FIELD OF THE INVENTION
[0001] The present invention relates to coating methods. More particularly, the invention
relates to an improved method for producing highly reflective coatings, on an automobile
or truck body or part thereof.
BACKGROUND OF THE INVENTION
[0002] Automobile and truck bodies are treated with multilayer coating systems that enhance
the aesthetic appearance of the vehicle and also provide protection from prolonged
exposure to the environment or weathering. Basecoat/clearcoat finishes for automobiles
and trucks have been commonly used for the past two decades.
U.S. Patent 4,728,543 and
U.S. Patent 3,639,347 disclose the application of a transparent protective clearcoat over a color coat
or pigmented basecoat in a "wet on wet" application, i.e., the clearcoat is applied
before the basecoat is completely cured. At the time of this application, it has become
popular to produce finishes on vehicles that are either solid color, pearlescent color,
or have a metallic sparkle. The metallic sparkle finishes are also described in the
art as metallic effect finishes, which utilize a metallic flake pigment, such as aluminum
flakes, in the pigmented basecoat layer to impart a glamorous, high gloss, metallic
appearance.
[0003] As is well known in the art, in producing a finish of automotive quality on a substrate,
multiple layers of coatings are generally used. A typical automobile steel panel or
substrate has, for example, several layers of coatings. The substrate is typically
first coated with an inorganic rust proofing zinc or iron phosphate layer over which
is provided a corrosion resistant primer, which can be an electrocoated primer or
a repair primer. A typical electrocoated primer, which is mainly used in original
equipment manufacturing (OEM) applications, comprises epoxy polyester and various
epoxy resins. Typically, a primer surfacer and/or sealer can be applied over the electrodeposited
primer to provide a smooth surface for better appearance and to which the overlying
layer or layers of basecoat will readily adhere. The cured primer layer can be sanded
to remove any defects present such as, for example, dust particles in or on the primer
or other imperfections.
[0004] In conventional practice, pigmented basecoat layers and/or "effect" basecoat layers
are applied over the primer layer. Multiple basecoat layers can be applied depending
upon the color and effect(s) that are desired in the finished product. The multiple
layers can either be the same as each other or different from each other. In applications
where two different basecoat layers are applied, such as for example when a metal
flake pigment layer is applied over a solid color pigment layer, it is a requirement
in the conventional art to use a forced drying or a curing step to rapidly dry or
cure the first layer prior to application of the second layer. If the first basecoat
layer is cured, the coated substrate is subjected to conditions such as, for example,
curing ovens, that cause crosslinking of the film forming binder. When rapid drying
is required in a painting process, it is conventional to use equipment such as blowers
and/or heaters to remove at least 50% of a dispersant solvent from a first coating
layer prior to application of a second coating layer having a different composition
during the period of time allotted for painting a vehicle substrate. Simple evaporation
under ambient conditions or reliance upon movement of air around a substrate as the
substrate is moved along a paint process line is not adequate for rapid drying processes
and, therefore, are not used conventionally where rapid drying processes -- such as
forced drying -- are required.
[0005] Metal flake pigments come in a variety of shapes and sizes. Conventional effect finishes
typically are relatively thick metal flake pigments that impart a sparkle to the finished
substrate. Several pigment manufacturers produce thin metal flake pigments. It is
possible to produce coatings using these thin metal flake pigments that have a polished
or anodized metal look without the metallic sparkle imparted by thick metal flake
pigments. However, thin metal flake pigments are difficult to use in a coating composition
as they allow underlying surface defects, such as sanding scratches, to be readily
visible in the finished substrate.
[0006] It is believed that the thin metal flake pigments are thin and flexible enough so
as to conform to the topography of the underlying substrate. In this manner, during
the solvent evaporation process, if thin metal flake pigments encounter a surface
defect such as a sanding scratch, the flakes align and follow the topography of the
defect. When the coating is dried and cured, the defect can be readily visible to
the naked eye. In contrast, traditional metal flake pigments are thick enough so that
they are able to lie flat on a substrate surface and bridge any sanding scratch defect
without deforming. Such small scratches do not significantly affect a basecoating
composition containing traditional metal flake pigments. Such traditional metal flake
pigments typically have an average thickness of about 300 to about 500 nanometers
whereas the thin metal flake pigments have an average thickness of only about 10 to
100 nanometers.
[0007] The desire for even more unique and attractive color effects has led the auto industry
to find ways to create even brighter metallic effects than available today. Vapor
metallized flake (VMF) pigments have been used in the basecoat layer to impart to
the finish an extremely smooth and fine-textured bright metallic appearance similar
to polished metal or an anodized metal with no perceptible "sparkle". This polished
or anodized metal appearance differs from traditional metallic finishes in that there
is a minimum of perceptible sparkle and the human eye cannot readily discern individual
metallic flakes.
[0008] In conventional practice, a polished or anodized metal appearance (also conventionally
known, and referred to herein, as the "polished metal effect") can be obtained using
organic solvent-borne paints. However, use of such paints requires a large amount
of surface preparation, and the paints are very difficult to produce. In a 2003 pre-print
publication of Kansai Paint entitled "Super Metallic Silver Colors" (Y. Mizutami,
Y. Nakao, and S. Nakamura) such a process is described where eight layers of paint
and six bakes are required. This process would require substantial reconfiguration
of a conventional paint line.
European Patent Application 1,591,492 A1 discloses a coating method for forming a chrome-like coating effect, but requires
that the effect layer be applied in multiple very thin coating layers. Such an application
method is not useful in an OEM automotive facility without substantially slowing down
the manufacturing process.
U.S. Patent No. 6,331,326 discloses a method for producing a plated metal effect on a substrate.
[0009] US 2004/02882 describes a process and materials for coating motor vehicles with flake containing
tricoat color finishes in a wet-on-wet-on-wet system on a continuously moving paint
application line It would be desirable to eliminate multiple spray passes and baking
steps in a process for manufacturing a vehicle having a polished metal appearance.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to the process according to claim 1.
[0011] In another aspect, the coating process for applying a multi-layer coating is carried
out using painting equipment that consists of two waterborne basecoat spray stations
and one clearcoat spray station.
[0012] The method of this invention can be operated in a single pass continuous in-line
paint application process or in stationary batch process such as a modular process.
[0013] The present invention eliminates the need for multiple bakes, while at the same time
provides a waterborne finish that is of automotive quality and appearance, substantially
free of sand scratch marks, and has smooth polished metal appearance with desired
brightness, flop and with a minimum of sparkle metallic effect.
[0014] Various aspects of the present invention can be realized by careful and thoughtful
modification of the claims using the details of the invention provided hereinbelow
in any combination or manner to further limit what is already claimed. It is anticipated
that any modification of what is claimed by what is disclosed is within the disclosed
scope and available to the inventors to be claimed.
BRIEF DESCRPTION OF THE DRAWINGS
[0015] FIG. 1 is a general flow diagram of one embodiment of the present invention to achieve
a polished metal appearance.
DETAILED DESCRIPTION OF THE INVENTION
[0016] In the description of the present invention that follows below, the context is generally
that of a process wherein an automotive substrate is coated on a continuously moving
assembly line in a standard basecoat/clearcoat paint application line, such as shown
in FIG.1. One of ordinary skill in the coating art would understand that the process
of the present invention could also be used in other types of continuous coating processes
or processes conventionally known in the art, such as, for example, batch processes.
[0017] In one embodiment, the present invention is a process for applying a multilayer coating
on a vehicle, wherein the coating provides a polished metal appearance to the coated
vehicle. The present invention provides such an appearance on a vehicle that is substantially
free from sand scratch marks, and thereby substantially reducing or eliminating altogether
the manifestation of scratches and/or sanding defects that can be discerned at the
outermost coating layer. By "substantially free of sand scratch marks" it is meant
that a substrate coated according to the present invention is high enough in quality
that no additional repair or retouching of the painted surface needs to be performed.
It should be noted that the cured coating might have defects that need to be repaired,
such as, for example, dust particles on or under the paint. However, small sanding
scratches that may be present in the primer layer are generally not visible after
application of the coating composition according to the present methods.
[0018] The terms "polished metal" or "anodized metal" appearance can be used interchangeably
and as used herein describe a coating having a high flop value and a low texture and
sparkle value. These values can be measured using a BYK-MAC 6-angle instrument, available
from Byk-Gardner USA, Columbia, Maryland. This instrument can measure reflected light
at several angles to determine the flop value, a "sparkle" value and a texture value
that is termed "graininess" or "coarseness" value. Flop is determined by measuring
the reflected light at several angles and applying those values to the following formula:
FLOP = (2.69) [L
*(15°)-L
*(110°)]
1.11/(L
*(45°))
0.88 where L*(n) is the value of reflected light at an incidence angle of n.
[0019] In general, larger metallic flakes exhibit higher flop values and correspondingly
high sparkle and graininess values. In contrast, the present method produces high
flop values but low sparkle and graininess values. Such an appearance is also known
in the art as a "polished metal effect".
[0020] The film-forming portion of the coating composition of this invention is referred
to as the "binder" or "binder solids". The binder generally includes all the film-forming
components that contribute to the solid organic portion of the cured composition.
Generally, catalysts, pigments, and non-polymeric chemical additives such as stabilizers
are not considered part of the binder solids. In this disclosure, the term "binder"
or "binder solids" refers to the curable film-forming materials, the crosslinking
agent and all other optional film-forming components, as are further described hereinbelow.
[0021] According to the practice of the present invention, a polished metal or anodized
metal looking finish of automotive quality that is substantially free of sand scratch
marks is produced in a single pass using conventional basecoat/clearcoat continuous
paint application lines typical of conventional automobile painting.
[0022] Prior to treatment, according to the process of this invention, a substrate optionally
can be primed or otherwise treated as may be conventional in the art. Preferably the
vehicle body is pre-primed with a primer surfacer (also known as a primer sealer)
layer and then sanded as needed to remove any defects, to a smooth finish as is conventional
in the art.
[0023] Referring to FIG. 1, in the first step 22 of the process of this invention, a first
waterborne basecoat is applied to the surface of the automotive substrate (10). The
first waterborne basecoat is substantially free from thin metal flake pigments. The
phrase "substantially free from" as used herein means that the first waterborne basecoat
comprises less than 1 percent by weight of a thin metal flake, such that the effects
of the thin metal flake are not discernable on coated surface. The first waterborne
basecoat functions (a) to form a layer that fills any sanding scratch defects and
(b) to provide a smooth surface on which the second waterborne basecoat can be applied.
This allows the thin metal flake pigment present in the second waterborne basecoat
to be oriented substantially parallel to the substrate and, after drying and curing
the combined layers according to the present invention, provides the desired optical
effect without allowing small sanding scratch defects that may be present in the primer
layer to be seen.
[0024] The first waterborne basecoat composition can be applied to the surface of the substrate
in this step by any suitable coating process well known to those skilled in the art.
A preferred method to apply the first waterborne basecoat is using electrostatic or
pneumatic spray equipment. The method and apparatus for applying the waterborne basecoat
composition to the substrate is determined in part by the configuration and type of
substrate material.
[0025] After application of a layer of the first waterborne basecoat composition, the process
of the present invention includes a second step 24 of applying the second layer of
waterborne basecoat composition containing thin metal flake pigment over the layer
of first waterborne basecoat composition. The second waterborne basecoat composition
can be applied to the surface of the substrate in this step by any suitable coating
process known to those skilled in the art. A preferred method of applying the second
waterborne basecoat is using pneumatic or electrostatic spray equipment. In the practice
of the present invention, the second waterborne basecoat composition can be applied
within about 10 to 300 seconds of the first waterborne basecoat application, preferably
within about 1 to 4 minutes of application.
[0026] The process of the present invention can take advantage of two conventional basecoat
zones 22 and 24 in a typical basecoat/clearcoat painting line without the need to
reconfigure the line. In FIG 1, basecoat application zone 22 and basecoat application
zone 24 can be individual spray booths or can be the same spray booth. In some existing
OEM automotive basecoat painting lines, basecoat zones 22 and 24 are the same spray
booth. Two separate sets of spray guns are used to apply the layers of the first and
second waterborne basecoat compositions and in many cases, the application of the
second waterborne basecoat (onto the first waterborne basecoat) begins prior to the
complete application of the first waterborne basecoat to the entire substrate.
[0027] In the practice of the present invention, the second waterborne basecoat is applied
over the first waterborne basecoat before the first waterborne basecoat is dry. In
a preferred embodiment, the second waterborne basecoat containing the thin metal flake
pigment can be applied to the first waterborne basecoat in such a manner that at least
50 percent, preferably at least 65 percent and more preferably, at least 80 percent
by weight of the carrier liquid of the first waterborne basecoat is still present
when the second waterborne basecoat is applied. In the practice of the present invention
a forced drying step or intermediate flash step before the application of the second
waterborne basecoat composition is optional. Forced drying, as one of ordinary skill
in the art would know, requires utilizing equipment such as blowers and/or heaters
to remove solvent at a faster rate than would occur under ambient conditions, or with
ambient (unforced) air flow such as, for example, the normal airflow resulting from
the movement of a substrate through space on a paint process line. It can be desirable
in the practice of the present invention to eliminate process steps that are not required,
and thereby improve efficiency and reduce costs associated with such steps. If no
forced drying step or flash step is practiced it is expected that the solvent content
of the first waterborne basecoat would not be reduced substantially - that is, not
greater than 5 wt% loss of solvent, compared with the weight of the applied first
waterborne basecoat -- prior to applying the second waterborne basecoat. Application
of the second waterborne basecoat composition can be done at essentially the same
temperature, humidity, and airflow conditions as used to apply the first waterborne
basecoat composition.
[0028] After application of the second waterborne basecoat composition, the process of the
present invention includes a third step 26 of subjecting the combined waterborne basecoat
layers to a forced drying or flash step to volatilize at least a portion of the volatile
materials from the liquid coating compositions and set, but not initiate curing or
crosslinking of, the basecoats on the substrate. By set, it is meant that the applied
basecoat is dried sufficiently that it is not disturbed or marred (waved or rippled)
by air currents that may blow past the surface. The flash step can be conducted in
heated and/or dehydrated air, such as, for example, using infra-red radiation and
convection drying. If the air is heated, it can be heated to a temperature in the
range of from about 60°C to 80°C. The volatilization or evaporation of volatiles from
the basecoat can be carried out in open air, but is preferably carried out in a flash
chamber (FIG. 1) in which heated and/or dehydrated air is circulated at low velocity
to minimize airborne particle contamination. A typical flash chamber has blowers or
fans positioned at the top and sides of the chamber so that the circulated air is
directed in a manner that is substantially perpendicular to the surface of the substrate.
The automobile body can be moved through the flash chamber in an assembly-line manner
at a rate that permits the volatilization of the applied basecoat compositions as
discussed above. The rate at which the automobile body is moved through the flash
chamber depends in part upon the length and configuration of the flash chamber. An
intermediate flash step can take from 30 seconds to 10 minutes. Preferably this step
can take from about 2-5 minutes, as in a conventional painting process.
[0029] Following application of the two basecoats to the surface of the automobile, the
body is dried sufficiently to enable application of the clearcoat composition such
that the quality of the finish will not be affected adversely by further drying and/or
curing of the basecoat. Preferably, the basecoats, after application to the surface
of the substrate, and having been subjected to the flash step, form a multilayer film
that is substantially uncrosslinked. During the flash: step, the applied basecoat
compositions must be sufficiently dried so that remaining water vapor does not evolve
to create defects in the layers of basecoat or clearcoat composition during the baking
and curing of the applied layers.
[0030] Referring again to FIG. 1, the process of the present invention comprises a next
step 28 of applying a liquid (solventborne or waterborne) or powder clear clearcoat
composition over the applied basecoat layers. The clearcoat can be applied by any
of the method known to those of ordinary skill in the art. A liquid clearcoat can
be applied over a basecoat by means of a wet-on-wet application, i.e., the clearcoat
can be applied to the basecoat without curing or completely drying the basecoat. The
clearcoat is preferably applied over partially layers of basecoat composition that
have been flashed, that is, partially dried. For the purposes of the present invention,
this is referred to herein as a "wet-on-wet" process because the basecoat is not completely
dried or cured. Although less preferred, the applied basecoat compositions can be
cured, if desired, before the clearcoat is applied.
[0031] According to the present invention, the first and second waterborne basecoat compositions
and the clearcoat compositions described above can be applied by conventional techniques
such as spraying, electrostatic spraying, high rotational electrostatic bells, and
the like. The preferred techniques for applying all three coatings are air atomized
(pneumatic) spraying with or without electrostatic enhancement, and high-speed rotational
electrostatic bells, since these techniques are typically employed in a continuous
paint application process.
[0032] Following the application of the clearcoat, the process of the present invention
preferably comprises a curing (i.e., baking) step 30 in which the coated substrate
is heated for a predetermined time period to allow simultaneous curing of the basecoats
and clearcoat. The composite coating composition is baked preferably at 60-150°C for
about 15-45 minutes to form a cured finish on the substrate. As used herein, "cured"
means that the crosslinkable components of the coatings are substantially crosslinked.
By the term "substantially crosslinked", it is meant that most of the crosslinking
has occurred, although further crosslinking may occur over time.
[0033] The process of the invention can optionally include a cooling step (not shown) after
the curing step to cool the composite finish to ambient temperatures before the vehicle
is further worked on during its manufacture.
[0034] The first waterborne basecoat functions to fill in defects, such as the sanding defects
present in the primer surfacer layer, and provide a smooth finish over which a second
waterborne basecoat layer containing an effective amount of thin metal flakes can
be applied. Preferably, the first basecoat is either a non-transparent solid color
(pigmented) basecoat or an unpigmented basecoat.
[0035] The term "non-transparent" as used herein means that the contrast between the black
and white fields of a black and white chart coated with the coating composition is
no longer visually discernible. ISO 6504-3:2006 (E), methods B is used to determine
the dry film thickness of a coating composition that is applied in a wedge shape to
a black and white chart at the point of complete hiding.
[0036] The first waterborne basecoat composition employed in the present invention is a
waterborne basecoat composition, preferably a solid color pigmented or an unpigmented
waterborne basecoat composition, more preferably a solid color black waterborne basecoat,
that is opaque and is applied at complete hiding. Other non-transparent colored compositions
can also be used, although black-pigmented compositions are preferred.
[0037] The first waterborne basecoat composition is preferably a crosslinkable composition
comprising a film-forming binder, volatile material, and optionally pigment. The film-forming
binder must contain at least one water-compatible aqueous microgel, at least one crosslinking
agent such as an amino resin and a sheet silicate. The film-forming binder also preferably
contains at least one other polyol polymer.
[0038] The aqueous microgels suitable for use in this invention may be composed of various
types of crosslinked polymers. Of particular interest for the purposes of this invention
are crosslinked acrylic microgel particles. Preparation of such acrylic microgels
may be carried out by methods that are well known and routinely practiced by those
of ordinary skill in the art. Typically, the microgels are acrylic addition polymers
mainly derived from one or more alkyl acrylates or methacrylates, optionally together
with other ethylenically unsaturated copolymerizable monomers like styrene and vinyl
esters. Suitable alkyl acrylates or methacrylates include, without limitation, alkyl
acrylates and methacrylates each having 1-18 carbon atoms in the alkyl group. Since
the microgel is required to be formed with internal crosslinking, there may be included
in the monomers from which the microgel is derived a minor proportion of a monomer
which is polyfunctional with respect to the polymerization reaction, such as ethylene
glycol dimethacrylate, allyl methacrylate or divinylbenzene.
[0039] Alternatively, there may be included in the monomers minor proportions of two other
monomers carrying pairs of functional groups which can be caused to react with one
another either during or after polymerization, such as epoxy and carboxyl (as for
example, in glycidyl methacrylate and methacrylic acid), anhydride and hydroxyl, or
isocyanate and hydroxyl. There also is preferably included in the monomers from which
the microgel is derived minor amounts of a hydroxy containing monomer for crosslinking
purposes after application of the composition to the substrate from the following
group: hydroxy alkyl acrylates or methacrylates, or any mixtures of other ethylenically
unsaturated hydroxy.
[0040] Acid functional monomers such as acrylic acid or methacrylic acid are also preferably
included in the monomer mix to ionically stabilize the microgels in the aqueous dispersion
medium by converting such groups to a suitable salt by reaction with a base, such
as dimethylaminoethanol, dissolved in the aqueous medium. Alternatively, the required
stability in the aqueous medium can be achieved by using an acrylate or methacrylate
monomer containing basic groups, for example, N,N-dimethylaminoethyl methacrylate
which is neutralized with a suitable acid, such as lactis acid. Stability in aqueous
medium can also be achieved through the use of surfactants or macromonomers that contain
water-soluble nonionic stabilizers such as materials that contain polyethylene glycol
structures.
[0041] Suitable acrylic microgels that can be used to form the waterborne basecoat composition
include crosslinked polymer microparticle aqueous dispersions such as disclosed in
Backhouse
U.S. Patent 4,403,003 issued Sep. 6, 1983 and Backhouse
U.S. Patent 4,539,363 issued Sep. 3, 1985. The microgel preferably contains appropriate functional groups, such as hydroxy
groups, whereby they can become crosslinked, after application of the composition
to the substrate by means of a crosslinking agent, e.g., the amino resin.
[0042] By "aqueous carrier", it is meant either water alone or water mixed with a water-miscible
organic co-solvent such as an alcohol. The crosslinked microgel particles so produced
are provided in colloidal dimensions. The microgel particles that are particularly
useful in this invention generally have a colloidal size from about 80 to 400 nanometers,
in diameter, preferably from about 90 to 200 nanometers.
[0043] In addition to the aqueous microgel, the first and second waterborne basecoat compositions
can each individually include other film-forming polymers, such as polyols. Suitable
polyols useful for preparing the waterborne basecoat composition include water-compatible
acrylic, polyester, polyurethane, polyether, or other polyol having a hydroxyl number
of 50-200, as are conventional in the art. Additional water-compatible film-forming
and/or crosslinking polymers may be included in the basecoat employed in the present
invention. Examples include water-compatible acrylics, polyurethane, epoxies, or mixtures
thereof.
[0044] Alternatively or in addition to the film-forming polymers mentioned above, film-forming
filler materials such as oligomeric polyether glycols of low volatility, for example,
low molecular weight polypropylene and/or polyethylene glycol, can be used to fill
the voids formed by the microgel particles upon drying and to improve the physical
properties of the resulting film or finish. These oligomeric substances can be converted
to high molecular weight polymer, after application of the basecoat composition, by
linking them through their hydroxyl groups or other groups that are reactive with
the crosslinking agent.
[0045] Suitable crosslinking agents include aminoplast resins that are soluble or partially
soluble in the aqueous medium of the composition, such as melamine-formaldehyde condensates
and in particular alkylated (e.g., methylated, butylated) melamine-formaldehyde condensates.
Other contemplated crosslinking agents are alkylated urea formaldehyde condensates,
benzoguanamine formaldehyde condensates and blocked polyisocyanates or compatible
mixtures of any of the forgoing.
[0046] A useful first waterborne basecoat composition comprises aqueous microgel in an amount
of from about 20-70% by weight of binder solids, preferably 45-65% by weight, in addition
to coloring pigments. Suitable aqueous microgels include but are not limited to the
crosslinked acrylic microparticle aqueous dispersions disclosed in
U.S. Patent 4,403,003, water-soluble or partially water-soluble aminoplast resin, preferably a methylated
melamine formaldehyde, from 10-35%, preferably 15-25%; water dispersible polyester
polyol resin from about 0-30%; polyurethane polyol aqueous dispersion from 0-35%,
preferably 5-15%; water soluble polyether filler from 0-15%; water-soluble acid catalyst
from about 0-2%, such as but not limited to a volatile amine blocked sulfonic acid
catalyst, to promote melamine or other crosslinking reaction. The first waterborne
basecoat composition also includes 0.1-1.6%, preferably 0.2-1%, based on the weight
of the total composition, sheet silicate particle, such as those disclosed in Berg
et al.
U.S. Patent 5,198,490 issued Mar. 30, 1993, to help give the desired holdout or resistance to strike-in and intermixing.
[0047] The overall solids content of the first waterborne basecoat composition can range
from about 10 to 50% by weight of the total composition. Preferably, the overall solids
content of the first waterborne basecoat can range from about 20 to 40% by weight
of the total composition.
[0048] A variety of pigments and/or metal flake pigments or other effect pigments can be
employed in the first waterborne basecoat composition, as would be apparent to those
skilled in the art. In a preferred embodiment, the first waterborne-basecoat composition
is a "straight-shade" or "solid color" coating that has no visible flop or two tone
metallic effect and primarily contains colored pigments other than flake.
[0049] Colored pigments useful in the practice of the present invention include, for example,
metal oxides such as titanium dioxide, zinc oxide, iron oxides of various colors;
carbon black; filler pigments such as talc, china clay, barytes, carbonates, silicates;
and organic colored pigments such as quinacridones, phthalocyanines, perylenes, azo
pigments, indanthrone blues, carbazoles such as carbazole violet, isoindolinones,
isoindolones, thioindigo reds, benzimidazolinones, diketo-pyrrolo-pyrroles (DPP).
[0050] Minor amounts of effect pigments such as aluminum flakes, copper bronze flakes, pearlescent
flakes, and the like, and optional other effect pigments, holographic flakes, glass
spheres, glass flakes, other non-flake effect pigments including micro titanium dioxide
pigments and GRAPHITAN
® pigments, and higher degree effect pigments including, for instance, CHROMAFLAIR
®, VARIOCHROME
®, and HELICONE
® pigments, can be optionally included in the first waterborne basecoat composition
to impart the desired color effect and hiding. The metal flake pigments optionally
used in the first waterborne basecoat are distinguished from the thin metal flake
pigments of the second waterborne basecoat composition. Metal flakes of the first
basecoat have an average particle thickness in the range of from 300 to 500 nanometers
and average particle diameters in the range of from 5 to 60 micrometers. They are
significantly thicker than the thin metal flake pigments of the second waterborne
coating.
[0051] It can be optional to include agents that inhibit the reaction of the traditional
metal flake pigments with water. Typical inhibitors are phosphated organic materials
such as phosphoric acid and other materials as described in
U.S. Pat. No. 4,675,358.
[0052] The specifc pigment to binder ratio of the first waterborne basecoat can vary widely
so long as it provides the requisite hiding at the desired film thickness and application
solids. The pigments can be introduced into either the first or second waterborne
basecoat compositions by forming a mill base or pigment dispersion with any of the
aforementioned polymers used in the coating compositions or with another compatible
polymer or dispersant by conventional techniques, such as high speed mixing, media
milling, sand grinding, ball milling, attritor grinding or two/three roll milling.
It is known conventionally that milling techniques are not applicable for metal flake
pigments. It is therefore conventional that mixing and slurry techniques are used
to disperse flake pigments. The pigment dispersion can be blended with the other constituents
used in the coating compositions.
[0053] The first and second waterborne basecoat compositions are formulated to have acceptable
hold-out or resistance to intermixing between the basecoats within about 10 to 300
seconds after application at ambient conditions between coats, preferably within 1
to 4 minutes under ambient conditions. Ambient conditions mean the environmental conditions
in a typical painting facility. Typical ambient conditions are: a temperature in the
range of from 15°C to about 35°C; a relative humidity in the range of from 5 percent
to 90 percent; and, for a continuous paint line, a line speed in the range of from
about 2 meters/minute to about 11 meters/minute. Preferably, the coating materials
described herein are formulated so that they can be applied in conditions ranging
from 18°C to 28°C and a relative humidity of 50 percent to 70 percent. An additional
step of flashing a portion of the aqueous carrier from the first waterborne basecoat
layer before applying the second waterborne basecoat composition is not required nor
is such a step desirable. In a continuous painting facility, that is, a painting facility
utilizing a continuously moving paint line using a "wet on wet" process, it is believed
that no substantial evaporation of the solvent from the first waterborne basecoat
occurs during the time between the completion of the first waterborne basecoat and
the start of the application of the second waterborne basecoat. The second waterborne
basecoat composition can be applied over the first layer under the same or similar
spraybooth conditions as used when applying the first waterborne basecoats without
sacrificing good control of the orientation of the thin metal flake pigments, and
without detracting from the desirable appearance (i.e. a minimum of perceptible sparkle,
high brightness, large flop value, polished or anodized metal appearance) of the overall
finish.
[0054] The first waterborne basecoat can be applied at such a rate as to achieve a dry film
thickness in the range of from 5 to 40 microns, preferably in the range of from 15
to 30 microns. The second waterborne basecoat can be applied so as to achieve a dry
film thickness in the range of from 2 to 10 microns, preferably in the range of from
2 to 4 microns. To achieve a thin dry film of the second waterborne basecoat, the
solids content of the second waterborne basecoat can be kept low relative to that
of the solids content of the first waterborne basecoat. Typically, the solids content
of the second waterborne basecoat can be in the range of from about 3% to about 30%
by weight of the total composition. Preferably, the solids content of the second waterborne
basecoat can be in the range of from 5% to 15%, by weight of the total composition.
[0055] The second waterborne basecoat composition employed in this invention provides the
polished metal effect and is a differently pigmented composition that its formulated
to be, like the first waterborne basecoat composition, non-transparent (opaque) and
is applied at complete hiding. The second waterborne basecoat composition comprises
an effective amount of thin metal flake pigment to impart the desired polished metal
effect. An effective amount of thin metal flake pigment, for the purposes of the present
invention, is the amount of thin metal flake contained in a binder composition in
a thin metal flake to binder ratio of from 1/100 up to 100/100 preferably from 3/100
up to 50/100, and most preferably from 10/100 up to 40/100.
[0056] The term "thin metal flake pigment" as used herein means a metal particle having
an average particle thickness in the range of from about 10 to 100 nanometers and
an average particle diameter in the range of from about 5 to 30 micrometers. Preferably,
the thin metal flake pigments have an average thickness in the range of from about
15 to 40 nanometers and an average particle diameter in the range of from about 8
to 20 micrometers. Such thin metal flake pigments have an aspect ratio (the ratio
of the flake diameter to the flake thickness) that is very high (in the hundreds rather
than traditional flake pigments in the tens). These thin metal flake pigments can
be produced by coating a very thin layer of metal vapor onto pretreated polyester
film in a vacuum chamber and then solvent stripping the deposited metal layer from
the carrier film. Other methods for producing these thin metal flake pigments include,
for example, physical vapor deposition, chemical vapor deposition, electrolysis, milling
and sputtering processes. The thin metal flake pigments may be unpassivated or passivated.
Passivated types are, for example, phosphated, chromated or coated with a silicon-oxygen
network. Passivated types are preferably used. Such thin metal flake pigments are
commercially available in passivated and unpassivated forms as pigment preparations
under the names HYDROSHINE
® and METALURE
®, both available from Altana/Eckart, Fürth, Germany; METASHEEN
® available from Ciba, Basel, Switzerland; DECOMET
® available from Schlenk, Roth, Germany and STARBRITE
®, available from Silberline, Tamaqua, Pennsylvania.
[0057] The second waterborne basecoat composition may optionally also contain one or more
other traditional flake pigments such as standard aluminum flake pigments and/or flake
pigments. It may also optionally contain other colored pigments to give the desired
color effect, such as any of those listed above. In one embodiment, the second waterborne
basecoat is a silver color basecoat.
[0058] Preferred second waterborne basecoat compositions contain film forming binders that
are similar to the first basecoat composition and include an aqueous microgel, such
as but not limited to the crosslinked aqueous microgel dispersions disclosed in aforementioned
U.S. Patent 4,403,003, optional polyol polymer, a crosslinking agent, such as an amino resin, an effective
amount of thin metal flake pigment and sheet silicate. Any of the microgels, polyols,
and crosslinking resins described as useful in the first basecoat can be used in the
second waterborne basecoat composition.
[0059] One useful second waterborne basecoat composition, in addition to the thin metal
flake pigments and optionally other pigments, comprises by weight of binder solids,
aqueous microgel from about 20-70%, preferably 45-65%, water-soluble or partially
water-soluble aminoplast resin, preferably a methylated melamine formaldehyde, from
about 10-35%, preferably 1-5-25%, water dispersible polyester polyol resin, from about
0-30%, polyurethane polyol aqueous dispersion from about 0-35%, preferably 15-25%,
water-soluble polyether filler from 0-10%, blocked acid catalyst from about 0-2%,
such as but not limited to amine blocked sulfonic acid catalyst, to promote melamine
or other crosslinking reaction. The composition also includes 0.1-1.6%, preferably
0.3-1%, based on the weight of the total composition, sheet silicate particle to help
give the desired holdout or resistance to strike-in and intermixing.
[0060] In addition to an effective amount of thin metal flake pigment, the second waterborne
basecoat composition can optionally include other pigments such as color providing
pigments or other flake effect pigments.
[0061] The pigments can be introduced into the second waterborne basecoat composition by
first forming a mill base or pigment dispersion with any of the aforementioned polymers
used in the coating composition or with another compatible polymer or dispersant by
conventional techniques, such as mixing/slurrying (i.e., for flakes), high speed mixing,
media milling, sand grinding, ball milling, attritor grinding or two/three roll milling.
Milling techniques may not be applicable for metal flake pigments. Mixing and slurry
techniques can be used to disperse flake pigments. The pigment dispersion can be blended
with the other constituents used in the coating composition.
[0062] Both first and second waterborne basecoat compositions employed in the present invention
may also include other conventional formulation additives such as wetting aids, surfactants,
defoamers, UV fortifiers, and rheology control agents, such as fumed silica, alkali
swellable emulsions, associative thickeners, or water compatible cellulosics. Both
first and second waterborne basecoat compositions employed in this invention also
include volatile materials such as water alone or water and a mixture of conventional
organic solvents and diluents, to disperse and/or dilute the above mentioned polymers
and facilitate formulation and spray application. Typical organic co-solvents and
diluents include hexyl CELLOSOLVE
®, toluene, xylene, butyl acetate, acetone, methyl isobutyl ketone, methyl ethyl ketone,
methanol, isopropanol, butanol, butoxyethanol, hexane, acetone, ethylene glycol, monoethyl
ether, VM and P naptha, mineral spirits, heptane and other aliphatic, cycloaliphatic,
aromatic hydrocarbons, esters, ethers and ketones and the like. However, in a typical
basecoat for this invention, water is used as the major diluent. Amines such as alkanolamine
can also be used as a diluent.
[0063] It is essential in the practice of the present process that both the first and second
waterborne basecoats include the required amounts of both aqueous microgel and sheet
silicate. The combination of the two in each' of the basecoat compositions functions
to provide coating compositions that once applied to a substrate, have the required
resistance to intermixing. This allows the first waterborne basecoat to provide a
flat and smooth surface on which to apply the second waterborne basecoat containing
the thin metal flake pigments and prevent intermixing of the two layers that would
destroy the desired polished metal effect.
[0064] The nature of the clearcoat composition employed in the process of the present invention
is not critical. Any of a wide variety of commercially available automotive clearcoat
compositions may be employed in the present invention including standard solventborne,
waterborne, or powdered clears. High solids solventborne clearcoats that have low
VOC (volatile organic content) and meet current pollution regulations are generally
preferred. Typically useful solventborne clearcoats include but are not limited to
2K (two-component) systems of polyol polymers crosslinked with isocyanate and 1 K
systems of acrylic polyol crosslinked with melamine or 1 K acrylosilane systems in
combination with polyol and melamine. Epoxy-acid systems can also be used. Suitable
1 K solventborne acrylosilane clearcoat systems that can be used in the process of
the present invention are known and disclosed in
U.S. Patent 5,162,426. Suitable 1 K solventborne acrylic/melamine clearcoat systems are disclosed in
U.S. Patent 4,591,533. Matte clearcoat finishes can be used as well to provide a delustered effect to the
applied coating compositions. Matte effect clearcoats are commercially available.
For example, Matte Clear HHC=5300
® can be obtained from DuPont, Wilmington, Delaware.
[0065] The above described multilayer coating composition can be used to provide automobiles
and trucks with a polished metal-like or anodized metal-like exterior finish having
an attractive aesthetic appearance, including high gloss and DOI (distinctness of
image), even on prolonged exposure to the environment and weathering. Matte finish
clearcoats can provide the same effect, without the high gloss and DOI traits of a
gloss clearcoat.
[0066] Useful substrates that can be coated according to the process of the present invention
include a variety of metallic and non-metallic substrates such as plastic substrates,
and combinations thereof. Useful metallic substrates that can be coated according
to the process of the present invention include unprimed substrates or previously
painted substrates, cold rolled steel, phosphatized steel and steel coated with conventional
primers by electrodeposition. Useful plastic materials include polyester reinforced
fiberglass, reaction-injection molded urethanes, partially crystalline polyamides,
and the like or mixtures thereof and their associated primers.
[0067] Preferably, the substrates are used as components to fabricate automotive vehicles,
including but not limited to automobiles, trucks, and tractors. The substrates can
have any shape, but are usually in the form of automotive body components such as
bodies, hoods, doors, fenders, bumpers and/or trim for automotive vehicles. The invention
is most useful in the context of coating automotive bodies and components thereof
traveling in continuous movement along an automotive assembly line.
[0068] While the current invention has been described in terms of application in an automotive
assembly plant, the invention can also be applied in an automotive refinish body shop.
In this manner, a damaged automobile finish can be repaired or an entire vehicle can
be painted with the described coating compositions.
[0069] Various other modifications, alterations, additions or substitutions of the components
of the processes and compositions of this invention will be apparent to those skilled
in the art without departing from the spirit and scope of this invention. This invention
is not limited by the illustrative embodiments set forth herein, but rather is defined
by the following claims.
EXAMPLES
[0070] Unless otherwise noted, all components of the following examples are believed to
be available from the Aldrich Chemical Company, Milwaukee, Wisconsin. The following
other components were used in the examples.
CYMEL® 303 melamine and DAOTAN® VTW 1236 aqueous aliphatic polyurethane dispersion are available from Cytec Industries,
West Patterson, New Jersey.
SOLSPERSE® 200000 dispersant is available from the Lubrizol Corporation, Wickliffe, Ohio.
SURFYNOL® 104 nonionic surfactant is available from Air Products and Chemicals, Inc., Allentown,
Pennsylvania.
PALIOGEN® Red L 3885 pigment is available from the BASF Corporation, Florham Park, New Jersey.
CARBON BLACK FW 200® pigment is available from Evonik Industries, Essen, Germany.
LAPONITE® RD sheet silicate is available from Southern Clay Products, Gonzales, Texas.
ACRYSOL® ASE 60 anionic thickener is available from Rohm and Haas (now part of the Dow Chemical
Company, Midland Michigan), Philadelphia, Pennsylvania.
HYDROSHINE® WS-3001 metal effect pigment is available from Altana/Eckart, Fürth, Germany.
Preparation of Black Pigment Dispersion
[0071] The following pigment slurry was prepared with 35.5 grams (g) of de-ionized water,
10.0g of a 30% non-volatile hydroxy functional aqueous acrylic microgel, 20.0g butoxyethanol,
15.0g CYMEL
® 303, 5.0g SOLSPERSE
® 20000 and 7.0g of 10% aqueous dimethylethanol amine solution and 0.5g SURFYNOL
® 104. The above components were mixed together, 7.0g of CARBON BLACK FW 200
® pigment was added and the resulting slurry was pre-dispersed using a Cowles blade.
The mixture was then ground in a horizontal beadmill until the desired particle size
of less than 0.5 micron was achieved.
Preparation of Red Pigment Dispersion
[0072] The following pigment slurry was prepared with 46.3g of de-ionized water, 15.0g of
a 30% non-volatile hydroxy functional aqueous acrylic microgel, 20.0g butoxyethanol,
8.0g CYMEL
® 303, 2.0g SOLSPERSE
® 20000, 0.2g of 10% aqueous dimethylethanol amine solution and 0.5g SURFYNOL
® 104. The above components were mixed together and 8.0g of PALIOGEN
® Red L 3885 pigment was added and the resulting slurry was pre-dispersed using a Cowles
blade. The mixture was then ground in a horizontal beadmill until the desired particle
size of less than 0.5 micron was achieved.
Preparation of Rheology Base
[0073] A homogeneous blend was prepared by mixing together and stirring 47.5g of a 30% non-volatile
hydroxy functional aqueous acrylic microgel, 2.0g of butoxyethanol and 0.5g of SURFYNOL
® 104. Following this, 50.0g of 3% LAPONITE
® RD in de-ionized water was added under stirring and homogenized and dispersed using
a horizontal beadmill.
Preparation of First Waterborne Black Basecoat Composition
[0074] A first waterborne black basecoat composition was prepared by mixing together the
following constituents under constant agitation in the order stated: 26.8 pbw of a
30% non-volatile hydroxy functional aqueous acrylic microgel, 16.2 pbw of black pigment
dispersion, 5.8 pbw of CYMEL
® 303, 13.8 pbw of rheology base, 1.0 pbw of SURFYNOL
® 104, and 2.0 pbw of butoxyethanol. The viscosity of the basecoat composition was
adjusted to within the desired range of 2000 - 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using 34.4 pbw
of a combination of (i) de-ionized water, (ii) a 10% (by non-volatiles (nv)) pre-neutralized
solution of ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Comparative First Waterborne Black Basecoat Composition A
[0075] This example shows the preparation of a first waterborne basecoat composition without
the addition of sheet silicate.
[0076] A waterborne black basecoat composition was prepared by mixing together the following
constituents under constant agitation in the order stated: 36.0 pbw of a 30% non-volatile
hydroxy functional aqueous acrylic microgel, 16:2 pbw of black pigment dispersion,
5.8 pbw of CYMEL
® 303, 1.0 pbw of SURFYNOL
® 104, and 2.0 pbw of butoxyethanol. The viscosity of the basecoat composition was
adjusted to within the desired range of 2000 - 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using 39.0 pbw
of a combination of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of
ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Comparative First Waterborne Black Basecoat Composition B
[0077] This example shows the preparation of a basecoat composition without the addition
of the aqueous acrylic microgel.
[0078] The preparation of the first waterborne black basecoat composition was repeated with
the difference that the entire portion of the 30% non-volatile hydroxy functional
aqueous acrylic microgel (including any aqueous acrylic microgel contained in the
premixes used) was replaced by an aqueous polyurethane dispersion DAOTAN
® VTW 1236. This replacement was performed according to an 1:1 replacement of binder
solids. The viscosity of the basecoat composition was adjusted to within the desired
range of 2000 - 4000 mPa·s at shear rate D=1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using a combination
of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Second Waterborne Silver Basecoat Composition
[0079] A waterborne silver color basecoating composition was prepared by mixing together
the following constituents under constant agitation in the order stated: 13.0 pbw
of a 30% non-volatile hydroxy functional aqueous acrylic microgel, 12.4 pbw of HYDROSHINE
® WS-3001, 3.4 pbw of CYMEL
® 303, 4.2 pbw of Rheology base, 1.0 pbw of butoxyethanol, and 1.0 pbw of SURFYNOL
® 104. The viscosity of the basecoat composition was adjusted to within the desired
range of 2000 = 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using 65.0 pbw
of a combination of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of
ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Comparative Second Waterborne Silver Basecoat Composition C
[0080] This examples shows the preparation of a basecoat composition without the addition
of sheet silicate.
[0081] A waterborne silver color basecoating composition was prepared by mixing together
the following constituents under constant agitation in the order stated: 15.9 pbw
of a 30% non-volatile hydroxy functional aqueous acrylic microgel, 11.7 pbw of HYDROSHINE
® WS-3001, 3.4 pbw of CYMEL
® 303, 1.0 pbw of butoxyethanol, and 1.0 pbw of SURFYNOL
® 104. The viscosity of the basecoat composition was adjusted to within the desired
range of 2000 - 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using 67.0 pbw
of a combination of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of
ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Comparative Second Waterborne Silver Basecoat Composition D
[0082] This example shows the preparation of a basecoat composition without the addition
of the aqueous acrylic microgel.
[0083] The preparation of the second waterborne silver basecoat composition was repeated
with the difference that the entire portion of the 30% non-volatile hydroxy functional
aqueous acrylic microgel (including any aqueous acrylic microgel contained in the
premixes used) was replaced by an aqueous polyurethane dispersion DAOTAN
® VTW 1236. This replacement was performed according to an 1:1 replacement of binder
solids. The viscosity of the basecoat composition was adjusted to within the desired
range of 2000 - 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using a combination
of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Preparation of Second Waterborne Silver-Red Basecoat Composition.
[0084] A waterborne silver-red color shade basecoating composition was prepared by mixing
together the following constituents under constant agitation in the order stated:
10.3 pbw of a 30% non-volatile hydroxy functional aqueous acrylic microgel, 7.5 pbw
of HYDROSHINE
® WS-3001, 2.5 pbw of CYMEL
® 303, 9.3 pbw of red pigment dispersion, 4.0 pbw of rheology base, 1.0 pbw of butoxyethanol
and 1.0 pbw. SURFYNOL
® 104. The viscosity of the basecoat composition was adjusted to within the desired
range of 2000 - 4000 mPa·s at shear rate D = 1 sec
-1, and the pH was adjusted to within the desired range of 8.2 - 8.8 using 64.4 pbw
of a_combination of (i) de-ionized water, (ii) a 10% nv pre-neutralized solution of
ACRYSOL
® ASE 60 in de-ionized water and (iii) a 10% aqueous dimethylethanol amine solution
in de-ionized water.
Solventborne Clearcoat Composition
[0085] The clearcoat composition used for the examples was a collision baking clear, commercially
available from Du Pont Performance Coatings (Standox), Christbusch 25, D-42285 Wuppertal,
Germany, prepared by mixing STANDOCRYL
® 2K-HS Clearcoat, 020-82497, with STANDOX
® 2K-HS Hardener, 020-82403, in a 2:1 volume ratio.
Application of two different Basecoats and Clearcoat (wet-on-wet-on-wet).
[0086] Standard automotive metal substrates (car doors) were processed and prepared with
standard automotive pre-treatment, and dried and cured layers of electrocoat and primer.
The substrates were then processed through a standard continuous basecoat/clearcoat
automotive type application line at a continuous line speed of approximately 4 m/min,
according to Table 1. In table 1, the first waterborne black basecoat composition
and comparative first waterborne black basecoat compositions A and B were applied
with an electrostatic bell at a flow rate of 120. cc/min. After 2 minutes under ambient
conditions (i.e. 22°C and 60% relative humidity), the second waterborne silver basecoat
composition, comparative second waterborne silver basecoat composition A, comparative
second waterborne silver basecoat composition B and second waterborne silver-red basecoat
composition were applied over the applied first waterborne basecoats according to
Table 1. Each of the second waterborne basecoat compositions were applied on top of
the first waterborne black basecoat compositions wet on wet, by pneumatic atomization
with robots, at a flow rate of 500 cc/min. The applied coatings were then dried by
a standard force dry in a drying tunnel for approximately 5 minutes at 60°C. Following
the drying step, the solventborne clearcoat composition was applied using electrostatic
spray gun, and the substrate was baked 10 minutes at 120°C. In each of the examples,
the film builds were as follows:
First waterborne basecoat: |
15 - 18 microns |
Second waterborne basecoat: |
2 - 4 microns |
Clearcoat: |
40 - 45 microns |
[0087] The multilayer coated car doors were in each case visually rated by 5 independent
individuals according to the following scale;
1 - Good polished metal effect; i.e., a highly reflective coating with a polished
or anodized metal effect was obtained. No occurrence of intermixing or strike-in phenomena.
2 - No polished metal effect. The system exhibited some intermixing and strike-in.
Some sparkling.
3 - No polished metal effect. The system exhibited strong intermixing and strike-in.
Greyish appearance.
TABLE 1
|
First Waterborne black basecoat composition |
Comparative first waterborne black basecoat composition A |
Comparative first waterborne black basecoat composition B |
Second waterborne silver basecoat composition |
1 |
3 |
2 |
Comparative second waterborne silver basecoat composition C |
n/t |
3 |
2 |
Comparative second waterborne silver basecoat composition D |
n/t |
3 |
2 |
Second waterborne silver-red basecoat composition |
1 |
n/t |
n/t |
n/t means that the particular combination of basecoat compositions was not sprayed. |
[0088] Subsequent work under a variety of application conditions (First waterborne basecoat
composition having a flow rate in the range of 90 to 160 cc/min; and the second waterborne
basecoat composition having a flow rate in the range of from 300 to 600 cc/min; varying
the flash off time in the range of from 1 to 5 minutes under ambient conditions) confirmed
that a coating composition according to the first waterborne black basecoat composition
and the second waterborne basecoat compositions exhibit a wide application window.