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BACKGROUMD OF THE INVENTInN
In recent years, the construction of sanitary napkins designed for catamenial protection in feminine - hygiene has changed from thick bulky pads having tab extensions, with the extensions being used to fasten ~the napkins to suspension belts or to buckle-equipped supporting garments, to less bulky pads devoid of tab extensions and having pressure sensitive adhesive means on the bottom surface for securing the napkins to snug-fitting undergarments. Representative U. S. patents descri~ing napkins of the latter type include: Chinai et al 4,023,570, Comerford et al 4,023,571, ~endricks 3,724,466, Roeder 3,672,371, McGuire et al 3,643,662, Sargent et al 3,595,237, McGuire 3,575,175, Sneider 3,570,491, Hendricks 3,508,549, Hendricks 3,463,154 and Hendricks 3,454,008.
~ nother recent development in the sanitary napkin art has been the introduction of hydrophobic, but fluid-pervious, outer wrappers of thermoplastic material comprised of filaments, fibers or fibrillated films. Such body-contacting wrappers permit body fluids to penetrate readily for absorption by an underlying absorbent core while the wrappers themselves retain little, if any, fluid. The body-contacting surface of the sanitary napkin thus remains in generally drier condition during use and the napkin thereby has a more comfortable feel. One such wrapper material is defined in U. S. patent 3,886,942 to Bernardin, which teaches the use of a sanitary napkin wrapper comprised of a non-woven web of thermoplastic hydrophobic fibers in which the fibers of the web are devoid of any fiber finishing treatment.
In fabricating these so-called tabless pads, it is necessary to seal together the short extensions of wrapper and other elemen~s which extend beyond the absorbent pad ends to provide a pad-confining closure.
Such sealing is now usually accomplished either by the us~ of a flexible adhesive, by mechanically crimping the multiple layers together, or by heat-sealing thermoplastic elements together when the latter are used in the napkin structure. However, each of these sealing methods has some disadvantages. For example, the initial softness and flexibility of the materials in the layers are often lost, and a stiff, sometimes harsh, product results.
Also, when the layers are thermoplastic and heat-sealing is employed, careful regulation of the temperature is needed, and such regulation or control is difficult to maintain during continuous production. If the heat is insufficient, the layers do not adhere well. A poor seal often results, and fre~uently fails. If too much heat is used, some of the thermoplastic elements in the seal are weakened, perforated, or even completely severed, resulting in a defective product with a weak seal or none at all.
When the napkin wrapper comprises a non-woven web of thermoplastic hydrophobic fibers, or the like, the problem of obtaining a proper seal becomes more difficult. Adhesives must be specifically compounded to secure the hydrophobic material, and oftentimes larger amounts of adhesive are found to be necessary to obtain secure seals. In the latter case a stiff, uncomfortable end structure results. Crimping does not work well with hydrophobic fibers, and thermoplastic sealing tends to melt the fibers excessively and weaken or perforate the wrapper.
~273~2 It has now been found that a ~oft flexible seal can be effected by using ultrasonic means to thermally activate and join together the multiple layers of thermoplastic wrapper and baffle material extending beyond the pad ends. Ultrasonic thermal activation forms a stronq seal, does not weaken the thermopla~tic materials adjacent the seal, and enables precise sizing and placement of the area of joinder.
In addition free end portions of the multiple layers can ~e left at the outer edges of the seal to facilitate manufacturing methods while contributing to product comfort.
This invention is directed to such a napkin structure and the method of obtaining it.
SUMMARY OF THE INVENTION
This inventivn is directed to a tabless sanitary napkin with sealed end portions of improved flexibility and softness. The napkin is comprised o an elongate absorbent pad enclosed in a fluid-permeable wrapper of thermopla~tic material. A fluid-impermeable baff~e of thin thermoplastic film is disposed between the wrapper and the lower surface of the pad and may also extend alongside and slightly over the pad edges. Both the wrapper and baffle extend beyond each end of the pad.
The~e wrapper and baffle exten~ions are fused to each other by an ultrasonically induced thermal seal in a transverse n~rrow band-like area disposed adjacent the - l~Z735Z
pad ends, while leaving free, unsealed end portions or short flaps of the wrapper and baffle extensions outward of the fused area. The fused band-like area of seal may be continuous or segmented. In the preferred em~odiment, the pad, fu~ed band area, and free end portions are rounded. Also in the preferred embodiment, the wrapper and baffle have substantially the same thermal melt characteristics. In still another preferred embodiment the top surface of the napkin and the underlying pad ; 10 are embossed with a spaced pattern of dimple embossments.
A method for providing the above-described tabless napkins comprises the steps of advancing a continuous web of fluid-pervious thermoplastic material along a selected path; depositing the elongate absorbent pads on the web in uniformly spaced relationship; intro-ducing a continuous strip of thin, fluid-impervious thermopIastic film over the pads; wrapping the web around and over the pad and film to overlap the longi-tudinal edges of the web; applying ultrasonic energy to selected band-like areas extending ~ransversely of the multiple layers of web and film spanning the space between the pads to thermally fuse together the web and film in a narrow transverse band of joinder adjacent each of the trailing and leading ends of adjoining pads with the bands of joinder also bPing spaced from each other; and severing the web and film layers between bands o-f joinder to provide individual sanitary napkins in which ~Z~35Z
the ~nds are transversely sealed with ultrasonically induced narrow bands of joinder and have flexible unfused extensions of web and film outwardly of the sealed area.
The above and other features and advantages of the invention will be described in more detail with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING~
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In the drawings:
FIG. 1 is a perspective view, partially cut away, of a sanitary napkin according to one embodiment of the invention;
FIG. 2 is a perspective view, also partially cut away, of another and preferred embodiment of the invention;
FIG. 3 is a schematic perspective representa-tion of means suitable for use in carrying vut the preferred method for providing sanitary napkins of this invention;
FIG. 4 is an enlarged fragmentary view o a suitable anvil means which cooperates with an ultra-sonic horn to provide the transverse narrow band-like seal in the preferred embodiment of the sanitary napkin of this invention.
DETAILÆD DESCRIPTION OF THE PREFERRED EMBODIMENTS
The perspective view of FIG. 1 illustrates one simplified embodiment of a sanitary napkin in accordance ~2735;~
with this invention. As shown therein, the sanitary napkin 10 is comprised of a central elongate absorbent pad 12, a fluid-impermeable baffle of thin, thermo-plastic film 14 underlying pad 12 and a thermoplastic fluid-permeable wrapper 16 encircling pad 12 and film 14.
Wrapper 16 is overlapped at the bottom ~urface of the napkin as indicated at 18. Longitudinal extensions of wrapper 16 and film 14 terminate beyond each of the pad ends and are fused to each other by ultrasonically-induced heating in a transverse narrow band-like se~l area 19 adjacent each end of pad 12, leaving free ends 16a and 16b of the wrapper and 14a of the film disposed outwardly of the narrow fused band-like area 19 at each end. The narrow fused band-like area 19 has a uniform transluc~nt appearance resembling a single layer of unitary film and the adjacent outwardly lying free-ends of wrapper and baffle film are soft and supple to the touch. Fused area 19 also forms a strong bond and leaves no weakened areas in adjacent portions of the constituent layers, which weakened areas often result when ordinary heat-sealing is used. Even though the layers in the ultrasonically fused area lose their individual identity and form a singIe fused layer, the portion of the layers immediately adjacent the fused area retain substantially their full strength at the point of joinder and a strong ~ond is achieved. This bond is demonstrably stronger than a conventional heat-seal.
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Sanitary napkin 10 may also be supplied on the lower surface with one or more strip-like layers of pressure-sensitive adhesive 15 covered by a removable protective sheet 17 of silicone-coated paper or the like.
A preferred embodiment of the sanitary napkin of this invention is shown in FIG. 2. As shown therein, sanitary napkin 20 is comprised of an elongate absorbent pad 22 with rounded ends 21, a fluid-impermeable baffle of thin thermoplastic film 24 which underlies pad 22 and extends upwardly alongside the pad edges and slightly over the top surface of the pad as shown at 23 and a thermoplastic fluid-permeable wrapper 26 encircling pad 22 and film 24. Wrapper 26 is overlapped at the bottom surface of the napkin as indicated at 28.
Extensions of wrapper 26 and film 24 terminate beyond each of the pad ends and are fused to each other by ultrasonically-induced heating in a transverse narrow band-like seal area 29 adjacent and parallel to the rounded pad ends, leaving free ends 26a and 26b of the wrapper and 24a of the film disposed outwardly of the narrow fused band-like area 29 at each end.
As in the napkin of FIG. 1, the narrow fused band-like seal area 29 has a uniform translucent appear-ance resembling a single uninterrupted layer of film and the adjacent outwardly disposed free ends of wrapper and baffle film are soft and supple to the touch.
While the narrow-fused band-like seal area in FIGS. 1 and 2 is shown as a continuous line or band, satisfactory results and an even more flexible end seal is obtained if the band is segmented or has a discontinuous broken-line pattern in the fused area.
Sanitary napkin 20 may also be provided with one or more strip-like layers of pressure-sensitive adhesive 25 covered with a removable protective strip 27.
In addition to rounded ends 21, the napkin 20 of FIG. 2 differs from the napkin of FIG. 1 in that napkin 20 is provided on its top surface with a spaced array of heat-set dimple-like embossments 30 which are also impressed into the absorbent pad 22 as shown at 30a.
These embossments provide fluid-receiving cavities which speed up the absorption of body fluids into absorbent pad 22 as the fluid is drawn into the cavities by gravity and which help keep unembossed surface areas of the wrapper relatively dry.
Napkin 20 also differs from napkin 10 in that the baffle 24 extends up and over the side edges as at 23.
; In the preferred embodiment of the napkin, the wrapper material is comprised of a spunbonded poly~
propylene web having a basis weight o~ about 12 grams per square yard. The thermoplastic film baffle is comprised of a .75 mil polypropylene film. The absor-bent pad is comprised of wood pulp fluff.
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It is understood of course that other known ab~orbent materials such as cotton, rayon or super-absorbent additives may be used in the absorbent pad structure, and that the wrapper and baffle film may be of different weight and thickness than are given for the preferred example.
Other known thermoplastic materials such as polyethylene, polyesters and polyvinyls may be used for the thermoplastic elements in the baffle and wrapper.
However, for best results, the wrapper and baffle should be made of material with the same thermal melt charac-teristics since the uniform melting po_nt thus obtained provides more uniform fusion and a better seal. Wrapper and baffle layers of polypropylene having uniform melt properties are preferred.
A method of fabricating the preferred napkin of this invention will now be described in connection with FIGS. 3 and 4.
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As shown therein a continuous web 31 of fluid-pervious thermoplastic material, such as spunbondedpolypropylene, is unrolled from supply roll 32 and ; advanced along a selected path. A supply of elongate absorbent pads 33 are deposited on web 31 at spaced intervals from supply trough 34. A continuous strip of fluid-impervious thermoplastic film 35 from supply roll 36 is then introduced on top of spaced pads 33.
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Film strip 35 should be at least as wide as pads 33, but preferably is wider so that it may be wrapped around the pad edges'as indicated.
After film 35 is introduced and wrapped around the pad edges, web 31 is wrapped over the pad and film layer and overlapped to provide a continuous sausage of intermittently spaced pads.
If the use of pressure-sensitive adhesive for garment attachmen,t use is desired, one or more strips of hot melt pressure-sensitive adhesive are extruded onto the back surface of the continuous sausage by extruder 37 and covered by a continuous strip of release paper 38 or the like.
In a preferred method the pressure-sensitive adhesive is first extruded onto the strip of release paper and then pressed into contact with the wrapped pads.
The sausage now passes through an ultrasonic sealing nip where an ultrasonic horn such as the type provided by Branson Sonic Power Company of Danbury, Connecticut cooperates with a rotating anvil roll 40 having an anvil means 41 of predetermined shape for transversely fusing a selected area of the folded wrapper and film layers into a narrow band-like pattern. FIG. 4 shows an enlarged partial view of an anvil design 41 suitable for forming the fused curved band in the pre-, ferred FIG. 2 napkin embodiment.
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The sausage then travels through a cuttingnip where a pinch cut roll 42 of predetermined contour cooperates with roll 43 to sever the continuous sausage into individual pads. The cu~ is made to provide free ends in the wrapper and film laminate adjacent and parallel to the narrow fused band as shown in FIGS.
1 and 2.
The individual pads then are conveyed into an embossing section where a heated embossing roll 45 provided with spaced nipples 46 provide one surface of the napkin and the underlying pad with heat-set, spaced, dimple-like embossments. The finished napkin is then transferred to stacking and packing e~uipment.
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