JP2663562B2 - Method for producing polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a polyester film having excellent thickness uniformity with high efficiency.

(Conventional technology) Saturated linear polyesters represented by polyethylene terephthalate have excellent mechanical properties, heat resistance, weather resistance, electrical insulation, chemical resistance, etc., and are therefore used for packaging, photography, electrical use, and magnetic tape. Are widely used in such a wide field. Usually, a polyester film is obtained by melt-extruding polyester and then biaxially stretching it. In this case, in order to increase the uniformity of the thickness of the film and the speed of casting, when the sheet-like material melt-extruded from the extrusion die is rapidly cooled on the surface of the rotary cooling drum, the adhesion between the sheet-like material and the drum surface is increased. Must be increased. As a method of increasing the adhesion between the sheet and the drum surface, a wire-shaped electrode is provided between the extrusion die and the rotary cooling drum, a high voltage is applied, and static electricity is deposited on the upper surface of the unfixed sheet. It is known that a method in which the sheet is rapidly cooled while being in close contact with the surface of the cooling body (hereinafter referred to as an electrostatic adhesion casting method) is effective (for example, Japanese Patent Publication No. 37-14142).

Film thickness uniformity is a very important property in film quality, and film productivity is directly dependent on casting speed, so increasing casting speed is extremely important to improve productivity. A great deal of effort has been put into improving the electrostatic adhesion.

It is known that electrostatic adhesion is an effective means to increase the amount of charge on the surface of a sheet.

In addition, it is known that in order to increase the amount of charge on the surface of a sheet-like material in the electrostatic adhesion casting method, it is effective to modify a polyester raw material used in forming a polyester film.

Conventionally, as the modification method, a method of adding an alkali metal compound, an alkaline earth metal compound, manganese or a zinc compound in a polyester production step is known. However, it is necessary to add a large amount of a metal compound in order to provide high electrostatic adhesion by the method. When these metal compounds are added, there is a problem that the stability of the polyester decreases. A method for improving stability by using a phosphorus compound in combination has been proposed, but it cannot be said that the method has reached a satisfactory level.

(Problems to be Solved by the Invention) In view of the above-mentioned circumstances, the present inventors have diligently studied a method for imparting high electrostatic adhesion with a small amount of a metal compound as much as possible, and completed the present invention.

(Means for Solving the Problems) According to the present invention, a polyester composition containing a zinc compound, an alkali metal compound and a phosphorus compound in an amount that simultaneously satisfies the following formulas (I) to (III) is melt-extruded into a film form. This is a method for producing a polyester film, wherein a melt-extruded film is electrostatically brought into close contact with a rotary cooling roll and rapidly cooled and solidified.

5 ≦ Zn ≦ 500 (I) 0.1 ≦ Zn / M ≦ 20 (II) 1.2 ≦ Zn / P ≦ 20 (III) A preferred embodiment of the present invention is a method for producing a polyester film, characterized in that at least one selected from phosphoric acid, phosphorous acid and esters thereof is used as the P compound in the present invention.

A further preferred embodiment of the present invention is a method for producing a polyester film in which the polyester film is stretched at least 1.1 times in one direction in the present invention.

The polyester of the present invention may be any polyester having a film-forming ability obtained from a dibasic acid and a dihydric alcohol or a copolymer thereof. Typical examples of the polyester include, but are not limited to, polyethylene terephthalate and a copolymer thereof.

The method of the present invention has a feature that the polymerization activity is higher than conventionally known methods, and therefore, it is particularly preferable to apply the method to a copolymer having a slow polymerization reaction. The method for producing the polyester of the present invention is not particularly limited as long as it is based on a usual melt polycondensation method, but is preferably applied to a so-called direct polymerization method produced by reacting a dicarboxylic acid with a glycol.

Further, the present invention can be applied to both batch and continuous production methods.

All Zn compounds used in the present invention can be used as long as they are soluble in the reaction system. Examples thereof include organic acid salts such as zinc acetate and zinc benzoate, halides such as zinc chloride, and acetylacetonate salt of zinc. As shown in the formula (I), the Zn compound is added in an amount of 5 to 500 ppm as a Zn atom to the finally obtained polyester in an amount of 20 to 300 ppm.
pm is particularly preferred.

If it is less than 5 ppm, the effect of improving the electrostatic adhesion is undesirably reduced. Conversely, if it exceeds 500 ppm, the effect of improving the electrostatic adhesion is saturated, and the heat resistance of the polyester is lowered, which is not preferable. Any alkali metal compound used in the present invention can be used as long as it is soluble in the reaction system. For example, Li, Na and K carboxylates, phosphates, carbonates, hydrides and alkoxides, specifically lithium acetate, sodium acetate, potassium acetate,
Lithium benzoate, sodium benzoate, potassium benzoate, potassium dihydrogen phosphate, sodium pyrophosphate,
Potassium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium bicarbonate, potassium bicarbonate, lithium hydride, sodium hydride, potassium hydride, lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium Ethoxide, potassium ethoxide and the like can be mentioned, but use of a carboxylate is particularly preferred. These compounds may be used alone or in combination of two or more.

The addition amount of the alkali metal compound must be in the range of 0.1 to 20 in the atomic ratio of Zn metal / alkali metal as shown by the formula (II). A range of 0.3 to 10 is particularly preferred. If the atomic ratio of the metal is out of the range of 0.1 to 20, the effect of improving the electrostatic adhesion is reduced, which is not preferable. On the other hand, if it is less than 0.1, precipitated particles due to the alkali metal are increased, which has an adverse effect such as a decrease in the transparency of the film and an increase in the generation of foreign substances, which is not preferable. The P compound used in the present invention is preferably selected from phosphoric acid, phosphorous acid and esters thereof.

For example, if another P compound such as phosphonic acid is used, precipitated particles due to the reaction with the metal compound, so-called internal particles, are deposited, which has an adverse effect such as a decrease in the transparency of the film and an increase in the generation of foreign substances. Specific P
Compounds include phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate,
Triphenyl phosphate, monomethyl phosphate, dimethyl phosphate, monobutyl phosphate, dibutyl phosphate, phosphorous acid, trimethyl phosphite, triethyl phosphite, tributyl phosphite, etc. can give. These may be used alone or in combination of two or more.

As shown in the formula (III), the addition amount of the P compound is Zn metal /
The atomic ratio of P atoms must be in the range of 1.2 to 20.
A range of 1.5 to 10 is particularly preferred. If it is less than 1.2, the effect of improving the electrostatic adhesion is undesirably small. It is not preferable because the thermal stability of the polyester exceeding 20 deteriorates.

The timing of adding the Zn compound, the alkali metal compound and the P compound is not particularly limited, and the addition can be carried out at any stage from the start of the production of the polyester to the time of melt extrusion into a film. It is preferable to add the compound in the polyester production process from the viewpoint of dissolving the compound in the polyester as uniformly as possible and suppressing generation of foreign matter. In particular, it is preferable to add it before starting the initial condensation. The compounds may be added simultaneously or separately.
The order of addition when added separately is not limited. Furthermore, a polyester containing a high concentration of a Zn compound, an alkali metal compound and a P compound, a so-called master polymer, is separately manufactured, and a master polymer system is employed in which the content is adjusted to a predetermined amount in a melt extrusion stage of film formation. Is also good.

When the above compound is added in the polyester production step, it is preferable to dissolve it in the glycol used for the production of the polyester and add it to the reaction system.

In the method of the present invention, since the Zn compound has polycondensation activity, the polyester may be produced without adding another polycondensation catalyst, but other polycondensation catalysts such as Sb, Ti and Ge may be used in combination. Is preferred. Stabilizers such as Co compounds and organic antioxidants may be used in combination for the purpose of improving thermal stability and color tone. Also, there is no limitation on the use of a lubricant or a lubricant made of inorganic or organic fine particles for the purpose of improving the slipperiness of the polyester film.

In the method of the present invention, there is no limitation on the structure of the electrostatic application device or the conditions for applying the static electricity, and they may be set arbitrarily. For example, the structure of the electrostatic application device includes an electrode structure, the presence or absence of a counter electrode, the positional relationship between the electrode, the counter electrode, an extrusion port, a cooling roll, and the like.
As the electrostatic application condition, a set voltage and a current value may be arbitrarily set.

The film in the method of the present invention may be any of an unstretched film, a uniaxially stretched film and a biaxially stretched film, but stretching in at least 1.1 times, preferably 2.5 times or more in one direction improves mechanical properties and other physical properties. It is preferable for providing various uses.

(Examples) Next, examples and comparative examples of the present invention will be described. All parts in the examples are parts by weight unless otherwise specified.
The measuring method used is shown below.

(1) Intrinsic viscosity The polymer is dissolved in a mixed solvent of phenol (6 parts by weight) and tetrachloroethane (4 parts by weight) and measured at 30 ° C.

(2) Electrostatic adhesion A tungsten wire electrode is provided between the die of the extruder and the cooling drum, and a voltage of 10 to 15 KV is applied between the electrode and the casting drum to perform casting.
The surface of the obtained casting material is visually observed, and evaluated by the casting speed at which pinner bubbles begin to occur. A polymer having a higher casting speed has better electrostatic adhesion.

(3) Thickness unevenness in the longitudinal direction The film thickness was measured for a film length of 10 m using a contact-type continuous thickness meter, and the thickness unevenness was calculated by the following equation.

Example 1 (1) Method for producing polyester 519 parts of terephthalic acid, ethylene glycol (EG) 357
Parts, neopentyl glycol 50 parts, antimony trioxide 0.
150 parts, sodium acetate 0.0214 parts, zinc acetate dihydrate 0.2
6 parts of the stirrer, a distillation column and a pressure regulator stainless steel autoclave was pressurized after charging nitrogen substitution gauge pressure 2.5 kg / cm ² to keep the water formed continuously from the top of the distillation column at 240 ° C. with The esterification reaction was performed while removing. 120 minutes after the start of the reaction, the pressure was released, and the esterification rate was 98.
% Product was obtained. 0.19 phosphoric acid is added to this esterification product.
Was added to a solution in which 1.9 parts of EG was dissolved and 1.2 parts of kaolinite having an average particle size of 0.7 μm to 8 parts by volume of EG.
After stirring at normal pressure and 240 ° C for 10 minutes, the mixture was transferred to a 240 ° C polycondensation reactor, and the temperature of the reaction system was gradually lowered to 0.05 mmHg while raising the temperature to 275 ° C in 45 minutes. A polycondensation reaction was conducted at the same temperature and pressure for about 70 minutes to obtain a polyester having an intrinsic viscosity of 0.675. The electrostatic adhesion of the obtained polyester is 60 m /
Minutes.

(2) Production of film A film was formed from the polyester obtained in (1) under the following conditions. Even if the film was formed at a take-up speed of 205 m / min, there was no defect on the film surface and the thickness was uneven in the vertical direction. Is 6.
High quality films of less than 5% were obtained.

Film forming conditions Film thickness: 12μ (after biaxial stretching) Extrusion temperature: 290 ° C Electrostatic contact condition: 0.25mmφ SUS electrode applied voltage 10-15KV Vertical stretching ratio: 3.5 times Vertical stretching temperature: 90 ° C Horizontal stretching ratio: 3.5 times Stretching temperature: 130 ° C. Heat setting temperature: 220 ° C. Comparative Example 1 A polyester was produced in the same manner as in Example 1, (1) except that sodium acetate was not added. The obtained polyester had a low electrostatic adhesion of 20 m / min.

This polyester was formed into a film by the same method as in Example 1 (2), but the maximum film formation speed was as low as 60 m / min.

Comparative Example 2 A polyester was produced in the same manner as in Example 1, (1) except that zinc acetate dihydrate was not added. The obtained polyester had a low electrostatic adhesion of 15 m / min.

The polyester was formed into a film in the same manner as in Example 1 (2), but the maximum film forming speed was low and was 50 m / min or less.

Examples 2 to 3 Polyesters having the composition shown in Table 1 were produced in accordance with (1) of Example 1, and the results obtained when the film was formed by the same method as in (2) of Example 1 are shown in Table 1. In each case, a high-quality film was obtained even when the film was formed at a high speed.

(Effects of the Invention) As shown in the above examples, the method of the present invention has an effect that a high-quality polyester film having excellent thickness uniformity can be formed at a high speed.

Claims (1)

(57) [Claims] 1. A polyester composition containing an amount of a zinc compound, an alkali metal compound and a phosphorus compound which simultaneously satisfies the following formulas (I) to (III) is melt-extruded into a film, and then the melt-extruded film is rotated and cooled. A method for producing a polyester film, wherein the polyester film is electrostatically adhered to a roll and rapidly cooled and solidified. 5 ≦ Zn ≦ 500 (I) 0.1 ≦ Zn / M ≦ 20 (II) 1.2 ≦ Zn / P ≦ 20 (III)