Surface protective film

Abstract

To provide a surface protective film which has adequate initial adhesive force as a masking material for protecting the surface of a smooth synthetic resin plate, is easily peeled because of less increase in adhesion even if it is placed under high temperature environment and is conveyed for a long time, and is excellent in appearance.SOLUTION: A surface protective film is formed by laminating a base material layer, and an adhesive layer, wherein the base material layer contains low density polyethylene (LDPE), the adhesive layer contains a hydrogenated product (SEBS) of a styrene-butadiene copolymer, and high density polyethylene (HDPE), a ratio (thickness of base material layer / thickness of adhesive layer) of the thickness of the base material layer to the thickness of the adhesive layer is 4.0 to 7.0, a mass ratio (SEBS:HDPE) of the SEBS to the HDPE is 70:30 to 55:45, a styrene content of the SEBS is 18 to 22 mass%, and molecular weight distribution of the HDPE is 4.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface protection film. [Background technology]

[0002] Conventionally, the surfaces of smooth-surfaced synthetic resin plates such as PMMA (polymethyl methacrylate) plates and PC (polycarbonate) plates, steel plates, and glass plates (hereinafter simply referred to as "synthetic resin plates, etc.") are easily damaged during transportation and storage. Therefore, surface protection films have been used to prevent this, and various surface protection films have been proposed. A commonly used surface protection film is a laminated film obtained by co-extrusion of a base layer made of PE (polyethylene) and a material that forms an adhesive layer. In the laminated film, the material that forms the adhesive layer is appropriately selected depending on the desired adhesive strength. Examples of materials that have been used for the adhesive layer include EVA (ethylene-vinyl acetate copolymer resin) and POE (ethylene-α-olefin copolymer).

[0003] The surface protection film is adhered to the synthetic resin plate etc. appropriately so as not to peel off during transportation of the synthetic resin plate etc. On the other hand, the surface protection film is required to be easily peeled off at the final stage of assembly etc. Therefore, the initial adhesive strength of the surface protection film is required to be 20 to 60 g / 25 mm at room temperature, preferably 20 to 50 g / 25 mm at room temperature, in a 180° peel test (peel speed 300 mm / min).

[0004] However, the adhesive strength of surface protection films attached to synthetic resin plates and the like often increases over time, and this increase accelerates as storage temperatures increase. Therefore, even if the film initially has adequate adhesive strength, it can become difficult to remove. This can lead to problems such as poor workability during the final assembly stage of synthetic resin plates and the like. Furthermore, when synthetic resin plates and the like are transported over long periods of time at high temperatures while the surface protection film is attached, such as during sea transport and subsequent land transport, this increased adhesive strength becomes even more pronounced. Therefore, a protective film is required that is resistant to increased adhesive strength, achieving an adhesive strength of approximately twice the initial adhesive strength (approximately 40 to 120 g / 25 mm, preferably approximately 40 to 100 g / 25 mm).

[0005] Although conventional EVA and POE have satisfactory initial adhesive strength, their adhesiveness increases significantly when placed in a high-temperature environment, so further improvement is required.

[0006] On the other hand, SEBS (a hydrogenated styrene-butadiene copolymer), a styrene-based thermoplastic elastomer, is a material that has a good balance of adhesive strength and adhesion resistance, and has traditionally been used in a wide range of applications as an adhesive layer material for surface protection films. However, because SEBS itself has high adhesive strength, it adheres excessively to smooth synthetic resin plates, making them difficult to peel. For this reason, a technology has been proposed in which SEBS is mixed with a thermoplastic resin such as PE to reduce the adhesive strength of SEBS and adjust the adhesive strength to an appropriate level.

[0007] As such a surface protection film, for example, Patent Document 1 discloses a surface protection film in which an adhesive layer is laminated on one side of a base film made of a thermoplastic resin, the adhesive layer comprising 30 to 70 mass % of a block copolymer represented by the general formula ABA (where A represents a styrene polymer block, and B represents an olefin polymer block obtained by hydrogenating a butadiene polymer or an isoprene polymer from these polymers) and 70 to 30 mass % of a polyolefin resin having an extractable content of less than 1.0 mass % by n-pentane extraction method.

[0008] Patent Document 2 discloses a surface protection film in which an adhesive layer is formed on one side of a base film made of a polyolefin resin, the adhesive layer being made of a resin composition comprising 50 to 75 mass % of a block copolymer represented by the general formula ABA (wherein A represents an aromatic vinyl polymer block, and B represents an isoprene polymer block or an olefin polymer block obtained by hydrogenating carbon-carbon unsaturated double bonds present in an isoprene / butadiene random copolymer block) and 25 to 50 mass % of a high-density polyethylene resin, to which 0 to 25 mass % of an ethylene-α-olefin copolymer is blended with respect to the resin composition.

[0009] Patent Document 3 discloses a surface protection film in which an adhesive layer (II) is laminated integrally onto a substrate layer (I) made of a polyolefin resin, the adhesive layer (II) containing a hydrogenated styrene-conjugated diene copolymer (a) and a polyethylene resin (b), and the blending ratio of the two components is 100 parts by mass of (a) and 10 to 50 parts by mass of (b). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 11-199839 [Patent Document 2] Japanese Patent Application Publication No. 9-143439 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-161882 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the surface protection film disclosed in Patent Publication 1 has a low initial adhesive strength of 12 to 18 g / 25 mm, which means that the surface protection film may lift off the surface of the synthetic resin plate or the like due to environmental changes in the storage location or over the storage period, contaminating the surface of the synthetic resin plate or the like, resulting in poor appearance.

[0012] Although the surface protection film in Patent Publication 2 has an adequate initial adhesive strength, the dispersion of the high-density polyethylene in the block copolymer is insufficient, resulting in an adhesive enhancement factor of more than 2, making it difficult to peel from smooth synthetic resin plates, etc. In addition, the block copolymer contains a large amount of aromatic vinyl polymer blocks, which results in insufficient affinity with the PE base layer material, making the co-extruded surface protection film prone to streaks and resulting in poor appearance. Streaks in the surface protection film can cause problems when inspecting the surface condition of synthetic resin plates, etc.

[0013] The surface protection film in Patent Publication 3 is intended for adherends with uneven surfaces, so the copolymer ratio is increased to adjust the adhesive strength to be high. Therefore, when it comes to smooth adherends, the film adheres too strongly and is difficult to peel off.

[0014] The present invention has been made in view of these problems, and aims to provide a surface protection film that has an appropriate initial adhesive strength as a masking material for protecting the surface of a smooth synthetic resin plate or the like, is easy to peel off because it does not increase in adhesiveness even when placed in a high-temperature environment or during long-term transportation, and has an excellent appearance. [Means for solving the problem]

[0015] As a result of extensive research into solving the above-mentioned problems, the inventors have discovered that the above-mentioned problems can be solved by using a surface protection film comprising a substrate layer and an adhesive layer laminated together, wherein the substrate layer contains low-density polyethylene (LDPE), the adhesive layer contains a hydrogenated styrene-butadiene copolymer (SEBS) having a specific styrene content and a high-density polyethylene (HDPE) having a specific molecular weight distribution (Mw / Mn) in a specific mass ratio, and the thickness of the substrate layer and the thickness of the adhesive layer are in a specific ratio, thereby completing the present invention.

[0016] That is, the present invention is as follows. [1] A surface protection film comprising a base layer and an adhesive layer laminated together, wherein the base layer comprises low-density polyethylene (LDPE), and the adhesive layer comprises a hydrogenated styrene-butadiene copolymer (SEBS) and high-density polyethylene (HDPE), the ratio of the thickness of the base layer to the thickness of the adhesive layer (thickness of the base layer / thickness of the adhesive layer) is 4.0 to 7.0, the mass ratio of the SEBS to the HDPE (the SEBS:the HDPE) is 70:30 to 55:45, the styrene content of the SEBS is 18 to 22 mass%, and the molecular weight distribution (Mw / Mn) of the HDPE, expressed as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) in terms of standard polystyrene, as measured by gel permeation chromatography (GPC), is 4.0 or less.

[0017] [2] The surface protection film according to [1], wherein the SEBS has a melt mass flow rate (MFR, 230° C., 2.16 kg load) of 11.0 to 15.0 g / 10 min.

[0018] [3] Melt viscosity of the SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of the HDPE (resin temperature: 210 ° C, shear rate: 121.6 s -1 The surface protection film according to [1] or [2], wherein the ratio of the melt viscosity of the SEBS to the melt viscosity of the HDPE (melt viscosity of the SEBS / melt viscosity of the HDPE) is 0.85 to 1.30.

[0019] [4] The surface protection film according to any one of [1] to [3], wherein the HDPE has a melt mass flow rate (MFR, 190°C, 2.16 kg load) of 2.0 to 6.0 g / 10 min. [Effects of the Invention]

[0020] According to the present invention, a surface protection film can be provided which has an appropriate initial adhesive strength as a masking material for protecting smooth synthetic resin plates and the like, is easy to peel off because it does not increase in adhesiveness even when placed in a high-temperature environment or during long-term transportation, and has an excellent appearance. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content, and the present invention can be carried out in various modified forms within the scope of its gist.

[0022] [Surface protection film] The surface protection film of this embodiment is a surface protection film comprising a substrate layer and an adhesive layer, the substrate layer comprising low-density polyethylene (LDPE), and the adhesive layer comprising hydrogenated styrene-butadiene copolymer (SEBS) and high-density polyethylene (HDPE). The ratio of the thickness of the substrate layer to the thickness of the adhesive layer (thickness of the substrate layer / thickness of the adhesive layer) is 4.0 to 7.0, the mass ratio of SEBS to HDPE (SEBS:HDPE) is 70:30 to 55:45, the styrene content of the SEBS is 18 to 22 mass%, and the molecular weight distribution (Mw / Mn) of the HDPE is 4.0 or less. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are values ​​measured by gel permeation chromatography (GPC) in terms of standard polystyrene. The molecular weight distribution (Mw / Mn) is expressed as the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn).

[0023] According to this embodiment, a surface protection film can be provided that has an appropriate initial adhesive strength as a masking material for protecting a smooth synthetic resin plate, etc., is easy to peel off due to little increase in adhesiveness even when placed in a high-temperature environment or during long-term transportation, is less likely to produce streaks or the like during film formation by co-extrusion molding, and has an excellent appearance. Although the reason for this is unclear, the inventors speculate as follows.

[0024] When mixing SEBS with PE to adjust the initial tack to an appropriate level, for example, if LLDPE (linear low-density polyethylene) and LDPE (low-density polyethylene) are used as PE, it is difficult to adjust the initial tack to an appropriate level because LLDPE and LDPE themselves are tacky. However, HDPE has relatively low tackiness by itself, so when mixed with SEBS, it is easy to adjust the initial tack to an appropriate level.

[0025] HDPE is available in two types: Ziegler catalyst-polymerized and metallocene catalyst-polymerized. HDPE obtained using a Ziegler catalyst has a wide molecular weight distribution, resulting in a high concentration of low-molecular-weight PE. This is thought to be the cause of thermal deformation and increased adhesion. HDPE obtained using a Ziegler catalyst also contains a high concentration of high-molecular-weight PE, making it difficult to deform at room temperature. This reduces adhesion to smooth synthetic resin plates and makes it difficult to adjust the initial adhesion to a suitable level. However, HDPE obtained using a metallocene catalyst has a narrow molecular weight distribution and contains relatively few low-molecular-weight and high-molecular-weight PE. Therefore, this HDPE is less susceptible to deterioration in adhesion due to thermal deformation. Furthermore, because it is easily deformed at room temperature, it also suppresses the loss of adhesion to smooth synthetic resin plates. This allows for the achievement of an optimal initial adhesion. Using HDPE in this way enables surface protection films to have excellent adhesion resistance and initial adhesion.

[0026] Furthermore, by using a specific mass ratio of HDPE with a narrow molecular weight distribution and SEBS with a styrene content within a specific range for the adhesive layer, the melt viscosities of HDPE and SEBS can be made similar, improving the dispersibility of HDPE in SEBS. Furthermore, the compatibility between HDPE and SEBS is also improved. As a result, the surface protection film can exhibit excellent adhesion resistance while maintaining adequate initial adhesion. Furthermore, streaks are less likely to occur during film formation, such as coextrusion molding, resulting in a surface protection film with excellent appearance.

[0027] It is believed that by laminating such an adhesive layer and LDPE as a base layer at a specific thickness ratio, it is possible to obtain a surface protection film that has an appropriate initial adhesive strength as a masking material for protecting smooth synthetic resin plates, etc., is easy to peel off because there is little increase in adhesiveness even when placed in a high-temperature environment or during long-term transportation, and is also less likely to produce streaks during film formation such as co-extrusion molding, resulting in an excellent appearance. However, the reasons for this are not limited to these.

[0028] Each layer in the surface protection film will be described below.

[0029] [Ratio of thickness of base layer to thickness of adhesive layer] The surface protection film has a base layer and an adhesive layer laminated thereon. The ratio of the thickness of the base layer to the thickness of the adhesive layer (thickness of base layer / thickness of adhesive layer) is 4.0 to 7.0. When the ratio is 4.0 or more, the decrease in mechanical strength of the base layer can be suppressed, and the film is less likely to stretch or tear during production or use. When the ratio is 7.0 or less, the decrease in adhesive strength can be suppressed, and the surface protection film is less likely to float and contaminate the surface of the synthetic resin plate. The ratio of the thickness of the base layer to the thickness of the adhesive layer is preferably 4.5 to 6.0. In this specification, the thicknesses of the base layer and the adhesive layer can be measured, for example, by observing the cross section of the surface protection film with an optical microscope. For specific measurement methods, see the Examples.

[0030] [Thickness of surface protection film] The total thickness of the surface protection film is preferably from 40 to 60 μm, more preferably from 43 to 57 μm, as this provides a better balance between film strength and adhesiveness.

[0031] [Base material layer] The surface protection film has a substrate layer laminated thereon.

[0032] The base layer contains low-density polyethylene (LDPE) because of its excellent formability, transparency, and flexibility. LDPE also has a relatively high melt tension, which tends to favorably suppress the occurrence of neck-in. LDPE's relatively high transparency allows for favorable visual inspection of the surface protection film while it is still attached to the synthetic resin plate. LDPE may be used alone or in combination of two or more types.

[0033] Furthermore, one or more types selected from the group consisting of HDPE and LLDPE may be added to the base layer, provided that transparency and moldability are not impaired. For HDPE, refer to the HDPE contained in the adhesive layer. For LLDPE, commercially available products may be used. Examples of commercially available products include Yumerit (registered trademark) manufactured by Ube Maruzen Polyethylene Co., Ltd., L-LDPE resin manufactured by NUC Corporation, and Sumikathene (registered trademark)-L, Sumikathene (registered trademark) E, Excellen (registered trademark) VL, and Excellen (registered trademark) FX manufactured by Sumitomo Chemical Co., Ltd.

[0034] The density of LDPE is usually 900-930 kg / cm 2 When the density of the LDPE is within the above range, the surface protection film tends to have better transparency and a better appearance. In this specification, density refers to a value measured in accordance with the density gradient tube method (23°C) described in JIS K7112 (1999). For specific measurement methods, see the examples.

[0035] The melt mass flow rate (MFR, 190°C, 2.16 kg load) of the LDPE is preferably 0.05 to 50.0 g / 10 min. When the MFR of the LDPE is within the above range, the surface protection film tends to have better transparency and a better appearance. In this specification, MFR refers to a value measured in accordance with ISO 1133 at a temperature of 190°C or 230°C under a load of 2.16 kg. For specific measurement methods, see the examples.

[0036] The molecular weight distribution (Mw / Mn) of the LDPE is preferably 2.0 to 30.0. When the molecular weight distribution (Mw / Mn) of the LDPE is within the above range, the surface protection film tends to have better transparency and better appearance.

[0037] The LDPE is preferably a high-pressure low-density polyethylene. The density of the high-pressure low-density polyethylene is preferably 910 to 930 kg / cm 2 and more preferably 911 to 929 kg / cm 2 The melt mass flow rate (MFR, 190°C, 2.16 kg load) of the high-pressure low-density polyethylene is preferably 0.1 to 5.0 g / 10 min, more preferably 0.2 to 4.0 g / 10 min. The molecular weight distribution (Mw / Mn) is preferably 2.0 to 30.0. When the density, MFR, and molecular weight distribution (Mw / Mn) of the high-pressure low-density polyethylene are within the above ranges, the surface protection film tends to have excellent transparency and appearance as well as even better formability.

[0038] Commercially available LDPE may be used, such as "Sumikathen (registered trademark) L211 (product name)" manufactured by Sumitomo Chemical Co., Ltd., and "L2340 (product name)" of the "Suntech (registered trademark)-LD" series manufactured by Asahi Kasei Corporation.

[0039] High-pressure low-density polyethylene can be produced by a generally known method, for example, by polymerizing ethylene and an α-olefin in an autoclave or a tube reactor at a high temperature and pressure of 100 to 300°C and 100 to 350 MPa in the presence of a free-radical generator such as peroxide.

[0040] [Adhesive layer] An adhesive layer is laminated on the surface protection film. The adhesive layer includes a hydrogenated styrene-butadiene copolymer (SEBS) and a high density polyethylene (HDPE).

[0041] (SEBS) SEBS is a copolymer obtained by hydrogenating a styrene-based block copolymer. The styrene-based block copolymer is generally a block copolymer represented by ABA or ABAB, or a mixture of a block copolymer represented by ABA and a block copolymer represented by AB, where A is a styrene polymer block and B is a hydrogenated butadiene polymer block. One type of SEBS may be used alone, or two or more types may be used in combination.

[0042] The SEBS preferably has a polymer block mainly composed of styrene. In this specification, "mainly composed of" means that the polymer block of the SEBS contains styrene units in an amount of 95% by mass to 100% by mass.

[0043] The SEBS is preferably a block copolymer represented by ABA or ABAB. The linking portion between the styrene polymer block and the butadiene polymer block may be a styrene-butadiene random copolymer.

[0044] The styrene content of SEBS is 18 to 22% by mass relative to the total amount of SEBS (100% by mass). When the styrene content is 18% by mass or more, the adhesive strength of the SEBS itself is favorable, and the amount of HDPE added can be adjusted within a suitable range, so the adhesive layer does not become too hard and a decrease in initial adhesive strength tends to be suppressed. When the styrene content is 22% by mass or less, the compatibility between SEBS and HDPE is favorable, streaks are unlikely to occur in the film, and the appearance of the synthetic resin plate with the surface protection film attached is excellent. Note that, in this specification, the styrene content and butadiene content can be measured, for example, by a nuclear magnetic resonance (NMR) spectrometer. The styrene content can be controlled by adjusting the amounts of styrene and butadiene added in the polymerization process, the timing of addition, etc.

[0045] The butadiene content of the SEBS is preferably 78 to 82 mass % relative to the total amount of SEBS (100 mass %).

[0046] The vinyl bond content of the butadiene portion is preferably 27 to 30% by mass relative to the total amount (100% by mass) of SEBS. In this specification, the vinyl bond content refers to the total content of 1,2-vinyl bonds (butadiene incorporated into the polymer via 1,2-bonds) and 3,4-vinyl bonds (butadiene incorporated into the polymer via 3,4-bonds) relative to the total butadiene (here, when 1,3-butadiene is used as the conjugated diene, it refers to the 1,2-vinyl bond content, and when isoprene is used as the conjugated diene, it refers to the 3,4-vinyl bond content). The vinyl bond content can be measured using a nuclear magnetic resonance (NMR) spectrometer. The butadiene-derived microstructure (cis / trans ratio, vinyl bond content) in SEBS can be controlled as desired by using known polar compounds, etc.

[0047] The hydrogenation rate of the butadiene-derived unsaturated double bonds in SEBS is preferably 70% by mass or more, more preferably 85% by mass or more, and even more preferably 95% by mass or more. The upper limit of the hydrogenation rate is usually 100% by mass or less, and may be 99% by mass or less. When the hydrogenation rate is within the above range, gelation during film formation of SEBS can be further suppressed, adhesive residue is improved, and a more excellent appearance tends to be obtained. The hydrogenation rate can be controlled, for example, by adjusting the amount of catalyst used during hydrogenation. The hydrogenation rate during polymerization can be controlled, for example, by adjusting the amount of catalyst used during hydrogenation, the amount of hydrogen feed, pressure, temperature, etc. The hydrogenation rate can be measured using a nuclear magnetic resonance (NMR) spectrometer.

[0048] The melt mass flow rate (MFR, 230°C, 2.16 kg load) of the SEBS is preferably 11.0 to 15.0 g / min, more preferably 12.0 to 14.0 g / min. When the MFR of the SEBS is within the above range, the dispersibility of HDPE in the SEBS becomes more favorable, and the balance between the initial adhesive strength and the resistance to adhesion enhancement tends to be better. In addition, favorable resistance to adhesion enhancement tends to be obtained. Streaks are less likely to occur in the film, and the appearance of the surface protection film tends to be less likely to be poor.

[0049] Melt viscosity of SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) is preferably 700 to 1000 mPa·s, more preferably 800 to 900 mPa·s. When the melt viscosity of SEBS is within the above range, the dispersibility of HDPE in SEBS becomes more favorable, and the balance between the initial adhesive strength and the resistance to adhesion enhancement tends to be better. Suitable resistance to adhesion enhancement tends to be obtained. In this specification, the melt viscosity is measured using a capillary rheometer at a resin temperature of 210°C and a shear rate of 12.2 s -1 ~12160 seconds -1 SEBS or HDPE was continuously measured under the conditions of a shear rate of 121.6 s -1 For specific measurement methods, see the Examples.

[0050] The number average molecular weight (Mn) of SEBS is preferably 50,000 to 150,000, more preferably 60,000 to 130,000, and even more preferably 70,000 to 120,000. When the number average molecular weight of SEBS is within the above range, the dispersibility of HDPE in SEBS becomes more favorable, and the balance between the initial adhesive strength and the resistance to adhesive enhancement tends to be better.

[0051] The molecular weight distribution (Mw / Mn) of SEBS is preferably less than 1.20, more preferably 1.15 or less, and even more preferably 1.13 or less. When the molecular weight distribution (Mw / Mn) of SEBS is within the above range, the mechanical strength of SEBS tends to be improved. SEBS does not have a branched structure and tends to be easily produced by sequential polymerization.

[0052] Commercially available SEBS products may be used, such as H1052 (trade name), H1062 (trade name), H1521 (trade name), and P1083 (trade name) from the Tuftec (registered trademark) series manufactured by Asahi Kasei Corporation.

[0053] SEBS can be produced by known methods, such as those disclosed in Japanese Patent Publication Nos. 36-19286, 43-17979, 46-32415, 49-36957, 48-2423, 48-4106, 51-49567, and 59-166518.

[0054] (HDPE) Examples of high density polyethylene (HDPE) include ethylene homopolymers and ethylene / α-olefin copolymers. HDPE itself has relatively low adhesiveness, so when it is mixed with SEBS, it is possible to suitably adjust the initial adhesive strength. HDPE may be used alone or in combination of two or more types.

[0055] Examples of the α-olefin include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, and 1-tetradecene. One type of α-olefin may be used alone, or two or more types may be used in combination.

[0056] The HDPE is preferably polyethylene containing less than 0.1% by mass of comonomer units such as α-olefins, and more preferably an ethylene homopolymer containing no comonomer units. In this specification, "high density" generally refers to a density of 930 to 970 kg / cm. 3 and preferably 940 to 960 kg / cm 3 is.

[0057] The molecular weight distribution (Mw / Mn) of HDPE is 4.0 or less, which is a narrow molecular weight distribution. When the molecular weight distribution of HDPE is 4.0 or less, the amount of low molecular weight components in the HDPE is relatively low, making it less likely to deform even in high-temperature environments, resulting in excellent adhesion enhancement resistance. In addition, the amount of high molecular weight components in the HDPE is relatively low, making it more likely to deform at room temperature and preventing a decrease in adhesion to smooth synthetic resin plates, etc. This allows for an appropriate initial adhesion strength to be obtained. By using HDPE, the surface protection film can have excellent adhesion enhancement resistance and initial adhesion strength. The molecular weight distribution of HEPD is preferably 3.8 or less. The lower limit of the molecular weight distribution is, for example, 3.2 or more.

[0058] The melt mass flow rate (MFR, 190°C, 2.16 kg load) of HDPE is preferably 2.0 to 6.0 g / 10 min, more preferably 3.0 to 5.5 g / 10 min. When the MFR of HDPE is within the above range, the dispersibility of HDPE in SEBS is improved, and the desired balance between adhesive strength and resistance to adhesion enhancement tends to be better. In addition, suitable resistance to adhesion enhancement tends to be obtained.

[0059] Melt viscosity of HDPE (resin temperature: 210°C, shear rate: 121.6 s -1 ) is preferably 700 to 1000 mPa·s, more preferably 800 to 900 mPa·s. When the melt viscosity of HDPE is within the above range, the dispersibility of HDPE in SEBS becomes more favorable, and the balance between initial adhesion and resistance to adhesion enhancement tends to be better. Also, suitable resistance to adhesion enhancement tends to be obtained.

[0060] Commercially available HDPE products may be used, such as "T4750 (trade name)" and "T701A (trade name)" from the "Creolex (registered trademark)" series manufactured by Asahi Kasei Corporation.

[0061] HDPE can be produced by a known method using a metallocene catalyst. For example, JP-A-2007-106857, JP-A-2015-89937, and JP-A-2013-249094 can be referenced for methods of producing HDPE.

[0062] [SEBS to HDPE mass ratio] The mass ratio of SEBS to HDPE (SEBS:HDPE) is 70:30 to 55:45. When the mass ratio of HDPE is 30 or more and the mass ratio of SEBS is 70 or less, the initial adhesion is 60 g / 25 mm or less and the adhesion after adhesion enhancement is 120 g / 25 mm or less, preferably the initial adhesion is 50 g / 25 mm or less and the adhesion after adhesion enhancement is 100 g / 25 mm or less, making it easy to peel the surface protection film from a synthetic resin board or the like. When the mass ratio of HDPE is 45 or less and the mass ratio of SEBS is 55 or more, the initial adhesion is 20 g / 25 mm or more, making it difficult for the surface protection film to lift off from a synthetic resin board or the like and making the surface of the synthetic resin board or the like less susceptible to contamination. Furthermore, when the mass ratio of HDPE is 45 or less and the mass ratio of SEBS is 55 or more, the adhesive strength after adhesion enhancement is 40 g / 25 mm or more, so that even when placed in a high-temperature environment or transported for a long time, the adhesive strength tends to be less enhanced and the film tends to be easier to peel off. In this specification, the initial adhesive strength and adhesive strength can be evaluated based on a "180° peel test" performed using a universal tension and compression tester at a temperature of 23°C and a relative humidity of 50% at a peel rate of 300 mm / min. For specific evaluation methods, see the examples.

[0063] [Melt viscosity ratio] Melt viscosity of SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of HDPE (resin temperature: 210°C, shear rate: 121.6 s -1 ) (melt viscosity of SEBS / melt viscosity of HDPE, hereinafter also referred to simply as "melt viscosity ratio") is preferably 0.85 to 1.30, more preferably 0.90 to 1.25, and even more preferably 0.95 to 1.20. When the melt viscosity ratio is within the above range, the viscosities of the SEBS and HDPE become similar, and the dispersibility of HDPE in the SEBS during kneading in the film extruder becomes better. Therefore, the surface protection film can exhibit even better adhesion enhancement properties while maintaining an appropriate initial adhesion strength.

[0064] (Other ingredients) The adhesive layer may contain other components such as other thermoplastic resins and thermoplastic elastomers, as well as ultraviolet absorbers, antioxidants, antioxidants, fillers, antiblocking agents, lubricants, antistatic agents, plasticizers, and colorants, within the range that does not impair the performance of the surface protection film. These other components may be used alone or in combination of two or more.

[0065] [Method for producing adhesive layer] The adhesive layer can be produced by a known method. The adhesive layer can be produced, for example, by using an adhesive layer material containing SEBS, HDPE, and, if necessary, other components.

[0066] The adhesive layer material can be produced, for example, by dry blending SEBS, HDPE, and, if necessary, other components, or by preparing the material using an apparatus typically used for mixing polymeric substances. The mixing device is not particularly limited, and examples thereof include kneading devices such as a Banbury mixer, a Laboplastomill, a single-screw extruder, a twin-screw extruder, etc. Production by a melt mixing method using an extruder is preferred from the viewpoints of productivity and good kneading ability.

[0067] In addition, the adhesive layer material may be produced by preparing SEBS pellets and HDPE pellets in advance and blending the pellets, or may be obtained as compound pellets by melt-kneading the SEBS pellets and HDPE pellets using a kneading device.

[0068] The melting temperature during kneading of the adhesive layer material can be set as appropriate, but is usually in the range of 130 to 300°C, preferably 150 to 250°C.

[0069] [Method for producing surface protection film] The surface protection film has an adhesive layer formed on one side of a base layer. The method for producing the surface protection film is not particularly limited, and examples thereof include methods for producing ordinary films, such as a T-die extrusion method, an inflation method, and a calendar roll method. Among these, it is preferable to produce the surface protection film by the T-die extrusion method.

[0070] A method for obtaining a surface protection film by the T-die extrusion method includes, for example, forming two streams in a melt co-extruder from a component capable of forming an adhesive layer, such as an adhesive layer material, and a component capable of forming a base layer, such as LDPE pellets, and then combining the two streams in the die opening to form a single fluid, which is then extruded to combine the adhesive layer and the base layer.

[0071] In the case of a method for obtaining a surface protection film using an extruder, the material for forming the adhesive layer can be produced by dry-blending the components for the adhesive layer in advance, which is a method with excellent productivity. Furthermore, when an adhesive film is extruded using an extruder, the adhesion and adhesive strength of the produced surface protection film tend to be better.

[0072] [Application] The surface protective film combines moderate initial adhesion and adhesion-enhancing resistance. Furthermore, the surface protective film is less likely to develop streaks or other defects during film formation, such as coextrusion molding, resulting in less appearance defects. Therefore, the surface protective film can be temporarily attached to the surfaces of optical molded bodies such as light guide plates and prism sheets, synthetic resin plates, metal plates, decorative plywood, coated steel plates, various nameplates, and the like, and is ideally used as a surface protective film to prevent scratches and dirt from being formed on these substrates during processing, transportation, and storage. The surface protective film is particularly suitable for protecting the surfaces of various smooth-surfaced plate-like objects, such as smooth-surfaced synthetic resin plates such as PMMA plates and PC plates used in the housings of IT information terminals, smooth-surfaced steel plates used in building materials, and glass plates. Because the effects of the surface protective film can be more effectively achieved, the surface protective film is even more ideally suited for use on synthetic resin plates. [Example]

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Measurement methods and methods for measuring physical properties applied to the examples and comparative examples are shown below.

[0074] <Measurement method> [MFR] The MFR (melt mass flow rate, g / 10 min) of SEBS (hydrogenated styrene-butadiene copolymer) was measured in accordance with ISO1133 at a temperature of 230°C and a load of 2.16 kg. The MFR (melt mass flow rate, g / 10 min) of HDPE (high density polyethylene) was measured in accordance with ISO1133 at a temperature of 190°C and a load of 2.16 kg.

[0075] [Styrene content of SEBS] The styrene content (mass%) of SEBS was measured by dissolving a certain amount of SEBS in chloroform and using an ultraviolet spectrophotometer (Shimadzu Corporation, UV-2450 (trade name)). Then, the content of styrene monomer units in SEBS (styrene content of SEBS) was calculated using a calibration curve based on the peak intensity at the absorption wavelength (262 nm) attributed to styrene.

[0076] [Melt viscosity ratio] The melt viscosity (mPa·s) of SEBS or SEPS was measured using a capillary rheometer (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name: Capilograph 1D, model: PM-C) at a resin temperature of 210°C and a shear rate of 12.2 s -1 ~12160 seconds -1 SEBS or SEPS was continuously measured under the conditions of a shear rate of 121.6 s -1 The value was calculated as The melt viscosity (mPa·s) of HDPE or LDPE was measured using a capillary rheometer in the same manner as above, with the resin temperature at 210°C and the shear rate at 12.2 s -1 ~12160 seconds -1 The HDPE was continuously measured under the conditions of a shear rate of 121.6 s -1 The value was calculated as Melt viscosity of SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of HDPE (resin temperature: 210°C, shear rate: 121.6 s -1 The ratio of the melt viscosity of SEBS to the melt viscosity of HDPE (melt viscosity ratio, melt viscosity of SEBS / melt viscosity of HDPE) was calculated using these values. Similarly, the melt viscosity of SEPS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of HDPE (resin temperature: 210°C, shear rate: 121.6 s -1 ) ratio (melt viscosity of SEPS / melt viscosity of HDPE), and the melt viscosity of SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of LDPE (resin temperature: 210°C, shear rate: 121.6 s -1The ratio (melt viscosity of SEBS / melt viscosity of LDPE) was also calculated using these values.

[0077] [Molecular weight distribution (Mw / Mn)] The molecular weight distribution (Mw / Mn) of HDPE was determined as the ratio (Mw / Mn) of the weight-average molecular weight (Mw) and number-average molecular weight (Mn) measured by GPC in terms of standard polystyrene. GPC measurements were performed using a Waters GPCV2000 (trade name) column, consisting of one Showa Denko UT-807 column and two Tosoh GMHHR-H(S)HT columns connected in series. The measurement conditions were trichlorobenzene (TCB) as the mobile phase, a column temperature of 140°C, a flow rate of 1.0 mL / min, a sample concentration of 20 mg / 15 mL (TCB), a sample dissolution temperature of 140°C, and a sample dissolution time of 2 hours. Molecular weight calibration was performed using 12 points of standard polystyrene manufactured by Tosoh Corporation, with Mw ranging from 1,050,000 to 2,060,000. The Mw of each standard polystyrene was multiplied by a coefficient of 0.43 to obtain the polyethylene-equivalent molecular weight. A primary calibration line was created from a plot of elution time versus polyethylene-equivalent molecular weight, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) were determined. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the LDPE were determined in the same manner as above.

[0078] [density] The density of HDPE and LDPE (kg / m) was measured in accordance with JIS K7112:1999, density gradient tube method (23°C). 3 ) was measured.

[0079] <Evaluation methods and properties of surface protection films> [Preparation of surface protection film] A T-die type three-layer film molding machine manufactured by Plastic Optics Research Institute, Inc. was used to produce the surface protection film. Specifically, LDPE pellets were fed into the hopper of the extruder for the base layer as the material for the base layer, and either pellets obtained by dry blending SEBS pellets and HDPE pellets, pellets obtained by dry blending SEPS pellets and HDPE pellets, or pellets obtained by dry blending SEBS pellets and LDPE pellets were fed into the hopper of the extruder as the material for the adhesive layer, and the surface protection film was produced by cast co-extrusion molding. The molding temperature was 210°C and the take-up speed was 7 m / min.

[0080] [Total film thickness and ratio of base layer thickness to adhesive layer thickness] The cross section of the surface protection film was cut with a razor. The cross section of the film was then observed with an optical microscope, and the thickness (μm) of the entire film, the thickness (μm) of the base layer, and the thickness (μm) of the adhesive layer were measured. The ratio of the thickness of the base layer to the thickness of the adhesive layer (thickness of the base layer / thickness of the adhesive layer) was calculated using the thickness values ​​of the base layer and the adhesive layer.

[0081] [PMMA adhesive strength] The adhesive strength of the surface protection film was measured using a universal tension and compression tester (Technograph TGE-500N (product name), manufactured by MinebeaMitsumi Inc.) Evaluation was carried out based on two types of properties: initial adhesive strength and resistance to adhesive enhancement, at a temperature of 23°C and a relative humidity of 50%, based on a "180° peel test" as follows.

[0082] (Initial adhesive strength) At a temperature of 23°C and a relative humidity of 50%, a 25mm wide surface protection film was laminated to a PMMA plate (polymethyl methacrylate, arithmetic mean surface roughness: 0.1μm), and then a 2kg rubber roll (diameter: 10cm) was rolled over the film to adhere it tightly. The film was then left for 30 minutes. The initial adhesive strength (g / 25mm) of the surface protection film was then measured at a peel rate of 300mm / min. Surface protection films with an initial adhesive strength of 20 to 50 g / 25 mm were considered acceptable.

[0083] (Adhesive strength) At 23°C and 50% relative humidity, a 25mm wide surface protection film was laminated to a PMMA plate (polymethyl methacrylate, arithmetic mean surface roughness: 0.1µm), and then a 2kg rubber roll (10cm diameter) was rolled over the film to adhere it tightly. The film was then left for 30 minutes. It was then heated in a gear oven at 80°C for 1 hour and returned to 23°C and 50% relative humidity. The adhesive strength (g / 25mm) of the surface protection film was then measured at a peel rate of 300mm / min.

[0084] (Adhesion resistance (adhesion increase ratio)) The adhesion enhancement ratio (adhesion strength value of the surface protection film / initial adhesion strength value of the surface protection film) was calculated using the adhesion strength value of the surface protection film obtained in the above measurement and the initial adhesion strength value of the surface protection film obtained in the above measurement. When the adhesion enhancement ratio was within 2.5 times, the adhesion enhancement resistance of the surface protection film was evaluated as good, and when the adhesion enhancement ratio was within 2.0 times, the adhesion enhancement resistance of the surface protection film was evaluated as best.

[0085] [Film formability] The film formability was evaluated by visually observing the appearance of the co-extruded surface protection film according to the following criteria. (standard) ◯: No defects in appearance such as streaks were observed. ×: Streaks and the like were observed, and poor appearance was observed.

[0086] [Adhesive residue (appearance evaluation)] The adhesive residue was evaluated by visually inspecting the surface of the PMMA plate after the above-mentioned adhesion test of the surface protection film (80°C, 1 hour) and using the following criteria. (standard) ◯: No adhesive residue (no traces of the film being applied). ×: Adhesive residue remains (traces of the film pasted on the film are visible).

[0087] Example 1 The material used for the base layer of the surface protection film was LDPE (Suntec (registered trademark)-LD L2340 (product name) manufactured by Asahi Kasei Corporation, high-pressure low-density polyethylene). The material for the adhesive layer of the surface protection film was a resin composition (pellets) obtained by dry blending 66% by mass of SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation, styrene content: 20% by mass, hydrogenated styrene-butadiene copolymer) and 34% by mass of HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation, molecular weight distribution: 3.7, high-density polyethylene). According to the above-mentioned surface protection film preparation method, the material for the base layer and the material for the adhesive layer were cast co-extruded into a surface protection film with a thickness of approximately 50 μm. The obtained surface protection film was transparent and had a good appearance. The physical properties of the obtained surface protection film were evaluated according to the above evaluation methods. The measurement results for SEBS and HDPE as well as the evaluation results are shown in Table 1.

[0088] Example 2 A surface protection film was formed in the same manner as in Example 1, except that the amount of SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) was changed from 66% by mass to 60% by mass, and the amount of HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation) was changed from 34% by mass to 40% by mass, and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0089] Example 3 A surface protection film was formed in the same manner as in Example 1, except that the amount of SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) was changed from 66% by mass to 58% by mass, and the amount of HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation) was changed from 34% by mass to 42% by mass, and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0090] Example 4 A surface protection film was formed in the same manner as in Example 1, except that the SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corp.) were replaced with SEBS pellets (Tuftec (registered trademark) H1062 (trade name) manufactured by Asahi Kasei Corp., styrene content: 18 mass%, hydrogenated styrene-butadiene copolymer), and the HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corp.) were replaced with HDPE pellets (Creolex (registered trademark) T701A (trade name) manufactured by Asahi Kasei Corp., molecular weight distribution: 3.5, high-density polyethylene). The measurement results for SEBS and HDPE are shown in Table 1, along with the evaluation results.

[0091] Example 5 A surface protection film was formed in the same manner as in Example 1, except that HDPE pellets (Asahi Kasei Corporation, Creolex (registered trademark) T4750 (trade name)) were used instead of HDPE pellets (Asahi Kasei Corporation, Creolex (registered trademark) T701A (trade name)), and the film was evaluated. The evaluation results are shown in Table 1, along with the measurement results for SEBS and HDPE.

[0092] Example 6 A surface protection film was formed in the same manner as in Example 1, except that the SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) were replaced with SEBS pellets (Tuftec (registered trademark) H1521 (trade name) manufactured by Asahi Kasei Corporation, styrene content: 18% by mass, hydrogenated styrene-butadiene copolymer), and the HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation) were replaced with HDPE pellets (Creolex (registered trademark) T701A (trade name) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE are shown in Table 1, along with the evaluation results.

[0093] Example 7 A surface protection film was formed in the same manner as in Example 1, except that the SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) were replaced with SEBS pellets (Tuftec (registered trademark) P1083 (trade name) manufactured by Asahi Kasei Corporation, styrene content: 20 mass%, hydrogenated styrene-butadiene copolymer), and the HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation) were replaced with HDPE pellets (Creolex (registered trademark) T701A (trade name) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE are shown in Table 1.

[0094] Example 8 A surface protection film was formed in the same manner as in Example 1, except that SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) were used instead of SEBS pellets (Tuftec (registered trademark) H1062 (trade name) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0095] Comparative Example 1 A surface protection film was formed in the same manner as in Example 2, except that HDPE pellets (Suntech (registered trademark)-HD J240 (trade name) manufactured by Asahi Kasei Corporation, molecular weight distribution: 7.3, high-density polyethylene) were used instead of HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0096] Comparative Example 2 A surface protection film was formed in the same manner as in Example 2, except that HDPE pellets (Suntech (registered trademark)-HD J320 (trade name) manufactured by Asahi Kasei Corporation, molecular weight distribution: 8.0, high-density polyethylene) were used instead of HDPE pellets (Creolex (registered trademark) T4750 (trade name) manufactured by Asahi Kasei Corporation) and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0097] Comparative Example 3 A surface protection film was formed in the same manner as in Example 2, except that HDPE pellets (Suntec (registered trademark)-HD B161 (registered trademark) manufactured by Asahi Kasei Corporation, molecular weight distribution: 10.0, high-density polyethylene) were used instead of HDPE pellets (Creolex (registered trademark) T4750 (registered trademark) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0098] Comparative Example 4 A surface protection film was formed in the same manner as in Example 2, except that SEBS pellets (SOES1613 (trade name) manufactured by Asahi Kasei Corporation, styrene content: 33 mass%, hydrogenated styrene-butadiene copolymer) were used instead of SEBS pellets (TUFTECH (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation) and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0099] Comparative Example 5 A surface protection film was formed in the same manner as in Example 2, except that SEBS pellets (G1657 (trade name) manufactured by KRATON, styrene content: 13 mass%, hydrogenated styrene-butadiene copolymer) were used instead of SEBS pellets (TUFTECH (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation), and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0100] Comparative Example 6 Instead of SEBS pellets (Tuftec (registered trademark) H1052 (trade name) manufactured by Asahi Kasei Corporation), SEPS pellets (Septon (registered trademark) 2002 (trade name) manufactured by Kuraray Co., Ltd.), MFR (230°C, 2.16 kg load): 70 g / 10 min, melt viscosity (resin temperature: 210°C, shear rate: 121.6 sec -1A surface protection film was formed in the same manner as in Example 2, except that a polyethylene terephthalate (SEPS, tensile strength: 230 mPa s, styrene content: 30 mass%, hydrogenated styrene-ethylene-propylene-styrene) was used, and HDPE pellets (Suntec (registered trademark)-HD B161 (registered trademark) manufactured by Asahi Kasei Corporation, molecular weight distribution: 10.0, high-density polyethylene) were used instead of HDPE pellets (Creolex (registered trademark) T4750 (registered trademark) manufactured by Asahi Kasei Corporation) and the evaluation results were evaluated. The measurement results of SEPS and HDPE are shown in Table 1.

[0101] Comparative Example 7 The content of SEBS pellets (manufactured by Asahi Kasei Corporation under the trade name Tuftec (registered trademark) H1052) was changed from 66% by mass to 50% by mass, and 34% by mass of HDPE pellets (manufactured by Asahi Kasei Corporation under the trade name Creolex (registered trademark) T4750) was replaced with LDPE (manufactured by Asahi Kasei Corporation under the trade name Suntec (registered trademark)-LD L2340), MFR (190°C, 2.16 kg load): 3.8 g / 10 min, melt viscosity (resin temperature: 210°C, shear rate: 121.6 sec -1 A surface protection film was formed in the same manner as in Example 1, except that the viscosity of the SEPS and HDPE films was changed to 537 mPa s, molecular weight distribution (Mw / Mn): 9.8, and the amount of high-pressure low-density polyethylene (HPE) was changed to 50 mass%, and the film was evaluated. The measurement results for the SEPS and HDPE films, as well as the evaluation results, are shown in Table 1.

[0102] Comparative Example 8 A surface protection film was formed in the same manner as in Example 1, except that the amount of SEBS pellets (Tuftec (registered trademark) H1052 (product name) manufactured by Asahi Kasei Corporation) was changed from 66% by mass to 75% by mass, and the amount of HDPE pellets (Creolex (registered trademark) T4750 (product name) manufactured by Asahi Kasei Corporation) was changed from 34% by mass to 25% by mass, and the film was evaluated. The measurement results for SEBS and HDPE, as well as the evaluation results, are shown in Table 1.

[0103] [Table 1]

Claims

1. A surface protection film including a base layer and an adhesive layer laminated thereon, the substrate layer comprises low-density polyethylene (LDPE), The adhesive layer contains a hydrogenated styrene-butadiene copolymer (SEBS) and a high-density polyethylene (HDPE), a ratio of the thickness of the base layer to the thickness of the adhesive layer (thickness of the base layer / thickness of the adhesive layer) of 4.0 to 7.0; a mass ratio of the SEBS to the HDPE (the SEBS:the HDPE) of 70:30 to 55:45; The styrene content of the SEBS is 18 to 22% by mass, A surface protection film, wherein the HDPE has a molecular weight distribution (Mw / Mn) of 4.0 or less, which is expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in terms of standard polystyrene, as measured by gel permeation chromatography (GPC).

2. 2. The surface protection film according to claim 1, wherein the SEBS has a melt mass flow rate (MFR, 230° C., 2.16 kg load) of 11.0 to 15.0 g / 10 min.

3. The melt viscosity of the SEBS (resin temperature: 210°C, shear rate: 121.6 s -1 ) and the melt viscosity of the HDPE (resin temperature: 210°C, shear rate: 121.6 s -1 2. The surface protection film according to claim 1, wherein the ratio of the melt viscosity of the SEBS to the melt viscosity of the HDPE is 0.85 to 1.

30.

4. 2. The surface protection film according to claim 1, wherein the HDPE has a melt mass flow rate (MFR, 190°C, 2.16 kg load) of 2.0 to 6.0 g / 10 min.

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