Incomplete curing is a common problem in the process of flexible packaging. Once it appears, it has a great impact on the performance of the composite film. The adhesive layer of the composite film is badly cured, which is similar to the state of the composite film that has not been matured just after the machine is off the machine. The adhesion between the film layers is large, which will directly affect the composite strength of the composite film. It is basically impossible to carry out post-processing. Even if it is forced to process, it will cause the sliding between the layers to form a tunnel or wrinkling due to the low composite strength between the layers; The slight poor curing phenomenon is that there is a slight adhesion between the film layers, and the composite strength is normal, but the heat sealing strength after bag making is poor, and the heat sealing area is easy to wrinkle.
In essence, the incomplete curing phenomenon is that the main agent and curing agent do not fully react according to the proportion. In the whole glue system, there are too few effective isocyanate groups which can react with the active hydrogen in the main agent of the adhesive, resulting in the "excess" of the main agent. Because the main agent is polyurethane resin, which is a viscous material, the adhesive layer of the composite film has viscosity. Under normal circumstances, if the amount of curing agent is enough, there will be enough isocyanate groups in the whole glue system to fully react with the active hydrogen of the main agent and completely solidify to form a cross-linked network structure material, which will become strong, tough and firm, and will no longer be sticky like the adhesive.
In general, for the use of two-component polyurethane adhesive, the supplier will provide a reference proportion to guide the packaging enterprises to produce. However, due to the complexity of flexible packaging production environment and process, even if the production is completely in accordance with the reference proportion, quality accidents may occur.
1、 The curing dose is less when mixing
1. Due to the differences in the number of molecular active groups and solid content of different types of adhesives, the proportion of the main agent and curing agent that is most suitable for composite flexible packaging will be different. Generally, the adhesive supplier will pack the main agent and curing agent according to the optimal proportion. In production, the main agent and curing agent should be mixed according to the fixed packaging, and then diluted to the required working concentration So long as the main agent and curing agent in the barrel are poured into the mixing barrel thoroughly, there will be no quality accident.
However, due to the change of production environment (such as temperature and humidity), sometimes it is inevitable to fine tune the proportion of main agent and curing agent, which involves the separation and weighing of the main agent or curing agent. Although there are automatic weighing and mixing equipment, most packaging enterprises still use manual weighing method, which may lead to inaccurate weighing The chemical dose is not enough. Therefore, for enterprises using manual weighing, electronic scales with sufficient precision should be used and calibrated regularly, and the weighing methods of employees should be standardized to prevent inaccurate weighing. Enterprises with conditions can also use automatic weighing and mixing equipment to ensure accurate weighing and even mixing of adhesives.
2. Due to the difference of molecular weight and solid content of various types of adhesive resin, the viscosity will also be different. The direct impact is that the fluidity will be different. The smaller the viscosity, the better the fluidity. The more viscosity, the worse the fluidity, and the harder to pour the glue. The viscosity of curing agent is generally higher than that of the main agent, and its fluidity is poor. It is not easy to pour out the curing agent in the barrel when mixing glue. If the curing agent is added into the mixing barrel without diluent, the amount of curing agent will be insufficient, resulting in insufficient isocyanate group which can react with active hydrogen of main agent during compounding, and cause incomplete curing quality accident. Therefore, it is necessary to pour out the curing agent patiently and carefully After the curing agent in the barrel is used, the curing agent attached to the barrel wall is washed with diluent and added into the mixing barrel.

3. The reaction rate between the main agent and curing agent of polyurethane adhesive is related to the concentration. The higher the concentration is, the greater the probability of reactive group collision in unit volume and the faster the reaction is. Therefore, the order in which the main agent, curing agent and diluent are added into the mixing barrel will also affect the amount of curing agent in the final glue system, and the reaction between water containing active hydrogen and curing agent is also affected It's the same thing.

The general mixing method of two-component polyurethane adhesive is to first pour the main agent into the mixing barrel, then add the diluent to mix evenly, and then add the curing agent for mixing. In this way, after mixing the main agent and the diluent, the concentration of diluent in the unit volume is reduced, and the concentration of micro water in the diluent is also reduced. After adding the curing agent, the water in the diluent consumes the curing agent It's a lot slower. However, some packaging enterprises use the curing agent to add the curing agent into the mixing barrel, then add the diluent for stirring, and finally add the main agent, which leads to a problem: if the diluent is added to the curing agent, the probability of hydrogen splashing reaction between the isocyanate in the curing agent and the trace moisture in the diluent is increased. When the main agent is added, some curing agent and moisture have already occurred Therefore, in the process of dispensing, packaging enterprises should pay attention to the invisible reduction of curing agent caused by the difference of glue mixing sequence.
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.
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