JP7017102B2 - Laminated polyester film - Google Patents

Description

The present invention relates to a laminated polyester film suitable as a surface protective film provided with an adhesive layer, and a surface protective film composed of the laminated polyester film.

Conventionally, synthetic resin plates, glass plates, metal plates, optical members (glass substrates, light diffusing films, liquid crystal displays, polarizing plates, retardation plates, light guide plates, prism plates, etc.), touch panels, automobile members, electrical / electronic members, A surface protective film with an adhesive layer on one side of a polyethylene film is used for the purpose of protecting the surface of various adherends, such as preventing dirt, scratches, dust, etc. on the surface of building materials, stationery, office supplies, etc. Has been done.

As the surface protective film, for example, a surface protective film using a low-density polyethylene resin as a base material and an ethylene-vinyl acetate copolymer (EVA) as an adhesive has been proposed (Patent Documents 1 and 2). ..

However, a surface protective film using a low-density polyethylene resin as a base film is subjected to heat treatment in a high-temperature atmosphere with the film still attached to the adherend, or in a high-temperature atmosphere during transportation or storage. When it is exposed to an environment, it is difficult to apply it because the base film is greatly deformed due to melting or shrinkage.

A surface protective film using a polyester film as a base film, which has better heat resistance than a low-density polyethylene resin, does not have such a problem of deformation due to heat, but the polyester film has a low molecular weight in the polyester film due to heat treatment. Visibility may decrease as the haze of the film rises due to the precipitation and crystallization of the oligomer (mainly the ester cyclic trimer) which is a substance. In addition, the precipitated oligomer may contaminate the film manufacturing process and significantly reduce the yield of the product. Therefore, the polyester base film is required to have an oligomer-sealing property.

Further, various members that are adherends protected by the surface protection film may be inspected for the adherend (foreign matter inspection or the like) by irradiating light from above the surface protection film. In the inspection accompanied by such an optical evaluation, with the recent improvement in the performance of the inspection apparatus, there is a tendency that even a foreign matter level, which has not been a problem in the past, is detected as a foreign matter and is regarded as a problem. For this reason, foreign substances existing inside or on the surface of the surface protective film may be mistakenly recognized as foreign substances existing in various members to be inspected.
Therefore, in order to improve the visibility of the polyester film in the inspection process, for example, when measures are taken to reduce the particle content in the film, the visibility is improved, but the slipperiness of the film surface is often found. Tends to decline. If the slipperiness of the film surface decreases, scratches will occur on the film surface in the film manufacturing process, and the product will be mistaken for a defective product at the time of inspection. Therefore, the yield of the product will decrease, especially in electronic component applications. , The improvement is desired.

For this reason, surface protective films used for the purpose of surface protection of various members are particularly easy to inspect even when an inspection involving optical evaluation is performed using a high-performance inspection device. Moreover, a film having a good oligomer-sealing property is required.

Japanese Unexamined Patent Publication No. 2006-299162 Japanese Unexamined Patent Publication No. 2008-68564

The present invention has been made in view of the above circumstances, and the problem to be solved thereof is that even if a high-performance inspection device is used, inspection accompanied by optical evaluation is easy while the inspection target member is still attached. It is an object of the present invention to provide a laminated polyester film and a surface protective film, which have good oligomer-sealing properties and are suitable as surface protective films for various members.

As a result of diligent studies in view of the above circumstances, the present inventor has found that a laminated polyester film having a specific configuration can easily solve the above problems, and has completed the present invention.

That is, the gist of the present invention is a base film which has a laminated structure of at least two polyester layers, and one surface layer (hereinafter, referred to as "surface layer A") is a polyester layer which does not substantially contain particles. A layer 1 having a cross-linking agent and / or a reaction product thereof formed on the surface layer A of the base film in an amount of 70% by weight or more and having a particle content of 0.1% by weight or more and less than 5% by weight. It resides in a laminated polyester film, which is characterized by having.

In one aspect of the present invention, the base film contains a titanium-based polymerization catalyst.
In one aspect of the present invention, the base film has a laminated structure of three or more layers having a polyester layer as an intermediate layer.

In one aspect of the present invention, a layer 2 containing a polyester resin and a cross-linking agent and / or a reaction product thereof is provided on the other surface layer (hereinafter referred to as “surface layer B”) of the base film.

In one aspect of the present invention, the adhesive layer is further provided on the layer 2.

In one aspect of the present invention, the pressure-sensitive adhesive layer is made of an acrylic pressure-sensitive adhesive.

The gist of the present invention also lies in a surface protective film made of such a laminated polyester film.

INDUSTRIAL APPLICABILITY According to the present invention, even if a high-performance inspection device is used, inspection with optical evaluation is easy and oligomer encapsulation is good in a state of being attached to the member to be inspected. A laminated polyester film and a surface protective film suitable as a surface protective film can be provided.
The laminated polyester film of the present invention is a surface protective film for various adherends such as synthetic resin plates, glass plates, metal plates, optical members, touch panels, automobile members, electrical / electronic members, building material members, stationery / office supply members, etc. Suitable for. When used for optical member applications that require a particularly high degree of visibility (for example, glass substrates, light diffusion films, liquid crystal displays, polarizing plates, retardation plates, light guide plates, prism plates, etc.) and touch panel applications, etc. Inspection with optical evaluation is possible (easy to inspect) with the surface protective film still attached, and the oligomer encapsulation property is good, and its industrial value is high.

Hereinafter, embodiments of the present invention will be described in detail.

The laminated polyester film of the present invention has a laminated structure of at least two polyester layers, and one surface layer (hereinafter, referred to as "surface layer A") is a base film which is a polyester layer containing substantially no particles. (Hereinafter, it may be referred to as "base film of the present invention") and contains 70% by weight or more of a cross-linking agent and / or a reaction product thereof formed on the surface layer A of the base film. It is characterized by having a layer 1 having a particle content of 0.1% by weight or more and less than 5% by weight.

<Base film>
The base film of the present invention has a laminated structure of at least two polyester layers. The base film of the present invention may have two or more polyester layers, and may have three layers, four layers or more, and is not particularly limited. The base film of the present invention may include a layer other than polyester. The layer other than polyester is not limited, and specific examples thereof include a polycarbonate layer, a polyamide layer, a polyolefin resin layer, an acrylic resin layer, and a polystyrene resin layer.
Among these, the base film is preferably formed of two or three polyester layers, and particularly preferably formed of three layers (two surface layers and an intermediate layer).
The base film of the present invention may be a non-stretched film (sheet) or a stretched film, but a stretched film is preferable, and a biaxially stretched film is more preferable.

The polyester used for the base film of the present invention may be a homopolyester or a copolymerized polyester. When it is made of homopolyester, it is preferably obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol. 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. Examples of typical polyesters include polyethylene terephthalate (PET) and the like. On the other hand, examples of the dicarboxylic acid component of the copolymerized polyester include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, sebacic acid, and oxycarboxylic acid, and examples of the glycol component include ethylene glycol and diethylene glycol. One or more of propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be mentioned. In any case, the polyester constituting the base film of the present invention is usually preferably 60 mol% or more, particularly preferably 80 mol% or more in an ethylene terephthalate unit.

In order to obtain the oligomer-sealing property which is the solution of the present invention, the polyester layer constituting the surface layer of the base film of the present invention has an oligomer (mainly ester cyclic trimer) content of 0.5% by weight or less. It is preferable to contain 80% by weight or more of a certain polyester. When the content of polyester having an oligomer content of 0.5% by weight or less is less than 80% by weight, the haze is significantly increased after the heat treatment step, and after processing, in terms of optical properties, for example, visibility. It may be unsuitable for optical members.

Further, it is more preferable that the base film of the present invention contains one or more of the titanium compound and / or the phosphorus compound in terms of reducing the oligomer content in the film. In this case, the preferable ranges of the titanium element content (Ti) and the phosphorus element content (P) in the polyester constituting the base film of the present invention are as follows.
0 <Ti ≦ 20 (ppm) ・ ・ ・ (1)
0 <P ≤ 20 (ppm) ... (2)
With respect to Ti, it is more preferably in the range of 2 to 10 ppm. If Ti exceeds the upper limit of the above formula (1), oligomers may be produced as a by-product in the step of melt-extruding the polyester chip, and a film having low oligomers and high transparency may not be obtained. It may be difficult to handle applications that place importance on. On the other hand, with respect to P, it is more preferably in the range of 5 to 15 ppm. If P exceeds the upper limit of the above formula (2), gelation may occur during polyester production, which may become a foreign substance and deteriorate the quality of the film, making it difficult to handle an inspection process involving optical evaluation, for example. ..
By simultaneously satisfying the above equations (1) and (2), it is possible to exert a remarkable effect on the reduction of the oligomer content in the polyester film.

The type of the titanium compound contained in the base film of the present invention is not particularly limited, but titanium-based polymerization catalysts such as tetraisopropyl titanate and tetrabutyl titanate are more preferable.
The type of phosphorus compound is also not particularly limited, but phosphoric acid esters such as ethyl acid phosphate, butyl acid phosphate, 2-ethylhexyl acid phosphate, and alkyl acid phosphate are more preferable.
The type and content ratio of the titanium compound and the phosphorus compound contained in the base film are preferably adjusted according to the type and amount of the catalyst used when producing the polyester used as the raw material of the base film.

The viscosity of the polyester constituting the base film of the present invention is not particularly limited, but the extreme viscosity measured by the method described in the section of Examples described later is 0.60 to 0.75 dl / g. In particular, it is preferably 0.60 to 0.70 dl / g. In order to keep the ultimate viscosity of the base film in the above range, it can be adjusted by the ultimate viscosity of polyester used as a raw material, the production conditions of the base film, and the like.

One surface layer (surface layer A) constituting the base film of the present invention, that is, the surface layer A on which the layer 1 described later is formed, substantially contains particles in order to facilitate an inspection involving an optical evaluation. do not do.

The term "substantially free of particles" as used in the present invention means that in the surface layer A, for example, in the case of inorganic particles, when the inorganic element is quantified by XRF (fluorescent X-ray) analysis, it is 50 ppm or less, preferably 10 ppm or less. , Most preferably defined as a particle content below the detection limit. This is because even if the particles are not intentionally contained in the surface layer A, the possibility of foreign matter being mixed from the outside is taken into consideration during the manufacturing process.

When the base film of the present invention is formed of two polyester layers, if at least one of them is the surface layer A, the other surface layer is not limited. That is, both surface layers may be composed of a layer corresponding to the surface layer A, but the other surface layer is preferably a layer corresponding to the surface layer B described later.
When the base film of the present invention is formed of three or more polyester layers, the surface layer is the same as that of the above two layers. When the base film has three or more layers, an intermediate layer exists, but the polyester layer forming the intermediate layer is arbitrary.
That is, the intermediate layer may contain particles or may have no particles, but it is preferable that the intermediate layer is a layer that does not substantially contain particles or has a low content of particles. In this case, the intermediate layer and the surface layer A have the same embodiment, but the intermediate layer may be a layer having a lower limit viscosity than the surface layer A, a layer not containing a titanium-based polymerization catalyst, or the lamination of the present invention. It can be differentiated from the surface layer A by using a raw material obtained by self-recycling the scraps of the polyester film.

It is preferable to add particles to the other surface layer (surface layer B) of the base film of the present invention, that is, the surface layer B on which the layer 2 described later is formed, mainly for the purpose of imparting slipperiness. The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness, and specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and magnesium phosphate. , Calcium, aluminum oxide, titanium oxide and the like. Further, heat-resistant organic particles described in Japanese Patent Publication No. 59-5216, Japanese Patent Application Laid-Open No. 59-217755, etc. may be used. Examples of other heat-resistant organic particles include thermosetting urea resin, thermosetting phenol resin, thermosetting epoxy resin, benzoguanamine resin and the like. Further, during the polyester manufacturing process, precipitated particles in which a part of a metal compound such as a catalyst is precipitated and finely dispersed can also be used.

The shape of the particles to be used is not particularly limited, and any of spherical, lumpy, rod-shaped, flat-shaped and the like may be used. Further, the hardness, specific gravity, color and the like are not particularly limited. Two or more kinds of these series of particles may be used in combination, if necessary.

The average particle size of the particles contained in the surface layer B is preferably in the range of 0.1 to 3.0 μm, more preferably 0. It is in the range of 1 to 1.0 μm. When the average particle size is less than 0.1 μm, the film surface may be too flat and the film winding property may be deteriorated. On the other hand, when the average particle size exceeds 3.0 μm, the presence of particles contained in the film may hinder the inspection process involving optical evaluation.

The particle content in the surface layer B is usually in the range of 0.001 to 3% by weight, preferably 0.01 to 2% by weight. If the particle content is less than 0.001% by weight, the slipperiness of the film may be insufficient, while if more than 3% by weight of particles are added, the transparency of the film is poor. It will be sufficient and may interfere with the inspection process involving optical evaluation.

The method of adding the particles to the surface layer B is not particularly limited, and a conventionally known method can be adopted. For example, particles can be added at any stage of producing the polyester constituting each layer, but are preferably added at the esterification stage or after the esterification reaction is completed in the polycondensation reaction step.
Further, a method of blending a slurry of particles dispersed in ethylene glycol or water with a polyester raw material using a kneaded extruder with a vent, or a method of blending dried particles with a polyester raw material using a kneading extruder. It can also be done by a method or the like.

In addition to the above-mentioned particles, various conventionally known additives such as antioxidants, antistatic agents, heat stabilizers, and lubricants are contained in each polyester layer constituting the base film of the present invention. Dyes, pigments and the like can be added.

The thickness of the base film of the present invention is not particularly limited as long as it can be formed as a film, but is preferably in the range of 12 to 250 μm and is preferably in the range of 25 to 125 μm for the purpose of use. Is more preferable.

The thickness of each polyester layer of the base film of the present invention is not particularly limited, but the thickness of the surface layers A and B is preferably 2 to 10 μm, particularly preferably 2 to 7 μm, respectively. When the thickness of the polyester layers of the surface layers A and B is not more than the above upper limit, for example, a larger amount of recycled raw materials and the like can be blended in the intermediate layer, which is effective in reducing the manufacturing cost. When the thickness is at least the above lower limit, the uniformity of the thickness of the polyester layer becomes good, which is preferable.

The preferred method for producing the base film of the present invention will be specifically described below, but the method for producing the base film of the present invention is not limited to the following production methods.

As a method for producing a base film of the present invention, a molten sheet extruded using an extruder having a plurality of dies using the polyester raw material described above is cooled and solidified with a cooling roll at 25 to 60 ° C. and not laminated. A method of obtaining a stretched sheet and biaxially stretching the sheet to obtain a biaxially stretched film is preferable. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and the electrostatic application adhesion method and / or the liquid coating adhesion method is preferably adopted. In order to stretch the obtained laminated unstretched sheet in the biaxial direction, first, the laminated 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 7.0 times, preferably 3.0 to 6.0 times. Then, it is stretched in a direction orthogonal to the stretching direction of the first stage, in which case the stretching temperature is usually 70 to 170 ° C., and the stretching ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6 times. It is 0.0 times. Then, heat treatment is subsequently performed at a temperature of 180 to 270 ° C. under tension or relaxation within 30% to obtain a laminated biaxially stretched oriented film. In the above stretching, a method of performing one-way stretching in two or more steps can also be adopted. In that case, it is preferable to finally set the draw ratios in the two directions within the above ranges.

Further, the base film of the present invention can also be produced by the simultaneous biaxial stretching method instead of the sequential biaxial stretching method described above. In the simultaneous biaxial stretching method, the laminated unstretched sheet is usually temperature-controlled at 70 to 120 ° C., preferably 80 to 110 ° C., in a mechanical direction (pick-up direction) and a width direction (direction orthogonal to the pick-up direction). It is a method of simultaneously stretching and orienting, and the stretching ratio is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area magnification. Then, the heat treatment is subsequently performed at a temperature of 170 to 250 ° C. under tension or relaxation within 30% to obtain a laminated biaxially stretched oriented film. As for the simultaneous biaxial stretching device that employs the above-mentioned stretching method, a conventionally known stretching method such as a screw method, a pantograph method, and a linear drive method can be adopted.

The layer 1 and the layer 2 described later may be formed by a so-called coating and stretching method (in-line coating) in which the film surface is treated during the above-mentioned stretching step. When the coating layer is provided on the polyester film by the coating and stretching method, the coating can be applied at the same time as stretching, and the thickness of the coating layer can be reduced according to the draw ratio, which is a suitable laminated polyester film as a surface protective film. Can be manufactured.

Further, in the base film of the present invention, in order to improve the coatability of the coating liquids 1 and 2 and the adhesion of the layers 1 and 2 described later, the film surface is chemically treated or corona discharged before the coating liquids 1 and 2 are applied. Treatment, plasma treatment, etc. may be performed.

<Layer 1>
Layer 1 is formed on the surface layer A of the base film of the present invention. The layer 1 contains a cross-linking agent and / or a reaction product thereof in an amount of 70% by weight or more and a particle content of 0.1% by weight or more in order to improve the oligomer-sealing property as a constituent member of the laminated polyester film. It is a layer of less than 5% by weight. This layer 1 contains a cross-linking agent of 70% by weight or more with respect to the non-volatile component, and the particle content in the non-volatile component is 0.1% by weight or more and less than 5% by weight of the coating liquid (hereinafter, “coating liquid 1”). It may be referred to as), preferably formed by coating, drying and curing. The layer 1 and the coating liquid 1 may contain other components as long as the gist of the present invention is not impaired.

In the present invention, the non-volatile component in the coating liquid 1 refers to the total of the components other than the solvent (including water) in the layer, and substantially refers to the layer 1 itself constituting the laminated polyester film of the present invention. As expected. The same applies to the coating liquid 2 described later.
The cross-linking agent contained in the coating liquid 1 is applied onto the base film, dried, and then undergoes a cross-linking reaction by energy such as light and heat. As a result, it is contained in the layer 1 as a crosslinked structure, that is, a reaction product of the crosslinked agent. Therefore, the content as a non-volatile component in the coating liquid 1 and the content as a reaction product in the layer 1 are substantially synonymous, and the same applies to the coating liquid 2 described later.

As the cross-linking agent, various known cross-linking agents can be used, and examples thereof include oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, and silane coupling compounds. Among these, an oxazoline compound is preferably used from the viewpoint of improving durability and adhesion, particularly when it is used for an application in which a functional layer is provided on the layer 1. Further, the melamine compound is preferably used from the viewpoint of preventing the precipitation of the oligomer on the film surface by heating and improving the durability and coatability of the layer 1.

As the oxazoline compound, a polymer containing an oxazoline group is particularly preferable, and it is produced by polymerization or copolymerization of an addition-polymerizable oxazoline group-containing monomer alone or with another monomer. Examples of the additive-polymerizable oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, and 2-isopropenyl-2-oxazoline. , 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. Among these, 2-isopropenyl-2-oxazoline is suitable because it is easily available industrially.

The other monomer may be a monomer copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and is not particularly limited. For example, alkyl (meth) acrylate (alkyl groups include methyl group, ethyl group, and n-propyl). (Meta) acrylic acid esters such as groups, isopropyl groups, n-butyl groups, isobutyl groups, t-butyl groups, 2-ethylhexyl groups, cyclohexyl groups); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid. , Crotonic acid, styrenesulfonic acid and unsaturated carboxylic acids such as salts thereof (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, (alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl Unsaturated amides such as groups (groups, 2-ethylhexyl groups, cyclohexyl groups, etc.); vinyl esters such as vinyl acetate and 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; α, β-unsaturated aromatic monomers such as styrene and α-methylstyrene can be mentioned, and one of them can be mentioned. Alternatively, two or more kinds of monomers can be used.

The amount of the oxazoline group of the oxazoline compound used in the coating liquid 1 is preferably in the range of 0.5 to 10 mmol / g, more preferably 3 to 9 mmol / g, and further preferably 5 to 8 mmol / g. By using the one in the above range, the durability of the formed coating film tends to be improved.

As the melamine compound, for example, an alkyrylated melamine derivative, a compound obtained by reacting an alkyrylated melamine derivative with an alcohol to partially or completely etherify, and a mixture thereof can be used. As the alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol and the like are preferably used. Further, the melamine compound may be either a monomer or a multimer of a dimer or more, or a mixture thereof may be used. Further, a melamine cocondensed with urea or the like can be used, or a catalyst can be used to increase the reactivity of the melamine compound.

Examples of the epoxy compound include epichlorohydrin and ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A and the like, and examples thereof include polyepoxy compounds, diepoxy compounds, monoepoxy compounds and glycidylamine compounds.
Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyltris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, and trimethylolpropane. Examples thereof include polyglycidyl ether. Examples of the diepoxy compound include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, and polypropylene glycol di. Examples thereof include glycidyl ether and polytetramethylene glycol diglycidyl ether.
Examples of the monoepoxy compound include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether and the like.
Examples of the glycidylamine compound include N, N, N', N'-tetraglycidyl-m-xylylenediamine, 1,3-bis (N, N-diglycidylamino) cyclohexane and the like.

The isocyanate-based compound is a compound having an isocyanate derivative structure typified by isocyanate or blocked isocyanate. Examples of the isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyldiisocyanate, phenylenedi isocyanate and naphthalenedi isocyanate, and aromatic rings such as α, α, α', α'-tetramethylxylylene diisocyanate. Aliphatic isocyanates such as aliphatic isocyanates, methylene diisocyanates, propylene diisocyanates, lysine diisocyanates, trimethylhexamethylene diisocyanates, hexamethylene diisocyanates, cyclohexane diisocyanates, methylcyclohexane diisocyanates, isophorone diisocyanates, methylenebis (4-cyclohexyl isocyanates), isopropyridene dicyclohexyldiisocyanates and the like. The alicyclic isocyanate of the above is exemplified. Further, polymers and derivatives such as burettes, isocyanurates, uretdiones, and carbodiimide-modified compounds of these isocyanates can also be mentioned. These may be used alone or in combination of two or more. 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, phenolic compounds such as heavy sulfites, phenol, cresol and ethylphenol, and alcoholic compounds 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 and dodecyl mercaptan, ε-caprolactam, δ-valerolactam, etc. Examples thereof include lactam compounds, amine compounds such as diphenylaniline, aniline, and ethyleneimine, acetanilide, acid amide compounds of acetate amide, formaldehyde, acetoaldoxime, acetone oxime, methyl ethyl ketone oxime, and oxime compounds such as cyclohexanone oxime. These may be used alone or in combination of two or more.

Further, the isocyanate-based compound in the present invention may be used alone, or may be used as a mixture or a bond with various polymers. It is preferable to use a mixture or a bond with a polyester resin or a urethane resin in the sense of improving the dispersibility and crosslinkability of the isocyanate compound.

The carbodiimide-based compound is a compound having one or more carbodiimide structures in the molecule, but a polycarbodiimide-based compound having two or more carbodiimide structures in the molecule is more preferable for better adhesion and the like.

The carbodiimide-based compound can be synthesized by a conventionally known technique, and a condensation reaction of a diisocyanate compound is generally used. The diisocyanate compound is not particularly limited, and any aromatic or aliphatic type can be used. Specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylenedi isocyanate, naphthalenedi isocyanate, hexa. Examples thereof include methylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexanediisocyanate, methylcyclohexanediisocyanate, isophorone diisocyanate, dicyclohexyldiisocyanate, and dicyclohexylmethane diisocyanate.

The content of the carbodiimide group contained in the carbodiimide-based compound is a carbodiimide equivalent (weight [g] of the carbodiimide compound for giving 1 mol of the carbodiimide group), and is usually 100 to 1000, preferably 250 to 700, and more preferably 300. It is in the range of ~ 500. By using the one in the above range, the durability of the formed coating film tends to be improved.

Further, in order to improve the water solubility and water dispersibility of the polycarbodiimide-based compound and the like, a surfactant may be added to the coating liquid 1 as long as the effect of the present invention is not lost, and the polyalkylene oxide and the dialkylaminoalcohol may be added. A hydrophilic monomer such as a quaternary ammonium salt or a hydroxyalkyl sulfonate may be added and used.

These cross-linking agents may be used alone or in combination of two or more types, but by combining two or more types, the adhesion between layer 1 or layer 2 and the functional layer, which was difficult to achieve at the same time, and after heating It is possible to improve the precipitation prevention property of the oligomer. Among them, a combination of an oxazoline compound effective for improving the adhesion between the layer 1 or the layer 2 and the functional layer and a melamine compound having a good anti-precipitation property of the oligomer after heating is particularly preferable and preferable.

Further, in order to further improve the adhesion between the layer 1 or the layer 2 and the functional layer, it is effective to combine three types of cross-linking agents. As a combination of three or more kinds of cross-linking agents, it is optimal to select a melamine compound as one of the cross-linking agents, and as a combination with the melamine compound, an oxazoline compound and an epoxy compound, and a carbodiimide-based compound and an epoxy compound are used. Especially preferable.

In addition, these cross-linking agents are used in the design of reacting in the drying process and the film forming process to improve the performance of the layer 1. It can be inferred that an unreacted product of these cross-linking agents, a compound after the reaction (reaction product), or a mixture thereof is present in the formed layer 1.

The content of the cross-linking agent with respect to the non-volatile component in the coating liquid 1, that is, the content of the cross-linking agent and / or the reaction product thereof in the layer 1 is usually 70% by weight or more, preferably 80% by weight or more, more preferably 90. It is more than% by weight. When the content of the cross-linking agent in the coating liquid 1, that is, the content of the cross-linking agent and / or the reaction product thereof in the layer 1 is less than 70% by weight, the precipitation of the oligomer after heating cannot be effectively suppressed. There is.
On the other hand, the upper limit of the content of the cross-linking agent and / or the reaction product thereof in the layer 1 is preferably 99.9% by weight or less, more preferably 99.5% by weight or less, still more preferably 99% by weight or less.

When a melamine compound is selected as one of the cross-linking agents from the viewpoint of preventing the precipitation of the oligomer after heating, the ratio of the melamine compound to the total non-volatile components in the coating liquid 1, that is, the melamine compound in the layer 1 and / or its The content of the reaction product is usually in the range of 5 to 95% by weight, preferably in the range of 15 to 80% by weight, and particularly preferably in the range of 30 to 65% by weight. When the ratio of the melamine compound (and / or its reaction product) is less than the above lower limit, the precipitation of the oligomer after heating may not be effectively suppressed. If the proportion of the melamine compound (and / or its reaction product) exceeds the above upper limit, the coating appearance may be deteriorated.

When the oxazoline compound and the epoxy compound are used in combination with the melamine compound as the cross-linking agent, the ratio of the oxazoline compound to the total non-volatile components in the coating liquid 1, that is, the content of the oxazoline compound and / or its reaction product in the layer 1. The amount is in the range of 15 to 70% by weight, preferably 30 to 60% by weight, and the ratio of the epoxy compound to the total non-volatile components in the coating liquid 1, that is, the epoxy compound in the layer 1 and / or its reaction formation. The content of the compound is preferably in the range of 15 to 70% by weight, preferably in the range of 30 to 60% by weight.
If the proportion of the oxazoline compound (and / or its reaction product) is less than the above lower limit, it may not be possible to effectively suppress the precipitation of the oligomer after heating. If the proportion of the oxazoline compound (and / or its reaction product) exceeds the above upper limit, the coating appearance may deteriorate. Further, when the ratio of the epoxy compound (and / or its reaction product) is less than the above lower limit, the adhesion of the coating film to the base film may be insufficient. If the proportion of the epoxy compound (and / or its reaction product) exceeds the above upper limit, the coating appearance may deteriorate.
When a carbodiimide compound and an epoxy compound are used in combination with a melamine compound as a cross-linking agent, the ratio of the carbodiimide compound to all the non-volatile components in the coating liquid 1, that is, the carbodiimide compound in the layer 1 and / or the reaction formation thereof. The content of the substance is in the range of 15 to 70% by weight, preferably 30 to 60% by weight, and the ratio of the epoxy compound to the total non-volatile components in the coating liquid 1, that is, the epoxy compound and / or the epoxy compound in the layer 1. The content of the reaction product is preferably in the range of 15 to 70% by weight, preferably in the range of 30 to 60% by weight.
When the ratio of the carbodiimide-based compound (and / or its reaction product) is less than the above lower limit, the precipitation of the oligomer after heating may not be effectively suppressed. If the proportion of the carbodiimide compound (and / or its reaction product) exceeds the above upper limit, the coating appearance may be deteriorated. Further, when the ratio of the epoxy compound (and / or its reaction product) is less than the above lower limit, the adhesion of the coating film to the base film may be insufficient. If the proportion of the epoxy compound (and / or its reaction product) exceeds the above upper limit, the coating appearance may deteriorate.

The coating liquid 1 may contain a component for promoting cross-linking, for example, a cross-linking catalyst, in addition to these cross-linking agents.

Further, in order to form the layer 1, a polymer can be used in combination in order to improve the appearance of the coating and to improve the adhesion when the functional layer is formed on the layer 1.

Specific examples of the polymer include polyester resin, acrylic resin, urethane resin, polyvinyl (polyvinyl alcohol and the like), polyalkylene glycol, polyalkyleneimine, methyl cellulose, hiroxycellulose, 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 the adhesion to various functional layers.

When a polymer is used, if the content of the polymer in the layer 1 is large, the precipitation prevention property of the oligomer after heating may deteriorate. Therefore, the content of the polymer is usually 29 with respect to the non-volatile component of the coating liquid 1. It is 9.9% by weight or less, preferably 20% by weight or less, and more preferably 10% by weight or less. If the polymer content of the coating liquid 1 exceeds the above range, it may not be possible to effectively suppress the precipitation of oligomers after heating. In order to effectively obtain the effect of improving the adhesion by using the polymer, the content of the polymer in the coating liquid 1 is preferably 5% by weight or more with respect to the non-volatile component. That is, the content of the polymer in the layer 1 is usually 29.9% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, and preferably 5% by weight or more.

Normally, polyester film has strong self-adhesion, so it is difficult for a film without any application to stick to it when it is wound into a roll, causing wrinkles or scratches, or to unwind it from the roll. .. Therefore, in general, the surface is roughened by adding particles to the surface layer of the film to ensure slipperiness. However, according to the present inventor, when a laminated polyester film is used as a surface protective film capable of inspecting an adherend for foreign matter, a conventional surface protective film is particularly used for high-precision inspection. It turned out that sufficient accuracy could not be obtained.
As a result of the examination, if the accuracy of the foreign matter inspection is improved, the particles added for the above purpose may cause slight non-uniformity of the film thickness, slight decrease in transparency, and the particles themselves may be mistaken for foreign matter. It was found to affect the inspection accuracy. It was also found that since the surface layer of the base film is relatively thick, even if particles are added to roughen the surface, the particles are buried in the surface layer and are not effective.

Therefore, if the surface layer A does not substantially contain particles and a predetermined amount of particles are contained in the layer 1 formed on the surface layer A, the inspection is performed with high accuracy without impairing the handleability of the film. It was found that it is possible to secure sex. If the layer 1 is provided by a method such as coating, it can be formed thinner than the surface layer of the base film, so that the added particles can directly contribute to the surface roughness and the laminated polyester film. It is also possible to make the thickness of the particles uniform.

Furthermore, surprisingly, if a method is adopted in which the surface layer A does not substantially contain particles and the particles are contained in the layer 1, the surface layer particles are mistakenly recognized as foreign substances even when performing a high-precision foreign matter inspection. It turned out that the particles were suppressed. It is considered that the reason is that if the particles are contained in the layer 1, it is possible to design such that the particles having a small particle size are contained in the minimum addition amount.
Further, as compared with the case where the particles are contained in the surface layer A, if the particles are contained in the layer 1, the effect of suppressing the precipitation of the oligomer can be expected in combination with the cross-linking agent. Therefore, by including the particles in the surface layer A, it is possible to suppress the misidentification that the oligomer precipitated from the surface protective film is a foreign substance of the adherend.

It was also found that the surface layer B does not have an adverse effect on high-precision foreign matter inspection even if it is designed as a layer containing particles as in the conventional case. It is considered that this is because, for example, if the surface layer B is covered with a thick adhesive layer or the like, the surface roughness of the surface layer B disappears, and therefore the hindrance to the inspectability due to the reflection of light or the like disappears. Therefore, if the surface layer B contains particles, for example, even if the base film is manufactured in advance and the layer 1 is applied in a later step, the base film is rolled into a roll. There is no problem in turning and unwinding.

In the present invention, the particle content in the layer 1 is 0.1% by weight or more and less than 5% by weight. By satisfying this range, good transparency can be ensured, which is suitable for optical applications such as inspection using transmitted light. When the particle content in the layer 1 is 5% by weight or more, the visibility is deteriorated when accompanied by an optical evaluation at a high level. The particle content in the layer 1 is preferably 3% by weight or less, while the content of the particles in the layer 1 is 0.5% by weight or more from the viewpoint of blocking and slipperiness improving effect by containing the particles. It is preferably 1% by weight or more, and more preferably 1% by weight or more. Therefore, the coating liquid 1 used for forming the layer 1 preferably contains 0.1% by weight or more and less than 5% by weight of particles with respect to the non-volatile component, and preferably contains 1 to 3% by weight.

The average particle size of the particles used in layer 1 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 film transparency. Further, the lower limit is preferably 0.01 μm or more, more preferably 0.03 μm or more in order to more effectively improve the slipperiness. Here, the average particle size of the particles is "d50" measured by the method described in the section of Examples described later.

The relationship between the average particle size d (μm) of the particles used in the layer 1 and the thickness t (μm) of the layer 1 is preferably 0.3 ≦ t / d ≦ 1.5, and above all, 0.5 ≦. It is more preferable that t / d or t / d ≦ 1.2.
When t / d is not more than the above upper limit value, the particles have a significant size with respect to the thickness of the surface layer 1, so that the slipperiness of the film can be maintained and good handling can be maintained. .. Further, since the particle size is not too small, it is not necessary to increase the particle content in order to improve the slipperiness of the film, and the transparency can be maintained. Therefore, when the laminated polyester film of the present invention is used as a surface protective film, high-precision inspection is possible. On the other hand, when t / d is at least the above lower limit value, the thickness of the surface layer 1 is not too thin, and it is possible to suppress the generation of high protrusions on the surface. Therefore, it is possible to prevent the particles from being mistakenly recognized as foreign substances at the time of inspection due to reflection by protrusions or the like, and further to prevent the particles from falling off from the surface layer 1.

Specific examples of the particles used in the layer 1 include those exemplified as the particles contained in the surface layer B described above, such as silica, alumina, kaolin, calcium carbonate, and organic particles.

Further, as long as the gist of the present invention is not impaired, a defoaming agent, a coatability improving agent, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant are necessary for forming the layer 1. , Foaming agents, dyes, pigments and other additives can also be used in combination, and therefore these additives may be blended in the coating liquid 1.

The layer 1 is preferably coated on the surface layer A surface of the base film of the present invention with a coating liquid 1 containing a cross-linking agent and particles, and if necessary, further containing a polymer or the like, and then dried and cured. It is formed.

As a method of applying the coating liquid 1 to the base film of the present invention, for example, an air doctor coat, a blade coat, a rod coat, a bar coat, a knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a transfer roll coat, and a gravure Conventionally known coating methods such as a coat, a kiss roll coat, a cast coat, a spray coat, a curtain coat, a calendar coat, and an extrusion coat can be used.
It is particularly preferable that the layer 1 is provided by an in-line coating in which the coating liquid 1 is applied during the film formation of the base film of the present invention.

When the layer 1 is provided on the polyester film being formed by in-line coating, the solid content concentration is adjusted to about 0.1 to 50% by weight by using the above-mentioned cross-linking agent, particles, etc. as an aqueous solution or an aqueous dispersion. It is preferable to apply the coated liquid 1 on the polyester film being formed. In this case, a small amount of an organic solvent may be added to the coating liquid 1 for the purpose of improving the dispersibility in water, improving the film-forming property, etc., as long as the gist of the present invention is not impaired. Only one kind of organic solvent may be used, and two or more kinds may be used as appropriate.

The drying and curing conditions of the coating film of the coating liquid 1 formed on the polyester film are not particularly limited. For example, when the coating layer is provided by offline coating, it is usually at 80 to 200 ° C. for 3 to 40 seconds. It is preferable to perform the heat treatment 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 the heat treatment at 70 to 280 ° C. for 3 to 200 seconds as a guide.

The thickness of the layer 1 is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.5 μm, and more preferably 0.005 to 0.5 μm as the thickness of the layer 1 of the laminated polyester film of the present invention finally obtained. It is in the range of 0.01 to 0.2 μm. When the thickness of the layer 1 is thinner than 0.003 μm, it may not be possible to sufficiently prevent the precipitation of the oligomer from the substrate film of the present invention. On the other hand, if it is thicker than 1 μm, problems such as deterioration of the appearance of layer 1 and easy blocking may occur. The thickness of the layer 1 is the thickness of the resin portion other than the particles when the cross section is observed with an electron microscope. The same applies to layer 2.

<Layer 2>
An arbitrary layer can be provided on the surface layer (surface layer B) on the side opposite to the surface layer A of the base film of the present invention, but for the purpose of improving the adhesiveness to the adhesive layer, the polyester resin and the cross-linking agent and / or the same thereof. It is preferable to form a layer 2 containing a reaction product, and the layer 2 is preferably formed by applying, drying and curing a coating liquid 2 containing a polyester resin and a cross-linking agent.

The polyester resin contained in the layer 2 is preferably a linear polyester containing a dicarboxylic acid component and a glycol component as constituent components. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, and phenylindandicarboxylic acid. Examples thereof include dimer acid and the like. Two or more of these components can be used. Further, along with these components, a small proportion of unsaturated polybasic acids such as maleic acid, fumaric acid, itaconic acid and the like, p-hydroxybenzoic acid, p- (β-hydroxyethoxy) benzoic acid and the like. It can also be used. The ratio of the unsaturated polybasic acid component and the hydroxycarboxylic acid component to all the constituent components of the polyester resin is preferably 10 mol% or less, more preferably 5 mol% or less.

The glycol components include ethylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylylene glycol, and dimethylolpropionic acid. , Glycerin, trimethylolpropane, poly (ethyleneoxy) glycol, poly (tetramethyleneoxy) glycol, alkylene oxide adduct of bisphenol A, alkylene oxide adduct of hydrogenated bisphenol A and the like can be exemplified. Two or more of these can also be used.

Among such glycol components, ethylene glycol and bisphenol A ethylene oxide adducts and propylene oxide adducts and 1,4-butanediol are preferable, and ethylene glycol and bisphenol A ethylene oxide adducts and propylene oxide adducts are preferable.

Further, it is more preferable that the layer 2 contains at least one kind of polyester resin having a sulfonic acid group or a sulfonic acid base in order to facilitate water dispersion or water solubility of the polyester resin used.

Examples of the polyester resin having a sulfonic acid group or a sulfonic acid base include 5-sodium sulfoisophthalic acid, 5-ammonium sulfoisophthalic acid, 4-sodium sulfoisophthalic acid, 4-methylammonium sulfoisophthalic acid, and 2-sodium sulfoisophthalic acid. , 5-Pultanic sulfoisophthalic acid, 4-potassium sulfoisophthalic acid, 2-potassium sulfoisophthalic acid, sulfonic acid alkali metal salt system such as sodium sulfosuccinic acid or sulfonic acid group or sulfonic acid base such as sulfonic acid amine salt system compound. It is preferable to use the dicarboxylic acid component having a dicarboxylic acid component as a copolymerization component in an amount of about 2 to 5 mol% with respect to the linear polyester.

In the polyester resin constituting the layer 2, the glass transition temperature (Tg) is preferably 40 ° C. or higher, more preferably 45 ° C. or higher. When the Tg of this polyester resin is less than 40 ° C., if the thickness of the layer 2 is increased for the purpose of improving the adhesiveness, problems such as easy blocking may occur.

The content of the polyester resin in the layer 2 is preferably 50% by weight or more, more preferably 60% by weight or more, from the viewpoint of improving the adhesiveness. On the other hand, from the viewpoint of combined use with other components, it is preferably 90% by weight or less, more preferably 80% by weight or less. Therefore, it is preferable that the coating liquid 2 contains 50 to 90% by weight of the polyester resin, particularly 60 to 80% by weight, in the non-volatile component thereof.

As the cross-linking agent constituting the layer 2, various known cross-linking agents described above can be used as the cross-linking agent contained in the coating liquid 1 used for forming the layer 1, and for example, an oxazoline compound, a melamine compound, an epoxy compound, and the like. Examples thereof include isocyanate-based compounds, carbodiimide-based compounds, and silane coupling compounds, and specific examples thereof, suitable compounds, and the like are as described in the above-mentioned layer 1 section. Among these, particularly when used for the purpose of providing a functional layer on the layer 2, an oxazoline compound and an epoxy compound are preferably used from the viewpoint of improving durability adhesion. Further, from the viewpoint of film-forming property, an epoxy compound is most preferable.

In the coating liquid 2, as in the coating liquid 1, one type of cross-linking agent may be used alone, or two or more types may be used in combination. Further, it may contain a component for promoting cross-linking, for example, a cross-linking catalyst or the like.

The content of the cross-linking agent and / or the reaction product thereof in the layer 2 is preferably 20% by weight or more, more preferably 30% by weight or more, from the viewpoint of improving the durability during the heat treatment after the layer is formed. On the other hand, from the viewpoint of combined use with other components, it is preferably 70% by weight or less, and more preferably 50% by weight or less. Therefore, it is preferable that the coating liquid 2 contains 20 to 70% by weight of the cross-linking agent, particularly 30 to 50% by weight, in the non-volatile component thereof.

Further, the layer 2 contains a polymer other than the polyester resin to the extent that the gist of the present invention is not impaired in order to improve the appearance and the adhesion when the adhesive layer is formed on the layer 2. May be good. Specific examples of the polymer other than the polyester resin that may be contained in the layer 2 include acrylic resin, polyurethane resin, polyvinyl (polyvinyl alcohol, etc.), polyalkylene glycol, polyalkyleneimine, methyl cellulose, hiroxycellulose, starches, and the like. Can be mentioned. Among these, it is preferable to contain an acrylic resin or a polyurethane resin from the viewpoint of improving the adhesiveness.

When the layer 2 contains a polymer other than the polyester resin, the content of the other polymer in the layer 2 is such that the polyester resin and the polyester resin have a sufficient effect of improving the adhesiveness by containing the other polymer. From the viewpoint of ensuring the required amount of the cross-linking agent and / or the reaction product thereof, it is preferably 5 to 20% by weight, particularly preferably 5 to 10% by weight. Therefore, it is preferable that the coating liquid 2 contains 5 to 20% by weight of other polymers, particularly 5 to 10% by weight, in the non-volatile component thereof.

Further, the layer 2 may contain particles for the purpose of blocking and improving slipperiness, as in the layer 1. Examples of the particles used for the layer 2 include the same particles as those described above as the particles used for the layer 1 and the surface layer B, and the average particle size thereof and specific examples of preferable particles are also the same.

When the layer 2 contains particles, the content of the particles in the layer 2 is preferably 1 to 10% by weight, more preferably 3 to 6 from the viewpoint of achieving both blocking, improving slipperiness and transparency. It is% by weight. Therefore, the coating liquid 2 preferably contains 1 to 10% by weight, particularly 3 to 6% by weight, of particles in the non-volatile component.

Further, to the extent that the gist of the present invention is not impaired, a defoaming agent, a coatability improving agent, a thickener, an organic lubricant, an antistatic agent, an ultraviolet absorber, and an antioxidant are necessary for forming the layer 2. , Foaming agents, dyes, pigments and other additives can also be used in combination, and therefore these additives may be added to the coating liquid 2.

The layer 2 is preferably coated with a coating liquid 2 containing a polyester resin, a cross-linking agent, and other polymers and particles used as necessary on the surface layer B surface of the base film of the present invention, and then dried and cured. It is formed by.
The method for forming the layer 2 in this case is the same as the method for forming the layer 1 described above, and the preferred conditions thereof are also the same.

When the layer 1 and the layer 2 are provided by in-line coating, for example, the coating liquid 1 is applied to one surface of the unstretched polyester film being formed, the coating liquid 2 is applied to the other surface, and then biaxial stretching is performed. The coating liquid 1 may be applied to one surface of the polyester film after the treatment or the uniaxial stretching treatment, the coating liquid 2 may be applied to the other surface, and then the stretching treatment may be performed. In this case, the coating film is dried and cured by heating during the stretching treatment or in the heat treatment step thereafter.

The thickness of the layer 2 is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.5 μm, more preferably 0.005 to 0.5 μm, as the thickness of the layer 2 on the finally obtained base film of the present invention. Is in the range of 0.01 to 0.2 μm. If the thickness of the layer 2 is thinner than 0.003 μm, the adhesiveness may be insufficient. If it is thicker than 1 μm, problems such as deterioration of the appearance of layer 2 and deterioration of blocking property may occur.

<Adhesive layer>
The adhesive layer of the laminated polyester film of the present invention, which is suitably used as a surface protective film, will be described below.
The adhesive layer is preferably provided on the layer 2 provided on one surface of the laminated polyester film of the present invention.

The adhesive layer means a layer composed of an adhesive material, and as the adhesive material, a silicone-based adhesive, an acrylic adhesive, etc. have been conventionally used as long as the gist of the present invention is not impaired. Known materials can be used. Among them, acrylic pressure-sensitive adhesives are preferable because they have a wide range of adjustment of pressure-sensitive adhesive properties and are widely used.
The case where the acrylic adhesive is used will be described below.

The acrylic pressure-sensitive adhesive means a pressure-sensitive adhesive containing an acrylic polymer formed as an essential monomer component of an acrylic monomer as a base polymer. The acrylic polymer contains a (meth) acrylic acid alkyl ester having a linear or branched alkyl group and / or a (meth) acrylic acid alkoxyalkyl ester 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 by using a (meth) acrylic acid alkyl ester having a linear or branched alkyl group and an acrylic acid alkoxyalkyl ester as an essential monomer component.

Further, as the monomer component forming the acrylic polymer which is the base polymer in the adhesive layer, a polar group-containing monomer, a polyfunctional monomer and other copolymerizable monomers are used as the copolymerizable monomer component. It may be included.

The above-mentioned "(meth) acrylic" means "acrylic" and / or "methacrylic", and the same applies to the others. Further, although not particularly limited, the content of the acrylic polymer as the base polymer in the pressure-sensitive adhesive layer according to the present invention is preferably 60% by weight or more, more preferably 60% by weight, based on the total weight (100% by weight) of the pressure-sensitive adhesive layer. Is 80% by weight or more.

The adhesive layer according to the present invention may contain a cross-linking agent, a cross-linking accelerator, a tackifier (for example, a rosin derivative resin, a polyterpene resin, a petroleum resin, an oil-soluble phenol resin, etc.), an antiaging agent, and a filler, if necessary. , Colorants (pigments, dyes, etc.), UV absorbers, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, antistatic agents, etc., as required within the scope of the present invention. Can be used.

For example, by blending the above-mentioned cross-linking agent, the gel fraction of the pressure-sensitive adhesive layer can be controlled by cross-linking the base polymer of the pressure-sensitive adhesive layer. Examples of the cross-linking agent include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, and melamine-based cross-linking agents exemplified as the cross-linking agent used for the above-mentioned layers 1 and 2, among which isocyanate-based cross-linking agents and epoxy-based cross-linking agents are used. It can be suitably used. Further, the cross-linking agent may be used alone or in combination of two or more. The cross-linking agent is preferably used in an amount of about 1 to 20 parts by weight based on 100 parts by weight of the base polymer.

The pressure-sensitive adhesive layer can be formed by applying a pressure-sensitive adhesive composition containing the above-mentioned acrylic pressure-sensitive adhesive or the like on the layer 2 of the laminated polyester film of the present invention and drying it.

The thickness of the adhesive layer (after drying) is preferably in the range of 10 to 100 μm, preferably 20 to 50 μm. If the thickness of the adhesive layer (after drying) is less than 10 μm, it may be difficult to obtain the desired adhesive force. On the other hand, if the thickness of the adhesive layer (after drying) exceeds 100 μm, the adhesive layer may not be sufficiently cured, and problems such as deterioration of workability may occur.

<Preferable physical characteristics of laminated polyester film>
Regarding the laminated polyester film (after forming the layer 1 and the layer 2) of the present invention, the haze measured by the method described in the section of Examples below is preferably 2% or less, more preferably 1% or less, particularly. It is preferably 0.6% or less, and most preferably 0.5% or less. If the haze of the laminated polyester film exceeds 2%, it may cause a problem when used as a constituent unit of the surface protective film for an inspection involving optical evaluation.

Further, with respect to the laminated polyester film (after formation of layer 1 and layer 2) of the present invention, the amount of change in film haze in the heat treatment (150 ° C., 90 minutes) of the surface of layer 1 measured by the method described in the section of Examples described later. (ΔH) is preferably 1.0% or less, more preferably 0.7% or less, still more preferably 0.3% or less. Various members may be heat-treated while being protected by a surface protective film or exposed to a high temperature atmosphere, but if ΔH exceeds 1.0%, the haze of the surface protective film due to the precipitation of oligomers As the temperature rises, the visibility deteriorates, which may be unsuitable for applications that require a high degree of visibility for inspections involving optical evaluation, such as touch panels.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

[Evaluation of physical properties / characteristics]
In the following, various physical properties and characteristics are measured or defined as follows.

(1) Measurement of extreme viscosity (dl / g) of polyester 1 g of polyester from which particles contained in polyester have been removed is precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added and dissolved. And measured at 30 ° C.

(2) Measurement of average particle size (d50) of particles The particle size of the integrated volume fraction of 50% in the equivalent spherical distribution measured using a centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type, manufactured by Shimadzu Corporation). The average particle size was d50.

(3) Measurement of Ester Cyclic Trimer (oligomer) Content in Polyester Raw Material About 200 mg of polyester raw material is weighed, and 2 ml of a mixed solvent having a volume ratio of chloroform / HFIP (hexafluoro-2-isopropanol) of 3: 2 is used. Dissolved in. After dissolution, 20 ml of chloroform was added, and then 10 ml of methanol was added little by little. The precipitate was removed by filtration, and the precipitate was washed with a mixed solvent having a volume ratio of chloroform / methanol of 2: 1 to recover the filtrate and washing liquid, concentrated by an evaporator, and dried. After dissolving the dry matter in 25 ml of DMF (dimethylformamide), this solution was supplied to liquid chromatography (“LC-7A”, manufactured by Shimadzu Corporation) to determine the content of the ester cyclic trimer in DMF. This value was divided by the amount of the polyester raw material dissolved in the chloroform / HFIP mixed solvent to obtain the ester cyclic trimer content (% by weight). The content of the ester cyclic trimer in the DMF was determined from the peak area ratio of the standard sample peak area and the measured sample peak area (absolute calibration curve method).
The standard sample was prepared by accurately weighing the pre-prepared ester cyclic trimer and dissolving it in the accurately weighed DMF.
The measurement conditions of the liquid chromatograph were as follows.
"Measurement condition"
Mobile phase A: Acetonitrile Mobile phase B: 2 wt% acetic acid aqueous solution Column: "MCI GEL ODS 1HU" manufactured by Mitsubishi Chemical Corporation
Column temperature: 40 ° C
Flow rate: 1 ml / min Detection wavelength: 254 nm

(4) Measuring the thickness of each layer of the laminated polyester film (base film) After fixing the sample film pieces before forming the adhesive layer to the stage with epoxy resin, cut them with a microtome, and take a cross section of the film into a transmission electron micrograph. I observed it. Two of the cross sections are almost parallel to the film surface, and the interface is observed by light and dark. The distance between the two interfaces and the film surface was measured from 10 photographs, and the average value was taken as the layer thickness.

(5) Measurement of the amount of metal elements and the amount of phosphorus elements in the film Using a fluorescent X-ray analyzer (“XRF-1500”, manufactured by Shimadzu Corporation), under the conditions shown in Table 1 below, simply by the film FP method. The amount of elements in the sample film (film after layer 1 and layer 2 formation) before the formation of the adhesive layer was determined by sheet measurement. The detection limit by this method is usually about 1 ppm.

(6) Haze (transparency) evaluation of film The sample film (film after layer 1 and layer 2 formation) before forming the adhesive layer is a haze meter "HM-150" (manufactured by Murakami Color Technology Laboratory) according to JIS K7136. The haze was measured by. After the measurement, transparency was evaluated according to the following criteria.
"criterion"
A: Haze is 0.5% or less B: Haze is more than 0.5% and 1.0% or less C: Haze is more than 1.0% and 2.0% or less D: Haze is more than 2.0%

(7) Heat treatment of film The measurement surface of the sample was exposed and fixed on top of Kent paper, and left at 150 ° C. for 90 minutes in a nitrogen atmosphere for heat treatment.

(8) Evaluation of film haze change amount (ΔH) (oligomer encapsulation) due to heat treatment Opposite to the surface of the sample film (film after layer 1 and layer 2 formation) provided with layer 1 before the formation of the adhesive layer. A coating agent having the following coating agent composition was applied to the side surface so that the thickness after curing was 3 μm, and dried in a hot air drying oven set at 80 ° C. for 1 minute. Next, using a high-pressure mercury lamp with an energy of 120 W / cm, irradiation was performed at an irradiation distance of 100 mm for about 7 seconds, curing was performed at 110 mJ / cm ² , and heat treatment was performed on the film to cause disturbance due to oligomer precipitation from the opposite surface. A laminated sample film provided with an active energy ray-curable resin layer for preventing factors was obtained.
<< Coating agent composition >>
A coating agent obtained by mixing "Shikou 7600B" manufactured by Nippon Synthetic Chemical Industry Co., Ltd. and "Irgacure 651" manufactured by Ciba Specialty Chemicals Co., Ltd. at a weight ratio of 100/5 and diluting them to a concentration of 30% by weight with methyl ethyl ketone. Haze was measured by the method of item (6) (Haze 1).
Next, the surface of the laminated sample film opposite to the active energy ray-curable resin layer was used as the measurement surface, and after heating by the method of item (7), the haze was measured by the method of item (6) (haze 2).
ΔH was calculated by the following formula and evaluated according to the following criteria.
ΔH = (Haze 2)-(Haze 1)
The lower the ΔH, the less the precipitation of the oligomer due to the high temperature treatment, and the better.
"criterion"
A: ΔH is 0.3% or less (especially good)
B: ΔH exceeds 0.3% and 0.7% or less (good)
C: ΔH exceeds 0.7% and 1.0% or less (may cause practical problems)
D: ΔH exceeds 1.0% (there is a practical problem)

(9) Evaluation of Adhesiveness with Adhesive Layer A pressure-sensitive adhesive layer composed of the following acrylic pressure-sensitive adhesive composition is applied onto layer 2 of the sample film (film after layer 1 and layer 2 formation) before the pressure-sensitive adhesive layer is formed. The film was applied using a baker-type applicator so that the amount (before drying) was 2 mil, and was heat-treated at 150 ° C. for 3 minutes in a hot air circulation furnace to prepare a sample film with an adhesive layer. The adhesive layer side of the sample film with the adhesive layer was overlapped with an untreated PET film (thickness 188 μm) and bonded with a 2 kg rubber roller. Next, the laminated body was cut into a size of 50 mm × 300 mm, and the peeling force after being left at room temperature for 1 hour was measured. The peeling force was 180 ° peeled under the condition of a tensile speed of 300 mm / min using a tensile tester (“Intesco model 2001 type”, manufactured by Intesco), and the adhesiveness was evaluated according to the following criteria.
《Adhesive composition》
Main agent: AT352 (manufactured by Saiden Chemical) 100 parts by weight Hardener: AL (manufactured by Saiden Chemical) 0.25 parts by weight Additive: X-301-375SK (manufactured by Saiden Chemical) 0.25 parts by weight Additive: X-301- 352S (manufactured by Saiden Chemical Co., Ltd.) 0.4 parts by weight Solvent: 40 parts by weight of toluene << Criteria >>
A: Peeling at the interface between the adhesive layer and the untreated PET film (no problem in practical use)
B: Peeling at the interface between the adhesive layer and the surface of layer 2 or at the interface between the base film and layer 2 (there is a problem in practical use).

(10) Visibility evaluation of surface protective film (I) (Practical property substitution evaluation of oligomer encapsulation)
After cutting out the surface protective film on which the adhesive layer is formed into a 5 cm square in advance, a hot air circulation furnace (size: 7 cm square, thickness 2 mm, conforming to JIS R3202) and the adhesive layer are bonded together. Made by TABAI: Heat-treated at 180 ° C. for 10 minutes in a model PVH-210). Then, in the state of being bonded, the visibility evaluation (I) was evaluated based on the following criteria as to whether or not the adhesive layer could be observed from the layer 1 side.
"criterion"
A: With the surface protection film still attached, the adhesive layer can be clearly observed without stagnation, and inspection is particularly easy (no problem in practical use).
B: The adhesive layer can be observed with the surface protective film attached, and inspection is easy (no problem in practical use).
C: It is possible to observe the adhesive layer with the surface protective film attached, but in rare cases it may be a little difficult to inspect (it may be a problem in practice).
D: Since the haze of the surface protective film is rising, it is difficult to observe the adhesive layer with the surface protective film attached, and it is difficult to inspect (there is a problem in practical use).

(11) Visibility evaluation of surface protective film (II) (Practical characteristic substitute evaluation of inspection ease with optical evaluation)
The adhesive layer side of the surface protective film on which the adhesive layer was formed was attached to a polarizing plate, and another polarizing plate was placed on the surface protective film so that the field of view became the darkest while rotating the polarizing plate. After that, the lower polarizing plate is observed using an optical microscope (transmitted light) with the laminated body configuration (polarizing plate / surface protective film (adhesive layer) / polarizing plate) as it is, and the observation state at that time is determined as follows. Visibility evaluation (II) was evaluated according to the criteria.
"criterion"
A: With the surface protection film still attached, the polarizing plate can be clearly observed without stagnation, and inspection is particularly easy (no problem in practical use).
B: The polarizing plate can be observed with the surface protective film attached, and inspection is easy (no problem in practical use).
C: It is possible to observe the polarizing plate with the surface protection film attached, but the inspection may be a little difficult (it may be a problem in practice).
D: It is difficult to observe the polarizing plate and inspect it with the surface protection film still attached (there is a problem in practical use).

(12) Comprehensive evaluation (practical characteristic substitute evaluation)
Each evaluation of (6) transparency evaluation, (8) oligomer sealing property, (9) adhesiveness evaluation with adhesive layer, (10) visibility evaluation (I), (11) visibility evaluation (II) The items were comprehensively evaluated according to the following criteria.
"criterion"
A: All are judged as A (no problem in practical use, especially good)
B: Except for the transparency evaluation, there is at least one B judgment, and all others are A judgments (no problem in practical use).
C: Except for transparency evaluation, at least one is judged as C, and the others are judged as A or B (may cause practical problems).
D: Transparency evaluation is B judgment, or at least one is D judgment in other items (there is a practical problem)

[Manufacturing of polyester]
The polyesters used in Examples, Comparative Examples and Reference Examples were produced as follows.

<Manufacturing method of 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 was taken in a reactor, the reaction start temperature was set to 150 ° C., and gradually with the distillation of methanol. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part by weight of ethyl acid phosphate was added to this reaction mixture, 0.04 part by weight of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually increased from 230 ° C to 280 ° C. On the other hand, the pressure was gradually reduced from the normal pressure to finally reach 0.3 mmHg. After the reaction was started, the reaction was stopped at the time when the ultimate viscosity corresponded to 0.63 dl / g due to the change in the stirring power of the reaction tank, and the polymer under nitrogen pressurization was discharged. The obtained polyester A had an ultimate viscosity of 0.63 dl / g and an ester cyclic trimer content of 0.97% by weight.

<Manufacturing method of polyester B>
Polyester A was pre-crystallized at 160 ° C in advance and then subjected to solid phase polymerization in a nitrogen atmosphere at a temperature of 220 ° C. Polyester B was obtained.

<Manufacturing method of polyester C>
Ester 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol, 30 ppm of ethyl acid phosphate with respect to the produced polyester, and 100 ppm of magnesium acetate / tetrahydrate as a catalyst with respect to the produced polyester at 260 ° C. Esterification reaction was allowed. Subsequently, 50 ppm of tetrabutyl titanate was added to the produced polyester, the temperature was raised to 280 ° C. over 2 hours and 30 minutes, the pressure was reduced to an absolute pressure of 0.3 kPa, and the mixture was further polycondensed for 80 minutes to obtain the ultimate viscosity. A polyester C having a viscosity of 0.61 dl / g and an ester cyclic trimer content of 1.02% by weight was obtained.

<Manufacturing method of polyester D>
After pre-crystallization of polyester C at 160 ° C, solid-phase polymerization was carried out in a nitrogen atmosphere at a temperature of 210 ° C, the ultimate viscosity was 0.71 dl / g, and the ester cyclic trimer content was 0.50% by weight. Polyester D was obtained.

<Manufacturing method of polyester E>
The method for producing polyester D is the same as that of polyester D, except that the polyester obtained by adding 0.3 parts by weight of silica particles having an average particle size (d50) of 2.3 μm to 100 parts by weight of polyester C and melt-kneading is used. Polyester E was obtained using the same method. The obtained polyester E had an intrinsic viscosity of 0.72 dl / g and an ester cyclic trimer content of 0.50% by weight.

<Manufacturing method of polyester F>
Method for producing polyester D, except that polyester obtained by adding 1.5 parts by weight of aluminum oxide particles having an average particle size (d50) of 0.3 μm to 100 parts by weight of polyester C and melt-kneading is used. Polyester F was obtained by the same method as in the above. The obtained polyester F had an ultimate viscosity of 0.72 dl / g and a content of an ester cyclic trimer of 0.50% by weight.

[Preparation of coating liquid]
The coating liquid used for forming the layers 1 and 2 in Examples, Comparative Examples and Reference Examples was prepared by mixing the following coating liquid materials.

<< Coating liquid sample >>
(A1): Hexamethoxymethylol melamine (A2): Epocross, which is an oxazoline compound (manufactured by Nippon Shokubai Co., Ltd., oxazoline group amount 7.7 mmol / g)
(A3): Polyglycerol polyglycidyl ether (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) emulsified polymer (emulsifier: anionic surfactant)
(C1): 2-Amino-2-methylpropanol hydrochloride (D1), which is a melamine cross-linking catalyst: An aqueous dispersion monomer composition of a polyester resin copolymerized with the following composition and having a glass transition point of 45 ° C. Monomer composition: (dicarboxylic acid component) Terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid // (diol component) ethylene glycol / 1,4-butanediol / diethylene glycol = 56/40/4 // 70/20/10 (mol%)
(F1): Silica particles having an average particle size of 0.07 μm (G1): Silica sol having an average particle size of 65 nm

≪Coating liquid composition≫
The compositions of the coating liquids 1-1 to 1-9 used for forming the layer 1 are as shown in Table 2 below, and the compositions of the coating liquids 2-1 to 2-5 used for forming the layer 2 are shown in Table 3 below. As shown in. All of these coating liquids were adjusted with water so that the solid content concentration was 2% by weight.

[Adhesive composition]
The pressure-sensitive adhesive compositions used for forming the pressure-sensitive adhesive layer in Examples, Comparative Examples, and Reference Examples are as follows.

<Acrylic adhesive layer composition>
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) and acrylic acid (6 parts by weight) in ethyl acetate by a conventional method (solid content 30 parts by weight). %) Was obtained. To 100 parts by weight (solid content) of the 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 Company), which is an epoxy-based cross-linking agent, are added. An acrylic pressure-sensitive adhesive layer composition was obtained.

<Silicone-based adhesive layer composition>
"SD4580" (silicone pressure-sensitive adhesive, manufactured by Toredau Corning Inc.) was used as a silicone-based pressure-sensitive adhesive layer composition.

[Example 1]
<Manufacturing of laminated polyester film F1>
The raw material of 100% by weight of polyester D is the raw material of the surface layer A, the raw material of blending polyesters D and F in the ratio of 90% by weight and 10% by weight, respectively, is used as the raw material of the surface layer B, and the raw material of 100% by weight of polyester C is used as the raw material of the intermediate layer. An unstretched sheet with a thickness of 1500 μm, which is supplied to three vented extruders, melt-extruded at 290 ° C, and then cooled and solidified on a cooling roll whose surface temperature is set to 40 ° C using an electrostatic application adhesion method. Got After this unstretched sheet is stretched 3.4 times in the mechanical direction at 85 ° C., the thicknesses (after drying) of the coating liquid 1-1 and the coating liquid 2-1 are 0.06 μm, respectively. After applying to each surface of the uniaxially stretched film, the film is guided to a tenter, stretched 4.0 times in the width direction at 100 ° C., heat-treated at 230 ° C., and then relaxed by 2% in the width direction. A laminated polyester film F1 having a layer 1 formed on the surface layer A and a layer 2 formed on the surface layer B of a base film having a thickness of 75 μm (thickness composition ratio = 6 μm / 63 μm / 6 μm) was obtained.

<Manufacturing of surface protection film>
An acrylic pressure-sensitive adhesive composition is applied to the surface of layer 2 of the laminated polyester film F1 so that the thickness (after drying) is 25 μm, and dried at 100 ° C. for 5 minutes to form an pressure-sensitive adhesive layer, and the surface of Example 1 is formed. Obtained a protective film.

[Examples 2 to 20, Comparative Examples 1 to 6, Reference Example 1]
In Example 1, the layers are laminated except that the polyester used for forming each polyester layer of the base film, the thickness of each layer, and the coating liquids 1 and 2 used for forming the layers 1 and 2 are shown in Tables 4 to 7. Laminated polyester films 2 to 26 were produced in the same manner as the polyester film F1. An acrylic pressure-sensitive adhesive composition or a silicone-based pressure-sensitive adhesive composition was used on the obtained laminated polyester film to form a pressure-sensitive adhesive layer in the same manner as in Example 1 to obtain a surface protective film.

Tables 4 to 7 show the evaluation results of the base film, the laminated polyester film and the surface protective film obtained in Examples 1 to 20, Comparative Examples 1 to 6 and Reference Example 1.

From Tables 4 to 7, it can be seen that the laminated polyester film and the surface protective film of the present invention of Examples 1 to 20 are excellent in all of transparency, oligomer encapsulation, visibility and the like.
On the other hand, in Comparative Example 1 in which the layer 1 is not formed, the oligomer encapsulation property is inferior, and therefore the visibility evaluation result is also poor.
Comparative Example 2 in which the particles are contained in the surface layer A of the base film is inferior in transparency and therefore has poor visibility evaluation.
Comparative Examples 3, 4 and 6 in which the content of the cross-linking agent in the coating liquid 1 used for forming the layer 1 was low were inferior in the oligomer-sealing property and the visibility evaluation result was also poor.
Comparative Example 5 in which the particle content of the coating liquid 1 used for forming the layer 1 is too large is inferior in transparency.
Reference Example 1 is inferior in transparency because the layer A contains particles, and the polyester used for producing the surface layer A and the surface layer B does not contain the Ti element and has a high ester cyclic trimer content. The haze is large and the amount of change in haze is remarkably large, and the transparency and visibility evaluation are remarkably inferior.

The laminated polyester film of the present invention is used 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 supply members, and the like. Can be suitably used for. Among them, for surface protection of 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, etc. When used in the above, the inspection with optical evaluation is easy and the oligomer encapsulation property is excellent with the surface protective film still attached, and its industrial value is high.

Claims (6)

A base film having a laminated structure of at least two polyester layers and one surface layer (hereinafter referred to as "surface layer A") being a polyester layer containing substantially no particles, and a surface layer of the base film. The base material having a layer 1 containing 70% by weight or more of a cross-linking agent and / or a reaction product thereof formed on A and having a particle content of 0.1% by weight or more and less than 5% by weight. A laminated polyester film comprising a layer 2 containing a polyester resin and a cross-linking agent and / or a reaction product thereof on the other surface layer of the film (hereinafter referred to as "surface layer B") . The laminated polyester film according to claim 1, wherein the base film contains a titanium-based polymerization catalyst. The laminated polyester film according to claim 1 or 2, wherein the base film has a laminated structure of three or more layers having a polyester layer as an intermediate layer. The laminated polyester film according to any one of claims 1 to 3, further comprising an adhesive layer on the layer 2. The laminated polyester film according to claim 4 , wherein the adhesive layer is made of an acrylic adhesive. A surface protective film made of the laminated polyester film according to claim 4 or 5 .