US3672371A

US3672371A - Sanitary napkin with improved adhesive fastening means

Info

Publication number: US3672371A
Application number: US35753A
Authority: US
Inventors: Robert J Roeder
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1970-05-08
Filing date: 1970-05-08
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27
Also published as: ZA712969B

Abstract

A sanitary napkin provided with improved pressure sensitive adhesive means for attaching the napkin to a supporting garment. The adhesive is applied to the bottom surface of the napkin and comprises at least two narrow parallel lines covered by a single overlying protective release sheet. Each strip has substantially less width and total surface area when compared with the width and area of adhesive strips or patches formerly used for attachment purposes. A typical adhesive pattern applied to an 8 X 2 5/8 in. napkin comprises a pair of centrally disposed parallel strips, each strip being approximately 6 in. long and one-eighth in. wide, and spaced about three-eighth in. from each other. The two strip pattern uses less adhesive, yet is more effective in preventing displacement of the napkin and in counteracting the shear forces exerted on the napkin by normal leg motion. The arrangement prevents failure of the wrapper when the protective sheet is removed by the user. It also reduces considerably the incidence of adhesive transfer to the garment at the time when the napkin is removed from the garment for disposal.

Description

United States Patent Roeder [451 June 27,1972

[54] SANITARY NAPKIN WITH IMPROVED ADHESIVE FASTENING MEANS [72] Inventor: Robert J. Roeder, Appleton, Wis.

Primary Examiner-Charles F. Rosenbaum Attorney-Daniel J. Hanlon, Jr. and Raymond J. Miller [57] ABSTRACT A sanitary napkin provided with improved pressure sensitive adhesive means for attaching the napkin to a supporting gar ment. The adhesive is applied to the bottom surface of the napkin and comprises at least two narrow parallel lines covered by a single overlying protective release sheet. Each strip has substantially less width and total surface area when compared with the width and area of adhesive strips or patches formerly used for attachment purposes. A typical adhesive pattern applied to an 8 X 2% in. napkin comprises a pair of centrally disposed parallel strips, each strip being approximately 6 in. long and one-eighth in. wide, and spaced about three-eighth in. from each other. The two strip pattern uses less adhesive, yet is more effective in preventing displacement of the napkin and in counteracting the shear forces exerted on the napkin by normal leg motion. The arrangement prevents failure of the wrapper when the protective sheet is removed by the user. It also reduces considerably the incidence of adhesive transfer to the garment at the time when the napkin is removed from the garment for disposal.

5 Claims, 8 Drawing Figures PATENTEDJUNN 1972 FIG.3

PATEEFJEQJUHZY 1972 3, 672 371 SHEET 2 OF 2 FIG.40

' F|G.6 (PRIOR ART) 1. SANITARY NAPKIN WITH IMPROVED ADHESIVE FASTENING MEANS BACKGROUND OF THE INVENTION 7 A number of sanitary napkins recently introduced into the market place employ a pressure sensitive adhesive means to attach the napkin to a to the more common prior art napkin which is constructed with wrapper extensions, called end tabs, by which the napkin is suspended from a body-encircling belt or the like. While commercial versions of adhesively-attached napkins are relativelynew, theprior art contains a number of patents describing' various embodiments of such products. Representative specifications include U.S. Pat. Nos. 2,295,016; 2,838,048; 3,044,467; 3,454,008; 3,463,154; and Swiss Pat. Nos. 295,532; 296, 828; and 306,502. In each of these patents the attachment means usually comprises one or several strips or patches of pressure sensitive adhesive disposed in various locations on the bottom surface of the napkin. These adhesive strips have substantial length and width dimensions which provide relatively large surface area for attachment purposes. For example, if the adhesive comprises alongitudinally extending strip centrally disposed on the bottom surface of the napkin, the strip is from 2% to 6 in. long, and may even extend the full length of the napkin, with widths of from about If; to in. If the adhesive means comprises multiple patches, such patches are from about 1 to 1% in. long by to as in. wide, and may be located near the ends and/or sides of the napkin or. both. While inmost cases, the size, arrangement and disposition of these adhesive strips serve to fasten the napkin to a supporting garment satisfactorily when the napkin is initially applied to the garment, each of the structures proposed in the art suffer from certain disadvantages which dictate against ready acceptance by the potential user.

Among these disadvantages the following are the most critical:

l. Shifting of the napkin from its original position on the supporting garment during use. This is attributed to periodic release and reattachment of the adhesive as shear forces are exerted on the pad and garment during normal body movement. v

2. Tearing of the napkin wrapper (a) when the protective strip is moved, (b) while the napkin is being worn, and when the napkin is removed for disposal or replacement.

3. A tendency for adhesive to be stripped fromthe pad (a) by remaining on the protective strip when it is removed prior to attachment and (b) by transfer to the supporting garment when the napkin is removed therefrom. v

4. The need to use relatively large amounts of expensive adhesive, or of still more expensive two-sided tape.

Accordingly, it is the primary object of this invention to provide a sanitary napkin with improved pressure sensitive adhesive attachment means which substantially eliminates the above problems.

SUMMARY OF THE INVENTION The sanitary napkin to which the improved adhesive fastening arrangement of this invention is applied may comprise the usual elongate pad of highly absorbent material enclosed in an outer wrapper of light-weight fluid pervious material. The wrapper is usually a rectangular sheet enveloping the pad and overlapped on the bottom side thereof. The pressure sensitive adhesive which is applied to the bottom side of the napkin comprises at least two narrow parallel lines of adhesive extending longitudinally of the napkin, and centrally disposed with respect to the sides and ends thereof. The individual lines of adhesive may be from about 4 to 8 in. long depending upon the size of the napkin, from about 1/1 6 to A in. wide, and are spaced from about A to in. from each other. A single sheet of protective release paper serves to cover the adhesive lines prior to use. The adhesive lines may be applied directly to the bottom surface of the napkin by printing or extrusion, being subsequently covered by the protective release sheet, or the supporting garment. This is in contrastadhesive lines may be first applied to the release sheet, with the combination then applied to the napkin.

It was found that with the above arrangement less adhesive is required to secure attachment, when compared to prior structures, yet the napkin is held in place on the supporting garment more securely. Apparently, when the adhesive comprises sets of narrow parallel lines rather than wide strips or patches, it provides a better distribution of the forces and stresses which act on the wrapper and adhesive over the length of the pad during use. In addition, while this new arrangement holds the napkin in place more securely, it was also found that the napkin could be stripped from the garment more easily at removal time, leaving substantially no adhesive residue on the garment.

Continuous lines of adhesive are preferred because they are easier to apply. However, broken or interrupted lines may also be employed.

The invention may be used in conjunction with most sanitary napkin constructions, but is especially useful with the recently developed flushable napkins in which an inherently weak wrapper is used to enclose the absorbent pad.

BRIEF DESCRIPTION OF THE DRAWINGS perspective bottom views of prior art DESCRIPTION OF THE PREFERRED EMBODIMENT In a preferred embodiment of the invention as shown in FIG. 1, the bottom side 11 of a sanitary napkin 13, comprising an absorbent pad enclosed in a fluid pervious wrapper overlapped at 12 and 120, has applied thereto parallel lines of pressure

sensitive adhesive

15 and 16 covered by a removable protective cover sheet 17, shown partially peeled back. In this particular embodiment, the napkin is approximately 8 in. long by 2% in. wide and in. thick. Each of the partial strips of

adhesive

15 and 16 are approximately 6 in. long and A; in. wide, and are spaced about $6 in. from each other.

.FIG. 2 shows a similar embodiment with release sheet 17 partially broken away. Adhesive lines and 16a are interrupted lines rather than being continuous as in FIG. 1. The individual adhesive segments comprising the

adhesive lines

15a and 16a are spaced about $4; in. apart, and are about I in. long by M; in. wide, extending along a substantial portion of the napkin length. FIG. 3 illustrates how a napkin of either embodiment may be positioned in a panty brief 19.

FIG. 4 shows one prior art embodiment of a napkin having pressure sensitive adhesive fastening means. In this embodiment, the pressure sensitive adhesive 21 comprises a 3% X W. in. strip centrally disposed on the back side of the napkin and covered by removable protective cover sheet 23.

The effective adhesive area of this prior art embodiment (3% X in.) is about 2% in. square inches, while the effective adhesive area of the arrangement comprising two narrow adhesive lines (6 in. X A in. X 2) is about l square inches.

Each of these napkins was fastened to a piece of fabric representing the crotch piece of a panty undergarment and torque applied to the ends to simulate normal leg motion. Even through the effective attachment area of the two strip arrangement was less than that of the one strip arrangement, it was found to offer more resistance to the shear stress resulting from the applied twisting forces than did the FIG. 4 arrangement. Thus, it became apparent that the two strip arrangement is more apt to prevent napkin displacement which might be caused by body movement during use. Subjective tests further confirmed this theory.

A solid strip of adhesive /5 in. wide and 6 in. long was also tested as an alternate attachment means and, as expected, was found to provide better resistance to torque than the FIG. 4 prior art arrangement. While this longer strip gave improved resistance to torque, it is obviously more expensive to use, and had other disadvantages discussed more fully below.

FIG. 5 shows another prior art embodiment in which two patches of adhesive and 26 covered by

protective release sheets

27 and 28 respectively are located near the opposite ends ofa napkin.

FIG. 6 shows still another prior art embodiment in which four patches of adhesive are used, two

patches

31 and 32 are disposed along each edge of the napkin and another two

patches

33 and 34 are disposed at the opposing ends of the napkin.

The FIG. 5 arrangement provided good attachment to the supporting garment when first applied. However, it was found that when the undergarment to which it was attached stretched during normal use, one end or the other, or both, of the napkin became detached from the garment as the result of such stretching, and when it was reaffixed by body pressures, tended to be displaced sideways out of its proper position, and on occasion even became completely displaced.

In the FIG. 6 arrangement which utilizes multiple patches at both sides and ends, there was less tendency for the napkin to be displaced by intermittent detaching action which occurs. However, it was found that

strips

31 and 32, by virtue of their close approximation to the edges of the napkin, often become wetted by body exudates and moisture whereby the tackiness of the adhesive was neutralized and rendered less effective, resulting in the aforesaid undesirable displacement. In addition the large number of adhesive areas required are difficult to apply and properly space on a mass production basis and obviously increase material costs.

In each of the prior art arrangements, the large areas of adhesive employed were themselves the source of problems. In some cases when the protective strip was removed, the stripping or peel force required, which is a function of width, was so large, that the adhesive tended to tear itself loose from the napkin fabric, rendering the napkin useless for its intended purpose.

In other cases, the attachment of the adhesive to the release paper was so strong that the wrapper fabric tore while the release paper was being peeled off. This too rendered the napkin useless.

The force required to remove the protective sheet from a pressure sensitive adhesive mass may be measured by a method devised by the Pressure Sensitive Tape Council in its publication entitled Test Methods for Pressure Sensitive Tapes." The method is identified as l80 Peel Adhesion" Call Letters PSTC-l, first issued in Sept, 1955 and revised in May, 1966.

Peel adhesion is defined as the force required to remove a pressure sensitive tape from a panel or its own backing at a specified angle and speed. The tape, or other adhesive carrying sheet stock, is applied to a standard test panel (stainless steel) using the defined pressure to make contact. The peel force is measured in kilograms with an Instron Tensile Tester.

Using this test, a pattern comprising two lines of adhesive 6 in. long by A; in. wide spaced $6 in. apart registered 0.17 kg of peel force, while a solid block pattern 3 in. long by in. wide registered 0.74 kg ofpeel force.

While the difference in total adhesive area for the two adhesive patterns tested made the above results predictable, the fact that the greatly reduced peel force of the two line pattern gave a better performing attachment means when applied to a napkin was totally unexpected.

In a large number of cases, when prior art napkins were successfully attached to garments another problem was found during subsequent removal. As the napkins were stripped Adhesive Transfer% of Pads Tested Complete Partial No Adhesive Pattern Transfer Transfer Transfer 3%" X block 63.7% 3l.4% 4.9% l.6% 12% 86.4%

6' X Mi" strips The dual narrow strip pattern is clearly superior in this respect.

In still further comparisons, when the protective cover sheets were stripped from the adhesive it was found that with the two line pattern, the sheets stripped off cleanly while on some of the others the adhesive itself stripped from the pad rendering those particular pads useless.

Thus it can be seen that the new arrangement of adhesive provides the user with more assurance that the adhesive will remain attached to the napkin when the protective cover sheet is removed; provides a napkin attachment means which has a greater ability to resist torque or shear forces; and provides attachment means which reduces transfer of adhesive to the supporting garment when the napkin is removed.

The slightly modified FIG. 2 example shows an adhesive pattern which also provides improved results. In this example

adhesive strips

15a and 16a comprise parallel segmented A; in. wide lines of a total length similar to the FIG. 1 arrangement, with spaces between segments about /4 in. and the individual segments being about I in. long. This broken line adhesive pattern performed substantially the same as the continuous lines of FIG. 1 except that it permitted the napkin wrapper to stretch and conform more closely with the stretch of the supporting garment.

While the improved adhesive pattern is useful which all types of napkin wrappers, it is especially advantageous when used with recently introduced napkins having flushable wrappers. In these napkins, the wrapper comprises a light-weight nonwoven fiber web bonded by a water soluble binder. In order to obtain in the wrapper the desired properties of fluid permeability when worn, as well as rapid dispersibility when the pad is dropped in the excess water of a toilet system for disposal, it is necessary to limit the overall amount of watersoluble binder which is used to give the non-woven fiber structure integrity. This results in a wrapper of much less strength than the nonflushable type wrappers in common use. Accordingly when napkins using such flushable wrappers are attached with pressure sensitive adhesive, supplemental strengthening as provided by the adhesive arrangement of this invention contributes to satisfactory performance.

While the two narrow strips reduce the total area of contact between napkin and garment, they provide larger perimeters of effective contact with the wrapper fabric, especially in the lengthwise direction, and thus provide at least double the resistance to edge tearing as compared to a wide single strip. At the same time the peel force necessary to strip the protective cover from the adhesive, or the napkin from the undergarment, is effectively reduced because of the narrow widths. Accordingly when either of these two operations are performed the chances for tearing a weak wrapper and/or causing adhesive transfer to the supporting garment are considerably reduced.

Another advantage arises from the method of applying the adhesive and this may be further illustrated by reference to FIG. 1a. The narrow

adhesive strips

15 and 16 are preferably applied directly to the wrapper fabric by extrusion, printing or hot melt techniques, and the release sheet 17 pressed in place over the strips. When this is done, the adhesive penetrates through at least both layers of 12 and 12a of the wrapper overlap and in effect doubles the potential tear strength.

Still further penetration is obtained if the release sheet is pressed in place over the adhesive with a hot calendering roll using a method similar to that disclosed in my copending application, Ser. No. 35,903, filed May 8, 1970. As described therein, pressure is applied to the back side of the release sheet while in place on the napkin at a temperature of about 325 F. for about 2 seconds. This causes the adhesive to penetrate not only layers 12 and 120 but also causes it to become attached to an area of absorbent pad 14 adjacent layer 12a. This penetration occurs without causing the pressure sensitive adhesive to lose any significant adhesive power when later attached to garments. In addition it was found that protective sheet 17 is more easily removable after such processing.

Comparison of this cross sectional structure should be made with the prior art structure as shown in FIG. 4a where the pressure sensitive adhesive 21 does not penetrate to any extent into the adjacent wrapper area and in effect is only an interfacial attachment between adhesive and wrapper.

Other advantages of the multiple narrow strip arrangements also may be found. As indicated above, crotch sections of the usual undergarments stretch and contract constantly when worn. A strong solid patch of adhesive does not conform to this dynamic stretching but is constantly torn loose and repositioned. Each time the adhesive attachment is broken, the napkin' in response to body movements must reattach itself properly. When this detaching-reattaching occurs repeatedly the napkin is often displaced and there is a danger that it may be lost. The narrow strips of adhesive of this invention are of such small mass that they permit some stretching and contracting of the attached areas of the wrapper with the garment and thus remain more securely in place. The portions which remain attached while other portions are detached also prevent the napkin from shifting. The increase in length which the lesser amount of adhesive permits from a cost standpoint also provides a larger contact perimeter between adhesive and wrapper fabric so that more points of the adhesive continually act as support areas.

It has also been found essential that the multiple narrow lines of adhesive be disposed near the longitudinal center of the pads. If disposed near the edges, or arranged in discrete patches at the ends and edges the napkins do not remain as securely in place as with a centrally disposed pattern. While no clear explanation can be found for this phenomenon, it has been observed as factual. Qne explanation suggested with respect to edge placement of adhesive, as noted earlier, is that body moisture often intervenes between adhesive and supporting garment during use to reduce the tackiness of the adhesive sufficiently to render it useless for its intended purpose.

While the specific examples given above show the preferred embodiments of the invention as comprising two narrow lines of adhesive, it will be seen that three or four lines can be used with equal effectiveness.

The adhesive used may comprise any of the large number presently available on the market. Such pressure sensitive adhesives are normally based on an elastomer selected from natural or synthetic rubbers, e.g. pale crepe rubber, smoked sheets, reclaimed rubber, Buna-S and Buna-N type rubbers, polyisoprene, polyisobutylene; and synthetic elastomers such as polyvinyl ethers, polyacrylates or the like. The adhesive mass may be especially compounded or inter-polymerized to provide the balance of adhesiveness characteristic of pressure sensitive adhesives in general. Any of the conventional tackifiers such as rosin, dehydrogenated and hydrogenated rosin, polyterpenes, coumarone-indene resins, polyalkyl styrene and the like may be used in proportions well known in the art. Other ingredients, fillers, antioxidants and pigments may also be included in the adhesive mass if desired.

What is claimed is:

1. In an elongate sanitary napkin structure provided with means for attaching said napkin to a supporting garment in which said means comprises pressure sensitive adhesive disposed on the bottom surface of said napkin comprises a pad of absorbent material enclosed in a fluid pervious non-woven wrapper comprising a substantially rectangular sheet enveloping said pad and overlapped on the bottom side thereof, the improvement wherein said adhesive comprises at least two narrow lines of adhesive parallely spaced from each other and extending longitudinally of said bottom surface, said spaced lines being centrally disposed thereon with respect to the sides and ends thereof, and said lines of adhesive penetrate both of said overlapped portions of said wrapper.

2. The improved napkin structure of claim 1 in which said lines of adhesive are from about 1/16 to V4 in. wide and are spaced from about $41 to about in. from each other.

3. The improved napkin structure of claim 1 in which said adhesive also penetrates partially into said pad.

4. The improved napkin structure of claim 1 in which said adhesive lines are divided into spaced elongate segments.

5. The improved napkin structure of claim 4 in which said adhesive also penetrates partially into said pad.

Claims

2. The improved napkin structure of claim 1 in which said lines of adhesive are from about 1/16 to 1/4 in. wide and are spaced from about 1/4 to about 3/4 in. from each other.