Waterborne Varnish Features and Usage

Waterborne varnish, also known as dispersion polish, has a colorless, odorless, transparent and non-toxic, non-organic volatiles (VOC), low cost, wide source of material, good gloss, and folding resistance The characteristics of abrasion resistance and chemical resistance are unmatched by other solvent-based coatings. In addition, adding other main agents and auxiliaries can also improve the gloss, flex resistance, abrasion resistance, and chemical resistance of aqueous coatings. As the water-based polish uses water as a diluent, a small amount of volatile ethanol is used as an auxiliary solution, there is no toxic and harmful volatilization, economic sanitation, and the harm to the human body and the pollution to the environment can be eliminated in operation, which is beneficial to safe production. And to improve the working conditions of employees, it is in line with environmental protection requirements, and is particularly suitable for use on food, cigarettes, pharmaceuticals and other packaging.

Water-based coating oil mainly consists of three main categories: main agent, solvent, and auxiliary agent. The main agent of waterborne coating is the film-forming resin, which is the film-forming material of the polishing agent and is usually a synthetic resin. It affects and dominates the various physical properties of the deep layer and the glazing quality of the film, such as gloss, adhesion Sex, dryness, etc. There are many types of aqueous film-forming resins, but the most common ones at home and abroad are acrylic resin copolymer resins. The properties of the waterborne acrylic copolymer resin depend on the composition of the monomer, the synthesis of the monomer, and the synthesis process. Waterborne acrylic copolymer resin has a series of excellent properties such as good film forming, good gloss, high transparency, rapid drying, wear resistance, and water resistance, and is widely used in water-based polishes and water-based gloss coatings.

Ancillary agents are used to improve the physical and chemical properties and processing properties of aqueous polishes. Adjuvants mainly include the following. 1 Curing agent: Improve the film forming property of the aqueous main agent and increase the cohesive strength of the film. 2 Surfactants: reduce the surface tension of aqueous solvents and improve leveling. 3 Defoamer: Long-term control of blistering of the polish, eliminating fisheye, pinhole and other quality defects. 4 Desiccant: Increase the drying rate of the water-based polish and improve the printability of the paper. 5 Adhesion Promoter: Improve the adhesion of the film forming material to the substrate. 6 wetting and dispersing agent: to improve the dispersion of the main agent to prevent stickiness and improve wear resistance. 7 other additives: plasticizers that can improve the folding performance.

There are many kinds of adjuvants, and they differ depending on the type of top polish. For example, the infrared waterborne varnish and the matt varnish are all different kinds of varnish, so the components of the assistant agent are also different. However, it should be noted that the use of various types of additives should not exceed 5% of the total amount, otherwise it will affect the processing suitability of the polish.

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. Colorless, odorless, non-toxic, widely sourced, and inexpensive. The volatility of water is almost zero. Its leveling performance is very good. However, the solvent of the water-based coating oil also has disadvantages, such as a slow drying speed, which may easily cause product failures and other process failures. Therefore, ethanol is often added during use to improve the drying performance of the aqueous solvent and improve the processing suitability of the aqueous coating. In addition, since the UV coating is ideal in terms of drying and the like, if it is used in an aqueous coating, it can complement each other. Based on this, a new drying method has now been developed for coating. Ultraviolet lacquer coatings can form bright films in a matter of seconds, as well as dry glazing coatings that use a combination of UV and IR radiation.

Compared to solvent-based coatings, aqueous coatings also have the following advantages.

(1) Strong transparency and good preservation. It can be stored for a long time on the prints it is applied to. Under long-term intense sunlight irradiation, water-based glazing oil is not easy to yellow and does not change color. (2) Good wear resistance. Packaging printed products need a strong abrasion resistance, measured with 50 pressures per square centimeter, generally can reach 50-70 brightness units, while the high-grade light type can exceed 80, non-absorbent substrates can reach 90. In particular, cigarette packs are subjected to high mechanical loads at high speeds of up to 300 to 500 packs per minute. 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. The drying process of the waterborne varnish is 30% by evaporation, 70% by the material penetration absorption, drying quickly, about a few seconds to complete. When the varnish still contains 20% to 30% of moisture, the film can be formed. Therefore, it does not require any drying method. If using infrared or hot air drying method, the drying speed is faster. (4) good heat sealing performance. In the current use of PP film as the outer package for cigarette packs, the water-based varnish has good heat-sealing properties. Even if celluloid is used, good heat-sealing effect can be obtained. (5) Finishing products have good flatness and strong anti-rolling force. One of the headaches in gravure printing is the continuous drying of printed materials through several color groups. The sweat rate of the paper is extremely low, and it is particularly prone to curling. This cannot be used at all in cigarette packs. The application of water-based varnish to the soft package, the product through the cut sheet, and then hot 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. The application of waterborne varnishes must be based on different glazing methods, paper types, product quality requirements and other factors in order to achieve good results. When using waterborne varnish, pay attention to the following issues.

(1) Viscosity control. In the coating process, the viscosity and solids content of the coating oil must be properly controlled. Therefore, dilution can only be performed within a certain range of solid content. Water-based glazing oil diluents generally use ethanol and water, a ratio of 1:1 mixture, a significant reduction in viscosity, should be strictly controlled.

(2) Select the paper type. Thick paper has good dimensional stability and thin paper has poor dimensional stability. Poor dimensional stability. Dimensional stability is one of the key indicators of print quality. It is closely related to the amount of water used in printing, the humidity control of paper, the time and method of drying, and the control of viscosity. If the printed product is less than 90 grams of paper, be cautious with the use of water varnish.

(3) Control of coating amount. The coating of waterborne coatings is not easily controlled. Because the evaporation speed of ethanol in the coating varnish is very fast, and the water is colorless and transparent, it is difficult to discriminate the amount of the transparent aqueous liquid on a white paper with the naked eye. Therefore, the control of viscosity is very important. Ethanol content must also be increased in time to ensure product stability.

(4) Use of anti-adhesion agent. In the use of water-based coating can completely eliminate or reduce the use of anti-adhesive dirty agent, because water-based coating has a complete curing, the surface is very smooth, very little sticky, and other polishing agents are different. The paper can be punched and indented with a press after printing (wet-wet printing) for 2 hours.

(5) Control of drying time. Solvent-based coating oils are almost all volatilized and dried, while the infiltration and drying of aqueous coating oils have great utility value. However, in multi-color printing, if the last color is coated with glazing oil, the drying time will be slow, because the paper has absorbed more ink and dampening water. If infrared water-based coating oils are used, drying is most successful with the aid of an infrared drying device. During the drying process, the coating oil is heated, the bottom layer penetrates quickly and dry, and at the same time, the moisture in the polishing agent is heated and evaporated by the high temperature, and is discharged through the exhaust pipe. Infrared drying device has good drying effect. Another way to increase the drying rate is to increase the ethanol content, but it depends on the actual conditions of the factory and the viscosity of the coating oil and cannot be arbitrarily adjusted.

Source: 21st Century Fine Chemicals Network