Easy to appear in the composite process of quality problems and solutions

Composite is an important process in the production and processing of flexible packaging, its common failures are: bubbles, low composite fastness, finished wrinkles and curled edges, composite products stretch or shrinkage. This section will focus on the analysis of wrinkles, crimping causes and methods of elimination.

01 Wrinkle phenomenon
In the dry composite failure in this phenomenon occupies a considerable proportion of the failure directly affects the quality of the finished bag.
The main reasons for the failure are as follows:

Composite materials or printing substrate itself is of poor quality, thickness deviation, film roll due to uneven winding tension and one end of the loose end of the tight. If the difference in tension between the two ends of the film roll is large, on the machine, the film up and down, left and right swing amplitude is also relatively large, it may result in wrinkles and curled edges.

Because when the material enters between the hot drum and the hot press roller, it can't be horizontal with the hot press roller, so it can't be extruded flat, resulting in wrinkled composite products and diagonal stripes, which leads to the scrapping of the products. When the composite material is PE or CPP, if the thickness deviation is more than 10μm, it is also easy to wrinkle, at this time, we can appropriately increase the tension of the composite material, as far as possible, so that it can be extruded with the hot rollers into a horizontal state.

However, it should be noted that the tension should be appropriate, the tension is too large and easy to make the composite material elongation, resulting in the bag mouth to the inward curling. If the composite material thickness deviation is too large, really can not be used, should be dealt with separately.

02 Composite white spots
Due to poor ink coverage produced by the white point: for composite white ink, when the ink absorbs the ethyl ester but volatilisation is not caused by the white point, can be used to improve the drying capacity of the method; if there is still a white point, the general solution is to improve the white ink coverage, such as checking the fineness of the white ink, because of the fineness of grinding good ink coverage rate is strong.

Adhesive coating uneven white spots: in the ink layer coated with glue, due to the underlying ink will absorb solvents, surface tension is smaller than the substrate, the levelling is inevitably inferior to the light film coated with glue, glue recesses and aluminium surface or aluminium foil is not close to the surface of the close fit, reflecting the light through the bubbles when encountered in the cross-section, it will be refracted or diffusely reflective, the formation of white spots.

The solution can be used to smooth the coating with a levelling roller, or increase the amount of coating.

03Composite bubbles

Composite bubbles are generated in the following situations and the corresponding methods:

1. Poor film wetting, should increase the concentration of glue and coating amount, MST, KPT surface is not easy to wet, easy to produce bubbles, especially in winter. Bubbles on the ink, use the method of increasing the amount of glue to remove.

2. Bumping and blistering on the surface of ink, the laminating temperature and pressure of laminating film should be increased.

3. The ink on the surface of the glue coating amount is small, should increase the composite roller pressure paste time and the use of smooth rollers, film preheating is sufficient, reduce the composite speed, select the wetting of good glue and the correct choice of ink.

4. The additives in the film (lubricant, antistatic agent) are penetrated by the glue, the glue with high molecular weight and rapid curing should be used, the concentration of the glue should be increased, the temperature of the oven should be increased to fully make the glue dry, and the film which has been stored for more than 3 months should not be used because the corona treatment has been lost.

5. Low temperature in winter, the binder on the film and ink transfer, wetting adhesion effect is not good, so the operation place to maintain a certain temperature.

6. Drying temperature is too high, the occurrence of rubber blistering or skin crust, not dry inside, should adjust the rubber drying temperature.

7. Composite roll film between the entrainment into the air, should improve the temperature of the composite roll, reduce the composite angle (film thick, hard, easy to produce air bubbles).

8. Due to the high barrier film, the CO2 gas produced during the curing of the glue, residual in the composite film, unprinted at the bubble, should increase the amount of curing agent, so that the glue in the drying of the curing.

9. The gum in the ethyl ester of lipoic acid is a good solvent for the ink binder, the gum soluble in ink, only in the ink on the bubbles, should avoid water infiltration into the gum and improve the gum drying temperature, reduce the solubility of the ink.

04 Poor peel strength

Peel strength is poor, is due to incomplete curing, or the amount of adhesive coating is too small, or the ink used with the adhesive does not match the situation and so on, although the curing has been completed, but the two layers of the composite film due to insufficient bonding strength to make the peeling force is reduced.

Factors affecting the reduction of peel strength of the final composite:

On the glue coating amount is too small, binder ratio is not appropriate, glue in the storage of deterioration, glue mixed with water and alcohol, etc., the film in the precipitation of additives, drying or maturation process is not in place and so on.

Help us to improve the composite peel strength of the poor problem of the method:

Pay attention to the proper storage of the glue for a maximum of 1 year (sealed tin cans);

Prevent foreign matter from entering the glue, especially water, alcohol and other easy to cause glue failure, double liquid type must be used with the allocation;

Already whitened glue can not be used. Can also be appropriate to increase the amount of glue coating;

Increase the drying temperature wind volume, reduce the composite speed. Secondary treatment of the film surface to improve the surface tension;

Reduce the use of additives in the film composite surface.

05 heat sealing bad

Composite bag heat sealing bad performance and its causes are basically the following cases:

1, poor heat sealing strength. The main causes of this phenomenon are binder curing is not complete or heat sealing temperature is too low. Optimise the maturation process or improve the sealing knife temperature can improve the problem.

2, heat sealing surface delamination, curling. The main reason for this phenomenon is that the binder is not cured. Adjusting the curing time or curing agent content can improve the problem.

3, Poor opening/poor opening of the inner film. The cause of this phenomenon is that the opening agent is too little, the binder (modifier) is too much, and the surface of the film is sticky or greasy. This problem can be improved by increasing the amount of opening agent, adjusting the amount of modifier, and avoiding secondary contamination of the film surface.