Precautions for composite processing under the hot

Precautions for composite processing under high temperature and high humidity environment

when the environment clearly shows the state of high temperature and high humidity, dry composite processing of thin films is carried out. A considerable number of composite color printing manufacturers have not paid attention to this potential change, and naturally there are many quality problems in the process of color printing composite. Then, in high temperature and high humidity weather, it shall not be greater than 0.5% of the load indication; What should we pay attention to in compound processing

first, high temperature and high humidity weather has an impact on dry compounding of a hydrated magnesium aluminosilicate nonmetallic mineral

then, most of the dry compounding uses two liquid reactive polyester and polyurethane adhesives. However, its performance is generally different from the selection of isocyanates, the molecular structure of polyester polyols, the degree of polymerization, the maintenance and inspection methods of pendulum impact testing machine, functional groups and mixing ratio. The two liquid reaction is a cross-linking reaction between the main agent containing hydroxyl at the end of the polymer and the curing agent containing isocyanate in the molecular structure to form polyurethane with high compactness. The curing agent containing isourethane group has strong activity, can react with substances containing hydroxyl and amino groups, and the reaction rate is more than 10 times faster than that with polymer polyester and polyurethane main agent. Such as methanol, ethanol, water and other amines. This is also the reason why most polyurethane adhesive manufacturers restrict water and esters in the instructions. In the process of dry compounding, the influence of high humidity on compounding is multifaceted, such as:

1 The adhesive is not hardened enough and remains sticky after composite curing, resulting in the reduction of peel strength

2. The optical coupling speed slows down, and the initial adhesion decreases, which is easy to cause the foaming phenomenon of the composite film

3. High temperature cooking film bag, the bag breaking phenomenon increases in the process of high temperature cooking

4. The solvent volatilization is not complete, and the peculiar smell of the composite membrane bag increases

5. When compounding, the foam phenomenon of the plastic disk increases, and the composite film is easy to have spots, white spots and crystal points

6. The composite membrane feels hard and brittle, and the phenomenon increases

II. Matters needing attention in high temperature and high humidity weather

through the above understanding, we have a general understanding of the impact of high temperature and high humidity weather on dry compounding, so in the process of dry compounding, we can carry out targeted control in each process:

1 All kinds of films must be controlled, such as nylon, cellophane and other moisture-absorbing films. When nylon is wrinkled, it may have absorbed moisture. Therefore, before compounding, wrap the film with metal aluminum foil or barrier film and put it on the shelf in a dry environment. Do not stack it directly on the ground

2. The amount of water and alcohol in ethyl acetate must be controlled. Try to buy Solvents from formal channels and store them in a closed manner. To detect the moisture content of ethyl acetate, one method is to mix half ethyl acetate and half toluene to detect the moisture content of ethyl acetate. If there are water drops and whitening at the bottom after mixing, it indicates that the moisture content of ethyl acetate is too high. In addition, a rapid moisture indicator can also be used to detect the moisture content

3. The compound environment must be controlled. Place an exhaust fan indoors to strengthen indoor air circulation, but be careful not to blow against the compound machine. Check whether there are water drops on the guide roller, compound roller and roller, and wipe it with a dry towel

4. When preparing the adhesive, the dosage should be appropriately reduced, and it should be used as it is prepared, and it should not be placed too long. At the same time, when preparing, ensure the amount of space stretching under the curing agent, make it close to the upper limit as far as possible, or appropriately increase the curing dosage (%), and increase the degree of cross-linking between the main agent and the curing agent

5. Changing the process parameters of the compounding machine, at present, the air outlet of most domestic compounding machines is small. During compounding, the air inlet speed is higher than the air outlet speed, which makes the formation of high pressure in the drying channel, which is easy to slow down the evaporation speed of the solvent and increase the residual solvent of the film after compounding. Therefore, increase the air outlet pipe. In addition, if the air outlet pipe is long, install the induced draft fan directly at the intersection of the air outlet pipe. Generally, imported composite machines have this device. In this way, the air outlet speed is greater than the wind shelter speed, so that a low pressure is formed in the drying channel, which is suitable for solvent volatilization and reduces residual solvent. In addition, if the temperature in the drying channel can be increased, it should be increased as much as possible (note that the first zone should not be too high, that is, into the film zone)

6. When compounding, always pay attention to the scraper and guide roller near the glue trough to see if there are water drops, and reduce the speed at the same time, because the speed is too fast, the solvent volatilization speed in the glue residue is accelerated, and the local temperature near the glue residue is too low, which directly causes water vapor condensation

when the factors in the above composite processes are controlled, the probability of quality problems in the composite process will be greatly reduced, thus avoiding some unnecessary losses and waste