The influence factors and problems of hot stamping process

Electro-aluminum hot stamping has advantages that can't be compared with other technologies in terms of improving packaging grades, brand identification, and product security. Therefore, it has been increasingly used in the surface decoration of folding cartons.

In the past two years, the materials used in folding cartons, printing processes, etc. have undergone major changes, such as: aluminum foil, laser cardboard, vacuum aluminum plating transfer paper and other packaging materials gradually applied, UV printing, UV coating, Screen printing (ice, refraction) and other printing and surface finishing processes have also been born one after another. All these have put forward higher requirements for hot stamping of aluminum foil.

This article analyzes the technical problems associated with the electro-aluminum hot stamping encountered in the actual production process of the printing plant, hoping to provide some reference for the printing factory.

First, the factors affecting the bronzing process

1. Hot stamping temperature

All of the aluminum alloys have their recommended hot stamping temperature, and the temperature variation is usually around ±10°C. In the production process, the elevated temperature is often the first solution that the operator thinks when he or she encounters issues such as poor heat or poor adhesion. However, excessively increasing the stamping temperature is not only unfavorable to the solution of the problem, but may cause the adhesive molecules of the adhesive layer to stick together and cause the paste plate, causing the dyeing layer to overheat and appear rainbow patterns and spots. The aluminum also undergoes an oxidation reaction at a high temperature to darken the color.

2. Stamping pressure

The adjustment of the pressure in the electro-aluminum hot stamping can not be ignored. The pressure is small, and the hot stamping or the hot stamping pattern cannot be adhered firmly; the pressure is high, which can cause problems such as paste printing and thickening of hot stamping lines.

Second, hot stamping process appears new situation and solution

1. Laser stamping on cardboard

When stamping on laser card paper, high-adhesion anodized aluminum should be selected. At the same time, when performing large-area hot stamping, care should be taken to ensure that bubbles are generated. Different from plain paper, there is no adsorption of gas by the fiber pores in the laser jam. Therefore, the air between the laser jam and the electrochemical aluminum will form bubbles if it escapes too late. In severe cases, it may pass through the aluminum. "Pinhole", in this case, the pad should be slightly higher than the middle to make the air easier to escape; or when ordering the electric engraving, the supplier needs to make the hot plate center slightly higher than the surrounding.

2. Reprint on hot stamping foil

In order to better reflect the design effect, some cartons use a hot stamping process (usually laser aluminum foil stamping) followed by a UV printing process. Pay attention to the following issues during the production process.

(1) Since the hot stamping plate is heated and swellable, if the overprinting precision of the printing pattern and the hot stamping pattern is required to be high, then the hot stamping film must be 0.02 mm in circumference when the hot stamping film is produced before printing.

(2) Select an electro-aluminum with a surface tension of (4.0 to 4.6) x 10-4N to ensure good adhesion of the printing ink.

(3) During the hot stamping process, attention should be paid to the quality of hot stamping. If the adhesion of electro-aluminum is not strong, there will be phenomena such as “flying gold” and stencil printing. In the offset printing process, metal powder will easily accumulate on the blanket, causing frequent shutdowns and affecting the production efficiency.

(4) After printing, the UV ink is printed on it, but it is not firmly attached and can be removed by hand. There are two reasons for this phenomenon: 1 During the hot stamping process, the wax in the aluminized peeling layer is not completely melted and remains on the surface of the aluminum foil. In this case, the temperature can be increased by 810°C during hot stamping to completely melt the wax. 2 The adhesion of the ink itself is not strong. Try other kinds of UV inks.
(5) If there is a phenomenon that the electrochemical aluminum powder is not accumulated on the blanket, it can be added to reduce the viscosity of the ink, or by changing the printing sequence.

3. Electrochemical aluminum hot stamping on UV varnish

Not all UV varnish can be stamped with anodized aluminum. UV Varnish contains acrylic acid monomer, silicone resin and other ingredients. Among them, the amount of silicone determines the glossy, smoothness, and abrasion resistance of the varnish, and it is also the most important factor that affects the UV varnish hot stamping applicability. During the curing process of the UV varnish, the silicone resin migrates to the surface of the varnish film, thereby affecting the embossing of the aluminum foil. In order to increase the hot stamping properties of UV varnish, varnish suppliers can use melamine resin to partially replace silicone, but this also reduces the gloss of UV varnish.

When a large-area hot stamping is performed on the surface of a UV varnish or a waterborne varnish layer, a "bubble" phenomenon may occur, that is, when the varnish or ink is not completely dried, an electro-aluminum hot stamping is performed. Under the hot pressure, moisture becomes steam, Unable to escape from the stamping pattern. The solution to this problem is to re-dry the printed or glossed prints. Of course, the best method is to first hot stamp, after the UV Varnish, this must confirm that the varnish can be stamped on the aluminum.

In addition, for some prints obtained by screen printing on UV laser paper to obtain special texture effects such as UV frosting, refraction, ice, etc., the part that needs to be stamped with anodized aluminum should be hollowed out on the screen plate to avoid electrification. Aluminum hot stamping is not on.

The emergence of new materials and new processes puts higher requirements on the traditional hot stamping process. The adjustment in the electro-aluminum hot stamping is no longer a simple adjustment of the temperature, pressure and speed (hot stamping time) balance point, hot stamping Problems that may arise in the course of time may be the result of the interaction of many factors, which requires the operator to learn more about materials and processes while mastering the hot stamping techniques. (Wen / Wang Weifeng)