TAPERED TIP NEEDLES FOR ADHESIVES AND SILICONES
I&J Fisnar has announced a tapered dispensing needle, which is a molded plastic tapered design that prevents, or at least, effectively reduces the tertiary pressure phenomenon. These needles are said to reduce the post dispensing ooze that can be experienced with blunt-end tips, particularly when using high viscosity fluid requiring higher pressure to dispense.
When dispensing high viscosity fluids with standard blunt-end tips extra pressure is required to overcome the resistance when entering the straight needle tube, the amount of resistance will depend on the internal bore of the tube, the company explained.
The effect of this extra pressure to overcome the resistance is to introduce a tertiary element in the control of the dispensing process, making an accurate deposit difficult or even impossible to achieve.
The tertiary element is the excess pressure, which shuts the fluid forward after the air pressure is released either from a syringe or valve. A few high pressure valves have a snuff-back feature but it is impossible to successfully apply snuff-back when using a syringe for high viscosity fluids.