JPH11156935A - Biaxially oriented polypropylene terephthalate film and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a polypropylene terephthalate film excellent in thickness uniformity, in which the film can be stably formed without break. SOLUTION: In a biaxially oriented polyester film consisting of polypropylene terephthalate, the refractive index Nz in the direction of the thickness is set to be 1.55 or less. Further, in obtaining a biaxially oriented polyester film made of the polypropylene terephthalate by a successive bixially orienting method, in which a lateral stretching is performed after a longitudinal stretching, the refractive index Nx in the stretching direction after longitudinal uniaxial stretching is set to be 1.63-1.585.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polypropylene terephthalate film which can be used for food packaging and the like by longitudinal and horizontal sequential biaxial stretching, and a method for producing the same. In particular, a film having excellent thickness uniformity and flexibility. And a method for stably forming and producing the film.

[0002]

2. Description of the Related Art Polypropylene terephthalate is known as a material having excellent flexibility, and it has been proposed to use it in a fibrous form for use as a material for carpet (Japanese Patent Publication No. 49-21256). Since the flexibility and the glass transition temperature and the melting point of such a material are very close to those of nylon 6, their properties are expected to be similar to those of a nylon film.

Furthermore, polyalkylene terephthalates such as polypropylene terephthalate generally have less influence on changes in physical properties due to moisture absorption than polyamides. It is expected that a film having small dimensional change due to moisture absorption can be obtained, and the change in size and strength due to moisture absorption of the nylon 6 film can be used for food packaging and the like in applications where problems have arisen.

[0004] However, a number of patents relating to films using polypropylene terephthalate have been proposed so far (for example, Japanese Patent Application Laid-Open No. 8-325391). The present invention is not a proposal to develop (for example, an elastic modulus of about 2 GPa), but to a film having an extremely low elastic modulus of 1 GPa or less. In such a case, it is necessary to form the film while keeping the stretching ratio in the longitudinal direction or the transverse direction at the time of film formation low, and there is a disadvantage that the thickness uniformity of the final film is poor. In addition, in order to obtain a film with good uniformity of thickness, generally, it is necessary to increase the vertical and horizontal magnifications to form a film.
Although preferable, the conditions for obtaining a biaxially stretched film that can be formed stably without breaking the film and have excellent thickness uniformity have not been clarified at present.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a polypropylene terephthalate having a tensile modulus of 1.5 GPa.
As described above, an object of the present invention is to provide a flexible polyester film having excellent thickness uniformity, which is not more than 3.5 GPa.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, a film having excellent thickness uniformity can be stably obtained by setting the following characteristic values of a uniaxially stretched film and a biaxially stretched film to certain values. It was found that a film could be formed. That is, in the biaxially stretched polyester film made of polypropylene terephthalate, the refractive index N in the thickness direction
z is 1.55 or less, and the tensile modulus is 1.5 GPa
As described above, the flexible polyester film is excellent in thickness uniformity and has a thickness of 3.5 GPa or less.

In order to obtain a biaxially oriented polyester film made of polypropylene terephthalate by a sequential biaxial stretching method in which transverse stretching is performed after stretching in the longitudinal direction,
The refractive index Nx in the stretching direction after the longitudinal uniaxial stretching is 1.63 or less;
It is a method for producing a biaxially stretched polyester film, which is 1.585 or more.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polypropylene terephthalate used in the present invention is a polyester containing terephthalic acid as a main acid component and 1,3-propanediol as a main glycol component. These acid components and / or glycol components include isophthalic acid, phthalic acid, and diphenyl- 4,4-
Dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, naphthalene-1,5
Dicarboxylic acid, diphenoxyethane-4,4-dicarboxylic acid, diphenylsulfone-4,4-dicarboxylic acid,
Acid components such as diphenyl ether-4,4-dicarboxylic acid, malonic acid, 1,1-dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, decamethylene dicarboxylic acid, and ethylene glycol, tetramethylene glycol, neopentyl Glycol components such as glycol, cyclohexane dimethanol, hydroquinone and bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymers thereof may be copolymerized.

As a method for producing the polyester in the present invention, a conventionally known method for directly obtaining a polyester by a reaction between dicarboxylic acid and glycol, or a method for transesterifying a lower alkyl ester of dicarboxylic acid with glycol, which is sodium, potassium or Heat-reacting using one or more of compounds containing magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt to obtain a low-polymerized polyester, and the obtained low-polymerized polyester is then subjected to the presence of a polymerization catalyst. And a method of heating and polymerizing at 200 to 260 ° C. under reduced pressure.

Preferred polymerization catalysts include antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds and titanium compounds.

Examples of the titanium compound include tetraalkyl titanate, tetraaryl titanate, titanyl oxalate, titanyl oxalate, chelate compounds containing titanium, tetracarboxylate of titanium, and the like. Specific examples include tetraethyl titanate and tetrapropyl titanate. , Tetraphenyl titanate or partial hydrolysates thereof, titanyl ammonium oxalate, potassium titanyl oxalate, titanium triacetylacetonate and the like.

The polyester film of the present invention may contain inorganic particles, organic salt particles and crosslinked polymer particles.

The inorganic particles include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, and fluorine oxide. Lithium oxide and the like.

Examples of the organic salt particles include calcium oxalate, terephthalate such as calcium, barium, zinc, manganese and magnesium.

Examples of the crosslinked polymer particles include divinylbenzene, styrene, acrylic acid, methacrylic acid, and homo- or copolymers of vinyl monomers of acrylic acid or methacrylic acid. In addition, organic particles such as polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester resin, thermosetting urea resin, and thermosetting phenol resin may be used.

[0016] The polyester film of the present invention may comprise a nucleating agent, an antioxidant, a coloring inhibitor, a pigment,
You may mix | blend a dye, an ultraviolet absorber, a mold release agent, a lubricant, a flame retardant, and an antistatic agent.

Next, a method for producing the film of the present invention will be described, but the method is not necessarily limited thereto. As described above, polypropylene terephthalate is polymerized by a known method, then chipped, and
Alternatively, after blending with other polymers and additives as required, the mixture is extruded into a sheet from an extruder equipped with a T-die, and while being applied with an electrostatic charge, the sheet is closely contacted with a cooled casting drum and solidified by cooling. Let it.

The unstretched film is stretched at a stretching temperature of 50 ° C.
After stretching from 2 to 5 times in the longitudinal direction with a roll-type vertical stretching machine at a temperature of from 100 to 100 ° C., it is guided into a tenter, and is horizontally stretched from 2 to 5 times, and heat-treated at from 120 to 220 ° C. If necessary, heat treatment may be performed while relaxing in the width direction.

The flexible polyester film of the present invention refers to a biaxially stretched polyester film having a tensile modulus of 1.5 GPa or more and 3.5 GPa or less. In other words, it has flexibility compared to ordinary polyethylene terephthalate, is about the same as the tensile modulus of nylon 6 film, and has practicality as a heavy weight film for food applications and a film for packaging water. To tell.

The biaxially stretched polyester film made of polypropylene terephthalate of the present invention needs to have a refractive index Nz in the thickness direction of 1.55 or less.

The present inventors have conducted intensive studies on a method for obtaining a biaxially oriented polypropylene terephthalate film having good thickness uniformity. As a result, the biaxially oriented polyester film made of polypropylene terephthalate has a refractive index Nz in the thickness direction of It was found that the film thickness uniformity was improved when the ratio was 1.55 or less.

In the present invention, in the above-mentioned sequential biaxial stretching, longitudinal stretching may be performed so that the longitudinal refractive index Nx of the uniaxially stretched film after longitudinal stretching is 1.63 or less and 1.585 or more. is necessary. When the longitudinal refractive index Nx of the uniaxially stretched film after the longitudinal stretching is larger than 1.63, the film is easily broken when the transverse stretching is performed after the uniaxial stretching, and the object of the present invention and the stability of the film are stabilized. I can't get it.

When the longitudinal refractive index Nx of the uniaxially stretched film after longitudinal stretching is smaller than 1.585, the refractive index Nz in the thickness direction of the biaxially stretched polyester film, which is the object of the present invention, is set to 1 It is difficult to set the thickness to .55 or less, irrespective of the transverse stretching conditions, and the thickness uniformity of the film is deteriorated.

[Method of Evaluating Physical Property Values] (1) Refractive index Nx in the longitudinal direction of the uniaxially stretched film after longitudinal stretching and refractive index Nz in the thickness direction of the biaxially stretched film
Measurement. Attach a polarizing plate to the eyepiece using an Abbe refractometer 4T manufactured by Atago Co., Ltd., adjust the direction of the polarizing plate and the direction of the film, and adjust the refractive indices Nx and Nz in the vertical, horizontal, and thickness directions of the film. Was measured. Diiodomethane was used as the intermediate liquid.

(2) Evaluation of thickness uniformity: TV% Using a continuous thickness gauge manufactured by Anritsu Electric Co., Ltd., the length of 5 m in the machine direction of the biaxially stretched film was measured.
The film thickness was continuously taken in, the difference R between the maximum value and the minimum value of the film thickness was divided by the average value Tave of the film thickness, and TV% was determined by the following equation. TV% = (R / Tave) × 100 A value of TV% of 10% or less was judged as good, and a value of more than 10% was judged as bad.

(3) Tensile Modulus (Kg / mm ² ) Measured at 23 ° C. and 65% relative humidity using a UMT-2-500 manufactured by Toyo Baldwin Co., Ltd. The sample shape is 100 mm long and the tensile speed is 1
00 mm / min.

[0027]

EXAMPLE 1 94 parts by weight of dimethyl terephthalate, 74 parts by weight of 1,3-propanediol and 0.0 parts of tetrabutyl titanate
35 parts by weight were charged into a reaction vessel, and the temperature in the vessel was gradually raised from 150 ° C. to 230 ° C. to carry out an esterification reaction, and 0.035 parts by weight of tetrabutyl titanate was added to the obtained reaction product. The temperature was gradually reduced and the temperature was raised to 260 ° C. and 1.0 mmHg or less in 60 minutes, and the polymerization reaction was performed for 2 hours. The intrinsic viscosity of the obtained polymer is 0.8
It was 4.

The propylene terephthalate polymer was vacuum-dried at 160 ° C. for 2 hours by a conventional method, extruded from a T-die, and brought into close contact with a casting drum by an electrostatic charge to obtain a cast film. The cast film is wound around a roll heated to 60 ° C., heated and then stretched 3.3 times in the machine direction, then preheated in a tenter at 60 ° C., and heated in the width direction while heating from 65 ° C. to 70 ° C. .5
The film was heat-treated at 180 ° C. for 15 seconds to obtain a biaxially oriented polypropylene terephthalate film having a thickness of 12 μm without breaking. The characteristics are as shown in Table 1.

Example 2 The film forming conditions were the same as in Example 1, except that the stretching ratio in the width direction was changed to 4.0. A biaxially oriented polypropylene terephthalate film was obtained without breaking.

Comparative Example 1 Film forming conditions were the same as in Example 1, except that the longitudinal stretching ratio was 2.5 times and the transverse stretching ratio was 3 times.

Comparative Example 2 In Example 1, the temperature of the roll during the longitudinal stretching was set to 90.
° C, the longitudinal stretch ratio was 3.3 times, and the transverse stretch ratio was 4 times, except that the film forming conditions were the same.

Comparative Example 3 In Comparative Example 1, the temperature of the roll during the longitudinal stretching was set to 60.
° C, the longitudinal stretching ratio to 4.0 times, and the transverse stretching ratio to 3.
The film forming conditions were the same except that the ratio was increased five times. At the time of horizontal stretching,
A film was not obtained because the film was broken.

Comparative Example 4 In Comparative Example 2, the longitudinal stretching ratio was set to 2.0 times and the transverse stretching ratio was set to 3. Except for doubling, the film forming conditions were the same. The thickness unevenness is large and the film appearance is poor.

Comparative Example 5 In Comparative Example 2, the longitudinal stretching ratio was 1.5 times, and the transverse stretching ratio was 3. Except for doubling, the film forming conditions were the same. The thickness unevenness is large and the film appearance is poor.

Comparative Example 6 Polyethylene terephthalate (intrinsic viscosity: 0.65) was vacuum-dried at 160 ° C. for 2 hours by a conventional method.
The film was extruded from a T-die and brought into close contact with a casting drum by an electrostatic charge to obtain a cast film. The cast film is wound around a roll heated to 94 ° C., heated, stretched 3.5 times in the machine direction, preheated in a tenter at 90 ° C., and stretched 4 times in the width direction while being heated to 110 ° C. Thereafter, a heat treatment was performed at 200 ° C. for 15 seconds while relaxing 5% in the width direction to obtain a biaxially stretched polyethylene terephthalate film having a thickness of 15 μm without breaking.

[0036]

[Table 1]

[0037]

The film of the present invention is a biaxially stretched film having excellent thickness uniformity, and is a production method capable of forming a film without breaking the film stably.

Claims (2)

[Claims] 1. A biaxially stretched polyester film made of polypropylene terephthalate, wherein the refractive index Nz in the thickness direction is 1.55 or less and the tensile elastic modulus is 1.5.
A flexible polyester film having excellent thickness uniformity, which is not less than GPa and not more than 3.5 GPa. 2. When a biaxially stretched polyester film made of polypropylene terephthalate is obtained by a sequential biaxial stretching method in which transverse stretching is performed after stretching in the longitudinal direction, the refractive index Nx in the stretching direction after longitudinal uniaxial stretching is 1. 63 or less;
585 or more, a method for producing a biaxially stretched polyester film.