CA1136324A - Hot melt adhesive for elastic banding and method for utilizing the same - Google Patents

Abstract

Abstract A purpose of the disclosed method is to impart gathers and elasticity to a relatively inelastic film, membrane, or web substrate, through elastic banding with a viscoelastic hot melt pressure-sensitive adhesive (PSA). Typically, the resulting elastic-banded substrate product (e.g. 40) will be cut into discrete units and formed into garments or body-encircling members such as disposable diapers. One step of the preferred method involves extruding a ribbon or band (13 or 113) comprising a viscoelastic hot melt PSA, which PSA has unusually high cohesion, stretchiness, and elasticity without excessive loss of adhesive bonding strength. (The viscoelastic behavior of the PSA is believed to be determined, at least in part, by the rela-tive size of its crystalline domains and its rubbery domains and the glass transition temperatures and soften-ing points of its components.) A second step of the preferred method involves bringing the band of hot melt (13 or 113) into adherent contact with a surface of a moving continuous substrate (22 or 32 or 132). A typical substrate would be the polyolefin film used is the manufacture of disposable diapers. The band can be bonded to the substrate through a pressure activation technique, wherein the band itself has the necessary inherent adhesive properties.

Description

~13~:i324 Technical Field This invention relates to a metllod for irnparting elastic characteristics to materials ~7hich are relatively inelastic through the US9 0~ a ho-t melt pressure-sensitive adhesive~ An aspect of this inven'ion relates to the formulation of a suitable hot melt pressure-sensitive adhesive composition for the aforementioned method. Still another aspect o this invention relates to the manufacture of garments or body-encircling members provided with an elastic band. Additional aspects of the .invention relate to the elastic banding of such garments or body-encircling members which are cut from a continuously moving film, membrane, or web-like substrate and hot melt pressure-sensitive compositions employed in the elastic banding process which compositions can take the form of extrudates, and elastic banding of discrete articles wherein the hot melt pressure-sensitive adhesive co~position can be in the form of a tape~
Description of the Prior Art In the garment industry, vulcanized rubber in sheet or thread orm is -t~pica~ly used for elastic banding purposes. Traditionally, the w lcanized rubber has been sewn, woven, or bonded to the garment . 25 or discrete unit of material. Crosslinked synthetic rubbers can be used in place of vulcanized natural rubber for this purpose.
Sewing or weaving or similar attachment techniques are not well suited to modern, high-production 3Q processes and may even be inconvenient or cumbersome to use in making homemade garments. A more efficient technique for attaching an elastic band involves the use of a heat-activated coating o~ the elastic or a separate adhesive, which adhesive can be coextensive in length with the elastic or merely applied in spots. Taking his cue from this more " ~L3~'24 eEficient ~pproach, the patentee of U.S. Paten' No 4,081,3~1 cBue~ issued ll~rch 28, 1~78 developed a high-production process particularly well sui~ed to providing disposable diapers with elas,ic l~g bands. Accordin~ to the Buell patent, glu~ applicators ca~ apply ~dhesive along the :Length of continuous bands of elas-tic which are applied, in a stretched condition, to the continuous web from WhiC'Q the disposable diapers are made. The patent further sugges-ts that the elastic band or ribbon can be coa~ed with a heat-activated adhesive prior to contact with the web. Still another sugges'ion relates to the use of a heat-sealable elastic ribhon which can be adhered to the web wikh the aid of a suitaDle heating means.
Still gxeater efficiency (with a concurrent simplification of the overall elastic banding process) could theroetically be provided if the adhesion of the elastic band to the substrate did not require either a separate adhesive or a heating means.
Unfortu~ately, there are few guidelines in the pxior art for one who would attempt to formula~e an adhesive which could itself be an elastic band It is known that "pressure-sensitive" adhesives do not require heat, solvents, moisture, or the like to form a reasonably stxong adhesive bond under normal ambient conditions. It is also known that such adhesives possess a degree of stretchiness, cohesion, and elasticity as well as adhesion characteristics However, the four-fold balance of adhesion, cohesion, stretchiness, and elasticity is a delicate one, and any substantial increases in the last three of these properties ~an result in unacceptable losses of adhesion.
Since the invention of pressure-sensitive adhesives, :Literally decades of research e-Ffort have yone into the investicJation oE the afore~entioned four-fold balance and the develo~ment of tes-ts for reproducibly measuring the desired properties. For example, the adhesive bond slrength or a pressure~
sensitive adhesive can ~e measured by 180~ peel resistance tests such ~s PSTC-l. The adhesive tack can be measured, for example, by probe tacX tests such as A.S.T.M. D2~79. ~Cohesion and stretchiness of adhesives can be measured with modern tensile testing equipmentO
A particularly unusual problem may be encountered when the adhesive is in a temperature envixonment which is continuously above normal ambient or room temperature. It has been found that some pressure-sensitive adhesives have their four-fold balance significantly altered when the environment is characterized by a modestly elevated temperature.
This finding is of great importance in the case of garments or body-encircling members which are i~ 20 continuously exposed to body temperature (e.g. 37 ~.).
Most modern pressure-sensitive adhesives ~t'PSA's") are applied tv a substrate by one of three techniques:
~oa~ing from an organic-solvent based solution ~e.g.
solvent castiny), coating from a suspension or dispersion such as an aqueous latex, and coating o-extruding of a hot melt pressure-sensitive composition.
The hot melt technique has a number of advantages;
for example, thicker layers of adhesive are readily obtainable, solvent recovery is unnecessary, and drying or "setting" time is minimal or nonexistent.
Research activity in the field of hot ~elt pressure-sensitive adhesives has been very extensive, and even a representative citation of references drawn from this field would be difficult to provide.
The following selection of patents and literature is believed to be reasonably representative.

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~3~3 U.S. P tent No. P~t ntee Issue Date 3,686,107 Russell Auyust 22, 1972 3,736,281 Russell May 29, 1973 3,827,999 Crossland Au~ust 6, 1974 5 3,935,338 Robertson et al Januar~ 27, 1976 3,954,692 Downey May 4, 1976 4,089,824 Bronstert et al May 16, 1978 British Patent Inventor Pùblica~ion Date 1,405,786 Crossland Septem~er 10, 197S
Xirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Volume l; John Wiley & Sons, Inc., New Yorkj New York, 1963, pages 381-384.
"SOLPRENE~ 418 in Pressure Sensitive Adhesives", Bulletin 304 o~ Phillips Chemical Co., a division of Phillips Petroleum Company.
Summary of the Invention It has now been found that a greatly simplified method for imparting elasticity to a relatively inelastic substrate can be provided if one extrudes a band comprising a suitable viscoelastic hot melt ~ pressure-sensitive adhesive, cools the thus-extruded ; band to a temperature below its softening point but above its glass transition temperature, and brings the thus-cooled band into contact with the substrate to form a pressure-sensitive adhesive ~PSA~
- bond, typically by means of pressure only, although modest amounts of heat can be used also, if desired.
The band of hot melt can be pre-extruded and ~ormed into a convoluted roll of hot melt pressure-sensitive adhesive tape. If the pre-extruded technique is used~
- a cooling step is ordinarily unnecessary, since the roll will ordinarily be stored and unreeled at ordinary ambient temperatures. Extruding the band of hot melt pressure-sensitive adhesive is by ~ar ~he most practical approach when applying the elastic band to a continuous non-elastomeric film, membrane, .
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or web substra-te which is subsequently cut into portions suitable or use as elastic~bancled articles.
The convoluted tape approach is very practical when a lengt'n of tape is to be applied to an individual ar-ticle.
In'the context o~ this inventionl a suitable hot melt pressure-sensitive adhesive will have viscoelastic behavior because of its glass transition and/or softening point characteristics and particularly because of a microstructure comprising the combination of crystalline domains with rubbery domains. The crystalline domains contribute -a pseudo-crosslinked character and greater elasticity and cohesion. High elasticity and elastomeric behavior are typically manifested by a stoxage modulus (G'~ which is higher, and a loss tangent (tan ~ or G"/G') which is lower, than most conventional PSA's~ ~owever, the storage modulus values cannot be so high as to preclude viscoelastic behavior in the temperature range o 25-50 C. A ~iscoelastic I solid, under stress, has some of the properties of a highly viscous liquid (e.g. "creep" or "cold flow") as well a3 some of the properties of an elastomer. A PSA with suitable "creep" or "cold flow" properties will have some tendency to flow in the temperature range ~f 25-50 C., but this tendency should be kept within limits, as manifested by a limited range of loss modulus (G") values.
~he followin~ are considered to be illustrative values for the Gl', G', and tan ~ (tan ~ = G~ f a suitable PSA. '-.

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*Values in 104 dynes/cm2 at Property 25-50 C. and 0.01-0.25 Hz Loss Modulus (G") 5 to 100*
Storage Modulus (G') 65 to 225*
Loss Tangent (tan 6= G.) 0.03 to 1.0 (no units) Some frequency-dependence of these values can be observed, but extreme temperature dependence is not desirable. For example, a loss of more than 50 x 104 dynes/cm2 in G' at 50 C., as compared to 25 C. indicates the likelihood of "heat set" or inadequate elastomeric behavior at moderately elevated temperatures. Permanent deformation due to elongation should not exceed about 1.5 times the original length of a sample of the PSA (i.e. a permanent increase in length equal to 50~ of the original length) throughout the 25-50 C. range, using the dead load creep test described subsequently.

Brief Description of the Drawing Figure 1 is a schematic illustration of a typical apparatus and typical method steps used in a preferred embodiment of this invention.
Figure 2 is a similar schematic illustration of another embodiment of this invention.

When used in this application, the following terms have the indicated meanings.
"Pressure-sensitive adhesive" denotes those adhesives which bond almost instantaneously when contact pressure is applied to force the mating surfaces together. Such adhesives have rather high cohesive strength, such that, if the adhesive is peeled away from a smooth surface to which it has adhered, no apparent offsetting occurs and no appreciable residue remains on the smooth surface.
True pressure-sensitive adhesives (PSA's) need not be ~ ( ~3~

in a liquid or mol-ten state in order to have adhesive properties. Similarly, moisture, solvents, heat, or the like are not needed to activate a PSA. Some PSA's have aggressive tack or "quic'~ stic~" at room temperature and tend to bond ins-tantly upon ~ontact.
The PSA's of this invention, on the o'her hand, ; typically raquire light pressure to form a bond of appreciable strength. In other words, the tack is relatively non-aggressive and ordinarily would not be sensed until some pressure were applied to the surface of the PSA, causing it to "cold flo~" in the manner of most viscoelas-tic materials. Thus, a PSA
of this invention has a rheology whicn permits sufficient flow under pressure to form a strong adhesive bond while nevertheless maintaining a high - level o cohesion, stretchiness, and elasticity.
"Hot melt" refers to thermoplastic solids with reasonably stable properties in the molten state, which are easily melted at modestly eleva'red temperatures (e.g. temperatures above 65 C.) and/or easily extruded, and which can be melted and resolidified a number of times without excessive degradation of the thermoplastic properties. A
"hot ~elt pressure-sensitive adhesive" or "hot melt PSA" refers to a hot melt adhesive having PSA
characteristics at temperatures below the softening point and above the glass transition temperature of the hot melt.
"Softening point" refers to a speciEic temperature or range of temperatures which can ba determined by any of the standard softening point tests such as the ring and ball ("R ~ B") testO
Accordingly, the term "softening point" includes --and subsumes "softening range".
"Elastomer" and "elastomeric" refer to a material which, in the form of an unsupportcd film ~,.v ~ .. .
~ ..

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g or layer can be elongated t~ at least 100% of it5 original length and which will return with force to substantially its original len~th when permitted to contract spontaneously. Thus, this invention contemplates a$ "elastomers" those ma-terials which would be defined as "elastomeric" by the American Society for Testing and Materials (A.S.T.M.).
"Non-elastomeric" materials are those which exhibit some degree of significant deformation or "set"
when elongated 100% of -their original length or less; that is, such non~elastomeric materials typically do not provide the elongation-resistant forces of an elastomer.
"Essentially hydrocarbon resin" refers to a resin in the molecular weight range of a few hundred up to several thousand ~e.g. 8,0003 which is obtained or . synthesized rom rather basic hydrocarbonaceous - materials such as petroleum, coal tar, turpentine, olefins and other unsaturated simple hydrocarbons, . 20 and the like. In the context of this inven-tion, an "essentially hydrocarbon resin" need not be a hydrocarbon in the strictest sense of the term and may contain oxygen, nitrogen, or sulfur, e.g. as hetero-atoms or as atoms of functional groups.
Thus, an "essentially hydrocarbon resin" can be made from a monomer such as coumarone (also known as benzofuran). And, in industrial practice, coumarone-indene resins are typically referred to as "hydrocarbon resins".
The terms "loss tangent" (tan ~ or G"/G'), "storage modulus ~G'), "loss compliance (J") and "storage compliancel' (J') are defined according to established principles of dynamic mechanics. These rheological quantities are measured on samples approximately 2.5 mm in -thickness placed ~etween 25 cm paral.lel plate fixtures of a Rheometrics , . , . ..... ..... . ... ., . ~ .. " , ......... ~ . . . . . .

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~ 10 -Mechanical Spectrometer (R~IS)~ The sample was allo~7ed -to equilibra-te ~7ith the test temperature (e g. 25 C. or 50 C.) A minicompu~er accura-tely g~verns the application of a 5% pea~-to-?eak shear strain to the sample. The frequency of the application can be accurately controlled to a fraction of a Hertz (Hz). The values of the complex modulus (G*) and loss tangent are calculated by the computer from geometry Eactors, pea~-to-peak amplitude of the torque signal, and phase lag of the torque output wave. The definition of loss tangent and the relationship between G*, G', and G"
provide two equations in two unknowns which can be - solved by the computer to provide G" and G', since G* and loss tangent are both known values calculated as described previously. The value for J' is gîven by the reciprocal of G' divided by the expression - 1 ~ tan2 ~ ; the ~alue of J" is given by ~he reciprocal of G" divided by 1 ~ (tan2 ~ ) 1 For any of these values, the fre~uency in Hz ~e.g.
0.25 Hz or 0.01 Hz) must be specified. Other instruments or measuring these rheological properties over a range of xequencies are known, e g. the "RHEOVIBRON".
The term "dead load deformation" or "dead load creep" refers to a measurement of "cold flow" or permanent deformation at one or more fixed test temperatures, e.g~ 23~ C. or 25 C., 40 or 41~ C., and 49 or 50 C. A sample of known length is suspended vertically in a chamber maintained at the test temperature~and a weight ~e.~. 1500 grams) is attached to the lower (free) end of the sample. The sample is cut to a size such that the force per unît area is 1500 g/cm~. After approximately 3 hours at 3S the test temperature, the sample is removed, the weight is detached, and the sample is allowed to relax ~3~

under the influence of its o~m inhere~t elastomeric forces. Th2 length oE the relaxed s3m~1e (I.~) is compared ko the oriyinal lencJth ~1)and t~e "d~ad load creep" (permanent deformation) is determined according to the formula (L2-Ll)/Ll x 100~.

Turning now to the Drawing, Figure 1 illustrates the use of a pre-tensioned, cooled band of hot melt PSA to bond two continuous substrates into a~ assembly having gathers all along the bond line. A hot melt reservoir 11 extrudes an elongated e~trudate ~re~erred to herein as a "band") by lorcing the hot melt PSA material in reservoir 11 throuyh an extrusion die 12. The hot melt PSA band 13 comes into contact with chill rolls 15 and 16 almost immediately after the extrusion step, so that band 13 will be cooled to a temperature below its softening point, e.g. to a normal ambient temperature such as ~0-25 C. (Typically, the hot melt PSA will be formulated to have a glass transition temperature below normal i ambient temperatures.) Chill rolls 15 and 16, in addition to cooling band 13, also advance it toward tensioning rolls 17 and 18. Accordingly, the portions 23 and 33 of band 13 ~Jhich are on either side of tensioning rolls 17 and 18 will be under tension and will be in an essentially elonyated state.
Tensionin~ rolls 17 and 18 advance portion 33 of band 13 to nip rolls 27 and 28. Substrates 22 and 32 are all the while being continuously unreeled from stoxa~e rolls 21 and 31, so that the pretensioned, c~olea band o hot melt PSA 33 and substrates 22 and 32 all enter the nip provided by rolls 27 and 28 to be ~ormed into the composite or assembled proauct 40 (i.e. the banded substrates). Although nip rolls 27 and 28 can be heated to a moderately elevated temperature, in the preferred embodiment of this .
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- 12 ~
invention, the modest pressure provided by the nip rolls is all that is needed to adhesively bond substrate 22 to substrate 32 with the hot melt PSA
band 33. Since the nip rolls 27 and 28 provide only line contact with the composite or assembly comprising substrate 22 and 32 and adhesive 33, it is difficult to expr ss the pressure applied by these rolls in conventional terms such as Kg/m2 or the like. Light pressure on the order o~ tens or hundreds o~ grams per square centimeter can be su~ficient; however, there is almost no upper limit on the pressure applied by nip rolls 27 and 28 so long as the rolls themselves or the substrates 22 and 32 are not damaged. The hot melt PSA in band 13 can be formulated to take into account the amount of pressure available at nip rolls 27 and 28.
Since band 13 is a viscoelastic hot melt PSA
which meets the definition of an elastomer, it will tend to contract spontaneously with force if the tension applied to banded substrates 40 is less than the tension on portion 33 o~ band 13. For example, additional rolls or conveying devices (not shown) can be used on banded substrates 40 merely to move the composite product along toward a cutting s-tation and not exert any significant tension upon the banded substrates. In such a situation, the portion 43 of band 13 on the exit side of nip rolls 27 and 28 will spontaneously cause the formation of gathers 41 all along the line of the adhesive bond between band 43 and substrates 22 and 32.
The banded substrate product 40 can be cut into individual elastic-banded articles such as disposable diapers by techniques known in the art.
In the embodiment of the invention shown in Figure 2, pre-tensioning of the hot melt PSA band 113 is not required. As in Figure 1, band 113 is extruded ~, ~

~36~Z4 ~ 13 -from reservoir 111 through exkrusion die 112. A
single substrate 132 is continuously unreeled from storage roll 131. Substra-te 132 is taken up by vacuum chill roll 127 at a point which permits 5 pre-gathering of the substrate. Teeth-like projections 129 on the surface of vacuum chill r~ll 127 create the ~lutes or yathers 141 in subs-trate 132. The two chill rolls 127 and 128 serve to cool band 113 in a manner analogous to the action of chill rolls lS
10 and 16 of Figure l; in addition, these chill rolls apply light pressure to the composite of the band 113 and the pre-gathexed substrate 132, so that the pressure-sensitive adhesive bond between band 113 and substrate 132 is formed without permanently 15 flattening out gathers 141. This re5ult occurs because, in the composite emerging from the exit side of rolls 127 and 128, band 113 tends to be bonded only to the peaks of gathers 141~
The foregoing methods are particularly well 7 20 5uited to high-volume production techniques using .
: continuous subs-trates. For low-volume or batch production, the elongation-resistant gathers can be imparted to portions of the substrate by means of ~- a pressure-sensitive adhesive tape. In this technique, 2S the desired length of tape is simply unreeled from a convoluted.roll of hot melt pressure-sensitive aahesive, which adhesive has been applied to a : flexible continuous backing. For good results in this technique, the pressure-sensitive adhesive 30 tape should have an extruded layer at least 50 micrometers (pM) in thickness, more typically at least 75 or 100 ,uM in thickness. I~ the flexible -continuous backing is relatively inelas~ic as compared to the ~ot melt PSA layer of the tape/ the backing 35 should have release characteristics, so that it can be delaminated from the tape structure in the manner ....... ~ .. . ... , ., , . . ... ... .. , .. .. , , ~, . . .

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o~ a transfer tape. The cohesive, sel~-supporting PSA layer removed from the tape can be elonyated and applied to, for ex~rnple, a garment in the stretche~
condition. Gathers will be in-troduced into the garment all along khe lines of ~he adhesive ~ond after pressure-sensitive bonding has been comple-ted. A
modest amount of pressure can be applied by machine or by hand to insure a strong adhesive bond. A
non-sticking coated roller or the like can be used to apply the pressure, paxticularly superior non-stick properties being obtained with ~luoropolymer or, less preferably, silicone coatings.
- Delamination of the tape is not necessary i~ the backing o~ the pressure-sensitive adhesive tape is itsel highly e~astomeric. Such a tape structure can be provided, for example, by coextruding the backing an~ the PSA through a single extrusion die.
The resulting stretchy tape can be rolled upon itsel~
or convoluted, particularly if the exposed side o~
the elastomeric backing is treated so as to be essentially non-sticky. Special sizings and the like which prevent the formation of a PSA bond are Xnown in the axt and can be employed for this purpose.
Viscoelastic hot melt pressure-sensitive adhesives (PSA's~ of this invention preferably comprise a rubbery block copolymer and at least two different types of resins which associate wi~h di~ferent parts of the rubbery block copolymer molecule.
The resin which associates with the crystalline vinyl arene end blocks o~ the block copolymer tends to increase the size of these crys~alline domains, there~y, it is bel~eved, decreasing the temperatur~
dependence of the elastic aspect of the viscoelastic behavior of the PSA. (However, this invention is not bound by any theoxy.) ~he adhesive character ; of the PSA i5 believed to be . . .

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dependent in part upon the high-viscosity liquid character of the PSA within the 25-50 C. temperature range. A characteristic of a viscous liquid is that it will yield to stress, and at least some strain (in an oscillating stress situation) will be up to 90 out of phase with the stress. By contrast, in a perfectly elas-tic solid the stress and strain would always be in phase. The previously given broad ranges of G", G', and loss tangent (and particularly the preferred and sptimum ranges given subse~uently) are believed to indicate a highly effective balance of viscoelastic properties in the 25-50 C range, whereby at leas-t some elasticity is provided (note the loss tangent ~ 1 and the G' ~f 65 x 104 dynes/cm2 or more), but in combination with some ability to flow or "wet out" a substrate ~note the loss tangent ~ 0.03, the Gl C 200 x 104 dynes/cm2, and G"c~ 100 x 104 dynes/cm2), without resulting in a viscosity so low as to permit excessive "creep"
or cold flow ~.note the 5" ~ 5 x 104).
i Although this invention is not bound by any theoxy, it is believed that enlargement of crystalline or vinyl arene domain~ will increase the storage modulus (G') and decrease the dead load creep, but some PSA behavior (e.g. peel strength) may be lost. Conversely, enlargement ~. midblock domains and/or increased tackifying of these domains may increase PSA behavior but also increase dead load creep and excessi.vely decrease loss modulus (G"~ and storage modulus (G'~ data. The ideal PSA
*or this invention appears to provide a balance of high-vi~cosity liquid and elastic solid behavior, resulting in low dead load creep, good PSA
properties, and properly balanced rheological data.
.35 The G', G", loss tangent, 3' and ~" data can be considered to he "parameters" of the ul~imate properties of dead load creep and PSA characteristics.

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~ tackifying resin with aliphatic character and relatively minim~l aromatic character can associa-te wi-th the midblock of -the block copolymer and, if properly selected, help provide this S viscoelastic balance in hot melt PS~ behavior Thus, a suitable viscoelastic hot melt PSA will typically co~prise:
(1) a rubbery block copol~mer w~ich includes a rubbery midblock portion and which is terminated with crystalline vinyl arene blocks, (2) 20-150 parks by weight, per 100 parts -, by weight o-E said rubbery block copolymer, o~
a tackifying resin generally compatible with and generally associated with the midbloc~
porti~n of the block copolymer, and

(3) 10-150 parts by weight, per 100 parts by weight of the rubbery blocX copolymer, of ~ an aromatic, essentiall~ hydrocarb~n resin - 20 havin~ a glass transition temperature and a i softening point above those of the tackifying resin and thè`end blocks of the block copolymer, which aromatic resin is qenerally compatible with and generally associated with ~5 the a~orementioned end-blocks.
The hot melt pressure-sensitive adhesive will typically have a ball and ring softening point within the range of 65~ to 240 C. It will exhi~it elastomeric behavior above its glass transition temperature and particularly for extended periods at body -tempera-ture ~e.g. 37 C.).
In addition to the block copolymer and resins, the hot melt PSA can contain the usual antioxidants or stabilizers and essentially inert ingredients which do not have a significant effect upon the properties of the combination of the rubbery bloc~ copolymer ' '' ~L3~

and the resins. For example, minor a~ounts of fillers and pigments can be included in the hot melt PS~r tyipcally in amounts less than 5% by weiyht of the total hot melt PSA compos;tion. Substantially inert extenders can also be included in the composition, e.g. the typical hydrocarbon process oils. The amount of process oil will typically also he kept below S weight-~ o~ the composition, since large amounts o oil can detract from the elastic recovery characteristics o~ the PSA.
Typical antioxidants useful in PSA's of this invention include the pentaerithritol phosphite ester type (e.g. di[stearyl~ pentaerithritol diphosphite), the hindered phenol or polyphenol type, and the like. Typical hindered phenol-type antioxidants include those in which a phenolic (i.e. hydroxyphenyl or hydroxybenzyl) group or - groups is or are substituted on a short hydrocarbon chain, and the hydroxy group of the phenolic substituent is hindered by nearby or adjacent alkyl groups su~stituted on the phenol nucleus. Such structures can be obtained, for example, by alkylating or styrenating hydro~yphenyl compounds such as phenols and cresols.
Typical pigments useful in formulating PSA's of this invention include titanium dioxide, typically having a particle size in the sub-micrometer range, and similar finely divided materials~
Fillers may tend to be a bit coarser in particle ; 30 size, though still typically smaller than 40 ~M
(minus 3~5 U.S. mesh), e.g. finely ground calcium salts or silicates.
The following description of the preferred ingredients of hot melt PSA's of this invention will concentrate on the block copolymers and the resins.

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~ number of rubbery block copol~mers can be tacki.fied to produce hot melt PSA com~os.i.-tions, as can be seen from the disclosu:res in the aforementioned U.S. Paten-t Nos. 3,686,107, 3,736,281, 3,827,999, 3,935,338, 3,954,692, and 4,089,824. Additional disclosures of this type can be found in British Patent 1,405,786 and trade literature of Phillips Petroleum Company and Shell Chemical Company. The block copolymers used in this invention are rubbery, i.e. elastomeric. Thouyh these copolymers are thermoplastic in the sense that they can he melted, formed, and resolidified several times with little or no change in physical proper-ties (assuming a minimum of oxidative degradation), they exhibit some o~ the characteristics of cross-linkea or vulcanized rubber. The apparent cross-linked character is provided by the aorementioned crystalline domains provided by vinyl arene terminal blocks or end blocks. The block copolymers also .~o include a rubbery midblock portion which can be either linear or hranched. In typical examples of a branched midblock, the midblock portion contains at least three branches which can be radiating out from a central hub or can be otherwise coupled together.
; 25 One way of synthesizing such rubbery block copolymers is to begin with the polymerization of the vinyl arene blocks which provide the end blocks.
Once the vinyl arene blocks have been formed, they can be linked to elastomeric blocks, which elas-tomeric blocks are typically obtained by polymerizing unsaturated hydrocarbons, e.g. dienes such as butadiene, isoprene, and dienes of higher hydrocarbons.
When an end block A is joined.to an elastomer block B, an A-B block copolymer unit is formed, which unit can be coupled by various techniques or with various coupling agents to provide a structure such as A-B-A, :

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which may in reality be two ~-B blocks joined together in a tail/tail arrangement.
By a similar technique, a radial blocX copolyrner can be formed having the formula (A-B)nX, wherein X
is the hub or central, polyfunctional coupliny acJent and n is a number grea-ter than 2~ (If n ~7ere 2, the polymex would be A-B-X-B-A, which is equi~alent to the A-B~A structure described previously and is essentially linear.) Usiny the coupling agent technique, the functionality of X determines the number of A-B bxanches.
Preferably, each block A has an average molecular weight between 1,000 and 60,000, and each block B has an average molecular weight between 5,000 and 450,000. The total molecular weight of the block copolymer is preferably in excess o~ lOO,Q00 or 200,00Q, e~g. 300,000. An extensive discussion o~
rubbery radial block copolymers can be founa in the disclosure of the aforementioned U.S.Patent No.

4,089,824. As pointed out by the '824 patent, the residual unsaturation in the midblock or diene-containing portion of the block copolymer molecule can be hydrogenated selectively so that the content of olefinic double bonds in tne radial block copolymers can be reduced to a residual proportion of less than 5~ or even less than 2%. Such hydrogenation tends to reduce sensitivity to oxidative degradation and may have bene~icial effects upon elastomeric properties.
P~eferred block copolymers used in this invention have styrene end blocks and an isoprene midblock portion. The isoprene typically comprises the major amount of the repeating units in the copolymer and can constitute, for example, 70% by weight or more o~ the copolymer molecule. The midblock, if bxanched, can have three or more branches, , .... , ,.. . ..... _~.. , . ,.. ~, .. .. ,. .. . .. .. . . ... .. . .. ... " .. . .. i . . .. .....

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and good results can be obtained with, for example, Eour, five, or six branches. The miclblock can be hydrogenated, if desired.
Linear or A~B-~ type block cop~lymers (including A-B-A-B-P, etc.) are preferably selected on the basis of end block conten-t, large end blocks being preferred. For S-I-S (styrene-isoprene-styrene) block copolymers, a styrene content in excess o~ 14%
by weight is preferred, e.g. 15-30% by weight. A
commercially available example of such a linear polymer is KRATOi~ 1111 rubber, an S-I~S polymer which contains about 21.5~ styrene units~
essentially the balance being isoprene units. Thus, the optimum styrene conten-t for linear S-I-S copolymers appears to be yreater than 20% by weight. As a result of -the higher styrene content, the polystyrene end blocks have a relatively high molecular weight.
Typical properties of KRATON~ 1111 are reported to include a tensile strength of 2900 psi (2.0 ~ 106 i 20 Kg/m~, a 300% modulus of 200 psi ~1.4 x 105 ~g/m2), an elongation of 1200% at break, a 10% set at break, and a Shore A hardness of 52; the Brookfield viscosity o a toluene solution is 1300 centipoise at room temperature, less than that of KRATO~ 1107~ -A variet~ of resins with tackifying properties are compatible with polymerized diene polymer blocks, including those diene blocks which have been hydrogenated 50 as to become virtually identical, - -chemically and physically, to polymerized mono-oleins ~e.g. polyethylene, polypropylene, polybutylene, etc.)~ These "miablock" tackifying resins tend to associate with the rubbery midblock of the linear - or radial block copolymer and thereby tend to extend or build up as well as tacki~y these rubbery domains.
Both natural and synthetic "essentially hydrocar~on resins" can be used as "midblock resins~ provided ~3~

th~t these resins con-tain at least sone aliphatic character, ~hich charac-ter can be provided by the aliphatic portion of rosin acids, repeating isvprene or other diene units (e.g. polymerized 1,3-pentadiene), polymerized cycloaliphaLics, and the like.
Although esters of polyhydric alcohols ~nd rosin acids will associate with a rubbery midblock, some of these esters tend to detract from the elastic recovery characteristics of the hot melt PSA and are not preferred. It is generally more pre~erable to use "essentially hydrocarbon resins", particularly the so-called "terpene" resins, i.e. polymers with xepeating C5H8 or CloH16 units. These polymers can be natural or synthetic and can be copolymers ;(including terpolymers, etc.), since isoprene is an olefin which can be copolymerized with other oleins.
Terpene-phenols have also been produced.
All terpene resins do not work wiLh equal ;20 effectiveness in this invention, and synthetic terpenes - having a softening point (ball and ring method) of about 80 to about 115~ C. are preferred, particularly the commercially available resin known as "WINGTA~K"
95. This commercially available terpene resin is reported to be derived from a mixed olefin feedstock as a by-product of isoprene or polyisoprene production. According to U.S.Patent ~o~ 3,935,338 and South Arican Patent No. 700,B81, "WINGTACK" 95 ~trademark of Goodyear Tire and Rubber Company) is a thermoplas~ic tackifying resin essentially comprising a copolymer of piperylene and 2-methyl-2-butene which results rom the cationic polymerization of 60%
piperylene, 10% isoprene, 5% cyclopentadiene, 15%
2-methyl-butene, and about 10% dimer. Other tackifying resins of the same yeneral type typically comprise 20-80 weight-~ of piperylene and 80-20 weight-% of 2-methyl-butene.

., . . ~ . . .. , . . . . ... . ~ . . . .. . . . .

Good elastic memory or elastic recovery characteristics can be obtained with natural hydrocarbon resins such as "PICCOLYTE D-135" (trademark), a natural dipentene terpene resin. However, this resin is not as effective as the "WINGTACK" 95 in providing good adhesive properties, e.g. good PSTC-l peel.
The naturally occurring terpenes can be classified as monocyclic (dipentene), dicyclic (pinene), or acyclic (micrene). A small amount of cyclic character is not detrimental in the context of this invention. A
significant amount of aromatic character in the terpene resin is, however, ordinarily avoided, if such aromatic character is sufficient to interfere with the midblock association properties of the resin.
As explained in British Patent No. 1,405,786, resins with aromatic character tend to associate with the vinyl arene end blocks. Such "end block"
resins include the coumarone-indenes, polystyrene, the polymethylstyrenes, the polyindenes, and other resins containing mono or polycyclic aromatic groups.
Such resins are commercially available, e.g. as "PICCOTEX 75" (low molecular weight alpha-methylstyrene-vinyl toluene synthetic copolymer), "PICCOTEX 100" (trademark for higher molecular weight version of "PICCOTEX 75"), "PICCOLASTIC D-150"
(trademark for polystyrene resin), and the "CUMAR"
resins (trademark for coumarone-indenes). It is particularly desirable that the "end block" resin have a glass transition temperature and a softening point above those of the end block and of the 'Imidblock" resin. Eor example, it would ordinarily not be desirable for the glass transition and for significant heat softening to occur in the 80-110 C.
range; hence, "end block" resins with somewhat ~r : .~ . , . : , , ,.. : .
:
,, .: , . : . : :
: . ~

( higher molecular weigilts and softening points above 115 C. are typically selec-ted. FrGm the standpoint of strong elastic recovery (hoth ini'ial and age~) and good adhesive proper-ties, the high soLtening point coumarone-indene resins appear to be by far the most effective. Such resins wi~h softening points within the ranye of 140-160 C. arP commercially available. -Considerable skill and knowledge already exist in.the PSA art with respect to determiningproportions of tackiEiers and rubbery block copolymers.
However, it has been found that these proportions cannot be selected with blind reliance upon prior experience. Nor can one rely too heavily upon PSTC-l or probe tack values. Probe tac'~ values and initial (immediate) PSTC-l values have keen found to be unreliable. or unreproducible indicators of performance in the context of this invention, whereas PSTC-l.values taken 24 hours ater the adhesive bond has been formed are relatively reliable and reproduc'ibla. I'Dead load deformation" ~"creep"~
and the rheological properties ~,G', G", loss tangent, J', an~ J") described previously have also been found to be reliable, reproducible parameters of PSA
and elastomeric behavior.
Preferrea PSTC-l values determined 24 hours after fo~mation of the PSA bond at room temperature on the standard steel plate using pressure from the standard 2 Kg roller include values in excess of 1 pound per inch wi~th ~1 p.i.w.), i.e. more than 450 grams 180~ peel Eorce is required to delaminate a tape/steel plate sample wherein the tape sample is 25.4 mm in width. 'PSTC-l values in excess of :. 1500g/25.4 mm-sample or even 3000g/25.4mm-sample can be obtained in practice~ These ~alues are ~ believed to indlcate a reasonably permanent or '............. semi-permanent bond between a band of PSA and a .

( -- 2~ --polymeric f.ilm subs-trate o~ t:he -type used in disposabl~
diapers.
Tensile strength values :Eo~ the PSA at 20-25 C.
can be determined as a measure or cohesive strenyth.

5 Values in excess oE 3 x 10 Kg/m (e,g. a~ove 33,000 Kg/m2) can be obtained in practice. "Dead load deformation" values (1500 g/cm for 3 hours at khe test temperature) can be well below 100% and even 4 . below 50% (L2 L1 x 100~) throughou~ the r~nge o~
,, .
25 C. to 50 C. I-t is particularly desirable that this deformation remain roughly constant over this temperature ranye and preferably show a gain of less than 509~ ~e.y. less than about 35~) at 49 or S0 C., as compared to the room temperature value.
Preferred and optimum rheological parameters are set forth below.
TABLE OF PREFERRED AND
OPTIMUM RHEOLOGICAL PROPERTIES
(All values in lOD" dynes/cm2 for G" and G' and in 10 8 cm2/dyne for ~' and J") PREFERRED OPTIMUM
(at 25-50 C.) (at 25-50 C.) at at at at Property 0.01 Hz 0.25 Hz 0.01 E~z 0.25 Hz Loss Modulus 5~25 10-100 8-16 15-35 ( ~ ) Storage Modulus 75-200 75-200 100-175 120-200 tG'3 Loss Tangent 0.05-.3 0.08- 0.07- . O.01-~tan ~; ) 1.0 0.10 0.25 Storage 40-100 40-100 60-80 50-70 Compliance (J') Loss Compliance 2-20 5-40 5-8 5-15 The temperature-dependence of these values over the 25-50 C. range is preferably minor, as indicated below.

_ .. . . ,. ~. -. - - ` !

~3~ 4 TABLE: OF BROAD ~ND PREFERP~ED LI~lITS
ON VA~IAI'IOI~S IN R~IEOLOGICAL PRO?E~<T~ES
(Ail values in 104 c1ynes/cm2, e~c over the 25- 5 0 C . ~ an~e ) Broad Limits Preferred I,imits Property 0.25 ~Iz 0 01 Hz 0.25 Hz 0.01 Hz G" (104 dynes/cm22 ~ 70 ~ 10 _ 25 ~ 10 G' ~104 dynes/cm2~ ~~ 40 ~ 15 ~ 2S ~ 8 Loss tangent ~ 0.6 ~ 0.2 ~ 0.5 ~ 0.15 1~ Actual test data indicate that an "ideal"
viscoelastic PSA, within the context of this invention, would have the following properties:
0.01 Hz 0.25 Hz G" (dynes/cm2) lol x 105 3 ~ 1~S
G' (dynes/cm2) 1.3 ~ 10 1.75 x 10 Loss tangent 0.085 0.2 J' (cm2/ayne) 7.7 x 10 7 6 ~ 10-7 J" ~cm2/dyne) 6 x 10 8 1 x 10 7 With these physical properties in mindr proportions of rubbery block copolymer and end block and midblock resins can be selected to provide an effec~ive PS~
with good elastic recover~ or elastic memory characteristics. The following Table of broad, preferred, and optimum proportions assumes that the 25 rubbery block copolymer is either (1~ "SOLPRENE~ -418", t~ademark of Phillips Chemical Company for a radial isoprene-styrene block copolymer having an approximate molecular weight o 300,000, a specific gravity of 0.92, an inherent viscosity in toluene 30 O~ 1.16, and an isoprene/styrene ratio of 85/lSr or (2~ KRATO~ 1111, trademark of Shell Chemical Co~ for a polystyrene-polyisoprene-polystyrene tS-I~S) block copolymer containing 21.5~ styrene, the balance being isoprene. This copolymer has the 35 previously reported tensile strength, 300 modulus, elongation at break, set at braak, and Shore A haraness.
The Brookfield viscosity in toluene is 1300 cps.

- . .. . .. .. .: .

SO~PRE~E~ 418 in toluene has a viscosity o' 2,900 centipoi~e at 25 C. Hydrogenated linear block copolymers, including those of the styrene-isoprene-styrene type are available according to U~S~ Patent No. 3,827,999; see also U.S. Pa-tent No. 4,089,824, which discloses the hydroc~enated butadiene analog. Such hydrogenated block cop~lymers can be used in the context of this invention.
Compounds of the "KR~rroN~ G" series (trademark of Shell Chemical Company~ have a saturated or essentially ~aturated ethylene-butylene midblock and, i used, are preferably used in combination with the KRATON~ 1111 or SOLPREME~ 418 type of rubbery block copol~mer.
The aforementioned Table of proportions is sek forth below.
T~BLE OF PROPORTIONS
FOR BLOCK COPO~YMER AND RESINS
Amount 20Broad Preferred Optimum ~ngredient ~ wt-% phr wt-% phr Rubbery block (100) 20-75 ~100) 35-45 ~100) copolymer Midblock resin 20-150 15-50 50-125 30-50 70-120 End block resin 10-150 10-40 40-65 15-30 40-55 NOTE: phr - parts per hundred by weight, based on 100 parts block copolymer.
wt-%= percentage by weight of total hot melt PSA composikion.
The nature o the block copolymer tlinear or branched, amount of vinyl arene units, etc.) can have a slight efect upon the optimum for~ula. The best balance of ~iscoelastic properties appears to be obtained with 100 paxts by weight linear, high-styrene block copolymer (35-45% by weight of the PSA), 7D-78 parts by weight of the synthetic polyterpene, and 45-55 parts by weight of a coumaron~~lndene resin having a soEteninc3 poin~ in excess of 145 C. About 0.005-1 part by ~;eiqh-~ oE
antioxidant should be added to such a formula.
Similar formulas can provlde similar results with branched block copolymers and low-styrene linear block copol~mers, but it may be useful to exten~ the ranges up to 85 phr of polyterpene and up to 65 phr of coumarone-indene resin~
The most effective criteria for the selection of amounts and ty~es of ingredients are believed to be (a) rheological properties such as Gl, Gl', loss tangent, ~' and J", and (b) dead load creep test results. New resins and new block copol~mers are constantly being discovered, and the formulation of suitable PSA's can be attempted with new materials by referring to these criteria.
It will be understood that variations in the aforementioned methods and proportions can be made without departing from the spirit and scope of this invention. For example, if the substrate to be elastic banaed is heat resistant, the extruded band need not be cooled very much below its softening point and -can be applied directly to the substrate while still relatively hot. However, even for such temperature 2S resistant substrates, maintaining the extruded band at or above its softening point is neither necessary nor desirable. In another variation of the method, the extruded band need not be applied as a line or linear bead, but can ~e "indexed" with a moving web to pro~ide a series of discrete circular or eliptical bands. Such "indexed" bands can provide a hat-banding effect ~e.g. for mass-produced surqical caps), a gathered, banded opening for a plastic bag, a waist band, or the~ like. In the case of disposable diapers, however, it is not necessary for the band to form a complete circle; the essential equi~alent :

J~æ4 of a circular leg band resul-ts when the diaper is pinned or snapped together at the child's hips.
The following non-limi~ing Examples illus-trate the preferred practice of this inven-tion. In these Examples, all pa~-ts and percentages are by ~eight unless otherwise indicated. The following raw materials were used in formulating the hot melt PSA's o~ the Examples:
"SOLPRENE~ 418": trademark for the radial block copolymer described previously.
"SO~PRENE~ 423": another trademark for essentially the same radial block copol~mer in a pellet form.
"KRATON~ 1111": trademark of Shell Chemical Co. for the polystyrene-polyisoprene-polystyrene copolymer described previously.
"KRATON~ 1107": trademark of Shell Chemical Co. for polystyrene-polyisoprene-pol~styrene linear ~locX copolymer having a styrene/isoprene xatio of 14/86.
"WI~GTACK 95": trademark for synthetic p~lyterpene resin described previously.
"KRYSTALEX~ 3100": trademark of Hercules Inc. for low molecular weight thermoplastic hydrocarbon resin of the alpha-methylstyrene type having a ring and ball softening point o 97-103 CO~ an acid number less than 1.0, a bromine number which is typically about 2, a specific gravity at 25 C. of 1.06, and a 3Q melt viscosity of 10,000 centipoise ~cps~ at 128 C., 1,O00 cps at 152 C., and lO0 cps at 190 C. The softening point substantially below 115 C. (typically not more than 103 C.) indicates a spectrum of molecular weig~ts, with a significant number of resin molecules having - . ...

-~3~2aJL
~ 29 -molecular ~eights well below -those of the rela-tively pure, narrow-spectrum co~arone-indene resins which are cornmercially available, e.g.
as the "CUMAR" (-trademark) series described subsequently. ~I-t has been found that the higher molecular weight, higher softening point, narrow-spectrum aromatic hydrocarbon resins are pxeferxed for use as "encLblock" association with - the rubbery block copolymers described previously.) 10 - "CUMAR LX-509": trademark of Ne~ille Chemical Company for coumarone-indene resin having a softening point CbY the ring and ball technique of ~.S.T.M. E-28) of at least about 155 C., a specific gravi-ty at 2S/15.6~ C. of 1.114, and an average molecular weigllt ~by osmometry) of 1,120.
"EASTMAN~ Resin H-100": trademark of Eas~man Kodak Company for a hydrocarbon resin produced from petroleum feedstock by polymerization, followed by hydrogenation.
This particular hydrocarbon resin has an acid number less than 0.1, a density at 23 C. of 1.04 g/cm3, a Brookfield viscosity at 190~ C.
of 200 centipoise, a bromine number of 11.1, ~5 and a rin~ and ball softening point ~A.S.T.~.
E-28) which i5 reported to be 100 C. and in any event is below lI5:C.
"IRGANOX 1010": trademark of Ciba-Geigy for an antioxidant and thermostabilizer of the hindered phenol type.
"SO~PRENE~ 420": trademark for a branched, teleblock copolymer having polystyrene Lerminal blocks and a structure essentially similar to . "SOLPRENE~ 423", except for a lower molecular ~leight.

..... .. . ... . . . .. .. ... .... .. ...

(~
~3L3~

"KR~TON~ 1102": -tradem~rlc for S-B-S
(styrene~butadiene-s-tyrene) bloc~ cop~lymer having a styrene/bu-tadiene ratio of 28/72, a BrookEield viscosity in toluene solu~ion (25 weiyh~-PO) of 1200 centipoise at 25 C., a speciic gravity of 0.94, a Shore A hardness o~
62, a set at break of 10~, an elongation of 880%
(A.S.T.M. method D412 with a tensile tester jaw separation speed of 25.4 cm/min.), a 300% modulus of 281,200 Kg/m2, and a tensile strength ~same A S.T.M. method as the elongation determination) of 3.23 x 10~ Kg/m2 determined on typical films cast from a toluene solution.
"WESTON~ 618": trademark of Borg'~7arner Corporation for an antioxidant described in U.S. Patent Nos. 3,047,608 and 3,205,26~, i.e.
an antioxidant which is reported to be di~stearyl) pentaerythritol diphosphite.
~or convenience of sample preparation, the ' antioxidants and pi~ments were sometimes omitted from the exemplary formulations which follow. Since incompatibility between resins and various portions of the rubbery block copolymer tend to be minimized in the molten state, the order of addition of ingredients is not usually critical. It is generally preferred to begin with one of the relativel'y larger components such as the rubbery block copolymer and add the tackifiers and other resins to it, e.g. adding ; the'synthetic terpene '!midblock" resin next, followed by the "endblock" resin. Samples can ~e Frepared by blending in a solvent mediumi however, the data obtained from such samples is believed to ~e less reliable as compared to samples formulated in the molten state. Samples can be solvent-cast to films ranging from 100 to 200 micrometers for test purposes, .

,, ~ .. ~ . ... . . ... ~ .. . ... . . .. .

: . ~

~ 3~;~;Z4 even though thP industrial practice of this invention involves ex-trusion of thc hot melt PSA.
Comparat,ive Example A
~ he following ingredients ~7ere blended in a heated mixer in the indicated amounts.
Wt.-% Ingredient 65.4 Radial isoprene-styrene elastomeric , block copolymer (SOLPRENE~ ~23)~
32.7 High softeniny-point, hiyh molecularweight c~umarone-indene resin (CU~AR~
LX-509) .
0.2 Phosphite ester antioxidant ~STON~
618).
0.2 Hindered phenol antioxidant ~"IRGANOX"
1010).
1.5 , Titanium dioxide pigment ~rutile, alumina-treated).
A pùrpose of this Example was to evaluate the effect upon rheology and room-temperature 180~ peel strength when the radial block copolymer/resin blend was provided with larye crystalline ~vinyl arene) domains and minimally tackified or plasticized rubbery (elastomeric) domains, in this case no "midblock"
resin. According to the scientific and patent literature, the coumarone-indene resin probably became associated with the polystyrene end blocks o-E
the raaial elasto~eric block copolymer.
Comparative Example B
The following formula is a rubbery block copolymer/tacki~ier resin blend which would have lo~ tack an~ peel and would have significant elastomeric kehavior at normal ambient temperatures. The formula , theoreticall~ contains no "endblock" resin.

.. , ... ~ ., . , ., ~ , ... . .. . .. .

2~

Wt.-% Ingredient Linear S-B-S (polystyrene-p~lybutadiene-pol~styrene) elastomeric block copolymer (~ATO`!~ 1102).
Hydrocarbon resin (EAST~ Resin ~-100) .
Skaybelite Ester 10 ~HERCULES~ glycerol es-ter of hydrogenated rosin, 83 C.
softening point).
-10 Compa~ative Example C
This formula was similar to that o~ Example B, except that an S-I-~polystyrene-polyisoprene-) radial block copolymer was blended with a different tackifier.
Wt.-% ~ngxedient Radial S-I- elastomeric block copolymer (SOLPRE~E~ 418).
Polyterpene resin ~WINGTACK~ 95).
Comparative Example D
This formula had both "endblock" resin and "midblock" resin in addition to the S-I-S bloc~
copolymer; however`, more than 80% by weight o~ the "endblockl' resin was a relatively low molecular weightl low so~ening point material~ The blocl,c copolymer was also a relatively lower molecular weight material. Room temperature performance of the formula would be expected to include poor PSA
properties and some elastomeric beha~ior, but at higher temperatures ~e.g. 37 C.), perormance would be unpredictab1e.

, .. ~ ~ .. . . . . .. . . . . .. . .... .. . . . . . . . .. .. . . ... .

~L3~
~ 33 ~It.-% Inyredient 40.0 Low molecular weight, radial, elastomeric block copolymer (SOLPP~E~ 420).
0.1 Phosphite ester an-tioxidant ~WESTo~
618~.
0.1. Hindered phenol antioxidant ~" IRGANOX"
1010) .
1.0 Titanium dioxicle pigment ~rutile, alumina-treated).
32.8 Hydrocarbon resin (EAST~N~ Resin ~I-lOQ)~
4.0 High molecular weigh~ co~marone-indene (CUM~R~ LX-509).
22.0 Alpha-methylstyrene resin ~typical lS softening point: 100 C.~ ~"KRYSTALEX"
3100 [trademark]).
Comparative Example E
This for~ula appeared to conform to all of the criteria of a formula of this invention, except that 20. the amount of "ena~loc~" resin was relatively high -and the amount of polyterpene tackifier was relati~ely low..
~t.-% Ingredient 4$.0 High molecular weight, radial S-I~
25 . elastomeric block copolymer ~SOLP~ENE~
418)-15.0 Polyterpene resin ~WINGTACK~ 95~ 7 40.0 High molecular ~eight, high so~tening point coumarone-indene ~CUMA~
LX-509)~
Examples 1 - 5 The formulas for Examples 1 through 5 are set .
forth in the following Table.

-- 3~ --~.~ -x .~ o Q) U~ r~?
.
U~ O
.. . . I
$ ~ r~~I r~ ~1 I H
. o~O ~
. ,_ ~ ~_ . c~ . o~d ' I X 1 .

C~ o ~.
o~o O ~ ~ ~I r-l r~
E-l C,) ~1 -- ~ ~ t~
~ _~ d.

~ ~. ~ 0-~
æ ~ ,¢ o s~
~ Z; ~ r~
Z; r-l 111 H. . . 1 O Q) ~t~
HPl P; ~ ~~') ~1 ~ ~ - 1 ~, æ '~' h ~ r~r~
H ~ ~ d'X
H O Q- ~ ~ O rl ~-1 h Q
I ~ O I I ~ I
U~ ) I I ~ I O ~ ~i ,4~
O ~ h h O
5,~ ~ C`l ~ ~ liS d~
I ~!) O
H ç: ~ ~ 0 ~1 ~1 o ~ d' I ~1 o ~
u~ ) ~ ~ W
x æ ~ ~
~ o o ~ ~

,~ E~ r~
~4 . U~
X O r-l N f~) ~ u~
~1 ,~ r U) z;
O

~ ~ .. .. .... .

~ 3~

heol ~i.cal Testing The G", G', loss tangent (G''/GI), J", and J' were determined, as described previously, at 25 and 50 C. and at 0.01 and 0.25 Hz,. The results for the Comparative ~xamples and Examples 1-5 are set forth below. All G" and G' data are .in 104 dynes/cm2, and all J" and ~' data are in lO ~
cm2/dyne. ~or purposes o~ comparison, typical data for natu~al rubber (at 0.25 Hz) are included.

.... . . . . . . .. .. .

3~
~ 36 -~ ~D O 0 O ~ ~r c~ ,~. . . . . ~
c, ~ n o o o Ln ~`I ~1 ~1 ~1 ~`I r ~D ~D co , _ L') ~ CO~n ~r ~ ~D ~
o. O'~ . ~ ' ' 0~> ' L') C~ r-l ,I r~ 10 cnL~ ,-1 tf) O
O ~ Ln ~ ~ .
Ln ~ ~ ~l ~ ~ n Ln L'l D

O CO
U~ ~ O U:> . . . . , t~ L~ 5> L') ~D t`l ~ C~
,~1 o CO o ~ n ~ ~ ~D ~ ~I
.~ o o ~ cn ~ o ~
U~ L~l ~ CJ~ ~ O ~r O O O O O O
/D N a5 In E~ ~:1 ~1 ~
In ~ o u~ In ~ ~ ~ O ~ o~
~ . O O t~l N ~ O In t~
~A o C~ ~1 L~) r-l O rl O ~ O O O ~ ' t~ t~ ~
O .. O
o ~ c~ u~
O ~ ~ ~ ,~ ~ ~ .
c~ a~ .. o ~ ~r ~ In ~ ~ L'l ~ ~ ~
~ Q) m , r~ ~ 1- ~ ~ ~1 ~1 ~1 ~1 ~D .
H O .L- _ 11 l ELl ~ . o I ~ ~ Ln C~ ~D r I O
~:1 O ~ Ln ~ ~ 1 . ~ Q . ~`1 o~
E~ ~ . ::
o o ~ ~ ~ . . .
O ~ ~ ~ ~1 ~ L'l O
L') r--l ~`I ~ ~J ~ C~ ~ ~ r~ In ' _ ~ ~ ~ L~ ~) ~ ~0 ~ ~ e~ ~
O r~
L'-) ~ D ~ O t~ ~1 ~ ~1 ~
~ ~ ~ ~r In ~a ~ ~ ~ ~1 ~
.

w ~ a F~

U~ O
'' , ... . . . . . .. ..... .

., ~ .

~L3~

.. "............... C~, O ~ 00 ~ CO ~D L~ ~ ~ ~0 ~ I

u~) N 0~ D N

o ' N . . . . . .

U~ 1-- ~D ~ ~D ~ Ct) U) C~ i~ ~ I

C~ C~

~ ~1 W O U~

o ~) ~1 ~ ~V O O

o . Lt~ . ~r . . . o . o I

u~ ~ ~ co ~ ~ ~ In ~I r- ~ I ,, _ ~ ~ ~ o r 7 ~ a~ ~D

o . N (`J -n ~ o ~ ~ . ~ . . o ~ I

. ~ ~ ~ ~ ~

~: t) ~1 o O ~ I` ~1 ~`J N Cl~
O o ~ t~ D O 0~ ~ O ~ In U~ ~ ~ O ~ ~ O ~ 0 ~1 0 0 ~ ~ O

E-~ ~: ~ ~ U') ,...........

d In ~ tn ~ 0 ~ a~ ~ ~ ~ co cn :

C~ O o ~ O C~ O ~r ~ co .,1 O ~ ~1 U~ ~t ~ ~ O ~ ~ ~ ~ ~D O
t~ N ,~ , . . . . . . . .
O o ,_1 .. L~
~0 ~ ~

o ~ O ~ C~ ~D O U~ O

. ~ ~ .. o ~ ~ ~ ~ r~

~ 0 . ~r~ ~
H 0 ~ V
H ~4 h o I co ~ ~ ~ ~ o a~ . LO ~ D ~ O
r- ~ ~ ~ ~ ~ ~1 ~ oo a) ~ E~ ~ cc~ ~-- o L~
o~ L~ . o :.

u~ o ~ , ._ o o . . o7 ~ -u~ c~ n ~ ~ ~ O

. c~ ~1 ~ ,1 ~ ~ ~ ~ ~ ~ 1-.

a, ~ ,~ ~ .
h 0-r~
~ ~Q~

It') o U'l ... .. . . .. , .. . . .. --~ ( ~3~

For Example A, the high G' values and the temperature dependency o these values indicat~
unsuitability, according to the principles of this invention. The high G' may, it is belie~d, indicate yood elastic behaviorl but, conversely, poor PSA
per~ormance. The rheological parameters were conEirmed by 180" peel data ~YSTC-l). Even 24 hours after for~ation of the PS~ bond, no PSTC-l value could be obtaine~. "Dead load deformation" ~alues were accepta~le, ranging from 0~ to only 6% throughout the 25-50 C. range.
For Example B, the tempera-ture dependenc~ of G' also lndicates unsuitability, which was reflected in the "dead load deformation" data. These data wer~ as follows: 20~ at room temperature, 3~4% at 37.8 C., and 528% at 43.3 C. Cohesive failure occurred at 48~9~ C.
For ~xample C, G" at .01 Hz ~25 C.) was - marginal~ an~1 at .2~ Hz (50 C.) was very low; G' data at .01 Hz were maryinal. This analysis of the rheological parameters was confirmed by "dead load Ae~ormation" data: 6~ at roo~ temperature, 44% at 37 8 C., 92~ at 43.3 C., and cohesive failure at 48.9 C. The PS~C-l values ater 24 hours were acceptable (2i70 g/25.4 mm-width), indicating the - abil ty to ~et out a substrate (but inadequate resistance to heat set).
Example D had poor PSA behavior, and performed poorly in the "dead load deforma-tion"
test. It is believed that the high G" and, most important, temperature dependence of G' were sig~ificant in these regards.
The high coumarone-indene content of Example E
was believed to be reflected in the high G' values.
The PSA behavior of Example E was marginal (e.g.

, .. , . ,:.. .... . . . . . . . . . .. .

~L~L3~Z4 - 39 ~
910 g/25.4 ~n-width in PSTC-l), but a sarnple of Example E performed adecluately in the "dead load deformation" test.
Examples 1-4 performed ~ell in terms of both (1) PSTC-l (180 peel) values taken at room te~perature after ~4 hours PSA bond formation and (2) "dead load deformation". Example 5 showed excellent PSTC-l performance but nearly ailed the "dead load deformation" test. The 24-hour PSTC-l values for Examples 1, 3, 4, and 5 are set forth below.
All samples tested were 25.~ mm in width, and the values are reported in grams per 25.~ mm~width.
E~ample 1: 2670 g/25.4 ~m Example 3: 2170 g/25.4 mm Example ~; 2130 g/25~4 mm Example 5: 3580 g/25.4 ~n*
*determined immediately rather than ater 24 hours PSTC-l values above 4500 g/~5.4 mm or even 400~
g/25.4 mm are difficult to o~tain in practice without sacrificing other desired properties.
Dead ~oad Deformation Test All of the products tested were manufactured using a high shear, double arm mixer heated to 200 C. Inert gas was used throughout processing to minimize degradation.
Samples taken fxom each batch were pressed between release paper using a Carver laboratory press. The release paper was heated in a forced air oven to 200 C. for 15 minutes to drive out residual moisture.
The press was equipped wi-th heated jaws set at 200 C. and was shimmed to yield an adhesive thickness of 50 microme~ers.
A dwell time of approximately 5 seconds at 3.5 x 106 KcJ/m was generally sufficient to form an air-free ilm.

.... . .

~ ~ 3~i3~ ~
-- ~0 --Dumbbell-shaped specimens were cut from the essentially air free films usiny a starldard striking die.
Marks were pla~ecl on the reduced section of a specimen approximately equidistant from its ~enter and perpendicular to its lon~itudinal axis. The centers of the marks were 25.0 mm ~ 0.5 mm apart.
The specimens were fastened in a ~ertical position at test temperature and weights e~ualling 1500 gms/cm2 of cross sec~ional area were attached. The specimens were conditioned in this mode for a period of 3 hours. After 3 hours, the weights ~ere removed and the specimens allowed to retract and equilibrate at 25 C. for 5 minutes. The distance ~et~Jeen marks was remeasured and the percent "dead load creep"
or elongation (permanent longitudinal deformation or set) was calculated as follows:
Elongation percent = L2 - Ll/Ll x 100 wherein L2 = measured distance between marks on the ~onditioned specimen, and Ll = original distance between marks.
This procedure is a modification of A.S.T.M.
D-412 (tension testing of vulcanized rubber) and the dumbbell-shaped samples were formed using Die C.
25The dead load deformation data for Examples 1, 3, 4, and 5 are se~ forth below.
TABLE III
PERM~NENT DEFORMATION FRQ~I 1500 gfcm AT ~RIOUS TE~ERATURES
30Room Example Temperature 37.8 C. 43.3~ C. 48.9 C~
l 2% 4% 8% 8~
3 2% 10% 30% 30%
4 2% 10% 24% 36%
35 5 6% 34% 56% 74%

, . . .

~ ~3~

In the case oE Example 5, some temperature ~ependency of G", G', and loss tang~nt should be noted at 0.25 Hz, and the deformation d~ta are believed to re~lect a similar temperature dependency.
S Furthermore, G' at 0.01 H~ was considered marginal for this formula.
The data for Examples 1-5 are believed to establish that a varie~y of relatively high molecular weight, relatively hiyh vinyl-arene elas-tomeric block copolymers can be used in this invention, e.g. both the radial and linear types~ Blends of these various types of block copolymers ~e~g.
1/9g - 99~1) will provide suitable elastomeric bases for admixture with endbloc~ and midblock resins or other PSA-forming materials. Examples 1-5 are also believed to demonstrate the value of a good balance between high softening point "endblock" resin and "midblock" resin in the preferred compositions.
Samples of Examples 1-5 were tested for tensile s~rength at 500% elongation at room temperature (20-25 C.). It was found that the tensile strength exceeded 35,000 Kg/m2 for all samples. For Examples 1-4, this measurement was significantly higher, generally in excess of 70,000 Kgtm2, indicating good cohesiveness.
To provide a further standard of comparison for the rheological data obtained from Examples 1-5, data regarding untackified, unextended, linear A-B-A block copolymers (e.g. of the KRAT0~ type) were obtained for 0.25 Hz/room temperature conditions.
These data indicate that G' is typically a~ove 300 x 104 dynes/cm2 and G" is typically above 50 x 104 dynes/cm~ and even, in some cases, above 100 x 104 dynesfcm . ~ike vulcanized natural rubber, these block copolymers exhibit excellent elastomeric behavior but, in the absence of tackifying resins, essentially no PSA behavior.

, ~ , . ~ . .

Claims (16)

WE CLAIM:

1. A method for imparting elongation-resistant gathers to portions of a generally non-elastomeric film, membrane, or web substrate, comprising the steps of:
(a) extruding a band comprising a viscoelastic hot melt pressure-sensitive adhesive, said ho-t melt pressure-sensitive adhesive comprising a rubbery block copolymer which includes a rubbery midblock portion and which is terminated with crystalline vinyl arene end blocks, said hot melt pressure-sensitive adhesive having a ball and ring softening point within the range of 65° to 240° C., being elastomeric above its glass transition temperature and at temperatures up to at least 37° C., and having the following rheological properties at 0.01-0.25 Hz and throughout the range of 25-50° C.:
loss modulus: 5 x 104 to 100 x 104 dynes/cm2 storage modulus: 65 x 104 to 225 x 104 dynes/cm2 loss tangent: 0.03 to 1.0;
(b) cooling the thus-extruded band to a temperature below its softening point but above its glass transition temperature;
(c) bringing the thus-cooled band into contact with a surface of a moveable, flexible, generally non-elastomeric continuous film, membrane, or web substrate having a thickness less than about 3 millimeters and forming a pressure-sensitive adhesive bond generally by means of pressure, whereby the thus-banded substrate can have elongation-resistant gathers at least along the area of the pressure-sensitive adhesive bond between said band and said substrate;

(d) cutting the resulting banded substrate into portions suitable for use as elastic-banded articles, said articles having elongation-resistant gathers at least along said area of the pressure-sensitive adhesive bond, due to the expandability of said gathers and the elastomeric properties of said band.

2. A method according to claim 1 in which said moveable flexible continuous film, membrane, or web substrate is kept continuously moving during said steps (a), (b), and (c).

3. A method according to claim 1 wherein said steps (b) and (c) are carried out simultaneously.

4. A method according to claim 3 wherein gathers are introduced into said banded substrate by placing said band under tension subsequent to said step (a) and prior to said step (d), whereby said substrate is wrinkled into gathers through contraction of the tensioned band.

5. A method according to claim 1, wherein said substrate is a polymeric film less than 0.5 mm thick or a woven or nonwoven web, and wherein said elastic-banded articles of step (d) are garments or body-encircling members.

6. A method according to claim 1 wherein said hot melt pressure-sensitive adhesive comprises:
(a) said rubbery block copolymer;
(b) 20-150 parts by weight, per 100 parts by weight of said rubbery block copolymer, of a tackifying resin generally compatible with and generally associated with said midblock portion;
and (c) 10-150 parts by weight, per 100 parts by weight of said rubbery block copolymer, of an aromatic, essentially hydrocarbon resin having a glass transition temperature and a softening point above those of the said end blocks and said tackifying resin; said aromatic, essentially hydrocarbon resin being generally compatible with and generally associated with said end blocks.

7. A method according to claim 1 wherein the said loss modulus, storage modulus, and loss tangent remain generally constant throughout the temperature range of 25-50° C. with respect to properties determined at both 0.25 and 0.01 Hz, at least within the following limits:
0.25 Hertz 0.01 Hertz loss modulus ? 70 x 10 ?10 x 104 dynes/cm2 dynes/cm2 storage modulus ? 40 x 104 ?15 x 104 dynes/cm2 dynes/cm2 loss tangent ? 0.6 ? 0.2.

8. A method according to claim 7 wherein said ..
pressure-sensitive adhesive has the following rheological properties throughout the temperature range of 25-50° C.:
0.01 Hz 0.25 Hz loss modulus, 5-25 10-100 104 dynes/cm2 storage modulus, 75-200 75-200 104 dynes/cm2 loss tangent 0.05-0.3 0.08-1.0 storage compliance, 40-100 40-100 10-8 cm2/dyne loss compliance, 2-20 5-40.
10-8 cm2/dyne

9. A method according to claim 8 wherein said rheological properties are as follows:

0.01 Hz 0.25 Hz loss modulus 8-16 15-35 104 dynes\cm2 storage modulus, 100-175 120-200 104 dynes\cm2 loss tangent 0.07-0.10 .01-0.25 storage compliance, 60-80 50-70 10-8 cm2/dyne

10. A method according to claim 1 wherein the dead load deformation of said pressure-sensitive adhesive, tested at room temperature, 37.8° C., 43.3° C., and 48.9° C. for 3 hours under 1500g/cm2, is less than 50%, where dead load deformation = the increased length minus the original length divided by the original length of a sample at least 25 mm in length.

11. A method for imparting elongation-resistant gathers to portions of a generally non-elastomeric substrate by means of a pressure-sensitive adhesive tape, comprising the steps of:
(a) unreeling a length of pressure-sensitive adhesive tape from a convoluted roll of hot melt pressure-sensitive adhesive tape comprising a hot melt pressure-sensitive adhesive layer adhered to a flexible continuous backing, said roll being maintained at a temperature below the softening point of said hot melt pressure-sensitive adhesive layer; said hot melt pressure-sensitive adhesive layer being an elongated extrudate at least 50 microns in thickness comprising (i) a rubbery block copolymer which includes a rubbery midblock portion and which is terminated with crystalline vinyl arene blocks; (ii) 20-150 parts by weight, per 100 parts by weight of said rubbery block copolymer, of a tackifying resin generally compatible with and generally associated with said midblock portion; and (iii) 10-150 parts by weight, per 100 parts by weight of said rubbery block copolymer, of an aromatic, essentially hydrocarbon resin having a glass transition temperature and a softening point above those of the said end blocks and said tackifying resin; said aromatic, essentially hydrocarbon resin being generally compatible and generally associated with said end blocks;
said hot melt adhesive having a ball and ring softening point within the range of 65° to 240°
C. and being elastomeric above its glass transition temperature and at temperatures up to at least 37° C.;
(b) placing said length of the pressure-sensitive adhesive layer of said tape under tension; and (c) bringing an exposed surface of the pressure-sensitive adhesive layer into contact with said substrate and forming a pressure-sensitive adhesive band generally by means of pressure; whereby the thus-banded substrate can have elongation-resistant gathers at least along the area of the pressure-sensitive adhesive bond between said band and said substrate.

12. A method according to claim 11, wherein the backing of said pressure-sensitive adhesive tape is a generally non-elastomeric release liner which is delaminated from said tape prior to said step (c).

13. A method according to claim 11, wherein the backing of said pressure-sensitive adhesive tape is elastomeric.

14. A method according to claim 13 wherein said tape has been formed by coextruding said backing and said pressure-sensitive adhesive layer, and wherein the exposed surface of said backing has been provided with release characteristics.

15. A viscoelastic hot melt pressure-sensitive adhesive consisting essentially of:
(a) 20-75% by weight of a rubbery block copolymer which comprises a rubbery polyisoprene midblock portion and a plurality of end blocks comprising a crystalline poly(vinylarene);
(b) 50-125 parts by weight, per 100 parts by weight of said block copolymer, of a terpene tackifying resin generally compatible with and generally associated with said midblock portion;
(c) 40-65 parts by weight, per 100 parts by weight of said radial block copolymer, of a coumarone-indene resin having a glass transition temperature and a softening point above about 115° C.;
the proportions of said components (a), (b), and (c) being selected to provide the following pressure-sensitive adhesive and rheological properties:
(i) a tensile strength at 500%
elongation, determined at 20-25° C., of at least 50 pounds per square inch;
(ii) a 180° peel resistance, according to PSTC-1, determined at 20-25° C. 24 hours after formation of the pressure-sensitive adhesive bond, of at least about 450 grams per 25.4 mm-width;
(iii) a dead load deformation, tested at room temperature, 37.8° C., 43.3° C., and 48.9° C. for 3 hours under 1500 g/cm2, is less than 50%, where dead load deformation = the increased length minus the original length divided by the original length of a sample at least 25 mm in length;
(iv) the following loss modulus, storage modulus, and loss tangent values at 0.01-0.25 Hz throughout the temperature range of 25-50° C.:
loss modulus: 5 x 104 to 100 x 104 dynes/cm2 storage modulus: 65 x 104 to 225 x 104 dynes/cm2 loss tangent: 0.03 to 1Ø

16. A viscoelastic hot melt pressure-sensitive adhesive according to claim 15, wherein said adhesive consists essentially of:
35-55% by weight of said block copolymer;
25-45% by weight of said terpene tackifying resin, said tackifying resin having been synthetically derived from a mixed olefin feedstock;
15-30% by weight of said coumarone-indene resin, said coumarone-indene resin having a softening point of at least about 140° C.;
0-5% by weight of substantially inert extenders, fillers, pigments, and antioxidants;
the foregoing proportions being selected to provide the following results for the properties defined in said paragraph (iv):

0 01 Hz 0.25 Hz loss modulus, 5-25 10-10 104 dynes/cm2 storage modulus, 75-200 75-200 104 dynes/cm2 loss tangent 0.05-0.3 0.08-1.0 storage compliance, 40-100 40-100 10-8 cm2/dyne loss compliance, 2-20 5-40.
10-8 cm2/dyne