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Printech Archives, May 1998: Re: Soy ink melting in laser printers, copiers

Re: Soy ink melting in laser printers, copiers

Robert Gifford (
Tue, 26 May 1998 14:30:48 -0500


This inquiry and response provides information from Wilson
Cunningham, a technical advisor to the National Soy Ink Information
Center. The Center's web page is <www.soyink.com>.
Fact sheets are available at <http://www.soyink.com/newfact.html>.
The 'laser proof' claim is made in <http://www.soyink.com/inkpromo.html>.

------- Forwarded Message Follows -------

Robert Gifford wrote:
> Mr. Cunningham:
> I have spoken with a printer who has experienced difficulties with soy ink
> on letterhead and forms which will be passed through hot environments like
> laser printers and photocopiers. The complaint was that constituents in
> the ink melted and transfered to machine parts. Parrafins in the ink were
> blamed.
> Are there any workable substitutes which are environmentally friendly?
> Are there 100% soy inks which can be used in these applications?
> Thank you for your assistance,
> Bob

Robert Gifford wrote:

>I have seen claims from the National Soy Ink Information Center
> that soy ink is 'laser proof' since the boiling point of soy oils is
> higher than petroleum oils.

Inks are mixture of 3 major components(account for about 97% by weigh),
pigment, resin, and liquid solvent. Soy oil or petroleum oil are
solvents. The advantage of soy oil over petroleum oil in heat stable
inks, like laser proof, is the higher boiling point soy oil is less
likely to "off gas" which will cause the resins to soften and release it
from the paper. This release is the seen as the unwanted transfer to the
hot patten of a laser printer.

Robert Gifford wrote:
>If parrafin is the culprit, then this does not
> seem to address the issue, especially for inks which are mixtures of soy
> and petroleum oils.
> What purpose does parrafin serve in a soy ink? How much is needed?

Parrafin waxes are used resin for some ink application but generally they
are not used for inks that are formulated for a secondary printing by a
laser printer. Similar to a candle, they become liquid when heated and
therefore it does not act as a pigment adhesive (one function for a
resin). If this is the printer's true problem, he/she is using the wrong
ink for the job and should contact the manufacturer for a better product
selection. Within the limited confines of chemical compatibility, you
should understand that resin and solvent are independent variables. In
other words, the choice of a parrafin resin is doomed to failure for this
type of printing - the properties of soy oil or petroleum oil will not
cure the problem.

There may be several things that the printer is doing that may be
affecting the "laser proofing" of the ink:

1) Printing an ink film thickness that exceeds the absorption capacity of
the paper stock. This becomes problematic when the sheet is not white.
The printer in an effort to give the color some visual contrast will
increase the inking level. This procedure is essentially printing ink on
ink and the secondary layer of ink is not adhered to the paper.
Non-adhered ink is prone to unwanted transfer to either the hands or
heated patten. Solutions require: reduction of the inking level, adjust
the ink-water balance, check roller settings. These actions should help
the unwanted transfer problem but the client may want more visual
contrast and the printing problem then becomes a client problem because
his/her expectations exceed the capacity of the printing system.

2) Inks, soy oil based or petroleum, that are designed for secondary
laser printing have a recommended curing interval. This time allows the
oils to dispate into the sheet and the resin to harden and adhere the
pigment. Exposure to heat before this alloted time will remove the
partially harden resin. Most ink manufacturers' product literature will
state this time.

3) The choice of paper stock may not have enough oil absorption capacity.
This causes the ink to be isolated on the paper's surface instead of
being drawn into the paper. Solutions require either a change in the
paper stock or a reformulation of the ink- which usually requires the
additon of petroleum oil that has a lower viscosity than soy oil.

At this time, there are no commercially available 100% soy resin-soy oil
inks. A 100% soy resin can only be maded by an oxidative polymerization
of the unsaturated fatty acids contained in the soy oil. These resins
can be used to formulate inks. Actually all inks formulated before the
1950's used this resin type. These resins lack many of the physical
requirements of the modern printing processes or diversity of product
types expected by the customers. Soy oil can be chemical reacted with
petrochemicals to form an array of different resins that are harder,
disperse pigments better and print better than oxidized soy oil.

If you need more information or need a better explanation, please contact

Wilson Cunningham



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