Application of post-press finishing process in label printing
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Application of some special finishing processes in the field of label printing
Label "light" finishing
In order to improve the surface gloss of the label print, we need to carry out "light" finishing, such as laminating, glazing and so on. From the perspective of reducing production costs and improving production efficiency, label printing companies use UV varnish to polish the label products.
According to the viscosity of UV varnish, the UV varnish can be divided into two categories: UV ink varnish and UV coating varnish. If the printing method is different, UV varnish can be divided into several types.
Because the UV ink fountain type varnish has large viscosity, poor leveling property, and the coating is extremely thin, the thickness is often only 1 to 5 μm, so the overall brightness is far less than the effect of the UV coating type varnish. Generally, when UV ink fountain type varnish is used for offset printing, we recommend that the front ink can be cured without UV lamp, and the "wet + wet" printing method can be used directly to improve the gloss of the label surface.
Labeled "matt (matte)" finishing
The commonly used "extinction (matte)" finishing process for labels can replace the previous matt film composite to a certain extent. At present, the best-effect "matt (matte)" finishing process is a screen printing matting oil, which has the advantages of thick ink layer and controllable hiding power, and the particles of the matting powder are coarse and have good refraction effect on light; The efficiency is low, it is not suitable for high-speed printing of labels, and it is used for the production of some high-end product labels.
Since the UV glazing process is closely related to the equipment used by the label printing company, we need to fully consider these constraints when selecting varnish, such as satellite or intermittent letterpress printing presses, which must be equipped with UV curing devices after each color group. In this way, the "wet + wet" printing method cannot be used, and the use of the UV ink fountain type varnish is inevitably ineffective. In view of such conditions, we usually choose to use UV matt oil, that is, to carry out the "dry + wet" printing method, and the front end color ink is cured and then printed with matt oil to achieve a better matt.
Labeled "snowflake and matte" finishing
In order to pursue the special effects of labels, some label printing companies choose UV snowflake oil for finishing. This finishing process can form very fine and even, smooth small wrinkles and flower patterns on the surface of label prints, accompanied by bright and matt two. Classes have different effects. The process generally uses a polyester screen of 200-350 mesh, and uses more than 3 UV curing lamps with a power of 5 kW, one of which is used for the formation of snowflakes and the other two tubes are used for complete curing. It is also conceivable to use an infrared lamp for pre-drying at the front end and then use multiple UV curing online operation modes.
Summarizing the past practical experience, the hue and tinting strength of the label background color will affect the size and uniformity of the "snowflake", especially the "snowflake" effect formed after printing is greatly affected by the transmission speed. Therefore, in the case of fixing other modes of operation, we should pay attention to adjusting the transmission speed to adjust the "snow" effect appropriately.
Label "wrinkle" finishing
“Wrinkle” finishing refers to the wrinkling caused by the different shrinkage of the surface layer and the bottom layer when the coating is dried at high temperature. This phenomenon is regarded as a unique decorative effect.
In the field of label printing, we often use UV curing to achieve "wrinkle" finishing, in order to solve the problem of deformation damage caused by high temperature. Usually we use the screen printing process to print UV crepe varnish on the surface of the substrate, through low-pressure UV lamps (low-power germicidal lamps with dominant wavelengths of 185 nm and 250 nm) and high-pressure mercury lamps (high-power mercury with dominant wavelengths of 360 and 385 nm) A combined illumination method produces a wrinkle visual effect on the surface of the label print.
It should be noted here that this type of process uses 100~250 mesh screens, the production speed is controlled at 20m/min, the overall production efficiency is not high, and the wrinkle effect is subject to various production conditions, which is difficult for ordinary people to operate. .
Label's "scented" finishing
Careful attention to the high-end label products on the market, we can find traces of the fragrance ink, can emit fragrance after wiping. The UV fragrance ink combines the microcapsule technology with the UV ink rapid curing process. When the UV ink is cured by irradiation, the fragrance wrapped in the sustained release capsule is solidified together with other components in the ink (see Figure 1). In this way, the printed matter is not volatile during storage and processing, and has a strong durability (more than one year). Only when the ink surface of the label print is touched, the pressure destroys the microcapsules and the fragrance is released.
For example, Hanghua's UV-SD scented varnish is a UV-curable varnish suitable for embossing and offset printing of resin plates. It uses microcapsule spice technology to keep the fragrance for a long time, suitable for all kinds of high-end gift boxes, greeting cards, books and metal signs. The UV scented inks currently on the market are available in the form of strawberries, roses, grapes, peaches, lemons, vanilla, apples, oranges, sandalwood, camphor, eucalyptus, jasmine, lavender, and mint.
Label "special UV suspected bump" process
The UV glazing process is not limited to a single device or a specific varnish product, but is often a combination of multiple types. The "UV suspected bump process" that is popular on the market today is a case where a typical varnish and matt oil are coated on the same label at a time.
The working principle of UV suspected concave and convex process: using the principle of "mutual exclusion" of UV varnish and UV underprint varnish (ink bucket type product), the printing effect of concave and convex is realized at one time, and it can be realized by controlling the coating amount of UV primer. The effect of light and dark after UV varnish coating.
It should be noted that under different printing conditions, the mutual repellency of varnish is different. For example, when UV underprint varnish is too dry, UV coated varnish may be easily peeled off when scratched. Therefore, in order to ensure the printing effect of the product, we need to strictly control the printing conditions.