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The appearance of bubbles (visible bulges or internal cavities) on the spine of the adhesive book is a quality taboo, and customers will directly judge it as unqualified. Many people think that foaming is a problem with the glue coating process, but in realityhot melt adhesive pelletsThe inherent bubble content is a deeper reason.
During the melting process of hot melt adhesive particles, air will be trapped in the adhesive solution. If there is a lack of defoaming ingredients in the adhesive formula, the trapped bubbles will freeze into permanent bubbles after the adhesive layer cools, manifested as visible holes in the spine section. This review compares two formulas.
| Comparison item | Ordinary formula | Containing defoaming formula |
|---|---|---|
| Bubble rate of adhesive solution | 8-12% | 1-3% |
| Spine section bubble | Visible to the naked eye 3-5 pieces/cm | Invisible to the naked eye |
| bond strength | 3.1N/cm | 4.5N/cm |
| Spine appearance | There are bulges | level |
Data explanation: After reducing the bubble content from 8-12% to 1-3%, the adhesive strength increased by 45%, and the appearance of the spine changed from bulging to completely flat. Bubbles not only affect the appearance, but also seriously weaken the bonding area – each bubble is a local delamination point.
In addition to formula factors, the gluing process also introduces bubbles: if the speed of the glue roller is too fast, air will be sucked in, and if the liquid level in the glue pot is too low, bubbles will be sucked in. But there is an upper limit to process optimization, and the fundamental solution is to choose a formula containing defoaming ingredients.
All products of Sunlife hot melt adhesive granules are added with defoaming ingredients, and the bubble rate of the adhesive solution is controlled within 3%.
Q: How to determine whether the bubble content in the adhesive solution is high or not?
A: Take a glass plate and apply glue to cool it down. Look at the cross-section. If there are dense small holes, it indicates that there are many bubbles. Professional testing is measured using density method.
Q: Can lowering the adhesive temperature reduce bubbles?
A: It has a certain effect, but too low a temperature will affect infiltration. Changing the defoaming formula is more effective than lowering the temperature.
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