Record numbers find out about rubber bonding

Rubber Bonding conference attracts record number of delegates and covers rubber and TPE materials, surface modification, new and improved adhesive systems and the chemistry of adhesion.

The Rubber Bonding conference organised by Rapra Technology on 21st and 22nd February in Dusseldorf had a record number of delegates and covered a wide topic range including rubber and TPE materials, surface modification, new and improved adhesive systems and the chemistry of adhesion.

The main challenges for the technical area remain the bonding of dissimilar materials, developing environmentally acceptable adhesives and increasing product performance.

Advances in analytical techniques are providing greater insights into adhesive technology.

Through low incidence x-ray diffraction analysis, William van Ooij from the University of Cincinatti demonstrated that the sulphide film formed on the surface of brass-plated tyre cord can become crystalline at high moulding temperatures causing a brittle interface and hence poor adhesion.

The addition of cobalt and resin systems improves aged adhesion as it delays the crystallinity of the sulphide film.

Current developments are examining the use of silanes to replace the brass and produce a more environmentally acceptable product.

Loughborough University presented a paper on the numerous surface treatments to improve the adhesion of rubber onto non-polar plastics.

The use of surface analysis techniques such as XPS, Sims and ATR has shown that the level of surface oxygen was not found to correlate with adhesion strength.

Although some success was found with some treatments, the health and safety issues have not been fully resolved.

This was also a limiting factor with a paper by Phoenix Rubber Industrial, on bonding rubber to PA11 and PVDF for hoses.

Premature failure of rubber-metal bonded pipelines has been experienced for a specific adhesive system.

Leaching of elements (chloride and bromide) from the primer and adhesive can create aggressive corrosive acids.

In addition, steel corrosion products can migrate into the rubber and accelerate rubber ageing, particularly at elevated service temperatures.

Chemical Innovations discussed the advantages and disadvantages of one-component bonding systems - the firm has modified the adhesive chemistry to offer improved heat and corrosion resistant grades.

Rohm and Haas presented data on environmentally friendly, robust rubber to metal bonding systems with resistance to boiling water, salt spray and glycol.

An adhesive system suitable for swaging applications was presented.

Lord has also been developing solvent-free systems.

The presentation by Henkel on the standard test method adopted by WDK for the development of lead-free bonding agents for car engines and bushes sparked debate on adhesive testing methods.

The flat metal stub method gives higher adhesion values and more rubber tear compared with the convex metal end stubs (ASTM D429 method F).

Tack Service, based in Germany, presented a machine that exposes polymers to ultraviolet light and ozone (Tack Treat AS3000).

The treatment was claimed to be more effective than corona or plasma treatment and enables a wide range of rubber and plastics to be bonded.

Initial take up has been in the shoe industry where it has permitted the use of water based PU adhesives and reduces VOC emissions.

For the TPE market, Exxon Mobil and Polyone presented polyolefin based TPV grades with improved adherence to polar materials in overmoulding applications.

Improved bond strength was achieved for the Exxon Mobil grades without the need for thick sections or high process temperature.

The proposed grades are not, however, a fix for all engineering thermoplastics.

Polyone also showed data for an improved TPE-S (Onflex S) with improved compression set and bonding to polar substrates.

Both materials enable greater design flexibility as softer, lower cost, higher temperature performance elastomers can be used compared with a polar TPE such as TPU.

Heat activated pressure sensitive tapes are gaining acceptance by the automotive industry for door and weather seals.

Boss Polymer Technologies from Australia presented a novel technology developed for use with TPE seals using generic double-sided PSA tape.

The tapes are used with a film interlayer, which is introduced directly into the extruder thereby eliminating post manufacturing operations.

Licensing agreements were being offered to promote applications across a range of industries.

For increased product performance, NGF presented details of its modified surface treatment for glass cords used in weather strips and timing belts.

The advantage for weather strips is that it permits highly extended, low cost EPDM compounds to be used without significant loss of adhesion.

For HNBR timing belts, improved product performance has enabled the belt to become a non-serviceable component.

This Rapra conference is biennial and the next event is scheduled for February 2008.

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