Reprinted from: China Printing Technology Association Fashion Leisure Backpack,Laptop Backpack,Leisure Backpack,Leisure School Backpack Gaobeidian Pengjie Leather Goods Co., Ltd. , http://www.pengjieluggage.com
Since 1996, this process route has spread to foreign countries with the entry of foreign companies, but the progress has not been smooth. The main problems are:
1. The competitors of the new technology market are traditional crafts, namely gravure printing and solvent compounding. The gravure printing plate of plastic film is commonly used in 175 lines, and the standard passed from abroad at that time is 120 to 133 lines. The anilox roller configuration is only in 600 to 700 lines. From the level of expression of the pattern, the flexo Too rough, far less than gravure, so the customer does not accept from the pattern printing.
2. The plastic film is gravure printing. The compounding process adopts no solvent. Due to environmental considerations, gravure printing uses alcohol ink containing no benzene solvent, but the result of this process is that the composite peeling strength of the product is low, and no The standard 2 N/15 mm to the original process can only reach 1 N/15 mm. Sometimes this strength will be better, but the quality will be unstable and the customer will not accept it.
3. Occasionally, it was found that thin films printed with benzene-based inks were solvent-free composites and the composite peel strength was fully up to standard. However, this is contrary to the original intention of using a solvent-free compound process to take the environmental protection route, so it is better to revert to the original process, and the country has not yet introduced mandatory standards to limit the application of benzene.
Although solvent-free compounding has small environmental impact, good product environmental characteristics, low production costs, and high production speed, it is the stripping strength that severely hinders the promotion of solvent-free compounding technology in the flexible packaging industry. Some companies have even changed their dual-use copiers into a single solvent compounder and a dedicated solventless compounder. Why is a very mature technology in foreign countries fall into such a situation in the country, where are the problems? I have done this research, and concluded that: This is the solvent residue in the film printing. We used the unprinted film to directly recombine, and the strength was up to standard. However, if the printed film was used for recombination, it was not up to the mark, and the printed film was originally up to standard when tested with 3M tape. As a result of the final peeling during the peel test, the ink was pulled away from the substrate and transferred to the adhesive layer. The adhesion of the ink to the substrate was significantly reduced. This indicates that the printed film had components that reacted with the adhesive. The printed film was detected by gas chromatography. The main residue was an alcoholic solvent. Its content was related to the proportion of the two-component adhesive compounded without solvent. We currently use a solvent-free adhesive, the end group of component A is OH group, the end group of component B is an NCO group, the control ratio of two components is 100:40, and the error is allowed to be about 100:42, but it cannot exceed 100:45. For this reason, the glue pump on the solvent-free compound machine is very precise, and the proportion control of the glue on the process is also very careful. If the mix ratio is not correct, the composite strength can not obviously reach the required peel strength.
The combined strength of printed films using benzene-based inks was significantly greater than that of alcohol-based inks, indicating that the OH groups of residual solvents in the latter were involved in the proportion of two-component adhesives. Therefore, even if the proportion of the adhesive is correct, the proportion of actual use is not correct. The key to solving the problem is to solve the residual problem of alcohol solvents. However, it is precisely this problem that gravure control is difficult to control. The gravure to control the residual solvent must take into account the depth of the plate, the fast and slow drying of the synthetic solvent, the size of the heat when the printing is dry, the speed of the printing, etc. The comprehensive control of these data depends on the management of the production site. Once there is a problem in one of the links, the residual amount of solvent must exceed the limit. The national standard for this issue is 10 mg/m2, and once it is out of control, 15 mg/m2 is possible. And without gas chromatograph, it is not easy to find the problem. Only when the printing film is released on the laminating machine to release the sticking sound, will cause the operator to be vigilant. Therefore, this results in instability of the composite peeling strength, resulting in a long-term unresolved quality problem. As a result of quality problems, sometimes when the OH ratio is low, we can increase the humidity in the curing chamber, use the OH groups in the air to make it into the reaction ratio to improve the composite performance, and when the proportion of OH is too large When we compare, we can't increase the proportion of NCO. The peel strength of the entire roll of material is not up to the mark, and it cannot be remedied.
The solution to the problem can be flexo. Solvent products have a much smaller residual solvent than gravure. We have measured a product with 200% of the inked area (CMYK four-color printing, white ink bottom), and the solvent residue is 2 mg/m2, which is much smaller than gravure printing. The flexo-printed film is solvent-free composite and there is no problem with peel strength. And it has been doing so in the soft packaging process in Europe and the United States. The problem once again returned to the level of expression of flexographic products. The requirements for flexible packaging in Europe and the United States are only 120 to 133 lines. The market has been accepting this for years, but this is not the case in Asia. The packaging market is not the same. Prior to 1992-1993, the domestic market demand was only 150 lines. With the improvement of ink and the advancement of electric engraving and gravure printing, gravure printing was raised to 175 lines. If we were to retreat to line 133 at a stroke, the concept of the Chinese people would be difficult to accept. Unless you take orders from European, American, and foreign companies, after all, they are the main part of the market. The key issue is whether flexo printing can achieve 150-175 lines. If we look at the flexo printing products for label printing, we found that flexo printing is completely okay. As long as some adjustments are made in the process, wide-format flexo printing can fully Meet the requirements of the domestic market.
The information on the excess of benzene residues in certain food packaging films in northern China, which was circulated in the previous phase, prompted green environmental packaging to once again refer to packaging companies. The current standard is that the total amount of solvent residues in composites should not exceed 10 mg/m2. The residual amount of benzene solvent does not exceed 3 mg/m2. This standard has lasted for many years. If the standards are to be in line with international standards and how many domestic soft packaging companies do, it is time to consider this issue. ※
Author: Cai Chengji
Author unit: United Printing Equipment Company
Solvent residue problem in packaging film printing
In the flexible packaging market in Europe and the United States, the wide-satellite flexo press has always been the main force: First, the wider the width of the door, the necessary side-filaments (for example, 10 to 15 mm per edge) are eliminated, per unit area. The higher the yield. The yield is profit. Secondly, wide-satellite flexographic printers use alcohol-soluble inks when printing films. The main solvent is alcohol, which has a large environmental tolerance. According to the relevant standards of our country, the allowable value of the environment is 1500 mg/m3. Compared to the 100 mg/m3 toluene and 300 mg/m3 ethyl acetate, the alcohol is indeed safer. Different from the commonly used domestic ethyl acetate-based polyurethane adhesive compounding process, the process used in Europe and the United States is solvent-free compounding. From the perspective of environmental protection, the influence of ethyl acetate solvent on the surrounding environment during volatilization is eliminated and the compound product is eliminated. Solvent residue; economically speaking, saving a lot of solvent costs, reducing production costs. Therefore, the flexible package market is dominated by satellite-based flexo and solvent-free composites.