Application and Development of Printing Coating Technology

The glazing process has a long history. With the development and progress of continuous application, the content of science and technology is also getting higher and higher, and the application range is becoming wider and wider, especially the rapid development of waterborne coatings and UV coatings that meet the requirements of safety and environmental protection. The extensive application of various online coating methods has greatly promoted the popularization and application of glazing technology and technological progress.

First, the printing coating vs traditional coating
The traditional laminating technology has come a long way, and we are no longer familiar with its technology. Compared with the glazing process, there are differences between them. The so-called printing glazing, is to complete the surface of the printed copy of the graphic, with a solid plate or graphic printing plate reprinted once or twice a varnish, so that the surface of the print to obtain a light and transparent film. The commonly used glazing methods are oily glazing, waterborne glazing and UV glazing.

Printing glazing can enhance the light resistance of the ink, increase the ink layer's ability to prevent heat and moisture, and protect the print, beautify the product, and replace the film. Compared with film lamination, printing glazing is cheap and easy to process. It can be full-coated or partially glazing.

(a) Environmental protection

First of all, from a purely environmental point of view, water and UV are in line with the trend. Because the film has two layers of pollution, white pollution and plastic film pollution. After the water-based coating and UV coating, the cover can be directly recycled without any further treatment.

In addition, from the perspective of the market environment, foreign jobs, in addition to food, medicine and cosmetics packaging, even those electronic products that are not in direct contact with the human body, because corporate culture advocates environmental protection and are proud of it, so it is gradually required Use this kind of pollution-free printing method.

With the economic exchanges and cooperation of various countries, a considerable number of printing and packaging companies in the coastal and inland areas have external single businesses, while Western countries have high requirements for environmental protection, and non-polluting water-based glazing and UV glazing have developed quite well. Especially in the fields of food packaging, pharmaceutical packaging, etc., Europe has established strict standards. The survival space for non-standard coatings and oily coatings is very small.

The traditional coating process will not completely fade out of the market because it can increase the thickness and toughness of the paper, as well as its good water resistance. However, in the face of global awareness of environmental protection, products are required to be recycled or biologically decomposed. The laminating process must strive to improve the product, operating environment and external environmental pollution in order to have a greater living space.

(B), cost and efficiency

According to the actual application, the cost of coating is higher than the cost of coating. In the industry, the quoting price of glazing is generally not more than half of the mulching, so the traditional lacquer coating has no advantage.

The laminating speed of the traditional laminating machine is in the range of 30m/min to 75m/min, and the current on-line coating equipment can completely match the speed of the printing press, and the stability of the coating quality has been greatly improved. Without considering the specific requirements of the customer, the glazing process is more economical in terms of efficiency.

It is worth noting that the repeated use of the transfer film process that has occurred in the past two years has broken through the boundaries of traditional film coating, and has already begun to show its advantages in the use of related color box and cigarette packs.

Second, the characteristics of polishing oil

There are many types of varnishes, but commonly used varnishes can be roughly classified into three categories: oily varnishes, waterborne varnishes, and UV varnishes. According to the actual application of Varnish and the improvement of environmental protection requirements, the use of oily glazing will be reduced. The application space of waterborne varnishes and UV varnishes is very broad. This section mainly introduces waterborne varnishes and UV varnish.

(A) Waterborne Varnish

Waterborne Varnish (English called WATERBASED VARNISH, also known as DISPEERSED VARNISH) consists mainly of water-soluble resin and water-dispersible resin.

Waterborne varnish is non-toxic and odorless, eliminating the harm to the human body and the pollution to the environment. It has the advantages of fast drying rate, good film transparency, stable performance, wide adaptability of equipment, good abrasion resistance and flatness on the surface, and printing. With the features of wide post processing flexibility, good heat sealing performance, safe and reliable use, convenient storage and transportation, etc., more and more attention has been paid to food, medicine, tobacco carton packaging and printing companies.

When UV waterborne varnish is used, the following typical problems should be noted:

1 How to ensure that the underlying ink can be sufficiently dried after coating with water-based varnishes, we must first ensure the air permeability of the water-based varnishes so that the wet ink layer can come into contact with the air and dry the oxidized conjunctiva; otherwise, it can also be improved The hot air temperature makes this problem solved.

2 The gloss of the waterborne varnish coating is lower than that of the UV varnish. In practice, a small amount of high boiling point solvent can be added to the aqueous varnish to moisturize the emulsion particles and promote the formation of a film with good flatness. Improve the surface smoothness of the coating, and ultimately achieve the purpose of improving the gloss of the waterborne coating.

(B), UV Varnish

UV glazing is a method of curing a glazing coating by irradiating with UV (abbreviation of Ultra viole, ie, ultraviolet ray). It has the characteristics of rapid solidification of coatings and low temperature curing inks that are not easily discolored, which helps to solve many problems in gloss processing of paper prints. Therefore, it has been widely used in the gloss processing of paper containers, trademarks, books, covers, and packaging boxes. application.

UV Varnish is almost solvent-free and emits very little organic volatiles, thus reducing air pollution. UV Varnish does not contain solvents and does not require heat for curing. The energy required for curing is relatively small. In addition, UV varnish has strong affinity for ink and strong adhesion; UV varnish has high active component, less volatilization, and relative saving in dosage; UV varnish has more abrasion resistance, chemical resistance, and resistance to the surface after printing. Chemical, good stability, able to scrub with water and ethanol; UV glazing products are not easy to adhere, can be stacked after curing, is conducive to post-processing operations.

When using UV varnish, pay attention to the following typical problems:

1 UV Varnish is not suitable for operation on osmotic paper. Because the low-molecular materials in the UV coating easily penetrate into the paper, causing the paper to become dark or even saturated. At present, most UV coatings are applied on printed paper with aluminum plating.

2 The main reason for the poor adhesion of UV varnish is: improper use of printing ink layer crystallization or ink additives and anti-slip agents, etc. The printing process should be improved, with or without ink additives;

3 UV Varnish gloss difference is mainly due to: poor paper quality, different surface roughness, uneven coating or coating oil is too thin, viscosity is too low and other reasons.

Third, polishing equipment

Printing glazing equipment is divided into glazing machines (including calenders) and printing glazing machines. The polishing machine is generally a stand-alone operation, the processing speed is slower, the quality stability is slightly worse, and the calendering process is often performed again. At present, large-scale offset printing companies at home and abroad mostly use on-line coating to improve the speed and quality of coating. It can be said that the on-line coating of coating is the development trend of coating machinery.

Print on-line coating can be roughly divided into two categories:

(A), printing glazing

The printing glazing unit is coated with a printing unit and its basic form is the coating of the last printing unit of a sheet-fed offset printing press. The use of printing units to coat the coating is generally of two forms: one is the use of a wetting device for coating, and the other is the use of an inking device for coating.

The use of existing printing units on a sheet-fed lithographic printing press for coating has the advantages of a small footprint and an additional investment in equipment. It is currently the simplest and most economical option. But its coating effect is not very good, only suitable for coating simple, less demanding products.

(B) Printing machine on-line glazing device

Online glazing with an independent glazing unit on the press, high production efficiency and stable coating quality. It can be coated with a resin plate or a conventional blanket. Like the printing device, it is monitored and controlled by the press control center, such as horizontal and circumferential register adjustment of the photosensitive resin plate, and diagonal lines. Register adjustment and so on.

The on-line coating device can apply thick and even coating on the entire surface or local image of the substrate. The coating can be applied on the blanket or on the flexible plate for fine partial coating. , can also be engaged in UV polishing.

When choosing the online coating system, the advantage of anilox roller coating is obvious, but the investment is relatively large. Anilox roller glazing can accurately control the thickness of the glazing coating, also does not depend on the printing speed, and is rarely affected by fluctuations in the viscosity of the glazing oil. More representative is the use of a closed ink knife system glazing device, the system consists of ceramic anilox roller, closed squeegee and flexible resin coated roller. This kind of on-line glazing has high speed and high efficiency. The anilox roller can be quickly replaced. Different anilox rollers can be used to accurately complete the coating according to requirements. It can not only obtain full glazing coating, but also can perform accurate partial glazing.

Glue has become an important means of post-press processing. With the constant maturation of glazing technology and the directional and non-polluting process of glazing, the consistency of operations, and the increasingly clear development of the diversified development direction of glazing products, it processes the packaging of foreign trade export products. China will also achieve great results. The glazing technology will be one of the most promising surface processing technologies for packaging and printing.

Source: Shaanxi Printing