In short, the climate change that affects the composite season is also the change of two major indexes of environment humidity and temperature: specifically, in spring and summer, especially in rainy season, the relative humidity of air is large, and even can reach saturation, while in autumn and winter, the air is dry and the humidity is small; in terms of temperature, summer is much higher than winter, and the maximum difference between the two can be close to 30-40 ℃ (in the South Region For example). If we don't pay attention to these differences, we may encounter the following problems in the preparation: when the air is wet, the glue often can't be completely cured, that is, it can't be completely dried, the residual viscosity is large and serious, and even the wire drawing phenomenon will occur when the composite film is peeled off, especially when the film itself has strong moisture absorption, for example, when nylon film is used for composite, this phenomenon is simpler; secondly, moisture The wet air will condense on the rubber roller, thus bringing water into the rubber basin. Over time, the glue will gradually become confused and white, thus losing the bonding effect. High temperature and humidity also make the glue difficult to preserve. If the working gel is not used up on the same day, it tends to turn white and agglomerate into a gel (jelly) gel. On the contrary, when it is cold in winter, the previously unused working adhesive will adhere to excellent transparent fluidity overnight, and can even be used directly on the machine without batch mixing in the newly prepared working adhesive. On the other hand, when the temperature is low in winter, the glue will thicken and the fluidity will decrease. When the laminating machine is running at high speed, a large number of bubbles simply accumulate on the glue surface and the edge of the upper glue anilox roll. At this time, there may be bubble transfer. Due to the insufficient amount of glue, the composite fastness may be affected. At the same time, due to the poor smoothness and relaxation of the composite film, the appearance of the composite film is also poor. For example, the flow pattern of glue is relatively obvious, sometimes in the form of orange peel. When it is used for lamination, if there is a large area of white ink or light color ink on the printing surface, small white spots and spots are more likely to form when the aluminum foil or aluminum coating is combined; otherwise, due to the low temperature in winter, the temperature of the curing room is very different from the external environment temperature. If the insulation method is not in place, the heat loss rate is far faster than that in high-temperature summer, which often makes the temperature in the curing room not reach the set temperature (generally 50 ℃). Therefore, ripening effect is also affected to some extent. In the same mature period, the composite fastness may be lower than that in summer.
In order to analyze the causes of the above phenomena, it is necessary to understand the influence of humidity and temperature on the adhesive. Firstly, the moisture content of two-component polyurethane adhesive is the same as that of polyester / polyether polyol, which can react with NCO group in curing agent. It is estimated that 1 g of water can consume 26-32 g of curing agent. Of course, this is the pure response component ratio. In fact, when the water in the working adhesive reacts with the curing agent, it competes with the main agent. However, no matter how much water is involved in the reaction, the curing agent will undoubtedly be consumed, so that the reaction amount between the curing agent and the main agent can not reach the original set working ratio, thus forming incomplete curing and residual viscosity. However, the viscosity and reactivity of adhesives are closely related to temperature. The viscosity value given by the adhesive manufacturer is measured with a rotary viscometer at a standard temperature of 25 ℃, which means that in practice, the temperature of the working environment in summer is more than 10 ℃ higher than that in summer, while the temperature of the working environment in winter may be 20 ℃ lower than that in cold weather. The viscosity of the glue is opposite to the temperature, that is, when the temperature is high, the viscosity of the same glue is low, the flow relaxation is good, the viscosity is high and the flow is good when the temperature is low.
The above is an introduction to the influence of seasonal climate on the glue in the two-component dispenser. For more information, please visit the official website http://emikasarl.com