JPH0455607B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing polyester, and more particularly to a method for producing polyester that can form a film with excellent surface properties. Conventional technology Polyethylene terephthalate, polyethylene
Polyesters, represented by 2,6-naphthalate, have excellent physical and chemical properties and are widely used in the film field, such as base films for magnetic recording media, films for electrical insulation, capacitors, and photographic films. , used in packaging films, etc. Polyester itself has poor passability during the film forming process and poor slipperiness of the product film.
A commonly used method is to disperse insoluble fine particles in the polyester to form appropriate irregularities on the film surface to improve surface smoothness. In this method, the properties of the film surface are greatly influenced by the properties of the insoluble particles, so conventionally it has been difficult to select the insoluble particles in terms of their type, particle size, particle size distribution, etc., and to control their content. Consideration has been given as to whether this should be done, and many proposals have been made. However, in recent years, the demand for higher quality polyester films has become stronger and stronger in various applications, and the situation has come such that conventional methods alone cannot adequately meet the demands. For example, in the field of high-grade magnetic tapes such as audio tapes, video tapes, and memory tapes, polyesters have finer particles, are completely finely dispersed in the polymer without secondary aggregation, and have an extremely low content of coarse particles. There has been a demand for a film with better quality, and conventional methods alone have become insufficient to meet this demand. Purpose of the Invention As a result of intensive research on a method for producing polyester that can meet such demands, the present inventor has discovered that the surface characteristics of polyester films are not caused solely by insoluble particles contained in the polymer as a lubricant, and that the difunctionality of the reaction raw material It is affected by particles mixed in small concentrations in lower alkyl esters of aromatic carboxylic acids and dihydroxy compounds, and no matter how you adjust the particle size, particle size distribution, etc. of the insoluble particles contained as a lubricant, the results will not be satisfied. The present invention has been made based on the discovery that a polymer capable of forming a film with excellent surface properties can be produced by reducing the number of particles of 4μ or more in the reaction raw material to a certain value or less. Reached. Therefore, an object of the present invention is to provide a method for producing polyester that can form a film with excellent surface properties. Structure and Effects of the Invention According to the present invention, a lower alkyl ester of a difunctional carboxylic acid and a dihydroxy compound are transesterified, and the resulting reaction product is then subjected to a polycondensation reaction to produce a polyester. In the manufacturing method, a lower alkyl ester of a difunctional carboxylic acid having an acid value of 0.1 or less and having a maximum length of 4 μ or more in 1 g of the lower alkyl ester is 30,000 or less, Furthermore, as the dihydroxy compound, the maximum length in 1 g of the dihydroxy compound
This is achieved by a method for producing polyester characterized by using a dihydroxy compound having 2500 or less particles of 4μ or more. In the present invention, difunctional carboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid and sebacic acid; and oxybenzoic acids such as oxybenzoic acid. Examples include carboxylic acids. Among these, aromatic dicarboxylic acids,
More preferred is 2,6-naphthalene dicarboxylic acid. In the present invention, such a difunctional carboxylic acid is used as a lower alkyl ester, and examples of the lower alkyl ester include dimethyl ester and diethyl ester. Among these, dimethyl ester is preferred. More specifically, 2,
6-naphthalene dicarboxylic acid dimethyl ester is preferred. Lower alkyl esters of difunctional carboxylic acids are usually produced by subjecting a difunctional carboxylic acid to an esterification reaction with a lower alcohol in the presence of a catalyst, and then purifying the reaction product. However, it is known from experience that a portion of the catalyst remains or unreacted difunctional carboxylic acid is mixed in the lower alkyl ester obtained. Furthermore, it is a common experience that impurities or foreign substances are mixed into the lower alkyl ester during storage or transportation, and that the acid value of the lower alkyl ester increases. Therefore, in conventional lower alkyl esters of difunctional carboxylic acids, there are particles with a maximum length of 4 μ or more in the range of 37,000 to 37,000.
It is mixed at a rate of 140,000 pieces/g. The "particles" referred to herein are particles that are suspended or precipitated in a solid state in a liquid when the lower alkyl ester is melted. These particles contain catalyst residues used in the production of lower alkyl esters of difunctional carboxylic acids, foreign substances such as packings mixed in from reaction tanks, storage tanks, piping, pumps, etc., and the lower alkyl esters. This is thought to be dust that gets mixed in during solidification, crushing, remelting, or during transportation. The lower alkyl ester of a difunctional carboxylic acid used in the present invention has the above-mentioned particles, that is, the number of particles with a maximum length of 4 μ or more is 30,000 or less, preferably 20,000 or less per gram of the lower alkyl ester. . Although it is preferable that the number of particles be as small as possible, in the production of lower alkyl esters on an industrial scale, reducing the number of particles to less than 1000 particles/g, particularly less than 500 particles/g, results in a significant increase in cost. From this point, the number of particles is 500
It is desirable that the number of particles/g is higher than that. the number of particles
When the number exceeds 30,000 pieces/g, it is difficult to produce a polyester that forms a film with good surface properties. The number of particles can be reduced by the acid value reduction method described below, but it is preferable to further reduce the number by filtration purification, for example, by filtering with a filter medium having an opening of 1 μm. Further, the lower alkyl ester of the difunctional carboxylic acid mentioned above must have an acid value of 0.1 or less, preferably 0.08 or less. If this acid value is higher than 0.1,
This is undesirable since agglomerated particles are significantly generated during polyester production. Methods to reduce this acid value include strengthening distillation purification, such as increasing the packing ratio of the distillation column to secure the specific surface area, increasing the height of the distillation column to secure the distillation time, and increasing the internal recirculation rate by increasing the capacity of the circulation heater in the distillation process. Preferred examples include enhancement of distillation capacity by In the present invention, the dihydroxy compound includes:
Ethylene glycol, trimethylene glycol,
Examples include aliphatic dihydroxy compounds such as triethylene glycol, tetramethylene glycol, and 1,4-cyclohexanedimethanol, and polyoxyalkylene glycols such as polyethylene glycol and polybutylene glycol.
Among these, ethylene glycol is particularly preferred. Such dihydroxy compounds usually also contain catalyst residues, foreign substances such as packings mixed in from reaction tanks, storage tanks, piping, pumps, etc., and particles caused by dust mixed in during transportation. For this reason, conventional dihydroxy compounds have a maximum diameter of
Particles of 4μ or more are mixed at a rate of 4,000 to 150,000 particles/g. The dihydroxy compound used in the present invention is
The number of particles having a maximum length of 4 μ or more is 2,500 or less, preferably 1,500 or less in 1 g of the dihydroxy compound. When the number of particles exceeds 2500, it is difficult to produce a polyester that forms a film with good surface properties. The smaller the number of particles, the better, but in the production of dihydroxy compounds on an industrial scale, this number of particles is
Setting the number to less than 200 pieces/g results in a significant cost increase. From this point of view, it is desirable that the number of particles be 200 particles/g or more. In the present invention, the above-mentioned lower alkyl ester of a difunctional carboxylic acid and a dihydroxy compound are first subjected to a transesterification reaction, and then the reaction product is subjected to a polycondensation reaction to produce a polyester.
At that time, the transesterification reaction and the polycondensation reaction are carried out under conditions conventionally known or accumulated in the art.
For example, it is preferable to use a transesterification catalyst, a stabilizer, a lubricant, etc. As is clear from the purpose of the present invention, these additives preferably do not contain particles with a maximum diameter of 4μ or more,
For example, the average particle diameter of the lubricant is preferably 1 μm or less, particularly 0.5 μm or less. In the present invention, polyesters include polyethylene-2,6-naphthalate and ethylene-2,
Particularly preferred are copolyesters having 6-naphthalate as the main repeating unit. Such polyesters are usually produced by melt polymerization. For example, dimethyl ester of 2,6-naphthalene dicarboxylic acid and ethylene glycol are transesterified to produce a monomer or initial polymer, which is then processed at a temperature above its melting point under vacuum or under inert gas flow. While stirring, the polycondensation reaction is carried out until the intrinsic viscosity becomes about 0.45 to 0.75. At this time, additives such as catalysts can be used as desired. When carrying out the transesterification reaction, if the acid value of the lower alkyl ester of the difunctional carboxylic acid used as a raw material is high, the amount of polymer-insoluble fine particles in the produced polyester will increase, which is undesirable. Moreover, if the number of particles of 4 μ or more mixed in the lower alkyl ester and dihydroxy compound is large, the amount of polymer-insoluble fine particles caused by these starting materials in the polyester to be produced increases, which is not preferable. Known methods such as centrifugation, filtration, adsorption with ion exchange resins, distillation, etc. can be used to reduce particles larger than 4μ in lower alkyl esters of difunctional carboxylic acids and particles larger than 4μ in dihydroxy compounds. The following method can be used. The present invention will be further explained below based on Examples.
The characteristics were evaluated using the following method. Parts in the examples mean parts by weight. 1 Acid value Dissolve the sample in paraxylene-ethanol mixed solvent system and add 1 volume of 0.1% phenol red aqueous solution.
A mixture of 1 volume of 0.1% bromothymol blue aqueous solution was used as an indicator, and titration was performed with potassium hydroxide. 2 Intrinsic viscosity Measured at 35°C in a mixed solvent of 40 parts of 1,1,2,2 tetrachloroethane and 60 parts of phenol. 3 Number of particles with a maximum length of 4μ or more Pass the sample through a tetrafluoroethylene resin filter with an opening of 0.22μ. This filter is 16
Divide into equal parts, observe the excess residue on the filter in one section under a microscope, and count the number of particles with a maximum diameter of 4μ or more in the microscope image using an image analyzer Luzetx 500 (manufactured by Nippon Regulator). The number of particles counted was calculated per 1 g of the sample.
Find the number of particles larger than 4μ. As the above samples, 240 mg of lower alkyl ester of difunctional carboxylic acid is used, and 2.4 g of dihydroxy compound is used. 4 Number of coarse particles in polymer 50 mg of polymer was sandwiched between two cover glasses and melt-pressed at 280℃, rapidly cooled, and then observed using a phase contrast microscope.
500, the number of particles with a maximum length of 4 μ or more in the microscopic image was counted, and the following judgment was made. Special grade: The number of particles larger than 4μ is less than 2 particles/mm ² Grade 1: The number of particles larger than 4μ is 2 to 10 particles/mm ² Grade 2: The number of particles larger than 4μ is 10 to 50 particles/mm ² Grade 3: The number of particles exceeding 4μ exceeds 50/mm ² Only special grade and grade 1 can be put to practical use. Example 1 Dimethyl 2,6-naphthalene dicarboxylate 100 with an acid value of 0.02 and a particle count of 4μ or more of 8100 pieces/1g
manganese acetate tetrahydrate in a mixture of 50 parts of ethylene glycol and 600 parts/g of particles larger than 4μ.
0.018 part was added, and the transesterification reaction was carried out while gradually increasing the temperature from 150°C to 240°C. After completing the transesterification reaction, add 0.013 parts of trimethyl phosphate, and further add 0.008 parts by weight of titanium acetate, heat the reaction product to 290°C, and perform a polycondensation reaction under high vacuum of 0.2 mmHg or less. Intrinsic viscosity 0.57
dl/g of polyethylene-2,6-naphthalate was obtained. The number of coarse particles of this polymer is as shown in Table 1. Example 2 The same procedure as in Example 1 was carried out, except that an ethylene glycol slurry in which 0.8 parts of silica particles having an average particle size of 0.28 μm were uniformly dispersed in 4 parts of ethylene glycol was added after the transesterification reaction was completed, and the intrinsic viscosity was 0.54 dl. /g of polyethylene-2,6-naphthalate was obtained. The number of coarse particles in this polymer is the first
As shown in the table. Comparative Example 1 Using 100 parts of dimethyl 2,6-naphthalene dicarboxylate having an acid value of 0.52 and having a particle count of 4μ or more at 48000 pieces/1g and 50 parts of ethylene glycol having a particle count of 4μ or more being 1200 pieces/1g. Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.58 dl/g was obtained in the same manner as in Example 1 in all other respects. The number of coarse particles of this polymer was as shown in Table 1, and it could not be put to practical use. Example 3 Dimethyl 2,6-naphthalene dicarboxylate with an acid value of 0.09 and a particle count of 4 μ or more of 30,000/1 g.
Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.57 dl/g was obtained in exactly the same manner as in Example 1, except that 100 parts of ethylene glycol and 50 parts of ethylene glycol having a particle size of 4 μ or more was 2400/g were used. The number of coarse particles of this polymer is as shown in Table 1. Comparative Example 2 Dimethyl 2,6-naphthalene dicarboxylate with an acid value of 0.69 and a particle count of 4μ or more of 25,000/1g.
Polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.54 dl/g was obtained in the same manner as in Example 1 except that 100 parts was used. The number of coarse particles of this polymer was as shown in Table 1, and it could not be put to practical use.

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Claims (1)

[Claims] 1. A method for producing a polyester by subjecting a lower alkyl ester of a difunctional carboxylic acid and a dihydroxy compound to a transesterification reaction, and then subjecting the resulting reaction product to a polycondensation reaction, wherein the lower alkyl ester has an acid value of 0.1 or less. Maximum length of 4μ in 1g of lower alkyl ester
Using a lower alkyl ester of a bifunctional carboxylic acid having 30,000 or less particles, and further using a dihydroxy compound having 2,500 or less particles with a maximum length of 4 μ or more in 1 g of the dihydroxy compound. A method for producing polyester, characterized in that it is used.