Stretched film and method for producing stretched film

Abstract

To provide a stretched film that exhibits excellent abrasion resistance while containing both ultra-high molecular weight polyethylene and polyethylene with an intrinsic viscosity [η] lower than that of the ultra-high molecular weight polyethylene.SOLUTION: There is provided a stretched film comprising: an ultra-high molecular weight polyethylene (A) satisfying requirement (a-1) of 5 to 40 pts.mass; and a low molecular weight or high molecular weight polyethylene (B) satisfying requirements (b-1) and (b-2) of 95 to 60 pts.mass (the total amount of (A) and (B) is 100 pts.mass). The intrinsic viscosity [η] measured in decalin solvent at 135°C falls within the range of 1.5 to 15 dL / g, and at least a portion of the stretched film forms 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; and (b-2) Density is 950 to 985 kg / m3.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oriented film containing ultra-high molecular weight polyethylene and a method for producing the oriented film. [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 composition obtained by blending 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 with a specific polyolefin resin composition. This composition produces molded articles with an excellent balance of abrasion resistance, appearance, and moldability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 12606 / 1983 [Patent Document 2] International Publication No. 2003 / 022920 Summary of the Invention [Problem to be solved by the invention]

[0007] As proposed in Patent Documents 1 and 2, when a resin obtained by blending ultra-high molecular weight polyethylene with polyethylene having a low intrinsic viscosity [η] is used, the film obtained by stretching may have insufficient abrasion resistance depending on the application. However, when attempting to melt-stretch ultra-high molecular weight polyethylene, there is a problem in that the ultra-high molecular weight polyethylene is prone to breakage during stretching due to the high degree of entanglement of molecular chains per molecular chain.

[0008] An object of the present invention is to provide a stretched film that contains ultra-high molecular weight polyethylene and polyethylene having a lower intrinsic viscosity [η] than that of the ultra-high molecular weight polyethylene, yet has excellent abrasion resistance. [Means for solving the problem]

[0009] 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.

[0010] [1] A composition comprising 5 to 40 parts by mass of an ultra-high molecular weight polyethylene (A) that satisfies the following requirement (a-1) and 95 to 60 parts by mass of a low-molecular weight or high-molecular weight polyethylene (B) that satisfies the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass), A stretched film having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 1.5 to 15 dl / g and at least a part of which forms 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.

[0011] [2] The stretched film according to [1], wherein the homogeneous phase is a phase in which no domains of 3 μm or more are observed when the cross section of the stretched film is observed with a laser microscope at a magnification of 1000 times.

[0012] [3] The stretched film according to [1] or [2], which has a thickness of 1 to 200 μm.

[0013] [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 step of producing a 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 and at least a part of which forms a homogeneous phase; a stretch-molding step of stretch-molding the polyethylene resin composition (X); A method for producing a stretched film, comprising: [Effects of the Invention]

[0014] According to the present invention, there is provided a stretched film which contains ultra-high molecular weight polyethylene and polyethylene having a lower intrinsic viscosity [η] than that of the ultra-high molecular weight polyethylene, and yet has excellent abrasion resistance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an example of a laser microscope photograph (magnification: 1000 times) of a cross section of the stretched film obtained in Example 1. [Figure 2] 1 is an example of a laser microscope photograph (magnification: 1000 times) of a cross section of the stretched film obtained in Example 2. [Figure 3] 1 is an example of a laser microscope photograph (magnification: 1000 times) of a cross section of a stretched film obtained in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Stretched film> The stretched film according to the present invention 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-1) and (x-2). In the following description, the resin composition that is the material for the stretched film according to the present invention will also be referred to as polyethylene resin composition (X) (or "resin composition (X)"). In other words, the stretched film according to the present invention is a stretched film obtained by stretching resin composition (X).

[0017] [Requirements (x-1)] The intrinsic viscosity [η] of the stretched film according to the present invention, measured in decalin at 135°C, is in the range of 1.5 to 15 dL / g, preferably 1.5 to 10 dL / g, more preferably 2.0 to 8.0 dL / g, and even more preferably 2.0 to 7.0 dL / g. That is, the intrinsic viscosity [η] of the resin composition (X) measured in decalin at 135°C satisfies the above range. 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 and high abrasion resistance, thereby achieving both abrasion resistance and moldability. As a result, the stretched film obtained from the resin composition (X) also has high abrasion resistance. If the intrinsic viscosity [η] in decalin solvent at 135°C is less than 1.5 dL / g, the abrasion resistance of the composition is impaired, and the abrasion resistance of the stretched film obtained from such a composition tends to be poor. 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 decreases, and the moldability is impaired.

[0018] [Requirements (x-2)] At least a portion of the stretched film according to the present invention forms a homogeneous phase. That is, in the stretched film according to the present invention, at least a portion thereof forms a homogeneous phase due to the compatibility of the ultra-high molecular weight polyethylene (A) and the polyethylene (B), and in the homogeneous phase portion, phase separation between the ultra-high molecular weight polyethylene (A) and the polyethylene (B) does not occur.

[0019] Whether at least a part of a stretched film is a homogeneous phase is determined based on the size of island phases (domains) observed when a thin section prepared by cutting the stretched film with a microtome is observed under a laser microscope under the conditions described in the Examples below. Homogeneous phase: The stretched film does not contain domains larger than 3 μm. Phase separation: A stretched film of the composition contains domains of 3 μm or larger. That is, it is preferable that the stretched film according to the present invention does not have a sea-island structure containing domains of 3 μm or more.

[0020] A stretched film in which the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are compatible with each other to form a homogeneous phase at least in part is preferred because it has excellent abrasion resistance and good surface smoothness. One reason why the stretched film of the present invention has excellent abrasion resistance is that the abrasion resistance derived from the ultra-high molecular weight polyethylene (A) is particularly strong in the parts where the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are compatible enough to form a homogeneous phase. Here, the stretched film of the present invention has particularly good abrasion resistance when parts in which the ultra-high molecular weight polyethylene (A) and the polyethylene (B) form a homogeneous phase are distributed throughout the stretched film, and when the entire stretched film is a homogeneous phase. The reason why the stretched film of the present invention has excellent surface smoothness is that the stretched film does not contain domains of 3 μm or more, and therefore does not cause roughness due to domains located on the surface of the stretched film.

[0021] 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 stretched film, so the polyethylene (B) portion wears off, and then the domains located on the abraded surface fall off, further increasing the abrasion, thereby impairing the abrasion resistance of the stretched film. Furthermore, when a stretched film is produced from a composition in which the ultra-high molecular weight polyethylene (A) and the polyethylene (B) are phase-separated, the domains formed by the ultra-high molecular weight polyethylene (A) are located near the surface of the stretched film, causing roughness and impairing the surface smoothness of the stretched film.

[0022] <Resin composition (X)> Resin composition (X) contains ultra-high molecular weight polyethylene (A) and polyethylene (B) and satisfies the requirements (x-1) and (x-2). That is, the intrinsic viscosity [η] of resin composition (X) measured in decalin solvent at 135°C satisfies the range described in relation to requirement (x-1). Furthermore, at least a portion of resin composition (X) forms a homogeneous phase.

[0023] The content of the ultra-high molecular weight polyethylene (A) in the resin composition (X) 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 resin composition (X) 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 resin composition (X) become good.

[0024] 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. As a result, the stretchability of the resulting film will be poor. 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 of the resulting composition will be poor because the abrasion resistance derived from the ultra-high molecular weight polyethylene (A) will be insufficient. As a result, the abrasion resistance of the resulting stretched film will also tend to be reduced.

[0025] It is believed that the formability and abrasion resistance of resin composition (X) are related not only to the contents of ultra-high molecular weight polyethylene (A) and polyethylene (B) but also to the fact that at least a portion of resin composition (X) forms a homogeneous phase. Specifically, it is believed that in areas where ultra-high molecular weight polyethylene (A) and polyethylene (B) form a homogeneous phase, film thickness unevenness is less likely to occur during stretch molding than in areas where ultra-high molecular weight polyethylene (A) and polyethylene (B) are phase-separated. As a result, it is believed that in areas where ultra-high molecular weight polyethylene (A) and polyethylene (B) form a homogeneous phase, there are fewer areas where strength is relatively weakened due to thickness unevenness, making breakage less likely to occur during stretch molding. Furthermore, because there are homogeneous phase areas where breakage due to thickness unevenness is less likely to occur, resin composition (X) has excellent formability and can be easily formed into a stretched film, despite being a resin containing a relatively large amount of ultra-high molecular weight polyethylene (A).

[0026] The resin composition (X) preferably has a melt flow rate (hereinafter also referred to as "MFR") of 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, measured at 190°C under a load of 10 kg in accordance with the measurement method of ASTM D-1238E. When the MFR of the resin composition (X) is in the above range, it is preferable because the stretch moldability is good.

[0027] <Ultra-high molecular weight polyethylene (A)> The ultra-high molecular weight polyethylene (A) blended into the resin composition (X) has an intrinsic viscosity [η] measured in decalin solvent at 135° C. of 8 to 50 dL / g, preferably 8.5 to 45 dL / g, more preferably 9 to 42 dL / g, even more preferably 9.5 to 40 dL / g, and particularly preferably 10 to 35 dL / g. When the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) is within the above range, the resin composition (X) can achieve both abrasion resistance and stretch formability, and as a result, a stretched film with excellent abrasion resistance can be obtained.

[0028] When an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of less than 8 dL / g measured in decalin at 135°C is used instead of the ultra-high molecular weight polyethylene (A), the abrasion resistance of the composition tends to deteriorate, and the abrasion resistance of the resulting stretched film tends to be poor. On the other hand, when an ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of more than 50 dL / g measured in decalin at 135°C is used instead of the ultra-high molecular weight polyethylene (A), the melt fluidity of the composition decreases, and the formability of the composition decreases, and as a result, the stretch formability of the film tends to deteriorate.

[0029] The ultra-high molecular weight polyethylene (A) is an ethylene homopolymer 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 an ethylene homopolymer or a copolymer of ethylene and the above α-olefin, a copolymer composed mainly of ethylene, and more preferably an ethylene homopolymer. Here, the term "main component" refers to the component with the highest content (mol %) of the structural units contained in the polymer.

[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, measured in decalin at 135°C. When the polyethylene (B) has an intrinsic viscosity [η] within the above range, a resin composition (X) having excellent abrasion resistance and stretch moldability can be obtained, and as a result, a stretched film having excellent abrasion resistance can be obtained.

[0031] When a low-molecular-weight 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, and the abrasion resistance of the resulting molded article tends to be inferior. On the other hand, when a low-molecular-weight 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 formability of the composition and, as a result, tends to deteriorate the stretchability and formability of the film.

[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 resin composition (X) having excellent abrasion resistance and stretch formability can be obtained, and as a result, a stretched film having excellent abrasion resistance and stretch formability 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 tendency for the abrasion resistance of the resulting stretched film to be poor. 3 Therefore, the resin composition (X) has a viscosity of 985 kg / m 3 Low 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] In addition, the copolymer of ethylene and an α-olefin preferably contains 90 mol % or more of structural units derived from ethylene, and more preferably 95 mol % or more of structural units derived from ethylene. When the polyethylene (B) is a copolymer of ethylene and an α-olefin, the greater the amount of structural units derived from ethylene, the better.

[0036] <Other ingredients> The resin composition (X) and the stretched film obtained from the resin composition (X) may contain other thermoplastic resins such as polyolefin resins (provided that they are different from the ultra-high molecular weight polyethylene (A) and the polyethylene (B)), 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 object of the present invention is not impaired. When the other components are contained, the total amount of the other components in the resin composition (X) (or in the stretched film obtained from 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 sum of the mass of the ultra-high molecular weight polyethylene (A) and the mass of the polyethylene (B) in the resin composition (X) to the 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. Similarly, the proportion of the sum of the mass of the ultra-high molecular weight polyethylene (A) and the mass of the polyethylene (B) in the stretched film obtained from the resin composition (X) to the mass of the stretched film is usually 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more.

[0037] <Method for producing polyethylene resin composition (X)> Hereinafter, a method for producing the resin composition (X) will be described, but the treatment carried out in the method for producing the resin composition (X) also serves as a production step in the method for producing a stretched film, which will be described later. Resin composition (X) is produced by a multi-stage polymerization method 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 a film 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 a film or the like, it is likely to form a sea-island structure, making it difficult to form a homogeneous phase.

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

[0041] <Method of manufacturing stretched film> The method for producing a stretched film according to the present invention includes a producing step of producing a resin composition (X) and a stretch molding step of stretch molding the resin composition (X). The producing step of producing the resin composition (X) is as described in the method for producing the resin composition (X).

[0042] [Stretch molding process] In the stretch-molding step, a film made of resin composition (X) is produced and then uniaxially stretched. In the stretch-molding step, the resin composition (X) may be molded into a film by T-die extrusion molding or the like at a temperature in the range of 200 to 300°C, and the resulting film may then be uniaxially stretched. Alternatively, the stretch-molding step may be carried out by using a single-screw extruder to melt the resin composition (X) at a temperature in the range of 200 to 300°C and melt-cast molding the melt while taking it up at a roll temperature of 60 to 90°C and a take-up speed of 0.2 to 1.8 m / min.

[0043] The stretching ratio, calculated in terms of length, is preferably 1.1 to 80, more preferably 1.5 to 60, and even more preferably 2 to 40. When the stretching ratio is within the above range, a stretched film having excellent abrasion resistance can be obtained.

[0044] The stretching temperature is preferably between the glass transition temperature (Tg) and the melting point (Tm) of the polymers, such as the ultra-high molecular weight polyethylene (A) and polyethylene (B), contained in the resin composition (X) used for stretching. For example, stretching at a temperature of 100 to 220°C provides a stretched film with excellent abrasion resistance.

[0045] <Applications of oriented film> The stretched film according to the present invention 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 resistance, such as various rubber reels for automobile glass run channels and automobile weather strips, conveyor guide covers for various transport devices, sliding surfaces for multifunction machines, guide rails for vending machines and store shelves, the bottom surfaces and mouse pads of PC mice, hopper linings, and sliding tapes.

[0046] <Physical properties of stretched film> The stretched film according to the present invention is obtained by stretching the resin composition (X), and therefore contains all of the components contained in the resin composition (X), and the amount of each component is the same as the amount in the resin composition (X). For example, the content of the ultra-high molecular weight polyethylene (A) in the stretched film according to the present invention 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). Similarly, the content of polyethylene (B) in the stretched film according to the present invention 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 the ultra-high molecular weight polyethylene (A) and the polyethylene (B) is 100 parts by mass).

[0047] The dynamic friction coefficient measured by bringing the stretched film according to the present invention into contact with glass (measurement conditions: counter material: glass plate (U-shaped), load: 250 g, speed: 150 mm / s, number of reciprocations: 5,000, stroke: 100 mm, measurement environment temperature: 23°C) is preferably in the range of 0.07 to 0.15, more preferably 0.07 to 0.10. When the dynamic friction coefficient of the stretched film is in the above range, it is expected that wear and heat generation due to friction will be suppressed and noise during sliding will be reduced.

[0048] When an abrasion test (counterpart: glass plate (U-shaped), load: 250 g, speed: 150 mm / s, number of reciprocations: 5000, stroke: 100 mm, measurement environment temperature: 23°C) is conducted on the stretched film of the present invention, the abrasion thickness is preferably 10 μm or less, more preferably 6 μm or less. The smaller the abrasion thickness, the better, but the lower limit is usually 2 μm or more. If the abrasion thickness of the stretched film in the abrasion test is within the above range, the abrasion resistance is sufficient in the usage environment of the stretched film of the present invention, and this is therefore preferred.

[0049] The surface roughness (arithmetic mean roughness (Ra)) of the stretched film according to the present invention is preferably less than 3.0 μm, more preferably 2.0 μm or less. The lower the surface roughness, the better, but the lower limit is usually 0.1 μm or more. When the surface roughness of the stretched film is in the above range, the surface smoothness is sufficient, which is preferable.

[0050] The thickness of the stretched film according to the present invention is not particularly limited, but is preferably 1 to 200 μm, more preferably 15 to 100 μm, and even more preferably 30 to 50 μm. [Example]

[0051] 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.

[0052] [Measurement conditions, etc.] The conditions for measuring each physical property are as follows:

[0053] [Intrinsic viscosity [η]] The intrinsic viscosity [η] of the various polymers and resin compositions obtained in the following Examples and Comparative Examples was measured at 135°C in decalin solvent. Hereinafter, the intrinsic viscosity of the ultra-high molecular weight polyethylene (A) will be referred to as "intrinsic viscosity [η] a Similarly, the intrinsic viscosity of polyethylene (B) is sometimes expressed as "Intrinsic viscosity [η] b " is sometimes written as ".

[0054] 〔density〕 The density of the polyethylene (B) was measured in accordance with ASTM D1505.

[0055] [MFR] The MFR of the compositions obtained in the following Examples and Comparative Examples was measured under a load of 10 kg at a temperature of 190°C in accordance with ASTM D1238E.

[0056] [Phase structure] The stretched films obtained in the following Examples and Comparative Examples were cut with a microtome to prepare thin sections of the stretched films. The cross sections of the films were then observed using a laser microscope (manufactured by Olympus) with a 1000x objective lens, and the homogeneity of the film was determined according to the following criteria. Homogeneous phase: No domains larger than 3 μm were observed in the cross section of the stretched film. Sea-island structure: Domains of 3 μm or more were observed in the cross section of the stretched film.

[0057] [Film surface roughness] The arithmetic mean roughness (Ra) of the surface of the stretched film obtained in the following Examples or Comparative Examples was determined by a method in accordance with JIS B 0601.

[0058] [Film wear thickness, dynamic friction coefficient] The stretched films obtained in the following examples or comparative examples were cut into strips (150 mm x 20 mm), and the thickness (fb) of each cut stretched film before the abrasion test was measured using a thickness gauge (Mitutoyo Corporation, ID-C112X). Each stretched film was then subjected to an abrasion test using a robotic arm friction and wear tester (Shinto Scientific Co., Ltd., TRIBOGEAR TYPE:31), and the dynamic friction coefficient was also measured. The test conditions for the abrasion test were: counter material: glass plate (U-shaped), load: 250 g, speed: 150 mm / s, number of reciprocations: 5,000, stroke: 100 mm, and measurement environment temperature: 23°C. The thickness (fa) after the abrasion test was also determined for each film after the abrasion test. For each film, the difference between the thickness (fb) before the abrasion test and the thickness (fa) after the abrasion test was calculated and used as the abrasion thickness of that film.

[0059] [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.

[0060] 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.

[0061] [Production of polyethylene resin composition (X1)] 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 (X1) weighed 190 g and had an intrinsic viscosity [η] in decalin solvent at 135° C. of 3.9 dl / g.

[0062] [Analysis of each component in polyethylene resin composition (X1)] Polyethylene (B1) content and properties Of the polymerizations carried out to produce polyethylene resin composition (X1), only the first stage polymerization was carried out separately under the same conditions as those used to produce polyethylene resin composition (X1). The yield of the resulting ethylene polymer was 162 g. Since polyethylene (B1) was produced by this polymerization, the content of polyethylene (B1) in polyethylene resin composition (X1) (yield 190 g) was calculated to be 85 mass %. The intrinsic viscosity [η] of the resulting polyethylene (B1) was measured in decalin solvent at 135°C and found to be 1.0 dl / g. The density of the resulting polyethylene (B1) was 971 kg / m 3 It was.

[0063] Ultra-high molecular weight polyethylene (A2) content and intrinsic viscosity [η] The first stage polymerization of the polymerization carried out to produce the polyethylene resin composition (X1) was omitted, and only the second stage polymerization was carried out separately under the same conditions as those used to produce the polyethylene resin composition (X1), thereby producing an 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). The results were compared with those of the polyethylene resin composition (X1) by GPC. 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 (X1). 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.

[0064] [Granulation of polyethylene resin composition (X1)] The obtained polyethylene resin composition (X1) 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 Co., Ltd., φ=15 mm, L / D=30, cylinder temperature: 200°C), and then granulated into pellets. The MFR was measured using the obtained pellets. The results are shown in Table 1.

[0065] [Production of stretched film] The pellets obtained above were melt-cast using a single-screw extruder (φ=20 mm, L / D=28) manufactured by Toyo Seiki Seisaku-sho, Ltd., under conditions of a cylinder temperature of 290°C, a die temperature of 290°C, a roll temperature of 80°C, and a take-up speed of 0.3 m / min to obtain a stretched film with a thickness of 50 μm. The stretching ratio was 20 times in terms of length. The stretching ratio was calculated from the ratio of the die thickness (1 mm) to the thickness of the stretched film (0.05 mm). The evaluation results of the obtained film are shown in Table 1, and a photograph of the cross section of the film is shown in Figure 1.

[0066] [Example 2] In the second-stage polymerization for producing the polyethylene resin composition, the ethylene polymerization temperature was changed from 53°C to 80°C, and the stretching ratio (equivalent to length) was changed to 40 times, but polymerization, granulation, and production and evaluation of a stretched film were carried out in the same manner as in Example 1. The thickness of the obtained film was 25 μm. The physical properties of the obtained composition and the evaluation results of the film are shown in Table 1, and a photograph of the cross section of the film is shown in Figure 2.

[0067] [Comparative Example 1] A composition was produced by exchanging the first-stage polymerization conditions and second-stage polymerization conditions of Example 1. Specifically, the catalyst component introduction temperature was changed from 80°C to 48°C, hydrogen was not fed in the first-stage polymerization, 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. Furthermore, in the second-stage polymerization, hydrogen was fed until the pressure inside the polymerization vessel reached 0.40 MPaG in 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. Granulation, production of a stretched film, and evaluation were carried out in the same manner as in Example 1. The physical properties of the obtained composition and the evaluation results of the film are shown in Table 1, and a photograph of the cross section of the film is shown in FIG.

[0068] [Table 1]

[0069] From the cross-sectional photographs of the films (FIGS. 1 to 3), it is clear that in Examples 1 and 2, stretched films were obtained that satisfied requirement (x-2) (i.e., at least a portion was a homogeneous phase). On the other hand, in Comparative Example, a sea-island structure was observed throughout the film, and no portion constituting a homogeneous phase was observed, so requirement (x-2) was not satisfied. In Examples 1 and 2, the abrasion thickness was smaller than in Comparative Example 1, so that Examples 1 and 2, which are stretched films that satisfy requirement (x-2), had superior abrasion resistance compared to the stretched film of Comparative Example 1, which does not satisfy requirement (x-2). Furthermore, the surface roughness Ra of the stretched films of Examples 1 and 2, which satisfy requirement (x-2), is lower than that of the stretched film of Comparative Example 1, which does not satisfy requirement (x-2). In other words, it was found that the stretched films satisfying requirement (x-2) have excellent surface smoothness. Furthermore, the cross-sectional views of the film cross sections (Figs. 1 to 3) also reveal that the surfaces of Examples 1 and 2 are smooth.

Claims

1. It comprises 5 to 40 parts by mass of an ultra-high molecular weight polyethylene (A) that satisfies the following requirement (a-1), and 95 to 60 parts by mass of a low-molecular weight or high-molecular weight polyethylene (B) that satisfies the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass), A stretched film having an intrinsic viscosity [η] measured in a decalin solvent at 135 ° C. in the range of 1.5 to 15 dl / g and at least a portion of which forms 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 stretched film according to claim 1, wherein the homogeneous phase is a phase in which no domains of 3 μm or more are observed when a cross section of the stretched film is observed with a laser microscope at a magnification of 1000 times.

3. The stretched film according to claim 1, having a thickness of 1 to 200 μm.

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- 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 production step of producing a 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 and at least a part of which forms a homogeneous phase; a stretch-molding step of stretch-molding the polyethylene resin composition (X); A method for producing a stretched film, comprising:

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