TW202434651A - Polyethylene composition and formed body - Google Patents

Abstract

The present invention provides a polyethylene composition having excellent stiffness during high temperature processing, less paste residue during high temperature processing, and thus excellent film processing properties. The polyethylene composition of the present invention satisfies conditions (A) to (D). ＜Condition (A)＞ The weight average molecular weight measured by gel permeation chromatography (GPC) is 40,000 g/mol or more and 350,000 g/mol or less. ＜Condition (B)＞ The crystallinity calculated by wide angle X-ray scattering (WAXS) is 60% or more and 75% or less. ＜Condition (C)＞ The crystallite size of the (110) plane calculated by the above wide angle X-ray scattering measurement is 17 nm or more and 32 nm or less. <Condition (D)> In temperature-variable wide-angle X-ray scattering measurement, the ratio of the peak intensity X originating from the (110) plane at 50°C to the peak intensity Y originating from the (110) plane at 130°C: Y/X is 0.40 or more and 0.80 or less.

Description

Polyethylene composition and formed body

The present invention relates to a polyethylene composition and a formed body.

Polyethylene compositions are formed by various molding methods and are used for various purposes. The properties required for these molding methods and purposes are also different. Films can be cited as a representative use of polyethylene compositions. Specifically, surface protective films for optical components are known. The purpose of the above-mentioned surface protective films is to prevent damage or stains from the outside during processing, transportation, and storage, and they are used by attaching to the surface of the adherend such as metal plates, resin boards, wooden makeup boards, nameplates, liquid crystal components, electrical and electronic components, building materials, and automotive parts.

In order to prevent wrinkles and improve the workability during peeling, the surface protective film is required to be stiff. In addition, from the perspective of reducing costs and reducing environmental load, the surface protective film is required to be thinned by high-speed extraction. On the other hand, when the polyethylene composition constituting the surface protective film does not contain low-density polyethylene or the content of the low-density polyethylene is extremely small, the film is unstable and easily shakes after coming out of the die, resulting in film breakage or uneven thickness and poor film appearance.

On the other hand, in the production step of the adherend, there are cases where the surface protective film is heated and processed in a state where it is attached to the adherend. Preferably, even if the surface protective film is exposed to high temperature, the surface protective film will not melt or deform, thereby achieving surface protection of the adherend, and the polyethylene composition will not remain in the adherend when peeled off. However, if low-density polyethylene is blended into the polyethylene composition constituting the above-mentioned surface protective film, the melting point of the surface protective film will be lowered, causing problems such as deformation or paste residue during high-temperature processing of the adherend.

In view of the above-mentioned problems of film breakage, uneven thickness, and poor film appearance of the surface protection film, Patent Document 1 discloses a polyethylene composition, which adds a small amount of low-density polyethylene to high-density polyethylene, thereby taking into account both FE (fish eye) reduction and sufficient stiffness at room temperature, thereby improving film breakage, uneven thickness, and film appearance. [Prior technical document] [Patent document]

[Patent Document 1] Japanese Patent No. 6792957

[The problem the invention is trying to solve]

However, the above-mentioned Patent Document 1 has the following problem: the paste residue during high-temperature processing of the adherend and the film forming processability have not been verified and there is no room for improvement.

Therefore, the present invention aims to provide a polyethylene composition having excellent stiffness during high-temperature processing of the film, less paste residue during high-temperature processing of the adherend, and excellent film processing properties. [Technical means for solving the problem]

The inventors of the present invention have conducted diligent research to solve the problems of the above-mentioned prior art, and as a result, they have found that a polyethylene composition having the specific properties shown below can solve the problems of the above-mentioned prior art, thereby completing the present invention. That is, the present invention is as follows.

[1] A polyethylene composition that satisfies the following <Condition (A)> to <Condition (D)>. <Condition (A)> The weight average molecular weight measured by gel permeation chromatography (GPC) is 40,000 g/mol or more and 350,000 g/mol or less. <Condition (B)> The crystallinity calculated by wide angle X-ray scattering (WAXS) is 60% or more and 75% or less. <Condition (C)> The crystallite size of the (110) plane calculated by the above wide angle X-ray scattering measurement is 17 nm or more and 32 nm or less. <Condition (D)> In temperature-variable wide-angle X-ray scattering measurement, the ratio of the peak intensity X derived from the (110) plane at 50°C to the peak intensity Y derived from the (110) plane at 130°C: Y/X is 0.40 or more and 0.80 or less. [2] The polyethylene composition as described in the above [1], wherein in pulse NMR (nuclear magnetic resonance) measurement at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components, the relaxation time _Tα of the low-mobility component α is 5 ms or more and 25 ms or less, and the abundance ratio _Rα of the low-mobility component α is 25% or more and 55% or less. [3] The polyethylene composition as described in [1] or [2] above, wherein the mass ratio of the component eluting before 80°C in the temperature rising elution fraction (TREF) of the cross fractionation chromatography (CFC) is not less than 1 mass % and not more than 35 mass % of the total elution amount. [4] A polyethylene composition as described in any one of [1] to [3] above, wherein the polyethylene composition is a mixture of a high-density polyethylene (A) having a density of 942 kg/ ^m3 or more and a low-density polyethylene (B) having a density of 930 kg/m3 or ^less , and when the free induction decay curve of the low-density polyethylene (B) obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components in a pulse NMR measurement at 180°C, the low-mobility component ratio calculated by the following (Formula I) based on the abundance ratio _Rα of the low-mobility component α and the abundance ratio _Rβ of the intermediate component β is 0.35 or more and 0.55 or less. (Ratio of low-mobility component) = R _α /(R _α +R _β ) •••(Formula I) [5] A polyethylene composition as described in any one of the above [1] to [3], wherein the above polyethylene composition is a mixture of a high-density polyethylene (A) having a density of 942 kg/m ³ or more and a low-density polyethylene (B) having a density of 930 kg/m ³ or less, and in a pulse NMR measurement of the above high-density polyethylene (A) at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components, the ratio of low-mobility components calculated by the following (Formula I) based on the existence ratio R _α of the low-mobility component α and the existence ratio R _β of the intermediate component β is greater than 0.50 and less than 0.70. (Ratio of low-mobility components) = R _α /(R _α +R _β )•••(Formula I) [6] The polyethylene composition described in [4] or [5] above, wherein the content ratio of the high-density polyethylene (A) is 70 mass % to 99 mass %, and the content ratio of the low-density polyethylene (B) is 1 mass % to 30 mass %. [7] A molded body comprising the polyethylene composition described in any one of [1] to [6] above. [8] The molded body described in [7] above, which is a film. [Effects of the invention]

According to the present invention, a polyethylene composition can be provided which has excellent stiffness during high-temperature processing of the film, less paste residue during high-temperature processing of the adherend, and thus excellent film-forming processability.

The following is a detailed description of the implementation method of the present invention (hereinafter referred to as "this implementation method"). Furthermore, the following this implementation method is an example for explaining the present invention and is not intended to limit the present invention to the following content. The present invention can be implemented in various ways within the scope of its main purpose.

[Polyethylene composition] The polyethylene composition of the present embodiment satisfies the following <Condition (A)> to <Condition (D)>. <Condition (A)> The weight average molecular weight measured by gel permeation chromatography (hereinafter, sometimes referred to as GPC) is 40,000 g/mol or more and 350,000 g/mol or less. <Condition (B)> The crystallinity calculated by wide-angle X-ray scattering (hereinafter, sometimes referred to as WAXS) is 60% or more and 75% or less. <Condition (C)> The crystallite size of the (110) plane calculated by the above WAXS measurement is 17 nm or more and 32 nm or less. <Condition (D)> In the temperature-variable WAXS measurement, the ratio of the peak intensity X originating from the (110) plane at 50°C to the peak intensity Y originating from the (110) plane at 130°C: Y/X is 0.40 or more and 0.80 or less.

By having a structure that satisfies the above conditions (A) to (D), a polyethylene composition having excellent stiffness during high-temperature processing of the film and less paste residue during high-temperature processing of the adherend can be obtained, thereby achieving excellent film processing properties.

The polyethylene composition of this embodiment preferably further satisfies at least one of the following <Condition (E)> to <Condition (H)>. Thus, a polyethylene composition having excellent stiffness during high-temperature processing of the film and less paste residue during high-temperature processing of the adherend can be obtained, thereby achieving excellent film processing properties.

<Condition (E)> When the free induction decay curve obtained by the Carr Purcell Meiboom Gill (hereinafter sometimes referred to as CPMG) method in pulse NMR measurement at 180°C is approximated into three components, the relaxation time _Tα of the low-mobility component α is from 5 ms to 25 ms, and the abundance ratio _Rα of the low-mobility component α is from 25% to 55%.

<Condition (F)> The mass ratio of the component eluted before 80°C in the temperature rising elution fraction (TREF) of the cross fractionation chromatography (CFC) is 1% by mass or more and 35% by mass or less of the total elution amount.

<Condition (G)> The polyethylene composition of this embodiment is a mixture of a high-density polyethylene (A) having a density of 942 kg/m ³ or more and a low-density polyethylene (B) having a density of 930 kg/m ³ or less. When the free induction decay curve of the low-density polyethylene (B) obtained by the CPMG method is approximated into three components in pulse NMR measurement at 180°C, the low-mobility component ratio calculated by the following (Formula I) based on the existence ratio R _α of the low-mobility component α and the existence ratio R _β of the intermediate component β is 0.35 or more and 0.55 or less. (Low-mobility component ratio) = R _α /(R _α +R _β ) •••(Formula I)

<Condition (H)> The polyethylene composition of this embodiment is a mixture of a high-density polyethylene (A) having a density of 942 kg/m ³ or more and a low-density polyethylene (B) having a density of 930 kg/m ³ or less. When the free induction decay curve of the high-density polyethylene (A) obtained by the CPMG method is approximated into three components in pulse NMR measurement at 180°C, the low-mobility component ratio calculated from the existence ratio R _α of the low-mobility component α and the existence ratio R _β of the intermediate component β obtained by the above (Formula I) is 0.50 or more and 0.70 or less. (Low-mobility component ratio) = R _α /(R _α +R _β ) •••(Formula I)

The polyethylene composition of this embodiment preferably contains a high-density polyethylene (A) having a density of 942 kg/m ³ or more and a low-density polyethylene (B) having a density of 930 kg/m ³ or less. Examples of the low-density polyethylene (B) include high-pressure low-density polyethylene, linear low-density polyethylene, and other special ultra-low-density polyethylene. Among them, high-pressure low-density polyethylene is preferred from the perspective of improving stability during film processing. Such a polyethylene composition tends to have both heat resistance and film processing stability.

The polyethylene contained in the polyethylene composition of the present embodiment may be a homopolymer of ethylene, a copolymer of ethylene and α-olefin or cyclic olefin, diene, and derivatives thereof, or a (co)polymer containing two or more thereof.

The polyethylene composition of the present embodiment is not particularly limited, and can be produced, for example, by melt-kneading a high-density polyethylene (A) and a low-density polyethylene (B). The production method of the polyethylene composition of the present embodiment is described in detail below. The density of the high-density polyethylene (A) is greater than 942 kg/ ^m3 , and the density of the low-density polyethylene (B) is ^less than 930 kg/m3. There is no particular limitation on the production method of the polyethylene used as the raw material, and any of the commonly used production methods such as the solution method, high-pressure method, high-pressure block method, gas method, slurry method, etc. can be applied.

(Weight average molecular weight) The polyethylene composition of this embodiment has a weight average molecular weight of 40,000 g/mol or more and 350,000 g/mol or less in GPC measurement as shown in the above <Condition (A)>. As the lower limit, it is preferably 60,000 g/mol or more, and more preferably 80,000 g/mol or more. As the upper limit, it is preferably 300,000 g/mol or less, and more preferably 250,000 g/mol or less. If the weight average molecular weight is 40,000 g/mol or more, the necking during film formation can be reduced, and the viscosity during extrusion is higher, and the fisheye (FE) is easily dispersed, so it is better. If the weight average molecular weight is 350,000 g/mol or less, the film breakage can be suppressed and the adhesion to the adherend is improved, so it is better. The weight average molecular weight of the polyethylene composition can be measured by the method described in the following examples.

The weight average molecular weight of the polyethylene composition can be controlled within the above numerical range by adjusting the polymerization conditions, selecting the type of raw materials, and adjusting the mixing ratio of the raw materials. As a method for controlling the molecular weight, for example, by using a highly active polymerization catalyst in the slurry method, or by reducing the concentration of hydrogen as a molecular weight regulator, the molecular weight tends to increase. In addition, by reducing the polymerization temperature, increasing the polymerization pressure, or not using a chain transfer agent in the high pressure method, the molecular weight tends to increase.

(Crystallinity) The polyethylene composition of this embodiment has a crystallinity of 60% or more and 75% or less as measured by wide-angle X-ray scattering (WAXS) as shown in the above <Condition (B)>. It is preferably 62% or more, and more preferably 64% or more. Also, it is preferably 73% or less, and more preferably 71% or less. If the crystallinity of the polyethylene composition of this embodiment is 60% or more, the stiffness during film forming is fully obtained, and the stiffness during high-temperature processing tends to be good, so it is better. Also, if the crystallinity is 75% or less, the neck of the film is reduced, and the high-speed processability tends to be good. In addition, FE can be reduced by branching components, so it is better. The crystallinity of the polyethylene composition of this embodiment can be measured by the method described in the following embodiment.

The crystallinity of the polyethylene composition calculated in the wide angle X-ray scattering (WAXS) measurement can be controlled within the above numerical range by adjusting the polymerization method, composition, and mixing method of the components contained in the polyethylene composition. As a method for controlling the crystallinity of the polyethylene composition, for example, in the slurry method, a method of mixing a comonomer, i.e., a monomer other than ethylene, with the ethylene raw material can be cited, whereby the crystallinity of the polyethylene composition tends to be reduced. In addition, a method of not using a chain transfer agent in the high pressure method can be cited, whereby the free radical polymerization is not easily stopped and long chain branching reaction is easily generated, so the crystallinity of the polyethylene composition tends to be reduced. In addition, the crystal structure of polyethylene is affected by the molecular structure and degree of interconnection of the components contained in the polyethylene composition. For example, the crystallization of polyethylene with a branched structure and polyethylene with an intertwined structure is easily hindered, so the polyethylene composition containing these tends to have a lower crystallinity. On the other hand, linear polyethylene and polyethylene with less intertwining are easy to crystallize, so the polyethylene composition containing these tends to have a higher crystallinity. In addition, when the polyethylene composition of the present embodiment is a mixture of polyethylenes, it is believed that the crystallinity will change according to the type and composition ratio of the polyethylene raw materials, and the secondary structure will change due to the difference in molecular structure, compatibility, and intertwining interaction.

(Crystalline size) The polyethylene composition of this embodiment, as shown in the above <Condition (C)>, has a crystallite size of 17 nm or more and 32 nm or less in the (110) plane calculated in the wide-angle X-ray scattering (WAXS) measurement. Preferably, it is 19 nm or more, and more preferably, it is 21 nm or more. The above crystallite size is preferably 30 nm or less, and more preferably, 28 nm or less. The crystallite size of the above (110) plane represents the crystal thickness in the direction perpendicular to the molecular chain. When the polyethylene composition is processed at high temperature, the low molecular weight components tend to be easily dissolved in the polyethylene composition. When the polyethylene composition is processed at high temperature, the polyethylene composition having a larger crystallite size has excellent heat resistance and low dissolution. On the other hand, the stress relaxation time becomes shorter and the necking during film formation tends to become larger. If the crystallite size of the (110) plane is 17 nm or more, there is a tendency that less paste residue is left during high-temperature processing of the adherend, which is preferred. In addition, if the crystallite size of the (110) plane is 32 nm or less, the necking during film formation becomes smaller and the yield is improved, and the film tends to be less prone to wrinkles, which is preferred. The crystallite size of the polyethylene composition of this embodiment can be measured by the method described in the following embodiment.

The crystallite size of the (110) plane of the polyethylene composition is affected by the composition of the polyethylene composition and the molecular structure of the components contained therein. For example, by including polyethylene having a branched structure or an interlaced structure in the polyethylene composition, there is a tendency for the crystallite size of the above (110) plane to become smaller. On the other hand, by including a linear polyethylene or a polyethylene with less interlacing, there is a tendency for the crystallite size of the above (110) plane to become larger. The branched structure or interlaced structure of the components contained in the polyethylene composition can be adjusted by changing the preparation method of the catalyst or the polymerization conditions, thereby controlling the crystallite size of the (110) plane of the polyethylene composition within the above numerical range. Specifically, when preparing the polymerization catalyst used in the slurry method, the loading times of the active species are adjusted to increase the loading concentration, thereby making the growth points of polyethylene on the catalyst surface dense and having multiple active species, so that the interlacing during the growth of polyethylene is promoted, and polyethylene with a large number of interlaced structures is obtained. More specifically, in order to obtain polyethylene with a large number of interlaced structures, it is preferred that in the step of synthesizing the Ziegler-Natta catalyst, when loading titanium as a catalyst species, the loading times are set to two times, and the molar ratio of the active species added in each loading operation is set to the first loading operation: the second loading operation = 1:3. On the other hand, polyethylene compositions polymerized using catalysts with lower active species loading density or using metallocene catalysts with one active species tend not to promote cross-linking, resulting in polyethylene with a linear structure or less cross-linking structure.

In addition, as a method for obtaining polyethylene having a large number of intertwined structures, for example, there can be cited: a method of mixing low-density polyethylene produced without adding a chain transfer agent into a polyethylene composition; or a method of mixing high-pressure low-density polyethylene produced by increasing the separation temperature and appropriately controlling the residence time in a gas separation device of unreacted ethylene gas in the production process of high-pressure low-density polyethylene into a polyethylene composition. By increasing the temperature of the gas separation device of unreacted ethylene gas to separate the unreacted ethylene gas immediately, it is easy to generate bonding reactions between polyethylenes by unreacted free radicals remaining in the system, and by controlling the residence time, it is not easy to generate decomposition of polyethylene. As a result, there is a tendency for low-density polyethylene with a long-chain branching structure to bond with each other to generate low-density polyethylene with a branching structure that expands into a tree shape. Specifically, in the gas separation device just after the reaction, the temperature of the gas separation device is set to above 220°C, and the retention time is set to below 15 minutes, thereby tending to generate high-pressure low-density polyethylene with a long-chain branching structure with a higher molecular weight. By including such low-density polyethylene with a long-chain branching structure, the intertwined structure becomes more, and polyethylene with a smaller crystallite size is obtained.

Furthermore, when the polyethylene composition of the present embodiment is a mixture of polyethylenes, the crystallite size of the (110) plane of the polyethylene composition varies depending on the type and composition ratio of the polyethylene raw materials. The reason is believed to be that the secondary structure changes due to differences in molecular structure, compatibility, and crosstalk. The WAXS measurement used to measure the crystallite size of the (110) plane of the polyethylene composition of the present embodiment can be implemented using a common wide-angle X-ray scattering measurement device, for example, it can be implemented using the method described in the following embodiment.

(Temperature-variable WAXS measurement) The polyethylene composition of this embodiment is as shown in the above <Condition (D)>. In the temperature-variable wide-angle X-ray scattering (WAXS) measurement, the ratio of the peak intensity X originating from the (110) plane at 50°C to the peak intensity Y originating from the (110) plane at 130°C: Y/X is 0.40 or more and 0.80 or less. Preferably, it is 0.45 or more, and more preferably, it is 0.50 or more. Preferably, it is 0.75 or less, and more preferably, it is 0.70 or less. Y/X is an index showing how much the crystalline structure of the polyethylene is maintained at 130°C. If Y/X is 0.40 or more, the peak intensity originating from the (110) plane is fully maintained at 130°C, and the surface protective film using the polyethylene composition of this embodiment has sufficient strength when subjected to high temperature treatment, and the paste residue on the adherend is reduced, so it is better. In addition, if Y/X is 0.80 or less, since the polyethylene composition of this embodiment contains a certain degree of low-density components, the film forming processability of the film using the polyethylene composition of this embodiment is improved, so it is better.

The method of temperature-variable WAXS measurement applied to the measurement of the polyethylene composition of this embodiment is not particularly limited, as long as the WAXS measurement is performed with the sample placed on a heating table. For example, it can be implemented using the method described in the following embodiment.

Y/X can be controlled within the above numerical range by adjusting the polymerization method, composition, and mixing method of the components contained in the polyethylene composition. The method is not particularly limited, and for example, Y/X can be controlled to be above 0.40 by making the polyethylene composition contain 75% by mass or more of a component with a density of 950 kg/m ³ or more (hereinafter, sometimes described as a high-density component). In addition, for example, Y/X can be controlled to be below 0.80 by making the polyethylene composition contain 1% by mass or more of a component with a density of 925 kg/m ³ or less (hereinafter, sometimes described as a low-density component).

The method for making the polyethylene composition contain a low-density component is not particularly limited, and examples thereof include a method of mixing a low-density polyethylene with a high-density polyethylene or a method of making a high-density polyethylene contain a low-density polyethylene by a multi-stage polymerization process.

On the other hand, in a polyethylene composition comprising a high-density component and a low-density component, the melting point of the high-density component tends to be lower than the melting point of the same high-density component alone. The reason for this is considered to be as follows: if a polyethylene composition comprising a high-density component and a low-density component in a solid state is heated, the low-density component will melt first. The melted low-density component will promote the crystallization and melting of the high-density component, and therefore, the melting point of the high-density component in the polyethylene composition tends to be lowered. Therefore, in a polyethylene composition comprising only a high-density component and a low-density component, in the temperature increase process of the temperature-variable WAXS measurement, the low-density component with a lower melting point melts first, and the melted low-density component will promote the crystallization and melting of the high-density component, so there is a tendency for the peak intensity Y originating from the (110) plane at 130°C to be greatly reduced. Therefore, by suppressing the promotion of crystal melting of the high-density component by the melted low-density component, the peak intensity Y originating from the (110) plane at 130° C. is prevented from decreasing, and the above Y/X can be set to 0.40 or more.

In order to control the above Y/X within the numerical range of 0.40 to 0.80, it is more effective to finely control the molecular mobility and molecular interconnection structure of the polyethylene composition. Polyethylene compositions with strong molecular interconnection tend not to reduce the peak intensity Y originating from the (110) plane even at 130°C. The reason is believed to be that part of the molecular chain of the low-density component is easily incorporated into the crystal structure formed by the high-density component, and tends to maintain the crystal structure even at 130°C. Furthermore, the molecular interconnection strength of the polyethylene composition can be evaluated by the following pulse NMR.

As a method for enhancing the molecular interconnection of the polyethylene composition, for example, a method of adjusting the preparation method of the polymerization catalyst or the polymerization conditions to control the molecular growth of the polyethylene can be cited. For example, when preparing the polymerization catalyst used in the slurry method, by adjusting the number of times the active species are loaded to increase the loading concentration, the growth points of the polyethylene on the catalyst surface are dense and have multiple active species. Thereby, there is a tendency to promote the molecular interconnection during the polyethylene growth process, and a polyethylene composition with stronger interconnection is obtained. Specifically, it is preferred that in the step of synthesizing the Ziegler-Natta catalyst, when loading titanium as a catalyst species, the loading times are set to two times, and the molar ratio of the active species added in each loading operation is set to the first loading operation: the second loading operation = 1:3. On the other hand, polyethylene compositions polymerized using catalysts with lower loading density of active species or polyethylene compositions polymerized using metallocene catalysts with active species as one species tend to be less likely to promote interlacing and tend to obtain polyethylene with less interlaced structure.

In addition, as a method for enhancing the mutual interlinking of the molecules of the polyethylene composition, for example, a method of making the polyethylene composition contain a component that easily forms physical crosslinking points can be cited. Such a polyethylene composition containing a component that easily forms physical crosslinking points is easy to crystallize in the state of molecular chain interlinking during the cooling step in the molding process, so it tends to be easy to maintain the crystalline structure even at 130°C. Furthermore, in the process of heating up such a polyethylene composition, the molecular chain of the low-density component that melts first is restrained by the interlinking, and the promotion of crystallization and melting of the high-density component tends to be suppressed. As a method for making the polyethylene composition contain a component that easily forms physical crosslinking points, for example, a method of making the polyethylene composition contain a low-density component with a long chain branching structure that expands into a tree shape can be cited. As a method containing such a low-density component, for example, there can be cited: a method of mixing a high-pressure low-density polyethylene produced without adding a chain transfer agent into a polyethylene composition; or a method of producing high-pressure low-density polyethylene by raising the separation temperature in a gas separation device for unreacted ethylene gas in the production process of high-pressure low-density polyethylene and appropriately controlling the residence time, and mixing the high-pressure low-density polyethylene into a polyethylene composition. As described above, by raising the separation temperature in a gas separation device for unreacted ethylene gas so that the unreacted ethylene gas is immediately separated, it is easy to generate a bonding reaction between polyethylenes by unreacted free radicals remaining in the system, and by appropriately controlling the residence time, there is a tendency that decomposition of polyethylene does not occur. As a result, there is a tendency for low-density polyethylene with a long-chain branching structure to bond with each other to generate low-density polyethylene with a branching structure that expands into a tree shape. Specifically, in the gas separation device just after the reaction, the temperature of the gas separation device is set to above 220°C, and the retention time is set to below 15 minutes, thereby tending to generate high-pressure low-density polyethylene with a long-chain branching structure with a higher molecular weight. As a result, as described above, the molecular interconnection of the polyethylene composition is enhanced.

In addition, in order to control Y/X within the above numerical range, a method of improving the dispersibility of the polyethylene composition in the extrusion step can be cited. By improving the dispersibility, the various components in the polyethylene composition in the molten state become uniform, and in this state, it is cooled in the cooling step in various molding methods, thereby crystallizing in the state of molecular chain interlacing, thereby suppressing the decrease of the peak intensity Y originating from the (110) plane at 130°C, so that the above Y/X can be controlled within the above numerical range. The method for improving the dispersibility of the polyethylene composition in the extrusion step is not limited to the following, and examples thereof include: a method of pre-granulating the low-density component and the high-density component and dry-blending them, and then melt-kneading them; or a method of melt-kneading the polyethylene composition containing the low-density component and the high-density component multiple times. Specifically, when the polyethylene composition containing the low-density component and the high-density component is melt-kneaded, a double-screw extruder and a single-screw extruder are used for two-stage extrusion, thereby the two components are fully mixed and the interweaving of the polyethylene composition tends to be enhanced. In addition, as a method for improving the dispersibility of the polyethylene composition in the extrusion step, a method of adding a low-density component to the production step of the high-density component and melt-kneading can be cited. Specifically, by adding a low-density component to a polyethylene powder of a high-density component produced by slurry polymerization and melt-kneading the two components, there is a tendency for the two components to be fully mixed and the dispersibility of the polyethylene composition to be improved. Furthermore, if the crystallinity of the high-density component and the crystallinity of the low-density polyethylene are similar in the initial stage of melt-kneading, the long chain branches of the low-density component are easily incorporated into the high-density component, so there is a tendency for the two components to be fully mixed and the dispersibility of the polyethylene composition to be improved. For example, by setting the temperature of the solvent used to polymerize the high-density component to a temperature below 1/2 of the polymerization temperature, the polymerized powder is quenched to reduce the crystallinity, and there is a tendency for the affinity with the low-density component to be improved. The polyethylene powder of the high-density component obtained in the above manner is melt-kneaded with the low-density component, thereby making it easier for the low-density component and the high-density component to disperse.

(Pulse NMR measurement at 180°C) The polyethylene composition of the present embodiment is preferably as shown in the above-mentioned <Condition (E)>, in the pulse NMR measurement at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated to three components, the relaxation time _Tα of the low-mobility component α is 5 ms to 25 ms, and the abundance ratio _Rα of the low-mobility component α is 25% to 55%. The relaxation time _Tα of the low-mobility component α is more preferably 8 ms or more, and more preferably 10 ms or more. Furthermore, it is more preferably 23 ms or less, and more preferably 20 ms or less. The abundance ratio _Rα of the low-mobility component α is more preferably 27% or more, and more preferably 30% or more. Furthermore, it is more preferably 52% or less, and further preferably 50% or less.

When the free induction decay curve obtained by the CPMG method in pulse NMR of the polyethylene composition of the present embodiment at 180°C is approximated into three components, it is considered that the low-mobility component α corresponds to the part where the molecular chains in the polyethylene composition in the molten state are firmly intertwined, and is a component that does not disentangle during the molding process and easily remains in the molded body. Therefore, if the existence ratio R _α of the low-mobility component α is 25% or more, the crystallization of the polyethylene composition is maintained by the intertwining of the molecular chains, thereby having sufficient strength when subjected to high-temperature treatment, and the dissolution amount of the low-density component is reduced, and in the surface protection film, etc. using the polyethylene composition of the present embodiment, the paste residue on the adherend is reduced, so it is more preferable. On the other hand, if the existence ratio R _α of the low-mobility component α is 55% or less, the stress when the polyethylene composition of this embodiment is formed into a film is reduced, the film forming processability is stable, and the film breakage and wrinkles during high-speed processing can be reduced, which is preferred.

In addition, the relaxation time _Tα of the low-mobility component α is an indicator of the degree of restraint of the molecular chain of the low-mobility component. The shorter the relaxation time in pulse NMR measurement, the more restrained the molecular chain is, and the stronger the interlocking in the molten state is. If the relaxation time _Tα of the low-mobility component α is 5 ms or more, the stress during the molding process into a film is reduced, the film forming processability is stable, the neck is small, and the film breakage and wrinkles can be reduced, so it is better. If the relaxation time _Tα of the low-motion component α is less than 25 ms, the crystallization of the polyethylene composition is maintained by the interweaving of the molecular chains, thereby having sufficient stiffness during high-temperature processing, and the dissolution amount of the low-density component is reduced, and the paste residue on the adherend is reduced, which is preferred.

The relaxation time _Tα and the existence ratio _Rα of the low-mobility component α of the polyethylene composition of the present embodiment can be controlled within the above numerical range by adjusting the composition ratio of the high-density component to the low-density component in the polyethylene composition, or adjusting the synthesis conditions or polymerization conditions of the polymerization catalyst, and adjusting the molecular growth of the polyethylene. For example, the method of setting the number of times of loading the active species to a certain number or more when synthesizing the polymerization catalyst, or the method of making the polyethylene composition contain a low-density component with a relatively high molecular weight and a moderately long-chain branched structure.

Specifically, the pulse NMR measurement of the polyethylene composition of the present embodiment can be performed by the following method. First, a sample tube filled with the polyethylene composition to a height of 1 cm from the bottom is placed in a TD-NMR device (model: minispec mq20) manufactured by Bruker Corporation and set so that the internal temperature of the sample tube becomes 30°C, and the sample tube is heated according to the <heating conditions> shown below. The temperature shown in the <heating conditions> below is the value obtained by measuring the internal temperature of the sample by a thermocouple. <Heating conditions> (1) Set to 30°C and let stand for 5 minutes. (2) Raise the temperature to 180°C at a rate of 5°C/min. (3) After heating to 180°C, let stand for 25 minutes.

After the temperature is raised by the above procedure, the rotation-rotation relaxation time (T ₂ , sometimes simply expressed as "relaxation time T" in this manual) of polyethylene is measured according to the <Measurement Conditions> shown below. <Measurement Conditions> Magnetic field strength: 0.47 T Measurement nucleus: ¹ H (20 MHz) Measurement method: Carr Purcell Meiboom Gill method Accumulation times: 256 times Repetition time: 3 seconds Interval between the initial 90° pulse and the 180° pulse (τ): 0.04 milliseconds Total number of echo signals: 6400 The free induction decay (FID) obtained by the above measurement is fitted using the analysis program TD-NMR-A manufactured by Bruker. The function shown in the following <Formula 1> is used for fitting. <Formula 1> f(t) = R _α eXp(-t/T _α ) + R _β eXp(-t/T _β ) + R _γ eXp(-t/T _γ ) (where R _α + R _β + R _γ = 100) t: variable (time elapsed from pulse irradiation) T _α : relaxation time of low-motility component α (ms) R _α : abundance ratio of low-motility component α (%) T _β : relaxation time of intermediate component β (ms) R _β : abundance ratio of intermediate component β (%) T _γ : relaxation time of high-motility component γ (ms) R _γ : abundance ratio of high-motility component γ (%)

Generally speaking, in the case of a polymer in a rubbery state where the molecular chain is actively moving, the free induction decay obtained by pulse NMR measurement can be represented by an exponential function. Therefore, in this measurement, the obtained free induction decay can also be fitted as the sum of three different components represented by the exponential function as shown in the above <Formula 1>. In addition, it is known that the higher the mobility of ¹ H, that is, the higher the mobility of the molecular chain, the slower the decay rate of the free induction decay. The relaxation time T in each exponential function is in the relationship of T _α ＜T _β ＜T _γ , therefore, the component with the lowest mobility is set as α, the component with intermediate mobility is set as β, and the component with the highest mobility is set as γ. Furthermore, component α corresponds to the part of the polyethylene composition where the molecular chains are strongly intertwined, component β corresponds to the part of the polyethylene composition where the molecular chains are weakly intertwined, and component γ corresponds to the part of the polyethylene composition where the molecular chains are not intertwined. More specifically, the pulse NMR measurement at 180° C. of this embodiment can be measured by the method described in the examples.

(Mass ratio of components eluted below 80°C) The polyethylene composition of this embodiment is as shown in the above <Condition (F)>, and the mass ratio of components eluted before 80°C in the temperature-elution fractionation (TREF) of the cross-fractionation chromatography (CFC) calculated from the elution temperature-elution amount curve obtained by the temperature-elution fractionation (TREF) measured by the cross-fractionation chromatography (CFC) is preferably 1 mass% or more and 35 mass% or less of the total elution amount. More preferably, it is 2 mass% or more, and further preferably, it is 5 mass% or more. Furthermore, it is more preferably 30 mass% or less, and further preferably, it is 25 mass% or less. The above-mentioned "total dissolution amount" is the total area of the dissolution temperature-dissolution amount curve within the range of 40°C to 120°C, and the mass ratio of the components dissolving below 80°C tends to be almost the same as the mass ratio of the low-density components contained in the polyethylene composition. By making the mass ratio of the components dissolving below 80°C more than 1% by mass of the total dissolution amount, the stress generated by the cross-linking effect of the long-chain branch components plays a role in the kneading step using the extruder, the stability of the film formation is improved, and the necking is reduced, so it is better. By making the mass ratio of the components dissolving below 80°C less than 35% by mass of the total dissolution amount, the dissolution components during high-temperature processing are less, so the paste residue is suppressed, so it is better. The mass ratio of the components eluted below 80°C can be controlled within the above numerical range by adjusting the amount of low-density components in the polyethylene composition, for example, by controlling the content of high-pressure low-density polyethylene to be above 1 mass % and below 35 mass % in the ethylene resin composition. The CFC measurement applied to the measurement of the polyethylene composition of this embodiment can be performed, for example, by the method of the embodiment.

(Ratio of low-mobility components of low-density polyethylene (B) at 180°C) As shown in the above <Condition (G)>, the polyethylene composition of the present embodiment is preferably a mixture of high-density polyethylene (A) having a density of 942 kg/ ^m3 or more and low-density polyethylene (B) having a density of 930 kg/m3 ^or less. In the pulse NMR measurement of the above-mentioned low-density polyethylene (B) at 180°C, when the free induction decay curve obtained by the CPMG method is approximated into three components, the ratio of low-mobility components calculated by the following (Formula I) based on the abundance ratio _Rα of the low-mobility component α and the abundance ratio _Rβ of the intermediate component β is preferably 0.35 or more and 0.55 or less. (Low-motility component ratio)=R _α /(R _α +R _β )•••(Formula I) The low-motility component ratio is more preferably 0.38 or more, and further preferably 0.40 or more. Further, it is more preferably 0.53 or less, and further preferably 0.50 or less.

The low-mobility component ratio calculated by the above formula (I) indicates the ratio of components with stronger cross-linking in a state where the molecular chains are restrained. Low-density polyethylene containing a large amount of such components is restrained by cross-linking, and the molecular motion is suppressed, so there is a tendency to suppress the promotion of crystallization and melting of high-density components. Therefore, if the above low-mobility component ratio is 0.35 or more, there is a tendency to suppress the promotion of crystallization and melting of high-density components by cross-linking, so it has sufficient strength when subjected to high-temperature treatment, and the dissolution amount of low-density components is reduced. In the surface protection film using the polyethylene composition of this embodiment, the paste residue on the adherend is reduced, so it is better. On the other hand, if the low-mobility component ratio is 0.55 or less, the film-forming processability of the polyethylene composition film of this embodiment is stable, and film breakage and wrinkles during high-speed processing can be reduced, which is preferred.

The low mobility component ratio of the low-density polyethylene (B) calculated by the above formula (I) in the polyethylene composition of this embodiment can be controlled within the above numerical range by adjusting the polymerization conditions such as polymerization temperature, polymerization pressure, type of initiator, type of chain transfer agent, etc., and controlling the amount of long-chain branched structure. For example, a method without using a chain transfer agent or a method of producing low-density polyethylene under forced stirring conditions can be adopted, thereby easily generating a starting point for free radical polymerization, having a large number of long-chain branched structures, and having a tendency to increase the low mobility component ratio. In addition, by increasing the separation temperature in the high-pressure separation device of the unreacted ethylene gas and appropriately controlling the residence time, the bonding reaction between polyethylenes is easily generated, and by controlling the residence time, the decomposition of polyethylene does not occur, so there is a tendency to generate a branched structure that expands into a tree shape, and the ratio of low-mobility components becomes higher.

(Ratio of low-mobility components in high-density polyethylene (A) at 180°C) As shown in the above <Condition (H)>, the polyethylene composition of the present embodiment is preferably a mixture of high-density polyethylene (A) having a density of 942 kg/ ^m3 or more and low-density polyethylene (B) having a density of 930 kg/m3 ^or less. In the pulse NMR measurement of the above high-density polyethylene (A) at 180°C, when the free induction decay curve obtained by the CPMG method is approximated into three components, the ratio of low-mobility components calculated by the following (Formula I) based on the abundance ratio _Rα of the low-mobility component α and the abundance ratio _Rβ of the intermediate component β is preferably 0.50 or more and 0.70 or less. (Low-motility component ratio) = R _α /(R _α +R _β ) (Formula I) More preferably, it is 0.52 or more, and further preferably, it is 0.55 or more. Further, it is more preferably 0.68 or less, and further preferably, it is 0.65 or less.

The ratio of the low-mobility component α indicates the ratio of components with stronger intertwining in a state where the molecular chains are restrained. In the high-density polyethylene (A), if the ratio of the low-mobility component calculated by the above formula (I) is 0.50 or more, the crystals of the polyethylene composition are maintained by intertwining, thereby having sufficient strength when subjected to high-temperature treatment, which is preferred. On the other hand, in the high-density polyethylene (A), if the ratio of the low-mobility component is 0.70 or less, it is easy to intertwine with the low-density polyethylene (B), and the film forming processability of the polyethylene composition of this embodiment is stable, and film breakage and wrinkles can be reduced, which is preferred. The ratio of low-mobility components in high-density polyethylene (A) can be controlled within the above numerical range by adjusting the synthesis conditions of the polymerization catalyst or the polymerization conditions such as polymerization temperature, polymerization pressure, and copolymerization monomer type to adjust the molecular growth of polyethylene. For example, when manufacturing the polymerization catalyst, by adjusting the number of times the active species are loaded to increase the loading concentration, the growth points of polyethylene on the catalyst surface are densely packed and have multiple active species, which tends to promote the crosstalk during the polyethylene growth process.

(Content ratio of high-density polyethylene (A) and low-density polyethylene (B)) When the polyethylene composition of the present embodiment is a mixture of high-density polyethylene (A) having a density of 942 kg/m ³ or more and low-density polyethylene (B) having a density of 930 kg/m ³ or less, it is preferred that the content ratio of the high-density polyethylene (A) is 70 mass % to 99 mass %, and the content ratio of the low-density polyethylene (B) is 1 mass % to 30 mass %. By making the existence ratio of the high-density polyethylene (A) and the low-density polyethylene (B) within the above range, a polyethylene composition having an excellent balance among the stiffness of the film during high-temperature processing, the paste residue during high-temperature processing of the adherend, and the film-forming processability of the film is obtained. More preferably, the content ratio of the high-density polyethylene (A) is 73 mass % to 97 mass %, and the content ratio of the low-density polyethylene (B) is 3 mass % to 27 mass %. Further preferably, the content ratio of the high-density polyethylene (A) is 75 mass % to 95 mass %, and the content ratio of the low-density polyethylene (B) is 5 mass % to 25 mass %.

[Method for producing polyethylene composition] The method for producing the polyethylene composition of the present embodiment is not particularly limited, and examples thereof include: a method of connecting a plurality of polymerization reactors so that the polyethylene composition contains a high-density component and a low-density component; or a method of producing a high-density component and a low-density component separately and mixing them. A method of mixing a high-density polyethylene (A) and a low-density polyethylene (B) produced by a high-pressure method in advance and melt-kneading them is particularly preferred. Here, the density of the high-density polyethylene resin is 942 kg/m ³ or more, and the density of the low-density polyethylene is 930 kg/m ³ or less.

There is no particular limitation on the method for premixing the high-density polyethylene (A) and the low-density polyethylene (B). For example, the high-density polyethylene (A) and the low-density polyethylene (B) produced by the high-pressure method are pre-granulated and the granules are dry-blended with each other; or in the production step of the high-density polyethylene (A), a granular low-density polyethylene (B) is added to the powdered high-density polyethylene (A). In particular, from the viewpoint of improving dispersibility, a method of performing dry blending for more than 1 hour is preferred. In addition, by adding the granular low-density polyethylene (B) to the powdered high-density polyethylene (A) and mixing them in a state where the high-density polyethylene (A) has a low crystallinity, the melting point of the high-density polyethylene is lowered, making it easier to mix with the low-density polyethylene (B), which is preferred.

As the melt kneading machine in the kneading operation, for example, a single-screw extruder, a double-screw extruder, an exhaust extruder, a tandem extruder, etc. can be used. In particular, it is preferred to perform melt kneading in two stages, a double-screw extruder or a single-screw extruder, because it is easy to disperse the high-density polyethylene (A) and the low-density polyethylene (B).

The high-density polyethylene (A) can be produced, for example, by a continuous slurry polymerization method. The catalyst used for production is not particularly limited, and for example, metallocene catalysts, Ziegler-Natta catalysts, Phillips catalysts, etc. can be used. The use of a Ziegler-Natta catalyst having multiple active sites is preferred because it promotes crosstalk during molecular growth.

The Ziegler-Natta catalyst used for producing high-density polyethylene (A) is not particularly limited, but is preferably a catalyst for olefin polymerization produced by carrying an organic magnesium compound and a titanium compound on a carrier prepared by reacting an organic magnesium compound with a chlorinating agent. The amount of the titanium compound used as an active site is not particularly limited, but from the perspective of increasing the amount of the titanium compound loaded in the pores of the carrier, the molar ratio of titanium to magnesium atoms contained in the carrier (Ti/Mg) is preferably 0.1 to 20, and more preferably 0.2 to 10. The method of loading the titanium compound on the carrier is not particularly limited, and a method of reacting the excess titanium compound with the carrier or a method of efficiently loading the titanium compound by using a third component may also be used. In particular, from the perspective of increasing the loading concentration on the carrier surface and promoting the interaction during molecular growth, it is preferred to perform the loading operation multiple times when loading the titanium compound, and it is further preferred to set the loading times to 2 times and set the molar ratio of the active species added in each loading operation to the first loading operation: the second loading operation = 1:3.

In general, in addition to adjusting the catalyst, physical properties such as molecular weight and density can also be controlled by adjusting the polymerization temperature, polymerization pressure, comonomer concentration or hydrogen concentration.

The comonomers that can be used to prepare the polyethylene composition of the present embodiment are not particularly limited, and examples thereof include: compounds selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, vinylcyclohexane, styrene, and derivatives thereof; compounds selected from the group consisting of cyclopentene, cyclopentene, A cyclic olefin having 3 to 20 carbon atoms selected from the group consisting of heptene, norpentene, 5-methyl-2-norpentene, tetracyclododecene, and 2-methyl-1,4,5,8-dimethoxy-1,2,3,4,4a,5,8,8a-octahydronaphthalene; a linear, branched, or cyclic diene having 4 to 20 carbon atoms selected from the group consisting of 1,3-butadiene, 1,4-pentadiene, 1,5-hexadiene, 1,4-hexadiene, 1,7-octadiene, and cyclohexadiene. Particularly preferred are propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. The density of high-density polyethylene can be adjusted by properly controlling the type and concentration of the comonomer.

The polymerization temperature is preferably 30°C or higher and 100°C or lower. When the polymerization temperature is 30°C or higher, more efficient production can be achieved industrially. On the other hand, when the polymerization temperature is 100°C or lower, more stable continuous operation can be achieved.

As the solvent used by the continuous slurry polymerization method, an inert carbonized hydrogen medium can be used, and further, the olefin itself can also be used as a solvent. The above-mentioned inert carbonized hydrogen medium is not limited to the following, and examples thereof include: aliphatic hydrocarbons such as propane, butane, isobutane, pentane, isopentane, hexane, heptane, octane, decane, dodecane, and lamp oil; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; aromatic hydrocarbons such as benzene, toluene, and xylene; halogenated hydrocarbons such as ethyl chloride, chlorobenzene, and dichloromethane, or mixtures thereof, etc. The temperature of the solvent supplied to the polymerization system is not particularly limited. From the perspective of reducing the crystallinity of the obtained high-density polyethylene (A) powder and improving the affinity with the low-density components, it is preferably set to a temperature below 1/2 of the polymerization temperature.

The polymerization pressure in the method for producing high-density polyethylene (A) of the present embodiment is usually preferably not less than normal pressure and not more than 2 MPa, more preferably not less than 0.1 MPa and not more than 1.5 MPa, and further preferably not less than 0.1 MPa and not more than 1.0 MPa.

The molecular weight of the high-density polyethylene (A) used in the polyethylene composition of this embodiment can be adjusted by allowing hydrogen to exist in the polymerization system or changing the polymerization temperature, as described in the specification of West German Patent Application Publication No. 3127133. It can be controlled within an appropriate range by adding hydrogen as a chain transfer agent to the polymerization system. As a solvent separation method, decanting method, centrifugal separation method, filter filtration method, etc. can be cited, and centrifugal separation method with good separation efficiency of ethylene polymer and solvent is more preferred. The polymer powder is granulated into granules by a single-screw extruder, a double-screw extruder, an exhaust extruder, a series extruder, etc. There is no particular limitation on the type of extruder and the number of extrusions, but it is preferred to use a double-shaft extruder for mixing.

The high-pressure low-density polyethylene (B) used in the polyethylene composition of this embodiment is not limited to the following, and can be obtained, for example, by free radical polymerization of ethylene in an autoclave or tubular reactor. When an autoclave reactor is used, the polymerization conditions only need to be set to the presence of peroxide, a temperature of 200 to 300°C, and a polymerization pressure of 100 to 250 MPa. On the other hand, when a tubular reactor is used, the polymerization conditions only need to be set to the presence of peroxide, a polymerization reaction peak temperature of 180 to 400°C, and a polymerization pressure of 100 to 400 MPa. In particular, the method of performing polymerization in an autoclave type reactor is preferred because forced stirring promotes the long-chain branching reaction. The molecular weight, density, molecular weight distribution, and molecular structure of the obtained low-density polyethylene are controlled by polymerization temperature, polymerization pressure, type of peroxide, and the presence or absence of chain transfer agents. Generally speaking, if the polymerization pressure is set higher, the molecular weight tends to increase, and by setting the polymerization pressure lower, the molecular weight tends to decrease. In addition, by adding chain transfer agents, the branching reaction can be inhibited, so there is a tendency for the density to increase and the molecular weight to decrease.

The peroxide is not limited to the following, and examples thereof include methyl ethyl ketone peroxide, peroxyketal (specifically, 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)octane, 4,4-bis(tert-butylperoxy)valerate n-butyl ester, 2,2-bis(tert-butylperoxy)butane, etc.), hydrogen peroxide (specifically, tert-butyl hydroperoxide, isopropyl hydroperoxide, diisopropyl hydroperoxide, peroxide, 1,1,3,3-tetramethylbutyl hydroperoxide, etc.), dialkyl peroxides (specifically, di-tert-butyl peroxide, diisopropylbenzene peroxide, di(tert-butylperoxyisopropyl)benzene, tert-butylisopropylbenzene peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyldi(tert-butylperoxy)hexane-3, etc.), diacyl peroxides (specifically, acetyl peroxide, isobutylene peroxide, octyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl oxide, etc.), peroxydicarbonates (specifically, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, dimethoxyisopropyl peroxydicarbonate, di(3-methyl-3-methoxybutyl) peroxydicarbonate, diallyl peroxydicarbonate, etc.), peroxyesters (specifically, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-butyl peroxyoctanoate, neodecyl peroxide, etc.), tert-butyl peroxide, tert-butyl peroxyneodecanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,6-trimethylhexanoate, tert-butyl peroxylaurate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, cumyl peroxyoctanoate, tert-hexyl peroxyneodecanoate, tert-hexyl peroxypivalate, tert-butyl peroxyneohexanoate, tert-hexyl peroxyneohexanoate, cumyl peroxyneohexanoate, etc.), acetyl cyclohexyl sulfonyl peroxide, tert-butyl peroxyallyl carbonate, etc. By selecting peroxides with particularly high reactivity, such as peroxyesters (specifically, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, t-butyl peroxyoctanoate, t-butyl peroxyneodecanoate, cumyl peroxyneodecanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy-3,5,6-trimethylhexanoate, t-butyl peroxylaurate, t-butyl peroxybenzoate, t-butyl peroxyisopropylcarbonate, cumyl peroxyoctanoate, t-hexyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxyneohexanoate, t-hexyl peroxyneohexanoate, cumyl peroxyneohexanoate, etc.), the long-chain branching reaction will be promoted, so it is better.

There is no particular limitation on the chain transfer agent. For example, hydrocarbon compounds such as propane, propylene, and butane can be used to adjust various physical properties by stopping the free radicals of the polymer in the growth process. In particular, it is better to perform polymerization without using a chain transfer agent, thereby generating a polymer with a higher degree of polymerization and more long chain branches.

The low-density polyethylene polymerized in the reactor is separated into unreacted ethylene gas components and polymer components by a gas separation device adjusted to any pressure. Multiple gas separation devices can be connected. From the perspective of safety, two or more gas separation devices are generally installed. In addition, the temperature of the gas separation device and the residence time of the low-density polyethylene in the gas separation device will affect the long-chain branching structure and decomposition degree of the low-density polyethylene. In particular, since there are unreacted peroxides and free radicals remaining in the low-density polyethylene in the gas separation device immediately following the reactor, the temperature of the gas separation device immediately following the reactor is set to be above 220°C and below 260°C, and the retention time is set to be below 20 minutes, so that the unreacted gas is separated immediately, the bonding between polyethylene chains is promoted, and the decomposition of the polymer chain due to degradation will not occur. Therefore, there is a tendency to generate high-pressure low-density polyethylene with a high molecular weight and a long-chain branching structure, which is better.

(Additives) The polyethylene composition, the components used as raw materials, and the molded product of this embodiment may further contain additives such as antioxidants, light stabilizers, lubricants, fillers, and antistatic agents.

[Molded body] The molded body of the present embodiment is a molded body of the polyethylene composition of the present embodiment. As an example of the molded body of the present embodiment, a film can be cited. When the above-mentioned film is a multi-layer film, the polyethylene composition of the present embodiment can be used in the outermost layer or the middle layer. As a specific use of the above-mentioned film, a surface protective film for optical components can be cited. [Example]

The present embodiment is described in detail below with reference to specific embodiments and comparative examples, but the present invention is not limited to the following embodiments and comparative examples. The measurement methods and evaluation methods of various physical properties and characteristics are described below. In addition, unless otherwise specified, the measurement and evaluation are performed at room temperature.

[Measurement method of physical properties] ((Physical property 1) Melt flow rate (MFR) at 190°C and 2.16 kg load) For each polyethylene composition obtained in the embodiments and comparative examples, and the high-density polyethylene (A) and low-density polyethylene (B) used as raw materials, the melt flow rate (g/10 minutes) was measured according to JIS K7210 code D: 1999 (temperature = 190°C, load = 2.16 kg).

(Physical Property 2) Density) The density (kg/m 3 ) of each polyethylene composition obtained in Examples and Comparative Examples, and the high-density polyethylene (A) and low-density polyethylene (B) used as raw materials was measured by the density gradient tube method (23° C.) in accordance with JIS ^K7112 :1999.

((Physical Property 3) Weight Average Molecular Weight in GPC Measurement) For each polyethylene composition obtained in the Examples and Comparative Examples, gel permeation chromatography (GPC) measurement was performed using a detector GPC-IR manufactured by Polymer Char and an IR5 manufactured by Polymer Char. 15 mL of o-dichlorobenzene as a mobile phase was introduced into 20 mg of each polyethylene composition obtained in the Examples and Comparative Examples, and stirred at 150°C for 1 hour to prepare a sample solution, which was then allowed to flow at a flow rate of 1.0 mL/min. As a column, UT-807 (1 column) manufactured by Showa Denko Co., Ltd. and GMHHR-H(S)HT (2 columns) manufactured by Tosoh Co., Ltd. were connected in series and used. The measurement was performed under the conditions of column temperature of 140°C, sample dissolution temperature of 140°C, and sample dissolution time of 90 minutes. The ratio (Mw/Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained by GPC was set as the molecular weight distribution. The molecular weight calibration is performed at 12 points in the range of Mw (Molecular weight) of standard polystyrene manufactured by Tosoh Co., Ltd. from 1,050 to 2,060,000. The Mw of each standard polystyrene is multiplied by a coefficient of 0.43 and used as the polyethylene-converted molecular weight. A primary calibration line is drawn based on the plot of dissolution time and polyethylene-converted molecular weight to determine the weight average molecular weight (Mw) and number average molecular weight (Mn).

(Physical Property 4) Crystallinity and crystallite size in wide-angle X-ray (WAXS) scattering measurement) The crystallinity and crystallite size of each polyethylene composition obtained in the embodiment and the comparative example were measured by transmission method wide-angle X-ray scattering measurement using the transmission X-ray scattering device NANOPIX manufactured by Rigaku Corporation. The sample cut into a thickness of 1 mm was irradiated with Cu-Kα rays, and the scattering was detected by the semiconductor detector HypiX-6000. The measurement was carried out under the conditions of a sample-detector distance of 96 mm, an output of 40 kV, 30 mA, an exposure time of 5 seconds, and a vacuum environment around the sample unit. The optical system adopts point focusing, and the slit diameter is the first slit: =0.55 mm, second slit: open, protection slit: =0.35 mm. In the case of wide-angle X-ray scattering measurement by transmission method, in the X-ray scattering pattern obtained by using a two-dimensional detector, when the position where the straight X-ray irradiated to the sample passes through the sample and reaches the two-dimensional detector is set as the center, the scattering intensity at the same distance from the center corresponds to the same scattering angle. Therefore, for the measured X-ray scattering pattern, the intensity average value (circular average value) at each scattering angle is calculated, thereby obtaining a one-dimensional scattering intensity distribution relative to the scattering angle 2θ. In the range of 2θ=10.0° to 2θ=29.0° of the obtained one-dimensional distribution, separation is performed into three diffraction peaks of the orthorhombic (110) plane of polyethylene, the diffraction peak of the orthorhombic (200) plane of polyethylene, and the amorphous peak of polyethylene. The reference line was drawn by connecting 2θ=10.0° to 2θ=29.0° with a straight line. The (110) plane diffraction peak and (200) plane diffraction peak of polyethylene were approximated by the Voigt function, and the amorphous peak of polyethylene was approximated by the Gauss function. In addition, the peak position of the amorphous peak was fixed under the conditions of 2θ=19.6° and half-maximum full width of 3.8°, and the peak position and half-maximum full width of the crystalline peak were not particularly fixed, and peak separation was performed. Based on the half-maximum full width of the (110) plane diffraction peak of polyethylene calculated by peak separation, the crystallite size (D) was calculated according to the Scherrer formula (the following formula). Furthermore, the crystallinity is obtained as a percentage of the area of the crystal peak relative to the sum of the areas of the separated crystal peak and amorphous peak. D = Kλ/(βcosθ)•••(Scherrer formula) D: crystallite size (nm) K: 0.9 (constant) λ: wavelength of X-ray (nm) β: (β ₁ ² -β ₂ ² ) ^0.5 β ₁ : half-maximum full amplitude of the (hkl) peak calculated from the results of peak separation (rad) β ₂ : half-maximum full amplitude of the diffusion of the incident beam (rad) θ: Bragg angle

((Physical Property 5) Y/X in Temperature-Variable Wide-Angle X-ray Scattering (WAXS) Measurement) The temperature-variable WAXS measurement of each polyethylene composition obtained in the examples and comparative examples was performed using the transmission X-ray scattering device NANOPIX manufactured by Rigaku Corporation. The sample cut into a thickness of 1 mm was irradiated with Cu-Kα rays, and the scattering was detected by the semiconductor detector HypiX-6000. The measurement was performed under the conditions of a sample-detector distance of 96 mm, an output of 40 kV, 30 mA, an exposure time of 10 seconds, and a vacuum environment around the sample unit. The optical system adopts point focusing, and the slit diameter is the first slit: =0.55 mm, Second slit: open, Protection slit: =0.35 mm. In addition, the sample was placed on a heating table and kept at 50°C for 10 minutes. After the temperature of the table and the sample was uniform, the temperature was raised at a rate of 2°C per minute, and WAXS measurements were performed at each temperature. In the X-ray scattering pattern obtained using a two-dimensional detector, when the position where the straight X-ray irradiated to the sample passes through the sample and reaches the two-dimensional detector is set as the center, the scattering intensity at the same distance from the center corresponds to the same scattering angle. Therefore, for the measured X-ray scattering pattern, the intensity average value (circular average value) at each scattering angle is calculated, thereby obtaining a one-dimensional scattering intensity distribution relative to the scattering angle 2θ. In the range of 2θ=10.0° to 2θ=29.0° of the obtained one-dimensional distribution, the diffraction peak of the orthorhombic (110) plane of polyethylene, the diffraction peak of the orthorhombic (200) plane of polyethylene, and the amorphous peak of polyethylene were separated into three peaks. The baseline was drawn by connecting 2θ=10.0° to 2θ=29.0° with a straight line. The diffraction peak of the (110) plane of polyethylene and the diffraction peak of the (200) plane of polyethylene were approximated by the Voigt function, and the amorphous peak of polyethylene was approximated by the Gauss function. In addition, the peak position of the amorphous peak was fixed under the conditions of 2θ=19.6° and the half-maximum full amplitude of 3.8°, and the peak position and half-maximum full amplitude of the crystalline peak were not particularly fixed, and the peak separation was performed. Regarding the peak intensity originating from the (110) plane in the one-dimensional distribution at each temperature obtained by the above measurement, the ratio of the peak intensity X originating from the (110) plane at 50°C to the peak intensity Y originating from the (110) plane at 130°C was calculated as Y/X.

((Physical Property 6) Pulse NMR measurement at 180°C, relaxation time T _α (ms) of low-mobility component α, abundance ratio R _α of low-mobility component α, ratio R _β of intermediate component β, ratio of low-mobility component) The pulse NMR measurement of each polyethylene composition obtained in the Examples and Comparative Examples and the high-density polyethylene (A) and low-density polyethylene (B) used as raw materials was carried out in the following manner. First, a sample tube filled with a sample to a height of 1 cm from the bottom was placed in a TD-NMR device (model: minispec mq20) manufactured by Bruker and set so that the internal temperature of the sample tube became 30°C, and the sample tube was heated according to the <Heating Conditions> shown below. The temperature shown in the <Heating Conditions> below is the value obtained by measuring the internal temperature of the sample by a thermocouple. <Heating conditions> (1) Set to 30°C and leave for 5 minutes. (2) Raise the temperature to 180°C at a rate of 5°C/min. (3) After reaching 180°C, leave for 25 minutes. After the temperature is raised through the above procedure, measure the rotation-rotation relaxation time (T ₂ , sometimes simply referred to as "relaxation time" in this manual) of the sample according to the <Measurement conditions> shown below. <Measurement conditions> Magnetic field strength: 0.47 T Species to be measured: ¹ H (20 MHz) Measurement method: Carr Purcell Meiboom Gill method Accumulated times: 256 times Repeat time: 3 seconds Interval between the initial 90° pulse and the 180° pulse (τ): 0.04 milliseconds Total number of echo signals: 6400 The free induction decay (FID) obtained by the above measurement was fitted using the analysis program TD-NMR-A manufactured by Bruker. The function shown in the following <Formula 1> was used for fitting. <Formula 1> f(t) = R _α eXp(-t/T _α ) + R _β eXp(-t/T _β ) + R _γ eXp(-t/T _γ ) (where R _α + R _β + R _γ = 100) t: variable (time elapsed from pulse irradiation) T _α : relaxation time of low-motility component α (ms) R _α : abundance ratio of low-motility component α (%) T _β : relaxation time of intermediate component β (ms) R _β : abundance ratio of intermediate component β (%) T _γ : relaxation time of high-motility component γ (ms) R _γ : abundance ratio of high-motility component γ (%) By fitting the curve of the free induction decay, the existence ratio R _α of the low-mobility component α and the relaxation time T _α of the low-mobility component α of each polyethylene composition obtained in the Examples and Comparative Examples are calculated. In addition, for the raw materials of each polyethylene composition obtained in the Examples and Comparative Examples, the low-mobility component ratio is calculated according to the relaxation time T and the existence ratio R obtained by the same method as above and by the (Formula I) shown below. (Low-mobility component ratio) = R _α /(R _α +R _β ) •••(Formula I)

((Physical Property 7) Dissolution temperature-dissolution amount curve in cross fractionation chromatography (CFC) measurement, mass ratio of components dissolved below 80°C to total dissolution amount) For each polyethylene composition obtained in the examples and comparative examples, CFC measurement was performed using Automated 3D analyzer CFC-2 manufactured by Polymer ChAR. A stainless steel microsphere column (outer diameter 3/8 inch × length 150 mm) was used as a TREF column. One GPC UT-807 manufactured by ShodeX and two GMHHR-H(S)HT manufactured by Tosoh, a total of three columns, were used as GPC columns. Ortho-dichlorobenzene (for high performance liquid chromatography) as an eluent was allowed to flow at a flow rate of 1.0 mL/min. The column containing the filler was heated to 140°C, and 20 mL of a sample solution (sample concentration: 1.0 g/mL) obtained by dissolving a polyethylene composition in o-dichlorobenzene was introduced and maintained for 120 minutes. Then, the temperature of the column was cooled to 40°C at a cooling rate of 0.5°C/min and maintained for 20 minutes. In this step, the sample precipitated onto the surface of the filler. Thereafter, the temperature of the column was adjusted as follows. First, the temperature was raised to 50°C and maintained at 50°C. Then, the temperature was raised to 60°C and maintained at 60°C. Furthermore, the temperature was raised from 60°C to 75°C and maintained at 5°C intervals, raised from 75°C to 90°C and maintained at 3°C intervals, raised from 90°C to 110°C and maintained at 1°C intervals, and raised from 110°C to 120°C and maintained at 5°C intervals. Furthermore, each temperature increase process was performed at a rate of 20°C/min, and each holding temperature was maintained for 21 minutes. The concentration (mass %) of the sample dissolved during the 21-minute holding at each holding temperature was detected, and the dissolution temperature-dissolution amount curve was obtained based on the holding temperature and the dissolution sample concentration. Furthermore, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the components dissolved during the 21-minute holding at each holding temperature were obtained using a GPC column connected to a TREF column. Based on the dissolution temperature-dissolution amount curve obtained as above, the mass ratio of the components dissolved below 80°C relative to the total dissolution amount is calculated.

[Evaluation method] (Evaluation 1) Stiffness during high temperature processing) Using a T-shaped film molding machine (HM40N manufactured by Beijin Industrial Co., Ltd., screw diameter 40 mm, mold width 300 mm), the polyethylene compositions obtained in the embodiments and comparative examples were formed at a cylinder temperature of 200°C, a mold temperature of 210°C, an extrusion volume of 5 kg/hour, an air gap of 10 cm, and a pulling speed of 9 m/min. Both ends were trimmed by 50 mm to obtain a film containing the polyethylene composition with a thickness of 35 μm. The obtained film was cut into 10 cm wide × 10 cm long, and the midpoint of a set of opposite sides was pulled with a clamp to eliminate wrinkles, and fixed in a manner that the deformation was 0% and horizontal to the ground. In this state, the stiffness evaluation test during high temperature processing was carried out in an environment of 2 atmospheres and 100% RH. The sample was placed in an oven under the above conditions and maintained for 5 minutes. The vertical distance from the lowest point of the film to the horizontal plane was set as the distance L (cm) that the film relaxed downward from the horizontal direction, and the stiffness during high temperature processing was evaluated based on the following criteria. ◎: less than 3 cm ○: more than 3 cm and less than 6 cm △: more than 6 cm and less than 9 cm ×: more than 9 cm or the film broke

((Evaluation 2) Residue after high temperature processing) The film obtained in the above (Evaluation 1) was cut into 5 cm wide × 5 cm long, attached to a new glass slide of 7.6 cm wide × 2.6 cm long in a way that no air bubbles would enter, and fixed at the four corners with transparent tape to make a sample. For this sample, an evaluation test of residue after high temperature processing was carried out in an environment of 130°C, 2 atmospheres, and 100%RH humidity. The sample was placed in an oven set to the above conditions, maintained for 60 minutes, and then the sample was taken out. After 1 minute, the membrane was peeled off with tweezers, and the surface of the slide glass with a width of 5 cm and a length of 2.6 cm where the membrane was in contact with the slide glass was visually observed. The residue after high temperature processing was evaluated according to the following criteria. ◎: No residue was found in the observed area. ○: Residue was found in less than 20% of the observed area. △: Residue was found in more than 20% and less than 40% of the observed area. ×: Residue was found in more than 40% of the observed area.

((Evaluation 3) Neck constriction) As an evaluation of high-speed film forming properties, a T-die film-making machine (HM40N manufactured by Beijin Industrial Co., Ltd., screw diameter 40 mm, die width 300 mm) was used to form each polyethylene composition obtained in the embodiment and comparative example at a cylinder temperature of 200°C, a die temperature of 210°C, an extrusion volume of 5 kg/hour, an air gap of 10 cm, and a pulling speed of 20 m/min. The difference between the width of the obtained film and the width of the T-die mouth was defined as neck constriction (mm), and the evaluation was performed according to the following evaluation criteria. Neck shrinkage is an indicator of film processability. The smaller the neck shrinkage under high-speed conditions, the less likely the film will break and the thin film can be processed. The higher the film yield, the better the film processability. ◎: 50 mm or less ○: 50 mm to 60 mm or less △: 60 mm to 70 mm or less ×: 70 mm or more or edge or film breakage

[Preparation of components used in the embodiments and comparative examples] (Preparation of catalyst) <Preparation of Ziegler-Natta catalyst (a-1)> Into an 8 L stainless steel autoclave fully purged with nitrogen, 1,000 mL of a 2 mol/L hexane solution of hydroxytrichlorosilane was added, and 2,550 mL of a hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OC ₄ H ₉ ) ₂ (equivalent to 2.68 mol of magnesium) was dropwise added while stirring at 65°C for 4 hours, and the reaction was continued while stirring at 65°C for 1 hour. After the reaction was completed, the supernatant was removed and washed four times with 1,800 mL of hexane to obtain a solid that became a carrier. The solid was analyzed and the result showed that 8.31 mmol of magnesium was contained in 1 g of the solid. Under the temperature condition of 10°C, 28 mL of 1 mol/L titanium tetrachloride hexane solution and 28 mL of 1 mol/L hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSiH) ₂ were added to 1,970 mL of hexane slurry containing 110 g of the above carrier while stirring for 1 hour. After the addition, the reaction was continued at 10°C for 1 hour. After the reaction was completed, 1100 mL of the supernatant was removed and washed twice with 1100 mL of hexane. Next, 1100 mL of hexane was added to the washed solid, and 82 mL of a 1 mol/L hexane solution of titanium tetrachloride and 82 mL of a hexane solution of an organic magnesium compound represented by 1 mol/L AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSiH) ₂ were added simultaneously over 1 hour. After the addition, the reaction was continued at 10°C for 1 hour. After the reaction was completed, 1100 mL of the supernatant was removed and washed twice with 1100 mL of hexane to prepare a Ziegler-Natta catalyst (a-1).

<Preparation of Ziegler-Natta Catalyst (a-2)> 1,000 mL of a 2 mol/L hexane solution of hydroxytrichlorosilane was added to an 8 L stainless steel autoclave that was fully purged with nitrogen. 2,550 mL of a hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OC ₄ H ₉ ) ₂ (equivalent to 2.68 mol of magnesium) was added dropwise at 65°C while stirring for 4 hours. The reaction was continued at 65°C while stirring for 1 hour. After the reaction was completed, the supernatant was removed and washed 4 times with 1,800 mL of hexane to obtain a solid that became a carrier. The solid was analyzed, and the result showed that the magnesium content per 1 g of the solid was 8.31 mmol. 82 mL of 1 mol/L titanium tetrachloride hexane solution and 82 mL of 1 mol/L hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSiH) ₂ were added to 1,970 mL of hexane slurry containing 110 g of the above-mentioned carrier while stirring at 10°C for 1 hour. After the addition, the reaction was continued at 10°C for 1 hour. After the reaction was completed, 1100 mL of the supernatant was removed and washed twice with 1100 mL of hexane. Next, 1100 mL of hexane was added to the washed solid, and 28 mL of a 1 mol/L hexane solution of titanium tetrachloride and 28 mL of a hexane solution of an organic magnesium compound represented by 1 mol/L AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSiH) ₂ were added simultaneously over 1 hour. After the addition, the reaction was continued at 10°C for 1 hour. After the reaction was completed, 1100 mL of the supernatant was removed and washed twice with 1100 mL of hexane to prepare a Ziegler-Natta catalyst (a-2).

<Preparation of Ziegler-Natta Catalyst (a-3)> 1,000 mL of a 2 mol/L hexane solution of hydroxytrichlorosilane was added to an 8 L stainless steel autoclave that was fully purged with nitrogen. 2,550 mL of a hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OC ₄ H ₉ ) ₂ (equivalent to 2.68 mol of magnesium) was added dropwise at 65°C while stirring for 4 hours. The reaction was continued at 65°C while stirring for 1 hour. After the reaction was completed, the supernatant was removed and washed 4 times with 1,800 mL of hexane to obtain a solid that became a carrier. The solid was analyzed, and the result showed that the magnesium content per 1 g of the solid was 8.31 mmol. 110 mL of a 1 mol/L titanium tetrachloride hexane solution and 110 mL of a 1 mol/L hexane solution of an organic magnesium compound represented by AlMg ₅ (C ₄ H ₉ ) ₁₁ (OSiH) ₂ were added to 1,970 mL of a hexane slurry containing 110 g of the above-mentioned carrier while stirring at 10°C for 1 hour. After the addition, the reaction was continued at 10°C for 1 hour. After the reaction was completed, 1100 mL of the supernatant was removed and washed twice with 1100 mL of hexane to prepare a Ziegler catalyst (a-3).

<Preparation of Ziegler-Natta Catalyst (a-4)> In the same manner as in Japanese Patent No. 6792957, 40 mL of a hexane solution of an organic magnesium compound represented by the formula: AlMg ₆ (C ₄ H ₉ ) ₁₂ (OC ₃ H ₇ ) ₃ (equivalent to 37.8 mmol in terms of the total amount of aluminum and magnesium) was added to a 200 mL stainless steel autoclave that was fully purged with nitrogen. 40 mL of hexane containing 2.27 g (37.8 mmol) of methyl hydropolysiloxane was added dropwise over 30 minutes at 25°C while stirring. After the addition, the temperature was raised to 80°C and the reaction was carried out while stirring for 3 hours to obtain an organic magnesium compound in contact with a titanium compound. 2400 mL of hexane was added to an 8 L stainless steel autoclave fully purged with nitrogen, and 1300 mL of a hexane solution of an organic magnesium compound represented by the formula AlMg ₆ (C ₄ H ₉ ) ₁₂ (OC ₃ H ₇ ) ₃ (equivalent to 521 mmol of magnesium) and 1300 mL of a hexane solution of 0.5 mol/L titanium tetrachloride were added simultaneously at -5°C for 2 hours while stirring. After the addition, the mixture was further stirred at 10°C for 1 hour while aging, and the supernatant was removed and washed 4 times with 3000 mL of hexane to prepare a Ziegler-Natta catalyst (a-4).

<Preparation of metallocene catalyst (b-1)> Similar to the method of Japanese Patent No. 6912290, 40 g of silica (average particle size 15 μm, compression strength 3 MPa) for catalyst carrier obtained by dehydration at 600°C was dispersed in 800 mL of hexane in a 1.8 L autoclave under a nitrogen atmosphere to obtain a slurry. The obtained slurry was maintained at 25°C and 84 mL of a hexane solution of triethylaluminum (concentration 1 mol/L) was added while stirring. Thereafter, the mixture was stirred for 2 hours to react triethylaluminum with the surface hydroxyl groups of silica, thereby obtaining a hexane slurry of component [a] in which the surface hydroxyl groups of silica were covered with triethylaluminum. On the other hand, 200 mmol of [(N-tert-butylamide)(tetramethyl-η5-cyclopentadienyl)dimethylsilane]titanium dimethyl (hereinafter referred to as "titanium complex") was dissolved in 1000 mL of Isopar E (registered trademark) (trade name of hydrocarbon mixture manufactured by Exon Chemical Company (USA)), 20 mL of a 1 mol/L hexane solution of n-butylethylmagnesium was added, and hexane was further added to prepare the titanium complex concentration to 0.1 mol/L, thereby obtaining component [b]. Furthermore, 5.7 g of bis(hydrogenated animal fat alkyl) methyl ammonium-tris(pentafluorophenyl)(4-hydroxyphenyl) borate (hereinafter referred to as "borate compound") was added and dissolved in 50 mL of toluene to obtain a 100 mmol/L toluene solution of the borate compound. 5 mL of a 1 mol/L hexane solution of diethylaluminum ethoxide was added to the toluene solution of the borate compound at room temperature, and hexane was further added to make the concentration of the borate compound in the solution 70 mmol/L. Thereafter, the mixture was stirred at room temperature for 1 hour to obtain a reaction mixture containing the borate compound [c]. After the temperature of the above-mentioned component [a] slurry is raised to 45-50°C, the stirring speed is set to 600 rpm, and 9.2 mL of the above-mentioned reaction mixture [c] and 6.4 mL of the above-mentioned component [b] are simultaneously added dropwise to the above-mentioned hexane slurry of the above-mentioned component [a] over 20 minutes, and then stirred at 50°C for 1 hour, thereby allowing the catalyst active species to penetrate into the interior of the silica. Thereafter, the supernatant containing the unreacted borate compound•titanium complex in the obtained reaction mixture is removed by clarification, thereby allowing the catalyst active species to be carried inside the silica. Then, after cooling to 10-15°C, 36.8 mL of the reaction mixture [c] and 25.6 mL of the component [b] were added dropwise over 80 minutes, and then stirred at 15-20°C for 3 hours to allow the titanium complex to react and precipitate with the borate, so that the catalyst active species were physically adsorbed on the surface of the silica. Then, the supernatant containing the unreacted borate compound and titanium complex in the obtained reaction mixture was removed by decanting, thereby obtaining a supported restricted geometric metallocene catalyst (b-1) in which the catalyst active species were formed on the surface and inside of the above-mentioned silica.

(High-density polyethylene (A)) ＜Production of high-density polyethylene (A-1)＞ A 280 L container-type polymerization reactor equipped with a stirring device was used to carry out continuous polymerization at a polymerization temperature of 70°C, a polymerization pressure of 0.80 MPa, and an average residence time of 1.6 hours. Dehydrated n-hexane as a solvent was supplied at 40 L/hour, the above-mentioned Ziegler-Natta catalyst (a-1) as a catalyst was supplied at 0.4 g/hour, and triisobutylaluminum as a liquid co-catalyst component was supplied at 24 mmol/hour in terms of Al atoms. Hydrogen for adjusting the molecular weight was supplied in such a manner that the gas phase concentration relative to ethylene was 40.2 mol%, thereby polymerizing ethylene. Furthermore, dehydrated n-hexane is supplied from the bottom of the polymerization reactor in a state of being cooled to 10°C by a heat exchanger, and hydrogen is supplied from the catalyst inlet line and the catalyst from the middle of the liquid surface and the bottom of the polymerization reactor in order to contact the catalyst in advance, and ethylene is supplied from the bottom of the polymerization reactor. The polymerization slurry in the polymerization reactor is introduced into a flash tank with a pressure of 0.08 MPa and a temperature of 75°C in a manner that the level of the polymerization reactor is kept fixed to separate the unreacted ethylene and hydrogen. Then, the polymerization slurry is continuously supplied to a centrifuge separator in a manner that the level of the polymerization reactor is kept fixed to separate the polymer and other solvents. At this time, the content of the solvent, etc. relative to the polymer is 45% by mass. The separated high-density polyethylene powder is dried at 85°C while blowing nitrogen. Then, 300 ppm by mass of tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate pentaerythritol ester] is added as an antioxidant to the obtained powder, thereby obtaining a powdery high-density polyethylene (A-1).

<Production of high-density polyethylene (A-2)> High-density polyethylene (A-2) was obtained by the same operation as the production of high-density polyethylene (A-1) except that the polymerization temperature was set to 70°C, the polymerization pressure was set to 1.0 MPa, the temperature of dehydrated n-hexane was set to 50°C, the gas phase concentration of hydrogen relative to ethylene was set to 28.6 mol%, and the gas phase concentration of 1-butene relative to ethylene was supplied to 0.58 mol%.

<Production of high-density polyethylene (A-3)> High-density polyethylene (A-3) was obtained by the same operation as the production of high-density polyethylene (A-1) except that the polymerization temperature was set to 65°C, the polymerization pressure was set to 1.0 MPa, the temperature of dehydrated n-hexane was set to 30°C, and the gas phase concentration of hydrogen relative to ethylene was set to 61.3 mol%.

<Production of high-density polyethylene (A-4)> Polymerization was performed in the same manner as the above-mentioned high-density polyethylene (A-1) except that the Ziegler-Natta catalyst (a-2) was used as a catalyst to obtain a high-density polyethylene resin (A-4).

<Production of high-density polyethylene (A-5)> Polymerization was performed in the same manner as the above-mentioned high-density polyethylene (A-1) except that the Ziegler-Natta catalyst (a-3) was used as a catalyst to obtain a high-density polyethylene resin (A-5).

<Production of high-density polyethylene (A-6)> Polymerization was performed in the same manner as the above-mentioned high-density polyethylene (A-2), except that the Ziegler-Natta catalyst (a-2) was used as a catalyst and the gas phase concentration of hydrogen relative to ethylene was set to 40.2 mol%, thereby obtaining a high-density polyethylene resin (A-6).

<Production of high-density polyethylene (A-7)> Polymerization was performed in the same manner as the above-mentioned high-density polyethylene (A-2) except that the Ziegler-Natta catalyst (a-3) was used as a catalyst, the polymerization temperature was set to 75°C, the gas phase concentration of hydrogen relative to ethylene was set to 54.3 mol%, and 1-butene was not supplied, to obtain a high-density polyethylene resin (A-7).

<Production of high-density polyethylene (A-8)> Referring to the method of Example (A-2) of Japanese Patent No. 6792957, a Ziegler-Natta catalyst (a-4) was used as a catalyst, and the polymerization temperature was set to 86°C. Except for this, polymerization was carried out in the same manner as the above-mentioned high-density polyethylene (A-2) to obtain a high-density polyethylene resin (A-8).

<Production of high-density polyethylene (A-9)> With reference to the method of Example (A-4) of Japanese Patent No. 6912290, a continuous polymerization was carried out using a container-type 340 L polymerization reactor equipped with a stirring device at a polymerization temperature of 80°C, a polymerization pressure of 0.98 MPa, and an average residence time of 3.2 hours. Dehydrated n-hexane as a solvent was supplied at 40 L/hour, the above-mentioned metallocene catalyst (b-1) as a catalyst was supplied at 1.4 mmol/hour in terms of Ti atom conversion, and triisobutylaluminum as a liquid co-catalyst component was supplied at 20 mol/hour in terms of Al atom conversion. Hydrogen for adjusting the molecular weight is supplied in a gas phase concentration of 0.47 mol% relative to ethylene, thereby polymerizing ethylene. Furthermore, dehydrated n-hexane is supplied from the bottom of the polymerization reactor at a temperature of 50°C. In order to contact the catalyst in advance, hydrogen is supplied from the catalyst inlet line and the catalyst from the middle of the liquid surface and the bottom of the polymerization reactor. Ethylene is supplied from the bottom of the polymerization reactor. The polymerization slurry in the polymerization reactor is introduced into a flash tank with a pressure of 0.08 MPa and a temperature of 75°C while keeping the level of the polymerization reactor fixed, and the unreacted ethylene and hydrogen are separated. Then, the polymer slurry is continuously supplied to a centrifuge while the level of the polymerization reactor is kept fixed, and the polymer and the solvents other than the polymer are separated. At this time, the content of the solvents relative to the polymer is 45% by mass. The separated high-density polyethylene powder is dried while blowing nitrogen at 85°C to obtain a powdered high-density polyethylene (A-9).

The physical properties of the obtained high-density polyethylene (A) are shown in Table 1 below.

[Table 1] High density polyethylene (A) A-1 A-2 A-3 A-4 A-5 A-6 A-7 A-8 A-9 density kg/m ³ 967 960 965 967 967 959 962 965 964 MFR g/10 min 12 5 20 12 14 12 20 5 14 Low athletic component ratio - 0.63 0.54 0.59 0.51 0.48 0.49 0.48 0.49 0.47

(Low-density polyethylene (B)) <Production of low-density polyethylene (B-1)> Using ethylene gas as a raw material, the polymer was polymerized in an autoclave reactor at a polymerization temperature of 255°C and a polymerization pressure of 130.0 MPa, using tert-butyl peroxyacetate as a polymerization initiator. Subsequently, the unreacted ethylene gas was separated in a gas separation device adjusted to 50.0 MPa and 240°C. Furthermore, the unreacted gas was separated in a gas separation device adjusted to 2.0 MPa and 240°C. In addition, the residence time of the polymer in each gas separation device was set to 15 minutes. Then, the molten polymer was pelletized by a single-screw extruder manufactured by Nippon Steel Corporation (screw diameter 100 mm, L/D = 24, L: distance from raw material supply port to discharge port (m), D: inner diameter of extruder (m), the same below) to obtain pelletized low-density polyethylene (B-1). The obtained low-density polyethylene (B-1) had a density of 919 kg/m ³ and an MFR of 4.0 g/10 min.

＜Production of low-density polyethylene (B-2)＞ Polymerization was carried out in the same manner as the above low-density polyethylene (B-1), except that the polymerization temperature was changed to 230°C, the polymerization pressure was changed to 150.0 MPa, and 1.2 mol% of the ethylene raw material was changed to propylene, to obtain low-density polyethylene (B-2). The obtained low-density polyethylene (B-2) had a density of 922 kg/m ³ and an MFR of 5.0 g/10 min.

<Production of low-density polyethylene (B-3)> Using ethylene gas as a raw material, the polymer was polymerized in a tubular reactor at a polymerization temperature of 270°C and a polymerization pressure of 230 MPa, using tert-butyl peroxy-2-ethylhexanoate as a polymerization initiator. Subsequently, the unreacted ethylene gas was separated in a gas separation device adjusted to 70.0 MPa and 230°C. Furthermore, the unreacted gas was separated in a gas separation device adjusted to 2.0 MPa and 230°C. In addition, the residence time of the polymer in each gas separation device was set to 20 minutes. Then, the molten polymer was pelletized by a single-screw extruder (screw diameter 100 mm, L/D = 24) manufactured by Nippon Steel Corporation to obtain pelletized low-density polyethylene (B-3). The obtained low-density polyethylene (B-3) had a density of 916 kg/m ³ and an MFR of 4.0 g/10 minutes.

＜Production of low-density polyethylene (B-4)＞ Polymerization was carried out in the same manner as the above low-density polyethylene (B-1), except that the polymerization temperature was changed to 220°C, the polymerization pressure was changed to 120.0 MPa, and 18.5 mol% of the ethylene raw material was changed to butane, to obtain low-density polyethylene (B-4). The obtained low-density polyethylene (B-4) had a density of 924 kg/m ³ and an MFR of 6.0 g/10 min.

<Production of low-density polyethylene (B-5)> Polymerization was carried out in the same manner as the above low-density polyethylene (B-1) except that the temperature of the gas separator was set to 200°C to obtain low-density polyethylene (B-5). The density of the obtained low-density polyethylene (B-5) was 919 kg/m ³ and the MFR was 4.0 g/10 min.

＜Production of low-density polyethylene (B-6)＞ Polymerization was carried out in the same manner as the above low-density polyethylene (B-1), except that the polymerization temperature was changed to 255°C, the polymerization pressure was changed to 130.0 MPa, 18.5 mol% of the ethylene raw material was changed to butane, the temperature of the gas separator was set to 265°C, and the residence time was set to 35 minutes, to obtain low-density polyethylene (B-6). The obtained low-density polyethylene (B-6) had a density of 925 kg/m ³ and an MFR of 8.0 g/10 minutes.

＜Production of low-density polyethylene (B-7)＞ Polymerization was carried out in the same manner as the above low-density polyethylene (B-3), except that the polymerization temperature was changed to 250°C, the polymerization pressure was changed to 200.0 MPa, 18.5 mol% of the ethylene raw material was changed to butane, the temperature of the gas separator was set to 200°C, and the residence time of the polymer in the gas separator was set to 15 minutes, to obtain low-density polyethylene (B-7). The obtained low-density polyethylene (B-7) had a density of 924 kg/m ³ and an MFR of 1.0 g/10 minutes.

<Production of low-density polyethylene (B-8)> With reference to the method of Example (B-10) of Japanese Patent No. 6912290, in an autoclave reactor, polymerization temperature was 256°C, polymerization pressure was 122 MPa, tert-butyl peracetate and tert-butyl peroctanoate were diluted in isododecane at a molar ratio of 1:9 to 30 mass % as an initiator, the temperature of the gas separator was set to 265°C, and the residence time of the polymer in the gas separator was set to 35 minutes. Except for this, polymerization was carried out in the same manner as the above-mentioned low-density polyethylene (B-1) to obtain low-density polyethylene (B-8). The obtained low-density polyethylene (B-8) had a density of 918 kg/m ³ and an MFR of 7.0 g/10 minutes.

The physical properties of the obtained low-density polyethylene (B) are shown in Table 2 below.

[Table 2] Low density polyethylene (B) B-1 B-2 B-3 B-4 B-5 B-6 B-7 B-8 Reactor High Pressure Kettle High Pressure Kettle Tube type High Pressure Kettle High Pressure Kettle High Pressure Kettle Tube type High Pressure Kettle density kg/m ³ 919 922 916 924 919 925 924 918 MFR g/10 min 4 5 4 6 4 8 1 7 Low athletic component ratio - 0.41 0.45 0.40 0.52 0.34 0.33 0.32 0.31

(Polyethylene composition) <Example 1 Preparation of polyethylene composition C-1> Low-density polyethylene (B-1) in granular form was added to high-density polyethylene (A-1) in powder form using a side feeder in an amount of 90% by mass of (A-1) and 10% by mass of (B-1). The mixture was melt-kneaded at a set temperature of 200°C using a twin-screw extruder (screw diameter 44 mm, L/D=35) manufactured by Nippon Steel Corporation. The mixture was then melt-kneaded at a set temperature of 200°C using a single-screw extruder (screw diameter 100 mm, L/D=24) manufactured by Nippon Steel Corporation to form granules.

<Example 2 Preparation of polyethylene composition C-2> Using a twin-screw extruder (screw diameter 44 mm, L/D = 35) manufactured by Nippon Steel Corporation, the powdered high-density polyethylene (A-1) was melt-kneaded at a set temperature of 200°C and granulated into granules. The obtained granular high-density polyethylene (A-1) and granular low-density polyethylene (B-1) were mixed in a tumble mixer in a ratio of 85% by mass and 15% by mass, respectively, for 2 hours. Using a single-screw extruder (screw diameter 100 mm, L/D = 24) manufactured by Nippon Steel Corporation, the blended mixture was melt-kneaded at a set temperature of 200°C and granulated into granules.

<Example 3 Preparation of polyethylene composition C-3> High-density polyethylene resin (A-2) and high-pressure low-density polyethylene resin (B-3) were used in an amount of 80% by mass and 20% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-1).

<Example 4 Preparation of polyethylene composition C-4> High-density polyethylene resin (A-2) and high-pressure low-density polyethylene resin (B-2) were used in an amount of 90% by mass and 10% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-1).

<Example 5 Preparation of Polyethylene Composition C-5> High-density polyethylene resin (A-3) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 70% by mass and 30% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Example 6 Preparation of Polyethylene Composition C-6> High-density polyethylene resin (A-4) and high-pressure low-density polyethylene resin (B-4) were used in an amount of 80% by mass and 20% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-1) to form granules.

<Example 7 Preparation of Polyethylene Composition C-7> High-density polyethylene resin (A-5) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 95% by mass and 5% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Example 8 Preparation of Polyethylene Composition C-8> High-density polyethylene resin (A-1) and high-pressure low-density polyethylene resin (B-5) were used in an amount of 80% by mass and 20% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-1).

<Example 9 Preparation of polyethylene composition C-9> High-density polyethylene resin (A-6) and high-pressure low-density polyethylene resin (B-3) were used in an amount of 85% by mass and 15% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-1).

<Example 10 Preparation of polyethylene composition C-10> High-density polyethylene resin (A-3) and high-pressure low-density polyethylene resin (B-6) were used in an amount of 90% by mass and 10% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-1), and granulation was performed into pellets.

<Example 11 Preparation of polyethylene composition C-11> High-density polyethylene resin (A-1) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 65% by mass and 35% by mass, respectively. The mixture was melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Comparative Example 1 Preparation of Polyethylene Composition C-12> High-density polyethylene resin (A-1) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 40% by mass and 60% by mass, respectively, and melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Comparative Example 2 Preparation of Polyethylene Composition C-13> High-density polyethylene resin (A-5) and high-pressure low-density polyethylene resin (B-5) were used in an amount of 90% by mass and 10% by mass, respectively, and melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-1).

<Comparative Example 3 Preparation of Polyethylene Composition C-14> High-density polyethylene resin (A-2) and high-pressure low-density polyethylene resin (B-8) were used in an amount of 65% by mass and 35% by mass, respectively, and melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Comparative Example 4 Preparation of Polyethylene Composition C-15> High-density polyethylene resin (A-6) and high-pressure low-density polyethylene resin (B-6) were used in an amount of 85% by mass and 15% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-1), and granulation was performed into pellets.

<Comparative Example 5 Preparation of Polyethylene Composition C-16> High-density polyethylene resin (A-7) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 80% by mass and 20% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-1), and granulation was performed into pellets.

<Comparative Example 6 Preparation of Polyethylene Composition C-17> High-density polyethylene resin (A-8) and high-pressure low-density polyethylene resin (B-3) were used in an amount of 90% by mass and 10% by mass, respectively, and melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Comparative Example 7 Preparation of Polyethylene Composition C-18> High-density polyethylene resin (A-9) and high-pressure low-density polyethylene resin (B-1) were used in an amount of 85% by mass and 15% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-1), and granulation was performed into pellets.

<Comparative Example 8 Preparation of Polyethylene Composition C-19> High-density polyethylene resin (A-1) and high-pressure low-density polyethylene resin (B-7) were used in an amount of 80% by mass and 20% by mass, respectively, and melt-kneaded and granulated into pellets in the same manner as the above-mentioned polyethylene composition (C-2).

<Comparative Example 9 Preparation of Polyethylene Composition C-20> High-density polyethylene resin (A-9) and high-pressure low-density polyethylene resin (B-8) were used in an amount of 80% by mass and 20% by mass, respectively. Melt-kneading was performed in the same manner as the above-mentioned polyethylene composition (C-2) to form granules.

The physical properties and evaluation results of the obtained polyethylene compositions are shown in Tables 3 and 4 below.

[Table 3] Polyethylene composition (C) Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9 C-10 C-11 density kg/m ³ 962 960 951 956 951 958 965 957 953 961 950 MFR g/10 min 11 11 5 5 12 10 13 10 10 18 8 Weight average molecular weight g/mol 119730 116660 193782 201291 67112 110553 88125 110168 113081 121288 117162 Crystallinity % 69 67 65 69 62 66 67 70 67 72 67 Crystallite size nm 24.2 27.1 23.3 30.8 23.5 26.6 29.1 29.2 24.8 25.7 23.4 Temperature-variable WAXS measurement (Y/X) - 0.69 0.61 0.64 0.59 0.57 0.66 0.53 0.48 0.49 0.54 0.55 Relaxation time of low-activity component T _α ms 18.3 15.6 14.2 23.1 9.8 21.4 26.1 19.4 12.6 15.9 7.9 The presence ratio of low-motility components R _α % 48.2 46.7 40.6 43.1 39.6 41.1 50.3 38.7 46.8 47.5 24.8 Total amount of dissolution before 80℃ wt% 12.1 16.8 21.2 9.3 31.5 20.1 5.4 19.3 14.6 9.4 36.2 Stiffness during high temperature processing ◎ ◎ ◎ ◎ ○ ○ ◎ ○ ○ ◎ ○ Residue after high temperature processing ◎ ○ ○ ◎ ○ ○ ◎ ○ ○ ◎ △ Neck ◎ ○ ◎ ○ ◎ ○ △ ○ ○ △ ◎

[Table 4] Polyethylene composition (C) Comparison Example 1 Comparison Example 2 Comparison Example 3 Comparison Example 4 Comparison Example 5 Comparative Example 6 Comparison Example 7 Comparative Example 8 Comparative Example 9 C-12 C-13 C-14 C-15 C-16 C-17 C-18 C-19 C-20 density kg/m ³ 938 962 945 954 953 960 957 958 955 MFR g/10 min 6 12 6 11 15 5 12 7 12 Weight average molecular weight g/mol 150925 83451 148872 100285 65464 157712 111464 127525 110332 Crystallinity % 55 72 59 66 70 71 72 74 76 Crystallite size nm 16.7 34.1 18.9 33.9 31 33.2 34.3 26.3 28.1 Temperature-variable WAXS measurement (Y/X) - 0.21 0.37 0.29 0.31 0.33 0.34 0.41 0.38 0.32 Relaxation time of low-activity component T _α ms 4.4 26.8 18.9 25.6 19.1 21.3 16.6 18.3 14.5 The presence ratio of low-motility components R _α % 24.1 56.3 44.8 55.8 48.6 41.1 29.5 38.7 24.9 Total amount of dissolution before 80℃ wt% 62.8 12.8 35.8 15.2 19.4 21.3 16.7 22.4 21.8 Stiffness during high temperature processing × △ × △ △ ○ △ △ △ Residue after high temperature processing × ○ × △ △ △ ○ △ △ Neck ◎ × ○ △ × × × △ × [Industrial Availability]

The polyethylene composition of the present invention has industrial applicability as a raw material for films that particularly require fisheye quality and heat resistance, such as surface protection films.

Claims (8)

A polyethylene composition that satisfies the following <Condition (A)> to <Condition (D)>: <Condition (A)> The weight average molecular weight measured by gel permeation chromatography (GPC) is 40,000 g/mol or more and 350,000 g/mol or less, <Condition (B)> The crystallinity calculated by wide-angle X-ray scattering (WAXS) is 60% or more and 75% or less, <Condition (C)> The crystallite size of the (110) plane calculated by the above wide-angle X-ray scattering measurement is 17 nm or more and 32 nm or less, <Condition (D)> In the temperature-variable wide-angle X-ray scattering measurement, the ratio of the peak intensity X originating from the (110) plane at 50°C to the peak intensity Y originating from the (110) plane at 130°C: Y/X is greater than 0.40 and less than 0.80. The polyethylene composition of claim 1, wherein in a pulse NMR measurement at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components, the relaxation time _Tα of the low-mobility component α is greater than 5 ms and less than 25 ms, and the abundance ratio _Rα of the low-mobility component α is greater than 25% and less than 55%. The polyethylene composition of claim 1, wherein the mass ratio of the component eluted before 80°C in the temperature rising elution fractionation (TREF) of the cross fractionation chromatography (CFC) is not less than 1 mass % and not more than 35 mass % of the total elution amount. A polyethylene composition as claimed in claim 1, wherein the polyethylene composition is a mixture of a high-density polyethylene (A) having a density of 942 kg/m3 ^or more and a low-density polyethylene (B) having a density of 930 kg/m3 ^or less; in a pulse NMR measurement of the low-density polyethylene (B) at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components, the low-mobility component ratio calculated from the existence ratio _Rα of the low-mobility component α and the existence ratio _Rβ of the intermediate component β by the following (Formula I) is greater than 0.35 and less than 0.55, (low-mobility component ratio) = _Rα /( _Rα + _Rβ )•••(Formula I). A polyethylene composition as claimed in claim 1, wherein the polyethylene composition is a mixture of a high-density polyethylene (A) having a density of 942 kg/m ³ or more and a low-density polyethylene (B) having a density of 930 kg/m ³ or less; in a pulse NMR measurement of the high-density polyethylene (A) at 180°C, when the free induction decay curve obtained by the Carr Purcell Meiboom Gill (CPMG) method is approximated into three components, the low-mobility component ratio calculated from the existence ratio R _α of the low-mobility component α and the existence ratio R _β of the intermediate component β by the following (Formula I) is greater than 0.50 and less than 0.70, (low-mobility component ratio) = R _α /(R _α +R _β )•••(Formula I). The polyethylene composition of claim 4 or 5, wherein the content ratio of the high-density polyethylene (A) is 70 mass % or more and 99 mass % or less, and the content ratio of the low-density polyethylene (B) is 1 mass % or more and 30 mass % or less. A shaped body comprising the polyethylene composition of claim 6. The formed body as claimed in claim 7 is a membrane.