Checklist for causes of white spots and bubbles in hot melt adhesive particles: 5 steps to locate the source of the problem

What causes white spots and bubbles in the adhesive layer?

Directly provide the order of investigation:Moisture absorption of adhesive particles → high temperature of adhesive glue → stirring and rolling into air → surface moisture of substrate → suction of adhesive pumpAccording to this order, over 90% of the white spot bubble problems can be located within half an hour. White spots are traces left by water vapor or air inside the adhesive layer, which not only affect the appearance, but also shrink the bonding area and decrease the strength. The following list has been compiled by the Trade and Technology Department of Guangzhou Sunlife.

5-Step Checklist

1. Check the moisture content of the rubber particles: Grab a handful of rubber particles and put them into the hot pot. If there is a “crackling” sound with foam, it is damp. Moisture affected rubber particles can be restored after 2 hours of drying at 60 ℃; After opening the bagged adhesive, be sure to tie the mouth to prevent moisture.
2. Check the melt adhesive temperatureExceeding the decomposition temperature will produce gas, manifested as fine bubbles and a slight burnt smell. According to the temperature limit indicated on Sunlife hot melt adhesive packaging, if it exceeds the limit, it will decrease.
3. Check mixing and refluxWhen the mixing blade of the glue pot is exposed to the liquid surface and stirred at high speed, air will be sucked in, keeping the glue surface submerged in the mixing blade by more than 2cm.
4. Check the moisture content of the substrateThe surface of cardboard that has just entered the factory from a cold storage or rainy weather has moisture, and when the glue is applied, the water vapor is heated and forms bubbles. The cardboard will be heated and equilibrated for 4 hours before going online.
5. Check if the glue pump is emptyWhen the glue level is too low, the pump sucks in air and intermittently produces bubbles when dispensing glue. Set low glue level alarm and replenish granules in a timely manner.

Quick Comparison Table

Frequently Asked Questions

Q: Do finished products with white spots and bubbles need to be scrapped in batches?
First, conduct a peel test to ensure that the strength meets the standard, which is only a visual issue. Ordinary parts for domestic sales can be released; Export parts and hardcover books are recommended to be reworked.

Q: How to prevent moisture in the southern region?
The adhesive particles should be stored off the ground and walls. They should be used up on the day of opening and sealed with desiccant if not used. Sunlife hot melt adhesive provides 5kg small packaging, which is the safest way to receive it on a daily basis when returning to Nantian.

Tick each item from the adhesive particles to the substrate according to the list, and the problem of white spots and bubbles is unlikely to recur.