For solvent-free compounding, we all recommend that customers isolate the solvent-free composite equipment, install air-conditioning, and achieve constant temperature dehumidification. This is very necessary for stabilizing product quality, but some manufacturers still do not adopt such isolation scheme.
The adverse effects of high temperature and humidity on solvent-free composite are as follows
1. Causes the deterioration of the adhesive
The a glue of solvent-free adhesive contains - NCO component, which is easy to cause side reaction with moisture in the air, and even cause the deterioration of the adhesive.
① When the dehumidification effect of the mixing system is poor, the moisture in the air will enter the rubber storage barrel and cross-linked with component A. when the situation is mild, the NCO group of the surface layer of glue will be consumed (equivalent to the decrease of the mole content of - NCO group). After automatic mixing, a small range of local drying phenomenon may occur; in serious cases, the surface will crust, which is very likely to result in The blockage of the rubber pipe leads to serious imbalance of the mixing ratio of the adhesive and the phenomenon that the glue does not dry.
② The adhesive between metering gap blocks is in direct contact with the air, especially the adhesive near the two side baffle blocks is replaced slowly. The reaction rate of solvent-free adhesive a and water molecules is much higher than that of solvent-free adhesive a and adhesive B. in other words, in the process of solvent-free compound operation, the solvent-free adhesive a reacts with the air moisture first, and the reaction exothermic accelerates the cross-linking of the adhesive itself The viscosity of the adhesive increases with reaction. The adverse effects are as follows: first, the adhesive increases, poor fluidity, coating amount decreases, affecting the amount of glue; second, water molecules consume excessive amount of - NCO in glue a, resulting in dry or unqualified peel strength. Solvent free one component adhesive is also NCO component and has the same adverse effect.
The above phenomenon is most obvious in the vicinity of the rubber block, and the most direct performance is that the glue liquor turns white and bubbles are produced during the startup process. Treatment measures: first, set the initial glue adding liquid level at a low level, so as to remove the glue as far as possible during the start-up process, so as to keep the glue liquid near the rubber block fresh; second, the displacement of the glue adding nozzle should be close to the rubber block as far as possible, so as to avoid the accumulation of old glue near the rubber block; third, the relative humidity in the environment should be controlled below 70%.
2. More prone to appearance of white spots
In addition to the adverse effects caused by the increase of residual solvents in the printing film, the high temperature and high humidity environment also has a negative impact on the production of white spots during solvent-free composite operation. The main reason is that water molecules react with the - NCO substrate in adhesive a to generate a large amount of CO2. If these gases cannot penetrate between the two films before the glue loses its fluidity, it will be completely solidified After that, it will show the appearance of white spots and bubbles. Of course, the better the barrier of the two-layer material, the more likely this appearance of white bubble phenomenon.

There are two main sources of influence: one is the adsorption of water molecules on the surface of materials. The polarity of the surface of materials commonly used by us is polar materials or after corona treatment, the adsorption capacity of water molecules will also increase. This part of influence is not only related to the relative humidity of solvent-free composite operation environment, but also needs to be traced back to the production and storage environment of raw materials; the other is to get off the machine There will be a certain amount of air between the two composite membranes. Obviously, the higher the relative humidity in the production environment, the more water molecules will be sandwiched in the air bubble between the two layers, and the more CO2 gas generated after reaction with curing agent, the greater the impact degree. At 20 ℃ 65% RH, the absolute humidity in the air is about 11g / m3; at 40 ℃ 85% RH, the absolute humidity in the air is about 43g / m3; assuming that all the moisture reacts with - NCO, the volume of CO2 generated is doubled, which undoubtedly increases the difficulty of eliminating white spots during curing.

3. Influence on dimensional stability of nylon membrane composite
Nylon film is a kind of water absorbent material. After moisture absorption, the size of nylon film is extended, and the tensile strength is reduced, so the printing film is easier to be elongated under the condition of composite tension.
At present, most solventless laminating machines are single station, so it is necessary to stop the machine for changing and unloading coils. In this way, when the nylon film in the channel is exposed to the air for a long time, the hygroscopic elongation is large; when it is running at a low speed, it also has the same effect; thus, the moisture absorption deformation of nylon film is not consistent with the normal production machine speed at shutdown, low speed and normal production machine speed, thus causing cursor If the distance is not consistent, it will affect the tracking and cutting accuracy of bags, and some will cause waste or shutdown.
4. Moisture proof is needed for nylon composite film at room temperature
In summer, many manufacturers adopt the way of natural aging at room temperature without entering the curing chamber. However, due to the moisture absorption characteristics of nylon membrane, the nylon film on the edge contacts with air for a long time, and the reaction rate of water molecules with adhesive a is much higher than that of adhesive a and adhesive B, which will reduce the phenomenon of insufficient crosslinking or slight non drying of the edge composite membrane. Therefore, for nylon composite membrane, if it is natural aging at room temperature, wrap a layer of moisture-proof film on the film roll to avoid moisture absorption reaction of the edge nylon film.
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