Overview
ISO 8226-1:1994 establishes a standardized method for the determination of hygroexpansivity of paper and board products when subjected to changes in relative humidity, specifically up to a maximum of 68% relative humidity. This international standard, developed by ISO Technical Committee 6/SC 2, replaces its first edition from 1985 with updated guidelines and procedures.
Hygroexpansivity refers to the dimensional change (expansion or contraction) in paper and board as a result of absorbing or desorbing moisture from their environment. Understanding this property is crucial for accurate control of processes such as printing, converting, and packaging, where dimensional stability is critical.
Scope
- Applicable to most paper and board grades
- Not suitable for crêpe papers and corrugated fibreboard, due to their specific structures
- Specifies the method for measurement between 33% and 66% relative humidity
Key Topics
- Hygroexpansivity Measurement: The standard defines hygroexpansivity as the percentage change in the length of a test strip conditioned at different relative humidity levels.
- Test Conditions: Emphasizes the necessity of controlled environments, including precise temperature (preferably 23°C ± 1°C) and humidity maintained by saturated salt solutions.
- Sample Preparation: Details on specimen selection, preparation, and conditioning to ensure test reliability and repeatability.
- Apparatus Requirements: Describes equipment for humidity and temperature control, accurate length measurement devices, and specific loading weights based on paper grammage.
- Test Procedure:
- Preliminary conditioning at low humidity
- Sequential exposure to 33% and 66% relative humidity
- Measurement of dimensional changes under controlled loads
- Expression of Results: Hygroexpansivity expressed as a percentage, with mean and standard deviation reported for both machine and cross directions of the paper.
Applications
ISO 8226-1:1994 is vital for industries where dimensional stability of paper and board affects product performance and quality:
- Printing and Publishing: Ensures precise alignment and registration during multi-color printing processes by predicting paper expansion or contraction.
- Packaging Manufacturing: Prevents warp or misfit in paperboard packaging due to environmental humidity changes.
- Paper Converting: Assists in process control for laminating, coating, and other operations sensitive to dimensional changes.
- Quality Control and Product Development: Enables manufacturers and laboratories to benchmark products and ensure compliance with industry requirements.
- Research and Development: Provides a framework for studying moisture-related behavior in new paper and board materials.
Related Standards
For comprehensive quality assurance and testing in the paper and board industry, the following ISO standards are often used in conjunction:
- ISO 186: Paper and board - Sampling to determine average quality
- ISO 187: Paper, board, and pulps - Standard atmosphere for conditioning and testing and procedures for monitoring the atmosphere and conditioning of samples
- ISO 536: Paper and board - Determination of grammage
Additionally, ISO 8226-2 covers hygroexpansivity measurement up to 86% relative humidity, suitable for applications where paper or board is exposed to higher humidity conditions.
In summary, ISO 8226-1:1994 provides a standardized, reliable method for assessing the hygroexpansivity of paper and board up to 68% relative humidity-a key quality characteristic for ensuring performance and consistency in paper-related industries.