What are the uses of minerals in Paper making
Pitch control - bentonite, talc
filler - cheaper than fibre
coating
ink qualities
Why was GCC and PCC not often used prior to 1980’s
Because the paper making process was acidic
define filler
minerals used in the wet end
define pigment
surface application
What does opacifying power depend on
Light scattering and therefore particle size
PCC better than GCC (Narrow psd can remove ultra small)
give a wishlist mineral
Chemically stable
Good light reflectivity across all wavelengths (TiO2 doesn’t fit this)
Free from impurities
Dispersible
Low density
Non abrasive
Low water absorption
Advantages of filler on paper
smoothness
brightness
opacity
density
aging resistance
ink receptivity
Disadvantages of filler on paper
Loss of strength (interrupts fibre bonding)
reduces bulk
dusting
advantages of coating
smoothness
Pourous structure changes liquid absorption
decrease dusting
gloss and opacity
disadvantages coating
loss mechanical strength and stiffness
How can you adjust opacity with particle size
Particle size has a heavy influence on scattering coefficient, ultrafine particles drop off a cliff
what is difference between narrow and broad psd
Broad has less void volume as different shapes can fill the holes. gives more closed surface structure.
Broad has better coating hold out as has less penetration
