Overview
ISO 5627:1995 - Paper and board: Determination of smoothness (Bekk method) defines the Bekk smoothness test, an air-flow based procedure to quantify the smoothness of paper and board surfaces. The standard replaces ISO 5627:1984 and is especially recommended for smooth papers and boards. It describes apparatus, sampling, conditioning, test procedure and reporting so laboratories and manufacturers can obtain comparable Bekk smoothness values.
Key topics and technical requirements
- Test principle: a test piece is clamped against a polished glass plate and a partial vacuum draws atmospheric air through the surface gap; the time for a specified vacuum change is recorded - the greater the time, the smoother the sample.
- Apparatus basics:
- Polished glass plate with a contact area of 10 cm² (±0.05 cm²) and a central vacuum connection.
- Pressure plate (≥45 mm diameter) and rubber pad (thickness ~4.0 mm ±0.2 mm; hardness 40 IRHD ±5).
- Vacuum containers: large (≈380 ml) and small (≈38 ml) volumes; manometer accurate to ±0.07 kPa.
- Timing device readable to the nearest second.
- Operating conditions:
- Apply a pressure of 100 kPa ±2 kPa to the test piece.
- Create a vacuum of 50.7 kPa, then measure time for drop to 48.0 kPa (or to 29.3 kPa in low-time cases).
- Use 10 test pieces per face (separate areas), conditioned per ISO 187.
- Expression of results:
- Arithmetic mean of 10 readings per face is reported as Bekk smoothness (in seconds).
- When the small vacuum container is used, multiply the mean by 10; when the larger vacuum drop (50.7→29.3 kPa) is used, divide the time by 10 to obtain the Bekk value.
- Limitations:
- Not recommended for materials thicker than 0.5 mm, very permeable papers/boards, newsprint, or rough surfaces.
- Extremely smooth samples may yield impractically long measurement times.
Applications and users
- Primary users: paper and board manufacturers, quality control laboratories, independent testing labs, converters and printing companies that require quantitative surface-smoothness data for process control, product specification, and printability assessment.
- Practical uses: incoming raw-material checks, production quality monitoring, comparative testing of coatings and calendering effects, and specifications for printing or finishing performance.
Related standards
- ISO 187 - conditioning and atmosphere for testing
- ISO 186 - sampling for average quality
- ISO 48, ISO 4662 - referenced for rubber pad properties and resilience
Keywords: ISO 5627:1995, Bekk method, Bekk smoothness, paper smoothness test, smoothness of paper and board, air-flow smoothness test, paper quality control.
