Aluminum phosphorus acid salts as epoxy resin cure inhibitors
View Patent ↗Certain aluminum salts of organic phosphorus acids are found to have a strong effect on inhibiting the epoxy cure rate in epoxy formulations. The substances act catalytically and can be used at a low level in an epoxy formulation to adjust the reactivity of a resin formulation to give longer gel times. Compositions and methods of preparing and using the compositions are disclosed.
1. A composition comprising
a) an epoxy resin,
b) a cross linker comprising a phenolic cross linker and wherein the composition comprises from about 50 to about 150% of the stoichiometric amount of hydroxy groups needed to cure the epoxy resin,
c) from 0.1 to 2 parts per hundred parts of epoxy resin of an aluminum phosphonate, phosphinate or phosphate salt cure inhibitor selected from compounds having the formula I:
wherein X and Y are independently selected from C 1-10 alkoxy, C 1-10 alkyl, C 6-10 aryl, C 6-10 aryl substituted by one or more C 1-10 alkyl, C 6-10 aryloxy and C 6-10 aryloxy substituted by one or more C 1-10 alkyl, and
d) a phosphorus containing flame retardant comprising from about 10 to 50 wt % of one or more compounds of formula (i)
from about 30 to 60 wt % of one or more compounds of formula (ii)
from about 10 to 50 wt % of one or more compounds of formula (iii)
and
from 0 to about 10 wt % tri-phenyl phosphine oxide based on the combined weight of compounds of formula (i), (ii), (iii) and tri-phenyl phosphine oxide,
wherein each R is independently hydrogen or an alkyl group containing from 1 to 6 carbon atoms, R 1 and R 2 are the same or different and each is an alkyl group containing from 1 to 6 carbon atoms, each of x and y is an integer from 0 through 4.
2. The composition according to claim 1 wherein each OR in the compounds of formulae (i), (ii) and (iii) are independently in the ortho- or para- position with respect to the bond between the P atom and the associated phenyl group.
3. The composition according to claim 2 wherein x and y are 0, R is hydrogen, and the ratio of the number of OR groups in the ortho-position with respect to the bond between the P atom and the associated phenyl group to the number of OR groups in the para-position with respect to the bond between the P atom and the associated phenyl group in the mixture is from about 20:80 to about 1:99.
4. The composition according to claim 3 wherein the ratio of the number of OR groups in the ortho-position with respect to the bond between the P atom and the associated phenyl group to the number of OR groups in the para-position with respect to the bond between the P atom and the associated phenyl group in the mixture is from about 10:90 to about 2:98.
5. The composition of claim 1 wherein the cure inhibitor c) is a aluminum phosphinate salt of formula I wherein X and Y are independently selected from C 1-10 alkyl, C 6-10 aryl and C 6-10 aryl substituted by one or more C 1-10 alkyl.
6. The composition of claim 1 wherein the epoxy resin a) comprises an epoxy novolac resin.
7. The composition of claim 1 wherein the cross linker b) comprises a novolac cross linker.
8. A process of slowing the cure rate of a curable epoxy composition by adding to an epoxy composition comprising an epoxy resin, a cross linker and a phosphorus containing flame retardant comprising from about 10 to 50 wt % of one or more compounds of formula (i)
from about 30 to 60 wt % of one or more compounds of formula (ii)
from about 10 to 50 wt % of one or more compounds of formula (iii)
and
from 0 to about 10 wt % tri-phenyl phosphine oxide based on the combined weight of compounds of formula (i), (ii), (iii) and tri-phenyl phosphine oxide,
wherein each R is independently hydrogen or an alkyl group containing from 1 to 6 carbon atoms R 1 and R 2 are the same or different and each is an alkyl group containing from 1 to 6 carbon atoms, each of x and y is an integer from 0 through 4,
from 0.1 to 2 parts per hundred parts of epoxy resin of an aluminum phosphonate, phosphinate or phosphate salt cure inhibitor selected from compounds having the structure I:
wherein X and Y are independently selected from C 1-10 alkoxy, C 1-10 alkyl, C 6-10 aryl, C 6-10 aryl substituted by one or more C 1-10 alkyl, C 6-10 aryloxy and C 6-10 aryloxy substituted by one or more C 1-10 alkyl.
9. A prepreg pepared by applying to, or impregnating into a substrate the composition according to claim 1 to obtain an epoxy coated substrate, heating the epoxy coated substrate at a temperature sufficient to draw off solvent from the epoxy formulation and optionally to partially cure the epoxy formulation to form the prepreg.
10. A laminate prepared by by stacking or layering sheets of prepreg according to claim 9 in alternating layers with one or more sheets of a conductive material, followed by processing to provide fully processed laminates.
11. The composition according to claim 1 further comprising e) an amine containing accelerant.
12. The process according to claim 9 wherein the curable epoxy composition further comprises an amine containing accelerant.