Thermal transfer is a process that is an important part of the entire printing process and is closely related to other processes. How to control the stability of this process is an important guarantee for the quality of printed matter. Let’s first look at the important factors affecting the thermal transfer process.
1. Thermal print head
The thermal print head is mainly composed of a surface film protective layer, a bottom film protective layer and a heating element. The heating element is a conductive mesh screen, and the heat generated by the voltage pulse is thermally diffused, so that the ink particles in the image portion are embossed and melted to complete the ink transfer.
The printing speed of thermal transfer depends on the time required for each line of text. Therefore, the thermal transfer head and the transfer paper should have good heat transfer properties, so that the heat generated by the heating element can be quickly transmitted to the surface of the substrate through the protective layer, the transfer paper substrate and the void to ensure that the ink has Enough transfer time.
The composition of the thermal transfer ink is generally three parts of a pigment (pigment or dye), a wax and an oil, wherein the wax is a main component of the thermal transfer ink.
3. Transfer medium
The substrate of the transfer paper is generally divided into a paper substrate, a polyester substrate and a celluloid substrate, and different substrates have different properties, so the following reference factors of the substrate should be noted when selecting the transfer paper.
● The thickness of the substrate should generally not exceed 20 μm;
● The substrate should have a high degree of smoothness to ensure the transfer rate of the ink;
● The substrate should have sufficient strength to ensure that it is not torn during transfer paper processing and printing.
2) Chemical properties
The uniform adhesion of the ink is two important manifestations of the chemical properties of the transfer paper substrate. The chemical properties of the transfer paper in production directly affect the quality of the print. If the transfer paper does not allow the ink to adhere well, or if the amount of ink is not well mastered in production, printing waste is caused. A good printing process and good prints must be based on a good grasp of the chemical properties of the transfer paper.
3) Good thermal performance
Since the transfer process is carried out by means of high temperature means, the material of the transfer paper must be able to withstand the influence of the transfer temperature and maintain the properties. In general, the thermal properties of the substrate of the thermal transfer paper are good and can be expressed by the following factors:
● The lower the heat resistance of the heat-resistant substrate, the thinner the thickness, the better the heat transfer, and the better the thermal properties;
● Smoothness The smoother the surface of the substrate, the lower the heat resistance, and the better the thermal performance;
●The heat-resistant thermal head temperature is generally around 300 °C.
Experience has shown that the print quality of a substrate with a rough surface is better, which is a remarkable feature of thermal transfer. Because the rough surface of the substrate indicates that the substrate has a large surface energy, the ink on the transfer paper can be transferred to the substrate well, and the desired level and tone are obtained. However, too rough will affect the normal transfer of ink, which is not conducive to the realization of the printing process.
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