To achieve high coverage of white ink heat transfer film on dark substrates, it is necessary to work together from three dimensions: ink, white ink heat transfer film, and process. As the core material, the hiding power of white ink mainly depends on the characteristics of the pigment. High-quality white ink usually uses titanium dioxide with a high refractive index as the pigment, which can effectively scatter light and block the absorption of light by the dark substrate, thereby improving the visual whiteness and coverage effect. At the same time, the formulation of the ink is also crucial. The rational use of dispersants can prevent pigment agglomeration, ensure uniform ink coating, and avoid light transmission caused by uneven pigment distribution.
The structural design of white ink heat transfer film directly affects the quality of the combination of ink and substrate. Common white ink heat transfer film consists of a base film, a release layer, and an ink layer. The base film needs to have good toughness and flatness to avoid wrinkles or blank areas during ink transfer due to film deformation. The release layer requires that during the heating and pressurization process, the white ink can be accurately and completely separated from the film and attached to the surface of the substrate. If the release effect is not good, some ink will remain, weakening the coverage effect.
Surface treatment of the substrate is a key pre-step to enhance coverage. If there is oil, dust or impurities on the surface of the dark substrate, it will hinder the adhesion of the ink. Therefore, it is necessary to improve the surface activity and roughness through pre-treatment methods such as cleaning and grinding. For example, metal substrates can be sandblasted, and fabrics can be pre-coated with primer to increase the intermolecular force between the substrate and the ink, so that the white ink can adhere more firmly and reduce the peeling or bottom penetration caused by insufficient adhesion.
Accurate control of thermal transfer process parameters is the decisive link to ensure the coverage effect. Temperature, pressure and time need to be balanced. Too low temperature will lead to insufficient ink fluidity and cannot fully fill the gaps on the surface of the substrate; too high temperature may cause the ink to carbonize or discolor, affecting whiteness. When the pressure is insufficient, the ink is not in close contact with the substrate, and it is easy to show the bottom; too high pressure may damage the film or substrate. The appropriate transfer time allows the ink to fully penetrate and solidify. Too short time will lead to incomplete transfer, and too long time may cause excessive diffusion of the ink and destroy the clarity of the pattern.
Multilayer coating technology is an effective means to improve hiding power. By applying white ink multiple times, the film thickness can be gradually increased to achieve more thorough hiding. After each coating, ensure that the ink is fully dried to avoid sticking or sagging. Although this method adds a process, it can significantly improve the coverage effect on high-contrast substrates such as dark leather and rubber.
The ink drying process should not be ignored. After thermal transfer, the ink needs to be dried and fixed quickly to prevent color migration or surface contamination. Common drying methods include hot air drying and infrared drying. Different drying methods will affect the curing speed and final performance of the ink. Reasonable selection of drying temperature and time can promote the cross-linking of internal molecules in the ink to form a dense protective film and enhance the stability and durability of the covering layer.
Finally, quality inspection and feedback optimization are the guarantee for continuous improvement of coverage effect. During the production process, it is necessary to promptly detect problems with insufficient coverage through visual inspection, glossiness testing, and other means, and trace whether it is caused by ink formula, process parameters, or equipment failure, so as to make targeted adjustments and optimizations, forming a closed-loop management from production to testing to improvement, thereby steadily improving the coverage performance of white ink heat transfer film on dark substrates.
