MEMBRANE ADHESIVE MEDIUM

Technical Field of Invention

Although the use of α-cyanoacrylate monomer- containing compositions as adhesives are well known, such compositions exhibit low viscosities and rapid polymerization and are thus incapable of broad area bonding and disparate non-continuous surface bonding. The present invention although exhibiting all of the favorable adhesive qualities of traditional α-cyano¬ acrylate monomer-containing compositions provide the user with a pliable web which extends the use of such compositions far beyond prior art adhesives.

Background of the Invention It has long been known that adhesive compositions containing monomeric α-cyanoacrylates exhibit high strength bonding characteristics for all kinds of materials, such as glass, metals, plastics, rubber, wood, cement, paper and cloth. However, these compositions exhibit very low viscosities in the range of 5 to 500 cps and, as such, the utilization of these adhesive compositions has been limited.

Recognizing this problem, applicant has proposed an α-cyanoacrylate monomerrcontaining composition in the form of a gel which is the subject of co-pending

Application Serial No. 639,340 , filed on 10 August 1984, Further, applicant has proposed a reinforced thixo- tropic α-cyanoacrylate containing gel composition which is not only thickened but, as the name implies, exhibits the rheological properties of a thixotrope. The later invention is the subject of co-pending Application Serial No. 639,339, filed on August 10, 1984.

Although the adhesive compositions referred to in the previous paragraph have vastly expanded the utility of α-cyanoacrylate monomer-containing adhesives, it has still not been possible, prior to the present

invention, to employ such compositions for broad area bonding and disparate non-continuous surface- bonding. As a result, when the practitioner _^ wished to adhesively bridge two or more surfaces to one another, an adhesive other than one containing α-cyanoacrylates was sought. As a result, the user was deprived of the fast setting tenacious bond achieved through the use of α-cyano¬ acrylate monomer-containing adhesives in such applica¬ tions. Although it is well recognized that adhesives containing α-cyanoacrylate monomers exhibit excellent bonding properties, such compositions do exhibit certain other drawbacks. Besides the viscosity limitation referred to above, such compositions tend to exhibit a certain degree of brittleness and lack of shock resistance resulting in their tendency to crack and pull away from a support surface under an applied bending or shear force. Although this tendency is somewhat modified by practicing the teachings of applicant's co-pending O.S. Application Serial No.

639,339, it was recognized that further improvement in the physical properties exhibited by such compositions could be made.

It is thus an object of the present invention to provide an α-cyanoacrylate' monomer-containing medium which does not exhibit the disadvantages which are exhibited by prior compositions when used as adhesives. It is yet another object of the present invention to provide a medium for the adhesive bonding of two or more surfaces which is capable of bridging said surfaces in a manner unobtainable by prior adhesive compositions.

It is yet a further object of the present invention to provide an α-cyanoacrylate containing medium which is tougher and more shock resistant than adhesive compositions of the prior art.

It is still another object of the present invention to provide an α-cyanoacrylate containing medium capable of broad area and disparate surface bon ing. These and further objects can be more readily appreciated when considering the following disclosure.

Summary of the Invention

The present invention deals with a medium for the adhesive bonding of two or more surfaces. The medium comprises a support membrane having been wetted with an α-cyanoacrylate monomer-containing composition. The membrane is comprised of filaments which are substan¬ tially insoluble in and inert to said α-cyanoacrylate monomer-containing composition. Although virtually any α-cyanoacrylate monomer- containing composition can be employed in practicing the present invention, it is preferred that, the gel composition disclosed and claimed in applicant's co- pending Application Serial No. 639 _t 340 _r t e disclosure of which is hereby incorporated by reference, be employed herein as the ideal adhesive component of the medium.

Detailed Description of th f'e I ^■ nvention

Broadly, the present invention comprises a support membrane which has been wetted with an α-cyanoacrylate monomer-containing composition. As previously noted, any conventional α-cyanoacrylate adhesive can be employed including thickened compositions such as those disclosed in U.S. Patent Nos. 3,178,379 and 2,794,788. hen employing gelled compositions of applicant's co- pending U.S. Application Serial No. .6.39,.340- ' it is contemplated that the composition include an α -cyanoacrylate monomer of the following structure:

CH - ? - C - 0 - R

CN 0

wherein R is a member selected from a group consisting of an alkyl from approximately 1 to 16 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl and amyl; phenyl, cyclohexyl, alkoxy, such as ethoxyethyl and ethoxyethyl, allyl and furfuryl groups. The composition further includes a dry colloidal fumed silica such as Cab-O-Sil N 70 TS which is available from Cabot Corporation. A plasticizer is also used to maintain the composition in a single phase and generally comprises a member selected from the group consisting of monofunctional aliphatic esters, difunctional aliphatic esters, difunctional aromatic esters, phosphate esters, phosphonate esters. and other well known materials. To further enhance the stability of the composition, a stabilizer is generally included. Suitable stabilizers include one or more members selected from the group consisting of sulfur dioxide, hydrogen fluoride, nitrogen oxide, phosporic acid, phosphorous acid, boron trifluoride, stannic chloride, ferric chloride, sultones and aromatic sulfonic acids.

As α-cyanoacrylates can polymerize by the free radical route, to enhance'shelf life, it is preferable that a free radical scavenger be included in the composition. Such scavengers include hydroquinone, monoethylether of hydroquinone, butylated hydroxy- anisole, butylated hydroxytoluene and t-butyl hydroquinone. It is important that the filaments which comprise the membrane of the present invention be of a material which is insoluble in and inert to the α-cyanoacrylate monomer containing composition. As such, the filaments should not contain significant amounts of residual catalyst, such as peroxides, which are used in certain manufacturing techniques for polyolefins etc. Thus,

although not an absolute requirement, it is preferable to employ filaments which were thermally polymerized and not catalytically polymerized wi their manufacture. In view of their inertness and relative availability, it has been found that polypropylene and polyethylene are preferred materials for use as filaments herein. These materials are available from Hercules Company and are sold under the trade names, type 151 and 153. Other fibers, both synthetic and natural, can be used as the filaments making up the web of the present invention including, besides polyolefins, polytetra- fluoroethylene, polyesters, polyamides and cellulose. When using cellulose, it is preferable to treat the material with an inerting agent, such as trimethyl- chlorosilane. Other filaments which may happen to have active hydroxyl groups can be employed if the hydroxyl groups have been rendered chemically neutral to α-cyanoacrylate monomer containing, compositions. Neutralization is generally carried out by silation, esterification and etherification.

Although a wide latitide can be employed in the selection of filaments of varying physical dimension, it was found appropriate to employ filaments of a denier between approximately 1 to 20 and more preferably between approximately 3 to 6 and most preferably between approximately 4 to 5. Depending upon the end use of the membrane medium of the present invention, a wide latitude can be exercised in fabricating membrane of varying weights. As a general rule, membrane having a weight between approximately

1.0 g/yd. 2 to 1,000 g/yd.2 can be employed in practicing the present invention. More specifically, weights between approximately 10 g/yd. 2 to 30 g/yd.2 have been found to be most appropriate for the average application of bonding two or more surfaces to one another.

The membrane should also be characterized as being of a physical structure which is capable of being wetted with the α-cyanoacrylate monomer containing composition. As such, the membrane can be woven, knitted or nonwoven from filaments which have been combined to satisfy the above-referenced requirement. Those support materials disclosed in U.S. Patent Nos. 4,376,438 and 4,411,262, the disclosures of which are incorporated by reference, can be used herein. From an economic standpoint, because the weaving of filaments to make a membrane is substantially more expensive, it is suggested that the membrane of the present invention preferably be composed of nonwoven filaments, such as those which have been thermally bonded to one another to make a composite structure. Such fabrication methods are notoriously well known in the art and include the techniques of spun bonding and calendering, thermally bonding of a carded web,, thermally bonding a needle punched web, and thermally bonding of an arachne web. It is preferred to employ a thermally bonded spun web. Such techniques are notoriously well known and are taught in Manual of Nonwovens by Prof. Dipl. Ing. Dr. Radko Krcma (1971), Nonwoven Fabrics by J. Robert Wagner (1982) and Nonwoven Materials - Recent Developments by M.T. Qillfes (1979), the disclosures of which are incorporated by reference herein.

Generally, the α-cyanoacrylate monomer containing composition can simply be applied to the above- described membrane by any well known technique. For example, kiss rollers and knife blades can be used to work the composition within the web after quenching in the adhesive solution. The rollers and blades should be composed of materials such as polytetrafluoro- ethylene or stainless steel which are inert to the α-cyanoacrylate monomer containing composition. Once saturation of the membrane is achieved, it can be rolled or folded into inert packaging such as

polypropylene pouches, bags or foils and sealed for later use.

Although the composition can -£>e added to the membrane without any extraordinary preparation, it is preferable that the web be treated prior to its contact with the α-cyanoacrylate monomer containing composition to enhance the stability of the final product. It is preferable to add the membrane to a container of non- ionic low-boiling solvent such as benzene, toluene, xylene, hexane, chloroform, dichloromethane, acetone, ethylene dichloride and ethyl acetate. Once the solvent and other impurities such as ethoxylated fatty acids are removed. by filtering the solvent from the filaments, further volatile materials such as gaseous HCl and water are stripped from the membrane under vacuum with or without the addition of further solvents. ^■

Example 1.

Approximately 500 mis of benzene was poured into an appropriately size flask which was then charged with 92 parts of ethoxyethyl α-cyanoacrylate monomer. With stirring, approximately 0.003 weight percent sulfur dioxide was added to stabilize the composition and the monomer was further protected with 0.07 weight percent hydroquinone as the free radical scavenger.

The viscosity of the above-described liquid composition was regulated by the addition of one part by weight polymethylmethacrylate and the possibility of phase separation minimized by the addition of one part by weight dioctylphthalate.

With good agitation, 6 parts by weight hydrophobic silated dry fumed silica was added slowly. In this instance, the fumed silica was Cab-O-Sil N 70 TS, which is available from the Cabot Corporation. Approximately 200 is of additional benzene was added to the above- recited composition and stirring continued for approxi-

mately 30 minutes. The flask, holding the composi¬ tion, was then fitted with dry nitrogen inlet and vacuum outlet lines whereupon the solvent was stripped from the composition at pressures of from 1 to 5 milli- meters Hg while bubbling nitrogen through the mix. The result was a stable thixotrope of an<5^-cyanoacrylate monomer containing adhesive.

Example 2

The adhesive composition of Example 1 was impreg- nated with a kiss roll applicator to approximately 100 percent pick-up level onto a 100 percent polypropylene, thermally bonded non-woven scrim which is available from International Paper Co. as Product No. 9317212.

2 The scrim was measured as being approximately 11 g/yd , while the adhesive was applied thereto at an additional

2 11 g/yd loading. The scrim, coated with the adhesive, was then stored in a suitable pouch and hermetically sealed to keep out moisture and air.

Example 3 Approximately 1/2 sq.ft. of the adhesive loaded scrim prepared pursuant to Example 2 was placed onto an equivalent size of 1/2 inch thick expanded honeycomb, which is available from Hexcel Corp. under the trademark NOMEX. This particular honeycomb possessed repeating cells of 1/8 inch spacing. On the other side of the loaded scrim was placed a 1/2 sq.ft. section of 1/2 inch thick coated paper honeycomb available from Honeycomb Structural Products. This particular structure displayed repeating honeycomb cells every 1/4 inch apart.

Manual pressure was supplied to the honeycombs for two minutes. The result was a significant bond which could not be manually deflected. It is clearly evident that the membrane of the present invention is capable

of bonding to compound surfaces which otherwise would be very difficult to combine.

•f Example 4

The forearm of a 40 year old male was prepared by placing onto the forearm an 18 inch tube of a stock¬ inette available from Isopedix Corporation under the trademark PROSET. The stockinette was sprayed lightly with the PROSET catalyst, which is dimethyltoluidine (in freon solvent). A polypropylene thermally bonded non-woven scrim, also available from International Paper Co. having a density of 24 g/yd 2 was impregnated with the gel prepared pursuant to Example 1. Prior to coating, the fabric was split into 4" x 36" strips. The fabric was coated with the gel by means of a kiss roll, such as that employed in Example 2 and the strips then wound to make short rolls which were thereupon applied to the PROSET stockinette to form a short arm orthosis. The resulting orthosis could not be deflected and proved an excellent, lightweight support for the forearm.