Subject:
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Re: Variations in dark blue color.
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Newsgroups:
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lugnet.color
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Date:
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Thu, 21 Feb 2008 05:21:47 GMT
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Viewed:
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9583 times
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In lugnet.color, David Eaton wrote:
> In lugnet.color, John Patterson wrote:
> > I was emailed by a former employee of Legoland and she said that the
> > bricks are sprayed with a chemical that what blocks UV light.
>
> I believe that although the chemical coating prolongs the life of the model, it
> doesn't mean it will last indefinitely or will never yellow. It just means it
> takes longer to do so.
It is absolutely impossible to create a clear coating that will shield the uv
light forever because of the fact that one has to incorporate some uv absorber
in the coating that will absorb the energy. And transparent ones are not nearly
as efficient as opaque ones. Sooner or later, that energy will degrade the
material that absorbs it and thus the film will fail--i.e. use up the uv
protector. That is the reason clear varnishes and sealers have a very limited
lifetime. Properly pigmented paint will last much longer. Now, the other
solution is to make a clear coating that is pretty much transparent to uv light.
For example, a clear acrylic finish. The finish will last well in uv, but will
not provide protection for the substrate. Therefore, say in the example of wood,
a clear coating of this sort is a poor protector of wood, as it allows the uv to
go through it and degrade the wood underneath.
We are talking clear films here--but if pigments are included then they act as
uv blockers and protect the resin (and also the substrate). In most coatings
systems, your main object is to protect the substrate. Transparent aluminum, a
la Star Trek Whale movie would be a great material to put into a clear acrylic
coating. lol
To me, the solution for LEGO Land models is simply put them under a giant tent
of some kind that would block the uv from reaching the models. Replace the tent
when it wears out. ABS is not an exterior grade material, and I have always
thought that it was pretty dumb to put wonderful expensive models outside.
When in Billund, they were experimenting with coating their models with
essentially an automotive grade acrylic clear coat with uv inhibitors in it.
Unprotected and exposed to direct uv from sun, the abs resin would degrade and
the when it did the gloss of the brick would diminish and the colors would fade.
Just like high gloss paint will eventually lose its shine.
Synthetic dyes--dyes are materials that actually dissolve in the resin-are in
most circumstances more susceptible to uv light because their organic chemical
bonds are broken down by the energy of uv.
Pigments, which are many times inorganic and do not dissolve but rather are
dispersed into the resin, most times provide a much better resistance to uv. For
example the TiO2 used in white bricks provides good uv resistance, but the abs
that wets the TiO2 is still susceptible to yellowing caused by the breakdown of
the bonds of the abs molecules. Perhaps a bit of zinc oxide in the pigment mix
would help mitigate yellowing--it does so in paint resins that are susceptible
to yellowing. I am not really an abs expert, but at one time was a paint
formulator. In fact worked for a company that was the first in USA to make and
sell a quality exterior Acrylic house paint. But I am confident that to get the
pigments to disperse, one had to add dispersing agents and it is a very
difficult thing to get just the right amount and right kind to maximize
dispersion. And these additions add further complexity to the system and in
most times cause undesirable side effects (as well as additional costs). Add
heat, shear of mixing, chemical changes induced by the heat, chemical changes
induced by the cooling process, etc. etc. and you come up with a very, very
complex system, Much trial and error and research has to be done to maximize qc.
Of course much of this is done by the resin and pigment suppliers—but each
recipe is unique and each is complex with all kinds of things going on at a
molecular and particle level.
Trust me--it is a very complex issue.
I know this is absolute heresy, but honestly speaking from a scientific point of
view, the best way to insure your mocs have consistent color and maximum
protection would be to --beware of heresy--paint them with a high quality, well
pigmented acrylic paint. And then keep them out of the sun.
Another alternative solution would be, that since many times the degradation
occurs at the surface of the plastic—simply resurface by sanding and polishing
and coating with clear coat.
.
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Message is in Reply To:
 | | Re: Variations in dark blue color.
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| (...) I believe that although the chemical coating prolongs the life of the model, it doesn't mean it will last indefinitely or will never yellow. It just means it takes longer to do so. I wish I remembered the stats, but I think it's something like (...) (16 years ago, 15-Feb-08, to lugnet.color)
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