JP2018002827A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface protective film for conductive films, a transparent conductive substrate film or the like, used when a conductive film is manufactured, resisting heat deformation even when used for a heating treatment at a high temperature, without causing the deterioration of transparency or processing defects such as curl or sag.SOLUTION: There is provided a polyester film containing a polyester resin as a main component and having a haze of 1.5% or less and a crystal fusion calorie ΔHm measured when temperature is raised at heating rate of 20°C/min. by differential scanning calorimetry of 13 cal/g to 30 cal/g.SELECTED DRAWING: None

Description

  The present invention is used for producing a conductive film, and it is difficult to be thermally deformed even when used for heat treatment at a high temperature, and the surface protection for a conductive film does not cause deterioration of transparency and processing trouble such as curling. The present invention relates to a film, a transparent conductive substrate film, and the like.

  Polyester films are excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, etc., and are used in various fields.

  In particular, in recent years, it has been increasingly used instead of glass as a base material for transparent conductive laminates used in touch panels, electronic paper, and the like. As such a transparent conductive laminate, there is one in which an ITO (indium tin oxide) film is formed by sputtering using a polyester film as a base material directly or via an anchor layer. The polyester film is generally heat processed.

  Moreover, in the process of manufacturing a transparent electrode for a touch panel, the transparent conductive film on which the transparent conductive film made of ITO is formed is subjected to many heating processes such as annealing, ITO crystallization, resist printing, and edging. It goes through a process and a chemical treatment process. In the manufacturing process of such a transparent electrode, in order to prevent the surface of the transparent conductive film opposite to the surface on which the transparent conductive film is formed from being stained or damaged, surface protection for the transparent conductive film is performed. The film is pasted and processed.

  In the manufacturing process, for example, heat treatment is performed at 130 ° C. in order to reduce the thermal shrinkage (Patent Document 1), or heat treatment is performed at 150 ° C. in order to crystallize ITO (Patent Document 2). For this reason, the polyester film used for the base film for transparent conductive film and the surface protective film for transparent conductive film is required to have heat-resistant deformation.

  However, when the polyester film is exposed to such a high temperature treatment, the film is deformed by heat, resulting in a decrease in conductivity and a decrease in visibility due to the deformation. The properties of the laminate were not sufficiently satisfactory in terms of heat distortion resistance.

As a measure for preventing the above-described thermal deformation, for example, a method of improving the heat distortion resistance by adding a crystal nucleating agent to the polyester resin constituting the polyester film to increase the crystallinity (Patent Document 3), or a high glass transition A method using a copolyester resin having a temperature (Patent Document 4) has been proposed.
However, in Patent Document 3, the transparency is likely to deteriorate, and the visibility is likely to deteriorate due to whitening of the film appearance. Moreover, in patent document 4, since the film tearing in a film manufacturing process is easy to generate | occur | produce, manufacturing stability is easy to deteriorate, and since a thermal contraction rate tends to become high, curl and sagging generate | occur | produce in the manufacturing process of a transparent electrode. Cheap. For this reason, the polyester film cannot be said to be sufficiently satisfactory for use as a surface protective film for a conductive film and a transparent conductive substrate film, and is required to be compatible with transparency and workability. .

JP 2007-42473 A JP 2007-200823 A JP 2011-213770 A JP 2007-224281 A

  Therefore, in view of the above-mentioned problems of the prior art, an object of the present invention is to hardly be thermally deformed even when used for a heat treatment at a high temperature used in producing a conductive film, resulting in deterioration of transparency, curl and sagging. An object of the present invention is to provide a surface protective film for a conductive film and a transparent conductive substrate film that do not cause such processing defects.

As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention. The present invention for achieving the above object is as follows.
1) A polyester film containing a polyester resin as a main component, having a haze of less than 1.5%, and a crystal melting heat amount ΔHm measured when the temperature is raised at a heating rate of 20 ° C./min by differential scanning calorimetry. The polyester film characterized by being 13 cal / g or more and 30 cal / g or less.
2) Thickness is 16 micrometers or more and 300 micrometers or less, The polyester film as described in 1) characterized by the above-mentioned.
3) Refractive index is 1.63 or more and 1.69 or less, The polyester film as described in 1) or 2) characterized by the above-mentioned.
4) The polyester film according to any one of 1) to 3), wherein the polyester resin is polyethylene terephthalate.
5) The polyester film according to any one of 1) to 4), wherein the polyester film is made of only a polyester resin, and the polyester resin is homopolyethylene terephthalate.
6) The polyester film according to any one of 1) to 5), wherein the content of the cyclic trimer is 0.01% by mass or more and 1.00% by mass or less.
7) The polyester film according to any one of 1) to 6), wherein the film has a heat shrinkage rate of 2.0% or less at 150 ° C. for 30 minutes.
8) The polyester film according to any one of 1) to 7), wherein a heat shrinkage rate in the film width direction at 150 ° C. for 30 minutes is 1.0% or less.
9) The polyester film according to any one of 1) to 8), which is used for optical applications.

  According to the present invention, a conductive film that is used in the production of a conductive film, hardly undergoes thermal deformation even when used for heat treatment at high temperatures, and does not cause processing problems such as deterioration of transparency, curl and sagging. Therefore, the industrial value of the present invention is high.

  Next, the form for implementing the polyester film of this invention is demonstrated in detail. The “film” in the present invention is used to mean a two-dimensional structure such as a sheet, a plate, and a film.

  It is important that the polyester film of the present invention contains a polyester resin as a main component. Polyester resin is excellent in transparency, dimensional stability, mechanical properties, heat resistance, electrical properties, etc. Polyester film made of polyester resin is used for surface protective film for conductive film and transparent conductive base film, for example Can be preferably used.

  It is important that the polyester film of the present invention has a haze of less than 1.5%. When the haze is 1.5% or more, the visibility is lowered, and for example, it is inappropriate for applications that require high visibility such as for touch panels. The haze of the polyester film of the present invention is preferably from 0.1% to 1.2%, particularly preferably from 0.1% to 1.0%.

  In the polyester film of the present invention, it is important that the heat of crystal fusion ΔHm measured when the temperature is raised at a heating rate of 20 ° C./min by differential scanning calorimetry is 13 cal / g or more and 30 cal / g or less. When the heat of crystal fusion ΔHm is less than 13 cal / g, thermal deformation is likely to occur during heat treatment at high temperatures when producing a conductive film, and as a surface protective film for a conductive film and a transparent conductive substrate film application. It becomes inappropriate. Further, when the heat of crystal fusion ΔHm exceeds 30 cal / g, the haze is often 1.5% or more, and it is difficult to achieve both transparency and transparency. The heat of crystal fusion ΔHm of the polyester film of the present invention is preferably 13 cal / g or more and 25 cal / g or less, more preferably 14 cal / g or more and 20 cal / g or less, and 15 cal / g or more and 18 cal / g or less. It is particularly preferred.

  Here, in calculating the crystal melting heat quantity ΔHm measured when the temperature is raised at a heating rate of 20 ° C./min by differential scanning calorimetry, a plurality of crystal melting peaks may be observed. When Tm1 and crystal melting temperature Tm2 are observed, ΣΔHmi (ΔHm1 is defined as the sum of two crystal melting heats of ΔHm1 applied to crystal melting temperature Tm1 and ΔHm2 applied to crystal melting temperature Tm2, i represents 1 to the total number of crystal melting peaks) as ΔHm. When a plurality of crystal melting peaks are observed, it is preferably 13 cal / g or more and 30 cal / g or less only by the amount of crystal melting heat ΔHmi applied to the main crystal melting peak.

  The means for adjusting the heat of crystal fusion ΔHm to 13 cal / g or more and 30 cal / g or less is not particularly limited. For example, it is adopted to increase the crystallinity of the film by a known method exemplified in Patent Document 3. Although it is possible, since these methods may cause deterioration of transparency, a method as described later, that is, a method of setting the content of the cyclic trimer in the polyester film to 1.00% by mass or less. Is particularly preferred.

  The mechanism that makes it easy to achieve a heat of crystal fusion ΔHm of 13 cal / g or more and 30 cal / g by setting the content of the cyclic trimer in the polyester film to 1.00% by mass or less is still unclear. Since the cyclic trimer can only exist in the amorphous part of the polyester resin, if there is little cyclic trimer in the whole of the polyester resin, the crystal of the polyester resin can be used in the stretching process in the film manufacturing process. When the crystallization proceeds, the energy required to drive the cyclic trimer to the amorphous part becomes relatively small, and the crystallization easily proceeds, that is, the crystallinity becomes high. Even when the film is produced under the film production conditions, the degree of crystallinity of the film is relatively high, and as a result, the heat of crystal fusion ΔHm is I guess it tends to grow.

  The polyester film of the present invention preferably has a thickness of 16 μm or more and 300 μm or less. When the thickness of the film is less than 16 μm or exceeds 300 μm, stable production as a film may be difficult, and in particular, when it exceeds 300 μm, it may be difficult to achieve both transparency. The thickness of the polyester film of the present invention is more preferably 18 μm or more and 260 μm or less, further preferably 20 μm or more and 250 μm or less, and particularly preferably 20 μm or more and 200 μm or less.

The polyester film of the present invention preferably has a refractive index of 1.63 or more and 1.69 or less. When the refractive index is less than 1.63, the heat distortion resistance may not be sufficient because it is difficult to proceed with crystallization of the film, and the film is used with a surface protective film for a conductive film or a transparent conductive substrate film. In some cases, sufficient mechanical properties may not be obtained. Moreover, when a refractive index exceeds 1.69, it becomes easy to generate | occur | produce a film tear in the extending | stretching process in a film manufacturing process, and manufacture stability may deteriorate. The refractive index of the polyester film of the present invention is particularly preferably 1.65 or more and 1.67 or less.
In addition, the refractive index said here means the average value of the refractive index of a film longitudinal direction and the refractive index of a film width direction. The refractive index can be measured with an Abbe refractometer using sodium D line (wavelength 589 nm) as a light source and diiodomethane as an intermediate solution. The method for setting the refractive index in the above range is not particularly limited, but in general, the refractive index can be controlled by adjusting the stretching ratio and temperature during stretching.

  Although the method for controlling the refractive index of the polyester film of the present invention is not particularly limited, it can be easily achieved by making the polyester film a biaxially oriented film. Here, “biaxial orientation” refers to a pattern showing a biaxial orientation pattern by wide-angle X-ray diffraction. A biaxially oriented film is generally a biaxially oriented method, that is, an unstretched sheet is stretched about 2.5 to 5.0 times in the sheet longitudinal direction and width direction, respectively, and then subjected to heat treatment to complete crystal orientation. Can be obtained. As the biaxial stretching method, a sequential biaxial stretching method may be used, or a simultaneous biaxial stretching method may be used. Further, after the biaxial stretching, a restretching method may be performed in which the film is stretched again in the film longitudinal direction or the film width direction.

  In the polyester film of the present invention, it is important that the resin that is the main component of the polyester film is a polyester resin. The polyester resin in the present invention is a polymer having an ester bond as a main bond chain. Is a general term. The polyester resin constituting the polyester film is selected from ethylene terephthalate, ethylene-2,6-naphthalate, butylene terephthalate, ethylene-α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, etc. It is preferable to use at least one component as a main component, but these components may be used alone or in combination of two or more. In consideration, polyethylene terephthalate is preferably the main component. Further, these polyester resins may be partially copolymerized with other dicarboxylic acid components and diol components, preferably 20 mol% or less.

The intrinsic viscosity of the above-described polyester resin when measured in o-chlorophenol at 25 ° C. according to JIS K7367 (2000) is preferably 0.4 dl / g or more and 1.2 dl / g or less. It is particularly preferably 5 dl / g or more and 0.8 dl / g or less.
Further, in this polyester resin, various additives such as an antioxidant, a heat stabilizer, a weather stabilizer, an ultraviolet absorber, an organic lubricant, a pigment, a dye, as long as the important requirements of the present invention are satisfied. Organic or inorganic fine particles, fillers, antistatic agents, nucleating agents, crosslinking agents and the like may be added. In particular, in the case of imparting an ultraviolet cut function, it is preferable to contain an ultraviolet absorber in the polyester resin. Preferred examples of the ultraviolet absorber include salicylic acid compounds, benzophenone compounds, benzotriazole compounds, cyanoacrylate compounds, benzoxazine compounds, and cyclic imino ester compounds, but ultraviolet rays at 380 nm. M + P and M / P of the polyester resin to be described later and M / P (M is the concentration of the catalytic metal element remaining in the film (mmol%)), P is the concentration of the phosphorus element remaining in the film (mmol%) A benzoxazine-based compound is most preferred from the viewpoint of the degree of expression of the effect of improving dispersibility by controlling. These compounds can be used alone or in combination of two or more. In addition, stabilizers such as HALS and antioxidants can be used in combination, and it is particularly preferable to use a phosphorus-based antioxidant in combination.

  Examples of the benzotriazole-based compound include 2- (2H-benzotriazol-2-yl) -4,6-bis (1-methyl-1-phenylethyl) phenol and 2- (2H-benzotriazole-2). -Yl) -4- (1,1,3,3-tetramethylbutyl) phenol, 2- (2H-benzotriazol-2-yl) -4-methylphenol, 2- (2H-benzotriazol-2-yl) ) -4,6-di-t-butylphenol, 2- (2H-benzotriazol-2-yl) -4,6-di-t-amylphenol, 2- (2H-benzotriazol-2-yl) -4 -T-butylphenol, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 ' It can be exemplified 5'-di -t- butyl-phenyl) -5-chloro-benzotriazole, or the like.

  Examples of the benzophenone compounds include 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, 2,2 ′, 4,4 ′. -Tetrahydroxybenzophenone, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid and the like can be mentioned.

  Examples of the benzoxazine-based compound include 2-p-nitrophenyl-3,1-benzoxazin-4-one, 2- (p-benzoylphenyl) -3,1-benzoxazin-4-one, and 2- (2 -Naphthyl) -3,1-benzoxazin-4-one, 2,2'-p-phenylenebis (3,1-benzoxazin-4-one), 2,2 '-(2,6-naphthylene) bis (3,1-benzoxazin-4-one) and the like can be exemplified.

  Moreover, as a polyester resin which comprises a polyester film, it is homopolyethylene terephthalate, Comprising: It is especially preferable that another copolymer component and / or another resin component are not included substantially. The polyester resin is homopolyethylene terephthalate and substantially does not contain other copolymer components and / or other resin components, it is easy to obtain high crystallinity, and the polyester film is an important requirement of the present invention. It becomes easy to set the heat of crystal fusion ΔHm to 13 cal / g or more and 30 cal / g or less. The term “substantially free of other copolymer components and / or other resin components” as used in the present invention means that the copolymer components include dicarboxylic acid components other than terephthalic acid as dicarboxylic acid components, and diols. It means that a diol component other than ethylene diol is not intentionally copolymerized as a copolymer component as a component. As other resin components, apart from homopolyethylene terephthalate, a resin that is compatible with homopolyethylene terephthalate, for example, a polyester resin other than homopolyethylene terephthalate, or incompatible with a dispersion size of 100 nm or less. It means a resin component added as a secondary component. That is, various additives as described above, as well as various catalysts added to polymerize homopolyethylene terephthalate, and for the purpose of imparting slipperiness and antiglare properties, etc., after film formation However, various particles such as polymer particles that maintain an arbitrary shape, impurities, and the like do not apply here.

  The polyester film of the present invention preferably has a cyclic trimer content of 0.01% by mass or more and 1.00% by mass or less. The cyclic trimer here means an ester cyclic trimer. When the content of the cyclic trimer exceeds 1.00% by mass, the crystal melting heat amount ΔHm measured when the temperature is raised at a heating rate of 10 ° C./min by differential scanning calorimetry, which is an important requirement of the present invention, is It may be less than 13 cal / g. In that case, thermal deformation is likely to occur during heat treatment at a high temperature when producing a conductive film, and as a surface protective film for a conductive film and a transparent conductive substrate film. May be inappropriate. In addition, it is substantially impossible to make the content of the cyclic trimer less than 0.01% by mass from the viewpoint of the generation mechanism of the cyclic trimer. The content of the cyclic trimer of the polyester film of the present invention is more preferably from 0.10% by mass to 0.80% by mass, and more preferably from 0.20% by mass to 0.60% by mass. More preferably, it is particularly preferably 0.30 mass% or more and 0.50 mass% or less.

  The means for setting the content of the cyclic trimer in the polyester film of the present invention to 0.01 mass% or more and 1.00 mass% or less is not particularly limited, but a polyester resin having a low content of the cyclic trimer is used as a raw material. Is a particularly preferred means. Various known methods can be used as a method for producing a polyester resin having a low cyclic trimer content. Examples thereof include a method of solid-phase polymerization after the production of the polyester resin.

  The polyester film of the present invention preferably has a heat shrinkage rate of 2.0% or less in the film longitudinal direction at 150 ° C. for 30 minutes. When the thermal shrinkage in the longitudinal direction of the film at 150 ° C. for 30 minutes exceeds 2.0%, curling is likely to occur during heat treatment at a high temperature when producing a conductive film, and a surface protective film for a conductive film, Moreover, it may become inappropriate as a transparent conductive substrate film application. In the polyester film of the present invention, the thermal shrinkage in the film longitudinal direction at 150 ° C. for 30 minutes is more preferably 1.6% or less, and particularly preferably 1.2% or less.

  The polyester film of the present invention preferably has a heat shrinkage rate of 1.0% or less in the film width direction at 150 ° C. for 30 minutes. When the thermal contraction rate in the film width direction at 150 ° C. for 30 minutes exceeds 1.0%, curling is likely to occur during heat treatment at a high temperature when producing a conductive film, and a surface protective film for a conductive film, Moreover, it may become inappropriate as a transparent conductive substrate film application. In the polyester film of the present invention, the thermal shrinkage in the film width direction at 150 ° C. for 30 minutes is more preferably 0.9% or less, and particularly preferably 0.8% or less.

  In the polyester film of the present invention, the difference between the heat shrinkage rate in the film longitudinal direction and the heat shrinkage rate in the film width direction at 150 ° C. for 30 minutes is preferably 1.0% or less. When the difference between the heat shrinkage rate in the film longitudinal direction and the heat shrinkage rate in the film width direction at 150 ° C. for 30 minutes exceeds 1.0%, curling may occur during heat treatment at a high temperature when producing a conductive film. It is easy to generate | occur | produce and may become unsuitable as a surface protection film for conductive films, and a transparent conductive base film use. In the polyester film of the present invention, the difference between the heat shrinkage rate in the film longitudinal direction and the heat shrinkage rate in the film width direction at 150 ° C. for 30 minutes is more preferably 0.9% or less, and 0.8% or less. It is particularly preferred that

  As long as the polyester film of this invention satisfies the important requirements of this invention, there is no restriction | limiting in the film structure, A single layer film or a laminated film may be sufficient. In the case of a laminated film, for example, a laminated film of layer A / layer B, that is, a two-type two-layer laminated film, a laminated film of layer B / layer A / layer B, that is, a two-type three-layer laminated film, or a layer B / layer A. / The structure of a laminated film of layer C, that is, a three-kind three-layer laminated film can be mentioned.

  When the polyester film of the present invention is used as a laminated film, the laminating method is not limited, and examples thereof include a laminating method by coextrusion method, a laminating method by bonding, and a method by a combination thereof. However, it is preferable to employ a coextrusion method from the viewpoint of transparency and production stability.

  When the polyester film of the present invention is used as a laminated film, different resin structures may be used for the purpose of imparting different functions to each layer. For example, when a laminated film of layer B / layer A / layer B, that is, a two-layer / three-layer laminated film is used, layer A is composed of homopolyethylene terephthalate from the viewpoint of transparency, and layer B is provided with slipperiness. For this purpose, a method such as adding particles can be used.

When the polyester film of the present invention is a laminated constitution film, a plurality of crystal melting peaks are obtained when calculating the crystal melting heat amount ΔHm measured when the temperature is raised at a heating rate of 20 ° C./min by differential scanning calorimetry. For example, when the crystal melting temperature Tm1 and the crystal melting temperature Tm2 are observed, the sum of two heats of crystal melting of ΔHm1 applied to the crystal melting temperature Tm1 and ΔHm2 applied to the crystal melting temperature Tm2 is observed. ΣΔHmi (i is 1 to the total number of crystal melting peaks) is read as ΔHm such that the heat of crystal fusion is ΔHm. When a plurality of crystal melting peaks are observed, it is preferably 13 cal / g or more and 30 cal / g or less only by the amount of crystal melting heat ΔHmi applied to the main crystal melting peak.
Next, the method for producing a polyester film of the present invention will be described by taking as an example the case where homopolyethylene terephthalate (hereinafter abbreviated as PET) is used as the polyester resin. However, the polyester film of the present invention is not limited to this.

  PET pellets (cyclic trimer content 1.0 to 0.3 mass%, intrinsic viscosity 0.5 to 0.8 dl / g) were vacuum dried and then fed to an extruder and melted at 260 to 300 ° C. An unstretched PET film is produced by extruding into a sheet form from a T-shaped base, winding around a mirror casting drum having a surface temperature of 10 to 60 ° C. using an electrostatic application casting method, and solidifying by cooling. This unstretched film is stretched 2.5 to 5.0 times in the longitudinal direction (referring to the traveling direction of the film and also referred to as “longitudinal direction”) between rolls heated to 70 to 100 ° C. Subsequently, the film is gripped with a clip, guided to a preheating zone, heated to a temperature of 75 to 95 ° C., and continuously in the heating zone of 90 to 115 ° C. in the transverse direction (perpendicular to the film traveling direction). The direction is also referred to as the “width direction”) and stretched 3.0 to 5.0 times, followed by heat treatment in a heating zone at 200 to 240 ° C. for 5 to 60 seconds, and crystallized through a cooling zone at 100 to 200 ° C. Obtain a fully oriented polyester film. In addition, you may perform a 3-12% relaxation process as needed during the said heat processing. Biaxial stretching may be either sequential stretching or simultaneous biaxial stretching, and may be re-stretched in either the longitudinal or transverse direction after longitudinal and transverse stretching. After cutting the end of the obtained biaxially oriented laminated polyester film, it is made into a winding intermediate product, then cut to a desired width using a slitter, and then wound around a cylindrical core to obtain a polyester film roll having a desired length. be able to. In addition, you may give an embossing process to both ends of a film for winding-up improvement at the time of winding.

  The polyester film of the present invention may be provided with a coating layer on one side of the film or on both sides of the film. Also, the coating layer may be a coating layer of two or more layers on one surface, and when a coating layer is provided on both surfaces, a different composition is applied on one surface and the opposite surface. You may do it.

  The coating layer provided on the surface of the polyester film of the present invention is not particularly limited as long as it satisfies the important requirements of the present invention, but various known coating layers can be provided, for example, for imparting slipperiness to the film. Particle-containing composition layer, a hard coat layer for supplementing the surface hardness and scratch resistance of the film, an easy-adhesion layer for supplementing the adhesion with a functional layer such as a separately provided hard coat layer, and a separate hard coat High refractive index layer for suppressing light interference unevenness caused by the refractive index difference between the layer and the base polyester film, oligomer block layer for suppressing whitening due to oligomer precipitation on the film surface, or other Examples thereof include an adhesive layer provided for bonding with a film.

  As a coating layer provided on the surface of the polyester film of the present invention, for example, it is possible to supplement a plurality of functions such as slipperiness and easy adhesion, or slipperiness and oligomer blockability with one coating layer. In addition, a coating layer that complements easy slipping and easy adhesion is provided on one side, a hard coat layer is provided on the other side, and a coating that complements both slipperiness and oligomer blockability is provided on the other side. There are no restrictions on the application surface, the function, the number and type of functions supplemented by one application layer, the combination of the number of application layers, and the like.

  In the case of providing a coating layer on the surface of the polyester film of the present invention, as a method of providing a coating layer, a method in which coating is performed in a process separate from the polyester film manufacturing process, a so-called offline coating method, and a polyester film manufacturing process. It is possible to use both of the so-called in-line coating methods, in which a polyester film coated with a coating layer is obtained at once. In the polyester film of the present invention, it is preferable to adopt an in-line coating method from the viewpoint of cost and uniform coating thickness, and the solvent of the coating liquid used in that case is an aqueous system from the viewpoint of environmental pollution and explosion-proof properties. It is preferable that

In the case where the coating layer is provided on the surface of the polyester film of the present invention, the method for carrying out the following steps 1) to 4) in this order using the in-line coating method as described above is used as the method for producing the polyester film. It is mentioned as a particularly preferable method from the viewpoint of expressing the characteristics of the coating layer and improving the productivity.
1) A process of applying a polyester film as a base An application process in which a coating liquid for forming a coating layer is applied to at least one surface of a film.
2) Process of polyester film serving as a base Heat drying process for forming a coating layer by heating and drying a coating liquid applied to a film.
3) A stretching process of stretching the process film on which the coating layer is formed.
4) A heat treatment step in which the stretched process film is heated and heat treated.

  The coating method in the coating process described in the above 1) is not particularly limited, and for example, a reverse coating method, a spray coating method, a bar coating method, a gravure coating method, a rod coating method, a die coating method, or the like may be used. However, from the viewpoint of reducing thickness unevenness of the coating layer, the gravure coating method and the bar coating method are preferably used, and the bar coating method using a measuring bar is particularly preferable. The diameter of the measuring bar used when the bar coating method using the measuring bar is used is not particularly limited, but is usually in the range of 10 to 30 mm. In addition, as a method for creating a groove for measurement, a wire bar method in which a wire is wound around a cylindrical member may be employed, or a method in which a spiral groove is dug on the member surface may be employed. From the viewpoint of coating uniformity, the deflection amount of the weighing bar is preferably 150 μm or less, and more preferably 100 μm or less.

  In the heat drying step described in the above item 2), it is preferable to adjust the temperature of the film surface of the coating layer surface after heat drying to a range of 75 to 95 ° C. When the temperature of the film surface of the coating layer surface after heat drying is less than 75 ° C., preheating of the film becomes insufficient, and there is a tendency that film tearing is likely to occur in the subsequent stretching step. Moreover, when the temperature of the film surface of the coating layer surface after heat drying exceeds 95 degreeC, the uniformity at the time of extending | stretching of a coating layer may be impaired, and there exists a tendency for the variation in the thickness of a coating layer to become large.

In addition, the heating and drying method in the heating and drying step is not particularly limited, and examples thereof include a method of blowing hot air and a method of heating with a non-contact type heater. It is preferable to employ a method of spraying. Further, the film surface of the coating layer surface after the heat drying process is measured with a non-contact thermometer, and the heat drying process is performed so that the measurement result is controlled to a target value determined to be within the above temperature range. The method of controlling the wind speed and / or temperature of the hot air at (lower the wind speed or lower the temperature if it becomes higher than the target temperature, increase the wind speed or raise the temperature if it becomes lower than the target temperature) This is preferable from the viewpoint of suppressing variation in coating thickness during long-time continuous production.
In the in-line coating method, the transverse stretching is usually performed after drying by heating in an oven. However, since both ends are held by clips, the application is often performed only at the center. For this reason, there may be a difference in the film temperature during stretching between the coated film center and the uncoated film end. In this case, the film end having a relatively high temperature. However, it is in a state where it is more easily stretched. In addition, when various cross-linking agents are contained in the coating layer, the coating thickness tends to decrease over time due to clogging of the measuring bar and gravure roll due to long-term continuous production. Since the film temperature at the center of the film during stretching rises, the center of the film tends to be relatively stretched, and the effective magnification of the transverse stretching at the center of the film increases, resulting in a thin coating layer thickness after transverse stretching. There is a case. In view of these circumstances, it is preferable to control the film temperature after the heat drying step to be constant over the film width direction or over time during continuous production.

  In the stretching step of the above item 3), it is preferable to stretch 3.0 to 5.0 times in the film width direction while blowing hot air set to 90 to 115 ° C. on the process film on which the coating layer is formed. It is. When the hot air temperature is less than 90 ° C., film breakage may occur during stretching. On the other hand, when the hot air temperature exceeds 115 ° C., as in the case of the heat drying, the coating layer Since the uniformity of thickness tends to deteriorate, it is not preferable. In addition, when the transverse stretch ratio of the film is less than 3.0 times, the strength in the film width direction tends to deteriorate, or the uniformity of the thickness in the film width direction tends to deteriorate, while the film In the case where the transverse stretching ratio exceeds 5.0 times, film tearing tends to occur during stretching, which is not preferable.

  In the heat treatment step of item 4), a method of blowing hot air set at 200 ° C. to 240 ° C. for 5 to 60 seconds is preferable. In this process, by promoting the crystallization of the process film, the secondary structure and tertiary structure of the polymer constituting the film are fixed, and the heat distortion resistance, thermal dimensional stability, chemical resistance, etc. of the film are improved. You can make it. About the temperature and time of a heat processing process, it can adjust according to the target film characteristic within the above-mentioned range.

  Hereinafter, the configuration and effects of the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to the following Example. Prior to describing each example, a method for measuring various physical properties will be described.

(1) Lamination ratio Using a Leica DMLM manufactured by Leica Microsystems Co., Ltd., the cross section of the polyester film is photographed with transmitted light at an arbitrary magnification of 100 to 1000 times, and the thickness of each layer is measured. Thus, the lamination ratio of each layer was calculated. When the interface of each layer is unclear, an arbitrary amount of dye was added to an arbitrary layer, a sample film was prepared without changing other production conditions, and the lamination ratio of each layer was calculated.

(2) Thickness Using a dial gauge (“No2110S-10” manufactured by Mitutoyo Corporation), 20 arbitrary points were measured, and the average value was defined as thickness (μm).

(3) Haze Based on JIS-K-7105 (1985), the haze was measured using a haze meter (“HGM-2GP” manufactured by Suga Test Instruments).

(4) Heat of crystal melting: ΔHm
Based on JIS-K-7122 (1987), the calculation was performed under the following conditions.
Apparatus: Differential scanning calorimeter (TA Instruments DSC “Q100 V9.8 Build 296”)
Measurement conditions: Measurement range under nitrogen atmosphere: 30 to 300 ° C. (1st RUN)
Temperature increase rate: 20 ° C./min Sample weight: 10 mg
(5) Refractive index Based on JIS-K-7142 (2008), measurement is performed under the following conditions, and the average value of the refractive index (nMD) in the film longitudinal direction and the refractive index (nTD) in the film width direction is calculated. Refractive index.

(6) Content of cyclic trimer 20 mg of a film piece was dissolved in OCP (o-chlorophenol) at 150 ° C. for 30 minutes and cooled at room temperature. Then, 1,4-diphenylbenzene was added as an internal standard, 2 ml of methanol was added, the polymer was separated with a high-speed centrifuge, and the liquid layer was used with a high-speed liquid chromatograph (“LC-10ADvp” manufactured by Shimadzu Corporation). Measured.

(7) Thermal contraction rate It measured based on ASTM-D1204 (1984). Specifically, on the film surface, a gauge point was given so that the measurement length was 200 mm, the distance L0 between the gauge points before heat treatment was measured, and the film sample was placed in an oven set at a temperature of 150 ° C. After holding for 30 minutes in an unstrained state, the distance L between the gauge points after the heat treatment is measured, and the thermal shrinkage rate in the film longitudinal direction and the thermal shrinkage rate in the film width direction are calculated by the following formula (1). The average value of the measurements was taken as the heat shrinkage rate.

Thermal contraction rate (%) = ((L0−L) / L0) × 100 (1)
(8) Transparency Based on the haze value obtained in the item of (1) haze, transparency was determined according to the following criteria.

(Transparency criteria)
A: The haze value was less than 1.0%.

  B: The haze value was 1.0% or more and less than 1.5%.

  C: The haze value was 1.5% or more.

(9) Heat-resistant deformation property A film sample cut into a 20 cm square was placed on a punching metal, held in an oven set at a temperature of 150 ° C. for 10 minutes in an unstrained state, and then the film sample was removed at room temperature for 10 minutes. After cooling for a minute, the state of the reflected image of the fluorescent lamp projected on the film surface was observed by the reflected light of the fluorescent lamp. The punching metal was evaluated using the following two types, and the heat deformation resistance was determined according to the following criteria.

・ Punching metal A: punching metal SUS304 embossed by Okutani Kinnet Seisakusho 1.5t × D4.5 × P7.5 60 ° plover ・ Punching metal B: punching metal SUS304 embossed by Okutani Kinnet Seisakusho 2t × D7 / H1.3 × P10 60 ° plover (Criteria for heat-resistant deformation)
A: In either case of punching metal A and punching metal B, no distortion was observed in the reflected image of the fluorescent lamp.

  B: Not applicable to A and B.

  C: In both the punching metal A and the punching metal B, the reflection image of the fluorescent lamp was distorted at the embossing pitch of the punching metal on a part or the entire surface of the film.

(10) Curling resistance A hard coat layer was disposed on both surfaces of the film in the following manner, and a transparent conductive layer was further disposed on the surface of one hard coat layer to obtain a transparent conductive film. The produced transparent conductive film is cut into a 20 cm square along the film longitudinal direction and the film width direction, and kept in an unstrained state for 90 minutes in an oven set at a temperature of 140 ° C. so that the transparent conductive layer is on the upper surface. The film sample was then cooled at room temperature for 10 minutes. After cooling, place the transparent conductive film on the flat surface so that the concave surface is on the top, measure the distance between the flat surface and the top of the transparent conductive film, calculate the average value of four points as the curl amount, The curling resistance was determined according to the criteria described above.

(Arrangement of hard coat layer)
The following raw materials were diluted with propylene glycol monomethyl ether (PGMA) and mixed, and each raw material was dispersed in a solvent to prepare a paint having a nonvolatile content of 25.5% by mass. The paint obtained here was applied on one side of the film so that the film thickness after drying was 1.0 μm, and the solvent in the coating film was removed by a drying furnace set at 80 ° C., followed by UV treatment. The coating film was cured by irradiating ultraviolet rays with an integrated light amount of 400 mJ / cm ² using the apparatus. A hard coat layer was provided on the other side of the film in the same manner, and the hard coat layer was disposed on both sides of the film.

Reactive group-decorated colloidal silica (dispersion medium: propylene glycol monomethyl ether acetate, nonvolatile content: 40% by weight): 100 parts by mass Dipentaerythritol hexaacrylate: 48 parts by mass 1,6-hexanediol diacrylate: 12 parts by mass Part / photopolymerization initiator (1-hydroxycyclohexyl phenyl ketone): 2.5 parts by mass (arrangement of transparent conductive layer)
A transparent conductive layer was formed on one side of the hard coat film provided with a hard coat layer on both sides of the film by using a sputtering method. Specifically, using a target obtained by adding 5% by mass of tin oxide to indium oxide, a film was formed in a mixed atmosphere composed of 98% by volume of argon gas and 2% by volume of oxygen gas. A transparent conductive layer made of the composite oxide was placed on the surface of one hard coat layer. Thereafter, the laminate was heated in an oven at 140 ° C. for 90 minutes to prepare a transparent conductive film.

(Criteria for curling resistance)
A: The curl amount was less than 10 mm.

  B: The curl amount was 10 mm or more and less than 15 mm.

  C: The curl amount was 15 mm or more.

(11) Comprehensive evaluation Based on the determination results in the above evaluation items, (7) transparency, (8) heat deformation resistance, and (9) curl resistance, the determination was made according to the following criteria.

  A: All items were judged as A.

  B: Not applicable to A and B.

  C: There were two or more items that were judged as B. Alternatively, there were one or more items that were judged as C.

[Polyester resin used]
(PET-1)
An esterification reaction product, which is a reaction product of terephthalic acid and ethylene glycol, is stored in a molten state at 255 ° C. in advance, and a slurry of terephthalic acid and ethylene glycol so that the molar ratio of ethylene glycol to terephthalic acid is 1.15. Then, a constant amount was supplied while maintaining the temperature of the esterification reaction tank, and the esterification reaction was carried out while distilling water to obtain an esterification reaction product. The obtained esterification reaction product is transferred to a polymerization reaction tank and contains an ethylene glycol solution containing phosphoric acid and an ethylene glycol solution containing magnesium acetate tetrahydrate, an ethylene glycol solution containing antimony trioxide, and potassium hydroxide. Separately add an ethylene glycol solution to the resulting polyester resin, adding an alkali metal element, an alkaline earth metal element, and a phosphorus element so that the M / P is 2.8 and the antimony element is 60 ppm. The pressure in the polymerization reaction vessel was gradually reduced to 0.13 kPa or less in 30 minutes, and at the same time, the temperature was gradually raised to 280 ° C. to carry out the polymerization reaction. Thereafter, the polycondensation reaction tank was returned to normal pressure with nitrogen gas, discharged into cold water from the base into cold water, pelletized into a cylindrical shape with an extrusion cutter, and pre-crystallized with a surface crystallization device to obtain a liquid polyester. . The liquid phase polyester obtained here was subjected to solid phase polymerization at a temperature of 215 ° C. for 20 hours under a reduced pressure of 0.13 KPa using a rotary vacuum dryer to obtain a polyester resin (PET-1). The obtained polyester resin (PET-1) had an intrinsic viscosity of 0.65 and a cyclic trimer content of 0.40% by mass.

(PET-2)
A polyester resin (PET-2) was obtained in the same manner as the polyester resin (PET-1) except that the solid phase polymerization time was changed to 30 hours. The intrinsic viscosity of the obtained polyester resin (PET-2) was 0.70, and the cyclic trimer content was 0.35% by mass.

(PET-3)
A polyester resin (PET-3) was obtained in the same manner as the polyester resin (PET-1) except that the solid phase polymerization time was changed to 50 hours. The intrinsic viscosity of the obtained polyester resin (PET-3) was 0.60, and the cyclic trimer content was 0.30% by mass.

(PET-4)
A polyester resin (PET-4) was obtained in the same manner as the polyester resin (PET-1) except that the solid phase polymerization time was changed to 10 hours. The obtained polyester resin (PET-4) had an intrinsic viscosity of 0.65 and a cyclic trimer content of 0.60% by mass.

(PET-5)
A polyester resin (PET-5) was obtained by the same method as the polyester resin (PET-1) except that the intrinsic viscosity was changed without performing solid phase polymerization. The intrinsic viscosity of the obtained polyester resin (PET-5) was 0.70, and the cyclic trimer content was 1.07% by mass.

(PET-6)
When adding an ethylene glycol solution of various polymerization catalysts after being transferred to the polymerization reaction tank, a polyester resin (PET-5) is used except that an ethylene glycol solution containing silica particles having an average particle diameter of 2 μm is further added. A polyester resin (PET-8) was obtained by the same method. The intrinsic viscosity of the obtained polyester resin (PET-8) was 0.70, the cyclic trimer content was 1.07% by mass, and the silica particle content was 0.02% by mass.

(PET-7)
When adding the ethylene glycol solution of various polymerization catalysts after transfer to the polymerization reaction tank, a polyester resin (PET-) was used except that an ethylene glycol solution containing crosslinked polystyrene particles having an average particle size of 0.3 μm was further added. A polyester resin (PET-9) was obtained by the same method as in 5). The obtained polyester resin (PET-9) had an intrinsic viscosity of 0.70, a cyclic trimer content of 1.07% by mass, and a crosslinked polystyrene particle content of 0.02% by mass.

(PET-8)
When adding the ethylene glycol solution of various polymerization catalysts after transfer to the polymerization reaction tank, a polyester resin (PET-) was used except that an ethylene glycol solution containing crosslinked polystyrene particles having an average particle size of 0.45 μm was further added. A polyester resin (PET-10) was obtained by the same method as in 1). The obtained polyester resin (PET-10) had an intrinsic viscosity of 0.65, a cyclic trimer content of 0.40% by mass, and a crosslinked polystyrene particle content of 0.01% by mass.

[Used coating liquid]
(Coating liquid-1)
Under a nitrogen gas atmosphere, 40 mol parts of 2,6-naphthalenedicarboxylic acid, 50 mol parts of terephthalic acid, 5 mol parts of sodium 5-sulfoisophthalate as dicarboxylic acid components, 95 mol parts of ethylene glycol and 5 mol parts of diethylene glycol as glycol components Was added to a transesterification reactor, 100 parts by mass of tetrabutyl titanate (catalyst) was added to 1 million parts by mass of the total dicarboxylic acid component, and the esterification reaction was carried out at 160 to 240 ° C. for 5 hours. The distillate was removed. Thereafter, 5 parts by mole of trimellitic acid and 100 parts by weight of tetrabutyl titanate were further added to 1 million parts by weight of all dicarboxylic acids, and the distillate was removed at 240 ° C. until the reaction product became transparent. The polyester (A) was obtained by performing a polycondensation reaction under reduced pressure at 220 to 280 ° C. Thereafter, 100 parts by weight of polyester (A) and 50 parts by weight of melamine-based crosslinking agent (“Nicarac” MW12LF manufactured by Sanwa Chemical Co., Ltd .: containing 70% by mass of active ingredient and 17% by mass of isopropyl alcohol) (in terms of active ingredient) ), 5.0 parts by mass of an active ingredient obtained by mixing 1.5 parts by mass of colloidal silica (particle size: 140 nm), 3.0 parts by mass of ethylene glycol mono-n-butyl ether, and 92.0 parts by mass of water Thus, a coating liquid-1 was obtained.

(Coating liquid-2)
In a nitrogen gas atmosphere, 85 mol parts of terephthalic acid as a dicarboxylic acid component, 5 mol parts of sodium 5-sulfoisophthalate, and 100 mol parts of ethylene glycol as a glycol component were charged into a transesterification reactor, and tetrabutyl titanate (catalyst). Was added at 100 parts by mass with respect to 1 million parts by mass of the total dicarboxylic acid component, and the esterification reaction was carried out at 160 to 240 ° C. for 5 hours, and then the distillate was removed. Thereafter, 10 parts by mass of 1,3,5-trimellitic acid and 100 parts by mass of tetrabutyl titanate are further added to 1 million parts by mass of all dicarboxylic acids, and the mixture is stored at 240 ° C. until the reaction product becomes transparent. After removing the effluent, a polycondensation reaction was performed under reduced pressure at 220 to 280 ° C. to obtain polyester (B). Then, except having changed polyester (A) into polyester (B), the coating liquid-2 was obtained by the method similar to the coating liquid-1.

(Coating liquid-3)
The active ingredient is 100 parts by weight of polyester (A) and 40 parts by weight of melamine-based crosslinking agent (“Nicarac” MW12LF manufactured by Sanwa Chemical Co., Ltd .: 70% by weight of active ingredient and 17% by weight of isopropyl alcohol) Component conversion), oxazoline-based crosslinking agent (“Epocross” WS500 manufactured by Nippon Shokubai Co., Ltd .: active ingredient 40 mass%, 1-methoxy-2-propanol 38 mass% contained) 10 parts by mass (active ingredient conversion), colloidal silica A coating liquid-3 was obtained in the same manner as the coating liquid-1, except that 1.5 parts by mass (particle size: 140 nm) was mixed.

(Coating solution-4)
The active ingredient is 100 parts by weight of polyester (A) and 40 parts by weight of melamine-based crosslinking agent (“Nicarac” MW12LF manufactured by Sanwa Chemical Co., Ltd .: 70% by weight of active ingredient and 17% by weight of isopropyl alcohol) Component conversion), carbodiimide-based crosslinking agent (“Carbodilite” V-04 manufactured by Nisshinbo Chemical Co., Ltd. V-04: active ingredient 40% by weight) 10 parts by mass (active ingredient conversion), colloidal silica (particle size 140 nm) 1.5 mass A coating liquid-4 was obtained in the same manner as the coating liquid-1, except that it was changed to part mixing.

[Create polyester film]
Example 1
After drying PET-1 in vacuum at 160 ° C. for 4 hours, it was supplied to an extruder and melt-extruded at 285 ° C. A stainless steel fiber is sintered and compressed with a filter having an average opening of 5 μm, and then a stainless steel powder with an average opening of 14 μm is filtered through a sintered filter, and then extruded into a sheet form from a T-shaped die and cast by applying electrostatic force. Using a method, it was wound around a mirror casting drum having a surface temperature of 20 ° C. and solidified by cooling. At this time, cold air having a temperature of 10 ° C. was blown from the opposite surface of the casting drum onto the film at a wind speed of 20 m / s from a slit nozzle having a gap of 2 mm provided in the longitudinal direction, and cooling was performed from both sides.
This unstretched film is preheated to 70 ° C. with a preheating roll, and then stretched 3.1 times in the longitudinal direction using the difference in peripheral speed between the rolls while heating up to 90 ° C. using a radiation heater from the top and bottom. It cooled to 25 degreeC with the cooling roll, and was set as the uniaxially oriented (uniaxial stretching) film. Both surfaces of the film were subjected to corona discharge treatment in air, and the surface tension of the film was 55 mN / m.

Subsequently, the coating liquid-1 was apply | coated to both surfaces of the said uniaxially stretched film using the bar coater. In addition, the metalling wire bar used the thing of diameter 13mm and wire diameter 0.1mm (# 4).
The uniaxially stretched film coated with the coating liquid was held with a clip and guided to an oven, and dried by hot air at a temperature of 120 ° C. and a wind speed of 20 m / min. Subsequently, the film was continuously led to a stretching process, and stretched 3.7 times in the width direction while being heated with hot air at a temperature of 100 ° C. and a wind speed of 15 m / min. The obtained biaxially oriented film was continuously heat-treated with hot air at a temperature of 230 ° C. and a wind speed of 20 m / min for 15 seconds, and then subjected to a 5% relaxation treatment while cooling from 230 ° C. to 120 ° C. Cooled to 50 ° C. Subsequently, after removing both ends in the width direction, the film was wound up to obtain a polyester film having a thickness of 125 μm.
The polyester film obtained here was excellent in transparency, heat distortion resistance, and curl resistance, and could be suitably used as a surface protective film application for a conductive film and a transparent conductive substrate film application.

(Examples 2, 6, and 8)
A polyester film was obtained in the same manner as in Example 1 except that the composition was changed to the configuration shown in Table 1 and the relaxation treatment was changed to 3%. The evaluation results of the obtained polyester film are shown in Table 1.

  Although the polyester films of Examples 2, 6, and 8 have slightly inferior curl resistance, they are excellent in transparency resistance and heat distortion resistance, and can be particularly suitably used as surface protective film applications for conductive films and transparent conductive substrate film applications. It was a thing.

(Examples 3-5, 7, 9-14)
A polyester film was obtained by the same method as in Example 1 except that the configuration was changed to the configuration shown in Table 1. The evaluation results of the obtained polyester film are shown in Table 1.

  The polyester films of Examples 3 to 5 and 7 were excellent in transparency, heat distortion resistance, and curl resistance, and were particularly suitable for use as surface protective film applications for conductive films and transparent conductive substrate film applications. . Although the polyester films of Examples 9 and 10 have slightly inferior heat resistance, they are excellent in transparency and curl resistance, and can be suitably used as surface protective film applications for conductive films and transparent conductive substrate film applications. . Although the polyester films of Examples 11 to 14 were slightly inferior in transparency, they were excellent in heat distortion resistance and curl resistance, and could be suitably used as surface protective film applications for conductive films and transparent conductive substrate film applications. .

(Examples 15 to 22)
Using the raw materials listed in Table 2, each was dried in an independent vacuum dryer at 160 ° C. for 4 hours in a vacuum, and then supplied to each independent separate extruder, and the layer configuration and lamination described in Table 2 as a film. A polyester film was obtained by the same method as in Example 1 except that the melt extrusion was performed by the coextrusion method so as to obtain a ratio. In addition, the notation of “B / A / B” in the item of the layer configuration described in Table 2 indicates that the layer B is arranged on both sides of the layer A as a film configuration, that is, the polyester film is layer B / layer A / layer. It means that it was constituted by the layer structure of B. The evaluation results of the obtained polyester film are shown in Table 2.

  The polyester films of Examples 15 to 17 were excellent in transparency, heat distortion resistance, and curl resistance, and were particularly suitable for use as surface protective film applications for conductive films and transparent conductive substrate film applications. The polyester films of Examples 18 and 19 are slightly inferior in heat distortion resistance, but are excellent in transparency and curl resistance, and can be suitably used as surface protective film applications for conductive films and transparent conductive substrate film applications. It was. Although the polyester films of Examples 20 to 22 are slightly inferior in transparency, they have excellent heat distortion resistance and curl resistance, and can be suitably used as surface protective film applications for conductive films and transparent conductive substrate film applications. It was.

(Examples 23 to 25)
Using the raw materials listed in Table 2, each was dried in an independent vacuum dryer at 160 ° C. for 4 hours in a vacuum, and then supplied to each independent separate extruder, and the layer configuration and lamination described in Table 2 as a film. A polyester film was obtained by the same method as in Example 1 except that the melt extrusion was performed by the coextrusion method so as to obtain a ratio. In addition, the notation of “A / B” in the item of the layer configuration described in Table 2 indicates that the layer B is disposed on one side of the layer A as the film configuration, that is, the polyester film is the layer configuration of the layer A / layer B. It means that it was configured. Moreover, when measuring haze or a refractive index, the layer A surface was made into the measurement surface. The evaluation results of the obtained polyester film are shown in Table 2.

  The polyester films of Examples 23 to 25 are slightly inferior in curl resistance but excellent in transparency and heat resistance moldability, and can be suitably used as a surface protective film application for conductive films and a transparent conductive substrate film application. It was.

(Examples 26 to 28)
Using the raw materials listed in Table 2, each was dried in an independent vacuum dryer at 160 ° C. for 4 hours in a vacuum, and then supplied to each independent separate extruder, and the layer configuration and lamination described in Table 2 as a film. A polyester film was obtained by the same method as in Example 1 except that the melt extrusion was performed by the coextrusion method so as to obtain a ratio. In addition, the notation of “B / A / C” in the item of the layer configuration described in Table 2 is that the layer B is arranged on one side of the layer A and the layer C is arranged on the other side as a film configuration, that is, It means that the polyester film was constituted by the layer constitution of layer B / layer A / layer C. Moreover, when measuring haze or a refractive index, the layer B surface was made into the measurement surface. The evaluation results of the obtained polyester film are shown in Table 2.

  Although the polyester films of Examples 26 and 27 are slightly inferior in transparency, they are excellent in heat distortion resistance and curl resistance, and can be suitably used as surface protection film applications for conductive films and transparent conductive substrate film applications. It was. The polyester film of Example 28 was slightly inferior in heat distortion resistance, but was excellent in transparency and curl resistance, and could be suitably used as a surface protective film application for a conductive film and a transparent conductive substrate film application.

(Comparative Examples 1-3)
A polyester film was obtained by the same method as in Example 1 except that the configuration was changed to the configuration shown in Table 3. In addition, the notation of “A” in the item of the layer configuration shown in Table 3 means that the film configuration is a single layer configuration of the layer A. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester films described in Comparative Examples 1 and 3 were inferior in heat-resistant deformation, and were difficult to use as surface protective film applications for conductive films and transparent conductive substrate film applications. The polyester film described in Comparative Example 2 was inferior in transparency and heat distortion resistance, and was difficult to use as a surface protective film application for conductive films and a transparent conductive substrate film application.

(Comparative Examples 4 and 5)
A polyester film was obtained in the same manner as in Example 2 except that the configuration was changed to the configuration shown in Table 3. In addition, the notation of “A” in the item of the layer configuration shown in Table 3 means that the film configuration is a single layer configuration of the layer A. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester films described in Comparative Examples 4 and 5 were inferior in heat-resistant deformation, and were difficult to use as surface protective film applications for conductive films and transparent conductive substrate film applications.

(Comparative Examples 6 and 7)
The polyester film was prepared in the same manner as in Example 1 except that the length was changed to 3.8 times and the width direction draw ratio was changed to 4.2 times. Got. In addition, the notation of “A” in the item of the layer configuration shown in Table 3 means that the film configuration is a single layer configuration of the layer A. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester films described in Comparative Examples 6 and 7 are inferior in transparency and have problems such as film tearing in the polyester film production process, and the use of surface protective films for conductive films and transparent conductive substrates. It was difficult to use as a film application.

(Comparative Examples 8 to 10)
A polyester film was obtained in the same manner as in Example 15 except that the configuration was changed to the configuration shown in Table 3. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester films described in Comparative Examples 8 and 9 are inferior in heat-resistant deformation and are difficult to use as surface protective film applications for conductive films and transparent conductive substrate film applications. Moreover, the polyester film described in Comparative Example 10 was inferior in transparency, and was difficult to use as a surface protective film application for conductive films and a transparent conductive substrate film application.

(Comparative Examples 11 and 12)
A polyester film was obtained in the same manner as in Example 23, except that the configuration shown in Table 3 was changed. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester film described in Comparative Example 11 was inferior in heat-resistant deformation and was difficult to use as a surface protective film application for conductive films and a transparent conductive substrate film application. Moreover, the polyester film described in Comparative Example 12 was inferior in heat distortion resistance and curl resistance, and was difficult to use as a surface protective film application for conductive films and a transparent conductive substrate film application.

(Comparative Examples 13 and 14)
A polyester film was obtained in the same manner as in Example 26 except that the configuration was changed to the configuration shown in Table 3. Table 3 shows the evaluation results of the obtained polyester film.

  The polyester films described in Comparative Examples 13 and 14 were inferior in heat-resistant deformation, and were difficult to use as surface protective film applications for conductive films and transparent conductive substrate film applications.

Claims (9)

  A polyester film containing a polyester resin as a main component, having a haze of less than 1.5%, and a heat of crystal melting ΔHm measured at a heating rate of 20 ° C./min by differential scanning calorimetry is 13 cal / g or more and 30 cal / g or less, The polyester film characterized by the above-mentioned. The polyester film according to claim 1, wherein the thickness is 16 μm or more and 300 μm or less.   The polyester film according to claim 1 or 2, wherein a refractive index is 1.63 or more and 1.69 or less.   The polyester film according to claim 1, wherein the polyester resin is polyethylene terephthalate.   The polyester film according to any one of claims 1 to 4, wherein the polyester film is made of only a polyester resin, and the polyester resin is homopolyethylene terephthalate.   The polyester film according to any one of claims 1 to 5, wherein the content of the cyclic trimer is 0.01% by mass or more and 1.00% by mass or less.   The polyester film according to any one of claims 1 to 6, wherein the thermal shrinkage in the longitudinal direction of the film at 150 ° C for 30 minutes is 2.0% or less.   The polyester film according to any one of claims 1 to 7, wherein the thermal shrinkage in the film width direction at 150 ° C for 30 minutes is 1.0% or less. It is used for an optical use, The polyester film in any one of Claims 1-8 characterized by the above-mentioned.