First, the characteristics and classification of waterborne coating products
Water-based coating oil is mainly composed of main agent, solvent and auxiliary agent. It is colorless, odorless, transparent and non-toxic, has no organic volatiles, low cost, and has a wide range of sources. It is a solvent-based coating. Oil can not be compared. If other main agents and auxiliaries are added, they can also have good gloss, abrasion resistance and chemical resistance, economical hygiene, and are particularly suitable for packaging printing.
Waterborne Varnish is mainly 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 coating machine coating process, online 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.
The solvent of water-based coating oil is mainly water, its volatility is almost zero, and the leveling performance is very good. However, water as a water-based coating solvent also has disadvantages, such as slow drying speed, which may easily cause product dimensional instability and other process failures. Therefore, proper use of ethanol is added to improve the drying performance of aqueous solvents and improve water-based coating. Oil processing suitability.
Use on the polishing machine: 6-10 g/m2
Second, the performance of waterborne coating products
As an emerging environmental protection printing material, waterborne varnish is environmentally friendly and safe, but as a new product, it has been competing with solvent-based varnish for a long time. Does not dominate. The state should strengthen its legislation and law enforcement efforts, strictly limit the VOC content in the exhaust gas from printing workshops, and strengthen the security testing of packaging prints to limit the use of solvent-based coating oil products as much as possible to protect the environment and the health of operators. In terms of the technical level achieved by current water-based varnishes, replacing solvent-based varnishes is not a problem, but due to the long history of solvent-based varnishes, the technology is mature and the price is low, and printing companies are also adapting. This process, coupled with the relative lag in national environmental legislation, will remain in the market for some time. UV Varnish is also an environmentally friendly material and has many technical characteristics. Therefore, it is impossible for water-based Varnish to completely replace it, and it will show a parallel development trend. As a new type of printing material, waterborne varnish is in the period of cultivation and development of the market, and the technology is changing with each passing day. At the same time, as the localization of major raw materials in water-based varnishes continues to increase, production costs will continue to decline, and market competitiveness will continue to increase. In the coming period, waterborne varnish, a green and environmentally friendly printing material, will be weak and strong, and will become the mainstream product in the printed surface finishing market. Varnish oil consumption is huge and will increase at a rate of 30% annually in the future.
1, the characteristics of waterborne varnish
Waterborne varnish (or dispersion polish) has a colorless, odorless, non-organic volatiles, low cost, a wide range of material sources, 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.
The use of waterborne varnish on the gravure printing machine is more convenient than the general solvent varnish, mainly controlling the viscosity of varnish, the depth of the anilox roller and the temperature of the oven. According to the experience, the viscosity of waterborne coating oil is generally controlled at about 15 seconds (measured at 20°C); the depth of the anilox roll is 20um, 200L/in; the oven temperature is 120°C (100Kw×2), and the condition is 150m/min. Light, the coating amount is 5g/m2, and the glazing oil is instantly 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 then apply it on the substrate. In general, the viscosity of the coating oil is about 20 seconds (measured at 20°C), the depth of the electric engraving of the metal anilox roll is 23μm, 150l/in, the coating amount is 5g/m2, the temperature is 65°C, and the infrared power is It is 5.4Kw x 5 pieces x 2 pieces, the total power is about 54Kw, the machine speed is 13000 pieces/h, instantaneous drying, no dusting, can be immediately hot stamping, die cutting, but special attention should be paid on the machine wet Under the conditions, the ink may not be fully dried and it may take about 4 hours to dry naturally.
In summary, the waterborne varnish has the advantages of advanced technology, convenient use, economical and practical, non-toxic and non-polluting, etc. It has broad development prospects and will gradually replace solvent varnish and oil varnish, occupying in the printing industry. leading position.
2, the composition of waterborne varnish
Waterborne varnish mainly consists of three main categories: main agent, solvent and auxiliary agent.
a. The main agent. The main agent of water-based coating oil is a film-forming resin, which is a film-forming substance of the polishing agent and is usually a synthetic resin. It affects and supports various physical properties of the deep layer and the coating quality of the film layer, such as gloss, adhesion Sex, dryness, etc.;
b. Additives. Auxiliaries are used to improve the physical and chemical properties and processing characteristics of aqueous polishes. The types of additives are: curing agents. Improve the film forming property of the aqueous main agent and increase the cohesive strength of the film; Surfactant. Reduce the surface tension of aqueous solvents and improve leveling; defoamers. Can long-term control of the blistering agent polish, eliminate fish eye, pinhole and other defects; desiccant. Increase the drying speed of water-based polish, improve the printability of paper; adhesion promoter. Improve the adhesion of the film-forming substance to the substrate; wetting and dispersing agent. Improve the dispersibility of the main agent, prevent stains and improve wear resistance; other additives are plasticizers that can improve folding resistance;
c. Solvent. The main role of the solvent is to disperse or dissolve synthetic resins and various additives.
The solvent of the aqueous coating oil is mainly water. The volatility of water is almost zero and its leveling performance is very good. However, water as a solvent for aqueous coating oils also has disadvantages such as a slow drying rate and a process defect that easily causes product dimensional instability.
3, the scope of application of water-based coating oil
With the rapid and steady development of market economy and commodity economy, people pay more and more attention to the printing and decoration of food packaging, books, magazines, covers, calendars, pictures, medicine boxes, and cigarette packs. With a splendid surface gloss, this glossiness is a special effect produced by applying varnish to the printed material. Applying varnishes to prints not only increases the value of printed products, but also enhances the resistance to optical rotation of inks, increases the heat and moisture resistance of inks, protects the imprints, improves the performance of printed products, and brings considerable benefits to printing houses. The economic benefits.
The coating glazing market is a diversified market. Food printing, book printing, commercial printing, trademark printing and folding carton printing plants all have varying degrees of glazing needs for various packaging products. The application of waterborne varnish must be comprehensively considered based on different glazing methods, paper types, product quality and other factors in order to achieve good results.
With the development of society, people’s awareness of the protection of the living environment has also been continuously improved. For the printing industry, it has gradually increased the requirements and restrictions on hygiene, environmental protection, labor protection and other aspects, especially the requirements for food packaging and printing. More stringent, and only in this way can we meet the requirements of international health standards. Therefore, it is imperative to develop and apply pollution-free, pollution-free “green†materials. Waterborne varnish has the characteristics of non-toxic, odorless, high glossiness, and easy to use. In recent years, it has been widely used in the field of packaging and printing, and has achieved a rising trend.