Thermal transfer technology film production process

1. Preparation of raw materials

a, preparation of the substrate film

There are many kinds of carriers for thermal transfer film, and PET is widely used. It has the characteristics of good dimensional stability, uniform tension, good heat resistance and good release property. In particular, there is a clear advantage in the reproduction of color tone manuscripts. 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 the material of the cylinder has "bumps" and "flank edges" and the like does 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, it is necessary to pay attention to controlling the viscosity during the coating process, that is, control. The solid content of the release agent 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 satisfactory. At the same time, pay attention to the transparency of the release agent, otherwise it will affect the effect of the printed layer.

c, ink preparation

The thermal transfer ink belongs to the gravure ink. The drying of the ink mainly depends on the volatilization of the solvent. After the substrate film is determined, the appropriate ink is selected according to the use of the printed matter and the nature of the printing material or according to the requirements of the construction sheet. Check the fineness, viscosity, hue, tinting strength and other indicators of the ink to see if all meet the printing quality requirements for the ink.

d, preparation of adhesive

The thermal transfer adhesive is a hot melt adhesive, which is a colorless transparent or light yellow viscous liquid. After coating and drying into a film, the film is transparent, and has a composite fastness on the surface of the release agent and the ink. Excellent flexibility, abrasion resistance, strong resistance to water, acid and alkali, and good weather resistance.

2. Precautions during the coating process

Once the material is ready, it can be printed on the 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

The substrate film is placed in the center of the take-up reel, passes between the embossing roller and the plate cylinder, and then passes through the constant tension traction roller to enter the reel, and the paper feeding force is adjusted according to the diameter of the reel, according to different materials coated. Set different drying temperatures.

b, coating release agent

Firstly prepare the release agent, pour into the coating tank and stir evenly, open the gravure printing machine, and coat the coated substrate film on the drying device. The drying temperature can be according to the temperature required by the release agent or The data provided by the manufacturer is set. The curing time of the release agent on the surface of the substrate film is very short, but in order to make the transfer effect better, the solvent must be completely evaporated before the coating ink is prepared, so the drying temperature can be appropriately higher, or in 2-4 colors. Dry on the group. The coating thickness of the release agent is controlled to be about 5 μm, and it should not be too thick or too thin. If the thickness is too thick, the release layer is easily peeled off from the substrate film, and too thin may cause the printed layer to be completely transferred during thermal transfer.

c, coating ink

The printed layer of the thermal transfer film is generally gravure printed. The substrate film roll coated with the release agent passes through the middle of the impression roller and the plate cylinder, the plate roller rotates in the ink tank, the graphic is printed, and after the drying device is printed The ink layer is dried to speed up the drying process. The drying of the thermal transfer ink is selected according to the solvent. If the solvent is a fast-drying toluene, the drying temperature can be appropriately lowered; if it is a 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, and the ink with low transparency is printed, and a layer of white ink is printed as needed. The function of the opaque white ink is to cover the color of the substrate itself, so that the image layer and color tone transferred to the colored object are not affected.

d, coating adhesive layer

In order not to destroy the graphic of the printed layer, the adhesive layer is to be carried out under the condition that the printed layer is completely dry. The adhesive layer can be directly coated in a color group of the gravure printing machine, and the coated base film is further dried. The drying temperature is determined according to different substrate films, and is wound up by the winding device.

e, winding and cutting

The inflation shaft of the winding is the same as the paper discharge shaft, and the winding force of the winding is controlled by the winding motor to control the traction force of the traction roller, which is generally the same as the tension of the paper feeding, so that the machine operates normally. When a take-up shaft is wound, it can be cut and then rolled onto another shaft. The thermal transfer film roll will be cut into finished products of different widths as required. In order to save cost, the thermal transfer image is usually uniformly 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 correcting device, otherwise it will affect the overall effect of the graphic.