Theory of color matching in powder coatings

Polyester powder coating is a thermosetting powder coating composed of polyester resin, curing agent, pigment, filler and additives In thermosetting powder coating, polyester powder coating is one of the main varieties of weather resistant powder coating In order to be different from polyester epoxy powder coating, it is usually called pure polyester powder coating   There are many kinds of polyester powder coating, including TGIC curing system for carboxyl polyester resin, HAA curing system for carboxyl polyester resin, pt910 curing system for carboxyl polyester resin, and powderlink 1 curing system for hydroxyl polyester resin 174) curing system, etc Hydroxypolyester resin is a closed polyisocyanate curing system, which is classified as polyurethane powder coating in China   In the formulation of polyester powder coating, for the selection of polyester resin, according to the user's requirements for the appearance and performance of the coating film, for the powder coating with high gloss and performance, the carboxyl polyester resin with the acid value of polyester resin of 28-35mgkoh / g and the glass transition temperature of more than 60 ℃ is generally selected; for the dry mixing method to manufacture the matt polyester powder coating, a polyester resin is selected For wrinkled (reticulated) polyester powder coating, hydroxypolyester with a hydroxyl value of 35-45mgkoh / G can be selected; for UV curing agent UV curing polyester powder coating, common carboxyl polyester resin can be selected On the basis of selecting polyester resin, select the corresponding curing agent and determine the dosage At present, TGIC and HAA are the main curing agents used in weather resistant polyester powder coatings Generally speaking, the appearance and properties of TGIC cured polyester powder coating are relatively good The disadvantage is that the baking temperature is a little higher and the toxicity is a little higher than HAA The disadvantage of HAA cured polyester powder coating is that pig pores are easy to appear when the coating is too thick, and the yellowing resistance of the coating is not as good as TGIC system when baking and curing Choose a more suitable curing system according to the user's requirements For the amount of curing agent, please refer to the recommended amount of the manufacturer, or make theoretical calculation: the amount of TGIC required by 100g polyester resin wtgic = APE / (etgic × 561) the amount of HAA required by 100g polyester resin WHAA = ape × hhaa / 561 In the HAA system, benzoin should be added less properly, and the leveling agent should be polyester or compound with good weather resistance as the carrier The brightener has little effect on the appearance of the film, but it has certain advantages in improving the dispersibility of pigments and fillers and reducing the disadvantages of the film The difference between the theoretical calculation results and the actual test results is inevitable The final formula must be determined on the basis of theory and practice Polyester powder coating is a thermosetting powder coating composed of polyester resin, curing agent, pigment, filler and additives In thermosetting powder coating, polyester powder coating is one of the main varieties of weather resistant powder coating In order to be different from polyester epoxy powder coating, it is usually called pure polyester powder coating   There are many kinds of polyester powder coating, including TGIC curing system for carboxyl polyester resin, HAA curing system for carboxyl polyester resin, pt910 curing system for carboxyl polyester resin, and powderlink 1 curing system for hydroxyl polyester resin 174) curing system, etc Hydroxypolyester resin is a closed polyisocyanate curing system, which is classified as polyurethane powder coating in China   In the formulation of polyester powder coating, for the selection of polyester resin, according to the user's requirements for the appearance and performance of the coating film, for the high gloss and high performance powder coating, generally choose the carboxyl polyester resin with the acid value of 28-35mgkoh / g and the glass transition temperature above 60 ℃; for the dry mixing method to produce Matt polyester powder coating, choose the acid value of a polyester resin Another kind of carboxyl polyester resin with an acid value of about 50mgkoh / G is selected when it is about 20mgkoh / g; for wrinkled (reticulated) polyester powder coating, the hydroxyl polyester with a hydroxyl value of 35-45mgkoh / G is selected; the commonly used carboxyl polyester resin can be selected when the extinction curing agent is extinction polyester powder coating On the basis of selecting polyester resin, select the corresponding curing agent and determine the dosage At present, TGIC and HAA are the main curing agents used in weather resistant polyester powder coatings Generally speaking, the appearance and properties of TGIC cured polyester powder coating are relatively good The disadvantage is that the baking temperature is a little higher and the toxicity is a little higher than HAA The disadvantage of HAA cured polyester powder coating is that pig pores are easy to appear when the coating is too thick, and the yellowing resistance of the coating is not as good as TGIC system when baking and curing Choose a more suitable curing system according to the user's requirements For the amount of curing agent, please refer to the recommended amount of the manufacturer, or make theoretical calculation: the amount of TGIC required by 100g polyester resin wtgic = APE / (etgic × 561) the amount of HAA required by 100g polyester resin WHAA = ape × hhaa / 561 In the HAA system, benzoin should be added less properly, and the leveling agent should be polyester or compound with good weather resistance as the carrier The brightener has little effect on the appearance of the film, but it has certain advantages in improving the dispersibility of pigments and fillers and reducing the disadvantages of the film The difference between the theoretical calculation results and the actual test results is inevitable The final formula must be determined on the basis of theory and practice Powder coating is not liquid, but a kind of powder coating The manufacture of powder coating is totally different from the traditional solvent coating or water-based coating The production process and equipment are similar to plastic processing to some extent, and the solvent is not needed in the application Therefore, compared with traditional coatings, there are different requirements for pigments Easy dispersion is an important requirement of powder coatings for pigments The dispersion of pigments in powder coatings is fundamentally different from that of liquid coatings in terms of technology or state of dispersed materials, and there is no comparability at all The retention time of the pre dispersed materials in the melt mixing equipment is very short, and it is very difficult to wet the pigment, so the dispersibility of the pigment becomes particularly important Generally, the pigments with good dispersibility in polyolefin plastic particles meet the requirements of powder coating The heat resistance of powder coating to pigment is mainly based on the following two considerations: on the one hand, the pigment must be able to withstand at least 210 ℃ for about 12 to 15 minutes of coating heating, melting, leveling and drying process; on the other hand, the powder coating on the surface of some end consumer products (barbecue rack, stove, etc.) must also withstand extremely high temperature The rheological system of powder coating requires that the pigment can not weaken the fluidity of the melted coating Only by ensuring the good fluidity of powder coating under low shear force, can the dense, smooth and continuous coating be formed in the process of heating, melting, leveling and curing after coating The coating thickness of the powder coating is generally in the range of 40 to 70 microns Only the excellent covering performance of the pigment can ensure the nearly perfect appearance of the powder coating In the field of outdoor decorative coating, the powder coating must go through at least one year's Florida exposure test, and the coating must maintain good color stability and light retention This puts forward high requirements for light and weather resistance of pigments The chemical resistance of powder coating mainly depends on its application, for example, the powder coating applied on the washing machine shell must have alkali resistance There are several kinds of pigments suitable for powder coatings: Yellow 53 Brown 24 blue 28 blue 36 and bismuth vanadium molybdenum yellow 184 Pigment yellow 34 and red 104 in lead containing pigments And organic synthetic pigment yellow 110; pigment red 112202254255 and 264; pigment purple 19 and 23; pigment blue 60 and 15:1 At present, the pigment preparation after surface treatment (for example, wrapped by urea formaldehyde resin) has also entered the field of powder coating.