The influence of moisture on the storage stability of polyester resin for powder coatings (1)

Abstract
The effect of moisture on the storage stability of polyester resins is determined by studying the water absorption of polyester resins by different endases, acid and hydroxy sizes, residual monomers, and particle size of polyester particles, and by comparing changes in the glassing temperature of test polyester resins with DSCs.
powder polyester absorbent
powder coating performance conditions, storage stability is an important indicator to evaluate the quality of a powder coating, and because polyester in polyester powder coating will generally account for more than 50% of the powder coating formulation, therefore, polyester resin storage stability will affect the storage stability of powder coating. Therefore, it is necessary to study the storage stability of polyester resin

. The poor stability of polyester storage is mainly due to the low glucification temperature of polyester and the reunification and lumping of polyester particles under certain environmental conditions. There are many factors that affect the temperature of polyester glassing, such as the flexibility of molecular chains, the interaction between molecular chains, crosslinking, co-concentration, molecular weight and molecular weight distribution, the amount and type of additives, moisture, and so on. Here we mainly study and analyze the effects of water, which is often the most common and common factor in the factors, because water in polyester played a role in plasticizer, will reduce the glass temperature of polyester, thereby affecting the storage stability of polyester. Then, the water absorbed by general polyester is mainly from gaseous water in the environment, and the polymer absorbs gaseous water mainly affected by the hydrophobial group contained in the polymer. Among them, there are many factors that affect the water absorption of polyester, we study and understand these factors, we can better understand the reasons for the poor stability of polyester storage, so as to guide the production and storage process of polyester and powder coatings.
Factors
1 The effect of polyester residual hydroxyl value on polyester absorbent and glassy temperature
because hydroxyl is hydrophobic group, polyester absorbs water, water on polyester has a plasticizer effect, will make polyester glass temperature lower, the more water absorption, the more the glass temperature will decrease. Figure 1 is a water-absorbing experimental comparison of three hydroxyl polyesters with different residual hydroxyl polyesters with the same acid value (acid value 35mg KOH/g), and Figure 2 is a comparison of the drop in polyester glassing temperature obtained by DSC testing after their corresponding water absorption experiments. From the two pictures we can see that the residual hydroxyl between 5-15 mg KOH/g, polyester absorbent difference is not large, glass temperature drop difference is not large. This shows that in a certain range, the residual hydroxyl value of polyester absorption is not very different, the effect on the glass temperature of polyester is not obvious. It is possible that the effects of residual hydroxy values are obscured by the absorbent nature of the carboxyl, which is more polar than hydroxyl.
Figure 1 The effect of the acid value of the same acid value (acid value 35mgKOH/g) on the suction of three hydroxyl polyesters with different residual hydroxyl polyesters



IPA-sealed polyester
Since the carbox is hydro-based and can form hydrogen bonds with water, it is worth exploring the effects of acidity on polyester absorption and glassing temperature. Figures 3 and 4 are the results of water-absorbing tests of several acid-sized polyester resins often used in 4 practical applications and the comparison of glassed temperature reductions. From this we can get that the higher the acid content, the greater the absorption rate, the greater the decreasing glassy temperature value.
results of the water-absorbing test of the polyester resin at the end of the IPA
and the results of the glassing temperature reduction after the water-absorbing test of the polyester resin at the end of the IPA seal in Figure 4
TMA-sealed polyester
Figure 5 Figure 6 is the TMA seal end polyester resin, four different acid values of the absorption rate and water absorption before and after the glass temperature drop results, from which we can conclude that with the increase of acid value, polyester absorbent, glass temperature drop more.
Figure 5 TMA end polyester resin absorbent test results
Figure 6 TMA sealing end polyester resin absorbent test after the glass temperature reduction value comparison results
finished to be continued
Source: 2018 China Powder Coatings and Coatings Industry Annual Meeting
Wei Haitao, Wang Shaofeng, Xu Guohui (Zhejiang Guanghua Technology Co., Ltd.)
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