Heat curable epoxy compositions

Details Heat curable epoxy compositions Heat curable epoxy compositions

2001-03-05

2003-05-13

Dawson, Robert (Department: 1712)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S487000, C428S413000, C525S507000, C528S088000, C528S089000, C528S092000, C528S094000, C528S119000

Reexamination Certificate

active

06562410

ABSTRACT:

The present invention refers to heat curable cationically polymerisable resin-systems comprising an improved initiator composition.
Initiator systems used for cationic polymerisation are known and often are based on latent curing agents in order to ensure sufficient storage stability. An important drawback of such initiator systems is that they often require relatively high curing temperatures in the curing process and an extended curing cycle to effect sufficient storage life. Therefore a need exists for initiating systems which provide a long shelf-life when added to the resin composition coupled with a high reactivity at relatively low curing temperatures.
The present invention refers to cationically polymerisable resin-systems comprising an improved redox initiator system. The compositions according to the present invention have a good latency and are sufficiently stable at room temperature. They further have a high reactivity at curing temperatures, a short curing time and offer a property profile suitable for e.g. casting, molding, adhesive and impregnation applications.
The cationic redox initiator system of the present invention is based on the combination of an aromatic N-heterocyclic ammonium salt with selected 1,1,2,2-substituted-1,2-ethane-diols and derivatives thereof, wherein the substituents in the 1- and 2-positions are selected aryl residues or aromatic heterocyclic ring systems as herein below defined as compounds of formula (I). The basic principle of using a combination of an aromatic N-heterocyclic ammonium salt and 1,1,2,2-tetraphenyl-1,2-ethane-diol(benzopinacol) is disclosed in EP-A-0 066 543. At elevated temperature benzopinacol forms free radicals. These radicals reduce the aromatic N-heterocyclic ammonium salt, for example N-methyl-quinolinium-hexafluorophosphate to yield free H
+
(PF
6
)
−
, which initiates the cationic polymerisation.
According to the present invention, selected compounds of formula (I) as defined below are combined with known aromatic N-heterocyclic ammonium salts to form new cationic redox initiator systems. Due to the lower cleavage temperatures of the benzopinacols used in these new combinations access is given to a wider range of cure conditions, especially to lowered cure temperatures and/or increased cure speeds for the cationic polymerisation of epoxides.
The present invention is defined in the claims. It refers to heat curable compositions capable of being cured by cationic polymerisation comprising:
(A) at least one compound which is capable of undergoing cationic polymerisation;
(B) at least one quaternary ammonium salt of an aromatic-N-heterocyclic cation which contains one or two N-atoms, and of a non-nucleophilic anion;
(C) at least one 1,1,2,2-substituted-1,2-ethane-diol and/or a derivative thereof, wherein the substituents in the 1- and 2-positions are selected aryl residues or aromatic-heterocyclic ring systems; and
(D) optionally further additives;
 which is characterised in that:
said component (B) is selected from the group of anions comprising BF
4
−
, PF
6
−
, SbF
6
−
, SbF
5
(OH)
−
, [B(X)
p
(Y)
q
]
−
, or CF
3
(CF
2
)
m
SO
3
−
, wherein
p and q are zero or an integer from 1 to 4, and wherein the sum of p and q is always 4;
each X (for p≧1) independently of the other is halogen, preferably fluorine or chlorine, or hydroxyl, wherein for halogen p is zero, 1, 2 or 3; and for hydroxyl p is zero, 1 or 2;
each Y (for q≧1) independently of the other is phenyl, optionally substituted with at least two halogen atoms, preferably fluorine or with one or two electron attracting groups, preferably —CF
3
, —OCF
3
, —NO
2
, —CN, or Y is an aryl residue with at least two aromatic rings, preferably naphthyl or biphenyl, optionally substituted with one or two halogen atoms, preferably fluorine, or with one or two electron attracting groups, preferably —CF
3
, —OCF
3
, —NO
2
or —CN; and m is zero or an integer from 1 to 17; and
said component (C) is a compound of formula (I):
 wherein
each of R
1
, R
2
and R
3
independently of the other is unsubstituted phenyl or has one of the meanings of R
4
;
R
4
is phenyl substituted by linear or branched (C
1
-C
12
)alkyl, (C
1
-C
8
)alkoxy-(C
1
-C
8
)alkyl, (C
1
-C
12
)alkyloxy, (C
1
-C
12
)alkylthio, (C
1
-C
12
)alkylcarbonyl, halogen, nitro, cyano, halo(C
1
-C
8
)alkyl, aryl, aryl-(C
1
-C
8
)alkyl; aryloxy, arylthio, benzoyloxy, benzoylmethyl and/or naphthoyloxy, or R
4
is &agr;-naphthyl or &bgr;-naphthyl, 1-, 2- or 3-pyridyl, N-substituted(1-, 2- or 3-)pyridyl, &agr;-quinolinyl, &bgr;-quinolinyl, N-substituted (&agr;- or &bgr;-)quinolinyl, and wherein said aryl and heterocyclic rings may be further substituted by linear or branched (C
1
-C
12
)alkyl or halogen; or
each of R
1
and R
2
and/or R
3
and R
4
independently of the other form a residue of formula (II):
 wherein
each of R
5
and R
6
independently of the other is hydrogen or (C
1
-C
4
)alkyl;
R
7
is —(CH
2
)
n
— or —S— or —O—;
n is 0, 1, 2 or 3; and
wherein the weight-ratio of component B) to component C) is from 0.05:1.0 to 1.0:0.05.
The invention also refers to a process for the thermal polymerisation of heat curable compositions capable of being cured by cationic polymerisation characterised in that said compositions are heated in the presence of an initiator combination of the components (B) and (C) as defined herein above.
The present invention further refers to novel compounds of formula (I), wherein each R
1
and R
3
independently of the other is phenyl or one of the meanings given for R
2
and each R
2
and R
4
independently of the other is 2-n-butylphenyl, 2-fluorophenyl or 2,6-difluorophenyl.
The invention further refers to novel N-benzyl-quinolinium salts having a N-benzyl-quinolinium cation and associated therewith a anion of the formula CF
3
(CF
2
)
3
SO
3
−
or the Anion A
4
and wherein each of R
8
independently of the other is linear or branched (C
1
-C
12
)alkyl, (C
1
-C
8
)alkoxy-(C
1
-C
8
)alkyl, (C
1
-C
12
)alkyloxy, (C
1
-C
12
)alkylcarbonyl, halogen or hydroxyl.
Compounds which are capable of undergoing cationic polymerisation are oxygen or sulphur containing saturated heterocyclic compounds, in particular those having 3, 4 or 5 ring members, and their derivatives. Examples of such compounds are compounds containing at least one epoxy group, such as ethylene oxide, propylene oxide, styrene oxide, phenyl glycidyl ether or butyl glycidyl ether; oxetanes, such as trimethylene oxide, 3,3-dimethyloxetane or 3,3-di(chloromethyl)oxetane; oxolanes such as tetrahydrofuran or 2,3-dimethyltetrahydrofuran; cyclic acetals such as trioxan, 1,3-dioxolane or 1,3,6-trioxacyclooctane; cyclic lactones such as &bgr;-propiolactone, &egr;-caprolactone and the alkyl derivatives thereof; thiiranes such as ethylene sulfide, 1,2-propylene sulfide or thioepichlorohydrin; and thietanes such as 1,3-propylene sulfide or 3,3-dimethylthietane.
Further polymerisable compounds of this invention are those ethylenically unsaturated compounds which are polymerisable by a cationic mechanism. Such compounds include mono- and diolefins, for example isobutylene, 1-octene, butadiene and isoprene; styrene, allylbenzene or vinylcyclohexane; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether or ethylene glycol divinyl ether; vinyl esters such as vinyl acetate or vinyl stearate; and dihydropyran derivatives, for example the 3,4-dihydro-2H-pyran-2-carboxylic acid esters of 2-hydroxymethyl-3,4-dihydro-2H-pyran.
Further polymerisable compounds of this invention are also the prepolymers of phenol-formaldehyde resins, acrylic resins, alkyd resins or polyester resins containing functional groups.
Still further polymerisable compounds of this invention are mixtures of cationically polymerisable compounds and compounds polymerisable by free radicals, for example mixtures of epoxy resins with monomeric or oligomeric acrylic or methacrylic acid esters. In this case, the polymerisation takes place by a cationic mechanism and a free radical mechanism.
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