Wax powder is a common additive for powder coatings. It mainly hardens the coating, makes it wear resistant and plays the role of degassing and defoaming with four varieties, polyethylene wax, polypropylene wax, polyamide wax and polytetrafluoroethylene wax. Different waxes perform differently in powder coatings and distinct in scratch resistance, film hardness, smooth feel, degassing, gloss, color vividness, texture effect, transfer tear paper, silver powder arrangement and effects on printing or recoating.
Tianshi Wax Powder has carried out a series of experiments from the perspective of the interaction between wax powder and other raw materials of powder coating to carefully study the mechanism ofaction of different types of wax powder in powder coating systems. This paper mainly analyzes the effect of different wax powders on the viscosity of polyester.
The most basic indicators of polyester for powder coatings are acid value, viscosity and Tg value. The addition of wax powder does not affect the acid value of the polyester, but has a certain influence on the viscosity and Tg value of the polyester. In this paper, DSM’s 4140 (6:4 hybrid) and 4900 (TGIC cured, 94:6) were selected as the base materials for the experiment.
Raw materials for the experiment
|Raw materials||Specification||Place of origin|
|Polyester resin 4140
|Wax powder PEW-0360||Micro powder of polyethylene wax, melting point 106°c, density 0.91g/cm3||Tianshi Wax Powder|
|Wax powder PEW-0211||Micro powder of polyethylene wax, melting point 110°c, density 0.94g/cm3||Tianshi Wax Powder|
|Wax powderPEW-0278||Micro powder of polyethylene wax, melting point 126°c, density 0.98g/cm3||Tianshi Wax Powder|
|Wax powder PEW-0510
|Oxidized polyethylene wax, melting point 110°c, density 0.94g/cm3||Tianshi Wax Powder|
|Wax powder PPW-0901||Micro powder of polypropylene wax, melting point 145°c, density 0.90g/cm3||Tianshi Wax Powder|
|Wax powder NEW-0401||Micro powder of polyamide wax, melting point 145°c, density 0.99g/cm3||Tianshi Wax Powder|
Rotating viscometer is used to measure the impact on the viscosity of the polyester resin after the wax powder of different varieties and proportions is added to the polyester resin with an additive amount of 1%, 2% and 4% of the polyester resin at160℃.
Considering that wax powder has completely melted at 160℃ and gelation process of the powder coating has not yet fully started, measurement of the viscosity at this temperature is to explore the impact of wax powder before the gelatinization temperature of the powder coating on the viscosity of the polyester resin.
The wax powder chosen includes polyethylene wax, oxidized polyethylene wax, polypropylene wax and polyamide wax, among which the polyethylene wax of low density (density 0.90-0.93 g/cm3), medium density (density 0.94-0.96 g/cm3) and high density (density 0.94-0.96 g/cm3) are all selected. These wax powders are quite representative in the production practice of powder coatings.
The viscosity data of the polyester resin 4900 with added wax powder is as follows:
Conclusion and analysis
The addition of wax powder has a certain viscosity-reducing effect on the polyester resin for powder coating. The degree of viscosity reduction varies greatly with different wax powders and polyester varieties.
Polyamide wax NEW-0401 has good viscosity-reducing properties to polyester. Oxidized polyethylene wax PEW-0510 has good viscosity-reducing properties to polyester. Different specifications of polyethylene wax have great difference in viscosity-reducing effect on polyester. Polyethylene wax powder of medium density PEW-0211 has good viscosity reduction, and polyethylene wax of high density PEW-0278 has good viscosity reduction in polyester 4140 but poor viscosity reduction in polyester 4900.Polyethylene wax of low density PEW-0360 has good viscosity reduction in polyester 4900 but poor viscosity reduction in polyester 4140. Polypropylene wax PPW-0901 may not be completely dissolved at 160 ° C andexperiments show that it does not have the ability to reduce viscosity at 160 ° C.
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