Coating compound common faults and solutions

There are many problems in the coating compounding process. This article introduces some troubleshooting solutions through examples.

Peeling strength difference causes:

1. The surface tension of the substrate is low, the surface treatment effect is poor, and the surface tension is not uniform, which affects the adhesion of the melt extrusion resin on the surface, resulting in low peel strength and uneven peel strength.

2. The surface of the substrate is not clean, and dirt, grease, and other contaminants are adhered, resulting in a decrease in the adhesive strength between the molten resin and the surface of the film.

3. Resin melt index (MI) is low. The higher the melt index of a typical resin, the better its fluidity and the greater the adhesion. Therefore, in the extrusion composite process, if the resin used has a low melt index and poor fusibility, it cannot bond well with the substrate to be coated, resulting in a decrease in peel strength.

4. Adjuvants (especially slip agents) in the resin can have an adverse effect on the peel strength of the extruded composite film.

5. The barrel temperature and the die temperature of the extruder are too low, and the resin is poorly plasticized. The molten resin flowing from the die cannot be well compounded with the coated substrate and the peel strength is reduced.

6. The low resin temperature and insufficient oxidation of the resin surface are not conducive to the wetting and penetration of the molten resin on the coated substrate, thereby affecting the peel strength of the extruded composite film.

7. In the extrusion process, the size of the air gap also has a great influence on the peel strength of the extruded composite film. The air gap is too small, the surface of the resin is not sufficiently oxidized, and the composite strength is deteriorated; the air gap is too large, the heat loss of the molten resin is large, and the temperature at the time of compounding is too low, and the peel strength may also be reduced.

8. The composite pressure is small, the adhesion between the molten resin and the substrate is not tight, and the peeling fastness is reduced.

9. The surface temperature of the cooling steel roller is too high, the cooling setting effect is not good, will reduce the composite fastness; if the surface temperature of the cooling steel roller is too low, the cooling rate is too fast, it will cause the decrease of the composite strength.

10. The thickness of the extruded composite layer is too thin, resulting in reduced peel strength.

11. Under the condition that the speed of the main motor of the extrusion is constant, the faster the composite line speed, the thinner the composite layer, the faster the temperature drop of the molten resin, the lower the adhesion force with the substrate, and the decrease of the peel strength.

12. The type of primer (AC agent) is improper or of poor quality.

13. The primer did not dry enough, leaving part of the solvent or water, causing the peel strength of the extruded composite film to decrease.

Solution:

1. Replace the coated substrate or re-corona treatment on the substrate to ensure that the surface tension is 4.0 x 10-2N/m or more and the corona treatment effect is uniform.

2. Clean the substrate surface or replace the substrate to ensure that the surface of the coated substrate is clean and clean.

3. Replace resin with appropriate melt index.

4. Extrusion-coated LDPE resins with or without a small amount of slip agent are used in the extrusion compounding process.

5. According to the production conditions, the temperature of each section of the extruder is adjusted and controlled to ensure the composite strength.

6. Appropriately increase the resin temperature to fully oxidize the resin and improve its wettability and adhesion to the substrate surface.

7. Adjust the size of the air gap according to the actual situation.

8. Adjust the complex pressure according to the specific situation.

9. The temperature of the surface of the cooling steel roller is controlled below 60c.

10. Appropriately increase the thickness of the extrusion coating to increase the peel strength.

11. According to the actual situation, control the production speed.

12. Replace the appropriate type of primer with good quality to ensure strong adhesion.

13. Properly reduce the compound line speed, increase the drying temperature and ventilation, ensure that the primer is fully dried, and increase the peel strength.