Stamping with a new type of silicone relief production process

With the advancement of society and the continuous improvement of people’s living standards, people’s demands for printed matter are getting higher and higher. Not only do they require a spectrum of colors—color printing, but they also require more advanced metallic colors on printed matter. If metal ink is used for printing, not only the cost is high, but also the metal ink is exposed to the air for a long time and is oxidized by the oxygen in the air to darken the color. The use of anodized aluminum stamping is not only durable metallic gloss, beautiful and generous, but also economic benefits, so in recent years, aluminum foil stamping call for its unique finishing effect has been favored by people.

Although electro-aluminum hot stamping has many advantages mentioned above, if it is improperly grasped on various factors that affect the effect of electro-aluminum hot stamping, not only the ideal hot stamping effect will be obtained, but also the waste of raw materials will be caused.

Electro-aluminum hot stamping uses the pressure and heat of the hot stamping to stamp the foil on the substrate. Therefore, the quality of the hot stamping plate becomes one of the key factors affecting the hot stamping effect.

Traditional electro-aluminum hot stamping generally adopts copper plate or zinc plate as the hot stamping plate, and requires the entire hot stamping surface to have an unevenness within 0.15 mm, and the bending degree (for example, 250 mm long product) should be between 1 and 1.5 mm. Hot stamping foils and hot stamping surfaces may not be firmly bonded, and even hot stamping patterns may be incomplete. In other words, when the hot stamping surface of the substrate is not a surface that satisfies the above requirements for unevenness and bending, the traditional hot stamping plate will be powerless.

Second, the traditional copper and zinc hotplates are not suitable for hot stamping materials with high surface hardness and relatively brittle texture. For example, glass is easily broken under the pressure of copper plates and zinc plates, and it is not suitable for hot stamping of aluminum foil with traditional copper and zinc hot plates.

In order to solve this technical problem, after repeated research and experimentation, we finally developed a new type of electro-aluminum hot stamping plate, silicone relief plate, which is simple and practical. The production process of this kind of hot stamping silicone relief is similar to the current popular manufacturing technique of the rubber relief printing for flexographic printing.

1. Selection of silicone relief materials

When making silicone stamping for hot stamping, plate material selection is one of the main factors affecting the performance of the hot stamping plate.

First, the hot stamping temperature of anodized aluminum is generally 120~180°C. If the silicone stamping used for stamping anodized aluminum does not have good high temperature resistance and aging resistance, it is necessary to frequently change the stamping printing plate in hot stamping production. The cost of hot stamping must surely increase. If the hardness of the silicone stamp is not properly selected, there will be insufficient cutting of the hot stamping pattern on the printed product or a thickening of the hot stamping pattern.

In view of the above two situations that may occur in silicone relief, we have repeatedly tested and modified the formulation of silicone rubber and finally formulated a silicone rubber formula based on Wacker rubber produced in Germany. With this silicone rubber can produce silicone convex suitable for different hardness requirements, after the final test, has completely reached the use of hot stamping.

Second, we chose Fe2O3 as an antioxidant when selecting antioxidants in rubber formulations. After testing, we have greatly improved the oxidation resistance and aging resistance of rubber.

Third, in the process of selecting rubber vulcanizing agents, we chose the more commonly used dicumyl peroxide (abbreviated as DCP) as the rubber vulcanizing agent in order to make the silica gel plate have better elasticity, so that the elasticity of the silicone plate can be achieved. Hot stamping requirements.

Fourthly, after the silica gel letterpress molding is completed, there is usually a revision process. In order to reduce the labor intensity of the revision workers and improve the revision efficiency, silicone extrusion must have good processability. Therefore, in the development of silicone rubber formulations, the choice of filler is very important. We finally chose a silicon powder that is both economical and practical to reduce its wear resistance.

2. Silicone letterpress molding process

Silicone relief molding process - molding process, is also one of the main factors affecting the performance of silicone relief.

First, in order to facilitate the installation of a hot stamping plate on the hot plate of a stamping machine, it is necessary to first adhere the silicone rubber plate to a metal plate, and then use the metal plate as a plate base to be fixed on the hot plate of the stamping machine. According to the actual needs of use, we chose a high thermal conductivity, flexible aluminum plate as a carrier, the thickness of the aluminum plate is usually selected 0.5 ~ 2.0mm.

Under normal circumstances, silicone extrusion and aluminum plate can not be directly bonded between, in order to make silica gel plate and aluminum plate can be bonded together, and has a certain degree of adhesive strength, after several experiments, we have developed a kind of adhesive, The adhesive was applied to an aluminum plate that had been sanded and washed with ethanol, and allowed to stand still for 12 hours at room temperature. After that, the aluminum plate and the silicone rubber were bonded with high strength at a high temperature during molding.

Second, in the case of already having a copper relief and a zinc relief, how to rapidly fabricate a silicone printing plate that is completely consistent with the copper relief and zinc relief is one of the most critical issues in this development work. After many analyses, discussions, and experiments, we developed the molding process of the "thermosetting resin transition mold."

This molding process is similar to the flexographic printing process. That is, first use a copper relief plate and a zinc relief plate as the upper mold to mold a plastic mold opposite to the yin and yang; then, use the plastic mold as a “master model” to mold the silicone rubber under certain process conditions; thereafter After revision, we have created a silicone relief for stamping anodized aluminum.

In this process, if the transition mold - the material of the plastic die is not properly selected, it will make the final stamped out of the hot stamping of the silicone printing plate incomplete or flash, thus affecting the effect of hot stamping.

When a rubber plate for flexographic printing is generally produced, a phenolic resin is used as the transition mold. However, the phenolic resin is prone to air bubbles during the high-temperature molding process, thereby affecting the flatness of the die surface of the plastic die and causing the above-mentioned defects to occur in the final hot stamped silicone hot stamping plate.

In response to this situation, we chose a reinforced unsaturated polyester with good flowability, high strength after molding, and low shrinkage to suppress the transition die. That is, the use of copper plate, zinc plate as a "master model" under certain conditions molded unsaturated polyester, will be made of transitional mode.

Once the die is made using this process, it is easy to mass produce hot stamping silica gel. Therefore, when a large quantity of anodized aluminum is used for hot stamping, the hot stamp manufacturing method is used, on the one hand, the operation is simple, the processing is quick, and on the other hand the cost is low.

In today's widespread use of electro-aluminum hot stamping, due to its many advantages, we believe its application prospects will be very broad.

Source: "Printing Technology - Packaging and Decoration Printing"

(Author/Wang Jingping Qian Junfeng Jing Xinli Guo Linghua)