Adhesive compositions

Abstract

An adhesive composition comprising an aromatic epoxy resin, an epoxy resin rubber adduct, an amine curing agent; and optionally one or more of an oil absorbent, a corrosion inhibitor and a urone accelerator, wherein the adhesive composition is curable at 150 C. in no more than 210 seconds.

Claims

1. An adhesive composition comprising: (a) 40 to 60 wt % aromatic epoxy resin, based on the total weight of said adhesive composition, said aromatic epoxy resin comprising a solid Bis-A epoxy resin having an epoxy equivalent weight of 450 to 465 and a semi-solid Bis-A epoxy resin having an epoxy equivalent weight of 300 to 340; (b) 20 to 35 wt % rubber adducted Bis-F epoxy resin, based on the total weight of said adhesive composition; (c) 3 to 7 wt % amine curing agent, based on the total weight of said adhesive composition; (d) 8 to 12 wt % oil absorbent, based on the total weight of said adhesive composition; (e) 0.1 to 2 wt % corrosion inhibitor, based on the total weight of said adhesive composition; and (f) 2 to 6 wt % urone based accelerator, based on the total weight of said adhesive composition, said urone based accelerator comprising 4,4-methylene diphenylene bis(N,N-dimethyl urea wherein said adhesive composition may be stored at 23 C. for at least 4 months prior to use.

2. The composition according to claim 1 wherein said aromatic epoxy resin further comprises a phenol novolac epoxy resin.

3. The composition according to claim 1, wherein said amine curing agent comprises dicyandiamide.

4. The composition according to claim 1, wherein said rubber adducted Bis-F epoxy resin comprises a nitrile rubber.

5. The composition according to claim 1, wherein said oil absorbent comprises CaCO.sub.3.

6. The composition according to claim 1, wherein said corrosion inhibitor is substantially free of chromium.

7. The composition according to claim 1, wherein the composition further comprises an ethylene vinyl acetate copolymer.

8. The composition according to claim 1, wherein the composition has a viscosity of at least 110,000 Pa.Math.s at 40 C.

9. The composition according to claim 8, wherein the viscosity of the composition at 80 C. is in the range of from 100 to 1000 Pa.Math.s.

10. A method for curing the composition according to claim 1, said method comprising heating the composition up to 150 C. for no more than 150 seconds.

11. A method of bonding two surfaces which comprises: contacting a first surface with the composition of claim 1 and curing the composition in contact with a second surface.

12. The method according to claim 11, wherein the curing comprises heating up to 150 C. for no more than 150 seconds.

13. The method according to claim 11, wherein at least one of the first and second surfaces is metal.

14. The method according to claim 13, wherein at least one of said first and second surfaces is contaminated with oil.

15. A composite article made by the method according to claim 11.

16. A prepreg comprising fibrous reinforcement and a composition according to claim 1.

Description

(1) The present invention will now be illustrated, but in no way limited, by reference to the following examples and drawings.

(2) In the drawings, FIG. 1 presents the viscosity in relation to the temperature for the compositions of Examples 5 and 10 according to embodiments of the invention, and;

(3) FIG. 2 presents the viscosity for the formulation of Example 10 during isothermal cure at 160 C.

EXAMPLES

(4) In this section, the viscoelastic properties, i.e. the storage modulus, loss modulus and (complex) viscosity were measured at 20 C. unless otherwise stated by using a Bohlin VOR Oscillating Rheometer with disposable 25 mm diameter aluminium plates. The measurements were carried out with the following settings: an oscillation test at increasing temperature from 50 C. to 150 C. at 2 C./mm with a controlled frequency of 1.59 Hz and a gap of 500 micrometer. Tan delta is defined as the ratio of the loss modulus to storage modulus. Loss modulus, storage modulus and tan delta are determined in accordance with ASTM D 4065.

Examples 1 to 5

(5) Lap shear testing was performed on Hot Dip galvanized steel that was cleaned with a volatile solvent (acetone) to give a grease and dirt free surface. The clean surface was then dosed with anticorrosion oil, Anticorit PL3802-39S (Fuchs), to give a coating of 3 g/m.sup.2. This was used as the substrate for lap shear testing. Adhesive compositions were applied to the oiled surface and a second, oiled, piece of steel was applied to form the other side of the lap shear joint.

(6) Prepared samples were held together with retaining bulldog style clips (51 mm long, Office Depot brand) on both sides of the adhesive joint and then placed into a pre-heated oven that had been equilibrated at 150 C. to allow the adhesive to cure for 3 minutes.

(7) The samples were then removed from the oven and allowed to cool to room temperature. Once cool the retaining clips were removed, a lap shear test was performed in accordance with ISO 527.

(8) The adhesive composition in accordance with the present invention (Example 4) is shown in Table 1 below.

(9) This was compared to industry standard one component paste adhesives for oiled steel. Comparative Example 1 was Araldite AV 4600 (Huntsman Corporation). Comparative Example 2 was Betamate 1460 (Dow Chemical Company). Comparative Example 3 was AF 126-2 (3M).

(10) The results are shown in Tables 2 and 3 below.

(11) TABLE-US-00001 TABLE 1 Example 4 formulation wt % by total Chemical weight Araldite GT6071 14 Solid Bis-A epoxy from Huntsman, EEW 450-465 PD3611 27 Rubber adducted bis-F epoxy from Schill & Seilacher LY1589 39 Semi Solid Bis-A epoxy from Huntsman, EEW 300-340 CaCO3 10 Mineral filler SAPPStrontium 1 Non chromium corrosion inhibitor aluminium polyphosphate hydrate Dyhard 100E 5 Amine curing agent from AlzChem Omicure U52 M 4 MDi urone accelerator from CVC 100.00

(12) TABLE-US-00002 TABLE 2 Lap shear test results (tested at 23 C.) Comparative Comparative Comparative Curing conditions Example 1 Example 2 Example 3 Press @ 150 C. No test possible, No test possible, No test for 3 mins sample fell apart sample fell apart possible, under its own under its own sample fell weight weight apart under its own weight

(13) TABLE-US-00003 TABLE 3 Lap shear test results (ISO 527, tested at 23 C.) Curing conditions Example 4 (MPa) Oven @ 150 C. for 15 mins 23.7 Press @ 150 C. for 4 mins 21.9 Press @ 150 C. for 3 mins 20.7 Press @ 150 C. for 2 mins 6.8

Examples 6 and 7

(14) TABLE-US-00004 TABLE 4 Examples 4 and 5 Example 4 Example 5 Chemical % by total weight % by total weight Araldite GT6071 14 15 PD3611 27 30 Advanced Bis A EEW 330 39 27 YD PN 638 10 CaCO3 10 8 SAPP 1 1 Dyhard 100E 5 5 U52 M 4 4

(15) Example 5 was based on Example 4 except that an advanced semi-solid bisphenol A epoxy resin having an EEW of 330 was used and a further resin component was included (YD PN638, a phenol novolac epoxy).

(16) Example 6 was designed to investigate the effect of the addition of a polyamide thermoplastic (ELVAX 40W). The same lap shear test was carried out in the same way as for Examples 1 to 5.

(17) TABLE-US-00005 TABLE 5 Examples 5 and 6 wt % by total weight of composition Example 5 Example 6 Araldite GT6071 15 15 PD3611 30 30 Advanced Bis A EEW 330 27 27 YD PN 638 10 10 Elvax 40W 5 CaCO3 8 8 SAPP 1 1 Dyhard 100E 5 5 U52 M 4 4 Results Lap shear strength, MPa 21.0 21.1 (ISO 527) Cured Tg, C. (D7028-07) 109.0 109.8 Tan Delta, C. (D4065) 129.6 126.6

(18) Examples 5 and 6 were press cured at 150 C. for 3 minutes. Although the results of Example 6 are equivalent to Example 5, it was observed that in a neat resin cure Example 6 had very low porosity in comparison to the very high porosity of the cured composition of Example 5.

Examples 7 to 9

(19) Compositions, by wt % of the total composition, for Examples 7, 8 and 9 are shown in Table 6.

(20) TABLE-US-00006 TABLE 6 Examples 7 to 9 compositions wt % by total weight Comparative of composition Example 7 Example 8 Example 9 Araldite GT6071, % 14 14 14 PD3611, % 27 PD3614, % 27 Advanced Bis A resin EEW 330, 39 39 66 % CaCO3, % 10 10 10 SAPPStrontium aluminium 1 1 1 polyphosphate hydrate, % Dyhard 100E, % 5 5 5 U52 M, % 4 4 UR200, % 4

(21) Example 7 corresponds to Example 4 except for replacement of 4,4-methylene diphenylene bis(N,N-dimethyl urea) (U52 M) urone accelerator with another urone accelerator (UR200).

(22) Example 8 corresponds to Example 4 except for the replacement of bisphenol F epoxy resin rubber adduct (PD3611) with bisphenol A epoxy resin rubber adduct (PD3614). The results show that bisphenol F epoxy resin rubber adduct (PD3611) achieves bonding to oily steel and forming a well cured joint in very short cure times.

(23) Comparative Example 9 corresponds to Example 4 except for replacement of bisphenol F epoxy resin rubber adduct (PD3611) with an advanced bisphenol a of EEW 330). The results show that the epoxy resin rubber adduct is required for bonding to oiled steel.

(24) The same lap shear tests were carried out as for Examples 1 to 6. All the Examples were cured for 2 and 3 min at 150 C. Results are shown in Table 7 below.

(25) TABLE-US-00007 TABLE 7 Examples 7 to 9 results Example 7 Example 8 Comparative Example 9 Lap shear strength (Mpa) Not tested (see Test not possible at Not tested (ISO 527) 3 min result) samples yielded/ (see 3 min result) 2 min cure elastic response from under cured adhesive Lap shear strength (Mpa) 1.5 Test not possible at Sample failed before (ISO 527) samples yielded/ testing, adhesive failure 3 min cure elastic response to the steel substrate from under cured showing no bonding to adhesive the oiled steel surface Cured Tg, C. (2 min cure, 62.9 70.2 98.3 ASTM D7028-07) Tan Delta, C. (2 min cure, 86.0 105.4 122.2 ASTM D4065) Cured Tg, C. (3 min cure, 86.0 80.9 103.6 ASTM D7028-07) Tan Delta, C. (3 min cure, 108.3 120.6 126.1 ASTM D4065)

(26) We will now describe a further exemplary formulation (Example 10) with reference to the below Table 8.

(27) TABLE-US-00008 TABLE 8 Examples 5 and 10 Wt % by total weight of composition Example 5 Example 10 Araldite GT6071 15 Epikote 1009 15 PD3611 30 30 Advanced Bis A EEW 330 27 27 YD PN 638 10 10 CaCO.sub.3 8 8 SAPP 1 1 Dyhard 100E 5 5 U52 M 4 4

(28) The viscosity in relation to the temperature of the compositions of Examples 5 and 10 is presented in FIG. 1.

(29) FIG. 2 presents the viscosity of the composition of Example 10 when cured at a fixed temperature of 160 C.

(30) A laminate was prepared using a carbon woven fabric (HexForce G0939 DA 1260 TCT HS03K as supplied by Hexcel Corporation) which was impregnated with the adhesive composition of Example 10 to result in an impregnated fabric having an overall weight of 340 gsm (g/m.sup.2). This material is referenced as Example 11. The prepared laminate was cured in a Stahl Clam press at a temperature of 150 C. for varying periods ranging from 2 to 5 minutes and the cured T.sub.g (ASTM standard D 7028-07) and storage modulus onset (ASTM standard D 4065) were measured. The results are presented in the below Table 9.

(31) TABLE-US-00009 TABLE 9 Cure time (mins) T.sub.g ( C.) Storage modulus, onset ( C.) 2 120 78 3 125 83 4 123 85 5 123 86

(32) An additional laminate (Example 11) was prepared from the same fabric G0939 impregnated with the adhesive composition of Example 10. This material was heated to 100 C. and then the temperature was increased from 100 C. to 150 C. at a rate of 3 C. per minute, and the temperature was held at 150 C. for 30 minutes (dwell). After this, the laminate was allowed to cool to room temperature. The laminate was cut into samples. One sample was tested for cured T.sub.g and another sample was left in ionised water at 70 C. for 2 weeks and following on from this, the cured T.sub.g was measured. The results are presented in the below Table 10.

(33) TABLE-US-00010 TABLE 10 Cured Tg, C. (ASTM D 7028-07) 103.71 Cured Tg after 2 weeks @70 C. in water, 70.15 C. (ASTM D 7028-07)

(34) Adhesive compositions of Example 10 in the form of films of 400 and 300 gsm (g/m.sup.2) were pressed with 50 gsm (g/m.sup.2) glass fleece (E glass random fibres) to form samples for Examples 12 and 13 respectively as outlined in below Table 11. As shown in Table 11 some 400 gsm specimens were conditioned in a humidity cabinet for up to 26 weeks at 24 C. 60% RH (relative humidity) or for up to 28 days at 40 C. 50% RH. Samples were prepared using the procedure described in Examples 1-5 to conduct measurements of SLSS (single layer shear strength), Bell peel strength and Flat wise tensile strength. SLSS was tested in accordance with ASTM standard D5868. The Bell peel strength test was determined in accordance with EN-2243-2. The flat wise tensile test was determined in accordance with ASTM C 297.

(35) The samples for which the SLSS was measured were cured at 150 C. for 3 min. The samples for which Bell peel and Flat wise tensile strength were measured were cured at an initial temperature of 100 C. which was ramped up at a rate of 3 C. per minute from 100 C. to 150 C., and held at a dwell temperature of 150 C. for 30 minutes and these samples were then allowed to cool to room temperature. Below Table 11 presents the results.

(36) TABLE-US-00011 TABLE 11 Example 12 Example 13 400 gsm 300 gsm SLSS on clean steel, MPa RT 28.8 SLSS on oiled steel, MPa RT 23.7 22.9 +65 C. 16 30 C. 34.2 SLSS, MPa 28 days at 24 C. RT 23.5 60% RH (relative humidity) +65 C. 12.5 30 C. 30.8 SLSS, MPa 26 weeks @24 C. RT 23.0 60% RH SLSS, MPa 28 days @ 40 C. RT 11.3 50% RH SLSS, MPa 21 days @ 40 C. RT 28.3 50% RH SLSS, MPa, 7 days @ 40 C. RT 25.3 50% RH Bell peel, N/25 mm RT 274 217 Flat wise tensile (MPa) RT 6.96 4.82