Crack powder coatings are thermosetting powder coatings. Crack powder coating not only has many advantages of thermosetting powder coating, but also forms a beautiful crack pattern after painting. It is natural, elegant and simple, and can be adjusted according to the shape of the workpiece and the shape of the crack. Crack powder coatings are widely used in the coating of toys, handicrafts and other fields.
The crack powder coating is a change in melt viscosity, surface tension, and curing speed of the powder coating during baking curing, causing shrinkage of the surface of the coating film to form a crack effect.
First, the method of forming cracks:
1. The amount of the filler can be increased, or the amount of the binder can be reduced. Generally, a filler having a higher oil absorption amount is selected to prevent the normal flow of the resin during film formation, so that the resin cannot be completely coated or the particles just covering the pigment filler are not used. Excess resin fills the voids between the pigment particles, thereby forming a three-dimensional structure with a pigment filler as a skeleton, and revealing the color of the primer at the crack.
2. By adding texture additives (such as scenting agents, wrinkles, etc.), the amount of such additives is small, and it is necessary to mix evenly when added, in order to obtain uniform and stable texture.
Main performance: the main performance of crack powder coating see below
Test item indicator
Gloss /% 65
Adhesion / level 0
Appearance, strong stereoscopic effect, obvious crack
The reference formula is as follows:
Precipitated barium sulfate 29
Carbon black 0.6
In the bottom powder, the addition of silver powder 80000A is added 0.6%, and the amount of floating agent is 0.1%. Need to be highly mixed.
Extrusion temperature: 110-120 baking temperature: 200*30
Second, the factors affecting the shape of the crack size:
Different base powders have different cracks. If you need to see clear cracks in a large space, you should choose a resin with lower viscosity to facilitate flow.
In the same system, due to the different content of pigments and fillers, the size and shape of cracks will be affected. The general rule is that as the content of pigments and fillers increases, the cracks of sprays will change from coarse and large cracks to relatively fine cracks.
Third, construction considerations:
1. During the powder coating construction process, the powder coating applied to the surface of the metal workpiece should be evenly distributed, and the coating thickness should be uniform and suitable. If the thickness is too thick, the crack boundary will be blurred; if it is too thin, it will easily cause problems such as bottoming and shrinkage.
A relatively small crack transition.
2. It is recommended that the spraying sequence be high to low. Spray the secondary surface first, then spray the main surface, preferably spray once. Some dead ends require partial touch up, which will cause the original part of the crack to disappear.
3, in order to achieve the best spraying effect, before the construction, the material is sieved slightly larger than the screen, through the fluidized bed system powder supply device to adjust the powder air pressure, atomizing air pressure, the distance between the nozzle and the workpiece, the spray gun The process parameters such as the removal speed are the best results;
4. Apply powder crack coatings to prevent them from contaminating other types of coatings. If there are conditions, it is best to have two sets of equipment to use separately.
5. When electrostatic spraying, the thermal spraying of the workpiece is better than the cold spraying texture. Since the thermal spraying is a rapid melting of the powder coating as soon as it contacts the workpiece, the coating begins to convect immediately (if the metal pigment is included, the pigment floats) So that it has enough time to rotate to the best angle of reflection. If cold spray is used, because the heat capacity of the workpiece is large (especially for thicker materials), it takes a long time for the room temperature to rise to the curing temperature, that is, the resin is at a high viscosity for a long period of time, and the internal resistance is hindered. The formation of the texture, if the gelling time of the coating is short, it gradually gels during the heating process, and when the curing temperature is reached, the coating has formed a gel, and the texture cannot be formed.