Surface protection film and optical component with the film attached thereto

Abstract

To provide a surface protective film high in an effect of suppressing occurrence of curling of an optical film, and improved in handling ability of an optical film adhered with a surface protective film, furthermore, easy in an operation of peeling a peeling film from an optical film with an adhesive, and easy to remove by peeling after use, and an optical component adhered therewith.SOLUTION: A surface protective film P is formed by laminating a first transparent film 1, a first adhesive layer 2, a second transparent film 3, and a second adhesive layer 4 in this order. The surface protective film P satisfies the following condition (1). Condition (1): When adhesive force to glass of the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 is set to adhesive force 1, and adhesive force to glass of the adhesive film formed of the second transparent film 3 and the second adhesive layer 4 is set to adhesive force 2, adhesive force 1<adhesive force 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a surface protection film and an optical component to which the same is adhered.

Background Art

[0002] Optical films such as polarizing plates, retardation plates, lens films for displays, antireflection films, hard coat films, and transparent conductive films for touch panels are used in optical products such as displays. When manufacturing and transporting these optical films or optical components, a surface protection film is adhered to the surface of the optical film to prevent surface contamination and damage in subsequent processes. In addition, when inspecting the appearance of an optical film, it may be performed with the surface protection film adhered.

[0003] Conventional surface protection films typically have a configuration in which an adhesive layer with a slightly adhesive force is provided on one side of a base film. The adhesive layer is a layer for adhering the surface protection film to an optical film or the like. The adhesive layer is made slightly adhesive in order to be able to peel off smoothly and without adhesive residue when peeling off the used surface protection film from the surface of the optical film.

[0004] In recent years, displays have been becoming thinner and higher in definition, and accordingly, optical films have also been becoming thinner. In addition, in order to make the optical film thinner, not only the thickness of each component member is reduced, but also the configuration is changed, such as omitting unnecessary members or combining the functions of a plurality of members into one member to reduce the number of members. For example, in polarizing plates, the number of polarizing plates having a configuration in which a polarizer protective layer is laminated only on one side instead of both sides of the polarizer layer is increasing. In the case of a polarizing plate in which the polarizer protective layer is provided only on one side with respect to the polarizer layer, the structure sandwiching the polarizer becomes asymmetric on the front and back sides, so it has a property of being easily bent (curled) on one side. Since curling significantly deteriorates the handleability of the optical film, a proposal for an optical film with suppressed curling has been disclosed.

[0005] For example, Patent Document 1 proposes a technique for suppressing the curl of a polarizing plate by laminating 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 is cited in which the thickness of a base film made of a biaxially stretched polyester resin is in the range of 25 μm or more and 120 μm or less.

[0006] Patent Document 2 proposes a polarizing plate that defines the Gurley stiffness of a laminate composed of a polarizing plate main body and a protective film (surface protective film). As a specific example, a polarizing plate using a protective film with a base film thickness of 50 μm made of a biaxially stretched polyester resin is cited.

[0007] Patent Document 3 proposes a protective film capable of favorably suppressing the warp (curl) of a polarizing plate. Specifically, a protective film having a first resin layer, an adhesive layer, a second resin layer, and an adhesive layer in this order is proposed. The value of the ratio of the thickness of the adhesive layer to the sum of the thicknesses of the first resin layer and the second resin layer is 0.40 or less. The storage elastic 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 integrally laminated on the surface of the polarizing plate and integrally peeled off.

[0008] The surface protective films shown in Patent Documents 1 to 3 increase the stiffness of the film by increasing the thickness of the base film or using a laminated film in which a resin layer / adhesive layer / resin layer is laminated as the base film, and a curl suppression effect for an optical film can be obtained. However, on the other hand, when peeling off and removing the surface protective film after use, there is a problem that the peeling force becomes strong.

[0009] When peeling off the surface protection film, the surface protection film is peeled off from the optical film at a peeling angle close to 180°. The peeling force of the surface protection film at this time is the sum of the force with which the adhesive of the surface protection film adheres to the optical film as the adherend and the force required to bend the surface protection film itself by 180°. When the stiffness of the surface protection film increases, the force required to bend the surface protection film itself by 180° also increases, so the peeling force of the surface protection film becomes stronger. In recent years, along with the thinning and high definition of displays, the size of displays has also been increasing in the applications of televisions and digital signage. For the optical films used in such large displays, the aforementioned surface protection film has a strong peeling force during peeling, so it is difficult to use.

[0010] In addition, optical films often have an adhesive layer for bonding to a panel or bonding to other optical films. For such optical films with an adhesive layer, a peeling film (sometimes called a separator or release film) is bonded to the adhesive layer for the purpose of protecting the adhesive layer. When bonding the optical film to a panel or other optical films, the peeling film is removed and used.

[0011] When thinning the optical film, it is possible to adjust the layer structure and manufacturing conditions of the optical film to produce an optical film that is difficult to curl. However, when removing the peeling film from the optical film with an adhesive layer, if the optical film is thin and has low stiffness, the optical film will be deformed by the peeling force when peeling off the peeling film, and there is a problem that the peeling film is difficult to peel off. A surface protection film with high stiffness also has the effect of making it easier to peel off the peeling film from the optical film with an adhesive by reinforcing the optical film.

[0012] Conventionally, in the manufacture of displays, parts such as liquid crystal panels, backlight units, and surface filters were procured in a form set by panel manufacturers (module procurement). However, in recent years, particularly in the case of televisions, a procurement form called "open cell procurement" has become mainstream. In open cell procurement, parts such as liquid crystal panels, backlight units, and surface filters are procured individually and assembled by television manufacturers, OEMs, etc. For this reason, the circulation of liquid crystal panels in a semi-finished state is increasing.

[0013] In module procurement, the surface protection film attached to the polarizing plate was peeled off after panelization. However, with the adoption of open cell procurement, in order to prevent the adhesion of dust and foreign matter during the transportation of liquid crystal panels, it has become common not to peel off the surface protection film until immediately before the set is made after panelization. When shipping and transporting liquid crystal panels, it is increasing to replace the surface protection film soiled during panelization or wipe off the dirt on the surface protection film to keep the surface of the surface protection film clean. In the surface protection films described in Patent Documents 1 to 3, operations such as replacing the surface protection film or wiping off the dirt on the surface protection film are required before shipping the liquid crystal panel, etc., which does not lead to process reduction and workability improvement.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0015] One aspect of the present invention has been made in view of the above circumstances, and has a high effect of suppressing the occurrence of curl of an optical film, improves the handleability of the optical film with a surface protection film attached, and further, the work of peeling the release film from the optical film with an adhesive is easy, and a surface protection film that is easy to peel off after use and an optical component to which the same is attached are provided.

Means for Solving the Problems

[0016] The inventors of the present invention have intensively studied to solve these problems. In order to suppress the curl of the optical film, improve the handleability of the optical film with the surface protection film attached, and further facilitate the work of peeling the release film from the optical film with an adhesive, it has been found that it is necessary to give the surface protection film laminated on the optical film a stiffness. However, it has been found that when the surface protection film has stiffness, the peeling force becomes strong when removing the surface protection film after use, and the surface protection film is difficult to peel off. It has been found that the curl suppression of the optical film, the improvement of handleability, the peelability of the release film, and the peelability of the surface protection film are in a contradictory relationship, and it is difficult to make these characteristics compatible only by considering the stiffness of the surface protection film.

[0017] In order to solve the above problems, the inventor of the present invention has studied whether there is a method in which the stiffness of the surface protection film is high when laminated on the polarizing plate and the stiffness of the surface protection film is low when removing the surface protection film. As a result, it has been found that any surface protection film that can change its form when laminated on the optical film and when peeling off the surface protection film can satisfy all the contradictory characteristics. One aspect of the present invention has a technical idea that it is a surface protection film that is integrated when laminated on the optical film and can be separated when peeled off after use.

[0018] One embodiment of the present invention provides a surface protection film in which a first transparent film, a first adhesive layer, a second transparent film, and a second adhesive layer are laminated in this order, and which satisfies the following condition (1). Condition (1): When the adhesive force of the adhesive film composed of the first transparent film and the first adhesive layer to glass is defined as adhesive force 1, and the adhesive force of the adhesive film composed of the second transparent film and the second adhesive layer to glass is defined as adhesive force 2, adhesive force 1 < adhesive force 2.

[0019] For the first adhesive layer, an acrylic adhesive or a urethane adhesive can be used.

[0020] The surface resistivity of the second adhesive layer is preferably less than 1×10 13 〔Ω / □〕.

[0021] Another embodiment of the present invention provides an optical component to which the surface protection film is attached.

Advantages of the Invention

[0022] According to one aspect of the present invention, there is provided a surface protection film that highly suppresses the generation of curl in an optical film, improves the handleability of the optical film to which the surface protection film is attached, and further facilitates the operation of peeling off the release film from the optical film with an adhesive. After use, it is easy to peel off and remove. It is possible to provide a surface protection film that does not require replacement or wiping of dirt of the surface protection film at the time of liquid crystal panel shipment, and an optical component using the same.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Best Mode for Carrying Out the Invention

[0024] Hereinafter, based on the embodiments, the present invention will be described in detail. FIG. 1 is a schematic configuration diagram of the surface protection film P of the embodiment. As shown in FIG. 1, on one side of the first transparent film 1, a first adhesive layer 2 is provided. On the side of the first adhesive layer 2 opposite to the transparent film 1, a second transparent film 3 is provided. On the side of the second transparent film 3 opposite to the first adhesive layer 2, a second adhesive layer 4 is provided. A release film 5 for protecting the adhesive surface is laminated on the surface of the second adhesive layer 4. That is, the surface protection film P is composed of the first transparent film 1, the first adhesive layer 2, the second transparent film 3, the second adhesive layer 4, and the release film 5 laminated in this order. Note that the film obtained by removing the release film 5 from the surface protection film P shown in FIG. 1, that is, the film in which the first transparent film 1, the first adhesive layer 2, the second transparent film 3, and the second adhesive layer 4 are laminated in this order may be referred to as the surface protection film P.

[0025] As the first transparent film 1 (base film), a plastic film having transparency is used. Since the first transparent film 1 and the second transparent film 3 have transparency, it becomes possible to perform an appearance inspection of the optical component while the surface protection film P is attached. As the plastic film for the first transparent film 1, preferably, a polyester film such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or polybutylene terephthalate is used. In addition to the polyester film, other plastic films can also be used as long as they have the required strength and optical suitability. The first transparent film 1 may be an unstretched film, or may be uniaxially or biaxially stretched. The first transparent film 1 may also be a plastic film in which the stretching ratio and the angle in the axial direction formed due to stretching crystallization are controlled.

[0026] "Transparent" means, for example, that the visible light transmittance calculated as the average value of the transmittance in the thickness direction over the entire wavelength range when measured within the range of a measurement wavelength of 380 nm to 780 nm is 50% or more (preferably 70% or more, more preferably 80% or more). The light transmittance can be measured in accordance with "Plastics - Methods of Test for Total Light Transmittance and Total Light Reflectance" specified in JIS K 7375:2008.

[0027] Although the thickness of the first transparent film 1 is not particularly limited, it is, for example, about 12 to 100 μm, and particularly often about 20 to 50 μm. On the first transparent film 1, if necessary, on the side opposite to the first adhesive layer 2 (the upper surface in FIG. 1), an antifouling layer for the purpose of preventing surface contamination, an antistatic layer, a hard coat layer for preventing damage, etc. may be provided, or an easy adhesion treatment such as corona discharge treatment or anchor coat treatment may be performed.

[0028] The first adhesive layer 2 is used for the purpose of absorbing and relaxing the stress associated with the curl of the optical film when the surface protection film P is adhered to the optical film, and for the purpose of peeling in two stages when the surface protection film is removed from the optical film. The first adhesive layer 2 is not particularly limited in terms of material as long as it satisfies characteristics such as having no adverse effect on the adhesion, adhesive properties, stability, etc. with the transparent film, and known materials can be used.

[0029] Examples of the material of the first adhesive layer 2 include adhesives such as rubber-based, acrylic-based, urethane-based, and silicone-based adhesives. The rubber-based adhesive is an adhesive in which an adhesion promoter, a softening agent, an antioxidant, a filler, etc. are blended with an elastomer such as natural rubber or synthetic rubber, and a crosslinking agent may be added if necessary. The acrylic-based adhesive is, for example, an adhesive in which a curing agent and an adhesion promoter are added to a (meth)acrylic-based polymer as necessary. The (meth)acrylic-based polymer is butyl acrylate (for example, n-butyl acrylate ), polymers copolymerized from main monomers such as 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, and comonomers such as acrylonitrile, vinyl acetate, methyl acrylate, methyl methacrylate, ethyl acrylate, and functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, glycidyl methacrylate, dimethylacrylamide, N-methylol methacrylamide, hydroxyl group-containing acrylic monomers, carboxyl group-containing acrylates, polyoxyalkylene group-containing acrylic monomers, etc. are common. For (meth)acrylic polymers, an appropriate composition may be selected according to the required properties. (Meth)acrylic polymers are used as base polymers.

[0030] Examples of curing agents include isocyanate compounds, epoxy compounds, melamine compounds, metal chelate compounds, etc. Examples of tackifiers include rosin-based, coumarone-indene-based, terpene-based, petroleum-based, phenol-based, etc. Additives such as curing catalysts, pot life extenders, antistatic agents, ultraviolet absorbers, antioxidants, etc. may be added to the first adhesive layer 2 as required. As the material of the first adhesive layer 2, an adhesive in which a photoinitiator and a monomer or oligomer capable of photocuring are added to the above adhesive, and the monomer or oligomer polymerizes after light irradiation and the adhesive force changes may also be used.

[0031] Polyurethane adhesives are polyurethane resins composed of a polyol component and a polyisocyanate component, and can be selected considering adhesiveness, wettability, adherend stainability, etc. The polyol component and the polyisocyanate component are not particularly limited. The polyurethane resin may be used alone or in a mixture of two or more. Polyurethane adhesives are sometimes simply referred to as "urethane adhesives".

[0032] Examples of the polyol component include polyester polyol, polyether polyol, polycaprolactone polyol, polycarbonate polyol, castor oil-based polyol, and the like. These polyol components may be used alone or in combination of two or more.

[0033] Examples of the polyisocyanate component include aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic polyisocyanate, and polyisocyanate dimer. These polyisocyanate components may be used alone or in combination of two or more.

[0034] Examples of commercially available polyurethane adhesives include Siavine (registered trademark) SH-101, SH-101M, SH-109, SP-205, SP-220 (manufactured by Toyochem Co., Ltd.), Arcot (registered trademark) FT100, FT200 (manufactured by Arakawa Chemical Industries, Ltd.), UN1175, UN1176 (manufactured by Daido Kasei Kogyo Co., Ltd.), and the like. The first adhesive layer 2 may be formed by crosslinking or curing a polyurethane adhesive.

[0035] Examples of silicone adhesives include addition reaction type and peroxide curing type. Since the addition reaction type has lower adhesive strength, it is more suitable. Silicone adhesives are generally those obtained by adding a silicone resin to a polyorganosiloxane polymer such as polydimethylsiloxane, but those not containing a silicone resin can also be used.

[0036] The first adhesive layer 2 may contain additives such as an antistatic agent, an adhesion improver, an ultraviolet absorber, a specific wavelength absorber, an antioxidant, a dye, and a pigment, if necessary.

[0037] As the material of the first adhesive layer 2, urethane adhesives and acrylic adhesives are particularly preferred in terms of heat resistance, durability, and adhesion to the second transparent film 3.

[0038] The adhesive force of the first adhesive layer 2 to the glass is lower than the adhesive force of the second adhesive layer 4 to the glass. If the adhesive force of the first adhesive layer 2 is equal to or greater than the adhesive force of the second adhesive layer 4, when removing the surface protection film, the surface protection film is likely to peel off from the interface between the second adhesive layer 4 and the optical film. Therefore, the peeling force of the surface protection film becomes high (strong), and there is a risk that the surface protection film becomes difficult to peel off.

[0039] The thickness of the first adhesive layer 2 is not particularly limited, but it is generally about 3 to 30 μm. By setting the thickness of the first adhesive layer 2 to 3 μm or more, a predetermined adhesive force can be obtained. By setting the thickness of the first adhesive layer 2 to 30 μm or less, the cost can be suppressed.

[0040] As a method for forming the first adhesive layer 2 on the first transparent film 1, a known method may be used. For example, a method of coating the first transparent film 1 with an adhesive and drying and curing it, or a method of coating the second transparent film with an adhesive, drying and curing it, and then bonding the first transparent film can be mentioned. Specifically, known coating methods such as reverse coating, comma coating, gravure coating, slot die coating, Mayer bar coating, and air knife coating can be used.

[0041] As the second transparent film 3, a plastic film having transparency is used. Since the first transparent film 1 and the second transparent film 3 have transparency, it becomes possible to perform an appearance inspection of the optical component while the surface protection film is adhered. As the plastic film for the second transparent film 3, preferably, a polyester film such as polyethylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or polybutylene terephthalate is used. In addition to the polyester film, other plastic films can be used as long as they have the required strength and optical suitability. The second transparent film 3 may be an unstretched film or may be uniaxially or biaxially stretched. The second transparent film 3 may also be a plastic film in which the stretching magnification and the axial angle formed with the crystallization of stretching are controlled.

[0042] Although the thickness of the second transparent film 3 is not particularly limited, for example, it is about 12 to 100 μm, and particularly often about 19 to 50 μm. If necessary, the second transparent film 3 may be subjected to an easy adhesion treatment such as a corona discharge treatment or an anchor coat treatment or an antistatic treatment on the side in contact with the first adhesive layer 2. Further, an antistatic layer or an easy adhesion treatment such as a corona discharge treatment or an anchor coat treatment may be performed on the opposite side (the lower surface in FIG. 1) of the first adhesive layer 2 of the second transparent film 3.

[0043] The second adhesive layer 4 is provided for adhering the surface protection film P to the optical film as the adherend. The second adhesive layer 4 is a layer made of an adhesive having a low adhesive force. The reason for using an adhesive having a low adhesive force is that the surface protection film P does not peel off during the manufacturing process 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 and there is no adhesive residue.

[0044] The material of the second adhesive layer 4 is not particularly limited, and known materials such as adhesives of rubber-based, acrylic-based, urethane-based, etc. can be used, but among them, acrylic-based adhesives are preferred. An acrylic adhesive is, for example, an adhesive obtained by adding a curing agent and a tackifier to a (meth)acrylic polymer as needed. The (meth)acrylic polymer is a copolymer of main monomers such as butyl acrylate (e.g., n-butyl acrylate ) , 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, etc., comonomers 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-methylol methacrylamide, hydroxyl group-containing acrylic monomers, carboxyl group-containing acrylates, polyoxyalkylene group-containing acrylic monomers, etc. The (meth)acrylic polymer may have an appropriate composition selected according to the required properties. The (meth)acrylic polymer is used as a base polymer.

[0045] Examples of the curing agent include isocyanate compounds, epoxy compounds, melamine compounds, metal chelate compounds, etc. Examples of the tackifier include rosin-based, coumarone-indene-based, terpene-based, petroleum-based, phenol-based, etc. Additives such as a curing catalyst, a pot life extender, an antistatic agent, an ultraviolet absorber, an antioxidant, etc. may be added to the acrylic adhesive as needed.

[0046] As the antistatic agent, those having good dispersion or compatibility with the (meth)acrylic polymer are preferable, and examples thereof include surfactant-based, ionic liquids, ionic solids, alkali metal salts, metal oxides, metal fine particles, conductive polymers, carbon, carbon nanotubes, etc. As the antistatic agent, surfactant-based, ionic liquids, ionic solids, alkali metal salts, etc. are preferable from the viewpoints of transparency and affinity for the (meth)acrylic polymer.

[0047] Surfactants used as antistatic agents in surfactant-based systems include nonionic, cationic, anionic, and amphoteric types. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid esters, glycerin fatty acid esters, propylene glycol fatty acid esters, polyoxyalkylene-modified silicones, and the like. Examples of cationic surfactants include alkyltrimethylammonium salts, dialkyldimethylammonium salts, alkylbenzyldimethylammonium salts, and the like. Examples of anionic surfactants include monoalkyl sulfates, alkyl polyoxyethylene sulfates, alkylbenzene sulfonates, monoalkyl phosphates, and the like. Examples of amphoteric surfactants include alkyldimethylamine oxide, alkyl carboxy betaine, and the like.

[0048] Ionic liquids are non-polymeric substances that contain anions and cations and are liquid at room temperature. Examples of the cationic part include cyclic amidine ions such as imidazolium ions, pyridinium ions, ammonium ions, sulfonium ions, phosphonium ions, etc. The anionic part includes C n H 2n+1 COO - 、C n F 2n+1 COO - 、N03 - 、C n F 2n+1 SO3 - 、(C n F 2n+1 SO2)2N - 、(C n F 2n+1 SO2)3C - 、PO4 2- 、AlCl4 - 、Al2Cl7 - 、ClO4 - 、BF4 - 、PF6 - 、AsF6 - 、SbF6- include the following.

[0049] An ionic solid is a non-polymeric substance that contains anions and cations and is solid at room temperature. Examples of the cationic part include nitrogen-containing onium ions such as pyridinium ion, imidazolium ion, pyrimidinium ion, pyrazolium ion, pyrrolidinium ion, ammonium ion, etc., and phosphonium ion, sulfonium ion, etc. Examples of the anionic part include inorganic or organic anions such as phosphate hexafluoride (PF6 - ), thiocyanate (SCN - ), alkylbenzene sulfonate (RC6H4SO3 - ), perchlorate (ClO4 - ), tetrafluoroborate (BF4 - ). By selecting the chain length of the alkyl group, the position and number of substituents, etc., a solid at room temperature can be obtained.

[0050] Examples of the alkali metal salt include metal salts containing alkali metals such as lithium, sodium, and potassium. For example, lithium trifluoromethyl sulfonate (CF3LiO3S) can be exemplified as the alkali metal salt. For the antistatic agent, a compound containing a polyoxyalkylene structure may be added to stabilize the ionic substance.

[0051] The addition amount of the antistatic agent component to the base polymer such as (meth)acrylic polymer varies depending on the type of the antistatic component and the degree of compatibility with the base polymer, and may be set in consideration of the surface resistivity, the contamination of the adherend, the adhesion characteristics, etc. Additives such as a curing catalyst, a pot life extender, an ultraviolet absorber, and an antioxidant may be added to the acrylic adhesive as necessary. The rubber-based and urethane-based adhesives may be the same as the adhesive used for the first adhesive layer 2.

[0052] When the surface protection film P is used in applications where there is a concern about the peeling charging voltage during peeling and removal, it is preferable 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 / sq]. When the surface resistivity of the second adhesive layer 4 is less than 1×10 13 [Ω / sq], the peeling charging voltage when removing the surface protection film can be lowered. Therefore, the antistatic performance can be enhanced.

[0053] Although the thickness of the second adhesive layer 4 is not particularly limited, for example, it is often about 3 to 50 μm, especially about 5 to 30 μm.

[0054] The adhesion of the second adhesive layer 4 to glass is higher than the adhesion of the first adhesive layer 2 to glass. If the adhesion of the second adhesive layer 4 is less than or equal to the adhesion of the first adhesive layer 2, when removing the surface protection film, the surface protection film is likely to peel off from the interface between the second adhesive layer 4 and the optical film. Therefore, the peeling force of the surface protection film becomes high (strong), and there is a risk that the surface protection film becomes difficult to peel off.

[0055] In other words, the surface protection film P satisfies the following condition (1). Condition (1): When the adhesion of the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 to glass is defined as adhesion 1, and the adhesion of the adhesive film composed of the second transparent film 3 and the second adhesive layer 4 to glass is defined as adhesion 2, "adhesion 1 < adhesion 2".

[0056] The second adhesive layer 4 is preferably a slightly adhesive micro-adhesive layer having a peel strength of about 0.03 to 0.3 N / 25 mm with respect to the surface of the adherend (optical film). When the adhesive force of the second adhesive layer 4 is 0.03 N / 25 mm or more, it is possible to suppress the surface protection film P from floating in the manufacturing process and the conveyance process of the optical film. When the adhesive force of the second adhesive layer 4 is 0.03 N / 25 mm or more, it is difficult for the surface protection film P to be peeled off by mistake. When the adhesive force of the second adhesive layer 4 is 0.3 N / 25 mm or less, workability can be improved.

[0057] The lamination of the second adhesive layer 4 on the second transparent film 3 may be performed by a known method and is not particularly limited. Specifically, (1) a method in which an adhesive that becomes 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 bonded to the surface of the second adhesive layer 4, (2) a method in which an adhesive that becomes the second adhesive layer 4 is applied to the release film 5, dried to form the second adhesive layer 4, and then the second transparent film 3 is bonded, etc. can be mentioned.

[0058] The formation of the second adhesive layer 4 on the second transparent film 3 may be performed by a known method. Specifically, an adhesive may be applied by coating means such as reverse coating, comma coating, gravure coating, slot die coating, Mayer bar coating, air knife coating, etc.

[0059] The surface protection film P generally has a configuration in which the surface of the adhesive layer 4 of the adhesive sheet formed with the first adhesive layer 2, the second transparent film 3, and the second adhesive layer 4 on the first transparent film 1 is protected by the release film 5. The surface protection film P can also be in a product form in which the first transparent film 1 / first adhesive layer 2 / second transparent film 3 / second adhesive layer 4 is wound in a tape shape without using the release film 5 if necessary.

[0060] The release film 5 is not particularly limited, and examples thereof include those 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, a non-silicone-based release agent, or a fluorine-based release agent. The release film 5 may also be a single film such as a polyolefin such as polypropylene or a fluorine film that can be used alone.

[0061] FIG. 2 is a schematic configuration diagram of an optical component D, which is an example of an optical component using the surface protection film P of the embodiment. As shown in FIG. 2, the optical component D is obtained by attaching the surface protection film P shown in FIG. 1 to the surface of the optical film C using the adhesive layer 4. Examples of the optical film C include a polarizing plate, a retardation plate, a lens film, a polarizing plate also serving as a retardation plate, and a polarizing plate also serving as a lens film. Such an optical component D can be used in the manufacture of liquid crystal display devices such as liquid crystal display panels and various instruments, optical system devices, etc.

[0062] Since the surface protection film P of the embodiment has a multilayer structure having two transparent films and two adhesive layers, it has a high effect of suppressing the curl of the optical film C. Due to the above-described structure, the surface protection film P is less likely to be folded or have irregularities on the optical film C. Therefore, the handleability of the optical film C can be improved.

[0063] Generally, when the surface protection film is formed thick, the curl suppression property and the handleability increase, while the peelability of the surface protection film decreases. In contrast, when the surface protection film P of the embodiment is peeled off after use, the first transparent film 1 and the first adhesive layer 2 are peeled off from the interface between the first adhesive layer 2 and the second transparent film 3, and then the second transparent film 3 and the second adhesive layer 4 are peeled off from the optical film, so that the surface protection film is easy to peel off.

[0064] When peeling off and removing the surface protection film P, first, the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 is peeled off and removed from other parts. For example, FIG. 3 is a schematic configuration diagram showing a configuration in which the adhesive film composed of the first transparent film 1 and the first adhesive layer 2 is peeled off and removed from the optical component D (see FIG. 2). As shown in FIG. 3, by peeling off and removing the adhesive film, a clean surface of the surface protection film can be exposed. Therefore, when shipping the liquid crystal panel, etc., it is not necessary to replace the surface protection film or wipe off dirt. Thus, man-hours can be reduced, and the yield can be improved, productivity can be enhanced, and workability can be improved.

[0065] In particular, the surface protection film P has a high effect of suppressing the occurrence of curl of the optical film that has been made thinner, and the handleability of the optical film with the surface protection film attached is improved. Furthermore, it is easy to peel off and remove after use. Therefore, it is possible to improve the yield, productivity, and workability in the manufacturing process of the thinner optical film.

Example

[0066] Next, the present invention will be further described with reference to examples. Hereinafter, "parts by mass" may be simply referred to as "parts". (Preparation of the surface protection film of Example 1) To 100 parts of a base polymer composed of 2-ethylhexyl acrylate and a hydroxyl group-containing acrylic monomer, 4 parts of an isocyanate-based curing agent was blended as a curing agent to obtain an adhesive A. The adhesive force of the adhesive layer (coating thickness after drying: 15 μm) formed by applying the adhesive A to a biaxially stretched polyester film with a thickness of 38 μm to glass was 0.10 N / 25 mm.

[0067] To 100 parts of a base polymer composed of 2-ethylhexyl acrylate, methyl acrylate, polyoxyethylene acrylate, and a hydroxyl group-containing acrylic monomer, 2 parts of an isocyanate-based curing agent was blended as a curing agent to obtain an adhesive B. The adhesive force of the adhesive layer (coating thickness after drying: 15 μm) formed by applying the adhesive B to a biaxially stretched polyester film with a thickness of 38 μm to glass was 0.15 N / 25 mm.

[0068] An adhesive A was applied to a colorless and transparent biaxially stretched polyester film (first transparent film) with a thickness of 38 μm so that the coating thickness after drying would be 15 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes. Next, a colorless and transparent biaxially stretched polyester film (second transparent film) with a thickness of 38 μm was laminated on the surface of the adhesive A (adhesive A-coated surface). An adhesive B was applied to the surface opposite to the adhesive A of the laminated biaxially stretched polyester film so that the coating thickness after drying would be 15 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes.

[0069] A release film (MRF-25 manufactured by Mitsubishi Chemical) obtained by coating a biaxially stretched polyester film with a thickness of 25 μm with a silicone-based release agent was laminated on the surface of the adhesive B (adhesive B-coated surface) so that the surface of the adhesive B and the release agent-treated surface (the surface coated with the silicone-based release agent) were in contact. The obtained sample was aged in a hot air circulation oven at 40°C for 3 days to obtain the surface protection film of Example 1. The adhesive layer formed of the adhesive A is the first adhesive layer. The adhesive layer formed of the adhesive B is the second adhesive layer.

[0070] (Preparation of the surface protection film of Example 2) To 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, a hydroxyl group-containing acrylic monomer, and a carboxyl group-containing acrylate, 2 parts of an isocyanate-based curing agent were blended as a curing agent to obtain an adhesive C. The adhesive force of the adhesive layer (coating thickness after drying: 15 μm) formed by applying the adhesive C to a biaxially stretched polyester film with a thickness of 38 μm to glass was 0.3 N / 25 mm. A surface protection film of Example 2 was obtained in the same manner as in Example 1, except that the adhesive C was used instead of the adhesive B. The adhesive layer formed of the adhesive A is the first adhesive layer. The adhesive layer formed of the adhesive C is the second adhesive layer.

[0071] (Preparation of the surface protection film of Example 3) To 100 parts of a base polymer composed of 2-ethylhexyl acrylate, methyl acrylate, polyoxyethylene acrylate, and a hydroxyl group-containing acrylic monomer, 2 parts of an isocyanate-based curing agent and 0.1 part of lithium trifluoromethanesulfonate as an antistatic agent were blended to obtain an adhesive D. The adhesive force of the adhesive layer (coating thickness after drying: 15 μm) formed by applying the adhesive D to a biaxially stretched polyester film with a thickness of 38 μm to glass was 0.12 N / 25 mm, and the surface resistance value of the adhesive surface was 4.2×10 11 Ω / □. A surface protection film of Example 3 was obtained in the same manner as in Example 1, except that the adhesive D was used instead of the adhesive B. The adhesive layer formed of the adhesive A is the first adhesive layer. The adhesive layer formed of the adhesive D is the second adhesive layer.

[0072] (Preparation of the surface protection film of Example 4) A 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 (second transparent film) with a thickness of 25 μm was used instead of the biaxially stretched polyester film (second transparent film) with a thickness of 38 μm. The adhesive layer formed of the adhesive A is the first adhesive layer. The adhesive layer formed of the adhesive B is the second adhesive layer.

[0073] (Production of the surface protection film of Example 5) As the urethane-based adhesive, 8 parts of the isocyanate-based curing agent Cyabine T-501 (manufactured by Toyochem Co., Ltd.) was blended with 100 parts of the urethane adhesive "Cyabine SH-109" manufactured by Toyochem Co., Ltd. to obtain Adhesive E. As the first adhesive layer, the surface protection film of Example 5 was obtained in the same manner as in Example 1, except that Adhesive E was used instead of Adhesive A. The adhesive layer formed of Adhesive E is the first adhesive layer. The adhesive layer formed of Adhesive B is the second adhesive layer.

[0074] (Production of the surface protection film of Comparative Example 1) On a colorless and transparent biaxially stretched polyester film with a thickness of 38 μm, Adhesive B was applied so that the coating thickness after drying was 15 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes. On the surface of Adhesive B (the surface where Adhesive B was applied), a release film (peel film) obtained by coating a silicone-based release agent on a biaxially stretched polyester film with a thickness of 25 μm was laminated so that the surface of Adhesive B and the release agent-treated surface (the surface where the silicone-based release agent was applied) were in contact. 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 becomes the adhesive layer.

[0075] (Production 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 with a thickness of 75 μm was used instead of the biaxially stretched polyester film with a thickness of 38 μm.

[0076] (Production of the 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.

[0077] (Production of the surface protection film of Comparative Example 4) A pressure-sensitive adhesive A and a pressure-sensitive adhesive B were used in the same manner as in Example 1 except that they were interchanged, and a surface protection film of Comparative Example 4 was obtained. The pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive B is the first pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive A is the second pressure-sensitive adhesive layer.

[0078] The method of the evaluation test is shown below. (Measurement of the adhesive strength of the pressure-sensitive adhesive layer) After applying a pressure-sensitive adhesive to a biaxially stretched polyester film with a thickness of 38 μm, it is dried in a hot air circulation oven at 120 °C for 2 minutes. A release film coated with a silicone-based release agent is laminated on the surface of the pressure-sensitive adhesive (the pressure-sensitive adhesive coating surface), which is a biaxially stretched polyester film with a thickness of 25 μm. The obtained sample is aged in a 40 °C hot air circulation oven for 3 days. The sample is cut into a width of 25 mm and a length of 150 mm. After peeling off the release film from the sample, this sample (surface protection film) is laminated on a glass plate. The sample is pressed against the glass plate by rolling a 2 kg rubber roller once back and forth on the sample. Then, after leaving the sample and the glass plate under the conditions of a temperature of 23 °C and a relative humidity of 50% for 1 hour, the strength when peeling off the surface protection film at a peeling angle of 180° and a peeling speed of 300 mm / min is measured using a tensile tester.

[0079] (Evaluation of handleability) A polarizing plate sample (total thickness 48 μm) obtained by laminating a triacetyl cellulose film on one side of a polarizer composed of iodine and polyvinyl alcohol is cut into A4 size (210 mm × 297 mm). Using a tabletop laminator, a surface protection film is laminated on the polarizing plate. Holding one of the four corners of the polarizing plate laminated with the surface protection film and shaking it back and forth 30 times, the presence or absence of appearance defects such as folds and unevenness on the polarizing plate is visually observed. Those without defects are marked as ○ (Good), and those with defects are marked as × (No Good).

[0080] (Evaluation of curl suppression) A polarizing plate sample (total thickness: 48 μm) consisting of iodine and polyvinyl alcohol with a triacetyl cellulose film laminated on one side is cut into A4 size (210 mm × 297 mm). Using a tabletop laminator, a surface protection film is laminated on the polarizing plate. Place it on the experimental bench with the convex side of the curl facing down. For the four corners, measure the floating distance from the surface of the experimental bench, and use the largest value as the curl amount. Those with a curl amount less than 10 mm are marked as ○ (Good), those with 10 mm or more and less than 20 mm are marked as △ (Fair), and those with 20 mm or more are marked as × (No Good).

[0081] (Evaluation of peelability of protective film) Prepare a polarizing plate (total thickness: 48 μm) with a triacetyl cellulose film laminated on one side of the polarizer. Cut a sample of the surface protection film (protective film) to a width of 25 mm and a length of 150 mm. After peeling off the release film from the sample, laminate this sample on the triacetyl cellulose film side of the polarizing plate. Press the sample against the polarizing plate by rolling a 2 kg rubber roller back and forth once on the sample. Then, after leaving the sample and the polarizing plate under the conditions of a temperature of 23°C and a relative humidity of 50% for 24 hours, use a high-speed peeling tester to measure the strength when peeling the surface protection film at a peeling angle of 180° and a peeling speed of 30 m / min. Those less than 1.5 N / 25 mm are marked as ○ (Good), those with 1.5 N / 25 mm or more and less than 2.5 N / 25 mm are marked as △ (Fair), and those with 2.5 N / 25 mm or more are marked as × (No Good).

[0082] (Peelability of release film of optically functional film with adhesive) A polarizing plate sample (total thickness: 48 μm) consisting of iodine and polyvinyl alcohol with a triacetyl cellulose film laminated on one side is cut into A4 size (210 mm × 297 mm). Using a tabletop laminator, a surface protection film is laminated on the polarizing plate.

[0083] On a 38-μm thick release film (MRF-38 manufactured by Mitsubishi Chemical), an adhesive F was prepared by blending 0.5 part of an isocyanate-based curing agent and 0.5 part of a silane coupling agent with 100 parts of a base polymer composed of butyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate, and acrylic acid. The adhesive F was applied with an applicator so that the thickness after drying would be 20 μm, and then dried in a hot air circulation oven at 120°C for 2 minutes. A surface protection film was laminated on the surface of the adhesive F (the surface where the adhesive F was applied), on the side opposite to the surface protection film of a polarizing plate with the surface protection film already laminated. The obtained sample was aged in a hot air circulation oven at 40°C for 5 days to produce a polarizing plate with an adhesive layer. From the polarizing plate with the release film laminated, the strength when peeling the release film at a peeling angle of 180° and a peeling speed of 30 m / min was measured using a high-speed peeling tester. Less than 1.0 N / 50 mm was rated as ○ (Good), and 1.0 N / 50 mm or more was rated as × (No Good).

[0084] The measurement results of each sample are shown in Table 1. Also, as reference values, the measurement results of the charging voltages when peeling the surface protection films in Example 1 and Example 4 are shown in Table 2.

[0085]

Table 1

[0086]

Table 2

[0087] From Table 1 and Table 2, the following can be understood. The surface protection films of Examples 1 to 5 had a high effect of suppressing the occurrence of curl in the optical film, and the handleability of the optical film with the surface protection film attached was good. The peelability when peeling the release film from the optical film with an adhesive was also good. Also, as can be seen from the results of the peel force, the surface protection films of Examples 1 to 5 were surface protection films that were easy to peel off and remove after use. Example 3 in which an antistatic agent was added to the second adhesive layer was a surface protection film with a low peel electrification voltage when removing the surface protection film.

[0088] On the other hand, the surface protection films of Comparative Examples 1 to 3 in which only the second adhesive layer was provided on the polyester film had improved handleability and curl suppression by increasing the film thickness, but the peelability when peeling the release film from the optical film with an adhesive and the peelability when removing the surface protection film decreased. That is, in the surface protection films of Comparative Examples 1 to 3, it was not possible to improve all of the curl suppression, handleability, peelability when peeling the release film from the optical film with an adhesive, and peelability when removing the surface protection film. The surface protection film of Comparative Example 4 with a high adhesive strength of the first adhesive layer had good handleability, curl suppression, and peelability when peeling the release film from the optical film with an adhesive, but the peel force of the surface protection film was not good.

Industrial Applicability

[0089] The present invention can be used, for example, in the production process of optical films such as polarizing plates, retardation plates, and lens films, and optical components, etc., to adhere to the surface of the optical components, etc. for protecting the surface. In particular, for a thinned optical film, it has a high effect of suppressing the generation of curl of the optical film, improves the handleability of the optical film with the surface protection film adhered thereto, and further, the operation of peeling the release film from the optical film with an adhesive is easy, and it is easy to peel off and remove after use. Therefore, it is possible to improve the yield and productivity in the manufacturing process of the thinned optical film. Further, since it becomes unnecessary to replace the surface protection film or wipe off dirt at the time of shipment, etc., it leads to an improvement in workability and productivity improvement.

Explanation of reference numerals

[0090] 1... First transparent film, 2... First adhesive layer, 3... Second transparent film, 4... Second adhesive layer, 5... Release film, C... Optical film, D... Optical component, P... Surface protection film.

Claims

1. A surface protection film in which a first transparent film, a first adhesive layer, a second transparent film, and a second adhesive layer are laminated in this order, the surface protection film has a multilayer structure having the first transparent film, the first adhesive layer, the second transparent film, and the second adhesive layer over the entire surface, the thickness of the first transparent film is 20 to 50 μm, the first adhesive layer uses an acrylic adhesive or a urethane adhesive, the thickness of the second transparent film is 19 to 50 μm, the second adhesive layer is provided for attaching the surface protection film to an optical film as an adherend, the second adhesive layer has an adhesiveness such that the peel strength with respect to the surface of the optical film as the adherend is 0.03 to 0.3 N / 25 mm, A surface protection film that satisfies the following condition (1). Condition (1): When the adhesive force of the adhesive film composed of the first transparent film and the first adhesive layer to glass is defined as adhesive force 1, and the adhesive force of the adhesive film composed of the second transparent film and the second adhesive layer to glass is defined as adhesive force 2, adhesive force 1 < adhesive force 2.

2. The surface resistivity of the second pressure-sensitive adhesive layer is less than 1×10 １３ 〔Ω / sq〕, and the surface protection film according to claim 1.

3. An optical component to which the surface protection film according to Claim 1 or Claim 2 is attached.

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