Thermal Transfer Technology Film Production Process

1. Preparation of raw materials

a. Preparation of substrate film

There are many kinds of carriers for thermal transfer film, and PET is widely used, which has the characteristics of good dimensional stability, uniform tension, good heat resistance effect and good release properties. In particular, it has obvious advantages in the reproduction of color tone originals. The specifications of the film such as width, thickness 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 there are "ribs" and "lotus leaf edges" in the tube material that do not meet the quality requirements.

b. Preparation of release agent

The release agent is a low-viscosity transparent resin with release, film-forming and adhesive properties. Because the solvent in the release agent volatilizes faster, during the coating process, attention should be paid to controlling the viscosity, that is, controlling The solid content of the release agent is generally controlled at about 23%. If the solid content is lower 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. The drying of ink mainly depends on the volatilization of solvent. After the substrate film is determined, select the appropriate ink according to the use of the printed matter and the properties of the printing material or according to the requirements of the construction sheet. Check the ink's fineness, viscosity, hue, tinting strength and other indicators to see if all meet the printing quality requirements for the ink.

d. Preparation of adhesive

The adhesive for thermal transfer printing is a hot melt adhesive, which is a colorless transparent or light yellow viscous liquid. After coating and drying to form a film, the film is transparent and has compound fastness and High flexibility, abrasion resistance, strong resistance to water and acid and alkali, and good weather resistance.

2. Precautions during the coating process

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

a. Unwinding

Install the substrate film in the center of the unwinding shaft, pass through the middle of the embossing roller and the printing plate cylinder, and then pass through the constant tension pulling roller into the winding shaft, adjust the feeding force according to the diameter of the roll, and coat different materials according to Set different drying temperatures.

b. Coating release agent

First prepare the release agent, pour it into the coating tank and stir evenly, start the gravure printing machine for coating, and dry the coated substrate film on a drying device. The drying temperature can be based on the temperature required by the release agent or Set 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, the solvent must be completely volatilized before preparing the ink for coating, so the drying temperature can be appropriately higher, or in 2-4 colors Dry on set. The coating thickness of the release agent is controlled at about 5μm, and it should not be too thick or too thin. Too thick will make the release layer easily 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. Pass the substrate film roll coated with the release agent through the middle of the embossing roll and the printing plate roll, and the printing plate roll rotates in the ink tank to print the pictures and texts, and then pass through the drying device to print after printing. The ink layer is dried to speed up the drying speed. The drying temperature of thermal transfer ink is selected according to its solvent. If the solvent is fast-drying toluene, the drying temperature can be appropriately lowered; if it is slow-drying xylene, the drying temperature should be increased. At the same time, note that the printing color sequence of the thermal transfer film is opposite to the general printing color sequence, that is, the ink with high transparency is printed first, then the ink with low transparency is printed, and a layer of white ink is printed as needed. The function of opaque white ink is to cover the color of the substrate itself, so that the level and tone of the image and text 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 when the printed layer is completely dry. The adhesive layer can be directly coated on one color group of the gravure printing machine, and the coated substrate film is then dried. The drying temperature is determined according to different substrate films, and is wound by the winding device.

e. Rewinding and cutting

The inflatable shaft of the rewinding is the same as the unwinding shaft, and the winding force of the rewinding is controlled by the rewinding motor to control the traction force of the traction roller, which is generally the same as the tension at the unwinding place, so that the machine can run normally. When one reel is finished, it can be cut and changed to another reel. The rolls of thermal transfer film are cut into finished products of different widths as required. In order to save costs, the thermal transfer graphics are usually evenly distributed on a printing plate according to the size, and then cut when used. At the same time, it is important that the cutting machine must have an automatic deviation correction device, otherwise it will affect the overall effect of the picture and text.