The good composite effect of two-component polyurethane adhesive is related to many conditions, among which the change of working environment is also a very important factor. In other words, with the change of season and climate, it is necessary to make some fine adjustments to the adhesive process in order to obtain the ideal composite effect.
In short, the seasonal climate change that affects the compound is the change of environmental humidity and temperature; In terms of temperature, the temperature in summer is much higher than that in winter, and the maximum difference between the two can be nearly 30-40 ℃ (this is to compare the southern area without indoor heating).
If we do not pay attention to these differences, it is likely that the following problems will occur in the process of lamination: when the air is wet, the adhesive is often not cured completely, that is, it is not dry, and the residual viscosity is large. In serious cases, the phenomenon of wire drawing can be observed when the composite film is peeled, especially when the film itself has high moisture absorption, such as nylon membrane composite;
Secondly, the moist air will condense on the roller, which will bring the water into the glue basin. As time goes on, the adhesive will gradually change from transparent to chaotic, white, and even lose the bonding effect; Wet heat and high temperature also make the storage of adhesives more difficult. If the work glue is not used, it will often lump and form gel (jelly shaped) after overnight.

On the contrary, when it is cold in winter, the working glue that has not been used up before still keeps good transparency and fluidity overnight. It can be directly used on the machine without mixing the new working glue in batches. On the other hand, in winter when the temperature is lower, the adhesive will become viscous and the leveling property will decrease. When the laminating machine is running at high speed, a large number of bubbles are easy to accumulate on the surface of glue and the edge of the roller, which may cause the transfer of vacuoles and the insufficient amount of upper adhesive, which will affect the composite fastness; At the same time, due to poor leveling and dispersion performance, the appearance effect of the composite film will also be poor. For example, the flow pattern of adhesive is obvious, sometimes orange peel. When used in composite aluminum foil or aluminum plating film, if there is a large area of white ink or light ink on the printing surface, it is easier to form small white spots and spots; in addition, due to the low temperature in winter, the temperature of the curing room is lower than that of the external environment If the insulation measures are not in place, the heat loss rate is much faster than that in summer, which often makes the temperature in the curing room not reach the set temperature (generally 50 ℃). Therefore, the effect of curing is also affected. Under the same aging time, the composite fastness may be lower than that in summer.

Analysis of the causes of the above phenomenon, it is necessary to understand the influence of moisture and temperature on the adhesive. First of all, for the two-component polyurethane adhesive, moisture can react with NCO group in curing agent just like polyester / polyether polyol. It is estimated that 1 g of water can consume 26-32 g of curing agent. Of course, in terms of the pure weight ratio of reaction, in practice, the water mixed into the working glue liquid competes with the main agent when it reacts with the curing agent. However, no matter how much water is involved in the reaction, this is undoubtedly the consumption of curing agent, which makes the amount of reaction with the main agent can not reach the original working ratio, thus resulting in incomplete curing and residual viscosity. The viscosity and reactivity of the adhesive are closely related to the temperature. The viscosity value given by the adhesive manufacturer is measured by rotary viscometer with 25 ℃ as the standard temperature, which means that the temperature of working environment can be more than 10 degrees higher in summer and 20 ℃ lower in winter when it is cold. The viscosity of the adhesive is just opposite to that of the temperature. That is to say, the viscosity of the same adhesive at high temperature is lower, and the flow dispersion performance is good. When the temperature is low, the viscosity is high.
In addition, the crosslinking and curing reaction between the two components of the adhesive is slow at low temperature and fast at high temperature, which is exactly why there is a curing room (speed up the curing reaction speed and improve the production efficiency).
In view of this situation, the following adjustments can be made according to the environmental changes when using the two-component polyurethane adhesive: if the air is humid and the air temperature is high, the amount of curing agent should be increased by 10% - 20% to make up for the consumption of moisture; the condensed water drops on the laminating machine should be sucked off with dry cotton yarn or cloth chips to prevent it from falling into the rubber basin; The unused working glue can be diluted with a small amount of solvent, and then sealed and stored. If conditions permit, it can be stored in a small refrigerator for better effect. When it is reused next time, it should be thawed under closed condition and mixed with the newly prepared working glue.
When the temperature is low in winter, more solvents can be added to the working glue solution to reduce the viscosity of the system, improve the flow dispersion, and reduce the generation of bubbles in the rubber basin. If the concentration of ethyl acetate and acetone is less than 3:3, the mixture of ethyl acetate and acetone can be used as the working solvent. In addition, in winter, the temperature of the curing room can be set slightly higher to ensure that the actual temperature can meet the requirements, so as not to affect the curing effect.
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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