US 3542028 A
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United States Patent  Patented Nov. 24, 1970 73], Assignee E. I. du'Pont de Nemours and Company Wilmington, Delaware a corporation of Delaware  FLUSIIABLE SANITARY NAPKINS 12 Claims, 2 Drawing Figs.
521 user s11 lnt.C|. A6lf13/l6 so] Fleldoi'Search 128/284,
287, 290. 296  References Cited UNITED STATES PATENTS 3,067,746 l2/l 962 Bletzinger et al. 128/290 3,370,590 2/l968 Hokanson et al. 128/290 128/290 3,407,814 10/1968 Georgeetal.
3,439,678. 4/l969 Thomas Primary Examiner-Charles F. Rosenbaum Attorney- Raymond P, Niro absorbent core of loosely felted fibrated wood pulp; a fluid barrier of a cellulosic fiber substrate coated with a fluoropolymer for retaining body fluids within the core, and a soft, water dispersible wrapper exhibiting pleasingaesthetics during use for encasing the core and fluid barrier and for maintaining the napkin in a unitary assembly during use, the wrapper being a nonwoven fabric of randomly entangled cellulosic fibers chemically modified to allow easy disintegration of the fabric in tap water for promoting flushability of the entire napkin, the wrapper is further characterized as having a unique combination of tensile properties while dry, or when wet with tap water, or while wet with body fluids. Also disclosed is a fluid barrier of a cellulosic sheet substrate coated with a fluoropolymer, or paraffin wax, the sheet having a combination of wet and dry tensile properties which yields good performance during use of the napkin of which it is a part while promoting flushability ofthe napkin.
- vPmnwil Ngw. 24, 1970 v Y 3,542,028
INVENTORS EDWIN V. BEEBE EDITH MAIER SINGH ATTORNEY doned.
perties sufficiently low BACKGROUND OE'IHEINVENTION 1. Field ofthe I nvention' This.inv'entio nrelates toabsorbent products in the form of sanitary napkins. More specifically, it'pr'ovides animproved' i and novel sanitary napkin which is genuinely'disposable by flus'hing in anyhome toilet facility. Dispbsable sanitarynapkins havebeencommercially available for many years'andh'ave met with great s'u'ccessand wide acceptance in'the more industrializedcountries of the world;
A long-felt need has existedfor a more convenientmethod forthe disposal of soiled-napkins. Numerous:sewers have been stopped up inattemp'ts to flush'awayconventional napkins to avoid the necessity of .disposalby' ordinary means. Although the absorbent 'coi'e of the napkin is usually composed mainly of wood fluff,which by itself would be easily flushable, the i moisture barrier and moreiespecially the fabric cover of the prior art napkins are relatively unaffected by water so that they maintain their structuralinteg'rity in flushing. The fabric cover of the napkin .of-the'present invention is water sensitive and has a unique combination of dry'and wettensile proper ties yieldinggoo'd performance in use with the;wet tensile pro-' home toilet. a j v 2. Description of the Prior Art 1 The need for a flushablenapkin was recognized early in the partial solution by providing 'ajflushable core and'a repellenttreatedbarrier which are separated from the nonflushable cover fabric and"flushed. -The cover fabric remainsto be disposed of otherwise, Other patents disclosing repellenttreated napkin barriers include the following U.S.-Pat. Nos.: Atkinson,-2,643,656,=dated'Jun. -30, 19.63; Harwo'od et jal.
3,029,8i 7,.d ated Apr fl7, r96 2; BletzingerEB,067;746,=dated.= Dec. 1 1962;andf1o'rr, 3,07 0,095,datedDec.25,1962. The" to give genuineflushability in ordinary x development of the art. British PatJ-No. 282,447 attempts a t Absorbency test to be described. For some types of fibers, ab-
last-mentioned patent also discloses the use of paper cover to achieve flushability forthe whole structure with'the resultant disadvantagesof harshness," noisiness, possible weakness,'and difficult flushability. Morse,fU.S ...Pat. No. 3,078,849, dated Feb. 26, 1963, discloses'a napkinincorporatinga fluid-sensitive, temporary barrierlwithin the absorbent core for spread ing the body fluids'g'but makes no provision for a water-sensitive cover fabric. .No commercially successful flushable sanita-' ry napkin has appeared'on the market in the history of the art.
' SUMMARY Orr n; INVENTION The present invention provides. an econ ornicak-soft, absorbent, easily conformable,strong-imusesanitarynapkin which I is fully flushablel in hometoil'etslby virtue of the easy water dispersibilityxof th'e jabsorbentcore, the repellent-treated barrie'r, and the novel water-sensitive-nonwoven fabric cover.;The
flushable sanitary'napkin of this invention comprises:
. 1. A flushable absorbent elongated wood pulp core covered on one sideand both edgesby; I '2.
A flush-able barrier consisting'ofone or mor'e cellulosic sheets'to one or both sides of Whichlhas been applied in a substantially uniform manner, ;a fluoropolymer water" household typej-paraffin waxfat the rate of 0.07 to 0.25
mg./cm'. the assembly'being enclosedin;
. A flush-able coversheet of nonwoven fabric given integrity by random fiber entan'glementin which from 10 to 100 percent of the fibers are wate r-.sen sitive fibers. Waterthe salt fre e'fibers beingxtested,which fibers must also be insoluble in synthetic urine.
Suitable 'water-sensitivefibers' may be homogeneous, i.e. have a substantially. uniform chemical composition throughout their cross-section, or may be heterogeneous,
thereby having an adherent coating or skin of a water-sensitive an Pat. -No. 706,510, granted May 14, 1968. Accordingly, the disclosure of BelgianPat. No. 706,5 l0,'gran'ted May 14, 1968,
is herein incorporated by reference. a
By flushable is meant the ability to pass the standard Flushability test to be described. It has been found that in order to ensure'flushability, the. nonwoven cover fabric should have an average'wet tensile strength'in distilled water of not more than about 0.1 lb./in. (l8 'g./cm.). At the same time. to ensure integrity in use, the fabric must have an average dry tensile strength of at least about 1.0 lb/in. g./cm.) and preferably about 1.5 lb./in. (2,68 gJcm.) and at least about 0.05 lb./in. (9 gJcm.) average tensile strength when wet witha test solution termed synthetic urine", to be described hereinafter. To ensure-softness and comfort, the'fabric should have a standard bending lengthofless than about 3 cm.
7 With reference tofithe fluid barrier, by the term fluoropolymer is meant vinyl-type polymers, copolymers, and
segmented or graft copolymers in which at least a major portion of the vinyl monomer units contain monovalent persorbencies'of 10 to 1'5 g./g. or even more maybe desirable.
, In,. addition, the absorbent nonwoven fabrics disclosed in Belgian' lat. No. 706,510,.granted May 14. 1968, are. also suitable for use in this inventions DESCRIPTION 0F-THE D A ING Inthe accompanying drawing FIGS. l and 2 illustrate a product of this invention. FIG. 1 is a view of a sanitary napkin which has been unwrapped atone end to reveal the assembly of the-innercore andbarrierwhile FIG. 2 represents a cross sectio'nof the center of the same napkin fully assembled. The
napkin comprises an absorbent core covered with a flushable fabric router wrapper 3 which. has endexten'sions forming attachment tabs in the usual manner. Within the cover is the ab-.
sorbentwco're'forrned of a composite of a fluid distributing member 5 such-as crepe' waddingor embossed wood fluff batting, and loosely felted fibrated wood pulp 4 commonly known as fluff. Surrounding the core on the bottom and sides is creped tissue 6 which hasbeen treatedwith a fluoropolymer or paraffin wax water repellent to act as a fluid barrier. The barrier-tissueis made substantially coextensive, longitudinally, with the absorbent core.
f DESCRIPTION or THE PREFERRED EMBODIMENTS A successful and'effective modern sanitary napkin must contain, in one form or'another, three major components: an absorbent core, a fluid barrier, and an outer wrapper.
The absorbent-core must soak up and immobilize the body fluids-deposited on. the napkin and should preferably have a physical structure contributing to shape retention in use. One or more layers of a fluid distributing material to cause the absorbed fluid to spread laterally, thus making more efficient use of theabsorptive capacity, is desirable. An economical and efficient absorbent is found in wood fluff, a comminuted wood pulp compacted to a density of about 1.5 to 5 lbs/ft. (0.024
A fluid barrier is used to prevent the absorbed fluid from penetrating to the outside or edges of the napkin, which might result in soiled clothing or other embarrassment. The barrier must be fluid-proof under use conditions and must have sufficient integrity to resist rupture due to the normal movements of the wearer. A thin polyethylene film is often used for this purpose. The barrierfmay be located near the center of the two-way napkin (which may be used with either side next to the body) or it may be located near or at one face of the core in the one-way napkin. Obviously, the latter arrangement makes more efficient use of the absorbent core and eliminates unnecessary useless bulk.
The outer wrapper holds the components of the assembly in place, prevents disintegration and shedding of the absorbent, provides tabs as a means of attachment to a supporting belt, and is the major load-bearing member of the structure. Since it is worn next to the body it must be soft, conformable, and nonchafing. The outer wrapper must be strong enough to support the strain imposed by motions of the'wearer in moving about, stooping, and the like. 1t must be soft and quiet and not emit papery sounds onbending and, further, it must not shed loose fibers when rubbed against the body while wet or dry, and it must transmit fluids readily. Commercially, sanitary napkin wrappers are often made of nonwoven fabrics in which textile fibers are held together by adhesive binders. Such fabrics have a weight of about 0.5 to 1.0 oz./yd.-(17 to 34 g./m.).
A flushable sanitary napkin must meet all of the structural requirements already mentioned in order to perform satisfactorily in use. In addition, all ofthe individual components and the structure as a whole must disintegrate in the flushing water of an ordinary toilet. It is not necessarily sufficient that the individual components be disposable by flushing as the entire combination must be flushable as a unit. The bulky core of a sanitary napkin, ifwrapped in sufficient toilet tissue to give mechanical integrity in use, would stop up ordinary toilets because the paper does not disintegrate easily enough, and the bulk of the entire unit is too large. On the other hand, in a flushable napkin the outer load-bearing wrapper and the fluidimpermeable barrier must maintain their strength and integrity in use even when wet with menstrual fluid. This difficult combination of properties plus easy biodegradability is attained for the first time by the novel combination of elements which constitutes the present invention.
The absorbent core ofthe flushable napkin of this invention is ofmore or less conventional construction. The main component is wood fluff, which easily disintegrates in water with mild turbulence to form a flushable slurry. The wood pulp, in the form of dry sheet material, may be comminuted in a hammer mill and collected from an air suspension in the form of a loose batt as is well known in the art. The absorbent core may contain a fluid-distributing layer of flushable crepe wadding. Alternatively, a ridged pattern may be embossed in the surfaces of the wood fluff batts, whose ridged faces are then brought into face-to-face contact at the center of the absorbent core to encourage the spread of fluid as described in U.S. Pat. No. 2,952,260. While the use of a fluid-distributing layer of some sort can be used, it is not essential in the flushable product of this invention.
The fluid barrier of the flushable sanitary napkin of this invention is formed from a water-dispersible cellulosic sheet material, preferably crepe wadding or crepe'd tissue, which is use are described in U.S. Pat. Nos. 3,068,187 and 3,171,861, Belgian Pat. No. 671,010 and French Pat. No. 1,462,332. It is preferred to use a solution or suspension of the repellent composition in an organic or nonaqueous liquid, since the use of an aqueous liquid may lead to the formation of pinholes or otherwise damage the crepe tissue to which it is applied.
The repellent materials are most conveniently applied by spraying a solution or suspension-of the active ingredients onto the sheet material which is to form the fluid barrier. The amount of material applied varies to some extent with the particular repellent formulation chosen and the cellulosic sheet material usedas a substrate. Too heavy an application may hinder the dispersibility of the barrier during flushing. Hence, some preliminary testing may be required for each specific set of materials. In general, the amount to be applied will fall within the range of 0.0001 g. to 0.0015 g./in. (0.0000155 to 0.000232 g./cm. and preferably 0.0002 to 0.0005 g./in. (0.000031 to 0.000077 g./cm.) for the fluoropolymers and .0005 to .0015 g./in. (.000077 to .000232 g./cm.) for the paraffin waxes.
The repellent may be applied to one or both sides of the barrier sheet, and the barrier maycontain one to three or even more layers of cellulosic material, depending on the weight and tensile strength of the material chosen.
' The barrier sheet is preferably of approximately the same length as the absorbent core with which it is used. The barrier should be at least wide enough to enclose one face and both edges of the absorbent core as shown in the drawings.
Optionally, the cellulosic sheet material which is to form the barrier may be of a width sufficient to completely wrap around the absorbent core with partial or complete overlap. In any case, the barrier repellent is applied to those areas of the sheet which are to cover the outside face and edges of the core. The repellent may be applied'before the sheet is assembled with the core, or may be sprayed on the outside after the sheet has been laid over or wrapped around the core material.
The cellulosic sheet material which makes up the bulk of the repellent barrier is preferably the material known in the trade as crepe wadding. This is a loosely-structured, lightweight, extensible creped product made from wood pulp.
It need not have great physical strength as itis supported in use by the external wrapper but the material should disintegrate quickly and easily in water.
A suitable cellulosic barrier substrate willhave a machinedirection dry tensile strength in the range of about 0.3 to 0.6 lbs./in. (54 to 107 gJcm.) coupled with anelongation of40 to 75 percent. These ranges are intended to indicate an area where satisfactory operation may be expected but are not intended to define the operable limits of the invention. There is a large number of cellulosic products on the market which can be adapted to use in barrier construction and which will be apparent to those skilled in the art. For example, a suitable cellulosic barrier substrate may also have a dry tensile strength in the principal direction of0.4 to 0.8 lbs./in. and an elongationat-break in the range of 10 to about 75 percent. The flushable nonwoven fabrics which are to be used as the outer wrapper may also be used to receive the repellent composition and form the inner barrier. Y
The outer wrapper of the flushable napkin of this invention is preferably made by the chemical modification of a nonwoven fabric of cellulose fibers held in place by random fiber entanglement. The chemical modification employed is one which makes the fibers water-sensitive and high-swelling in water.
The water sensitivity of the fibers cooperates with the entanglement-type of fiber-to-fiber fastening in the nonwoven fabric to yield a product which will disperse in water by fiber slippage and fiber breakage. In this .way it is possible to provide an economical, lightweight, soft, drapeable fabric with high dry strength which is easily flushable in the ordinary toilet. ln use, as the outer wrapper of the sanitary napkin of this invention, the front or outside area of the fabric is kept dry by the repellent barrier and thus retains full strength in use.
' The outer wrappers suitable-for. use-in-the ,flushable napkin of this. invention include theabsorbentmonwoven. fabrics described and disclosedin-BelgianPat. No. 706,510, granted May 14, 1968.1Accordihgly,thedisclosure of'Belgian Pat. No.
706,510, granted May l4,- l96 8, is herein incorporated by reference.
Such absorbent nonwovenfabrics have dry strength-andin- ,tegrity in theaabsence.ofresinousor fusion-.bonds -cornprising,
from l to .100percent waterwsensiti-ve fibers characterizedin that: l
l. the water-sensitive fibers are less-than 3 inches (7'.6 crn.)'
iniengt'h, the balanceof the fibers consistingof nonwatersensitive fibers of lessthan 0.5 inch.( 1 3 cm.) in length; 2. said fabriehas'a dry coherencevalue (C, dry) of at least 0.2 -an'd a wetjcoherence:value- (C,, wet) ofless than 0.3 bothmeasured in the absence of resinous orfusion bonds;
and. r 3. withthe provisothat the ratio Chdry, a a-1.3
Preferably-thefabricihas a'weight of,0.3 to 5 oz./yd. to 170 g./m. and most preferably hasan average wet strip tensile strength ofless than-0.;1 lb,/in. 1 8' g,/cm.). ln a .prefe'rred embodiment,.the, fabrics haye; an elongation at-breakxin two directions at right angiesto each otherof at least 20 percent,
the C wet islessth'an 0.115" and thefabric contains at least 40 percent.water-sensitive fibers. in another preferred embodiment, the fabric hasan: average tensilestrength in synthetic to. and a length of between 0.25 v to 2'inches (0.6 to 5.1
cm.). Thepreferred water-sensitive fibers are those of cellulosic esters and ethers whose AOH compound is soluble in water at to an extent of at least 3 percent. Two preferred products consist either (a) essentially of water-sensitive fibers or (b) are layered,the.surface layer containing at least 80 percent nonwater-sensitive fibersandthe centerlayer containing at least 70 percent water-sensitive fibers, the overall structure comprising to 90 percent water-sensitivecellulosic f bers.
The coherence value (C )isa.measurement of the degree to which the fabric comes aparfby-fiber-to-fiber slippage as opposed to fiber-breakage whenever along stripof'the fabricjs pulled apart and is thus a measure of interfiber friction from which the fabric derives its strength.
Nonwovenfabric means a structure having drape asmeasured by a bending length ofless than 3.0 cm. in two directions at right angles to each other andelongation-at-break of at ;least 9 percent in atileast one direction.
Water-sensitive fibers are those with we; coefficient'of. sliding friction ,ofless than 0.9 (preferably :less than 0.70) as measured on a nonwoven fabric consisting essentially of the salt free fibersbeing tested, which fibers alsozmustbe insolu- T ble'in synthetic urine.
The fibers may be homogeneous, i,e. have a substantially uniform'chernical compositionthroughout theircross section, onmaybe heterogeneous, thereby having an adherentcoating or skin of la water-sensitive composition.
A C wet oftles's than about ,0.30 characterizes behavior such .t hat entangled fibers will breakupinto smaller pieces in water afterdipping by the'relatively mildforces of the turbulent flow ina toilet-bowl. I
The preferredproducts of this invention have .C,, (wet) values of less than about 0. l5. Thisclass .of products is flushaconvert the cellulosic, fibers to polyeiectrolytes by attaching ionizinggroups to the cellulose chain. Polyelectrolytesfare generally solubleor highly swollenin waterbut have been found to be highly sensitive to.the,desweilingeffect of dissolved ionizingsalts. Body fluids suchas urine, blood,.menstrual fluid, and perspiration allcontain dissolved ionizing salts in sufficient concentration to permit the water-dispersible cover fabric to maintain adequate strength and integrity in use when wet with such body fluidsrsuitablepolyelectrolyte cellulosederivatives made from rayon generally have a degree of substitution of from,0.2 to 0.4 andpreferably from about 0.22 to about 0.30 groups per glucose unit,.on.the average.'
The nonwoven fabrics u'sed forchemical modificationare preferably made from regenerated cellulose, fiberssuch as 'rayonrather than natural fibers like cotton. The regenerated cellulose fibers aresignificantly more reactiveto themodifying reagentsused, and are adaptable .to high-speed, continuous operation in thechemical conversion.
Any regenerated cellulose fibers can be used, but preferably, they are viscose rayonfibers of 1 .5 to 2 denier per filament. These arepreferablycut into staple lengths of 0.25 inch to 2 inches (0.635..to 5.08 cm.), with fibers from .0.75 inch to 1.56 inches 1.9 to 3.97 cm.), being especially suitable. The fibers arepreferably converted into a nonwovenweb of random fiber orientation by an air deposition process but the wet paper machine methods may be used for-the shorter fibers. Air-deposition may be. accomplished by means of a Rando-Webber machine made by the Curlator Corp. of Rochester, N.Y. Nonwoven fabricsfor use in the products of this invention may also be prepared from more oriented webs.
streams of water delivered atrelatively high pressures. The
process and apparatus involved are described in detail in Belgian Pat. Nos. 673,199 and 706,510. The product ob.- tained, when dried, is suitable for immediate chemical conversion to the flushable form. 4
The preferredchemicalderivatives of cellulose for use as flushable fabrics include the sodium salts of the partial carboxymethyl-ether, the p artialmonoester of phosphoric acid, and the partial monoester of succinic acid. Other less preferred derivatives include the hydroxyethyl ether and the sodium salts of: the carboxyethyl ether, the monoester of sulfuric acid, the monoester of phthalic acid, and the monoesters of other dibasic organic acids. All of these derivatives can be made by methodsknown in the art and the three preferredderivatives can easily be made by direct, rapid, continuous-process, hightemperature methods. These methods are illustrated in the examples.
As illustratedin the examples the water-sensitive nature of the fabrics of this inventionrequires special treatmentfor the V fabrics when wet with water. High-swelling fabrics containing .ble, in the form of relatively large fabrics .(suchas 13 in. X 17 in.) with reduced turbulence of water, without the need of predipping beforeflushing.
A potential problem remains in the possibility of weakening the suspending .tabs'by moistening with perspiration, and the necessity of maintaining reasonable fabricintegrityin the area wet by the-menstrualfluid. For these reasons it ispreferred to substitutents which are salts of .weak acids may be converted to a low-swelling free-acid form by treatment witha dilute solution of-a.strong acidlike' H In this free-acid form, the fabrics may be washed free of impurities in plain water quickly and without damage. They may then be converted to the more useful high-swelling form by treatment with a slightly alkaline buffer such as disodium phosphate to reform the sodium salt of-the acidgroups. in order to preventexcessive swelling and,
possible solution or other damage in the alkaline medium, the buffer is mixed with a solution of a deswelling ionized salt such as sodium sulfate. Other strongly ionizing salts such as animonium sulfate or sodium citrate may also be used, but sodium sulfate appears to be they most effective and economical, and the most desirable as a minor residual solid in the final fabric. in order to prevent stiffening or harsheningduring drying, the fabric is dried directly while still wet with the deswelling buffered saltsolution. Mechanical working during drying helps to soften the fabric and remove excess free salt. If a saltrfree final productis desired, it may be obtained in a softened form by extracting the buffered salt solution with aqueous alcohol or acetone, rinsingin dry alcohol or acetone, and drying with heat. Alternatively, the use of salt may be minimized by neutralizing the free acid form of the fabric with an aqueous alcohol solution of a buffer or dilute alkali, followed by an alcohol or acetone wash and drying with heat.
The nonwoven fabric used for chemical modification may contain a small amount of less reactive or noncellulosic fibers. For example, cotton, nylon, or polyester fibers may be mixed with the rayon staple prior to formation of the initial nonwoven batt or web. The amount of unreactive fiber will depend on length of the fibers used, the degree of entanglement, and the degree of substitution imposed on the cellulosic fiber. The unreactive fibers should be one-half inch (1.27 cm.) or less in length. It should be noted that the addition of such unreactive fibers to the fabric tends to reduce the biodegradabilityof the product which may be undesirable where the products are to be disposed of in septic tanks.
TESTING PROCEDURES Samples used for-tensile tests, and fabric weight are conditioned at 70F. (21C.) and 65 percent relative humidity for at 7 least 24 hours before testing under these conditions.
Tensile strengths and elongations are measured on 1.0 X 2 inch (2.54 X 5.08 cm.) samples at an elongation of 50 percent per minute on an lnstron testing machine. The results are in pounds/inch (grams/centimeter), herein designated as lbs./in. (g./cm.).
Samples are soaked for 5 minutes in distilled water at 21C. and then clamped in the tester and broken in air to determine wet tensile strength in water. In determining wet tensile strength in synthetic urine or other liquid, the soaking is done in synthetic urine or the test liquid specified.
Fabric weights are expressed .in ounces/square yard (grams/square meter), herein designated as oz./yd. (g./m. and are based on the weight of the air-dry fabric. Correction is made for salt content on high-swelling fabrics containing sodium sulfate.
For the purposes of this invention and to evaluate the effects of body fluids on the fabrics, a salt solution termed synthetic urine" with a composition similar to human urine g. NaCl, 24 g. urea, 0.6 g. MgSO and 0.7 g. calcium acetate monohydrate'per 964.7 g. distilled water is employed.
-The dispersibility is determined in a 250 ml. filter flask having an added side arm at the bottom of the conical wall and containing a magnetically rotated bar. The bar is 3.8 cm. long by 8 mm. in diameter, weighs 11.73 grams and is rotated at 500 revolutions per minute. A 3 X 3-inch (7.62 X 7.62 cm.)
sample is folded in half and inserted under the surface of the' arm is filtered and the residue dried to constant weight at l 00C. to give the weight of fibers dispersed. The contents of the filter flask are filtered after the test and dried to yield the weight of undispersed fibers. The percent dispersibility is equal to 100 times the, weight of fibers dispersed divided by the total weight of fibers recovered. Conventional toilet tissues have a dispersibility ofabout 7 percent.
The flushability of a napkin or piece 'of fabric is determined by dropping it into the bowl of a household toilet (Model' F- 2122 made by. the American Radiator and Standard Sanitary Corporation of New York, NY.) and flushing. The discharge from the toilet is passed through a length of glass pipe 2.33 feet (71 cm.) long and 10.8 cm. inside diameter containing an artificial obstruction. The obstruction is constructed of standard flattened expanded metal with 0.5-inch (1.27 cm.) wide diamond perforations, formed into a cylinder one foot (30.5 cm.) long and about 10.3 cm. in diameter and provided with ing parallel pairs of cuts about 0.25 to 0.75 inch (0.63 to 1.9 cm.) long and about 0.3 inch (0.76 cm.) apart. and bending the cut sections to stand perpendicular to the walls of the cylinder. One flushing gives a flow of 18 to 20 liters of water in 20 seconds. The toilet is flushed twice for each sample, if necessary. If no more than minor fragments of fibers are retained by the obstruction, the sample is termed F lushable".
It has been observed that coverv fabric samples termed Flushable" by the above test usually have a dispersibility of at least about 20 percent in 2 minutes, in the small-scale dispersion test. Preferred fabrics have a dispersibility of at least 40 percent.
Bending length is 0.5 the length of a strip of sample that bends under its own weight to a 45 angle. 1t is determined on a 1 X 6-inch sample on a Drape-Flex Stiffness Tester made by Fabric Development Tests. Brooklyn 32, N.Y. The procedure followed in making thistest is given in ASTM method D1388- 5ST.
The liquid absorbency ofa sample is determined by soaking a small sample in an excess of the liquid at 25C. unless otherwise designated (lg. in 3,000 g. liquid). The sample is removed from the liquid and spread to cover a 5 X 5 cm. area on a bleached sulfite blotter paper. The sample is placed between layers of blotter paper and loaded with a 3 kilogram weight to give a pressure of 120 g./cm. Pressure is applied for 5 minutes after which the sample is removed and weighed, giving the net weight. The sample is then dried to constant weight using a Nobel and Woods sheet dryer at C. Absorbency equals the water absorbed which is the wet weight minus the dry weight divided by the dry weight of the sample. In the case of absorbency determinations in body fluids or synthetic urine, the dry weight must be corrected for solids dissolved in the liquid absorbed. All absorbencies are measured in distilled water unless otherwise noted. I
Coherence Value (C,,)
The coherence value (C,.) is a measure of the degree to which the fibers within the fabric break as opposed to slipping apart whenever a long strip of the fabric'is pulled apart.
The test comprises measuring the tensile strength of a long strip of the fabric and dividing this value by the tensile strength of the strip as determined at substantially zero length (lnstron clamping jaws together). It is a readily apparent that during the zero length strip-tensile measurement fiber slippage cannot occur and hence the maximum tensile strength for the strip is obtained. Therefore the maximum (C is 1 with lower C values indicating fiber slippage. A C,, wet ofless than about 0.3 is necessary to achieve the desired dispersibility of the products of this invention while a C,, dry of at least 0.2 is required to yield adequatein-use strength.
Samples of salt-free fabrics are cut into 4.1 cm. wide strips. The strips are then cut to about 5 and 2.5 cm. long adjacent samples. The longer samples is broken using 3.8 cm. initial distance between the rubber-coated jaws of the lnstron Tester. The shorter sample is broken using zero initial distance between the jaws. The coherence value (C is the breaking strength of the longer sample'divided by the breaking strength ofthe shorter sample. The average results from at least 3 pairs of such breaks in each direction of the fabric is reported as C,, in the examples.
For C,.- wet values, a bath of distilled water is raised around the sample which is clamped in the lnstron machine and the sample soaked for at least 1 minute before breaking it in the bath. All samples are elongated at a rate of 12.7 mm. per minute.
Salt-free fabrics for use in coherence value determinations are prepared by extracting with a solution made from 60 percent methanol and 40 water by volume. About 100 g. of the fabric (divided into 4 portions of 25 g. each) is placed in 1500 ml. of solution, then gently worked to insure saturation, soaked 15 minutes, and then gently squeezed and pressed between blotters. This is repeated using fresh solution until the solution is clear (normally three washes). Three additional I treatments of the 4 9 portions simultaneously are then given followed by .a final" treatment in 100* percent methanol. The blotted samplesare opened anddried 'in 'air. Twisting or pulling of the fabric during the treatments is avoided.
Rayon fibers of '1 .56 inches ('3.'97-'crn.') length and 1.5 denier pertilament' are made into a'batt'o f randomly oriented fibers by an air-deposition"process using a Rando-Webber machine. The 'batt has a weight of about 0.8 ozI/yd. (27 g./m'.) and it is made into a n onwoven fabric by the process of Belgian Pat. No. 673,199; In this process; the batt of random fiber s is supported on a screen'having 24 wires per inch (2.54 cm.) in each direction with 16' percent open'area and is passed 7 at yards (4:5' 7-meter's) per minuteunder' 5 rows of oscillating jets supplied with' waterat20Q; 300; 400; 500ahd600 lbs/inf 14.1; 2 1 .1, 28.1;351'2; and 42,2 k /cm?) respeetivelyl Each .row of jets contains 40 ho1e's/ihch"'( 40 holes/2.54 cm.) which are-,0.005 inch (0. 127 mm.) indiameter. The columnar streams of waterdeliver energy at the rate of 0.96 horsepowerhour pei pound"(0.9 6 horsepower-hour per 0.454
about 0.8 oz./yd. (27 g./in and"a dry tensile strength of 6.1 7.
lbs/in; (1.1 kg./cm.).'
The-"dry fabric is thoroughly wet out inan aqueous reagent bath.containi'ng 2.1 percent of sodium hydroxide and. 15.8, percent of sodium monochloro 'ce'tate. Excess reagent is pressed out of the fabric withfsque'eze rolls so'tha't the fibers retain 1;] times their own weight of liquid. The moist 'fibers are immediatelydried and caused to react by passing them through a c'ircuIating air oven 0.46 meterslong at a rate of 1.53 meters-per minute whileatatemperaturebf approximately 140C. The "carboxyinethylated fabric is then passed under a spray of 5"percentsulfuric acidto conve rti'it to the i low-swelling free acid'form after which it is thoroughly washed with waternlt is thenconvertedto'the high-swellingsodium saltform in a deswelling neutralizing bath containing 8.5 percent sodium-sulfat'e and-Tperc'entdisodium phosphate. The fabric-is passed between squeeze rolls to' 'remove'as inuch salt solution as possible; c'ut into'convenient lengths, and dried at 40C. in a laundry drier'containing'several baseballs 9.7 cm. in
diameter to soften the fabric by mechanicalworkin'g and to remove excess salt. The dried'fabricis cut into 7 X"1'9inch (17.8 X 48.3 cm.)piece's foruse as the Wrapper elementsof sanitary napkins. The-fabric has the following properties:
Fabric weight-1.5 oz./yd. (51 g./m.
Tensile strength, dry (MD)%3;34l b./in. (597 g./cm.).
Tensile strength; 1 wet (MD) tap (12.5 g./cm.):- 1
Tensile'. strength, wet synthetie urine0.2 3 1b./in.
Absorbency..About 10 to 15 g./g.
Degree of SubstitutionAbout 0. 25, .7
In the construction of a sanitary napkin, a wood fluff core having. embossed layjers to encourage the distribution of ab- Workto-break(XD)- 0.014 in. Ibs./;in. (1.5 g.em./
Bending Length-(MD)1.48 cm.
Density.-1.15 5 gJem.
Thickness0.0049 in. (0.124 mm.).
The crepe tissue on the back side and edges of the wrapped absorbent core are sprayed with an organosol of a;
fluoropolymer water repellent so that 0.0064 g. of solid remain after the solvent has evaporated. The corners of the assembly are cutoff to give roundedends as shown in the drawing and the core assembly is then wrapped in.a piece of the water sensitive outer wrappernfabric. The edges of the outer wrapper on the back of the napkin are secured in place with small spots of an adhesive polyvinyl alcoholat intervals along theoverlap.
The repellent organosol used in constructing the repellent barrier is made in accordance with'the teachings of'Belgian methacrylate specieshavingthe general formula ll t CFz(CF2)n-CH2,CHzO =CH2 wherein the speciesn being S, 7 and 9 are'in relative-weight proportions of 3:2:1 respectively and constituteat least 90 percent of the monomer mixture; higher species constitute up to IOpercentl- In preparing the fluoropolymer the following ingredients are used (Buton 100 is a Enjay Company of 60 W.. 49th Street, New-York; N.Y.).
cm.) thick, 2.5-"inches"'(6. 35 cm. 'wide,'andl7i. 6 inches (19.3 cm.) long is wrapped' in acrepe""tissuewra'pper about 7.6 inches 19:3cm.)"1o'ng*and 7;75 inches19.7 ch1;)wide so that the overlap forms a'doi ble thic kness 'on part of the back side, These t'w'b thicknesses are glued together i with a light: continuous-line of polytvinyla1cohdl)-adhesive;'Thecrepe tis sue usediis found to be too we tote'st'when' wet with water. The physical propertiesmeasured on I X cm.] samples of th'e'dry'sheet inthetr'isiile tests ar'e as follows:
The ingredients. of Part A ,are charged in ordergiven with agitation into a: reactor. and heated t0,9597:C'. and held-at this.ternpe raturefor 2 hours and 1.5 minutes,
The components of Part Bare premixedand adde'd to Part A reaction product. Combined Parts Aand B are reheated to 9 7C., held at this temperature for 2 hours and" 1 5 minutes and then cooled .to 65C.
Part C is added to Parts A-B over a 10-minute period, maintaining the temperature at about 65C. The composition is agitated for 20 minutesat.6 5 ".C, and then cooled to room temperature and filtered. Theresultingmixture, containing flap proximately 20 percent nonvolatile material y is diluted to about05 percent concentration with methyl. chloroform be fore use.
In an experimental wear test..all of the napkins perform in a satisfactory manner, comparable to. commercialnonflushable sanitary napkins The test napkinsare disposed of in the standard flushabil ity test without difficulty.
EXAMPLE I] Rayon fibers of 0.75 inch.(l;9 cm.) length and 1.5 denier per filament are made into a batt having a weight of I32 oz./yd. 40.7 g./m.
Pat. No. 671,010. The fluoromonomer" is; a mixture of" commercially available product of.
v and entangled into a'nonwoven-fabric I by the method of example I, using 0.96 horsepower-hoursper pound of fiber, the fiber being supported on a screen having wires per inch (2.54 cm.) in both directions and 36 percent open area. The dried nonwoven fabric has a tensile strength of 6.6 lb./in. (1,180 g./cm.) in the machine direction and 4.6 lbs./in. (821 g./cm.) in the cross direction.
The dry fabric is cut into pieces about 20 inches (50.8 cm.) long and 10 inches (25.4 cm.) wide. These are soaked for 2 minutes in a 17 percent solution of succinamic acid at about 50C. The fabric is removed and pressed between blotters until it retains three times its weight of succinamic acid solution. The fabric is then dried and a chemical reaction is effected by placing the sheet in a circulating hot-air oven for 4 min. during which time the air temperature is raised from 135C. to 163C. The cellulose is thus converted to the free acid form of the partial hemisuccinate ester at a degree of substitution of 0.3 acid succinate groups per glucose unit. It is converted to the high-swelling sodium salt by soaking it for 5 minutes in a buffered salt solution containing 3 percent disodium phosphate and 17 percent sodium sulfate and maintained at a pH of 8.5 to 9.0 by the addition of small amounts of sodium hydroxide solution as needed. The fabric is then squeezed as free of salt solution as possible, air-dried, and mechanically worked by hand to remove excess salt. The final fabric has the following properties:
cm. Tensile Strength, wet (syn. urine)0.2l8 lb./in. (39
g. cm. Elongation, wet (tap water)13.4%. Elongation, wet (syn. urine)33.6%.
The fabric is used in the construction of sanitary napkins as in example I. In a use test, the napkins perform fully as well as the usual commercial sanitary napkin. All the test napkins flush easily in the experimental test toilet facility.
EXAMPLE III Crimped rayon staple fiber of 0.75 inch (1.9 cm.) length and 1.5 denier per filament is fed in sequence to a Garnett feeder, a Garnett card, a Rando-Feeder", and a Rando- Webber to form a l oz./yd. web. The rayon fibers are entangled to give strength and integrity to the web using the method of Belgian Pat. No. 673,199. In this process, the web of rayon fibers is supported on a screen containing 24 wires per inch (2.54 cm.) in both directions, with 16 percent open area, and passed at 5 yards (4.57 meters) per minute under 4 rows of oscillating jets supplied with 65C. water at 200, 500, 700, and 800 lbs./in. 14.1, 35.2, 49.2, and 56.2 kg./cm. respectively. Each row of jets contains 40 holes/inch (40 holes/2.54 cm.), each hole being 0.005 inch (0.127 mm.) in diameter. The columnar streams of water deliver energy at the rate of 1.03 horsepower-hours per pound (0.454 kg.) of fibers. The dried nonwoven fabric has a weight of 1.10 oz./yd. (37.3 g./m. and a tensile strength of 5.08 lbs./in. (907 g./cm.) in the machine direction with a tenacity of2.97 lbs./in. (530 g./cm.) in the cross direction.
The nonwoven fabric is uniformly padded with 2.02 times its weight of a reagent solution prepared by dissolving 100 parts of shotted commercial urea in 56.5 parts of deionized water at 185F. (85C.) and adding 43.5 parts of commercial 85 percent phosphoric acid to the solution. The web fabric is fastened on a tenter frame and passed through a circulating air oven with exposure to balanced-flow low-velocity air at 315F. (157C.) for 2 minutes. The resulting cellulose phosphate ester fabric is cut into pieces which are washed in 5 percent sulfuric acid, squeezed free of excess liquid, and neutralized to the high-swelling form in a buffered salt solution containing 2 percent disodium phosphate and 8 percent sodium sulfate. adjusted to a pH of about 8.5. The pieces of fabric are squeezed free of excess liquid, pressed between blotters to reduce the amount of retained salt solution, and dried as in example 1. The final product has the following properties:
wet syn. urine-0.375 lb./in.
The fabric is used as the wrapper fabric in the construction of sanitary napkins as in example 1. These napkins easily pass the standard flushability test.
EXAMPLE IV The napkins of this example are constructed solely to evaluate the barrier structure and are not flushable as an assembled unit. They are made using a wood pulp core as in example l, The nonflushable outer cover fabric is a resin-bonded non- I woven scrim removed from a commercial napkin. The repellent barrier is similar to that in example 1, except that the portion of the crepe tissue which is to cover the back and sides of the core is sprayed with repellent on both sides before it is wrapped around the wood fluff core. In this case, the repellent contains as active ingredient, a segmented copolymer of about 76 percent of 2-(N-ethyl, heptadecafluoro-l-octanesulfonamide)-ethyl methacrylate and about 24 percent methyl methacrylate, as described in US. Pat. No. 3,068,187. A total of about 0.034 g. of repellent per gram of substrate is applied to the barrier sheet.
The napkins are subjected to a static loading test designed to be more severe than any actual conditions to be encountered in use. The napkin is placed, with the outside down, on a resilient felt flock protected with a thin polyethylene film. A 9- pound (4.1 kg.) lead block is placed on top of the napkin, subjecting it to a pressure of about 0.5 lb./in. (35 g./cm. Through a l-inch (2.54 cm.) hole in the center of the lead block, oxalated bovine blood is introduced into the napkin at the rate of 10 cc./min. After 20 cc. has been added in 2 minutes, the bottom is inspected, and the test is resumed if no stain shows. After 30 ml. of blood has been added, the lead block is shifted to apply pressure uniformly to the wet area for 10 seconds. If the barrier does not pass a stain under these conditions it is considered more than adequate for general use. The napkins of this example do not show any stain on the back side in this test. The repellent barriers easily disintegrate in mildly circulating water, indicating easy flushability.
EXAMPLE V A nonwoven entangled rayon fabric is made by a process closely similar to that in example I using a supporting screen having 20 wires per inch (2.54 cm.) in both directions. The dried fabric has a weight of0.95 oz./yd. (32.2 g./m.) and the tensile strength is 3.2 lbs./in. (572 g./cm.) with 31 percent elongation in the machine direction while the cross direction exhibits a tensile strength of 2.24 lbs/in. (400 g./cm.) with 72 percent elongation.
A reagent solution is prepared containing 4.50 percent sodium hydroxide, 20 percent sodium monochloroacetate and 0.75 percent Kelzan, a polysaccharide thickener made by the Kelco Company of Chicago, lllinois. This solution is applied uniformly to the nonwoven fabric by means of a pad roll etched with 2.5 mil (0.0635 mm.) lines so that the fabric picks up 1.87 g. reagent per gram of air-dry cellulose. The fabric is passed through a circulating hot air oven at 136144C. at 6 feet (183 meters) per minute, for a reaction time of 15 Degree of substitution0.32. Absorbency-10.2 g./g. y Disp'ersibility 59. 1 Fabric weight-about 1.5 oz./yd. (51 g./m.
Tensile strength, dry (M-D)4.56 lbs/in. (815 g./cm.).
dry (XD).1.55-lbs./in. (277 g./cm.). Tensile strength,
wet (MD) tap water0.044 lbs./in.
' g-/ m-) K v Tensile strength, 'wet (XD) tap water-0.002 lbs/in.
(0.4 g./em.). Tensile strength, wet (MD) syn. urine0.13 lbs./in.
Wet l yn. urine0.10 lbs/in. (17.9 g./cm.) y, Y r
The fabric is cut into pieces 7 inches l 7.8 cm.) wide and 19 inches (48.2 cm.) long which are used as wrapper in the construction offlushable sanitary napkins. The absorbent core of the napkins is wood fluff wrapped in crepe tissue as in example I. In this case, however, a separate barrier is constructed of crepe tissue having the, following properties:
Sheet weight-0.6 oz./yd. (20.4 g./m. Thickness-0.0074 in. (0.188 mm). Bursting,strength.6.0 p.s.i. (422 g./cm. Bending length-. 28 Tensile strength, MD.0.251b./in. (44.7 g./cm.). Tensilestrength, XD-0.14lb./in. (25 g./cm.). Elongation, MD70.6%. Elongation, XD?12%.
The crepe tissue is treated on both sides with the fluoropolymer repellent of example IV, so that the sheets retain about percent of their original weightof repellent material. The sheets are about 7.5 inches (19 cm.) long and are assembled into a barrier three sheets thick with a 5-sheet thick overlap at the center. Thebarrier is 11 inches (28 cm.) long, and-3.5.i nc hes (8.9 cm.) ;wide so as to cover the back and sides of the wrapped absorbent core. These assemblies are enclosed in the flushable nonwoven fabric wrappers, after two notches about L25 inch-(3.18 cm.) wide and 4 inches (10.5 cm.) longare cut out ofeach end of the-wrapper fabric to reduce the bulk of the fastening tab. =In experimental test usage, none of the barriers permit the passage of menstrual fluid and the, napkins are easily flushable in the standard flushability test.
Thefluid barriers of the napkins of this invention can optionally be made by using the outer wrapper comprised of modified cellulosicfibers as theasubstrate and coating the inside portion of the wrapper that is to be away from the user directly with the fluoropoiymer, thereby converting'the outer wrapper into an effective barrier. The barrier, when so constructed restricts then apkin to use as a one-way type of napkin. t t t EXAMPLE VI In the construction ofa flushable sanitary napkin, an absorbent core fabricated from crepe tissue and wood fluff batts is used. The cores are formedby laying up three layers of wood fluff, each layer being contained between single plies of crepe tissue, and stamping out the individual cores, with a suitable die cutter, of about 7.5 inch long X 2.5 inch wide X 0.875 inch thick, ends rounded. A suitable wood fluff for these absorbent cores is prepared by processingpulp sheets of Weyerhaueser Soft Alpha M through a hammermill followed by further processing through a Rando-Webber (or similar air laydown) machine to give batts of material of 8 oz./yd. basis weight and a thickness of three-eighths inch. In the absorbent cores, the crepe tissue carriers of the wood fluff are alined with the creping direction of the tissue running parallel to the long dimension of the core. Suitable tissues, of the grade known as white facial toilet tissue, have the following specifications:
Basis weight0.47-0.57 oz./yd.
Tensile strength (MD)0.410.71 1b./in. Tensile strength (XD)0.120.30 lb./in. Elongation (MD)1058%.
Elongation (X D) 514%.
Work-to-break (MD)0.09-0.105 in. lbs/in Work-to-break (XD)0.0070.014 in. lbs./in. Beading length (MD)-1.482.2 em. Thickness-About 0.005 in.
The absorbent cores are wrapped in a single ply crepe tissue wrapper (of the preceding specifications) about 7.25 inches long and 14 inches wide. The tissue wrapper is rolled over core in such a way that a two ply wrapper results. The second ply of tissue is glued to the first ply, on the bottomside of the core, with a light continuous line ofeither an aqueous poly(vinyl alcohol) adhesive or a poly(vinyl acetate) emulsion type of adhesive.
The crepe tissue on the back wrapped absorbent core is household type 122-124F.) in l,l,l-trichloroethane (2 g. ofwax in 98 ml. of solvent) so that 0.07 to 0.25 mg./cm. of wax remains, on the treated area, after the solvent evaporates.
This core assembly is then wrapped in a 7 inch wide and 19 inch long piece of cellulose phosphate ester fabric prepared as described below.
Crimped dull rayon staple fiber of 0.75 inch (1.9 cm.) length and 1.5 denier per filament is fed in sequence to a Garnett Feeder, a Garnett card, a Rando-Feeder., and a Rando-Webber to form a l oz./yd. (34 g./m. web. The web of rayon fibers is supported on a screen containing 24 wires per inch (2.54 cm.) in both directions, with 16 percent open area, and passed at 6 yards (5.5 meters) per minute under 4 rows of jets supplied with 60C. water at 300, 600 and 700 lbs./in." (21.2, 42.4 and 49.2 kg./cm. respectively. Each row of jets contains 40 holes/inch (40 holes/2.54 cm.), each hole being 0.005 inch (0.127 mm.) in diameter. The dried nonwoven fabric has a weight of 1.05 ozl/yd strength is 4.1 lbs./in. (476 g./cm.) in the cross direction.
The nonwoven fabric is uniformly padded wi th'1.95 times its weight of a reagent solution prepared by dissolving 100 parts of commercial urea pellets in 62.4 parts of tap water, heated to maintain about 45C., and adding 37.6 parts ofcommercial percent phosphoric acid to the solution. The ratio (bottom) side and edges of the of phosphoric acid to urea in the reagent solution is 1/3. l2 and the fabric retains 0.31 times its weight of H PO The wet fabric is supported on a meshed wire conveyor and passed through a circulating air oven with exposure to through-flow, low velocity air at 376F. (191C.) for 0.25 minutes. The heated air is recirculated and fresh air addition is minimized to maintain a concentration of urea vapor in the air. The resulting cellulose phosphate ester fabric supported on a screen conveyor is assed at 12 yd./min. (11.0 m./min.) under three flows of 1 percent Na SO /2 percent Na HPO /3 percent sodium hexametaphosphate containing 0.2 percent Du Pont Paper white SP solution sprayed with a solution of a. paraffin wax water repellent (freezing point (35.6 g./m. The tensile and 0.05 percent Merpol* ON adjusted to Water-.02 (est.).
The edges of the outer wrapper described above are secured in place with small spots of an adhesive poly(vinyl alcohol) or poly(vinyl acetate) at intervals along the overlap.
In experimental wear tests, the napkins perform in a satisfactory manner, comparable to commercial nonflushable sanitary napkins. The test napkins are disposed of in the standard flushability test without difficulty.
Other solvents may be used for the spray application of the paraffin wax water repellent barrier. Suitable solvents are V.M. & P. Naptha, paraffin distillate, and ethylene dichloride, among others. The paraffin wax may also be used to treat the tissue substrate through the use of hot melt printing techniques. For example, a hand gravure roller containing 180 pyramidal shaped cells per inch has been used in the laboratory to apply the paraffin wax, at a temperature of 190-2 10F., to a single ply of the various tissues at a loading of about 0.62 to 1.09 mg./cm. per pass ofthe roller. At this loading, the tissue has a slight waxy feel but is not stiffened noticeably. Although this printed tissue is not quite as water repellent as the 0.07 to 0.25 mg./cm. waxed tissue obtained by spray application (as judged by beading of droplets of water on the surfaces), it may be rendered equally repellent by a post heat treatment at 81 to 150C. In none of these application methods is a continuous film of wax applied, as judged visually under the microscope. When a loading of about of to 27 mg./in. of the wax is applied to the tissue by the printing technique (repeated passes), the tissue becomes quite waxy and is stiffened somewhat.
Other paraffin waxes are suitable as water repellent barriers on the tissue. Blends of paraffin wax and microcrystalline waxes and/or ethylene/vinyl acetate-type copolymers with the wax are also operable. In addition, other barrier candidates which can pass a laboratory screening test similar to that described in example IV when sprayed onto the crepe tissue wrapper, include: Zelan" S (durable water repellent) (0.54 mg./in."), Zepel S-l (fabric fluoridizer) (1.14 mg./in. TLF-2005 (a polyhydroxy titanium stearate) (0.78 mg./in. Zonyl" S-13 (fluorochemical surfactant) (about 0.5-1.0 mg./in. poly(acrylic acid), (0.2 mg./in. and poly(vinyl alcohol) (0.15 mg./in.
EXAMPLE VII Example V1 is repeated except that an alternate core construction is used in which one layer of wood fluff is prepared from Weyerhaueser soft Alpha M pulp. The core is contained between the same single plies of tissues and cut to the same dimensions described in example VI. The wood fluff batt has a basis weight of 21 oz./yd." and a thickness of about 1 inch. In experimental wear tests, the napkins perform in a satisfactory manner and are disposed of in the standard flushability test without difficulty.
The flushable fabrics of examples I, II, 111, V, VI and VII have a dry coherence value (C dry) of at least 0.2 and a wet coherence value (C wet) of less than 0.3, both measured in the absence of resinous or fusion bonds. In addition, the fabrics have a wet coefficient of sliding friction of less than 0.90.
The following procedure is used to determine the water-sensitive fiber frictional characteristics of the flushable fabrics used in this invention.
WATER-SENSITIVE FIBER FRICTIONAL CHARACTERISTICS The coefficient of sliding friction, 8 (or kinetic friction) is the ratio of the force F needed to pull one surface over another to the force N normal to the surfaces in contact.
A piece of fabric of about 2 inches X 6 inches (5.1 X 15.3 cm.) is placed on the horizontal bottom of a metal tank with the longer length in the direction of sliding and one end held in place with a heavy metal block. A second portion of fabric of 1 inch X 3 inches (2.5 X 7.6 cm.) is wrapped around a sled so that the bottom, front and back faces of the sled have one thickness of cloth and the top face has one to two thicknesses. A 5 gram brass weight is placed on top of the fabric. The sled consists ofa l X 1 X 0.063 inches (25 X 25 X 1.6 mm.) piece of poly(methyl methacrylate) plastic with an outer layer of crocus cloth (abrasive face out) held to the plastic with double-faced adhesive tape. The sled has a filament attached to each side near the forward edge forming a yoke. A 0.1 percent aqueous solution of NaCl is slowly added to the tank to a depth of about 8 mm., the sled, fabric and weight placed on top of the lower fabric, the yoke attached to a filament leading under a pulley in the tank and upward to the crosshead of an Instron Tester and the tester started so as to pull to sled at a rate of 2 inches (5.0 cm.) per minute. The sliding is continued for about seconds. The charted force from 30 seconds to the end is averaged and reported as F after suitable correction for the force necessary to overcome the friction of the pulley. Force N is the sum of the sled weight (1.9 g.), the fabric (normally about 0.15 g.) and the 5.0 g. weight, minus the buoyancy of the solution. The solution completely covers the sled and about 50 percent of the weight. (Total effective force, N, 5.8 gms.)
The above conditions should be followed sincefvaries with N.
The test is made on a nonwoven fabric consisting of percent of the water-sensitive fibers. Fabric pattern or structure variation has been found to have little effect on the sliding friction with essentially planar fabrics. We claim:
1. A flushable sanitary napkin comprising in combination an elongated absorbent core ofloosely felted fibrated wood pulp, said core having a density in the range of 1.5 to 5 lbs./ft."; a fluid barrier for retaining body fluids within the core; a wrapper encasing the core and fluid barrier for maintaining said napkin in a unitary assembly during use, the wrapper being a nonwoven fabric of randomly entangled, chemicallymodified cellulosic fibers, of 1.5 to 3 dpf and a length within the range of 0.25 to 2.0 inches, selected from the group consisting of sodium carboxymethyl cellulose of0.2 to 0.4 degree of substitution, the sodium salt of cellulose acid succinate of 0.2 to 0.4 degree of substitution, and the sodium salt of monocellulose dihydrogen phosphate of 0.15 to 0.35 degree of substitution; said wrapper being further characterized as a soft, water-dispersible, nonwoven fabric of 0.5 to about 2.0 oz./yd. fabric weight with a bending length ofless than 3 cm., having a tensile strength in synthetic urine within the range of about 0.1 to 0.5 lbs./in., and having a tap-water wet tensile strength within the range of 0 to about 0.09 lbs./in., the wrapper corresponding to a fabric weight within the range of 0.5 to about 1.0 oz./yd. having a dry-strip tensile strength within the range of 1 to 5 lbs/in. in the principal fabric directions and the wrapper of a fabric weight within the range of about 1.0 to 2.0 oz./yd. having a dry-strip tensile strength within the range of 3 to about 10 lbs/in.
2. The sanitary napkin of claim I wherein the fluid barrier is a cellulosic substrate coated with an organosol of a fluoropolymer to yield about 0.0001 to 0.0005 gram of fluoropolymer per square inch of barrier surface.
3. The sanitary napkin of claim 2 wherein the fluoropolymer is the polymerization product of:
a. a fluoromonomer comprising about 85 percent by weight of the reaction mixture consisting essentially of a mixture of wherein the compounds corresponding to n of 5, 7 and 9 are in the relative weight proportions of about 3:221 respectively and constitute at least 90 percent of the monomer mixture, the remainder of the monomer mixture being the compounds corresponding to n values greater than 10; and
b. a styrene/butadiene copolymer which comprises about percent of the reaction mixture.
4. The sanitary napkin of claim 2 wherein the fluoropolymer coating consists essentially of the segmented copolymer of:
a. about 76 percent of Z-(N-ethyl, heptadecafluoro-l-octanesulfonamido)-ethyl methacrylate; and
b. about 24 percent methyl methacrylate.
S. The sanitary napkin of claim 2 wherein the barrier substrate comprises a cellulosic crepe sheet having a dry tensile strength in the principal direction of 0.4 to 0.8 lbs/in. and an elongation at break in the range of 10 percent to about 75 percent at a basis weight of about 0.4 to to 0.7 oz./yd. the substrate having a bending length of l to 2.5 centimeters.
6. The sanitary napkin of claim 2 wherein the barrier substrate is the outer wrapper of said napkin.
7. The sanitary napkin of claim 1 wherein the fluid barrier is a cellulosic substrate coated with compounds selected from the group consisting of a paraffin wax, blends of paraffin wax and microcrystalline wax and blends of paraffin wax and an ethylene-vinyl acetate copolymer to yield about 0.0005 to 0.0015 gram of wax per square inch of barrier surface.
8. The sanitary napkin of claim 7 wherein the barrier substrate. comprises a cellulosic crepe sheet having a dry tensile strength in the principal direction of 0.4 to 0.8 lbs/in. and an elongation at break in the range of 10 percent to about 75 percent at a basis weight of about 0.4 to 0.7 oz./yd. the substrate having a bending length of l to 2.5 centimeters.
9. The sanitary napkin of claim 7 wherein the barrier substrate is the outer wrapper of said napkin.
10. A flushable sanitary napkin comprising in combination an elongated absorbent core of loosely felted fibrated wood pulp, said core having a density in the range of 1.5 to 5 lbs/ft; a fluid barrier for retaining body fluids within the core, and a wrapper encasing the core and fluid barrier for maintaining said napkin in a unitary assembly during use; said wrapper being an absorbent nonwoven fabric weighing 0.35 oz./yd. having dry strength and integrity in the absence of resinous or fusion bonds and comprising from 10 to percent water-sensitive fibers characterized in that:
l. the water-sensitive fibers are less than three inches (7.6
cm.) in length, the balance of the fibers consisting of nonwater-sensitive fibers of less than 0.5 inch (1.3 cm.) in length;
2. said fabric has a dry coherence value (C, dry) of at least 0.2 and a wet coherence value (C, wet) of less than 0.3 both measured in the absence of resinous or fusion bonds,
3. with the proviso that the ratio Ch dry Ch wet 213 11. The sanitary napkin of claim 10 in which the nonwoven fabric comprising the wrapper has an average wet strip tensile strength of less than 0.1 lb./in.
l2. The'sanitary napkin of claim 11 in which the nonwoven fabric comprising the wrapper has an elongation at break in two directions at right angles to each other of at least 20 percent.