Performance comparison of different polishing methods

Common coating processes in China include solvent-based, oil-based, water-based, and UV coating, each with its own advantages and disadvantages.

I. Solvent-based Coating

(1) Advantages

① Low equipment investment

② Standardized coating process, relatively stable quality.

③ Good gloss, adhesion, dimensional stability, and post-processing adaptability.

④ Low overall cost.

(2) Existing Problems

① Slow coating speed, low production efficiency.

② Poor chemical resistance, coating may yellow.

③ 50% of the organic solvent in the coating volatilizes, resulting in high coating oil consumption; solvent volatilization pollutes the environment and is harmful to human health.

④ Organic residue remains in the coating, limiting its application; it is being replaced and phased out.

II. Oil-based Coating

(1) Advantages

① Using an offset press for coating reduces equipment investment.

② Offset presses are fast, resulting in high coating efficiency.

③ Good adhesion, dimensional stability, and post-processing adaptability.

(2) Existing Problems

① Slow coating drying speed, requiring 4-8 hours to dry, so it cannot be used for inline coating or immediate post-processing.

② General gloss, poor chemical resistance, coating may yellow.

③ General coating quality, suitable for small-batch general printing coating.

III. Water-based Coating

(1) Advantages

① Colorless, odorless, good transparency, high gloss.

② No solvent volatilization, non-toxic, non-irritating, harmless to human health, environmentally friendly.

③ Fast drying speed, stable performance, coating does not yellow or discolor.

④ Tough, wear-resistant, high-temperature resistant, good heat sealing, good post-processing adaptability.

⑤ Convenient and safe transportation.

(2) Existing Problems

① Low grammage paper is prone to dimensional deformation.

② It is necessary to control the viscosity of the coating, printing speed, coating application amount, and drying time.

③ For offset inline printing and coating, the principle of oil and water immiscibility should be considered, and the compatibility of the water-based varnish with the ink should be noted when selecting it.

IV. UV Coating

(1) Advantages

① Fast coating speed, instant curing, allowing for inline coating and simultaneous coating and printing, allowing for immediate post-processing.

② High gloss, brighter than lamination.

③ Good chemical resistance, good adhesion, wear-resistant, heat-resistant, water-resistant, and light-resistant.

④ No solvent release during photocuring, 100% participation in the reaction, no environmental pollution, harmless to human health.

⑤ Meets the diverse requirements of printed products, allowing for full and partial coating; enhances product grade and added value.

(2) Existing Problems

① UV coating quality control is more complex and difficult than other coating processes. There are many types of film-forming resins (oligomers) in UV coating materials, with different properties. Different UV coating materials should be selected according to different printing processes, substrates, and post-processing suitability to obtain ideal results.

② Currently, domestic UV coating materials still have a certain gap compared with foreign ones, such as the coating being light yellow, affecting the color effect of printed products; the coating has a small amount of odor, although non-toxic, but affecting the use effect.

③ The cost of UV coating is lower than lamination and higher than other coating processes.

④ UV coating should pay attention to safe operation, such as UV coating irritating to the skin, if the skin accidentally contacts UV coating should be immediately washed with soapy water, otherwise it will swell and blister; operation should avoid UV light direct irradiation to the human body.

⑤ UV drying produces ozone, which should be ventilated and removed.

V. Coating and Calendering

(1) Advantages

① After calendering, the printed matter has a mirror-like reflection, smooth, delicate surface, high gloss, and can replace expensive glass-coated paper in packaging printing.

② Improves the quality of printed packaging products.

③ Improves moisture resistance, water resistance, no sticking, no yellowing.

④ Good post-processing adaptability.

⑤ Relatively low overall processing cost.

(2) Existing Problems

① Multiple processing steps are required, coating must be applied first, and then calendering can be performed after drying.

② Slow calendering speed, low production efficiency.

③ Slightly lower folding and wear resistance.