GB2263479A

GB2263479A - Epoxy resins

Info

Publication number: GB2263479A
Application number: GB9201388A
Authority: GB
Inventors: Stephen Mortimer; Anthony John Ryan; John Lawrence Stanford
Original assignee: Kobe Steel Europe Ltd
Current assignee: Kobe Steel Europe Ltd
Priority date: 1992-01-22
Filing date: 1992-01-22
Publication date: 1993-07-28
Anticipated expiration: 2012-01-22
Also published as: JPH05222161A; GB2263479B; GB9201388D0

Abstract

The invention provides a complex of a Lewis acid and an epoxy functionalised compound containing a secondary or tertiary amino group or a thioether group. This complex is useful as a latent catalyst in epoxy resin formulations.

Description

EPOXY RESINS This invention relates to epoxy resins, and more particularly to latent catalysts for epoxy resins and their use.

Epoxy resin formulations containing latent catalysts are known. A latent catalyst is one which is inactive at ambient temperature, but which becomes active upon heating. Latent catalysts are therefore useful in epoxy resin systems where the curing stage involves heating, such as resin transfer moulding, pultrusion, filament winding, compression moulding and other routes to pre-pregs. Examples of latent catalysts which are known for this purpose are complexes of boron trifluoride with nitrogen-containing compounds.

A problem with conventional pre-pregs is that the resin can migrate during storage, and thus become unevenly distributed throughout the structural fibres.

Another problem is that of resin advancement (curing) during storage which, to minimise, requires storage in the cold and dark. Further problems arise with conventional resin transfer moulding systems. The latent catalyst has to be blended with the epoxy system, and uneven distribution gives rise to inferior products on curing. Furthermore, the nitrogen-containing compound in the latent catalyst is usually an amine, and residual amine can migrate to the surface and cause discolouration.

The present invention overcomes the above problems by combining nitrogen or sulfur atoms, which complex with the Lewis acid, with epoxy groups in the same component.

The present invention thus provides a complex of a Lewis acid and an epoxy functionalised compound containing a secondary or tertiary amine group or a thioether group.

The invention also provides an epoxy resin formulation which comprises a complex as defined above as a latent epoxy resin catalyst.

Furthermore, the invention provides use of a complex as defined above as a latent catalyst for epoxy resins.

Liquid epoxy resin formulations suitable for preparation of composites by resin transfer moulding, pultrusion, filament winding, compression moulding and other routes to pre-pregs have thus been developed. The materials of the invention are stable at room temperature but react at elevated temperatures to form glassy crosslinked polymers. The most basic formulation will consist simply of the complex of the Lewis acid with the epoxy functionalised compound.

However, the basic formulation may also contain a low viscosity polyepoxy monomer. Additional low-viscosity comonomers and/or reactive prepolymers may be included to modify the viscosity and reactivity to give controllable gel times.

The invention thus has the following features: The formation of Lewis acid-organic base complexes functionalised with epoxy groups; The dissolution of such complexes in diluents such as low viscosity comonomers and/or inert solvents to give reactive epoxy resin formulations; The heat-activated curing of the Lewis acid-organic base epoxy monomer formulations to form polymers, either without fillers or containing e.g.

particulate fillers; The curing of formulations of monomers in the presence of fiber reinforcements in a hot mould (for example resin transfer and compression moulding); and The formulation of stable, gelled pre-pregs suitable for compression moulding applications.

The formation of pre-pregs involves two processing stages. The fiber reinforcements are first impregnated with liquid resin (optionally with an inert solvent) and then pre-reacted to form a partly cured product (Bstage). At this stage, the pre-preg is storable and can be moulded for suitable applications. Final curing of the pre-preg takes place under heat and pressure (final stage). Careful selection of the epoxy monomer containing an organic base, the diluent and the polyepoxy monomers allows control of (i) the initial viscosity, (ii) the time for gel formation at low temperatures, and (iii) the time taken for complete cure at elevated temperatures (e.g. greater than 1000C). For pre-preg applications, such control is highly desirable in terms of B-stage and final-stage processing.

The properties of the epoxy resin polymer and its composite materials are determined by the compositions of the formulations, the nature and amounts of fillers and reinforcements used, and the thermal history.

The epoxy resins of the invention are particularly useful in the preparation of composite mouldings, either by filling hot mould cavities containing pre-placed, long-fiber reinforcements (resin transfer moulding) or by impregnating fibers with material with a low geltemperature to form a stable pre-preg, and providing shaping during a higher temperature curing step.

The particular components and reaction conditions used in the present invention will now by described in more detail.

Complex of Lewis Acid and Epoxy Functionalised Compound In principle, any Lewis acid can be used, but it is preferred to use readily available ones. Examples include boron trifluoride, boron trichloride, boron tribromide, aluminium trichloride and antimony pentafluoride. Boron trifluoride is most preferred.

The complex is readily formed from the Lewis acid and the epoxy functionalised compound. For example, commercially available boron trifluoride etherate is reacted with the epoxy functionalised compound, and the ether is distilled off under vacuum. If the other Lewis acids are to be used they will generally be reacted directly. BBr3 BC13 SbCl5 are supplied as pure liquids.

AlCl3 is supplied as a solid and must generally first be dissolved.

The epoxy functionalised compound may have 1 to 4 epoxy groups. Each of the epoxy groups may be linked to an amine nitrogen atom or thioether sulfur atom as in formulae (I) or (II):

The epoxy groups may be linked to a tertiary nitrogen atom as in formula (III):

The complex may also contain at least one epoxy group bonded through an ether linkage as in formula (IV):

The epoxy functionalised compound is preferably of the general formula (V)::

A is an aromatic, aliphatic or mixed aromatic-aliphatic, carbocyclic or heterocyclic group, comprising at least one ring, and in the case where there is more than one such ring, the rings are fused, linked by a single bond or linked by an intermediate group; L and L' each independently represent a single bond or a C1-C4 alkylene group; p is an integer of from 1 to 4; and q is 0 or an integer of from 1 to 4.

In formula (V), A is preferably a benzene ring (optionally substituted by C1-C4 alkyl, halo C1-C4 alkyl or halogen), a cyclohexane ring (optionally substituted by C1-C4 alkyl, halo C1-C4 alkyl or halogen) or is of the formula (VI):

in which R represents a single bond or a linking group, preferably C1-C4 alkylene; and preferably p is 1 or 2 and q is 0 or 1.

The epoxy functionalised compound may also have the general formula (VII):

EPoxy Resin Formulation The epoxy resin formulation comprises a complex as defined above as a latent epoxy resin catalyst. The complex may be the only epoxy component in the formulation, or the formulation may contain the complex and at least one other epoxy component. The other epoxy component may be an epoxide pre-polymer having at least one epoxide group, preferably a glycidyl mono- or polyether of a monohydric or polyhydric phenolic compound, most preferably a diglycidyl ether of Bisphenol A.

The formulation may also contain phenyl glycidyl ether or butyl glycidyl ether as a reactive diluent, and/or a cyclic aliphatic compound having at least one0- group in the ring. The cyclic aliphatic compound may comprise a 5-, 6- or 7-membered ring having 1 or 2 -0groups and optionally a -CO- group next to an -0- group.

The cyclic aliphatic compound is preferably butyrolactone, caprolactone, tetrahydrofuran or dioxane.

The formulation may also contain a functionalised rubber or a functionalised thermoplastic, where the functionalities are thiol, hydroxy, carboxy, epoxy or anhydride, for example, selected from acrylic rubber particles, functionalised polybutadiene, butadieneacrylonitrile copolymer, polyolefin, polyethersulfone, polyetherimide, p olydim ethy ls i loxane, polyetheretherketone or functionalised polycarbonate.

The formulation may also contain a filler, for example, a particulate filler. However, the filler preferably comprises structural fibres.

In a further aspect, the invention provides a prepreg comprising structural fibres impregnated with a stable, gelled but not fully cured composition prepared from a formulation as defined above.

Advantaaes of the Invention The invention in principle provides a one component system, and thereby avoids prior art problems with blending. Furthermore, in the present invention there is no residual amine which might migrate to the surface of a moulding and cause discolouration. When the compositions of the present invention are used in pre pregs, the fibers become coated with an elastic solid, which is preferable to the liquid resin compositions used in the prior art, as the resin is less likely to migrate in the pre-pregs.

The invention is illustrated by the following Examples: Example 1 The latent catalyst complex was formed by mixing 0.2 ml (0.23 g) of boron trifluoride etherate with 34 g of compound 1 in acetone (-200 ml) solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a stable, liquid catalyst-epoxy mixture. The mixture was poured into a glass mould where an exothermic reaction resulted in a solid product in 10 minutes at 180 CC. The highly crosslinked polymer thus formed had a glass-to-rubber transition at 110 CC, a glassy modulus of -3 GPa, and a rubbery modulus of -100 MPa.

Compound 1 Example 2 The latent catalyst complex was formed by mixing 0.2 ml (0.23 g) of boron trifluoride etherate with 34 g of compound 2 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a stable, liquid catalyst-epoxy mixture. The mixture was poured into a glass mould where an exothermic reaction resulted in a solid product in 10 minutes at 180 OC. The highly-crosslinked polymer thus formed had a glass-to-rubber transition at 85 "C, a glassy modulus of -3 GPa, and a rubbery modulus of -100 MPa.

Compound 2 Example 3 The latent catalyst complex was formed by mixing 0.2 ml (0.23 g) of boron trifluoride etherate with 34 g of compound 3 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a stable, liquid catalyst-epoxy mixture. The mixture was poured into a glass mould where an exothermic reaction resulted in a solid product in 10 minutes at 180 OC. The highly-crosslinked polymer thus formed had a glass-to-rubber transition at 110 "C, a glassy modulus of -3 GPa, and a rubbery modulus of -100 MPa.

Compound 3 Example 4 The latent catalyst complex was formed by mixing 0.2 ml (0.23 g) of boron trifluoride etherate with 34 g of compound 4 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a liquid, catalyst-epoxy mixture. The mixture was poured into a glass mould containing a preplaced glass fibre mat. Partial reaction (B -stage) gave a rubbery pre-preg product, which remained storage-stable for several months at room temperature. Curing of the pre-preg at 80 OC for 1 hour gave a highly-crosslinked, rigid composite material which was then post-cured at 200 "C for 1 hour.The composite material thus formed contained - 15 % by weight of glass, and showed no evidence of a glass-to-rubber transition below 250 OC and up to this temperature, the composite material had a glassy modulus of -6 GPa.

Compound 4 Example 5 The latent catalyst complex was formed by mixing 0.8 ml (0.92 g) of boron triflouride etherate with 17 g of compound 4 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a liquid, catalyst-epoxy mixture. One part of the latent catalyst was mixed with nine parts of DGEBA (DER 332) and initially cured at 80 OC for 1.5 hour to give a rubbery solid. Final curing at 200 OC for one hour gave a lightly-crosslinked polymer with a glass-to-rubber transition of - 10 OC. a glassy modulus of-3 GPa, and a rubbery modulus of -10 MPa.

Example 6 The latent catalyst complex was formed by mixing 0.8 ml (0.92 g) of boron triflouride etherate with 17 g of compound 4 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a liquid, catalyst-epoxy mixture. One part of the latent catalyst was mixed with four parts of DGEBA (DER 332) and initially cured at 80 OC for half an hour to give a rubbery solid. Final curing at 200 OC for one hour gave a highly-crosslinked polymer with a glass-to-rubber transition of z 70 OC, a glassy modulus of -3 GPa, and a rubbery modulus of -100 MPa.

Example 7 The latent catalyst complex was formed by mixing 0.8 ml (0.92 g) of boron triflouride etherate with 17 g of compound 4 in acetone solution in a florentine flask. The diethyl ether and acetone were distilled off using a rotary film evaporator at 50 OC and 10 mm Hg to give a liquid, catalyst-epoxy mixture. Three parts of the latent catalyst were mixed with seven parts of DGEBA (DER 332) and initially cured at 80 OC for ten-minutes to give a rubbery solid.

Final curing at 200 OC for one hour gave a highly-crosslinked polymer with a glass-to-rubber transition of = 100 OC, a glassy modulus of -3 GPa, and a rubbery modulus of -150 MPa.

Claims

CLAIMS:

1. A complex of a Lewis acid and an epoxy functionalised compound containing a secondary or tertiary amine group or a thioether group.

2. A complex according to claim 1, in which the Lewis acid is boron trifluoride, boron trichloride, boron tribromide, aluminium trichloride or antimony pentafluoride.

3. A complex according to claim 1 or 2, in which the Lewis acid is boron trifluoride.

4. A complex according to any of claims 1 to 3, in which the epoxy functionalised compound has 1 to 4 epoxy groups.

5. A complex according to any of claims 1 to 4, in which each of the epoxy groups is linked to an amine nitrogen atom or thioether sulfur atom as in formulae (I) or (it):

6. A complex according to any of claims 1 to 4, in which the epoxy groups are linked to a tertiary nitrogen atom as in formula (III):

7. A complex according to claim 5 or 6, also containing at least one epoxy group bonded through an ether linkage as in formula (IV):

8.A complex according to any of claims 1 to 7, in which the epoxy functionalised compound is of the general formula (V):

9. A complex according to claim 8, in which A is a benzene ring (optionally substituted by C1-C4 alkyl, halo C1-C4 alkyl or halogen), a cyclohexane ring (optionally substituted by C1-C4 alkyl, halo C1-C4 alkyl or halogen) or is of the formula (VI):

in which R represents a single bond or a linking group, preferably C1-C4 alkylene.

10. A complex according to claim 8 or 9, in which p is 1 or 2 and q is 0 or 1.

11. A complex according to any of claims 1 to 7, in which the epoxy functionalised compound has the general formula (VII):

12. An epoxy resin formulation which comprises a complex according to any of claims 1 to 11 as a latent epoxy resin catalyst.

13. A formulation according to claim 12, in which the complex is the only epoxy component in the formulation.

14. A formulation according to claim 13, containing the complex and at least one other epoxy component.

15. A formulation according to claim 14, in which the other epoxy component is an epoxide pre-polymer having at least one epoxide group.

16. A formulation according to claim 15, in which the epoxide pre-polymer is a glycidyl mono- or polyether of a monohydric or polyhydric phenolic compound.

17. A formulation according to claim 16, in which the epoxide pre-polymer is a diglycidyl ether of Bisphenol A.

18. A formulation according to any of claims 12 to 17, also containing phenyl glycidyl ether or butyl glycidyl ether as a reactive diluent.

19. A formulation according to any of claims 12 to 18, also containing a cyclic aliphatic compound having at least one -0- group in the ring.

20. A formulation according to claim 19, in which the cyclic aliphatic compound comprises a 5-, 6- or 7membered ring having 1 or 2 -o- groups and optionally a -CO- group next to an -0- group.

21. A formulation according to claim 20, in which the cyclic aliphatic compound is butyrolactone, caprolactone, tetrahydrofuran or dioxane.

22. A formulation according to any of claims 12 to 21, also containing a functionalised rubber or a functionalised thermoplastic, where the functionalities are thiol, hydroxy, carboxy, epoxy or anhydride.

23. A formulation according to claim 22, in which the functionalised rubber or functionalised thermoplastic is selected from acrylic rubber particles, functionalised polybutadiene, butadiene-acrylonitrile copolymer, polyolefin, polyethersulfone, polyetherimide, polydimethylsiloxane, polyetheretherketone or functionalised polycarbonate.

24. A formulation according to any of claims 12 to 23, also containing a filler.

25. A formulation according to claim 24, in which the filler is a particulate filler.

26. A formulation according to claim 25, in which the filler comprises structural fibers.

27. A pre-preg comprising structural fibers impregnated with a stable, gelled but not fully cured composition prepared from a formulation according to any of claims 12 to 26.

28. Use of a complex according to any of claims 1 to 11 as a latent catalyst for epoxy resins.

29. Use according to claim 28, in which the epoxy resin is for resin transfer moulding, pultrusion, filament winding, compression moulding, pre-pegs and other routes to composites.

30. Use according to claim 29, in which the epoxy resin forms a pre-preg.

31. A method of forming a cured epoxy resin product, which comprises heating, optionally under pressure, a curable epoxy resin formulation according to any of claims 12 to 27.

32. A cured epoxy resin which has been obtained by curing an epoxy resin formulation according to any of claims 12 to 27.