Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
This invention relates to a metallic urethane paint
film having a high degree of geometric metamerism. More
particularly," this invention relates to a high-solids paint
composition containing isocyanate-terminated urethane resins
57~
and metal flake pigmen-t, which resins are moisture curable
to produce a decorative topcoat wherein the flakes are
substantially uniformly oriented parallel -to the topcoat
surface to provide an aesthetical:Ly pleasing finish having
a high degree of geometric metamerism.
Geometric metamerism is the ability of a paint film
to exhibit subtle variations in color and appearance depending
upon the directions from which it is illuminated and viewed.
This effect is produced by metal flakes incorporated into the
film at varying depths and lying substantially parallel to
the film surface. Light rays traveling through the film are
reflected by the flakes to the viewer. For a paint film also
containing a color-producing pigment, the degree of inter-
action between that agent and a light ray -- that is, the
degree of color or hue -- depends upon the distance traveled
by the light ray through the film. Light rays reflected
from flakes at varying film depths travel different distances
through the film. Thus, the viewer perceives a combination
of light rays having different degrees of color. More
importantly, the distance traveled by light rays reflected
off ihe flakes depends upon the angle of incidence and the
angle of reflection. Light rays traveling normal to the
flake surface travel a shorter distance than light rays
traveling at acu-te angles. Thus, the "average" color is
directly related to the illumination and viewing angles.
The combination of these phenomena makes a film having
geometric metamerism appear to be brighter and have a lighter
hue when viewed normal to its surface -than when viewed at
an acute angle. That is, a viewer looking directly down
upon the film surface observes a light, bright color.
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Flakes near the film sur~ace reflect ligh-t that only
slightly interacts with the color-producing pigmen~ and
so appear to sparkle. When the viewer shif-ts to look at
the film at an acute angle to its surface, a darker, more
intense color is perceived. Because of the gxeater degree
of interaction, less sparkling is observed and the film
appears generally deeper or thicker. At very shallow angles
approaching the plane of the film surface, multiple reflections
between metal flakes dramatically increase the light-pigment
interaction and thereby makes the film appear extremely
dar~ and deep.
Geometric metamerism, also referred to as
goiniochromatism or simply "flop"~ makes an overall aesthetically
` pleasing impression upon the viewer. For this reason, it is
highly preferred in decorative finishes and particularly in
automotive topcoats. The subtle color variations helps to
hide surface irregularities and highlight styling lines and
contours. It is known that the degree of geometric metamerism
is greatest when the metal flakes are oriented uniformly and
substantially parallel to the film surface. More random
metal flake orientation decreases the degree of geometric
metamerism.
A typical prior art topcoat exhibiting a high
degree of geometric metamerism is formed by the spray appli-
cation of an aluminum flake-containing acrylic lacquer having
a nonvolatiles content of between lS and 35 weight percent.
The viscosity of the low-solids lacquer is sufficiently low
to permit the flakes to move and become approximately oriented
as desired during film leveling immediately after application.
The massive solvent evaporation during curing creates
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turbulence within the film and causes the film to shrink
toward the substrate surface, thereby providing additional
aligning forces to orient the flakes as desired. The result
is a coating wherein the metal flakes are oriented substantially
parallel to the film surface and thereby provide a high
degree of geometric metamerism. Heretofore, the geometric
metamerism obtained with low-solids lacquers has not been
reproduced with paints having higher solids concentrations,
such as 60 to 70~/O~ because the higher viscosity and the lower
solvent evaporation of such paints do not produce the same
uniformity of flake orientation.
It is also known that suitably formulated poly-
urethane resins provide a tough, yet flexible finish that
has improved chip and impact resistance. Polyurethane paint
compositions formulated with a high solids concentration are
known to reduce solvent emissions during curing. While such
properties recommend polyurethane paint binder resin for
applications such as automotive topcoats, the use of such
resins has heretofore been deterred because they did not
display adequate resistance to degradation and fading when
exposed to outdoor conditions and because they did not
provide the good geometric metamerism obtained using low-
solids lacquers.
~ ccordingly, it is an object of my invention to
provide an improved polyurethane paint film that exhibits
the high degree of geometric metamerism typically associated
with metal flake-containing, acrylic lacquer finishes.
It is a further object of my invention to provide an
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improved paint composition containing an isocyana-te-terminated,
polyurethane prepolymer resin and aluminum flakes and having
a high nonvolatiles concentration, said resin being moisture
curable to produce a decorative coating wherein the metal
flakes lie at varying depths and are oriented substantially
parallel to the film sur~ace to provide a high d~gree of
geometric metamerism. The uniformity of flake orientation
in the subject coating and, therefore, the degree of geometric
metamerism are compara~le to acrylic lacquer topcoats applied
with significantly higher solvent concentrations.
It is a still further object of one aspect of my
invention to provide a high-solids urethane paint composition
that is moisture curable to produce a decorative topcoat
having improved resistance to de~radation and fading when
exposed to outdoor conditions and also having a high degree
of geometric metamerism. A urethane paint having these
properties is particularly useful as an automotive topcoat.
Summary of the Invention
; In accordance with a preerred em~odiment of my
invention, these and other objects are accomplished by a
paint composition having a nonvolatiles concentration of 60 70
weight percent or higher and containing aluminum flake pigment
and a binder comprising a particular isocyanate-terminated
polyether urethane resin. The particular urethane formulation
produces a composition having a surprisingly low viscosity in
consideration of its high-solids conte~t~ The paint compos.ition
is spray applied to a substrate and moisture cured to produce
a tough, impact-resistant finish~ The particular resin
structures and the low viscosity o* the composition cause the
aluminum flakes to orient substantially parallel to the paint
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surface and to be distributed generally uniformly across
the thickness of the film. The aluminum flake orientation is
substantially similar to previous metal flaXe orientation
obtained in acrylic lacquer films applied at significantly
lower solvent concentrations. Thus, the urethane paint
composition of my invention produces a film having a high
degree of geometric metamerism.
The urethane resin in my paint composition is formed
by mixing and coreacting an appropriate amount of an aliphatic
diisocyanate, preferably methylene bis (4-cyclohexyl isocyanate),
with a polyoxypropylene diol and a higher-functional polyoxy-
propylene polyol, preferably in the presenceof a suitable organotLn
catalyst,to form a prepolymer having urethane linkages. The
ratio of isocyanate groups to total hydroxyl groups is
initially at least 1.5 to 1 and preferably greater than 2 to 1
to produce a relatively low molecular weight, isocyanate-
terminated resin. The molecular weights and proportions of
the diols and higher-functional polyols are balanced to
provide proper viscosity in the uncured resins and suitable
chemical and physical properties in the cured paint. After
application, the paint film is cured by exposing it to water
vapor at slightly elevated temperatures. In the presence of
water, the terminal isocyanate groups react to form primarily
urea linkages and thereby polymerize the film. In one
embodiment, an ultraviolet light stabilizer capable of
reacting with isocyanate or hydroxyl groups is advantageously
added to the diisocyanate-diol-polyol mixture and coreacted
into the prepolymer molecule, thereby ultimately producing a
coating having resistance to degradation and fading when
exposed to outdoor conditions.
~2~;72
To the resin is added aluminum flake, other
pigments and solvents. The pigments preferably include a
color-producing agent. The total amount of solvent added
does not exceed 30 to 4~/O by weight of the total paint
composition as needed for spray application~ A blend of
organic solvents is preferred. A suitable low boiling
solvent is typically added to lower the compositional
viscosity to permit spraying, yet evaporate sufficiently fast
to prevent sagging of the uncured film on the substrate.
A high boiling solvent component permits the composition
to flow out and level on the substrate and also controls
the curing rate. The particular choice of solvents is
governed by conditions under which the composition is applied
to the substrate, such as the distance from the spray nozzle
to the substrate and the ambient temperature. It is an
important feature of this invention thàt the particular
urethane resin structures are such that a small amount of-
solvent is effective to lower the viscosity to permit spray
application, good film formation, and preferred orientation
of the metal flakes.
Detailed Description of the Invention
An isocyanate-terminated urethane resin mixture
was prepared as follows:
Methylene bis (4-cyclohexyl isocyanate) obtained
from E. I. DuPont de Nemours & Company was employed. This
diisocyanate is a liquid stereoisomeric mixture sold under
the trade name of "Hylene*W". The material is sometimes
generically referred to as H12MDI. Analysis showed it to be
of greater than 99.2% purity. A polyoxypropylene diol having
a number average molecular weigh-t of approximately 1000 was
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*Trademark
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employed. It was obtained from sAsF Wyandotte Corporation
under the trade designation "P1010" and had a hydroxyl number
of 10~. A combination of two polyoxypropylene triols was
also used. The triols were based on trimethylol propane
and obtained from BASF Wyandotte Corporation under the
trade designation "TP440" and "TP1540". They had hydroxyl
numbers of 395 and 107, respectively, and number average
molecular weights of about 425 and 1500, respectively. Also,
included in the reactive mixture was bis (2,2,6,6 tetramethyl
10 piperidinyl-4) sebacate. This compound is an ultraviolet light
stabilizer that improves the resistance of the paint film to
degradation and fading when exposed to outdoor conditions.
It is manufactured by Ciba-Geigy under the trade designation
"Tinuvin 770 ". Dibutyltin dilaurate catalyst was preferably added.
The following proportions of each of the above
ingredients was employed in the preparation of the urethane
resin prepolymer:
Constituent Parts BY Weight rlilliequivalents
Diisocyanate-Hylene* li~ 58.8 449
20 Diol -- P1010 17.3 33
Triol - TP440 14.2 100
Triol - TP1540 8.7 17
Catalyst - Dibutyltin 0.02 --
Dilaurate
Bis 2,2,6,6 Tetramethyl 1.0 4
Piperidinyl-4) Sebacate -
Tinuvin 770
The rat:io of isocyanate groups to hydroxyl groups
is 3.0 to 1. The ratio of triols to total polyols in terms of
chemical equ`ivalents was about 0.78. The above constituents
30 were mixed with approximately 10 parts by weight of dry n-butyl
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acetate. The mixture was reacted for twenty-four hours at
room temperature. During the reaction, the hydroxyl groups
react with the isocyanate to form a polymer having urethane
linkages. The excess of isocyanate groups to hydroxyl groups
produces a reaction product containing a plurality of isocyanate-
terminated molecules of relatively low molecular weight. It
is an important feature of this embodiment of my invention that
the isocyanate groups also react with the reactive amine groups
of the stabilizer. Thus, the stabilizer is chemically reacted
into the prepolymer resin, while maintaining its stabilizing
properties, so that it can neither diffuse out of the final
topcoat film nor undergo phase separation or aggregation.
secause the number of reactive sebacate amine qroups was
small in comparison to the total hydroxyl groups present,
the sebacate had a negligible effect upon the overall resin
molecular structure and the prepolymer properties necessary
to produce the desired geometric metamerism. Thus, in this
example, the prepolymer resin fomulation was accurately
defined by reference to the diisocyanate, diol and triols
present and their ratios, without including the sebacate.
The previously prepared prepolymer binder was then
mixed with phthaloblue pigment (obtained from E. I. DuPont de
Nemours & Company~ and with solvents. To aid in dispersing
the color producing pigment in the paint composition, a small
quantity of the binder was first milled with the pigment and
a small amount of solvent in the following proportions:
Constituent Parts BY Weiqht
Binder 77
Phthaloblue 75
n-Butyl Acetate 3.5
Cellosolve Acetate* 3.5
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*Trademark
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The mixture was milled until a pigment particle size under
20 microns was obtained. This mill paste was then mixed
with additional urethane prepolymer binder resin and solvent
to obtain the following formulation:
ConstituentParts By Weight
Binder 100
Phthaloblue .5
Cellosolve Acetate* 8.5
` n-Butyl Acetate 8.5
Methyl Ethyl Ketone 17.1
The aluminum flake pigment was then added to complete
forming the desired paint composition. A non~leafing aluminum
pigment of typical automotive grade was employed. It was
obtained from Silberline Manufacturing Co. under the trade
designation "Coarse Aluminum Paste ~o. 3141 AR". The paste
contains about 50O/o by weight of aluminum flake and the balance
essentially mineral oil and acetone. To assist in dispersing
the flake in the previously prepared blue resin formulation,
the desired amount of aluminum paste was initially mixed with
approximately equal amounts of resin and solvent, thereby
lowering the paste viscosity and initially wetting the flakes.
The mixture containing coarse aluminum flake was added to the
above blue pigmented formulation along with additional solvent
and catalyst to ohtain a blue metallic moisture-curing urethane
paint of the following composition, wherein the amount of
aluminum flake is reported as a dry flake weight and the amounts
oE other material present in the commercial aluminum paste
are ignored:
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ConstituentParts By Weight
Binder 100
Phtaloblue 0,5
Aluminum Flake 1.6
Methyl Ethyl Ketone 34
n-Butyl Acetate 17
Cellosolve Acetate* 17
Dibutyltin Dilaurate 0.06
The urethane paint composition had a nonvolatiles concentration
0 of 6~/o by weight. The pigment (including flake~ to binder
ratio was 2.1:100. The viscosity of the above paint formulation
was 0.5 poise(Zahn 2 Cup viscosity of 27.6 sec.), suitably low
for spray application.
The above paint composition was spray applied over
Bonderite* 40 phosphated steel substrates which had been primed
using a commercially available primer obtained from the PPG
Industries, Inc., under the trade designation 80.593. The
topcoats were applied using standard siphon fed spray guns
and cured for 30 minutes at 88 C. and 45% relative humidity
in a Tenney-Mite*5 temperature/humidity chamber.
The cured topcoats were decorative and glossy and
found to have excellent mechanical properties. They were tough,
flexible and resistant to chipping and other mechanical failure.
The coatings exhibited excellent stability when exposed to
ultraviolet radiation. Visual examination of the coatings
demonstrated that they displayed a high degree of geometric
metamerism that was qualitiatively comparable to conventional
metallic acrylic lacquer topcoats.
An effort was made to quantitatively compare the
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aluminum flake orientation obtained with the above-mentioned
urethane paint composition and that obtained with a conventional
acrylic lacquer. The flake orientation was determined by
removing a portion of the urethane topcoat along with about one
, mil of primer from the steel substrate. The coating was then
sectioned on a microtome. The sections were then photographed
end on using Leitz* optical microscope in the reflectance mode.
From the photomicrographs, the ori~entation of all aluminum flake
in the coating section were determined relative to the coating
10 surface. The results of this analysis for the blue metallic
coating of this embodiment are presented in Table 1.
TABLE 1
- Distribution of Flake Orientations
Conventional
Acrylic
Blue Metallic Urethane Topcoat Lacquer
Angle of
Flake Relative Number of Percent of Percent of
to Film Surface Flakes in Flakes in Flakes in
(Deqrees)Interval Interval Interval
0-4.5 79 42.2 42.7
5-9.5 40 21.4 23.8
10-14.5 24 12.8 14.7
15-19.5 18 9.6 7.9
20-24.5 6 3.2 1.2
25-29.5 5 2.7 1.8
30_34.5 4 2.1 ]
35~39-5 4 2.1 2.5
40-44.5 1 0.6 ]1 2
45-49.5 1 0.6
50-54.5 2 1.2 ]
55-59.5 1 0.6 2
60-64.5 0 0 ]
65-69.5 0 0 1.2
70-74.5 1 0.6 ]
75-79.5 1 0.6 1.2
80-84.5 0 0
85-90 0 0 ]1.2
Total 187
*Trademark
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For purposes of illustration, the total number of ~lakes having
orientation angles ~alling with 5 intervals is presented.
~ It is seen that over 4~/O of the flakes are oriented within 5
; of the surface and over 70~/O of the flakes are within 10. The
data was also used to calculate an average orientation angle
for the aluminum flakes by multiplying each orientation angle
by the number of flakes having that angle, summing this value
over all angles and dividing by the total number of flakes.
The average orientation angle for the above-described blue
metallic urethane coating was 10.5.
Table 1 also presents the results of a similar analysis
conducted on a conventional acrylic lacquer film having a high
degree of geometric metamerism. The acrylic lacquer was a
commercial automotive topcoat obtained from the E. I. DuPont
de Nemours and Company under the trade designation 927-AF156.
The lacquer was applied at a nonvolatile concentration of 19%
by weight. comparison of the values presented in Table 1 shows
that the subject urethane paint composition produces a
distribution of flake orientation substantially similar to that
obtained using conventional acrylic lacquers. The average
flake orientation for the acrylic lacquer in this test was 10.9
and compared favorably with the subject urethane paint. similar
tests preformed on several conventional lacquers indicate that
suitable films generally have average orientation angles of
between about 6.9 and 12.7 .
It is apparent to one skilled in the art that other
color producing agents can be substituted for the phthaloblue
pigment in the above embodiment without substantially affecting
the aluminum flake orientation. A green metallic coating was
produced using a paint composition containing a phthalogreen
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pi~meIIt and ~he resin binder described above. The green paint
composition was prepared similar to the blue composition, but
had a nonvolatiles content of 7~/~ by weight. The compositional
viscosi-ty was 1.0 poise (43.4 seconds for a Zahn 2 Cup) and
the phthalogreen pigment to binder weight ratio was 2.5:100.
The paint composition contained 5 gram (dry) of aluminum flake
for each 100 grams of isocyanate~terminated resin. The
composition was applied to primed substrates and cured. The
coating had a generally dark green color and displayed a high
degree of geometric metamerism. Analysis of the coating
indicated that it had an average orientation angle of 7.3
and that over 70~/O of the flakes were oriented within 10
of the surrace, surprising in view of its high solids content.
A second green coating was produced using the same
isocyanate-terminated resin. It had a nonvolatile concentration
of 68% by weight, a viscosity of 1.2 poise (46.0 seconds for '
a zahn 2 Cup), and a phthalogreen pigment to binder weight
ratio of 2.9:100. The dry concentration of the aluminum flake
was 1.0 grams for every 100 grams of resin binder. Thus, this
second green coating differed primarily from the previously
described green coating in the proportion of aluminum flake.
This resulted in a coating having an overall lighter green hue,
in spite of the slightly larger phthalogreen concentrationO
This light green coating also displayed a high degree of geometric
metamerism. Analysis of the aluminum flake in the finished
coating indicated that the average orientation angle was 12.0C
and that over 60% of the flakes had an orientation of less
than 10 rela-tive to the finished surface.
In the above examples, the high solids content, moisture
curable urethane paint compositions of my invention produced
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decorative metallized topcoats in which a large n~mber of
aluminum Elakes were distributed generally uniformly across
the thic]cness o~ -the film. EIowever, the flakes were also
arranged in a preferred orientation in which a major portion
of their number were substantially parallel to the film surface.
This orientation was surprisingly ob-tained despite the high
solids content of the paint formulation. The result is -that
my paints provide attractive and durable topcoat surfaces
with less solvent disposal effort~
To a great extent the degree of geometric metamerism
is related to the orienlation of the aluminum flakes with
respect to the Eilm surface. A high degree of geometric
metamerism is generally obtained where the average aluminum
flake orientation is 15 or less, and preferably 12 or lessO
Typically, the coatings of my invention have an average flake
orientation angle of between 5 and 12. Besides the average
orientation angle, it is also important in obtaining a high
degree of geometric metamerism that the majority of flakes
are oriented at a low angle relative to the surface, In the
above coatings, the great preponderance of the flakes -60 to
700/O- lie within 10 of being parallel to the surface. While
flaXe orientation is important, other factors also contribute
to the overall effect of geometric metamerism, particularly
the refractive index of the film, and thereby prevent a more
direct comparison of the color variations.
In the above examples, the diisocyanate employed in
the preparation of the prepolymer resin was methylene bis
(4-cyclohexyl isocyanate). Other aliphatic diisocyanates
could be suitably employed to prepare urethane prepolymer resins
useful for forming the high-solids, low-viscosity paint
~2~
compositions of my invention. Suitable isocyanates include
isophorone diisocyanate, lysine diisocyanate, and the biuret
oE hexamethylene diisocyanate.
n the preparation of the prepolymer resin, it is
preferred that a mixture of polyoxpropylene diols and higher
functional polyols be used. Polyoxypropylene diols having
molecular weights in the range of about 200 to ~,000 may be
used. Polyoxypropylene triols or higher functional pc~~ols with
molecular weights in the range of about 400 to 4,000 are suitable.
The presence of higher functional polyols provides chain
branching and ultimately cross-linking so that a suitable
tough, flexible, chip resistant paint is obtained. Good
coating properties are obtained where the ratio of e~uivalents
of triol or higher functional polyols to total polyol is in the
range of 0.1 to 0.9.
Of importance in obtainin~ a resin binder capable of
forming a low viscosity, high-solids pain-t composition is the
ratio of isocyanate groups to the total of hydroxyl groups.
In general, ratios of 1.5:1 or greater are suitable and ratios
in the range of 2:1 to 3:1 are preferred. Where the reactants
are mixed at the desired ratio, the reaction between an
aliphatic isocyanate with both polyoxypropylene diol and higher
functional polyol forms aurethane prepolymer resin having low
molecular weight and capable of forming paint compositions
that are moisture curable to produce topcoatsdisplaying
geometric metamerism.
In the preferred embodiment, a small amount of
bis (2,2,6,6 tetramethyl piperidinyl-~) sebacate was coreacted
with the diisocyanate and the polyols during the preparation
of the moisture curable, isocyanate-terminated urethane prepolymer
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resin. The llindered bis-piperidinyl material is a known
ultraviolet light stabilizer. I have found that it is
particularly advantageous to react -this type oE stablizer with
my isocyanate so as to incorporate this stabilizer directly
into the prepolymer resin molecular structure. IncorporatiOn
of the stabilizer in this manner produces a coating having
improved resistance to degradation and fading when exposed to
; outdoor conditions. While the aforementioned hindered
piperidinyl sebacate is preferred, other bis-piperidinyls of
aliphatic dicarboxylic acids are known light stabilizers and
may be similarly employed. Other types of stabilizers capable
of reacting with isocyanate or hydroxyl groups may also be
advantageous coreacted into the prepolymer molecule in accordance
with the practice of my invention.
I have found that the amount of the preferred
hindered sebacate effective to produce the desired film stability
is normally from 0.1% to about 2% by weight of the resin.
The incorporation of a small amount of the stabilizer in the
aforementioned manner has no noticeable effect upon the
orientation of the aluminum flakes. Coatings displaying a
high degree of geometric metamerism have been produced with
similar isocyanate-terminated, polyether-urethane prepolymer
resins that do not contain a stabilizer. When the a~ount of
stabilizer is small, its effect upon the overall prepolymer
resin molecular structure and the properties necessary to
produce the desired aluminum flake orientation is small. Thus,
the prepolymer resin formulation is essentially defined by the
amounts and ratios of the diisocyanate, diol and higher-
functional polyols initially present and it is unnecessary to
consider the stabilizer. When larger proportions of stabilizer
~25~2
are incorporatecl into the prepolymer resin structure,
the resin binder is more accurately dcscribed by including
the stabilizer. That is, ~or a stabilizer concentration of about
2% or greater, a suitable prepolymer resin is obtained where
the ratio of the diisocyanate to t;he total of the hydroxyl
groups and the reactive groups of the stabilizer is 1.5:1 or
greater and preferably between 2:1 and 3:1.
It is apparent that other color-producing pigments
may be substituted for the phthaloblue and phthalogreen pigments
employed in the examples set forth herein. Thus, urethane top
coats having a wide range of colors and displaying geometric
metamerism may be produced. It is also apparent that small
amounts of other pigments could be added without substantially
detering the desired aluminum flake orienta-tion. For example,
an ultraviolet light stabili2er might be added in the conventional
fashion as a pigment, rather than reacted into the urethane resin
..ructure. It is also within the skill of the art to vary the
catalyst and its concentration to obtain a satisfactorily
cured coating. In comparison with the resin structure, the use
of other pigments or catalysts has a negligible effect on the
degree of geometric metamerism.
Subsequent experiments wherein the urethane paint
composition was analysized immediately after application to a
metal substrate indicated that the solids content of the freshly
applied film was typically about 85% by weight. The change in
solvent concentration is attributed to evaporation occurring
after the spray leaves the gun. Solvent continues to evaporate
after the film is applied. However, from these experiments, it
is believed that the on-panel film viscosity necessary to obtain
good flake orientation needs to be less than 10 poise at a shear
18
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rate of 15.7 sec and preferably between 1 and 5 poise.
Obviously, the viscosity should not be so low as to permit
the paint to run or sag before it is cured. Solvent systems
of varying concentration or containing compounds other than
methyl ethyl ketone, n~butyl acetate or cellosolve acetate
may be formulated to provide the Idesired flake orientation
without causing sagging.
The maximum advantages of my invention are obtained
where the total solvent concentration is no greater than 40
weight percent. The use of a low solvent spray composition
minimizes the ~uantity of solvents that must-be evaporated
during paint drying and permits lower drying temperatures
in the paint curing oven. It is an important fea-ture of my
invention that the particular resin structures may be applied
- using a minimal solvent concentration
While my invention has been described in terms of
certain specific embodiments thereof, it will be appreciated
that other forms could readily be adapted by those skilled
in the art and, accordingly, the scope of my invention is
to be considered limited only by the following claims.
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