JP2821936B2 - Method for producing biaxially stretched polyester film - Google Patents

Description

The present invention relates to a method for producing a biaxially stretched polyester film,
In particular, in the method of stretching in the machine direction (MD) after trimming both ends of the film stretched in the transverse direction (TD),
The present invention relates to a method for stably producing a biaxially oriented polyester film by preventing breakage of a film generated during MD stretching and heat fixing, and further relates to a method for stably producing a biaxially oriented polyester film having a high MD strength. Things.

(Prior art)

Conventionally, as a method of manufacturing a biaxially stretched film, a method of MD stretching after TD stretching is known. In this method, after the TD stretching, the portion gripped by the clip is trimmed to form a film having a constant thickness, and then the MD stretching is usually performed. However, when the end of the film after the above-mentioned trimming is scratched during MD stretching, there is a problem that the film breaks therefrom. In addition, there has been a problem that the clip gripping portion breaks during heat fixing. I mentioned earlier
As a method for preventing breakage during MD stretching, there is known a method in which both ends of a film are further bent after trimming to form a double structure (Japanese Patent Publication No. 51-32669).

[Problems to be solved by the invention]

However, the method of bending both ends as described above not only reduces the yield in the width direction of the film, but also requires the provision of a special device for bending, and has the problem of causing scratches during bending. Was.

An object of the present invention is to solve such problems and to produce a biaxially stretched polyester film with a high yield, and in particular to produce a highly stable MD strength biaxially stretched film. Things.

[Means for solving the problem]

The present invention relates to a method for producing a biaxially stretched polyester film, in which a film is first stretched in the horizontal direction, then trimmed at both ends, and then stretched in the vertical direction. A method for producing a biaxially stretched polyester film, characterized in that the stretching is performed at a position having a thickness greater than the thickness at the center of the stretched film.

Polyesters usable in the present invention include polyesters comprising ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, ethylene 2,6-naphthalenedicarboxylate units, and the like. Particularly preferred is polyethylene terephthalate.

The polyester film may be added with known internal particles or external particles as a lubricant in order to impart appropriate lubricity after the biaxial stretching, or the surface may be lubricious until the stretching is completed. It is needless to say that the coating can be performed as required, for example, by performing a coating for imparting a surface treatment or performing an electric discharge machining process.

Further, in order to improve thermal stability, a relaxation treatment can be performed before and after the heat setting treatment.

The present invention has been completed as a result of researching various methods to improve the disadvantages of the conventional methods. In other words, as a method of completely preventing breakage due to defects at the ends, when trimming both ends after TD stretching, cut a position 10 mm or more from the film end and a thickness greater than the thickness of the central part of the film after TD stretching. It is based on finding out what to do.

[Action]

In the present invention, when trimming both ends, the reason for cutting at a position 10 mm or more from both ends of the film and larger than the thickness of the center part of the film after TD stretching is that if it is less than 10 mm, it is mainly at the clip gripping part during TD stretching. This is because breakage, which is considered to be caused by the generated defects, occurs, and it is difficult to perform stable MD high-magnification stretching. Also, the reason for cutting at a position thicker than the center of the film after TD stretching is that it is difficult for cutting defects to occur in places thicker than the center of the film. This is because no break occurs even in the case of. Generally, the extruded sheet has a large thickness at the end,
The present inventors have found that this portion remains undrawn after TD drawing, and that cutting at this position can significantly improve the MD draw ratio. Also,
Since the thickness of both ends of the film is larger than the thickness of the central portion, it is possible to prevent breakage from the clip gripping portion during heat setting after MD stretching.

According to the method of the present invention, the film formation stability of a thin material is improved,
It is possible to prevent a decrease in productivity due to breakage.
After trimming the film into a uniform thickness
A decrease in film width due to neck-in caused by MD stretching can be suppressed more than in the case of MD stretching, and a portion having a uniform thickness of the film increases, thereby improving the yield.

〔Example〕

 The present invention will be described with reference to examples.

Example 1 A melt-extruded unstretched polyethylene terephthalate film (123 μm in thickness at the center) was first placed on a TD at 95 ° C. for 3.5
It was stretched twice. The thickness of the central part of the obtained film is 35 μm
It was. Next, after performing trimming while changing the cutting position from the end of the film in various ways, the MD stretching ratio was changed, and the ratio at which a 1000 m film was continuously obtained without breaking was measured as the highest stable stretching ratio. The results are shown in Table 1. After MD stretching, fixing was performed at 200 ° C.

Front page of the continuation (72) inventor off the coast Masashi Tsuruga, Fukui Prefecture Toyo-cho, No. 10 No. 24 Toyobo Co., Ltd. Research Institute Tsuruga minute indoor (58) investigated the field (Int.Cl. ^6, DB name) B29C 55 / 02-55/14

Claims (1)

(57) [Claims] 1. A method for producing a biaxially stretched polyester film, comprising first stretching in the horizontal direction, then trimming both ends, and then stretching in the vertical direction, wherein the trimming is performed at least 10 mm from the end of the film. A method for producing a biaxially stretched polyester film, which is performed at a position where the thickness is greater than the thickness of the central portion of the film after the transverse stretching.