Digital BW, The Print

I have found a U.S. Army Corps of Engineers Engineering and Design manual on
line that is an excellent source of information on coatings.  Chapter 4 is
devoted to "Coating Types and Characteristics."  See
www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-3400/c-4.pdf

The two types of coatings that are of most interest to me now are the
water-borne acrylics and aliphatic polyurethanes.  With respect to the
water-borne acrylics the manual notes that they "provide coatings with
unexcelled color retention and have excellent exterior weathering and
durability properties." (p. 4)

On p. 9 the polyurethanes are discussed.  These cross-linking co-polymers
work due to the affinity of their isocyanate groups for active hydrogens.
The isocyanates can be either aromatic (containing the benzene ring) or
aliphatic (straight chain or cyclical) hydrocarbons.  "Aromatic
polyurethanes are prone to darkening and yellowing on exposure to sunlight
because of the chromophoric nature of the benzene ring.  Because aliphatic
polyurethanes, by definition, do not contain the benzene right, they do not
yellow or darken and are preferred for exterior use."

The aliphatic isocyanates are more expensive, but they "allow the
formulation of non-yellowing, light stable, high gloss finish coats. The
appearance of polyurethane coatings formulated with aliphatic isocyanates
are unsurpassed in this regard by any of the epoxies, acrylics, or other
coating materials."

I currently favor the polyurethanes because they are tougher and non-porous.
The non-cross-linked acrylics are porous and relatively soft/tacky.  The
Golden technical representative led me to Hydrocote Polyshield, which is
currently what I am using. It is a water-borne, single-solution, aliphatic
polyurethane that, from what I have read and what the Golden technical
person reports from their tests, does not yellow.  Long term experience will
probably be needed to be sure of this.

While Hydrocote appears to be excellent product (one coat on Eclipse kicks
the dMax to over 2, doesn't yellow the whites, and provides a satin/pearl
finish that is tough enough to clean with a damp paper towel), I am
searching for an aliphatic, water-borne polyurethane that has a higher
solids content.  So far, I have not had any luck.  All the higher-solids
aliphatic polyurethanes that I've found so far are solvent-based.  (If a
company doesn't or won't say whether it's polyurethane is aliphatic, assume
that it uses the cheaper aromatic [yellowing] isocyanates [read Varathane].)

If anyone knows of a high-solids water-borne aliphatic poly, please let me
know.

Paul
http://www.PaulRoark.com

Paul,

Just wondering what the brand name of the spray you use is and 
where you can get it.  Is there an online resource that you buy it 
from?  I'd like to try coating some of my prints and was intrigued 
by your comment on the Satine paper.  Thanks.

Andy





--- In DigitalBlackandWhiteThePrint@y..., "Paul Roark" <
paul.roark@v...> wrote:
> I have found a U.S. Army Corps of Engineers Engineering and 
Design manual on
> line that is an excellent source of information on coatings.  
Chapter 4 is
> devoted to "Coating Types and Characteristics."  See
> www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-
2-3400/c-4.pdf
> 
> The two types of coatings that are of most interest to me now 
are the
> water-borne acrylics and aliphatic polyurethanes.  With respect 
to the
> water-borne acrylics the manual notes that they "provide 
coatings with
> unexcelled color retention and have excellent exterior 
weathering and
> durability properties." (p. 4)
> 
> On p. 9 the polyurethanes are discussed.  These cross-linking 
co-polymers
> work due to the affinity of their isocyanate groups for active 
hydrogens.
> The isocyanates can be either aromatic (containing the 
benzene ring) or
> aliphatic (straight chain or cyclical) hydrocarbons.  "Aromatic
> polyurethanes are prone to darkening and yellowing on 
exposure to sunlight
> because of the chromophoric nature of the benzene ring.  
Because aliphatic
> polyurethanes, by definition, do not contain the benzene right, 
they do not
> yellow or darken and are preferred for exterior use."
> 
> The aliphatic isocyanates are more expensive, but they "allow 
the
> formulation of non-yellowing, light stable, high gloss finish 
coats. The
> appearance of polyurethane coatings formulated with aliphatic 
isocyanates
> are unsurpassed in this regard by any of the epoxies, acrylics, 
or other
> coating materials."
> 
> I currently favor the polyurethanes because they are tougher 
and non-porous.
> The non-cross-linked acrylics are porous and relatively soft/
tacky.  The
> Golden technical representative led me to Hydrocote 
Polyshield, which is
> currently what I am using. It is a water-borne, single-solution, 
aliphatic
> polyurethane that, from what I have read and what the Golden 
technical
> person reports from their tests, does not yellow.  Long term 
experience will
> probably be needed to be sure of this.
> 
> While Hydrocote appears to be excellent product (one coat on 
Eclipse kicks
> the dMax to over 2, doesn't yellow the whites, and provides a 
satin/pearl
> finish that is tough enough to clean with a damp paper towel), I 
am
> searching for an aliphatic, water-borne polyurethane that has a 
higher
> solids content.  So far, I have not had any luck.  All the higher-
solids
> aliphatic polyurethanes that I've found so far are solvent-
based.  (If a
> company doesn't or won't say whether it's polyurethane is 
aliphatic, assume
> that it uses the cheaper aromatic [yellowing] isocyanates [read 
Varathane].)
> 
> If anyone knows of a high-solids water-borne aliphatic poly, 
please let me

> know.
> 
> Paul
> http://www.PaulRoark.com

Andy,

I don't recommend sprays except to slightly increase resistance to physical
abrasion.  For deeper blacks, use a wire-wound rod to apply the coating.
(#15, 1/2 inch wide, length dependent on print width; from Diversified
Enterprises, 800-833-4644)

I have been using Hydrocote Polyshield clear gloss (800-229-4937).  It's a
water-borne, aliphatic polyurethane that is easy to use, tough, and
hopefully relatively impermeable.  I will probably be trying and testing
different coatings for a while -- there are a lot of interesting
alternatives.

I published the whole procedure in mid-October on the forum.  Check the
archives.

Paul
______________________________

  -----Original Message-----
  From: akivisuals [mailto:akivisuals@...]
  Sent: Tuesday, November 12, 2002 11:14 AM
  To: DigitalBlackandWhiteThePrint@yahoogroups.com
  Subject: [Digital BW] Re: Coatings -- High Solids Aliphatic Polyurethane
search


  Paul,

  Just wondering what the brand name of the spray you use is and
  where you can get it.  Is there an online resource that you buy it
  from?  I'd like to try coating some of my prints and was intrigued
  by your comment on the Satine paper.  Thanks.

  Andy





  --- In DigitalBlackandWhiteThePrint@y..., "Paul Roark" <
  paul.roark@v...> wrote:
  > I have found a U.S. Army Corps of Engineers Engineering and
  Design manual on
  > line that is an excellent source of information on coatings.
  Chapter 4 is
  > devoted to "Coating Types and Characteristics."  See
  > www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-
  2-3400/c-4.pdf
  >
  > The two types of coatings that are of most interest to me now
  are the
  > water-borne acrylics and aliphatic polyurethanes.  With respect
  to the
  > water-borne acrylics the manual notes that they "provide
  coatings with
  > unexcelled color retention and have excellent exterior
  weathering and
  > durability properties." (p. 4)
  >
  > On p. 9 the polyurethanes are discussed.  These cross-linking
  co-polymers
  > work due to the affinity of their isocyanate groups for active
  hydrogens.
  > The isocyanates can be either aromatic (containing the
  benzene ring) or
  > aliphatic (straight chain or cyclical) hydrocarbons.  "Aromatic
  > polyurethanes are prone to darkening and yellowing on
  exposure to sunlight
  > because of the chromophoric nature of the benzene ring.
  Because aliphatic
  > polyurethanes, by definition, do not contain the benzene right,
  they do not
  > yellow or darken and are preferred for exterior use."
  >
  > The aliphatic isocyanates are more expensive, but they "allow
  the
  > formulation of non-yellowing, light stable, high gloss finish
  coats. The
  > appearance of polyurethane coatings formulated with aliphatic
  isocyanates
  > are unsurpassed in this regard by any of the epoxies, acrylics,
  or other
  > coating materials."
  >
  > I currently favor the polyurethanes because they are tougher
  and non-porous.
  > The non-cross-linked acrylics are porous and relatively soft/
  tacky.  The
  > Golden technical representative led me to Hydrocote
  Polyshield, which is
  > currently what I am using. It is a water-borne, single-solution,
  aliphatic
  > polyurethane that, from what I have read and what the Golden
  technical
  > person reports from their tests, does not yellow.  Long term
  experience will
  > probably be needed to be sure of this.
  >
  > While Hydrocote appears to be excellent product (one coat on
  Eclipse kicks
  > the dMax to over 2, doesn't yellow the whites, and provides a
  satin/pearl
  > finish that is tough enough to clean with a damp paper towel), I
  am
  > searching for an aliphatic, water-borne polyurethane that has a
  higher
  > solids content.  So far, I have not had any luck.  All the higher-
  solids
  > aliphatic polyurethanes that I've found so far are solvent-
  based.  (If a
  > company doesn't or won't say whether it's polyurethane is
  aliphatic, assume
  > that it uses the cheaper aromatic [yellowing] isocyanates [read
  Varathane].)
  >
  > If anyone knows of a high-solids water-borne aliphatic poly,
  please let me
  > know.
  >
  > Paul
  > http://www.PaulRoark.com


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