Techspectacular.com

A blood test tube required for medical use needs to be perfectly smooth, transparent and dimensionally exact. For this reason glass has long appeared to be the only suitable material. However, PET-blood test tubes produced with moulds from MHT Mold & Hotrunner Technology now fulfil all the necessary requirements – and offer additional advantages such as low weight and infrangibility.

The tool development presented certain challenges as, production-wise, the ratio of small diameter to considerable length is rather unfavourable.

Particular attention was therefore paid to the achievement of an optimal injection point and a uniform melt flow. The narrow wall thickness can only undergo process-stable manufacture by means of a thermal and rheological precisely balanced hot runner. In addition, the MHT team have developed a special needle duct (locking needle with pre-alignment), to take into account the high sprue quality requirements.

The close-contoured tool cooling at the core and along the cavity guarantees, in addition to the necessary dimensional exactitude, low crystallinity, and with it, absolute transparency of the blood test tube. A smooth surface (average roughness value RA &t;0.05µm) is achieved by means of mirror finish. Even during prefabrication utmost surface quality has to be taken into consideration.

Where plastic is injection molded, there is a sprue. Should ridges or edges appear in the case of the blood test tubes, these could damage the protective gloves worn in the laboratory. For this reason, MHT have sunk the sprue into the base of the test tube.

The aperture of the blood test tube is provided with a curved lip which later secures the sealing plug. This retaining ring is dimensioned in such a way that an enforced demolding is made possible.

With less than 4g the PET blood test tube is a true lightweight, and yet, in comparison to its glass competitor, functionally an absolute equal; and it even survives a fall onto the tiled floor.

Blood test tubes – specifications:
Part weight: &t;4g
Average roughness value: RA &t;0.05µm
Dimensions: Diameter of 12.8mm / 75mm resp. 100 mm