KR102775982B1 - Surface-protective film and optical component attached with the same - Google Patents

Abstract

The present invention provides a surface protection film which can be bonded to an optical film having an uneven surface, causes little contamination of an adherend, and further, has low contamination properties of an adherend that do not change over time, does not deteriorate over time, and has excellent peeling antistatic performance, and an optical component using the same. A surface protection film (5) in which a release agent layer (2) containing an antistatic agent (3) composed of an alkali metal salt and a release agent is formed on one surface of a base film (1) made of a transparent resin, and an adhesive layer (4) is formed on the other surface of the base film (1), wherein the antistatic agent (3) component composed of an alkali metal salt is present only on the surface of the adhesive layer (4).

Description

SURFACE-PROTECTIVE FILM AND OPTICAL COMPONENT ATTACHED WITH THE SAME

The present invention relates to a surface protection film bonded to the surface of an optical component (hereinafter, also sometimes referred to as an optical film). More specifically, the present invention relates to a surface protection film that causes little contamination of an adherend and, further, which does not change in contamination of the adherend over time, and to an optical component using the same. In addition, the present invention provides a surface protection film that suppresses a peeling voltage at the time of peeling the surface protection film to a low level even when a constituent member of a polarizing plate, which is an optical component, is replaced (changed from a TAC film to an acrylic film or polyester film, or from a water-based adhesive to an ultraviolet-curable adhesive), and to an optical component bonded thereto.

Here, the optical components in the present invention refer to polarizing plates, phase difference plates, display lens films, etc.

When manufacturing or returning optical films such as polarizing plates, phase difference plates, display lens films, antireflection films, hard coat films, transparent conductive films for touch panels, and optical products such as displays using the same, a surface protection film is bonded to the surface of the optical film to prevent contamination or scratches on the surface during subsequent processes. In order to reduce the effort of peeling off and then re-bonding the surface protection film and to increase work efficiency, the appearance inspection of the optical film as a product is sometimes performed with the surface protection film bonded to the optical film.

Conventionally, surface protection films having an adhesive layer formed on one side of a base film have been generally used to prevent the attachment of scratches or contamination in the manufacturing process of optical products. The surface protection film is bonded to an optical film via a non-adhesive adhesive layer. The non-adhesive adhesive layer is intended to enable easy peeling when the surface protection film after use is peeled off from the surface of the optical film and to prevent the adhesive from being attached to the optical film of the adherend and remaining therein (so-called prevention of adhesive residue).

Recently, in the production process of liquid crystal display panels, there have been a small number of cases in which circuit components such as driver ICs for controlling the display screen of a liquid crystal display are destroyed or the alignment of liquid crystal molecules is damaged due to the peeling voltage generated when peeling and removing a surface protection film laminated on an optical film.

In addition, in order to reduce the power consumption of liquid crystal display panels, the driving voltage of liquid crystal materials is lowered, and accordingly, the breakdown voltage of driver ICs is also lowered. Recently, it has been required to set the peeling voltage within the range of +0.7 kV to -0.7 kV.

In addition, conventional polarizing plates were manufactured by bonding triacetyl cellulose films (TAC films) to both sides of a polarizer made of iodine-impregnated polyvinyl alcohol (PVA) with an aqueous adhesive to protect the polarizer, but recently, polarizing plates using acrylic films, cyclic polyolefin films, or polyester films instead of the TAC film, and polarizing plates using ultraviolet-curable adhesives instead of aqueous adhesives have also been used. As the constituent materials of the polarizing plate change, there is also a problem that the peeling voltage generated when the surface protection film is peeled and removed is higher than when a polarizing plate with a conventional configuration is used.

In addition, with the recent spread of 3D displays (stereoscopic displays), there are those in which an FPR (Film Patterned Retarder) film is bonded to the surface of an optical film such as a polarizing plate. The FPR film is bonded after the surface protection film bonded to the surface of the optical film such as a polarizing plate is peeled off. However, if the surface of the optical film such as a polarizing plate is contaminated with an adhesive or antistatic agent used in the surface protection film, there is a problem in that the FPR film is difficult to adhere. Therefore, the surface protection film used for the purpose is required to have little contamination of the adherend.

Meanwhile, some liquid crystal panel manufacturers have adopted a method of evaluating the degree of contamination of the surface protection film on the adherend by peeling off the surface protection film adhered to an optical film such as a polarizing plate, re-adhering it while mixing in air bubbles, heat-treating it under specified conditions, and then peeling off the surface protection film to observe the surface of the adherend. In this evaluation method, even if the surface contamination of the adherend is trace, if there is a difference in the surface contamination of the adherend between the part where the air bubbles were mixed and the part where the adhesive of the surface protection film was in contact, traces of the air bubbles (sometimes called air bubble stains) will remain. For this reason, this is a very strict evaluation method for evaluating the degree of contamination of the surface of the adherend. Recently, there has been a demand for a surface protection film that has extremely little contamination of the surface of the adherend and can pass the judgment by this strict evaluation method.

In order to prevent problems caused by high peeling voltage that occurs when peeling the surface protection film from the adherend after bonding the surface protection film to the optical film as an adherend, a surface protection film using an adhesive layer containing an antistatic agent for suppressing the peeling voltage to a low level has been proposed.

For example, Patent Document 1 discloses a surface protection film using an adhesive composed of an alkyltrimethylammonium salt, an acrylic polymer containing a hydroxyl group, and a polyisocyanate.

In addition, patent document 2 discloses an adhesive composition comprising an ionic liquid and an acrylic polymer having an acid value of 1.0 or less, and an adhesive sheet using the same.

In addition, Patent Document 3 discloses an 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.

In addition, Patent Document 4 discloses an 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.

Japanese Patent Publication No. 2005-131957 Japanese Patent Publication No. 2005-330464 Japanese Patent Publication No. 2005-314476 Japanese Patent Publication No. 2006-152235

In the surface protection films described in the above patent documents 1 to 4, an antistatic agent is added to the inside of the adhesive layer. Therefore, as the thickness of the adhesive layer increases, and as time elapses after bonding the surface protection film to the adherend, the amount of the antistatic agent transferred from the adhesive layer to the adherend tends to increase with respect to the adherend to which the surface protection film is bonded. In addition, if the amount of the antistatic agent transferred to the adherend increases, there is a possibility that the appearance quality of the optical film as the adherend deteriorates, or the adhesiveness of the FPR film deteriorates when bonding the FPR film.

In this way, if the thickness of the adhesive layer is made thin to reduce the change in the antistatic agent over time that transfers from the adhesive layer to the adherend, other problems arise. For example, when used on an optical film with a rough surface, such as a polarizing plate that has been anti-glare treated to prevent glare, the adhesive layer cannot follow the roughness of the optical film surface, causing bubbles to be mixed in, or the bonding area between the optical film and the adhesive layer is reduced, resulting in a decrease in adhesive strength and a problem in which the surface protection film comes off or peels off during use.

In addition, if the amount of antistatic agent added to the adhesive layer is reduced in order to reduce the change in antistatic agent over time that occurs when the surface protection film is peeled off from the adherend, there is a risk that the peeling voltage generated when the surface protection film is peeled off from the adherend may increase, resulting in the destruction of circuit components such as driver ICs or damage to the alignment of liquid crystal molecules.

The present invention has been made in consideration of the above circumstances, and has as its object the provision of a surface protection film that is bonded to the surface of an optical film, which can be bonded even to an optical film having an uneven surface, causes very little contamination of an adherend, and further, has low contamination of an adherend that does not change over time, and an optical component using the surface protection film.

In addition, the present invention aims to provide a surface protection film and an optical component using the same, which suppresses the peeling voltage at the time of peeling the surface protection film to a low level even when the component of a polarizing plate, which is an optical component, is replaced (changed from a TAC film to an acrylic film or polyester film, or from a water-based adhesive to an ultraviolet-curable adhesive).

The inventors of the present invention have conducted careful studies to solve these problems. In order to reduce contamination of the adherend and also to reduce the change in contamination over time, it is necessary to reduce the content of the antistatic agent, which is presumed to be the cause of contamination of the adherend. However, when the content of the antistatic agent is reduced, the peeling voltage when peeling the surface protection film from the adherend increases.

Accordingly, the inventors of the present invention studied a method for suppressing the peeling voltage when peeling a surface protection film from an adherend without increasing the content of an antistatic agent.

The present inventors first produced a surface protection film by coating and drying an adhesive composition not including an antistatic agent on one side of a substrate to laminate an adhesive layer, and laminating a release agent layer containing an antistatic agent on the other side of the substrate. Thereafter, the surface protection film was wound into a roll shape with the adhesive layer facing inward, so that the antistatic agent component contained in the release agent layer was transferred to the surface of the adhesive layer, and existed only on the surface of the adhesive layer. They found that when this surface protection film was once bonded to an optical film as an adherend, the peeling voltage was suppressed low when peeling it from the adherend, and furthermore, it was difficult for the adherend to be contaminated, and thus the present invention was completed.

The surface protection film of the present invention is formed by coating and drying an adhesive composition that does not contain an antistatic agent on one side of a substrate to laminate an adhesive layer, laminating a release agent layer containing an antistatic agent on the other side of the substrate, and then winding the surface protection film so that the adhesive layer faces inward to form a roll, thereby transferring an antistatic agent component contained in the release agent layer to the surface of the adhesive layer. The present invention is a technical idea in which, when the surface protection film wound in this roll shape is rewound from the roll shape and bonded to an adherend, contamination of the adherend is suppressed to a low level, and a peeling voltage is suppressed to a low level when peeling the surface protection film from an optical film, which is an adherend.

In order to solve the above problem, the present invention provides a surface protection film in which a release agent layer containing an antistatic agent and a release agent made of an alkali metal salt is formed on one side of a base film made of a transparent resin, and an adhesive layer is formed on the other side of the base film, characterized in that the antistatic agent component made of the alkali metal salt exists only on the surface of the adhesive layer.

In addition, it is preferable that the adhesive layer is an acrylic adhesive layer containing a crosslinked (meth)acrylate copolymer.

In addition, it is preferable that the unfolding force from the state of being rolled into a roll shape of the surface protection film be 0.03 to 0.3 N/50 mm.

In addition, it is preferable that the surface potential when peeling the adhesive layer from the optical film, which is the adherend, is +0.7 kV to -0.7 kV.

In addition, it is preferable that the substrate film is wound in a roll shape with the adhesive layer facing inward so that the release agent layer and the adhesive layer are in contact with each other.

In addition, the present invention provides an optical component formed by bonding the surface protection film with the adhesive layer interposed therebetween.

The surface protection film of the present invention is a surface protection film that is bonded to the surface of an optical film, and can also be bonded to an optical film having an uneven surface.

In addition, according to the present invention, it is possible to provide a surface protection film and an optical component using the same, which causes very little contamination of an adherend and whose contamination of an adherend does not change over time.

In addition, according to the present invention, even if the constituent elements of a polarizing plate, which is an optical component, are changed (changed from a TAC film to an acrylic film, a ring-shaped polyolefin film or a polyester film, or from a water-based adhesive to an ultraviolet-curable adhesive), a surface protection film that suppresses the peeling voltage when peeling the surface protection film to a low level and an optical component using the same can be provided.

In addition, the surface protection film rolled into a roll shape of the present invention is a surface protection film rolled into a roll shape with the adhesive layer facing inward so that the release agent layer and the adhesive layer are in contact with the base film, and the antistatic agent component comprising the alkali metal salt is transferred from the release agent layer to the surface of the adhesive layer, and exists only on the surface of the adhesive layer.

That is, the present invention has the characteristics of reducing the peeling voltage when peeling the surface protection film from the adherend after attaching the surface protection film, which is rewound from a surface protection film wound in a roll shape, to the adherend, and also reducing the change in peeling antistatic performance over time and contamination of the adherend, thereby making it possible to improve the productivity and yield of optical components as adherends.

Figure 1 is a conceptual cross-sectional view showing a surface protection film rolled into a roll shape according to the present invention.
Figure 2 is a conceptual cross-sectional view showing a state in which a release agent layer and an adhesive layer are in contact with each other in a state in which the surface protection film of the present invention is rolled into a roll shape.
FIG. 3 is a cross-sectional view showing one example of bonding a surface protection film of the present invention to an optical component.

Hereinafter, the present invention will be described in detail based on embodiments.

Fig. 1 is a conceptual cross-sectional view showing a surface protection film (10) in a roll-shaped state of the present invention. The surface protection film (10) in a roll-shaped state shown on the right side of Fig. 1 is a surface protection film (5) according to the present invention wound in a roll shape with the adhesive layer (4) facing inward (roll body of the surface protection film (5)). In addition, the left side of Fig. 1 is a conceptual cross-sectional view showing the surface protection film (5) rewound from a roll shape in the direction of the arrow, enlarged in the thickness direction.

This surface protection film (5) has a release agent layer (2) containing an antistatic agent (3) made of an alkali metal salt on one side of a transparent base film (1), and an adhesive layer (4) formed on the other side of the base film (1). By winding the surface protection film (5) having the release agent layer (2) on one side of the base film (1) and the adhesive layer (4) on the other side of the base film in a roll shape with the adhesive layer (4) facing inward so that the release agent layer (2) and the adhesive layer (4) are in contact, a surface protection film (10) wound in a roll shape is obtained in which the antistatic agent (3) component contained in the release agent layer (2) is transferred to the surface of the adhesive layer (4), and exists only on the surface of the adhesive layer (4).

As the base film (1) used in the surface protection film (5) according to the present invention, a base film made of a resin having transparency and flexibility is used. As a result, the surface protection film (5) can be bonded to the optical component as an adherend, and an external appearance inspection of the optical component can be performed. As the film made of a transparent resin used as the base film (1), a polyester film such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or polybutylene terephthalate is preferably used. In addition to the polyester film, a film made of another resin can also be used as long as it has the necessary strength and optical properties. The base film (1) may be a non-stretched film, or a uniaxially or biaxially oriented film. In addition, the stretching ratio of the stretched film or the axial orientation angle formed along with the crystallization of the stretched film may be controlled to a specific value.

The thickness of the base film (1) used in the surface protection film (5) according to the present invention is not particularly limited, but for example, a thickness of about 12 to 100 ㎛ is preferable, and a thickness of about 20 to 75 ㎛ is more preferable because it is easy to handle.

In addition, if necessary, easy-adhesion treatment such as surface modification by corona discharge or application of an anchor coat agent may be performed on the surface of the substrate film (1).

The release agent layer (2) formed on the surface protection film (5) according to the present invention is formed using a release agent containing an antistatic agent (3) composed of an alkali metal salt. Examples of the release agent include a silicone-based release agent, a release agent containing a long-chain alkyl group, a fluorine-based release agent, a release agent composed of a copolymer of silicone or fluorine and an organic material, and a release agent composed of a mixture of an organic resin and the above-described release agent.

Examples of the silicone-based release agent include known silicone-based release agents such as addition reaction type, condensation reaction type, cationic polymerization type, and radical polymerization type. Commercially available products of addition reaction type silicone-based release agents include, for example, KS-776A, KS-847T, KS-779H, KS-837, KS-778, KS-830 (manufactured by Shin-Etsu Chemical Co., Ltd.), SRX-211, SRX-345, SRX-357, SD7333, SD7220, SD7223, LTC-300B, LTC-350G, LTC-310 (manufactured by Dow Corning Toray Co., Ltd.). Commercially available products of the condensation reaction type include, for example, SRX-290, SYLOFF-23 (manufactured by Dow Corning Toray Co., Ltd.). Examples of products commercially available as cationic polymerization types include TPR-6501, TPR-6500, UV9300, UV9315, UV9430 (manufactured by Momentive Performance Materials), and X62-7622 (manufactured by Shin-Etsu Chemical Co., Ltd.). Examples of products commercially available as radical polymerization types include X62-7205 (manufactured by Shin-Etsu Chemical Co., Ltd.). In addition, in order to adjust the peeling performance of these peeling agents, silicone resin (silicon resin composed of R3SiO1/2 units and SiO4/2 units), silica, ethyl cellulose, etc. may be added.

Examples of the long-chain alkyl group-containing stripping agent include known long-chain alkyl group-containing stripping agents, such as long-chain alkyl group-containing amino alkyd resins, long-chain alkyl group-containing acrylic resins, and long-chain aliphatic pendant resins (reaction products of at least one active hydrogen-containing polymer selected from the group of compounds consisting of polyvinyl alcohol, ethylene/vinyl alcohol copolymers, polyethyleneimine, and hydroxyl group-containing cellulose derivatives, and long-chain alkyl group-containing isocyanates). It may be a stripping agent that performs a curing reaction by adding a curing agent and an ultraviolet initiator, or a stripping agent that solidifies by volatilizing a solvent.

As the "long-chain alkyl group", an alkyl group having 8 to 30 carbon atoms is preferable, and may also have 10 or more, 12 or more, 18 or less, or 24 or less carbon atoms, and among these, a linear alkyl group is preferable. Specific examples thereof include one or more alkyl groups selected from a decyl group, an undecyl group, a lauryl group, a dodecyl group, a tridecyl group, a myristyl group, a tetradecyl group, a pentadecyl group, a cetyl group, a palmityl group, a hexadecyl group, a heptadecyl group, a stearyl group, an octadecyl group, a nonadecyl group, an icosyl group, a docosyl group, and the like.

Examples of products commercially available as long-chain alkyl group-containing removing agents include Ashio Resin (registered trademark) RA-30 manufactured by Ashio Sangyo Co., Ltd., Piroyl (registered trademark) 1010, Piroyl 1010S, Piroyl 1050, Piroyl HT manufactured by Ipposha Yuchi Kogyo Co., Ltd., Resem N-137 manufactured by Chukyo Yuchi Co., Ltd., Exepal (registered trademark) PS-MA manufactured by Kao Co., Ltd., and Tespine (registered trademark) 303 manufactured by Hitachi Chemical Co., Ltd.

Examples of fluorine-based stripping agents include vinyl ether polymers containing perfluoroalkyl groups, and coating agents in which fluorine resins such as tetrafluoroethylene and trifluoroethylene are dispersed in a binder resin.

Examples of release agents composed of copolymers of silicone or fluorine and organic materials include those obtained by graft copolymerizing silicone or fluorine resin onto acrylic resin, and those obtained by copolymerizing silicone onto alkyd resin. Examples of commercially available release agents composed of copolymers of silicone or fluorine and organic materials include Cymac (registered trademark) manufactured by Toa Synthetic Co., Ltd. and Tespine (registered trademark) manufactured by Hitachi Chemical Polymer Co., Ltd.

Examples of the organic resin used in the release agent comprising a mixture of an organic resin and the release agent include polyester resin, epoxy resin, acrylic resin, urethane resin, phenol resin, alkyd resin, amino alkyd resin, polyolefin resin (polyethylene, polypropylene, cyclic polyolefin), polyvinyl alcohol, cellulose resin, melamine resin, etc.

The selection of the release agent used in the surface protection film of the present invention needs to be done in consideration of the unfolding force of the surface protection film. In the surface protection film according to the present invention, the surface protection film wound in a roll shape has a release agent layer and an adhesive layer in contact. When using the surface protection film according to the present invention, it is used by unwinding from the surface protection film wound in a roll shape, but if the unfolding force when unwinding the surface protection film is large, there is a concern that the workability when unwinding the surface protection film deteriorates, or the surface of the adhesive layer of the surface protection film becomes rough (the surface is not smooth but becomes uneven), and air bubbles are likely to be included when bonding to an adherend. On the other hand, if the unfolding force when unrolling from a surface protection film wound in a roll shape is too low, there are concerns that the roll shape of the surface protection film may collapse during storage or transportation, the surface protection film may unroll more than necessary when used, wrinkles may be mixed in during bonding work with an adherend, or the bonded product of the surface protection film and the adherend may curl. For this reason, the unfolding force of the surface protection film from a roll state is preferably 0.03 to 0.3 N/50 mm. Depending on the adhesive used, a release agent having the aforementioned unfolding force of the surface protection film may be selected.

In addition, when the surface protection film (5) according to the present invention is bonded to an optical component (6) via an adhesive layer (4) (see FIG. 3), a release agent layer (2) is exposed on the surface of the surface protection film (5). However, when the surface protection film is used for the purpose of protecting a polarizing plate, when shipping the polarizing plate, etc., there are cases where the polarizing plate to which the surface protection film is bonded is cut to a predetermined size, and a plurality of polarizing plates on which the cut surface protection films are formed are overlapped. At that time, if the release agent layer is difficult to slip, a problem occurs in that multiple polarizing plates have to be lifted when lifting one polarizing plate on which the surface protection film is formed. In addition, if the release agent layer is excessively slippery, a problem also occurs in that the polarizing plates slip and are difficult to overlap when multiple polarizing plates on which the surface protection films are formed are overlapped. Therefore, when selecting a release agent constituting the release agent layer, it is necessary to consider slipperiness.

As the antistatic agent (3) included in the release agent layer (2), it is preferable that it has good dispersibility in the release agent solution and does not inhibit the curing of the release agent. In addition, in order to transfer the antistatic agent (3) component included in the release agent layer (2) to the surface of the adhesive layer (4) in contact with the release agent layer (2) and impart an antistatic function to the surface of the adhesive layer (4), an antistatic agent that does not react with the release agent is preferable. Such an antistatic agent is preferably an alkali metal salt.

As the alkali metal salt, metal salts composed of lithium, sodium, and potassium can be mentioned. Specifically, for example, a metal salt composed of a cation selected from Li ⁺ , Na ⁺ , and K ⁺ and an anion selected from Cl ^- , Br ^- , I ^- , BF ₄ ^- , PF ₆ ^- , SCN ^- , ClO ₄ ^- , CF ₃ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (C ₂ F ₅ SO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₃ C ^- is preferably used. Specific examples of alkali metal salts include lithium salts such as LiBr, LiI, LiBF ₄ , LiPF ₆ , LiSCN, LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, Li(C ₂ F ₅ SO ₂ ) ₂ N, and Li(CF ₃ SO ₂ ) ₃ C. These alkali metal salts may be used alone, or two or more types may be mixed and used. In order to stabilize the ionic substance, a compound containing a polyoxyalkylene structure may be added.

The amount of antistatic agent to be added to the release agent varies depending on the type of antistatic agent or the degree of compatibility with the release agent, but may be set by considering the desired peeling voltage when peeling the surface protection film from the adherend, contamination of the adherend, adhesive characteristics, etc. When the release agent is a silicone-based release agent, the mixing ratio (weight ratio) of the silicone-based release agent and the antistatic agent is preferably a value of 5 to 100 in terms of solid content of the antistatic agent with respect to 100 in terms of solid content of the silicone-based release agent, and more preferably a ratio of 5 to 60. If the amount of the antistatic agent added in terms of solid content is less than a ratio of 5 with respect to 100 in terms of solid content of the silicone-based release agent, the amount of antistatic agent transferred to the surface of the adhesive layer also decreases, and it becomes difficult for the adhesive to exhibit an antistatic function. In addition, if the amount of the antistatic agent added in terms of solid content exceeds a ratio of 100 to 100 of the solid content of the silicone-based release agent, the silicone-based release agent component is transferred to the surface of the adhesive layer together with the antistatic agent, which may reduce the adhesive properties of the adhesive.

The release agent layer (2) is composed of at least a release agent and an antistatic agent that does not react with the release agent. The method of mixing the release agent and the antistatic agent is not particularly limited. Any method may be used, such as a method of adding the antistatic agent to the release agent, mixing them, and then adding and mixing a release agent curing catalyst, a method of diluting the release agent in advance with an organic solvent, and then adding and mixing the antistatic agent and the release agent curing catalyst, or a method of diluting the release agent in advance with an organic solvent, adding and mixing the catalyst, and then adding and mixing the antistatic agent. In addition, the release agent layer (2) may contain, as necessary, an adhesion improver such as a silane coupling agent, a material that assists an antistatic effect such as a compound containing a polyoxyalkylene group, a material that imparts tensile properties such as a cellulose-based compound, a material that adjusts slipperiness, etc.

The formation of a release agent layer (2) on the surface of the substrate film (1) can be carried out by a known method. Specifically, a known coating method such as gravure coating, Meyer bar coating, or air knife coating can be used.

In the adhesive layer (4) formed on the surface protection film (5) according to the present invention, the antistatic agent (3) component included in the release agent layer (2) does not exist inside (other than the surface) of the adhesive layer (4), but exists only on the surface of the adhesive layer (4). As a result, changes in the antistatic performance of the surface protection film (5) over time and contamination of the adherend can be suppressed.

The adhesive layer (4) formed on the surface protection film (5) according to the present invention is not particularly limited as long as it is an adhesive layer that adheres to the surface of an adherend, can be easily peeled off after use, and is also unlikely to contaminate the adherend. Considering that durability is required after the surface protection film (5) according to the present invention is bonded to an optical film, it is preferably an acrylic adhesive layer formed by crosslinking a (meth)acrylate copolymer.

Examples of (meth)acrylate copolymers include copolymers copolymerized with main monomers such as n-butylacrylate, 2-ethylhexylacrylate, isooctyl acrylate, and isononyl acrylate, with comonomers such as acrylonitrile, vinyl acetate, methyl methacrylate, and ethyl acrylate, and functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutylacrylate, glycidyl methacrylate, and N-methylolmethacrylamide. The (meth)acrylate copolymer may have all of the main monomer and other monomers be (meth)acrylates, or may contain one or more monomers other than (meth)acrylate as monomers other than the main monomer.

In addition, a compound containing a polyoxyalkylene group may be copolymerized or mixed with the (meth)acrylate copolymer. Examples of the compound containing a copolymerizable polyoxyalkylene group include polyethylene glycol (400) monoacrylic acid ester, polyethylene glycol (400) monomethacrylic acid ester, methoxypolyethylene glycol (400) acrylate, methoxypolyethylene glycol (400) methacrylate, polypropylene glycol (400) monoacrylic acid ester, polypropylene glycol (400) monomethacrylic acid ester, methoxypolypropylene glycol (400) acrylate, and methoxypolypropylene glycol (400) methacrylate. By copolymerizing these monomers containing a polyoxyalkylene group with the main monomer or functional monomer of the (meth)acrylate copolymer, an adhesive made of a copolymer containing a polyoxyalkylene group can be obtained.

As a compound containing a polyoxyalkylene group that can be mixed in a (meth)acrylate copolymer, a (meth)acrylate copolymer containing a polyoxyalkylene group is preferable, and a polymer of a (meth)acrylic monomer containing a polyoxyalkylene group is more preferable, and examples thereof include polymers such as polyethylene glycol (400) monoacrylic acid ester, polyethylene glycol (400) monomethacrylic acid ester, methoxypolyethylene glycol (400) acrylate, methoxypolyethylene glycol (400) methacrylate, polypropylene glycol (400) monoacrylic acid ester, polypropylene glycol (400) monomethacrylic acid ester, methoxypolypropylene glycol (400) acrylate, and methoxypolypropylene glycol (400) methacrylate. By mixing a compound containing these polyoxyalkylene groups with the (meth)acrylate copolymer, an adhesive to which a compound containing a polyoxyalkylene group is added can be obtained.

As a curing agent added to the adhesive layer (4), crosslinking agents that crosslink (meth)acrylate copolymers, such as isocyanate compounds, epoxy compounds, melamine compounds, and metal chelate compounds, can be exemplified. In addition, as an adhesive agent, rosin-based, coumarone-indene-based, terpene-based, petroleum-based, and phenol-based can be exemplified.

The thickness of the adhesive layer (4) formed on the surface protection film (5) according to the present invention is not particularly limited, but is preferably about 5 to 40 μm in thickness, and more preferably about 10 to 30 μm in thickness. It is preferable that the adhesive layer (4) have a micro-adhesive strength of about 0.03 to 0.3 N/25 mm in peel strength (adhesive force) of the surface protection film to the surface of the adherend, in that the operability when peeling the surface protection film from the adherend is excellent.

The method for forming the adhesive layer (4) on the base film (1) of the surface protection film (5) according to the present invention may be performed by a known method, and is not particularly limited. Specifically, a known coating method such as reverse coating, comma coating, gravure coating, slot die coating, Meyer bar coating, or air knife coating can be used.

The surface protection film (5) according to the present invention having the above configuration preferably has a surface potential of +0.7 kV to -0.7 kV when peeling the adhesive layer (4) from the optical film as the adherend. Furthermore, it is more preferable that the surface potential is +0.5 kV to -0.5 kV, and it is particularly preferable that the surface potential is +0.2 kV to -0.2 kV. This surface potential can be adjusted by adding or subtracting the type and amount of the antistatic agent (3) contained in the release agent layer (2). The type and amount of the antistatic agent (3) of the release agent layer (2) may be adjusted in consideration of the surface contamination of the optical film as the adherend after peeling the surface protection film (5) from the optical film as the adherend.

Fig. 2 is a conceptual cross-sectional view showing a state in which a release agent layer (2) and an adhesive layer (4) are in contact with each other when the surface protection film (5) of the present invention is rolled into a roll shape. A surface protection film (5) formed by forming a release agent layer (2) containing an antistatic agent (3) on one surface of a substrate film (1) and forming an adhesive layer (4) not containing an antistatic agent (3) on the other surface of the substrate film (1) is rolled into a roll shape with the adhesive layer (4) facing inward, thereby forming a state in which the release agent layer (2) and the adhesive layer (4) are in contact with each other in the radial direction of the roll. As a result, a part of the antistatic agent (symbol 3) component contained in the release agent layer (2) is transferred to the surface of the adhesive layer (4). Fig. 3 shows a state in which a surface protection film (5) released from a surface protection film (10) in a roll shape obtained in this manner is bonded to an optical component (6). Since the antistatic agent (3) component is transferred from the release agent layer (2) to the surface of the adhesive layer (4), the peeling voltage when the surface protection film (5) is peeled from the adherend after bonding the surface protection film (5) to the adherend is reduced compared to the adhesive layer (4) before the antistatic agent (3) component is transferred. Here, the peeling voltage when the surface protection film (5) of Fig. 1 is peeled from the adherend can be measured by a known method. For example, after attaching a surface protection film (5) to an adherend such as a polarizing plate, the surface protection film (5) is peeled at a peeling speed of 40 m per minute using a high-speed peeling tester (manufactured by Tester Industry), and the surface potential of the surface of the adherend is measured every 10 ms using a surface electrometer (manufactured by Keyence Co., Ltd.). The maximum value of the absolute value of the surface potential is measured as the peeling voltage (kV).

In the surface protection film (10) in a roll shape according to the present invention, when the surface protection film (5) that has been rewound from the roll shape is attached to an adherend, the antistatic agent (3) transferred to the surface of the adhesive layer (4) comes into contact with the surface of the adherend. As a result, the peeling voltage when the surface protection film (5) is peeled from the adherend again can be suppressed low. In addition, in the surface protection film (10) in a roll shape according to the present invention, the release agent layer (2) is on the outside and the adhesive layer (4) is on the inside, so that the surface of the adhesive layer (4) is protected without being exposed in the roll shape. Even after the surface protection film (5) is rewound from the roll shape, since the release agent layer (2) is integrated with the base film (1), removal or disposal of the release agent layer (2) is unnecessary.

Fig. 3 is a cross-sectional view showing an optical component (7) having a surface protection film formed thereon, as one example of bonding the surface protection film (5) of the present invention to an optical component. The optical component (7) having a surface protection film formed thereon is obtained by unwinding the surface protection film (5) of the present invention from a surface protection film (10) wound in a roll shape, and bonding it to an optical component (6) as an adherend via the adhesive layer (4). Examples of the optical component (6) include optical films such as a polarizing plate, a phase difference plate, a lens film, a phase difference plate combined polarizing plate, and a lens film combined polarizing plate. Such optical components are used as constituent parts of liquid crystal display devices such as liquid crystal display panels, optical systems of various instruments, and the like. In addition, examples of the optical component include optical films such as an antireflection film, a hard coat film, and a transparent conductive film for a touch panel.

When the surface protection film (5) of the present invention is unwound from a surface protection film (10) in a roll shape, and is bonded to an optical component (optical film) as an adherend, and then the surface protection film (5) is peeled off from the adherend, the peeling voltage can be sufficiently suppressed to be low. Therefore, there is no concern about destroying circuit components such as a driver IC, a TFT element, a gate line driving circuit, etc., and the production efficiency in the process of manufacturing a liquid crystal display panel, etc. can be increased, and the reliability of the production process can be maintained.

Example

Next, the present invention will be described in more detail by examples.

(Example 1)

(Production of surface protection film)

3.125 parts by weight of a long-chain alkyl group-containing release agent (manufactured by Hitachi Chemical Co., Ltd., product name: Tespine 303), 7.5 parts by weight of a 10% ethyl acetate solution of lithium bis(fluorosulfonyl)imide, 89.375 parts by weight of a 50:50 mixed solvent of toluene and ethyl acetate, and 0.09 parts by weight of a catalyst (manufactured by Hitachi Chemical Co., Ltd., product name: Dryer 900) were mixed and stirred to prepare a paint forming the release agent layer of Example 1.

Meanwhile, 100 parts by weight of a 40% ethyl acetate solution of an adhesive composed of a copolymer of 90 parts by weight of 2-ethylhexyl acrylate, 7 parts by weight of methoxypolyethylene glycol (400) methacrylate, and 3 parts by weight of 2-hydroxyethyl acrylate was stirred and mixed with 2 parts by weight of an isocyanate curing agent (Coronate (registered trademark) HX manufactured by Tosoh Corporation), thereby producing an adhesive composition of Example 1.

On the surface of a polyethylene terephthalate film having a thickness of 38 ㎛, a paint forming a release layer of Example 1 was applied with a Meyer bar so that the thickness after drying would be 0.2 ㎛, and dried in a hot air circulation oven at 120°C for 1 minute to form a release layer. Next, on the surface of the polyethylene terephthalate film on which the release layer is not formed, the prepared adhesive composition was applied so that the thickness after drying would be 20 ㎛, and then dried in a hot air circulation oven at 100°C for 2 minutes to form an adhesive layer. Thereafter, the film having the release layer formed on one surface of the obtained base film and the adhesive layer formed on the other surface was wound into a roll shape with the adhesive layer facing inward so that the release layer and the adhesive layer were in contact with each other. The adhesive film obtained by rolling into a roll shape was kept in an environment of 40°C for 5 days to harden the adhesive layer, thereby obtaining a surface protection film rolled into a roll shape of Example 1.

(Example 2)

8.33 parts by weight of a long-chain alkyl group-containing release agent (manufactured by Itposa Yuji Kogyo Co., Ltd., product name: Pyrolyl HT), 7.5 parts by weight of a 10% ethyl acetate solution of lithium bis(trifluoromethanesulfonyl)imide, and 84.17 parts by weight of a 50:50 mixed solvent of toluene and ethyl acetate were mixed and stirred to prepare a paint forming a release agent layer of Example 2. A surface protection film in a roll shape of Example 2 was obtained in the same manner as in Example 1, except that the paint forming a release agent layer was the paint of Example 2.

(Example 3)

A paint forming a release agent layer of Example 3 was prepared by mixing and stirring 14 parts by weight of a 10% toluene solution of ethyl cellulose (manufactured by Dow Chemical Co., Ltd., product name: Ethocel FP100), 0.67 parts by weight of an addition-reactive silicone (manufactured by Dow Corning Toray Co., Ltd., product name: SRX-345), 7.5 parts by weight of a 10% ethyl acetate solution of lithium bis(fluorosulfonyl)imide, 77.83 parts by weight of a 1:1 mixed solvent of toluene and ethyl acetate, and 0.07 parts by weight of a 10% toluene solution of a platinum catalyst (manufactured by Dow Corning Toray Co., Ltd., product name: SRX-212), and stirring the mixture. A surface protection film forming a release agent layer of Example 3 was obtained in a roll shape in the same manner as in Example 1, except that the paint forming a release agent layer was the paint of Example 3.

(Example 4)

A paint forming a release agent layer of Example 4 was prepared by mixing and stirring 5 parts by weight of an addition-reactive silicone (manufactured by Dow Corning Toray Co., Ltd., product name: SRX-345), 7.5 parts by weight of a 10% ethyl acetate solution of lithium bis(fluorosulfonyl)imide, 87.5 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 Dow Corning Toray Co., Ltd., product name: SRX-212). A paint forming a release agent layer of Example 4 was prepared in the same manner as in Example 1, except that the paint forming a release agent layer was the paint of Example 4, to obtain a surface protection film in a roll shape of Example 4.

(Comparative Example 1)

A surface protection film in a roll shape of Comparative Example 1 was obtained in the same manner as in Example 1, except that lithium bis(fluorosulfonyl)imide, an antistatic agent, was not added.

(Comparative Example 2)

Instead of adding lithium bis(fluorosulfonyl)imide to the release agent, 0.67 parts by weight of lithium bis(fluorosulfonyl)imide was added to the adhesive side per 100 parts by weight of a 40% ethyl acetate solution, in the same manner as in Example 1, to obtain a surface protection film in a roll shape of Comparative Example 2.

Below, the method and results of the evaluation test are presented.

〈Method for measuring the unfolding power of surface protection film〉

A sample of a surface protection film that has been rolled up from a surface protection film in a roll shape is cut into two overlapping layers to a width of 50 mm and a length of 150 mm. The strength when peeled in a 180° direction at a peeling speed of 300 mm/min using a tensile tester under a test environment of 23°C×50%RH is measured, and this is taken as the unfolding force (N/50 mm) of the surface protection film.

(Surface resistivity of the release layer and adhesive layer)

The surface resistivity (Ω/□) of the release agent layer and adhesive layer of a sample of a surface protection film rewound from a roll shape was measured using a high-performance high-resistivity meter (Hiresta (registered trademark)-UP manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under the conditions of an applied voltage of 100 V and a measurement time of 30 seconds.

〈Method for measuring the adhesive strength of surface protection film〉

An anti-glare, low-reflection polarizing plate (AG-LR polarizing plate) was used as the adherend by bonding an acrylic film to a polarizer (polyvinyl alcohol film containing iodine) using an ultraviolet-curable adhesive. The polarizing plate was bonded to the surface of a glass plate using a bonding machine with a double-sided adhesive tape. Thereafter, a surface protection film cut to a width of 25 mm was bonded onto the acrylic film on the surface of the polarizing plate, and then stored in a test environment of 23°C × 50%RH for 1 day. Thereafter, the strength when the surface protection film was peeled in the 180° direction at a peeling speed of 300 mm/min using a tensile tester was measured, and this was taken as the adhesive strength (N/25 mm).

〈Method for measuring peeling voltage of surface protection film〉

An anti-glare, low-reflection polarizing plate (AG-LR polarizing plate) was used as the adherend by bonding an acrylic film to a polarizer (polyvinyl alcohol film containing iodine) using an ultraviolet-curable adhesive. The polarizing plate was bonded to the surface of a glass plate using a bonding machine with a double-sided adhesive tape. Thereafter, a surface protection film cut to a width of 25 mm was bonded onto the acrylic film on the surface of the polarizing plate, and then stored in a test environment of 23°C × 50%RH for 1 day. Thereafter, a high-speed peeling tester (manufactured by Tester Sangyo) was used to peel the surface protection film at a peeling speed of 40 m/min, and the surface potential of the surface of the polarizing plate was measured every 10 ms using a surface electrometer (manufactured by Keyence Co., Ltd.). The maximum absolute value of the surface potential was taken as the peeling voltage (kV).

〈Method for checking surface contamination of surface protection film〉

An anti-glare, low-reflection polarizing plate (AG-LR polarizing plate) was used as the adherend by bonding an acrylic film to a polarizer (polyvinyl alcohol film containing iodine) using an ultraviolet-curable adhesive. The polarizing plate was bonded to the surface of a glass plate using a bonding machine with a double-sided adhesive tape. Thereafter, a surface protection film cut to a width of 25 mm was bonded onto the acrylic film on the surface of the polarizing plate, and then stored for 3 days and 30 days in a test environment of 23°C × 50%RH. Thereafter, the surface protection film was peeled off, and the presence or absence of contamination on the surface of the polarizing plate was visually observed to confirm the surface contamination. As a criterion for judging the surface contamination, a case where no contamination was transferred to the polarizing plate was marked (○), and a case where contamination was confirmed to be transferred to the polarizing plate was marked (×).

The measurement results for the surface protection films wound in a roll shape of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1. "2EHA" stands for 2-ethylhexyl acrylate, "HEA" stands for 2-hydroxyethyl acrylate, "#400G" stands for methoxypolyethylene glycol (400) methacrylate, "AS agent (1)" stands for lithium bis(fluorosulfonyl)imide, "AS agent (2)" stands for lithium bis(trifluoromethanesulfonyl)imide, "303" stands for Tespaine 303, "Dryer" stands for Dryer 900, "HT" stands for Pyrol HT, "FP-100" stands for Ethocel FP100, "SRX-345" stands for SRX-345, "SRX-211" stands for SRX-211, and "SRX212" stands for platinum catalyst SRX-212. Also, "3.7E11" of surface resistivity means 3.7×10 ¹¹ , and "over-range" means exceeding the measurement limit of the measuring instrument, meaning 1.0×10 ¹³ Ω／□ or more.

From the measurement results shown in Table 1, the following can be known.

The surface protection film in a roll shape of Examples 1 to 4 according to the present invention has an appropriate adhesive strength and does not cause contamination of the surface of an adherend when rewound from the roll shape and used. In addition, even if the adherend is a polarizing plate using an acrylic film, the peeling voltage when the surface protection film is once bonded to the adherend and then peeled from the adherend is low.

Meanwhile, in the case of the surface protection film in a roll shape and in Comparative Example 1, in which no antistatic agent was added to the release agent layer, the peeling voltage when the surface protection film that was rewound from the roll shape was once attached to the adherend and then peeled off from the adherend was high. In addition, in the case of the surface protection film in a roll shape and in Comparative Example 2, in which the antistatic agent was contained in the adhesive layer instead of the release agent layer, the peeling voltage when the surface protection film that was rewound from the roll shape was once attached to the adherend and then peeled off from the adherend was low and thus good, but the adherend became more contaminated after the surface protection film was peeled off.

That is, it is difficult for the surface protection films rolled in a roll shape of Comparative Examples 1 to 2 to achieve both a reduction in peeling voltage and low contamination of the adherend. On the other hand, the surface protection films rolled in a roll shape of Examples 1 to 4, in which an antistatic agent was added to the release agent layer and the antistatic agent component was transferred only to the surface of the adhesive layer, had good compatibility between a reduction in peeling voltage and low contamination of the adherend.

The surface protection film of the present invention can be used to protect the surface of, for example, optical films such as polarizing plates, phase difference plates, lens films, antireflection films, hard coat films, transparent conductive films, and other various optical components in the production process, by bonding it to the surface of the optical component, etc. In addition, the surface protection film of the present invention can suppress the peeling voltage that occurs when the surface protection film is peeled from the adherend after bonding it to the optical component (optical film) which is the adherend, and further, the change in peeling antistatic performance over time and the contamination of the adherend are small, and the yield of the production process can be improved, so it has great industrial utility value.

1… substrate film, 2… release agent layer, 3… antistatic agent, 4… adhesive layer, 5… surface protection film, 6… optical component (optical film), 7… optical component having surface protection film formed thereon, 10… surface protection film wound in a roll shape.

Claims (3)

A release agent layer containing an antistatic agent made of an alkali metal salt and a release agent is formed on one side of a base film made of a transparent resin, and an adhesive layer is formed on the other side of the base film.
By winding the above-mentioned base film into a roll shape with the adhesive layer facing inward so that the release agent layer and the adhesive layer are in contact with each other,
The antistatic agent comprising the alkali metal salt is transferred only to the surface of the adhesive layer,
A method for producing an antistatic surface protective film, characterized in that the above-mentioned releasing agent is a releasing agent containing a long-chain alkyl group having 8 to 30 carbon atoms. In the first paragraph,
A method for producing an antistatic surface protection film, characterized in that the adhesive layer is an acrylic adhesive layer containing a compound containing a polyoxyalkylene group and a (meth)acrylate copolymer. delete