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Some notices for using glue in seasonal change

Some notices for using glue in seasonal change

The good composite effect of two-component polyurethane adhesive is related to many factors, and the change of working environment is also an important factor. That is to say, with the change of seasonal climate, in order to achieve the ideal compound effect, it is necessary to make some fine adjustments to the technology of glue use.


In a simple way, the seasonal climate change that affects the compound is also the two major changes in the humidity and temperature of the environment. In the spring, summer and two seasons, especially in the Meiyu season, the relative humidity of the air is larger, even the air is saturated and the air is dry and the humidity is small in the two quarter of autumn and winter; as far as the gas temperature is concerned, the summer is much higher than the winter. The maximum difference between the two is nearly 30~40 degrees centigrade. If you don't pay attention to these differences, it is likely to produce the following problems when the air is mixed: when the air is wet, the glue is often cured, that is, dry, the residual viscosity is large, and even when the composite film is stripped, the phenomenon of drawing is observed, especially when the thin film itself has a large moisture absorption, such as nylon. When the membrane is combined, it is easier to produce this phenomenon; secondly, the moist air will be condensed on the reticulated roll, and then the water is brought into the rubber basin. As the time goes on, the glue gradually becomes chaotic and white, so that the adhesion is lost, and the hot and hot high temperature also makes the retention of the glue more difficult and matches well. If the working glue is not used up for the same day, it will often lump and form gel (jelly gel) after overnight. In contrast, during the cold winter, the working glue that has not been used up before the night still maintains a good transparent fluidity, even if it does not have to be added into the new working glue in batch, and can be used directly to the machine. On the other hand, in the winter with low temperature, the glue becomes sticky and levelling down. When the composite machine runs at a high speed, a large number of bubbles are easily accumulated on the surface of the glue and the edge of the reticulated roll. At this time, it may cause the vacuolation, the amount of glue is insufficient, and the compound fastness is affected. At the same time, the appearance of the composite film will become worse because of the poor dispersing performance, such as the flow pattern of the glue. It is more obvious, sometimes in the form of orange peel. When it is used for compound aluminum foil or aluminum coating, it is easier to form white spots and spots if the printing surface has large area of white ink or light color ink. In addition, because of low temperature in winter, the temperature of the curing room is very different from the ambient temperature, if the insulation measures are not done enough, The heat loss rate is much faster than that of high temperature in summer, which often causes the temperature in the curing room to be below the set temperature (usually 50 degrees Celsius). Therefore, the effect of ripening is also affected. Under the same curing time, the composite fastness may be lower than that in summer.


The reason for the above phenomena is to understand the influence of moisture and temperature on the adhesive. First, for two component polyurethane adhesives, the water can react with the NCO group in the curing agent, like polyester / polyether polyols. It is estimated that the water of 1G can consume 26 to 32g of the curing agent. Of course, this is the pure reaction weight ratio. In practice, the water in the mixture in the mixture is competing with the main agent when it reacts with the curing agent. However, no matter how much water is involved in the reaction, it is no doubt that it consumes the curing agent so that the amount of the reaction to the main agent is less than the original work ratio, and thus causes the uncomplete and residual viscosity of the curing. The viscosity and reactivity of adhesives are strongly related to temperature. The viscosity values given by the adhesives are measured at 25 degrees centigrade at the standard temperature by a rotating viscometer, which means that the temperature of the working environment is more than 10 higher in summer than in the winter when it is used in the winter, and it may be more than 20 degrees centigrade in winter. The viscosity of the glue is exactly the opposite of the temperature, that is, the viscosity of the same glue is lower when the temperature is high, the flow and dispersion performance is good, the temperature is low, the viscosity is high, and the flow is poor. In addition, the crosslinking curing reaction between the two components of the adhesive has a slow reaction speed at low temperature and high reaction speed when the temperature is high. This is precisely why the curing room is required (quickening the curing rate and improving the production efficiency).


In this case, the following adjustments can be made in the use of a double component polyurethane adhesive according to the environmental changes: if the air is wet and the temperature is high, the dosage of the curing agent is increased by 10% to 20% to make up for the consumption of water. Drop, prevent it from falling into the rubber basin; use a small amount of solvent to add a small amount of solvent to dilute it, and then seal it. If conditions permit, it can be kept in a small refrigerator, so that the effect is better, the next reoccupy, in the closed condition thawing, and mixed with the new working glue mixture. When the temperature is low in winter, some solvent can be properly added to reduce the viscosity of the system, improve the dispersion of the flow, and reduce the production of bubbles in the working bowl. However, the concentration of the working glue will be reduced. If the working concentration is not changed, a small amount of acetone can be used to replace the ethyl acetate, that is, the mixture of acetone and ethyl acetate can be used as a diluent, the proportion of which is 2:8 or 3:7. In addition, the temperature setting of the curing room can be adjusted slightly at low temperature in winter to ensure that the actual temperature can meet the requirements, so as to avoid affecting the curing effect.


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