Glue is used in the production of a wide range of products. Gluing two parts together is an extremely common process. And yet, many of the very serious quality issues coming out of China come from the use of an improper glue.
Let's dig into this with David...
Four Key Questions & Answers On Glue Process Control
I asked my partner David Collins for his input on four key questions about glue process control and the use of glue in manufacturing:
"What are the most important process controls during the production of glue?"
Obviously it is important not to use inferior polymers. Those polymers might not be fully reacted. There might be many monomers or oligomers (short-chain polymers) and this will affect the glue properties.
During the manufacturing process, these variables absolutely have to be controlled:
- Quality of the water – in particular there should not be many ions in it, as some of those ions can react with some of the polymer chains and inhibit the glue from reaching its maximum potential.
If you work with a supplier who doesn’t do all this properly, your products might not be held together properly and it might cause serious customer complaints. (See question 4 below). Think of baking a cake only halfway. When you eat it, there is still a lot of dough.
"How should a factory test the glue before using it in production?"
It makes sense to test these 2 properties:
- The amount of solids in the glue – if there is only a 30% proportion of solids instead of 50%, strong savings have been pocketed by the supplier but the amount of coverage (i.e the performance) is not the same. The vehicle (the water and the solvent) is not what “does the work”…
Give feedback to your supplier about your findings, to keep them on their toes. And don’t use clearly inferior glue, or your company might face very expensive failures in the hands of customers…
"How to confirm if a certain glue can be used for a certain application?"
Ask a few suppliers. We are amazed by how many Chinese manufacturers assume the cheap glue they usually buy will also work on a new type of material and don’t ask their supplier!
There are many types of glues that are quite different from each other. The polymer groups might stick to a certain material… or not.
For example, a glue that works on some plastics won’t work on wood or rubber; some other glues work on many more materials but are more expensive.
"Why might glue ‘hold’ parts together now but fail in a few weeks/months?"
Exposure to the sun, heat, and/or to humidity can have a very strong impact on glue and reduce its ability to hold things together:
- UV rays break down double bonds and the polymer chain if there are no UV absorbers in it. (Years ago, one could see faded paint on many cars because their paint had no UV absorbers – now it is included in the paint of all cars.)
- If the glue is made of inferior polymers, its polymer chain can break down quickly due to heat and other factors.
- Humidity can cause certain chemical reactions, especially in water-based glues (which are very common).
Imagine a shipment that goes across the ocean in a container. There is much heat and humidity. If the products are held together by inferior glue, their quality will quickly degrade during that 2-4 week journey. Or it might take a few months and many customers will complain and return products.
Have you had issues with glue, or do you have other questions on this topic? Write a comment below and David and I will be happy to respond.
We hope these explanations have been useful. Digging deep into the technical reasons behind common manufacturing issues is something we plan to do more of in the future (If you have suggestions, they are welcome, tell us in the comments!).