TWO COMPONENT (2K) CURABLE ADHESIVE COMPOSITION

Abstract

The present invention is directed to a curable and debondable two-part (2K) adhesive composition comprising: i) a first part comprising: a) epoxy resin; b) an electrolyte; c) optionally, a solubilizer; and, ii) a second part comprising: a) a curing agent consisting of at least one compound possessing at least two epoxide reactive groups per molecule; and, b) an accelerator; wherein said composition further comprises an electrically non-conductive filler and, optionally a toughener.

Claims

1. A curable and debondable two-part (2K) adhesive composition comprising: a first part comprising: a) epoxy resin; b) an electrolyte; c) optionally, a solubilizer; and a second part comprising: a) a curing agent consisting of at least one compound possessing at least two epoxide reactive groups per molecule; and, b) an accelerator; wherein said composition further comprises an electrically non-conductive filler and, optionally a toughener.

2. A curable and debondable two-part adhesive composition according to claim 1, wherein said epoxy resin is selected from the group consisting of bis-phenol A epoxy resin, bis-phenol F epoxy resin, mixture of bis-phenol A epoxy resin and bis-phenol F epoxy resin, cycloaliphatic epoxy resin and mixtures thereof.

3. A curable and debondable two-part adhesive composition according to claim 1, wherein said epoxy resin is present in an amount of from 30 to 70% by weight of the composition.

4. A curable and debondable two-part adhesive composition according to claim 1, wherein said electrolyte is selected from the group consisting of 1-ethyl-3-methylimidazolium methansulfonate, 1-ethyl-3-methylimidazolium methyl sulfate, 1-hexyl-3-methylimidazolium 2-(2-fluoroanilino)-pyridinate, 1-hexyl-3-methylimidazolium imide, 1-butyl-1-methyl-pyrrolidinium 2-(2-fluoroanilino)-pyridinate, 1-butyl-1-methyl-pyrrolidinium imide, trihexyl (tetradecyl) phospholium 2-(2-fluoroanilino)-pyridinate, cyclohexyltrimethylammonium bis (trifluormethylsulfonyl) imide, di(2-hydroxyethyl) ammonium trifluoroaetate, N,N-dimethyl (2-hydroxyethyl) ammonium octanoate, methyltrioctylammonium bis (trifluoromethylsulfonyl) imide, N-ethyl-N-N-N-N-tetramethylguanidinium trifluoromethanesulfonate, guanidinium trifluoromethanesulfonate, 1-butyl-4-methylpyridinium bromide, 1-buthyl-3-methylpyridinium tetrafluoroborate, 1-butyl-3-hydroxymethylpyridinium ethylsulfate, 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, 1-butyl-methylpyrrolidinium tris (pentafluoroethyl) trifluorophosphate, 3-methyl imidazolium ethylsulfate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-ethyl-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-octyl-3-methylimidazolium chloride, 1-methyl-3-octylimidazolium chloride, 1-propyl-3-methylimidazolium iodide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-butylimidazol, 1-methylimidazolium tetrafluoroborate, tetrabutylphosphonium tris (pentafluoroethyl) trifluorophosphate, trihexyl (tetradecyl) phosphonium tetrafluoroborate and mixtures thereof.

5. A curable and debondable two-part adhesive composition according to claim 1, wherein said electrolyte is present in an amount of from 2 to 25% by weight of the total weight of the composition.

6. A curable and debondable two-part adhesive composition according to claim 1, wherein said electrically non-conductive filler is selected from the group consisting of calcium carbonate, calcium oxide, talcum, fumed silica, silica, wollastonite, barium sulphate, glass beads and mixtures thereof.

7. A curable and debondable two-part adhesive composition according to claim 1, wherein said filler is present in an amount of from 1 to 50% by weight of the total weight of the composition.

8. A curable and debondable two-part adhesive composition according to claim 1, comprising solubilizer in an amount of from 0.5 to 15% by weight of the total weight of the composition.

9. A curable and debondable two-part adhesive composition according to claim 8, wherein said solubilizer is selected from: polyphosphazenes; polymethylenesulfides; polyoxyalkylene glycols; polyethylene imines; silicone surfactants and fluorinated silicone surfactants; co-polymers of functionalized polyalkysiloxanes and epoxy resins; polyhydric alcohols; and, sugars.

10. A curable and debondable two-part adhesive composition according to claim 1 further comprising electrically conductive particles selected from the group consisting of carbon black, silver and mixtures thereof.

11. A curable and debondable two-part adhesive composition according to claim 1, comprising electrically conductive particles in an amount of from 0.05 to 10% by weight of the total weight of the composition.

12. A curable and debondable two-part adhesive composition according to claim 1, wherein said curing agent comprises at least one polyamine having at least two amine hydrogens reactive toward epoxide groups, said polyamine being further characterized by containing primary and/or secondary amine groups and having an equivalent weight per primary or secondary amine group of not more than 150 g/eq.

13. A curable and debondable two-part adhesive composition according to claim 1, wherein said accelerator is selected from the group consisting of tertiary amines, quaternary ammonium salts, amidines, guanidines and mixtures thereof, wherein said accelerator is selected from the group consisting of imidazole, methylimidazole, benzyldimethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,4-diazabicyclo(2,2,2) octane and mixtures thereof.

14. A curable and debondable two-part adhesive composition according to claim 1, wherein said accelerator is present in an amount of from 0.1 to 15% by weight of the total weight of the composition.

15. A bonded structure comprising a first material layer having an electrically conductive surface; a second material layer having an electrically conductive surface; wherein a cured debondable two-part adhesive composition as defined in claim 1 is disposed between the first and second material layers.

16. A method of debonding said bonded structure according to claim 15, the method comprising the steps of: 1) applying a voltage across both surfaces to form an anodic interface and a cathodic interface; and 2) debonding the surfaces, wherein the voltage applied in step 1 is from 0.5 to 200 V and it is applied from 1 second to 120 minutes.

Description

[0209] The present invention will be described with reference to the appended drawings in which:

[0210] FIG. 1a illustrates a bonded structure in accordance with a first embodiment of the present invention.

[0211] FIG. 1b illustrates a bonded structure in accordance with a second embodiment of the present invention.

[0212] FIG. 2a illustrates the initial debonding of the structure of the first embodiment upon passage of a current across that structure.

[0213] FIG. 2b Illustrates the initial debonding of the structure of the second embodiment upon passage of a current across that structure.

[0214] FIGS. 3a and 3b illustrate the results of lap shear strength testing of aluminium substrates bonded with a cured adhesive composition in accordance with an embodiment of the present invention.

[0215] As shown in FIGS. 1a appended hereto, a bonded structure is provided in which a layer of cured adhesive (10) is disposed between two conductive substrates (11). A layer of non-conductive material (12) may be disposed on the conductive substrates (11) to form the more complex bonded structure as depicted in FIG. 1b. Each layer of conductive substrate (11) is in electrical contact with an electrical power source (13) which may be a battery or an AC-driven source of direct current (DC). The positive and negative terminals of that power source (13) are shown in one fixed position but the skilled artisan will of course recognize that the polarity of the system can be reversed.

[0216] The two conductive substrates (11) are shown in the form of a layer which may be constituted by inter alia: a metallic film; a metallic mesh or grid; deposited metal particles; a resinous material which is rendered conductive by virtue of conductive elements disposed therein; or, a conducting oxide layer. As exemplary conductive elements there may be mentioned silver filaments, single-walled carbon nanotubes and multi-walled carbon nanotubes. As exemplary conducting oxides there may be mentioned: doped indium oxides, such as indium tin oxide (ITO); doped zinc oxide; antimony tin oxide; cadmium stannate; and, zinc stannate. The selection of the conductive material aside, the skilled artisan will recognize that the efficacy of the debonding operation may be diminished where the conductive substrates (11) are in the form of a grid or mesh which offers limited contact with the layer of cured adhesive (10).

[0217] As depicted in FIGS. 2a and 2b, the debonding occurs at the positive interface, that interface between the adhesive composition (10) and the electrically conductive surface (11) that is in electrical contact with the positive electrode. By reversing current direction prior to separation of the substrates, the adhesive bond may be weakened at both substrate interfaces.

[0218] It is however noted that the composition of the adhesive layer (10) may be moderated so that debonding occurs at either the positive or negative interface or simultaneously from both. For some embodiments, a voltage applied across both surfaces so as to form an anodic interface and a cathodic interface will cause debonding to occur simultaneously at both the anodic and cathodic adhesive/substrate interfaces. In an alternative embodiment, reversed polarity may be used to simultaneously disbond both substrate/adhesive interfaces if the composition does not respond at both interfaces to direct current. The current can be applied with any suitable waveform, provided that sufficient total time at each polarity is allowed for debonding to occur. Sinusoidal, rectangular and triangular waveforms might be appropriate in this regard and may be applied from a controlled voltage or a controlled current source.

[0219] Without intention to limit the present invention, it is considered that the debonding operation may be performed effectively where at least one and preferably both of the following conditions are instigated: a) an applied voltage of from 0.5 to 200 V; and, b) the voltage being applied for a duration of from 1 second to 120 minutes, for example from 1 second to 60 minutes or 1 second to 30 minutes. Where the release of the conductive substrate from the cured adhesive is to be facilitated by the application of a force—exerted via a weight or a spring, for instance—the potential might only need to be applied for the order of seconds.

[0220] The following examples are illustrative of the present invention and are not intended to limit the scope of the invention in any way.

EXAMPLES

[0221] The following materials were employed in the Examples: [0222] Cab-O-Sil 720: Fumed silica which has been surface treated with polydimethylsiloxane (PDMS) available from Cabot Corporation. [0223] Casiflux G20: Particulate wollastonite, available from Sibelco. [0224] KBM-4803: 8-glycidooxyoctyl trimethoxysilane, available from Shinetsu. [0225] EMIM-MS 1-Ethyl-3-methylimidazolium methansulfonate, available from TCI America Inc. [0226] B-Tough A3 Epoxy-silicone elastomer adduct, available from Croda Europe Limited. [0227] DER 330EL: Low viscosity bisphenol A epoxy resin, available from Olin. [0228] DER 337: Intermediate epoxy equivalent weight semi-solid resin based on Bisphenol-A epoxy, available from Olin. [0229] DER 337-X80: Intermediate epoxy equivalent weight semi-solid resin based on Bisphenol-A epoxy in xylene, available from Olin. [0230] Jeffamine® D-230: Ether group-containing aliphatic primary polyamine, available from Huntsman. [0231] PEG400: Polyethylene glycol, available from Sigma Aldrich. 2-piperazin-1-ylethanamine Tertiary amine, available from Acros Organics.

Example 1

[0232] Parts (A) and (B) of the two-part (2K) compositions were independently prepared in accordance with Table 1 herein below:

TABLE-US-00001 TABLE 1 Wt. % (based on Ingredient weight of composition) Part A 1 D.E.R. 337 52.81 2 B-tough A3 4.18 3 Casiflux G20 4.18 4 EMIM MS 18 5 PEG 400 4.57 6 ShinEtsu KBM-4803 0.76 7 Cab-o-Sil TS 720 1.52 Part B 1 2-piperazin-1-ylethanamine 6.99 2 Jeffamine D230 6.99

[0233] The individual parts (A, B) were loaded into separate compartments of a 50 g cartridge and sealed at both ends. The cartridge was then loaded into a cartridge-gun and a mixing tip was installed on the front end. By application of constant pressure on the trigger, the two parts were pushed into the mixing tip to ensure sufficient mixing before application to the stated substrate.

[0234] The substrates were aluminium (AA6016) and stainless steel (1.4301) each with a thickness of 1.25 mm for aluminium and 1.5 mm for steel and 1 mm for copper. Substrates were cut into 2.5 cm×10 cm (1″×4″) in size for tensile testing. Tensile lap shear (TLS) test was performed according to test method described on page 5.

[0235] The applied two-part (2K) adhesive compositions were cured in the overlapping region by the application of a temperature of 65° C. for 120 minutes. Subsequently, the samples were stored at 25° C. with 20% humidity in a climate chamber.

[0236] For each substrate, tensile lap shear strength was investigated after said 24-hour storage period both prior and subsequent to the application of a constant potential of 50V across the adhesive layer for a duration of 20 minutes. The results are documented in Table 2 herein below.

TABLE-US-00002 TABLE 2 Initial Bond Bond Strength after Substrate Strength (MPa) 50 V, 20 minutes (MPa) Aluminium 15.16 (±1.79) 5.9 (±1.9) Stainless Steel 19.11 (±0.88) 5.14 (±1.42) Copper 15.21 (±0.48) 1.88 (±0.28)

Example 2

[0237] For the adhesively bonded aluminium substrate (AA6016), lap shear strength (MPa) was investigated under two conditions: a) over a period of 120 minutes applying a constant potential (75 V) across the overlapping bonded area; and, b) applying different potentials across the overlapping bonded region for a fixed period of time (30 minutes) at each applied potential. The results of these investigations are given in FIGS. 3a and 3b appended hereto.

Example 3

[0238] Stability test was conducted for the composition of example 1. For this test, normal lap shear samples were prepared and cured at 65° C. for 120 min. Aluminium and steel substrates were used. Subsequently, the samples were stored at 25° C. with 20% humidity in a climate chamber.

[0239] The las shear was measured after one day, seven days, 14 days, 21 days and 30 days. The results are documented in Table 3 herein below.

TABLE-US-00003 TABLE 3 Initial Bond Bond Strength after Aluminium Strength (MPa) 75 V, 1 hour (MPa)  1 day 15,155 (+/−) 1.79.sup.  5.9 (+/−)1.89  7 days  16.8 (+/−) 0.68 4.97(+/−) 2.12 14 days  17.4 (+/−) 1.19 3.04(+/−) 0.17 21 days 12.11(+/−) 0.79 4.54(+/−) 0.82 30 days 14.57(+/−) 2.21 4.32(+/−) 0.42

[0240] The stability results are illustrated in FIG. 4. FIG. 4 illustrates adhesion properties and debonding effect on aluminium and steel. The test results show that the composition according to the present invention has good initial adhesion properties and does not lose them over the time. In addition, the composition according to the present invention has good initial debonding effect and maintains it over the time.

Example 4

[0241] Parts (A) and (B) of the two-part (2K) compositions were independently prepared in accordance with Table 4 herein below:

TABLE-US-00004 TABLE 4 Wt. % (based on Ingredient weight of composition) Part A 1 D.E.R. 330-EL 52.81 2 B-tough A3 4.18 3 Casiflux G20 4.18 4 EMIM MS 18.00 5 PEG 400 4.57 6 ShinEtsu KBM-4803 0.76 7 Cab-o-Sil TS 720 1.52 Part B 1 1-(2-aminoethyl)piperazin 6.99 2 Jeffamine D230 6.99

[0242] The composition and samples were prepared as in described in example 1. The results are documented in Table 5 herein below.

TABLE-US-00005 TABLE 5 Initial Bond Bond Strength after Substrate Strength (MPa) 50 V, 20 minutes (MPa) Aluminium 18.20 (±0.925) 10.02 (±0.8)  Stainless Steel 27.38 (±0.81)  16.31 (±4.99)

[0243] In view of the foregoing description and examples, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.

Example 5

[0244] Parts (A) and (B) of the two-part (2K) compositions were independently prepared in accordance with Table 6 herein below:

TABLE-US-00006 TABLE 6 Wt. % (based on Ingredient weight of composition) Part A 1 D.E.R. 337-X80 55.83 2 B-tough A3 4.18 3 Casiflux G20 4.18 4 EMIM MS 18.00 5 PEG 400 4.57 6 ShinEtsu KBM-4803 0.76 7 Cab-o-Sil TS 720 1.52 Part B 1 1-(2-aminoethyl)piperazine 5.48 2 Jeffamine D230 5.48

[0245] The composition and samples were prepared as in described in example 1. The results are documented in Table 7 herein below.

TABLE-US-00007 TABLE 7 Initial Bond Bond Strength after Substrate Strength (MPa) 50 V, 20 minutes (MPa) Aluminium 6.43 (±0.75) 0.95 (±0.23)

Example 6

[0246] Parts (A) and (B) of the two-part (2K) compositions were independently prepared in accordance with Table 8 herein below:

TABLE-US-00008 TABLE 8 Wt. % (based on Ingredient weight of composition) Part A 1 D.E.R. 337 61.63 2 B-tough A3 4.72 3 Casiflux G20 4.72 4 EMIM MS 8.77 5 PEG 400 5.15 6 ShinEtsu KBM-4803 0.86 7 Cab-o-Sil TS 720 1.72 8 GPX 801 (Cabot) 0.09 Part B 1 1-(2-aminoethyl)piperazine 6.17 2 Jeffamine D230 6.17

[0247] The composition and samples were prepared as in described in example 1. The results are documented in Table 9 herein below.

TABLE-US-00009 TABLE 9 Initial Bond Bond Strength after Substrate Strength (MPa) 50 V, 20 minutes (MPa) Aluminium 17.69 (±1.64) 3.21 (±0.91)

[0248] In view of the foregoing description and examples, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.

Example 7

[0249] Two two-part (2K) compositions were independently prepared in accordance with Table 10 herein below with the difference that the composition 1a contains a non-electrically conductive filler (fumed silica) whereas composition 1b does not contain a non-electrically conductive filler.

TABLE-US-00010 TABLE 10 Wt. % (based Wt. % (based on weight of on weight of composition) composition) Ingredient Composition 1a Composition 1b Part A 1 D.E.R. 337 61.63 63.30 2 B-tough A3 4.72 4.84 3 Casiflux G20 4.72 4.84 4 EMIM MS 20.48 20.84 5 PEG 400 5.15 5.29 6 ShinEtsu KBM-4803 0.86 0.89 7 Cab-o-Sil TS 720 1.72 0.00 Part B 1 1-(2-aminoethyl)piperazine 6.17 6.17 2 Jeffamine D230 6.17 6.17

[0250] The composition and samples were prepared as in described in example 1. The results are documented in Table 11 herein below.

TABLE-US-00011 TABLE 11 Initial Bond Bond Strength after Substrate Strength (MPa) 75 V, 20 minutes (MPa) Aluminium 1a 16.17 5.91 Aluminium 1b 12.89 11.07

[0251] The results indicate that the use of non-conductive filler, and especially fumed silica, improves the initial strength and debonding effect. The results are also illustrated in FIG. 5.

[0252] In view of the foregoing description and examples, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.