Heat transfer printing technology began to be put into production in some printing plants in the early 1970s. However, at this stage, most of the patterns of transfer printing paper are transferred to chemical fiber fabrics such as clothes, ready-made clothes, bags, or cut pieces. In the mid-1970s, transfer printing technology began to be put into continuous production like traditional printing. Due to the improvement of printing equipment, the quality of transfer printing base paper was correspondingly improved. Its machine printing paper production energy was generally 2000-3000 m / h.
Heat transfer printing is usually divided into heat melt transfer printing and heat sublimation transfer printing. Heat melt transfer printing is commonly used in all-cotton products. Thermal sublimation transfer printing is often used in polyester transfer printing, but its disadvantage is that the plate-making cost is high.
The sublimation method is commonly used in heat transfer printing. The principle is to transfer dispersed dyes to synthetic fibers such as polyester and fix them at high temperatures by using the sublimation characteristics of disperse dyes.
The specific process is to print the pattern on the paper with dispersed dye or ink through the roller or flat-screen after plate making, or the circular screen printing machine. Then, the transfer printing paper with patterns will be combined with the fabric through the transfer printing machine under the applicable temperature and pressure conditions. Through the physical and chemical action, the patterns on the paper will be sublimated and transferred to the fabric surface instantly, and at the same time, the patterns will diffuse and penetrate into the fiber’s inner layer to be fixed. This is the process of heat transfer printing on polyester fabric.
Heat sublimation transfer printing can be divided into offset printing, gravure printing, silk screen printing, and data printing according to different printing methods.
Advantages and disadvantages
Compared with traditional processes, heat transfer printing has the following advantages:
- Small floor space and short process flow;
- Because of the use of dispersed dyes sublimation fixation properties can be completely hair color fixation;
- It eliminates the post-treatment processes such as fixation and washing, thus eliminating the sewage problem. It is an environmentally friendly printing and dyeing method.
- Because the dye absorption of transfer printing base paper is much less than that of direct printing on the fabric, the cost is relatively reduced.
- The defects caused by complex color blending and pattern matching can be found when printing pattern paper and the defective pattern paper can be cut off before being transferred to the fabric, so as to ensure the genuine rate of the finished cloth after transfer printing.
- Due to the minimum width and permeability of the base paper, the transfer printing cloth has clearer patterns, clearer layers, and more uniform colors. The strong stereoscopic effect, especially in the halftone effect.
- It is suitable for small batch, multi-variety, and short delivery products.
- There are limitations in the scope of fiber application. The transfer process requires high temperature and high pressure, so it is mainly used for chemical fiber fabrics, mainly polyester fiber. The disadvantage of heat transfer printing is that it is difficult to achieve satisfactory scale production on natural fiber fabrics.
- Transfer paper requires a high and large amount.
Conditions affecting heat transfer printing
The temperature depends on the sublimation dyeing temperature of the dye, the heat resistance of the fiber, and the heat transfer time.
For disperse dyes used in heat transfer printing, the sublimation temperature should be lower than the melting point of fiber macromolecules and do not damage the fabric strength. The suitable processing temperature for polyester is 180 ℃ to 210 ℃.
Plate press: take 10KPA as the standard transfer pressure. If the pressure is insufficient, the transfer paper and the printed fabric are not closely matched, the printed pattern is uneven and the color is not bright; On the contrary, if the pressure is too high, the feel and style of the printed fabric will also change.
Roller transfer printing machine: in order to make the transfer paper closely coincide with the printed fabric, the blanket must be tightly wrapped on the surface of the hot roller, and the appropriate pressure is generally controlled at 12kpa.
Vacuum negative pressure heat transfer machine: under the negative pressure condition (13.3kpa), good coloring and penetration effects can be obtained, and the printed fabric feels very good.