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

6.6 Filter
6.6.1 General The filter media is that part of the system which influences the differential pressure used as the basic data for determining the results of the test. The differential pressure increase is dependent on the retention characteristics of the filter media. In order to have comparable results it is important that the filter media is defined in detail and assembled exactly to specification. Screen-packs are used as filter media.
The screen-pack is assembled from ultrasonically cleaned filter discs, having a filter diameter of 33,8 mm (± 0,1 mm), in a multi-layer construction, preferably held together in an aluminium frame. All screens shall be made from a suitable material appropriate to the polymer used, e.g. stainless steel in accordance with EN 1 0088-1 , Type 1 .4404.
Any change in specification (e. g. weaving pattern, surface condition, number of apertures per unit length or aperture width) can lead to a different test result.
6.6.2 Screen-pack 1 Two-layer construction, where the first layer is a reverse plain dutch weave 61 5/1 08 warp/weft per 25,4 mm with a wire diameter of 0,042 mm/0,1 4 mm and the second layer (support mesh) is a square mesh plain weave 0,63 mm aperture width with a wire diameter of 0,40 mm calendered (for further details see ISO 9044).
6.6.3 Screen-pack 2 Two-layer construction, where the first layer is a reverse plain dutch weave 61 5/1 32 warp/weft per 25,4 mm with a wire diameter of 0,042 mm/0,1 3 mm and the second layer (support mesh) is a square mesh plain weave 0,63 mm aperture width with a wire diameter of 0,40 mm calendered (for further details see ISO 9044).
6.6.4 Screen-pack 3 Three-layer construction, where the first layer is a twilled dutch weave 1 65/1 400 warp/weft per 25,4 mm with a wire aperture width with a wire diameter of 0,1 6 mm and the third layer (support mesh) is a square mesh plain weave diameter of 0,071 mm/0,040 mm and the second layer (support mesh) is a square mesh plain weave 0,25 mm 0,63 mm aperture width with a wire diameter of 0,40 mm calendered (for further details see ISO 9044).
NOTE 1 The use of further finer screen-packs than described in 6.6.2 may be agreed between the interested parties.
NOTE 2 It is recommended to request confirmation from the supplier that the above specifications are used for the screenpack. Especially the number of apertures per unit length and the wire diameters of the individual layers are extremely critical for the result of the filter pressure value test. m 6.7 Sealing ring The sealing ring or aluminium frame of the filter disc should have a diameter of 33,8 mm ± 0,1 mm and an inside diameter of 28 mm ± 0,1 mm.
If the screen-pack has no aluminium frame a sealing ring is to be used. 7 Preparation of test mixtures 7.1 General The colour concentrate (5.1 ) and the basic test polymer (5.2) are mixed together, for example in a glass or plastics container, to provide the homogeneous test mixture.
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