Digital BW, The Print

My first post to this list.
For a good few years now I've seen TiO2 mentioned in New Scientist magazine
as useful in breaking down organic compounds in the presence of UV. An
example application is self-cleaning windows. I've also seen references
elsewhere to self-cleaning Japanese toilets. This is more or less what the
article at ingentaconnect is about. This admittedly non-academic link seems
to illustrate the process well, for anyone who is interested:
http://tekoneast.com/titania/Green%20Quest%20-%20Photocatalyst%20Mechanism.htm

Wikipedia:
http://en.wikipedia.org/wiki/Titanium_dioxide

And an interesting and more technical article:
http://www.threebond.co.jp/en/technical/technicalnews/pdf/tech62.pdf

Two things stand out:
1. in the presence of water, TiO2 produces hydroxyl radicals which are
extremely reactive and could certainly damage paper and/or ink
2. TiO2 is hydrophilic

Neither of these sound like great things for the paper that holds the TiO2.
On the other hand, if the TiO2 particles are coated to prevent such contact
it could have a protective effect. It is the key component to any sunscreen,
due to its being highly reflective to UV light. So if the particles are
coated, it could be beneficial in reflecting away any UV.

Tom

On 06/04/07, Paul Roark <paul.roark@...> wrote:
>
> {snip}
> My questions with respect to the TiO2 claim are more with respect to
> whether
> it is a true OBA and whether it has other properties that make it
> undesirable in papers.
>
> "Titanium dioxide (TiO2) reflects ultraviolet light, ...
> [I]n the presence of sunlight and water, TiO2 catalyzes the formation of
> hydrogen peroxide, ..."
>
> http://www.ingentaconnect.com/content/klu/bico/2003/00000048/00000005/05122462
>
>
> If TiO2 reflects UV rather than absorbs it and re-emits it as blue light
> like the OBAs we usually talk about, it might still be considered a
> "brightener" in that it is very white, but it is not the same as the dyes
> that convert UV to visible light.  This might explain why with respect to
> at
> least one Premier Art paper claimed to be "Bright White" I did not detect
> fluorescence under my UV light.
>
> TiO2's catalytic properties were apparently what caused the polyethylene
> cracking in the original RC papers (according to an old Kodak
> publication).
> I wonder if that same property has any effects on fading, which, after
> all,
> is an oxidation process.
>
> On the other hand the above paper, which is not talking of paper, mentions
> that TiO2 can be coated to eliminate the catalytic properties.  So, it may
> be that the coating companies are using an advanced form of the very white
> pigment to make their papers very white, even if not fluorescent.
>


[Non-text portions of this message have been removed]