(This article is an original article from Bisheng. It is forbidden to reprint, and reprinting must be corrected)
In modern packaging and printing, the surface finishing of printed products is becoming more and more important. The most widely used is film coating and glazing, and glazing is due to its unique advantages (environmental protection, short production cycle, production cost) Low), and gradually showing a stronger and stronger momentum, playing an irreplaceable role in the field of post-press processing.Why polish on the surface of the printed matter?
First of all, the glazing on the surface of the printed matter can greatly increase the surface gloss of the printed matter, and at the same time the surface smoothness of the printed matter has also been improved, which has also improved the design grade of the printed matter; Play a protective role in the graphic of printed matter. Therefore, the glazing process can be widely used in the fields of packaging and decoration, book covers, trademarks, advertisements, calendars and other fields.
What are the glazing processes?
The glazing process of printed matter is generally composed of two steps: coating and calendering of glazing paint. The classification of glazing coating methods can be divided into ordinary printing equipment glazing and special glazing machine glazing (online and offline); according to the type of glazing coating, it can be divided into oxidative polymer coating Varnishing, solvent volatile coating varnishing, photocuring coating varnishing, and thermal curing coating varnishing; according to the type of product coated, it can be divided into whole varnishing, partial varnishing, extinction, artistic varnishing .
Is glazing and calendering the same thing?
If it is not according to the more general term, we generally refer to the process of applying glazing paint in glazing. Calendering is the follow-up process of glazing coating, which is generally processed according to customer requirements. It is a special production process carried out on special glazing equipment after the glazing paint is dried. Calendering is mainly due to the high temperature and pressure provided by the calender to make the surface smoother and the visual experience brighter.
What are the most popular glazing paints in printing houses? Introduce the process characteristics.
Relatively popular glazing coatings now include UV glazing and water-based glazing, while solvent-based glazing coatings have gradually become obsolete because of their environmental and hazardous effects. The following describes the respective characteristics of UV and water-based varnish.
UV coating
UV varnishing is ultraviolet ray curing and glazing, which belongs to a kind of light curing glazing. The varnish is mainly composed of photosensitive resin prepolymer, reactive solvent, photoinitiator and other additives. Its reaction mechanism is that after the unsaturated double bond in the prepolymer absorbs the energy emitted by ultraviolet rays, the double bond is opened. Under the action of the initiator, it cross-links with the monomer and undergoes a polymerization reaction, thereby curing to form a film. Due to the instant curing, the UV varnish has a fast glazing speed and full gloss, and the surface resistance performance after film formation is considerably improved. In addition, UV varnish has good adsorption performance on different surfaces and has little impact on the environment, so it is generally favored.
Equipment conditions for UV coating
Rubber roller: must choose the ink roller that can resist the corrosion of UV varnish, such as EPDM, nitrile rubber, etc.
Light source: UV lamp with power of 80 ～ 120W / cm and wavelength spectrum of 200 ～ 450nm. If the glazing speed needs to be increased, the power of the UV lamp needs to be increased accordingly (or 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 glazing.
Use of UV varnish
①The UV varnish must be kept in a dark room at 15 ～ 20 ℃
â‘¡ Stir before use, and do the necessary tests (for different printed surfaces, different UV varnish adsorption capacity will be different)
â‘¢ During the glazing process, a reasonable thickness of the light film should be paid attention to. Although it is UV light curing, the problem of incomplete curing, residual odor, and deformation of the substrate may also occur for the thick film layer.
â‘£ For papers with different surface smoothness, pay attention to choosing varnishes with different viscosity and leveling. For papers with rough surface, choose varnishes with low viscosity and good leveling.
⑤ The UV varnish used for special products must consider the corresponding varnish performance. If it is used for the outer packaging of washing products, then the UV varnish must choose chemical resistance, especially alkali resistance.
â‘¥ In the printing production, attention should be paid to the change of the UV varnish on the color of the ink, and the sensitive ink pigments (light blue, gold red, etc.) should be applied with caution.
Water-based varnish
The water-based varnish is mainly composed of water-soluble polymer resin and a small amount of additives. Its main solvent is water, which has the characteristics of high solid content, colorless and odorless, good transparency, non-toxic and no organic volatiles.
Equipment condition of water-based varnish
Plate material: Water-based glazing usually adopts flexographic plate glazing, so various flexographic resin plates can be used, but washed resin plates cannot be used. Various glazing roll coatings can also be used.
Use of water-based varnish
①Store at 15 ～ 20 ℃, especially avoid storage or transportation below 0 ℃.
â‘¡ The use of water-based varnish is basically the same as water-based ink. The PH value of the glazing process should be steadily controlled between 8.5 and 9.5, otherwise it will affect the glazing intensity.
â‘¢ In the coating process, the viscosity must be in the range of 25 ~ 35S, otherwise there will be quality problems.
Which of water-based varnish and UV varnish is more advantageous?
From the perspective of quality and production efficiency, UV varnish has obvious advantages, mainly reflected in the high gloss of the product surface, good surface resistance, and short production cycle.
In consideration of cost and environmental protection, water-based varnish has great advantages. The application of water-based varnish does not require special equipment (special ink roller, special drying system, etc.) like UV varnish coating, and it is optional to use Larger, water-based varnish itself is cheaper than UV varnish, without any environmental pollution.
From the above, it can not be concluded arbitrarily whether UV or water-based varnish is more advantageous, but we also find that with the continuous improvement of water-based varnish itself, the development of water-based varnish has been a good trend. The UV varnish will also firmly occupy the market due to its unique and irreplaceable characteristics.
What are the more common polishing equipment?
We mentioned above that there are several types of glazing coating equipment, including glazing by glazing machine, glazing by printing unit, and online glazing.
How to use unit glazing?
There are generally two ways to use the unit for glazing, one is to use the wetting device to glaze, and the other is to use the inking part of the printing machine to glaze through the printing plate or blanket. Below we introduce separately:
Varnishing with wetting device
This kind of glazing method is more typical of KBA RAPIDA sheet-fed lithographic multi-color printing machine. It can be equipped with a wetting and glazing conversion device. The operator only needs a very simple manual operation to quickly perform the wetting operation. The state transitions to glazing operation. When the wetting and glazing functions are converted, the wetting fluid is changed to glazing liquid, and the wetting and glazing device can be set to a forward running glazing mode at this time.
You can select the state of Figure a or the state of Figure b during the transition. As shown in Figure a above, the rotation speed of the water bucket roller runs at a speed of 1/3 to 2/3 of the rotation speed of the water transfer roller, so that the pre-glazing is formed by this speed difference, and the real coating is still through the water bucket roller Speed ​​to adjust.
If it is adjusted as shown in Figure b, it can achieve better glazing effect and better eliminate ghost phenomenon.
Use the inking device to polish
The operation of using the printing machine to transfer ink to glaze is the same as printing with ordinary ink, the difference is that the water roller of the offset press does not work when glazing at full width. In addition, screen printing machine, flexographic printing machine, gravure printing machine, resin printing machine can be used for glazing, and these models are very commonly used for local glazing. In addition, for local polishing products that require less precision, a lithographic offset press can also be used to directly engrave the blanket. In particular, sheet-fed printing presses (whether flat, concave, convex, or perforated) are often used for offline polishing of various products. It is very practical and practical for small printing plants that cannot make large and complete products. of.
How many kinds of online polishing? What are the characteristics of the organization? What are the advantages of each?
There are two common types of online glazing, roller glazing and blade glazing. The following is a separate introduction to the two forms of online coating:
Roller coating
Heidelberg Speedmaster102-4 CD type machine, ROLAND700, Mitsubishi DIAMOND3000, Komori LITHRONE40 type machine are all roller glazing device.
Roller glazing device 1. Liquid bucket roller; 2. Liquid bucket disk; 3. Liquid loading roller; 4. Polishing coating roller; 5. Impression roller; 6. Metering roller
The roller glazing mechanism of these models is basically the same. As shown in the above figure, the glazing amount and pressure of the on-line glazing unit of this type of printing press are controlled by the printing press control center, like the Heidelberg glazing device for printing presses. The glazing liquid supply mechanism can control the whole process of glazing. The polishing liquid is pumped from the storage tank through the hose to the polishing liquid hopper tray by the electronic double diaphragm. The liquid level and the circulation of the polishing liquid are monitored by the potentiometer to ensure the uniform supply of the polishing liquid. Ultrasonic monitoring can be carried out at any time Monitor the amount of coating liquid.
KBA Rapida 105 machine roller glazing device
The KBA Rapida 105 glazing unit can be used as a two-roller system in forward operation or as a three-roller system in reverse operation. As shown in (b) and (c) above, when the two-roller forward operation works, the metering roller 6 is disengaged. At this time, the coating liquid is adjusted by the pressure between the coating liquid bucket roller 2 and the application roller 3 Light quantity, simple structure. When the three-roller reverse operation works, the glazing roller and the hopper roller operate in reverse to obtain good gloss. At the same time, when using a high-viscosity glazing liquid, it is not necessary to increase the pressure between the rollers to achieve a thin and uniform coating. purpose.
The benefits of this roller glazing are many:
The transmission path of the glazing liquid from the hopper tray to the glazing roller is very short, and there are few contact points. It is directly transmitted from the hopper roller to the glazing coating roller, so that the glazing liquid is not easy to dry inside the glazing unit. Use quick-drying varnish.
Even if there are few transfer contact points, it can make the very thick coating liquid evenly transmitted. The maximum thickness of the coating liquid wet film can reach 8g / ?, and the thickness of the coating liquid can reach 3 ~ 4g /? After drying;
The replacement operation or the operation of replacing the varnish are simple and convenient.
Scraper glazing
Squeegee-type glazing devices are more and more widely used in modern printing equipment. It is usually made up of two polishing blades
It consists of a closed blade box and a ceramic anilox roller that functions as a metering roller. The upper and lower scrapers and the anilox roller form a closed "glazing box". The polishing liquid is input through the pipeline. Heidelberg SM102-4CD, ROLAND700, KBA RAPIDA105, Mitsubishi DIAMOND 3000, Komori LITHRONE 40, etc. all have scraper-type polishing devices , Their mechanism is basically the same, as shown in the figure below for Heidelberg SM102-4 machine blade glazing device.
This type of glazing device has many irreplaceable advantages:
â‘ Stable and excellent coating quality. The upper and lower scrapers in the scraper-type polishing structure are pneumatically coupled to the anilox roller. Due to the effect of the upper blade, the coating amount of the polishing liquid can be uniform and unaffected by the change of printing speed. Even if it is a continuous printing operation for many days, the polishing effect can be kept constant and consistent. In the traditional glazed structure, the change in color tone due to the change in coating thickness no longer exists in this mechanism.
â‘¡ Conducive to environmental protection. The squeegee-type glazing structure is a closed structure, requiring only a small amount of glazing liquid to circulate, and there is no problem of odor emission. The waste to be cleaned is also reduced to a minimum.
â‘¢ Glazing is more economical. Generally, during the plate-changing operation, the glazing liquid can be directly cleaned with a cleaning agent. Only when the ordinary glazing is converted into gold or silver glazing, the squeegee system needs to be cleaned manually. If multiple such scraper-type glazing devices are used instead, the time for plate change and cleaning operations can be further shortened. Selection of qualified automatic cleaning device can also greatly improve work efficiency.
â‘£ This structure is a closed system, even if using extremely low viscosity glazing liquid, it can be glazed at the same time as high speed printing.
⑤ Because of the use of anilox rollers, the thickness of the glazing liquid layer can be accurately set over the entire width of the paper to ensure glazing of the printed matter, especially when the thin paper is glazed. The coating amount is the lowest range, and the coating is uniform at the same time. Changing the thickness of the coating is determined by the density of the anilox roller.
Varnishing gold. This glazing device can adapt to the gold and silver glazing printing gold containing different elements, and achieves a very high wear resistance.
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