Epoxies/adhesives needles

These syringe applicators with very fine needles may apply very small dots or drops down to one hundredth of a milligram. They are widely used in electronics for surface mounting, chips bonding and in jewellery and watches. The application of the adhesive may be controlled with a special camera or an optical fibre detector. The viscosities of the adhesives may range from 100 mPas (cyanoacrylates) to 20,000 mPas (epoxies, silicones). 

Needle bonding has long been a major application for adhesives. The bonding of stainless-steel needles in glass syringes that are prefilled with pharmaceuticals was traditionally done using heat-cured two-component epoxies, but toughened UV acrylic adhesives have led to dramatic increases in productivity. 

Adhesives are used to bond the stainless steel cannulae to the plastic hubs (Figure 10.1) and in this high-volume application (up to ten assemblies per second) it is essential that every needle assembly is bonded. The adhesive used (typically either a UV acrylic or a single-part epoxy) fluoresces at about 450 nm and so the presence of adhesive on the cannula can be verified automatically using inspection cameras and if it does not see the adhesive fillet, it will eject the part off the line. 

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