JP4887698B2 - Biaxially stretched polyester film for shining packaging - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a biaxially stretched polyester film for shining packaging, and more particularly, to a biaxially stretched polyester film having excellent film forming properties and uniformity in thickness, and having excellent heliness aptitude.

  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 _1, was satisfied _{0.003 ≦ N 1 -N 0 ≦ 0.021} ) polyester film is disclosed. (For example, refer to Patent Document 1). In addition, a mixed polyester composed of polyethylene terephthalate, a polyester having a glass transition temperature of 35 ° C. or higher and a polyester having a glass transition temperature of 34 ° C. or lower is biaxially stretched, and then subjected to a tension heat treatment at a relatively high temperature (210 to 220 ° C.). A polyester film having a ratio of falling yield stress / upper yield stress of 0.95 or less is disclosed. (For example, refer to Patent Document 2).

  However, although these polyester films are excellent in the 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 was a drawback.

  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 3).

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 2003-31828 A 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 biaxially stretched polyester film that is excellent in film formability and thickness uniformity, and has excellent shininess aptitude.

A sheet obtained by cooling and solidifying a molten resin of a mixed polyester having a mixing ratio of 100: 0 to 50:50 (% by weight) of a polyester mainly composed of an ethylene terephthalate component and a polyester mainly composed of a butylene terephthalate component is first in the transverse direction. perform stage stretching, then longitudinally performing a second-stage stretching, be further manufactured to a heat treatment under tension line cormorants method, the second stage draw ratio is 2.0 to 4.5 times, strain the heat treatment temperature is 80 to 130 ° C., and the product of the second stage stretching magnification and tension the heat treatment temperature is a biaxially oriented polyester film for twist wrapping prepared by the process is 200 to 600, and stress -A cypress characterized by the fact that the average value of the value in the vertical direction and the value in the horizontal direction of the difference in yield point stress (difference between the upper yield point stress and the lower yield point stress) in the strain curve is 2 MPa or more. It is a biaxially stretched polyester film for repackaging.

  The biaxially stretched polyester film for shining wrapping of the present invention is an extremely useful polyester film because it is excellent in film formability and thickness uniformity, and has excellent shininess aptitude.

The polyester film of the present invention is obtained by cooling and solidifying a molten resin of a mixed polyester having a mixing ratio of 100: 0 to 50:50 (% by weight) of a polyester mainly composed of an ethylene terephthalate component and a polyester mainly composed of a butylene terephthalate component. performing a first-stage stretching a sheet in the transverse direction and then longitudinally performing a second-stage stretching, be further manufactured to a heat treatment under tension line cormorants way, the second stage draw ratio from 2.0 to 4 a .5 times, tension heat treatment temperature is 80 to 130 ° C., and the second-stage stretching magnification and tension heat treatment temperature and twist packaging biaxially oriented polyester product is manufactured in a manner that is 200 to 600 of The average value of the value in the longitudinal direction and the value in the transverse direction of the yield point stress difference (difference between the upper yield point stress and the lower yield point stress) in the stress-strain curve is 2MP. A biaxially stretched polyester film for velvet packaging characterized by being a or more.

  In the present invention, the polyester constituting the film yields in a film in which the mixing ratio of the polyester mainly composed of the ethylene terephthalate component and the polyester mainly composed of the butylene terephthalate component is 100: 0 to 50:50. This is necessary in order to develop a point stress difference and to secure good film forming properties such as heat resistance, water resistance and transparency.

  When the amount of the polyester having a butylene terephthalate component as a main component exceeds 50% by weight, not only the yield point stress difference is hardly exhibited but also the film forming property is deteriorated.

  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. In addition, as glycol components, aliphatic glycols such as propanediol, pentanediol, hexanediol and neopentylglycol, alicyclic glycols such as cyclohexanedimethanol, ethylene oxide adducts of bisphenol A, ethylene oxide adducts of bisphenol S, etc. Aromatic glycol, 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, a sheet obtained by cooling and solidifying a polyester melt-extruded by a known extruder is subjected to first-stage stretching 3.0 to 4.5 times in the transverse direction at a temperature equal to or higher than the glass transition temperature of the polyester, 2nd stage stretching in the longitudinal direction 2.0 to 4.5 times at a temperature equal to or higher than the glass transition temperature of, and further, heat-fixing treatment with a certain length in the known width direction (for example, both ends of the film with clips It is preferable to carry out the heat setting treatment by gripping at 80 to 130 ° C. for 1 to 20 seconds.

  In the present invention, in the film forming method described above, the product (M × · T) of the second stage draw ratio (M × (−)) and the heat setting temperature (T (° C.)) is controlled to 200 to 600. However, it is necessary to improve the film formability and thickness uniformity, improve the appearance of the product roll, and develop a yield point stress difference in the obtained film. When Mx · T is less than 200, the yield stress difference of the obtained polyester film is sufficiently developed, but when cutting both ends of the film after biaxial stretching or when cutting to finish into a product roll It is not preferable because it is easy to break and wrinkles due to the above-mentioned tarmi are likely to occur in the product roll. On the contrary, when M × T exceeds 600, the film forming property and the product roll appearance are excellent, but it is not preferable because the yield point stress difference of the obtained polyester film becomes difficult to express.

  In the present invention, as the third stage stretching, re-stretching of 1.05 to 1.4 times may be performed at a temperature equal to or higher than the glass transition temperature of the polyester. Further, relaxation treatment (treatment of relaxing 0.5 to 8% in the width direction at 100 to 140 ° C.) may be performed in the width direction.

  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.

The evaluation methods used in the examples and comparative examples will be described.
(1) Yield point stress difference (Δσ (MPa))
The stress-strain curve was measured according to JIS C 2151 (5 points each in the vertical and horizontal directions), and the difference between the upper and lower yield stresses in the vertical and horizontal directions (the value in the vertical direction and the value in the horizontal direction). (Average value) is the yield point stress difference.
(2) 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
(3) Intrinsic viscosity of polyester 0.1 g of polyester is dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane (3/2 by volume) and measured at 30 ° C. using an Ostwald viscometer.
(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 75 to 85 °
×: Twist return angle is 85 ° or more

Table 1 shows the polyester raw materials, film forming conditions, M × T, thickness uniformity, yield point stress difference, and swellability used in Examples and Comparative Examples.
(1) A: Polyethylene terephthalate (Intrinsic viscosity: 0.62 dl / g, average particle diameter: 1.3 ppm of agglomerated silica of 1000 ppm)
(2) B: Polyethylene terephthalate / isophthalate (containing 10 ppm of repeating unit of ethylene isophthalate, intrinsic viscosity: 0.62 dl / g, average particle size: 1.3 ppm of agglomerated silica of 1000 ppm)
(3) C: Polybutylene terephthalate (Intrinsic viscosity: 1.2 dl / g)

[Example 1]
A mixture of B and C (B / C: 75/25% by weight) as a polyester raw material was dried under reduced pressure (1.3 hPa) at 120 ° C. for 24 hours, and melted at 280 ° C. using a single screw extruder, Cast onto a cooling roll (peripheral speed 50 m / min) from a 45 cm wide T-die (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, A non-stretched sheet was obtained by applying a current of 2 mA for electrostatic contact. 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 preheated at 80 ° C. and stretched at 95 ° C. in the longitudinal direction of 3.6 °. The film was stretched twice (second-stage stretching), further re-stretched 1.05 times at 100 ° C. (third-stage stretching), and then heat-fixed at 100 ° C. to obtain a polyester film having a thickness of 18 μm. It was.
As can be seen from Table 1, the method of this example has a yield point stress difference of 4 MPa, and can be said to be an excellent biaxially stretched polyester film for velvet packaging.

[Example 2]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the second stage draw ratio was 4.2 times and the constant length width heat setting treatment temperature was 120 ° C.
As can be seen from Table 1, the method of this example has a yield point stress difference of 3 MPa, and can be said to be an excellent 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 second stage draw ratio was 3.0 times.
As can be seen from Table 1, the method of this example has a yield point stress difference of 5 MPa, and can be said to be an excellent biaxially stretched polyester film for velvet packaging.

[Example 4]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 3 except that A was used as the polyester raw material.
As can be seen from Table 1, the method of this example has a yield point stress difference of 3 MPa, and can be said to be an excellent biaxially stretched polyester film for velvet packaging.

[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 constant length width heat fixing treatment temperature was set to 170 ° C.
As can be seen from Table 1, this method has a yield point stress difference of 0 MPa (no yield point and only increases the stress) and is inferior in the formability, and thus is not preferable as a biaxially stretched polyester film for wrapping.

[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 polyester raw material was a mixture of B and C (B / C: 40/60 wt%) and cast to a cooling roll having a peripheral speed of 30 m / min. .
As can be seen from Table 1, this method has a yield point stress difference of less than 1 MPa (an upper yield point is recognized, but a clear lower yield point is not recognized), and is less suitable for heliness. It is not preferable as an axially stretched polyester film.

[Comparative Example 3]
A polyester film was obtained in the same manner as in Example 1 except that the polyester raw material was a mixture of B and C (B / C: 20/80% by weight) and cast to a cooling roll with a peripheral speed of 30 m / min. After cooling with a cooling roll, both ends of the sheet were often cracked, and a polyester film could not be obtained stably.
This method is not preferable as 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 fixed length width heat fixing treatment temperature was set to 50 ° C., but the film was severely damaged after the heat fixing treatment. A polyester film could not be stably obtained because it was easily broken. This method is not preferable as a biaxially stretched polyester film for shining packaging.

[Comparative Example 5]
A polyester film having a thickness of 18 μm was obtained in the same manner as in Example 1 except that the second stage draw ratio was 1.6 times.
As can be seen from Table 1, this method has a yield point stress difference of 6 MPa and good shining suitability, but is not preferable as a biaxially stretched polyester film for shining wrapping due to poor thickness uniformity.

  The polyester film of the present invention is excellent in film formability and appearance of a product roll, and has excellent yield resistance because the obtained film has sufficient yield point stress, and is extremely useful as a biaxially stretched polyester film for hinelli packaging. You can say that.

Claims (3)

A sheet obtained by cooling and solidifying a molten resin of a mixed polyester having a mixing ratio of 100: 0 to 50:50 (% by weight) of a polyester mainly composed of an ethylene terephthalate component and a polyester mainly composed of a butylene terephthalate component is arranged in the transverse direction. perform first-stage stretching, then longitudinally performing a second-stage stretching, be further manufactured to a heat treatment under tension line cormorants method, the second stage draw ratio is 2.0 to 4.5 times, tension heat treatment temperature is 80 to 130 ° C., and a biaxially oriented polyester film for twist wrapping prepared in the second stage stretching magnification and the method the product of the tension heat treatment temperature is 200 to 600, and The average value of the value in the vertical direction and the value in the horizontal direction of the difference in yield point stress (difference between the upper yield point stress and the lower yield point stress) in the stress-strain curve is 2 MPa or more. Biaxially stretched polyester film for wrapping. 2. The biaxially stretched polyester film for shining packaging according to claim 1, wherein the thickness uniformity in the longitudinal direction is 8% or less. The biaxially stretched polyester film for shining packaging according to claim 1 or 2, wherein the film thickness is 9 to 25 µm.