Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention rela`tes to a process for the
production of protective and decorative coatings upon
surfaces, particularly the surfaces of automo~ile bodies.
It is well known to formulate coating compositions,
especially those for use in the automobile industry, upon
polyester resins. Such resins may be of the air-drying
alkyd type, containing autoxidisable groupings derived from
natural drying oil 57 in which case curing of the resin to
form a film occurs by the action of atmospheric oxygen~
Alternatively, they may contain no autoxidisable qroupings
but instead rely for curing upon the reaction of residual
hydroxyl or carboxyt groups present with a cross-linking
agent such as an amino resin, effected in a curing step
su~sequent to the application of the coating composition
to the substrate. A combination of both curing mechanisms
is frequently utilisedO These po~yester-based compositions,
however, give rise to certain difficulties, especially under
the conditions of spray application as normally used in the
painting of car bodies. In those cases where such a composition
is employed for the final finishing of the car body, the need
to achieve good flow-out of the coating after application,
in order to maximise gloss, may require the incorporation of
~ilm-forming components of very low molecular weightf these,
however, tend to cause excessive flow o the composition
during the spraying operation, with the occurrence of
"sagging"7 In other cases, where a polyester-based composition
is used as a pigmented basecoat, especially one containing
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metallic flake pigment, upon which an unpigmented topcoat
is subsequently applied by the conventional wet-on-wet
procedure, there is a prime requirement that the application
of the topcoat shall not soften the basecoat and hence
disrupt the control of orientation o the metallic flake
(whereby a "glamour metallic" or "flip" effect is achieved).
To meet this reguirement, film-forming material of high
molecular weight is needed, but it is often difficult to
select appropriate polyester formulations which will enable
high molecular weights to be obtained without accompanying
problems of high viscosity or a risk of gelation during
manufacture.
It has now been found that an improvement in the
spray application properties of a coating composition based
on a polyester resin can be achieved by incorporating in the
composition a proportion of polymer microparticles of
specified type.
According to the present invention there is :-
provided a process for the production of a surface coating
upon a substrate which comprises applying by spray to the
substrate surface a composition comprising (A) a film-forming :
polyestsr resin as hereinafter defined; (B) a volatile organic
liquid diluent in which the polyester resin (A) is dissolved;
(C) polymer microparticles as hereinafter defined, in an
amount of at least 3% of the aggregate weight of the resin (A)
and the microparticles, which are insoluble in and stably
dispersed in the solution of the polyester resin (A) in the
diluent (B) 9 and subsequently evaporating the volatile diluent
to form a polymer film upon the surface.
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By the term ~'film-forming polyester resin" we
mean any of those resin~ which are known in the art for use
in surface coating compositions and which are essentially
the products of condensation of polyhydric alcohols and
polycarboxylic acids. We include in this term the alkyd
resins which are obtained from such starting materials with
the addition of constituents supplying residues of fatty
acids derived from natural drying oils, or semi-drying oils,
or even oils having no air-drying capabilities. We also
include polyester resins not incorporating any natural oil
residuesO All these resins normally contain a proportion o~
free hydroxyl and/or carboxyl groups which are available for
reaction with suitable cross-linking agents, ~hich are
discussed in more detail below. Where a cross-lin~ing agent
is employed, this is, for the purposes of the foregoing
de~inition of the invention, considered to be a part of the
film-forming constituent (A~.
Suitable;polyhydric alcohols for the production of
polyester resins include ethylene glycol, propylene glycol,
butylene glycol, 1:6-hexylene glycol, neopentyl glycol,
diethylene glycol, triethylene glycol, tetraethylene glycol,
glycerol, trimethylolpropane, trimethylolethane, pentaeryth-
ritol, dipentaerythritol, tripentaerythritol, hexane triol,
oligomers of styrene and allyl alcohol (for example that sold
by Monsanto Chemical Company under the designation RJ 100)
and the condensation products of trimethylolpropane with
ethylene oxide or propylene oxide ~such as the produ~ts known
commercially as "Niax" triols). Suitable polycarboxy~ic acids
* Trade Mark
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include succinic acid (or its anhydride), adipic acid, azelaic
acid, sebacic acid, maleic acid (or its anhydride), fumaric acid,
muconic acid, itaconic acid, phthalic acid (or its anhydride),
isophthalic acid, terephthalic acid, trimellitic acid (or its
anhydride) and pyromellitic acid (or its anhydride). Where it is
desired to produce air-drying alkyd resins, suitable drying oil
fatty acids which may be used include those derived from iinseed
oil, soya bean oil, tall oil, dehydrated castor oil, fish olls or
tung oi?. Other oil fatty acids, of semi-drying or non-drying
types, which may be used include those derived from sa~flower oil,
sunflower oil and cottonseed oil~ Normally it is preferred that
the oil length of such an alkyd resin should not exceed 50%.
Monofunctional saturated carboxyl acids may also be incorporated
in order to confer plasticity on the polyester. Such acids may be,
for example, C4 - C20 saturated aliphatic acids benzoic acid,
p-tertbutyl benzoic acid and abietic acld; these may, in fact,
be the only fatty acids present, in those cases where the poly-
ester resin is to be cured by subsequent reaction of residual
hydroxyl or carboxyl groups with a cross-linking agent. In addition,
monofunctional hydroxy compounds may be incorporated in order to
control the chain length of the polyester or to confer certain
desirable compatibility properties upon it; suitable monohydroxy
compounds include benzylalcohol, cyclohexyl alcohol, saturated or
unsaturated fatty alcohols and condensation products of ethylene
oxide or propylene oxide with monofunctional alcohols (e.g. the
methoxy-polyethylene glycol obtained by reaction of ethylene oxide
with methanol).
Suitable film-forming polyester resins also include
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'lmodified" alkyd resins, for example styrenated or
methacrylated alkyds, urethane alkyds and epoxy alkyds.
The volatile organic liquid constituent (B) o~ the
composition used in the process may be any of the liquids, or
mixtures of liquids, which are conventionally used as polymer
solvents in coating compositions, for example aromatic
hydrocarbons such as toluene and xylene and petroleum fractions
of various boiling point ranges having a significant aromatic
content, esters such as butyl acetate, ethylene glycol
diacetate and 2-ethoxyethyl acetate, ketones such as acetone
and methyl isobutyl ketone, and alcohols such as butyl alcohol.
The actual liquid or mixture of liquids selected as the diluent
(B) will depend upon the nature of the polyester resin (A~,
according ~o principles which are well ~nown in the coatings
art, in order that the resin shall be soluble in the diluent.
The polymer microparticles (C) present in the
composition used according to the invention are polymer
particles of colloidal dimensions, having a diameter of from
0.01 - 10 microns, which are insoluble in the solution of the
polyester resin (A) in the diluent (B) and which are stably
dispersed therein (in the sense that they do not undergo
flocculation or aggregation) whilst dispersed in that medium.
The insolubility of the microparticles may be achieved by
suitable selection of the composition of the microparticle
polymer, that is to say, the polymer may be one which is
inherently insoluble in that solution, but preferably it is
achieved by introducing a su~ficient degree of cross-linking
into a polymer which, if not cross-linkec3, would actually be
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soluble in the solution of the polyester resin (A) in the
diluent (B). Where insolubility of the microparticles is
achieved through cross-linking, it is preferred that the
degree of cross-linking should not be greater than that
5 necessary to render the polymer insoluble. Insolubility of
the microparticles in the solution of polyes~er resin (A) in
diluent (B) may be checked by means of the following test.
The microparticles (1 part by weight) are shaken for 30
minutes with the diluent (B) ~100 parts by weight); the
suspension is then centrifuged at 17,000 r p.m. for 30 minutes. ~
The supernatant liquid is decanted off and the residual polymer ~-
then dried for 30 minutes at 150C, after which its weight is
compared with that of the microparticles originally taken.
This test may be difficult to apply where the specific gravity
of the diluent is close to or greater than that of the micro-
particles, but such diluents ~e5g. chlorinated solvents) would
not normally be used in the compositions under consideration.
Where the result of this test indicates that the microparticles
are acceptably insoluble in the diluent (B) alone9 it can be
assumed that the particles will be at least equally insoluble
when the polyester resin tA) is a~so present in solution in
the diluent; there would be practical dificulties in carrying
out the test actually in a solution of polyester resin (A) in
diluent (B).
The microparticulate polymer may be of various types~
It may, for example, be an addition polymer, derived from one
or more ethylenically unsaturated monomers; in particular, it
may be a polymer or copolymer of one or more alkyl esters of
:
:
acrylic acid or methacrylic acid, optionally together with
other monomers such as vinyl acetate, acrylonitrile, styrene,
acrylic acid or methacrylic acid. Suitable acrylic and
methacrylic esters include methyl methacrylate, ethyl metha-
crylate, propyl methacrylate, butyl methacrylate9 ethylacrylate, butyl acrylate and 2-ethylnexyl acrylate. Where it
is desired that such a polymer should be cross-linked, this
may be achieved by either of two general methods : firstly,
by including in the monomers from which the polymer is derived
a minor proportion of a monomer which is polyfunctional with
respect to the polymerisation reaction, e.g. ethylene glycol
dimethacrylate or divinylbenzene; or secondly, by including
in those monomers minor proportions of two othe~ monomers
carrying pairs of chemical groupings which can be caused to
react with one another either during or after the polymerisation
reaction, such as epoxy and carboxyl (e.g. glycidyl methacrylate
and methacrylic acid)~ anhydride and hydroxyl or isocyanate
and hydroxyl. Alternatively, the microparticles may be composed
of a condensation polymer, for example a polyester prepared
2 from any of the polyhydric alcohols and polycarboxylic acids
described above. Again, such polymers may be cross-linked if
desired, by the incorporation of materials of functionality
greater than two, in the starting composition, although in this
case, because of the characteristically broad distribution of
molecular species formed in a condensation polymerisation, it
may be difficult to ensure that all those species are in fact
cross-linked. ~
The chemical compositions and degree of cross-linking
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of the microparticulate polymer may be such that it has a
Tg (glass-rubber transition temperature) below room
temperature~ in which case the microparticles will be rubbery
in nature; alternatively it may be such that the Tg is above
room temperature9 that is to say the particles will be hard
and glassy.
As already stated9 it is necessary that the polymer
microparticles be stably dispersed in the solution of the
polyester resin in the liquid diluent. By "stably dispersed"
is meant that the particles are prevented from flocculating
or aggregating by means of a steric barrier around the
particles, of polymer chains which are solvated by the said
solution and hence are in a chain-extended configuration. In
this context the term "solvated" implies that the polymer
chains in question, if they were independent molecules, would
be actually soluble in the polyester resin solution; however,
because the chains are in fact attached to the microparticles
at one or more points along thelr length, the steric barrier
remains permanently attached to the particles. It will be
understood that the stabilising polymer chains to be used in
any particular instance will be selected with reference to
the nature of the liquid diluent and film-forming polyester
resin concerned. In general terms this means that the chains
will be of a degree of polarity similar to that of the
dlluent and film~forming resin, so that the combination of
the latter will be inherently a solvent for the polymer of
which the chains are composed. Since, in the automobile
finishes to which the present invention is primarily directed,
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the liquid diluent will conventionally be of a relatively
high degree of polarity ~containing, for example, a
substantial proportion of "strong" ester and ketone solvents)
it follows that the stabilising chains on the microparticles
will usually require to be o~ a composition such that they
are inherently soluble in that ty~e of liquid.
The mode of anchoring of the stabilisinq chains to
the microparticles is conveniently discussed in connection
with methods of making the particles, as ~ollows.
The polymer microparticles may be produced in a
variety of ways. Preferably they are produced by the
dispersion polymerisation of monomers, in an organic liquid
in which the resulting polymer is insoluble~ in the presence
of a steric stabiliser for the particles. Suitable processes
of dispersion polymerisation are well-known and extensively
described in the literature. Thus, so far as the dispersion
polymerisation of ethylenically unsaturated monomers such as
acrylic or methacrylic acid esters, vinyl esters and styrene
or its derivatives are concerned, the procedure is basically
one of polymerising the monomers in an inert liquid in which
the monomers are soluble but the resulting polymer is not
soluble, in the presence dissolved in the liquid of an
amphipathic stabilising agent or of a polymeric precursor
which, by copolymerisation or graftin~ with a portion of the
monomers, can give rise in situ to such a stabilising agent.
Reerence may be made, for example, to British Patent
Speciications Nos. 941,305; 1,052,Z41; 1,122,397 and 1,231,614
for a general description of the principles involved, as well
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as to "Dispersion Polymerisation in Oryanic Media~ ed~
K.E.J. Barrett (John Wiley and Sons, 1975). Suitable ethylen-
ically unsaturated monomers include methyl methacrylate, ethyl
methacrylate, butyl methacrylate~ ethyl acrylate, butyl
acrylate, 2-hydroxyethyl acrylate, vinyl acetate, vinyl
propionate, styrene and vinyl toluene. The production
specifically of dispersions of cross-linked addition polymer
particles can be achieved by including, in the monomers
selected, pairs of monomers containing (in addition to the
polymerisable unsaturated groups~ groups capable o~ entering
into chemical reaction with each other; for example, the
epoxide and carboxyl groups contained in glycidyl methacrylate
and methacrylic acid. By following the procedures
particularly described in British Patent Specifications Nos.
1,095,288 and 1,156,012, for example, particles are obtained
in which there are present such complementary groups which,
although not at that stage co-reacted, can be caused to
co-react and so ~orm cross-links by subsequently heating the
dispersion to a suitably elevated temperature~ Cross-linked
addition polymers may also be prepared in dispersion by
including in the monomers undergoing dispersion polymerisation
a minor proportion of a monomer which is difunctional with
respect to the polymerisation reaction, such as ethyleneglycol
dimethacrylate or divinylbenzene.
O~ the unsaturated monomers mentioned above, methyl
methacrylate is an appropriate choice where it is desired that
the polymer microparticles should have a high Tg value. Where
the microparticles are required to be of low Tg, ethyl acrylate
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or vinyl acetate may be used, but it may be a more
convenient alternative to copolymerise methyl methacrylate
with minor proportions of '7softeninq" monomers such as butyl
acrylate or butyl methacrylate. The proportions used of such
softening monomers may, however, need to be limited; otherwise
there is a risk that the resulting copolymer may be too
soluble, even in low-polarity hydrocarbon diluents, for stable
dispersion of microparticles to be obtained. With butyl
acrylate as the softening monomer, for example, a proportion
of 15% by weight of the total monomers should not be exceeded.
Certain other softening monomers such as 2-ethoxyethyl
acrylate or 2-ethoxyethyl methacrylate, may be used in greater
proportions than this if desired, but these monomers are not
as readily accessible as the corresponding lower alkyl esters~
Small proportions of comonomers incorporating carboxyl- groups,
e.g. acrylic acid or methacrylic acid may be included ~where
the microparticles are to be cross-linked, such proportions
would be in excess of those used in order to achieve cross-
llnking by reaction with a co-reactive monomer such as glycidyl
methacrylate). Conversely, small (additional) proportions of
an epoxide monomer, e.g. glycidyl methacrylate, may be included.
Other functional monomers, such as hydroxyethyl acrylate or
acrylamide, may also be included in minor proportions in ~he
monomers from which the microparticles are to be derived.
The production of dispersions of condensation
polymers is described, for example, in British Patent
Specifications Nos~ 1,373,531; 1,403,794 and 1,419,1g9 and
methods of obtaining cross-linked polymer particles are
~! included in these descriptions. The general principles
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involved here are the same as those referred to above in
connection with addition polymer dispersions, but there is
a difference of detail arising from the commonly more highly
polar nature of the monomers or starting materials from which
condensation polymers are derived. This is, namely, that
the monomers in question are usually insoluble in the inert
liquid in which the polymerisation is to be carried out~
Accordingly the first step in the dispersion polymerisation
of the monomers is to bring them into a state of colloidal
10 dispersion in the inert liquid, either as liquid or as
solid particles. In the second step, polymerisation of the
monomers takes place within those same particles. An
amphipathic stabilising agent is required in each stage,
firstly in order to stabilise the particles of monomer and
~5 secondly in order to stabilise the particles of polymer formed,
but in suitable cases a single sta~ilising aqent can be
~ found which will perform both these functions. In place of
; using a preformed amphipathic stabilisin~ agent in this
process, there may be employed instead a suitable polymeric
precursor which, by copolymerisation or grafting with a
portion of the monomers being polymerised, can give rise to
such a stabilising agent in_situ. Reference may be made in
this connéction to our Canadia~ Patent Serial ~o. 1079884,
published ~une 17, 1980
Suitable monomeric starting materials for preparing
condensation polymer microparticles are those which are well
known for use in making such polymers by melt or solution
polymerisation techniques~ For example, suitable materials
in the case o~ polyester microparticles are the polyhydric
alcohols and polycarboxylic acids mentioned above in connection
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with the fil~-forming polyester resin (A). In the case of
polyamide microparticles, suitable monomeric starting makerials
are amino-acids, such as 6-aminocaproic acid or 11-amino-
undecanoic acid, or the corresponding lactams, and/or polyamines,
such as ethyl~ne diamine, propylene diamine, hexamethylene
diamine, diethylene triamine, triethylene tetramine or tris
(aminoethyl) methane, in conjunction with the polycarboxylic
acids mentioned above. It will, of course~ be understood that,
in the case of both polyester and polyamide microparticles, the
mixture to be polymerised must incorporate some proportion of
a starting monomer which has a functionality greater than two,
where it is desired that the microparticles should be cross-linkedO
In all the above-described dispersion polymerisation
processes, the amphipathic steric stabilisin~ agent is a
substance the molecule of which contains a polymeric component
which is solvatable by the liquid in which the dispersion is
made and another component which is relatively non-solvatable
by that liquid and is capable of associating with the polymer
par~icles producedO Such a stabilising agent will be soluble
as a whole in the dispersion liquid, but the resulting solution
will usually contain both individual molecules and micellar
aggregates of molecules, in equilibrium with each other. The
type of stabilising agent preferred for use in the invention
is a block or graft copolymer containing in the molecule two
types of polymeric component : one type consists, as stated
above, of polymer chains which are solvatable by the dispersion
liquid and the other type consists of polymer chains of
different polarity from the first type which accordingly are
,
not solvatable by that liquid and are capable of becoming
anchored to the polymer microparticles. A particularly
useful form of such a stabilising agent is a graft copolymer
comprising a polymer backbone, which is the non-solvatable
or "anchor~ component, and a plurality of solvatable polymer
chains pendant from the backbone. Specific examples of such
graft copolymers include those in which the backbone is an
acrylic polymer chain, derived predominantly from methyl
methacrylate, and the pendant chains are residues of poly
(12-hydroxystearic acid~ which are readily solvatable by an
aliphatic hydrocarbon medium. These copolymers may be made,
for example, by first reacting poly~12-hydroxystearic acid)
with glycidyl acryIate or glycidyl methacrylate, whereby the
terminal - COOH yroup in the polymeric acid is converted to
an ester derivative containing a polymerisable unsaturated
grouping, and then copolymerising that derivative with methyl
methacrylate, optionally together with minor proportions of
other copolymerisable monomers. By employing acrylic acid or
methacrylic acid as such minor comonomers, it is possible to
introduce carboxyl groups into the backbone chain of the graft
copolymer with beneficial results inasmuch as the backbone is
thereby rendered more polar than it is if composed of methyl
methacrylate units alone. This incraased polarity causes the
backbone to be even less solvatable by a non-polar diluent
such as an aliphatic hydrocarbon, and in consequence enhances
the force whereby it becomes anchored to the microparticle.
Although it is preferred to prepare the polymer
microparticles by means of dispersion polymerisation processes
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as just described9 it may be necessary to subject the
particles so obtained to a further treatment in order to
render them suitable for incorporation in the compositions
used according to the invention~ This need may arise in the
following way. The most convenient inert liquids in which to
carry out dispersion polymerisations are liquids of low
polarity, for example aliphatic or aromatic hydrocarbons or
mixtures thereof; this is because such liquids are non solvents
for the majority of polymers, whether of the addition or of the
condensation type, and therefore, give scope for the widest ~
choice of polymer or copolymer compositions according to the :
properties which it is desired the microparticles should
possess. From the foregoing discusslon it will, however,
be appreciated that steric stabilising agents which are
suitable for stabilising the microparticles in a simple low
polarity liquid environment may no longer effectively stabilise
them when they are transferred to the environment of the
solution of the film-forming polyester resin (A) in the liquid
diluent (B)~ One relevant factor is that (B) is likely to be
a relatively highly polar liquid, where the formulation of
automobile finishes is concerned, and another, perhaps more
important, factor is that the polyester molecules (A) will now
be competing with the chains of the stabilising agent for the
solvating action of the diluent. The consequence is that
transfer of the microparticles to the new environment will
result in their de-stabilisation and flocculation~
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It is, therefore, a preferred feature of the
invention that microparticles which have been made by a
dispersion polymerisation process are further associated
with a polymer which is soluble in the volatile organic
S liquid constituent (B) of the base-coat composition and is
also compatible with the film-forming polyester resin (A).
This further polymer, hereinafter referred to as the
"auxiliary" polymer, is essentially non-crosslinked. It
is believed that, when microparticles with which it is
associated are introduced into the more highly polar
environment of the solution of film-forming polyester resin
(A) in the organic liquid (B), the chains of the auxiliary
polymer now become solvated and take over at least in part
from the original amphipathic stabiliser the function of
1~ maintaining the microparticles in a deflocculated, dispersed
state. The scope of the present invention is not, however,
in any way limited by the extent to which this belief is correct.
The microparticles are most conveniently brought into
association w~th the auxiliary polymer by following up the
dispersion polymerisation process immediately with the
polymerisation of further monomer, from which the auxiliary
polymer is to be derived, in the original inert liquid
medium and in the presence of the original stabilising agent.
In general, the auxiliary polymer will be required
to have a composition such that it is compatible with the
film~forming polyester resin (A). The monomer or monomers
from which the auxiliary polymer is to be derived will be
chosen with this requirement in mind, as will be apparent to
those skilled in the art.
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On introducing the microparticles so treated into
the solution of the polyester resin (A) in the liquid (B),
part of the auxiliary polymer may be dissolved away by that
more polar medium, but it is believed that a substantial
portion of the auxiliary polymer chains remainsattached to the
microparticles (albeit now solvated by the medium), for example
by virtue of their having become entangled with the chains of
the microparticle polymer during their formation, or as a
result of actual grafting on to those chains. If desired, the
stability of the treated microparticles in the more polar medium
may be enhanced by ensuring that covalent linkages are
developed between the chains of the auxiliary polymer and those
of the microparticlès. This may be done, for example, by
including an unsaturated carboxylic acid in the monomers from
which the auxiliary polymer is derived. The carboxyl groups
so introduced are able to react with epoxide groups, present
in the microparticle polymer as the result of the use of a
slight excess of the latter groups for the purpose of cross-
linking that polymer by reaction with carboxyl groups in the
manner described above.
The incorporation of the microparticles, macle by
dispersion polymerisation, into the coating composition may
be effected by blending the dispersion of the microparticles
(whether treated with auxiliary polymer or not) with a
solution of the film-forming polyester resin (A) in a suitable
diluent (B). Another possibility is to separate the micro~
particles from the dispersion in which they are made, for
example by centrifuging, filtration or spray-drying, and then
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to blend the microparticles with a solution of a polyester
resin (A) in a diluent (B) as before.
~ i~l b~ ~ e-r-st-oo~--f-E~om--t-h~--oreg~1F~g---de-sGr~ t~ n
that, for the purposes of the definition of the
hereinbefore given, the film-forming con~iXuent ~A) is
considered to comprise that ~ ~t- f the auxiliary polymer,
if such po ~ ~ ~yed, which is dissolved away from the
micro ~ when the latter are incorporated into the
As an alternative to the use of dispersion poly~er-
isation methods, the polymer microparticles may, for example,
be produced by aqueous emulsion polymerisation of suitable
unsaturated monomers, using procedures well~known in the art.
The microparticles are then obtained in the form of a charge-
stabilised dispersion, from which the particles themselves can
be separated, e.g. by spray drying. For incorporation into
the coating composition, the microparticles are then re-dispersed
in the solution in the diluent of the film-forming polyester
resin, preferably by methods imparting high shear to the
mixture such as pug milling or triple roll milling, in an
analogous fashion to the dispersion of a pigment By further
analogy to pigment dispersion, the requisite steric stability
of the microparticles may then be achieved simply as a result
of an innate tendency of the film-forming polyester resin
~which by definition is solvated by the diluent) to associate
with the particles, for example through the interaction of
polar groups present in the polyester resin and in the micro-
particle respectively. In producing the microparticles by
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aqueous emulsion polymerisation, some difunctional
unsaturated compounds may be included in the polymerising
monomers in order to give rise to a cross-linked polymer
which will be insoluble in the solution of the film-forming
polyester resin (A) in the diluent (B), whatever the nature
of the latter. Here again 9 as in the case of microparticles
made by dispersion polymerisation~ it may be desirable to
continue the emulsion polymerisation with a second feed of
monomers which does not include any difunctional (iOe. cross-
linking) material and which gives rise to a polymer which iscompatible with the solution of polyester resin (A) in diluent
(B), in other words to associate with the microparticles an
'auxiliary' polymer having the same function as that previously
described.
As has already been stated, the polymer microparticles
(C) are present in the compositions used according to the
invention in an amount of at least 3% of the aggregate weight
of the film-forming polyrner (A~ and of the microparticles.
For the purposes of this definition, the term "polymer
microparticles" is to be understood as referring, in the case
where auxiliary polymer is employed, to the microparticles
proper together with that part of the auxiliary polymer
associated therewith which cannot be dissolved away from the
particles by the diluent (B), under the conditions of the
insolubility test described above. When the compositions are
intended for use in the production of f;nishing coats (as
distinct from their use as basecoats, mentioned below), the
amount of the po]ymer microparticles incorporated is preferably
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from 3% to 30% of the aggregate weight of the film-forminy
polymer and the microparticles~
The compositions used in the process of the invention
may incorporate, in addition to the polyester resin (A)g the
diluent (B) and the polymer microparticles ~C), pigments as
conventionally used in the coatings art. Such pigments may
range in particle size from 1 to 50 m~crons and may be ~
inorganic in nature, for example titanium dioxide, iron oxide,
chromium oxide, lead chromate or carbon black, or organic in
nature, for example phthalocyanine blue, phthalocyanine green,
carbazole violet, anthrapyrimidine yellow, flavanthrone yellow,
isoindoline yellow, indanthrone blue, quinacridone violet and ~ i~
perylene red. Of particular interest in the context of the
invention are metallic pigrnents consisting of flat flakes of
aluminium, copper, tin, nickel or stainless steel, by the use
of which there may be obtained the so-called "glamour metallic"
finishes whereby a differential light reflection effect,
depending upon the viewing angle, is achieved. Any of the
above pigments may be present in the coating compositions in a
proportion of from 2% to 50% of the aygregate weight of all
the film-forming material present. The term "pigment" is-
. _. . , :
here meant to embrace also cpnventional fillers ~ j
and extenders, such as talc or kaolin.
Such pigments, whether metallic or otherwise, may
be incorporated into the compositions with the ald of knowndispersants, for example an acrylic polymer, which are
compatible with the polyester resin (A).
, . . . i
- 21 -
;:
... .
. ~ :
- ' . ~ .
,:
If desired, the compositions may additionally
incorporate other known additives, for example viscosity
modifiers such as bentone or cellulose acetate butyrate.
As already indicated, there may further be
incorporated a cross-llnking agent to effect or assist the
curing of the polyester resin ~A). Suitable types of
cross-linking agents include diisocyanates, diepoxides and,
especially, aminoplast resins, t~at is to say, condensates
of formaldehyde with nitrogenous compounds such as urea,
melamine, thiourea or benzoguanamine, or the lower alkyl
ethers of such condensates in which the alkyl groups contain
from 1 to 4 carbon atoms. Particularly suitable are melamine-
formaldehyde condensates in which a substantial proportion of
the methylol groups are etheriied by reaction with butanol.
The proportion of cross-~inking agent to cross-linkable
acrylic or other polymer in the composition may vary widely,
but in general a ratio of from 50:50 to 90:10 by weight of
polymer to cross-linking agent is satisfactory. The precise
proportion to be employed depends upon the properties required
in the final ~ilm, but a preferred range afording a good
balance of properties is from 60:40 to 85:15 by weight of
polymer to cross-linklng agent.
The composition may also incorporate a suitable
catalyst for the cross-linking reaction, for example an acid-
reacting compound such as acid butyl maleate, acid butylphosphate or p-toluene sulphonic acid. Alternatively, the
required catalytlc effect may be provided by carboxyl groups
present ln the film-forming polyester resin (A). ~;
!
- 22 -
. , . . . - . . .
`~ ~6:~)3
Following spray application of the coating
composition to the substrate surface and evaporation of the
volatile liquid diluent so as to form a polymer fiim upon
the surface, the polyester resin constituent (A) may then be
allowed to cure by atmospneric oxidation, or it may be
reacted with a cross-linking agent present, as appropriate.
If desired, the cur;ng process may be assisted by heating the
coating, for example to a temperature of up to 160C.
Any of the known spraying procedures may be used
for applying the composition, such as compressed air spraying,
electrostatic spraying, hot spraying and airless spraying~
and either manual or automatic methods are suitable. Under
these conditions of application, coatings of excellent gloss
are obtained which possess advantages over the coatings
obtained according to the prior art in respect of the reduction
of excessive flow on application, particularly at sharp edges
or corners of a substrate of complicated shape, or the
obliteration of scratch marks in the surface to be coated.
Films of up to 4 mils dry thickness may be applied without
any tendency for sagging, or "sheariness" of any metallic
pigment present, to occur.
- Alternatively~ the proceSs of the invention may
be modified to a two-coat procedure, commonly referred to as
a "base-coat/clear-coat" procedure and of special relevance
to the productlon of the "glamour metallic" finishes referred
to earlier, in which there is first applied to the surface of
the substrate a base-coat containing the metallic pigment and
formulated to give the maximum "flip" tone effect, and there
- 23 -
-- . . : . . . .. :
.
.
. , ~ . . -: ,
LlZ6~3
is then applied over the base-coat an unpigmented top-coat
which yields a high degree of gloss without in a~y way
modifying the characteristics of the base-coat. The process
according to the invention as hereinbefore defined in which
metallic pigment is employed is of special value ~or the
production of the base-coat in this type of application
procedure.
Thus, according to a further aspect of the invention,
there is provided a process for the production of a multilayer
coating upon the surface of a substrate, which comprises the
steps of : `
(1) applying by spray to the surface a base-coat
comprising:-
(A) a film-forming polyester resin as hereinbefore
defined;
(~) a volatile organic liquid diluent in which
the polyester resin (A) is dissolved;
(C) polymer microparticles as hereinbefore defined
which are insoluble in and are stably dispersed
in the solution of the film-forming polymer in
the liquid diluent7 in an amount of at least :
10% of the aggregate weight of the film-forming
polymer and the microparticles;
(D) pigment particles also dispersed in the solution
of the film-forming polyester resin in the
liquid diluent;
(2) forming a polymer filrn upon the surface from the
cornposition applied in step (1);
~ y
- 24 - :
.
.
: : , : .
.
.. ~ : . ... :
26~3
(3) applying to the base-coat film so obtained a
transparent top-coat composition comprising:
(E) a film forming polyrner;
(F) a volatile carrier liquid for the polymer tE);
(4) forming a second polymer film upon the base-coat
film from the composition applied in step (3)~
The polyester resins (A), the diluents (B) and the
polymer microparticles (C) which are suitable for use in the
above process are those previously described herein. The
pigment particles (D) may be any of those already described
but, as already indicated~ the process is of special relevance
to the use of metallic pigments. }t will be noted that a
higher maximum proportion of the microparticl s is specified
for use in this process~ as compared with the process
; described earlier. This stipulation takes into account the
fact that, in a base-coat composition, especially one containing
a metallic pigment, a rather higher degree of control of flow
of the material during application is required than in a
omposition intended for the production of a finishing coat.
Preferably the amount of the microparticles used is from 10%
to 30% of the aggregate weight of the film-forming polymer (A)
and the microparticles.
If desired, the base-coat composition may -
additionally incorporate other known additives, for example
viscosity modifiers such as bentone or cellulose acetate
butyrate.
~ 25 -
)3
The polymer constituent (E) of the top-coat
composition employed in step (3) of the process may in
general be any suitable film-forming polymer. Thus, it may
be a film-forming polyester resin of any of the types
previously described, in which case the top coat composition
may additionally contain a cross-linking agent. Alternatively,
the polymer (E) may be one of the known acrylic ~ilm-forming
polymers, derived predominantly from esters of acrylic or
methacrylic acid. Such polymers may be of the thermoplastic
type, in which case the step (4) of forming the second polymer
film may require no more than evaporation of the volatile
carrier liquid; alternatively9 they may be of the thermo-
setting type, which require the assistance of a cross-linking
agent of similar type to those already descrîbed in connection
with the polyester resins, and may also require khe application
of heat in step (4). Unlike the polyester resin in the base-
coat composition, the polymer (E) in the top-coat composition
may be either in solution or in stable dispersion in the
volatile carrier liquid (F3 of the composition.
Thus, the carrier liquid (F) may be either a
solvent or a non-solvent for the top-coat polymer. Where the
liquid is to be a solvent, it may be any of the volatile
organic liquids or mixtures thereof previously mentioned as
suitable for use in a composition containing the polyester
resin. Where the liquid i5 to be a non-solvent, ik will tend
to be of rather lower polarity than the former and may consist
of one or more aliphatic hydrocarbons such as hexane, heptane
or petroleum fractions of low aromatic content, optionally in
;~
- 26 -
--: ,. , . - . - i .
-: :. : :- : .
:: , : : : - : ~ .: : :: . . ~ :
.
6~3
admixture with liquids of high polarity as already referred
to~ provided that the total mixture is a non-solvent for the
top-coat polymer.
Where the top-coat composition is a polymer
dispersion, this will in general be a sterically stabilised
dispersion in which the polymer particles are stabilised by
means of a block or graft copolymer, one polymeric constituent
o which is non-solvatable by that liquid and is associated
with the disperse polymer. The well-known principles
according to which such dispersions may be prepared have been
referred to above in connection with the making of the micro-
particles of the base-coat composition.
The top coat composition may in some cases contain
both polymer in solution and polymer in dispersion. The soluble
polymer may be a preformed polymer of different monomer
composition from the dispersed polymer which, unlike the latter,
is soluble in the carrier liquid (F) and is added as a solution
therein to the dispersion. It may alternatively arise during
the formation of the disperse polymer as the result of
preferential polymerisation of certain of the monomers present.
Again, it may be polymer which is originally formed in dispersion
but which, unlike t~e main film-ormer, passes into solutlon
when there are added to the continuous phase liquid of the
dispersion other liquids o~ stronger solvency than the latter
in the course of formulating a paint with the required application
characteristics.
Usually, the top-coat composition will be substant-
ially colourless so that the pigmentation effect due to the
t
- 27 -
.
base-coat is not significantly modified, but it may be
desirable in some cases to provide a transparent tinting
of the top-coat composition.
In the first operational step of the process, the
base-coat composition is applied to the surface of the
substrate9 which may be previously primed or otherwise
treated as conventional in the art. The substrates which are
of principal interest in the context of the invention are
metals such as steel or aluminium which are commonly used
for the fabrication of automobile bodies, but other materials
such as glass, ceramics, wood and even plastics can be used ; --
provided they are capable of withstanding the temperatures
at which final curing of the multilayer coating may be
effected. After application of the base-coat composition, a
polymer film is formed therefrom upon the surface of the
substrate. If desired, this may be achieved by s~bjecting
; the substrate and the applied coating to heat in order to
volatilise the organic liquid diluent, and it lies within the
scope of the invention to employ a heating temperature
sufficient to cross-link the base-coat film in those cases
where curing of the polyester resin requires such a procedure.
However, a particular merit of the present process is that
it is sufficient to allow only a short period of drying at
or about room temperature, i.e. without effecting curing
of the polyester resin, in order to ensure that the top-~oat
composition can be applied to the base-coat film without
there being any tendency for the former to mix with or dissolve
the latter in a way which can interfere with the correct
... ; ~
~ ~ :
- ,:
.
Z~ 3
orientation of a metallic pigment, whereby optimum "flip"
effect is achieved. Typically, a drying time of from 1 to
5 minutes at a temperature of from 15Q to 30C ensures that
mixing of the two coats is prevented. At the same time, the
base-coat film is adequately wetted by the topcoat composition,
so that satisfactory intercoat adhesion is obtained.
After application of the top-coat composition to
the base-coat film, the coated substrate is subjected to a
curing operation in which the base-coat, and optionally the
top-coat also, is cured by autoxidation and/or cross-linking
with the aid of the cross-linking agent(s) present, as
appropriate. This curing operation is carried out at an
elevated temperature as is conventional in the thermosetting
coating composition art, usually at a temperature in the
lS range 100 - 140C, but, if desired, at a lower temperature
provided the cross-linking system is sufficiently reactive.
The base-coat composition may be applied to the
substrate by any of the spray techniques described above. The
top-coat compo~ition may subsequently be applied by any
convenient method such as brushing, spraying, dipping or
flowing, but it is pre~erréd that spray application again be
used since the best results are thereby achieved in regard to
gloss o~ the final finish. The use of the base-coat
composition containing both polyester resin and polymer micro-
particles is found to give a signiicantly improved degree ofcontrol over the orientation of metallic pigment under the
conditions of spray application, so ~hat enhanced "flip" can
be achieved~
- 29 -
The invention is illustrated but not limited by
the following Examples, in which parts and percentages are :-
by weight.
EXAMPLE 1
~A) Alkyd resin finish composition containing polymer :
., - .
(1) Pre~at~on of Pol~mer_Microparticle_
To a vessel fitted with stirrer, thermometer an~
reflux condenser the following were added:-
Aliphatic hydrocarbon ~boiling
range 140 - 156C : zero aromatlc
content) 20.016 parts
Methyl methacrylate 1.776 parts
Methacrylic acid 0.036 part
lS Azo-diisobutyronitrile 0.140 part
Graft copolymer stabiliser
~ ~ (33% solution) (as described below) 0.6~2 part
:~ : The vessel and contents were purged with inert gas
~and the temperature then raised to 100 and held there for
1 hour in order to produce a disperse polymer "seed". The
following ingredients were pre-mixed and were fed into the
:vessel at a uniform rate over a perlod of 6 hours, maintaining
; stirring and heating at 100C :
Methyl methacrylate 32.459 parts ~-
Glycidyl methacrylate 0~331 part
Methacrylic acid 0.331 part
Azo-diisobutyronitrile 0.203 part
Dimethylaminoethanol 0.070 part
- 30 -
.~,",, .
.
Graft copolymer stabiliser
solution (as described below)6.810 parts . .
Aliphatic hydrocarbon (boiling
range 140 - 156C) 33.166 parts
100.000 parts
The contents of the vessel were held at 100C for
a further 3 hours, to give full conversion of the monomers to
a fine dispersion containing insoluble polymer gel microparticles
(21 - 22% of the total dispersion) together with uncross-linked
polymer particles (23% of the total dispersion).
The graft copolymer stabiliser used in the above
procedure was obtained as followsO 12-hydroxystearic acid
was self-condensed to an acid value of about 31 - 34 mg KOH/g
(corresponding to a molecular weight of 1650 - 1800) and~then
reatced with an ~quivalent amount of glycidyl methacrylate.
The resulting unsaturated ester was copolymerised at a weight
ratio of 2:1 with a mixture of methyl methacrylate and acrylic
acid in the proportions o~ 95:5.
(2) Modification oE Microparticles with
Auxiliary Polymer
To a vessel fitted as described in step (a), there
were charged 63.853 parts of the dispersion obtained in step
(a) above. The dispersion was heated to 115C and the vessel ~ :
.
was purged with inert gas. The following ingredients were
pre-mixed and were ~ed at a steady rate, over a period of 3
hours, to the stirred contents o~ the vessel, the temperature
being maintained at 115C :
: .
''~':;' ; ~
~: ,.
... ~ . . . .. .. . .. . .. . . .
Methyl methacrylate 3.342 parts
Hydroxyethyl acrylate 1.906 parts
Methacrylic acid 0.496 part
Butyl acrylate 3.691 parts
2-Ethylhexyl acrylate 3.812 parts
Styrene 5~712 parts
Azo-diisobutyronitrile 0.906 part
Prim-octyl mercaptan 0.847 part
Graft copolymer stabiliser
solution (as described in 1.495 parts
step (a).)
On completion of the addition, the contents of the
vessel were held at 115C for a further 2 hours to achieve
full conversion of the monomers, and 13.940 parts of butyl
1~ acetate were finally added, bringing the total charge to
100.000 parts~ The dispersion so obtained had a total film-
forming solids content of 45 - 46%; the content of insolu~le
~el polymer microparticles was 27.0 - 27~5%.
(3) Preparation of Millbase
The following ingredients were ground together in
a ball mill ~
Titanium dioxide pigment 7.8 parts
Middle chrome " 27.8 p~rts
Scarlet chrome " 18.1 parts
Disperslng resin (49% solids
solution in xylene) 29.6 parts
Xylene 16.7 parts
- 32 -
:
,~
- , . ~ :
"` ~ 3
(4) Preparation of finish composition
The following ingredients were blended :
Millbase (as described in (3) abo~e) 150.34 parts
Melamine/formaldehyde resin (62%
solids solution in butanol)63.52 parts
Alkyd resin solution ~as
described below) 133~43 parts
Polymer microparticle dispersion
(as described in (2) above)35.46 parts
Dipentene 24.00 parts
Butyl acetate 8.00 parts
Xylene 51.00 parts
The alkyd resin solUtion used in the above
formulatlon was a 63% solids solution in xylene of a 34%
: 15 oil length resin made by condensing coconut oil, trimethylol-
propane, glyceroll benzoic acid and phthalic anhydride in the
molar proportions 00806 : 3.273 : 0~192 : 0.581 : 3.906
respectively.
~: (B) Alkyd res;in finish not containing polymer
The ~ollowing ingredients were blended:-
Millbase as described in A(3) above 150.34 parts
Melamine/formaldehyde resin (62%
solids solution in butanol)63.52 parts
25 . Alkyd resin solution tas
described in A(4) above) 157.58 parts
Dip~ntene 24.00 parts
Butyl acetate 8.00 parts
Xylene 51.00 parts
; ~3
.
.
.. . .
6~3
(C) Applicat_on of finishes
The compositions prepared as described in (A) and(B) above were applied by spray on to vertical primed steel
panels which were punched with 0.25" diameter holes at l"
intervals, in such a way that the film thickness progressively
increased from the top to the bottom of the panel~ The applied
coatings were allowed to flash off for 45 minutes and were
then stoved at 130C for lO minutes.
The film thickness at which sagging of the coatings
at the rims of the holes first occurred was then estimated.
For the composition (A) containing polymer micropartic:Les,
the minlmum film thickness was 0.0038"; for the composîtion (B)
not containing the microparticles, the minimum film thickness
was only 0.0024"~
lS EXAMPLE 2
Base-coat/clear~top coat process utilising base-coat
(A) Preparation of Base-coat compos_tion
The following ingredients were blended:
Melamine/formaldehyde resin (67%
solution in butanol) 38.0Q parts
Polymer microparticles dispersion
: ~ (as described in Example:l,
part A(2)~) 83.56 parts
Alkyd resin soIution (as
described below) 26.64 parts
Dispersion of Carbazole Violet
(6.1% in xylene) lO.12 parts
Dispersion of Phthalocyanine Blue
(9.7% in xylene) 20.28 parts
Dispersion of Carbon Black
(14.2% in xylene) 2.52 parts
- 34 ~
,
Dispersion of Aluminium ~lake
(35% paste in xylene) 81.04 parts
2-Ethoxyethyl acetate 50.64 parts
Butyl Acetate 35.00 parts
The alkyd resin solution used in the above
formulation was a 70% solids solution in xylene of a
resin made by condensing coconut oil, trimethylolpropane,
glycerol and phthalic anhydride in the molar proportions
1.0 : 4.05 : 0.5 : 5.14 D
B. Coati q process
100 parts of the basecoat composition prepared
as in (A) was thinned by addition of 87 parts of butyl
acetate, to give a viscosity of 23.25 secs. in a B.S. B3
cup at 25C. The thinned paint was applied by spray to
a primed metal panel so as to give a film of thickness
0.000~3" after loss of all solvents. After a 2 minute
flash-off period at room temperature, the panels were
over-coated with two coats of a thermosetting acrylic ~-
clear composition, a 2 minute flash-off period being
allowed between coats9 The dry film thickness of the
clear coat was 0.0025". A~ter a final flash-off period
of 10 minutes at room temperature~ the panels and coatings
were stoved at 127C for 30 minutes.
The finishes thus obtained were of excellent
appearance, having an even aluminium metal effect with
no trace oP movement of the metal flake (i.e. absence
of "shear"). There was no sinkage of the clear top coat
into the basecoat7 50 that the very high gloss level
associated with the clear coat was in no way impaired by
- 35 -
!
'
,: , . .. . ~
., : ` ', , . :, : , : .
~2~ 3
the basecoat, and yet there was excellent intercoat
adhesion of the stoved panels. The coating also had
good flexibility and humidity resistance.
The acrylic clear composition used as the
topcoat in the above procedure was made up as follows:-
Butylated melamine-formaldehyde
resin, 60% solution in butanol 22.0 parts
Dipentene 9.5 parts
Butyl ~lycollate 4.5 parts
Butanol ~ 2~5 parts
2% solution of silicone oil0.4 part
Non aqueous dispersion in aliphatic/
aromatic hydrocarbon mixture of
thermosetting acrylic resin? 42~
solids 50.0 parts
;~ ~ Solution of thermosett1ng acrylic
resin, in xylene/butanol, 50%
solids 19.8 parts
:: : : :
The COmpoSItiOn had a viscosity of 60 seconds
when measured at 25C in`a B3 cup according to B.S. 1733:
1955.
The~procedure of Example 2 was repeatéd, except
tha~ the 26.64 parts of allcyd resin solution there described
; ~ 25 were replaced by 31.07 parts o~ a 60% solution in xylene
of an alkyd resin obtained by condensing azel.aic acid,
phthalic anhydride,~ trimethylolpropane and neopentylglycol ;~
in the molar proportions of 0.346 : 0.654 : 0.369 : 0.777
respectively.
~C~
Alkyd resin finish compositions containing polymer
~ ~5~ _Ies at different _ight proportions
:; ~ ' :'" ' :
~; - 36 -
~6~
, ~
Three compositions, designated I, II and III,
were obtained by blending the following ingredients in
the proportions shown:-
I II III
Melamine/formaldehyde resin
(62% solids solution in
Butanol) 60.0 72.560~0
White mill base containin~
TiO2 119.2 119.2 119~2
Alkyd resin solution (as
described in Example 2)143.1 107.9128.2
Silicone oil solution ~2%) 1~2 1~2 1.2
Isobutyl alcohol 8.0 8.0 8.0
Dipentene 20.0 20~0:20.0 :~
Xylene 56.0 50.083~0 ;
: Polymer microparticle
dispersion ~as described
in Example 1, part A t2)) 32.965.8
Thermosetting acrylic
~; 20 polymer, (65%:solution) - - 22.9
~:: : Determined solids
content, % ~ 51.14 50.59 50.03
Microparticle content,
% non-volatile (based on
non-volatile resin components 5 10 0
Primed metal panels were sprayed with each of
the three composltions so as to give a "wedge" coat of
gradually varying film thickness. Each panel was allowed
to stand vertically for 45 minutes and was then stoved,
again in a vertical position, for 10 minutes at 130C.
The film thickness at which "sagging" first .occurred was
then determined each case. The panel ~inished with
- 37 _
~ ~:
- : .: .: . , . : .: . : ~
composition III sagged at a film thickness of 60 - 65
microns and above, but the panels finished with
compositions I and II sagged only at a film thickness
of 75 microns and above.
Example 5
Polyester rinish composition containing polymer
microparticles, using an alternative cross-
The ~ollowing ingredients were ground in a ball
mill:-
Hydroxyl group-containing polyester,
(hydroxyl content 801%~ 90% solution
in 2-butoxyethyl acetate) 17.1l parts
Polymer microparticle dispersion
(as described in Example 1, part
A (2)~ 8.39 parts
Butyl acetate 6.20 parts
Titanium dioxide 34.30 parts
After grinding and removal from the ball mill,
the following ingredients were added:- ~
Zinc octoate (containing 22% Zn) 0.8~0 part
Silicone oil solution (2%)2.00 parts
2 Ethoxyethyl acetate 3.10 parts
Butyl acetate 2.80 parts
To the above charge there was added 15.i5 parts
of an aliphatic polyisocyanate (100% non-volatile content,
NC0 content 23.5%). After mixing, the resulting
composition was sprayed on to a primed panel in the manner
described in Example 4, allowed to flash off for 30 minutes
and then stoved for 30 minutes at 80C.
A similar composition was prepared but omitting
the polymer microparticles. On spray application as
described in Example 4, this was observed to have
significantly poorer resistance to sagging then the above
composition containing the microparticles.
5xam~1e 5
Polyester "metallic" finish composition, with
The following series of ingredi~nts, identified
in columns I and II respectively, were blended
I II
Butylated melamine/formalde-
hyde resin (67% solids in
butanol) 39.3 parts 39.3 parts
Dispersion of phthalocy-
anine blue (9.7% in xylene) 3063 parts 3.83 parts
Dispersion of phthalocy-
anine green-blue (8.65%
in xylene)2.34 parts 2.34 parts
Alkyd resin solution (as
described below)59783 parts 117.6 parts
Butyl acetate20.1 parts 20.1 parts
Methyl ethyl ketone20.1 parts 20.1 parts
Flow-promoting polymer
(10% solution in xylene) 0.9 parts 0.9 parts
Dipentene30.0 parts 30.0 parts
Modified microparticle
dispersion (as described
in Example 1 A (2))77.31 parts
Dispersion of aluminium
flake (20% paste in xylene)18.15 parts 18.14 parts
Xylene - 20.0 parts
- 39 -
- : . ~ . : . , ~ :, . ,. . , : . . - . , , .: : : :~ :
: ~: . , .: . : :,
Læ~3
The alkyd resin used in the above formulation
was a 70% solids solution in a 4:1 by weight ~ixture of
xylene and isobutanol of a 34% oil length resin made by
condensing coconut oil, trimethylolpropane, glycerol and
phthalic anhydride in the molar proportions 1.0 : 4.05 :
0.5 : 5 14 respectively.
Both compositions I and II had a viscosity of
33 secs. measured in B.S. B3 cup at 25C.
Four coats of each composition were applied
wet-on-wet to primed metal panels, allowing a l-minute
flash-off period between coats. After a final 10-minute
flash-off period, the panels were stoved at 127C for 30
minutesO
The control of the aluminium flake pigment on
: 15 application, as observed by absence of "shear" effects
and "black-edginy" in the coatings obtained, was found
to be superior in the case of composition I to that in
the case of composition II.
- 40 -
~, :. . , -
~ , , , . '
: . , ~
