Heat activated silicon-based adhesive

Adhesive compositions affording strong bonds of high environmental resistance between elastomers and substrates such as metals are provided. The adhesive compositions comprise an admixture of (i) olefinic organosilane, (ii) water, and (iii) an alumino zirconium metallo-organic complex of chelated aluminum moiety, an organofunctional ligand and zirconium oxyhalide. The adhesive composition preferably includes a polymer resin selected from phenolic-formaldehyde resins, urea-formaldehyde resins, resorcinol-formaldehyde resins or melamine-formaldehyde resins.

FIELD OF THE INVENTION 
This invention relates to adhesive compositions suitable for bonding 
elastomeric materials to other substrates. More particularly the invention 
is directed to adhesive compositions which afford strong bonds of high 
environmental resistance between elastomers and substrates such as metal. 
BACKGROUND OF THE INVENTION 
Compositions, including silicon-based adhesive compositions, for bonding 
rubber to metal and other substrates are well known in the art. 
In the search for the ideal all-purpose adhesive there have been developed 
a variety of adhesive compositions which have been utilized with varying 
degrees of success in bonding elastomeric materials to themselves or to 
other substrates such as metal substrates. As a general rule, the known 
adhesives which have been effective as simple rubber-to-metal bonding 
agents are limited with respect to the type of elastomer to be bonded. 
That is to say, an adhesive which is capable of providing an acceptable 
bond with butadiene/styrene elastomers may be unsatisfactory with 
ethylene/propylene/ nonconjugated diene terpolymer (EPDM) elastomer or 
polyisobutylene/ isoprene elastomer. 
In addition to the problem of lack of versatility prior art adhesive 
compositions, including silicon-based adhesives, tend to suffer from one 
or more other disadvantages, including a general inability to afford 
optimum adhesion, particularly at elevated service temperatures; poor 
storage stability at room and/or elevated temperatures; poor resistance to 
prebake. Moreover, the resistance of the adhesive bond to environmental 
conditions such as oils, solvents and moisture is often poorer than 
normally desired in many commercial applications. Thus, there remains a 
need for more effective silicon-based adhesive formulations which can be 
employed in the bonding of various elastomeric materials to substrates 
such as metal and which exhibit an adhesive bond of improved resistance to 
degradation from environmental factors. 
It is an object of the invention to provide adhesive compositions for 
bonding a variety of elastomers to various substrates, particularly metal 
substrates. 
Another object of the invention is to provide adhesive compositions which 
afford strong elastomer-substrate adhesive bonds which exhibit high 
environmental resistance. 
SUMMARY OF THE INVENTION 
These and other objects of the invention are obtained by an adhesive 
composition comprising: 
(i) about 2.5 to 70% by weight of an olefinic organosilane 
(ii) about 0.25 to 32% by weight water; and 
(iii) about 0.25 to 20% by weight on a dry basis of an aluminum zirconium 
metallo-organic complex of chelated aluminum moiety, an organofunctional 
ligand and a zirconium oxyhalide, the organofunctional ligand being 
complexed with and chemically bound to the chelated aluminum moiety and 
the zirconium; 
said aluminum moiety having the formula: 
Al.sub.2 (OR.sub.1 O).sub.2 A.sub.a .sub.b B.sub.c wherein A or B is 
hydroxy or halogen and a, b and c are numerical values such that 2a+b+c=6, 
and (OR.sub.1 O) is an alpha, beta or alpha, gamma glycol group in which 
R.sub.1 is an alkyl group having 1 to 6 carbon atoms or an alpha-hydroxy 
carboxylic acid residue having the formula: 
##STR1## 
wherein R.sub.3 is H or an alkyl group having 1 to 4 carbon atoms; 
said organofunctional ligand is an amino functional carboxylic acid having 
2 to 18 carbon atoms or a mercaptofunctional carboxylic acid having 2 to 
18 carbon atoms; and 
said zirconium oxyhalide moiety has the formula: 
EQU ZrA.sub.d B.sub.e 
wherein A and B are as above defined and d and e are numerical values such 
that d+e=4; the molar ratio of chelated aluminum moiety to zirconium 
oxyhalide moiety being from 1.5 to 10, and the molar ratio of 
organofunctional ligand to total metal being from about 0.05 to 2. 
In a preferred embodiment, the adhesive compositions of the invention 
optionally include about 1 to 95% by weight, preferably 30% to 70% by 
weight as measured dry weight, of a polymer resin selected from the group 
consisting of phenolic-formaldehyde resins, urea-formaldehyde resins, 
resorcinol-formaldehyde resins and melamine-formaldehyde resins. 
The adhesive compositions are preferably diluted with an inert solvent to a 
total solids content of 1 to 55% by weight, preferably from 1 to 12% by 
weight. Particularly preferred are adhesive compositions of the invention 
including phenolic-formaldehyde resins, diluted to a total solids content 
of about 7% by weight. 
DETAILED DESCRIPTION OF THE INVENTION 
The olefinic organosilane component of the invention can broadly be 
described as those organosilane compounds capable of undergoing both the 
hydrolytic reactions typical of alkyl esters of silicic acid and free 
radical reactions via the alpha-olefin unsaturated bond that characterizes 
the compounds. 
The preferred organosilanes have the structure: 
##STR2## 
wherein R.sup.1 is a monovalent aliphatic, cycloaliphatic or aromatic 
radical having from 1 to 20 carbon atoms, and is preferably selected from 
the group consisting of alkyl radicals having from 1 to 4 carbon atoms, 
cycloalkyl radicals having from 4 to 7 ring carbon atoms, aryl radicals 
having 6, 10 or 14 nuclear carbon atoms, and such aryl radicals containing 
one or more substituent alkyl groups having from 1 to 4 carbon atoms; 
R.sup.2 is a monovalent aliphatic, cycloaliphatic or aromatic organic 
radical containing from 1 to 8 carbon atoms and is preferably selected 
from the group consisting of alkyl radicals having from 1 to 4 carbon 
atoms, --R.sup.3 --O--R.sup.4 --, and 
##STR3## 
where R.sup.3 is an alkylene group having from 1 to 4 carbon atoms and 
R.sup.4 is an alkyl group having from 1 to 4 carbon atoms; 
x is zero or 1, and preferably is zero; 
R.sup.5 is a divalent hydrocarbon radical, including aliphatic, 
cycloaliphatic and aromatic divalent radicals, having from 1 to 20 carbon 
atoms, and is preferably an alkylene of 1 to 4 carbon atoms, cycloalkylene 
of 4 to 7 carbon ring carbon atoms and arylene of 6 to 14 nuclear carbon 
atoms; and n is 0 or 1. 
Representative organosilanes which are suitable for use in the practice of 
the invention include without limitation vinyltrimethoxysilane, 
vinyltriethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, 
vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, 
vinylethyldimethoxysilane, vinylethyldiethoxysilane, 
vinylphenyldimethoxysilane, vinylphenyldiethyloxysilane, 
vinylcyclohexyldimethoxysilane, 2-propenyltrimethoxysilane, 
2-propenyltriethoxysilane; 2-propenylmethyldiethoxysilane, 
2-propenylmethyldimethoxysilane, 2-propenylphenyldiethoxysilane, 
2-propenylcyclohexyldimethexysilane, 3-butenyltrimethoxysilane, 
3-butenyltriethoxysilane, 4-pentenyltriethoxysilane, 
4-pentenyltrimethoxysilane, 5-hexenetrimethoxysilane, 
5-hexenemethyldimethoxysilane, and the like. 
The aluminum zirconium metallo-organic complexes useful in the present 
invention are commercially available and their preparation is described in 
detail in U.S. Pat. No. 4,539,049, hereby incorporated by reference. 
In the aluminum moiety Al.sub.2 (OR.sub.1 O).sub.a A.sub.b B.sub.c, pairs 
of aluminum atoms are joined by bidentate chelating ligands wherein 
(1) --OR.sub.1 O-- is an alpha, beta or alpha, gamma glycol in which 
R.sub.1 is an alkyl, alkenyl, alkynyl, or aralkyl group having from 1 to 6 
carbon atoms, most preferably 2 to 3 carbon atoms, such ligands to be used 
exclusively or in combinations within a given composition, or 
(2) --OR.sub.1 O-- is an alpha-hydroxy carboxylic acid 
##STR4## 
having from 2 to 6 carbon atoms, preferably R.sub.1 is 2 to 3 carbon 
atoms. In each instance the organic ligand is bound to two aluminum atoms 
through two oxygen heteroatoms. 
Examples of chelating ligands (--OR.sub.1 O--) include: ethylene glycol, 
propylene glycol, glycerol, etc. Examples of alpha-hydroxy acids R.sub.3 
CH(OH)COO-- are glycolic, lactic, alpha-hydroxybutyric, and tartaric acids 
and those known in the art. 
The organofunctional ligand --OC(R.sub.2)O-- is a moiety which can be 
derived from an aminofunctional carboxylic acid having from 2 to 36 carbon 
atoms, the preferred range being 4 to 18 carbon atoms. 
Examples of specific aminofunctional carboxylate anions, --OC(R.sub.2))-- 
include the anions of glycine, alanine, beta-alanine, valine, leucine, 
isoleucine, phenylalanine, tyrosine, serine, threonine, methionine, 
cysteine, cystine, proline, hydroxyproline, aspartic, and glutaric acids. 
The stabilized chelated aluminum complex can be prepared by complexing a 
dimeric aluminum chlorohydrate moiety with bidentate chelating ligand 
which imparts hydrolytic stability, such as an alpha, beta, or alpha, 
gamma glycol of 1 to 6 carbon atoms. Complexation of the organofunctional 
ligand can be achieved by either introducing the ligand to a solution 
containing only zirconium oxyhalide, preferably zirconium oxychloride, or 
after the introduction and reaction of the zirconium oxyhalide with the 
stabilized aluminum chlorohydride. Details of the complexing reactions are 
given in full in U.S. Pat. No. 4,539,049. 
The polymeric resins which may be optionally included in the adhesive 
compositions of the invention are, for example, condensation products of 
an aldehyde having from 1 to 8 carbon atoms and phenolic, resorcinol, urea 
or melamine compounds, all well known and commercially available. 
Representative of aldehydes employed in the preparation of these polymer 
resins are formaldehyde, acetaldehyde, isobutyraldehyde, ethylhexaldehyde 
and the like and compounds known to be methylene bridge donors. 
The phenolic and resorcinol resins are conventionally prepared from the 
condensation of from about 0.8 to about 3 moles of aldehyde per mol of 
phenol or resorcinol compound in the presence of basic, neutral or acidic 
catalysts to afford an organic solvent-soluble resin having a molecular 
weight in the range of about 300 to 4,000, preferably about 300 to 1200. 
The presently preferred phenolic resins are the phenolic resols which are 
condensation products of formaldehyde and phenols. 
The urea-aldehyde and melamine resins of similar molecular weight are 
usually prepared by condensing aldehyde, preferably formaldehyde, with an 
excess of urea compounds and melamine compounds, respectively, in the 
presence of a basic catalyst such as pyridine, ammonia or 
hexamethylenetetramine. 
In cases where it is desired to increase or enhance the crosslink state of 
the polymer resin, the present invention contemplates employing in 
combination therewith a suitable methylene donor such as 
hexamethylenetetramine (HEXA) and hexamethoxymelamine (HMMA). 
As aforementioned, the components of the adhesive compositions of the 
invention are preferably dispersed in a solvent and adjusted to a solids 
content of up to 55%, preferably below 12%. Suitable solvents include 
polar solvents such as methyl alcohol, ethyl alcohol, propyl alcohol, 
isopropyl alcohol, butyl alcohol, isobutyl alcohol, ethylene glycol, 
propylene glycol, butylene glycol, acetone, methyl isobutyl ketone, ethyl 
acetate, butyl acetate, monoethylether and other aliphatic, 
cycloaliphatic; aromatic alcohols, ethers, esters and aromatic hydrocarbon 
solvents such as toluene, xylene, and the like. 
The adhesive compositions of this invention may be formulated in any 
suitable manner using conventional blending techniques. As a general rule, 
the organosilane and aluminum zirconium metallo-organic complex are first 
blended together in a portion of the solvent used. The polymeric resin, if 
employed, is then added either as a solid material or dissolved in the 
solvent. Finally the mixture is adjusted to the desired solids content. 
The thus-prepared admixture is itself suitable for use as an adhesive but 
the composition can include conventional additives, for example, fillers 
such as carbon black; pigments, extenders, diluents, corrosion inhibitors 
and the like, employing conventional techniques for formulating adhesive 
compositions. 
The adhesive compositions of the present invention have been found to be 
particularly suitable for bonding a wide variety of peroxide-cured 
elastomeric materials, especially vulcanizable elastomeric materials, to 
themselves or to other substrates, particularly inorganic substrates. 
Elastomers which can be bonded include, without limitation, peroxide-cured 
ethylene/propylene copolymer rubber (EPM); ethylene/propylene/diene 
terpolymer rubber (EPDM); silicon rubber, fluoroelastomers and the like. 
Substrates other than the elastomers per se which can be effectively 
bonded include fabrics such as fiberglass, polyamides, polyesters, 
aramids, metals and their alloys such as steel, stainless steel, lead, 
aluminum, copper, brass, bronze, zinc, and the like, including treated 
metals such as phosphatized steel, galvanized steel, and the like. 
The adhesive compositions are applied to the substrate surfaces in a 
conventional manner such as by dipping, spraying, brushing, and the like. 
Preferably, the substrate surfaces are allowed to dry after coating before 
being brought together. After the surfaces have been joined, the composite 
structures are heated in a conventional manner to effect curing of the 
adhesive compositions and simultaneous vulcanization of uncured elastomer 
stock. 
The following examples are provided for purposes of illustrating the 
invention, it being understood that the invention is not limited to the 
examples nor the specific details therein enumerated. In the examples, 
amounts are parts by wet weight unless otherwise specified. 
In the examples, the substrate to which the elastomeric material was bonded 
was not primed, unless otherwise noted. The composite assembly was cured 
at conventional conditions of time and temperature pressure for the 
specific elastomer. The adhesive bond was tested according to ASTM 
standard D-429-B at either 45.degree. and 90.degree. peel angles. 
The bonded assemblies are subjected to various tests, including room 
tempertures (RT) pull, the boiling water test and the hot oil test. In the 
RT pull test, the rubber body is peeled from the metal at a 45.degree. or 
90.degree. angle using a Scott tensile tester and the force required in 
pounds is recorded. In the boiling water test, bonded samples, after 
having been scored at the bond line and prestressed by bending the rubber 
body back from the metal, are immersed in boiling water for 2 hours. In 
the hot oil test, the bonded samples are immersed in 5W-30 motor oil at 
300.degree. F., for 70 or 120 hours. The samples so treated are tested for 
relative bond strength by pulling the rubber body from the metal. 
In the data given in the Examples, failure is expressed in terms of percent 
of failure in the rubber body, e.g., 95 R means that 95 percent of the 
failure occurred in the rubber body, with the remaining failure being 
between the adhesive composition and the metal.

EXAMPLE 1 
An adhesive formulation was prepared by first adding to an agitated blend 
tank at room temperature the following ingredients in order: 
______________________________________ 
Adhesive % Weight 
______________________________________ 
Vinyltriethoxysilane 6.53 
Aluminum Zirconate.sup.(1) 
2.33 
Deionized Water 1.85 
Methyl Alcohol 89.27 
Total Solid Cotent Approx. 7.0% 
100.00 
______________________________________ 
.sup.(1) Amino aluminum zirconium complex prepared by complexing 
propanolato aluminum chlorohydrate zirconium oxychloride and NH.sub.2 
CH.sub.2 CH.sub.2 COOH at a Al:Zr mole ratio of 9:1. 
The thus-prepared adhesive composition was coated on iron phosphatized cold 
rolled steel coupons and allowed to dry. The coated coupons were then 
placed into contact with silicone rubber and each assembly cured at 
360.degree. F. for 8 minutes at a pressure of 800 psi. 
The bonded assemblies were evaluated under the room temperature (RT) pull 
test and the hot oil test with the following results: 
______________________________________ 
Hot Oil 
RT Pull* Test** 
Lbs. Pull Failure, % 
Failure, % 
______________________________________ 
18.6 100 R 100 R 
______________________________________ 
*90.degree. peel angle 
**at 100.degree. F. for 70 hours 
EXAMPLE 2 
An adhesive formulation was prepared by first adding to an agitated blend 
tank at room temperature the following ingredients in order: 
______________________________________ 
% Weight 
Adhesive (Wet) 
______________________________________ 
Vinyltriethoxysilane 3.82 
Aluminum Zirconante.sup.(1) 
9.55 
Deionized Water .636 
Phenolic Resin 1.27 
Methyl Alcohol 84.72 
Total Solid Content Approx. 7.0% 
100.00 
______________________________________ 
.sup.(1) Amino aluminum zirconium complex prepared by complexing 
propanolato aluminum chlorohydrate zirconium oxychloride and NH.sub.2 
CH.sub.2 CH.sub.2 COOH at a Al:Zr mole ratio of 9:1. 
Bonded assemblies were prepared using the procedure described in Example 1 
and evaluated under the room temperature pull test and the hot oil test as 
in Example 1 except that the latter was conducted for 120 hours at 
300.degree. F. The results of the test were as follows: 
______________________________________ 
Hot Oil 
RT Pull* Test 
Lbs. Pull Failure, % 
Failure, % 
______________________________________ 
17.8 100 R 75 R 
______________________________________ 
*90.degree. peel angle 
EXAMPLE 3 
The thus-prepared adhesive composition of Example 2 was coated on 
vapor-degreased, cold rolled steel coupons and allowed to dry. The coated 
coupons were then placed into contact with EPDM rubber and each assembly 
cured at 425.degree. F. at 800 psi pressure. Another group of bonded 
assemblies were similarly prepared except that the coated coupons after 
drying were prebaked at 260.degree. C. for 5 minutes before contact with 
the EPDM rubber substrate. The bonded assemblies thus-prepared were 
subjected to the room temperature pull test with the following results: 
______________________________________ 
RT Pull* 
Adhesive Lbs. Pull 
Failure, % 
______________________________________ 
0' Prebake 45 95 R 
5' Prebake 38 95 R 
______________________________________ 
*90.degree. peel angle 
EXAMPLE 4 
An adhesive formulation was prepared by first adding to an agitated blend 
tank at room temperature the following ingredients in order: 
______________________________________ 
% Weight 
Adhesive (Wet) 
______________________________________ 
Vinyltriethoxysilane 2.66 
Aluminum Zirconate.sup.(1) 
12.99 
Phenolic Resin 10.49 
Carbon Black 2.35 
Ethyl Alcohol 62.90 
Toluene 8.61 
Total Solid Content Approx. 18.0% 
100.00 
______________________________________ 
.sup.(1) Amino aluminum zirconium complex prepared by complexing 
propanaltoaluminum chlorohydrate zirconium oxychloride and NH.sub.2 
CH.sub.2 CH.sub.2 COOH at a Al:Zr mole ratio of 9:1. 
The thus-prepared adhesive composition was coated on zinc phosphatized cold 
rolled steel coupons and allowed to dry. One group (0' Prebaked) of the 
coated coupons were contacted with a silicone rubber substrate and each 
assembly cured at 340.degree. F. for 15 minutes. Another group of coated 
coupons (5' Prebaked) were prebaked at 260.degree. C. for 5 minutes before 
contact and curing with the silicone rubber. 
The bonded assemblies were subjected to the RT pull test and the boiling 
water test with the following results: 
______________________________________ 
Boiling 
RT Pull* Water Test 
Adhesive Lbs. Pull Failure, % 
Failure, % 
______________________________________ 
0' Prebake 
30 100 R 98 R 
5' Prebake 
20 100 R 98 R 
______________________________________ 
*90.degree. peel angle 
Further bonded assemblies were prepared by repeating the above procedure 
but substituting an EPDM rubber substrate for the silicone rubber 
substrate and curing at 425.degree. F. for 2 minutes. The bonded 
assemblies were subjected to the RT pull test with the following results: 
______________________________________ 
RT Pull* 
Adhesive Lbs. Pull 
Failure, % 
______________________________________ 
0' Prebake 50 100 R 
5' Prebake 45 93 R 
______________________________________ 
*90.degree. peel angle 
The data of the foregoing examples demonstrate the strong adhesion provided 
by the adhesive compositions of the invention in the bonding of elastomers 
to metal substrates and also the high environmental resistance that 
characterizes the adhesive composition of the invention.