FAST CURING COMPOSITIONS

Abstract

This invention relates to an epoxy resin formulation containing a curative that can be cured at 150° C. to 95% cure in no more than 150 seconds, and can be cured at 120° C. to 95% cure in no more than 4 minutes. This results in a cured resin having a Tg no greater than 140° C. wherein the formulation further contains a mould release agent.

Claims

1. An epoxy resin formulation containing a curative that can be cured at 150° C. to 95% cure in no more than 150 seconds, and can be cured at 120° C. to 95% cure in no more than 4 minutes to provide a cured resin having a glass transition temperature as determined in accordance with astm d7028 of no greater than 140° C. wherein the formulation further contains a mould release agent.

2. An epoxy resin formulation according to claim 1 in which the cured epoxy resin formulation has a Phase angle below 20° at a temperature below 140° C.

3. An epoxy, resin formulation according to claim 2 in which the phase angle is above 10° at a temperature below 140° C.

4. An epoxy resin formulation containing a curative, the formulation comprising a phase angle below 30° when cured at 120° C. for less than 600 seconds wherein the formulation further contains a mould release agent.

5. (canceled)

6. An epoxy resin formulation according to claim 1, wherein the release agent comprises unsaturated fatty acids and/or saturated fatty acids.

7. An epoxy resin formulation according to claim 1, wherein the release agent comprises components selected from triglycerides.

8. An epoxy resin formulation according to claim 1, wherein the release agent comprises polyunsaturated fatty acids and/or mono saturate fatty acids and/or saturated fatty acids.

9. An epoxy resin formulation according to claim 1, wherein the release agent comprises one or more components selected from alpha linoleic acid, linoleic acid, oleic acid, stearic acid, and palmitic acid.

10. A prepreg containing an epoxy resin formulation according to claim 1.

11. A prepreg comprising fibrous reinforcement and an epoxy resin formulation that can be cured at 150° C. in no more than 150 seconds, can be cured at 120° C. in no more than 4 minutes to provide a cured resin having a glass transition temperature no greater than 140° C., and a Phase angle of 20° or less at a temperature of 140° C. or below wherein the epoxy resin contains a mould release agent.

12. (canceled)

13. An epoxy or a prepreg according to claim 1 containing from 0.25 to 5 wt % of the mould release agent.

14. An epoxy resin formulation or a prepreg according to claim 1 in which the mould release agent is a blend of organic fatty acid derivatives with surface active agents.

15. An epoxy resin formulation or a prepreg according to claim 1 in which the curative is a urea based curing agent.

16. An epoxy resin formulation or a prepreg according to claim 1 in which the epoxy resin contains from 4 to 10 wt % based on the weight of the epoxy resin of the curing agent.

17. An epoxy resin formulation or a prepreg according to claim 1 in which the epoxy resin has a functionality of at least 2.

18. (canceled)

19. (canceled)

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. A method of demoulding a moulding comprising an epoxy resin formulation according to claim 1, wherein the moulding has a glass transition temperature within 20% of the temperature of the moulding.

Description

EXAMPLES

[0133] The present invention is illustrated by reference to the following Examples.

Example 1

[0134] Samples of neat resin containing 0.5%, 1% or 2% of release agent were mixed and cast into 200 gsm films. The films were pressed into 150 by 150 mm squares of G803 fabric (Hexcel Reinforcements, Les Avenieres, France) to form a prepreg. A fast cure resin system sold by Hexcel Corporation under the tradename of M77 was used as the neat resin. Four plies of prepreg were laid up onto a plate of degreased aluminium. Samples were hot loaded into a press and press cured at 150° C. for 6 minutes at 7.2 bar. Once cooled, the cured laminate and the aluminium to which it was adhered were removed from the press and cut into a smaller 50 mm by 50 mm square. In the centre of each of these squares a 10 mm radius bore cutting drill bit was used to cut through the laminate into the aluminium below. A dolly was attached to the circles of prepreg using Redux 810 adhesive. The dolly was then connected to an Instron materials testing rig, the force required to remove the prepreg circle from the aluminium sheet was measured using the Instron. The pull off force was compared as a percentage of the pull off force for an identical prepreg free from any release agent.

[0135] The results were as follows.

TABLE-US-00001 TABLE 1 Percent reduction of pull off Release agent Weight percent force Stearate 1% 65%

[0136] A resin formulation according the invention was produced comprising the following: [0137] 0.5% by weight of Release Agent Axel INT-1324 [0138] 95% by weight of M77 Hexcel Corporation

[0139] Moulding compound was produced from a prepreg comprising the resin formulation. the prepreg comprised 150 gsm of unidirectional carbon fibre and 38% by weight of the resin formulation. The prepreg was cut into 0.85 by 5 cm chips and pressed into a sheet to form the moulding compound.

[0140] Samples of moulding compound measuring 100 mm by 100 mm squares were cut and press cured between two steel plates at 150° C. for 2 minutes under 75 bar of applied pressure. Both mould surfaces were initially treated with externally applied Airtech Cirex 043 release agent before the first sample of moulding compound was applied.

[0141] Eighty eight samples were cured in this manner, all of which were easily removed from the mould. The first 20 required very easily removed from the mould, but as the number of cures rose this increased slightly. After the first 20 samples the force to remove did not increase, suggesting the initial application of external release agent has been disrupted beyond that point. Because the remaining samples were successfully demoulded further samples would continue to be demoulded without an additional externally applied release agent.

Example 2

[0142] A second resin formulation was made as above only the weight % of release agent was doubled to 1%. Samples were cured in the mould as described above. Forty two samples were successfully demoulded without reapplication of an external mould release.

Example 3

[0143] Neat resin samples were prepared from M77 resin as supplied by Hexcel Corporation in which the resin samples contained commercially available release agents as follows:

TABLE-US-00002 TABLE 2 Weight % based on total Sample Release agent weight of resin A INT 1324LE (Axel) 0.5%   B INT 1888LE (Axel) 2% C INT 1888LE (Axel) 1% D Byk 9912 (Altana) 2%

[0144] Films were cold pressed in the form of discs, 50 mm in diameter to a thickness of 1 mm. The films were loaded into an Instron 5969 Dual Column Tabletop Testing System (compression/tensile tester) on corresponding circular disc shaped test surfaces of 50 mm in diameter.

[0145] The disc shaped test surfaces were prepared to have varying surface roughness as set out in the below Table 3. The surface roughness was measured using a Mitotoyo Surftest 301.

TABLE-US-00003 TABLE 3 Sample A Sample B Sample C Sample D Pull force Pull force Pull force Pull force Roughness (μm) (MPa) (MPa) (MPa) (MPa) 2.5 5.0 2.6 4.0 2.3 1 4.8 3.2 — 1.8 0.4 3.7 2.2 4.2 1.7

[0146] The samples were cured at an isothermal temperature of 150° C. for 2 minutes. Directly following cure, the disc shaped surfaces were moved apart and the force was measured to separate the cured neat resin disc from a disc surface as the pull force in MPa (Pull force=separation force, F/ surface area of the disc, A). The results are presented in Table 3.