Thermal transfer technology of membrane process

Film making process of heat transfer printing technology

1. Preparation of raw materials

a. Preparation of substrate film

There are many kinds of carriers for heat transfer film. 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 tone original. Film specifications such as width, thickness, size and brand are selected according to the manufacturer's requirements. At the same time, check the flatness of the film, whether there are "protruding ribs" and "ruffles" in the cylinder material that do not meet the quality requirements.

b. Preparation of release agent

Release agent is a kind of low viscosity transparent resin with release property, film-forming property and adhesiveness. Because the solvent in the release agent volatilizes faster, in the coating process, we should pay attention to controlling the viscosity, that is, 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 heat 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

Heat transfer ink belongs to gravure printing ink. The drying of ink mainly depends on the volatilization of solvent. After the substrate film is determined, the appropriate ink should be selected according to the purpose of the printed matter and the nature of the substrate material or according to the requirements of the construction order. Check the ink fineness, viscosity, hue, coloring power and other indicators to see if all meet the printing quality requirements for the ink.

d. Preparation of adhesive

The adhesive for heat transfer printing is hot-melt adhesive, which is colorless, transparent or light yellow viscous liquid. After coating and drying, the film is transparent. It has compound fastness and flexibility on the surface coated with release agent and ink, strong abrasion resistance, water resistance, acid and alkali resistance, and good weather resistance.

2. Precautions in coating process

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

a. Unwinding

The substrate film is placed in the center of the unwinding roll, passes through the middle of the imprint roll and the plate cylinder, and then passes through the constant tension traction roll to enter the unwinding roll. The paper feeding tension is adjusted according to the diameter of the roll, and different drying temperature is set according to different materials.

b. Coating release agent

First, the release agent is prepared, poured into the coating tank and stirred evenly. Then, the gravure printing machine is started for coating. 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. Release agent in the surface of the substrate film curing time is very short, but to make the transfer effect is better, we must let the solvent volatilize completely before preparing the coating ink, so the drying temperature can be appropriately higher, or in 2-4 color group drying. Release agent coating thickness control in 5 μ It is not too thick or too thin, too thick will make the release layer easy to fall off from the substrate film, too thin will lead to the printing layer can not be completely transferred.

c. Coating ink

The printing layer of heat transfer film is generally gravure printing. The substrate film reel coated with release agent passes through the middle of the embossing roller and the plate roller. The plate roller rotates in the ink tank to print 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 heat transfer ink is selected according to its solvent. If the solvent belongs to fast drying toluene, the drying temperature can be appropriately reduced; For slow drying xylene, the drying temperature should be increased. At the same time, pay attention to the printing color sequence of the heat transfer film, which is opposite to the general printing color sequence, that is, first print the ink with high transparency, then print the ink with low transparency, and then print a layer of white ink as needed. 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 image and text of the printing layer, the adhesive layer should be carried out when the printing layer is completely dry. The adhesive layer can be directly coated in one color group of gravure printing machine, and then the coated substrate film is dried. The drying temperature is determined according to different substrate film, and the winding device is used for winding.

e. Winding and cutting

The air expansion 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, which is generally the same as the tension at the paper discharge position, so that the machine can operate normally. When one winding 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 according to the requirements. In order to save the cost, the heat transfer image and text are usually evenly distributed on a plate according to the size, and then cut when used. At the same time, it is important that the cutting machine must have automatic correction device, otherwise it will affect the overall effect of graphics.