ISO 18903 pdf download – lmaging materials.-Films and paper —Determination of dimensional change.
5 Sampling
5.1 SelectIon of specimens
Specimens intended for cmensional stability tests shall exhibit no obvious physical defects, be representative of the whole of the material being tested, be handled in the same manner as in actual use, and be treated uniformly. When different materials are to be compared, they shall have been subjected to the same conditioning history. The length direction should be indicated if known.
5.2 Handling of specimens
Specimens shall be prepared under controlled conditions and then separated into groups which are subjected to different atmospheric conditions. The operator shall take care not to breathe on the specimens and shall wear moisture-resistant gloves while handling them, since moisture from the skin may reduce the accuracy of the results.
3.3 Conditioning of specimens
5.3.1 General
Specimens shall be SUSpended in the conditioning atmosphere by means o4 a hook or a rod through a hole In the middle of one end near the edge of the specimen. The specimens shall be separated to prevent contact with each other. An alternative method of conditioning is to place specimens in racks spaced so that there is free circulation of the air on both sides of the material.
Specimens shall not be removed from the conditioning atmosphere for measuring. Condition specimens until practical moesture equilibrium has been reached. The time required to achieve this condition shall be established by actual measurements on representative specimens ci’ based on prior experience.
5.3.2 Film
The conditioning time for film will be about 4 Ii, but will vary according to access of the conditionmg air, the film type, base thickness, etc. Conditioning time shall not exceed 24 h.
At relative humidities of 60 $ and above, fikiis and papers sometimes undergo an irreversible change In size with time. For this reason, the conditioning time shall be standardized for comparison purposes.
5.3.3 Paper
Double.weight fibre.base papers will require about 1 d of conditioning; resin-coated papers require at least 7 d.
The otmensions of the unprocessed specimen at a geren relative humidity can be dependent to a large extent upon the earlier humidity used for precondiiioning (preconditioning humidity history). This is due to the hysteresis and relaxation effects described in annex C.
It is necessary to specify whether the specimen had been preconditioned from a lower humidity or from a higher humidity prior to the orinal measurement on the unprocessed matenal, This is indicated by the letter L for the former and H for the latter, When a specimen is measured from the original box (or packaging) without preconditioning. the letter B is used
9.1.3 Relative humidity for preconditioning of a processed specimen
The preconditloning humidity history Is as Imporlant for the dimensions of the processed specimen as for the raw specimen described In 9.1.2. The letters ‘V and H” are also used to indicate the humidity history of the processed material. The letter ‘H is also used when the specimen Is dried after processing at the measuring humidity.
Although the dryng conditions after processing affect the dimensional change due to processing, the effect is eliminated when the processed specimen is preconditioned. If measurements are made on a processed specimen that is not preconditioned after processing. the letter ‘M is used.
9.1.4 Relative humidity condition
Specimens shall be contioned to moisture equilibrium using the same relative humidity for both the raw and processed measurements, Otherwise, a reversible humidity change will be included in the measured dwnensaonal change However. The dimensional change due to processing can be very dependent upon the relative humidity at which those measurements are made and this shall be indicated when reporting the results
9.2 Coding system
A wide variety of test procedures can be used for the measurement of dimensional change due to processing by varying the preconditioning history of the raw and processed specimens and the relative humidity at which these measurements are made.
To characterize the procedure used, a coding system Is used. For example, procedure LH-50 slgnif*s that the raw specimen had been preconditioned from a low humidity (L), the processed specimen had been preconditioned from a high humidity (H). and all measurements were made at 50 % RH. Likewise, procedure LL-1O indicates that both the raw and processed specimen had been preconditioned at a lower humidity than the 10 % RH at which the specimens were measured. In practice, the range encompassed by LH-50 (tray processed and air dried) and HL-50 (machine processed and machine dried) generally reflects the expected variation in processing dimensional change The procedure BM-50 indicates that no preconditioning was done for either the raw specimen from the original box (or packaging), or the processed specimen from the machine.
ISO 18903 pdf download – lmaging materials.-Films and paper —Determination of dimensional change
