Preparation and use of water-soluble glazing ink

Water-based glazing ink (WaterBase Varnish) / water-based glazing coating (Water Base Coating) is abbreviated as water-based varnish or water-oil, which is used for full coating or spot coating. On printed matter, it can protect printed matter and enhance gloss. The advantages are non-toxic, no environmental pollution, no solvent volatilization (low residual odor), can improve the production environment, is beneficial to the health of the operator; and can meet the environmental protection import standards in Europe and the United States. The water-based varnish has fast conjunctiva, strong wear resistance, is not easy to turn yellow, and has high gloss. It is widely used in various types of paper. The specially formulated water-based varnish can be applied to non-absorbent materials, such as gold and silver cards, PET, PP, PVC, etc.

Water-based varnish is generally composed of 80-90% water-based resin and 10-20% other additives. After coating and glazing, a thin layer of polymer is left on the surface of the substrate, which gives the coating different characteristics due to different formula combinations. Such as high gloss, matte, wear-resistant and so on.

Water-based resin is the most important component in water-based varnish. It determines and affects the characteristics of water-based varnish, such as gloss, adhesion, wear resistance, drying, etc., so the proper selection of water-based resin is the key to the success of water-based varnish.

There are many types of resin, including water-based rosin modified maleic acid resin, water-based polyurethane resin, water-based acrylic resin, water-based alkyd resin, water-based amino resin and so on. For water-based varnish, the resin selected should have the characteristics of easily soluble salts, good water release, good gloss after film formation, heat resistance, chemical resistance, and fast drying speed, while water-based acrylic copolymer resin It can meet the requirements of printing and glazing to the greatest extent, so when formulating water-based varnish, the copolymer resin of water-based acrylic system becomes our best choice.

Waterborne acrylic copolymer resins can be divided into waterborne acrylic resin solutions, waterborne acrylic dispersions, and acrylic emulsions. The acrylic emulsion can be divided into film-forming acrylic emulsion and non-film-forming acrylic emulsion. The performance of the waterborne acrylic copolymer resin is composed of monomers. The performance and synthesis process vary. Some monomers can improve gloss and hardness, while others can provide chemical resistance and adhesion. After a large number of experiments, it is proved that the performance of the water-based varnish made by scientifically compounding water-based acrylic solution and acrylic emulsion is ideal.

Other additives also play an important role in improving and improving the performance of water-based varnish. Such as leveling agent, wetting agent, defoaming agent, anti-wear agent, etc. The leveling agent is to improve the fluidity, extend the leveling time, help the coating form a smooth coating after drying, and avoid the appearance of water marks and streaks. The wetting agent mainly reduces the surface tension of the water-based varnish system and improves the wetting ability of the coating on the substrate surface. The antifoaming agent can just suppress and eliminate the foaming of the water-based varnish in the circulation system, avoiding excessive foaming to affect the operation. Anti-wear agents can improve the anti-friction, anti-scratch and slip properties of water-based varnish. In addition, adding a small amount of auxiliary solvent in the formulation can make the components of the water-based varnish better miscible with each other, reduce the cohesion of the system, and improve the adaptability of the glazing.

Water-based varnish is suitable for special line coating unit, offline roller coating machine, flexographic coating, gravure coating, etc., and the main applications are mainly line coating (such as KBA104, KBA105), offline Roller coated. In particular, line polishing, in addition to less use and no need for powder spraying, can also greatly improve printing efficiency (reduction of spacers) and reduce the waiting time required for post-processing. The printed product after the line is polished can generally be processed after die cutting and other processing after 2 to 6 hours.

However, no matter what kind of glazing you choose, if you want to achieve a satisfactory glazing effect. You must master the use of water-based varnish. Therefore, in the process of using water-based varnish, we suggest to carefully master the following three factors:

1) Coating amount: After a uniform and proper amount of coating is formed, the gloss is good and the wear resistance is high. If the coating amount is small, the water-based varnish cannot form a complete and continuous coating film, resulting in poor gloss and insufficient protection and decoration effects. However, if the amount of coating is large, the thickness of the coating film will increase the cost of glazing, and also affect the drying speed. Seriously, there will be a sticky back. We generally recommend that the wet coating film should be 4 ~ 10g / ?, and the specific coating amount will require customers to vary according to the characteristics of paper and equipment.

2) Viscosity: The viscosity of the off-line roller is generally recommended to be 18 ~ 25 seconds (DIN4, 25 ℃). The viscosity of the glazed wire (such as Roland 705) is generally recommended to be 40 to 70 seconds (DIN4, 25 ° C). If the viscosity is too low, it will not be able to protect and decorate; if the viscosity is high, the leveling may be poor and the drying may be slow. The water-based varnish and diluent are generally water, or a 1: 1 mixture of isopropyl alcohol: water can be used as the diluent according to specific conditions. The specific viscosity should be adjusted according to the characteristics of the paper and equipment.

3) Drying temperature and time: water-based varnish mainly depends on penetration drying and also has crosslinking and curing. Common drying devices include hot air drying and infrared drying. It is generally accepted that infrared drying works best. Because the main solvent of water-based varnish is water, and the fluidization heat of water is relatively high, so the drying speed is slower than oily. For the same reason, the drying temperature is higher than that of oily varnish. Generally recommended at 80 ~ 100 ℃, drying channel is about 2m. If the temperature is not enough and the drying tunnel is too short, the coating film will not dry, and sticky back and rubbing will seriously occur, but if the temperature is too high, the drying time is long, the paper fiber loses too much water, the paper becomes brittle, and it is easy to Breaking and bursting occurred during processing.

The above is just a brief description of the three key issues when using water-based varnish, but the use of water-based varnish is also considered according to different printing methods, printing equipment, paper type, ink characteristics and glazing equipment to make water-based varnish The superiority of the show.

Due to the advantages of environmental protection and ease of use, water-based varnish has gradually replaced solvent-based varnish and oil-based varnish. In the future, it will inevitably be adopted by more and more printing companies.

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