Note: Descriptions are shown in the official language in which they were submitted.
200~7[D~
FA-036~
URETHANE DIOL EXTENDED
CATHODIC ELECTRODEPOSITION RESINS
The field of art to which this invention
pertains is electrodepositable epoxy resins chain
extended with urethane diols containing crosslinking
agents to be used in cathodic electrocoat processes.
BACKGROUND ART
The coating of electrically conductive
substrates by electrodeposition is a well known and
important industrial process. (For instance,
electrodeposition is widely used in the automotive
industry to apply primers to ~utomotive substrates).
In this process, a conductive article is immersed as
one electrode in a coating composition made from an
aqueous emulsion of film-forming polymer. An electric
current is passed ~etween the article and a
counter-electrode in electrical contact with the
aqueous emulsion, until a ~esired coating is produced
on the article. The article to be coated is made the
cathode in the electrical circuit with the
counter-electrode being the anode.
Resin compositions used in cathodic
electrodeposition baths are also well ~nown in ~he art.
These reslns are typically manufactured from
polyepoxide resins which have been chain extended and
adducted to include a nitrogen. The nitrogen is
typically introduced through reaction with an amine
compound. Typically these resins are blended with a
crosslin~ing agent and then salted with an acid to ~orm
a water emulsion which is usually referxed to as a
princ~pal emulsion.
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The principal emulsion is combined with a
pigment paste, coalescent solvents, water, and other
additives to foFm the electrodeposition bath. The
electrodeposition bath is placed in an insulated tank
containing the anode. The article to be coated is made
the cathode and is passed through the tank containing
the electrodeposition bath. The thickness of the
coating is a function of ~he bath characteristics, the
electrical operating characteristics, the immersion
tim~, and so forth.
The coated objec~ is removed from the bath
after a certain period of time. The object is rinsed
with deionized water and the coating is cured typically
in an oven at sufficient temperature to produce
~rosslinking-
Prior art of cathodic electrodepositable
resin compositions, coating baths, and cathodic
electrodeposition processes are disclosed in U.S.
Patent Numbers 3,922,253; 3,984,299; 4,093,594;
2Q 4,134,864; 4,137,140; 4,419,467; and 4,468,307, the
disclosures of which are incorporated by reference.
An important ch,aracteristic of the
electrodeposition bath is its throw power. Throw power
concerns the ability of the cationic resin to coat the
recessed areas and shielded portions of the cathode. Asecond important characteristic of the final coating is
chip resistance. This has become increasingly
important to automobile manufacturers as cars have
become more aerodynamic in shape and therefore are more
susceptible to being chipped by pebbles or other
debris. What is nPeded is an electrodepositable resin
which ha~ increased throw power and greater chip
resistance.
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SUMMARY OF THE INVENTION
In accordance with the present invention, an
electrodepositable resin is provided. The resin is
typical of the well known aromatic polyepoxide resins
except that it has been internally plasticiz~d by
reacting the aromatic polyepoxide with a urethane diol
which has been found to give improved throw power and
chip resistance without adversely affecting other
important electrodepositable resin characteristics.
DETAILED D~SCRIPTION
As discus~ed above, it is well known that
most principal emulsions in electrodeposition coatings
comprise an epoxy amine adduct blended with a
crosslinking agent and salted with an acid in order to
get a water soluble product.
The polyepoxide resins which are used in the
practice of the invention are polymers having a
1,2 epoxy equivalency greater than one and preferably
abou~ two, that is, polyepoxides which have on an
average basis two epoxy groups per molecule. The
preferred polyepoxides are polyglycidyl ethers of
cyclic polyols. Particularly preferred are polygly-
cidyl ethers o~ polyhydric phenols such as bisphenol A.
These polyepoxides can be produced by etherification of
polyhydric phenols with epihalohydrin or dihalohydrin
such as epichlorohydrin or dichlorohydrin in the
presence of alkali. Examples of polyhydric phenols are
2,2-bis-(4-hydroxy-3-tertiarybutylphenyl)-propane,
1,1-bis-(4-hydroxyphenyl)ethane, 2-methyl-1,1-bis-
~4-hydroxyphenyl) propane, 2,2-bis-(4-hydroxy-3-
tertiarybutylphenyl~propane, bis-(2-hydroxynaphthyl)
methane, 1~5-dihydroxy-3-naphthalene or ~he like~
Besides polyhydric phenols, other cyclic
polyols can be used in preparing the polyglycidyl
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ethers of cyclic polyol derivatives. Examples of other
cyclic polyols would be alicyclic polyols, particularly
cycloaliphatic polyols, such as 1,2-cyclohexanediol;
1,4-cyclohexanediol, 1,2-bis(hydroxymethyl)cyclohexane,
1,3-bis-(hydroxymethyl)cyclohexane and hydrogenated
bisphenol A.
The polyepoxides have molecular weights of at
least 200 and preferably within the range of 200 to
2000, and more preferably about 340 to 2000.
To be useful as an electrocoat, the
polyepoxide must be chain extended by an intèrnal
flexibilizer. The internal flexibilizer enhances flow
and coalescence and increases rupture v~ltage of the
composition. Currently, internal flexibilization is
usually accomplished by chain extending the polyepoxide
with a polyether or a polyester polyol.
It has been found that substituting a
urethane diol for the polyether polyol or polyester
polyol results in both improved throw power and better
chip resistance. These improvements are realized while
maintaining the flow and coalescence characteristics of
a polyepoxide resin chain extended with a polyether
polyol or polyester polyol.
The urethane diol is formed in one of two
ways: (1) mixing diisocyanate and polyol; or (23
mixing alkylene carbona~e and diamine. The reac~ion
condition for the diisocyanate-polyol route is to add
diisocyanate to polyol at 25-100C for about two hours.
Prefered diisocyanates are aliphatic diisocyantes such
as hydrogenated methylene diphenyl diisocyanate.
Prefered polyols are diols such as butane diol, hexane
diol t ethoxylated bisphenol A and so forth. The
pre~ered eguivalsnt ratio of diisocyanate ~o ~olyol is
1:2.
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The prefered method for making the urethane
diol is the alkylene carbonate-diamine route. In this
method alkylene carbonate is added to a diamine at
25-100~C for about three hours. Prefered alkylene
carbonates are ethylene carbonate and propylene
carbonate. The prefered diamines are hexamethylene
diamine and 2-methyl pentane diamine. The prefered
equivalent ratio of alkylene carbonate to diamine is
~ his method is disclosed in U.S. Patent
lo No.3,248,373. The urethane diol molecular weight should
be between 250-2000 and most preferably 270-600~
Urethane diol is commercially available from
Xing Industries under the tradename ~K-Flex UD
320-100~.
In addition, the urethane diol can be chain
extended by reacting it with an alkylene oxide to make
a polyether urethane diol.
The urethane diol chain extended polyepoxide
is reacted with a cationic group former, ~or example,
an amine.
The amines used to adduct the epoxy resin are
monoamines, particularly secondary amines with primary
hydroxyl groups. When you react the secondary amine
containing the primary hydroxyl group with the terminal
epoxide groups in the polyepoxide ~he result is the
amine epoxy adduct in which the amine has become
ter~iary and contains a primary hydroxyl group.
Typical amines that can be used in the invention are
methyl ethanol amine, diethanolamine, and so forth.
Our preferred amine is diethanol amine.
Mixtur~s of the various amines described
above can be used. ~he reaction of the secondary amine
with the polyepoxide resin takes place upon mixing the
amine with the product. The reaction can be conducted
neat, or, optionally in the presence of ~uitable
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solvent. The reaction may be exothermic and cooling
may be d2sired. However, heating to a moderate
temperature, that is, within the range of 50 to 150C,
may be used to hasten the reaction.
The reaction product of secondary amine with
the polyepoxide resin attains its cationic character ~y
at least partial neutralization with acid. Examples of
suitable acids include organic and inorganic acids such
as formic acid, acetic acid, lactic acid, and
phosphoric acid. The extent of neutralization will
depend upon the particular product involved. It is
only necessary that sufficient acid be used to disperse
the product in water. Typically, the amount of acid
used will be sufficient to provide at least 30 percent
of the ~otal theoretical neutraliæation. Exces~ acid
beyond that required for lQ0 percent total theoretical
neutralization can also be used.
The extent of cationic group formation of the
resin should be selected such that when the resin is
mixed with aqueous medium, a stable dispersion will
form. A stable dispersion is one which does not settle
or is one which is easily redispersible if some
sedimentatisn occurs. In addition, the dispersion
should be of sufficient cationic character that the
dispersed resin particles will migrate towards the
cathode when there is an electrical potential between
the anode and cathode immersed in the aqueous
d~sperslon .
In general, most of the cationic resins
prepared by the process of the invention contain ~rom
about 40 to 80, preferably ~rom about 50 to 70
milliequivalents of cationic group per hundred grams of
resin solids.
The cationic resinous binder should
prefPrably have average molecular weights, as
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determined by yel permeation chromatography using a
polystyrene standard, of less than 10,000, more
preferably less than 5,000 and most preferably less
than 3,000 in order to achieve high flowability.
After forming the above described cationic
resin, it is mixed with a crosslinking agent.
The crosslinking agents o~ our novel process
are well known in the prior art. Typical crosslinkers
are aliphatic and aromatic isocyanates such as
hexamethylene diisocyanate, toluene diisocyanate,
methylene diphenyl dii~ocyanate and so forth. These
isocyanates can also be react~d with a polyol such as
trimetholpropane to form a polyisocyanate. The
isocyanate is then pre-reacted with a blocking agent
such as methyl ethyl ketoxime or ethylene glycol mono
butyl ether to block the isocyanate functionality
(i.e., the crosslinking functionality). Upon heating
the blocking agent seperates and crosslinking occurs.
The preferred crosslinking agent for our invention is
toluene diisocyanate (TDI) reacted with trimethyol
propane (TMP) and blocked with ethylen~ glycol mono
butyl ether.
The ratio of TDI to TMP i~ about 3:1, The
ethylene glycol mono butyl ether is usually added in an
equivalent ratio of about 1:1 to the TDI~TMP
polyisocyanate. Reaction conditions for the above
reactions are well known in the art and are disclosed
in the following patents. U.S. Patent~ No. 4,031,050
and 3,~47,35~.
The cationic resin and the blocked isocyanate
are the principal resinous ingredients in the
electrocoating composi~ion and are usually present in
amounts of about 30 to 50 percent by weight of solids.
Besides the resinous ingredients described
above, the electrocoating compositions usually contain
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a pigment which is incorporated into the composition in
the form o~ a paste. The pigment paste is prepared by
grinding or dispersing a pigment into a grinding
vehicle and optional ingredients such as wetting
agents, surfactants and-defoamers. Pigment grinding
vehicles are well known in the art. After grinding,
the particle size of the pigment should be as small as
practical, generally, a Hegman grinding gauge of about
6 to 8 is usually employed.
Pigments which can be employed i~ the
practice of the invention include titanium dioxide,
basic }ead silicate, strontium chromate, carbon black,
iron oxide, clay and so forth. Pi~ments with high
surface areas and oil absorbencies should be used
judiciously because they can have an undesirable effect
on coalescence and flow.
The pigment-to-resin weight ratio is also
fairly important and should be preferably less than
0.5:1, more pre~erably less than 0.4:1, and usually
about 0.2 to 0.4:1. Higher pigment-to-resin solids
weight ratios have also been found to adversely affect
coalescence and flow~
The coating compositions of the invention can
contain optional ingredients such as wetting agents,
surfactants, defoamers and so forth. Examples of
surfactants and wetting agents include alkyl
imidazolin~s such as those available from Ciba~~eigy
Industrial Chemicals as ~Amine C,~ These optional
ingredients, when present, constitute from ahout 0 to
20 peroent by weight of resin solids. Plasticizers are
optional ingredients because ~hey promote flow.
Examples are high boiling water immiscible materials
such as ethylene or propylene oxide adducts o~ nonyl
phenols or bisphenol A. Plasticizers are usually used
in amounts sf about 0 to 15 percent by weight resin
solidsO
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Curing catalysts such as tin catalysts are
usually present in the composition. Examples are
dibutyltin dilaurate and dibutyltin oxide. When used,
they are typically present in amounts o~ abo~t 0.05 to
1 percent by w2ight tin based on weight of total resin
solids.
The electrodepositable coating compositions
of the present invention are dispersed in aqueous
medium. The term ~dispersion~ as used within the
~0 context of the present invention is believed to be a
two-phase translucent or opaque aqueous resinous system
in which the resin is in the dispersed phase and water
the continuous phase. The average particle size
diameter ~f the resinous phase is about 0.1 to 10
microns preferably less than 5 microns. The
concentration of the resinous products in the aqueous
medium is, in general, not critical, but ordinarily the
major portion of the a~ueous dispersion is water. The
aqueous dispersion usually contains from about 3 to 50
percent typically 5 to 40 percent by weight resin
solids. Fully dilu~ed electrodeposition baths
generally have solids contents of about 3 to 25 percent
by weight.
Besides water,~the aqueous medium may also
contain a coalescing solven~. Useful coalescing
solvents include hydrocaxbons, alcohols, esters, ethers
and ketones. The preferred coalescing solvents include
alcohols, polyols and ketones. Specific coalescing
solvents include monobutyl ~nd monohexyl etbers of
ethylene glycol, and phenyl ether of propylene glycol.
The amount of coalescing solvent is not unduly critical
and is generally between about 0 to lS percent by
weight, preferably about 0.5 to 5 percent by weighk
bas~d on weight of resin solids.
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EXAMPLE T
W~. NV
~Epon X28~ 1~6~ 1216.9
Xylene 60
Bisphenol A 355 355
Benzyl Dimethyl Amine 2~1
nK-Flex UD 320-100~ 288 276.5
Benzyl Dimethyl Amine 4.2
Diethanol Amine202.7 202.7
Methyl Isobutyl Ketone577.3
"Epon 828n~ a diglycidyl ether of ~isphenol A from
Shell Chemical Co.) and xylene were charged to a
reaction vessel and heated with nitrogen sparge to
145C. The reaction was held at reflux for about 1/2
hour to remove water. The reaction mixture was cooled
to 140C and the bisphenol A and Benzyl dimethyl amine
added. The reaction mixture was heated to 160~-190C
and held at this temperature for about an hour and then
cooled to 120C. nK-Flex UD 320-100~ (a uretha~e diol
from King Industries3 and a second portion of benzyl
dimethyl amine were then added. The reaction was
heated to 140C and held at 140C ~or 2~ hours until
the proper weight per epoxide was obtained. The
reaction mixture was cooled to 100C. Diethanol amine
was then added. The reaction mixture was held at 120C
for one hour after methyl isobutyl ketone was added to
reduce the non-volatiles (NV) to 75%.
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EXAMPL~ II
Wt._ _NV
BacXbone resin from Example I570.5 427.9
Capped Isocyanate Crosslinkerl 324.4 230.3
~WP 1~ Plasticizer ~rom Rohm & Haas 20.0 20.0
~ownol PPH" from Dow 23.0
Surfactant2 7.0
De~onized Water 1261.0
Lactic acid 22.8
1 Polyurethane crosslinker formed from half-capping
toluene diisocyanate (80/20 2,~/2,6 isomer mixtuxe)
with hexyl cellosolve and reacting this product with
tri methylol propane in a 3:1 molar ratio. The
crosslinker is present as a 71 percent solids
solution in a 90/10 mixture of methyl isobutyl ]cetone
and n-butanol.
2 Sur~actant is a mixture of 120 parts ~mine C;' from
Ciba-Geigy, 120 parts acetylenic alcohol,
commercially available as "Surfynol 104", 120 parts
of 2-butyoxy ethanol and 221
parts by weight of deionized water and 19 parts
glacial acetic acid.
Thoroughly mix the bac~bone resin from Example I,
polyurethane crosslinker,~WP~n, nDownol PPH~, lactic
acid, and surfactant. Then add the deionized water
under agitation. This mixture was allowed to mix until
majority of the organic ketone solvent evaporated. The
dispersion has a solid con~ent of 36%.
EX~MPLE III
Q~ATERNIZING AGENT
Wt. NV
2-Ethylhexanol half 320.0 304
capped TDI in MIBK
Dimethylethanolamine 8i.2 87~2
A~ueous Lactic Acid Solution117~6 B8.2
~-~utoxyethanol 39~2
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- PIGMENT GRINDING VEHICLE
~Epon 829~ 720 682
Bisphenol A 289.6 289;6
2-Ethylhexanol half 406.4 386.1
capped T~I in MIBK
Quaternizing Agent (from above3 496.3 421.9
Deionized Water 71.2
2-Butoxyethanol 149.Q
The quaternizing agent was prepared by adding
dimethylethanolamine to the ethylhexanol half-ca~ped
Toluene diisocyanate in a suitable reaction ~essel at
room temperature. The mixture exothermed and was
stirred for one hour at 80C. Lactic acid was then
charged followad by the addition of 2-butoxyethanol.
The reaction mixture was stirred for about one hour at
65C to form the desired quaternizing agent.
To form the pigment grinding vehicle "Epon
829~ (a diglycidyl ether of bisphenol A from Shell
Chemical Co.) and Bisphenol A were charged under a
nitrogen atmosphere to a suitable reaction vessel and
heated to 150-160C to initiate an exothermic
reaction. The reaction mixture was permitted to
exotherm for one hour at 150-160C. The reaction
mixture was then cooled to 120C and the 2-ethylhexanol
half-capped toluene diisocyanate was added. The
temperature of the reaction mixture was held at
110-120'C ~or one hour, followe~ by the addition of the
2-butoxyethanol. The reaction mixture was then cooled
to 85~-90C, homogenized and then charged with water,
followed by the addition of the quaternizing agent
~prepared above). The ~emperature of the reaction
mixture was held at ~0-85C until an acid value of
about 1 was obtained. The reaction mixture had a
solids content of ~5 percent.
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PIGMENT P~STE
Wt~
Grind Vehicle 266.62
Deionized Water 385. oa
Carbon Black 10.81
Aluminum Silicate 25.92
Lead Silicate 51.83
Basic Lead Silica Chromate 22.21
Dibutyl Tin Oxide 29~.23
Deionized Water 59.0
The above ingredients were mixed together and ground in
a mill to a Hegman NG. 7 grind.
EXAMPLE IV
Wt. NV
Emulsion from Example II 344.4 12~
Pigment Paste 73.0 365
Deionized Water 385.1
A co~position was prepared by blending the above
ingredients. The coating composition has a pH of 5. 4,
a bath conductivity of 1620 micro Siemens. ~he zinc
phosphate cold roll steel panels were cathodically
electrocoated in the electrodeposition bath at 250
volts for 2 minutes at a bath temperature of 83'F. The
wet ~ilms were cured at 360~F for 15 minutes. The film
appearance is smooth with good corrosion resistance.
The chip resistance is better than current commercially
available systèms at an equal film thickness. The
gravilometer ra~ings were 7 in SAE-400 test metho~. The
bath has 15.5 inches of throw power at 275 volts.
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