Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 94/14867 215 0 4 7 g PCT/US93/12259
RAPID CIJRE: T~ ruN~;~ lONAI. PO~Dl~R COATING8
Field of the Invention
This invention provides thermosetting powder
coatings for functional applications (i.e., protective
rather than decorative) which are very rapidly cured
while at the same time having extended shelf lives in
the powder state, and which show excellent protective
characteristics.
Background of the Invention
Thermosetting epoxy resin powders enjoy wide
use as protective (i.e., functional) coatings for a
variety of materials such as steel pipe, metal sheets
or bars, and other materials where flexibility,
abrasion-resistance, and corrosion-resistance of the
coatings are required. These coatings are described in
"Epoxy Surface Coatings," by E. Linak, Chemical
Economics Handbook, SRI International, October, 1991.
Such coatings are advantageous because of these
superior protective properties, and also because the
powders are applied in the absence of any volatile
solvents and curing of the powders does not release
harmful vapors. In addition, when properly formulated,
such powder resins exhibit very long shelf lives yet
cure rapidly on application to a hot substrate.
While powder coatings which generally fit
these criteria are known, they usually suffer from two
deficiencies. First, many powder coatings exhibit
unsatisfactory shelf lives at ambient conditions, by
clumping or fusing in the presence of moisture or
35 slightly elevated temperatures. Typically, this is due
to the presence of added curing catalyst in the powder
formulation which promotes some cure even at ambient
WO94/1~67 21~ O ~ 7 9 PCT~S93/12259
temperatures. Second, even with added catalyst, many
powder coatings do not cure rapidly enough for the high
volume production required in industry. A gel time on
the order of ten seconds at application temperatures of
180-C or greater is often required for economical
production.
JP 62-104837, published May 15, 1987, by
E. Hosokawa and M. Fukushima, assigned to Showa Densen
Denzoku K.K., describes a powder coating consisting of
Scotchcast~ 5256 epoxy resin (available from 3M), PBOX,
trimellitic anhydride, and Modaflow~ leveling agent
(available from M~ncA~to). While a powder coating
inco~o~ating PBOX is described in JP '837, it requires
a monocarboxylic acid anhydride, which also bears a
free carboxyl group, as the preferred embodiment. Such
anhydrides are known to react differently from
dianhydrides having no free carboxyl groups, in resin
formulations.
Several formulations of liquid epoxy resin
coatings con~; n; ng PBOX are known. U.S. Patent No.
4,652,620 describes a resin comprising PBOX, Epon~ 828
liquid epoxy resin, and Alnovol~ PN320 phenol resin.
The presence of PBOX reportedly increases the T~ of the
product resin from 117-C to 150 C. The resultant resin
is a li~uid, not a powder. In addition, U.S. Patent
No. 4,652,620 requires a minimum of 20~ PBOX in any
coating composition.
European Patent Application No. 342,035,
assigned to the assignee of the present application,
describes powdered coating compositions for metal
substrates comprising uncured epoxy resins and aromatic
compounds having hyd~oxy y ou~s in adjacent or
available adjacent positions, including catechol
novolak resins. The incorporation of PBOX is not
disclosed therein.
Epoxy-based protective powder coatings are
well-known, having the desirable characteristics of
W094/1~67 215 0 4 7 9 PCT~S93/12259
high temperature stability, toughness, corrosion-
resistance, and flexibility. However, uncatalyzed
powder coatings suffer from slow gel times, and
catalyzed compositions often have poor shelf-life. A
need exists for a powder resin system with rapid gel
time and cure time and which is also stable on the
shelf for periods of six to twelve months.
Brief Description of the Invention
We have discovered such a protective powder
coating. The present invention relates to powder
coating compositions which are nonblocking or storage
stable between about 15-C and about 50 C, preferably
between about 20 C and about 45 C, and most preferably
lS between about 22 C and about 40 C, comprising the
reaction product of a composition comprising:
(a) about 4 to about 40 percent by weight of
l,3-phenylenebis-2-oxazoline;
(b) optionally about lO to about 70 percent
by weight of a nucleophilic material selected from the
group consisting of
(i) phenolic novolac compounds,
(ii) bisphenols,
(iii) bisphenol-terminated epoxy resins,
and
(iv) non-heat-reactive aromatic
hydroxy-functional compo~ln~, having an average of
greater than one aromatic hydroxyl group per molecule,
and
(v) mixtures thereof,
wherein, for the nucleophilic material, at least
one of the following (l) and (2) is true:
(l) the nucleophilic material has a
ring-and-ball softening point above about 70 C;
(2) the nucleophilic material has a
crystalline melting point above about 40 C;
WO94/1~67 2 ~ 7 9 PCT~S93112259
(c) optionally about 4 to about 70 percent
by weight of an electrophilic material selected from
the group consisting of polyanhydrides and mixtures
thereof;
(d) optionally about 20 to about 80 percent
by weight of an epoxy resin wherein for the epoxy resin
at least one of the following (i) and (ii) is true:
(i) the epoxy resin has a ring-and-ball
softe~;~g point above about 70 C;
(ii) the epoxy resin has a crystalline
melting point above about 40 C;
wherein the composition comprises one of the
following combinations of components: (a) (b) and (c);
(a) (b) and (d); and (a) (c) and (d);and
wherein the weight percentages are based upon
the total weight of (a) plus any optional components
selected from the group consisting of (b), (c) and (d).
The term "non-heat-reactive" as used herein
refers to materials which will not homopolymerize when
subjected to a temperature of about 100-C to about
300 C.
Another aspect of this invention relates to
protective coatings prepared from the powder coating
compositions of the invention.
This invention demonstrates PBOX (1,3-
phenylene bisoxazoline) as a latent curing agent in a
variety of thermosetting resin systems. Three unique
aspects of the present systems are emphasized, in
contrast to known systems: 1) no catalysts are
required to achieve the rapid and thorough cures seen
with the present system; 2) the present invention
demonstrates that PBOX is an effective curing agent
even at concentrations much less than 20% by weight;
and 3) the present system features a flexible
combination of three active materials, allowing for
improved tailoring of the properties of the coating.
W094/1~67 ~ 4 7 D PCT~S93/12259
PBOX chemistry is unusual in that the
oxazoline ring of PBOX is susceptible to attack by both
electrophilic agents (at the ring nitrogen) and
nucleophilic agents (at the unsubstituted carbon
s adjacent to the ring oxygen). It is this duality that
makes it an effective curing agent in a multi-component
system such as the present invention. Electrophiles
such as acidic hydrogen, an unsubstituted carbon of an
epoxide ring, and an anhydride carbonyl carbon readily
attack the ring nitrogen, highly activating the
unsubstituted carbon adjacent to the ring oxygen to
nucleophilic attack. Since the system is rich in
nucleophiles such as phenolic oxygen, epoxide oxygen,
amines, or the free oxygen of cleaved anhydrides,
reactions in this system are quite rapid at coating
temperatures. The thorough crosslinking which results
contributes to higher T~ and ~hAnce~ thermal stability
of the coatings.
The composition of the present invention is
advantageous in that it is coatable as a powder.
Powder coatings are advantageous due to their lack of
solvents, and hence are environmentally superior.
Powder coatings are also more efficient than solvent-
based spray coatings, in that there is virtually no
overspray or excess material usage.
The composition of the present invention is
also advantageous in that it does not require the use
of catalyst. The present invention, using a three-
component or four-component system, provides polymer
gellation and curing at a rate equal to or greater than
what is now available only with the use of a catalyst.
Catalysts can be ~Yp~ncive and/or toxic and can
contribute to decreased shelf life.
The composition of the present invention is
also advantageous in that PBOX is very versatile as a
coreactant and curative. Very few three-part systems
incorporating PBOX have been described. The
W094/1~67 PCT~S93/12259
4 7 9
composition which can comprise a variety of components
is highly tailorable and versatile.
PBOX has been found to be a very effective
latent curing agent; one that is completely unreactive
at room temperature, but which is very fast at coating
temperatures typically used for functional powder
coatings. Epoxy resins need not be present to afford
powder coatings of the present invention, since one
skilled in the art can envision a number of
combinations of PBox/electrophile/nucl~srh;le~ as
outlined above, which do not include epoxy resins.
The present invention provides for flexible,
rapid curing thermosetting powder coatings for
protection of metallic surfaces under adverse
conditions of heat, moisture, and corrosive materials.
Typical substrates include steel reinforcing bars for
cement constructions ("rebar"), steel pipelines,
especially those that are buried (both interior and
exterior coatings), deep well petroleum drilling pipes,
and electrical cable.
Detailed Descri~tion of the Invention
The powder coating compositions are cured
using 1,3-phenylene-b;soY~7oline (PBOX) as a coreactant
with a nucleophile/ele~L~G~hile pair to form a coating.
A wide variety of resin formulations are shown to
accommodate the PBOX, all of which are characterized by
rapid onset of gelation and rapid cure at working
temperatures. All formulations of the present
invention are three-component: PBOX, a suitable
nucleophilic moiety capable of participating in
polymerization reactions, such as a (poly)phenol or a
(poly)epoxide, and a suitable electrophilic moiety also
capable of participating in polymerizations, such as a
multifunctional anhydride or a (poly)epoxide. The
choice of starting materials is further limited to
those which produce powders suitable for coating that
WO94/1~67 ~ 79 PCT~S93/12259
are solid and are nonblocking (i.e., non-fusing) at
room temperatures. Surprisingly, the powder coating
compositions described by this invention do not require
a catalyst to effect the observed rapid curing.
Preferred concentrations of each of the three
components of the present powders vary widely as a
, function of which components are present and on the
desired properties of the resulting coating, as will be
seen from the enabling examples presented herein.
PBOX
PBOX is referred to by various names
including the following: 1,3-phenylenebis-2-oxazoline;
meta-phenylenebis-2-oxazoline; 2,2'-(1,3-
phenylene)bis(2-oxazoline); 2,2'-m-phenylenebis(2-
oxazoline); 1,3-bis(2-oxazolin-2-yl)benzene; and
isophthaloyl bisoxazoline. The preferred Chemical
Abstracts name for PBOX is 2,2'-(1,3-phenylene)bis[4,5-
dihydro-]oxazole, CAS Registry No. 34052-90-9.
As a percentage of the total weight of the
powder coating composition, PBOX can be present in a
concentration ranging from about 4% to about 40%. PBOX
is commercially available from a number of sources
including the Ashland Oil Co. PBOX is an essential
component of the powder coatings of this invention. If
it is left out, the resulting binary mixtures of
nucleophiles and ele~LLophiles are very slow to react,
or are not reactive at all, especially in the absence
of any catalyst.
NucleoDhilic Materials
Nucleophilic materials of the invention are
normally solid at s~An~Ard temperature and pressure, by
which is meant that they exhibit a ring-and-ball
softening point of at least about 70 C or exhibit a
crystalline melting point of at least about 40 C.
Examples of suitable nucleophilic materials include
WO94/1~67 PCT~S93/12259
7 ~
those selected from the group consisting of phenolic
novolac compounds, bisphenols, bisphenol-terminated
epoxy resins, and non-heat-reactive aromatic-hydroxy-
functional compounds having an average of more than one
aromatic hydroxyl group per molecule which may be ring-
substituted or ring-unsubstituted, wherein the ring
substituents include but are not limited to those
selected from the group consisting of alkyl
substituents having from about l to about 4 carbon
atoms not including alkylene bridges between aromatic
rings; halogen atoms such as fluorine, chlorine,
bromine and iodine; amines; N-alkyl and N, N-di-
alkylamines having from about 1 to about 8 carbon atoms
in the alkyl group(s); nitro; amides; N-alkyl and N, N-
dialkylamides having from about 1 to about 8 carbonatoms in the alkyl group(s), and mixL~ e~ thereof. The
choice of preferred nucleophilic material is made based
on the end use and desired properties of the coating.
When a high-Tg coating is desired, ring-substituted or
ring-unsubstituted phenolic novolac resins are the
preferred nucleophile. When a flexible coating is
required, aromatic-hydroxy-functional phenolic-
terminated epoxy resins are the preferred nucleophile.
When toughness and adhesiveness of the coating is
desired, phenolic novolac resins bearing more than one
aromatic hydroxyl group per aromatic ring are the
preferred nucleophile.
Reagents that donate an electron pair in
chemical reactions are said to be nucleophilic
("nucleus loving"), according to Roberts and Caserio,
Basic Principles of Or~anic Chemistry, 2nd Edition, W.
A. Benjamin, Menlo Park, CA, 1977, p. 208. In the
present invention, a nucleophilic material, if
included, can react with PBOX by attacking the C-4
carbon atom of the oxazoline ring in a ring-opening
reaction, which contributes to the polymer crosslinking
and/or chain extension that is critical to the high Tg
-8-
W094/1~67 ~l 5 ~ 4 7 9 PCT~S93/12259
values of the cured powder coating compositions of the
invention.
Among the phenolic compounds useful in the
present invention are bisphenols such as Bisphenol A
alone or in combination with an aromatic hydroxy-
functional phenolic-terminated epoxy resin such as
DEH~-85, from Dow Chemicals, or Bisphenol F, phenolic
novolac resins and substituted and modified phenolic
novolac resins.
Bisphenol-A is an aromatic phenolic compound
which has been extensively described in the literature.
Chapter 2 of the ~ndbook of Epoxy Resins, H. Lee and
K. Neville, McGraw Hill, New York, 1967, describes
Bisphenol-A and its reactions with epoxy com~u,.ds.
Phenolic novolac resins are obtained by the
polycon~ tion of phenol (or a substituted phenol)
with formaldehyde to form a resin of idealized
structure C6HsoH-tcH2-c6HsoH]n~ wherein n is an integer of
about l to about lO. A special case, where n=l, is
known in the art as Bisphenol F. An i~lLLod~ction to
the preparation of such resins can be found in the
Handbook of Epoxy Resins, (supra), pages 2-lO. In
contrast to resole resins, in which the reactive
functional groups are methylols (i.e., -CH2OH), novolac
reactive functional yLou~ are phenols (i.e., -C6H50H).
Representative novolac resins include Borden Durite~ SD
series resins. The generic term "phenolic novolac
resins" is meant to specifically include novolac resins
obtained by reaction of aromatic rings bearing more
than one hyd1oxyl group, examples of which include but
are not limited to catechol, resorcinol, hydroquinone,
pyrogallol and related naphthalenic com~ou~.ds with
formaldehyde, usually in the presence of acid and a
stoichiometric excess of the phenolic reactant. In
addition to more than one hydroxyl group, aromatic
rings of phenolic novolac resins of the invention may
bear substituents which include but are not limited to
WO94/1~67 21 ~ ~ ~ 7 ~ PCT~S93/12259
those selec~ed from the group consisting of alkyl
su~stituents having from about 1 to about 4 carbon
atoms not including alkylene bridges between aromatic
rings; halogen atoms such as fluorine, chlorine,
bromine and iodine; amines; N-alkyl and N, N-di-
alkylamines having from about 1 to about 8 carbon atoms
in the alkyl group(s); nitro; amides; and N-alkyl and
N, N-dialkylamides having from about 1 to about 8
carbon atoms in the alkyl group(s).
Nucleophiles useful in the ~L es~nt invention
are selected from the group consisting of nucleophiles
having a ring-and-ball softening point above about
70 C, those having crystalline melting points above
about 40 C, and mixtures thereof. That is, they are
generally friable solid materials at room temperature.
Epoxides and epoxy resins, while certainly
nucleophilic, are ~;C~ e~ below and are not
considered in this section.
Ele~L~hilic Materials
Reagents that acquire an electron pair in
chemical reactions are said to be electrophilic
("electron loving")", according to Basic Principles of
Orqanic Chemistry, (Supra), p. 208. Electrophilic
reagents participate in reactions with PBOX by
attacking the electron-rich nitrogen atom of the
oxazoline ring, a process which apparently highly
activates the C-4 carbon atom to nucleophilic attack.
In the present invention, the use of polyfunctional
electrophiles such as polyanhydrides and epoxy resins
adds to the strength of the resulting coating through
the many crosslinks thus formed. In addition, ring
activation by ele~Lrop11iles apparently contributes
significantly to the observed high reaction rate.
Examples of electrophiles of element (c) useful in the
present invention include but are not limited to those
selected from the group consisting of polyanhydrides
--10--
W094/1~67 ~1 5 0 4 7 9 PCT~S93/12259
such as aliphatic and aromatic dianhydrides, and
mixtures thereof.
Dianhydrides comprise a large group of acid
anhydride materials which are suitable for these
formulations. Dianhydrides have traditionally been
employed as crosslinkers for hydroxy-containing
polymers via esterification reactions of the -OH with
anhydride carbonyl. However, in the present case,
carbonyl carbons of the anhydride act as electrophilic
agents in attacking the PBOX ring nitrogen. This
apparently activates the PBOX ring carbon adjacent to
the ring oxygen, rendering it susceptible to attack by
oxygen of phenolic hyd~vxyls in a PBOX ring-opening
reaction. Likewise, this ring carbon can attack an
oxirane oxygen in a crossli nk; ng step. Thus, both the
dianhydride and PBOX act as crosslinking agents for the
epoxy resin. The dianhydride appears to act as an
accelerator for the PBOX reactions; in the absence of a
dianhydride these curing reactions are noticeably
slower. Examples of typical dianhydrides include but
are not limited to those selected from the group
consisting of benzophenone tetracarboxylic acid
dianhydride (BTDA), pyromellitic dianhydride, and
mixtures thereof. BTDA is preferred.
The known electrophilic nature of epoxies and
epoxy resins is ~u~osefully excluded from the above
discussion and will be dealt with below.
EPOXY Resins
D~r~n~;ng on the nature of the other reactive
species in the powder coating mixture, epoxy resins
participate as either electrophilic or nucleophilic
reactants with PBOX. EPOXY resins useful in the
invention are well-known in the literature. Examples
of such epoxy resins are disclosed in U.S. Patent No.
3,971,745, assigned to the assignee of the present
case. Monomeric or polymeric polyepoxides suitable for
WO94/1~67 21~ ~ 4 7 ~ PCT~S93/12259
use in the present invention ço~mprise any of the
conventional polyepoxid~es contAi n; ~g more than one 1,2-
epoxide (i.e., oxirane) ring per molecule, the two
carbon atoms of the epoxide ring being catenary atoms
of an acyclic aliphatic chain which can be straight or
branched. The epoxide rings of the polyepoxide may be
in internal and/or terminal positions. The backbone
structure connecting the epoxide rings may comprise
aliphatic, cycloaliphatic, hete~o~yelic and/or aromatic
constituents and may also contain hetero atoms such as
oxygen, nitrogen or sulfur.
For purposes of brevity, polyepoxide is often
referred to herein as epoxy or epoxy resin.
Polyepoxides having glycidyl ether yLOU~ are the
preferred type of polyepoxides to be used in this
invention because of the commercial availability
thereof. One class of polyglycidyl ether polyepoxides
can be prepared by the reaction of epichlorohydrin and
a polyol or polyphenol such as 2,2-bis(4-
hyd~oxy~llenyl)propane (Bisphenol A). Other commonpolyepoxide forming reactants useful in this invention
are disclosed in the literature. See, for example,
U.S. Patent Nos. 2,840,541; 2,892,809; 2,921,049;
2,921,923; 2,943,096; and 3,629,167. A wide variety of
polyepoxide resins useful in this invention is
commercially available with a wide range of epoxide
equivalents, e.g., about 100 to about 1,500, such as
those commercially available under the trademark Epon
which are available from the Shell Chemicals Company,
and Araldite, available from the Ciba-Geigy Company.
A class of epoxy resins useful in the present
invention are the "aromatic epoxy resins," which are
herein defined as resins comprising at least aromatic
or fused aromatic rings and epoxy groups. Typically,
such aromatic epoxy resins arise from the reaction of
epichlorohydrin and a compound having at least one
aromatic hydroxy substituent.
-12-
WO94/1~67 2 ~ 5 0 ~ 7 9 PCT~S93/12259
Another class of useful epoxy resins includes
those resins that are solid aliphatic and aromatic
copolymeric epoxy resins produced by the
copolymerization of a mixture of aliphatic epoxy resins
and aromatic epoxy resins with a bisphenol compound
such as Bisphenol-A.
An additional comprehensive description of
typical epoxy resins can be found in U.S. Patent No.
5,013,791 (assigned to PPG Industries). Epoxy resins
are also thoroughly described in the monograph Handhook
of Ep~xy Res; nC, H. Lee and K. Neville, McGraw-Hill,
New York, 1967 and in EPOXY Resin Technology, P. F.
Bruins, ed., Interscience Publishers, New York, 1968.
The ~IO~G} ~ion of epoxy resin, if used, in
the final coating composition is determined by the
nature of the other constituents and the use to which
the powder coating will be put. Preferably the epoxy
resin selected comprises from about 20% to about 80% by
weight in order to assure good coating performance.
Epoxy resins selected from the group consisting of
epoxy resins and polyepoxide monomers having a ring-
and-ball softeni~g point above about 70 C, those having
crystalline melting points above about 40 C, and
mixtures thereof are useful herein. That is, epoxy
resins useful in the present invention are generally
solid friable materials at room temperatures, and may
herein be described as "solid epoxy resins."
Within the scope of the present invention,
numerous combinations of PBOX, nucleophile, and
electrophile can be envisioned. Preferred embodiments
are dictated by the desired properties of the resultant
coating. A preferred combination to produce a coating
having a high T~ value comprises PBOX, BTDA
(electrophile), and a phenolic resin (nucleophile). A
preferred combination to produce a coating showing good
toughness and durability comprises PBOX, an epoxy resin
(electrophile) and a phenolic resin (nucleophile). To
WO94/1~67 215 ~ ~ 7 9 PCT~S93/12259
obtain a coating with excellent flexibility, one would
advantageously combine PBOX, either of a novolac resin
or a bisphenol-A en~cApped epoxy resin, especially
long-chain aliphatic polyepoxides (nucleophile), and
any of a number of solid epoxy resins (electrophile).
To obtain a powder coating which gels and cures at low
temperatures, ~g~, about 190C, a preferable
combination would be PBOX, a difunctional phenolic
resin such as Bisphenol A (nucleophile) and BTDA
(electrophile). A preferred combination for a coating
with good hydrolytic stability comprises PBOX, a
phenolic novolac resin (nucleophile) and an epoxy resin
(electrophile).
Optional Com~onents
Typically, a flow CO~I~LO1 agent such as a
Modaflow~ acrylate flow control agent material,
available from M~nc~to, is included in the final
powder formulation. Examples of useful flow control
agents which the coating composition may further
comprise include but are not limited to those selected
from the group consisting of acrylic polymers and/or
copolymers such as polylauryl acrylate, polybutyl
acrylate, poly(2-ethylhexyl)acrylate, poly(ethyl 2-
ethylhexyl)acrylate, polylauryl methacrylate,polyisodecenyl methacrylate, and mixtures thereof.
Flow control agents prevent cratering of the cured
coating. Flow control agents, when used, are present
in amounts of less than about 3 % by weight of the
powder coating composition. Typically, flow control
agents, if used, comprise from about 0.5% to about 2%
percent by weight of the powder coating composition.
Additional optional components which the
powder coating composition may further comprise may be
selected from the group consisting of reinforcing
fillers, such as ground silica, talcs, clays, calcium
carbonate, and the like; pigments; fumed silica;
~ wo 94~1~67 ~ 1 5 ~ 4 7 9 PCT~S93/12259
adhesion promoters or coupling agents well known in the
art, such as silanes; and mixtures thereof.
Method of Use
A thermosetting powder coating comprising a
mixture of 1~3-phenylenebi roX~ ~oline, a reactive
nucleophilic polymer-forming material and a reactive
- ele~LLo~hilic polymer forming material is prepared and
ground to a fine powder, then applied by conventional
powder coating means to various substrates such as
steel reinforcing rod for concrete structures (rebar),
petroleum pipelines or drills, or other materials in
need of protection from heat, moisture and/or corrosive
materials. The result is a smooth, pinhole-free,
tough, co~losion-resistant, and yet flexible,
protective coating. The three-part composition affords
rapid cure without the need for added catalyst.
Typically, the powder coating is prepared by
dry gr;nAing a mixture of PBOX and the other
ingredients - nucleophile and ele~LL~hile as well as
other additives as outlined above - to a mean grain
size of about 44 microns. Optionally, the mixture of
ingredients can be melt-blended, e.g., in a twin-screw
extruder, quenched, then ground to a powder using,
e.g., a hammer mill. The powder is sprayed onto a
metal surface that has been heated to a temperature of
about 180C to about 230C. Gel times for the coatings
after application to the heated substrate from about 1
to about 15 seconds are preferred in order to maintain
efficient production. Gel times can be controllably
varied by varying the p~o~oLLion of one or more of the
essential components in the mixture.
Storaqe Stability
An exceptional feature of the resin powder
coatings of the invention is their nonblocking, or
WO94/1~67 ~ 15 0 4 7 ~ PCT~S93/12259
storage stable, character. Blocking is defined as
clumping or coalescing of the powder which renders it
incapable of being effectively applied to the substrate
which is to be coated. Blocking occurs in powder
coatings when they begin to cure under the action of
ambient moisture or by self-condensation. Many
commercial products are not storage stable for useful
lengths of time, such as months, even at moderate
temperatures and humidities. Refrigerated storage is
usually recommended. Often, however, powder coatings
must be stored in situations where no refrigeration is
available, and they subsequently have a rather limited
shelf life. In contrast, the powder coatings of the
invention exhibit excellent storage stability between
about 15-C and about 50 C, preferably between about
20 C and about 45 C, and most preferably between about
22 C and about 40 C, without refrigeration or other
unusual precautions. The latent, higher temperature
cure afforded by the use of PBOX as a curative accounts
for the excellent storage stability of the powder
coatings of the invention. While we have described
powders that are stable up to at least 40 C, that
temperature is considered to be a minimum temperature
requirement at which the powders are to be storage
stable. Indeed, many of the powders described herein
are stable at temperatures significantly in eYcess of
40 C.
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~ WO94/1~67 21~ 0 4 7 9 PCT~S93112259
GlossarY
The following trade names and abbreviations
are used herein.
BPA: Bisphenol A
BTDA: Benzophenone 3,4,3',4'-
tetracarboxylic acid dianhydride
DSC/TGA: Differential Sc~nn;~g Calorimetry /
Thermal Gravimetric Analysis
Durite~ SD-7280 Phenolic novolac resin available
from Borden.
EPON~2004 Solid DGEBA, from Shell Chemical
Company
PBOX: 1,3-Phenylenebis-2-oxazoline
DGEBA: diglycidyl ether of Bisphenol A
PhYsical Tests and Methods
The test substrate is typically a 2.54 cm x
4.0 cm strip of 0.005 mil copper or steel.
Gel Time: A st~n~rd surgical scalpel is
dragged across the hot resin immediately after it is
sprayed onto the test substrate, preheated to the
specified temperature. The time at which the scalpel
no longer makes a visible impression in the resin is
measured and recorded, along with the temperature at
which the test was performed. The method is also known
as the "Scalpel Drag Test (SDT)".
Flexibility: Flexibility of the coating is
measured by observing the effect on the coating of
h~n~; ~g the test substrate at a 90 angle. Results are
quantified as:
1 - Poor: significant delamination
2 - Fair: noticeable stress cracking with
some delamination
3 - Good: minor cracking observed; no
delamination
WO94/1~67 2 ~ n ~7 9 PCT~S93/12259
4 - Excellent: 90 bend exhibits no stress
fractures
Adherence: Adherence is measured by
attempted scratching of the cured coating from the test
substrate, using a st~n~Ard surgical scalpel. Results
are quantified as:
l - Poor: delaminates in flakes when
scratched
2 - Fair: significant delamination when
scratched
3 - Good: slight delamination along leading
edge when scratched
4 - Excellent: no delamination along leading
edge when scratched.
Differential ScA~n; nq Calorimetry ~DSC):
Industry-st~n~rd DSC equipment is used to determine
the glass transition temperature (T,) of a sample of the
powder coating resin in powder form. Typically, the
powder sample is heated to 300 C at a rate of 20 per
minute, and the melting temperature is determined by
the observed endotherm. A Peak Exotherm temperature
is observed when the polymerization reaction reaches
its maximum rate during the programmed DSC heating.
The sample is cooled, then reheated to determine the
glass transition temperature (T,). Results are obtained
in graphic form as stAn~Ard ouL~L from the test
equipment.
Thermal Gravimetric Analysis (TGA~
TGA data is obtained using a Perkin-Elmer 7-
Series Thermal Analysis System. A powder sample is
heated at 20 C per minute and the temperatures at which
1% weight loss occurs and at which thermal degradation
begins are recorded.
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W094/1~67 21~ ~ 4 7 9 PCT~S93/12259
Ring-and-Ball Softeninq Point
The ring-and-ball softening point of a resin
is determined according to ASTM test method E 28 - 67.
The softening point is defined as the temperature at
which a disk of the sample held within a horizontal
ring is forced downward a distance of 2.54 cm under the
weight of a steel ball as the sample is heated at a
prescribed rate in a water bath or glycerin bath.
In a typical determination, a 25-50 g sample
of resin is heated above its melting point and poured
into a preheated brass ring (l.9 cm outside diameter x
l.6 cm inside diameter) until the ring is completely
full. The resin-filled ring is allowed to cool until
the sample solidifies, then is positioned 2.54 cm above
a receiving plate in a stirred ethylene glycol bath
which also contains an ASTM High Softening Point
Thermometer. A 9.5 mm diameter steel ball weighing
between 3.45 and 3.55 g is placed on the sample in the
ring, and the ethylene glycol bath is heated at a rate
of not more than 5 C per minute. The softening point
is determined as the temperature at which the sample
touches the receiving plate.
Storaqe Stability
Storage stability of a powder coating resin
is determined by placing a 5 g sample of the formulated
powder, as described in Examples 1-5, in a sealed 8-
dram vial in an air-circulating oven for two hours at
40 C in an upright position. The vial is removed and
immediatly tipped to a horizontal position. To be
considered "storage stable," or "nonblocking," the
powder must freely flow within the vial with no
evidence of lumps or of clumping together.
--19--
WO94/1~67 2 ~ 5 ~ PCT~S93/12259
Exam~les
All parts, percentages, ratios, etc. in the
Examples and the rest of the specification are by
weight unless indicated otherwise.
Example 1
PBOX / CATECHOL NOVOLAC / EPOXY RESIN
A mixture of 12 parts 1,3-phenylenebisoxazoline
(PBOX, Ashland Oil Co.), 24 parts catechol novolac
resin (comprising approximately a 4:3 ratio of catechol
to formaldehyde) and 64 parts Epon~2004 (Shell
Chemicals) epoxy resin was ground into a fine powder
and applied to a preheated copper strip at about 235 C.
The coating gelled in 15 seconds then was cured at the
application temperature for 1 minute, and finally
removed from the heat source for cooling and testing.
The coating exhibited a composite adherence and
flexibility rating of 4. Analysis of the powder by
DSC/TGA showed a glass transition temperature (T~) of
102 C and a 1% weight loss at 205 C.
Example 2
PBOX / PHENOLIC NOVOLAC / EPOXY
A mixture of 25 parts PBOX, 25 parts Durite~SD-
7280 phenolic novolac resin (Borden Co.) and 50 parts
Epon~2004 (Shell Chemicals) epoxy resin was ground into
a fine powder and applied to a copper strip preheated
to 235 C. The powder coating gelled in 20 seconds then
was cured at the application temperature for 1 minute,
and finally removed from the heat source for cooling
and testing. On cooling, the coating exhibited a
composite adherence and flexibility rating of 2.5. The
powder showed a T~ of 96 C and a 1~ weight loss at 171-C
by DSC/TGA.
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~ WO94/1~67 2 I ~ ~ 4 7 9 - - PCT~S93112259
Example 3
PBOX / DIANHYDRIDE / EPOXY RESIN
A mixture of 5 parts PBOX, 13 parts BTDA
(3,3',4,4'-benzophenone tetracarboxylic acid
dianhydride, from Allco Chemical Co.) and 87 parts
Epon~2004 (Shell Chemicals) epoxy resin was ground into
a fine powder and applied to a copper strip preheated
to 235 C. The coating gelled in 6 s~con~ then was
cured at the application temperature for 1 minute, and
finally removed from the heat source for cooling and
testing. On cooling, the coating exhibited a composite
adherence and flexibility rating of 2.5. DSC/TGA
analysis of the powder showed T~s at 114-C and 205 C and
1% weight loss at 263 C.
Example 4
PBOX / PHENOLIC RESIN / DIANHYDRIDE
A mixture of 42 parts BTDA and 29 parts PBOX was
stirred and heated at 215-C until all of the BTDA was
dissolved, then cooled to room temperature. The solid
mixture was mixed with 29 parts Bisphenol A and ground
to a fine powder, then applied to a copper strip
preheated to 190-C. The coating gelled in 8 seconds
then was cured at the application temperature for 1
minute, and finally removed from the heat source for
cooling and testing. On cooling, the coating exhibited
a composite adherence and flexibility rating of 3.
Analysis of the powder by DSC/TGA showed a T~ of 136-C
and a 1% weight loss at 224 C
~ Example 5
J 35 PBOX / BISPHENOL A~ ~ATED EPOXY / DIANHYDRIDE
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WO94/1~67 2 1~ 0 4 7 ~ PCT~S93/12259 ~
A mixture of 26 parts BTDA, 37 parts PBOX and 37
parts DEH~-85 (aromatic hydroxy-functional phenolic-
terminated epoxy resin cont~;ning an ~C~fiS of
Bisphenol A, from Dow Chemical) was ground to a fine
powder and applied to a copper strip preheated to
205 C. The powder coating gelled in 10 seconds then
was cured at the application temperature for 1 minute,
and finally removed from the heat source for cooling
and testing. On cooling, the coating exhibited a
composite adherence and flexibility rating of 2. The
powder showed a T~ of 200 C and a 1~ weight loss at
178-C by DSC/TGA.
Reasonable modifications and variations are
possible from the foregoing disclosure without
departing from either the spirit or scope of the
present invention as defined by the claims.
