Polyethylene resin composition and method for producing the polyethylene resin composition

Abstract

To provide a polyethylene resin composition that has a well-balanced combination of a high melt fluidity of the level to facilitate molding and fabrication, and a wear resistance under high load condition.SOLUTION: A polyethylene resin composition (X) is provided, including: 5 to 35 pts.mass of high molecular weight polyethylene (A) satisfying requirement (a-1); and 95 to 65 pts.mass of polyethylene (B) satisfying requirements (b-1) and (b-2) (here, the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 pts.mass), the polyethylene resin composition (X) satisfies requirement (x-1) and (x-2). (a-1) the intrinsic viscosity [η] measured in decalin solvent at 135°C is 33 to 50 dl / g; (b-1) the intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5.0 dl / g; (b-2) density is 950 to 985 kg / m3; (x-1) the intrinsic viscosity [η] of the polyethylene resin composition (X) measured in a decalin solvent at 135°C is in the range of 1.5 to 15 dl / g; (x-2) the difference between the intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A) and the intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is in the range of 32 to 49 dl / g.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Ultra-high molecular weight polyethylene (ULME) exhibits superior sliding properties compared to general-purpose resins like ordinary polyethylene. Its weaker intermolecular cohesive forces, symmetrical molecular structure, and high crystallinity result in excellent impact resistance, abrasion resistance, and tensile strength, making it suitable for use as a sliding material. However, due to its high molecular weight, ULME is difficult to manufacture molded products from, and it is often challenging to directly utilize the molding methods employed for 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 with a low intrinsic viscosity [η].

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

[0005] Patent Document 2 discloses a polyethylene resin composition in which a specific polyolefin resin composition is blended with a polyethylene resin composition containing 35% to 90% by weight of ultra-high molecular weight polyethylene with an intrinsic viscosity [η] of 10 to 40 dl / g and 10% to less than 65% by weight of low molecular weight or high molecular weight polyethylene with an intrinsic viscosity [η] of 0.1 to 5 dl / g. From this composition, a molded article with an excellent balance of abrasion resistance, appearance, and moldability can be obtained.

[0006] Furthermore, Patent Document 3 describes a material comprising 5-18% by weight of ultra-high molecular weight polyethylene with an intrinsic viscosity [η] of 10-40 dl / g, and 82-95% by weight of low-molecular-weight or high-molecular-weight polyethylene with an intrinsic viscosity [η] of 0.1-5 dl / g, with a density of 955-970 kg / m³. 3 A polyethylene resin composition is disclosed.

[0007] Furthermore, Patent Document 4 discloses a composition comprising 100 parts by mass of polyethylene resin containing 5 to 25% by mass of ultra-high molecular weight polyethylene with an intrinsic viscosity [η] of 10 to 40 dl / g and 75 to 95% by mass of low molecular weight or high molecular weight polyethylene with an intrinsic viscosity [η] of 0.1 to 5 dl / g, and 0.1 to 10 parts by mass of polyorganosiloxane with 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 Publication No. 2012-25904 [Patent Document 4] Japanese Patent Publication No. 2016-204405 [Overview of the project] [Problems that the invention aims to solve]

[0009] Although the compositions disclosed in Patent Documents 1 to 4 all exhibit excellent moldability and abrasion resistance, in recent years there has been a demand for polyethylene resins with even higher abrasion resistance than these compositions, and in particular, for resins that exhibit abrasion resistance even under high load conditions (e.g., 25 kg load). However, improving the abrasion resistance of polyethylene resin compositions tends to result in a loss of melt fluidity and poor moldability, so no resin composition that achieves both abrasion resistance under high load conditions and moldability is known.

[0010] The present invention aims to provide a polyethylene resin composition that possesses a good balance between high molten fluidity, which facilitates molding, and wear resistance under high load conditions. [Means for solving the problem]

[0011] As a result of the inventor's research, it was found that the above-mentioned problems can be solved according to the following configuration example. The configuration example of the present invention is as follows. In this specification, "A~B" indicating a numerical range means A or greater and B or less.

[0012] In other words, the present invention has, for example, the following [1] to [4].

[0013] [1] 5 to 35 parts by mass of ultra-high molecular weight polyethylene (A) that meets the following requirement (a-1), It contains 95 to 65 parts by mass of low molecular weight or high molecular weight polyethylene (B) that meet the following requirements (b-1) and (b-2) (however, the total amount of ultra-high molecular weight polyethylene (A) and low molecular weight or high molecular weight polyethylene (B) shall be 100 parts by mass), A polyethylene resin composition (X) that satisfies the following requirements (x-1) and (x-2). (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 33-50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5.0 dl / g; (b-2) Density of 950-985 kg / m³3 which is; (x-1) the intrinsic viscosity [η] of said polyethylene resin composition (X) measured in a decalin solvent at 135°C is in the range of 1.5 to 15 dl / g; (x-2) the difference between the intrinsic viscosity [η] of said ultra-high molecular weight polyethylene (A) and the intrinsic viscosity [η] of said low molecular weight to high molecular weight polyethylene (B), measured in a decalin solvent at 135°C, is in the range of 32 to 49 dl / g.

[0014] [2] The polyethylene resin composition (X) according to [1], wherein the melt flow rate measured in accordance with ASTM D1238E at 190°C under a 10 kg load is 3 to 50 g / 10 min.

[0015] [3] A molded article comprising the polyethylene resin composition (X) according to [1] or [2].[1END]]

[0016] [4] a first step of producing an ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C of 33 to 50 dl / g, and a low molecular weight to high molecular weight polyethylene (B) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 0.1 to 5.0 dl / g, a difference from the intrinsic viscosity [η] of said ultra-high molecular weight polyethylene (A) measured in a decalin solvent at 135°C in the range of 32 to 49 dl / g, and a density of 950 to 985 kg / m 3 , a second step of producing the low molecular weight to high molecular weight polyethylene (B), by a multi-stage polymerization method including at least the two steps of a method for producing a polyethylene resin composition (X), which produces the polyethylene resin composition (X) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 1.5 to 15 dl / g. Effects of the Invention

[0017] According to the present invention, there is provided a polyethylene resin composition that has a good balance of high melt fluidity sufficient to facilitate molding processing and abrasion resistance under high load conditions. Brief Description of the Drawings

[0018] [Figure 1] This is a photograph of a test piece formed from the polyethylene resin composition (X3) obtained in Example 3, after undergoing a sliding abrasion test under high load (25 kg) conditions. [Figure 2] This is a photograph of a test piece formed from the polyethylene resin composition (CX1) obtained in Comparative Example 1, after undergoing a sliding abrasion test under high load (25 kg) conditions. [Modes for carrying out the invention]

[0019] Polyethylene resin composition The polyethylene resin composition (X) according to the present invention (hereinafter also referred to as "resin composition (X)") comprises a specific ultra-high molecular weight polyethylene (A) and a specific low molecular weight to high molecular weight polyethylene (B) (hereinafter also referred to as "polyethylene (B)").

[0020] <Ultra-high molecular weight polyethylene (A)> Ultra-high molecular weight polyethylene (A) satisfies the following requirement (a-1).

[0021] [Requirement (a-1)] Ultra-high molecular weight polyethylene (A) has an intrinsic viscosity [η] of 33-50 dl / g, preferably 35-45 dl / g, more preferably 38-45 dl / g, and even more preferably 38-42 dl / g, as measured in decalin solvent at 135°C.

[0022] When the intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A), measured in decalin solvent at 135°C, is 33 dl / g or higher, the abrasion resistance of the resin composition (X) tends to be good, and as a result, the abrasion resistance of the molded article obtained from the resin composition (X) tends to be good. Furthermore, when the intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A), measured in decalin solvent at 135°C, is 50 dl / g or lower, the melt fluidity of the resin composition (X) containing ultra-high molecular weight polyethylene (A) tends to be high. In other words, when the intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A) is within the above range, the resin composition (X) can achieve both abrasion resistance and moldability under high load conditions.

[0023] Ultra-high molecular weight polyethylene (A) is a homopolymer of ethylene, or a copolymer of ethylene and α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, or 3-methyl-1-pentene. Preferably, ultra-high molecular weight polyethylene (A) is a homopolymer of ethylene, or a copolymer of ethylene and the above-mentioned α-olefins, and is a copolymer mainly composed of ethylene; more preferably, it is a homopolymer of ethylene. Here, the main component refers to the component with the highest content ratio (mol%) among the constituent units contained in the polymer.

[0024] <Low molecular weight or high molecular weight polyethylene (B)> Polyethylene (B) satisfies the following requirements (b-1) and (b-2).

[0025] [Requirement (b-1)] The intrinsic viscosity [η] of polyethylene (B), measured in decalin solvent at 135°C, is 0.1 to 5.0 dl / g, preferably 0.5 to 3.0 dl / g, more preferably 0.7 to 2.0 dl / g, and even more preferably 0.8 to 1.5 dl / g.

[0026] When the intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is 0.1 dl / g or more, the abrasion resistance of the resin composition (X) tends to be favorable, and as a result, the abrasion resistance of a molded article obtained from the resin composition (X) tends to be favorable. Further, when the intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is 5.0 dl / g or less, the melt fluidity of the resin composition (X) tends to increase. That is, when the intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is 0.1 to 5.0 dl / g, it is easy to obtain a resin composition (X) excellent in both abrasion resistance and moldability under high load conditions.

[0027] [Requirement (b-2)] Polyethylene (B) has a density of 950 to 985 kg / m 3 , preferably 960 to 980 kg / m 3 , more preferably 960 to 975 kg / m 3 , still more preferably 965 to 975 kg / m 3 . When the density of polyethylene (B) is 950 kg / m 3 or more, the crystallinity of polyethylene (B) tends to be high enough to prevent polyethylene (B) from being easily abraded, and as a result, the resulting resin composition (X) tends to be excellent in abrasion resistance under high load conditions. Further, since the density of polyethylene is usually 985 kg / m 3 or less, polyethylene having a density of 985 kg / m 3 or less is used as the polyethylene (B).

[0028] Polyethylene (B) is a homopolymer of ethylene or a copolymer of ethylene and an α-olefin. It is preferably a homopolymer of ethylene. Examples of α-olefins constituting the copolymer include 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, or 1-eicosene. Of these, propylene and 1-butene are preferred due to their relationship with the density range of polyethylene (B).

[0029] Furthermore, it is more preferable that the copolymer of ethylene and α-olefin contains 90 mol% or more of constituent units derived from ethylene, and even more preferable that it contains 95 mol% or more of constituent units derived from ethylene. Also, it is more preferable that the copolymer of ethylene and α-olefin contains 10 mol% or less of constituent units derived from α-olefin, and even more preferable that it contains 5 mol% or less of constituent units derived from α-olefin. When polyethylene (B) is a copolymer of ethylene and α-olefin, a higher amount of constituent units derived from ethylene is preferable.

[0030] <Other ingredients> The resin composition (X) may also contain other thermoplastic resins such as polyolefin resins, or resin additives (for example, stabilizers such as heat-resistant stabilizers and weather-resistant 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 they do not impair the objectives of the present invention. If the above-mentioned other components are included, the total amount of the above-mentioned other components in the resin composition (X) 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 ultra-high molecular weight polyethylene (A) and polyethylene (B) in the resin composition (X) to the total mass of the resin composition (X) is usually 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more.

[0031] <Resin composition (X)> The content of ultra-high molecular weight polyethylene (A) in the resin composition (X) is 5 to 35 parts by mass, preferably 8 to 30 parts by mass, and more preferably 8 to 25 parts by mass (provided that the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass). The polyethylene (B) content in the resin composition (X) is 65 to 95 parts by mass, preferably 70 to 92 parts by mass, and more preferably 75 to 92 parts by mass (provided that the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass).

[0032] When the content of ultra-high molecular weight polyethylene (A) in the resin composition (X) is 35 parts by mass or less and the content of polyethylene (B) is 65 parts by mass or more, the melt fluidity of the resin composition (X) can be made relatively high, so the moldability of the resin composition (X) tends to be good. On the other hand, when the content of ultra-high molecular weight polyethylene (A) is 5 parts by mass or more and the content of polyethylene (B) is 95 parts by mass or less, the resin composition (X) obtains sufficient abrasion resistance derived from the ultra-high molecular weight polyethylene (A), so the abrasion resistance of the resin composition (X) is good and tends to be excellent in abrasion resistance under high load conditions.

[0033] The resin composition (X) satisfies the following requirements (x-1) and (x-2). Preferably, the resin composition (X) satisfies requirement (x-3) in addition to requirements (x-1) and (x-2).

[0034] [Requirements (x-1)] The intrinsic viscosity [η] of the resin composition (X), measured in decalin solvent at 135°C, is in the range of 1.5 to 15 dl / g, preferably in the range of 1.5 to 10 dl / g, more preferably in the range of 2.0 to 8.0 dl / g, and even more preferably in the range of 2.0 to 7.0 dl / g. When the intrinsic viscosity [η] in decalin solvent at 135°C is 1.5 dl / g or higher, the abrasion resistance of the resin composition (X) is good, and it tends to exhibit excellent abrasion resistance under high load conditions. On the other hand, when the intrinsic viscosity [η] in decalin solvent at 135°C is 15 dl / g or lower, the fluidity of the resin composition (X) does not decrease, and the moldability of the resin composition (X) tends to be good. In other words, when the intrinsic viscosity [η] of the resin composition (X) in decalin solvent at 135°C satisfies the above range, the resin composition (X) has high melt fluidity that facilitates molding, while also exhibiting good abrasion resistance under high load conditions, thus achieving both abrasion resistance and moldability.

[0035] [Requirements (x-2)] In a decalin solvent at 135°C, the difference between the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) and the intrinsic viscosity [η] of the polyethylene (B) is in the range of 32 to 49 dl / g, preferably in the range of 34 to 44 dl / g, more preferably in the range of 37 to 44 dl / g, and even more preferably in the range of 37 to 41 dl / g. When the difference in intrinsic viscosity [η] between the ultra-high molecular weight polyethylene (A) and polyethylene (B) is 49 dl / g or less, the resulting resin composition (X) exhibits good abrasion resistance and tends to have excellent abrasion resistance under high load conditions. This is presumed to be because, as the molecular chains of ultra-high molecular weight polyethylene (A) lengthen, even if friction occurs between the molded body obtained from the resin composition (X) and the mating material, the ultra-high molecular weight polyethylene (A) contained in the molded body of resin composition (X) becomes less likely to break. Furthermore, it is presumed that if the difference in intrinsic viscosity [η] between ultra-high molecular weight polyethylene (A) and polyethylene (B) is 32 dl / g or more, it is possible to ensure abrasion resistance derived from ultra-high molecular weight polyethylene (A) while exhibiting melt fluidity derived from polyethylene (B), thus improving the moldability of the resin composition (X).

[0036] [Requirements (x-3)] The resin composition (X) has a melt flow rate (hereinafter also referred to as "MFR") measured at 190°C and a 10 kg load in accordance with the ASTM D1238E measurement method, which is preferably 3 to 50 g / 10 min, more preferably 5 to 40 g / 10 min, and even more preferably 5 to 35 g / 10 min. An MFR within the above range of the composition is preferable because it provides good moldability.

[0037] <Method for producing polyethylene resin composition (X)> The method for producing the resin composition (X) is not particularly limited as long as it is a method that can contain ultra-high molecular weight polyethylene (A) and polyethylene (B) in a predetermined ratio, but preferred methods include the following methods (M-1) to (M-3).

[0038] Method (M-1): A method for producing ultra-high molecular weight polyethylene (A) and polyethylene (B) by first producing each in the presence of an olefin polymerization catalyst, and then blending these ultra-high molecular weight polyethylene (A) and polyethylene (B) so as to satisfy the conditions that the resin composition (X) should satisfy, such as (x-1) and (x-2). Method (M-2): A multi-stage polymerization method comprising at least two steps: a first step of producing ultra-high molecular weight polyethylene (A) in the presence of an olefin polymerization catalyst, and a second step of producing polyethylene (B). The second step is carried out in the presence of the ultra-high molecular weight polyethylene (A) produced in the first step. The polymerization conditions for the first and second steps are selected to satisfy the conditions that the resin composition (X) should satisfy, such as (x-1) and (x-2) described above. Method (M-3): A multi-stage polymerization method comprising at least two steps: a first step of producing polyethylene (B) in the presence of an 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 polyethylene (B) produced in the first step. The polymerization conditions for the first and second steps are selected to satisfy the conditions that the resin composition (X) should satisfy, such as (x-1) and (x-2) above. Furthermore, ultra-high molecular weight polyethylene (A) and polyethylene (B) can be produced, for example, by polymerizing an ethylene-containing monomer in the presence of a known olefin polymerization catalyst described in WO2008 / 013144, WO2010 / 074073, under polymerization conditions (temperature 70°C to 85°C, polymerization time 45 minutes to 300 minutes) such that the resin composition (X) has the desired physical properties.

[0039] Of methods (M-1) to (M-3), methods (M-2) and (M-3) using multi-stage polymerization are more preferred, and method (M-2) in which ultra-high molecular weight polyethylene (A) is produced in the first step is even more preferred. Using multi-stage polymerization is preferable because it makes it easier to achieve both abrasion resistance and moldability, as the ultra-high molecular weight polyethylene (A) and polyethylene (B) contained in the resin composition (X) become compatible and dispersibility is improved. Furthermore, when this composition is produced using method (M-2), the molecular weight of the polyethylene (polyethylene (B)) obtained in the second step can be easily adjusted to be lower than the molecular weight of the polyethylene (ultra-high molecular weight polyethylene (A)) obtained in the first step by adding a chain transfer agent to induce a chain transfer reaction and raising the polymerization temperature in the second step, thus being preferable in terms of superior production efficiency.

[0040] In this process, the olefins used for polymerization, such as ethylene, can be any of the various olefins listed in the sections on ultra-high molecular weight polyethylene (A) and polyethylene (B) without limitation.

[0041] Molded body The resin composition (X) can be molded into containers, trays, sheets, rods, films, or coatings for various molded bodies by conventionally known methods, specifically, for example, injection molding, shape extrusion molding, pipe molding, tube molding, coating molding of different molded bodies, injection blow molding, direct blow molding, T-die sheet or film molding, inflation film molding, press molding, etc.

[0042] The molded articles obtained by the above molding method can be widely used in conventional polyethylene applications, but they are particularly abrasion-resistant, and are therefore used in applications where this is required, such as coatings for metals like steel pipes, electric wires, and automobile slide rails; pressure-resistant rubber hoses; gaskets for automobile doors; gaskets for cleanroom doors; various rubber reels such as automobile glass run channels and automobile weatherstrips; sliding materials such as various guide rails and elevator rail guides; and various protective liner materials.

[0043] When a molded article obtained from resin composition (X) is subjected to a high-load abrasion test (test temperature 23°C, mating material S45, load 25 kg, speed 30 m / min, sliding distance 3 km), the amount of abrasion is preferably 1000 mg or less, more preferably 500 mg or less. A smaller amount of abrasion is preferable, but the lower limit is usually 0.1 mg or more. When the amount of abrasion obtained from the abrasion test under the above conditions is within the above range, it is preferable because the abrasion resistance of the molded article obtained from resin composition (X) is sufficient in the usage environment. [Examples]

[0044] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0045] [Measurement conditions, etc.] The measurement conditions for each physical property are as follows:

[0046] [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. In the following, the intrinsic viscosity of ultra-high molecular weight polyethylene (A) is referred to as "intrinsic viscosity [η]". u It is sometimes written as "intrinsic viscosity [η]" for polyethylene (B). Similarly, the intrinsic viscosity of polyethylene (B) is sometimes written as "intrinsic viscosity [η] h It is sometimes written as follows: "Intrinsic viscosity [η] u It is sometimes written as "."

[0047] 〔density〕 The density of polyethylene (B) was measured in accordance with ASTM D1505.

[0048] [MFR] The MFR of the resin compositions obtained in the examples or comparative examples was measured under a 10 kg load in accordance with ASTM D1238E. The measurement temperature was 190°C.

[0049] [Example 1] [Preparation of solid titanium catalyst component [C1]] 75.0 g of anhydrous magnesium chloride, 280.3 g of decane, and 308.3 g of 2-ethylhexyl alcohol were placed in a reaction vessel and heated at 130°C for 3 hours. Then, 19.9 g of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added, and the mixture was stirred and mixed at 100°C for 1 hour. The homogeneous solution obtained in this manner was cooled to room temperature. Then, the entire 30 ml of the homogeneous solution was added dropwise over 45 minutes with stirring to 80 ml of titanium tetrachloride kept at 0°C to form a mixture. After the dropwise addition was complete, the resulting mixture was heated to 110°C over 6 hours, and 0.55 g of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added. The mixture was then kept at 110°C with stirring for 2 hours. After the 2-hour reaction was complete, the solid portion was collected by thermal filtration and washed with 90°C decane until no free titanium compounds were detected in the washings, followed by thorough washing with hexane at room temperature.

[0050] The solid titanium catalyst components prepared by the above procedure were stored as a decance slurry, and a portion of it was dried in order to investigate the catalyst composition. The composition of the dried solid titanium catalyst component [C1] was 2.8% by mass of titanium, 18.1% by mass of magnesium, 58.2% by mass of chlorine, 19.6% by mass of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane, and 1.4% by mass of 2-ethylhexyl alcohol residues.

[0051] [Manufacturing of polyethylene resin composition (X1)] 500 ml of purified decane was charged into a 1-liter polymer chamber that had been thoroughly purged with nitrogen. At a temperature of 65°C, 0.5 mmol of triisobutylaluminum and solid titanium catalyst component [C1] (0.01 mmol in terms of titanium atoms) were added. Then, ethylene was fed into the polymer chamber until the pressure reached 0.40 MPaG gauge pressure, and the first stage of ethylene polymerization was carried out at a temperature of 70°C. When 14 liters of ethylene had been fed, the ethylene feed was stopped, the temperature was rapidly cooled to 45°C, and then depressurization and nitrogen purging were performed. By performing the first stage of ethylene polymerization under the above conditions, ultra-high molecular weight polyethylene (A1) is obtained as the first stage polyethylene.

[0052] Next, hydrogen was fed into the polymerizer until the pressure inside the polymerizer reached 0.40 MPaG gauge pressure, and then ethylene was fed in until the pressure inside the polymerizer reached 0.60 MPaG gauge pressure. The second stage of ethylene polymerization was carried out at a temperature of 85°C. When 128 liters of ethylene had been fed, the ethylene feed was stopped, the temperature was rapidly cooled to 40°C, and then depressurization and purging were performed. By performing the second stage of ethylene polymerization under the above conditions, low molecular weight or high molecular weight polyethylene (B1) can be obtained as the second stage polyethylene.

[0053] The slurry containing the solid prepared above was filtered and dried under reduced pressure at 80°C overnight. The resulting polyethylene resin composition (X1) was 178 g, and its intrinsic viscosity [η] was 3.2 dl / g. The polymerization was repeated multiple times to obtain the amount required for evaluation.

[0054] [Analysis of each component in polyethylene resin composition (X1)] • Content and intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A1) When only the first stage of polymerization, which was carried out during the production of polyethylene resin composition (X1), was performed separately under the same conditions as during the production of the polyethylene resin composition, the yield of the resulting ethylene polymer was 17.8 g. Since ultra-high molecular weight polyethylene (A1) was produced by this polymerization, the content of ultra-high molecular weight polyethylene (A1) in the polyethylene resin composition (yield 178 g) was calculated to be 10.0 mass%. Furthermore, the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A1) contained in polyethylene resin composition (X1) was measured to be 39.0 dl / g.

[0055] • Polyethylene (B1) content and physical properties Polyethylene (B2) was produced by omitting the first stage of polymerization during the production of polyethylene resin composition (X1) and separately performing only the second stage of polymerization under the same conditions as during the production of polyethylene resin composition (X1). The intrinsic viscosity [η] of polyethylene (B2) was 1.0 dl / g, and its density was 971 kg / m³. 3 That was the case. Next, the molecular weight distribution of polyethylene (B2) was measured by gel permeation chromatography (GPC), and compared with the results of the GPC molecular weight distribution measurement for polyethylene resin composition (X1). The peak positions and shapes of the chromatograms were consistent with those of the lower molecular weight component (polyethylene (B1)) contained in polyethylene resin composition (X1). The GPC analysis conditions were the same for both the analysis of polyethylene (B2) and the analysis of polyethylene resin composition (X1). Based on these results, the physical properties of polyethylene (B1) were considered to be the same as those of polyethylene (B2). Specifically, the intrinsic viscosity [η] of polyethylene (B1) was set to 1.0 dl / g, and the density of polyethylene (B1) was set to 971 kg / m³. 3 That's what I decided.

[0056] [Granulation of polyethylene resin composition (X1)] The polyethylene resin composition (X1) obtained above was dry-blended with Irganox 1010 (BASF), Irgaphos 168 (BASF), and calcium stearate (NOF Corporation). The blending amounts of each substance were 0.1% by mass for Irganox 1010, 0.2% by mass for Irgaphos 168, and 0.12% by mass for calcium stearate, relative to 100% by mass of the dry-blended composition. The dry-blended composition was melt-kneaded using a twin-screw extruder (Technovel Co., Ltd., φ=15mm, L / D=30, cylinder temperature: 200℃), and then granulated into pellets. The physical properties of the polyethylene resin composition (X1) were measured using the resulting pellets. The results are shown in Table 1.

[0057] [Molding of molded bodies] The pellets obtained as described above were injection molded using an injection molding machine (NEX30-3E, manufactured by Nissei Plastic Industrial Co., Ltd.) to produce test specimens measuring 30 cm in length, 30 cm in width, and 2 mm in thickness.

[0058] [Evaluation of slip resistance and abrasion resistance (ring abrasion test)] Using the test specimens obtained above, the specific wear was measured using a Suzuki friction and wear tester in accordance with JIS K 7218 "Sliding and Wear Test Method for Plastics". The test conditions were: mating material: S45C, speed: 30 m / min, sliding distance: 3 km, load: 25 kg, and measurement ambient temperature: 23 °C.

[0059] [Example 2] Except for changing the amount of ethylene feed in the first polymerization stage from 14 liters to 18 liters and the amount of ethylene feed in the second polymerization stage from 128 liters to 120 liters, the polyethylene resin composition (X2) was manufactured, analyzed, granulated, molded, and its physical properties were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0060] [Example 3] Except for changing the amount of ethylene feed in the first polymerization stage from 14 liters to 26 liters and the amount of ethylene feed in the second polymerization stage from 128 liters to 112 liters, the polyethylene resin composition (X3) was manufactured, analyzed, granulated, molded, and its physical properties were evaluated in the same manner as in Example 1. The results are shown in Table 1. Furthermore, Figure 1 shows a photograph of a specimen of a polyethylene resin composition (X3) after a sliding abrasion test performed under a 25 kg load. In the specimen shown in Figure 1, although a ring-shaped area was worn away at the friction point with the mating material, the friction point was only shallowly worn.

[0061] [Comparative Example 1] [Preparation of solid titanium catalyst component [C2]] 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 at 130°C for 1 hour to obtain a homogeneous solution. The homogeneous solution obtained in this way was cooled to room temperature. Then, the entire 50 ml of the homogeneous solution was added dropwise to 200 ml of titanium tetrachloride, which was kept at 0°C, over 60 minutes with stirring to form a mixture. After the dropwise addition was complete, the resulting mixture was kept at 0°C for 1 hour. The temperature of the mixture was then raised to 20°C over 1 hour, and then 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 carried out for 2 hours while maintaining the temperature at 80°C. After the 2-hour reaction was complete, the solid portion was collected by thermal filtration, and this solid portion was resuspended in 200 ml of titanium tetrachloride. A second heating reaction was then carried out at 90°C for 2 hours. After the second heating reaction was complete, the solid portion was again collected by thermal filtration, washed with decane at 90°C until no free titanium compounds were detected in the washings, and then thoroughly washed with hexane at room temperature.

[0062] The solid titanium catalyst components prepared by the above procedure were stored as a decance slurry, and a portion of it was dried in order to investigate the catalyst composition. The composition of the dried solid titanium catalyst component [C2] was 3.1% by mass of titanium, 18% by mass of magnesium, 60% by mass of chlorine, 15.4% by mass of ethyl benzoate, and 1.5% by mass of 2-ethylhexyl alcohol residues.

[0063] [Manufacturing of polyethylene resin composition (CX1)] A polyethylene resin composition (CX1) was produced in the same manner as in Example 1, except that the catalyst component was changed from [C1] to [C2], the catalyst component input temperature was changed from 65°C to 48°C, the ethylene polymerization temperature in the first stage of polymerization was changed from 70°C to 53°C, the amount of ethylene fed in the first stage was changed from 14 liters to 21 liters, and the amount of ethylene fed in the second stage was changed from 128 liters to 119 liters. Analysis of each component in the polyethylene resin composition (CX1) was performed in the same manner as in Example 1, and it was found that the polyethylene resin composition (CX1) contained 15% by mass of ultra-high molecular weight polyethylene (CA1) (intrinsic viscosity [η] = 30 dl / g in decalin at 135°C) and 85% by mass of polyethylene (B) (intrinsic viscosity [η] = 1.0 dl / g in decalin at 135°C) per 100% by mass of polyethylene resin composition (CX1). The obtained polyethylene resin composition (CX1) was granulated, molded, and its physical properties were evaluated in the same manner as in Example 1. Furthermore, Figure 2 shows a photograph of a test piece after a sliding abrasion test performed on a molded polyethylene resin composition (CX1) under a 25 kg load. From Figure 2, it can be seen that the ring formed at the friction point with the mating material penetrates the test piece.

[0064] [Comparative Example 2] Except for changing the amount of ethylene feed in the first polymerization stage from 21 liters to 28 liters and the amount of ethylene feed in the second polymerization stage from 119 liters to 112 liters, the polyethylene resin composition (CX2) was manufactured, analyzed, granulated, molded, and its physical properties evaluated in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0065] [Comparative Example 3] Except for changing the amount of ethylene feed in the first polymerization stage from 21 liters to 33.6 liters and the amount of ethylene feed in the second polymerization stage from 119 liters to 106.4 liters, the polyethylene resin composition (CX3) was manufactured, analyzed, granulated, molded, and its physical properties evaluated in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0066] [Table 1]

[0067] The amount of wear in the sliding abrasion test (25 kg load) of molded articles obtained from the polyethylene resin compositions was smaller in all of Examples 1 to 3 than in Comparative Examples 1 to 3, demonstrating that the polyethylene resin compositions of Examples 1 to 3 have high abrasion resistance under high loads.

Claims

1. 5 to 35 parts by mass of ultra-high molecular weight polyethylene (A) that meets the following requirement (a-1), It contains 95 to 65 parts by mass of low molecular weight or high molecular weight polyethylene (B) that meet the following requirements (b-1) and (b-2) (provided that the total amount of ultra-high molecular weight polyethylene (A) and low molecular weight or high molecular weight polyethylene (B) is 100 parts by mass), A polyethylene resin composition (X) that satisfies the following requirements (x-1) and (x-2). (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 33–50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 to 5.0 dl / g; (b-2) Density of 965-985 kg / m³ 3 It is; (x-1) The intrinsic viscosity [η] of the polyethylene resin composition (X), measured in decalin solvent at 135°C, is in the range of 1.5 to 15 dl / g; (x-2) The difference between the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) and the intrinsic viscosity [η] of the low molecular weight or high molecular weight polyethylene (B), measured in decalin solvent at 135°C, is in the range of 32 to 49 dl / g.

2. The polyethylene resin composition (X) according to claim 1, wherein the melt flow rate measured at 190°C and a 10 kg load in accordance with ASTM D1238E is 3 to 50 g / 10 min.

3. The polyethylene resin composition (X) according to claim 1, wherein the difference between the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) and the intrinsic viscosity [η] of the low molecular weight or high molecular weight polyethylene (B), measured in a decalin solvent at 135°C, is in the range of 37 to 44 dl / g.

4. A molded article comprising the polyethylene resin composition (X) according to any one of claims 1 to 3.

5. A first step to produce ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] of 33 to 50 dl / g as measured in a decalin solvent at 135°C, and, The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 0.1 to 5.0 dl / g, and the difference between this and the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) measured in decalin solvent at 135°C is in the range of 32 to 49 dl / g, and the density is 965 to 985 kg / m³. 3 The second step is to produce low molecular weight or high molecular weight polyethylene (B), A multi-stage polymerization method including at least two steps, A method for producing a polyethylene resin composition (X), wherein the polyethylene resin composition (X) has an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 1.5 to 15 dl / g.

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