Re: Selling RP, color question

From: Nkin (
Date: Mon May 04 1998 - 15:44:31 EEST


In a message dated 98-05-04 06:13:35 EDT, you write:

> but i too agree with Mr Rees on WYSIWYG for the sales
> presentation/mockups.....but remembering colours can be further divided
> into can we encompass the production for all the various
> shades that may be required???

You've noted a "color" limitation which may be significant for systems which
must place
colored material in "conventional" fashion. For instance, a machine which
must extrude a
different colored filament to achieve variation would indeed seem limited
(unless it could
color the material as, or after, it is extruded).

There's another method, however, which can more closely approximate the color
resolution of 2D printing. Lacking a better term, I call it "indirect
coloration." It has
long-term potential for use with several existing technologies - any system
which "adds" a
material which has the ability to absorb ink or the ability to diffuse light.
{This includes
powder systems and systems which can add a material which could be "inked"
destroying layer bonding capabilities}

Perhaps the simplest embodiment is with "cut-on-the-stack" lamination. When
laminate a layer of material, you can color the top surface with a suitable 2D
system (an ink jet could be used after lamination or a laser printer could be
used before
lamination). If the material is suitably absorbent (such as some papers) or
has the ability
to diffuse light (such as translucent acrylic - but not clear acetate), the
layer will expose
color throughout its depth after it has been cut to shape with a knife.
{Quality varies, but
three tests can be used to prequalify a material: a stack must appear white on
its side, a
single layer must show color on the bottom when colored on the top, the edge
must not
discolor when cut}

In lamination, it's also helpful to use the same printing device to achieve
"selective bonding"
 - either by applying the bonding agent or by applying a release agent. The
samples I've
fabricated use thin butcher paper, a pen plotter (for placing black ink and a
release agent)
and a sign cutter. I see no reason why additional research will not allow a
range of better
materials, improved color resolution, and user-friendly "unshelling" of
laminated products.
 Fortunately, no laser necessary.

In contrast to placing precolored material, "indirect coloration" can use well
printing methods, including dithering. The bulk of the material is
inexpensive and
"uncolored." Only a relatively small perimeter band must be colored on the
top surface.
In that crucial area, near the cut edge, a very small volume of ink transforms
the full depth
of a layer to the "edge color" which is desired. Moreover, this "edge color"
can also be extended any required depth into the model so that it is not
removed when abraded or polished.

So much room for research!

Norm Kinzie


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