Note: Descriptions are shown in the official language in which they were submitted.
~9 E;~30
, .
GRAFT POLYMER CO~0SITIONS OF TERMINATED EPOXX RESIN,
PRocEssEs FOR MAKING AND USING SAME,
AND SUBSTRATES COATED THEREWITH
Field of the Invention
This invention relates to novel polymeric blends and processes
for making them. It is particularly concerned with coating compositions
and their production, especially ones that are to be dispersed in water.
Background
In our copending Patent Application 27~058, identified
above, coating compositions are described that comprise a compatible
blend of film-forming polymeric constituents in a liquid vehicle wherein
the polymeric blend is, in a preferred embodiment of the invention,
an associatively-formed mixture of a carboxylic acid-functional
graft polymer and carboxylic acid~functional addition copolymer.
In the embodiments of the invention of our copending application 278058,
the graft polymer has an epoxy resin component that has an integral
aliphatic carbon chain, onto which i5 grafted at aliphatic carbons
thereof an addition copolymer component that contains carboxylic acid
units derived from a carboxylic acid monomer, which units constitute
at least 1% by weight of the graft polymer. The grafting amounts to
at least 1-1/2 parts by weight of the addition copolymer component for
each 100 parts by ~7eight of the epoxy resin component. The acid
number of the blend falls in the range from about 3Q to about 220.
Said copending application, also describes processes for
making such coating compositions. One such process involves reacting
an epoxy resin with a mixture of monomers containing ethylenic un-
saturation, which monomers are copolymerizable to form the addition
copolymer. These materials are reacted in the presence of at least
3% o benzoyl peroxide by weight based on the weight of the mixture
of monomers, at about 110C ,to about 120C. Instead of benzoyl
peroxide, any other free radical initiator may be used that furnishes
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~ ~ ~. A r r~ ') q ~ A
53(~
equivalent free radical initiating activity for this reaction a~ that
temperature. The epoxy resin reactant generally amounts to from 5%
to 95% of the initial reaction mixture, preferably at least 50%, and
for highly demanding can coating compositions, from 60% to 90%.
In those processes of Application No. 278058 the presence
of the unusually large amount of free radical initiator, based on the
weight of polymerizable monomer, together with the strong orienting
influence of the epoxy resin groups, favored the formation of a graft
polymer in which the grafting was predominantly on aliphatic backbone
carbon atoms of the epoxy resin. Some grafting, in minor amount,
occurred at other locations as well. Grafting of other types occurred,
particularly ester grafting in which carboxylic acid groups reacted
with epoxy groups. Ester-type grafting is less desirable than aliphatic
carbon-to-carbon grafting because the linkage is less resistant to
hydrolysis and weathering.
U.S. Application No. 788,454 from which the present case claims
priority spoke of capping the epoxy resin9 the term "capping" being
used in a broad sense whexein some or all of the oxirane (epoxy)
groups of the starting epoxy resin are eliminated. Such capping is
not reversible in the sense that the word "capping" sometimes is used
in connection with some other organic reactions, and the resulting
"caps" cannot be removed readily to restore the original oxirane
configuration. Hence the word "terminating" is believed to be better
here than "capping" to describe this oxirane elimination.
The "capping" or termination can be done to oxirane(epoxy)
groups on the starting epoxy resin either without extension of the
starting epoxy resin molecules (e.g. using benzoic acid), or with
extension which might even be substantial (e.g. using oxirane-terminated
epoxy resin reacted with more or less of a diphenol such as bisphenol A).
In such non-extension instance there are, of course, residues of the
carboxylic acid projecting from where eliminated oxirane groups were;
in such extension instance, the resin chain becomes generally much
longer as little such diphenol reactant is used, and less long as more
, "~ -3
~9&53(;~
such diphenol is used.
Summary oE the Invention
In one aspect, the present invention is a process for producing
coating compositions, similar to those exemplified in our copending
Patent Application 278058 by a process which eliminates at least
some oxirane groups from the epoxy resin. Thus, production of graft
polymer where the grafting of addition polymer is at aliphatic carbons
is favored and vagaries of oxirane (epoxy) reactions are suppressed,
thereby making the production process more efficient in those respects
than that of the copending Application 278058. The invention is~ also
concerned with the novel coating compositions produced by the instant
process, and with their uses.
However, a more basic concern of the invention is the
provision of a process for modifying grat polymer-addition polymer
blends, to improve their properties9 and for other purposes. This
is accomplished by reacting the epoxide moieties with a chemical
terminating agent, so that the blend not only will be partly free
or substantially free of epoxy groups, but also possess properties
imparted by the terminating agent. This may be done either before,
2~ during or after grafting.
In one embodiment of the process of the invention that
is useful in the production of coating compositions, a preliminary
terminating reaction is used, between any epoxy resin, that has
aliphatic backbone carbon chains, and a chemical terminating agent,
to eliminate substantially all of the epoxide groups of the resin
and for~ modified resin. The subsequent step of the process then
involves reacting
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this modified resin with addition polymerizable monomer in the
presence of at least 3~ of benzoyl perbxide by weight based on
the weight of the monomer, or the free radical initiating
equivalent thereof. Suitable chemical terminating agents in-
clude phenols, carboxylic and other acids, amines, mercaptans,
alcohols, water ~all having hydrogen atoms reactable with
o~irane groups) and other terminating agents also reactable with
oxirane groups, eg " acyl halides, alkyl halides, ketones,
Girgnard reagents (RMgX)~ cyanates, cyanoacetates, diborane,
C02 and CS2. Most of these need to be reacted in an operation
apart from the addition polymerization, but some such as
benzoic acid can be used simultaneously~
The end products of this process are reaction product
mixtures similar to those of our copendlng application. That
i~, the reaction product mixture, if made with polymer~zable
monomer that includes an acrylic acid, contains carboxylic acid-
functional graft polymer and carboxylic acid-functional ad~ition
copolymer. The graft polymer is predominantly in the con-
figuration in which the grafting onto the epoxy resin component
i at aliphatic backbone carbon atoms, These reaction product
mlxtures, produced in accordance with the present invention, are
sati~factory as is for formulation into coating compositions.
Because of the hiyh carboxyl content o the graft
polymer and addition copolymer in such a reaction mixture, the
reaction mixture is easily ionized wi~h base such as an amine to
form a 3table aqueous dispersion. Whether applied in a
sslvent system or in an aqueous vehicle, ooatlngs prepared in
accordance with the present invention are useful for a wide
variety of purposes and can be formulated to be particularly
suitable for coatiny both two-piece and three-piece cans.
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The present invention is useful for the production of
polymer ~lends and particularly, coating compositions, for
application from a variety o different kind~ of liquid vehi-
cles, including organic solvent system~. The invention is gen-
erally applicable for the production of novel polymeric com-
positions that are u3eful for many film-forming applications
In our earlier patent application identified above, we
described our surprising discovery that under proper conditions,
grafting can be caused to ocau~ between an epoxy resin compon~nt
and addition polymerizable monomer, gen~rally onto aliphatic
backbone carbons of the epoxy resin component. Sanitary coating
compositions were made that were suitable for beveragP can coat-
ing application~, by the reaction of a mixture of ethylenically
unsaturated monomers that can copolymerize to ~orm an addition
copolymer in the presence ~f the epoxy resin and an unusually
large amount of benz~yl peroxide or equivalent free radical
ini~iatorO In that pr~cess~ however, a small but measurable
amount of grating ~ccurred at other location~, and parti-
cularly, estex grating apparently oc~rred, to some extent,through the reactlon of carb~xyl groups with epoxy group~.
The present inven~ion provides a technique to favor
grafting of the desired kind, without requiring the large amount
of free radical initiator than might otherwise be n cessary
ThiA is accomplished through the use of ohemical terminating
agents, that are used to eliminate substantialLy all of tha
epoxy groups of the epoxy r~in, so that e~er-typ~ grafting
between acid and epoxy groups cannot occur and vagaries of epoxy
grol~p reactions are eliminated. When the chemical terminating
agent is properly ~elected, it need not b removed thereafter,
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~3&~ii30
since if properly selected, it will either not have a material
effect on the properties of the final reaction mixtu~e, or it
will impart some desired properties.
While preliminary terminating, just de~cribed, is an
important way to practice the invention, the tcrminating step
may al90 be done during or after grafting. Thi~ is a useful way
to control properties. For example, epoxy yrOUpB exe~t an
important effect on the propertie~ of polymer blends that contain
them. By eliminating the epoxy groups, whether before, during,
or after gra~ting, and whether completely or only partially,
property modification can be accompli~hed easily and u~ually
inexpen~ively.
To effect terminating in accordance with the present
invention, a large numbqr of satisfaatory material are available
or u e as the terminati~g agent3, including tho~e liRted above.
With monofunctional reaativity towards 2pOXy groups ~uch agenta
do not extend the epoxy resin while eliminating such epoxy groupsO
With difunctionality such as in a dicarboxyli~ acid or dipheno~,
thP average molecular weight o the epoxy resin can be built up
to terminate with a aarboxylic or phenolic hydr~xyl groupO With
a primary amine used in fairly high concentration and reacted
rapidly, termination can take place without extension of the
epoxy resin, wherea~ with low amine concentration extension of
the epoxy resin can be made to occur during termination~
The grafting step involves reacting an epoxy re in,
whlch may or may not be terminated to make mod~fied resin, with
addition polymerizable monomer, that may be in the form of
either a singl~ monomer of a mixture of monomers that contain
ethyleni~ unsaturation and that are c~polymerizable to orm an
addition copolymer. Where the end product is to be a coating
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~965~(~
composition, and particularly where he composition is to be
dispersed in an aqueous vehicle, at least one of these monomers
is a carboxylic acid1 The epoxy resin ca~nent and the monomer
mixture are reacted together in the presence of at least 3~ of
benzoyl peroxide, by weight of the polymerizable monomer, at
about 110C. to about 120C. or alternatively, any other free
radical initia~or can be used that furnishe3 equivalent free
radical initiating activity in the reaction temperature r~nge.
When such proportion of free radical initiator
employed is less than the equivalent o~ at least 3% by weight of
benzoyl peroxide, based on the polymerizable monomer, ester-type
graft polymers apparently predominate ~unless the epoxide groups
have been terminated and thus eliminated)~ When ~uch proportion
of free radical initiator is sufficient to be the equivalent of
at least 3% by weight of benzoyl peroxide, and up to about 7% or
more by weight of benzoyl peroxide, the pre~x~n~ type of
grafting that occurs i9 at aliphatic carbons of the epoxy resin
or the thus modified epoxy resin. When a greater amount of
benzoyl peroxide that about 7% is employed, or equivalPnt,
greater expense is incurred without any particular advantage yet
noted. However, amounts Qf free radical initiator as high as
15% equivalent of benzoyl p~roxide by weight of the addition
polymerizable monomer can be used.
The products produced by this invention are an a -
sociatively-formed resinous blend of grafts of addition polymer
to the terminated ep~xy resin structure wherein such grafting is
mainly to aliphatic carbon atoms of the terminated resin
(usually to aliphatic backbone carbon atoms), ungrafted modified
epoxy resin ~i.e. an epoxy resin that ha~ had some or all of
it~ oxirane groups reacted with a terminating agent such as a
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carboxylic acid, phenol, or the like), and ungrafted addition
polymer. The backbone of a starting epoxy re~in is the resin
other than its oxirane groups; of an epoxy resin modified by
the instant termination thP backbone also includes those carbons
that formerly were oxirane carbons where an oxirane group has
be~n eliminated by the te~mination,
The grafting forms especially durable linkages for
modifying sufficient of the terminated epoxy resin pxesent in
the graft to exert a profound influence on the properties of
the product blend as well as to impart la ting characteristics
of the grafted-on addition polymer to the terminated epoxy resin
receptor. Thus, for example, such grafted addition polymer rich
in acrylic ester units would be expected to improve such
receptor's resistance to outdoor expo~ure. Also, for example,
such a graft polymer that is rich in carboxyl groups imparts to
the product blend superior characteristics for making water-
reduced sanitary coatings used inside beverage and like cans
provided that there are a few parts by weight o~ grafted car-
boxylic acid containing addition polymer supplying at least about
two weight parts of carboxyl units per 100 part8 of starting
epoxy resin. Such a blend is highly resi~tant to undesirablP
reaction in and precipitation from a mildly alkaline aqueous
disper ion and the suspending influenca of the ionized graft
pslymer in co~bination with associatively-forme~ corrssponding
carboxylic acid-containing copolymer on other components in
~uch re~inous blend appears to be remarkable.
However, to obtain even qo modest a proportion of this
durable grafting and its attendant influence upon properties of
the a~soci~tively-formed blend, it is essential to commence the
addition polymerization with an unusually large proportion
_g_
~0~653Y~
of free radical initiation with re~pect to the polymerizing tem-
perature and amount of polymerizable monomer being u~ed, e.g.
4% to 7% or more by weight of benzoyl peroxide based on weight
of such monomer when using a temperature of about 115C.
to 130C.
While the invention is particularly useful as ~ tech-
nique for the production of coating compositions similar to
tho~e disclosed in our copending patent application mentioned
above, the pre~ent invention is important also, for it broader
aspects, For example, epoxy resinc have less resistance to out-
doox expo ure conditions than some of the other synthetic poly-
meric materials. Epoxy resins are also subject to attack by
some materials such as, fox example, strong alkalis, or even
soaps.
The present invention provides a technique for making
modified polymer blends that contain graft polymer~ and ungrafted
addition polymers, so as to improve their properties, by partly
or completely eliminating th~ epoxy groups, Since the modi-
fication can be done prior to, during, or after the formationof the gxa~t polymer with the proper selection of terminating
agent, the i~vention is very versatil~.
The gra~ting that OCCU~8 at the aliphatic backbone
carbon~ exerts a pro~ound influence on the proper ies of the
reaction mixture. Thus, when the addition polymerizable monomer
includes a major amount of an acrylic acid, both the graft
polymer and the ungra~ted adclition polymer, ~hat are produced,
are carboxylic acid-functional, and in the presence of a suit-
able neutraLizing or ionizing agent, the reaction product may
be stably dispersed in an aqueous vehicle. For satisfactory
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3C~
dispersion in an aqueous vehicle, the Acid Number sf the reaction
mixture should be sufficient for establishing and maintaining
the polymer blend in the dispersion.
The effects of graft polymerization in accordance with
this invention can be ob~erved, in the case of water-reducible
coatings, when there is sufficient carboxylic acid functionality
o that stable dicpersions are formed. There are different ways
in which this can be measured. Thus, the addition polymer, when
formed from an acrylic acid rontaining polymerizable monomer,
will contain caxboxyli~ a~id units. m ese - COOH units should
constitute at least 2% by weight of the graft polymer, for ease
of dispersion. However, when the initial reaction mixture is
low in either epoxy resin or ln an aorylic acid, this measure-
ment alone may not suffice. Accordingly, it i8 best to couple
this measUrement with an Acid Number value for the entire re-
action mixture, which value should be above 30 and generally
will not exceed 220. A preferred range is from about 45 to
about 150; a more pre~erred range, for sanitary coating com-
position hinders, is 80 to 9~.
~ven when the initial ~starting) ep~xy resin reactant
constitute3 a major part of the reaction mixture, surprisingly
little gra~ting may take place, while nevertheless pxoducing a
reaction mixture which i5 apparently profoundly influenced by
the novel graft polymer m us, ths grating of the addition
polymer on~o the epoxy resin may be as low as to the extent of
1-1/2 parts by weight of addi.tion polymer for 100 parts by
weight of the epoxy resin. Generally, to secure the benefits
of the invention, the amount of starting epoxy reQin should ~e
~ufficient ~o that quch epoxy resin constitutas at least 5% of
the initial reac~ion mixtu~e by weight, and preferably at least
'~
o
10%. Superior binder klends are obtained when the amsunt of
epoxy resin is 40% or more by weight of the initial reactant3,
and 50% or more produces preferred binders, although for sanitary
coating composition binders, the amount should be from 60% to
90% starting epoxy resin,
One important feature of the procesq of the invention
is the unusually high proportion of free radical initiator
relative to addition polymerizable monomer that is used in the
reactionO For practical results such proportion ~hould be u~ed
to initiate the addition polymerization and grafting reactions
ra~her than to use some of ~uch proportion to finish off such
reactions. If such latter addition is practiced, additional
catalyst is best added. The proportion of benzoyl peroxida,
used at about 110C. to 120~C. or so must be at least 3% based
on the weight of addition polymeriæable monomer, and preferably
is at least 4%. A useful practical preferred range is 6~ to
7%, although up to 15% or more can be used. When other fre
radical initiatorq are used, the amount c~n be adjusted to be
equivalent in activity for khi~ particular reaction, tak~ng
the temperature of use into account.
E~ter-type graft polymers apparently are formed when
the polymerizable monomer includes an acrylic acid, unless pre-
vented by eliminating oxirane group~. Whan the proportion of
peroxide-type free radical initiator i sufficient to be the
equivalent of at lea~t 3% or more by weight based on weight of
addition polymerizable monomer, of ben20yl peroxide, and of up
to about 7~ or more by w~ight of benzoyl peroxide, the pre-
dsminant 'cype of grafting that occurs with any kind of poly-
merizable monomer, even without terminating the epoxy resin to
m~ke modified resin, is at aliphatic backbone carbons of the
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epoxy resin or modified resin, and particularly, at those
aliphatic carbons that have either one or two hydrogens bonded
thereto in the ungrafted state. With prior terminating no acid
to epoxy group ester gra~ting occurs, and the free radical in-
itiator i~ employed to greatest effect When a greater pro-
portion of peroxide-type free radical initiator is employed than
the equivalent of about 7~ of benzoyl peroxide at 110C. to
120C. generally greater expense is incurred without any
accompanying advantage.
While the preferre~ grafting reaction technique in-
volves placing the epoxy component and a solvent for it in a
reactor, and then 810wly adding the monomer mixture, catalyst
(i.e. free radical initiator), and solvent over a period o time
that permit6 facility o control over the exothermic heat, other
approaches to the procQs~ can be employed. For example, ~hs
epoxy resin or the modified resin and a s~lvent for it could be
placed in a reactor, thçn all of the catalyit and part of the
monomer mixture could be added. After an initial reaction,
taking place upon heating, the remainder of the monomer mixture
could be added slowly over a period of time. A~ a variation on
this process, some of the free radical lnitiator ml~ht ~e re-
tained for addition to the reac~or alsng with the monomer mix-
ture. As a further alternative, the monomer mixture, epoxy or
modified resin component, and any desired solvent~, could be
placed in a reactor, and the catalyst added slowly~
For priox te~minating, the termina~ing agent is re-
acted wit~ the epoxy resin before the grating reaction. For
terminating at the same time as grafting, the reaction technique
employed will depend on the terminating agent selected (eg so
as not to alternate the free radical initiator action
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531~
appreciably).
Once the final reaction product is obtained, it isgenerally useful to suspend it in an aqueous vehicle, to facil-
itate its applicati~n as a coating composition.
The process of converting the polymeric blend contain-
ing appreciable carboxyl group~ and solvent Rystem to a ~table
water-borne system requires the utilization of a base or mix-
tures of baqes. The preferred neutralizing base is dimethyl-
ethanolamine, and it is normally used at 4~ to 12% by weight
based on the total weight of polymer in the associatively-formed
blend. For a givsn dispersion the proportion of ba~e us~d
determines the resulting viscosity of the water-b~rne system,
which in turn affects application characteristicq. Higher
levels of base give higher viscosities and require larger
amounts of water dilution for viscosity control.
Two different processing procedures can be us~d to
convext th~ reaction product blend to a ~table water-borne
system. For ease of manufacture, the preferred procedure in-
volves adding the produc~ blend with organic svlvent to a
mixture o~ water and dimethylethanolamine, with mixing Usually
a small amount of hy~rophilic solvent ~ethylene glycol monobutyl
ether or the like) i5 included in the water to aid dispersing
the resin therein.
In khe second procedure, water and amine are added to
the product blend and solvent, with mixing. While the water-
borne sy~tem prepared by thi~ proces~ is satisfactory as to
quality, ~his procedure i~ not preferred for best equipment
utilization.
Wat~r~borne sy~tems prepared as described above nor-
mally have a pH in the range from about 7.5 to 8.0, and have
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~09~3~
been found to be stable fsr storage periods of over one year.
Products so produced do not ahange unduly in viscosity, there
is lit~le or no settling or separation, and application char-
acteristics remain satisfactory after storage.
To operate within the most preferred ranges for
practiciny the present invention, for the production of sanitary
coating compositions for soft drink and beer can3, the amount
of starting diepoxid~ resin should preferably be ~bout 80% by
weight, and the amount of monomer mixture employed, for reaction
with the epoxy component and by i~self, should be about 20% ~y
weight. The amount of benzoyl peroxide present during the
reaction ~hould be from about 6% to about 7% by weight based on
monomers, and preferably, about 6.7% to 6.8%. The amount of
me~hacrylic acid in the monomer mixture is reflected in the
Acid Number of the final reactisn product mixture that is
obtained. For present purposes, this Acid Number should be
in the range from 45 to 150, and preferably, from about 80 to
90, and mosk preferably, about 85.
For a beverage can coating composition, for use in an
80 parts of dlepoxide to 20 parts of monomer mixture reaction
mixture, with 1~3 part~ benzoyl peroxide, a preferred monomer
mix~ure composition i5 70 parts methacrylic acid to 30 parts
styrene with one wt. p~rcent ethyl acrylate. The final reaction
product mixture obtained should have all of the monomer mixture
copolymerized to an addlti~n copolymer, with about 2-1/2 weight
parts grafted to the diepoxide resin, at aliphatic backbone
carbon~, a~d with the balance of the addition copolymer blended
with the graft polymer in th~ r~action product mixture.
Both the graft polymer and the addition copolymer thus
produced are carboxylic acid-functional. They have enough
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~&53i~
ionizable groups to ~e hydrophilic and are readily blenda~le.
With the 80/20 preferred reaction mixture of star~ing
diepoxide to monomer mixture, for beverage can coating, reacted
at a level of 3~ by weight Q~ benzoyl peroxide base on monomers,
generally about 1-1/2% to 2% of the addition copolymer is
grafted (based on total addition copolymer formed from the
monomer mixture), and dispersibility in water i5 poor. At 5%
benzoy~ perQxide, about 8% of the addition ~opolymer is grafted;
at 7% benzoyl peroxidel about 12% of the addition copolymer is
grafted; at 9% benzoyl peroxide, close to 20% is graf~ed; and
at 15% benzoyl per~xide, over 40% of the addition copolymer is
grafted. For clarity, it is emphasized that when 10% of the
addition polymer is grafted, this means that the final reaction
product mixture consists o~ about 82% graft polymer and ungrafted
diepoxide resin and about 18~ of associatively-formed addition
copolymer. Termination to eliminate epoxy groups, particularly
termination without extensi~n, would not be expected to detract
appreciably from the water dispersibilty of the re~ulting
associatively-formed blend.
For good coating compositions generally, at least about
1-1~2 parts by weight of the ~d~ition cop01ymer should be grafted
for each 100 parts by wçight of starting epoxy resin component
in the graft polymer~ The amount ~f addition copolymer grafted
can be as high as 1~ parts, i~ en~ugh benzoyl peroxide is used,
but a level of 5-1/2 parts or so is a pxactical upper limit for
most purposes, and values of 2-1/2 to 3 parts are generally
preferred for can coatings.
Generally the reaction product mixture obtained, from
the 80/20 preferred xeaction mixture o starting diepoxide resin
to monomer mixture, will contain up to 18-1/2 parts of ungrafted
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l~9~;S3~
addition copolymer 9 For many coating applications, even more
addition copolymer can be tolerated, and separately formed
compatible addition copolymer, preferably of substantially
the same compo~ition as that present, can be added, up to a
total of about 40 or so parts of ungrafted addition copolymer
in the reaction product mixture. Similarly, additional un-
grafted diepoxide resin can be tolerated, generally up to
a total of about 10~ by weight of the reaction produat mixture~
For aqueous dispersions at high epoxy content, prior
~ermination is preferred and, t~e carboxyl content of the
reaction product mixture, mea3ured as - COOH, should be at least
2% by weight of the reaction product mixture. For stability of
dispersion, the amount may be substantlally higher. ~he
practioal range is at least about 5% generally. When the car-
boxyl content is below about 2%, polymer blends are produced
that are useful in sol~ent vehicles.
me several individual features of the invention will
now be discussed in detail.
The epoxy r sin component may be eith~r an aliphatic
epoxide resin or an aromatic epoxide resin. For preparing
coating compositions for cans in which aomestibles suitable for
human consumption are preserved, the aromatic ~poxy resins
a~e preferr~d.
The most preferred epoxy resins are polyglycidyl
ethers of bisphenol A, especially thos2 having 1, 2-epoxy
equivalency of from about 1.3 to about 2, and preferably about
2. The molecular weight of the epoxy resin used hould be from
about 350 to about 20,000, and preferably, for sanitary coating
compositions, from about 4,000 to about 10,000. Low moleculax
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~,
~96S3(3
weight epoxy resins are ordinarily ~elected for use when the
epoxy resin content of the polymeric binder is to be low, that
is, from about 10% to about 30% by weight. Low molecular weight
epoxy re ins, for present purpose~, are considered to be those
having a molecular weight of le s than 1,000.
Ordinarily, when the polymeric blend is intended to
contain from 50~ to 90% by weight of epoxy resin ba~ed on tstal
polymer solids, the epoxy resin selected will be one having a
molecular w~ight in the ~ange from about 4,000 to about 19,000,
particularly for the preparation of sanitary coating compo-
sitions, for which i~ is preferred ~hat the epoxy resin con-
tribute at least 60% to total solids.
While it is sometimes convenient to u~e a finished
epoxy resin at the desired molecular weight, it is often more
practical to start with bi~phenol A and the bi glycidyl ether
of bisphenol A, which is available from commercial sources.
The bis~lycidyl ether of bisphenol A, known in the industry as
liquid epoxy resin, i~ available in precatalyzed form not only
from Dow Chemical Company under the trade name DER 333, con-
taini~g as the cat lyst the complex of ethyl triphenyl phos-
phonium acetate with acetic acid, but also from Shell Chemical
C~mpany under the trade name Epon 829 (Epon is a trademark) and
these are convenient initial starting materials. Uncatalyzed
liquid epoxy resins are alBo available and hav been found to
be suitable for u~e when the proper catalyst is employed.
The precatalyzed liquid epoxy resin from Dow Chemical
Company, DER 333, has the following physical properties:
, -18-
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Table I
Appearance Clear, viscou~ liquid
Color (Gardner) 1-2
Specific gravity 1.15
Weight per gallon 9.65
Nonvolatile by weight 96 + 1%
Volatile Xylsne
Nonvolatile by volume 95% avg.
Viscosity at 25C~ 2300-4600 cps.
Epoxide equivalent weight* 199-202
*Epoxide equivalent weight is the grams of re in con-
taining one gram equivalent weight of epoxide.
T~ inareaqe the initial molecular weight of a liquid
epoxy resin to a level that is more sa~isactory for many
coa~ing applications, the initial liquid epoxy resin may be
reacted not only with a~ditional bi~phenol A but al~o with other
matarials. Other polyfunctional a~omatia alcohols can be u3ed
to make glycidyl ether and to increase molecular weight, in-
cluding such materials as bis(4-hydroxyphenyl)methane; bicphenol
F;2,2-bis(4'-hydroxy-2',2',5',6'-tetrachlorophenyl)propane;
tetrachloro~i~phenol A; 4, 4-bi~ (hydroxyphenyl) pentanoio acid;
diphenolic acid; novolacs or low molecular weigh phenolform-
aldehyde polymers; 1, 8 bis~hydroxyphenyl) pentadecane; resorcinol;
2,2,5,5-tetrakis (4'-hydroxyphenyl)hexane; and others. However,
the p~eerred material, for prac~ical contr~l over the proce3s,
for increasi~g the weight of the initial liquid epoxy resin,
is bisphenol A.
The ratio of bisphenol ~ ~o DER 333 used to produce
the moak desirahle molecular weight i~ from 65% to 66.5% by
weight ~ER 333 and 35% to 33.5% by weight bisphenol A. The
fsllowing table list~ the aharacteris~ic~ of the inished epoxy
resins:
-19
~6~3~
Table II
~3~_
DE~ 333 level by wt. 65 66.5
Bisphenol A level by wt. 35 33.5
Approximate molecular wt. 9000 5000
% Epoxide oxygen .4 .6
Gardner visaosity range Z~ ~Z3 X-Z
at 40% wt. nv. in ethylene-
glycol mono butyl ether
The reaction conditions employed to increase the mole-
cular weight o~ the liquid epoxy resin, or other low molecular
weight epoxy resins, include a reaction temperature of about
175C. and atmospheric p~essure. While this reaction can be
conducted without a sclvent, it i8 preferred to use ethylene
glycol mono butyl ethe~ a~ about 15% by weight based on total
raaction charge.
For many ooating applications, the epoxy resin, ordin-
arily a diepoxide, may have a molecular weight in the range from
about 350 to about 20,000. However, for more demanding appli-
cations, particularly for applications where the end product
is to be sanitary coating, epoxy resin m~lecular wei~ht values
in the range from about 4,000 to about 10,00~ are preerred,
These and other molecular weight determinations of the epoxy
resin components are made by gel permeation chromatography,
preferably, but any other standard technique may be employed.
Epoxy resin~ tha~ are u~eful al~qo can be modified
; with othex condensates such as phenolic resin , phenols, and
polyols~ Typical modified epoxy resins are: epoxidizad poly-
butadiene; glycidyl ethers f~rmed by reacting phenol novolak
resins with epichlorohydrin; 4, 4'-isopropylidenediphenolepi-
chlorohydrin; 4, 4l-sec-butylldened~phenol-epichlorohydrin
reacted with one or more of the following drying oils or atty
acid~: beechnut, candlenut, castor ~including dehydrated), tung,
-20-
... ~
~9653~
coconut, corn, cottonseed, i~h (reined), hempseed, lin3eed,oiticica, perilla, poppyseed, pumpkinseed, safflower, seasame,
soybean, sunflower, tall oil, and walnut; 4, 4'-isopropyli-
denediphenol-epichlorohydrin chemicall~ treated with one or more
of the following: allyl ether of mono~, di-, or trimethylol
ph~nol; 4, 4'-isopropylidenediphenol-formaldehyde; 4, 4-sec-
butylidenediphenol-formaldehyde, melamine formaldehyde, and
ur~a-formaldehyde.
Commercial epoxy resins that have useful molecular
weight values and tha~ are suitable for use as i~, without
furth~r incraa~e in molecular weight, include DER 662, 664,
667; 668, and 669, all solid epoxy resin products of Dow
Chemical Company ~with calculated average molecular weight,
respectively, of 1,275; 1,850; 3,690; 5,500; and 9,000): and
EPON 836, 1007 and 1009, all products of Shell Chemical Company
(with calculated average molecular weights, respectively, of
625 ~semi solid); 4,500; and 6,500 ~ Epon is a Trademark).
~ hile preferred diepoxide materialR, for use in the
practice of the invention, are prepared by reacting epichloro-
hydrin wi~h bisphenol A, other satisfactory diepoxide include3uch initial material~ as khe followlng, provided the molecular
weightc are adjusted to the proper range:
Diepoxide 1
H2-O-~-~CH2)2 ~ H2
H3 H3
~096~3~
Diepoxide 2
O o
H 2C--CHCH 20 ~ CH2 ) 2CH2CH--CH 2
Diepoxide 3
O O
Diepoxide 4
0~
\I" Lc@--CH2
Diepoxide 5
~ 12-o 3~
.,, ~
~0~6~
Diepoxide 6
/ 0\ ~ fH3
CH2 CH- CH2 0 ~ CH~
fH ~ fH3 ~
tCH2 CH~CH2 O~C
~O\
~)- ~2 -CH CH2
N -- O, 1 or more
A furth~r way of charaoterizing the epoxy re~in com-
ponen~ n terms of its oxirane content. Thi~ value can be
anythi~g from zero to about 8%o ~ zero value Dxirane content
would indicate tha~ ~h~ epoxy group~ have been compl~ely
reac~d, a~, for exampl~, wi~h exc~s ~i~phenol A. The epOxy
group~ may no be ne~ded ~or applioa~ion~ other ~han ~or good
can co~ting3. The oxirane aontent i~ de~erminated in the
ollbwing way.
Det0rmlnakion o~ Oxiran~ Content
A ~ampl~ o~ kncwn weight i8 placed into a 50 millili~er
Erle~meyex flask, ~nd di~solved in 10 milllliter~ of chloro-
benzene. To the s~lution i~ added 10 milliliters of tetraethyl-
a~moniu~ bromide ~olutlon and 2 ~o 3 drope of 2~ crystal violet
indicatox solutlon in gla¢i~l acetic acid. The re~ulting
~olution i~ then titrat~d ~o ~lue-green end point with a
~tandardized 0.1 N perchloric acid ~HC104) U8i~g a 10 milliliter
misroburet, % oxir~n~ i~ calculated from ~he following ~quation:
-23-
~al96~
% Oxirane = ~ml, X N of HC104)X 1.600
Wt. of sam~e in grams~
The 0.1 N HC104 solution was prepared by mixing 8.5
ml. of 72% HC104 with 300 ml~ of glacial acetic acid (99,5~),
20 ml. of acetic anhydride was added, and the solution was
diluted to 1 liter with glacial acetic acid and allowed to stand
overnight. It was then standardized against pota sium acid
phthalate.
The tetraethylammonium bromide solution re~uired above
wa~ prepared by dissolvin~ 100 g. of tetraethylammonium bromide
in 400 ml. of glacial acetic acid (99.5%). To neutralize basic
impurities, a few drops of 2~ crystal violet indicator solution
was added and the solution was titra~ed dropwise with the
standard 0.1 HÇ104 to the end point color change.
This determination is applicable to both the initial
epoxy resin and to the reaction mixture that include~ the graft
polymer.
Materials that are generally u~eul as terminating
agents for the epoxy groups have been mentioned above and in-
clude the phenols, many of the carboxylic acids, primary and~econdary amines, msrcaptans, alcohol~, and water. While some
ethylenically unsaturated terminating agents can be used, gen-
erally it is preferxed to avoid materials of thi kind in order
to avoid possible addition polymerizakion reactions with the
addition polymerizable monomer during grafting.
A preferred terminating agent fox obtaining extension
of the epoxy resin i~ bisphenol A. This is used very simply,
particulaxly when terminating is done prior to gra~ting, in
which case a molar excess of bisphanol A over epoxy resin can
-24-
~6~3D
be used when the molecular weight of an initial liquid epoxideresin is ~o be increased. Thus, per slightly less than 64
weight parts of Dow DER 333 liquid resin per 36 weight parts of
bisphenol A (where the modified resin reaches about Z3 4
Gardner-Holdt viscosity at 25C. 40% by weight resin dissolved
in ethylene glycol monobutyl ether) down to about 60 parts D~R
333 liquid resin per 40 parts of bisphenol A ~where the modified ~-
re in like viscosity is a little above U) represent the useful
range for these reactants in such terminating aromatic alcohols,
that are useful for increasing the molecular weight of the
liquid epoxide resin, are useful as such terminating agents.
Also useful are phenol, the cresols, and the xylenols.
Saturated ~atty acids and aromatic monocarboxylic
acids such as benzoic are particularly useful for terminating
epoxy resin "without extension", especially where they can
impart ~esirable properties to the end product, Ordinarily the
fatty acid~ can be used in a variety of commercial forms ~nd
need not be highly purified. However, aaids such as palmitic,
lauric, myristic, and stearic are very useful, in either refined
form or as highly purified acids.
Generally the primary and ~econdary amines are satis-
faatory capping agent~, par~icularly hydroxyl ~mines 3uch as,
for example, ethanolamine and diethanolamine. While not wishing
to be bound by any par~icular theory, and recognizing that a
large numbex of t~rminating agents are readily available, it
appears thak the prese~ce of a hydrogen atom reactable with an
oxirane group i~ preferable~ It is for ~his raason, among
other~, that the tertiary amines are not considered ~uitable.
-2~-
53~
Addition Polymerizable Monomer
Another important group of materials, for use in
practicing the present invention, consists of addition poly-
merizable materials.
To practice the pre~ent in~ention in its broadest as-
pects, the addition polymerizable monomer, that is reacted in
the presence of thç epo~y resin or modified ~e~in and the fre~
radical initiator to form the reaction mixture including the
graft polymer, may be a -~in~le monomer, or a mixture of copoly-
merizabie monomers. The material selected will depend upon theobjactives ~o be achieved in ~erms of properties and economics.
S~yrene is a valuable monomer, for example, because it acts as
an extender and i8 economlcal. Acrylamide is interesting be-
cause it en~ances a self-curing capability, whether used alone
or as a part of a mi~tUre. The acrylic acids impart carboxylic
a~id functionality.
~ urrently approved 8pOXy ac~ylic coating for b~verage
can use include thr~e or more monomers in admixture, i.e.,
styrene, metacryliP a~id, and ethyl a~rylate, and optionally,
2Q me~hylme~hacrylate. However, very use~ul water-reducibl
coating~ can be produced from mixtures of methacrylic acid and
sytrene, such acid normally being the major component, in order
to develop ~ufficient acid unctionaliky for forming stable
aqueou dispersions o~ the resulting addi ion copolymer.
Generally, ~or making coating compositions in accord-
ance with the present invention, the addition polymerizabla
monomer will be selected from classes of such monomeric
materials, The selee~ion may be a single monomer, or a mixture
o~ such mo~omers that is designed to achieve some particular0 sbjective such as, fo~ example, acid functionality.
-26-
6530
The first class of monomers, that may be u3ed in thepreparation of coating compo~ition~, a~e the acrylic acids.
This category in~ludes true acrylic acid and lower alkyl sub- ^-
stituted acrylic acids, that is, those acids having ethylenic
unsaturation in a position tha~ is alpha, beta to a single car-
boxyllc acid group. The preferred acrylia acid is methacrylic
acid.
A second clas6 of mo~omer that may be employed can be
identified as inal~din~ tho~e readily commercially avallable
monomers that have vinyl unsaturation and that do not impart
ionizing fun~tionality~ Thi~ would include s~yreNc monomers,
such as styrene, vinyl toluene, and divinyl benzene. Other
suitable monomers include i~oPrene, conjugated butadiene, and
the likaO
A third cla3s of monomers that are useful, particularly
to comply with current rqgulations that apply to sanitary coat-
ing~ for addition to a methacrylic acid-styrene mixture, are
the alkyl ester3 o~ an acryl1c aci~, generally the lower alkyl
e~ters, that is, tho~e es~rs in which the esterifying group
contains from 1 to ~ aarbon atoms, and particularly, ethyl
acrylate. Other useful monomers in thi~ class include other
Cl 15 alkyl acrylate ester.~ and methacrylate esters such as,
~or example, propyl acrylate, isopropyl acrylate, butyl
acrylate, i~obutyl acrylate, tertiary butyl acrylate, pentyl
acrylate, hexyl acrylate, 2-~thyl hexyl acrylate, octyl
acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate,
osibornyl acrylate, methyl me~hacrylate, butyl methacrylate,
isobutyl methacrylate, hexyl methacrylate, 2-e~hyl hexyl
methacrylate, octyl methaorylate, and nonyl methacrylate.
Acrylamide and aarylonitrile are al~o u3eful, although not
-27-
3~
for foods.
Generally, ~ho e addition polymerizable monomers that
are readily polymerizable under solution polymerization con-
dition, typically those that contain ethylenic unsaturation,
are suitable for use. This would lnclude also acetylenically
unsaturated materials such as, for example, acetylenic glycols.
When a mixture of monomers is used in the production of a water-
redu~ibla coating, those monomers selected, other than an
acrylic acid monsmer sho~ld oopolymerlz well with acrylic acid
monomers, and should fo~m copolymers that by themselves are not
cro~s-linked at least until cured in o a finished coating.
For most water-reducible coating compositions, gen-
erally the monomer mixture will con ain a major proportion of
an acxylic acid, and a minor proportion of a styrenic monomer,
gen rally styrene. For those ~oating compositions that may
come in contact with food, in general, and for the preparation
of besr can coating compositions in particular, one preferred
addition polymerizable monomer mixture is m~de from 70 parts by
weight of methacrylic acid to 30 parts by weight of styr~ne,
together with 1 wt. percent of ethyl acrylate. Another pre-
ferred monomer mixture includes methacrylic acid, styrene, and
ethyl acrylate, in the approximate weight ratio of 65:34:1,
respectively.
Free Radical Initiator
____
The epoxy resin and the mixture of polymerizable
monomer ~re reacted toyether in the presence of a free radical
initiator, preferably of the peroxide type.
Many ~ree radical initiating materials may be used,
butyl benzoyl peroxide is preferred. Those materials that may
be used generally include the material of~en referred to as
-28-
~a~9~3~ -
peroxide-type catalysts. The clas~ of free radical initiators
is generally well-known and is generally useful to 30me degree,
including combination~ of free radical initiators and activators
for the free radical initiators~ including ultraviolet light
and high energy elctron b~ams, under proper conditions. Typical
practical free radical initiators that are in common use include
cumene hydroperoxide, ~enzoyl per~xide, t-butyl perbenzoate,
t-butyl peroxide, lau~oyl peroxide, methyl ethyl ketone peroxide,
chlorobenzoyl peroxide, and the like. Benzoyl peroxide i~ pre-
ferr~d as the ~ree radical initiator for u~e in the practice ofthe present invention, to initiate and to conduct grafting and
addition polymerization together (that is, associatively).
The amount of f~ee radical initiating activity i~
important. That amount is expressed herein in terms of percentage
by weight of benzoyl pe~oxide based on the total weight of the
polymerizable monomer, or equivalent, at the temperature of use,
which is generally from about 110C. to 130C. ~r so. Such
proportion should be at lea~ 3%, and preferably more than 4%
by weight of benzsyl peroxide or equivalent. Since benzoyl
peroxide i6 an expen~ive material, no more should be uRed than
i~ neces~ary to produce the de~lred reæults.
When the amount of benzoyl peroxide or equivalent used
i5 about 3~ by weight on monomers, minimum desired grafting
occurs. A~ such propor~ion of free radical initiator used is
increa~ed, grafting at the aliphatic backbone carbons is
favored. At a level of free radical initiator equivalent to
6% to 7% of benzoyl peroxide based on polymerlzable monomer,
with a reaction mixture o~ about 80% by w~ight epoxy resin ko
20% polymerizable monomex by weight, about 12% by weight of
the initial monomer gra~ts to ~he epoxy, onto aliphatic backbone
-29-
carbons that have either one or two hydrogens bonded thereto ~n
the ungrafted state. While grafting appears to occur at those
aliphatic backbone aarbons that are in positions alpha to
terminal epoxy groups, where the epoxy resin has not yet been
modified per the instant proaessing, there is some grafting,
apparently, at other locations. This type of grafting can be
illustrated thus:
~0--CH--1H--CH2--
CH2--C--[--CH2--C--~--
y y
and
O--CH2 1H--CH~
CH2 c _ ~CH2 f ~_
Y
where X is CH3 or H, and
Y is phenyl, CO2H, or CO2Et, for example.
The ari~hmetic of thus having 12% of the polymerizable monomer
graft to the epoxy re~in indicates that the addition polymer,
that is fo~med from the monomer, and that grafts, amounts to
about 2.4 parts of addi~ion polymer out of about 82.4 parts of
graft polymer, assuming that all of the epoxy resin grafts.
mi8 means ~hat ~he addition p~lymer ~omponent amounts to about
2.9% of such as~umed graft polymer by we~ght. Actually a
sizable percentage of the epoxy resin may not be grafted, but
the free epoxy resin i~ difficult to detect; it may evan be as
much as 50~ or more of the original epoxy resin that remains
-30-
,,,J"~
653(~
ungrafted. When epoxy group~ in the resulting resinous blendare eliminated by reacting them with a terminating agent to
farm modified resin~ the foregoing grafting survives.
The Graftin~ Reaction Proce~s
A typical grafting r2action prior to resin modification
generally con~ists o~ ~eacting the starting epoxy resin com-
ponent with p~lymerizable monomer that constitu~es from absut
5~ to about 95~ of the reaction mixture ky weight, in the pre-
sence of a peroxide-type free radical initiator, preferably
benæoyl peroxide, in an amount that is the free radi~al in-
itiating equivalent of ~t least 3% of benzoyl peroxide by wsight
of the monomer. While the reaction may be conducted in the
absence of a solvent, ordinarily a solvent system i~ employed
for coating produation. A preferred solvent system is one made
up of two miscible 501v~nt9.
A pre~erred ~echnique or conducting such reaction i9
to pla~e a solution of the epoxy resin ln a reactor, heat, ~nd
then ~lowly add, over a pexiod of two ~o three hours, with
mixing, ~he polym~riza~le monomer, and the fxee radiGal in-
itiato~. Sinc~ ~he rea~tion is exothermic, this techniqueenablea the temperature to be maintained at ~ desired tem-
pe~ature and reaction ra~e with some deqree of control.
At the end of the additi~n to ~he reactox, the content of the
reactor may be maintained at a presele~tQd holding temperature
for some addition pe~iod of time, to make sure that the reaction
ha~ gone forward to tha desired extant.
The particular solvents that may be employed are well-
known in t~e art. Solvents such as xylene are satisfactory for
the epoxy re in componen~. Other suitable solvents include
benzene, ethyl kenzene, toluene, and the alkoxy alkanols.
-31~
~09~
For the addi~ion polymerizable monomer, alcoh~ls such as
methanol, ethanol, propanol, butanol, and the like, are suitable
with n-butanol being preferred. Ethylene glycol monobutyl
ether, ethylene glycol monobutyl ether acetate, and the like,
and hexane, mineral spirits, and the like, are also suitable.
If the end product is to ~e used in an aqueous vehicle, then
the solvents selected should be water-soluble materials.
Solvents for thinning may be introduced into the
3y~tem during the initial reaction of a precatalyzed liquid
epoxy resin to increase its molecular weight. For thi~ purpose,
a preferred solvent is ethylane glycol monobutyl e~her, at 15%
by weight ~ase~ on total reactants. It is also preferred to use
a mixture of ethylene glycol monobutyl ether and normal butyl
alcohol at about 40/60 by ratio, for efficiency in term of per-
formance or can coating Most o the -~olvent is usually
pre~ent to moderate viscosity and some ~olvent is generally
added to the monomer to moderate reactivity.
The pressure during such grafting reaction ordinarily
is atmospheric, but it can be higher or lower~ The reaction
temperature pref~rably i~ maintained in the range f~om about
80C, to about 130~C. although the temperature may be adjusted
within a relatively wide range to a~commodate the reactivity of
the mixture~ Thus operating temperatuxes in the range from
about 30C. to about 200C. are feasible~ depending upon the
end results and operating conditions selected.
As noted before, the grafting is done in conjunction
with the formation of the addition polymer. The product
resinous blend generally is made t~ have no more than about
3~ oxirane content, with zaro ~o 1% oxirane content r~presenting
a typical level.
-32-
~9~3~
While the u~e of 3 solvent i5 optional, and the re-
action may go forward in the absence of solvent, ordinarily the
amount of solvent may be in the range from about 5% to 30% by
weight of the sum of the other components.
To conclude, conventional soluti~n copolymerization
conditions are preferably employed for such grafting reaction.
The monomer and free radical initiator can bs batch charged to
the epoxy re~in but metered addi~ion i9 praferred for exotherm
control. The reaction mixture is normally held for up to three
hours at reaction temperature, after addition of monomar has
been completed, to complete monomer conversion. When the ep~xy
resin is terminated with terminating agent to eliminate at least
a portion of the epoxy gr~ups, the foregoing techni~ue is used
also, al~h~ugh more solvent can be used i the viscs~i~y of the
modified resin i~ ~aised esp~cially.
'~_
Und~r tha reaotion aonditions described, and with at
lea~t 4% and preferably 6% to 7% G~ benzoyl peroxide by weight
of the monomer mixture, tw~ re~ction products are formed at the
same time, in assocaition with one anoth~r. This i5 referred
to herein a~ a sociative formation.
One product, that i~ presen~ in the final reaction
mixture, is a graft polymer. Under the grafting conditions
described, grafting take~ plaae onto aliphatic backbone carbons
of the epoxy re~in, at those aliphatic backbone carbon atoms
that have either one or two hydrogens bonded therets in the un-
grafted stake. When the proportion of free radical initiator
to copolymerizable monomer i~ at about 34 of benzoyl peroxida
or equivalent, or below that level, ~he grafting at the ali-
phatic backbone carbon atoms i9 le~æ predominant than when
-33-
53(~
higher amounts are employed. Under all conditions, when tha
addition polymerizable monomer includes an acrylic acid, some
ester-type grafting apparently may occur, particularly in the
presence of an amine, bu~ when the amount of benzoyl peroxide
is above 3%, and particularly, above 6%, and such ester direct-
ing nitrogenous cataly~t is not present, the amount of ester
grafting that occurs become$ relatively unimportant compared to
carbon-to-carbon backbone grafting.
Es~er-type grafting can be almost csmpletely elimi-
nated, however, by terminating substantially all of the epoxidegroups prior to grafting. The terminating reaction is a simple
one and may involve the use of more than usual bi~phenol A.
Ths particular reaction conditions required for terminating are
those that are appropriate t~ the particular terminating agent
~elected.
Whether the terminating i6 done prior to, during, or
after grafting, in addition to the graft polymer, the reaction
mixture also cvntains associatively-forme~, ungrafted addition
polymer~ formed fxom the addition polymerizable monomer. Un-
reacted modified resin is dificult o detect in the reaction
mixture, but up to about 10% by weight of the re in solids
present in the reaction mixture may be auch unreacted resin,
and in some cases, particularly wh~re the starting epoxy resin
constitutes a very high percentage by weight of the total
materials reacted, as much a~ 50~ by weight may be unreacted
modified resin. When the starting epoxy resin is as little as
5~ of the initial reaction mixture, a higher proportion of it
may be grafted, and little may be present, ungrafted, in tha
final reaction mixture.
The epoxy resin or modified resin may have very little
-34
531~3
graf~ing on it, but what is there, is important in terms of
properties. It i9 generally preferred that ther~ be sufficient
starting epoxy resin present initially, and sufficient grafting,
so that the epoxy resin component of the graft pol~mer con-
stitutes at least about 5% by weight of the final reaction mix-
ture. To demonstrate what occurs in the production of a resin
binder blend for a sanitary coating composition for the interior
of beverage cans, for example, when the reaction product mixture
i5 formed from initial reactants made up o~ 80 parts by weight
of a diepoxide resin to about 20 parts by weight of a monomer
mixture containing primarily methacrylia acid and styrene, to-
gether with a minor amount of ethyl acrylate, in a weight ratio
of 65:34.:1 respectively, with the reaction t~king place in an
ethylene glycol monobutyi ether/n-butan~l solvent system in the
presence of from about 6~ to about 7% benzoyl per~xide by weight
of the mo~omer mixture, then of the initial 20 parts by weight
of the monomer mixture, about 2-1/2 parts of such monomer appear
combined in the graft polymer, and the remaining 17-1/2 parts
form ungrafted addition copolymer. Prior terminating doe~ not
seem to have a material effect of these proportions.
Because of the difficulty of sepaxating the graft
p~lymer from the other components of the reaction mixture,
molecular- weight measurements on it have been difficult to make
and at best a~e probably only approximations, The indications
are that the molecular weight of the graft polymer is in the
range from ~bout 5,000 to about 40,000.
For coating compositions, the grafting between the
addition polymer component and khe epoxy resin or modified resin
component should take place to the extent of at least 1-1/2
3~ weight parts of the addition polymer aomponent for each 100
-35-
~6~3(~
weight parts of the epoxy resin component. Generally, most of
such grafting i5 at aliphatic backbone carbons that have either
one or two hydrogen~ bonded thereto in the ungrafted state,
with or without prior terminating to eliminate epoxid~ group~.
In other words, eliminating the epoxide group~ does not 3eem to
have a material effect, in most ca~es~ on the de~ired type of
grafting, although prior terminating doe prevent
esterification.
There are ~everal items of evidence indicating that
the graft pol~x~ ~hat is obtained does have the structure des-
cribed~ One important piece of evidence i8 that in the absence
of prior capping, the Acid Numb~r that would be expected to be
obtained from a ~imple mixtu~e of the components, i~ close to
the AGid Numbex that is ob~erved in the ~inal reaction mixture.
This indicate~ that there i~ little ~ster formation during
gxaf~ing. In addition, the evidence obtained through the use
of carbon 13 nuclear magnetic resonance Spe~troBOQpy tend to
confirm a~ do chemiaal reaotions with epoxy fragments ~model
strU~:tureR ),
For coating comp~itions, tha Acid Number of the
resinou~ reaction pro~uct mixture (excluding ~olvents) 3hould
be in the range from abou~ 30 to about 220, or preferably, from
about 45 ~o 150, and for ~anitary coaking compositions, such
acid number ~hould ba in th~ range from about 80 to about 90,
and preferably alo~e to about 85.
When benzoyl peroxide i~ employed at a level greater
than about 3% by weighk o the polymerizable monomer, free
radical grafting to carbon~ in the alipha~i~ backbone chains of
the epoxide xesin compo~ant is fav~red over other type3 of
3~ grafting, but at ths 3% level of benzoyl peroxide, little of
-36-
~91Ei~3~
such grafting occurs with or without prior terminating to elimi-
nate epoxide groups. ~hen the amount of ben~oyl peroxide is
increased to a preferred operating level of about 6% to 7%,
optimum results in terms o$ production of the desired kind of
grafting and economy for making good coating materials are
usually attained.
Resinous xeaction mi~tures prepared in accoxdance with
this invention ~ill con~ain modified resin partially or com-
pletely devoid of epoxy group~. However, the procedure for con-
ve~ting the reaction mixture to a dispersion in an aqueous
vehicle may be the same as in our copending application S.N.
685,24~, in som~ cases. I~ the ~eaction mixture ha~ an Acid
Number of 30 to 220, or prafera~ly 45 to 159, the suspension sr
dispersing procedure i~ generally that describe~ below ~and is
essentially similar to that described in such copending appli-
cation~. If the r~action ml~ture i8 not readily ionizable, a
solvent vehicle may be ~e~ui~ed~ If the terminating agent con-
tributed to acid or baaic functionality, the dispersion step
may be facilita~ed. For the purpoaes of the following dis~
cussion, and to illustrate the aqueous dispersing technique, it
is assumed that the reaation mlxture i8 highly acid-functional.
To convert acid~functional reaction mixtures produced
in accordance with tha present invention to aqueous suspension,
the techniques employed are esaentially conventional. The graft
polymer is dispersed in deionlzed water, using a fugitive base
(under curing conditions for th~ coating~ such as primary, sec-
ondary, and t~r~iary alkyl, alkanol, and aromatic amines and
alkanol-alkyl mixed amines; e.g. monoethanolamine, dimethyl-
ethanolAmine, diethanolamine, triethylamine, dimethylaniline,
-37-
~r
~09~53(~
ammonium hydroxide, or the like. Ordinarily this is done by
adding an amine with some deionized water to the resinou~ blend
and mixing vigorou~ly while ~optionally) warming, then diluting
the reaction mixture with more deionized water as i~ desirea.
The amount of water in the final disper~ion depends
on the vi~cosity desired, which, in turn, is related to the
method of application. For spraying the dispersion, water
amounting ~o about 60~ by weight of the dispersion repre~en~
a typical level, within a preferred r~nge for compssition for
the di3persion of from 10~ to 30% by weight of re~in ~olid~ and
about 70% to 90~ of volatiles, that is, base, water, and sol-
ven~3. The basic is usually about 2% to ~%, water about 30% to
90%, and the organic solvents from about zero to 40%~ the~e
percentages being by weight based on the sprayable dispersion.
The solids comprise the reaction mixture solids, about 9~ to
23%, and cross-linking agents, abQut 1~ to 10%, based on the
weight of sprayable dispersion.
As to applications other than spraying, the aqueous
dispersion may comprise: 10% t~ 40% 601ids, which are pro-
portioned as follows: 0.1% t~ 16% by weight of a cros~-linking
agent, and 6% ~o 39.9~ by weight of the reaa~ion mixtur~7 and
60% ~o 90~ volatile ~ornponents, generally divided into organic
~olvent, 6% to 35%, and water, 25% ko 80%. It i9 preferred
that ome organic solvent b~ used to fa~ tate appliaation,
and it iB ~enerally u~ed in the ra~io of one part by wPight
of solvent to about three parts by weight of water.
The organic solvent oan be made up of one or more of
the known ~olvent~ such as butanol (normal), 2-butoxy-ethanol-1,
xylene, tolu~ne, and othsr ~olvents. It is often preerred to
use n-butanol in combination with 2-butoxy-ethanol-1, in equal
-38-
, ,~,
~o~
amou~ts. ` ;
An aminoplast re~in can be utilized for cros3-linking
with the graft polymer. I~ can be added to the graft polymer
before neutralization and diluting, or thereafter. Typical
aminoplasts include melami~e, benzoguanamine, acetoguanamine,
and urea resins such as urea formaldehyde. Commercially avail-
able aminoplast which are water soluble or water disper3ible
for the instant puxpo8e include Cymel 301, Cymel 303, Cymel 370,
and Cymel 373 (all bei~g pr~ducts of American Cyanamid,
Stamford, Connecticut, a~d baing melamin~ based, e.g., hexa-
methoxymethyl melamine or Cymel 301), and Beetle 80 ~product
of American Cyanamid which a~e methylated or butylated urea~).
"Cymel" and "Beetle" ar~ ~ra~emarks.
Oth~r suitable amin~plast resins are of the type pro-
duced by the reaction of al~hyde and formoguanamine, ammeline,
2-chloro-4, 6-diamine-1,3,5'triazin~;2 phenyl-p-oxy-4, 6-diamino-
1, 3, 5-triazine; 2-phenyl-p-oxy-4, 6-krihydrazinel, 3,5-
triazine, and 2, 4, 6-kriethyl-~xiamino-1, 3t 5-txiazine. The
mono-,di-, or triaryl melamines, or instance, 2, 4, 6-tri-
phenyltriamino-l, 3, 5-triazine, are pre~erred. Other aldehydes
u~ed to react with the amino aompound to form the resinous
material are croto~ic aldehyde, acrolein, or compound which
generate aldehydes, such aQ hexamethylene-tetramine, par-
aldehyde, and the lik9.
If there is little or no oxirane functionality in the
graft polymer, ~hen a cross-linker i~ necessary; otherwise, it
i9 de~irable, but the graft polymer i9 self cross-linking with
heat.
Another way ko introduce cros~-linking capability into
the reaction mixture and the grat polymer i9 by utilizing as
-39-
31al~653(~
all or part of the addition polymerizable monomer, in the initial
reaction mixture, a matexial such a~ a crylamide or an alkyl
derivative thereof, or a material such as bis maleimide.
The coating composition of the present invention can
be pigmented and/or opacified with known pigment~ and opacifiers.
For many uses, including food uses, the preferred pigment is
titanium dioxide. Generally the pigment is used in a pigment- -
to-binder ratio of 0.1:1 to 1:1, by weight. Thus ti~anium
dioxide pigment can be incorporated into the composition in
amounts of from about 5% to 40% by weight, based on ~olids in
the compo~ition.
Tha resulting a~ueous coating composition can be
applied satisfactorily by a conventi~nal method known in the
coating industry. Thus, spraying, rolling, dipping, electro-
depo~ition, or flow csating applications can be u~ed for both
clear and pigmented films. Ofken spraying is preferred. After
application onto the metal substxate, the coating is cure~
thermally at t~ra ~ e~ in the range from about 95C. to about
235C or hi~her, for perio~s in the range from l to 20 minutes,
~uch time being sufficient to effect complete curing as well as
volatilizing of any fugitive aomponent ~herein. Further, films
may be air dried at ambient b~xa~e~ for longer periods of
time.
For sheet metal ~ub~trates intended for use in the
manufacture of beverage containers and particularly for car-
bonated beverages such as b~er, the coating shsuld be applied
at a rate in the range fr~m O.5 to 15 milligrams of polymer
coating per square inch of exposed metal surface. To attain
the foregoing, ~he wa~er-dispersible co~ting a~ applied can be
as thick as l/lOth to l mil.
-40-
For a bet~er understanding of the present invention,
the following examples are provlded. In this application, all
parts are parts by weight, all percentages are weight percent-
ages, and temperatures are degree~ Centigrade unles3 otherwise
expressly noted. The amine-containing a~ueous dispersions of
the first five examples were all stable at room temperature for
long periods.
EXAMPLE 1
Terminating Prior to Grafting, UQing Phenol
as the Terminatlnq Aqent
877.5 Grams of solid epoxy re~in (DER 661), a trade-
mark of the Dow Chemical Comp~ny, average molecular weight lOiO
and oxirane oxygen (3.05%) was charged to a 5-liter, 4-neck,
agitated, glass flask heated by a mantle. The flask was purged
with nitrogen, and 52 gram3 of phenol was added thereto.
Reactor contents were h~ated to 200C., and this temperature
was maintained for three hour~. The oxirane oxygen of the
resinous mixture then was determined to be 2.29%. 0.5 ml. of
ethyl triphenyl ph~sphine acatate cataly~t was added to the flask
to facilitate the reaction between the phenol and the epoxy
re~in. The temperature was maintained at 203C. for two more
hours, ater which the oxirane oxygen measured 1.56~. An ad-
ditional 1 mil. of said phosphine aoetate catalyst was added,
and the reaction was continued at 203C. or 1.5 hours. The
oxirane oxygen measuremenk showed no change ?
254 Gram6 of ethylene glycol monobutyl ether was added
310wly to the r~actor, this followed by the 910w addition of
430 grams of n-butanol. The mixture was allowed to cool and
stand overnight at room temperature. The reactor then was
heated under nitrogen to 117C. and held at that temperature
for two hours.
-41-
~0~6~
In a separate vessel, a monomer mixture of 150 grams
of methacrylic aid, 78 gram~ of styrene, 2 grams of ethyl acry-
late, and 20 grams of wat benzoyl peroxide (78% BP in water;
amount on dry basis = 15.6 g. or 6.8% by weight based on the
total weight of polymerizable monomers) was prepared in 59 grams
of ethylene glycol monobutyi ether. Thie monomer mixture was
added ~1QW1Y to the agitated reactox contents over a 2-hour
period while maintaining khe temperature of the contents at
117C. After the monomer were added, the reactor temperature
w~s main ained at 117C. for ~ne moxe hour, then 33 grams of
n-butanol was added.
1500 Grams of the foregoing reaction product was then
placed in an agitated vessel, and the following diluents were
added: l9a7 grams of deionized water, 108 grams of ethylene
glycol monobutyl ether, and 85 grams of dimethyl ethanolamine.
These last three items were added to the vessel as a neutraliz-
ing mixture calcula ed to produce about 70% neutralization of
the carboxylic acid groups pr~sent in the reaction product. The
resistivity of the deionlzed water was at least 50,000 ohm-cm.
This addition cooled the con~ent~ of the vessel to about 50C.,
and a~ter a short time the content~ of the vessel were cooled
further by an addition of 313 more grams of deionized water,
with mixing throughou~ the ~ilu ion operation.
The disper~ion ~mul~ion) thu~ produced was a further
water-reducible re~in~us c~ating compo~ition having the follow-
ing properties:
Nonvolatiles 24.3%
Viscosity ~Ford NoO 4 Cup at 25C.) 23 seconds
~ Neutralization 70
Aci~ Number of composition 95
The emulsion was stable an~ suitabl~ for formulating into a
sprayed-on sanitary coating for cans.
-~2-
~e~9~;5~
EXAMPLE 2
Terminating Prior to Grafting, Using
A Saturated Fatty Acid AB Terminating Agen~
An agitated reaction vessel was charged with 1289
grams of DER 661 ~olid epoxy resin and 466 grams of a com-
mercially available ~aturated C12 fatty acid (NEOFAT-12, a
trademark of Armour Industxial Chemical Co.). This product is
regarded as a commercially pure lauric acid. The molar ratio
of ~uch acid to epoxy xesin was about 2.33 to 1.22. ~For com-
plete termination, a mol ratio of at least 2.44 of thi3 acid to
1.22 of the epoxy resin would be raquired.) The theoretical
Acid Number of the initial reaç~ion mixture, based on the
acidity of the lauric acid, is 74.5. The progress of the re-
action wa~ monito~ed by observing the decrease in Acid NumbPr.
The vessel was h~atad to 180C. and held at this temperature
for about two ho~r~ under a nitrogen purge. The Asid Number of
a sample of the mixtu~e, taken at that point, was 12.73, and the
oxirane ~ntent was 0.33%. Tha temperatuxe was then increased
to 195C.
A~ter a 9ho~t period of tLme, the contents of the re-
actor were diluted by tha addition of 480 grams of ethylene
glycol monobutyl ethex and 826 gram3 of n-butanol. After mix-
ing, the diluted reacti~n mixtur~ was allowed to stand over-
night, with gradual loss of tempera~ure on stan~ing.
~he dilu~ed reaction mixture wa8 then heated under
nitrogen to a temperature between about 113C. to about 117C.
M~anwhile, in a g~parate ve sel, a mixture was made up of 283
grams of methacrylic aaid, 148 grams of styrena, 4 grams of athyl
acrylate, 38.5 gram~ of wet benzoyl paroxide ~78~ in water,
about 6.9% by weight ben~oyl peroxide basad on wPight of poly-
merizable monomers) and 111 grams of ethylene glycol monobutyl
-43-
"
~9~
ether. This mixture was added gradually to the reactor, with
the reactor temperature baing maintained at about 115C. An-
other 62 grams of n-butanol was added, and the reactor was main-
tained at about 115C. for an additional period of thrse hours.
At the end of that time, a quantity of 2,683 grams of
the diluted reaction mixture was transferred to a large agitated
vessel, and was treated with a neutralizing mixture made up of
3,411 grams of deionized water, 193 grams of ethylene glycol
monobutyl ether, and 152 gram~ of dimethyl ethan~lamineO This
is calculated to give 70% neutralizatiQn. After a short period
to permit equilibration, a final ~ilution was made by adding 560
grams of dionized water. The final dispersion had the following
properties:
Nonvolatiles 21.8%
Visco~ity (Ford No. 4 Cup at 25C.) 21 seconds
Acid Number of Final Disper~ion 22~88
Acid Number of Nonvolatile Portion 105
This disper ion of a reaction produot made from the
above partially fatty acid-terminated epoxy resin has excellent
characteristics for coating applications.
EX~IPLE 3
Terminating Prior to Gxafting, Uc~ing
The starti~g material was a liquid epoxide resin~ DER
333, that is reported by its manufa¢turer, Dow Chemical Company,
to have an epoxide equi~alent weight of 197 to 200, and a weight
of about 9.65 lb /gal. The calculated average molecular weight
~8 399. A reacto~ was ~h~rged with 1,1~7 grams of this low
molecular weight resin, to which wa~ added 310 grams of ethylane
glycol monobutyl ether. The content~ were reacted with 588
grAms of bi~phenol A at 150C. to increase its molecular weight.
The reaction wa aLlowed to equilibrate at 175-183C. for about
--44--
~653~
three hours and then was deemed to be complete, (the oxirane
content was measured as 0.586%. The Gardner-Holdt viscosity
was X-Y.)
To terminate ~he epoxy resin, 83 grams of benzoic acid
was added to the reactor, al~ng with 2 grams of benzyl dimethyl-
amine aR a cataly~t for such terminating reaction. The reactor
was heated to 160C. and wa~ then maintained at about 150C.
for three hours. At that time a ~ample was determined to have
an oxirane content of O.Q35~ on nonvolatiles and an Acid Num~er
of 8.48. Accordingly, the reaction waR continued for an
additional hour, aftex which the oxirane content was found _o
be 0.026%, and the AGid Number was 4.
The contents of the reactor were then diluted by the
addition 183 grams of ethylene glycol monobutyl ether and 85
gram~ of n-butanol. ~he temperature was then maintained at
118C under a nitrogen blanket over a two hour period, during
which a monomer mixture was lswly added to the reactor. The
monomer mixture was made up of 294 grams of methylacrylic acid,
154 grams of styrene, 4 grams of ethyl acrylate and 39 grams of
benzoyl peroxide (approximately 8.6% by weight ~a~ed on poly-
merizable monomer). The reacti~n mixture was then further
diluted by the addition of 62 grams of n-butanol.
A neutr~lizin~ ~olukisn was made up of deionized water
and dimethyl ethanolamine, toge~her with about 10% weight o
the mixture of ethylene glycol monobutyl ether. ~he neu-
tralizing mixture wa~ added to the diluted reaction product,
with mixing, until the Acid Number of the resulting di~persion
measured 21.8.
-45-
'.~
~L~g~3C~
EXAMP~E 4
Low Molecular Weight Epoxy Resin
Terminated with Bispheno ~
An agitated, nitrogen-purged reaction ves~el was
charged with 1,079 grams of the liquid epoxy resin, DER 333,
310 grams of ethylene glycol monobutyl ether, and 676 grams of
bisphenol A. The content6 were heated to 140C., and the heat
turned off. Temper~ture rose to 170C., at which temperatur2
the reaction was held or 5 h~urs. At ths end of this time the
oxirane content was 0.~74%. 701 Grams of n-butanol were added
and the ~ontents were allowe~ to aool overnight.
The bisphenol A terminated epoxy resin was heated to
117C. and then reacted with a m~nomer mixture that was added
810wly to the terminated epoxy resin over a two-hour period.
The monomer mixture wa~ made up o~ 365 grams of methacrylic
acid, 191 grams of styrene, 6 gram~ of ethylacrylate, 4B grams
of wet benzoyl peroxide ~78% BP in water or about 6.7% by weight
of the dry free radical initiator based on weight of the monomer
mixture) and 157 grams of ethylene ylycol monobutyl eth~rO
After this period the Acid Number of the product was 104.
A neutralizing solution ~f 4248 grams of deionized
water, 132 grams o dimethylanolamine, and 120 gram3 of ethylene
glycol monobutyl ether. At that point~ the nonvolatile cont~nt
of the emulsion was 27.1~, and the viscosity as measured by a
No, 4 Ford cup a~ 25C. was 105 second~.
Upon evaluation in a spxayable coating composition
for beverage cans, the dispersion was found to be quite
satis~actory.
-46-
EXAMPLE S
Production of a Powdered Product_for Aqueous Di~persion
Coating composition~ prepared in accordance with this
invention can be applied from purely organic solvent vehicles
and from aqueous vehicles. For many coating purposes, however,
it is very convenient and economical if the end product is
available in the form of a readily water-dispersible powder that
can be ma~e up into an aqueouC coating f~r spraying as needed.
Some of the obviou~ advantages of ~uch 301id product are that
it requires less space ~or storage and is at mimimum weight for
shipm~nt. Thi~ example describes the production of such a
powder product.
3 mols DER 333 resin ~1200g) was reacted with 4 mols
of bisphenol A (912g) to make a bi~phe~ol A-terminated modified
resin in the ab3ence of 601vent, using a nitrogen blanket. m e
reactants were charged together into an agitated reactor fitted
with a trap and condenser, and the mixture was heated to 165C.
to initiate the reac~ion. The exothermic heat of reaction was
allowed to dissipate~
~he molten mass thus pr~duced was thlnned with 125 ml
(lOOg3 methyli~obutylket~ne to make it mo~e readily stirrable
at eleva~ed temperatures. A meaqured quantity of 2212 weight
part~ of this ~lightly thinned ma~ was maintained with
agitation at 139C. initially while a mixture of vinyl and
acrylic monomer~ was dripped into it. Addition of the monomers
; took two hours, with temperalture o~ the ma~s ri~ing to 158C
during this time. The mass wa~ then 3tirred ~or an additional
hour. The momomers were a mixture o~ 30.6 weight percent (276g)
methacrylic acid, 35 weight parcent (316g~ styrene, and 34.4
weight percent ~311g) ethyl acrylate, do~ed with 5% by weight
-47-
",~
~653~
(45 . lg) dicumyl peroxide based on the weight of these mixed
monomers.
The mass was permitted to cool and sclidi~y, then
pulverized. The Acid Number of the product was 46.3. When 40
parts of the powder were di~lved in 60 parts of 2-butoxy-
ethanol-}, the Gardner-Holdt vi8c03ity was X-Y and a slight
haze could be observed in the solution. me pulveri~ed product
did not adhere together ~block) at 120F, but did so slightly
at 135F.
A 100 gram ~ample o~ the pow~ered produst was mixed
with 267 grams of water~ 7.4 grams of dimethylethanolamine, 18
grams of h~methoxymethylmelamine resin (Cymel 370, a product
of American Cyanamid Company) and 50.6 grams of 20butoxy-
ethanol-l. The powdered bl~nd dispersed well, and the resulting
dispersion was ~hinned with 60 gram~ of wa~er to give a coating
product having 23.6 weight percent resin solids and Number 4
Ford Cup viscosity of 35 secondg.
This ~hinned ~isp~rsion had the following coating
characteri~tics on tin-free ~eel and aluminum. The dispersion
was ~pread wi~h rods on the~e substrates and b~ked for 3 minutes
at 196C. to cure the wet film~. The first rub test below had
wet film thickne~ before cure of 1.5 mil. Ths econd rub test
below and the rei~t of the tests below were made on cured residues
of 1.4 mil thick wet ~ilms, The cured film is about one-fifth
as thick.
Test Tin-Free Steel Aluminum
Methylsthylketone ru~s to 100 more than
film rupture; 1st te~t 120
Methylethylketone rubs t~
film rupture; 2nd te~t 55 70
Blushing of cured c~a~ing from
-48-
3~)
Test Tin-Free Steel Aluminum
pasteurization tretment; 3rd test none none
Test Tin-Free Steel Aluminum
Adhesion by Scotch tape method 0 2
0=no coating removed
10=all coating removed
The aqueQUS dispersion was stored at 120F. and lost
very little viscosity and only A minute bit of alkalinity in a
week. After about 5 week~ storage at 120F. vi~cosity declined
from 35 seconas to 20 seaonds a6 measured by a Number 4 Ford
Cup, but this was not ~onsidered 3arious because the product
still remained well-dispe~ed and useful. It would not be ex-
pected to be stored a~ a wet dispersion for long periods at
high temperature, par~icularly beoau e ordinarily the p~wdered
product would be stored.
EX~MPLE 6
COMPOSITION USEFU~ FOR CAT~O~IC E~ECTROCOATING
450 grams of DER 331 rasin and 400 grams of a~hylene
glycol monobutyl ether were mixed in a reactor ~4 liter, 4-neck
agitated, glass flask) and heated to 100C. under a nitrogen
atmosphere.
This monomer mixture was made in a separate vessel:
1080 grams butyl acrylate, 540 grams styrene, 180 grams of
hydroxy ethyl acrylate, 155 gram~ of 78% benæoyl peroxide in
water, (130 grams BP on dry basis), and in 340 grams of ethylene
glycol monobutyl ether.
The reactor containing the epoxy resin was heated to
118. Then the monomer mixture was added over a 2-hour period.
The temperature was held at 118 for 3 additional hours. At
-48a-
~6~3~
this stage the following propertie~ were determined.
Visc05ity = X (Gardner-Holdt at 25C~
Non-Volatile Matter = 70.9%
Oxirane Oxygen = 1.5% on nonvolatile matter
In an agitated vessel 1027 grams of the above reaction
product ~70.9~ re~in in solvent) was heated to 116C. 84 grams
of diethanolamine then was added, and the temperature held at
116C. $or 1.5 hours~
The purpo~e of so adding the amine was to eliminate
oxirane groups and produoe a cathodiaally-attractable, modified
re~in paint binder u~eful for formulating into an aqueous
painting bath for direct current cathodic electrocoating.
EXAMPLE ~
Investiga~ion o the_Grafting Mechani m
A polymeric bl~nd i prepared by reacting an epoxy
resin with an addition polymerizabla monomer mixture in an 80
to 20 weight ratio, in ~he following manner.
Fir t, a DER 333 li~uid epoxy xe~in is reacted with
bi ph~nol A in the proportion of a~out 65% of the resin to
20 about 35~ by weight o~ bigphenol A. In a separate vessel a
mixture is made of methacrylic acid, styrene, and ethyl acxy-
late, in the weight ratio of 65 to 34 to 1, re~pectively.
About 6.8% sf kenzoyl peroxid~ i5 added by weight of the mixture
i~ then graduall~ added to the epoxy resin at a reaction tem-
perature of ahout 120C. during a two hour perio~ After an
additional holding perisd of about ~wo hours a~ the samP
eleva~sd temperature, ~ample~ of the product are taken for
structural evaluation.
Carbon 13 nuclear magnel:ic reqonance spactro~copy
indicates that most of the grafting between the addition
-48b-
~"~
6~30
copolymer and the epoxy re~in i re~tricted to what had been,
before the grafting aliphatic secondary ~and po~sibly aliphatic
tertiary) backbone carbon atoms of the epoxy resin bac~bone.
In order to delineate further such grafting, several
different model compounds, each having an aliphatic carbon atom
arrangement like some of those present in the epoxy resin, are
reacted separately with the same mixture ~f monomer~ under con-
ditions comparable to the grafting con~itions described abo~e.
Carbon 13 nuclear magnetic resonance spectroscopy on thPse re-
sulting analog pr~duct~ indicate~ that grafting on aliphaticbackbone carbon atoms of the model compounds occurs practically
entirely on those carbons which had been aliphatic secondary
carbonR alpha to oxirane groups prior to grafting. This sug-
gests a fair likeliho~d of the same situation prevailing in
- the instant resinou~ blend reacti~n product, A small decrease
is noted in the Acid Number of the reaction product, relative
to the Acid Number calculated or the equival~nt mass but based
upon all of the methaorylic acid charged to the reactor, and
thi~ small decrease in Acid N~mber tends to sorroborate the
20 f indings made through Carb~n 13 spectroscopy.
Hence, it is concluded that while oth r grafting to
aliphatic carbon atoms of the epoxy resin backb~ne may occur,
the propor~ion is minor r~lative ~o the grafting on those
aliphatic backbone carbon atoms in po~i~ions alpha to the
oxirane groups and on other aliphatic backbone carbon that
have either one or two hydrogen~ in the ungraftQd stateO
The foregoing polymeric blend can be reacted with
benzoic acid in the manner of Example 4 (using catalyst~ to
eliminate virtually all oxirane content in the graft polymer
39 ~between the epoxy resin and the copolymerizable monomers) and
-48c-
53C~
unreacted 2poxy resin presentO BY so doing, the possibility of
uncontrolled subsequent reaction of oxirane groups is precluded.
The resinous product then can be formulated into stable aqueous
compositions for coating in the manner of Example 4.
Our sub~equent experience with epoxy resina that have
been reacted with chemical terminating agent3 to eliminate
epoxide gr~ups and make modified resin preparatory to the
gra~ting reaction with additlon polymerizable monomer indicates
no material difference in performance of the resulting resinous
blends made up into aqu~ous coating compositions with amine
from those wherein such termination i3 done after the grafting.
Accordingly we conclude that the grafting to aliphatic carbon
atoms in such instance i8 enough like that described in this
Example 7 to give substantially the same practiced results.
E~A
Effect of Using Different
Amount of Benzo~l Peroxide
_____ .
A s2ries of resinou~ blends are prepared in assentially
the same manner as described in Example 7, but with each addition
polymerizakion operation u3ing a diferent per~en,age of benzoyl
peroxide free radical initiator based on the weight of the
mixed m~nomers~
The approximate weight fraction of t~tal mixed monomers
charged that grafts ~nko the epoxy resin i~ estimated by solvent
extraction, The blend~ are observed for their ease of dis-
per6ibility in aqueous amine solution, and the resulting aqueous
dispPrsion~ are observed for their resistance to precipitation
~stability) for a week. The ollowing observations for this
work are typical.
-48d-
~,;.
~i96530
Table V
~t. % Benzoyl Approximate wt. % total
Peroxide based on Mixed monomer~ grafted
Mixed monomersto epoxy resin _ Remarks
3 3.0 marginally dis-
per6ible, tending
to separate in
about a day ~1)
11.5 very stable aqueous
alkaline dispersion
made readily
7 15.0 "
9 28.2 .,
45.0 " (2)
(1) Would be considexed borderline at best for sanitary coating
use and most likely would require considerable extra
hydr~philic organi~ solvent for ease of aqueous dispersion.
~2) The high pxopsrtion of free radical initiator not only gives
rise to concern~ about high cos~s, but also concerns about
the possibility of free radical initiator fragments~e.g.
benzoic acid) giving rise to undesirable organsleptic and
other properties, e.g. tending ts produce components
extractable into beverages, varioUs low mol weight~sub-
stances, etc.
The foregoing polymeric blend can be reacted with ben-
zoic acid in the manner of Example 4 (using catalyst) to elimi-
nate virtually all oxirane content in the graft polymer (between
the epoxy resin and the copolymerizable monomers~ and unreactPd
epoxy resin present. By so doing the pQssibility of uncontrolled
~ubsequent reaction of oxirane groups i5 precluded. The product
can be formulated into a table aqueous composition for coating
in the manner of Example 4.
EXAUPLE 9
Terminating Prior to Grafting Using
921 Gram~ of liquid epoxy resin (DER 333, average M.
W,=399) and 591 grams of bisphenol A were charged to ~ 5-liter
4-neck reactor flask placed in a heating mantle. The flask was
-48e-
~)96~5~
then heated ~ntil the temperature of the reactants reached
150C. at which point the heat wa~ turned off. The reaction
temperature continued to rise to 187C. which was maintained
for one hour. The oxirane oxygen of the reaction mixture then ^~
was measured at 0.048%. 582 Gram~ of ethylene glycol monobutyl
ether was added slowly to the reaction mixture followed by the
~low addition of 872 grams of nwbutanol. The reaction mixture
comprising the bisphenol A terminated epoxy was ailowed to cool
to 120C.
In a separate ve~sel the following monomer mixture
was made: 282 grams of methacrylic acid, 173 gram of styrene,
193 grams of ethyl acrylate, and 44 grams of benzoyl peroxide
(about 6.8% by weight based on the weight of monomers). This
monomer mixture wa~ added to ~he reactor containing the
bisphenol A terminated epoxy over a two hour period ~hile main-
taining the temperature at 120C. The entire contents were
maintained at 120C. for an additi~nal three hours with mixing
after which ~he Acid ~umber wa~ dete~mined aæ 91.
3169 Grams ~f the reaction mixture was placed in a
20 large stirred ves~el and heated to 100C. at which point 3824
grams of deionized water and 207 grams of dimethylethano amine
were added. The neu~ralizlng ingredient was proportioned to
provide about 80% neutralization. The contents were maintained
at lO9~C. for one hour, then cooled with the addition of 1800
grams of additional deionized water. The neutralized dispersion
was allowad to stand at room temperature overnight~
The disper~ion thUC~ produced was a resinous sanitary
coating composikion for beverage canq having the following
propertieCl:
~48f-
~9~i~i3~
Nonvolatiles: 20%
Viscosity (Ford No. 4 Cup at 25C): 14 sec.
pH: 7.4
% Neutralization: 80%
Such di~persion showed no measurable change in viscosity or
pH even after stsrage at 49C. f~r a period o~ two weeks, and
dispersion stability was shown by no precipitation in this
period.
General Comments
To sum Up, this invention proYide3 a330ciatively-
. formed resinous blend of ungra~t~d ep3xy re6in that has been
.~ modi~ied ~o eliminate at least a part of its epoxide groups,
ungrafted addition polymer, and grafts of addition polymer onto
the modifiad resin structure wherein ~uch grafting is r~stricted
mainly to what were, bef~re such grafting~ aliphatic secondary
(and possibly aliphatic tertiary) oarbon atoms of the epoxy
resin or modified resin aliphatic carbon backbone.
This grafting provides an sspecially durable linkage
for further redesigning the epoxy resin ~o as to exert a pro-
found influence on the properties of the ~esinous blend product
as well as ko impart lasting characteristics of the grafted-on-
addition poIymer to the epoxy re~in or modified resin receptor.
Thu6, for example, such a graft polymer that is rich in carboxyl
groups imparts to the resinous blend product superior char-
acteristic~ for making water-re~uced sanitary ooatings used in-
side cans for beverage3 and the like, provided that there are
a few parts by weight of grafted carboxylic acid-containing
addition polymer supplying at least about one weight part of
carbcxyl groups per 100 parts of starting epoxy resin. Such a
blend i8 highly resis~an~ to undeRirable reaction in and pre-
cipitation from mildly alkaline aqueous dispersion.
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530
To obtain even so modest a proportion of this durable
grafting and attendant influence upon properties of the
associatively-formed blend, it is es ential to commence the
addition polymerization with an unu~ually large amOunt of free
radical initiation relative to the polymerizing temperature and
amount o polymerizable monomer being used, e.g. from 4~ to 7%
or more by weight of benzoyl peroxide baæed on weight of such
monomer when reacting at a temperature abouk 115C. to about
125C.
In its preferred embodiments, then, this invention is
primarily concerned with the production of re~inous compositions
that are intended for use in coating cans for items for human
con~umption, and particularly, for soft drinks and beer. There
are sevaral tests that are applied in order to determine whether
a particular coating composition is sati factory for these
surprisingly deman~in~ en~ . uses. Some of the
~48h-
`~
536~
more important tests are described briefly below. Whenever a coating
composition has been indicated in this application to be acceptable for
use as a sanitary coating composition, it can pass many of these tests.
The Flavor Test. The cured coating in the can should impart
no discernible flavor to the contents of the can, nor should it alter the
flavor of the can contents in any way. This test is particularly important
with respect to beer can coatings.
Adhesion. The adhesion test is conducted at room temperature
under ambient humidity conditions. The coated panel to be tested is cross-
hatched by cutting three parallel lines, each approximately 1l' long, about
1/8" apart. These lines are intersected at 90 with thre,e identical lines
similarly spaced. Usually a knife edge or razor blade is used to cut the
lines. A strip of Scotch cellophane tap~e is then firmly pressed diagonally
across the scribed squares. "Scotch" is a Trademark. The tape is pulled
off with a quick continuous pull, using a peeling back motion at an angle
of pull of about 150 . The cross-hatched area of the panel is then
inspected for removal of coating. If any coating is removed, the percentage
is recorded as a numerical rating in the range of zero to 10. A ~ero rating
indicates a perfect score, with no removal, and a 10 rating indicates
100~ removal.
Storage Stability. Water reducible coatings must demonstrate
acceptable hydrolytic stability on extended storage. This is determined
by making an initial measurement of all of the properties of the coating
composition and then redetermining them after a period of storage, on
samples stored no~ only at room temperature but also at 50C. Some of
the most significant parameters, with respect to stability, are freedom
from gelation, fr edom from precipitation, and freedom from changes in
pH. To be acceptable as a sanitary coating composition, there should be
little discernible change in viscosity after room temperature storage for
12 months or after storage at 50 C for 8 months, indicating the absence of
gelation.
Thermal Stability. In some can manufacturing processes, after
the coating has been applied, the coated metal is dipped in a solder bath
- ~ at a temperature
~9 _/.n_
in the range from about 340C. to 370~C. for a period up to
about 5 seconds. The amount of discoloration of the coating i3
an indication of tha extent of dec~mposition. In other can
fabricating operations, where US9 iS made of ends that are die-
stamped, the assembled cans are usually immer3ed in a bath of
acidic copper sulfate for 5 minutes, to test for any cracking
in the coating during the fabrication. The pxesence of a crack
will be indioated by the deposition of a small amount of copper
on the metal of the can.
Water Pasteurization Test. This test is often oer-
formed on curPd coatings that have been sprayed and baked on
the interi~rs of two-pi~ce al~minum cans for beverages. The
test is al~o used to measure the resis~ance of a coating
material to water and to water vapor at pasteurization ~m-
perature. For test purposes, the c~ating weight iB from 12 to
16 milligrams per 4 square inches of panel. A~ter the coating
has been applied and cured by baking for about 2 minutes at
about 218C. (390F.), tw~ test strips are cut from the coated
panel, each approximately l-l/2"X 9". The top ~" ~f each test
strip is bent back upon it~elf, with the coated side exposed~
Each te~t 5trip iB th~n half-immerse~ in a water bath at about
94C.(170F.) by handing each strip over the edge of the water
bath. After immersion for 1/2 hour, the ~trips are cooled under
running tap water at room temperatuXe, dried, and examined
immediately for blush and for adhesion.
Any blush (whitening) indiaate~ the absorption of
water during pasteurization and is rated on a scale from zero
to 10, zero being per~ect and indicating no blush, and 10 in-
dicating complete whitening. Both the immersed area and the
area exposed only to water vapor are rated. A blush rating
-5~-
: ~,
~0~s3~
range of zero to 2 is acceptable.
The adhesion test, as described above, is applied to
both the immersed area and the water vapor expo~ed area, and i5
rated accordingly, again on a scale of zero to 10. Coating
removal from a test strip in the range from zero to 1 is
acceptable.
namel Rat-r 5~ct. This is a test employed by canners,
to evaluate metal exposure in c~ated cans. Under the conditions
of the te8t, a low voltage is applied between an electrode that
is immersed in an electrolyte-filled can, and the can body.
When the coating on th~ can i~ imper ect, metal i5 exposed and
current flows. The flow o current i9 indicated on a meter,
and the magnl~ude of the current i8 related to-the total area
of metal that is expo~çd to the electrolyte. m us, the size of
the current flow, as indicated by the reading on the milliam-
meter, provides a relativ~ measure of the total metal exposure.
Ge~erally, each canner has his own specification a~ to the
permis3ible current flow.
The conditions of the test involve the use of a
standardized electrolyte, ~nd a coating weight of 2.5 mgs, per
square inch. For a 12 ounce b~verage can, this coating weight
i8 approximately 110 to 120 ~g~. per can. Und~r the usual test
conditions, a aurr~nt flow rate bel~w 25 milliampere~ is accep~-
able for alu~inum beer can~, for many brewer~.
The requiremenk~ for soft drink cans are more stringent
and the normal requirement for alumlnum qot drink canQ in pro-
duction is a current ~low rate of less than 5 milliamperes.
Accordingly, higher coating w~ights are normally applied to
coatings for ~oft drink cans, normally about 4.5 mgs./in.2,
which amount~ to about 160 to 200 mgs. for a 12-ounce ~oft
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, ~
~09G53V
drink can.
The following characteri3tics are also often evaluated
for sprayable coating compositions for two-piece cans.
Wetting. The composition on the coated surface must
have the ability to form a continuous wet film. This is a par-
ticularly critical requirement with respect to the lower wall
area of two-pieoe cans because this is where the can is farthest
from the spray gun.
Blister Re3istanoe. Som~ applications, such ~s single
coat~ for two-piece tin plated cans, require high coating
weights. No~mally the highe3t wet film concentration will occur
in the moat area. Because of the great thickness of the film
in ~his area, there i9 a tendency to blister, which is a dis-
ruption o~ the film urface by vol~tilization o~ liquid.
Foaming, When applied by~an airless spray hy 1,000 psi,
the coating must not ~oam on the can. When foaming occurs, it
causes film discontinuity and a rough urface.
COWCLUSION
Water dispersion sanitary coating compositions made
in accordance with embodiments of this invention can pass many
of the te t~ mention~d above. Such compositions perform excep-
tionally well when spray0d by both air and airless d~vices.
Excellent atomization can be obtained regardless of the type of
nozzle or pressure, that is, excellent spraying applications
can be obtained at pressures in the range from 2 psi up to
1590 psi.
Coating materials ma~a in aGcordance with the invention
have been applied to tin plate, aluminum, to metal coated with
primers, to plastics made ~rom ABS, polyolefins, polyesters,
polyamides, and the like, in a range o~ application thicknesses
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producing cured weights per 12-ounce can in the range from 1
to 10 mgs/in, which i5 50 to 300 mgs. per 12-ounce can. Film
continuity generally has been excellent throughout this range.
Moreover, these compositions have excellent application
properties and generally their u e is free from problems with
respeçt to blistering, sagging, solvent washing, foaming, and
excess flow. It is common with water-reducible coatings to
encounter odor problems in the spraying equipment, but no such
problems have been ena~untered with compositions pr~pared in
aocordance with this invention.
While the specific examples demonstrate, generally,
preferred embodimen~s of the invention, other preferred embodi-
- ments and practices als~ lead to excellent coating compositions.
Thus, if the procedure of Ex. 3 is followed, and then diluent
addition copolymer made by the addition copolymerization of the
same monomer mixture a~ u~ed in that example, i~ added to the
reaction pr~duct mix~ure, quite satisfactory coatings can be
obtained, ~enerally at lower cost, up to addition levels
vielding an ungrafted total of about 40% of a~dition polymer
based on the mixturP, an~ even more may be tolerated. Similar
re~ults are obtained when the only diluent used is ad~ed apoxy
re~in, i.e., when ther~ i~ no addi~ion to the reaotion mixture
of separately polymeriz~d addition copolymer. However, any
addi~ion o~ epoxy resin generally i~ for properties rather than
for economy. Both epoxy ~esin and eparateiy formed addition
polymer may be added, however, f~r a combination of property
modification and economy.
While the compositions described generally have been
tho~e using liquid vehicle~, the binders may be prepared in
the absence of ~olvent~, coolad, and pulverized to form powdered
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~r
~"~
~9~53~
products, as in Example 5. TheRe powdered products can be
dissolved in solvent vehicles, and can be dispersed in aqueous
vehilces if some amine is added at the time of use. Concentrates
may also ba useful for economical shipping.
The amount of the prefsrred free radical initiator,
benzoyl peroxide, has been expressed in terms of percentage base
on weight of the addition polymerizable monomer. Based on the
entire reaction mixture, it is preferred that the amounts be in
the range from not below 0.6~ to not above 5%.
lo While the invention ha~ been disclosed by reference to
the details of preferred embodiments thereof, it is to be under-
stood that such di~closure is intended in an illustrative,
rather than in a limiting sense, and it is contemplated that
various modifications in the compositions and processing tech-
niques, in particular, will readily occur to those skilled in
the art, within the spirit of the invention and the scope
of the appended claim~.
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