Innovative Application of Paper Packaging Printing Technology (5)

3.4 Screen Printing New Technology

Screen printing has the characteristics of thick ink layer, rich graphic layers, strong three-dimensional sense, and wide printing materials, etc. The application of high-grade tobacco and alcohol, food packaging cartons has gradually increased. The use of UV screen inks to print frosted, refraction, ice, wrinkles and other effects on cigarette packs has greatly stimulated consumers' desire to purchase. However, due to the flat screen printing method, the printing speed is low, the ink curing speed is slow, the printing quality is difficult to control, and the printing material consumes a large amount, which can not meet the needs of cigarette cartons in scale and mass production. High-speed rotary screen printing production line, fast printing speed, high productivity, stable quality of printing products, low consumption, change the traditional flat pressure flat screen printing, manual feeding, ink supply, suitable for high-speed automatic, large-scale mass production of exquisite Fold the tray.

Web Rotation Screen printing uses a nickel metal round screen plate, a built-in doctor blade, and an automatic ink supply system. The doctor blade transfers the printing ink from the circular screen plate to the surface of the substrate supported by the impression cylinder. The entire printing process from paper feeding, ink supply, ink color registration, UV dry bath, etc. are fully controlled by the computer. The round screen printing plate adopts 100% nickel non-woven fabric material, and the mesh is hexagonally shaped by electroforming. The entire mesh surface is even and thin to ensure the stability and precision of the imprinting. Suitable for large format rotary printing, the maximum speed can reach 125m/min, and the screen can be reused 15 times. Therefore, roll web screen printing can not only meet the requirements of special effects such as printing frosting and ice flowering, but also can be used for hot stamping holographic anti-counterfeit labels, embossing, and die-cutting molding. It is easy to realize high-speed automatic printing paper boxes.

Environmentally-friendly UV screen printing imitation metal etching ink is mainly composed of an oligomer (ie, a photocurable resin), a reactive diluent (ie, a photosensitive cross-linking monomer), an optical (polymerization) initiator, and an additive. Printing on gold and silver card paper, UV screen printing imitation metal etching ink is rapidly cured under ultraviolet light irradiation, and the printed surface produces a frosted effect.

Under irradiation with xenon light, the photopolymerization initiator in the UV ink absorbs photons of a certain wavelength, excites excited states, and forms radicals or ions. Then, through intermolecular energy transfer, polymers such as polymerizable prepolymers and photosensitive monomers are brought into an excited state to generate charge transfer complexes; UV inks selectively absorb UV photons, and the drying of UV inks is influenced by the total energy of the UV light source and the distribution of light energy at different wavelengths. Solve the UV ink and UV light source match, help to speed up the ink drying speed, improve labor productivity and energy utilization, reduce production costs.

4. Surface finishing and forming technology

4.1 Waterborne and UV Polishing

The lamination process is simple and inexpensive, but because the coated paper is difficult to recycle, it is non-degradable and can easily cause white pollution. Long-term use will also endanger the health of workers. Therefore, the traditional instant coating type adhesive material will be replaced by a high quality, environmentally friendly new type of adhesive. Coating not only enhances the surface brightness and protects printed graphics, but also does not affect the recycling and reuse of paper, saving resources and protecting the environment. Therefore, it is widely used in the surface processing of paper packaging printing products. The glazing coatings mainly include solvent coatings, waterborne coatings, and UV coatings. Due to the poor efficacy of solvent varnish and its unfavorable environmental protection, the application range is greatly limited.

Waterborne varnish uses water as solvent, non-toxic and odorless, eliminating the harm to the human body and the pollution to the environment. It has the advantages of fast drying speed, stable performance, good abrasion resistance on the light surface, wide applicability after printing, and heat Sealing performance, use of safe and reliable, and other characteristics, more and more food, medicine, tobacco carton packaging and printing companies pay attention.

UV coating depends on the irradiation of ultraviolet light to make chemical reaction inside the UV coating to complete the curing process. Due to the effect of ultraviolet rays, UV light is instantly dried when it is glazing, and there is no volatilization of the solvent during curing, which will not cause environmental pollution. Printed products using UV varnish have high surface gloss, heat resistance, abrasion resistance, water resistance, and light resistance. However, due to the high price of UV varnish, high requirements are imposed on machine performance. Therefore, they are currently used only on high-grade paper boxes. Light.

(to be continued)

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