Thermal transfer technology film production process

1. Preparation of raw materials

a. Preparation of substrate film

There are many kinds of carriers for heat transfer film, and PET is widely used. It has the characteristics of good dimensional stability, uniform tension, good heat resistance and good release. In particular, it has obvious advantages in the reproduction of color gradation originals. The specifications of the film, such as width, thickness, size and grade, are selected according to the manufacturer's requirements. At the same time, it is necessary to check the flatness of the film and whether the barrel material has "protruding ribs", "flounces" and other conditions that do not meet the quality requirements.

B. Preparation of release agent

The release agent is a low-viscosity transparent resin with release property, film-forming property and adhesion. Because the solvent volatilizes faster in the release agent, attention should be paid to controlling the viscosity during the coating process, I .e. controlling the solid content of the release agent. The solid content is generally controlled at about 23%. If the solid content is less than 19%, the transfer effect of the thermal transfer film after coating the release agent is not ideal. At the same time, pay attention to the transparency of the release agent, otherwise it will affect the effect of the printing layer.

c. Preparation of ink

Thermal transfer ink belongs to gravure printing ink, ink drying mainly depends on the volatilization of solvent, substrate film to determine after, according to the use of printed matter and the nature of the printing material or according to the construction of a single request to choose the appropriate ink. Check the ink fineness, viscosity, hue, tinting strength and other indicators to see if all meet the printing quality requirements of the ink.

d. Preparation of adhesive

The adhesive for thermal transfer is hot melt adhesive, which is colorless, transparent or light yellow viscous liquid. After coating and drying to form a film, the film is transparent. It has composite fastness and flexibility on the surface coated with release agent and ink. It has strong resistance to water, acid and alkali and other media and good weather resistance.

2. Precautions in the coating process

When the material is fully prepared, it can be printed on the printing machine. Generally, the release layer, the printing layer and the adhesive layer are coated and printed on the same gravure printing machine.

a. unwinding

The substrate film is installed in the center of the unwinding shaft, passes through the middle of the impression roller and the printing plate cylinder, and then passes through the constant tension traction roller to enter the winding shaft. The paper conveying tension is adjusted according to the diameter of the winding shaft, and different drying temperatures are set according to different materials coated.

B. Coating release agent

First, the release agent is prepared, poured into the coating tank, stirred evenly, opened the gravure printing machine for coating, and the coated substrate film is dried on the drying device. The drying temperature can be set according to the temperature required by the release agent or the data provided by the manufacturer. The curing time of the release agent on the surface of the substrate film is very short, but to make the transfer effect better, it is necessary to let the solvent volatilize completely before preparing to coat the ink, so the drying temperature can be appropriately higher, or dry on 2-4 color groups. The coating thickness of the release agent is controlled at about 5μm, and cannot be too thick or too thin. Too thick will make the release layer easy to fall off from the substrate film, and too thin will cause the printing layer to not be completely transferred during thermal transfer.

C, coating ink

The printing layer of the thermal transfer film generally adopts gravure printing. The substrate film roll coated with the release agent passes through the middle of the embossing roller and the printing plate roller, the printing plate roller rotates in the ink tank to print out pictures and texts, and then the printed ink layer is dried by the drying device to speed up the drying speed. The drying temperature of thermal transfer ink is selected according to its solvent. If the solvent belongs to fast-drying toluene, the drying temperature can be appropriately reduced; if it is slow-drying xylene, the drying temperature should be increased. At the same time, attention should be paid to the printing color sequence of the thermal transfer film, which is opposite to the general printing color sequence, I .e. printing ink with high transparency first, then printing ink with low transparency, and printing a layer of white ink as required. The function of opaque white ink is to cover the color of the substrate itself, so that the graphic level and tone transferred to the colored object are not affected.

d. Coating adhesive layer

In order not to damage the graphics of the printed layer, the adhesive layer should be carried out under the condition that the printed layer is completely dried. The adhesive layer can be directly coated on a color set of the gravure printing machine, and the coated substrate film is dried again. The drying temperature is determined according to different substrate films and is wound by the winding device.

E, winding and cutting

The inflatable axis of winding is the same as the paper discharge axis, and the winding force of winding is controlled by the winding motor to control the traction force of the traction roller, which is generally the same as the tension at the paper discharge position, so that the machine can operate normally. When one take-up shaft is finished, it can be cut and changed to another shaft. The heat transfer film roll will be cut into finished products of different widths as required. In order to save costs, the thermal transfer graphic is usually made on a printing plate according to the size of the uniform distribution, and then cut when in use. At the same time, it is important that the cutting machine has an automatic correction device, otherwise it will affect the overall effect of the graphic.