JP4793073B2 - Method for producing biaxially stretched polyester film - Google Patents

Description

  The present invention relates to a method for producing a biaxially stretched polyester film. More specifically, the biaxially stretched film has excellent film handling and appearance, and has easy tearability and handleability suitable for stick packaging applications and lid material applications. The present invention relates to a method for producing a polyester film.

  Cellophane with good transparency has been widely used as a film having excellent tearability. 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. . Polyethylene terephthalate film, on the other hand, has excellent properties such as toughness, heat resistance, water resistance, and transparency, but has the disadvantage that it cannot be used for stick packaging or lid material applications due to its poor tearability. It was.

  As a method for eliminating such drawbacks, it is disclosed that a polyester film having a thickness of 3 to 9 μm and a total elongation in the machine direction and transverse direction of 200% or less exhibits easy tearability. (For example, refer to Patent Document 1).

  Further, as a method for controlling the total elongation in the machine direction and the transverse direction of the polyester film to 190% or less, micropores are provided on the entire surface of the polyester film obtained by stretching in the longitudinal direction and then stretching in the transverse direction. A method is disclosed. (For example, refer to Patent Document 2).

However, since this method requires a step of providing micropores, it not only leads to an increase in cost, but also has a problem of causing tearing variation due to nonuniformity of the micropore depth.
JP 2003-165174 A JP 2002-178450 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 that is excellent in film handleability and appearance, and has excellent easy tearability and handleability.

  In the invention of the present application, after the polyester resin is melt-extruded, the sheet solidified with a cooling roll is first subjected to the first stage stretching in the transverse direction, then the second stage stretching in the longitudinal direction, and then at least 140 to 200 ° C. It is a manufacturing method of the biaxially stretched polyester film whose thickness is 3-9 micrometers characterized by performing a 1-8% relaxation process in the temperature range.

  In this case, 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 2.5 to 4.5 times.

  Furthermore, in this case, it is preferable that the total breaking elongation (TE) in the machine direction and the transverse direction of the film is 190% or less.

  The method for producing a polyester film of the present invention is a method for producing a biaxially stretched polyester film suitable for stick packaging use, lid material use, etc., because it has excellent film handleability and appearance and has excellent easy tearability. I can say that.

  In this invention, it is preferable that the polyester which comprises a film makes an ethylene terephthalate component the main structural component from the point which ensures the heat resistance, water resistance, etc. of a film.

  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.

  When the thickness of the polyester film is less than 3 μm, the handleability in printing and / or laminating is inferior, which is not preferable. Conversely, if it exceeds 9 μm, the tearability is poor, which is not preferable.

  Even if the thickness of the polyester film is 3 to 9 μm, if the sum of the breaking elongation (TE) in the longitudinal direction and the transverse direction exceeds 200%, the tearability is poor, which is not preferable.

  In the present invention, the polyester film after biaxial stretching has a thickness of 3 to 9 μm, and the polyester sheet obtained by melt extrusion is subjected to the first stage stretching in the transverse direction and then the second stage stretching in the longitudinal direction. Then, by performing 1 to 8% relaxation treatment at least in the temperature range of 140 to 200 ° C., the total of the elongation at break (TE) in the longitudinal direction and the transverse direction of the polyester film can be 190% or less.

  Furthermore, it is preferable to control the 5% elongation strength (F5) in the transverse direction to 95 MPa or more and the thermal shrinkage (HS) at 105 ° C. to 0.5% or less.

  By making the 5% elongation strength (F5) in the transverse direction of the polyester film 95 MPa or more and the thermal shrinkage rate (HS) at 105 ° C. 0.5% or less, it is possible to dry or extrude during printing or dry laminating. This is preferable because wrinkles are less likely to occur during lamination.

  In the present invention, after stretching from the first stage to the second stage or the third stage, heat fixing with a certain length in the width direction (for example, heat fixing performed by holding both ends of the film with clips) is performed. It is carried out in the above temperature range, and then a relaxation treatment is performed in the width direction. In this relaxation treatment, 5% elongation strength in the transverse direction of the polyester film is to be relaxed by 1 to 8% in a temperature range of at least 140 to 200 ° C. While suppressing the decrease in (F5), the thermal contraction rate (HS) at 105 ° C. in the lateral direction can be controlled within a range of 0.5% or less.

When the relaxation treatment is performed in a temperature range of less than 140 ° C., it is difficult not only to control the thermal shrinkage rate (HS) at 105 ° C. in the lateral direction of the polyester film to a range of 0.5% or less, but also the relaxation rate is large. In such a case, the polyester film loosens after the relaxation treatment and comes into contact with the heat setting device, so that the polyester film is easily scratched. In addition, when the relaxation temperature is low, the polyester film is loosened after the relaxation treatment, and is not preferable because the polyester film is liable to come into contact with the heat setting device.
On the contrary, when relaxation treatment is performed in a temperature range exceeding 200 ° C., it is not preferable because it is difficult to control the 5% elongation strength (F5) in the transverse direction of the polyester film to a range of 95 MPa or more.

  Moreover, even if it is the said temperature range, when a relaxation rate is less than 1%, since it is difficult to control the thermal contraction rate (HS) of 105 degreeC of the polyester film in the horizontal direction to the range of 0.5% or less, it is preferable. Absent. Conversely, when the relaxation rate exceeds 8%, the thermal shrinkage rate (HS) at 105 ° C. in the transverse direction of the polyester film can be controlled within a range of 0.5% or less, but the 5% elongation strength (F5) is 95 MPa. It is difficult to control within the above range.

  In the present invention, as long as the effect of the relaxation is not hindered, a relaxation treatment in a temperature range exceeding 200 ° C. may be used in combination.

  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 5 to 4.5 times in the longitudinal direction. When the first stage draw ratio is less than 3.0 and / or when the second stage draw ratio is less than 2.5, the flatness of the easily tearable biaxially stretched polyester film is poor and the pitch in the printing process This is not preferable because it tends to cause a shift. On the contrary, when the first stage stretch ratio exceeds 4.5 times and / or when the second stage stretch ratio exceeds 4.5 times, wrinkles often occur in the second stage stretching. It is not preferable.

  In the present invention, it is preferable to further increase the 5% elongation strength (F5) by stretching 1.05 to 1.50 times in the transverse direction at a temperature equal to or higher than the glass transition temperature of the polyester as the third stage stretching.

  In the present invention, the intrinsic viscosity of the polyester film is preferably 0.50 to 0.65 dl / g.

  When the intrinsic viscosity is less than 0.50 dl / g, it is not preferable because breakage tends to occur during the production of the polyester film. On the contrary, when the intrinsic viscosity exceeds 0.65 dl / g, it is not preferable because a dimensional defect is likely to occur in the cutting process to a predetermined product width.

  In the present invention, after the relaxation treatment in the width direction is performed, the wet tension may be adjusted to 44 to 58 mN / m by performing corona treatment on one side or both sides of the polyester film before winding.

  The biaxially stretched polyester film obtained by the production method of the present invention can be combined with other base materials or used alone as a constituent material for stick packaging and lid materials.

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

(1) Polyester film thickness Measured according to JIS-Z-1702.

(2) Elongation at break (TE) of polyester film and 5% elongation strength in the transverse direction (F5)
Measured according to JIS-C-2151.

(3) Thermal shrinkage (HS) at 105 ° C in the transverse direction of the polyester film
Measured according to JIS-C-2151.

(4) 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.

(5) Tearability of polyester film A piece of polyester film of 20 cm in the tearing direction and 4 cm in the orthogonal direction is cut out. Ten samples each having a notch of 5 mm in length at the center of one short side of the film piece are prepared in each of the vertical direction and the horizontal direction. Next, it tears by hand from the notch and evaluates that the tear propagation end condition is ○ as practical.
○: The propagation end reaches within 5 mm from the center of the short side facing the notched side. Δ: The propagation end reaches at least 5 mm from the center of the short side facing the notched side. Has not reached the short side

(6) Handling property of polyester film Practical use of wrinkle generation condition by visual observation when applying a tension of 80 N / m with a dry laminator with a drying temperature set to 140 ° C. and running at 120 m / min. Evaluate it.
○: No wrinkle △: Wrinkle at the end ×: Wrinkle on the entire surface

(8) Scratches The presence or absence of scratches on both sides of the film was visually confirmed.

  Table 1 shows the film forming conditions, film thickness, elongation at break (TE), 5% elongation strength (F5), thermal shrinkage (HS) at 105 ° C., tearability, and handleability in Examples and Comparative Examples. Show.

[Example 1]
Polyethylene terephthalate (intrinsic viscosity: 0.58 dl / g, average particle diameter: 1000 ppm of agglomerated silica having an average particle size of 1.3 μm) was dried under reduced pressure (1.3 hPa) for 24 hours at 120 ° C., and 280 using a single screw extruder. After melting at ℃, cast onto a cooling roll (circumferential speed 50 m / min) from a 45 cm wide T-die (7.2 kV from a tungsten wire electrode with a diameter of 30 μm installed so as to face the circumferential surface of the cooling roll) Was applied, and a 0.2 mA current was applied to cause electrostatic contact) to obtain an unstretched sheet. The unstretched sheet was stretched 4.0 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 105 ° C. in the longitudinal direction of 4.1. Double-stretched (second-stage stretching), subjected to constant length width heat treatment at 216 ° C., relaxed by 1.0% in the transverse direction at 216 ° C., and then 2.0% in the transverse direction at 170 ° C. A 7 μm polyester film was obtained.
As can be seen from Table 1, the method of this example can be said to be a method for producing a biaxially stretched polyester film having excellent tearability.

[Example 2]
A polyester film having a thickness of 7 μm was obtained in the same manner as in Example 1 except that the first stage stretching ratio was 3.5 times and the third stage stretching was performed 1.2 times at 150 ° C.
As can be seen from Table 1, the method of this example can be said to be a method for producing an excellent easily tearable biaxially stretched polyester film.

[Example 3]
A polyester film having a thickness of 7 μm was obtained in the same manner as in Example 1 except that the second stage draw ratio was 3.85.
As can be seen from Table 1, the method of this example can be said to be a method for producing an excellent easily tearable biaxially stretched polyester film.

[Comparative Example 1]
A polyester film having a thickness of 2.5 μm was obtained in the same manner as in Example 1.
As can be seen from Table 1, this method is not preferred as a method for producing an easily tearable biaxially stretched polyester film because of poor handling.

[Comparative Example 2]
A polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1.
As can be seen from Table 1, this method is not preferable as a method for producing an easily tearable biaxially stretched polyester film because tearability is poor.

[Comparative Example 3]
A polyester film was obtained in the same manner as in Example 1 except that the relaxation treatment after the constant length heat treatment was changed to 1.0% in the lateral direction at 216 ° C. and then 10.0% in the horizontal direction at 170 ° C. The polyester film slackened after the relaxation treatment in the heat setting device, and the polyester film was scratched in contact with the heat setting device.
This method is not preferable as a method for producing an easily tearable biaxially stretched polyester film.

[Comparative Example 4]
A polyester film having a thickness of 7 μm was obtained in the same manner as in Example 1 except that the relaxation treatment after the constant-length heat treatment was changed to 3.0% at 216 ° C.
As can be seen from Table 1, this method is not preferable as a method for producing an easily tearable biaxially stretched polyester film because the 5% elongation strength is small and the handleability is poor.

[Comparative Example 5]
A polyester film having a thickness of 7 μm was obtained in the same manner as in Example 1 except that the relaxation treatment after the constant-length heat treatment was 1.0% at 216 ° C. and then 2.0% at 130 ° C.
As can be seen from Table 1, this method is not preferable as a method for producing an easily tearable biaxially stretched polyester film because the elongation at break and thermal shrinkage ratio are large and the tearability and handleability are poor.

  The method for producing a polyester film of the present invention is excellent in film handleability and appearance, and is excellent in tearability and handleability, and can be said to be extremely useful as a method for producing an easily tearable biaxially stretched polyester film.

Claims (3)

  After the polyester resin is melt-extruded, the sheet solidified with a cooling roll is first stretched in the first stage in the transverse direction, then stretched in the second stage in the longitudinal direction, and then 1 in a temperature range of at least 140 to 200 ° C. A method for producing a biaxially stretched polyester film having a thickness of 3 to 9 μm, characterized by performing a relaxation treatment of ˜8%.   2. The method for producing a biaxially stretched polyester film according to claim 1, wherein the first-stage stretching is performed in a 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 the second step. A process for producing a biaxially stretched polyester film, characterized by stretching in the longitudinal direction 2.5 to 4.5 times at a temperature equal to or higher than the glass transition temperature of polyester as stage stretching.   The method for producing a biaxially stretched polyester film according to claim 1, wherein the total of the breaking elongation (TE) in the machine direction and the transverse direction of the film is 190% or less. Manufacturing method.