paper sizing agents (was Re: fabriano paper)

From: "Christina Z. Anderson" <zphoto@bellsouth.net>
Subject: Re: fabriano paper
Date: Thu, 06 May 2004 10:27:36 -0400

> Ryuji asks> Besides gelatin and "starches" what are used as sizing material?
> > I wonder if the sizing in this paper is retained in my processing,
> > where the sensitizer is coated at 35-40C.
>
> Now THAT'S the question to ask. I know there are such things as:
> alkyletene dimer or aquapel, whatever the heck that is. You chemists can
> tell us laypersons.

Dimeric alkylketenes can form strong covalent bond with hydroxyl
groups of cellulose under certain conditions to make the fiber
hydrophobic or less absorbent (Weisgerber, C. A. and Hanford, C. B.,
1960. Tappi, Vol 43, No 12) so it's a useful sizing agent. Indeed,
this seems to be one of the preferred neutral internal sizing agent
for silver gelatin paper stocks, as paper that is heavily sized with
this agent doesn't absorb too much processing chemicals and wash more
readily (Of course typical commercial baryta papers have surface
sizing and baryta sizing on top of that.) It seems that Aquapel is a
product consisting of blends of dimerric alkylketenes in emulsion form
and maybe some other additives.

Why gelatin sizing isn't used so much? I couldn't find an answer to
that, but it seems to be related to that the way papers are made in
industry is rather incompatible with gelatin.

Why dimeric alkylketenes are preferred as the internal sizing agent?
I think older materials used aluminum sulfate or some other things in
part, and this rendered the paper acidic, and the paper became brittle
over time -- archival problems.

Anyway, Aquapel-type internal sizing is most likely safe with my
coating temperature, but I'm not certain about other sizing agents
that are often used in conjunction with these material. (such as
modified starches)

--
Ryuji Suzuki
"All the truth in the world adds up to one big lie." (Bob Dylan 2000)