2、 The water content or other active hydrogen substances in the diluent are high.
1. The reaction process of two-component polyurethane adhesive is the cross-linking reaction between the active hydrogen in the main agent and isocyanate in curing agent to form a three-dimensional network structure. Isocyanate can easily react with substances (water, alcohol, amine) containing hydroxyl and amino groups. In the use of polyurethane adhesives, combined with the properties of solvents (boiling point, solubility), ethyl acetate is generally used as the diluent of adhesives. However, because ethyl acetate contains carboxyl group and has good affinity to water, it is inevitable that water will be mixed in the production process of ethyl acetate. According to the national standard gb3728-91 for industrial grade ethyl acetate, ethyl acetate is divided into several grades. The moisture content of superior product is less than 1000ppm (0.1%), and that of first grade is less than 2000ppm (0.2%).
The reaction formula of water with - NCO group is as follows:
—NCO+H20→—NHCOOH→—NH2+CO2
—NCO+—NH2→—NHCONH
It can be seen from the above formula that one water molecule consumes two isocyanate groups, that is, 18G water can react with 84g isocyanate group. Therefore, the quality of diluent should be strictly controlled when choosing and using diluent, and ethyl acetate with alcohol, ammonia or moisture greater than 0.2% should not be used. At the same time, the purity and moisture of ethyl acetate should be strengthened in the incoming inspection.
2. In the actual compound production process, a considerable part of the water and alcohols in the diluent will be volatilized in the drying channel, but if the water or alcohol in the diluent is slightly higher, the consumption of curing agent will be accelerated. Before entering the drying channel, part of the curing agent in the glue liquid will be consumed by water or alcohol, resulting in insufficient curing dose and incomplete curing.
3、 The consumption of curing agent and the influence of production environment on curing.
1. Consumption of curing agent by ink
In recent years, non benzene and ketone free polyurethane ink has been more and more widely used to adapt to the trend of environmental protection. However, with the use of polyurethane ink, the problem of glue drying caused by the consumption of curing agent by polyurethane ink often occurs. The hydroxyl terminated polyurethane resin and alcohol solvent containing hydroxyl group used in polyurethane ink have great interference on the composite processing. When the curing agent in the adhesive is consumed to a critical state by other factors, plus the consumption of hydroxyl groups in the ink, it is very easy to cause the ink part of the glue not dry. Therefore, when using polyurethane ink, alcohol solvent should be avoided as far as possible, even if it is used, the residual amount of solvent should be controlled to the minimum; for products with white substrate, a small amount of curing agent should be added to the white ink as far as possible, and the printing film should be aged for several hours before compound production, so as to reduce the consumption of curing agent by ink.
2. The humidity of production environment is too high
The humidity of the production environment is too high, which means that the moisture content in the air is too high. During the production process, the moisture in the air will continuously enter the rubber tray or recycling rubber bucket with the evaporation of ethyl acetate, which will increase the water content of the whole glue system, and the water will consume the curing agent of the glue system, causing incomplete curing problem. Generally, packaging enterprises will adopt the method of increasing curing dose in the season of high temperature and humidity, but the more effective method should be to control the environment of compound production, strengthen the monitoring of temperature and humidity, place exhaust fan in the workshop, and strengthen the air circulation. For enterprises with good conditions, sealed dust-free air-conditioning workshop can be used, and the temperature and humidity can be more effective Control.
summary
Incomplete curing problem is closely related to production environment, quality of ink, diluent, glue mixing operation and other factors. In the production process, it is necessary to strengthen the control of environmental humidity and diluent quality, and pay attention to the influence of printing process ink, glue mixing operation and other details, so as to effectively avoid the occurrence of incomplete curing problem.
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.