Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-06-19
2002-06-25
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C106S287110, C106S287130, C156S326000
Reexamination Certificate
active
06409874
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods for adhering rubber to metal surfaces.
BACKGROUND OF THE INVENTION
Reliable metal to rubber adhesion is required for many commercial and industrial parts. For example, rubber to metal adhesion is required in the automotive, medical, appliance and other industries where basic functions such as fluid control, energy conversion, sealing, vibration isolation and/or combinations of these functions are required. Additionally, tire to metal, metallic reinforcement of conveyor belts and hoses, and vibration dampening on motor and railroad mounts are further examples of industrial situations in which a variety of metals need to be adhesively bound to an associated rubber substrate.
Fluorosilicone elastomers have become increasingly popular due to their excellent high and low temperature performance. These elastomers also demonstrate advantageous resistance to fuels, oils, chemicals etc. due to the presence of the trifluoropropyl moiety in their repeat unit formula
The polysiloxanes are crosslinked via pendent vinyl moieties by curing with peroxides. Compounds of fluorosilicones are formulated with reinforcing silica, various processing aids and other additives. These elastomers ar of special interest in the automotive industry where they can be used as conduits, valves or diaphragms and the like if properly adhesively bound to ancillary metal equipment.
It has however been difficult to bond these surfaces to metals, especially in those instances in which the adhesively bound surfaces are subjected to fuels, oils and other organic solvents.
Accordingly, it is an object of the present invention to provide methods for effectively adhesively bonding metal to rubber surfaces. It is an even more especially preferred object to provide a method for bonding fluorosilicone rubbers to a variety of metallurgies including, stainless steel, mild steel, brass, and aluminum.
SUMMARY OF THE INVENTION
These and other objects are met by the instant invention. Effective adherence of rubber, especially flourosilicone rubbers, to a variety of metal surface has been shown by use of an adhesive treatment comprising (I) an organofunctional silane and (II) a non-organofunctional silane.
The silanes (I) and (II) are partially hydrolyzed by addition thereof to an acidic aqueous or alcoholic medium. Solutions or dispersions of the silanes (I) and (II) are then applied to the requisite rubber or metal surface by dip coating, spraying, roller coating etc. After application of adhesive treatment to the surfaces, the surfaces may be blow dried or heated.
Although emphasis has been placed on effective adhesive bonding of fluorosilicone rubbers to a variety of metal surfaces, the adhesive treatment may also be used in conjunction with other rubber types such as EPDM, fluorocare rubber, and vinyl methyl silicone rubber. Tested metals with which the adhesive treatment has demonstrated efficacy include brass, stainless and mild steel and aluminum.
The invention will now be more specifically described in the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The adhesive treatment of the invention comprises use of an organofunctional silane (I) and a non-organofunctional silane (II).
I. Organofunctional Silane
This is a substituted silane compound having at least one free organofunctional moiety attached to an Si atom wherein the organofunctional moiety is adapted to react with the rubber substrate. More preferably, the organofunctional moiety is attached to one end of the Si atom with the remaining Si valences bonded to groups selected from C
1
-C
6
alkoxy or acetoxy. More particularly, suitable organofunctional silane compounds can be represented by the formula
wherein R is chosen from amino, C
1
-C
6
alkylamino, vinyl, ureido, ureido substituted C
1
-C
6
alkyl, epoxy, epoxy substituted C
1
-C
6
alkyl, mercapto, mercapto substituted C
1
-C
6
alkyl, cyanato, cyanato subsituted C
1
-C
6
alkyl, methacrylato, methacrylato substituted C
1
-C
6
alkyl, and vinyl benzyl moieties. The most preferred R substituent is vinyl. R
1
, R
2
, and R
3
are independently selected from C
1
-C
6
alkyl and acetyl groups.
Exemplary organofunctional compounds include &ggr;-aminopropyltriethoxysilane (&ggr;-APS); &ggr;-mercaptopropyltrimethoxysilane (&ggr;-MPS); &ggr;-ureidopropyltrialkoxysilanes (&ggr;-UPS); &ggr;-glycidoxypropyltrimethoxysilane (&ggr;-GPS); and a host of vinyl silanes (wherein R is vinyl). Most preferred are vinytrimethoxysilane, vinyltriethoxysilane and vinyltriacetoxysilane with vinyltrimethoxysilane (VS) most preferred.
II. Non-Organofunctional Silane
These are substituted silane compounds wherein one or a plurality of the Si valences are bonded to C
1
-C
6
alkoxy and/or acetoxy groups. These may be represented by the formula II
wherein m is 0 or 1; n is 0 or 1; and p is 0 or 1; with R
4
selected from an aliphatic (saturated or unsaturated) group; aromatic group, or C
1
-C
6
alkoxy or acetoxy; R
5
, R
6
, R
7
, R
8
, R
9
, and R
10
may be the same or different and are chosen from C
1
-C
6
alkoxy, H, or acetoxy; X, when present, is alkylene, alkenylene, phenylene or amino.
Exemplary non-organofunctional silanes include methyltrimethoxysilane (MS); propyltrimethoxysilane (PS); 1,2bis(triethoxysilyl)ethane (BTSE); bis(methyl diethoxysilyl)ethane (BDMSE); 1,2-bis(trimethoxysilyl)ethane (TMSE); 1,6-bis(trialkoxysilyl)hexanes; 1,2-bis-(triethoxysilyl)ethene; and 1,2-bis-(timethoxysilyipropyl) amine. Preferred are BTSE and BDMSE with BTSE most preferred.
The non-organofunctional silanes (I) and the non-organofunctional silanes (II) are both partially hydrolyzed by addition thereto into an aqueous/alcoholic solution including preferably a 40/60 vol % mix of ethanol/water. The silanes are added in an amount by volume of 0.5-10% based on the volume of the aqueous/alcoholic solution. Preferably, the silanes are present in an amount by volume of from about 1-5 vol %. Optimal adhesion has been shown when the pH of the solution is adjusted to between about 1-7. Most preferred is a pH of about 4.
The hydrolyzation of the silanes I and II is dependent on the pH of the solution. For example, acetic acid, oxalic acid and phosphoric acid may be mentioned as exemplary pH adjustment agents. Based on presently available data, it is preferred to use acetic acid as the pH adjustment agent.
Preliminary results indicate that the solution should be an ethanol/water solution with a 40/60 ethanol:water volumetric ratio being presently preferred.
The intended interfacial surfaces of the metal to rubber parts are contacted by the silanes (I) and (II) by dipping, spraying, painting etc. The following procedures were tried and found effective:
(1) blow drying—the metal parts are dipped in the silane solution for at least 30 s and then are blown dry by filtered air;
(2) air drying—the metal parts are dipped into the silane solution for at least 30 s and are allowed to dry for at least 30 min in the air;
(3) prebaking—the metal parts are dipped into the silane solution for at least 30 s and then dried in an air circulated oven for 20 min at 120° C.;
(4) spraying—the silane solution was sprayed on the metal parts and the parts were blown dry by filtered air; and
(5) preheated spraying—the silane solution was sprayed onto the metal parts which were then preheated in an air circulated oven for 20 min and then blown dry by filtered air. In those situations in which brass metallurgy is to be adhesively bound to desired rubber, the blow drying and spraying techniques appear optimal.
When brass and fluorosilicone substrates are to be bonded, a mixture of VS and BTSE should be used in a single layer approach. A mixture of 3% VS and 2% BTSE in EtOH/H
2
O appears optimal in this situation.
Surprisingly it was found that a two step or two layer coating system appeared optimal for Al, SS and MS metals. That is, a first layer of non-organofunctional silane (II) is applied to the metal surface. Then, the organofunctional silane (I) is applied over the first layer as a se
Van Der Aar Cornelis P. J.
Van Ooij Wim J.
Biebel & French, L.P.A.
Gallagher John J.
Vernay Laboratories, Inc.
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