How to reduce the influence of compound process on solvent residue?

- Dec 01, 2020-

The most important factor that causes peculiar smell in composite flexible packaging materials comes from the solvent residues of inks and adhesives, especially solvent residues in dry compounding. For this reason, the soft package factory can usually take the following measures to avoid or reduce the ambiguity.


1. Choose a two-component adhesive compatible with the ink, and the diluent should also meet the requirements of no peculiar smell.


2. Control the amount of glue applied. If the amount of glue is too large or the glue layer is too thick, it is not conducive to the volatilization of the solvent, resulting in an increase in the amount of solvent residue.


3. Adjust the viscosity of the adhesive according to the speed of the laminating machine, so that the solvent can dissolve the adhesive well, and the coating roller can not use the corroded plate. Use a laser roller, an electric engraving roller or a knurled roller to make the glue layer Uniform, consistent solvent volatilization.


Through testing, it is found that using a larger coating roller with a lower operating viscosity, while ensuring the coating amount, the total solvent residue combined is smaller than that of a small-size coating roller with high viscosity glue.

This reminds us that we can’t just consider the cost of the volatilized solvent and ignore the difficulty of volatilization of the solvent in the glue. Excessively high working viscosity makes the solvent release of the adhesive layer worse. The adhesive layer just coated on the film is skinned by the high temperature of the oven and the blowing of hot air so that the solvent inside the adhesive layer cannot be completely volatilized.


4. In dry compounding, the drying tunnel is usually divided into three zones, and the temperature setting is usually: zone 1 50-65℃, zone 2 60-75℃, zone 3 70-85℃, and the speed is usually 100-150 m/min, and some manufacturers have a compound speed of 180-250 m/min.


In fact, the internal air outlet design, air supply and exhaust air volume, and wind speed design of the drying oven produced by many machinery factories are not completely scientific and reasonable, or the length of the drying tunnel is insufficient, which cannot match the actual operating speed of the machine. In the case of insufficient drying capacity and discharge capacity and insufficient drying tunnel length, the excessively high compounding speed is undoubtedly prone to excessive residual solvents in the compound semi-finished products and odor.


The reasonable compounding speed should be based on the vehicle speed when the gas chromatograph test the lowest value of the solvent residue of the compound semi-finished product is the appropriate speed of the machine under the coating amount and drying conditions. The speed cannot be increased simply for the pursuit of productivity, let alone Consider how many meters the designed vehicle speed of a machine is when it leaves the factory and set the machine's operating speed.


5. The curing should be carried out after compounding. The curing time and temperature should be well controlled. The curing time is generally 36 to 48 hours, and the temperature is about 45-50°C. Incomplete curing will not only produce peculiar smell, but also seriously affect the peel strength.


At the same time, the air inlet and exhaust ducts of the curing chamber should be smooth. When conditions permit, the semi-finished product after maturation is reversely rewound and assisted by air cooling, which is also very helpful for reducing the peculiar smell of the final product.

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