TW202413082A - Surface-protective film and optical component attached with the same - Google Patents

Abstract

A surface-protective film and an optiacla compoenet attached with the same are provided by the present invention. The surface-protective film has a good effect of inhibiting the curl of the optical film, improves handling ability of optical film attached with the surface-protective film, is easily to be peeled off after used, and the does not required reattached and wipped out dirt when shipment. The surface-protective film (P) has a first transparent film (1), a first adhesive layer (2), a second transparent film (3), and a second adhesive layer (4) laminated in this order. The storage modulus of the first adhesive layer (2) at 23℃ is equal to or more than 1.0×10 ⁴Pa and is less than 8.0×10 ⁴Pa, and the adhesive force of the first adhesive layer (2) to glass is equal to or less than 5N/25mm.

Description

Surface protection film and optical component with the surface protection film attached thereto

The present invention relates to a surface protection film and an optical component with the surface protection film attached thereto.

Optical films such as polarizing plates, phase difference plates, lens films for displays, anti-reflection films, hard coating films, and transparent conductive films for touch panels are used in optical products such as displays. When manufacturing and transporting optical films or optical components, a surface protection film is attached to the surface of the optical film to prevent dirt and scratches on the surface in subsequent steps. Sometimes, the appearance inspection of the optical film is performed directly with the surface protection film attached.

The surface protection film based on the prior art typically has a structure in which a slightly adhesive adhesive layer is provided on one side of a base film. The adhesive layer is used to attach the surface protection film to the optical film. The reason for setting the adhesive layer to be slightly adhesive is that when the surface protection film is peeled off from the surface of the optical film after use, it can be peeled off smoothly without generating adhesive residue.

In recent years, displays have been thinning and becoming more precise, and the thinning of optical films has also been developing. In addition, in order to make optical films thinner, not only the thickness of each component is reduced, but also the structure is changed to remove unnecessary components or reduce the number of components by integrating the functions of multiple components into one component. For example, among polarizing plates, the number of polarizing plates with a structure in which a polarizing protective layer is laminated only on one side of a polarizer instead of on both sides is increasing. In the case of a polarizing plate in which only one polarizing protective layer is provided for a polarizer, since the structure sandwiching the polarizer is asymmetrical inside and outside, it has the property that one side is easy to bend (easy to warp). Therefore, a method of suppressing the warping of optical films has been proposed.

For example, Patent Document 1 proposes a manufacturing method for suppressing warping of a polarizing plate by attaching a protective film (surface protective film) having a Gurley stiffness of 1.0×10 ² mgf or more and 1.0×10 ⁵ mgf or less. As a specific example, a protective film having a base film made of a biaxially stretched polyester resin and a thickness in the range of 25 μm or more and 120 μm or less can be cited.

Patent Document 2 proposes a polarizing plate that specifies the rigidity of a laminate composed of a polarizing plate body and a protective film (surface protective film). As a specific example, a polarizing plate using a protective film having a thickness of 50 μm and a base film composed of a biaxially stretched polyester resin can be cited.

Patent document 3 proposes a protective film that can effectively suppress the crook of a polarizer. Specifically, a protective film having a first resin layer, an adhesive layer, a second resin layer, and an adhesive layer in sequence is proposed. The ratio of the thickness of the adhesive layer to the sum of the thickness of the first resin layer and the thickness of the second resin layer is 0.40 or less. The storage modulus of the adhesive layer at 23°C is 8.0×10 ⁴ Pa or more and less than 1.0×10 ⁷ Pa. The protective film is bonded to the surface of the polarizer as a whole and is peeled off as a whole.

The surface protection film shown in Patent Documents 1 to 3 has a thicker base film or uses a laminated film with a resin layer/adhesive layer/resin layer as the base film. Therefore, although the elasticity of the film becomes stronger and the warping suppression effect of the optical film can be obtained, on the other hand, there is a problem that the peeling force becomes stronger when the surface protection film is peeled off after use. When peeling the surface protection film, the surface protection film is peeled off at a peeling angle of nearly 180° relative to the optical film. The peeling force of the surface protection film at this time is the total force of the adhesive of the surface protection film adhering to the optical film as the adherend and the force required to bend the surface protection film itself 180°. If the elasticity of the surface protective film increases, the force required to bend the surface protective film by 180 degrees also increases, resulting in a stronger peeling force for the surface protective film. In recent years, in the use of televisions and digital signage, the size of displays has been increasing along with the thinning and high-precision of displays. For optical films used in such large displays, the above-mentioned surface protective films have a strong peeling force when peeled off, making them difficult to use.

In the past, in the manufacture of displays, LCD panels, backlight modules, surface filters and other parts were purchased by panel manufacturers in the form of sets. This is called module procurement. However, in recent years, a procurement method called "open cell procurement" has become mainstream, especially for TV applications. In open cell procurement, parts such as LCD panels, backlight modules, surface filters, etc. are purchased separately and assembled at TV manufacturers, OEM destinations, etc. Therefore, the circulation of LCD panels in a semi-finished state is increasing.

In module procurement, the surface protection film attached to the polarizer is peeled off after panelization. However, with the adoption of open cell procurement, in order to prevent the adhesion of dust and foreign matter when transporting the LCD panel, the surface protection film is not peeled off from the panelization to the assembly (set) more and more. When shipping and transporting the LCD panel, the surface protection film that was contaminated during panelization is re-attached or the stains on the surface protection film are wiped off to make the surface protection film clean. For the surface protection film shown in patent documents 1 to 3, the surface protection film must be re-attached or the stains on the surface protection film must be wiped off before the LCD panel is shipped, etc., and it is impossible to reduce steps or improve operability. Prior art literature Patent literature

Patent document 1: Japanese Patent Publication No. 2012-053078 Patent document 2: Japanese Re-publication No. WO2016/039296 Patent document 3: Japanese Patent Publication No. 5461640

Technical Problems to be Solved by the Invention

One embodiment of the present invention is completed in view of the above-mentioned actual situation. The technical problem is to provide a surface protection film and an optical component using the surface protection film. The surface protection film has a high effect of suppressing the warping of the optical film, and the handling performance of the optical film bonded with the surface protection film is improved. It is easy to peel off and remove after use, and there is no need to re-stick the surface protection film or wipe off stains when shipping. Technical means to solve the technical problem

An embodiment of the present invention provides a surface protection film, which comprises a first transparent film, a first adhesive layer, a second transparent film and a second adhesive layer stacked in sequence, wherein the storage modulus of the first adhesive layer at 23°C is greater than 1.0×10 ⁴ Pa and less than 8.0×10 ⁴ Pa, and the adhesion of the first adhesive layer to glass is less than 5N/25mm.

The second adhesive layer can use a (meth)acrylic polymer as a base polymer.

Preferably, the adhesion of the second adhesive layer to the glass is less than 0.5 N/25 mm, and the adhesion of the first adhesive layer to the glass is higher than the adhesion of the second adhesive layer to the glass.

It is preferred that the surface resistivity of the second adhesive layer is less than 1×10 ¹³ [Ω/□].

Another embodiment of the present invention provides an optical component with the surface protection film attached thereto. Effect of the invention

According to an embodiment of the present invention, a surface protective film and an optical component using the surface protective film can be provided. The surface protective film has a high effect of suppressing the warp of the optical film, and the handling performance of the optical film bonded with the surface protective film is improved. The surface protective film can be easily peeled off and removed after use, and there is no need to re-stick the surface protective film or wipe off stains when shipping liquid crystal panels.

Methods for implementing the invention

The present invention is described in detail below based on the implementation method. FIG. 1 is a schematic structural diagram of a surface protection film P of an implementation method. As shown in FIG. 1 , the surface protection film P is provided with a first adhesive layer 2 on a single surface of a first transparent film 1. A second transparent film 3 is provided on the side of the first adhesive layer 2 opposite to the first transparent film 1. A second adhesive layer 4 is provided on the side of the second transparent film 3 opposite to the first adhesive layer 2. A peeling film 5 for protecting the adhesive surface is overlapped on the surface of the second adhesive layer 4. That is, the surface protection film P is formed by sequentially stacking the first transparent film 1, the first adhesive layer 2, the second transparent film 3, the second adhesive layer 4 and the peeling film 5. In addition, a film obtained by removing the release film 5 from the surface protection film P shown in FIG. 1, that is, a film on which the first transparent film 1, the first adhesive layer 2, the second transparent film 3, and the second adhesive layer 4 are sequentially stacked is sometimes referred to as the surface protection film P.

As the first transparent film 1 (base film), a transparent plastic film is used. By making the first transparent film 1 and the second transparent film 3 transparent, it is possible to perform an appearance inspection of optical components with the surface protection film P attached. As the plastic film used for the first transparent film 1, polyester films such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, and polybutylene terephthalate are suitable. In addition to polyester films, other plastic films can also be used as long as they have the required strength and optical suitability. The first transparent film 1 can be a non-stretched film or can be uniaxially or biaxially stretched. The first transparent film 1 can also be a plastic film with controlled stretching ratio, axial angle formed by crystallization accompanying stretching, etc.

The thickness of the first transparent film 1 is not particularly limited, and is, for example, about 12 to 100 μm, and is particularly preferably about 20 to 50 μm. An antifouling layer, an antistatic layer, or a hard coating layer for preventing surface dirt, or a corona discharge treatment, an anchor coat treatment, or other easy-adhesion treatment may be provided on the first transparent film 1 on the side opposite to the first adhesive layer 2 (the upper surface in FIG. 1 ), as required.

When the surface protection film P is bonded to the optical film, the first adhesive layer 2 is used to absorb and relieve the stress accompanying the warping of the optical film. The first adhesive layer 2 is not particularly limited in material as long as it satisfies the characteristics of not adversely affecting the adhesion, adhesion characteristics, stability, etc. with the transparent film, and a known material can be used.

As the material of the first adhesive layer 2, rubber, acrylic, urethane and other adhesives can be listed. Rubber adhesives can be adhesives in which tackifiers, softeners, anti-aging agents, fillers and the like are mixed in elastomers such as natural rubber and synthetic rubber, and crosslinking agents can be added as needed. Acrylic adhesives are adhesives in which curing agents, tackifiers and the like are added to (meth) acrylic polymers as needed. (Meth) acrylic polymers are usually polymers copolymerized with main monomers such as butyl acrylate (e.g. n-butyl acrylate), 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, etc.; copolymer monomers such as acrylonitrile, vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, etc.; and functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, glycidyl methacrylate, dimethylacrylamide, N-hydroxymethylmethacrylamide, hydroxyl-containing acrylic monomers, carboxyl-containing acrylic esters, polyoxyalkylene-containing acrylic monomers, etc. (Meth) acrylic polymers can be selected with appropriate composition according to the required characteristics. (Meth) acrylic polymers can be used as base polymers.

As curing agents, isocyanate compounds, epoxy compounds, melamine compounds, metal chelate compounds, etc. can be listed. As thickeners, rosin, coumarone-indene, terpenes, petroleum, phenols, etc. can be listed. Additives such as curing catalysts, pot life extenders, antistatic agents, ultraviolet absorbers, and antioxidants can also be added to the first adhesive layer 2 as needed. As the material of the first adhesive layer 2, an adhesive in which a photoinitiator and a photocurable monomer or oligomer are added to the above-mentioned adhesive, and the monomer or oligomer is polymerized after light irradiation to change the adhesive force can also be used.

Urethane adhesives include urethane adhesives in which the types and composition ratios of hard segments and soft segments are adjusted. As the material of the first adhesive layer 2, acrylic adhesives are particularly preferred from the perspectives of heat resistance, durability, and adhesion to the second transparent film 3.

The first adhesive layer 2 may also use an adhesive whose adhesive force is reduced by irradiation with ultraviolet rays, wherein the adhesive contains an ultraviolet initiator and an ultraviolet curable monomer or oligomer. By using this adhesive, the first transparent film and the first adhesive layer can be easily peeled off and removed from the second transparent film when the liquid crystal panel is shipped and transported. The first adhesive layer 2 may also use an adhesive whose adhesive force is reduced by heating by adding a thermal foaming agent within a range that does not reduce transparency.

The first adhesive layer 2 has an adhesive force of 5N/25mm or less to the glass. Preferably, the first adhesive layer 2 has an adhesive force of 5N/25mm or less to the glass at a 180° peeling speed of 300mm/min. If the adhesive force of the first adhesive layer 2 to the glass is greater than 5N/25mm, the peeling force when peeling off the surface protection film P becomes larger, which may reduce the operability. In addition, if the adhesive force of the first adhesive layer 2 to the glass is greater than 5N/25mm, it may be difficult to peel the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 from the second transparent film 3 when necessary (when shipping liquid crystal panels, etc.).

The adhesion of the first adhesive layer 2 to the glass can be set to, for example, 1 N/25 mm or more. If the adhesion of the first adhesive layer 2 to the glass is 1 N/25 mm or more, the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 is unlikely to be accidentally peeled off.

Considering the workability when peeling and removing the surface protection film P, it is preferable that the adhesive force of the first adhesive layer 2 is higher than the adhesive force of the second adhesive layer 4. Thus, when shipping liquid crystal panels, the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 can be easily peeled off from the second transparent film 3.

The storage modulus of the first adhesive layer 2 at 23°C is 1.0×10 ⁴ Pa or more and less than 8.0×10 ⁴ Pa. If the storage modulus of the first adhesive layer 2 is less than 1.0×10 ⁴ Pa, when the surface protection film P is rolled up and stored, the adhesive may be squeezed out from the edge, and foreign matter may be easily attached to the edge. In addition, the warp suppression effect of the optical film may be reduced. If the storage modulus of the first adhesive layer 2 is 8.0×10 ⁴ Pa or more, the peeling force when peeling off the surface protection film P becomes large, and the workability may be reduced.

The thickness of the first adhesive layer 2 is not particularly limited, but is generally about 3 to 30 μm. By setting the thickness of the first adhesive layer 2 to be 3 μm or more, a predetermined adhesive force can be obtained. By setting the thickness of the first adhesive layer 2 to be 30 μm or less, the cost can be suppressed.

As a method for forming the first adhesive layer 2 on the first transparent film 1, a known method may be used. For example, there may be a method of applying an adhesive on the first transparent film 1, drying and curing the adhesive, or a method of applying an adhesive on the second transparent film, drying and curing the adhesive, and then bonding the first transparent film. Specifically, known coating methods such as reverse coating, comma coating, gravure coating, slot die coating, meyer bar coating, and air knife coating may be used.

As the second transparent film 3, a transparent plastic film can be used. By making the first transparent film 1 and the second transparent film 3 transparent, it is possible to perform an appearance inspection of optical components in a state where a surface protection film is attached. As the plastic film used for the second transparent film 3, polyester films such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, and polybutylene terephthalate are suitable. In addition to polyester films, other plastic films can also be used as long as they have the required strength and optical suitability. The second transparent film 3 can be a non-stretched film or can be stretched uniaxially or biaxially. The second transparent film 3 can also be a plastic film with controlled stretching ratio, axial angle formed by crystallization accompanying stretching, etc.

The thickness of the second transparent film 3 is not particularly limited, for example, it is about 12 to 100 μm, and in particular, it is usually about 19 to 50 μm. The second transparent film 3 may also be subjected to an easy-adhesion treatment or anti-static treatment such as a corona discharge treatment or a primer treatment on the side in contact with the first adhesive layer 2 as needed. In addition, an easy-adhesion treatment such as an anti-static treatment, a corona discharge treatment, a primer treatment, etc. may also be applied to the side of the second transparent film 3 opposite to the first adhesive layer 2 (the lower surface in FIG. 1).

The second adhesive layer 4 is provided to adhere the surface protection film P to the optical film as an adherend. The second adhesive layer 4 is a layer composed of a slightly adhesive adhesive. The slightly adhesive adhesive is used so that the surface protection film P does not peel off during the manufacturing step of the optical film, and after use, when the surface protection film P is peeled off from the surface of the optical film, it can be peeled off smoothly without generating adhesive residue.

The material of the second adhesive layer 4 is not particularly limited, and known materials such as rubber, acrylic, and urethane adhesives can be used, among which acrylic adhesives are suitable. Acrylic adhesives are, for example, adhesives in which a curing agent, a thickening agent, etc. are added to a (meth)acrylic polymer as needed. (Meth) acrylic polymers are usually polymers copolymerized with main monomers such as butyl acrylate (e.g. n-butyl acrylate), 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, etc.; copolymer monomers such as acrylonitrile, vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, etc.; and functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, glycidyl methacrylate, dimethylacrylamide, N-hydroxymethylmethacrylamide, hydroxyl-containing acrylic monomers, carboxyl-containing acrylic esters, polyoxyalkylene-containing acrylic monomers, etc. (Meth) acrylic polymers can be selected with appropriate composition according to the required characteristics. (Meth) acrylic polymers can be used as base polymers.

Examples of curing agents include isocyanate compounds, epoxy compounds, melamine compounds, metal chelate compounds, etc. Examples of tackifiers include rosins, coumarone-indene compounds, terpenes, petroleum compounds, phenols, etc. Additives such as curing catalysts, pot life extenders, antistatic agents, ultraviolet absorbers, and antioxidants may be added to acrylic adhesives as needed.

The antistatic agent may be one that has good dispersion or compatibility with the (meth)acrylic polymer, and examples thereof include surfactants, ionic liquids, ionic solids, alkali metal salts, metal oxides, metal particles, conductive polymers, carbon, carbon nanotubes, etc. As the antistatic agent, surfactants, ionic liquids, ionic solids, alkali metal salts, etc. are preferred from the perspective of transparency, affinity with the (meth)acrylic polymer, etc.

As surfactants, nonionic, cationic, anionic, amphoteric, etc. can be listed. As nonionic surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid esters, glycerol fatty acid esters, propylene glycol fatty acid esters, polyoxyalkylene modified silicones, etc. can be listed. As cationic surfactants, alkyl trimethylammonium salts, dialkyl dimethylammonium salts, alkyl benzyl dimethylammonium salts, etc. can be listed. As anionic surfactants, monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkyl benzene sulfonates, monoalkyl phosphates, etc. can be listed. As amphoteric surfactants, alkyl dimethyl amine oxide, alkyl carboxy betaine, etc. can be listed.

Ionic liquids are non-polymeric substances that contain anions and cations and are liquid at room temperature. Examples of cations include cyclic amidine ions such as imidazole ions, pyridinium ions, ammonium ions, cobalt ions, and phosphonium ions. As the anion part, _there can ^be listed _{CnH2n +} ^1COO- , _{CnF2n +} 1COO- ^, _{NO3- ,} ^CnF2n _{+ 1SO3-} , ( _{CnF2n+1SO2 )} ^2N- _, ( _{CnF2n + 1SO2} ) ^{3C- ,} _PO42- ^{, AlCl4- ,} _Al2Cl7- ^, _{ClO4- , BF4- , PF6-} ^, _{AsF6- , SbF6-} ^{, etc.}

Ionic solids are non-polymeric substances that contain anions and cations and are solid at room temperature. Examples of cations include pyridine ions, imidazole ions, pyrimidine ions, pyrazolium ions, pyrrolidinium ions, nitrogen-containing onium ions such as ammonium ions, or phosphonium ions, coronium ions, etc. Examples of anions include hexafluorophosphate (PF ₆ ^- ), thiocyanate (SCN ^- ), alkylbenzenesulfonate (RC ₆ H ₄ SO ₃ ^- ), perchlorate (ClO ₄ ^- ), tetrafluoroborate (BF ₄ ^- ), etc. as inorganic or organic anions. By selecting the chain length of the alkyl group, the position and amount of the substituents, an ionic solid that is solid at room temperature can be obtained.

Examples of the alkaline metal salt include metal salts containing alkaline metals such as lithium, sodium, and potassium. Examples of the alkaline metal salt include lithium trifluoromethanesulfonate (CF ₃ LiO ₃ S). In order to stabilize the ionic substance, a compound containing a polyoxyalkylene structure may be added to the antistatic agent.

Although the amount of antistatic agent components added to base polymers such as (meth) acrylic polymers varies depending on the type of antistatic component or the degree of compatibility with the base polymer, it can be set in consideration of surface resistivity, adherend contamination, adhesive properties, etc. Additives such as curing catalysts, pot life extenders, ultraviolet absorbers, and antioxidants can be added to acrylic adhesives as needed.

When the surface protection film P is used for peeling and removal, in which case peeling electrostatic voltage may be generated, it is appropriate to add an antistatic component (antistatic agent) to the second adhesive layer 4. In this case, the surface resistivity of the second adhesive layer 4 is preferably less than 1×10 ¹³ [Ω/□]. If the surface resistivity of the second adhesive layer 4 is less than 1×10 ¹³ [Ω/□], the peeling electrostatic voltage when removing the surface protection film can be reduced. Therefore, the antistatic performance can be improved.

The thickness of the second adhesive layer 4 is not particularly limited, and is, for example, about 3 to 50 μm, and is often about 5 to 30 μm.

The adhesion of the second adhesive layer 4 to the glass depends on the type of surface treatment of the optical film to which the surface protection film P is attached, but is preferably 0.5 N/25 mm or less. Preferably, the adhesion of the second adhesive layer 4 to the glass at 180° peeling and a peeling speed of 300 mm/min is 0.5 N/25 mm or less. If the adhesion of the second adhesive layer 4 is 0.5 N/25 mm or less, the peeling force when peeling and removing the surface protection film P becomes low, thereby improving workability.

The second adhesive layer 4 is preferably a slightly adhesive layer with a peeling strength of about 0.03 to 0.3 N/25 mm on the surface of the adherend (optical film). If the adhesive force of the second adhesive layer 4 is 0.03 N/25 mm or more, it is possible to suppress the floating (i.e., partial peeling) of the surface protection film P during the manufacturing step and the conveying step of the optical film. In addition, it is not easy to accidentally peel off the surface protection film P. When the adhesive force of the second adhesive layer 4 is 0.3 N/25 mm or less, the operability can be improved.

The second adhesive layer 4 may be deposited on the second transparent film 3 by a known method without particular limitation. Specifically, there are (1) a method in which an adhesive for forming the second adhesive layer 4 is applied to the second transparent film 3, dried to form the second adhesive layer 4, and then a release film 5 is attached to the surface of the second adhesive layer 4; (2) a method in which an adhesive for forming the second adhesive layer 4 is applied to the release film 5, dried to form the second adhesive layer 4, and then a second transparent film 3 is attached.

The second adhesive layer 4 may be formed on the second transparent film 3 by a known method. Specifically, the adhesive may be applied by reverse coating, comma coating, gravure coating, nip extrusion coating, Mayer bar coating, air knife coating, or the like.

The surface protection film P is generally a structure in which the surface of the adhesive layer 4 of an adhesive sheet having a first adhesive layer 2, a second transparent film 3, and a second adhesive layer 4 formed on a first transparent film 1 is protected by a release film 5. If necessary, the surface protection film P may be a product in which the first transparent film 1/first adhesive layer 2/second transparent film 3/second adhesive layer 4 are rolled into a tape without using the release film 5.

The release film 5 is not particularly limited, and examples thereof include a release film obtained by subjecting the surface of a film such as a polyester film to a release treatment using a release agent such as a silicone-based release agent.

FIG2 is an example of an optical component using a surface protection film P of an implementation method, which is a schematic structural diagram of an optical component D. As shown in FIG2, the optical component D is formed by bonding the surface protection film P shown in FIG1 to the surface of an optical film C using an adhesive layer 4. As the optical film C, there can be listed polarizing plates, phase difference plates, lens films, polarizing plates used as phase difference plates, and polarizing plates used as lens films. This optical component D can be used to manufacture liquid crystal display devices such as liquid crystal display panels, optical system devices of various measuring instruments, etc.

Since the surface protection film P of the embodiment has a multi-layer structure, it has two transparent films and two adhesive layers, so it has a high effect of suppressing the warping of the optical film C. The surface protection film P makes it difficult for the optical film C to bend, bump, etc. due to the above structure. Therefore, the handling performance of the optical film C can be improved. Generally, when a thicker surface protection film is formed, although the warping suppression and handling performance become higher, the peeling property of the surface protection film decreases. In contrast, the surface protection film P of the embodiment uses the first adhesive layer 2 having the above characteristics, so it has the advantage of being easy to peel and remove after use.

Since the surface protection film P uses the first adhesive layer 2 having the above-mentioned characteristics, the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 can be peeled off and removed from other parts. For example, FIG3 is a schematic structural diagram showing the structure of peeling off and removing the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 from the optical component D. As shown in FIG3. By peeling off and removing the adhesive film, the clean surface of the surface protection film can be exposed. Therefore, when shipping the liquid crystal panel, there is no need to re-stick the surface protection film and wipe off the stains. Therefore, the number of steps can be reduced, and it is possible to seek improvements in productivity, productivity, and operability. In particular, for thin-film optical films, the surface protection film P has a high effect of suppressing the warping of the optical film, and the handling performance of the optical film bonded with the surface protection film is improved, and it is easy to peel off and remove after use. Therefore, it is possible to seek to improve the yield of the manufacturing step of the thin-film optical film, increase the productivity, and improve the operability. Example

Next, the present invention is further described by way of examples. Hereinafter, "parts by mass" may be referred to simply as "parts". (Preparation of surface protective film of Example 1) 0.3 parts of isocyanate curing agent are mixed as curing agent with 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, dimethyl acrylamide, and hydroxyl-containing acrylic monomer to obtain adhesive A. The adhesive layer formed by applying adhesive A to a biaxially stretched polyester film having a thickness of 38 μm (the coating thickness after drying is 10 μm) has an adhesion to glass of 3.8 N/25 mm.

100 parts of a base polymer composed of 2-ethylhexyl acrylate and a hydroxyl-containing acrylic monomer were mixed with 3 parts of an isocyanate curing agent as a curing agent to obtain an adhesive B. The adhesive layer formed by applying the adhesive B on a biaxially stretched polyester film having a thickness of 38 μm (the coating thickness after drying was 20 μm) had an adhesion to glass of 0.2 N/25 mm.

Adhesive A was applied to a colorless and transparent biaxially stretched polyester film (first transparent film) with a thickness of 25 μm so that the coating thickness after drying was 10 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes. Then, a colorless and transparent biaxially stretched polyester film (second transparent film) with a thickness of 38 μm was bonded to the surface of adhesive A (adhesive A coated surface). Adhesive B was applied to the surface of the bonded biaxially stretched polyester film opposite to adhesive A so that the coating thickness after drying was 20 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes.

A release film (release film) coated with a silicone release agent on a biaxially stretched polyester film having a thickness of 25 μm was attached to the surface of adhesive B (adhesive B coated surface) in such a manner that the surface of adhesive B was in contact with the release agent treated surface (the surface coated with the silicone release agent). The obtained sample was aged in a hot air circulation oven at 40°C for 3 days to obtain a surface protective film of Example 1. The adhesive layer formed with adhesive A was the first adhesive layer. The adhesive layer formed with adhesive B was the second adhesive layer.

(Preparation of surface protective film of Example 2) 0.5 parts of isocyanate curing agent were mixed into 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, dimethyl acrylamide, hydroxyl-containing acrylic monomer, and carboxyl-containing acrylic ester as a curing agent to obtain adhesive C. The adhesive layer formed by applying adhesive C on a biaxially stretched polyester film with a thickness of 38 μm (the coating thickness after drying was 10 μm) had an adhesion to glass of 4.8 N/25 mm. The surface protective film of Example 2 was obtained in the same manner as Example 1 except that adhesive C was used instead of adhesive A.

(Preparation of surface protective film of Example 3) 1.5 parts of isocyanate curing agent were mixed into 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, dimethyl acrylamide, and hydroxyl-containing acrylic monomers to obtain adhesive D. The adhesive layer formed by applying adhesive D to a biaxially stretched polyester film with a thickness of 38 μm (the coating thickness after drying was 10 μm) had an adhesion to glass of 1.6 N/25 mm. The surface protective film of Example 3 was obtained in the same manner as Example 1, except that adhesive D was used instead of adhesive A.

(Preparation of the surface protection film of Example 4) The surface protection film of Example 4 was obtained in the same manner as in Example 1 except that a colorless and transparent biaxially stretched polyester film with a thickness of 25 μm was used instead of the biaxially stretched polyester film with a thickness of 38 μm (second transparent film).

(Preparation of surface protective film of Example 5) 0.1 parts of lithium trifluoromethanesulfonate as an antistatic agent and 3.0 parts of an isocyanate curing agent as a curing agent were mixed with 100 parts of a base polymer composed of 2-ethylhexyl acrylate, a polyoxyalkylene-containing acrylic monomer, and a hydroxyl-containing acrylic monomer to obtain an adhesive E. The adhesive layer formed by applying the adhesive E to a biaxially stretched polyester film having a thickness of 38 μm (the coating thickness after drying was 20 μm) had an adhesion to glass of 0.15 N/25 mm, and the surface resistance value of the adhesive surface was 6.0×10 ¹¹ Ω/□. The surface protective film of Example 5 was obtained in the same manner as in Example 1, except that the adhesive E was used instead of the adhesive B.

(Preparation of surface protection film of Comparative Example 1) Adhesive B was applied to a colorless and transparent biaxially stretched polyester film having a thickness of 38 μm so that the coating thickness after drying was 20 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes. A release film (peeling film) coated with a silicone peeling agent on a biaxially stretched polyester film having a thickness of 25 μm was attached to the surface of adhesive B (adhesive B coated surface) so that the surface of adhesive B was in contact with the peeling agent treated surface (the surface coated with silicone peeling agent). The obtained sample was aged in a hot air circulation oven at 40°C for 3 days to obtain the surface protection film of Comparative Example 1. Adhesive B became an adhesive layer.

(Preparation of the surface protection film of Comparative Example 2) The surface protection film of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that a colorless and transparent biaxially stretched polyester film having a thickness of 75 μm was used instead of the biaxially stretched polyester film having a thickness of 38 μm.

(Preparation of surface protection film of Comparative Example 3) The surface protection film of Comparative Example 3 was obtained in the same manner as in Comparative Example 1 except that a colorless and transparent biaxially stretched polyester film with a thickness of 100 μm was used instead of the biaxially stretched polyester film with a thickness of 38 μm.

(Preparation of surface protection film of comparative example 4) 0.2 parts of isocyanate curing agent were mixed into 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, dimethyl acrylamide, hydroxyl-containing acrylic monomer, and carboxyl-containing acrylic ester as a curing agent to obtain adhesive F. The adhesive layer formed by applying adhesive F on a biaxially stretched polyester film with a thickness of 38 μm (the coating thickness after drying was 10 μm) had an adhesion to glass of 6.5 N/25 mm. The surface protection film of comparative example 4 was obtained in the same manner as in Example 1 except that adhesive F was used instead of adhesive A.

(Preparation of surface protective film of comparative example 5) 0.3 parts of isocyanate curing agent were mixed into 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and hydroxyl-containing acrylic monomers to obtain adhesive G. The adhesive layer formed by applying adhesive G to a biaxially stretched polyester film with a thickness of 38 μm (the coating thickness after drying was 10 μm) had an adhesion to glass of 3.2 N/25 mm. The surface protective film of comparative example 5 was obtained in the same manner as in Example 1 except that adhesive G was used instead of adhesive A.

(Preparation of surface protective film of comparative example 6) 2.0 parts of isocyanate curing agent were mixed as curing agent to 100 parts of base polymer composed of 2-ethylhexyl acrylate, hydroxyl-containing acrylic monomer, and carboxyl-containing acrylic monomer to obtain adhesive H. The adhesive layer formed by applying adhesive H to a biaxially stretched polyester film with a thickness of 38 μm (the coating thickness after drying was 20 μm) had an adhesion to glass of 0.6 N/25 mm. The surface protective film of comparative example 6 was obtained in the same manner as in Example 1 except that adhesive H was used instead of adhesive B.

The following is a method for the evaluation test. (Measurement of Adhesion of Adhesive Layer) After applying the adhesive to a biaxially stretched polyester film having a thickness of 38 μm, the film was dried in a 120°C hot air circulation oven for 2 minutes. A release film on which a silicone release agent was applied to a biaxially stretched polyester film having a thickness of 25 μm was bonded to the surface of the adhesive (adhesive coating surface). The obtained sample was aged in a 40°C hot air circulation oven for 3 days. The sample was cut into a width of 25 mm and a length of 150 mm. After peeling off the release film from the sample, the sample (surface protection film) was bonded to a glass plate. The sample is pressed against the glass plate by rolling a 2kg rubber roller back and forth on the sample once. Then, the sample and the glass plate are placed at a temperature of 23°C and a relative humidity of 50% for 1 hour, and the strength of the surface protective film is measured using a tensile tester at a peeling angle of 180° and a peeling speed of 300mm/min.

(Determination of storage modulus) After applying the adhesive to a biaxially stretched polyester film with a thickness of 38 μm, dry it in a hot air circulation oven at 120°C for 2 minutes. A release film coated with a silicone release agent on a biaxially stretched polyester film with a thickness of 25 μm is attached to the surface of the adhesive (adhesive coating surface). The obtained sample is aged in a hot air circulation oven at 40°C for 3 days. The adhesive becomes an adhesive layer. After peeling off the release film from the sample, the storage modulus of the adhesive layer at 23°C is measured using a viscoelasticity measuring device (dynamic viscoelasticity test device Rheogel-E4000 manufactured by UBM).

(Evaluation of handling performance) A polarizing plate sample (total thickness 48μm) with a triacetylcellulose film laminated on one side of a polarizer made of iodine and polyvinyl alcohol was cut into A4 size (210mm×297mm). The surface protection film was laminated to the polarizing plate using a table laminating machine. The polarizing plate laminated with the surface protection film was held at one of the four corners and shaken back and forth 30 times, and then the polarizing plate was visually observed for appearance defects such as bends and bumps. The case without defects was rated as ○, and the case with defects was rated as ×.

(Evaluation of warp suppression) A polarizing plate sample (total thickness 48μm) with a cellulose triacetate film bonded to one side of a polarizing lens made of iodine and polyvinyl alcohol was cut into A4 size (210mm×297mm). The surface protective film was bonded to the polarizing plate using a table laminator. It was placed on the experimental table with the convex surface of the warp facing downward. The distance that the four corners floated from the surface of the experimental table was measured, and the largest value was set as the warp amount. The case where the warp amount was less than 10mm was rated as ○, the case where it was more than 10mm and less than 20mm was rated as △, and the case where it was more than 20mm was rated as ×.

(Evaluation of protective film peeling properties) A polarizing plate (total thickness of 48μm) with a cellulose triacetate film laminated on one side of a polarizer was prepared. A sample of the surface protective film (protective film) was cut into a width of 25mm and a length of 150mm. After peeling off the release film from the sample, the sample was bonded to the cellulose triacetate film surface of the polarizing plate. A 2kg rubber roller was rolled back and forth on the sample once, and it was pressed toward the polarizing plate. Then, the sample and the polarizing plate were placed at a temperature of 23°C and a relative humidity of 50% for 24 hours, and then the strength of the surface protective film when peeled off at a peeling angle of 180° and a peeling speed of 30m/min was measured using a high-speed peeling tester. The value of less than 1.8N/25mm was evaluated as ○, the value of more than 1.8N/25mm and less than 2.5N/25mm was evaluated as △, and the value of more than 2.5N/25mm was evaluated as ×.

(Releasability of the first adhesive layer) A polarizing plate (total thickness of 48 μm) was prepared in which a cellulose triacetate film was laminated on one side of a polarizing filter, and an adhesive layer and a release film bonded to the surface of the adhesive layer were provided on the side of the polarizing filter opposite to the cellulose triacetate film. A sample of the surface protective film was cut into a width of 25 mm and a length of 150 mm. After peeling off the release film from the sample, the sample was bonded to the cellulose triacetate film surface of the polarizing filter to obtain a polarizing filter with a surface protective film. The sample was pressed toward the polarizing filter by rolling a 2 kg rubber roller back and forth once on the sample. Then, the release film attached to the polarizing plate was peeled off, and the polarizing plate with the surface protection film was attached to the glass plate using a bench-type laminating press. Then, the polarizing plate with the surface protection film and the glass plate were placed at a temperature of 23°C and a relative humidity of 50% for 24 hours, and the adhesive film composed of the first transparent film and the first adhesive layer was peeled off from the second transparent film while pressing the second transparent film part by hand. If the adhesive film was peeled off without peeling the second adhesive layer, it was rated as good (○), and if peeling or floating occurred on the second adhesive layer, it was rated as bad (×).

The measurement results of the samples are shown in Table 1. In addition, the measurement results of the electrostatic voltage when the surface protection film of Example 1 and Example 5 was peeled off are shown in Table 2 as reference values.

[Table 1]

[Table 2] Project Unit Embodiment 1 Embodiment 5 Surface resistance of the second adhesive layer Ω/□ 5.80E+13 6.00E+11 Stripping static voltage kV 1.2 0.1

From Table 1 and Table 2, the following can be seen. The surface protection films of Examples 1 to 5 have a high effect of suppressing the warping of the optical film, and the optical film bonded with the surface protection films has good handling performance. From the results of the peeling force, it can be seen that the surface protection films of Examples 1 to 5 are surface protection films that are easily peeled off and removed after use. According to the results of the peelability of the first adhesive layer, the surface protection films of Examples 1 to 5 can peel off and remove the adhesive film composed of the first transparent film and the first adhesive layer. Example 5 in which an antistatic agent is added to the second adhesive layer is a surface protection film with a low peeling electrostatic voltage when the surface protection film is removed.

In contrast, the surface protective films of Examples 1 to 3, which only have a second adhesive layer on a polyester film, have improved handling performance and warp suppression by increasing the thickness of the film, but have reduced releasability. That is, the surface protective films of Examples 1 to 3 cannot improve all of the warp suppression, handling performance, and releasability. The surface protective film of Example 4, in which the adhesion of the first adhesive layer is high, has good handling performance and warp suppression, but the releasability of the releasability of the first adhesive layer cannot be called good. The surface protective film of Example 5, in which the storage modulus of the first adhesive layer is low, has poor warp suppression. The releasability may be deteriorated due to warping. The surface protection film of Example 6, in which the adhesion of the second adhesive layer is high, has good handling performance and warp suppression, but cannot be called good in peeling properties. Industrial Applicability

The present invention can be used, for example, in the production steps of optical films such as polarizers, phase difference plates, lens films, and optical components, to be bonded to the surface of the optical component to protect the surface. In particular, for thin-filmed optical films, the effect of suppressing the warp of the optical film is high, and the handling performance of the optical film bonded with the surface protection film is improved, and it is easy to peel off and remove after use. Therefore, it is possible to seek to improve the yield and increase the productivity of the manufacturing steps of thin-filmed optical films. In addition, since there is no need to re-stick the surface protection film or wipe off stains when shipping, it is possible to improve operability and productivity.

1: First transparent film 2: First adhesive layer 3: Second transparent film 4: Second adhesive layer 5: Peeling film C: Optical film D: Optical component P: Surface protection film

FIG. 1 is a schematic structural diagram of a surface protective film of an embodiment. FIG. 2 is a schematic structural diagram of an example of an optical component using a surface protective film of an embodiment. FIG. 3 is a schematic structural diagram showing a structure after an adhesive film composed of a first transparent film and a first adhesive layer is peeled off from the optical component shown in FIG. 2 .

1: First transparent film

2: First adhesive layer

3: Second transparent film

4: Second adhesive layer

5: Peel off the membrane

P: Surface protection film

Claims (4)

A surface protection film is provided, which comprises a first transparent film, a first adhesive layer, a second transparent film and a second adhesive layer stacked in sequence, wherein the surface resistivity of the second adhesive layer is less than 1×10 ¹³ [Ω/□], the adhesion of the first adhesive layer is higher than the adhesion of the second adhesive layer, the adhesion of the second adhesive layer to glass is less than 0.5N/25mm, and the adhesive film composed of the first transparent film and the first adhesive layer can be peeled off from the second transparent film. The surface protection film according to claim 1, wherein the second adhesive layer uses a (meth)acrylic polymer as a base polymer. The surface protection film according to claim 1 or 2, wherein a release film is bonded to the surface of the second adhesive layer. An optical component having a surface protection film as described in any one of claims 1 to 3 attached thereto.