Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2~33S
COLOR PLUS CLEAR COATING METHOD UTILIZING ADDITIO~ INTERPOLYMERS
CO~TAI~ING ALROXY SILAN~ ANDtoR ACYLOXY SILANE GROUPS
Background of the Invention
..
A coating system becoming incseasingly popular, particularly in
the automotive industry, i one known a~ "color plu8 clear." In this
~ystem the substrate i8 coa ed with one or more spplications of a pigmented
basecosting composition to form a ba3ecoat which thereafter i8 coated with
one or more applica~ions of an easentially clear topcoating composit~on to
form a topcoat.
~owever, there are several tisadvflntage~ with known color plu~ -
clesr costing systems. After conventional ba~ecoatin~ compositions are
applied to the substrate a rathes long period of time, on the order o~
about 30 minutes or more, may be required between the application of the
conventional basecoating composition and the conventional topcoating compo-
sition. Such a period i9 needed to prevent adver3e attack by components of
~he conventional topcoating composition, particularly solventa, on the bsse-
coating composition at the interface of the two, a phenomenon often referred
to a9 strike-in. Strike-in adversely af~ects the final appearance proper-
ties of the coated product. Strike-in is an especially seriou~ problem
when metallic-flake pigments are employed in the bssecoating composition.
Strike-in, among other ~hings, can destroy the desired metallic-flake
orientation in the basecoat.
Often, known color plus clear systems based on thermoaetting
resins require elevated temperatures typically of at lea3t 120C for
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3;~i
curing. It would be desirable to provide a color plus clear coating method
in which relatively low temperatures, for example, below about 82C, and
preferably ambient temperatures, could be utilized. Previous attempts to
develop such coating systems resulted in systems which had the disadvantages
of being too time consuming and/or energy intensive or resulted in cured
films which were deficient in various combinations of physical properties.
- In addition to the need for a color plus clear coating system
which can utilize low temperature curing, it would be desirable that the
composite coating on a substrate from a color plus clear coating system
exhibit excellent long term durability as evidenced, for example, by
excellent long term gloss retention after long term outdoor exposure or
excellent gloss retention aEter accelerated weathering.
In accordance with the present invention, a color plus clear
coating system has been developed which can provide an acceptable rate of
cure at low or even ambient temperatures and results in coated products in
which the films exhibit an excellent combination of good appearance and
physical properties such as good solvent resistance, high gloss, surpris-
ingly excellent gloss retention, good durability, good visual appearance of
depth, substantial absence of strike-in, and good metallic pattern control
when metallic-flake pigments,are employed. Additionally the color plus
clear system of the present invention can be utilized with either a reduc-
tion of or even elimination of the use of organic isocyanates without
sacrificing the attendant advantages of the present invention.
Summary of the Present Invention
The present invention provides a method for coating a substrate
comprising the steps of (a) forming a basecoat by coating the substrate
5~
with one or more applications of a pigmented basecoating composition
containing an addition interpolymer having alkoxy silane moieties and/or
acyloxy silane moieties; and (b) thereafter forming a topcoat by coating
the basecoat with one or more applications of an essentially clear top-
coating composition containing a film-forming thermoplastic resin and/or
film-forming thermosetting resin, hereinafter referred to for convenience
as "a film-forming resin", which may be the same or different from the
addition interpolymer of the basecoating composition.
The present invention also provides a method for coating a
substrate comprising the steps of (a) forming a basecoat by coating the
substrate with one or more applications of a pigmented basecoating com-
position containing a film-forming thermoplastic resin and/or film-
forming thermosetting resin, referred to above for convenience as "a
film-forming resin," which film-forming resin is not an addition inter-
polymer having alkoxy silane moieties and/or acyloxy silane moieties;
and (b) thereafter forming a topcoat by coating the basecoat with one or
more applications of an essentially clear topcoating composition contain-
ing aD addition interpolymer havlng alkoxy silane and/or acyloxy silane
moletles .
The addition interpolymer containing alkoxy silane moieties
and/or acyloxy silane moieties for the basecoating composition, and/or for
the topcoating composition, is prepared by reaction of a mixture of mono-
mers consisting essentially of (i) at least one ethylenically unsaturated
monomer which does not contain silicon atoms, hereinafter referred to for
convenience as an ethylenically unsaturated silicon-free monomer, and (ii)
a copolymerizable ethylenically unsaturated alkoxy silane monomer and/or a
33~ .
copolymerizable e~hylenically unsaturated acyloxy silane monomer. The
basecoating composition, and/or the topcoating composition, containing
the addition interpolymer, herein referred to for convenience as the
"silane addition interpolymer", may be cured at low temperature, pref-
erably ambient temperature, in the presence of moisture. Certain of these
silane addition interpolymers are a fiubject of U.fi. Patont 4,499,~50 of
R. Dowbenko and M. e~ Hartman titled "Low ~olecuIar
Weight Addition Interpolymer~ Containing Alkoxysilane and/or Acyloxysilane
Groups."
Detailed De~cription of the Invention
m e basecoating composition and/or topcoating composition contain-
ing the silane addition interpolymer is moisture-curable at low temperature,
preferably at ambient temperature.
The silane addition interpolymer i9 prepared by in~espolymerizing
at least one ethylenically unsaturated silicon-free monomer, which pref-
erably is substantially ~ree of active hydrogen atoms, with a silane
monomer selected from an ethylenically unsaturated alkoxy fiilane monomer
and/or an ethylenically unsaturated acyloxy silane monomer.
The ethylenically unsaturated silicon-free monomer employed in
making the ailane addition interpolymer is any monomer containing at least
one ~ C~C ~ group which monomer preferably is substantially free of active
hydrogen atoms, i.e., monomers which are sub~tantially free of moieties
containing active hydrogen atoms such as hytroxyl, carboxyl or unsubstituted
amide groups. Monomers containing such functional groups preferably are
avoided in preparihg the interpolymer since they can caufie premature
gelation of the interpolymer. However, amounts of such fiilicon-free
-- 4 --
~"
. .
;6335
monomers containing active hydrogen atoms insufficient to cause pre-
mature gelation of the interpolymer may be utilized in preparing the
interpolymer. As used herein, an amount of silicon-free monomers consid-
ered to be substantially free of active hydrogen atoms would represent
less than 10% by weight of silicon-free monomers containing active hydro- -
gen atoms based on the total weight of silicon-free monomers. Preferably
less than 0.5% by weight of such silicon-free monomers containing active
hydrogen atoms, based on the total weight of silicon-free monomers, is
employed.
As indicated above, the silane addition interpolymer for the
method of the invention is formed from at least two components, i.e., an
ethylenically unsaturated silicon-free monomer containing at least one
~C=C~ group and which is preferably substantially free of active
hydrogen atoms and an ethylenically unsaturated compound selected from an
alkoxysilane monomer, an acyloxysilane monomer or a mixture thereof. The
term "ethylenically unsaturated" is employed in a broad sense and is
intended to encompass, for example, vinyl compounds, acrylic compounds and
methacrylic compounds. The basic criteria with respect to the ethyleni-
cally unsaturated monomer are that it contains at least one ~C=C~
group, that it is copolymerizable without gelation with the silane monomer
component, and that it does not otherwise preclude the utilization of the
finished interpolymer.
Examples of suitable ethylenically unsaturated silicon-free
monomers employed in forming the silane addition interpolymer herein
include the alkyl acrylates, such as methyl acrylate, ethyl acrylate, butyl
acrylate, propyl acrylate, and 2-ethylhexyl acrylate; the alkyl methacry-
lates, such as methyl methacrylate, butyl methacrylate, 2-ethylhexyl
3~5
methacrylate, decyl methacrylate, and lauryl methacrylate; and unsaturated
nitriles, such as acrylonitrile, methacrylonitrile and ethacrylonitrile.
Still other unsaturated monomers which can be used include: vinyl aromatic
hydrocarbons such as styrene, alpha methyl styrene, and vinyl toluene;
vinyl acetate; vinyl chloride; and epoxy functional monomers such as
glycidyl methacrylate.
In practice, in order to produce desirable properties in the
silane addition interpolymer, it is preferred to use combinations o~
ethylenically unsaturated silicon-free monomers which form hard polymer
segments, such as styrene, vinyl toluene and alkyl methacrylates having
from 1 to 4 carbon atoms in the alkyl group with monomers which form soft
polymer segments, such as the alkyl esters of acrylic or methacrylic acid,
the alkyl groups having from 1 to 1~ carbon atoms in the case of acrylic
esters and from 5 to 16 carbon atoms in the case of methacrylic esters.
Illustrative of monomers which form soft polymer segments are ethyl acry- -
late, butyl acrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate,
decyl methacrylate, and lauryl methacrylate. In addition to the hardening
and softening monomers, as previously indicated, other monomers such as
vinyl acetate, vinyl chloride, vinyl toluene, and acrylonitrile may be
included to achieve specific properties in the interpolymer. The silane
addition interpolymer is formed from about 50 percent to about 95 percent,
preferably from about 70 percent to about 90 percent, by weight of these
ethylenically-unsaturated silicon-free monomers.
The other component of the silane addition interpolymer is an
organosilane compound, specifically an ethylenically unsaturated alkoxy- -
silane, an ethylenically unsaturated acyloxysilane or a mixture thereof.
Alkoxysilanes which can suitably be employed and are preferred are the
33~
acrylatoalkoxysilanes, such as gamma-acryloxypropyltrimethoxysilane and the
methacrylatoalkoxysilanes, such as gamma-methacryloxypropyltrimethoxysilane,
gamma-methacryloxypropyltriethoxysilane and gamma-methacryloxypropyltris-
(2-methoxyethoxy)silane. Among the above listed alkoxysilanes, gamma-
methacryloxypropyltrimethoxysilane is especially preferred due to its
greater reactivity. Other alkoxysilanes are the vinylaikoxysilanes such as
vinyltrimethoxysilane, vinyltriethoxysilane and vinyltris(2-methoxyethoxy)- ~
silane. Ethylenically unsaturated acyloxysilanes include acrylato-,
methacrylato- and vinyl-acetoxysilanes, such as vinylmethyldiacetoxysilane,
acrylatopropyltriacetoxysilane, and methacrylatopropyltriacetoxysilane.
The silane addition interpolymer contains from about 5 percent to about 50
percent by weight, preferably from about 10 percent to about 30 percent by
weight, of the above described silane monomer.
The silane addition interpolymer is formed by interpolymerizing
the ethylenically unsaturated silicon-free monomer or monomers with the
ethylenically unsaturated silane monomers in the presence of a vinyl
polymerization catalyst. The preferred catalysts are azo compounds such
as, for example, alpha alpha'-azobis(isobutyronitrile)j peroxides such as
benzoyl peroxide and cumene hydroperoxide and tertiary butyl peracetate,
isopropyl percarbonate, butyl isopropyl peroxy carbonate and similar com-
pounds. The quantity of catalyst employed can be varied considerably,
however, in most instances, it is desirable to utilize from about 0.1 to 10
percent based on the weight of monomer solids. A chain modifying agent or
chain transfer agent may be added to the polymerization mixture. The
mercaptans, such as dodecyl mercaptan, tertiary dodecyl mercaptan, octyl
mercaptan, hexyl mercaptan and the mercaptoalkyl trialkoxysilane, e.g.,
3-mercaptopropyltrimethoxysilane may be used for this purpose as well as
other chain transfer agents such as cyclopentadiene, allyl acetate, allyl
~5~;~35
carbamate, and mercaptoethanol. The mercaptoalkyl trialkoxysilanes have
been found to be especially useful where increased durability is needed.
Thus, a level the mercaptoalkyl trialkoxysilane at a level of 0.5 to
15 parts per 100 parts monomer substantially increases the durability of
coatings based on silane addition interpolymer.
For certain coatings applications it is preferable that the peak
molecular weight, as determined by gel permeation chromatography, of the
silane addition interpolymer when in the pigmented basecoating composition
be at least about 2,000, more preferably at least about 10,000. If the
peak molecular weight is low, the time required for drying or curing the
basecoating composition to a degree at least sufficient to allow application
of the topcoating composition without undesirable strike-in may be undesir-
ably long for certain coatings applications. An advantage of the method of
the invention utilizing the silane addition interpolymer for the basecoating
composition is that the topcoating composition typically can be applied to
the basecoat after the basecoat has remained at ambient temperature in atmo-
spheric moisture for a short period of time, sometimes as short as 2 minutes,
without, for example, the topcoating composition undesirably striking-in to
the basecoat. Often, the peak molecular, as determined by gel permeation
chromatography, of the silane addition interpolymer when in the pigmented
basecoating composition is in a range of from about 2,000 to about 20,000,
preferably from about 10,000 to about 18,000.
On the other hand, if the peak molecular weight of the silane
addition interpolymer of the basecoating composition is high, for example
greater than about 20,000, the spray application properties of the compo-
sition at a desirably high solids content may be undesirably affected.
However, while a basecoating composition containing the silane addition
interpolymer can be applied by any conventional method such as brushing,
~-%~
dipping, flow coating, spraying, etc., an advantage of the method of the
present invention is that where desired it allows a basecoating composition
containing silane addition interpolymer to be spray applied at a high
solids content, i.e., 40 percent by weight total solids, preferably 50
percent by weight total solids and higher. ~loreover, convention~l spraging
techniques and equipment can be utilized.
When the topcoating composition contains a silane addition inter- -
polymer, the peak molecular weight of the silane addition interpolymer
as determined by gel permeation chromatography typically is at least about
2,000, and often is in a range of from about 2,000 to about 20,000, pref- -
erably from about 2,000 to about lS,000, and more preferably from about
4,000 to about 10,000. The peak molecular weight of a silane addition
interpolymer Eor the topcoating composition typically can be rather low
since the degree of cure to prevent, for example, strike-in is not an
important consideration with respect to the topcoating composition.
Conventional techniques for applying coating compositions to sub
strates such as those described previously can be employed to apply the
topcoating composition in the present invention. However, spraying is the
usual method oE application. Preferably, the basecoating composition and
topcoating composition are spray applied to the substrate at high solids
contents, i.e., 40 percent by weight total solids, preferably 50 percent by
weight total solids and higher. ~oreover, compositions containing silane
addition interpolymer can be spray applied at the aforesaid high solids
contents utilizing conventional spraying techniques and equipment.
The polymerization reaction for the mixture of monomers to
prepare the silane addition interpolymer is carried out in an organic
solvent medium utilizing conventional solution polymerization procedures
which are well known in the addition polymer art as illustrated with
6335
particularity in, for example, U.S. Patents 2,978,~37; 3,079,434 and
31307~963. Organic solvents which may be utilized in the polymerization
of the monomers include virtually any of the organic solvents heretofore
employed in preparing conventional acrylic or vinyl polymers such as, for
example, alcohols, ketones, aromatic hydrocarbons or mixtures thereof.
Illustrative of organic solvents of the above type which may be employed
are alcohols such as lower alkanols containing 2 to 4 carbon atoms includ-
ing ethanol, propanol, isopropanol, and butanol; ether alcohols such as
ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene
glycol monomethyl ether, and dipropylene glycol monoethyl etherj ketones
such as methyl ethyl ketone, methyl N-butyl ketone, and methyl isobutyl
ketone; esters such as butyl acetate, and aromatic hydrocarbons such as
xylene, toluene, and naphtha.
Preferably, choice of the specific ethylenically unsaturated
silicon-free monomers and ethylenically unsaturated silane monomers is made
so that the silane addition interpolymer for the basecoating composition
will have a calculated glass transition temperature (Tg) of at least about
25C, more preferably from about 30C to about 105C. The calculated Tg of
a silane addition interpolymer for the topcoating composition preferably is
at least about 25C, and more preferably is at least about 45 C. The Tg is
calculated using a generally Xnown equation as found, for example, in "Funda-
mentals of Acrylics" by W. H. Brendley, Jr., Paint and Varnish Production,
Vol. 63 No. 7, July 1973, pages 13-27. If the glass transition temperatures
of the silane addition interpolymers are low, for example less than about
25C, the physical properties of the cured films for certain protective
coatings applications may be adversely affected. Such physical properties
include, for example~ the gloss retention of the topcoat films which is a
measure of long term durability, the mar resistance of the films, the
abrasion resistance of the films, and the desired hardness of the films for
certain protective coatings applications.
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The silane addition interpolymers serve as film-forming resins
in the color plus clear coating method of the invention. Typically, the
basecoating composition, and/or the topcoatiDg composition, contains a
silane addition interpolymer, catalyst and, for application purposes,
often a solvent. The cure accelerating catalyst may be an organic acid,
such as, Eor exa~ple, p-toluenesulfonic acid, and n-butylphosphoric acid,
or a metallic salt of an organic acid, such as, for example, tin naphthenate,
tin benzoate, tin octoate, tin butyrate, dibutyltin dilaurate, dibutyltin
diacetate, iron stearate, and lead octoate, or an organic base, such as,
for example, isophorone diamine, methylene dianiline, and imidazole. The
preferred cure accelerating catalysts are the organotin salts, such as
dibutyltin dilaurate.
The specific amounts of cure accelerating catalyst which are
included in the compositions containing silane addition interpolymer vary
considerably depending upon factors such as the rate of cure desired, the
specific composition of the silane addition interpolymer component, the
amount of moisture present in the ambient atmosphere and the like. However,
in general, the coating compositions containing silane addition interpolymer
utilized in the method of the invention may contain from about 0.1 parts to
about 5 parts by weight of cure accelerating catalyst based on 100 parts by
weight of silane addition interpolmer solids.
In addition to the foregoing components, the coating compositions
containing silane addition interpolymer employed in the method of this
invention may contain optional ingredients, including various pigments of
the type ordinarily utilized in coatings of this general class. In addi-
tion, various fillers; plasticizers, antioxidants; mildewcides and fungi-
cides; surfactants; various flow control agents including, for example,
-- 11 --
thixotropes and additives for sag resistance and/or pigment orientation
b2sed on poly~er microparticles (sometimes referred to as ~icrogels~
described for example in U.S. Patents 4,025,474; 4,055,607; 4,075,141;
4,115,472; 4,147,688; 4,180,489; 4,242,384; 4,268,547j 4,220,679; and
4,290,932 and other such ormulating
addltives maY be employed in some instances. A
pri~ary thiol, e.g., dodecylmercaptan, isooctylthioglycolate, and the
mercaptoalkyl trialkoxysilanes~ surprisingly, when inoluded in the coating
compositions conta~ning silane addition interpolymer enhance~ the gloss of
the cured coatings. A level of about 0.1 p~rts to about 5 parts primary
thiol per 100 parts silane addition interpolymer provides the enhanced
gloss effect. A composition containing the silaae addition i~terpolymer
i~ ordinarily applied in sn organic solvent which may be sny ~olvent or
solvent mixture in which the materials employed are compa~ible and soluble
to the de6ired extent.
The method of the invention may be e~ployed utilizing a wide
variety o~ substrates such a8 wood, metals, glass, cloth, plastics, foams
and the like, as well as over primers. The method of the invention is
especially useful for coating automobiles, particulsrly for automobile
refinishing
As indicated, the coating compositions containing ~ilane addition
interpolymer can be cured by heating or typically by exposure to atmospheric
moi~ture at ambient temperature. Thus, once the silane addition interpoly-
mer component and cure accelerating catalyst component are brought into con-
tact with each other, as by mixing, and exposed to the ambient atmosphere,
the composition will begin to cure. Accordingly, it is desirable in some
ins~ances to prepare the compositions containing silane addition interpolymer
.
- 12 -
. .,
~ f~
~L~5~3~
in the form of a two package system, i.e., one package containing the
addition interpolymer component along with any desired optional ingredients
and a second package containing the cure accelerating catalyst component.
The silane addition interpolymer component of the composition in the
absence of the cure accelerating catalyst exhibits good pot life, i.e., 6
months or more when stored at temperatures of 120F (48.9C~ or less. When
it is desired to coat a substrate with the composition of silane addition
interpoiymer, the components of the two packages are merely mixed together
~ust prior to application and the resulting composition applied to the
substrate by one of the methods described above.
As indicated previously at least one of the basecoating composi-
tion and topcoating composition contains as film-forming resin a silane
addition interpolymer either as the sole film-forming resin or optionally
in combination with an additional film-forming thermoplastic resin and/or
thermosetting resin. Examples of such additional film-forming thermoplas-
tic and/or thermosetting resins include the generally known cellulo&ics,
acrylics, aminoplasts9 urethanes, polyesters, epoxies or mixtures thereof.
Additionally when only one of the basecoating and topcoating compositions
contains the silane addition interpolymer, the other contains a film-forming
resin typically selected from the generally known cellulosics, acrylics,
aminoplasts, urethanes, polyesters, epoxies or mixtures thereof mentioned
immediately above. These film-forming resins can be employed optionally in
combination with various ingredients generally known for use in coating
compositions containing film-forming resins of these general classes.
Examples of these various ingredients include: fillers; plasticizers;
antioxidants; mildewcides and fungicides; surfactant~; various flow control
agents including, for example, thixotropes and also additives described
previously for sag resistance and/or pigment orientation based on polymer
microparticles.
- 13 -
Cellulosics refer to the generally known thermoplastic polymers
which are derivatives of cellulose, examples of which include: nitrocellu-
lose; organic esters and mixed esters of cellulose such as cellulose
acetate, cellulose propionate, cellulose butyrste, and preferably cellulose
acetate butyrate (CAB); and organic ethers of cellulose auch as ethyl
cellulose.
Acrylic resins refer to the generally known addition polymers and
copolymers of acrylic and methacrylic acids and their ester derivatives,
acrylamide and methacryla~ide, and acrylonitrile and methacrylonitrile.
Additional examples of acrylic monomers which can be addition pol-ymerized
to form acrylic resins include the alkyl acrylates and the alkyl methacry-
lates previously set forth under the description of suitable ethylenically
unsaturated silicon-free monomers for preparing the addition interpolymer
containing alkoxy silane ~nd/or acyloxy silane moieties some further
examples of which include hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxyethyl methacrylate, and hydroxypropyl methacrylate. Moreover, where
desired, various other unsaturated monomers can be employed in the prepara-
tion of the acrylic resins examples of which include: vinyl aromatic
hydrocarbons such as styrene, alpha methyl styrene, and vinyl toluene;
vinyl acetate; vinyl chloride; and unsaturated epoxy functional monomers
such as glycidyl methacrylate.
Aminoplast resins refer to the generally known condensation
products of an aldehyde with an amino- or amido-group containing substance
examples of which include the reaction products of formaldehyde, acetalde-
hyde, crotonaldehyde, benzaldehyde and mixtures thereof with urea, melamine,
or benzoguanimine. Preferred aminoplast resins include the etherified
products obtained from the reaction of alcohols and formaldehyde with urea,
~5~33~ .
melamine, or benzoguanimine. Examples of suitable alcohols for preparing
these etherified products include: methanol, ethanol, propanol, butanol,
hexanol, benzylalcohol, cyclohexanol, 3-chloropropanol, and ethoxyethanol.
Urethane resins refer to the generally known thermosetting or
thermoplaAtic urethane resins prepared from organic polyisocyanates and
organic compounds containing active hydrogen atoms as found for example in
- hydroxylS and amino moieties. Some examples of urethane resins typically
utilized in one-pack coating compositions include: the isocyanate-modified
alkyd resins sometimes referred to as "uralkyds"; the isocyanate-modified
drying oils commonly referred to as "urethane oils" which cure with a drier
in the presence of oxygen in air; and isocyanate-terminated prepolymers
typically prepared from an excess of one or more organic polyisocyanates
and one or more polyols including, for example, simple diols, triols and
higher alcohols, polyester polyols and polyether polyols. Some examples of
systems based on urethane resins typically utilized as two-pack coating
compositions include an organic polyisocyanate or isocyanate-terminated
prepolymer (first pack) in combination with a substance (second pack) con-
taining active hydrogen as in hydroxyl or amino groups along with a cata-
lyst (e.g., an organotin salt such as dibutyltin dilaurate or an organic
amine such as triethylamine or 1,4-diazobicyclo-(2:2~2) octane). The
active hydrogen-containing substance in the second pack typically is
a polyester polyol, a polyether polyol, or an acrylic polyol known for use
in such two-pack urethane resin systems. Many coating compositions based
on urethanes (and their preparation) are described extensively in Chapter X
Coatings, pages 453-607 of Polyurethanes: Chemistry and Technology, Part II
by H. Saunders and K. C. Frisch, Interscience Publishers (N.Y., 1964).
33~i .
Polyester resins are generally known and are prepared by collven-
tional techniques utilizing polyhydric alcohols and polycarboxylic acids.
Examples of suitable polyhydric alcohols include: ethylene glycol; propyl-
ene glycol; diethylene glycol; dipropylene glycol; butylene glycol; gly-
cerol; trimethylolpropane; pentaerythritol; sorbitol; 1,6-hexanediol; 1,4-
cyclohexanediol; 1,4-cyclohexanedimethanol; 1,2-bis(hydroxyethyl)cyclohexane;
and 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate. Examples
of suitable polycarboxylic acids include: phthalic acid; isophthalic acid;
terephthalic acid; trimellitic acid; tetrahydrophthalic acid; hexahydrophtha-
lic acid; tetrachlorophthalic acid; adipic acid; azelaic acid; sebacic acid;
succinic acid; maleic acid; glutaric acid; malonic acid; pimelic acid;
suberic acid; 2,2-dimethylsuccinic acid; 3,3-dimethylglutaric acid; 2,2-
dimethylglutaric acid; maleic acid; fu~aric acid; and itaconic acid.
Anhydrides of the above acids, where they exist, can also be employed and
are encompassed by the term "polycarboxylic acid." In addition, certain
substances which react in a manner similar to acids to form polyesters are
also useful. Such substances include lactones such as caprolactone,
propylolactone and methyl caprolactone, and hydroxy acids such as hydroxy
caproic acid and dimethylol propionic acid. If a triol or higher hydric
alcohol is used, a monocarboxylic acid, such as acetic acid and benzoic
acid may be used in the preparation of the polyester resin. Moreover,
polyesters are intended to include polyesters modified with fatty acids or
glyceride oils of fatty acids (i.e., conventional alkyd resins). Alkyd
resins typically are produced by reacting the polyhydric alcohols, poly-
carboxylic acids, and fatty acids derived from drying, semi-drying, and
non-drying oils in various proportions in the presence of a catalyst such
as litharge, sulfuric acid, or a sulfonic acid to effect esterification.
~;2 56~
Examples of suitable fatty acids include saturated and unsaturated acids
such as stearic acid, oleic acid, ricinoleic acid, palmitic acid, linoleic
acid, linolenic acid, lîcanic acid, elaeostearic acid, and clupanodonic
acid.
Epoxy resins, often referred to simply as "epoxies", are generally
known and refer to compounds or mixtures of compounds containing more than
/o\
one 1,2-epoxy group of the formula - C - C -, i.e., polyepoxides. The
polyepoxides may be sa~urated or unsaturated, aliphatic, cycloaliphatic,
aromatic or heterocyclic. Examples of suitable polyepoxides include the
generally known polyglycidyl ethers of polyphenols and/or polyepoxides
which are acrylic resins containing pendant and/or terminal 1,2-epoxy
groups. Polyglycidyl ethers of polyphenols may be prepared, for example,
by etherification of a polyphenol with epichlorohydrin or dichlorohydri~ in
the presence of an alkali. Examples of suitable polyphenols include:
1,1-bis(4-hydroxyphenyl)ethane; 2,2-bis(4-hydroxyphenyl)propane; 1,1-bis(4- -
hydroxyphenyl)isobutane; 2,2-bis(4-hydroxytertiarybutylphenyl)propane;
bis(2-hydroxynaphthyl)methane; 115-dihydroxynaphthalene; 1,1-bis(4-hydroxy-
3-allylphenyl)ethane; and the hydrogenated derivatives thereof. The
polyglycidyl ethers of polyphenols of various molecular weights may be
produced, for example, by varying the mole ratio of epichlorohydrin to
polyphenol in known manner.
~poxy resins also include the polyglycidyl ethers of mononuclear
polyhydric phenols such as the polyglycidyl ethers of resorcinol, pyrogallol,
hydroquinone, and pyrocatechol.
Epoxy resins also include the polyglycidyl ethers of polyhydric
alcohols such as the reaction products of epichlorohydrin or dichlorohydrin
:~563~
with aliphatic and cycloaliphatic compounds containing from two to four
hydroxyl groups including, for example, ethylene glycol, diethylene glycol,
triethylene glycol, dipropylene glycol, tripropylene glycol, propane diols,
butane diols, pentane diols, glycerol, 1,2,6-hexanetr;ol, pe~taerythritol,
and 2,2-bis(4-hydroxycyclohexyl)propane.
Epoxy resins additionally include polyglycidyl esters of polycar--
boxylic acids such as the generally known polyglycidyl esters of adipic
acid, phthalic acid, and the like.
Addition polymerized resins containing epoxy groups may also be
employed. These polyepoxides may be produced by the addition polymeriza- -
tion of epoxy functional monomers such as glycidyl acrylate, glycidyl
methacrylate and allyl glycidyl ether optionally in combination with
ethylenically unsaturated monomers such as styrene, alpha-methyl styrene,
alpha-ethyl styrene, vinyl toluene, t-butyl styrene, acrylamide, methacryl-
amide, acrylonitrile, methacrylonitrile, ethacrylonitrile, ethyl methacry-
late, methyl methacrylate, isopropyl methacrylate, isobutyl methacrylate,
and isobornyl methacrylate.
Many additional examples of epoxy resins are described in the
Handbook of Epoxy Resins, Henry Lee and Kris Neville, 1967, McGraw Hill
Book Company.
Pigments suitable for the pigmented basecoating composition
include a wide variety of pigments generally known for use in coating
compositions. Suitable pigments include both metallic-flake pigments and
various white and colored pigments.
Examples of metallic-flake pigments include the conventional
metallic flakes such as aluminum flakes, nickel flakes, tin flakes, silver
flakes, chromium flakes, stainless steel flakes, gold flakes, copper flakes
and combinations thereof. Of the metallic-flake pigments, nonleafing alu-
minum flakes are preferred.
- 18 -
-~5~;33~
Examples of ~ite and colored pigments include generally known
pigments based on metal oxides; metal hydroxides; metal sulfides; metal
sulfates; metal carbonates; carbon black; china clay; phthalo blues and
greens, organo reds, and other organic dyes.
In the method of the invention the pigmented basecoating composi- -
t-on, preferably containing silane addition interpolymer, is first applied -
to the substrate. The pigmented basecoating composition, depending on the
choice of thermoplastic and/or thermosetting resin or silane addition
interpolymer, may be dried or cured at ambient temperature or with applied
heat to a degree at least sufficient to allow the clear topcoating composi-
tion to be applied to the basecoat without undesirable strike-in. When
optional heat curing is employed, it is sometimes desirable to allow the
basecoating composition to flash for up to about 30 minutes at ambient
temperature. Such solvent flashing may be utilized with either basecoating
compositions containing thermoplastic resins or with basecoating compositions
containing thermosetting resins (i.e., those which involve some degree of
crosslinking during cure). ln particular, a basecoating composition based
on a silane addition interpolymer typically is cured at ambient temperature;
although curing by the application of heat may be utilized. However, a dis-
tinct advantage of the method of the present invention is that the topcoating
composition may be applied essentially "wet on wet," i.e., without first
drying or curing the basecoat and with a minimum of flash time for the
basecoat, for example of only about 2 to about 5 minutes at ambient tem-
perature, before the topcoating composition is applied to the basecoat.
The topcoating composition is applied directly over the basecoat.
Depending for example on the choice of thermoplastic and/or thermosetting
resin or silane addition interpolymer, the topcoating composition is air
- 19 -
335
dried or cured at ambient temperature or with applied heat to form the
topcoat. An advantage of utilizing topcoating compositions containing
silane addition interpoly~er is that they can be cured to durable, trans-
parent, high gloss films under ambient conditions of temperature and
moisture. Additionfllly, these moisture-cured films exhibit excellent gloss
retention.
The topcoating composition is formulated so that when it is
applied to the basecoat, it for~s a clear topcoat 90 that the pigmentation
of the basecoat will be visible through the topcoat. It should be under-
stood that the topcoat, while being transparent, may contain small amounts
of dyes and/or tints to modify the overall appearance where desired. How-
ever, it is usua~ly prefer~ble not to employ even small amounts of dyes
and/or tints in the topcoating composition. Although the topcoating compo-
sition may contain transparent extender pigments and optionally a small
amount of coloring pigment, it should not contain 80 much coloring pigment
that it interferes with the general transparency of the topcoat. Usually,
it is preferable not to utilize even small amounts of coloring pigment in
the topcoating composition~
Thermoplastic topcoating compositions usually are hardened by
evaporation of the volatile solvent or dispersant.
Thermosetting topcoating compositions may be crosslinked (cured)
in various ways, typically at temperatures ranging from about 20C to about
260C. Some film-forming resins such as the air-curable alkyds may be
cured by exposure to atmospheric oxygen. When a cros~linking agent is
present (i.e., an agent other than a silane addition interpolymer which
itself contains moisture curable alkoxy silane and/or acyloxy silane
groups) the topcoating compositions may be cured by heating. The curing
- 20 -
~2~335
temperatures may vary widely, but usually are in the range of from about
80C to about 150C. Similarly the curing times may be subject to wide
variation but usually are in the range of from about 10 minutes to
about 45 minutes. As a rule, an increase in the curing temperature for
the topcoating composition permits a reduction in the curing time. Where
a plurality of superimposed basecoats and/or topcoats are to be applied,
each coat may be dried or cured prior to application of the next coat-
ing composition. It is preferable, however, to utilize coating sys-
tems which will permit the application of two or more superimposed
coatings which can be dried or cured together in a single drying or curing
operation.
An advantage of employing a silane addition interpolymer, as
described previously, for the topcoating composition, is that such a top-
coating composition may be cured at ambient temperature in atmospheric
moisture in a relatively short period of time.
The Examples which follow are submitted for the purpose of fur-
ther illustrating the nature of the present invention and should not be
regarded as a limitation on the scope thereof.
As used in the body of the specification, examples, and claims,
all percents, ratios and parts are by weight unless otherwise specifically
indicated.
Example I
This example illustrates the preparation of a silane addition
interpolymer, especially useful in a basecoating composition as illustrated
in Example III. The following monomers are used: -
i33~i
Percent by Wei~ht
Methyl methacrylate 40.0
Butyl methacrylate 7.5
2-ethylhexyl acrylate 10.0
Styrene 25.0
Gamma-methacryloxy- 17.5
propyltrimethoxysilane
A reaction vessel equipped with condenser, stirrer, thermometer
and means for maintaining a nitrogen blanket is charged with 336.0 parts
butyl acetate, 144.0 parts VM & P naphtha, and 96.0 parts toluene. The
contents of the vessel are then heated to reflux, about ll9DC, while under
a nitrog~n blanket and agitation. Three charges are next made simultane-
ously while maintaining the vessel at reflux conditions. Charge I consists
of a mixture of 896.0 parts methyl methacrylate, 168.0 parts butyl methacry-
late, 224.0 parts 2-ethylhexyl acrylate, 560.0 parts styrene and 392.0 parts
gamma-methacryloxypropyltrimethoxysilane. Charge II consists of 192.0
parts butyl acetate and 4~.8 parts di-tert-butyl peroxide catalyst. Charge
III consists of 192.0 parts butyl acetate and 56.0 parts 3-mercaptopropyl-
trimethoxysilane chain transfer agent. The three charges are completed
after 2 hours, at which time another 9.0 parts di-tert-butyl peroxide cata-
lyst is added. The vesse]'s contents are maintained at reflux for another
hour. Still another 9.0 parts of the peroxide catalyst is added and the
vessel's contents is allowed to reflux for 1.5 hours. The heat is removed
from the vessel after the 1.5 hours and allowed to cool.
The resultant product mixture is thinned with 400 parts butyl
acetate, 80.0 parts VM ~ P naptha and 53.3 parts toluene. The mixture has
a solids content of 58.2%, a viscosity of 18.23 Stokes and an acid value of
O . 1 .
- 22 -
3~
An analysis of the silane addition interpolymer shows it to have
a peak molecular weight of 17,400 as-determined by gel permeation chroma-
tography, using a styrene standard and a calculated Tg of 55C.
Example II
The following monomers are used to make a silane addition inter- -
- polymer, the use of which is illustrated in Example III:
Percent by Weight
Methyl methacrylate 40
Butyl acrylate 20
Styrene 25
Gamma-methacryloxy- 15
propyltrimethoxysilane
A reaction vessel equipped as in Example I is initially charged
with 336.0 parts butyl acetate, 144.0 parts VM & P naphtha and 96.0 parts
toluene and then heated to reflux, about 119C. A nitrogen blanket is
provided and maintained throughout the reaction. After the solvent has
reached reflux conditions three charges are simultaneously added over a two
hour time period. Charge I consists of 896.0 parts methyl methacrylate,
448.0 parts butyl acrylate, 560.0 parts styrene and 336.0 parts gamma-
methacryloxypropyltrimethoxysilane. Charge II consists of 192.0 parts
butyl acetate and 112.0 parts di-tert-butyl peroxide catalyst. Charge III
consists of 192.0 parts butyl acetate and 112.0 parts 3-mercaptop~opyltri-
methoxysilane. After the three charges are added, 9.0 parts of the peroxide
catalyst is added and the reaction mixture held at reflux for 1 hour.
Another 9.0 parts of the peroxide catalyst is added and the mixture is held
for 1.5 hours at reflux.
- 23 -
5633~
An analysis of the resultant product shows the solids content of
the silane addition interpolymer is 66.9%, the viscosity of the product is
26.8 Stokes and the acid value of the product is 0.1.
The silane addition interpolymer has a peak molecular weight
of 6800 as determined by gel permeation chromatography, using a styrene
standard and a calculated Tg of 50C.
- Example III
This example illustrates the advantages achieved when a basecoat-
ing composition containing a siLane addition interpolymer is applied to a
substrate, flashed for a short period of time, and has applied to it a clear
topcoat. The formulations of the basecoating composition and clear topcoat-
ing composition are as set forth in the following TABLES 1 and 2 respectively.
TABlE 1
Basecoating CompositionPercent by Weight
Acrylic silane solution l18.0
Pigment paste 2 4.7
UV absorber 3 0.3
Polysiloxane solution 0.3
(0.5% solids)4
Pattern control agentS 3.8
Triethylorthoformate 0.6
Dibutyltin dilaurate solution 1.5
~10% solids)
Butyl acetate 13.6
Acetone 19.0
Toluene 26.8
Xylene 9.2
Diethylene glycol monobutyl 2.2
ether acetate
- 24 -
3~j
lAs made in Example I.
2 The pigment paste has a pigment weight concentration (PWC) o~ 62.3% and
is composed of 31.5X by weight pig~ent solids, 19.1X by weight acrylic
copolymer resin solids, and 49.4% by weight solYents. The pigmen~
solids are composed o~ 85X by weight nonleafing aluminun flakes and
15%.by weight phthalo blue. The pigments are di3persed in the acrylic
copolymer resin ha~ing a peak molecular weight o~ 20,000 determined by
gel permeation chromatography (54~ by weight methyl methacrylate, lOg
by weight butyl methacrylate, 10% by weight 2-ethylhexyl acrylate,
25X by weight styrene, snd 1% by weight acrylic acid which has been
partially reacted with hydroxyethyleneimine) at 48% by weight resin
solids in a ~ixture of solven~s (8.92% by weight toluene, 12.11% by
weight naphtha, and 78.97% by weight butylacetate).
3Available ~rom Ciba-Geigy Corp. a~ TINUVIN ~28.
4The polysiloxane is available from DOW Corning Corpora~ion as DC~200, 135 ~k.
5Prepared as described in U.S. Patent 4,147,688, Example II.
TABLE 2
Clearcoating Compo~iti_nPercent by Weight
Silane addition interpolymer ~olutionl 49.6
UV absorber2 0 7
Polysiloxane solution3 0.9
Triethylorthoformate 1.7
Dibutyltin dilaurate solution2.5
(lOX solids)
Butyl acetate 7.8
Acetone 10.8
Toluene 15.2
Xylene 5.1
Ethylene glycol monoethyl 3.6
ether acetate
Diethylene glycol monobutyl 2.1
ether acetate
- 25 -
- *Trade Mark
~25~ 5
lAs made in Example II.
2As used in the basecoating composition.
3As used in the basecoating composition.
The above compositions are each applied at 21C and 40% relative
humidity to a previously painted used car. The compositions are spray
applied in amounts sufficient to give a 0.5 mil dry film thickness of base-
coat and 1.5 mil dry film thickness of clear coat. The clear coat applica-
tion is begun about 5 minutes after the basecoat application is completed.
The appearance of the resultant coatings is excellent thereby
showing the ability of the basecoat to receive a subsequent coating shortly
after its own application. The film properties of the coatings are also
excellent as evidenced by the following tests and results set forth in the
following TABLE 3.
TABLE 3
Tape-free time 47 hours
20 gloss 87 (after 24 hours)
87 (after 144 hours)
Sward hardness 14 (after 24 hours)
30 (after 144 hours)
Pencil hardness 3B (after 24 hours)
HB (after 144 hours)
Three minute gasoline soak Good (after 24 hours)
Excellent (after 144 ~lours)
Distinctness of image 65 (after 24 hours)
60 (after 144 hours)
Percent gloss retention 90 (after 12 months in Florida)
EXA~PLE IV
This example illustrates the method of applying a high solids
clear topcoating composition containing a silane addition interpolymer over
- 26 -
i3~
a basecoat prepared from a high solids, pigmented basecoating composition
containing a silane addition interpolymer.
A basecoating composition is prepared consisting of the ingredi-
ents in the relative amounts set forth in the following TABLE 4.
TABLE 4
Basecoating Composition_r ent by Weight
Silane addition interpolymer solutionl 63.9
Nonleafing aluminum pigment paste2 11.5
Polysiloxane solution3 1.0
Ultraviolet light (UV) absorber4 1.0
Triethylorthoformate 2.5
Dibutyltin dilaurate solution5 6.5
Butyl acetate 13.6
1 As prepared in Example II.
2 Contains 65æ by weight nonleafing aluminum flakes in hydrocarbon
solvents available as Sparkle Silver 5500 from Silberline Manufac-
turing Company, Inc.
3 The polysiloxane is available from DOW Corning Corporation as DC 200, 135 csk.
Dissolved in xylene to give a 0.5 percent polysiloxane content.
4 Available from Ciba-Geigy Corp. as TIN WIN 328.
5 A solution of 10 percent by weight dibutyltin dilaurate in xylene.
The basecoating composition set forth in TABLE 4 has a total
solids content of 50~ by weight and a pigment weight concentration (P~C) of
15 percent by weight.
The basecoating composition is spray applied to 24 gauge cold
3~
rolled steel panels treated with BONDERITE 40 and primed with a two compo-
nent epoxy/polyamide primer available as DP 40/401 from DITZLER Automotive
~ , k
- 27 -
~5~33~i
Finishes, PPG INDUSTRIES, INC., to form a basecoat. The basecoat is allowed
to flash for 5 minutes at room temperature. Immediately thereafter, a
clear topcoating composition consisting of the ingredients set forth in the
following TABLE 5 is spray applied at 50% by weight total solids to the
basecoat to form a clear topcoat.
TABLE 5
.,
Topcoating CompositionPercent by Weight
Silane addition interpolymer solutionl 75.2
Polysiloxane solution2 1.3
Ultraviolet light stabilizer3 1.0
Triethylorthoformate 2.5
Dibutyltin dilaurate solution4 3.7
Butyl acetate 16.3
1 As prepared in EXA~PLE II.
2 As described in footnote 3 to TABLE 4.
3 As described in footnote 4 to TABLE 4.
4 As described in footnote 5 to TABLE 4.
The basecoat and topcoat are allowed to moisture cure at room
temperature for 24 hours under ambient atmospheric conditions to a dry film
thickness of the basecoat of 1.0 mil and a dry film thickness of the topcoat
of 3.5 mils.
The properties of the resulting cured composite basecoat/topcoat
are as set forth in the following TABLE 6.
TABLE 6
20 Gloss 81
Distinctness of Image (DOI) 50
Sward Hardness 6
Pencil Hardness B
Resistance to gasolinel Excellent
- 28 -
i3~i
1 Determined by immersing the cured coated panel in unleaded gasoline for
3 minutes after which the panel is removed and the gasoline is
allowed to evaporate for 1 minute before the coated panel is
visually inspected.
EXAMPLE V - ~
This example illustrates the method of applying a clear topcoating
composition which does not contain a silane addition interpolymer over a
basecoat prepared from a high solids, pigmented basecoating composition
containing a silane addition interpolymer.
A basecoating composition is prepared consisting of the ingredi-
ents in the relative amounts set forth in TABLE 4 above. The basecoating
composition has a total solids content of 50X by weight and a pigment
weight concentration (PWC) of 15 percent by weight.
The basecoating composition is spray applied to the same type of
treated and primed steel panel as described in EXAMPLE IV to form a basecoat.
The basecoat is allowed to flash for 5 minutes at room temperature. Imme-
diately thereafter, a clear topcoating composition is spray applied to
the basecoat to form a clear topcoat. The clear topcoating composition is
~ a two component acrylic urethane composition available as DAU 82/DAU 2 from
DITZLER Automotive Finishes, PPG INDUSTRIES, INC.
The basecoat and topcoat are allowed to cure at room temperature
for 24 hours under ambient atmospheric conditions to a dry film thickness of
the baseco2t of 1.0 mil and a dry film thickness of the topcost of 2.0 mils.
The properties of the resulting cured composite basecoat/topcoat
are as set forth in the following TABLE 7.
~ r~c~ k .
i3~
TABLE 7
20 Gloss . 65
Distinctness of Image (DOI) 30
Sward Hardness 6
Pencil Hardness 2B
Resistance to gasolinel Excellent
1 Determined using the sar~e procedure described in footnote 1 to TABLE 6.
EXAMPLE VI
This example illustrates the method of the invention employing
heat curing.
A basecoating composition is prepared consisting of the ingredi-
ents in the relative amounts set forth in the following TABLE 8.
TABLE 8
Basecoating CompositionPercent by Weight
Silane addition interpolymer solutionl 20.9
Nonleafing aluminum pigment paste2 3.7
Polysiloxane solution3 0.3
Ultraviolet light (UV) absorber4 0.3
Triethylorthoformate 0.6
Anhydrous ethanol 0.6 _
Butyl acetate 15.0
Dibutyltin dilaurate solution~ 1.7
Acetone 24.7
Toluene 24.2
Xylene 8.0
- 30 -
1 As prepared in EXAMPLE I.
2 As described in footnote 2 to TABLE 4.
3 As described in footnote 3 to TABI.E 4.
4 As described in footnote 4 to TABLE 4.
5 Contains 10% by weight dibutyltin dilaurate in a mixture of solvents
consisting of 43.5% by weight acetone, 42.4% by weight toluene and
14.0~ by weight xylene.
The basecoating composition is spray applied to the same type of
treated and primed steel panel as described in EXAMPLE IV to form a basecoat.
The basecoat is allowed to flash for 5 minutes at room temperature. Imme- -
diately thereafter, a clear topcoating composition is spray applied to the
basecoat to form a clear topcoat. The clear topcoating composition is
Corostar 434 Acrylic Urethane, a two component clear coating composition
available from Peinturas Corona, Department Carrosserie, La Courneuve, France.
The resulting basecoat and topcoat are allowed to flash at room
temperature for 30 minute~ and thereafter are force-dried Eor 45 minutes in
air at 140F (60.0C) to a dry film thickness of the basecoat of 0.7 mils and
a dry film thickness of the topcoat of 1.5 mils.
The properties of the resulting cured composite basecoat/topcoat
are as set forth in the following TABLE 9. These properties are measured
after drying at room temperature for an additional 24 hours and 96 hours
respectively.
TABLE 9
24 Hours 96 Hours
20 Gloss 89 88
Distinctness of Image (D~I) 45 45
Sward Hardness 22 34
Pencil Hardness 2B HB
Resistance to gasolinel Good Excellent
~d~ ~-~k - 31 -
;3~5
1 Determined using the same procedure described in footnote 1 to TABLE 6.
EXA~PLE VII
The silane addition interpolymer illustrated in this example is
used in the coating compositions of EXAMPLE VIII. The silane addition
interpolymer is prepared from the following monomers: -
Percent by Weight
Methyl methacrylate 40.0
Butyl methacrylate 10.0
Butyl acrylate 10.0
Styrene 25.0
Gamma-methacryloxypropyltrimethoxysilane 15.0
The process utilized for preparing the interpolymer is that
illustrated in EXAMPLE II. Following this process there is obtained a
reaction product having a solids content of 67.7% by weight, a viscosity of
45.6 Stokes and an acid value of 0. The silane addition interpolymer has a
calculated Tg of 653C and a peak molecular weight of 6800 as determined by
gel permeation chromatography using a styrene standard.
.
EXAMPLE VIII
A basecoating composition is prepared consisting of the ingredients
in the relative amounts set forth in the following TABLE 10. -
TABLE 10
Basecoating Composition Percent by Weight
Silane addition interpolymer solutionl 37.6
Pigment paste2 4.3
Polysiloxane solution3 0.3
Ultraviolet light (UV) absorber4 0.5
- 32 -
Gamma-methacryloxypropyltrimethoxysilane 0.1
Triethylorthoformate 2.7
Dibutyltin dilaurate solution5 il.9
Xylene 10.2
Butyl acetate 8.6
Acetone 8.5
Methylethyl Ketone 3~4
Solvesso 1006 5.1
Lactol spirits 5.1
Diethylene glycol monobutyl ether acetate 1. 7
1 As prepared in EXAMP~E YII.
2 The pigment paste has a pigment weight concentration (PWC) of 46~4%
where PWC equals 100 times weight of pigment solids divided by (weight
of pigment solids + weight of acrylic copolymer resin solids), and
is composed of 20.4% by weight pigment solids, 23.6% by weight
acrylic copolymer resin solids, and 50.6% by weight solvents. The
pigment solids are composed of 71% by weight nonleafing aluminum
flakes, 18% by weight phthalo blue, and 11% by weight anthraquinone.
The pigments are dispersed in the acrylic copolymer resin having a
peak molecular weight of 20,000 determined by gel permeation chro-
matography (54% by weight methyl methacrylate, 10% by weight butyl
methacrylate, 10% by weight 2-ethylhexl acrylate, 25~o by weight sty-
rene, and 1% by weight acrylic acid which has been partially reacted
with hydroxyethyl ethyleneimine) at 48% by weight resin solids in a
mixture of solvents (8~92% by weight toluene, 12.11% by weight
naphtha, and 78~97% by weight butyl acetate).
3 As described in footnote 3 to TABLE 4.
4 As described in footnote 4 to TABLE 4.
- 33 -
5 A solution of 2.2 percent by weight dibutyltin dilaurate in toluene.
6 An aromatic hydrocarbon solvent commonly referred to as a "high flash
naphtha" having a flash point of 100F ~37.8C).
The basecoating composition is spray applied to the same type of
treated and primed steel panel as described in EXAMPLE IV to form a basecoat.
The basecoat is allowed to flash for 45 minutes at room temperature. Imme-
diately thereafter, a clear topcoating consisting of the ingredients in
the relative amo~mts set forth in the following TABLE 11.
TABLE 11
Topcoating CompositionPercent by Weight
Silane addition interpolymer solutionl 45.5
Polysiloxane solutionZ 0.3
Ultraviolet light (UV) stabilizer3 0.6
Triethylorthoformate 1.8
Gamma-mercaptopropyltrimethoxysilane 0.1
Dibutyltin dilaurate solution4 13.3
Butyl acetate 12.2
Acetone 6.5
Methylethyl ketone 2.6
Xylene 7.8
Solvesso 1005 3.9
Lactol spirits 3.9
Diethylene glycol monobutyl ether acetate 1.5
1 As prepared in EXAMPLE VII.
2 As described in footnote 3 to TABLE 4.
3 As described in footnote 4 to TABLE 4.
4 As described in footnote 5 eo TABLE 10.
5 As described in footnote 6 to TABLE 10.
- 34 -
The resulting basecoat and topcoat are allowed to cure at room
temperaLure to a dry film thickness of the basecoat of 1.7 mils and a dry
film thickness of the topcoat of 1.2 mils. The following properties as
set forth in the following TABLE 12 for the composite basecoat/topcoat are
determined after 24 hours and 168 hours respectively from when the topcoat- -
ing composition is applied to the basecoat.
TABLE 12
24 Hours 168 hou_
20 Gloss 86 86
Distinctness of Image (DOI) 75 70
Sward Hardness 8 24
Pencil Hardness 6B HB
Resistance to gasolinelFair Excellent
1 Determined using the same procedure described in footnote 1 to TABLE 6.
EXAMPLE IX
This example illustrates the preparation of a high molecular
weight silane addition interpolymer, especially useful in a basecoating
composition as illustrated in EXAMPLE X.
The following monomers are used:
Percent by Weight
Methyl methacrylate 40
Butyl acrylate 10
Butyl methacrylate 10
Styrene 25
Gamma-methacryloxypropyltrimethoxysilane 15
- 35 -
~i6~
A reaction vessel equipped as in EXAMPLE I is initially charged
with 896.0 parts of xylene and then heated to reflux, about 140 C. A
nitrogen blanket is provided and maintained throughout the reaction. After
the solvent has reached reflux conditions, two charges are simultaneously
added over a two hour time period. Charge I consists of 832.0 parts methyl
methacrylate, 208.0 parts butyl acrylate, 520.0 parts styrene, 312.0 parts
gamma-methacryloxypropyltrimethoxysilane and 208.0 parts of butyl methacry-
late. Charge II consists of 224.0 parts xylene and 41.6 parts di-tert-butyl
peroxide initiator. After the two charges are added, 8.32 parts of the
peroxide initiator is added and the reaction mixture held at reflux for 1
hour. Another 8.32 parts of the peroxide initiator is added along with
581.8 parts xylene and the mixture is held for 1.5 hours at reflux.
An analysis of the resultant product shows the solids content of
the silane addition interpolymer is 53.9 percent by weight, the viscosity
of the product is Z4~ Stokes and the acid value of the product is 0.1.
The silane addition interpolymer has a peak molecular weight of
64,861 as determined by gel permeation chromatography using a styrene stand-
ard and a calculated Tg of 70C.
_AMPLE X
This example illustrates the excellent long term durability of
a cured coating prepared by the method of the invention as evidenced by
surprisingly excellent gloss retention after accelerated weathering in a
QUV Accelerated Weathering Tester from Q PA~EL Company.
The formulations of the basecoating composition and clear top-
coating composition are as set forth in the following TABLES 13 and 14
respectively.
- 36 -
3~
TAB1E 13
_ _
Basecoating Composit on Percent by Weight
Silane addition interpolymer solutionl 19.6
Nonleafing aluminum pigment paste2 3.4
Polysiloxane solution3 0.2
Ultraviolet light absorber4 0.3
Triethylorthoformate 0.7
Butyl acetate 9.0
Dibutyltin dilaurate 0.2
10- Acetone 22.2
Toluene 31.4
Xylene 10.4
Diethylene glycol monobutyl ether acetate 2.6
1 As prepared in EXAMPL~ IX.
2 Contains 65% by weight nonleafing aluminum flakes in hydrocarbon solvents
available as Sparkle Silver 5500 from SiLberline Manufacturing Company, Inc.
3 The polysiloxane is available from DOW Corning Corporation as DC-200,
135 csk. dissolved in xylene to give a 0.5 percent polysiloxane content.
4 Available from Ciba-Geigy Corp. as TINUVIN 328.
TABLE 14
_pcoating Compo_ t n Percent by Weight
Silane addition interpolymer solutionl 34.6
Butyl acetate 11.5
Triethylorthoformate 1.0
Flow control agent2 0.1
Ultraviolet light absorber3 0.4
Dibutyltin dilaurate a. 1
Acetone 15.7
Toluene 21.0
Xylene 7.8
Propylene glycol monomethyl ether acetate 5.2
Diethylene glycol monobutyl ether acetate 2.6
~1 ~5~
1 As prepared in EXAMPLE IX~
2 Available as BYK 300 from BYK Mallinekrodt Chem. Produkte GmbH.
3 Available from Ciba-Geigy Corp. as TIN WI~ 328.
The basecoating composition is spray applied to 24 gauge cold
rolled steel panels treated with BONDERITE 40 and primed with a two compo- -
nent epoxy/polyamide primer available as DP 40/401 from DITZLER Automotive
Finishes, PPG INDUSTRIES, INC. to form a basecoat. The basecoat is allowed ~
to flash for 5 minutes at room temperature. Immediately thereafter, the
clear topcoating composition is spray applied to the basecoat to form a
clear topcoat.
The basecoat and topcoat are allowed to moisture cure at room
temperature for 24 hours under ambient atmospheric conditions to a dry film
thickness of the basecoat of 1.0 mil and a dry film thickness of the
topcoat of 3.5 mils.
The properties of the resulting cured composite basecoat/topcoat
as prepared according to the method of the present invention are as set
forth in the following TABLE 15.
For comparison purposes, a basecoating composition of DITZLER
DURACRYL lacquer DMA-310 to which sufficient Sparkle Silver 5500 from
Silberline Manufacturing Company is added to obtain a total pigment weight
concentration of 17 percent and a topcoating composition of DITZLER DURACRYL
clear lacquer DCA-468 are applied to the same type of substrate utilizing
the same procedures as set forth in this EXAMPLE X for the application of
the basecoating and topcoating compositions containing the silane addition
interpolymers. Likewise the same flashing and curing procedures are employed
in this comparative example. l'he resulting dry film thickness of the compa-
rative basecoat and topcoat are 1.0 mil and 3.5 mils respectively. The prop-
erties of the resulting cured composite basecoat/topcoat of this comparative
example are also set forth in the following TABLE 15.
- 38 -
As used in TABLE 15, the time periods "24 hours" and "96 hours"
represent the periods after the topcoating composition is applied to the
basecoat when the applicable measurements are made. The terms "initial"
and "700 hours" refer to the results of 20 gloss measurements made ini-
tially after the topcoating composition is applied to the basecoat and
after 700 hours in the QUV Accelerated Weathering Tester operating at the
conditions set forth in footnote 1 of TABLE 15.
TABLE 15
. _ _ _~ _
EXAMPLE X Comparative Example
10 Tape Time >4 hrs 4 hrs
.
24 hrs 96 hrs 24 hrs96 hrs
20 Gloss 68 66 60 60
¦ Sward Hardness 8 14 lO 12
I Pencil Hardness 3B B HB H
Resistance to Gasoline ~Good ExcellentGood Excellent
Initial700 hrs Initial700 hrs
QUV Resistancel 166 63 75 3*
1 QUV cycle: 8 hours ultraviolet light at 50C, 4 hours condensing humidity
at 40C.
* The comparative composite basecoat/topcoat is yellowed and cracked
at 700 hours in the QUV Accelerated Weathering Tester.
As can be seen from the QUV data in TABLE 15, the cured composite
basecoat/topcoat prepared according to the method of the invention demon-
strated substantially improved long term weathering resistance as evidenced
by the substantially higher 20 gloss reading of 63 after 700 hours in the
QUV Accelerated Weathering Tester as compared to a 20 gloss reading of
only 3 for the comparative composite basecoat/topcoat after the 700 hour
period.
- 39 -
