JPS6143378B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyethylene resin composition, and more specifically, the present invention relates to a polyethylene-based resin composition, and more specifically, an ethylene homopolymer having a relatively high molecular weight and a high density of 0.955 or more or a copolymer of ethylene and α-olefin, and a relatively high molecular weight and a high density. A blow molding having improved environmental stress cracking resistance (hereinafter abbreviated as ESCR) made by mixing a low density copolymer of 0.91 to 0.95 ethylene and an α-olefin having 4 or more carbon atoms. and a polyethylene resin composition suitable for extrusion molding. Polyethylene is used in a wide range of applications, but when used in applications such as pipes and bottles, these molded products tend to crack after long periods of use, which poses a major practical problem. There is. This phenomenon is called environmental stress cracking, and is a phenomenon in which cracks occur over a relatively long period of time when the molded product is under stress from the outside or when there is residual strain from the molding process. It is.
Moreover, this limitation may be increased depending on the environmental conditions in which the molded article is used. Methods to improve the ESCR of polyethylene include blending polyethylene with rubbers such as natural rubber, SBR, butyl rubber, and ERR, polybutene-1, polycarbonate, ethylene-vinyl acetate copolymer, and low molecular weight and low melting point. A method of blending paraffin wax has been proposed. However, these methods are not practically satisfactory for resin compositions for blow molding and extrusion molding in some or all of the following respects. (1) ESCR is still not practically satisfactory. (2) Mechanical properties of the molded product, where the rigidity decreases. (3) The mixture is eluted in certain solvents at low temperatures. (4) The materials to be mixed are expensive and economically disadvantageous. Additionally, as mentioned above, methods for improving the ESCR of polyethylene without mixing other polymers include copolymerizing ethylene with α-olefins such as proprene and butene-1 to lower the density. methods of increasing molecular weight (i.e. generally decreasing melt index);
Modification methods such as grafting and crosslinking are known. However, these methods may not be practical depending on the application due to insufficient ESCR, decreased mechanical properties, or decreased fluidity during molding. There are many. In recent years, as the uses and demands for polyethylene have increased, even higher performance has been required, and the required performance also differs depending on the use. The physical properties required for polyethylene for blow molding and extrusion molding include good ESCR, high density and excellent mechanical properties, especially high rigidity, good processing characteristics, and a certain level of quality. can give. Generally, the ESCR of polyethylene is better as the density is lower, or as the melt index is lower and the molecular weight is higher. However, when the density is lowered, mechanical strength such as rigidity decreases. On the other hand, when the melt index is decreased (the molecular weight is increased), the fluidity during processing deteriorates and processing becomes extremely difficult. Therefore, improving the ESCR and improving the processing properties, especially the fluidity during processing, are contradictory to each other. The present inventors have conducted various studies to solve the above-mentioned difficult problems and obtain a polyethylene resin composition suitable for blow molding and extrusion molding. (A) α having ethylene and 4 or more carbon atoms - Olefin is polymerized in the presence of hydrogen and a catalyst system containing at least one of a chromium compound and a titanium compound, and the density is 0.91 to 0.91, obtained without substantially removing the catalyst and the low molecular weight polymer.
0.95, the number of branches per 1000 skeletal carbon atoms is 2 or more, and the ratio of this to the number of branches per 1000 skeletal carbon atoms in the boiling cyclohexane extraction residue is 1:
Branching degree distribution ranges from 1 to 1:01 at 130℃
A catalyst containing 10 to 65% by weight of an ethylene copolymer having an intrinsic viscosity of 2.5 to 8.2 as measured in tetralin, and (B) ethylene alone or ethylene and α-olefin, and at least one of a chromium compound and a titanium compound. Ethylene polymers having a density greater than 0.955 and an intrinsic viscosity of less than or equal to 1.7, measured in tetralin at 130° C., obtained by polymerization in the presence of a system and hydrogen without substantially removing the catalyst and the low molecular weight polymer. A polyethylene resin composition with a melt index of 0.05 to 2.0 and a density of 0.930 to 0.960, which is made by mixing 35% by weight, has a good balance of ESCR, density and processability, and is suitable for blow molding and extrusion molding. It was discovered that it is extremely suitable as a polyethylene resin composition, and the present invention was achieved. The content of the present invention will be explained in more detail below. The present inventors previously proposed an accurate and reproducible ESCR evaluation method and device (Japanese Patent Application Laid-open No. 109988/1983).
The present inventors conducted various studies on the ESCR of olefin polymers and olefin polymer compositions according to Example 1 of JP-A-52-109988, and found the following fact. 1. When two types of olefin polymers exhibiting mutually different ESCRs are mixed, the ESCR has additivity. For example, as shown in Figure 1, polyethylene A (melt index 0.53, density 0.944,
ESCR F ₅₀ 202) and polyethylene B (melt index 8.1, density 0.962, ESCR F ₅₀ 8.4), the F ₅₀ value of the mixture (time until 50% of 10 test samples break) in,
The logarithm of ), which is an indicator of ESCR quality, corresponds to the sum of the products of the logarithm of the F ₅₀ value of each component and its weight percentage. 2 In the case of olefin polymer alone, ethylene and α
-The ESCR of copolymers with olefins is better than that of ethylene homopolymers with the same molecular weight. Furthermore, the ESCR of a copolymer of ethylene and α-olefin differs depending on the type of comonomer used even if the molecular weight and density are the same, and the comonomer with a larger carbon number improves the ESCR of the copolymer. For example, as shown in Table 1, when comparing ethylene/propylene copolymer, ethylene/butene-1 copolymer, and ethylene/hexene-1 copolymer, which have almost the same intrinsic viscosity and density,
ESCR is an ethylene/propylene copolymer,
Ethylene/butene-1 copolymer, ethylene/
Hexene-1 copolymer is the best. That is, when α-olefins such as butene-1 and hexene-1 having 4 or more carbon atoms are used as comonomers, the polyethylene copolymer
ESCR will be dramatically improved. However, when the comonomer is propylene, the improvement rate is small.

[Table] 3 The copolymer of ethylene and α-olefin is
The higher the molecular weight, the better the ESCR. For example, as shown in Figure 2, a low molecular weight copolymer can be produced even if the degree of branching (the number of branches per 1000 carbon atoms, which usually corresponds to the proportion of comonomer in the copolymer) is increased. The effect of improving ESCR from a homopolymer with a degree of branching of 0 is small, and on the contrary, the ESCR of a high molecular weight copolymer is dramatically improved even if the degree of branching is small. In addition, short chain branching is measured by infrared absorption spectroscopy.
Using the absorption at 4255 cm ^-1 as an internal standard ^, it was measured by the method of Willborn [A. Etsuchi. AHWillbourn, Journal of Bolimar Science
Polymer Science) Volume 34, Page 569, (1959
year). In addition, those with an F ₅₀ of 1000 hours or more, which is an indicator of ESCR quality, are mixed with polyethylene with an F ₅₀ of 8.4 hours, and calculated from the F ₅₀ of the mixture according to the additivity described above. It is. 4 Closely related to the fact in 3, the distribution of short chain branches with respect to molecular weight (branching degree distribution) has a close relationship with ESCR, and the olefin copolymer with more branches in the high molecular weight part has a higher ESCR. is in good condition.

[Table] For example, as shown in Table 2, ethylene/butene-1 copolymer B has many branches in the low molecular weight part extracted with boiling cyclohexane and has few branches in the extraction residue. Ethylene/butene-1
ESCR is poor compared to copolymer A. Also, Table 2
Copolymers A and B shown in 1 were subjected to molecular weight fractionation using a column fractionation method, and the distribution of the degree of branching (branching degree distribution) with respect to the molecular weight was determined. The detailed method of column separation can be found in J. Etsuchi. Eliot (JH
Elliot) in “Polymer Fractionation” edited by MJRCantow 67~
93 pages [Academic Press (Academic
Press). [Published in 1967], but the method will be briefly described below. Approximately 5 g of a sample is deposited on Celite 545 as a carrier in xylene, and then packed into a column. Then, heat the column to 120℃
The mixture is heated to , and allowed to flow down the column while changing the mixing ratio of butyl cellulose xylene to separate the low molecular weight fraction to the high molecular weight fraction. After adding methanol to the effluent and collecting the precipitated polymer,
Dry under reduced pressure and separate. The molecular weight (M) of the obtained fractionated fraction is calculated from the limiting viscosity ([η]) measured in tetralin at 130°C using the following formula. [η]=4.71×10 ^-4 M ^0.71 The degree of branching of the fractionated sections was determined by the above-mentioned infrared absorption spectroscopy. Copolymers A and B of ethylene and butene-1 obtained in this way
Figure 3 shows the branching degree distribution of . Figure 3 shows that copolymer A with good ESCR has a uniform branching degree distribution, and there are many branches even in the molecular weight portion of 100,000 or more.
Copolymer B with poor ESCR has a nonuniform distribution of branching degrees, and shows that there is almost no branching in the molecular weight part of 100,000 or more, and the branches in the high molecular weight part are
This shows that ESCR is dramatically improved. The present invention was achieved based on the above findings, and the high molecular weight and low density ethylene copolymer (hereinafter abbreviated as component A) used in the present invention is composed of ethylene and 4 or more carbon atoms. A copolymer with α-olefin having a density of 0.91 to 0.95 is preferable. In addition, producing an ethylene copolymer with too large a molecular weight will cause it to gel easily and be difficult to mix with other polyolefins, so the intrinsic viscosity will be 2.5~2.5.
Preferably 8.2, more preferably 3.0
~6.5. When an ethylene copolymer produced without hydrogen is mixed with another polyolefin in the presence of a catalyst system that further includes at least one of a chromium compound and a titanium compound, the composition
It shows too large a balancing effect, and when used for blow molding and extrusion molding, it has poor processability, such as poor high-speed processability and difficulty in parison control, making it difficult to obtain complex shapes. Preferred is a copolymer of In addition, copolymers with uneven branching degree distribution are
It is undesirable because it contains a large number of branches in the low molecular weight portion, which is less effective in improving ESCR, and undesirably lowers the density. Therefore, it has two or more branches per 1000 skeletal carbon atoms, and the ratio of this to the number of branches per 1000 skeletal carbon atoms in the boiling cyclohexane extraction residue is preferably from 1:1 to 1:0.1. More preferably, one having a branch distribution in the range of 1:1 to 1:0.5 is used. Such copolymers are made by combining ethylene and α-olefins such as butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, etc. as catalysts in medium pressure or low pressure processes, especially up to high molecular weight components. It is obtained by copolymerizing in the presence of a carrier-supported catalyst that copolymerizes uniformly and hydrogen. Examples of such catalyst systems include so-called Phillips type catalysts and Ziegler type catalysts. Specifically, catalysts whose main component is silica or silica alumina supported with 0.5 to 6% by weight of chromium oxide; Catalyst supported on a magnesium compound such as alkoxide or magnesium hydroxide, or whose main components are a reaction product of these and an organic aluminum compound such as triethylaluminum or triisobutylaluminum; titanium tetrachloride and metal aluminum Catalysts whose main components are a reaction product with an organic aluminum compound and the like can be mentioned. On the other hand, the low molecular weight and high density ethylene polymer (hereinafter referred to as component B) used as another component in the present invention is obtained by combining ethylene alone or ethylene and α-olefin with a chromium compound and a titanium compound. It can be produced by polymerizing in the presence of a catalyst system containing at least one of the above and hydrogen by a generally well-known medium pressure method or low pressure method. This component B preferably has a density of 0.955 or more and an intrinsic viscosity of 1.7 or less. More preferably, the density is 0.960 or more, and the intrinsic viscosity is
1.5 or less. When the density is less than 0.955, the density of the composition becomes low and a good composition with high mechanical strength such as rigidity cannot be obtained. Furthermore, if the intrinsic viscosity is 1.7 or more, a composition with good fluidity during processing cannot be obtained. Therefore, the polyethylene resin composition of the present invention obtained by mixing such component A and component B,
For use in blow molding and extrusion molding,
The melt index measured by JISK-6760 is preferably in the range of 0.05 to 2.0, and the density is preferably in the range of 0.930 to 0.960.
More preferably, it is in the range of 0.940 to 0.960. In the present invention, there are no particular restrictions on the mixing method for producing the polyethylene resin composition, including a method in which component A and component B are produced independently and then mixed in a kneader, and a method in which one component is polymerized. Various mixing methods that provide a uniform composition can be arbitrarily used, such as a method in which other components are subsequently polymerized using the same catalyst and mixed in a reactor (two-stage polymerization method). The mixing ratio and combination of component A and component B are closely related to the ESCR, density and processability of the composition, and in particular, the density is roughly expressed by the following equation and is proportional to the mixing ratio. 1/d=1/d _A W _A +1/d _B W _B (where d, d _A , and d _B represent the densities of the composition, component A, and component B, respectively; W _A and W _B are Each represents the weight fraction of component A and component B. 1=W
_A + W _B. ) Therefore, regarding the mixing ratio of component A and component B, it is preferable that component A, which has a large intrinsic viscosity, accounts for 100 to 65% by weight of the entire composition, and the difference in density between component A and component B is 0.01 or more. , more preferably 0.02 or more, and the intrinsic viscosity of component A is equal to that of component B.
Suitable combinations are 1.5 times or more, preferably 2 times or more. The polyethylene resin composition of the present invention obtained in this way has excellent ESCR when subjected to blow molding and extrusion molding, so there is no risk of environmental stress fracture, and furthermore, since it has a high density,
It has high mechanical strength, particularly excellent rigidity, and allows molded products to be made thinner. Furthermore, since the resin composition of the present invention has a wide molecular weight distribution,
Good fluidity during processing. That is, a high extrusion amount can be obtained at low pressure, and there is no fear that roughening will occur on the surface of the molded product even when processed at high extrusion speed. The compositions of the invention include antioxidants, antistatic agents,
Conventional additives such as UV absorbers, color pigments, and lubricants can be added. Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist of the present invention is exceeded. In the Examples and Comparative Examples, the flow rate ratio is the flow rate when a load of 21.60 kg is applied and the flow rate when a load of 2.16 kg is applied according to the melt index measurement method specified in JIS K-6760. is defined as the ratio of the outflow of This outflow ratio is an index representing the pressure dependence of flow; when this value is large, fluidity at high pressures is excellent and melt fracture does not occur even at high shear rates. Furthermore, the swelling ratio is expressed as the ratio of the diameter of the extruded strand to the diameter of the orifice when measuring the melt index, and is an index of the balance effect. ESCR's
_F50 was measured by the method and apparatus described in Example 1 of JP-A-52-109988, and was approximately 2.8 of the value determined by the bent-stop method specified in ASTM D-1693-70. Indicates the double value. Example 1 20 g of anhydrous magnesium chloride and 6 g of benzoyl chloride were co-milled in a vibrating ball mill. 15 g of the obtained co-pulverized material was placed in a 500 ml flask, and a solution obtained by previously mixing and reacting 125 ml of toluene, 86.3 g of titanium tetrachloride, and 12.4 g of dimethyldimethoxysilane at room temperature was added. The co-pulverized product and the mixed reaction solution were mixed at a temperature of 65°C.
Stir and mix for hours. The obtained solid product was filtered,
After washing with toluene, a powdery catalyst component was obtained by drying at 40° C. under reduced pressure. 20.1 mg of this catalyst component, 0.54 g of triethylaluminum, 1
Kg of isobutane, 0.09 g of hydrogen and 18.2 g of butene-1 were charged to 3 autoclaves. The autoclave was heated to 85°C, and polymerization was carried out for 30 minutes while maintaining the partial pressure of ethylene at 10 kg/cm ² . After the polymerization was completed, the monomer and solvent were removed by distillation under heating, and the sample was used as it was without removing the catalyst and low-molecular components. Similar treatments were carried out in the following Examples and Comparative Examples. The copolymer of ethylene and butene-1 thus obtained has an intrinsic viscosity of
6.2, density is 0.915, degree of branching is 14.8/1000℃, degree of branching of boiling cyclohexane extraction residue is 13.5/
1000C, and the ratio was 1:0.91. On the other hand, without using butene-1, 0.31g of hydrogen
Homopolymerization of ethylene was carried out in the same manner as above, except that the amount of ethylene was increased. The polyethylene thus obtained had an intrinsic viscosity of 1.2 and a density of 0.962. 25% by weight of the copolymer of ethylene and butene-1 thus obtained and 75% by weight of polyethylene
The mixture was mixed by roll kneading at 145°C for 10 minutes. When the physical properties of the obtained polyethylene resin composition were measured, the results shown in Table 3 were obtained. Table 3 Melt index 0.22 Outflow ratio 103 Swelling ratio 1.31 Density 0.950 ESCR (F ₅₀ ) Example 2 Silica without being destroyed in 2000 hours. Chromium oxide-silica prepared by supporting 1% by weight of chromium oxide on an alumina support and activating it in air at 700°C for 10 hours. Alumina catalyst 105
mg, 500 g of isobutane, 28.8 g of hexene-1,
Charge 0.15g of hydrogen into a 1.5 autoclave.
The temperature was raised to 90℃. Thereafter, polymerization was carried out for 1 hour while maintaining the partial pressure of ethylene at 23 kg/cm ² . The thus obtained copolymer of ethylene and hexene-1 has an intrinsic viscosity of 3.9 and a density of
The amount of branching was 0.928 g/cm ³ , the degree of branching was 8.1 pieces/1000C, and the degree of branching of the boiling cyclohexane extraction residue was 7.5 pieces/1000C, and the ratio was 1:0.92. On the other hand, silica.
232 mg of a chromium oxide-silica alumina catalyst supported on an alumina carrier with 2% by weight of chromium oxide and activated at 850° C. for 10 hours in air, 1 kg of cyclohexane, and 0.35 g of hydrogen were charged into an autoclave No. 3. Then, the temperature was raised to 160℃, and the temperature was increased to 350℃.
g of ethylene was injected under pressure while maintaining its partial pressure at 10 kg/cm ² to carry out polymerization. The polyethylene thus obtained has an intrinsic viscosity of
0.78, and the density was 0.970. Thus obtained, 36% by weight of copolymer of ethylene and hexene-1 and 64% by weight of ethylene homopolymer.
and were mixed by roll kneading at 145°C for 10 minutes. The physical properties of this polyethylene resin composition were measured and the results shown in Table 4 were obtained. Table 4 Melt index 0.11 Outflow ratio 179 Swelling ratio 1.62 Density 0.954 FSCR F ₅₀ 285 Comparative example 1 Homopolymerization of ethylene and copolymerization of ethylene and propylene in the presence of hydrogen using the same catalyst and equipment as used in Example 1. I did this. The intrinsic viscosity of the obtained polyethylene was 6.3. Also, the intrinsic viscosity of ethylene/propylene copolymer is
7.6, and the density was 0.917. This polyethylene 25
Weight %, intrinsic viscosity 1.2 and density used in Example 1
Composition A was obtained by roll kneading and mixing 75% by weight of 0.962 polyethylene at 145°C. Similarly, 25% by weight of the above ethylene/propylene copolymer and Example 1
Polyethylene with an intrinsic viscosity of 1.2 and a density of 0.962 used in
Composition B was obtained by mixing 75% by weight. These physical properties were measured and the results shown in Table 5 were obtained.

[Table] Comparative Example 2 Copolymerization of ethylene and butene-1 was carried out in the absence of hydrogen using the same catalyst and equipment as used in Example 1. The intrinsic viscosity of the obtained copolymer was 11.5,
The density was 0.911. 15% by weight of this copolymer and 85% by weight of the polyethylene having an intrinsic viscosity of 1.2 and a density of 0.962 used in Example 1 were roll-kneaded at 145°C for 10 minutes. The resulting composition has a melt index of
3.3, the ESCR (F ₅₀ ) was 3 hours, indicating that the mixing was not intense. Comparative Example 3 Titanium tetrachloride, triethylaluminum and isobutane were charged into the autoclave in step 3,
The temperature was raised to 85°C, and ethylene, butene-1, and hydrogen were pressurized to a total pressure of 26 kg/cm ² to carry out polymerization. The ethylene/butene-1 copolymer thus obtained has an intrinsic viscosity of 6.5, a density of 0.921, and a degree of branching.
19.8 pieces/1000C, the degree of branching of the boiling cyclohexane extraction residue was 1.6, and the ratio was 1:0.08. Intrinsic viscosity used in Example 1 with 25% by weight of this copolymer
1.2, 75% by weight of polyethylene having a density of 0.962 was mixed in the same manner as in Example 1. This composition was measured and the results shown in Table 6 were obtained. Table 6 Melt index 0.19 Outflow ratio 110 Swelling ratio 1.30 Density 0.951 ESCR F ₅₀ 41 As shown above, even if the composition has a different distribution of the degree of branching and the conditions are the same as in Example 1, the ESCR
It can be seen that there is a large difference in Examples 3 to 9 A co-pulverized product obtained by co-pulverizing anhydrous magnesium chloride and trichloroacetyl chloride was reacted with a reaction product of titanium tetrachloride and tetraethoxylan in toluene to obtain a catalyst component. Ethylene copolymerization was carried out in the same manner as in Example 1 using this catalyst and triethylaluminum as cocatalysts.
However, the comonomers used were changed as shown in Table 7.

[Table] Intrinsic viscosity of each copolymer in Table 7 and used in Example 2
Polyethylene with a density of 0.78 and 0.970 was mixed using a roll in the proportions shown in Table 8. When the physical properties of each of the obtained compositions were measured, the results shown in Table 8 were obtained.

【table】 [Brief explanation of the drawing]

Figure 1 shows that when polyethylene A and polyethylene B having different ESCRs are mixed,
This is a diagram showing an example where ESCR has additivity, and Figure 2
is a diagram showing the relationship between the degree of branching and ESCR due to differences in the molecular weight of ethylene copolymers, and Figure 3 shows the relationship between the molecular weight and ESCR of ethylene and butene-1 copolymers with different ESCR.
It is a relationship diagram of ESCR.

Claims (1)

[Claims] 1 (A) α having ethylene and 4 or more carbon atoms
-Olefin is polymerized in the presence of hydrogen and a catalyst containing at least one of a chromium compound and a titanium compound, and the catalyst and low molecular weight polymer are substantially removed, and the density is 0.91 to 0.95 g/ cm ³ , the number of branches per 1000 skeletal carbon atoms is 2 or more, and the ratio of this to the number of branches per 1000 skeletal carbon atoms in the boiling cyclohexane extraction residue is 1:1 to 1:0.1. (B) 10 to 65% by weight of an ethylene copolymer with a branching degree distribution in the range of 2.5 to 8.2 dl/g and an intrinsic viscosity measured in tetralin at 130°C; (B) ethylene alone or ethylene and α-olefin; is polymerized in the presence of hydrogen and a catalyst system comprising at least one of a chromium compound and a titanium compound, and the density is obtained without substantially removing the catalyst and the low molecular weight polymer.
A melt index of 0.05 to 2.0 g/10 made by mixing 90 to 35% by weight of an ethylene polymer larger than 0.955 g/cm ³ and having an intrinsic viscosity of 1.7 g/g or less when measured in tetralin at 130°C. minute, the density is
A polyethylene resin composition suitable for blow molding and extrusion molding that has excellent environmental stress cracking resistance of 0.930 to 0.960 g/cm ³ .