Application of Waterborne Varnish and Problems to Be Noted (I)

First, what is printing

The so-called printing glazing is the surface of the replica that has been completely printed in the graphic and text printing process. The printing plate is printed once or twice with a solid printing plate or a graphic plate, and the surface of the printing object is given a bright film layer. method. Printing glazing can enhance the lightfastness of the ink, increase the heat resistance and moisture resistance of the ink layer, and play a role in protecting the print and beautifying the product.

Printing glazing and other methods are more cost-effective, easy-to-manufacture, easy-to-operate, and have the greatest advantage over the treatment methods that add glossy film to the surface of the printed product. , Selective glazing, both full version glazing (no special plate, no flat plate for letterpress printing, offset printing, no special new plates, the use of the original plate on the machine), or partial glazing Because the principle of transfer between printing and printing is the same as the principle of printing and graphic printing, the printing plate is used to transfer the adsorption layer on the substrate, and the principle of non-adsorption of the blank is used. According to the customer's requirements and the special requirements of the actual printing process, the coating is applied. .

Second, the characteristics of waterborne varnish

Waterborne Varnish (or Dispersion Coating) has a colorless, odorless, VOC-free, low cost, wide source of material, good gloss, folding resistance, abrasion resistance and Chemical resistance, economic health and other characteristics. Waterborne Varnish can be divided into three types: high gloss, ordinary luster and matt luster. From the processing technology can be divided into: ink fountain coating process, scouring process (using ordinary offset printing machine water, ink fountain) special glazing machine polishing process, on-line coating process. Waterborne varnish can eliminate the harm to the human body and the pollution brought to the environment during operation, and has been paid more and more attention by food and tobacco printing enterprises. Compared with solvent-based varnish, water-based varnish has advantages in terms of environmental protection. What are the advantages? The following can be summarized:

1. Strong transparency, bright printed materials

It can be stored for a long time on the prints it is applied to. Under long-term intense sunlight irradiation, waterborne varnish is not easy to yellow and does not change color.

2. Strong wear resistance

Packaging type prints require strong abrasion resistance, measured with 50 pressures per square centimeter, generally capable of reaching 150 wipes per minute. Brightness generally can reach 50-70 brightness units, high-grade light can exceed 80, non-absorbing The substrate can reach 90, especially cigarette packs, and at high speeds with speeds of up to 300-500 packs/minute, the cigarette labels are subjected to a large mechanical load. For this reason, printed products not only need to be glazed, but also wear-resistant, while water-based coating oils can fully meet this requirement.

3. Conjunctival speed

Dry quickly, water-based paint drying process 30% by evaporation, 70% by the material absorption, drying quickly, about a few seconds to complete. When the varnish still contains 20% -30% of moisture, it can be conjunctiva. Therefore, it does not need any drying method. However, if infrared or hot air drying methods are used, the drying speed can be increased.

4. Easy to use and store, safe, safe to produce and improve labor conditions

Due to the fact that solvent-based coatings are dangerous goods, transportation, storage and use are quite inconvenient. The waterborne varnish uses water as the solvent without any danger. It is safe and reliable to use and can be cleaned with water.

5. Non-toxic and odorless Because water-based varnish uses water as a solvent and a small amount of volatile edible ethanol as an auxiliary solvent, it is particularly suitable for use on food and tobacco packaging. Tobacco is a very easy-to-smell plant, and the application of water-based gloss oil fundamentally eliminates the possibility of odor.

6. High temperature resistance, good heat sealing performance

At present, cigarette packs are widely used as outer packagings of PP film. Waterborne varnish has good heat sealing properties, and even with Celluloid, good heat sealing effect can be obtained.

7. Good finished product flatness, strong anti-rolling force

One of the headaches in gravure printing is the continuous drying of the printed material through several color groups. The moisture content of the paper is extremely low, and it is particularly prone to curling, so that the tobacco factory cannot use it. The use of water-based varnish to soften the package, the product through the cut sheet, and then bronzing cut, still maintain a good flatness and roll resistance. This will provide a new way for gravure to change the gravure, especially the need for hot stamping to change gravure.

8. Reasonable price

At present, the market price of water-based varnish is RMB 26 (including tax) per kilogram, solvent-based varnish is RMB 10 (per tax), but the coating amount of varnish is only 30% of solvent-based varnish. %, so the actual cost is about 80% of solvent-based varnish.

In addition to the above advantages, the use of waterborne varnish on gravure printing machines is more convenient than that of general solvent varnish. It is mainly to control the viscosity of the varnish, the depth of the anilox roller and the temperature of the oven. According to our experience, the viscosity of waterborne coating is generally controlled at about 15 seconds (measured at 4° DIN cup at 20°C). The anilox roll depth is 20 μm, 200 l/in: oven temperature 120°C (100kw x 2) at 150m Under the conditions of /min coating, the coating amount is 5g/m2, and the coating oil is instantaneously dried and can be directly hot stamped and die cut. Waterborne varnish differs from oily coatings in the way it is used on offset presses. Oily glazing can use the original printing unit, ink fountain, printing directly using the PS version of the glazing. The disadvantage of this glazing method is that the brightness is not enough, the fastness is not strong, easy to fade, and wet wet glazing, especially the full version of the field printing. On the offset printing line, water is coated on the surface by applying the coating method. It is different from the oil offset printing on the original offset printing set. It uses the principle of gravure ink transport, through the metal anilox roller and squeegee, transfer the varnish to the blanket or resin plate, and finally coated on the substrate. Under normal circumstances, the viscosity of the coating oil is about 20 seconds (measured at 3#ZAHN measuring cup 20°C), the electric engraving depth of the metal anilox roll is 23 μm, 150l/m2, the coating amount is 5g/m2, and the temperature is 65 °C, infrared power is 5.4kw x 5 x 2 groups, the total power is about 54Kw, the machine operating speed is 13000 / hour, instant dry, not dusting, can immediately bronzing, die-cutting, but to pay special attention is Even under the wet and wet conditions of the machine, the ink may not be fully dried, and it may take about 4 hours to dry naturally before it is bronzing.

In summary, the waterborne varnish has the advantages of advanced technology, convenient use, economical application, non-toxic and non-polluting, etc. It has a wide range of development prospects and will gradually replace solvent varnish and oil varnish, occupying in the printing industry. leading position.

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