CA1071519A - Absorbent article with adhesive strip - Google Patents

Abstract

Abstract of the Disclosure The disclosed article (e.g. a sanitary napkin) typically comprises (1) an elongated absorbent pad, (2) an outer covering layer in adherent contact with at least one surface of the pad, (3) an adhesive strip or layer on the exposed surface of the outer layer, and (4) a release liner for protecting the adhe-sive layer. The adhesive layer is useful for removably attach-ing the article to the inside of an undergarment or the like.
Production of the article can be greatly simplified by using a hot-melt pressure sensitive adhesive (PSA) as the adhesive layer. However, the rubbery base for the hot-melt PSA should be very carefully selected. Two types of rubbery polymers pro-vide good results, i.e. (a) an A-B-A block copolymer having polystyrene end blocks and a rubbery poly(ethylene-butylene) midblock and (b) a radial teleblock copolymer with branches having polystyrene terminal blocks and a butadiene segment in the center. One or both of these rubbery polymers is used to formulate the hot-melt PSA along with a suitable tackifier and a process oil.

Description

~ G 219 ~lljUSA

Field of the Invention This invention relates to arti~les for absorbiny fluids.
An aspect of this invention relates to articles for ~bsorbing body fluids such as blood, uxine~ menses, and other exuda,es, secretions, and excreta (including fecal matter). Still another - aspect of this invention relates to a sanitary napkin provided with a pressure-sensiti~e adhesive means for attaching the napkin to a supporting garment. . - .
. ' ; ' .
: . . Description of the Prior Art 10 Absorb~nt structuxes have been developed which are parti~- .
ularly well-suited for use with a supporting garment or body-en~ ¦
circling membex, wherein the absorh~nt structure is temporarily attached to the me~ber or gaxment with a pressure-sensitive adhe-sive means. Typical examples of such absorb~nt structures include.
sanitary napkins an~ diaPer-like inserts or attachmen~ to the inside of rubber panties. The inserts for rubber panties which serve, in combination with the panties, as diapers, are similar in structure to the ~anitary napkins, except that they are wider ;; and are designed to receive and absor~ uxine and ~ecal matt~r, The sani~ary napkins a~e generally of two types--a highly absorb~
ent type for periods of hea~y menstrual flow and a far-less absorbtive type or the so-called light ~low (which typically - occurs near the end o a menstrual period). An example. OL the :: highly absorbtive type of sanitary napkin is described in U. S.
Patent 3,672,371 (Roeder) issued ~une 27, 1972.

All of the aforementioned absorbent structures generally comprise: (1) an elongated absorbent pad having essentially t~,Jo major surfaces, (2) an outer covering layer adhered to one . ' ' ~ .

: .
, or both or the two major sur~aces J (3) an adhesive layer on the outer layer ~hich is intended for co~tact with the garment or b~dy-encircling member, and (4) a release liner means for cover-ing and protecting the a~hesive layer until the absorb~nt struc-ture is put to use Several ~ypes of pressure-sensitive adhesive systems have been suggested for use as the aforementioned pressure-sensitiva adhe~ive layer on the outwardly-facing surface of the outer layer of the absorbent structure. For example, some work has been done with solvent-based pressure-sensitive adhesive ~PS~) systems.
However, ~he genexally low-viscosity o~ such PSA systems can ~
result in a xapid penetration or impxegnation of the a~sorb~nt pad, leading to poorly control~ed results with respect to coating of th~ PSA system. Furthermore, any solvent-based system can -have the usual problems of health 'nazards from solvent vapors, solvent recovery to xeduce costs, etc~, associated with it.

Water-based adhesive systems have also been suggested for providing the PSA layer on the outer surface of the absorbent pad structure. It has been generally found~ however, that the water~
based adhesives tend to "set" ~ dry down rather slowly, particu-larly as compared to the solvent-based t~pP.

Still another approach which has been attempted is the use of transfer tapæs to transfer a coherent layer of PSA onto the desired portion of the pad structure. One difficulty with this approacn is that the resulting coherent la~er of adhesive can be used only as~t~e PSA means for adhering the pad to the garment.
Since there is no impregnation of the absorbant pad structure with the trans~erred adhesive, the adhesive cloes not ordinarily add to or reinforce the integrity of the absorb~nt pad structure. With ., ~7~

a more fluid adhesive, it is a-t least possi~le to use the PSA
system for a double purpose; as the PSA layer on the outer surace and as a means for cementiny together seams (or the like) i~ the struc$ure.

So-called hot-melt PSA's are known. However, these PSA s~s-tems typically lack one or more performance requirements for a sanitary napkin or diaper pad P5A.
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Summar~ of the In~ention A hot-melt PSA system has now been discovered which can be used as the PSA for adhesive-coated absorh~nt structures. Like many hot-melt systems, the hot-melt PSA used in this invention comprises a tackifier, a rubbery-basP material, and a plasticize~
ox diluent~ e.g~ a hydrocarbon process oil, for adju~ting the tackt the viscosity, and the like. It has been ound that the -rubbery base used in the hot-melt PSA should comprise a xub~e~y block copolymer which imparts a varie~y of desired characteris- -tiCS~ Two different types of block copolymers have been found t~
meet the requirements of a PSA for sanitary napkins and, fu~thar, to provide some surprising advantages. These two types of bloc~
copolymers both contain rubber~ mid-blocks and relativel~ stiffer polystyrene terminal blocks. ~n one pre~erred embodimen~ of the invention, th block copolymer is of the A-B-A type wherein the A blocks comprise polystyrene and $he B block is a rubbery poly (ethylene-butylene) center block~

In a second pre~exred embodiment, the polymer is a tele-block copolymer comprising molecules having at least thres brancnes radially branching out from a central hub, each of the branches having polystyrene blocks and a hutadiene segment in the center.

( Thus, a typical absorbent structure of this invention comprises:
(a) an elongated absorb~nt pad having essentially two major surfaces;
~b) an outer layer in adherenk contact with at least one of the two major surfaces;
~c) ~he hot-melt pressure-sensitive adhesive layer, whic~
is adhered to the outwardly-facing surface of the outer layer, i.e. the surface which is designed to-come in con-tact with the garment or body-encircling member; and (d) a sheet-like removable protective release liner means : covPri~ ~he hot-melt pressure~-sensiti~e adhesive layer~
' Detailed Descri ~
; As pointed out previously, a typical abs~rbent struc ure of this invention is a sanitary napkin of the type disclosed in U.S. Patent 3,672,371 t~oeder)~ issued June 27, 1972. A structur~
of this general type can include an absorb~nt pad enclosed ln a fluid-pervious wrapper which is overlapp~d to pxovide a seamr the seam typically running lengthwise through the middle of a maj or surface of the pad. The layer ~or layers) of PSA tPxes5ure~

sensitive adhesive) can be applied to this seam ~overlapped~ area f luidity If the PSA has suffLcient / when applied, it can permeate the seam, binding to~ether the overlapped area and sealing the absorb-~n~ pad inside the fluid-pervious ~rapper. A release liner ovex the PSA layer protects it until the napkin is to b~ used, at which Lime the liner is peeled off and the PSA layer is pressed against the inside of an underwear ~arment or the like. The major surface on ~7hich the PSA is coa-ted does not ackually have to be fluid-pervious, since the body f~uids enter the absorbent . ~o structure from the opposi~e surface. For this reason, the 1071~19 ~ I
absorbent structure can contain other elements such as a 1uid-impervious film integral with the PSA coa-ted surface and the absorbent pad. Furthermore, the liner or envelope enclosing the absorb~nt pad can comprise a plurality of.layers of matexial such .
as waterlaid sheets~ nonwoven webs, and -the like. The absorbent pad itself can be a batt or frictionally entangled mass of ~ihers with properties similar to an absorbent cotton mass. Absorb~nt cotton itself can also be used as the absorb~nt pad material~.
.' .
When the purpose of the absorb~nt structure is to a~sorb .
a very light flow of blood and menses~ the total stxucture can be :
: simpler. In khis case the absorb~ pad can be much thinne~ and .
need not be surrounded or sealed in completely by a fluid-pervious layer, due to the inherently greater integrity of the thinner pad.
~or example, the entire structure ~an consist essentially o~.the thin pad (totally exposed on one major. surface), a fluid-impervi~ .
ous film in adherent contact with the other major surface of the pad (this ilm serves as the outer c~vering layer), the PSA layer coated on the exposed surface of the impervious film, and the .
relea~e li.ner protec ting the PSA layar.
~ ' ' ' ' ; .
In any of these structures, the PSA layer need no~ be .~ coextensive in area with the major surface on which it is coated.
On the contrary, the typical PSA layer is very muc~ narrower in ;. width and can be somewhat shorter in length.

When the absoxb~nt structure is an insert for rubber pant-ies and is intended to serve as a diaper, it is typically wider than a sanitary napkin and may be somewhat longer. Otherwise, : the structure is similar. On the other hand, i~ the absor~nt structure is intended for receiving wound exudat~s, a differ2nt - arrangemen-t of e1.ements i~ generally desirable.

The properties of the PSA layer are peculiar to this art.
Por example~ the PSA, when applied, should have a low enough vis-cosity to flow into place readily and pre' erably also to permeate the aformentioned seam axea or overlap area. However, the yiscos~
ity must not be so low that the PSA composition will permeate through ~he outer covering layer and into the absorbant pad itself.
~urthermore, the viscosity should be high ~nough to permit some degree of a pr~perty similar to "hold-out"--that is, a significant amount of the PSA composition should remain on the exposed surface of thP covering layer and form a coherent PSA layer. This "hold~
out" effect can be most effecti~tely obl:ained i:E the PSA, duxing application to the outer covering layer, has a signi~icant amount of thixotropy. ~or a hot-melt PSA, it is ordinarily prefexxed that ~he composition have a viscosity rangln~ from about 500 to 10,000 centipose ~cps) in the pour temperature range, which would typicall~ be 100 - 250C., more typ:ically 150 - 200C. (e~g.
300 - 400F.)~

Another impoxtant property i9 the ability to soLidify or .. congeal or "se~" ver~r rapidly--p~e:Eerably a~nost instantaneouslyO
Hot-melt PSA's are particuharl~ desixable in this re~ard, since they can cool down from-the application temperature to a solidifi-cation temperature almost instantly under noxmal ambient conditions.

~mong the most peculiar properties needed for the PSA are the adhesive bond characteristics. These characteristics must be obtained without sacrificing room temperature tack ("probe tack"
or "wet grab") and without creatin~ a situation where the adhe-sive will offset or transfer to the garment. The requirements .. . ..
for the adhesive bond are that the PSA should have ade~uate peel stxen~th and yet have the ability to release itself from the --7-- .

5~

undergarment wit~out pulling G.fibers or tearing the garm~nt.
There are presently no adeguate standardized tests ~or measurin~
these adhesive bond properties; however, the PSTC-l test i5 help-ful to give some indication of the required amount of peel strenyth.
See U.S. Patent 3,672J371r colum~ 3, line 51 et seq. Standard 180 peel and shear tests are also helpful~ For example, a PS~ o~
th~ inven~ion has been found to have a 180 peel strength.("klylar'~
~ subs-trate, 12 in./min) ranging from about 4 to about 5 or 6 ~ound.
:. per inch width ~piwS and a tensile shear strength ~0~1 in/min).o~ .
. 10 about 15 to about 35 pounds per s~uare inch (psi).

.
The hot-melt PSA compositions which have been foun~ to ha~e the best combination of properties for use in sanitar~ napkins and ~:~ diaper inserts comprise a rubbery or elastomeric block copolymer~
.- an essentially h~drocarbon oil, and a tackifier resin, all of which iare descri~ed in more detail subsequen~ly.

. . - .
- The Rubbery Copolymer The two basic types o~ rubb~ry or elastomeric blosk co~o~-mers particularly we~l~suited for use in this invention are:
~a) an A-B A block copolymer having polystyrene ena block~
: 20 and a rubbery polyole~in ~e.~ter or mid-block, the polyolefin being a rubbery poly~ethylene-bukylene~ ~lock, and (b) a teleblock copolymer comprising molecules having at .. least three branches radi~ly branching ou-t from a central `~ hub, each said branch having polystyrene te~minal blocks and a butadiene se~ment in the center.

The A-B-A block copolymer is consldered a t~o-phase pol~-mer comprising polystyrene domains.in.a rubbery poly(ethylene~
bu~ylene) matr.ix. In order to obtain desired levels o~ tack, i~ :
,. .

~ 8-`: ( ( (and this is alsb true of the teleblock copolymer) is tackified with a resin and an oil. The A-B-A polymer is a true elastomer (according to ~h~ ASTM ~efinition of "elastomer"~ and has an elongation at bxeak well in excess of 200%, e.g. 500%. The elonga~
tion at break ~or the teleblock kadial) copol~mex is in approxi-mately the same range ~r slightly higher, e.g. 590%.

To ensure rubberiness or elastomeric behavior in the radial copolymer, the number of butadiene units should be greater than the number of styrene units. Shore A hardness for the telebloc~ ~rad~
ia-l) copolymers can be in the range typical of true rubbers, e.g~
above 60 or 70.

.. . .
.~ The ultimate tensile strength o~ the ru~ber~ copol~mer .- ~whether of the A-B-A type or the radial type3 is moderately ~igh, e.gO above 2000 p.s.i., more ~ypically above 3000 psi~ Tensile strengths~abo~re 5000 psi are possible w ith the A-B-A structure.
~ . .
~ The Essentiall~ ~ydrocarbon Oil . . .
The oily liquids used i~ compounding PSA~s of this inven-tion are essentially h~drocarbon process oils whic~-are pr~erably . , .
low i~ aromati~ content. ~or example, an analysis of the types of carbon atoms i~ oils used in this invention indicate that~aro-:: matic carbons comprise less than 5~ of the oil, while naphthenic ... .
carbons ~i.e. carbons of c~cloalipha-tic compounds and the like) ;. can range ~rom about 25 to 60~ and paraf~inic car~ons can range from abou~ 35 to 75~. Accordinyly, these oils are typically referred to as ~'naphthenic" or "paraffinic" process oils~
,' ' , ,.
: Th~se oils are preferably very low in volatility. Initial boiling points, under normal ambient pressure conditions, can range from ~Jell over 400F. (i.e. above about 200~C.) to almos-t 800F~ ~almost 430C.). The least ~olatile ~raction in the pro-cess oils can have a boiling point inexcess o~ about 1000F.
(about 535C.), so that the entire boiling range can cover several hundred degrees, e.g. 600-1100F. ~315 - 600C~).

The_aroma~ic content of the oils as determined by clay gel analysi~ (in weight percent) can range from less tha~ 1% up to 15 or more; however, ar~matic content should be low and should not exceed about 20~ by weigh~. The molecular weight of the oil is ~ypically above 200 and can be above 600. Most naph~he~ic and paraffinic proc ss oils, however, tend to have a molPcular weight within the xange of 250 ~ 600.

. . .
.-. .
The Tacki~ er Resi~
lthough various t~pes of tackifier resi~s are known, such as hydrogenated rosin esters, esters o~ polyhydric a7cohols, -phenol-aldehyde resins, and the like, the preferred tacki~iers are ~ . .
of the ~ype known as "hydrocarbon resins". In industrial practice . . "hydrocarbon resin" is a term of art relating to resin~ in the ,, .
molecular weight range of a few hundred up to about 6,000 or ~,000 `~ ~ which are obtained or synthesized from rather basic hydrocarbon-.: .
~, aceous materials such as petroleu~, coal tar, turpentine~ and the like. A good description of "hydrocarbon resins" can be ~ound in Kirk-Othmer, Enc~clopedia of Chem cal Technology, Second Edition, Volumne 11, Interscience, New YorX, 1966, pp242. rlany of the so-~ .:
called "hydrocarbon xesins" com~excially available today are 'Iterpenel' resins, i.e. polymers with r~peating terpene units.
These polymers can be homopol~mers, or copolymers, (including terpolymers, etc.), since terpene is an olefin which can be co-olymerized with other olefins. Terpene-phenols are also produced.

,. I
":
;, ~' All hydrocarbon resins do not wor~ ~ith equal e~fective-ness, and a commercially available resin k~Lown as 7'wingtacX" 95 ttrademar~ of Goodyear Chemical Company) is especially suited for use in this invention. This hydrocarbon resin is compatible with other components of the hot-melt PSA and has a softening point ~ball and ring me~hod) of 100C.+ 5. "Wingtack" 95 is believed to be a by-product of isoprene or polyisoprene production and is also belie~ed to be a s~nthe~ic terpe~e xesin derived fxom a mixed olefin feed stock.

.
- The hot melt PSA compositi~s of this invention can be formulated with techniques known in the art using heated mixers and the like. The rubbery copolymer and the oil can be blended together readil~ at moderately eleva~ed temperature~ ~e.g. 150 -300F.)~ The tackifier resin can be added to the copolymex oil ~ixture. If a pigment is included in the PSA composition, it should be added to the copolymer/oil blend before the tackifier xesin is introduced into the composition.
., ' ' ' . .
The resulting hot-melt PSA, once it is heated ~o the temp-erature whex~ it will flow readily, can be applied to the outer covering layer of the absoxbent structure or article by any of the techni~ues known in the art, including flow coating, roller coa~ing, knife coating, or the like. The PSA can also be ex~rud~
ed into place by using a hot extruder or die face~

The P~eSulting Hot-k!el-t PSA Compositions As is known in the art, various other components can be added to modify the tack, rheology characteris-tics ~including melt viscosity, thixotxopy), adhesive bond streng~h characteris-tics, rate of "set", low teMperature flexibiility, ~tcn ~ colorr . .
odor, etc., of a hot-melt PSA. For example, liquid resins are sometimes used as a partial or total replacemen~ or substitution for process oils, although such a substitution is not preferred in the contex~ of this invention~

The proportions o~ components in a hot-meLt PSA of this invention are pre~erabl~ selected to provide the adhesive bond characteristics described previously. It is also important khat - these adhesive characteristics remain reaso~ably constant during s-torage or ~on-use in a hot-melt applicator and during normal io skorage of the article (e.gA a sanitary napkin) prior to use~
Still further, it is d sirabl~ that adhesive properties remain generally within the prescribed ranges from one production batch to another. "Aging" tests of the A-B-A block copolymer embodiment o~ the PSA indicate generally stabLe adhesive propexties at hot~
melt applicator temperatures ~e.g. with the range of ~00 -~S0C~
more typically lS0 - 200C.~ and, after coating onto the article, with the range of temp~ratures typically associated with storage and shipping (e.~ from about -20C. to about ~50C. ? ~
.... .
With respect to this embodiment, the most noticeable down-ward trend in adhesive properties detectable upon storage of coated samples in 1 to 24--week agin~ tests appears to be in the peel strength of samples stored at 120F. ~48.9C.). Even this trend does not indicate a si~nificant deterioration in peel strength.

In shor~, these da-ta generally indicate a reasonable degree of stability in the internal structure of the hot-melt PSA
~or example, the process oil is reasonably w~ll retained within a matrix or the like provided b~ the tackifi~r resin andfor the rubbery block copolymer.
. . .

. . .

The tackifier resin (e.g. "Wingtack" 95, trademark of Goodyear ChemLcal Company), provides a number oE desired proper ties (e.g. increased shear strength of the adhesive bond) partic-ularly at levels in excess of 30 weight-~ teOg. 40 weight-% ox more) However, if the resin is increased at the expense of the process ; oil conten~, there can be a significant loss of tack and undesir able increases in viscosity. Accordingly, the amounts of tacki-fier resin is preferably less than 70 weight-% of the-composition ~e.g. 6S weight-~ or less, more typically 50-60 weight~
,. . . :
The process oil content is preferably above 10~ by weiyht (e.g. at least 15 weight-~) to provide suf~cient ~ack and a low enough viscosity at the pour temperature or temperature of appli-cation (e.ga 150 - 200C.). However, excessive amounts of oil ~or a ~iven content of rub~ery base~ can reduce shear strength and cohesiv~ strength and possibly lead to transference of PSA
~rom the article to the undergarment. ~ccordingly, it is ordin-arily preferred that the amount of process oil in the PSA be less than 40 weight-~.
.' ' . . .:
The rubbery copol~mer base assiists in providing manyr if not most, of the key properties contemplated for hot-melt PSA's of ~his invention. However, minor amounts of these rubbery mat-erials are effective, and excessive amounts can increase th~ vis-cosity drastically, inter~ering with ~low properties in the 100 -250C. range discussed previously~ At amounts below 5% by weight, ; the oontriblltion of the rubbery base to the PSA is ordinaril~
insu Eicient, and amounts of 10 weight-~i or more are~preferred.
At rubbery copolymer amounts above 30~ (e.g. 35%), the increase in viscosity (even at elevated pour temperatures such as 350F.~
rapidly approaches inconvenient levels. Accordingly, the op~imum , ., ; ~

amount of rubbery copolymer appears to be wi~hin the range of 10 ~ 20 weight~

The principle and practice of this. invention is illustrated in the following nonlimiting examples.

~'' ' ' ' .
Example 1 In this Example, a block copolymer with the A-B-A struc-ture was used. The commerical e~bodiment of the copolyme~ is ~ : sold by Shell chemical Company under the trademark "KRATO~"
; GX 6500 (more recently eeferred to as "KRATO~" 1650). This .

. - .
~ ,.

co~mercially available material is a three block copolymer wi~h polystyrene end~locks and a rubbery poly~ethylene-bu-~ylene) mid-bloc~. It is considered a t~o-phase pol~mer consisting of polysty-rene domains in a rubbery polytethylene-butylene)matrix. Typical properties of the copolymer are as follows: .
Tensile strength psi: 6000 Elongation at break: 500-g .
Modulus at 300~ extension, psi: 950 Solutio~ viscosity (measured with a Brookfield Model RVT :

Viscometer)~ 20~ by weight in toluene, centipoise: 2000 .
25% by w ight in toluene, centipolse: 12000 The proauct is available in particulate form, e.g, in crumbs about 1/8 inch in size. .
. : .:

The foxmula for the hot-melt PSA of this Example, was as :

' :Eollowso Parts by Weight Ingredienl:=
.. .. ~
30.0 Naphthenic process oil*
15.0 "KRA~ON" 1650 (traaemark; formc~l~ sold under the trademark "KRATOW" GX 6500) 201.0 Pisment dispersion 643 parts b~ wei~ht : of pigment dispersed in 57 parts by .
weight of the naphthenic process oil) 54.0 "Wingtack" 95 (trademarX of Goodyear . Chemical Co. for hydrocarbon tackifie.
resi~) *See detailed description which follows, .
'" . ,. I

' - After the "KR~TON" was completely blended into the process oil, ~he pigment dispersio~ was added under high shear mixing.
The mixing ~emperature was maintained below 300F. After the pigment was dispersed in the "KRATON"~oiL composition~ the "Wing~
tack" 95 was added, and mixing was continued until a uniform com-position was obtained.

The naphthenic process oil used in the composition wa~
"Tufflo 6204" (trademark). This pxocess oil has a viscosity (SUS/lQ0~F.) of 1965, a specific gravity (60~60) o~ 9.9206, a flash point (COC) of 440F., a pour point of 0F~, and a sulfur content which is less than 0.001%. The molecular weight of the .. . . .
; oil is 440, and clay gel analysis indicates 0~ asphaltenes, 9%
polar compounds, or reslns~ 14.8~ aromatics, and 85.2~ saturates~
Carbon type analysis indicates 2% aromatic carbons, 52% naph~
thenic carbons, and 46% paraffinic car~ons The boiling range is 630 1018F., the initial boiling point being 630F~ r and 95% of the oil being distilled at 1018F. Only S~ Of the oil distills at 630~F. and 50~ distills at 710F.

Ten po~nds o~ the resultin~ hot-melt PSA ~as tested for peel strength and shear strength. The 180 peel strength was conducted at 12 inches per minute and the tensils shear test was conaucted at 0.1 inches per minute. Results wexe as follows:

Aging Time* Peel (plw) Shear (psi) : . , ; Zero 4.9 29.1 8 hours 5.2 30.7 24 hours 4O6 2908 48 hours 4.8 32.3 *Length of time adhesive was held in the hot-melt applicator pot at 193C. ~380F.~ prior to application to the test specimens.
Three sa~ples were tested and averaged to arrive at the val~es given in the above table.
-16~

.
~ Propexties of the resulting hot-melt PSA wexe as follows:
. .
Ring and ball softening point: 202 - 240F.
Specific ~ravity: OD 922 Brookfield Viscosity (Brook~ield ~hermosel speed 20 rpm : spindle SC-4-27~ 8 gram sample):
1,300-1,650 cps at 350~F.
`~ 3,800-5,000 cps at 325~. . .
700-gob cps at 375F.
This hot-melt PSA was ~ound to be particularly well-suited f~r sanitary napkin structures of the type described in U.S~
Patent 3,672,371 ' ' Example ~
This Example illustrates the use of a radial ~teleblock) copolymer, the commercial embodiment: in this case being "SOLP~E~E"
50~, a trademark of Philips Petroleum Company; typical properties of "SOLPRENE" ~trademaxk) 50Z-CX are as follows:
. , . : - .
.; Speci~ic gravity. 0O91 rielt flow, 190~C./21~6K~: 0.2 Molecular weig~t: siooo ~ ~o Shore A hardness: ?9 ;;~ Butadiene/styrene ratio. 70/30 Tensile strength, psi: 3900 Modulus at 300% extension, psi: 540 ~lgonation at break: 590%
; Compression set ~Method B) 22 hours, 78F.: 35~

The formula used in the case of the "SOLPRENE" pol~m~r was as follows:
' ' -17-' Parts b~ l~?eight Ingredient _ -. 29~0 ~aph~henic process oil ~"Tuf~lo" 6204, see Example 13 15~0 "SOLPRENE" 502 (see preceding `. description) : 2.0 Pigment dispersion (see Example 1) 54.0 "Winstack" 95 (trademark; see Example 1) .

, The procedure for preparing the hot-melt PSA was the sam~
as that of Example ls The specific gravity of the resulting pro- .
, . .
~: 10 ~uct was O~g22. The ri~g and ball softeningpoint was 204 - 240~F~, : ~ . the viscosity at 350F. was 750 - 940 centipoise ~cps) t determined .: on a Brookfield Thermosel at a speed of 20 rpm, spindle SC-4-27, ~ with an 8 gram sample~ . .
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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An article for absorbing fluids, the structure comprising:
(a) an elongated absorbent pad having essentially two major surfaces;
(b) an outer layer in adherent contact with at least one of said two major surfaces;
(c) a tacky hot-melt pressure sensitive adhesive layer adhered to the outwardly-facing surface of said outer layer, said tacky hot-melt pressure-sensitive adhesive comprising -(i) a rubbery copolymer selected from the group consisting of a radial block-copolymer, an A-B-A block copolymer, and mixtures thereof, said radial block copolymer being a teleblock copolymer comprising molecules having at least three branches radially branching out from a central hub, each said branch having polystyrene terminal blocks and a butadiene segment in the center, and said A-B-A block copolymer being a three-block polymer, the B block of said A-B-A
block copolymer being a poly(ethylene-butylene) midblock and the A blocks being stiffer than the B block;
(ii) an essentially hydrocarbon oil having an initial boiling point above 200° C., said essentially hydrocarbon oil containing a naphthenic oil, or a paraffinic oil;
(iii) a tackifier resin; and (d) a sheet-like removable protective release liner means covering said hot-melt pressure sensitive adhesive layer.

2. An article according to claim 1 wherein said structure is a sanitary napkin, and wherein said outer layer means is a fluid-pervious non-woven wrapper comprising a substantially rectangular sheet enveloping said absorbent pad.

3. An article according to claim 1 or 2 wherein the A blocks of said A-B-A block copolymer are polystyrene.

4. An article according to claim 2 wherein said hot-melt pressure sensitive adhesive layer comprises an elongated strip of said adhesive, narrower in width than the with of said absorbent pad, which has at least partially impregnated said non-woven wrapper along a seam of said wrapper, thereby holding said wrapper in adherent contact with said major surface of said absorbent pad.

5. A sanitary napkin comprising:
(a) an elongated absorbent pad having essentially two major surfaces;
(b) an outer envelope means comprising a fluid-pervious non-woven sheet-like wrapper encircling said absorbent pad having a seam therein running lengthwise along a said major surface;
(c) a hot-melt pressure sensitive adhesive layer impregnated into said seam and thereby adhered to the outwardly facing surface of said wrapper, said hot-melt pressure sensitive adhesive consisting essentially of a rubbery polymer blended with an essentially hydrocarbon oil having an initial boiling point above 200°C and a hydrocarbon tackifier resin, said rubbery polymer being a three-block A-B-A block copolymer, said A blocks being polystyrene and said B block being a rubbery ethylene-butylene polymer;
and (d) a sheetlike, removable protective release liner means covering said hot-melt pressure sensitive adhesive layer.

6. An article according to claim 5 wherein the hot-melt pressure sensitive adhesive in said layer consists essentially of:
(i) 10-30% by weight of said rubbery polymer;
(ii) 15-35% by weight of said essentially hydrocarbon oil; and (iii) 40-65% by weight of said hydrocarbon tackifier resin.

7. An article according to claim 1 wherein the hot-melt pressure sensitive adhesive in said layer consists essentially of:
(i) 10-30% by weight of said rubbery copolymer;
(ii) 15-35% of said essentially hydrocarbon oil;
and (iii) 40-65% by weight of said tackifier resin.