Chemical Bonding Systems

As chemical bonding systems use solvents and adhesives to join both similar and dissimilar materials, they usually do not require additional fasteners.  They are well suited to applications where a liquid or gas seal is required and where the use of fasteners would create a problem.  These joining methods generally do not create assembly stresses, but they do require appropriate joint design, fixtures, and proper safety precautions.  Depending on the system used, preparation and cure times may be long.

Solvent Welding:
A fast and economical method using a liquid solvent to dissolve the surfaces of the joint areas sufficiently to bond them, this method requires little or no part preparation or special equipment.  It is limited to compatible materials that dissolve in the same solvent or combination of solvents, and may not be applicable to many semi-crystalline resins.  Care must be taken for worker protection, ventilation, and solvent recovery.

Adhesive Bonding:
The excellent chemical resistance of Ticona’s engineering resins limits them to adhesive bonding, using a third substance that adheres to both parts to join them.  Adhesives of various types - contact, two-component, hot melt, and polymerizable – and different chemistries - epoxy, acrylic, polyurethane, phenolic, rubber, polyester, or vinyl – may be   used with thermoplastics.  Some systems incorporate solvents to improve adhesion by partially dissolving the plastic surface.  Adhesive bonding is generally slow, requiring more fixtures and longer clamp times.  Special ovens or curing conditions may be necessary.  Surface preparation can be critical since any contamination such as grease, oil, mold release, or even fingerprints can spoil a bond.

Key criteria in selecting a system are good adhesion and avoidance of chemical attack on the plastic material(s).  Other factors include cure temperature, which must be low enough not to cause part distortion, and joint functional requirements such as sealing quality, isolation, energy transmission and so on.  Specific adhesive recommendations can be obtained from both the plastic and adhesive suppliers; however, the designer must test the performance of the joint in the actual end-use environment.  

Pretreatments may involve chemical or solvent cleaning; mechanical abrasion such as sandblasting or grinding; acid etching, fluorination or ozonation; or flame, corona or plasma treatment.