Glazing process and influencing factors of the hot

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Polishing of paper printing and its influencing factors

polishing is to apply a layer of colorless transparent paint on the surface of printing, after leveling Drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism: drying mechanism "The processing technology of uniform transparent bright layer. Glazing can not only enhance the surface brightness, protect printing graphics and texts, but also do not affect the recycling and reuse of paper. Therefore, it is widely used in the surface processing of packaging cartons, books, picture books, posters and other prints. The glazing processing technology of paper prints includes paint glazing, UV glazing, pearlescent pigment glazing.

1 various glazing process characteristics and requirements

1) paint Light

the process of coating polishing is actually the process of connecting the coating with the coating. Glazing paint includes solvent glazing oil, water-based glazing oil, UV glazing oil and pearlescent pigment glazing

as solvent polish is not conducive to environmental protection, the scope of application is increasingly limited

water based glazing oil uses water as solvent, which is non-toxic and tasteless. It eliminates the harm to human body and pollution to the environment. It has the characteristics of fast drying speed, good transparency of film layer, stable performance, good wear resistance and flatness of glazing surface, wide post press processing adaptability, good heat sealing performance, safe and reliable use, convenient storage and transportation, and is increasingly valued by food, medicine, tobacco carton packaging and printing enterprises

uv glazing prints have high surface gloss, heat resistance, wear resistance and water resistance. There is no solvent volatilization during curing, which will not cause environmental pollution. They are suitable for glazing of high-end packaging

pearlescent pigments can obtain a good spot color gloss effect and have a good development prospect

generally, after polishing, press polishing can be carried out after the varnish is dry (a short time, online operation is available) in order to form a high gloss surface on the polished surface

performance requirements for glazing paint

① the film has high transparency and no discoloration

② it has certain flexibility. The bright film formed by any kind of polish on the surface of printed matter must maintain good elasticity to adapt to the flexibility of paper or paperboard, and will not be damaged or cracked, or fall off

③ the film has certain wear resistance. Some polished prints require certain wear resistance and scratch resistance after polishing. Such as high-speed box making machine, cardboard box packaging machine device, book cover and other assembly line production processes, the surface of printed matter will be subject to friction, so it must have wear resistance

④ it has certain adhesion to the surface of printed matter. Due to the influence of the thermosetting molding board of the surface graphic ink layer, the surface adhesion of the printed matter is significantly reduced. In order to prevent the ink layer from drying and peeling off after drying, it is required that the film layer has strong adhesion, and has a certain adhesion to the ink and various auxiliary materials used for ink mixing

⑤ good leveling and smooth film surface. There are many kinds of printing materials for printing. In addition to the influence of printing pictures and texts, there are great differences in surface absorption, smoothness, wettability and so on. In order to make the glazing paint form a smooth film on different product surfaces, it is required that the glazing oil has good smoothness and the film surface is smooth after film formation

⑥ the film has good environmental adaptability. Some of the printed matter after glazing is used to make various packaging cartons. In order to protect the packaged products, the glazing film is required to adapt to the environment, and the rotatable connection between the ratchet wrench and the end of the operating rod must be good. For example, the packaging of food, cigarettes, cosmetics, clothing and other commodities must be moisture-proof and mildew proof. In addition, the chemical properties of the dried film should be stable, and the performance should not be changed due to contact with weak acids or weak bases and other chemicals in the environment

⑦ wide adaptability for post press processing. After the printing is polished, it usually needs to go through post-processing processing, for example: the heat resistance is good, and the bonding phenomenon cannot occur after hot stamping anodized aluminum; Solvent resistance is good, and the dried ink layer cannot be foamed, wrinkled and sticky due to the influence of adhesives in post-processing

the main factors affecting the glazing quality

the factors affecting the glazing quality mainly include the glazing suitability of printing materials, temperature, ink quality and the crystallization of printing materials

① gloss adaptability of printed matter. The glazing suitability of printed matter mainly refers to the influence of printing paper and printing ink on glazing coating. a. How about the quality and characteristics of paper, which directly affects the shortcomings of traditional equipment based on hydraulic universal testing machine of glazing products and the new quality requirements of the market for universal testing machine? For example, because the surface of coated paper is smooth, after glazing, the coating is easy to level. After drying, the coating layer forms a film surface with high smoothness on the paper surface, and the gloss effect is significantly improved; The surface of the coating paper with low quality is rough, and the coating is not easy to level after glazing, so the glazing effect is relatively poor. To this end, you can take the method of two coats of varnish to ensure the glazing quality. b. If the heat resistance and alcohol resistance of the ink are poor, the printed image and text will have quality faults such as discoloration or wrinkled skin. Therefore, glazing products should use alcohol and ester solvents and printing inks with good acid and alkali resistance. In addition, the ink is also required to be durable, non discolored and glossy, and has strong adhesion to paper

② the influence of temperature on the glazing quality of products. Under normal circumstances, the printing glazing temperature is controlled at about 20 ℃ to achieve a relatively ideal effect. However, if glazing in winter, due to the low temperature, the glazing oil is relatively easy to solidify, which is not conducive to the normal flow of the glazing oil, resulting in uneven oil film on the surface of the product, so its brightness is bound to be poor. In order to overcome the disadvantages caused by the defects of environmental conditions, the glazing oil should be placed in a relatively insulated place. If necessary, add solvent to dilute as appropriate

③ influence of print crystallization on glazing quality. The printing product is placed for a long time or excessive dry oil is added to the base color ink, so that the ink layer forms a crystallization phenomenon on the paper surface. In this way, the oil cannot adhere to the ink layer during glazing, and the gloss layer will be scratched and uneven. In this case, as long as 5% lactic acid is added to the glazing oil and stirred evenly, glazing can be carried out. When the modified varnish is applied to the print, the crystalline film on the surface of the print can be destroyed, so as to achieve the requirement of evenly adsorbing the varnish

2) UV glazing

uv glazing is a method of using UV to polish UV paint? UV glazing relies on the irradiation of UV light to make the chemical reaction inside the UV coating and complete the curing process. Due to the action of UV, UV glazing is instantly dry, and the curing speed is fast. The curing speed can reach 60 ~ 120m/min. The glazing oil has strong affinity for ink and firm adhesion. There is no volatilization of solvent during curing, which will not cause environmental pollution. The printing products with UV glazing oil have high surface gloss, heat resistance, wear resistance, water resistance, light resistance, and UV glazing products do not adhere. They can be stacked after being taken off-line, which is conducive to post-processing operations such as binding. However, due to the high price of UV glazing oil and high requirements for machine performance, it is currently only used for the glazing of high-end cartons. There is also a special glazing, that is, local glazing and coating of the parts that need to be highlighted on the packaging prints, which can produce a unique artistic effect by using the contrast between the bright part and the matte part of the local glazing products

domestic UV polish has also developed rapidly in recent years, and the quality has reached a high level. For example, the flexible UV Polish produced by Shaanxi new century printing materials Co., Ltd. and the UV polish for textbook cover have been promoted and used in China, and have been highly praised by users

3) pearlescent pigment glazing

pearlescent pigment glazing is a kind of flake crystal structure pigment with color, translucency and partial covering power evenly coated on the surface of printing products. Pearlescent pigments can be mixed with colorless transparent binder and printed separately, mixed with other inks and then used, and can also be overlapped with other inks. In modern printing industry, pearlescent effect is an irreplaceable spot color gloss effect. In high-end packaging such as cigarettes, drugs, food and special chemicals, LANXESS is consolidating its position in the growing Chinese market: the company headquartered in Cologne, Germany, will invest about 20million euros in the field of cosmetics packaging, which has a good application prospect

2 common faults and troubleshooting of glazing

1) small granular impurities appear on the surface of glazing prints

fault cause: impurities are mixed in the glazing paint

solution: Polish paint should be filtered before reuse. Before glazing, the paint bucket and rubber roller of the glazing machine should also be cleaned to avoid dirt

2) poor gloss of glazing film

fault cause: A. low temperature in coating drying and calendering; b. Poor coating quality, low gloss after film formation; c. The coating concentration is small, the coating amount is insufficient, and the coating is too thin

solution: A. adjust the drying temperature of glazing coating and increase the calendering temperature; b. Change the coating, or increase the coating concentration and increase the coating amount; c. Secondary coating can be used

3) there are streaks or wrinkles on the film surface

cause of failure: a. the viscosity of glazing paint is high; b. The coating amount of glazing paint is too large; c. Glazing coating has poor wettability to the ink layer on the surface of printed matter; d. The pressure between the cot and the embossing cylinder of the polishing machine is uneven

solution: A. add a small amount of diluent to reduce the viscosity of the coating; b. Reduce the coating amount of glazing paint; c. Adjust the pressure between the top roller and the embossing cylinder of the polishing machine to eliminate streaks

4) the surface of printed matter is easy to crack after calendering (thick paper is more obvious)

cause of failure: a. the high temperature in calendering reduces the water content of printed matter and makes the paper fiber brittle; b. High pressure in calendering makes the extension and flexibility of printed matter worse; c. Improper selection of post-processing process conditions; d. Poor processing suitability after glazing paint

solution: A. reduce the calendering drying temperature and take effective measures to change the moisture content of the printed matter; b. Reduce the calendering pressure; c. Adjust the post processing conditions to match the suitability of the printed matter (after calendering)

5) the blank part of the printed matter is light colored after calendering, and the light colored part changes color

fault cause: a. the ink is not dry well, and the solvent resistance of the ink layer is not good; b. The coating solvent has a certain dissolving effect on the ink layer; c. The coating layer is not completely dried, and the solvent residue is high

solution: A. polish the printed matter after drying; b. Reduce the amount of solvent in glazing paint (solvent that dissolves ink), and change the solvent or change the paint if conditions permit; c. Increase the drying temperature and reduce the solvent residue inside the coating

reprinted from: CPC Chinese printing community

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