On-line glazing environmental protection analysis

Due to the deteriorating global environment, environmental protection has become a major issue that affects the survival and development of the entire human race. Printed matter, which is one of the products that penetrate the most extensive human lives, is naturally taken care of by everyone.

Waterborne gloss environmental protection analysis

1. Waterborne Varnish is safe and reliable

The main raw materials of water-based coating oil are water-based acrylic resin and water-based acrylic emulsion; the additives are mainly defoamers and film-forming aids, all of which are free of organic volatiles; the main solvent is water, and the volatilization amount of harmful substances is zero. The flat performance is good and it is a true "green material". However, the drying speed of waterborne varnish is slow, so many companies currently use a small amount of volatile edible ethanol as an auxiliary solvent, which not only improves the drying performance of the aqueous solvent, but also improves the processing adaptability of the aqueous varnish. Of course, more importantly, this mixed solvent does not contain solvents such as acids, ethers, ketones, esters, and aromatic hydrocarbons, so the aqueous coating oil is basically colorless, odorless, non-toxic, and safe and reliable.

2. The glazing process has no harmful substances added

The waterborne varnish is applied to the surface of the printed matter, and after drying it reaches a bright effect, that is, the glazing process is completed. Waterborne varnish is water when it is coated and dried. It is harmless to the environment and the human body. Even if the operator comes into contact with the water-based varnish, it can be rinsed with clean water and it will not harm the skin. After glazing, you can wash the plate, wash the car, and wash the tank directly with clean water, without using any other solvent, so as to ensure no pollution to the environment during the glazing process. In addition, the drying equipment of the water-based coating oil is an infrared drying oven, which avoids that the UV coating must be dried with ultraviolet rays of a certain wavelength to generate ozone (O3) and the solvent-based coating oil contains a large amount of harmful substances that volatilize or remain in the printed matter. The disadvantages that cause harm to the environment and the human body.

3. Polishing products can be recycled

After the glazing process, during the subsequent storage and transportation, during the use, the varnish is further dried and the conjunctiva is dried. Although the solvent is still volatilized in the process, the water-soluble varnish is still water. In addition, if the printed matter after use is recycled, the acrylic resin and a small amount of auxiliaries left on the print can be easily decomposed without leaving any harmful substances. For consumers, buy prints that contain water-based polish, and don't worry about taking toxic odors home.

On-line water coating application

In on-line water-based coating, the coating effect is affected by the printing process. The effects of many factors, such as printing equipment, printing materials, printing speed, and product use, are not easy to achieve perfect results. The following is a summary of the current problems encountered with on-line waterborne coating and the solutions to the problem after interviewing industry experts.

1. The impact of the printing process

Water-based coating oils have a wide range of applications and can be used for online operations such as offset printing, flexo printing, and gravure printing. The effect of different printing methods on the glazing effect is mainly reflected in the speed of the glazing and the thickness of the glazing oil, and the printing method has the same effect on the printing speed and the ink film thickness. There are many types of waterborne coating on the market, and different viscosities should be used for different printing methods. Varnish for different drying speeds.

Flexo Inline Coating uses an ink roller-squeegee short ink inking system. The viscosity of the waterborne varnish is required to be 50-60s (coating 4# cups) and the drying speed is 8-10m/s. The thickness of the coating film is usually controlled by adjusting the number of screen lines of the anilox roller. Since the anilox roller has uniform ink transfer, a flexo coating is used to make the coating layer more uniform.

In the on-line offset coating, the water-based coating oil is liable to be incompatible with the ink. Therefore, in the selection of the resin in the aqueous coating oil, the varnish should be similar to the offset ink or have similar compositions. Offset printing ink systems have a plurality of uniform ink rollers, requiring the drying speed of waterborne coating oil to be relatively slow, otherwise it will dry on the surface of the rubber roller and cannot print normally. In addition, the printing speed of the offset press is much slower than the flexo press, which makes the problem of the drying speed of the aqueous coating oil more prominent.

The gravure printing machine uses an anilox roller-squeegee short ink inking system, but the gravure roll used by the gravure printing machine has a lower number of lines than that used in flexo printing. More rough. In order to avoid the coating layer being too thick or dry, the viscosity should generally be low. Fast drying waterborne coating.

In short, the viscosity of waterborne varnish is relatively low, and there are some special requirements for the ink supply system of printing equipment. Generally, the ink supply systems of flexographic and gravure printing machines are more suitable for on-line water-based coating, while the ink supply systems of offset printing machines are relatively unsuitable for water-based coating, and water-based coating oils with suitable viscosity must be used.

2. The impact of the printing process

In the printing process, aqueous coatings are usually used in two process steps. One is to base oil for the substrate before printing to increase its surface smoothness, glossiness, prevent fluffing, and improve printing quality. The other is water-based coating after the printing of yellow, magenta, cyan, black and spot colors to improve the surface gloss and wear resistance of printed products, and the solvent resistance and scratch resistance of printed products are also improved. As the semi-finished products after water-based coating are printed with other colors, the ink is difficult, and even cannot be left on the prints. Therefore, the water-based coating oil is always arranged for the final coating. In addition, the glazing of the printing surface is more conducive to hot stamping and other post-press processing, generally using the following process: printing → water-based coating → hot stamping → die-cutting.

3. Impact of printing materials

Waterborne varnish has a wide range of applications and can be used for paper. Aluminum foil, aluminized paper, gold/silver cardboard, etc. The type and quality of printing materials have a great influence on the glazing effect.

For paper. on the one hand. Different papers have a great difference in absorbency, that is, when the same coating oil is used, the coating effect will be different. Therefore, according to the different absorption of paper, choose different viscosity and solid content of Varnish. On the other hand, the smoothness of the paper surface also has a direct effect on the gloss effect, especially on the brightness of the gloss. Paper with a high surface smoothness has a good effect after glazing, and has a higher lightness, whereas it has a lower lightness. For example, when the front surface of ordinary white cardboard is lighted, the effect is good; when it is reversed, light effects are basically not seen.

4. Impact of printing speed

When the printing speed is too slow, the water-based coating oil will dry on the surface of the printing plate, resulting in a paste plate and a dirty plate. In this case, a small amount of water and glycerol should be added to the water-based coating for humidity conditioning to slow the drying speed. When the printing speed is too fast, the water-based coating on the prints is too late to dry, and the prints are stacked together, causing the back of the print to stick. In this case, an appropriate amount of ethanol and isopropanol should be added to the aqueous coating oil to adjust the drying speed.

5. Effect of product use

Waterborne gloss products are soft and delicate on the look and feel. Bright, bright colors and other characteristics. At the same time, water-based coating can also improve the brightness and metallic feeling of gold and silver on the product, but the water-resistance is worse than that of other varnish oils. Varnish should be selected according to different product applications. White box paper or white cardboard printing hard box cigarette packs, because it must be equipped with a long dry track on the packet machine. Therefore, it is required that the waterborne varnish have a high wear resistance. The use of coated paper printed soft box cigarette labels, there is a high requirement for the smoothness of water-based coating oil, which has a lot to do with the type of cigarette packaging equipment used by cigarette factories. Beer labels, especially beer labels, are resistant to waterborne paints due to the fact that they need to be refrigerated, transported, etc. Alcohol resistance and abrasion resistance are very high. In addition to cigarette packs and labels, water-based polishes are also widely used in kits. Food packaging. In short, according to the different uses of the product, so that after polishing the product is increasing the gloss. Improve wear resistance and safety and environmental protection at the same time, with anti-oil, anti-alkali, high temperature resistance, baking resistance, anti-solvent and other properties.

In the domestic market, the prospects for the development of water-based varnishes are unanimously optimistic. We believe that with the improvement of technology and the enhancement of environmental awareness among the general public, the environmental protection department, together with printing companies and equipment suppliers, will be able to achieve a more healthy and rapid development of the water-based glazing technology in China and make it more suitable for the printing industry in China. Big contribution.