JPS6140538B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing thermoplastic polyester films without surface defects with high efficiency. In the production of films made of thermoplastic resin, when a melt-extruded sheet material is rapidly cooled on the surface of a rotating cooling body such as a rotating drum, a wire-shaped electrode is provided between the extrusion die and the surface of the rotating cooling body to apply the voltage. An electrostatic casting method in which a uniform film is obtained by charging the upper surface of an unsolidified sheet with an electrostatic charge and rapidly cooling the sheet while closely contacting the surface of a cooling body is disclosed in Japanese Patent Publication No. 37-6142. It is known from et al. However, even in such an electrostatic 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 obtain a uniform film. Moreover, air being drawn in between the sheet material and the rotary cooling body causes defects on the film surface. Increasing productivity and reducing manufacturing costs in film manufacturing is an important issue as well as improving quality, and to achieve this, it is effective to increase the peripheral speed of the rotary cooling body and increase the film forming speed. This is a typical method. In the electrostatic casting method, as the circumferential speed of the rotary cooling body is increased in order to increase the film forming speed, the amount of electrostatic 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. As a result, as mentioned above, the adhesion between the sheet-like material and the rotary cooling body decreases, causing defects on the film surface. To solve this problem, the voltage applied to the electrode installed between the extrusion die and the extrusion die is usually increased to increase the adhesion between the sheet-like material and the rotary cooling body, thereby reducing the static charge on the surface of the sheet-like material. A method is taken to increase the amount of charge, but if the applied voltage is too high, arc discharge will occur between the electrode and the surface of the cooling body, which will destroy the sheet-like material on the surface of the cooling body and cause damage to the surface of the cooling body. It will cause damage. 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. In order to overcome the limitations of the electrostatic casting method, increase the film forming speed, and obtain a highly efficient, uniform polyester film with no surface defects, the
Japanese Patent No. 40231 proposes a method of controlling the resistivity of a molten polymer by incorporating an alkali metal, an alkaline earth metal, or a compound thereof to produce a polyester film with high efficiency. However, in this method, the adhesion between the polyester sheet and the rotary cooling body is improved by incorporating an alkali metal or alkaline earth metal compound in the polymer in an amount of 0.005 to 1% by weight, preferably 0.07 to 0.3% by weight. However, when such large amounts of alkali metals and alkaline earth metals are contained, particles will precipitate inside the polyester, and the coarse precipitated particles may cause pinholes in the film or cause arcing during film formation. This is undesirable because it may induce electric discharge, and the color tone of the polyester itself may be significantly deteriorated, resulting in a polyester film with a strong yellowish tinge. The present invention has been made through intensive studies to overcome these drawbacks, and aims to produce polyester films with high efficiency by improving the adhesion between the melt-extruded sheet material and the surface of the rotary cooling body without changing the physical properties of the polyester film itself. They discovered a method and arrived at the present invention. That is, the present invention provides a method for producing a film by melt-extruding thermoplastic polyester, comprising:
A method for producing a polyester film, characterized in that the thermoplastic polyester contains 0.01 to 2 parts by weight of inorganic fine powder and 0.0001 to 0.0025 parts by weight of an ethylene glycol-soluble alkali metal compound in terms of metal, per 100 parts by weight of polyester. It is. The present invention will be explained in detail below. The thermoplastic polyester in the present invention mainly refers to polyethylene terephthalate, but some of them include dibasic acids such as isophthalic acid and adipic acid, triethylene glycol, 1,4-
It may be a polyester copolymerized with a dihydric alcohol such as butanediol, or a polyoxyalkylene glycol such as polyethylene glycol, polybutylene glycol, etc., and a stabilizer,
It may also contain additives such as colorants. Such thermoplastic polyesters are usually produced by melt polymerization. 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 through an inert gas flow. It can be produced by carrying out a polycondensation reaction under stirring until the intrinsic viscosity (measured at 35°C using an orthochlorosolvent) reaches about 0.45 to 0.75. At this time, additives such as catalysts can be used as desired. Preferable examples of the ethylene glycol-soluble alkali metal compound used in the present invention include sodium hydroxide and aliphatic carboxylate, and particularly preferred examples include sodium hydroxide,
Examples include 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 substances in polyester due to aggregation or the like, they may cause defects such as pinholes, which is undesirable. Further, as the inorganic fine powder used in the present invention, clay, kaolin, talc, silica, alumina, calcium phosphate, etc. can be preferably mentioned.
These are usually used for the purpose of improving the slipperiness of polyester films. If the polyester simply contains these inorganic fine powders, it is not expected that the film forming rate will increase much due to improved adhesion of the sheet-like material to the surface of the cooling body, and even if there is an increase, it will be very small. Further, when the polyester contains only an alkali metal compound, only a slight increase in the film forming rate is expected. However, the effect increases dramatically by combining an alkali metal compound and an inorganic fine powder. These inorganic fine powders and ethylene glycol-soluble alkali metal compounds may be added at any time as long as they are uniformly dispersed in the polyester, but they should be added while the polycondensation reaction is progressing and the intrinsic viscosity does not exceed 0.2. It is preferable to do so. Further, the inorganic fine powder and the alkali metal compound may be mixed in advance outside the system and added, or the effect will not change even if each is added independently. Furthermore, there is no problem in adding the ethylene glycol-soluble alkali metal compound simultaneously with catalysts and additives commonly used in polyester production. In the present invention, the inorganic fine powder contained in the polyester is 0.01 parts by weight per 100 parts by weight of the polyester.
-2 parts by weight, more preferably 0.03-1.5 parts by weight. If the amount is less than 0.01 part by weight, no synergistic effect with the alkali metal compound coexisting in the polyester can be expected, and rather the state is equivalent to adding the alkali metal compound alone, making it difficult to increase the film forming rate due to improved adhesion. Become. In addition, if the content of the inorganic fine powder exceeds 2 parts by weight, the content of the inorganic fine powder in the polyester film becomes too large, which impairs the original transparency and uniformity of the polyester film. Furthermore, agglomeration is induced due to the inclusion of a large amount of inorganic fine powder particles,
It becomes difficult to obtain high quality polyester film. In addition, the ethylene glycol-soluble alkali metal compound coexisting with the inorganic fine powder in the polyester is calculated in terms of metal per 100 parts by weight of the polyester.
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 due to the synergistic effect with the inorganic fine powder in the present invention cannot be expected, and if it exceeds 0.0025 parts by weight, the color tone of the polyester film will worsen and yellowing will occur. This is undesirable as it results in a polyester film having a tinge of color. Furthermore, even if more than 0.0025 parts by weight of alkali metal is contained, the effect of increasing the film forming speed has almost reached saturation, but rather increases the frequency of arc discharge, which is not suitable for obtaining polyester films with high efficiency. It is. Normally, when obtaining a polyester film containing inorganic fine powder, a polyester containing a high concentration of inorganic fine powder is produced in the polycondensation reaction process, and then in the process of melt extrusion to obtain the film, a polyester film containing no inorganic fine powder is produced. A method is used to obtain a polyester film having the desired composition by diluting it in an arbitrary ratio, and the same method can be used in the present invention. Diluting to a predetermined concentration with a polyester that does not contain will not prevent the effects of the present invention in any way. In this case, it is preferable to coexist the inorganic fine powder and the alkali metal compound in the same polyester because the effects of the present invention can be more effectively expressed. Producing a polyester containing an alkali metal compound and a polyester containing an inorganic fine powder separately, and then mixing the inorganic fine powder and the alkali metal compound in the film forming process tends to reduce the effects of the present invention by half. The reason for this is not clear, but it suggests that the synergistic effect between the inorganic fine particles of the present invention and the alkali metal compound improves the adhesion between the polyester sheet and the surface of the rotary cooling body. . The present invention will be explained in detail below based on Examples.
The evaluation method is as described below. (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 a few minute surface defects. Rank-3: There are relatively many minute surface defects. Rank-4: There are relatively many large surface defects. Rank -5 Large surface defects exist on one side. Example 1 Polyethylene terephthalate was polymerized according to a conventional method using manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, and trimethyl phosphate as a thermal stabilizer. At this time, before the transesterification reaction was completed, 0.25 parts by weight of clay and 0.0005 parts by weight (metal equivalent) of sodium acetate were added per 100 parts by weight of polyethylene terephthalate obtained. The obtained polyethylene terephthalate having an intrinsic viscosity of 0.62 was dried and formed into a film under the following conditions. Extrusion temperature: 285℃ Electrostatic casting conditions:
Electrode 0.25mmφSUS applied voltage 6500V Cooling drum temperature: 25℃ Longitudinal stretch ratio: 3.6 times Lateral stretch ratio: 3.9 times Heat setting temperature: 225℃ Film forming speed: 180 m/min Surface defects of biaxially stretched film after film formation are removed. A uniform film was obtained, which was ranked -1 without any hardness. Comparative Example 1 Polyethylene terephthalate was obtained under the same conditions as in Example-1 except that sodium acetate was not added, and a biaxially stretched film was obtained under the same conditions. In this case, the surface defects are rank -
5, and no film that could be used as a product was obtained. Example 2 Polyethylene terephthalate was obtained in the same manner as in Example-1 except that 0.0006 parts by weight (metal equivalent) of sodium hydroxide was added in place of sodium acetate, and then produced under exactly the same conditions as in Example-1. It was filmed. The surface of the obtained film was ranked -1, and a uniform film was obtained. Examples 3, 4, 5 and Comparative Examples 2, 3 Polyethylene terephthalate was obtained in the same manner as in Example 1, except that the type of inorganic fine powder and the type of alkali metal compound were changed as shown in Table 1.
The polyethylene terephthalate was formed into a film under the same conditions as in Example 1, except that only the film forming speed was changed as shown in Table 1. Table 1 shows the results obtained.
Shown below.

[Table] In Comparative Example 3, the polymer color tone was yellowish, and furthermore, it was difficult to obtain a product film by arc discharge. Examples 6 and 7 When obtaining a polyethylene terephthalate film containing an inorganic fine powder and an alkali metal compound, firstly, polyethylene terephthalate containing a high concentration of an inorganic fine powder and/or an alkali metal compound was prepared, and then a predetermined proportion of these was used and Table 2 shows an example in which the film was diluted to a predetermined concentration with unadded polyethylene terephthalate at the film forming stage. Example 6 is an example in which an inorganic fine powder and an alkali metal compound are contained in the same polyethylene terephthalate, and Example 7 is an example in which polyethylene terephthalate containing an inorganic fine powder and an alkali metal compound separately are mixed at the film forming stage. This is an example.

【table】

Claims (1)

[Claims] 1. A method for producing a film by melt extruding a thermoplastic polyester, in which 0.01 to 2 parts by weight of an inorganic fine powder and an ethylene glycol-soluble alkali metal compound are added to the thermoplastic polyester per 100 parts by weight of the polyester. From 0.0001 to metal equivalent
A method for producing a polyester film characterized by containing 0.0025 parts by weight. 2. The method for producing a polyester film according to claim 1, wherein the alkali metal compound is at least one compound selected from sodium hydroxide and aliphatic carboxylate. 3. The method for producing a polyester film according to claim 1 or 2, wherein the inorganic fine powder is at least one kind of fine powder selected from clay, kaolin, talc, silica, alumina, and calcium phosphate. 4. The method for producing a polyester film according to any one of claims 1 to 3, wherein the thermoplastic polyester is a polyester whose main repeating unit is ethylene terephthalate.