JP2016164259A - Polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film good in underlying concealing property and processing suitability at high temperature even as a thin film.SOLUTION: There is provided a polyester film having thickness of 10 to 40 μm and an L value in a Hunter colorimetric system of 80 or more and thermal shrinkage rate (Sx) in a direction X at 190°C for 20 minutes and thermal shrinkage rate (Sy) in a direction Y satisfying the following formula, where the direction X is any direction in a film face and the direction Y is a direction orthogonal to the direction X. |Sx-Sy|≤4% (I) Sx≤5% (II) Sy≤5% (III).SELECTED DRAWING: None

Description

  The present invention relates to a polyester film that is suitably used for applications requiring concealment properties such as a laminated metal plate and a light shielding tape.

  Thermoplastic resin films, especially biaxially oriented polyester films, have excellent properties such as mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance. It is widely used as a substrate film in the above applications. In addition, for metal can applications, studies have been made to make a white laminated metal plate obtained by laminating a white film on a metal plate in order to perform vivid printing on the surface of the can (for example, Patent Documents 1 to 3) and painting. Therefore, it has been proposed as a low environmental load material that does not use organic solvents.

JP 2000-177085 A JP 2001-212918 A JP-A-11-262987

  However, when a white pigment such as titanium oxide is contained in the film at a high concentration in order to conceal the base of the metal plate, the white pigment becomes the starting point during film production, and the film is likely to break. For this reason, in Patent Documents 1 to 3, a method of suppressing crystallization of a polymer by polymerizing a copolymer component with polyester used in film production is applied. However, when applying a polyester containing a copolymer component, the melting point is lowered. For example, if the heat setting temperature after biaxial stretching is set in a range exceeding 190 ° C., the flatness and brittleness resistance may be lowered. In addition, there is a problem that it is difficult to produce a high-quality film in which the shrinkage rate at 190 ° C. is sufficiently suppressed.

  Therefore, the present invention aims to solve the above-mentioned drawbacks and provide a polyester film that is a thin film but has excellent base concealing properties and high processability at high temperatures.

The present invention for solving the above problems has the following configuration.
(1) A polyester film having a thickness of 10 to 40 μm and an L value of 80 or more in the Hunter color system, wherein one direction in the film plane is the direction X and the direction perpendicular to the direction X is the direction Y. A polyester film in which the heat shrinkage rate (Sx) in the direction X and the heat shrinkage rate (Sy) in the direction Y at 190 ° C. for 20 minutes satisfy the following formulas.
| Sx-Sy | ≦ 4% (I)
Sx ≦ 5% (II)
Sy ≦ 5% (III)
(2) The polyester film according to (1), wherein the surface roughness SRa of at least one surface is 7 nm or more and 30 nm or less, and the glossiness at an incident angle of 60 ° of at least one surface is 80% or more and 120% or less.
(3) Assuming that one arbitrary direction in the film plane is the direction X and the direction perpendicular to the direction X is the direction Y, the breaking strength (Fx) in the direction X, the breaking strength (Fy) in the direction Y, and the breaking elongation in the direction X The polyester film according to (1) or (2), in which the degree (Lx) and the breaking strength (Ly) in the direction Y satisfy the following formulas, respectively.
| Fx−Fy | ≦ 30 MPa (IV)
140 MPa <Fx ≦ 200 MPa (V)
140 MPa <Fy ≦ 200 MPa (VI)
| Lx−Ly | ≦ 30% (VII)
80% <Lx ≦ 195% (VIII)
80% <Ly ≦ 195% (IX)
(4) The polyester film according to any one of (1) to (3), wherein a change in gloss at an incident angle of 60 ° before and after heat treatment at 120 ° C. for 10 minutes is 0% or more and 15% or less on at least one side.
(5) The polyester film according to any one of (1) to (4), wherein a change in glossiness at an incident angle of 60 ° before and after stretching by 50% is 0% or more and 20% or less on at least one side.
(6) The polyester film according to any one of (1) to (5), wherein the melting point of the film is 230 ° C. or higher and 265 ° C. or lower.
(7) The polyester film according to any one of (1) to (6), wherein the white pigment contained in the film is anatase-type titanium oxide.
(8) The polyester film according to any one of (1) to (8), wherein the polyester B layer has a polyester B layer on at least one side, and the polyester B layer does not contain a white pigment.
(9) The polyester film according to any one of (1) to (8), which is used by being laminated on a metal plate.
(10) A light shielding tape using the film according to any one of (1) to (8).

  When the polyester film of the present invention is bonded to a metal plate or used as a light-shielding tape, the polyester film has an effect of imparting high concealability to the metal plate or tape and enabling processing at a high temperature.

Hereinafter, the polyester film of the present invention will be described in detail.
The polyester in the present invention refers to a polymer bonded by an ester bond of a structural unit derived from a dicarboxylic acid (dicarboxylic acid component) and a structural unit derived from a diol (diol component).
Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, Aromatic dicarboxylic acids such as 4,4′-diphenyl ether dicarboxylic acid and 4,4′-diphenylsulfone dicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid and cyclohexanedicarboxylic acid And ester derivatives with various aromatic dicarboxylic acids and aliphatic dicarboxylic acids. These diol components may be used alone or in combination of two or more in addition to ethylene glycol.
Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis (4-hydroxyethoxy) Phenyl) propane, isosorbate, spiroglycol and the like. These dicarboxylic acid components may be used alone or in combination of two or more in addition to ethylene glycol.
Among these dicarboxylic acid components and diol components, from the viewpoint of solvent resistance and heat resistance, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid are preferable as the dicarboxylic acid component, and ethylene glycol is preferable as the diol component. 1,4-butanediol, 1,4-cyclohexanedimethanol, isosorbate and spiroglycol are preferably used. In addition to solvent resistance and heat resistance, a combination of terephthalic acid and ethylene glycol is most preferable from the viewpoint of manufacturing cost.
When the polyester constituting the polyester film of the present invention is a so-called polyethylene terephthalate comprising a combination of terephthalic acid and ethylene glycol, the dicarboxylic acid component other than terephthalic acid is based on 100 mol% of the total dicarboxylic acid component constituting the polyester. 0 mol% or more and 20 mol% or less is preferable, 0 mol% or more and 10 mol% or less is more preferable, 0 mol% or more and 2 mol or less is more preferable, and particularly preferably 0 mol%, that is, the dicarboxylic acid component is terephthalic acid. It is the structure which consists only of a component. When the dicarboxylic acid component other than the terephthalic acid component exceeds 20 mol% with respect to 100 mol% of all dicarboxylic acid components, the melting point of the polyester film is lowered or the crystallinity is lowered, resulting in insufficient heat resistance. Or thickness unevenness may increase.
When the polyester constituting the polyester film of the present invention is polyethylene terephthalate, the diol component other than ethylene glycol is preferably 0 mol% or more and 33 mol% or less with respect to 100 mol% of all diol components constituting the polyester. 0 to 10 mol% is more preferable, and 0 to 5 mol% is more preferable. Particularly preferred is 0 mol%, that is, the diol component consists of ethylene glycol only. When the diol component other than ethylene glycol exceeds 33 mol% with respect to 100 mol% of all diol components, the melting point of the polyester film is lowered or the crystallinity is lowered, resulting in insufficient heat resistance, thickness. The unevenness may become large.

  It is important that the polyester film of the present invention has a thickness of 10 to 40 μm. When the thickness is less than 10 μm, handling at the time of processing may be difficult, base concealing property may be insufficient, or film forming property may be insufficient. Also, if the thickness exceeds 40 μm, lamination with a metal plate becomes difficult, and when used as a double-sided adhesive light shielding tape for electronic components, the thickness of the electronic components increases, which is disadvantageous for use in small products. Sometimes. The polyester film of the present invention is preferably 6 to 30 μm, more preferably 8 to 25 μm, and particularly preferably 10 to 20 μm from the viewpoints of handleability, laminating properties, and product thickness.

  Examples of a method for adjusting the thickness of the polyester film of the present invention to 10 to 40 μm include a method of adjusting production conditions such as a polymer discharge rate, a cast drum speed, and a draw ratio.

  It is important that the polyester film of the present invention has an L value of 80 or more in the Hunter color system. If the L value in the Hunter color system is less than 80, the base concealing property for metal and electronic parts may be insufficient.

  The L value of the polyester film of the present invention is preferably 82 or more, more preferably 84 or more, and particularly preferably 86 or more, from the viewpoint of better concealment. Further, the greater the L value of the polyester film of the present invention, the better the base concealing property. However, from the viewpoint of improving the film forming property, the L value is preferably 100 or less.

  Examples of the method for setting the L value of the polyester film of the present invention to 80 or more include a method in which a predetermined amount of white pigment is contained in the film. Examples of white pigments include titanium oxide, barium sulfate, calcium carbonate, silica, and alumina. Among these, titanium oxide is preferable. When titanium oxide is included as the white pigment, either anatase type titanium oxide or rutile type titanium oxide may be included. Among these white pigments, anatase-type titanium oxide is preferable from the viewpoint of slit property during production. In the case of using, for example, anatase titanium oxide as the polyester film of the present invention, in order to make the L value 80 or more, an embodiment containing 5% by mass to 40% by mass with respect to the whole film is preferable although it varies depending on the film thickness. Preferably it is 7 mass% or more and 35 mass% or less, More preferably, it is 10 mass% or more and 30 mass% or less, Especially preferably, it is the aspect containing 15 mass% or more and 25 mass% or less. When the white pigment is contained in an amount of less than 5% by mass with respect to the entire film, the L value may be less than 80. In addition, when the white pigment exceeds 40% by mass with respect to the entire film, the crystallization of the polyester constituting the film proceeds excessively with the white pigment as the starting point, and breaks at the time of transverse stretching and biaxially stretches. A polyester film may not be obtained.

In laminating to a metal plate, suitability for processing at 190 ° C. is important in order to prevent the film from being deformed by heat applied during laminating, printing, and can manufacturing. Therefore, the polyester film of the present invention has a thermal contraction rate (Sx) in the direction X at 190 ° C. for 20 minutes, where the direction X is an arbitrary direction in the film plane and the direction Y is a direction perpendicular to the direction X. It is important that the thermal contraction rate (Sy) in the direction Y satisfies the following formulas (I) to (III).
| Sx-Sy | ≦ 4% (I)
Sx ≦ 5% (II)
Sy ≦ 5% (III)
When | Sx-Sy | of the polyester film of the present invention exceeds 4%, wrinkles may occur when laminating with metal or when processing into adhesive tape, or misalignment may occur after printing There is.
| Sx-Sy | of the polyester film of the present invention is preferably 3% or less, more preferably 1.5% or less, and particularly preferably 0.6% or less.

As a method for setting the | Sx-Sy | of the polyester film of the present invention to 4% or less, the effective magnifications of the longitudinal stretching and the lateral stretching are substantially the same (for example, the longitudinal stretching is 3 times and the transverse stretching is performed). 3 times, etc.), a method of setting the plane orientation coefficient to 0.8 to 1.4, a method of setting Δn to 0 to 30 × 10 ^−3, and the like. Here, the plane orientation coefficient refers to an index of orientation in the in-plane direction of the film, and the refractive index (nX) in any one direction X in the film plane and the refractive index (nY) in the direction Y orthogonal to the direction X. ), The refractive index (nZ) in the thickness direction Z is measured, and can be calculated from the formula fn = (nX + nY) / 2−nZ. In addition, Δn refers to the birefringence in the in-plane direction of the film, and is obtained by Δn = nX−nY.

  When Sx and Sy of the polyester film of the present invention exceed 5%, the width shrinkage increases when laminating with metal or processing into adhesive tape, and the yield of laminated metal plate or double-sided adhesive light-shielding tape is increased. May decrease. Sx and Sy are each preferably 4% or less, more preferably 3% or less, and particularly preferably 2% or less.

  As a method for making each of Sx and Sy of the polyester film of the present invention 5% or less, a method of setting a heat setting temperature after biaxial stretching to 190 ° C. or higher, biaxial stretching, longitudinal stretching and / or transverse Examples include a method of stretching and increasing the plane orientation to suppress thermal shrinkage. The heat setting temperature after biaxial stretching is preferably 190 ° C. or higher and 250 ° C. or lower, more preferably 200 ° C. or higher and 240 ° C. or lower, and particularly preferably 210 ° C. or higher and 230 ° C. or lower. In addition, when performing longitudinal stretching and / or lateral stretching again after biaxial stretching, do not perform heat setting after the first lateral stretching, or perform longitudinal stretching and / or lateral stretching again in a state set to 100 to 120 ° C. It is preferable to carry out in the range of 130-150 degreeC.

  In the polyester film of the present invention, in order to set the heat setting temperature after biaxial stretching to 190 ° C. or higher, the melting point of the polyester film is 230 ° C. or higher and 265 ° C. or lower from the viewpoint of film quality and brittle resistance. preferable. The melting point of the polyester film is more preferably 246 ° C. or higher and 260 ° C. or lower, further preferably 250 ° C. or higher and 260 ° C. or lower, and particularly preferably 253 ° C. or higher and 257 ° C. or lower. If the melting point of the polyester film is less than 230 ° C., the film is heated to near the melting point when the heat setting temperature is set to 190 ° C. or higher. In some cases, the melting of polyester crystals starts, the film orientation becomes low, and the film becomes brittle. Moreover, when melting | fusing point of a polyester film exceeds 265 degreeC, melt extrudability falls, extrusion accuracy becomes inadequate, and the thickness nonuniformity of a film may become large.

  In the polyester film of the present invention, it is not easy to obtain a film having all the characteristics of thickness, L value in Hunter color system, 190 ° C., and heat shrinkage at 20 minutes. For example, when trying to make the Hunter color system L value more than a specific range in a thin film of 40 μm or less, it is necessary to contain a large amount of white pigment such as titanium oxide, but if a large amount of white pigment is contained, As described above, the crystallization of the polymer constituting the film proceeds excessively and breaks easily during transverse stretching. On the other hand, by applying a copolyester such as isophthalic acid copolymerized polyethylene terephthalate, 1,4-cyclohexanedimethanol copolymerized polyethylene terephthalate, etc., and reducing crystallinity, it is possible to suppress breakage during transverse stretching. When the copolyester is applied, the melting point of the polyester is also lowered, so that the heat setting temperature of the film cannot be sufficiently increased from the viewpoint of flatness and brittleness resistance, and it is difficult to reduce the 190 ° C. heat shrinkage rate. It may become.

  In order to achieve the present invention, in order to suppress the heat shrinkage by setting the heat setting temperature after biaxial stretching to a high temperature of 190 ° C. or higher, the polyester copolymerization amount is small, that is, the melting point is high and the crystallinity is high. It is important to apply polyester. On the other hand, it is necessary to contain a large amount of white pigment in order to make the L value in the Hunter color system 80 or more with a small thickness, but since the crystallinity of the polyester becomes high and breakage during stretching tends to occur. In order to achieve the present invention, it is important to use a highly crystalline polyester having a high melting point and containing a large amount of white pigment, and to suppress crystallization so that breakage does not occur even when a thin film is stretched. Become.

  Examples of techniques for suppressing crystallization during stretching while using polyester with high crystallinity include thermal crystallization suppression during casting and orientation crystallization suppression by performing stepwise stretching during longitudinal stretching.

  Specifically, the suppression of thermal crystallization during casting is a method in which the surface temperature of the cast drum is set to 15 ° C. or less so that a temperature history at which the polymer on the cast drum crystallizes is not given as much as possible. The surface temperature of the cast drum is preferably 13 ° C. or less, and preferably 10 ° C. or less. However, if the surface temperature of the cast drum is too low, the drum surface may condense, so it is preferable to keep the humidity low. As a method of setting the surface temperature of the cast drum to 15 ° C. or less, a method of decreasing the temperature of the refrigerant circulating in the cast drum or a method of increasing the flow rate per unit time, or blowing cool air on the surface of the cast drum with an air chamber A method and a method using these in combination are used. The method using an air chamber is also preferably used from the viewpoint of directly cooling the film on the cast drum with cold air.

  Specifically, the technology for suppressing crystallization by stepwise stretching at the time of longitudinal stretching is not to stretch the sheet obtained in the casting process to a desired ratio at the same time when stretching the sheet in the longitudinal stretching process. This is a method of suppressing orientation crystallization during stretching by repeatedly stretching at a low magnification in stages or more. In stretching at a low magnification, the stretch ratio at one time is preferably 3 times or less, more preferably 2 times or less, still more preferably 1.8 times or less, and particularly preferably 1.5 times or less. Moreover, the draw ratio in the longitudinal stretch total is preferably 2.5 times or more, more preferably 2.7 times or more, and particularly preferably 3 times or more.

  The polyester film of the present invention preferably has a surface roughness SRa of at least one side of 7 nm or more and 30 nm or less, and a glossiness of at least one side at an incident angle of 60 ° is 80% or more and 120% or less. By setting the surface roughness SRa of at least one surface to 7 nm or more and 30 nm or less, the rollability of the film and the gloss of the printed portion are improved. At least one surface roughness SRa is more preferably 7 nm or more and 20 nm or less, and further preferably 7 nm or more and 10 nm or less. Moreover, the polyester film of this invention can make the glossiness of the part which has not been printed especially favorable by making glossiness 80 degree% or more and 120% or less at the incident angle of 60 degrees of at least one side. The glossiness at an incident angle of 60 ° is more preferably 80% or more and 110% or less, and particularly preferably 85% or more and 100% or less.

  As a method of setting the surface roughness SRa of at least one side and the glossiness at an incident angle of 60 °, which is a preferable configuration of the present invention, to a predetermined range, the polyester film of the present invention has a configuration of two or more layers, Examples of the layer include making the content of the white pigment constituting the layer smaller than the layer on the remaining surface.

In the polyester film of the present invention, the direction X is the arbitrary direction in the film plane, and the direction Y is the direction perpendicular to the direction X. The breaking strength (Fx) in the direction X, the breaking strength (Fy) in the direction Y, and the direction It is preferable that the breaking elongation (Lx) of X and the breaking strength (Ly) in the direction Y satisfy the following expressions, respectively.
| Fx−Fy | ≦ 30 MPa (IV)
140 MPa <Fx ≦ 200 MPa (V)
140 MPa <Fy ≦ 200 MPa (VI)
| Lx−Ly | ≦ 30% (VII)
80% <Lx ≦ 195% (VIII)
80% <Ly ≦ 195% (IX)
By satisfying the formula (IV), the balance of strain in two directions becomes good and curling of the film after biaxial stretching hardly occurs. In addition, satisfying the formulas (V) and (VI) makes it difficult to break even when a film is applied with high tension when it is put into a continuous conveyance process by laminating with a metal plate or printing on a film. , Handling becomes good. When the film is deformed together with the metal plate, the film can be deformed without generating a crack. Moreover, by satisfy | filling (VII) Formula, the balance of the distortion of two directions becomes favorable and it becomes difficult to occur the film of the film after biaxial stretching. Further, by satisfying the formulas (VIII) and (IX), the film can be deformed without generating a crack when it is deformed together with the metal plate.

In the polyester film of the present invention, as a method for satisfying the formulas (IV) to (IX), a method of reducing the copolymerization amount of the polyester constituting the polyester film and adjusting the longitudinal and lateral stretch ratios, respectively. Etc.

  The polyester film of the present invention has a change in glossiness at an incident angle of 60 ° before and after heat treatment at 120 ° C. for 10 minutes at least on one side of 0% or more and 15% or less when heated by molding or print drying. It is preferable from the viewpoint that the appearance does not become non-uniform even when uneven heating occurs. The change in glossiness at an incident angle of 60 ° before and after heat treatment at 120 ° C. for 10 minutes is more preferably 0% or more and 10% or less, and further preferably 0% or more and 5% or less.

As a method of setting the change in glossiness at an incident angle of 60 ° before and after the heat treatment at 120 ° C. for 10 minutes according to the present invention within a predetermined range, the polyester film of the present invention is composed of two or more layers, and at least in one layer. For example, making the content of the white pigment to be smaller than the layer of the remaining surface. A film containing inorganic particles such as a white pigment has irregularities formed on the surface due to inorganic particles present in the vicinity of the surface, but when this film is heated above the glass transition temperature, the surface area becomes small. Film deformation occurs. This deformation causes the white pigment on the film surface to dive inside the film, and the uneven shape on the film surface becomes small. Therefore, it is considered that the glossiness of the film changes after the heat treatment. Therefore, if the content of the white pigment is reduced in at least one layer, the amount of the white pigment that is submerged in the film after the heat treatment is reduced, so that the change in glossiness can be reduced.

  In the polyester film of the present invention, the gloss after heat treatment at 120 ° C. for 10 minutes is preferably 80% or more, and more preferably 83% or more, from the viewpoint of improving the glossiness after canning. Further, from the viewpoint of improving the slipperiness during can making, the glossiness after heat treatment at 120 ° C. for 10 minutes is preferably 120% or less. As a method for setting the gloss after heat treatment at 120 ° C. for 10 minutes to 80% or more, the polyester film of the present invention is composed of two or more layers, and the content of the white pigment constituting at least one layer is set to the remaining surface. It is possible to make it smaller than this layer.

  In the polyester film of the present invention, at least on one side, the change in glossiness at an incident angle of 60 ° before and after stretching by 50% is 0% or more and 20% or less because the surface appearance change before and after the molding of the film is small. preferable. The change in glossiness at an incident angle of 60 ° before and after 50% stretching is more preferably 0% or more and 15% or less, further preferably 0% or more and 10% or less, and particularly preferably 0% or more and 5% or less. It is.

  As a method for bringing the change in the glossiness at an incident angle of 60 ° before and after 50% stretching into a specific range on at least one side of the present invention, the polyester film of the present invention is composed of two or more layers, and at least on one side. Then, by making the content of the white pigment to be smaller than the layer of the remaining surface and by orienting the major axis of the white pigment in the plane direction in advance by stepwise stretching during the longitudinal stretching, 50 For example, a method of making the direction of the white pigment difficult to change even when stretched by%.

  In the polyester film of the present invention, the glossiness at an incident angle of 60 ° after stretching by 50% is preferably 80% or more, and more preferably 83% or more, from the viewpoint of improving the glossiness after canning. Further, from the viewpoint of improving the slipperiness during can making, the glossiness at an incident angle of 60 ° after stretching by 50% is preferably 120% or less. As a method of setting the glossiness at an incident angle of 60 ° after stretching by 50% to 80% or more, the polyester film of the present invention is composed of two or more layers, and at least in one layer, the content of the white pigment to be constructed is It is possible to make it smaller than the remaining surface layer.

The polyester film of the present invention has a polyester B layer on at least one side of the polyester A layer in order to make the surface roughness of at least one side, glossiness, before and after heat treatment, and particularly a change in glossiness before and after stretching in a particularly favorable range, The structure which does not contain a white pigment in the polyester B layer is preferable. However, the polyester B layer may contain known slippery particles other than the white pigment as long as the surface roughness on one side, the glossiness, before and after the heat treatment, and the glossiness change before and after stretching are not impaired. The polyester film of the present invention is not particularly limited in the number of layers and the layer structure, but from the viewpoint of suppressing curling of the film and achieving both reduction in warpage and suppression of interference color when bonded to a polarizer, B layer / A layer A configuration in which the film is symmetrical with respect to the thickness direction, and both surface layers are polyester B layers, such as / B layer, B layer / A layer / B layer / A layer / B layer, is preferable.
When the cross-sectional observation confirms the laminated structure, a layer in which a large amount of inorganic material can be seen by visual observation of the cross-sectional observation photograph can be identified as a polyester A layer, and a layer in which a small amount of inorganic material appears can be identified as a polyester B layer.

  Since the polyester film of the present invention is a thin film, it has excellent surface concealing properties and good processability at high temperatures. Therefore, it is possible to apply various surface treatments such as plating on the steel plate, aluminum plate, or the steel plate, which is a metal can material. A film is laminated on the applied metal plate, and the obtained metal plate is preferably used for applications such as drawing or ironing to produce a metal can.

  In addition, the polyester film of the present invention is preferably used as a light-shielding tape that is used by further laminating an adhesive layer or performing printing to attach to a base of a plastic member or glass member that is a constituent material of an electronic component. .

  The polyester film of the present invention has various additives such as antioxidants, heat stabilizers, weathering stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, antistatic agents. Further, a nucleating agent or the like may be contained so as not to deteriorate the characteristics.

  Next, although the preferable manufacturing method of the polyester film of this invention is demonstrated below, this invention is limited to this example and is not interpreted.

Polyester is fed to a vented twin screw extruder and melt extruded. At this time, it is preferable to control the resin temperature to 265 ° C. to 295 ° C. under an atmosphere of flowing nitrogen in the extruder, with an oxygen concentration of 0.7% by volume or less. Also, when laminating two or more different types of layers, each melt-extruded polymer is joined using a feed block, multi-manifold, etc., after being fed into separate vented twin-screw extruders and melt-extruded. To make a laminated state.
Next, foreign matter is removed and the amount of extrusion is leveled through a filter and a gear pump, respectively, and discharged from the T die onto a cooling drum in a sheet form. At that time, an electrostatic application method in which the cooling drum and the resin are brought into close contact with each other by static electricity using an electrode applied with a high voltage, a casting method in which a water film is provided between the cast drum and the extruded polymer sheet, The sheet-like polymer is brought into close contact with the cast drum, cooled and solidified by a method of adhering the polymer extruded at a glass transition point to (glass transition point−20 ° C.) or a combination of these methods, and unstretched. Get a film. Among these casting methods, when using polyester, a method of applying an electrostatic force is preferably used from the viewpoint of productivity and flatness. The surface temperature of the cast drum is preferably 15 ° C. or less from the viewpoint of both concealability, processability at high temperatures, and stretchability. The polyester film of the present invention is from the viewpoints of processability at high temperatures and suppression of thickness unevenness. A biaxially oriented film is preferable. The biaxially oriented film is obtained by stretching an unstretched film in the longitudinal direction and then stretching in the width direction, or by stretching in the width direction and then stretching in the longitudinal direction, or by the longitudinal direction of the film. It can be obtained by stretching by a simultaneous biaxial stretching method in which the width direction is stretched almost simultaneously.

  As the draw ratio in such a drawing method, preferably 2.8 times or more and 3.5 times or less, more preferably 3 times or more and 3.3 times or less in the longitudinal direction. The stretching speed is preferably 1,000% / min or more and 200,000% / min or less. The stretching temperature in the longitudinal direction is preferably 95 ° C. or higher and 130 ° C. or lower, and it is preferable to preheat at 85 ° C. for 1 second or longer before stretching.

When stretching a highly crystalline unstretched film containing a high concentration of white pigment in order to achieve both concealability and processability at high temperatures, the desired magnification can be achieved at a time in order to suppress breakage during subsequent lateral stretching. A method is preferably used in which the stretching at a low magnification is repeated in two or more stages and the orientation crystallization at the stretching is suppressed. In stretching at a low magnification, the stretch ratio at one time is preferably 3 times or less, more preferably 2 times or less, still more preferably 1.8 times or less, and particularly preferably 1.5 times or less. Moreover, the draw ratio in the longitudinal stretch total is preferably 2.5 times or more, more preferably 2.7 times or more, and particularly preferably 3 times or more.
The stretching ratio in the width direction is preferably 2.8 times or more and 3.5 times or less, more preferably 3 times or more and 3.5 times or less, and it is preferable to match the stretching ratio in the longitudinal direction. The stretching speed in the width direction is desirably 1,000% / min or more and 200,000% / min or less. In order to suppress the heat shrinkage rate of 85 ° C., the first half temperature of stretching is 100 ° C. or more and 120 ° C. or less, the middle temperature of stretching is 105 ° C. or more and 130 ° C. or less, and the second half temperature of stretching is 110 ° C. or more and 150 ° C. or less. It is preferable to preheat at 85 ° C. for 1 second or longer.
Then, you may perform the 2nd longitudinal stretch as needed. The stretching ratio in the second longitudinal stretching is preferably 1 to 2 times, more preferably 1.2 to 1.6 times. The stretching temperature is preferably 140 ° C. or higher and 160 ° C. or lower.

  Furthermore, the film is heat-treated after biaxial stretching or second longitudinal stretching. The heat treatment can be performed by any conventionally known method such as in an oven or on a heated roll. This heat treatment is performed at a temperature of 120 ° C. or higher and below the crystal melting peak temperature of the polyester, preferably 190 ° C. or higher. The heat treatment time can be arbitrarily set within a range not deteriorating the characteristics, and is preferably 5 seconds to 60 seconds, more preferably 10 seconds to 40 seconds, and most preferably 15 seconds to 30 seconds. Good.

  Furthermore, in order to improve the adhesive force with a printing layer, an adhesive layer, etc., at least one surface can be subjected to corona treatment or an easy adhesion layer can be coated. As a method of providing the coating layer in the film production process, at least uniaxially stretched film is uniformly applied using a metalling ring bar, gravure roll, or the like in which the coating layer composition is dispersed in water, A method of drying the coating agent while stretching is preferred, and the easy-adhesion layer thickness is preferably 0.01 μm or more and 1 μm or less. Also, various additives such as antioxidants, heat stabilizers, ultraviolet absorbers, infrared absorbers, pigments, dyes, organic or inorganic particles, antistatic agents, nucleating agents, etc. may be added to the easy-adhesion layer. Good. The resin preferably used for the easy-adhesion layer is preferably at least one resin selected from an acrylic resin, a polyester resin, and a urethane resin from the viewpoint of adhesiveness and handleability. Furthermore, off-annealing under conditions of 140 to 200 ° C. is also preferably used.

  The polyester film of the present invention can be preferably used as a metal can produced by drawing or ironing after being laminated on a metal plate or the like. Moreover, it can use preferably as a light shielding tape installed in the window frame of electronic devices, such as a smart phone and a tablet, by printing black.

  The characteristic measuring method and the effect evaluating method in the present invention are as follows.

(1) Polyester composition The polyester resin and film were dissolved in hexafluoroisopropanol (HFIP), and the content of each monomer residue component and by-product diethylene glycol was quantified using ¹ H-NMR and ¹³ C-NMR. In the case of a laminated film, each layer of the film was scraped off in accordance with the laminated thickness to collect and evaluate the components constituting each single layer. In addition, about the film of this invention, the composition was computed by calculation from the mixing ratio at the time of film manufacture.

(2) Intrinsic viscosity of polyester The intrinsic viscosity of the polyester resin and the film was measured at 25 ° C. using an Ostwald viscometer after dissolving the polyester in orthochlorophenol. In the case of a laminated film, the intrinsic viscosity of each layer was evaluated by scraping each layer of the film.

(3) Film thickness and layer thickness The film was embedded in an epoxy resin, and the film cross section was cut out with a microtome. The cross section was observed with a transmission electron microscope (TEM H7100, manufactured by Hitachi, Ltd.) at a magnification of 5000 times to determine the film thickness and the thickness of the polyester layer.

(4) Measurement and analysis were performed in accordance with JIS K7121-1987 and JIS K7122-1987 using a melting point differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd., RDC220). Using 5 mg of the polyester film as a sample, the temperature at the top of the endothermic peak obtained from the DSC curve when the temperature was raised from 25 ° C. to 300 ° C. at 20 ° C./min was defined as the melting point of the film. When two or more melting points were observed, the largest endothermic peak was taken as the melting point of the film.
(5) In the case of a melting point laminated film of each layer of the film, the melting point of each layer can be measured by the method of (4) by scraping off each layer of the film. In the case of a laminated polyester film having a polyester A layer and a polyester B layer, when it is confirmed as a laminated structure by cross-sectional observation in (3), a layer in which a lot of inorganic substances are visually observed in a cross-sectional observation photograph is polyester A layer, The layer that appeared to have a small amount of inorganic matter was designated as polyester B layer. In each layer, when two or more melting points were observed, the largest endothermic peak was adopted as the melting point of each layer.

(6) Using an L value color meter (manufactured by Suga Test Instruments, SM-T) in the Hunter color system, the value measured in the transmission mode in the Hunter system according to JIS P81213-1961 was measured. The light incident surface was measured 5 times on each side for a total of 10 times on both sides. The average of 10 measurement values in total was obtained, and this was taken as the L value in the Hunter color system of the film.

(7) Surface roughness The surface roughness was measured using a surface roughness meter (SE4000, manufactured by Kosaka Laboratory). Measured under the conditions of a stylus tip radius of 0.5 μm, measuring force of 100 μN, measuring length of 1 mm, low-frequency cutoff of 0.200 mm, and high-frequency cutoff of 0.000 mm, and arithmetic average roughness SRa according to JIS B0601-2001 (Nm) was determined.

(8) Glossiness According to the method defined in JIS Z-8741-1997, the 60 ° specular glossiness was measured using a glossiness meter (digital variable angle glossiness meter UGV-5D manufactured by Suga Test Instruments Co., Ltd.). The measurement was performed at n = 10, and the average value of eight measured values excluding the maximum value and the minimum value was defined as the glossiness.

(9) A heat shrinkage film at 190 ° C. for 20 minutes was cut into a rectangular shape having a length of 70 mm and a width of 10 mm in an arbitrary direction X and a direction Y orthogonal to the X direction, and used as samples. Marks were drawn on the sample at intervals of 50 mm, and a heat treatment was performed by placing it in a hot air oven heated to 190 ° C. with a 3 g weight suspended for 20 minutes. The distance between the marked lines after the heat treatment was measured, and the thermal contraction rate was calculated from the change in the distance between the marked lines before and after heating by the following formula. For each film, three samples were measured in the X direction and the Y direction for each film, and the average value was evaluated.
Thermal shrinkage (%) = {(distance between marked lines before heat treatment) − (distance between marked lines after heat treatment)} / (distance between marked lines before heat treatment) × 100.

(10) Breaking elongation, breaking strength Any one direction in the film plane is the direction X, and the direction orthogonal to the direction X is the direction Y. The sample is cut into a rectangle of 150 mm × 10 mm (direction X × direction Y). . Using a tensile tester (Orientec Tensilon UCT-100), the initial tensile chuck distance is set to 50 mm (L0), the tensile speed is set to 300 mm / minute, the tensile test is performed, and the chuck distance when the sample breaks ( L). With respect to the value obtained by the formula of (L−L0) / L0 × 100, the average value of 10 measurements was defined as the elongation at break (%) in direction X. Moreover, the strength measured immediately before the break was defined as the break strength (MPa). A sample was prepared by cutting into a rectangle of 150 mm × 10 mm (direction Y × direction X), and the elongation at break in direction Y was determined in the same manner.

(11) Using a film stretcher (Browner, KARO-IV) after 50% stretching, a sample was prepared according to the following criteria for the film surface appearance after stretching the film under the following conditions. Then, the glossiness was evaluated.
Initial sample: 100 mm × 100 mm, preheating / stretching temperature: 120 ° C., preheating time: 20 s, stretching speed: 20% / s, stretching ratio: 2 ×× 1 gloss change rate (%) = | gloss before stretching− Glossiness after stretching | / Glossiness before stretching × 100
(12) A sample cut to 100 mm × 100 mm is hung on the middle part of the ceiling of the oven in a hot air oven set at 120 ° C. and a glossiness change rate of 120 ° C. after 10 minutes of heat treatment, and left for 10 minutes. After 10 minutes, a sample was taken out and evaluated for glossiness.
Gloss change rate after heat treatment at 120 ° C. for 10 minutes (%) = | Glossiness before heat treatment−Glossiness after heat treatment | / Glossiness before heat treatment × 100
(13) Processability evaluation An A4 size film was sandwiched between two A4 size metal frames (a shape in which four sides were left 20 mm each, and the center was cut out) and fixed with a metal clip. The center part of the mark of 50 mm × 50 mm square (A4 size long side direction (hereinafter referred to as long side direction) × A4 size short side direction (hereinafter referred to as short side direction)) overlaps with the center part of the A4 size film. Then, it was put into a 5 m hot air drying furnace set at 160 ° C. at a conveying speed of 2.5 m / min. The cell size and film state of the film that came out of the hot air drying furnace were confirmed and evaluated according to the following criteria.
A: The rate of change in the mesh size of the film was less than 1% in both the long side direction and the short side direction, and no film wrinkles were observed.
B: The rate of change in the mesh size of the film was less than 1% in either the long side direction or the short side direction, and the other was 1% or more, and no film wrinkles were observed.
C: The rate of change in the size of the grid of the film was 1% or more in both the long side direction and the short side direction, and no film wrinkles were observed.
D: Wrinkles were found on the film.
(14) Evaluation of concealment After filling in three types of lines of 50 mm in length, 0.3 mm in width, 1 mm in width, and 1.5 mm in width on a tin-free steel plate (steel plate) heated to a temperature 5 ° C. lower than the melting point. The tin steel plate was heated to a temperature 5 ° C. lower than the melting point of the film, and the film was laminated on the plate using a rubber roll. The obtained laminated steel sheet was visually observed and evaluated according to the following criteria.
A: All three types of lines were not visible at all.
B: Only one type of line was visible among the three types of lines.
C: Two types of lines were visually recognized among three types of lines.
D: Three types of lines were visually recognized.

(15) Formability evaluation The laminated steel sheet obtained in (14) was drawn with a drawing ratio of 3, and the resulting can was visually confirmed and evaluated according to the following criteria.
A: The film surface was not broken or cracked on the film surface.
B: Breaking and cracking of a film portion of 2 mm or less were observed on the film surface.
C: Breaks and cracks of the film part exceeding 2 mm and 5 mm or less were observed on the film surface.
D: Breaking and cracking of a film part having a size exceeding 5 mm were observed on the film surface.

(16) Gloss evaluation (15) The can obtained by the evaluation was evaluated according to the following criteria.
A: When a fluorescent lamp is projected on the can, the outline is clearly visible with respect to the entire surface of the can.
B: When a fluorescent lamp is projected on the can, the outline of either the bottom or the trunk of the can is visually blurred and the other is clearly visible. The glossiness is weak, and the other has a sufficient glossiness.
C: When a fluorescent lamp is projected on the can, the outline is visually blurred with respect to the entire surface of the can.
D: When a fluorescent lamp is projected on the can, at least one of the bottom surface and the trunk surface of the can is very rough, and the outline is hardly visible.

(Manufacture of polyester)
The polyester resin used for film formation was prepared as follows.

(Polyester A)
Polyethylene terephthalate resin (intrinsic viscosity 0.65) in which the terephthalic acid component is 100 mol% as the dicarboxylic acid component and the ethylene glycol component is 100 mol% as the glycol component.

(Polyester B)
1,4-cyclohexanedimethanol copolymerized polyethylene terephthalate resin (intrinsic viscosity 0.75) in which 10 mol% of 1,4-cyclohexanedimethanol is copolymerized with respect to the glycol component.

(Polyester C)
Isophthalic acid copolymerized polyethylene terephthalate resin (inherent viscosity 0.7) having 80.4 mol% terephthalic acid component as dicarboxylic acid component, 19.6 mol% isophthalic acid component, and 100 mol% ethylene glycol component as glycol component .

(White pigment master D)
A polyethylene terephthalate white pigment master (inherent viscosity 0.65) containing polyester anatase-type titanium oxide particles having a number average particle diameter of 1 μm at a particle concentration of 50% by mass.
(White pigment master E)
Polyethylene terephthalate white pigment master (intrinsic viscosity 0.65) containing a rutile type titanium oxide particle having a number average particle size of 1 μm in polyester A at a particle concentration of 50 mass%.

(Particle Master F)
Polyethylene terephthalate particle master (intrinsic viscosity 0.65) containing agglomerated silica particles having a number average particle size of 2.2 μm in polyester A at a particle concentration of 2 mass%.

(Particle Master G)
A polyethylene terephthalate particle master (specific concentration 0.65) containing polyester carbonate A with calcium carbonate particles having a number average particle diameter of 0.7 μm at a particle concentration of 2% by mass.

Example 1
The composition is as shown in the table, and the raw material is supplied to a vented co-directional twin-screw extruder having an oxygen concentration of 0.2% by volume. The raw material is melted at an extruder cylinder temperature of 280 ° C., and the die temperature is 280 ° C. The sheet was discharged from a T die onto a cooling drum whose temperature was controlled at 10 ° C. At that time, a wire-like electrode having a diameter of 0.1 mm was applied electrostatically, closely contacted with the cooling drum, and an unstretched sheet was obtained while blowing cold air of 15 ° C. on the polymer on the cast drum by an air chamber method. . Next, preheating was performed for 1.5 seconds at a preheating temperature of 85 ° C. in the longitudinal direction, the film was stretched 3 times in the longitudinal direction at a stretching temperature of 115 ° C., and immediately cooled with a metal roll whose temperature was controlled at 40 ° C. Next, it is preheated at a preheating temperature of 85 ° C. for 1.5 seconds with a tenter type horizontal stretching machine, stretched 3.5 times in the width direction at a stretching first half temperature of 115 ° C., a stretching middle temperature of 135 ° C., and a stretching second half temperature of 145 ° C. In the tenter, a heat treatment was performed at a heat treatment temperature of 210 ° C. while relaxing 5% in the width direction to obtain a biaxially oriented polyester film having a film thickness of 20 μm.
(Examples 2 and 3)
A biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was changed as shown in the table.
(Examples 4, 5, and 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the thickness was changed as shown in the table.
(Example 7)
The composition is as shown in the table, and the raw materials are supplied to separate bent co-directional twin-screw extruders each having an oxygen concentration of 0.2% by volume, the A layer extruder cylinder temperature is 280 ° C., and the B layer extruder cylinder temperature is Melt at 270 ° C., and merge into a three-layer configuration of A layer / B layer / A layer in the feed block. The sheet was discharged on a cooling drum controlled in temperature. Thereafter, a biaxially oriented polyester film having a thickness of 20 μm was obtained in the same manner as in Example 1.
(Examples 8, 9, 10, 13, 14, 15, 16, 17)
A biaxially oriented polyester film was obtained in the same manner as in Example 7 except that the composition was changed as shown in the table.
(Examples 11 and 12)
A biaxially oriented polyester film was obtained in the same manner as in Example 7 except that the lamination ratio was changed as shown in the table.
(Comparative Examples 1, 2, 3, 5, 7)
A biaxially oriented polyester film was obtained in the same manner as in Example 7 except that the composition, thickness, and production conditions were changed as shown in the table.
(Comparative Example 4)
A biaxially oriented polyester film was obtained in the same manner as in Example 6 except that the thickness was changed as shown in the table.
(Comparative Example 6)
A biaxially oriented polyester film was obtained in the same manner as in Example 5 except that the thickness was changed as shown in the table.

The present invention relates to a polyester film that is suitably used for applications that require concealment properties such as a laminated metal plate and a light shielding tape, and by setting the thickness, L value by a hunter color system, and heat shrinkage in a specific range. Although it is a thin film, it is suitable for applications requiring concealment properties such as a laminated metal plate and a light-shielding tape because of its excellent base concealing property and high processability at high temperatures.

Claims (10)

When the thickness is 10 to 40 μm, the L value in the Hunter color system is 80 or more, and when one direction in the film plane is the direction X and the direction perpendicular to the direction X is the direction Y, 190 ° C., A polyester film in which the heat shrinkage rate (Sx) in the direction X and the heat shrinkage rate (Sy) in the direction Y in 20 minutes satisfy the following expressions.
| Sx−Sy | ≦ 4% (I) Sx ≦ 5% (II) Sy ≦ 5% (III)   2. The polyester film according to claim 1, wherein at least one surface has a surface roughness SRa of 7 nm or more and 30 nm or less, and at least one surface has a glossiness of 80% or more and 120% or less at an incident angle of 60 °. Assuming that one arbitrary direction in the film plane is the direction X and the direction perpendicular to the direction X is the direction Y, the breaking strength in the direction X (Fx), the breaking strength in the direction Y (Fy), and the breaking elongation in the direction X (Lx ), And the breaking strength (Ly) in the direction Y satisfies the following formula, respectively.
| Fx−Fy | ≦ 30 MPa (IV)
140 MPa <Fx ≦ 200 MPa (V)
140 MPa <Fx ≦ 200 MPa (VI)
| Lx−Ly | ≦ 30% (VII)
80% <Lx ≦ 195% (VIII)
80% <Lx ≦ 195% (IX)   The polyester film according to any one of claims 1 to 3, wherein a change in glossiness at an incident angle of 60 ° before and after heat treatment at 120 ° C for 10 minutes is 0% or more and 15% or less on at least one side.   The polyester film according to any one of claims 1 to 4, wherein a change in glossiness at an incident angle of 60 ° before and after stretching by 50% is 0% or more and 20% or less on at least one side.   The polyester film according to claim 1, wherein the film has a melting point of 230 ° C. or higher and 265 ° C. or lower.   The polyester film according to any one of claims 1 to 6, wherein the white pigment contained in the film is anatase type titanium oxide.   The polyester film according to any one of claims 1 to 8, wherein the polyester A layer has a polyester B layer on at least one side, and the polyester B layer does not contain a white pigment.   The polyester film according to any one of claims 1 to 8, which is used by being laminated on a metal plate. The light-shielding tape using the film in any one of Claim 1 to 8.