Heat-curing epoxy resin composition containing non-aromatic ureas as accelerator

Abstract

Heat-curing epoxy resin compositions are characterized by high impact strength, good storage stability, and a low curing temperature. The epoxy resin compositions are suitable for use as a construction shell adhesive and for producing structural foams. They can already be cured in so-called bottom-baking conditions. Furthermore, it has been found that the use of an accelerator of the formula (Ia) or (Ib) results in an increase of the impact strength of heat-curing epoxy resin compositions.

Claims

1. A method of adhesively bonding heat-stable materials with improved impact peel strength, comprising: contacting a first heat-stable material with a heat-curing epoxy resin composition; applying a second heat-stable material to said heat-curing epoxy resin composition on said first heat-stable material; and curing the heat-curing epoxy resin composition at a temperature of from 100 to 220° C. to bond the first and second heat-stable materials together; wherein the heat-curing epoxy resin composition comprises: 10% to 85% by weight, based on the overall weight of the composition, of (A) at least one epoxy resin having on average more than one epoxide group per molecule; 0.1% to 30% by weight, based on the weight of (A), of (B) a dicyandiamide hardener; 0.02% to 0.85% by weight, based on the weight of (A), of (C) an accelerant; 0.1% to 50% by weight, based on the overall weight of the composition, of (D) at least one toughener; 2% to 50% by weight, based on the overall weight of the composition, of (F) at least one filler; and 0.1%-20% by weight, based on the overall weight of the composition, of (G) at least one reactive diluent which carries one or more epoxy groups per molecule; wherein (A) comprises a liquid epoxy resin having the formula (A-II) and optionally a solid epoxy resin of the formula (A-I): ##STR00023## wherein R′″ and R″″ independently of one another are either H or CH.sub.3, and r is from 0 to 1, and ##STR00024## wherein R′ and R″ independent of one another are either H or CH.sub.3, and s is >1.5; wherein (C) is selected from compounds of formula (Ia) and compounds of formula (Ib): ##STR00025## wherein: R.sup.1 is H or an n′-valent aliphatic, cycloaliphatic or araliphatic radical; R.sup.2 and R.sup.3 either each independently of one another are an alkyl group or aralkyl group; or together are a divalent aliphatic radical having 3 to 20 C atoms which is part of an optionally substituted heterocyclic ring having 5 to 8 ring atoms; R.sup.1′ is an n′-valent aliphatic, cycloaliphatic or araliphatic radical; R.sup.2′ is an alkyl group or aralkyl group; R.sup.3′ independently at each occurrence is H or an alkyl group or aralkyl group; and n and n′ are each from 1 to 4; wherein (D) comprises a blocked polyurethane polymer and optionally further comprises one or more of liquid rubbers, epoxy-modified liquid rubbers, and core-shell polymers; and wherein the heat-cured epoxy resin composition provides an impact peel strength between the first and second heat-stable materials that is higher than an impact peel strength of a similar heat-cured epoxy resin composition, which is formulated with components (A), (B), (D), (F), and (G), but not with component (C).

2. The method of claim 1, wherein (A) is present in an amount of 15% to 70% by weight, based on the overall weight of the composition.

3. The method of claim 1, wherein (A) is present in an amount of 15% to 60% by weight, based on the overall weight of the composition.

4. The method of claim 1, wherein (B) is present in an amount of 0.2% to 10% by weight based on the weight of (A).

5. The method of claim 1, wherein n is 1 or 2.

6. The method of claim 1, wherein R.sup.2 and R.sup.3 are each a methyl, ethyl or propyl group.

7. The method of claim 1, wherein n is 2 and R.sup.1 is selected from: an alkylene group having 4 to 10 carbon atoms; ##STR00026## hexamethylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, biuret, or m-xylylene diisocyanate, following removal of the isocyanate groups; and a xylylene group.

8. The method of claim 1, wherein (C) is 1,1-dimethylurea.

9. The method of claim 1, wherein (D) is present in an amount of 0.5% to 40% by weight, based on the overall weight of the composition.

10. The method of claim 1, wherein (D) further comprises a core-shell polymer.

11. The method of claim 1, wherein (D) further comprises a liquid rubber, which is an acrylonitrile/butadiene copolymer terminated with carboxyl groups or (meth)acrylate groups or epoxide groups, or is a derivative thereof.

12. The method of claim 1, wherein the blocked polyurethane polymer has the formula (II): ##STR00027## where Y.sup.1 is a linear or branched polyurethane polymer PU1 terminated with m+m′ isocyanate groups, following the removal of all of the terminal isocyanate groups; Y.sup.2 independently at each occurrence is a blocking group which is eliminated at a temperature above 100° C.; Y.sup.3 independently at each occurrence is a group of the formula (II′) ##STR00028## where R.sup.4 is a radical of an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide, containing a primary or secondary hydroxyl group following the removal of the hydroxide groups and epoxide groups; p is 1, 2 or 3; and m and m′ are each between 0 and 8, with the proviso that m+m′ is from 2 to 8.

13. The method of claim 12, wherein Y.sup.2 is a radical which is selected from the group consisting of ##STR00029## where: R.sup.5, R.sup.6, R.sup.7, and R.sup.8 each independently of one another is an alkyl or cycloalkyl or aryl or aralkyl or arylalkyl group; or R.sup.5 together with R.sup.6, or R.sup.7 together with R.sup.8, form part of a 4- to 7-membered ring which if desired is substituted; R.sup.9, R.sup.9′ and R.sup.10 each independently of one another is an alkyl or aralkyl or aryl or arylalkyl group or is an alkyloxy or aryloxy or aralkyloxy group; R.sup.11 is an alkyl group, R.sup.12, R.sup.13, and R.sup.14 each independently of one another are an alkylene group having 2 to 5 C atoms, which optionally has double bonds or is substituted, or are a phenylene group or a hydrogenated phenylene group; R.sup.15, R.sup.16, and R.sup.17 each independently of one another are H or are an alkyl group or are an aryl group or an aralkyl group; and R.sup.18 is an aralkyl group or is a mono- or polycyclic substituted or unsubstituted aromatic group which optionally contains aromatic hydroxyl groups.

14. The method of claim 12, wherein m is other than 0.

15. The method of claim 1, wherein (G) is selected from the group consisting of: monofunctional glycidyl ethers of monofunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain C.sub.4-C.sub.30 alcohols; difunctional glycidyl ethers of difunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain C.sub.2-C.sub.30 alcohols; trifunctional or polyfunctional glycidyl ethers of trifunctional or polyfunctional, saturated or unsaturated, branched or unbranched, cyclic or open-chain alcohols; glycidyl ethers of phenol compounds and aniline compounds; epoxidized amines; epoxidized monocarboxylic or dicarboxylic acids; and epoxidized difunctional or trifunctional polyether polyols.

16. The method of claim 15, wherein: the monofunctional glycidyl ethers are selected from the group consisting of butanol glycidyl ether, hexanol glycidyl ether, 2-ethylhexanol glycidyl ether, allyl glycidyl ether, tetrahydrofurfuryl glycidyl ethers, furfuryl glycidyl ethers, and trimethoxysilyl glycidyl ether; the difunctional glycidyl ethers are selected from the group consisting of ethylene glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, octanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and neopentyl glycol diglycidyl ether; the trifunctional or polyfunctional glycidyl ethers are selected from the group consisting of epoxidized castor oil, epoxidized trimethylolpropane, epoxidized pentaerythritol, and polyglycidyl ethers of aliphatic polyols; the glycidyl eithers of phenol compounds and aniline compounds are selected from the group consisting of phenyl glycidyl ether, cresol glycidyl ether, p-tert-butylphenyl glycidyl ether, nonylphenol glycidyl ether, 3-n-pentadecenyl glycidyl ether, and N,N-diglycidylaniline; the epoxidized amines are selected from the group consisting of N,N-diglycidylcyclohexylamine; the epoxidized monocarboxylic or dicarboxylic acids are selected from the group consisting of: glycidyl neodecanoate, glycidyl methacrylate, glycidyl benzoate, diglycidyl phthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, and diglycidyl esters of dimeric fatty acids; and the epoxidized difunctional or trifunctional polyether polyols are selected from the group consisting of polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether.

17. The method of claim 16, wherein (G) is selected from the group consisting of hexanediol diglycidyl ether, cresol glycidyl ether, p-tert-butylphenyl glycidyl ether, polypropylene glycol diglycidyl ether, and polyethylene glycol diglycidyl ether.

18. The method of claim 1, wherein the heat-curing epoxy resin composition is free from organic carboxylic acids.

19. The method of claim 1, wherein the heat-curing epoxy resin composition further comprises at least one chemical blowing agent.

20. The method of claim 1, wherein the heat-curing epoxy resin composition is free of an aromatic urea compound.

21. The method of claim 1, wherein the heat-cured epoxy resin composition provides an impact peel strength between the first and second heat-stable materials that is at least 15% higher than an impact peel strength of a similar heat-cured epoxy resin composition, which is formulated with components (A), (B), (D), (F), and (G), but not with component (C).

22. The method of claim 1, wherein a fracture energy of the heat-cured epoxy resin composition, as measured at 23° C. according to ISO 11343, is at least 16.3 J.

Description

EXAMPLES

(1) Curing Agents for Epoxy Resins

N,N-Dimethylurea (=1,1-dimethylurea)(“asym DMH”)

(2) n=1, R.sup.1=H, R.sup.2=R.sup.3=CH.sub.3

(3) N,N-Dimethylurea was obtained from Aldrich, Switzerland.

N′,N′-Dimethyl-N-butylurea (=3-butyl-1,1-dimethylurea) (“BuDMH”)

(4) n=1, R.sup.1=n-butyl, R.sup.2=R.sup.3=CH.sub.3

(5) 50 ml of tetrahydrofuran (THF) and 20.0 g of an approximately 33% strength solution of dimethylamine in ethanol (Fluka) (about 146 mmol of amine) were charged to a 100 ml two-neck flask with reflux condenser. Subsequently, over 30 minutes, 14.5 g of butyl isocyanate (Fluka) (about 146 mmol of NCO) were slowly added dropwise, producing a slight exothermic response. After 3 hours of stirring at ambient temperature, the solvent was stripped off on a rotary evaporator at 80° C. under vacuum. This gave about 21.0 g of a slightly yellowish, low-viscosity liquid. The desired adduct was used further without other purification.

Hexamethylenebis(1,1-dimethylurea) (=1,1′-(hexane-1,6-diyl)bis(3,3-dimethylurea) (“HDIDMH”)

(6) n=2, R.sup.1=—(CH.sub.2).sub.6—, R.sup.2=R.sup.3=CH.sub.3

(7) 50 ml of THF and 20.0 g of an approximately 33% strength solution of dimethylamine in ethanol (Fluka) (about 146 mmol of amine) were charged to a 100 ml two-neck flask with reflux condenser. Subsequently, over 30 minutes, 10.0 g of hexamethylene diisocyanate (Fluka) (about 119 mmol of NCO) were added slowly dropwise, producing a slight exothermic response and immediately precipitating a white solid. After 2 hours of stirring at ambient temperature, the suspension was filtered. The filter product was washed 3× with 20 ml of THF each time. The crude product obtained was dried under vacuum at 80° C. for 3 h. The desired product was obtained in the form of 12.3 g of a white powder.

(8) Adduct of Desmodur N-100 with dimethylurea (“N100DMH”)

(9) n=3, R.sup.1=formula (IX), R.sup.2=R.sup.3=CH.sub.3

(10) ##STR00020##

(11) 30 ml of THF and 20.0 g of an approximately 33% strength solution of dimethylamine in ethanol (Fluka) (about 146 mmol of amine) were charged to a 100 ml two-neck flask with reflux condenser. Subsequently, over 30 minutes, 18.7 g of the hexamethylene diisocyanate trimer Desmodur N-100 (Bayer) (about 118 mmol of NCO) in 20 ml of THF were slowly added dropwise, producing a slight exothermic response. After 2 hours of stirring at ambient temperature, the solvent and also the excess dimethylamine were evaporated first at 100° C. under a stream of nitrogen and collected in a gas wash bottle with acidic water, followed by further drying on a rotary evaporator at 80° C. under vacuum. Decanting from the flask gave about 21.5 g of a virtually colorless, high-viscosity product. The desired adduct was used further without other purification.

(12) Benzyldimethylurea (“BzDMH”)

(13) n=1, R.sup.1=—(CH.sub.2)—C.sub.6H.sub.5, R.sup.2=R.sup.3=CH.sub.3

(14) 15.0 g (139.5 mmol) of N,N-dimethylcarbamoyl chloride and 80 ml of dioxane were charged to a 250 ml two-neck flask with reflux condenser. Subsequently 13.66 g (135 mmol) of triethylamine and 14.89 g (139 mmol) of benzylamine were added. After the exothermic response had subsided, the mixture was stirred at 90° C. for 5 h, during which there was rapid formation of a slightly orange suspension. The resulting suspension was filtered while hot. The turbidity which developed as the solution cooled was removed by further filtration. The solvent was stripped off on a rotary evaporator at 60° C. This gave above 14.0 g of a slightly orange, waxlike solid.

3,3′-(4-Methyl-1,3-phenylene)bis(1,1-dimethylurea) (“TDIDMH”)

(15) n=2, R.sup.1=formula (X), R.sup.2=R.sup.3=CH.sub.3

(16) ##STR00021##

(17) 3,3′-(4-Methyl-1,3-phenylene)bis(1,1-dimethylurea) was obtained from Fluka, Switzerland.

N,N′-Dimethylurea (=1,3-dimethylurea) (“sym DMH”)

(18) n=1, R.sup.1=CH.sub.3, R.sup.2=H, R.sup.3=CH.sub.3

(19) N,N′-Dimethylurea was obtained from Fluka, Switzerland.

N,N,N′,N′-Tetramethylurea (=1,1,3,3-tetramethylurea) (“TMH”)

(20) ##STR00022##

(21) N,N,N′,N′-Tetramethylurea was obtained from Fluka, Switzerland.

(22) TABLE-US-00001 TABLE 1 Raw materials used. D.E.R. 330 (Bisphenol A diglycidyl ether = “DGEBA”) Dow Polypox R7 (tert-butylphenyl glycidyl ether) = “Polypox”) UPPC Polydis 3614, epoxy-resin-modified CTBN (= “Polydis‘”’) Struktol Dicyandiamide (= “Dicy”) Degussa PolyTHF 2000 (difunctional polybutylene glycol BASF (OH equivalent weight = about 1000 g/OH equivalent) Liquiflex H (hydroxyl-terminated polybutadiene) Krahn (OH equivalent weight = about 1230 g/OH equivalent) Isophorone dicyanate (= “IPDI”) Evonik Cardolite NC-700 (Cardanol, meta-substituted Cardolite alkenyl-mono-phenol)

(23) Preparation of a Toughness Improver (“D-1”)

(24) 150 g of poly-THF 2000 (OH number 57 mg/g KOH) and 150 of Liquiflex H (OH number 46 mg/g KOH) were dried at 105° C. under vacuum for 30 minutes. When the temperature had been reduced to 90° C., 61.5 g of IPDI and 0.14 g of dibutyltin dilaurate were added. The reaction was continued at 90° C. under vacuum until the NCO content was constant at 3.10% after 2.0 h (calculated NCO content: 3.15%). Then 96.1 g of Cardanol were added as a blocking agent. Stirring was continued at 105° C. under vacuum until the NCO content had dropped, after 3.5 h, below 0.1%. The product in this form was used as toughness improver D-1.

(25) Preparation of the Compositions

(26) In accordance with the details in table 2, the reference compositions Ref.1-Ref. 4 and also the inventive compositions 1, 2, 3, 4 and 5 were prepared. In the reference examples there were in each case no accelerant (Ref.1) or accelerants not conforming to the formula (Ia) used, whereas this was the case for examples 1, 2, 3, 4 and 5. The amount of accelerants used was calculated such that the overall concentration of urea groups was constant.

(27) Test Methods:

(28) Tensile Shear Strength (TSS) (DIN EN 1465)

(29) The specimens were produced from the above-described compositions and with electrolytically galvanized DC04 steel (eloZn) with dimensions of 100×25 5×0.8 mm, the bond area being 25×10 mm with a layer thickness of 0.3 mm. Curing took place for 30 minutes at 180° C. (“TSS.sub.180”), or for 10 min at 165° C. (“TSS.sub.165”), in a forced-air oven. Measurement took place after cooling to room temperature, after one day, with a pulling speed of 10 mm/min.

(30) Impact Peel Energy (ISO 11343)

(31) The specimens were produced from the above-described compositions and with electrolytically galvanized DC04 steel (eloZn) with dimensions of 90×20×0.8 mm, the bond area being 20×30 mm with a layer thickness of 0.3 mm. Curing took place for 30 minutes at 180° C. The impact peel energy was measured in each case at 23° C. The peeling speed was 2 m/s. The fracture energy (“FE”) reported, in joules, is the area under the measurement curve (from 25% to 90%, in accordance with ISO 11343).

(32) As the increase in impact toughness relative to reference example Ref.1, the “Δ.sub.FE” value in the table was determined in accordance with the following formula:
Δ.sub.FE=[FE/FE(Ref.1)]−1.

(33) Viscosity

(34) The adhesive samples were measured on a Bohlin CVO 120 plate/plate viscometer (diameter 25 mm, gap dimension 1 mm), frequency 5 Hz, 0.01 deflection, temperature 23-53° C., 10° C./min. The viscosity in this case was determined as the complex viscosity at 25° C. from the measurement plot.

(35) Following their preparation, the adhesives were stored at 25° C. for 1 day or at 60° C. for one week. After they had cooled to room temperature, the viscosity was measured, and was reported as “Visc (Id, 25° C.)”, or as “Visc (1 w, 60° C.)” in table 2. Viscosity increase (Δ.sub.visc) was calculated in accordance with the formula
[Visc (1w, 60° C.)/visc (1d, 25° C.)]−1.

(36) The results of these tests are summarized in table 2.

(37) TABLE-US-00002 TABLE 2 Compositions and results. Ref. 1 Ref. 2 Ref. 3 Ref. 4 1 2 3 4 5 DGEBA [pbw.sup.1] 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 Polypox [pbw.sup.1] 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Polydis [pbw.sup.1] 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 D-1 [pbw.sup.1] 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 Dicy [pbw.sup.1] 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 TDIDMH [pbw.sup.1] 0.51 TMH [pbw.sup.1] 0.45 sym-DMH [pbw.sup.1] 0.34 asym-DMH [pbw.sup.1] 0.34 BuDMH [pbw.sup.1] 0.56 HDIDMH [pbw.sup.1] 0.50 N100DMH [pbw.sup.1] 0.79 BzDMH [pbw.sup.1] 0.69 Filler mixture [pbw.sup.1] 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 19.0 TTS.sub.180 [MPa] 21.4 21.7 21.4 21.7 21.7 22.2 22.0 21.8 22.4 TTS.sub.165 [MPa] n.m..sup.2 20.1 n.m..sup.2 n.m..sup.2 19.8 21.2 21.1 21.0 21.1 FE [J] 14.2 16.1 13.9 14.4 16.5 17.5 17.4 16.3 17.3 Δ.sub.FE[%] 13 −2 1 16 23 23 15 22 Visc (1 d, 25° C.)[mPas] 395 350 345 360 255 310 360 320 335 Visc (1 w, 60° C.)[mPas] 395 1340 420 455 305 325 370 335 405 Δ.sub.visc [%] 283 22 26 20 5 3 5 21 .sup.1pbw = parts by weight .sup.2n.m. = not measurable

(38) The examples Ref.1, Ref.3, and Ref.4 show such inadequate curing at 165° that the specimens fell apart as early as during the removal of the fixing clamps following withdrawal from the oven; accordingly, it was not possible to measure a tensile shear strength. In these cases, the adhesive was still of low viscosity even after cooling to room temperature. Ref. 2, based on a urea with aromatic radicals, does exhibit good cure behavior even at 165° C., but has a very low storage stability.

(39) The inventive examples 1, 2, 3, 4, and 5 exhibit good mechanical values even after curing at 165° C., and also good storage stability.

(40) Furthermore, it is apparent from a comparison of examples Ref.1 with Ref.4 or 1 that it is possible when using accelerants of the formula (Ia) in adhesives which already have a high degree of impact toughness to achieve further sharp improvement in impact toughness, while this is not the case for the corresponding aliphatic accelerants that do not conform to the formula (Ia). In the case of the aromatic accelerants (Ref.2), it was in fact also possible to find this kind of increase in impact toughness, but not to the same extent.