Digital BW, The Print

Ernst Dinkla wrote:

> Henry Wilhelm says something about Barium Sulfate versus 
> Titanium DiOxide and analogue RC papers but it goes a bit 
> further than just RC papers. Interesting comments about 
> Barium Sulfate and the use of OBAs in the second one.

> http://www.wilhelm-research.com/pdf/HW_Book_17_of_20_HiRes_v1a.pdf

Following up on the comment above.

In the euphoria about Baryta papers it would be good to 
check one thing thoroughly: to get a whiteness equal to the 
TiO2 coating whitener as used in RC polyethylene and nonRC 
paper coatings a thicker Baryta coating is needed and I 
suspect more optical brightener. The Barium Sulfate 
refractive index is way lower than that of TiO2. The link 
above describes the advantage of barium sulfate not blocking 
UV light and by that giving the optical brighteners their 
best effect. The optical brightener can be added to the 
paper base instead or additional to the coating for the same 
reason. There are reservations about the use of optical 
brighteners and alternative whiteners. UV stability of both 
are not at the level of TiO2. That alternatives for TiO2 are 
sought is not just for nostalgic (darkroom) reasons, TiO2 is 
more expensive so blends with other (cheaper) whiteners are 
made and other whiteners are developed to give them TiO2 
specs, primarily by getting the particle size and uniformity 
close to that of TiO2. The new Alumina mentioned is one 
example but Alumina itself in clay coatings isn't new. What 
Baryta content actually is used in the paper coatings is a 
mystery. The Sihl Baryta specs mention a high Barium Sulfate 
content but not that it is the sole whitener in the coating. 
There is little or no optical brightener in that paper and 
both base and coating color are warm. It is hard to check 
how good development has been on substitutes for TiO2 not 
just in their opacity and whiteness but also in relation to 
stability in time. One thing is sure, the Baryta coating on 
inkjet papers of today isn't an exact copy of the analogue 
Baryta coating of >10 years ago.


This was written in 1999 (hard to read in Firefox, Explorer 
is good):

http://www.allbusiness.com/manufacturing/plastics-rubber-products-manufacturing/294696-1.html


-- 
Met vriendelijke groeten,  Ernst


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