A brief discussion on curl deformation control of cigarette packets

To this end, we have formulated the following options.
(1) Curl control of soft pack products
When printing soft package products, single-sided coated paper of 80 g/m2 or 90 g/m2 or 95 g/m2 of transfer paper is generally used. The paper is curled and deformed mainly in the gravure printing process, and the offset printing process is natural drying of the ink. The deformation of the paper is much smaller. The following are several ways to control the curl deformation of gravure soft packs.
1 back coating. In general, the last color group of the gravure printing machine is used to print the back coating liquid on the back of the paper. The key is to select a suitable back coating liquid, and the appropriate coating amount is also very important, and the general control is about 1.0 g/m2. However, using this method does not completely solve the problem because, under high humidity conditions, slight changes in humidity can cause large deformation of the paper. If the amount of coating is not controlled or the formula of the back coating solution is not stable, the moisture content on the front and back sides of the paper will be uneven, and the dimensions of the paper on both sides will be different. As a result, the curl of the paper may be more serious.
In particular, it is necessary to remind that the back coating solution needs to be specially modulated and no wax-like slip agent can be added. Otherwise, the cigarette package may not be firmly bonded. Some cigarette printing companies use ordinary water-based varnish diluted with water as the back. Liquid coating, it is prone to such quality problems. If the dryness of the back coating solution is not good, alcohol additives such as alcohol may be appropriately added.
2 coating anti-curling varnish. The choice of varnish type is important, and the thickness of the varnish coating must be moderate. Some of the varnish (mainly oily varnish) have good anti-curling effect, but the residual odor may be large and need to be carefully selected.
3 Adjust the temperature of each oven of the gravure printing machine to reduce the decrease of moisture content of the paper caused by high temperature drying. After testing, we found that this method works best, but it does not completely eliminate the paper deformation. After all, the temperature reduction limit is limited, otherwise the temperature will be too low to cause ink drying. The problem that easily arises in the initial adjustment is that the individual printing plates are not overprinted due to the decrease in the oven temperature, and at the same time, the indicators such as the drying speed and wear resistance of the inks need to be monitored, and the ink formulation must be adjusted to meet the quality requirements.
4 Replace the paper. If the above three measures cannot achieve the desired results, it is recommended to replace the paper for testing. Our company's "big harvest", "Bamboo plum", "Doubao" and other soft products, previously used a domestic paper company 90g/m2 single-sided coated paper, because the workshop is more decentralized, the ambient temperature and humidity Difficult-to-stable control Within the previously mentioned reference range, there is always a problem with curling in soft pack products. After adjusting for the above three measures, the degree of curling has been reduced, but it has not yet reached our expected effect. Later it was replaced with Taiwan's Yongfengyu 90g/m2 single-sided coated paper, with the previous three measures, basically solved this problem.
After testing, we found that the Yongfengyu 90g/m2 single-sided coated paper has more long fibers in the pulp, high pulp content, relatively small amount of filler, and relatively stable performance; however, the surface smoothness of this paper is not as good as the paper used before the replacement. Gravure printing on a large area of ​​the ground is relatively poor, need to adjust the parameters in the gravure plate, while adjusting the gravure ink to improve the leveling problem.
(2) Curl control of hard pack products
The curl of hard package products mainly occurs on composite gold paperboard, transfer gold paperboard, and transfer laser paper. White paperboard is much better than coated paper due to its thickness and stiffness. Whether offset or gravure printing is used, the paper is warped and curled. The situation is relatively less.
The structure of the composite paper we use is generally: through the wet composite method, a 12-μm, 16-μm or 18-μm thick aluminized film (or aluminized laser film) and 220-230 g/m 2 white card bottom paper are bonded together. Aluminum layer as the printing surface.
Due to the layer of PET or BOPP film on the surface of the composite paper, its air permeability is limited. The moisture absorption and moisture release of the paper are mainly performed on the back of the composite paper. In addition, most of the wet compound uses water-based adhesives, which also increases the moisture content of the paper. For the transfer of aluminum spray paper, the surface is less of this layer of PET or BOPP film.
At present, most of cigarette paper printing composite paper and transfer paper use UV offset printing or gravure printing. If it is UV offset printing, the UV curing system of non-cold light source will emit a large amount of heat at the same time of curing, so the UV lamp will emit out of the printing press. The paper temperature is generally high, sometimes up to 50 °C. If the product still needs to use screen printing to print certain special inks (such as ice ink), it needs a relatively large curing energy, the drying tunnel temperature is relatively high, and the paper deformation is relatively large.
The curl control methods of hard package products mainly include the following.
1 Back-coating when producing base paper can control the moisture absorption and release rate of the fibers on the back side of the paper. The main component of the back coating solution is an aqueous resin solution, and the coating amount is generally 1.0 to 1.5 g/m2. For the selection of the back coating solution, reference may be made to the related introduction in the curl control of the front soft package product.
2 For double-coated gold cardboard, there are two issues to be noted in the production of base paper. First, the thickness of the film, generally using 16μm or 18μm film, try not to use 12μm film, so that although the cost will be higher, but when The deformation is relatively small; the second is to control the composite tension, if the composite tension is not well controlled, the film is stretched after the special composite paper, production often curled to the printing surface, while die-cutting at the indentation line at the film and the bottom Paper will separate.
3 In the production process, shrink paper should be used to tightly pack each bundle of paper, even if the workshop has a constant temperature and humidity control system.
4 die-cutting process control. Many cigarette pack printing companies have encountered this kind of situation: sometimes the printed large-format prints are relatively flat, but the cigarette pack products after die-cutting are curled more severely, especially in the case of laminated gold card paper. More.
This situation is often related to die-cutting processes and operations. In particular, the relationship between the height of die-cut creasing lines and the depth and width of the bottom die must be checked. Ordinary wood die-cutting plates mostly use an indentation line with a thickness of 0.71mm and a height of 23.2mm. Many cigarette package printing companies use a bottom mold of 1.1mm x 0.35mm, regardless of what kind of hard paper they produce. I consider this practice to be a common practice. Unscientific, because the thickness of different bottom papers is different, it is necessary to make bottom molds with different widths and depths. Our experience is: the use of 0.35mm x 1.1mm bottom mold for white cardboard, 0.35mm x 1.2mm bottom mold for composite gold paperboard, 0.35mm x 1.1mm if the bottom paper of laminating paper is thin The bottom mold.
Die-cut tobacco products are best to use steel template (in order to save the cost of the mold, you can use sandwich steel mold), because the steel template uses 0.71mm thick, 23.8mm high indentation line and thickness 0.71mm, height 23.2mm Steel knives, the supporting bottom mold indentation line is completely concave, the steel knife in the same plane, the bottom mold for the steel plate, the indentation is relatively full, curved. In addition, the strength of the steel stencil is much higher than that of the wooden stencil. For long-lived orders, the unit cost is actually much lower.
The above is a summary of the process control of the paper curl of the cigarette package product by the company combined with the production situation of the company. It is only for the sake of process control. Due to the different product requirements of various manufacturers, the materials used are not the same, the environment is also different, but also we need to adjust according to the actual situation.