KR102559867B1 - polyester film - Google Patents

Abstract

The ratio of optical density to thickness (μm) (optical density (OD) / thickness (T)) is 0.22 or more and 2.0 or less, and in differential scanning calorimetry (DSC), the crystallization temperature (Tmc) on cooling when cooled at a temperature cooling rate of 10 ° C. / min after holding in a molten state for 5 minutes is 180 ° C. or more and has a peak in the range of 210 ° C. or less. A polyester film excellent in shrinkage when illuminated and suitably used as a light-shielding base material for electronic devices is provided.

Description

polyester film

[0001] The present invention relates to a polyester film that is excellent in hiding properties and film forming properties, and also excellent in shrinkage property when irradiated with light.

Polyester (particularly, polyethylene terephthalate, polyethylene 2,6-naphthalene dicarboxylate, etc.) resin has excellent mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and is used for various applications. A polyester film obtained by forming the polyester into a film, in particular, a biaxially oriented polyester film, is used for various applications such as materials for solar battery back sheets, electrical insulation materials for water heater motors, electrical insulation materials for car air conditioner motors and drive motors, tape materials, condenser materials, packaging materials, building materials, photographic applications, graphic applications, thermal transfer applications, etc., due to its mechanical properties and electrical properties.

Among these uses, concealability is required for materials for solar cell back sheets and tape materials used inside electronic devices. For example, in the solar cell back sheet material, from the viewpoint of design, it is preferable that the wiring to the power generation element is not visible from the outside. [0004] As for materials for solar battery back sheets, a method of using a polyester film containing a black pigment such as carbon black has been studied to improve the concealability (Patent Documents 1 and 2). In addition, in tape materials, with the recent spread of smart phones, tapes used inside electronic devices are required to have high concealment properties in order to block internal light. Along with miniaturization and thinning of electronic devices, tape materials are required not only to have concealability but also to be thin. In tape materials, as a method of improving concealability, a method of providing a printed layer containing a large amount of black pigment on a polyester film having a thin film thickness has been studied (Patent Document 3).

Japanese Unexamined Patent Publication No. 2008-56871 Japanese Unexamined Patent Publication No. 2011-119651 Japanese Patent No. 5651012

However, as in the methods described in Patent Literatures 1 and 2, when carbon black is added to impart hiding properties to polyester, the carbon black serves as a crystallization nucleus and the polyester crystallization rate is increased. Therefore, when carbon black is contained in a large amount, a problem of deterioration in film forming properties occurs. Therefore, in the methods described in Patent Literatures 1 and 2, since there is a limit to the concentration of carbon black contained in the film, there is a problem that sufficient hiding property cannot be obtained. This subject was remarkable in the case of a film with a thin film thickness especially. On the other hand, in the method described in Patent Document 3, although sufficient concealability can be obtained even in a thin film, there is a problem of environmental pollution caused by printing ink and a problem of shrinkage of the film due to heat generated when light is absorbed because the thickness ratio of the polyester film having excellent mechanical properties is small.

An object of the present invention is to provide a polyester film that is excellent in hiding properties (hereinafter sometimes referred to as light-shielding properties) and film forming properties in view of such prior art, and also excellent in shrinkage property when exposed to light (hereinafter sometimes referred to as light shrinkability).

In order to solve the above problems, the present invention takes the following configuration. in other words,

[I] The ratio of optical density and thickness (optical density (OD) / thickness (T)) is 0.22 or more and 2.0 or less, and the cooling crystallization temperature (Tmc) in differential scanning calorimetry (hereinafter referred to as DSC) is 180 ° C. or more and 210 ° C. or less. Polyester film.

[II] The polyester film according to [I], which contains 4% by mass or more and 25% by mass or less of the black pigment.

[III] In [I] or [II], the 10-point average roughness (Rz) (μm) of at least one surface is the ratio of Rz (μm) to thickness (μm) (10-point average roughness (Rz) / thickness (T)) A polyester film that satisfies 0.30 or less.

[IV] The polyester film according to any one of [I] to [III], wherein the polyester resin constituting the film contains an isophthalic acid component and/or a cyclohexanedimethanol component as constituent components of the polyester.

[V] The polyester film according to [IV], wherein the polyester constituting the film contains 0.5 mol% or more and 20 mol% or less of an isophthalic acid component with respect to all dicarboxylic acid components, or 0.5 mol% or more and 20 mol% or less of a cyclohexanedimethanol component with respect to all diol components.

[VI] The polyester film according to any one of [I] to [V], wherein the film thickness is 28 µm or less.

[VII] The polyester film according to any one of [I] to [VI], which is used as a light-shielding substrate for electronic devices.

[VIII] A light-shielding tape using the polyester film described in any one of [I] to [VI].

ADVANTAGE OF THE INVENTION According to this invention, the polyester film which is excellent in concealment property, film forming property, and also excellent in light shrinkage resistance can be provided. In addition, such a film can be suitably used as a light-shielding substrate used inside electronic devices.

The polyester film of the present invention has a polyester resin as a main component. Here, using a polyester resin as a main component means that the polyester resin is contained in an amount of 60% by mass or more relative to the components constituting the film.

The polyester resin constituting the polyester film of the present invention can be obtained by 1) polycondensation of a dicarboxylic acid or an ester-forming derivative thereof (hereinafter, collectively referred to as “dicarboxylic acid component”) and a diol component or an ester-forming derivative thereof (hereinafter, collectively referred to as “diol component”), 2) polycondensation of a carboxylic acid or carboxylic acid derivative and a compound having a hydroxyl group in one molecule, and 1) a combination of 2). In addition, polymerization of the polyester resin can be performed by a conventional method.

In 1), as the dicarboxylic acid component, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, ethylmalonic acid, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin Alicyclic dicarboxylic acids such as dicarboxylic acids, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, Representative examples include aromatic dicarboxylic acids such as 4,4'-diphenylsulfone dicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylendane dicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorenic acid, or ester derivatives thereof. In addition, these may be used independently or may be used in multiple types.

Further, dicarboxylic compounds obtained by condensing oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid and derivatives thereof, or condensing a plurality of oxyacids such as hydroxybenzoic acid to at least one carboxy terminal of the dicarboxylic acid component can also be used.

Next, as the diol component, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol, alicyclic diols such as cyclohexanedimethanol, spiroglycol, and isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, and 9,9' - Aromatic diols, such as bis(4-hydroxyphenyl) fluorene, are mentioned as a representative example. In addition, even if these are used independently, even if they use multiple types as needed, they are not cared about. Dihydroxy compounds formed by condensing diols to at least one hydroxy terminal of the diol component can also be used.

Examples of the compound having a carboxylic acid or a carboxylic acid derivative and a hydroxyl group in 2) include oxyacids such as l-lactide, d-lactide, and hydroxybenzoic acid, derivatives thereof, oligomers of oxyacids, and those obtained by condensation of an oxyacid with one carboxyl group of a dicarboxylic acid.

Further, as the polyester resin constituting the polyester film of the present invention, a trifunctional component (a trivalent or higher valent carboxylic acid, a trivalent or higher valent diol, a trivalent or higher valent oxyacid and their ester-forming derivatives) may be contained within a range not impairing the properties of the present invention.

Specific examples of the polyester resin include homopolymers such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, and polylactic acid, and copolymers thereof. The polyester resin constituting the polyester film of the present invention may be selected from the above homopolymers and copolymers and used, or homopolymers or homopolymers and copolymers may be blended for use.

Here, as the homopolymer of the polyester resin, polyethylene terephthalate, polyethylene-2,6-naphthalate, polybutylene terephthalate, and polylactic acid are preferable from the viewpoint of film forming properties. Among them, polyethylene terephthalate and polyethylene-2,6-naphthalate are more preferable from the viewpoint of easy processability, and polyethylene terephthalate is particularly preferable from the viewpoint of excellent film forming properties.

In addition, the polyester resin copolymer represents a copolymer composed of either or both of the other dicarboxylic acid component and the diol component for less than 50 mol% of the total polyester resin, and when a blend with a homopolymer is assumed, it is preferable to use a copolymer in which the same molecular structure as the target homopolymer constitutes 50 mol% or more of the total.

Here, as the copolymer of the polyester resin, from the viewpoint of excellent polymerization suitability, thermal stability, and compatibility with the homopolymer, alicyclic dicarboxylic acid, isophthalic acid, or naphthalene dicarboxylic acid as the dicarboxylic acid component, and butanediol, ethylene glycol, spiroglycol, or cyclohexane dimethanol as the diol component are preferably used, and these may be used alone or in combination as necessary. Among them, those containing isophthalic acid as a copolymer component as a dicarboxylic acid component and those containing cyclohexanedimethanol as a copolymer component as a diol component are more preferably used from the viewpoint of improving film forming properties.

In the polyester resin constituting the polyester film of the present invention, the ratio of the copolymerization component is 0.5 mol% or more and 20 mol% or less with respect to the total polyester resin components. By reducing the crystallinity of the polyester by introducing a copolymerization component into the polyester resin, a polyester film having excellent film formability and light shrinkage resistance can be obtained even if a large amount of the color pigment described later is contained. More preferably, the proportion of the copolymerization component is 1.0 mol% or more and 15 mol% or less, still more preferably 2.0 mol% or more and 10 mol% or less, and particularly preferably 2.5 mol% or more and 7.5 mol% or less.

The copolymerization component as used herein refers to a dicarboxylic acid component and a diol component other than the first component contained in the polyester resin in an amount of less than 50 mol% when the dicarboxylic acid component and the diol component of the polymer constituting more than 50 mol% of the total polyester resin are used as the first component. In addition, the copolymerization component of the polyester film can be analyzed by proton nuclear magnetic resonance spectroscopy ( ¹ H-NMR) or carbon nuclear magnetic resonance spectroscopy ( ¹³ C-NMR) after solvent extraction of the polyester film.

When the ratio of the copolymerization component of the polyester resin is less than 0.5 mol%, the crystallinity cannot be suppressed, the film formability is insufficient, or the orientation at the time of stretching takes too long, and the light shrinkage resistance may also be reduced. On the other hand, when the ratio of the copolymerization component of the polyester resin is more than 20 mol%, the crystallinity of the polyester resin is too low and the film forming property is rather deteriorated, or the film shrinks too much due to heat generated when irradiated with light due to insufficient mechanical strength without orientation, and the light shrinkage resistance may be insufficient. That is, in the polyester resin constituting the polyester film of the present invention, by setting the ratio of the copolymerization component to 0.5 mol% or more and 20 mol% or less with respect to all polyester resin components, a polyester film having both excellent film formability and light shrinkability can be obtained. In addition, as the copolymerization component, an isophthalic acid component is included in an amount of 0.5 mol% or more and 20 mol% or less with respect to all dicarboxylic acid components, or a cyclohexanedimethanol component is included in an amount of 0.5 mol% or more and 20 mol% or less with respect to all diol components. Since the film formability and light shrinkage of the polyester film can be further improved, it is more preferable.

Moreover, it is preferable that the polyester resin which comprises the polyester film of this invention is a crystalline polyester resin from a viewpoint of biaxial stretchability. Crystallinity as used herein refers to a chart obtained when a polyester film is heated from a solid state to a molten state at a heating rate of 10 ° C. / min in differential scanning calorimetry in accordance with JIS K7122 (1987). It indicates that an endothermic peak due to thermal crystallization is observed.

The polyester film of the present invention preferably has a color pigment in order to impart concealability. As a color pigment, a black pigment is preferable from a viewpoint of being excellent in light-shielding property. Specific examples of the black pigment include carbon-based compounds such as carbon black, graphite, fullerene, and carbon fibers, and oxide-based inorganic particles such as titanium black. In addition, it is preferable to use carbon black because it is compatible with hiding property and film forming property, and among these, it is more preferable to use carbon black produced by a furnace method from the viewpoint of being inexpensive and excellent in hiding property.

The primary particle diameter of the color pigment is preferably 5 nm or more and 100 nm or less, more preferably 10 nm or more and 50 nm or less, still more preferably 15 nm or more and 30 nm or less. When the primary particle size of the color pigment is less than 5 nm, the formation of defects due to aggregation or excessive acceleration of crystallization of the polyester resin may reduce film forming properties. On the other hand, when the primary particle size of the color pigment exceeds 100 nm, the hiding property may be lowered or the film may be easily torn during film formation.

Moreover, as for content of the said color pigment, 0.5 mass % or more and 40 mass % or less are preferable. In the present invention, in the case of containing a black pigment as a color pigment, it is preferably 3.5% by mass or more and 30% by mass or less, more preferably 4.0% by mass or more and 25% by mass or less, still more preferably 5.0% by mass or more and 15% by mass or less, particularly preferably 6.0% by mass or more and 10% by mass or less. In the present invention, if the content of the black pigment is less than 3.5% by mass, the light-shielding property may not be satisfied because the hiding property is insufficient. On the other hand, when content of a black pigment exceeds 30 mass %, film forming property may deteriorate. That is, by containing 3.5% by mass or more and less than 30% by mass of a black pigment in the polyester film of the present invention, even if it is a thin film with a film thickness of 28 μm or less, excellent concealment and film forming properties are compatible.

Further, the polyester film of the present invention may contain other additives (eg, heat-resistant stabilizer, ultraviolet absorber, weathering stabilizer, organic lubricant, filler, antistatic agent, flame retardant, etc.) within a range that does not impair the effects of the present invention. For example, when the polyester film of the present invention is used for applications requiring flame retardancy, the flame retardancy of the polyester film can be improved by containing an organic flame retardant such as halogen or phosphorus or an inorganic flame retardant such as antimony or metal hydroxide. As the flame retardant, organic flame retardants are preferably used from the viewpoint of maintaining film forming properties even when used in combination with color pigments, and phosphorus-based flame retardants are more preferably used among organic flame retardants from the viewpoint of reducing environmental impact.

The polyester film of the present invention needs to have a cooling crystallization temperature (Tmc) of 180°C or more and 210°C or less in differential scanning calorimetry (DSC). It is more preferably 186°C or more and 206°C or less, more preferably 192°C or more and 203°C or less, still more preferably 197°C or more and 201°C or less. The temperature-decreasing crystallization temperature (Tmc) in differential scanning calorimetry as used herein refers to heat generation obtained when a polyester film is heated from 25°C to the melting point (Tm) of the polyester resin + 50°C at a heating rate of 10°C/min in accordance with JIS K7122 (1987), and then maintained in a molten state at the melting point (Tm) +50°C for 5 minutes and then cooled to 25°C at a cooling rate of 10°C/min. Indicates the temperature of the peak top of the peak. In the case of having a plurality of exothermic peaks, the peak top temperature located at the highest temperature is shown. Here, the melting point (Tm) of the polyester resin is the chart obtained when the polyester film is heated from the solid state to the molten state at a heating rate of 10 ° C. / min in differential scanning calorimetry. The cooling crystallization temperature (Tmc) is used as an indicator of the crystallinity of the polyester resin, and a high temperature of the cooling crystallization temperature (Tmc) indicates high crystallinity, and a low temperature of the cooling crystallization temperature (Tmc) or cooling If the crystallization temperature (Tmc) is not detected, it indicates low crystallinity.

In the polyester film of the present invention, since the crystallinity is too low when the cooling crystallization temperature (Tmc) is less than 180 ° C., when a high concentration of black pigment is included, the film shrinks during light irradiation or the film is bent during stretching, resulting in deterioration of stretchability. In particular, this problem appears remarkably in a thin film having a film thickness of 28 μm or less. On the other hand, when the cooling crystallization temperature (Tmc) exceeds 210°C, the crystallinity is too high, making film formation difficult. In addition, orientation is easily applied, and light shrinkage resistance is lowered due to residual stress after stretching. That is, in the present invention, by setting the crystallization temperature (Tmc) on cooling to within the range of 180°C or more and 210°C or less, a polyester film having both excellent film forming properties and light shrinkage properties can be obtained.

In addition, the crystallization temperature (Tmc) on cooling in the present invention can be adjusted by the type and content of the color pigment and the ratio of the copolymerization component in the polyester resin when the color pigment is contained in the polyester resin constituting the polyester film. Moreover, in order to aim at compatibility with hiding property, the method of adjusting with the ratio of the copolymerization component in a polyester resin is the most preferable.

The polyester film of the present invention, even if it is a thin film, has excellent concealment, film formability, and light shrinkage, so that it can be suitably used as a tape base material used inside electronic devices requiring thinness such as smart phones.

The thickness (T) of the polyester film of the present invention is preferably 28 μm or less, more preferably 25 μm or less, still more preferably 20 μm or less, and particularly preferably 16 μm or less. Further, the lower limit of the thickness is not particularly limited, but it is realistic to be 3.0 μm or more in view of deterioration of film formability and deterioration of light shrinkage.

The polyester film of the present invention preferably has an optical density (OD) of 3.5 or more, more preferably 4.0 or more, even more preferably 5.0 or more, and particularly preferably 6.0 or more. By setting the optical density (OD) of the polyester film of the present invention to 3.5 or more, it can be suitably used as a tape base material that requires light-shielding properties used in electronic devices in which light is generated inside. Moreover, when using as a base film of a light shielding tape, the number of times of printing of a black ink layer can be reduced. In addition, although there is no particular limitation on the upper limit of the optical density, 9.0 or less is realistic from the viewpoint of the amount of particles that can be incorporated into the film.

The polyester film of the present invention requires a ratio of optical density to thickness (μm) (optical density (OD)/thickness (T)) of 0.22 or more and 2.0 or less. As can be understood from Lambert-Ber's law, the optical density, which is an indicator of the concealment properties of a film, tends to be high when the thickness of the film increases (when the light transmission path becomes longer). Therefore, as long as the optical density is increased, even in a conventional polyester film in which the amount of color pigment that can be contained in the film is limited from the viewpoint of film formability and light shrinkage, it was possible to achieve this by increasing the film thickness. However, in a conventional polyester film in which the amount of color pigment that can be contained in the film is limited from the viewpoint of film forming property and light shrinkage, it is difficult to set the optical density to thickness (μm) ratio (OD/T) to 0.22 or more. As described above, by controlling the crystallinity of the polyester film of the present invention to a preferred range, it became possible to contain a color pigment at a high concentration, and as a result, a ratio (OD / T) of optical density and thickness (μm) that could not be reached conventionally is 0.22 or more, preferably 0.25 or more, 1.5 or less, more preferably 0.30 or more, 1.0 or less, still more preferably 0.35 or more, 0.5 or less.

In the present invention, a polyester film having a ratio (OD/T) of optical density to thickness (μm) of less than 0.22 shows that the hiding property is insufficient compared to the thickness. On the other hand, when the ratio (OD/T) of the optical density to the thickness (μm) exceeds 2.0, it is thin and excellent in hiding properties, but the film formability is reduced, and the film is excessively shrunk by heat generated by absorbing light during light irradiation. Therefore, it is not suitable as a substrate used inside electronic devices.

That is, in the polyester film of the present invention, by setting the ratio (OD/T) of the optical density to the thickness (μm) in the range of 0.22 or more and 2.0 or less, even if it is a thin film, it has excellent light-shielding properties, and it is possible to make a film excellent in film formability and light shrinkability. Therefore, it can be suitably used as a tape base material inside an electronic device that requires thinness like a smart phone and also requires light-shielding properties.

The 10-point average roughness (Rz) (μm) of at least one surface of the polyester film of the present invention is preferably 3.0 μm or less, more preferably 2.5 μm or less, still more preferably 2.0 μm or less. The 10-point average roughness (Rz) herein is a value obtained by measuring the 10-point average roughness (Rz) of at least one surface of the polyester film with a contact-type three-dimensional surface roughness meter in a measuring method described later. If the 10-point average roughness (Rz) exceeds 3.0 μm, the unevenness of the surface may become too large, resulting in a thick film thickness required to block light. Further, the lower limit of the 10-point average roughness (Rz) is not particularly limited, but is preferably 0.1 µm or more from the viewpoint of deterioration in windability. Further, it is more preferable that the 10-point average roughness (Rz) (μm) of both surfaces of the film satisfy the above range.

The polyester film of the present invention has a 10-point average roughness (Rz) (nm) of at least one surface, and the ratio (10-point average roughness (Rz) / thickness (T)) of Rz (μm) and thickness (μm) preferably satisfies 0.30 or less, more preferably 0.25 or less, and still more preferably 0.20 or less. When (Rz/T) exceeds 0.30, the unevenness of the surface becomes too large, and the film thickness necessary for blocking light is insufficient, and the light-shielding property may decrease. In addition, there are cases where the unevenness of the surface becomes too large relative to the film thickness, and the film formability is lowered. The lower limit of (Rz/T) is not particularly limited, but is preferably 0.07 or more, more preferably 0.10 or more, and even more preferably 0.12 or more from the viewpoint of improving the light-shielding property by light diffusion on the film surface.

In order to set the ratio (Rz/T) of the 10-point average roughness (Rz) (μm) and the thickness (μm) of the polyester film of the present invention to 0.30 or less, when the color pigment is contained in the polyester resin constituting the polyester film, the 10-point average roughness (Rz) (μm) can be adjusted by the film forming conditions of the polyester film. Details are described later.

Even if the polyester film of this invention is a single film film, it does not matter which structure is selected from the laminated|multilayer film which consists of two or more layers. The manufacturing process can be simplified by using the polyester film of this invention as a single film. In addition, in the case of a laminated film of two or more layers, by using a two-type three-layer configuration of P2 layer / P1 layer / P2 layer, for example, the P2 layer is a layer that does not contain a color pigment, and the P1 layer is a layer containing a color pigment. By separating the functions as a layer, it is possible to create a film that has both concealment and new functions. Moreover, light-shielding property can be improved more by making the said p2 layer contain a color pigment and containing the cavity which has light diffusivity to the p1 layer.

(Method for producing polyester film)

Next, a specific example is given and demonstrated about the manufacturing method of the polyester film of this invention. The present invention should not be construed as being limited only to substances obtained by these examples.

First, the method for producing the polyester resin constituting the polyester film can be produced by the following method.

A polyester resin can be obtained by subjecting a dicarboxylic acid or its ester derivative to a diol to a transesterification reaction or an esterification reaction by a known method. Examples of conventionally known reaction catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and phosphorus compounds. Preferably, in any step prior to completion of the method for producing the polyester resin, it is preferable to add an antimony compound, a germanium compound, or a titanium compound as a polymerization catalyst. As such a method, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

Next, as a method for producing a polyester film, a method (melt casting method) in which raw materials constituting the polyester film are heated and melted in an extruder and extruded from a mold onto a cooled cast drum to be processed into a sheet shape (melt casting method) is preferably used. In addition, when the polyester film has a laminated structure, the raw materials of each layer to be laminated are introduced into two extruders, melted, and then joined, and then coextruded from a mold onto a cooled cast drum to form a sheet. A method (coextrusion method) can be preferably used. In addition, an unstretched sheet having suppressed crystallization can be produced by bringing the melt-extruded sheet into close contact with a cast drum with static electricity and fixing it by cooling. Further, as a method of bringing the melt-extruded sheet into close contact with the cast drum, a method of blowing air to the melt-extruded sheet through a thin groove and bringing it into close contact with the melt-extrusion sheet or a method of drawing the melt-extrusion sheet through a vacuum chamber and bringing it into close contact can also be selected.

Next, the polyester film of the present invention is preferably at least uniaxially stretched, more preferably biaxially stretched. By obtaining by stretching the polyester film of the present invention, it can be made into a polyester film that can be thinned and has excellent mechanical properties.

As the stretching method, the unstretched sheet is drawn into a group of rolls heated to a temperature of 70 to 140 ° C., stretched in the longitudinal direction (longitudinal direction, that is, the direction in which the sheet travels), and cooled in a group of rolls at a temperature of 20 to 50 ° C. A uniaxially stretched sheet can be obtained.

In the case of biaxial stretching, the both ends of the uniaxially stretched sheet obtained above are then held by clips while leading to a tenter, and transversely stretched in a direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated at a temperature of 70 to 150 ° C. to obtain a biaxially stretched polyester film.

At this time, the draw ratio is 2 to 5 times in the longitudinal direction and the width direction, respectively, but the area magnification (longitudinal stretch ratio x transverse stretch ratio) is preferably 8 times or more, more preferably 9 times or more, still more preferably 10 times or more. The lower limit of the plane magnification is not particularly limited, but if it is less than 6 times, the mechanical properties of the film may be insufficient or thinning may be difficult.

As a method of biaxial stretching, in addition to the sequential biaxial stretching method in which stretching in the longitudinal direction and the width direction are separately performed, a simultaneous biaxial stretching method in which stretching in the longitudinal direction and the width direction are performed simultaneously, or an impension film forming method may be used.

Here, in order to adjust the 10-point average roughness (Rz) (μm) of the polyester film to a preferred range, it is preferable to select biaxial stretching, and the film temperature immediately before uniaxial stretching (immediately before starting simultaneous stretching in the case of simultaneous biaxial stretching) is adjusted to a range of 80 ° C. or more and 100 ° C. or less, and the first-axis stretching ratio is 2.8 times or more and 3.6 times or less, or the preheating temperature of the second-axis stretching is set. It is more preferable to form a film in the range of 70°C or higher and 125°C or lower.

In order to reduce the 10-point average roughness (Rz) of the polyester film, since it is important to suppress the generation of coarse crystals during stretching, Rz may increase in unstretched sheets and uniaxially stretched sheets. In the case where the stretching temperature during the first stretching exceeds 100°C or the stretching ratio is less than 2.8 times, thermal crystallization of the polyester is excessively promoted, and the 10-point average roughness (Rz) may rather increase. In addition, when the stretching temperature is less than 80°C or when the stretching ratio exceeds 3.6 times, orientation crystallization in the first axis may be excessively promoted. In addition, when the preheating temperature of the second-axis stretching exceeds 125 ° C., the polyester crystals formed on the first axis grow with heat, and coarse crystals remain on the polyester film, and some have large surface irregularities. On the other hand, if the preheating temperature for the second-axis stretching is lower than 70°C, the amount of heat may be insufficient and tearing in the stretching may occur.

That is, when the polyester film of the present invention is produced by biaxial stretching, by performing film formation under the above conditions, it becomes possible to suppress the crystallization of polyester and the growth of crystals, and the 10-point average roughness (Rz) of the polyester film can be adjusted to a preferred range, thereby further improving the light blocking properties of the polyester film.

As a method for incorporating the color pigment into the polyester film of the present invention, a method of preparing a raw material obtained by master batching the color pigment at a high concentration and diluting the polyester resin containing no color pigment to a desired concentration when introduced into an extruder (master batch method) is preferably used.

Further, in the present invention, it is more preferable to use a copolymerized polyester resin as a base material for master batching, and the master batch obtained in this way can further increase the dispersibility of the color pigment, and improve light-shielding and film forming properties.

The polyester film of this invention can be manufactured by the said manufacturing method. The obtained polyester film is excellent in hiding properties and film forming properties, and also has excellent shrinkage properties when exposed to light. Therefore, it can be suitably used for a variety of applications, such as industrial materials such as cover films, films for solar cell back sheets, insulating films for motors, and the like, packaging materials such as external films for lithium ion batteries, design films, and protective films, films for ink ribbons, films for building materials, and thermal transfer films, as well as light-shielding substrates used inside electronic devices.

In addition, as a light-shielding base material for electronic devices that can be suitably used for the polyester film of the present invention, cell phones, smartphones, disk top-type PCs, notebook PCs, tablet-type PCs, electronic dictionaries, car navigation systems, GPS navigation systems, digital cameras, video cameras, and the like. By using the polyester film of the present invention, it is possible to further reduce the size or thickness while preventing internal light from leaking to the outside of the electronic device.

The polyester film of the present invention is excellent in hiding properties and film forming properties, and has excellent shrinkage properties when exposed to light, so that it can be suitably used for light-shielding tapes. As a structure of the light-shielding tape which can be used for the polyester film of this invention, what provided the adhesive layer on one side or both surfaces of the polyester film of this invention is mentioned, for example. The pressure-sensitive adhesive used in the pressure-sensitive adhesive layer is not particularly limited, but an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, and the like are preferably used.

When the light-shielding tape of the present invention lacks light-shielding properties, a black ink layer may be provided between the polyester film and the pressure-sensitive adhesive layer in a configuration in which the pressure-sensitive adhesive layer is provided on the side or both surfaces of the polyester film where the pressure-sensitive adhesive layer is not provided. Moreover, it is also possible to mix a black pigment in an adhesive and install it as a black adhesive layer. The black ink component is not particularly limited, but a component in which the above-described black pigment is contained in a binder made of an acrylic resin or a urethane resin is preferably used.

Further, within a range where the effect of the present invention is not impaired, a functional layer containing other additives may be newly formed, or may be combined with the pressure-sensitive adhesive layer or the black ink layer. For example, a light-shielding tape having matte properties can be obtained by providing a layer containing particles having a large particle size on a polyester film on the opposite side of the pressure-sensitive adhesive layer. Moreover, it can be set as a light-shielding tape excellent in heat dissipation property by adding heat dissipation particles to the black ink layer.

Next, as a method of providing the layer on the polyester film, surface treatment such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and coating with an undercoat is performed on the surface, and then a roll coating method, dip coating method, bar coating method, a coating method such as a die coating method and a gravure roll coating method, or a printing method such as offset printing, gravure printing, flexographic printing, silk screen printing, and inkjet printing. Moreover, the method of using a well-known coating method in-line during film formation of a polyester film is also a preferable method from the point of simplifying a process.

As described above, since the light-shielding tape using the polyester film of the present invention that is thin and has excellent light-shielding properties can eliminate the black ink layer conventionally used for imparting light-shielding properties or reduce the number of layers, it is possible to reduce the environmental load due to organic solvents used as solvents and simplify the manufacturing process.

[Measurement method and evaluation method of characteristics]

(1) Differential Scanning Calorimetry (DSC)

In accordance with JIS K7122 (1987), Seiko Instruments Inc. Using the manufactured differential scanning calorimetry device “Robot DSC-RDC220” and the disk session “SSC/5200” for data analysis, 5 mg of polyester film was weighed on a sample pan and heated from room temperature to 300° C. at a heating rate of 10° C./min (called 1st RUN), held for 5 minutes in that state, then cooled to 25° C. at a cooling rate of 10° C./min, and the measurement charts for the heating and cooling processes were got it

(1-1) Measurement of cooling crystallization temperature (Tmc)

Regarding the exothermic peak appearing in the cooling process obtained in (1), the temperature at the peak top was defined as the temperature cooling crystallization temperature (Tmc) of the polyester film. In addition, when a plurality of exothermic peaks appear, the peak on the highest temperature side is taken as the temperature cooling crystallization temperature (Tmc).

(2) optical density measurement

The optical density of the polyester film was measured using a spectral densitometer manufactured by X-lite. The measurement was performed 5 times at a distance of 5 cm or more on a straight line in the longitudinal direction and the width direction, and the average value of 10 times in total was taken as the optical density. In addition, when directionality was unclear or when there was no concept, measurement was performed on an arbitrary straight line and on a straight line in the vertical direction.

(3) measurement of three-dimensional surface roughness (Rz)

The 10-point average roughness (Rz) of the polyester film was obtained from Kosaka Laboratory Ltd. 3D surface roughness meter (model ET-4000A) manufactured by Kosaka Laboratory Ltd. Using a three-dimensional surface roughness analysis system (type TDA-31), the stylus has a tip radius of 0.5 μmR, a diameter of 2 μm, is made of diamond, and a needle pressure of 100 μN. 100, Z measurement magnification: 20000, hysteresis: 0.006 μm was set, and the average value obtained by measuring twice in the film length direction and width direction was taken as the three-dimensional surface roughness (Rz). In addition, the measurement was performed on both surfaces, and the three-dimensional surface roughness of the lower value was described in the table. In addition, when directionality was unclear or when there was no concept, measurement was performed on an arbitrary straight line and on a straight line in the vertical direction.

(4) film formation

The film-forming property of the polyester film was determined as follows from the stretched surface magnification at which film tearing did not occur during continuous film-forming for 1 hour. In addition, both the longitudinal stretch and the transverse stretch magnification are at least 2.5 times or more, and the transverse stretch magnification here represents the machine magnification, which is the ratio of the tenter entrance width to the maximum width. In addition, you may change conditions other than a draw ratio freely.

Face magnification 10 times or more: A

Face magnification 9 times or more: B

Face magnification 8 times or more: C

Face magnification 6x or higher: D

Face magnification is less than 6x, or film cannot be formed: E

The film forming properties are good for A to D, and among them, A is the most excellent.

(5) Evaluation of light-shielding properties

(5-1) Fabrication of pseudo-LED lighting stand for light-shielding evaluation

Hayashi Watch-Works Co., Ltd. To the LED light source for the optical fiber light guide (model: LA-HDF108AS, rated voltage AC100-240V, rated power consumption 20W, rated frequency 50/60Hz), the company's optical fiber light guide with a binding diameter of 4 mmφ was connected, and the LED light was prepared by setting the control scale of the LED light source body to 8. Next, a light guide was inserted from the lower part of the sample stand having a hole of the diameter of the tip of the light guide, and the tip of the LED light was fixed at a position 5 mm away from the flat surface of the sample stand to produce a pseudo-LED light stand.

(5-2) Evaluation of similar light blocking properties

The pseudo-LED lighting stand obtained in (5-1) was covered with a polyester film, and the presence or absence of an LED light source penetrating the polyester film was visually confirmed when the input voltage was adjusted, and the light-shielding property of the polyester film was determined as follows. In addition, the said evaluation was performed 5 times by selecting the location separated by 5 cm or more on the straight line of the longitudinal direction and the width direction, and it was set as the average value of 10 times in total. In addition, when the shape of the transmitted light was not circular, the location with the longest diameter was measured.

No transmitted light is visible even at an input voltage of 5 V: A

Transmitted light is not visible when the input voltage is more than 3 V and less than 5 V: B

Transmitted light is not visible when the input voltage is 2 V or more and less than 3 V: C

Transmitted light is not visible when the input voltage is 1V or more and less than 2V: D

Transmitted light is visible even when the input voltage is less than 1 V: E

Light-shielding properties are good for A to D, and among them, A is the most excellent.

(6) Evaluation of light shrinkage

Write a square with a side of 1 cm on one side of the polyester film, and measure the length of two diagonals to Techno Needs Company Ltd. It was measured using a manufactured universal projector (AMM-1 unit), and the average value of the two lengths was taken as L0. Next, the pseudo LED light stand used in (4) was covered with a polyester film so that the center of the square was the center of the LED light, and the input voltage was set to 5 V and the light was illuminated for 30 seconds. The average value when the lengths of two diagonals of the square were similarly measured was set as L, and the light shrinkage was calculated from the following formula. In addition, the said evaluation was performed 5 times by selecting a location separated by 5 cm or more on a straight line in the length direction and width direction, and it was set as the average value of 10 times in total.

Optical shrinkage (%) = (L0 - L) / L0 × 100

From the obtained light shrinkage rate, the light shrinkage resistance of the polyester film was determined as follows.

Light shrinkage less than 2%: A

Light shrinkage of 2% or more and less than 3%: B

Light shrinkage of 3% or more and less than 5%: C

Light shrinkage of 5% or more and less than 10%: D

Light shrinkage greater than 10%, or not measurable: E

The light shrinkage properties of A to D are good, and among them, A is the most excellent.

(7) Required characteristics of light-shielding materials for electronic devices

From the evaluation of the thickness of the polyester film, the light-shielding property of item (5), and the light shrinkage resistance of item (6), it was determined as follows.

When the thickness is 16 μm or less, both the light-shielding properties and the light-shrinkability evaluation are judged as A: A

Thickness is 20 μm or less, and both light-shielding and light shrinkage evaluations are B judgment or better: B

Thickness is 25 μm or less, and both light-shielding and light shrinkage evaluations are C judgment or higher: C

The thickness is 28 μm or less, and both light-shielding and light-shrinkability evaluations are more than D judgment: D

The thickness exceeds 28 μm, or either the light-shielding property or the light-resistance shrinkage evaluation is E judgment: E

As a light-shielding substrate for electronic devices, A to D are good, and among them, A is the most excellent.

(8) the number of times the black ink layer is printed

In the light-shielding tape using a polyester film, the light-shielding tape evaluation was determined as follows from the number of times a black ink layer was printed on the polyester film in order to achieve A in (5-1) Similar light light-shielding property evaluation of (5) light-shielding property evaluation. Evaluation was performed 5 times and determined from the average value.

No need to print: A

Less than 2 prints: B

The number of prints is 2 or more but less than 4: C

More than 4 but less than 6 prints: D

More than 6 prints: E

As light-shielding tape evaluation, from the viewpoint of reducing the environmental load and simplifying the manufacturing process, A to D are good, and among them, A is the most excellent.

Example

Hereinafter, the present invention will be described by giving examples, but the present invention is not necessarily limited to these.

(Method for producing polyester resin)

1. Polyethylene terephthalate (PET)

100 parts by mass of dimethyl terephthalate, 57.5 parts by mass of ethylene glycol, 0.03 parts by mass of magnesium acetate dihydrate, and 0.03 parts by mass of antimony trioxide were melted at 150°C in a nitrogen atmosphere. While stirring this melt, the temperature was raised to 230°C over 3 hours, methanol was distilled out, and the transesterification reaction was completed. After completion of the transesterification reaction, an ethylene glycol solution (pH 5.0) in which 0.005 parts by mass of phosphoric acid was dissolved in 0.5 parts by mass of ethylene glycol was added. The intrinsic viscosity of the polyester composition at this time was less than 0.2. Thereafter, a polymerization reaction was carried out at a final attained temperature of 285°C and a degree of vacuum of 0.1 Torr to obtain polyethylene terephthalate having an intrinsic viscosity of 0.65 and a terminal carboxyl group weight of 34 equivalents/ton.

2. Polyethylene naphtharate (PEN)

Except for using 2,6-naphthalene dicarboxylic acid as the dicarboxylic acid component, polymerization was carried out in the same manner as in the polyethylene terephthalate of the above item 1., and polyethylene naphthalate having an intrinsic viscosity of 0.61 and a terminal carboxyl group weight of 36 equivalents/ton was obtained.

3. Polyethylene terephthalate-IPA copolymer 1 (PET/I-1)

As the dicarboxylic acid component, except that 82.5 parts by mass of dimethyl terephthalate and 25 parts by mass of dimethyl isophthalate were mixed, polymerization was carried out in the same manner as in the polyethylene terephthalate of the above item 1. to obtain a polyethylene terephthalate copolymerized with 17.5 mol% of isophthalic acid (IPA).

4. Polyethylene terephthalate-IPA copolymer 2 (PET/I-2)

As the dicarboxylic acid component, except that 75 parts by mass of dimethyl terephthalate and 25 parts by mass of dimethyl isophthalate were mixed, polymerization was performed in the same manner as in polyethylene terephthalate to obtain polyethylene terephthalate copolymerized with 25 mol% of isophthalic acid (IPA).

5. Polyethylene terephthalate-NDC copolymer (PET/N)

Except for using 2,6-naphthalene dicarboxylic acid as the dicarboxylic acid component, polyethylene terephthalate copolymerized with 17.5 mol% of naphthalene dicarboxylic acid (NDC) was obtained in the same manner as the polyethylene terephthalate copolymer of the above 3. item.

6. Polyethylene terephthalate-CHDM copolymer (PET-G)

As polyethylene terephthalate copolymerized with 30 mol% of cyclohexane dimethanol (CHDM), a polyester resin "Eastar™ Copolyester 6763" manufactured by Eastman Chemical Company was used.

7. Polybutylene terephthalate (PBT)

As a polybutylene terephthalate whose diol component is butanediol (BDO), Toray Industries, Inc. Production "TORAYCON 1200S" was used.

8. CB Masterbatch 1 (CB-MB1)

CB master batch 1 was prepared by melting and kneading 80 parts by mass of polyethylene terephthalate obtained in the above item 1. and 20 parts by mass of carbon black (CB-1) produced by a furnace method having a primary particle size of 18 nm in a vented 280 ° C. extruder.

9. CB Masterbatch 2 (CB-MB2)

CB master batch 2 was produced in the same manner as in CB master batch 1, except that carbon black (CB-2) produced by the acetylene method having a primary particle size of 23 nm was used.

10. CB Masterbatch 3 (CB-MB3)

CB master batch 3 was produced in the same manner as in CB master batch 1, except that polyethylene terephthalate-IPA copolymer 1 obtained in the above 3. was used as the base polyester resin.

11. Titanium oxide master batch (TiO ₂ -MB)

50 parts by mass of polyethylene terephthalate obtained in the above item 1. and 50 parts by mass of rutile titanium dioxide particles having a primary particle size of 200 nm were melt-kneaded in a vented 280°C extruder to prepare a TiO ₂ masterbatch.

(Production method of light-shielding tape)

1. Adhesive layer

98.9 parts by weight of isononyl acrylate, 0.1 part by weight of acrylic acid, 1.0 part by weight of N-vinyl caprolactam, 0.05 part by weight of n-dodecyl mercaptan as a chain transfer agent, and 80 parts by weight of ethyl acetate as a solvent were added to a 5-necked flask equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, and after stirring, it was purged with nitrogen gas for about 30 minutes to remain in the monomer solution. oxygen was removed. Thereafter, the air in the flask was purged with nitrogen gas, the temperature was raised while stirring and maintained at 70° C., and a solution of 0.03 parts by weight of benzoyl peroxide as a thermal polymerization initiator in 1 part by weight of ethyl acetate was added dropwise from a dropping funnel. After the start of the reaction, it was made to react at the same temperature for 10 hours, and an acrylic copolymer solution was obtained.

Subsequently, the acrylic copolymer solution was applied to one side of the polyester film by a die coating method to form an adhesive layer having a thickness of 8 μm.

2. Black ink layer

To the carbon black (CB-1) used in CB master batch 1 (CB-MB1), a commercially available medium for ink (polyurethane-based/salt/acetic non-copolymer) and a solvent (ketone/aromatic hydrocarbon/alcohol) were added and mixed and stirred to prepare a black ink having a carbon content of 50% by weight after solvent drying.

Subsequently, using the black ink, a black ink layer having a thickness of 2 μm after drying was provided on the polyester film at the number of times and offset according to the required characteristics of the light-shielding property.

(Example 1)

34 parts by mass of polyethylene terephthalate prepared in the preceding paragraph as a polyester raw material and 26 parts by mass of polyethylene terephthalate-isophthalic acid (IPA) copolymer 1 and 40 parts by mass of CB master batch 1 were blended so as to have the composition shown in the table, and vacuum dried at 180 ° C. for 2 hours. Then, it was melted and discharged in an extruder heated to 280 ° C., and the molten sheet extruded from the T die was cooled and fixed in close contact with an electrostatic application method on a casting drum maintained at a surface temperature of 25 ° C. to obtain an unstretched sheet.

Subsequently, the obtained unstretched sheet was preheated with a roll group heated to a temperature of 80 ° C., and then stretched three times in the longitudinal direction (machine direction) by adding a three-fold speed difference between the roll heated to a temperature of 85 ° C. and the roll adjusted to a temperature of 25 ° C. After that, it was cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched sheet. Further, while holding both ends of the obtained uniaxially stretched sheet with a clip, it was led to a preheating zone at a temperature of 80 ° C. in the tenter, and then in a direction perpendicular to the longitudinal direction (width direction) in a heating zone continuously maintained at 90 ° C. It was stretched 3.6 times. Subsequently, heat treatment was performed at 230° C. for 20 seconds in the heat treatment zone in the tenter, followed by uniform slow cooling while performing relaxation treatment in the 6% width direction to form a polyester film. Subsequently, the discharge amount of the extruder and the line speed after the casting drum were adjusted so that the thickness of the polyester film after film formation was 16 μm, and the polyester film described in Example 1 was obtained. The film forming property was very excellent, and even when the film forming was performed continuously for 1 hour under the above conditions, film tearing did not occur even once. When the obtained polyester film was evaluated for light-shielding properties and light-shrinkability, it was found that both had very excellent light-shielding properties and light-shrinkability. In addition, it was found that the polyester film can be suitably used as a light-shielding substrate used in electronic devices by satisfying the above characteristics while being very thin.

Furthermore, a light-shielding tape was produced by providing an adhesive layer on one side of the polyester film. It was found that the obtained light-shielding tape was very excellent in light-shielding property and did not need to provide a black ink layer, and thus was a very excellent light-shielding tape from the viewpoint of reducing the environmental load and simplifying the manufacturing process.

(Examples 2-7)

A polyester film was obtained in the same manner as in Example 1 except that the film forming conditions were adjusted so that the amount of CB master batch 1 and the thickness described in the table were obtained so as to have the color pigment concentration shown in the table. In Examples 4 and 5, since film tearing occurred during film formation, film formation was performed with the draw ratio lowered compared to Example 1.

As shown in the table, the properties of the obtained polyester film were poor in Example 1, but showed good properties, and it was found that the properties were good as a light-shielding substrate for electronic devices.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to have good characteristics as a light-shielding tape, although it was inferior to Example 1.

(Examples 8 to 13)

A polyester film was obtained in the same manner as in Example 1 except that the amount of the polyethylene terephthalate-isophthalic acid (IPA) copolymer 1 was adjusted so as to be the ratio of the copolymerization components shown in the table. In cases other than Example 8, since film tearing occurred during film formation, film formation was performed with a lower draw ratio compared to Example 1, and among them, Example 13 had poor film formation properties, but was within a problem-free range.

As shown in the table, the properties of the obtained polyester film were inferior to those of Example 1, but exhibited good properties and were also good as a light-shielding substrate for electronic devices. Among them, Example 9 was found to have the most excellent properties. In Example 12, although the light shrinkage was poor, it was within a satisfactory range.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to be a very excellent light-shielding tape.

(Examples 14 to 18)

A polyester film was obtained in the same manner as in Example 1 except that the amounts of the polyethylene terephthalate-naphthalene dicarboxylic acid (NDC) copolymer, polyethylene terephthalate-cyclohexanedimethanol (CHDM) copolymer, and polybutylene terephthalate (PBT) described in the preceding paragraph were adjusted so as to have the types and ratios of the copolymerization components shown in the table. In all cases other than Example 17, since film tearing occurred during film formation, film formation was performed at a lower draw ratio compared to Example 1, and among them, Example 14 had poor film formation properties, but was within a problem-free range.

As for the properties of the obtained polyester film, as shown in the table, Example 17 using CHDM as the diol component as a copolymerization component and using a copolymerization component ratio of 9 mol% had very excellent light-shielding properties and light shrinkage resistance similarly to Example 1. It was found. In addition, it was found that the other examples showed good characteristics, although inferior to Examples 1 and 17, and also had good characteristics as a light-shielding substrate for electronic devices.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to be a very excellent light-shielding tape.

(Examples 19 to 21)

As shown in the table, a polyester film was obtained in the same manner as in Example 1 except that the type and content of the color pigment were changed using CB master batch 2, CB master batch 3, and titanium oxide master batch described in the preceding paragraph. Example 20 was poor in film forming property, but within a problem-free range.

As for the properties of the obtained polyester film, as shown in the table, Example 19 has poor light-shielding properties and light shrinkage properties compared to Example 1, but has excellent properties, and Example 20 has a color pigment concentration compared to Example 1. In Example 21, although the light-shielding property was poor, it was within a problem-free range.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to have good characteristics as a light-shielding tape, although it was inferior to Example 1.

(Example 22)

A polyester film was obtained in the same manner as in Example 1 except that the polyethylene naphthalate described in the preceding paragraph was used as the constituent component and the polyethylene terephthalate described in the preceding paragraph in which the dicarboxylic acid component was terephthalic acid (TPA) was prepared as a copolymerization component so as to be in the ratio shown in the table.

As for the properties of the obtained polyester film, as shown in the table, it was found that the light shrinkage resistance was inferior to that of Example 1, but the properties were excellent.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to be a very excellent light-shielding tape.

(Example 23)

A polyester film was obtained in the same manner as in Example 1 except that the thickness of the film was 10 µm. The properties of the obtained film are as shown in the table, and compared to Example 1, it was found that the light-shielding property was inferior, but it was excellent.

Further, when a light-shielding tape was produced in the same manner as in Example 1, it was found to be an excellent light-shielding tape.

(Examples 24 to 35)

As shown in the table, a polyester film was obtained in the same manner as in Example 23 except that the film forming conditions were changed. In Examples 25 to 35, film formation was performed by installing an infrared heater (RH) with an inter-film distance of 400 mm, a heater capacity of 6.6 kW, and a heating length of 800 mm between the preheating roll and the stretching roll during longitudinal stretching. The obtained polyester film was found to change the ratio (Rz/T) of the optical density, 10-point average roughness (Rz) (μm), and film thickness (μm) by changing the film temperature at the time of longitudinal stretching in the film forming conditions, the draw ratio, and the preheating temperature at the time of transverse stretching. In Example 35, although the film forming property was poor, it was within a problem-free range.

As the characteristics of the obtained polyester film are shown in the table, Examples 25, 34, and 35 were found to be superior in light-shielding properties compared to Example 23.

Further, when light-shielding tapes were produced in the same way as in Example 1, it was found that Examples 25, 34, and 35 were excellent light-shielding tapes compared with Example 23.

(Comparative Example 1)

As shown in the table, it was the same as Example 1 except that the homopolymer of polyethylene terephthalate was used alone, but the light shielding and light shrinkage properties were very excellent, but the film forming property was poor.

(Comparative Example 2)

As shown in the table, except that polyethylene terephthalate-isophthalic acid (IPA) copolymer 2 was used alone, it was the same as in Example 1, but the light shielding property was very excellent and the film forming property was good, but the light shrinkage resistance was poor.

(Comparative Example 3)

As shown in the table, it was the same as in Example 12 except that the color pigment was highly concentrated, but the light-shielding property was excellent, but the film forming property and light shrinkage resistance were poor.

(Comparative Example 4)

As shown in the table, it was the same as in Example 1 except that the color pigment was reduced in concentration, but the film formability and light shrinkage resistance were very excellent, but the light shielding property was poor.

The polyester film of the present invention is a thin film and has excellent hiding and film forming properties, and excellent shrinkage when exposed to light, and can be suitably used not only for light-shielding substrates used inside electronic devices, but also for applications such as cover films, solar cell back sheets, industrial materials such as insulating films for motors, packaging materials such as exterior films for lithium ion batteries, design films, and protective films, films for ink ribbons, films for building materials, and thermal transfer films.

Claims (8)

The ratio of optical density and thickness (μm) (optical density (OD) / thickness (T)) is 0.22 or more and 2.0 or less, and the polyester constituting the film contains 0.5 mol% or more and 20 mol% or less of an isophthalic acid component with respect to all dicarboxylic acid components, or contains 0.5 mol% or more and 20 mol% or less of a cyclohexanedimethanol component with respect to all diol components, and in differential scanning calorimetry (DSC), A polyester film having a temperature cooling crystallization temperature (Tmc) of 180 ° C. or higher and 210 ° C. or lower when cooled at a cooling rate of 10 ° C./min after holding for 5 minutes in a molten state. According to claim 1,
A polyester film containing 3.5% by mass or more and 30% by mass or less of a black pigment. According to claim 1 or 2,
The 10-point average roughness (Rz) (μm) of at least one surface satisfies that the ratio (10-point average roughness (Rz)/thickness (T)) of Rz (μm) and thickness (μm) is 0.30 or less. A polyester film. delete delete According to claim 1 or 2,
A polyester film having a film thickness of 28 µm or less. According to claim 1 or 2,
A polyester film used as a light-shielding substrate for electronic devices. A light shielding tape using the polyester film according to claim 1 or 2.