JPS6317105B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyester resin composition for powder coatings with stable quality and economically. In recent years, powder coatings have been steadily increasing in demand as resource-saving and non-polluting coatings in various industries such as building materials, home appliances, agricultural machinery, and automobiles. In this case, as materials for powder coatings, polyester resins are also used in large quantities in addition to epoxy resins and acrylic resins. Among them, polyester resin compositions consisting of saturated polyester resins whose terminal groups are mainly carboxyl groups and epoxy resins have almost no volatile components during the curing reaction, so they can be used over a wide range of film thicknesses of about 20 to 200 microns. It is one of the most preferred materials for powder coatings, as it is capable of forming a smooth and beautiful coating film without (boiling), and is also capable of forming a physically or chemically excellent coating film. However, the above-mentioned polyester resin composition consisting of a polyester resin whose terminal group is mainly a carboxyl group and an epoxy resin reacts and hardens itself when the temperature exceeds a certain temperature. Uniform mixing at a low temperature and/or in a short time is essential in order to form a smooth and beautiful coating film. Furthermore, powder coatings are often used continuously in large quantities, and since the recovered coating materials are reused, it is extremely important to provide materials that are stable over a long period of time. The present inventors have conducted intensive research to produce such a polyester resin composition for powder coatings in a stable and economically advantageous manner, and have found that the objective can be achieved by developing the following method. did it. That is, the present invention has a softening point of 60 to 120°C and an acid value of
20 to 80 and in which at least 60% of the terminal groups are carboxyl groups, and an epoxy resin having two or more glycidyl groups in the molecule. , an epoxy resin that is liquid at room temperature is used as the epoxy resin, and a saturated polyester resin in a molten state maintained at a temperature of 140°C to 200°C and an epoxy resin in a molten state held above the melting temperature are simultaneously used. A method for producing a polyester resin composition for powder coatings, which comprises quantitatively supplying the composition to a kneader equipped with one or more screws and continuously mixing and discharging at a temperature of 120 to 150°C. It is. The polyester resin used when carrying out the method of the present invention has aromatic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid. group, alicyclic, aliphatic dicarboxylic acids or their lower dialkyl esters, trimellitic acid,
Polyhydric carboxylic acids such as trimezic acid and pyromellitic acid, their anhydrides, and lower alkyl esters are used as acid components, and ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,3-butane are used as acid components. Diol, 1,4-
Butanediol, 1,5-pentanediol,
Dialcohols such as 1,6-hexanediol, diethylene glycol, neopentyl glycol, and 1,4-cyclohexanedimethanol, and polyhydric alcohols such as trimethylolethane, trimethylolpropane, and pentaerythritol are used as alcohol components. Then, if necessary, esterification or transesterification is carried out in the presence of a catalyst at a temperature of 150 to 250°C, and a polycondensation catalyst such as antimony trioxide, germanium oxide, or tetrabutyl titanate is added to the resulting low polymer. hand
A polyester with a high degree of polymerization is obtained by performing a polycondensation reaction at a temperature of 200 to 300°C under reduced pressure of 0.5 mmHg or less. Furthermore, using the above-mentioned dicarboxylic acid or/and polycarboxylic acid in the necessary amount depending on the acid value and average degree of polymerization of the polyester resin for this purpose, the temperature is 200 to 280°C.
A depolymerization reaction is carried out to obtain a polyester resin, which is one of the most preferable methods in terms of stable quality.
It is one. This may be a polyester resin obtained simply by an esterification reaction, or a polyester resin obtained by a polycondensation reaction in addition to an esterification reaction. However, when using polyester resin produced by any method as a material for powder coatings, its softening point is
It is necessary to adjust the temperature to 60-120°C, preferably 80-100°C. In other words, resins with a softening point of 60°C or lower may have storage stability problems when used as such or when prepared as a powder coating, while resins with a softening point of 120°C or higher may be mixed with pigments etc. and used as a powder. The workability when preparing a body paint becomes extremely poor, and it becomes difficult to form a smooth and beautiful paint film by painting or baking. Further, it is very important to adjust the acid value of the polyester resin to a range of 20 to 80 in order to balance the workability of forming a paint, the storage stability of the paint, and the performance of the coating film. In other words, polyester resins with an acid value of less than 20 usually have a high average degree of polymerization and a high melt viscosity, making it difficult to work with paints, and making it difficult to form a smooth and beautiful paint film during coating and baking. Become. On the other hand, polyester resins with an acid value exceeding 80 have a low average degree of polymerization, and this also results in poor storage stability of the paint. In addition, 60% or more, preferably 80% or more of the terminal groups of such polyester resin are carboxyl groups, and the reaction with the glycidyl group contained in the epoxy resin becomes dominant in the curing reaction when baking the coating film. Therefore, it is desirable that the volatile components be so small as to be almost negligible. In carrying out the method of the present invention, epoxy resins that can be used include, for example, epoxy resins that are liquid at room temperature, such as epi-bis type epoxy resins. When melt-mixing polyester resin and epoxy resin, uniform mixing is achieved by quantitatively feeding the molten polyester resin and epoxy resin to a mixer, mixing them continuously, and discharging them. It also becomes possible to prepare extremely stable polyester resin compositions. In this case, conventionally,
Compared to the usual process of cooling and powdering polyester resin produced in a molten state, premixing it with epoxy resin, and then remelting and mixing it, temperature control during the preparation of polyester resin compositions is much easier and quality can be improved. Not only can this be stabilized, but energy consumption can also be significantly reduced. The temperature of the polyester resin supplied to the kneader is selected within the range of 140 to 200°C. In other words, in the case of high temperatures exceeding 200°C, even if mixing and dispensing are performed in a relatively short time, the mixture will partially react with the epoxy resin, so even slight variations in conditions will cause uneven quality. On the other hand, at a low temperature of less than 140°C, the melt viscosity becomes high and the power consumption of the kneading machine increases, and if the difference in viscosity from the epoxy resin is too large, the kneading state becomes poor. Polyester resin and epoxy resin are continuously supplied to the mixer using a metering pump such as a gear pump. The kneader is equipped with one or more screws and has mixing and conveying functions at the same time. A kneader that circulates a heat medium through the barrel of the kneader and, if necessary, the screw, and is capable of heating or cooling, is the polyester that consumes the least amount of power in the kneader in the range of 120 to 150°C and can be dispensed. The heating medium temperature is set and used so that the temperature of the resin composition becomes the lowest. Next, the method of the present invention will be specifically explained with reference to Examples and Reference Examples. Example 1 Terephthalic acid 747Kg, ethylene glycol 279
Kg, neopentyl glycol 468Kg was taken, 150~
A low polymer is prepared by carrying out an esterification reaction at 250°C and removing 160 kg of water. Next, 262g of antimony trioxide was added as a catalyst and a polycondensation reaction was carried out at 280°C under reduced pressure of 0.2mmHg to prepare a highly polymerized polyester, and then 47kg of trimellitic acid was added and a depolymerization reaction was carried out at 250°C to soften it. A polyester resin having a temperature of 95°C, an acid value of 35, and a hydroxyl value of 3 was prepared. Subsequently, an epoxy equivalent of 190 g/equivalent at room temperature (25
℃) in a twin-screw kneader (Ikegai Iron Works RC) under the conditions shown in Table 1 below.
-100 type) using a gear pump together with polyester resin, and continuously mixed and dispensed. In this way, polyester resin compositions shown in Table 2 were prepared.

【table】

【table】

[Table] Reference Example 1 A polyester resin composition was prepared in the same manner as in Example 1 under the conditions shown in Table 3 below, and the results shown in Table 4 were obtained.

【table】

【table】

[Table] Reference Example 2 Polyester resin was supplied in pellet form (at room temperature) using a rotary valve in the same manner as No. 1 of Example 1, and mixed and dispensed, but semi-molten material accumulated in the receiving hole of the kneader. Therefore, continuous operation was extremely difficult. Reference Example 3 Nos. 1 to 9 of Example 1 and Nos. 1 and 34 of Reference Example 1
Per 100 parts by weight of each polyester resin composition, 30 parts by weight of titanium oxide, 1 part by weight of calcium stearate as a catalyst, 1 part by weight of Modaflow (trade name) manufactured by Monsanto Co. as a coating surface conditioner, and PR manufactured by Busu Co., Ltd.
- After kneading into powder using a 46 type co-kneader, BT
It was painted on a #37 steel plate and baked at 190°C for 30 minutes to evaluate the coating film performance, and the results shown in Table 5 were obtained.

【table】

[Table] However, the coating film performance was evaluated using the following method. 60° specular reflectance: According to JIS Z8741. Erichsen test: According to JIS Z2247. Impact resistance test: Measured at 1/2″-1Kg using a Dupont impact tester. Boiling water resistance test: Perform Erichsen test after processing according to JIS K6902. Salt water resistance test: Cut a cut on the surface of the test piece. Soaked at 40℃
in a 5% sodium chloride aqueous solution spray atmosphere.
After standing for 250 hours, remove the coating using adhesive tape and measure the peeling width. As is clear from a comparison between Examples and Reference Examples, implementing the method of the present invention exhibits exceptionally superior actions and effects compared to conventional methods. This achieves uniform mixing of the polyester resin whose terminal group is mainly a carboxyl group and the epoxy resin with virtually no reaction, making it possible to produce polyester resin for powder coatings with stable quality. It shows that.

Claims (1)

[Claims] 1 Powder coating made of a saturated polyester resin with a softening point of 60 to 120°C, an acid value of 20 to 80, and at least 60% of the terminal groups are carboxyl groups, and an epoxy resin having two or more glycidyl groups in the molecule. In the method for producing a polyester resin composition for use, an epoxy resin that is liquid at room temperature is used as the epoxy resin, a saturated polyester resin that is in a molten state maintained at a temperature of 140 ° C to 200 ° C, and a saturated polyester resin that is maintained at a temperature above the melting temperature. The molten epoxy resin is simultaneously fed quantitatively to a kneader equipped with one or more screws at 120 to 150°C.
A method for producing a polyester resin composition for powder coatings, which comprises continuously mixing and dispensing at a temperature of .