99.9% of people will fall into the misunderstanding
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Curing is also called curing. In most cases, it is a necessary procedure to maintain the composite in a constant temperature room at 40~70 °C for more than 48 hours. The purpose is to make the main component of the two-component polyurethane adhesive and the curing agent chemically. The molecular weight is multiplied to form a network crosslinked structure, thereby having higher composite fastness, better heat resistance and stability against dielectric attack. Regarding the curing temperature, don't fall into a misunderstanding of "the higher the better."
The chemical reaction of the polyurethane adhesive will proceed slowly under the condition of low temperature, but the slow cycle is too long and the efficiency is too low, so it is not feasible in industrial production.
When the temperature is increased, the reaction rate is increased, and the final effect, that is, the bonding fastness is also good. However, the temperature should not be too high, because the heat resistance of the film such as LDPE used is not high enough. If the curing temperature reaches 80 to 90 ° C or higher, the film of the film may shrink and deform, even to the point where the adhesion is melted. Therefore, most occasions are 45~55 °C.
Of course, if the substrate used is heat resistant, such as a high temperature resistant cooking film, it is compounded by PET, M-PET, BOPA, AL and CPP, so that it can be quickly cured at a higher temperature. For example, at 50 to 55 ° C, the curing time is 48 hours or more, and at 70 ° C, it is only 24 hours, and at 80 ° C, it is only 6 to 8 hours. However, the temperature of the curing chamber is too high, and people can't get in. It is not convenient to feed and discharge. Only in the case of highly modernized and automated, it is suitable for high temperature and rapid curing.
In order to speed up material circulation, shorten production cycle and quickly deliver to customers, in recent years, there has been a rapid curing adhesive which can shorten the curing time from 48h to 24h or 12h, which provides flexible packaging processing enterprises. The help of reducing the space of the curing room, reducing energy consumption, and improving economic efficiency has been welcomed by users. Among the fast-curing adhesives, there are imported LX770A type, etc., as long as they are aged at 45~50 °C for 16~24h; domestically produced LY-50FT and LY-75FT type, mature at 45~50 °C 12~20h will be fine; recently, the domestic adhesive has been fully cured as long as 4~6h.
Regarding the fast-curing adhesive, don't fall into the trap of "the sooner the better."
Foreign fast-curing adhesives have shortened the ripening from the original 48h to 24h. The domestic products have been shortened from the original 48h to 12h under the premise of ensuring the quality and operating solution have a normal long service life. It is the limit.
Why? Because we can't just pursue the rapid ripening of the compound and ignore the maintenance of other properties.
If the curing time is shortened to 4h, not only the performance of the composite is degraded, but also the service life of the prepared operating solution is too short, and the viscosity is quickly increased. The blocking phenomenon occurs during the gluing process, which causes economic loss. . Therefore, we must remind users not to excessively pursue unilateral rapid maturity, but to comprehensively consider them comprehensively.