What should I do if the composite packaging bag has small spots, fog, wavy fish scales, and mushroom cloud patterns?

Many plastic composite packaging bags require high transparency and use large areas of blank base films BOPP and CPP composite. However, in the composite process, sometimes the transparency of plastic composite flexible packaging is poor or decreases, such as the finished product showing a "foggy" appearance, with "small spots", "wavy fish scales", "silk lines", "mushroom clouds", "water drop splashing", etc., affecting the transparency of the composite product, and in severe cases, even causing the composite product to be scrapped.

Shunxingyuan Packaging, a professional flexible packaging manufacturer, now analyzes the reasons for this phenomenon.

1. "Foggy" phenomenon and countermeasures

1. Poor transparency of the composite material or printing substrate

Before compounding, the film material is generally tested.

The detection method is: Take a small piece of film and observe it through light. The film material should be smooth, without small spots, no sticking, no unevenness, and no hazy impurities.

Therefore, only by choosing high-quality materials from regular manufacturers can good finished products be produced.

2. Influence of adhesive

If the adhesive is too dark, with a deep yellow or yellowish-red color, after drying, this darker part will remain on the film. Therefore, when the composite product requires high transparency, a light yellow or even colorless adhesive should be used.

The correct selection of two-component adhesives can reduce the probability of the composite product showing a "foggy" appearance, or even eliminate the "foggy" phenomenon.

3. Operational errors or insufficient drying temperature

Operational errors or insufficient drying temperature can also produce a "foggy" phenomenon.

For example, the amount of adhesive is uneven, thicker on one side and thinner on the other. Therefore, uniform coating is crucial in the dry lamination process.

2. "Small spots" phenomenon and countermeasures

1. Dust and other particles mixed in the adhesive

There is too much dust in the air of the workshop, and there is also dust in the hot air blown from the drying tunnel after applying the adhesive. The dust sticks to the adhesive layer, and when compounded, it is sandwiched between the two base films, causing the composite product to be opaque.

Solution:

Filter the adhesive with a 180-mesh metal wire mesh to remove insoluble particles from the adhesive. At the same time, attention should be paid to the cleanliness of the workshop, keeping the ground clean and dust-free.

In dry lamination, the glue bucket and glue tray must be cleaned before the end of the shift. Especially in summer, the indoor temperature is high and the drying is fast. Before the end of each shift, the remaining adhesive should be poured into the bucket and sealed separately.

In addition, a high-mesh filter screen or other filter material should be used at the air intake of the drying tunnel to remove dust from the hot air.

Two-component reactive adhesives are easily affected by temperature and become white and cloudy. "Cloudy white" adhesives cannot be used anymore, otherwise, uneven distribution of the adhesive layer will occur, resulting in an increase in "small spots".

2. The quality of the base film and composite film does not meet the requirements

If the OPP heat-sealing material is yellow and old, it should be carefully checked.

First, the surface tension value should be tested. The surface tension of BOPP needs to reach 38 mN/m, and the surface tension of PET needs to reach 50 mN/m. Low surface tension will lead to poor wetting effect on the material surface, uneven coating of the adhesive, resulting in gaps, and small spots in the finished composite product.

Therefore, films that do not meet the surface tension requirements must be processed before use.

Secondly, use a magnifying glass to check the smoothness of the base film and composite film. It should be smooth without any unevenness. If the surface of the material is uneven and the depth is inconsistent, it cannot be completely bonded to the adhesive film after being pressed by the hot press roller, resulting in "small spots". Therefore, material selection is crucial.

3. Poor flatness of the adhesive roller, insufficient fluidity of the adhesive, and poor leveling will lead to "small spots"

The adhesive roller should be fine and smooth, preferably made of silicone rubber.

Good adhesive fluidity, excellent leveling, and uniform coating can reduce the probability of "small spots", and the transparency of the composite product is also improved.

3. "Fish scales" phenomenon and countermeasures

1. The PE film itself shows a "fish scale" phenomenon, which appears in the blank area after compounding, causing a decrease in composite transparency. The solution is to replace the material.

2. Accidental shutdown during production, the adhesive pressure roller is not relaxed in time, or the adhesive roller is not separated from the adhesive, and the hot press roller and the hot drum are not separated.

Generally, wavy irregular transverse indentations will appear in the blank area under 30 minutes of tight pressure, resulting in poor transparency.

Therefore, in a non-working state, the adhesive roller and the gravure roller should be isolated and cleaned, the hot press roller and the hot drum should be separated, and the power of the hot drum should be turned off.

4. "Mushroom cloud", "water drop splashing", "silk lines", etc. causes and countermeasures

1. Poor material itself, irregular patterns appear

Just replace it.

2. Influence of adhesive and drying tunnel

When entering the drying tunnel, the temperature is too high and the drying speed is too fast, causing the solvent on the surface of the adhesive layer to evaporate rapidly, forming a skin. When the heat penetrates into the interior of the adhesive layer, the solvent under the film vaporizes, breaking through the film surface, forming ring-shaped structures similar to volcanic craters, like "mushroom clouds" distributed on the adhesive film surface, leading to uneven and opaque adhesive layers.

Therefore, the drying tunnel temperature should gradually increase from low to high, allowing the solvent to evaporate completely from the inside out in an orderly and uniform manner, leaving no peculiar smell.

In addition, solvents with different boiling points can be mixed and used. In this way, during heat evaporation, high-boiling-point solvents on the surface of the adhesive layer will remain for a longer time, preventing the surface film from skinning. However, it must be ensured that the residual solvent amount meets the requirements and there are no unpleasant odors or peculiar smells.

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