UV glazing is a new way of glazing that has emerged in recent years. It uses ultraviolet light to cure varnish. At present, our offset printing cigarette packs use UV varnish in addition to the low-grade cigarettes, and UV varnish is used because UV varnish products cure fast, cure instantly, and have high gloss and good mirror finish. As a result, the print has excellent rubbing resistance. At the same time, the merger and reorganization of cigarette factories will also make the design and printing of cigarette packs towards “luxury” development. It requires the majority of product designers and process designers to choose UV glazing when developing new products. These have greatly stimulated the popularity and development of UV coating.

However, with the increase in the variety and production of cigarette packs using UV varnish, problems in the printing process have followed. The author is in the company's development of new products, understand the UV Varnish brings many problems to the production.

Smoke film fog problem analysis

There is a new type of packaging using cylindrical laser holographic paper offset proofing, using UV inks and UV Varnish, printed ink full of ink, high gloss, soon was selected by the cigarette factory. When the first batch of samples was made, the staff at the workshop noticed a large amount of odor, so we opened up the finished product and sent it to the cigarette factory for cigarette smoking. But on the sample packaging machine coated with tobacco film when Changde Jinpeng gravure Printing Co., Ltd. Ou Liguo is now a problem of fog, and the residual odor on the cigarette package has not been eliminated.

In response to these two problems, our company immediately organized technical personnel to tackle the problem. At that time, we reviewed and researched a great deal of information on UV varnish, combined with the experience and opinions of the ink manufacturer's technicians, and summed up two points of the haze of the torch pack. the reason.

1. The UV varnish has poor curing properties or the UV lamp power is not high, resulting in incomplete curing of the UV varnish, and the internal moisture or auxiliaries do not evaporate.

2. The smoothness of the surface of the cigarette pack is too high. During the film coating process of the packaging machine, the high temperature causes residual moisture and additives to dissipate to the surface. However, because the paper is too smooth, the film and the paper are attached very tightly and moisture and auxiliary agents cannot be discharged.

Smoke film fog problem solution

Several solutions have been formulated to address the causes of the problem.

1. Reduce the number of anilox roller screens of the coating machine and reduce the coating amount of varnish.
2. Increase UV lamp power and reduce printing speed.

3. Add an additional process, namely offset UV glazing followed by flat concave UV glazing, from full-page glazing to line glazing, because the gravure used UV refractive light oil layer is thick, the hand feels can feel the convex The lines that make up the packaging film are in multi-line contact with the surface of the paper rather than the original full-size stickers.

Finally, we solved the problem of fog completely by the third method. One more condition is that there are lines in the printed pattern of this product. If other manufacturers also have such troubles, they can add some net line patterns when designing the cigarette label, so that the contact area between the surface of the cigarette label and the packaging film can be reduced to prevent fogging of the torch film.

Cause of odor

Before discussing the causes of residual odor after UV polishing, we first understand the reaction principle of the UV varnishes: the main components of the UV varnishes are monomers and oligomers. The UV curing mechanism is to use photoinitiators to promote freedom. Base reaction, UV curing first from the surface, from the surface to the curing, and ultimately achieve complete curing effect. Therefore, it is odorless to want to print a production line. Theoretically, this is impossible and impractical. We can only require that the prints have no residual odor after going through the entire curing process.

1. On an uncured UV varnish surface, the odor comes from the following aspects.

(1) The nature of the monomers and oligomers themselves.
(2) The odor of photoinitiator, which is the main factor of residual odor.

(3) The odor of the solvent in the UV varnish. Because many manufacturers add a part of organic solvents, such as xylene, to reduce the cost, when xylene is coated with UV varnish, xylene volatilizes will produce unpleasant odor.

2. The possible causes of residual odor after UV varnish curing are as follows.

(1) The intensity of the UV light source does not conform to the standard, and the curing time of the UV varnish is not enough, which will cause the product to have a strong residual odor.

(2) The photoinitiator plays a key role in the residual odor of the coating film. The UV varnish has poor curing properties or the vehicular speed is too fast to cure the UV varnish. A small amount of the photosensitizer does not react immediately but remains in the paper.

(3) Residual solvent. Most solvents in the UV varnish system have been volatilized after irradiation with UV light. In many cases, the unpleasant residual odor is not generated by organic solvents.

(4) The light box or the oven is not conducive to the ventilation, resulting in a high concentration of residual gas in the tank and part of the gas is absorbed by the reverse side of the sheet. Because the back of the paper is fluffy and not exposed to UV light throughout the production process, it has been pressed tightly underneath; the gas simply cannot be emitted.

(to be continued)