Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-1- 21 ~8529
CURABLE PULVERULENT MIXTURES
Background of the Invention
Powder coatings are used, inter alia, for coating
metal furniture such as camping equipment, refrigerators,
garden furniture, and shelving, and for coating small
objects and workpieces of complex shape, bicycles, sewing
machines, and other metal articles. It is largely metal
articles which are coated by this process, but powder
coating technology can also be used to coat plastics, for
example.
Compared with other coating processes, powder
coating technology has a number of advantages. For
instance, powder coating is a solvent-free operation and
is thus environmentally friendly and more cost-effective.
The process is also advantageous with regard to waste
disposal, workplace safety due to the absence of
flammable solvents, industrial hygiene and environmental
protection. In addition there is no need to wait for the
coats to dry initially. The coated article is conveyed
directly to the baking oven, thereby reducing the time
expended on the overall coating procedure.
In addition to the production of coatings, powder
resins can also be employed as adhesives. This is of
advantage if, for example, it is necessary to adhesively
bond nonporous materials such as metals from which it is
not possible for volatile components to escape
subsequently.
However, adhesive systems which are solvent-free and
which do not give off elimination products are
increasingly being preferred for the processing of porous
materials too. These requirements are met by adhesives
based on epoxy resins.
Among the heat-curable powder coating systems, it is
predominantly epoxy resin combinations which are
employed. These epoxy resins are mixed with curing
agents, for example with amines, polyamides, acid
-2- 21 ~8~29
anhydrides, boron trifluoride complexes, or dicyandi-
amide. Many of these mixtures have disadvantages which
restrict their industrial application. Both from an
environmental standpoint and given economic
considerations, there is currently a requirement for
coating materials and adhesives which are free from
solvent and from elimination products and which can be
processed extremely rapidly.
It has now been found in practice that, for many
applications, the curing time of the powder mixtures of
the prior art is too long, since the reactivity of the
known powder mixtures and methods is not sufficiently
high. Thus the powder coating mixture should cure fully
at the lowest possible temperature in the shortest
possible time. A further requirement is that of good
storage stability.
The curing of epoxy resins, especially glycidyl
ethers, with numerous anhydrides, di- and polyanhydrides
and various compounds in combination with anhydrides is
known (cf. Lee, Neville, Handbook of Epoxy Resins,
McGraw-Hill Book Company, Chapter 12 Acid-Anhydride
Curing Agents for Epoxy-Resins).
As long ago as in the published German Patent
Application D 7193 (September 4, 1952), resinous
condensation products were described which comprise
compounds containing ethyleneoxy or propyleneoxy groups
in the molecule and polyanhydrides. According to
published German Patent Application H 9989 (September 10,
1953) synthetic resins can be obtained by heating
polyepoxy compounds which contain at least two glycidyl
ether groups and are not derived from phenolic hydroxyl
groups with anhydrides of polybasic carboxylic acids.
From among the plethora of patents, further mention may
be made, for example, of GB-A 744,388, in which mixtures
of epoxy resins and hexachloroendomethylenetetrahydro-
phthalic anhydride and the full curing thereof are
disclosed, and of GB-A 1,264,647, which discloses the
curing of epoxy resins with polycarboxylic anhydrides
containing at least one carbocyclic ring in the presence
215852~
of acidic polyesters which themselves contain carbocyclic
and/or heterocyclic rings.
According to Patent SU 328134, epoxy block
copolymers are prepared by condensation of carboxyl-
containing compounds with excess epoxide. In this case,
linear polyanhydrides of dicarboxylic acids or acidic
polyesters are employed as acid component.
Summary of the Invention
Accordingly, it is an object of the invention to
provide epoxy compositions of improved storage stability
and faster drying time.
It is also an object of the invention to provide
methods of making and using such compositions.
It has now surprisingly been found that it is
possible, by using specific epoxide compounds, to prepare
powder mixtures which are stable on storage and which
have a distinctly higher reactivity than the powder resin
systems known from the prior art.
In accordance with these objectives, in accordance
with a first aspect of the present invention there is
been provided a curable pulverulent mixture including:
(A) a compound containing at least two 1,2-epoxide groups
which is the reaction product of (Al) a compound having
at least two 1,2-epoxide groups per molecule and (A2) a
cyclic carboxylic anhydride, and optionally (B) a curing
agent.
In accordance with other aspects of the invention,
there is provided a substrate coated with a coating
obtained by curing a mixture as described above.
Further objects, features, and advantages of the
invention will become apparent from the details from the
detailed description of preferred embodiments that
follows.
21 58529
Detailed Description of the Preferred Embodiments
The epoxide compound (A) employed in accordance with
the invention contains on average at least 2 epoxide
groups per molecule. Any such compound or mixtures of
such compounds prepared using (A1) and (A2) is useful.
Epoxy compound (A) may have any desired properties
depending on the intended use of the composition.
The epoxide equivalent weight of (A) (molar mass
divided by the number of epoxide groups in the molecule)
is in general between 300 and 1500 g/mol, preferably
between 400 and 800 g/mol and, in particular, between 500
and 700 g/mol, while the acid number is usually from 0.01
to 20 mg of KOH/g, preferably from 0.01 to 2 mg of KOH/g.
Furthermore, the epoxide (A) generally possesses a
number-average molar mass Mn of from 500 to 10,000 g/mol,
preferably from 800 to 3000 g/mol. Depending on the
starting components (Al) and (A2) and their molar ratio
and on the molar mass of (A), these epoxide compounds are
generally solid products having a usual glass transition
temperature (Tg) of at least 20C, preferably from at
least 35 to 60C.
The epoxide compounds (A) are prepared by reacting
the compounds (Al) with the cyclic carboxylic anhydrides
(A2) in any desired manner, generally by heating the
components for several hours with exclusion of oxygen at
temperatures from 100 to 200C, preferably 120 to 160C,
generally until an acid number of less than 20 mg of
KOH/g, preferably of 2 mg of KOH/g or less, is reached.
In this context it is possible to employ as (A1) both
epoxy resins which have been prepared in a one-stage
process (for example from bisphenol and epichlorohydrin)
and those which are obtainable in a two-stage process
(for example from a low molar mass liquid epoxy resin and
bisphenol). The epoxide compounds (A) are preferably
prepared such that the synthesis of the epoxy resin (A1)
is followed immediately by the reaction with the cyclic
anhydride (A2).
2ls8529
The 1,2-epoxide compounds employed in accordance
with the invention as component (A1) have on average at
least two 1,2-epoxide groups per molecule. Any such
epoxide compounds or mixtures can be used. Generally the
compounds have an epoxide equivalent weight of from 160
to 1000 g/mol, preferably from 160 to 600 g/mol, and a
glass transition temperature of at least 10C and up to
140C. They may be either saturated or unsaturated and
aliphatic, cycloaliphatic, aromatic, or heterocyclic, and
may also contain hydroxyl groups. They may additionally
contain substituents which do not give rise, under the
conditions of mixing or reaction, to any interfering side
reactions, examples being alkyl or aryl substituents,
ether groups, or the like.
Examples of such polyepoxide compounds (A1) include
those based on polyhydric phenols, for example
resorcinol, hydroquinone, 4,4'-dihydroxydiphenylmethane,
isomer mixtures of dihydroxydiphenylmethane (bisphenol
F), 4,4'-dihydroxy-3,3'-dimethyldiphenylmethane,
2,2-bis(4-hydroxyphenyl)propane (bisphenol A),
4,4'-dihydroxydiphenylcyclohexane, 2,2-bis(3-methyl-
4-hydroxyphenyl)propane, 4,4'-dihydroxydiphenyl,
4,4'-dihydroxydiphenyl sulfone, tris(4-hydroxy-
phenyl)methane, 4,4'-dihydroxybenzophenone,
1,1-bis(4-hydroxyphenyl)isobutane, 2,2-bis(4-hydroxy-
3-tert-butylphenyl)propane, bis(2-hydroxy-
naphthyl)methane, 1,5-dihydroxynaphthalene,
bis(4-hydroxyphenyl) ether, and also those from the
hydrogenation, chlorination and bromination products of
the above-mentioned compounds, and from novolaks (i.e.,
from reaction products of mono- or polyhydric phenols
with aldehydes, especially formaldehyde, in the presence
of acidic catalysts).
The polyglycidyl ethers of polyhydric alcohols are
also suitable as (Al). Examples of such polyhydric
alcohols which may be mentioned are trimethylolpropane
and 2,2-bis(4-hydroxycyclohexyl)propane.
Also suitable with or as component (Al) are solid
acrylate resins which are compatible with any other
-6- 21 S8529
components of (Al) and contain glycidyl groups, for
example suitable polymers based on glycidyl methacrylate.
Other compounds which are suitable as (A1) are those
such as (poly)glycidyl esters of the formula (I)
R C--C--OCH2--CH--/H2)n C 1~
in which R' is a linear or branched, saturated or
unsaturated hydrocarbon radical having from 1 up to 40,
preferably up to 10, carbon atoms or a substituted or
unsubstituted phenyl radical, the substituents being
selected from among C1- to C8-alkyl and alkoxy radicals
and halogen atoms, and n is at least 2, preferably from
2 to 5. Such polyglycidyl esters of polycarboxylic acids
are obtained by reacting epichlorohydrin or similar epoxy
compounds with an aliphatic, cycloaliphatic or aromatic
polycarboxylic acid, such as oxalic acid, adipic acid,
glutaric acid, terephthalic acid, hexahydrophthalic acid,
2,6-naphthalenedicarboxylic acid and dimerized fatty
acids. Examples of these esters are diglycidyl tereph-
thalate and diglycidyl hexahydrophthalate.
Also suitable as polyepoxides (Al) are compounds
such as triglycidyl isocyanurate and its oligomers and
triglycidyl urazole and its oligomers, and corresponding
mixtures.
These polyepoxide compounds can also be employed as
a mixture with one another and, if desired, as a mixture
with monoepoxides, with care preferably being taken to
ensure that the mixture of the 1,2-epoxide compounds
possesses a glass transition temperature of at least
10C. If 1,2-epoxide compounds having lower glass
transition temperatures are used in the mixture, then
they should preferably be employed only in a minor
proportion and only in combination with correspondingly
high-melting 1,2-epoxide compounds, so that the glass
transition temperature of component (Al) is in the
preferred range of at least 10C.
_7_ 21 $8529
Examples of suitable monoepoxides include epoxidized
monounsaturated hydrocarbons (butylene oxide, cyclohexene
oxide and styrene oxide), halogen-containing epoxides,
for example epichlorohydrin, epoxide ethers of monohydric
alcohols (methyl, ethyl, butyl, 2-ethylhexyl and dodecyl
alcohol); epoxide ethers of monohydric phenols (phenol,
cresol and other o- or p-substituted phenols); glycidyl
esters of unsaturated carboxylic acids, epoxidized esters
of unsaturated alcohols or unsaturated carboxylic acids,
and the acetals of glycidaldehyde.
Other epoxide compounds having suitable melting
points useful in or as component (A1) are described in
the handbook "Epoxidverbindungen und Epoxidharze"
[Epoxide compounds and epoxy resins] by A.M. Paquin,
Springer Verlag, Berlin 1958, Chapter IV, in Lee, Neville
"Handbook of Epoxy Resins", 1967, Chapter 2 and in
Wagner/Sarx, "Lackkunstharze" [Synthetic resins for
coatings], Carl Hanser Verlag (1971), p. 174 ff.
Preferred epoxide compounds (Al) are:
20 poly(epoxyalkyl) ethers of aliphatic or
cycloaliphatic polyhydroxy compounds, such as of
trimethylolethane, trimethylolpropane, tris(hydroxy-
ethyl) isocyanurate and pentaerythritol;
reaction products of epihalohydrins such as
epichlorohydrin with monomeric polyhydric phenols
such as 2,2-bis(4-hydroxyphenyl)propane,
1,1-bis(4-hydroxyphenyl)ethane, bis(4-hydroxy-
phenyl)methane, 4,4'-dihydroxydiphenyl sulfone,
hydroquinone, resorcinol, dihydroxybiphenyl,
dihydroxynaphthalene, and also trisglycidyl
isocyanurate;
glycidyl ethers of polyhydric phenolic compounds,
such as novolaks and resols obtained from the
condensation of phenol and/or cresols with
formaldehyde;
polyglycidyl esters of polycarboxylic acids, such as
diglycidyl esters of phthalic acid, isophthalic
acid, terephthalic acid, tetrahydrophthalic acid,
hexahydrophthalic acid, polyglycidyl esters derived
2l~8529
--8--
from polyesters, or else compounds containing free
carboxyl groups.
It is particularly preferred to use as (A1), epoxy
resins based on bisphenol A and/or bisphenol F with
epichlorohydrin, having epoxide equivalent weights in the
range from 160 to 1000 g/mol.
Suitable cyclic carboxylic anhydrides (A2) include
any known in the art and are expediently those containing
from 4 to 20, and preferably from 4 to 10 carbon atoms,
which may if desired also contain substituents such as
halogen, especially chlorine, and/or carboxyl groups.
They may be derived from (cyclo)aliphatic, olefinically
unsaturated or aromatic polycarboxylic acids having 2 or
more carboxyl groups. Examples which may be mentioned
include succinic anhydride, alkenylsuccinic anhydrides
such as, for example, dodecenylsuccinic anhydride,
glutaric anhydride, maleic anhydride, citraconic
anhydride (methylmaleic anhydride), dichloromaleic
anhydride, aconitic anhydride (l-propene-
1,2,3-tricarboxylic 1,2-anhydride), tricarballylic
anhydride (propane-1,2,3-tricarboxylic anhydride),
itaconic anhydride (methylenesuccinic anhydride),
cyclopentanetetracarboxylic dianhydride, ~4-tetrahydro-
phthalic anhydride, 4-methyl-~4-tetrahydrophthalic
anhydride, hexahydrophthalic anhydride, 4-methylhexa-
hydrophthalicanhydride,3,6-endomethylene-~4-tetrahydro-
phthalic anhydride (= nadic anhydride), 4-methyl-
3,6-endo-methylene-~4-tetrahydrophthalic anhydride
(= methylnadic anhydride); 3,4,5,6,7,7-hexachloro-
3,6-endomethylenetetrahydrophthalic anhydride
(= chlorendic anhydride), the Diels-Alder adduct of 2 mol
of maleic anhydride and 1 mol of 1,4-bis(cyclopenta-
dienyl)-2-butene or Diels-Alder adducts of maleic
anhydride and conjugated fatty acids such as 2,4-hexa-
dienoic acid (sorbic acid), 9,11-octadecadienoic acid
(ricinenic acid), 9,11,13-octadecatrienoic acid
(eleostearic acid), 9,11,13,14-octadecatetraenoic acid,
and also aromatic polycarboxylic anhydrides such as
phthalic anhydride, trimellitic anhydride, pyromellitic
2ls8529
- 9 -
anhydride or benzophenonetetracarboxylie bisanhydride.
It is also useful to use other cyclic polycarboxylic
anhydrides whose carboxyl groups are on different rings,
whieh may be fused, one example of such compounds being
1,8-naphthalenedicarboxylic anhydride.
Particular preference is given to succinic
anhydride, phthalic anhydride and the cycloaliphatic
dicarboxylic anhydrides which can be obtained by Diels-
Alder addition from inexpensive petrochemical raw
materials, for example ~4-tetrahydrophthalic anhydride or
hexahydrophthalic anhydride.
Components (A1) and (A2) are employed in quantities
to give the desired product and are usually employed in
quantities such that in general 0.01 - 1 mol, preferably
0.05 - 0.5 mol and particularly preferably 0.1 - 0.4 mol
of cyclic anhydride (A2) is used per mole of epoxide
compound (A1).
Catalysts can optionally be used in the reaction of
(A1) and (A2) to form (A). Examples of catalysts which
ean be employed for the targeted and aecelerated reaction
of the anhydride and/or carboxyl groups of component (A2)
and of the epoxide groups of component (A1) include
Bronsted bases such as sodium hydroxide, potassium
hydroxide, lithium hydroxide, sodium earbonate; ehromium
eompounds such as CrCl3, CrO3, ehromium aeetyl aeetonate;
imidazoles; quaternary ammonium and phosphonium eompounds
sueh as benzyl-trimethylammonium ehloride, tetraethyl-
ammonium ehloride, tetramethylammonium ehloride, benzyl-
trimethylammonium ehloride, benzyldodeeyldimethylammonium
ehloride, methyltriphenylphosphonium iodide,
triphenyl(2,5-dihydroxyphenyl)phosphonium hydroxide,
ethyltriphenylphosphonium aeetate, triphenylethyl-
phosphonium bromide and Lewis bases, sueh as organie
phosphines (e.g., triphenylphosphine, trieyelohexyl-
phosphine, tributylphosphine, eyelohexyloetylphosphine)and amines, whieh may be aromatic (N,N-dimethylaniline,
N,N-diethylaniline, N,N-dimethyl-p-toluidine, N,N-di-
ethyl-p-toluidine) and (cyclo)aliphatic (triethylamine,
tributylamine, benzyldimethylamine, benzyldiethylamine,
21 58529
--10--
triethylenediamine, N-methylmorpholine, N-methyl-
piperidine, N-butylamine) as well as alkanolamines such
as diethanolamine, dimethylethanolamine, diethylethanol-
amine, dibutylethanolamine, methyldiethanolamine and
di(3-phenoxy-2-hydroxypropyl)alkylamines, for example
di(3-phenoxy-2-hydroxypropyl)-n-butylamine.
Preferred catalysts in this context are those of the
formula (II)
/R1 OH
R--N ~ I 1)
R1 OH
in which0 R = hydrogen, a branched or unbranched alkyl
radical having 1 to 18, preferably 1 to 4,
carbon atoms, a cycloaliphatic alkyl radical
having 5 to 12, preferably 5 to 8, carbon
atoms, or is -R10H;5 R1 = a branched or unbranched alkylene radical
having 2 to 6, preferably 2 or 3, carbon
atoms, which may additionally carry
substituents -OR2,
R2 = a branched or unbranched alkylene radical
having 2 to 6, preferably 2 or 3, carbon atoms
or a substituted or unsubstituted aromatic
ring.
Particularly preferred compounds of the formula (II)
are triisopropanolamine and/or triethanolamine.
These optional catalysts when employed, are employed
in a catalytic effective amount and in general in
quantities of from 0.01 to 1~, preferably from 0.05 to
2%, based on the sum of the masses of (Al) and (A2).
The reaction products (A) of (Al) and (A2) can be
used in compositions with known epoxy resins, for example
those based on bisphenol A or bisphenol F, in which case
their proportion is preferably allowed to be between 5
-11- 21 ~8~29
and 70% of the overall mass of the epoxide components
(A).
Suitable curing agents (B) include all compounds
which are known for this purpose, especially anhydride
curing agents such as, for example, phthalic anhydride,
tetrahydrophthalic anhydride, 4-methyltetrahydrophthalic
anhydride, hexahydrophthalic anhydride, 4-methylhexa-
hydrophthalic anhydride, methylnadic anhydride (trivial
name for isomers ofmethylendomethylenetetrahydrophthalic
anhydride), chlorendic (HET) anhydride (3,4,5,6,7,7-hexa-
chloro-3,6-endomethylenetetrhydrophthalic anhydride),
pyromellitic dianhydride, benzophenonetetracarboxylic
dianhydride, trimellitic anhydride, curing agents in
accordance with component (B) of DE-A 25 56 182 (hereby
incorporated by reference), dodecenylsuccinic anhydride,
isooctenylsuccinic anhydride, other acidic curing agents,
dicyandiamide, phenolic curing agents such, for example,
as the Dow hardeners ~D.E.H. 80, ~D.E.H. 82, ~D.E.H. 84,
carboxylic salts of imidazole or imidazoline compounds,
meltable, soluble adducts which are obtained by reacting
an epoxide compound with imidazole or imidazoline
compounds or the carboxylic salts thereof (cf.
DE-C 19 10 758, hereby incorporated by reference).
Polyesters which contain carboxyl groups are
preferred as curing agents (B). The epoxide compounds
(A) and the carboxyl polyesters as curing agents (B) are
present in the mixture according to the invention, in
general, in quantities such that the ratio of equivalents
of carboxyl groups of the curing agents to epoxide and
hydroxyl groups in (A) is from 0.7 to 1.3, preferably
from 0.9 to 1.1. For this to apply, the quantity of
carboxyl polyesters as curing agent (B) will usually be
from 50 to 90~, preferably from 65 to 85~, based on the
sum of the masses of (A) and (B). In this way, a suffi-
cient crosslinking density is generally obtained.
The carboxyl-containing polyesters employed as
component (B) usually possess an acid number of from 15
to 150 mg of KOH/g, preferably from 30 to 100 mg of KOH/g
and a glass transition temperature of at least 35C, pre-
2158529
-12-
ferably from at least 40 to 60C. The number-average
molar mass Mn (gel chromatography, polystyrene standard)
is in general between 600 and 12,000 g/mol, preferably
between 2000 and 8000 g/mol. The carboxyl groups are
preferably disposed at the ends of the molar chains,
which may be linear or branched. The end groups of the
carboxyl polyester in general consist of carboxyl groups
to the extent of more than 70%, preferably more than 90%.
The chain ends preferably predominantly have on average
2 or more carboxyl groups, some of which are present as
carboxylic anhydride groups.
The melt viscosities of the carboxyl polyester at
200C are in general between 1000 and 8000 mPa.s,
preferably between 2000 and 6000 mPa.s.
The carboxyl polyesters are prepared in a known
manner in a one-stage process or, preferably, in a two-
stage process as described, for example, in
DE-A 2 163 962 (hereby incorporated by reference), by
reacting appropriate polyols with appropriate poly-
carboxylic acids or derivatives thereof, especially
anhydrides. In this context, the polycarboxylic acids
and anhydrides are employed in excess. The quantitative
ratio is generally such that the ratio of equivalents of
hydroxyl to acid and/or anhydride groups is from 1:3 to
1:1.1, preferably from 1:2.2 to 1:1.8.
Compounds which are especially suitable as polyol
component include those having hydroxyl numbers in the
range from 10 to 80 mg of KOH/g, preferably from 15 to
40 mg of KOH/g, and number-average molar masses Mn (gel
chromatography) of from 600 to 10,000 g/mol, preferably
from 2000 to 8000 g/mol, and also softening points of
from 35 to 110C, preferably from 40 to 90C (differen-
tial thermal analysis). Examples which may be mentioned
here include OH-containing polyesters, polyethers, poly-
thioethers, polyacetals, polycarbonates and polyester-
amides. Linear or branched polyesters are preferred in
this context.
Examples of such hydroxyl-containing polyesters are
reaction products of polyhydric, preferably dihydric and,
-13- 21 ~8529
if desired, additional trihydric, alcohols with poly-
basic, preferably dibasic, carboxylic acids. In place of
the free polycarboxylic acids it is also possible to use
the corresponding polycarboxylic anhydrides or polycarb-
oxylic esters of alcohols having 1 to 6 carbon atoms,
mixtures thereof, to prepare the polyesters. The reac-
tion can also be carried out in the presence of conven-
tional esterification catalysts. The polycarboxylic
acids may be aliphatic, cycloaliphatic, aromatic and/or
heterocyclic in nature and may, if desired, be substi-
tuted, for example, by halogen atoms, and/or unsaturated.
Examples of useful carboxylic acids and derivatives
thereof for making the polyester curing agents include
the saturated aliphatic dicarboxylic acids, succinic
acid, adipic acid, suberic acid, azelaic acid, sebacic
acid; also phthalic acid, isophthalic acid, trimellitic
acid, phthalic anhydride, tetrahydrophthalic anhydride,
hexahydrophthalic anhydride, tetrachlorophthalic anhyd-
ride,endomethylenetetrahydrophthalicanhydride,glutaric
anhydride, maleic acid, maleic anhydride, fumaric acid,
dimerized and trimerized unsaturated fatty acids, if
desired as a mixture with monomeric unsaturated fatty
acids, such as oleic acid, and also dimethyl terephtha-
late and bisglycol terephthalate.
Examples of suitable polyhydric alcohols useful in
making the polyester curing agents include ethylene
glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-buty-
lene glycol, 1,6-hexanediol, 1,8-octanediol, neopentyl-
glycol, 1,4-bishydroxymethylcyclohexane, 2-methyl-
1,3-propanediol, glycerol, trimethylolpropane,
1,2,6-hexanetriol, 1,2,4-butanetriol, trimethylolethane,
pentaerythritol, quinitol, mannitol and sorbitol, methyl-
glycoside, and also diethylene glycol, triethylene
glycol, tetraethylene glycol and higher polyethylene
glycols, dipropylene glycol and higher polypropylene
glycols, and dibutylene glycol and higher polybutylene
glycols. It is also useful to employ polyesters of
lactones, for example, ~-caprolactone, or of hydroxy-
carboxylic acids, for example, ~-hydroxycaproic acid.
2ls8529
- -14-
Examples of the anhydrides useful as curing agents
(B) are, in particular, trimellitic anhydride (TMAA) and
pyromellitic anhydride or maleic anhydride adducts with,
for example, piperylene.
Further carboxyl-containing polyesters which are
suitable in accordance with the invention as curing
agents (B) are, for example, those described in
DE-C 36 18 355 and in DE-A 21 63 962, and 26 18 729, each
of which are hereby incorporated by reference.
Particularly preferred curing agents are carboxyl-
containing polyesters whose acid number is between 15 and
150 mg of KOH/g and whose number-average molar mass is
between 600 and 12,000 g/mol.
Other preferred curing agents are imidazolines of
the formula (III)
R ¦ ¦ R
R--N~ N
R
in which each substituent R, independently of the others,
is hydrogen or a C1 to C20-alkyl, aryl, aralkyl,
cycloalkyl or heterocyclic radical, R' is the same as R
or is an alkylene or arylene radical connecting two
imidazole or imidazoline groups, any of R and R' may
possibly be substituted by one or more C1 to C20-alkyl,
aryl, aralkyl, cycloalkyl or heterocyclic radicals, and
where two or more radicals may be connected, possibly
also by heteroatoms, and/or imidazoles of the formula
(IV)
R R
H N~N ~ I V~ '
in which R and R' are as defined for formula (III).
-15- 21 58529
Examples of suitable imidazolines include the
following compounds: 2-methylimidazoline, 2-ethyl-
4-methylimidazoline, 2-phenylimidazoline, 2-undecyl-
imidazoline, 2-heptadecylimidazoline, 2-ethylimidazoline,
2-isopropylimidazoline, 2,4-dimethylimidazoline,
2-phenyl-4-methylimidazoline, 2-benzylimidazoline,
2-(o-tolyl)imidazoline, 2-(p-tolyl)imidazoline, tetra-
methylenebisimidazoline,1,1,3-trimethyl-1,4-tetramethy-
lenebisimidazoline, 1,3,3-trimethyl-1,4-tetramethylene-
bisimidazoline, 1,1,3-trimethyl-1,4-tetramethylenebis-
4-methylimidazoline, 1,2-phenylenebisimidazoline,
1,3-phenylenebisimidazoline,1,4-phenylenebisimidazoline
and 1,4-phenylenebis-4-methylimidazoline. It is also
useful to employ any desired mixtures of the imidazo-
lines.
Examples of suitable imidazoles include imidazole
itself, 1-methylimidazole, 2-methylimidazole, 4-methyl-
imidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethyl-
imidazole, 1-propylimidazole, 2-propylimidazole,
2-isopropylimidazole, 1-butylimidazole, 2-octylimidazole,
2-undecylimidazole, 2-heptadecylimidazole, 2-cyclohexyl-
imidazole, 1-phenylimidazole, 2-phenylimidazole,
2,4-dimethylimidazole, 1,2-dimethylimidazole,
4,5-dimethylimidazole, 2-ethyl-4-methylimidazole,
1-ethyl-2-methylimidazole, 1-methyl-2-isopropylimidazole,
4-butyl-5-ethylimidazole, 2-cyclohexyl-4-methylimidazole,
1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole,
4,5-diphenylimidazole, 2-ethyl-4-phenylimidazole,
2,4,5-trimethylimidazole, 2,4,5-tricyclohexylimidazole,
1,2,4,5-tetramethylimidazole and benzimidazoles and
derivatives thereof. It is also useful to employ any
desired mixtures of the imidazoles and/or imidazolines.
The quantity of curing agents in the pulverulent
mixtures according to the invention depends on the nature
of the curing agent and can fluctuate within wide limits
to give the desired curing. The quantity of curing agent
is generally from 0.01 to 90%, preferably from 0.5 to
85%, based on the sum of the masses of the two components
-16- 21 58529
(A) and (B). In the case of imidazoles or imidazolines,
a mass fraction of 0.01 to 70%, preferably of 0.5 to 40%,
of curing agent in the composition is usually chosen.
In addition to components (A) and (B), the mixtures
according to the invention may contain additives which
are conventional for powder coatings, such as leveling
agents or anticrater agents, dyes, pigments, fillers,
matting agents, thixotropic agents, deaerating agents, W
stabilizers, oxidation inhibitors, quenchers (free-
radical scavengers, for example, N-alkyl-substituted
piperidines), catalysts for accelerating the crosslinking
reaction, plasticizers, additional curing agents, addi-
tional curable resins, and the like. Any of these addi-
tives or mixtures thereof can be used. These additives
are generally employed in effective quantities of from 0
to 50%, preferably from 0.1 to 40%, based on the overall
mass of the powder coating mixture. Any liquid or pasty
additives here can be used, inter alia, as a mixture with
highly active silicic acid as a masterbatch (see
DE-A 22 02 907).
Leveling agents which can be employed include, for
example, acetals such as polyvinylformal, polyvinyl-
acetal, polyvinylbutyral, polyvinylacetobutyral, and the
like, polyethylene glycols and polypropylene glycols,
silicone resins, mixtures of zinc soaps, of fatty acids
and aromatic carboxylic acids, and in particular commer-
cially available products based on polyacrylates. The
leveling agents can be added to component (A) in effec-
tive quantities, for example, of from 0.1 to 4%, prefer-
ably from 0.2 to 2.0%.
Examples which may be mentioned of the dyes or
pigments, which may be inorganic or organic in nature,
are titanium dioxide and zinc oxide. The organic dyes or
pigments should of course be selected such that they are
stable at the curing temperatures and do not lead to any
intolerable alterations in shade.
Examples of suitable fillers include ground quartz,
silicates, chalk and gypsum.
-17- 21 S8529
The stabilizers can be aromatic diketones such as
benzoin, which prevent localized decomposition and thus
suppress the formation of pores.
The stabilizers are generally added in quantities of
from 0.1 to 3%, preferably from 0.2 to 2~, based on the
mass of the overall binder mixture.
In order to prepare the pulverulent mixtures
according to the invention for testing, processing and
practical application, the individual components are
generally mixed with one another. When using liquid
constituents, generally the solid components are finely
ground and the liquid components are distributed uniform-
ly therein. In order to prepare the curable mixtures
according to the invention, the components are homo-
genized in the melt after mixing. This can take place in
suitable equipment, for example, heatable kneading appa-
ratus, double-Z mixers, or extruders, preferably the
latter, the extrusion temperature being chosen such that
maximum shear force acts on the mixture. In this con-
text, an upper temperature limit of 130C should not be
exceeded. When using catalysts it may be advantageous to
add these to component (A) or (B). This addition can
also be made, for example, during the preparation of
component (A).
The homogenized mass is then allowed to cool to room
temperature and, after suitable precomminution, is ground
to give a curable, pulverulent mixture (powder coating).
The target average particle sizes depend on the intended
use and are generally from about 40 to 90 ~m, but pre-
ferably about 50 ~m. Any oversize present, with a
particle size of more than 90 ~m, is generally removed by
screening.
On the basis of their high reactivity, the mixtures
according to the invention are particularly suitable as
adhesives and coating compositions. The mixture can be
made solvent free, thereby achieving the advantages
mentioned at the outset.
The powder coatings thus produced can be applied to
suitable substrates, for example, metal, wood, glass,
21$8S29
-18-
concrete, plastic and ceramic, by known methods, for
example, by electrostatic powder spraying, powder
application by the triboelectric method, fluidized-bed
sintering, electrostatic fluidized-bed sintering or by
flame spraying.
After the powder coating has been applied by one of
the methods mentioned, the coated workpieces are general-
ly heated, to achieve full cure, to a temperature of from
90 to 270C, preferably from 120 to 220C, for a time
which is sufficient to achieve full curing, in general
from 0.5 to 60 minutes. The resulting coatings are
distinguished by good properties in terms of paint
technology, such as good mechanical properties, good
chemical resistance, good weathering resistance and good
adhesion. The powder coatings according to the invention
are consequently suitable, in particular, for coating
materials such as, for example, metal, glass, fabrics,
paper, and ceramic.
In addition to the use as coatings, the mixtures
according to the invention can also be employed as
adhesives. The production of adhesive formulations is in
principle carried out in the same way as described for
the powder coating mixtures. In other words the solid
epoxy resins (component A) are first comminuted and then
intimately mixed with the curing agent (B), care being
taken to ensure uniform distribution of the components.
The formulations thus obtained may if desired be
admixed with conventional additives as described above,
such as fillers, pigments, and/or dyes. The mixtures
according to the invention can be used for adhesive
bonding of all types of materials, for example, metals,
light metals, but also nonmetallic materials such as
ceramic, glass, leather, rubber, paper, cardboard, wood
and plastics with themselves or with other materials.
They can also be employed in the preparation of sandwich
constructions of metals and other materials.
A point worthy of particular emphasis is the
possibility of constructing sandwich systems from wood
(chipboard, plywood, etc.) and fabrics, for example,
2l5852~
--19--
polyester fibers (~Trevira). In the course of the
adhesion process the fabric is embedded completely in the
binder system, forms a homogeneous surface and adheres in
an optimum manner to the substrate. The laminate
obtained in this way, even with a lower thickness of
material, has a high flexural strength in relation to
plain chipboard or plywood panels. This procedure makes
it possible to obtain panels which, while of the same
quality, are of lower weight in comparison to standard
materials.
When the mixtures according to the invention are
used for adhesive bonding they can be applied by
electrostatic means, for example, with an electrostatic
powder spray gun. In this way it is possible to apply
uniformly thin coats, for example, on films. Because of
the rapid reaction of the individual components of the
mixtures according to the invention at low temperatures,
it is also possible to achieve high rates of production
throughput.
An outstanding advantage in this application means
is that yellowing, combustion, and gas escape can be
avoided. The pulverulent mixture on the coated materials
generally cures fully at temperatures of from 120 to
220C, preferably from 130 to 210C, in an adequate time
of from 2 to 60 minutes.
The compositions according to the invention are
particularly suitable for the coating of filter papers
which can be used in the production of filters for low-
and medium-viscosity liquids, for example, oils. In this
case either the epoxy resin/curing agent mixture is
applied to untreated filter paper in the form of a fine
powder and incipiently melted for a brief period, or the
paper is coated with a melt of the mixture. Full curing
is then carried out at the stage of ultimate fabrication
and adhesive bonding.
The present invention is further illustrated by the
following examples, which are for illustrative purposes
only and do not limit the invention.
- 2158529
-20-
EXAMPLES:
Epoxy resin I (comparison)
Commercially available bisphenol A epoxy resin for
the preparation of powder coatings, having the following
characteristics:
Epoxide equivalent weight about 800 g/mol
Viscosity at 25C about 500 mPa.s
40% strength in butyldiglycol
in accordance with DIN 53 015
Melting point about 70C
Capillary method in accordance
with DIN 53 015
Glass transition temperature about 50~C
Epoxy resin II (according to the invention)
Preparation
1464 g of a liquid bisphenol A epoxy resin having an
epoxide equivalent weight of 183 g/mol (8 mol of epoxy
groups) and 456 g of bisphenol A (2 mol) are heated to
125C in a four-necked flask with stirring under a
nitrogen atmosphere, and 4 g of triethanolamine are
added. By exothermic reaction and additional heating,
the temperature is brought to 160C over the course of 15
minutes and maintained for 4.5 hours. The epoxide
equivalent weight is then 468. After a holding time of
a further hour at 160C, the temperature is reduced to
150C and 91. 4 g (0. 6 mol) of tetrahydrophthalic
anhydride are added. After 1. 25 hours, the acid number
is 0.9 mg of KOH/g. After a further 0. 5 hour, the flask
is emptied.
Characteristics:
Epoxide equivalent weight 601 g/mol
Acid number (toluene/ethanol) 0. 2 mg of KOH/g
Viscosity 25C (40% in butyldiglycol 519 mPa.s
Glass transition temperature 45.7C
21~8529
-21-
Example 1
Gel time determination
The gel time was measured in accordance with
DIN 16 916 Part 2 (September 1987) section 5.7.1,
"Determination of the B-stage time", at 180C. The
results for various mixtures according to the invention
in comparison with those of the prior art are listed in
Table 1.
The pulverulent mixtures according to the invention
exhibit surprisingly short gel times in comparison with
the mixtures containing a prior art epoxy resin. This is
a measure of the high reactivity of the mixtures accord-
ing to the invention which are used, and demonstrates the
great influence of the epoxy resin component A on the
rate of reaction of the overall system.
- 21S8~29 -
-22-
Table 1: Gel time determinations at 180C
Epoxy Curing agentParts by wt. (pbw) of curing Seconds
resin agent per 100 pbw of epoxy
resin
2-Heptadecylimidazole 0.5 > 600
II 2-Heptadecylimidazole 130
2-Heptadecylimidazole 1 > 600
II 2-Heptadecylimidazole 62
2-Heptadecylimidazoline2.5 725
II 2-Heptadecylimidazoline 172
1 0 I 2-Ethyl~methylimidazoline 1 219
II 2-Ethyl~methylimidazoline 35
2-Methylimidazoline 1 282
II 2-Methylimidazoline 111
2-Phenylimidazole 2.5 85
1 5 II 2-Phenylimidazole 37
2-Phenylimidazoline 2.5 337
II 2-Phenylimidazoline 103
Curing agent B31 (Huls) 1 > 600
II Curing agent B31 (Huls) 376
I Curing agent B31 (Huls) 2.5 324
II Curing agent B31 (Huls) 79
Curing agent B68 (Huls) 2.5 > 600
II Curing agent B68 (Huls) 221
Curing agent B55 (Hals) 2.5 > 600
II Curing agent B55 (Huls) 190
Curing agent EH 694 (Hoechst) 15 234
II Curing agent EH 694 (Hoechst) 80
Trimellitic anhydride 6 587
II Trimellitic anhydride 108
3 0 I Pyromellitic anhydride 5 314
II Pyromellitic anhydride 112
Dicyandiamide 2.5 684
II Dicyandiamide 280
Dyhard~ lW (SKW Trostberg) 2.7 623
II Dyhard~ 100 (SKW Trostberg) 225
Curing agent B31: cyclic amidine
Curing agent B55:~ salt of a polycarboxylic acid and of a
Curing agent B68:J cyclic amidine
Curing agent EH694: resinous anhydride
Dyhard~ 100: dicyandiamide
2l~8.529
-23-
Example 2
Coatings testing
The powder coatings tested in Table 3 were prepared
by extruding the powder coating mixtures comprising
carboxyl polyester, epoxy resin, pigment and additives in
the mixing ratio given in Table 2 and are comparable with
one another in respect of the preparation process and the
particle size distribution (average particle size 50 ~m).
The extruded powder coating mixtures were applied to
degreased steel panels using a Corona spray gun. The
coating thickness was on average about 63 ~m and the
stoving temperature was 160C (see Table 3). The tests
were carried out in accordance with the standards
indicated.
The tendency toward yellowing was determined by
dividing the coated panels together with the baked films
and overbaking one half at 200C. The ~E color differ-
ence measurement was carried out on a Tricolor LFM 3
colorimeter from Lange in accordance with DIN 6174,
CIE-LAB 1976, against a white standard or, in the case of
the overbaked films, against the portion of the film
which was not overbaked.
- 21s8s29
-24-
Table 2: Powder coating mixtures (composition in
parts by weight)
FY~mpl~. 2 a)Example 2 b)
Comparison
Epoxy resin I 170
Epoxy resin II - 157
Polyesterl) 397 410
Titanium dioxide2)300 300
Blanc fixe F 100 100
Leveling agent3) 30 30
Benzoin 3 3
l) Carboxyl polyester~ Alftalat AN 770 (Hoechst) having
the following characteristics:
Acid number (DIN 53 402): 34 + 4 mg of KOH/g
Glass transition temperature: 53 + 2C
(measured by DSC, Mettler TA 3000, at 10C/min)
Viscosity at 200C: 5,000 to 6,500 mPa.s
(measured with ICI Cone & Plate)
2) ~Kronos 2160 from Kronos Titan
3) ~Additol XL 396 (Hoechst)
- 21 S85~9
-25-
Table 3: Test results for the coating films
Example 2c Example 2d Example 2e Example 2f
(Co~)dlis(,ll)(C~ lis~,ll)
Powder coating mixture 2a 2a 2b 2b
example
Overbaking Ov~ kii.g
Drying temperature (C) 160 200 160 200
5 Drying time (min) 10 60 10 60
Coat thickness (~Im)60 - 66 56 - 62 60 - 66 66 - 70
Gloss 60 perspective DIN 95 94 95 94
67 530 (%)
Leveling (+) 2 2
Cratering (+) 0 0
Erichsen indentation11.2 11.8 11.5 11.7
DIN 53 156 (mm)
Impact testing ASIIM
D 2794
direct Nm (Ib-in) 1 8 (16) 18.1 (160) 6.8 (60)18.1 (160)
indirect NM (Ib-in)<0.5 (<4) 18.1 (160) 4.5 (40)18.1 (160)
Butyl acetate test 3 min 5 4 4 3
(+)
Xylene test 30 min (+) 5 5 5 4
I~E rel. to powder white 1.21 1.35
standard
AB rel. to powder white 0.12 0.04
standard
AE rel. to normal curing 3.15 1.94
~B rel. to normal curing 2.79 1.93
Blocking resistance of the
powder coating mixture 2 2
40C acc. to DIN 55990 7
days
3 0 Gel time of the powder
coating mixture at 180C 197 85
(S)
( + ) = visual assessment in accordance with DIN 53 230
0 = very good, 5 = very poor
` -26- 21 58529
From the examples in Table 3 it is evident that the
powder coating films of the powder coating mixture
according to the invention give test results which are
equal to (gloss, leveling, cratering, Erichsen
indentation) and in some cases better than (solvent test,
yellowing resistance) those of the comparison powder
coating mixture. In particular, the powder coating
mixture 2 b (2 e) according to the invention exhibits
substantially greater reactivity (lower gel time) than
that of the prior art 2 a (2 c). Furthermore, it was
found that the impact testing values of the coating film
according to the invention (2 e) at the chosen baking
temperature are higher than those of the comparison
(2 c). In practice, therefore, powder coating films can
advantageously be stoved at lower temperatures with the
resins according to the invention than with those
according to the prior art.
Example 3
Bonding of polyester fabric
The resin/curing agent mixture (e.q., 92 parts by
weight of epoxy resin II and 8 parts by weight of curing
agent B 31, cyclic amidine from Huls Aktiengesellschaft)
is mixed in an MTI mixer to a particle size of < 5 mm and
extruded at 80C with a residence time of 10-15 seconds,
and the liquid melt of the binder/curing agent mixture,
directly after the dispersion in the extruder, is passed
together with the polyester fabric through a calender, in
the course of which operation the liquid melt material is
distributed uniformly on the fabric. The coated fabric
is stored at ambient temperature prior to its subsequent
use or adhesive bonding.
The fabric treated with the powder mixture is
punched out, cut and then adhesively bonded with
chipboard panels under a pressure of 40 bar over
40 seconds at 200C. Under the process conditions chosen,
the powder mixture melts, wets the substrate (chipboard
and fabric) very thoroughly and then cures fully. In
21 ~8~2g
-27-
this procedure the polyester fabric is completely
embedded in the binder system, forms a homogeneous
surface and adheres to the substrate in an optimum
manner.
Example 4
Bonding of polyester fabric
The resin/curing agent mixture (e.q., 92 parts by
weight of epoxy resin II and 8 parts by weight of curing
agent B 31, cyclic amidine from Huls Aktiengesellschaft)
is mixed in an MTI mixer to a particle size of < 5 mm and
is extruded at 80C with a residence time of
10-15 seconds. The extrudate emerging at 100C is
cooled, broken, ground and screened to a particle size of
< 125 ~m.
The powder mixture obtained in this way is applied
using an electrostatic powder spray gun to polyester
fabric and the coated material is processed further
either by
a) immediately pressing and adhesively bonding the
polyester fabric provided with the powder mixture
onto chipboard to be laminated, or by
b) fusing the powder mixture for 2 minutes at 100C
onto the Trevira fabric, placing the material in
intermediate storage and then adhesively bonding it
to chipboard.
The adhesive bonding of the fabric treated in this
way is carried out under pressure (40 bar) over 40
seconds at 200C to chipboard. Owing to the chosen
process conditions, the powder mixture melts, wets the
substrate (chipboard and fabric) very thoroughly and then
cures fully.
Example 5
Filter paper coating
The epoxy resin/curing agent mixture (e.g., 92 parts
by weight of epoxy resin II and 8 parts by weight of
curing agent B 31, cyclic amidine from Huls
Aktiengesellschaft) is mixed in an MTI mixer to a
2l58s29
-28-
particle size of < 5 mm and is extruded at 80C with a
residence time of 10-15 seconds.- The extrudate emerging
at 100C is cooled, broken, ground and screened to a
particle size of < 125 ~m.
The powder mixture obtained in this way is applied
using an electrostatic powder spray gun to filter paper,
fused to the paper at about 100C for 2 minutes, and
placed in intermediate storage until adhesive bonding is
carried out.
An alternative procedure which is possible is to cut
the filter paper, which has been provided with the as yet
unfused powder coating, to the desired shape, to punch it
out and then immediately to carry out adhesive bonding.
Instead of the electrostatic application, the liquid
melt of the binder-curing agent mixture can be applied
directly, following its dispersion in an extruder, to the
paper. To this end the liquid material is passed
together with the filter paper through a calender,
resulting in a uniform coat on the paper. The coated
filter paper is then placed in intermediate storage until
adhesive bonding is carried out.
The papers treated with the powder coating are
punched out to shape, cut and then bonded to one another
under pressure and with heating. Owing to the chosen
process conditions, the powder melts, sufficiently wets
the papers to be bonded and cures in a very short time
(e.g., a few seconds at 180C) to give adhesive bonds
which are suitable for the production of oil filters.
While the invention has been described with
reference to certain preferred embodiments, numerous
modifications, alterations, and changes to the preferred
embodiments are possible without departing from the
spirit and scope of the invention.
