Re-stretched film and method for manufacturing a re-stretched film

Abstract

This invention provides polyethylene resin compositions that can be used to manufacture films with higher elastic modulus and tensile strength. [Solution] A re-stretched film (Y) is formed from a polyethylene resin composition (X) comprising 5 to 40 parts by mass of polyethylene (A) satisfying requirement (a-1) and 95 to 60 parts by mass of polyethylene (B) satisfying requirements (b-1) and (b-2) (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass), wherein the intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1.0 to 15 dl / g: (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 5 to 50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 dl / g or more and less than 5 dl / g; (b-2) The density is 950 to 985 kg / m³ 3 That is the case.

Description

[Technical Field]

[0001] This invention relates to a re-stretched film and a method for producing a re-stretched film. [Background technology]

[0002] Ultra-high molecular weight polyethylene has weaker intermolecular cohesive forces, a symmetrical molecular structure, and high 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. Furthermore, among high-density polyethylenes (HDPE), high molecular weight polyethylene with relatively high density and large molecular weight can also be used as a sliding material due to its excellent sliding properties, impact resistance, abrasion resistance, and tensile strength.

[0003] However, ultra-high molecular weight polyethylene and high molecular weight polyethylene with relatively high density and large molecular weight are difficult to manufacture molded products from due to their high molecular weight, and it is often difficult to use the same methods as those used for molding general-purpose polyethylene.

[0004] Therefore, various methods have been proposed to improve the moldability of ultra-high molecular weight polyethylene and high molecular weight polyethylene without impairing their excellent properties, such as blending these resins with polyethylene having a lower intrinsic viscosity [η].

[0005] For example, Patent Document 1 contains 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.

[0006] Furthermore, Patent Document 2 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]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-25904 [Patent Document 2] Japanese Patent Publication No. 2016-204405 [Overview of the project] [Problems that the invention aims to solve]

[0008] The compositions proposed in Patent Documents 1 and 2 exhibited excellent moldability. Furthermore, molded articles such as films obtained by stretch molding the compositions of Patent Documents 1 and 2 also exhibited excellent sliding properties, but depending on the application, their elastic modulus and tensile strength were sometimes insufficient.

[0009] The present invention aims to provide a polyethylene resin composition that can be used to produce films with higher elastic modulus and tensile strength. [Means for solving the problem]

[0010] 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.

[0011] [1] 5 to 40 parts by mass of polyethylene (A) that meet the following requirement (a-1), 95 to 60 parts by mass of polyethylene (B) satisfying the following requirements (b-1) and (b-2) (assuming the total amount of polyethylene (A) and polyethylene (B) is 100 parts by mass), A re-stretched film (Y) formed from a polyethylene resin composition (X) having an intrinsic viscosity [η] measured in a decalin solvent at 135 °C in the range of 1.0 to 15 dl / g: (a-1) The intrinsic viscosity [η] measured in a decalin solvent at 135 °C is 5 to 50 dl / g; (b-1) The intrinsic viscosity [η] measured in a decalin solvent at 135 °C is 0.1 dl / g or more and less than 5 dl / g; (b-2) The density is 950 to 985 kg / m 3 is.

[0012] [2] The re-stretched film (Y) according to [1], having a thickness of 1 to 500 μm.

[0013] [3] The re-stretched film (Y) according to [1] or [2], having a tensile strength in the MD direction of the re-stretched film of 30 MPa or more.

[0014] [4] A step of producing polyethylene (A) having an intrinsic viscosity [η] measured in a decalin solvent at 135 °C in the range of 5 to 50 dl / g, The intrinsic viscosity [η] measured in a decalin solvent at 135 °C is 0.1 dl / g or more and less than 5 dl / g, and the density is 950 to 985 kg / m 3 is a step of producing polyethylene (B), 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 1.0 to 15 dl / g, An extrusion molding step of extruding the polyethylene resin composition (X) to form a film, A stretching molding step of stretching the film, including A method for producing a re-stretched film (Y).

Advantages of the Invention

[0015] The present invention provides a polyethylene resin composition that can be used to produce a film having a higher elastic modulus and tensile strength.

Mode for Carrying Out the Invention

[0016] ≪Rewound Film (Y)≫ The rewound film (Y) according to the present invention contains specific polyethylene (A) and specific polyethylene (B), and is composed of a polyethylene resin composition (X) (hereinafter also referred to as "resin composition (X)") that satisfies the following requirement (x-1). That is, the rewound film (Y) is a rewound film obtained by molding the resin composition (X).

[0017] 〔Requirement (x-1)〕 The intrinsic viscosity [η] measured in a decalin solvent at 135 °C using the resin composition (X) as a sample is in the range of 1.0 to 15 dl / g, preferably in the range of 1.2 to 10 dl / g, more preferably in the range of 1.4 to 8.0 dl / g, still more preferably in the range of 1.6 to 6.0 dl / g, and particularly preferably in the range of 1.6 to 4.0 dl / g. That is, the intrinsic viscosity [η] measured in a decalin solvent at 135 °C using the rewound film (Y) as a sample satisfies the above range. When the intrinsic viscosity [η] of the resin composition (X) in a decalin solvent at 135 °C satisfies the above range, the resin composition (X) has a high melt fluidity that facilitates molding, a high abrasion resistance, and a high slidability, and thus has both abrasion resistance, moldability, and slidability. As a result, the rewound film (Y) obtained from the resin composition (X) also has a high abrasion resistance and a high slidability. When the intrinsic viscosity [η] in a decalin solvent at 135 °C is less than 1.0 dl / g, the abrasion resistance of the composition is impaired, and thus the abrasion resistance of the rewound film obtained from such a composition tends to deteriorate. On the other hand, when the intrinsic viscosity [η] in a decalin solvent at 135 °C exceeds 15 dl / g, the fluidity of the composition decreases, and the moldability tends to be impaired.

[0018] <Resin composition (X)> The resin composition (X) comprises polyethylene (A) and polyethylene (B) and satisfies requirement (x-1). That is, the intrinsic viscosity [η] of the resin composition (X), measured in decalin solvent at 135°C, satisfies the range described in relation to requirement (x-1).

[0019] The polyethylene (A) content 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 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 polyethylene (A) and polyethylene (B) is 100 parts by mass). When the content of polyethylene (A) and polyethylene (B) is within the above range, the moldability and abrasion resistance of the resin composition (X) are improved. Furthermore, by including polyethylene (A), which has a relatively high intrinsic viscosity and high molecular weight, in the above range proportions, the sliding properties of the re-stretched film (Y) obtained from the resin composition (X) are improved.

[0020] When the polyethylene (A) content in the composition exceeds 40 parts by mass and the polyethylene (B) content falls below 60 parts by mass, the melt-flowability of the composition tends to be low. As a result, the stretch-formability of the resulting film tends to deteriorate. On the other hand, when the polyethylene (A) content falls below 5 parts by mass and the polyethylene (B) content exceeds 95 parts by mass, the abrasion resistance and sliding properties derived from polyethylene (A) are insufficient, so the abrasion resistance and sliding properties of the resulting composition tend to deteriorate. As a result, the abrasion resistance and sliding properties of the resulting re-stretched film also tend to decrease.

[0021] 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 measurement method of ASTM D-1238E, 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 of MFR for resin composition (X) is preferable because it provides good stretch moldability.

[0022] <Polyethylene (A)> The polyethylene (A) blended into the resin composition (X) has an intrinsic viscosity [η] of 5 to 50 dl / g, preferably 6.0 to 40 dl / g, more preferably 6.5 to 35 dl / g, even more preferably 6.5 to 30 dl / g, particularly preferably 7.0 to 20 dl / g, and especially most preferably 7.5 to 15 dl / g, as measured in decalin solvent at 135°C. When the intrinsic viscosity [η] of polyethylene (A) is within the above range, the resin composition (X) can achieve both abrasion resistance and stretch moldability, resulting in a re-stretched film (Y) with excellent abrasion resistance. Furthermore, when the intrinsic viscosity [η] of polyethylene (A) is within the above range, relatively high molecular weight polyethylene is included in the resin composition (X), which tends to result in good sliding properties of the re-stretched film (Y) obtained from the resin composition (X).

[0023] When polyethylene with an intrinsic viscosity [η] of less than 5 dl / g, measured in decalin solvent at 135°C, is used instead of polyethylene (A), the abrasion resistance of the composition deteriorates, and the resulting re-stretched film tends to have poor abrasion resistance. On the other hand, when polyethylene with an intrinsic viscosity [η] of more than 50 dl / g, measured in decalin solvent at 135°C, is used instead of polyethylene (A), the melt fluidity of the composition decreases, reducing the moldability of the composition, and consequently, the stretch moldability of the film tends to deteriorate.

[0024] Polyethylene (A) is a homopolymer of ethylene, or a copolymer of ethylene and an α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, or 3-methyl-1-pentene. Polyethylene (A) is preferably a homopolymer of ethylene, or a copolymer of ethylene and the above-mentioned α-olefins, and is a copolymer mainly composed of ethylene, and more preferably 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.

[0025] <Polyethylene (B)> The intrinsic viscosity [η] of polyethylene (B), measured in decalin solvent at 135°C, is 0.1 dl / g or more and less than 5 dl / g, preferably 0.5 to 2.0 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 stretch moldability is obtained, and as a result, a re-stretched film (Y) with excellent abrasion resistance is obtained.

[0026] When polyethylene with an intrinsic viscosity [η] of less than 0.1 dl / g, measured in decalin solvent at 135°C, is used instead of polyethylene (B), the abrasion resistance of the composition deteriorates, and the resulting molded articles tend to have poor abrasion resistance. On the other hand, when polyethylene with an intrinsic viscosity [η] of 5 dl / g or more, measured in decalin solvent at 135°C, is used instead of polyethylene (B), the melt fluidity of the composition decreases, which reduces the moldability of the composition, and consequently, the stretch moldability of the film tends to deteriorate.

[0027] Polyethylene (B) has a density of 950-985 kg / m³. 3 And preferably 960-980 kg / m 3 More preferably, 960-975 kg / m³ 3 And more preferably 965-975 kg / m3 It is so. When the density of polyethylene (B) is within the above range, a resin composition (X) excellent in both abrasion resistance and stretch molding properties can be obtained, and as a result, a re-stretched film excellent in both abrasion resistance and stretch molding properties can be obtained.

[0028] When polyethylene with a density less than 950 kg / m is used instead of polyethylene (B), the crystallinity of 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 obtained re-stretched film tends to be inferior. Also, since the density of polyethylene is usually 985 kg / m or less, polyethylene with a density of 985 kg / m or less is used for the resin composition (X). 3 When polyethylene with a density less than 950 kg / m is used instead of polyethylene (B), the crystallinity of 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 obtained re-stretched film tends to be inferior. Also, since the density of polyethylene is usually 985 kg / m 3 or less, polyethylene with a density of 985 kg / m 3 or less is used.

[0029] Polyethylene (B) is a homopolymer of ethylene or a copolymer of ethylene and an α-olefin. Preferably, it is a homopolymer of ethylene. Examples of the α-olefin 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, etc. can be mentioned. Among these, propylene and 1-butene are preferably used in relation to the density range of polyethylene (B).

[0030] 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.

[0031] <Other ingredients> The resin composition (X) and the re-stretched film (Y) obtained from the resin composition (X) may contain other thermoplastic resins such as polyolefin resins (but different from polyethylene (A) and polyethylene (B)) and 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 re-stretched film (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 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 polyethylene (A) and polyethylene (B) in the re-stretched film (Y) obtained from the resin composition (X) to the mass of the re-stretched film (Y) is usually 95% by mass or more, preferably 98% by mass or more, and more preferably 99% by mass or more.

[0032] <Method for producing 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 polyethylene (A) and polyethylene (B) in a predetermined ratio, but preferred methods include the following methods (M-1) to (M-4).

[0033] Method (M-1): A multi-stage polymerization method comprising at least two steps: a first step of producing polyethylene (A) and a second step of producing polyethylene (B) in the presence of an olefin polymerization catalyst. The second step is carried out in the presence of polyethylene (A) produced in the first step. Method (M-2): 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 polyethylene (A). The second step is carried out in the presence of polyethylene (B) produced in the first step. Method (M-3): Blend multiple resin compositions (X) obtained by Method (M-1) or Method (M-2). Method (M-4): Blend the resin composition (X) obtained by methods (M-1), (M-2), and (M-3) with one or more materials selected from polyethylene (A) and polyethylene (B). Furthermore, 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 and WO2010 / 074073, under polymerization conditions such that the resin composition (X) has the desired physical properties.

[0034] Comparing method (M-1) and method (M-2), method (M-1) is preferable because, when resin composition (X) is produced using method (M-1), the molecular weight of the polymer (polyethylene (B)) obtained in the second step can be easily adjusted to be lower than that of the polymer (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 offering superior production efficiency.

[0035] On the other hand, when polyethylene (A) is produced in the presence of polyethylene (B) using method (M-2), the resulting resin composition (X) tends to be less likely to form a sea-island structure and more likely to form a homogeneous phase. This is presumed to be because when polyethylene (A) is produced in the presence of polyethylene (B), a granular polyethylene resin composition is obtained in which polyethylene (A) particles are coated with polyethylene (B). It is presumed 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 more likely to form a homogeneous phase during molding.

[0036] In any of methods (M-1) to (M-4), the olefins used for polymerization, such as ethylene, can be any of the various olefins described in the sections on polyethylene (A) and polyethylene (B) without limitation. From the viewpoint of obtaining a re-stretched film (Y) with higher elastic modulus and tensile strength, the method for producing the resin composition (X) is preferably method (M-1) or method (M-2), and more preferably method (M-2).

[0037] The resin composition (X), polyethylene (A), and polyethylene (B) (referred to as the resin composition and polymer, etc., according to the present invention) may use only biomass-derived raw materials (e.g., monomers such as ethylene and α-olefin) as their raw materials, or only fossil fuel-derived raw materials, or both biomass-derived and fossil fuel-derived raw materials. Biomass-derived raw materials are raw materials made from any (renewable) natural raw materials and their residues, including fungi, yeasts, algae, and bacteria, which are of plant or animal origin, for example, as carbon. 14 1 × 10¹¹ C isotopes -12 ~1 × 10 -14 Examples of raw materials include those containing a certain proportion and having a biomass carbon concentration (unit: pMC) of approximately 100 pMC, as measured in accordance with ASTM D6866. Biomass-derived raw materials (e.g., monomers such as ethylene and α-olefins) can be obtained, for example, by conventionally known methods. It is preferable from the viewpoint of reducing environmental impact (mainly greenhouse gas reduction) that the resin compositions and polymers, etc., according to the present invention include constituent units derived from biomass-derived raw materials. The resin compositions and polymers according to the present invention, even if they contain biomass-derived raw materials, are acceptable as long as the manufacturing conditions such as polymerization catalyst, polymerization process, polymerization temperature, and kneading method are equivalent. 14 1 × 10¹¹ C isotopes -12 ~1 × 10 -14 Aside from the proportion of biomass-derived materials present, the molecular structure and physical properties are equivalent to those of resin compositions and polymers made from fossil fuel-derived raw materials. Therefore, it is considered that resin compositions and polymers containing biomass-derived raw materials have no difference in performance compared to those made from fossil fuel-derived raw materials.

[0038] <Method for manufacturing re-stretched film (Y)> The method for producing the re-stretched film (Y) includes a production step for generating a resin composition (X), an extrusion molding step for forming a film by extruding the resin composition (X), and a stretch molding step for stretching the film obtained in the extrusion molding step. In the extrusion molding step, the resin composition (X) is extruded while being slightly stretched to form an extruded stretched film, so the stretch molding step is equivalent to re-stretching the extruded stretched film. The production step for generating the resin composition (X) is as described in the method for generating the resin composition (X).

[0039] [Extrusion molding process and stretch molding process] There are no particular restrictions on the extrusion molding and stretch molding processes. Examples of stretch molding methods include uniaxial stretching and biaxial stretching, and in the case of biaxial stretching, it may be simultaneous or sequential stretching. When using biaxial stretching as the stretch molding method, examples of the extrusion molding and stretch molding processes include the tenter method and the tube method.

[0040] In the tenter method, a resin composition (X) is typically melted and kneaded in an extruder and extruded from a T-die. The resulting molten mixture is then cooled and solidified on a casting drum, and introduced between a slow (front) drive roll and a fast (rear) drive roll to be stretched longitudinally to a predetermined magnification. Subsequently, the longitudinally stretched film is placed in a tenter, and while holding both transverse ends and heating, it is further stretched transversely to produce a re-stretched film (Y). At this time, further heat treatment may be performed in the tenter for purposes such as fixing the molecular orientation of the film. In addition, the means for obtaining the film used in the stretch molding process in the tenter method (i.e., the extruded stretched film) is usually the T-die molding method, but the film may also be obtained by other known methods.

[0041] In the tube method, a resin composition (X) is typically melted and kneaded in an extruder, the molten polymer is extruded in a tube shape from a ring die, and after rapid cooling in a cooling tank, this tube-shaped material (tubular extruded stretched film) is heated, air is introduced into the interior and pressurized, or the outside of the tube is depressurized, and while being stretched laterally, tension is applied in the longitudinal direction to stretch it again in the longitudinal direction, thereby producing a re-stretched film (Y).

[0042] In the uniaxial method, a film of the resin composition (X) obtained by T-die molding or inflation molding (the film used in the stretch molding process) is cooled and then introduced between a slow (front) drive roll and a fast (rear) drive roll, and stretched to a predetermined magnification in the longitudinal direction to produce a re-stretched film (Y). Furthermore, heat treatment may be performed for purposes such as fixing the molecular orientation of the film.

[0043] When manufacturing by the tenter method using an extruder equipped with a T-die, the temperature at the inlet side of the extruder is typically set to a temperature range of 150-250°C, the temperature at the outlet side of the extruder is set to a temperature range of 200-280°C, and the die temperature is set to a temperature range of 200-280°C. The resin is then extruded from the T-die so that the resin temperature is in the range of 180-300°C, and the re-stretched film (Y) is obtained by stretching it to the desired aspect ratio.

[0044] When using the tube method, the temperature at the inlet of the extruder is typically set to a temperature range of 150-250°C, the temperature at the outlet of the extruder to a temperature range of 180-280°C, and the die temperature to a temperature range of 180-280°C. The resin is then extruded from the ring die so that the resin temperature is in the range of 180-300°C, and the re-stretched film (Y) is obtained by stretching it to the desired aspect ratio.

[0045] When unstretching an unstretched film obtained by T-die molding, the temperature at the inlet of the extruder is typically set to a range of 150-250°C, the temperature at the outlet of the extruder to a range of 180-280°C, and the die temperature to a range of 180-280°C. The film is then extruded from the T-die so that the resin temperature is in the range of 180-300°C, and stretched to the desired longitudinal magnification.

[0046] In the present invention, a re-stretched film (Y) is obtained by the extrusion molding process and the stretch molding process described above. The re-stretched film (Y) may be a single-layer film or a multi-layer film. A single-layer film is obtained by the stretch molding process described above. A multi-layer film can be produced, for example, by melting and kneading the resin compositions that form each layer of the film in separate extruders, injecting the molten mixture into a die for co-extrusion, and then simultaneously extruding these molten mixtures through the slits of the die and stretching them using the uniaxial stretching method or biaxial stretching method described above.

[0047] The stretching ratio is preferably 1.2 to 20 times, more preferably 1.3 to 18 times, even more preferably 1.4 to 16 times, even more preferably 1.5 to 13 times, and particularly preferably 1.5 to 10 times in terms of length. When the stretching ratio is within the above range, a re-stretched film (Y) is obtained that has excellent abrasion resistance as well as excellent elastic modulus (tensile modulus) and tensile strength.

[0048] <Applications of re-stretched film (Y)> The re-stretched film (Y) can be widely used in conventional polyethylene applications, but it is particularly excellent in abrasion resistance, elastic modulus (tensile modulus), and tensile strength, as well as in sliding properties, and can be used in applications where these are required. Such applications include, for example, automotive glass run channels, various rubber reels such as automotive weatherstrips, conveyor guide covers for various transport equipment, sliding surface lubricants for multifunction printers, guide rails for vending machines and product shelves, PC mouse bottoms and mouse pads, hopper linings, sliding surface linings, pipe linings, sliding tapes, adhesive tapes, masking tapes, packaging films, and protective films.

[0049] <Physical properties of re-stretched film (Y)> Since the re-stretched film (Y) is obtained by extruding and stretching the resin composition (X), it contains all the components of the resin composition (X), and the amount of each component is the same as the amount in the resin composition (X). For example, the polyethylene (A) content in the re-stretched film (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 polyethylene (A) and polyethylene (B) is 100 parts by mass). Similarly, the polyethylene (B) content in the re-stretched film (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 polyethylene (A) and polyethylene (B) is 100 parts by mass).

[0050] The coefficient of dynamic friction measured by bringing the re-stretched film (Y) into contact with glass (measurement conditions: mating material: glass plate (U-shaped), load: 250g, speed: 150mm / s, number of reciprocations: 5000 times, stroke: 100mm, measurement ambient temperature: 23℃) is preferably in the range of 0.05 to 0.15, and more preferably in the range of 0.07 to 0.12. When the coefficient of dynamic friction of the re-stretched film (Y) is within the above range, it is expected that wear and heat generation due to friction will be suppressed, and noise during sliding will be reduced.

[0051] The tensile strength of the re-stretched film (Y) in the machine direction (MD direction) is preferably 30 MPa or higher, more preferably 32 MPa or higher, and even more preferably 34 MPa or higher. A higher tensile strength in the MD direction is preferable, but the upper limit is usually 300 MPa. The tensile strength of the re-stretched film (Y) in the MD direction can be determined by the method described in the examples. It is preferable that the tensile strength of the re-stretched film (Y) in the MD direction is within the aforementioned range, because the tensile strength of the re-stretched film (Y) is sufficient for the intended use of the re-stretched film (Y).

[0052] The elastic modulus (tensile modulus) of the re-stretched film (Y), as determined by a tensile test, is preferably 500 MPa or higher, more preferably 750 MPa or higher, even more preferably 1000 MPa or higher, and particularly preferably 1500 MPa or higher. A higher elastic modulus of the re-stretched film (Y) is preferable, but the upper limit is usually 6000 MPa. The elastic modulus of the re-stretched film (Y) is determined by the method described in the examples. It is preferable that the elastic modulus of the re-stretched film (Y) is within the aforementioned range, as this ensures sufficient durability of the re-stretched film (Y) in applications where its use is anticipated.

[0053] The thickness of the re-stretched film (Y) according to the present invention is not particularly limited, but is preferably 1 to 500 μm, more preferably 1 to 300 μm, even more preferably 3 to 250 μm, and particularly preferably 5 to 200 μm. [Examples]

[0054] 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 following polymerization may be carried out multiple times to obtain the necessary amount of polymer and resin composition for evaluation.

[0055] [Measurement conditions, etc.] The measurement conditions for each physical property are as follows:

[0056] [Intrinsic viscosity [η]] The intrinsic viscosity [η] of the various polymers and resin compositions obtained in the examples was measured at 135°C in decalin solvent. In the following, the intrinsic viscosity of polyethylene (A) may be referred to as "intrinsic viscosity [η]a". Similarly, the intrinsic viscosity of polyethylene (B) may be referred to as "intrinsic viscosity [η]b".

[0057] 〔density〕 The density of polyethylene (B) was measured in accordance with ASTM D1505.

[0058] [MFR] The MFR of the resin compositions obtained in the examples was measured under a 10 kg load in accordance with ASTM D1238E. The measurement temperature was 190°C.

[0059] [Film thickness] The film thickness of the re-stretched film obtained in the example was measured using a thickness gauge (Mitutoyo ID-C112X).

[0060] [Strength, elastic modulus] The re-stretched films obtained in the examples were cut into dumbbell-shaped pieces conforming to ASTM D-638 size (total length 115 mm, parallel section: 6 mm, grip width: 19 mm, gauge length: 25 mm), and the tensile modulus and tensile breaking strength were measured using a precision universal testing machine (Shimadzu Corporation, AGX-V). The test conditions were a tensile speed of 50 mm / min, a grip distance of 65 mm, a gauge length of 25 mm, and a measurement ambient temperature of 23°C.

[0061] [Coefficient of kinetic friction] The re-stretched film obtained in the example was cut into strips (150 mm x 20 mm), and the coefficient of dynamic friction of the film was measured using a JSPS abrasion tester (TRIBOGEAR TYPE31, manufactured by Shinto Kagaku Co., Ltd.). The test conditions were: mating material: glass plate (U-shaped), load: 250 g, speed: 150 mm / s, number of reciprocations: 5000 times, stroke: 100 mm, measurement ambient temperature: 23 °C.

[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)] In a 1-liter polymer chamber that had been thoroughly purged with nitrogen, 500 ml of purified decane was charged at room temperature. At 80°C, 0.5 mmol of triisobutylaluminum and solid titanium catalyst component [C1] (0.01 mmol in terms of titanium atoms) were added. Next, 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. After feeding 119 liters of ethylene, the ethylene feed was stopped, the temperature was rapidly cooled to 45°C, and then depressurization and nitrogen purging were performed. Polyethylene (B1) was obtained by performing 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 80°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. Polyethylene (A1) was obtained by carrying out the second stage of ethylene polymerization under these conditions. The slurry containing the generated solid was filtered and dried under reduced pressure overnight at 80°C. The intrinsic viscosity [η] (in decalin solvent at 135°C) of the obtained polyethylene resin composition (X1) is shown in Table 1.

[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 during the production of polyethylene resin composition (X1), was performed separately under the same conditions as during the production of polyethylene resin composition (X1), the yield of polyethylene obtained 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] • Polyethylene (A1) content and intrinsic viscosity [η] Polyethylene (A2) was produced by omitting the first stage of polymerization during the production of polyethylene resin composition (X1) and separately carrying out 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 (A2) was 10 dl / g. Next, the molecular weight distribution of polyethylene (A2) 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 high molecular weight component (polyethylene (A1)) contained in polyethylene resin composition (X1). Based on these results, the physical properties of polyethylene (A1) were considered to be the same as those of polyethylene (A2). That is, the intrinsic viscosity [η] of polyethylene (A1) was set to 10 dl / g.

[0067] [Granulation of polyethylene resin composition (X1)] The polyethylene resin composition (X1) obtained above was dry-blended with a known antioxidant, heat stabilizer, and hydrochloric acid absorbent commonly used in polyolefins. The total amount of these antioxidants, heat stabilizers, and hydrochloric acid absorbents blended was approximately 0.42% by mass, with the dry-blended composition being 100% by mass. The dry-blended composition was melt-kneaded using a twin-screw extruder (Technovel Co., Ltd., φ=15mm, L / D=30, cylinder temperature: 230℃) to form a polyethylene resin composition, which was then granulated into pellets. The MFR was measured using the obtained pellets. The results are shown in Table 1.

[0068] [Manufacturing of stretched film] The pellets obtained as described above were melt-cast molded using a single-screw extruder (manufactured by Toyo Seiki Seisakusho Co., Ltd., φ=20mm, L / D=28) under the conditions of cylinder temperature 290°C, die temperature 290°C, roll temperature 80°C, and take-up speed 0.3m / min to obtain a stretched film with a thickness of approximately 40μm.

[0069] [Re-stretching of film] The obtained stretched film was re-stretched using a batch-type stretcher (Bruckner, KARO IV). A re-stretched film with a thickness of approximately 20 μm was obtained by stretching it to approximately twice its original size at a stretching temperature of 130°C. The strength, modulus of elasticity, and coefficient of dynamic friction of the obtained re-stretched film were measured using the method described above. The evaluation results are shown in Table 1.

[0070] [Example 2] The composition was manufactured by swapping the polymerization conditions for the first and second stages of Example 1, and the production of the resin composition and granulation, production of the stretched film and re-stretching, and evaluation were carried out in the same manner as in Example 1, except that a stretched film with the thickness shown in Table 1 was used. Specifically, the polymerization conditions were modified by changing the catalyst component input temperature from 80°C to 48°C, not feeding hydrogen during the first stage of polymerization, changing the ethylene polymerization temperature from 85°C to 53°C, and changing the ethylene feed amount 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, changing the ethylene polymerization temperature from 80°C to 85°C, and changing the ethylene feed amount from 21 liters to 119 liters. The evaluation results are shown in Table 1.

[0071] [Examples 3-5] Except for changing the stretching ratio shown in Table 1, the resin composition was manufactured and granulated, the stretched film was manufactured and re-stretched, and the evaluation was carried out in the same manner as in Example 2. The evaluation results are shown in Table 1.

[0072] [Table 1]

Claims

1. 5 to 40 parts by mass of polyethylene (A) that meet the following requirement (a-1), It contains 95 to 60 parts by mass of 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 re-stretched film (Y) formed from a polyethylene resin composition (X) having an intrinsic viscosity [η] in decalin solvent at 135°C in the range of 1.0 to 15 dl / g: (a-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 5 to 50 dl / g; (b-1) The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 dl / g or more and less than 5 dl / g; (b-2) Density of 950-985 kg / m³ ３ That is the case.

2. The re-stretched film (Y) according to claim 1, having a thickness of 1 to 500 μm.

3. The re-stretched film (Y) according to claim 1, wherein the tensile strength of the re-stretched film in the MD direction is 30 MPa or more.

4. A process for producing polyethylene (A) having an intrinsic viscosity [η] in decalin solvent at 135°C in the range of 5 to 50 dl / g, The intrinsic viscosity [η] measured in decalin solvent at 135°C is 0.1 dl / g or more and less than 5 dl / g, and the density is 950 to 985 kg / m³. ３ The process for producing polyethylene (B), 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 1.0 to 15 dl / g, An extrusion molding process in which the polyethylene resin composition (X) is extruded to form a film, A stretch molding process for stretching the aforementioned film, including, A method for manufacturing a re-stretched film (Y).

Images