Single-component thermosetting epoxy resin having high scouring resistance

Abstract

A single-component thermosetting epoxy resin adhesives, including: a) at least one epoxy resin having, on average, more than one epoxy group per molecule; b) at least one latent hardener for epoxy resins; and c) 2-7 wt % aerogel particles, relative to the total weight of the single-component thermosetting epoxy resin adhesive, wherein the epoxy resin adhesive has a viscosity of 1000-4000 Pas, in particular 1000-3500 Pas, at 25° C., wherein the viscosity is oscillographically determined by means of a rheometer having a heatable plate (MCR 301, AntonPaar) (gap 1000 μm, measurement plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 25° C.). The epoxy resin adhesives are characterized in that they can be easily applied in the temperature range from 40° C. to 70° C. and are scouring-resistant, even at higher temperatures.

Claims

1. A one-component thermosetting epoxy resin adhesive comprising: a) at least one epoxy resin having an average of more than one epoxy group per molecule, wherein the at least one epoxy resin includes a liquid epoxy resin, and a proportion of the at least one epoxy resin is in a range of from 15% to 60% by weight, based on a total weight of the one-component thermosetting epoxy resin adhesive; b) at least one latent curing agent for epoxy resins, wherein the at least one latent curing agent includes dicyandiamide, and an amount of the at least one latent curing agent is 1-8% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive; and c) 2-5% by weight of aerogel particles, based on the total weight of the one-component thermosetting epoxy resin adhesive, d) at least one filler that is not the aerogel particles, and an amount of the at least one filler is 5-40% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive; e) at least one toughness improver D that is a terminally blocked polyurethane polymer D1, a terminally blocked polyurethane prepolymer of the formula (I) and a proportion of the terminally blocked polyurethane prepolymer of the formula (I) is in a range of from 20% to 40% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive, wherein the formula (I) is: ##STR00011## where R.sup.1 is a p-valent radical of a linear or branched polyurethane prepolymer terminated by isocyanate groups after the removal of the terminal isocyanate groups; p has a value of 2 to 8; and R.sup.2 is independently a substituent selected from the group consisting of ##STR00012## where R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are each independently an alkyl or cycloalkyl 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, optionally substituted ring; R.sup.9, R.sup.9′ and R.sup.10 are each independently an alkyl or aralkyl or arylalkyl group or an alkyloxy or aryloxy or aralkyloxy group; R.sup.11 is an alkyl group, R.sup.12, R.sup.13 and R.sup.14 are each independently an alkylene group which has 2 to 5 carbon atoms and optionally has double bonds or is substituted, or a phenylene group or a hydrogenated phenylene group; R.sup.15, R.sup.16 and R.sup.17 are each independently H or an alkyl group or 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 optionally having aromatic hydroxyl groups; R.sup.4 is a radical of an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide containing a primary or secondary hydroxyl group after the removal of the hydroxyl and epoxy groups; and m has a value of 1, 2 or 3; and f) optionally at least one of a reactive diluent and an accelerator; wherein the one-component thermosetting epoxy resin adhesive has a viscosity of 1000-4000 Pas at 25° C., as determined by oscillography using a rheometer with a heatable plate, the rheometer is MCR 301 available from Anton Paar, and rheometer conditions include a 1000 μm gap, a measurement plate diameter of 25 mm, plate/plate, deformation 0.01 at 5 Hz, and a temperature of 25° C.

2. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, comprising amorphous silicon dioxide aerogel particles.

3. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein a particle density of the aerogel particles is 90-200 kg/m.sup.3.

4. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the aerogel particles have an average particle size of 0.01-5 mm.

5. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the one-component thermosetting epoxy resin adhesive has a viscosity between 1000 Pas and 3000 Pa.Math.s at 25° C.

6. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the at least one latent curing agent is selected from dicyandiamide, guanamines, guanidines, aminoguanidines and derivatives thereof, substituted ureas, imidazoles, and amine complexes.

7. A method of bonding substrates, comprising the steps of a) applying the one-component thermosetting epoxy resin adhesive as claimed in claim 1, to a first substrate; b) contacting the applied one-component thermosetting epoxy resin adhesive with a second substrate, to form an adhesive bond; and c) curing the one-component thermosetting epoxy resin adhesive in the adhesive bond at a temperature in the range from 100 to 220° C.

8. The method as claimed in claim 7, further comprising a step b′) between step b) and step c), wherein step b′) comprises: contacting the substrates and the one-component thermosetting epoxy resin adhesive in contact therewith with a wash liquid at a temperature between 20 and 100° C.

9. An article comprising a cured adhesive bond, wherein the adhesive bond is obtained by the method as claimed in claim 7.

10. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the aerogel particles are effective to increase washout resistance of the one-component thermosetting epoxy resin adhesive.

11. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the aerogel particles are effective to increase impact peel, I-peel, strength to ISO 11343, of the one-component thermosetting epoxy resin adhesive.

12. The one-component thermosetting epoxy resin adhesive as claimed in claim 1, wherein the amount of the at least one latent curing agent is 1-4% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive.

Description

EXAMPLES

(1) Production of the Compositions

(2) According to the details in tables 1 and 2, the reference compositions Ref. 1-Ref. 6 and the inventive compositions Ex. 1 and Ex. 2 were produced. The stated amounts in tables 1 and 2 are stated in parts by weight.

(3) TABLE-US-00001 TABLE 1 raw materials used for composition ZA Raw materials (% by wt.) Liquid epoxy resin, D.E.R. 331 50 (bisphenol A diglycidyl ether), Dow Reactive diluent, hexanediol glycidyl ether, 1 Denacol EX-212, Nagase America Toughness improver D-1 20 Curing agent, dicyandiamide (= “Dicy”) 4 Accelerator, substituted urea 0.2 Filler mixture, mixture of calcium 24.8 carbonate and calcium oxide Total (% by wt.) 100

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

(5) 150 g of poly-THF 2000 (OH number 57 mg/g KOH) and 150 g of PolyBD R45V (OH number 46 mg/g KOH) were dried under reduced pressure at 105° C. for 30 minutes. Once 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 carried out under reduced pressure at 90° C. until the NCO content was constant at 3.10% after 2.0 h (calculated NCO content: 3.15%). Subsequently, 96.1 g of cardanol were added as blocking agent. Stirring was continued at 105° C. under vacuum until it was no longer possible to detect any free NCO. The product was used as such as toughness improver D-1.

(6) TABLE-US-00002 TABLE 2 Poly-THF 2000 (difunctional polybutylene glycol) (OH equivalent weight = about 1000 g/OH equivalent), BASF PolyBD R45V (hydroxyl-terminated polybutadiene) (OH equivalent weight = about 1230 g/OH equivalent), Cray Valley Isophorone diisocyanate (=“IPDI”), Evonik Cardolite NC-700 (cardanol, meta-substituted alkenylmonophenol), Cardolite Ref1 Ref2 Ref3 Ref4 Ref5 Ex1 Ex2 Ref6 Composition ZA (% by wt.) 100 98 96 93.5 98.4 96.7 93.5 92 Aerogel particles (% by wt.) — — — — 1.6 3.3 6.5 8 Fumed silica (% by wt.) —   1.6   3.3  6.5 — — — — Total (% by wt.) 100 100  100  100   100 100 100 100 IP (23° C.) (MPa) <15 n.d. n.d. n.d. 18.6 22.3 n.d. n.d. IP (−30° C.) (MPa) <8 n.d. n.d. n.d. 11.2 13.2 8.0 n.d. Washout 6  6  4 1  6 1 0 0 Viscosity (Pas) <500 n.d. n.d. n.d. n.d. 1000-2000 3000-4000 6500 “n.d.” = not determined, fumed silica: Wacker, aerogel particles: Aerogel Cabot P300, Cabot Corp. (Billerica, MA, USA).

(7) Washout Resistance

(8) To determine washout resistance, the respective composition was applied at room temperature as a triangular bead (width 8 mm, height 10 mm) to an oiled metal sheet (200×25 mm, electrolytically galvanized). The sheet has one hole at each end of the sheet (Ø 8 mm, central, distance 10 mm from the end of the sheet) for securing to the pivot mount. Thereafter, the sample was conditioned at room temperature for one hour.

(9) Subsequently, these metal sheets were mounted on a pivot mount and suspended in a vessel filled with water at 55° C. with half of them in the water at a stirrer speed of 60 rpm and rotated for 10 min. The distance of the metal sheets measured from the axis of the pivot mount is 120 mm.

(10) After the test had been performed, the deformation of the bead was assessed by the following scale:

(11) 0: unchanged compared to original state

(12) 1: slight deformation

(13) 2: distinct deformation without material washed off

(14) 3: significant deformation, but without material washed off

(15) 4: very significant deformation with material washed off

(16) 5: loss of material, but the originally wetted area still covered with material

(17) 6: almost complete loss of material apart from small residues

(18) Those samples that had a value from 0 to 3 were designated as washout-resistant.

(19) Viscosity

(20) Viscosity was measured by oscillography by means of a rheometer having a heatable plate (MCR 301, AntonPaar) at the stated temperature (1000 μm gap, measurement plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, heating rate: 10° C./min).

(21) Impact Peel Strength (I-Peel) (to ISO 11343)

(22) The specimens were produced with the adhesive and DC04+ZE steel with dimensions of 90×20×0.8 mm. The bonding area here was 20×30 mm at a layer thickness of 0.2 mm with glass beads as spacer. The samples were cured for 25 minutes at oven temperature 180° C.

(23) Impact peel strength was measured in each case at the temperatures specified (23° C., −30° C.) as a triple determination on a Zwick 450 impact pendulum. The impact peel strength reported is the average force in N/mm under the measurement curve from 25% to 90% to ISO11343.

(24) Results

(25) It is apparent from table 2 that adequate washout resistance is not achieved when less than 2% by weight of aerogel particles is used, and the viscosity reaches too high a value when more than 7% by weight of aerogel particles is used.

(26) It has been found that, surprisingly, very good washout resistance superior to the use of fumed silica is obtained in the range of 2-7% by weight of aerogel particles.

(27) Moreover, it has been found that, surprisingly, compositions containing 3.3% by weight of aerogel particles have high impact peel strength values at −30° C. compared to compositions containing zero or 1.6% by weight of aerogel particles. The same behavior was also observed for impact peel strength at 23° C.