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| |
|
It is true that where LEGO used to receive color-molded pellets for
> molding, and now the ABS is clear/uncolored and colors are injected during
> molding.
Scott, a question, why is it more difficult to control the color with clear
plastic than it was to control the color in the older method of using colored
plastic? Is it not the same problem to insure that the colored pellets are the
same color? They probably made countless runs of the same color pellets without
changing color. Its hard to believe that they had quality control in the 60s,
70s, 80s, 90s, but can't contol it now. Is it possible that Lego has reduced
each brick run and they have the problem when making a second brick run?
Your post on the making of the bricks and injection molding was most helpful and
useful. It was like watching the Discovery Channel's How Its Made. Thank you.
One personal question. I have a model of the White House that was on display in
Lego's corporate office in Denmark. It is glued together. At some point in its
history it was outside. It is all white bricks and there is yellowing. What I
don't understand in that the yellow bricks are not consistent. They are 1x8,
one next to another and one maybe yellow and the other is pure white. About
every fifth brick is yellowed in random patterns all over the piece. Any reason
that you can think of? This has puzzeled me for some time now.
Thanks
John P
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<snip> > At some point in its
> history it was outside. It is all white bricks and there is yellowing. What I
> don't understand in that the yellow bricks are not consistent. They are 1x8,
> one next to another and one maybe yellow and the other is pure white. About
> every fifth brick is yellowed in random patterns all over the piece. Any reason
> that you can think of? This has puzzled me for some time now.
> Thanks
> John P
As someone who has had the dubious pleasure of maintaining a piece like that, I
can tell you that it had gotten damaged. (Little curious fingers, pulling,
pushing, etc.) When something like that receives damage, someone has to repair
it. You use what you have on hand, and replace with appropriate pieces what is
too damaged to re-use. The more recent the repair, the newer the pieces look.
I hope that satisfies your curiosity.
Have Fun!
C-Ya!
Rich
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In lugnet.color, Richard W. Schamus wrote:
> <snip> > At some point in its
> > history it was outside. It is all white bricks and there is yellowing. What I
> > don't understand in that the yellow bricks are not consistent. They are 1x8,
> > one next to another and one maybe yellow and the other is pure white. About
> > every fifth brick is yellowed in random patterns all over the piece. Any reason
> > that you can think of? This has puzzled me for some time now.
> > Thanks
> > John P
>
> As someone who has had the dubious pleasure of maintaining a piece like that, I
> can tell you that it had gotten damaged. (Little curious fingers, pulling,
> pushing, etc.) When something like that receives damage, someone has to repair
> it. You use what you have on hand, and replace with appropriate pieces what is
> too damaged to re-use. The more recent the repair, the newer the pieces look.
>
> I hope that satisfies your curiosity.
>
> Have Fun!
> C-Ya!
>
>
> Rich
Hi Rich
I don't think that is the problem in that it is random all over the piece and
there is no way these could have been damaged. There will be a row with 30 pure
white and 20 yellowed and the new row is both also. This is from the bottom of
the piece to the top on all sides. There is now way these could have come loose
or have been repaired. I would say that 1/5 of the bricks are yellowed,
randomly on all walls. It would have destroyed the piece to replace any on the
walls in this number. Any other thoughts? Thanks
John P
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In lugnet.color, John Patterson wrote:
> I don't think that is the problem in that it is random all over the piece and
> there is no way these could have been damaged.
I've been told this is common among white elements especially-- that they're
more susceptible to light damage (or perhaps just that it's more noticeable in
white). I was told (IIRC this was from master builders in Enfield) that even the
tiniest of tiny variations can make a white piece go yellow, such that even
elements in the same batch of bricks can behave differently.
From the sounds of it, though, I'd guess that when it was being constructed, it
was being built from several different batches of white, a few of them being
more vulnerable to light.
DaveE
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In lugnet.color, David Eaton wrote:
> In lugnet.color, John Patterson wrote:
> > I don't think that is the problem in that it is random all over the piece and
> > there is no way these could have been damaged.
>
> I've been told this is common among white elements especially-- that they're
> more susceptible to light damage (or perhaps just that it's more noticeable in
> white). I was told (IIRC this was from master builders in Enfield) that even the
> tiniest of tiny variations can make a white piece go yellow, such that even
> elements in the same batch of bricks can behave differently.
>
> From the sounds of it, though, I'd guess that when it was being constructed, it
> was being built from several different batches of white, a few of them being
> more vulnerable to light.
>
> DaveE
Thanks David, that makes sence
John P
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In lugnet.color, David Eaton wrote:
> In lugnet.color, John Patterson wrote:
> > I don't think that is the problem in that it is random all over the piece and
> > there is no way these could have been damaged.
>
> I've been told this is common among white elements especially-- that they're
> more susceptible to light damage (or perhaps just that it's more noticeable in
> white). I was told (IIRC this was from master builders in Enfield) that even the
> tiniest of tiny variations can make a white piece go yellow, such that even
> elements in the same batch of bricks can behave differently.
>
> From the sounds of it, though, I'd guess that when it was being constructed, it
> was being built from several different batches of white, a few of them being
> more vulnerable to light.
>
> DaveE
ABS in and of itself will yellow. With white the yellowing is just more evident.
Yellowing occurs in blue and red and all the other colors but is masked. It is
analogous in paint to the fact that certain resins will yellow with age. Acrylic
is perhaps the best of the bunch and very, very little yellowing if any . Hence
the widespread use of acrylic resin in white paint. There is no solution I can
think of for yellowing of white bricks--except to change from ABS. ABS however
has other qualities that make it a good plastic for LEGO bricks. The human eye
can discern millions of different combinations of hues and values.
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In lugnet.color, John Patterson wrote:
> Hi Rich
> I don't think that is the problem in that it is random all over the piece and
> there is no way these could have been damaged. There will be a row with 30 pure
> white and 20 yellowed and the new row is both also. This is from the bottom of
> the piece to the top on all sides. There is now way these could have come loose
> or have been repaired. I would say that 1/5 of the bricks are yellowed,
> randomly on all walls. It would have destroyed the piece to replace any on the
> walls in this number. Any other thoughts? Thanks
> John P
Is there any consistency of fading by brick type, that could be explained by
different molding batch?
I have huge constructions of white and yellow bricks which were not consistent
from the factory. The 1x4s and 2x2s were obviously differently colored right out
of the box. Generally, they exhibited differing bluish tints when new (this is
particularly ghoulish on the yellow bricks.) Over time the distinctions have
become more obvious.
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In lugnet.color, Erik Olson wrote:
> In lugnet.color, John Patterson wrote:
>
> > Hi Rich
> > I don't think that is the problem in that it is random all over the piece and
> > there is no way these could have been damaged. There will be a row with 30 pure
> > white and 20 yellowed and the new row is both also. This is from the bottom of
> > the piece to the top on all sides. There is now way these could have come loose
> > or have been repaired. I would say that 1/5 of the bricks are yellowed,
> > randomly on all walls. It would have destroyed the piece to replace any on the
> > walls in this number. Any other thoughts? Thanks
> > John P
>
> Is there any consistency of fading by brick type, that could be explained by
> different molding batch?
>
> I have huge constructions of white and yellow bricks which were not consistent
> from the factory. The 1x4s and 2x2s were obviously differently colored right out
> of the box. Generally, they exhibited differing bluish tints when new (this is
> particularly ghoulish on the yellow bricks.) Over time the distinctions have
> become more obvious.
Thanks, that makes sense too. I wish I could replace these as this is a great
display piece. It is so large I have it on the patio.
John P
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In lugnet.color, John Patterson wrote:
> It is true that where LEGO used to receive color-molded pellets for
> > molding, and now the ABS is clear/uncolored and colors are injected during
> > molding.
>
> Scott, a question, why is it more difficult to control the color with clear
> plastic than it was to control the color in the older method of using colored
> plastic? Is it not the same problem to insure that the colored pellets are the
> same color? They probably made countless runs of the same color pellets without
> changing color. Its hard to believe that they had quality control in the 60s,
> 70s, 80s, 90s, but can't contol it now. Is it possible that Lego has reduced
> each brick run and they have the problem when making a second brick run?
> Your post on the making of the bricks and injection molding was most helpful and
> useful. It was like watching the Discovery Channel's How Its Made. Thank you.
> One personal question. I have a model of the White House that was on display in
> Lego's corporate office in Denmark. It is glued together. At some point in its
> history it was outside. It is all white bricks and there is yellowing. What I
> don't understand in that the yellow bricks are not consistent. They are 1x8,
> one next to another and one maybe yellow and the other is pure white. About
> every fifth brick is yellowed in random patterns all over the piece. Any reason
> that you can think of? This has puzzeled me for some time now.
> Thanks
> John P
John,
Adding color dye to clear ABS is like taking a bowl of flour, and adding food
coloring to it. You will find that as you mix the flour, some of the flour will
wind up being tinted a little darker than other areas. It depends on your
mixing technique, and all the relative aspects (i.e. how fast your mixing, the
way you are mixing, what you are mixing with, etc).
Now, if it were possible to buy a bag of flour with the flour colored the way
you wanted it, you could have a better guarantee of the consistiency, as the
company (i.e. vendor) producing the flour that you purchased would be doing
their own quality checks.
Now, if you needed a lot of different colored flour, would you be better off
buying several different bags of flour each with a specific color, knowing you
wouldn't be using the entire bag each time, or would you be better off buying a
huge amount of flour, then only taking what you needed from the large portion
(which is probably cheaper per use due to size and economies of scale), and
mixing your own colors?
I figure this is pretty close to how things are happening now. Using your own
color, you are now taking color consistency QC into your own hands, and not
using the vendors QC in addition to your own.
Transitions from the "norm" of 30 years, to newer methods are never seamless.
There's always going to be bumps. Any consultant that guarantees "seamless
transition" doesn't fully know the process.
As for the yellowing--on top of other posts in the thread about yellowing,
another thing to consider is the display was probably static, and you should
consider the position of the sun in relation to how much sun bricks are getting.
I'd dare say that bricks exposed to sunlight for a longer period of time are
bound to yellow faster.
Scott
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In lugnet.color, Scott Lyttle wrote:
> In lugnet.color, John Patterson wrote:
> > It is true that where LEGO used to receive color-molded pellets for
> > > molding, and now the ABS is clear/uncolored and colors are injected during
> > > molding.
> >
> > Scott, a question, why is it more difficult to control the color with clear
> > plastic than it was to control the color in the older method of using colored
> > plastic? Is it not the same problem to insure that the colored pellets are the
> > same color? They probably made countless runs of the same color pellets without
> > changing color. Its hard to believe that they had quality control in the 60s,
> > 70s, 80s, 90s, but can't contol it now. Is it possible that Lego has reduced
> > each brick run and they have the problem when making a second brick run?
> > Your post on the making of the bricks and injection molding was most helpful and
> > useful. It was like watching the Discovery Channel's How Its Made. Thank you.
> > One personal question. I have a model of the White House that was on display in
> > Lego's corporate office in Denmark. It is glued together. At some point in its
> > history it was outside. It is all white bricks and there is yellowing. What I
> > don't understand in that the yellow bricks are not consistent. They are 1x8,
> > one next to another and one maybe yellow and the other is pure white. About
> > every fifth brick is yellowed in random patterns all over the piece. Any reason
> > that you can think of? This has puzzeled me for some time now.
> > Thanks
> > John P
>
> John,
> Adding color dye to clear ABS is like taking a bowl of flour, and adding food
> coloring to it. You will find that as you mix the flour, some of the flour will
> wind up being tinted a little darker than other areas. It depends on your
> mixing technique, and all the relative aspects (i.e. how fast your mixing, the
> way you are mixing, what you are mixing with, etc).
>
>
> Now, if it were possible to buy a bag of flour with the flour colored the way
> you wanted it, you could have a better guarantee of the consistiency, as the
> company (i.e. vendor) producing the flour that you purchased would be doing
> their own quality checks.
>
> Now, if you needed a lot of different colored flour, would you be better off
> buying several different bags of flour each with a specific color, knowing you
> wouldn't be using the entire bag each time, or would you be better off buying a
> huge amount of flour, then only taking what you needed from the large portion
> (which is probably cheaper per use due to size and economies of scale), and
> mixing your own colors?
>
> I figure this is pretty close to how things are happening now. Using your own
> color, you are now taking color consistency QC into your own hands, and not
> using the vendors QC in addition to your own.
>
> Transitions from the "norm" of 30 years, to newer methods are never seamless.
> There's always going to be bumps. Any consultant that guarantees "seamless
> transition" doesn't fully know the process.
>
> As for the yellowing--on top of other posts in the thread about yellowing,
> another thing to consider is the display was probably static, and you should
> consider the position of the sun in relation to how much sun bricks are getting.
> I'd dare say that bricks exposed to sunlight for a longer period of time are
> bound to yellow faster.
>
> Scott
Thanks for the explanitation. I still would think that if the supplier of the
pellets starts off with a clear plastic and then adds color, it would be the
same for Flextronics starting with a clear plastic and adding color to make the
pellets. Perhaps I am a little dense, but when the pellet supplier added the
color they were the same as Lego or Flexrtonics adding color. They all start
with clear plastic and add color.
As for the yellowing on the bricks, perhaps i didn't explain it well enough.
There is a row with every fifth brick yellowed and a row below it with every
fifth colored but spread in a different pattern. There is no way that one brick
yellowed next to on that did not to get more sun. They all would have gotten
the same amount of light. One yellower right next to one that did not, no
bricks are half yellow and half white. This is from the builders in Denmark and
I would think that they all had the same bricks while building this.
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. At this point I
guess that they were using bricks that were presprayed and some that were not.
She did make sence, except that the models were sprayed after it is built.
Perhaps they sprayed the bricks before the early models were built and used
bricks that were sprayed and not sprayed for an inside creation, and now at
Legoland spray the bricks after the model is built.
John P
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| |
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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. I wish I remembered the stats, but I think it's something
like a few months to a year for an untreated model, and 5-10 years for a treated
model, before they start looking sun-and-weather-beaten.
I imagine that the treatment they get also helps prevent damage from rain and
humidity, as I'm told these affect the bricks as well. In particular, I was
relayed a story about master builders constructing a large Naboo fighter model
for a Star Wars convention in ... 1999 I think? Anyway, it had been raining and
humid for a few days straight, and the bricks wouldn't retain their clutch
power, despite being kept under a tent.
Of course, models for displayed are typically glued, so clutch power in
particular isn't as much of an issue, but still, I'm sure the other elements
(other than just the sun) don't do the bricks any good with continuous exposure.
DaveE
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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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In lugnet.color, John Patterson wrote:
| |
In lugnet.color, Scott Lyttle wrote:
| |
In lugnet.color, John Patterson wrote:
Scott
|
Thanks for the explanitation. I still would think that if the supplier of the
pellets starts off with a clear plastic and then adds color, it would be the
same for Flextronics starting with a clear plastic and adding color to make
the pellets. Perhaps I am a little dense, but when the pellet supplier added
the color they were the same as Lego or Flexrtonics adding color. They all
start with clear plastic and add color.
-SNIP-
John P
|
John:
Not quite. Flextronics is a molder, while the suppliers they would buy
precolored pellets from are compounders. The difference is all in the method
and intensity of mixing. When a compounder colors a resin like ABS, they do
start with a natural. The pellets are pre-blended with the pigments and/or dyes
along with stabilizers, lubes, and other additives. The preblend is then put
through an extruder. The extruder consists of a metal screw wrapped by a heated
barrel. The preblend is fed in at one end and comes out the other end in molten
strands which are typically cooled in a water bath. The design of the screw
along with the processing conditions (temperature, screw RPM) determines how
much mixing occurs. This is the heart of compounding technology. Most
precolors are done on twin-screw extruders because they offer the best mixing
capabilities.
In contrast when a molder colors resin “at the press”, they are adding the
colorant in some way (liquid color, masterbatch/concentrate, etc.) at the hopper
of the injection molding machine. Mixing is less effective in injection molding
machines because they are primarily designed to melt and convey materials rather
than mix them. The L/d (length/diameter) ratio of the screw along with the
profile of the screw play a part in how much mixing occurs. Injection molding
machines typically have low L/d ratios and low-compression or general purpose
screws which means that minimal mixing occurs in a molding machine. You can
improve mixing by adjusting some processing parameters, but in the end, it will
never be as efficient as a twin-screw compounding extruder.
Here’s a very basic overview of
compounding.
In my experience, the control over color consistency diminishes the farther you
take the colorant away from the compounder. Precolor is usually the most
consistent, followed by masterbatches/concentrates, followed by liquid color or
“at the press” blending. Granted, I’m probably a little biased as I work for a
specialty compounder. :-) Some molders are better than others at maintaining
consistency and liquid color can be done well. It just takes someone dedicated
to learning the process and all the intricacies.
Also, some machine companies are also starting to come out with
“compounding/injection molding machines” which basically combine an extruder
with a molding machine. These new machines will allow molders to compound their
own materials right at the press. The downside is that they will have to hire
engineers who are experienced in materials development to put together the
formulations for them. :-)
-Dave
| | | | | | | | | | | | | | | | | |
In lugnet.color, Dave Sterling wrote:
| |
In lugnet.color, John Patterson wrote:
| |
In lugnet.color, Scott Lyttle wrote:
| |
In lugnet.color, John Patterson wrote:
Scott
|
Thanks for the explanitation. I still would think that if the supplier of
the pellets starts off with a clear plastic and then adds color, it would be
the same for Flextronics starting with a clear plastic and adding color to
make the pellets. Perhaps I am a little dense, but when the pellet supplier
added the color they were the same as Lego or Flexrtonics adding color.
They all start with clear plastic and add color.
-SNIP-
John P
|
John:
Not quite. Flextronics is a molder, while the suppliers they would buy
precolored pellets from are compounders. The difference is all in the method
and intensity of mixing. When a compounder colors a resin like ABS, they do
start with a natural. The pellets are pre-blended with the pigments and/or
dyes along with stabilizers, lubes, and other additives. The preblend is
then put through an extruder. The extruder consists of a metal screw wrapped
by a heated barrel. The preblend is fed in at one end and comes out the
other end in molten strands which are typically cooled in a water bath. The
design of the screw along with the processing conditions (temperature, screw
RPM) determines how much mixing occurs. This is the heart of compounding
technology. Most precolors are done on twin-screw extruders because they
offer the best mixing capabilities.
In contrast when a molder colors resin “at the press”, they are adding the
colorant in some way (liquid color, masterbatch/concentrate, etc.) at the
hopper of the injection molding machine. Mixing is less effective in
injection molding machines because they are primarily designed to melt and
convey materials rather than mix them. The L/d (length/diameter) ratio of
the screw along with the profile of the screw play a part in how much mixing
occurs. Injection molding machines typically have low L/d ratios and
low-compression or general purpose screws which means that minimal mixing
occurs in a molding machine. You can improve mixing by adjusting some
processing parameters, but in the end, it will never be as efficient as a
twin-screw compounding extruder.
Here’s a very basic overview of
compounding.
In my experience, the control over color consistency diminishes the farther
you take the colorant away from the compounder. Precolor is usually the most
consistent, followed by masterbatches/concentrates, followed by liquid color
or “at the press” blending. Granted, I’m probably a little biased as I work
for a specialty compounder. :-) Some molders are better than others at
maintaining consistency and liquid color can be done well. It just takes
someone dedicated to learning the process and all the intricacies.
Also, some machine companies are also starting to come out with
“compounding/injection molding machines” which basically combine an extruder
with a molding machine. These new machines will allow molders to compound
their own materials right at the press. The downside is that they will have
to hire engineers who are experienced in materials development to put
together the formulations for them. :-)
-Dave
|
Thanks, it is starting to clear things up for me. Would a solution be to make
the bricks from one batch, or at least put bricks into the box from the same
mixture? I am somewhat familiar with dye lot variations as I worked in the
needlecraft industry for a number of years and it was critical to match dye
lots. Stitchers were always told to buy enough thread from the same dye lot.
The thread manufactures made it easier in that the box of thread sent to the
stores with 10 balls of yarn or 12 skeins of yarns always came from the same
lot. I see that it is a lot harder in the plastic industry. Around the time
Lego changed the greys, the yarn suppliers changed their grey dye also. There
was such an uproar that they had to go back to the original dye lot and the
wholesale price of all the colors of the yarn from the manufacture went up. John
P
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In lugnet.color, John Patterson wrote:
| |
In lugnet.color, Dave Sterling wrote:
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In lugnet.color, John Patterson wrote:
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In lugnet.color, Scott Lyttle wrote:
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In lugnet.color, John Patterson wrote:
Scott
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Thanks for the explanitation. I still would think that if the supplier of
the pellets starts off with a clear plastic and then adds color, it would
be the same for Flextronics starting with a clear plastic and adding color
to make the pellets. Perhaps I am a little dense, but when the pellet
supplier added the color they were the same as Lego or Flexrtonics adding
color. They all start with clear plastic and add color.
-SNIP-
John P
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John:
Not quite. Flextronics is a molder, while the suppliers they would buy
precolored pellets from are compounders. The difference is all in the
method and intensity of mixing. When a compounder colors a resin like ABS,
they do start with a natural. The pellets are pre-blended with the pigments
and/or dyes along with stabilizers, lubes, and other additives. The
preblend is then put through an extruder. The extruder consists of a metal
screw wrapped by a heated barrel. The preblend is fed in at one end and
comes out the other end in molten strands which are typically cooled in a
water bath. The design of the screw along with the processing conditions
(temperature, screw RPM) determines how much mixing occurs. This is the
heart of compounding technology. Most precolors are done on twin-screw
extruders because they offer the best mixing capabilities.
In contrast when a molder colors resin “at the press”, they are adding the
colorant in some way (liquid color, masterbatch/concentrate, etc.) at the
hopper of the injection molding machine. Mixing is less effective in
injection molding machines because they are primarily designed to melt and
convey materials rather than mix them. The L/d (length/diameter) ratio of
the screw along with the profile of the screw play a part in how much mixing
occurs. Injection molding machines typically have low L/d ratios and
low-compression or general purpose screws which means that minimal mixing
occurs in a molding machine. You can improve mixing by adjusting some
processing parameters, but in the end, it will never be as efficient as a
twin-screw compounding extruder.
Here’s a very basic overview
of compounding.
In my experience, the control over color consistency diminishes the farther
you take the colorant away from the compounder. Precolor is usually the
most consistent, followed by masterbatches/concentrates, followed by liquid
color or “at the press” blending. Granted, I’m probably a little biased as
I work for a specialty compounder. :-) Some molders are better than others
at maintaining consistency and liquid color can be done well. It just takes
someone dedicated to learning the process and all the intricacies.
Also, some machine companies are also starting to come out with
“compounding/injection molding machines” which basically combine an extruder
with a molding machine. These new machines will allow molders to compound
their own materials right at the press. The downside is that they will have
to hire engineers who are experienced in materials development to put
together the formulations for them. :-)
-Dave
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Thanks, it is starting to clear things up for me. Would a solution be to
make the bricks from one batch, or at least put bricks into the box from the
same mixture? I am somewhat familiar with dye lot variations as I worked in
the needlecraft industry for a number of years and it was critical to match
dye lots. Stitchers were always told to buy enough thread from the same dye
lot. The thread manufactures made it easier in that the box of thread sent to
the stores with 10 balls of yarn or 12 skeins of yarns always came from the
same lot. I see that it is a lot harder in the plastic industry. Around the
time Lego changed the greys, the yarn suppliers changed their grey dye also.
There was such an uproar that they had to go back to the original dye lot and
the wholesale price of all the colors of the yarn from the manufacture went
up. John P
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John:
That might work if you were using precolored pellets...but honestly...if you
were using precolor, you wouldn’t see the variation. :-) With both
concentrates and liquid color, there can easily be shot-to-shot variation if
mixing/dispersion is not optimized and/or controlled.
Imagine grabbing a handful of snow. Now take a drop of red food coloring and
drop it on that snow. Now you have a small speck that is really red surrounded
by a bunch of white. This equates to a bunch of natural pellets surrounding a
concentrate red pellet. Now mix the snow up. As you start to mix, the red
spreads out. But it spreads slowly and requires a lot of mixing to get to
uniform color dispersion. Herein lies the problem. You have to put a lot of
work into mixing to get even color.
Now, as a materials supplier, we can add things to the concentrate to aid
dispersion of the color. I can’t comment on any specifics...but the technology
is out there. Most color concentrates can be fairly evenly dispersed and many
companies use this technology. One other thing to keep in mind though is that
certain pigments are harder to disperse due to their chemical makeup/structure.
Organic based pigments can be particularly tricky to disperse. Perhaps some of
the inconsistency comes from the pigment type? I’m not sure, but it’s another
piece of the puzzle to look at. I can almost guarantee that LEGO is looking at
this though. I firmly believe that the inconsistency you saw is just “start-up
jitters” with a new color and new color technology.
Interestingly enough (speaking of new colors and technology), I’ve never heard
anyone make mention of the flow-lines that were present in some of the metallic
colors produced recently. And I’ll quell any complaining right now by telling
everyone that the flow lines in metallics cannot be eliminated...period. :-)
We’ve been trying for years. The only thing you can do is try and gate the part
to hide the flow lines.
Anyway, I’m babbling now. Hope this information is useful.
Best Regards,
Dave
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Hope this information is useful.
Best Regards,
Dave
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It is useful, thanks Dave
John P
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In lugnet.color, Dave Sterling wrote:
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Interestingly enough (speaking of new colors and technology), I’ve never
heard anyone make mention of the flow-lines that were present in some of the
metallic colors produced recently. And I’ll quell any complaining right now
by telling everyone that the flow lines in metallics cannot be
eliminated...period. :-) We’ve been trying for years. The only thing you
can do is try and gate the part to hide the flow lines.
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Do you mean the ‘swirl’ effect seen on some metallized bricks? I actually like
that effect. :)
Steve
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In lugnet.color, Dave Sterling wrote:
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...
In my experience, the control over color consistency diminishes the farther
you take the colorant away from the compounder. Precolor is usually the most
consistent, followed by masterbatches/concentrates, followed by liquid color
or “at the press” blending. Granted, I’m probably a little biased as I work
for a specialty compounder. :-) Some molders are better than others at
maintaining consistency and liquid color can be done well. It just takes
someone dedicated to learning the process and all the intricacies.
...
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Excellent lesson. This kind of material would have been welcome in this group a
couple of years ago. Better late than never. Thanks for the info.
Doug
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