Causes and Elimination of Odor in Soft Packaging Bags

With the wide application of composite flexible packaging in the food industry, the problem of odor in plastic packaging bags has attracted more and more attention. This odor can lead to skewing of the packaged food, and even affect the quality of food, pollute the environment and endanger consumers. Health. The country has also attached increasing importance to the problem of odor problems in flexible packaging. The relevant standards have been gradually standardized. It not only requires the food itself to comply with international standards, but also requires that flexible packaging from raw materials to finished products must be in line with international standards.

The odor produced by the soft packaging is mainly affected by the ink solvent, plastic film, and composite technology. The following sections will be analyzed one by one.

Ink solvent effects

In gravure printing, mixed solvents are often used in the ink in order to improve the printability of the ink, increase the ink transfer rate, and make the print color more saturated and real. After the ink is transferred to the film, the solvent on the surface evaporates, and the ink layer quickly crusts, hindering the volatilization of the solvent in the ink layer, resulting in the solvent residue in the printed matter, resulting in an odor, and the residual solvent of the ink during surface printing is higher than that in the printing process. many. The residual amount of this solvent can be measured with a special instrument to facilitate quantitative management.

There are several sources of excessive residual solvents in the ink.

(1) The affinity between the solvent molecules in the ink and the binder resin molecules is too large, which leads to an increase in residual problems. Therefore, when using a new ink, it must be handled according to the characteristics of the solvent.

(2) The ink uses a mixed solvent. The volatilization rate of different solvents is different. If they are not properly controlled, the slow-evaporating solvent will stay in the inner layer of the ink film, resulting in residue.

(3) The ink is not dry enough. In this regard, the following measures can be taken: to reduce the amount of slow-drying solvents; to increase the drying temperature, increase the amount of air blowing, and to use double-bake warming equipment; printing speed is too fast to ensure complete volatilization of solvents, a large amount of residues and odors, Therefore, the speed can be properly reduced; the humidity in the printing shop should not be too large, otherwise the ink film will absorb the moisture in the air, so that the solvent in the ink cannot be fully volatilized, and the residual odor is generally required to have a humidity of 65% to 75% in the workshop. Between the temperature is appropriate at 25 °C; gravure cylinder using electronic engraving or laser engraving plate, do not try to manually etched version, to avoid the network site is too deep, uneven network, especially for large area network requirements should be more stringent, because the network point Non-uniformity, it is not easy to dry when printing; the winding tension during printing cannot be too large, otherwise it is not conducive to the volatilization of residual solvents; the printed matter after winding should be placed in a dry and ventilated place for more than 24 hours before compounding to reduce the residual solvent .

Effect of film material

Different film materials have different absorption properties for solvents. For example, polyester (PE film) is a non-absorbent film with less residual solvents; polypropylene film tends to retain hydrocarbon solvents; nylon-based water-absorbing films tend to retain alcohol. Solvents. Therefore, as far as possible, the film produced by corona treatment should be selected as soon as possible to prevent the moisture and corona treatment of the film from being in place. During the printing and drying process, the water in the film is analyzed and the volatilization of the solvent is affected. For materials that absorb moisture easily, keep them before and after printing.

The impact of the composite process

Improper operation of the compounding process and loss of control of the temperature will cause the plastic bags to have different defects. Usually, the following measures can be taken to avoid or reduce the difference.

(1) Use two-component adhesives that are compatible with the ink. Diluent should also be odor-free.

(2) Control the amount of glue applied, if the amount of glue applied is too large or the glue layer is too thick, it is not conducive to the volatilization of the solvent, which leads to an increase in the amount of residual solvent.

(3) According to the speed of the composite machine, the viscosity of the adhesive is properly formulated so that the solvent can dissolve the adhesive well, and the adhesive cannot have glue particles, so that the coating is uniform and the solvent is volatilized uniformly.

(4) When compounding, the section temperature of the oven should be set according to the machine speed. When the machine speed is 80 meters/minute, the section temperature is generally about 70 degrees Celsius, 80 degrees Celsius, and 90 degrees Celsius, and it should be added. The amount of ventilation in the large oven drains the odor on the plastic package.

(5) Curing after compounding, curing time and temperature should be controlled well, the curing time is generally 24 to 28 hours, and the temperature is about 45°C. Incomplete curing not only produces odor, but also seriously affects peel strength. At the same time, the inlet and outlet ducts of the curing chamber should be smooth.

There are many reasons for the odor produced in the packaging bag. Here, we only summarize the main reasons. We hope that everyone will observe it in practice, discover problems, and earnestly sum up experiences.