7.13.1.4 Additives
Additives are used in coating formulations for specificp urposes andi n
small, sometimes even tracea mounts. Some typical additives and their
purposesa re as follows:
Phenylmercury,z inc, cuprous compounds: mildew inhibitors
Cobalt and manganese naphthanates: aidt os urfacea nd thorough
drying
Zincoxide: protection of the resin from heat and sun
Latex paints have anumber of additives that act as stabilizers, coalescing
aids, emulsion stabilizers, freeze–thaw stabilizers, and so on.
7.13.1.5 Solvents
Organic solvents are usually required only to apply the coating and after
application are designed to evaporate from the wet paintfi lm. Water is
considered eithera sasolvent or an emulsifier.T he rate that solvents
evaporate at influences the applicationc haracteristicso ft he coating. It is
imperative that the solvent completely evaporate.Ifthe solventsare partially
retained and do notevaporate completely,premature failure by blisteringor
pinholing is likelyt oo ccur.
Most coatings are formulated to be applieda ta mbient conditions of
approximately 758 F/248 Cand a50% relative humidity.Ifambient conditions
are considerably higher or lower,itisconceivablethat solvent release could
pose ap roblem. This potential problem can be eased by changing the
“solventb alance.” Generally,f aster evaporating solvents should be used in
colder weather, and slower evaporating solvents should be used in hot
weather.Classes and characteristics of some common solventsare shown in
Table 7.16.
Low viscosity and two component epoxiesa nd powder coatings are
examples of paint systems referred to as solvent-free. The epoxy coatings
may be mixed and appliedw ithout the use of as olvent,a st he two
components typically have alow viscosity.
Powder coatings are cured by sintering. Before applicationthermoplastic
powder coatings consisto falarge number of smallb inder particles. These
particles ared eposited on am etal surfaceu sings pecial application
techniques. Subsequently, the paintisbaked in an oven to form acontinuous
film by sintering.
7.13.2S urface Preparation
For apainttoprovide maximum protection, it is essential that the surfaceto
whicht he painti st ob ea pplied is properlyp repared.T he specific
preparation system willb ed ependent on the coating system to be applied
Coatings
469
CAT8247—CHAPTER 7—17/10/2006—15:03—TRGANESH—XMLM ODEL B–pp. 403–485
Additives are used in coating formulations for specificp urposes andi n
small, sometimes even tracea mounts. Some typical additives and their
purposesa re as follows:
Phenylmercury,z inc, cuprous compounds: mildew inhibitors
Cobalt and manganese naphthanates: aidt os urfacea nd thorough
drying
Zincoxide: protection of the resin from heat and sun
Latex paints have anumber of additives that act as stabilizers, coalescing
aids, emulsion stabilizers, freeze–thaw stabilizers, and so on.
7.13.1.5 Solvents
Organic solvents are usually required only to apply the coating and after
application are designed to evaporate from the wet paintfi lm. Water is
considered eithera sasolvent or an emulsifier.T he rate that solvents
evaporate at influences the applicationc haracteristicso ft he coating. It is
imperative that the solvent completely evaporate.Ifthe solventsare partially
retained and do notevaporate completely,premature failure by blisteringor
pinholing is likelyt oo ccur.
Most coatings are formulated to be applieda ta mbient conditions of
approximately 758 F/248 Cand a50% relative humidity.Ifambient conditions
are considerably higher or lower,itisconceivablethat solvent release could
pose ap roblem. This potential problem can be eased by changing the
“solventb alance.” Generally,f aster evaporating solvents should be used in
colder weather, and slower evaporating solvents should be used in hot
weather.Classes and characteristics of some common solventsare shown in
Table 7.16.
Low viscosity and two component epoxiesa nd powder coatings are
examples of paint systems referred to as solvent-free. The epoxy coatings
may be mixed and appliedw ithout the use of as olvent,a st he two
components typically have alow viscosity.
Powder coatings are cured by sintering. Before applicationthermoplastic
powder coatings consisto falarge number of smallb inder particles. These
particles ared eposited on am etal surfaceu sings pecial application
techniques. Subsequently, the paintisbaked in an oven to form acontinuous
film by sintering.
7.13.2S urface Preparation
For apainttoprovide maximum protection, it is essential that the surfaceto
whicht he painti st ob ea pplied is properlyp repared.T he specific
preparation system willb ed ependent on the coating system to be applied
Coatings
469
CAT8247—CHAPTER 7—17/10/2006—15:03—TRGANESH—XMLM ODEL B–pp. 403–485