Standard sets the Standard

It does exactly what it says in the title

It is rare, in these obfuscating days, to read a standard which is intelligible at first reading, clear in its intentions, original, and relevant. Such a standard has been received covering a method of evaluating the dispersion of pigments in plastics.1 It is doubly pleasant to note that the standard text originates from CEN, an organisation hitherto seriously in need of a study of good communication.

The method itself has modest aims. It describes a quality control test which assesses the performance of a specimen masterbatch in a controlled environment, using the rheology of a resultant coloured plastic as a proxy for the dispersibility of the pigment. There is no attempt to produce an academic basis for the test, nor to relate the figure which emerges (a 'filter pressure value FPV') to any absolute property either of the plastic or the pigment. It is an 'European Standard Rigmarole' and of a type which will be long familiar to technicians and technologists who have worked with British, US, and other standards whose basis is pragmatic, rather than academic.

What happens is that a three-stage trial is carried out. The first stage uses uncoloured plastic which is extruded at a known rate in a molten state and driven through a filter of defined size. The pressure in the line immediately in front of the filter is measured at a steady state. The second stage adds a concentrated colourant to the plastic and continues the test extrusion and 'filtration', measuring the maximum pressure reached immediately prior to the filter. The final stage purges the apparatus. A simple calculation then assesses the increase in pressure which the colour concentrate causes, discounted for the quantity of concentrate used.

What the standard does well is to illustrate the operation of the process with a clear diagram of the apparatus used, and the resulting graph of the rises of pressure which occur during the stages of the test. Those quantities which are necessary to be defined, are defined, with appropriate tolerances. Those quantities, which are controlled variables, are highlighted, and those quantities which are not, and cannot be defined, are, as far as it is possible to tell, pointed out in sufficient cautionary detail. The limitations of the process and any measurements arising from it are fully identified. The authors have resisted any temptation to relate what is measured to any traditional measurement, such as shear rate, viscosity, or thixotropy. The operation of the equipment is very properly left in the hands of the operator, and a considerable discretion is given in the matter of operational characteristics, such as temperature.

What emerges is a parameter, the FPV, which is a useful quality control tool, provided that the limitations of the test are fully understood. There is, again very properly, no precision data quoted, although the text makes clear that participants in the preparation of the document have enjoyed an enviable degree of interlaboratory collaboration

What the standard could do, and doesn't, is to acknowledge the copyright and intellectual property rights which were used in the preparation of the standard. It is appreciated that, under its rules, CEN does not have to. However, it would not only be a polite thing to do, but would also encourage those who have intellectual property, patent, or commercial rights in their own knowledge to participate in the development of standards.

Conclusion

For those with an interest in the dispersion of colourants in plastics, this document could be a useful contributor. As an exemplar of good standards writing and communication, this document would rank highly. It is not entirely clear whether this standard meets a long-felt want, or whether other methods already extant would not be better or more universal. Judged by the accepted criteria of the surface coatings industry, it does exactly what it says in the title. It deserves to succeed.

TEXT

TEXT

Career development - an opportunity

Mr John Balfour FTSC has advised the Association that he is no longer able to represent the Association on standards committees. This news is received with considerable regret. John has been very active in promoting the interests of the Association through his standards work for very many years, and his wide knowledge and wise professionalism will be greatly missed by his colleagues within the Association and in the standardisation field.

However, the Association now has a not inconsiderable hole to fill, and is therefore seeking representatives to participate in the work of the following BSI committees:

• STI/001 Pigments
• STI/010 Test methods for paints
• STI/028 Paint systems for non-metallic substrates
• PRI/021 Testing of plastics
• CW/015/0-/04 Chemical requirements

Participation in BSI Committees gives opportunities to influence, and participate in, European and international standards making activities, and is both a valuable source of up-to-date technical advances and career development opportunities. Service on BSI committees is recognised by OCCA as part of continuous professional development, and would be important to any aspiring Chartered Scientist wishing to enhance his or her portfolio of accredited experience.

Members interested in representing the Association on the above committees should contact Yvonne Waterman (yvonne@occa.org.uk) at Eden Court.

References

1. BS EN 13900-5: 2005 Pigments and Extenders - Methods of dispersion and assessment of dispersibility in plastics. Part 5: Determination by filter pressure value test [Return ]

British Standards are available from BSI, 384 Chiswick High Road, London W4 4AL, or from the Association at 1st Floor, 3 Eden Court, Eden Way, Leighton Buzzard, Bedfordshire LU7 4FY, UK