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IS0
I N T E R NAT1 O N AL OR GAN I ZATl O N FOR S TAN DARD 12 AT1 ON
IS0 RECOMMENDATION
R 535
DETERMINATION OF THE WATER ABSORPTION
OF PAPER OR BOARD (COBS METHOD)
1st EDITION
January 1967
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The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 535, Determination of the Water Absorption of Paper or Board
(Cobb Method), was drawn up by Technical Committee ISO/TC 6, Paper, Board and Pulps, the
Secretariat of which is held by the Association Française de Normalisation (AFNOR).
Work on this question by the Technical Committee began in 1960 and led, in 1964, to the
adoption of a Draft IS0 Recommendation.
In April 1965, this Draft IS0 Recommendation (No.791) was circulated to all the IS0
Member Bodies for enquiry. It was approved, subject to a few modifications of an editorial
nature, by the following Member Bodies :
Germany Portugal
Argentina
Greece Republic of South Africa
Australia
Austria India Romania
Belgium Israel Spain
Brazil Italy Sweden
Japan Switzerland
Canada
Morocco Turkey
Czechoslovakia
Netherlands U.A.R.
Chile
Denmark New Zealand United Kingdom
Finland Norway U.S.S.R.
France Poland Yugoslavia
Two Member Bodies opposed the approval of the Draft:
Ireland
U.S.A.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in January 1967, to accept it as an IS0 RECOMMENDATION.
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ISOIR 535 - 1967 (E)
M
IS0 Recommendation R 535 January 1967
DETERMINATION OF THE WATER ABSORPTION
OF PAPER OR BOARD (COBB METHOD)
INTRODUCTION
This test permits the determination of the quantity of water that can be absorbed by a paper or
board in a given time.
Water absorption capacity is a function of various characteristics of paper or board such as
sizing, porosity, etc. It cannot be used for a precise appreciation of the writing properties.
1. SCOPE
This IS0 Recommendation describes a method of determining the water absorption capacity of
paper or board under standard conditions.
2. DEFINITION
Water absorption of paper or board (Cobb value). The amount of water in grammes absorbed by
1 m2 of paper or board in a specified time under a head of 1 cm of water and at 20 f 1 "C or at
one of the other temperatures specified in IS0 Recommendation R 187*.
3. PFUNCIF'LE
To weigh the test piece immediately before beginning the test and again after exposure to water
under the conditions stated in the test method.
4. REAGENTS
Use distilled or de-mineralized water.
The temperature of the water is important and should be maintained at 20 & 1 "C or at one of
the other temperatures specified in IS0 Recommendation R 187, at the time of test.
5. APPARATUS
5.1 The Cobb absorbency tester
For determining water absorption capacity, any type of apparatus may be used which permits
- an immediate and uniform contact of the water with the part of the test piece submitted
to the test and
- the rapid withdrawal of the test piece without the risk of contact with the water outside
the test area.
The test area is 100 cm2.
In its simplest form, the apparatus consists of a rigid metal cylinder of 100 f 0.2 cm2 internal
cross sectional area (corresponding to a diameter of 112.8 & 0.2 mm) and about 5 cm high
with means for clamping it on the surface of the test piece. The thickness of the cylinder
wall is not important but should be such as not to damage the surface of the test piece.
The lower edge of the cylinder in contact with the test piece should be flat and machined
smooth.
The test piece is placed on a flat base which has been previously covered with a piece of sheet
rubber so that a leakproof seal is formed when the cylinder is clamped in the testing position.
* IS0 Recommendation R 187, Method for the Conditioning of Paper and Board Test Samples.
See also IS O Recommendation R 554, Standard Conditioning andlor Test Atmospheres - Standard Reference Atmosphere
- Specifications.
-3-
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SOIR 535 - 1867 (E)
5.2 Blotting apparatus
Blotting paper having a substance of 200 to 250 g/m2 and having absorbent properties,
measured by the Klemm method (see Appendix Z), around 75 mm.
A smooth metal roller, face width 20 cm and weighing 10 f 0.5 kg is used for blotting.
5.3 Auxiliary apparatus
An analytical balance, sensitive to 1 mg over the working range corresponding to the test
piece having an area of 100 cm2
A stop-watch
A glass measuring cylinder.
6. SAMPLING, CONDITIONING AND PREPARATION OF TEST PIECES
6.1 Sampling and conditioning should be carried out in accordance with IS0 Recommendation
R 186* and R 187 respectively.
6.2 The standard Cobb method recommends a standard test area of 100 cm2 and states that
sufficient material should be available to provide at least 10 test pieces 12.5 cm square (5 for
each side of the paper or board, unless otherwise stated). When the test pieces available are
too small to conform with standard conditions, a smaller test area may be used, by agree-
ment between buyer and seller.
7. PROCEDURE
The test should be carried out in a standard reference atmosphere in accordance with IS0
Recommendation R 187.
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