WO2006005559A1

WO2006005559A1 - Stable curable epoxy resin compositions and uses thereof

Info

Publication number: WO2006005559A1
Application number: PCT/EP2005/007473
Authority: WO
Inventors: Alain Robert Louis Leroy; Marianne Norbertine Marcella Godts
Original assignee: Hexion Specialty Chemicals Research Belgium S.A.
Priority date: 2004-07-13
Filing date: 2005-07-11
Publication date: 2006-01-19

Abstract

The invention belongs to the field of epoxy resin curable compositions, more particularly intend for the impregnation of fibers applicable to the manufacturing of composite structures and as adhesives thereof. The objects of the present invention are achieved by a curable or polymerizable epoxy resin characterized in that the hardener part comprises a combination of: (i) at least a liquid carrier, (ii) dicyandiamide and (iii) an amine functional catalyst the amount of the hardener over the epoxy resin being 8 to 20 part by weight, the operating window of the composition being between 12 hours to 30 days at room temperature.

Description

STABLE CURABLE EPOXY RESIN COMPOSITIONS AND USES THEREOF

The invention relates to epoxy resin curable compositions, more particularly intended for the impregnation of fibers applicable to the manufacturing of composite structures and as adhesives therefore.

Epoxy resin curable compositions are well known in the art to provide excellent properties of cured material after impregnation of fibers. The epoxy resins are curable with for example poly-acids and/or poly-anhydride or poly-amines. Although these compositions are currently used for industrial applications some drawbacks are well recognized. The acid and/or anhydride cured systems are often water sensitive and lead to hydrolysis of the cured matrix. The amine cured compositions are more resistant to hydrolysis but have a stability drawback and often the amine-epoxy reaction occurs at .storage temperature. It is • the object of this invention to provide a curable epoxy resin composition with a polyamine curative with an controllable stability/reactivity profile.

EP 0 621 879 discloses a hardenable or polymerizable epoxy composition comprising an epoxy resin and about 5 to about 50 wt % of a hardener based on the total weight of the composition, said hardener including the combination of: (a) at least one imidazole that only polymerizes said epoxy resin at temperatures above 75°C; and(b) at least one polyamine that only polymerizes said epoxy resin at temperatures below 75⁰C. said composition having a lifetime (shelf life) of at least 21 days and a water uptake of the composition measured in accordance with standard ISO 75 for 14 days at 70⁰C; being at most 2%. The proposed composition works with latent (at storage temperature) imidazole derivatives. Therefore the technical solution to the abovementioned problem is solved by the use of sophisticated and expensive imidazole derivatives, while the industry is still looking for a amine curable epoxy composition that has long stability at storage temperature and that is based on low cost chemicals. After extensive research and experimentation, it has now surprisingly been found that dicyandiamide dispersed in at least a member of the group consisting of a polyamine, polyamidoamide, polyetherpolyamine, polyol and polyetherpolyol in the presence of at least an imidazole derivative or other amine catalyst such as the urone derivatives, provides a curable epoxy resin composition with an adjustable stability/reactivity profile or an adjustable operating window. By the term "operating window" as used throughout the present specification is meant maximum time interval during which the composition is suitable for producing a composite structure, that is retains its handling properties and its mechanical performance after full polymerization or hardening.

With the term "fibrous reinforcements" as used throughout the present invention are meant as all types of woven and/or nonwoven textile reinforcements comprising natural and/or synthetic and/or technical textile material such as flax, glass, polyester, polyamide, aramid, carbon, silicon and a combination thereof.

An object of this invention is to provide an epoxy resin curable composition with an adjustable "operating window" from 12 hours to more that 30 days.

Another object of the present invention is formed by curable epoxy resin compositions, which have a reactivity such that they can be used in formulations which can be "B-staged", which means that the reaction has been progressed until before the gelation point, while keeping the impregnated object further processable. So the advancement of the reaction (with increases in Tg and viscosity) will occur at low temperature (about 65⁰C) and that the full cure of the pre-impregnated fibrous reinforcements, in a so called "B-stage" , with the composition of the invention will take place at moderate temperature (not higher than 130⁰C) .

Another object of the invention is formed by the curable epoxy resin compositions which can be suitably used for the manufacturing of composite structure under moderate curing conditions and can be specially designed for use for large fibrous reinforcements such as wind turbine blades, ship/boat- building parts, car-body and aircraft structures.

These objects of the present invention are achieved by a curable or polymerizable epoxy resin characterized in that the hardener part comprises a combination of: (i) at least a liquid carrier, (ii) dicyandiamide and (iii) an amine functional catalyst

Preferred hardener parts to be used according the present invention comprise at least (i) from 40-70 part by weight of a liquid carrier, (ii) from 25-45 part by weight of dicyandiamide and (iii) from 5-25 part by weight of an amine functional catalyst ^{' ■}

More preferred weight ratios of the components (i) , (ii) , and (iii) are from 45-65 part by weight of (i) , from 30-40 part by weight of (ii) and from 10 to 20 of (iii) .

The epoxy resin used in the composition of this invention is a liquid or medium molecular weight solid resin or a mixture thereof. The epoxy resins used could also contain an additive known in the art to improve flexibility and/or the adhesion capacity to the various substrates mentioned earlier in the description.

The preferred epoxy resins for the composition of this invention are the diglycidyl ether of Bisphenol A, and/or Bisphenol F and/or polyglycidyl ethers of phenol/cresol-formaldehyde novolacs, and the like. Example of such resins are: EPIKOTE 828, EPIKOTE 834, EPIKOTE 835, EPIKOTE 836, EPIKOTE 1001, EPIKOTE 1002, EPIKOTE 154, EPIKOTE 164, EPON SU-8 (EPIKOTE, EPON are a .Resolution Performance Products Trademark)

The main feature of the composition according to this invention is the selection of liquid carrier that provides the convenient reactivity and the correct viscosity to maximize the processing parameters for the mixing with the resin, for the impregnation of the fibers or the wetting of the substrate for adhesive applications.

The preferred liquid carriers are polyamines or polyether- polyamines. The most preferred are the polyether-polyamines which can be obtained by reaction of polyethers with phosgene or thionyl chloride followed by amination to give the polyether- amine. The polyether-polyamines employed in accordance with the invention are commercially available (for example) under the name JEFFAMINE (JEFFAMINE is a Huntsman trademark) , such as JEFFAMINE, D400, JEFFAMINE D2000, JEFFAMINE T403, JEFFAMINE T5000 and derivatives based on these JEFFAMINE such as reaction products with epoxy resins. Other poly-etherdiamines based on ethylene or propylene glycol with lower molecular weight are available from BASF, e.g 4,7 dioxadecane-1, 10 diamine or 4,7,10- trioxatridecanel, 13 diamine.

Suitable amine functional catalysts are imidazoles, such as, for example, imidazole, 2-ethylimidazole, 2-phenylimidazole, 1- methylimidazole, l-cyanoethyl2-ethyl-4-methylimidazole, 2-ethyl- 4-methylimidazole or adduct of an imidazole with epoxy resin.

Other suitable amine functional catalysts are tertiary amines, such as benzyldimethylamine or 2,4, 6-tris (dimethylaminomethyl) phenol.

Another class of suitable amine functional catalysts are, for example, urea derivatives, such as N, N-dimethyl-N' - (3-chloro- 4-τnethylphenyl)urea (chlortoluron) , N, N-dimethyl-N'- (4- chlorophenyl) urea (tnonuron) or N, N-dimethyl-N' - (3, 4- dichlorophenyl) urea (diuron) , 2,4-bis (N¹, N¹ -dimethylureido) toluene or 1,4-bis (N¹, N' -dimethylureido) benzene. Commercially available products of this urone family are available as DYHARD Urones from Degussa, e.g. DYHARD UR 200, UR300, and UR 500 (DYHARD is a trademark) .

The above suitable amine functional catalysts are used alone or as a mixture thereof such as for example a mixture of an imidazole and an urone derivative.

It will be appreciated that another aspect of the present inventions is formed by a composite structure derived from at least one curable or polymerisable epoxy resin compositions as herein before defined and in particularly those wherein the epoxy resins composition is selected from a liquid resin or medium molecular weight solid resin or a mixture thereof. Another aspect of the invention is formed by laminated composite structures which comprises fibrous reinforcements as all types of woven and/or nonwoven textile reinforcements comprising natural and/or synthetic and/or technical textile material such ^• as flax, glass, polyester, polyamide, aramid, carbon, silicon and a combination thereof. Still another aspect of the invention is formed by an adhesive composition comprising a curable or polymerizable epoxy resin as herein before specified.

The following examples illustrate the invention however without limiting the scope of these specific embodiments.

Testing and analytical methods used in this invention.

Viscosity, reported in Pa. s, was measured at different temperature by means of a Brookfield LTDV-III viscometer equipped with a thermosel unit. Most measurements were made using spindle 21.

DSC Perkin Elmer DSC-7 Less than 10 mg was taken from the samples for DSC analysis. For all scans closed 50μl aluminium pans were used with a self-made hole in the lid.

Following sequence was applied for determining uncured Tg. 1. Hold at -20⁰C for 5' 2. Heat from -2O⁰C to 100⁰C at 20°C/min

Following sequence was applied for determining cured Tg.

1. Hold for 60 min at 100⁰C

2. Cool from 100⁰C to 20⁰C at 40°C/min 3. Hold for 2 min at 20⁰C

4. Heat from 20⁰C to 200⁰C at 20°C/min

All Tg' s reported are the transition mid-point temperatures.

EXAMPLES Example 1 preparation of curative part based on JEFFAMINE D400.

The ingredients of the curative composition were mixed using a Molteni (DISSMAX) vacuum mixer equipped with a disc saw mixing unit. Charges of 350 g were prepared allowing production of good quality and uniform white creamy paste.

51.8 parts by weight JEFFAMINE D400 (liquid phase) 38.0 parts by weight Dicy DYHARD 100s 10.2 parts by weight DYHARD UR500 (DYHARD is a Trademark from Degussa)

Examples 2 and 3

The preparation of the curative paste were carried out according to the same method as example 1. The composition are given in Table 1. Example 4 epoxy composition based on Example 1. Curative paste of Example 1 and EPIKOTE 834. The resin EPIKOTE 834 was pre-heated at 40⁰C in order to facilitate the mixing. The resin and the curing agent were mixed by hand at a 100 parts resin to 10 parts hardener ratio. Once mixed the composition is stored at 23⁰C and 50%RH. The system stability is followed by looking at the uncured Tg (in ⁰C) versus the storage time (in days) as given in Table 2.

Examples 5 and 6

The composition was in both examples based on EPIKOTE 834 the hardener according to examples 2 and 3 respectively. The same conditions and ratio as for example 4 were applied.

TABLE 1: Curative compositions of Examples 1-3

All expressed in parts hy weight. EPIKURE is a Resolution Performance Products Trademark. TABLE 2: Storage stability of the compositions 4-6

Example 1 is a composition offering a long pot-life at storage temperature (<25°C) , a possibility to be B-staged (pre-gelation temperature at 65 °C) and a moderate cure temperature (90-120°C) Example 2 is a composition offering a long pot-life at storage temperature (<25°C) and a moderate cure temperature (90-120⁰C). Example 3 is a composition offering a limited pot-life at storage temperature (<25°C) and curing at a moderate cure temperature (90-120 ⁰C) .

Claims

STABLE CURABLE EPOXY RESIN COMPOSITIONS AND USES THEREOFC L A I M S

1. A curable or polymerizable epoxy resin composition characterized in that the hardener part comprises a combination of at least :

(i) a liquid carrier, (ii) dicyandiamide and

(iii) an amine functional catalyst the hardenerf (i) + (ii) + (iii) } relative to the epoxy resin being 8 to 20 part by weight, the "operating window" of the composition being between 0.5 to 30 days at room temperature.

2. The curable or polymerizable epoxy resin composition according to claim 1, characterized in that the hardener part comprises a combination of at least :

(i) from 40-70 part by weight of a liquid carrier, (ii) from 25-45 part by weight of dicyandiamide and

(iii) from 5-25 part by weight of an amine functional catalyst.

3. The epoxy composition according to claim 1 characterized in that compound (i) is selected from polyamines or polyether- polyamines.

4. The epoxy composition according to claim 1 characterized in that compound (ii) is ^'dicyandiamide in powder form with a particle size between 1 and 250 microns and preferably lower than 10 microns.

5. The epoxy composition according to claim 1 characterized in that compound (iii) is selected from to the family of the imidazole or urone derivatives .

6. The epoxy composition according to claim 1 characterized in that compound (iii) comprises at least one imidazole-epoxy resin adduct .

7. The epoxy composition according to claim 1 characterized in that compound (i) is selected from polyether-polyamines which are based on polypropylene oxide/polyethylene oxide and diol or triol copolymer.

8. The epoxy composition according to claim 1 characterized in that (i) derives from polyether-polyamines polypropylene oxide/polyethylene oxide and diol copolymer and subsequently reacted with an epoxy resin

9. A composite structure derived from a composition according to any one of claims 1 to 8 characterized in that the epoxy resin is selected from a liquid resin or medium molecular weight solid resin or a mixture thereof.

10. A laminated composite structure according to claim 9 characterized in that it comprises fibrous reinforcements as all types of woven and/or nonwoven textile reinforcements comprising natural and/or synthetic and/or technical textile material such as flax, glass, polyester, polyamide, aramid, carbon, silicon and a combination thereof.

11. The composite structure according to claim 9 in the form of windmill blades, ship/boat-building parts, car-body and aircraft structures.

12. An adhesive composition comprising a composition according to any one of claims 1 to 8.