Note seasonal environmental changes using glue
Time：2012-10-08 15:04:41 Hits：1905
Two component polyurethane adhesive composite effect is related to many other conditions, including changes in the environment is also a very important factor. That is, with the seasonal climate change, in order to obtain the desired composite effect, it is necessary to make some fine-tuning of glue to use technology.
Simply put, seasonal climate changes affect the composite that is humidity environment, changes in temperature of the two indicators: specifically, especially in the spring and summer rainy season, larger relative humidity of the air, even up to saturation autumn and winter air drying, humidity and small; the temperatures terms, much higher in summer than in winter, the maximum difference between the nearly 30 ~ 40 ℃ (here in the southern areas of the room is not heating an example for comparison). For these differences, such as inattention, it is likely that in the composite will produce the following issues: the air is humid, the glue is often not completely cured, that is dry impervious residual stickiness large, serious or even composite membrane peeling observed the drawing phenomenon, especially when the film itself moisture absorption is large, such as nylon film composite even more prone to this phenomenon; Secondly, moist air will be generated in the upper gum anilox condensing moisture brought into a plastic pot, with the passage of time, the glue gradually becomes chaotic made of a transparent, whitish, and even loss of cohesive effect; moist heat high temperature such that the glue is stored more difficult, with a good working glue such day not finished, placed overnight, often whitish lumps, to form a gel (jelly jelly-like). By contrast, in the winter when it's cold, did not run out of work before the glue overnight after remains good transparent liquidity in batches do not even have to work glue incorporation of new distribution, you can take a direct come on the machine to use. On the other hand, in the low winter temperatures, the glue will become sticky, leveling decline. When the high-speed operation of the composite machine, glue basin prone to the accumulation of a large number of air bubbles in the anilox roll edge of the glue surface and on the plastic, then there may cause vacuolar transfer, the amount of glue is insufficient to affect the composite fastness; Also, since the flow Ping dispersed poor performance composite film appearance will deteriorate, such as the flow of glue plain obvious, and sometimes was orange peel-like, when used in composite aluminum foil or aluminized white ink printing surface area or when the light-colored ink, the formation of white spots, spots easier; addition, due to the low winter temperatures, ripening room temperature and the temperature of the external environment is very different, If not doing enough insulation measures in place, the dissipation of the heat faster than the high-temperature The summer quickly, which often makes the ripening room temperature of less than the set temperature (typically 50 ° C). So the effect of aging also affected to some degree, under the same aging time, the composite fastness than summer low.
Analysis of the reasons for the above phenomenon, we must understand the impact of moisture and temperature on adhesives. Firstly, for the two-component polyurethane adhesive, moisture match wherein a main agent, polyester / polyether polyols can be reacted with the NCO groups in the curing agent. According to calculations, 1g of the water may be consumed by the curing agent of 26 ~ 32g and, of course, which is on the sheer weight of the reaction ratio, in practice, in the reaction with the curing agent and the main agent mixed into the water within the working glue compete. But regardless how much moisture is involved in the reaction, which undoubtedly consumed curing agent, making its reaction with the primary agent in the end amounted to less than the original set ratio, thus causing the curing is not complete and residual stickiness . The viscosity and the reactivity of the adhesive and the temperature has a great relevance. Viscosity values given by the adhesive manufacturer in the 25 ° C standard temperature measured using a rotational viscometer This means that the actual use, the temperature of the working environment comparable to their more than 10 degrees higher in the summer and winter when it's cold than low on 20 ℃ how. The viscosity of the glue is coincided with the temperature level of opposite, i.e. the same glue manifested in the high temperature low viscosity values, good dispersion flow, low temperature, high viscosity, and flow adjustment. In addition, the a crosslinking curing reaction between the two components of adhesives, in the low temperature reaction is slow, fast response, high temperature, precisely why should there be ripening room reasons (to speed up the curing reaction, improve production efficiency).
For this situation, two component polyurethane adhesive for composite according to the environmental changes make some adjustments: If the air is humid, high temperatures, the amount of curing agent appropriately increased by 10% to 20% to make up for the water to its of consumption; often with a dry cotton or rags siphoning off the complex machine condensed water droplets, to prevent its falling into the plastic basin; work used up the the glue may add a small amount of solvent dilution, then sealed and stored, if conditions allow, can be set refrigerated in a small freezer storage, which is better, then the next thaw in a sealed case and glue mixed with. When the low winter temperatures, the preparation work glue may be appropriate to consider adding some solvent to reduce the viscosity of the system, to improve leveling dispersed, but will also reduce the generation plastic basin bubble work. But doing work glue concentration will decrease, such as do not wish to change the working concentration, can replace a portion of ethyl acetate with a small amount of acetone, i.e. by using a mixed solvent of acetone and ethyl acetate as a diluent, both The ratio may be 2:8 or 3:7. In addition, the low temperature in winter when the temperature setting of the ripening room slightly raised, to ensure that the actual temperature can meet the requirements, so as not to affect the maturation effect.
