ISO QMS Certified
"Our Science ... Your Success"

Solvent welding – your days are numbered!

What is solvent welding?

Solvent welding is a method of joining two plastic substrate materials. The solvent chemical (often dichloromethane-based) or solvent cement attacks the surface of the plastic, dissolving it. The liquid polymers from substrate 1 are free to combine with those of substrate 2, the solvent evaporates and Hey Presto, the parts are welded together!

Sounds pretty nifty but shipping,storing and handling those nasty solvent-based flammable chemicals can be the stuff of nightmares. Not forgetting to mention weakening the substrate, attacking areas outside of the bond and in general leaving a scruffy appearance (which for clear coloured plastics gives a really poor finish).

What plastics are often solvent welded?

Typically, polycarbonate, polystyrene, PVC, ABS, acrylic, Perspex® are the usual victims of solvent welding. Often they are weakened, deformed, stress cracked or can lose their “lustre” when attacked with solvent.

Are there any good points for solvent welding?!

Solvents appear cheap to purchase compared to adhesives – although when you add up how much you get through, the extra cost of shipping and storing plus also consumption of volatile solvent materials will most likely be considerably more. This is due to evaporation – whereas adhesives are 100% solids. Solvent cement is popular for bonding and sealing PVC water pipes together, its use is widespread in the plumbing industry.

Many manufacturers of clear displays (so things like menu racks, display units, display boxes, signage, literature racks etc.) use solvent welding techniques. Due to tightening of materials handling in the workplace plus the drive to improve product quality, there is now a strong demand for clear, non-yellowing adhesive products.

Types of clear adhesive

The simplest clear adhesives are cyanoacrylates. For a high quality finished appearance, a low odour, non-blooming grade is preferred (blooming is the white powdery residue associated with cyanoacrylate adhesive). Permabond offers its 940 series cyanoacrylates. These cure inside the closed joint in seconds.UV-cure adhesives are very easy to apply; they are single component and remain liquid until you flash the joint with UV light. This makes positioning and clean-up very easy and offers the perfect finished appearance with a crystal clear joint. Choosing the appropriate viscosity product will help minimise any air bubbles in the joint. With cheap lamps available to any Tom, Dick or Harry on eBay these days, even a small user with limited budget can still afford this type of system.  UV adhesives cannot be used on parts if they’re opaque and block UV light, you must be able to cure through one of them.

New crystal clear methyl methacrylate adhesives are now available – check out Permabond TA4204. This type of product offers a clear, non-yellowing finish and simplicity of application. Whack the cartridge into a handgun, attach the mixing nozzle and away you go – no need for UV lights, curing ovens or anything. You have several minutes to assemble parts before the adhesive starts curing. Bond strength normally exceeds that of the substrate material.

TABLE SUMMARISING PROS AND CONS OF SOLVENT WELDING

Solvent welding2

For more information, samples or to discuss your application, please contact Permabond!