METHOD FOR CURING CURABLE COMPOSITIONS

Abstract

The invention relates to a process for the curing of latently reactive, heat-curable compositions which do not harden at room temperature. The composition includes a polymer obtainable via reaction of certain compounds having two aldehyde groups with polyacrylate compounds having two or more acrylate groups, and also a compound which bears at least two thiol groups.

Claims

1. A process for the curing of curable compositions the process comprising: providing at least one heat-curable composition, and hardening the composition by heating to temperatures greater than or equal to 60° C., wherein the curable composition comprises: (a) at least one polymer (S) obtainable via reaction of at least one compound having two aldehyde groups and of at least one acrylate compound (B) selected from the group consisting of acrylate compounds having more than two acrylate groups (By) and diacrylate compounds (B2), wherein the at least one compound having two aldehyde groups is an aromatic dialdehyde having a molecular structure wherein the bonds to the two aldehyde groups are at an angle to one another, and (c) at least one compound (C) which bears at least two thiol groups.

2. The process according to claim 1, wherein the curable composition exhibits a viscosity increase of less than 100 000 mPa s within a period of 4 h at room temperature.

3. The process according to claim 1, wherein the compound having two or more aldehyde groups is selected from the group consisting of phthalaldehyde, isophthalaldehyde, and a mixture of these.

4. The process according to claim 1, wherein the diacrylate compounds (B2) are difunctional acrylates of one of alkanediols, cycloalkanediols, lower polyalkylene glycols and diamines, and wherein the acrylate compounds (By) are selected from the group consisting of polyether acrylates, polyester acrylates, acrylated polyacrylatols, urethane acrylates, and acrylic esters of alkoxylated polyols.

5. The process according to claim 1, wherein the acrylate compounds (By) and (B2) are selected from the group consisting of ethylene glycol diacrylate, 1,2-propanediol diacrylate, 1,3-propanediol diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, 1,8-octanediol diacrylate, neopentyl glycol diacrylate, 1,1-cyclohexanedimethanol diacrylate, 1,2-cyclohexanedimethanol diacrylate, 1,3-cyclohexanedimethanol diacrylate, 1,4-cyclohexanedimethanol diacrylate, 1,2-cyclohexanediol diacrylate, 1,3-cyclohexanediol diacrylate, 1,4-cyclohexanediol diacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, N,N′-bisacryloyl-2,2-diaminoethane, N,N′-bisacryloyl-1,6-diaminohexane, N,N′-bisacryloylpiperazine, trimethylolpropane triacrylate, ditrimethylolpropane pentaacrylate, ditrimethylolpropane hexaacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol diacrylate, glycerol triacrylate, di- or polyacrylates of sugar alcohols, di- or polyacrylates of polyTHF with molecular weight from 162 to 2000, di- or polyacrylates of poly-1,3-propanediol with molecular weight from 134 to 1178, di- or polyacrylates of polyethylene glycol with molecular weight from 106 to 898, urethane di- and polyacrylates and polycarbonate di- and polyacrylates.

6. The process according to claim 1, wherein the acrylate compound is a diacrylate compound (B2) and is selected from the group consisting of ethylene glycol diacrylate, 1,2-propanediol diacrylate, 1,3-propanediol diacrylate, 1,4-butanediol diacrylate, and 1,6-hexanediol diacrylate.

7. The process according to claim 1, wherein the at least one compound (C) having at least two thiol groups are one of compounds (C1) of the formula ##STR00010## or compounds (C2) of the formula ##STR00011## or compounds (C3) of the formula ##STR00012## in which Z.sup.1, Z.sup.2, Z.sup.3, Z.sup.4, Z.sup.5 and Z.sup.6 are in each case mutually independently a single bond or a moiety of the formula —(C═O)—R.sup.3—S—, R.sup.3 is a divalent C.sub.1- to C.sub.6-alkylene moiety, p, q, r, s, t, u are in each case mutually independently zero or a positive integer from 1 to 5, each X.sub.i for i=from 1 to p, from 1 to q, from 1 to r, from 1 to s, from 1 to t and from 1 to u can be selected mutually independently from the group consisting of —CH.sub.2—CH.sub.2—O—, —CH.sub.2—CH(CH.sub.3)—O—, —CH(CH.sub.3)—CH.sub.2—O—, —CH.sub.2—C(CH.sub.3).sub.2—O—, —C(CH.sub.3).sub.2—CH.sub.2—O—, —CH.sub.2—CHVin-O—, —CHVin-CH.sub.2—O—, —CH.sub.2—CHPh-O— and —CHPh-CH.sub.2—O—, wherein Ph is phenyl and Vin is vinyl, wherein when the at least one compound (C) comprises compound (C1) at least four of the moieties Z.sup.1 to Z.sup.6 are a group of the formula —(C═O)—R.sup.3—S—, and wherein when the at least one compound (C) comprises one of compounds (C2) or (C3) at least three moieties Z.sup.1 to Z.sup.4 are a group of the formula —(C═O)—R.sup.3—S—.

8. The process according to claim 1, wherein the at least one compound (C) having at least two thiol groups are di- or trifunctional compounds (C4) of the formula ##STR00013## in which R.sup.1 and R.sup.2 are in each case mutually independently hydrogen or a C.sub.1- to C.sub.4-alkyl moiety, R.sup.4 is methylene or 1,2-ethylene, k, l, m, n are in each case mutually independently zero or a positive integer from 1 to 5 each Y.sub.i for i=from 1 to k, from 1 to l, from 1 to m, and from 1 to n can be selected mutually independently from the group consisting of —CH.sub.2—CH.sub.2—O—, —CH.sub.2—CH(CH.sub.3)—O—, —CH(CH.sub.3)—CH.sub.2—O—, —CH.sub.2—C(CH.sub.3).sub.2—O—, —C(CH.sub.3).sub.2—CH.sub.2—O—, —CH.sub.2—CHVin-O—, —CHVin-CH.sub.2—O—, —CH.sub.2—CHPh-O— and —CHPh-CH.sub.2—O—, wherein Ph is phenyl and Vin is vinyl.

9. The process according to claim 1, wherein the at least one compound (C) is selected from the group consisting of ethylene glycol di(3-mercaptopropionate) (GDMP), trimethylolpropane tri(3-mercaptopropionate) (TMPMP), trimethylolpropane trimercaptoacetate (TMPMA), 3-mercaptopropionic ester of poly-1,2-propylene glycol with molar mass from 500 to 2500 g/mol, 3-mercaptopropionic ester of ethoxylated trimethylolpropane with molar mass up to 1500 g/mol, pentaerythritol tetra(3-mercapotopropionate) (PETMP), pentaerythritol tetramercaptoacetate (PETMA), dipentaerythritol tetra(3-mercaptopropionate), dipentaerythritol tetramercaptoacetate, dipentaerythritol penta(3-mercaptopropionate), dipentaerythritol pentamercaptoacetate, dipentaerythritol hexa(3-mercaptopropionate), dipentaerythritol hexamercaptoacetate, ditrimethylolpropane tetra(3-mercaptopropionate), ditrimethylolpropane tetramercaptoacetate, and alkoxylated products of these.

10. The process according to claim 1, wherein the curable composition further comprises a catalyst (E) which can accelerate the addition reaction between the thiol groups, wherein the catalyst (E) is selected from the group consisting of primary, secondary, and tertiary amines, primary, secondary, and tertiary phosphines, quaternary ammonium and phosphonium salts, imines, and iminium salts.

11. The process according to claim 1, wherein the process is selected from the group consisting of injection molding, injection-compression molding, flow molding, reaction injection molding (RIM), RTM (resin transfer molding), VARTM (vacuum assisted RTM), tape layup processes, coil coating, filament winding, manual lamination, pultrusion, hot reactive adhesive bonding, and high-temperature-hardening coating processes.

12. The process according to claim 1, wherein the curable composition comprises: (a) from 10 to 80% by weight of the polymer (S), (b) in total from 0 to 80% by weight of at least one nonpolymeric compound selected from compounds (S1) having an α-(1′-hydroxyalkyl)acrylate group and compounds (S2) having two or more α-(1′-hydroxyalkyl)acrylate groups, (c) from 10 to 70% by weight of the compound (C), (d) from 0 to 60% by weight of at least one reactive diluent (D) having a number-average molar mass M.sub.n that is less than 1000 g/mol, (f) from 0 to 10% by weight of at least one photoinitiator (F), wherein the sum is always 100% by weight, wherein the stoichiometric ratio of thiol groups in (C) to acrylate groups in (S), (S1), and (S2) is from 0.2:1 to 3.8:1.

13. The process according to claim 1, further comprising producing moldings from the cured composition, wherein the composition is introduced by means of VARTM technology into a mold for hardening to give the molding.

14. A curable composition suitable for a process according to claim 1, wherein the composition is curable via heating to temperatures greater than or equal to 60° C. and comprises: (a) at least one polymer (S) obtainable via reaction of at least one compound having two aldehyde groups and of at least one acrylate compound (B) selected from the group consisting of acrylate compounds having more than two acrylate groups (By) and diacrylate compounds (B2), wherein the at least one compound having two aldehyde groups is an aromatic dialdehyde having a molecular structure wherein the bonds to the two aldehyde groups are at an angle to one another, and (c) at least one compound (C) which bears at least two thiol groups.

15. The curable composition according to claim 14, wherein the at least one compound having two aldehyde groups is selected from the group consisting of phthalaldehyde, isophthalaldehyde, and a mixture of these.

16. (canceled)

17. A cured composition that can be produced via the process according to claim 1.

18. The cured composition according to claim 17, wherein the cured composition is a polymer composite material.

19. The cured composition according to claim 18, wherein the cured composition is one of a glass fiber composite material or a carbon fiber composite material.

20. The curable composition according to claim 14 further comprising: (b) at least one compound (S1) having an α-(1′-hydroxyalkyl)acrylate group, (d) at least one reactive diluent (D) with number-average molar mass Mn that is less than 1000 g/mol, (e) at least one catalyst (E) which can accelerate the addition reaction between thiol groups and acrylate groups, and (f) at least one photoinitiator (F).

Description

EXAMPLES

Example 1: Production of the Binder of the Invention, Resin A

[0212] DABCO (1,4-diazabicyclo[2.2.2]octane; 0.0375 mol; 4.2065 g) was added to a suspension of 1,4-butanediol diacrylate (0.900 mol; 178.3942 g) and isophthalaldehyde (0.750 mol; 100.5990 g) in THF (150 ml). The resultant mixture was stirred at 50° C. for 48 h and then THF was removed in vacuuo. The residue was taken up in ethyl acetate and washed with 10% HCl. The organic fraction was dried over MgSO.sub.4, and the solvent was removed in vacuuo (80° C., 1 mbar). The product was obtained in the form of a viscous, clear, and colorless liquid.

Example 2 (Comparison), Resin B

[0213] DABCO (0.075 mol; 8.413 g) was added to a suspension of 1,4-butanediol diacrylate (1.800 mol; 356.788 g) and terephthalaldehyde (1.500 mol; 201.198 g) in tetrahydrofuran (THF, 300 mL). The resultant mixture was stirred at 60° C. for 48 h. THF was then removed in vacuuo. The remaining mixture was taken up in ethyl acetate and washed with 10% HCl in order to remove the catalyst residues. The organic fraction was then dried over magnesium sulfate (MgSO.sub.4), and filtered, and the solvent was removed in vacuuo. For further purification the mixture was treated at 80° C. and 1 mbar for 12 h.

[0214] Gel permeation chromatography (GPC) in THF with PMMA standard gave M.sub.w 1100 g/mol and M.sub.n 910 g/mol. The product was a clear, yellow viscous liquid.

Example 3: Hardening

[0215] 9 g of resin λ=component 1 (binder)

[0216] 10.4 g of pentaerythritol tetrakis(3-mercaptopropionate) (crosslinking agent) mixed with 170 mg of PC-Kat® NP112 (N-methyldicyclohexylamine, catalyst)=component 2

[0217] Components 1 and 2 were Mixed.

[0218] No hardening was observed at room temperature for >16 h (long pot life).

[0219] Very rapid hardening (“snap cure”) takes place in less than 1 h at 70° C.

[0220] The product is a solid, transparent, clear and colorless material with Shore hardness 88 A and 56 D.

Example 4: Comparative Example

[0221] 9 g of resin B=component 3 (binder)

[0222] 10.4 g of pentaerythritol tetrakis(3-mercaptopropionate) (crosslinking agent) mixed with 80 mg of N-methyl-dicyclohexylamine (catalyst)=component 4

[0223] Component 3 was Mixed with Component 4.

[0224] After 2 h: tack-free hardening at room temperature; Shore A hardness 76.

[0225] When 170 mg of catalyst were used instead of 80 mg, tack-free curing in bulk takes place at room temperature within as little as 20 minutes in a highly exothermic reaction. This gives an irregular surface with many undesired blisters.

[0226] The use of the system of the invention therefore gives a longer pot life with a two-step hardening profile, whereas the comparative example hardens after only a short time at room temperature.

Example 5

[0227] The initial charge comprises a mixture made of 201 g (1.5 mol) of isophthalaldehyde, 148 g (0.5 mol) of trimethylolpropane triacrylate, 192 g (1.5 mol) of butyl acrylate, and 3.74 g (0.0333 mol) of DABCO. The mixture is stirred at 60° C. for 48 hours.

[0228] The product has low to moderate viscosity.

[0229] Gel permeation chromatography (THF): Mn=680; Mw=1220;

[0230] Polydispersity 1.8

Example 6: Hardening

[0231] Hardening was carried out with the components specified in Table 1, using the catalyst still present from example 5.

[0232] Hardening can be achieved in from 5 to 60 minutes (typically 30 minutes) at 70° C. or in from 1 to 5 minutes at 120° C.

[0233] The glass transition temperatures of the hardened products were as set out in table 1.

TABLE-US-00001 TABLE 1 Polymer from ex. 5 [g] BADGE [g] PE-SH TMP-SH Tg [° C.] 6A 10 — 10 — 50.0 6B 10 — — 10 40.3 6C 10 10 10 — 21.5 6D 10 10 — 10 Tg: Glass transition temperature, determined via differential scanning calorimetry (ASTM 3418/82, “midpoint temperature”) BADGE: bisphenol A diglycidyl ether PE-SH: pentaerythritol tetrakis(3-mercaptopropionate) TMP-SH: trimethylolpropane tris(3-mercaptopropionate)

Example 7

[0234] The initial charge comprises a mixture made of 134 g (1 mol) of isophthalaldehyde, 396 g (2 mol) of butanediol diacrylate, and 8.98 g (0.08 mol) of DABCO. The mixture is stirred at 60° C. for 48 h.

[0235] The product is viscous.

[0236] Gel permeation chromatography (THF): Mn=770; Mw=1330;

[0237] Polydispersity 1.73

Example 8

[0238] 1.44 g of benzoic acid were admixed with 80 g of product from example 7, and the mixture was stirred at 60° C. for 3 h.

Example 9

[0239] 1.35 g of benzoic acid were mixed with 150 g of product from example 7, and the mixture was stirred at 60° C. for 2 h.

Example 10: Hardening

[0240] Hardening was carried out with the components specified in Table 2, using the catalyst still present respectively from examples 7 to 9.

[0241] Hardening can be achieved in from 5 to 60 minutes (typically 30 minutes) at 70° C. or in from 1 to 5 minutes at 120° C.

[0242] The glass transition temperatures of the hardened products were as set out in table 2.

TABLE-US-00002 TABLE 2 Polymer Polymer Polymer from from from Tg ex. 7 [g] ex. 8 [g] ex. 9 [g] PE-SH TMP-SH [° C.] 10A 10 — — 10 — 38.0 10B 10 — —  8 — 45.8 10C 10 — — — 10 25.2 10D 10 — — —  8 16.5 10E — 10 — 10 — 26.1 10F — 10 —  8 — 17.3 10G — — 10 10 — 35.3 10H — — 10  8 — 22.2 10I — — 10 — 10 11.7