IMPROVED FAST CURE EPOXY RESINS AND PREPREGS OBTAINED THEREFROM

Abstract

This invention relates to a composition comprising a semisolid epoxy resin containing a curative dispersed therein. The curative has a particle size such that at least 90% of the particles have a size below 25 pm at ambient temperature of 21° C., wherein the composition further comprises a diluent containing a particulate filler. The composition is used as matrix in prepregs. The use of the diluent increases peel strength of the composition when brought into contact with metal or wood substrate.

Claims

1. A composition comprising a semisolid epoxy resin containing a curative dispersed therein, said curative having a particle size such that at least 90% of the particles have a size below 25 μm at ambient temperature of 21° C., as determined in accordance with ASTM D1214), wherein the composition further comprises a diluent.

2. A composition according to claim 1, wherein the diluent comprises a particulate filler.

3. A composition according to claim 2, wherein the particulate filler is selected from micro balloons, glass, carbon, metal and/or combinations of the aforesaid tillers.

4. A composition to claim 1 wherein the composition comprises a fibrous reinforcement material.

5. A composition according to claim 4, wherein the fibrous reinforcement material comprises a fleece.

6. A composition ccording to claim 4, wherein the composition is in the form of a prepreg.

7. A composition according to claim 4, wherein the diluent is present on the surface of the fibrous reinforcement material.

8. (canceled)

9. A composition according to claim 1 in which at least 90% of the curative has an average particle size below 10 μm.

10. (canceled)

11. (canceled)

12. (canceled)

13. A composition according to claim 1 in which the curative comprises dicyandiamide.

14. A curative account to claim 13 in which the curative comprises a urea derivative.

15. (canceled)

16. A composition according to claim 1 that can be cured to provide a 95% cure at 120° C. in no more than 10 minutes and a 95% cure at 130′C in no more than 6 minutes.

17. A composition according to claim 1, wherein the composition further comprises a toughener or modifier in the range of from 3 to 15% by weight of the composition.

18. A composition according to claim 17, wherein the toughener or modified comprises a nitrile rubber which is in the form of a nitrile rubber modified bis F epoxy block copolymer.

19. (canceled)

20. (canceled)

21. (canceled)

22. (canceled)

23. (canceled)

24. A process for the continuous manufacture of a prepreg comprising mixing a semisolid epoxy resin and a curative of particle size such that at least 90% of the particles have a size below 25 μm at ambient temperature, heating the mixture to a temperature of between 35 to 80° C., and continuously dispensing the mixture onto a moving fibrous reinforcement material and providing a particulate filler based diluent onto the dispensed mixture to produce a prepreg.

25. (canceled)

26. (canceled)

27. (canceled)

28. A composite structure comprising a cured prepreg comprising a fibrous material and a semisolid epoxy resin containing a curative of particle size such that at least 90% of the particles have a size below 25 μm at ambient temperature and a particulate filler based diluent, said fibrous material and semisolid epoxy resin being bonded to a substrate.

29. A structure according to claim 28 in which at least 90% of the curative has an average particle size below 10 μm.

30. (canceled)

31. (canceled)

32. (canceled)

33. A composite structure according to claim 28 in which the curative comprises dicyandiamide.

34. A composite structure according to claim 33 in which the curative comprises a urea derivative.

35. A composite structure according to claim 28 in which the substrate is a metal such as aluminium or wood.

36. A composite structure according to claim 35 in which the peel strength of the bond between the cured prepreg and the aluminium is greater than than 3 N/mm.sup.2.

37. (canceled)

38. (canceled)

Description

EXAMPLE 1

[0085] A composition called Invention 1 is prepared from 85.65 wt % of a semisolid bisphenol-A based resin LY1589 from Huntsman which was mixed with 14.35 wt % of a powdered curative system comprising:

[0086] 62 wt % Dicyandiamide (DICY)

[0087] 31 wt % Dyhard UR500 (blend of 2,4-toluene bis dimethyl urea and 2,6-toluene bis dimethyl urea accelerator) 7 wt % Sipernat D17 (silica based anticaking agent from Evonik)

[0088] The powdered curative system was mixed or blended so that 98% of the particles were of a size smaller than 10 microns.

[0089] The resin system has a viscosity at 25° C. of 1.18 MPas. It had a cold Tg of 17.29° C. Onset of cure occurred at 128.26° C. and the peak temperature during cure was 139° C.

[0090] A composition called Invention 2 was prepared from 81.37 wt % of a semisolid bisphenol-A based resin LY1589 from Huntsman which was mixed with 13.63 wt % of the powdered curative system of Invention 1, together with 5.00 wt % of a nitrile modified bis F epoxy block copolymer containing 40% by weight of nitrile rubber, available under the trade name Polydis PD3611.

[0091] A composition called Invention 3 was prepared from 77.08 wt % of a semisolid bisphenol-A based resin LY1589 which was mixed with 12.92 wt % of the powdered curative system of Invention 1, together with 10.00 wt % of a nitrile modified bis F epoxy block copolymer containing 40% by weight of nitrile rubber, available under the trade name Polydis PD3611.

[0092] The resin of the various Invention compositions was applied to a glass fibre web (LT570 from Hexcel) by the process illustrated in FIG. 1 to form a prepreg comprising 34 wt % glass fibre and 66 wt % of the resin system as is typical for a winter sports prepreg used in ski manufacture.

[0093] The product was characterised in terms of peel strength to aluminium (using standard test DIN 53295), mechanical performance tests (tensile strength and tensile modulus in accordance with DIN EN ISO 527−4), isothermal cure was measured at 120° C. for 15 minutes and at 130° C. for 15 min by DSC in accordance with ASTM D3418, and also the resin flow was measured. The resin flow was measured as follows.

[0094] A round prepreg coupon having a surface area of 100 cm.sup.2 is cut from the prepreg. The mass m.sub.1 of the coupon is determined. The coupon is subsequently cured in a heated press at a temperature of 130° C. for 10 minutes and at a pressure of 5 bar. A circular coupon with diameter 50 mm is then cut from the cured coupon and the mass m.sub.2 is determined. The resin flow R (%) is then calculated as follows:

R(%)=(m.sub.1−(m.sub.2×f))/m.sub.1×100

[0095] Wherein f=5.09.

[0096] The prepregs containing the resin composition of the Inventions 1 to 3 were compared to a comparable prepreg also containing 34 wt % glass fibre prepared from the Hexcel product

[0097] Hexply using an X1 resin formulation which contains two liquid bisphenol-A based epoxy resins in combination with 69 wt % dicyandiamide, and 31 wt % Dyhard UR500. This formulation is also compared with a pre-reacted (B-staged) commercial system with long open time (SLOT) based prepreg as conventionally used in the production of wintersports goods, having a glass fibre content of 39 wt %.

[0098] The results are shown in the below Table 1.

TABLE-US-00001 TABLE 1 Results. The data is normalised to reflect a 50% by volume glass fibre material. Method/ standard Invention 1 Invention 2 Invention 3 X1 SLOT Peel Strength DIN53295 2.19 N/mm.sup.2 3.1 N/mm.sup.2 5.8 N/mm.sup.2 4.6 N/mm.sup.2 1.61 N/mm.sup.2 Resin Flow 15.0% 15.0% 15.0% 15.0% NA Isothermal 95% 8 min 9.2 min 9.7 min 8.3 min 15 min Cure @ conv. 126° C. 124° C. 122° C. 125° C. −80° C. 120° C., 15 min Tg (DSC) Isothermal 95% 4.7 min 5.6 min 5.8 min 5 min NA Cure @ Tg 125° C. 117° C. 115° C. 135° C. NA 130° C., 15 min (DSC) Mechanical Tensile 750 MPa 790 MPa 826 MPa 850 MPa 870 MPa Performance Strength Mechanical Tensile 30.5 GPa 31.9 GPa 32.3 GPa 32 GPa 32 GPa Performance Strength

[0099] Once prepared the prepreg containing the resin formulation of the invention could be rolled-up, so that it can be stored for a period of time. It can then be unrolled and cut as desired and optionally laid up with other prepregs to form a prepreg stack in a mould or in a vacuum bag which is subsequently placed in a mould.

EXAMPLE 2

[0100] The composition of Invention 3 is combined with fabric of different weights F35 fleece, 35 g/m.sup.2 and F65 fleece, 55 g/m.sup.2 both supplied by Hexcel Corporation. The fabrics were impregnated with the composition. In addition in Samples B and D a diluent in the form of glass spheres (Spheriglass A glass 2227 as supplied by Potters Industries LLC) was added. The resulting resin contents in the composition as wt % based on the overall weight of the composition are present in the below Table 2. This Table also shows the relative peel strength in relation to Sample A when each of the compositions is applied to an aluminium sheet and cured for 7 minutes at a temperature of 130° C. The 2227 content in Samples B and D is 70 g/m.sup.2.

TABLE-US-00002 TABLE 2 Relative peel strength Resin fiber (in relation content weight to Sample A) - Sample Composition (wt %) (g/m.sup.2) ASTMD1876 A Invention 3/F35 80% 35 1 B Invention 3/F35 + 2227 57% 35 1.3 C Invention 3/F65 80% 55 2.0 D Invention 3/F65 + 2227 64% 55 2.2

[0101] There is thus provided a composition and a process as herein before described. The composition and process is particularly suited to the manufacture of winter sports equipment in combination with fibrous reinforcement and/or polyurethane core materials.