The good compound effect of two-component polyurethane adhesive is related to various conditions, and the change of working environment is also an important factor. That is to say, with seasonal climate change, in order to obtain the ideal compound effect, it is necessary to make some fine tuning of the adhesive use process.
in a nutshell, compound of seasonal climate change is also the change of environmental humidity, temperature, two major indicators, specifically in the spring and summer, especially in the rainy season, the relative humidity of air is larger, even can reach saturation and the air is dry, the autumn and winter seasons humidity is small; In terms of temperature, many higher in summer than in winter, maximum difference between nearly 30 ~ 40 ℃ (here is indoor without heating southern region as an example to compare).
For these differences such as no heed, probably in a composite will produce the following problem: when the air is humid, adhesive curing incomplete, often also is dry, residual viscosity big, serious and even can be observed during for composite membrane stripping has the phenomenon of wire drawing, especially when the film itself sucks tide sex is larger, such as nylon membrane composite was more prone to this kind of phenomenon;
Second, moist air can produce condensation on the gluing anilox roll, forcing the water into plastic basin, with the passage of time, gradually by transparent adhesive become chaotic, pale, even lose bonding effect; Hot and humid heat also makes the preservation of adhesive is difficult, with good working gel fluid such as the day after use, place overnight, often hair white clumps, formation of gels (jelly - like).
In contrast, when the day is cold in winter, unused work before glue solution overnight after still keep good transparent liquid, don't even have to partial points into the liquid mixed with the work of the new with glue, can be directly used to computer use. On the other hand, in colder temperatures, the binder will become thicker and less fluid. When composite machines, high-speed operation, plastic basin prone to piled up a large number of bubbles on the surface of glue and glue anilox roll edge, is likely to cause cavitation transfer at this moment, on glue dosage is insufficient, affect composite fastness; At the same time, due to the poor flow flat dispersion performance, the appearance of the composite membrane effect will be worse, such as adhesive flow tabby is obvious, it is sometimes orange peel, when used for composite aluminum foil or aluminum plating film, if there is a large area of white ink printing surface or light color ink, it is easier to form white spots, spots; In addition, because of the low winter temperatures, the temperature of curing room temperature difference with the outside world is very big, if insufficient heat preservation measures, the heat loss is far less than the summer heat is fast, which often makes the curing room temperature to reach the set temperature (typically 50 ℃). Therefore, the effect of maturation is also affected, and at the same time, the composite fastness may be lower than in summer.
To understand the causes of the above phenomena, we need to understand the influence of moisture and temperature on adhesives. First, for the two-component polyurethane adhesive, water is the same as the main agent, polyester/polyether polyol, which can be reacted with the NCO group in the curing agent. According to calculation, 1 g of water can burn 26 ~ 32 g curing agent, of course, this is just pure reaction in terms of weight ratio, in actual work with the moisture inside the glue solution when react with curing agent to compete with the main agent. But no matter how much water in the reaction, it was definitely consumes curing agent, has not reach its reaction with the main agent of the original set of job matching, thus causing curing not thorough and residual viscosity. The viscosity and reaction activity of adhesives have a great correlation with temperature. Adhesive manufacturer gives the viscosity value of 25 ℃ temperature on rotational viscometer was used to measure, this means that the actual use, the temperature of the working environment than the above 10 degrees in the summer, when the cold winter days May 20 ℃ lower than the how. The viscosity of the adhesive is exactly the opposite of that of temperature. The same adhesives show lower viscosity when the temperature is high, the flow dispersion is good, the temperature is low and the viscosity is high, the flow adjustment is poor.
In addition, the adhesive between the two components of crosslinking curing reaction, slow reaction in low temperature, at high temperature reaction speed, which is precisely why have the cause of the aging room, speed up the curing reaction, improve production efficiency.
Against such a situation, when using a two-component polyurethane adhesive for composite can be adjusted according to the environment changes to do the following: if the air is humid, the temperature on the high side, increasing the dosage of 10% ~ 20%, the solidifying agent in order to make up for the consumption of water for its; Use dry cotton yarn or cloth to remove the condensation water from the compound and prevent it from falling into the plastic basin. To burn work adhesive solution can add a small amount of solvent dilution, and then sealed preservation, if conditions permit, may be placed on a small freezer refrigerated storage, better effect, so the next time, thawing in an airtight case, and work with the new adhesive solution mixed use.
When the winter temperature is low, the preparation of the working gel can be used to reduce the system viscosity, improve the dispersion and reduce the production of air bubbles in the gel basin at work. But do such work adhesive solution concentration will be reduced, such as do not wish to change jobs concentration, you can use a small amount of acetone instead of part of the ethyl acetate, using mixed solvent of acetone and ethyl acetate as thinner, both for the proportion of 2:8 or 3:7. In addition, the temperature of the cooked room can be set at a slightly higher temperature during the cold winter, so as to ensure that the actual temperature can meet the requirements, so as to avoid the effect of the curing effect.