KR20200093634A - Surface protective film and optical member having protective film - Google Patents

Abstract

The surface protection film 10 is provided with the adhesive layer 2 adhered and laminated on the main surface of the film base material 1. The front retardation of the film base material 1 is 100 nm or less. The surface protective film 10 has a moisture permeability of 300 g/m2·24h or less at a temperature of 60° C. and a relative humidity of 90%, and a 180° peel force of 30 m/min of tensile speed to an acrylic plate is 3 N/25 mm or less. By bonding the surface protective film to the surface of the optical member, an optical member having a protective film is obtained.

Description

Surface protective film and optical member having protective film

The present invention relates to a surface protection film provided with an adhesive layer on a film substrate, and an optical member to which the surface protection film is adhered.

Surface protective films are provided on the surfaces of optical devices such as displays, electronic devices, and films or glass materials that are components of these devices for the purpose of surface protection and imparting impact resistance. The surface protection film is provided with an adhesive layer on the main surface of the film base material, and is bonded to the surface of the adherend to be protected through the adhesive layer.

As a base material of a surface protection film, a biaxially stretched polyester film or a biaxially stretched polypropylene film is generally used from the viewpoint of excellent mechanical strength and transparency. Since the biaxially stretched polyester film and the biaxially stretched polypropylene film have a large phase difference, light leakage, coloring, rainbow stains, and the like due to the phase difference of the film base material are generated in inspection using polarized light. Moreover, when the phase difference of a film base material is large, transmitted light and reflected light are colored in a rainbow shape, and it is easy to be recognized, and it becomes a factor which interferes with optical inspection, such as a lighting test, such as a liquid crystal panel and an organic EL panel.

Regarding such a problem, in Patent Document 1, it is proposed to use a low-phase difference film such as a cellulose-based resin film, a cyclic olefin-based resin film, and a non-stretched polypropylene film as the film substrate.

Japanese Patent Publication No. 2017-190406

As a low-phase difference film, a film of a non-stretched or low-stretch magnification or a film made of a low birefringent material is generally used. However, a polyester film, a polypropylene film, or the like, usually has a mechanical strength of a non-stretched film because the mechanical strength is increased by aligning the molecules in the in-plane direction of the film by biaxial stretching and crystallization. Further, a film made of a low birefringent material such as cyclic olefin or acrylic may be a stretched film, but mechanical strength is often small compared to a biaxially stretched polyester film or the like. Therefore, when peeling and removing the surface protection film from the adherend, rupture or breakage of the film base material is likely to occur, and peeling may be difficult, and the tendency is particularly prominent when peeling at a high speed.

The cellulose-based film has a property that molecules are easily oriented in the in-plane direction even in a non-stretched state, and has high mechanical strength as compared to a cyclic olefin-based film. However, the surface protection film using a cellulose-based film base material has a problem that, when exposed to a high temperature and high humidity environment in a state where it is bonded to an adherend, peeling or lifting from the adherend is likely to occur.

In view of the above, the present invention aims to provide a surface protection film that does not interfere with optical inspection in a state bonded to an adherend, has excellent moisture resistance, and is easily peelable from the adherend.

The present invention relates to a surface protection film comprising an adhesive layer adhered and laminated on a first main surface of a film substrate. The front retardation of the film base material is 100 nm or less. The thickness direction retardation of the film base material is preferably 100 nm or less. The tensile strength at break of the film substrate is, for example, 200 MPa or less, and may be 120 MPa or less or 100 MPa or less. As a film base material, a cyclic olefin type film, an acrylic type film, etc. are mentioned.

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

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

The thickness of the pressure-sensitive adhesive layer is preferably 1 to 50 μm. In particular, in order to suppress the cloudiness of the pressure-sensitive adhesive layer in a high-humidity environment and maintain transparency, the thickness of the pressure-sensitive adhesive layer is preferably 25 μm or less. As the 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 be provided with an antistatic layer 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 phase difference, it is possible to prevent light leakage, coloring, rainbow stains, and the like in optical inspection of an adherend to which the protective film is bonded. Therefore, the protective film of this invention is suitable as a protective film for various optical members. The surface protection film of the present invention has a high humidification reliability of adhesion, and even when the adherend on which the surface protection film is attached is exposed to a high-humidity environment, it is difficult for the surface protection film to be lifted or peeled. In addition, since the peeling force from the adherend of the surface protective film of the present invention is small, even when the film base material is low in strength, rupture or breakage during high-speed peeling is unlikely to occur.

1 is a cross-sectional view showing a laminated structure of a surface protection film.
It is sectional drawing which shows the laminated|stacked structure of the surface protection film to which a separator was temporarily attached.

[Structure of surface protection film]

1 is a cross-sectional view showing an embodiment of a surface protection film. The surface protection film 10 is provided with an adhesive layer 2 on the first main surface of the film substrate 1. The pressure-sensitive adhesive layer 2 is adhered and 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, the separator 5 may be temporarily attached to the pressure-sensitive adhesive layer 2 of the surface protection film 10. The surface of the adherend can be protected by peeling off the separator 5 temporarily attached to the surface of the pressure-sensitive adhesive layer 2 and bonding the exposed surface of the pressure-sensitive adhesive layer 2 to the adherend. In addition, "fixation" is a state in which two stacked layers are strongly adhered, and peeling at both interfaces is impossible or difficult. "Temporary adhesion" is a state in which the adhesive force between two stacked layers is small and can be easily peeled off at both interfaces.

The surface protection film 10 has a 180° peel force (tensile 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 described as “peel force”. When the peeling force is 3 N/25 mm or less, high-speed peeling of the protective film from the adherend is easy, and the workability is excellent.

The peeling force of the surface protection film 10 is preferably 2.5 N/25 mm or less. Particularly, when the strength of the surface protection film 10 is small (for example, when the tensile breaking strength of the film base material is 120 MPa or less), the peel force is preferably 2 N/25 mm or less, and 1.7 N/25 mm or less It is more preferable, and 1.5 N/25 mm or less is more preferable. When the peeling force is within the above range, even when the strength of the film base material is small, it is possible to prevent film rupture or breakage during high-speed peeling. From the viewpoint of ensuring adhesion with the adherend, the peeling 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 peeling force of the surface protection film 10 mainly depends on the properties of the pressure-sensitive adhesive layer 2.

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

If the moisture permeability at a temperature of 60°C and relative humidity of 90% is 300 g/m 2 ·24h or less, adhesion can be maintained even when the adherend to which the surface protective film 10 is bonded is exposed to a high temperature and high humidity environment, and the surface is protected from the adherend Lifting and peeling of the film 10 can be suppressed. The moisture permeability of the surface protection film 10 is preferably 200 g/m 2 ·24h or less, more preferably 150g/m 2 ·24h or less, and even more preferably 100g/m 2 ·24h or less.

The moisture permeability of the surface protection film 10 is affected by both the film base 1 and the pressure-sensitive adhesive layer 2, but mainly depends on the moisture permeability of the layer having low moisture permeability. Although it depends on the material and thickness of the film base material 1 and the pressure-sensitive adhesive layer, in general, the moisture permeability of the surface protective film 10 is the film base material ( It is roughly equivalent to the moisture permeability of 1).

[Film description]

As the film base 1, a plastic film is used. The thickness of the film substrate is, for example, about 5 to 500 μm. From the viewpoint of achieving both the protective performance and flexibility for the adherend, 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.

When the optical inspection of the adherend is performed in a state where the surface protective film 10 and the adherend are joined, the film substrate 1 is preferably transparent. The total light transmittance of the film substrate 1 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the film base material 1 is preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less.

The front retardation Re of the film base material 1 is 100 nm or less. Since the front retardation of the surface protection film 10 becomes small by using the film base material 1 with a small front retardation Re, light leakage, coloring, rainbow in optical inspection of the adherend to which the protective film is bonded It can prevent stains and the like. The front 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 base material 1 is preferably 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. Since the thickness direction retardation Rth of the film base material 1 is small, light leakage, coloring, rainbow stains, and the like can be prevented even during observation from the oblique direction. Therefore, in a wide range of photographed images by a fixed camera, the difference in color or luminance between the center portion (front direction) and the peripheral portion (inclination direction) becomes small, and data processing becomes easy.

The front retardation Re and the thickness direction retardation Rth are defined below, and are all measured values at a wavelength of 590 nm unless otherwise specified.

nx is a refractive index in the in-plane slow axis direction, ny is a refractive index in the in-plane progressive axis direction, nz is a refractive index in the thickness direction, and d is thickness.

In general, the pressure-sensitive adhesive layer has a smaller phase difference than the film substrate. Therefore, the front retardation Re and the thickness direction retardation Rth of the surface protection film 10 provided with the adhesive layer 2 on the film base material 1 are respectively the front retardation Re and the thickness direction of the film base material 1. It is roughly equivalent to the retardation Rth. Therefore, by using the film base material in which the front retardation Re and the thickness direction retardation are the said range, the front retardation Re and the thickness direction retardation Rth of the surface protection film 10 also become said range.

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, even more preferably 150 g/m 2 ·24h or less, and 100 g/m 2 ·24h or less Especially preferred. When the moisture permeability of the film substrate 1 is within the above range, even if the moisture permeability of the pressure-sensitive adhesive layer 2 is high, intrusion of moisture into the adhesive interface between the pressure-sensitive adhesive layer 2 or the pressure-sensitive adhesive layer 2 and the adherend can be suppressed. Can. Therefore, even when the adherend to which the surface protective film 10 is bonded is exposed to a high temperature and high humidity environment, lifting or peeling of the surface protective film 10 from the adherend can be suppressed.

Although the resin material which comprises a film base material is not specifically limited, As a material which can satisfy the requirement of high transparency, low phase difference, and low moisture permeability, cyclic olefin resin and acrylic resin are mentioned.

As a cyclic olefin resin, polynorbornene is mentioned, for example. Examples of commercial products of the cyclic olefin-based resins include Zeonoa and Zeonex manufactured by Nippon Xeon, Atone manufactured by JSR, Apel manufactured by Mitsui Chemicals, and Topas manufactured by TOPAS ADVANCED POLYMERS. It is preferable that a cyclic olefin type film contains 50 weight% or more of cyclic olefin type resins.

As an acrylic resin, 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, (meth)acrylate methyl-styrene copolymer (MS resin, etc.), a polymer having an alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, methacrylic acid) Methyl-(meth)acrylic acid norbornyl copolymer, etc.). As a commercial item of acrylic resin, Mitsubishi Chemical's acripet is mentioned. 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 constituent materials of the film substrate 1. It is preferable that an acrylic film contains 50 weight% or more of acrylic resins.

The film base material may contain an antioxidant, an ultraviolet absorber, a light stabilizer, a nucleating agent, a filler, a pigment, a surfactant, and an antistatic agent.

The film base material 1 may be a stretched film or a non-stretched film as long as the front retardation Re is within the above range. For example, by using a low-refractive-index material, a low-retardation film having a front retardation within the above range is obtained even if it is a stretched film. In addition, if the stretching ratio in the vertical and horizontal directions is appropriately controlled, even a material having large birefringence can reduce front retardation.

As described above, transparency, low moisture permeability, and low phase difference can be realized by using a cyclic olefin-based film or an acrylic film as the film substrate 1. However, these materials have low mechanical strength, and in either case of a stretched film or a non-stretched film, the tensile breaking strength is generally 120 MPa or less. In order to make a low phase difference, when using an unstretched film or a low stretch magnification film, the tensile strength at break is smaller and often becomes 100 MPa or less. In addition, since the pressure-sensitive adhesive layer 2 is highly viscous and easy to deform, the rupture or fracture of the surface protection film 10 provided with the pressure-sensitive adhesive layer 2 on the film substrate 1 mainly depends on the strength of the film substrate. Therefore, the tensile breaking strength of the surface protection film 10 is approximately equal to the tensile breaking strength of the film substrate 1.

The surface protection film 10 using such a low-strength film base material 1 is liable to cause rupture or breakage when peeling from an adherend. In the present invention, by controlling the properties of the pressure-sensitive adhesive layer and reducing the peeling force, even when a low-strength film substrate is used, it is possible to prevent rupture or breakage when peeling the surface protective film from the adherend.

The film base 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 base material 1 on the opposite side of the pressure-sensitive adhesive layer laying surface. When the antistatic layer is provided on the film substrate, the surface resistivity of the surface on which the antistatic layer is formed is preferably 1.0×10 ¹² Ω/□ or less, more preferably 1.0×10 ¹¹ Ω/□ or less, and 1.0×10 ¹⁰ Ω/ □ The following is more preferable.

When the film base 1 is provided with an antistatic layer, adhesion of dust and degradation of workability due to static electricity of the surface protection film 10 can be suppressed. When the film base material 1 is provided with an antistatic layer, when conducting a lighting test such as a liquid crystal panel or an organic EL panel as an adherend, defects in the panel due to static electricity can be prevented. In addition, by providing the antistatic layer of the film base 1, the generation of static electricity at the time of peeling the surface protective film 10 from the adherend is suppressed, adhesion of dust to the adherend caused by static electricity, and defect of the adherend , It is possible to prevent problems such as deterioration of workability.

Examples of the antistatic layer include a layer formed by containing an antistatic component in various resins. Examples of the resin include various types of resins such as thermosetting resins, ultraviolet curing resins, electron beam curing resins, and two-liquid mixed resins. Can be employed. Examples of the antistatic component include organic or inorganic conductive materials, various antistatic agents, and the like. As the organic conductive material, various conductive polymers can be preferably employed. Examples of such conductive polymers include polyaniline, polypyrrole, polythiophene, polyethyleneimine, and allylamine-based polymers. Examples of the inorganic conductive material include various metals, alloys, and conductive metal oxides. The inorganic conductive material is preferably contained in the antistatic layer as fine particles having a particle diameter 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, a positive ion antistatic agent, or a nonionic antistatic agent.

[Adhesive layer]

It is preferable that the pressure-sensitive adhesive layer 2 is transparent. In particular, when the adherend (protection target) of the surface protection film is an optical device such as a display or a component thereof, a highly transparent pressure-sensitive adhesive is used. In addition, it is preferable to use a highly transparent pressure-sensitive adhesive even when optical inspection is performed while the surface protection film 10 is attached to the adherend. The total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The haze of the pressure-sensitive adhesive layer 2 is preferably 10% or less, more preferably 5% or less, further preferably 2% or less, and particularly preferably 1% or less.

The composition of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer 2 is not particularly limited, and acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy-based, A polymer such as a rubber-based polymer such as fluorine-based, natural rubber or synthetic rubber can be appropriately selected and used. In particular, from the viewpoint of excellent optical transparency, an acrylic pressure sensitive adhesive using an acrylic polymer as a base polymer is preferably used.

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

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester having 1 to 20 carbon atoms in the alkyl group is suitably used. For example, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate , (Meth)acrylic acid isopentyl, (meth)acrylic acid neopentyl, (meth)acrylic acid hexyl, (meth)acrylic acid heptyl, (meth)acrylic acid 2-ethylhexyl, (meth)acrylic acid octyl, (meth)acrylic acid isooctyl, ( Nonyl meth)acrylate, isononyl methacrylate, decyl (meth)acrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, isotridecyl methacrylate, (meth)acrylate ) Tetradecyl acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, ( And nonadecyl methacrylate, 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 with respect to the total amount of the monomer components constituting the base polymer. The acrylic polymer may be a copolymer of a plurality of (meth)acrylic acid alkyl esters. The arrangement of the constituent monomer units may be random or may be a block.

It is preferable that an acrylic polymer contains the monomer component which has a crosslinkable functional group as a copolymerization component. Examples of the monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxyl group-containing monomer. Especially, it is preferable to contain a hydroxy group containing monomer as a copolymerization component of a base polymer. The hydroxy group or carboxy group of the base polymer serves as a reaction point with a crosslinking agent described later. When the crosslinked structure is introduced into the base polymer, the cohesive force of the pressure-sensitive adhesive improves, and while exhibiting proper adhesion to the adherend, the peeling force when peeling the surface protective film from the adherend tends to decrease. Therefore, at the time of peeling of the surface protection film, tensile stress and strain applied to the film are reduced, and rupture and fracture can be prevented.

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

As the copolymer of the acrylic polymer, an acid anhydride group-containing monomer, acrylic acid caprolactone adduct, sulfonic acid group-containing monomer, and phosphoric acid group-containing monomer may be used as the copolymerization monomer component. In addition, as modified monomers, vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole Vinyl monomers such as vinyl oxazole, vinyl morpholine, N-vinyl carboxylic acid amides, styrene, α-methyl styrene, and N-vinyl caprolactam; Cyanoacrylate-based monomers such as acrylonitrile and methacrylonitrile; Epoxy group-containing acrylic monomers such as (meth)acrylic acid glycidyl; Glycol-based acrylic ester monomers such as (meth)acrylic acid polyethylene glycol, (meth)acrylic acid polypropylene glycol, (meth)acrylic acid methoxyethylene glycol, and (meth)acrylic acid methoxy polypropylene glycol; Acrylic acid ester monomers, such as tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and 2-methoxyethylacrylate, can also be used.

Although the proportion of the copolymerized monomer component in the acrylic polymer is not particularly limited, for example, when a hydroxy group-containing monomer or a carboxyl group-containing monomer is used as the copolymerized monomer component for the purpose of introducing a crosslinking point, the content of the hydroxy group-containing monomer and the carboxyl group-containing monomer is The total is about 1 to 20% of the total amount of the monomer components constituting the base polymer, and more preferably about 2 to 15%.

An acrylic polymer as a base polymer is obtained by polymerizing the monomer component by various known methods such as solution polymerization, emulsion polymerization, bulk polymerization, and suspension polymerization. From the standpoint of balance of properties such as adhesive strength and holding power of the pressure-sensitive adhesive, cost, and the like, a solution polymerization method is preferred. As a solvent for solution polymerization, ethyl acetate, toluene, or the like is used. The solution concentration is usually about 20 to 80% by weight. As a polymerization initiator, various well-known things, such as azo type and peroxide type, can be used. In order to adjust the molecular weight, a chain transfer agent may be used. The reaction temperature is usually about 50 to 80°C, and the reaction time is usually about 1 to 8 hours.

The molecular weight of the base polymer is appropriately adjusted so that the pressure-sensitive adhesive layer 2 has a desired adhesive strength, but for example, the weight average molecular weight in terms of polystyrene is about 50,000 to 2 million, preferably about 70 to 1.8 million, more Preferably about 100,000 to 1.5 million, more preferably about 200 to 1 million. Moreover, when a crosslinked structure is introduce|transduced into a base polymer, it is preferable that the molecular weight of the base polymer before introducing a crosslinked structure is the said range.

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

For the purpose of adjusting the adhesive force of the pressure-sensitive adhesive layer 2, a crosslinked structure may be introduced into the base polymer. For example, a crosslinking structure is introduced by adding a crosslinking agent to the solution after polymerization of the base polymer and heating as necessary. As a crosslinking agent, an isocyanate type crosslinking agent, an epoxy type crosslinking agent, an oxazoline type crosslinking agent, an aziridine type crosslinking agent, a carbodiimide type crosslinking agent, a metal chelate type crosslinking agent, etc. are mentioned. Among them, an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent are preferable from the viewpoint of high reactivity of the hydroxy group or carboxyl group of the base polymer and easy introduction of the crosslinking structure. These crosslinking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the base polymer to form a crosslinked structure.

As an isocyanate crosslinking agent, polyisocyanate which has 2 or more isocyanate groups in 1 molecule is used. Examples of the isocyanate-based crosslinking agent 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 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate; Trimethylolpropane/tolylene diisocyanate trimer adduct (e.g., dosing agent ``Coronate L''), trimethylolpropane/hexamethylene diisocyanate trimer adduct (e.g., dosing agent ``Coronate HL'') , Trimethylolpropane adduct of xylylene diisocyanate (for example, Mitsui Chemicals "Takenate D110N"), hexamethylene diisocyanate isocyanurate body (for example, tosohide "Coronate HX"), etc. And isocyanate adducts.

As an epoxy crosslinking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy group of the epoxy-based crosslinking agent may be a glycidyl group. Examples of the epoxy-based crosslinking agent include N,N,N',N'-tetraglycidyl-m-xylenediamine, diglycidylaniline, and 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, poly Propylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane Polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris (2-hydroxyethyl) isocyanurate, resorcin diglycidyl ether, bisphenol- And S-diglycidyl ether. As the epoxy-based crosslinking agent, commercial products such as "Denacol" manufactured by Nagase Chemtex and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical Co., Ltd. may be used.

By adding a crosslinking agent to the base polymer after polymerization, a crosslinking structure is introduced into the base polymer. The amount of the crosslinking agent to be used may be appropriately adjusted depending on the composition, molecular weight of the base polymer, desired adhesive properties and the like. The amount of the crosslinking agent used is preferably 1.5 parts by weight or more with respect to 100 parts by weight of the base polymer, in order to provide a suitable cohesive force to the pressure-sensitive adhesive and to adjust the peel force when peeling the protective film from the adherend to an appropriate range, 2 It is more preferably at least parts by weight, and even more preferably at least 2.5 parts by weight. In order to have proper adhesion to the adherend, the amount of the crosslinking agent is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and even more preferably 10 parts by weight or less, based on 100 parts by weight of the base polymer. .

When the crosslinked structure is introduced into the base polymer, the gel fraction of the pressure-sensitive adhesive increases, and as the viscous behavior decreases, the peeling force at the time of peeling the protective film from the adherend tends to be small. The gel fraction of the pressure-sensitive adhesive layer 2 is preferably 70.0% or more, more preferably 80.0% or more, and even more preferably 90.0% or more. When the gel fraction of the pressure-sensitive adhesive layer 2 is excessively large, wettability to the adherend is lowered, and the adhesive force may be insufficient. Therefore, the gel fraction of the pressure-sensitive adhesive layer 2 is preferably 99.5% or less, more preferably 98.5% or less, and even more preferably 97.5% or less. The gel fraction can be determined as an insoluble content for a solvent such as ethyl acetate, and specifically, the weight fraction (unit: of the insoluble component after immersing the pressure-sensitive adhesive layer in ethyl acetate at 23°C for 7 days, before immersion) Weight%). Generally, the gel fraction of the polymer is equivalent to the degree of crosslinking, and the more crosslinked portions in the polymer, the larger the gel fraction.

The storage elastic modulus G'at 23°C of the pressure-sensitive adhesive layer 2 at 23°C is 5.0×10 ⁴ from the viewpoint of giving the pressure-sensitive adhesive layer 2 an appropriate hardness and reducing the peeling force when peeling the protective film from the adherend. Pa or more is preferable, 7.5 x 10 ⁴ Pa or more is more preferable, and 1.0 x 10 ⁵ Pa or more is more preferable. When the storage elastic modulus of the pressure-sensitive adhesive layer 2 is excessively large, wettability to the adherend is lowered, and the adhesive force may be insufficient. Therefore, the storage elastic modulus G'at 23°C of the pressure-sensitive adhesive layer 2 is preferably 5.0×10 ⁶ Pa or less, more preferably 2.5×10 ⁶ Pa or less, and even more preferably 1.0×10 ⁶ Pa or less. Do. Storage modulus G'is a dynamic viscoelasticity measuring device (for example, "ARES" manufactured by Rheometrics) using a frequency of 1 Hz, a temperature range of -70°C to 150°C, and a heating rate of 5°C/min in shear mode. It is obtained by performing viscoelasticity measurement.

The storage elastic modulus of the pressure-sensitive adhesive layer can be adjusted by the composition of the pressure-sensitive adhesive. For example, the use of a base polymer having a high glass transition temperature tends to increase the storage modulus. In addition, when the gel fraction is increased by the introduction of a crosslinked structure to the base polymer, the storage elastic modulus tends to be large.

The pressure-sensitive adhesive composition, in addition to each of the components exemplified above, additives such as silane coupling agent, tackifier, plasticizer, softener, deterioration inhibitor, filler, colorant, ultraviolet absorber, antioxidant, surfactant, antistatic agent, properties of the present invention It may contain in the range which does not damage.

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

The adhesive composition is applied onto the substrate by roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat, lip coat, die coat, etc. The adhesive layer is formed by applying and drying and removing the solvent as necessary. As a drying method, a suitable method can be suitably employed. The heating and 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, still more preferably 10 seconds to 10 minutes, particularly preferably 10 seconds to 5 minutes.

When the pressure-sensitive adhesive composition contains a crosslinking agent, it is preferable to advance the crosslinking by heating or aging simultaneously with drying of the solvent or after drying of the solvent. The heating temperature and the heating time are appropriately set depending on the type of the crosslinking agent to be used, and usually crosslinking is performed in the range of 20°C to 160°C by heating for about 1 minute to 7 days. The heating for drying and removing the solvent may also serve as heating for crosslinking.

Although the thickness of the pressure-sensitive adhesive layer 2 is not particularly limited, the thickness of the pressure-sensitive adhesive layer 2 is preferably 1 to 50 μm, from the viewpoint of achieving both the adhesive strength to the adherend and the peelability from the adherend. 40 µm is more preferable, and 3 to 35 µm is even more preferable. The smaller the thickness of the pressure-sensitive adhesive layer 2, the more the peelability from the adherend tends to be improved. In particular, when the breaking strength of the film base material 1 is small, the thickness of the pressure-sensitive adhesive layer 2 is 25 μm from the viewpoint of preventing film rupture or breakage when the surface protective film 10 is peeled from the adherend at high speed. The following is preferable, and 20 µm or less is more preferable. In addition, from the viewpoint of suppressing cloudiness 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, and more preferably 20 µm or less.

In the case of forming the pressure-sensitive adhesive layer 2 on a substrate other than the film substrate 1, the surface protective film 10 is obtained by drying the solvent on the substrate and then transferring the pressure-sensitive adhesive layer 2 on the film substrate 1 . The base material used for forming the pressure-sensitive 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 film 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. On the contact surface of the separator 5 with the pressure-sensitive adhesive layer 2, it is preferable that a mold release agent such as silicone-based, fluorine-based, long-chain alkyl-based or fatty acid amide-based, or shelf silica powder is applied. The plastic film constituting the separator 5 may contain an antistatic agent.

[Physical properties of surface protection film]

As described above, the surface protection film 10 has a tensile force of 30 m/min with respect to an acrylic plate and a 180° peel force of 3 N/25 mm or less, and preferably 2.5 N/25 mm or less. Particularly, when the film base material 1 having a tensile breaking strength of 120 MPa or less is used, peeling from the viewpoint of preventing peeling or breaking of the surface protection film 10 upon peeling from the adherend and improving peeling workability The force 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 force of the adhesive layer 2, the peeling force of the surface protection film 10 can be made into the said range. As described above, the smaller the thickness of the pressure-sensitive adhesive layer 2, the smaller the peel force tends to be. Moreover, by increasing the amount of the crosslinked structure introduced into the base polymer constituting the pressure-sensitive adhesive layer 2, the gel fraction is increased, and the peeling force tends to be small.

From the viewpoint of suppressing the 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, when peeling off the surface protective film from the adherend, rupture or breakage is likely to occur. The moisture permeability of the surface protective film is preferably 300 g/m 2 ·24h or less from the viewpoint of improving the adhesion reliability in a humidified environment without excessively increasing the peel force, and suppressing peeling or lifting of the surface protective film from the adherend. , 200 g/m 2 ·24h or less is more preferable, 150g/m 2 ·24h or less is more preferable, and 100g/m 2 ·24h or less is particularly preferable.

As described above, the moisture permeability of the surface protective film 10 is approximately equal to the moisture permeability of the film substrate 1. Therefore, in order to set the moisture permeability of the surface protection film 10 within the above range, it is preferable to use a low moisture permeability film substrate 1 such as a cyclic olefin-based film or an acrylic film.

When optical inspection is performed in a state where the surface protection film 10 is bonded to the adherend, the phase difference of the surface protection film 10 becomes a cause of coloring of the inspection light. From the viewpoint of preventing light leakage, coloring, rainbow stains, and the like during optical inspection, the front retardation Re of the surface protection film 10 is preferably 100 nm or less, more preferably 50 nm or less, and further 30 nm or less It is preferred, and 20 nm or less is particularly preferred. From the same viewpoint, 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 front retardation Re and the thickness direction retardation Rth of the surface protection film 10 provided with the pressure-sensitive adhesive layer 2 on the film substrate 1 are respectively the front retardation Re of the film substrate 1 and It is roughly equivalent to the thickness direction retardation Rth. Therefore, in order to make Re and Rth of the surface protection film 10 into the said range, it is preferable to use a low birefringent material film or a film of non-stretching or low stretching ratio as the film base material 1. In the present invention, since the peeling force of the surface protective film 10 is appropriately adjusted, even when a film having a low strength (for example, a tensile breaking strength of 120 MPa or less) is used as the film substrate 1, it is high speed. Film rupture or breakage during peeling can be prevented.

The peeling voltage when peeling the surface protection film from the adherend is preferably 2.5 kPa or less, more preferably 2 kPa or less. In particular, in the case of bonding the surface protective film to an adherend susceptible to static electricity, the peeling voltage is preferably 1.5 kV or less, and more preferably 1 kV or less. For example, by providing an antistatic layer on the non-laying surface of the pressure-sensitive adhesive layer of the film substrate 1, the peeling voltage of the surface protection film 10 can be reduced.

The adherend to which the surface protection film of the present invention is bonded can prevent damage to the surface or damage due to impact. Since the surface protective film has a low moisture permeability and high humidification reliability of adhesion, even when the adherend on which the surface protective film is attached is exposed to a high-humidity environment, lifting or peeling of the surface protective film is unlikely to occur.

The adherend of the surface protection film is not particularly limited. The surface protection film of this invention can be used as a surface protection film of various optical members, for example. Examples of the optical member include an optical film such as a polarizing plate, a retardation plate, an optical compensation film, a viewing angle enlargement film, a visual control film, a brightness enhancing film, an antireflection film, a reflective sheet, a transparent conductive film, a prism sheet, and a light guide plate; Image display panels such as liquid crystal panels and organic EL panels; And an image display device incorporating an image display panel. The assembly may be performed in a state where the surface protective film is bonded to the optical film as an optical component, and an image display panel or an image display device may be formed.

Since the surface protection film of the present invention has a low phase difference, even when an optical inspection is performed while the surface protection film is bonded to the optical member, it is difficult to interfere with the optical inspection, which contributes to the improvement of inspection efficiency and certainty. Moreover, since the peeling force of the surface protection film of this invention is small, even when the film base material is low-strength, it is hard to generate|occur|produce rupture and fracture at the time of high-speed peeling, and it is excellent in workability.

Example

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 property and evaluation of the film base material and the surface protection film were performed by the following method.

<Front retardation and thickness direction retardation>

The film substrate was cut into a size of 50 mm x 50 mm, and measured under a polarization/phase difference measurement system ("AxoScan" manufactured by Axometrics) under an environment of 23% relative humidity of 50% (hereinafter referred to as "standard environment"). The retardation in the state in which the film was inclined by 40° was measured with the front retardation at a wavelength of 590 nm and the slow axis direction as the center of rotation. From these measurements, front retardation Re and thickness direction retardation Rth were calculated. When calculating the thickness direction retardation, the average refractive index measured by the Atago-made Abe refractive index meter was used.

<Peeling power>

The surface protective film was cut to a size of 25 mm in width and 100 mm in length, and after the separator was peeled off, the pressure was applied to an acrylic plate ("Acrylite" manufactured by Mitsubishi Chemical, thickness: 2 mm, width: 70 mm, length: 100 mm). Roll compression was performed at a rate of 0.25 MPa and a feed rate of 0.3 m/min. After the sample was allowed to stand for 30 minutes in a standard environment, under the same environment, a peel test was performed at a peel angle of 180°, a tensile speed of 0.3 m/min or 30 m/min, and the 180° peel force at each tensile speed was measured. Did.

<break strength>

A test piece (5 mm in width) in the form of a dumbbell type 3 was cut out from the surface protection film, and the separator was peeled to adhere the powder to the adhesive surface, and the influence of the adhesive was eliminated. A tensile tester was used, and in accordance with JIS K7311: 1995, under a standard environment, a tensile test was performed under a condition of a tensile speed of 0.3 m/min, and the tensile strength at break in each of the MD direction and the TD direction was measured.

<Water permeability>

After leaving the surface protection film under a standard environment for 24 hours, the separator is peeled off, and the surface protection film is removed for 24 hours under an environment at a temperature of 60°C and a relative humidity of 90% according to JIS Z0208: 1976, a moisture permeability test (cup method). The moisture permeability was calculated from the weight of the water vapor permeated and the sample area.

<Surface resistivity>

Under a standard environment, a resistivity meter (Mitsubishi Chemical Analtech's "High Resta UP MCP-HT450 type") was used, and the URS probe was brought into contact with the non-laying surface of the pressure-sensitive adhesive layer of the film base, and the applied voltage was 10 V and the applied voltage was 30. The surface resistivity was measured in seconds.

<rainbow stain>

The separator was peeled from the surface protection film, and bonded so that the direction of the transmission axis of the polarizing plate and the direction of MD of the film base material were parallel. Another polarizing plate was placed on the surface protective film so that the polarizing plate bonded to the surface protective film would be cross nicol. The light of a fluorescent lamp was irradiated from the lower side of one polarizing plate, and the presence or absence of rainbow stain was evaluated by looking through the eyes of the transmitted light. It was set as OK that rainbow stain was not confirmed and NG that rainbow stain was confirmed.

<rupture of peeling city>

The surface protection film was cut out to a size of 25 mm in width and 100 mm in length, and the separator was peeled off. A surface protective film was pressed with a hand roller on the hard coat layer forming surface of the hard coat polarizing plate (made by Nitto Denko, width 50 mm, length 100 mm) bonded to a glass plate having a thickness of 1 mm. This sample was taken out for 5 days in a constant temperature and humidity tank at a temperature of 60°C and a relative humidity of 90%, and then taken out and left for 30 minutes under a standard environment. Thereafter, under a standard environment, peel tests were performed at a peel angle of 180°, a tensile speed of 0.3 m/min or 30 m/min, and evaluated based on the following criteria based on the presence or absence of rupture of the surface protection film at each speed.

A: No rupture occurs at any tensile speed and peeling is possible.

B: No tearing occurred at a tensile speed of 0.3 m/min, but peeling was possible, but tearing occurred at a tensile speed of 30 m/min.

NG: Burst occurs at any tensile speed

<Humidity adhesiveness>

The surface protection film was cut to a size of 25 mm in width and 50 mm in length, and the separator was peeled off. The hard coat layer forming surface of the hard coat polarizing plate (made by Nitto Denko, width 50 mm, length 70 mm) bonded to a glass plate having a thickness of 1 mm was intentionally bonded so that bubbles of about 10 mm were mixed. This sample was taken out after standing for 5 days in a constant temperature and humidity bath at a temperature of 60°C and a relative humidity of 90%, and after standing for 30 minutes under a standard environment, the floating state of the surface protection film from the surface of the polarizing plate was observed by visual observation. . It was OK that the change was not seen before and after humidification, and after the humidification, the peeling area of the surface protective film increased, and the tunnel-like excitation so as to penetrate the bubbles was taken as NG.

<Moisture transparency>

The surface protection film was cut out to a size of 25 mm in width and 50 mm in length, and the separator was peeled off. A surface protective film was pressed with a hand roller on the hard coat layer forming surface of a hard coat polarizing plate (made by Nitto Denko, width 50 mm, length 70 mm) bonded to a glass plate having a thickness of 1 mm. This sample was taken out after standing for 5 days in a constant temperature and humidity bath at a temperature of 60°C and a relative humidity of 90%, and after standing for 30 minutes in a standard environment, the presence or absence of cloudiness of the surface protective film was observed by visually viewing under a fluorescent lamp in a dark room. It was observed. What cloudiness was not observed was set to OK, and what cloudiness was seen was set to NG.

<Peeling off voltage>

The surface protection film was cut to a size of 70 mm in width and 130 mm in length, and the separator was peeled off. A hard coat-based polarizing plate (made by Nitto Denko, width 50 mm, length 70 mm) was bonded to the surface of a glass plate having a thickness of 1 mm, and one end of the surface protection film was protruded 30 mm from the end of the polarizing plate on the polarizing plate. , Compressed with a hand roller. This sample was allowed to stand for 24 hours in a standard environment, and then set in a sample holder having a height of 20 mm under a standard environment. The end portion of the surface protective film protruding 30 mm from the polarizing plate is fixed with an automatic winding machine, and the surface protective film is peeled from the polarizing plate under conditions of a peeling angle of 150° and a tensile speed of 30 m/min, and an adherend generated at this time (polarizing plate) The potential of the surface of the was measured with a potential measuring device ("KSD-0103" manufactured by Denki Denki Co., Ltd.) fixed at a position 100 mm in height from the center of the polarizing plate.

[Acrylic polymer polymerization]

<Acrylic polymer A>

In a reaction vessel equipped with a thermometer, stirrer, cooler, and nitrogen gas introduction tube, 96.2 parts by weight of 2-ethylhexyl acrylate (2EHA), and 3.8 parts by weight of hydroxyethyl acrylate (HEA) as a monomer component, and a polymerization initiator As 2,2'-azobisisobutyronitrile (AIBN), 0.2 parts by weight of ethyl acetate was added together with 150 parts by weight of ethyl acetate, and nitrogen gas was introduced while gently stirring at 23°C to perform nitrogen substitution. Thereafter, the liquid temperature was maintained at about 60°C, and polymerization reaction was carried out for 6 hours to prepare a solution of acrylic polymer A (concentration 40% by weight). The Tg of acrylic polymer A calculated from Fox's formula is -66°C.

<Acrylic polymer B>

In a reaction vessel equipped with a thermometer, stirrer, cooler, and nitrogen gas introduction tube, as monomer components, 2EHA: 54.1 parts by weight, vinyl acetate (Vac): 43.2 parts by weight, and acrylic acid (AA): 2.7 parts by weight, and polymerization initiator As benzoyl peroxide (BPO; Nichiyu Co., Ltd. "Nyper BW"): 0.3 parts by weight was added together with 143 parts by weight of toluene, and nitrogen gas was introduced while gently stirring at 23°C to perform nitrogen substitution. Thereafter, the liquid temperature was maintained at around 60°C to conduct a polymerization reaction for 6 hours, the liquid temperature was raised to 80°C, and aged for 6 hours to obtain a solution of acrylic polymer B (concentration 41% by weight). The Tg of acrylic polymer B calculated from Fox's formula is -26°C.

<Acrylic polymer C>

The monomer component was changed to 91 parts by weight of 2EHA and 91 parts by weight of 4-hydroxybutyl acrylate (4HBA). Other than that, nitrogen substitution and polymerization were carried out in the same manner as in the above acrylic base polymer A to obtain a solution of acrylic polymer C (concentration 40% by weight). The Tg of the acrylic polymer C calculated from Fox's formula is -67°C.

[Film description]

The details of the film substrate used in the production example are as follows.

Cyclic olefin film 1 (COP1): Nippon Xeon agent "Zeonoa film ZF-16" (thickness 40 µm, Re = 1.8 nm, Rth = 8.6 nm)

Cyclic olefin film 2 (COP2): Nippon Xeon agent "Zeonoa film ZF-14" (thickness 40 µm, Re = 0.8 nm, Rth = 3.5 nm)

Antistatic cyclic olefin film (AS-COP): An antistatic layer is provided on one side of the Nippon Xeon agent "Zeo Noah Film ZF-16" by a method described later.

Acrylic film: Biaxially oriented film made of an imidized MS resin prepared in the same manner as in "Transparent protective film 1A" described in Examples of Japanese Patent Publication No. 2017-26939 (thickness 40 µm, Re=0.4 nm, Rth=0.7 nm)

Polyethylene terephthalate film (PET): "Diafoil T100C38" manufactured by Mitsubishi Chemical (38 µm thick, Re=180 nm, Rth=812 nm)

Triacetyl cellulose film (TAC): Konica Minolta "KC4CT1" (thickness 40 µm, Re = 0.8 nm, Rth = 3.8 nm)

Biaxially stretched polypropylene film (OPP): "PA30" made by Suntox (60 µm thick, Re=195 nm, Rth=555 nm)

<Formation of antistatic layer>

To form the antistatic layer of the antistatic cyclic olefin film (AS-COP), a dispersion of a polyester resin as a binder resin ("Bylonal MD-1480" manufactured by Toyo Co., Ltd.) was 100 parts by weight as a solid content, and poly(3) as a conductive polymer. ,4-ethylene dioxythiophene) and an aqueous solution containing polystyrene sulfonate ("Clevios P" manufactured by Heraeus) as a solid content of 50 parts by weight, 10 parts by weight of a melamine-based crosslinking agent, and an aqueous dispersion of carnauba wax as a lubricant 40 parts by weight of a coating solution having a solid concentration of 0.3% mixed in a mixed solvent of water and ethanol was used. The coating solution was applied to the COP film with a bar coater and dried by heating at 130° C. for 10 seconds to form an antistatic layer having a thickness of 25 nm.

[Production Example 1]

To the solution of acrylic polymer A, ethyl acetate was added and diluted 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 the dosing agent "Coronate HX" as a crosslinking agent, and ethyl acetate solution of dioctyl tin dilaurate as a crosslinking catalyst (Tokyo Fine Chemicals "Envy") Riser OL-1") was added and stirred as a solid content by 0.02 parts by weight, and an acrylic pressure-sensitive adhesive solution was prepared.

The acrylic pressure-sensitive adhesive solution was applied to a release treatment surface of a separator (a biaxially stretched polyethylene terephthalate film having a thickness of 25 µm with a silicone release treatment on one side) and heated at 130° C. for 20 seconds to form a pressure-sensitive adhesive layer having a thickness of 10 µm. Did. This pressure-sensitive adhesive layer was bonded to a corona-treated surface of a COP film on one side of which was corona-treated to obtain a surface protection film provided with a separator.

[Production Examples 2 to 17]

A separator was prepared in the same manner as in Production Example 1, except that the type of the film substrate, the composition of the acrylic pressure-sensitive adhesive solution (type of the acrylic polymer, and the type and amount of the crosslinking agent) and the thickness of the pressure-sensitive adhesive layer were changed as shown in Table 1. One surface protection film was obtained. In addition, the detail of the crosslinking agent used in each example is as follows. The addition amount of the crosslinking agent in Table 1 is the solid content of the crosslinking agent with respect to 100 parts by weight of the polymer. In Preparation Examples 11 and 12 using only the epoxy-based Tetrad C as the crosslinking agent, a crosslinking catalyst was not added in the preparation of the pressure-sensitive adhesive solution.

Coronate HX: an isocyanurate body of hexamethylene diisocyanate (manufactured by Tosoh Corporation)

Coronate L: 75% solution of trimethylolpropane adduct of tolylene diisocyanate (toso)

Tetrad C: 4-functional epoxy compound (Mitsubishi Gas Chemical Co., Ltd.)

Table 1 shows the composition of the surface protective film of each production example (type of film substrate, composition and thickness of the adhesive), and evaluation results of the surface protective film. The surface resistivity of Production Example 2 using an antistatic cyclic olefin (AS-COP) film was 8.1×10 ⁸ Ω/□, and the surface resistivity of the other example exceeded 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 stains were observed under cross nicol due to the large retardation of the substrate film, resulting in poor optical inspection. In Production Example 18 using the TAC film base material, rainbow stain under cross nicol was not observed, but peeling of the surface protection film was likely to occur after the humidification test, and humidification reliability was poor. This is considered to be due to the low moisture permeability of the film substrate and a large amount of moisture intrusion into the adhesive interface.

In Production Examples 1 to 15 using a low phase difference and a low moisture permeability film substrate, rainbow stain under cross nicol was not observed, and the peeling area of the surface protective film was not increased even after the humidification test.

In Production Example 8, rupture occurred in either low-speed peeling or high-speed peeling after the humidification test. In Production Example 8, since the mechanical strength (tensile breaking strength) of the film base material is small and the peel strength is large, it is considered that the film base material is liable to cause rupture due to the stress applied to the film base material during peeling.

In Production Example 7 and Production Example 10, no rupture occurred at low-speed peeling after the humidification test. In Production Examples 1 to 6, 9 and 11 to 15, no rupture occurred in any of the low-speed peeling and the high-speed peeling after the humidification test. From these results, by designing the pressure-sensitive adhesive layer so that the peeling force from the adherend is small, even when a film substrate having a low mechanical strength is used in a low phase difference, a surface protection film that is unlikely to cause rupture or breakage during high-speed peeling is obtained. You can see that

When attention is paid to the relationship between the composition of the pressure-sensitive adhesive layer and the peeling force, the peel strength is reduced by increasing the amount of the crosslinking agent in the pressure-sensitive adhesive composition from the contrast of Production Examples 1, 4, 5 to 7 using the pressure-sensitive adhesive layer. It can be seen that there is a tendency. The same tendency can be seen from the contrast of Production Example 3 and Production Example 8, and the contrast of Production Example 11 and Production Example 12. In addition, it can be seen from the contrast of Production Examples 1, 3, and 10 using the pressure-sensitive adhesive having the same composition that the smaller the thickness of the pressure-sensitive adhesive layer, the lower the peeling force, and the higher the peeling speed can be prevented.

In Production Example 10 in which an adhesive layer having a thickness of 30 µm was formed on a film substrate, cloudiness of the film was observed after the humidification test. From these results, it can be said that the thickness of the pressure-sensitive adhesive layer is preferably smaller from the viewpoint of transparency as well as preventing rupture during peeling.

In Production Example 2 using a film base material having an antistatic layer, the peeling voltage is smaller than in other examples. From these results, it can be said that it is preferable to provide an antistatic layer on the film base material as a surface protection film used in a device susceptible to static electricity.

As can be understood from the contrast of the above production example, by adjusting the thickness or composition of the pressure-sensitive adhesive layer to set the peel force to a predetermined range, even when a film substrate having low mechanical strength is used in a low phase difference, rupture or breakage occurs at high speed peeling. It can be seen that a surface protective film that is difficult to obtain is obtained.

1: Film substrate
2: Adhesive layer
5: separator
10: surface protection film

Claims (10)

It is a surface protection film provided with a film base material and the adhesive layer adhered and laminated on the first main surface of the film base material,
The film substrate has a front retardation of 100 nm or less,
The surface protection film is a surface protection film having a moisture permeability of 300 g/m 2 ·24h or less at a temperature of 60° C. and a relative humidity of 90%, and a 180° peel force of a tensile speed of 30 m/min to an acrylic plate of 3 N/25 mm or less. According to claim 1,
The surface protective film whose thickness direction retardation of the said film base material is 100 nm or less. The method according to claim 1 or 2,
A surface protective film having a tensile breaking strength of 120 MPa or less. The method according to any one of claims 1 to 3,
The said film base material is a cyclic olefin type film or an acryl-type film, The surface protection film. The method according to any one of claims 1 to 4,
The thickness of the pressure-sensitive adhesive layer is 1 to 50㎛, surface protection film. The method according to any one of claims 1 to 5,
The pressure-sensitive adhesive layer, a surface protection film comprising an acrylic base polymer having a cross-linked structure. The method of claim 6,
A surface protective film having a crosslinked structure introduced into the base polymer. The method according to any one of claims 1 to 7,
An antistatic layer is provided on the second main surface of the film substrate, and the surface protection film. The method of claim 8,
The surface protection film, wherein the surface resistivity of the antistatic layer is 1.0×10 ¹² Ω/□ or less. An optical member having a protective film, wherein the surface protective film according to any one of claims 1 to 9 is bonded to the surface of the optical member.

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