Talking about the influencing factors and improvement methods of polyester powder coating's water seepage resistance

Wen/Hong Xianbo, Cai Jinshu
Guangdong Huajiang Powder Technology Co., Ltd.
Summary: This paper mainly from the polyester resin type, special water-resistant polyester resin type, filler and curing conditions and other aspects of the impact on the polyester powder coating water-resistant properties and improvement methods.
1 Foreword
Aluminum alloy building profiles are the main structural materials of doors, windows and curtain walls today, widely used in the world, unscathed aluminum alloy profile appearance is single, and easy to be corroded in the humid atmosphere, so it is difficult to meet the requirements of high decoration and weather resistance of buildings, in order to improve decorative effects, enhance corrosion resistance and extend service life, aluminum profiles generally have to be surface treatment, and powder spraying is an important trend in the development of aluminum profiles at this stage.
with the progress of science and technology, environmental protection, the market demand for powder coatings is also growing, the quality of powder requirements will be higher and higher

. Building powder coatings are usually thermoclytic powder coatings, which react with each other between reactive groups of thermosolytic resins and reactive groups of curing agents, and eventually cure into coatings of polymer compounds. Although the coating film is not a strong water seepage substance, but in the closed and high heat and high humidity environment, moisture is not volatile, it will penetrate through the gap between the coating film to the inside leading to film color change, loss of light. The relative humidity in the south is large, the temperature is high, sometimes dark brown powder aluminum profile after tearing off the protective film will appear "water spot" phenomenon, the relevant parties may have a certain quality dispute, so it is necessary to explore the reasons affecting the aluminum profile with dark brown polyester powder coating water resistance. This paper mainly studies and analyzes the types of polyester resins, the types of special water-resistant polyester resins, fillers and curing conditions, etc.
2 Experimental part
2.1 Experimental raw materials and laboratory equipment
2.1.1 Experimental raw materials
polyester resin, special water-resistant polyester resin, TGIC, highlighter, filler, leveling agent, brightener, wax powder, resting incense, titanium white powder, carbon black, iron red, iron yellow and so on.
2.1.2 Experimental equipment
electronic scales, extruders, grinders, golden horse guns, electric ovens, gloss meters, color difference meters, impact testers and so on.
2.2 Experimental process
according to the actual formula of the experiment weighing raw materials, physical mixing uniformly through the extruder melt extrusion, and finally made in line with the requirements of the dark brown model, according to the requirements to detect water seepage performance.
2.3 detection method
to expand the full text 2.3.1 detection method of the specific steps
a, 5 layers of diameter 55mm of circular qualitative filter paper stacked together on the surface of the sample;
b, drop 1.5 ml 0.1 ml distilled water, and then cover the sample with a surface dish, seal the edge of the surface dish with glass glue to prevent steam leakage;
c, put the sample covered with surface dish in a constant temperature tank at 58 degrees C for 4 hours;
d, cool 15min, remove the surface dish and filter paper.
2.3.2 Chroma Measurement
The color difference after the experiment was measured with a chroma meter, i.e. the color difference between the covered part of the filter paper and the unsealed color difference, measuring 3 points, taking the color difference value from the middle point, and remembering E, L, a, and b.
3 Experimental results and analysis of the effect of
3.1 polyester resin on the water-resistant properties of powder coatings
Polyester resins, as one of the main film-forming substances of outdoor powder coatings, are the most important components that determine the coating properties of powder coatings. Saturated polyester resin is polyols and polyacids after esterification, polymerization reaction, alcohols are mainly used in new glycol (NPG), glycol (EG), glycol (DEG), propylene glycol and so on, acids are mainly benzoic acid (PTA), interbenzene (IPA), hexic acid, fumaric acid and so on. Among them, alcohol NPG and propylene glycol have a stable chemical structure, water-resistant performance after synthetic polyester resin is also superior to other alcohols, of which acid PTA, IPA have benzene ring structure, because its benzene ring structure has a very stable chemical structure, after synthetic polyester water-resistant properties are also more than hetdiacids, fumaric acid and other fatty family acids have obvious advantages.
3.1.1 Effect of polyester resins with different acid values on the water-resistant properties of powder coatings

can be seen from Table 1, Formula 1 has the best water resistance, followed by Formula 2 and Formula 3, followed by Formula 4, and the worst is Formula 5. It is stated that the water resistance of polyester resins with different acid values is larger, the greater the acid value, the better the water resistance, and the smaller the acid value, the worse the water resistance. The reason is that the higher the acid value, the more curing agents required for crosslinking reaction, the greater the cross-linking degree of the coating film formed, the denser the coating film, the more difficult it is for water molecules to penetrate into, the less obvious the water spots tested for seepage. On the contrary, the smaller the acid value, the smaller the cross-linking of the coating film, the less water resistance. However, it can also be seen from the table that the higher the acid level, the worse the acid value, the better.
3.1.2 Effect of polyester resins of the same type of acid on the water-resistant properties of powder coatings

table 2 shows that Formula 9 has the best water resistance, followed by Formula 8, followed by Formula 6, and the worst is Formula 7. Explain that the same type of acid value of different polyester resin water-resistant properties are significantly different, although the coating cross-linking degree - the same, but the performance of the performance of water seepage is not the same - the reason is because of the synthetic polyester resin raw materials and content is different, indicating that different polyester resin varieties and different manufacturers between the composition of a large difference, the more permeable performance of the monomer, polyester resin impermeable water performance is better, including acid and alcohol.
3.1.3 Effects of different polyester resin collations on the water-resistant properties of powder coatings
The water-resistant properties of the same type of polyester resin are also different, and the polyester A1, polyester B1 and polyester E with better comprehensive properties are selected to explore the effects of collation on the water-resistant properties of powder coatings, and the specific experimental formulations and results are shown in Table 3.
can be seen from Table 3, formula 14 and formula 13 have the best and close water resistance, followed by formula 12, the worst formula 10 and formula 11. It is explained that different polyester resins are mixed with different proportions to make the powder coating water-resistant performance is different, the proportion of polyester resin added with good water-resistant water resistance is good, the contrast is good, but the coating surface leveling has the opposite result, the proportion of polyester resin added with good permeable water resistance is poor, and the reverse is good. A balance point of water-resistant properties and leveling needs to be selected for the following experiments.
3.2 Effects of special water-resistant polyester resins on water seepage resistance of powder coatings
Special water-resistant resins on the market are also available for spraying aluminum profiles due to their excellent heat resistance and boiling water resistance. Two types of special water-resistant polyester resins are selected to explore the effects on water-resistant properties of powder coatings, and the specific experimental formulations and results can be found in Table 4.
table 4 shows that Formula 17 has the best water resistance, followed by Formula 15, then Formula 18, and worst formula 16. It is stated that adding special water-resistant polyester can improve the water seepage resistance of powder coatings, and the effect of only 5% of the formula weight is more significant. The main reason is the special water-resistant polyester structure, as well as synthetic monomer than ordinary polyester synthesis of monomer water-resistant performance. From the table can also be seen that different models of special water-resistant polyester water resistance is also different, special water-resistant polyester F is significantly better than G; Then choose to use 5% content of special water-resistant polyester F to continue to do the following experiments.
3.3 Effect of fillers on water seepage resistance of powder coatings
Filler H consists of complex compounds with special structures, heat resistance and good water resistance. Add different contents of filler H to do water-resistant experiments, the specific experimental formula and results can be found in Table 5.
From Table 5, it can be seen that adding filler H can effectively improve the water-resistant performance of powder coatings, the formulation of different content of filler H water-resistant performance is slightly different, but not significant, but with the increase of filler H content, surface level will be worse, mechanical performance will be worse. The reason is that the special structure of filler H can effectively block the penetration of water vapor, so that the coating film has a certain hydrophobic properties, can improve the water penetration performance of the coating film, but because of the brittleness of filler H, and will also affect the melting fluidity of powder coating, so the content plus more surface leveling and mechanical properties will be worse, comprehensive aspects, so choose to add 5% content of filler H.
3.4 Effects of curing conditions on water seepage resistance of powder coatings
Powder coatings are manufactured with little involved in chemical reactions, but cross-linking reactions occur when used by downstream customers to produce coatings with certain physical and chemical properties. Therefore, in order to produce qualified products, we must choose the right curing conditions. The water-resistant properties of the test models with powder coatings made in formula 19 are seen in Table 6 under different curing temperature conditions, and the water-permeable properties of the test models under different curing time conditions are seen in Table 7.
From the experimental results of Table 6, it can be seen that the water-resistant performance of the coating film is very poor at the baking temperature of 180 degrees C, and the water-resistant performance of the coating film is significantly improved and not much difference when the baking temperature is 200 degrees C. From the experimental results of Table 7, it can be seen that the water-resistant performance of the 6min coating film baked at 200 OC is very poor, and the water-resistant performance of the 10min and above coating film baked at 200 OC is very good and not much different. The experimental data from Tables 6 and 7 show that different curing temperatures or curing times have a great influence on the water-resistant properties of powder coating coating, and are more effective than other factors. This is mainly because it takes a certain temperature and time for polyester resins to cross-link with curing agents. At the lower curing temperature, the activity of the resin and curing agent reaction can not reach, the reaction is not completely up to the due cross-link density, so the water resistance of the coating film is very poor. Shorter curing time resin and curing agent cross-linking reaction is not complete, the cross-link density of the coating film also did not reach the due cross-link density, so the coating film water resistance performance is also very poor. Aluminum profile factory complaints powder coating suppliers a batch of products impermeable water performance is poor, may also be related to the oven's actual effective curing temperature is low or effective curing time is too short. Therefore, in order to make the powder coating film curing completely, baking should control the effective curing temperature and time.
, there are many factors that affect the water seepage resistance of powder coatings: the type of polyester resin, the type of special water-resistant polyester resin, the filler and the curing condition. In this paper, the water-resistant properties of polyester powder coatings are improved by comparing polyester resins, combining special water-resistant polyester resins, collation filler H, and selecting suitable curing conditions.
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