RAPID CURING EPOXY-RESIN COMPOSITION FOR FIBER-MATRIX SEMIFINISHED PRODUCTS

Abstract

The present invention relates to an epoxy-resin composition as matrix component for sheet molding compounds (SMC) and/or bulk molding compounds (BMC), comprising a resin component comprising at least one epoxy resin and a hardener component comprising at least one aminoalkylimidazole compound, at least one diazabicycloalkylen compound and at least one latent hardener. In said epoxy-resin composition, the amount of the aminoalkylimidazole compounds used is in the range from 0.007 to 0.025 mol per mole of epoxy groups of the entire composition. The invention also relates to a fiber-matrix-semifinished-product composition (SMC composition or BMC composition) with, as matrix component, the epoxy-resin composition mentioned, and with, suspended therein, short reinforcement fibers with an average length of from 0.3 to 5.0 cm. The invention also relates to the corresponding semisolid fiber-matrix composite, in particular to the semisolid SMC and to the corresponding cured fiber-matrix semifinished product, in particular the cured SMC.

Claims

1. An epoxy-resin composition comprising a resin component (A) which comprises at least one epoxy resin (A1), and a hardener component (B) which comprises at least one aminoalkylimidazole compound (B1), at least one latent hardener (B2) and at least one diazabicycloalkylen compound of the general formula I (B3) ##STR00003## where X and Y are respectively mutually independently an alkylen group, preferably having from 3 to 5 carbon atoms, where the amount of the aminoalkylimidazole compounds (B1) used is in the range from 0.007 to 0.025 mol per mole of epoxy groups of the entire composition, and where the total amount of primary aliphatic amine groups of the aminoalkylimidazole compounds (B1) and any further primary amines optionally comprised does not exceed a proportion of 0.09 mol per mole of epoxy groups of the entire composition.

2. The epoxy-resin composition according to claim 1, where the epoxy resin (A1) is a diglycidyl ether of monomeric or oligomeric diol, where the diol is one selected from the group consisting of bisphenol A or bisphenol F, or hydrogenated bisphenol A or bisphenol F.

3. The epoxy-resin composition according to claim 1, where the aminoalkylimidazole compound (B1) is an aminoalkylimidazole compound of the general formula II ##STR00004## where R1 is a hydrogen atom, an alkyl group, an aryl group, or an arylalkyl group, R2 and R3 are respectively mutually independently a hydrogen atom or an alkyl group, and R4 is an aminoalkyl group.

4. The epoxy-resin composition according to claim 3, where R1 is a hydrogen atom, an alkyl group having from 1 to 4 carbon atoms, an aryl group having from 3 to 7 carbon atoms, or an arylalkyl group having from 4 to 10 carbon atoms, R2 and R3 are respectively mutually independently a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms, and R4 is an aminoalkyl group having from 2 to 4 carbon atoms.

5. The epoxy-resin composition according to claim 1, where the latent hardener (B2) is dicyandiamide.

6. The epoxy-resin composition according to claim 1, where the amount of the diazabicycloalkylen compounds of the general formula I (B3) used is in the range from 0.5 to 3.0% by weight based on the amount of epoxy resin (A1).

7. The epoxy-resin composition according to claim 1, where the diazabicycloalkylen compound of the general formula I (B3) is 7,8-diazabicyclo[5,4,0]undec-7-ene (DBU) or 1,5-diazabicyclo[4,3,0]non-5-ene or a mixture thereof.

8. The epoxy-resin composition according to claim 1, where the epoxy-resin composition comprises, as further constituent of the resin component (A), alongside the epoxy resin (A1), a reactive diluent (A2).

9. The epoxy-resin composition according to claim 1, where the epoxy-resin composition comprises, as further constituent short reinforcement fibers (C) with an average length of from 0.3 to 5.0 cm suspended in the epoxy-resin composition.

10. The epoxy-resin composition according to claim 9, where the short reinforcement fibers (C) have an average length of from 1.2 to 5.0 cm.

11. A process for producing an epoxy-resin composition, comprising the mixing of the constituents of the epoxy-resin composition according to claim 1 at a temperature at which the epoxy resin (A1) used does not react significantly with the latent hardener (B2) used.

12. A process for producing matured semisolid fiber-matrix semifinished product comprising the provision of an epoxy-resin composition according to claim 9 and the maturing of the composition at a temperature at which, for at least the duration of the maturing time, the epoxy resin (A1) used does not react significantly with the latent hardener (B2) used, where the maturing time is the period that starts with the provision of the epoxy-resin composition according to claim 9 and ends at the point in time from which the viscosity of a specimen of 2 g of the corresponding epoxy-resin composition rapidly heated at 0.5 C./sec to 140 C. is then never less than 0.5 Pa*sec.

13. A matured semisolid fiber-matrix semifinished product which can be produced by the process according to claim 12.

14. A cured fiber-matrix semifinished product which can be produced via curing of the semisolid fiber-matrix semifinished product according to claim 13.

15. The use of the epoxy-resin composition according to claim 9 for producing semisolid sheet molding compounds or for producing cured sheet molding compounds.

16. The use of an epoxy-resin composition according to claim 1 as matrix component for producing semisolid sheet molding compounds or for producing cured sheet molding compounds.

Description

EXAMPLES

Example 1

[0074] Production of Epoxy-Resin Compositions E1 to E11 (of the Invention) and C1 to C6 (for Comparison)

[0075] In each case, 100 g of DEGBA (Epilox A 18-00, Leuna Harze GmbH, EEW=180 g/eq) were mixed together with 6.5 g of DICY (Dyhard 100 SH, AlzChem, Mw 84 g/mol) and 1 g (0.014 mol per mole of epoxy group in the entire epoxy-resin composition) of API (Lupragen API, BASF SE) and a curing accelerator in a mixing apparatus at room temperature (comparison example C1 is without curing accelerator). Table 1 collates the constituents including the various used curing accelerators, and also the amounts of these (in g per 100 g of the epoxy resin), for the hardener components of the compositions E1 to E5 and C1 to C4.

TABLE-US-00001 TABLE 1 Composition of the hardener component for epoxy- resin compositions C1 to C4 and E1 to E5 Dyhard DICY API UR500 TMG DMP30 DBU DBN C1 6.5 1 C2 6.5 1 1 C3 6.5 1 1 C4 6.5 1 1 E1 6.5 1 1 E2 6.5 1 2 E3 6.5 1 0.5 E4 6.5 1 0.75 E5 6.5 1 1

Example 2

[0076] Measurement of Glass Transition Temperature and of Viscosity for the Epoxy-Resin Compositions E1 to E3, E5 and C1 to C4 Over the Course of Time

[0077] Differential scanning calorimetry (DSC) was used in accordance with the standard DIN 53765 to measure the glass transition temperature for the epoxy-resin compositions E1 to E11 and C1 to C4 immediately after the mixing of the constituents of the respective epoxy-resin compositions, and then in each case once daily during the storage of the corresponding epoxy-resin compositions at 25 C. Table 2 collates the glass transition temperatures thus determined as a function of the storage time for the respective epoxy-resin compositions E1 to E3, E5 and C1 to C4.

[0078] Immediately after the mixing of the constituents for the respective epoxy-resin compositions E1 to E3, E5 and C1 to C4, and then in each case once daily during storage at 25 C., the minimum of the viscosity curve resulting from rapid heating of the specimen was determined. To this end, in each case a specimen (about 2 g) of the respective epoxy-resin composition was taken and heated at 0.5 C./sec from the storage temperature (25 C.) to the hardening temperature (140 C.), while viscosity was measured as a function of time. The viscosity was measured by using a rheometer (Anton Paar MCR 301, FW3.30 viscometer (plate-on-plate configuration; diameter 25 mm; gap 1000 m, oscillation, shear rate 10 Hz)). The heating of the specimen initially reduces the viscosity, but then it rises rapidly over the further course of time because of the onset of latent curing. Table 3 collates the minimum of the viscosity curve here as a function of storage time for the respective epoxy-resin compositions E1 to E3, E5 and C1 to C4.

TABLE-US-00002 TABLE 2 Glass transition temperature (in C.) over the course of time (from 0 to at most 7 days) for the epoxy-resin compositions E1 to E3, E5 and C1 to C4 Storage time in days at 25 C. 0 1 2 3 4 5 6 7 C1 16 14 11 9 7 2 3 7 C2 16 13 11 7 5 3 1 12 C3 17 11 4 10 17 C4 16 11 7 6 12 E1 17 12 8 6 5 0 10 12 E2 17 10 3 2 0 4 15 E3 16 11 8 5 0 9 18 E5 17 7 2 5 6 18

TABLE-US-00003 TABLE 3 Viscosity minimum (in mPa*sec) over the course of time from 0 to at most 5 days (until a viscosity minimum of at least 500 mPa*sec is reached) for the epoxy-resin compositions E1 to E3, E5 and C1 to C4 - at the time when a viscosity minimum of at least 500 mPa*sec is reached, a sample is sufficiently matured to allow for curing under SMC molding conditions at e.g. 140 C. Storage time in days at 25 C. 0 1 2 3 4 5 C1 15 25 59 113 245 >500 C2 16 28 51 85 282 >500 C3 17 50 167 451 >500 C4 28 81 246 >500 E1 24 34 86 119 238 >500 E2 34 94 229 >500 E3 22 53 172 320 >500 E5 61 75 179 >500

Example 3

[0079] Measurement of Glass Transition Temperature for the Epoxy-Resin Compositions E1 to E3, E5 and C1 to C4

[0080] Immediately after the mixing of the constituents for the respective epoxy-resin compositions E1 to E5 and C1 to C4, and then in each case the glass transition temperature (Tg) was measured by DSC in accordance with ASTM D3418, and the temperature profile used here was as follows: 3 min 50 C..fwdarw.5K/min 250 C..fwdarw.10 min 250 C..fwdarw.20K/min 0 C..fwdarw.20K/min 250 C. In each case, 2 procedures were carried out, and Tg here was in each case determined in the 2nd procedure. Table 4 collates the results.

TABLE-US-00004 TABLE 4 Glass transition temperature (in C.) for the epoxy-resin compositions E1 to E3, E5 and C1 to C4 Glass transition temperature ( C.) C1 148 C2 143 C3 144 C4 145 E1 150 E2 145 E3 145 E5 148

[0081] The addition of the diazabicycloalkylen accelerator according to the invention does not impair the glass transition temperature of the cured epoxy resin.

Example 4

[0082] Measurement of Gel Time and Cure Time for the Epoxy-Resin Compositions E1 to E5 and C1 to C4

[0083] Immediately after the mixing of the constituents for the respective epoxy-resin compositions E1 to E5 and C1 to C4, and then in each case the loss modulus (G) and the storage modulus (G) was measured at a hardening temperature of 140 C. over time in accordance with standard ASTM D4473 by using a rheometer (Anton Paar MCR 301, FW3.30 viscometer (plate-on-plate configuration; diameter 25 mm; gap 1000 m, oscillation, shear rate 10 Hz)). The point of intersection of G and G provides the gel time and the time taken to reach the maximum G provides the curing time. Table 5 collates the results.

TABLE-US-00005 TABLE 5 Gel time (in min) and curing time (in min) at 140 C. for the epoxy-resin compositions E1 to E5 and C1 to C4 Gel time (min) Curing time (min) C1 3.5 6.9 C2 2.9 6.1 C3 2.6 5.6 C4 2.3 5.1 E1 1.5 4.1 E2 1.0 2.8 E3 1.8 3.6 E4 2.0 3.8 E5 0.8 2.8

[0084] The epoxy-compositions of the present invention which comprise diazabicycloalkylen compounds as curing accelerators show a significantly reduced gel time and curing time, compared to epoxy-resin compositions with other curing accelerators such as Dyhard UR500, TMG or DMP30. At the same time, the handling time and the maturing time and the glass transitions temperature of the cured epoxy resin are not impaired for the epoxy-compositions of the present invention compared to the epoxy-resin compositions with other curing accelerators.

Example 5

[0085] Measurement of the Resin Squeeze Out of Fiber-Matrix Semifinished Product Based on the Epoxy-Resin Composition C1, C3 and E1

[0086] SMCs were prepared on a SMC pilot line based on the epoxy-resin compositions C1, C3 and E1 and having a glass fiber content of 55% b.w. (2.5 cm fiber length). The SMCs were stored at 23 C. The resin squeeze out (measured as weight loss) was determined over the course of time by means of a press device as described in EN ISO 12114 II. The following molding conditions have been applied: a mold coverage of 66%, a molding time of 5 min, a temperature of 140 to 145 C. and a pressure (in mold) of 66 bar. The start of molding window was defined by a resin loss of 5%, and the end of the molding window was defined by a resin loss of 0% and incomplete flow of SMC. The length of the molding window in days is presented in Table 6.

TABLE-US-00006 TABLE 6 Molding window in days for SMCs based on the epoxy-resin compositions C1, C3 and E1 Length of molding window (days) C1 6 C3 2 E1 6

[0087] The length of the molding window of the SMC according to the invention (E1) using the curing accelerator DBU is comparable to that of the comparison example (C1, without curing accelerator). In contrast, curing accelerator TMG (as used in comparison example C3) substantially reduces the applicable molding time.