Underwater Bonding of Surface-Forming Material

United States Patent [191 Card et al. [54] [75] [73] [ ‘ l [21] [22] [63] [51] [52] [581 UNDERWATER BONDING OF SURFACE-CONFORMING MATERIAL Inventors: Steve W. Card, Minden; Joseph R. West, Bossier City, both of La. Assignee: Morton Thiokol, Inc., Chicago, 111. Notice: The portion of the term of this patent subsequent to Dec. 27, 2005 has been disclaimed. Appl. No.: 57,567 Filed: Jun. 1, 1987 Related U.S. Application Data Continuation-in-part of Ser. No. 884,443, Jul. 11, 1986. Int. Cl.4 ............ .. C09J 3/14; C09J 5/02 U.S. Cl. ............................... .. 156/307.3; 102/321; 156/331.2; 248/205.3; 523/177 Field of Search ........................ .. 156/331.2, 307.3; 523/177; 248/205.3; 102/321 [11] Patent Number: 4,793,887 [45] Date of Patent: * Dec. 27, 1988 [56] References Cited U.S. PATENT DOCUMENTS 3,896,077 7/1975 Leonard et al. ............... .. 156/331.2 FOREIGN PATENT DOCUMENTS 2078763 l/1982 United Kingdom ........... .. 156/331.2 Primary Examz’rzer—John J. Gallagher Attorney, Agent, or Fz'rm——Wayne E. Nacker; Gerald K. White [57] ABSTRACT Surface-conforming materials, such as sheets, ribbons, tapes or moldable material may be adhered to a wide variety of underwater target surfaces with a cyanoacry- late adhesive. The cyanoacrylate adhesive is evacuated from its container under water, applied to a surface of the surface-conforming material, and then the surface- conforrning material is pressed against the target surface for a relatively short period of time. The method pro- vides a method, for example, of attaching a plastic ex- plosive to the hull of a ship entirely under water. 9 Claims, No Drawings 4,793,887 1 UNDERWATER BONDING OF SURFACE-CONFORMING MATERIAL 2 DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS In accordance with the present invention, it is found This application is a continuation-in-part of U.S. pa- 5 that CYaI103CYY13t€ 3-dhe5iV€5 may be applied to an ex‘ tent application Ser. No. 884,443, filed July 11, I986. The teachings of said parent application are incorpo- rated herein by reference. The present invention is directed to underwater bonding of surface-conforming materials to target sur- faces. BACKGROUND OF THE INVENTION There exists a need for a system of adhering surface- conforming material of some significant weight to an underwater target. In particular, military applications require a non-invasive means of attaching a plastic ex- plosive to an underwater target surface, such as a sub- merged surface of a hostile ship. The target surface may be made of a variety of substances and may be rough or uneven. It is necessary that the plastic explosive remain adhered for a sufficient period of time for personnel to remove themselves from the site, and in many cases, it may be desirable that the device remain adhered to the site for a period of several days. For some time now the U.S. Army has been using a two-sided tape to bond plastic explosives to target sur- faces. If the target surface is very cold or is under water, an adhesive (unlike those used in accordance with the present invention) is applied to the surfaces of the tape prior to bonding. This bonding system has proven to be particularly unsatisfactory for underwater bonding, and for some time the Army has waived its target specifica- tions for lack of a bonding system which meets its re- quirements. It is therefore a general object of the pres- ent invention to provide a system for bonding surface- conforming materials, such as plastic explosives, to underwater target surfaces. Although the present invention was developed in response to a military requirement, the invention is applicable to civilian applications where bonding of a surface-conforming material to an underwater target surface is required. SUMMARY OF THE INVENTION In accordance with the invention, a non-invasive method of adhering a somewhat weighty, surface-con- forming object to a variety of underwater target sur- faces, including rough or uneven surfaces, comprises applying a cyanoacrylate adhesive or glue to a surface of the surface-conforming material, and pressing the surface-conforming material against the target surface so as to conform the material to the target surface and provide a layer of cyanoacrylate adhesive between the material and the target surface and continuing to apply pressure to the surface-conforming material for a suffi- cient period of time that a bond forms which is suffi- cient to support the weight of the surface-conforming material from the target surface. In a variation of the method, the cyanoacrylate is applied to the target sur- face, and the surface-conforming material is then pressed against the cyanoacrylate-covered target sur- face. The entire bonding procedure surprisingly may be carried out under water, including evacuating the cya- noacrylate adhesive from its container under water and applying it to the target surface. 10 15 20 25 30 35 40 45 50 55 65 posed surface of a surface-conforming material and that the cyanoacrylate-covered material may be pressed against an underwater target surface, including rough surfaces of a variety of materials, and adhesively bond the conforming material to the target surface within a very short period of time so as to support the weight of the conforming material from the target surface. The fact that a cyanoacrylate adhesive can be used to effect a bond entirely under water which meets previ- ously unachieved specifications is very surprising and unexpected and is contrary to what is generally ac- cepted regarding the properties of cyanoacrylate adhe- sives. A discussion of cyanoacrylate adhesives is provided in Kirk-Othmer Encyclopedia of Chemical Technology, H. F. Mark et. al. eds. John Wilson & Sons, New York, Vol. 1, pp 408-413. Among the teachings in this refer- ence are that: highly exothermic polymerization which can result from the direct addition of alcohols, bases (including weak amines), water, or surface activating agents should also be avoided; that cyanoacrylate adhe- sives should be protected from moisture; and that mois- ture deteriorates cyanoacrylate polymer bonds. That underwater bonds which are unachievable using other adhesive materials can be achieved with cyanoacrylate is therefore entirely opposite to conventional under- standing. Furthermore, the reference teaches that stron- gest bonds are obtained when the bond thickness is less than 50 microns. Bond strengths decrease and set times generally increase if the gap is greater than 50 microns thickness. Generally, cyanoacrylates are known to be most useful for forming bonds between smooth surfaces which promote formation of very thin cured adhesive layers and, thus, strong bonds. Hence, it is further sur- prising and unexpected that reasonably strong bonds can be formed between a surface of a surface-conform- ing material and rough target surfaces. Although Applicants are not bound by any particular theory as to why bonds can be formed with cyanoacry- lates under conditions which “fly in the face” of con- ventional understanding about the nature of cyanoacry- late adhesives, it is theorized that although moisture does effect a very rapid cure of cyanoacrylates, under rapid cure and heat-extracting conditions, cyanoacry- lates are self-encapsulating. Thus, when a cyanoacrylate is expelled from its container under water, a surface cure is immediately effected, providing a thin protec- tive casing or film around a volume of uncured cyano- acrylate. Such encapsulation may actually take the form of production of multiple microcapsules. Although water-initiated cure is known to be highly exothermic, the volume of water surrounding the cyanoacrylate represents a heat sink which is probably responsible for limiting the rate and extent of water-catalyzed cure. When the encapsulated-cyanoacrylate is pressed, e.g., through the surface-conforming material against the target surface, water is locally pushed out from along the target surface and the encapsulating fi1m(s) is rup- tured, contacting yet uncured cyanoacrylate directly with both the surface of the surface-conforming mate- rial and the target surface in the localized presence of a sufficiently low concentration of water for an effective bond to be formed. 4,793,887 3 The surface-conforming nature of the material to be attached helps to ensure that a substantial degree of close contact may be established even with a rough or uneven surface to provide a sufficiently strong bond. It is known that the most secure cyanoacrylate bonds are formed between smooth surfaces; nevertheless, effec- tive bonds are formed in accordance with the invention between surface-conforming materials and rough and uneven target surfaces. When pressed against the sur- face, sufficient localized regions of the conforming ma- terial come into very close proximity to regions of the target surface, establishing localized bonding regions. It is appreciated that the invention does not generally provide bonds that anywhere near approach the hold- ing power of cyanoacrylate bonds which normally form between smooth, dry surfaces, but that sufficient micro regions of strong bonding between the surface-con- forming material and the target surface provide suffi- cient holding power per unit area to hold objects of at least § lb. per in2 of surface area (8.8 gm per cmz) from either a vertical surface or from a downward-facing horizontal (underside) target surface. Between micro regions of effective bonding, excess cyanoacrylate may not form strong bonds but may nev- ertheless cure to form polymeric mass which surrounds the micro regions of effective bonding. The bonds in the presence of water are not permanent, and it is believed that water eventually degrades the cyanoacrylate poly- mer; however, the bonding regions may be protected from water attack for a period of time until the sur- rounding polymeric mass is sufficiently degraded by water attack. Bonds formed in accordance with this invention are nevertheless demonstrated to have a suffi- cient life-expectancy appropriate for certain military applications and certain other applications, such as short-term emergency repairs. Surface-conforming material may include flexible material with a well-defined configuration, such as a strip or a tape. Some plastic explosive material, for example, may take the form of an elastomer and may be applied to a target surface as strips or the like. The surface-conforming material may have some resiliency or tendency to assume a particular configuration; how- ever, any such resiliency has a tendency to act against bond formation. Of course, the extent that resiliency tends to act against bond formation depends upon the‘ degree of distortion required to conform the material to the target surface. In attaching a strip of plastic explo- sives to a target surface, resiliency is generally not of great concern because small amounts of plastic explo- sive surface bonding may be required and relatively regular regions of the target surface may be available for attachment of the plastic explosive. Surface-con- forming material, including some plastic explosives, may be putty-like and moldable to assume the configu- ration of the target surface without tendency to reas- sume an original configuration. Such materials are typi- cally flattened to provide a generally broad surface to which the cyanoacrylate adhesive is applied. The cyanoacrylate adhesive may be evacuated from its container, e.g., by squeezing a tube, while under water and applied to a submerged surface of the sur- face-conforming material. In such case, the encapsula- tion as described above occurs immediately. Within a relatively short period of time, the surface-conforining material is then pressed against the target object. Gener- ally, after application of the cyanoacrylate to the sur- face-conforming material, not more than about 15 min- l0 l5 20 25 30 35 40 45 50 55 65 4 utes should elapse until application of the conforming material to the target surface. Typically, the time be- tween cyanoacrylate application to the conforming material and application of the conforming material to the target surface will be much less, e.g., less than a minute. It is necessary to press the conforming material against the target surface for a time sufficient to effect at least a partial cure in the micro bonding regions; how- ever, this is generally about 30 seconds or less, a conve- nient amount of time for the material to be hand-held. It is also within the scope of the present invention to initially apply the cyanoacrylate directly to an under- water target surface and then press the surface-con- forming material against the target surface and hold the material against the target surface until the bond forms. In most cases, however, it is easier to apply the adhesive to the surface-conforming material, particularly if the surface-conforming material is easily handled and/ or if the target surface is rough or uneven. It is a convenience, rather than a requirement, that the cyanoacrylate be evacuated from its container un- derwater, and the cyanoacrylate may be applied in air to the surface-conforming material and then submerged for attachment to the underwater target surface. If a plastic explosive is to be attached surreptitiously to a target surface, it is desirable to perform the whole pro- cess underwater. On the other hand, for emergency underwater repairs, particularly when the repairer does not have underwater breathing equipment, it may be preferred to apply the cyanoacrylate to a surface of the conforming material above the surface and then apply the material to the target surface under water. An apparent advantage to evacuating the cyanoacry- late from its container under water is that the viscosity of the cyanoacrylate formulation is considered less im- portant if evacuated from the container under water. Cyanoacrylate formulations having viscosities ranging from 75—10,000 cps (preferably 75 to 5000 cps and most preferably between about 2000 and about 2500 cps) are used to provide successful bonds under water. As noted above, cure to form an encapsulating film appears to be extremely rapid when applied under water, and it is likely that even the most fluid cyanoacrylates will self- encapsulate to a significant extent under water. On the other hand, if the cyanoacrylate is to be applied to the surface-conforming material in air, a more viscous cya- noacrylate formulation is preferred, i.e., in the range of from about 1000 to 10,000 cps. Curing is more uniform in air than in water, and although a protective film will form on globules of thickened cyanoacrylate adhesive formulations, highly fluid cyanoacrylate adhesive for- mulations may cure completely on the surface-conform- ing material before the surface-conforrning material can be applied to an underwater target surface. Even for underwater application, thickened cyanoacrylate for- mulations are preferred for ease of workability and to ensure encapsulation of sufficient quantities of uncured cyanoacrylates. That is, it is generally preferred to use cyanoacrylate compositions having viscosities above about 1000 cps. The higher viscosity cyanoacrylate formulations comprise, in addition to cyanoacrylate monomers, vis- cosity regulators or thickeners, which are soluble in the cyanoacrylate monomer such as polymethacrylates, cellulose esters and prepolymerized cyanoacrylic esters, as is known in the art, and these thickened cyanoacry- late formulations are considered within the scope of the 4,793,887 5 invention, and in fact, represent preferred aspects of the invention. The cyanoacrylate monomers are selected from among those known in the art, particularly alkyl 2- cyanoacrylates where the alkyl is a short, straight or branched-chain alkyl group having from one to five carbon atoms. The preferred cyanoacrylate monomer for purposes of this invention is ethyl 2-cyanoacrylate. It is further preferred that the cyanoacrylate adhesive formulation include polymerization inhibitors to in- crease shelf-life. Preferably, a combination of an anionic and a free-radical inhibitor is used for shelf-life exten- sion. Known anionic inhibitors include phosphorus pentoxide, phosphoric acid, nitric oxide, sulfur dioxide and propane sulfone. Known free-radical inhibitors include hydroquinone, catechol and derivatives of hy- droquinone and catechol. It is further found that shelf-life is enhanced if the cyanoacrylate formulation is packaged in metal contain- ers, e.g., aluminum tubes. It is found that water mole- cules can slowly enter containers formed of polymeric material, initiating premature polymerization of the monomers. EXAMPLE 1 Underwater tests were conducted to test bonding of ribbons of tape. The tape was weighted with § lb. per inz of surface area. Approximately 3 gm of adhesive was used for bonding each ribbon to the surface. Tests were conducted in tap water and in 4% sodium chloride solution (simulated seawater) and on vertical and hori- zontal (underside) surfaces. The cyanoacrylate adhesive used is sold under the trademark “Permabond 240” and is a thickened ethyl 2-cyanoacrylate with a viscosity range of 2,000-2,400 cps. The cyanoacrylate was ap- plied to a surface of the ribbon and then either immedi- ately or after 10 minutes (delayed), the ribbon was pressed to a submerged surface for 30 seconds. The table below specifies the number of hours the bond adhered. An asterisk (") shows that the bond ad- hered for the maximum time of 72 hours. A number shows the time of failure in hours. Unsalted Unsalted Water Water Immediate Delayed Target Surface Bonding Bonding New Steel Horizontal 48 " ‘ ‘ New Steel Vertical 24 ‘ 48 ‘ Weathered Steel ' ‘ ‘ ‘ Horizontal Weathered Steel ‘ ‘ ' . ‘ Vertical Painted Steel 24 72 48 ‘ Horizontal Painted Steel 24 24 48 ‘ Vertical New Wood Horizontal ‘ ‘ ‘ ' New Wood Vertical ‘ ‘ ‘ ' Weathered Wood ‘ ‘ ‘ ‘ Horizontal Weathered Wood ' ‘ ' ‘ Vertical Painted Wood Horizontal “ ‘ ‘ “ Painted Wood Vertical ‘ ‘ ‘ “ New Concrete Horizontal ‘ ‘ ‘ ‘ New Concrete Vertical ‘ ‘ ‘ ‘ Weathered Concrete ’ ‘ ’ ‘ Horizontal Weathered Concrete * ' ‘ ‘ Vertical Painted Concrete ‘ ' ‘ " 10 15 20 25 30 35 45 50 55 65 6 -continued Horizontal Painted Concrete ‘ ’ ‘ " Vertical Salted Salted Water Water Immediate Delayed Target Surface Bonding Bonding New Steel Horizontal 24 24 72 72 New Steel Vertical 24 24 72 ‘ Weathered Steel ‘ ‘ “ ’ Horizontal Weathered Steel ‘ ’ 72 * Vertical Painted Steel 24 ‘ 72 72 Horizontal Painted Steel 24 ‘ 72 72 Vertical New Wood Horizontal New Wood Vertical Weathered Wood Horizontal Weathered Wood 24 ' ‘ ‘ Vertical Painted Wood Horizontal ‘ ‘ ‘ ‘ Painted Wood Vertical ‘ " ‘ ‘ New Concrete Horizontal ‘ ’ ‘ ' New Concrete Vertical ‘ ’ ’ ‘ Weathered Concrete ‘ ‘ ’ ’ Horizontal Weathered Concrete ' ' ’ ' Vertical Painted Concrete ‘ ‘ " ‘ Horizontal Painted Concrete ' ' ' ’ Vertical EXAMPLE 2 A further test was performed under water as per Example 1 with painted steel substrates only. The steel surfaces were first stripped of all old paint and treated with a zinc phosphate solution, primed and painted. The paint was then baked on the surface. This further test was performed due to a large number of underwater strength test failures on painted steel target surface in Example 1. These failures were due to the paint strip- ping from the steel (a bad paint application). Weighted ribbons were applied to 6 vertical surfaces and 6 hori- zontal underside surfaces. In each case, the bonds re- mained for 120 hours. This test shows that the adhesive will adhere a surface-conforming material to a painted steel surface. EXAMPLE 3 Putty-like patches of C-4 explosive (1.17 lbs. each, about 25 square inch surface area) were bonded with permabond 240 to underwater steel, rusted steel, ce- ment and wood surfaces. In each case, the bonded ex- plosive was transported from the place of bonding to a bunker and detonated. Of course, in adhering a material to a surface, it is not always possible to select the surface; however, this test shows that early failures on painted steel surfaces were not the result of poor bonding of the surface-conforrn- ing material to the target surface, but rather a failure of the paint to steel. Advantages of the invention may now be more fully appreciated. The invention provides for attachment of surface-conforming materials, such as a plastic explo- sive, to a variety of underwater target surfaces, includ- ing concrete, metallic and wooden materials which may be weathered or new, painted or unpainted, smooth or 4,793,887 7 rough or wet or dry. Underwater adhesion, either in salt water or in fresh water, for at least 3 days is often achieved. Attachment may be to any portion of a target surface, including vertical and underside surfaces. The bond can withstand motion or vibration. Attachment is often accomplished within 30 seconds. At least 8.8 gm of material is attachable per cm2 of surface area. The material can be quickly, easily, quietly and safely ap- plied, even by an unskilled person. Less than & pound of adhesive is required for application of 20 pounds of object. While the invention has been described in terms of certain preferred embodiments, modifications obvious to one with ordinary skill in the art may be made with- out departing from the scope of the present invention. Various features are set forth in the following claims. What is claimed is: 1. A method of adhering a surface-conforming mate- rial to a target surface which is submerged underwater, the method comprising applying to a surface of said conforming material or to said target surface a cyanoacrylate formulation consisting essentially of cyanoacrylate monomers with or without dissolved thickening agents, said cyanoacrylate formulation having a viscosity be- tween about 75 cps and about 10,000 cps, and pressing said conforming material against said target surface to establish contact of said conforming 10 15 20 25 30 35 45 50 55 65 8 material surface with said target surface and for a period of time sufficient to effect a cure of said cyanoacrylate adhesive formulation to form a bond adequate to support said conforming material from said target surface. 2. A method according to claim 1 wherein said cya- noacrylate adhesive formulation is evacuated from a container and applied to a surface while submerged under water. 3. A method according to claim 1 wherein said cya- noacrylate adhesive formulation has a viscosity of be- tween about 1000 cps and about 10,000 cps. 4. A method according to claim 1 wherein said cya- noacrylate adhesive formulation has a viscosity of be- tween about 2000 cps and about 2500 cps. 5. A method according to claim 1 wherein said sur- face-conforming material is a sheet, tape or ribbon. 6. A method according to claim 1 wherein said sur- face-conforming material is a moldable material. 7. A method according to claim 1 wherein said sur- face-conforming material is a plastic explosive. 8. A method according to claim 1 wherein said sur- face-conforming material weighs at least about 8.8 gm per cm2 of bonding surface area. 9. A method according to claim 1 wherein said sur- face-confonning material is pressed against said target surface for about 30 seconds or more. 3 * # II #