Tube and method for manufacturing a tube

Abstract

The present invention provides a tube containing ultra-high molecular weight polyethylene and polyethylene with a lower intrinsic viscosity [η] than ultra-high molecular weight polyethylene, resulting in superior surface smoothness. [Solution] A tube (Y) formed from a polyethylene resin composition (X) comprising 5 to 40 parts by mass of ultra-high molecular weight polyethylene (A) satisfying requirement (a-1) and 95 to 60 parts by mass of low molecular weight or high molecular weight polyethylene (B) satisfying requirements (b-1) and (b-2) (provided that the total amount of (A) and (B) is 100 parts by mass), wherein the intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1.5 to 15 dl / g, and at least a portion forms a homogeneous phase; (a-1) Intrinsic viscosity [η] measured in decalin solvent at 135°C is 8 to 50 dl / g; (b-1) 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 / m³ 3 That is the case.

Description

[Technical Field]

[0001] This invention relates to a tube and a method for manufacturing a tube. [Background technology]

[0002] Ultra-high molecular weight polyethylene has weaker intermolecular cohesive forces, a symmetrical molecular structure, and a higher degree of crystallinity compared to general-purpose resins such as ordinary polyethylene. Therefore, it exhibits excellent sliding properties, as well as superior impact resistance, abrasion resistance, and tensile strength, making it suitable for use as a sliding material. However, due to its high molecular weight, ultra-high molecular weight polyethylene is difficult to mold, and it is often difficult to directly utilize the molding methods used 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 product obtained by injection molding is excellent in that it has the excellent sliding properties and wear resistance of an 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. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 12606 / 1983 [Patent Document 2] International Publication No. 2003 / 022920 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, as proposed in Patent Documents 1 and 2, tubes obtained by molding a resin obtained by blending ultra-high molecular weight polyethylene and polyethylene with low intrinsic viscosity [η] sometimes have insufficient surface smoothness depending on the application.

[0008] The present invention aims to provide a tube that contains ultra-high molecular weight polyethylene and polyethylene with a lower intrinsic viscosity [η] than ultra-high molecular weight polyethylene, and has superior surface smoothness. [Means for solving the problem]

[0009] 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.

[0010] [1] 5 to 40 parts by mass of ultra-high molecular weight polyethylene (A) that meets the following requirement (a-1), It contains 95 to 60 parts by mass of low molecular weight or high molecular weight polyethylene (B) that meet the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) is 100 parts by mass), A tube (Y) formed from a polyethylene resin composition (X) having an intrinsic viscosity [η] measured in decalin solvent at 135°C in the range of 1.5 to 15 dl / g, and in which at least a portion forms a homogeneous phase. (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 8-50 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 of 950-985 kg / m³ 3 That is the case.

[0011] [2] The tube (Y) described in [1], wherein the roundness of the outer surface of the tube (Y), which has an outer diameter of 6 mm and a thickness of 1 mm, is 0.3 mm or less as measured by the diameter method.

[0012] [3] The tube (Y) described in [1] or [2], wherein the coefficient of kinetic friction with respect to glass is 0.2 or less.

[0013] [4] A tube (Y) as described in any one of [1] to [3], wherein the surface roughness of the outer surface is 2.0 μm or less.

[0014] [5] The intrinsic viscosity [η] measured in decalin solvent at 135°C was 0.1–5 dl / g, and the density was 950–985 kg / m³. 3 The first step involves producing low molecular weight or high molecular weight polyethylene (B), Following the first step, a second step is performed to produce ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] in the range of 8 to 50 dl / g, as measured in decalin solvent at 135°C. By a multi-stage polymerization method including at least two steps, A production process for producing a polyethylene resin composition (X) having an intrinsic viscosity [η] measured in a decalin solvent at 135 °C within the range of 1.5 to 15 dl / g, and A molding process for molding the polyethylene resin composition (X), A method for manufacturing a tube (Y), which includes these processes.

Advantages of the Invention

[0015] According to the present invention, a tube is provided that includes ultra-high molecular weight polyethylene and polyethylene having a lower intrinsic viscosity [η] than ultra-high molecular weight polyethylene, and has excellent surface smoothness.

Brief Description of the Drawings

[0016] [Figure 1] It is an example of a laser microscope photograph of a cross-section of the tube (Y1) obtained in Example 1 (magnification 1000 times). [Figure 2] It is an example of a laser microscope photograph of a cross-section of the tube (Y2) obtained in Example 2 (magnification 1000 times). [Figure 3] It is an example of a laser microscope photograph of a cross-section of the tube (CY1) obtained in Comparative Example 1 (magnification 1000 times).

[0017] ≪Tube (Y)≫ The tube (Y) according to the present invention includes 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)"), and is formed from a polyethylene resin composition (X) (hereinafter also referred to as "resin composition (X)") that satisfies the following requirements (x-1) and requirement (x-2). That is, the tube (Y) is a tube obtained by molding the resin composition (X).

[0018] 〔Requirement (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. That is, the intrinsic viscosity [η] of the resin composition (X) measured in decalin solvent 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 aforementioned range, the resin composition (X) possesses high melt fluidity sufficient to facilitate molding and high abrasion resistance, thus achieving both abrasion resistance and moldability. As a result, the tube (Y) obtained from the resin composition (X) also possesses high abrasion resistance. Furthermore, if the intrinsic viscosity [η] in decalin solvent at 135°C is less than 1.5 dl / g, the abrasion resistance of the composition tends to be impaired, and the abrasion resistance of tubes obtained from such compositions also tends to be impaired. On the other hand, if the intrinsic viscosity [η] in decalin solvent at 135°C exceeds 15 dl / g, the fluidity of the composition decreases, which tends to impair its moldability.

[0019] [Requirements (x-2)] At least a portion of the resin composition (X) forms a homogeneous phase. That is, in the resin composition (X), at least a portion of it forms a homogeneous phase due to the compatibility of ultra-high molecular weight polyethylene (A) and polyethylene (B), and in the portion of the homogeneous phase, phase separation between ultra-high molecular weight polyethylene (A) and polyethylene (B) does not occur. In this case, in the tube (Y) obtained from the resin composition (X), at least a portion of it also forms a homogeneous phase due to the compatibility of ultra-high molecular weight polyethylene (A) and polyethylene (B), and in the portion of the homogeneous phase, phase separation between ultra-high molecular weight polyethylene (A) and polyethylene (B) does not occur.

[0020] Whether at least a portion of the resin composition (X) is a homogeneous phase is determined by the size of the island phases (domains) observed when a cross-section of a thin section prepared by cutting a tube (Y) obtained by molding the resin composition (X) with a microtome is observed with a laser microscope using a 1000x objective lens, as follows: Homogeneous phase: The cross-section of the tube (Y) does not contain domains larger than 3 μm. Phase separation: The cross-section of tube (Y) contains domains larger than 3 μm. In other words, it is preferable that, in tube (Y), a sea-island structure containing domains of 3 μm or larger is not formed in at least a portion of it.

[0021] A tube (Y) obtained from a resin composition (X) in which ultra-high molecular weight polyethylene (A) and polyethylene (B) are compatible in at least part to form a uniform phase is preferred because it has excellent abrasion resistance and good surface smoothness on the outer surface of the tube (Y). The reason why the tube (Y) has excellent surface smoothness is presumed to be that the tube (Y) contains portions that do not contain domains of 3 μm or more, so roughness caused by domains located on the surface of the tube (Y) is less likely to occur.

[0022] Furthermore, when ultra-high molecular weight polyethylene (A) and polyethylene (B) are in phase separation, a sea-island structure is formed in which the ultra-high molecular weight polyethylene (A) forms domains (island phases) and polyethylene (B) forms the matrix (sea phase). When a tube (Y) is manufactured from such a phase-separated composition, the domains formed by the ultra-high molecular weight polyethylene (A) are located near the surface of the tube (Y), which tends to cause roughness and impair the surface smoothness of the tube (Y).

[0023] <Resin composition (X)> The resin composition (X) comprises ultra-high molecular weight polyethylene (A) and polyethylene (B), and satisfies requirements (x-1) and (x-2). Specifically, the intrinsic viscosity [η] of the resin composition (X), measured in decalin solvent at 135°C, satisfies the range described in requirement (x-1). Furthermore, at least a portion of the resin composition (X) forms a homogeneous phase.

[0024] The content of 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 (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 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 (provided that the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass). When the content of ultra-high molecular weight polyethylene (A) and polyethylene (B) is within the above range, the moldability and abrasion resistance of the resin composition (X) are improved.

[0025] When the content of ultra-high molecular weight polyethylene (A) in the composition exceeds 40 parts by mass and the content of polyethylene (B) falls below 60 parts by mass, the melt-flowability of the composition tends to decrease, resulting in poor moldability. On the other hand, when the content of ultra-high molecular weight polyethylene (A) falls below 5 parts by mass and the content of polyethylene (B) exceeds 95 parts by mass, the abrasion resistance derived from ultra-high molecular weight polyethylene (A) is insufficient, resulting in poor abrasion resistance of the resulting composition. Consequently, the abrasion resistance of the resulting tube also tends to decrease.

[0026] It is presumed that not only the content of ultra-high molecular weight polyethylene (A) and polyethylene (B), but also the fact that at least a portion of the resin composition (X) forms a homogeneous phase, is related to the moldability of the resin composition (X). Specifically, in the parts where ultra-high molecular weight polyethylene (A) and polyethylene (B) form a homogeneous phase, it is thought that unevenness in the thickness of the tube (Y) during molding is less likely to occur compared to the case where ultra-high molecular weight polyethylene (A) and polyethylene (B) are phase-separated. As a result, the parts where ultra-high molecular weight polyethylene (A) and polyethylene (B) form a homogeneous phase exhibit superior surface smoothness.

[0027] The resin composition (X) has a melt flow rate (hereinafter also referred to as "MFR") measured at 190°C and a 10kg load in accordance with the ASTM D-1238E measurement method, which 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. The above range for the MFR of the resin composition (X) is preferable because it provides good moldability.

[0028] <Ultra-high molecular weight polyethylene (A)> The ultra-high molecular weight polyethylene (A) incorporated into the resin composition (X) has an intrinsic viscosity [η] 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, as measured in decalin solvent at 135°C. 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 moldability, resulting in a tube (Y) with excellent abrasion resistance.

[0029] When ultra-high molecular weight polyethylene (A) is used instead of ultra-high molecular weight polyethylene (A) with an intrinsic viscosity [η] of less than 8 dl / g as measured in decalin solvent at 135°C, the abrasion resistance of the composition deteriorates, and the resulting tubes tend to have poor abrasion resistance. On the other hand, when ultra-high molecular weight polyethylene (A) is used instead of ultra-high molecular weight polyethylene (A) with an intrinsic viscosity [η] of more than 50 dl / g as measured in decalin solvent at 135°C, the melt fluidity of the composition decreases, which reduces the moldability of the composition, and as a result, the moldability of the tubes tends to deteriorate.

[0030] 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.

[0031] <Low molecular weight or high molecular weight polyethylene (B)> The intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is 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. When the intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135°C is within the above range, a resin composition (X) with excellent abrasion resistance and moldability is obtained, and as a result, a tube (Y) with excellent abrasion resistance is obtained.

[0032] When using low molecular weight to high molecular weight polyethylene with an intrinsic viscosity [η] measured in a decalin solvent at 135°C less than 0.1 dl / g instead of polyethylene (B), the abrasion resistance of the composition deteriorates, and the abrasion resistance of the resulting molded product tends to be inferior. On the other hand, when using low molecular weight to high molecular weight polyethylene with an intrinsic viscosity [η] measured in a decalin solvent at 135°C exceeding 5 dl / g instead of polyethylene (B), the melt fluidity of the composition becomes low, so the moldability of the composition tends to decrease.

[0033] Polyethylene (B) has a density of 950 - 985 kg / m 3 and preferably 960 - 980 kg / m 3 and more preferably 960 - 975 kg / m 3 and even more preferably 965 - 975 kg / m 3 When the density of polyethylene (B) is within the above range, a resin composition (X) excellent in both abrasion resistance and moldability can be obtained, and as a result, a tube (Y) excellent in abrasion resistance can be obtained.

[0034] When using low molecular weight to high molecular weight polyethylene with a density less than 950 kg / m instead of polyethylene (B), the crystallinity of the low molecular weight to high molecular weight polyethylene is low and it has a property of being easily shaved. As a result, the abrasion resistance of the composition deteriorates, and the abrasion resistance of the resulting tube tends to be inferior. Also, since the density of the low molecular weight to high molecular weight polyethylene is usually 985 kg / m 3 or less, low molecular weight to high molecular weight polyethylene with a density of 985 kg / m 3 or less is used for the resin composition (X). 3

[0035] Polyethylene (B) is a homopolymer of ethylene or a copolymer of ethylene and an α-olefin, and 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).

[0036] 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. When polyethylene (B) is a copolymer of ethylene and α-olefin, a higher amount of constituent units derived from ethylene is preferable.

[0037] <Other ingredients> The resin composition (X) and the tube (Y) obtained from the resin composition (X) may contain other thermoplastic resins such as polyolefin resins (however, different from ultra-high molecular weight polyethylene (A) and polyethylene (B)) 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 aforementioned other components are included, the total amount of the aforementioned other components in the resin composition (X) (or in the tube (Y) 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 total mass of ultra-high molecular weight polyethylene (A) and 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 total mass of ultra-high molecular weight polyethylene (A) and polyethylene (B) in the tube (Y) obtained from the resin composition (X) to the mass of the tube (Y) is usually 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more.

[0038] <Method for producing polyethylene resin composition (X)> The following describes the method for producing the resin composition (X). The processes performed in the method for producing the resin composition (X) are also the production steps in the method for producing the tube (Y), which will be described later. The resin composition (X) is produced by a multi-stage polymerization method comprising at least two steps: a first step of producing polyethylene (B) and a second step of producing ultra-high molecular weight polyethylene (A) in the presence of a known olefin polymerization catalyst. The second step is carried out in the presence of the polyethylene (B) produced in the first step.

[0039] It is hypothesized 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 the particles of ultra-high molecular weight polyethylene (A) are coated with polyethylene (B). It is hypothesized that when the particle surface of the polyethylene resin composition is coated with polyethylene (B), the polyethylene resin composition is less likely to form a sea-island structure and is more likely to form a homogeneous phase when molded into tubes or the like.

[0040] On the other hand, even when using a multi-stage polymerization method, 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 easily form a homogeneous phase. This is presumed to be 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 tube or the like, it tends to form a sea-island structure, making it difficult to form a homogeneous phase.

[0041] Furthermore, when producing the resin composition (X), the olefins used for polymerization, such as ethylene, can be any of the various olefins described in the sections on ultra-high molecular weight polyethylene (A) and polyethylene (B) without limitation.

[0042] The monomers (ethylene, α-olefin) contained in the ultra-high molecular weight polyethylene (A) and polyethylene (B) according to the present invention may be monomers derived from fossil fuels, monomers derived from biomass, or a combination of monomers derived from fossil fuels and monomers derived from biomass. Biomass-derived raw materials are raw materials made from any (renewable) natural raw materials and their residues, including fungi, yeasts, algae, and bacteria, and of plant or animal origin.

[0043] <Method for manufacturing tube (Y)> The method for manufacturing a tube (Y) according to the present invention includes a production step for generating a resin composition (X) and a molding step for molding the resin composition (X). The production step for generating the resin composition (X) is as described in the method for generating the resin composition (X).

[0044] [Molding process] The resin composition (X) of the present invention is formed into a tube (Y) using a known tube molding method. One method of tube molding is to extrude molten resin into a cylindrical shape using a cylindrical die, and then shape it by sizing.

[0045] The die used is not particularly limited, but straight dies are generally used, and spiral dies and spider dies are preferred shapes for straight dies. The sizing method used is not particularly limited. Suitable sizing methods include vacuum sizing, air-pressurized sizing, multi-plate sizing, sliding sizing, internal sizing, and roll sizing.

[0046] <Applications of Tube (Y)> Applications of tube (Y) include shrink tubing, plumbing tubing, medical tubing, heavy-duty bag tubing, hoses, and pipes.

[0047] <Physical properties of tube (Y)> The tube (Y) is a hollow molded body formed from a resin composition (X), and is preferably a hollow cylindrical molded body. Since the tube (Y) according to the present invention is obtained by molding a resin composition (X), it contains all 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 ultra-high molecular weight polyethylene (A) in tube (Y) 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 (provided that the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass). Similarly, the polyethylene (B) content in tube (Y) 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 (provided that the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) is 100 parts by mass).

[0048] The coefficient of dynamic friction measured by bringing the tube (Y) into contact with glass (measurement conditions: mating material: flat glass, load: 1 kg, speed: 150 mm / s, number of reciprocations: 1000 times, stroke: 100 mm, measurement ambient temperature: 23 °C) is preferably 0.2 or less, more preferably 0.08 to 0.18, and even more preferably 0.10 to 0.16. When the coefficient of dynamic friction of the tube (Y) is within the above range, it is expected that wear of the tube (Y) due to friction will be suppressed, heat generation on the surface of the tube (Y) will be suppressed, and noise will be reduced when the tube (Y) is slid.

[0049] The surface roughness (arithmetic mean roughness (Ra)) of the tube (Y) is preferably less than 2.0 μm, and more preferably 1.0 μm or less. A lower surface roughness is preferable, but the lower limit is usually 0.5 μm or more. A surface roughness within the above range of the tube (Y) is preferable because it provides sufficient surface smoothness.

[0050] The outer diameter of tube (Y) is not particularly limited, but is preferably 1 to 300 mm, and more preferably 2 to 100 mm. The thickness of tube (Y) is not particularly limited, but is preferably 0.1 to 50 mm, more preferably 0.3 to 30 mm, even more preferably 0.5 to 10 mm, and especially preferably 0.8 to 3 mm.

[0051] The roundness of tube (Y) determined by the following measurement conditions (diameter method) is preferably 0.3 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. The lower limit of the roundness of tube (Y) determined by the following measurement conditions is preferable as it is, but is usually 0.05 mm or more. (Measurement conditions) For the cross-section of tube (Y), the outer diameter is measured at five points using a micrometer, and the roundness is calculated by (maximum outer diameter - minimum outer diameter) ÷ 2. [Examples]

[0052] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. Note that the polymerization described below may be carried out multiple times to obtain the necessary amount of polymer and composition for evaluation.

[0053] [Measurement conditions, etc.] The measurement conditions for each physical property are as follows:

[0054] [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. In the following, the intrinsic viscosity of ultra-high molecular weight polyethylene (A) is referred to as "intrinsic viscosity [η]". A 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] B It is sometimes written as "."

[0055] 〔density〕 The density of polyethylene (B) was measured in accordance with ASTM D1505.

[0056] [MFR] The MFR of the compositions obtained in the following examples or comparative examples was measured under a 10 kg load in accordance with ASTM D1238E. The measurement temperature was 190°C.

[0057] [Tube dimensions] The dimensions of the tubes obtained in the examples or comparative examples were measured using a micrometer for the outer diameter and a dial gauge for the thickness.

[0058] [Circularity of the tube] For the cross-sections of the tubes obtained in the examples or comparative examples, the outer diameter was measured at five points using a micrometer, and the roundness was calculated by (maximum outer diameter - minimum outer diameter) ÷ 2.

[0059] [Surface roughness of the tube] The arithmetic mean roughness (Ra) of the tube surfaces obtained in the examples or comparative examples was determined using a method compliant with JIS B 0601.

[0060] [Coefficient of dynamic friction of a tube] The dynamic friction coefficient of the tubes obtained in the examples or comparative examples was measured using a robotic arm type friction and wear tester (Shinto Kagaku Co., Ltd., TRIBOGEAR TYPE:31). The test conditions were: mating material: flat glass, load: 1 kg, speed: 150 mm / s, number of reciprocations: 1000, stroke: 10 cm, and measurement ambient temperature: 23 °C.

[0061] [Phase structure] Thin sections of the tubes obtained in the following examples and comparative examples were prepared by cutting them with a microtome. Then, the cross-sections of the thin sections were observed using a laser microscope (Olympus) with a 1000x objective lens, and it was determined whether they were a homogeneous phase according to the following criteria. Homogeneous phase: No domains larger than 3 μm were observed in the cross-section of the tube. Sea-island structure: Domains larger than 3 μm were observed in the cross-section of the tube.

[0062] [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 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 90°C decane until no free titanium compounds were detected in the washings, and then thoroughly washed with hexane at room temperature.

[0063] 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 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.

[0064] [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 80°C, 0.5 mmol of triisobutylaluminum and solid titanium catalyst component [C1] (0.01 mmol in terms of titanium atoms) were added. Hydrogen was fed into the polymer chamber until the pressure reached 0.406 MPaG gauge pressure, and then ethylene was fed into the polymer chamber until the pressure reached 0.66 MPaG gauge pressure. The first stage of ethylene polymerization was carried out at 85°C. The ethylene feed was stopped when 119 liters of ethylene had been fed, the temperature was rapidly cooled to 45°C, and then depressurization and nitrogen purging were performed. Polyethylene (B1) was obtained by carrying out the first stage of ethylene polymerization under the above conditions. Next, ethylene was fed into the polymerizer until the pressure inside the polymerizer reached a gauge pressure of 0.60 MPaG, and the second stage of ethylene polymerization was carried out at a temperature of 53°C. When 21 liters of ethylene had been fed, the feeding of ethylene 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 these conditions, ultra-high molecular weight polyethylene (A1) was obtained. The slurry containing the generated solid was filtered and dried under reduced pressure overnight at 80°C. The resulting ethylene resin composition (X1) was 190 g and had an intrinsic viscosity [η] of 3.9 dl / g in decalin solvent at 135°C.

[0065] [Analysis of each component in polyethylene resin composition (X1)] • Polyethylene (B1) content and physical properties When only the first stage of polymerization, which was carried out when polyethylene resin composition (X1) was produced, was performed separately under the same conditions as when polyethylene resin composition (X1) was produced, the yield of the resulting ethylene polymer was 162 g. Since polyethylene (B1) was produced by this polymerization, the polyethylene (B1) content in polyethylene resin composition (X1) (yield 190 g) was calculated to be 85% by 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 / m³ 3 That was the case.

[0066] • Content and intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A2) Ultra-high molecular weight polyethylene (A2) 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 ultra-high molecular weight polyethylene (A2) was 30 dl / g. Next, the molecular weight distribution of ultra-high molecular weight polyethylene (A2) was measured by gel permeation chromatography (GPC), and compared with the results of GPC molecular weight distribution measurements for polyethylene resin composition (X1). The peak positions and shapes of the chromatograms were consistent with those of the high molecular weight component (ultra-high molecular weight polyethylene (A1)) contained in polyethylene resin composition (X1). Based on these results, the physical properties of ultra-high molecular weight polyethylene (A1) were considered to be the same as those of ultra-high molecular weight polyethylene (A2). That is, the intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A1) was set to 30 dl / g.

[0067] [Granulation of polyethylene resin composition (X1)] The obtained polyethylene resin composition (X1) 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 MFR was measured using the obtained pellets. The results are shown in Table 1.

[0068] [Tube molding] The pellets obtained above were used to form tubes using a tube molding extruder (IKG, PMS65) at a temperature of 230°C and a mold diameter (outer diameter / inner diameter) of 8.0 / 5.4 mm. The winding speed was adjusted so that the tube reached the target dimensions (outer diameter 6.0 mm / inner diameter 4.0 mm, thickness 1.0 mm), and the tube (Y1) was obtained by sizing and cooling in a 7°C vacuum water bath. Table 1 shows the evaluation results for tube (Y1), and Figure 1 shows a photograph of the cross-section of tube (Y1). In Figure 1, no domains larger than 3 μm were observed, confirming that a homogeneous phase was formed in at least a portion of tube (Y1).

[0069] [Example 2] In the second stage of polymerization for producing the polyethylene resin composition, polymerization, granulation, and tube molding were carried out in the same manner as in Example 1, except that the ethylene polymerization temperature was changed from 53°C to 80°C, to obtain tube (Y2). Table 1 shows the physical properties of the obtained composition and the evaluation results of the tube (Y2). Figure 2 shows a photograph of the cross-section of the tube (Y2).

[0070] [Comparative Example 1] The composition was manufactured by swapping the polymerization conditions for the first and second stages in the example. Specifically, the catalyst component input temperature was changed from 80°C to 48°C, hydrogen was not fed during the first stage of polymerization, the ethylene polymerization temperature was changed from 85°C to 53°C, and the ethylene feed amount was changed from 119 liters to 21 liters. Furthermore, during the second stage of polymerization, hydrogen was fed until the pressure inside the polymerizer reached a gauge pressure of 0.40 MPaG, the ethylene polymerization temperature was changed from 53°C to 85°C, and the ethylene feed amount was changed from 21 liters to 119 liters. Granulation, tube molding, and evaluation were performed in the same manner as in Example 1. Table 1 shows the physical properties of the obtained composition and the evaluation results of the obtained tube (CY1). Figure 3 shows a photograph of the cross-section of the tube (CY1). In Figure 3, domains larger than 3 μm were observed, so it was evaluated as a sea-island structure.

[0071] [Table 1]

Claims

1. 5 to 40 parts by mass of ultra-high molecular weight polyethylene (A) that meets the following requirement (a-1), It contains 95 to 60 parts by mass of low molecular weight or high molecular weight polyethylene (B) that meet the following requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass), A tube (Y) formed from a polyethylene resin composition (X) having an intrinsic viscosity [η] in decalin solvent at 135°C in the range of 1.5 to 15 dl / g, and in which at least a portion 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 of 950-985 kg / m³ ３ That is the case.

2. The tube (Y) according to claim 1, wherein the roundness of the outer surface of the tube (Y), which has an outer diameter of 6 mm and a thickness of 1 mm, is 0.3 mm or less, as measured by the diameter method.

3. The tube (Y) according to claim 1, wherein the coefficient of dynamic friction with respect to glass is 0.2 or less.

4. The tube (Y) according to claim 1, wherein the surface roughness of the outer surface is 2.0 μm or less.

5. The intrinsic viscosity [η] measured in decalin solvent at 135°C was 0.1–5 dl / g, and the density was 950–985 kg / m³. ３ The first step is to produce low molecular weight or high molecular weight polyethylene (B), Following the first step, a second step is performed to produce ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] in decalin solvent at 135°C in the range of 8 to 50 dl / g. A multi-stage polymerization method including at least two steps, A production step for producing a polyethylene resin composition (X) having an intrinsic viscosity [η] in decalin solvent at 135°C in the range of 1.5 to 15 dl / g, and A molding step for molding the polyethylene resin composition (X), A method for manufacturing a tube (Y), including the tube.

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