With the rapid development of packaging and printing industry, the application of hot stamping process is more and more extensive, especially in the packaging box of goods. Its application can often play the role of finishing touch, highlight the design theme, and improve the added value of products to meet the requirements of different printing customers. This article is edited by Shanghai rainbow package to share three technology applications that are difficult to control in hot stamping process
The gilding process is to transfer the aluminum layer in the anodized aluminum to the substrate surface using the principle of hot press transfer to form a special metal effect. According to the specification, gilding refers to the thermal transfer printing process of stamping anodized hot stamping foil (hot stamping paper) to the substrate surface under a certain temperature and pressure. Since the main material used for gilding is anodized aluminum foil, gilding is also called anodized hot stamping.
01 Stamping on UV varnish
UV glazing can improve the gloss of printed products, and its unique high gloss effect is recognized by the majority of customers. Hot stamping on UV varnish can obtain very good visual effect, but its process is difficult to control. This is mainly because the hot stamping suitability of UV varnish is not yet mature, and the resin composition and additives of UV varnish are not conducive to hot stamping.
However, when processing some products, the process of hot stamping on UV varnish cannot be avoided. The original production process needs to go through three processes of offset printing, hot stamping and polishing. After the new materials are used, offset printing and polishing can be completed once and then hot stamping can be done. In this way, one process can be reduced and the impact of one UV curing can be reduced, thus avoiding the phenomenon of paper die cutting color explosion, greatly improving the production efficiency and reducing the scrap rate.
However, at this time, it is necessary to hot stamp on UV varnish, which puts forward quite high requirements for UV varnish and hot stamp anodized. Attention should be paid to the following aspects.
1) When glazing, pay attention to controlling the amount of varnish. UV varnish must have a certain thickness to achieve the effect of high brightness, but too thick varnish is bad for hot stamping. Generally, when the UV varnish layer is coated by offset printing, the polishing amount is about 9g/m2. After reaching this value, if the brightness of the UV varnish layer needs to be improved, the flatness and brightness of the varnish layer can be improved by adjusting the coating process parameters (coating roller screen wire angle and number of screen wires, etc.) and the performance of the printing equipment (printing pressure and printing speed, etc.).
2) Try to ensure that the varnish coating of the whole batch of products is relatively stable, and the varnish layer should be thin and flat.
3) Reasonable selection of hot stamping materials. It is required that hot stamping materials have high temperature resistance, good adhesion, and good affinity between its adhesive layer and UV varnish resin.
4) Accurately adjust the temperature and pressure of the hot stamping version, because too high pressure and temperature will damage the ink performance and make hot stamping more difficult.
5) Hot stamping speed should not be too fast.
02 Hot before printing
The process of hot stamping followed by printing is generally to enhance the metal visual sense of the printed pattern, and to adopt a process method of hot stamping followed by four color printing on the hot stamping pattern. Usually, the gradual and metallic color patterns can be printed with dot overlay, which has good visual performance. The following matters shall be noted during the actual operation of this process:
1) The requirements for hot stamping anodized aluminum are very high. At the same time, the hot stamping position is required to be very accurate. The surface of the hot stamping pattern is smooth and bright, without bubbles, paste, obvious scratches, etc., and the edges of the hot stamping pattern cannot have obvious indentation;
2) For white cards and glass cards, special attention should be paid to the protection of semi-finished products, and the influence of various adverse factors such as paper deformation should be minimized during the production process, which will greatly help the smooth process of hot stamping and the improvement of product qualification rate;
3) The adhesive layer of anodized aluminum shall have very high adhesion (special adhesive layer shall be developed for cigarette package products if necessary), and the surface tension of anodized aluminum shall not be less than 38mN/m;
4) Before hot stamping, it is necessary to output positioning film, and ensure the accuracy of hot stamping and printing overprint by adjusting the exact position of the hot stamping plate;
5) Before mass production, the products that are hot before printing must be subject to film pulling test. The method is to use 1 inch transparent tape to directly pull the hot stamped anodized aluminum, and observe whether there is gold powder falling, incomplete or insecure hot stamping, which can prevent a large number of waste products in the printing process;
6) When making the film, pay attention to the unilateral expansion range, which should generally be within 0.5mm.
03 Holographic positioning hot stamping
Holographic positioning hot stamping can be applied to prints with anti-counterfeit patterns, greatly improving the anti-counterfeit ability of products, and also improving the quality of products. Holographic positioning hot stamping requires very high control of temperature, pressure and speed, and the hot stamping model also has a great impact on its effect.
In holographic positioning hot stamping, the accuracy of overprint is directly related to the quality of the product. The hot stamping film should be shrunk and expanded by 0.5mm on one side. Generally, holographic positioning hot stamping adopts hollow hot stamping. In addition, the cursor of the holographic positioning hot stamping material should be uniform, and the pattern should be evenly spaced, so that the machine can accurately track the hot stamping cursor.
04 Other precautions：
1) The appropriate anodized aluminum must be selected according to the type of substrate. When hot stamping, you must master the temperature, pressure and speed of hot stamping, and treat them differently according to different hot stamping materials and areas.
2) Paper, ink (especially black ink), dry oil, composite adhesive, etc. with appropriate properties shall be selected. The hot stamping parts must be kept dry to avoid oxidation or damage to the hot stamping layer.
3) Generally, the specification of anodized aluminum is 0.64m × One 120m roll, one box for every 10 rolls; Large rolls with width of 0.64m, length of 240m or 360m or other special specifications can be customized.
4) During storage, anodized aluminum shall be protected against pressure, moisture, heat and sun, and placed in a cool and ventilated place.
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Post time: Oct-19-2022