CA1108484A - Self-adhering material - Google Patents

Abstract

SELF-ADHERING MATERIAL
Abstract of the Disclosure A novel adhesive material comprising a plastic foam having at least a surface layer of open cells in which the surface layer of cells contains a pressure-sensitive adhesive composition formed by applying the adhesive to the foam, while the foam is maintained under pressure sufficient to cause the cell walls of the surface layer of cells to be exposed and be relatively flat so as to receive the adhesive. Upon the release of pressure, the cellular structure returns to its normal state and does not exhibit a tacky surface but will adhere to itself upon the application of pressure sufficient to expose the adhesive-containing cell walls.

Description

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This invention pertains to a novel adhesive-containing material. More particularly, the invention reLates to an adhesive-containing material which exhibits the unique S ability to adhere to itself, or to a non-ad~esive~contain-` ing material of similar physical structure, but which does not have a tacky surface and exhlbits lit~le or no tendency to adhere to other objects or surfaces in its normal state.
The use of pressure-sensitive adhesives as coatings for tapes, wallcoverings, floor tiles and in other similar applications where a permanently tacky adhesive film or coating capable of firmly adhering to a wide variety of surfaces is required is extremely well-known~ Although such adhesive coatings have a high degrée of utility, their desirable properties are also responsible for cer-. ; 1. .
tain limitations on their usefulness. For example, in many instances the ability of the adhesive to aggressive-ly adhere to a wide variety of surfaces requires that the adhesive coating be covered with silicone-treated paper, or other similar material, to mask the adhesive prior to actual use. Without such a covering layer, the adhesive would indiscrimi~ately stick to any surface with which it comes in contact. Thus, where the adhesive coating is applied to a tape, for example, the tape can~
not readily be unwound from a roll because of the aggres-sive adherence o~ the adhesive to the back of the tape.
; Great care must be taken in using such adhesively-coated materials since, once they are contacted with any surface,

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B4~4 they are not easily peelabLe or otherwise re~novable, particularLy in those instances wllere the adhesive bond may be substantially in excess of the cohesive or tear strength of the object to which they are applied. Ac-- 5 cordingly, the us~Lal pressure-sensitive adhesive-coated tape, wallcovering or the like is designed for use in - permanent applications where it will not be subjected to repeated application and removal.
need exists in the art ~or an a-lhesive system which exhibits selective adherence properties, such that it will not finnly adhere to most surfaces or objects but will ~irmly ad4ere to itself, or to a limited number of other sur~aces and will exhibit the additional prop-erty oE being readily separable from itself~ so that it can be re-used if desired. It will be readily apparent .~
~- to those persons skilled in the art that such an adhesive system would be extremely useful as a low cost closure system which could be utilized in lieu of hooks, snaps, or the ~astening systems sold under the trademark "Velcro";
as a bandage; or in any other environment where a self-closing or self-sealing property would be desirable.
It is an object of this invention to provide a novel adhesive-containing material exhibiting the ability to selectively adhere to itsel~, or to a non-adhesive-con-~5 taining matérial having similar physical prop~r-~ies.
It is another object o~ this invention to provicle a novel adhesive-containing material which is capable of adhering to itsel, but which is rea~ily separable to ~reak the adhesive ~ond, withou-t destruction of the materlal to which the adhesive is applied.
Yet another object o~ this invention is to pxovid~ a novel adhesive-containin~ material which is usefui in self~
sealing and self-closure applications.
~ ccordingly, the present in~en ion provides an adhe-si~e-containing material comprising a plastic foam material and a dry, solvent~ree permanently ~acky adhesive composi-tion, said plastic foam having a cellular structure includ-ing a surface layer o open cells, the actua' sur~ace o~
said foam bein~ defined by the leading ed~es of the side-walls o said surface layer of open cells, said sidewalls of ~aid sur~ace layer o~ open cells being coated with said adhesive composition~ the amount of sa~d adhesive composi~
tion being insu~icient to 'orm a continue.us adhesive ~ilm on the actual surface of saia plastic foam or to coat a substantial number of cells below said surface layer o~
open cells, said adhesive~containing material being incap~
able o~ adhering to any opposed suxface without the appli=
cation of pressure~
The material of tha in~ention is readil~ distinguish-able ~rom prior art adhesi~e~coated oam materials Csee, for example, U.S. Patent No. 3,847,647~" in that the oam.
material o~ the invention is not provided with a continu-ous adhesiva surface coating and there~ore~ does not have the tacky feel normally associate~ with su~h sur'ace coat-ings, or the a~ility to aggressively stick to any sur~ace with which it may come in contact. In the absence o~ such a sur~ace coating, the novel adhesive~containing foam material exhibits little or no tendency to stick to any surface, except to itself or to a non-adhesive-containing ~oam matexial; and then, only upon ~he application o~ ~
pressure sufficient to expose the F.ressure-sensitive ~ .

adhesive composition ~hich is ~ithin the sux~ce c~ll la~e~.
The no~eL adhesiYe m~terial is ~oxmed h~ ~p~l~ing the adhesive to the plastic foam while the ~oam is maintai}led under a pressure sufficient to pre~ent a relativel~ ~lat surface to be adhesi~ely coated and it is ~elieved the novel proper~ies o~ the adhesive of ~he invention are the xesult of th~ combination of the physical propertiQs o~ the oam materi~l and the method o~ application of the pressure~sensiti~e adhesi~e to the ~oam material. More ~articularl~, microscopic examination o~ a typical ~oam material having a surface layer o~ open cells reveal~ that the cells appear to be irxegularly-shaped 3, 4, and 5 sided, intexconnected cup-like structures which are dis~
posed at vaxious angles to the surface of the ~oam mate-xial. Indeed, when the ~oam material is in thP relaxed state, i.e., is not under pressuret the actual sux~ace -,~
o~ the foam is defined by the leading edges of the sid~-~alls of the cells ~hich axe disposed at various angles - to the actual sux~ace o~ the ~oam and the open spaces thexebetween. Accordingly, the actual su~ace o~ a layer of foam material is an open latticework and has relatively little solid sur~ace. The application of pressure to the æoam causes the cells to ~latten-outr such that they present a relatively flat, solid surface to be coated with the pressure-sensitive adhesive. ~hen the pressure is released, after application of the ad-hesi~e, the cells o~ the foam material return to their o~i~inal shape, taking the ~dhesive with them. As a - result, the cell walls which are beneath the plane de~
fining the actual suxface of the foam are coated with , i . -s- . .
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a~hesive but there is no continuous aclhesive film on the sur~ace o-E the ~oam, because of the open la-tticework structure. As a result, the surEace o~ the ~oam does not present a ta-ky feel to the hand and will not stick to most s-urfaces. For illustrative purposes,the foam surface and method of application o~ a~hesive can be compared to an accordion. The relaxed state of the foa;n is comparable to the compr~ssed state o~ the accordion~
in that only edges are exposed and the bulk of the av~
able surEace is below the plane defined by these edges.
The extension o~ an accordion would be comparable to the application of pressure to the ~oam, since it exposes the maximum surfaee.
It appears to be a unique characteristic of the adhesive-containing material of the invention that it is capable o finnly adhering to itself when two opposed surfaces of the adhesive-containing material are pressed ~ogether, utiliæing ordinary hand or ~inger pressure, despite the fact that it will not adhere to any sur~ace absent such pressure. Moreover, ~mder ordinary conditions, the adhesive-containing material will not firmly adhere to most surfaces, e.g.g to paper, wood, plasticg metal or glass surfaces, even when pressure is appLied, although adhesion for such uses can be improved by employing larger amounts of adhesive or nlaterials exhibiting greater ad-hesion. However, the novel adhesive-containing material of the invention does exhibit an ability to adhere to a non-adhesive-containing plastic foam material when pressure - is applied. It is believed that this phenomenon is the result of the flattening and exposure of the cell walls hy th~ application o~ pressuxer ~oupled ~ith the inability of the foam to return to its rela~ed state upon release o~
the pressure, due to the bond created between the adhesive coating on the cell walls and the opposing cell walls~
This would appear to be particularly true where both foam materials have been treated with adhesive in accordance .
with the invention, since the possibility of an adhesive~
to-ad~esivc bond is likely.
The nature o~ the foam material employed in the described em~odiment is not critical, provided only that `~ the surace layer of cells of the ~oam has an open-cell structure and the foam has sufficient flexi~ility such that the cell walls can ~e brought into substantial align-ment with the sur~ace of the foam, upon the application of pressurel to expose the concealed adhesive deposited in I those cells in accordance with the invention. Although i ~lexible foams are pre~erred, because of the relative ~ase ; I with which the cell walls will move into substantial align-ment with the plane defining the surface of the foam to be-~0 come exposed upon application o pressure, the invention is not limlted to conventional flexible foamed plastics. It I ~ill be~readily appreciated by those persons skilled in the art that so-called "rigid" foams may also be employed, :
provided that the surface layer of cells can be flexed as heretofore stated, and that the ability to achieve such flexing under normal hand or finger pressure will be dependent upon the thickness of the foam layer.
It is also well-known in the plastics art that mos~

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plastic materials c~n be ~ormed into foame~ plas~ics by the proper in~rod-uction of a gas and the setting o F the expanded plastic mass and thaL this can be accomplished - by various technlques, including the introduction of gaseous blo~ing a~en~s; whipping a gas into a viscous plastic mass; ox the release oF gas as a reaction prod uct o~ ~he ingredients in the plastic m~xture. Further, it is welL~known that the foamed plastic structures thereby produced may consist oE discrete closed-cell units, or interconnected cells and that the size of the cells and the density o~ the foam may be controlled, de pending upon the method employed to produce the foamed plasticO The present invention is not limited to any particular foa~ing techn~que or the chemical nat~e of the foamed plastîc, provided only that it e~hibits su~
~Li-~îcient flexibîlity as heretofore stated, and that the sur~ace layer of cells is open. To the extent that a partîcular foamed plastic is formed under~condîtions producing a closed-cell structure, an open-cell structure may be readîly produced, in accordance with technîques which are well-known in the art, by cutting a fîlm of the required thickness for the intended end-use from a block of the foa.~ This process, known a~s "peelînO" which is well known in the art, res--lts în open cells which are exposed to the surface of the foam material.
Among the foamed plastic materials which may be utîlized în accordance with the învention, are latex rubber foams; polyurethane foams 9 îrrespectîve of whether th~y are ~crived from reactlons with polyethers or poly~
es~ers; polyoleEin ~oams, s~lch as polyethylene and poly~
propylene; vinyl foamsl such as those derived from vinyl chloricle polymers; styrene polymer foams, such as poly-styrene or those derived from acrylonitrile-styrene polymers; and foams derived froM cellulose acetate, epoxy, phenolic, urea or silicone resins. The flexible ~oams : ormed from polyurethane, polyolefins and v;nyl polymers are particularly preferred, but are not critical to the invention.
It will be readily appreciated that the thick~ess oE the foamed plastic material is not a critical feature o~ the invention and will largely depend upon the desired end-use of the adhesive-containing material. For example, where the adhesive-containing material of the invention '~ 1~'' is intended for use in a self-adhering tape, such as a bandage or in a closure system, the layer of foam mate-rial may be quite thin; e.g.~ 10-100 mils, and be appr~-priately laminated to a backing material to satisfy ;~ 20 strength, decorative or other requirements. On the other hand, it is equally possible to ~orm thick blocks o~ foam having an adhesive-containing surface in accordance with the invention which could be utillzed, for example, in combination with other self-adhering blocks or shapes o~
foam material to create packing systems for odd-shaped instruments or machines.
The nature of the pressure-sensitive adhesive mate~
rial which is utilized in conjunction with the foamed plastic material .is not a cri.tical featur~ of the ln-~en-tiOIl, T~e term "pressure-sensitive adhesive" as used in this application is intended to re~er to those ad-hesive3 which, in dr~, solven~-~ree form, are pennanently tacky at no-~mal ambient temperat~lres and firmly adhere - to a variety o~ dissimilar surfaces without the need for activation by water, solvent or heat~ An extensive variety of s~lch a.~hesives has been developed and is well-known in the artO Generally, such alkesives are composed o~ a rubbery-type elastomer, combined wi~h a liquid or solid resiQ tacki:fier component. Typical ela3tomeric materials include reclaimed rubber, styrene-butadiene .~ rubber, polyisobutylene or butyl rubber, butadiene-acrylo-nitrile rubber, polyvinyl ethers and polyacrylate ester~.

L~- 15 Typical tackifie~s inc1ude polyterpene resins, gum rosin, rosin esters and other rosin derivati~es, phenolic resins, ; coumarone-indene resins and petroleum hydrocarbon resins.
~: The pressure-sensitive adhesives may also include plas-ticizers, fillers, pig~ents, an~i-oxidants and other materials designed to control viscosity9 color or the like, or to protect the adhesive against degradationO
It is also well-known in the art that, depending upon the specific ingredients employed, the adhesive may be . applied from a water-based or solvent-based fo~nula, or may even be a 100% solids formula which is heat-cured into positionO
Although the amount of adhesive applied to the foam-ed plastic material may vary over wide limits, depending 10 ~

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; upon such.~actors ~s the naiure of the c~llular structure of the foamed plastic material: the nature o~ the adhesive and the desired degree o~ adhesion in the final product J
~` the amount o~ adhesi~e employed is subject to certain im-poxtant ~unctional limitations in order to achieve the - basic objects o~ the invention. More paxticularly, the - , amount o~ adhesive put into the ~oamed plastic material ; should be suffi.cient to coat a substantial portion of the cell walls of the suxface la~er Oæ cells but should be : 10 insu~icient to eithe~ ~orm a continuous adhes~ve ~ilm ox co~ting on the surace of the ~oamed plastic material, o.r to cause intexnal adhesion which would inter~exe.with the , abilit~ o~ the ~oamed plastic material to be flexed in oxder to expose the cell ~alls of the sur~ace la~ex of . . cells, Such internal adhesion could xesult from the ap-' plication o~ the adhesiva composition to a substantial . I number o~ cells below the sur~ace layer o~ cells.
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~ I As pre~iousl~ indicated, it is to be noted that the :~ I pressuxe~sensitive adhesive ma~ be applied ~o the plastic ? 20 ~oam material while maintaining the ~oam under suf~icient ., ' pressure to substantially align the cell walls with theplane defining the surface of the foam, i.e., to expose ; . the walls o~ the sur~ace layer ~f cells, so that they may - be coated with adhesive~ A vari~y o~ techniques may be employed ~or that puxpose. For example, the'adhesive may be sprayed onto the ~oam material while the ~oam mat xial is maintained under sufficient pressure, to expose thecell walls. Alternativaly, a conventional xoll coating -~ 11~ .
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,, 34~4 or kni~e-coa~ing t~chniq~le may be employecl. In the former technique, adhesive material is transferrecl from a trough to a pick-up roller il~mersecl in it and ~oam ma-terial main~
tained under pressure is continuously coated with adhesive S when fed between the transfer roller and a pressure roller.
In the latter method, an adjustable knife-blade9 bar or ; rod is employed to control the deposition of adhesîve flow-ing onto a s~eet of oam moving u~der the blade, while the foam is maintained under pressure su~Eicient to expose the cell walls.
; In the pre~erred method o~ applying the pressure-sensitive adhesive to the plastic foam material, the adhesive îs applied by means of an engraved roll having cells in the surface capable of temporarily holding the adhesive compo-sition. The engraved roll, which is rotatable, is rotated in a pa~ contai1ling the adhesive composition,having the ex-cess adhesive removed by means o~ a doctor blade,and comes dir~ctly i~ contact with the ~ace of the plastic foam mate-.~ rial and a second roll, located behind the foam, acts as a substantially rigid support. Pressure is asserted against the engraved roller as it rotates in contact with the plas~ic foam layer, sufficient to ensure that the sur~ace layer o~
cell walls is exposedO This technique is preferred, because it gives a substantial degree o~ control over the amount of adhesive actually deposited on the ~oam layer. For example, in a preferred embodiment, an engraved roll having a 150 line to 180 line screen with a quadrangular cell will de-posit approximately 2.72 to 1~96 lbso of adhesive solids, respectively, from solutions contai~ing approxirnately 50%
solids. Although the solids concentration of a ~articular adhesive composition is not a critical feat~e of the in-vention; conventional practice, well-known to those persons skilled in the art, has established that a smooth flow from an engraved applicator roller is accomplished by adhesive solutions containing roughly 50% solvent and 50% solids.
Moreover3 most water-based adhesives are made co~mercially available in solids contellts varying from ~7% to 55%.
The pressure between the engraved applicator roller ` and the back-up roller is not critical and will vary, de-pendlng upon the pressure required in order to expose the cell walls of the surface layer o cells which, in turn, ; will depend upon the nature of the plastic foam materiaL.
Ordinarily, the pressure will not be less than 10 psi.
The invention will bP further understood by reference to the following illustrative example:
- In one preferred embodiment of the invention, a .031 thlck open-cell vinyl foam is employed to form a bandage designed to hold a sterile pad in place on an extremity. The foam material is re-ceived in roll form and would be fed into a coater equipped with means for unwinding and txansport-ing the foam, including tension controls, speed controls, means of applying pressure to the foam so that the surface layer o~ cells lays flat, means of winding up the finished product, and means for trimming and slitting the material to form finished products of various sizes.

; Internal to -the machine, an engraving mounted on appropria~e journals ancl operatlng against a rubber impression roll, with a durometer of ~bout - 60 shore would be appropriately equipped with a pan to handle the adhesive and a doctor blade to remove the excess. Such an engraving would be a 150 line electro-engraving3 calculated to deposit out of its quadrangular cells about 2.75 pounds of a 50% solids adhesive for each ream o~ 3,000 square eet.
The adhesive used may be an acrylic latex~ sus-pended in water, having approximately a 50%
solids content and a viscosity of about 2000 centepoise. The machine is equipped with heated rolls, which may be either steam, oil or hot water heated, sufficient in quantity and heat capacity to drive off the moisture contained in the adhesive~ or an enclosed oven with supporting idle rolls suitably heated with gas or steam heated air of sufficient temperature and viscosity to drive off the water The vinyl foam is fed frvm the unwind stand around such rolls as are required to maintain layflat, then fed through the nip created by the engraved roll and its rubber impression roll; -thence to and through the hot roll section of the machine, and thence to the rewind section Nip pressure between the engraving and impression roll should be about 20 p5 i .

A~ the rewind, trim kniv~s are used to trim any ragged edges and internal score cut knives may be used to trim ~o desired widths ill the manufac-turing process.
It will be apparent to those persons sk;lled in the art, that ~he absence of a continuous pressure-sensitive adhesive film on the surface of the foam not only prevents the adherence o~ the adhesive-contalning material to other :, .
;; surfaces in the absence of the application of pressure, but also eliminates the problem o~ "blocking", i.e., the ~`; sticking together of layers of a rolled-up web of foam which would inter~ere with or prevent the unwinding of that web. Moreover, separation of the adhesive-containing foam material from itself, or another piece of ~oam, after it has been adhered together by the applica~ion of hand or ~inger pressure is greatly simplified, as compared to adhesive systems containing continuous adhesive films.
Because the adhesive is discontinuous, the separation is self-propagating to a substantial degree and the dif~icult peeling and stripping action which is characteristic of most continuous pressure-sensitive adhesive films, is not present in the material o~ the invention. This character-istic renders the adhesive-containing material of the in-vention highly desirable as a closure means such as, for example, as part of disposable garments or masks in the health-care ~ield. Closure can be simply accomplished by pressing together two opposed faces of adhesive-containing foam material, and opening is readily accomplished by the : 15.

simple act of pulling the two layers apart.
It will be readiLy apparent to those persons skilled in the art that the ad~esive-containing material of the inventi.on may be laminated to a wide variety of films, fabrics, papers and the like, in order to form tapes~
decorative coverings or other devices in which the selec-tive adherence3 self-adherence and easy removal character . istics are desired. For example, the foam may be lamlnated `~ to polyethylene or to non-woven materials to orm a bandage;
laminated to decorative paper or plastics, which would be useful in self-closlng packaging; or, laminated to cloth or non-woven fabrics, as fillers and sti~feners for cloth-: ing. A wide variety of other combinations and applications : which take advantage of the unique features of this novel material will readily occur to persons of ordinary skill in the art.
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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An adhesive-containing material comprising a plas-tic foam material and a dry, solvent-free permanently tacky ad-hesive composition, said plastic foam having a cellular struc-ture including a surface layer of open cells, the actual surface of said foam being defined by the leading edges of the sidewalls of said surface layer of open cells, said sidewalls of said sur-face layer of open cells being coated with said adhesive composi-tion, the amount of said adhesive composition being insufficient to form a continuous adhesive film on the actual surface of said plastic foam or to coat a substantial number of cells below said surface layer of open cells, said adhesive-containing material being incapable of adhering to any opposed surface without the application of pressure.

2. The material of claim 1, wherein said plastic foam is capable of being flexed by the application of pressure so as to cause said adhesive composition to be exposed at the plane defin-ing the actual surface of said plastic foam.

3. The material of claim 1, wherein opposed surfaces of said adhesive-containing material may be adhered to each other by the application of pressure.

4. The material of claim 1, wherein said adhesive com-position is applied to said foam while said foam is maintained under a pressure sufficient to cause said sidewalls of said sur-face layer of open cells to be substantially aligned with the surface of said plastic foam.

5. The material of claim 1, wherein said plastic foam is flexible.

6. The material of claim 1, wherein said plastic foam is a polyurethane foam.

7. An adhesive-containing material comprising a plas-tic foam material and a dry, solvent-free, permanently tacky ad-hesive composition, said plastic foam having a cellular struc-ture including a surface layer of open cells, the actual surface of said foam being defined by the leading edges of the sidewalls of said surface layer of open cells, said plastic foam being suf-ficiently flexible such that the cell walls of said surface layer of open cells may be moved into substantial alignment with the actual surface of said plastic foam upon the application of pres-sure, said surface layer of open cells being coated with said ad-hesive composition, said adhesive composition having been applied to said plastic foam while said foam was maintained under a pres-sure sufficient to bring said cell walls into substantial align-ment with the actual surface of said plastic film such that a sub-stantial portion of said adhesive composition is located below the actual surface of said plastic foam in the absence of pres-sure on said foam, the amount of said adhesive composition being insufficient to form a continuous adhesive film on the surface of said plastic foam and insufficient to coat a substantial num-ber of cells below said surface layer of open cells, said adhes-ive-containing material being incapable of adhering to any opposed surface without the application of pressure.