Adhesives suitable for use in bonding applications

Abstract

The present invention relates to adhesives that are suitable for use in a broad variety of bonding applications. In particular, the present invention relates to adhesives that are suitable for use in polymer-to-metal, for example elastomer-to-metal, such as rubber-to-metal bonding applications, wherein the adhesives comprise at least one halogenated polyolefin, at least one epoxysilane having at least one terminal alkoxy silane group, at least one bis-silane, and optionally at lease one organic solvent.

Claims

1. An article comprising an adhesive layer, comprising: i) at least one halogenated polyolefin having a weight average molecular weight of 200,000 to 400,000, wherein the halogen content ranges from 55 to 90 percent by weight, present in an amount in the range of 1 to 30 wt.-%, based on the weight of the adhesive; ii) at least one epoxysilane having at least one terminal alkoxy silane group wherein the epoxysilane is present in an amount of 0.2 to 5 wt.-%, based on the weight of the adhesive; iii) at least one bis-silane, wherein the bis-silane has two silicon atoms per molecule, wherein the two silicon atoms are linked with each other by a divalent linkage group and each silicon atom carries three additional substituents, wherein at least one of the three additional substituents is an alkyl or alkoxy residue, and the bis-silane is present in an amount of 0.1 to 2 wt.-%, based on the weight of the adhesive; iv) optionally at least one organic solvent, wherein the weight ratio of epoxysilane to bis-silane in the adhesive is from 1:0.2 to 1:0.8 wherein the adhesive layer is, disposed between (a) a polar elastomeric substrate selected from the group consisting of nitrile butadiene rubber, hydrogenated nitrile butadiene rubber and ethylene acrylic elastomers, and (b) a metallic substrate.

2. The article of claim 1, wherein the halogenated polyolefin is selected from chlorinated polyolefins.

3. The article of claim 1, wherein the epoxysilane comprises a single epoxy group and a single terminal alkoxy silane group per molecule.

4. The article of claim 1, wherein the epoxysilane is represented by formula (I) ##STR00015## wherein R.sup.a is a divalent linkage group, comprising 1 to 24 carbon atoms, R and R.sup.3 independently of one another are selected from C.sub.1-24 alkyl, C.sub.2-24 alkenyl, C.sub.1-24 alkoxyl or C.sub.3-24 acyl, and R.sup.2 is selected from C.sub.1-24 alkyl or C.sub.3-24 acyl, A is either ##STR00016## where R, R.sup.o and R.sup.d independently of one another are hydrogen or C.sub.1-6 alkyl; or ##STR00017##

5. The article of claim 1, wherein the epoxysilane is represented by formula (II), ##STR00018## wherein n is an integer from 1 to 10, m is an integer from 0 to 14, R.sup.1a and R.sup.3a independently of one another are selected from C.sub.1-24 alkyl, C.sub.2-24 alkenyl, C.sub.1-24 alkoxyl or C.sub.3-24 acyl, and R.sup.2a is selected from C.sub.1-24 alkyl or C.sub.3-24 acyl; or is represented by formula (IIa), ##STR00019## wherein v is an integer from 1 to 10, R.sup.1b and R.sup.3b independently of one another are selected from C.sub.1-24 alkyl, C.sub.2-24 alkenyl, C.sub.1-24 alkoxyl or C.sub.3-24 acyl, and R.sup.2b is selected from C.sub.1-24 alkyl or C.sub.3-24 acyl.

6. The article of claim 1, wherein the epoxysilane is selected from 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltri-n-propoxysilane, 3-glycidyloxypropyltri-iso-propoxysilane, 3-glycidyloxypropyltri-n-butoxysilane, 3-glycidyloxypropyltri-iso-butoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltriethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltri-n-propoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltri-iso-propoxysilane, gamma-(3,4-epoxycyclohexyl)-propyltrimethoxysilane, gamma-(3,4-epoxycyclohexyl)-propyltriethoxysilane, gamma-(3,4-epoxycyclohexyl)-propyltri-n-propoxysilane, gamma-(3,4-epoxycyclohexyl)-propyltri-iso-propoxysilane, and/or combinations thereof.

7. The article of claim 1, wherein the bis-silane is represented by formula (III),
(R.sup.5O).sub.(3-q)(R.sup.4).sub.qSiBSi(R.sup.6).sub.p(OR.sup.7).sub.(3-p)formula (III) wherein p is 0 to 3, q is 0 to 3, B represents a divalent linkage group comprising 1 to 24 carbon atoms and at least one heteroatom selected from N, S or O, each R.sup.4 and each R.sup.6 is independently selected from hydrogen, halogen, C.sub.1-24 alkyl, C.sub.2-24 alkenyl, C.sub.1-24 alkoxyl or C.sub.3-24 acyl, and each R.sup.5 and each R.sup.7 is independently selected from C.sub.1-24 alkyl or C.sub.3-24 acyl.

8. The article of claim 1, wherein the bis-silane is represented by formula (IV),
(R.sup.15O).sub.3Si(R.sup.14).sub.k-D-(R.sup.14).sub.kSi(OR.sup.15).sub.3formula (IV) where k is 0 or 1, each R.sup.15 is independently selected from C.sub.1-4 alkyl or C.sub.1-4 acyl, each R.sup.14 is independently selected from C.sub.1-6 alkylene or C.sub.6-12 arylene, and D is selected from one of the following divalent groups: ##STR00020## where R.sup.8a is selected from hydrogen, C.sub.1-24 alkyl or C.sub.6-18 aryl; ##STR00021## where each R.sup.9a is independently selected from hydrogen, C.sub.1-24 alkyl, or C.sub.6-18 aryl, and R.sup.10a is selected from C.sub.1-24 alkylene or C.sub.6-18 arylene; ##STR00022## where Y is selected from O, S or NR.sup.11a, Z is selected from O, S, and NR.sup.12a, wherein R.sup.11a and R.sup.12a independently of one another are selected from hydrogen, C.sub.1-24 alkyl or C.sub.6-18 aryl, and X is the selected from O or S, with the proviso that Y and Z are not both O or S.

9. The article of claim 1, wherein the bis-silane is selected from bis-(trimethoxysilylethyl)amine, bis-(triethoxysilylethyl)amine, bis-(tri-n-propoxysilylethyl)amine, bis-(tri-iso-propoxysilylethyl)amine, bis-(trimethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)amine, bis-(tri-n-propoxysilylpropyl)amine, bis-(tri-iso-propoxysilylpropyl)amine, bis-(trimethoxysilylethyl)urea, bis-(triethoxysilylethyl)urea, bis-(tri-n-propoxysilylethyl)urea, bis-(tri-iso-propoxysilylethyl)urea, bis-(trimethoxysilylpropyl)urea, bis-(triethoxysilylpropyl)urea, bis-(tri-n-propoxysilylpropyl)urea, bis-(tri-iso-propoxysilylpropyl) urea, and combinations thereof.

10. The article of claim 9, wherein the adhesive is substantially free of nitroso-containing compounds.

11. The article of claim 1, wherein the adhesive is a one-part adhesive.

Description

EXAMPLES

A. Sample Preparation

(1) The adhesive formulations were prepared by combining the listed ingredients in a solvent mixture of methoxy propyl acetate and xylene.

(2) The metal substrates (mild steel, size of 10.2 cm2.5 cm) were prepared by removing all surface contaminations, such as oil grease and rust. The adhesive formulations were applied on the metal surfaces at a film thickness of 8 m using an applicator (nozzle diameter 2 mm, air pressure 3.5 bar; distance approx. 50 cm), wherein a surface area of 6.45 cm2 was covered by the adhesive. After a thin and uniform coating was formed on the metal substrates, the coated metal substrates were dried at 22 C. for 20 min.

(3) The formed coated metal substrates where then bonded to DOTG-free Vamac or HNBR (elastomeric substrates) by injection molding the elastomeric substrates onto the coated metal substrates under a pressure of >5 MPa at a temperature of 160 C. for 12 min.

(4) The formed assembly was cooled to 20 C. and the initial bond strength was determined as described below. By additionally exposing the aforementioned assembly to a temperature of 175 C. for 4 hours the vulcanization reaction of the elastomeric substrate was completed and the post-cured bond strength of the fully vulcanized assembly was determined as described below.

B. Test Methods

(5) Initial Bond Strength

(6) Bonded parts were pulled to destruction according to ASTM Test D429Method B. Bonded parts were tested in peel with a peel angle of 45 degrees using an Instron 5567A. The tests were conducted at 22 C. with a test speed of 50 mm per minute.

(7) Post Cured Bond Strength

(8) After 4 hours at 175 C. the formed assembly was allowed cool to 20 C. and then the post cured bond strength was determined according to ASTM Test D429Method B as described above.

(9) Stressed Boiling Water Test

(10) The formed assembly was stressed at a 90 angle using a 2 Kg weight attached to the elastomeric substrate. The stressed assembly was then placed in boiling water for an extended period to ascertain how long the assembly can withstand the conditions before failure occurs. Details of the stressed boiling water tests can be found in Handbook of rubber bonding, Smithers Rapra Press, Bryan Crowther, chapter 3.8, pages 110-112.

C. Adhesive Formulations and Bonding Performance

(11) In the following examples of Table 1 and 2, a number of adhesive formulations are given on a weight percent basis. The adhesive formulations were evaluated for bonding performance on polar elastomeric substrates, such as NN-di-ortho-tolyl guanidine (DOTG)-free Vamac and HNBR.

(12) TABLE-US-00001 TABLE 1 Initial and post-cured bond strengths on DOTG-free Vamac Formulation (wt.- % basis) Ingredient 1 2 3 4 Halogenated polyolefin 10 10 13 13 Superchlon HE1200.sup.[1] Carbon black 2.5 2.5 2.5 2.5 Epoxysilane 1 1.6 1 1.5 3-Glycidyloxypropyltrimethoxysilane Bis-silane 0.3 0.6 0.3 0.6 Bis-(trimethyoxysilylpropyl)urea Methoxy propyl acetate 6 6 6 6 Xylene 80.2 79.3 77.2 76.4 Initial Bond Strength (N/mm) 22.6 21.9 20.9 21.0 Post-cured bond strength (N/mm) 27.2 27.3 22.9 30.2 .sup.[1]Chlorinated polyethylene

(13) TABLE-US-00002 TABLE 2 Initial bond strengths and stressed boiling water tests were performed on HNBR Formulation (wt.- % basis) Ingredient 6 7.sup.[a] 8 Halogenated polyolefin 1 10 10 13 Superchlon HE1200.sup.[1] Carbon black 2.5 2.5 2.5 Epoxysilane 1 1.6 1 3-Glycidyloxypropyltrimethoxysilane Bis-silane 0.3 0.3 Bis(trimethyoxysilylpropyl) urea Methoxy propyl acetate 6 6 6 Xylene 80.2 79.9 77.2 Initial Bond Strength (N/mm) 29.5 11.2 34.4 Stressed (2 Kg) boiling water test >8 hrs <1 hr >8 hrs .sup.[1]Chlorinated polyethylene .sup.[2]Comparative formulation

(14) Comparative formulation 7 demonstrates that an insufficient bonding strength is obtained, when an adhesive formulation is used which does not comprise a combination of halogenated polyolefin, epoxysilane and bis-silane.