ISO 18903:2002 pdf download
ISO 18903:2002 pdf download.lmaging materials -Films and paper —Determination of dimensional change.
3.12
width direction
direction of the film or paper at right angles to the length direction
NOTE This is also termed “cross direction”.
4 Measurement technique
There are a number of different techniques used for measuring the dimensional change of sensitized materials. Specifications of measuring equipment are beyond the scope of this International Standard, but several approaches are described in annex B.
5 Sampling
5.1 Selection of specimens
Specimens intended for dimensional 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.
5.3 Conditioning of specimens
5.3.1 General
Specimens shall be suspended in the conditioning atmosphere by means of 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 moisture equilibrium has been reached. The time required to achieve this condition shall be established by actual measurements on representative specimens or based on prior experience.
5.3.2 Film
The conditioning time for film will be about 4 h, but will vary according to access of the conditioning air, the film type, base thickness, etc. Conditioning time shall not exceed 24 h.
At relative humidities of 60 % and above, films 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 I d of conditioning; resin-coated papers require at least 7 d.
Specimens may be developed as negatives or as positives, but this can affect the dimensional change properties of some materials. Silver-gelatin films generally show less dimensional change when they have low density rather than high density.
6.1.1 General
Either a walk-in constant humidity room or a cabinet may be used.
6.1.2 Constant humidity room
The relative humidity (RH) shall be held constant to ± 1 % or better in areas of the room where specimens are measured. The room shall be vapour sealed, insulated on all six sides, and shall be mechanically air-conditioned. Air shall be circulated at a linear velocity of at least 15 cm/s. The number of personnel permitted in the room at any one time during testing shall be limited.
The relative humidity of the room shall be checked regularly, preferably by means of an electric hygrometer calibrated by a dew-point method.
Humidity measurements to within ± 1 % RH are difficult and are to be carried out in accordance with
ISO/TR 18931.
6.1.3 Constant humidity cabinet
A convenient size for a humidity cabinet is approximately 1 m in height and 0,5 m in width and depth. It shall be constructed of materials that will ensure good insulation. Suitable provision shall be made for thermostatically controlling the temperature within the cabinet. Air shall be circulated throughout the cabinet at a linear velocity of at least 30 cm/s.
The cabinet shall be equipped with ports filled with moisture-impermeable (e.g. rubber or plastic) gloves for entrance of the operator’s hands. The relative humidity of the cabinet shall be checked regularly, preferably by means of an electric hygrometer calibrated by a dew-point method.
The relative humidity within the cabinet shall be controlled as closely as possible. Where the cabinet is mechanically air-conditioned, the relative humidity shall be maintained to ± I % or better. Where a saturated salt solution is used for control, provision shall be made at the bottom of the cabinet for inserting suitable trays, which shall hold about I I of salt solution. A solution tray with a large surface area is needed and about 100 cm2 is suitable.
6.2 Standard temperature and humidity.
