WO2015083535A1 - Surface protection film - Google Patents

Abstract

Provided is a surface protection film able to exhibit, at a high level, conflicting characteristics, namely the prevention of oligomer precipitation following heat treatment and adherence with respect to a functional layer such as a hard coat layer. The surface protection film is obtained by forming a coating layer on both surfaces of a multilayer polyester film, which has a laminated structure having at least three layers and in which the softening point of the outermost surface polyester layers is higher than the softening point of an intermediate layer, and forming a pressure-sensitive adhesive layer on the surface of one of the coating layers. The coating layers are formed from a coating liquid that contains a crosslinking agent at a quantity of 70wt% or higher relative to involatile components.

Description

Surface protection film

The present invention relates to a surface protective film, such as a synthetic resin plate, a glass plate, a metal plate, an optical member, an automobile member, an electric / electronic member, a building material member, a stationery / office supplies member, and the like. The present invention relates to a surface protective film suitable for protection. More specifically, for optical members that require particularly high visibility, for example, glass substrates, light diffusion films, liquid crystal displays (polarizing plates, retardation plates, light guide plates, prism plates, etc.), touch panels, When used in an organic EL display, a plasma display, etc., the present invention relates to a surface protective film having good visibility after heat treatment and adhesion to a hard coat layer.

Conventionally, synthetic resin plates, glass plates, metal plates, optical members (glass substrates, light diffusion films, liquid crystal display members (polarizing plates, retardation plates, light guide plates, prism plates, etc.), touch panels, organic EL displays, plasma displays In order to prevent surface contamination, scratches, dust, etc., such as automobile parts, electrical / electronic parts, building material parts, stationery / office supplies parts, etc. A surface protective film provided with an adhesive layer on one side is used.

As the surface protective film, for example, a surface protective film using a low density polyethylene resin as a substrate and an ethylene-vinyl acetate copolymer (EVA) as an adhesive has been proposed (for example, Patent Document 1). ).

For example, in a state where such a surface protective film is stuck to an adherend, a heat treatment step in a high temperature atmosphere, or a situation where the surface protection film is exposed to a high temperature atmosphere during transportation or storage (for example, Patent Document 1, When used in 2), deformation due to melting or shrinkage of the base film is large, making it difficult to use.

Therefore, when using a surface protection film based on a polyester film having better heat resistance, after heat treatment in a high temperature atmosphere, low molecular weight substances and oligomers in the polyester film constituting the surface protection film ( Visibility may decrease as the film haze rises mainly due to precipitation and crystallization of the ester cyclic trimer).

For this reason, in order to solve the above problems, when taking an oligomer precipitation prevention measure, for example, when the oligomer precipitation prevention layer described in Patent Document 3 is laminated on the polyester film surface, the oligomer precipitation is suppressed, Adhesion with the functional layer, for example, adhesion with the hard coat layer is poor.

On the other hand, when an easy-adhesion layer for a hard coat layer (for example, Patent Document 4) that is generally used is laminated on a polyester film, adhesion to the hard coat layer is good, but oligomer precipitation is prevented. The situation was inadequate. For this reason, when used as a surface protective film, a coating layer is required which is compatible with a high level of conflicting characteristics such as prevention of oligomer precipitation after heat treatment and adhesion to a functional layer, for example, a hard coat layer. .

JP 2006-299162 A JP 2008-68564 A Japanese Patent No. 5236586 JP 2010-89307 A JP 2012-173354 A

The present invention has been made in view of the above circumstances, and the problem to be solved is to prevent oligomer precipitation after heat treatment by using a coating film having a coating layer having a specific configuration as a constituent unit of a surface protection film. Another object of the present invention is to provide a surface protective film that can achieve a high level of conflicting properties such as adhesion to a functional layer, for example, a hard coat layer.

As a result of intensive studies in view of the above circumstances, the present inventors have found that the above problems can be easily solved by a surface protective film having a specific configuration, and have completed the present invention.

That is, the gist of the present invention is to form a coating layer on both sides of a multilayer polyester film having a laminated structure of at least three layers, and the softening point of both outermost polyester layers is higher than the softening point of the intermediate layer, A surface protective film comprising an adhesive layer on the surface of the coating layer, wherein the coating layer is formed from a coating solution containing 70% by weight or more of a crosslinking agent with respect to the nonvolatile component. It exists in the surface protection film.

The surface protective film of the present invention is suitable for surface protection of various adherends such as synthetic resin plates, glass plates, metal plates, optical members, automobile members, electrical / electronic members, building material members, stationery / office supplies members, etc. It is. For optical members that require particularly high visibility (for example, glass substrates, light diffusion films, liquid crystal displays (polarizing plates, retardation, light guide plates, prism plates, etc.), touch panels, organic EL displays, plasma displays, etc.) When used as, the visibility after heat treatment and the adhesion to the hard coat layer are good, and its industrial value is high.

The polyester film constituting the surface protective film of the present invention is required to have a laminated structure of at least 3 layers. For example, as long as it does not exceed the gist of the present invention other than the three-layer configuration, it may be a multilayer of four layers or more, and is not particularly limited.

The polyester may be a homopolyester or a copolyester. In the case of a homopolyester, those obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol are preferred. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyester includes polyethylene terephthalate (PET) and the like. On the other hand, examples of the dicarboxylic acid component of the copolyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (eg, P-oxybenzoic acid). One or two or more types can be mentioned, and examples of the glycol component include one or more types such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like. In any case, the polyester referred to in the present invention refers to a polyester that is usually 60 mol% or more, preferably 80 mol% or more of polyethylene terephthalate or the like which is an ethylene terephthalate unit.

The polyester film constituting the surface protective film of the present invention must have a multilayer structure of at least three layers, and it is essential that the softening point of both outermost polyester layers is higher than the softening point of the intermediate layer It is a requirement. Preferably, the difference in softening point between the polyester layers of the outermost layers and the intermediate layer is 3 ° C. or higher, preferably 5 ° C. or higher.

As a specific method for satisfying the conditions, preferably by containing 80% or more of polyester having an oligomer (cyclic trimer) content of 0.5% by weight or less in the polyester layer constituting both outer layers The difference between the softening points can be further increased.
When polyester with an oligomer content of more than 0.5% by weight is used, or when the content is less than 80%, the coated film is subjected to heat treatment for a long time at 150 ° C or high tension. When used in processing processes under severe conditions, such as under-sputtering processes and durability tests in high-temperature and high-humidity atmospheres, the film haze increases greatly, and after processing, the optical properties or visibility In some cases, it may be inappropriate for an optical member.

In the polyester layer, it is preferable to mix particles for the main purpose of imparting slipperiness. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and magnesium phosphate. , Particles of kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

The average particle size of the particles contained in the polyester film is preferably in the range of 0.2 to 1.5 μm. When the average particle size is less than 0.2 μm, the film surface may be flattened and the winding characteristics in the film production process may be inferior. On the other hand, when the average particle size exceeds 1.5 μm, it may be difficult to adapt to applications in which visibility is important due to generation of bright spots due to particles contained in the film.

Furthermore, the particle content in the polyester layer is usually in the range of 0.001 to 5% by weight, preferably 0.005 to 3% by weight. When the particle content is less than 0.001% by weight, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 5% by weight, the transparency of the film is insufficient. There is.

The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage of producing the polyester constituting each layer, but preferably a polycondensation reaction may be carried out after the esterification stage or after the transesterification reaction.

Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, thermal stabilizers, lubricants, dyes, pigments, and the like can be added to the polyester film as necessary.

The thickness of the polyester film is not particularly limited as long as it can be formed as a film, but is preferably 20 to 250 μm, more preferably 25 to 125 μm, for use. .

Next, a production example of the polyester film will be specifically described, but is not limited to the following production example.

First, a method in which the polyester raw material described above is used and the molten sheet extruded from the die is cooled and solidified with a cooling roll to obtain an unstretched sheet is preferable. In this case, in order to improve the flatness of the sheet, it is necessary to improve the adhesion between the sheet and the rotary cooling drum, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably employed. Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the unstretched sheet is stretched in one direction by a roll or a tenter type stretching machine. The stretching temperature is usually 70 to 120 ° C., preferably 80 to 110 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the stretching temperature orthogonal to the first-stage stretching direction is usually 70 to 170 ° C., and the draw ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a biaxially oriented film. In the above-described stretching, a method in which stretching in one direction is performed in two or more stages can be employed. In that case, it is preferable to carry out so that the draw ratios in the two directions finally fall within the above ranges.

Also, the simultaneous biaxial stretching method can be adopted for the production of the polyester film. The simultaneous biaxial stretching method is a method in which the unstretched sheet is usually stretched and oriented simultaneously in the machine direction and the width direction in a state where the temperature is controlled at 70 to 120 ° C, preferably 80 to 110 ° C. The area magnification is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times. Subsequently, heat treatment is performed at a temperature of 170 to 250 ° C. under tension or under relaxation within 30% to obtain a stretched oriented film. With respect to the simultaneous biaxial stretching apparatus that employs the above-described stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be employed.

Furthermore, a so-called coating stretching method (in-line coating) for treating the film surface during the above-described polyester film stretching step can be performed. When a coating layer is provided on a polyester film by a coating stretching method, coating can be performed simultaneously with stretching and the thickness of the coating layer can be reduced according to the stretching ratio, producing a film suitable as a polyester film. it can.

The coating layer constituting the surface protective film of the present invention has good adhesion to the adhesive layer, and the film haze is increased even after heat treatment in a high-temperature atmosphere (for example, 150 ° C., 90 minutes). It is preferable to be as small as possible.

The coating layer constituting the surface protective film of the present invention has an essential requirement to have a coating layer formed from a coating solution containing 70% by weight or more of a crosslinking agent as a nonvolatile component. The coating solution may contain other components as long as the gist of the present invention is not impaired.

As the crosslinking agent, various known crosslinking agents can be used, and examples thereof include an oxazoline compound, a melamine compound, an epoxy compound, an isocyanate compound, a carbodiimide compound, and a silane coupling compound. Among these, especially when using for the use which provides a functional layer on a coating layer, an oxazoline compound is used suitably from a viewpoint that durable adhesiveness improves. Moreover, a melamine compound is used suitably from a viewpoint of prevention of precipitation of the ester cyclic trimer on the film surface by heating and improvement of durability and applicability of the coating layer.

The oxazoline compound is a compound having an oxazoline group in the molecule, and is particularly preferably a polymer containing an oxazoline group, and can be prepared by polymerization of an addition polymerizable oxazoline group-containing monomer alone or with another monomer. Addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, Examples thereof include 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like, and one or a mixture of two or more thereof can be used. Of these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer is not particularly limited as long as it is a monomer copolymerizable with an addition polymerizable oxazoline group-containing monomer. For example, alkyl (meth) acrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, (Meth) acrylic acid esters such as n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene Unsaturated carboxylic acids such as sulfonic acid and its salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); Unsaturated nitriles such as acrylonitrile, methacrylonitrile; (meth) acrylamide, N-alkyl ( (Meth) acrylamide, N, N-dialkyl (meth) acrylamide, Examples of the alkyl group include unsaturated amides such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc .; vinyl acetate Vinyl esters such as vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α, β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride And α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene, and the like, and one or more of these monomers can be used.

The amount of the oxazoline group of the oxazoline compound contained in the coating solution is usually in the range of 0.5 to 10 mmol / g, preferably 3 to 9 mmol / g, more preferably 5 to 8 mmol / g. By using it in the above range, the durability of the coating film is improved.

The melamine compound is a compound having a melamine structure in the compound, for example, an alkylolated melamine derivative, a compound partially or completely etherified by reacting an alcohol with an alkylolated melamine derivative, and these Mixtures can be used. As alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used. Moreover, as a melamine compound, either a monomer or a multimer more than a dimer may be sufficient, or a mixture thereof may be used. Further, a product obtained by co-condensing urea or the like with a part of melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include condensates of epichlorohydrin with ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A and the like hydroxyl groups and amino groups, There are polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like. Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane. Examples of the polyglycidyl ether and diepoxy compound include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and propylene glycol diglycidyl ether. , Polypropylene glycol diglycidyl ether, poly Examples of tetramethylene glycol diglycidyl ether and monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, and glycidyl amine compounds such as N, N, N ′, N′-tetraglycidyl-m-xylyl. Examples include range amine and 1,3-bis (N, N-diglycidylamino) cyclohexane.

The isocyanate compound is a compound having an isocyanate derivative structure typified by isocyanate or blocked isocyanate. Examples of isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate, and aromatic rings such as α, α, α ′, α′-tetramethylxylylene diisocyanate. Aliphatic isocyanates such as aliphatic isocyanate, methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis (4-cyclohexyl isocyanate), isopropylidene dicyclohexyl diisocyanate Ne Alicyclic isocyanates such as bets are exemplified. Further, polymers and derivatives such as burettes, isocyanurates, uretdiones, and carbodiimide modified products of these isocyanates are also included. These may be used alone or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to avoid yellowing due to ultraviolet rays.

When used in the state of blocked isocyanate, the blocking agent includes, for example, bisulfites, phenolic compounds such as phenol, cresol, and ethylphenol, and alcohols such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol. Compounds, active methylene compounds such as methyl isobutanoyl acetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, acetylacetone, mercaptan compounds such as butyl mercaptan, dodecyl mercaptan, ε-caprolactam, δ-valerolactam, etc. Lactam compounds, amine compounds such as diphenylaniline, aniline, ethyleneimine, acetanilide, acetic acid amide acid amide compounds, Examples include oxime compounds such as rumaldehyde, acetoaldoxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime, and these may be used alone or in combination of two or more.

Further, the isocyanate compound may be used alone, or may be used as a mixture or a combination with various polymers. In the sense of improving the dispersibility and crosslinkability of the isocyanate compound, it is preferable to use a mixture or a bond with a polyester resin or a urethane resin.

A carbodiimide-based compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in the molecule, but for better adhesion, etc., the polycarbodiimide having two or more in the molecule More preferred are system compounds.

The carbodiimide compound can be synthesized by a conventionally known technique, and generally a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and any of aromatic and aliphatic compounds can be used. Specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexa Examples include methylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

The content of the carbodiimide group contained in the carbodiimide compound is carbodiimide equivalent (weight of the carbodiimide compound to give 1 mol of carbodiimide group [g]), and is usually 100 to 1000, preferably 250 to 700, more preferably 300. It is in the range of ~ 500. By using it in the above range, the durability of the coating film is improved.

Furthermore, in order not to lose the effect of the present invention, in order to improve the water solubility and water dispersibility of the polycarbodiimide compound, adding a surfactant, polyalkylene oxide, quaternary ammonium salt of dialkylamino alcohol, You may add and use hydrophilic monomers, such as a hydroxyalkyl sulfonate.

These cross-linking agents may be used singly or in combination of two or more kinds, but by combining two or more kinds, adhesion to the functional layer, which has been difficult to be compatible, and oligomer after heating (ester cyclic trimer) ) Was improved. Among them, a combination of an oxazoline compound that can improve adhesion to a functional layer and a melamine compound that is excellent in preventing precipitation of an oligomer (ester cyclic trimer) after heating is optimal and preferable.

Further, the present inventors have found that it is particularly effective to combine three kinds of crosslinking agents in order to further improve the adhesion with the functional layer. As a combination of three or more kinds of cross-linking agents, it is preferable to select a melamine compound as one of the cross-linking agents. As a cross-linking agent to be combined with the melamine compound, an oxazoline compound, an epoxy compound, and a carbodiimide type are used. Particularly preferred are compounds and epoxy compounds.

When such a crosslinking agent is contained, a component for promoting crosslinking at the same time, for example, a crosslinking catalyst can be used in combination.

In addition, in the formation of the coating layer, a binder polymer is used in combination within the range not impairing the gist of the present invention in order to improve the coating appearance and the adhesion when the functional layer is formed on the coating layer. It is also possible. The binder polymer is a polymer compound safety evaluation flow scheme (November 1985, sponsored by the Chemical Substances Council) with a high number average molecular weight (Mn) of 1000 or more by gel permeation chromatography (GPC) measurement. It is defined as a molecular compound having film-forming properties.

Specific examples of the polymer include polyester resin, acrylic resin, urethane resin, polyvinyl (polyvinyl alcohol, etc.), polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, starches and the like. Among these, it is preferable to use a polyester resin, an acrylic resin, or a urethane resin from the viewpoint of improving adhesion with various surface functional layers. However, when the content increases, the precipitation prevention property of the ester cyclic trimer after heating may deteriorate, and it is usually 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less. When the ratio which occupies in a coating layer exceeds the said range, the precipitation inhibitory effect of the oligomer (ester cyclic trimer) after a heating may become inadequate.

In addition, particles can be used in combination for the purpose of blocking and improving slipperiness in forming the coating layer. The average particle diameter is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.2 μm or less from the viewpoint of transparency of the film. Further, the lower limit is preferably 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably a range larger than the film thickness of the coating layer in order to improve the slipperiness more effectively. Specific examples of the particles include silica, alumina, kaolin, calcium carbonate, and organic particles.

Further, in the range not impairing the gist of the present invention, an antifoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant are formed as necessary for forming the coating layer. It is also possible to use a foaming agent, a dye, a pigment and the like in combination.

As a ratio to the total nonvolatile components in the coating liquid, the ratio of the crosslinking agent is 70% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more as described above. When the ratio of the crosslinking agent is less than 70% by weight, it is difficult to suppress the precipitation of the oligomer (ester cyclic trimer) after heating the polyester film.

From the viewpoint of preventing oligomer (ester cyclic trimer) precipitation after heat treatment, when melamine is selected as one of the crosslinking agents, the ratio of melamine as the ratio to the total nonvolatile components in the coating liquid forming the coating layer is: The range is usually 5 to 95% by weight, preferably 15 to 80% by weight, particularly preferably 30 to 65% by weight. When the ratio of the crosslinking agent is out of the above range, precipitation suppression of the ester cyclic trimer after heating may be insufficient, or the coating appearance may be deteriorated.

Further, the thickness (after drying) of the coating layer of the coating film is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.5 μm, more preferably 0.01 to 0.2 μm. It is. When the thickness is less than 0.003 μm, the amount of ester cyclic trimer precipitated from the film may not be sufficiently reduced. On the other hand, when the thickness is larger than 1 μm, there are cases where problems such as deterioration of the appearance of the coating layer and lowering of the blocking property may occur.

Examples of methods for applying a coating solution to a polyester film include air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, and kiss roll coating. Conventional coating methods such as cast coating, spray coating, curtain coating, calendar coating, and extrusion coating can be used.

In order to improve the coating property and adhesion of the coating agent to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment or the like before coating.

The analysis of various components in the coating layer can be performed by analysis of TOF-SIMS, ESCA, fluorescent X-rays, and the like.

When providing a coating layer by in-line coating, apply the above-mentioned series of compounds as an aqueous solution or water dispersion on a polyester film with a coating solution adjusted to a solid content concentration of about 0.1 to 50% by weight. It is preferable to produce a laminated polyester film. Moreover, in the range which does not impair the main point of this invention, a small amount of organic solvents may be contained in the coating liquid for the purpose of improving dispersibility in water, improving film-forming properties, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

The drying and curing conditions for forming the coating layer on the polyester film are not particularly limited. For example, when the coating layer is provided by off-line coating, it is usually preferably 3 to 40 seconds at 80 to 200 ° C. Is preferably heat-treated at 100 to 180 ° C. for 3 to 40 seconds as a guide.

On the other hand, when the coating layer is provided by in-line coating, it is usually preferable to perform heat treatment at 70 to 280 ° C. for 3 to 200 seconds as a guide.

In addition, regardless of off-line coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as necessary. The polyester film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

In the double coated film, the film haze is preferably 10% or less. More preferably, it is 5% or less, More preferably, it is 3% or less. When the film haze of the coating film exceeds 10%, it may be difficult to cope with an application requiring particularly high visibility as a surface protective film of the optical member.

Further, the coating film constituting the surface protective film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

Next, the adhesive layer constituting the surface protective film of the present invention will be described below.

In the surface protective film of the present invention, it is an essential requirement to provide an adhesive layer on one coating layer.

By adopting the above configuration, the characteristics of the coating layer are utilized, and the film surface is protected by the coating layer having high heat resistance even when the film surface is exposed to a severe heat treatment process for a long time. Precipitation can be suppressed.

The pressure-sensitive adhesive layer means a layer composed of an adhesive material, and conventionally known materials such as silicone pressure-sensitive adhesives and acrylic pressure-sensitive adhesives can be used as long as the gist of the present invention is not impaired. . As one specific example, the case where an acrylic adhesive is used will be described below.

The acrylic pressure-sensitive adhesive means a pressure-sensitive adhesive layer containing, as a base polymer, an acrylic polymer formed using an acrylic monomer as an essential monomer component. The acrylic polymer has (meth) acrylic acid alkyl ester and / or (meth) acrylic acid alkoxyalkyl ester having a linear or branched alkyl group as an essential monomer component (more preferably as a main monomer component). ) It is preferably an acrylic polymer to be formed. Further, the acrylic polymer is particularly preferably an acrylic polymer formed using (meth) acrylic acid alkyl ester and acrylic acid alkoxyalkyl ester having a linear or branched alkyl group as essential monomer components. That is, the pressure-sensitive adhesive layer is particularly an acrylic pressure-sensitive adhesive layer formed using (meth) acrylic acid alkyl ester and acrylic acid alkoxyalkyl ester having a linear or branched alkyl group as essential monomer components. preferable.

In addition, the monomer component that forms the acrylic polymer that is the base polymer in the pressure-sensitive adhesive layer further includes a polar group-containing monomer, a polyfunctional monomer, and other copolymerizable monomers. May be included.

In addition, said "(meth) acryl" represents "acryl" and / or "methacryl", and others are the same. Although not particularly limited, the content of the acrylic polymer as the base polymer in the adhesive layer is preferably 60% by weight or more, more preferably 80% by weight, based on the total weight (100% by weight) of the adhesive layer. That's it.

As an essential monomer component for forming the acrylic polymer, a (meth) acrylic acid alkyl ester having a linear or branched alkyl group (hereinafter simply referred to as “(meth) acrylic acid alkyl ester”) may be used. ) Can be suitably used. Specific examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, (meth ) Isobutyl acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate , Octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, (meth) acrylic acid Isodecyl, undecyl (meth) acrylate, dodecyl (meth) acrylate, (Meth) acrylic acid tridecyl, (meth) acrylic acid tetradecyl, (meth) acrylic acid pentadecyl, (meth) acrylic acid hexadecyl, (meth) acrylic acid heptadecyl, (meth) acrylic acid octadecyl, (meth) acrylic acid nonadecyl, (meta Examples thereof include (meth) acrylic acid alkyl esters having 1 to 20 carbon atoms, such as eicosyl acrylate. Moreover, the (meth) acrylic acid alkyl ester may be used alone or in combination of two or more. Among them, (meth) acrylic acid alkyl esters having 2 to 14 carbon atoms in the alkyl group are preferable, and (meth) acrylic acid alkyl esters having 2 to 10 carbon atoms in the alkyl group are more preferable. In particular, 2-ethylhexyl acrylate (2EHA) is preferred.

Further, (meth) acrylic acid alkoxyalkyl ester [alkoxyalkyl (meth) acrylate] can also be suitably used as the essential monomer component (more preferably, the main monomer component) for forming the acrylic polymer. Particularly preferred is an acrylic acid alkoxyalkyl ester [alkoxyalkyl acrylate]. The (meth) acrylic acid alkoxyalkyl ester is not particularly limited. For example, (meth) acrylic acid 2-methoxyethyl, (meth) acrylic acid 2-ethoxyethyl, (meth) acrylic acid methoxytriethylene glycol, (meth) ) 3-methoxypropyl acrylate, 3-ethoxypropyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, 4-ethoxybutyl (meth) acrylate, and the like. The said (meth) acrylic-acid alkoxyalkylester can be used individually or in combination of 2 or more types. Among these, 2-methoxyethyl acrylate (2MEA) is preferable.

In addition, the content of the essential monomer component [(meth) acrylic acid alkyl ester and / or (meth) acrylic acid alkoxyalkyl ester] forming the above acrylic polymer is selected from the viewpoint of adhesiveness of the pressure-sensitive adhesive layer. The amount is preferably 5% by weight or more (for example, 5 to 100% by weight), more preferably 5 to 95% by weight, based on the total amount (100% by weight) of monomer components forming the system polymer. In addition, when both (meth) acrylic acid alkyl ester and (meth) acrylic acid alkoxyalkyl ester are used as monomer components, the content of (meth) acrylic acid alkyl ester and (alkyl) alkoxyalkyl (meth) acrylate The total amount of ester content (total content) only needs to satisfy the above range.

Among the above, it is preferable that both (meth) acrylic acid alkyl ester and acrylic acid alkoxyalkyl ester are used as essential monomer components for forming the acrylic polymer. In that case, the content of the (meth) acrylic acid alkyl ester is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, based on the total amount of monomer components (100% by weight) forming the acrylic polymer. %, More preferably 65 to 80% by weight, most preferably 65 to 75% by weight. If the content exceeds 95% by weight, the adhesiveness may decrease, and if it is less than 5% by weight, the elastic modulus of the pressure-sensitive adhesive layer may be too high. Further, the content of the alkoxyalkyl ester of acrylic acid is preferably 10 to 45% by weight, more preferably 10 to 40% by weight, and still more preferably relative to the total amount (100% by weight) of monomer components forming the acrylic polymer. 20 to 35% by weight. If the content exceeds 45% by weight, the elastic modulus of the pressure-sensitive adhesive layer may be too high, and if it is less than 10% by weight, the adhesiveness may decrease.

Examples of the polar group-containing monomer include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid and other carboxyl group-containing monomers or anhydrides thereof (maleic anhydride, etc. ); Hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, etc. Hydroxyl group (hydroxyl group) -containing monomers such as vinyl alcohol and allyl alcohol; (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-hydride Amide group-containing monomers such as xylethylacrylamide; amino group-containing monomers such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, and t-butylaminoethyl (meth) acrylate; ) Glycidyl group-containing monomers such as glycidyl acrylate and methyl glycidyl (meth) acrylate; Cyan group-containing monomers such as acrylonitrile and methacrylonitrile; N-vinyl-2-pyrrolidone, other than (meth) acryloylmorpholine , N-vinyl pyridine, N-vinyl piperidone, N-vinyl pyrimidine, N-vinyl piperazine, N-vinyl pyrrole, N-vinyl imidazole, N-vinyl oxazole and other heterocyclic ring-containing vinyl monomers; sodium vinyl sulfonate, etc. Sulfonic acid group-containing monomer of 2-hydroxyethyl Acrylate phosphoric acid group-containing monomers such as acryloyl phosphate; cyclohexyl maleimide, imide group-containing monomers such as isopropyl maleimide; 2-methacryloyloxy such acryloyl isocyanate group-containing monomers such as methacryloyloxyethyl isocyanate. The said polar group containing monomer can be used individually or in combination of 2 or more types. Among the above-mentioned polar group-containing monomers, carboxyl group-containing monomers or acid anhydrides thereof, hydroxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, heterocyclic-containing vinyls Monomers are preferred, and acrylic acid (AA), 4-hydroxybutyl acrylate (4HBA), N-vinyl-2-pyrrolidone (NVP), and N-hydroxyethylacrylamide (HEAA) are particularly preferred.

The content of the polar group-containing monomer is preferably 15% by weight or less with respect to 100% by weight of the monomer component forming the acrylic polymer. When it exceeds 15% by weight, the cohesive force of the pressure-sensitive adhesive layer becomes too high. As a result, the storage elastic modulus (23 ° C.) becomes too high, and the stress relaxation property may be lowered. If it is less than 0.01% by weight, the adhesion may be lowered.

Among these, the content of the hydroxyl group-containing monomer is preferably 5% by weight or less with respect to 100% by weight of the monomer component forming the acrylic polymer. When the content exceeds 5% by weight, the cohesive force of the pressure-sensitive adhesive layer becomes too high, the storage elastic modulus (23 ° C.) becomes too high, and the stress relaxation property may be lowered. Content of polar group-containing monomers other than hydroxyl group-containing monomers (particularly carboxyl group-containing monomers, amide group-containing monomers, amino group-containing monomers, heterocyclic-containing vinyl monomers) Is preferably 15% by weight or less with respect to 100% by weight of the monomer component forming the acrylic polymer. When the content exceeds 15% by weight, the cohesive force of the pressure-sensitive adhesive layer becomes too high, the storage elastic modulus (23 ° C.) becomes too high, and the stress relaxation property may be lowered.

Examples of the polyfunctional monomer include hexanediol di (meth) acrylate, butanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meth) acrylate. , Neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylol methanetri (meth) ) Acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate and the like. The said polyfunctional monomer can be used individually or in combination of 2 or more types. Among the above, as the polyfunctional monomer, trimethylolpropane triacrylate (TMPTA) is preferable.

The content of the polyfunctional monomer is preferably 0.5% by weight or less with respect to 100% by weight of the total amount of monomer components forming the acrylic polymer. When the content exceeds 0.5% by weight, for example, the cohesive force of the pressure-sensitive adhesive layer becomes too high, and the stress relaxation property may be lowered.

Examples of copolymerizable monomers (other copolymerizable monomers) other than the above polar group-containing monomers and polyfunctional monomers include cyclopentyl (meth) acrylate and cyclohexyl (meth). (Meth) acrylates having an alicyclic hydrocarbon group such as acrylate and isobornyl (meth) acrylate, and (meth) acrylates having an aromatic hydrocarbon group such as phenyl (meth) acrylate and the like (meth ) (Meth) acrylic acid esters other than alkyl acrylates, alkoxyalkyl (meth) acrylates, polar group-containing monomers and polyfunctional monomers; vinyl esters such as vinyl acetate and vinyl propionate; styrene , Aromatic vinyl compounds such as vinyl toluene; ethylene, butadiene, isoprene, isobutylene, etc. Vinyl ethers such as vinyl alkyl ethers; olefins or dienes and vinyl chloride.

The acrylic polymer can be prepared by polymerizing the above monomer components by a conventionally known or conventional polymerization method. Examples of the polymerization method of the acrylic polymer include a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, and a polymerization method by active energy ray irradiation (active energy ray polymerization method). Among them, the solution polymerization method and the active energy ray polymerization method are preferable in terms of transparency, water resistance, production cost and the like, and particularly when forming a relatively thick pressure-sensitive adhesive layer, active energy ray polymerization (photopolymerization and Method), and an ultraviolet polymerization method by ultraviolet irradiation is particularly preferable.

Examples of the active energy rays irradiated in the above active energy ray polymerization (photopolymerization) include ionizing radiation such as α rays, β rays, γ rays, neutron rays, electron rays, and ultraviolet rays, among others. Ultraviolet light is preferred. Further, the irradiation energy, irradiation time, irradiation method, and the like of the active energy ray are not particularly limited as long as they do not impair the gist of the present invention.

In the solution polymerization, various common solvents can be used. Examples of such solvents include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; cyclohexane and methylcyclohexane Organic solvents such as ketones such as methyl ethyl ketone and methyl isobutyl ketone. A solvent can be used individually or in combination of 2 or more types.

In preparing the acrylic polymer, a polymerization initiator such as a thermal polymerization initiator or a photopolymerization initiator (photoinitiator) can be used depending on the type of polymerization reaction. A polymerization initiator can be used individually or in combination of 2 or more types.

The photopolymerization initiator is not particularly limited, and examples thereof include benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketol photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, and photopolymerization initiators. An active oxime photopolymerization initiator, a benzoin photopolymerization initiator, a benzyl photopolymerization initiator, a benzophenone photopolymerization initiator, a ketal photopolymerization initiator, a thioxanthone photopolymerization initiator, and the like can be used. The amount of the photopolymerization initiator used is not particularly limited. For example, it is preferably in the range of 0.01 to 0.2 parts by weight with respect to 100 parts by weight of the total amount of monomer components forming the acrylic polymer.

Specific examples of the benzoin ether photopolymerization initiator include, for example, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one And anisole methyl ether. Examples of the acetophenone photopolymerization initiator include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4- (t-butyl). Examples include dichloroacetophenone. Examples of the α-ketol photopolymerization initiator include 2-methyl-2-hydroxypropiophenone, 1- [4- (2-hydroxyethyl) phenyl] -2-methylpropan-1-one, and the like. . Specific examples of the aromatic sulfonyl chloride photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the photoactive oxime photopolymerization initiator include 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime. Examples of the benzoin photopolymerization initiator include benzoin. Examples of the benzyl photopolymerization initiator include benzyl.

Specific examples of the benzophenone photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3,3′-dimethyl-4-methoxybenzophenone, polyvinylbenzophenone, α-hydroxycyclohexyl phenyl ketone, and the like. Specific examples of the ketal photopolymerization initiator include benzyldimethyl ketal. Specific examples of the thioxanthone photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, dodecylthioxanthone, and the like.

Specific examples of the thermal polymerization initiator include azo polymerization initiators [for example, 2,2′-azobisisobutyronitrile, 2,2′-azobis-2-methylbutyronitrile, 2,2′-azobis. (2-methylpropionic acid) dimethyl, 4,4′-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [ 2- (5-Methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis (2-methylpropionamidine) disulfate, 2,2′-azobis (N, N′-di) Methyleneisobutylamidine) dihydrochloride], peroxide polymerization initiators (eg, dibenzoyl peroxide, tert-butylpermaleate, etc.), red Box-type polymerization initiators and the like. The amount of the thermal polymerization initiator used is not particularly limited as long as it does not impair the gist of the present invention, and may be any range that can be conventionally used as a thermal polymerization initiator.

For the adhesive layer, a crosslinking agent, a crosslinking accelerator, a tackifier (for example, a rosin derivative resin, a polyterpene resin, a petroleum resin, an oil-soluble phenol resin, etc.), an anti-aging agent, a filler, a colorant (as required) Pigments, dyes, etc.), UV absorbers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, and the like can be used as needed within the range not impairing the properties of the present invention. .

The cross-linking agent can control the gel fraction of the pressure-sensitive adhesive layer by cross-linking the base polymer of the pressure-sensitive adhesive layer. As crosslinking agents, isocyanate crosslinking agents, epoxy crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents Agents, carbodiimide crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, amine crosslinking agents, and the like, and isocyanate crosslinking agents and epoxy crosslinking agents can be preferably used. A crosslinking agent can be used individually or in combination of 2 or more types.

The thickness of the adhesive layer (after drying) is 10 to 200 μm, preferably 20 to 150 μm, and more preferably 25 to 100 μm. When the thickness of the adhesive layer (after drying) is less than 10 μm, it may be difficult to obtain a desired adhesive force. On the other hand, when the pressure-sensitive adhesive layer thickness (after drying) exceeds 200 μm, the pressure-sensitive adhesive layer may be insufficiently cured, resulting in problems such as workability deterioration.

In the surface protective film of the present invention, a heat treatment (150 ° C., 90 minutes) is performed in order to ensure good visibility even in a step of heat treatment in a high temperature atmosphere, or in a situation where it is exposed to a high temperature atmosphere during transportation and storage. ) The rate of change in film haze before and after (ΔH) is preferably 1.0% or less. More preferably, ΔH is 0.7% or less. When ΔH exceeds 1.0%, the visibility decreases as the film haze increases due to precipitation of the oligomer (ester cyclic trimer). For example, for optical members (for example, glass substrates, light diffusion films, When used in a liquid crystal display (polarizing plate, retardation plate, light guide plate, prism plate, etc.), touch panel, organic EL display, plasma display, etc., it may be difficult to apply.

In order to prevent failure and malfunction when using electronic devices that are adherends with a surface protective film attached to display devices and input devices, the adherends may not be corroded. preferable. (For example, Patent Document 5 also describes.)

From such a viewpoint, in the surface protective film of the present invention, not only the pressure-sensitive adhesive layer but also the double-sided coating film to be configured, the material constituting the coating layer should be a material that does not substantially contain a halogen element. preferable. Specifically, the total amount of halogen ions detected after leaving the coated film in pure water for 24 hours at room temperature is preferably 1 ppm or less.

As a countermeasure against corrosion in the adhesive layer, for example, a technique described in Japanese Patent Publication No. 2012-246407 can be employed.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist. The measuring method used in the present invention is as follows.

(1) Measurement of intrinsic viscosity (dl / g) of polyester:
1 g of polyester from which other polymer components and pigments incompatible with polyester were removed was precisely weighed, 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) was added and dissolved, and measurement was performed at 30 ° C.

(2) Average particle diameter (d50):
The average particle size d50 was defined as the particle size having an integrated volume fraction of 50% in an equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 type) manufactured by Shimadzu Corporation.

(3) Measuring method of contained ester cyclic trimer contained in polyester raw material:
About 200 mg of the polyester raw material is weighed and dissolved in 2 ml of a mixed solvent of chloroform / HFIP (hexafluoro-2-isopropanol) in a ratio of 3: 2. After dissolution, add 20 ml of chloroform, and then add 10 ml of methanol little by little. The precipitate is removed by filtration, and the precipitate is washed with a mixed solvent of chloroform / methanol ratio 2: 1. The filtrate / washing solution is collected, concentrated by an evaporator, and then dried. After the dried product was dissolved in 25 ml of DMF (dimethylformamide), this solution was supplied to liquid chromatography (“LC-7A” manufactured by Shimadzu Corporation) to determine the amount of ester cyclic trimer in DMF. The value is divided by the amount of the polyester raw material dissolved in the chloroform / HFIP mixed solvent to obtain the amount of ester cyclic trimer (weight%). The amount of ester cyclic trimer in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method).

Preparation of the standard sample was performed by accurately weighing the ester cyclic trimer previously collected and dissolving it in DMF accurately weighed.

The conditions for the liquid chromatograph were as follows.

Mobile phase A: Acetonitrile Mobile phase B: 2% acetic acid aqueous solution Column: “MCIGEL ODS 1HU” manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(4) Thickness of the laminated polyester layer:
The film piece was fixed with an epoxy resin and then cut with a microtome, and the cross section of the film was observed with a transmission electron micrograph. Two of the cross-sections are observed almost in parallel with the film surface, and the interface is observed by contrast. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was defined as the laminated thickness.

(5) Measurement of softening point of each polyester layer of the multilayer polyester film:
After confirming the layer structure of the sample film in advance as described in (4) above, in the exposed film cross-section, one central part of each polyester layer is placed at Nano Navi II / E-Sweep / nano-TA2 (SII Nano (Manufactured by Technology Co., Ltd.) under the following measurement conditions, and the average value of N = 3 was used as the softening point of the polyester layer. In addition, regarding the measured value, the tangent in each curve of a temperature rising curve and a temperature falling curve was drawn from the obtained measurement chart, and the intersection of the tangent was calculated | required. Next, a point passing through the intersection of the obtained tangent lines and intersecting the measurement temperature axis perpendicularly was defined as a softening point.
"Measurement condition"
Temperature increase rate: 5 ° C / sec
Probe: Thermal cantilever AN2-200
Measurement temperature range: normal temperature (23 ° C) to 300 ° C
Measurement atmosphere: atmospheric pressure

(6) Measurement of film haze:
The film haze of the sample film for measurement was measured according to JIS-K-7136 using a haze meter “HM-150” manufactured by Murakami Color Research Laboratory Co., Ltd.
(7) Measurement of rate of change in film haze (ΔH) of surface protective film before and after heat treatment (practical property substitution evaluation):
In a hot air circulating furnace (TABAI: model PVH-210), heat treatment is performed at 150 ° C. for 90 minutes with a sample film (10 cm square) suspended by a clip. Thereafter, the film haze was measured by the method of (4) (haze 1). Using the same sample, ΔH was calculated with a difference from the unprocessed film haze (haze 2).

ΔH = (Haze 1)-(Haze 2)
The lower ΔH, the less oligomer precipitation due to the wet heat treatment, which is better.

(Criteria)
ΔH is 0.3% or less: Visibility is particularly good ΔH is over 0.3% and 0.7% or less: Visibility is good ΔH is over 0.7% and 1.0% or less: Visibility may be a problem ΔH exceeds 1.0%: Level where visibility is a problem in practical use

(8) Adhesion evaluation with hard coat layer:
An active energy ray curable resin composed of the following active energy ray curable resin composition is applied to the coating layer surface of the obtained coated film with a # 16 wire bar, dried at 80 ° C. for 1 minute to remove the solvent, and then irradiated with ultraviolet rays. A hard coat layer having a thickness (after drying) of 5 μm was provided by irradiating ultraviolet rays from a machine with a metal halide lamp 120 w / cm so that the integrated light amount was 180 mJ / cm ² . Next, using the hard coat layer surface of the obtained sample film, 100 grid-shaped cuts were made using a cutter guide with a gap interval of 1 mm. Next, an 18 mm wide tape (Cellotape (registered trademark) CT-18 manufactured by Nichiban Co., Ltd.) was applied to the cut surface on the grid, and a 2.0 kg roller was reciprocated 20 times to completely adhere to it. The peeled surface after peeling off rapidly at the peeling angle was observed and judged according to the following criteria.

<Active energy ray curable resin composition>
A mixed coating solution of 72 parts by weight of dipentaerythritol acrylate, 18 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate, 1 part by weight of a photopolymerization initiator (Irgacure 651, manufactured by Ciba Specialty Chemicals), and 200 parts by weight of methyl ethyl ketone.
(Criteria)
A: Peeling area is less than 5% B: Peeling area is 5% or more and less than 20% C: Peeling area is 20% or more and less than 50% D: Peeling area is 50% or more

(9) Determination of the amount of halogen ions in the coated film:
A sample film (coated film) is cut into a 10 cm square and immersed in pure water at room temperature for 24 hours. Thereafter, the amount of halogen ions detected was measured by an iochromatography method under the following measurement conditions.
(Ion chromatograph measurement conditions)
Analytical device: DX-320, manufactured by DIONEX
Separation column: Ion Pac AS15 (4 mm x 250 mm)
Guard column: Ion Pac AG15 (4mm x 50mm)
Removal system: ASRS-ULTRA (external mode, 100 mA)
Detector: Electrical conductivity detector Eluent: 7 mM KOH (0 to 20 minutes)
45 mM KOH (20-30 minutes)
(Using eluent generator EG40)
Eluent flow rate: 1.0 ml / min Sample injection volume: 250 μl
(Criteria)
A: Halogen ion content is 1 ppm or less (practically acceptable level)
B: Halogen ion amount exceeds 1 ppm (concern is practically concerned)

(10) Corrosion resistance evaluation of surface protective film (practical property substitution evaluation):
A test piece was prepared by pasting the adhesive surface of the sample film on the surface of a copper foil having a thickness of 70 μm. Using a test piece, after holding in a constant temperature and humidity chamber at 60 ° C. and 95% RH for 200 hours, peel off the surface protective film on the surface of the copper foil where the surface protective film is bonded. Then, visual observation was performed, and the degree of discoloration (corrosion) on the copper foil surface was determined according to the following criteria.
(Criteria)
A: No discoloration (corrosion) is observed on the copper foil surface B: Slight discoloration (corrosion) is confirmed on the copper foil surface

(11) Visibility evaluation after heat treatment of surface protective film (I):
(Practical property substitution evaluation of oligomer sealing)
After cutting out each surface protection film of an Example and a comparative example in 5 cm square beforehand, in the state which bonded the float glass plate (size: 7 cm square, thickness 2mm, based on JISR 3202) and the adhesion layer, it is a hot-air type. Heat treatment was performed at 150 ° C. for 90 minutes in a circulating furnace (manufactured by Tabai: model PVH-210). Thereafter, whether or not the adhesive layer is observable was determined according to the following criteria in the state of being bonded.
(Criteria)
A: The adhesive layer can be inspected with the surface protective film still attached, and the inspection is particularly easy (practically no problem level).
B: The adhesive layer can be inspected while the surface protective film is still adhered, and inspection is easy (practical level).
C: The adhesive layer can be inspected while the surface protective film is still bonded, but in rare cases, the inspection may be slightly difficult.
(Practical level that may cause problems)
D: Since the film haze of the surface protective film is rising, it is difficult to inspect the adhesive layer with the surface protective film still attached (practically problematic level)

(12) Visibility evaluation after heat treatment of surface protective film (II):
(Practical property substitution evaluation of oligomer sealing)
After applying an anchor layer composed of the following anchor layer composition on one side of a 50 μm thick PET film (Mitsubishi Resin Co., Ltd .: Diafoil T600 type) to a thickness (after drying) of 30 nm, the anchor layer A thickness of 25 nm is formed by a reactive sputtering method using a sintered body material of 95% by weight of indium oxide and 5% by weight of tin oxide in an atmosphere of 0.4 Pa composed of 95% argon gas and 5% oxygen gas. An ITO film (transparent conductive thin film) was formed.
Next, on the surface of the ITO layer, the pressure-sensitive adhesive layer surface of each surface protective film obtained in Examples and Comparative Examples in the present invention was bonded to obtain a laminate.
The obtained layered product was subjected to a heat treatment at 180 ° C. for 90 minutes in a hot air circulating furnace (manufactured by Tabai: model PVH-210) to crystallize the ITO layer.
<< Anchor layer composition >>
Colcoat P (manufactured by Colcoat)
A 1% strength solution was prepared using isopropyl alcohol.
Thereafter, whether or not the ITO layer can be observed was determined according to the following determination criteria in the state of being bonded.
(Criteria)
A: It is possible to inspect the ITO layer with the surface protective film still attached, and the inspection is particularly easy (practically no problem level).
B: The ITO layer can be inspected while the surface protective film is still bonded, and inspection is easy (practically no problem level).
C: The ITO layer can be inspected with the surface protective film still attached, but in rare cases, the inspection may be slightly difficult.
(Practical level that may cause problems)
D: Since the film haze of the surface protective film is rising, it is difficult to inspect the adhesive layer with the surface protective film still attached (practically problematic level)

(13) Comprehensive evaluation (practical property substitution evaluation):
Using the surface protective films produced in the examples and comparative examples, comprehensive evaluation was performed according to the following criteria for each evaluation item of visibility after heat treatment, hard coat adhesion, and corrosion resistance.
(Criteria)
A: Visibility after heat treatment, hard coat adhesion, and corrosion resistance are all B or more, and at least two are A (a level that causes no problem in practical use).
B: Visibility after heat treatment, hard coat adhesion, and corrosion resistance are all B or more and A is at most one (practically no problem level)
(Practical, no problem level)
C: At least one of visibility after heat treatment, hard coat adhesion, and corrosion resistance is C (a level that may cause a problem in practical use)
D: At least one of visibility (hard coat adhesion) and corrosion resistance after heat treatment is D (practically problematic level)

The polyester used in the examples and comparative examples was prepared as follows.
<Manufacture of polyester>
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 part of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.63 and an ester cyclic trimer content of 0.97% by weight.

<Method for producing polyester (B)>
The polyester (A) is pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C., and has an intrinsic viscosity of 0.75 and an ester cyclic trimer content of 0.46% by weight. Polyester (B) was obtained.

<Method for producing polyester (C)>
100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 30 ppm of ethyl acid phosphate with respect to the resulting polyester, and 100 ppm of magnesium acetate tetrahydrate with respect to the resulting polyester as the catalyst at 260 ° C. in a nitrogen atmosphere at 260 ° C. The reaction was allowed to proceed. Subsequently, 50 ppm of tetrabutyl titanate was added to the resulting polyester, the temperature was raised to 280 ° C. over 2 hours and 30 minutes, the pressure was reduced to 0.3 kPa in absolute pressure, and melt polycondensation was further carried out for 80 minutes. A polyester (C) having a polyester (A) ester cyclic trimer content of 0.61 and a content of 1.02% by weight was obtained.

<Method for producing polyester (D)>
Polyester (C) was pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 210 ° C., with an intrinsic viscosity of 0.72 and an ester cyclic trimer content of 0.50 wt%. Polyester (D) was obtained.

<Method for producing polyester (E)>
In the production method of polyester 1, after adding 0.04 part of ethyl acid phosphate, 0.5 part of silica particles having an average particle diameter (d50) of 1.6 μm dispersed in ethylene glycol and 0.04 of antimony trioxide are added. A polyester (C) was obtained using the same method as the production method of polyester 1 except that the polycondensation reaction was stopped at a time corresponding to an intrinsic viscosity of 0.65. The obtained polyester (C) had an intrinsic viscosity of 0.65 and an ester cyclic trimer content of 0.82% by weight.

(Manufacture of polyester film F1)
Polyester B and E are blended at a ratio of 90% and 10%, respectively, as surface layer raw material, and polyester A 100% raw material as intermediate layer raw material is supplied to two vented extruders and melt extruded at 290 ° C. After that, an amorphous film having a thickness of about 1500 μm was obtained by cooling and solidifying on a cooling roll whose surface temperature was set to 40 ° C. using an electrostatic application adhesion method. This film was stretched 3.4 times in the machine direction at 85 ° C. Thereafter, a coating layer comprising the following coating solution was coated on both sides so that the coating thickness (after drying) was 0.04 g / m ² , and then the film was guided to a tenter and 4.0 sideways at 100 ° C. After double-stretching and heat treatment at 230 ° C., a relaxation treatment of 2% in the transverse direction was performed to obtain a polyester film F1 having a thickness of 50 μm (thickness ratio = 2.5 μm / 45 μm / 2.5 μm).

Moreover, the following was used as a composition contained in a coating liquid.
(A1): Hexamethoxymethylolmelamine (A2): Epocross which is an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd.) Oxazoline group amount 7.7 mmol / g
(A3): Epocros which is an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd.) Oxazoline group amount 4.5 mmol / g
(A4): Polyglycerol polyglycidyl ether

(A5): Block polyisocyanate synthesized by the following method 1000 parts of hexamethylene diisocyanate was stirred at 60 ° C., and 0.1 part of tetramethylammonium capryate was added as a catalyst. After 4 hours, 0.2 part of phosphoric acid was added to stop the reaction, and an isocyanurate type polyisocyanate composition was obtained. 100 parts of the obtained isocyanurate type polyisocyanate composition, 42.3 parts of methoxypolyethylene glycol having a number average molecular weight of 400, and 29.5 parts of propylene glycol monomethyl ether acetate were charged and maintained at 80 ° C. for 7 hours. Thereafter, the reaction solution temperature was kept at 60 ° C., 35.8 parts of methyl isobutanoyl acetate, 32.2 parts of diethyl malonate, and 0.88 part of 28% methanol solution of sodium methoxide were added and kept for 4 hours. Block polyisocyanate obtained by adding 58.9 parts of n-butanol and maintaining the reaction solution temperature at 80 ° C. for 2 hours, and then adding 0.86 part of 2-ethylhexyl acid phosphate

(A6): Carbodilite (manufactured by Nisshinbo Chemical Co., Ltd.) which is a polycarbodiimide compound Carbodiimide equivalent 340
(B1): Acrylic resin aqueous dispersion polymerized with the following composition and having a glass transition point of 40 ° C. Ethyl acrylate / n-butyl acrylate / methyl methacrylate / N-methylol acrylamide / acrylic acid = 65/21/10/2 / 2 (% by weight) emulsion polymer (emulsifier: anionic surfactant)

(B2): 315 parts by weight of terephthalic acid, 299 parts by weight of isophthalic acid, 74 parts by weight of ethylene glycol, and 265 parts by weight of diethylene glycol as the component (B2a), (B2a) 953 parts by weight, isophorone diisocyanate Polyester polyurethane comprising 267 parts by weight, ethylene glycol 56 parts by weight, and dimethylolpropionic acid 67 parts by weight neutralized with ammonia and dispersed in water (concentration 23%, viscosity at 25 ° C., 30 mPa · s) )
(B3): Polymer having a pyrrolidinium ring in the main chain (Daiichi Kogyo Seiyaku Co., Ltd .: Charol DC902P)
(C1): 2-amino-2-methylpropanol hydrochloride (F1), which is a melamine crosslinking catalyst: silica particles having an average particle size of 0.07 μm.

(Manufacture of polyester films F2 to F31)
F1 was manufactured in the same manner as F1 manufacturing method 5 except that the type of polyester film and the type of coating layer were different, and a polyester film was obtained.

Example 1:
A pressure-sensitive adhesive layer composed of the following pressure-sensitive adhesive layer composition was applied to the surface of one coating layer of the polyester film F1 so that the thickness (after drying) was 25 μm and dried at 100 ° C. for 5 minutes to obtain a surface protective film. .
(Adhesive layer composition A)
A solution of an acrylic copolymer having a weight average molecular weight of 600,000 (polystyrene equivalent) by copolymerizing butyl acrylate (100 parts by weight, acrylic acid 6 parts by weight) in ethyl acetate by a conventional method (solid content 30% by weight) ) To 100 parts by weight (solid content) of an acrylic copolymer, 0.2 part by weight of N, N-dimethylaminoethyl acrylate and 6 parts by weight of Tetrad C (manufactured by Mitsubishi Gas Chemical) as an epoxy-based crosslinking agent are added. An adhesive layer composition was obtained.

Examples 2 to 22:
In Example 1, it manufactured similarly to Example 1 except changing the kind of polyester film, and a coating liquid composition, and obtained the surface protection film.

Example 23:
In Example 1, it manufactured similarly to Example 1 except having changed the adhesion layer composition into the following adhesion composition, and obtained the surface protection film.
(Adhesive layer composition B)
A solution of an acrylic copolymer having a weight average molecular weight of 600,000 (polystyrene equivalent) by copolymerizing butyl acrylate (100 parts by weight, acrylic acid 6 parts by weight) in ethyl acetate by a conventional method (solid content 30% by weight) ) To 100 parts by weight (solid content) of the acrylic copolymer, 6 parts by weight of tetrad C (manufactured by Mitsubishi Gas Chemical) as an epoxy crosslinking agent was added to obtain an adhesive layer composition B.

Comparative Examples 1 to 9:
In Example 1, it manufactured similarly to Example 1 except changing the kind of polyester film, and a coating liquid composition, and obtained the surface protection film.
Comparative Example 1 is an example in which no coating layer is provided, and Comparative Examples 2 to 5 are examples in which the softening points of both outermost polyester layers of the multilayer polyester film are the same as the softening point of the intermediate layer. Examples 9 to 9 are examples in which the content of the crosslinking agent (A1 to A6 in Table 4) in the coating solution is less than 70% by weight.

The characteristics of the surface protective films obtained in the above examples and comparative examples are shown in Tables 1 to 6 below.

The surface protective film of the present invention is for surface protection of various adherends such as synthetic resin plates, glass plates, metal plates, optical members, automobile members, electric / electronic members, building material members, stationery / office supplies members, etc. Can be suitably used.

Claims (3)

1. A coating layer is formed on both surfaces of a multilayer polyester film having a laminate structure of at least three layers, and the softening point of both outermost polyester layers is higher than the softening point of the intermediate layer, and an adhesive layer is formed on one coating layer surface A surface protective film comprising: a coating film comprising a coating solution containing 70% by weight or more of a crosslinking agent based on a non-volatile component.
2. The surface protective film according to claim 1, wherein the coating solution contains oxazoline and melamine.
3. The surface protective film according to claim 1 or 2, wherein the adhesive layer is formed of an acrylic adhesive.