More than 15 years successful in the determination of the pressure filter value during the production of masterbatches and compounds

In 1998, all started – at that time, several companies founded the „CEN Committee Filtertest “consisting of masterbatch producing companies and manufacturers of laboratory lines for the processing of plastic. Aim of this initiative was to develop a standardized method for the determination of the pressure filter value.

In 2004, with EN 13900-5, the CEN Committee finally presented a uniform measuring method with which the suitability of pigments for colouring plastic can be described and which, in the meantime, as ISO 23900-5 has become international standard.

The pressure filter test is used to detect quality differences in a polymer caused by agglomerates, fillers, which are not completely dispersed resp. impurities.

It can be used e. g.

  • in the field of product development for optimizing the colour etc.
  • for quality control resp. outgoing and incoming goods control of masterbatches, compounds or polymers

The material to be tested is melted and homogenized in an extruder and via a melt pump, it is guided through a screen with a defined and constant volume flow. The screen is clogged by particles with a certain size, which results in a reduced opening of the screen. At a constant volume flow, this causes a pressure increase in front of the screen, which is determined by a sensor and which is used for the determination of the sample quality.

Special characteristics

  • A filter cassette system allows a filter change within a few seconds
  • For changing the filter, via a bypass valve, the melt flow can be deflected in front of the filter. This allows an interruption of the melt flow by the filter without having to stop the extruder and the melt pump and to start them again after having finished the filter change
  • Integrated pre-heating of the screen
  • Easy-to-use software for calculating the pressure filter value and determining a listing

How can the filter be changed within less than 10 seconds?

  1. Insert the cassette with filter (S1) into the guiding rail
  2. By swivelling the polymer valve (W), the melt flow is deflected into the bypass (B)
  3. Release the filter cassette fixation (P) (not shown)
  4. Push the inserted filter cassette (S1) into the pre-heating position (S2) and push the filter cassette in the pre-heating position (S2) into the testing position (S3). At the same time, the used filter (S3) is moved into the removal position (S4)
  5. Fix the filter cassette (S3)
  6. By moving back the polymer valve, the melt flow is returned through the filter
  7. Remove the filter cassette (S4).

Ex Extruder with screw (shown schematically)
Mp Melt pump (shown schematically)
P1 Melt pressure in the extruder
P2 Melt pressure in front of the filter

Measuring value detection

A pressure filter test unit with an integrated touch panel CMI 7 detects the test data:

  • Melt pressure in front of the filter
  • Melt temperature
  • Melt pump speed

The time curves of melt pressure and temperature are represented in a diagram.

Via a start and stop button, the operator defines the start (filling in the sample) and the end of the test. The calculation of the pressure filter value (FPV = Filter Pressure Value) is effected at the end of the test by determining the initial pressure PStart resp. the maximum pressure Pmax during the test and by using the formula:

FPV = (Pmax– PStart) / m

*m is the pigment weight in the sample

The recorded data can be stored in the Collin microcontroller and a test protocol can be printed.

Je kleiner der Druckfilterwert ist, desto besser ist das Pigment dispergiert und umso höher ist die Produktqualität.