JP5225697B2 - Method for producing uniaxially oriented polyester film - Google Patents

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 suitably used 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, forming an endless circulation track between the drive sprocket on the film outlet side and the free sprocket on the inlet side, and the clips grip 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 both ends are wound while being slit.

According to the tenter type stretching device, although there is a merit that a wide film can be easily obtained, in the production of a uniaxially oriented film, the film is oriented in the direction perpendicular to the running direction of the film. Since it is easy to tear along a direction and there are many film breaks in a manufacturing process, the low productivity has been a problem. The rupture at both ends of the film cut after the tenter stretching apparatus is as important as the rupture of the film, and the rupture at both ends of the film has an important influence on the production stability.
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-type stretching device, except for the weight (A) of both ends of the film that is cut in the steps after the tenter-type stretching device and both ends. It exists in the manufacturing method of the uniaxially-oriented polyester film characterized by the relationship with film weight (B) satisfying following formula (1).
0.61 ≦ B / (A + B) ≦ 0.69 (1)

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 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 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, a uniaxially oriented polyester film is produced by transversely stretching an unstretched polyester sheet in a stretching zone in a tenter stretching apparatus. The lateral stretching is performed by gradually increasing the width of the tenter rail.

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

In the present invention, normally, an unstretched sheet is used for transverse stretching. However, the unstretched sheet is longitudinally stretched at a temperature not lower than the glass transition point and not higher than the melting point, and birefringence Δn (refraction between the longitudinal direction and the transverse direction). A longitudinally stretched film having a rate difference of 40 × 10 ⁻³ or less can also be used. A longitudinally stretched film having an Δn exceeding the above range is not preferable because the variation in the orientation angle becomes large.

  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. When 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 is too high when the film comes out of the tenter stretching apparatus, and the flatness of the film is deteriorated.

  In the present invention, the film stretched by the tenter-type stretching apparatus is cut and removed at both ends, and then guided to a winding process and wound into a roll. At this time, if the weight of both ends of the film cut after the tenter type stretching apparatus is A and the weight of the wound film other than both ends is B, the relationship of 0.60 ≦ B / (A + B) ≦ 0.75 is established. It is necessary to satisfy, and it is preferable that the relationship of 0.65 ≦ B / (A + B) ≦ 0.70 may be satisfied. When B / (A + B) is greater than 0.75, the width of both ends cut after the tenter-type stretching apparatus is too narrow or the thickness becomes thin, so that it is easy to break and productivity is increased. Will result in a decline. On the other hand, when B / (A + B) is small, the above-mentioned productivity problem does not occur, but the weight of the cut ends increases, and the ratio of the wound product to the amount of raw material used decreases, resulting in a yield. Will cause a decline. In order to increase the production amount, it is necessary to increase the discharge amount, which is not preferable in terms of production efficiency. For this reason, B / (A + B) needs to be 0.60 or more.

  The ratio between the weight A and the weight B is mainly determined by the ratio of the film thickness seen in the width direction in the film forming process and the position where cutting is performed. The thickness ratio can be adjusted, for example, by adjusting the slit width of the discharge amount portion in the polyester extrusion step, taking-out conditions of the molten sheet, or the like.

  The film of the present invention can be provided with a coating layer for the purpose of improving the adhesion of the surface or 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) Film-forming stability Film-forming stability was evaluated according to the following criteria.
A: The state of both ends of the film cut after the tenter type stretching apparatus is very stable, and the number of breaks at both ends of the film per day is 0. ○: The film is cut after the tenter type stretching apparatus. The state of both ends of the film is stable, and the number of breaks at both ends of the film per day is 1-2. ×: Both ends of the film that are cut after the tenter type stretching device are easily broken. The number of breaks at both ends of the film is 3 or more. (2) Production efficiency Production efficiency was evaluated according to the following criteria.
○: The weight of both ends of the film cut after the tenter type stretching apparatus is not too large and the production efficiency is good. X: The weight of both ends of the film cut after the tenter type stretching apparatus is large and the production efficiency is not good.

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 tenter-type stretching device, preheated in a preheating zone at 90 ° C., stretched in a transverse stretching zone having a stretching temperature of 100 ° C. and a stretching ratio of 4.0, and then heat treated in a heat setting zone at 220 ° C. And it cooled in the 150 degreeC cooling zone, and obtained the 40-micrometer-thick polyester film. B / (A + B) = 0.61, where A is the weight of both ends of the film cut after the tenter type stretching apparatus, and B is the weight of the film other than both ends.

Example 2:
In Example 1, the weight of both ends of the film cut after the tenter type stretching apparatus is A, the weight of the film other than both ends is B, and B / (A + B) = 0.66. A polyester film was obtained.

Example 3:
In Example 1, the weight of both ends of the film cut after the tenter type stretching apparatus is A, the weight of the film other than both ends is B, and B / (A + B) = 0.69. A polyester film was obtained.

Comparative Example 1:
Example 1 is the same as Example 1 except that B / (A + B) = 0.74, where A is the weight of both ends of the film cut after the tenter type stretching apparatus, B is the weight of the film other than both ends. A polyester film was obtained.

Comparative Example 2 :
In Example 1, the weight of both ends of the film cut after the tenter type stretching apparatus is A, the weight of the film other than both ends is B, and B / (A + B) = 0.50. A polyester film was obtained.

Comparative Example 3 :
In Example 1, the weight of both ends of the film cut after the tenter type stretching apparatus is A, the weight of the film other than both ends is B, and B / (A + B) = 0.80. A polyester film was obtained.

  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 that is stretched by a tenter-type stretching device, and the relationship between the weights (A) of both ends of the film that are cut in the steps subsequent to the tenter-type stretching device and the film weights (B) other than both ends. Satisfies the following formula (1): A process for producing a uniaxially oriented polyester film.
0.61 ≦ B / (A + B) ≦ 0.69 (1)