Analysis on the development and raw material selection of wood grain thermal transfer series powder coatings

Abstract: Overview of the development history of thermal transfer technology, introduction to powder spraying and thermal transfer production processes, selection of raw materials for wood grain thermal transfer powder coatings, choice of wood grain transfer paper and wood grain powder coatings, and expounds on low energy consumption , Environmental protection, the inevitable development trend of wood grain powder coatings

1.

The powder coating is the powder state coating, the coating process is also carried out in the powder state, only when it is baked to form a film, it has a molten and formed liquid process

The development of powder coatings began in the early 1950s.

In the late 1950s, Shell Chemical Company was the first to develop thermosetting epoxy powder coatings, but the performance was not ideal due to poor dispersion uniformity

Until 1962, Shell Chemical Company developed the melt extrusion process to improve the problem of poor dispersion uniformity.

The development of powder coatings in China is more lagging.

In the 1990s, through the introduction of foreign capital and the import of more advanced powder coating production equipment and application equipment, domestic powder coatings began to develop on a large scale

With the development of powder coatings, some fine-art powder coatings have gradually come into people's field of vision
.

2.
Application of thermal transfer technology

Thermal transfer printing technology has long been used in the production of fabric thermal transfer printing.
With the rapid development of high technology, thermal transfer printing technology has become more and more widely used
.
There are heat transfer type and sublimation transfer type from the classification of ink types
.

The application of thermal transfer technology on aluminum profiles brings unlimited vitality to powder coatings for profiles and enriches the versatility of powder coatings
.

Thermal transfer printing is a dry production process.
According to the principle of thermal sublimation, the ink can quickly transfer the required wood grain, marble grain or other characteristic textures to the surface of the aluminum powder coating within 3-5 minutes, and can penetrate into The inside of the coating is 40-60μm without any gaps
.

With the rich selection of the development process of thermal transfer, there are roughly three types of thermal transfer processes currently: glue bonding thermal transfer, ironing thermal transfer and vacuum thermal transfer
.

2.
1 The development of wood grain thermal transfer powder coatings

As a kind of fine art powder coating, wood grain thermal transfer powder coating requires thermal transfer process and deep processing after spraying and curing.
At the initial stage of development, it is limited by technology, equipment, process and other aspects, so it has not been widely used
.

Compared with functional coatings, the added value of thermal transfer coatings is not high.
For a long time, large foreign companies with technical background and financial strength have not invested more research and development costs in thermal transfer coatings.
The focus is on functional coatings with high added value
.

After the wood grain thermal transfer powder coating passes through the thermal transfer process, colorful patterns are obtained, especially the visual effects of simulated logs.
The application on aluminum profiles and aluminum veneers such as furniture, doors and windows has been favored and recognized by customers
.

Thanks to the development of domestic real estate in recent years and the concentration of Guangdong's aluminum processing industry, thermal transfer powder coatings have developed well in southern China
.

3.
Selection of raw materials for wood grain thermal transfer powder coatings

At present, the heat transfer method of aluminum profiles is mainly vacuum transfer.
The heat transfer powder used must ensure that the paper is not sticky, the transfer is clear, the leveling is good, and the mechanical properties are excellent
.
In the Chinese market, wood grain powder coatings are mainly polyester/TGIC and polyurethane/blocked isohydrogen acid, which are the two main types
.

3.
1 Selection of carboxyl polyester

Polyester/TGIC type wood grain powder has better mechanical properties than polyurethane wood grain powder, and the price is also relatively advantageous.
However, if polyester is selected, unreasonable formulation design will easily cause problems such as poor leveling, unclear transfer, and sticky paper.

.

According to the technical principle of thermal transfer, the main technical characteristics of resins used in this field are rapid curing and a denser surface after curing, which can ensure clear transfer and non-stick paper, but it is easy to cause poor leveling and poor appearance.
Good
.

How to make polyester/TGIC powder coatings with good leveling, clear transfer, and non-sticky paper is to choose low-viscosity polyesters with different acid values ​​and make a reasonable combination
.

The experiment in Table 1 shows that the acid value of the resin directly affects the clarity of the heat transfer and the tearing of the paper.
The heat transfer polyester resin chooses high acid value and low viscosity; if the high acid value polyester is used alone, the leveling effect of the coating film is not Good
.

At this time, adding an appropriate amount of low acid value polyester with moderate reactivity can properly adjust the leveling effect, and the transfer effect is also improved
.

3.
2 Selection of Hydroxy Polyester

Polyurethane wood grain powder coating has good leveling properties.
As the hydroxyl value of the resin increases, the transfer effect becomes clearer and clearer, but the mechanical properties of the coating film become worse and worse
.

The test results in Table 2 show that the transfer effect of the hydroxyl resins with different hydroxyl values ​​is superior, but the impact performance of the high-strength resin is poor, the gloss of the coating film is lower, and the raw material cost of polyurethane wood grain powder coatings using high-hydroxy polyester is ridiculously high
.

In addition, its mechanical properties and boiling water resistance are poor, so it is recommended to use medium and low hydroxyl value resins, or with a proper amount of high hydroxyl resins, which can meet the good transfer effect
.

3.
3 Pigment selection

Regarding the selection of wood grain powder coating pigments, considering its weather resistance, inorganic pigments are the first choice.
The selection of inorganic pigments will not be described in detail here
.
When inorganic pigments cannot meet the color requirements of customers, we can reasonably choose organic pigments with high color strength, bright colors and complete color spectrum
.

Choosing organic pigments should mainly have the following characteristics:

(l) Excellent heat resistance stability, to prevent powder coatings from being decomposed or crystallized to change color during hot melt extrusion, heating curing process and thermal transfer process;

(2) Good fastness to light and weather.
Wood grain products are mostly used in doors, windows and furniture to avoid obvious discoloration of the coating film in the course of use;

(3) It has good dispersibility and can be evenly dispersed in the coating film during the powder coating production process
.

(4) It is necessary to have good rubbing fastness (the pigments migrate from the cured coating to the surface of the coating, and the phenomenon of "blooming" or "copper light" occurs, resulting in poor rubbing fastness of the pigments.
Wood grain products are mostly used for people The doors, windows and furniture that have been in contact for a long time in daily life use pigments with poor rubbing fastness, which affects the normal use of consumers
.

3.
4 Packing selection

Taking into account the high requirements for weather resistance and apparent leveling of wood grain products, barium sulfate is basically used as the main filler at present.
The original ore barium sulfate that has not been pickled contains more calcium carbonate and has poor batch stability.
Performance is poor
.
It is recommended to use pickled barium sulfate and precipitated barium sulfate as the main fillers
.

The transfer clarity of wood grain powder products is directly proportional to the transparency of the coating, that is, the light transmittance
.
Theoretically speaking, the refractive index of the filler is similar to that of the substrate, and it has little effect on the transparency of the coating, that is, the light transmittance
.

However, there are still slight differences in fillers with different refractive indices, and the clarity of wood grain texture formed by using different varieties of barium sulfate is also slightly different
.

3.
5 Selection of transfer paper

There are currently two types of transfer materials: transfer film and transfer paper.
Due to cost reasons, most of the domestic use of transfer paper is the choice of transfer paper
.

Rough surface transfer paper is prone to sticky paper during the transfer process, and fibrous lint remains at the right corners of the transfer profile
.
Transfer paper that is too smooth will not have sticky paper, but its ink permeability is poor, resulting in poor transfer clarity
.

In the selection of heat transfer paper, higher tensile strength and heat resistance are required.
The tightness of the transfer paper should be larger and the air permeability should be smaller
.
If the transfer paper is too tight and has greater air permeability, the sublimated ink will diffuse outward through the back of the base paper during the sublimation transfer process, which will affect the transfer effect
.

It can be seen from the experiment in Table 3 that the same wood grain powder coating, using wood grain paper with different textures, has different transfer adhesive properties
.
We conclude: light-colored wood-grain paper has superior tearing performance, and dark-colored wood-grain paper has poor tearing performance
.

Our in-depth research on wood-grain transfer paper found that the amount of ink used for printing wood-grain paper and the solid content are the main reasons for the above differences
.
For light-colored wood-grain paper (with less ink consumption), the transfer tearability is good, so these factors can be ignored
.

For wood-grain paper with dark colors (with large amounts of ink), attention should be paid to the selection of inks, and the content of butyral of different viscosities in the inks should be reasonably controlled
.

4 Conclusion

In recent years, thanks to the rapid development of the aluminum profile market, thermal transfer powder coating products have been loved by users with their realistic decorative effects and brilliant colors.
The colorful wood grain colors satisfy consumers' desire for a natural and comfortable life.
Pursuit
.

The wood grain transfer process can make the produced wood grain profiles have clear texture and strong three-dimensional effect, and can better reflect the natural feeling of wood grain.
It is an ideal energy-saving and environmentally friendly material to replace wood, which is in line with the current green concept of "substituting aluminum for wood".
, Wood grain series powder coatings have also been widely used in the door and window industry, and the next all-aluminum furniture will also shine
.