In modern packaging and printing, the surface finishing in the later period of printed matter is more and more important. The most widely used is the lamination and coating, and the glazing is due to its unique advantages (environmental protection, short production cycle, and production cost). Low), and gradually showing a growing momentum, playing an irreplaceable role in the field of post-press processing.
Why light on the print surface?
Firstly, the glazing on the surface of the printed matter can greatly increase the surface glossiness of the printed product, and at the same time, the surface smoothness of the printed product is also improved, which also improves the design grade of the printed product; secondly, it can improve the abrasion resistance of the printed surface. Protect the printed images. Therefore, the glazing process can be widely applied in the fields of package decoration, books and magazine covers, trademarks, advertisements, calendars, and the like.
What are the glazing processes?
The glazing process of printed products is generally composed of coating and calendering of glazing coatings. The classification of coating methods can be divided into ordinary printing equipment polishing, special coating machine polishing (with online and offline points); according to the type of coating coating can be divided into, oxidation polymerization coating Glossing, solvent evaporating coating glazing, light-curing coating glazing, heat-curing coating glazing; according to the coated product form can be divided into: whole glazing, partial glazing, extinction, artistic glazing, etc. .
Is glazing and calendering the same thing?
If it is not according to the more common name, we generally call the coating process of coating coating directly in production. The calendering is a follow-up process of coating and is usually processed according to customer requirements. It is a special production process carried out on a special coating machine after the coating coating has dried. The calendering is mainly effected by the high temperature and pressure provided by the calender, so that the surface is smoother and the visual feeling is brighter.
What are the most popular glazing coatings in the printing industry now? Introduce the process features.
Nowadays, relatively popular coatings for glazing have UV glazing and water-based gloss glazing, while solvent-based glazing coatings have gradually become obsolete due to their environmental and hazardous properties. The following describes the respective characteristics of UV and waterborne varnish.
1.UV polishing
UV coating is UV light curing, which belongs to the light curing coating. The coating oil is mainly composed of a photosensitive resin prepolymer, a reactive solvent, a photoinitiator and other auxiliary agents. The reaction mechanism is that after the unsaturated double bonds in the prepolymer absorb the ultraviolet emission energy, the double bonds are opened. Under the action of the initiator, crosslinking occurs with the monomer and a polymerization reaction takes place to cure the film. Because it is an instant cure, UV varnish has a high speed of glazing and full luster, and the surface resistance of the film after the film formation is considerably improved. In addition, the UV light oil has good adsorption performance on different surfaces and has a small impact on the environment, so it is generally favored.
(1) UV polishing equipment conditions
Rubber roller: must choose the ink roller which can resist the corrosion of UV varnish, such as EPDM, nitrile rubber, etc.
Light source: UV lamp with a power of 80 to 120 W/cm and a wavelength spectrum in the range of 200 to 450 nm. If you need to increase the speed of the glazing, then the power of the UV lamp will need to be increased (or increased by the number of lamps).
Mirror: It is very important to keep the mirror clean and intact. If it is not clean or damaged, it will affect the curing speed of the coating.
(2) Use of UV Varnish
1UV Varnish must be kept away from light at 15 to 20°C indoors
2 Stir before use, and do necessary tests (there will be some differences in the different UV light oil adsorption capacity for different print surfaces)
3 in the coating process should pay attention to a reasonable thickness of the film, although it is UV light solid, but too thick film layer will also appear incomplete curing, residual odor, resulting in substrate deformation and other issues.
4 For papers with different surface smoothness, care should be taken to choose different viscosities with different viscosity and leveling. For paper with rough surface, choose low gloss and good leveling.
5 The UV varnish used for special products must consider the properties of the varnish. If it is used for the outer packaging of detergents, then the varnish must be chosen to have chemical resistance, especially alkali-resistant varnish.
6 In the printing production, attention should also be paid to the change of the color of the ink by the UV varnish. Care must be taken in the case of more sensitive ink pigments (light blue, gold red, etc.).
2. Waterborne Varnish
Waterborne gloss oil is mainly composed of water-soluble polymer resin and a small amount of additives. Its main solvent is water, which has high solid content, colorless, odorless, good transparency, non-toxicity, and no organic volatiles.
(1) Equipment conditions for waterborne varnish
Plate: Water-based coating is usually applied with a flexo plate, so a variety of flexo-resin plates can be used, but it is not possible to use a water-based resin plate. Various coating rollers can also be used for coating.
(2) Use of Waterborne Varnish
1 Stored at 15 to 20 °C, especially to avoid storage or transportation below 0 °C.
2 The use of water-based gloss oil is basically the same as that of water-based ink. The PH value of the polishing process must be controlled between 8.5 and 9.5. Otherwise, the gloss intensity will be affected.
3 in the coating process to ensure its viscosity in the range of 25 ~ 35S, otherwise there will be quality problems.
Which are the advantages of waterborne varnish and UV varnish?
From the point of view of quality and production efficiency, UV Varnish has obvious advantages, mainly in terms of high surface gloss, surface resistance, and short production cycle.
From the viewpoint of cost and environmental protection, waterborne varnish has great advantages. The coating of waterborne varnish does not require special equipment such as UV varnish coating (special ink roller, special drying system, etc.) Larger, waterborne varnish itself is less expensive than UV varnish, without any environmental pollution.
From the above perspective, whether UV and water-based gloss oils are more advantageous and cannot be concluded arbitrarily, but we also found that with the continuous improvement of water-based gloss oils, the development of waterborne gloss oils has been a good trend. And because of its unique and irreplaceable characteristics, UV Varnish will also firmly occupy a market.
What are the more common coating equipment?
We mentioned above that there are several kinds of coating equipment, including coating machine, coating machine, on-line coating.
What is the operation of the unit glazing?
There are generally two ways to use the glazing unit. One is the use of a moistening device for glazing, and the other is the use of the ink transfer section of the printing machine for glazing through a printing plate or a blanket. Here we introduce:
1. Polishing with dampening device
This kind of glazing method is more typical of the KBA RAPIDA sheet-fed multicolor printing press. It can be equipped with wetting and glazing conversion devices. The operator can quickly wet the job with a simple manual operation. The status changes to the glazing job status operation. When the wetting and glazing functions are switched, the wetting fluid is converted into a coating liquid, and the wetting and glazing device can be set to run in glazing mode.
1. Plate cylinder 2. Metering roller; 3. Liquid (water) roller; 4. Liquid (water) roller; 5. Liquid (water) roller; 6. Liquid (water) roller; 7. Blank cylinder
The state of graph b may be selected in the transition and the state of graph b may also be selected. As shown in figure a, the speed of the roller is running at a speed of 1/3 to 2/3 of the rotation speed of the water transfer roller, so that a pre-gloss is formed by this rotation speed difference, and the true glazing still passes through the water roller. Speed ​​to adjust. If you adjust it as shown in Figure b, you can achieve a better glazing effect and better eliminate ghosting.
2. Polishing with inking device
The operation of applying ink to the printer is the same as printing using ordinary inks. The difference is that the offset roller does not work when full width is applied. In addition, screen printing machines, flexographic printing presses, gravure printing presses, and resin printing presses can all be used for polishing, and these types of machines are commonly used for partial coating. In addition, for those parts that require less detail, it is also possible to use a lithographic offset press to directly engrave the blanket. In particular, sheet-fed printing presses (whether flat, concave, convex, or stencil) are often used for off-line glazing of various products, and are very practical and practical for small-scale printing plants that cannot do great work. of.
There are several kinds of online coating? What are the characteristics of the organization? What are the advantages?
The more common online coating, roller glazing and squeegee coating two. The following is a brief introduction to the two forms of online glazing:
Roll coating
Heidelberg Speedmaster102-4CD machine, ROLAND700, Mitsubishi DIAMOND3000, Komori Lithrone 140 are all roller glazing units.
Roller glazing device 1. Liquid hopper roller plate; 2. Liquid hopper plate; 3. Liquid immersion roller; 4. Coating coating roller; 5. Stamping roller; 6. Metering roller
The principle of roller glazing mechanisms of these types of machines is basically the same. As shown in the above figure, the amount of glazing and the pressure of the on-line glazing unit are controlled by the printing press control center, such as the glazing unit of Heidelberg presses. The coating liquid supply mechanism can control the entire process of coating. The glazing liquid is pumped from the liquid storage tank through the hose through the electronic double diaphragm to the glazing tank. The height of the liquid level and the circulation of the glazing fluid are monitored by the potentiometer cycle to ensure that the glazing liquid is evenly supplied. Ultrasonic monitoring can be performed at any time. Monitor the gloss of the coating solution.
KBA Rapida 105 roller coating machine
The KBARapida 105 machine coating machine can be used as a two-roller system that runs in a forward direction, and can also be used as a three-roller system that operates in reverse. As shown in (b) and (c) above, the metering roller 6 is disengaged when the two-roller forward operation is performed, and the gloss liquid is adjusted by the pressure between the glossing liquid roller 2 and the liquid charging roller 3 Light quantity, simple structure. When the three-roller reverse running is operated, the coating roller and the liquid-foil roller run in the reverse direction, and a good gloss can be obtained. At the same time, when the high-viscosity coating liquid is used, it is not necessary to increase the pressure between the rollers to achieve a thin and uniform coating. purpose.
The advantages of this type of roller coating are many: The transfer path of the coating liquid from the liquid tray to the coating drum is very short, and the contact point is relatively small. It is directly transferred from the liquid fountain roller to the coating coating drum, so that the coating liquid It is not easy to dry inside the coating unit, and quick-drying coating can be used.
Even if there are few contact points,