Filter papers
Raw materials and manufacture
For production of the high quality MN filter papers
we use cotton linters, refined pulp with a high level
of
µ
-cellulose as well as glass fibres. Cotton linters
are short-fibred seed hairs from cotton seeds,
which cannot be used for textile purposes, but
which are highly suitable for the manufacture of
soft and absorbent filter papers.
In addition to cotton linters we use mainly pulp,
which is obtained by chemical treatment of plant
materials, e.g. coniferous or deciduous wood.
At MACHEREY-NAGEL only the most experienced
paper specialists select the raw materials in order
to ensure the continuosly high quality of our filter
papers.
For the manufacturing of MN glass fibre filters we
use staple fibres made from borosilicate glass
(exception: paper from quartz fibres). With a
diameter of 0.5 – 1.5 µm these glass fibres are
considerably thinner than cellulose fibres. One of the most important feature of glass fibre filters is their resistance to almost all
chemicals (exception e.g. hydrogen fluoride).
Important technical parameters of filter papers
The ash content is determined in accordance with DIN 54370: 10 g filter paper are weighed after
ignition in a platinum crucible at 800 °C. Results are expressed as % of original paper weight.
For determination of the dry bursting strength the paper is clamped over a rubber diaphragm with an area
2
of 10 cm . The strain on the paper is then increased by applying an increasing air pressure, until the paper
bursts. The dry bursting strength in accordance with DIN 53113 is stated in Kpa.
For determination of the tensile strength a paper strip (measuring 180 x 15 mm) is subjected to vertical
strain by applying increasing weight. The force expended at the moment of tearing represents the tensile
strength. Results are expressed in N/15 mm.
The thickness of a paper is measured with a touch pressure device. Especially for soft and creped papers it
is important that the touch pressure is not too high. Otherwise the papers are compressed and a falsely low
thickness is obtained.
For determination of the filtration speed in accordance with DIN 53137 the duration of flow of 10 ml distilled
water through a quadrant-folded, freely suspended filter circle of 12.5 cm diameter is measured. Results are
expressed in seconds.
2
The basis weight is determined for a sample of 10 x 10 cm. It is measured in g/m .
The Gurley test measures the time required for filtration of 100 ml air at a water column pressure of 31 mm.
The sample has an area of ¼ sq. inch.
The wet strength of a paper is a measure for the mechanical stability of a paper in a wet or moist condition.
For example, it can be determined as the tensile strength or the bursting strength (see above).
The retention efficiency of a filter paper is influenced by several factors. Since filter papers are deep-bed
filters, one usually refers to a mean particle retention.
The capillary rise according to Klemm indicates how far a strip of filter paper is moistened in 10 min when
vertically dipped with one end into distilled water (20 °C).
Particle retention refers to the efficiency of filter papers in retaining certain precipitates. It is characterised by
the permeability of the paper for precipitates of iron(III) oxyhydrate, lead sulphate, calcium oxalate and
barium sulphate.
Ash content/
residue on ignition
Dry bursting strength
Tensile strength
Thickness
Filtration speed
Basis weight
Gurley test
Wet strength
Pore size
Capillary rise according
to Klemm
Particle retention
Parameter
Description
Filtration Products
MN
4
