Precautions for water-based composite adhesive
2020-12-28
Causes and prevention of white spots in composite products: Water-based composite adhesives typically contain 50% water, which must be completely volatilized in a short time, requiring sufficient temperature and airspeed. There are two reasons for white spots in composite products: insufficient water-based composite adhesive and incomplete drying. White spots that may disappear after short-term aging indicate incomplete drying, as aging can further help evaporate moisture; otherwise, it indicates insufficient adhesive. To avoid incomplete drying, adjust the temperature and airspeed of the drying channel. The temperature of the drying channel can be set to 70℃～80℃～90℃; however, we find that the actual temperature of many composite equipment is much lower than the set temperature. Therefore, calibration must be performed if possible to avoid large errors. The airspeed is particularly important for the drying of water-based adhesives. Ensure the airspeed is above 6m/s, and regularly clean the air outlet and inlet of the equipment to prevent blockage. In addition, the temperature of the composite roller will also affect the appearance of the composite and the initial bonding. Ensure the actual temperature of the composite roller reaches above 50°C.
Matching issues between water-based composite adhesives and inks: Will water-based composite adhesives affect the adhesion of inks on films? Why is there a significant difference in the appearance of composite films printed with different inks? Water-based composite adhesives have good adaptability to both water-based and solvent-based inks. Ink transfer is usually related to the quality of the ink. If the ink has poor affinity with the film, the adhesive may pull the ink from the film; therefore, this problem will not occur when using high-quality inks.
Inks contain different waxes, antifoaming agents, plasticizers, etc. These components may adversely affect the water-based composite adhesive, affecting the appearance of the composite. Therefore, the water-based composite adhesive should be tested after changing the ink to avoid losses.
Surface tension of the composite substrate: When the surface tension of the composite film is below 38 dynes, the water-based composite adhesive is difficult to wet, and the peel strength after compositing will be greatly reduced. Therefore, the surface tension of the composite film is usually required to be no less than 38 dynes. However, the surface tension of the aluminum film in the plastic film and coating will slowly decrease during storage. Therefore, the surface tension of the film should be tested before rolling. If large drops are found, small-batch tests should be conducted first to check whether the strength after mixing meets the standard before regular mixing.
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