Note: Descriptions are shown in the official language in which they were submitted.
BRANCHED POLYESTER POLYMERS
AND SOFT TOUCH COATINGS COMPRISING THE SAME
FIELD OF THE INVENTION
[0002] The present invention relates to crosslinkable branched polyester
polymers
prepared by free radical polymerization of the double bonds of a first
unsaturated
polyester prepolymer and a second unsaturated polyester prepolymer. The
polyester
polymers have a Tg of 25 C or less. The present invention further relates to
coatings
comprising such polyesters and substrates to which such coatings are applied;
the
coating, when cured, imparts a soft touch to the substrate.
BACKGROUND OF THE INVENTION
[0003] Conventional linear and branched polyester resins produced by the
polycondensation of different combinations of polyols and polyacids have been
widely used in the coatings industry. They have been used to coat a wide range
of
metallic and non-metallic substrates used in a number of different industries.
These
industries particularly include those in which flexible coatings are desired.
Particularly suitable examples include substrates used in the packaging
industry, coil
coatings, and certain industrial and automotive coatings. It is often desired
that
coatings have a particular "touch feel"; in the consumer electronics industry,
for
example, it is often desired to have a coating with a "soft feel" or "soft
touch". A
soft touch coating can impart a range of touch feel, for example, a velvety
feel, a
silky feel, or a rubbery feel, to a substrate. Notwithstanding the feel of the
coating, it
would also be desired that the coating have at least some degree of resistance
to
abrasion, marring, scratching and/or staining. Soft touch coatings having
acceptable
performance properties are therefore desired.
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SUMMARY OF THE INVENTION
[0004] The present invention is directed to a crosslinkable branched polyester
polymer prepared by free radical polymerization of a double bond of a first
unsaturated polyester prepolymer and a double bond of a second unsaturated
polyester
prepolymer, wherein each prepolymer independently comprises: a) a polyol
segment;
and b) an unsaturated polycarboxylic acid and/or an anhydride and/or ester
thereof;
wherein the branched polyester polymer has a Tg of 25 C or less. Coatings
comprising such polyesters are also within the scope of the present invention,
as are
substrates coated at least in part with such coatings.
DETAILED DESCRIPTION OF THE INVENTION
[0005] The present invention is directed to crosslinkable branched polyester
polymers generally comprising a reaction product of prepolymers, which
prepolymers
are the reaction product of components comprising a polyol segment and an
unsaturated polycarboxylic acid and/or an anhydride and/or ester thereof The
prepolymers are unsaturated polyesters, and are sometimes referred to herein
as an
"unsaturated polyester prepolymer", "prepolymer" or like terms. Free radical
initiators are used to initiate polymerization through the unsaturation of the
unsaturated polyester prepolymers, thereby resulting in a branched polyester.
The
branched polyester is crosslinkable, which means that it can undergo
crosslinking
with another compound. That is, the polyester has functionality that will
react with
functionality on another compound, such as a crosslinker. Reaction of the
unsaturation of the prepolymers results in the crosslinkable branched
polyester. This
polyester is a polymer. It is not a cured coating. The present invention is
therefore
distinct from art in which crosslinking the points of unsaturation on monomers
and/or
polymers results in a cured coating.
[0006] The unsaturated polyester prepolymer comprises a polyol segment.
"Polyol"
and like terms, as used herein, refers to a compound having two or more
hydroxyl
groups. The polyol used to form the polyol segment is sometimes referred to
herein
as the "polyol segment monomer". Polyols can be chosen to contribute softness
to the
prepolymer. Polyols can also contribute hardness, however, so the polyol(s)
used and
amount of each should be selected so that the unsaturated prepolymers, when
reacted,
result in a branched polyester having a Tg of 25 C or less. Suitable polyols
for use in
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the invention may be any polyol or mixtures thereof known for making
polyesters.
Examples include, but are not limited to, alkylene glycols, such as ethylene
glycol,
propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, hexylene glycol, polyethylene glycol, polypropylene
glycol and
neopentyl glycol; hydrogenated bisphenol A; cyclohexanediol; propanediols
including
1,2-propanediol, 1,3-propanediol, butyl ethyl propanediol, 2-methyl-1,3-
propanediol,
and 2-ethy1-2-buty1-1,3-propanediol; butanediols including 1,4-butanediol, 1,3-
butanediol, and 2-ethyl-1,4-butanediol; pentanediols including trimethyl
pentanediol
and 2-methylpentanediol; cyclohexanedimethanol; hexanediols including 1,6-
hexanediol; caprolactonediol (for example, the reaction product of epsilon-
caprolactone and ethylene glycol); hydroxy-alkylated bisphenols; polyether
glycols,
for example, poly(oxytetramethylene) glycol; trimethylol propane,
pentaerythritol, di-
pentaerythritol, trimethylol ethane, trimethylol butane, dimethylol
cyclohexane,
glycerol and the like. Suitable unsaturated polyols for use in the invention
may be
any unsaturated alcohols containing two or more hydroxyl groups. Examples
include,
but are not limited to, trimethylol propane monoallyl ether, trimethylol
ethane
monoallyl ether and prop-1-ene-1,3-diol. The polyol segment can also comprise
some
mono-ol, such as up to 10 weight (N), or 5 weight %, based on the total weight
of the
polyol segment. In certain embodiments, the polyol segment comprises 10 to 90
weight % of the polyester prepolymer, such as 30 to 50 weight %. The percent
of
polyol in the prepolymer can vary widely depending on the molecular weight of
the
polyol segment.
[0007] The unsaturated polyester prepolymer further comprises an unsaturated
polycarboxylic acid/anhydride/ester. Suitable unsaturated polyacids for use in
the
invention may be any unsaturated carboxylic acid containing two or more
carboxy
groups and/or an ester and/or anhydride thereof, or mixtures thereof. Examples
include, but are not limited to, maleic acid, fumaric acid, itaconic acid,
citraconic
acid, mcsaconic acid and teraconic acid, and/or esters and/or anhydrides
thereof.
Where the unsaturated polyacid is in the form of an ester, these esters may be
formed
with any suitable alcohol, such as Cl-C18 alkyl esters formed by reaction of a
Cl-
C18 alcohol (e.g. methanol, ethanol, 1-propanol, 1-butanol, 2-butanol,
isobutanol, 1-
pentanol, 1-pentanol and 1-hexonol) with the polyacid. A particularly suitable
unsaturated polyacid is maleic acid, maleic anhydride or a C1-C6 alkyl ester
of maleic
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acid. In certain embodiments the unsaturated polycarboxylic
acid/anhydride/ester
comprises 3 to 25 weight % of the polyester prepolymer, such as 5 to 20 weight
%.
[0008] The polyester prepolymer can further comprise one or more monomers that
contribute to the overall properties of the polyester, including "softness".
For
example, one or more monomers that contribute a "soft segment" can be used
with the
one or more polyols and one or more unsaturated polycarboxylic
acids/anhydrides/esters. As used herein, "soft segment" and like terms refers
to a
monomer or residue thereof or mixtures thereof that contribute flexibility to
the
prepolymer, and can help to obtain the desired Tg and/or viscosity of the
branched
polyester. The soft segment can be the residue of, for example, a polyacid.
"Polyacid" and like terms, as used herein, refers to a compound having two or
more
acid groups and includes the ester and/or anhydride of the acid. Such acids
can
include, for example, linear acids that impart flexibility. Examples include
but are not
limited to saturated polyacids such as adipic acid, azelaic acid, sebacic
acid, succinic
acid, glutaric acid, decanoic diacid, dodecanoic diacid and esters and
anhydrides
thereof. Suitable monoacids include CI-CB aliphatic carboxylic acids such as
acetic
acid, propanoic acid, butanoic acid, hexanoic acid, oleic acid, linoleic acid,
undecanoic acid, lauric acid, isononanoic acid, other fatty acids, and
hydrogenated
fatty acids of naturally occurring oils; and/or esters and/or anhydrides of
any of these.
[0009] In certain embodiments, one or more additional acids can also be used.
For
example, the additional acid can be an aromatic acid or a cycloaliphatic acid,
suitable
examples of which include, but are not limited to, phthalic acid, isophthalic
acid, 5-
tert-butylisophthalic acid, tetrachlorophthalic acid, benzoic acid, t-
butylbenzoic acid,
tetrahydrophthalic acid, naphthalene polycarboxylic acid, terephthalic acid,
hexahydrophthalic acid, methylhexahydrophthalic acid, dimethyl terephthalate,
cyclohexane dicarboxylic acid, chlorendic anhydride, 1,3-cyclohexane
dicarboxylic
acid, 1,4-cyclohexane dicarboxylic acid, tricyclodecane polycarboxylic acid,
endomethylene tetrahydrophthalic acid, endoethylenc hexahydrophthalic acid,
cyclohexanetetra carboxylic acid, cyclobutane tetracarboxylic acid and esters
and
anhydrides thereof and/or combinations thereof. It will be appreciated that
some of
the additional acids listed above may impart rigidity to the branched
polyester and
therefore cause the Tg of the branched polyester to increase. When one or more
of
the above acids are used, therefore, the acids used and amounts of each acid
should be
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selected so that, when the prepolymers are reacted, the branched polyester has
a Tg of
25 C or less.
[0010] Other monomer components can also be used in formation of the
prepolymer
to impart one or more additional properties to the branched polyester and/or
coating
comprising the same. For example, phthalic anhydride can be included, such as
in
amounts of 2 to 20 weight % of the prepolymer; phthalic anhydride might impart
greater stain resistance to the coating. In addition, copolymerization of the
unsaturated prepolymer with PDMS silmer acryl ate could impart flexibility
and/or
improve fingerprint resistance in the final coating. Such silmer acrylate
monomer can
be used in any suitable amount, such as 0.1 to 10 wt %. Fatty diacids could be
added
to increase hydrophobicity, while a polyether such as poly THF could be used
to
make the branched polyester more hydrophilic.
[0011] The unsaturated polyester prepolymer can be prepared by any means known
in the art. In one embodiment, a soft segment and polyol segment are
prereacted to
form what is sometimes referred to herein as a "polyol prepolymer", and then
further
reacted with the unsaturated polycarboxylic acid/anhydride/ester. In another
embodiment, the polyol segment and unsaturated polycarboxylic
acid/anhydride/ester
are reacted together either with or without the soft segment. The polyol is
typically in
excess as compared to the soft segment when a soft segment is included. For
example, the ratio of reactive groups on the soft segment monomer to reactive
groups
on the polyol segment monomer may be 1:2, 2:3 or even higher. The higher the
ratio,
the higher the molecular weight of the reaction product. Because an excess of
polyol
is used, the reaction product has terminal hydroxyl functionality. This
functionality
remains unreacted in the preparation of the branched polyester, thereby
rendering the
polyester "crosslinkable" with another compound. Similarly, when a soft
segment is
not used, the prepolymer has terminal hydroxyl or acid functionality that can
be
crosslinked with another compound.
[0012] As noted above, according to the present invention, the Tg of the
crosslinkable, branched polyester is 25 C or less. In certain embodiments, the
Tg of
the prepolymers reacted to form the branched polyester is also 25 C or less.
In other
embodiments, the Tg of one or more prepolymers may be greater than 25 C while
the
Tg of one or more prepolymers may be 25 C or less, such that, when reacted,
the
resulting branched polyester has a Tg of 25 C or less.
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[0013] Following formation of the unsaturated polyester prepolymers, the
prepolymers are then polymerized in the presence of a free radical initiator.
That is,
the unsaturation on a first polyester prepolymer is reacted with the
unsaturation on a
second polyester prepolymer. It will be appreciated that reaction occurs
through free
radical polymerization. Any free radical initiator typically used to initiate
the
polymerization of unsaturated compounds containing double bonds may be used in
the free radical polymerization. For example, the free radical initiator can
be an azo
initiator or a peroxide initiator, such as tert-butyl peroxy-2-ethylhexanoate,
tert-butyl
peroxybenzoate or dibenzoyl peroxide. The ratio of initiator to unsaturated
acid/anhydride/ester may be varied depending upon the degree of branching of
the
chains of the polyester that is desired. For example, the molar ratio of the
initiator to
the double bonds may be 0.001 to 1.0, such as 0.01 to 0.9 or 0.5 to 1.
[0014] If a higher amount of initiator is used, the more branching will be
achieved.
Increased branching typically means higher functionality in the polyester. In
certain
embodiments, a lower amount of initiator may be used, such as 0.1, so as to
minimize
the amount of branching and retain some unsaturation in the polyester. Such
embodiment might provide particularly desirable flexibility in the final
coating.
[0015] Unsaturation from one acid/anhydride/ester moiety in the prepolymer
reacts
with the unsaturation of another prepolymer. The result is a branched
polyester
polymer. At least some if not all of the branches will have terminal hydroxyl
groups.
There may also be pendant functionality in the branched polyester as well,
depending
on the starting materials used. Typically, when initiator is used in
conjunction with
unsaturated acid/anhydride/esters, a linear polymer results. It was therefore
a very
surprising and unexpected result to achieve a branched polyester according to
the
present invention. It will be appreciated that the branching in the present
invention is
predominantly achieved through reaction of the unsaturation. It is possible to
contribute a minor degree of branching through the use of a tri- or tetra-ol,
although
the amount of such compound should be selected to avoid gellation. It will be
appreciated that the present methods for achieving branching through the use
of
polymerizing the unsaturation of a polycarboxylic acid and polyesters
resulting
therefrom are quite unique when compared with conventional branched
polyesters,
such as those made through the use of tri- or tetra-ols.
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[0016] In certain embodiments, the present branched polyesters have a degree
of
branching or Mark-Howink parameter of less that 0.58, such as 0.50 or less or
0.48 or
less as measured by triple detector GPC.
[0017] Depending upon the degree of control of the polymerization that is
desired,
the initiator can be added in different portions at different times. For
example, all of
the free radical initiator may be added at the start of the reaction, the
initiator may be
divided into portions and the portions added at intervals during the reaction,
or the
initiator may be added as a continuous feed. It will be appreciated that the
addition of
initiator at set intervals or in a continuous feed will result in a more
controlled process
than adding all of the initiator at the start. In certain embodiments, the
initiator is
added over 10 minutes, until the molecular weight of the polyester doubles or
triples.
The free radical polymerization can be conducted under various conditions
allowing
for parameters such as the molecular weight of the branched polyester, the
degree of
functionality, the amount of branching and the like to be controlled so as to
obtain the
branched polyester that gives the desired feel and properties to the final
coating.
[0018] Regardless of the manner in which the polyester prepolymer is made,
whether a polyol prepolymer is formed first or a soft segment monomer, if
used, and
polyol segment monomer are reacted directly with the polycarboxylic
acid/anhydride/ester, how and when the initiator is added, and the like, the
resulting
branched polyester will actually be a mixture of polyesters with varying
degrees of
unsaturation, chain length, branching and the like. Some of the resulting
product may
even be a monoester, but is still encompassed by the term "polyester" as used
herein.
[0019] The temperature at which the free radical polymerization reaction is
conducted may be varied depending on factors such as the composition of the
unsaturated acid/anhydride/ester, the polyol segment monomer, the soft segment
monomer, if used, the initiator, the solvent and the properties that are
desired in the
polyester. Typically, the free radical polymerization is conducted at a
temperature of
from 50 C to 150 C. In a typical polymerization, such as an acrylic
polymerization,
the higher temperature results in a higher concentration of free radical
initiator, which
in turn results in more chains being polymerized, each with a relatively low
molecular
weight. It has been surprisingly discovered in the present system,
particularly when
maleic is used, the higher the initiator concentration, the higher the
molecular weight
of the resulting polymer. This is a surprising result as those skilled in the
art would
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not have expected the present polymerization to occur. Too much initiator,
however,
can lead to gellation. In certain embodiments, therefore, the polyester of the
present
invention is ungelled.
[0020] While any means can be used to effect the polymerization, for ease of
handling, the free radical polymerization can be performed using solutions of
the
unsaturated acid/anhydride/ester and polyol prepolymer (or soft segment
monomer
and polyol segment monomer). Any solvent may be used, as long as it is able to
dissolve the components including the free radical initiator to a sufficient
degree to
allow the polymerization to take place efficiently. Typical examples of
suitable
solvents include butyl glycol, propylene glycol mono methyl ether, methoxy
propyl
acetate and xylene. Preparation of the polyester in solvent is sometimes
referred to
herein as a "solvent-based system", which means that greater than 50%, such as
up to
100%, of the solvent is an organic solvent, and less than 50% of the solvent,
such as
less than 20%, less than 10%, less than 5%, or less than 2% of the solvent is
water.
[0021] Alternatively, the polyester can be prepared in a water-based system. A
"water-based system" is one in which greater than 50%, such as up to 100%, of
the
solvent is water, and less than 50% of the solvent, such as less than 20%,
less than
10%, less than 5%, or less than 2% of the solvent is an organic solvent. In
certain
embodiments, however, the polymerization is done without solvent; that is, all
steps
from making the prepolymer to making the polyester, can be done in the absence
of
solvent.
[0022] In any of the solvent-based systems, the water-based system, or solvent-
free
system, the resulting polyester can be a liquid, such as a viscous liquid.
[0023] As noted above, the branched polyesters of the present invention are
formed
by free radical polymerization via the double bonds of a first and second
unsaturated
polyester prepolymer. The first and second prepolymers can be the same or
different.
In certain embodiments, two or more different unsaturated polyester
prepolymers can
be reacted together. "Different", in this context, means that one or more
components
used in the unsaturated polyester prepolymers and/or the amount of one or more
components used in the unsaturated polyester prepolymers can be different. For
example, polyester according to the present invention can be prepared using
polyol
prepolymers comprised of the same components, while in other embodiments they
can be prepared by using two or more polyol prepolymers that are formed by
different
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components. That is, a first polyol prepolymer comprising a terminal hydroxyl
group
and a second polyol prepolymer comprising a terminal hydroxyl group are
reacted
with an unsaturated acid/anhydride/ester; the components used to make the
first and
second prepolymers can be different, and/or can have one or more different
components and/or can have one or more different amounts if the same
components
are used. In this embodiment, the resulting polyester is likely to have random
units
derived from each type of prepolymer used. Thus, the present invention
encompasses
polyesters prepared by prepolymers having the same or different polyol
segments
monomers, and/or unsaturated acids/anhydrides/esters and/or the same or
different
amounts of any of these; moreover, each of the prepolymers can have the same
or
different soft monomers and/or additional acid monomers and/or the same or
different
amounts of any of these. Use of different polyol prepolymers, soft segment
monomers, polyol segment monomers, additional monomers, unsaturated
acids/anhydrides/esters and/or amounts of any of these may result in
polyesters
having different properties. In this manner, polyesters can be formed that
have a Tg
of 25 C or less and possibly other desirable properties deriving from the use
of the
particular components used in the prepolymers.
[0024] In particularly suitable embodiments, prepolymers used according to the
present invention comprise adipic acid (soft segment) such as in an amount of
10 to
60 weight %, 2-methyl-1,3-propanediol (polyol segment) such as in an amount of
0 to
50 weight %, and maleic anhydride, such as in an amount of up to 25 weight %,
such
as 5 to 20 weight %, with weight % based on total monomer weight in the
prepolymer. Additional monomer can also be used, such as isophthalic acid or
terephthalic acid, phthalic acid, succinic acid, and neopentyl glycol.
[0025] As noted above, the branched polyester is formed by using free radical
polymerization, wherein the unsaturation of the polycarboxylic
acid/anhydride/ester
moieties in the prepolymers polymerize. In certain embodiments as noted above,
the
reaction is run such that substantially all of the unsaturation is reacted in
the formation
of the branched polyester, while in other embodiments the resulting polyester
also
comprises some degree of unsaturation. For example, the resulting polyester
can
comprise enough unsaturation to render the polyester reactive with other
functional
groups through the points of unsaturation.
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[0026] Because the branched polyester according to the present invention is
formed
primarily through the free radical polymerization of the unsaturation in the
prepolymers, the terminal hydroxyl groups will remain unreacted in the
branched
polyester of the present invention. These unreacted hydroxyl groups can then
be
crosslinked with another component. Thus, the present invention is distinct
from art
in which gelled polyesters, that is extensively networked polyesters, arc
formed. The
present polyesters are thermoset, and therefore also distinct from art that
teaches
thermoplastic polyesters.
[0027] In certain embodiments it may be desirable to convert some or all of
the
hydroxyl functionality on the unsaturated polyester prepolymer before
polymerization
takes place, and/or on the branched polyester, to another functionality. For
example,
the hydroxyl can be reacted with a cyclic anhydride to result in acid
functionality.
Acid esters can also be formed.
[0028] In certain other embodiments, the unsaturated polyester prepolymer may
comprise linkages in addition to the ester linkages. For example, the
polyester
prepolymer may further comprise one or more urethane linkages. Urethane
linkages
could be introduced by reacting an excess of the polyol prepolymer or the
unsaturated
polyester polymer with a polyisocyanate. The resulting unsaturated polyester
prepolymer will still have terminal functionality and unsaturation, but will
have
urethane linkages in addition to ester linkages. Other chemistries could also
be
introduced. Accordingly, in certain embodiments, the unsaturated polyester
prepolymer comprises one ore more linkages in addition to ester linkages.
[0029] In certain other embodiments, the use of unsaturated monomers other
than
the unsaturated polyacid/anhydride/ester of the prepolymer product is
excluded. For
example, the use of vinyl monomers such as (meth)acrylates, styrene, vinyl
halides
and the like can be excluded in certain embodiments. In such embodiments, PDMS
silmer acrylate can still be used if the double bond of the acrylate moiety is
reacted in
the formation of the prepolymer. Similarly, or any other acrylate or
methacrylate
containing monomer or polymer can be used if the double bond of the acrylate
moiety
is reacted in the formation of the prepolymer. That is, the acrylate double
bond is
reacted and therefore unavailable to react with the unsaturation of a second
prepolymer during free radical polymerization. It will be appreciated that the
present
branched polyesters are not polyester/acrylic graft copolymers, which are
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known in the art and are not formed by reaction of unsaturation on first and
second
polyester prepolymers.
[0030] In certain embodiments, the present polyesters specifically exclude
polyesters prepared from prepolymers that are formed by the reaction with
aldehydes;
thus, in this embodiment, acyl succinic acid polyesters are specifically
excluded.
Similarly, use of aldehyde in the solvent is specifically excluded in certain
embodiments of the invention.
[0031] The branched polyesters of the present invention can have a relatively
high
molecular weight and functionality as compared to conventional linear
polyester
resins. Typically, the ratio of the weight average molecular weight ("Mw") of
the
branched polyester of the present invention to the Mw of the unsaturated
polyester
prepolymer is from 1.2 to 100, such as 4 or 5 to 50, although in certain
embodiments,
it can be as higher.
[0032] In certain embodiments, the polyester prepolymers can have an Mw of
1,000
to 50,000, such as 5,000 to 10,000 or 7,000 to 8,000. In addition, the final
branched
polyester can have an Mw in the range of 2,000 to 100,000, such as 4,000-
10,000.
The prepolymer Mw can be related to the properties of the branched polyester
as well
as a coating comprising the polyester. For example, a branched polyester with
an Mw
at the lower end of the range, such as less than 10,000, might give a higher
crosslink
density or hardness in the coating as there would be higher functionality, and
might
have better flow and lower viscosity, while a branched polyester with an Mw
higher
than 10,000 might provide a coating with a lower crosslink density or
hardness, but
with a different touch feel.
[0033] In certain embodiments, the equivalent weight of the polyester is 1000
or
less. Equivalent weight is the Mw divided by the average functionality.
Equivalent
weight contributes to the crosslink density, which, as noted above, may affect
the
properties of soft touch coatings. For example, a higher equivalent weight may
give a
lower crosslink density.
[0034] In addition to the molecular weight described above, the branched
polyesters
of the present invention can also have a relatively high functionality; in
some cases
the functionality is higher than would be expected for conventional polyesters
having
such molecular weights. The average functionality of the polyester can be 2.0
or
greater, such as 2.5 or greater, 3.0 or greater, or even higher. "Average
functionality"
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as used herein refers to the average number of functional groups on the
branched
polyester. The functionality of the branched polyester is measured by the
number of
hydroxyl groups that remain unreacted in the branched polyester, and not by
the
unreacted unsaturation. In certain embodiments, the hydroxyl value of the
branched
polyesters of the present invention can be from 10 to 500 mg KOH/gm, such as
30 to
250 mg KOH/gm. In certain embodiments, the present branched polyesters will
have
both high Mw and high functionality, such as a Mw of? 15,000, such as 20,000
to
40,000, or higher than 40,000, and a functionality of? 100 mg KOH/gm.
[0035] Because the polyester of the present invention comprises functionality,
it is
suitable for use in coating formulations in which the hydroxyl groups (and/or
other
functionality) are crosslinked with other resins and/or crosslinkers typically
used in
coating formulations. Thus, the present invention is further directed to a
coating
comprising a branched polyester according to the present invention and a
crosslinker
therefor. The crosslinker, or crosslinking resin or agent, can be any suitable
crosslinker or crosslinking resin known in the art, and will be chosen to be
reactive
with the functional group or groups on the polyester. It will be appreciated
that the
coatings of the present invention cure through the reaction of the hydroxyl
groups
and/or other functionality and the crosslinker and not through the double
bonds of the
polycarboxylic acid/anhydride/ester moiety, to the extent any such
unsaturation exists
in the branched polyester.
[0036] Non-limiting examples of suitable crosslinkers include phenolic resins,
amino resins, epoxy resins, isocyanate resins, beta-hydroxy (alkyl) amide
resins,
alkylated carbamate resins, polyacids, anhydrides, organometallic acid-
functional
materials, polyamines, polyamides, aminoplasts and mixtures thereof In certain
embodiments, the crosslinker is a phenolic resin comprising an alkylated
phenol/formaldehyde resin with a functionality > 3 and difunctional o-
cresol/formaldehyde resins. Such crosslinkers are commercially available from
Hexion as BAKELITE 6520LB and BAKELITE 7081LB.
[0037] Suitable isocyanates include multifunctional isocyanates. Examples of
multifunctional polyisocyanates include aliphatic diisocyanates like
hexamethylene
diisocyanate and isophorone diisocyanate, and aromatic diisocyanates like
toluene
diisocyanate and 4,4'-diphenylmethane diisocyanate. The polyisocyanates can be
blocked or unblocked. Examples of other suitable polyisocyanates include
12
isocyanurate trimers, allophanates, and uretdiones of diisocyanates and
polycarbodiimides such as those disclosed in United States Patent 8,389,113.
Suitable polyisocyanates are well known in the art and widely available
commercially.
For example, suitable polyisocyanates are disclosed in United States Patent
Number
6,316,119 at columns 6, lines 19-36. Examples of commercially available
polyisocyanates include DESMODUR VP2078 and DESMODUR N3390, which are
sold by Bayer Corporation, and TOLONATE HDT90, which is sold by Rhodia Inc.
[0038] Suitable aminoplasts include condensates of amines and/or amides with
aldehyde. For example, the condensate of melamine with formaldehyde is a
suitable
aminoplast. Suitable aminoplasts are well known in the art. A suitable
aminoplast is
disclosed, for example, in United States Patent Number 6,316,119 at column 5,
lines
45-55.
[0039] In preparing the present coatings, the branched polyester and the
crosslinker
can be dissolved or dispersed in a single solvent or a mixture of solvents.
Any solvent
that will enable the formulation to be coated on a substrate may be used, and
these will
be well known to the person skilled in the art. Typical examples include
water,
organic solvent(s), and/or mixtures thereof. Suitable organic solvents include
glycols,
glycol ether alcohols, alcohols, ketones, and aromatics, such as xylene and
toluene,
acetates, mineral spirits, naphthas and/or mixtures thereof "Acetates" include
the
glycol ether acetates. In certain embodiments, the solvent is a non-aqueous
solvent.
"Non-aqueous solvent" and like terms means that less than 50% of the solvent
is
water. For example, less than 10%, or even less than 5% or 2%, of the solvent
can be
water. It will be understood that mixtures of solvents, including or excluding
water in
an amount of less than 50%, can constitute a "non-aqueous solvent". In other
embodiments, the coating is aqueous or water-based. This means that 50% or
more of
the solvent is water. These embodiments have less than 50%, such as less than
20%,
less than 10%, less than 5% or less than 2% solvent.
[0040] In certain embodiments, the coatings of the present invention further
comprise a curing catalyst. Any curing catalyst typically used to catalyze
crosslinking
reactions between polyester resins and crosslinkers, such as phenolic resins,
may be
used, and there are no particular limitations on the catalyst. Examples of
such a curing
catalyst include dibutyltin dilaurate, phosphoric acid, alkyl aryl sulphonic
acid,
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dodecyl benzene sulphonic acid, dinonyl naphthalene sulphonic acid, and
dinonyl
naphthalene disulphonic acid.
[0041] It will be appreciated that a number of factors should be balanced to
give the
desired "touch" to the final coating. As noted above, monomer selection and
content
may play a role, as might Mw, equivalent weight, and degree of branching. The
Tg of
the branches can be decreased so as to increase the "soft touch" quality of
the coating.
In addition, the selection of crosslinker can also contribute to the soft
touch. For
example, the crosslinker and amount of crosslinker used can be selected to
give the
desired crosslink density, which, as noted above, relates to touch feel. In
certain
embodiments, the gloss of the coating at 600 is 0.5- 1.5.
[0042] If desired, the coating compositions can comprise other optional
materials
well known in the art of formulating coatings, such as colorants,
plasticizers, abrasion
resistant particles, anti-oxidants, hindered amine light stabilizers, UV light
absorbers
and stabilizers, surfactants, flow control agents, thixotropic agents,
fillers, organic
cosolvents, reactive diluents, catalysts, grind vehicles, slip agents and
other customary
auxiliaries.
[0043] As used herein, the term "colorant" means any substance that imparts
color
and/or other opacity and/or other visual effect, e.g. gloss, to the
composition. The
colorant can be added to the coating in any suitable form, such as discrete
particles,
dispersions, solutions and/or flakes. A single colorant or a mixture of two or
more
colorants can be used in the coatings of the present invention.
[0044] Example colorants include matting pigments, dyes and tints, such as
those
used in the paint industry and/or listed in the Dry Color Manufacturers
Association
(DCMA), as well as special effect compositions. A colorant may include, for
example, a finely divided solid powder that is insoluble but wettable under
the
conditions of use. A colorant can be organic or inorganic and can be
agglomerated or
non-agglomerated. Colorants can be incorporated into the coatings by grinding
or
simple mixing. Colorants can be incorporated by grinding into the coating by
use of a
grind vehicle, such as an acrylic grind vehicle, the use of which will be
familiar to one
skilled in the art.
[0045] Example pigments and/or pigment compositions include, but are not
limited
to, carbazole dioxazine crude pigment, azo, monoazo, disazo, naphthol AS, salt
type
(lakes), benzimidazolone, condensation, metal complex, isoindolinone,
isoindoline
14
and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo
pyrrole, thioindi go, anthraquinone, indanthrone, anthrapyrimidine,
flavanthrone,
pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone
pigments,
diketo pyrrolo pyrrole red ("DPPBO red"), titanium dioxide, carbon black,
carbon
fiber, graphite, other conductive pigments and/or fillers and mixtures thereof
The
terms "pigment" and "colored filler" can be used interchangeably.
[0046] Example dyes include, but are not limited to, those that are solvent
and/or
aqueous based such as acid dyes, azoic dyes, basic dyes, direct dyes, disperse
dyes,
reactive dyes, solvent dyes, sulfur dyes, mordant dyes, for example, bismuth
vanadate,
anthraquinone, perylene aluminum, quinacridone, thiazole, thiazine, azo,
indigoid,
nitro, nitroso, oxazine, phthalocyanine, quinoline, stilbene, and triphenyl
methane.
[0047] Example tints include, but are not limited to, pigments dispersed in
water-
based or water-miscible carriers such as AQUA-CHEM 896 commercially available
from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL
COLORANTS commercially available from Accurate Dispersions division of
Eastman Chemicals, Inc.
[0048] As noted above, the colorant can be in the form of a dispersion
including,
but not limited to, a nanoparticle dispersion. Nanoparticic dispersions can
include one
or more highly dispersed nanoparticle colorants and/or colorant particles that
produce
a desired visible color and/or opacity and/or visual effect. Nanoparticle
dispersions
can include colorants such as pigments or dyes having a particle size of less
than 150
nm, such as less than 70 nm, or less than 30 nm. Nanoparticles can be produced
by
milling stock organic or inorganic pigments with grinding media having a
particle size
of less than 0.5 mm. Example nanoparticle dispersions and methods for making
them
are identified in United States Patent Number 6,875,800 B2. Nanoparticle
dispersions
can also be produced by crystallization, precipitation, gas phase
condensation, and
chemical attrition (i.e., partial dissolution). In order to minimize re-
agglomeration of
nanoparticles within the coating, a dispersion of resin-coated nanoparticles
can be
used. As used herein, a "dispersion of resin-coated nanoparticles" refers to a
continuous phase in which is dispersed discreet "composite microparticles"
that
comprise a nanoparticle and a resin coating on the nanoparticle. Example
dispersions
of resin-coated nanoparticles and methods for making them are described, for
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example, in United States Patent Number 7,605,194 at column 3, line 56 to
column 16,
line 25.
[0049] Example special effect compositions that may be used include pigments
and/or compositions that produce one or more appearance effects such as
reflectance,
pearlescence, metallic sheen, phosphorescence, fluorescence, photochromism,
photosensitivity, thermochromism, goniochromism and/or color-change.
Additional
special effect compositions can provide other perceptible properties, such as
opacity or
texture. In a non-limiting embodiment, special effect compositions can produce
a
color shift, such that the color of the coating changes when the coating is
viewed at
different angles. Example color effect compositions are identified in United
States
Patent Number 6,894,086, incorporated herein by reference. Additional color
effect
compositions can include transparent coated mica and/or synthetic mica, coated
silica,
coated alumina, a transparent liquid crystal pigment, a liquid crystal
coating, and/or
any composition wherein interference results from a refractive index
differential
within the material and not because of the refractive index differential
between the
surface of the material and the air.
[0050] In certain non-limiting embodiments, a photosensitive composition
and/or
photochromic composition, which reversibly alters its color when exposed to
one or
more light sources, can be used in the coating of the present invention.
Photochromic
and/or photosensitive compositions can be activated by exposure to radiation
of a
specified wavelength. When the composition becomes excited, the molecular
structure is changed and the altered structure exhibits a new color that is
different from
the original color of the composition. When the exposure to radiation is
removed, the
photochromic and/or photosensitive composition can return to a state of rest,
in which
the original color of the composition returns. In one non-limiting embodiment,
the
photochromic and/or photosensitive composition can be colorless in a non-
excited
state and exhibit a color in an excited state. Full color-change can appear
within
milliseconds to several minutes, such as from 20 seconds to 60 seconds.
Example
photochromic and/or photosensitive compositions include photochromic dyes.
[0051] In a non-limiting embodiment, the photosensitive composition and/or
photochromic composition can be associated with and/or at least partially
bound to,
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such as by covalent bonding, a polymer and/or polymeric materials of a
polymerizable component. In contrast to some coatings in which the
photosensitive
composition may migrate out of the coating and crystallize into the substrate,
the
photosensitive composition and/or photochromic composition associated with
and/or
at least partially bound to a polymer and/or polymerizable component in
accordance
with a non-limiting embodiment of the present invention, have minimal
migration out
of the coating. Example photosensitive compositions and/or photochromic
compositions and methods for making them are identified in United States
Patent
8,153,344.
[0052] In general, the colorant can be present in any amount sufficient to
impart the
desired visual and/or color effect. The colorant may comprise from 1 to 65
weight
percent of the present compositions, such as from 3 to 40 weight percent or 5
to 35
weight percent, with weight percent based on the total weight of the
compositions.
[0053] An "abrasion resistant particle" is one that, when used in a coating,
will
impart some level of abrasion resistance to the coating as compared with the
same
coating lacking the particles. Suitable abrasion resistant particles include
organic
and/or inorganic particles. Examples of suitable organic particles include but
are not
limited to diamond particles, such as diamond dust particles, and particles
formed
from carbide materials; examples of carbide particles include but are not
limited to
titanium carbide, silicon carbide and boron carbide. Examples of suitable
inorganic
particles, include but are not limited to silica; alumina; alumina silicate;
silica
alumina; alkali aluminosilicate; borosilicate glass; nitrides including boron
nitride and
silicon nitride; oxides including titanium dioxide and zinc oxide; quartz;
nepheline
syenite; zircon such as in the form of zirconium oxide; buddeluyite; and
eudialyte.
Particles of any size can be used, as can mixtures of different particles
and/or different
sized particles. For example, the particles can be microparticles, having an
average
particle size of 0.1 to 50, 0.1 to 20, 1 to 12, 1 to 10, or 3 to 6 microns, or
any
combination within any of these ranges. The particles can be nanoparticles,
having an
average particle size of less than 0.1 micron, such as 0.8 to 500, 10 to 100,
or 100 to
500 nanometers, or any combination within these ranges.
[0054] Any slip agent can be used according to the present invention such as
those
commercial available from BYK Chemie or Dow Corning.
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[0055] In certain embodiments, the polyesters of the present invention are
used as
coating additives. For example, it has been discovered that the present
polyesters can
replace all or part of the sag control agent, such as cellulose esters, used
in coating
formulations comprising metallic flake. It will be appreciated that the
branched
polyester of the present invention and crosslinker therefor can form all or
part of the
film-forming resin of the coating. In certain embodiments, one or more
additional
film-forming resins are also used in the coating. For example, the coating
compositions can comprise any of a variety of thermoplastic and/or
thermosetting
compositions known in the art. The coating compositions may be water-based or
solvent-based liquid compositions, or alternatively, may be in solid
particulate form,
i.e. a powder coating.
[0056] Thermosetting or curable coating compositions typically comprise
film-forming polymers or resins having functional groups that are reactive
with either
themselves or a crosslinking agent. The additional film-forming resin can be
selected
from, for example, acrylic polymers, polyester polymers, polyurethane
polymers,
polyamide polymers, polyether polymers, polysiloxane polymers, copolymers
thereof,
and mixtures thereof. Generally, these polymers can be any polymers of these
types
made by any method known to those skilled in the art. Such polymers may be
solvent-borne or water-dispersible, emulsifiable, or of limited water
solubility. The
functional groups on the film-forming resin may be selected from any of a
variety of
reactive functional groups including, for example, carboxylic acid groups,
amine
groups, epoxide groups, hydroxyl groups, thiol groups, carbamate groups, amide
groups, urea groups, isocyanate groups (including blocked isocyanate groups)
mercaptan groups, and combinations thereof Appropriate mixtures of film-
forming
resins may also be used in the preparation of the present coating
compositions.
[0057] Thermosetting coating compositions typically comprise a crosslinking
agent
that may be selected from any of the crosslinkers described above. In certain
embodiments, the present coatings comprise a thermosetting film-forming
polymer or
resin and a crosslinking agent therefor and the crosslinker is either the same
or
different from the crosslinker that is used to crosslink the branched
polyester. In
certain other embodiments, a thettnosetting film-forming polymer or resin
having
functional groups that are reactive with themselves are used; in this manner,
such
thermosetting coatings are self-crosslinking.
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[0058] The coatings of the present invention may comprise 1 to 100, such as 10
to
90 or 20 to 80 weight %, with weight % based on total solid weight of the
coating, of
the branched polyester of the present invention. The coating compositions of
the
present invention may also comprise 0 to 90, such as 5 to 60 or 10 to 40
weight %,
with weight % based on total solids weight of the coating, of a crosslinker
for the
branched polyester. Additional components, if used, may comprise 1 weight %,
up to
70 weight %, or higher, with weight % based on total solids weight of the
coating.
[0059] Coating formulations according to the present invention can have a soft
touch and/or smooth feel when cured on a substrate. For example, the coating
can
have a softness as measured by the Fischer Micro-hardness test of 1 to 20
N/mm2,
such as 2 to 10 N/mm2. The coating can further have a coefficient of friction
as
measured by ASTM Method D1894 of 0.01 to 0.5, such as 0.05 to 0.2.
"Coefficient
of friction" refers to the ratio of the force that maintains contact between
an object
and a surface and the frictional force that resists the motion of the object.
The
coating, at 50 micron thickness, can have an abrasion resistance as measured
by
ASTM Method F2357 of 50 to 500 cycles, such as 250 to 500. The cured coating
can
also have a surface roughness of 1 pm to 80 pm, such as 10 [um to 60 pm, 20
[tm to 50
[tm, or 35 [tm to 45 pm as measured by a Taylor Hobson Precision Duo
Profilometer.
Surface roughness can be altered through formulation, such as through the use
of
additives, an example of which is silica. It will be appreciated by those
skilled in the
art that achieving this level of hardness, coefficient of friction, abrasion
resistance,
and surface roughness in the same coating is a remarkable accomplishment. The
result is a coating that is soft to the touch, but durable. While the
inventors believe
this combination of properties is achieved due to the branching of the
polyester, they
do not wish to be bound by any mechanism.
[0060] In certain embodiments, the prepolymers, the branched polyester and/or
the
coatings of the present invention, may be substantially free, may be
essentially free
and/or may be completely free of bisphenol A and derivatives or residues
thereof,
including bisphenol A ("BPA") and bisphenol A diglycidyl ether ("BADGE"). Such
prepolymers, branched polyesters andlor coatings are sometimes referred to as
"BPA
non intent" because BPA, including derivatives or residues thereof, are not
intentionally added but may be present in trace amounts because of impurities
or
unavoidable contamination from the environment. The prepolymers, branched
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polyesters and/or coatings can also be substantially free and may be
essentially free
and/or may be completely free of bisphenol F and derivatives or residues
thereof,
including bisphenol F and bisphenol F diglycidyl ether ("BFDGE"). The term
"substantially free" as used in this context means the prepolymers, branched
polyesters and/or coatings contain less than 1000 parts per million (ppm),
"essentially
free" means less than 100 ppm and "completely free" means less than 20 parts
per
billion (ppb) of any of the above mentioned compounds, derivatives or residues
thereof.
[0061] The present coatings can be applied to any substrates known in the art,
for
example, automotive substrates, industrial substrates, packaging substrates,
wood
flooring and furniture, apparel, electronics including housings and circuit
boards
including consumer electronics such as housings for computers, notebooks,
smartphones, tablets, televisions, gaming equipment, computer equipment,
computer
accessories, MP3 players, and the like, glass and transparencies, sports
equipment
including golf balls, and the like. These substrates can be, for example,
metallic or
non-metallic. Metallic substrates include tin, steel, tin-plated steel,
chromium
passivated steel, galvanized steel, aluminum, aluminum foil. Non-metallic
substrates
include polymeric, plastic, polyester, polyolefin, polyamide, cellulosic,
polystyrene,
polyacrylic, poly(ethylene naphthalate), polypropylene, polyethylene, nylon,
EVOH,
polylactic acid, other "green" polymeric substrates,
poly(ethyleneterephthalate)
("PET"), polycarbonate, polycarbonate acrylobutadiene styrene ("PC/ABS"),
polyamide, wood, veneer, wood composite, particle board, medium density
fiberboard, cement, stone, glass, paper, cardboard, textiles, leather both
synthetic and
natural, and the like. The substrate can be one that has been already treated
in some
manner, such as to impart visual and/or color effect.
[0062] The coatings of the present invention can be applied by any means
standard
in the art, such as electrocoating, spraying, electrostatic spraying, dipping,
rolling,
brushing, and the like.
[0063] The coatings can be applied to a dry film thickness of 0.04 mils to 4
mils,
such as 0.3 to 2 or 0.7 to 1.3 mils. In other embodiments the coatings can be
applied
to a dry film thickness of 0.1 mils or greater, 0.5 mils or greater 1.0 mils
or greater,
2.0 mils or greater, 5.0 mils or greater, or even thicker. The coatings of the
present
invention can be used alone, or in combination with one or more other
coatings. For
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example, the coatings of the present invention can comprise a colorant or not
and can
be used as a primer, basecoat, and/or top coat. For substrates coated with
multiple
coatings, one or more of those coatings can be coatings as described herein.
The
present coatings can also be used as a packaging "size" coating, wash coat,
spray coat,
end coat, and the like.
[0064] It will be appreciated that the coatings described herein can be either
one
component ("1K"), or multi-component compositions such as two component ("2K")
or more. A 1K composition will be understood as referring to a composition
wherein
all the coating components are maintained in the same container after
manufacture,
during storage, etc. A 1K coating can be applied to a substrate and cured by
any
conventional means, such as by heating, forced air, and the like. The present
coatings
can also be multi-component coatings, which will be understood as coatings in
which
various components are maintained separately until just prior to application.
As noted
above, the present coatings can be thermoplastic or thermosetting.
[0065] In certain embodiments, the coating is a clearcoat. A clearcoat will be
understood as a coating that is substantially transparent or translucent. A
clearcoat
can therefore have some degree of color, opacity provided it does not make the
clearcoat opaque or otherwise affect, to any significant degree, the ability
to see the
underlying substrate. The clearcoats of the present invention can be used, for
example, in conjunction with a pigmented basecoat. The clearcoat can be
foimulated
as is know in the coatings art.
[0066] In certain other embodiments the coating comprises a colorant, such as
a
pigmented basecoat used in conjunction with a clearcoat, or as a pigmented
monocoat.
Such coating layers are used, for example, in the automotive industry to
impart a
decorative and/or protective finish to a vehicle. "Vehicle" is used herein in
its
broadest sense and includes all types of vehicles, such as but not limited to
cars,
trucks, buses, vans, golf carts, motorcycles, bicycles, railroad cars and the
like. It will
be appreciated that the portion of the vehicle that is coated according to the
present
invention may vary depending on why the coating is being used. For example,
anti-
chip primers may be applied to some of the portions of the vehicle as
described above.
When used as a colored basecoat or monocoat, the present coatings will
typically be
applied to those portions of the vehicle that are visible such as the roof,
hood, doors
trunk lid and the like, but may also be applied to other areas such as inside
the trunk,
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inside the door and the like; they can also be applied to those portions of
the car that
are in contact with the driver and/or passengers, such as the steering wheel,
dashboard, gear shift, controls, door handle and the like. Clearcoats will
typically be
applied to the exterior of a vehicle.
[0067] In another embodiment, the present invention is directed to a substrate
coated at least in part with the coating of the present invention, wherein the
substrate
comprises a consumer electronic part. "Consumer electronic part" includes, for
example, any part or housing of computers, notebooks, smartphones, tablets,
televisions, gaming equipment, computer accessories, MP3 players, and the
like. The
coatings are typically applied to at least the exterior of the housing of such
equipment,
but may also be applied in whole or in part to the interior of such housing as
well.
The present coatings are particularly suitable for application to consumer
electronics
as they can provide the desired soft touch and durability.
[0068] Coil coatings, having wide application in many industries, are also
substrates
that can be coated according to the present invention; the present coatings
are
particularly suitable as coil coatings due to their unique combination of
flexibility and
hardness, as discussed above. Coil coatings also typically comprise a
colorant.
[0069] The coatings of the present invention are also suitable for use as
packaging
coatings. The application of various pretreatments and coatings to packaging
is well
established. Such treatments and/or coatings, for example, can be used in the
case of
metal cans, wherein the treatment and/or coating is used to retard or inhibit
corrosion,
provide a decorative coating, provide ease of handling during the
manufacturing
process, and the like. Coatings can be applied to the interior of such cans to
prevent
the contents from contacting the metal of the container. Contact between the
metal
and a food or beverage, for example, can lead to corrosion of a metal
container, which
can then contaminate the food or beverage. This is particularly true when the
contents
of the can are acidic in nature. The coatings applied to the interior of metal
cans also
help prevent corrosion in the headspace of the cans, which is the area between
the fill
line of the product and the can lid; corrosion in the headspace is
particularly
problematic with food products having a high salt content. Coatings can also
be
applied to the exterior of metal cans. Certain coatings of the present
invention are
particularly applicable for use with coiled metal stock, such as the coiled
metal stock
from which the ends of cans are made ("can end stock"), and end caps and
closures
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are made ("cap/closure stock"). Since coatings designed for use on can end
stock and
cap/closure stock are typically applied prior to the piece being cut and
stamped out of
the coiled metal stock, they are typically flexible and extensible. For
example, such
stock is typically coated on both sides. Thereafter, the coated metal stock is
punched.
For can ends, the metal is then scored for the "pop-top" opening and the pop-
top ring
is then attached with a pin that is separately fabricated. The end is then
attached to
the can body by an edge rolling process. A similar procedure is done for "easy
open"
can ends. For easy open can ends, a score substantially around the perimeter
of the lid
allows for easy opening or removing of the lid from the can, typically by
means of a
pull tab. For caps and closures, the cap/closure stock is typically coated,
such as by
roll coating, and the cap or closure stamped out of the stock; it is possible,
however,
to coat the cap/closure after formation. Coatings for cans subjected to
relatively
stringent temperature and/or pressure requirements should also be resistant to
popping, corrosion, blushing and/or blistering.
[0070] Accordingly, the present invention is further directed to a package
coated at
least in part with any of the coating compositions described above. In certain
embodiments, the package is a metal can. The term "metal can" includes any
type of
metal can, container or any type of receptacle or portion thereof used to hold
something. One example of a metal can is a food can; the term "food can(s)" is
used
herein to refer to cans, containers or any type of receptacle or portion
thereof used to
hold any type of food and/or beverage. Metal "bottles" that mimic the shape of
glass
bottles are also "metal cans" according to the present invention. The term
"metal
can(s)" specifically includes food cans and also specifically includes "can
ends",
which are typically stamped from can end stock and used in conjunction with
the
packaging of beverages. The term "metal cans" also specifically includes metal
caps
and/or closures such as bottle caps, screw top caps and lids of any size, lug
caps, and
the like. Metal cans can be used to hold other items as well as food and/or
beverage,
including but not limited to personal care products, bug spray, spray paint,
and any
other compound suitable for packaging in an aerosol can. The cans can include
"two-piece cans" and "three-piece cans" as well as drawn and ironed one-piece
cans;
such one-piece cans often find application with aerosol products. Packages
coated
according to the present invention can also include plastic bottles, plastic
tubes,
laminates and flexible packaging, such as those made from PE, PP, PET and the
like.
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Such packaging could hold, for example, food, toothpaste, personal care
products and
the like.
[0071] The coating can be applied to the interior and/or the exterior of the
package.
For example, the coating can be rollcoated onto metal used to make a two-piece
food
can, a three-piece food can, can end stock and/or cap/closure stock. In some
embodiments, the coating is applied to a coil or sheet by roll coating; the
coating is
then cured by radiation and can ends are stamped out and fabricated into the
finished
product, i.e. can ends. In other embodiments, the coating is applied as a rim
coat to
the bottom of the can; such application can be by roll coating. The rim coat
functions
to reduce friction for improved handling during the continued fabrication
and/or
processing of the can. In certain embodiments, the coating is applied to caps
and/or
closures; such application can include, for example, a protective varnish that
is
applied before and/or after formation of the cap/closure and/or a pigmented
enamel
post applied to the cap, particularly those having a scored seam at the bottom
of the
cap. Decorated can stock can also be partially coated externally with the
coating
described herein, and the decorated, coated can stock used to form various
metal cans.
[0072] Substrates coated according to the present invention can be coated with
any
of the compositions described above by any means known in the art, such as
spraying,
rolling, dipping, brushing, flow coating and the like; the coating may also be
applied
by electrocoating when the substrate is conductive. The appropriate means of
application can be determined by one skilled in the art based upon the type of
substrate being coated and the function for which the coating is being used.
The
coatings described above can be applied over the substrate as a single layer
or as
multiple layers with multiple heating stages between the application of each
layer, if
desired. After application to the substrate, the coating composition may be
cured by
any appropriate means.
[0073] As used herein, unless otherwise expressly specified, all numbers such
as
those expressing values, ranges, amounts or percentages may be read as if
prefaced by
the word "about", even if the term does not expressly appear. Also, any
numerical
range recited herein is intended to include all sub-ranges subsumed therein.
Singular
encompasses plural and vice versa. For example, although reference is made
herein
to "a" polyester, "a" branched polyester, "an" unsaturated
acid/anhydride/ester, "a"
polyol pre-polymer, "a" soft segment, "a" soft monomer, "a" polyol segment,
"a"
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polyol segment monomer, "a" prepolymer, "a" crosslinker, and the like, one or
more
of each of these and any other components can be used. As used herein, the
term
"polymer" refers to oligomers and both homopolymers and copolymers, and the
prefix
"poly" refers to two or more. Including, for example and like terms means
including
for example but not limited to. When ranges are given, any endpoints of those
ranges
and/or numbers within those ranges can be combined within the scope of the
present
invention.
EXAMPLES
[0074] The following examples are intended to illustrate the invention and
should
not be construed as limiting the invention in any way.
[0075] Hardness was measured with the HM2000S Fischer Microhardness
Instrument following the instruction described in the Fischerscope HM2000
Manual.
Three measurements were conducted and the average hardness value was recorded
and reported.
[0076] Coefficient of Friction testing was conducted using a Dynisco 1055
Coefficient of Friction Tester, a Chatillion DGGS Force Gauge and a green felt
sled.
Five tests were run on each sample. Five measurements were conducted and the
average hardness value was recorded and reported.
[0077] Surface roughness was measured by a Taylor Hobson Precision Surtronic
Duo Profilometer, following the instructions provided by the manufacturer.
[0078] Abrasion resistance was measured according to ASTM Method F2357.
Example 1
[0079] A branched polyester according to the present invention was prepared as
follows. 650 grams of 2-methyl-1,3-propanediol, 177 grams of adipic acid, 287
grams of isophthalic acid, 179 grams of phthalic anhydride, 223 grams of
maleic
anhydride and 1.5 grams of butylstannoic acid were added to a 3-liter, 4-neck
round
bottom flask equipped with a stirrer, a steam-cooled column topped with a
distillation
head and a thermocouple. The contents were heated slowly under a flow of
nitrogen
gas. The contents of the flask were heated to about 95 C at which time they
were
melted and stirring was started. The batch was heated to 155 C at which time
water
began distilling. Heating was continued to a batch temperature of 220 C. 160
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of water was removed from the reaction. The final acid value of the resin was
measured as 3.8. The contents of the batch were cooled to 150 C and 316 grams
of
Aromatic 100 was added. The material in the flask was then cooled and poured
out.
The solids content was 81% by weight. The OH number of the resin was 50.2 at
81%
solids. The weight average molecular weight of the product was 5700 against a
polystyrene control. The Tg of the prepolymer was -11 C.
[0080] 988 grams of the above resin were placed in a 3-liter, 4-neck round
bottom
flask equipped with a stirrer, a water-cooled condenser, an addition funnel
and a
thermocouple. The contents of the flask were heated to 120 C. 2 grams of tert-
butyl
peroctoate and 153 grams of butyl acetate were mixed and placed into the
addition
funnel. The contents of the funnel were added to the flask over 10 minutes.
The
temperature of the reaction was maintained at 120 C for one hour. It was then
cooled
and the contents poured out. The final resin had a solids content of 70% by
weight.
The OH number of the resin was 41 at 70% solids. It had a weight average
molecular
weight of 7900 as measured against a polystyrene standard. The Tg of the
polyester
was -18 C as measured with Dynamic Scanning Calorimetry.
Example 2
[0081] A branched polyester according to the present invention was prepared as
follows. 650 grams of 2-methyl-1,3-propanediol, 282 grams of adipic acid, 166
grams of isophthalic acid, 179 grams of phthalic anhydride, 223 grams of
maleic
anhydride and 1.5 grams of butylstannoie acid were added to a 3-liter, 4-neck
round
bottom flask equipped with a stirrer, a steam-cooled column topped with a
distillation
head and a thermocouple. The contents were heated slowly under a flow of
nitrogen
gas. The contents of the flask were heated to about 95 C at which time they
were
melted and stirring was started. The batch was heated to 155 C at which time
water
began distilling. Heating was continued to a batch temperature of 220 C. 162
grams
of water was removed from the reaction. The final acid value of the resin was
measured as 6.1. The contents of the batch were cooled to 150 C and 313 grams
of
Aromatic 100 was added. The material in the flask was then cooled and poured
out.
The solids content was 81% by weight. The OH number of the resin was 43 at 81%
solids. The weight average molecular weight of the product was 6600 against a
polystyrene control and the Tg of the prepolyrner was -18 C.
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[0082] 988 grams of the above resin were placed in a 3-liter, 4-neck round
bottom
flask equipped with a stirrer, a water-cooled condenser, an addition funnel
and a
thermocouple. The contents of the flask were heated to 120 C. 2 grams of tert-
butyl
peroctoate and 153 grams of butyl acetate were mixed and placed into the
addition
funnel. The contents of the funnel were added to the flask over 10 minutes.
The
temperature of the reaction was maintained at 120 C for one hour. It was then
cooled
and the contents poured out. The final resin had a solids content of 71% by
weight.
The OH number of the resin was 32 at 71% solids. It had a weight average
molecular
weight of 9300 as measured against a polystyrene standard. The Tg of the
polyester
was -22 C as measured with Dynamic Scanning Calorimetry.
Example 3
[0083] A branched polyester according to the present invention was prepared as
follows. 650 grams of 2-methyl-1,3-propanediol, 711 grams of adipic acid, 152
grams of maleic anhydride and 1.5 grams of butylstannoic acid were added to a
3-
liter, 4-neck round bottom flask equipped with a stirrer, a steam-cooled
column
topped with a distillation head and a thermocouple. The contents were heated
slowly
under a flow of nitrogen gas. The contents of the flask were heated to about
112 C at
which time they were melted and stirring was started. The batch was heated to
173 C at which time water began distilling. Heating was continued to a batch
temperature of 220 C. A total of 196 grams of water was removed from the
reaction.
The final acid value of the resin was measured as 2.6. The contents of the
batch were
cooled to 150 C and 307 grams of Aromatic 100 was added. The material in the
flask
was then cooled and poured out. The solids content was 81% by weight. The OH
number of the resin was found to be 52 at 81% solids. The weight average
molecular
weight of the product was found to be 5700 against a polystyrene control. The
Tg of
the prepolymer was -47 C.
[0084] 982 grams of the above resin were placed in a 3-liter, 4-neck round
bottom
flask equipped with a stirrer, a water-cooled condenser, an addition funnel
and a
thermocouple. The contents of the flask were heated to 120 C. 2 grams of tert-
butyl
peroctoate and 158 grams of butyl acetate were mixed and placed into the
addition
funnel. The contents of the funnel were added to the flask over 10 minutes.
The
temperature of the reaction was maintained at 120 C for one hour. It was then
cooled
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and the contents poured out. The final resin had a solids content of 71% by
weight.
The OH number of the resin was found to be 50 at 71% solids. It had a weight
average molecular weight of 6700 as measured against a polystyrene standard
and a
Tg of -48 C.
Example 4
[0085] A coating according to the present invention was prepared as follows:
59
grams of polyester resin from Example 1, 17 grams of ethyl acetate, 5 grams of
diacetone alcohol, 5 grams of PM acetate, and 0.4 grams of DISPERBYK-103 (a
wetting and dispersing additive commercially available from BYK) were added to
a
half pint metal can equipped with an overhead mechanical stirrer. The above
mixture
was gently mixed for 5-10 minutes, and 6.5 grams of ACEMATT TS-100 silica
(thermal silica commercially available from Evonik Industries) was
subsequently
added. The mixture was continued to mix under high speed for 20-30 minutes. A
total of 1 gram of SILOK-3200 (a coating feeling agent commercially available
from
Guangzhou Silok Polymers Co., Ltd.), 0.6 grams of BLS 292 (a light stabilizer
from
Mayzo, Inc.) and 0.1 grams of dibutyltin dilaurate were finally added to the
metal can
and mixed for another 5 minutes. The resulting mixture was mixed with 21 grams
of
XPH80002 hardener (HDI trimmer that is commercially available from PPG
Industries, Inc.) and reduced with GXS73037 reducer (organic solvent mixture
available from PPG Industries, Inc.) to an appropriate spray viscosity. The
resulting
soft touch paint was sprayed on a polycarbonate substrate and cured at 60 C
for 30
mins with a dry film build around 50 pm. The final soft touch coating on
polycarbonate substrate showed hardness of 4.2 N/mm2, a coefficient of
friction of
0.06, a surface roughness of 42, and an abrasion resistance of 480 cycles. The
coating
was tested for stain resistance against common household products and
exhibited stain
resistance to mustard, ketchup, lipstick, sunscreen, petroleum jelly and hand
lotion.
Example 5
[0086] A coating according to the present invention was prepared as follows:
59
grams of polyester resin from Example 2, 17 grams of ethyl acetate, 5 grams of
diacetone alcohol, 5 grams of PM acetate, and 0.4 grams of DISPERBYK-103 were
added to a half pint metal can equipped with an overhead mechanical stirrer.
The
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above mixture was gently mixed for 5-10 minutes, and 6.5 grams of ACEMATT TS-
100 silica was subsequently added. The mixture was continued to mix under high
speed for 20-30 minutes. A total of 1 gram of SILOK-3200, 0.6 grams of BLS 292
and 0.1 grams of dibutyltin dilaurate were finally added to the metal can and
mixed
for another 5 minutes. The resulting mixture was mixed with 16 grams of
XPH80002
hardener and reduced with GXS73037 reducer to an appropriate spray viscosity.
The
resulting soft touch paint was sprayed on a polycarbonate substrate and cured
at 60 C
for 30 mins with a dry film build around 55 pm. The final soft touch coating
on
polycarbonate substrate showed hardness of 3.3 N/mm2, a coefficient of
friction of
0.07, a surface roughness of 44 and an abrasion resistance of 300 cycles. The
coating
was tested for stain resistance against common household products and
exhibited stain
resistance to ketchup, lipstick, sunscreen, petroleum jelly and hand lotion,
while slight
staining occurred with mustard.
Example 6
[0087] A coating according to the present invention was prepared as follows:
59
grams of polyester resin from Example 3, 17 grams of ethyl acetate, 5 grams of
diacetone alcohol, 5 grams of PM acetate, and 0.4 grams of DISPERBYK-103 were
added to a half pint metal can equipped with an overhead mechanical stirrer.
The
above mixture was gently mixed for 5-10 minutes, and 6.5 grams of ACEMATT TS-
100 silica was subsequently added. The mixture was continued to mix under high
speed for 20-30 minutes. A total of 1 gram of SILOK-3200, 0.6 grams of BLS 292
and 0.1 grams of dibutyltin dilaurate were finally added to the metal can and
mixed
for another 5 minutes. The resulting mixture was mixed with 26 grams of
XPH80002
hardener and reduced with GXS73037 reducer to an appropriate spray viscosity.
The
resulting soft touch paint was sprayed on a polycarbonate substrate and cured
at 60 C
for 30 mins with a dry film build around 55 ium. The final soft touch coating
on
polycarbonate substrate showed hardness of 3.0 N/mm2, a coefficient of
friction of
0.07, a surface roughness of 38, and an abrasion resistance of 350 cycles when
measured after initial cure and 600 cycles after 5 days. The coating was
tested for
stain resistance against common household products and exhibited stain
resistance to
ketchup, sunscreen, petroleum jelly and hand lotion, while slight staining
occurred
with mustard and lipstick.
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