JP2010082953A - Successively biaxially oriented polyester film and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film with a low degree of undermining of laminate breaking tenacity at the end part, achieved through inhibiting cleavage, and a method of manufacturing the same. <P>SOLUTION: A successively biaxially oriented polyester film in which the laminate breaking tenacity T10 in a position 10 cm distant widthwise from a clip grab mark of the film stretched transversely by a tenter, satisfies an expression T10>0.6N/cm. Further, the film can be stretched longitudinally 4-5 times as much at a draft temperature of 125-135°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polyester film. In particular, the present invention relates to a polyester film with little decrease in laminate strength at the edge.

  For packaging applications such as foods, a biaxially stretched polyester film is used after being laminated with a sealant film or the like because of its excellent heat resistance, mechanical strength, dimensional stability, printability and the like.

  However, a polyester film that has been biaxially stretched and highly oriented and crystallized often cleaves on the surface layer, so that it tends to cause delamination even when laminated, and has become a fatal defect in packaging applications. There was a problem that the vicinity of the laterally stretched clip grip was particularly easy to cleave. This is presumably because the clip is cooled to prevent cutting, so that the heat setting is low in the vicinity of the clip gripping trace, and the orientation is hardly relaxed.

  In order to prevent cleavage, Patent Document 1 discloses a polyester film having a balanced and appropriate plane orientation coefficient as a biaxially oriented polyester film for packaging.

  However, since the draw ratio is appropriately reduced so as not to be over-oriented, and the longitudinal draw ratio and the transverse draw ratio are made the same in order to obtain a balanced orientation, the longitudinal draw ratio is at most 3.8 times. It was.

In recent years, demand for cost reduction has been increasing in order to absorb the rise in raw material prices, and if the longitudinal draw ratio is lowered, the production speed becomes slow, which is disadvantageous in cost. Moreover, it did not respond to the problem that the end portion was easily cleaved.
JP 2007-118476 A

  The present invention is intended to solve the above-mentioned problems of the prior art, and to provide a polyester film that suppresses cleavage and has a small decrease in laminate strength at the end and a method for producing the same. .

As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by performing longitudinal stretching under specific conditions, and have reached the present invention.
That is, the gist of the present invention is as follows.
(1) A sequentially biaxially stretched polyester film in which a laminate strength T10 at a position of 10 cm in the width direction from a clip grip mark of a film stretched laterally by a tenter satisfies the following formula.
T10> 0.6 N / cm
(2) The sequential biaxially stretched polyester film according to claim 1, wherein the laminate strength T100 at a position of 100 cm in the width direction from the clip grip trace satisfies the following formula.
T100> 1.0 N / cm
(3) The method for producing a successively biaxially stretched polyester film according to claim 1 or 2, wherein the film is longitudinally stretched 4 to 5 times at a stretching temperature of 125 to 135 ° C.
(4) The method for producing a successively biaxially stretched polyester film according to claim 3, wherein the film is stretched transversely at a stretching temperature of 80 to 140 ° C and 3.5 to 6.0 times after the longitudinal stretching.

  According to the present invention, since the longitudinal stretching is performed at a temperature of 125 to 135 ° C., the degree of orientation does not increase so much even if the stretching ratio is increased, and the film is less cleaved. Therefore, it can be used as a wider range of products, and a higher longitudinal draw ratio can be adopted, so that a high cost reduction effect can be obtained.

  In the present invention, the polyester film is preferably a film mainly composed of the following polyester resin. Examples of the polyester resin include polyalkylene terephthalates such as polyethylene terephthalate, polybutylene terephthalate, and polypropylene terephthalate, polyalkylene-2,6-naphthalates such as polyethylene-2,6-naphthalate, polybutylene-2,6-naphthalate, and polylactic acid. It is done. These are not limited to homopolymers, and may be copolymers obtained by substituting dicarboxylic acid and / or diol components, which are constituent components of polyester, with other dicarboxylic acids and / or diols. Furthermore, the polyester resin used in the present invention may be a mixture of other polyester resins as long as the effects of the present invention are not impaired.

  From the viewpoint of excellent mechanical characteristics and thermal characteristics, the polyester film is preferably composed mainly of polyethylene terephthalate.

  Furthermore, various additives and modifiers that are usually blended as necessary, for example, lubricants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, antistatic agents, tackifiers, seals A property improver, an antifogging agent, a crystal nucleating agent, a release agent, a plasticizer, a crosslinking agent, a flame retardant, and a colorant (pigment, dye, etc.) may be added.

  The sequential biaxially stretched polyester film of the present invention is produced by longitudinally stretching an unstretched film and then laterally stretching.

  In the present invention, the film forming method is not particularly limited, but an electrostatic application method capable of high speed film formation with a high cooling rate is preferable.

  In the present invention, it is preferable to perform longitudinal stretching 4 to 5 times at a stretching temperature of 125 to 135 ° C. The stretching temperature is particularly preferably 127 to 130 ° C. The draw ratio is particularly preferably divided into 2 to 3 times and 1.5 to 2.5 times, and the total is 4 to 5 times. When the stretching temperature is less than 125 ° C., cleavage is likely to occur as a result of an increase in the degree of orientation in the longitudinal direction. When the stretching temperature exceeds 135 ° C., a peeling failure from the longitudinal stretching roll is likely to occur, resulting in stretch spots. When the draw ratio is less than 4, the production speed is not increased, which is disadvantageous in cost. When the draw ratio exceeds 5 times, cleavage is likely to occur as a result of an increase in longitudinal orientation. The stretching in two stages is particularly preferable because it makes it easy to suppress the longitudinal orientation.

  Next, transverse stretching is performed. It is preferable that both ends of the longitudinally stretched film are gripped by a clip and stretched at a temperature of 80 to 140 ° C. at a magnification of 3.5 to 6.0 times. When the stretching temperature is less than 80 ° C., stretching breakage may occur. If the stretching temperature exceeds 140 ° C, the tensile strength at break may be lowered. When the draw ratio is less than 3.5 times, the tensile strength at break may be lowered. When the draw ratio exceeds 6.0 times, cleavage may be likely to occur as a result of the increase in lateral orientation, or stretch breakage may occur.

  The temperature of the clip immediately before gripping the film is preferably 50 to 100 ° C. In order to keep the temperature of the clip in this range, it can be cooled with cold air. If the temperature of the clip is less than 50 ° C. or exceeds 100 ° C., stretch cutting tends to occur. If it is less than 50 ° C., even when stretch cutting does not occur, the film temperature in the vicinity of the clip does not rise, and the laminate strength at the end described below becomes small. The clip temperature can be measured using an infrared radiation thermometer or the like.

  The biaxially stretched film is subsequently subjected to a heat treatment, and the maximum temperature of the heat treatment is preferably 240 to 260 ° C. When the heat treatment temperature is lower than 240 ° C., the orientation of the film surface is not relaxed easily and cleavage is likely to occur, and the shrinkage rate of the film increases. If it is higher than 260 ° C., the film may melt, and the tensile strength at break will be low.

  Subsequently, it is preferable to perform a relaxation treatment of 2 to 6% in the width direction. The relaxation treatment temperature is preferably 200 to 240 ° C.

  The polyester film of the present invention can be subjected to an easy-adhesion coat or a surface treatment such as corona treatment in order to increase the laminate strength.

In the polyester film of the present invention, the laminate strength (T10) measured at a position 10 cm in the width direction from a portion (hereinafter referred to as a grip mark) gripped by a clip when transversely stretched by a tenter is represented by the following formula:
T10> 0.6 N / cm
It is necessary to satisfy the relationship. Since the area outside 10 cm from the grip mark is usually trimmed and recycled as a stretched ear, the position 10 cm from the grip mark is positioned as the end of the product. If the cleavage occurs, the laminate strength becomes 0.6 N / cm or less, so T10 needs to be larger than 0.6 N / cm, and preferably larger than 1.0 N / cm.

Further, in the polyester film of the present invention, the laminate strength (T100) measured at a position of 100 cm in the width direction from the grip mark is represented by the following formula:
T100> 1.0 N / cm
Is preferably satisfied. The center from 100 cm from the grip mark is a position where the influence of the grip mark is considered to be eliminated. Considering the influence of the distance from the grip mark on the opposite side, the film width is preferably 200 cm or more, and more preferably 300 cm or more in terms of productivity. More preferably, T100 is greater than 1.5 N / cm.

  In addition, if the laminate strength exceeds 1.0 N / cm, it can be used without any problem for ordinary packaging applications.

  Moreover, as a packaging use, it is preferable that at least one of MD and TD is 200 MPa or more as for the tensile fracture strength of a polyester film.

  Although the thickness of the polyester film of this invention is not specifically limited, If it is the range of 9-50 micrometers, it is preferable.

  The laminate strength and tensile breaking strength were measured by the following methods.

(Strong laminate)
The laminate strength is measured by taking a test piece of MD100 mm × TD15 mm from the laminate film and using a tensile tester (AGS-100B type, manufactured by Shimadzu Corp.) in an atmosphere of 23 ° C. and 50% RH by the T peel method. The film interface was peeled from the end of the test piece under the condition of a tensile speed of 300 mm / min, and the strength was measured.

(Tensile strength at break)
The measurement was performed according to the method described in JIS K-7127. Measurement was carried out at 10 cm from the grip mark and at the center position in the width direction of the film, and an average value was adopted.

Example 1
After melting polyethylene terephthalate with an intrinsic viscosity of 0.69 dl / g with an extruder, it is extruded from a T-die and brought into close contact with a cooling drum whose surface temperature is adjusted to 20 ° C. by an electrostatic application method. An unstretched film of 280 μm was obtained. Next, after preheating with a preheating roll group adjusted to 90 ° C., the stretching speed was adjusted to 2.3 times by changing the peripheral speed between the drawing rolls adjusted to 130 ° C., and further adjusted to 130 ° C. A longitudinally stretched film having a thickness of 50 μm was obtained by longitudinally stretching 2.0 times while changing the peripheral speed. Subsequently, the longitudinally stretched film is guided to a tenter type stretching machine, and is stretched transversely at a preheating temperature of 90 ° C. and a stretching temperature of 120 ° C. by 5 times, followed by heat treatment at 255 ° C., and a relaxation treatment of 3% in the transverse direction at 200 ° C. Also went. Trimming was performed at a position of 10 cm from the grip mark, and after corona treatment, winding was performed to obtain a biaxially stretched polyester film having a width of 480 cm and a thickness of 12 μm.

The wound film was slit with a width of 900 mm from the end to obtain an original film for lamination. A dry laminate adhesive (Dick Dry LX401 / SP60, manufactured by Dainippon Ink & Chemicals, Inc.) is applied to the corona-treated surface so that the coating amount is 3.5 g / m ^2, and the adhesive-coated surface and the corona-treated surface of the sealant film (unfinished) A stretched low-density polyethylene film; manufactured by Tosero Co., Ltd., TUX-FCS, 50 μm) was bonded with a nip roll (nip condition: 80 ° C.) and subjected to adhesive recommended aging to obtain a laminate film. As for both ends of the obtained 900 mm wide laminate film, one end is a portion 10 cm from the grip mark, and the other end is a portion 100 cm from the grip mark. The laminate strength was measured at the positions at both ends, and T10 and T100 were obtained.

Examples 2-6, Comparative Examples 1-3
A biaxially stretched polyester film was produced in the same manner as in Example 1 except that the conditions were changed as shown in Table 1. In Example 6, longitudinal stretching was performed in one stage, and the stretching ratio at this time was 4.6 times.

  As can be seen from Table 1, in each Example, a film having T10 of 0.6 N / cm or more was obtained.

  In Examples 4 and 5, since the transverse stretching temperature was high or the transverse stretching ratio was low, the tensile rupture strength in the TD direction was low, but the film physical properties were in a range where there was no practical problem.

  As can be seen from the comparison between Example 1 and Example 6, the laminate strength was improved when the longitudinal stretching was performed in two stages.

  Since Comparative Examples 1 and 3 were highly oriented, cleavage occurred and the laminate strength was low.

  Since Comparative Example 2 became stretch spots due to poor peeling from the longitudinal stretching roll, the laminate strength and tensile breaking strength were not evaluated.

Claims (4)

A sequentially biaxially stretched polyester film in which a laminate strength T10 at a position 10 cm in the width direction from a clip grip mark of a film stretched laterally by a tenter satisfies the following formula.
T10> 0.6 N / cm Furthermore, the successive biaxially stretched polyester film according to claim 1, wherein the laminate strength T100 at a position of 100 cm in the width direction from the clip grip trace satisfies the following formula.
T100> 1.0 N / cm The method for producing a successively biaxially stretched polyester film according to claim 1 or 2, wherein the film is longitudinally stretched 4 to 5 times at a stretching temperature of 125 to 135 ° C. 4. The method for producing a successively biaxially stretched polyester film according to claim 3, wherein after the longitudinal stretching, the film is laterally stretched 3.5 to 6.0 times at a stretching temperature of 80 to 140 ° C. 5.