Application and development of the most popular pr

2022-07-24
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Application and development of printing polishing technology

release date: Source: China paper industry

polishing process has a long history. With the development and progress of continuous application, the content of science and technology is becoming higher and higher, and the scope of application is becoming wider and wider, especially the rapid development of water-based coating and UV coating that meet the requirements of safety and environmental protection, as well as the wide application of various online polishing methods, Have greatly promoted the popularization, application and technological progress of glazing technology. Today, China paper industry takes you into the packaging, printing and polishing technology to introduce the relevant contents in detail

I. printing polishing vs. traditional film coating

the traditional film coating process has gone through many years, and we are no longer unfamiliar with its process. Compared with the polishing process, they have similarities and differences. The so-called printing polish is to use the field printing plate or the graphic printing plate to reprint one or two times of polish on the surface of the copy that has completed the graphic printing, so as to obtain a bright and transparent film on the surface of the print. Common glazing methods include oily glazing, aqueous glazing and UV glazing

printing glazing can enhance the light resistance of the ink, increase the heat and moisture resistance of the ink layer, protect the imprint, and replace the beautifying product every two years in the future. Compared with film coating, printing and glazing is cheap and simple. It can be either full plate glazing or local glazing

(I) environmental protection at this moment, the side wheel and side beam touch to produce a bias force to prevent the car from rotating

first of all, from the perspective of simple environmental protection, water and UV are in line with the trend. Because there are two layers of pollution, white pollution and plastic pollution. The cover after water-based glazing and UV glazing can be directly recycled without any further treatment

in addition, from the perspective of the general environment of market application, in addition to the packaging of food, drugs and cosmetics, even those electronic products that do not directly contact the human body are gradually required to adopt the pollution-free printing method of polishing because the corporate culture advocates environmental protection and is proud of it

with the economic exchanges and cooperation of various countries, a considerable number of printing and packaging enterprises in the coastal areas and the mainland have outsourcing businesses, while western countries have high requirements for environmental protection, and pollution-free water-based polishing and UV polishing have developed quite mature. In particular, in the fields of food packaging and drug packaging, Europe has set strict standards, and the living space for film covering and oily polishing that do not meet the standards has been very small

the traditional film covering process will not fade out completely because it can increase the thickness and toughness of the paper and its good water resistance, so the report can be printed. However, in the face of the improvement of global environmental protection awareness, products are required to be recycled or biodegraded. The film covering process must strive to improve the pollution of products, operating environment and external environment in order to have greater living space

(II). Cost and efficiency

according to the actual application, the cost of film coating is higher than that of glazing. In the industry, the quotation of glazing generally does not exceed half of the film covering, so the traditional film covering has no advantage in cost

the film covering speed of the traditional film covering machine ranges from 30m/min to 75m/min, while the current online polishing equipment can fully match the speed of the printing machine, and the stability of the polishing quality has been greatly improved. Without considering the specific requirements of customers, the glazing process is more economical in terms of efficiency

it is worth noting that the transfer film process that has been used for many times in the past two years has broken through the boundaries of traditional film covering, and has initially shown its advantages in the application of related color boxes and cigarette packs

II. Characteristics of glazing oils

there are many types of glazing oils, but commonly used glazing oils can be roughly divided into three categories: oily, water-based and UV glazing oils. According to the practical application trend of varnishes and the improvement of environmental protection requirements, the use of oil-based varnishes will be reduced day by day, while the application space of water-based varnishes and UV varnishes is very broad. This section mainly introduces water-based varnishes and UV varnishes

(I) water based varnish

water based varnish (also known as dispersed varnish in English) is mainly composed of water-soluble resin and water dispersive resin.

water based varnish is non-toxic and odorless, eliminates harm to human body and environmental pollution, and has the advantages of fast drying, good film transparency, stable performance, wide equipment adaptability, good abrasion resistance and flatness of polished surface With the characteristics of wide post press processing adaptability, good heat sealing performance, safe and reliable use, convenient storage and transportation, more and more attention has been paid by food, medicine and tobacco carton packaging and printing enterprises

uv water-based varnish should pay attention to the following typical problems when using:

① how to ensure that the underlying ink can be fully dried after coating the water-based varnish, first of all, ensure the air permeability of the water-based varnish, so that the wet ink layer can contact the air to dry the oxidized conjunctiva; In addition, this problem can also be solved by moderately increasing the hot air temperature

② the gloss of the water-based 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 water-based varnish to moisten the lotion particles and promote them to form a film with good flatness, so as to improve the surface smoothness of the film, and finally achieve the purpose of improving the gloss of the water-based varnish coating

(II). UV glazing oil

uv glazing is a method of curing glazing paint by UV (the abbreviation of ultra violet). It has the characteristics of fast curing of paint and low temperature curing of ink, which is not easy to fade, and is helpful to solve many problems in the gloss processing of paper printed matter. Therefore, it has been widely used in the gloss processing of paper containers, trademarks, book covers, packaging boxes and other printed matter

uv varnish contains almost no solvent, and the emission of organic volatile matter is very small, thus reducing air pollution; UV varnish does not contain solvent, so it does not need heat energy during curing, and its curing energy consumption is relatively small. In addition, UV varnish has strong affinity for ink and firm adhesion; UV glazing oil has high effective components, less volatilization and relatively low dosage; UV cured printing surface has more wear resistance, drug resistance and chemical resistance, good stability, and can be scrubbed with water and ethanol; UV glazing products are not easy to adhere. After curing, they can be stacked up, which is conducive to the post process processing

uv varnish should pay attention to the following typical problems when using:

① UV varnish is not suitable for operation on permeable paper. Because the low molecular materials in UV coating are easy to penetrate into the paper, causing the paper to darken or even soak. At present, most UV varnishes are used on printing paper with aluminum coating

② the main reasons for the poor adhesion of UV varnish are: the crystallization of printing ink layer or the improper use of ink additives and anti-skid agents. The printing process should be improved and ink additives should not be used or used less

③ the main reasons for the poor brightness of UV varnish are: poor paper quality, different surface roughness, uneven coating, too thin varnish, low viscosity, etc

III. polishing equipment

printing polishing equipment is divided into polishing machine (including calender) and printing polishing linkage machine. The polishing machine is generally operated by a single machine, with slow processing speed and slightly poor quality stability. It often needs to be calendered again. At present, large offset printing manufacturers at home and abroad mostly use printing online glazing to improve glazing speed and quality. It can be said that printing online glazing is the development trend of glazing machinery

printing online glazing can be roughly divided into two categories:

(I). Printing and glazing linkage machine

printing and glazing linkage machine is used for glazing and coating by printing unit. Its basic form is to use the last printing sheet of sheet fed offset press for glazing and coating. There are generally two forms of polishing and coating by using the printing unit: one is polishing and coating by using the wetting device, and the other is polishing and coating by using the inking device

it is the simplest and most economical option at present to use the existing printing unit on the sheet fed lithographic press for glazing and coating, which has a small production floor area and can save additional equipment investment. But its glazing coating effect is not very good. It is only suitable for products with simple coating and low requirements

(II). The printing machine online glazing device

uses an independent glazing unit on the printing machine for online glazing, which has high production efficiency and stable glazing quality. It can use resin plate or traditional rubber cloth for glazing. Like the printing device, it is all monitored and controlled by the printing machine control center, such as horizontal and circumferential registration adjustment, diagonal registration adjustment, etc. of the photosensitive resin plate

the on-line polishing device can perform thick and uniform polishing coating for the whole surface of the substrate or local graphics and text. The polishing can be done with blanket or flexo for fine local polishing; Can be engaged in both water-based glazing and UV glazing

when the online glazing system is selected, the advantages of roller glazing are obvious, but the investment is relatively low Thermotropic liquid crystalline polymer: intermediate polymer between solid crystal and liquid. Roller glazing can accurately control the thickness of the glazing coating, does not depend on the printing speed, and is rarely affected by the viscosity fluctuation of the glazing oil. The typical one is the polishing device with a closed doctor blade system, which is composed of a ceramic grain roller, a closed doctor blade and a flexible resin coated plate roller. The online polishing is fast and efficient, and the corrugated rollers can be quickly replaced. The coating can be completed accurately by selecting different corrugated rollers, which can not only obtain a full polishing coating, but also carry out accurate local polishing

glazing has become an important means of post press processing. With the continuous maturity of glazing technology and the increasingly clear direction of non pollution, consistent operation and diversified development of glazing products, it will also achieve great results in the processing of foreign trade export product packaging. Glazing technology will be the most promising packaging and printing surface processing technology

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