UV Partial Silk Screen Coating Process (I)

In the printing industry, the integration of several printing methods seems to have become a trend. The comprehensive application of UV screen printing and offset printing is a good example. The author writes this article, is to introduce the reader to this industry and introduce the reader to the technical details of the UV partial silk screen coating process.

UV glazing is divided into overall glazing and local glazing. It should be said whether the overall UV glazing or the local glazing of printed materials is rapidly growing. The overall application of glazing roller coating process, speed, high efficiency, as an alternative to the film has a very good environmental protection effect, but its disadvantage is the high-speed operation of the machine, the coating is thin, the brightness is not very satisfactory.

Compared with the UV local silk screen coating process, the process freedom is much greater. At present, it is mainly used in the publishing industry and packaging industry. Its process features are: the use of silk on the surface of ordinary offset paper products, or BOPP matte film The web printing process coats the paper product pattern to form a strong contrast between the coated area and the matte surface, and achieves the finishing touch to the graphics and text that need to be emphasized.

Silk screen printing process freedom is large, because the thickness of the screen can be adjusted by forming a variety of effects, you can choose ordinary coating, you can also perform thick film coating, replace the crystal ink, you can also make a local crystal embossed. By adjusting the film ~ texture, you can make a variety of effects on the paper, to beautify the product has become a finishing touch. At present, the silk screen local glazing industry is mainly concentrated in Beijing and several cities in the south. It is expected that the industry will be further developed within a few years and it will achieve the same status as embossing, drumming, laminating, and bronzing. Less post-processing processes have a place in the industry.

As early as in the early 1990s, this process became popular in Taiwan, Hong Kong, and Southeast Asia, and the real-scale industrial application in China was in the late 1990s. Represented by Beijing Michelangelo and Weicai, these companies seized the opportunity to develop a silkscreen business with a certain scale.

Compared with other screen printing processes, UV partial silk coating coating process should be said to be less difficult, but there are still many technical details for simple technical processes. This is an industry that is interested in UV technology and should pay attention. First of all, talk about printing materials, UV part of the silk screen coating generally use coated paper, offset paper and BOPP film coating.

Practice has shown that direct glazing on paper: the use of paper varnish, adhesion is good or bad, the reason for this, different offset printing inks used by manufacturers are not the same, some brands of ink contains UV varnish oil is not easy to adhere to Additives, sometimes you will find that even if the corona treatment, some paper ink surface adhesion is still not ideal. Therefore, the author suggests that before UV glazing, we must do a good adhesion test to prevent loss to the company. Suppliers of general UV varnish products offer a range of products to meet their production needs, including paper varnish, BOPP matte film polish, and some other specialty varnish. When selecting varnish, it should be noted that the photocuring energy of different manufacturers is not the same. Saving energy and realizing low energy curing should be an important standard. Brightness, photocuring energy and the product must be applied to varnish before use. Adaptability makes a comprehensive assessment.

In the BOPP matt film coating process, the film surface must be corona-treated. In order to save this process, some polishing manufacturers simply cover the surface of the offset printing product directly with double-sided corona film (commonly known as electrostatic film). Light manufacturers have purchased corona treatment equipment. The corona discharge treatment method is a hybrid plasma method under atmospheric pressure. The principle is to generate high-frequency high-voltage current and produce a uniform and fine EDM under certain conditions, on the surface of BOPP film. For processing, the electrons, protons, excited atoms, and ions in the plasma region break the carbon-carbon bonds on the plastic surface, and the carbon-hydrogen bonds generate a large amount of free radicals. The generated radicals can exist in the air for a long time, in the air, with oxygen and nitrogen. As a result of the reaction, the polar groups are introduced onto the plastic surface, so that the plastic surface is easily wetted, which is advantageous for the ink adhesion. The depth of the corona discharge treatment is 5 to 50 μm, so that it is not easily perceived by human eyes and does not have a destructive effect on the surface of the BOPP film.

There are several points to pay attention to, the treated film surface is best not to contact with the metal surface, such as temporary printing oil after treatment, should be stacked in order to maintain the treatment effect. The treated film still needs to be tested for adhesion to verify the effectiveness of the corona treatment. Prints containing gold and silver ink cannot be corona treated.

UV screen printing generally use 150-34 and 165-34 type screens, the final tension is recommended to be above 18N/cm, this can guarantee the instant off-grid and precise registration in the printing process, using the 150-34 type screen The amount of ink is relatively large, and the brightness is also relatively good. If there is a part of the convex process after polishing, then the use of a 165-34 screen will be better, such a small amount of ink under the net, the ink layer is also thinner, No cracking of the ink layer occurs when it is convex.

The weakness of the UV ink layer is that once the ink layer is thick, it is easily broken. However, thick film can also achieve a very high brightness. Understanding these advantages and disadvantages requires that the company's customer service staff have a good communication with the customer.

UV screen printing process equipment generally use semi-automatic screen printing machine. Can also use automatic roller printing machine, or even hand-glazed, semi-automatic machine is generally about 800 India / hour, fully automatic machine is generally about 3000 India / hour, which according to the needs of enterprises, generally speaking, fully automatic machine positioning There is no semi-automatic manual reloading to get accurate, and the time for the version is relatively long, generally it may reach more than one hour. Therefore, semi-automatic can be said to be the first choice of UV partial glazing technology. Of course, this depends on the amount of business and order nature to make decisions. The light-curing equipment is very similar, and it is recommended that the width should be set at 70cm or more to ensure that the paper can be over 60cm×90cm. Many manufacturers put a conveyor belt of about 5m long before the light curing machine to make the UV printable. Varnish has a dry process to ensure the UV surface finish.

The technical details of UV coating on the local glazing technology are far more than these. The printing alignment and film processing will involve some details. The entire process is a complete process. Only by controlling every link in the process can a qualified product be produced. On this basis, efforts to open up the market will certainly lead to a big development in business management. Print glazing technology and other glazing methods have been favored by printing users in recent years as a method of finishing the surface of printed products. The reason is that a thin and uniform transparent and bright layer formed on the surface of printed matter after being coated with a colorless and transparent coating on the surface of the printed matter can effectively improve the surface properties of the printed matter, and can not only enhance the printability. The glossiness of the surface makes the printed matter or packaged product more visible on the shelf, and adds value to the product, which can protect the printed material from moisture and corrosion. The special gloss effect caused by the gold, silver and pearlescent glazing process, the surface three-dimensional effect brought by the foam coating, and the olfactory feeling brought by the scent coating to match the visual impact make the glazing process more extensive .

One kind of polishing process

The glazing process can be divided into off-line glazing and on-line glazing according to its processing method. Off-line glazing, namely printing and glazing, are carried out on special machines, and special glazing machines or calenders are required for glazing. For some folding carton manufacturers, off-line glazing is a very good choice not only because it can obtain higher gloss than on-line glazing, but also because of its high flexibility and equipment. Small investment. However, off-line glazing systems have increased transport efficiency between printing and glazing operations, so most off-line glazing has lower production efficiency than on-line light.

After the glazing unit is connected to the printing unit, the printing and coating are completed once. Current offset presses, gravure presses, and some screen printers can all accomplish this. No additional special glazing equipment is required, which not only improves work efficiency, but also overcomes various types of quality failures caused by offset printing and dusting. Therefore, on-line coating has become an attractive glazing solution. However, on-line coating has high requirements for coating technology, coating oil, drying equipment and coating equipment.
And the glazing part of the printing press is several times more expensive than the stand-alone glazing unit.