Adhesives Magazine

Ask Dr. Dave - August 2002

August 1, 2002
E-mail your questions to Dr. Dave at DrDave242@att.net



Q

We use cyanoacrylates in our assembly operation but spend a lot of time cleaning up the trays that our parts are on because of excess glue spilling on them. How can we avoid this, or can we spray a mold release on them to help in cleaning?

A

There are several things I would suggest. First, you should investigate acquiring a modern applicator for the adhesive. Many available dispensers will place a precise drop of adhesive exactly where you want it, with no spillage at all. If this is not possible, then you could make the trays out of PTFE or line them with PTFE to aid in cleaning. One other option is to use disposable trays -- polyethylene film would be a good material for these. I would not recommend using any type of mold release on your trays because of the possibility of contaminating your parts or the adhesive and ruining the adhesion.

Q

We are a food company looking at assembling two-layer plastic-film stand-up pouches for fruit-juice products. What are the best types of adhesives for laminating these films?

A

I would suggest first that you deal with a supplier that only uses FDA-approved ingredients in its adhesives. You have several options for adhesives. The two most common types used for flexible packaging are polyurethanes and acrylics, and they are available in solvent- and water-based versions. They can be used in one of two ways -- either the adhesive is applied on each surface and then allowed to dry before assembly (dry-bond adhesives), or the adhesive can be applied and assembled when wet (wet-bond adhesives).

In either case, the assembled substrates are usually run through a heated nip-roller to optimize the bond and speed up the curing. Water-based wet-bond adhesives require one of the substrates to be porous to allow removal of the solvent or water, so they are not suitable for your particular application. Some newer liquid adhesives are 100% solids, i.e., they contain no solvents, but some problems still remain in ensuring that the systems do not contain residual monomers, which might contaminate the food.

All the systems described above require some time to get full strength, ranging from a few hours up to 24 hours. New systems being worked on are cured with UV light or electron beams and promise to give virtually instant cures.

Q

We custom-mold seals and gaskets and would like to lower the cost of making custom molds. I have read about new systems that can make gaskets from liquid sealants using UV light, rather than compounded rubber. Can I get these to have the same properties and meet the specifications of my customers? We use a lot of rubbers, particularly FKM (fluoroelastomers), ACM (acrylic rubber) and HNBR (hydrogenated nitrile rubber).

A

The systems you refer to are called "cure-in-place" or sometimes "form-in-place." They allow you to take a pail or drum of sealant, apply it with a robotic applicator in any size or shape you want and then cure it quickly using UV light or heat. Obviously, you don't need a new mold for each new gasket, but you do need to be a manufacturer with large volumes to justify the capital cost of the applicator and curing equipment. Two types of sealant are currently available, silicone-based and flexible acrylics. These materials will probably not meet your current automotive specifications, but you will have to work with the suppliers to discuss each specific application. The good news is that patents have appeared in the last couple of years on the UV curing of conventional elastomers like FKM, ACM and HNBR, so it is quite likely that we may have the required products very soon.