JP4935087B2 - Method for producing biaxially stretched polyester film for shining packaging - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for producing a biaxially stretched polyester film for shining packaging, and more particularly, to a method for producing a biaxially stretched polyester film having excellent film formability and thickness uniformity and having excellent velvet suitability.

  Cellophane, which has good transparency, has been widely used as a film having excellent suitability. However, since cellophane has hygroscopicity, its characteristics fluctuate depending on the season, it is difficult to always supply a certain quality, and poor workability due to uneven thickness has been a drawback. . On the other hand, the polyethylene terephthalate film has excellent properties such as toughness, heat resistance, water resistance, and transparency, but has a disadvantage that it cannot be used for wrapping due to its poor heelability.

As a method for eliminating such drawbacks, the copolyester was biaxially stretched and then subjected to tension heat treatment at a relatively high temperature (140 to 235 ° C., preferably 150 to 230 ° C.) to reduce the degree of orientation (unstretched film). the average refractive index of the N _0, when the average refractive index of biaxially oriented film was N _0, was satisfied _{0.003 ≦ N 1 -N 0 ≦ 0.021} ) polyester film is disclosed. (For example, refer to Patent Document 1).

  However, although the polyester film is excellent in suitability, since the tension heat treatment is performed at a relatively high temperature, the thickness uniformity is not good, and as a result, wrinkles are likely to occur in processing steps such as printing and vapor deposition. There were drawbacks.

  As a method for eliminating such drawbacks, a polyester film having a crystallinity of 40% or less obtained by biaxially stretching polyethylene terephthalate is disclosed. (For example, refer to Patent Document 2).

However, the polyester film is excellent in the suitability and thickness uniformity, but it tends to generate tarmi after biaxial stretching, and it is cut when both ends of the film are cut after biaxial stretching or for finishing into a product roll. At the same time, there was a drawback that the product roll was easily broken and wrinkles due to the tarmi were likely to occur on the product roll, which was not yet satisfied.
Japanese Patent No. 2505474 JP 2005-513225 A

  The object of the present invention is to solve the problems of the prior art. That is, the present invention provides a method for producing a biaxially stretched polyester film having excellent film formability and thickness uniformity, excellent appearance when formed into a product roll, and further having excellent fining aptitude.

This onset Ming after melt-extruding the polyester, performing a first stage stretching in the first lateral direction a solidified sheet with a cooling roll, and then was heat-treated fixed length under the width direction, the second-stage stretching in the longitudinal direction a method of manufacturing a twist packaging biaxially oriented polyester film to do so, a glass transition temperature - glass transition temperature heat treatment of the polyester between the stretching of stretching and longitudinal direction of the second-stage transverse direction of the first stage Hinel wrapping, which is performed at a temperature of + 20 ° C. for 0.5 to 3 seconds , and further heat-fixed at a temperature of 80 ° C. or higher after biaxial stretching so that the maximum height of the film surface is 5 to 7 μm. It is a manufacturing method of the biaxially stretched polyester film.

The method for producing a polyester film of the present invention is excellent in film formability and uniformity of thickness, has an excellent appearance when formed into a product roll, and has an excellent shininess aptitude. It can be said that this is a method for producing a polyester film.

  In this invention, the polyester which comprises a film is preferable from the point which ensures the heat resistance, water resistance, etc. of the film obtained by making an ethylene terephthalate component into a main structural component.

  In this invention, the polyester which comprises a film can contain another copolymerization component in the range which does not inhibit the objective. Among other copolymerizable components that can be used, aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, diphenylsulfone dicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, decane Aliphatic dicarboxylic acids such as dicarboxylic acid, maleic acid, fumaric acid and dimer acid, oxycarboxylic acids such as p-oxybenzoic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be used.

  As glycol components, aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol and neopentylglycol, alicyclic glycols such as cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, ethylene oxide of bisphenol S Aromatic glycols such as adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can be used. In addition, a small amount of a compound containing an amide bond, a urethane bond, an ether bond, a carbonate bond, or the like may be included.

  In the present invention, the first-stage stretching is performed in the transverse direction, followed by constant length heat treatment in the width direction for 0.5 to 3 seconds at a temperature of the glass transition temperature of the polyester to the glass transition temperature + 20 ° C., and then in the longitudinal direction. It is necessary to perform the second stage stretching.

  When no heat treatment is performed between the first-stage transverse stretching and the second-stage longitudinal stretching, or when heat treatment is performed at a temperature lower than the glass transition temperature of the polyester, or the heat treatment time is 0.5 seconds. If it is less than 1, the maximum height of the obtained polyester film is less than 5 μm, which is unfavorable because the aptitude is poor. Conversely, when heat treatment is performed at a temperature exceeding the glass transition temperature + 20 ° C. and / or a time exceeding 3 seconds, the maximum height of the obtained polyester film exceeds 7 μm, and the suitability is good. This is not preferable because the film tends to break when the second stage stretching is performed.

  In the present invention, as the first stage stretching, the film is stretched in the transverse direction by 3.0 to 4.5 times at a temperature equal to or higher than the glass transition temperature of the polyester, and as the second stage stretching at a temperature equal to or higher than the glass transition temperature of the polyester. It is preferable to stretch in the longitudinal direction from 0 to 4.5 times.

  When the first-stage draw ratio is less than 3.0 and / or when the second-stage draw ratio is less than 2.0, the resulting polyester film has poor thickness uniformity or flatness, and a slick wrapping machine. This is not preferable because the running property of the film is poor. Conversely, when the first stage stretch ratio exceeds 4.5 times and / or when the second stage stretch ratio exceeds 4.5 times, wrinkles are generated in the second stage stretching, and third This is not preferable because it often breaks during stage stretching.

  In the present invention, after the second stage of longitudinal stretching, re-lateral stretching of 1.05 to 1.4 times may be performed as the third stage of stretching at a temperature equal to or higher than the glass transition temperature of the polyester.

  In the present invention, after the second stage of longitudinal stretching or after the third stage of re-lateral stretching, a heat setting treatment is performed with a known width direction as a constant length, and the heat setting temperature is 80 ° C. or more. preferable.

  When the heat setting treatment temperature is less than 80 ° C., the obtained polyester film is excellent in suitability, but it breaks when it is cut at both ends of the film after biaxial stretching or when it is cut to finish into a product roll. This is not preferable because it is easy to cause wrinkles due to the above-mentioned tarmi on the product roll.

  In the present invention, the intrinsic viscosity of the polyester is preferably 0.5 dl / g or more. When the intrinsic viscosity is less than 0.5 dl / g, breakage tends to occur when forming a polyester film, which is not preferable.

  In this invention, it is preferable that the thickness of a polyester film is 9-25 micrometers. When the thickness of the polyester film is less than 9 μm, when the obtained film is used for the wrapping packaging, it is not preferable because the film feels poor. On the other hand, when the thickness exceeds 25 μm, the obtained film is inferior in the swellability, which is not preferable.

  Hereinafter, the present invention will be described based on examples. First, evaluation methods used in Examples and Comparative Examples will be described.

(1) Intrinsic viscosity of polyester 0.1 g of polyester was dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane (3/2 by volume) and measured at 30 ° C. using an Ostwald viscometer.

(2) Glass transition temperature of polyester After heating and melting polyester at 300 ° C. for 5 minutes, 10 mg of sample obtained by quenching with liquid nitrogen was used, and 10 ° C. using a differential scanning calorimeter (DSC) in a nitrogen stream. An exothermic / endothermic curve (DSC curve) was measured at a rate of temperature rise per minute, and the glass transition temperature was determined by the tangential method.

(3) a three-dimensional non-contact surface shape measuring system up to the height of three polyester film pieces Corporation Ryoka Systems of the polyester film (KP-MI monochrome CCD camera, MICROSCOPE MM-40 camera, universal lighting device EPI- The measurement was carried out under the following optical conditions and measurement conditions . Average of three Rt (difference between the highest and lowest points from the center line) was maximum height ri.

(Optical conditions)
Wavelength: 5600 mm, objective lens: 10 times, zoom lens: 0.5 times, relay lens: unused, CCD camera: 2/3 inch.

(Measurement condition)
Mode: Wave 560M, repetitive measurement cycle: 1, measurement area: FieldX: 480, Field Y: 480, sampling interval: 1.

(3) Uniformity of polyester film thickness (TV (%))
A piece of film having a width of 4 cm and a length of 3 m is cut out in the longitudinal direction from the center of the polyester film, and a sample obtained by dividing the film piece into three pieces having a length of 1 m is used as a measurement sample. The measurement sample is measured under the following conditions using a continuous thickness meter (micrometer: K306C, recorder: K310C) manufactured by Anritsu Electric Co., Ltd. The (maximum value−minimum value) in the measurement sample 1m is obtained, and the average value of three (ΔT average) is calculated. Next, the average thickness (T average: three film pieces after continuous thickness measurement were stacked and measured at 18 points using a dial gauge at a 5 cm pitch on the basis of 5 cm from one end. The value obtained by dividing the total value by 54) is calculated. Next, TV = (ΔT average / T average) × 100 (%) is calculated, and TV is evaluated as practical if 8% or less.

[Conditions for continuous thickness measurement]
Film feed rate: 1.5 m / min Micrometer scale: ± 5 μm
Recorder high cut: 5Hz
Recorder scale: ± 2 μm
Recorder chart speed: 2.5 mm / sec Recorder measurement range: × 1

(4) Hinel suitability A 10 cm × 10 cm sample piece is cut out from the polyester film and wound in the longitudinal direction so as to protrude 5 cm from a round bar having a diameter of 2 cm. Next, the protruding portion is twisted 360 °, and the angle returned from 360 ° is measured (n = 100). The average value of these is obtained, and ○ is evaluated as practical.
○: Twist return angle is 75 ° or less ×: Twist return angle is more than 75 °

Table 1 shows the polyester raw materials, film forming conditions, maximum film height (average Rt), thickness uniformity, and suitability used in Examples and Comparative Examples.
(1) A: Polyethylene terephthalate (Intrinsic viscosity: 0.62 dl / g, glass transition temperature: 74 ° C., average particle size: 1.3 ppm of agglomerated silica containing 1000 ppm)
(2) B: Polyethylene terephthalate / isophthalate (ethylene isophthalate repeating unit 10 mol%, intrinsic viscosity: 0.62 dl / g, glass transition temperature: 72 ° C., average particle size: 1.3 μm of agglomerated silica blended in 1000 ppm )

[Example 1]
Polyester A as a polyester raw material is dried under reduced pressure (1.3 hPa) at 120 ° C. for 24 hours, melted at 280 ° C. using a single screw extruder, and then cooled from a 45 cm wide T-die (peripheral speed 50 m / min). ) Cast upward (applying a voltage of 7.2 kV from a tungsten wire electrode with a diameter of 30 μm placed so as to face the circumferential surface of the cooling roll, and applying a 0.2 mA current to make it electrostatically adhere) A stretched sheet was obtained. The unstretched sheet was stretched 3.7 times in the transverse direction at a preheating temperature of 95 ° C. and a stretching temperature of 92 ° C. (first stage stretching), and heat treated at 78 ° C. for 1 second, preheating temperature of 80 ° C., stretching temperature of 105 ° C. The film was stretched 4.2 times in the machine direction at 2 ° C. (second-stage stretching), and further re-stretched 1.05 times at 100 ° C. (third-stage stretching). A polyester film having a thickness of 18 μm was obtained.
As can be seen from Table 1, the method of this example has a maximum height of 5.2 μm, and can be said to be a method for producing a biaxially stretched polyester film excellent in fining suitability.

[Example 2]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was changed to 82 ° C. after the first stage stretching.
As can be seen from Table 1, the method of this example has a maximum height of 6.2 μm, and can be said to be an excellent method for producing a biaxially stretched polyester film for velvet packaging.

[Example 3]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the first stage draw ratio was 3.5 times and the third stage draw ratio was 1.2 times.
As can be seen from Table 1, the method of this example has a maximum height of 5.7 μm, and can be said to be a method for producing a biaxially stretched polyester film having excellent twistability.

[Example 4]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that a raw material obtained by mixing 80% by weight of A and 20% by weight of B was used as the polyester raw material.
As can be seen from Table 1, the method of this example has a maximum height of 5.1 μm, and can be said to be a method for producing a biaxially stretched polyester film excellent in fining suitability.

[Comparative Example 1]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the heat treatment temperature was changed to 70 ° C. after the first stage stretching.
As can be seen from Table 1, this method is not preferable as a method for producing a biaxially stretched polyester film for hinelli wrapping because the maximum height is 4.3 μm and the shininess suitability is poor.

[Comparative Example 2]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the heat treatment was not performed after the first stage stretching.
As can be seen from Table 1, this method is not preferable as a method for producing a biaxially stretched polyester film for hinelli wrapping because the maximum height is 4.0 μm and the heliness aptitude is poor.

[Comparative Example 3]
An attempt was made to obtain a polyester film having a thickness of 18 μm in the same manner as in Example 1 except that the heat treatment temperature after the first-stage stretching was 100 ° C. A polyester film could not be obtained.
As can be seen from Table 1, this method had a maximum height of 7.3 μm and was excellent in the suitability, but the film-forming property was inferior, which is not preferable as a method for producing a biaxially stretched polyester film for shining packaging. .

[Comparative Example 4]
A polyester film was obtained in the same manner as in Example 1 except that the heat setting treatment temperature was 50 ° C., but the film was severely damaged after the heat setting treatment, and the film was broken when both ends of the film were cut. Since it was easy, the polyester film was not obtained stably.
This method is not preferred as a method for producing a biaxially stretched polyester film for shining packaging.

  The method for producing a polyester film of the present invention is excellent in film-forming properties, is excellent in uniformity of the thickness of the obtained film and is suitable for shining, and is extremely useful as a method for producing a biaxially stretched polyester film for shining packaging. It can be said.

Claims (1)

After melt extrusion of the polyester, the sheet solidified with a cooling roll is first stretched in the first step in the transverse direction, then heat treated under a constant length in the width direction, and then stretched in the second step in the longitudinal direction. A method for producing an axially stretched polyester film, wherein the heat treatment between the first-stage transverse stretching and the second-stage longitudinal stretching is performed at a temperature of polyester glass transition temperature to glass transition temperature + 20 ° C. Biaxially stretched polyester for helmet wrapping, which is performed for 0.5 to 3 seconds , and further heat-fixed at a temperature of 80 ° C. or higher after biaxial stretching to make the maximum film surface height 5 to 7 μm. A method for producing a film.