Research and Application of Environmental Performance of Waterborne Varnish

At present, the coating glazing technology has been adopted by more and more printing manufacturers, and the demand for glazing oil continues to increase. Due to the characteristics of non-toxic, odorless, transparent, non-organic volatile matter (VOC) emissions, low cost, and wide source of raw materials, the waterborne varnish can impart good glossiness and folding resistance to the printed materials. Abrasion resistance and chemical resistance, especially its environmental performance, are particularly suitable for the processing of packaging and printing materials in the food, pharmaceutical and tobacco industries.

Keywords: Waterborne Varnish Environmental Performance Development Application

I. Introduction

With the increasing awareness of human environmental protection, people have paid more and more attention to the impact of ecological environment changes in activities such as production operations and household consumption. In the field of printing, the importance of environmental protection is no exception. The printing industry has also increased many requirements and restrictions on hygiene, environmental protection, and labor protection. Especially for food packaging, the printing requirements are more stringent. At present, the coating glazing technology has been adopted by more and more printing plants, and the demand for glazing oil is increasing. After years of hard work, the environmentally friendly waterborne varnish developed by Wuhan Modern Industrial Technology Research Institute has made a breakthrough and it can completely replace solvent-based varnish and oil varnish. This article discusses the development and application of environment-friendly waterborne varnish.

Second, the development of environmentally friendly waterborne coating

Waterborne coating mainly consists of resin, solvent and functional additives.

1. Resin

Aqueous film-forming resins are the most important components in aqueous coatings. It influences and dominates the gloss, adhesion, abrasion resistance, water resistance, flexibility and drying properties of the coating layer of the varnish, and plays a role in the protection of the paper and ink surface.

There are many types of aqueous film-forming resins, such as rosin-modified maleic resin, water-soluble acrylic resin, styrene-modified maleate wax, water-based amino resin, and polyvinyl alcohol. It generally has three forms, the characteristics of which are detailed in Table 1.

Table 1 Characteristics of Aqueous Film-forming Resins

Morphology Water-soluble dispersion type Appearance Transparent Translucent Milky white Particle size 0.1μm
Low Molecular Weight - Medium to Medium Large Viscosity High, Medium, and Low Solid Content Low, Medium, High Leveling, Good Poor, Poor, Poor, Dry, Poor, Good, Low Film Strength

Since the choice of suitable resin is the key to water-based coating, it must possess the advantages of easy formation of salt solution, high adhesion after filming, good heat resistance, good anti-sticking performance, good water release performance, and rapid drying. Characteristics, so the use of more common outside the country is the acrylic copolymer resin. The performance of the waterborne acrylic copolymer resin depends on the composition, properties and synthesis process of the monomer. Choosing monomers with different properties can result in hard-to-soft copolymer resins to suit different printing methods, printing equipment, printing speeds, printing papers and quality requirements of aqueous coatings. After analyzing the formulas at home and abroad, the hospital conducted trial and error, selected acrylic acid and its acrylic monomer copolymers, and used scientific methods to compound the water-soluble resin and the emulsion. The varnish developed with this composite resin achieves the best effect of use, fully satisfies the current printing requirements for the packaging of food, medicine, tobacco and daily necessities, and imparts good glossiness, folding resistance and abrasion resistance to the printed matter. And chemical resistance.

2. Solvent

The main role of the solvent is to dissolve and decompose the dilutable composite resin and various functional additives. Used to adjust the viscosity and drying properties of the coating. The solvent of environment-friendly waterborne varnish is mainly water, its water volatility is zero, its leveling performance is good, its source is extensive, and it is colorless, non-toxic, and odorless. It belongs to “green material” and cannot be phased by other solvents. The disadvantage is that the drying speed is slower. Generally, the mixed solution of ethanol and water is used in the use, which can improve the drying performance of the aqueous solvent and improve the processing adaptability of the aqueous coating oil.

3. Functional additives

The role of functional auxiliaries is to improve the transfer, leveling, drying, and slip properties of the waterborne varnish; to adjust the viscosity, improve gloss and processing characteristics. There are many kinds of additives and they are generally added according to the method used for coating.

The defoamer can be used to control the bubbling of the varnish, solve the problems of fish eye, pinhole and other defects in the application of the varnish; use the surfactant to reduce the surface tension of the aqueous solution and improve the leveling; Dispersants to improve the dispersion properties of tree shit, to prevent stickiness and improve wear resistance; to enhance the adhesion of the film-forming substance to the substrate with the coating film enhancer; to provide folding endurance after coating with a plasticizer Use matting agent to use the gloss oil is good, transparent and strong.

4. Based on the above, after several trials and repeated tests, the following formulas for the formulation of the following aqueous coating oils were formulated using the orthogonal design method:

Water-soluble acrylic resin: 20~30%
Acrylic emulsion: 40~50%
Water + Ethanol: 30~40%
Functional additives: 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 technical process is: adding a certain amount of water-soluble acrylic resin and two or more acrylic emulsions with water and ethanol, stirring uniformly, and then adding the additives etc. After being evenly dispersed, detecting relevant indexes, and then filtering and packaging after being qualified. Storage.

5. The main technical indicators of the waterborne varnish developed by the above method are as follows:

Appearance: white emulsion PH value: 8~9
Solid content: ≥30%
Viscosity (coating ~ 4 cups) 25°C ≥ 30 seconds

The coating oil has the characteristics of non-toxic, odorless, strong transparency, no organic volatile matter (VOC) emission, 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 in food, medicine and tobacco industries.

Third, the application of water-based coating oil

In recent years, based on our experience in practical applications, we believe that waterborne varnish has the following advantages:

(1) High transparency and good gloss. There is no adverse effect on the color of the printed matter. Even under long-term intense sunlight, the coating film of waterborne varnish is not easily yellowed.

(2) Strong wear resistance and scratch resistance. The surface of the printed material is hard-wearing, non-fading, water-repellent, and oil-repellent, and is well received and relied on by users. Waterborne coating oils are used in cigarette packs. At high speeds of up to 300 to 500 packs per minute, the cigarette labels are subjected to a large mechanical load, while the aqueous coating oils fully satisfy this requirement. It was found that neither the gravure printing nor the offset printing showed a phenomenon that the cigarette pack was discolored.

(3) Non-toxic and odorless, easy to use, transport and store, and safe. The water-based coating oil uses water as the solvent, and only a small amount of edible ethanol, which is volatile, can be used as an 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, and it was fully dried at a printing speed of 13,000 sheets/hour, infrared drying, power of 5.4 kw×5 sticks×2 sets, and a temperature of 65° C., and satisfactory application results were obtained. . The cigarette packs use PP film as the outer package, and the waterborne varnish shows a good heat seal performance.

(5) Good flatness and strong anti-rolling force. Water-based coating oils have no excessive temperature requirements and are more convenient to use on gravure machines than general solvent-based coatings. 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, making it unusable. The water-based coating was not applied to the flexible packaging. The product was cut into large sheets, and then bronzing and slitting. The flatness and roll-resistance were still maintained. The user was satisfied after use.

It is worth noting that the application of waterborne varnish must be based on different printing methods, printing equipment, printing speed, type of paper, printing equipment, printing speed, paper type, product quality requirements and other factors in order to achieve good effect. The main points to note are the following:

(1) Viscosity control. In the process of coating and glazing, the viscosity and solid content of coating oil should be reasonably controlled, and dilution can only be performed within a certain range of solid content.

(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 one of the key indicators of print quality. It is related to the amount of water used in printing, the temperature adjustment of paper, the time and method of drying, and the control of viscosity.

(3) Coating amount control. Water-based coating oil coating is not easy to control, generally should be combined with the actual situation of the factory, to determine.

(4) Drying time control. The use of water-based varnishes, if using infrared drying device, the best effect, because in the drying process coating oil is increased, the bottom quickly penetrated and dried, while the middle of the water heated by high temperature evaporation, discharged through the exhaust pipe, This is the best way to coat the last color in multicolor printing.

In summary, the waterborne varnish can eliminate the harm to the human body and the pollution to the environment during operation, and has been increasingly favored by food and tobacco packaging and printing companies. Its advanced technology, convenient use, and economical and reasonable advantages have great prospects for development. It has gradually replaced solvent-based coatings and oil-based coatings, and will dominate the packaging and printing industry.

Reprinted from: China Packaging Industry

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