Small Pockmarks, Fog, Wavy Fish Scales, Mushroom Umbrella Cloud, How To Deal With It?

"Small pockmarks, fog, wavy fish scales, mushroom umbrella cloud", how to deal with it?

Many plastic composite flexible packaging products require high transparency, and use a large area of blank base film for BOPP and CPP composites. However, in the dry composite process, sometimes the transparency of plastic composite flexible packaging is poor or decreased. For example, the finished product is "Fog", "small pits", "wave fish scales", "silk patterns", "mushroom umbrella clouds", "splashing water" and other phenomena, which affect the transparency of the composite product, and even make the composite product in severe cases. scrapped. The reasons for this phenomenon are analyzed as follows.

"Fog" phenomenon and countermeasures

1. The transparency of the composite material or the printing substrate itself is poor

Before lamination, the film material is generally tested. The detection method is: take a small section of the film and observe it through the light, and the film material is required to be smooth, free of small spots, no sticky dirt, no unevenness of unevenness, and no dusty impurities. Therefore, only high-quality materials produced by regular manufacturers can be compounded to produce good finished products.

2. The influence of adhesives

The color of the adhesive is too dark, dark yellow or yellow-red. After drying, this part of the dark color will stay on the film accordingly. Therefore, when the composite product is required to have high transparency, it is necessary to use yellowish or even colorless. adhesive. The correct selection of two-component adhesives can reduce the probability of "fog" in the composite product, and even eliminate the "fog" phenomenon.

3. Operation error or insufficient drying temperature

Misoperation or insufficient drying temperature will also produce "fog" phenomenon. For example, the amount of glue applied is uneven, one side is thicker and the other side is thinner. Therefore, uniform coating is very important in the dry lamination process.

"Small pockmarks" phenomenon and countermeasures

1. The adhesive is mixed with dust and other particles. There is too much dust in the air of the workshop environment. There is also dust in the hot air blown out of the drying tunnel after gluing. Causes the composite finished product to be opaque.

Solution: Use a 180-mesh wire mesh to filter the adhesive to remove insoluble particles in the adhesive. At the same time, attention should be paid to the cleanliness of the workshop, keeping the floor clean and free of floating dust. In dry lamination, the glue bucket and glue tray must be cleaned before leaving get off work. Especially in summer, the indoor temperature is high and drying is fast. The residual adhesive should be poured into the bucket before each shift and should be sealed and handled separately.

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

Two-component reactive adhesives are easily affected by temperature and become white and turbid. The "turbid white" adhesive can not be used again, otherwise there will be uneven distribution of the adhesive layer, resulting in the increase of "small pits".

2. The quality of base film and composite film is not good enough. If the OPP heat compound is yellow and old, it should be checked carefully. First, the surface tension value should be detected. The surface tension of BOPP should reach 38mN/m, and the surface tension of PET should reach 50mN/m. Low surface tension will lead to poor wetting effect on the surface of the material, uneven coating of the glue solution, resulting in voids, and small pitting in the finished product after compounding. Therefore, the film whose surface tension value does not meet the requirements should be used after passing the treatment.

The second is to use a magnifying glass to detect the smoothness of the base film and the composite film, requiring no unevenness. If the surface of the material is uneven and different in depth, it cannot be completely adhered to the film after being squeezed by the hot pressing roller, and "small pits" will appear. So material selection is critical.

3. Poor flatness of the top roller, insufficient fluidity of glue, and poor flatness will lead to "small pits". The cots are required to be fine and smooth, preferably cots made of silicone rubber. The glue has good fluidity, excellent flatness, and even coating, which can reduce the probability of "small pockmarks", and at the same time, the transparency of the composite product has also been improved.

"Fish scales" phenomenon and countermeasures

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

2. Accidental shutdown during the production process, the gluing roller is not released in time, or the gluing roller is not separated from the glue liquid, and the hot pressing roller is not separated from the hot drum. Generally, wavy and irregular transverse indentation will appear in the blank space under the compressed state for 30 minutes, resulting in poor transparency. Therefore, in the non-working state, the top roller and the anilox roller should be isolated and cleaned, the hot pressing roller and the hot drum should be separated, and the power of the hot drum should be turned off at the same time.

Reasons and countermeasures for phenomena such as "mushroom umbrella cloud", "splashing water" and "silk pattern"

1. The material itself is not good, and irregular patterns appear. Just replace it.

2. The influence of adhesives and drying channels. When entering the drying tunnel, the temperature is too high and the drying speed is too fast, so that the solvent on the surface of the adhesive layer volatilizes rapidly, and the surface is crusted. The ring of the mouth, like a "mushroom cloud", is distributed on the surface of the adhesive film, resulting in an uneven and opaque adhesive layer. Therefore, the temperature of the drying tunnel should be increased sequentially from low to high, so that the solvent can be completely volatilized from the inside to the outside in an orderly and uniform manner, leaving no odor. In addition, solvents with different boiling points can be mixed to use, so that when heated and evaporated, the high-boiling point solvent on the surface of the adhesive layer will remain for a long time, and the surface film will not be crusted, but it is necessary to ensure that the amount of residual solvent meets the requirements and does not exist. Odor and odor problems.