Abstract: This paper introduces the synthesis of a kind of polyester resin for outdoor TGIC curing physical matting powder coating. The resin has high Tg. The effects of the storage, weatherability of polyester resin and coating as well as different matting agent, dosage of matting agent and extrusion process conditions on the comprehensive properties of the coating film are investigated.
The polyester has low selectivity to the matting agent, and the prepared low gloss powder coating has excellent surface leveling and matting effect.
1. With the continuous pursuit of fashion life and the change of aesthetic concept, low light powder coating is more and more popular, and its proportion in the product structure of powder coating is also increasing.
With the increasing market demand, more and more enterprises begin to pay attention to the production and application of low gloss powder coating.
Polyester resin as the main raw material of powder coating will directly determine the performance of powder coating. At present, TGIC curing physical extinction system is more difficult than indoor epoxy curing physical extinction system in technology.
It is unsatisfactory in the aspects of extinction effect, surface fineness, gloss stability, and the selectivity of extinction agent. It is of great significance to develop an excellent TGIC curing physical extinction polyester resin.
In this paper, a special polyester resin for TGIC curing physical matting powder coating was synthesized. Tg of polyester resin was analyzed by DTA. The storage stability, weatherability of low light type coating and the influence of different kinds of physical matting agent, dosage of matting agent and extrusion process on the coating performance were tested.
2. Experimental part
2.1 experimental materials and instruments neopentyl glycol; 1,4-cyclohexanedimethanol (CHDM); terephthalic acid (PTA); isophthalic acid (IPA); adipic acid; azelaic acid;
1,4-cyclohexanedicarboxylic acid (CHDA); esterification catalyst (f4100); antioxidant 168, antioxidant 1010; curing accelerator; physical matting agent.
Keywords 3000ml small glass reactor complete set and mixing motor; cdr-4p differential thermal analyzer; dv-ii rotary viscometer; DF-4 computer asphalt softening point tester; qcj film impactor;
GT-III type gel time tester; TT210 coating thickness gauge; Micro-tri-gloss gloss tester. QUV / basic accelerated weathering test chamber manufactured by q-panel company of the United States.
2.2 for the synthesis of polyester resin, the raw material diol, dicarboxylic acid and other reaction materials are put into the reactor according to the formula amount, and nitrogen is filled for protection. When the temperature rises to 170 ℃, esterified water begins to be produced, and continues to rise to 255 ℃, when there is no esterified water in the reaction, colorless and transparent resin is obtained.
Add polyacid end capping agent, and keep the temperature at 255 ℃ for 90 minutes. After the reaction, gradually vacuumize to (- 0.095mpa), react to the acid value between 28-34mgkoh / G under the vacuum condition of 255 ℃, stop the vacuum, cool to 200 ℃, add various additives, stir for 10 minutes, and discharge.
2.3 preparation of low gloss powder coating sample: the polyester resin, physical matting agent, pigment, filler, leveling agent, etc. are added into the batch container according to the formula amount, fully stirred and evenly, then the powder coating is obtained by melting extrusion and crushing by the extruder.
Electrostatic spray on the sample plate and place it in the curing oven to obtain the curing film. The basic formula of coating is shown in Table 1.
2.4 the determination of acid value and softening point of performance characterization polyester resin shall be determined according to the corresponding national standard. The melting viscosity was measured by dv-ii rotary viscometer. TG was measured by cdr-4p differential thermal analyzer at 10 ℃ / min. The coating performance shall be determined according to the corresponding national standard test method. The storage stability of powder shall be tested in accordance with GB / T 21782.8-2008 evaluation of storage stability of thermosetting powder. The aging evaluation of paint film shall be carried out in accordance with GB / T 1766-2008 aging rating method for paints and varnishes. Artificial accelerated aging test conditions shall be tested in accordance with GB / T 14522-93 (accelerated test method for artificial climate of plastics, coatings and rubber materials for mechanical industrial products).
3. Results and discussion
3.1 physical and chemical properties of polyester resin appearance: colorless or light yellow transparent particles; acid value: 28.0-34.0mgkoh/g; melt viscosity (200 ℃): 1000-3000cp; glass transition temperature (TG) 64.2 ℃; softening point (TF): 110-125 ℃. Polyester resin TG is shown in Figure 1.
Through the complex multi-level chemical reaction and incompatibility between the polyester resin and the physical matting agent in the process of powder melting and curing, the micro uneven surface of the film is produced, the light scattering is enhanced, the reflection is weakened, and the glossiness is reduced.
The gloss and leveling of low gloss powder coating film are affected by the base material, filler and matting agent. For polyester resin, improving the leveling of low gloss powder coating and reducing the gloss of powder can be realized by reducing the viscosity of polyester resin and the reaction speed of polyester resin.
Reduce the viscosity of polyester resin, increase the area of film leveling and curing in unit time, so as to achieve good leveling.
The curing accelerator is used to adjust the reaction speed of polyester resin, so that when it is mixed with the matting agent, it can not only play the role of matting, but also prevent the film from leveling and curing too fast, resulting in the poor leveling of the film.
3.2 the storage stability test results of polyester resin and coating are shown in Table 2, and the storage stability of powder coating is shown in Table 3.
It can be seen from the data in Table 2 and table 3 that the storage stability of the polyester resin is very good, and there is no agglomeration after 28d.
After 28 days' experiment, it was found that the less the amount of matting agent, the less the gelation time fluctuation, and the higher the gloss stability.
At the same time, the gloss of low gloss powder coating increases with time, and the leveling is also worse. The main reason is that the composition of the matting agent has changed under long-term storage at 40 ℃.
3.3 the influence of different matting agent and dosage on the comprehensive performance of the film the composition of outdoor physical matting agent produced by different auxiliary manufacturers is different. When it is used with polyester resin to prepare low gloss powder coating, there will be some differences in matting effect, leveling, fineness and other aspects. Figure 4 and figure 5 show that the difference of the matting agent results in the difference when the film solidifies.
As shown in Figure 4, there are many differences in the composition of the three kinds of physical matting agents from different manufacturers, resulting in the difference of the initial curing temperature in the preparation of low light powder coating as shown in Figure 5.
When the curing condition is taken as the fixed value and the glossiness of the film is fixed, the dosage of the three matting agents is different. In the case of a certain amount of matting agent, there will be differences in glossiness.
Table 6 shows that the comprehensive performance of the film varies with the amount of matting agent from different manufacturers; table 7 shows that the comprehensive performance of the film will change with the amount of matting agent.
At the same time, it can be seen from the peak valley temperature of the glass transition in Fig. 5 that there are certain differences in the storage stability of the low light powder prepared by each matting agent.
3.4 influence of extrusion process on comprehensive properties of coating
It can be seen from table 8 that the extrusion process has a great influence on the comprehensive properties of low gloss powder coating. Too high extrusion temperature will cause sanding on the surface of the film; the faster the rotation speed is, the faster the local temperature in the screw rises, which will easily lead to the poor leveling; the worse the mixing effect is, the better the extinction effect is.
3.5 the weatherability of low gloss powder prepared by different matting agents is a very important indicator for outdoor powder coatings. The weatherability of the polyester resin is different from that of the low gloss powder coating prepared by different manufacturers with the gloss below 20%, as shown in Table 9, and the effect is not very good.
4. Conclusion
(1) In this paper, an outdoor TGIC curing physical matting polyester resin ts2700 was synthesized. The resin has high glass transition temperature and good storage stability.
(2) The low gloss powder coating made from ts2700 has low gloss, excellent leveling, general weather resistance, low selectivity for matting agent, and good matching with most matting agents on the market.
(3) There are some differences in the matting agents from different manufacturers, which will lead to the differences in the comprehensive properties of powder coatings. Matting agents often play a decisive role in the comprehensive properties of coatings. Source: Zhejiang Tiansong New Material Co., Ltd
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