How to avoid bubbles in the finished product of dry laminating machine?
Understanding and mastering the operation skills of dry laminating machine is of great help to improve the quality of packaging bags. Dry composite packaging bags often have defects such as bubbles, so some adjustments should be made to each part during operation. Here are some tips to avoid bubbles in the finished product.
1. Increase the concentration of the adhesive or choose an adhesive with good wetting properties
Adhesives that are too thin or have poor wetting properties tend to flow, resulting in uneven adhesion on the substrate and resulting in longitudinal or transverse water marks. Bubbles may occur in areas of low adhesive application. The generation of bubbles can be reduced by increasing the concentration of the binder or selecting a binder with good wetting characteristics.
2. Substrate corona treatment
In order to improve the adhesion ability of the substrate surface and ensure the coating quality, the surface tension of the substrate should reach about 42-56mn/cm. Before coating, an additional corona treatment device can be added to the substrate surface for corona treatment to blur the surface and enhance the surface tension. This may increase the amount of adhesive applied to the substrate surface to avoid the formation of bubbles.
3. Correct installation and adjustment of scraper
When coating, if the pressure applied by the doctor blade on the screen roller is too low, impurities may be mixed in, causing the doctor blade to lift and form a gap, resulting in uneven coating.
Due to the uneven surface of the net roller, if the installation angle of the scraper is too large, the elastic scraper is prone to vibration or beating during high-speed operation, causing mucus to bounce and increase the difference in coating amount. The radial angle between the contact point of the scraper and the web roll is usually selected between 15-30 °.
4. Suitable drying temperature
An appropriate drying temperature can sufficiently dry the adhesive on the surface of the substrate. Generally, the drying temperature should be adjusted to 80~100 ℃. If the drying temperature is too high, the surface of the adhesive has formed a hard skin, and the part below the surface is not completely dried, making it difficult for exhaust gas to escape, which can easily lead to foaming. Conversely, if the drying temperature is too low, the adhesive does not dry completely. After a period of mixing, the finished product will also form bubbles due to the natural evaporation of the adhesive. Increasing the temperature of the composite heating roller and reducing the compounding angle during the compounding process are beneficial to remove bubbles in the composite film.
5. Adjust compound pressure and speed
Insufficient compound pressure is easy to produce bubbles. Increasing the compression temperature and compounding pressure of the composite membrane can greatly reduce bubbles.
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