At present, the vast majority of China's flexible packaging inks contain benzene solvent ink. With the strengthening of domestic awareness of environmental protection and sound health and safety regulations, China's flexible packaging ink products are rapidly developing in the direction of environmental protection and hygiene. Polyurethane inks account for more than a year each year, and at the same time solve the problem of poor strength of chlorinated polypropylene inks on PET and nylon, while chlorinated polypropylene inks release Hcl during use. Hazards to the human body are gradually reduced. However, some characteristics of polyurethane inks have not yet been understood by the majority of users. After printing, compounding fails to gain attention, and it is often prone to some details. If it is a cooking bag, it is often prone to bag breakage and wrinkling, and ordinary bags are compounded. Poor fastness and quits.
I will give two examples: one is a color printing plant in Inner Mongolia using a retort-resistant polyurethane ink, printing nylon and then compounding CPP. After the bag has not been subjected to a cooking test, it is sent to the food factory packaged food, but after the cooking, the bag is found to have printing ink. The place where the nylon delaminated wrinkled. Another is a color printing factory in Guangdong using PET special ink (polyurethane system), printing PET and then composite PE aging, found that the fastness of the thick ink printing is not satisfactory, but there is still a little stickiness, and the ink layer shallow place and the prison The degree is very good.
To analyze the above two examples, we must first analyze the polyurethane ink system, polyurethane ink composition: pigments, polyurethane resins, additives, solvents and so on. Dilution solvent composition of polyurethane ink generally include: butanone, ethyl ester, butyl ester, isopropyl alcohol, toluene and so on.
Adhesive bonding mechanism of polyurethane adhesive: The main agent is -OH-terminated polyurethane and curing agent with -NCO-terminated polyurethane, which react to produce larger molecular weight polyurethane and form adhesive force. Therefore, the alcohol with -OH and the material with -NH2 interfere with the post-composite processing.
For the same reason, the polyurethane resin in the ink itself is also -OH-terminated and can also react with the curing agent of the polyurethane adhesive. Therefore, it is not difficult to explain the phenomena in the above two examples.
The solution is, first, to solve the composition of the diluted solvent in the polyurethane ink, as far as possible without alcohol dilution solvent. If alcohol diluents must be used during printing, it is also necessary to minimize residual solvents during printing.
Second, if there is a white ink bottom of the printed film, it is best to add a small amount of hardener in white ink, can increase the composite fastness. However, the hardened ink is used for a short period of time. If there is any surplus, the interval time is longer and should not be used in principle. (However, this operation is wasteful and is for reference only.)
Third, the preparation of adhesive dilution of ethyl acetate with high purity, including water and alcohol content as low as possible, this is to ensure the quality of cooking bag, in addition to the preparation of adhesives, the appropriate increase in the amount of curing agent (increased proportion is Curing dose between 5% and 10%, which means that adding 1kg of curing agent needs to add 0.05 to 0.1kg curing agent) to ensure that the adhesive main agent and the curing agent are fully cross-linked.
The ink of polyurethane system is the current development direction of printing ink, and the ink of chlorinated polypropylene system will be phased out. Therefore, only the characteristics of the ink of the polyurethane system can be well mastered, so as to effectively avoid some of the quality problems on the composite.
(Author/Zhejiang New Oriental Ink Group Co., Ltd. Xiao Haiyi)
Guangdong packaging