CA2210336C - Hot melt adhesive having improved wet strength properties - Google Patents

Abstract

A hot melt adhesive is described which possesses superior properties for the construction of disposal soft articles and more specifically disposable soft articles which may be exposed to moisture for prolonged periods of time. The adhesive composition includes about 10 % to about 60 % by weight of a butene-1-ethylene copolymer, about 20 % to abou t 80 % by weight of a tackifying resin; about 5 % to about 30 % by weight of a plasticizer; and about 0.1 % to about 3 % by weight of a n antioxidant. >

Description

2 PCT/US96/00438 HOT MELT ADHESIVE HAVING
IMPROVED WET STRENGTH PROPERTIES
Background of the Invention The present invention relates to hot melt adhesives which exhibit improved open-times, and more specifically to hot melt adhesives having improved wet strength properties and which find usefulness in the manufacture of disposable nonwoven garments.
Description of the Prior Art The prior art is replete with numerous examples of hot melt adhesives which are employed for the construction of disposable soft goods.
Specific applications for these prior art adhesives have included disposable ri diapers, sanitary napkins, surgical drapes, hospital pads and adult incontinence products to name but a few. Moreover the prior art methods of application of these prior art adhesives have included but are not limited to extrusion (mufti-bead or slot) and spray or wheel application systems.
Those skilled in the art will readily recognize that many different polymers have been used in adhesives employed in the construction of disposable soft goods. In this regard typical hot melt adhesives have em-ployed polymers which have included S-I-S (styrene-isoprene-styrene); SBS
(styrene-butadiene-styrene); SEBS (styrene-ethylene-butylene-styrene); EVA
(ethylene vinyl acetate); and APAO (amorphous poly alpha olefin). While these polymers, when properly blended provide acceptable adhesion to most substrates employed in typical diaper construction, and further provide acceptable adhesion under dry conditions, they have had several shortcomings which have detracted from their usefulness.
One of the most noteworthy shortcomings of the prior art adhesives concerns the manner in which the adhesive reacts when exposed to liquids, such as water, urine, or the like. For example, when the prior art adhesives are applied to polyolefin substrates (such as polyethylene, polypropylene or nonwoven substrates, as the case may be), almost all adhe-sives will give good dry bonds and will normally maintain an acceptable bond strength when wet. However, when substrates such as tissue or core fluff are SUBSTITUTE SHEET (RULE 26~

WO 96!23042 PCTIUS96100438 used, certain problems present themselves. For example, while many of the adhesives formulated with the polymers, noted above, will give excellent dry bond strengths, these same adhesive bonds appear to be easily broken when the substrates are exposed to water, urine, or other water-based discharges or solutions. This bond delamination of the various substrates can cause the fluff ' core to sag, and further results in a poor fit, absorption problems and leaking of the garment especially when the garment is of the type which includes disposable diapers, or incontinence products.
More recently, manufacturers of disposable nonwoven garments such as diapers have endeavored to produce products which are much thinner in their overall thickness and profile and which incorporate super absorbent materials in place of the fluff, which is normally in the core.
In this regard, it should be understood that the nonwoven fibers comprise long wood pulp fibers which are interwoven together to form a given mass. In contrast, super absorbent material includes small sphere shaped particles which are not connected together to form a coherent mass like the nonwoven material. Therefore, core integrity becomes an even more important issue with these thinner garments. Therefore, it has long been known that it would be desirable to have a hot melt adhesive which is useful for bonding to substrates which are typically employed in the construction of nonwoven garments, such as polyethylene; polypropylene; nonwoven; tissue; or fluff and which further maintains acceptable bond strength with the above identified substrates following exposure of same for prolonged periods of time to water, urine or similar materials, and which further is substantially nonblocking under normal storage, and usage conditions.
Summary of the Invention It is therefore an object of the present invention to provide an improved hot melt adhesive which is useful for the manufacture of dispos-able soft goods.
A further object of the present invention is to provide a hot melt adhesive which can be employed as a construction adhesive, and which further can be applied by employing extrusion, or spray techniques to at least SUBSTITUTE SHEET (RULE 26~

-3-one polyolefin, or nonwoven substrate and at least one polyethylene, polypropylene, nonwoven, tissue or fluff.
Another object of the present invention is to provide a hot melt adhesive which has the following preferred composition:
about 25%, by weight, of a butene-1-ethylene copolymer;
about SO%, by weight, of a tacldfying resin;
about 25%, by weight, of a plasticizer; and about 0.1 to about 3%, by weight, of a hindered phenolic antioxidant, and wherein the hot melt adhesive composition displays an improved open-time and room temperature flow properties, and further has a viscosity of about 2,000 cP at 325°F, and a melting point of about 170°F to about 200°F.
Another object of the present invention is to provide an adhesive composition which, when applied to a tissue laminate in an amount equal to about 3 milligrams per square inch and at a temperature of about 300°F, and further with an open time of about 1 second, produces a peel strength, when measured by utilizing a dry Instron peel strength evaluation, of about 100 grams.
Another object of the present invention is to provide a hot melt adhesive composition and wherein the adhesive composition is substan-tially nonblocldng under normal storage conditions, and further when applied to a nonwoven, and tissue substrate in an amount which is equal to about 2 milligrams per square inch, and at a temperature of about 300°F, forms a bond which has an average peel strength of about 50 grams following expo-sure to water for at least one hour duration.
Another object of the present invention is to provide a hot melt adhesive composition which utilizes a butene-1-ethylene copolymer, and wherein the adhesive composition possesses an excellent balance of high specific adhesion, elevated temperature resistance and acceptable viscosity during normal application temperatures.

-3a-In an embodiment of the invention the hot melt adhesive will bind to polyethylene, polypropylene, absorbent core, and nonwoven top sheet or tissue of a disposable article and further has a propensity to flow into the fibers of the absorbent core or tissue thereby establishing a mechanical bond which resists degradation when exposed to a solution which includes or comprises water.
Further objects and advantages of the present invention are to provide a hot melt adhesive composition for the purposes described, and

-4-which is durable, easy to apply utilizing conventional manufacturing tech- -niques; and which further does not have the numerous shortcomings attribut-able to the prior art adhesives used for substantially identical.purposes heretofore.
De~,~~'~n off' t~ eferred Embo l anent The preferred adhesive composition of the -present invention w includes:
about 10% to about 60%, by weight, of a butene-1-ethylene copolymer;
about 20% to about 80%, by weight, of a tackifying resin;
about 5% to about 30%, by weight, of a plasticizer; and about 0.1% to about 3%, by weight, of an antioxidant, and wherein the hot melt adhesive composition has a viscosity of about 1,000 to about 50,000 cP at 325°F, and a melting point of about 170°F -200°F.
IS Butene-1-homopolymers and copolymers which are useful in the present invention are primarily linear chain molecules with regular and spatially ordered arrangements of ethyl side groups. These side groups are the result when butene-1 is polymerized across the 1, 2, carbon double bond, and along an ethylene chain backbone. This is described in further detail in U.S. Patent Number 3,362,940. When cooled from a melt, the ethyl side groups initially align in a tetragonal spatial arrangement. With time the tetragonal crystalline phase form transfers into a stable hexagonal spatial arrangement with a subsequent development of improved physical properties.
A more thorough discussion of the polymer utilized herein may be found in the reference to Mostert, U.S. Patent Number 4,937,138. As will be seen from the disclosure above, the present polymer is useful in amounts of about 10% to about 60%, by weight.
A suitable commercially available butene-1-ethylene copoly-mer.can be secured from Shell Chemical Company of Houston, Texas under the trade-mark Duraflex 8910 PC.

. S -As noted above, tackifying resins which are useful within the scope of the present invention have a weight of about 20% to about 80%, by weight. The tackifyi.ng resins can be selected from any of the nonpolar types, which are commercially available. An example of a commercially available tac~fying resin which is useful for the present invention ,includes the resin which is identified commercially by the- trade-mark-Escorez 1310 LC
and which is manufactured by Exxon Chemical Company. Normally, nonpolar tackifying resins which are useful with the present invention include resins which have partially, or completely hydrogenated C9 or Cs based hydrocarbon resins with softening points that are in a range of approximately 70°C
to approximately 125°C. Tackifying resins which are useful for the present invention can perhaps include polar tac)afying resins, however, the choice of available polar tacldfying resins is limited in view of the fact that many of the polar resins appear only partially compatible with the butene-1-homopolymer, and copolymers. As nosed above, the tackifying resin selected which is useful with the present invention will be about 20% to about 80%, by weight, of the entire adhesive composition and more preferably about 50% thereof.
The plasticizer that finds usefulness in the present invention can be any number of different plasticizers but the inventors have discovered that a plasticizer which includes a mono-olefin po~,lymer such as what is commercially available under the trade-mark lndopol H~ 100, and which is manufactured by Amoco, is particularly useful in the present invention. As will be appreciated, plasticizers have typically been employed to lower the viscosity of the overall adhesive composition without substantially decreasing the adhesive suength and/or the service temperature of the adhesive. As noted above, the present adhesive composition has a viscosity of about 2,000 cP to about 50,000 cP at 325°F, and a melting point of about 170°F to about 200°F. In view of the unexpectedly favorable viscosities, the adhesive compo-sition of the present invention has improved spraying characteristics when employed with conventional manufacturing equipment.
As earlier discussed, the hot melt adhesive composition of the present invention includes about 0.1% to about 3%, by weight, of an antioxi-dant. As a general matter it is understood that antioxidants and stabilizers are important to protect the otherwise vulnerable copolymer and thereby the adhesive composition from the deleterious effects of thermal and oxidative degradation which is frequently experienced during the manufacture and application of adhesive compounds as well as in the ordinary use of the final product. It should be understood that this degradation usually manifests itself by the deterioration of the adhesive composition in appearance, physical properties and performance. Among the most useful stabilizers are high molecular weight hindered phenols, and multifunctional phenols, such as sulfur, and phosphorous-contain phenols. In this regard, hindered phenols are well known to those skilled in the art, and may be characterized as phenolic compounds which also contain sterically bulky radicals in close proximity to the phenolic hydroxyl group thereof. In particular, tertiary butyl groups generally are substituted onto the benzene ring in at least one of the ortho positions relative to the phenolic hydroxyl groups. The presence of the sterically bulky substituted radicals in the vicinity of the hydroxyl group is believed to retard its stretching frequency and correspondingly its reactivity.
This steric hindrance is believed to provide the phenolic compounds with its stabilizing properties.
A suitable antioxidant for use with the present invention is commercially available from CIBA-GEIGY Company under the trade-mark Igranox 1010.
The performance of these stabilizers are well known in the art and may be further enhanced by utilizing in conjunction therewith, syner-gists such as for example, thiodipropionate esters and phosphites; and chelating agents and metal deactivators, such as, for example, ethylenedi-aminetetraacetic acid, salts thereof and disalicylalpropylenediimine.
The hot melt adhesive composition of the present invention may be formulated using any of the techniques known in the art. A represen-tative example of the prior art procedure involves placing all of the plasticizes and stabilizer in a jacketed mixing kettle, and preferably in a jacketed heavy duty mixer of the Baker-Perkins* or Day* type and which is equipped with * trade-mark rotors and thereafter raising the temperature of this mixture to a range of about 250° to about 350°F. It should be understood that the precise tempera-ture to be used in this step will depend upon the melting point of the particu-lar ingredients. When the initial mixture, noted above, has been heated, the mixture is blanketed in carbon dioxide at a slaw flow rate, and the resin described above is slowly added. When the resin i~ melted; and the desired temperature is reached, the copolymer is added to the mixture. The resultant adhesive composition mixture is then agitated until the copolymer is com-pletely dissolved. A vacuum is then applied to the mixture to remove any entrapped air.
Optional additives may be incorporated into the hot melt construction adhesive compasition in order to modify particular physical properties. These additives may include colorants, such as titanium dioxide and fillers such as talc and clay. However, these additional additives do not include nucleating agents such as those that are described in U.S. Patent Number 4,937,138 to Mostert, in view of the undesirable effects imparted to the adhesive composition when these nucleating agents are added to same.
The invention is further illustrated by way of the examples noted below. In this regard, an adhesive composition in accordance with the teachings of the present invention was made by the general procedure de-scribed above. This adhesive composition had the following constituent elements:
about 25%, by weight, of a butene-1-ethylene copolymer;
about SO%, by weight, of a tackifying resin;
about 25%, by weight, of a plasticizer; and about 0.1% to about 3%, by weight, of a hindered phenolic antioxidant and wherein the hot melted adhesive composition following application displayed an improved open time, and room temperature flow properties, and further had a viscosity of about 2,000 cP at 325°F, and a melting point of about 17Q°F.
More specifically, butene-1-ethylene copolymer was commer-dally secured from Shell Chemical Company under the trade-mark Duraflex . g.
8910-PC; the tackifying resin was commercially secured from Exxon Chemical Company under the trade-mark Escorez 1310 LC; the plasticizes was commercially secured from Amoco Chemical Company under the trade-mark Indopol H-100*; and the antioxidant was commercially secured under the trade-mark Irganox 1010 from $ the CEBA-GEIGY.
The resulting hot melt adhesive composition, upon testing, was found useful for a multibead or multiline construction of nonwoven garments. Further it was sprayed and extruded on various substrates and found to be generally acceptable for all intended purposes. The specific performance characteristics of this preferred formulation and the examples which follow are discussed in greater detail hereinafter.
A second example of the adhesive composition was formulat-ed and had the following cha.racteristia:
about 40%, by weight, of a butene-1-ethylene copolymer;
about 40%, by weight, of a tackifying resin;
about 20%, by weight, of a plasticizes, and about 1%, by weight, of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about 4000 cP at a temperature of about 325°F and a melting point of about 180°F.
A third example of the adhesive composition was formulated and had the following characteristics:
about $0%, by weight, of a butene-1-ethylene copolymer;
about 30%, by weight, of a tackifying resin;
about 20%, by weight, of a plasticizes; and about I %, by weight, of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about

5$00 cP at a temperature of about 325°F and a melting point of about 188°F.
A fourth example of the adhesive composition was formulat-ed and had the following characteristics:
about 25%, by weight, of a butene-1-ethylene copolymer;
about 65%, by weight, of a tackyif~ring resin;
about 10%, by weight, of a plasticizes; and * Indopol H-100 is a polybutene plasticizes.

about 1%, by weight, of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about 1500 cP at 325°F and a melting point of about 173°F.
In each of the examples, noted above, it was found that ' S adhesives formulated in accordance with these examples were useful for constructing nonwoven, disposable soft goods.
As noted earlier, traditional hot melt adhesives which have been formulated using SIS, SBS, SEBS and APAO have a propensity when exposed to water for prolonged periods of time, to lose their bond strengths, with the result that laminations prepared with such adhesives will fail when exposed for prolonged periods of time to water.
As should be understood, such delaminations, of a nonwoven garment, such as a diaper or the like may cause the garment's core integrity to fail with resulting undesirable effects such as leaking or poor fit.
In order to demonstrate the novel and unexpected results achieved by the present invention, the inventors compared and contrasted the adhesive compositions of the present invention with the prior art adhesive compositions which have been commercially available for some time and which further utilize the polymers, such as SIS, SBS, SEBS, and APAO, as noted above. For example, the prior art adhesive compositions were applied in an amount equal to about approximately three milligrams per square inch and at a temperature of 300°F, and further with an open time of about 0.5 seconds to form a tissue laminate. It was discovered that the present adhe-sive, when measured by a dry Instron peel strength evaluation, under similar coating conditions, produced a bond strength of approximately 100 grams, this bond strength being comparable to more traditional adhesive compositions.
However, when the same adhesive composition was compared to the more traditional adhesives following a one hour soak in tap water, it was discovered that the traditional adhesives, as noted above, produced bond strengths in the range of approximately 5 to about 25 grams. In contrast, adhesives manufac-tured in accordance with the teaching of the present invention produced bond strengths in excess of SO grams thereby making them a very attractive adhe-SUBSTITUTE SHEET (RULE 26~

to -sive for use in constructing a nonwoven garment,-and more specifically a diaper which may be exposed to water for prolonged periods of time.
The present composition was further tested by means of applying it to a nonwoven, and tissue substrate to form a laminate. The adhesive was applied in an amount equal to about 2 milligrams per square inch and at a temperature of about 300°F and further with .an open time of about 1.0 second. Following formation of the laminate, it was submerged in water for approximately one hour. Following submersion, the peel strength of the adhesive was tested in a manner similar to that which was discussed above. The test results demonstrated that the lamination had an average peel strength of about 50 grams following exposure to water for one hour. Tradi-tional adhesive compositions displayed greatly reduced bond strengths along the ranges noted above. What was surprising, however, was the percentage' of bond strength retained. For example, a standard adhesive such as H2120-O1 and which may be secured from Findley Adhesives, had a bond strength following a soak of one hour of about 5.7 grams which represents about 2% of its dry bond strength. In contrast, the adhesive of the present invention, following a one hour soak retained a bond strength of about 56.6 grams, which represents approximately 36% of its dry bond strength.
When tested relative to multibead construction, and wherein polyethylene, and polypropylene are bound together to form a lamination, the present adhesive composition when applied to the selected substrates, as discussed above, in an amount equal to about 1.5 milligrams per square inch of adhesive at 300°F and at a 0.5 second open time produced a bond equal to about $55 grams. In contrast, when compared to prior art adhesive composi-tions, the average peel strength under the same coating conditions resulted in bond strengths of about 661 grams. When further compared against tradition-al adhesive compositions which are used to form laminations of polyethylene, and polypropylene and wherein the adhesive composition of the present invention is applied to the selected substrates in an amount equal to about 3 milligrams per square inch, and at a temperature of 300°F, the present formulation produced bond strengths, as reflected by an average peel strength * trade-mark as measured by an Instron tensile tester, which are comparable to that produced by the conventional hot melt adhesives. Still further, when laminations were formed uzider the same conditions and which included a polyethylene substrate which is bound to a nonwoven, the average peel strength of the present adhesive was significantly improved and quite unex-pected relative to that produced by a conventional hot melt- adhesive composi-lion. For example, under the conditions noted above, the average peel strength for a lamination which is composed of a polyethylene and nonwoven substrate, and wherein the adhesive composition of the present invention was applied in an amount equal to about 3 milligrams per square inch, and at a temperature of about 300°F, was about 339 grams, as compared to traditional hot melt adhesive compositions which may be commercially secured from Findley Adhesive Inc. under the trade-mark H2275-02 and which produced an average peel strength of about 208 grams.
As noted earlier, the adhesive composition of the present invention is substantially nonblocking under normal storage conditions. For example, the inventors prepared a lamination of poly~;thylene which was combined with a nonwoven to form a laminate. The adhesive of the present invention was applied to form the laminate in an amount equal to about 1.5 milligrams per square inch, and at a temperature of about 300°F. The adhesive was applied with about a 0.5 second open time. Further, a laminate was prepared under identical coating conditions by using a traditional hot melt adhesive composition such as what is commercially available from Findley Adhesives Inc, of Wauwatosa, Wisconsin and which can be purchased under the trade-mark H2275-02. When identical blocking samples were prepared and were aged in an oven for 48 hours and at a temperature of 140°F, the traditional hot melt adhesive, such as the formulation I-I2275-02, displayed an average peel strength of approximately 35 grams. In comparison, the adhesive composition of the present invention displayed an average peel strength of about 8.5 grams. These results were surprising in view of the fact that the present adhesive blocking values were significantly less than the state-* trade-mark of the-art adhesive which is considered to be an excellent non-blocking adhesive for nonwoven garment assembly.
These results are significant in view of the conditions under which most nonwoven garments are employed. It is important, to understand that it is very beneficial that an adhesive composition flow for a time thereby allowing it to penetrate the nonwoven fibers thus establishing a mechanical bond with same. Once the flowing has occurred, however, it is important that 'the hot melt adhesive set up and be relatively hard and nontacky (non-blocking). This, of course, decreases the potential for blocking (sticking) to an adjoining substrate or surface such as may be the case when diapers are packed in a box and shipped at elevated temperatures; or worse yet, the possibility that the adhesive will, under some conditions, such as elevated temperature, adhere to the skin of a young infant, or during storage, flow completely out of the bond interface. As would be expected, an adhesive which would remain tacky under these circumstances could make an associat-ed nonwoven article extremely uncomfortable to wear, as might be the case when such adhesives are utilized in garments such as incontinence garments, and feminine care articles or the like, which may be placed in an orientation where it is exposed to body hair.
In all the tests noted above, the peel strengths were measured at a rate of 12 inches per minute. Further, five samples were tested in each instance. Additionally, the blocking test was employed to simulate compact packaging. More specifically, the laminations employed in the blocking test were placed on top of nonwoven garments such as a diaper or the like with the nonwoven portion of the laminate placed in contact with the nonwoven substrate of the diaper. Samples were then compressed with a weight of 200 grams per square centimeter for a period of 48 hours, and at a temperature of 140°F. The samples were then allowed to cool to room temperature. The samples were then tested for their peel strength in an Instron tensile tester at a rate of 12 inches per minute.
A review of the information above will reveal that the adhesives of the present invention give similar peel strengths as compared SUBSTITUTE SHEET (RULE 26) with more traditional hot melt adhesives such as Findley Adhesives H2275-0Z, and further show improved bond strengths when exposed to water. Further, the present adhesive composition appears to exhibit no noteworthy blocking characteristics, thereby suggesting that the adhesive will be very useful for S assembling nonwoven goods which will be packaged in a compact fashion.
In addition to the foregoing, the adhesive composition of the present invention has a low viscosity, and melting point, which makes this a very desirable adhesive for use with the more traditional application methods.
Therefore, it will be seen that the hot melt adhesive of the present invention provides a fully dependable and practical means for adhe-sively assembling a disposable soft good such as a disposable diaper, feminine napkin or the like, and which further avoids the detriments associated with the prior art practices which includes, among others, employing several different adhesive compositions for assembling a disposable soft good. In addition to the foregoing, the improved hot melt adhesive of the present invention shows surprising and unusually desirable manufacturing viscosities when compared with the prior art, and further has peel strengths, following exposure to water which are greatly improved in relative comparison to the prior art.
It will be apparent to those skilled in the art that the forego-ing example has been made for the purpose of illustration and that variations may be made in the proportions, procedures, and material without departing from the scope of the present invention. Therefore, it is to be understood that this invention not be limited except by the claims which follow:
SUBSTITUTE SHEET (RULE 26)

Claims (11)

CLAIMS:

1. A hot melt adhesive composition having improved wet strength characteristics comprising a formulation having the following ingredients:
about 10% to about 60%, by weight, of a butene-1-ethylene copolymer;
about 20% to about 80%, by weight, of a tackifying resin;
about 5% to about 30%, by weight, of a low molecular weight liquid plasticizer having a molecular weight less than about 2000; and about 0.1% to about 3%, by weight, of an antioxidant, wherein the ingredients total 100%, by weight, based on the weight of the entire adhesive composition and the hot melt adhesive composition has a viscosity of 1,000 to 50,000 cP at 325 °F and a melting point of about 170°F to about 200°F.

2. A hot melt adhesive composition as claimed in Claim 1, wherein the tackifying resin is compatible with the butene-1-ethylene copolymer, and the antioxidant is a hindered phenolic antioxidant.

3. A hot melt adhesive composition as claimed in Claim 1, wherein the plasticizer comprises a mono-olefin polymer.

4. A hot melt adhesive composition as claimed in Claim 1, wherein the formulation comprises about 25% by weight of said butene-1-ethylene copolymer, about 49%
by weight of said tackifying resin, about 25% by weight of said low molecular weight plasticizer, and about 1 % by weight of said antioxidant.

5. A hot melt adhesive composition as claimed in Claim 1, wherein the adhesive composition, when applied to a tissue laminate in an amount of about 3.0 mg/in2 and at a temperature of 300°F, and with an open time of about 1 second, produces a peel strength of about 100 grams.

6. A hot melt adhesive composition as claimed in Claim 1, wherein the adhesive composition is non-blocking when exposed to elevated temperatures of about 140°F.

7. A hot melt adhesive composition as claimed in Claim 1, wherein the tackifying resin is compatible with the butene-1-ethylene copolymer, and the plasticizer comprises mono-olefin polymers.

8. A hot melt adhesive composition as claimed in Claim 1, wherein said low molecular weight plasticizer is polybutene.

9. A hot melt adhesive composition as claimed in Claim 1, wherein said low molecular weight plasticizer has a molecular weight less than about 1000.

10. A hot melt adhesive composition as claimed in Claim 9, wherein the hot melt adhesive will bind to a polyethylene, polypropylene, absorbent core, and nonwoven top sheet or tissue of a disposable article and further has a propensity to flow into the fibers of the absorbent core or tissue thereby establishing a mechanical bond which resists degradation when exposed to a solution which comprises water.

11. A hot melt adhesive composition as claimed in Claim 10, wherein the plasticizer comprises a mono-olefin polymer, and the hot melt adhesive composition remains non-blocking when exposed to elevated temperatures of about 140°F.