JP2000256582A - Production of polyester resin for powdered coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for economically producing a polyester resin for a coating material by reusing distillate distilled from a production process for esterification reaction as a polyol component without rectifying operation. SOLUTION: When producing a polyester resin for a coating material from terephthalic acid or acid components principally comprising it and polyol components principally comprising two or more kinds of 2-8C diols through at least both an esterification process and a polycondensation one, distillate distilled from the polycondensation process following the esterification process is reused as part of the polyol components in the esterification process after the solid content contained in the distillate is removed down to <=1 wt.%. On that occasion, the weight ratio of reused polyol to refined polyol is 0.05-0.49.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for economically producing a polyester resin for powder coatings.

[0002]

2. Description of the Related Art Polyesters represented by polyethylene terephthalate have excellent physical and chemical properties, and are widely used as molded articles such as fibers and films for clothing and industrial materials. On the other hand, attempts have been made to use polyethylene terephthalate as a powder coating utilizing the excellent properties of polyethylene terephthalate.However, if polyethylene terephthalate is used directly as a resin for powder coating, it has a high softening point and poor pulverizability. Has disadvantages.

In order to lower the softening point of polyethylene terephthalate and improve the pulverizability, an aromatic polycarboxylic acid other than terephthalic acid and / or an aliphatic polycarboxylic acid other than terephthalic acid, and an aliphatic diol other than ethylene glycol as a polyol component are used. It is known that copolymerization of aliphatic polyols having 3 or more valences is effective.

[0004] The production of polyester-based powder coating resins generally involves an esterification reaction between an acid component mainly composed of terephthalic acid and a polyol component mainly composed of two or more diols having 2 to 8 carbon atoms. This is usually performed by a two-step method or a three-step method as described later.

[0005] In recent years, the demand for cost reduction of resin for powder coating has become increasingly severe. In order to respond to this demand, for example, reuse of the distillate can be considered. As one of them, it is conceivable that the distillate distilled out in the polycondensation step is recovered as a high-purity diol by a rectifying operation and reused, but the cost of recovery is naturally high, so the merit of cost reduction is reduced. I will.

[0006]

Therefore, if the polyol distilled out in the polycondensation step can be directly reused in the esterification step without performing the rectification operation, it would be very difficult in terms of production cost. It is advantageous. In the prior art, the distillate distilled off through the separation tower in the polycondensation step contains a high melting point substance attached to the separation tower, and the high melting point substance does not dissolve when the distillate is reused directly. For this reason, the quality of the resin for powder coating is not stable, and there is a defect that unevenness is generated on the surface of the coating film and the gloss is poor. An object of the present invention is to provide a method for economically producing the polyester resin for powder coatings having a low melting point.

[0007]

Means for Solving the Problems In producing a polyester resin for powder coating, the present inventors directly reuse the distillate generated in the polycondensation step in the esterification step without performing a rectification operation. As a result of intensive studies on the method of performing, the distillate generated in the polycondensation step, the solid component contained therein was removed, and it was found that it was extremely effective to use the distillate at a specific ratio, and the present invention was reached. .

[0008] That is, the present invention relates to a method for preparing a powder from terephthalic acid or an acid component mainly containing terephthalic acid and a polyol component mainly containing two or more diols having 2 to 8 carbon atoms through an esterification step and a polycondensation step. In producing a polyester resin for body coating, a distillate generated as a part of the polyol component in the esterification step in the subsequent polycondensation step is removed so that the solid component contained therein becomes 1% by weight or less. A method for producing a polyester resin for powder coating, characterized in that the recycled polyol used in the esterification step has a weight ratio of 0.05 to 0.49 with respect to 1 of the purified polyol. It is the gist.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below in the order of steps. As a method for producing a polyester resin for powder coating, terephthalic acid or an acid component mainly containing terephthalic acid and an esterification reaction of a polyol component mainly containing two or more diols such as ethylene glycol and neopentyl glycol are used. An esterification step of obtaining a low polymer, and a polycondensation step of obtaining a powder coating resin having a desired degree of polymerization from the low polymer, in some cases, the esterification step and the desired degree of polymerization or more There are a three-step method including a polycondensation step for once increasing the degree of polymerization and a depolymerization step for depolymerizing the same to a desired degree of polymerization, and the method of the present invention can be applied to either method.

The acid component used in the present invention is terephthalic acid or a substance mainly composed of terephthalic acid. A dicarboxylic acid or an anhydride thereof such as dodecane dicarboxylic acid, an oxycarboxylic acid such as paraoxybenzoic acid, or the like can be used.

The polyol component is mainly composed of two or more diols selected from ethylene glycol, diethylene glycol, triethylene glycol, 1,6-hexanediol, neopentyl glycol, propylene glycol, cyclohexanedimethanol and the like. A small amount of a trivalent or higher polyol such as trimethylolpropane or pentaerythritol can be used in combination. As the combination of the polyol components, ethylene glycol / neopentyl glycol, ethylene glycol / neopentyl glycol / trimethylolpropane and the like are preferably used.

First, in the esterification step, terephthalic acid or an acid component mainly composed of terephthalic acid and a polyol component mainly composed of two or more diols in an amount of 1.01 to 2.0 times the mol of the acid component are mixed at a temperature of 200 to 290 ° C. For about 2 to 10 hours to obtain a low polymer. Water generated in the esterification step is distilled off through the separation tower, but excess polyol may be extracted from the bottom of the separation tower. In some cases, the extracted polyol can be reused as well as the recovered polyol at the time of polycondensation.

When the esterification reaction is carried out, a known esterification catalyst or polycondensation catalyst, a color tone improver such as a cobalt compound, a fluorescent agent or a dye, a pigment such as titanium dioxide, a bromine compound or a phosphorus compound may be used. An additive such as a flame retardant may coexist.

The polycondensation step is carried out under reduced pressure at a temperature of 200 to 290 ° C. until a desired degree of polymerization (usually 3 to 50) is obtained.
Polycondensation is usually performed with antimony, titanium, germanium,
The reaction is performed in the presence of a catalyst selected from compounds such as tin and zinc, and a stabilizer such as phosphoric acid, phosphorous acid, trimethyl phosphate, or triethyl phosphate is used as needed.

In the case of going through the depolymerization step, the degree of polymerization is once increased to a desired degree of polymerization or higher (usually 80 to 120) in the polycondensation step which is the previous step, and then the depolymerization agent And a required amount of a polyol such as trimethylolpropane and neopentyl glycol and / or a polycarboxylic acid such as isophthalic acid and trimellitic acid or an acid anhydride thereof, at a temperature of 200 to 290 ° C. and at normal pressure and / or pressure. The depolymerization reaction is carried out under pressure for about 1 to 3 hours.

In the present invention, it is necessary to remove the solid components contained in the distillate, and to reuse the obtained polyol in the esterification reaction at a weight ratio of 0.05 to 0.49 with respect to 1 of the purified polyol. Here, the purified polyol is obtained by purifying an unused high-purity polyol and / or a polyol distilled off in a process for producing a polyester resin for powder coating by distillation, and having a boiling point of 150 to 250 ° C under normal pressure. Minute purity is usually 97 to 100%.

When the recovered polyol is used in a weight ratio of 0.05 to 0.49, preferably 0.15 to 0.49, and most preferably 0.25 to 0.49 with respect to the purified polyol 1, the color tone of the polyester resin for powder coating obtained becomes It is almost the same as that of the case using only. When this ratio exceeds 0.49, the color tone becomes poor, and when it is less than 0.05, the amount of the polyol to be reused is small, so that the cost is not substantially reduced and both are not preferable. On the other hand, when the solid component contained in the distillate is used after being removed so as to be 1% by weight or less, the amount of the insoluble matter described below of the obtained resin for powder coating is smaller than that when only the purified polyol is used. It is almost the same as the one without any difference. If this proportion exceeds 1% by weight, the amount of insolubles increases and the solubility deteriorates, which leads to unevenness on the coating film surface and poor gloss, which is not preferred.

The solid components contained in the distillate can be removed by general-purpose techniques such as centrifugation and filtration. Any means can be used so long as the solid components can be substantially reduced to 1% by weight or less. There is no particular limitation.

According to the present invention, a polyester resin for powder coating having the same quality as that obtained when a fully purified polyol is used as the polyol can be obtained, but in addition to this, the polymerization catalyst contained in the recovered polyol can be recovered. is there. For example, in the case of an antimony compound, about 20% of the charged amount is contained in the recovered polyol, and in the case of a germanium compound, about 30% of the charged amount is contained in the recovered polyol. Therefore, when the recovered polyol is used, the amount of the catalyst can be reduced. It has the following effects,
This also leads to cost reduction.

[0020]

Next, the method of the present invention will be described more specifically with reference to examples. In addition, each characteristic value in a reference example, an example, and a comparative example is a thing measured by the following method. (a) Intrinsic viscosity [η] It was determined from the solution viscosity measured at 20 ° C in a mixed solvent of an equal weight of phenol and ethane tetrachloride. (b) Color Tone A resin that passes through a 7-mesh screen and does not pass through a 16-mesh screen is packed in a cell for powder measurement, and is measured using a Hunter-type color difference meter conforming to the ASTM standard in UCS system L, a, and b displays. Then, the b value was obtained. (c) Amount of Insolubles After dissolving 300 g of the resin in tetrahydrofuran, the resin was filtered through a 300-mesh filter to determine the weight (mg) of the insolubles on the filter.

Reference Example 1 1545 parts of terephthalic acid (TPA) and 172 parts of isophthalic acid (IPA) as raw materials for the acid component, 538 parts of ethylene glycol (EG), 765 parts of neopentyl glycol (NPG) and 765 parts of trimethylolpropane as the polyol component (T
P) 54 parts were charged into the esterification reaction tank in about 1 hour, and after the completion of the charging, the temperature was raised to 250 ° C. in about 4 hours with stirring and kept for 2 hours with stirring to increase the reaction rate. Next, the esterification reaction completed oligomer was transferred to a polymerization tank. Antimony trioxide as a polymerization catalyst
After adding 40 parts of 1.5% by weight EG solution, the pressure in the bath was reduced to 50 Torr in 30 minutes while maintaining the temperature in the bath at 250 ° C., and a polycondensation reaction was performed for a total reaction time of 2 hours and 30 minutes. I got The properties of the obtained resin are intrinsic viscosity [η] 0.29
6, the color tone (b value) was 8.6, and the content of insolubles was 0.1 mg. (Reference Example 1 in Table 1) By this reaction, 448 parts of a distillate was distilled. The operation of Reference Example 1 was repeated for four batches, and they were mixed to obtain a re-used distillate, which was used after being subjected to the following pretreatment. Pretreatment 1 of Reused Distillate 448 parts of the reused distillate were removed of solid components with a 10 μ filter to obtain 436 parts of a recovered polyol. When the composition of this recovered polyol was analyzed, 178 parts of EG, NP
G of 254 parts and 4 parts (0.9% by weight) of solid components. Pretreatment 2 of re-used distillate The composition of 435 parts of the re-used distillate was analyzed without removing solid components. The result was 178 parts of EG, 251 parts of NPG and 6 parts (1.4% by weight) of solid components. Was. Pretreatment 3 of Reused Distillate 476 parts of the reused distillate were removed of solid components with a 10 μ filter to obtain 466 parts of a recovered polyol. When the composition of this recovered polyol was analyzed, 192 parts of EG, NP
G of 270 parts and 4 parts of solid components (0.9% by weight). Pretreatment 4 of Reused Distillate The solid component was removed from 381 parts of the reused distillate with a 10 μ filter to obtain 373 parts of a recovered polyol. When the composition of this recovered polyol was analyzed, 152 parts of EG, NP
G, 218 parts, and 3 parts (0.8% by weight) of a solid component.

Example 1 Instead of 538 parts of purified EG, 765 parts of NPG and 54 parts of TP (total of 1357 parts) used in Reference Example 1, 360 parts of purified EG,
511 parts of NPG and 54 parts of TP (925 parts in total) and a total of 436 parts of the recovered polyol obtained by removing the solid components in the pretreatment 1 of the reused distillate (178 parts of EG, 254 parts of NPG, 4 parts of solid components) ), That is, the reaction was carried out in exactly the same manner as in Reference Example 1 except that 0.47 of a recovered polyol containing 0.9% by weight of a solid component was used with respect to the purified polyol 1 in a weight ratio to obtain a polyester resin for powder coating. The properties of the obtained resin were almost the same as those of the resin of Reference Example 1 with an intrinsic viscosity [η] of 0.297, a color tone (b value) of 8.6 and an insoluble content of 0.2 mg. (Example 1-1 in Table 1) The distillate distilled out in Example 1 was reused in the same manner as in Example 1, and was repeatedly used for the next reaction. A polyester resin was obtained. The characteristics of the resin obtained in the 10th batch were intrinsic viscosity [η] 0.299, color tone (b value) 8.8, and content of insoluble matter 0.1 mg. It was quality. (Example 1-10 in Table 1)

Comparative Example 1 Instead of 538 parts of purified EG, 765 parts of NPG and 54 parts of TP (1357 parts in total) used in Reference Example 1, 360 parts of purified EG,
514 parts of NPG and 54 parts of TP (928 parts in total) and were obtained without removing solid components in pretreatment 2 of the re-used distillate.
Total amount of recovered polyol containing 1.4% by weight of solid components 435
Parts (EG 178 parts, NPG 251 parts, solid component 6 parts), the reaction was carried out in exactly the same manner as in Reference Example 1 to obtain a polyester resin for powder coatings. The characteristics of the obtained resin were an intrinsic viscosity [η] of 0.295, a color tone (b value) of 8.7, and an insoluble content of 5.2 mg. (Comparative Example 1-1 in Table 1) The distillate distilled out in Comparative Example 1 was reused in the same manner as in Comparative Example 1 and repeatedly used for the next reaction. A resin was obtained. The characteristics of the resin obtained in the fifth batch were an intrinsic viscosity [η] of 0.297, a color tone (b value) of 8.8, and an insoluble content of 4.9 mg.
(Comparative Example 1-5 in Table 1) As is clear from the results of Comparative Example 1, when a recovered polyol containing more than 1% by weight of a solid component was used, insolubles were reduced as compared with the characteristics of the resin of Reference Example 1. Many were not preferred.

Comparative Example 2 In place of 538 parts of purified EG, 765 parts of NPG and 54 parts of TP (1357 parts in total) used in Reference Example 1, 346 parts of purified EG,
495 parts of NPG and 54 parts of TP (a total of 895 parts) and a total of 466 parts of the recovered polyol obtained by removing the solid components in the pretreatment 3 of the reused distillate (192 parts of EG, 270 parts of NPG, 4 parts of solid components) That is, the reaction was carried out in exactly the same manner as in Reference Example 1 except that 0.52 of a recovered polyol containing 0.9% by weight of a solid component was used with respect to the purified polyol 1 in a weight ratio to obtain a polyester resin for powder coating. The properties of the obtained resin are as follows: intrinsic viscosity [η] 0.299, color tone (b value) 9.5, and insoluble content.
0.2 mg. (Comparative Example 2-1 in Table 1) The distillate distilled out in Comparative Example 2 was reused in the same manner as in Comparative Example 2 and repeatedly used for the next reaction. A resin was obtained. The characteristics of the resin obtained in the fifth batch were an intrinsic viscosity [η] of 0.298, a color tone (b value) of 12.0, and an insoluble content of 0.2 mg.
(Comparative Example 2-5 in Table 1) As is clear from the results of Comparative Example 2, purified polyol 1
If the recovered polyol was used in an amount exceeding 0.49 (parts by weight) with respect to (parts by weight), the color tone of the resin gradually deteriorated each time the reaction was repeated, which was not preferable.

Reference Example 2 1444 parts of TPA as a raw material for an acid component and 378 parts of EG and 779 parts of NPG as a polyol component were added to an esterification reaction tank in about 1 part.
After the charging, the raw materials are stirred for about 4 hours.
The temperature was raised to 250 ° C. over a period of time and maintained for 2 hours while stirring to increase the reaction rate. Next, the esterification reaction completed oligomer was transferred to a polymerization tank. After adding 40 parts of an EG solution containing 1.5% by weight of antimony trioxide as a polymerization catalyst, the temperature in the vessel was raised from 250 ° C. to 280 ° C. in one hour while the temperature was increased by 3 hours.
The pressure was reduced to Torr, and a polycondensation reaction was performed for a total reaction time of 3 hours and 30 minutes to obtain a polymer having a desired degree of polymerization or more. After adding 84 parts of trimellitic acid as a depolymerizing agent to this, a depolymerization reaction was performed for 2 hours during a total reaction time of 2 hours while the temperature in the tank was lowered from 280 ° C to 250 ° C in 1 hour under normal pressure. A polyester resin was obtained. The properties of the obtained resin were an intrinsic viscosity [η] of 0.259, a color tone (b value) of 7.4, and an insoluble content of 0.1 mg. (Reference Example 2 in Table 1)

Example 2 Instead of 378 parts of purified EG and 779 parts of NPG (total of 1157 parts) used in Reference Example 2, 226 parts of purified EG and NPG were used.
561 parts (787 parts in total) and a total of 373 parts (EG 152) of a recovered distillate of a brand different from that of Reference Example 2 obtained by removing solid components in pretreatment 4 of the reused distillate of Reference Example 1 Department, NPG 218
Parts, 3 parts of solid components), that is, a recovered polyol containing 0.8% by weight of solid components with respect to 1 purified polyol
The reaction was carried out in exactly the same manner as in Reference Example 2 except that 0.47 was used, to obtain a polyester resin for powder coating. The properties of the obtained resin were almost the same as those of Reference Example 2 with an intrinsic viscosity [η] of 0.260, a color tone (b value) of 7.6, and an insoluble content of 0.1 mg. (Example 2 of Table 1)

Table 1 shows the production conditions and characteristic values of the polyester resin in Reference Examples, Examples and Comparative Examples.

[0028]

[Table 1]

[0029]

According to the present invention, the distillate distilled in the production process can be reused in the esterification reaction as a polyol component without performing a rectifying operation. The present invention provides a method for producing a polyester resin for powder coating, which is advantageous to the present invention.

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Claims (3)

[Claims] 1. A polyester for powder coatings comprising at least an esterification step and a polycondensation step from terephthalic acid or an acid component mainly containing the same and a polyol component mainly containing two or more diols having 2 to 8 carbon atoms. In producing the resin, the distillate generated as a part of the polyol component in the esterification step in the subsequent polycondensation step is removed so that the solid component contained therein becomes 1% by weight or less. In this case, the ratio of the reused polyol used in the esterification step was 0.05% with respect to the purified polyol 1.
A method for producing a polyester resin for powder coating, wherein the weight ratio is adjusted to 0.49. 2. The process for producing a polyester resin for a powder coating according to claim 1, wherein isophthalic acid is used together with terephthalic acid as an acid component. 3. The method according to claim 1, wherein the diol is ethylene glycol or neopentyl glycol.