Powder coating is a thermosetting powder coating composed of polyester resin, curing agent, pigment, filler and auxiliary. Among thermosetting powder coatings, polyester powder coatings are one of the main varieties of weather-resistant powder coatings. In order to distinguish them from polyester epoxy powder coatings, they are customarily called pure polyester powder coatings.
There are also many varieties of polyester powder coatings. The main varieties include TGIC curing systems for carboxy polyester resins; hydroxyalkylamides (HAA, trade name Primid XL522 or T105) for carboxy polyester resins. Curing system; epoxy compound (PT910) curing system for carboxy polyester resin; tetramethoxymethyl glycoluril (Powderlink 1174) curing system for hydroxy polyester resin, etc. A blocked polyisocyanate curing system for hydroxy polyester resin is classified as a polyurethane powder coating in China.
In the formulation of polyester powder coatings, for the selection of polyester resins, according to the user's requirements for the appearance and performance of the coating film, for high gloss and high performance powder coatings, the polyester resin acid value is generally selected from 28 to 35 mgKOH / g. Carboxylic polyester resin with a glass transition temperature above 60 ° C. For the manufacture of matte polyester powder coatings by dry blending method, one polyester resin is selected with an acid value of about 20 mgKOH / g, and the other is selected with an acid value of 50 mgKOH / g Left and right carboxy polyester resins; For wrinkle (reticulate) type polyester powder coatings, choose a hydroxy polyester with a hydroxyl value of 35 to 45 mgKOH / g; matte curing agent dull polyester powder coatings, you can choose a commonly used carboxy polyester Resin.
Based on the selection of polyester resin, select the corresponding curing agent variety and determine the amount. In weather-resistant polyester powder coatings, the main curing agents currently used are TGIC and HAA. Generally speaking, the appearance and coating film performance of TGIC cured polyester powder coating are better. The disadvantage is that the baking temperature is a bit higher and the toxicity is higher than HAA. The disadvantage of HAA cured polyester powder coating is that the coating film is too Pig pores tend to appear when thick, and the yellowing resistance of the coating film is not as good as that of the TGIC system when cured.
The amount of TGIC required for 100g of polyester resin WTGIC = APE / (ETGIC × 561)
HAA (Hydroxyalkylamide) required for 100g of polyester resin WHAA = APE × HHAA / 561
In the HAA system, benzoin should be added appropriately, and the leveling agent should be based on a weather-resistant polyester or compound. The brightener has little effect on the appearance of the coating film, but it can improve the dispersion of the pigment and filler and reduce the Membrane ills have certain benefits. The difference between the theoretical calculation results and the actual test results is inevitable. The final formula must be determined based on theory and combined with practice.