Polyethylene resin composition

Abstract

To provide a polyethylene resin composition which has both high melt flowability to facilitate molding treatment, and high abrasion resistance to have abrasion resistance against abrasive wear in a well-balanced manner, and is usable for manufacturing an extrusion molding excellent in surface smoothness.SOLUTION: A polyethylene resin composition contains 5-40 pts.mass of ultrahigh molecular weight polyethylene (A) satisfying (a-1), and 95-60 pts.mass of low molecular weight or high molecular weight polyethylene (B) satisfying (b-1) and (b-2) (the total of (A) and (B) is 100 pts.mass), has intrinsic viscosity [η] in a decalin solvent at 135°C of 2.0-15 dl / g, and forms a uniform phase. (a-1) Intrinsic viscosity [η] measured in a decalin solvent at 135°C of 8-50 dl / g; (b-1) intrinsic viscosity [η] measured in a decalin solvent at 135°C of 0.1-5 dl / g; and (b-2) density of 950-985 kg / m3.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyethylene resin composition, a molded article using the composition, and a method for producing the composition. [Background technology]

[0002] Compared to general-purpose resins such as ordinary polyethylene, ultra-high molecular weight polyethylene has weaker intermolecular cohesion, a symmetrical molecular structure, and a high degree of crystallinity, resulting in excellent sliding properties, as well as excellent impact resistance, abrasion resistance, tensile strength, etc., making it suitable for use as a sliding material, etc. However, because ultra-high molecular weight polyethylene has a high molecular weight, it is difficult to produce molded articles from it, and it is often difficult to directly use methods used to mold general-purpose polyethylene.

[0003] Therefore, various methods have been proposed to improve the moldability of ultra-high molecular weight polyethylene without impairing its excellent properties, such as blending ultra-high molecular weight polyethylene with polyethylene having a low intrinsic viscosity [η].

[0004] For example, Patent Document 1 discloses a polyolefin composition for injection molding, which is composed of 15 to 40% by weight of an ultra-high molecular weight polyolefin having an intrinsic viscosity [η] of 10 to 40 dL / g and 85 to 60% by weight of a low- to high-molecular weight polyolefin having an intrinsic viscosity [η] of 0.1 to 5 dL / g. This composition has the advantage that it can be injection molded despite containing an ultra-high molecular weight polyolefin, and furthermore, molded articles obtained by injection molding are excellent in that they retain the excellent sliding properties and wear resistance of the ultra-high molecular weight polyolefin.

[0005] Patent Document 2 discloses a polyethylene resin composition containing more than 35% by weight but not more than 90% by weight of ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 10 to 40 dL / g and 10% by weight or more but less than 65% by weight of low-molecular-weight or high-molecular-weight polyethylene having an intrinsic viscosity [η] of 0.1 to 5 dL / g, blended with a specific polyolefin resin composition. This composition produces molded articles with an excellent balance of abrasion resistance, appearance, and moldability.

[0006] Patent Document 3 also describes a polymer composite containing 5 to 18% by weight of ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 10 to 40 dL / g and 82 to 95% by weight of low-molecular weight or high-molecular weight polyethylene having an intrinsic viscosity [η] of 0.1 to 5 dL / g, and having a density of 955 to 970 kg / m 3 A polyethylene resin composition is disclosed in which

[0007] Furthermore, Patent Document 4 discloses a composition comprising 100 parts by mass of a polyethylene resin containing 5 to 25 mass% of an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 10 to 40 dL / g and 75 to 95 mass% of a low-molecular weight or high-molecular weight polyethylene having an intrinsic viscosity [η] of 0.1 to 5 dL / g, and 0.1 to 10 parts by mass of a polyorganosiloxane having an intrinsic viscosity [η] of 0.1 to 10 dL / g. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 12606 / 1983 [Patent Document 2] International Publication No. 2003 / 022920 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-25904 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-204405 Summary of the Invention [Problem to be solved by the invention]

[0009] Although the compositions disclosed in Patent Documents 1 to 4 are all excellent in moldability and wear resistance, in recent years there has been a demand for polyethylene resins with even higher wear resistance than these compositions, and in particular for resins that exhibit wear resistance even against abrasive wear, a type of wear in which the sliding surface is scraped by hard particles or protrusions, etc. However, when the wear resistance of a polyethylene resin composition is improved, the melt fluidity tends to be lost and moldability deteriorates, so no resin composition is known that combines abrasive wear resistance and moldability. Furthermore, there are increasing demands for the appearance of molded articles obtained from the composition, and in particular, there is a demand for improved surface smoothness of molded articles obtained by extrusion molding.

[0010] An object of the present invention is to provide a polyethylene resin composition that has a good balance of high melt fluidity that facilitates molding processing and high wear resistance that provides resistance to abrasive wear, and that can be used to produce extrusion-molded articles that have excellent surface smoothness. [Means for solving the problem]

[0011] As a result of further research, the present inventors have found that the above-mentioned problems can be solved by the following configuration example. In this specification, the numerical range "A to B" indicates A or more and B or less.

[0012] [1] A polyethylene resin composition comprising 5 to 40 parts by mass of an ultra-high molecular weight polyethylene (A) satisfying the following requirement (a-1) and 95 to 60 parts by mass of a low-molecular weight to high-molecular weight polyethylene (B) satisfying the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass): A polyethylene resin composition having an intrinsic viscosity [η] measured in decalin solvent at 135°C in the range of 2.0 to 15 dl / g and forming a homogeneous phase: (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 8 to 50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5 dl / g; (b-2) Density is 950 to 985 kg / m 3 is.

[0013] [2] The polyethylene resin composition according to [1], wherein the homogeneous phase is a phase in which no domains of 1 μm or more are observed when a thin section of the resin composition is observed under an optical microscope at a magnification of 400 times.

[0014] [3] A molded article of the polyethylene resin composition according to [1] or [2].

[0015] [4] The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5 dl / g, and the density is 950 to 985 kg / m 3 a first step of producing a low-molecular-weight to high-molecular-weight polyethylene (B), a second step of producing, after the first step, an ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 8 to 50 dl / g; by a multi-stage polymerization method including at least two steps of A method for producing a polyethylene resin composition, which produces a polyethylene resin composition having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 2.0 to 15 dl / g and forming a homogeneous phase. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a polyethylene resin composition that has a good balance of high melt fluidity that facilitates molding processing and high wear resistance that provides resistance to abrasive wear, and that can be used to produce an extrusion-molded article that has excellent surface smoothness. [Brief explanation of the drawings]

[0017] [Figure 1]1 is an example of an optical microscope photograph of the polyethylene resin composition obtained in Example 1. [Figure 2] 1 is an example of an optical microscope photograph of the polyethylene resin composition obtained in Example 2. [Figure 3] 1 is an example of an optical microscope photograph of the polyethylene resin composition obtained in Example 3. [Figure 4] 1 is an example of an optical microscope photograph of the polyethylene resin composition obtained in Comparative Example 1. [Figure 5] FIG. 1 is a graph showing an example of the relationship between the abrasion loss in a Taber abrasion test and the MFR of a polyethylene resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Polyethylene resin composition> The polyethylene resin composition according to the present invention (hereinafter also referred to as "the composition") contains a specific ultra-high molecular weight polyethylene (A) and a specific low- to high-molecular weight polyethylene (B) (hereinafter also referred to as "polyethylene (B)"), and satisfies the following requirements (X) and (Y):

[0019] Requirement (X): The intrinsic viscosity [η] of the composition measured in decalin solvent at 135°C is in the range of 2.0 to 15 dl / g, preferably in the range of 2.5 to 10 dl / g, more preferably in the range of 3.0 to 8.0 dl / g, and even more preferably in the range of 3.5 to 7.0 dl / g. When the intrinsic viscosity [η] of the present composition in decalin solvent at 135°C satisfies the above range, the present composition has high melt fluidity to an extent that it facilitates molding processing, and high wear resistance to an extent that it is resistant to abrasive wear, thereby achieving both wear resistance and moldability. If the intrinsic viscosity [η] in decalin solvent at 135°C is less than 2.0 dL / g, the abrasion resistance of the composition is impaired. On the other hand, if the intrinsic viscosity [η] in decalin solvent at 135°C is more than 15 dL / g, the fluidity of the composition is reduced, resulting in impaired moldability.

[0020] Requirement (Y): The polyethylene resin composition forms a homogeneous phase. In this composition, the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are compatible with each other to form a homogeneous phase, and no phase separation occurs between the ultra-high molecular weight polyethylene (A) and the polyethylene (B).

[0021] Whether the composition is a homogeneous phase or not is judged as follows based on the size of islands (domains) observed when a thin section prepared by cutting the composition with a microtome is observed under an optical microscope, where the observation conditions under the optical microscope are as described in the examples below. Homogeneous phase: composition does not contain domains larger than 1 μm Phase separation: the composition contains domains larger than 1 μm That is, in this composition, a sea-island structure containing domains of 1 μm or more is not formed.

[0022] It is preferable that the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are compatible to form a homogeneous phase, since this results in excellent abrasion resistance and good surface smoothness of the molded article obtained by extrusion molding. The reason why this composition has excellent abrasion resistance is that the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are compatible to the extent that they form a homogeneous phase, thereby exhibiting the abrasion resistance inherent to the ultra-high molecular weight polyethylene (A). The reason why this composition has excellent surface smoothness is that the composition does not contain domains of 1 μm or more, and therefore does not cause roughness due to domains located on the surface of the molded article.

[0023] When the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are phase-separated, an island-sea structure is formed in which the ultra-high molecular weight polyethylene (A) forms domains (island phases) and the polyethylene (B) forms the matrix (sea phase). In this case, the abrasion resistance inherent in the ultra-high molecular weight polyethylene (A) is not exerted throughout the composition, so the polyethylene (B) portion wears away, and then the domains located on the abrasion surface fall off, further increasing the abrasion resistance of the composition. Furthermore, when the composition is extrusion-molded, the domains formed by the ultra-high molecular weight polyethylene (A) are located near the surface of the molded article, causing roughness and impairing the surface smoothness of the molded article.

[0024] The content of the ultra-high molecular weight polyethylene (A) in the composition is 5 to 40 parts by mass, preferably 8 to 30 parts by mass, more preferably 10 to 25 parts by mass, and even more preferably 12 to 20 parts by mass (where the total amount of the ultra-high molecular weight polyethylene (A) and the polyethylene (B) is 100 parts by mass). The content of polyethylene (B) in the composition is 60 to 95 parts by mass, preferably 70 to 92 parts by mass, more preferably 75 to 90 parts by mass, and even more preferably 80 to 88 parts by mass (where the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass). When the contents of the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are within the above ranges, the moldability and abrasion resistance of the composition are improved.

[0025] If the content of ultra-high molecular weight polyethylene (A) in the composition exceeds 40 parts by mass and the content of polyethylene (B) is less than 60 parts by mass, the melt fluidity of the composition will be low, resulting in poor moldability of the composition. On the other hand, if the content of ultra-high molecular weight polyethylene (A) is less than 5 parts by mass and the content of polyethylene (B) is more than 95 parts by mass, the abrasion resistance derived from the ultra-high molecular weight polyethylene (A) will be insufficient, resulting in poor abrasion resistance of the resulting composition.

[0026] The melt flow rate (hereinafter also referred to as "MFR") of the present composition, measured in accordance with the measurement method of ASTM D-1238E at 190°C under a load of 10 kg, is preferably 0.01 to 500 g / 10 min, more preferably 0.1 to 100 g / 10 min, and even more preferably 1.0 to 50 g / 10 min. If the MFR of the composition is within the above range, it is preferable because the moldability is good.

[0027] <Ultra-high molecular weight polyethylene (A)> The ultra-high molecular weight polyethylene (A) blended in the present composition has an intrinsic viscosity [η] measured in decalin solvent at 135° C. of 8 to 50 dL / g, preferably 8 to 45 dL / g, more preferably 10 to 45 dL / g, even more preferably 15 to 45 dL / g, and particularly preferably 18 to 42 dL / g. When the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) is within the above range, the composition can preferably achieve both abrasion resistance and moldability.

[0028] If an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of less than 8 dL / g measured in decalin solvent at 135°C is used instead of the ultra-high molecular weight polyethylene (A), the abrasion resistance of the composition will deteriorate, and the abrasion resistance of the resulting molded article will be inferior, which is not preferred. On the other hand, if an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of more than 50 dL / g measured in decalin solvent at 135°C is used instead of the ultra-high molecular weight polyethylene (A), the melt fluidity of the composition will be reduced, and the moldability of the composition will be reduced, which is not preferred.

[0029] The ultra-high molecular weight polyethylene (A) is a homopolymer of ethylene or a copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, or 3-methyl-1-pentene. The ultra-high molecular weight polyethylene (A) is preferably a homopolymer of ethylene or a copolymer of ethylene and the above α-olefin, a copolymer composed mainly of ethylene, and more preferably an ethylene homopolymer.

[0030] <Low-molecular-weight or high-molecular-weight polyethylene (B)> The polyethylene (B) has an intrinsic viscosity [η] of 0.1 to 5 dl / g, preferably 0.5 to 2 dl / g, more preferably 0.7 to 1.5 dl / g, and even more preferably 0.8 to 1.2 dl / g, as measured in decalin at 135°C. When the polyethylene (B) has an intrinsic viscosity [η] within the above range as measured in decalin at 135°C, a composition excellent in both abrasion resistance and moldability can be obtained.

[0031] If a low- or high-molecular-weight polyethylene having an intrinsic viscosity [η] of less than 0.1 dL / g measured in decalin at 135°C is used instead of polyethylene (B), the abrasion resistance of the composition deteriorates, resulting in inferior abrasion resistance of the resulting molded article, which is undesirable. On the other hand, if a low- or high-molecular-weight polyethylene having an intrinsic viscosity [η] of more than 5 dL / g measured in decalin at 135°C is used instead of polyethylene (B), the melt fluidity of the composition decreases, which reduces the moldability of the composition, which is undesirable.

[0032] Polyethylene (B) has a density of 950 to 985 kg / m 3 and preferably 960 to 980 kg / m 3 and more preferably 960 to 975 kg / m 3 and more preferably 965 to 975 kg / m 3 When the density of the polyethylene (B) is within the above range, a composition excellent in both abrasion resistance and moldability can be obtained.

[0033] Instead of polyethylene (B), the density is 950 kg / m 3 When a low-molecular-weight or high-molecular-weight polyethylene having a density of less than 985 kg / m is used, the low-molecular-weight or high-molecular-weight polyethylene has a low crystallinity and is easily scraped, which results in a deterioration in the abrasion resistance of the composition and a poor abrasion resistance of the resulting molded article, which is therefore undesirable. 3 Therefore, the composition has a strength of 985 kg / m 3Low to high molecular weight polyethylenes of the following densities are used:

[0034] The polyethylene (B) is an ethylene homopolymer or a copolymer of ethylene and an α-olefin, preferably an ethylene homopolymer. The α-olefin constituting the copolymer includes linear or branched α-olefins having 3 to 20 carbon atoms, specifically propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 3,4-dimethyl-1-pentene, 4-methyl-1-hexene, 3-ethyl-1-pentene, 3-ethyl-4-methyl-1-pentene, 3,4-dimethyl-1-hexene, 4-methyl-1-heptene, 3,4-dimethyl-1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, etc. Among these, propylene and 1-butene are preferably used in view of the density range of the polyethylene (B).

[0035] The ethylene and α-olefin copolymer preferably has an ethylene content of 90 mol% or more, and more preferably 95 mol% or more. When polyethylene (B) is an ethylene and α-olefin copolymer, the higher the ethylene content, the better.

[0036] <Other ingredients> The present composition may contain other thermoplastic resins such as polyolefin-based resins, and resin additives (for example, stabilizers such as heat stabilizers and weather stabilizers, crosslinking agents, crosslinking aids, antistatic agents, slip agents, antiblocking agents, antifogging agents, lubricants, dyes, pigments, fillers, mineral oil-based softeners, petroleum resins, waxes, etc.), as long as the addition does not impair the object of the present invention. When the other components are contained, the total amount of the other components in the composition is usually 5% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less. In other words, the proportion of the total mass of the ultra-high molecular weight polyethylene (A) and the polyethylene (B) in the composition to the mass of the composition is usually 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more.

[0037] <Method of producing polyethylene resin composition> The composition is produced by a multi-stage polymerization process comprising at least two steps: a first step of producing polyethylene (B) in the presence of a known olefin polymerization catalyst; and a second step of producing ultra-high molecular weight polyethylene (A). The second step is carried out in the presence of the polyethylene (B) produced in the first step.

[0038] It is presumed that when ultra-high molecular weight polyethylene (A) is produced in the presence of polyethylene (B), a granular polyethylene resin composition is obtained in which particles of ultra-high molecular weight polyethylene (A) are coated with polyethylene (B). It is presumed that when the particle surfaces of the polyethylene resin composition are coated with polyethylene (B), the polyethylene resin composition is less likely to form a sea-island structure and more likely to form a homogeneous phase when molded into pellets or the like.

[0039] On the other hand, even when a multi-stage polymerization method is used, if ultra-high molecular weight polyethylene (A) is produced before polyethylene (B), and polyethylene (B) is produced in the presence of ultra-high molecular weight polyethylene (A), the resulting composition does not form a homogeneous phase. This is presumably because, in the composition obtained when polyethylene (B) is produced in the presence of ultra-high molecular weight polyethylene (A), polyethylene (B) is coated with ultra-high molecular weight polyethylene (A), and when the polyethylene resin composition is molded into pellets or the like, it is prone to form a sea-island structure, making it difficult to form a homogeneous phase.

[0040] In producing the present composition, the olefin such as ethylene used in the polymerization can be any of the various olefins described in the sections on ultra-high molecular weight polyethylene (A) and polyethylene (B) without any restrictions.

[0041] <Molded body> The present composition can be molded into containers, trays, sheets, rods, films, or coatings for various molded articles by conventionally known methods, specifically, for example, extrusion molding, coextrusion molding, injection molding, profile extrusion molding, pipe molding, tube molding, coating molding for heterogeneous molded articles, injection blow molding, direct blow molding, T-die sheet or film molding, inflation film molding, press molding, or other molding methods.

[0042] The molded article obtained by the above molding method can be widely used for conventionally known polyethylene applications, but since it has particularly excellent abrasion resistance, it can be used for applications requiring this, such as coatings for metals such as steel pipes, electric wires, and automobile slide rails, pressure-resistant rubber hoses, gaskets for automobile doors, gaskets for clean room doors, automobile glass run channels, and various rubber reels such as automobile weather strips, various guide rails, elevator rail guides, and sliding materials such as various protective liner materials.

[0043] When a Taber abrasion test (test temperature 23°C, grinding wheel H22, load 1000 g, rotation speed 60 rpm, test rotation number 10800 (3 hours)) is performed on a molded article obtained from this composition, the amount of wear is preferably 100 mg or less. The smaller the amount of wear, the better, but the lower limit is usually 0.1 mg or more. If the amount of wear in the Taber abrasion test is within the above range, the molded article obtained from this composition will have sufficient wear resistance in the usage environment, and this is preferable. Note that in the above Taber abrasion test, since there are small protrusions on the surface of the grinding wheel (H22) used, the above Taber abrasion test is a test for abrasive wear.

[0044] The surface roughness (arithmetic mean roughness (Ra)) of the molded article obtained by extrusion molding of the present composition is preferably 3.0 μm or less, more preferably 2.0 μm or less. The smaller the surface roughness, the better, but the lower limit is usually 0.1 μm or more. It is preferable that the surface roughness of the extrusion molded article is within the above range, as this provides sufficient surface smoothness. [Example]

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In some cases, the following polymerization was carried out multiple times to obtain the amounts of polymer and composition required for evaluation.

[0046] [Measurement conditions, etc.] The conditions for measuring each physical property are as follows:

[0047] [Intrinsic viscosity [η]] The intrinsic viscosity [η] of the various polymers and resin compositions obtained in the examples and comparative examples was measured at 135°C in decalin solvent. Hereinafter, the intrinsic viscosity of the ultra-high molecular weight polyethylene (A) may be referred to as "intrinsic viscosity [η]u." Similarly, the intrinsic viscosity of the polyethylene (B) may be referred to as "intrinsic viscosity [η]h."

[0048] 〔density〕 The density of the polyethylene (B) was measured in accordance with ASTM D1505.

[0049] [Phase structure] The pellets of the resin compositions obtained in the Examples and Comparative Examples were cut using a microtome to prepare thin sections of the resin compositions. The thin sections were then observed under an optical microscope at a magnification of 400 times, and judged to be homogeneous based on the following criteria. Homogeneous phase: No domains larger than 1 μm were observed in thin sections of the composition. Phase separation: Domains of 1 μm or more were observed in thin sections of the composition.

[0050] [MFR] The MFR of the compositions obtained in the Examples and Comparative Examples was measured under a load of 10 kg in accordance with ASTM D1238E at a temperature of 190°C.

[0051] [Wear Amount of Molded Body] The compositions obtained in the Examples and Comparative Examples were molded into square plates measuring 10 cm square and 2 mm thick, and the resulting molded bodies were weighed. The resulting molded bodies were subjected to a Taber abrasion test in accordance with JIS K7204. The test conditions were as follows: Polishing stone: H22 Test load: 1000g Rotation speed: 60 rpm Test rotation speed: 10,800 times (3 hours) Test temperature: 23℃ After the test, the molded body was weighed again, and the difference in mass of the molded body before and after the test was taken as the amount of wear of the molded body in the Taber abrasion test.

[0052] [Surface roughness of molded body] The compositions obtained in the Examples and Comparative Examples were used to produce ram-extrusion molded articles and / or laminates coextruded with ethylene-propylene-ethylidenenorbornene copolymer (hereinafter also referred to as "EPDM") by the method described below. The arithmetic mean roughness (Ra) of the surfaces of the resulting molded articles (the surfaces of the laminates facing the polyethylene resin composition obtained in the Examples or Comparative Examples) was determined by a method in accordance with JIS B 0601.

[0053] [Example 1] [Preparation of solid titanium catalyst component [C1]] 95.2 g of anhydrous magnesium chloride, 398.1 g of decane, and 306 g of 2-ethylhexyl alcohol were placed in a reaction vessel and heated at 140°C for 6 hours. After the solution in the reaction vessel was cooled to 50°C, 17.6 g of ethyl benzoate was added, and the mixture was stirred and mixed at 130°C for 1 hour to obtain a homogeneous solution. The homogeneous solution thus obtained was cooled to room temperature, and then 50 ml of the homogeneous solution was added dropwise over 60 minutes with stirring to 200 ml of titanium tetrachloride maintained at 0°C. After the addition, the resulting mixture was maintained at 0°C for 1 hour, then the temperature of the mixture was raised to 20°C over 1 hour, and then further raised to 80°C over 30 minutes. When the temperature of the mixture reached 78°C, 2.35 g of ethyl benzoate was added to the mixture, and the reaction was continued for 2 hours while maintaining the temperature at 80°C. After the 2-hour reaction, the solid was collected by hot filtration, resuspended in 200 ml of titanium tetrachloride, and then heated again at 90°C for 2 hours. After the second heating reaction, the solid was collected again by hot filtration, washed with 90°C decane until no free titanium compounds were detected in the washes, and then thoroughly washed with room-temperature hexane.

[0054] The solid titanium catalyst component prepared by the above procedure was stored as a decane slurry, and a portion of this was dried to examine the catalyst composition. The composition of the dried solid titanium catalyst component [C1] was 3.1 mass% titanium, 18 mass% magnesium, 60 mass% chlorine, 15.4 mass% ethyl benzoate, and 1.5 mass% 2-ethylhexyl alcohol residue.

[0055] [Production of polyethylene resin composition] A 1-liter polymerization vessel, thoroughly purged with nitrogen, was charged with 500 ml of purified decane at room temperature, and 0.5 mmol of triisobutylaluminum and a solid titanium catalyst component [C1] (0.01 mmol of titanium atom equivalent) were added at 80°C. Hydrogen was then fed until the pressure inside the polymerization vessel reached 0.406 MPaG (gauge pressure), followed by ethylene feeding until the pressure inside the polymerization vessel reached 0.66 MPaG (gauge pressure). First-stage ethylene polymerization was carried out at 85°C. The ethylene feed was stopped when 119 liters of ethylene had been fed, and the vessel was rapidly cooled to 45°C. The vessel was then depressurized and purged with nitrogen. By carrying out the first-stage ethylene polymerization under these conditions, polyethylene (B1) was obtained. Next, ethylene was fed into the polymerization reactor until the pressure inside the polymerization reactor reached 0.60 MPaG in gauge pressure, and second-stage ethylene polymerization was carried out at a temperature of 53°C. When 21 liters of ethylene had been fed, the ethylene feed was stopped, the temperature was rapidly cooled to 40°C, and then the pressure was released and purging was carried out. Note that by carrying out the second-stage ethylene polymerization under the above conditions, ultra-high molecular weight polyethylene (A1) can be obtained. The resulting slurry containing the solid was filtered and dried under reduced pressure overnight at a temperature of 80° C. The resulting ethylene resin composition weighed 190 g and had an intrinsic viscosity [η] in decalin solvent at 135° C. of 3.9 dl / g.

[0056] [Analysis of Components in Polyethylene Resin Composition] Polyethylene (B1) content and properties Of the polymerizations carried out when producing the polyethylene resin composition, only the first stage polymerization was carried out separately under the same conditions as when producing the polyethylene resin composition, and the yield of the obtained ethylene polymer was 162 g. Since polyethylene (B1) was produced by this polymerization, the content of polyethylene (B1) in the polyethylene resin composition (yield 190 g) was calculated to be 85 mass %. The intrinsic viscosity [η] of the obtained polyethylene (B1) was measured in decalin solvent at 135°C and was found to be 1.0 dl / g. The density of the obtained polyethylene (B1) was 971 kg / m 3 It was.

[0057] Ultra-high molecular weight polyethylene (A2) content and intrinsic viscosity [η] The first stage polymerization was omitted from the polymerization carried out to produce the polyethylene resin composition, and only the second stage polymerization was carried out separately under the same conditions as in the production of the polyethylene resin composition, thereby producing ultra-high molecular weight polyethylene (A2). The ultra-high molecular weight polyethylene (A2) had an intrinsic viscosity [η] of 30 dL / g. Next, the molecular weight distribution of the ultra-high molecular weight polyethylene (A2) was measured by gel permeation chromatography (GPC). When the results were compared with those of the polyethylene resin composition, the peak position and shape of the chromatogram were consistent with those of the high molecular weight component (ultra-high molecular weight polyethylene (A1)) contained in the polyethylene resin composition. Based on this result, the physical properties of the ultra-high molecular weight polyethylene (A1) were considered to be the same as those of the ultra-high molecular weight polyethylene (A2). In other words, the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A1) was determined to be 30 dL / g.

[0058] [Granulation of polyethylene resin composition] The obtained polyethylene resin composition was dry-blended with Irganox 1010 (manufactured by BASF), Irgafos 168 (manufactured by BASF), and calcium stearate (manufactured by NOF Corporation). The blend amounts of each substance were 0.1% by mass for Irganox 1010, 0.2% by mass for Irgafos 168, and 0.12% by mass for calcium stearate, assuming the composition after dry blending to be 100% by mass. The composition after dry blending was melt-kneaded using a twin-screw extruder (manufactured by Technovel, φ=15 mm, L / D=30, cylinder temperature: 200°C), and then granulated into pellets.

[0059] The resulting pellets were used to measure the physical properties of the polyethylene resin composition. The results are shown in Table 1. An optical microscope photograph of a thin section obtained from the pellets is shown in Figure 1. Figure 1 shows that the polyethylene resin composition formed a homogeneous phase.

[0060] [Ram extrusion molding] The furnace (inner diameter 10 mm) of a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho) equipped with a slit die (1 mm × 6 mm) was heated to 230°C, and the polyethylene resin composition was extruded at a piston speed of 200 mm / min. The extruded polyethylene resin composition was water-cooled to obtain a molded article. The arithmetic mean roughness (Ra) of the surface of the obtained molded article was then determined. The results are shown in Table 1.

[0061] [Co-extrusion] Ethylene-propylene-ethylidene norbornene copolymer (EPDM) (Shore A hardness = 75, including vulcanizing agent) was formed into sheets, which were then cut into square pellets using a sheet cutter. Each of the resulting EPDM pellets was extruded at 80°C, and a polyethylene resin composition was coextrusion laminated onto the surface at 200°C to obtain a coextrusion laminate. The EPDM layer in the coextrusion laminate had a thickness of 1.0 mm, and the polyethylene resin composition layer had a thickness of 0.1 mm. The coextrusion laminate was then heated to 230°C and held there for 5 minutes to vulcanize and crosslink the EPDM layer. The arithmetic mean roughness (Ra) of the surface of the polyethylene resin composition layer of the coextrusion laminate was then measured. The results are shown in Table 1.

[0062] [Example 2] Polymerization, analysis, and granulation were carried out in the same manner as in Example 1, except that the ethylene polymerization temperature was changed from 53°C to 68°C in the second-stage polymerization during production of the polyethylene resin composition, and various physical properties were measured. The analytical results and the results of measuring the physical properties are shown in Table 1. FIG. 2 shows an optical microscope photograph of a thin section obtained from the pellets. FIG. 2 shows that the polyethylene resin composition formed a homogeneous phase.

[0063] [Example 3] [Preparation of solid titanium catalyst component [C2]] 75.0 g of anhydrous magnesium chloride, 280.3 g of decane, and 308.3 g of 2-ethylhexyl alcohol were charged into a reaction vessel and heated at 130°C for 3 hours, after which 19.9 g of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added and the mixture was stirred and mixed at 100°C for another hour. The homogeneous solution thus obtained was cooled to room temperature, and then a total of 30 ml of the homogeneous solution was added dropwise over 45 minutes with stirring to 80 ml of titanium tetrachloride maintained at 0°C to obtain a mixed solution. After the dropwise addition was completed, the resulting mixed solution was heated to 110°C over 6 hours, and 0.55 g of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added, followed by maintaining the mixture at 110°C for 2 hours with stirring. After the 2-hour reaction was completed, the solid portion was collected by hot filtration and washed with 90°C decane until no free titanium compounds were detected in the washings, followed by thorough washing with room temperature hexane.

[0064] The solid titanium catalyst component prepared by the above procedure was stored as a decane slurry, and a portion of this was dried to examine the catalyst composition. The composition of the dried solid titanium catalyst component [C2] was 2.8 mass% titanium, 18.1 mass% magnesium, 58.2 mass% chlorine, 19.6 mass% 2-isobutyl-2-isopropyl-1,3-dimethoxypropane, and 1.4 mass% 2-ethylhexyl alcohol residue.

[0065] [Production of polyethylene resin composition] A 1-liter polymerization vessel that had been thoroughly purged with nitrogen was charged with 500 ml of purified decane at room temperature, and 0.5 mmol of triisobutylaluminum and a solid titanium catalyst component [C2] (0.01 mmol in terms of titanium atom) were added at a temperature of 75°C. Hydrogen was then fed until the pressure in the polymerization vessel reached 0.24 MPaG (gauge pressure), and ethylene was then fed until the pressure in the polymerization vessel reached 0.44 MPaG (gauge pressure), and first-stage ethylene polymerization was carried out at a temperature of 85°C. When 130 liters of ethylene had been fed, the ethylene feed was stopped, and the vessel was rapidly cooled to 45°C, followed by depressurization and nitrogen purging. Next, 0.75 micromoles of titanocene dichloride in terms of titanium atom was added to the polymerization vessel, and ethylene was fed until the pressure inside the polymerization vessel reached 0.66 MPaG in gauge pressure, and second-stage ethylene polymerization was carried out at a temperature of 70° C. When 25 liters of ethylene had been fed, the ethylene feed was stopped, and the temperature was rapidly cooled to 40° C., followed by depressurization and purging.

[0066] The analysis, granulation, and measurement of the physical properties of the obtained polyethylene resin composition were carried out in the same manner as in Example 1. The analysis results and the measurement results of the physical properties are shown in Table 1. An optical microscope photograph of a thin section obtained from the pellets is shown in Figure 3. Figure 3 shows that the polyethylene resin composition formed a homogeneous phase. For the composition of Example 3, co-extrusion molding with EPDM and measurement of the arithmetic mean roughness (Ra) were not carried out.

[0067] [Comparative Example 1] A composition was produced by interchanging the first-stage and second-stage polymerization conditions of the example. Specifically, the catalyst component introduction temperature was changed from 80°C to 48°C. In the first-stage polymerization, hydrogen was not fed, the ethylene polymerization temperature was changed from 85°C to 53°C, and the ethylene feed rate was changed from 119 liters to 21 liters. In the second-stage polymerization, hydrogen was fed until the pressure inside the polymerization vessel reached 0.40 MPaG (gauge pressure), the ethylene polymerization temperature was changed from 53°C to 85°C, and the ethylene feed rate was changed from 21 liters to 119 liters. Other conditions were the same as in the example. Analysis, granulation, and coextrusion molding with EPDM were then performed as in the example, and physical properties were measured. The analytical and physical property measurement results are shown in Table 1. An optical microscope photograph of the resulting composition is shown in Figure 4. Figure 4 reveals that the composition obtained in Comparative Example 1 has a sea-island structure.

[0068] Comparative Example 2 Polymerization was carried out in the same manner as in Comparative Example 1, except that the ethylene feed rate in the first polymerization stage was changed from 21 liters to 33.6 liters and the ethylene feed rate in the second polymerization stage was changed from 119 liters to 106.4 liters. Analysis and granulation were then carried out, and various physical properties were measured. The analytical results and the results of measurement of physical properties are shown in Table 1. Note that for the composition of Comparative Example 2, ram extrusion molding and coextrusion molding with EPDM, and measurements of the arithmetic mean roughness (Ra) of the molded articles obtained by these molding processes were not performed.

[0069] [Table 1]

[0070] The polyethylene resin compositions obtained in Examples 1 to 3 have a good balance of high melt fluidity that facilitates molding and high wear resistance that provides resistance to abrasive wear. Furthermore, the polyethylene resin compositions of Examples 1 to 3 have a relatively small arithmetic mean roughness of the coextruded product surface, and therefore can be used to produce extrusion-molded products with excellent surface smoothness. These results are thought to be due to the fact that the polyethylene resin compositions of the Examples contain ultra-high molecular weight polyethylene (A) and polyethylene (B) in the specified ratio, have a specified intrinsic viscosity, and form a homogeneous phase.

[0071] FIG. 5 is a graph showing an example of the relationship between the abrasion loss in a Taber abrasion test and the MFR of a polyethylene resin composition. In the composition of Comparative Example 1, the content of the ultra-high molecular weight component was reduced to improve moldability, resulting in reduced abrasion resistance. Furthermore, the arithmetic mean roughness of the surface of the coextrusion molded product of Comparative Example 1 was greater than that of the Examples, resulting in insufficient surface smoothness. The reason why the composition of Comparative Example 1 is inferior in abrasion resistance and surface smoothness to the polyethylene resin compositions of the Examples is thought to be due to the fact that the composition of Comparative Example 1 has a sea-island structure. In Comparative Example 2, the content of the ultra-high molecular weight component was increased to improve abrasion resistance, resulting in reduced moldability. On the other hand, the plots for Examples 1 to 3 show smaller abrasion amounts and have melt fluidity to the extent that moldability is good compared to Comparative Examples 1 and 2. That is, the compositions of the Examples have both high melt fluidity to the extent that molding processing is easy and high abrasion resistance.

Claims

1. A polyethylene resin composition comprising 5 to 40 parts by mass of an ultra-high molecular weight polyethylene (A) satisfying the following requirement (a-1) and 95 to 60 parts by mass of a low- to high-molecular weight polyethylene (B) satisfying the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass): A polyethylene resin composition having an intrinsic viscosity [η] measured in decalin solvent at 135°C in the range of 2.0 to 15 dl / g and forming a homogeneous phase: (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 8 to 50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5 dl / g; (b-2) Density is 950 to 985 kg / m 3 is.

2. 2. The polyethylene resin composition according to claim 1, wherein the homogeneous phase is a phase in which no domains of 1 μm or more are observed when a thin section of the resin composition is observed under an optical microscope at a magnification of 400 times.

3. A molded article of the polyethylene resin composition according to claim 1 or 2.

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