Effect of Rubber Accelerator on Properties of Polyester Epoxy Powder Coatings

1. As is known to all, polyester epoxy powder coating is composed of polyester resin, epoxy resin, makeup filler and additives. In addition to the commonly used leveling agent, dispersant, degassing agent, loose agent, etc., in order to meet the reactivity of powder coating, that is, to meet the curing conditions and need to add curing accelerator, so that the film performance to meet the requirements of users. With the rapid development of Chinese powder coating and coating industry, in order to meet the needs of various uses, there are many varieties of polyester resin and epoxy resin developed, which can basically meet the general needs, but can not completely meet the needs of special use. In the development of polyester resin varieties for powder coating, although different amounts of curing accelerator should be added, but because of the distance of the raw material production unit, product price, resin compatibility and other aspects of the reasons did not find the ideal resin variety, should consider the activity of the familiar resin varieties to adjust the use, One of the concrete measures is to add accelerators to the formula. In powder coating formulation, the main role of accelerator is to improve the reactivity of resin and curing agent (or resin), improve the curing reaction rate of the film or shorten the curing reaction time, or adjust the gel time and melt level fluidity of powder coating.

There are many kinds of accelerators used in the polyester epoxy powder coating system, the commonly used varieties are metal oxide (zinc oxide), tertiary amine (imidazoles), quaternary amine (ammonium ammonium salt), etc. To understand the effects of different promoters on the properties of epoxy powder coatings prepared with the same polyester resin. The effect of the same kind of accelerator on the properties of polyester epoxy powder coatings prepared by different manufacturers or different types of polyester resin from the same manufacturer; The effects of different amounts of accelerators on powder coating and film properties of the same kind of polyester resin are of great significance for the design of polyester powder coating, the selection of the type and amount of accelerators and the selection of polyester resin.

2 Test part

2.1 Test equipment and instruments

Test equipment for laboratory twin screw extruder, crusher, electrostatic powder spraying equipment; Instruments include color difference meter, gelation time and melt fluidity tester, refrigerator, film gloss and impact strength tester, etc.

2.2 Test raw materials

Raw materials: polyester resin -1, polyester resin -2, polyester resin -3, polyester resin -4, epoxy resin E-12, accelerator -1 (imidazoline), accelerator -2 (imidazoline), promoter -3 (onium salt), titanium dioxide R940, precipitated barium sulfate, leveling agent, dispersant, degasifier and other additives.

2.3 Test method

According to the formula of powder coating weighing, with the general powder coating preparation method, through "melting extrusion → grinding → screening (180 mesh)" powder coating, and then determine the gel time and melt horizontal fluidity of powder coating, in 0.5 mm cold rolled steel plate after electrostatic spraying at 180℃, 190℃, respectively, After curing at 200℃ for 15 min, the coating performance was tested.

3 Results and discussion

3.1 Effects of different accelerators on properties of the same polyester epoxy powder coating Promoter-1, promoter-2 and promoter-3 were selected to prepare polyester epoxy powder coating with polyester resin-1 and epoxy resin E-12 respectively. The test results of different accelerators on the properties of polyester epoxy powder coatings and coatings are shown in Table 1.

Table 1 Test results show that different accelerator varieties have different effects on the gelation time, melting leveling property, film luster and impact strength of the same polyester epoxy powder coating, especially on the impact strength of frozen film is significantly different. This is because the structure of different accelerators is different, the catalytic mechanism is different, so the promotion effect is different. Therefore, it is necessary to select the appropriate promoters according to the requirements of powder coating and film performance.

The powder coatings prepared with three different accelerators and the powder coatings without accelerators (empty white) were cured for 15 min at 180℃, 190℃ and 200℃ respectively. The changes of color difference (ΔE) of the coatings were compared, and the test results were shown in Table 2.

The test results in Table 2 show that the color difference of accelerant -3 is small, no matter the sample baked and cured at 180 ° C with accelerator or the sample baked and cured at 180 ° C without accelerator. For this reason, considering the color resistance and heat resistance of the film, the choice of accelerant -3 is better.