UV Varnish on the Finished Surface of Paper Products II

  IV. Selection of UV Varnish for Paper Products

There are many types of UV varnish, which are classified into UV varnish for UV inks, UV varnish for oily varnish, and UV varnish for both, depending on the type of base color ink. It can also be divided into off-line UV varnish, on-line UV varnish, or both UV varnish in accordance with the method of processing.

Coating on UV inks, because the compositional structure of UV ink and UV light oil is basically the same, so overprinting, dryness, gloss, adhesion, odor, post processing suitability, rub resistance, finger resistance, Yellowing in local production can get better results.

Applying UV Varnish to the oil ink has the advantages of reducing the dusting process and improving the rubbing resistance. However, it is necessary to select the type of UV Varnish that is suitable for the base oily ink, otherwise it will affect overprinting, gloss, and dryness. Enthusiasm and so on.

When UV Varnish is used, the final processing of the Varnish should be based on the production conditions. For example, in the post-processing process, there are sizing, hot galvanized aluminum and other requirements, when selecting the UV oil, you should choose a varnishes adaptability, hot-aluminum adaptability of UV Varnish. It is best to select glue and aluminum foil in advance and carry out appropriate tests. In general, the printed matter is conveyed at high speed on the box making machine or on the packaging line in the box making process, and it needs to slide without stopping. In order to impart good slidability to the printed matter, polyolefin waxes, petroleum liquid waxes, and silicon UV varnish can be added to improve the slipperiness of the print surface.

Here are some of the UV Varnish used for surface treatment of paper products produced by Japan TK TOKA, which is a world-renowned manufacturer of UV technology, as well as its uses, characteristics, and applicable coating machines.

Among them, VECTA YM-GA is an on-line, off-line type varnish used on UV inks, and UV PC-3, UV PC-O, and UV PC-K1 are UV varnish oils that can be used on oily inks on UV inks. It can also be used. UV matte Varnish differs depending on the model, both for types that can be used on oily inks, and types that can only be used on UV inks.

V. Use of UV Varnish

Viscosity: generally controlled in about 20 seconds or less (4 Zahn Cup), printing effect is better. However, UV Varnish does not have a diluent with a low viscosity such as solvent or water, and it is difficult to adjust the viscosity during the operation. Generally, the UV Varnish viscosity is adjusted by controlling the temperature of the Varnish container.

Edition: When printing on the spot, you can use PS and water printing. The resin plate can be directly used for partial printing.

Blanket: It is more suitable to use UV. Because UV varnish makes it easier for the rubber to expand than UV inks, it is recommended to use UV-specific ones.

Cleaning fluid: Oily cleaning fluid cannot be used. After the cleaning operation, it should be cleaned by cleaning. If it is directly coated with cleaning fluid, it will greatly affect the drying time of the varnish. Therefore, it is better to use a more volatile cleaning fluid.

UV curing device: According to the drying mechanism of UV varnish and other various conditions required to select the appropriate UV lamp. It should be noted that UV varnish uses a homogenous initiator with little yellowing. The initiator absorbs ultraviolet rays at a wavelength of 365 nm and must use ultraviolet rays at a wavelength of 253 nm. From the viewpoint of curing efficiency, high-pressure mercury lamps are generally better than metal halide lamps, and metal halide lamps are better than no-ozone lamps (there is no use of ozone-free lamps in the absence of the ozone lamps, and the efficiency of the use of these lamps is greatly affected, so do not use them as much as possible).

Storage: Use UV light to avoid direct sunlight and store in a cool place below 30 degrees Celsius. When adjusting the viscosity by heating, avoid high temperatures or prolonged heating so as not to cause gelation or deterioration of the varnish.

Labor protection: UV varnish is irritating to the skin, and is non-volatile. When it is attached to the skin or clothes, it may enter the skin and cause inflammation with sweat if it is in the hot summer weather. Therefore, if the skin is stained with UV Varnish, it should be washed with soapy water as soon as possible, and change the clothes.

VI. Problems to be solved and future development directions

UV coating materials have the advantages of high processing speed, high gloss, abrasion resistance, and blocking resistance. In the box making process or circulation process is not easy to damage, product appearance, rapid development in recent years. Initially subject to price constraints, but as the amount increases, prices gradually decline. If all aspects of processing speed and quality are taken into consideration, the overall cost will not be much worse than that of general varnish coating or calendering, and thus it will be accepted by customers. Currently, the proportion of UV varnish in the paper printing industry is increasing. Gradually increase. However, the following problems still need to be solved in UV varnish.

1) Odor

At present, although it is gradually developing toward low odor, odor problems still exist. In the future, it is necessary to increase the molecular weight and reactivity of prepolymerization, monomers, etc., and develop odorless materials including photoinitiators.

2) Security

The currently used sharp diluents have a skin irritation (pH) of 3 or less, but further development of a reactive diluent with a PH value of 1 or less is required to improve product safety.

If we can produce more environmentally friendly Varnish in the future, I believe that the demand will increase.

In addition, UV varnish is inferior to water varnish in terms of odor and food hygiene. UV coatings have not been approved by the FDA (US Food and Drug Administration) and cannot be in direct contact with food.

3) Adhesion to Oxidation Polymeric Inks

Printing trays and publications generally use an oxidized polymeric offset ink. Some printers also use relatively high-priced UV inks to reduce dusting processes and improve station attachment.

Applying UV varnish to an oxidative polymerization type ink may cause odor, low gloss, and the like, and the adhesion to an oxidative polymerization type ink is not ideal. Although off-line processing can be applied in the middle of the coating, and then coated with UV light oil, but the two-layer coating to increase the cost, so need to improve the compatibility of UV Varnish and oily ink.

4) Recycling of UV-coated paper

Although UV processing paper has good film performance, there are still some problems in the paper regeneration. In particular, the solvent-free UV varnish coating is required to be improved in the future due to the high cross-linking density and difficulty in recycling the paper.

5) Reduce costs

In recent years, although it has dropped a lot, it is still too high compared with the general ink, and it is necessary to further reduce the operating costs of varnish, coating cost, and irradiation equipment.

On the whole, UV light oil has the above problems. However, UV varnish has great advantages in protecting the environment, saving energy, simplifying operations, and increasing the added value of products. With the advent of UV technology, there will be greater development in the future.

Source: Printing Technology