properties. The final coating is formed as ar esult of the drying oil reacting
with the resin that is combined with pigments and solvents. The paint is
packaged in asingle can that can be opened, mixed, and the paintapplied.
Since oxygen reacts with the coating, introducing additional cross-linking,
final film properties can take weeks or even months to attain.
Autooxidative cross-linking type paints includea lkyds, epoxies, esters,
oil-modifiedurethanes, and so on. These are commonly used, when properly
formulated, to resist moisture and chemical fume environments. They can be
applied over wood, metal, or masonrysubstrates.
The advantage of thesec oatings is their ease of application, excellent
adhesion, relatively good environmental resistance (in all but immersion
and high chemical fume environment), and tolerance for poorer surface
preparation. Their major disadvantage, compared with others ynthetic
resins, is their lessened moisture and chemical resistance.
7.13.1.1.8 Water Soluble Resins and Emulsion Coatings
By introducing sufficient carboxylg roups into ap olymer,a ny type of resin
can be made water soluble. These groups are then neutralized with avolatile
bases uch as ammonia or an amine, rendering the resin ap olymeric salt,
soluble in water or water/ether–alcohol mixtures. The major disadvantage
to such resins is that polymersdesigned to be dissolved in water will remain
permanentlys ensitivet ow ater.B ecause of this, they are not widely
used industrially.
However, water emulsions are widely accepted.T he water-based latex
emulsions aref ormulated with high molecular weight resins in the form
of microscopicallyfi ne particles of high molecular weight copolymers
of polyvinyl chloride,p olyvinyl acetate, acrylic esters,s tryren–butadiene,
or other resins combined with pigments, plasticizers, UV stabilizers, and
otheri ngredients. Water-based epoxy formulationsa re also available. The
epoxy resin and ap olyamide copolymer are emulsified and packaged in
separate containers.A fter mixing, coalescence, andu ltimate drying, the
polyamide reacts with the epoxy to form the final film.
The majora dvantage of the emulsion coatings is their ease of cleanup.
Their disadvantage is the permanent water sensitivity of the coating, making
them unsuitable foru se in continually wet environments. Water-based
coatings cannot be applied to blast-cleaned steel surfaces with the same
confidence as solvent-based coatings.
7.13.1.1.9 Zinc-Rich Coatings
In all of the abovementioned coatings, the final film properties of corrosion
protection and environmental resistance have been attributed to organic
composition of their constituent resin or binder. The pigment, although
playing an importantr ole in the final film properties, is secondary to the
resistance of the organic binders.
Corrosion of Linings and Coatings
466
CAT8247—CHAPTER 7—17/10/2006—15:03—TRGANESH—XMLM ODEL B–pp. 403–485
with the resin that is combined with pigments and solvents. The paint is
packaged in asingle can that can be opened, mixed, and the paintapplied.
Since oxygen reacts with the coating, introducing additional cross-linking,
final film properties can take weeks or even months to attain.
Autooxidative cross-linking type paints includea lkyds, epoxies, esters,
oil-modifiedurethanes, and so on. These are commonly used, when properly
formulated, to resist moisture and chemical fume environments. They can be
applied over wood, metal, or masonrysubstrates.
The advantage of thesec oatings is their ease of application, excellent
adhesion, relatively good environmental resistance (in all but immersion
and high chemical fume environment), and tolerance for poorer surface
preparation. Their major disadvantage, compared with others ynthetic
resins, is their lessened moisture and chemical resistance.
7.13.1.1.8 Water Soluble Resins and Emulsion Coatings
By introducing sufficient carboxylg roups into ap olymer,a ny type of resin
can be made water soluble. These groups are then neutralized with avolatile
bases uch as ammonia or an amine, rendering the resin ap olymeric salt,
soluble in water or water/ether–alcohol mixtures. The major disadvantage
to such resins is that polymersdesigned to be dissolved in water will remain
permanentlys ensitivet ow ater.B ecause of this, they are not widely
used industrially.
However, water emulsions are widely accepted.T he water-based latex
emulsions aref ormulated with high molecular weight resins in the form
of microscopicallyfi ne particles of high molecular weight copolymers
of polyvinyl chloride,p olyvinyl acetate, acrylic esters,s tryren–butadiene,
or other resins combined with pigments, plasticizers, UV stabilizers, and
otheri ngredients. Water-based epoxy formulationsa re also available. The
epoxy resin and ap olyamide copolymer are emulsified and packaged in
separate containers.A fter mixing, coalescence, andu ltimate drying, the
polyamide reacts with the epoxy to form the final film.
The majora dvantage of the emulsion coatings is their ease of cleanup.
Their disadvantage is the permanent water sensitivity of the coating, making
them unsuitable foru se in continually wet environments. Water-based
coatings cannot be applied to blast-cleaned steel surfaces with the same
confidence as solvent-based coatings.
7.13.1.1.9 Zinc-Rich Coatings
In all of the abovementioned coatings, the final film properties of corrosion
protection and environmental resistance have been attributed to organic
composition of their constituent resin or binder. The pigment, although
playing an importantr ole in the final film properties, is secondary to the
resistance of the organic binders.
Corrosion of Linings and Coatings
466
CAT8247—CHAPTER 7—17/10/2006—15:03—TRGANESH—XMLM ODEL B–pp. 403–485