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APPLICATION OF SUBLIMATION TRANSFER PRINCIPLE FOR POWDER COATING

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APPLICATION OF SUBLIMATION TRANSFER PRINCIPLE FOR POWDER COATING

Numerous studies have being performed and various methods and techniques of metal decorating have being developed for the last 30 years.

The most extensive of them include:

  1. Decorating by destruction of surface layer (all kinds of engraving).
  2. Decorating of metal structure by Metalphoto, Gedacolor, Polychromal technologies.
  3. Surface decoration of metal items: silk printing, Grawerton and Colorton sublimation printing on metal.
  4. Implementation of organic dyes in the pores of metal by metallographic.
  5. Decoration by technology of sublimation thermal transfer.
  6. And the most obvious is using of various painting techniques.

Each technology is unique and has its area of use. Therefore, selection of technology is primarily determined by specific quality requirements and their performance characteristics.

If you consider aluminum as a building material (window, door, facade, sliding systems etc.), it is primarily an alternative to the wood. That is why, while choosing a decorating method, priority requirements were claimed. They were aimed to ensure maximum visual similarity with wooden elements on large formats and they are suitable for external application.

Studies have shown that method of polymer decorating by using of sublimation thermal transfer

is not complicated for mass production applications and is optimally fits into the process of powder coating.

Businesses engaged in powder coating, can easily implement this technology in their production line, and thus to diversify their production and increase its profitability.
Sublimation technology is a method of image transfer.

First drawing is formed by ink on the intermediate surface, as a rule, this is transfer paper. Then, there is a transition of ink from solid into gas state is happened. This happened due to temperature and pressure impact. Further dye penetrates into the structure of specially treated primer surface.

A prerequisite for image transfer on primer surface is either a polymeric structure of material itself, or the presence of a polymer coating on its surface.

The term “sublimation thermal transfer” involves the usage of physical phenomena “sublimation”, i.e. changing of substance physical state.

Then the decorating mechanism can be described as follows: first of all heating increases the kinetic energy of dye’s molecules. As soon as it becomes greater than the sublimation energy Eo, the particles are able to leave dye’s surface.

The speed of sublimation process is given by formula:

(1)
Where:
C – constant which depends on material of transfer paper, ink, and number and range of dispersion dyes in it;
T – temperature;
K – Boltzmann constant.

Molecules of dyes included in sublimation ink, have the ability to diffuse inside the structure of certain materials (e.g. polyesters).

Therefore, when heated molecules are “sandwiched” between the primer surface, which is coated with powder paint and transfer paper, the contact transfer process of pattern preserving the geometry and contrast happens.

The dependence of diffusion coefficient Do of temperature is the following:

(2)
Where:
C – constant which depends on the physical-chemical characteristics of polymeric primer;
ε — the activation energy.

Formula (1) and (2) shows only the general behavior of curves of these two processes. The choice of optimum modes with consideration of all variables is far beyond the scope of our review.