JP2013189591A - Biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film excellent in heat resistance and optical properties used for various optical members used for liquid crystal displays, touch panels, etc., protective films and release films used in the manufacturing process of optical products. I will provide a.
A polyester composed of a diol unit in which 0.25 to 30 mol% of diol units is isosorbide and 0.38 to 45 mol% is 1,4-cyclohexanedimethanol and a dicarboxylic acid unit. A biaxially oriented polyester film characterized in that the film has a thickness of 25 to 250 μm.
[Selection figure] None

Description

  The present invention relates to a biaxially oriented polyester film, and more specifically, to various optical members used for liquid crystal displays, touch panels, etc., and protective films and release films used in the manufacturing process of optical products. The polyester film is preferably used and particularly relates to a biaxially oriented polyester film having excellent heat resistance.

  Conventionally, polyester film, especially polyethylene terephthalate biaxially oriented film has excellent mechanical properties and chemical resistance, magnetic tape, ferromagnetic thin film tape, photographic film, packaging film, electronic component film, electrical It is widely used as a material for insulating films, metal laminate films, protective films for various members, and the like.

  In recent years, polyester films are often used for various optical films, such as prism sheets for LCD members, light diffusing sheets, reflectors, touch panels, and other base films, antireflection base films, and display explosion-proof base films, It is used for various applications such as PDP filter films and touch panel films. In these optical products, in order to obtain a bright and clear image, the base film used as an optical film has good transparency from its usage pattern and has defects such as foreign matter and scratches that affect the image. It is necessary not to. In recent years, LEDs are often used as light sources in LCDs, and the amount of heat applied to optical films tends to increase.For touch panels, the processing temperature tends to rise to improve the performance of transparent conductive films. In these optical base films, the heat resistance of the film is an important factor.

  Polyethylene terephthalate (PET) is often used as an optical base film. However, in the above-mentioned recent trend, the glass transition point of polyethylene terephthalate (PET) may have insufficient performance.

  In order to increase the heat resistance of the film, a method of increasing the thickness of the film can be considered. The polyester film is usually obtained by subjecting an amorphous sheet obtained by melt extrusion to a sheet shape and rapid cooling and solidification to the longitudinal direction and the transverse direction, followed by heat treatment. When increasing the thickness of the polyethylene terephthalate film, the sheet is not cooled sufficiently in the process of rapidly solidifying the melt-extruded sheet, and the crystallization of the raw material proceeds, so that it is sufficiently transparent for optical use. May not be obtained.

  In order to increase the heat resistance of the base film, the use of a special resin having excellent heat resistance can be considered, but this is not preferable because the cost is significantly increased.

JP 2007-178997 A JP 2000-238124 A JP-A-11-222529

  This invention is made | formed in view of the said actual condition, Comprising: The solution subject is various optical members used for a liquid crystal display, a touchscreen, etc., and the protective film and release film used in the manufacturing process of the product of an optical field | area It is providing the biaxially-oriented polyester film excellent in heat resistance and an optical characteristic used for the above.

As a result of intensive studies in view of the above problems, the present inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention.
That is, the gist of the present invention is that a diol unit in which 0.25 to 30 mol% of diol units is isosorbide and 0.38 to 45 mol% is 1,4-cyclohexanedimethanol, and a dicarboxylic acid unit. It is a film made of a configured polyester, and exists in a biaxially oriented polyester film characterized in that the film has a thickness of 25 to 250 μm.

  According to the present invention, biaxial shafts excellent in heat resistance and optical properties, used for various optical members used in liquid crystal displays, touch panels, etc., and protective films and release films used in the manufacturing process of optical products. An oriented polyester film can be provided, and the industrial value of the present invention is high.

  The polyester film referred to in the present invention is a film obtained by stretching a sheet melt-extruded from an extrusion die according to a so-called extrusion method.

  The polyester constituting the above film refers to a polyester obtained by polycondensation of a dicarboxylic acid unit and a diol unit. Examples of the dicarboxylic acid unit include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the diol unit include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like.

  In the present invention, 0.25 to 30 mol% in the diol unit is isosorbide and 0.38 to 45 mol% is required to be 1,4-cyclohexanedimethanol, preferably 1 in the diol unit. ~ 20 mol% is isosorbide, 1.5-30 mol% is 1,4-cyclohexanedimethanol, more preferably 5-10 mol% in the diol unit is isosorbide, 7.5-20 mol % Is 1,4-cyclohexanedimethanol.

  When the isosorbide in the diol unit is less than 0.25 mol% or 1,4-cyclohexanedimethanol is less than 0.38% mol, sufficient heat resistance cannot be obtained. When isosorbide in the diol unit exceeds 20 mol%, or when 1,4-cyclohexanedimethanol exceeds 30 mol%, the heat resistance is sufficient, but the low cost cannot be maintained, which is not preferable.

  The isosorbide referred to in the present invention is 1,4: 3,6-dianhydro-D-sorbitol having the following structure.

  As a method of containing such a component, a copolymer polyester contained as a predetermined amount of a copolymer component as a raw material for producing a film may be used, or a copolymerized polyester film containing a copolymer component larger than a predetermined amount; You may use the raw material obtained by blending copolymer polyester or homopolyester of content with little copolymerization component.

  The polyester in the present invention is obtained by a conventionally known method, for example, a method of directly obtaining a low polymerization degree polyester by reaction of a dicarboxylic acid and a diol, or after reacting a lower alkyl ester of a dicarboxylic acid and a diol with a conventionally known transesterification catalyst. It can be obtained by a method of conducting a polymerization reaction in the presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony catalyst, a germanium compound, or a titanium compound may be used. Preferably, the amount of antimony compound is zero or 100% or less as antimony to reduce film dullness. .

  The polyester used in the present invention may be obtained by forming a chip after melt polymerization and further subjecting it to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.4 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  In order to facilitate handling, the polyester film in the present invention may contain particles under conditions that do not impair transparency. Examples of particles used in the present invention include inorganic particles such as calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, and crosslinked polymers. Examples thereof include organic particles such as particles and calcium oxalate. Examples of the method of adding particles include a method of adding particles in a polyester as a raw material, a method of adding directly to an extruder, and the like. Two methods may be used in combination.

  The particle size of the particles used is usually 0.05 to 5.0 μm, preferably 0.1 to 4.0 μm. When the average particle size is larger than 5.0 μm, the haze of the film increases and the transparency of the film may be lowered. If the average particle size is smaller than 0.1 μm, the surface roughness becomes too small, and the film may be difficult to handle. The particle content is usually 0.001 to 30.0% by weight, preferably 0.01 to 10.0% by weight, based on the polyester. If the particle content is high, the haze increases and the transmittance in the visible light region may be reduced. If the particle content is low, the film may be difficult to handle.

  The method of adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a method of blending dried particles and a polyester raw material using a kneading extruder. It is performed by the method of blending.

  In the present invention, additives may be added in addition to the above particles as necessary. Examples of such additives include stabilizers, lubricants, cross-linking agents, anti-blocking agents, antioxidants, dyes, pigments, and ultraviolet absorbers.

  In the present invention, a single-layer film using one polyester melt extruder can be used, and two or three or more can be used to form a laminated film of at least three layers by a so-called coextrusion method. . As the structure of the layer, an A structure using only the A raw material, an A / B / A structure using the A raw material and the B raw material, an A / B / C structure using the C raw material, or other three or more layers. It can be set as the film of a structure.

  The thickness of the polyester film of the present invention is 25 to 250 μm, preferably 25 to 188 μm, and more preferably 25 to 125 μm. When the film thickness is thicker than 250 μm, the heat resistance is sufficient, but it is not preferable in terms of product design for optical applications competing for weight reduction and thinning.

  In the present invention, the haze is usually 5.0% or less, preferably 3.0% or less. If the haze is higher than 5.0%, the transparency is lowered, which may be undesirable for use in optical applications.

  The film of the present invention may be provided with a coating layer on one side or both sides of the film. Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As a coating method of the coating agent, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or a coating apparatus other than these can be used.

  In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

  The thickness of the coating layer is usually in the range of 0.02 to 0.5 μm, preferably 0.03 to 0.3 μm, as the final dry thickness. When the thickness of the coating layer is less than 0.02 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above problem of sticking appears particularly when the same coating layer is formed on both sides of the film.

  In addition, you may coat by the method called offline coating which coats after manufacture of a film as needed. Moreover, single side | surface and both surfaces are not ask | required. The coating material may be either water-based and / or solvent-based in the case of off-line coating.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. Various physical properties and characteristics are measured or defined as follows. In the examples, “%” means “% by weight”.

(1) Measurement of glass transition point Tg Using a differential scanning calorimeter (DSC7 type manufactured by PerkinElmer Co., Ltd.), a sample of 5 mg was heated from room temperature at a heating rate of 10 ° C./min in a nitrogen atmosphere, and a secondary transition type. The change point of the specific heat associated with was taken as the glass transition point Tg.

(2) Measurement of haze The haze of a film was measured using a Nippon Denshoku Industries Co., Ltd. haze meter.

(3) Evaluation of heat resistance The film was cut into a size of 150 mm x 150 mm, treated with a hot air circulation oven at 100 ° C for 24 hours, and then the flatness of the film was evaluated according to the following criteria. In the following criteria, “Δ” or more is considered acceptable.
A: The flatness of the film is almost the same before and after the heat treatment. ○: The flatness of the film is slightly deteriorated before and after the heat treatment, but it is an acceptable level. Δ: The flatness of the film is deteriorated before and after the heat treatment. The flatness of the film greatly deteriorates before and after, and is at a rejected level.

(4) Comprehensive evaluation Comprehensive evaluation was performed according to the following criteria.
A: It has sufficient heat resistance and can be suitably used particularly for optical applications from the viewpoint of physical properties and cost.
(Double-circle): It has sufficient heat resistance, and can be used suitably for an optical use from the surface of a physical property or cost.
○: It has heat resistance and can be used for optical applications.
(Triangle | delta): Although heat resistance is inferior, it can barely be used for an optical use.
X: Insufficient heat resistance and difficult to use for optical applications.

Example 1:
(Polyester chip manufacturing method)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and chipped into a polyester (A) according to a conventional method. The solution viscosity IV of the obtained polyester chip was 0.66.

  Moreover, when manufacturing the said polyester (A), 1000 ppm of amorphous silica with an average particle diameter of 2 micrometers was added, and polyester (B) was created.

  In the production method of the polyester (A), the polyester (C) is produced by using the same method as the production method of the polyester (A) except that ethylene glycol, isosorbide, and 1,4-cyclohexanedimethanol are used as starting materials as the diol component. Got. The obtained polyester (C) contained 30 mol% of isosorbide and 45 mol% of 1,4-cyclohexanedimethanol as diol units.

(Manufacture of polyester film)
The polyesters (A), (B), and (C) were mixed at a ratio of 88.4%, 10.0%, and 1.6%, respectively, and melt-extruded by a melt extruder to obtain a single-layer amorphous sheet. . Subsequently, the sheet was coextruded on a cooled casting drum and solidified by cooling to obtain a non-oriented sheet. Next, the film was stretched 3.2 times in the longitudinal direction at 95 ° C., further subjected to a preheating step in the tenter, stretched 4 times in the transverse direction at 95 ° C., and subjected to heat treatment at 230 ° C. for 10 seconds, and 100 μm thick polyester A film was obtained.

Example 2:
A polyester film is obtained in the same manner as in Example 1 except that raw materials in which the polyesters (A), (B), and (C) are mixed in the proportions of 83.3%, 10.0%, and 6.7%, respectively, are used. It was.

Example 3:
A polyester film is obtained in the same manner as in Example 1 except that a raw material in which polyesters (A), (B), and (C) are mixed at a ratio of 70.0%, 10.0%, and 20.0%, respectively, is used. It was.

Example 4:
A polyester film is obtained in the same manner as in Example 1 except that raw materials in which the polyesters (A), (B), and (C) are mixed in the proportions of 63.3%, 10.0%, and 26.7%, respectively, are used. It was.

Example 5:
A polyester film is obtained in the same manner as in Example 1 except that raw materials in which the polyesters (A), (B), and (C) are mixed in the proportions of 43.3%, 10.0%, and 46.7%, respectively. It was.

Example 6:
A polyester film is obtained in the same manner as in Example 1 except that a raw material in which polyesters (A), (B), and (C) are mixed in proportions of 30.0%, 10.0%, and 60.0%, respectively, is used. It was.

Example 7:
A polyester film is obtained in the same manner as in Example 1 except that a raw material in which the polyesters (A), (B), and (C) are mixed at 1.1%, 10.0%, and 89.9%, respectively, is used. It was.

Example 8:
A polyester film was obtained in the same manner as in Example 6 except that the thickness was 25 μm.

Example 9:
A polyester film was obtained in the same manner as in Example 6 except that the thickness was 125 μm.

Example 10:
A polyester film was obtained in the same manner as in Example 6 except that the thickness was 188 μm.

Example 11:
A polyester film was obtained in the same manner as in Example 6 except that the thickness was 250 μm.

Example 12:
A polyester film is obtained in the same manner as in Example 1 except that a raw material in which the polyesters (A), (B), and (C) are mixed at a ratio of 65.0%, 5.0%, and 30.0%, respectively, is used. It was.

Example 13:
A polyester film was obtained in the same manner as in Example 1 except that the raw materials in which the polyesters (A), (B), and (C) were mixed at a ratio of 50.0%, 20.0%, and 30.0, respectively, were used. .

Comparative Example 1:
A polyester film was obtained in the same manner as in Example 6 except that the raw materials in which the polyesters (A) and (B) were mixed at a ratio of 90.0% and 10.0%, respectively, were used.

Comparative Example 2:
In the manufacturing method of polyester (C), polyester was obtained using the method similar to the manufacturing method of polyester (C) except the addition amount of ethylene glycol, isosorbide, and 1, 4- cyclohexanediol added as a diol component. The obtained polyester contained 40 mol% isosorbide and 60 mol% 1,4-cyclohexanedimethanol as diol units. A polyester film was obtained in the same manner as in Example 1 except that raw materials in which the polyester and the polyester (B) were mixed at a ratio of 95.0% and 5.0% were used.

Comparative Example 3:
A polyester film was obtained in the same manner as in Example 6 except that the thickness of the film was 16 μm.

Comparative Example 4:
A polyester film was obtained in the same manner as in Example 6 except that the thickness of the film was 300 μm.

  The film of the present invention can be suitably used for, for example, various optical members used for liquid crystal displays, touch panels, and the like, protective films and release films used in the manufacturing process of products in the optical field.

Claims (1)

0.25-30 mol% in the diol unit is isosorbide, 0.38-45 mol% is a film composed of a polyester composed of a diol unit composed of 1,4-cyclohexanedimethanol and a dicarboxylic acid unit. A biaxially oriented polyester film, wherein the film has a thickness of 25 to 250 μm.