Gravure printing has always been an important part of the printing process, and it consists of four major printing process systems: offset printing, flexo printing, and screen printing. The gravure printing process has the advantages of being very clear and the printing pattern is bright. With rich level reproduction capability, the printing plate is resistant to printing, and the high-speed operation can reach 250m/min or more. The suitable printing substrate is more extensive. In China, gravure printing is mainly used for plastic packaging and printing. With the development of printing technology and technological changes, gravure printing has expanded from flat printing to curved three-dimensional printing, especially in decorative printing. In the traditional plastic packaging gravure printing, the plastic film is the final printing printing product. In the new decorative gravure printing, the plastic film is the carrier of the printing ink pattern, and finally printed to the flat or curved price through various transfer methods. . There are many ways to transfer based on the different printing carriers. This paper mainly introduces plastic film as the carrier to introduce two new special gravure printing technologies; plastic film thermal transfer printing and water transfer printing (water drape).
The plastic film thermal transfer printing process refers to using a plastic film (usually a PET film) as a printing carrier, first applying a separation layer on the PET, and then printing various patterns on the separation layer, and then applying a thermal melting layer on the pattern. This completes the printing process of the thermal transfer film. Using this transfer printed film, the transfer pattern of the printed pattern is completed by pressing at a high temperature (typically 120 to 220° C.) in a certain thermal transfer machine. The thermal transfer printing process has a wide range of applications, such as architectural decoration accessories, furniture imitation wood-grained plates, daily-use plastic products, and stationery gifts.
The analysis of thermal transfer printing process is basically the same as traditional plastic packaging and printing, but it must be targeted and professional in the selection of raw materials. The carrier PET film of the film is generally an ordinary 12-15 μm film. The choice of ink and coating is the key to the production of thermal transfer printing film. Because this process has not been around for a long time in China, there are only a few specialized manufacturers engaged in the production of thermal transfer inks and coatings. Zhejiang New Oriental Ink Group introduced foreign technology through technical exchanges to produce plastic film thermal transfer matching inks and coatings. Fully meet the production requirements of the process. The separation layer requires high transparency and gloss, light color, blocking the adhesion of the printing ink to the PET film, and can also have a good affinity with the ink, and at the same time, needs excellent wear resistance. Due to the instant high temperature, the printing ink must be guaranteed not to fade or stick. It can be attached to various plastic substrates to ensure smooth processing of the transfer process. The hot-melt primer requires a good instant hot-melt effect and excellent adhesion, and works well with the ink layer. The thermal transfer ink produced by New Oriental Ink Company is A003 ink, the separation layer (bottom adhesive) is A001, and the hot melt adhesive is A007. The price of primers and hot melt adhesives produced in Taiwan or Japan is very high, and the compatibility with domestic thermal transfer inks is poor, and there is a lack of technical after-sales support. This series of products of New Oriental Ink Company has been confirmed by the use of many domestic manufacturers, three The cooperation between the good, after-sales service in place.
The success of thermal transfer printing film production directly affects the quality of transfer processing. According to our application experience, whether the transfer of the printing pattern is thorough, in addition to the temperature and contact time, the compatibility of the separation layer and the printing ink is a key factor, and the separation layer must not only have a certain fastness to the PET film, but also ensure The ink layer does not permeate in the past and has a fastness to the PET film. If the separation layer is poor in compatibility with the ink, it will affect the printing effect of the ink, and even the printed pattern will not color, and the transitional dots in the shallow printing area will be missing. . In the traditional plastic film printing, the transparent and glossy effects of the film itself greatly promote the gloss of the printed pattern. In the thermal transfer printing, the gloss of the pattern itself depends on the ink itself and the separation due to the separation of the final PET film from the printed pattern. The gloss and transparency of the layer (bottom adhesive), so we need to consider the transparency and gloss effect of the separation layer, and its wear resistance when selecting the ink and coating, especially the furniture panel, thermal transfer film for daily necessities plastic products During the production, in addition, we need to pay attention to the safety and sanitation of the printing ink itself when making thermal transfer film, such as heavy metal content. Especially when exporting products for export, Europe and the United States have relevant regulations and standards.
The water transfer printing process includes the production of a water transfer film, water transfer, and finishing. The water transfer film is produced by a gravure printer and a special ink to print a pattern (eg, wood grain, marble) on a water soluble film (PVA). The water transfer has a special set of forming equipment, and the general process is as follows: After the printing coil is sprayed with activating agent, it is immersed in hot water of a certain temperature, and the object to be printed is pressed into water to contact the printing film, and the pattern covers the surface of the object, due to water The dissolution, PVA film dissolution, price cleaning and drying. Finishing refers to the process of painting, painting, etc. on objects with transfer patterns. Water transfer technology has not been developed in China for a long time, but its development speed is very fast. Its application range is very wide, especially in automotive interior trim, furniture and communication products.
In the water transfer process, the most critical process is the production of a water transfer film. At present, domestically produced water-soluble printing films have a considerable gap with imported products in terms of flatness of the film and print applicability, although the price of domestically produced films is only 1/2 of that of imported films. The water-soluble printing film is mainly composed of polyvinyl alcohol (PVA) and soluble modified starch. The degree of alcoholysis and degree of polymerization of PVA are the main factors affecting the printing and post-processing performance of the film. In general, the degree of alcoholysis increases, the solubility of the film in cold water decreases, the solubility in hot water increases, the degree of polymerization increases, the strength and solvent resistance after film formation increase, and the solubility in water decreases. Increased stretch resistance. Moisture and temperature have a great influence on the water-soluble film. The printing shop should be able to keep constant temperature and humidity. Otherwise, due to the effect of moisture, the reel-up printing film is prone to anti-adhesion and stretching, resulting in a lot of film waste; when printing, Road temperature does not allow more than 50 °C, otherwise there will be due to the film softening and stretching caused by overprinting is not allowed.
The ink used for water-soluble film printing is dedicated, and not all inks are suitable for the printing of PVA film. ABC001 produced by Zhejiang New Oriental Ink is an ink specially used for water transfer printing. Compared to traditional plastic film printing, in addition to the above differences, the composition of the printing plate is also slightly different. In general, the number of printing plates for water transfer printing will not exceed three colors, the pattern is mainly some stripes plus For wood grain, etc., the last color needs to be coated with transparent varnish, which serves as the basis for the attachment of the independent pattern, preventing the floating of the pattern due to the dissolution of the water-soluble film and affecting the integrity of the printed pattern. Chao Lifu ABC001 water transfer printing ink and its matching varnish, with good printability, excellent solvent release, excellent anti-blocking properties, New Oriental Ink Company is also the only one in China's water transfer (water slope cover) Special ink manufacturers.
Plastic thermal transfer printing and water transfer printing processes are new special printing processes derived from traditional plastic gravure printing. They use gravure printing to expand into curved printing fields, inject new vitality into plastic gravure printing, and provide us with color printing manufacturers. New development opportunities. Because of the huge market potential and the rapid development of the transfer technology, due to the lack of related technologies and the lack of supporting raw materials, most of China's transfer printing films in the land area, especially the water transfer film, are mostly imported (including from Taiwan Into the mainland, so its profit margin is very large, and the ordinary color printing competition is fiercely abnormal. If our color printing manufacturers can accelerate technological development and occupy the market in advance, it is a very good opportunity for development. New Oriental Ink Company is willing to cooperate with us color printing manufacturers. Work together to provide advice for the development of ethnic enterprises and create a better tomorrow.
Author: Yu Yongyue
Source: Zhejiang New Oriental Ink Group Co., Ltd.