Self-supporting adhesive body for structural bonds

Abstract

A composition having at least one structural adhesive and at least one chemically crosslinked elastomer based on the silane-functional, non-polar polymer, said elastomer being provided in the form of a penetrating polymer network in the structural adhesive. Self-supporting adhesive bodies, particularly in the form of adhesive tapes, can be produced from such compositions and can be used for structural bonds and to reinforce metal structures.

Claims

1. A composition comprising at least one structural adhesive, and at least one chemically crosslinked elastomer based on a silane-functional apolar polymer that is a reaction product of a silane and an apolar polymer, wherein the apolar polymer is a polyether in which a ratio of carbon atoms to oxygen atoms of monomers in the polyether is on average greater than 3:1, and the silane has epoxide groups and the apolar polymer has epoxide-reactive groups, or the silane has epoxide-reactive groups and the apolar polymer has epoxide groups.

2. The composition as claimed in claim 1, wherein the chemically crosslinked elastomer is present as an interpenetrating polymer network in the structural adhesive.

3. The composition as claimed in claim 1, wherein the silane-functional apolar polymer comprises silane groups of formula R.sup.4Si(OR.sup.1)(OR.sup.2)(OR.sup.3) or R.sup.4SiR.sup.1(OR.sup.2)(OR.sup.3), where: R.sup.1, R.sup.2, and R.sup.3 are alike or different and denote alkyl groups which optionally contain at least one ether function, and R.sup.4 is a linear or branched divalent hydrocarbyl radical having 1 to 12 carbon atoms and optionally one or more heteroatoms.

4. The composition as claimed in claim 1, wherein the structural adhesive is a thermosetting epoxy resin composition comprising at least one epoxy resin and at least one hardener for epoxy resins which is activated by elevated temperature.

5. The composition as claimed in claim 4, wherein the epoxy resin comprises diglycidyl ethers of Bisphenol-A.

6. The composition as claimed in claim 1, wherein a fraction of the structural adhesive is in a range of from 50 to 85 wt %, and a fraction of the chemically crosslinked elastomer based on the silane-functional apolar polymer is in a range of from 15 to 50 wt %.

7. The composition as claimed in claim 6, wherein the fraction of the structural adhesive is in a range of from 70 to 80 wt %, and the fraction of the chemically crosslinked elastomer is in a range of from 20 to 30 wt %.

8. The composition as claimed in claim 1, wherein the chemically crosslinked elastomer has been obtained using an aminosilane as a crosslinking assistant.

9. The composition as claimed in claim 1, wherein the apolar polymer is based on polybutylene glycol and/or poly(tetramethylene) glycol.

10. A method for producing an adhesive body composed of a composition as claimed in claim 1, comprising reacting the silane with the apolar polymer; mixing the resulting silane-functional apolar polymer with the structural adhesive; shaping the resulting mixture, optionally on a carrier or substrate; and storing the shaped mixture under conditions under which the silane-functional apolar polymer crosslinks with water.

11. The method as claimed in claim 10, wherein the silane-functional apolar polymer is crosslinked with water in the form of atmospheric moisture.

12. An adhesive body composed of a composition comprising: at least one structural adhesive, and at least one chemically crosslinked elastomer based on a silane-functional apolar polymer that is a reaction product of a silane and an apolar polymer, wherein the apolar polymer is a polyether in which a ratio of carbon atoms to oxygen atoms of monomers in the polyether is on average greater than 3:1, and the silane has epoxide groups and the apolar polymer has epoxide-reactive groups, or the silane has epoxide-reactive groups and the apolar polymer has epoxide groups.

13. The adhesive body as claimed in claim 12, wherein it has a thickness in a range of from 0.1 to 5 mm.

14. A method comprising joining two substrates with an adhesive body as claimed in claim 12.

15. The method as claimed in claim 14, comprising: applying the adhesive body to a first substrate, contacting the adhesive body on the first substrate with a second substrate, and curing the adhesive body.

Description

EXAMPLES

(1) Set out below are exemplary embodiments which are intended to elucidate in more detail the invention described. It will be appreciated that the invention is not confined to these exemplary embodiments described.

(2) Commercial Substances Used

(3) TABLE-US-00001 Hypro Amine-terminated butadiene-acrylonitrile 1300X16 ATBN copolymer; Mw = about 3600 g/mol; equivalent weight 900 g/eq, from Emerald Performance Materials Jeffamine Polyetheramine based on poly(tetramethylene) THF-170 glycol; Mw = about 1700 g/mol; equivalent weight 380 g/eq, from Huntsman Dynasilan 3-Glycidoxypropyltriethoxysilane, from Evonik GLYEO Araldite Transesterification product of 3-glycidoxy- DY 1158 propyltrimethoxysilane with diethylene glycol monomethyl ether; Mw = about 500, from Huntsman MS Polymer Trimethoxysilane-terminated polypropylene S303H glycol having an average functionality of 2.3 and an Mw of about 12 000 g/mol, from Kaneka Silyl Trimethoxysilane-terminated polypropylene SAX400 glycol having an average functionality of 3 and an Mw of about 24 000 g/mol, from Kaneka PolyTHF Poly(tetramethylene) glycol having an Mw of 2000 about 2000 g/mol, from BASF Vestanat Isophorone diisocyanate, from Evonik IPDI DBTDL Dibutyl tin dilaurate, from Fluka Silquest N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane, A-1120 from Momentive Araldite Liquid epoxy resin based on DGEBA, Mw = GY 250 about 375 g/mol, from Huntsman Dicyandiamide from Evonik Tyzor Bis(ethylacetoacetato)diisobutoxytitanium(IV), IBAY from Dorf Ketal

(4) Test Methods

(5) The impact peel strength was determined on the basis of ISO 11343, the measurements being carried out at 23 C.

(6) The lap shear strength was determined on the basis of EN1465 on a strip measuring 525 mm, 2 mm thick, mounted on a 0.8 mm-thickness strip of HDG steel (H380) cleaned with acetone

(7) The gel content was determined in accordance with method A of ASTM 2765. For this purpose, two containers made of a 100 mesh polyamide fabric and each containing 0.3 g of ground sample material were stored in an excess of methyl ethyl ketone (MEK) at room temperature for at least 40 hours. Thereafter the containers were washed with MEK and dried at room temperature for at least 5 hours. This was followed by further drying under reduced pressure at 50 C. for at least 18 hours. The insoluble weight fraction remaining in the container corresponds to the gel content or the gel fraction.

(8) Production of Inventive Compositions and Adhesive Tapes obtained from them

(9) In accordance with the quantity data in Table 1, a liquid rubber and an epoxy silane were in each case mixed in a vessel and heated to a temperature of 80 C. for 1 hour. The course of reaction was ascertained by means of the NIR absorbance of the epoxy peak at about 4522 cm.sup.1, it being found that the epoxy groups had substantially been consumed by reaction after a reaction time of 1 hour. After heating had taken place, the resultant silane-functional apolar polymer was admixed with the liquid epoxy resin, which was mixed in with the aid of a centrifugal mixer at 3500 rpm for 2 minutes. The hardener for epoxy resins (dicyandiamide) was then added and likewise mixed in. The completed mixtures were used to produce adhesive tapes, by being applied in a thickness of 5 mm to PTFE casting molds and also in a thickness of 0.3 mm directly to the steel substrate of the test specimens, and left to stand in air at room temperature, at 23 C., for 7 days, during which the silane groups crosslinked with moisture. The adhesive tape thus produced was tested for gel content. Additionally, the adhesive tape was cured in a forced air oven first at 80 C. for 2 hours and then at 180 C. for 1.5 hours, and was tested for lap shear strength and impact peel strength.

(10) As comparative examples, as silane-functional polymer, two different silane-terminated polyethers based on polypropylene glycol (MS Polymer 5303H and Silyl SAX400) were used in combination with a catalyst for silane crosslinking.

(11) The compositions of the individual formulations, and also the mechanical properties, are reported in Table 1 below.

(12) TABLE-US-00002 TABLE 1 Inv. ex. 1 Inv. ex. 2 Inv. ex. 3 Inv. ex. 4 Comparative ex. 1 Comparative ex. 2 in wt % in wt % in wt % in wt % in wt % in wt % Component (designation) Liquid rubber Hypro 1300X16 ATBN 17.8 14.9 Jeffamine THF-170 13.3 9.9 Epoxysilane Dynasilan GLYEO 5.8 10.3 Araldite DY 1158 8.7 13.7 Silane-terminated polyether MS Polymer S303H 30.6 Silyl SAX400 30.6 Catalyst for silane crosslinking DBTDL 0.3 0.3 Silquest A-1120 1 1 Liquid epoxy resin Araldite GY 250 70.8 70.8 70.8 70.8 62.8 62.8 Hardener for epoxy resins Dicyandiamide 5.6 5.6 5.6 5.6 5.3 5.3 Properties Adhesive tape Gel content (after 7 d/RT) 22 20 20 19 28.5 30.3 Cured adhesive tape Tensile shear strength in 7.5 6.2 9.7 11.8 0.6 0.6 MPa (after 7 d/RT & 1.5 h/180 C.) Impact peel strength in 6.5 10.5 1 2 not measurable not measurable N/mm (after 7 d/RT & (too soft) (too soft) 1.5 h/180 C.)

(13) In a further series of experiments, a silane-functional apolar polymer in the form of a silane-functional poly(tetramethylene) glycol (S-PTMEG) was first produced. For this purpose, a hydroxysilane was first prepared by reaction of 3-aminopropyltriethoxysilane with L-lactide. Moreover, an isocyanate-functional poly(tetramethylene) glycol was by reaction of PolyTHF 2000 with Vestanat IPDI in a ratio of 1:2. The hydroxysilane was subsequently reacted at 80 C. with the isocyanate-functional poly(tetramethylene) glycol at an OH/NCO ratio of 1.1/1, to give the S-PTMEG.

(14) The S-PTMEG was mixed subsequently by means of a centrifugal mixer with liquid epoxy resin, hardener, catalyst for silane crosslinking (Tyzor IBAY), and optionally aminosilane (Silquest A-1120), the further procedure being as described for example 1. The precise compositions of the materials investigated, and the physical properties ascertained, are reproduced in Table 2 below.

(15) TABLE-US-00003 TABLE 2 Ex. 5 Ex. 6 Ex. 7 Ex. 8 in wt % in wt % in wt % in wt % Component (designation) Silane-functional apolar polymer S-PTMEG 17.5 24.5 17.5 24.5 Liquid epoxy resin Araldite GY 250 47.8 41.3 47.1 40.6 Hardeners Dicyandiamide 3.7 3.2 3.6 3.2 Tyzor IBAY 1.1 1.1 1.1 1.1 Silquest A-1120 0.7 0.7 Properties Adhesive tape Gel content (after 15.9 23.2 27.3 35.2 7 d/RT) Cured adhesive tape Tensile shear strength 10.8 9.2 12.5 11.2 in MPa (after 7 d/RT & 1.5 h/180 C.) Impact peel strength in 0.5 2.9 1.2 4 N/mm (after 7 d/RT & 1.5 h/180 C.)

(16) From the results of the investigations it is evident that by adding Silquest A-1120 it is possible to improve the lap shear strength and the peel strength further by about 20%. In the case of the examples with a relatively high fraction of liquid epoxy resin, moreover, slightly better lap shear strengths are obtained.