TW202020041A - Substrate for surface protective film, method for manufacturing the substrate, surface protective film using the substrate, and optical film with surface protective film including forming a film-forming material comprising an acrylic resin and an elastomer into a film shape, and sequentially or biaxially stretching the molded film - Google Patents

Abstract

The present invention provides a substrate for a surface protective film, which has excellent flexibility or bending resistance, and can favorably suppress light leakage, coloring, and rainbow stains during optical inspection. The substrate for the surface protective film of the present invention is composed of a film comprising an acrylic resin and an elastomer, has in-plane retardation Re (550) of 30 nm or less, and the number of bending times to break in the MIT test is 500 or more. A method for manufacturing the substrate for the surface protective film of the present invention comprises: molding of a film forming material comprising the acrylic resin and the elastomer into a film; and sequential biaxial stretching or simultaneous biaxial stretching of the molded film.

Description

Substrate for surface protection film, method for producing the substrate, surface protection film using the substrate, and optical film with surface protection film

Field of invention The present invention relates to a substrate for a surface protection film, a method for manufacturing the substrate, a surface protection film using the substrate, and an optical film with a surface protection film.

Background of the invention For the optical film (for example, a polarizing plate, a laminate including the polarizing plate), in order to protect the optical film (eventually the image display device) until the actual use of the image display device to which the optical film is applied, it is peelable A surface protection film is attached. In practice, an image display device is produced by laminating an optical film/surface protective film laminate to a display unit, and the image display device is subjected to an optical test (for example, a lighting test) with the laminate attached. After the appropriate time, the surface protection film is peeled off and removed. The surface protective film typically has a resin film as a base material and an adhesive layer. With the conventional surface protection film, light leakage, coloring, rainbow-like unevenness, etc. may occur during optical inspection, which may cause a decrease in the accuracy of optical inspection. As a result, although there is no problem with the image display device itself, it may be judged to be defective in the optical inspection before shipment, and thus there is a problem that the efficiency from the manufacture of the image display device to the shipment is reduced. Furthermore, the surface protection film (substantially a base material) requires excellent flexibility in consideration of handling properties during bonding and peeling. Existing technical literature Patent Literature

Patent Document 1: Japanese Patent Laid-Open No. 2017-190406

Summary of the invention Problems to be solved by the invention The present invention has been made to solve the above-mentioned existing problems, and its main object is to provide a surface protection film having excellent flexibility or bending resistance and capable of suppressing light leakage, coloring, and rainbow-like unevenness during optical inspection Substrate. Means to solve the problem

The substrate for a surface protection film according to an embodiment of the present invention is composed of a film containing an acrylic resin and an elastomer, the in-plane retardation Re (550) is 30 nm or less, and the number of bending times until breakage in the MIT test is 500 or more. It contains 6 parts by weight or more of the elastomer with respect to 100 parts by weight of the acrylic resin. In one embodiment, the acrylic resin has at least one selected from the group consisting of glutarimide units, lactone ring units, maleic anhydride units, maleimide units, and glutaric anhydride units 1 of them. In one embodiment, the above-mentioned elastomer is at least one selected from the group consisting of rubber-like polymers, polyamide-based elastomers, polyethylene-based elastomers, styrene-based elastomers, and butadiene-based elastomers. In one embodiment, the total light transmittance of the substrate for a surface protection film is 80% or more, and the haze is 1.0% or less. According to another aspect of the present invention, there is provided a method for manufacturing the substrate for a surface protection film. The manufacturing method includes: forming a film-forming material containing an acrylic resin and an elastomer into a film shape; and successively biaxially stretching or simultaneously biaxially stretching the formed film. In one embodiment, in the manufacturing method described above, the stretching temperature in the sequential biaxial stretching or simultaneous biaxial stretching is Tg+10°C to Tg+30°C. According to yet another aspect of the present invention, a surface protection film is provided. The surface protection film includes the substrate for the surface protection film and the adhesive layer. According to yet another aspect of the present invention, an optical film with a surface protective film is provided. The optical film with a surface protection film includes an optical film and the surface protection film, and the surface protection film is attached to the optical film in a peelable manner. Effect of invention

According to an embodiment of the present invention, by stretching a film containing an acrylic resin and an elastomer under predetermined stretching conditions (for example, stretching temperature and stretching speed), it is possible to achieve a balance between very small in-plane retardation and Base material for surface protection film with excellent flexibility or bending resistance.

Detailed description of preferred embodiments Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

A. Base material for surface protection film The substrate for a surface protection film according to an embodiment of the present invention is composed of a film including acrylic resin and elastomer.

As the acrylic resin, any appropriate acrylic resin can be used. The acrylic resin typically contains alkyl (meth)acrylate as the main component in the monomer unit. In this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid. As the (meth)acrylic acid alkyl ester constituting the main skeleton of the acrylic resin, a linear or branched alkyl group having 1 to 18 carbon atoms (meth)acrylic acid alkyl ester can be exemplified. They can be used alone or in combination. Furthermore, any appropriate comonomer can be introduced into the acrylic resin by copolymerization. The kind, number, copolymerization ratio, etc. of such a comonomer can be appropriately set according to purposes. The constituent components (monomer units) of the main skeleton of the acrylic resin will be described later with reference to the general formula (2).

The acrylic resin preferably has a structural unit selected from glutarimide units, lactone ring units, maleic anhydride units, maleimide units, and glutaric anhydride units. The acrylic resin may have only one kind of these structural units, or plural kinds. An acrylic resin having a lactone ring unit is described in, for example, Japanese Patent Laid-Open No. 2008-181078, and the description of this publication is incorporated by reference in this specification. Glutarimide units are preferably represented by the following general formula (1).

[Chemical Formula 1]

In the general formula (1), R ¹ and R ² each independently represent hydrogen or a C 1-8 alkyl group, R ³ represents a C 1-18 alkyl group, a C 3-12 cycloalkyl group, or Aryl groups with 6 to 10 carbon atoms. In the general formula (1), it is preferred that R ¹ and R ² are each independently hydrogen or methyl, and R ³ is hydrogen, methyl, butyl, or cyclohexyl. More preferably, R ¹ is methyl, R ² is hydrogen, and R ³ is methyl.

The above-mentioned alkyl (meth)acrylate is typically represented by the following general formula (2).

[Chemical Formula 2]

In the general formula (2), R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom, or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. Examples of the substituent include halogen and hydroxyl. Specific examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, Tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, (meth) 2-hydroxyethyl acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate and 2,3,4,5 (meth)acrylate -Tetrahydroxypentyl ester. In the general formula (2), R ⁵ is preferably a hydrogen atom or a methyl group. Therefore, a particularly preferred alkyl (meth)acrylate is methyl acrylate or methyl methacrylate.

The acrylic resin may include only a single glutarimide unit, or may include multiple glutarimide units different in R ¹ , R ^2, and R ³ in the general formula (1).

The content ratio of glutarimide units in the acrylic resin is preferably 2 mol% to 50 mol%, more preferably 2 mol% to 45 mol%, and still more preferably 2 mol% to 40 mol Ear %, particularly preferably 2 mol% to 35 mol %, most preferably 3 mol% to 30 mol %. If the content ratio is less than 2 mol%, the effects derived from glutarimide units may not be fully exhibited (for example, high optical characteristics, high mechanical strength, excellent adhesion to polarizers, thinning) Worry. If the content exceeds 50 mol%, for example, heat resistance and transparency may be insufficient. Furthermore, in the acrylic resin, the glutarimide unit is substituted for or has a lactone ring unit, maleic anhydride unit, maleimide unit and/or glutaric anhydride unit on the basis of the glutarimide unit. In the case of the above, the above content ratio may be the total content ratio of these structural units.

The acrylic resin may include only a single alkyl (meth)acrylate unit, or may include multiple alkyl (meth)acrylate units having different R ⁴ and R ⁵ in the general formula (2).

The content ratio of the (meth)acrylic acid alkyl ester unit in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, and still more preferably 60 mol% ~98 mol%, particularly preferably 65 mol% to 98 mol%, most preferably 70 mol% to 97 mol%. If the content ratio is less than 50 mol %, there is a possibility that the effects (for example, high heat resistance and high transparency) derived from the alkyl (meth)acrylate unit cannot be fully exhibited. If the above content ratio is more than 98 mol%, the resin may become brittle and easily break, and the high mechanical strength may not be fully exhibited, and productivity may be poor.

唑啉、2-乙烯基

唑啉、2-丙烯醯基

唑啉、N-苯基馬來醯亞胺、甲基丙烯酸苯基胺基乙酯、苯乙烯、α-甲基苯乙烯、對環氧丙基苯乙烯、對胺基苯乙烯、2-苯乙烯基

唑啉等。這些可以單獨使用，也可以組合使用。優選為苯乙烯、α-甲基苯乙烯等苯乙烯系單體。其他乙烯基系單體單元的含有比例優選為0~1重量%、更優選為0~0.1重量%。若為這樣的範圍，能夠抑制不期望的相位差展現及透明性降低。The acrylic resin may contain other than alkyl (meth)acrylate units, glutarimide units, lactone ring units, maleic anhydride units, maleimide units and/or glutaric anhydride units Unit. For example, the acrylic resin may contain vinyl monomer units (other vinyl monomer units) that can be copolymerized in addition to the above. Examples of other vinyl-based monomers include acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl epoxypropyl ether, maleic anhydride, itaconic anhydride, and N-methylmaleimide. Imine, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, methyl Ethylaminopropyl acrylate, cyclohexylaminoethyl methacrylate, N-vinyl diethylamine, N-acetyl vinylamine, allylamine, methallylamine, N-methyl Allylamine, 2-isopropenyl

Oxazoline, 2-vinyl

Oxazoline, 2-propenyl

Oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-epoxypropylstyrene, p-aminostyrene, 2-benzene Vinyl

Oxazoline etc. These can be used alone or in combination. Styrene-based monomers such as styrene and α-methylstyrene are preferred. The content ratio of other vinyl-based monomer units is preferably 0 to 1% by weight, and more preferably 0 to 0.1% by weight. Within such a range, it is possible to suppress undesired phase difference development and decrease in transparency.

The amidation rate of the acrylic resin is preferably 2.5% to 20.0%. When the imidate ratio is in such a range, a resin excellent in heat resistance, transparency, and moldability can be obtained, and the occurrence of scorching during film formation and reduction in mechanical strength can be prevented. In the above-mentioned acrylic resin, the imidate ratio is expressed by the ratio of glutarimide units to alkyl (meth)acrylate units. This ratio can be obtained from, for example, NMR spectrum, IR spectrum, etc. of acrylic resin. In the present embodiment, the imidate ratio can be determined by ¹ H-NMR measurement of the resin using ¹ HNMR BRUKER Avance III (400 MHz). More specifically, the peak area of the O-CH ₃ proton derived from the alkyl (meth)acrylate near 3.5 to 3.8 ppm is set to A, and the glutarimide-derived one near 3.0 to 3.3 ppm is used. The area of the peak of the N-CH ₃ proton is defined as B, and it is determined by the following formula. Acetylimidization rate Im(%)={B/(A+B)}×100

The acid value of the acrylic resin is preferably 0.10 mmol/g to 0.50 mmol/g. When the acid value is in such a range, a resin having an excellent balance of heat resistance, mechanical properties, and moldability can be obtained. If the acid value is too small, there may be problems such as an increase in cost due to the use of the modifier to adjust to the desired acid value, generation of a gel-like substance due to residual modifier, and the like. If the acid value is too large, it tends to cause foaming during film forming (for example, during melt extrusion), and the productivity of the molded product tends to decrease. In the acrylic resin, the acid value is the content of carboxylic acid units and carboxylic anhydride units in the acrylic resin. In this embodiment, the acid value can be calculated by, for example, the titration method described in WO2005/054311 or JP-A-2005-23272.

The details of the acrylic resin, its manufacturing method, and its characteristics are described in, for example, Japanese Patent Laid-Open No. 2016-139027, Japanese Patent Laid-Open No. 2007-316366, and Japanese Patent Laid-Open No. 2008-181078. It is cited in this specification.

As the elastomer, any appropriate elastomer can be used. Elastomers typically have a hard segment that can function as a pseudo-crosslinking point and a soft segment that mainly contributes to elasticity. Representative examples of the elastomer include rubber-like polymers, polyamide-based elastomers, polyethylene-based elastomers, styrene-based elastomers, and butadiene-based elastomers. The elastomer can be used alone or in combination. The elastomer can be appropriately selected according to the desired characteristics. For example, from the viewpoint of easy design of optical characteristics, a styrene-based elastomer can be used. Representative examples of styrene-based elastomers include polystyrene having hard segments and polybutadiene, polyisoprene, or polybutadiene and polyisoprene as soft segments. Copolymers of styrene elastomers and their hydrides. In addition, the hydride may be obtained by partially hydrogenating polybutadiene, polyisoprene, or the like, or may be obtained by hydrogenating all of them. As the styrene-based elastomer, commercially available products can be used. Examples of commercially available styrene elastomers include Tuftec, Tufprene (manufactured by Asahi Kasei Chemicals Corporation above), Kraton (manufactured by Kraton Corporation), DYNARON, JSR TR, and JSR SIS (manufactured by JSR Corporation). , SEPTON (manufactured by KURARAY CO., LTD), RABALON (manufactured by Mitsubishi Chemical Corporation), etc. As the polyethylene-based elastomer, a polyethylene-based elastomer having 50 parts or more of ethylene blocks is preferable, and examples of commercially available products include EXCELLEN FX (Sumitomo Chemical Co., Ltd.) and the like. The polyamido-based elastomer preferably has a polyether block. Examples of commercially available products include Pebax (manufactured by Tokyo Materials Co., Ltd.) and the like. The rubber-like polymer is preferably a core-shell type particle, and as a commercially available product, W-300 (manufactured by Mitsubishi Chemical Corporation) and the like can be cited.

The compounding amount of the elastomer is 6 parts by weight or more relative to 100 parts by weight of the acrylic resin, preferably 6 to 30 parts by weight, and more preferably 8 to 20 parts by weight. When the blending amount of the elastomer is within such a range, it is possible to realize a substrate for a surface protection film that combines both very small in-plane retardation and excellent flexibility or bending resistance.

In the embodiment of the present invention, the in-plane retardation Re(550) of the substrate for a surface protection film is 30 nm or less, preferably 10 nm or less, more preferably 5 nm or less, further preferably 3 nm or less, and particularly preferably 2.5 nm or less. The smaller the in-plane phase difference Re(550) is, the more preferable. The lower limit is ideally 0 nm, for example, it may be 0.1 nm. When the in-plane retardation Re(550) is in such a range, when the surface protective film using the substrate for surface protective film of the present invention is used for optical inspection of an image display device, light leakage, coloring, and iridescence can be suppressed well Uneven. As a result, the optical inspection accuracy of the video display device can be significantly improved, and the efficiency from the manufacturing of the video display device to the shipment can be improved. Such an in-plane retardation Re (550) can be achieved by stretching a film containing the above-mentioned specific acrylic resin and a specific elastomer under predetermined stretching conditions described below. In addition, in this specification, "Re(λ)" is an in-plane phase difference measured with light of a wavelength λnm at 23°C. Re (λ), when the thickness of the layer (thin film) is d (nm), is calculated according to the formula: Re=(nx-ny)×d. Therefore, "Re(550)" is the in-plane retardation measured at 23°C with light having a wavelength of 550 nm. Here, "nx" is the refractive index in the direction in which the in-plane refractive index becomes maximum (that is, the slow axis direction), and "ny" is the refractive index in the direction orthogonal to the slow axis (that is, the fast axis direction) in the plane.

The thickness direction phase difference Rth(550) of the substrate for a surface protection film is preferably 50 nm or less, more preferably 25 nm or less, still more preferably 15 nm or less, and particularly preferably 10 nm or less. The smaller the thickness direction phase difference Rth(550), the more preferable, and the lower limit is ideally 0 nm, for example, 0.5 nm. When the thickness direction phase difference Rth(550) is within such a range, light leakage, coloring, and rainbow-like unevenness in the oblique direction in the optical inspection can be suppressed well. As a result, it is possible to significantly improve the accuracy even in the optical inspection of a large image display device. The Nz coefficient of the substrate for surface protection film is preferably 1.1 to 20, and more preferably 1.5 to 5.4. Therefore, the refractive index characteristic of the base material for surface protection films can show the relationship of nx>ny>nz, for example. When the Nz coefficient is in such a range, light leakage, coloring, and rainbow-like unevenness in the oblique direction during optical inspection can be further satisfactorily suppressed. "Rth(λ)" is a phase difference in the thickness direction measured at 23°C with light having a wavelength of λnm. Regarding Rth(λ), when the thickness of the layer (thin film) is d (nm), it is obtained from the formula: Rth=(nx-nz)×d. Therefore, "Rth(550)" is the phase difference in the thickness direction measured at 23°C with light having a wavelength of 550 nm. Here, "nz" is the refractive index in the thickness direction. Furthermore, the "Nz coefficient" is obtained by Nz=Rth(λ)/Re(λ).

The substrate for surface protective film can display the inverse dispersion wavelength characteristic that the in-plane phase difference becomes larger according to the wavelength of the measurement light, or the positive wavelength dispersion characteristic that the in-plane phase difference becomes smaller according to the measurement light wavelength, or The flat-wavelength dispersion characteristic that the in-plane phase difference basically does not change with the wavelength of the measurement light.

The total light transmittance of the substrate for a surface protective film is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, and particularly preferably 95% or more. Furthermore, the haze of the substrate for a surface protection film is preferably 1.0% or less, more preferably 0.7% or less, still more preferably 0.5% or less, and particularly preferably 0.3% or less. According to the embodiment of the present invention, it is possible to realize a substrate for a surface protection film having a very small in-plane retardation Re (550) as described above and having such a very excellent transparency.

In the embodiment of the present invention, the number of times the substrate for a surface protective film is bent until fracture in the MIT test is 500 or more, preferably 1000 or more, more preferably 1500 or more, and still more preferably 2000 or more. That is, the substrate for a surface protective film can have very excellent flexibility or bending resistance. Due to the excellent flexibility or bending resistance of the substrate for a surface protection film, it is possible to obtain a surface protection film which is excellent in handleability at the time of bonding and peeling and which suppresses cracking. According to the embodiment of the present invention, such excellent flexibility or bending resistance and the very small in-plane retardation Re(550) as described above can be reconciled. Being able to achieve such a balance is one of the achievements of the present invention. Furthermore, the MIT test can be performed in accordance with JIS P 8115.

The elastic modulus of the substrate for surface protection film is preferably 50 MPa to 350 MPa at a stretching speed of 100 mm/min. When the elastic modulus is in such a range, a surface protective film excellent in transportability and handleability can be obtained. According to the embodiments of the present invention, excellent elastic modulus (strength) and excellent flexibility or bending resistance (flexibility) as described above can be reconciled. In addition, the elastic modulus is measured according to JIS K 7127:1999.

The tensile elongation of the substrate for surface protection film is preferably 70% to 200%. When the tensile elongation is within this range, there is an advantage that it is not easily broken during transportation. In addition, the tensile elongation is measured according to JIS K 6781.

The thickness of the substrate for the surface protection film is typically 10 μm to 100 μm, preferably 20 μm to 70 μm.

B. Manufacturing method of base material for surface protection film The method for manufacturing a substrate for a surface protection film according to an embodiment of the present invention includes forming a film-forming material (resin composition) containing an acrylic resin and an elastomer as described in the above item A into a film shape, and forming the The film is stretched.

The film-forming material may contain other resins in addition to the acrylic resin and the elastomer, and may contain additives or solvents. As the additive, any appropriate additive can be adopted according to the purpose. Specific examples of additives include reactive diluents, plasticizers, surfactants, fillers, antioxidants, anti-aging agents, ultraviolet absorbers, leveling agents, thixotropic agents, antistatic agents, conductive materials ，Flame retardant. The number, kind, combination, amount of additives, etc. of the additives can be appropriately set according to the purpose.

As a method of forming a thin film from a thin film forming material, any appropriate forming method can be adopted. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (for example, casting method), Calendering method, hot pressing method, etc. The extrusion molding method or the cast coating method is preferred. This is because the smoothness of the obtained film can be improved, and good optical uniformity can be obtained. The molding conditions can be appropriately set according to the composition and type of the resin used, desired characteristics of the substrate for surface protection film, and the like.

The film stretching method is typically biaxial stretching, more specifically, sequential biaxial stretching or simultaneous biaxial stretching. This is because a substrate for a surface protection film having a small in-plane retardation Re (550) and excellent flexibility or bending resistance can be obtained. Successive biaxial stretching or simultaneous biaxial stretching is typically performed using a tenter. Therefore, the stretching direction of the film is typically the longitudinal direction and the width direction of the film.

The stretching temperature can be changed according to the desired in-plane retardation and thickness of the substrate for a surface protective film, the type of resin used, the thickness of the film used, the stretching ratio, and the like. Specifically, the stretching temperature relative to the glass transition temperature (Tg) of the film is preferably Tg+5°C to Tg+50°C, and more preferably Tg+10°C to Tg+30°C. By stretching at such a temperature, in the embodiment of the present invention, a substrate for a surface protection film having appropriate characteristics can be obtained.

The stretching ratio can be changed according to the desired in-plane retardation and thickness of the substrate for a surface protection film, the type of resin used, the thickness of the film used, the stretching temperature, and the like. When using biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching), the stretching ratio in the first direction (for example, the longitudinal direction) and the stretching in the second direction (for example, the width direction) The magnification is preferably as small as possible, and is more preferably substantially equal. With such a configuration, a substrate for a surface protection film having a small in-plane retardation Re (550) and excellent flexibility or bending resistance can be obtained. In the case of biaxial stretching (for example, sequential biaxial stretching or simultaneous biaxial stretching), the stretching ratio is for each of the first direction (for example, the longitudinal direction) and the second direction (for example, the width direction) For example, it can be 1.1 times to 3.0 times.

In the embodiment of the present invention, the stretching speed is preferably 10%/sec or less, more preferably 7%/sec or less, still more preferably 5%/sec or less, and particularly preferably 2.5%/sec or less. By stretching the film containing the specific acrylic resin and the specific elastomer as described above at such a small stretching speed, it is possible to obtain a small in-plane retardation Re (550) and excellent flexibility or bending resistance Substrate for surface protection film. The lower limit of the stretching speed may be, for example, 1.2%/sec. If the drawing speed is too low, the productivity may become impractical. Furthermore, in the case of biaxial stretching (eg, sequential biaxial stretching or simultaneous biaxial stretching), the stretching speed in the first direction (eg, longitudinal direction) and the second direction (eg, width direction) The stretching speed of is preferably as small as possible, and is more preferably substantially equal. With such a configuration, the in-plane retardation Re (550) can be further reduced, and the flexibility or bending resistance can be further improved.

C. Surface protection film The substrate for a surface protection film described in the above items A and B can be suitably used for the surface protection film. Therefore, the embodiment of the present invention also includes a surface protection film. The surface protection film of the embodiment of the present invention includes the substrate for a surface protection film and the adhesive layer described in the above items A and B.

As the adhesive forming the adhesive layer, any appropriate adhesive can be used. Examples of the base resin of the adhesive include acrylic resins, styrene resins, silicone resins, urethane resins, and rubber resins. Such a base resin is described in, for example, Japanese Patent Laid-Open No. 2015-120337 or Japanese Patent Laid-Open No. 2011-201983. The descriptions of these publications are incorporated into this specification by reference. From the viewpoints of chemical resistance, adhesion for preventing penetration of the treatment liquid during immersion, freedom from adherends, and the like, acrylic resins are preferred. Examples of the crosslinking agent that can be included in the adhesive include isocyanate compounds, epoxy compounds, and aziridine compounds. The adhesive may include, for example, a silane coupling agent. The compounding prescription of the adhesive can be appropriately set according to the purpose and desired characteristics.

The storage elastic modulus of the adhesive layer is preferably 1.0×10 ⁴ Pa to 1.0×10 ⁷ Pa, and more preferably 2.0×10 ⁴ Pa to 5.0×10 ⁶ Pa. When the storage elastic modulus of the adhesive layer is within such a range, it is possible to suppress blocking during roll formation. In addition, the storage elastic modulus can be obtained from, for example, dynamic viscoelasticity measurement at a temperature of 23° C. and an angular velocity of 0.1 rad/s.

The thickness of the adhesive layer is preferably 1 μm to 60 μm, and more preferably 3 μm to 30 μm. If the thickness is too thin, the adhesiveness may become insufficient, and bubbles and the like may be mixed at the adhesive interface. If the thickness is too thick, defects such as adhesive bleed are likely to occur.

Practically, before the actual use of the surface protection film (that is, bonding to the optical film or image display device), the separator is temporarily attached to the surface of the adhesive layer in a peelable manner. By providing the separating member, the adhesive layer can be protected, and the surface protection film can be wound into a roll shape. As the separator, for example, a plastic (for example, polyethylene terephthalate) surface-coated with a release agent such as a silicone-based release agent, a fluorine-based release agent, or a long-chain alkyl acrylate-based release agent is used. Glycol ester (PET), polyethylene, polypropylene) film, non-woven fabric or paper, etc. For the thickness of the separator, any appropriate thickness can be adopted according to the purpose. The thickness of the separator is, for example, 10 μm to 100 μm.

D. Optical film with surface protection film The surface protection film described in the above item C is used to protect the optical film (actually, an image display device) before actually using the optical film. Therefore, the embodiment of the present invention also includes an optical film with a surface protective film. The optical film with a surface protection film according to an embodiment of the present invention includes an optical film and the surface protection film described in item C above that is peelably attached to the optical film.

The optical film may be a single film or a laminate. Specific examples of the optical film include polarizers, retardation films, polarizing plates (typically laminates of polarizers and protective films), conductive films for touch panels, surface treatment films, and A laminated body obtained by appropriately laminating them (for example, a circular polarizing plate for antireflection, a polarizing plate with a conductive layer for a touch panel, a polarizing plate with a retardation layer, and a polarizing plate integrated with a sheet). Examples

Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited to these examples. The measuring method of each characteristic in an Example is as follows. Furthermore, unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) In-plane phase difference Re (550) and thickness direction phase difference Rth (550) The base material for surface protection films (biaxially stretched film) obtained in Examples and Comparative Examples was cut into a length of 4 cm and a width of 4 cm, and used as a measurement sample. For this measurement sample, in-plane retardation and thickness direction retardation were measured using the product name "Axoscan" manufactured by Axometrics. The measurement wavelength was 550 nm and the measurement temperature was 23°C. (2) Haze For the same measurement sample as the above (1), the haze was measured using a haze meter (manufactured by Murakami Color Technology Research Institute, model HM-150). The measurement temperature was 23°C. (3) MIT test The MIT test was conducted in accordance with JIS P 8115. Specifically, the substrate for a surface protection film (biaxially stretched film) obtained in Examples and Comparative Examples was cut into a length of 15 cm and a width of 1.5 cm, and used as a measurement sample. The measurement sample was mounted on the MIT Folding Fatigue Tester Model BE-202 (manufactured by TESTER SANGYO CO., LTD.) (load 1.0 kgf, R of the fixture: 0.38 mm), and the test speed was 90 cpm and the bending angle was 90°. Bending was repeated with 2000 times as the upper limit, and the number of times of bending at the time of measuring the sample fracture was taken as the test value. (4) Rainbow-like unevenness The base material (biaxially stretched film) for the surface protection film obtained in Examples and Comparative Examples was placed between two polarizing plates in a crossed state. At this time, the substrate for the surface protection film is arranged so that the longitudinal direction of the substrate for the surface protection film is parallel to the transmission axis direction of one polarizing plate. In this state, the light of the fluorescent lamp is irradiated from the lower side of the lower polarizing plate, and the presence or absence of rainbow-like unevenness is visually observed. The evaluation was performed according to the following criteria. ○: Rainbow-like unevenness was not observed △: Rainbow-like unevenness is slightly observed ×: Rainbow-like unevenness is significantly observed (5) Flexibility or bending resistance The substrate for surface protection film (biaxially stretched film) was repeatedly subjected to a 180° bending test 100 times to confirm the presence or absence of breakage. The evaluation was performed according to the following criteria. ○: No fracture was observed ×: Fracture observed

>Example 1> 1-1. Polymerization of acrylic resin and compounding of elastomer 229.6 parts of methyl methacrylate (MMA), 33 parts of 2-(hydroxymethyl) methyl acrylate (MHMA), toluene were put into a reaction vessel equipped with a stirring device, a temperature sensor, a condenser tube, and a nitrogen introduction tube 248.6 parts and 0.19 parts of n-dodecyl mercaptan were introduced into it, and the temperature was raised to 105°C. At the beginning of the reflux with the temperature rise, 0.28 parts of tert-amyl isononyl peroxide ("Luperox (registered trademark) 570" manufactured by ARKEMA Yoshitomi, Ltd.) was added as a polymerization initiator, and the solution was added dropwise over 2 hours. 0.56 parts of oxidized tert-amyl isononanoate and 12.4 parts of styrene were subjected to solution polymerization at a reflux of about 105° C. to 110° C. After completion of the dropwise addition, aging was further performed at the same temperature for 4 hours. Next, 0.21 part of stearyl phosphate ("Phoslex A-18" manufactured by Sakai Chemical Industry Co., Ltd.) which is a catalyst for the cyclization condensation reaction (cyclization catalyst) is added to the resulting polymerization solution at about 90 to 110 The cyclization condensation reaction for forming a lactone ring structure was carried out under reflux at 2°C for 2 hours. Next, the obtained polymerization solution was passed through a multi-tube heat exchanger heated to 240°C to complete the cyclization condensation reaction. In this way, an acrylic resin having a lactone ring unit is obtained. Next, after the completion of the cyclization condensation reaction, the resin solution was introduced at a processing speed of 31.2 parts/hour (resin amount conversion) to a cylinder temperature of 250° C., with a rear vent hole and four front vents Holes (referred to as the first exhaust hole, the second exhaust hole, the third exhaust hole, the fourth exhaust hole from the upstream side) and the side feed between the third exhaust hole and the fourth exhaust hole A feeder, an exhaust-type screw twin-screw extruder (L/D=52) with a disc-type polymer filter (filter accuracy of 5 μm) arranged at the front end. At this time, ion exchange water was introduced from behind the second exhaust hole at an input rate of 0.47 parts/hour, and an ultraviolet absorber (manufactured by ADEKA Corporation) was introduced from behind the third exhaust hole at an input rate of 0.59 parts/hour. "ADK STAB (registered trademark) LA-F70") 0.66 parts of a solution prepared by dissolving in 1.23 parts of toluene, and ion exchange water was added from behind the fourth exhaust hole at a feed rate of 0.47 parts/hour. Furthermore, pellets of a polyethylene-based elastomer (manufactured by Sumitomo Chemical Co., Ltd., product name "EXCELLEN FX") were fed from a side feeder at a feed rate of 0.63 parts/hour. In this way, pellets containing an acrylic resin having a lactone ring unit and a polyethylene-based elastomer are produced. The obtained pellet contained 10 parts by weight of elastomer relative to 100 parts by weight of acrylic resin.

1-2. Manufacture of film containing acrylic resin and elastomer After the obtained pellets were vacuum-dried at 80°C for 5 hours, a single screw extruder (all made by Isuzu Chemical Industries, screw diameter 25 mm, barrel setting temperature: 250°C), T die (width 200 mm, setting Temperature: 250°C), a cooling roll (set temperature: 120 to 130°C) and a film-making device of a winder to produce a film containing acrylic resin and elastomer with a thickness of 160 μm. The glass transition temperature (Tg) of the film containing the acrylic resin and the elastomer was 121°C.

1-3. Fabrication of substrates for surface protection films The film containing the acrylic resin and the elastomer obtained above was simultaneously biaxially stretched to twice the length and width directions, respectively. The stretching temperature is [Tg+10°C] (that is, 131°C), and the stretching speed is 1.4%/sec in both the length direction and the width direction. In this way, a substrate for a surface protection film (thickness 40 μm) was obtained. Re (550) of the obtained substrate for surface protection films was 0.3 nm, Rth (550) was 1.6 nm, haze was 0.6%, and the MIT test value exceeded 2000 times as an upper limit. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 2> Except that the compounding amount of the elastomer was 15 parts by weight and the stretching temperature was [Tg+20° C.], the same procedure as in Example 1 was carried out to obtain a substrate for a surface protection film. Re (550) of the obtained substrate for surface protection films was 0.5 nm, Rth (550) was 9 nm, haze was 0.2%, and the MIT test value exceeded 2000 times as an upper limit. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 3> Except that the compounding amount of the elastomer was 8 parts by weight and the stretching temperature was [Tg+30° C.], the same procedure as in Example 1 was carried out to obtain a substrate for a surface protection film. Re (550) of the obtained substrate for surface protection films was 2 nm, Rth (550) was 20 nm, haze was 0.3%, and the MIT test value was 1032 times. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 4> Use 10 parts by weight of styrene-based elastomer (manufactured by Asahi Kasei Co., Ltd., product name "Tuftec") instead of 10 parts by weight of polyethylene-based elastomer, and set the stretching temperature to [Tg+20°C], otherwise In the same manner as in Example 1, a substrate for a surface protection film was obtained. Re (550) of the obtained substrate for surface protection films was 0.8 nm, Rth (550) was 3 nm, haze was 0.3%, and the MIT test value exceeded the upper limit 2000 times. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 5> Except that the compounding amount of the elastomer was 15 parts by weight and the stretching temperature was [Tg+30° C.], the same procedure as in Example 4 was carried out to obtain a substrate for a surface protection film. Re (550) of the obtained substrate for surface protection films was 1.2 nm, Rth (550) was 5.1 nm, haze was 0.4%, and the MIT test value exceeded 2000 times as an upper limit. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 6> Instead of 10 parts by weight of polyethylene-based elastomer, 20 parts by weight of polyamide-based elastomer (manufactured by Tokyo Materials Co., Ltd., product name "Pebax") was used, and the stretching temperature was set to [Tg+20°C], except Except this, it carried out similarly to Example 1, and obtained the base material for surface protection films. Re (550) of the obtained substrate for surface protection films was 2.3 nm, Rth (550) was 3.1 nm, haze was 0.8%, and the MIT test value exceeded 2000 times as an upper limit. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Example 7> 10 parts by weight of core-shell rubber-like particles (manufactured by Mitsubishi Chemical Corporation, product name "W-300") were used instead of 10 parts by weight of the polyethylene-based elastomer, and the stretching temperature was set to [Tg+20°C], Except this, it carried out similarly to Example 1, and obtained the base material for surface protection films. Re (550) of the obtained substrate for surface protection films was 0.3 nm, Rth (550) was 1 nm, haze was 0.3%, and the MIT test value was 592 times. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Comparative example 1> A commercially available norbornene-based resin film (manufactured by Zeon Corporation, trade name "ZEONOR", Tg: 150°C) was used instead of a film containing an acrylic resin and an elastomer, and the stretching temperature was set to [Tg+20°C ] Except this, it carried out similarly to Example 1, and obtained the base material for surface protection films. Re (550) of the obtained substrate for surface protection films was 2 nm, Rth (550) was 8 nm, haze was 0.1%, and the MIT test value was 150 times. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Comparative example 2> Ultra-high phase difference polyethylene terephthalate (manufactured by Mitsubishi Chemical Corporation, trade name "Diafoil", Tg: 81°C) was used instead of the film containing acrylic resin and elastomer, and the stretching temperature was set to Except [Tg+20 degreeC], it carried out similarly to Example 1, and obtained the base material for surface protection films. Re (550) of the obtained substrate for surface protection films was 4500 nm, Rth (550) was 6000 nm, haze was 1.3%, and the MIT test value exceeded 2000 times as an upper limit. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

>Comparative Example 3> Except that the compounding amount of the elastomer was 5 parts by weight and the stretching temperature was [Tg+20° C.], the same procedure as in Example 1 was carried out to obtain a substrate for a surface protection film. Re (550) of the obtained substrate for surface protection films was 0.6 nm, Rth (550) was 1.3 nm, haze was 0.2%, and the MIT test value was 412 times. The obtained substrate for surface protection films was used for the evaluation of (4) and (5) above. The results are shown in Table 1.

[Table 1]

>evaluation> It is clear from Table 1 that the substrates for surface protection films of the examples of the present invention can prevent rainbow-like unevenness and have excellent bending resistance (or flexibility). It is speculated that this can be achieved by stretching a film containing a specific acrylic resin and a specific elastomer under predetermined stretching conditions. Furthermore, from the results of Comparative Example 3, it can be seen that there may be a critical value where the bending resistance (or flexibility) is lower than the allowable range in the vicinity of the compounding amount of the elastomer exceeding 5 parts by weight. In addition, with regard to light leakage and coloration, it has been confirmed that the same results as rainbow-like unevenness are obtained.

Industrial availability The base material for surface protection films of the present invention is suitable for surface protection films. The surface protection film of the present invention can be used to protect the optical film (eventually the image display device) before it is actually used. By using the substrate for a surface protection film and the surface protection film of the present invention, the accuracy of optical inspection of an image display device can be significantly improved.

(no)

Claims (8)

A substrate for a surface protection film, which is composed of a film containing an acrylic resin and an elastomer, and the in-plane retardation Re (550) is 30 nm or less, and the number of bending times until breakage in the MIT test is 500 or more, relative to 100 parts by weight of the acrylic resin contains 6 parts by weight or more of the elastomer. The substrate for a surface protection film according to claim 1, wherein the acrylic resin has a unit selected from the group consisting of glutarimide units, lactone ring units, maleic anhydride units, maleimide units and glutaric anhydride units At least one of the formed group. The substrate for a surface protection film according to claim 1, wherein the elastomer is selected from rubber-like polymers, polyamide elastomers, polyethylene elastomers, styrene elastomers and butadiene elastomers At least one of them. For the substrate for the surface protection film of claim 1, the total light transmittance is 80% or more, and the haze is 1.0% or less. A method for manufacturing a substrate for a surface protection film, which manufactures a substrate for a surface protection film as claimed in claim 1, the method comprising: forming a film-forming material containing an acrylic resin and an elastomer into a film shape; and The formed film is subjected to successive biaxial stretching or simultaneous biaxial stretching. The method for manufacturing a substrate for a surface protection film according to claim 5, wherein the stretching temperature in the sequential biaxial stretching or simultaneous biaxial stretching is Tg+10°C to Tg+30°C. A surface protection film comprising the substrate for a surface protection film according to any one of claims 1 to 4 and an adhesive layer. An optical film with surface protective film, including: Optical film; and The surface protection film according to claim 7, which is peelably attached to the optical film.