Preparation method and application of sand pattern powder coating

Introduction: Thermosetting sand grain powder coating not only has many advantages of general thermosetting powder coating, but also has beautiful patterns and strong decoration.

This type of powder coating is widely used in the coating of instruments and meters, power distribution cabinets, security doors, home appliances, furniture, lighting and other fields

1.

Sand grain type powder coatings are prepared by baking and curing the powder coating's melt viscosity, surface tension and curing speed, etc.

1.

The principle of adding fillers to produce sand grain powder coatings: increase the amount of fillers, or use high oil absorption fillers to hinder the normal flow of the resin during melting;

The resin cannot completely contain or can just contain the pigment and filler particles, and there is no excess resin to fill the gaps between the pigment and filler particles, thereby forming a three-dimensional structure with the pigment and filler particles as the skeleton

It should be noted that when using this method, the oil absorption of different fillers is different.

The advantage of the sand grain produced by this method is that its cost is lower, but if the amount of filler is not properly controlled, the construction performance of the powder coating, the mechanical properties of the coating film, and the chemical resistance will be affected

Generally, this method is used to produce products with high efficiency and good stability, and some adjustments can be made in the production process

Chemical composition mass fraction/%; epoxy resin 25; polyester resin 25; auxiliary 5; pigment and filler 45
.

1.
2 Add incompatible substances

Adding incompatible materials to produce sand grain powder coatings refers to adding some incompatible polymers to the powder coatings, whose melting point is higher than the melting temperature of the resin base material of the powder coating;

The pre-mixed powder coating containing incompatible substances is incompatible with other resin curing agents during melt extrusion, and the resin constituting the base material is coated on the polymer particles during curing to form a film, thereby forming a texture
.

It should be noted that this method needs to strictly control the type and amount of incompatible substances, otherwise the mechanical properties of the coating film will be affected
.
The sand grain powder coating produced by this method has better chemical resistance and corrosion resistance
.
The reference formula is as follows:

Chemical composition mass fraction/%; epoxy resin 31; polyester resin 31; incompatible polymer 3; additives 5; pigments and fillers 30
.

1.
3 Add rheological additives

Adding rheology additives to produce sand grain powder coatings: the powder coating will have a normal viscosity when the powder coating is melted and extruded with high shear force.
In the melting and solidification stage, the system has a high viscosity and cannot flow, thus forming Sand pattern
.

It should be noted that when using this method, the amount of rheological additives is very small when producing sand grains, generally accounting for 1-2% of the total, so the pre-dispersion must be evenly dispersed
.

The advantage of this method over the filler method is that the decorative effect of the coating is similar, the protective ability of the coating film is improved, the powder is easy to be sprayed, the spraying area is large, and the decrease in the amount of filler is easy to squeeze.
Out of production
.
The reference formula is as follows:

Chemical composition mass fraction/%; epoxy resin 31; polyester resin 31; rheology additive 1.
5; additive 5; pigment and filler 31.
5
.

1.
4 Add sand texture agent

Generally, powder coating manufacturers often add sand texture agents
.
The principle of adding sand-graining agent to produce sand-grain powder coating is:

When the powder coating is melted and leveled, since the surface tension of the sand texture agent is lower than the surface tension of the normal powder coating film, the sand texture agent dispersed at each point of the coating film changes the local tension of the coating film, making the base material with high surface tension.
To wrap the sand texture agent with the surface tension bottom, the final coating film surface presents a uniformly distributed sand texture
.

The sand grain powder coating produced by this method has good decorative and protective properties.
It not only has excellent mechanical properties, but also has stable texture reproduction, smooth hand feeling, easy extrusion and stable effect.
The main disadvantage is that the cost of materials is relatively high.
High
.
The reference formula is as follows:  

Chemical composition mass fraction/%; epoxy resin 32; polyester resin 32; sand texture agent 3; auxiliary agent 5; pigments and fillers 28
.

The production method of the above four kinds of sand grain powder coatings is to produce the coatings at one time by pre-mixing, melt-extrusion, tableting, cooling, crushing, sieving, and packaging to finished products.

.

In addition, according to the actual situation, the above-mentioned four sand grain powder coating preparation methods can be organically combined to produce high-quality and inexpensive products
.

2.
Painting construction

Due to its special film-forming principle and production process, sand grain powder coatings should pay attention to its special operability when painting.
It is necessary to make appropriate adjustments to its coating equipment and construction process to meet the requirements of sand grain coating curing.
Membrane requirements
.

2.
1 Spraying environment

The particularity of the raw materials used in sand grain powder coatings, although it is not very sensitive to incompatible substances, but if the spraying equipment is not cleaned, and there are many impurities in the air, if it is contaminated on the coating film, it will cause its surface It is difficult to form texture and strong pattern
.
Therefore, the spraying environment should be clean
.

2.
2 Painting parameters

When spraying sand grain powder coatings, the electrostatic voltage is generally controlled at 60-80kv.
The voltage is too low and the powder is not easy to attach to the workpiece; if the voltage is too high, the powder coated on the workpiece will rebound.
After the coating surface is baked There are protruding star-shaped dots, commonly known as "pitting"
.

The powder delivery air pressure should not be too high, generally controlled at 4.
9-15*104pa.
Too high air pressure will cause uneven coating thickness, resulting in inconspicuous pattern size, which will affect the overall three-dimensional feeling
.

2.
3 Curing conditions

The curing temperature of sand grain powder coatings is similar to that of general powder coatings.
It must be baked at a specified temperature and time to completely crosslink and cure the powder coatings
.

The specified baking temperature refers to the temperature that the surface of the painted workpiece should actually reach, and the powder is maintained at this temperature for a certain period of time to solidify into a film
.

In the coating construction process, some customer manufacturers often implement baking curing when the actual surface temperature of the workpiece does not reach the specified curing conditions, which causes defects such as incomplete curing of the powder coating film and obvious decline in mechanical properties
.

Therefore, we can take corresponding measures according to its curing conditions, such as increasing the temperature in the oven and extending the curing time
.
Conditional manufacturers can have an oven temperature tracker to detect the temperature of the oven in order to better grasp the curing conditions of the coating film
.

2.
4 Coating film thickness

The length of the powder leveling time, the thickness of the coating film directly affects the size of the pattern after the powder is formed, usually the film thickness of the sand pattern powder coating is controlled at 70-100um, the coating thickness, the powder melting and leveling time is long, the pattern becomes flat and blurred strong;

The coating film is thin, the powder melting and leveling time is short, the pattern becomes broken and clear, but it should not be too thin.
When it is too thin, the surface of the workpiece will be exposed, and it should not be too thick.
When it is too thick, pitting and pitting will appear on the surface of the workpiece.
Electrostatic breakdown phenomena such as pits
.

Therefore, during the construction of sand grain powder coatings, the thickness of the coating film must be kept uniform to prevent the above-mentioned quality defects
.

3.
Conclusion

Sand grain type powder coating has simple production process, stable quality performance and superior decorative performance.
It has been widely used in the coating of general metal surfaces
.

Sand grain type powder coating has its own particularity, suitable for various systems, and develops with the development of powder coatings
.
Further research on sand grain powder coatings will be very valuable
.

references:

1.
Zhang Huadong, etc.
, Precautions for the application of additives in powder coatings, Shanghai Paint,

2.
Chen Zhenfa, Zhou Shiyue, etc.
, Powder Coating Technology, Shanghai Science and Technology Literature Press

3.
Nan Renzhi Powder Coating and Painting Technology Chemical Industry Press

4.
Zhang Huadong and Zhang Jun UV-curable powder coating technology and abstracts