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UDC 678.51.8 : 620.193.6
IS0
FOR STAND AR D 1 ZATl O N
O R G A N IZ AT I O N
I N T ER N AT I ON A L
IS0 RECOMMENDATION
R 878
P LAST I CS
DETERMINATION OF RESISTANCE OF PLASTICS
TO COLOUR CHANGE UPON EXPOSURE TO LIGHT
OF THE ENCLOSED CARBON ARC
1st EDITION
December 1968
COPYRIGHT RESERVED
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 878, Plastics - Determination of resistance of plastics to colour change
upon exposure to light of the enclosed carbon arc, was drawn up by Technical Committee ISOlTC 61, Plastics,
the Secretariat of which is held by the United States of America Standards Institute (USASI).
Work on this question led, in 1963, to the adoption of a Draft IS0 Recommendation.
L'
In August 1964, this Draft IS0 Recommendation (No. 758) 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 :
Argentina Hungary Romania
Austria India South Africa, Rep. of
Belgium Israel Switzerland
Canada Japan Turkey
Czechoslovakia Korea, Rep. of U.A.R.
Finland Netherlands United Kingdom
France New Zealand U.S.A.
Germany Poland U.S.S.R.
Two Member Bodies opposed the approval of the Draft :
Italy
Sweden
The Draft IS0 Recommendation was then submitted by correspondence to the IS0 Council, which decided,
in December 1968, to accept it as an IS0 RECOMMENDATION.
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ISO/R 878-1968 (E
IS0 Recommendation R 878 Decem ber 1968
PLASTl CS
DETERMINATION OF RESISTANCE OF PLASTICS
TO COLOUR CHANGE UPON EXPOSURE TO LIGHT
OF THE ENCLOSED CARBON ARC
1. SCOPE
This IS0 Recommendation describes a procedure for assessing the resistance of plastics to colour change upon
exposure to light of an enclosed carbon arc.
2. PRINCIPLE OF METHOD
2.1 Specimens of the plastics material to be tested are exposed to light, together with pieces of the dyed wool
standards specified in IS0 Recommendation R lOS/I, Tests for colour fastness of textiles (First series),
Part 11 : “Colour fastness to light : Daylight”. These standards vary in colour fastness to light, No. 8
being the most stable and No. 1 the least stable.
After specified exposure, the degree of contrast between exposed and unexposed portions of the test
specimens is compared with that of the dyed wool standards, and the fastness number obtained from the
number of the standard which shows a degree of contrast similar to that of the test specimen.
Provision is also made in this IS0 Recommendation for the use of other standards and other means of
measurement. Related methods are described in the following IS0 Recommendations :
IS0 Recommendation R 877, Determination of resistance of plastics to colour change upon
exposure to daylight;
IS0 Recommendation R 879,
Determination of resistance of plastics to colour change upon
exposure to light of a xenon lamp.
2.2 The quality and intensity of solar radiation at the earth’s surface vary with climate, location and time.
Consequently, uniform, reproducible exposure ordinarily is not achieved under natural conditions.
Laboratory sources of radiation vary among themselves, with ambient conditions and with usage. These
variations should be recognized both in measuring the effects of exposure on plastics and in interpreting
the results of such measurements. The use of dyed wool standards as a reference provides a means for
minimizing the effects of these variables. The carbon arc apparatus permits controlled and rapid evaluation
of the resistance of plastics to radiation rich in ultra-violet energy. While radiation may affect other
properties of plastics, this method pertains only to its effect on colour.
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iSO/R 878-1968 (E
3. APPARATUS
3.1 Radiation source
The source of light is provided by an enclosed single or twin carbon arc lamp with automatic carbon feed
and controls to maintain a current of 15 to 17 A at a potential of 125 to 145 V (r.m.s.) for each arc. The
pure carbon electrodes are of the solid or cored type, or both, 13 mm in diameter and of proper length.
3.2 Globe
Each arc is enclosed in a bell-shaped globe made of heat-resistant glass having a lower transmission cut-off
at 275 nm and a transmittance of at least 91 at 370 nm and in the visible region of the spectrum. The
globe should fit securely, it should be clean and free of chips or cracks, and it should be so maintained at
each change of electrodes. It is discarded whenever noticeable discoloration (as compared with an unused
globe) occurs, or in any event after 2000 hours of use.
3.3 Test chamber
3.3.1 Ventilation control. Clean air is circulated through the test chamber and over the test specimens and
standards, to prevent excessive rise in temperature.
The air velocity or air temperature may be adjusted to control the temperature. If wet and dry bulb
thermometers are used to measure relative humidity in the test chamber, the air velocity at this point
should be not less than 3 m per second.
3.3.2 Temperature measurement. Temperature is measured by a black panel thermometer (see Note below) or
mercury thermometer with a blackened bulb, mounted in the position normally occupied by the test
specimen.
The black panel temperature should not exceed 55 OC.
NOTE. - The black panel thermometer consists of a 0.9 t 0.1 mm thick steel panel, of a size to fiU completely one
specimen holder and finished with a black glossy enamel having good resistance to light. The panel is provided with
means for measuring its temperature at the centre. A thermocouple or bimetallic thermometer making intimate contact
with the panel is suitable.
3.3.3 Relative humidity measurement and control. Relative humidity may be determined by means of wet and
dry bulb thermometers mounted on the specimen holder, but shielded from the radiation. If means for
control are available, relative humidity is adjusted to the value specified for the material. In a test
chamber not equipped for such adjustment, the relative humidity prevailing in it is measured and
reported. Materials highly sensitive to humidity should only be tested in a test chamber capable of
control.
3.4 Specimen holders
A cylindrical frame between the arc and the shell of the test chamber supports specimen holders which
accurately position the test specimens so that they face the arc at a distance of 25.4 cm from the effective
centre, with no part more than 6.5 cm above or below the horizontal plane passing through the centre of
the source. (For twin arcs, the test specimens are 38 cm from a point midway between the arcs).
3.5 Standards
Blue dyed wool standards No. 1 to No. 8, as specified in IS0 Recommendation R 105/1, Part 11,
clause 3.1.1 .* (See Appendix, section Z. 1, of this IS0 Recommendation).
3.6 Grey scale
Grey scale for assessing change of colour, as specified in IS0 Recommendation R 105/I, Part 2.* (See
Appendix, section 2.2, of this IS0 Recommendation). In this scale, Grade 1 corresponds to the greatest
degree of contrast, and grade 5 to zero contrast (two patterns of identical colour).
*
See IS0 Recommendation R 105/I, Tests for colour fastness of textiles (First series)
Part 2 : “Grey scale for assessing change in colour”,
Part 11 : “Colour fastness to light : Daylight”.
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iSO/R 878-1968 (E)
4. TEST SPEClMEN
The test specimen may conveniently be 60 to 70 mm in length and 20 mm or more in width, according to
4.1
the dimensions of the specimen holders used.
For film and sheet, the test specimen is cut to size and is of the thickness of the film or sheet.
For moulding materials, a moulded sheet of thickness 3 i O. 15 mm is prepared and the test specimen cut
from this, unless other methods of preparation or other thicknesses are prescribed in the specification for
the material.
For materials which may shrink in one direction during the test, the test specimen should be cut with its
long dimension at right angles to this direction, since a change in the length of the test specimen may
displace the limiting line between exposed and unexposed parts and thus diminish the sharpness of
contrast.
4.2 One test specimen is used. More may be required for materials which are not of a uniform colour.
A further control specimen (or specimens) is required for comparison.
5. PROCEDURE
5.1 When a number of specimens are to be tested simultaneously, the test specimens are mounted in the
specimen holders facing the source, both above and below the horizontal c
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