Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~lZ~941
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention is concerned with thermosettable,
highly aromatic polyestèr resins and coating compositions
based on such resins.
1124941
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SUMMARY OF THE INVENTION
We have discovered a new and useful type of polyester
resin compositions which, when combined with a suitable
solvent and appropriate ad~uvants, provide thermosettable
coating compositions of superior qualities which are parti-
cularly well suited for app~iancecoating applications. The
resins are the polyester condensation products of a reaction
mixture comprising:
a) about 40% to about 60% by weight benzenedicarboxylic
acid [e.g~: 1,3-benzenedicarboxylic acid];
b2 about 2% to about 18% by weight of a trihydroxy
alkyl component [e.g.: 2-ethyl-2-(hydroxymethyl)-
1,3-propanediol];
C2 about 9% to about 23% by weight of a short chain
alkylene diol component having four or less carbon
; atoms in the primary carbon chain between the hydroxyl
moieties [e.g.: 2,2-dimethyl-1,3-propanediol]2
d2 about 9% to about 30% by weight of a dihydroxy alkyl
compound having four to ten carbon atoms in the
primary carbon chain between the hydroxyl moieties
[e.g~: 1,6-hexanediol]; and
e2 0% to about 10% by weight of an alkyl dicarboxylic
acid component [e.g~: 1,6-hexanedioic acid].
The monomers are combined in ratios substantially
within the stated ranges, such that the resulting polyester
has a number average molecular weight of from about 1,400
to about 5,000, a combined acid and hydroxyl value of about 40
to about 160 milligrams of KOH per gram of polyester, and a
glass transition temperature of about -15 to +25C.
l~Z4941
The highly aromatic polyester resins disclosed
herein are readily solvated in coventional coating composition
solvent vehicles to form stable coating solutions. When
` combined with an appropriate aminoplast and acid catalyst,
such coating solutions may be applied to a suitable substrate
and cured to produce coatings exhibiting an outstanding
combination of hardness, adhesion, stain resistance,
water resistance, extendability and dry heat resistance.
1124941
DESCRIPTION OF SPECIFIC EMBODIMENTS
Polyester Resins
The benzenedicarboxylic acid component of the
polyester resins of the present invention is preferably one
of the nonsymmetrical isomers of that compound, and most
preferred is l,3-benzenedicarboxylic acid ~isophthalic acid].
1,2-Benzenedicarboxylic acid [phthalic acid], or its anhydride,
may also be used to advantage as the aromatic acid component,
either by itself or in combination with 1,3-benzenedicarboxylic
acid. The benzenedicarboxylic acid component is used in an
amount between about 40 percent and about 60 percent by weight
of the reaction mixture, based on the total weight of the
` reactants.
The trihydroxy alkyl component may be a linear or
i 15 branched hydrocarbon compound and the three hydroxyl functions
are attached to either terminal or to nonterminal carbon atoms
in the molecule. It has been found that triol compounds
having an internal tertiary carbon atom in the hydrocarbon
skeleton, such that each of the hydroxyl groups is on a different
terminal carbon atom, result in the most desirable configurations
: for the polyester product. For this reason the preferred
trihydroxy compounds are those exemplified by 2-ethyl-2-
(hydroxymethyl)-1,3-propanediol [trimethylolpropane; TMP] and
2-(hydroxymethyl)-2-methyl-1,3-propanediol [trimethylolethane,
TME; pentaglycerol]. The trihydroxy alkyl component is used
in an amount between about 2 percent and about 18 percent by
weight of the reaction mixture, based on the total weight of
the reactants.
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The preferred short chain alkylene dlol component,
which constitutes between about g percent and about 23 percent
by weight of the reaction mixture, comprises one or more of those
short chain alkylene diol compounds having rour or less carbon
atoms in the hydrocarbon chain between the two hydroxy groups.
It is preferred that this diol component be 2,2-dimethyl-
1,3-propanediol [neopentyl glycol], elther by itself or in
admixture with other short chain alkylene diol compounds.
Other diol compounds (such as 1,2-ethanediol, 1,2-propanediol
and 1,3-butanediol~ are similarly useful in the preparation of
the resins disclosed herein and are preferably used in ad-
mixture with 2,2-dimethyl-1,3-propanediol.
The second dihydroxy component of the polyester
resins of this invention comprises a dihydroxy alkyl compound
having four to ten carbon atoms in the primary carbon chain
between the two hydroxyl groups~ The preferred compound is
1,6-hexanediol [hexamethylene glycol], but other similar com-
pounds wherein the hydroxyl groups are separated by a chain of
four to ten carbon atoms may be successfully substituted
therefore. Examples of other useful compounds include, but
are not limited to: 1,4-butanediol; 1,5-pentanediol; 1,7-
heptanediol; 1,8-octanediol, l,9-nonanediol; and 1,10-decanediol.
This component is used in an amount between about 9 percent
and about 30 percent by weight of the reaction mixture, based
on the total weight of the reactants.
An alkyl dicarboxylic acid component, such as
1,6-hexanedioic acid, may optionally be included in the formul-
ation. When included, such constituent is preferably in the
range of 0 percent to about 10 percent by weight of the reaction
mixture and replaces a corresponding portion of the aromatic
acid component.
~Z494~
The esterlfication reaction is normally carried out
at temperatures between about 175C and about 250C, for a
period of time ranging between about 3 hours and about 10
hours. A conventional catalyst for the promotion of
esterification reactions, such as dibutyltin oxide, dibutyltin
dilaurate, or triphenyl phosphite, can be used in catalytic
amounts (e.g.: 0.01 to 1.0 percent by weight) to aid in the
reaction. During the reaction it is advantageous to remove
the water evolved from the esterification, for instance by
means of a suitable trap which condenses and draws off the
water vapors, by azeotropic distillation with toluene or
xylene, or by flushing the reactor with an inert gas to sweep,
the vapors away from the reactants. The reactants are com-
blned in appropr ate relative amounts, substantially within
the specified ranges, such that the polyester product of the
above reaction process is a substantially noncrystalline resin
-material having a number average molecular weight of from
about 1,400 to about 5,000, combined acid and hydroxyl values
of about 40 to about 160 milligrams of KOH per gram of
polyester, and a glass transition temperature of about
-15 to +25C.
1124941
Coating Compositions
The essential components of the coating compositions
of this invention are the foregoing polyester resin, an aminoplast,
an acid catalyst, and an inert organic solvent.
; The material used to thermoset the coating is a
conventional aminoplast cross-linking agent. Such agents are
well known in the art. There can be used any of the thermo-
setting alkylated aminoplast resins, such as the urea-aldehyde
resins, the melamine-aldehyde resins, the dicyandiamide-
aldehyde resins, and other aminoplast-aldehyde resins such as
those triazine resins produced by the reaction of an aldehyde
with formoguanamine, ammeline, 2-chloro-4,6-diamino-1,3,5-triazine,
6-methyl-2,4-diamino-1,3,5-triazine, 2,4,5-trihydrazine-1,3,5-
triazine, and 2,4,6-triethyl-triamino-1,3,5-triazine. Generally,
such resins are alkylated with an alcohol, such as methanol
or butanol. As aldehydes used to react with the amino compounds
to form the resinous material, one may use such compounds
as formaldehyde, acetaldehyde, crotonaldehyde, acrolein, or
compounds which engender aldehydes, such as hexamethylene-
tetramine, paraldehyde, paraformaldehyde, and the like. Theamount of aminoplast used is between about 5 weight percent
and about 25 weight percent on resin solids.
The acid catalyst may be the acid itself or a
derivative that will generate the acid in situ, such as
commercially available Aerosol~OT which generates sulfonic acid
and ammonium nitrate which can be decomposed to form nitric acid~
Acids that generally are used to cure aminoplast systems
include p-toluenesulfGnic acid (pTSA), benzenesulfor.ic acid,
methylsulfonic acid, cyclohexyl sulfonic acid, phosphoric
acid, mono- or dialkyl acid phosphates, and many others
indicated in the art as suitable curing catalysts. The amount
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112~941
of acid catalyst used is usually between about 0.1 weight
percent and about 1.0 weight percent, based upon total resin
solids.
~ The solvents utilizable in the coating compositions
of this invention are the usual volatile solvents used in
paints and enamels. Aromatic hydrocarbons are useful, such as
toluene, xylene, and aromatic petroleum cuts, e.g.: Hi-Sol
4-1 (boils 190.6 - 260.0C) and Solvesso 100 (boils 155.6 -
172.2C). Useful ketones include methyl isobutyl ketone (MIBK),
isophorone, ethyl amyl ketone, and methyl n-amyl ketone.
Alcohols are utilizable, such as butanol, amyl alcohol,
2-ethylhexanol, and cyclohexanol. Also of use are the ether
alcohols and their acetate esters, such as methoxyethanol,
ethyoxyethanol, butoxyethanol, hexoxyethanol, methoxypropanol,
methoxyethyl acetate, and ethoxyethyl acetate. It is within
the contemplation of this invention to use mixture of two or
more solvents. The proportion of solvents included is not
critical, since they primarily serve as the volatile vehicle
to convey the solid material to the substrate to be coated.
The total amount of solvents used will be sufficient to
provide a solids content (% NVM) of between about 35 weight
percent and about 55 weight percent in the coating composition
prior to pigmentation.
It is preferred to incorporate a pigment into the
coating compositions of this invention. The preferred pigment
is titanium dioxide, but any conventional pig~ent can be used,
such as zinc oxide, bentonite, silica, and chrome yellows,
greens, oranges, etc. Sufficient pigment is included to
provide an opaque or colored film of the desired intensity and
appearance.
1124941
The coating composltions of this invention may be
, applied to any of the usual substrates, i.e.: metal, paper,leather, cloth, etc., using any of the usual methods of application
including spraying, direct rollcoating, reverse rollcoating,
~ 5 electrodeposition, flow coating, and the like. The coating
,~ composition is primarily useful for coating aluminum, steel,
tin plated steel, electro-galvanized steel, and hot dipped
galvanized steel. Such metal substrates are usually cleaned
and chemically treated to improve the wettlng and adhesion of
subsequent organic coatings. The coating compositions of
this invention are equally useful for primers or as topcoats
deposited over base layers of either the same or different
types of resinous composltlons. After coating the substrate
the coating is cured, preferably by baking for about 5 seconds
to about 25 minutes at between about 120C and-about 315C.
A typical fast bake is for about 40 seconds at about 240C -
255C.
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The following examples demonstrate the preparation of
the polyester resins of thls invention and coating compositions
containing them, along with performance characteristics of
such coatings.
;; 5 Example 1
~,
A ten gallon reactor was charged with 1100.0
grams of 2-ethyl-2-(hydroxymethyl~-1,3-propanedlol, 3845.6_grams
of 2,2-dimethyl-1,3-propanediol, 4395.6 grams of 1,6-hexanediol,
12,636.8 grams of 1,3-benzenedicarboxyllc acid and 22 grams of
dlbutyltin oxlde. The contents of the reactlon vessel were
gradually heated to 225C whlle removing the water of reactlon
through a steam ~acketed dlstlllatlon column. When an acld
number of 10.0 was obtalned, the resultlng polyester was
reduced with Hi-Sol 4-1 solvent to afford a materlal wlth a
final acid number of 9.3 at 60.5% N~M (Non-Volatlle Materlal),
a hydroxyl number of 54.6, a Gardner Holdt viscosity of Z3+,
a Gardner Color of 1+, and a welght of 8.87 lbs per gallon.
Examples 2 - 11
The followlng table contains examples of polyesters
whlch were prepared by the same technlque as that of Example
.
llZ~941
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` Example 12
, Paint was made from the polyester solution of Example
~ 1 by combining it with 15% of hexamethoxymethylmelamine cross-
S linker on resin solids, pigmented with TiO2 pigment at a
pigment/resin ratio of 0.9~1, catalyzed with 0.1% on resin
solids of a 20% pTSA solution and reduced to 68.4% NVM with
isophorone and Solvesso~3100. This paint was applied on Bonderite~
901 treated cold rolled steel panels at 0.9 mils dry film
thickness and baked at 266C for 40 seconds. The cured coating `
showed a 95 gloss, an H to 2H pencil hardness and passed a
O T-Bend and 120 inch/lb reverse impact with no microfractures
or loss of Scotch~tape adhesion. Stain resistance of this paint
was excellent when tested with iodine, mustard, shoe polish,
lipstick, catsup, and chlorox, which are typical reagents used
to test appliance coatings.
`` The glo~s was determined in accordance with ASTM
Designation D-523-67, the reverse impact resistance according
to ASTM Designation D-2794-69 and adhesion via ASTM Designation
D-3359-76. The other test procedures were as follows:
Fabrication 180 Bend (O T-Bend) - The panel is
manually bent into a U-shape. A number of thicknesses of the
substrate (in this case, no-thicknesses or OT) are placed in
the bend area and the entire assembly is placed in the ~aws of
a press and pressed. Scotch tape is applied across the bend
and removed quickly. The adhesion of the coating after bending
is rated on a scale of 0 to 10 with 10 representing perfect,
i.e., no coating was pulled off with the tape.
B
llZ4941
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Pencil Hardness Test - A set of pencils ranging from
6B (soft) to 6H (hard) are used, starting with the hard end of
the set. These pencils are pushed in turn into the film.
The first pencil which crumbles instead of penetrating indicates
the pencil hardness.
MEK Double Rubs - A pad of felt (2" square) soaked
in MEK (methylethyl ketone) is rubbed back and forth across
the coated surface, while the panel is resting on a firm
surface. Each stroke is 2 l/2-3" in length at a uniform
pressure of about 900 grams and at a rate of about 100 rubs
per minute. The pad is re-soaked with MEK after 50 double
rubs, or before, if lncrease in friction makes it necessary.
One double rub is considered as one back and forth stroke.
Fifty double rubs should only slightly dull the surface in
the center area of the rub.
Stain Resistance - One ml of reagent is placed on a
coated panel and covered with a watch glass for 96 hours.
Then the watch glass is removed and the panel is washed with
soap and water and the degree of staining is rated versus a
high quality appliance coating used on refrigerators as a
control.
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, ,
Example 13
A portion of the polyester resin solution of Example
2 was combined with 16% on resin solids of a hexamethoxymethyl-
melamine crosslinker, pigmented with TiO2 at a pigment/binder
ratio of 0.9/1, catalyzed with 0.25% on resin solids of a 20%
pTSA solution and reduced to 67.7% N~M with Cellosolve Acetate
and Solvesso~100. At this reduction the paint viscosity was
40-50 seconds #4 Zahn Cup. It was applied at o.8 mils dry
film thickness on 20 mil Bonderite~901 treated cold rolled
steel panels and baked at 266C for 40 seconds. The cured
coating showed 4H to 5H pencil hardness, passed a 5T-Bend with
no microfracture or loss of Scotch~3tape adhesion. Stain
resistance of this paint was excellent when tested with iodine,
mustard, shoe polish, lipstick, catsup and chlorox.
Example 14
A portion of the polyester resin solution from Example
2 was combined with 30% on resin solids of a hexamethoxymethyl-
melamine crosslinker, pigmented with TiO2 solution, and reduced
to 70.1% NVM with Cellosolve Acetate and Solvesso 100. This
paint was applied at 0.8 mils dry film thickness on 20 mil
Bonderite 901 cold rolled steel and baked 40 seconds at 254C
or 213C peak metal temperature. The cured coating showed an
85 gloss, greater than 100 MEK double rubs, a 2H to 3H pencil
hardness, and passed a 4T-Bend and 80 inch/lb reverse impact
with no cracks or loss of Scotch tape adhesion. Stain
resistance of this paint was excellent when tested with the
reagents mentioned above.
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B
11~4941
Example 15
A portion of the polyester resin from Example 3
was made into a white paint by using 15% hexamethoxymelthyl-
melamine as a crosslinker based on resin solids, 0.2% of a
20% solution of pTSA as a catalyst, and pigmenting it with
TiO2 at a pigment/binder ratio of 0.9~1. This paint was
reduced to 35-40 seconds #4 Zahn Cup and 68.1% NVM with Solvesso
100 and Cellosolve Acetate. It was applied at 0.9 mils dry
film thickness on 20 mil cold rolled steel panels treated with
Bonderite 901 and baked at 266C for 40 seconds. When tested
this coating showed a Knoop Hardness Number of 20.7, greater
than 100 MEK double rubs, and passed an 80 inch/lb reverse
impact and 5T-Bend with no cracks or loss of Scotch tape
adhesion.
Example 16
The polyester resin solution from Example 4 was
formulated into a paint by combining it with 15% of hexameth-
oxymethylmelamine crosslinker, pigmented with TiO2 at a pigment/
binder ratio of 0.9/1, catalyzed with 0.2% on resin solids of
a 20% pTSA solution and reduced to a viscosity of 36 seconds
#4 Zahn Cup and 68.2% NVM with Cellosolve Acetate and Solvesso
100. This coating was applied at 0.85 mils dry film thickness
on a 20 mil cold rolled steel panels treated with Bonderite
901 and baked at 266C for 40 seconds. The cured coating
showed a Knoop Hardness Number (KHN) of 17.9, a gloss of
87, and it passed a 4T-Bend and 80 inch/lb reverse impact with-
out showing any microfractures or loss of adhesion when tested
with Scotch tape.
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llZ~941
Example 17
The resin solution from Example 5 was made into a
high solids paint by blending it with 20% hexamethoxymethyl-
melamine, pigmenting it with TiO2 at a pigment/binder ratio
of 0.8/l and reducing it to 80.2% NVM with Cellosolve Acetate,
plus 1.0% on resin solids of a 20% pTSA solution. This coating
was checked for film properties by applying it at o.85 mils
dry film thickness on 20 mil cold rolled steel panels treated
with Bonderite 901 and baking at 266C for 40 seconds. When
coated thus the paint showed a gloss of 88, pencil hardness
of 2H to 3H and passed an 80 inch/lb reverse impact plus
Scotch tape with no loss of adhesion.
.. . ., . ... _ _
Although the present invention has been described
.. .. . .. . . . _ . . . . .
with reference to preferred embodiments, it is to be understood
that modifications and variations may be resorted to without
departlng from the spirit and scope of this invention, as
those skilled in the art will readlly understand. Such
modifications and variations are considered to be within the
purview and scope of the appended claims.
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