Development and Application of Environment-friendly Waterborne Varnish
BNF HARDWARE CO., LTD , https://www.bnfhandles.com
Second, the development of environmentally friendly waterborne varnish Waterborne varnish mainly consists of resin, solvent functional additives.
1. Resin Waterborne molding resin is the most important component in waterborne varnish. It influences and dominates the gloss, adhesion, abrasion resistance, water resistance, flexibility of the coating layer of the varnish oil and protects the surface of the paper and the ink with the drying performance.
There are many types of aqueous film-forming resins, such as rosin-modified melamine resin, water-soluble acrylic resin, styrene-modified maleic resin, water-based amino resin, and polyvinyl alcohol.
It generally has three forms, which are characterized by wind:
Morphology/Item Water-Soluble Dispersion Emulsion Appearance Transparent Translucent Milky White Granular Type 0.001μm 0.001-0.1μm > 0.1μm
Low molecular weight - Medium to medium viscosity High to medium low solids content Low to medium high leveling agents Good slightly poor poor dryness Good poor Good film strength Low to medium High Selecting the right resin is the key to the aqueous coating, which must have High adhesion fastness, good heat resistance, good antifouling performance, good water release, and rapid drying. Therefore, acrylic resins are widely used at home and abroad. The performance of the aqueous acrylic copolymer resin depends on the monomer composition, performance and synthesis process. Choose water-based varnishes with different printing methods, different printing equipment, printing speeds and different printing paper and quality requirements. After analyzing the domestic and foreign formulations, we have passed several tests. Acrylic acid and its acrylic monomer copolymers were selected, and the water soluble resin and the emulsion were compounded scientifically. The varnish developed with this composite resin achieves the best effect of use, fully satisfies the current requirements for the packaging and printing of foods, pharmaceuticals, tobacco and daily necessities, and can impart good glossiness, folding-resistance and abrasion resistance to printed products. And chemical properties.
2, the solvent The main role of the solvent is to dissolve, decompose or dilute the composite resin and various functional additives. Used to adjust the viscosity and drying properties of the coating. The solvent of the environment-friendly aqueous coating oil is mainly water. Water's volatility is zero, its leveling performance is good and its source is wide, colorless, non-toxic and odorless. It is a "green material". These advantages are unmatched by other solvents. Its disadvantages are slow drying speed. Generally, the mixed solution of ethanol and water is used in the use, so that the drying performance of the aqueous solvent can be improved and the processing suitability of the waterborne oil can be improved.
3. Function Additives The role of functional auxiliaries is to improve the transfer, leveling, drying, and slip properties of water-based varnishes; to adjust the viscosity, improve gloss, and processing characteristics. There are many types of auxiliaries, generally based on glazing. How to use the oil to add it properly.
The commonly used antifoaming agent is to control the bubbling of the varnish and solve the problems of fisheye, pinhole and other defects in the application of the varnish.
Use surfactants to reduce the surface tension of aqueous solvents and improve leveling; Use dispersants to improve the dispersion of resins to prevent stickiness and improve wear resistance; Use coating enhancers to improve the film-forming substances and substrates Adhesion ability; Use plasticizers to improve the folding resistance after polishing; Use gloss improver to make the gloss of gloss and transparency.
4. According to the above, after repeated trials, we used the orthogonal design method to formulate the following formula for water-based oiling. Water-soluble domestic and foreign acid resin: 20-30%
Acrylic emulsion resin: 40-50%
Water + Ethanol: 30-40%
Functional auxiliaries: 3-5%
The production process is carried out in two steps. The composite resin is first prepared and then the coating oil is synthesized. The technological process is to add water and ethanol evenly to a water-soluble acrylic resin and other kinds of acrylic emulsions, and then add additives, etc., and then uniformly detect the relevant indicators. After passing the test, the filter can be filtered and stored. .
5. The main technical indexes of the waterborne coating oil developed by the above method are as follows:
Appearance: White lotion
P H value: 8---9
Solid content: ≥30%
Viscosity (coating -4 cup) 25°C ≥30%
The modified gloss oil has the characteristics of non-toxic and odorless, strong transparency, no organic volatile matter (VOC) emissions, low cost, and wide source of raw materials. In use, it has good gloss, folding resistance, abrasion resistance and chemical resistance, especially its environmental performance is particularly suitable for the processing of packaging and printing materials for industries such as food, medicine and tobacco.
Third, the application of waterborne varnish In recent years, based on our experience in practical applications, we feel that waterborne varnish has the following advantages:
(1) High transparency, good gloss, and no adverse effect on the color of printed matter. Under long-term strong sunlight, the coating film of waterborne varnish is not easy to yellow.
(2) Strong wear resistance, scratch resistance, abrasion resistance on the surface of the printed material, no fading, water repellent, oil repellent, and very popular with users. Waterborne varnish is used on cigarette packs. At high speeds of up to 300-500 packs per minute, the cigarette labels are subjected to a large mechanical load, while the waterborne varnish completely fulfills this requirement, and whether it is gravure or None of the offsets was found to have been discolored.
(3) Non-toxic, odorless, easy to use, transport, store, and safe. Water-based glazing oil uses water as the solvent, and only a small amount of volatile edible ethanol is the auxiliary solvent, which is conducive to safe production and improvement of employees' working conditions. After finishing the light, the equipment can be washed directly with water without any danger.
(4) Conjunctiva fast, dry quickly, and high temperature resistance, heat sealing performance. The waterborne varnish was applied on the Heidelberg CD five-color stencil offset printing machine. The printing speed was 13,000 sheets/hour, infrared drying, power 5.4kw × branch × 2 groups, and the temperature was 65°C. The drying was complete, and satisfactory application results were obtained. The cigarette pack is made of PP film as the outer package, and the water-based coating oil shows a good heat sealing performance.
(5) Good flatness, strong anti-rolling force, water-based coating oil is not excessively high in temperature, and it is more convenient to use on the gravure printing machine than general solvent-type coating oil. One of the most difficult problems 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 and can not be used. The water-based varnish was used to polish the flexible package. The product was cut into large sheets, and then bronzing and slitting. The flatness and roll resistance were still maintained. The user was satisfied with the application.
It is worth noting that the application of waterborne varnish must be based on different printing methods, printing equipment, printing speed, paper type, product quality requirements and other factors in order to achieve good results. Mainly pay attention to the following points:
(1) Viscosity control: During the coating process, the viscosity and solid content of the coating oil should be reasonably controlled. Dilution can only be performed within a certain solid content range.
(2) Different types of paper are closely related to the process of coating the coating. Thick paper has good dimensional stability, thin paper has poor dimensional stability, and dimensional stability is a key indicator of print quality. With the amount of printing water, the humidity of the paper. Drying time and method, viscosity control are all related.
(3) Control of coating amount: The coating amount of the aqueous coating oil is not easy to control. Generally combined with the factory's actual situation and experience to determine.
(4) Drying time control: The use of water-based glazing oils is best if an infrared drying device is used because during the drying process, the coating oil is heated, the bottom layer penetrates quickly and dry, and the middle moisture is heated and evaporated by high humidity. The exhaust pipe is discharged, which is the best way to coat the last color in multi-color printing.
In summary, waterborne coating can eliminate the harm to the human body and the pollution brought to the environment in operation. It has been increasingly favored by food and tobacco printing companies. It has advanced technology, convenient use, and economical and reasonable. Its advantages have great development prospects, and it has gradually replaced solvent-based coating oils and oil-based coating oils, which will dominate the printing industry.