A. What is glazing?
Glossing is a colorless and transparent coating (varnish) coated (or sprayed, printed) on the surface of a print. After being leveled, dried, and calendered, it forms a thin, uniform, transparent layer of light on the surface of the print. . Coatings include full gloss, partial gloss, glossy gloss, matt (matte) gloss, and special coatings.
B. Why do you need to polish your print?
The glazing is to beautify the printed matter, protect the printed matter, strengthen the publicity of the printed matter and increase the practical value of the printed matter. The surface of the printed surface after polishing is even smoother, resulting in uniform reflection of the incident light and a brighter ink layer. Glazing is the use of varnish for surface coating of printed products. Before the final processing of the prints after printing, take appropriate measures to protect the surface of the paper or paperboard prints. After the printing, the surface is covered with a glossy film. Its application scope includes:
1 The binding of books, such as covers, covers, inserts, and calendars, calendars, advertisements, and promotional samples, etc., can increase the gloss and bright colors of printed materials through polishing.
2 Packing and decorating paper products, such as Paper Bags, envelopes, trademarks, etc., play a role in beautifying and protecting commodities after polishing.
3 Cultural articles, such as playing cards, postcards, and gold patterns, can resist mechanical abrasion and chemical corrosion when glazing.
4 daily necessities, foods, etc. Such as cigarettes, food, detergents and other trademarks can play a role in moisture, mold.
5 Pressing the copper foil on the hard cover can make the appearance beautiful, and its brightness is very high, very much like gold. If the combination of copper and Kiko is not strong, good adhesion properties can be obtained after polishing.
C. What are the technical requirements for coating oil?
In addition to having a colorless, odorless, strong gloss, rapid drying, and chemical resistance, the ideal coating oil must also have the following properties.
1 film transparency, no discoloration. Decorative prints to obtain excellent glazing effect depends on the formation of a colorless, transparent film on the surface of the printed sheet, and the graphic does not change color after drying. And it should not be discolored or yellowed due to sun exposure or long use.
2 film has a certain degree of wear resistance. Some glossy prints require some abrasion resistance and scratch resistance after polishing. Because of the assembly line production processes such as high-speed box-making machines, cardboard boxes and packaging machines, and book covers, the surface of prints is subject to friction and must therefore have wear resistance.
3 has a certain degree of flexibility. The glossy film formed on the surface of any type of varnish must maintain good elasticity so that it can adapt to the flexibility of paper or paperboard, and it will not be damaged or cracked or peeled off.
4 Film resistance to environmental performance is better. After glazing, some of the printed matter is used to make all kinds of packaging cartons. In order to be able to protect the products being packaged, the glazing film layer must have good environmental resistance. For example: The packaging of food, cigarettes, cosmetics, clothing and other commodities must have moisture-proof and mildew-proof properties. In addition, the chemical properties of the dried film must be stable. Do not change the performance due to contact with a weak acid or weak base or other chemical substance in the environment.
5 has a certain adhesion to the print surface. Due to the integral density value of surface ink layers, the printability of the printed matter is greatly reduced. In order to prevent the dry and cracked film from drying after use, it is required that the film has strong adhesion, and the ink and ink transfer are used in various types. Accessories have a certain degree of adhesion.
6 Good leveling and smooth film surface. There are various types of materials for printing materials, and the effects of printed graphics, such as the surface absorptivity, smoothness, and wettability, are very different. In order to make the coating on the surface of different products can form a smooth film layer, it requires coating oil. Leveling is good, film surface is smooth after film formation.
7 Printability is wide after printing. After the glazing of prints, it is generally required to go through the post-process processing, such as: molding processing, stamping and electro-aluminum processing. therefore. It is required that the post-printing processing of the coating film should be wide enough. For example, the heat resistance is better. After the electro-aluminization is stamped, no sticking phenomenon can occur; the solvent resistance is high, and the dried film cannot be blisters, wrinkles, and hair due to the influence of the adhesive in the post-processing. Viscosity phenomenon.
D. How to choose varnishes?
The choice of glazing oil must meet the basic principles of science, economy and practicality.
The so-called science refers to the need to study whether Varnish meets the physical and chemical properties of the glazing and use of printed materials. For example, the covers and seals of books, catalogs, and albums require that glazing oil not only has high transparency, but also has better abrasion resistance and folding resistance; Food Packaging varnish must first be non-toxic and have certain moisture-proof and anti-corrosion properties; The packaging paper carton is varnished and requires high chemical stability. It cannot be discolored or yellow due to placement (sunlight or light), or sticking and other phenomena occur due to stacking.
The economy means that when choosing a varnishes, the varnishes must be commensurate with the prints to avoid the use of high-grade varnishes for medium and low-grade prints. For example, for high-grade printed products, you can use solvent-based coating with high cost, good quality calendering, UV-curing, or acrylic resin as the main agent; on the contrary, if the printed matter is a bulk product such as textbooks, It is advisable to use a general solvent type coating oil whose quality is moderate and whose quality can meet the processing requirements.
Practicality means that the choice of varnish must be matched with the varnishing equipment. For example, solvent-based coating oils are only suitable for ordinary coating machines; UV-curable coating oils must be used on machines equipped with an ultraviolet drying device; alcohol-soluble or water-soluble coating oils must be satisfactorily applied to the coating machine. Varnish drying requirements (generally require a drying path length of more than 6m, temperature above 65 °C). In addition, we must also consider the need to save labor and materials, but also suitable for mechanical mass production, try to reduce production costs, less investment, more output. The choice of coating oil must also pay attention to safety, hygiene and environmental protection requirements. From the perspective of safety, we should use varnishes with good storage properties and non-flammable properties. We should use odorless, non-toxic and odorless varnishes in consideration of hygiene and environmental protection. The production site and the ventilation conditions of the machine are good, and the selection range can be appropriately wider. On the contrary, the coating oil with aromatic substances as the solvent should not be used to prevent the operator's physical health and environmental pollution.
E. What are the requirements for the quality of the varnish coating?
In order to obtain the desired glazing effect, in the coating process, the coating of the varnish should meet the following requirements: (1) The coating layer of the coating is uniform, free of blisters, free from bubbles, and free of paint. 2 The coating amount is appropriate, and the coating can be dried and dried at a certain temperature and a coating speed. 3 coating is not affected by printing ink performance, printing image area and integral density value, leveling is good, and has a certain adhesion with the print surface. 4 coating in the calendering, can adhere to the surface of the calender belt, after cooling it can be easily peeled off.
F. What are the factors affecting the quality of glazing?
The main factors affecting the quality of glazing are: paper properties, temperature, ink, and crystallization of printed materials.
1 Effect of paper properties on gloss quality. The effect of paper on coating quality is mainly reflected in the effect of paper smoothness on coating quality. High-smoothness papers have a significant effect upon polishing, while papers or paperboards with low smoothness have a poor effect after polishing, since the varnish is almost completely absorbed by rough paper or paperboard. In order to solve this problem, you can use a casein base or two times before the application of light.
2 The effect of temperature on polish quality. Glossing temperature between 18 °C ~ 20 °C, can achieve the best results. In winter, the varnish is easily solidified, and the surface film of the varnish product is uneven. In order to solve this problem, the coating oil needs to be stored in a warm place. If the temperature of the coating oil is too low—below 10, even though the coating oil is put in a room with room temperature of 20° C. for a day and night, it cannot be used. The coating oil must also be properly diluted in the solvent.
3 printing ink on the quality of the coating. Printing inks used for products that need to be applied after printing must have solvent resistance and heat resistance, otherwise the printed matter will be discolored or wrinkled. The solution is to pay attention to the following points when selecting printing inks: a. Must use alcohol-resistant, ester-based solvents, and acid-base inks. B. Must use durable ink with good color and good gloss. C. Must choose ink with good adhesion to paper.
4 The effect of crystallization on the quality of glazing. The phenomenon of crystallization of printed matter is mainly due to the fact that the printed matter is left for too long, the ink area at the bottom of the print is too large, and the dry oil is excessively added. The ink film has a crystallization phenomenon on the surface of the paper, which often causes glazing or printing to fail. "Face", "matt" and other problems.
In order to solve this problem, 5% lactic acid is generally added to the varnish and it can be used after stirring. The modified varnish is applied to the printed matter so that the vitrified film on the surface of the printed matter is damaged, and the varnish can be evenly applied to the surface of the printed matter to form a glossy film.
G. What is calendering?
The calendering is performed on two units of varnishing and varnishing. The printed product is first coated with an glazing oil on an ordinary glazing machine, and after being dried and then hot-pressed by the stainless steel belt of the calender, after cooling and peeling, the surface of the printed matter is formed with a mirror reflection effect, thereby obtaining high gloss.
H. What are the factors that affect the quality of calendering?
The main factors affecting the calender quality are: calendering temperature, pressure and speed
1 calendering temperature. Appropriate calendering temperature can increase the molecular heat movement ability of coating film layer, accelerate the diffusion speed, and is beneficial to the secondary wetting, adhesion and penetration of the main agent molecules in the coating on the surface of the printed matter. In addition, the appropriate temperature will increase the plasticity of the coating film layer. Under the effect of pressure, the smoothness of the surface will be greatly improved. The appropriate calendering temperature is beneficial to improve the quality of the calendered film layer, but the temperature is too high or too low is not conducive to Calendered. If the temperature is too high, the adhesion strength of the paint layer decreases, and the moisture content of the paper drops rapidly, which is not conducive to glazing and peeling. When the temperature is too low, the paint layer cannot be completely plasticized, and the paint layer does not adhere well to the surface of the calender plate and the printed matter, and the calendering effect is poor, and it is not easy to form a film layer with high smoothness after calendering.
2 pressure. The effect of pressure is to compress and thin the coating layer so that it forms a smooth surface layer. However, if the pressure is too large, the printability, plasticity, and toughness of the printed matter will be deteriorated, and the phenomenon of difficulty in peeling will not easily occur.
3 speed. The pressure speed is the curing time of the coating in the calendering. If the curing time is short (speed is fast), the coating oil molecules can not fully function with the ink layer on the surface of the printed matter. After drying, the smoothness of the film surface is poor, and the adhesion of the coating layer to the ink layer is poor.
Source: Saint Gerkan Design Print