Some Problems in the Printing of Tobacco Labels and Their Solutions

First, aluminizing film printing adaptability

Direct printing on the surface of the aluminized film, whether using lithography, flexo or gravure, has problems such as printability and print uniformity. In order to obtain better printing effect, the surface of the aluminized film must be processed. The usual method is to coat the surface of the aluminized film with a layer of base oil and then carry out the post-sequence printing. At present, the bottom oil used in mainland China is almost 100% solvent-based. However, with the requirements of environmental protection, water-based primers are gradually being applied. The use of acrylic based aqueous base oils on aluminum foils is relatively mature, but its application on aluminum coatings still has its own problems. Recent studies have shown that polyester base oils have satisfactory results in terms of compatibility, adhesion, transparency, etc., especially hot stamping performance, but they are not yet widely understood and applied in industry in China. .

Second, the UV light oil smell

In China, cigarette label printing has almost become the highest level in the printing industry. In order to be more competitive, most printers installed UV drying devices using UV inks and UV light oils. For most manufacturers, the residual odor of the UV system becomes a thorny issue regardless of the printing process used.

The main components of the system are monomers and oligomers. The UV curing mechanism uses photoinitiators to promote free radical reactions. The UV curing process begins with the surface first, and then the surface-to-inside post-cure process finally achieves complete curing effect. . Therefore, it is odorless to want to print a production line. Theoretically, this is impossible and impractical. All we require is that there is no residual odor after the print has passed the post-curing process. Let me discuss the odor issue as follows:

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

The nature of the monomers and oligomers; the odor of the photoinitiator, which is the main factor of the residual odor; the solvent in the UV varnish. Because many manufacturers add a part of organic solvents, such as xylene, to reduce the cost, in fact, when UV varnish is coated, xylene volatilizes to produce an unpleasant odor.

2. Possible causes of residual odor after UV curing of UV Varnish:

The intensity of the UV light source does not meet the standard, and the curing time of the UV varnish is not enough, which will have a strong residual odor. The choice of photoinitiator, the photoinitiator plays a key role in the residual odor of the coating. Residual solvent: However, most of the solvents in the UV varnish system have evaporated after irradiation with a UV light source. In many cases, the unpleasant residual odor is not caused by organic solvents.

3. The solution:

1) Printing and packaging manufacturers should ask suppliers to use the monomers, oligomers, and photoinitiators with the least odor when producing UV-varnish.

2) With a suitable formulation, the printing and packaging plant will not only get a satisfactory surface curing effect, but also a good post-curing effect.

3) Printing and packaging plants should use UV varnish with a solid content of at least 99.5%.

4) Note that the test of UV varnish performance should be performed 24 hours after the coating is cured.

Third, some problems in the printing of aluminized paper and their solutions

In general, the flatness, smoothness and gloss of the surface of the aluminized paper are not as good as those of the PET aluminum film. The unevenness of the surface of the aluminized paper makes the printing uneven. In addition, its roughness poses a greater challenge for printers, especially lithographers, because the varnish coated with a lithographic press is thinner than a flexo gravure printer. If the printed image is not flat, cracks are easily formed at the crease lines when the box is folded, exposing the bottom paper. It is therefore recommended to coat the base oil before printing, which not only improves surface smoothness, but also provides a printing surface with better printability for subsequent printing. When selecting the base oil, note that:

1. Base oil flexibility

The surface of the aluminized paper is composed of a layer of fine aluminum particles, which has a tendency of deformation, breakage, and shrinkage during folding. The smaller the humidity of the cardboard surface, the easier it is to cause such problems. In addition to the ink formulator's adjustment of ink properties, the flexibility of the base oil must be considered.

Coefficient of friction

The coefficient of friction on the cardboard surface is a key factor in determining whether the sequential printing process can achieve continuous feeding. The friction coefficient of the cardboard surface is determined by the nature of the base oil, so the choice of base oil is critical. In general, the harder the film is, the smoother the coefficient of friction is, the more suitable it is for the machine. The control of the coefficient of friction must be carefully tested to meet the specific requirements of each machine.

We recently made a technological breakthrough: we studied a specially formulated aqueous base oil. It is a neutral liquid that does not contain ammonia. The stability of this base oil is superior to the waterborne base oils that are currently being widely used. In addition, its fast drying and residue-free odor is another advantage. What's more important is that this special varnish and aluminized paper surface has excellent adhesion and leveling properties compared to the general acrylic type of base oil. It also has excellent transparency without darkening metallic luster.