Application of the hottest water-based glazing oil

The application of water-based glazing oil and the problems that should be paid attention to

first, what is printing glazing

the so-called printing glazing is a method to obtain a bright film layer on the surface of the printed object by printing once or twice with a field printing plate or a graphic printing plate on the surface of the replica that has completed the graphic printing process. Printing glazing can enhance the light resistance of the ink, increase the heat and moisture resistance of the ink layer, and protect the imprint and beautify the product

compared with other methods to increase the gloss film on the surface of printing products, such as laminating, plastic pasting, spray brushing, etc., it is not only cheap, simple and easy to operate, but also has the greatest advantage that it can be selectively polished according to the actual needs, which can not only polish the full plate (no special plate is required, relief printing can use light lithography, offset printing, no special new plate is required, and the original plate on the machine is used), It can also be locally polished, because the printing glazing is the same as the transfer principle of printing pictures and texts. Using the principle that the printing plate pictures and texts are partially transferred to the adsorbed film on the substrate, while the blank part is not adsorbed, the printing glazing is carried out according to the needs of customers and the special requirements of the actual printing process

II. Characteristics of aqueous glazing oil

aqueous glazing oil (or dispersion coating) has the characteristics of colorless, tasteless, no organic volatile matter (VOC), low cost, wide source of materials, good gloss, folding resistance, wear resistance, chemical resistance, economy and health

water based polish can be divided into three types according to the purpose of the product: high gloss, ordinary gloss and matte gloss. In terms of processing technology, it can be divided into: ink bucket polishing process, water bucket can consume high-quality powder inventory accumulated when profits are rich, and today's transaction is still dominated by medium and low-grade powder ore polishing process (using water and ink bucket of ordinary offset press), special polishing machine polishing process, online polishing process. Waterborne Varnish can eliminate the harm to human body and the pollution to the environment in the operation, and has been paid more and more attention by food and tobacco printing enterprises

compared with solvent based glazing oil, in addition to the advantages of environmental protection, what are the other advantages of water-based glazing oil? It can be summarized as follows:

1. It has strong transparency, and the printed matter is bright

it can be stored for a long time on the printed matter it is coated. Under the long-term strong sunlight, the water-based varnish is not easy to yellowing and discoloration

2. Strong wear resistance

packaging printing materials need strong wear resistance. Measured with 50 pressures per square centimeter, it can generally reach 150 rubs per minute, the brightness can generally reach 50-70 brightness units, the high-end bright type can exceed 80, and the non absorbable base material can reach 90, especially the cigarette box. In the high-speed operation with the speed of 300-500 bags/minute, the cigarette label has to bear a lot of mechanical load. For this reason, printing materials not only need to be polished, but also wear-resistant, and water-based polish can fully meet this requirement

3. the conjunctiva is fast

it dries rapidly. 30% of the drying process of water-based varnish is through evaporation, and 70% depends on material penetration and absorption. It dries rapidly, which can be completed in a few seconds. When the Polish still contains 20% - 30% water, the conjunctiva can be formed. Therefore, it does not need any drying method. However, if various methods are used to dry the components of materials with infrared or hot air, the drying speed can be improved

4. It is convenient and safe to use and store, which is conducive to safe production and improving the working conditions of employees

because solvent based varnish belongs to the category of dangerous goods, it is quite inconvenient to transport, store and use. The water-based glazing oil uses water as the solvent, which is safe and reliable, and can be cleaned with water

5. non toxic and tasteless because water-based varnish uses water as solvent and a small amount of volatile edible ethanol as auxiliary solvent, it is particularly suitable for use in food and tobacco packaging. Tobacco is a kind of plant that is easy to absorb flavor. The application of water-based varnish fundamentally eliminates the possibility of cross flavor

6. high temperature resistance, good heat sealing performance

at present, PP film is widely used as the outer packaging of cigarette packs. Water based varnish has good heat sealing performance. Even if cellulite is used, good heat sealing effect can be obtained

7. the finished product has good flatness and strong roll resistance

a headache in gravure printing is that the printed matter is continuously dried by several color groups, and the moisture content of the paper is extremely low, which is particularly easy to curl, so that the cigarette factory cannot use it. Apply water-based varnish to polish the soft package. The product is cut into large sheets, then bronzed and cut, and still maintains good flatness and roll resistance. This provides a new way for offset printing to gravure printing in the future, especially for cigarette labels that need bronzing to gravure printing

8. The price is reasonable

at present, the water-based varnish on the market is 26 yuan per kilogram (tax included), and the solvent based varnish is 10 yuan per kilogram (tax included), but the coating amount of the water-based varnish is only 30% - 40% of the solvent based varnish, so its actual cost is about 80% of the solvent based varnish

in addition to the above advantages, water-based varnish is more convenient to use on gravure printing machines than general solvent based varnish. The main thing is to control the viscosity of the varnish, the depth of the wrinkle roll and the temperature of the oven. According to our experience, the viscosity of water-based glazing oil is generally controlled at about 15 seconds (measured by 4 DIN measuring cup at 20 ℃) and the depth of the roller is 20 μ m. 200L/in: the oven temperature is 120 ℃ (100kW x 2). Polish under the condition of 150m/min, the coating amount is 5g/m2, and the polish is instantly dry, which can be directly bronzed and die cut

when water-based glazing oil is used on offset press, it is different from oil-based glazing in method. Oily glazing can use the original printing unit and ink bucket, and use PS plate to directly print and polish. The disadvantage of this glazing method is that the brightness is not enough, the fastness is not strong, the color is easy to fade, and the wet glazing cannot be overlapped, especially for full-scale field printing. Offset printing line glazing is the application of coating method for water-based glazing, which is different from the original offset printing unit oil-based imprint glazing. It uses the ink conveying principle of gravure printing, transfers the varnish on the blanket or resin plate through the metal roller and the doctor blade, and finally applies it on the substrate. In general, the viscosity of the polishing oil is about 20 seconds (measured at 20 ℃ with 3 Zahn measuring cup), and the electric engraving depth of the metal stripe roller is 23 μ m. 150L/㎡, the coating amount is 5g/㎡, the temperature is 65 ℃, the infrared power is 5.4kw x 5 pieces x 2 groups, the total power is about 54kw, the running speed of the machine is 13000 sheets/hour, it is instantly dry without powder spraying, and it can be bronzed and die-cut immediately, but it should be noted that under the wet upper wet strip of the machine, the ink may not be fully dried, and it needs to be naturally dried for about 4 hours before bronzing

to sum up, water-based varnish has the advantages of advanced technology, convenient use, economic applicability, non-toxic and pollution-free, and has a broad development prospect. It will gradually replace solvent-based varnish and oily varnish, and occupy a leading position in the printing industry

III. composition of water-based glazing oil

water based glazing oil is mainly composed of main agent, solvent and auxiliary agent

1. main agent

the main agent of aqueous glazing oil is film-forming resin, which is the film-forming material of glazing agent, usually synthetic resin. It affects and dominates various physical properties in the deep layer and the glazing quality of the film layer, such as gloss, adhesion, dryness, etc

2. additives

additives are to improve the water-based standard, strengthen the compliance and safety management of food contact materials from the perspective of supply chain, and polish the physical and chemical properties and processing characteristics. The types of additives are: ① curing agent: improve the film-forming property of water-based main agent and increase the cohesive strength of the film

② surfactant: reduce the surface tension of aqueous solvents and improve leveling

③ defoamer: it can control the foaming of polish for a long time and eliminate quality defects such as fish eyes and pinholes

④ desiccant: increase the drying speed of water-based polish and improve the suitability of paper prints

⑤ adhesion aid: improve the adhesion between film-forming material and substrate

⑥ wetting dispersant: improve the dispersibility of the main agent, prevent dirt and improve wear resistance

⑦ other additives are plasticizers that can improve the folding resistance

3. solvent

the main function of solvent is to disperse or dissolve synthetic resins and various additives

the solvent of aqueous polish is mainly water. Water is colorless, tasteless, non-toxic, widely sourced and cheap. The volatility of water is almost zero. Its leveling performance is very good. However, as the solvent of water-based glazing oil, water also has shortcomings, such as slow drying speed, easy to cause process failures such as unstable product size. Therefore, add ethanol in use to improve the drying performance of aqueous solvents and improve the processability of aqueous glazing oils

IV. application of water-based varnish

with the rapid and steady development of market economy and commodity economy, people pay more and more attention to the printing and decoration of books, magazines, covers, calendars, pictures, medicine boxes, cigarette packs. Printing requires not only beautiful color pictures, but also magnificent surface gloss. This gloss is the special effect produced by coating varnish on the printed object. Coating varnish on printed matter can not only increase the value of printed products, but also enhance the light resistance of the ink, increase the heat and moisture resistance of the ink, protect the imprint, improve the use performance of printed products, and bring considerable economic benefits to the printing factory

the coating and glazing market is a diversified market. All kinds of book printing plants, commercial printing plants, trademark printing plants and folding carton printing plants have different degrees of glazing needs for a variety of packaging products. The application of water-based glazing to better produce various experimental oils must be comprehensively considered according to different glazing methods, paper types, product quality requirements and other factors in order to achieve good results

v. the main problems affecting the glazing quality include paper performance, paper type, viscosity, coating amount, drying conditions, etc

1. paper performance

the influence of paper on glazing quality is mainly reflected in the influence of paper smoothness on glazing quality. The paper with high smoothness has a significant effect after polishing, while the paper or paperboard with low smoothness has a poor effect after polishing, because the polishing oil is almost completely absorbed by the paper or paperboard with rough surface. In order to solve this problem, you can apply primer once or twice before glazing

2. paper type

thick paper has good dimensional stability, while thin paper has poor dimensional stability. Dimensional stability is one of the key indicators of print quality, which is closely related to the amount of water in printing, the water content of paper, the drying time and method, and the control of viscosity. If the printing product is less than 90g/㎡ paper, please carefully use water-based polish

3. viscosity and solid content of glazing oil

in the coating process, the viscosity and solid content of glazing oil must be reasonably controlled. Therefore, dilution can only be carried out within a certain range of viscosity and solid content. The diluent of water-based glazing oil is generally a mixture of ethanol and water with a ratio of 1:1. The dilution amount is 10% - 30%, which should not be too large and should be strictly controlled

4. coating amount

the coating amount of water-based varnish should be controlled at 4-6g/㎡. Because in the coating varnish, the evaporation rate of ethanol is very fast, so the viscosity control is very important. The content of ethanol should also be increased in time to ensure the stability of the product

5. Drying conditions

almost all solvent based varnishes