JP2009166442A - Method for producing uniaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably producing a uniaxially oriented polyester film which can appropriately be used as, for example, the substrate of a liquid crystal display, specifically the protective film of a polarizing film or plate. <P>SOLUTION: In the method for producing the uniaxially oriented polyester film stretched by a tenter type drawing machine, the polyester film, before being stretched by the drawing machine, is stretched by 1.05-1.20 times in the film progress direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a uniaxially oriented polyester film, and specifically relates to a method for producing a uniaxially oriented polyester film that is suitably used, for example, as a liquid crystal display substrate.

  A liquid crystal display generally has a configuration of backlight / polarizing plate / liquid crystal film / polarizing plate, and in particular, a polarizing plate generally has a configuration of protective film / polarizing film / protective film or protective film / polarizing film / retardation film. . In recent years, uniaxially oriented polyester films have superior optical properties, such as less variation in the main orientation angle with respect to an arbitrary reference direction in the film plane than biaxially oriented films. Attempts have been made to use as a protective film for a polarizing film or a protective film for a polarizing plate.

  As a method for producing a uniaxially oriented polyester film, a method of stretching an unstretched sheet obtained by melting and continuously extruding a polyester resin and then rapidly cooling it with a tenter-type stretching apparatus is known. A number of clips are mounted at equal intervals on the tenter stretching device, and an endless circulation track is formed between the drive sprocket on the film outlet side and the free sprocket on the inlet side, and the clip grips both ends of the film on the inlet side. Then, the film is stretched in the stretching zone through the preheating zone in the direction perpendicular to the direction of travel, through the heat setting zone and the cooling zone, the clip opens the end of the film at the tenter outlet, and then is taken up by the take-up roll. In this step, the film is manufactured by a method in which the ears at both ends are wound while being slit.

In the manufacturing method of the uniaxially oriented polyester film by the tenter type stretching device, there is a method of manufacturing using the tenter type stretching device of the existing sequential biaxial stretching device, and in terms of cost compared with the case of constructing a new stretching device. Is also advantageous. The sequential biaxial stretching apparatus is an apparatus that stretches an unstretched sheet in the traveling direction and / or the vertical direction of the film by the longitudinal stretching process and the tenter type stretching process, and by using the tenter type stretching apparatus of the sequential biaxial stretching apparatus, It is possible to produce a uniaxially oriented polyester film that extends in the vertical direction of the film. When producing a uniaxially oriented polyester film using a sequential biaxial stretching device, in order to co-produce with a sequential biaxially stretched film, the longitudinal stretching process is also used during the production of the uniaxially oriented polyester film from the point of reducing production loss as much as possible. It is necessary to raise the temperature condition of the roll to some extent. The longitudinal stretching process of a sequential biaxial stretching apparatus generally consists of a number of preheating rolls, stretching rolls, and cooling rolls. In the production of a uniaxially oriented polyester film, the unstretched sheet sticks to the roll mainly in the stretching roll of the longitudinal stretching process. Thus, color unevenness in the case of inspecting the obtained uniaxially oriented film under crossed Nicols becomes a problem.
Japanese Patent No. 3840937 JP 2003-89152 A

  This invention is made | formed in view of the said actual condition, Comprising: The solution subject is providing the manufacturing method which produces stably the uniaxially-oriented polyester film used suitably as a base material of a liquid crystal display.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by a specific film manufacturing method, and has completed the present invention.

  That is, the gist of the present invention is a method for producing a uniaxially oriented polyester film that is stretched by a tenter stretching device, and is stretched by 1.05 to 1.20 times in the traveling direction of the film before stretching by the stretching device. The present invention resides in a method for producing a uniaxially oriented polyester film.

Hereinafter, the present invention will be described in detail.
The polyester film referred to in the present invention is a film obtained by stretching an unstretched sheet melt-extruded from an extrusion die by a so-called extrusion method.

  The polyester constituting the above film refers to a polymer containing an ester group obtained by polycondensation from dicarboxylic acid and diol or from hydroxycarboxylic acid. Examples of dicarboxylic acids include terephthalic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and diols include ethylene glycol and 1,4-butane. Examples include diol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol and the like, and examples of hydroxycarboxylic acid include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. be able to.

  Typical examples of such polyester include polyethylene terephthalate, polyethylene-2,6-naphthalate, polytetramethylene terephthalate, polytetramethylene-2,6-naphthalate, and the like. These polyesters may be homopolymers or may be those obtained by copolymerizing a third component. As described above, among the exemplified polyesters, polyethylene terephthalate is excellent in transparency, water resistance, chemical resistance, mechanical strength, dimensional stability, and the like, and is preferably used.

  The polyester in the present invention is 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 a reaction of a lower alkyl ester of a dicarboxylic acid and a diol with a conventionally known ester exchange catalyst. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst.

  The polyester used in the present invention may be converted into chips after melt polymerization, and further subjected to solid phase polymerization as necessary under heating and reduced pressure or in an inert gas stream such as nitrogen.

  In order to prevent blocking and 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. Well, you may use two methods together.

  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 wt%, preferably 0.01 to 10.0 wt%, based on the polyester. If the particle content is high, the haze increases and the transparency of the film decreases, and if the particle content is low, handling of the film may be difficult.

  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 of producing the polyester, but preferably after the esterification stage or after the transesterification reaction, particles may be added to proceed the polycondensation 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 blend of dried particles and a polyester raw material using a kneading extruder It is done by the method to do.

  In this invention, you may add an additive other than the said particle | grain as needed. 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 melt-extruded using a single polyester melt extruder can be used, or two or three or more layers can be used to laminate two or more layers by a so-called coextrusion method. It can also be a film. The layer structure includes a single layer structure using only the A raw material, an A / B structure using the A raw material and the B raw material, or an A / B / A structure, and an A / B / C structure using the C raw material or It can be set as the film of the structure of other than that. For example, the surface shape of the A layer can be designed using specific particles as the A raw material, and a film having an A / B or A / B / A structure can be formed using a raw material not containing particles as the B raw material. Further, even if the recycled material of the film is blended with the B layer, the surface roughness can be designed by the surface A layer, so that the cost advantage is further increased.

  In the present invention, the uniaxially oriented polyester film is a polyester film that is remarkably stretched in one direction, and has a refractive index (nγ) in the main orientation direction and a refractive index in the direction perpendicular to the main orientation direction in the film plane. The difference Δn (Δn = nγ−nβ) with respect to (nβ) is 80 or more, preferably 100 or more.

  In the present invention, an unstretched polyester sheet is stretched by 1.05-1.20 times in the film traveling direction in a longitudinal stretching process using a sequential biaxial stretching apparatus, and is laterally stretched in a stretching zone in a tenter stretching apparatus. Thus, a uniaxially oriented polyester film is produced. The lateral stretching is performed by gradually increasing the width of the tenter rail.

  The unstretched sheet can be obtained by melt-extruding polyester and rapidly solidifying it on a rotating cooling drum.

  In the present invention, an unstretched sheet is introduced into the longitudinal stretching step to perform longitudinal stretching in the film traveling direction. The longitudinal stretching ratio is 1.05-1.20 times, preferably 1.05-1.15 times. More preferably, it is 1.05 to 1.10 times. When the longitudinal stretching ratio is 1.05 or less, the unstretched sheet adheres to the stretching roll in the longitudinal stretching step, and the polarizing plate with the protective film using the obtained film as a base material is crossed Nicol When inspecting with, the color unevenness becomes large and hinders the inspection. When the longitudinal draw ratio is larger than 1.20 times, the variation of the angle of the main orientation with respect to an arbitrary reference direction in the film surface becomes large, and a polarizing plate with a protective film pasted using the obtained film as a base material, etc. When testing under crossed Nicols, the difference between light and dark becomes large, which hinders testing.

  The film of the present invention is produced by a method of stretching with a tenter type stretching apparatus. The tenter stretching apparatus generally comprises a preheating zone, a stretching zone, a heat setting zone, and a cooling zone. The tenter stretching apparatus grips both ends of the unstretched sheet with clips and guides the sheet to the preheating zone. The temperature of the preheating zone is preferably not less than the glass transition point and not more than 140 ° C.

  In the present invention, the stretching zone of the tenter stretching apparatus comprises one or more stretching zones defined by a predetermined stretching ratio and / or stretching temperature. The stretching temperature is not lower than the glass transition point. The stretch ratio is not particularly limited, but a range of 2 to 8 times is preferable. When the stretch ratio is less than 2 times, the thickness fluctuation becomes large, and when it exceeds 8 times, the film is easily broken during transverse stretching.

  In the present invention, the angle formed by the running direction between the tenter rail and the film center in the stretching zone is preferably 10 ° or less. If the angle formed by the running direction between the tenter rail and the film center in the stretching zone exceeds 10 °, the variation in the orientation angle increases.

  In the present invention, the heat setting zone is composed of one or more zones. In the heat setting zone, the film can be relaxed in the same direction as the film stretching direction in order to obtain an appropriate value for the heat shrinkage rate. The relaxation rate is preferably 10% or less. If the relaxation rate in the heat setting zone is 10% or more, the flatness and the sagging of the film may be deteriorated.

  In the present invention, the cooling zone is composed of one or more zones. The temperature of the cooling zone is preferably 30 ° C. or lower than the maximum temperature of the heat setting zone. When the temperature of the cooling zone is within 30 ° C. compared to the maximum temperature of the heat setting zone, the film temperature may be too high when the film comes out of the tenter stretching device, and the flatness of the film may be deteriorated. .

  The film of the present invention can be provided with a coating layer for the purpose of improving the surface adhesion and providing an antistatic effect. The coating layer may be provided on one side of the film or on both sides, and different coating layers may be provided on the front and back sides.

  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, for example, 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.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the stable uniaxially-oriented polyester film can be provided, and the industrial value of this invention is high.

  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.

(1) Color unevenness under crossed Nicols A polarizing plate with a protective film using the obtained film as a base material is inspected under crossed Nicols, and color unevenness under crossed Nicols is evaluated according to the following criteria. I did it.
A: There is no color unevenness under crossed Nicols, and it can be inspected well.
○: Color unevenness can be confirmed under crossed Nicols, but inspection does not hinder.
X: Color unevenness under crossed Nicols becomes large and hinders inspection.

(2) Measurement of angle of main orientation Using a polarization microscope manufactured by Carl Zeiss, the orientation of the polyester film is observed, and the direction of the main orientation axis in the plane of the polyester film is tilted several times with respect to the width direction of the polyester film. To determine the orientation angle. This measurement was carried out for a total of three locations, the center and both ends of the film, and the deviation was taken as the value of the variation in the angle of the main orientation with respect to an arbitrary reference direction in the film plane.

(3) Light / dark unevenness under crossed Nicols A polarizing plate with a protective film using the obtained film as a base material is inspected under crossed Nicols, and evaluation of light / dark unevenness under crossed Nicols is performed according to the following criteria. went.
◎: There is no unevenness of light and darkness under crossed Nicols, and it can be inspected well ○: Lightness and darkness unevenness can be confirmed under crossed Nicols, but there is no problem in inspection ×: Lightness and darkness unevenness under crossed Nicols increases Disturbed

(4) Productivity ◎: There was no quality defect under the crossed Nicols and the deflection of the main orientation angle, and the productivity was greatly improved. ○: There was little quality failure under the crossed Nicols and the deflection of the main orientation angle. Productivity improved ×: Poor quality under crossed nicols and fluctuation of main orientation angle, resulting in poor productivity

Example 1:
Polyethylene terephthalate having 0.2% of amorphous silica having an average particle size of 1.3 μm was melt extruded at 285 ° C., cast on a cooling drum at 30 ° C., and rapidly cooled to obtain an unstretched sheet having a thickness of 160 μm. The obtained unstretched sheet is guided to a longitudinal stretching step, stretched 1.06 times in the film traveling direction, then guided to a tenter-type stretching device, preheated in a preheating zone of 90 ° C, a stretching temperature of 100 ° C, a stretching ratio of 4 After stretching in a 0.0 transverse stretching zone, heat treatment was performed in a 220 ° C. heat setting zone and cooling was performed in a 150 ° C. cooling zone to obtain a 40 μm thick polyester film.

Example 2:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the stretching ratio in the traveling direction of the film in the longitudinal stretching step was 1.09.

Example 3:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the draw ratio in the traveling direction of the film in the longitudinal drawing step was 1.16.

Comparative Example 1:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the draw ratio in the traveling direction of the film in the longitudinal drawing step was 1.00.

Comparative Example 2:
In Example 1, a polyester film was obtained in the same manner as in Example 1 except that the draw ratio in the traveling direction of the film in the longitudinal drawing step was 1.50.
The obtained results are summarized in Table 1 below.

  The present invention can be suitably used, for example, as a method for producing a substrate for a liquid crystal display.

Claims (1)

A method for producing a uniaxially oriented polyester film stretched by a tenter-type stretching device, wherein the film is stretched by 1.05 to 1.20 times in the traveling direction of the film before stretching by the stretching device. A method for producing a polyester film.