Talk about the improvement of edge coverage of epoxy polyester powder coating

China Coatings Network
News: China
Coatings Network
News:
NanRenzhi, Jinshunyu, Cheng Jun, Pan , Zhou Jianxin, Chen Yifeng
(Jiangsu Lanling Polymer Materials Co., Ltd., Jiangsu Changzhou 213119)
Summary: Discussion of epoxy polyester
powder coatings
polyester resin varieties, powder
coatings
formulation of catalyst varieties and dosages, corner covering force modifier varieties and dosages,
pigments
varieties and dosages on the powder coating melting level flow and collation time, through the adjustment of these factors can improve the epoxy polyester powder coating corner covering.
key words: epoxy polyester; powder coating; corner covering force; Improvements in figure
Classification number: TQ633 Document identification code: A Article No. 1007-9548 (2012)2012) 10-0012-04
0 Introduction
Epoxy polyester powder coating is the most produced in China's powder coating, coating appearance type and color varieties are also the most, the widest range of applications of powder coating varieties. In order to meet the needs of various applications, it is often necessary to adjust the powder coating's various technical parameters, such as curing speed, melting viscosity, covering force, powder rate, corner covering force, etc., wherein the corner covering force of powder coating is one of the important technical parameters for the work piece that requires a thick coating or a uniform thickness of the workmange. The corner covering force of powder coating is closely related to the melting viscosity and collification time of powder coating. Generally speaking, the melting viscosity of powder coating is affected by the melting viscosity of resin, the content of pigment and the amount of oil absorption, the greater the melting viscosity of powder coating, the better the edge coverage;
In the design of powder coating formulation, first of all, in the selection of raw materials, we should consider the selection of powder coating melting viscosity has a greater impact on the varieties; Specifically, in the choice of polyester resin, as far as possible to consider the melting viscosity at the curing temperature of polyester resin varieties, in addition to the formulation design by adding curing promoter to shorten the gel time of powder coating, and add corner covering force modifier, increase the content of pigments and other methods to improve the melting viscosity of powder coating, so as to improve the edge coating coverage. The following is a detailed description of the research experiment.
1. Test Part
1.1 Test Equipment
Laboratory with twin screw extruder, small high-speed shredder, electrostation powder spraying equipment, powder coating gel time and melting fluidity meter, coating performance measurement equipment.
1.2 Test raw materials
epoxy polyester powder coatings with general raw materials (including different specifications of different merchants polyester resin), E-12 epoxy resins, leveling agents, brighteners, resting incense, magenta
titanium white powder
, precipitation sulfate, promoter, gas phase silicon dioxide and so on.
1.3 Test Method
After selecting the classic formula of epoxy polyester powder coating (m epoxy/m polyester x 50/50), polyester resin variety, promoter variety and dosage, corner covering force modifier variety and dosage, pigment content, etc., the change of melting flow and gluing time of powder coating was examined.
2. Results and discussion of the effects of
2.1 polyester resins
The formulation and coating performance indicators for the formulation and coating of epoxy polyester powder coatings with 4 polyester resins (m epoxy/m polyester x 50/50) from different merchants are below Table 1.
Table 1 The formulation and coating properties of polyester powder coatings formulated by different merchant polyester resins
The test results of Table 1 show that the same formula of epoxy polyester powder coatings formulated by four different merchants' polyester resins, although the coating The appearance, luster and impact resistance of the film are similar, the gel time of powder coating is not very different, however, the melting viscosity of polyester resin is different, the melting level of powder coating is different, among which the flow of co-polyester resin preparation powder coating is minimal. Therefore, in order to get a good edge covering of epoxy polyester powder coating, it is best to choose co-production polyester resin. When choosing polyester resin, it is best to choose polyester resin varieties with high melting viscosity or low melting level of preparation powder coating under curing temperature conditions.
2.2 Effects of promoter variety and dosage
2-benzodialyc and 2-methyl-methylene are selected to be formulated with epoxy polyester powder coatings, and the formulation and coating properties of epoxy polyester powder coatings formulated with 2-benzene-based methylene are available in Table 2;
Table 2 Formulation and coating performance of epoxy polyester powder coatings made with 2-benzene methane
Table 3 Formulation and coating properties of epoxy polyester powder coatings with 2-methyl methane
The amount of dosing increased, the appearance and gloss of the coating film did not change significantly, but the impact resistance of the coating film has been significantly improved, and the gel time of the powder coating has been significantly shortened, the melting flow of the powder coating is also significantly smaller, that is to say, by adjusting the amount of 2-benzene-based mite, you can improve the coating edge coverage.
test results of table 3 show that with the increase of 2-methyl mide, the appearance of the coating film becomes worse and the gloss decreases, however, the impact resistance of the coating film has a tendency to get better. With the increase of 2-methyl mide dosing, the gel time of powder coating is obviously shorter, and the melting level flow of powder coating is obviously smaller, which is conducive to the improvement of coating angle coverage.
When the powder coating containing 2 promoters is compared, the gel time of powder coating containing 2-methylmide is shorter, the melting level flow of powder coating is smaller, indicating that the effect of 2-methyl mide on the coating corner coverage of powder coating is better than that of 2-benzene mide.
2.3 Effects of corner covering force modifiers
In epoxy polyester powder coatings, gas-phase silica, gas-phase alumina, nano-calcium carbonate, etc. can be used as coating film corner covering force modifiers. The results of the experiments with different amounts of gas-phase silica and nano-calcium carbonate are below Table 4 to 5.
Table 4 Test results of different amounts of gas-phase silicon dioxide and nano-calcium carbonate
Table 5 Effects of different amounts of nano-calcium carbonate on the performance of epoxy polyester powder coating and coating
For powder coatings, with the increase in the amount of gas-phase silicon dioxide, the gel time of the powder coating becomes longer, and the melting level of the powder coating fluidity becomes smaller, indicating that by adjusting the amount of gas-phase silica in the formula, the edge coverage of the powder coating is improved, but the amount added is determined according to the requirements of the mechanical properties of the coating film, adding too much will affect the mechanical properties of the coating film.
The experimental results of table 5 show that with the increase of nano-calcium carbonate dosing, the effect of coating film gloss and impact resistance is not obvious, however, it has a certain effect on the appearance of coating film, when increased to a certain amount, the coating film orange grain becomes heavier. With the increase of the amount of nano-calcium carbonate, the collification time of powder coating is shorter, and the melting level of powder coating is significantly smaller, indicating that adjusting the amount of nano-calcium carbonate in the formula can improve the edge coverage of powder coating.
2.4 Effects of pigment and filler dosing
In powder coating formulations, pigments and fillers are an indispensable component and are used in large quantities. Therefore, the choice of variety and dosing has a great impact on the technical index of powder coating and the performance of coating film, including the adhesion time and fluidity of powder coating. If the right pigments and fillers and dosing are selected, the corner covering of powder coatings can be improved by adjusting the content of pigments and fillers in the formulation. The effects of different filler (ultra-fine heavy crystal powder) on epoxy polyester powder coatings can be seen in Table 6, and the effects of different pigments and filler combinations on epoxy polyester powder coatings can be seen in Table 7.
Table 6 Effects of different pigment and filler combinations on epoxy polyester powder coatings
Table 7 Effects of different pigment combinations on epoxy polyester powder coating and coating properties
There is no obvious change in film gloss and impact resistance, the gel time of powder coating is also very small, however, the melting level of powder coating fluidity changes significantly, with the increase of ultra-fine heavy crystal powder amount of powder coating melting level fluidity is smaller, can be appropriately increased filler dosing to improve the coating corner coverage.The results of Table
show that when the ratio of the three pigments of gold-redstone titanium white, sharp titanium-type titanium white and precipitated nihric sulfate is adjusted, the appearance, gloss and impact resistance of the powder coating film do not change much, the adhesion time of the powder coating changes significantly, and the melting level flow of the powder coating changes significantly, indicating that the coating angle covering capacity of formula 27 has significantly improved compared to formula 25. That is to say, through the adjustment of different pigment dosing ratio, the coating angle coverage of powder coating can be improved.
3. Conclusion
test results show that to improve the edge coverage of epoxy polyester powder coating, can be considered in the following aspects:
1) from the polyester resin, as far as possible to choose a high melting viscosity polyester resin varieties at curing temperature, so that the powder coating melting viscosity is high when curing, the coating of the corner covering is good.
2) The addition of suitable curing promoter varieties and dosages can adjust the gel time of the powder coating, so that the melting level of the powder coating flow is smaller, can improve the corner coverage of the powder coating film.
3) Add angle covering force modifiers that can increase the molten viscosity of powder coatings, such as gas phase silicon dioxide, nano calcium carbonate and other additives, can improve the corner covering force of powder coating film.
4) According to the oil absorption and activity of pigments and fillers, by changing the variety, dosing and ratio of pigments to adjust the melting viscosity, gel time and melting level flow of powder coatings, the corner coverage of powder coatings can be improved.