Methods of powder coating matting agent realization

2021-09-15   Pageview:197

Generally speaking, the matting of powder coatings can be achieved by the following methods.
( 1) Filler addition method
( 2) Adding incompatible substances
( 3) Dry mixing method
( 4) One time extrusion method

 

 

 

 

 

 

 

 

 

( 1) Filler addition method
Adding fillers such as BaSO4, CaCO3, kaolin, barite, pyrogenic silica, mica powder, etc. to the coating components can theoretically produce a matting effect from high gloss to non-glossy surface, but with the increase of fillers the mechanical properties of the coating film drop sharply and the leveling deteriorates, so this method is only suitable for the preparation of glossy coating films above 60b, and its application is limited.

( 2) Adding incompatible substances
When incompatible substances are added to the resin, they can still flow freely but in a non-homogeneous state during the high temperature baking stage, and will precipitate out of the system after cooling and arrange in a non-homogeneous distribution on the surface, forming a rough surface and scattering light, thus reducing the light. For example, polyvinyl acetate derivatives, cellulose esters, etc. Firstly, it is difficult to prepare powders with less than 30% gloss, and excessive addition of wax-based compounds may cause bleeding from the surface, paraffin wax and ptfe causing processing problems; secondly, the inhomogeneous distribution of components is often influenced by extrusion conditions, resulting in fluctuations in gloss. However, there are now non-reactive matting additives for non-wax systems, which not only produce good matting effect, but also do not yellow, and are suitable for hybrid or TGIC systems, and the minimum gloss can be reduced to below 20b.

( 3) Dry mixing method
Dry mixing of two different reactive powders or two incompatible types of powder can produce matting effect. In order to improve the mixing effect is usually crushed together rather than the two powders simply mechanical dry mixing, the two systems of powder its gel time is not the same, the faster reaction of the powder part first cross-linked into a mesh structure, reducing the fluidity of the system. The stress contraction of the two different reactions forms a microscopic rough surface, leading to matting. A good example is the mixing of two polyester powders with different reactivities, such as 90:10 and 96:4 powders based on polyester/TGIC, and 90:10 and 96:4 (9615:315) powders based on polyester/hydroxyalkylamide. In general, the greater the difference in reactivity, the better the matting effect obtained. Mixing powders with different chemical reaction mechanisms, melt viscosities, and surface tensions can also result in a disorganized (sometimes referred to as contaminating) coating surface that produces matting. A simple example is the dry blending of high gloss hybrid and TGIC polyesters, hybrid / pure epoxy, polyurethane / TGIC systems, etc. These combinations can produce matting ranging from 30% to 40%, where the different polyester resins have a significant impact on the sensitivity of the gloss. Dry blending is a very time consuming method of matting. Sometimes the difference in mixing effect can lead to poor reproducibility, and sometimes produce uneven surfaces.

( 4) One time extrusion method
The primary extrusion method overcomes the instability of the dry mixing method, which is chemically incompatible and consists of at least two chemical reactions with different reaction rates of the film-forming resin during the reaction. It is based on the principle of one resin and a bifunctional curing agent, or one resin and two curing agents, or two different resins and one curing agent, or different resins and two (or three) curing agents. In general, the greater the difference in reaction rate, the lower the gloss of the coating film obtained.

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