Surface protection film

Abstract

To provide a surface protective film that can be used for an optical film having irregularity on a surface, causes less contamination to an adherend, has unchanged low contamination performance to the adherend despite passage of time, is not degraded with time, and has excellent release anti-static performance.SOLUTION: A release film 5 for surface protective film is formed by laminating a release agent layer 4 containing a release agent having dimethyl polysiloxane as a main component, an anti-static agent which does not react with the release agent, and an anti-static auxiliary agent on one face of a resin film 3, a component of the anti-static agent is an ionic compound (which is not alkali metal salt) having a melting point of less than 30°C, the anti-static auxiliary agent is polyether-modified silicone, and when the release film 5 is adhered to a surface of an adhesive agent layer 2 via the release agent layer 4, the component of the anti-static agent and the anti-static auxiliary agent of the release agent layer 4 are transferred onto the surface of the adhesive agent layer 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface protection film to be attached to the surface of optical components (hereinafter sometimes referred to as optical films) such as polarizing plates, retardation plates, lens films for displays, etc. More specifically, the present invention provides a surface protection film that causes little contamination to the substrate, and further, a surface protection film that does not deteriorate over time and has excellent antistatic properties upon peeling, and optical components using the same. [Background technology]

[0002] Conventionally, when optical films such as polarizing plates, retardation plates, lens films for displays, antireflection films, hard coat films, and transparent conductive films for touch panels, and optical products such as displays using the same, are manufactured and transported, a surface protective film is attached to the surface of the optical film to prevent the surface from being soiled or scratched in later processes. In order to improve work efficiency by eliminating the need to peel off and reattach the surface protective film, visual inspection of the optical film product is sometimes performed with the surface protective film attached to the optical film.

[0003] Generally, a surface protection film having a pressure-sensitive adhesive layer provided on one side of a base film is used in the manufacturing process of optical products to prevent scratches and dirt from adhering. The surface protection film is attached to the optical film via a pressure-sensitive adhesive layer with weak adhesive strength. The pressure-sensitive adhesive layer has weak adhesive strength so that when a used surface protection film is peeled off and removed from the surface of the optical film, it can be easily peeled off and the pressure-sensitive adhesive does not adhere to and remain on the optical film of the adherend (preventing the occurrence of so-called adhesive residue).

[0004] In recent years, during the production process of liquid crystal display panels, there have been a few cases where the peeling charge voltage generated when peeling off and removing the surface protection film attached to the optical film has destroyed circuit components such as driver ICs that control the display screen of the liquid crystal display panel, or damaged the alignment of liquid crystal molecules. Furthermore, in order to reduce the power consumption of LCD panels, the driving voltage of liquid crystal materials has been lowered, and as a result, the breakdown voltage of driver ICs has also been lowered.Recently, there has been a demand for the peeling electrification voltage to be within the range of +0.7kV to -0.7kV.

[0005] Furthermore, with the recent spread of 3D displays (stereoscopic displays), there are some optical films, such as polarizing plates, that have an FPR (Film Patterned Retarder) film laminated to their surfaces. The FPR film is laminated after peeling off the surface protective film that was previously laminated to the surface of the optical film, such as a polarizing plate. However, if the surface of the optical film, such as a polarizing plate, is contaminated by the adhesive or antistatic agent used in the surface protective film, there is a problem in that the FPR film is difficult to adhere to. For this reason, surface protective films used in such applications are required to be ones that cause minimal contamination to the adherend.

[0006] Additionally, some LCD panel manufacturers have adopted a method for evaluating the fouling properties of surface protection films on substrates, in which the surface protection film attached to an optical film such as a polarizing plate is first peeled off, reattached in a state where air bubbles are mixed in, and then heat-treated under specified conditions. The surface protection film is then peeled off and the surface of the substrate is observed. With this evaluation method, even if the surface contamination of the substrate is minimal, if there is a difference in the surface contamination between the area where the air bubbles are mixed in and the area where the adhesive of the surface protection film was in contact, air bubble marks (sometimes called "bubble stains") will remain. Therefore, this is a very strict evaluation method for the fouling properties of the substrate surface. In recent years, there has been a demand for surface protection films that do not have problems with fouling properties on the surface of the substrate, even when judged by such a strict evaluation method.

[0007] In order to prevent problems caused by high peeling electrification voltage when peeling a surface protection film from an optical film as an adherend, a surface protection film has been proposed that uses a pressure-sensitive adhesive layer containing an antistatic agent to keep the peeling electrification voltage low.

[0008] For example, Patent Document 1 discloses a surface protection film that uses a pressure-sensitive adhesive made of an alkyltrimethylammonium salt, a hydroxyl group-containing acrylic polymer, and a polyisocyanate. Furthermore, Patent Document 2 discloses a pressure-sensitive adhesive composition comprising an ionic liquid and an acrylic polymer having an acid value of 1.0 or less, and pressure-sensitive adhesive sheets using the same. Furthermore, Patent Document 3 discloses a pressure-sensitive adhesive composition comprising an acrylic polymer, a polyether polyol compound, and an alkali metal salt treated with an anion-adsorbing compound, and a surface protection film using the same. Furthermore, Patent Document 4 discloses a pressure-sensitive adhesive composition comprising an ionic liquid, an alkali metal salt, and a polymer having a glass transition temperature of 0° C. or lower, and a surface protection film using the same. Furthermore, Patent Document 5 discloses a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that are used for a surface protection sheet for optical members, which are made of a polymer containing a liquid ionic salt. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-131957 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-330464 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-314476 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-152235 [Patent Document 5] Japanese Patent Application Laid-Open No. 2008-069261 Summary of the Invention [Problem to be solved by the invention]

[0010] In the above Patent Documents 1 to 5, an antistatic agent is added to the inside of the adhesive layer. However, as the thickness of the adhesive layer increases and as time passes after bonding to the adherend, the amount of antistatic agent that migrates from the adhesive layer to the adherend to which the surface protective film is bonded increases. If the amount of antistatic agent that migrates to the adherend increases, the appearance quality of the optical film that is the adherend may deteriorate, and the adhesiveness of the FPR film may decrease when the FPR film is bonded.

[0011] If the thickness of the pressure-sensitive adhesive layer is reduced in order to reduce the increase over time in the amount of antistatic agent that migrates from the pressure-sensitive adhesive layer to the adherend, other problems arise. For example, when used with an optical film having an uneven surface, such as a polarizing plate that has been anti-glare treated to prevent glare, the pressure-sensitive adhesive layer may be unable to conform to the unevenness of the optical film surface, resulting in the inclusion of air bubbles, or the adhesive strength may decrease due to a reduced adhesive area between the optical film and the pressure-sensitive adhesive layer, causing the surface protection film to float or peel off during use.

[0012] For this reason, there is a demand for a surface protection film to be used on optical films, which can be used even on optical films with uneven surfaces, which causes very little contamination to the adherend and does not increase contamination of the adherend over time, and which has a low peeling electrification voltage when the surface protection film is peeled off from the adherend.

[0013] The present inventors have conducted extensive research into this issue. In order to reduce the contamination of the adherend and to minimize the increase in contamination over time, it is necessary to reduce the amount of the antistatic agent component in the pressure-sensitive adhesive layer, which is presumed to be contaminating the adherend. However, if the amount of the antistatic agent component in the pressure-sensitive adhesive layer is reduced, the peeling electrification voltage increases when the surface protection film is peeled from the adherend. Therefore, we investigated a method for reducing the peeling electrification voltage when the surface protection film is peeled from the adherend without increasing the absolute amount of the antistatic agent component in the pressure-sensitive adhesive layer. As a result, the inventors discovered that, rather than forming a pressure-sensitive adhesive layer by applying and drying a pressure-sensitive adhesive composition containing an antistatic agent to one side of a substrate film, it is possible to reduce the peel electrification voltage when peeling the surface protection film from the optical film to be adhered by applying and drying a pressure-sensitive adhesive composition that does not contain an antistatic agent to laminate the pressure-sensitive adhesive layer, and then applying an appropriate amount of an antistatic agent component only to the surface of the pressure-sensitive adhesive layer, thereby completing the present invention.

[0014] The present invention has been made in consideration of the above circumstances, and has as its object to provide a surface protection film that can be used for optical films having an uneven surface, that causes little contamination to the adherend, that maintains its low contamination property to the adherend over time, that does not deteriorate over time, and that has excellent antistatic performance against peeling, and an optical component using the same. [Means for solving the problem]

[0015] In order to solve the above problems, the surface protection film of the present invention has the technical concept of coating and drying an antistatic agent-free pressure-sensitive adhesive composition on one side of a base film to form a pressure-sensitive adhesive layer, and then applying an appropriate amount of antistatic agent to the surface of the pressure-sensitive adhesive layer, thereby minimizing contamination of the adherend and minimizing peel electrification voltage when peeled off from the adherend, i.e., the optical film.

[0016] In order to solve the above-mentioned problems, the present invention provides a surface protection film comprising a substrate film made of a transparent resin on one side of which a pressure-sensitive adhesive layer is formed, and a release film having a release agent layer laminated on the pressure-sensitive adhesive layer, wherein the release film comprises a resin film on one side of which a release agent layer is laminated, the release agent layer containing a release agent mainly composed of dimethylpolysiloxane, an antistatic agent that does not react with the release agent, and an antistatic aid, the antistatic agent component being an ionic compound having a melting point of less than 30°C, and the antistatic aid being a polyether-modified silicone, and the antistatic agent component and the antistatic aid are transferred from the release agent layer of the release film to the surface of the pressure-sensitive adhesive layer, thereby reducing the peel electrification voltage when the pressure-sensitive adhesive layer is peeled from an adherend.

[0017] The pressure-sensitive adhesive layer is preferably formed by crosslinking a pressure-sensitive adhesive composition containing a (meth)acrylate copolymer and a crosslinking agent.

[0018] It is also preferable that the peeling force when peeling the release film from the pressure-sensitive adhesive layer is 0.2 N / 50 mm or less.

[0019] The present invention also provides an optical component having the above-described surface protection film attached thereto. [Effects of the Invention]

[0020] The surface protective film of the present invention causes little contamination of the adherend, and the low contamination of the adherend does not change over time. Furthermore, the surface protective film of the present invention can be used even when the adherend is an optical film with an uneven surface, such as an AG polarizing plate. Furthermore, according to the present invention, the peeling electrification voltage generated when peeling from the adherend, i.e., the optical film, can be kept low, and a surface protective film having excellent peeling antistatic performance without deterioration over time, and optical components using the same can be provided. The surface protective film of the present invention can reliably protect the surface of an optical film, thereby improving productivity and yield. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view illustrating the concept of a surface protection film of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a state in which a release film has been peeled off from the surface protection film of the present invention. [Figure 3] FIG. 1 is a cross-sectional view showing one embodiment of an optical component of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail below based on embodiments. 1 is a cross-sectional view showing the concept of the surface protection film of the present invention. This surface protection film 10 has a pressure-sensitive adhesive layer 2 formed on one surface of a transparent substrate film 1. A release film 5, which has a release agent layer 4 formed on the surface of a resin film 3, is attached to the surface of this pressure-sensitive adhesive layer 2.

[0023] The substrate film 1 used in the surface protection film 10 of the present invention is made of a transparent and flexible resin. This allows for visual inspection of the optical component, which is the adherend, with the surface protection film attached to the optical component. The transparent resin film used as the substrate film 1 is preferably a polyester film such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or polybutylene terephthalate. In addition to polyester films, films made of other resins can also be used as long as they have the required strength and optical suitability. The substrate film 1 may be an unstretched film or a uniaxially or biaxially stretched film. The stretching ratio of the stretched film and the axial orientation angle formed due to crystallization of the stretched film may be controlled to specific values. The thickness of the substrate film 1 used in the surface protection film 10 according to the present invention is not particularly limited, but is preferably about 12 to 100 μm, and more preferably about 20 to 50 μm for ease of handling. If necessary, an antifouling layer for preventing surface contamination, an antistatic layer, a hard coat layer for preventing scratches, etc. may be provided on the surface of the base film 1 opposite to the surface on which the pressure-sensitive adhesive layer 2 is formed. The surface of the base film 1 may also be subjected to an adhesion-enhancing treatment such as surface modification by corona discharge or application of an anchor coating agent.

[0024] Furthermore, the adhesive layer 2 used in the surface protection film 10 of the present invention is not particularly limited as long as it adheres to the surface of the adherend, can be easily peeled off after use, and is unlikely to contaminate the adherend. However, taking into consideration durability after application to an optical film, it is common to use an adhesive made by crosslinking a (meth)acrylate copolymer.

[0025] Examples of (meth)acrylate copolymers include copolymers obtained by copolymerizing a main monomer such as n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, or isononyl acrylate with a comonomer such as acrylonitrile, vinyl acetate, methyl methacrylate, or ethyl acrylate; a functional monomer such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, glycidyl methacrylate, or N-methylol methacrylamide; or a polyoxyalkylene group-containing monomer such as methoxypolyethylene glycol methacrylate. The (meth)acrylate copolymer may contain both the main monomer and other monomers as (meth)acrylates, or may contain one or more monomers other than (meth)acrylates as other monomers besides the main monomer. The other monomers besides the main monomer can be selected without particular limitation from the above-mentioned comonomers, functional monomers, and polyoxyalkylene group-containing monomers.

[0026] Examples of the curing agent added to the adhesive layer 2 include crosslinking agents that crosslink the (meth)acrylate copolymer, such as isocyanate compounds, epoxy compounds, melamine compounds, and metal chelate compounds. Examples of the tackifier include rosin-based, coumarone-indene-based, terpene-based, petroleum-based, and phenol-based agents.

[0027] The thickness of the pressure-sensitive adhesive layer 2 used in the surface protection film 10 according to the present invention is not particularly limited, but is preferably about 5 to 40 μm, and more preferably about 10 to 30 μm. Furthermore, a pressure-sensitive adhesive layer 2 having a weak adhesive strength, i.e., a peel strength (adhesive strength) of the surface protection film to the surface of the adherend, of about 0.03 to 0.3 N / 25 mm, is preferred, as this provides excellent operability when peeling the surface protection film from the adherend. Furthermore, to provide excellent operability when peeling the release film 5 from the surface protection film 10, the peel force when peeling the release film 5 from the pressure-sensitive adhesive layer 2 is preferably 0.2 N / 50 mm or less, and more preferably 0.14 N / 50 mm or less.

[0028] The release film 5 used in the surface protection film 10 according to the present invention has a release agent layer 4 laminated on one side of a resin film 3. The release agent layer 4 contains a release agent mainly composed of dimethylpolysiloxane, an antistatic agent that does not react with the release agent, and an antistatic auxiliary. In the release film used in the surface protection film according to the present invention, it is preferable that the antistatic agent component is an ionic compound having a melting point of less than 30°C, and that the antistatic auxiliary is polyether-modified silicone.

[0029] Examples of the resin film 3 include polyester film, polyamide film, polyethylene film, polypropylene film, and polyimide film, but polyester film is particularly preferred because of its excellent transparency and relatively low price. The resin film may be an unstretched film or a uniaxially or biaxially stretched film. Furthermore, the stretching ratio of the stretched film and the axial orientation angle formed by crystallization of the stretched film may be controlled to a specific value. The thickness of the resin film 3 is not particularly limited, but is preferably about 12 to 100 μm, and more preferably about 16 to 50 μm, for ease of handling. If necessary, the surface of the resin film 3 may be subjected to an easy-adhesion treatment such as surface modification by corona discharge or application of an anchor coating agent.

[0030] The release agent containing dimethylpolysiloxane as a main component that constitutes the release agent layer 4 includes known silicone-based release agents such as addition reaction type, condensation reaction type, cationic polymerization type, and radical polymerization type. Examples of commercially available products as addition reaction type silicone-based release agents include KS-776A, KS-847T, KS-779H, KS-837, KS-778, and KS-830 (manufactured by Shin-Etsu Chemical Co., Ltd.), SRX-211, SRX-345, SRX-357, SD7333, SD7220, SD7223, LTC-300B, LTC-350G, and LTC-310 (manufactured by Dow Corning Toray Co., Ltd.). Examples of commercially available products as condensation reaction type release agents include SRX-290 and SYLOFF-23 (manufactured by Dow Corning Toray Co., Ltd.). Examples of commercially available cationic polymerization products include TPR-6501, TPR-6500, UV9300, VU9315, and UV9430 (manufactured by Momentive Performance Materials), and X62-7622 (manufactured by Shin-Etsu Chemical Co., Ltd.). Examples of commercially available radical polymerization products include X62-7205 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0031] The antistatic agent constituting the release agent layer 4 is preferably one that has good dispersibility in a release agent solution containing dimethylpolysiloxane as a main component and that does not inhibit the curing of the release agent containing dimethylpolysiloxane as a main component. Furthermore, since the antistatic agent is transferred from the release agent layer 4 to the surface of the pressure-sensitive adhesive layer 2 and imparts antistatic properties to the pressure-sensitive adhesive layer 2, it is preferable that the antistatic agent does not react with the release agent containing dimethylpolysiloxane as a main component. As such an antistatic agent, an ionic compound with a melting point of less than 30°C is preferred.

[0032] Examples of ionic compounds having a melting point of less than 30°C include ionic compounds having a cation and an anion, and the cation may be a cyclic amidine ion such as an imidazolium ion, a pyridinium ion, an ammonium ion, a sulfonium ion, a phosphonium ion, or the like. Examples of an anion include C n H 2n+1 COO - , C n F 2n+1 COO - , NO3 - , C n F 2n+1 SO3 - , (C n F 2n+1 SO2)2N - , (C n F 2n+1 SO2)3C - , PO4 3- , AlCl4 - , Al2Cl7 - , ClO4 - , BF4 - , PF6 - , AsF6 - , SbF6 - etc. The amount of antistatic agent added to a release agent containing dimethylpolysiloxane as a main component varies depending on the type of antistatic agent and the degree of affinity with the release agent. The amount of antistatic agent added can be determined taking into consideration the desired peeling electrification voltage when the surface protection film is peeled from the adherend, the staining properties of the adherend, the adhesive properties, etc.

[0033] The antistatic aid constituting the release agent layer 4 is used to improve the antistatic properties of the surface of the pressure-sensitive adhesive layer. A suitable antistatic aid is polyether-modified silicone. The polyether chain in the polyether-modified silicone is composed of ethylene oxide, propylene oxide, or the like. For example, by selecting the molecular weight of the polyethylene oxide used in the side chain, physical properties such as compatibility with the silicone release agent and antistatic effect can be adjusted. In addition, examples of commercially available polyether-modified silicone products include KF-351A, KF-352A, KF-353, KF-354L, KF-355A, and KF-642 (manufactured by Shin-Etsu Chemical Co., Ltd.), SH8400, SH8700, and SF8410 (manufactured by Dow Corning Toray Co., Ltd.), TSF-4440, TSF-4441, TSF-4445, TSF-4446, and TSF-4450 (manufactured by Momentive Performance Materials), and BYK-300, BYK-306, BYK-307, BYK-320, BYK-325, and BYK-330 (manufactured by BYK-Chemie). The amount of polyether-modified silicone added to a release agent containing dimethylpolysiloxane as its main component varies depending on the type of polyether-modified silicone and the degree of compatibility with the release agent, but can be set taking into consideration the desired peel electrification voltage, staining properties on the adherend, adhesive properties, etc. when peeling the surface protection film from the adherend.

[0034] There are no particular limitations on the method for mixing the dimethylpolysiloxane-based release agent with the antistatic agent and antistatic aid. Any of the following methods may be used: adding the antistatic agent and antistatic aid to the dimethylpolysiloxane-based release agent, mixing, and then adding and mixing a catalyst for curing the release agent; diluting the dimethylpolysiloxane-based release agent with an organic solvent, then adding and mixing the antistatic agent, antistatic aid, and release agent curing catalyst; or diluting the dimethylpolysiloxane-based release agent with an organic solvent, adding and mixing a catalyst, and then adding and mixing the antistatic agent and antistatic aid. If necessary, an adhesion improver such as a silane coupling agent or a material that enhances the antistatic effect, such as a compound containing a polyoxyalkylene group, may be added.

[0035] The mixing ratio of the dimethylpolysiloxane-based release agent to the antistatic agent and antistatic aid is not particularly limited, but a ratio of about 5 to 100 parts by weight of the combined solids of the antistatic agent and antistatic aid to 100 parts by weight of the dimethylpolysiloxane-based release agent is preferred. If the combined solids content of the antistatic agent and antistatic aid is less than 5 parts by weight per 100 parts by weight of the dimethylpolysiloxane-based release agent, the amount of the antistatic agent and antistatic aid transferred to the surface of the adhesive layer will be reduced, making it difficult for the adhesive to exhibit its antistatic function. Furthermore, if the combined solids content of the antistatic agent and antistatic aid is more than 100 parts by weight per 100 parts by weight of the dimethylpolysiloxane-based release agent, the dimethylpolysiloxane-based release agent, along with the antistatic agent and antistatic aid, will be transferred to the surface of the adhesive layer, potentially reducing the adhesive properties of the adhesive.

[0036] The method for forming the pressure-sensitive adhesive layer 2 on the base film 1 of the surface protection film 10 according to the present invention and the method for laminating the release film 5 thereto may be any known method and are not particularly limited. Specifically, examples include (1) a method in which a resin composition for forming the pressure-sensitive adhesive layer 2 is applied to one side of the base film 1, followed by drying to form a pressure-sensitive adhesive layer, and then laminating the release film 5, and (2) a method in which a resin composition for forming the pressure-sensitive adhesive layer 2 is applied to the surface of the release film 5, followed by drying to form a pressure-sensitive adhesive layer, and then laminating the base film 1, and either method may be used.

[0037] The pressure-sensitive adhesive layer 2 may be formed on the surface of the base film 1 by a known method. Specifically, known coating methods such as reverse coating, comma coating, gravure coating, slot die coating, Mayer bar coating, and air knife coating can be used.

[0038] Similarly, the release agent layer 4 may be formed on the resin film 3 by a known method. Specifically, known coating methods such as gravure coating, Mayer bar coating, and air knife coating can be used.

[0039] The surface protection film 10 according to the present invention having the above configuration preferably has a surface potential of +0.7 kV to -0.7 kV when the pressure-sensitive adhesive layer is peeled off from the adherend, i.e., the optical film. The surface potential is more preferably +0.5 kV to -0.5 kV, and particularly preferably +0.1 kV to -0.1 kV. This surface potential can be adjusted by adjusting the types and amounts of the antistatic agent and antistatic auxiliary contained in the release agent layer.

[0040] FIG. 2 is a cross-sectional view showing the surface protection film of the present invention with the release film peeled off. When the release film 5 is peeled off from the surface protection film 10 shown in FIG. 1, a portion of the antistatic agent and antistatic aid (reference numeral 7) contained in the release agent layer 4 of the release film 5 is transferred (adhered) to the surface of the pressure-sensitive adhesive layer 2 of the surface protection film 10. Therefore, in FIG. 2, the antistatic agent and antistatic aid transferred to the surface of the pressure-sensitive adhesive layer 2 of the surface protection film 11 in a state where the release film has been peeled off are schematically shown by spots reference numeral 7. The transfer of the antistatic agent and antistatic aid components 7 from the release film 5 to the surface of the pressure-sensitive adhesive layer 2 reduces the peel electrification voltage when the pressure-sensitive adhesive layer 2 is peeled off from the adherend, compared to the pressure-sensitive adhesive layer 2 before transfer. The peel electrification voltage when the pressure-sensitive adhesive layer is peeled off from the adherend can be measured by a known method. For example, after a surface protection film is attached to an adherend such as a polarizing plate, the surface protection film is peeled off at a peeling speed of 40 m per minute using a high-speed peel tester (manufactured by Tester Sangyo Co., Ltd.), while the surface potential of the adherend surface is measured every 10 ms using a surface potential meter (manufactured by Keyence Corporation). The maximum absolute value of the surface potential is measured as the peel electrification voltage (kV). In the surface protection film of the present invention, when the surface protection film 11 from which the release film shown in Fig. 2 has been peeled is attached to an adherend, the antistatic agent and antistatic auxiliary transferred from the release agent layer to the surface of the pressure-sensitive adhesive layer 2 come into contact with the surface of the adherend, thereby making it possible to keep the peeling electrification voltage low when the surface protection film is peeled off from the adherend again.

[0041] FIG. 3 is a cross-sectional view showing an embodiment of an optical component according to the present invention. The release film 5 is peeled off from the surface protection film 10 of the present invention, and in a state where the pressure-sensitive adhesive layer 2 is exposed, the surface protection film 10 is attached to an optical component 8 as an adherend via the pressure-sensitive adhesive layer 2 . 3 shows an optical component 20 to which a surface protective film 11 of the present invention is attached. Examples of optical components include optical films such as polarizing plates, retardation plates, lens films, polarizing plates that also serve as retardation plates, and polarizing plates that also serve as lens films. Such optical components are used as components of liquid crystal display devices such as liquid crystal display panels, optical devices for various instruments, and the like. Other examples of optical components include optical films such as anti-reflection films, hard coat films, and transparent conductive films for touch panels. According to the optical component of the present invention, peeling electrification voltage can be kept sufficiently low when the surface protection film 11 is peeled off from the adherend, that is, the optical component (optical film). As a result, there is no risk of damaging circuit components such as driver ICs, TFT elements, and gate line driving circuits, and production efficiency in the process of manufacturing liquid crystal display panels and the like can be improved and the reliability of the production process can be maintained. [Example]

[0042] The present invention will now be further illustrated by examples. Example 1 (Preparation of surface protection film) 5 parts by weight of an addition reaction type silicone (Dow Corning Toray Co., Ltd., product name: SRX-345), 7.5 parts by weight of a 10% ethyl acetate solution of tri-n-butylmethylammonium bistrifluoromethanesulfonimide (FC-4400, 3M Co.), an ionic compound with a melting point of 27.5°C, 0.3 parts by weight of a polyether-modified silicone (Dow Corning Toray Co., Ltd., product name: SH8400), 95 parts by weight of a 1:1 mixed solvent of toluene and ethyl acetate, and 0.05 parts by weight of a platinum catalyst (Dow Corning Toray Co., Ltd., product name: SRX-212) were mixed and stirred to prepare a coating material for forming the release agent layer of Example 1. The coating material for forming the release agent layer of Example 1 was applied to the surface of a 38 μm-thick polyethylene terephthalate film using a Mayer bar to a dried thickness of 0.2 μm, and the mixture was dried in a hot air circulating oven at 120°C for 1 minute to obtain the release film of Example 1. Separately, 30 parts by weight of an acrylate copolymer with a weight average molecular weight of 470,000, obtained by copolymerizing 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate in a weight ratio of 96:4, was dissolved in 70 parts by weight of ethyl acetate to prepare an adhesive polymer solution (ethyl acetate solution with a solid content of 30%). 1.2 parts by weight of an HDI-based curing agent (manufactured by Tosoh Corporation, product name: Coronate (registered trademark) HX) was added to and mixed with this to prepare the adhesive composition of Example 1. Note that "HDI-based" refers to "hexamethylene diisocyanate-based." The pressure-sensitive adhesive composition of Example 1 was applied to the surface of a 38 μm-thick polyethylene terephthalate film so that the thickness after drying would be 20 μm, and then dried for 2 minutes in a hot air circulating oven at 100°C to form a pressure-sensitive adhesive layer. The release agent layer (silicone-treated surface) of the release film of Example 1 prepared above was then attached to the surface of this pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive film was kept warm in an environment of 40°C for 5 days to cure the pressure-sensitive adhesive layer, thereby obtaining a surface protection film of Example 1.

[0043] (Comparative Example 1) 5 parts by weight of addition reaction type silicone (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-345), 95 parts by weight of a 1:1 mixed solvent of toluene and ethyl acetate, and 0.05 parts by weight of a platinum catalyst (manufactured by Toray Dow Corning Co., Ltd., product name: SRX-212) were combined, stirred, and mixed to prepare a coating material for forming the release agent layer of Comparative Example 1. The coating material for forming the release agent layer of Comparative Example 1 was applied to the surface of a polyethylene terephthalate film with a thickness of 38 μm using a Mayer bar so that the thickness after drying would be 0.2 μm, and the coating was dried for 1 minute in a hot air circulating oven at 120°C to obtain the release film of Comparative Example 1. On the other hand, 3 parts by weight of a 10% ethyl acetate solution of tri-n-butylmethylammonium bistrifluoromethanesulfonimide (FC-4400 manufactured by 3M), an ionic compound with a melting point of 27.5°C, and 1.2 parts by weight of an HDI-based curing agent (manufactured by Tosoh Corporation, product name: Coronate (registered trademark) HX) were added to and mixed with 100 parts by weight of the adhesive polymer solution of Example 1 (ethyl acetate solution with a solid content of 30%) to prepare an adhesive composition of Comparative Example 1. The pressure-sensitive adhesive composition of Comparative Example 1 was applied to the surface of a 38 μm-thick polyethylene terephthalate film so that the thickness after drying would be 20 μm, and then dried for 2 minutes in a hot air circulating oven at 100°C to form a pressure-sensitive adhesive layer. The release agent layer (silicone-treated surface) of the release film of Comparative Example 1 prepared above was then attached to the surface of this pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive film was kept warm in an environment of 40°C for 5 days to cure the pressure-sensitive adhesive layer, thereby obtaining a surface protection film of Comparative Example 1.

[0044] (Comparative Example 2) The surface protection film of Comparative Example 2 was obtained in the same manner as Comparative Example 1, except that the adhesive layer did not contain tri-n-butylmethylammonium bistrifluoromethanesulfonimide, an ionic compound with a melting point of 27.5°C.

[0045] (Comparative Example 3) A surface protection film of Comparative Example 3 was obtained in the same manner as in Example 1, except that the release agent layer did not contain polyether-modified silicone.

[0046] Example 2 The surface protection film of Example 2 was obtained in the same manner as in Example 1, except that instead of the adhesive composition of Example 1, an adhesive composition was used in which 30 parts by weight of an acrylate copolymer having a weight average molecular weight of 480,000, which was copolymerized with 2-ethylhexyl acrylate, butyl acrylate, and 2-hydroxyethyl acrylate in a weight ratio of 60:36:4, was dissolved in 70 parts by weight of ethyl acetate, and 1.2 parts by weight of an HDI-based curing agent (manufactured by Tosoh Corporation, product name: Coronate (registered trademark) HX) was added to and mixed with 100 parts by weight of an adhesive polymer solution (ethyl acetate solution with a solids content of 30%).

[0047] Example 3 The surface protection film of Example 3 was obtained in the same manner as in Example 1, except that instead of the adhesive composition of Example 1, an adhesive composition was used in which 30 parts by weight of a (meth)acrylate copolymer having a weight average molecular weight of 380,000, which was copolymerized in a weight ratio of 86:10:4, was dissolved in 70 parts by weight of ethyl acetate to form 100 parts by weight of an adhesive polymer solution (ethyl acetate solution with a solids content of 30%), to which 1.2 parts by weight of an HDI-based curing agent (manufactured by Tosoh Corporation, product name: Coronate (registered trademark) HX) was added and mixed.

[0048] The evaluation test methods and results are shown below. <Method for measuring the peel strength of release film> A sample of the surface protection film was cut to a width of 50 mm and a length of 150 mm. Under a test environment of 23°C x 50% RH, the release film was peeled off in a 180° direction at a peeling rate of 300 mm / min using a tensile tester, and the strength was measured, which was taken as the peel strength of the release film (N / 50 mm).

[0049] <Method for measuring adhesive strength of surface protection film> An anti-glare, low-reflection treated polarizing plate (AG-LR polarizing plate) was attached to the surface of a glass plate using a laminating machine with double-sided adhesive tape. A surface protection film cut to a width of 25 mm was then attached to the surface of the polarizing plate, and the plate was then stored for one day in a test environment of 23°C and 50% RH. The surface protection film was then peeled off in a 180° direction at a peeling rate of 300 mm / min using a tensile tester, and the strength was measured, which was taken as the adhesive strength (N / 25 mm).

[0050] <Method for measuring the peeling electrification voltage of surface protection film> An anti-glare, low-reflection treated polarizing plate (AG-LR polarizing plate) was attached to the surface of a glass plate using a laminating machine with double-sided adhesive tape. A surface protection film cut to a width of 25 mm was then attached to the surface of the polarizing plate, and the plate was then stored for one day in a test environment of 23°C and 50% RH. The surface protection film was then peeled off at a peeling speed of 40 m / min using a high-speed peel tester (manufactured by Tester Sangyo Co., Ltd.), while the surface potential of the polarizing plate surface was measured every 10 ms using a surface potential meter (manufactured by Keyence Corporation). The maximum absolute value of the surface potential was recorded as the peeling electrification voltage (kV).

[0051] <Method for checking the surface contamination of surface protection films> An anti-glare, low-reflection treated polarizing plate (AG-LR polarizing plate) was attached to the surface of a glass plate using a laminating machine with double-sided adhesive tape. A surface protection film cut to a width of 25 mm was then attached to the surface of the polarizing plate, and the plate was then stored in a test environment of 23°C and 50% RH for 3 and 30 days. The surface protection film was then peeled off, and the polarizing plate surface was visually inspected for contamination. The evaluation criteria for surface contamination were as follows: no contamination transfer to the polarizing plate was marked with (○), and contamination transfer to the polarizing plate was marked with (×).

[0052] The results of measurements of the obtained surface protection films of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Tables 1 and 2. "2EHA" means 2-ethylhexyl acrylate, "HEA" means 2-hydroxyethyl acrylate, "BA" means butyl acrylate, "#400G" means methoxypolyethylene glycol (400) methacrylate, and "FC4400" means tri-n-butylmethylammonium bistrifluoromethanesulfonimide. In Tables 1 and 2, the composition of the adhesive layer is expressed in parts by weight so that the total amount of the adhesive polymer (solid content) is approximately 100 parts by weight. Therefore, in the adhesive layer of Comparative Example 1, the weight ratio of the adhesive polymer (solid content) to FC4400 was 30 parts by weight:0.3 parts by weight = 100 parts by weight:1.0 part by weight.

[0053] [Table 1]

[0054] [Table 2]

[0055] The measurement results shown in Tables 1 and 2 reveal the following: The surface protection films of Examples 1 to 3 according to the present invention have suitable adhesive strength, do not contaminate the surface of the adherend, and have low peel electrification voltage when peeled from the adherend. On the other hand, the surface protection film of Comparative Example 1, which contained an antistatic agent in the adhesive layer, had a low and favorable peeling electrification voltage when the surface protection film was peeled off from the adherend, but caused a lot of contamination on the adherend after peeling. Furthermore, the surface protection film of Comparative Example 2, in which neither the adhesive layer of the surface protection film nor the release agent layer of the release film contained an antistatic agent, exhibited good stain resistance to the adherend, but the peeling electrification voltage was high when the surface protection film was peeled from the adherend. In other words, it is difficult to achieve both reduced peeling electrification voltage and resistance to contamination of the adherend in the surface protection film of Comparative Example 1, in which an antistatic agent is contained in the adhesive layer of the surface protection film, and the surface protection film of Comparative Example 2, in which an antistatic agent is not contained in either the adhesive layer of the surface protection film or the release layer of the release film. On the other hand, in the surface protection films of Examples 1 to 3, in which an antistatic agent and an antistatic auxiliary were incorporated into the release agent layer of the release film and then the antistatic agent and antistatic auxiliary from the release agent layer were transferred only to the surface of the adhesive layer, the addition of a small amount of antistatic auxiliary had the effect of significantly reducing the peeling electrification voltage, so there was no contamination of the adherend and the peeling antistatic performance was also good. Furthermore, the surface protection film of Comparative Example 3, in which only an antistatic agent but no antistatic auxiliary was contained in the release agent layer, did not stain the adherend and had good antistatic performance upon peeling. However, the peeling electrification voltage was higher than that of the surface protection films of Examples 1 to 3, in which the release agent layer contained both an antistatic agent and an antistatic auxiliary. [Industrial Applicability]

[0056] The surface protection film of the present invention can be used to protect the surface of, for example, optical films such as polarizing plates, retardation plates, and lens films, as well as various other optical components, in the production process of the optical components, etc. Furthermore, the surface protection film of the present invention can reduce the amount of static electricity generated when peeled from an adherend, and reduces changes over time in antistatic performance upon peeling and contamination of the adherend, thereby improving the yield of the production process and having great industrial utility value. [Explanation of symbols]

[0057] 1...base film, 2...adhesive layer, 3...resin film, 4...release agent layer, 5...release film, 7...antistatic agent and antistatic auxiliary, 8...adherend (optical component), 10...surface protection film, 11...surface protection film with release film removed, 20...optical component with surface protection film attached.

Claims

1. A surface protection film comprising a base film having a pressure-sensitive adhesive layer formed on one side thereof and a release film for surface protection films, capable of transferring an antistatic agent, attached to the surface of the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer is obtained by crosslinking a pressure-sensitive adhesive composition containing a (meth)acrylate copolymer and a crosslinking agent, and does not contain an antistatic agent; the release film for surface protective films is formed by laminating, on one surface of a resin film, a release agent layer containing a release agent mainly composed of dimethylpolysiloxane, an antistatic agent that does not react with the release agent, and an antistatic auxiliary; the antistatic agent component is an ionic compound (but not an alkali metal salt) having a melting point of less than 30°C, and the antistatic auxiliary is a polyether-modified silicone; the ionic compound is an ionic compound having a cation and an anion, when the release film for a surface protective film is attached to the surface of the pressure-sensitive adhesive layer via the release agent layer, the antistatic agent component and the antistatic auxiliary of the release agent layer are transferred to the surface of the pressure-sensitive adhesive layer, A surface protection film characterized in that after the surface protection film is attached to an adherend, the surface potential when the pressure-sensitive adhesive layer of the surface protection film is peeled off from the adherend is +0.7 kV to −0.7 kV.

2. 2. The surface protective film according to claim 1, wherein the cation is one selected from the group consisting of an imidazolium ion, a pyridinium ion, an ammonium ion, a sulfonium ion, and a phosphonium ion.

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