Surface properties

Question 1

Why is air permeability an important measurement?

Answer 1

How much air can pass through the sample
An indirect measure of refining
Filtering efficiency
Absorbency
And how the paper will react to printing!

Question 2

How is air permeability influenced

Answer 2

Surface finish - coating and calendaring (denser sheet)
Fibre type and length - short fibres decrease air permeability - they fill in gaps
Fillers - more fillers will decrease air permeance - fill in gaps

Question 3

Which air permeability testers do you know

Answer 3

Bendtsen
Sheffield
Gurley
All measuring air going through the paper

Question 4

What are the traditional instruments to measure smoothness?

Answer 4

Bendtsen (ml/min)
PPS (micrometers)
Bekk (seconds)
Usually measured through air leakage principle, device is placed on paper - if a lot of air is leaking the surface must be rougher with grooves allowing it to escape

Question 5

Which unit are Bendtsen, PPS, and Bekk (Roughness testers)

Answer 5

Bendtsen - ml/min
PPS - micrometers
Bekk - seconds

Question 6

Do you expect a higher roughness for the top or for the wire side and why?

Answer 6

On the wire side
Fillers and fines are likely to pass through the wire, until a mat of fibres builds up which can catch the smaller particles. Thus the top side has higher amount which help fill in gaps contributing to smoothness
Will also have the wire marks

Question 7

Which factors can affect the surface properties of a paper

Answer 7

Whether the paper has been calendared - this helps to smooth out the paper
If a coating has been applied - this can change the smoothness and gloss