JP2014234403A - Polyethylene resin composition and blow-molded body comprising the same - Google Patents

Abstract

A polyethylene resin composition excellent in transparency, heat resistance, and blow moldability is provided. A crystalline polymer block (hard segment) mainly composed of ethylene satisfying specific requirements and at least one α-olefin selected from α-olefins having 3 to 30 carbon atoms and ethylene. An olefin block copolymer [A] containing an amorphous polymer block (soft segment) and a high-density polyethylene [B] satisfying specific requirements, wherein [A] / [B] (weight ratio) is 99 Polyethylene resin composition characterized by being 5 / 0.5 to 70/30. [Selection figure] None

Description

  The present invention relates to a polyethylene resin composition excellent in transparency and heat resistance and a blow molded article comprising the same.

  In recent years, a material having excellent transparency for observing contents as a medical container has been desired. As materials, polyethylene, crosslinked polyethylene, polypropylene and the like are distributed.

  In general, high-density polyethylene has remarkably poor transparency, and the thickness has to be extremely reduced in order to observe the contents. However, the problem that load resistance is inferior when the thickness is reduced is inevitable.

  Moreover, although the low density polyethylene has good transparency, the melting point is lowered, so the problem of poor heat resistance is inevitable.

  In recent years, due to an increase in awareness regarding safety and hygiene, sterilization tends to be performed at a higher temperature, and a material having higher heat resistance is desired as a container material. When sterilization is performed at 121 ° C. or higher, polypropylene having excellent heat resistance and transparency is used, but there are problems in flexibility and low temperature impact. On the other hand, for the purpose of improving the heat resistance of low density polyethylene, an attempt has been made with a polyethylene composition comprising an ethylene / α-olefin copolymer, a low density polyethylene by a high pressure radical polymerization method, or a mixture thereof (see Patent Documents 1 and 2). However, the physical properties required for pharmaceutical containers have not been satisfied.

  In addition, radiation cross-linking is carried out for the purpose of improving heat resistance. However, when installing cross-linking equipment, it is not only expensive, but also costs are incurred for safety measures and maintenance when using the equipment. It was a problem.

JP-A-3-168231 JP-A-3-29659

  An object of the present invention is to provide a pharmaceutical container that does not deform even when subjected to high-temperature heat sterilization, and that is excellent in flexibility and transparency.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have processed a specific olefin block copolymer [A] by blending a specific high density polyethylene (hereinafter referred to as HDPE) [B]. An unprecedented suitable polyethylene resin composition having excellent properties, high transparency, and excellent heat resistance was obtained, and the present invention was completed.

That is, the present invention is an amorphous material mainly composed of at least one α-olefin selected from a crystalline polymer block (hard segment) mainly composed of ethylene and an α-olefin having 3 to 30 carbon atoms and ethylene. An olefin block copolymer [A] containing the following polymer blocks (soft segments) and satisfying the following requirements (a) to (d) and a high density polyethylene [B] satisfying the following requirements (e) to (h): In addition, the present invention relates to a polyethylene resin composition [I] having an [A] / [B] (weight ratio) of 99.5 / 0.5 to 70/30.
(A) Density measured according to JIS K 7112: 1999 is 870 to 900 kg / m ³
(B) Measured according to JIS K 7210: 1999 under a load of 190 ° C. and 21.18 N. Melt flow rate (MFR) is 0.1 to 100 g / 10 min (c) Ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) is 2.0 to 3.0
(D) In a differential scanning calorimeter, the endothermic curve obtained when melting at 220 ° C. for 5 minutes and then cooling to −40 ° C. at 10 ° C./min is substantially increased at 10 ° C./min. The crystal melting peak temperature (Tm (° C.)) is 121 ° C. or higher (e) The density measured in accordance with JIS K 7112: 1999 is 935 kg / m ³ or higher (f) JIS K7210: Melt flow rate (MFR) measured under a load of 190 ° C. and 21.18 N measured in accordance with K7210: 1999 is 0.01 to 1.0 g / 10 min (g) Weight average molecular weight (Mw) and number average molecular weight The ratio (Mw / Mn) of (Mn) is 6.0-30.
(H) Melt tension is 2.0-40 cN

  The polyethylene resin composition [I] of the present invention is excellent in heat resistance, transparency, flexibility and the like, and is suitably used as a blow molded pharmaceutical container.

  The present invention is described in detail below.

  The olefin block copolymer [A] constituting the polyethylene resin composition [I] of the present invention comprises a crystalline polymer block (hard segment) mainly composed of ethylene and an α-olefin having 3 to 30 carbon atoms. An olefin block copolymer comprising at least one selected α-olefin and ethylene, and preferably an amorphous polymer block (soft segment) in which the proportion of the latter ethylene is less than that of the hard segment, It is a multiblock copolymer in which two or more, preferably three or more blocks are connected alternately.

  The olefin block copolymer [A] is a block copolymer different from an ethylene / α-olefin random copolymer conventionally synthesized using a general metallocene catalyst or the like as an α-olefin copolymer with ethylene. is there. A block copolymer obtained by hydrogenating a block copolymer of butadiene (for example, Dynalon CEBC manufactured by JSR) is a polyethylene block (hard segment) that is a hydrogenated product of 1,4-polybutadiene block and ethylene. However, the olefin block copolymer [A] is essentially different from this. The olefin block copolymer [A] is a multi-block copolymer in which a crystalline hard segment and an amorphous soft segment are precisely controlled. When the block copolymer obtained by hydrogenation is used, Compared with various properties such as heat resistance.

  The hard segment of the olefin block copolymer [A] in the present invention is a crystalline polymer block mainly composed of ethylene. A hard segment refers to a block of polymerized units in which ethylene is present in an amount ranging from about 60% to about 95% by weight, preferably from about 70% to about 85% by weight, based on the weight of the polymer. Crystallinity refers to a polymer having a primary transition point or crystalline melting point (Tm) measured by differential scanning calorimetry (DSC) or equivalent technique.

  The soft segment of the olefin block copolymer [A] in the present invention is an amorphous polymer block mainly composed of at least one α-olefin selected from α-olefins having 3 to 30 carbon atoms and ethylene. . A soft segment is a comonomer content (content of monomers other than ethylene) in the range of about 30% to about 80% by weight, preferably about 35% to about 80% by weight, based on the weight of the polymer. Refers to a block of polymer units. Amorphous refers to a polymer that lacks a crystalline melting point as measured by differential scanning calorimetry (DSC) or equivalent technique.

  The latter is preferably an amorphous polymer block in which the proportion of ethylene is less than that of the hard segment.

  As an alpha olefin which comprises the soft segment of the olefin block copolymer [A] in this invention, C3-C30, Preferably it is C4-C20, More preferably, it is C4-C8 linear or or Branched α-olefins such as propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1- Examples include octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadedecene, 1-octadecene, 1-eicocene. Among them, the case where 1-octene is mainly used is most preferable from the viewpoint of compatibility.

  As an optimal structure of the olefin block copolymer [A] in the present invention, the hard segment is a crystalline block containing 1-octene mainly composed of ethylene, and the soft segment has a higher 1-octene content ratio than the hard segment. 1) An amorphous block mainly composed of 1-octene and ethylene, and each block has a multi-block structure in which 2 or more, preferably 3 or more are alternately connected.

In the olefin block copolymer [A] in the present invention, the ethylene content is preferably 25 to 97%, more preferably 40 to 96%, and even more preferably 55 to 95%.
Moreover, in the olefin block copolymer [A] in this invention, a density (measured based on JISK7112: 1999) is 870-900 kg / m < ³ >, Preferably it is 875-895 kg / m < ³ >. From the viewpoint of transparency and heat resistance.

  In the olefin block copolymer [A] in the present invention, the melt flow rate (based on JIS K 7210: 1999, measurement temperature: 190 ° C., load: 21.18 N) is 0.1 to 100 g / 10 min. In terms of blow moldability, it is preferably 0.3 to 30 g / 10 min.

  In the olefin block copolymer [A] in the present invention, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined from gel permeation chromatography (GPC) is 2.0. It is -3.0, Preferably it is 2.3-2.7 from the point of blow moldability.

  In the olefin block copolymer [A] in the present invention, the melting point by DSC is preferably 121 ° C. or higher, more preferably 125 ° C. or higher, from the viewpoint of heat resistance.

  Here, the melting point by DSC is obtained when a differential scanning calorimeter is melted at 220 ° C. for 5 minutes and then cooled to −40 ° C. at 10 ° C./min and then heated again at 10 ° C./min. The endothermic curve has a substantially single peak and is the peak temperature of crystal melting observed (Tm (° C.)).

  The olefin block copolymer [A] can typically be synthesized using the catalyst composition disclosed in JP-T-2007-529617. For example, (C) a first olefin polymerization catalyst and (D) a second polymer capable of preparing a polymer that differs in chemical or physical properties from the polymer prepared by catalyst (C) under equivalent polymerization conditions. A composition comprising a mixture or reaction product obtained by combining an olefin polymerization catalyst and (E) a chain transfer agent is prepared, and the ethylene and α-olefin are contacted with the composition under addition polymerization conditions. It can manufacture through the process of making it.

  For the polymerization, a continuous solution polymerization method is preferably applied. In continuous solution polymerization, catalyst components, chain transfer agents, monomers, and optionally solvents, adjuvants, scavengers and polymerization aids are continuously fed to the reaction zone from which the polymer product is continuously removed. It is. The length of the block can be changed by controlling the ratio and type of the catalyst, the ratio and type of the chain transfer agent, the polymerization temperature, and the like.

  Detailed conditions in the production of the olefin block copolymer [A] can typically be set according to various conditions disclosed in JP-T-2007-529617.

  The olefin block copolymer [A] is commercially available, for example, from Dow Chemical Company under the trade names INFUSE D9000, D9007, D9100, D9107, D9500, D9507, D9530, D9817, D9807, and the like.

  The high-density polyethylene [B] constituting the polyethylene resin composition [I] of the present invention is HDPE produced using a Ziegler catalyst, and commercially available products can be used.

In the high density polyethylene [B] constituting the polyethylene resin composition [I] of the present invention, the density (measured in accordance with JIS K 7112: 1999) is 935 kg / m ³ or more. When the density is less than 935 kg / m ³ , the molded body has low rigidity and it is difficult to maintain the strength of the thin product. Moreover, it is inferior in heat resistance, and cannot be sterilized at a high temperature.

  In the high density polyethylene [B] in the present invention, the melt flow rate (based on JIS K 7210: 1999, measurement temperature: 190 ° C., load: 21.18 N) is 0.01 to 1.0 g / 10 min. . When the MFR is less than 0.01 g / 10 min, the resin pressure increases during molding and the resin temperature tends to increase. There is also a problem that the skin surface of the molded product is not smooth. On the other hand, if the MFR exceeds 1.0 g / 10 min, the uneven thickness increases, for example, the drawdown is large and the thicknesses of the upper and lower parts of the product are different.

  In the high density polyethylene [B] in the present invention, the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined from gel permeation chromatography (GPC) is 6.0 to 30. . If Mw / Mn is less than 6.0, the surface of the molded body tends to be rough. When Mw / Mn exceeds 30, the pinch-off strength and the weld strength tend to decrease.

  In the high-density polyethylene [B] in the present invention, the melt tension is 2.0 to 40 cN. When the melt tension is less than 2.0 cN, the drawdown property tends to be lowered, and when it exceeds 40 cN, uniform stretching becomes difficult, and the resin pressure and the resin temperature tend to increase.

  The polyethylene resin composition [I] of the present invention has an olefin block copolymer [A] / high-density polyethylene [B] (weight ratio) of 99.5 / 0.5 to 70/30. When the weight ratio of the high density polyethylene [B] is less than 0.5, the molding processability is inferior, and when it exceeds 30, the transparency deteriorates.

  The haze (measured according to JIS K7105) of the polyethylene resin composition [I] of the present invention is preferably 30% or less at which transparency is good.

  In the polyethylene resin composition [I] of the present invention, the melting point by DSC is preferably 121 ° C. or higher, more preferably 125 ° C. or higher, from the viewpoint of heat resistance.

  Here, the melting point by DSC is obtained when a differential scanning calorimeter is melted at 220 ° C. for 5 minutes and then cooled to −40 ° C. at 10 ° C./min and then heated again at 10 ° C./min. The endothermic curve has a substantially single peak and is the peak temperature of crystal melting observed (Tm (° C.)).

  The polyethylene resin composition [I] of the present invention can be obtained by mixing [A] and [B] by an arbitrary method. As a mixing method, a single-screw or twin-screw extruder, an open roll mill, a Banbury mixer, a kneader, a kneader ruder, a method of mixing under mechanical mixing conditions, a method of dry blending to mix at the time of container molding, etc. are adopted. be able to.

  The polyethylene resin composition [I] of the present invention is added with additives usually used for polyolefins, such as antioxidants, weathering stabilizers, antistatic agents, lubricants, antiblocking agents, and organic / inorganic pigments, as necessary. It doesn't matter. The method of mixing the above-mentioned additives in the resin composition is not particularly limited, but for example, a method of adding to [A], [B] constituting the polyethylene resin composition [I], For example, a high concentration master batch is prepared in advance, and this is dry blended during molding.

  The method for molding the polyethylene resin composition [I] of the present invention is not particularly limited and may be a generally known method, for example, water-cooled or air-cooled inflation molding, blow molding, tube molding, rotational molding, injection molding, injection blow. Examples of the molding method include molding, and blow molding and injection blow molding are preferred. Moreover, you may shape | mold a container by a single layer or a multilayer using these shaping | molding methods.

  Examples of the use of the blow molded article of the polyethylene resin composition [I] of the present invention include a medical container, an optical film, and the like, preferably a medical container. As a medical container, it is suitably used for a blood bag, a blood collection container, a blood product container, an infusion container, an infusion set, an eye drop container, an internal use container, a urine bag, an external liquid container, and the like.

  Examples of the sterilization method of the polyethylene resin composition [I] of the present invention include a high pressure steam method (autoclave), a heat sterilization method such as a dry heat method, an irradiation method such as a radiation method and a high frequency method, a gas method, and a filtration method. Can be mentioned. In particular, the sterilization temperature during high-pressure steam sterilization is preferably 115 to 121 ° C. from the balance between heat resistance and transparency. After containing the chemical solution, it is preferable to perform sterilization at 115 to 121 ° C.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
The materials used are shown below.

Olefin block copolymer [A];
Ingredient (A-1): INFUSE D9530 (product of Dow Chemical Company)
(A block copolymer composed of (alternately) blocks made of ethylene (crystalline hard segments) and blocks made of 1-octene and ethylene (amorphous soft segments). MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 5.3 g / 10 min, density (JIS K 7112) 887 kg / m ³ , melting point 122 ° C.)
Ingredient (A-2): INFUSE D9500 (product of Dow Chemical Company)
(A block copolymer composed of (alternately) blocks made of ethylene (crystalline hard segments) and blocks made of 1-octene and ethylene (amorphous soft segments). MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 4.5 g / 10 min, density (JIS K 7112) 877 kg / m ³ , melting point 123 ° C.)
Ingredient for comparison (A-3): Engage EG8100 (product of Dow Chemical Company)
(Metalocene-catalyzed LLDPE elastomer (random copolymer of ethylene and octene-1). MFR (JIS K 7210: 1999, 190 ° C., load 2.16 kg): 1.0 g / 10 min, density 872 kg / m ³ (ASTM D −792), melting point 58 ° C.)
Component for comparison (A-4): Dynalon DR6201B (manufactured by JSR)
(Ethylene-ethylene-butene-ethylene block copolymer (CEBC). Styrene content 0% by weight, MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 0.5 g / 10 min, density (JIS K 7112) 880 kg / m ³ , melting point peak not observed)
High density polyethylene [B];
Ingredient (B-1): Nipolon Hard, Grade: 8600A (manufactured by Tosoh Corporation)
(MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 0.03 g / 10 min, density (JIS K 7112) 950 kg / m ³ , Mn / Mn 16.1, melt tension 17 cN)
Ingredient for comparison (B-2): Nipolon hard, Grade: 2000 (manufactured by Tosoh Corporation)
(MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 15 g / 10 min, density (JIS K 7112) 960 kg / m ³ , Mn / Mn 4.1, melt tension 3 cN)
Ingredient for comparison (B-3): Nipolon-L, Grade: M50 (manufactured by Tosoh Corporation)
(MFR (JIS K 7210: 1999, 190 ° C., 2.16 kg) 3.0 g / 10 min, density (JIS K 7112) 936 kg / m ³ , Mn / Mn 3.3, melt tension 2 cN)
The evaluation method is as follows.

  The density was measured by the density gradient tube method according to JIS K7112 (1999).

  The melt flow rate was measured at 190 ° C. under a load of 2.16 kg according to JIS K7210 (1999).

  For Mw / Mn, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC). Tosoh Co., Ltd. HLC-8121GPC / HT is used as the GPC apparatus, Tosoh Co., Ltd. TSKgel GMHhr-H (20) HT is used as the column, the column temperature is set to 140 ° C., and 1 is used as the eluent. Measurement was performed using 2,4-trichlorobenzene. A measurement sample was prepared at a concentration of 1.0 mg / mL, and 0.3 mL was injected and measured. The calibration curve of molecular weight is calibrated using a polystyrene sample having a known molecular weight.

  The peak temperature of crystal melting was measured using DSC (manufactured by Perkin Elmer, trade name: DSC-7). A sample of 5 to 10 mg is inserted into an aluminum pan and placed on the DSC, then heated to 230 ° C. at a heating rate of 80 ° C./min, and left at 230 ° C. for 3 minutes. Thereafter, the temperature is cooled to −10 ° C. at a rate of temperature decrease of 10 ° C./min, and the temperature is increased / decreased from −10 ° C. to 150 ° C. at a rate of temperature increase of 10 ° C./min. The number of endothermic curves observed at the time of temperature increase was evaluated.

  The sample for evaluation of the polyethylene resin composition and the measurement of the melt tension was obtained by adding a heat resistance stabilizer (manufactured by Ciba Specialty Chemicals, Irganox 1010TM; 1,500 ppm, Irgaphos 168TM; 1,500 ppm) to the sample. What knead | mixed for 30 minutes at 190 degreeC and rotation speed 30rpm under nitrogen stream using Null mixer (the Toyo Seiki Seisakusho make, brand name Labo Plast Mill) was used.

  To measure the melt tension, a capillary viscometer (Toyo Seiki Seisakusho, trade name Capillograph) with a barrel diameter of 9.55 mm is attached with a die with a length of 8 mm and a diameter of 2.095 mm so that the inflow angle is 90 °. It was measured. The temperature was set to 190 ° C., the piston lowering speed was set to 10 mm / min, the stretch ratio was set to 47, and the load (cN) required for take-up was taken as the melt tension. When the maximum draw ratio was less than 47, the load (cN) necessary for taking-up at the highest draw ratio that did not break was taken as the melt tension.

  The evaluation of the polyethylene resin composition is based on evaluation of heat resistance from the peak temperature of crystal melting, and the haze value (%) of the film using a haze meter (manufactured by Nippon Denshoku Co., Ltd., model NDH-20D) (based on JIS K7105) ) Was evaluated for transparency.

In addition, the evaluation of blow moldability was evaluated by observing the appearance of the container produced by the method shown in [Molding of Blow Molded Product] for the following items. The drawdown property and the thickness uniformity were observed, and a good one was marked with ◯ and a molding with poor molding was marked with ×.
[Molding of blow molded product]
Using a single-layer blow molding machine (made by Plako Co., Ltd.) having a 65 mmφ extrusion screw, a 0.2 μm filter was attached to the blowing air port, a cylinder temperature of 220 ° C., a thickness of 1.5 mm, and a container volume of 1000 ml. A container was formed.
(Examples 1-3, Comparative Examples 1-7)
Table 1 shows the blow molded product evaluation results of the polyethylene resin composition of the present invention containing the olefin block copolymer [A] and the high density polyethylene [B] in a predetermined amount ratio.

表１の実施例１〜３の評価結果が示すように、オレフィンブロック共重合体［Ａ］と高密度ポリエチレン［Ｂ］を所定量比で含む本願発明のポリエチレン樹脂組成物では、耐熱性、透明性、ブロー成形性のいずれもバランスよく備えていることが分かる。

As shown in the evaluation results of Examples 1 to 3 in Table 1, in the polyethylene resin composition of the present invention containing the olefin block copolymer [A] and the high-density polyethylene [B] in a predetermined amount ratio, the heat resistance and transparency It can be seen that both the moldability and the blow moldability are well balanced.

  On the other hand, as in Comparative Example 1 and Comparative Example 2 in Table 1, when the composition is single, only the olefin block copolymer [A] has a problem in blow moldability, and high density polyethylene [B]. There are problems with transparency alone.

  As shown in Comparative Example 3 in Table 1, when the composition ratio of the olefin block copolymer [A] and the high density polyethylene [B] does not satisfy the claims of the present application, transparency and blow moldability are not satisfied.

  As shown in Comparative Example 4 in Table 1, when a random copolymer is used instead of the olefin block copolymer [A], heat resistance and blow moldability are not satisfied.

  When using ethylene-ethylene butene-ethylene block copolymer (CEBC) instead of the olefin block copolymer [A] as shown in Comparative Example 5 in Table 1, transparency, heat resistance and blow moldability are obtained. I'm not satisfied.

  In high density polyethylene [B] as shown in Comparative Example 6 and Comparative Example 7 in Table 1, when MFR does not satisfy 0.01 to 1.0 g / 10 minutes, transparency and blow moldability are not satisfied, Not suitable for practical use.

  The present invention can be used for a pharmaceutical container. In particular, it is possible to provide an elastomer composition useful as a blow molded article that does not deform even when subjected to high-temperature heat sterilization treatment and is excellent in flexibility and transparency.

Claims (5)

A crystalline polymer block (hard segment) mainly composed of ethylene and an amorphous polymer block composed mainly of at least one α-olefin selected from α-olefins having 3 to 30 carbon atoms and ethylene Olefin block copolymer [A] satisfying the following requirements (a) to (d) including the segment) and high density polyethylene [B] satisfying the requirements (e) to (h) below: [A] / [B] A polyethylene resin composition [I] having a weight ratio of 99.5 / 0.5 to 70/30.
(A) Density measured according to JIS K 7112: 1999 is 870 to 900 kg / m ³
(B) Melt flow rate (MFR) measured in accordance with JIS K 7210: 1999 under a load of 190 ° C. and 21.18 N is 0.1 to 100 g / 10 minutes (c) Weight average molecular weight (Mw) and number average Molecular weight (Mn) ratio (Mw / Mn) is 2.0 to 3.0
(D) In a differential scanning calorimeter, the endothermic curve obtained when melting at 220 ° C. for 5 minutes and then cooling to −40 ° C. at 10 ° C./min is substantially increased at 10 ° C./min. The crystal melting peak temperature (Tm (° C.)) is 121 ° C. or higher (e) The density measured in accordance with JIS K 7112: 1999 is 935 kg / m ³ or higher (f) JIS K7210: Melt flow rate (MFR) measured under a load of 190 ° C. and 21.18 N measured in accordance with K7210: 1999 is 0.01 to 1.0 g / 10 min (g) Weight average molecular weight (Mw) and number average molecular weight The ratio (Mw / Mn) of (Mn) is 6.0-30.
(H) Melt tension is 2.0-40 cN   The polyethylene resin composition [I] according to claim 1, wherein the α-olefin in component [A] has 4 to 20 carbon atoms.   The polyethylene resin composition [I] according to claim 1 or 2, wherein the α-olefin in the component [A] is octene-1. The polyethylene resin composition [I] according to any one of claims 1 to 3, wherein the following requirements (i) to (j) are satisfied.
(I) In accordance with JIS K7105, measured haze is 30% or less. (J) In a differential scanning calorimeter, melted at 220 ° C. for 5 minutes and then cooled to −40 ° C. at 10 ° C./min. The endothermic curve obtained when the temperature is raised at 0 ° C / min has a substantially single peak, and the observed crystal melting peak temperature (Tm (° C)) is 121 ° C or higher.   A blow molded article comprising the polyethylene resin composition [I] according to claim 1.