Digital BW, The Print

Paul, you wrote:
>
> >I would also advise you to make sure the Hydrocote is stirred
> >very well.
> >...
> >... open the lid, stir it, get what you need out,
> >and then reseal the lid.
>
> I am down to near the bottom of the quart can of Hydrocote I first
> purchased, and I think I've noticed a  viscosity increase.  I now usually
> stir the PUR just before using, but admit that I have not always been so
> vigilant.  It may also be that the air in the can, with repeated openings,
> causes some viscosity increase.  At an rate, the symptoms I see are
streaks
> in the coating that were not there before.  It is the same type of
streaking
> I saw with Liquitex acrylic before I diluted it 3:1.

Is there any chance the viscosity increase is actually 'Hydrocote
polymerised' or just solids sinking / solvents evaporating ? One would
expect polymerisation to happen on top of the liquid of course.

Ernst

Ernst,

>> I am down to near the bottom of the quart can of Hydrocote I first
>> purchased, and I think I've noticed a  viscosity increase.  ...

>Is there any chance the viscosity increase is actually 'Hydrocote
>polymerised' or just solids sinking / solvents evaporating ? One would
>expect polymerisation to happen on top of the liquid of course.

I think some polymerization is a distinct possibility.  I'd be most
concerned if it occurred in clumps -- making a smooth application tough.

I'm wondering if we ought to stir the mix very well when first purchased and
pour it into several smaller bottles.  The 4 oz./ 110 ml. ink bottles come
to mind as possible candidates.

Paul

Paul,

> >> I am down to near the bottom of the quart can of Hydrocote I first
> >> purchased, and I think I've noticed a  viscosity increase.  ...
>
> >Is there any chance the viscosity increase is actually 'Hydrocote
> >polymerised' or just solids sinking / solvents evaporating ? One would
> >expect polymerisation to happen on top of the liquid of course.
>
> I think some polymerization is a distinct possibility.  I'd be most
> concerned if it occurred in clumps -- making a smooth application tough.
>
> I'm wondering if we ought to stir the mix very well when first purchased
and
> pour it into several smaller bottles.  The 4 oz./ 110 ml. ink bottles come
> to mind as possible candidates.

I have not the faintest idea how fast it polymerises. Whether they have done
any stuff in it to prevent polymerisation in the can itself. Mixing the
varnish first with the Fish Eye/Leveling additive and then pouring it in
smaller polyethylene bottles where you can squeeze out the extra air may be
a good idea. Put a marble in too. Then you can shake the bottle without
mixing air in the liquid. But I have not the fainte ........

Erns

On 12/10/02 7:59 AM, "Ernst Dinkla" <E.Dinkla@...> wrote:

> Paul,
> 
>>>> I am down to near the bottom of the quart can of Hydrocote I first
>>>> purchased, and I think I've noticed a  viscosity increase.  ...
>> 
>>> Is there any chance the viscosity increase is actually 'Hydrocote
>>> polymerised' or just solids sinking / solvents evaporating ? One would
>>> expect polymerisation to happen on top of the liquid of course.
>> 
>> I think some polymerization is a distinct possibility.  I'd be most
>> concerned if it occurred in clumps -- making a smooth application tough.
>> 
>> I'm wondering if we ought to stir the mix very well when first purchased
> and
>> pour it into several smaller bottles.  The 4 oz./ 110 ml. ink bottles come
>> to mind as possible candidates.
> 
> I have not the faintest idea how fast it polymerises. Whether they have done
> any stuff in it to prevent polymerisation in the can itself. Mixing the
> varnish first with the Fish Eye/Leveling additive and then pouring it in
> smaller polyethylene bottles where you can squeeze out the extra air may be
> a good idea. Put a marble in too. Then you can shake the bottle without
> mixing air in the liquid. But I have not the fainte ........

Hydrocote is a polyurethane that is already polymerized!...that's why it is
called "poly".  There are coatings which you add a cross-linker to but they
are not available in water-based formula.  The problem with viscosity is a
universal problem with water-based polyurethanes.  They are not really
soluble in water so people add cosolvents to them.  If the cosolvent (which
is more volatile than water) begins to evaporate the polymer starts to drop
out of solution.  The polymer itself is much more viscous than the solution.
Personally, I don't fine polyurethanes to be a good solution for print
coating...there are just too many variables that can go wrong.  Acrylics are
a much better solution and they are commonly used for artists
materials...polyurethanes...are not.

Robert

On 12/10/02 7:36 AM, "Paul Roark" <paul.roark@...> wrote:

> Ernst,
> 
>>> I am down to near the bottom of the quart can of Hydrocote I first
>>> purchased, and I think I've noticed a  viscosity increase.  ...
> 
>> Is there any chance the viscosity increase is actually 'Hydrocote
>> polymerised' or just solids sinking / solvents evaporating ? One would
>> expect polymerisation to happen on top of the liquid of course.
> 
> I think some polymerization is a distinct possibility.  I'd be most
> concerned if it occurred in clumps -- making a smooth application tough.
> 
> I'm wondering if we ought to stir the mix very well when first purchased and
> pour it into several smaller bottles.  The 4 oz./ 110 ml. ink bottles come
> to mind as possible candidates.
> 
Incidentally, don't put the polyshield in plastic...only glass or metal
cans...the cosolvent will absorb into the plastic and this could also cause
a viscosity change.  If you are also using syringes for application you may
experience a problem here as well...I believe that neoprene is what is used
for the black seals in syringes...and on the short run it is resistant to
N-methyl Pyrrolidinone (the cosolvent in Hydrocote Polyshield), but in the
long run it will swell.  Neoprene are the best regularly available gloves
for handling NMP (you can order them through a chemical supply company), but
they should be changed regularly for the same reason.  I believe it goes
right through latex.  Lastly, here is the warning from the safety sheet on
the cosolvent:  "Repeated or prolonged contact with skin may cause
dermatitis. Animal tests show that this substance possibly causes toxic
effects upon human reproduction".  When we used the solvent in the plant
(back in my chemistry days), operators were required to wear respirators,
gloves and full body jumpsuits because of the "sensitization hazard".
Hydrocote Polyshield uses NMP at 5-10% concentrations...but it is very
hydroscopic...so if you get the Hydrocote on your skin the NMP will be
immediately absorbed.  It also has a relatively high vapor pressure
(compared to water)...so it starts coming off the can as soon as you open
it.

Here's the safety sheet for NMP:

http://www.cdc.gov/NIOSH/ipcsneng/neng0513.html

And the MSDS for Hydrocote Polyshield:

http://www.hydrocote.com/msds.htm



Robert

Robert wrote:

>Hydrocote is a polyurethane that is already polymerized!...
>that's why it is called "poly".  There are coatings which you
>add a cross-linker to but they are not available in
>water-based formula.

My understanding is that the water-based, single-component polyurethanes do
cross-link after application, whereas the acrylics do not.  Both are (I've
been told) soft "golf balls" in suspension.  While the best cross-linking is
with the 2-component, solvent-based polyurethanes, the single-component
water-borne version is said to be about half way between the acrylics and
the industrial-strength PURs.

As I understand it, the importance of the cross-linking is that without it
the coating is porous and cannot achieve as high hardness relative to
brittleness.  Many seem to recommend that a water-borne acrylic be coated
with a solvent-based polymer to seal it and reduce the "tackiness" of the
surface.  My hope with the PUR is to get a single-step coating procedure
that is tough enough to withstand some abuse.

For a tough, durable coating, the aliphatic PURs are the standard, as far as
I can tell.  The 2-component, solvent-borne versions just seem like they'd
be too much of a hassle to use.

One company has said it will send a formula to me/us that will make a
2-component water-based PUR.  This is the next step even for industrial
PURs, in part due to the pressure on VOCs.  This would probably be the
strongest water-based coating possible today, but I have yet to receive the
materials.

Paul
http://www.PaulRoark.com

Paul,

One thing to remember here...is that the technology that you are being
handed from these companies is for coating wood...a rigid, hard surface.
The demands on a coating for a flexible, porous substrate like paper are
very different.  That's one reason why no artist's materials companies use
polyurethanes.  

Regardless of what you are being told about the aliphatic water-based
polyurethanes...no significant crosslinking occurs after the original
emulsion polymerization reaction...that's marketing hype.  The film cure is
very similar between the polyurethanes and the acrylics.  The difference is
that the polyurethane polymer is harder and more light sensitive than some
acrylics.  Because of the huge range of acrylics polymers, products can be
formulated with a considerable variance in hardness.

The key in this application is to get something that is just hard enough
that there isn't a tack problem, but not as hard as polyurethane so that
there is still flexibility.  Of course this isn't an issue with wood.

Robert

On 12/10/02 9:59 AM, "Paul Roark" <paul.roark@...> wrote:

> Robert wrote:
> 
>> Hydrocote is a polyurethane that is already polymerized!...
>> that's why it is called "poly".  There are coatings which you
>> add a cross-linker to but they are not available in
>> water-based formula.
> 
> My understanding is that the water-based, single-component polyurethanes do
> cross-link after application, whereas the acrylics do not.  Both are (I've
> been told) soft "golf balls" in suspension.  While the best cross-linking is
> with the 2-component, solvent-based polyurethanes, the single-component
> water-borne version is said to be about half way between the acrylics and
> the industrial-strength PURs.
> 
> As I understand it, the importance of the cross-linking is that without it
> the coating is porous and cannot achieve as high hardness relative to
> brittleness.  Many seem to recommend that a water-borne acrylic be coated
> with a solvent-based polymer to seal it and reduce the "tackiness" of the
> surface.  My hope with the PUR is to get a single-step coating procedure
> that is tough enough to withstand some abuse.
> 
> For a tough, durable coating, the aliphatic PURs are the standard, as far as
> I can tell.  The 2-component, solvent-borne versions just seem like they'd
> be too much of a hassle to use.
> 
> One company has said it will send a formula to me/us that will make a
> 2-component water-based PUR.  This is the next step even for industrial
> PURs, in part due to the pressure on VOCs.  This would probably be the
> strongest water-based coating possible today, but I have yet to receive the
> materials.
> 
> Paul
> http://www.PaulRoark.com
> 
> 
> 
> 
> 
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On Tuesday, December 10, 2002, at 02:22  PM, Robert Morrison wrote:

> Paul,
>
> One thing to remember here...is that the technology that you are being
> handed from these companies is for coating wood...a rigid, hard 
> surface.
> The demands on a coating for a flexible, porous substrate like paper 
> are
> very different.  That's one reason why no artist's materials companies 
> use
> polyurethanes.
>
> Regardless of what you are being told about the aliphatic water-based
> polyurethanes...no significant crosslinking occurs after the original
> emulsion polymerization reaction...that's marketing hype.  The film 
> cure is
> very similar between the polyurethanes and the acrylics.  The 
> difference is
> that the polyurethane polymer is harder and more light sensitive than 
> some
> acrylics.  Because of the huge range of acrylics polymers, products 
> can be
> formulated with a considerable variance in hardness.
>
> The key in this application is to get something that is just hard 
> enough
> that there isn't a tack problem, but not as hard as polyurethane so 
> that
> there is still flexibility.  Of course this isn't an issue with wood.
>
> Robert
>
Some of the prints I coated with  AquaZar water based poly on Sunday 
curled quite badly while drying and today the coating started to crack. 
  Humidity was extremely low  during this period.  These were on 190 gsm 
eclipse satine.  Don't know if the AquaZar is  an aliphatic poly or not 
- label on the can says "non yellowing".  The dried coating was 
beautiful, but I won't be using this product again because of the 
cracking.  Any problems like this with the Hydrocote?

>
>Hydrocote is a polyurethane that is already polymerized!...that's why it is
>called "poly".  There are coatings which you add a cross-linker to but they
>are not available in water-based formula.  The problem with viscosity is a
>universal problem with water-based polyurethanes.  They are not really
>soluble in water so people add cosolvents to them.  If the cosolvent (which
>is more volatile than water) begins to evaporate the polymer starts to drop
>out of solution.  The polymer itself is much more viscous than the solution.
>Personally, I don't fine polyurethanes to be a good solution for print
>coating...there are just too many variables that can go wrong.  Acrylics are
>a much better solution and they are commonly used for artists
>materials...polyurethanes...are not.
>
>Robert
>


I have been following this with interest...and even posted several 
times in the past month or two about the virtues of coating with 
acrylic varnish...I agree with Robert that acrylics are a much more 
elegant solution chemically.  Find a good quality artist acrylic 
varnish and intermix the gloss and the matte together until you get 
the degree of gloss you want....Blow it through the same spray 
gun...easy clean up...as long as you don't let the thing dry....I 
shoot a lot of plain water through it after the job and follow it 
with some denatured alcohol to clear our the water...Never had a clog 
problem with the gun...Oh, it doesn't hurt to take an artists brush 
and scrub the tip lightly with some plain water during a long session 
so you don't get build up on the tip.

Bill Agee
-- 

bill agee studio
capistrano beach, ca / laguna beach, ca

http://www.redsilver.com

>....  Many seem to recommend that a water-borne acrylic be coated
>with a solvent-based polymer to seal it and reduce the "tackiness" of the
>surface.  My hope with the PUR is to get a single-step coating procedure
>that is tough enough to withstand some abuse.
>
>
>Paul
>http://www.PaulRoark.com
>
>


Paul,

I had some early problems with "tackiness" when shooting acrylic 
coatings on photographs...however, I talked with the chemist of the 
supplier I use

http://www.novacolorpaint.com/

and they eventually developed a hard surface acrylic varnish with no 
tacky feel.  The reason they had tacky versions was that a lot of it 
was used in coating painted murals on sides of buildings and it was 
more flexible.

#216 is a hard surface semi gloss varnish....add #206 to it until you 
get the gloss you want....All pure acrylic...

Bill Agee
-- 

bill agee studio
capistrano beach, ca / laguna beach, ca

http://www.redsilver.com