JPS636097B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyester film with excellent adhesiveness and printability with high efficiency. In recent years, the demand for polyester films as packaging materials for foods, miscellaneous goods, etc. has been increasing.
Originally, polyester had low surface free energy and poor adhesiveness and printability with hydrophilic inks. In order to improve these, attempts have been made to copolymerize polyether segments to improve the surface free energy. (Refer to Japanese Patent Publication No. 54-17350) Usually, improving the adhesion of polyester films,
Furthermore, block copolymerization of polyalkylene glycol has been carried out for the purpose of improving printability, but in order to obtain films useful as packaging materials using these block copolymers, it was necessary to
An electrostatic casting method known from Publication No. 37-6142 and the like is used. What is the electrostatic casting method? When rapidly cooling a sheet-like material made by melting and extruding a thermoplastic resin on the surface of a cooling body such as a rotating drum, a wire-shaped electrode is installed between the extrusion die and the surface of the rotating cooling body. In this method, a uniform film is obtained by depositing electrostatic charges on the upper surface of an unsolidified sheet-like material and rapidly cooling the sheet-like material while closely contacting the surface of a cooling body. However, even in such an electrostatic charge application casting method, as the circumferential speed of the rotary cooling body is increased to improve the film forming speed, the adhesion of the sheet material to the surface of the cooling body decreases, making it difficult to form a uniform film. Moreover, air is trapped between the sheet-like material and the rotary cooling body, causing defects on the film surface. Reducing the manufacturing cost in film production is an important issue, and for this purpose, it is effective to increase the peripheral speed of the rotary cooling body to improve the film production speed. However, as mentioned above, as the circumferential speed of the rotary cooling body is increased, the amount of static charge per unit area on the surface of the sheet-like object that is in close contact with the surface of the cooling body decreases, and the Adhesion is reduced and defects appear on the film surface. Therefore, in order to increase the adhesion between the sheet material and the rotary cooling body, the voltage applied to the electrode provided between the extrusion die and the surface of the rotary cooling body is increased, and the electrostatic charge on the surface of the sheet material is reduced. A method of increasing the amount of precipitation is considered, but if the applied voltage is too high, arc discharge will occur between the electrode and the surface of the cooling body, destroying the sheet-like material on the surface of the cooling body, and causing damage to the surface of the cooling body. This will cause damage to the top. Therefore, it is virtually impossible to increase the voltage applied to the electrodes above a certain level, and the conventional electrostatic casting method has a limit in increasing the film forming speed and obtaining a uniform film. . Polyester resins made by block copolymerizing polyalkylene glycol, etc. have a significant drop in adhesion to the surface of a rotary cooling body in the electrostatic casting method described above, making it difficult to efficiently obtain a film with a uniform surface. Ta. The present inventor has conducted extensive studies on a method for highly efficient production of a polyester film with excellent adhesiveness and printability by improving the adhesion between a melt-extruded sheet material and the surface of a rotary cooling body, and has developed the present invention. has been reached. That is, the present invention melt-extrudes a block copolymer consisting of a polyester segment containing terephthalic acid as the main acid component, ethylene glycol as the main glycol component, and 0.5 to 10% by weight of polyalkylene glycol with a molecular weight of 400 to 8,000. When forming a film, the block copolymer
The amount of ethylene glycol-soluble alkali metal compound in 100 parts by weight is 0.0001~
This is a method for forming a polyester film, characterized in that 0.0025 parts by weight is blended. The present invention will be explained in detail below. The polyester segment in the present invention is
The main target is polyethylene terephthalate, but polyesters in which dibasic acids such as isophthalic acid and adipic acid, and dihydric alcohols such as triethylene glycol and 1,4-butanediol are copolymerized may also be used. The block copolymer in the present invention is usually produced by a melt polymerization method. For example, terephthalic acid or its lower alkyl ester is subjected to an esterification or transesterification reaction with ethylene glycol to form a monomer or an initial polymer, which is then heated at a temperature above its melting point under vacuum or under a flow of inert gas. The intrinsic viscosity is 0.45~ while stirring
Polycondensation reaction is carried out until it reaches about 0.75. At this time, polyalkylene glycol is added before the intrinsic viscosity of the polymer exceeds 0.2 to obtain a block copolymer. In this process, catalysts, stabilizers, etc. can be used as desired, and additives such as colorants can also be used as desired. Further, the polyalkylene glycol component in the present invention needs to have a molecular weight of 400 to 8000,
If the molecular weight is less than 400, no improvement in adhesion or printability can be expected, and if the molecular weight exceeds 8000, it will not be possible to create a block copolymer, and the polyalkylene glycol component will separate into the polyester. When a film is formed, the polyalkylene glycol component leaches out onto the surface, which is undesirable as it causes fogging of printing ink. Further, the proportion of polyalkylene glycol in the block copolymer needs to be 0.5 to 10% by weight. If it is less than 0.5% by weight, no improvement in adhesion or printability can be expected, and if it exceeds 10% by weight, the properties of the polyester itself will change, reducing the physical properties such as tensile strength necessary for the film. Therefore, it becomes essentially unable to function as a film. The polyalkylene glycol in the present invention preferably has -O(-CH ₂ ) _o -O- [n is 2 to 4] as a repeating unit. If n exceeds 4, it will be difficult to obtain a block copolymer, and even if it is obtained, it will be difficult to contribute to improved printability. Further, preferable examples of the ethylene glycol-soluble alkali metal compound used in the present invention include sodium hydroxide and aliphatic carboxylate, and particularly preferable examples include sodium hydroxide and sodium acetate. Compounds that are not soluble in ethylene glycol are difficult to uniformly disperse in polyester, and if they are present as coarse foreign matter in the polyester film due to aggregation or the like, they may cause defects such as pinholes, which is undesirable. Furthermore, the proportion of these alkali metal compounds in the block copolymer is calculated as metal per 100 parts by weight of the block copolymer.
It is necessary that it is 0.0001 to 0.0025 parts by weight,
More preferably, it is 0.0003 to 0.0020 parts by weight. If the content is less than 0.0001 parts by weight, the effect of increasing the film forming speed cannot be expected, and even if the alkali metal content exceeds 0.0025 parts by weight, the effect of increasing the film forming speed has almost reached saturation, and rather the arc discharge This results in an increase in the frequency of , making it unsuitable for obtaining a polyester film with high efficiency. Such an ethylene glycol-soluble alkali metal compound may be added at any time as long as it is uniformly dispersed in the polyester, but it is preferable to add it while the polycondensation reaction is progressing and the intrinsic viscosity does not exceed 0.2. . Furthermore, even if a polyester-alkylene glycol copolymer containing a high concentration of an alkali metal compound is manufactured in advance and diluted appropriately during film formation, it is possible to produce a polyester with high efficiency and excellent printability as referred to in the present invention. It does not have any adverse effect on the effectiveness of forming the film. Furthermore, when obtaining a polyester-based stretched film, a lubricant is generally used to improve film forming workability and runnability of the product film, but it is not possible to add inorganic fine particles such as calcium carbonate, kaolin, and silica, which are commonly used in the present invention. Not subject to any restrictions. Further, the stretched film may be subjected to heat treatment, corona discharge treatment, etc. Further, there is no problem in incorporating appropriate additives such as antioxidants, ultraviolet absorbers, etc. The present invention will be explained in detail below based on Examples. Furthermore, evaluation methods related to the present invention will be described. (Surface defect evaluation method) The surface of the formed film is observed under a polarized lens and ranked as follows. Rank-1: Uniform surface with no visible surface defects. Rank-2: There are many minute surface defects. Rank-3: There are many large surface defects. (Adhesion with printing ink) Tape peeling Using a commercially available adhesive tape (trade name: cellophane tape), apply it to the printing ink layer side without air bubbles and quickly peel it off.The peeling condition is classified as follows. and evaluated. ◎ No peeling at all. Good. 〇 Almost no peeling. Good (10% or less) △ 10% to 50% peeling. Somewhat good. × 50% or more ~ Almost completely peeled off. Defective comparative example When polyethylene terephthalate was obtained according to a conventional method using manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, and trimethyl phosphate as a heat stabilizer, polyalkylene glycol and Irganox 1010 as an antioxidant were used at the end of transesterification. (manufactured by Ciba Geigy) and further added sodium acetate. A stretched film was obtained using the obtained polyester resin by a normal sequential biaxial stretching film forming method. Table 1 shows the results of evaluating surface defects and adhesion of these.

【table】

[Table] The stretched film contains 0.1 part by weight of kaolin to impart slipperiness. As is clear from Table 1, by incorporating a trace amount of alkali metal compound into the polyalkylene glycol-polyethylene terephthalate copolymer, it is possible to produce a stretched film with excellent uniform surface adhesion with high efficiency. It is. Example 5 A stretched film was obtained by forming a polyester resin in the same manner as in Example 1, except that 0.001 parts by weight of sodium hydroxide (calculated as metal) was contained in place of sodium acetate. When this film was evaluated, the following results were obtained. Film forming speed 120m/min Surface defects Rank 1 Adhesion ◎

Claims (1)

[Scope of Claims] 1. A polyester segment containing terephthalic acid as the main acid component and ethylene glycol as the main glycol component, and 0.5 to 10% by weight of a polyester segment having a molecular weight of 400 to 10% by weight.
When forming a film by melt-extruding a block copolymer consisting of 8,000% polyalkylene glycol, 0.0001 to 0.0025 parts by weight of an ethylene glycol-soluble alkali metal compound is added to 100 parts by weight of the block copolymer. 1. A method for forming a polyester film characterized by blending. 2. The method for forming a polyester film according to claim 1, wherein the alkali metal compound is at least one compound selected from sodium hydroxide and fatty acid carboxylate. 3. The method for forming a polyester film according to claim 1 or 2, wherein the polyalkylene glycol has -O( _-CH2 ) _-oO- [n is 2 to 4] as a repeating unit.