Digital BW, The Print

Ernst,

This is probably the article I recall: 
http://www.geocities.com/thombell/rcvsfiber.html 

It notes, among other things, "Intensive research at Kodak and among the
other manufacturers finally pointed to the culprit - the white pigment
titanium dioxide (TiO2) that was added to the polyethylene resin layer on
the face side of the print to make it white and reflective. While the prints
were on display, the TiO2 pigment absorbed light energy and generated a very
active form of oxygen that attacked the resin layer and caused the
cracking."

So, the TiO2 was not an OBA but more like what you described.

The author of this article, James M. Reilly, Director of the Image
Permanence Institute, Rochester Institute of Technology, concludes that the
RC papers can be as long lived as the fiber based prints.

But I'm sure that won't stop the skepticism.

Paul
www.PaulRoark.com 




> -----Original Message-----
> From: DigitalBlackandWhiteThePrint@yahoogroups.com
> [mailto:DigitalBlackandWhiteThePrint@yahoogroups.com] On Behalf Of Ernst
> Dinkla
> Sent: Sunday, February 19, 2006 1:53 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: Re: [Digital BW] Crane SR & Da Vinci Fibre Gloss Paper
> 
> Paul Roark wrote:
> > Kodak's story (working from memory here) with respect to the RC cracking
> was
> > that the OBAs were originally titanium dioxide.
> 
> Paul, if I recall it correctly, titanium dioxide is a highly
> opaque white pigment only but it can not be combined with OBAs
> as it reacts with the OBAs causing  yellowing. I saw that
> information not so long ago when I checked whether transparent
> OBAs exist. TiO2 is still used in thin polyethylene foils to
> give the foils a high white opacity  despite their thickness.
> 
> They put out a strong
> > oxidant that attacked the polyethylene and cracked it.  In response, a
> > number of companies put anti-oxidants in the coating to deal with this
> > problem, but they yellowed.  Now, presumably, there is a combination of
> less
> > reactive OBAs and non-yellowing anti-oxidants that solve the RC problems
> --
> > according to the manufacturers.
> >
> > Polyethylene is apparently a broad category of materials, within which
> there
> > can be significant performance differences.  Whether what is used in the
> > papers is up to the job might depend on more than just what the common
> name
> > is for the material.
> 
> There are several grades and copolymeres. For foils like that
> you would use high density polyethylene. Main problem of
> plastics like polyethylene and polypropylene is getting a
> bond between the coating and the plastic itself. The foil has
> to be corona treated to change the polarity on the surface
> after that there's a short time to create the better bond. In
> time that may be lost again. Polyethylene will have
> plasticisers added if there's a need for more flexibility,
> paraffin wax is the more ordinary one. In itself not a nice
> material to create a bond on. It also migrates from the
> polyethylene in time. For this barrier purpose I do no think
> that it is needed, the foil is thin enough to be flexible. For
> outdoor use polyethylene has one bad property, it is easily
> attacked by UV light that will shorten the long molecules to
> shorter ones and make the material brittle in time.
> 
> >
> > One industry person I spoke with thought the new technology did involve
> a
> > barrier, but it might not be polyethylene.
> 
> Enough other barriers possible and most likely it will be a
> sandwich of more plastic foils. PVA for example often is used
> in combination with other foil(s) to combine a gas and fluid
> barrier in one layer and/or to create a better bond to paper
> or coating.
> 
> >
> > Lots of uncertainty here ...
> 
> Right, you only have to check who supplies what in the coating
> industry to know that there are a thousand combinations possible.
> 
> Ernst
> 
>                     --
>            Ernst Dinkla
> 
> 
> www.pigment-print.com
> (         unvollendet         )
> 
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