JP2013199046A - Polyester film for surface protection film and surface protection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for surface protection films, which exhibits excellent image clarity after stuck to a display screen and which has a coating layer having both of excellent antistatic properties and easy adhesiveness and to provide the surface protection film.SOLUTION: The polyester film for surface protection films is obtained by forming the coating layer on at least one side of a multilayer polyester film. The coating layer is formed from a coating liquid containing: an acrylic resin having a reactive emulsifying agent-derived hydrophilic group in one molecule thereof; an oxazoline compound; and a compound having a quaternary ammonium group. The multilayer polyester film has ≥89% of a value of image representing properties. The surface protection film is obtained by forming a slightly tacky-adhesive layer on at least one side of the polyester film.

Description

  The present invention relates to a polyester film for a surface protective film and a surface protective film, and more particularly to a polyester film for a surface protective film and a surface protective film having both excellent antistatic performance and easy adhesion performance.

  Biaxially stretched polyester film excels in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, gas barrier properties, chemical resistance, etc., packaging materials, plate making materials, display materials, transfer materials, building materials, It is used for window paste materials, membrane switches, antireflection films used for flat displays, optical films such as diffusion sheets and prism sheets, and transparent touch panels. However, when other materials are applied and laminated on the polyester film in such applications, there is a drawback that the adhesiveness is poor depending on the materials used. As one of the methods for improving the adhesiveness of the biaxially stretched polyester film, there is known a method of applying various resins to the surface of the polyester film and providing a coating layer having easy adhesion performance (Patent Documents 1 and 2). .

  However, such an existing easily-adhesive coating layer may still not have sufficient adhesion depending on the type of the topcoat layer. For example, when a so-called solventless UV curable coating is used as the topcoat, the solventless topcoat has a low penetration and swelling effect on the easy-adhesion layer compared to the solvent-based topcoat, and therefore has poor adhesion. It tends to be enough.

  For these problems, for example, by providing an easy-adhesion layer having a specific composition, a method for imparting better adhesiveness has been proposed and improved (Patent Documents 3 to 5).

  Recently, however, it has been increasingly used as a protective film for information terminal display screens such as mobile phones and tablet PCs based on polyester film. Especially when used outdoors, it is not only adhesive. In addition, there is a demand for adhesion weather resistance that maintains adhesion over a long period of time.

  Surface protective films for display screens of mobile phones, tablet PCs, etc. are widely used with a configuration in which a thin adhesive layer is provided on one side of a polyester film substrate and a hard coat layer is provided on the opposite side. It is known to provide a silicone-based fine-adhesive layer that can be applied and peeled off many times without causing paste residue or oozing out of the paste (Patent Document 6).

  In addition, polyester film is easily charged during friction, peeling, etc., and when applying a silicone coating solution, there is a problem of uneven coating due to charging of the base material. There is also a demand for imparting antistatic performance.

  Therefore, a coating layer having adhesion weather resistance and antistatic properties as described above is required, but any conventional easy adhesion coating layer and easy adhesion coating layer having antistatic properties still have sufficient effects. It is not done.

  Furthermore, as the display screens of mobile phones, tablet PCs, and the like become higher in definition, the surface protection film is also required to have sharpness after being attached to the display screen.

JP-A-2002-53687 Japanese Patent Laid-Open No. 11-286092 JP 2009-220376 A JP 2009-221359 A JP 2010-13550 A JP 2007-136985 A

  The present invention has been made in view of the above circumstances, and its solution is a film excellent in sharpness after being attached to a display screen, and an application layer having both excellent antistatic properties and easy adhesion properties. It is providing the polyester film and surface protection film which have these.

  As a result of intensive studies on the above problems, the present inventors have found that the above problems can be solved by providing a specific polyester film with a coating layer containing a specific type of compound. It came to complete.

  That is, the gist of the present invention is a laminated polyester film having a coating layer on at least one side of the polyester film, the coating layer having an acrylic resin having a hydrophilic group derived from a reactive emulsifier in the molecule, and an oxazoline compound. A polyester film for a surface protective film comprising a coating solution containing a compound having a quaternary ammonium group, wherein the image clarity value of the laminated polyester film is 89% or more, and the polyester film It exists in the surface protection film characterized by having a slightly adhesion layer at least on one side.

  According to the present invention, it is possible to provide a polyester film having a coating layer excellent in antistatic property and easy adhesion to a topcoat with a film excellent in sharpness after being attached to a display screen. The industrial value of the present invention is high.

The base film used in the present invention is made of polyester. Such polyesters include dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, 4,4′-diphenyldicarboxylic acid, 1,4-cyclohexyldicarboxylic acid or esters thereof. It is a polyester produced by melt polycondensation with glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol. Polyesters composed of these acid components and glycol components can be produced by arbitrarily using a commonly used method.
For example, a transesterification reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or a direct esterification of an aromatic dicarboxylic acid and a glycol, to form a substantially bisglycol of an aromatic dicarboxylic acid A method is employed in which an ester or a low polymer thereof is formed and then polycondensed by heating under reduced pressure. Depending on the purpose, an aliphatic dicarboxylic acid may be copolymerized.

  Typical examples of the polyester of the present invention include polyethylene terephthalate, polyethylene-2,6-naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, and the like. It may be a polymerized polyester and may contain other components and additives as necessary.

  The polyester film in the present invention can contain particles for the purpose of ensuring the film runnability and preventing scratches. Examples of such particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium phosphate, kaolin, talc, aluminum oxide, titanium oxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. Further, organic particles such as crosslinked polymer particles and calcium oxalate, and precipitated particles during the polyester production process can be used.

  The film of the present invention has an image clarity value of 89% or more, preferably 93%. When the image clarity value is less than 89%, the visibility of the display screen as a protective film is impaired because the visibility is impaired.

  The particle size and content of the particles used are selected according to the use and purpose of the film, but the average particle size is usually in the range of 0.01 to 5.0 μm. If the average particle size exceeds 5.0 μm, the surface roughness of the film becomes too rough, or the particles are likely to fall off from the film surface. When the average particle size is less than 0.01 μm, the surface roughness is too small and sufficient slipperiness may not be obtained.

  In addition, when it is particularly desired to ensure the transparency and smoothness of the film, the film may be substantially free of particles. Further, various stabilizers, lubricants, antistatic agents and the like can be appropriately added to the film.

  As a film forming method of the film of the present invention, a generally known film forming method can be adopted, and there is no particular limitation. For example, a sheet obtained by melt extrusion is first stretched 2 to 6 times at 70 to 145 ° C. by a roll stretching method to obtain a uniaxially stretched polyester film, and then perpendicular to the previous stretching direction in the tenter. A film is obtained by extending | stretching 2 to 6 times at 80-160 degreeC to the direction, and also heat-processing at 150-250 degreeC for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the heat treatment zone and / or the cooling zone at the heat treatment outlet is preferable.

  The polyester film in the present invention has a single layer or multilayer structure. In the case of a multilayer structure, the surface layer and the inner layer, or both the surface layer and each layer can be made of different polyesters depending on the purpose.

  The polyester film of the present invention has a coating layer on at least one surface, but even if a similar or other coating layer or functional layer is provided on the opposite surface of the film, it is naturally included in the concept of the present invention.

  In the present invention, the coating layer may be provided by various coating methods. However, it is desirable to provide the coating layer by a so-called in-line coating in which a coating layer is formed during film formation, particularly by a coating stretching method in which stretching is performed after coating.

  In-line coating is a method of coating within the process of manufacturing a polyester film. Specifically, it is a method of coating at any stage from melt extrusion of polyester to biaxial stretching and then heat setting and winding. is there. Normally, it is coated on either a substantially amorphous unstretched sheet obtained by melting and quenching, then a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction), or a biaxially stretched film before heat setting. To do. In particular, as a coating stretching method, a method of stretching in the transverse direction after coating on a uniaxially stretched film is excellent.

  According to such a method, since film formation and coating layer coating can be performed simultaneously, there is an advantage in manufacturing cost, and since the film is stretched after coating, it becomes a uniform coating with a thin film, so that the adhesive performance is stable. To do. Moreover, the polyester film before biaxially stretching is first covered with an easy-adhesive resin layer, and then the film and the coating layer are stretched simultaneously, whereby the base film and the coating layer are firmly adhered.

  In addition, biaxial stretching of the polyester film is achieved by stretching the film in the lateral direction while holding the film edge with a tenter, so that the film is constrained in the longitudinal / lateral direction. High temperature can be applied while maintaining Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the film forming property of the coating layer is improved, and the coating layer and the polyester film are firmly adhered. As an easily-adhesive polyester film, the uniformity of the coating layer, the improvement of the film-forming property, and the adhesion between the coating layer and the film often produce favorable characteristics.

  In this case, the coating solution to be used is preferably an aqueous solution or an aqueous dispersion for safety reasons in terms of handling, working environment, and may contain an organic solvent if water is the main medium.

  Next, the coating layer provided on the film in the present invention will be described.

  The coating layer of the present invention is a coating layer containing a coating solution containing an acrylic resin having a hydrophilic group derived from a reactive emulsifier in the molecule, an oxazoline compound, and a compound having a quaternary ammonium group. It can be obtained by drying and curing. The coating solution may contain other components.

  When each component is not completely reacted, the resulting coating layer contains both unreacted products and reaction products of each component, and the ratio of the reaction product and unreacted product depends on the curing conditions. It can be changed as appropriate.

  As described above, in the conventional technique, adhesion and antistatic performance are not compatible at a sufficient level. The reason for this is not always clear, but it is thought that there are the following reasons.

  That is, in order to obtain sufficient antistatic performance by coating, it is necessary to increase the thickness of the coating layer in order to obtain the necessary amount of antistatic component. When the forced peeling test is performed after the top coat is processed, the coating layer itself tends to cohesive failure in addition to peeling at the interface between the coating layer and the top coat layer. Therefore, sufficient adhesion cannot be ensured. In order to prevent this cohesive failure, if the cohesive force of the coating layer itself is increased by using, for example, a crosslinking agent, the antistatic component network in the coating layer is inhibited, and the antistatic performance is reduced, or the coating layer is coated to prevent cohesive failure. When the layer is thinned, the total amount of antistatic components is reduced, and the antistatic performance is lowered. In addition, when the ratio of the antistatic component to the effective component of the entire coating layer is increased instead of increasing the thickness of the coating layer, if these components have poor adhesion, the resulting coating layer also has high adhesion. I couldn't.

  In other words, in order to achieve both antistatic performance and adhesion, it was necessary to find a new combination in the selection of materials to be used and the configuration of the coating layer.

  In the present invention, the acrylic resin contained in the coating solution for forming the coating layer is composed of a polymerizable monomer having a carbon-carbon double bond, as typified by acrylic and methacrylic monomers. It is a polymer.

  Examples of the polymerizable monomer having a carbon-carbon double bond include various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, citraconic acid, and the like. Various hydroxyl group-containing monomers such as salts, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, monobutylhydroxyfumarate, monobutylhydroxyitaconate , Various (meth) acrylic esters such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate, (meth) acrylimide, di Acetone acrylamide Various nitrogen-containing vinyl monomers such as N-methylolacrylamide or (meth) acrylonitrile, various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, vinyltoluene, vinyl acetate, vinyl propionate, etc. Various vinyl esters are exemplified, and in the present invention, a copolymer containing at least one of acrylic acid, methacrylic acid, acrylic acid ester, and methacrylic acid ester is particularly preferable.

  Moreover, when polymerizing such monomers to obtain an acrylic resin, the present invention is preferably obtained in the form of an aqueous dispersion using an emulsion polymerization method in which the monomers are dispersed and polymerized in water. An emulsifier is used to disperse the monomer in water. In the present invention, it is preferable to use a nonionic or anionic reactive emulsifier. In acrylic resins obtained using other emulsifiers, the resulting coating layer often does not exhibit sufficient adhesion. The reactive emulsifier here refers to an emulsifier having a radical polymerizable double bond in the molecule and copolymerizing in the resin during the polymerization of the acrylic resin. It is particularly preferable that it is nonionic, and in that case, a hydrophilic group using an alkylene oxide is preferable. In the case of an anionic property, a sulfate group is preferable as the hydrophilic group.

  The obtained acrylic resin aqueous dispersion preferably has an average dispersed particle size in the range of 0.01 to 0.2 μm, more preferably 0.02 to 0.09 μm. When the average dispersed particle size is larger than the above range, the appearance and adhesion of the resulting coating layer tend to be inferior. Moreover, when smaller than the said range, there exists a tendency which is still inferior to adhesiveness.

  In the present invention, the compound having a quaternary ammonium group contained in a coating solution for forming a coating layer refers to a compound having a quaternized ammonium group in the molecule, and particularly a polymer compound. Is preferred. Moreover, it is preferable that it is a water-soluble compound.

  In the present invention, for example, a polymer containing as a component a monomer having a quaternary ammonium group and an unsaturated double bond can be used.

  Specific examples of such a polymer include a polymer having a constituent represented by the following formula 1 or 2 as a repeating unit. These homopolymers and copolymers, and other plural components may be copolymerized.

In the above formula, R ¹ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ² is —O— or —NH—, R ³ is an alkylene group having 1 to 6 carbon atoms or the structure of formula 1 Other possible structures, R ¹ , R ² and R ³ are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and X ⁻ is a monovalent anion.

In the above formula, R ¹ and R ² are each a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and X ⁻ is a monovalent anion.

The polymer having the component represented by the above formula 1 is excellent in transparency of the resulting coating layer and is preferable. However, in the coating stretching method, heat resistance may be inferior, and when used in the coating stretching method, X ⁻ is preferably not a halogen.

  The compound represented by the above formula 2 and other compounds having a quaternary ammonium base in the polymer skeleton are excellent in heat resistance, and antistatic properties are easily obtained even in the coating stretching method.

  Moreover, in this invention, it is necessary to contain an oxazoline compound in the coating liquid for forming a coating layer.

  The oxazoline compound in the present invention refers to a compound having an oxazoline group in the molecule, and can be synthesized using a monomer containing an oxazoline group as at least one raw material monomer. Examples of such monomers include 2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2- Vinyl-5,6-dihydro-4H-1, -oxazine, 4,4,6-trimethyl-2-vinyl-5,6-dihydro-4H-1,3-oxazine, 2-isopropenyl-2-oxazoline, 4,4-dimethyl-2-isopropenyl-2-oxazoline, 4-acryloyl-oxymethyl-2,4-dimethyl-2-oxazoline, 4-methacryloyl-oxymethyl-2,4-dimethyl-2-oxazoline, 4 -Methacryloyl-oxymethyl-2-phenyl-4-methyl-2-oxazoline, 2- (4-vinylphenyl) -4,4-dimethyl-2-o Oxazoline, 4-ethyl-4-hydroxymethyl-2-isopropenyl-2-oxazoline can be exemplified 4-ethyl-4-ethoxymethyl-2-isopropenyl-2-oxazoline and the like. One or more of these or other oxazoline group-containing monomers can be used.

  Moreover, in this invention, it is preferable to copolymerize the other component which does not contain an oxazoline group. Here, the other component is not particularly limited as long as it is a monomer that can be copolymerized with an oxazoline group-containing monomer. For example, a resin copolymerized with a vinyl oxazoline monomer using a monomer containing a vinyl group, such as (meth) acrylic acid esters, (meth) acrylamides, and styrene monomers, has high reactivity and is industrially obtained. Cheap.

  The coating solution may contain other cross-linking agents.

  The coating solution for providing the coating layer can contain components other than those described above as necessary. For example, surfactants, other binders and antistatic agents, lubricants, particles, antifoaming agents, coatability improving agents, thickeners, antioxidants, ultraviolet absorbers, foaming agents, dyes, pigments and the like. These additives may be used alone or in combination of two or more as necessary.

  The upper limit of the thickness of the coating layer as the film thickness on the finally obtained film is 0.07 μm, preferably 0.05 μm or less. The lower limit is 0.01 μm, preferably 0.02 μm or more. When the composition of the coating layer is limited as described above and the thickness of the coating layer is within the above range, both adhesion and antistatic performance can be achieved at a high level.

The antistatic property of the coating layer is measured by the surface specific resistance of the coating layer. It can be said that the lower the surface resistivity, the better the antistatic property. If the surface resistivity is 1 × 10 ¹³ Ω or less, it can be said that there is no problem with antistatic properties, and if it is 1 × 10 ¹² Ω or less, it can be said that the antistatic properties are extremely good.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In addition, the evaluation method in an Example and a comparative example is as follows.

(1) Measurement of intrinsic viscosity of polyester 1 g of polyester from which other polymer components and pigments incompatible with polyester have been removed are precisely weighed, and 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio) is added. It was dissolved and measured at 30 ° C.

(2) Average particle size of particles added to the polyester film (d50)
The size of the particles was measured by a sedimentation method based on Stokes' resistance law using a Shimadzu centrifugal sedimentation type particle size distribution analyzer SA-CP3 type.

(3) Average particle diameter of coating composition The aqueous dispersion of the coating composition was diluted to an appropriate concentration, and the 50% average diameter of the number average was measured with a Nikkiso Microtrac UPA.

(4) Thickness of coating layer A film was fixed with an embedding resin, a cross section was cut with a microtome, and a sample was prepared by staining with 2% osmic acid at 60 ° C. for 2 hours. The obtained sample was observed with a transmission electron microscope (JEM2010 manufactured by JEOL Ltd.), and the thickness of the coating layer was measured. Measure a total of 15 points on the film, and use the average of 9 points excluding 3 points from the larger value and 3 points from the smaller value as the coating layer thickness.

(5) Image clarity value According to JIS-K-7105, the image clarity value of the film was measured by the transmission method with image clarity measuring device ICM-1 manufactured by Suga Test Instruments Co., Ltd. The value is read from an optical comb of 0.125 mm.

(6) Adhesiveness The active energy ray-curable resin composition as shown below was applied onto the coating layer of the sample so that the thickness after curing would be 7 μm, and the hot-air drying oven set at 80 ° C. And dried for 1 minute. Next, using a high-pressure mercury lamp with an energy of 120 W / cm, curing was performed by irradiation for about 7 seconds at an irradiation distance of 100 mm to obtain a laminated film in which an active energy ray-curable resin layer was provided on the film. The integrated light amount of the active energy ray at this time was measured using an ultraviolet integrated light amount meter UIT-250 and a light receiver UVD-C365 (manufactured by USHIO INC.), And was about 110 mJ / cm ² . The active energy ray-cured resin layer of the obtained laminated film is cross-cut so that there are 100 grids per inch, and 18 mm wide tape (Nichiban cello tape (registered trademark) CT-18) Was attached, a rapid peel test was performed, and the adhesion was evaluated based on the peeled area. The judgment criteria are as follows.
A: Number of cross-cuts = 0
○: 1 ≦ Number of cross cuts ≦ 10
Δ: 11 ≦ number of cross-cuts ≦ 20
×: 21 <Number of cross-cuts peeled ××: Whole surface peeled Cured resin composition: 80 parts by weight of KAYARAD DPHA manufactured by Nippon Kayaku, 20 parts by weight of KAYAARD R-128H manufactured by Nippon Kayaku, 5 IRGACURE651 manufactured by Ciba Specialty Chemical A composition in which a mixture by weight is diluted with toluene to a concentration of 30% by weight.

(7) Surface resistivity (Ω / □)
Using a high resistance measuring instrument: HP4339B and measuring electrode: HP16008B manufactured by Hewlett-Packard Japan, the sample was conditioned for 30 minutes in a measurement atmosphere at 23 ° C. and 50% RH, and then the surface resistivity was measured. It can be said that if the surface specific resistance is 1 × 10 ¹² Ω or less, it can be said that there is good antistatic performance, and if it is 1 × 10 ¹⁰ Ω or less, it can be said that there is sufficient antistatic performance.

(8) Visibility After providing a hard coat layer similar to the above (1) on the opposite side of the film provided with a slightly adhesive layer, it is actually pasted on the display screen of a mobile phone, for clarity and visibility. The determination was made according to the following criteria.
<Criteria>
◎: Vividness and visibility, particularly good (practically satisfactory level)
○: Vividness / Visibility is good (a level that is practically acceptable)
×: Vividness / visibility poor (practically problematic level)

(9) Comprehensive evaluation as a protective film ○: Adhesiveness, antistatic property and visibility are all good and suitable for a protective film ×: Any of adhesiveness, antistatic property and visibility Inferior and unsuitable for protective film

The polyester raw materials used in Examples and Comparative Examples are as follows.
(Polyester 1): Polyethylene terephthalate having an intrinsic viscosity of 0.66 that does not substantially contain particles (Polyester 2): containing 0.3% by weight of amorphous silica having an average particle diameter (d50) of 1.6 μm, Polyethylene terephthalate (polyester 3) having an intrinsic viscosity of 0.65: polyethylene terephthalate having an intrinsic viscosity of 0.61 (polyester 4) containing 0.5% by weight of a crosslinked polymer fine powder having an average particle diameter (d50) of 0.5 μm : Polyethylene terephthalate having an intrinsic viscosity of 0.61 containing 1.5% by weight of γ-type aluminum oxide fine aggregated particles having an average primary particle size of 20 nm and an average particle size (d50) of 0.1 μm. Was used.
(E1): a polymer compound having a number average molecular weight of 20000, obtained by copolymerizing a structural unit of the following formula 1-1 and a structural unit of the following formula 1-2 at a weight ratio of 95/5.

(E2): a polymer compound composed of a structural unit of the following formula 2-1

(E3): a polymer compound having a structure in which a structural unit of the following formula 3-1 and an acrylate ester are copolymerized

(A1):
In the presence of alkoxy polyethylene glycol methacrylate as a reactive emulsifier, copolymerization was carried out with alkyl acrylate, alkyl methacrylate, methacrylic acid and N-methylol acrylamide as the main components, glass transition point of 50 ° C., acid value of 14 mg KOH, Acrylic resin (C1) having an average particle size of 0.05 μm: Epocross WS-500 (manufactured by Nippon Shokubai Co., Ltd.), which is a polymer type cross-linking agent in which an oxazoline group is branched to an acrylic resin
(C2): Becamine J-101 (made by Nippon Materials), which is methoxymethylol melamine.
(C3): Denacol EX-521 (manufactured by Nagase ChemteX) which is polyglycerol polyglycidyl ether
(F1): Silica sol aqueous dispersion having an average particle size of 0.07 μm (S1): Surfactant Surfinol 465 (manufactured by Air Products)

Comparative Example 1:
Each of the above-mentioned polyester 1 and polyester 2 is mixed at 83% and 17%, respectively, and the mixed raw material is used as the raw material for the A layer, and 100% raw material is used as the raw material for the B layer. Then, after melting at 285 ° C., the layer A is the outermost layer (surface layer), the layer B is the intermediate layer, and on the casting drum cooled to 40 ° C. : B: A = 6: 88: 6 was coextruded and cooled and solidified to obtain a non-oriented sheet. Next, the film was stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the roll peripheral speed difference, then led to a tenter, stretched 4.0 times at 120 ° C. in the transverse direction, and heat-treated at 230 ° C. Thereafter, the film was wound on a roll to obtain a laminated polyester film having a thickness of 50 μm. The properties of the obtained film are shown in Table 2 below.

Example 1:
A coating solution as shown in Table 1 below was applied to both surfaces of the uniaxially oriented film obtained in the same process as Comparative Example 1. Next, the film was guided to a tenter stretching machine, and the coating composition was dried using the heat, and the film was formed on a biaxially oriented polyethylene terephthalate film having a film thickness of 50 μm by the same process as in Comparative Example 1. A laminated polyester film provided with a coating layer having a thickness shown in 1 was obtained. The properties of this film are shown in Table 2 below.

Examples 2-4, Comparative Examples 2-6:
In the same process as in Example 1, the coating solution was changed as shown in Table 1 to obtain a laminated polyester film in which a coating layer was provided on a base film having a film thickness of 50 μm. The properties of this film are shown in Table 2.

Example 5:
A laminated polyester is produced in the same manner as in Example 1 except that the raw material of layer A is a mixed raw material in which polyester 1, polyester 3 and polyester 4 are mixed at a weight ratio of 60%, 30% and 10%, respectively. A film was obtained. The properties of the obtained film are shown in Table 2 below.

Comparative Example 7:
A laminated polyester film was obtained in the same manner as in Example 1 except that the raw material in which the polyester 1 and the polyester 2 were mixed at a weight ratio of 40% and 60%, respectively, was used as the raw material for the A layer. The properties of the obtained film are shown in Table 2 below.

  Next, on one side of this film, 100 parts of silicone coating liquid (linear polyorganosilicone having a vinyl group only at the terminal group (“X-62-1347” manufactured by Shin-Etsu Chemical Co., Ltd.)) as a fine adhesion layer (solid weight) 2 parts) of platinum catalyst (“CAT-PL-56” manufactured by Shin-Etsu Chemical Co., Ltd.) using a bar coater, and drying and curing the coating film at 150 ° C. for 2 minutes. A thin adhesive layer having a thickness of 25 μm was provided, and the film thus obtained has excellent properties as shown in Table 2. Therefore, the film was actually attached to a display screen of a mobile phone as a protective film. The visibility when used was good except for Comparative Example 7 and could be used preferably.

  The film of the present invention can be suitably used as a polyester film for a surface protective film that requires excellent antistatic properties and easy adhesion.

Claims (2)

A laminated polyester film having a coating layer on at least one surface of a polyester film, the coating layer having a hydrophilic group derived from a reactive emulsifier in the molecule, an oxazoline compound, and a compound having a quaternary ammonium group A polyester film for a surface protective film, wherein the image quality value of the laminated polyester film is 89% or more. A surface protective film comprising a slightly adhesive layer on at least one surface of the polyester film according to claim 1.