WO2005030853A1

WO2005030853A1 - Epoxy compositions and methods of detecting cure

Info

Publication number: WO2005030853A1
Application number: PCT/NZ2004/000237
Authority: WO
Inventors: Gregory John LEWIS
Original assignee: Nuplex Industries Limited; TOWNSEND, Sharon, Lee
Priority date: 2003-09-30
Filing date: 2004-09-30
Publication date: 2005-04-07

Abstract

The present invention incorporates triaryl compound dyes, particularly triarylmethane dyes, into epoxy compositions that are cured using a hardener. The dye allows a user to monitor the degree of curing of compositions. The dye also provides means to identify if hardener has been added to the epoxy composition, and whether the hardener has been mixed properly into the composition. The dye provides an indicator which reacts with the components of the epoxy when mixed at room temperature and produces a colour change. On heat curing further a secondary colour change is produced, preferably above about 50oC. A further final colour change at post cure created at about 75oC enables a visible determination of the status cure of the resulting epoxy composite.

Description

EPOXY COMPOSITIONS AND METHODS OF DETECTING CURE

Field

The present invention relates to epoxy compositions and to their preparation and use. The invention has particular application to ascertaining the degree of mixing and cure of an epoxy resin composition.

Background

Advanced components using room temperature gel or pre-preg epoxies are used extensively in the Marine and Aerospace Industries. In the case of these composite materials, differences in cure temperatures often mean that the performance limit of known epoxy systems may not be reached. In most applications, the epoxy composites require post-cure at elevated temperatures to achieve full mechanical properties. Post-curing is generally done at temperatures above 80 °C and for particular time periods as specified by the manufacturer of the epoxy resin. Determining if full cure has been obtained is difficult and little is known about post-cure variations that occur.

Object

It is an object of the present invention to provide an epoxy composition or a method of making, applying, using or curing an epoxy composition which will provide an indication of the degree of cure. Alternatively, it is an object of the present invention to at least go some way toward overcoming disadvantages of known compositions or to at least provide the public with a useful choice.

Summary of the Invention

Accordingly in one aspect the invention consists in an epoxy resin composition including a triaryl compound dye which indicates mix homogeneity when the composition is mixed with a hardener. Preferably the triaryl compound is a triarylmethane dye.

Preferably the amount of dye is in the general range 0.01%-3.0% by weight of the epoxy resin, and most preferably 0.05%-0.25% by weight of the total composition.

In a second aspect the invention consists in a hardener composition for an epoxy resin, the hardener composition including a triaryl compound dye which indicates mix homogeneity when the composition is mixed with the resin.

Preferably the triaryl compound comprises a triarylmethane dye.

In a third aspect the invention consists in an epoxy resin composition including a triaryl compound dye which indicates the degree of cure by providing a visible colour change as cure occurs after the composition is mixed with a hardener.

Preferably the triaryl compound comprises a triarylmethane dye.

In a fourth aspect the invention consists in a hardener composition for an epoxy resin, the hardener composition including a triaryl compound dye which indicates the degree of cure by providing a visible colour change as cure occurs after the composition is mixed with the resin.

Preferably the triaryl compound comprises a triarylmethane dye.

In a fifth aspect the invention consists in a method of for determining the degree of cure of an epoxy resin system, the method including the steps of: mixing a triaryl compound dye with an epoxy resin composition and a hardener; and allowing a colour change to occur to indicate a property of the system.

Preferably the colour change indicates that the system has been mixed and the step of mixing is continued until the colour change occurs. Alternatively or additionally the colour change indicates that a first stage of a cure process has occurred .

Preferably the method includes the application of heat, and wherein the colour change indicates that a stage of a cure process has occurred, such as a second or post cure stage.

Preferably the method includes the step of mixing until a mixing colour change occurs.

Preferably the method includes the step of forming the mixture into a shape after mixing, and/or applying the mixture to a substrate after mixing.

Preferably the method includes the steps of allowing a first cure colour change to occur, then heating, and allowing a second cure colour change to occur.

In a sixth aspect the invention consists in a kit of parts including an epoxy resin, a hardener, and a triaryl compound dye.

Preferably the triaryl compound comprises a trialymethane dye.

In a seventh aspect the invention consists in an epoxy composition based on amine curable compounds, which includes an epoxy resin, hardener and a dye as an indicator of cure and/or mix homogeneity which changes colour to indicate one or more of: a) that hardener has been added; b) whether excess or insufficient hardener has been added; c) whether post cure has been applied at correct temperatures; d) whether sufficient post cure has been applied; e) that the colo ur change corresponds with the amount of un- reacted amine and epoxy in the cured laminate.

Preferably the composition includes: a) at least one dye selected from the group of triaryl compound dyes. b) A liquid epoxy resin containing Bisphenol A and or Bisphenol F or Novolac, and/or Diluents such as benzyl alcohol, plasticisers and additives. c) An epoxy hardener.

Preferably the triaryl compound comprises a triarylmethane dye.

Preferably the dye is in an amount to insure adequate indication when excess amine is available and further colour change when insufficient amine is present (reacted amine).

Preferably the amount of dye in the general range 0.01 %-3.0% by weight of the epoxy resin is sufficient for this purpose, and preferably 0.05%-0.25% by weight of the composition.

Preferably the hardener comprises a room temperature or above epoxy hardener.

Preferably the hardener comprises one or more of: a) triethylene tetramine; b) Isophorone diamine; c) adducts of aliphatic and/or cycloaliphatic amines.

Preferably the composition includes: a) 20%-99% by weight of the liquid epoxy resin/s; and b) 0%-30% by weight of the benzyl alcohol or additives; and c) 0.005%- 3.0% of the triaryl compound dye/s.

Preferably the dye is selected from triarylmethane or mixtures thereof. Preferably the composition includes one or more diluents selected from benzyl alcohol and/or acetone.

Preferably the hardener includes compounds from Mannich bases and/or cycloaliphatic amines or aliphatic amines.

Preferably the hardener includes co-components which initiate polymerisation for use as accelerators.

Preferably the components of the hardener are used in the following concentrations by weight, based in each case on the overall mixture: a) reactive compounds, from 5%-50%, b) additive compounds, from 1%-5% c) diluting agents, from 0%-30%.

Preferably the dye colour change takes place from blue to colourless on mixing.

Alternatively or additionally the dye colour change takes place from colourless on mixing to light blue or colourless on room temperature cure (0°C-35°C).

Alternatively or additionally the dye colour change takes place from colourless or light blue on room temperature cure to red, green yellow or blue on heating (35°C- 100°C).

Alternatively or additionally a further dye colour change takes place from red, green, yellow on post cure temperature (50°C - 175°C) to blue or the complementary colours of red, green or yellow.

Preferably the hardener further includes co-components which may be used as accelerators, such as tertiary amine catalysts, phenolic accelerators.

Preferably the composition is mixed in liquid form at room temperature or incorporated with fibreglass material in pre-preg form. In an eighth aspect the invention consists in a method for applying an epoxy resin composition according to any one or more of the preceding statements, said method comprising: a) applying to at least one of the materials: i) Fibreglass mat ii) Aramid fibre iii) Carbon fibre iv) E glass b) Consolidating (for applying to a fibreglass or similar fabric) the materials at room temperature or below, c) Allowing to cure at room temperature or above, d) Curing the composition at elevated temperatures.

Preferably the dye indicator colour change takes place from blue, red, green or yellow to clear or to the complementary colours of red, blue, green, and yellow.

Alternatively or additionally the dye indicator colour change takes place from clear or to blue, red, green or yellow to the complementary colours of red, blue, green, or yellow on heating.

Alternatively or additionally the dye indicator colour change takes place from blue, red, green or yellow to the complementary colours of red, blue, green, or yellow on further heating.

Preferably the dye is selected from the chemical group consisting of triaryl compound dyes.

Preferably the dye is selected from the chemical group consisting of triarylmethane dyes. Preferably the method includes providing at least one amine hardener compound selected from one or more of the following: a) Aliphatic amines b) Cycloaliphatic amines c) Mannich bases d) Adducts of above

Preferably the method includes providing one or more diluents, wherein said composition comprises b) 0%-30% by weight of the diluents benzyl alcohol or acetone. c) 0.005%-3.0% of dye

Preferably the method includes using a composition comprising: a) 20%-99% by weight of the liquid epoxy and b) 0-30% by weight of the diluents. c) 0.005%-3.0% of dye

Preferably the method includes using an epoxy resin selected from Bisphenol A Bisphenol F and/or Novolac epoxy resins.

Preferably the method includes using a hardener comprising amine compounds.

Preferably the components of the hardener are used in the following concentrations by weight, based on the overall mixture: (i) 1%-50% by weight.

Preferably the materials to be laminated are identical or different materials selected from fibreglass, aramid, carbon, glass or cloth materials.

Preferably the materials to be fabricated comprise marine or aerospace components. Detailed Description

The present invention incorporates dyes into epoxy compositions that are cured using a hardener. The dye has significant advantage of allowing a user to monitor the degree of curing of compositions. The dye also provides means to identify if hardener has been added to the epoxy composition, and whether the hardener has been mixed properly into the composition. Therefore the dye provides an indicator which reacts with the components of the epoxy when mixed at room temperature and produces a colour change. On heat curing further a secondary colour change is produced, preferably above about 50°C. A further final colour change at post cure created at about

75°C enables a visible determination of the status cure of the resulting epoxy composite.

The compounds of the present invention include: a) at least one liquid epoxy; b) at least one hardener, preferably an amine hardener; c) a dye.

A diluent may also be preferable.

These compounds can be prepared in accordance with processes known per se by knowing mixing and blending steps. It is also possible, as known to those skilled in the art to which the invention relates, to use other epoxy hardeners and resins apart from those described as being most preferred in the description below.

In general, a very wide variety of two component epoxy systems can be used in accordance with the present invention. These need only be stable in storage, substantially liquid in their application form (most preferably water to honey like fluid), and should have pot life sufficient for processing, but should then cure after mixing with the hardener to a dimensionally stable form by the simple action of ambient air with optional final cure at elevated temperatures. Additionally, the compositions of the invention may include agents having an accelerator effect.

In the preferred form a substantially liquid epoxy resin is provided containing Bisphenol A and/or Bisphenol F or Novolac. The resin composition may also include diluents, for example benzyl alcohol, plasticisers and/or additives.

An epoxy hardener is also provided. In general, substantially any conventional room temperature or above epoxy hardener may be used with the present invention. Specific examples which we have found to be effective include triethylene tetramine, lsophorone Diam^'me and adducts of aliphatic and cycloaliphatic amines.

Together with these known epoxy resins and hardeners is added at least one dye. In use the dye provides an indicator of cure of the resultant epoxy composition. It also preferably provides an indicator of mixed homogeneity. In particular, the dye changes colour to indicate one or more of the following: a) that hardener has been added to the composition; b) whether excess or insufficient hardener has been added; c) whether the post cure has been applied at correct temperatures; whether sufficient post cure has been applied. e) that the colour change corresponds with the amount of un- reacted amine and epoxy in the cured laminate.

In a preferred embodiment the dye is specifically selected from the group of triaryl compound dyes, most preferably triarylmethane dyes. The dye is provided in an amount to ensure that a good indication when excess amine is available and further colour change occurs when insufficient amine is present (reactive amine). In general an amount of dye in the range .01 %-3% by weight of the epoxy resin is sufficient for this purpose, and preferably .05%- .25% by weight of the composition. In a preferred embodiment of the invention an epoxy composition is formed from 20 to 99% by weight of liquid epoxy resin(s), 0%-30% by weight of one or more diluents such as benzyl alcohol or additives, and 0.01 %-3% by weight of triaryl compound dye(s), preferably triarylmethane dyes.

The hardener system preferably includes compounds from Mannich bases and/or cycloaliphatic amines or aliphatic amines.

The composition may also include co-components with which initiator polymerisation are used as accelerators.

The hardener system is preferably used in the following concentrations by weight, based on the overall mixture: a) elective compounds, from 5%-50%; b) additive compounds, from 1%-5%; c) diluting agents, from 0%-30%

We have found that with these compositions the dye provides at least one or more of the following colour changes:

1. The dye change takes place from colourless on mixing to light blue or colourless on room temperature cure (approximately 0° C to 35°C).

2. The dye colour change takes place from colourless or light blue on room temperature cure to red, green, yellow or blue on heating (approximately 35°C to 100°C).

3. The dye colour change takes place from red, green, yellow on post cure temperatures (approximately 50°C to 175°C) to blue or the complementary colours of red, green or yellow.

In practice, a composition as described above is mixed in liquid form at room temperature or incorporated within a substrate material in pre-preg form. An appropriate material may be a fiberglass material such as fiberglass mat or another fibre based material such as aramid fibre, carbon fibre material or E glass. Also, the composition may be firstly mixed and then applied to a material such as a fibre glass mat, an aramid fibre, carbon fibre material or E glass. This can occur at room temperature or below room temperature if desired.

Once the composition has been applied in a known way to such a substrate, then the composition is allowed to cure at room temperature or above room temperature if desired in the known way. A post cure step can then occur at elevated temperatures if desired.

Throughout the steps outlined above, the dye indicator, which is included in the composition of the invention, provides the colour changes outlined above which allow the user to ascertain whether the correct quantify of hardener has been added and mixed correctly, and at what stage of the cure process the composition is at any point in time. In particular, when the composition is curing, either at room temperature or at temperatures above room temperature and in particular during post cure operations, the dye will provide an indication of the amount of hardener which has reacted in any region in which the composition has been applied and/or the temperature of the composition in any particularly region. Therefore, a user can detect regions that may not have sufficiently cured and apply further heat or allow further time to assist curing of those regions. In a number of marine or aerospace products inadequate cure in a particular inadequate post cure in particular religions of the product in which the epoxy composition is used can create areas of significant mechanical weakness and therefore defective product. One particular example is manufacture of a boat hull from fibre glass material which is laminated using an epoxy resin composition. The present invention may be used to determine the degree of cure throughout the manufacture of the hull. In particular, if post cure does not occur in any region/s of the hull, then this can be determined by a simple visual inspection and remedied at the appropriate time. Indication of incorrect hardener levels will occur at post cure stage where the final colour will not develop under correct post cure temperature and time.

We have found from experimental results that it is clear that the colour change provided by the dye indicator correlates unambiguously with the amine (i.e. the hardener in the mixed epoxy compound).

Similarly, with the dye indicator, we found there were an unambiguous correlation of the clearly visible colour changes with the cure of the mixed epoxy composition and a correlation between un-reacted amine and colour change.

Two examples of compositions and detected colour changes according to the invention are described below:

Example 1. (Room Temperature and post -cure system)

Part A

Bisphenol A resin 62.00%

Bisphenol F resin 27.97% Benzyl Alcohol 10.00%

Basonyl Blue 636* (dye) 0.03%

Polyoxyalkylamine 15% Isophorone Diamine 20%

Triethylene Tetramine 30%

1 ,5-pentanediamine, 2-methyl 15%

Benzyl alcohol 8%

Bisphenol A resin 12%

Bisphenol A resin - Araldite GY9708-1 from Vantico

Bisphenol F resin- Kukdo YD-114EF FROM Kukdo, Sth Korea

Basonyl Blue 636 - BASF

Product mixed 5 parts by weight of Part A with 1 part by weight of part B. Colour changes Recorded: Ambient mix Blue to clear after 30 seconds stirring

Product laminated with fibreglass mat - remain clear to gel stage 2-3 hrs and remain clear until full room temperature cure for 5 days. Post cure in oven at 65°C for 2 hours- allow to cool -colour change clear to red. Post cure in oven 4 hours at 80° C- allow to cool - colour change red to blue

Example 2 Room Temperature cure system (Using resin of Part A from example 1)

Part B

Isophorone Diamine 20%

Triethylene Tetramine 20% Mannich Base 60%

Product mixed 5 parts by weight of Part A with 1 part by weight of part B.

Colour changes Recorded:

Ambient mix Blue to clear after 30 seconds stirring

Product laminated with fibreglass mat - remain clear to gel stage 1-3 hrs and changes blue and darkens at room temperature - optional post cure lightens colour.

The triarlymethane die is referred to above by its trade name. The chemical formula of the preferred dye is C33 - H40 - N3.CI. Alternative names include the following:

* Ethanaminium,

N-(4-((4-(diethylamino)phenyl)(4-(ethylamino)-1-naphthalenyl)meth- ylene)-2,5-cyclohexadien-1-ylidene)-N-ethyl-, chloride

* N-(4-((4-(Diethylamino)phenyl)(4-(ethylamino)-1-naphthalenyl)meth- ylene)-2,5-cyclohexadien-1-ylidene)-N-ethylethanaminium chloride

Systematic Name

(4-(4-(Diethylamino)-alpha-(4-(ethylamino)-1-naphthyl)benzylidene)cycloh exa-2,5-dien-1-ylidene)diethylammonium chloride Ethanaminium,

N-(4-((4-(diethylamino)phenyl)(4-(ethylamino)-1-naphthalenyl)methylene)- 2,5-cyclohexadien-1-ylidene)-N-ethy]-, chloride

The scope of the invention is not limited to the specific embodiments described above but also includes those modifications, additions, improvements, equivalents and substitutions which a person skilled in the art would appreciate are within the scope of the invention.

The words "comprise" or "comprises" or "comprising" are used in this specification in a manner which is intended to be inclusive rather than restricting.

Claims

1. An epoxy resin composition including a triaryl compound dye which indicates mix homogeneity when the composition is mixed with a hardener.

2. A resin composition as claimed in claim 1 wherein the triaryl compound is a triarylmethane dye.

3. A resin composition as claimed in claim 1 or claim 2 wherein the amount of dye is in the general range 0.01 %-3.0% by weight of the epoxy resin.

4. A resin composition as claimed in any one of claims 1 to 3 wherein the dye is 0.05%-O.25% by weight of the total composition.

5. A hardener composition for an epoxy resin, the hardener composition including a triaryl compound dye which indicates mix homogeneity when the composition is mixed with the resin.

6. A hardener composition as claimed in claim 5 wherein the triaryl compound comprises a triarylmethane dye.

7. A hardener composition as claimed in claim 5 or claim 6 wherein the amount of dye is in the general range 0.01%-3.0% by weight of the epoxy resin.

8. A hardener composition as claimed in any one of claims 5 to 7 wherein the dye is 0.05^<%-0.25% by weight of the total composition.

9. An epoxy resin composition including a triaryl compound dye which indicates the degree of cure by providing a visible colour change as cure occurs after the composition is mixed with a hardener.

10. An epoxy resin composition as claimed in claim 9 wherein the triaryl compound com prises a triarylmethane dye.

11. An epoxy resin composition as claimed in claim 9 or claim 10 wherein the amount of dye is in the general range 0.01 %-3.0% by weight of the epoxy resin.

12. An epoxy resin composition as claimed in any one of claims 9 to 11 wherein the dye is 0.05%-0.25% by weight of the total composition.

13. A hardener composition for an epoxy resin, the hardener composition including a triaryl compound dye which indicates the degree of cure by providing a visible colour change as cure occurs after the composition is mixed with the resin.

14. A hardener composition as claimed in claim 13 wherein the triaryl compound comprises a triarylmethane dye.

15. A hardener composition as claimed in claim 13 or claim 14 wherein the amount of dye is in the general range 0.01 %-3.0% by weight of the epoxy resin.

16. A hardener composition as claimed in any one of claims 13 to 15 wherein the dye is 0.05%-0.25% by weight of the total composition.

17. A method of for determining the degree of cure of an epoxy resin system, the method including the steps of: mixing a triaryl compound dye with an epoxy resin composition and a hardener; and allowing a colour change to occur to indicate a property of the system.

18. A method as claimed in claim 17 wherein the colour change indicates that the system has been mixed and the step of mixing is continued until the colour change occurs.

19. A method as claimed in claim 17 wherein the colour change indicates that a first stage of a cure process has occurred.

20. A method as claimed in claim 17 including the application of heat, and wherein the colour change indicates that a stage of a cure process has occurred, such as a second or post cure stage.

21. A method as claimed in any one of claims 17 to 20 including the step of mixing until a mixing colour change occurs.

22. A method as claimed in any one of claims 17 to 21 including the step of forming the mixture into a shape after mixing.

23. A method as claimed in any one of claims 17 to 22 including the step of applying the mixture to a substrate after mixing.

24. A method as claimed in any one of claims 17 to 23 including the steps of allowing a first cure colour change to occur, then heating, and allowing a second cure colour change to occur.

25. A kit of parts including an epoxy resin, a hardener, and a triaryl compound dye.

26. A kit of parts as claimed in claim 25 wherein the triaryl compound comprises a trialymethane dye

27. An epoxy composition based on amine curable compounds, which includes an epoxy resin, hardener and a dye as an indicator of cure and/or mix homogeneity which changes colour to indicate one or more of: a) that hardener has been added; b) whether excess or insufficient hardener has been added; c) whether post cure has been applied at correct temperatures; d) whether sufficient post cure has been applied; e) that the colour change corresponds with the amount of un- reacted amine and epoxy in the cured laminate.

28. A composition as claimed in claim 27 including: a) at least one dye selected from the group of triaryl compound dyes. b) A liquid epoxy resin containing Bisphenol A and or Bisphenol F or Novolac, and/or Diluents such as benzyl alcohol, plasticisers and additives, c) An epoxy hardener.

29. A composition as claimed in claim 27 or claim 28 wherein the triaryl compound comprises a triarylmethane dye.

30. A composition as claimed in any one of claims 27 to 29 wherein the dye is in an amount to insure adequate indication when excess amine is available and further colour change when insufficient amine is present

(reacted arnine).

31. A composition as claimed in any one of claims 27 to 30 wherein the amount of dye in the general range 0.01 %-3.0% by weight of the epoxy resin is sufficient for this purpose, and preferably 0.05%-0.25% by weight of the composition.

32. A composition as claimed in any one of claims 27 to 31 wherein the hardener comprises a room temperature or above epoxy hardener.

33. A composition as claimed in any one of claims 27 to 32 wherein the hardener comprises one or more of: a) triethylene tetramine; b) Isophorone diamine; c) adducts of aliphatic and/or cycloaliphatic amines.

34. A composition as claimed in any one of claims 27 to 33 wherein the composition includes: a) 20%-99% by weight of the liquid epoxy resin/s; and b) 0%-30% by weight of the benzyl alcohol or additives; and c) 0.005%- 3.0% of the triaryl compound dye/s.

35. A composition as claimed in any one of claims 27 to 34 wherein the dye is selected from triarylmethane or mixtures thereof.

36. A composition as claimed in any one of claims 27 to 35 including one or more diluents selected from benzyl alcohol and/or acetone.

37. A composition as claimed in any one of claims 27 to 36 wherein the hardener includes compounds from Mannich bases and/or cycloaliphatic amines or aliphatic amines.

38. A composition as claimed in any one of claims 27 to 37 wherein the hardener includes co-components which initiate polymerisation for use as accelerators.

39. A composition as claimed in any one of claims 27 to 38 wherein the components of the hardener are used in the following concentrations by weight, based in each case on the overall mixture: a) reactive compounds, from 5%-50%, b) additive compounds, from 1%-5% c) diluting agents, from 0%-30%.

40. A composition as claimed in any one of claims 27 to 39 wherein the dye colour change takes place from blue to colourless on mixing.

41. A composition as claimed in any one of claims 27 to 40 wherein the dye colour change takes place from colourless on mixing to light blue or colourless on room temperature cure (0°C-35°C).

42. A composition as claimed in any one of claims 27 to 41 wherein the dye colour change takes place from colourless or light blue on room temperature cure to red, green yellow or blue on heating (35°C- 100°C).

43. A composition as claimed in any one of claims 27 to 42 wherein a further dye colour change takes place from red, green, yellow on post cure tem erature (50°C - 175°C) to blue or the complimentary colours of red, green or yellow.

44. A composition as claimed in any one of claims 27 to 43 wherein the hardener system further includes co-components which may be used as accelerators, such as tertiary amine catalysts, phenolic accelerators.

45. A composition as claimed in any one of claims 27 to 44 wherein the co position is mixed in liquid form at room temperature or incorporated with fibreglass material in pre-preg form.

46. A method for applying an epoxy resin composition according to any one or more of the preceding statements, said method comprising: a) applying to at least one of the materials: i) Fibreglass mat ii) Aramid fibre iii) Carbon fibre iv) E glass b) Consolidating (for applying to a fibreglass or similar fabric) the materials at room temperature or below, c) Allowing to cure at room temperature or above, d) Curing the composition at elevated temperatures.

47. A method as claimed in claim 46 wherein the dye indicator colour change takes place from blue, red, green or yellow to clear or to the complementary colours of red, blue, green, and yellow.

48. A method as claimed in claim 46 wherein the dye indicator colour change takes place from clear or to blue, red, green or yellow to the complementary colours of red, blue, green, or yellow on heating.

49. A method as claimed in claims 46 wherein the dye indicator colour change takes place from blue, red, green or yellow to the complementary colours of red, blue, green, or yellow on further heating.

50. A method as claimed in any one of claims 46 to 49 wherein the dye is selected from the chemical group consisting of triaryl compound dyes.

51. A method as claimed in any one of claims 46 to 50 wherein the dye is selected from the chemical group consisting of triarylmethane dyes.

52. A method as claimed in any one of claims 46 to 51 including providing at least one amine hardener compound selected from one or more of the following: a) Aliphatic amines b) Cycloaliphatic amines c) Mannich bases d) Adducts of above

53. A method as claimed in any one of claims 46 to 52 including providing one or more diluents, wherein said composition comprises b) 0%-30% by weight of the diluents benzyl alcohol or acetone. c) 0.005%-3.0% of dye

54. A method as claimed in any one of claims 46 to 53 including using a composition comprising: a) 20%-99% by weight of the liquid epoxy and b) 0-30% by weight of the diluents. c) 0.005%-3.0% of dye

55. A method as claimed in any one of claims 46 to 53 including using an epoxy resin selected from Bisphenol A Bisphenol F and/or Novolac epoxy resins.

56. A method as claimed in any one of claims 46 to 55 including using a hardener comprising amine compounds.

57. A method as claimed in claim 56 wherein the components of the hardener are used in the following concentrations by weight, based on the overall mixture: (i) 1%-50% by weight.

58. A method as claimed in any one of claims 46 to 57 wherein the materials to be laminated are identical or different materials selected from fibreglass, aramid, carbon, glass or cloth materials.

59. A method as claimed in any one of claims 46 to 58 wherein the materials to be fabricated comprise marine or aerospace components.

60. An epoxy resin composition substantially as herein described with reference to any one of the examples.