JP4979104B2 - Method for producing polyethylene terephthalate film - Google Patents

Description

  The present invention relates to a method for forming a polyethylene terephthalate film.

  Polyethylene terephthalate films are widely used as base materials for various sheet-like products as typical polyester films due to their excellent mechanical properties, transparency, heat resistance, chemical resistance, and other characteristics.

  As the manufacturing method, the extruded amorphous sheet is stretched in the longitudinal direction with a roll stretching machine, then stretched in the transverse direction with a tenter stretching machine, and further fixed with heat while the film width is fixed in the tenter stretching machine. The so-called sequential biaxial stretching method in which width relaxation is performed after heat fixing, if necessary, is widely employed.

  However, when transverse stretching and heat setting are performed with a tenter stretching machine after longitudinal stretching, the center region of the film shrinks in the longitudinal direction, resulting in a bowing phenomenon, so that the alignment axis of the polyethylene terephthalate molecular chain is in the film end region after heat setting. It has been known that wrinkles and sagging may be generated when heat is applied in a state where tension is applied in the longitudinal direction because the oblique direction is different from the longitudinal direction and the lateral direction.

When processing such end parts, such as providing a functional layer, wrinkles and talmi are generated when heated, which may hinder processing and, in severe cases, cannot be made into products, greatly affecting yield. There is a demand for means for stably obtaining a film with less wrinkles and tarmi.
JP 2004-358742 A

  The present invention has been made in view of the above circumstances, and a problem to be solved thereof is to provide a film forming method that is unlikely to cause wrinkles and tamil when heated.

  As a result of intensive studies, the present inventors have found that the above-mentioned problems can be easily solved by adopting a specific method, and the present invention has been completed.

That is, the gist of the present invention is a method for producing a biaxially stretched polyethylene terephthalate film having a thickness of 50 to 100 μm, and the biaxially stretched film is 1.04 to 1 in the transverse direction at a temperature in the range of 180 to 237 ° C. A method of producing a polyethylene terephthalate film is characterized in that the film is stretched 10 times and subjected to heat fixing without shrinking the rail width of the tenter at 225 to 237 ° C. to be relaxed 5 to 10% in the width direction.

Hereinafter, the invention will be described in detail.
The polyethylene terephthalate referred to in the present invention refers to a polyester obtained by polycondensation of terephthalic acid or a derivative thereof and ethylene glycol. In addition to about 1 mol% of diethylene glycol produced in the polycondensation process, the third component may be copolymerized as long as the total is up to about 5 mol%. Examples of these copolymer components include aromatic dicarboxylic acids such as isophthalic acid and 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid and cyclohexanedicarboxylic acid, 1,3-propanediol, Examples thereof include aliphatic glycols such as 1,4-butanediol, triethylene glycol, 1,4-cyclohexanedimethanol and neopentyl glycol, and oxycarboxylic acids such as p-hydroxybenzoic acid.

  A uniaxially stretched film (longitudinal stretched film) as a pre-stage for applying the transverse stretching method of the present invention can be obtained by a conventional method. An example is disclosed here, but is not limited to the described method.

  First, polyethylene terephthalate is melted by a melt extruder, and the melt sheet extruded from the T die is immediately cooled to below the glass transition temperature by a cooling drum to obtain an amorphous sheet.

  The amorphous sheet is stretched 3 to 5 times at a temperature of 80 to 120 ° C. using a roll stretching machine to obtain a uniaxially stretched film. At this time, longitudinal stretching may be performed in multiple stages, and when multiple stages are used, the stretching temperature in each stage may be different. As a heating method, in addition to contact heating with a heating roll, radiation heating with an infrared heater or the like may be used in combination. When performing in-line coating, the coating is usually performed before and / or after longitudinal stretching.

  The uniaxially stretched film thus obtained is guided to a tenter stretching machine and subjected to transverse stretching. After predetermined transverse stretching, it is subjected to 1.04 to 1.10 times stretching in a temperature range of 180 to 237 ° C. and transverse stretching. It is indispensable to give 5-10% width relaxation without passing through heat fixation later, and a conventional method can be applied about the other elements.

  In addition, the maximum transverse stretch ratio as used in the field of this invention means the value which remove | divided the width | variety at the time of the widest during a film forming process by the tenter stretcher entrance width.

  A typical example of the transverse stretching method combining the ordinary method and the method of the present invention is disclosed. That is, in the tenter stretching machine, first, the longitudinally stretched film is preheated at 90 to 115 ° C., and then stretched at 120 to 160 ° C. corresponding to 93 to 95% of the maximum transverse stretching ratio. Subsequently, transverse stretching corresponding to 96 to 98% of the maximum transverse stretching ratio is performed at 180 to 237 ° C. Immediately after that, a width relaxation corresponding to 5 to 10% of the total film width is usually performed at 225 to 237 ° C., and finally, cooling is performed to a level of 80 to 100 ° C. with a constant width.

  In order to obtain a film that is unlikely to cause wrinkles and tamil when heated in the present invention, the maximum transverse draw ratio must be reached in the stretching process before 120-160 ° C., ie, the orientation-induced thermal crystallization proceeds. In accordance with the progress of orientation-induced thermal crystallization, lateral stretching corresponding to about 93 to 95% of the maximum lateral stretching ratio is performed, then width relaxation is performed before heat fixing, and heat fixing is performed at a constant width. It is necessary not to perform. A considerable portion of the width obtained by transverse stretching at 180 to 237 ° C. is offset by the relaxation of the width. However, in the conventional method, that is, the method in which transverse stretching at 180 to 237 ° C. is not performed, the customer performs various conversions. Talmi cannot be sufficiently suppressed when heated. Although heat fixation with a constant width after width relaxation may be carried out, it is possible to obtain a generally sufficient crystal higher order structure in the process of transverse stretching and width relaxation in accordance with the progress of orientation-induced thermal crystallization. Since the number of zones in the stretching machine is limited, it is not always necessary to perform these zones because it is advantageous in terms of characteristics to be assigned to lateral stretching and width relaxation according to the progress of orientation-induced thermal crystallization. .

  The present invention is suitable as a method for producing polyethylene terephthalate used as various processed substrates, and its industrial value is very high.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example. In the examples and comparative examples, “parts” means “parts by weight” as a solid content. The evaluation method used in the present invention is as follows.

(1) Evaluation of Tarmi A sample film roll having a width of 1000 mm is prepared and passed through a furnace in an atmosphere at 160 ° C. over 15 seconds. At this time, a load of 100 N is applied to the film in the longitudinal direction. While visually checking the fluttering situation of the film passing through the furnace and the sagging condition after passing, the amount of the sagging is evaluated according to JIS C2151 winding property (Method A).

Example 1:
Polyethylene terephthalate having an intrinsic viscosity of 0.65 dl / g and containing 0.1 part of amorphous silica particles having an average particle diameter of 1.5 μm was melted at 290 ° C. with a vented twin screw extruder. The melt sheet extruded from the T die was adhered to a cooling drum maintained at a surface temperature of 40 ° C. by an electrostatic adhesion method to obtain an amorphous sheet. This amorphous sheet was subjected to longitudinal stretching at 90 ° C. and 3.6 times by a roll stretching machine to obtain a uniaxially oriented film. This uniaxially oriented film was guided to a tenter stretching machine, preheated at 110 ° C., and then stretched 4.2 times in a zone having a temperature gradient from 125 ° C. to 145 ° C. in multiple stages. Further, 1.06 times transverse stretching was performed in a zone having a temperature gradient of 180 to 220 ° C. in multiple stages. Immediately thereafter, the rail width was narrowed in a zone of 235 ° C. to give a width relaxation of 6.5%. Thereafter, it was cooled by passing through a zone having a temperature gradient of 150 to 80 ° C. to obtain a polyethylene terephthalate film having a width of 7000 mm and a thickness of 75 μm. When this film was passed through a furnace at 160 ° C., there was no fluttering of the film, and the amount of tarmi after passing was 17 mm.

Comparative Example 1:
The process up to the preheating zone in the tenter stretching machine was the same as in Example 1. After preheating, 4.45 times transverse stretching was performed in a zone with a temperature gradient of 125 to 145 ° C in multiple stages, 7.0% width relaxation was performed at 235 ° C, and a constant width was obtained at 235 ° C. It was kept and heat-set, and then cooled in the same manner as in Example 1 to obtain a polyethylene terephthalate film having a width of 7000 mm and a thickness of 75 μm. When this film was passed through a furnace at 160 ° C., the film fluttering in the furnace was large, and the amount of tarmi after passing was 24 mm.

  The manufacturing method of this invention can be utilized as a manufacturing method of the polyester film useful as a base material of various sheet-like products, for example.

Claims (1)

A method for producing a biaxially stretched polyethylene terephthalate film having a thickness of 50 to 100 μm. The biaxially stretched film is stretched by 1.04 to 1.10 times in the transverse direction at a temperature in the range of 180 to 237 ° C. A method for producing a polyethylene terephthalate film, wherein the film is relaxed by 5 to 10% in the width direction by shrinking the rail width of the tenter at 225 to 237 ° C. without fixing.