JP2015174933A - Polyester film for surface protective film, and laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for a surface protective film that is stuck with a transparent conductive film and excellent in handleability, inspectability, and surface properties.SOLUTION: A polyester film for a surface protective film has a thickness of 100 μm or more, a haze in the range of 5-20%, and a roughness (Ra) of one film surface of 30 nm or less. A laminate is formed by sticking the polyester film with a conductive film via an adhesive layer.

Description

  The present invention relates to a polyester film for a surface protective film and a laminate used in combination with a transparent conductive film. More specifically, the present invention relates to a polyester for a surface protective film having excellent handling properties, inspectability, and surface characteristics. The present invention relates to a film and a laminate.

  Conventionally, synthetic resin plates, glass plates, metal plates, optical members (glass substrates, light diffusion films, liquid crystal displays (polarizing plates, retardation plates, light guide plates, prism plates, etc.), touch panels, organic EL displays, plasma displays, etc. ), Automobile parts, electrical / electronic parts, building materials, stationery / office supplies, etc., in order to prevent surface contamination, scratches, dust, etc. A surface protective film having an adhesive layer on one side is used. However, such a surface protective film is still attached to the adherend, and is subjected to a heat treatment process in a high temperature atmosphere, or in a high temperature atmosphere during transportation and storage (Patent Documents 1 and 2). When it is used, the deformation due to melting or shrinkage of the base film is large and it is difficult to use.

  On the other hand, biaxially stretched polyester film is excellent 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, It is used for building materials, window paste materials, membrane switches, antireflection films used for flat displays, optical films such as diffusion sheets and prism sheets, and transparent touch panels. Since a material called polyester is obtained at a relatively low cost, it is suitably used as a base material for a protective film used in the process of various functional films described above (Patent Document 3).

  In recent years, electronic displays having a touch panel function have been rapidly penetrating into daily life because of their convenience. However, in order to further improve the convenience, thinning of the electronic display itself is progressing. Along with this, various members used in the electronic display also need to be thinned, and the transparent conductive film, which is an essential member for developing the touch panel function, is also being thinned. However, as the thinning of the transparent conductive film progresses, the handling properties and processability in the manufacturing process deteriorate, so the surface protective film used in the transparent conductive film manufacturing process is opposite to the thinning process. It tends to be thicker.

  In the inspection carried out in the final step of the production process of the transparent conductive film, it is inspected in the form of a laminate in which the transparent conductive film and the surface protective film are bonded together, but with the progress of thinning of the transparent conductive film, Because of the increased transparency of the laminate, when using a conventional surface protection film, surface glare causes problems such as poor visual inspection and excessive detection of automatic defect detectors. The protective film is also required to have appropriate optical characteristics.

  The surface protective film is a member that is peeled off when mounted on an electronic display, but when peeled off, the surface shape is transferred to the surface of the adhesive layer. It is required to hold.

JP 2006-299162 A JP 2008-68564 A JP 2012-232488 A

  An object of the present invention is to provide a polyester film for a surface protective film, which is used by being bonded to a transparent conductive film, and has excellent handling properties, inspection properties, and surface characteristics.

  As a result of intensive studies on the above problems, the present inventors have solved the above problems by controlling the particles prescribed for a specific polyester film and controlling the optical characteristics and surface characteristics within a certain range. As a result, the present invention has been completed.

  That is, the gist of the present invention is a polyester film having a thickness of 100 μm or more, characterized in that the haze is in the range of 5 to 20%, and the roughness (Ra) of one film surface is 30 nm or less. The present invention resides in a laminate comprising the polyester film for a surface protective film and the polyester film bonded to a conductive film through an adhesive layer.

  According to the present invention, it has excellent handling properties and inspection properties when used in combination with a transparent conductive film, and also has surface characteristics that make a release surface suitable when peeled off from a transparent conductive film. A polyester film for a surface protective film and a laminate can be provided, and the industrial value of the present invention is high.

  The optical laminated polyester film of the present invention is preferably a multilayer film having at least 3 layers. The laminated polyester film for optics referred to in the present invention is a polyester film extruded by a so-called extrusion method that is melt-extruded from an extrusion die, and is oriented in the biaxial direction of the vertical direction and the horizontal direction as necessary. Film.

The base film of 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.

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

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

  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. If the average particle size is less than 0.01 μm, the surface roughness is too small and sufficient slipperiness may not be obtained, and the polyester film may not be adjusted to a desired haze range.

  Regarding the particles to be used, it is preferable to add two or more kinds of particles. For the purpose of imparting slipperiness, it is preferable to prescribe particles having a relatively large particle size within a range that does not adversely affect the surface shape of the pressure-sensitive adhesive layer applied in the subsequent step. The range of 1.0 to 5.0 μm is preferable, and it is more preferable to add particles in the range of 1.5 to 3.0 μm. The particles added for the purpose of imparting slipperiness are preferably added to the outermost layer of the polyester film.

  On the other hand, for the purpose of adjusting the haze, it is preferable to formulate particles having a relatively small particle size. Specifically, the particle size is preferably in the range of 0.01 to 1.5 μm, more preferably 0.1 to 0.1 μm. It is preferable to add particles in the range of 1.2 μm. The particles added for the purpose of adjusting the haze may be any of the outermost layer and the inner layer of the film, and the existing layer is not particularly limited.

  Furthermore, the particle content in the polyester layer is usually in the range of 0.0005 to 0.5% by weight, preferably 0.001 to 0.3% by weight. When the particle content is less than 0.0005% by weight, the slipperiness of the film is insufficient, and appearance defects such as scratches may occur during film processing, and the desired haze characteristics may not be obtained. high. On the other hand, when adding over 0.5% by weight, there is a high possibility that a polyester film having a desired surface roughness (Ra) cannot be obtained, and there is a high possibility that a desired haze characteristic cannot be obtained. .

  The polyester of the film of the present invention has an essential condition that the haze of the film is in the range of 5 to 20%, and preferably in the range of 7 to 15%. When the haze is less than 5%, surface glare is confirmed by inspection with reflected light after forming a surface protective film / transparent conductive film laminate using the film of the present invention, and the inspectability is poor. On the other hand, when the haze is higher than 20%, inspecting the transmitted light after forming the surface protective film / transparent conductive film laminate causes poor lamination and the inspectability is poor.

  The polyester of the film of the present invention has an essential condition that the roughness (Ra) of one film surface is 30 nm or less, and preferably 20 nm or less. If the surface roughness (Ra) exceeds 30 nm, the surface of the pressure-sensitive adhesive layer becomes rough when the surface protective film is peeled off after the surface protective film / transparent conductive film laminate is prepared. This causes problems such as distortion and blurring in the image of an electronic display incorporating the transparent conductive film.

  In the present invention, various stabilizers, lubricants, antistatic agents, ultraviolet absorbers and the like can be appropriately added to the film.

  The thickness of the polyester film of the present invention is essentially 100 μm or more, more preferably 125 μm or more. When the film thickness is less than 100 μm, the thickness of the laminate after being bonded to the transparent conductive film is not sufficient, so that wrinkles are generated during processing, or there is a problem when the laminate is cut into single sheets. The stability of the laminate that is generated or cut into single sheets is insufficient. In addition, if the thickness is 350 μm or more, the film becomes too strong, and the laminate after being bonded to the transparent conductive film is unwound from the roll form and is curled and curled when actually used. May occur and there may be problems in actual use.

  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.

  In addition, in this invention, in order to make the planarity in the laminated body state after bonding together with the film with an ITO layer favorable about the polyester film as a protective film base material, for example, the draw ratio of the vertical direction is 3. 5 times or less, preferably 3.2 times or less. The heat setting temperature is preferably 223 ° C. or higher, more preferably 227 ° C. or higher.

  In the optically laminated polyester film of the present invention, a coating layer may be provided for the purpose of improving the adhesion to the layer processed thereon, improving the slipperiness during processing, and the like. Regarding the coating layer, it may be provided by in-line coating which treats the film surface during the process of forming a polyester film, or offline coating which is applied outside the system on a once produced film may be adopted. Since the coating can be performed simultaneously with the film formation, the production can be handled at a low cost, and therefore in-line coating is preferably used.

  The in-line coating is not limited to the following, but for example, in the sequential biaxial stretching, the coating treatment can be performed particularly before the lateral stretching after the longitudinal stretching is finished. When the coating layer is provided on the polyester film by in-line coating, it is possible to apply at the same time as the film formation, and the coating layer can be processed at a high temperature in the heat treatment process of the polyester film after stretching. Performances such as adhesion to various surface functional layers that can be formed on the layer and heat-and-moisture resistance can be improved. Moreover, when coating before extending | stretching, the thickness of an application layer can also be changed with a draw ratio, and compared with off-line coating, uniform coating can be performed with a thin film. That is, a film suitable as a polyester film can be produced by in-line coating, particularly coating before stretching.

  Moreover, the coating layer of the film of the present invention comprises a surfactant, an antifoaming agent, a coating property improving agent, a thickener, an organic lubricant, organic particles, inorganic particles, an antioxidant, an ultraviolet absorber, a foaming agent, It may contain additives such as dyes and pigments. These additives may be used alone or in combination of two or more as necessary.

As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, amides such as N-methylpyrrolidone Can be mentioned.
These organic solvents may be used in combination of two or more as required.

  Moreover, you may use together heat treatment and active energy ray irradiation, such as ultraviolet irradiation, as needed irrespective of offline coating or in-line coating as needed. The polyester film constituting the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for off-line coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, when the polyester film of the present invention is used for optics, a colorant, a conductive material, etc. may be added, and further, reflection of external light, electric shock due to static electricity, prevention of dust adhesion, and further electromagnetic wave shielding. An intended functional multilayer thin film may be formed.

  The coating liquid used in the present invention is preferably an aqueous solution or an aqueous dispersion in terms of handling and working environment, but contains water as the main medium and contains an organic solvent as long as it does not exceed the gist of the present invention. You may do it.

  Although there is no restriction | limiting in particular in the solid content density | concentration of a coating liquid, Usually, 0.3 to 65 weight%, Preferably it is 0.5 to 30 weight%, More preferably, it is 1 to 20 weight%. When the concentration is too high or too low than these ranges, it may be difficult to provide a coating layer having a thickness necessary for fully expressing the function.

  The thickness of a coating layer is dry thickness, and is 0.003-1.5 micrometers normally, Preferably it is 0.01-0.5 micrometer, More preferably, it is 0.01-0.3 micrometer. If the thickness of the coating layer is less than 0.003 μm, sufficient performance may not be obtained, and if it exceeds 1.5 μm, blocking between films tends to occur.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipping property, the fixing property and the like. The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the transparency of the film is hindered and the sharpness of the image tends to be lowered.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes.

  Examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound (for example, divinylbenzene) containing two or more carbon-carbon double bonds in one molecule.

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. The content of the particles in the coating layer is preferably 10% by weight or less, more preferably 5% by weight or less as an appropriate addition amount that does not impair the transparency.

  The coating layer may contain an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  The polyester film of the present invention is used as a surface protective film by coating an adhesive layer on one side. In addition, a release layer is usually provided below the adhesive layer. The material constituting the release layer is not particularly limited as long as it has releasability, and may be a type mainly composed of a curable silicone resin, or an organic resin such as a urethane resin, an epoxy resin, or an alkyd resin. A modified silicone type by graft polymerization with a resin or the like may be used. Among them, when the curable silicone resin is a main component, the release property is good. Types of curable silicone resins include solvent addition type, solvent condensation type, solvent ultraviolet ray curable type, solventless addition type, solventless condensation type, solventless ultraviolet ray curable type, solventless electron beam curable type, etc. Can be used.

  The material constituting the adhesive layer is not particularly limited as long as it has adhesiveness, and suitable examples include acrylic resins, olefin resins, urethane resins, polyether resins, Examples thereof include vinyl acetate resins, ethylene-vinyl acetate resins, epoxy resins, vinyl chloride resins, polyamide resins, and the like, but acrylic resins that can easily adjust the adhesive strength are particularly preferably used. Although the thickness of an adhesion layer is not specifically limited, Usually, it is the range of 1-100 micrometers, Preferably it is 2-50 micrometers, More preferably, it is 2-30 micrometers. If it is thinner than 1 μm, there is a high possibility that sufficient adhesive strength cannot be obtained, and if it is thicker than 100 μm, the ratio of the adhesive layer in the entire laminate of the surface protective film and transparent conductive film is too high, and the stability as a laminate. May be lacking.

  The surface protective film using the polyester film of the present invention as a base material is bonded to the transparent conductive film via an adhesive layer and used as a surface protective film / transparent conductive film laminate. Has a configuration in which a conductive film is laminated on a transparent substrate. The transparent substrate is not particularly limited as long as sufficient transparency, dimensional stability, mechanical properties, heat resistance, etc. are ensured, but the material is generally polyester, polyacryl, polycarbonate, Acetyl cellulose, aliphatic cyclic polyolefin and the like are preferably used. Although the thickness of the base material of a transparent conductive film is not specifically limited, Usually, it is the range of 5-100 micrometers, Preferably it is 7-50 micrometers, More preferably, it is 10-30 micrometers. If the thickness is less than 5 μm, wrinkles and the like are likely to be formed during the processing of the transparent conductive layer coating, and the workability may be lost. If the thickness is more than 100 μm, the productivity at the time of coating the transparent film is poor.

As a constituent material of the transparent conductive film, a metal oxide is preferably used from the viewpoint of transparency, durability, and weather resistance. In particular, indium tin oxide (ITO), antimony-containing indium tin compound (ATO), and oxidation are used. Tin, zinc oxide (ZnO), indium zinc oxide (In ₂ O ₃ —ZnO) and the like are particularly preferably used. The method for forming the transparent conductive film is not particularly limited, and a conventionally known method can be employed. Specific examples include vacuum deposition, sputtering, and ion plating.

  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 particle size 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) Thickness of polyester film The thickness of the polyester film was measured using a Digimatic standard outside micrometer (MDC-SB) manufactured by Mitutoyo Corporation.

(4) Measurement of film haze Film haze was measured for the sample film in accordance with JIS-K-7136 using a haze meter “HM-150” manufactured by Murakami Color Research Laboratory.

(5) Surface roughness of the polyester film (Ra)
Parallel to the average line of the portion (hereinafter referred to as the extracted portion) extracted by the reference length (2.5 mm) from the cross-sectional curve obtained by the surface roughness measuring device “SE-3F” manufactured by Kosaka Laboratory Ltd. 2 When the extracted portion was sandwiched by straight lines, the distance between the two straight lines was measured in the direction of the longitudinal magnification of the cross-sectional curve, and the value expressed in units of micrometers (μm) was defined as the maximum height of the extracted portion. The maximum height was expressed as an average value of the maximum heights of the extracted portions obtained from 10 cross-sectional curves obtained from the sample film surface. The radius of the stylus used at this time was 2.0 μm, the load was 30 mg, and the cutoff value was 0.08 mm.

(6) Application of release layer and adhesive layer to polyester film
An anchor layer composed of the following anchor layer composition was coated on the polyester film so that the coating amount (after drying) was 0.05 g / m 2, and then dried at 120 ° C. for 30 seconds. Next, 100 parts of a curable silicone resin (“KS-779H” manufactured by Shin-Etsu Chemical), 1 part of a curing agent (“CAT-PL-8” manufactured by Shin-Etsu Chemical), a methyl ethyl ketone (MEK) / toluene mixed solvent system on the anchor layer A release agent consisting of 2200 parts was applied so that the coating amount was 0.1 g / m ² and dried at 170 ° C. for 10 seconds to obtain a release film.
<< Anchor layer composition >>
Aluminum tris (acetylacetonate): 19.5% by weight
Γ-glycidoxypropyltrimethoxysilane: 80% by weight
Dibutyltin diacetate: 0.5% by weight
Then, the adhesive layer comprised from the following adhesion layer composition was apply | coated to the surface which carried out the mold release process of this polyester film so that thickness (after drying) may be 25 micrometers, and it was made to dry at 100 degreeC for 5 minutes, and a surface protection film was obtained. Obtained.
(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, acrylic acid 6 parts by weight) in ethyl acetate by a conventional method (solid content 30% by weight) ) To 100 parts by weight (solid content) of an acrylic copolymer, N, N-dimethylaminoethyl acrylate, 0.2 parts by weight, and 6 parts by weight of Tetrad C (manufactured by Mitsubishi Gas Chemical), which is an epoxy-based crosslinking agent, are added. An adhesive layer composition was obtained.

(7) Processability of surface protective film / transparent conductive film laminate Using a polyester film (Diafoil “T600E38”, manufactured by Mitsubishi Plastics Co., Ltd.) with a thickness of 38 μm, from 95% argon gas and 5% oxygen gas In an atmosphere of 0.4 Pa, an ITO film (transparent conductive thin film) having a thickness of 25 nm is formed by a reactive sputtering method using a sintered body material of 95% by weight of indium oxide and 5% by weight of tin oxide. A conductive film was created. The transparent conductive film is disposed so that the adhesive surface of the surface-protective film subjected to the above-mentioned adhesive processing is in contact with the surface opposite to the surface on which the ITO film is formed, and bonded together. did. The obtained surface protective film / transparent conductive film laminate was cut into a size of 21 cm × 30 cm to form a single wafer, and then subjected to a heat treatment at 180 ° C. for 1 hour to carry out a crystallization treatment of the ITO film. The processability of the laminate was evaluated according to the following criteria. ○: When the laminate is cut into single sheets, it can be cut without the film edge adhering to the cutter, etc., and no curling or the like occurs during crystallization treatment. Δ: When cutting the laminate into single sheets The film can be cut without adhering to the end of the film, and curl slightly occurs during crystallization, but there is no practical problem. ×: When cutting the laminate, Adhesion may scatter, curl of the laminate may occur during crystallization treatment, and the laminate may be curved after crystallization treatment.

(8) Curling property of the surface protective film / transparent conductive film laminate The laminate was cut out so that each piece was a 10 cm square and used as a measurement sample, and then this sample was set in a hot air circulating furnace set at 180 ° C. Then, heat treatment is performed for 60 minutes. Next, the sample was placed on a horizontal base, the heights of the four corners floating from the horizontal plane were measured, and this average value was taken as the curl value.
(Criteria)
○: Curl value is 3 mm or less (practically no problem level)
Δ: The curl value exceeds 3 mm and is 5 mm or less (a level that may cause a problem in practical use)
X: The curl value exceeds 5 mm. (Practical problem level)
By performing the laminate planarity evaluation after the heat treatment based on the above determination, a more accurate film laminate can be obtained.

(9) Inspectability of surface protective film / transparent conductive film laminate The surface protective film / transparent conductive film laminate product prepared as described above is transmitted / reflected in a dark room under irradiation with a three-wavelength fluorescent lamp. Under these conditions, the protective film side was visually inspected, and the inspectability was evaluated according to the following criteria.
○: Glare and cloudiness are not confirmed during visual inspection, and sufficient inspection performance is ensured. △: Reflected light from the fluorescent lamp is strong during reflected light inspection during visual inspection, and hinders visual inspection. The laminate is cloudy during the transmitted light inspection during inspection, which hinders visual inspection.

(10) Evaluation of the surface of the adhesive layer after peeling the surface protective film The surface protective film of the surface protective film / transparent conductive film laminate prepared as described above is peeled off, and the surface is irradiated with a three-wavelength fluorescent lamp in a dark room. The observation was made through reflected light below, and the evaluation was made according to the following criteria.
○: Adhesive layer surface is not rough and sufficient flatness is ensured ×: Adhesive layer surface is rough, so diffuse reflection of fluorescent lamp reflected light can be visually confirmed

(Production method of polyester chip A)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and chips were obtained according to a conventional method to obtain polyester A.

(Production method of polyester chip B)
When manufacturing the said polyester A, 6000 ppm of silica particles with an average particle diameter of 3.0 micrometers were added, and the polyester B was obtained.

(Production method of polyester chip C)
When manufacturing the said polyester A, 5000 ppm of calcium carbonate with an average particle diameter of 0.8 micrometer was added, and the polyester C was obtained.

Example 1:
The mixed raw material in which the polyester A and the polyester B are mixed at a ratio of 85% and 15% is used as the raw material for the A layer, and the mixed raw material in which the polyester A and the polyester C are mixed at a ratio of 98% and 2% is the raw material for the B layer. Each was supplied to two extruders and each was melted at 285 ° C., and then two layers and three layers on a casting drum cooled to 40 ° C. with the A layer as the outermost layer (surface layer) and the B layer as the intermediate layer In (ABA), a non-oriented sheet was obtained by coextrusion and cooling solidification so that the thickness composition ratio was A: B: A = 5: 115: 5. Next, the film was stretched 3.1 times in the machine direction at a film temperature of 85 ° C. by utilizing the difference in peripheral speed of the roll, and this longitudinally stretched film was guided to a tenter and stretched 4.3 times at 120 ° C. in the transverse direction. After performing the heat treatment, a polyester film having a thickness of 125 μm was obtained. The characteristics of the obtained polyester film are shown in Table 1 below.

Example 2:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that polyester A and polyester C were mixed in the proportions of 92% and 8% as raw materials for the B layer. The characteristics of the obtained polyester film are shown in Table 1 below.

Example 3:
In Example 1, polyester A and polyester B were mixed at a ratio of 77% and 23% as raw materials of the A layer, and polyester A and polyester C were mixed at a ratio of 97% and 3% as raw materials of the B layer. Obtained a polyester film in the same manner as in Example 1. The characteristics of the obtained polyester film are shown in Table 1 below.

Example 4:
In Example 1, it was coextruded so that the film thickness composition ratio was A: B: A = 7.5: 173: 7.5, and the final polyester film thickness was 188 μm. A polyester film was obtained in the same manner as in Example 1 except that the film was formed. The characteristics of the obtained polyester film are shown in Table 1 below.

Example 5:
In Example 1, the film was stretched 3.4 times in the machine direction at a film temperature of 85 ° C. using the difference in peripheral speed of the roll, and this longitudinally stretched film was guided to a tenter and stretched 4.3 times at 120 ° C. in the transverse direction. A polyester film was obtained in the same manner as in Example 1 except that heat treatment was performed at 223 ° C.

Comparative Example 1:
In Example 1, polyester A and polyester B were mixed at a ratio of 77% and 23% as raw materials for the A layer, and polyester A was mixed at a ratio of 100% as a raw material for the B layer. A polyester film was obtained by the method. The characteristics of the obtained polyester film are shown in Table 1 below.

Comparative Example 2:
In Example 1, polyester A and polyester B were mixed at a ratio of 80% and 20% as raw materials of the A layer, and polyester A and polyester C were mixed at a ratio of 90% and 10% as raw materials of the B layer. Obtained a polyester film in the same manner as in Example 1. The characteristics of the obtained polyester film are shown in Table 1 below.

Comparative Example 3:
In Example 1, polyester A and polyester B were mixed at a ratio of 70% and 30% as raw materials of the A layer, and polyester A and polyester C were mixed at a ratio of 95% and 5% as raw materials of the B layer. Obtained a polyester film in the same manner as in Example 1. The characteristics of the obtained polyester film are shown in Table 1 below.

Comparative Example 4:
In Example 1, the film was formed so that the film thickness ratio was A: B: A = 3: 69: 3 and the final polyester film had a thickness of 75 μm. Except for the above, a polyester film was obtained in the same manner as in Example 1. The characteristics of the obtained polyester film are shown in Table 1 below.

  The film of the present invention can be suitably used, for example, as a surface protective film used by being bonded to a transparent conductive film.

Claims (2)

A polyester film for a surface protective film, which is a polyester film having a thickness of 100 μm or more, has a haze in a range of 5 to 20%, and has a roughness (Ra) of one film surface of 30 nm or less. A laminate comprising the polyester film according to claim 1 bonded to a conductive film through an adhesive layer.