Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 2117141
93/K 024
Curable pulverulent mixtures
Powder coatings are used inter alia for aoating metal
; furniture such a6 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 metallic
articles that are coated by this process, but powder
coating technology can al60 be used to coat pla6tics, for
example.
Compared with other coating processes, powder coating
'. technology ha6 a number ~o;f advantages. For instance,
powder coating i6 a solvent-free operation and is thu6
environmentally friendly and more co6t-effective. The
proce6s i6 also advantageous with regard to waste dis~
posal, workplace safety (absence of combustible 601-
vents), 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 furnace, thereby reducing the time expended on the
20 overall coating procedure. ~ ~
- ..:
In addition to the production of coatings, powder resins
can also be employed as adhesives. This iB of advantage
if, for example, it is required to adhesively bond
nonporous materials such as metals, from which it is not
25 possible or volatile components to subsequently escape. ;`
However, adhesive systems which are 601vent-free and
which do not give off elimination products are in-
creasingly being preferred for the procesQing of porous
materials too. These requirements are met by adhesives
based on epoxy resin6.
Among heat-curable powder coating systems it is predomi-
nantly epoxy re~in ao~binatione whi~h are e~ployed. These
~ . . - ... . . .. . .
- 2 - 2117141
epoxy resins are mixed with curing agents, for example
with amine~, polyamides, anhydrides, boron trifluoride
complexefl or dicyandiamide. Many of these mixtures have
disadvantages which restrict their industrial
application. For example, mixtures of polyepoxides and
aliphatic amines solidify fairly rapidly, making it
necessary to avoid mixing the components until shortly
before use and to use the mixtures rapidly before the
process of curing sets in. Although the use of aromatic
amines enables the processing time to be extended, curing
then again requires relatively high temperatures and
relatively long times. In addition, yellowing phenomena
occur at the curing temperatures.
" DE 22 48 776 and DE 27 31 335 disclose the use of
imidazoline derivatives as curing agents for powder coat-
ings based on epoxy resin~i. DE 23 24 696 describes the
use of ~alts of polycarboxylic acids and imidazoline
derivatives for the same purpose. The use of adducts of
epoxide~ and imidazole compounds as curing agents for
powder coatings is also known (DE 19 10 758). EP 387 692
describes powder coatings based on polyepoxides which are
1 modified with aromatic dicarboxylic acids, which coatings
are cured using polyesters containing carboxyl groups.
Both environmental aspects and economic considerations
currently necessitate coating materials and adhesives
which are free from solvent and elimination products and
which can be processed extremely rapidly.
It has now been found in practice that, for many applica-
tions, the curing time of the powder mixtures of the
prior art is too long, because 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 for good storage
stability.
2117141
- - 3 -
Surpri~ingly it ha~ now been found that it i~ posslble by
using specific epoxide compound~ 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. This is also valid, in
! particular, in relation to the powder coatings according
to EP 387 692.
The present invention relates to curable pulverulent mix-
tures comprising
A) epoxide compounds which are a reaction product of
A1) compounds having at least two 1,2-epoxide
groups per molecule and epoxide equivalent
weights of from 160 to 600, and
A2) aromatic dicarboxylic acids or a mixture there-
of with compounds from the group comprising
(cyclo)aliphatic dicarboxylic acids, monocar-
boxylic acids and/or monohydric phenols, and
A3) if desired, cyclic anhydrides, and
.
B) a curing agent.
Polyesters containing carboxyl groups are excluded as
curing agents in this context.
The epoxide compounds A) employed in accordance with the
invention contain on average at least 2 epoxide groups
, per molecule. The epoxide equivalent weight is in general
between 300 and 1,200, preferably between 400 and 800 and
in particular between 450 and 700, while the acid number
i8 u~ually from 0.01 to 20 and preferably from 0.01 to
2 mg of XO~/g. Furthermore, the epoxides A) possess
average molecular weights M~ (number average; determined
by gel chromatography) of from 500 to lO,000, preferably
from 800 to 3,000. Depending on the starting components
A1), A2) and if desired A3), on the molar ratio thereof
21~7141
- 4 -
and on the molecular weight of A), these epoxide com-
pounds are solid products having glass transition tempsr-
atures (Tg) of at least 20C, preferably of at least 35
to 60C.
The epoxide compounds A) are prepared in a known manner
by reacting the compounds A1) with the acids or the acid
mixtures according to A2), for example by heating the
components for two or more hours while excluding oxygen
at temperatures of from 100 to 250C, preferably from 140
to 180C, advantageously in the presence of a eatalyst.
When component A3) is also used, the preparation is a~ a
rule earried out in two stages. The proeedure in this
ease is, in the first stage, initially as described
above, the aim being in general to prepare a product with
acid numbers of less than 20 mg of ROH/g, preferably less
than 2 mg of KOH/g. Subsequently, in a second stage, the
reaction product of A1) and A2) is reacted with the
eyelie anhydride A3) by heating the components for two or
more hours while exeluding oxygen at temperatures of from
100 to 200C, preferably from 120 to 160C, until an aeid
number is reaehed of less than 5 mg of KOH/g, preferably
less than 2 mg of KOH/g.
The 1,2-epoxide eompounds employed in accordance with the
invention aa eomponent A1) have on average at least two
1,2-epoxide groups per moleeule, thus representing
polyepoxide eompounds, and generally have a glass transi-
tion temperature of at least 10C. They may be either
saturated or unsaturated and may be aliphatic, cy~loali-
phatie, aromatie and heterocyclic, and may also contain
`30 hydroxyl groups. In addition, it is possible for them to
;eontain tho~e substituents whieh do not eause any disrup-
tive secondary reaetions under the mixing or reaction
conditions, for example alkyl or aryl substituents, ether
groups or the like.
Examples of sueh polyepoxide compounds A1) are those
: ,: . - :
, : . . - . : . ~ : . -
- --` 2117~41
s
ba~ed on polyhydric phenols, for example resorclnol,
hydroquinone, 4,4'-dihydroxydiphenylmethane, lsomer
mixtures of dihydroxydiphenylmethane (bisphenol F),
4,4'-dihydroxy-3,3'-dimethyldiphenylmethane, 4,4'-dl-
5 hydroxydiphenyldimethylmethane (bisphenol A), 4,4'-di-
' hydroxydiphenyldicyalohexane, 4,4'-dihydroxy-3,3'-di-
methyldiphenylpropane, 4,4'-dihydroxybiphenyl, 4,4'-di-
hydroxydiphenyl sulfone, tris(4-hydroxyphenyl)methane,
4,4'-dihydroxybenzophenone, 1,1-bis(4'-hydroxyphenyl)iso-
10 butane, 2,2-bis(4'-hydroxy-tert-butylphenyl)propane,
bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene, . -
bis(4-hydroxyphenyl) ether, and also those from the
hydrogenation, chlorination and bromination products of
the abovementioned compounds, from novolaks (i.e. from
4 15 reaction products of mono- or polyhydric phenols with
aldehydes, especially formaldehyde in the presence of
acidic catalysts).
The polyglycidyl ethers of polyhydric alcohols are al~o
suitable as Al). Examples of such polyhydric alcohols
20 which can be mentioned are trimethylolpropane and 2,2-
bis(4'-hydroxycyclohexyl)propane. ~ :
:
Solid acrylate resins which contain glycidyl groups and
are compatible with component Al) also come into con-
sideration, for example suitable polymers based on
glycidyl methacrylate.
Other compounds which are suitable as Al) are those such . .
as (poly)glycidyl e~ters of the formula
R/(-l~-ocH2-c!~H2)n - '~
in which R' is a linear or branched, saturated or un-
saturated hydrocarbon radical having up to 40, preferably
up to 10, carbon atoms or a substituted or unsubstituted
phenyl radical 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
....' ', ~ ~ ,'
2117141
- - 6 -
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 A1) are compounds such as
triglycidyl isocyanurate and/or its oligomers and trigly-
cidyl urazole and its oligomers, and corresponding
mixtures.
These polyepoxide compounds can also be employed as a
mixture with one another and, if desired, a~ a mixture
with monoepoxides, care being taken to ensure that the
mixture of the 1,2-epoxide compounds possesses a gla~s
transition temperature of at least 10C. If 1,2-epoxide
compounds having lower glass transitions temperatures are
used in the mixture then they can only be employed in a
minor proportion and only in combination with correspond-
ingly high-melting 1,2-epoxide compounds, 80 that the
glass transition temperature of component A) is at least
10C.
Examples of suitable monoepoxides are epoxidized mono-
unsaturated hydroearbons (butylene oxide, cyclohexene
oxide and styrene oxide), halogen-eontaining epoxides
sueh as epiehlorohydrin, epoxide ethers of monohydric
alcohols (methyl, ethyl, butyl, 2-ethylhexyl and dodeeyl
aleohol), epoxide ethers of monohydric phenols (phenol,
eresol and other o- or p-substituted phenols), glyeidyl
esters of unsaturated earboxylie aeids, epoxidized esters
of unsaturated aleohols or unsaturated carboxylic acid~
and the acetals of glycidaldehyde.
Other epoxide compounds with suitable melting points are
described in the handbook "Epoxidverbindungen und
Epoxidharze" lEpoxide Compounds and Epoxy Resins] by
A.M. Paquin, Springer Verlag, Berlin 1958, chapter IV, in
, . .:
. . ::: . :
, - , ~ : .
: .:: . :: :
-~ 2~17141
_ 7
Lee, Neville "Handbook of Epoxy Resins", 1967, chapter 2
and in Wagner/Sarx, "Lackkunstharze" [Synthetic Re0in~
for Coatings], Carl Hanser Verlag (1971), p. 174 ff.
Preferred epoxide compounds A1) are:
- poly(epoxyalkyl) ethers of aliphatic or cycloali-
phatic polyhydroxy compounds, such as of trimethyl-
olethane, trimethylolpropane, tris(hydroxyethyl)
isocyanurate, pentaerythrit~l;
- reaction products of epihalohydrin~ such as epi-
chlorohydrin with monomeric polyhydric phenols such
as 2,2-bis(4-hydroxyphenyl) propane,
1,1-bis(4'-hydroxyphenyl)ethane, bis(4-hydroxyph-
enyl)methane, 4,4'-dihydroxydiphenyl sulfone, hydro-
quinone, resorcinol, dihydroxybiphenyl, dihydroxyna-
phthalene, 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 formal-
dehyde;
- polyglycidyl esters of polycarboxylic acids, such as
diglycidyl esters of phthalic acid, isophthalic
acid, terephthalic acid, tetrahydrophthalic acid,
hexahydrophthalic acid, polyglycidyl esters derived
from polyesters, or else compounds containing free
carboxylic acid groups.
It is particularly preferred to use as A1) epoxy resins
based on bisphenol A and epichlorohydrin, having epoxide
equivalent weights in the range from 160-600, preferably
! 160-200.
.~
The compounds A2) represent aromatic dicarboxylic acids
or mixtures of these aromatic dicarboxylic acids with
(cyclo)aliphatic dicarboxylic acids, monocarboxylic acids
and/or monohydric phenols.
Examples of the aromatic dicarboxylic acids used are
terephthalic acid, isophthalic acid, o-phthalic acid or
2117141
-- 8
various naphthalene dicarboxylic acids, for example
2,6-naphthalene dicarboxylic acid. Particularly preferred
in this context is terephthalic acid. It is also posslble
to employ mixtures of the aromatic dicarboxylic acids.
5 Other suitable aromatic carboxylic acid~ are those of the
type
HOOC- ~ -X- ~ COOH,
in which X is a chemical bond, an alkylene radical of 1
to 6 carbon atoms, or 0, SO2 or CO.
The term "(cyclo)aliphatic" dicarboxylic acids is in-
tended to comprise corresponding aliphatic or cycloali-
phatic acid~ and mixtures thereof.
Examples of aliphatic dicarboxylic acids whose aliphatic
radical in general contains from 1 to 20 and preferably
from 2 to 12 carbon atoms are succinic acid, glutaric
acid, adipic acid, suberic acid, azelaic acid, sebacic
acid and dodecanedioic acid.
' '
Examples of suitable aliphatic carboxylic acids whose
cycloaliphatic radical generally comprises from 5 to 12
and preferably from 6 to 8 carbon atoms are the various
cyclohexanedicarboxylic acid isomers, hexahydrophthalic
acid and tetrahydrophthalic acid.
Examples of suitable monocarboxylic acids containing in
general from 3 to 20 and preferably from 3 to 12 carbon
atoms are benzoic acid, ~- or ~-naphthoic acid, 'o-, m-
and p-toluic acid, anisic acid, veratric acid, and also
branched or unbranched aliphatic monocarboxylic acids
such as acetic acid, propionic acid, butyric acid, lauric
acid, stearic acid, isooctanoic acid, i~ononanoic acid,
trialkylacetic acid such as neo acid C5 (2,2-dimethyl-
propionic acid), neo acid C10 or hydroxymonocarboxylicacids such as glycolic acid, lactic acid and dimethylol-
propionic acid.
: .: '
.. . :
.. , , . . : -: .. :
: ' ' ' ' . ' ~
21171~1
g
The monohydric phenols may be mono- or polycyclic.
Examples which may be mentioned here are phenol, o-, m-
and p-cre~ol, xylenol~, guaiacol, thymol, carvacrol, a-
or ~-naphthol, p-tert-butylphenol and the like.
If component A2) represent~ a mixture of an aromatic
dicarboxylic acid with (cyclo)aliphatic dicarboxylic
acids, monocarboxylic acids and/or aromatic alcohols,
then the guantity of these components which are present
in addition to the aromatic dicarboxylic acid is usually
from 0.1 to 20% by weight, preferably from 1 to 5% by
weight, based on the aromatic dicarboxylic acid.
Components A1) and A2) are conventionally employed in
amounts such that the ratio~of equi~alents of epoxide to
carboxyl groups i~ from 6 . 5 to 2 : 1, preferably from
3 : 2 to 2 : 1. When A3) is used in addition, in general
from 0.01-1 mol, preferably 0.1-0.4 mol, of cyclic
anhydride A3) is to be used per mole of reaction product
of A1) and A2).
~ . .
Suitable cyclic polycarboxylic anhydrides A3) are ex-
pediently those containing from 4 to 20 and preferably
from 4 to 10 carbon atoms, which may if desired also
contain substituents such as halogen, in particular
chlorine, and carboxyl groups. They may be derived from
(cyclo)aliphatic, olefinically unsaturated or aromatic
polycarboxylic acids. Examples which may be mentioned
here are succinic anhydride, alkenylsuccinic anhydrides,
such as, for example, dodecenylsuccinic anhydride,
glutaric anhydride, maleic anhydride, citraconic an-
hydride (methylmaleic anhydride), dichloromaleic an-
hydride, aconitic anhydride (l-propene-1,2,3-tricarboxy-
lic 1,2-anhydride), tricarballylic anhydride (propane-
1,2,3-tricarboxylic anhydride), itaconic anhydride
(methylenesuccinic anhydride), cyclopentanetetracar-
boxylic dianhydride, ~-tetrahydrophthalic anhydride,
4-methyl-~-tetrahydrophthalic anhydride, hexahydroph-
thalic anhydride, 4-methylhexahydrophthalic anhydride,
, : : . ,. . . : . " . ~ , :.,, - -. . , . .: ~ - : . ...
21 I 71 41
- 10 -
3,6-endomethylene-~4-tetrahydrophthalic anhydride
(= nadic anhydride), 4-methyl-3,6-endomethylene-Q~-tetra-
hydrophthalic anhydride (= methylnadic anhydride),
3,4,5,6,7,7-hexachloro-3,6-endomethylenetetrahydroph-
thalic anhydride (~ chlorendic anhydride), theDiels-Alder adduct of 2 mol of maleic anhydride and 1 mol
of 1,4-bis(cyclopentadienyl)-2-butene or Diels-Alder
adducts o~ maleic anhydride and conjugated ~atty acids
such as 2,4-hexadienoic acid (sorbic acid), 9,11-octa-
decadienoic acid (ricinenic acid), 9,11,13-octadeca-
trienoic acid (eleostearic acid), 9,11,13,14-octadeca-
tetraenoic acid, and also aromatic polycarboxylic an-
hydrides such as phthalic anhydride, trimellitic an-
hydride, pyromellitic anhydride or benzophenonetetracar-
boxylic anhydride. It is, however, also possible to use
other cyclic polycarboxylic anhydrides containing car-
boxycyclic rings, in which the carboxyl groups are on
different rings which may be fused, one example of such
compounds being 1,8-naphthalenedicarboxylic anhydride.
Particular preference is given to nuccinic anhydride,
phthalic anhydride and the cycloaliphatic dicarboxylic
anhydrides which can be obtained by Diels-Alder addition
from inexpensi~e petrochemical raw materials, for example
~-tetrahydrophthalic anhydride or hexahydrophthalic
anhydride.
Examples of catalyst~ which can be employed to target and
accelerate the reaction of the carboxyl groups of com-
ponent A2) with the epoxide groups of component A1) are
sodium hydroxide, potassium hydroxide, lithium hyd'roxide,
sodium carbonate, chromium compounds such as CrCl3, CrO3,
chromium acetylacetonate, imidazoles, quaternary ammonium
and phosphonium compounds such as benzyltrimethylammonium
chloride, tetraethylammonium chloride, tetramethylam-
monium chloride, benzyldodecyldimethylammonium chloride,
methyltriphenylphosphonium iodide, triphenyl(2,5-di-
hydroxyphenyl)phosphonium hydroxide, ethyltriphenyl-
phosphonium acetate, triphenylethylphosponium bromide and
2117141
organic phosphanes such as triphenylphosphane, tricyclo-
hexylphosphane, tributylphosphane and cyclohexyloctyl-
phosphane, and also aromatic amines such a~ N,N-dlmethyl-
aniline, N,N-diethylaniline, N,N-dimethyl-p-toluidine,
N,N-diethyl-p-toluidine, and amines such as triethyl-
amine, tributylamine, benzyldimethylamine, benzyldiethyl-
amine, triethylenediamine, N-methylmorpholine, N-methyl-
piperidine, N-alkylamines such as N-butylamine, and
alkanolamines su~h as diethanolamine, dimethylethanol-
amine, diethylethanolamine, dibutylethanolamine, methyl-
diethanolamine and di(3-phenoxy-2-hydroxypropyl)alkyl
amines such as, for example, di(3-phenoxy-2-hydroxy-
propyl)n-butyl amine. Preferred compounds in this context
are those of the formula (I)
/ 1-;OH
R-N (I)
R1- OH
15 in which -
R = hydrogen, a branched or unbranched alkyl radical
having from 1 to 18, preferably from 1 to 4, carbon
atoms, a cycloaliphatic alkyl radical having from 5
to 12, preferably from 5 to 8 carbon atoms, or is
equal to -RlOH;
R1 = a branched or unbranched alkylene radical having
from 2 to 6, preferably 2 or 3, carbon atoms which
may additionally carry substituents -OR2, in which
R~ = Rl or is a substituted or unsubstituted aromatic
ring.
Particularly preferred representatives of this formula
(I) are triisopropanolamine and/or triethanolamine.
These catalysts are generally employed in amounts of from
0.01 to 1%, preferably from 0.05 to 2%, based on the sum
of Al) and A2).
These reaction products of Al) and A2) and, if desired,
A3) can also be used as a mixture with the known epoxy
resins, for example those based on bisphenol A or
... . .. . ....
``` 21171~
- 12 -
bisphenol F.
Suitable curing agents B) are, in quite general term~,
all compounds which are known for this purpose, in
particular anhydride curing agents such as, for example:
phthalic anhydride, tetrahydrophthalic anhydride,
4-methyltetrahydrophthalic anhydride, hexahydrophthalic
anhydride, 4-methylhexahydrophthalic anhydride, methyl-
nadic anhydride (trivial name for isomers of methyl-
endomethylenetetrahydrophthalic anhydride), chlorendic
(HET) anhydride (3,4,5,6,7,7-hexachloro-3,6-endomethyl-
enetetrahydrophthalic anhydride), pyromellitic dian-
hydride, benzophenonetetracarboxylic dianhydride, trimel-
litic anhydride, curing agents in accordance with com-
ponent B) of DE 25 56 182, dodecenylsuccinic anhydride,
isooctenylsuccinic anhydride etc., dicyandiamide which is
prepared, for example, under the trade name Dyhard of
SKW Trostberg, phenolic curing agents such as the Dow
curing agents D.E.H. 80, D.E.H. 82, D.E.H. 84, carboxylic
acid salts of imidazole or imidazoline compounds, mel-
table, soluble adducts which are obtained by reacting an
epoxide compound with imidazole or imidazoline compounds
or their carboxylic acid salts (cf. DE-C-19 10 758).
Polyesters which contain carboxyl groups are excluded as
curing agents. -~
Preferred curing agents are imidazolines or imidazoles,
in particular those of the formula (I)
R R
R ¦ ¦ R
R -N N
.' ~,D
.
! R'
ln which each R, independently of the others, is hydrogen
or an alkyl, aryl, aralkyl, cycloalkyl or heterocyclic
radical, R' is the same as R or is an alkylene or arylene
30 radical which may possibly be ~ubstituted by one or more ~ ~
alkyl, aryl, aralkyl, cycloalkyl or heterocyclic radi- ~ -
cals, and where two or more radicals may be connected,
~ 2117141
- 13 -
possibly also by heteroatoms, and/or of the formula (I~)
HN N
!
R'
in which R and R' are as defined in formula (I).
Specific examples of suitable imidazolines are 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-methylimidazo~ine, 2-benzylimidazoline,
2-(o-tolyl)imidazoline, 2-(p-tolyl)imidazoline, tetra-
methylenebisimidazoline, 1,1,3-trimethyl-1,4-tetra-
methylenebisimidazoline, 1,3,3-trimethyl-1,4-tetra-
methylenebisimidazoline, 1,1,3-trimethyl-1,4-tetra-
methylenebis-4-methylimidazoline, 1,2-phenylenebisimid-
azoline, 1,3-phenylenebisimidazoline, 1,4-phenylenebis-
imidazoline and 1,4-phenylene-bis-4-methylimidazoline.It
is also possible to employ any desired mixtures of the
imidazolines.
Examples of suitable imidazoles are imidazole itsQlf,
l-methylimidazole, 2-methylimidazole, 4-methylimidazole,
5-methylimidazole, l-ethylimidazole, 2-ethylimidazole,
l-propylimidazole, 2-propylimidazole, 2-isopropyl-
! imidazole, l-butylimidazole, 2-octylimidazole, 2-undecyl-
imidazole, 2-heptadecylimidazole, 2-cyclohexylimidazole,
l-phenylimidazole, 2-phenylimidazole, 2,4-dimethyl-
imidazole, 1,2-dimethylimidazole, 4,5-dimethylimidazole,
2-ethyl-4-methylimidazole, 1-ethyl-2-methylimidazole,
l-methyl-2-isopropylimidazole, 4-butyl-5-ethylimidazole,
2-cyclohexyl-4-methylimidazole, 1-benzyl-2-methyl-
imidazole, 2-phenyl-4-methylimidazole, 4,5-diphenyl-
imidazole, 2-ethyl-4-phenylimidazole, 2,4,5-trimethyl-
imidazole, 2,4,5-tricyclohexylimidazole, 1,2,4,5-tetra-
-:
:: : , ,
.
. - - , . . .
- 2117141
- 14 -
methylimidazole, and benzimidazoles and derivatives
thereof. It is also po~sible to employ any desired
mixtures of the imidazole~.
The amount of curing agent in the pulverulent mixtures
~ 5 acaording to the invention depends on the nature of the
curing agent, and can fluctuate within wide limit~. The
quantity of curing agent i~ generally from 0.01 to 60% by
weight, preferably from 0.5 to 40% by weight, based on
the sum of the two components A) and B).
10 In addition, the mixtures according to the invention may
contain the additives which are conventional for powder
coatings, such as leveling agent~ or anticrater agents,
? dyes, pigments, fillers, matting agents, thixotropic
agents, deaerating agents, UV stabilizers, oxidation
15 inhibiters, quenchers (free-radical scavengers, for
example N-alkyl-substituted piperidines), crosslinking
catalysts, plasticizers, additional curing agents,
additional curable resins and the like. These additives
are generally employed in amounts of from 0 to 50% by
20 weight, preferably from 0.1 to 40% by weight, based on
the overall powder coating mixture. Any liquid or pasty
additives here can be used inter alia as a mixture with
highly active silicic acid, as a master batch (see
DE 22 02 907).
25 The leveling agents which can be employed are, 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
30 and aromatic carboxylic acids, and in particular com-
mercially available products based on polyacrylates. The
leveling agents can also be added to component A) in
amounts of from 0.1 - 4% by weight, preferably from
0.2 - 2.0% by weight.
35 Examples which may be mentioned of the dyes or pigments,
2117141
- 15 -
which may be inorganic or organic in nature, are titanium
dioxide and zinc oxide. The organic dyes/pigment~ should
naturally be selected 80 that they are stable at the
curing temperatures and do not lead to any lntolerable
alteration~ in shade.
Examples of suitable filler~ are ground quartz, sili-
cates, chalk, gypsum and the like.
The ~tabilizers can also be aromatic diketones such as
henzoin, which prevent highly localized decompositions
and thus reduce the formation of pores. They are general-
ly added in amounts of from 0.1 to 3% by weight,
preferably from 0.2 to 2~ by weight, based on the overall
binder mixture.
In order to prepare pulverulent mixtures according to the
invention for testing, processing and practical applica-
tion, the individual components are generally mixed with
one another. When using liquid components the solid
components are finely ground and the liquid components
are admixed to these until they are uniformly distri-
buted. In order to prepare the curable mixtures accordingto the invention the components are homogenized in the
melt after mixing. Thi~ can take place in suitable
equipment, for example heatable kneeding equipment,
double-Z mixers or extruders, preferably the latter, the
extrusion temperature being selected 80 that a maximum
shear force acts on the mixture. In thi~ context an upper
temperature limit of 130C should not be exceeded. When
using catalysts it may be advantageou~ to add these to
component A) or B). This addition can also be made, for
30 example, during the preparation of component A). ~ -
The homogenized mass i8 then allowed to cool to room
temperature and, after a suitable precomminution, is
ground to give a curable pulverulent mixture (powder
coating) the target average particle sizes depending on
the intended use and being from about 40 to 90 ~m, but
,.
: .
.
2~1714~
- 16 -
pre~erably about 50 ~m. Any oversize present, with a
particle size of more than 90 ~m, is removed by screen-
ing.
The powder coatings thus produced can be applied to
suitable substrates, for example metal, wood, glass,
concrete, plastic, ceramic etc., by known methods, for
example by electrostatic powder spraying, powder applica-
tion by the triboelectric method, fluidized-bed sinter
ing, eleatrostatic fluidized-bed sintering or by flame
~praying.
After the powder coating has been applied by one of the
methods mentioned, the coated workpieces are heated, to
achieve full cure, to a tem~perature of from 90 to 270C,
preferably $rom 120 to 220C, for a time which i8 suffi-
cient to achieve full curing, in general from 0.5 to60 minutes. The resulting coating~ are distinguished by
good properties in terms of paint technology, such as
good mechanical properties, good chemical resistance,
good weathering resietance, good adhesion etc. Conse-
quently the powder coatings according to the inventionare suitable, in particular, for coating materials such
as metal, glass and ceramic.
In addition to this the mixtures according to the inven-
! tion can also be employed as adhesives. The production of
adhesive formulations is carried out in principle 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, together with the curin'g agent
C, intimately mixed with one another, care being taken to
ensure uniform distribution of the components.
The resulting formulations may if desired be admixed withthe conventional additives described above such as
fillers, pigments, dyes and the like. The mixtures
according to the invention can be used for adhesively
bonding a great variety of materials, for example metals,
.:~ . .' ~'
2~17141
- 17 -
light metals, but also nonmetallic materials such as
ceramic, glass, leather, rubber, wood, plastlc et¢., wlth
themselves or with other materials. They can al~o be
employed in the preparation of sandwich constructions of
metals and other materials.
Because of their high reactivity the mixtures according
to the invention are particularly suitable as adhesives
and coating compositions. A point worthy of particular
emphasis is the possibility of constructing ~andwich
systems from wood (chipboard, plywood etc.) and fabrics,
for example polyester fibers (Trevira). In the course of
the adhesion process the fabric is embedded completely in
the binder system, forms a homogenous 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 produce panels which, while of the same
quality, axe of lower weight in comparison to standard
materials.
When the mixtures according to the invention are used for
adhesive bonds they can be applied by electrostatic
means, for example with an electrostatic powder spray
gun. In this way it i8 po~sible to apply uniformly thin
coats (for example on films). Becau~e 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 context is that yellow-
ing, combustion and gas escape can be avoided. The
pulverulent mixture on the coated materials generally
cures fully at temperatures of from 120 to 220C, prefer-
ably from 130 to 210C, in a sufficient time of from 2 to
60 minutes.
, .::. :
21171~1
- 18 -
~poxy resin I (comparison)
Commercially available bisphenol A epoxy resin for the
preparation of powder coating~, having the ~ollowing
chara~teristics:
!
5 epoxide equivalent about 800
viscosity 25C about 500 mPa.s
40% strength in butyldiglycol
in accordance with DIN 53 015
melting point about 70C
10 capillary method in accordance
with DIN 53 015
glass transition temperature about 50C
J
~poxy resin II (according to the invention)
Preparation
1,552 g of a liguid bisphenol A epoxy resin having an
epoxide equivalent of 183 (8.48 eq) and 352 g of tereph-
thalic acid (4.24 eq) were heated to 170C in a four-
necked flask under a nitrogen atmosphere with stirring,
2 g of triethanolamine were added, and the mixture was
maintained at 170C. After 4 hours the acid number was
0.6 mg of KOH/g and the epoxide equivalent was 459. The
reaction product was then cooled at 140C and 97 g of
tetrahydrophthalic anhydride (0.64 mol) were added. The
temperature wa~ maintained at 140C. After 1.5 hours the
acid number wa~ 1.4 mg of KOH/g. The reaction was ended
after a further hour by emptying the flask.
Characteristic data: '
epoxide equivalent 582
acid nu~ber (toluene/ethanol) 0.5 mg KOH/g
30 vi~cosity 25C (40% in butyldiglycol) 541 mPa.s
glass transition temperature 43.4C
~po~y re~in III (according to the invention)
Preparation
1,549 g of a liguid bisphenol A epoxy resin having an
~: . ' ~'
2117141
- 19 -
epoxide equivalent of 183 (8.46 eq) and 448 g of
terephthalic acid (5.39 eq) were heated at 170C in a
four-necked 1ask with stlrring and under a hydrogen
atmosphere, 2 g of triethanolamine were added and tho
mlxture was maintained at 170C. After 7 hours the acld
number was 0.6 mg of KOH/g. The reaction was ended after
a further hour by emptying the flask.
Characteristic data:
epoxide equivalent 688
10 acid n~ber (toluene/ethanol) 0.3 mg KOH/g
viscosity 25C (40% in butyldiglycol) 443 mPa.
Glass transition temperature 49.9C
- Xxa~ple 1
Gel ti~e determination
The gel time was determined 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 according to the prior art are compiled in Tables
!' 20 1 and 2.
The pulverulent mixtures according to the invention
exhibit surprisingly short gel time~ in comparison with
the mixtures containing a prior art epoxy resin. This i8
a measure of the high reactivity of the mixtures accord-
ing to the invention which are used, and demonstrates thegreat effect of epoxy resin component A on the rate of
j reaction of the overall system.
,j
2~17141
- 20 -
Table 1
Gel time determinations at 180C
, ... _
Epoxy Curing agent Parta by Seconds
resin wt. of
curing
agent per
100 part~
, by wt. of
epoxy re~ in
: . ,
I 2-Heptadecylimidazole 0.5 ~ 600
II 2-Heptadecylimidazole l 69
I 2-Heptadecylimidazole 1 ~ 600 - -
II 2-Heptadecylimidazole 47 ~ ;
III 2-Heptadecylimidazole 70
': . ~
I 2-Heptadecylimidazoline 2.5 725
II 2-Heptadecylimidazoline 64
I 2-Undecylimidazole 2.5 ~ 600
II 2-Undecylimidazole 45
-
I 2-Ethyl-4-methylimidazoline 1 219
II 2-Ethyl-4-methylimidazoline 35
.,
I 2-Methylimidazoline 0.5 ~ 600
II 2-Methylimidazoline 93
___ _
I 2-Me~hylimidazoline 1 '282
II 2-Methylimidazoline 25 -~
_ -~
I 2-Phenylimidazole 2.5 85
II 2-Phenylimidazole 46 ~
.. _ . ::~,
I 2-Phenylimidazoline 2.5 337
II 2-Phenylimidazoline 42
III 2-Phenylimidazoline 57
2117141
- 21 -
Table 1 continued
Epoxy Curing agent Parts by Soconds
resin wt. of
. 5 curing
agent per
100 parts
by wt. of
. , epoxy resin
', 10 .
I Curing agent B 31 (Hul~) 1 ~ 600
II Curing agent B 31 (Huls) 162
..
I Curing agent B 31 (Huls) 2.5 324
II Curing agent B 31 (Huls) 37
III Curing agent B 31 (Huls) 68
.
I Curing agent B 68 (Huls) 2.5 ~ 600
II Curing agent B 68 (Huls) 149
III Curing agent B 68 (Huls) 196
_
I Curing agent B 55 (Huls) 2.5 ~ 600
II Curing agent B 55 (Hul~) 147
III Curing agent B 55 (Huls) 195
I Curing agent EH 694 (Hoechst) 15 234
II Curing agent EH 694 (Hoechst)67
III Curing ag-nt EH 694 (Hoechst~65
' 30 I Trimellitic anhydride 6 587
., II Trimellitic anhydride ' 115
;t III Trimellitic anhydride 180
. ~.
2117141
- 22 -
Table 1 continued
Epoxy Curing agent Parts by Seco=dE
resin curing ;~
. 100 parts
by wt. of
epoxy res Ln
I Pyromellitic anhydride 5 314 . -
II Pyromellitic anhydride 83
III Pyromellitic anhydride 125
' .".
15 I Dicyandiamide 2.7 684 - :::
II Dicyandiamide 246 : .
III Dicyandiamide ~ 370
." '.
I Dyhard~lO0 (SKW Trostberg) 2.7 623
II Dyhard~100 (SKW Trostberg) 157
III Dyhard~100 (SKW Trostberg) 251
Curing agent B31: cyclic amidine
Curing agent B55: salt of a polycarboxylic
acid and a
Curing agent B68: cyclic amidine
Dyhard 100: dicyandiamide
,~:
~a~ 2
f
92 parts by weight of epoxy resin II and 8 parts by
weight of the curing agent B 31 (cyclic amidine from
Huls AG) were mixed in a MTI mixture to a particle size
of c 5 mm and extruded at 80 with a reElidence time of
from 10 - 15 seconde, and the liquid melt of the binder-
curing agent mixture, directly after dispersion in the
;35 extruder, was passed together with the Trevira fabric
;through a calender, in the course of which the liquid
'.'. ~
: ~ '
~' - 23 - 2117141
melt was di~tributed uniformly on the fabric.
The coated fabric was stored at ambient temperature prior
to its further processing or adhesive bondlng.
The fabrics treated with the powder mixture were punched
out, cut and then adhesively bonded with chipboard 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 this procedure the Trevira fabric is
completely embedded in the binder system, forms a homo-
genous surface and adheres to the substrate in an optimum
manner.
~xample 3
92 parts by weight of epoxy resin II and 8 parts by
weight of the curing agent B 31 (cyclic amidine from
Huls AG) were mixed in an MTI mixer to a particle size of
c 5 mm, and extruded at 80C with a residence time of
from 10 - 15 seconds. The extrudate emerging at 100C was
cooled, broken, ground and screened to a particle size c
20 125 ~m.
The powder mixture obtained in this way was applied using
an electrostatic powder spray gun to Trevira fabric, and
the coated material was processed further either by
a) immediately pressing and adhesively bonding the
Trevira fabric provided with the powder mixture onto
chipboards to be laminated, or
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 fabrics treated in this way
was carried out under pressure (40 bar) over 40 seconds
, ~ . ., : -: .
- 24 - 2 1 171 gl
at 200C, to chipboard. Under the choeen procee~ condi-
tion~ the powder mixture melts, wets the substrate (chlp-
board and fabric) very thoroughly and then curee fully.
- .,';
