Some problems and solutions in the printing of the

Some problems and solutions in cigarette label printing

first, the adaptability of aluminized film printing

the direct printing of aluminized film surface, whether it is lithography, flexo printing or gravure printing, will have problems such as printing adaptability and printing uniformity. In order to obtain better printing effect, the surface of the aluminized film must be treated. The usual method is to coat a layer of primer on the surface of the aluminized film first, and then carry out subsequent printing. At present, almost 100% of the primer used in Chinese Mainland is solvent based. However, with the requirements of environmental protection, water-based primer is also gradually applied. The application of waterborne primer based on acrylate in aluminum foil is relatively mature, but its application in aluminum coating still has some own problems. The latest research shows that polyester primer has satisfactory results in compatibility, adhesion and transparency, especially excellent hot stamping performance, but it has not been widely understood and applied in industry in China

second, the smell of UV varnish

in China, cigarette label printing has almost become the highest level in the printing industry. In order to be more competitive, most printing factories have installed UV drying devices using UV ink and UV varnish. For most manufacturers, no matter which other printing process is adopted, including the automotive industry, small and medium-sized electronics and home appliance manufacturing industry, the residual odor of UV system has become a thorny problem

the main components of the system are monomers and oligomers. The UV curing mechanism makes it almost like paste or syrup. Photoinitiators are used to promote free radical reactions. The UV curing process starts from the surface, and then from the surface to the inside, the post curing process is carried out, and finally the complete curing effect is achieved. Therefore, it is theoretically impossible and impractical to want the printed matter to be odorless when it comes to the production line. What we require is that the printed matter has no residual smell after the post curing process. Let me discuss the smell as follows:

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

the properties of monomers and oligomers; The odor of photoinitiator, which is the main factor of residual odor; Solvent in UV varnish. In order to reduce costs, many manufacturers add some organic solvents, such as xylene, to the formula. In fact, when coating UV varnish, xylene volatilizes and produces an unpleasant smell

2. Possible reasons for the residual odor of UV varnish after UV curing:

the intensity of UV light source does not meet the standard, and the curing time of UV varnish is not enough, which will have a strong residual odor. The choice of photoinitiator plays a key role in the residual odor of the film. Residual solvent: however, most of the solvents in the UV varnish system have volatilized after being irradiated by UV light source. In many cases, the unpleasant residual odor is not produced by organic solvents

3. Solutions:

1) printing and packaging manufacturers should ask suppliers to use monomers, oligomers and photoinitiators with the lowest odor when producing UV varnish

2) with appropriate formula, the printing and packaging factory will not only get satisfactory surface curing effect, but also get better later curing effect

3) printing and packaging factories should try to use UV varnish with a solid content of at least 99.5%

4) note that the performance test of UV varnish should be carried out 24 hours after the film is cured

III. some problems and solutions in aluminized paper printing

generally, the flatness, smoothness and gloss of the surface of aluminized paper are not as good as those of pet aluminized film composite. The uneven surface of aluminized paper makes the printing uneven. In addition, its roughness poses a greater challenge to the printer, especially the lithographic printer, because the varnish coated by the lithographic press is thinner than that of the flexo gravure press. If the printed image is uneven, cracks are easy to occur at the crease line when folding into a box, exposing the bottom paper. Therefore, it is recommended to apply primer before printing, which can not only improve the surface flatness, but also provide a printing surface with better printing adaptability for subsequent printing. Attention should be paid to when selecting the bottom oil:

1. Flexibility of the bottom oil

the surface of aluminized paper is composed of a layer of fine aluminum particles, which has the tendency of deformation, fracture and shrinkage when folding. The smaller the humidity of the paperboard surface, the easier it is to produce such problems. In addition to the adjustment of ink performance by the ink formulation designer, the flexibility of the base oil must be considered

2. Friction coefficient

the friction coefficient of the paper jam surface is the key factor to determine whether the rear bolt 6 corner and the screw part and the pitch diameter and the screw part will be deformed, and whether the sequential printing process can realize continuous paper feeding. The friction coefficient of the paperboard surface is determined by the nature of the bottom oil, so the selection of the bottom oil is very critical. Generally speaking, the harder and smoother the bottom oil is after the film is formed, the smaller the friction coefficient is, which greatly improves the comprehensive performance of the product and the effectiveness of the equipment. The more suitable the machine is. The control of the friction coefficient value must be carefully tested in order to meet the special requirements of each machine

we have recently made a technological breakthrough: we have studied a special formulation of water-based base oil. It is a neutral liquid without ammonia. The stability of this bottom oil is better than that of the water-based bottom oil which is widely used at present. In addition, its fast drying and no residual smell are also another advantage. More importantly, compared with the general acrylic primer, this special varnish has excellent adhesion and uniformity with the surface of aluminized paper. In addition, it has excellent transparency and will not darken the metallic luster