In recent years, based on our experience in practical applications, we believe that water-based pressure-sensitive adhesives have the following advantages:
(1) High transparency and good gloss. It has no adverse effect on the color of printed matter. Even under long-term strong sunlight, the coating of water-based varnish is not easy to yellow.
(2) Strong abrasion resistance and scratch resistance. The surface of the printed material is wear-resistant, does not fade, is repelled by water and oil, and is welcomed and relied by users. Water-based varnishes are used on cigarette cases. During high-speed operation at speeds of up to 300 to 500 packs / minute, the cigarette labels are subject to large mechanical loads. Water-based varnishes fully meet this requirement, No phenomenon was found in cigarette packs whether it was gravure or offset printing.
(3) Non-toxic and tasteless, convenient to use, transport and store, and safe. Water-based varnishes use water as the solvent, and only a small amount of edible edible ethanol as the auxiliary solvent, which is conducive to safe production and improve working conditions for employees. After glazing, the equipment can be washed directly with water without any danger.
(4) The conjunctival speed is fast, the drying is fast, and the high temperature resistance and heat sealing performance are good. Water-based varnish is applied on Heidelberg CD five-color continuous glazing offset printing machine. It is completely dried at a printing speed of 13,000 sheets / hour, infrared drying, power of 5.4kw × 5 pieces × 2 groups, and a temperature of 65 ° C. It has achieved satisfactory application results. . Cigarette packs use PP film as the outer packaging. Water-based varnishes show good heat-sealing performance.
(5) Good flatness and strong anti-rolling force. Water-based varnishes do not have excessive temperature requirements, and their use on gravure printing machines is more convenient than that of general solvent-based varnishes. A difficult problem in gravure printing is that after the printed matter is continuously dried in several color groups, the moisture content of the paper is extremely low, and it is particularly easy to curl, making it unusable. The flexible packaging was not glazed with water-based glazing. The product was cut into large sheets, and then bronzed and slit. It still maintained good flatness and anti-rolling resistance, and the users were satisfied with it.
It is worth noting that the application of water-based pressure-sensitive adhesive must be comprehensively considered according to different printing methods, printing equipment, printing speed, paper type, printing equipment, printing speed, paper type, product quality requirements and other factors in order to obtain a good effect. The main points to note are:
(1) Viscosity control. During the coating and varnishing process, the viscosity and solid content of the varnish must be reasonably controlled. Dilution can only be performed within a certain range of solid content.
(2) The different paper types are closely related to the coating process. 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 of the paper, the time and method of drying, and the control of viscosity.
(3) Control of coating amount. The coating amount of water-based varnish is not easy to control. Generally, it should be determined in combination with the actual situation and experience of our factory.
(4) Control of drying time. Using water-based varnish, if infrared drying device is used, the effect is good, because the varnish is boosted during the drying process, the bottom layer quickly penetrates to dry, and the middle water is heated and evaporated at high temperature, which is discharged through the exhaust pipe. It is a good way to apply varnish to the last color in multi-color printing.
To sum up, water-based varnish can eliminate the harm to the human body and the pollution to the environment during operation, and it has been more and more favored by food and tobacco packaging and printing enterprises. It has the advantages of advanced technology, convenient use, and economical reasonableness, and has great development prospects. It has gradually replaced solvent-based varnishes and oily varnishes, and will occupy a dominant position in the packaging and printing industry.