Postpress Technology 1000 (3)

twenty four. What are the main varieties of calender coating resins?

Calendered coatings, like general coatings, consist of resins, solvents, and small amounts of additional components. At present, the resins used for coating calendering at home and abroad mainly have the following varieties (see Figure 3).

Figure 3

25. Coating calendering process should pay attention to what issues?

1 temperature. The temperature of the heat roll for coating calendering is generally 100~200°C. When the temperature is too high and the humidity of the paper is too high, blistering and paper delamination may occur. If the temperature is too low, the gloss may be poor.

2 pressure. When the pressure is too great, the pressure is uneven, and the humidity of the paper is too large, and the humidity is uneven, the wrinkle of the printed matter may occur.

3 speed. The calendering speed is the curing time of the varnish in calendering. If the curing speed is short (speed is fast), the coating oil molecules can not fully function with the ink layer on the surface of the printed matter. After drying, the surface smoothness of the film layer is poor, and the adhesion of the coating oil to the ink layer is poor.

4 gloss. Ensure that the coating has a certain thickness, the temperature is slightly higher in the possible range, and the light band is clean to ensure the production of high-gloss paint press prints.

5 sticky tape. The stainless steel belt is not cleaned and polished in time, the hot-pressing temperature is too high, the calendered resin is not suitable, and the coating is too thin, etc., all of which are likely to cause a sticking phenomenon and are not easily peeled off.

26. What is the application range of coating calendering?

The coating calendering is suitable for glazing of high-grade trademarks, product brochures, and art photos, postcards, etc. It is also suitable for coating white paper prints for packaging to replace expensive glass paperboard.

27. What is the process characteristic of coating calendering?

The paint press prints have strong gloss, smooth and delicate surface, no stickiness and yellowing, moisture resistance, water resistance, etc. The processing cost is relatively low, but there are many processes and the production efficiency is not high. In addition, the resistance to folding and abrasion of the paint calendered prints is not as good as that of paper-plastic composite processing, but it does not cause various problems caused by the use of films and poor adhesion of paper-plastic composites.

28. What is UV polishing?

UV coating is a method of curing varnish coating using uV (abbreviation of UltraViolet, ie, ultraviolet light) irradiation.

29. Why UV glazing is more suitable for paper print processing?

The characteristics of rapid solidification and low-temperature curing of uV coatings help solve many problems in gloss processing of paper prints. Therefore, they have been widely used in the gloss processing of paper printers, trademarks, seals, pictures, and tape covers. In foreign countries, the glossy finish of books, magazines, and covers is painted with uV, which is also common.

30. Why does UV Varnishing have great potential to replace plastic composites?

uV glazing has rapidly emerged and has largely replaced plastic composites in many products, depending on its own characteristics:

1 The air pollution is small. Since uV coating oil contains almost no solvent, organic volatiles emissions are minimal, thus reducing air pollution, improving the working environment, and reducing the risk of fire.

2 Curing speed. Shaanxi New Century Printing Material Co., Ltd. has developed a special coating for textbooks to meet the needs of the UV cover of the textbook cover. This coating oil has a strong affinity for ink and is firmly attached. The curing speed can reach 60 to 120 m/Min.

3 Polishing quality is good. After being processed by uV coating process, the color of the printed matter is obviously brighter than other processing methods, the luster is plump and moist, and the cured coating is slippery and wear-resistant. It is also more resistant to chemicals and chemicals, and has good stability. Can scrub with water and ethanol.

4 Low cost. uV coating oil has many active components and less volatilization. Therefore, the amount of coating is usually 4 g/m2, and the cost is about 60% of the cost of coating film.

5 can avoid the plastic film coating process often appears defects. Avoid the phenomenon of edging, blistering, wrinkling, delamination, etc. Uv glazing products do not stick, after stacking, they can stack up, which is conducive to post-processing operations such as binding.

6 can be recycled. For example, recycled papermaking solves the problem of environmental pollution caused by the failure of paper-based plastic recycling.

31. What is the basic composition of UV coating paint?

The UV coating used for UV curing and drying varies depending on the composition, the type of resin, and the curing device. Its main classification is shown in Table 3:

table 3

At present, the vast majority of foreign paper printing Uv coating products, the use of free radical polymerization acrylic.

32. What is the curing mechanism of uV coating varnish?

Solvent-based coatings are almost always cured by solvent evaporation and drying, while uV coatings rely on the power of ultraviolet light to cure them. After the uV coating is irradiated with ultraviolet rays, the photoinitiator in its component absorbs the ultraviolet light energy, generates free radicals after being excited, and initiates the polymerization reaction.

33. What kind of uV polish oil?

There are many kinds of uV varnish. According to the color ink type, it is divided into uV varnish for uV ink, uV varnish for oil varnish, and uV varnish for both. It can be divided into off-line UV varnish, on-line UV varnish, or both UV varnish, depending on the coating process. According to the use of sub-paper bags with UV Varnish, the general box with UV Varnish, medicines, food packaging with UV Varnish and so on.