JP7126306B2 - Surface protective film and optical member with protective film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface protective film having a pressure-sensitive adhesive layer on a film substrate, and an optical member to which the surface protective film is adhered.

Surface protective films are provided on the surfaces of optical devices such as displays, electronic devices, and films and glass materials that are components of these devices for the purpose of surface protection, impact resistance, and the like. A surface protective film is provided with an adhesive layer on the main surface of a film substrate, and is attached to the surface of an adherend to be protected via this adhesive layer.

Biaxially oriented polyester films and biaxially oriented polypropylene films are generally used as substrates for surface protective films because of their excellent mechanical strength and transparency. Since the biaxially stretched polyester film and the biaxially stretched polypropylene film have a large retardation, light leakage, coloration, iridescent unevenness, etc. due to the retardation of the film substrate occur in an inspection using polarized light. In addition, when the retardation of the film substrate is large, the transmitted light and reflected light are colored in a rainbow pattern and are easily visible, which is a factor that hinders optical inspections such as lighting tests of liquid crystal panels, organic EL panels, etc. .

To address such problems, Patent Document 1 proposes using a low retardation film such as a cellulose resin film, a cyclic olefin resin film, or an unstretched polypropylene film as a film substrate.

JP 2017-190406 A

As the low retardation film, a non-stretched or low-stretching film, or a film made of a low birefringence material is generally used. However, polyester films, polypropylene films, and the like are generally biaxially stretched to orient molecules in the in-plane direction of the film and crystallize them to increase their mechanical strength. Therefore, non-stretched films have low mechanical strength. In addition, films made of low birefringence materials such as cyclic olefins and acrylics often have lower mechanical strength, even when stretched films, compared to biaxially stretched polyester films and the like. Therefore, when the surface protective film is removed from the adherend by peeling, the film substrate tends to tear or break, and peeling may become difficult. Cheap.

A cellulose-based film has a property that molecules are easily oriented in an in-plane direction even in an unstretched state, and has higher mechanical strength than a cyclic olefin-based film. However, a surface protective film using a cellulose-based film base has a problem in that when it is exposed to a high-temperature and high-humidity environment in a state where it is attached to an adherend, it tends to peel off or float from the adherend.

In view of the above, it is an object of the present invention to provide a surface protective film that does not interfere with optical inspection in a state where it is attached to an adherend, has excellent moisture resistance, and is easy to peel off from the adherend. do.

TECHNICAL FIELD The present invention relates to a surface protection film provided with an adhesive layer fixedly laminated on the first main surface of a film substrate. The in-plane retardation of the film substrate is 100 nm or less. The retardation in the thickness direction of the film substrate is preferably 100 nm or less. The tensile breaking strength of the film substrate is, for example, 200 MPa or less, and can be 120 MPa or less or 100 MPa or less. Examples of film substrates include cyclic olefin films and acrylic films.

The surface protective film has a moisture permeability of 300 g/m ² ·24 h or less at a temperature of 60° C. and a relative humidity of 90%. In order to make the moisture permeability of the surface protective film within the above range, the moisture permeability of the film substrate is preferably within the above range.

The surface protective film has a 180° peeling force of 3 N/25 mm or less, preferably 2.5 N/25 mm or less against an acrylic plate at a tensile speed of 30 m/min. In particular, when the film substrate has a low breaking strength (for example, a tensile breaking strength of 120 MPa or less), in order to prevent tearing or breaking of the film during high-speed peeling, the tensile speed of the surface protective film is 30 m / min. The 180° peeling force is preferably 2 N/25 mm or less.

The thickness of the adhesive layer is preferably 1 to 50 μm. In particular, the thickness of the pressure-sensitive adhesive layer is preferably 25 μm or less in order to suppress white turbidity of the pressure-sensitive adhesive layer in a high-humidity environment and maintain transparency. As a pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, an acrylic pressure-sensitive adhesive containing an acrylic base polymer is preferable. A crosslinked structure may be introduced into the base polymer.

The surface protection film may have an antistatic layer provided on the second main surface of the film substrate. The surface resistivity of the antistatic layer is preferably 1.0×10 ¹² Ω/□ or less.

Since the surface protective film of the present invention has a low retardation, it can prevent light leakage, coloration, iridescent unevenness, etc. in optical inspection of an adherend to which the protective film is laminated. Therefore, the protective film of the present invention is suitable as a protective film for various optical members. The surface protective film of the present invention has high humidity-reliability of adhesive strength, and even when the adherend to which the surface protective film is attached is exposed to a high-humidity environment, the surface protective film is less likely to lift or peel off. Furthermore, since the surface protective film of the present invention has a low peeling force from an adherend, it is less likely to tear or break during high-speed peeling even when the film substrate has low strength.

FIG. 3 is a cross-sectional view showing a laminated structure of a surface protective film; FIG. 4 is a cross-sectional view showing a laminated structure of surface protective films to which separators are temporarily attached;

[Structure of surface protection film]
FIG. 1 is a cross-sectional view showing one embodiment of the surface protection film. The surface protection film 10 has an adhesive layer 2 on the first main surface of the film substrate 1 . The adhesive layer 2 is fixedly laminated on the first main surface of the film substrate 1 . An antistatic layer (not shown) may be provided on the second main surface of the film substrate 1 .

As shown in FIG. 2 , a separator 5 may be temporarily attached to the adhesive layer 2 of the surface protection film 10 . The surface of the adherend can be protected by peeling off the separator 5 temporarily adhered to the surface of the adhesive layer 2 and bonding the exposed surface of the adhesive layer 2 to the adherend. The term "fixed" refers to a state in which two laminated layers are strongly adhered to each other and it is impossible or difficult to separate them at the interface between them. "Temporarily adhered" means a state in which the adhesive strength between two laminated layers is small and the layers can be easily separated at the interface between them.

The surface protective film 10 has a 180° peeling force (pulling speed: 30 m/min) to an acrylic plate of 3 N/25 mm or less. Hereinafter, unless otherwise specified, the peel force in the 180° peel test at a tensile speed of 30 m/min against an acrylic plate is simply referred to as "peel force". If the peeling force is 3 N/25 mm or less, the protective film can be easily peeled off from the adherend at high speed, resulting in excellent workability.

The peel strength of the surface protection film 10 is preferably 2.5 N/25 mm or less. In particular, when the strength of the surface protective film 10 is small (for example, when the tensile strength at break of the film substrate is 120 MPa or less), the peel force is preferably 2 N/25 mm or less, more preferably 1.7 N/25 mm or less, and 1 0.5 N/25 mm or less is more preferable. If the peel force is within the above range, tearing or breakage of the film during high-speed peeling can be prevented even when the strength of the film substrate is low. From the viewpoint of ensuring adhesion to the adherend, the peel force is preferably 0.1 N/25 mm or more, more preferably 0.2 N/25 mm or more, and even more preferably 0.3 N/25 mm or more. The peel strength of the surface protective film 10 is mainly affected by the properties of the pressure-sensitive adhesive layer 2 .

The surface protective film 10 has a moisture permeability of 300 g/m ² ·24 h or less. Moisture permeability is a value measured according to the moisture permeability test (cup method) of JIS Z0208: 1976, in an environment with a temperature of 60 ° C and a relative humidity of 90%, the amount of water vapor that permeates a sample with an area of 1 m ² in 24 hours. Weight. Below, the water vapor permeability measured under this condition is simply referred to as "water vapor permeability" unless otherwise specified. The JIS Z0208 moisture permeability is measured at a temperature of 25° C. or 40° C. and a relative humidity of 90%, whereas the moisture permeability measured at a higher temperature of 60° C. tends to be a higher value.

If the moisture permeability at a temperature of 60° C. and a relative humidity of 90% is 300 g/m ² ·24 h or less, the adherend to which the surface protection film 10 is laminated can maintain its adhesiveness even when exposed to a high-temperature and high-humidity environment. It is possible, and it is possible to suppress lifting and peeling of the surface protection film 10 from the adherend. The moisture permeability of the surface protective film 10 is preferably 200 g/m ² ·24h or less, more preferably 150 g/m ² ·24h or less, and even more preferably 100 g/m ² ·24h or less.

The moisture permeability of the surface protection film 10 is affected by both the film substrate 1 and the pressure-sensitive adhesive layer 2, but mainly depends on the moisture permeability of the low moisture permeability layer. Although it depends on the material and thickness of the film substrate 1 and the adhesive layer, generally the film substrate 1 has a lower moisture permeability than the adhesive layer 2. Almost equal to the moisture permeability of material 1.

[Film substrate]
A plastic film is used as the film substrate 1 . The thickness of the film substrate is, for example, about 5 to 500 μm. The thickness of the film substrate 1 is preferably 10 to 300 μm, more preferably 15 to 200 μm, and even more preferably 20 to 150 μm, from the viewpoint of achieving both protection performance for an adherend and flexibility.

When the adherend is optically inspected with the surface protective film 10 and the adherend bonded together, the film substrate 1 is preferably transparent. The total light transmittance of the film substrate 1 is preferably 80% or higher, more preferably 85% or higher, even more preferably 90% or higher. The haze of the film substrate 1 is preferably 10% or less, more preferably 5% or less, even more preferably 2% or less.

The in-plane retardation Re of the film substrate 1 is 100 nm or less. By using the film substrate 1 with a small in-plane retardation Re, the in-plane retardation of the surface protective film 10 is reduced, so that light leakage, coloration, iridescent unevenness, etc. in optical inspection of the adherend to which the protective film is attached are reduced. can be prevented. The in-plane retardation Re of the film substrate 1 is preferably 50 nm or less, more preferably 30 nm or less, and even more preferably 20 nm or less.

The thickness direction retardation Rth of the film substrate 1 is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. Since the retardation Rth in the thickness direction of the film substrate 1 is small, it is possible to prevent light leakage, coloration, iridescent unevenness, etc. even when observing from an oblique direction. Therefore, in a wide range image captured by a fixed camera, the difference in color and luminance between the vicinity of the center (frontal direction) and the peripheral portion (oblique direction) is reduced, and data processing is facilitated.

The in-plane retardation Re and the thickness direction retardation Rth are defined below and are measured values at a wavelength of 590 nm unless otherwise specified.
Re=(nx−ny)×d
Rth=(nx−nz)×d
nx is the refractive index in the in-plane slow axis direction, ny is the refractive index in the in-plane fast axis direction, nz is the refractive index in the thickness direction, and d is the thickness.

In general, the pressure-sensitive adhesive layer has a smaller retardation than the film substrate. Therefore, the in-plane retardation Re and the thickness direction retardation Rth of the surface protection film 10 in which the pressure-sensitive adhesive layer 2 is provided on the film substrate 1 are respectively equal to the in-plane retardation Re and the thickness direction retardation Rth of the film substrate 1. approximately equal to Therefore, by using a film substrate having the in-plane retardation Re and the thickness direction retardation within the above ranges, the surface protection film 10 also has the in-plane retardation Re and the thickness direction retardation Rth within the above ranges.

The moisture permeability of the film substrate 1 is preferably 300 g/m ² ·24h or less, more preferably 200 g/m ² ·24h or less, further preferably 150 g/m ² ·24h or less, and 100 g/m ² ·24h. The following are particularly preferred. If the moisture permeability of the film substrate 1 is within the above range, even if the moisture permeability of the adhesive layer 2 is high, the penetration of moisture into the adhesive layer 2 or the adhesive interface between the adhesive layer 2 and the adherend is prevented. can be suppressed. Therefore, even when the adherend to which the surface protection film 10 is attached is exposed to a high-temperature and high-humidity environment, the surface protection film 10 can be prevented from lifting or peeling off from the adherend.

The resin material constituting the film substrate is not particularly limited, but examples of materials that can satisfy the requirements of high transparency, low retardation and low moisture permeability include cyclic olefin resins and acrylic resins.

Examples of cyclic olefin resins include polynorbornene. Commercially available cyclic olefin resins include ZEONOR and ZEONEX manufactured by Nippon Zeon, ARTON manufactured by JSR, APEL manufactured by Mitsui Chemicals, TOPAS manufactured by TOPAS ADVANCED POLYMERS, and the like. The cyclic olefin film preferably contains 50% by weight or more of the cyclic olefin resin.

Examples of acrylic resins include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate- Acrylic acid ester-(meth)acrylic acid copolymer, methyl (meth)acrylate-styrene copolymer (MS resin, etc.), polymer having an alicyclic hydrocarbon group (e.g., methyl methacrylate-cyclohexyl methacrylate copolymers, methyl methacrylate-norbornyl (meth)acrylate copolymers, etc.). Commercially available acrylic resins include ACRYPET manufactured by Mitsubishi Chemical. A (meth)acrylic resin having a lactone ring structure, a (meth)acrylic resin having an unsaturated carboxylic acid alkyl ester unit and a glutarimide unit, and the like are also applicable as the constituent material of the film substrate 1 . The acrylic film preferably contains 50% by weight or more of acrylic resin.

The film substrate may contain antioxidants, ultraviolet absorbers, light stabilizers, nucleating agents, fillers, pigments, surfactants, antistatic agents, and the like.

The film substrate 1 may be either a stretched film or a non-stretched film as long as the in-plane retardation Re is within the above range. For example, by using a low refractive index material, a low retardation film having an in-plane retardation within the above range can be obtained even with a stretched film. In addition, by appropriately controlling the draw ratio in the vertical and horizontal directions, it is possible to reduce the in-plane retardation even with a material having a large birefringence.

As described above, by using a cyclic olefin film or an acrylic film as the film substrate 1, transparency, low moisture permeability, and low retardation can be achieved. However, these materials have low mechanical strength, and the tensile strength at break is generally 120 MPa or less in both stretched and unstretched films. When a non-stretched film or a film with a low stretch ratio is used to obtain a low retardation, the tensile strength at break is even smaller, often 100 MPa or less. Since the pressure-sensitive adhesive layer 2 is highly viscous and easily deformed, tearing or breakage of the surface protective film 10 having the pressure-sensitive adhesive layer 2 on the film substrate 1 mainly depends on the strength of the film substrate. Therefore, the tensile strength at break of the surface protective film 10 is approximately equal to the tensile strength at break of the film substrate 1 .

The surface protective film 10 using such a low-strength film substrate 1 is likely to tear or break when peeled from the adherend. In the present invention, by controlling the properties of the pressure-sensitive adhesive layer to reduce the peeling force, even when a low-strength film substrate is used, tearing or breaking occurs when the surface protective film is peeled off from the adherend. can be prevented.

The film substrate 1 may be subjected to a surface treatment such as corona treatment or easy-adhesion treatment. An antistatic layer may be provided on the main surface of the film substrate 1 opposite to the pressure-sensitive adhesive layer-attached surface. When an antistatic layer is provided on the film substrate, the surface resistivity of the antistatic layer-forming surface is preferably 1.0×10 ¹² Ω/□ or less, more preferably 1.0×10 ¹¹ Ω/□ or less, 1.0×10 ¹⁰ Ω/□ or less is more preferable.

By providing the film substrate 1 with an antistatic layer, it is possible to suppress adhesion of dust and deterioration of workability due to static electricity of the surface protection film 10 . By providing the film substrate 1 with an antistatic layer, it is possible to prevent damage to the panel caused by static electricity when a lighting test is performed on an adherend such as a liquid crystal panel or an organic EL panel. In addition, since the film substrate 1 is provided with an antistatic layer, the generation of static electricity when peeling the surface protective film 10 from the adherend is suppressed, and the adhesion of dust to the adherend caused by static electricity. It is possible to prevent defects such as loss of body and deterioration of workability.

The antistatic layer includes, for example, a layer formed by adding an antistatic component to various resins, and the resin includes a thermosetting resin, an ultraviolet curable resin, an electron beam curable resin, and a two-liquid mixture. Various types of resins may be employed, such as mold resins. Antistatic components include organic or inorganic conductive substances, various antistatic agents, and the like. Various conductive polymers can be preferably employed as the organic conductive substance. Examples of such conductive polymers include polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine-based polymers. Inorganic conductive materials include various metals, alloys, and conductive metal oxides. The inorganic conductive substance is preferably contained in the antistatic layer as fine particles having a particle size of 0.1 μm or less (typically 0.01 μm to 0.1 μm). The antistatic component may be a cationic antistatic agent, an anionic antistatic agent, an amphoteric ionic antistatic agent, a nonionic antistatic agent, or the like.

[Adhesive layer]
The adhesive layer 2 is preferably transparent. In particular, when the adherend (target to be protected) of the surface protective film is an optical device such as a display or its constituent parts, a highly transparent pressure-sensitive adhesive is used. Also, when an optical inspection is performed with the surface protective film 10 attached to an adherend, it is preferable to use a highly transparent pressure-sensitive adhesive. The total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or higher, more preferably 85% or higher, even more preferably 90% or higher. The haze of the adhesive layer 2 is preferably 10% or less, more preferably 5% or less, still more preferably 2% or less, and particularly preferably 1% or less.

The composition of the adhesive constituting the adhesive layer 2 is not particularly limited, and may be acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy, fluorine, It is possible to appropriately select and use rubber-based polymers such as natural rubber and synthetic rubber as base polymers. In particular, an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer is preferably used because of its excellent optical transparency.

As the acrylic base polymer, one having a monomer unit of (meth)acrylic acid alkyl ester as a main skeleton is preferably used. In addition, in this specification, "(meth)acryl" means acryl and/or methacryl.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms is preferably used. For example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, (meth) ) Pentyl acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, ( meth) isooctyl acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, (meth) ) isotridodecyl acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate , iso-octadecyl (meth)acrylate, nonadecyl (meth)acrylate, aralkyl (meth)acrylate, and the like.

The content of the (meth)acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more, relative to the total amount of the monomer components constituting the base polymer. The acrylic polymer may be a copolymer of multiple (meth)acrylic acid alkyl esters. The arrangement of the constituent monomer units may be random or block.

The acrylic polymer preferably contains a monomer component having a crosslinkable functional group as a copolymer component. Monomers having a crosslinkable functional group include hydroxy group-containing monomers and carboxy group-containing monomers. Above all, it is preferable to contain a hydroxy group-containing monomer as a copolymerization component of the base polymer. The hydroxy group and carboxy group of the base polymer serve as reaction points with a cross-linking agent, which will be described later. By introducing a crosslinked structure into the base polymer, the cohesive force of the pressure-sensitive adhesive is improved, the adhesive exhibits appropriate adhesive strength to the adherend, and the peeling force when peeling the surface protective film from the adherend is reduced. Tend. Therefore, when the surface protective film is peeled off, tensile stress and strain applied to the film are reduced, and tearing and breakage can be prevented.

Examples of hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and (meth)acrylate. Examples include 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate and (4-hydroxymethylcyclohexyl)-methyl acrylate. Carboxy group-containing monomers include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid and the like.

In addition to the above, the acrylic polymer can also use an acid anhydride group-containing monomer, a caprolactone adduct of acrylic acid, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, etc. as a copolymerizable monomer component. Further, as modifying monomers, vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, N -Vinyl-based monomers such as vinylcarboxylic acid amides, styrene, α-methylstyrene and N-vinylcaprolactam; Cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; Epoxy-group-containing acrylic monomers such as glycidyl (meth)acrylate ; glycol-based acrylic ester monomers such as polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; tetrahydrofurfuryl (meth)acrylate , fluorine (meth)acrylate, silicone (meth)acrylate, acrylic acid ester monomers such as 2-methoxyethyl acrylate, and the like can also be used.

The ratio of the copolymerization monomer component in the acrylic polymer is not particularly limited. The total content of the contained monomers is preferably about 1 to 20%, more preferably about 2 to 15%, relative to the total amount of monomer components constituting the base polymer.

An acrylic polymer as a base polymer can be obtained by polymerizing the above monomer components by various known methods such as solution polymerization, emulsion polymerization, bulk polymerization and suspension polymerization. A solution polymerization method is preferable from the viewpoint of the balance of properties such as the adhesive strength and holding power of the pressure-sensitive adhesive and the cost. Ethyl acetate, toluene and the like are used as solvents for solution polymerization. The solution concentration is usually about 20 to 80% by weight. As the polymerization initiator, various known ones such as azo type and peroxide type can be used. A chain transfer agent may be used to control molecular weight. The reaction temperature is generally about 50-80° C., and the reaction time is generally about 1-8 hours.

The molecular weight of the base polymer is appropriately adjusted so that the pressure-sensitive adhesive layer 2 has the desired adhesive strength. about 100,000 to 1,500,000, more preferably about 200,000 to 1,000,000. When a crosslinked structure is introduced into the base polymer, the molecular weight of the base polymer before the introduction of the crosslinked structure is preferably within the above range.

In order to obtain the pressure-sensitive adhesive layer 2 having appropriate adhesiveness to the adherend in a normal temperature environment, the glass transition temperature (Tg) of the base polymer converted to the Fox formula is preferably 0° C. or lower. The Tg of the base polymer is preferably -10 to -80°C, more preferably -15 to -75°C, and still more preferably -20 to -70°C.

A crosslinked structure may be introduced into the base polymer for the purpose of adjusting the adhesive strength of the pressure-sensitive adhesive layer 2 or the like. For example, a cross-linked structure is introduced by adding a cross-linking agent to the solution after polymerization of the base polymer, and heating if necessary. Examples of cross-linking agents include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, carbodiimide-based cross-linking agents, and metal chelate-based cross-linking agents. Among these, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferred because they are highly reactive with the hydroxy groups and carboxy groups of the base polymer and facilitate the introduction of a cross-linked structure. These cross-linking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the base polymer to form a cross-linked structure.

A polyisocyanate having two or more isocyanate groups in one molecule is used as the isocyanate-based cross-linking agent. Examples of isocyanate-based cross-linking agents include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; Aromatic isocyanates such as isocyanate, 4,4′-diphenylmethane diisocyanate, and xylylene diisocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct (for example, “Coronate L” manufactured by Tosoh), trimethylolpropane/hexamethylene Diisocyanate trimer adduct (e.g., Tosoh "Coronate HL"), trimethylolpropane adduct of xylylene diisocyanate (e.g., Mitsui Chemicals "Takenate D110N", isocyanurate of hexamethylene diisocyanate (e.g., Tosoh " and isocyanate adducts such as "Coronate HX").

A polyfunctional epoxy compound having two or more epoxy groups in one molecule is used as the epoxy-based cross-linking agent. The epoxy group of the epoxy-based cross-linking agent may be a glycidyl group. Examples of epoxy-based cross-linking agents include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1, 6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, penta erythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipate diglycidyl ester, o-phthalate diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether and the like. As the epoxy-based cross-linking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX, "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical may be used.

A crosslinked structure is introduced into the base polymer by adding a crosslinking agent to the base polymer after polymerization. The amount of the cross-linking agent used may be appropriately adjusted according to the composition and molecular weight of the base polymer, the desired adhesive properties, and the like. In order to give the pressure-sensitive adhesive an appropriate cohesive force and adjust the peeling force when peeling the protective film from the adherend to an appropriate range, the amount of the cross-linking agent used is 100 parts by weight of the base polymer. , preferably 1.5 parts by weight or more, more preferably 2 parts by weight or more, and even more preferably 2.5 parts by weight or more. The amount of the cross-linking agent used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, more preferably 10 parts by weight or less, with respect to 100 parts by weight of the base polymer in order to provide appropriate adhesion to the adherend. is more preferred.

By introducing a crosslinked structure into the base polymer, the gel fraction of the pressure-sensitive adhesive increases, and along with the decrease in viscous behavior, there is a tendency for the peeling force when peeling the protective film from the adherend to decrease. The gel fraction of the pressure-sensitive adhesive layer 2 is preferably 70.0% or higher, more preferably 80.0% or higher, even more preferably 90.0% or higher. If the gel fraction of the pressure-sensitive adhesive layer 2 is excessively high, the wettability with respect to the adherend may decrease, resulting in insufficient adhesive force. Therefore, the gel fraction of the adhesive layer 2 is preferably 99.5% or less, more preferably 98.5% or less, even more preferably 97.5% or less. The gel fraction can be determined as an insoluble content in a solvent such as ethyl acetate. Specifically, the insoluble content after immersing the adhesive layer in ethyl acetate at 23 ° C. for 7 days is It is obtained as a weight fraction (unit: % by weight). In general, the gel fraction of a polymer is equal to the degree of cross-linking; the more cross-linked moieties in the polymer, the higher the gel fraction.

From the viewpoint of reducing the peeling force when the protective film is peeled from the adherend by giving the pressure-sensitive adhesive layer 2 an appropriate hardness, the storage elastic modulus G' of the pressure-sensitive adhesive layer 2 at 23°C is 5.0. ×10 ⁴ Pa or more is preferable, 7.5 × 10 ⁴ Pa or more is more preferable, and 1.0 × 10 ⁵ Pa or more is even more preferable. If the storage elastic modulus of the pressure-sensitive adhesive layer 2 is excessively high, the wettability with respect to the adherend may decrease, resulting in insufficient adhesive strength. Therefore, the storage elastic modulus G′ of the adhesive layer 2 at 23° C. is preferably 5.0×10 ⁶ Pa or less, more preferably 2.5×10 ⁶ Pa or less, and further preferably 1.0×10 ⁶ Pa or less. preferable. The storage elastic modulus G′ is measured using a dynamic viscoelasticity measuring device (eg, “ARES” manufactured by Rheometrics Co., Ltd.) under the conditions of a frequency of 1 Hz, a temperature range of −70° C. to 150° C., and a heating rate of 5° C./min. It is obtained by performing viscoelasticity measurement.

The storage elastic modulus of the adhesive layer can be adjusted by the composition of the adhesive. For example, using a base polymer with a high glass transition temperature tends to increase the storage modulus. In addition, when the gel fraction increases due to the introduction of a crosslinked structure into the base polymer, the storage elastic modulus tends to increase.

In addition to the components exemplified above, the pressure-sensitive adhesive composition contains a silane coupling agent, a tackifier, a plasticizer, a softening agent, an anti-degradation agent, a filler, a coloring agent, an ultraviolet absorber, an antioxidant, and a surfactant. Additives such as agents and antistatic agents may be contained within a range that does not impair the characteristics of the present invention.

By laminating the adhesive layer 2 on the film substrate 1, the surface protection film 10 is obtained. The pressure-sensitive adhesive layer 2 may be directly formed on the film substrate 1 , or may be transferred onto the film substrate 1 from a pressure-sensitive adhesive layer formed in a sheet form on another substrate.

The pressure-sensitive adhesive composition is applied to the substrate by roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, die coating, or the like. A pressure-sensitive adhesive layer is formed by applying it on the material and removing the solvent by drying if necessary. As a drying method, an appropriate method can be adopted as appropriate. The heat drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, still more preferably 70°C to 170°C. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, even more preferably 10 seconds to 10 minutes, particularly preferably 10 seconds to 5 minutes.

When the pressure-sensitive adhesive composition contains a cross-linking agent, it is preferable to promote cross-linking by heating or aging at the same time as drying the solvent or after drying the solvent. The heating temperature and heating time are appropriately set according to the type of cross-linking agent used, and generally cross-linking is carried out by heating in the range of 20° C. to 160° C. for about 1 minute to 7 days. The heating for removing the solvent by drying may also serve as the heating for cross-linking.

The thickness of the adhesive layer 2 is not particularly limited, but from the viewpoint of achieving both adhesive strength to the adherend and releasability from the adherend, the thickness of the adhesive layer 2 is preferably 1 to 50 μm, more preferably 2 to 40 μm. is more preferable, and 3 to 35 μm is even more preferable. As the thickness of the pressure-sensitive adhesive layer 2 becomes smaller, the releasability from the adherend tends to improve. In particular, when the breaking strength of the film substrate 1 is small, the thickness of the pressure-sensitive adhesive layer 2 is preferably 25 μm or less from the viewpoint of preventing tearing or breaking of the film when the surface protective film 10 is peeled off from the adherend at high speed. , 20 μm or less. From the viewpoint of suppressing white turbidity of the pressure-sensitive adhesive layer 2 in a high-humidity environment and maintaining transparency, the thickness of the pressure-sensitive adhesive layer is preferably 25 μm or less, more preferably 20 μm or less.

When the adhesive layer 2 is formed on a substrate other than the film substrate 1, the surface protection film 10 is obtained by transferring the adhesive layer 2 onto the film substrate 1 after drying the solvent on the substrate. be done. The base material used for forming the adhesive layer may be used as the separator 5 as it is.

As the separator 5, plastic films such as polyethylene, polypropylene, polyethylene terephthalate and polyester films are preferably used. The thickness of the separator is usually 3 to 200 μm, preferably about 10 to 100 μm, more preferably about 15 to 50 μm. The contact surface of the separator 5 with the pressure-sensitive adhesive layer 2 is subjected to release treatment with a release agent such as a silicone, fluorine, long-chain alkyl, or fatty acid amide release agent, silica powder, or the like. is preferred. The plastic film forming the separator 5 may contain an antistatic agent.

[Physical properties of surface protective film]
As described above, the surface protective film 10 has a 180° peeling force of 3 N/25 mm or less, preferably 2.5 N/25 mm or less against an acrylic plate at a tensile speed of 30 m/min. In particular, when using a film substrate 1 having a tensile breaking strength of 120 MPa or less, the surface protective film 10 is prevented from tearing or breaking when peeled from the adherend, and the peel strength is preferably 2 N/25 mm or less, more preferably 1.7 N/25 mm or less, and even more preferably 1.5 N/25 mm or less.

By adjusting the adhesive strength of the pressure-sensitive adhesive layer 2, the peel strength of the surface protection film 10 can be within the above range. As described above, the peel strength tends to decrease as the thickness of the pressure-sensitive adhesive layer 2 decreases. Also, by increasing the amount of the crosslinked structure introduced into the base polymer that constitutes the pressure-sensitive adhesive layer 2, the gel fraction tends to increase and the peeling force tends to decrease.

From the viewpoint of suppressing peeling of the surface protective film 10 from the adherend in a high-temperature and high-humidity environment, it is preferable that the peeling force (adhesive force) of the surface protective film 10 is large. On the other hand, as described above, when the peeling force is large, tearing or breakage is likely to occur when the surface protective film is peeled from the adherend. From the viewpoint of improving adhesion reliability in a humid environment without excessively increasing the peeling force and suppressing peeling and lifting of the surface protective film from the adherend, the moisture permeability of the surface protective film is 300 g/m ² ·. 24 hours or less is preferable, 200 g/m ² ·24 hours or less is more preferable, 150 g/m ² ·24 hours or less is even more preferable, and 100 g/m ² ·24 hours or less is particularly preferable.

As described above, the moisture permeability of the surface protection film 10 is substantially equal to that of the film substrate 1 . Therefore, in order to keep the moisture permeability of the surface protection film 10 within the above range, it is preferable to use a film substrate 1 with low moisture permeability such as a cyclic olefin film or an acrylic film.

When optical inspection is performed with the surface protective film 10 attached to an adherend, the retardation of the surface protective film 10 causes the inspection light to be colored. From the viewpoint of preventing light leakage, coloring, iridescent unevenness, etc. during optical inspection, the in-plane retardation Re of the surface protection film 10 is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 20 nm or less. . From the same point of view, the thickness direction retardation Rth of the surface protection film 10 is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less.

As described above, the in-plane retardation Re and the thickness direction retardation Rth of the surface protective film 10 in which the pressure-sensitive adhesive layer 2 is provided on the film substrate 1 correspond to the in-plane retardation Re and the thickness direction retardation Rth of the film substrate 1, respectively. Approximately equal to the retardation Rth. Therefore, in order to make the Re and Rth of the surface protection film 10 within the above ranges, it is preferable to use a low birefringence material film or a non-stretched or low stretch ratio film as the film substrate 1 . In the present invention, since the peeling force of the surface protection film 10 is appropriately adjusted, even when a film having a low strength (for example, a tensile strength at break of 120 MPa or less) is used as the film substrate 1, even when peeling at high speed It can prevent tearing and breakage of the film.

The peeling electrostatic voltage when peeling the surface protective film from the adherend is preferably 2.5 kV or less, more preferably 2 kV or less. In particular, when the surface protection film is attached to an adherend that is susceptible to static electricity, the peeling electrification voltage is preferably 1.5 kV or less, more preferably 1 kV or less. For example, by providing an antistatic layer on the surface of the film substrate 1 on which the pressure-sensitive adhesive layer is not attached, the peeling electrostatic voltage of the surface protection film 10 can be reduced.

An adherend to which the surface protection film of the present invention is attached can prevent the surface from being scratched or damaged by impact. Since the surface protective film has low moisture permeability and high humidification reliability of adhesive strength, even when the adherend to which the surface protective film is attached is exposed to a high humidity environment, the surface protective film is less likely to lift or peel off. .

The adherend of the surface protective film is not particularly limited. The surface protective film of the present invention can be used, for example, as a surface protective film for various optical members. Optical members include polarizing plates, retardation plates, optical compensation films, viewing angle expansion films, viewing angle control films, brightness enhancement films, antireflection films, reflection sheets, transparent conductive films, prism sheets, optical films such as light guide plates; image display panels such as liquid crystal panels and organic EL panels; and image display devices incorporating image display panels. An image display panel or an image display device may be formed by assembling an optical film as an optical component with a surface protection film laminated thereon.

Since the surface protective film of the present invention has a low retardation, even when optical inspection is performed in a state where the surface protective film is attached to an optical member, it hardly interferes with the optical inspection, and contributes to improving the efficiency and accuracy of the inspection. . In addition, since the surface protective film of the present invention has a small peeling force, even when the film base material has low strength, tearing or breakage is unlikely to occur during high-speed peeling, and workability is excellent.

The present invention will be further described below with reference to production examples of the surface protective film, but the present invention is not limited to these examples.

[Measurement method and evaluation method]
Each physical property and evaluation of the film substrate and the surface protective film were performed by the following methods.

<Front retardation and thickness direction retardation>
Cut out the film substrate to a size of 50 mm × 50 mm, using a polarization / phase difference measurement system ("AxoScan" manufactured by Axometrics), under an environment of 23 ° C. relative humidity of 50% (hereinafter "standard environment"), at a measurement wavelength of 590 nm The in-plane retardation and the retardation in a state in which the film was tilted at 40° around the slow axis direction were measured. From these measured values, the in-plane retardation Re and the thickness direction retardation Rth were calculated. In calculating the retardation in the thickness direction, an average refractive index measured by an Abbe refractometer manufactured by Atago Co., Ltd. was used.

<Peeling force>
Cut the surface protective film into a size of 25 mm in width and 100 mm in length, and after peeling off the separator, on an acrylic plate ("Acrylite" manufactured by Mitsubishi Chemical, thickness: 2 mm, width: 70 mm, length: 100 mm), pressure 0.25 MPa , and a feed rate of 0.3 m/min. After allowing this sample to stand under a standard environment for 30 minutes, a peel test was performed under the same environment at a peel angle of 180° and a tensile speed of 0.3 m/min or 30 m/min. was measured.

<Breaking strength>
A No. 3 dumbbell-shaped test piece (width 5 mm) was cut out from the surface protection film, and after peeling off the separator, powder was adhered to the adhesive surface to remove the influence of the viscosity of the adhesive. Using a tensile tester, according to JIS K7311:1995, a tensile test was performed under a standard environment at a tensile speed of 0.3 m/min to measure the tensile strength at break in each of the MD and TD directions.

<Moisture permeability>
After leaving the surface protective film under a standard environment for 24 hours, the separator was peeled off, and in accordance with the moisture permeability test (cup method) of JIS Z0208: 1976, the temperature was 60 ° C. 24 in an environment with a relative humidity of 90%. The moisture permeability was calculated from the weight of the water vapor permeating the surface protection film during the time and the sample area.

<Surface resistivity>
Under a standard environment, using a resistivity meter (Mitsubishi Chemical Analytic "Hiresta UP MCP-HT450 type"), the URS probe is brought into contact with the adhesive layer non-attached surface of the film substrate, and the applied voltage is 10 V for the voltage application time. The surface resistivity was measured under the condition of 30 seconds.

<Rainbow unevenness>
The separator was peeled off from the surface protection film, and the polarizing plate and the MD direction of the film substrate were bonded together so that they were parallel to each other. Another polarizing plate was placed on the surface protective film so as to form cross Nicols with the polarizing plate attached to the surface protective film. Light from a fluorescent lamp was irradiated from the lower side of one of the polarizing plates, and the presence or absence of iridescent unevenness was evaluated by visual observation of the transmitted light. A case where rainbow unevenness was not observed was evaluated as OK, and a case where rainbow unevenness was confirmed was evaluated as NG.

<Tears during peeling>
The surface protection film was cut into a size of 25 mm in width and 100 mm in length, and the separator was peeled off. A surface protective film was crimped with a hand roller to the hard coat layer forming surface of a hard coat polarizing plate (manufactured by Nitto Denko, width 50 mm, length 100 mm) laminated to a glass plate having a thickness of 1 mm. This sample was placed in a constant temperature and humidity chamber at a temperature of 60° C. and a relative humidity of 90% for 5 days, then taken out and left to stand for 30 minutes under a standard environment. After that, a peel test was performed under a standard environment at a peel angle of 180° and a tensile speed of 0.3 m/min or 30 m/min, and evaluation was made according to the following criteria based on the presence or absence of tearing of the surface protective film at each speed. .
A: Peelable without cracking at any tensile speed B: Peelable without cracking at tensile speed of 0.3 m / min, but cracking at tensile speed of 30 m / min NG: Any tensile Tear occurs even at high speed

<Humidified adhesion>
The surface protection film was cut into a size of 25 mm in width and 50 mm in length, and the separator was peeled off. A hard coat polarizing plate (manufactured by Nitto Denko, width 50 mm, length 70 mm) laminated to a glass plate having a thickness of 1 mm was intentionally laminated so as to contain air bubbles of about 10 mm. After leaving the sample in a constant temperature and humidity chamber at a temperature of 60° C. and a relative humidity of 90% for 5 days, the sample was taken out and allowed to stand under a standard environment for 30 minutes. observed at. When no change was observed before and after humidification, it was evaluated as OK.

<Humidification transparency>
The surface protection film was cut into a size of 25 mm in width and 50 mm in length, and the separator was peeled off. A surface protective film was crimped onto the hard coat layer formed surface of a hard coat polarizing plate (manufactured by Nitto Denko, width 50 mm, length 70 mm) bonded to a glass plate having a thickness of 1 mm using a hand roller. This sample is taken out after standing for 5 days in a constant temperature and humidity chamber at a temperature of 60 ° C. and a relative humidity of 90%. The presence or absence of cloudiness was observed. A sample in which cloudiness was not observed was evaluated as OK, and a sample in which cloudiness was observed was evaluated as NG.

<Peeling electrification voltage>
The surface protective film was cut into a size of 70 mm wide and 130 mm long, and the separator was peeled off. A hard-coated polarizing plate (manufactured by Nitto Denko, width 50 mm, length 70 mm) was attached to the surface of a glass plate with a thickness of 1 mm, and one end of the surface protective film was placed on the polarizing plate from the edge of the polarizing plate. It was crimped with a hand roller so as to protrude by 30 mm. After this sample was allowed to stand under standard environment for 24 hours, it was set on a sample fixing table having a height of 20 mm under standard environment. The end of the surface protective film protruding from the polarizing plate by 30 mm is fixed to an automatic winding machine, and the surface protective film is peeled from the polarizing plate under the conditions of a peeling angle of 150 ° and a tensile speed of 30 m / min. The potential of the surface of the adherend (polarizing plate) was measured with a potential measuring device (“KSD-0103” manufactured by Kasuga Denki) fixed at a position 100 mm in height from the center of the polarizing plate.

[Polymerization of acrylic polymer]
<Acrylic polymer A>
96.2 parts by weight of 2-ethylhexyl acrylate (2EHA) and 3.8 parts by weight of hydroxyethyl acrylate (HEA) were added as monomer components in a reaction vessel equipped with a thermometer, a stirrer, a condenser and a nitrogen gas inlet tube. 0.2 parts by weight of 2,2′-azobisisobutyronitrile (AIBN) as a polymerization initiator was charged together with 150 parts by weight of ethyl acetate, and nitrogen gas was introduced while gently stirring at 23° C. to perform nitrogen substitution. rice field. After that, a polymerization reaction was carried out for 6 hours while keeping the liquid temperature around 60° C. to prepare a solution of acrylic polymer A (concentration: 40% by weight). The Tg of Acrypolymer A calculated from the Fox equation is -66°C.

<Acrylic polymer B>
2EHA: 54.1 parts by weight, vinyl acetate (Vac): 43.2 parts by weight, and acrylic acid (AA): 2.7 parts by weight, and 0.3 parts by weight of benzoyl peroxide (BPO; "NIPER BW" manufactured by NOF Corporation) as a polymerization initiator, were charged together with 143 parts by weight of toluene, and nitrogen gas was added while gently stirring at 23 ° C. was introduced to perform nitrogen substitution. After that, the liquid temperature was maintained at about 60° C. and the polymerization reaction was carried out for 6 hours. The Tg of acrylic polymer B calculated from the Fox equation is -26°C.

<Acrylic polymer C>
The monomer components were changed to 2EHA: 91 parts by weight and 4-hydroxybutyl acrylate (4HBA): 9 parts by weight. Other than that, nitrogen substitution and polymerization were carried out in the same manner as for the acrylic base polymer A to obtain a solution of acrylic polymer C (concentration: 40% by weight). The Tg of acrylic polymer C calculated from the Fox equation is -67°C.

[Film substrate]
The details of the film substrate used in the production examples are as follows.
Cyclic olefin film 1 (COP1): Nippon Zeon "Zeonor Film ZF-16" (thickness 40 μm, Re = 1.8 nm, Rth = 8.6 nm)
Cyclic olefin film 2 (COP2): Nippon Zeon "Zeonor Film ZF-14" (thickness 40 μm, Re = 0.8 nm, Rth = 3.5 nm)
Antistatic cyclic olefin film (AS-COP): One side of Nippon Zeon's "Zeonor Film ZF-16" provided with an antistatic layer by the method described later Acrylic film: Examples of JP-A-2017-26939 Biaxially stretched film made of imidized MS resin (thickness 40 μm, Re = 0.4 nm, Rth = 0.7 nm) prepared in the same manner as “transparent protective film 1A” described in
Polyethylene terephthalate film (PET): Mitsubishi Chemical "Diafoil T100C38" (thickness 38 µm, Re = 180 nm, Rth = 812 nm)
Triacetyl cellulose film (TAC): "KC4CT1" manufactured by Konica Minolta (thickness 40 µm, Re = 0.8 nm, Rth = 3.8 nm)
Biaxially oriented polypropylene film (OPP): Santox "PA30" (thickness 60 µm, Re = 195 nm, Rth = 555 nm)

<Formation of antistatic layer>
For the formation of the antistatic layer of the antistatic cyclic olefin film (AS-COP), 100 parts by weight of a solid content of a polyester resin dispersion (Toyobo "Binalol MD-1480") as a binder resin and a conductive polymer An aqueous solution containing poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (50 parts by weight of "Clevios P" manufactured by Heraeus in solid content, 10 parts by weight of a melamine-based cross-linking agent, and an aqueous dispersion of carnauba wax as a lubricant 40 parts by weight of the solid content in a mixed solvent of water and ethanol to obtain a coating liquid having a solid content of 0.3%.This coating liquid is applied to the above COP film with a bar coater, and and dried for 10 seconds to form an antistatic layer with a thickness of 25 nm.

[Production example 1]
Ethyl acetate was added to the acrylic polymer A solution to dilute it to a concentration of 25% by weight. To 400 parts by weight of this solution (100 parts by weight of solids), 4 parts by weight of "Coronate HX" made by Tosoh as a cross-linking agent and an ethyl acetate solution of dioctyltin dilaurate as a cross-linking catalyst ("Enbi" by Tokyo Fine Chemicals) were added. Riser OL-1”) was added in solid content of 0.02 parts by weight and stirred to prepare an acrylic pressure-sensitive adhesive solution.

The above acrylic pressure-sensitive adhesive solution is applied to the release-treated surface of a separator (25 μm-thick biaxially oriented polyethylene terephthalate film with silicone release treatment on one side) and heated at 130° C. for 20 seconds to obtain a thickness of 10 μm. to form an adhesive layer. This pressure-sensitive adhesive layer was attached to the corona-treated surface of a COP film, one surface of which was corona-treated, to obtain a separator-attached surface protective film.

[Production Examples 2 to 17]
Preparation Example 1 except that the type of film substrate, the composition of the acrylic pressure-sensitive adhesive solution (the type of acrylic polymer and the type and amount of the cross-linking agent added), and the thickness of the pressure-sensitive adhesive layer were changed as shown in Table 1. In the same manner as above, a surface protective film with a separator was obtained. The details of the cross-linking agents used in each example are as follows. The amount of the cross-linking agent added in Table 1 is the solid content of the cross-linking agent with respect to 100 parts by weight of the polymer. In Production Examples 11 and 12, in which only the epoxy-based Tetrad C was used as the cross-linking agent, no cross-linking catalyst was added in the preparation of the adhesive solution.

Coronate HX: isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh)
Coronate L: 75% solution of trimethylolpropane adduct of tolylene diisocyanate (manufactured by Tosoh)
Tetrad C: Tetrafunctional epoxy compound (manufactured by Mitsubishi Gas Chemical)

Table 1 shows the structure of the surface protective film of each production example (kind of film substrate, composition and thickness of adhesive) and evaluation results of the surface protective film. The surface resistivity of Preparation Example 2 using an antistatic cyclic olefin (AS-COP) film is 8.1×10 ⁸ Ω/□, and the surface resistivity of other examples is the upper measurement limit (1×10 ¹³ Ω/ □).

In Production Example 16 using a biaxially stretched PET film substrate and Production Example 17 using an OPP film substrate, rainbow unevenness was observed under crossed Nicols due to the large retardation of the substrate film. Poor optical inspection. In Production Example 18 using the TAC film substrate, no iridescent unevenness was observed under crossed Nicols, but the surface protective film was easily peeled off after the humidification test, and the humidification reliability was poor. It is considered that this is due to the fact that the moisture permeability of the film substrate is low and the amount of moisture entering the adhesive interface is large.

In Production Examples 1 to 15 using film substrates with low retardation and low moisture permeability, rainbow unevenness was not observed under crossed Nicols, and the peeled area of the surface protective film did not increase even after the humidification test.

In Production Example 8, tearing occurred in both low-speed peeling and high-speed peeling after the humidification test. In Production Example 8, the mechanical strength (tensile breaking strength) of the film substrate is small and the peeling force is large, so the film substrate is likely to tear due to the stress applied to the film substrate during peeling. Conceivable.

In Production Examples 7 and 10, no tear occurred in low-speed peeling after the humidification test. In Production Examples 1 to 6, 9, and 11 to 15, no tear occurred in either low-speed peeling or high-speed peeling after the humidification test. From these results, by designing the adhesive layer so that the peeling force from the adherend is small, tearing and breaking during high-speed peeling can be prevented even when using a film substrate with low retardation and low mechanical strength. It can be seen that a surface protective film that is difficult to be produced can be obtained.

Focusing on the relationship between the configuration of the pressure-sensitive adhesive layer and the peel strength, from the comparison of Preparation Examples 1, 4, and 5 to 7 using the pressure-sensitive adhesive layer with the same thickness, the amount of the cross-linking agent used in the pressure-sensitive adhesive composition is increased. Therefore, it can be seen that the peel force tends to decrease. A similar tendency can be seen from the comparison between Production Examples 3 and 8 and the comparison between Production Examples 11 and 12. In addition, from the comparison of Production Examples 1, 3, and 10 using adhesives of the same composition, it can be seen that the thinner the thickness of the adhesive layer, the lower the peeling force and the more the tearing during high-speed peeling can be prevented.

In Production Example 10, in which a pressure-sensitive adhesive layer having a thickness of 30 μm was provided on the film substrate, cloudiness of the film was observed after the humidification test. From this result, it can be said that the thickness of the pressure-sensitive adhesive layer is preferably as small as possible from the viewpoint of transparency as well as prevention of tearing at the time of peeling.

In Preparation Example 2 using the film substrate provided with the antistatic layer, the peeling electrification voltage was smaller than in the other examples. From this result, it can be said that it is preferable to provide an antistatic layer on the film substrate as the surface protective film used for devices susceptible to static electricity.

As can be understood from the comparison of the above production examples, by adjusting the thickness and composition of the adhesive layer to keep the peeling force within a predetermined range, even when using a film substrate with low retardation and low mechanical strength, high-speed peeling can be achieved. It can be seen that a surface protective film that is less likely to tear or break during peeling can be obtained.

REFERENCE SIGNS LIST 1 Film substrate 2 Adhesive layer 5 Separator 10 Surface protection film

Claims (9)

A surface protective film comprising a film substrate and an adhesive layer fixedly laminated on a first main surface of the film substrate,
The in-plane retardation of the film substrate is 30 nm or less,
An antistatic layer is provided on the second main surface of the film substrate,
The surface protective film has a moisture permeability of 300 g/m ² 24 h or less at a temperature of 60° C. and a relative humidity of 90%, and a 180° peeling force of 1.5 N/25 mm or less against an acrylic plate at a tensile speed of 30 m/min. , surface protection film. 2. The surface protection film according to claim 1, wherein the thickness direction retardation of the film substrate is 100 nm or less. 3. The surface protection film according to claim 1, which has a tensile strength at break of 120 MPa or less. The surface protection film according to any one of claims 1 to 3, wherein the film substrate is a cyclic olefin film or an acrylic film. The surface protection film according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer has a thickness of 1 to 50 µm. The surface protection film according to any one of claims 1 to 5, wherein the adhesive layer contains an acrylic base polymer having a crosslinked structure. 7. The surface protection film according to claim 6, wherein a crosslinked structure is introduced into said base polymer. 8. The surface protection film according to claim 1, wherein the antistatic layer has a surface resistivity of 1.0×10 ¹² Ω/□ or less. An optical member with a protective film, wherein the surface protective film according to any one of claims 1 to 8 is attached to the surface of an optical member.

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