I. Effect of high temperature and high humidity weather on dry composite
We all know that most of the dry compounding is a two-liquid reaction type polyester or polyurethane type binder. However, its performance generally differs depending on the choice of isocyanate, the molecular structure of the polyester polyol, the degree of polymerization, the functional group, and the mixing ratio. The two-liquid reaction is a cross-linking reaction between a main component containing a hydroxyl group component at a terminal portion of the polymer and a curing agent containing an isocyanate group in the molecular structure, and is combined into a polyurethane having a high degree of tightness. The curing agent containing an isocyanate group component has a strong activity and reacts with a substance having a hydroxyl group or an amine group, and the reaction rate is more than 10 times faster than that of the polymer polyester or the polyurethane main agent. Such as methanol, ethanol, water and other amines. This is why most polyurethane adhesive manufacturers have restrictions on water, alcohols and amines in the instructions.
Then in the dry compounding process, the effect of the composite on the high humidity is multifaceted, such as:
1. The adhesive is insufficiently hardened, and remains sticky after the composite curing, resulting in a decrease in peel strength;
2. The crosslinking speed is slowed down, and the initial adhesive force of the adhesive is lowered, which easily causes the composite film to tunnel;
3. The high temperature cooking film bag increases the bag breaking phenomenon during the high temperature cooking process;
4, the solvent volatilization is not complete, the odor of the composite film bag increases;
5. When the composite is compounded, the foam phenomenon increases, and the composite film is prone to spots, white spots and crystal spots;
6, the composite film feels hard and brittle phenomenon.
Second, the high temperature and high humidity weather should pay attention to matters.
Through the above understanding, we have a general understanding of the effects of high temperature and high humidity weather on dry recombination, then in the dry recombination process we carry out targeted control in each process:
1, we must control a variety of films, such as nylon, cellophane and other moisture-absorbing film, when the nylon wrinkles, it may have absorbed moisture, so in the absence of composite, with metal foil or good barrier properties The film is wrapped in a dry environment on the shelf and remembered to be stacked directly on the ground.
2. We must control the amount of water, alcohol and amine in the solvent used, and try to buy the solvent in the regular channel.
3. We must control the composite environment, place exhaust fans indoors, and strengthen indoor air circulation, but be careful not to blow against the compound machine, and check the guide rolls, composite rolls and net rolls for waterless beads at any time, and wipe them with a dry towel. Again.
4. When disposing the adhesive, the amount of the compound is appropriately reduced, and it should not be placed too long when it is used. When the configuration is made, the amount of the curing agent is ensured so as to be as close as possible to the upper limit, and the curing dose can be appropriately increased (5) ~10%) increase the degree of crosslinking between the main agent and the curing agent.
5. Change the process parameters of the compound machine. At present, most of the composite machines in China have smaller air outlets. When compounding, the air inlet speed is higher than the air outlet speed, which causes high air pressure to form in the drying tunnel, causing the solvent to evaporate at a slower rate. The residual solvent of the film is increased. Therefore, the outlet pipe is increased. In addition, if the outlet pipe is long, an induced draft fan should be installed at the outlet of the outlet, and the general imported composite machine has this device. In this way, the outlet air velocity is greater than the inlet air velocity, so that a low air pressure is formed in the drying tunnel, which is suitable for solvent evaporation and reduction of residual solvent. In addition, the temperature in the drying tunnel can be increased as much as possible (note that the first zone should not be too high - that is, the film entering zone).
6. When compounding, pay attention to the scraper and guide roller near the glue tank at any time, and produce waterless beads, and at the same time reduce the speed of the vehicle and reduce the residual of solvent. The high temperature and high humidity weather will easily accelerate the solvent evaporation rate in the glue tank, and the vicinity of the glue tank If the temperature is too low, it will easily cause water vapor to condense.