Surface protective film

Abstract

The present invention provides a surface protective film that does not cause surface contamination, dents, deformations, or other dents or transfer defects on adherends such as polarizing plates and phase difference plates. [Solution] A surface protection film having a back layer, an intermediate layer, and an adhesive layer, wherein the back layer and the adhesive layer are mainly composed of a polyolefin resin without antioxidants, the adhesive layer and a biaxially oriented polyester film are bonded at room temperature, and the change in the water contact angle of the surface of the biaxially oriented polyester film from before bonding to after peeling, when stored for 7 days at a temperature of 23°C and a humidity of 65%, is less than 20°.

Description

[Technical Field]

[0001] This invention relates to a surface protective film used as a component in optical products. [Background technology]

[0002] Surface protection films are used to protect optical products such as optical films or sheets. When surface protection films used for such optical products are laminated to an optical film or other substrate, it is strictly required that no additives originating from the surface protection film, defects in the adhesive layer or back surface, or foreign matter from the environment are transferred to the substrate due to stress during lamination or stress from winding and storage in a roll, resulting in surface transfer contamination or dents.

[0003] These requirements have become increasingly stringent in recent years, and there is a strong demand for surface protection films that are less prone to surface transfer contamination and dents, even when the film is laminated onto a substrate, wound into a roll, and stored for long periods as a rolled-up product.

[0004] For this reason, in order to eliminate the indentation deformation (dents or transfers) on the substrate caused by defects such as fisheyes on the protective film, proposals have been made to use a polyethylene resin with a metallocene catalyst in the base layer and a specified cross-fractionation extraction ratio (Patent Document 1), or to use a polypropylene resin polymerized using a metallocene catalyst (Patent Document 2). However, these have not yet reached a level that is sufficiently satisfactory in eliminating additive transfer contamination from the protective film and dents on the substrate caused by minute fisheyes, etc.

[0005] Furthermore, a proposal has been made (Patent Document 3) for surface protection films with specific surface shapes by using a special nip roller for film formation. However, further improvements are desired in terms of preventing contamination from additive transfer from the surface protection film to the substrate, as well as in preventing dents caused by minute fisheyes and protrusions on the back surface.

[0006] Therefore, there is a need for a surface protection film that can simultaneously prevent contamination from additive transfer from the surface protection film to the adherend and eliminate dents. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-111208 [Patent Document 2] Japanese Patent Publication No. 2009-143215 [Patent Document 3] International Publication No. 2013 / 80925 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention aims to provide a surface protection film that does not cause surface transfer contamination or dents, etc., in order to meet the high demands of optical films such as polarizers and phase difference plates. [Means for solving the problem]

[0009] As a result of extensive research to solve the above problems, the present invention has found that by forming a specific surface shape using a film-forming nip roller with a film composition and structure made of a certain polyolefin, the effect of reducing additive transfer defects and indentation transfer due to protrusions can be obtained.

[0010] To solve these problems, the present invention employs the following means.

[0011] That is, the present invention is a surface protection film having a back layer, an intermediate layer, and an adhesive layer, wherein the back layer and the adhesive layer are mainly composed of a polyolefin resin without an antioxidant, and the adhesive layer and the biaxially stretched polyester film are pressure-bonded at room temperature, and the water contact angle on the surface of the biaxially stretched polyester film has a change amount of less than 20° after peeling after storage for 7 days at a temperature of 23°C and a humidity of 65% from before bonding.

Advantages of the Invention

[0012] According to the present invention, in a configuration made of a specific polyolefin, by using a film-forming nip roller and forming a surface shape, an effect of reducing indentations or transfers can be obtained.

Embodiments for Carrying Out the Invention

[0013] The surface protection film of the present invention has at least a three-layer structure of a back layer, an intermediate layer, and an adhesive layer.

[0014] The above back layer is preferably composed mainly of a polyolefin resin without an antioxidant, as it causes less contamination in the film-forming process and less contamination to the adherend. Here, the main component means 50% by mass or more of the total amount of the back layer resin.

[0015] Conventionally, polyolefin resins have been added with antioxidants for the purpose of preventing oxidative degradation during melt extrusion or long-term storage. Therefore, when the film is melt-extruded and wound into a roll for storage, the antioxidant bleeds out onto the film surface, causing contamination of the die in the film-forming process, contamination of the roll surface, and when the surface protection film is bonded to the adherend and then wound into a roll and stored as a roll weight for a long time, the antioxidant may transfer to the surface of the adherend and cause surface contamination.

[0016] The above polyolefin resin without an antioxidant refers to a resin obtained by not adding an antioxidant when polymerizing and chipping the polyolefin resin.

[0017] Examples of polyolefin resins without antioxidants used in the back layer include, for example, polyethylene resins, propylene copolymers, and blends thereof.

[0018] Preferred examples of the polyethylene resins mentioned above include high-density polyethylene, linear low-density polyethylene, high-pressure low-density polyethylene, and blends thereof, particularly those with a density of 0.900 to 0.925 (g / cm³). 3 Preferably, the material is high-pressure low-density polyethylene with a melt flow rate (hereinafter sometimes abbreviated as MFR(190℃)) measured at 190℃ in the range of 1 to 10 g / 10 min.

[0019] Examples of the propylene copolymers mentioned above include, but are not limited to, ethylene-propylene random copolymers, ethylene-propylene-butene random copolymers, ethylene-propylene block copolymers, and blends thereof. In particular, ethylene-propylene random copolymers obtained by a metallocene catalyst method are preferred, having an ethylene content of 1 to 6% by mass and a melt flow rate (hereinafter sometimes abbreviated as MFR(230°C)) measured at 230°C in the range of 1 to 10 g / 10 min.

[0020] In the present invention, the arithmetic mean roughness (Ra) of the backing layer surface is preferably 0.50 μm or less, more preferably 0.4 μm or less, and the ten-point mean roughness (Rz) is preferably 2 to 5 μm, more preferably 2.5 to 4 μm. By setting the surface roughness of the backing layer within this range, the transfer of the surface shape to the film is further suppressed.

[0021] While it is preferable to use 100% by mass of the above-mentioned polyolefin resin without the above-mentioned antioxidant for the back layer, if a polyolefin resin containing other antioxidants is mixed in, or if the antioxidant migrates from the intermediate layer using a resin containing antioxidants, it is preferable that the antioxidant content of the back layer be 200 ppm or less, preferably 100 ppm or less, because this reduces contamination during the film-forming process and reduces transfer contamination to the adherend when the surface protective film is laminated to the adherend, wound into a roll, and stored as a rolled weight for a long period of time.

[0022] The intermediate layer in the present invention is preferably made of polypropylene resin, high-density polyethylene, high-pressure low-density polyethylene, linear low-density polyethylene, and blends thereof, with a blend of high-density polyethylene and high-pressure low-density polyethylene being particularly preferred. A preferred specific example is an MFR(190) of 3 to 12 g / 10 min and a density of 0.940 to 0.970 g / cm³. 3 High-density polyethylene in the range of ) and MFR (190℃) of 1-7 g / min and density of 0.900-0.925 (g / cm³) 3 It is a blend with high-pressure low-density polyethylene within the specified range. When blending these high-density polyethylenes with high-pressure low-density polyethylenes, a preferred blending ratio is high-density polyethylene:high-pressure low-density polyethylene = 95:5 to 60:40 (by mass). When the intermediate layer is within this preferred range, the lamination properties with the back layer and adhesive layer, film formation properties when using a film-forming nip roller, thickness accuracy, and adhesion to the substrate are stable and preferable.

[0023] The antioxidant content of the polypropylene resin, high-density polyethylene, high-pressure low-density polyethylene, and linear low-density polyethylene in the intermediate layer is preferably 5000 ppm or less, more preferably 2000 ppm or less. If the antioxidant content of the intermediate layer exceeds 5000 ppm, it may migrate to the back layer and adhesive layer and bleed out, potentially contaminating the film-forming process and the adherend.

[0024] Furthermore, in the manufacturing process of the surface protective film of the present invention, if the intermediate layer is self-recoverable, a small amount of the resin used in the back layer and adhesive layer may be mixed in, to the extent that it does not degrade the film properties.

[0025] The above adhesive layer is mainly composed of polyolefin resin without antioxidants. Here, "main component" refers to 50% by mass of the total amount of adhesive layer resin.

[0026] Examples of polyolefin resins without antioxidants used in the adhesive layer include, for example, polyethylene resins, propylene copolymers, and blends thereof.

[0027] Examples of the polyethylene resins mentioned above include high-density polyethylene, high-pressure low-density polyethylene, linear low-density polyethylene, and blends thereof. Preferably, high-pressure low-density polyethylene, linear low-density polyethylene, and blends thereof are used, and in particular, the density is 0.870 to 0.925 (g / cm³). 3 Preferably, the high-pressure low-density polyethylene has an MFR (190°C) in the range of 1 to 7 g / 10 min. When the density and MFR of the high-pressure low-density polyethylene are within the above range, the lamination properties with respect to the back layer and intermediate layer, the film-forming properties when using a film-forming nip roller, the thickness accuracy, etc. are stable, changes in adhesive strength with the adherend are less likely to occur, the adhesiveness is stable, and the surface roughness is stable when using a film-forming nip roller, which is preferable. The antioxidant-free polyolefin resins used in the back layer and adhesive layer may be the same or different.

[0028] The above adhesive layer has an antioxidant content of 0 ppm by using a polyolefin resin without the above antioxidant. However, when other antioxidant-containing resins are mixed in, or when resins containing antioxidants are used in the back layer and intermediate layer, it is preferable that the amount of antioxidant that migrates from the back layer and intermediate layer to the adhesive layer is 200 ppm or less, as this prevents transfer contamination to the adherend.

[0029] The arithmetic mean roughness (Ra) of the adhesive layer is preferably in the range of 0.01 to 0.20 μm, more preferably 0.02 to 0.05 μm, and the ten-point mean roughness (Rz) is preferably in the range of 0.1 to 0.5 μm, more preferably 0.2 to 0.4 μm. By setting the adhesive layer to such a roughness range, the adhesive force to the adherend becomes more stable, and the transfer of the film surface shape is more easily suppressed.

[0030] In the present invention, it is preferable to impart an embossed shape to one side (the surface) of the surface protection film using a film-forming nip roller. Any film-forming nip roller capable of forming the surface shape of the surface protection film of the present invention can be used without particular limitations, but film-forming nip rollers such as those disclosed in International Publication No. 2013 / 80925 and Japanese Patent Application Publication No. 2020-55189 are preferably used. Specifically, an embossing nip roller having an arithmetic mean roughness Ra of 0.20 μm or less, a ten-point mean roughness Rz of 2 to 8 μm, and an average spacing Sm of irregularities of 90 μm or less is preferred.

[0031] In the present invention, it is preferable to form the back layer in an embossed shape using a film-forming nip roller. According to the inventors' findings, defects on the film-forming nip roller can cause defects on the back side of the surface protective film corresponding to the roller's cycle. If the defect height of the back layer is high, it can cause indentations on the adherend when the film is bonded to it. In addition, fisheyes caused by foreign matter or gel-like substances in the film can protrude on the adhesive layer side, and if their maximum height is high, they can similarly cause indentations on the adherend. Therefore, the surface protective film of the present invention is preferable because, by using a specific film-forming nip roller and a specific resin composition, the protrusions on the back side and the protrusions on the adhesive layer caused by fisheyes can be suppressed, thereby reducing indentations on the adherend.

[0032] As a method for manufacturing the surface protective film of the present invention, preferred examples include a method in which a film obtained by inflation molding is reheated and nipped with the film-forming nip roller, and a method in which the molten resin extruded from the T-die in T-die molding is nipped with a cooling roll and the film-forming nip roller. In particular, a method using a mirror-finish type cooling roll with a surface roughness of 0.2s or less and the film-forming nip roller to nip the molten resin extruded from the T-die is preferred. More preferably, a method using a mirror-finish type cooling roll with a surface roughness of 0.15s or less and the film-forming nip roller to nip the molten resin extruded from the T-die is preferred.

[0033] The surface protection film of the present invention provides a protective film free of defects such as wrinkles when wound during film formation, can be easily unwound when unwinding for bonding to an adherend, and has good thickness uniformity, making it easy to handle and process during bonding to an adherend. In particular, it can reliably provide a surface protection film that prevents dents, deformation, scratches, and transfer contamination of additives to the adherend caused by the maximum fisheye height, the height of periodic protrusions on the back surface, and various wrinkles in the film, which are required for optical films such as polarizing plates and phase difference plates.

[0034] The surface protective film of the present invention preferably has a back layer thickness of 0.3 to 30 μm, more preferably 0.5 to 20 μm, and more preferably 0.7 to 15 μm; an intermediate layer thickness of 3 to 200 μm, more preferably 5 to 150 μm, and more preferably 7 to 100 μm; and an adhesive layer thickness of 0.3 to 30 μm, more preferably 0.5 to 20 μm, and more preferably 0.7 to 15 μm.

[0035] The total thickness is preferably 3.6 to 260 μm, more preferably 6 to 190 μm, and more preferably 8.4 to 130 μm.

[0036] The surface protection film of the present invention is formed by bonding an adhesive layer and a biaxially oriented polyester film at room temperature, and the change in the water contact angle of the surface of the biaxially oriented polyester film from before bonding to after peeling, when stored for 7 days at a temperature of 23°C and a humidity of 65%, is less than 20°. The biaxially oriented polyester film is a substitute film for easily evaluating the transfer contamination of the surface protection film of the present invention to optical films such as polarizers and phase difference plates of the target substrate. If the change in the water contact angle exceeds 20°, the film becomes impractically unusable due to transfer contamination of optical films such as polarizers and phase difference plates of the substrate.

[0037] The thickness unevenness in the width direction (TD direction) of the surface protective film of the present invention is preferably less than 1%, and more preferably 0.5% or less, because if the thickness unevenness exceeds 1%, uneven adhesion with the adherend may occur. This is preferable for stable peelability from the adherend.

[0038] As a simple evaluation of the adhesive strength of the adherend to optical films such as polarizing plates and phase difference plates, it is preferable that the adhesive strength to the acrylic plate is in the range of 0.02 to 0.15 N / 50 mm after storage in a 23°C atmosphere for 24 hours and after being left in an oven at 50°C for 3 days and then removed and stored in a 23°C atmosphere for 24 hours. If the adhesive strength is less than 0.02 N / 50 mm, lifting may occur due to insufficient adhesion to the adherend, and if it exceeds 0.15 N / 50 mm, peeling marks may occur. Furthermore, it is preferable that the difference in adhesive strength between storage in a 23°C atmosphere for 24 hours and storage in a 23°C atmosphere for 24 hours after being left in an oven at 50°C for 3 days and then removed and stored in a 23°C atmosphere for 24 hours is 0.02 N / 50 mm or less. [Examples]

[0039] The surface protective film of the present invention will be described in detail below based on specific examples, but the present invention is not limited to these examples. The measurement and evaluation were performed using the methods shown below.

[0040] (1) Melt Flow Rate (MFR) Using a melt indexer manufactured by Toyo Seiki Seisakusho Co., Ltd., measurements were taken in accordance with JIS K7210-1997, at a temperature of 230°C and a load of 2.16 kg for polypropylene resins, and at a temperature of 190°C and a load of 2.16 kg for polyethylene resins. All units are g / 10 min.

[0041] (2) Confirmation that polyolefin resin is free of antioxidants. The presence or absence of antioxidants can be confirmed by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0042] (3) Surface roughness Using a fully automatic micro-shape measuring machine (SURFCORDER ET4000A) manufactured by Kosaka Laboratory Co., Ltd., measurements were taken 10 times in the transverse direction (TD direction of the film) with a measurement length of 4 mm and in the longitudinal direction (machine direction) with a pitch of 10 μm, in accordance with JIS B0601-1982. Three-dimensional analysis was performed to determine the arithmetic mean roughness (Ra) and the ten-point mean roughness (Rz) (units are μm). A diamond stylus with a tip radius of 2.0 μm and an apex angle of 60° was used, with a measuring force of 100 μN and a cutoff of 0.8 mm.

[0043] (4) Evaluation of transfer contamination on the surface of the adherend As an alternative film for easily evaluating transfer contamination of the adherend to optical films such as polarizers and phase difference plates, Toray Industries, Inc.'s biaxially oriented polyester film "Lumirror®" #50-U483 (hereinafter abbreviated as PET film) was used as the adherend to be bonded, and the water contact angle of the surface was measured. Next, the adhesive layer of a protective film was placed on top of the PET film, and the film was bonded using a special pressure roller manufactured by Yasuda Seiki Co., Ltd. at a temperature of 23°C, a pressure of 9,100 N / m, and a speed of 300 cm / min. After that, the film was cut to 100 mm x 100 mm, sandwiched between smooth boards, and stored at a temperature of 23°C and a humidity of 65% for 7 days. After that, the surface protective film was peeled off and the water contact angle of the surface of the PET film was measured.

[0044] At this time, using the water contact angle of the PET at the initial stage of bonding as a reference, the water contact angle of the PET surface after peeling off the protective film was measured, and the following judgment was made. Transcription contamination detection criteria: ○: Water contact angle after peeling - Water contact angle at the initial stage of application is less than 20° ×: Water contact angle after peeling - Water contact angle at the initial stage of application is 20° or more.

[0045] (5) Adhesive strength The adhesive strength was measured by peeling off the surface protective film using a tensile testing machine at a tensile speed of 300 mm / min and a peeling angle of 180°C.

[0046] (6) Film thickness unevenness in the width direction (TD direction) The film was divided into 10 sections in the width direction (TD direction), and the thickness at these 10 points was measured using a dial gauge. The value calculated using the following formula was defined as the thickness variation (%). Thickness variation (%) = (((Maximum thickness) - (Minimum thickness)) / (Average thickness)) × 100.

[0047] <Example 1> The back layer resin has a density of 0.922 g / cm³. 3 Low-density polyethylene with no antioxidants added, processed using the high-pressure method with an MFR (190℃) of 5.0 g / 10 min, as an intermediate layer, with a density of 0.961 g / cm³. 3 , MFR (190℃) 7.5g / 10min, antioxidant-free high-density polyethylene 80% by mass, density 0.924g / cm³ 3 A blend of 20% by mass of low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 5.8g / 10min (190℃), used as an adhesive layer, with a density of 0.922g / cm³. 3, Using antioxidant-free high-pressure low-density polyethylene with an MFR (190 °C) of 5.0 g / 10 min, a T-die type composite film forming machine with a die width of 1800 mm having three extruders with diameters of 65 mm φ (for the back layer), 100 mm φ (for the intermediate layer), and 65 mm φ (for the adhesive layer) respectively was used. The prepared resin composition was introduced into each extruder, and the discharge amounts of each extruder were adjusted so that the back layer thickness ratio was 25%, the intermediate layer thickness ratio was 50%, and the adhesive layer thickness ratio was 25%. It was extruded from the T-die at an extrusion temperature of 220 °C, nipped between the film-forming nip roller described in JP-A-2020-55189 and a casting drum with a surface roughness of 0.1 s, and simultaneously quenched at a temperature of 30 °C, and wound into a roll to obtain a three-layer laminated surface protection film with a film thickness of 30 μm.

[0048] Table 1 shows the surface roughness and characteristics of the back layer and the adhesive layer of the obtained surface protection film. This film has little TD thickness unevenness, no increase in adhesion after storing at 50 °C for 3 days in the state of being laminated on the surface of the biaxially stretched polyester film, the change amount after peeling after storing at a temperature of 23 °C and a humidity of 65% for 7 days is 0, and there is no transfer contamination to the surface of the adherend.

[0049] <Example 2> As the intermediate layer, except that it was a blend of 80% by mass of high-density polyethylene with a density of 0.965 g / cm 3 and an MFR (190 °C) of 7.0 g / 10 min with 1000 ppm of antioxidant added and 20% by mass of antioxidant-free high-pressure low-density polyethylene with a density of 0.922 g / cm 3 and an MFR (190 °C) of 5.0 g / 10 min, a three-layer laminated surface protection film was obtained in the same manner as in Example 1.

[0050] Table 1 shows the surface roughness and characteristics of the back layer and the adhesive layer of the obtained surface protection film. This film has little TD thickness unevenness, no increase in adhesion after storing at 50 °C for 3 days in the laminated state, although migration of the antioxidant to the adhesive layer was observed, the water contact angle on the surface of the biaxially stretched polyester film has a change amount of 3° after peeling after storing at a temperature of 23 °C and a humidity of 65% for 7 days after lamination, and there is no transfer contamination to the surface of the adherend.

[0051] <Example 3> A three-layer laminated surface protective film was obtained in the same manner as in Example 2, except that the back layer was an ethylene-propylene random copolymer without antioxidants, obtained by a metallocene catalyst method with an ethylene content of 4% by mass and 5 g / 10 min at MFR (230°C).

[0052] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protective film. This film had small TD thickness variations, no increase in adhesion after storage at 50°C for 3 days in the laminated state, and migration of the antioxidant to the adhesive layer was observed. However, the change in the water contact angle of the biaxially oriented polyester film surface after peeling following storage at 23°C and 65% humidity for 7 days after lamination was 3°, and there was no transfer contamination to the substrate surface.

[0053] <Example 4> The backing layer and adhesive layer resin have a density of 0.923 g / cm³. 3 Using low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 5.0 g / 10 min, the intermediate layer has a density of 0.965 g / cm³. 3 High-density polyethylene with 50% mass and density of 0.922 g / cm³, with 1000 ppm antioxidant added, MFR (190℃) 7.0 g / 10 min. 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that it was a blend of 50% by mass of low-density polyethylene with 1000 ppm of antioxidant added and processed by high-pressure method using MFR (190℃) 5.0 g / 10 min.

[0054] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protective film. This film had small TD thickness variations, no increase in adhesion after storage at 50°C for 3 days in the laminated state, and migration of the antioxidant to the adhesive layer was observed. However, the change in the water contact angle of the biaxially oriented polyester film surface after peeling following storage at 23°C and 65% humidity for 7 days after lamination was 5°, and there was no transfer contamination to the substrate surface.

[0055] <Example 5> The back layer has a density of 0.922 g / cm³. 3 , MFR (190℃) 5.0g / 10 min with 500ppm antioxidant added, high-pressure method, low-density polyethylene 50% by mass, density 0.922g / cm³ 3 The blend consists of 50% by mass of low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 5.0 g / 10 min, and the intermediate layer has a density of 0.965 g / cm³. 3 High-density polyethylene with 50% mass and density of 0.922 g / cm³, with 1000 ppm antioxidant added, MFR (190℃) 7.0 g / 10 min. 3 A blend of 20% by mass of low-density polyethylene with 1000 ppm antioxidant added and MFR (190℃) 5.0 g / 10 min, and an adhesive layer with a density of 0.922 g / cm³. 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that it was low-density polyethylene processed by high-pressure method without antioxidants, using MFR (190℃) 5.0 g / 10 min.

[0056] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protective film. This film had small TD thickness variations, no increase in adhesion after storage at 50°C for 3 days in the laminated state, and migration of the antioxidant to the adhesive layer was observed. However, the change in the water contact angle of the biaxially oriented polyester film surface after peeling following storage at 23°C and 65% humidity for 7 days after lamination was 10°, and there was no transfer contamination to the surface of the adherend.

[0057] <Example 6> The back layer has a density of 0.922 g / cm³. 3 The material is low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 5.0 g / 10 min, and the intermediate layer has a density of 0.965 g / cm³. 3 High-density polyethylene with 50% mass and density of 0.922 g / cm³, with 1000 ppm antioxidant added, MFR (190℃) 7.0 g / 10 min. 3 A blend of 50% by mass of low-density polyethylene with 1000 ppm antioxidant added, processed by high-pressure method using MFR (190℃) 5.0 g / 10 min, and used as an adhesive layer, with a density of 0.922 g / cm³. 3, MFR (190℃) 5.0g / 10 min with 1000ppm antioxidant added, high-pressure method, low-density polyethylene 10% by mass, density 0.922g / cm³ 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that it was a blend of 90% by mass of low-density polyethylene processed by high-pressure method without antioxidants using MFR (190℃) 5.0 g / 10 min.

[0058] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protective film. This film had minimal TD thickness variation, no increase in adhesion after storage at 50°C for 3 days in a laminated state, a low amount of antioxidant in the adhesive layer, a change of 15° after peeling following storage at 23°C and 65% humidity for 7 days, and no transfer contamination to the substrate surface.

[0059] <Comparative Example 1> The back layer resin has a density of 0.925 g / cm³. 3 The material is low-density polyethylene produced by high-pressure method with 1000 ppm antioxidant added, using MFR (190℃) 0.5 g / 10 min, and the intermediate layer has a density of 0.961 g / cm³. 3 High-density polyethylene with 1000 ppm antioxidant added, MFR (190℃) 7.5 g / 10 min, 50% by mass, density 0.924 g / cm³ 3 A blend of 50% by mass of low-density polyethylene using the high-pressure method, with 1000 ppm of antioxidant added at MFR (190℃) 0.8 g / 10 min (190℃), used as an adhesive layer, with a density of 0.925 g / cm³. 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that low-density polyethylene was used, which was subjected to a high-pressure method with 1000 ppm of antioxidant added, and subjected to MFR (190℃) 0.5 g / 10 min.

[0060] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protection film. Due to the large amount of antioxidant in the adhesive layer, the water contact angle of the biaxially oriented polyester film surface changed by more than 30° and 20° after peeling following 7 days of storage at 23°C and 65% humidity after lamination, indicating antioxidant transfer contamination to the substrate surface. In addition, the low MFR of the high-pressure low-density polyethylene used resulted in large TD thickness variations, high surface roughness, and indentation of the substrate, as well as high adhesive strength to the substrate.

[0061] <Comparative Example 2> The back layer resin has a density of 0.925 g / cm³. 3 The material is low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 5.0 g / 10 min, and the intermediate layer has a density of 0.961 g / cm³. 3 High-density polyethylene with 80% mass and a density of 0.924 g / cm³, with 1000 ppm antioxidant added, and MFR (190℃) 7.5 g / 10 min. 3 A blend of 20% by mass of low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 7.5g / 10min (190℃), and an adhesive layer with a density of 0.922g / cm³. 3 70% by mass of low-density polyethylene with a density of 0.922 g / cm³, processed by high-pressure method using MFR (190℃) 5.0 g / 10 min with 1000 ppm antioxidant added. 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that it was a blend of 30% by mass of low-density polyethylene processed by high pressure method without antioxidants, with an MFR (190℃) of 5.0 g / 10 min.

[0062] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protective film. Due to the large amount of antioxidant in the adhesive layer, the water contact angle of the biaxially oriented polyester film surface changed from 25° to 20° after peeling following 7 days of storage at 23°C and 65% humidity after lamination, resulting in transfer contamination to the substrate surface.

[0063] <Comparative Example 3> The back layer resin has a density of 0.925 g / cm³. 3The material is low-density polyethylene produced by high-pressure method with 1000 ppm antioxidant added, and the intermediate layer has a density of 0.961 g / cm³. 3 High-density polyethylene with 50% mass and a density of 0.924 g / cm³, containing 4000 ppm antioxidant, with an MFR (190℃) of 7.5 g / 10 min. 3 A blend of 50% by mass of low-density polyethylene produced by high-pressure method without antioxidants, with an MFR (190℃) of 7.5g / 10min (190℃), and an adhesive layer with a density of 0.925g / cm³. 3 A three-layer laminated surface protective film was obtained in the same manner as in Example 1, except that high-pressure low-density polyethylene without antioxidants was used, with an MFR (190℃) of 5.0 g / 10 min.

[0064] Table 1 shows the surface roughness and characteristics of the back layer and adhesive layer of the obtained surface protection film. Due to the large amount of antioxidant migration from the central layer to the adhesive layer, the water contact angle of the biaxially oriented polyester film surface changed from 22° to 20° after peeling following 7 days of storage at 23°C and 65% humidity after lamination, resulting in transfer contamination to the substrate surface.

[0065] [Table 1-1]

[0066] [Table 1-2]

Claims

1. A surface protective film having a back layer, an intermediate layer, and an adhesive layer, The aforementioned back layer and adhesive layer are mainly composed of a polyolefin resin without antioxidants. A surface protective film is formed by bonding the adhesive layer and a biaxially oriented polyester film at room temperature, wherein the change in the water contact angle of the surface of the biaxially oriented polyester film from before bonding to after peeling, when stored for 7 days at a temperature of 23°C and a humidity of 65%, is less than 20°.

2. The surface protective film according to claim 1, wherein the polyolefin resin without antioxidants is selected from the group consisting of high-pressure low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

3. The surface protective film according to claim 1, wherein the polyolefin resin without antioxidants is a propylene copolymer.

4. The surface protective film according to claim 1, wherein the arithmetic mean roughness (Ra) of the surface of the back layer is 0.50 μm or less and the ten-point mean roughness (Rz) is 2 to 5 μm, and the arithmetic mean roughness (Ra) of the surface of the adhesive layer is 0.01 to 0.20 μm and the ten-point mean roughness (Rz) is 0.1 to 0.5 μm.

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