Peter Swanson explains why developing an adhesives process requires more than just the data sheet
The question “it works in practice, but does it work in theory?” is commonly used to describe situations in economics. But the same concept can be applied to adhesives applications, where the data sheet may not always give the same insights as your practical observations and tests.
Every adhesives application is unique. Specifying materials and equipment for an adhesives process requires detailed discussions and testing to establish what works for your application. The data sheet offers some insight – but may not tell you everything.
Why you should look past the data sheet for your adhesive manufacturing process
The data for an adhesive or coating mostly comes from laboratory test procedures, which are well understood, usually in the public domain, universal and repeatable. That means this information is great for characterising the material for properties such as how hard or soft it is, whether it is rigid or elastic, how much force will it take before it breaks, and how much it will stretch before it does so. However, in many cases, this data needs interpretation and extrapolation to fit with the designer’s circumstances.
A survey of product datasheets may allow the design engineer to narrow down the candidate list from many thousands to, hopefully, a handful. This selection can then be put forward to practical testing for their specific application. Testing production parts provides assurance that what is specified will meet the unique and distinct requirements.
So although data sheets and specification documents are useful when deciding on what material or equipment to consider for an application, the selection of a product based on the data sheet alone is not recommended – there may be factors that the designer hasn’t considered.
Intertronics’ approach is always “this material would be a good candidate for you to test”, or “let’s evaluate this proposed process with some trials”. This doesn’t mean the firm doesn’t know what it’s talking about – it’s quite the opposite; years of experience have shown that what might appear simple is often complex.
Unanswered adhesives process questions
One reason an adhesives process may not work in theory is because data sheets are not exhaustive – they may not answer all of the questions. For example, the data sheet may say that the adhesive bonds to ABS and PC, but not mention the bond strength to PMMA or glass. This may be that the adhesive is not recommended for those substrates, or perhaps alternatively that the adhesion to those substrates has not been tested, or if tested, published. Good suppliers may be able to fill in those data sheet gaps from experience.
You may have other questions. How does the published pot life relate to the working life I need for my process? The stated intensity of that UV curing lamp looks strong, but is it the correct wavelength for my material? How will the published cure time differ with mass? With temperature? With humidity? The performance of that adhesive looks like it will more than meet my needs, but how will my production manager fit it into our assembly process?
It’s not unusual that the cost of applying and curing the adhesive – the process – is more significant than the cost of the material itself. To keep the process simple, designers may want to consider automation, single part materials with no requirement for mixing, fast in-line cure and process friendly packaging. Keeping the process simple will reduce costs and help make productivity gains.
A good supplier will be able to add considerable knowledge to the facts on the data sheets, using its experience of successful implementations. It could clarify whether, from its experience, the adhesive does bond to glass, even if it’s not mentioned. Or, whether the UV curing lamp will cure a specific coating, even though the data sheet mentions another wavelength. The supplier may recommend a different adhesive that won’t cause a bottleneck in production.
Simple statements rarely match complex reality – working together to understand that what may work in theory will work for you in practice is the best philosophy.
Peter Swanson is managing director of Intertronics