Introduction: The glazing process has a long history and is an important method of post-press processing. With the continuous maturity of glazing technology and the directional pollution-free glazing process, the diversified development direction of glazing finished products is becoming more and more clear. Today, I will share about the glazing process Knowledge points, content for the reference of friends:
Coating is to apply (or spray or print) a layer of colorless transparent paint on the surface of the printed matter, which will protect and increase the gloss of the printed matter after drying. Coat (or spray or print) a layer of colorless and transparent paint on the surface of the printed matter. After leveling, drying, calendering and curing, a thin and uniform transparent bright layer is formed on the surface of the printed matter to enhance the smoothness of the carrier surface. The process of protecting the finishing function of printed graphics is called glazing process. The glazing process of printed matter can be divided into paint glazing, paint pressure glazing, UV glazing, pearlescent pigment glazing, etc.
Printing glazing and traditional laminating
The traditional laminating process has gone through many years, and we are no longer unfamiliar with its process. Compared with the glazing process, there are similarities and differences between them. The so-called printing and glazing is to use a solid printing plate or a graphic printing plate to print one or two glazing oils on the surface of the finished copy to make the surface of the printed matter obtain a bright and transparent film. Commonly used glazing methods include oily glazing, water-based glazing and UV glazing.
Printing and glazing can enhance the light resistance of the ink, increase the heat and moisture resistance of the ink layer, and play the role of protecting imprints, beautifying products, and replacing film. Compared with laminating film, printing glazing is low in price and simple in process. It can be used for full-page glazing or partial glazing.
First of all, from a purely environmental perspective, water-based and UV are in line with the trend. Because the film has two layers of pollution, white pollution and film glue pollution. The cover after water-based glazing and UV glazing can be recycled directly without any further treatment.
In addition, from the perspective of the market application environment, foreign jobs, except for food, medicine and cosmetics packaging, even those electronic products that do not directly contact the human body, because the corporate culture advocates environmental protection and is proud of it, it gradually requires Adopt the non-polluting printing method of varnish.
With the economic exchanges and cooperation of various countries, a considerable number of printing and packaging companies in the coastal and inland areas have foreign order business. Western countries have high requirements for environmental protection, and pollution-free water-based coating and UV coating have been developed quite mature. Especially in the fields of food packaging and pharmaceutical packaging, Europe has established strict standards, and the survival space for non-compliant film and oily glazing is very small.
The traditional laminating process will not completely fade out of the market because it can increase the thickness and toughness of the paper combined with its good water resistance. However, in the face of increasing global environmental awareness, products require recycling or biodegradation. The coating process must strive to improve the pollution of products, operating environment and external environment in order to have more room for survival.
Cost and efficiency
According to the actual application, the cost of coating is higher than the cost of glazing. In the industry, the quotation of glazing generally does not exceed half of that of laminating, so traditional laminating has no advantage in cost.
The laminating speed of the traditional laminating machine is 30m/min~75m/min, while the current online coating equipment can fully match the speed of the printing machine, and the stability of the coating quality has been greatly improved. Without considering the specific requirements of customers, the glazing process is more economical in terms of efficiency.
Characteristics of varnish
There are many types of varnishes, but the commonly used varnishes can be roughly divided into three categories: oily varnishes, water-based varnishes and UV varnishes. According to the actual application trend of glazing oil and the improvement of environmental protection requirements, the use of oily glazing will decrease day by day, and the application space of water-based glazing oil and UV glazing oil is very broad.
Water-based glazing oil is mainly composed of water-soluble resin and water-dispersible resin. Water-based glazing oil is non-toxic and tasteless, eliminating the harm to human body and pollution to the environment. It has fast drying speed, good film transparency, stable performance, and equipment. Wide adaptability, good abrasion resistance and flatness of the glazing surface, wide post-press processing adaptability, good heat sealing performance, safe and reliable use, convenient storage and transportation, etc., are more and more popular for food, medicine, tobacco carton packaging and printing The attention of the enterprise.
The following typical problems should be paid attention to when using UV water-based varnish:
① The question of how to ensure that the underlying ink can be fully dried after applying water-based glazing oil. First of all, to ensure the air permeability of the water-based glazing oil, so that the wet ink layer can be exposed to air to dry the oxidized conjunctiva; in addition, it can also be improved The hot air temperature solves this problem.
② The gloss of water-based varnish coating is lower than that of UV varnish. In practice, a small amount of high-boiling solvent can be added to the water-based varnish to moisten and swell the emulsion particles and promote the formation of a smooth coating film. Improve the surface flatness of the coating film, and finally achieve the purpose of improving the gloss of the water-based varnish coating.
UV glazing is a method of curing glazing paint by UV irradiation. It has the characteristics of rapid curing of coatings and low-temperature curing inks that are not easy to fade, which helps to solve many problems in the gloss processing of paper printed products. Therefore, it has been widely used in the gloss processing of paper containers, trademarks, book covers, packaging boxes, etc. application.
UV glazing oil contains almost no solvents, and the emission of organic volatiles is very small, thus reducing air pollution; UV glazing oil does not contain solvents, does not require heat during curing, and requires relatively little energy consumption for curing. In addition, UV glazing oil has a strong affinity for inks and strong adhesion; UV glazing oil has high effective ingredients, less volatilization, and relatively low consumption; the surface of the printed product after UV glazing is more wear-resistant, chemical-resistant and resistant Chemical properties, good stability, can be scrubbed with water and ethanol; UV glazing products are not easy to stick, and can be stacked and stacked after curing, which is conducive to subsequent processing operations.
The following typical problems should be paid attention to when using UV varnish:
① UV varnish is not suitable for operation on permeable paper. Because the low-molecular materials in UV coatings easily penetrate into the paper, causing the paper to darken or even soak. At present, most UV varnishes are applied to printed paper with aluminized film.
② The main reason for the poor adhesion of UV varnish is: the crystallization of the ink layer of the printed matter or the improper use of ink additives and anti-slip agents. The printing process should be improved, and no or less ink additives should be used;
③ The main reasons for the poor brightness of UV varnish are: poor paper quality, different surface roughness, uneven coating, too thin varnish, and low viscosity.
Printing and glazing equipment is divided into glazing machines (including calenders) and printing and glazing linkages. The glazing machine is generally a stand-alone operation, the processing speed is slow, the quality stability is slightly worse, and the calendering treatment is often required. At present, large-scale offset printing manufacturers at home and abroad mostly use online printing to improve the speed and quality of the coating. It can be said that online printing is the development trend of coating machinery.
Printing and coating linkage
The printing and glazing linkage is used for glazing and coating by a printing unit, and its basic form is to glazing and coating by the last printing unit of a sheet-fed offset press. There are generally two forms of glazing and coating with printing units: one is glazing and coating with a dampening device, and the other is glazing and coating with an inking device.
It is the simplest and most economical option to use the existing printing unit on the sheet-fed lithographic printing machine for coating, which has a small production area and can save additional equipment investment. However, the glazing coating effect is not very good, and it is only suitable for coating simple, less demanding products.
Online glazing device for printing machine
The independent coating unit on the printing machine is used for online coating, which has high production efficiency and stable coating quality. It can use the resin plate or the traditional blanket for glazing. Like the printing device, it is all monitored and controlled by the printing press control center, such as the lateral and circumferential register adjustment and the diagonal line of the photosensitive resin plate. Register adjustment, etc.
The online glazing device can apply thick and uniform glazing to the entire surface or partial graphics of the substrate. The glazing can use either a blanket or a flexographic plate for fine local glazing; it can be used in water-based glazing , Can also be engaged in UV coating.
When choosing an online coating system, the advantages of anilox roller coating are obvious, but the investment is relatively large. Anilox roller glazing can accurately control the thickness of the glazing coating, does not depend on the printing speed, and is rarely affected by the fluctuation of the glazing oil viscosity. The most representative is the use of a closed ink knife system glazing device, which consists of a ceramic anilox roller, a closed doctor blade and a flexible resin coated plate roller. This kind of online coating has fast speed and high efficiency. The anilox rollers can be quickly replaced. Different anilox rollers can be selected to complete the coating accurately as required, which can not only obtain a full coating, but also perform precise partial coating.