Label printing and ink analysis (middle)
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Second, the choice of label ink
There are many types of label printing inks, which can be divided into three categories according to the solvent used: water-based label printing ink, solvent-based label printing ink and UV label printing ink.
Water-based ink is safe, hygienic, non-polluting, and meets environmental protection requirements, which is conducive to human health; but it also has shortcomings, such as slow drying speed, low color saturation, poor stability, etc. It is not suitable for printing large areas, and it is easy to precipitate and divide. Layer phenomenon.
Solvent-based label printing inks have strong adaptability to label materials, stable performance, and high printing quality; however, there are environmental pollution problems, and some volatile solvents are harmful to the human body.
UV label printing inks have excellent performance, reliable quality and wide application range; however, the price is high, and special drying equipment is required, and there are certain requirements for supporting materials.
When selecting the label printing ink, it is necessary to comprehensively consider the type of printing material, printing method and printing conditions, customer's special requirements, post-press processing, label use, use conditions, cost and other factors. The performance of label printing inks mainly includes hue, fineness, saturation, gloss, adhesion, viscosity, dryness, etc. These properties have an important influence on the printing process and printing quality.
Third, self-adhesive printing process
Flexographic printing is a new type of printing process generally promoted in the international printing industry. Its advantages are simple machine structure, low cost, comparable printing quality to gravure printing, and the advantage of thick ink layer not available in offset printing; Its ink uses water-based inks and does not pollute the environment. Some developed countries have legislation that requires packaging labels for food and medicine to be printed flexibly.
Currently, the flexographic printing plates of the self-adhesive labels are mostly made of a solid resin plate, and the inks are generally ink or UV ink. Although the flexo has the advantage of full ink color, the printing network cable is limited, generally only 133 lines/inch, which is far from satisfying the requirements of the sticker users for the higher quality of the printed products.
The flexographic self-adhesive label printing equipments are all narrow-format flexographic printing machines. They are mainly made in China. The equipment has two characteristics: one is to use UV ink instead of water-based ink. UV inks are stable and avoid frequent cleaning of the plates and inking systems. More importantly, the color density of UV inks is greater than that of water-based inks, which improves the print quality of labels. Another feature is the widespread use of film-free direct laser plate-making technology, which avoids the loss of small dots, the level of large dots, improves the image level, and greatly improves the image clarity and printing quality.
Flexographic printing, with its high-quality prints, the unique advantage of what is called "green printing" will become the trend of future self-adhesive label printing. Therefore, it is no exaggeration to say that flexographic printing self-adhesive labels are the future development direction. At present, the flexographic printing equipment produced by domestic enterprises using domestic resources and foreign technology is gradually being used by domestic printing enterprises in terms of printing quality and price. Accepted, the market share of applying flexographic stickers is growing rapidly.
Fourth, self-adhesive materials
Self-adhesive labels are mainly used for decorative materials and trademark materials. The decoration materials are mainly film, mainly used for decorative decals on automobiles and motorcycles, logo characters on trademark windows, reflective films on highways, markings on containers, etc. The trademark materials are mainly paper and film, and are subdivided into basic labels and variable information labels according to the scope of application. The basic labels mainly include labels for foods and beverages, chemical products, pharmaceuticals, office supplies, toys, shampoos, electrical appliances, and sanitary products. Variable information labels include lot number, sequence code, barcode, date of manufacture, expiration date, price, postal process information processing, distribution, warehouse management, inventory data, and more.
The self-adhesive material consists of three parts: face material, glue and backing paper. Choosing a suitable customer's self-adhesive product is by no means an easy task. According to the experience of professional workers, we should understand the following aspects:
1. The permanent and removable nature of the adhesive. In terms of the performance of the adhesive, the overall can be divided into two categories: permanent and removable.
2. Emphasize the meaning of the label surface. Labels processed with self-adhesive materials may be labeled on the surface of various materials, and different label surfaces have a great influence on performance.
3. The surface structure and shape of the substrate. Intuitively, a rough label surface requires a more viscous glue. The surface of the label substrate has a flat surface and a curved surface. If the surface of the label has a certain curvature (for example, the surface of a vial having a diameter of less than three centimeters), the surface paper may have a good conformability or a relatively strong viscosity.
4. The cleaning condition of the label surface. Adhesive materials are best suited for label substrates with clean, dry, oil-free and dust-free surfaces.
5. The adverse effect of plasticity on the glue is the requirement of climate tolerance. For example, whether the viscosity of the adhesive needs to be applied under cold, hot, humid or room temperature conditions; whether the self-adhesive label is exposed to the environment below freezing point; whether it is used outdoors, under high temperature, humidity or under ultraviolet light, And whether it is close to a car engine with a higher temperature.
6. Printing methods and processing methods for the requirements of self-adhesive materials. After choosing different printing methods (such as flexographic printing, letterpress printing, offset printing, thermal transfer and laser printing) and processing methods (such as roll-to-roll, roll-to-sheet, folding feed, single to single) Before you can decide on the printed materials.