JP6899339B2 - Surface protective film and optical member with protective film - Google Patents

Description

The present invention relates to a surface protective film having an adhesive layer on a film substrate, and an optical member to which the surface protective film is attached.

A surface protective film is provided on the surface of optical devices such as displays and image pickup devices, electronic devices, and films and glass materials that are components of these devices for the purpose of surface protection and impact resistance imparting. .. Surface protective films include those that are temporarily attached before use, such as when assembling, processing, and transporting devices, and then re-peeled before using the device (used as a process material), and those that use the device. Some are used as they are stuck on the surface of the device (for the purpose of permanent adhesion).

Both the surface protective film used as a process material and the surface protective film for the purpose of permanent adhesion have an adhesive layer on the main surface of the film base material, and the adherend to be protected is provided through the adhesive layer. It is attached to the surface of the body (see, for example, Patent Document 1).

As a base material for the surface protective film, a polyester film is widely used because of its excellent mechanical strength and transparency. In general, polyester films have improved slipperiness, winding characteristics, and the like by blending particles in a resin to form fine protrusions on the surface (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2013-793360 Japanese Unexamined Patent Publication No. 2006-176685

When a conventional surface protection film using a polyester film is attached to an adherend and the transmitted light from the adherend is visually recognized, the transmitted light is distorted or the transmitted light is glaring and visually recognized. May decrease. In particular, when a surface protective film is attached to the surface of a display device such as a display and visually recognized from a short distance, this tendency becomes remarkable. Image distortion and glare caused by such a surface protective film hinder optical inspection and imaging.

In view of the above, it is an object of the present invention to provide a surface protective film having good adhesiveness to an adherend and which does not easily interfere with visual recognition and imaging of transmitted light from the adherend.

The surface protective film of the present invention includes an adhesive layer fixed and laminated on the main surface of the film base material. The haze of the surface protective film is 2% or less. The adhesive strength of the surface protective film to the acrylic plate is 0.03 N / 25 mm or more. The adhesive force is a value measured by a peeling test at a tensile speed of 30 m / min and a peeling angle of 180 °. The surface protective film preferably has a total scratch amount of 3000 or less calculated from a 200 × 200 pixel image obtained from an inspection area of 5 mm × 5 mm.

The thickness of the pressure-sensitive adhesive layer is preferably 2 μm or more. The pressure-sensitive adhesive layer preferably contains one or more selected from the group consisting of an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive.

It is preferable that the film substrate is substantially free of particles.

Since the surface protective film of the present invention has good adhesiveness to the adherend, it is difficult for air bubbles to get caught in the bonding interface, and visibility in a state where the surface protective film is bonded to the adherend. Excellent for. Further, since the surface protective film has a low haze and is less likely to cause light scattering, it is less likely to interfere with the visibility and imaging of transmitted light from the adherend, and has good visibility.

It is sectional drawing which shows the laminated structure of the surface protection film. It is sectional drawing which shows the laminated structure of the surface protection film which a separator was temporarily attached.

[Structure of surface protective film]
FIG. 1 is a cross-sectional view showing an embodiment of a surface protective film. The surface protective film 10 includes an adhesive layer 2 on the first main surface of the film base material 1. The pressure-sensitive adhesive layer 2 is fixedly laminated on the first main surface of the film base material 1.

As shown in FIG. 2, the separator 5 may be temporarily attached to the pressure-sensitive adhesive layer 2 of the surface protective film 10. The surface of the adherend can be protected by peeling off the separator 5 temporarily adhered to the surface of the pressure-sensitive adhesive layer 2 and adhering the exposed surface of the pressure-sensitive adhesive layer 2 to the adherend. In addition, "fixation" is a state in which two laminated layers are firmly adhered to each other, and peeling at the interface between the two layers is impossible or difficult. "Temporary adhesion" is a state in which the adhesive force between the two laminated layers is small and can be easily peeled off at the interface between the two layers.

<Adhesive strength>
The surface protective film preferably has an adhesive force to the acrylic plate of 0.03 N / 25 mm or more. When the adhesive strength is 0.03 N / 25 mm or more, air bubbles are less likely to be caught between the pressure-sensitive adhesive layer 2 of the surface protective film and the adherend, and the reproducibility tends to be improved. The adhesive force of the surface protective film to the acrylic plate is more preferably 0.05 N / 25 mm or more, and further preferably 0.07 N / 25 mm or more.

The upper limit of the adhesive force of the surface protective film to the acrylic plate is not particularly limited. When a surface protective film is used as a process material and removability from an adherend is required, the adhesive force with respect to the acrylic plate is preferably 10 N / 25 mm or less, more preferably 5 N / 25 mm or less, and 3 N / 25 mm or less. Is even more preferable. When removability is required, the adhesive force of the surface protective film to the acrylic plate is preferably 1 N / 25 mm or less.

The adhesive force to the acrylic plate is the peeling force when a surface protective film is attached to the acrylic plate, left to stand in an environment of 23 ° C. for 30 minutes, and then subjected to a 180 ° peeling test at a tensile speed of 30 m / min. The smaller the adhesive force, the easier it is for the surface protective film to be peeled off from the adherend at high speed, and the adhesive residue on the adherend at the time of peeling and the breakage of the surface protective film are less likely to occur, and the workability is excellent. The adhesive strength of the surface protective film 10 mainly depends on the characteristics of the pressure-sensitive adhesive layer 2.

<Haze>
The haze of the surface protective film is preferably 2% or less, more preferably 1.5% or less. Since the haze of the surface protective film is small, the visibility when the adherend is visually recognized through the surface protective film is excellent.

<Total amount of scratches>
The total scratch amount of the surface protective film is preferably 3000 or less, more preferably 2500 or less, and even more preferably 2000 or less. The smaller the total scratch amount, the smaller the uneven brightness of the light transmitted through the surface protective film, and the more the glitter tends to be suppressed. Further, the smaller the total amount of scratches, the better the imageability tends to be.

The total amount of scratches is determined by irradiating a sample with a surface protective film attached to a glass plate at a linear speed of 5 m / min and irradiating light from the glass plate side with a surface light source, and using a line scan camera (Keyence's "Keyence". It is obtained by taking a picture with "XG-HL04M") and analyzing the obtained image with a scratch inspection tool manufactured by KEYENCE. The distance between the light source and the sample at the time of photographing is 200 mm, and the distance between the sample and the line scan camera is 210 mm. The segment size at the time of analysis is 4, and the scratch level threshold is 3.

For the total scratch amount, the segment in which the difference in brightness (scratch level) of the image (grayscale 256 gradations) taken by the line scan camera exceeds the threshold value is counted as a "scratch", and is within the shooting area. The number of segments counted as "scratches". The scratch level is the difference between the maximum value and the minimum value of lightness in four small areas in the direction of movement of the set segment. When the difference between the maximum value and the minimum value of lightness in the four small areas exceeds the threshold value, the segment consisting of the four small areas is counted as a "scratch".

<Mapability>
The surface protective film preferably has a transmissivity of 92.5% or more at an optical comb width of 0.125 mm. The transmissivity is measured according to JIS K7374 (Plastic-How to determine image sharpness) using a sample in which a surface protective film is attached to a glass plate. The higher the transmissibility, the less glare of the light transmitted from the adherend through the surface protective film, and the more the visibility tends to be improved. When the transmissivity is less than 92.5%, when the adherend to which the surface protective film is attached is visually recognized from a short distance (for example, within 200 mm), glare is felt and the visibility is deteriorated. If the transmissivity is small, it may adversely affect the imaging performed at a short distance from the subject such as fingerprint authentication. From the viewpoint of reducing the glare of the transmitted light, the transmissivity of the surface protective film is preferably 93% or more, more preferably 94% or more, still more preferably 95% or more. If the transmitted image property is 95% or more, even when the adherend is observed from a close distance, the glare of the transmitted light is hardly felt.

[Film substrate]
As the film base material 1, a transparent plastic film is used. The total light transmittance of the film substrate 1 is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more. The haze of the film substrate 1 is preferably 1.5% or less, more preferably 1% or less, still more preferably 0.5% or less. The thickness of the film base material is, for example, about 5 to 500 μm. From the viewpoint of achieving both protection performance against an adherend and flexibility, 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.

As the resin material constituting the film base material, a resin material having excellent transparency, mechanical strength, and thermal stability is preferable. Specific examples of the resin material include cellulose-based resins such as triacetyl cellulose, polyester-based resins, polyether sulfone-based resins, polysulfone-based resins, polycarbonate-based resins, polyamide-based resins, polyimide-based resins, polyolefin-based resins, and acrylic-based resins. , Cyclic polyolefin resin (norbornen resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, and mixtures thereof. A polyester resin is particularly preferable, and a low oligoma polyester resin is particularly preferable.

The film substrate may contain an antioxidant, an ultraviolet absorber, a light stabilizer, a nucleating agent, a filler, a pigment, a surfactant, an antistatic agent and the like. An easy-adhesion layer, an easy-slip layer, an antiblocking layer, an antistatic layer, an antireflection layer, an oligomer prevention layer, and the like may be provided on the surface of the film base material.

The film substrate preferably contains substantially no particles. Since the film base material does not contain particles, light scattering by the surface protective film is unlikely to occur, and the in-plane uniformity of the surface shape is improved. Along with this, the total amount of scratches on the surface protective film is reduced, and the transmitted light reproducibility is improved. When the film substrate is "substantially particle-free", it means that the particles do not affect the surface shape of the film. Even when the particles do not affect the surface shape, the reproducibility may be deteriorated due to light scattering at the interface between the resin component of the film base material and the particles. Therefore, the content of the particles in the film substrate is preferably 100 ppm or less, more preferably 50 ppm or less, further preferably 30 ppm or less, and particularly preferably 10 ppm or less. Most preferably, the particle content of the film substrate is zero.

A film substrate that is substantially free of particles has a smooth surface and low slipperiness, which may cause blocking, transfer failure in a roll-to-roll process, and winding failure. Examples of prevention of blocking and poor transport due to high smoothness include a method of attaching another highly slippery film to the film base material and a method of providing an easy-slip layer on the surface of the film base material. The easy-to-slip layer provided on the surface of the film substrate may contain fine particles. When the slippery layer contains fine particles, if the particle size of the fine particles is small, the slipperiness becomes insufficient. On the other hand, if the particle size of the fine particles contained in the slippery layer is excessively large, the total amount of scratches on the surface protective film may increase due to the scattering of visible light, and the transmitted light reproducibility may deteriorate. From the viewpoint of both suppressing the scattering of visible light by the slippery layer and imparting slipperiness, the number average particle size of the fine particles is preferably 1 to 200 nm, more preferably 3 to 150 nm, and even more preferably 5 to 100 nm.

[Adhesive layer]
A highly transparent pressure-sensitive adhesive is used for the pressure-sensitive adhesive layer 2. The total light transmittance of the pressure-sensitive adhesive layer 2 is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more. The haze of the pressure-sensitive adhesive layer 2 is preferably 1% or less, more preferably 0.7% or less, still more preferably 0.5% 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, fluorine-based, A polymer based on a rubber-based polymer such as natural rubber or synthetic rubber can be appropriately selected and used. In particular, because of its excellent adhesiveness and optical transparency, acrylic adhesives based on acrylic polymers, urethane adhesives based on urethane polymers, and silicones based on silicone polymers. Adhesives are preferably used.

<Acrylic adhesive>
As the acrylic base polymer of the acrylic pressure-sensitive adhesive, those having a monomer unit of (meth) acrylic acid alkyl ester as a main skeleton are preferably used. In addition, in this specification, "(meth) acrylic" means acrylic 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 , (Meta) isooctadecyl acrylate, (meth) nonadecil 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, still more preferably 60% by weight or more, based on the total amount of the monomer components constituting the acrylic 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 block.

The acrylic polymer preferably contains a monomer component having 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 carboxy group-containing monomer. Above all, it is preferable to contain a hydroxy group-containing monomer as a copolymerization component. The hirodoxy group and the carboxy group serve as reaction points with the cross-linking agent described later. By introducing the crosslinked structure into the base polymer, the cohesive force of the pressure-sensitive adhesive is improved, the adhesive force is moderately adhered to the adherend, and the surface protective film tends to be easily peeled off from the adherend. ..

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

In addition to the above, the acrylic polymer may also use an acid anhydride group-containing monomer, a caprolactone additive of acrylic acid, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, or the like as a copolymerization monomer component. Further, as the modifying monomer, vinyl acetate, vinyl propionate, N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazin, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholin, N. -Vinyl carboxylic acid amides, vinyl monomers such as styrene, α-methylstyrene, N-vinylcaprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing acrylic monomers such as glycidyl (meth) acrylate. Glycol-based acrylic ester monomers such as (meth) polyethylene glycol acrylate, (meth) polypropylene glycol acrylate, (meth) methoxyethylene glycol acrylate, and (meth) methoxypolypropylene glycol acrylate; (meth) tetrahydrofurfuryl acrylate. , Acrylic acid ester-based monomers such as fluorine (meth) acrylate, silicone (meth) acrylate and 2-methoxyethyl acrylate can also be used.

The ratio of the copolymerization monomer component in the acrylic polymer is not particularly limited. For example, when a hirodoxy group-containing monomer or a carboxy group-containing monomer is used as the copolymerization monomer component for the purpose of introducing a cross-linking point, the hirodoxy group-containing monomer and the carboxy group are used. The total content of the contained monomers is preferably about 1 to 20%, more preferably about 2 to 15%, based on the total amount of the monomer components constituting the acrylic polymer.

An acrylic polymer can be obtained by polymerizing the above-mentioned monomer components by various known methods such as solution polymerization, emulsion polymerization, bulk polymerization and suspension polymerization. The solution polymerization method is preferable from the viewpoint of the balance of characteristics such as the adhesive force and the holding force of the pressure-sensitive adhesive and the cost. Ethyl acetate, toluene and the like are used as the solvent 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. Chain transfer agents may be used to adjust the molecular weight. 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 acrylic polymer is appropriately adjusted so that the pressure-sensitive adhesive layer 2 has the desired adhesive strength. For example, the polystyrene-equivalent weight average molecular weight is about 50,000 to 2 million, preferably 70,000 to 180. It is about 10,000, more preferably about 100,000 to 1,500,000, and even more preferably about 200,000 to 1,000,000. When the crosslinked structure is introduced into the acrylic base polymer, the molecular weight of the polymer before the introduction of the crosslinked structure is preferably in the above range.

A crosslinked structure may be introduced into the base polymer for the purpose of adjusting the adhesive force of the pressure-sensitive adhesive layer 2. For example, a cross-linked structure is introduced by adding a cross-linking agent to the solution obtained by polymerizing the acrylic polymer and heating as necessary. Examples of the cross-linking agent 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. Of these, isocyanate-based cross-linking agents and epoxy-based cross-linking agents are preferable because they have high reactivity with hydroxy groups and carboxy groups of acrylic polymers and can easily introduce a cross-linked structure. These cross-linking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the polymer to form a cross-linked structure.

As the isocyanate-based cross-linking agent, polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate-based cross-linking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate and isophorone diisocyanate; 2,4-tolylene diisocyanate. Aromatic isocyanates such as isocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate; trimethylolpropane / trimylene diisocyanate trimer adduct (eg, "Coronate L" manufactured by Toso), trimethylolpropane / hexamethylene Diisocyanate trimeric adduct (eg, "Coronate HL" manufactured by Tosoh), trimethylolpropane adduct of xylylene diisocyanate (eg, "Takenate D110N" manufactured by Mitsui Chemicals, isocyanurate of hexamethylene diisocyanate (eg, "Tosoh" Examples thereof include isocyanate additives such as "Coronate HX").

As the epoxy-based cross-linking agent, a polyfunctional epoxy compound having two or more epoxy groups in one molecule is used. The epoxy group of the epoxy-based cross-linking agent may be a glycidyl group. Examples of the epoxy-based cross-linking agent include N, N, N', N'-tetraglycidyl-m-xylene diamine, diglycidyl aniline, 1,3-bis (N, N-diglycidyl aminomethyl) 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 Ellisritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipate diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris (2-hydroxyethyl) isocyanurate, Examples thereof include resorcin diglycidyl ether and bisphenol-S-diglycidyl ether. As the epoxy-based cross-linking agent, commercially available products such as "Denacol" manufactured by Nagase ChemteX and "Tetrad X" and "Tetrad C" manufactured by Mitsubishi Gas Chemical Company may be used.

A crosslinked structure is introduced by adding a crosslinking agent to the polymerized acrylic polymer. The amount of the cross-linking agent used may be appropriately adjusted according to the composition and molecular weight of the 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 within an appropriate range, the amount of the cross-linking agent used is 100 parts by weight of the acrylic polymer. Therefore, 1.5 parts by weight or more is preferable, 2 parts by weight or more is more preferable, and 2.5 parts by weight or more is further preferable. In order to have an appropriate adhesiveness to the adherend, the amount of the cross-linking agent used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and 10 parts by weight with respect to 100 parts by weight of the acrylic polymer. The following is more preferable.

<Urethane adhesive>
As the urethane-based base polymer of the urethane-based pressure-sensitive adhesive, a reaction product of a polyol and a polyisocyanate compound is used.

(Polyol)
As the polyol, a polyol having two hydroxy groups in one molecule (diol), a polyol having three hydroxy groups in one molecule (triol), and a polyol having four hydroxy groups in one molecule (tetra All), a polyol having 5 hydroxy groups in 1 molecule (pentaol), a polyol having 5 hydroxy groups in 1 molecule (pentaol), a polyol having 6 hydroxy groups in 1 molecule (ol) Hexaol) and the like.

As the polyol component of the urethane-based base polymer, polymer polyols such as polyester polyols, polyether polyols, polycarbonate polyols, and caprolactone polyols are preferable. The number average molecular weight of the polyol is preferably about 400 to 30,000, more preferably about 1,000 to 25,000, and even more preferably about 3,000 to 20,000.

The polyester polyol is a polyester having a hydroxyl group at the terminal, and is obtained by reacting a polybasic acid with a polyhydric alcohol so that the alcohol equivalent is excessive with respect to the carboxylic acid equivalent. As the polybasic acid component and the polyhydric alcohol component constituting the polyester polyol, a combination of dibasic acid and diol is preferable.

As the dibasic acid component, aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, and terephthalic acid; alicyclics such as hexahydrophthalic acid, tetrahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Formula dicarboxylic acid; aliphatic dicarboxylic acids such as oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decandicarboxylic acid, dodecandicarboxylic acid, octadecanedicarboxylic acid; Examples thereof include acid anhydrides of dicarboxylic acids and lower alcohol esters.

Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, 1,6-hexanediol, and the like. 1,8-octanediol, 1,10-decanediol, diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, bisphenol F , Hydrogenated bisphenol A, hydrogenated bisphenol F and the like.

The polyether polyol is obtained by ring-opening addition polymerization of an alkylene oxide on a polyhydric alcohol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and tetrahydrofuran. Examples of the polyhydric alcohol include the above-mentioned diol, glycerin, trimethylolpropane and the like.

The polycarbonate polyol is a polycarbonate polyol obtained by subjecting a diol component and phosgen to a polycondensation reaction; the diol component, dimethyl carbonate, diethyl carbonate, diprovyl carbonate, diisopropyl carbonate, dibutyl carbonate, ethylbutyl carbonate, ethylene carbonate, propylene carbonate, and carbonic acid. Polycarbonate polyol obtained by ester exchange condensation with carbonic acid diesters such as diphenyl and dibenzyl carbonate; copolymerized polycarbonate polyol obtained by using two or more kinds of polyol components in combination; the above-mentioned various polycarbonate polyols and carboxy group-containing compounds are esterified. Polycarbonate polyol obtained by reaction; Polycarbonate polyol obtained by etherifying the various polycarbonate polyols and hydroxyl group-containing compounds; Polycarbonate polyol obtained by ester exchange reaction between the various polycarbonate polyols and ester compounds; Polycarbonate polyol obtained by ester exchange reaction between a polyol and a hydroxyl group-containing compound; Polycarbonate-based polycarbonate polyol obtained by polycondensation of the above-mentioned various polycarbonate polyols and a dicarboxylic acid compound; Examples thereof include the obtained copolymerized polyether-based polycarbonate polyol.

Examples of the polycaprolactone polyol include a caprolactone-based polyester diol obtained by ring-opening polymerization of a cyclic ester monomer such as ε-caprolactone and σ-valerolactone.

It is preferable that the urethane-based base polymer contains triol as the polyol component because the cohesive force of the pressure-sensitive adhesive is improved, the adhesive force is moderately adhered to the adherend, and the removability from the adherend is excellent. .. As the high molecular weight triol, a polyether polyol obtained by ring-opening addition polymerization of alkylene oxide to triol such as glycerin and trimethylolpropane is preferably used.

The content of triol with respect to the entire polyol component constituting the urethane-based base polymer is preferably 50% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, still more preferably 90% by weight or more.

When high molecular weight triol is used as the polyol component of the urethane-based base polymer, triol having a number average molecular weight of 7,000 to 20,000, triol having a number average molecular weight of 2000 to 6000, and triol having a number average molecular weight of 400 to 1900 are used in combination. It is more preferable to use a triol having a number average molecular weight of 8000 to 15000, a triol having a number average molecular weight of 2000 to 5000, and a triol having a number average molecular weight of 500 to 1800 in combination, and the number average molecular weight is 8000. It is more preferable to use a triol of ~ 12000, a triol having a number average molecular weight of 2000 to 4000, and a triol having a number average molecular weight of 500 to 1500 in combination. By using three types of triols having different molecular weights in combination, it is easy to obtain a urethane-based pressure-sensitive adhesive capable of achieving both adhesiveness to an adherend and removability.

(Polyisocyanate)
The polyisocyanate used for forming the urethane-based base polymer may be any of an aliphatic polyisocyanate, an alicyclic polyisocyanate, and an aromatic polyisocyanate.

Aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene. Examples thereof include diisocyanate.

Examples of the alicyclic polyisocyanate include 1,3-cyclopentenediisocyanate, 1,3-cyclohexanediisocyanate, 1,4-cyclohexanediisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, and hydrogenated triisocyanate. Examples thereof include range isocyanate and hydrogenated tetramethylxylylene diisocyanate.

Examples of aromatic polyisocyanates include phenylenediocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, and 4,4'-toluene. Examples thereof include diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalenediocyanate, and xylylene diisocyanate.

As the polyisocyanate, a derivative of the above polyisocyanate compound can also be used. Derivatives of the polyisocyanate compound include a dimer of polyisocyanate, a trimer of polyisocyanate (isocyanurate), a polypeptide MDI, an adduct with trimethylolpropane, a biuret modified product, an allophanate modified product, a urea modified product, and the like. Can be mentioned. The polyisocyanate may be one in which a protecting group such as oxime or lactam is added to the terminal isocyanate group. Since the protecting group is desorbed from the isocyanate group by heating, the isocyanate group and the hydroxy group of the polyol react with each other.

As the polyisocyanate, a urethane prepolymer having an isocyanate group at the terminal may be used. By reacting the polyol and the polyisocyanate so that the polyisocyanate becomes excessive, a urethane prepolymer having an isocyanate group at the terminal can be obtained.

(Other ingredients)
A urethane-based base polymer can be obtained by mixing the above polyol and polyisocyanate. The urethane-based pressure-sensitive adhesive may contain a reactive component other than the polyol and the polyisocyanate.

For example, the urethane-based pressure-sensitive adhesive may contain a chain lengthing agent as a copolymerization component in addition to the polyol and polyisocyanate. Chain length agents include sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitan, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerin, trimethylolethane, Polyformates having 3 or more hydroxyl groups such as trimethylolpropane and pentaerythritol; ethylene glycol, diamine glycol, triethylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol , Pentandiol, 1,6-hexanediol, propylene glycol and other diols; dimethylolacetic acid, dimethylolbutanoic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolpentanoic acid and other dialkyralkanoic acids, dihydroxysuccinic acid and the like. Compounds having a free carboxy group; aliphatic diamines such as ethylenediamine, propylenediamine, hexamethylenediamine, 1,4-butanediamine, aminoethylethanolamine; alicyclic diamines such as isophoronediamine and 4,4′-dicyclohexylmethanediamine. Diamine; Examples thereof include aromatic diamines such as xylylene diamine and tolylene diamine.

The urethane-based pressure-sensitive adhesive may contain a fatty acid ester. As the fatty acid ester, one having a molecular weight of about 200 to 400 is preferably used. Specific examples of the fatty acid ester include polyoxyethylene bisphenol A laurate ester, butyl stearate, 2-ethylhexyl palmitate, 2-ethylhexyl stearate, monoglyceride behenate, cetyl 2-ethylhexanoate, and isopropyl myristate. Isopropyl palmitate, cholesteryl isostearate, lauryl methacrylate, methyl palm fatty acid, methyl laurate, methyl oleate, methyl stearate, myristyl myristate, octyldodecyl myristate, pentaerythritol monooleate, pentaerythritol monostearate, penta Examples thereof include erythritol tetrapalmitate, stearyl stearate, isotridecyl stearate, triglyceride 2-ethylhexanoate, butyl laurate, and octyl oleate.

The blending ratio of the fatty acid ester in the urethane-based pressure-sensitive adhesive is, for example, preferably 5 to 50% by weight, more preferably 8% to 40% by weight, still more preferably 10 to 30% by weight, based on 100 parts by weight of the polyol.

The urethane-based pressure-sensitive adhesive may contain a modified silicone oil such as a polyether-modified silicone oil. Examples of the modified silicone oil include side chain type polyether-modified silicone oil, double-ended type polyether-modified silicone oil, and the like. Among these, double-ended type polyether-modified silicone oil is preferable.

<Silicone adhesive>
Examples of the silicone-based base polymer of the silicone-based pressure-sensitive adhesive include peroxide-crosslinked silicone and addition-reaction silicone. Of these, addition reaction type silicone is preferable, and phenyl group-containing organopolysiloxane is particularly preferable. Examples of the phenyl group-containing organopolysiloxane include polyalkylphenylsiloxanes such as polymethylphenylsiloxane and polyethylphenylsiloxane. The addition reaction type silicone-based pressure-sensitive adhesive composition preferably contains a silicone rubber and a silicone resin.

(silicone rubber)
As the silicone rubber, a phenyl group-containing organopolysiloxane is preferable, and among them, a silicone rubber composed of an organopolysiloxane having methylphenylsiloxane as a main constituent unit is preferable. The organopolysiloxane in the silicone rubber may have a functional group such as a vinyl group, if necessary. The weight average molecular weight of the organopolysiloxane is preferably 150,000 to 1,500,000, more preferably 280,000 to 1,000,000, and even more preferably 500,000 to 900,000.

(Silicone resin)
The silicone resin, for example, M units consisting of constituent units _"R 3 _{-Si 1/2"} Q unit consisting of structural units "SiO _2", T units consisting of the structural units _{"R-SiO 3/2",} and Examples thereof include those containing an organopolysiloxane composed of a (co) polymer having at least one unit selected from the D unit consisting of the structural unit "R _2-SiO". In addition, R in the said structural unit is a hydrocarbon group or a hydroxy group. Examples of the hydrocarbon group include an alkyl group, a cycloalkyl group, an aryl group and the like. The ratio of "M unit" in the silicone resin is preferably 0.3 to 1.5 times, preferably 0.5 to 1.3 times, that of "at least one unit selected from Q unit, T unit and D unit". Is more preferable.

The organopolysiloxane in the silicone resin may have a functional group such as a vinyl group, if necessary. The weight average molecular weight of the organopolysiloxane in the silicone resin is preferably 1000 to 20000, more preferably 1500 to 10000.

The blending ratio of the silicone rubber and the silicone resin in the silicone-based adhesive is preferably 100 to 220 parts by weight, more preferably 120 to 180 parts by weight, based on 100 parts by weight of the silicone rubber. ..

(Crosslinking agent)
In the silicone-based pressure-sensitive adhesive, the silicone rubber and the silicone resin may be in a mixed state, or the silicone rubber and the silicone resin may react to form a condensate or a partial condensate. Silicone rubbers, silicone resins, or silicone rubbers and silicone resins may be bonded to each other via a cross-linking agent. As the cross-linking agent, a siloxane-based cross-linking agent, a peroxide-based cross-linking agent, and the like are preferable.

As the siloxane-based cross-linking agent, polyorganohydrogensiloxane containing two or more hydrosilanes (SiH) in one molecule is preferable. A crosslinked structure is introduced by a hydrosilylation reaction between a vinyl group contained in silicone rubber or silicone resin and hydrosilane. In polyorganohydrogensiloxane, various organic groups may be bonded to the silicon atom to which the hydrogen atom is bonded in addition to the hydrogen atom. Examples of the organic group include an alkyl group such as a methyl group and an ethyl group; an aryl group such as a phenyl group; and an alkyl halide group. Of these, an alkyl group is preferable, and a methyl group is particularly preferable, from the viewpoint of synthesis and handling. The skeleton structure of the polyorganohydrogensiloxane may be linear, branched, or cyclic, but linear is preferable.

As the silicone-based pressure-sensitive adhesive composition, a commercially available product such as "X-40-3306" manufactured by Shin-Etsu Chemical Co., Ltd. may be used.

<Adhesive composition>
The pressure-sensitive adhesive composition contains a base polymer (or its constituent monomer components) and, if necessary, a cross-linking agent and a solvent. The pressure-sensitive adhesive composition includes a polymerization catalyst, a cross-linking catalyst, a silane coupling agent, a tackifier, a plasticizer, a softening agent, an antioxidant, a filler, a colorant, an ultraviolet absorber, an antioxidant, a surfactant, and the like. Additives such as antistatic agents may be contained within a range that does not impair the characteristics of the present invention.

<Formation of adhesive layer>
The adhesive composition is based on 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. A pressure-sensitive adhesive layer is formed by applying on a material and, if necessary, drying and removing the solvent. As a drying method, an appropriate method can be appropriately adopted. The heating and drying temperature is preferably 40 ° C. to 200 ° C., more preferably 50 ° C. to 180 ° C., and even 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, and particularly preferably 10 seconds to 5 minutes.

When the pressure-sensitive adhesive composition contains a cross-linking agent, it is preferable to proceed the cross-linking by heating or aging at the same time as the drying of the solvent or after the drying of the solvent. When the pressure-sensitive adhesive composition contains a constituent monomer component of the base polymer, it is preferable to carry out the polymerization by heating or aging. The heating temperature and heating time are appropriately set depending on the type of monomer and cross-linking agent used, and are usually in the range of 20 ° C. to 160 ° C. for about 1 minute to 7 days. The heating for drying and removing the solvent may also serve as the heating for polymerization or cross-linking.

The thickness of the pressure-sensitive adhesive layer 2 is preferably 2 μm or more, and more preferably 3 μm or more, from the viewpoint of increasing the adhesive force to the adherend and suppressing the deterioration of the mapping property due to the mixing of air bubbles or the like. The upper limit of the thickness of the pressure-sensitive adhesive layer is not particularly limited. From the viewpoint of maintaining transparency, the thickness of the pressure-sensitive adhesive layer 2 can be 150 μm or less, 100 μm or less, 75 μm or less, 60 μm or less, 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, or 20 μm or less. When the surface protective film is required to be peeled off again, the thickness of the pressure-sensitive adhesive layer 2 is preferably 100 μm or less from the viewpoint of facilitating the peeling off from the adherend.

A surface protective film can be obtained by laminating the pressure-sensitive adhesive layer 2 on the film base material 1. The pressure-sensitive adhesive layer 2 may be formed directly on the film base material 1, or the pressure-sensitive adhesive layer formed in a sheet shape on another base material may be transferred onto the film base material 1. By attaching the separator 5 on the pressure-sensitive adhesive layer 2, a surface protective film with a separator can be obtained. The base material used for forming the pressure-sensitive adhesive layer may be used as it is as the separator 5.

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

[Use of surface protective film]
By adhering the surface protective film of the present invention to various adherends, it is possible to prevent scratches on the surface of the adherend and damage due to impact.

The surface protective film of the present invention has good adhesiveness to glass, an acrylic plate, etc., has high transparency, and has high reproducibility of transmitted light, so that it can be used as a surface protective film for various optical members. Optical members include polarizing plates, retardation plates, optical compensation films, viewing angle enlargement films, viewing angle control films, brightness improving films, antireflection films, reflective sheets, transparent conductive films, prism sheets, light guide plates, and other optical films; Image display panels such as liquid crystal panels and organic EL panels; image display devices incorporating image display panels; lenses and the like can be mentioned. An image display panel or an image display device may be formed by assembling the optical film as an optical component with the surface protective film attached.

Since the surface protective film of the present invention has high reproducibility of transmitted light, it does not easily interfere with optical inspection. Therefore, it is possible to accurately perform an optical inspection such as a luminance inspection with the surface protective film attached, which contributes to the improvement of the efficiency and accuracy of the optical inspection. Further, since the surface protective film of the present invention has small light scattering and is less likely to cause glare of transmitted light, it is also suitably used as a surface protective film for displays such as liquid crystal display devices and organic EL display devices.

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

[Example 1]
<Polymerization of acrylic polymer A>
In a reaction vessel equipped with a thermometer, a stirrer, a cooler and a 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 monomer components, and 3.8 parts by weight of hydroxyethyl acrylate (HEA), and 0.2 parts by weight of 2,2'-azobisisobutyronitrile (AIBN) was charged as a polymerization initiator together with 150 parts by weight of ethyl acetate, and nitrogen gas was introduced while gently stirring at 23 ° C. to perform nitrogen substitution. It was. Then, the liquid temperature was maintained at around 65 ° C. and a polymerization reaction was carried out for 6 hours to prepare a solution of acrylic polymer A (concentration: 40% by weight). The weight average molecular weight of the acrylic polymer A was 540,000.

<Preparation of adhesive composition>
Ethyl acetate was added to the solution of acrylic polymer A to dilute it to a concentration of 20% by weight. 1.5 parts by weight (solid content 0.) of a solution obtained by diluting a polyether compound (“Aqualon HS-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to 10% with ethyl acetate in 500 parts by weight (solid content 100 parts by weight) of this solution. 15 parts by weight), 5 parts by weight of an isocyanurate compound of hexamethylene diisocyanate as a cross-linking agent (“Coronate HX” manufactured by Toso), and 3 parts by weight of dibutyltin dilaurate (1 wt% ethyl acetate solution) as a cross-linking catalyst (solid content 0. 03 parts by weight) was added and stirred to prepare an acrylic pressure-sensitive adhesive solution.

<Preparation of surface protection film>
The above acrylic pressure-sensitive adhesive solution is applied to the non-slip layer non-forming surface of a particle-free polyester film (“Lumilar U41” manufactured by Toray Co., Ltd., thickness 38 μm) having a nano-particle-containing easy-slip layer on one side, and the temperature is 130 ° C. for 2 minutes. By heating, a pressure-sensitive adhesive layer having a thickness of 10 μm was formed. A release-treated surface of a separator (a polyester film having a thickness of 25 μm with one side treated with silicone) was bonded to the surface of the pressure-sensitive adhesive layer to obtain a surface protective film with a separator.

[Example 2]
<Polymerization of acrylic polymer B>
Ethyl acetate 186 with 95 parts by weight of butyl acrylate and 5 parts by weight of acrylic acid as a monomer component and 0.2 parts by weight of AIBN as a polymerization initiator in a reaction vessel equipped with a thermometer, agitator, a cooler and a nitrogen gas introduction tube. It was charged together with the parts by weight, and nitrogen gas was introduced while gently stirring at 23 ° C. to perform nitrogen substitution. Then, the liquid temperature was maintained at around 63 ° C. and a polymerization reaction was carried out for 10 hours to prepare a solution of acrylic polymer B (concentration: 35% by weight). The weight average molecular weight of the acrylic polymer B was 500,000.

<Preparation of adhesive composition and preparation of surface protective film>
Ethyl acetate was added to the solution of acrylic polymer B to dilute it to a concentration of 20% by weight. To 500 parts by weight of this solution (100 parts by weight of solid content), 7 parts by weight of a tetrafunctional epoxy compound (“Tetrad C” manufactured by Mitsubishi Gas Chemical Company) was added as a cross-linking agent and stirred to prepare an acrylic pressure-sensitive adhesive solution. Using the obtained acrylic pressure-sensitive adhesive solution, a surface protective film with a separator was prepared in the same manner as in Example 1.

[Example 3]
As a polyol, a polyether polyol having a number average molecular weight of 10000 having 3 hydroxy groups ("Preminol S3011" manufactured by Asahi Glass Co., Ltd.) is 85 parts by weight, and a polyether polyol having a number average molecular weight of 3000 having 3 hydroxy groups (Sanniks manufactured by Sanyo Kasei). GP3000 ") 13 parts by weight, and 2 parts by weight of a polyether polyol (manufactured by Sanyo Kasei" Sanniks GP1000 ") having a number average molecular weight of 1000 having three hydroxy groups; an isocyanurate of hexamethylene diisocyanate as a polyisocyanate (manufactured by Toso). "Coronate HX") 13.3 parts by weight; as a catalyst, 0.12 parts by weight of Nasem ferric iron (manufactured by Nippon Kagaku Sangyo); 0.5 parts by weight of hindered phenolic antioxidant ("Irganox 1010" manufactured by BASF); 5 parts by weight of cetyl 2-ethylhexanoate (“Saracos 816T” manufactured by Nisshin Oillio) as a fatty acid ester; 1-ethyl-3-methylimidazolium bis (fluoromethanesulfonyl) imide (“AS110” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0 .5 parts by weight; 0.025 parts by weight of double-ended type polyether-modified silicone oil (KF-6004, manufactured by Shin-Etsu Chemical Industry Co., Ltd.); and 210 parts by weight of ethyl acetate as a diluting solvent, and a urethane-based pressure-sensitive adhesive The solution was prepared.

Using the obtained urethane-based pressure-sensitive adhesive solution, a surface protective film with a separator was produced in the same manner as in Example 1.

[Example 4]
100 parts by weight of addition reaction type silicone adhesive ("X-40-3306" manufactured by Shin-Etsu Chemical Co., Ltd.), 0.2 parts by weight of platinum catalyst ("CAT-PL-50T" manufactured by Shin-Etsu Chemical Co., Ltd.), and 100 parts of toluene as a solvent. The parts by weight were mixed to prepare a silicone-based pressure-sensitive adhesive solution.

Using the obtained silicone-based pressure-sensitive adhesive solution, a surface protective film with a separator was prepared in the same manner as in Example 1.

[Examples 5 to 7, Comparative Examples 1 to 3]
The amount of the epoxy-based cross-linking agent (Tetrad C) added in Example 2 and the thickness of the pressure-sensitive adhesive sheet were changed as shown in Table 1. A surface protective film with a separator was produced in the same manner as in Example 2 except for the above.

[Example 8 , Reference Examples 9, 10, Comparative Examples 4, 5]
In Example 1, the film base material shown in Table 1 was used instead of the particle-free polyester film (Lumira U41). A surface protective film with a separator was produced in the same manner as in Example 1 except for the above.

[Comparative Example 6]
The amount of the epoxy-based cross-linking agent (Tetrad C) added in Example 2, the thickness of the pressure-sensitive adhesive sheet, and the type of the film base material were changed as shown in Table 1. A surface protective film with a separator was produced in the same manner as in Example 2 except for the above.

[Measurement method and evaluation method]

<Adhesive strength>
The surface protective film is cut into a size of 25 mm in width and 100 mm in length, and after peeling off the separator, it is placed on an acrylic plate (Mitsubishi Chemical "Acrylite", thickness: 2 mm, width: 70 mm, length: 100 mm) at a pressure of 0.25 MPa. The roll was crimped at a feed rate of 0.3 m / min. This sample was allowed to stand in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 30 minutes, and then a peel test was conducted under the same environment at a peeling angle of 180 ° and a tensile speed of 30 m / min to measure the 180 ° peeling force. ..

<Haze>
The separator was peeled off from the surface protective film, and the haze was measured according to JIS K7136 by irradiating light from the film substrate side of the surface protective film with a haze meter (“NDH-5000” manufactured by Nippon Denshoku Kogyo Co., Ltd.).

<Total amount of scratches>
The surface protective film was cut into a size of 100 mm × 100 mm, the separator was peeled off, and then pressure-bonded to a microslide glass (“Microslide Glass S” manufactured by Matsunami Glass Ind., Thickness: 1.35 mm, 100 mm × 100 mm) with a hand roller. While moving this sample in one direction at a linear speed of 5 m / min, a surface light source (light source: CCS "LT-200SW", lighting amplifier: CCS "PSB3-30024", lighting cable: FCB-10-1, 24SQ-ME7 ”) irradiates light from the glass plate side, and the transmitted light is photographed by a 4096 pixel line scan camera (“XG-HL04M” manufactured by Keyence), and 8 bits (102.4 mm × 12.5 mm area) (8 bits). 256 gradations) A grayscale photographed image was obtained. The scan rate of the line scan camera was adjusted so that one pixel in the feed direction corresponds to 25 μm. The distance between the light source and the sample at the time of photographing (distance in the normal direction of the surface protective film) was set to 200 mm. The distance between the sample and the line scan camera was 210 mm, and the horizontal position of the line scan camera was set so that the amount of received light was half of the maximum amount of light (about 120 gradations). In this measurement, one pixel of the line scan camera corresponds to the area of 25 μm × 25 μm of the sample.

A 200 x 200 pixel area (corresponding to a 5 mm x 5 mm area of the sample) was cut out from the obtained photographed image, and a scratch inspection tool manufactured by KEYENCE was used under the conditions of segment size: 4 and scratch level threshold value: 3. , Scratch detection was performed, and the total scratch amount in the analysis area was determined.
<Adhesion and mapping>
The surface protective film is cut into a size of 45 mm in width and 50 mm in length, and after peeling off the separator, it is made into a water-rimmed slide glass (Matsunami Glass Ind. "S200200", thickness: 1.3 mm, width: 45 mm, length: 50 mm). It was crimped with a hand roller. This sample was visually observed and the presence or absence of air bubbles between the surface protective film and the glass plate was evaluated according to the following criteria.
A: Almost no bubbles are seen B: Bubbles are seen locally C: Bubbles are seen on the entire surface

The mapping property of the above sample was measured by a transmission method according to JIS K7374 with a mapping property measuring device (“ICM-1” manufactured by Suga Test Instruments Co., Ltd.). An optical comb of 0.125 mm was used.

<Visibility>
Peel off the separator from the surface protection film, attach it on the screen of a smartphone equipped with an organic EL display (Samsung Electronics "Galaxy S8 +"), and with the green image displayed, visually check the screen from a distance of 150 mm. Therefore, the presence or absence of glare was evaluated according to the following criteria.
A: No glare at all B: Almost no glare C: Glitter is felt D: Very glare is felt

Table 1 shows the composition of the surface protective film of each production example (type of film base material, composition and thickness of adhesive), and the evaluation result of the surface protective film. The details of the film base material are as follows.

U41: Particle-free biaxially stretched polyester film with an easy-slip layer on one side (Toray's "Lumirror U41", thickness 38 μm)
TA044: Particle-free birefringent high birefringence polyester film with an easy-slip layer on one side (Toyobo "Cosmo Shine TA044", thickness 80 μm)
T101: Particle-containing low-haze biaxially stretched polyester film (Mitsubishi Chemical "Diafoil T101-38", thickness 38 μm)
T100: Particle-containing biaxially stretched polyester film (Mitsubishi Chemical "Diafoil T100-75S", thickness 75 μm)
T100C: Particle-containing biaxially stretched polyester film (Mitsubishi Chemical "Diafoil T100C # 38", thickness 38 μm)
Acrylic: A biaxially stretched film (thickness: 40 μm) made of an imidized MS resin prepared in the same manner as the “transparent protective film 1A” described in Examples of Japanese Patent Application Laid-Open No. 2017-26939.
COP: Cyclic olefin film (Zeon Corporation "Zeonoa film ZF-16", thickness 40 μm)

The surface protective films of Examples 1 to 9 all had good adhesion to the acrylic plate and good visibility of transmitted light. From the comparison between Example 5 and Example 6, it was found that the thicker the pressure-sensitive adhesive layer, the greater the adhesive force to the acrylic plate. Further, from the comparison between Example 2 and Example 5 and the comparison between Example 6 and Example 7, the adhesive force to the acrylic plate decreases as the amount of the cross-linking agent added to the pressure-sensitive adhesive composition increases. There was a tendency.

In Comparative Example 1 in which the thickness of the pressure-sensitive adhesive layer was small, the adhesiveness to the adherend was low, and a large number of bubbles were observed between the adhesive layer and the adherend. Further, in Comparative Example 1, the transmitted light was remarkably glaring and visually recognized, and the visibility was inferior. In Comparative Example 2, the adhesive strength was increased by reducing the amount of the cross-linking agent as compared with Comparative Example 1, but the imageability was low and the transmitted light was glaringly visually recognized. From this result, it can be seen that even when the adhesiveness is high, when the thickness of the adhesive layer is small, minute bubbles are likely to be mixed in the adhesive interface and the visibility is lowered. In Comparative Example 3, the thickness of the pressure-sensitive adhesive layer was made larger than that of Comparative Example 1, but the pressure-sensitive adhesive was hard due to the large amount of the cross-linking agent, and the adhesiveness to the adherend was insufficient.

In Comparative Examples 4 and 5 in which the same adhesive as in Example 1 was used and the type of the film base material was changed, the adhesiveness and adhesion between the surface protective film and the adherend were good, but the imageability was good. It was low and the transmitted light was glaring and visible. In Comparative Example 6, the amount of the cross-linking agent added to the pressure-sensitive adhesive composition was reduced and the adhesive strength was significantly increased, but the visibility was not improved. The decrease in visibility in Comparative Examples 4 to 6 is considered to be due to the particles contained in the film substrate.

In Examples 1 to 8, Reference Examples 9 and 10, and Comparative Examples 1 to 6, a high correlation was observed between the total amount of scratches on the surface protective film and the transmissibility. Further, the higher the transmissibility, the less glaring of the transmitted light was, and the better the visibility tended to be.

From the above results, by adjusting the type of film base material, the composition of the pressure-sensitive adhesive, the thickness of the pressure-sensitive adhesive layer, etc., the total amount of scratches on the laminate (surface protective film) of the film base material and the pressure-sensitive adhesive can be reduced. It can be seen that a surface protective film having high transmitted light reproducibility and excellent visibility of transmitted light from the adherend can be obtained.

1 Film base material 2 Adhesive layer 5 Separator 10, 13 Surface protective film

Claims (4)

A surface protective film comprising a film base material and an adhesive layer fixed and laminated on the first main surface of the film base material.
The film base material has an easy-to-slip layer containing fine particles having a particle content of 100 ppm or less and a particle size of 1 to 200 nm on the surface thereof.
Haze is less than 2%
The adhesive force to the acrylic plate at a tensile speed of 30 m / min and a peeling angle of 180 ° is 0.03 N / 25 mm or more.
A surface protective film having a total scratch amount of 3000 or less calculated from a 200 × 200 pixel image obtained from a 5 mm × 5 mm inspection area. The surface protective film according to claim 1, wherein the pressure-sensitive adhesive layer has a thickness of 2 μm or more. The surface protective film according to claim 1 or 2 , wherein the pressure-sensitive adhesive layer contains at least one selected from the group consisting of an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, and a silicone-based pressure-sensitive adhesive. An optical member with a protective film, wherein the surface protective film according to any one of claims 1 to 3 is attached to the surface of the optical member.

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