Note: Descriptions are shown in the official language in which they were submitted.
~CKGROUND OF THE INVENTION
Field of Invention
_.
This invention is related to lo~ molecular wei~ht
polyesters and coatings based thereon and partlcularly to
blends of low molecular weight hydroxy-terminated polyesters
and thermosetting coating compositions prepared therefrom.
Description of Prior Art
Polyesters are well known in the prior art~ Their
preparation and utilization in a large ~ariety of coating
applications have been amply documented. The prior art
is replete with polyesters of various end groups and of wldely
varying molecular weights.
United States Patent 3,296,211, issued January 3,
1967 to J. Winkler, et al., discloses hydroxy-terminated
polyesters prepared from a mixture of di-primary and primary-
:, ,
secondary diols and aliphatic diacids. Such compositionsare not commonly useful as coati~gs and suffer from the dis-
advantage that during their preparation the components link
up in a random fashion and there~ore it i~ difficult to control
final properties, such as stain and salt spray resistance.
United Stated Patent 3,819,757, issued June 25, 1974
to J. Dorffel, et al., discloses coating compositions containing
low molecular weight hy~roxy-terminated polyesters which require
maleic or oxalic aclds for curing. Again, a possible dis-
advantage of these compositions resides in the use of mixtures
of different diol~ and mixturesof different diacids
Conventional coating compositions comprise
one or more film-formin~ constituents which, as the name im-
plies, are primarily responsible for the formation of the
~30 coating film on the substrate. In the case of thermosetting
2 -
s
compositions, it is common -to select as the film-formin~
I constituents of the compositions, blends of rnaterials, at
least one oE which is polymerlc and has a typical number average
molecular wei~ht of at least about 2,000, whi.ch co-react during the
curin~ process to form a crosslinked polymeric film of very
high molecular weight. For example, suitable known compo~ :
sitions of ~his type are blends of alkyd resins with melamine-
formaldehyde or urea-formaldehyde resins. The resins them-
selves are normally solid or semi-solid at ambient temperature
and hence 1n order to:formulate coating compositions which.
are sufficiently fluid to be applied to substrates by con
ventional means, the compositions usually include solvents for
the resins, to lower the composition viscosity. A typical
coating composition of this type can contain 40 percent or
more by weight of solvent, usually a volatile organic liquid,
~ which must be removed during the curing process, thus presenting
- a waste disposal and potential atmospheric pollution p~obIem.
United 5tates Patent~3,857,817, issued December 31, 1974 to
B. C. Henshaw, et al., discloses high solids coating compo
sitions.based on low molecular weight polyesters and thereby
obviating the need for the inclusion of large amounts of organic
solv.entsO However, in Example lO of this patent it is pointed
; out that any deviation from the indicated structures results
in films having markedly inferior properties. -.
Vnited States Patent 3,893,959, issued July 8, 1975
to R. E. Layman, discloses alkyd resins which are polyesters
of rather complex compositions. A mixture of mono~, di , and
tri-carboxylic acids is utilized. The dicarboxylic acid compo-
nent is made up of at least three different varieties, among
3Q which are the phthalic acids and, optionally, aliphatic di-
carboxylic acids. The diol component comprises at least two
: 3 -
.~
.~3~ 5
kinds, one of which is a hindered diol such as 2,2,4-trl--
methyl-1,3-pentane diol. Such compositions suEfer from the
above described d.isadvantage of randomness and are too viscous
for high solids applications.
SUMMARY OF THE INVENTION
According to the present invention there is
provided a blend of hydroxy-terminated polyesters consisting
essentially of:
(A) 20-80 parts by weight, based on the weight of
the blend,of a polyester of th~ following struc-ture: :
.~ '
C,H3 ~~ 1 ~CH3
HO - - CH-C-CH2-OC-X-Co - -CH2-C - CH- OH
CH3CH CH3 CH3 CHCH3
CH3 CH3
_ -n
or the isomeric ester through the secondary hydroxyl group,
wherein X~ CH-CH~
:~ and wherein n=0-10 with n=0-3 predominating; and
(B) 80-20 parts by weight, based on the weight of the
blend, of a polyester of the following general structure:
.~'' ' .
.~
. CH3 O " ~3
HO - -~ CH-C-CH2-OC~cH2~mcO ~ - CH2-C --CH -- OH
CH3CH CH3 CH3 CHCH3
CH3 CH3
_ ~ n
~: - 4 -
~3 ~
or the isomeric ester throu~h the secondary hydroxyl group,
wherein n=0-10 with n=0-3 predominatlng and wherein m-2-12
with m-2-4 predominating.
According to the present inve~tion there is further
provided a high solids coating composition consisting essen-
tially of:
(A) 30-80 parts by weight, based on the weight of
(A) plus (B), of a blend of hydroxy-terminated polyesters
described above; and
(B) 70~20 parts by weight) based on the weight of
(A) plus (B), of a nitrogen resin crosslinking agent or a
polyisocyanate.
It is also contemplated that the coating composition
of this invention can contain rheology control agents, pigments,
dispersants, adhes~on promoters, and other adjuvants.
DESCRIPTION OF THE INVENTION
~: .
The blend of low molecular weight hydroxy-texminated
polyesters of this invention comprises polyesters based on
2,2,4-trimethyl-1,3-pentane diol (TMPD) as the diol coMponent.
It has been found unexpectedly that the exact ~ature
- of the diol can be determinative of the properties of the poly-
ester blend of this invention. When neopentyl glycol was used
in place of TMPD, the polyester components were of very high
viscosity, partially solid at room temperature.
To obtain the two polyester componenlts of the blend,
- TMPD is reacted separately with iso-phthalic acid (IP~ or its
esters such as dimethyl iso-phthalate, other phthalic acids and
their esters, male.ic acid and its esters or ~etrahydrophthalic
acid, its anhydride or esters, cyclohexane 1,2-dicarboxylic acid,
it~ anhydride or esters, and the isomeric naphthalene dicarboxylic
5 _
acids, their esters or anhydrides and with an aliphatic
dicarboxylic acid, its esters or mixtures thereof. The
aliphatic dicarboxylic acid is of the general formula
HooctcH2~ COOH, where m is generally 2-4, although m=l
or 4-12 is also possible. In one preferred composition,
a mixture of dicarboxylic acids or their esters is utilized,
the mixture containing succinic, glutaric, and adipic acids.
The choic~ of a speciEic ratio of aliphatic esters can depend
on the final polyester property desired, such as flexibility
lQ or softness. In one preferred composition this ratio is
1:2:1 by weight.
During the preparation of the two components o
the blend of polyesters, the starting diol component, TMPD,
can and probably does react at either of its two hydroxyl groups.
Although the polyester components are represented by the following
two formulae, it is contemplated that the isomeric products,
; through the secondary hydroxyl groups, can also be present:
. CH3 0 ,CH3
HO - - CH-C-CH2-OC-X--CO - 1 2 : ,
CH3CH C~3 CH3 CHCH3
CH3 CH3
n
where X = -CH=C~
2~ ~ , ~ , ~ ,
,~ .
and n = 0-10, and
,
~3~
C 8 ~ CH3
HO - ~ CH-C-CH2-OC~Cl~2tmCO - - CH2-C ~ CEI ~ OH
CH3Cll CH3 C~3 C~CH3
_ CH3 ~ ~H3
.
where n = 0-10 and m = 2-12.
For optimum final coating properties it has been
found that it is important to control not only the composi-
tion of each component of the blend and their ratios to each
other but also the molecular weight of each of the components
of the blend. The average number average molecular weight
must not exceed approximately 1,000. It is of course recog-
nized by the skilled workers, that a polyester itself is a
mixture of different molecular weight species, that is the
value of n~in the above structures can vary. I~ is preferred
that ~alues of n be 0, l, 2 or 3, although there are usually
obtained smaller amounts of higher molecular weight species
also, n up to and including 10. In some typical reactions
for the preparation of the components of the blend of poly~
esters o~ this invention, the following data show the molecular
weight species obtained by gel permeation chromatography
uti}izing a polypropylene glycol standard and the corresponding
values of n. For the TMPD/IPA reactions a molar ratio of 2.1:1
of the reactants is utilized, for the TMPD/ aliphatic carboxylic
methyl esters (dimethyl succinate:dimethyl glutarate:dimethyl
adipate = 1:2:1, by weight) reactions the molar ratio is 1O8:1.
3~
TM~D/IPA
run #1:
molecular weight: 150 410 680 980 1040
(shoulder)
n: 0 1 2 3
run #2:
molecular weight: 140 380 640 910-970
( shoulder)
n: 0 1 2 3
It is contemplated that, on the average, at least 70% by weight
of this polyester component is n = 3 or less.
TMPD/aliphatic:
.
run #1:
molecular weight: 142 230 390 650 9S0
n: 0 (half- 1 2 3
ester)
run #2:
; molecular weight: 143 220 390 640 940
n: 0 (half~ 1 2 3
ester)
It is contemplated that, on the average, at least 55~ by weight
of this polyester component is n = 3 or less.
~ .
For best overall properties for the coating composition
of this invention a low final acid number is desired for the poly-
ester components of the blend. The acid number is usually 40 or
~; below but it is preferred that the acid number not exceed 12.
The acid number is the number of milligrams of potassium hydroxide
required to neutralize a l-gram sample of the polyester.
-- 8
C~
The individual polyeste.r components of the blend
can be present in the relative weight ratios of from 10:90
to 90:10. It is preferred for op-timum final coating properties
that the ratio of the polyester containing the aromatic di-
carboxylic acid moiety to the polyester containing the
aliphatic dicarboxylic acid moiety be from 80:20 to 40:60
and most preferably 65:35.
The blend of hydroxy-terminated polyesters of this
invention can comprise 30~80~ by weight of ~he film-forming
composition and preferably 50-70%. The relative amounts of
the polyester blend to the crosslinking agent, the total
comprising the film-forming composition, can depend on the
type of crosslinking agent utilized and on the amount and
type of catalyst to be included.
The Eormulated high solids coating compositions of
this invention can he applied to a substrate at.a solids
content of approximately 95% by weight. A chaxacteristic
property of these compositions is the pronounced lowering of
viscosity with only a slight increase in temperature from ambient.:
This property can be utilized to enhance, ~O,the spray atomiza-
tion during application. In contrast, conventional coating
compositions usually exhibit a more linear lowering of viscosity
with inoreased temperatures.
: The blend of hydroxy-terminat~d polyesters o~ this
invention,~when combined with a crosslinking agent such as a
nitrogen resin crosslinking agent or a polyisocyanate, form the
coating compositi.on of this invention.
The nitrogen resin crosslinking agents are well known
in the art. They are the alkylated products of amino resins,
g _ /
the latter prepared by the condensations of at least one
aldehyde with at least one oE urea, N,N'-ethyleneurea,
dicyandiamide, and aminotriazines such as melamines and
guanamines. Among the aldehydes -that are suitable are
formaldehyde, revertable polymers thereof such as paraformal-
dehyde, acetaldehyde, crotonaldehyde, and acrolein. Pre~
ferred are formaldehyde and revertable polymers thereof.
The amino-resins are alkylated with at least one and up to
six alkanol molecules containing 1 to 6 carbon atoms. The
alkanols can be straight chain, branched, cyclic or mixtures
thereof. Among preferred members of this class are the
methylated melamine-formaldehyde resins such as hexam thoxy-
methylmelamine. These liquid crosslinking agen~s have sub-
stantially 100~ non-volatile content as measured by the oil
method at 45C for 45 minutes. For the purposes of this
invention it is important not to introduce extraneou~
diluents that would lower the final solids content of the
coating. The hexamethoxymethylmelamines also offer fast
rates and high efficiency of cure and result in coatings of
high gloss and excellent chemical and stain resistance.
The polyisocyanates that can be utilized to cross-
link or extend the hydroxy~terminated polyester blend are
also well known. Among the preferred ones are included:
the biuret of hexamethylene dilsocyanate and various pre-
polymers of isophorone diisocyanate and methylene bis~cyclo~
hexylisocyanate). Diisocyanates can also be utilized.
A preferred composition contains a polyester blend of
TMPD/IPA and TMPD/aliphatic in an approximate weight ratio of
65:35, 55~75 parts, and a crosslinking agent, 45 25 parts.
-- 10 --~
~ ~.3~
For optimum properties in a final coatiny Eor use in the
appliance industry, 65 parts of the above b:lend is pre-
ferred together with 35 parts of a nitrogen resin cross-
linking agent. It is understood that, in addition to the
above components, the final coating composition can contain
a vari~ty of additives and modifiers.
The coating composition of this invention can be
cured to a tough, flexible coating upon haating in the
absence or presence of additional catalyst. The use o~
acidic catalysts to cure coating compositions based on
hydroxy-functional polyesters and complementary cross-
linkers is well known in the art, para-toluenesulfonic acid
~PTSA) being a commonly used catalyst.
The amount and type of acid catalyst can depend,
among other factors, on the amount and type of crosslinking
agent utilized in the coating com~osition of this invention,
on the desired curing temperature and time or on the method
of application of the coating composition. For example, it
was found that utilizing 20 parts by weight of a melamine-
formaldehyde crosslinker with 80 parts of the hydroxy-
terminated polyester blend of this invention required 0.4
part by weight of PTSA, while a 35/65 ratio of the same
materials required approximately 0.5 part by weight of PTSA
to achieve the same approximate level of curing.
The method of application of ~he coating composition
can affect the catalyst level when electrostatic spray appli-
cation is utilized. For this application it is important that
the coating compositio~ have high resistivity. As can be seen
from the data below, increasing the level of catalyst, which
;~ 30 allows a higher rate of cure or curing at a lower temperature,
3~
decreases th~ resistivity of the composition as measured
by a Ransburg Resistivity Meter having a pre~set gap
between the electrodes and thereby providing relative
resistivity values in megaohms. The pigmented coating
composition utilized in this test is based on a poly-
ester blend containing a polyester prepared from TMPD and
IPA and a polyester prepared from TMPD and dimethyl
aliphatic carboxylates (succina-te glu-tarate: adipate in
a 1:2:1 approximate weight ratio), in a weight ratio of
approximately 1O4/ and hexamethoxymethylmelamine, in a
weight ratio of polyesters:crosslinker of approximately
2:1; measurements are at 25C:
Catal~st Level (~) Relative Resistivity (Megaohm)
o 10
0.20 3.~
0.25 ~ l.g
.: , .
0.30 1.75
0.35 1.4
0.40 1.2
Curing of the coating composition of this lnvention
can be carried out at various temperatures, usually between
125~180C and preferably between 150-17SC. The length of
time of curing can also vary but 20-30 minutes afEord well
cured coatings.
The coating composition of this invention can contain,
in additi~n to a blend of polyesters and a crosslinking agent,
other components to enhance various properties of the composi-
tlon or the final coating therefrom, such as pigments, pigment
- 12 ~
~.t3~
stabilizers, rheology ccntrol agen-ts, for example acrylic
polymers, cellulosics, finely divided fumed ~silicas, dis-
persants, adhesion promoting agents, e.g. epoxy resins,
colorants, and the like.
For purposes of this invention, the coating
composition can be prepared from the polyester blends
followed by the addition of the o~her ingredients or by
premixing the ingredients with each of the polyester com-
ponents followed by blending.
The coating compositions of this invention are
designed for application to metallic substratesl such as
steel and` aluminum and can be applied with or without the
presence of a primer. They can be applied by any conven-
tional method of application such as spray-, dip-, roll-
or brush-coating or by electrostatic methods. In this
latter case~ high resistivity of the coating composition
is an important factor.
The coating composition of this invention are
useful as general industrial coatings, for example in the
appliance industry, and provide coatings having excellent
s~lvent and stain resistance, resistance to weathering
and corrosive conditions, forward and reverse impact,
hardness, high gloss, etc.
In the following Examples, illustrating the
invention, all parts are by weight, unless otherwise
lndicated.
.
.
- 13 -
EXAMPLE I
A. Preparation of a Polyester from
2,2 t 4-Trimethylpentane 1,3 diol
and Iso~hthalic acid
.
Into a five liter three necked flaslc equipped w.ith
stirrer, thermometer, a packed column, condenser, and a
Dean-Stark trap are placed TMPD, 1839.6 g; isophthalic acidr
996.0 g; oluene, 54.0 g; and dibutyltin dilaurate, 3.0 g.
The contents of the flask are heated to a maximum temperature
of 208C for a total of eleven hours during which time a
water-toluene a~eotrope is collected to remove the theoretical
amount of water. The final pro~uct has a solids content of
98% in toluene, a viscosity of 32,750 centipoises, measured
on a Brookfield viscometer, and an acid number o 5~4.
~ B. Preparation of a Polyester from
- . 2,2,4-Trimethylpentane-1,3-diol
and a Mixture of Dimethyl aliphatic
arboxylates ~ _
: .~
Into an apparatus:described in A above are charged
TMPD, 1839.6 g; a mixture of dimethyl succinate, dimethyl
glutarate, and dimethyl adipate J in a weight ratio of 1:2.1, ~ :
~: 972.0 ~; and dihutyltin dilaurate, 3 g. The contents of the
vessel are heated to a maximum of 202C for a total of nine
hours during which time the theoretical amount of ~ethanol is
collected. The final product has a Gardner~oldt viscosity of
Q and a hydroxyl number of 213.
C. Preparation of_ Polyester Blend
A blend of polyesters is prepared by stirrincJ
ogether 80 g of the polyester from A above and 20 q of
the polyester from ~ above.
- 14 -
~3~5
D. Preparation of a Co~olyester Control
Utilizing the apparatus described :in A above,
the following components are placed in the reaction vessel:
; TMPD, 1839.6; dimethyl isophthalate~ 931.2 g; the mixed methyl
esters of the aliphatic carboxylic acids shown in B above,
194.4 g; and dibutyltin dilaurate, 3 g. The contents are heated
at a maximum temperature of 196C for 7.5 hours to remove the
theoretical amount of methanol.
EXAMPLE II
A. Pigment Disp~sion
; A pigment dispersion is prepared from the following
ingredients, by sand milling:
HexamethQxymethy1melamine 463.0 g.
Acrylic rheology control agent,
at 60% solids, composition:
butyl-acrylate/styrene/hydroxyethyl
acrylate/acrylic acid//38/50/8/4,
solvent composition:cellosolve
acetate/n-butanol/aliphatic hydro-
carbon//61/8/31 234.9 g.
Dispersant, at 48~ solids, an
isocyanate-modified methyl
methacrylate/2-ethylhexyl
acrylate//63/37 polymer,
capped with mèrcaptosuccinic
acid; described in Canadian
~ ~ Patent 968,092, Example I 9.1 g.
Amyl acetate 279.5 g.
Tio~ (rutile) 2013.4 g.
.~
B. Coating Composition Based on
Polyester Blend from Exam~le IC
A coating composition is prepared by mixing together
the following:
Pigment dispersion fxom A above 400.0 g.
Polyester Blend from Example IC 172.0 g.
Hexamethoxymethylmelamine18.8 g.
Toluene 12.0 g.
PTSA 120% in isopropanol)2.6 g.
C. Coating Composition Based on a
Copolyester Con-trol from Example ID
A coating composition is prepared by mixing together
the following:
lU~ Pigment dispersion from A above 400.0 g.
Copolyester Control from Example ID 169.1 g~
Hexamethoxymethylmelamine~ 18.8 g.
Toluene 12~0 g.
PTSA (20~ in lsopropanol~~.6 g.
D Preparation of Coatings
The compositions from B and C above are applied to
cold--rolled steel panels, treated with an iron phosphate con-
version coating, by spraying and are cured at 163C for 30
min. The tabulation below shows that the coating composition
20 of this invention has ~xcellent stain and sQlvent resistance
while the control fails to meet minimum requirements.
,~
, .
- 16 -
i~
~t3~ 5
Coating Composition Based On:
Test B C (control)
Pencil hardness 4H 2H
Solvent resistance ~as measured
by pencil hardness testing
immediately after 50 double
rub~ with methyl ethyl ketone) 4H F
Direct impact resistance
30 inch pound 10 10
40 inch pound 10 9~5 (some cracking)
50 inch pound 10 9.5 (some cracking)
Reverse impact resistance
30 inch pound 9.0 9.0
40 inch pound 9.0 8.5 (cracking,
delamination)
50 inch pound 8~5 8.5 (crackiny,
delamination~
Stain resistance(l)
.
mustard 10
lipstick 10 9
orange dye 10 8
Test carried out by placing staining agent on coating for
a 72-hour period, followed by washing with soap and water.
The coating i~ rated immediately after the washing. A value
of 10 indicates no effect by the staining agent. Minimum
aaceptable value for most applications is 9.5.
11 --
EXAMPLE II_
A. Prepara~ion of a Polyester from Neopentyl
~ Iso-Dhthalic Acid - Control
The procedure of Example IA is repeated, substituting
neopentyl glycol (NPG) for TMPD. The -Einal product is a
semi-solid at room temperature.
B. Preparation of a Polyester ~rom Neopentyl
Glycol and a ~ixture of Dlmethyl Aliphatic
Carboxvlates Control
__
The procedure of Example IB is repea~ed, substituting
neopentyl glycol for TMPD~ The final product is quite viscous
and crystals are deposited upon standlng at room temperature.
C. Coating Composition Based on Control
Polyester A ' ' ''' ' ' '''''
A coating composition is prepared by mixing together
the pigment dispersion from Example IIA, 2643~0; the NPG ~ based
polyester from ~ above, 1078.9 g.; an epoxy resin (available
from Shell Chemical CoO as EPON* 828), 71.0 g. hexamethoxymethyl
melamine, 124.1 g., and amyl acetate, 83.4 g. The final volume
soli~s i5 80%.
D. Coating Composition Based on Control
Polyester B''' ''' '''' ''
A coating composition is prepared as above but
substituting the NP& - based po3yester prepared in B above.
The final volume solids is 80%~
* denotes trade mark
- 18
~,0~."
~3~
E. Comparison oE Control Coating Compositions
from C and D above with Coating Compositions
Based on Polyes_ers from Example IA and_B
Coating compositions ~ased on polyesters from
Example IA and B are prepared as in C above utili~ing the
individual polyester components from Ex~mple IA and IB.
A comparison of these coating compositions, at 80% volume
solids, with the control compositions prepared in C and D
above, at the same volume solids, shows that the latter
. 10 are very viscous and thereafter are unsuitable, when blended,
as high solids coating compositions in most applications:~
Viscosity (cps, BrookEield,
. 2 rpm, 32C.)
TMPD~IPA-based ~Ex. IIIE)580 (~3 spindle)
NPG/IPA-based (control, Ex. IIIC) 2750 ~#3 spindle).
; ~ .
TMPD/aliphatic diesters (Ex.IIIE) 180 (~1 spindle) ; -~
: NPG/aliphatic diesters ~controlj 310 (~1 spindle)
- Ex.IIID)
., ~ ~
'
-- 19 --
