Digital BW, The Print

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
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  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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