Contact person
Mikolaj Malinowski
Forsknings-och utvecklingsingenjör
Contact Mikolaj
Optical formation measurement
Optical formation is the variation you see when looking through a paper illuminated from the back side. Fibre flocks of different sizes and shapes can be seen as well as wire marks.
For coated paper qualities the coating can reduce paper thickness variations but then the coating layer thickness will have a variation, and this can cause mottle.
Purpose
Measurements of the optical formation is a tool that shows how smooth the paper machine makes the paper. Fibre flocs of different sizes are unwanted but always present to some extent.
The formation is important for the wet pressing and drying in the papermaking process, as well as for the end use properties of the paper.
Note: The optical formation depends on the light-absorption and light-scattering properties of the material. Coating will more effective prevent the light from passing the paper compared to fibres and filler.
An alternative method is to use beta formation. The beta radiation method is directly dependent on the mass of the material in contrast to optical formation.
The measurements can be used for:
- Measure if the optical formation is acceptable and stable over time
- Monitor how new settings in the productions affect the optical formation
- Check if new products are better or not when it comes to optical formation
Method
The samples are scanned in a flatbed scanner with a transparence unit in 300 dpi resolution or higher. Frequency analysis is applied to divide the variations coming from flocs into size intervals.
Deliveries
The optical formation value, which is the gray level variations as Coefficient of Variation in size interval (wavelengths) 1-8 mm and also, detailed optical formation divided in spatial octave bands, ex. 0.25-0.5 mm, 0.5-1 mm, 1-2 mm, 2-4 mm, 4-8 mm and 8-16 mm revealing the optical formation in fine scale, medium scale and large scale.
The results are saved in an Excel file.
