Surface protective film and method for producing the same

Abstract

To provide a surface protective film having sufficient adhesive strength, suppressed adhesion enhancing and sufficiently low thermal shrinkage.SOLUTION: There is provided a surface protective film in which a backing layer (X), an intermediate layer (Y) and an adhesive layer (Z) are laminated in this order, wherein the intermediate layer (Y) is composed of a resin composition (E) comprising 50 to 95 pts.mass of a propylene polymer (A) and 5 to 50 pts.mass of a 4-methyl-1-pentene-α-olefin copolymer (B) satisfying the following requirement (B-a) (provided that the total of the propylene polymer (A) and the 4-methyl-1-pentene-α-olefin copolymer (B) is defined as 100 pts.mass) and the adhesive layer (Z) contains a polystyrene-based elastomer (C). Requirement (B-a): the copolymer (B) contains 60 to 90 mol% of a structural unit (i) derived from 4-methyl-1-pentene and 10 to 40 mol% of a structural unit (ii) derived from an α-olefin having 2 to 4 carbon atoms.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protection film and a method for producing the same. [Background technology]

[0002] Surface protection films with an adhesive layer on one side are used to protect metal plates such as synthetic resin plates, glass plates, stainless steel plates, aluminum plates, and copper plates, as well as coated plates of these materials, and products and parts made from these materials. The surface protection film is peeled off during or after the molding process of the material.

[0003] A surface protection film is required to be able to adhere to an adherend and to be easily bonded thereto, not to peel off spontaneously when the adherend is transported, and to be easily peeled off when or after the adherend is processed. Therefore, a surface protection film is required to have various properties, such as appropriate adhesion to the surface of the adherend to be protected, flexibility to the extent that the surface protection film itself does not damage the surface to be protected, mechanical properties such as elongation characteristics according to the molding and processing of the adherend, and heat resistance. Furthermore, depending on the application, good transparency and color are required, and the surface protection film is also required to be free from defects such as gel components and fish eyes.

[0004] For example, by laminating a surface protection film to a prism sheet used in a liquid crystal display or the like, the liquid crystal display or the like can be protected from adhesion of dust, dirt, etc. Prism sheets are generally adherends having an uneven shape on at least one surface, and when laminating the surface protection film and the prism sheet, the adhesion area between the prism sheet and the adhesive layer of the surface protection film becomes small, so the adhesive used in the adhesive layer must have high adhesive strength.

[0005] However, when a surface protection film having a highly adhesive adhesive is rolled up as a film roll, the adhesive layer, which is one of the outermost layers of the surface protection film, and the base layer, which is the other outermost layer, are strongly adhered to each other. Therefore, when the surface protection film is unrolled and unfolded, deformation of the base layer and peeling of the adhesive itself in the adhesive layer occur, which raises concerns that the function of the surface protection film may be impaired.

[0006] Furthermore, when a surface protection film with a highly adhesive adhesive is attached to the surface of an adherend, the problem of so-called increased adhesion may occur due to factors such as the elapsed time and environmental temperature. Increased adhesion occurs due to an increase in the adhesive area at the interface between the adherend, particularly an adherend with an uneven surface, and the adhesive layer of the surface protection film. Even in the case of adherends with relatively small uneven surfaces, such as diffusion films and reflective films, the adhesive area increases significantly, making increased adhesion likely to occur. The increased adhesion can make it difficult to peel the surface protection film from the surface of the adherend, and can also cause problems such as adhesive residue, where adhesive components partially remain on the surface of the adherend.

[0007] Patent Documents 1 and 2 disclose surface protection films having an adhesive layer containing a styrene elastomer, which is an isobutylene block copolymer, and a tackifier, while Patent Documents 3 and 4 disclose resin compositions and surface protection films that use a styrene elastomer in the adhesive layer and are less likely to develop adhesion. Patent Document 5 also discloses a surface protection film that uses a highly adhesive styrene elastomer and an aliphatic amide composition containing a fatty acid amide compound in the adhesive layer to suppress adhesion development. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-126512 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-255071 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-274213 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-126169 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-121989 [Patent Document 6] International Publication No. 2015 / 12274 Summary of the Invention [Problem to be solved by the invention]

[0009] It was found that the surface protection films described in Patent Documents 1 and 2 had insufficient adhesive strength when attached to an adherend with a surface having large irregularities.

[0010] The surface protection films described in Patent Documents 3 and 4 are intended for use on smooth substrates such as polyethylene terephthalate (PET) substrates and acrylic substrates, and therefore have low adhesive strength, making it difficult to apply the surface protection films to substrates with large irregularities. In the surface protection film described in Patent Document 5, the aliphatic amide compound is a low molecular weight compound, and so there is a concern that components of the adhesive layer may migrate to the adherend and cause contamination.

[0011] Furthermore, it is desirable that the surface protection film have a low thermal shrinkage rate. Therefore, an object of the present invention is to provide a surface protection film that has sufficient adhesive strength both to adherends with flat surfaces and to adherends with uneven surfaces, that suppresses adhesion buildup, and that has sufficiently small thermal shrinkage. [Means for solving the problem]

[0012] The present invention relates to, for example, the following items [1] to [5].

[0013] [1] The back layer (X), the middle layer (Y) and the adhesive layer (Z) are laminated in this order, the intermediate layer (Y) is made of a resin composition (E) containing 50 to 95 parts by mass of a propylene polymer (A) and 5 to 50 parts by mass of a 4-methyl-1-pentene-α-olefin copolymer (B) satisfying the following requirement (Ba) (where the total of the propylene polymer (A) and the 4-methyl-1-pentene-α-olefin copolymer (B) is taken as 100 parts by mass), The adhesive layer (Z) contains a polystyrene-based elastomer (C), Surface protection film. Requirement (Ba): The 4-methyl-1-pentene·α-olefin copolymer (B) contains 60 to 90 mol % of structural units (i) derived from 4-methyl-1-pentene and 10 to 40 mol % of structural units (ii) derived from an α-olefin having 2 to 4 carbon atoms (provided that the total of structural units (i) and structural units (ii) is 100 mol %).

[0014] [2] The surface protection film according to [1], wherein the resin composition (E) has a tanδ peak temperature in the range of 10 to 40°C and a tanδ peak value in the range of 0.10 to 0.40, as determined by dynamic viscoelasticity measurement under the conditions of a temperature range of -40 to 150°C, a deformation mode of a torsional deformation mode, a frequency of 1.0 Hz, a heating rate of 4°C / min, and a strain of 0.5%.

[0015] [3] The surface protection film according to [1] or [2], which has a heat shrinkage rate of 0.5% or less when measured after heating at a temperature of 60°C for 24 hours.

[0016] [4] The method includes a step of laminating a back layer (X), an intermediate layer (Y), and an adhesive layer (Z) in this order, the intermediate layer (Y) is made of a resin composition (E) containing 50 to 95 parts by mass of a propylene polymer (A) and 5 to 50 parts by mass of a 4-methyl-1-pentene-α-olefin copolymer (B) satisfying the following requirement (Ba) (where the total of the propylene polymer (A) and the 4-methyl-1-pentene-α-olefin copolymer (B) is taken as 100 parts by mass), The adhesive layer (Z) contains a polystyrene-based elastomer (C), A method for manufacturing a surface protection film. Requirement (Ba): The 4-methyl-1-pentene·α-olefin copolymer (B) contains 60 to 90 mol % of structural units (i) derived from 4-methyl-1-pentene and 10 to 40 mol % of structural units (ii) derived from an α-olefin having 2 to 4 carbon atoms (provided that the total of structural units (i) and structural units (ii) is 100 mol %).

[0017] [5] The method for producing the surface protection film according to [4], comprising the step of forming and laminating the back layer (X), intermediate layer (Y) and adhesive layer (Z) by co-extrusion molding. [Effects of the Invention]

[0018] The surface protection film of the present invention has sufficient adhesive strength to both adherends with flat surfaces and adherends with uneven surfaces, suppresses adhesion buildup, and exhibits sufficiently small heat shrinkage. DETAILED DESCRIPTION OF THE INVENTION

[0019] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention.

[0020] In this specification, a range of values ​​expressed using "to" means a range that includes the values ​​before and after "to" as the lower and upper limits. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, it means the total amount of multiple substances present in the composition, unless otherwise specified.

[0021] [Back layer (X)] The surface protection film according to the present invention includes a back layer (X). The back layer (X) contains, for example, a thermoplastic resin. Examples of the thermoplastic resin include polyolefin, polyester, and polyamide. Examples of polyolefin include ethylene polymer, propylene polymer, 4-methyl-1-pentene polymer, and 1-butene polymer. Examples of ethylene polymer include high-density polyethylene, medium-density polyethylene, high-pressure low-density polyethylene, and linear low-density polyethylene. Examples of polyester include polyethylene terephthalate and polyethylene naphthalate. Examples of polyamide include polyamide 6, polyamide 66, polyamide 12, and polyamide 6-66 copolymer. The thermoplastic resin may be one type or two or more types.

[0022] From the viewpoint of the heat resistance of the surface protective film, the back layer (X) preferably contains a polyolefin, more preferably an ethylene polymer and / or a propylene polymer, and even more preferably a propylene polymer.

[0023] Examples of propylene polymers include propylene homopolymers and copolymers mainly containing structural units derived from propylene. When the propylene polymer is a copolymer, it may be a random copolymer or a block copolymer. Examples of monomers copolymerizable with propylene include α-olefins other than propylene and diene compounds.

[0024] Examples of α-olefins other than propylene include α-olefins having 2 to 20 carbon atoms (excluding propylene), such as ethylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene.

[0025] The content of structural units derived from propylene in the propylene polymer is preferably 85 to 100 mol %, more preferably 90 to 100 mol %. When the propylene polymer is a copolymer, the content of structural units derived from propylene in the copolymer is preferably 85 to 99.9 mol %, more preferably 90 to 99.5 mol %, and the content of structural units derived from other monomers (content of structural units derived from monomers other than propylene) is preferably 0.1 to 15 mol %, more preferably 0.5 to 10 mol %.

[0026] The propylene polymers may be used alone or in combination of two or more. Propylene polymers can be produced by polymerizing monomers in the presence of known catalysts such as Ziegler-Natta catalysts and metallocene catalysts by known polymerization methods such as gas phase, bulk and slurry methods. Commercially available propylene polymers may be used, such as Novatec PP (registered trademark) manufactured by Japan Polypropylene Corporation, Sumitomo Noblen (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., Prime Polypro (registered trademark) manufactured by Prime Polymer Co., Ltd., and Sunallomer (registered trademark) manufactured by Sunallomer Co., Ltd.

[0027] From the viewpoint of film-forming properties of the surface protection film, the melt mass flow rate (MFR) of the propylene polymer is preferably in the range of 0.5 to 50 g / 10 min, more preferably 1.0 to 40 g / 10 min, and even more preferably 2.0 to 30 g / 10 min. The MFR can be measured in accordance with ASTM D1238 at a temperature of 230°C and a load of 2.16 kg.

[0028] From the viewpoint of film-forming properties of the surface protection film, the melting point (Tm) of the propylene polymer is preferably 100 to 190° C., more preferably 110 to 180° C., and even more preferably 120 to 170° C. The melting point can be measured, for example, by using a differential scanning calorimeter (DSC) to heat the polymer to 250° C., melt it by heating for 5 minutes, and then quench it with liquid nitrogen to obtain a sample. When the exothermic curve and endothermic curve are observed in a nitrogen gas flow at a heating rate of 10° C. / min, the melting point can be measured as the maximum temperature of the endothermic peak associated with melting.

[0029] The back layer (X) preferably contains a propylene homopolymer from the viewpoint of providing the surface protective film with both appropriate rigidity and heat resistance. From the viewpoint of improving the interlayer adhesive strength between the back layer (X) and the intermediate layer (Y), the back layer (X) also preferably contains the same propylene polymer as the propylene polymer (A) used in the intermediate layer (Y).

[0030] The back layer (X) may contain additives such as antioxidants, fibers, fillers, ultraviolet absorbers, crystal nucleating agents, pigments, hydrochloric acid absorbers, crosslinking agents, crosslinking aids, softeners, and flame retardants, as long as the effects of the present invention are not impaired. The total content of the additives is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 1% by mass or less, relative to 100% by mass of the back layer (X).

[0031] Middle layer The surface protection film includes an intermediate layer (Y). The intermediate layer (Y) is made of a resin composition (E) containing a propylene polymer (A) and a 4-methyl-1-pentene-α-olefin copolymer (B).

[0032] <Propylene polymer (A)> Examples of the propylene polymer (A) include a homopolymer of propylene, and a random copolymer and a block copolymer of propylene with a small amount of an α-olefin. Examples of the α-olefins include α-olefins having 2 to 20 carbon atoms (excluding propylene), such as ethylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene. The propylene polymer (A) may be one type or two or more types.

[0033] The content of structural units derived from propylene in the propylene polymer (A) is preferably from 85 to 100 mol %, more preferably from 90 to 100 mol %. When the propylene polymer (A) is a copolymer, the content of structural units derived from propylene in the copolymer is preferably 85 to 99.9 mol %, more preferably 90 to 99.8 mol %, from the viewpoint of dispersibility of the 4-methyl-1-pentene-α-olefin copolymer (B), and the content of structural units derived from other monomers (the content of structural units derived from monomers other than propylene) is preferably 0.1 to 15 mol %, more preferably 0.2 to 10 mol %.

[0034] The propylene polymer (A) is preferably a propylene homopolymer from the viewpoints of dispersibility of the 4-methyl-1-pentene·α-olefin copolymer (B) and rigidity and heat resistance of the surface protection film. The monomer constituting the propylene polymer (A) may be a monomer derived from a fossil fuel or a monomer derived from biomass, and these monomers may be used alone or in combination of two or more.

[0035] From the viewpoint of film-forming properties of the surface protection film, the melt mass flow rate (MFR) of the propylene polymer (A) is preferably in the range of 0.5 to 50 g / 10 min, more preferably 1.0 to 40 g / 10 min, and even more preferably 2.0 to 30 g / 10 min. The MFR can be measured in accordance with ASTM D1238 at a temperature of 230°C and a load of 2.16 kg.

[0036] From the viewpoint of film-forming properties of the surface protection film, the melting point (Tm) of the propylene polymer (A) is preferably 100 to 190° C., more preferably 110 to 180° C., and even more preferably 120 to 170° C. The melting point can be measured, for example, by using a differential scanning calorimeter (DSC) to heat the polymer to 250° C., melt it by heating for 5 minutes, and then quench it with liquid nitrogen to obtain a sample. When the exothermic curve and endothermic curve are observed in a nitrogen gas flow at a heating rate of 10° C. / min, the melting point can be measured as the maximum temperature of the endothermic peak associated with melting.

[0037] The propylene polymer (A) may be a commercially available product, such as Novatec PP (registered trademark) manufactured by Japan Polypropylene Corporation, Sumitomo Noblen (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., Prime Polypro (registered trademark) manufactured by Prime Polymer Co., Ltd., and Sunallomer (registered trademark) manufactured by Sunallomer Co., Ltd.

[0038] <4-methyl-1-pentene / α-olefin copolymer (B)> 4-methyl-1-pentene-α-olefin copolymer (B) (hereinafter sometimes abbreviated as "copolymer (B)") is a copolymer of 4-methyl-1-pentene and an α-olefin, and satisfies the following requirement (Ba).

[0039] <Requirements (Ba)> Copolymer (B) contains 60 to 90 mol % of structural units (i) derived from 4-methyl-1-pentene and 10 to 40 mol % of structural units (ii) derived from an α-olefin having 2 to 4 carbon atoms (provided that the total of structural units (i) and structural units (ii) is 100 mol %).

[0040] The content of each structural unit in the copolymer (B) was determined by carbon-13 nuclear magnetic resonance (hereinafter referred to as 13 The content of each structural unit was calculated using the measurement method described in the Examples section under the equipment and conditions. 13 It can be calculated by measuring the C-NMR spectrum.

[0041] The content of the structural unit (i) is 60 to 90 mol %, preferably 65 to 89 mol %, more preferably 68 to 88 mol %, and even more preferably 70 to 87 mol %. When the content of the structural unit (i) is at least the above lower limit, the copolymer (B) has excellent dispersibility in the propylene polymer (A). Furthermore, when the content of the structural unit (i) is at least the above lower limit, the surface protective film can maintain the transparency of the propylene polymer (A) without deterioration. When the content of the structural unit (i) is equal to or less than the upper limit, the surface protection film exhibits excellent conformability to the irregularities of the surface of the adherend.

[0042] The content of the structural unit (ii) is 10 to 40 mol %, preferably 11 to 35 mol %, more preferably 12 to 32 mol %, and even more preferably 13 to 30 mol %. When the content of the structural unit (ii) is at least as large as the above lower limit, the surface protection film exhibits excellent conformability to the irregularities of the surface of the adherend. When the content of the structural unit (ii) is equal to or less than the upper limit, the copolymer (B) has excellent dispersibility in the propylene polymer (A). Furthermore, when the content of the structural unit (ii) is equal to or less than the upper limit, the surface protective film can maintain the transparency of the propylene polymer (A) without deterioration.

[0043] Examples of the α-olefin having 2 to 4 carbon atoms from which the structural unit (ii) is derived include ethylene, propylene, and 1-butene. The α-olefin may be one type, or two or more types. The α-olefin is preferably propylene, which provides good dispersibility in the propylene polymer (A). The monomers constituting the 4-methyl-1-pentene·α-olefin copolymer (B) may be monomers derived from fossil fuels or monomers derived from biomass, and these monomers may be used alone or in combination of two or more.

[0044] The copolymer (B) can improve the conformability of the surface protection film to the irregularities of the adherend surface and suppress the increase in adhesion. To improve the conformability to the adherend and suppress the increase in adhesion, it is preferable that the copolymer (B) not only imparts flexibility to the surface protection film but also has high stress relaxation properties. Stress relaxation can be evaluated, for example, by the loss tangent tanδ, which is the ratio (G'' / G') of the storage modulus G' to the loss modulus G'', measured by dynamic viscoelasticity measurement. The storage modulus G' is the elastic component that stores the energy internally and maintains the stress when stress is applied. The loss modulus G'' is the viscous component that converts the energy into heat and releases it (diffuses it to the outside) when stress is applied. Therefore, the higher the loss tangent tanδ of a material under a specific temperature environment, the easier it is to absorb shock and the higher the stress relaxation will be.

[0045] The tan δ peak value of copolymer (B) determined by dynamic viscoelasticity measurement under the conditions of a temperature range of -40 to 150°C, a deformation mode of a torsional deformation mode, a frequency of 1.0 Hz, a heating rate of 4°C / min, and a strain of 0.5% is preferably in the range of 0.5 to 5.0, more preferably 0.6 to 4.5, even more preferably 0.7 to 4.0, and particularly preferably 1.0 to 3.5. The maximum value of the loss tangent tan δ measured in the dynamic viscoelasticity measurement is defined as the tan δ peak value.

[0046] The tanδ peak temperature of copolymer (B) determined by dynamic viscoelasticity measurement in a temperature range of -40 to 150°C, a torsional deformation mode, a frequency of 1.0 Hz, a heating rate of 4°C / min, and a strain of 0.5% is preferably in the range of -20 to 60°C, more preferably -10 to 55°C, and even more preferably 0 to 50°C. The temperature at which the loss tangent tan δ measured in the dynamic viscoelasticity measurement reaches a tan δ peak value is defined as the tan δ peak temperature.

[0047] When the tan δ peak value and tan δ peak temperature of the copolymer (B) are within the above ranges, the surface protection film has excellent conformability to the irregularities of the adherend surface and sufficient adhesive strength. Specific methods for measuring the tan δ peak value and tan δ peak temperature of the copolymer (B) are as described in the Examples section below. The tan δ peak value and tan δ peak temperature can be adjusted by changing the composition of the structural units (i) and (ii) in the copolymer (B).

[0048] The intrinsic viscosity [η] of copolymer (B) measured in decalin solvent at 135°C is preferably in the range of 0.5 to 5.0 dL / g, more preferably 0.6 to 4.0 dL / g, and even more preferably 0.8 to 3.0 dL / g. When the intrinsic viscosity [η] of copolymer (B) is in the above range, the content of low molecular weight components is low, thereby reducing stickiness and facilitating film formation. The intrinsic viscosity [η] can be calculated by measuring the specific viscosity under the conditions described in the Examples section.

[0049] The melting point (Tm) of the copolymer (B) measured by differential scanning calorimetry (DSC) is preferably not observed or is in the range of less than 160° C. When the copolymer (B) has a melting point, the melting point is preferably 150° C. or lower, more preferably 145° C. or lower, and even more preferably 140° C. or lower.

[0050] The melting point can be adjusted by changing the stereoregularity of copolymer (B), the type of α-olefin that derives structural unit (ii), and the content of structural unit (ii). The melting point can be adjusted by adjusting the composition to the desired level using an olefin polymerization catalyst, which will be described later. The melting point (Tm) is measured using a differential scanning calorimeter (DSC), and details of the measurement method are described in the Examples section.

[0051] The density of the copolymer (B) is preferably 820 to 860 kg / m 3 , more preferably 825 to 855 kg / m 3 , and more preferably 830 to 850 kg / m 3 When the density of the copolymer (B) is within the above range, flexibility can be imparted to the surface protection film. The density can be measured using a density gradient tube in accordance with JIS K7112.

[0052] The molecular weight distribution (Mw / Mn) of the copolymer (B), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) as measured by gel permeation chromatography (GPC), is preferably in the range of 1.0 to 4.0, more preferably 1.2 to 3.5, and even more preferably 1.5 to 3.0. When the molecular weight distribution (Mw / Mn) of the copolymer (B) is in the above range, the influence of low molecular weight and low stereoregularity polymers is reduced, and the rigidity of the surface protection film is improved.

[0053] The weight average molecular weight (Mw) of the copolymer (B) in terms of polystyrene, measured by gel permeation chromatography (GPC), is preferably in the range of 500 to 10,000,000, more preferably 1,000 to 5,000,000, and even more preferably 5,000 to 2,500,000. When the weight average molecular weight (Mw) of the copolymer (B) is in the above range, the rigidity of the surface protection film is improved. Details of the methods for measuring Mw, Mn and Mw / Mn are described in the Examples section.

[0054] From the viewpoint of facilitating the formation of the surface protection film and facilitating the adjustment of the film thickness, the melt mass flow rate (MFR) of the copolymer (B) is preferably in the range of 0.5 to 50 g / 10 min, more preferably 1.0 to 40 g / 10 min, and even more preferably 2.0 to 30 g / 10 min. The MFR can be measured in accordance with ASTM D1238 at a temperature of 230°C and a load of 2.16 kg.

[0055] <Method for producing copolymer (B)> The copolymer (B) can be produced, for example, by polymerizing 4-methyl-1-pentene and the above-mentioned α-olefin having 2 to 4 carbon atoms using an appropriate polymerization catalyst such as a magnesium-supported titanium catalyst or a metallocene catalyst. The polymerization catalyst may suitably be a conventionally known catalyst, such as a magnesium-supported titanium catalyst or the metallocene catalysts described in International Publication No. 01 / 53369, International Publication No. 01 / 27124, JP-A-3-193796, JP-A-2-41303, WO 2011 / 055803, or WO 2014 / 050817. The polymerization may be carried out by a method appropriately selected from liquid phase polymerization methods including solution polymerization and suspension polymerization, and gas phase polymerization methods.

[0056] In the liquid phase polymerization method, an inert hydrocarbon solvent can be used as a solvent constituting the liquid phase. Examples of the inert hydrocarbon include aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, decane, dodecane, and kerosene, alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane, aromatic hydrocarbons such as benzene, toluene, and xylene, halogenated hydrocarbons such as ethylene chloride, chlorobenzene, dichloromethane, trichloromethane, and tetrachloromethane, and mixtures thereof.

[0057] In the liquid phase polymerization method, bulk polymerization can also be performed using the monomer corresponding to the structural unit (i) derived from 4-methyl-1-pentene (i.e., 4-methyl-1-pentene) or the monomer corresponding to the structural unit (ii) derived from an α-olefin having 2 to 4 carbon atoms (i.e., an α-olefin having 2 to 4 carbon atoms) itself as a solvent.

[0058] By copolymerizing 4-methyl-1-pentene with an α-olefin having 2 to 4 carbon atoms in a stepwise manner, it is also possible to adjust the compositional distribution of the structural units (i) derived from 4-methyl-1-pentene and the structural units (ii) derived from the α-olefin having 2 to 4 carbon atoms that constitute the copolymer (B).

[0059] The polymerization temperature when producing the copolymer (B) is preferably −50 to 200° C., more preferably 0 to 100° C., and even more preferably 20 to 100° C. The polymerization pressure when producing the copolymer (B) is preferably normal pressure to 10 MPa gauge pressure, and more preferably normal pressure to 5 MPa gauge pressure.

[0060] During the production of copolymer (B), hydrogen may be added for the purpose of controlling the molecular weight and polymerization activity of the resulting polymer. The amount of hydrogen added is suitably about 0.001 to 100 nL per 1 kg of the total amount of 4-methyl-1-pentene and the α-olefin having 2 to 4 carbon atoms.

[0061] <Resin composition (E)> The resin composition (E) contains 50 to 95 parts by mass, preferably 52 to 94 parts by mass, more preferably 54 to 93 parts by mass, and even more preferably 55 to 92 parts by mass of the propylene polymer (A), and 5 to 50 parts by mass, preferably 6 to 48 parts by mass, more preferably 7 to 46 parts by mass, and even more preferably 8 to 45 parts by mass of the copolymer (B) (where the total of the propylene polymer (A) and the copolymer (B) is 100 parts by mass).

[0062] When the content of copolymer (B) is at least the above lower limit, the surface protection film can easily conform to the irregularities of the adherend surface and has sufficient adhesive strength. When the content of copolymer (B) is equal to or less than the upper limit, the surface protection film has good rigidity, making it easy to attach the surface protection film to an adherend. In addition, the surface protection film does not have a high heat shrinkage rate, and after attaching the adherend to the adhesive layer, there are less likely to be any loose portions at the interface between the adherend and the adhesive layer, resulting in sufficient adhesive strength.

[0063] The propylene polymer (A) and the copolymer (B) are polymers that are highly compatible with each other. The resin composition (E) essentially has a sea-island structure in which the propylene polymer (A) phase is a so-called sea phase and the copolymer (B) phase is a so-called island phase. However, since the size of the dispersed phase of the copolymer (B) phase is very small, the surface protection film can be easily formed.

[0064] The resin composition (E) may contain an antioxidant to the extent that the effects of the present invention are not impaired. Examples of antioxidants include known antioxidants, such as hindered phenol compounds, sulfur-based antioxidants, lactone-based antioxidants, organic phosphite compounds, organic phosphonite compounds, and combinations of several of these. Examples of antioxidants include phenol-based antioxidants (e.g., 2,6-di-t-butyl-4-methylphenol), polycyclic phenol-based antioxidants (e.g., 2,2'-methylenebis(4-methyl-6-t-butylphenol)), phosphorus-based antioxidants (e.g., tetrakis(2,4-di-t-butylphenyl)-4,4-biphenylenediphosphonate), and amine-based antioxidants (e.g., N,N-diisopropyl-p-phenylenediamine).

[0065] The resin composition (E) may contain additives such as fibers, inorganic or organic fillers, ultraviolet absorbers, crystal nucleating agents, pigments, hydrochloric acid absorbers, crosslinking agents, crosslinking aids, softeners, and flame retardants, as long as the effects of the present invention are not impaired.

[0066] The total content of the antioxidant and additives is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the total of the propylene polymer (A) and the copolymer (B).

[0067] The resin composition (E) may contain a resin other than the propylene polymer (A) and the copolymer (B) within a range that does not impair the effects of the present invention. The content of the resin other than the propylene polymer (A) and the copolymer (B) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, per 100 parts by mass of the total of the propylene polymer (A) and the copolymer (B).

[0068] The resin composition (E) is obtained by mixing the propylene polymer (A) and the copolymer (B) in the above-mentioned ratio. The resin composition (E) can be produced by various known methods, such as dry blending the propylene polymer (A) and the copolymer (B) using a Henschel mixer, a tumbler blender, a V-blender, or the like, dry blending the propylene polymer (A) and the copolymer (B) and then melt-kneading them using a single-screw extruder, a twin-screw extruder, a Banbury mixer, or the like, and stirring and mixing them in the presence of a solvent.

[0069] When the resin composition (E) contains an antioxidant or the like, the resin composition (E) may be produced by adding the antioxidant or the like when mixing the propylene polymer (A) and the copolymer (B), or the resin composition (E) may be produced by mixing the copolymer (B) with the antioxidant or the like, and then mixing the propylene polymer (A) and the copolymer (B).

[0070] The tan δ peak temperature of the resin composition (E) determined by dynamic viscoelasticity measurement in a temperature range of -40 to 150°C, a torsional deformation mode, a frequency of 1.0 Hz, a heating rate of 4°C / min, and a strain of 0.5% is preferably in the range of 10 to 40°C, more preferably 15 to 35°C, and the tan δ peak value is preferably in the range of 0.10 to 0.40, more preferably 0.10 to 0.30. When the tan δ peak temperature of the resin composition (E) is within the above range, the surface protection film has excellent conformability to the irregularities of the adherend surface at room temperature (e.g., 23°C), has sufficient adhesive strength, and is sufficiently suppressed from increasing adhesion.

[0071] When the tan δ peak temperature is within the above range and the tan δ peak value is equal to or greater than the above lower limit, the surface protection film has excellent conformability to the irregularities of the adherend surface, sufficient adhesive strength, and sufficient suppression of adhesion. Also, when the tan δ peak temperature is within the above range and the tan δ peak value is equal to or less than the above upper limit, the surface protection film has sufficient adhesive strength and also has good rigidity, making it easy to attach the adhesive layer to the adherend. The tan δ peak temperature and tan δ peak value can be increased or decreased, for example, by changing the content of copolymer (B) in resin composition (E).

[0072] [Adhesive layer (Z)] The surface protection film includes an adhesive layer (Z). The adhesive layer (Z) contains a polystyrene elastomer (C) from the viewpoints of preventing damage to the adherend due to the occurrence of fisheyes, improving the adhesive strength of the surface protective film, and suppressing the progression of adhesion.

[0073] Examples of polystyrene elastomers (C) include styrene-butadiene-styrene block copolymers (SBS), which consist of a rigid hard segment of polystyrene and a flexible soft segment of butadiene, styrene-butadiene-butylene-styrene block copolymers (SBBS), hydrogenated styrene-butadiene-styrene block copolymers (HSBR), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene-ethylene-butylene-styrene block copolymers (SEBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isobutylene-styrene block copolymers (SIBS), and styrene-isobutylene block copolymers (SIB). The polystyrene elastomer (C) may be one type alone or two or more types.

[0074] As the polystyrene elastomer (C), commercially available products can also be used. Commercially available styrene-butadiene-styrene block copolymers (SBS), in which the butadiene-derived components of styrene-butadiene copolymers are hydrogenated and styrene moieties are copolymerized in the flexible segments, include SOE (registered trademark) and Tufprene (registered trademark) manufactured by Asahi Kasei Corporation, and Dynalon (registered trademark) manufactured by ENEOS Materials Corporation.

[0075] Commercially available styrene-butadiene-butylene-styrene block copolymers (SBBS) include, for example, the Tuftec (registered trademark) P series manufactured by Asahi Kasei Corporation. Commercially available styrene-isoprene-styrene block copolymers (SIS) include, for example, JSR SIS (registered trademark) manufactured by JSR Corporation, Hybler (registered trademark) manufactured by Kuraray Co., Ltd., and Kraton (registered trademark) D SIS manufactured by Kraton Polymer Japan, Ltd.

[0076] Commercially available styrene-ethylene-butylene-styrene block copolymers (SEBS) include, for example, the Tuftec H series manufactured by Asahi Kasei Corporation and Kraton G manufactured by Kraton Polymer Japan Co., Ltd. Commercially available styrene-isobutylene-styrene block copolymers (SIBS) and styrene-isobutylene block copolymers (SIB) include, for example, SIBSTAR (registered trademark) manufactured by Kaneka Corporation. The monomers constituting the polystyrene elastomer (C) may be fossil fuel-derived monomers or biomass-derived monomers, and these monomers may be used alone or in combination of two or more.

[0077] The styrene content in the polystyrene elastomer (C) is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 8% by mass or more, and is preferably 50% by mass or less, relative to 100% by mass of the polystyrene elastomer (C). When the styrene content in the polystyrene elastomer (C) is within the above range, the interfacial adhesive strength between the adhesive layer (Z) and the intermediate layer (Y) is good, and the surface protection film has suitable formability.

[0078] The adhesive layer (Z) may contain additives such as a tackifier, an antioxidant, a fiber, a filler, an ultraviolet absorber, a crystal nucleating agent, a pigment, a hydrochloric acid absorber, a crosslinking agent, a crosslinking aid, a softener, and a flame retardant, as well as an olefin polymer, within a range that does not impair the effects of the present invention. Examples of olefin polymers include homopolymers and copolymers of α-olefins having 2 to 20 carbon atoms, and copolymers of ethylene and unsaturated carboxylic acids or unsaturated carboxylic acid esters.

[0079] Examples of the tackifier include chroman-based resins such as chroman-indene resin; phenol-based resins such as phenol-formaldehyde resin and xylene-formaldehyde resin; terpene-based resins such as terpene-phenolic resin, terpene resin (α,β-pinene resin), aromatic-modified terpene resin, and hydrogenated terpene resin; petroleum-based hydrocarbon resins such as synthetic polyterpene resin, aromatic hydrocarbon resin, aliphatic hydrocarbon resin, aliphatic cyclic hydrocarbon resin, aliphatic-alicyclic petroleum resin, aliphatic-aromatic petroleum resin, unsaturated hydrocarbon polymer, and hydrocarbon-based tackifying resin; hydrogenated petroleum-based hydrocarbon resin; and rosin-based resins such as rosin pentaerythritol ester, rosin glycerin ester, hydrogenated rosin, hydrogenated rosin ester, special rosin ester, and rosin-based tackifier.

[0080] Examples of the α-olefin homopolymers include propylene homopolymers and 1-butene homopolymers. Examples of the α-olefin copolymer include ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, propylene-ethylene copolymer, propylene-1-butene copolymer, propylene-ethylene-1-butene copolymer, 1-butene-ethylene copolymer, and 1-butene-propylene copolymer. Examples of copolymers of ethylene and unsaturated carboxylic acids or unsaturated carboxylic acid esters include ethylene-vinyl acetate copolymers, ethylene-methacrylic acid copolymers, and ethylene-methyl methacrylate copolymers.

[0081] The total content of the additives and the olefin polymer is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and particularly preferably 1% by mass or less, relative to 100% by mass of the adhesive layer (Z).

[0082] [Surface protection film] In the surface protection film, the back layer (X), the intermediate layer (Y) and the adhesive layer (Z) are laminated in this order. The surface protective film may include layers other than the back layer (X), the intermediate layer (Y) and the adhesive layer (Z).

[0083] The thickness of the surface protection film is not particularly limited and may be appropriately selected depending on the desired application, but is preferably 10 to 300 μm, more preferably 10 to 200 μm, even more preferably 10 to 150 μm, and particularly preferably 10 to 100 μm. When the thickness is equal to or greater than the lower limit, the film has sufficient rigidity and is easy to handle during production and use. When the thickness is equal to or less than the upper limit, the surface protection film can easily conform to the irregularities of the adherend surface when attached to the adherend. In addition, the mass of the surface protection film is not too large, and the surface protection film has appropriate rigidity, resulting in good productivity in film production.

[0084] From the viewpoint of conformability to the irregularities of the adherend surface, the thickness ratio of the backing layer (X) to the adhesive layer (Z) (thickness of the backing layer (X) / thickness of the adhesive layer (Z)) is preferably 1 / 3 to 3 / 1, more preferably 1 / 2 to 2 / 1. In addition, the thickness ratio of the intermediate layer (Y) to the adhesive layer (Z) (thickness of the intermediate layer (Y) / thickness of the adhesive layer (Z)) is preferably 2 / 1 to 10 / 1. The thickness ratio of the back layer (X), intermediate layer (Y) and adhesive layer (Z) (thickness of back layer (X) / thickness of intermediate layer (Y) / thickness of adhesive layer (Z)) is preferably 1 / 2 / 1 to 1 / 10 / 1. When the thickness ratio of the intermediate layer (Y) is equal to or greater than the lower limit, the surface protection film can easily conform to the irregularities of the adherend surface when it is attached to the adherend, improving adhesive strength. When the thickness ratio of the intermediate layer (Y) is equal to or less than the upper limit, the surface protection film is less likely to stretch when it is attached to the adherend and then peeled off, facilitating peeling from the adherend.

[0085] According to JIS K7133, the surface protection film is heated at 60°C for 24 hours, allowed to cool naturally to 23°C, and measured after 24 hours. The heat shrinkage of the surface protection film is preferably 0.5% or less, more preferably 0.45% or less. It is preferable that both the heat shrinkage in the MD and TD directions are within the above range. A surface protection film having a heat shrinkage within the above range has dimensional stability and is less likely to shrink. When the heat shrinkage is below the upper limit, the surface protection film is less likely to wrinkle or lift even when exposed to a high-temperature environment, and is less likely to spontaneously peel after being attached to an adherend. Details of the method for measuring the heat shrinkage are described in the Examples section.

[0086] The heat shrinkage rate can be increased or decreased, for example, by changing the content ratio of the propylene polymer (A) to the copolymer (B) in the intermediate layer (Y). When the mass ratio of the content of the copolymer (B) to the content of the propylene polymer (A) in the intermediate layer (Y) is small, the heat shrinkage rate tends to be small.

[0087] The surface protection film can be produced by laminating the back layer (X), intermediate layer (Y), and adhesive layer (Z) in this order. Examples of methods for producing the surface protection film include a method in which the back layer (X), intermediate layer (Y), and adhesive layer (Z) are formed and laminated by coextrusion molding or extrusion lamination using polymers that constitute each of the back layer (X), intermediate layer (Y), and adhesive layer (Z), respectively; a method in which extrusion coating is performed on a layer previously obtained by extrusion molding using a T-die device or inflation film molding; and a method in which films that will become each layer are laminated by dry lamination or the like. Among these, the co-extrusion molding method is preferred because it allows the surface protection film to be easily produced and high quality to be maintained.

[0088] The surface protection film obtained by the above method may be stretched. Conventionally known stretching methods can be appropriately adopted, including, for example, a tenter method and a roll stretching method. Stretching may be uniaxial stretching or biaxial stretching. Biaxial stretching may be sequential biaxial stretching or simultaneous biaxial stretching. When the surface protection film is stretched using a stretching roll immediately after extrusion or coextrusion molding, the stretching direction is the MD direction, i.e., the extrusion direction. The extrusion direction is a direction parallel to the die line generated on the film surface and can be easily identified from the die line. When the surface protection film is a biaxially stretched film, the heat shrinkage rates in both the MD and TD directions are preferably within the above ranges.

[0089] The surface protection film is usually used so that the adhesive layer (Z) adheres to the adherend. The surface protection film has sufficient adhesive strength both to adherends with smooth surfaces and to adherends with uneven surfaces. Furthermore, the surface protection film has excellent conformability to the uneven surface of the adherend, which increases the adhesion area with the adherend, stabilizes the adhesive strength, and suppresses adhesion buildup. The surface protection film can have sufficient adhesive strength and the adhesion increase is sufficiently suppressed, so that, for example, the adherend tends not to be contaminated.

[0090] The surface protection film has excellent flexibility and stretchability due to the inclusion of the intermediate layer (Y), and therefore can be easily adhered to an adherend and has excellent handleability.

[0091] The surface protective film is not limited to applications for preventing damage and staining of adherends having an uneven surface, and can also be preferably used to protect metal plates such as synthetic resin plates, glass plates, stainless steel plates, aluminum plates, and copper plates, as well as coated plates thereof, and products and parts made of these materials. [Example]

[0092] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. The methods for measuring the physical properties of polymers, the polymers used, the methods for preparing test pieces, and the evaluation methods in the following examples and comparative examples are as follows.

[0093] [Method for measuring polymer properties] <Content of constituent units> The content of the structural unit derived from 4-methyl-1-pentene and the content of the structural unit derived from α-olefin in the copolymer (B) were measured using the following apparatus and conditions: 13 The content of structural units derived from α-olefins in this measurement result does not include the content of structural units derived from 4-methyl-1-pentene. Using a nuclear magnetic resonance spectrometer (ECP500 model manufactured by JEOL Ltd.), solvent: o-dichlorobenzene / deuterated benzene (80 / 20% by volume) mixed solvent, sample concentration: 55 mg / 0.6 mL, measurement temperature: 120 °C, observation nuclei: 13C (125 MHz), sequence: single pulse proton decoupling, pulse width: 4.7 μsec (45° pulse), repetition time: 5.5 sec, number of accumulations: 10,000 or more, chemical shift reference value: 27.50 ppm 13 The C-NMR spectrum was measured. 13 The composition of copolymer (B) was quantified based on the C-NMR spectrum.

[0094] <Intrinsic viscosity〔η〕> The intrinsic viscosity of the copolymer (B) was measured at 135° C. in a decalin solvent using an Ubbelohde viscometer. First, approximately 20 mg of copolymer (B) was collected. The copolymer (B) may be in the form of a polymer powder, pellets, or resin block. The collected copolymer (B) was then dissolved in 15 mL of decalin, and the specific viscosity ηsp was measured in an oil bath heated to 135°C. This decalin solution was diluted with 5 mL of decalin solvent, and the specific viscosity ηsp was measured in the same manner. This dilution procedure was repeated two more times, and the value of ηsp / C when the concentration (C) was extrapolated to 0 was used to calculate the intrinsic viscosity (see the formula below). [η]=lim(ηsp / C) (C→0)

[0095] <Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn)> The molecular weight of copolymer (B) was measured by gel permeation chromatography (GPC). Specifically, a Waters ALC / GPC150-Cplus liquid chromatograph (integrated with a differential refractometer detector) was used, and two Tosoh GMH6-HT and two Tosoh GMH6-HTL columns were connected in series. The mobile phase consisted of o-dichlorobenzene and 0.025% by mass dibutylhydroxytoluene (Fujifilm Wako Pure Chemical Industries, Ltd.) as the antioxidant. The mobile phase was run at 1.0 mL / min, the sample concentration was 15 mg / 10 mL, the sample injection volume was 500 μL, and a differential refractometer was used as the detector. Standard polystyrenes with weight-average molecular weights (MW) ranging from 1,000 to 4,000,000 were used. The weight-average molecular weight (Mw), number-average molecular weight (Mn), and molecular weight distribution (Mw / Mn) were calculated by analyzing the obtained chromatogram using a calibration curve prepared by a known method using a standard polystyrene sample. The measurement time per sample was 60 minutes.

[0096] <Melt flow rate (MFR)> The MFR of the copolymer (B) was measured in accordance with ASTM D1238 at a temperature of 230° C. and a load of 2.16 kg.

[0097] <Melting point (Tm)> The melting point (Tm) of copolymer (B) was measured using a differential scanning calorimeter (DSC200, Hitachi High-Tech Corporation) in accordance with JIS K7121. Approximately 5 mg of sample was placed in a measurement aluminum pan and heated to 200°C at a heating rate of 10°C / min. The temperature at the highest melting peak among the measured melting peaks was taken as the melting point. If no melting peak appeared, it was evaluated that no melting point was observed.

[0098] <density> The density of the copolymer (B) was measured using a density gradient tube in accordance with JIS K7112.

[0099] <Dynamic viscoelasticity measurement> After a predetermined amount of pellet-like copolymer (B) was filled into a SUS mold, the heating plate was set to 200°C, and using a hydraulic heat press (NSF-50 manufactured by Shinto Metal Industry Co., Ltd.), the mixture was preheated for 7 minutes and pressed at a gauge pressure of 10 MPa for 2 minutes. The mixture was then transferred to a cooling plate set to 20°C, compressed at a gauge pressure of 10 MPa, and cooled for 2 minutes to produce a 2 mm thick press sheet for measurement. Using the measurement press sheet, the temperature dispersion of dynamic viscoelasticity was observed from -40 to 150°C using a rheometer (MCR301 manufactured by Anton Paar) under the following conditions: deformation mode: torsional deformation mode, frequency: 1.0 Hz, heating rate: 4°C / min, strain amount: 0.5%, and the tan δ peak value and tan δ peak temperature were measured.

[0100] [Propylene polymer (A)] The following propylene polymer (A) was used. Propylene polymer (A-1): Prime Polypro F107BV manufactured by Prime Polymer Co., Ltd. (MFR = 7 g / 10 min (230 °C, 2.16 kg), melting point 160 °C)

[0101] [Copolymer (B)] As copolymer (B), copolymers (B-1) and (B-2) were used, which were prepared so as to have different contents of structural units derived from 4-methyl-1-pentene and different contents of structural units derived from α-olefins having 2 to 4 carbon atoms.

[0102] <Preparation Example 1: Preparation of Copolymer (B-1)> A 1.5 L stainless steel autoclave equipped with a stirring blade and thoroughly purged with nitrogen was charged with 300 mL of n-hexane (dried over activated alumina under a dry nitrogen atmosphere) and 450 mL of 4-methyl-1-pentene at 23° C. 0.75 mL of a 1.0 mmol / mL toluene solution of triisobutylaluminum (TIBAL) was then charged into the autoclave and stirred.

[0103] The autoclave was then heated to an internal temperature of 60°C and pressurized with propylene to a total pressure (gauge pressure) of 0.40 MPa. Subsequently, 0.34 mL of a previously prepared toluene solution containing 1 mmol of methylaluminoxane (calculated as aluminum) and 0.01 mmol of diphenylmethylene(1-ethyl-3-t-butylcyclopentadienyl)(2,7-di-t-butylfluorenyl)zirconium dichloride was introduced into the autoclave under pressure with nitrogen to initiate the polymerization reaction. During the polymerization reaction, the internal temperature of the autoclave was adjusted to 60°C. Sixty minutes after the start of polymerization, 5 mL of methanol was introduced into the autoclave under pressure with nitrogen to terminate the polymerization reaction, and the autoclave was then depressurized to atmospheric pressure. After depressurization, acetone was added to the reaction solution while stirring.

[0104] The resulting powdery copolymer containing the solvent was dried at 100°C under reduced pressure for 12 hours. The mass of the product, copolymer (B-1), was 36.9 g. In copolymer (B-1), the content of structural units derived from 4-methyl-1-pentene was 72.4 mol%, and the content of structural units derived from propylene was 27.6 mol%. DSC measurement showed no melting point. The measurement results of each physical property of copolymer (B-1) are shown in Table 1.

[0105] Next, 100 parts by weight of the copolymer (B-1) were blended with 0.1 parts by weight of tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]pentaerythritol as a heat stabilizer and 0.1 parts by weight of tris(2,4-di-t-butylphenyl)phosphate as a secondary antioxidant. The resulting strand was extruded using a twin-screw extruder (TEX25αIII, manufactured by The Japan Steel Works, Ltd., screw diameter 25 mm, L / D = 52) at a cylinder temperature of 200 °C, an extrusion rate of 5 kg / h, and a screw rotation speed of 100 rpm. The strand was then immersed in a water bath and introduced into a pelletizer (KM-100, manufactured by Katsumik Co., Ltd.) for pelletization to obtain pellets. The results of dynamic viscoelasticity measurements using the pellets are shown in Table 1.

[0106] <Preparation Example 2: Preparation of Copolymer (B-2)> A 1.5 L stainless steel autoclave equipped with a stirring blade and thoroughly purged with nitrogen was charged with 300 mL of n-hexane (dried over activated alumina under a dry nitrogen atmosphere) and 450 mL of 4-methyl-1-pentene at 23° C. 0.75 mL of a 1.0 mmol / mL toluene solution of triisobutylaluminum (TIBAL) was charged to the autoclave and stirred.

[0107] The autoclave was then heated to an internal temperature of 60°C and pressurized with propylene to a total pressure (gauge pressure) of 0.19 MPa. Subsequently, 0.34 mL of a previously prepared toluene solution containing 1 mmol of methylaluminoxane (calculated as aluminum) and 0.01 mmol of diphenylmethylene(1-ethyl-3-t-butylcyclopentadienyl)(2,7-di-t-butylfluorenyl)zirconium dichloride was introduced into the autoclave under nitrogen pressure to initiate the polymerization reaction. During the polymerization reaction, the autoclave's internal temperature was adjusted to 60°C. Sixty minutes after the start of polymerization, 5 mL of methanol was introduced into the autoclave under nitrogen pressure to terminate the polymerization reaction, after which the autoclave was depressurized to atmospheric pressure. After depressurization, acetone was added to the reaction solution while stirring.

[0108] The resulting powdery polymer containing the solvent was dried at 130°C under reduced pressure for 12 hours. The mass of the product, Copolymer (B-2), was 44.0 g. In Copolymer (B-2), the content of structural units derived from 4-methyl-1-pentene was 84.1 mol%, and the content of structural units derived from propylene was 15.9 mol%. DSC measurement revealed that the melting point was 130°C. The measurement results of each physical property of Copolymer (B-2) are shown in Table 1.

[0109] Next, 100 parts by weight of the copolymer (B-2) were blended with 0.1 parts by weight of tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]pentaerythritol as a heat stabilizer and 0.1 parts by weight of tris(2,4-di-t-butylphenyl)phosphate as a secondary antioxidant. The mixture was extruded into a twin-screw extruder (TEX25αIII, manufactured by The Japan Steel Works, Ltd., screw diameter 25 mm, L / D = 52) at a cylinder temperature of 200 °C, an extrusion rate of 5 kg / h, and a screw rotation speed of 100 rpm. The strand was then immersed in a water bath and introduced into a pelletizer (KM-100, manufactured by Katsumik Co., Ltd.) for pelletization to obtain pellets. The results of dynamic viscoelasticity measurements using the pellets are shown in Table 1.

[0110] [Polystyrene elastomer (C)] The following polystyrene elastomers were used as the polystyrene elastomers (C): Polystyrene elastomer (C-1): Tuftec (registered trademark) H1052 manufactured by Asahi Kasei Corporation (hydrogenated styrene-ethylene-butylene-styrene copolymer (SEBS), styrene content 19% by mass, MFR = 14 g / 10 min (230 °C, 2.16 kg))

[0111] [Polyolefin elastomer] The polyolefin elastomer used was a propylene-ethylene random copolymer (ExxonMobil Chemical Company, Vistamaxx 6202: MFR = 20 g / 10 min (230 °C, 2.16 kg), ethylene content 15 mass%).

[0112] [Table 1]

[0113] [Example 1] A resin composition (E-1) was prepared by dry blending 90 parts by mass of a propylene polymer (A-1) and 10 parts by mass of a copolymer (B-1) containing a heat stabilizer and a secondary antioxidant using a tumbler blender.

[0114] Then, propylene polymer (A-1) was loaded into the back layer hopper of a three-type three-layer co-extrusion molding machine equipped with a T-die (screw diameter 25 mm, L / D = 24, T-die width 350 mm, lip opening 2 mm), resin composition (E-1) was loaded into the middle layer hopper, and polystyrene-based elastomer (C-1) was loaded into the adhesive layer hopper. The cylinder temperature was set to 220 to 240°C, and the T-die temperature was set to 240°C, and the molten resin was extruded from the T-die. The casting roll temperature was set to 40°C, and the take-up speed was set to 3.0 m / min, and the screw rotation speed was adjusted to form a surface protection film such that the layer thicknesses of the back layer (X), intermediate layer (Y), and adhesive layer (Z) were 10 μm, 30 μm, and 10 μm, respectively. The physical properties of the surface protective film and the loss tangent tan δ of the resin composition (E-1) were measured according to the methods described below. The results are shown in Table 2.

[0115] [Example 2] Resin composition (E-2) was prepared using 80 parts by mass of propylene polymer (A-1) and 20 parts by mass of copolymer (B-1), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-2) was used instead of resin composition (E-1). The results of measuring the physical properties of the surface protective film and the results of measuring the loss tangent tanδ of resin composition (E-2) are shown in Table 2.

[0116] [Example 3] Resin composition (E-3) was prepared using 70 parts by mass of propylene polymer (A-1) and 30 parts by mass of copolymer (B-1), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-3) was used instead of resin composition (E-1). The results of measuring the physical properties of the surface protective film and the results of measuring the loss tangent tanδ of resin composition (E-3) are shown in Table 2.

[0117] [Example 4] Resin composition (E-4) was prepared using 60 parts by mass of propylene polymer (A-1) and 40 parts by mass of copolymer (B-1), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-4) was used instead of resin composition (E-1). Table 2 shows the measurement results of the physical properties of the surface protective film and the measurement results of the loss tangent tanδ of resin composition (E-4).

[0118] [Example 5] Resin composition (E-5) was prepared using 60 parts by mass of propylene polymer (A-1) and 40 parts by mass of copolymer (B-2), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-5) was used instead of resin composition (E-1). The results of measuring the physical properties of the surface protective film and the results of measuring the loss tangent tanδ of resin composition (E-5) are shown in Table 2.

[0119] [Comparative Example 1] A surface protective film was produced in the same manner as in Example 1, except that only the propylene polymer (A-1) was used instead of the resin composition (E-1). The results of measuring the physical properties of the surface protective film and the loss tangent tanδ of the propylene polymer (A-1) are shown in Table 2.

[0120] Comparative Example 2 Resin composition (E-7) was prepared using 96 parts by mass of propylene polymer (A-1) and 4 parts by mass of copolymer (B-1), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-7) was used instead of resin composition (E-1). The results of measuring the physical properties of the surface protective film and the results of measuring the loss tangent tanδ of resin composition (E-7) are shown in Table 2.

[0121] Comparative Example 3 Resin composition (E-8) was prepared using 40 parts by mass of propylene polymer (A-1) and 60 parts by mass of copolymer (B-1), and a surface protective film was produced in the same manner as in Example 1, except that resin composition (E-8) was used instead of resin composition (E-1). The results of measuring the physical properties of the surface protective film and the results of measuring the loss tangent tanδ of resin composition (E-8) are shown in Table 2.

[0122] Comparative Example 4 A resin composition (E-9) was prepared using 60 parts by mass of the propylene polymer (A-1) and 40 parts by mass of a polyolefin elastomer, and a surface protection film was produced in the same manner as in Example 1, except that the resin composition (E-9) was used instead of the resin composition (E-1). The measurement results of the physical properties of the surface protection film and the measurement results of the loss tangent tanδ of the resin composition (E-9) are shown in Table 2.

[0123] [Measurement of dynamic viscoelasticity of resin composition (E)] Resin compositions (E-1) to (E-5), propylene polymer (A-1), and resin compositions (E-7) to (E-9) were fed into a twin-screw extruder (TEX25αIII manufactured by The Japan Steel Works, Ltd., screw diameter 25 mm, L / D=52) through a hopper. Strands were extruded under the conditions of a cylinder temperature setting of 200°C, an extrusion rate of 5 kg / hour, and a screw rotation speed of 100 rpm. The strands were then immersed in a water tank and introduced into a pelletizer (KM-100 manufactured by Katsumik Co., Ltd.) for granulation, thereby obtaining pellets.

[0124] After filling a specified amount of the pellets into a SUS mold, the heating plate was set to 200°C and a hydraulic heat press (NSF-50 manufactured by Shinto Metal Industry Co., Ltd.) was used to preheat for 7 minutes and pressurize for 2 minutes at a gauge pressure of 10 MPa. The pellets were then transferred to a cooling plate set to 20°C, compressed at a gauge pressure of 10 MPa, and cooled for 2 minutes to produce a 2 mm thick press sheet for measurement. Using the measurement press sheet, the temperature dispersion of dynamic viscoelasticity was measured at -40 to 150°C using a rheometer (MCR301 manufactured by Anton Paar) under the following conditions: deformation mode: torsional deformation mode, frequency: 1.0 Hz, heating rate: 4°C / min, and strain: 0.5%, and the tan δ peak value and tan δ peak temperature were determined.

[0125] [Measurement of physical properties of surface protection films] <Tensile modulus> The surface protection film was cut into strips of 15 mm width x 180 mm length to form test pieces, and the tensile modulus was measured in the machine direction (MD) of the test pieces in accordance with JIS K7127 using a tensile testing machine (Shimadzu Corporation universal testing machine AG-X-5) under the following conditions: chuck distance: 100 mm, tensile speed: 200 mm / min, and temperature: 23°C.

[0126] <Initial adhesive strength at 23°C (acrylic plate)> The surface protection film was cut to a width of 60 mm, and an acrylic plate (Acrylite L manufactured by Mitsubishi Chemical Corporation, thickness 2 mm) 50 mm wide x 150 mm long was used as the adherend. The surface protection film and the adherend were bonded together by moving a pressure roller (urethane rubber hardness A80, roller mass 4 kg) back and forth twice in a direction perpendicular to the width direction.The surface protection film that protruded from the acrylic plate was then cut off, and a sample was prepared by bonding the surface protection film to the acrylic plate.

[0127] The surface roughness in the width direction of the acrylic plate was measured in accordance with JIS B0601, and the arithmetic mean roughness Ra was 0.0045 μm. The obtained sample was stored in a room at 23°C for 24 hours, and then the adhesive strength was measured using a peel tester (Shimadzu Corporation, universal testing machine AGS-X) under the conditions of a tensile speed of 300 mm / min and a peel angle of 180°.

[0128] <Adhesive strength after aging at 60°C (acrylic plate)> The sample obtained by bonding the surface protection film obtained by the above method to an acrylic plate was aged in a heating oven at 60°C for 24 hours, and then left in a room at 23°C for 24 hours, and the adhesive strength was measured in the same manner as in measuring the initial adhesive strength (acrylic plate) at 23°C.

[0129] <Initial adhesive strength at 23°C (prism sheet)> The surface protection film was cut to a width of 50 mm, and a prism sheet 25 mm wide x 150 mm long was used as the adherend. The surface protection film and the adherend were bonded together by moving a pressure roller (urethane rubber hardness A80, roller mass 4 kg) back and forth three times in a direction perpendicular to the width direction (in the direction of the ridge of the prism sheet).The surface protection film that protruded from the prism sheet was then cut off, and a sample was produced by bonding the surface protection film and the prism sheet together.

[0130] The prism sheet used had a length between prism ridges of 21 μm, a height (mountain height) of prism ridges of 14 μm, and an angle of the tip of the prism ridges of 52°. The obtained sample was stored in a room at 23°C for 24 hours, and then the adhesive strength was measured using a peel tester (Texture Arazaizer TA.XTplusC manufactured by Eiko Seiki Co., Ltd.) under the conditions of a pulling speed of 100 mm / min and a peel angle of 180°.

[0131] <Adhesive strength after aging at 60°C (prism sheet)> The sample obtained by bonding the surface protection film obtained by the above method with the prism sheet was aged for 24 hours in a heating oven at 60°C, and then left in a room at 23°C for 24 hours, and the adhesive strength was measured in the same manner as in measuring the initial adhesive strength (prism sheet) at 23°C.

[0132] <Adhesive excitement rate> For each adhesive force measured by the above method, the adhesiveness increase rate (%) was calculated using the following formula. Adhesion enhancement rate (%) = [{(adhesion strength after aging at 60°C) - (initial adhesive strength at 23°C)} / (initial adhesive strength at 23°C)] x 100

[0133] <Heat shrinkage rate> A square test piece with dimensions of 120 mm in both the MD (Machine Direction) and TD (Transverse Direction) directions was obtained from the surface protection film, and benchmark lines were marked in each direction so that the distance between benchmark lines was 100 mm. Next, in accordance with JIS K7133, the specimen was heated at 60°C for 24 hours, then allowed to cool naturally to 23°C. After 24 hours, the dimensions were measured and the heat shrinkage was calculated using the following formula. The results are shown in Table 2. Heat shrinkage rate (%) = [{(gauge length after heating) - (gauge length before test)} / (gauge length before test)] x 100

[0134] [Table 2]

[0135] The surface protection films of Examples 1 to 5 have sufficient adhesive strength to adherends both with smooth surfaces and with uneven surfaces. Furthermore, the surface protection films of Examples 1 to 5 are sufficiently suppressed from increasing adhesiveness and have sufficiently small heat shrinkage rates.

[0136] On the other hand, the surface protection films of Comparative Examples 1 and 2 have sufficiently strong initial adhesive strength to adherends with smooth surfaces, but do not suppress adhesion progression, and also have weak adhesive strength to adherends with uneven surfaces such as prism sheets.

[0137] The surface protection film of Comparative Example 3 has a sufficiently strong initial adhesive strength and inhibits adhesion progression to adherends such as prism sheets with uneven surfaces. However, due to its large thermal shrinkage, the surface protection film may wrinkle or lift when exposed to high temperatures, making it unsuitable as a surface protection film.

[0138] The surface protection film of Comparative Example 4 does not suppress the increase in adhesion, and does not have sufficient initial adhesion to an adherend having an uneven surface, making it unsuitable as a surface protection film.

Claims

1. A back layer (X), an intermediate layer (Y) and an adhesive layer (Z) are laminated in this order, The intermediate layer (Y) contains a resin comprising 50 to 95 parts by mass of a propylene polymer (A) and 5 to 50 parts by mass of a 4-methyl-1-pentene·α-olefin copolymer (B) satisfying the following requirement (Ba-a) (where the total of the propylene polymer (A) and the 4-methyl-1-pentene·α-olefin copolymer (B) is taken as 100 parts by mass): Composition (E) The adhesive layer (Z) contains a polystyrene-based elastomer (C), Surface protection film. Requirement (Ba-a): The 4-methyl-1-pentene / α-olefin copolymer (B) contains 60 to 90 mol % of structural units (i) derived from 4-methyl-1-pentene and 10 to 40 mol % of structural units (ii) derived from an α-olefin having 2 to 4 carbon atoms (provided that the total of structural units (i) and structural units (ii) is 100 mol %).

2. The tanδ peak temperature of the resin composition (E) obtained by dynamic viscoelasticity measurement in a temperature range of −40 to 150 ° C., a deformation mode of a torsional deformation mode, a frequency of 1.0 Hz, a heating rate of 4 ° C. / min, and a strain amount of 0.5% is in the range of 10 to 40 ° C., and the tanδ peak value is in the range of 0.10 to 0.

40. The surface protection film according to claim 1.

3. 2. The surface protection film according to claim 1, which has a heat shrinkage of 0.5% or less when measured after heating at a temperature of 60°C for 24 hours.

4. The method includes a step of laminating a back layer (X), an intermediate layer (Y), and an adhesive layer (Z) in this order, The intermediate layer (Y) contains a resin comprising 50 to 95 parts by mass of a propylene polymer (A) and 5 to 50 parts by mass of a 4-methyl-1-pentene·α-olefin copolymer (B) satisfying the following requirement (Ba-a) (where the total of the propylene polymer (A) and the 4-methyl-1-pentene·α-olefin copolymer (B) is taken as 100 parts by mass): Composition (E) The adhesive layer (Z) contains a polystyrene-based elastomer (C), A method for manufacturing a surface protection film. Requirement (Ba-a): The 4-methyl-1-pentene / α-olefin copolymer (B) contains 60 to 90 mol % of structural units (i) derived from 4-methyl-1-pentene and 10 to 40 mol % of structural units (ii) derived from an α-olefin having 2 to 4 carbon atoms (provided that the total of structural units (i) and structural units (ii) is 100 mol %).

5. The method for producing a surface protective film according to claim 4, comprising a step of forming and laminating the back layer (X), the intermediate layer (Y) and the adhesive layer (Z) by co-extrusion molding.

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