JP2013194144A - Easily-stretchable polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easily-stretchable polyester film unable to undergo low-stress stretching at about 80°C but able to undergo low-stress stretching at about 130°C.SOLUTION: An easily-stretchable polyester film includes a polyester having its carboxylic acid unit constituent component comprising 95-85 mol% of terephthalic acid units and 5-15 mol% of isophthalic acid units, and its glycol unit constituent comprising 90-80 moL% of ethylene glycol units and 10-20 mol% of 1,4-cyclohexanedimethanol units. This film has a stress at 5% elongation (F5-value) of 0.5-2.1 MPa at 130°C and a F5-value of 9.5 MPa or greater at 80°C.

Description

  The present invention relates to an easily stretched polyester film. More specifically, the present invention relates to an easily stretched polyester film that cannot be stretched at a low stress at a temperature around 80 ° C. but can be stretched at a temperature near 130 ° C.

  In recent years, a method of widely producing a resin sheet having excellent flatness by casting an optical resin sheet on a polyester film, drying and solidifying it, and then peeling it off from the polyester film has been widely adopted. The peeled resin sheet is provided with various optical values by giving a shaping process or providing a phase difference by 5 to 15% of a stretching process, and has been commercialized. If the optical resin sheet is continuously cast on the polyester film and then stretched by 5 to 15%, and the optical resin sheet having a retardation can be peeled after stretching, the productivity of the retardation resin sheet is improved. Although greatly improved, a polyester film that can be easily stretched as such has not been found.

  That is, in order to further stretch the polyester film generally obtained by the biaxial stretching treatment, high stress is generated. Therefore, even if the stretching temperature is increased to around 130 ° C., it is necessary to apply a high tension, and it is difficult to stretch under the same conditions as the optical resin sheet that can be stretched with low stress.

JP 2008-279705 A

  The present invention has been made in view of the above circumstances, and the problem to be solved is to provide an easily stretched polyester film that cannot be stretched at a low stress at a temperature near 80 ° C. but can be stretched at a temperature near 130 ° C. There is to do. The term “stretching treatment” as used herein means a stretching treatment in a relatively small strain range with an elongation of about 5 to 15%.

  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 film having a specific configuration, and has completed the present invention.

  That is, the gist of the present invention is that 95 to 85 mol% of terephthalic acid units and 5 to 15 mol% of isophthalic acid units are constituents of carboxylic acid units, 90 to 80 mol% of ethylene glycol units and 1,4-cyclohexanedimethano- It is a film made of polyester containing 10 to 20 mol% of a glycol unit as a constituent component of glycol units, and the 5% elongation stress (F5 value) at 130 ° C. of the film is in the range of 0.5 to 2.1 MPa. And it exists in the easily stretched polyester film characterized by F5 value in 80 degreeC being 9.5 Mpa or more.

  According to the present invention, it is possible to industrially provide a polyester film that is not easily stretched at a low temperature of 80 ° C. or less, but can be stretched with a remarkably low stress at a processing temperature near 130 ° C. Such a film can be stretched before the peeling step in a production method in which an optical resin sheet is cast-molded, dried and solidified, and then peeled off from the polyester film, and the optical resin sheet has high productivity. It is useful for the purpose of imparting a phase difference to the surface, and its industrial value is very large.

  The polyester used as the raw material for the easily stretched polyester film of the present invention is a polyester capable of forming an oriented structure by stretching. The constituent component is required that the carboxylic acid unit is composed of 95 to 85 mol% of terephthalic acid units and 5 to 15 mol% of isophthalic acid units. In addition, for example, dicarboxylic acid units such as orthophthalic acid, 2,7-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,2-biphenyldicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, etc. You may contain.

  The ratio of preferred isophthalic acid units is 6 to 14%, more preferably 7 to 13 mol%. If the ratio of isophthalic acid units is less than 5 mol%, the F5 value in a 130 ° C. atmosphere tends not to be sufficiently lowered. On the other hand, if the ratio of isophthalic acid units exceeds 15 mol%, the film tends to be too soft and easily broken in the stretching process.

  Although the main glycol unit is composed of an ethylene glycol unit as the other constituent component, it contains a considerable amount of 1,4-cyclohexanedimethanol unit in order to express a particularly easy stretchability in a high temperature region around 130 ° C. It will be necessary. The ratio of both units needs to be in the range of 90 to 80 mol% of ethylene glycol units and 10 to 20 mol% of 1,4-cyclohexanedimethanol units. Further, it contains other glycol units such as propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol in a small proportion. It may be.

  The easily stretched polyester film of the present invention needs to have a stress at 5% elongation (F5 value) in an atmosphere of 130 ° C. within the range of 0.5 to 2.1 MPa, preferably 0.6 to 2.2. It is 0 MPa, more preferably in the range of 0.8 to 1.5 MPa. When the F5 value at 130 ° C. exceeds 2.1 MPa, when used as a cast film of an optical resin sheet, high tension is required for the stretching process in the process, and the optical resin sheet is not uniformly stretched. This tends to cause problems. On the other hand, if the F5 value at 130 ° C. is less than 0.5 MPa, the same vertical wrinkles are generated in the stretching process, which tends to be inferior in practical aptitude.

  On the other hand, the easily stretched polyester film of the present invention needs to have an F5 value in an atmosphere of 80 ° C. of 9.5 MPa or more, and preferably 11 MPa or more. If the F5 value at 80 ° C. is less than 9.5 MPa, the film tends to be stretched from a relatively low temperature range, so that there is a tendency for problems such as difficulty in stretching integrally with the optical resin sheet. .

  It is preferable to add particles to the easily stretched polyester film of the present invention for the purpose of improving the slipperiness. For example, known inert particles such as kaolin, clay, various calcium carbonates, silicon oxide, aluminum oxide, titanium oxide, and carbon black can be used. These particles preferably have a content of 0.002 to 2% by weight with respect to the layer constituting the surface in the film, and preferably have an average particle size in the range of 0.001 to 5 μm.

Moreover, various additives can be contained in the range which does not impair the objective of this invention. If necessary, components such as conventionally known antioxidants, heat stabilizers, lubricants, fluorescent brighteners, dyes, ultraviolet absorbers, near infrared absorbers and the like can be contained.
The thickness of the easily stretched polyester film of the present invention is not particularly limited, but as a film used for resin casting, it preferably has an appropriate waist strength, usually in the range of 12 to 300 μm, preferably It is in the range of 25 to 200 μm, more preferably 38 to 150 μm.

  Here, although an example at the time of using biaxial stretching is demonstrated in detail, unless the summary of this invention is exceeded, this invention is not limited to the following examples.

First, the raw material which comprises a polyester film is supplied to an extruder, is extruded after melt-kneading. Next, the molten sheet extruded from the die is rapidly cooled and solidified on the rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature, thereby obtaining a substantially amorphous unoriented sheet. In this case, in order to improve the planar uniformity and cooling effect of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum, and in the present invention, an electrostatic application adhesion method is preferably employed. Next, the obtained sheet is stretched in a biaxial direction to form a film. First, the unstretched sheet is stretched under the conditions of a stretching temperature of usually 65 to 130 ° C., preferably 70 to 110 ° C., usually 2.0 to 6.0 times, preferably 2.5 to 5.0 times. Stretch in one direction (longitudinal direction). A roll and tenter type stretching machine can be used for such stretching. Next, at a stretching temperature of usually 80 to 150 ° C., preferably 90 to 130 ° C., usually orthogonal to the first stage under conditions of a stretching ratio of 2.0 to 6.0 times, preferably 2.5 to 5.0 times. The film is stretched in the direction (transverse direction) to obtain a biaxially oriented film. For such stretching, a tenter type stretching machine can be used. A method of performing the above-mentioned unidirectional stretching in two or more stages can also be adopted, but in this case as well, it is preferable that the final stretching ratio falls within the above-described range.
Next, heat treatment is performed in the tenter. In this step, it is also an object to lower the orientation structure of the polyester film produced by biaxial stretching. Therefore, the heat treatment temperature is preferably a temperature close to the melting point of the polyester film. In particular, a film containing 1,4-cyclohexanedimethanol units and isophthalic acid units in a considerable ratio as in the present invention shows a decrease in melting point, so that the heat treatment is preferably carried out at a relatively low temperature. Usually, it is carried out at 140 to 200 ° C., preferably 150 to 190 ° C. for 1 second to 5 minutes. In this heat treatment step, it is effective to reduce the stretching stress at 130 ° C. by relaxing 1-25% in the transverse direction between the zone of the highest temperature of the heat treatment and the cooling zone immediately before the heat treatment outlet ( Orientation relaxation). A preferable relaxation rate is in the range of 10 to 20%.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples, unless the summary is exceeded. In addition, the various physical property in this invention, its measuring method, and a definition are as follows.

(1) Average particle diameter of added particles (μm)
Using a centrifugal sedimentation type particle size distribution analyzer SA-CP3 manufactured by Shimadzu Corporation, the particle size was measured by a sedimentation method based on Stokes' resistance law. The average particle diameter was determined by using a value of 50% of integration (volume basis) in the equivalent spherical distribution of particles obtained by measurement.

(2) Intrinsic viscosity IV (dl / g)
A mixed solvent of phenol / tetrachloroethane: 50/50 (weight ratio) was added to 1 g of polyester at a ratio of 100 ml, and the mixture was measured at 30 ° C.

(3) Stress at 5% elongation in a heated atmosphere (MPa)
About the obtained film, the sample of 150 mm of longitudinal directions x width direction 15 mm was extract | collected, respectively. Next, using a tensile tester (trade name “Autograph AG-I (1 kN)” manufactured by Shimadzu Corporation), the sample is sandwiched and fixed on a chuck set at an interval of 50 mm, and then stabilized in a predetermined heating atmosphere. The load was measured with a load cell attached at a speed of 200 mm / min. Then, the load at 5% elongation was read, and the stress (MPa) was calculated by dividing by the sample cross-sectional area before pulling.

(4) Stretch processability test A 250 mm wide film was passed to a roll-to-roll stretching apparatus, the film actual temperature in the stretching section was set to 130 ° C., a tension of 1.5 MPa was applied, and fine stretching was performed in the flow direction. It was evaluated from the viewpoint of whether a film having a uniform elongation rate of 10% could be obtained and whether there were no significant vertical wrinkles.

Stretching evaluation ◎: A film having a uniform elongation of 10% was obtained. ○: Uniform stretching was possible in the range of 5 to 9%. ×: Elongation did not reach 5%, and the desired stretching was performed. Processing was not possible / wrinkle evaluation ○: Wrinkle was not generated after stretching processing △: Minor wrinkles were observed after stretching processing, but it was within the usable range ×: Wrinkles after stretching processing It was remarkable and unsuitable for practical use

Example 1:
Polyester raw material A (TPA as carboxylic acid unit: 91 mol% + IPA: 9 mol%, EG as glycol unit: 84 mol% + CHDM: 16 mol%, IV = 0.73 dl / g) having an average particle size of 4.2 μm A mixture containing 0.1% by weight of amorphous silica was supplied to an extruder, melted at 280 ° C., extruded onto a casting drum, and rapidly solidified by applying an electrostatic application method to obtain an unstretched sheet. . The obtained sheet was stretched 3.6 times in the machine direction at 78 ° C. in the longitudinal direction, further stretched 3.8 times in the transverse direction at 85 ° C., heated stepwise and then heat treated at 181 ° C. for 3 seconds, Heat treatment relaxation (to narrow the tenter rail width) by 18% in the direction. Finally, a film having a thickness of 75 μm was obtained.

Example 2:
A film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that the carboxylic acid unit of the raw material A was changed to TPA: 93 mol% + IPA: 7 mol%.

Example 3:
A film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that the carboxylic acid unit of the raw material A was changed to TPA: 89 mol% + IPA: 11 mol%.

Comparative Example 1:
A film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that the carboxylic acid unit of the raw material A was changed to TPA: 100 mol%.

Comparative Example 2:
A film having a thickness of 75 μm was obtained in the same manner as in Example 1 except that the carboxylic acid unit of the raw material A was changed to TPA: 100 mol% and the glycol unit was changed to EG: 74 mol% + CHDM: 26 mol%.

Comparative Example 3:
A film having a thickness of 75 μm was obtained in the same manner as in Example 1, except that the carboxylic acid unit of raw material A was TPA: 100 mol%, the glycol unit was EG: 100 mol%, and the heat treatment temperature was changed to 235 ° C. It was.

  Table 1 below shows the conditions used for forming each film and the evaluation results of the polyester film. In addition, about the polyester structural component in following Table 1, TPA means terephthalic acid, IPA means isophthalic acid, EG means ethylene glycol, and CHDM means 1,4-cyclohexanedimethanol.

The film of the present invention can be suitably used as a process film for casting, drying and solidifying, finely stretching (retarding) and peeling an optical resin sheet.

Claims (1)

The terephthalic acid unit 95 to 85 mol% and the isophthalic acid unit 5 to 15 mol% are used as the carboxylic acid unit constituents, the ethylene glycol unit 90 to 80 mol% and the 1,4-cyclohexanedimethanol unit 10 to 20 mol%. It is a film comprising a polyester as a glycol unit constituent, and the 5% elongation stress (F5 value) at 130 ° C. of the film is in the range of 0.5 to 2.1 MPa, and the F5 value at 80 ° C. Is an easily stretched polyester film characterized by being 9.5 MPa or more.