Some flexible packaging manufacturers often encounter the phenomenon that the composite products still do not dry after 24-28 hours of aging. Some manufacturers also found that the aging products wrinkled during heat sealing, and the peel strength between layers was relatively good. I don't know what the reason is. In fact, this is directly related to the composite film adhesive layer is not completely cured. The phenomenon of non drying often occurs in spring and summer with high temperature and humidity, but it is not easy to appear in dry autumn and winter. 1、 The composite film does not dry phenomenon. After the composite product is aged for a certain temperature and time, the interlayer peeling off of the composite film adhesive layer still has a certain viscosity, that is, after the composite film is peeled, the two-layer film can be glued together again by hand. If the adhesive layer of the composite film is not dry seriously, it will directly affect the peeling strength of the composite film. However, if it is not dry slightly, the heat sealing strength is poor after bag making, and there is stickiness after peeling between layers, and the heat sealing place is easy to wrinkle. There are also no wrinkle phenomenon in the processing of the composite film after aging, but the packaging bag wrinkle phenomenon appears after storage for a week or half a month, resulting in a large loss. 2、 From the adhesive analysis: the main agent of polyurethane adhesive has high peel strength only by reacting with isocyanogen in curing agent to produce network cross chain structure. The isocyanogen in the curing agent of polyurethane adhesive is easy to react with the substances containing hydroxyl and amino groups (moisture, alcohols, amines). 1. Water molecules can react with two isocyanate groups. The content of curing agent in dry curing agent is about 75%, and the consumption of curing agent in dry curing agent is about 75%. We assume that the moisture content of 20 kg of ethyl acetate is 0.2% according to the national standard), then the moisture content in 20 kg of ethyl acetate is 40 G. If the reaction is complete, 1.4 kg of curing agent will be consumed. The reaction rate between the main agent of polyurethane adhesive and curing agent is generally related to the amount of catalyst, temperature and concentration. The more catalyst is used, the faster the reaction speed is. The higher the temperature is, the faster the reaction speed is. The same is true for the reaction of water and small molecule alcohols with curing agent. Their reaction also takes a certain time, but the reaction speed is 10-20 times faster than that of the main agent and curing agent. In the actual compound, the moisture and alcohol in the solvent will be volatilized in the drying channel, so what we have to do is to let the moisture and alcohol volatilize in the drying channel as much as possible, so as to reduce the occurrence of non drying phenomenon. From the above analysis, the main reason why the adhesive layer does not dry is that the main agent does not react with curing agent completely, that is, some main agent does not react with curing agent. Because the main agent is a viscous material, the adhesive layer of the composite film is viscous, which affects the quality of the product. The reason of incomplete crosslinking between main agent and curing agent is that a large amount of isocyanate group in curing agent is consumed by water or alcohol. 2. When the PET film containing K coating is compounded, it will not dry, which is often related to the coating. Therefore, it is necessary to do a good job of prevention when compounding. The preventive method is to increase the dosage of curing agent appropriately (increase the amount by 5-10%). The quality of PET film is poor, and the additives contained in the film are unstable, which can also cause non drying phenomenon, because the amine components contained in the additives will react with the curing agent to form powdery white substances.But this kind of dry phenomenon is often relatively rare. The use of polyurethane, polyester ink is also easy to cause dry phenomenon. First of all, we should analyze the polyurethane ink system, the composition of polyurethane ink: pigment, polyurethane resin, additives, solvents and so on. The diluting solvent components of polyurethane ink are butanone, ethyl ester, butyl ester, isopropanol, toluene, etc. Alcohols with hydroxyl group and substances with amine group have great interference on the post-processing of composite. The polyurethane resin in the ink itself is also hydroxyl terminated and can react with polyurethane adhesive curing agent. (due to the use of fast curing polyurethane adhesives, and some fast curing polyurethane adhesives often increase the reaction speed of the main agent and curing agent by increasing the amount of catalyst, and at the same time, the reaction speed of moisture and alcohols with curing agent is also increased. If the moisture content or alcohols in the concentrated agent are slightly higher, the curing agent in the glue liquid will be eliminated by water or alcohol before entering the drying channel And there's not much left. This will cause the phenomenon of not doing. 3、 Based on the above analysis, we believe that there are several reasons for the non drying of the adhesive layer: 1. The proportion of the curing agent provided by the glue manufacturer is not accurate, the proportion of curing agent is too small or the proportion of the curing agent is out of balance when preparing the glue solution, and the curing agent is too few or invalid; 2. The water content of the diluted solvent or the content of small molecular alcohol is too high, and a large amount of curing agent is consumed; 3 Film moisture absorption, especially NY and cellophane, is prone to dry phenomenon; 4. The ink used contains alcohol solvent, which does not volatilize, causing the adhesive layer to dry completely; 5. Using polyurethane and polyester ink to cause the adhesive layer not dry; 6. The environment temperature and humidity are too high, the prepared adhesive is placed for a long time, resulting in the curing agent reacting with moisture for a long time. 7. The composite of PET film containing coating and the effect of additives in PET film. 4、 Generally speaking, the ratio provided by the adhesive manufacturer is the reasonable ratio obtained through a large number of tests conducted by the adhesive manufacturer. Therefore, there will be no inaccurate proportioning. It is necessary to replace the adhesive if it is due to the quality of the adhesive itself; 2. Reduce the total content of water and alcohol in ethyl acetate (replace the better ethyl acetate, the total content of water and alcohol is less than 0.2%); 3. When the film of NY and cellophane which is easy to absorb moisture is compounded, the proportion of curing agent (5-10%) should be adjusted and increased, and the damp film should not be used; 4. Reduce the amount of residual solvent in printing ink as far as possible; 5. When using polyurethane ink: first of all, solve the composition of diluted solvent in polyurethane ink, and try not to use alcohol dilution solvent. If the alcohol diluent must be used in printing, it should also minimize the residual solvent during printing. Secondly, if there is a white ink low printing film, it is best to add a small amount of hardener in the white ink, which can increase the composite fastness. However, the service life of the ink added with hardener is short. If there is surplus and the interval is long, it should not be reused in principle (but this operation wastes a lot, only for reference.) 6. The purity of ethyl acetate for diluting adhesive should be high, and the content of water and alcohol should be as low as possible, which is the quality assurance of cooking bag and dry composite. In addition, when preparing the adhesive, the amount of curing agent should be increased appropriately (the increase ratio is between 5% and 10% of the curing dosage) to ensure the full crosslinking between the main agent and the curing agent. 7. It is necessary to control the compound environment, such as placing the exhaust fan indoors to strengthen the indoor air circulation, but pay attention not to blow against the compound machine. At the same time, pay attention to the speed of the squeegee at the same time when there is no glue bead in the vicinity of the squeegee. Because the vehicle speed is too fast, the solvent volatilization speed in the glue tank should be accelerated, and the local temperature near the glue tank should be too low, which should cause steam condensation; 8. Shorten the storage time of the prepared adhesive, reduce the amount of each preparation, increase the preparation times, shorten the storage time, and increase the drying channel temperature to reduce the amount of residual solvent. In this way, the influence of water and alcohol on curing agent can be reduced, and as much water and alcohol as possible can be volatilized in the drying channel.Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.