Absorbent pad and method for making same

Abstract

An elongate, disposable absorbent pad having an elongate, absorbent, fluff batt of cellulosic fibers enclosed within a fibrous envelope having a fluid pervious facing layer and a backing layer. The fibrous envelope has end margins which extend beyond end margins of the fluff batt, and the end margins of the fibrous envelope are closed by transverse end seal bands having seal rows with opposed surfaces defined by transversely adjacent ridges and valleys interconnected by lateral walls. The lateral walls of the seal rows are compressed to define seal regions characterized by interlocked fibers of the envelope; said seal regions, in the plane of the absorbent pad, extending in the direction of elongation of the absorbent pad. The method for continuously manufacturing elongate, disposable absorbent pads having end margins which are closed by transverse end seal bands as described above forms a part of the present invention.

Parent Case Text

RELATED APPLICATIONS

This application is a division of U.S. Pat. application Ser. No. 137,839, filed Apr. 27, 1971, now abandoned, entitled ABSORBENT PAD AND METHOD FOR MAKING SAME.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an elongate, disposable absorbent pad, and to the method for manufacturing such pad. More specifically, this invention relates to an elongate, disposable absorbent pad having unique transverse end seal bands, and to a continuous method for manufacturing such absorbent pads.

2. Description of the Prior Art

Continuous methods for forming disposable absorbent pads are known in the prior art. The absorbent pads formed by such continuous methods are used in absorbent products such as sanitary napkins, disposable diapers and the like. One specific use for such disposable absorbent pads is in a two-piece diaper system which comprises, in addition to an absorbent pad, a fluid impermeable retaining garment. The retaining garment is adapted to be fastened about an infant with the absorbent pad fastened to said garment and positioned within the perineal region of the infant.

An absorbent pad for use in a two-piece diaper system is presently manufactured by Scott Paper Company and is sold under its trademark babyScott. This absorbent pad is comprised of a fluff batt of cellulosic fibers enclosed within a fibrous envelope having a fluid pervious facing layer which is adapted to face the infant during use of the diaper system. The fibrous envelope has end margins which extend beyond end margins of the fluff batt, and the end margins of the fibrous envelope are closed by transverse end seal bands which retain the fibers of the fluff batt within the confines of the absorbent pad during use.

In a continuous process for forming absorbent pads, such as the absorbent pads described in the preceding paragraph, individual fluff batts are spaced from each other in the direction in which they are fed through sequential pad forming operations. A continuous composite structure is formed by disposing the spaced, fluff batts between continuous fibrous webs which define a continuous fibrous envelope for such spaced fluff batts. The webs of the continuous fibrous envelope are closed by transverse seal bands intermediate adjacent fluff batts, and the elongate, disposable absorbent pads are formed from the above-described continuous composite structure by transversely severing said composite structure along a substantially transverse medial line of each transverse seal band. In forming the discrete absorbent pads, the continuous composite structure is maintained under constant tension in its direction of feed through the above-described sequential pad forming operations to prevent undesirable sideways movement, or tracking of said composite structure.

The prior art transverse seal bands which close the webs of the continuous fibrous envelope in regions intermediate adjacent fluff batts; and accordingly, the prior art transverse end seal bands closing opposite ends of discrete, absorbent pads, are defined by a plurality of transversely spaced seal rows, each of which extends in the direction of elongation of the continuous composite structure. Each of the opposed surfaces of the fibrous envelope in each seal row is defined by adjacent ridges and valleys interconnected by lateral walls. The lateral walls have seal regions therein characterized by interlocked fibers of the webs of the fibrous envelope. These seal regions, in the plane of the continuous composite structure, extend transversely to the elongate direction of said composite structure, i.e., transversely to the direction of the tension forces applied to the continuous composite structure during the sequential pad forming operations.

The application of tension to the continuous composite structure resulted, in many instances, in an opening of the webs of the continuous fibrous envelope within the confines of the prior art transverse seal bands to thereby destroy the sealing effect of such bands in the completed, disposable absorbent pads. Large compressive forces applied to the continuous fibrous envelope formed sufficient fiber interlock in the seal regions of the prior art transverse seal bands to prevent the opening of said seal bands. Unfortunately, these large compressive forces required to prevent the webs from opening in the transverse seal bands created a thinning and weakening of said transverse seal band in the seal regions, and in some instances, the webs actually tore in said seal regions. This weakening and/or tearing of the seal regions resulted, in many instances, in a separation of discrete sections from the continuous composite structure at the transverse seal bands prior to the completion of the pad forming operations. This separation was caused by the tension forces applied to the continuous composite structure to prevent undesirable sideways movement of said composite structure. The separation of discrete sections from the continuous composite structure required machine down time to reposition the continuous composite structure for proper feed through the sequential pad forming operations.

SUMMARY OF THE INVENTION

Applicant recognized that the problem of separation of discrete sections from the continuous composite structure prior to the completion of the pad forming operations could be alleviated by changing the orientation of the weakened seal regions, in the plane of the continuous composite structure (which is the same as the plane of the discrete absorbent pads formed from the composite structure). Specifically, applicant discovered that the weakened seal regions in the prior art transverse seal bands had a considerable dimension transverse to the elongate direction of said composite structure, i.e., transverse to the direction of the tension forces, and that this considerable dimension of the weakened seal regions was responsible for the separation of discrete sections from the continuous composite structure under the tension forces applied normal to said transverse direction.

The elongate, disposable absorbent pad of this invention comprises an elongate, absorbent fluff batt of cellulosic fibers disposed within a fibrous envelope which has end margins extending beyond end margins of the fluff batt, said end margins of the fibrous envelope being closed by unique transverse end seal bands. Each transverse end seal band is defined by at least one transversely extending seal row comprising transversely adjacent ridges and valleys interconnected by lateral walls. The lateral walls have seal regions therein characterized by interlocked fibers of the fibrous envelope, and these seal regions, in the plane of the elongate, disposable absorbent pad, extend in the direction of elongation of said absorbent pad, i.e., parallel to the direction of application of the tension forces. Therefore, the dimension of the seal regions taken transverse to the direction of the tension forces, and therefore transverse to the elongate direction of the absorbent pad, is relatively small and is actually equal to the thickness of the fibrous envelope in the seal regions.

This invention also relates to the continuous method for forming the above-described elongate, disposable absorbent pad having unique transverse end seals. More specifically, this invention relates to a unique method for forming transverse seal bands in a continuous composite structure which comprises a plurality of elongate, absorbent fluff batts spaced from each other in their direction of elongation and disposed within a continuous fibrous envelope. The continuous fibrous envelope is closed by the unique method of this invention for forming transverse seal bands in the region of the fibrous envelope disposed between adjacent, elongate fluff batts. The transverse seal bands are formed by passing the continuous composite structure through the nip defined between upper and lower sealing dies which are mounted for rotation about axes which are substantially transverse to the direction of feed of the continuous composite structure. The upper sealing die has a row of axially spaced projections defining depressions therebetween, and the lower sealing die has a row of axially spaced projections defining depressions therebetween. The row of projections of one sealing die are axially offset from the row of projections of the other sealing die such that the projections on each sealing die mesh with the depressions on the other sealing die. This meshing of projections and depressions, as the continuous fibrous envelope passes through the nip of said sealing dies, results in the closing of the fibrous envelope by a transverse seal band defined by a transversely extending seal row of alternate ridges and valleys interconnected by lateral walls. The axial space between side walls of each lower projection and the side walls of its adjacent upper projections is less than the thickness of the fibrous envelope passing through the nip of said sealing dies; therefore, the fibrous envelope is transversely compressed between the side walls of adjacent upper and lower projections to form the thin seal regions characterized by interlocked fibers of the continuous fibrous envelope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an elongate, disposable absorbent pad of this invention showing details of its forward surface, and having parts broken away to show internal details of construction;

FIG. 2 is an isometric view of the absorbent pad shown in FIG. 1 showing details of the back surface;

FIG. 3 is a plan view of an absorbent pad of this invention in folded condition;

FIG. 4 is a schematic view, in side elevation, showing a continuous method for manufacturing the absorbent pad shown in FIG. 3;

FIG. 5 is an enlarged plan view showing a portion of a prior art transverse end seal band;

FIG. 6 is a sectional view taken along line 6--6 of FIG. 5;

FIG. 7 is a side elevation view of end sealing dies utilized to form the prior art transverse end seal bands;

FIG. 8 is an enlarged plan view of the blocked portion 8 of FIG. 3 showing a portion of a transverse end seal band of this invention;

FIG. 9 is a sectional view taken along line 9--9 of FIG. 8;

FIG. 10 is an exploded isometric view showing a portion of the end sealing dies utilized to form the transverse end seal bands of this invention;

FIG. 11 is a transverse sectional view taken along line 11--11 of FIG. 10 with the dies in position to form an end seal; and

FIG. 12 is a sectional view taken along line 12--12 of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THIS INVENTION

This invention relates to an elongate, disposable absorbent pad 10 having unique transverse end seal bands 12, 14; and to the method for manufacturing such pads. The elongate, disposable absorbent pad 10 of this invention is shown in FIGS. 1-3, and has an elongate, fluff batt 16 of cellulosic fibers, such as short paper-making fibers, disposed within a fibrous envelope 18. The fibrous envelope 18 has forward and rearward end margins 20, 22, respectively, which extend beyond end margins of the fluff batt 16, and which are closed by the transverse end seal bands 12, 14, respectively.

In the preferred embodiment of this invention, the fibrous envelope 18 is defined by fluff batt supporting webs comprising upper and lower layers of creped paper wadding 24 and 26; an elongate, backing cover web 28 of a suitable wet strength paper stock; and an elongate, fluid pervious, facing cover web 30 of nonwoven, adhesively bonded fibers. Preferably, the facing cover web 30 is an adhesively bonded, hydrophobic, carded rayon web. The upper and lower layers of creped paper wadding 24 and 26 are disposed in contact with opposite surfaces of the elongate, fluff batt 16 to support said fluff batt during the formation of the absorbent pad 10, and also during use of said absorbent pad. The number of plies of creped paper wadding which is utilized in each of the upper and lower layers can be varied within wide limits. In practice, two plies of creped paper wadding in each of the upper and lower layers has proved satisfactory to support the fluff batt 16. The elongate, backing cover web 28 is disposed adjacent the lower layer 16 of creped paper wadding and has greater wet strength than the layers of creped paper wadding to aid in maintaining the structural integrity of the absorbent pad 10 during use. The fluid pervious, elongate, facing cover web 30 extends over the upper layer 24 of creped paper wadding and has side margins 32, 34 extending around the back side of the pad 10 and secured to the backing cover web 28 by elongate securing stripes 36 of glue, adhesive, or the like (FIG. 2). The facing cover web 30 has a high wet strength to aid in maintaining the structural integrity of the absorbent pad 10 during use, and also is permeable to body fluids to permit passage of such fluids into the fluff batt 16 which has a high absorptive capacity, i.e., ability to retain large quantities of fluid without leaking. The backing cover web 28 has a lower toughness (energy absorbing capacity) than the facing cover web 30. Therefore, the backing cover web 28 will tear and leave the facing cover web 30 intact when the energy applied to the fibrous envelope during use of the absorbent pad 10 exceeds the energy absorbing levels of the backing cover web 28. Since the facing cover web 30 is in contact with the child during use of the absorbent pad 10, it is desirable to maintain the integrity of said facing cover web to prevent inner components of the pad, such as the fluff batt 16, from coming into contact with, and sticking to the child's skin. The use of a backing cover web having a lower toughness than the facing cover web accomplishes this objective.

Side regions of the absorbent pad 10 are infolded along elongate, fold lines 38, 40 to form side panels 42, 44 which are in overlying relationship with the elongate, facing cover web 30 in center region 46 of said pad (FIG. 3). The elongate, backing cover web 28 terminates in elongate side margins (not shown) disposed adjacent the fold lines 38, 40 so that the backing cover web 28 is not included in the side panels. The pad construction wherein the backing cover web 28 is omitted from the side panels is the invention of Richard W. Schutte and will be covered in a subsequently filed patent application.

The side panels 42, 44 are retained in their infolded position by suitable securing means, such as securing dots, or tacks 48, 49, of adhesive, glue, or the like (FIG. 3). The securing tacks 48, 49 are disposed between the center region 46 of the absorbent pad 10 and the side panels 42, 44, respectively, adjacent the forward end margin 20 of said absorbent pad 10.

Fibrous envelopes other than the one described in the preceding paragraph can be utilized in the absorbent pads 10 of this invention. Fibrous envelopes utilized in the absorbent pads 10 of this invention must have sufficient wet strength to assure that the structural integrity of the absorbent pads is not unduly impaired during use. Also the fibrous envelopes must have a fluid pervious facing layer to assure that body fluids impinged on said facing layer pass through it for retention in the fluff batt 16. Reference to a "fibrous envelope" in the specification and claims of this application is intended to include all fibrous envelopes meeting the above criteria, and is not intended to be limited to any specific number or types of webs unless there is clear indication to the contrary.

The folded, elongate, disposable absorbent pad 10 shown in FIG. 3 is specifically adapted for use as an absorbent component in a two-piece diaper system such as is disclosed in U.S. Pat. application Ser. No. 101,292, filed Dec. 24, 1970 now U.S. Pat. No. 3,693,621, and assigned to the same assignee as this application. The two-piece diaper system comprises, in addition to the absorbent pad 10, a fluid impermeable retaining garment which is adapted to be fastened about an infant with the absorbent pad 10 positioned within the perineal region of the infant. The absorbent pad 10 can be held in the retaining garment by any suitable means, but preferably the absorbent pad 10 is held in position within the retaining garment by the unique holding device disclosed in the above-mentioned application Ser. No. 101,292. This holding device is fastened to the forward margin of the retaining garment and has a rearwardly extending member terminating in a cross member. The cross member is positioned rearwardly of securing tacks 48, 49, between the center region 46 and the side panels 42, 44 of the absorbent pad 10. In use the rear section of the absorbent pad 10 can be flared out as shown in FIG. 3 to provide sufficient area for containing fecal matter. The forward portion of the absorbent pad 10 has a substantial amount of absorbent material to retain urine by virtue of the folded arrangement of said absorbent pad. The fluid impervious retaining garment, and the holding device for holding the absorbent pad 10 within the retaining garment do not form a part of the present invention and have been described to indicate the reason for providing tacked side panels 42, 44 as shown in FIG. 3, and to indicate one specific environment in which absorbent pads 10 of this invention are useable.

A continuous process for manufacturing the elongate, disposable absorbent pad 10 shown in FIG. 3 is schematically represented in FIG. 4. The continuous elements utilized in this process which correspond to the discrete elements of the elongate, disposable absorbent pad 10 will be described by the same numerals as said discrete elements but with a prime (') suffix thereafter. A continuous, loosely matted fluff batt 16' of cellulosic fibers is formed by any suitable batt forming apparatus 50, such as as Joa Fiberizer, Hammermill, etc. The continuous fluff batt 16' is fed by a batt feed conveyor 52 to a severing station 54. The severing station 54 comprises a driven knife carrier roll 56 with a knife 58 mounted therein. The knife 58 cooperates with a backing roll 60 to sever the continuous fluff batt 16' at spaced intervals into discrete, individual fluff batts 16. These individual fluff batts 16 are directed onto a batt spacing conveyor 62 which is operated at a faster linear speed than the batt feed conveyor 52 to space apart the discrete fluff batts 16. The discrete fluff batts 16 are sandwiched, or disposed between fluff batt supporting webs comprising continuous layers of creped paper wadding 24', 26' concurrently with the transfer of the discrete fluff batts 16 onto the batt spacing conveyor 62. A continuous backing cover web 28' of a suitable wet strength paper stock is superimposed on the continuous layer 26' of creped paper wadding, and a continuous adhesively bonded, carded rayon facing cover web 30' is disposed adjacent the continuous layer of creped paper wadding 24' as said continuous layer of creped paper wadding 24' passes onto a feed conveyor 64. The continuous composite structure formed thus far is directed past a folding station schematically shown at 66 at which side margins of the continuous facing cover member 30' are folded around the side margins of the discrete fluff batts 16 into overlying relationship with the continuous backing cover web 28'. As the continuous backing cover web 28' enters the folding station 66 it passes under a pair of stationary, transversely spaced, extruders 68 (only one of which is shown in FIG. 4) which apply continuous securing stripes of glue, adhesive, or the like, in transversely spaced elongate lines to the continuous backing cover web 28'. The side margins of the continuous facing cover member 30' are folded into overlying relationship with the continuous securing stripes to firmly secure the continuous facing cover web 30' to the continuous backing cover web 28', whereby a continuous composite structure is formed which comprises a continuous fibrous envelope 18' disposed about the spaced, discrete fluff batts 16. The continuous composite structure is then fed past a sealing station 70 comprising opposed upper and lower driven sealing die carrier rolls 72, 74, respectively, into which are secured upper and lower sealing dies 76, 78, respectively. The continuous fibrous envelope 18' is compressed by the sealing dies 76, 78, intermediate fluff batts 16 to form transverse seal bands 80 intermediate adjacent discrete fluff batts 16. The continuous composite structure is then fed past a second folding station, schematically shown at 82 at which continuous side margins of the continuous composite structure are infolded to form continuous side panels. Prior to the completion of the side panel forming operation a pair of transversely spaced securing tacks of glue, adhesive, or the like, are provided through a pair of extruders 84 (only one of which is shown in FIG. 4). The extruders 84 are operated to apply the transversely spaced securing tacks to the continuous cover web 30' at longitudinally spaced intervals to position the tacks in the completed absorbent pad 10 as indicated at 48, 49 in FIG. 3. The folded, continuous side panels will overlie the transversely spaced securing tacks and will be firmly adhered to the continuous facing cover web 30' by said securing tacks. The composite structure is then severed at a pad separating station 86 to form the elongate, disposable absorbent pads 10 shown in FIG. 3. The pad separating station 86 comprises a driven knife carrying roll 88 into which a knife 90 is fixed. The knife 90 cooperates with an anvil 100 mounted within a driven anvil carrying roll 102. The knife is synchronized to sever the composite structure along a transversely extending medial line of each transverse seal band 80 to form the forward transverse end seal band 12 and the rearward transverse end seal band 14, respectively, of the elongate, disposable absorbent pad 10.

A driven belt assembly 106 comprising opposed driven belts 108, 110, is disposed between the folding station 82 and the pad separating station 86 and is driven at a speed for maintaining a constant tension on the continuous fibrous envelope 18' in the direction of feed of said continuous composite structure. This tension is required to prevent unwanted transverse movement or "tracking" of the continuous composite structure as it is fed through the sequential pad forming operations. Transverse movement of the continuous composite structure could result in the placement of the continuous securing stripes on the continuous backing cover web 28' in regions which do not align with the folded side margins of the continuous cover web 30'. In such a situation the facing cover web 30 would not be retained to the backing cover web 28 in the completed absorbent pad 10. Additionally, unwanted transverse movement could result in the positioning of the securing tacks onto the continuous facing cover web 30' outside of the region which the side panels overlie to thereby prevent engagement of the side panels with such securing tacks in the absorbent pads 10. The improper location of the securing stripes and tacks results in the formation of unacceptable absorbent pads 10; and therefore, should be avoided.

The sequence of operations described with reference to FIG. 4 is the same for forming both the prior art disposable absorbent pads; and the elongate, disposable absorbent pads 10 of this invention having unique transverse end seal bands 12, 14, respectively. The continuous method for forming absorbent pads 10 of this invention utilizes a unique step for forming the transverse seal bands 80 in the continuous composite structure (FIG. 4). The continuous composite structure is severed along the transverse medial lines of respective seal bands 80 to form the elongate, disposable absorbent pads 10 of this invention having unique transverse end seal bands 12, 14 (FIG. 3). The contribution of this invention to the state of the art can be best understood with reference to the discussion which follows relating to the problems encountered in the prior art method for continuously forming disposable absorbent pads, and to the specific step utilized to form the transverse seal bands 80 in such prior art method.

PRIOR ART

In the prior art method for forming absorbent pads the tension applied to the continuous fibrous envelope 18' by the driven belt assembly 106 resulted, in many instances, in an opening up of the webs of said continuous fibrous envelope 18' within the confines of the transverse seal bands 80 to thereby destroy the sealing effect of such bands. This problem was overcome by applying large compressive forces through sealing dies 76p, 78p (FIG. 7) to form the transverse seal bands 80. Unfortunately, these large compressive forces create excessive weakness of the continuous fibrous envelope 18' in the transverse seal bands which results, in many instances, in a separation of discrete sections from the continuous composite structure at the transverse seal bands prior to the completion of the pad forming operations. This separation of discrete sections requires machine down time to reposition the continuous composite structure for proper feed through the pad forming operations. The present invention resides in the recognition of the specific problem causing the unwanted separation of discrete sections, and to the unique solution to this problem.

The prior art method for forming transverse seal bands 80 in the continuous composite structure, and the construction of the seal bands formed by such prior art method will be described in detail with reference to FIGS. 5-7. The transverse end seal bands in the completed absorbent pads are substantially identical to the transverse seal bands 80 formed in the continuous composite structure since the end seal bands in the completed absorbent pads are defined by portions of transverse end seal bands 80 resulting from the severing of the transverse seal bands 80 along their respective transverse medial lines. Therefore, the only difference between the seal bands 80 formed in the continuous composite structure, and the end seal bands of the completed absorbent pad, is that the end seal bands have a dimension in the elongate direction of the completed absorbent pad which is approximately one half of the corresponding dimension of the seal bands 80 formed in the continuous composite structure.

Referring to FIG. 7, an upper sealing die 76p is mounted within an upper driven carrier roll 72 and cooperates with a lower sealing die 78p which is mounted within a lower driven carrier roll 74. The continuous composite structure from which the discrete absorbent pads are formed is fed between the sealing dies 76p, 78p in the direction indicated by arrow 112, and the sealing dies are driven in the direction indicated by arrows 114, 116, respectively. These sealing dies are utilized in the process schematically represented in FIG. 4 to form the prior art transverse seal bands 80 which are subsequently severed along a transverse medial line to form the forward and rearward seal bands in the prior art absorbent pads. A cooperating set of projections on the upper and lower sealing dies 76p, 78p, respectively, is shown in FIG. 7, and comprises an upper row of circumferentially spaced projections 118 and a lower row of circumferentially spaced projections 118'. A plurality of such cooperating sets of projections are provided on the sealing die 76p, 78p; each such set being axially spaced from its adjacent sets, and being separated from its adjacent sets by grooves, relief recesses, or the like (not shown).

The spaced projections 118 on each upper row define depressions 120 therebetween, and have end walls 122 which join bottom walls 124 of the depressions 120 with crests 126 of said projections 118. The spaced projections 118' on each lower row define depressions 120' therebetween and have end walls 122' which join bottom walls 124' of the depressions 120' with crests 126' of said projections 118'. The row of projections 118' on the lower sealing die are circumferentially offset from, and in axial alignment with a cooperating row of projections 118 such that the cooperating row of projections on each of the sealing dies will mesh with the depressions on the other sealing die during the sealing operation. As stated above, the upper and lower sealing dies 76p, 78p are provided with a plurality of cooperating sets of projections which are identical to the set just described, and each cooperating set of projections is axially spaced from adjacent sets by grooves, relief recesses, or the like.

Referring to FIGS. 5 and 6, the structure of the transverse end seal bands formed by the sealing dies 76p, 78p will be described. The transverse end seal bands are each defined by a plurality of transversely spaced seal rows 149; each seal row 149 being formed by a cooperating set of projections on the sealing dies 76p, 78p. Each seal row 149 extends in the direction of elongation 151 of the absorbent pad, and this direction of elongation corresponds to the direction in which the tension forces are applied to the continuous composite structure by the driven belt assembly 106. The spaces, or regions 158 between adjacent seal rows 149 are not compressed, and represent the regions of the continuous composite structure which pass between the upper and lower sealing dies 76p, 78p in alignment with the grooves, or relief recesses (not shown) that separate cooperating sets of projections.

The opposed surfaces in each seal row 149 are defined by adjacent ridges 150 and valleys 152 interconnected by lateral walls 154. The valleys 152 on each surface are aligned with the ridges 150 on the other surface (FIG. 6). The continuous fibrous envelope 18' is compressed in the region of the lateral walls 154 to form the seal regions 156 which are characterized by interlocked fibers of the webs of said continuous fibrous envelope 18'. The compressive forces for forming the seal regions 156 are applied by adjacent end walls 122, 122' of adjacent meshing projections 118, 118', respectively. The magnitude of the compressive forces required to prevent the transverse end seal bands from opening during the pad forming operations also causes a thinning and weakening of the webs in the seal regions 156 (FIG. 6). In some instances, these compressive forces cause the webs to actually tear in said seal regions 156. These weakened and/or torn seal regions 156, in the plane of the absorbent pad, extend transversely to the direction in which the tensioning forces are applied by the driven belt assembly 106 during the formation of the absorbent pads. The magnitude of the tensioning forces required to prevent undesired sideways movement or tracking have, in many instances, exceeded the tensile strength of the continuous fibrous envelope 18' along the transverse seal bands 80 to thereby cause a separation of discrete sections from the continuous composite structure at said transverse seal bands 80 prior to the completion of the pad forming operations. As stated earlier, this separation of discrete sections requires machine down time to permit the continuous composite structure to be repositioned for proper feed through the sequential pad forming operations.

THE INVENTION

Applicant has discovered that transversely adjacent weakened, or torn seal regions 156 in adjacent seal rows 149 define transverse lines of weakness characterized by transversely spaced, weakened seal regions 156 interconnected by the uncompressed regions 158. A substantial transverse extent of these lines of weakness is defined by the transversely extending, weakened, or torn seal regions 156. This fact that the weakened seal regions 156 constitute a substantial portion of the transverse lines of weakness was determined to be the cause of the undesirably low tensile strengths of the webs in the transverse seal bands.

Applicant recognized that the tensile strength of the continuous fibrous envelopes 18' in the transverse seal bands could be enhanced by reducing the transverse dimension of the weakened seal regions. Applicant's unique method for reducing this transverse dimension of weakened seal regions in the lines of weakness will now be described with reference to FIGS. 8-12.

Referring first to FIGS. 10-12, the sealing dies which are utilized at the sealing station 70 (FIG. 4) for forming transverse seal bands according to the teachings of this invention will be described. An upper sealing die 76 is fixed within the upper carrier roll 72 and a lower sealing die 78 is fixed within the lower carrier roll 74. The continuous fibrous envelope 18' is fed between the sealing dies 76, 78 in the direction indicated by arrow 200, and the sealing dies are driven in the direction indicated by arrows 202, 204, respectively (FIGS. 10 and 12).

The cooperation between the upper and lower sealing dies 76, 78 can be best understood with reference to FIG. 11 which shows one cooperating set of projections. This cooperating set of projections comprises a row of axially spaced projections 218 on the upper sealing die and a cooperating row of axially spaced projections 218' on the lower sealing die. The row of axially spaced projections 218 define depressions 220 therebetween and have side walls 222 which join bottom walls 224 of the depressions 220 with crests 226 of said projections 218. The row of axially spaced projections 218' define depressions 220' therebetween and have side walls 222' which join bottom walls 224' of the depressions 220' with crests 226' of said projections 218'.

The rows of projections 218' on the lower sealing die 78 are axially offset from, and in circumferential alignment with its cooperating row of projections 218 of the upper sealing die 76 such that the projections in each row of projections mesh with the depressions between spaced projections of the other row as indicated in FIG. 11.

The upper and lower sealing dies are provided with a plurality of cooperating sets of projections which are identical to the set described with reference to FIG. 11, and each cooperating set of projections is circumferentially offset from adjacent sets by rows of axially aligned grooves 228, 228' in the upper and lower sealing dies, respectively (FIGS. 10 and 12). Each row of axially aligned grooves in one sealing die is in circumferential alignment with a cooperating row of axially aligned grooves in the other sealing die. When the upper and lower sealing dies 76, 78 are in cooperating, sealing relationship with each other, the bases of opposed, circumferentially aligned rows of grooves 228, 228' are spaced from each other a greater distance than the thickness, or caliper of the webs of the continuous fibrous envelope 18' passing between said dies (FIG. 12). Therefore, the regions of the continuous fibrous envelope 18' which pass between aligned rows of grooves 228, 228' will not be compressed.

Referring to FIGS. 8 and 9 the unique transverse end seal bands 12, 14 of this invention will be described. The end seal bands 12, 14 are identical and therefore the description which follows will be limited to end seal band 14 (FIG. 8). The transverse end seal band 14 is defined by a plurality of transversely extending seal rows 249 which are spaced from each other in the direction of elongation of the elongate, disposable absorbent pad 10. This direction of elongation is indicated by arrow 151, and corresponds to the direction of feed of the continuous composite structure through the pad forming operations, and to the direction in which the tension forces are applied through the driven belt assembly 106. Each seal row 249 is created by a cooperating set of projections 218, 218' on the upper and lower sealing dies 76, 78 respectively. Opposed surfaces of each seal row 249 are defined by transversely adjacent ridges 250 and valleys 252 interconnected by lateral walls 254, and the valleys on one opposed surface are aligned with the ridges on the other opposed surface. Each lateral wall 252 has a seal region 256 characterized by interlocked fibers of the webs in said seal regions. These seal regions 256 are formed by compressive forces applied to the webs of the continuous fibrous envelope 18' by adjacent side walls 222, 222' of adjacent, meshing projections 218, 218', respectively. As stated above, the regions of the webs of the continuous fibrous envelope 18' which align with the grooves 228, 228' of the upper and lower sealing dies 76, 78, respectively, are not compressed, and define unweakened transversely extending regions 258 between adjacent seal rows 249 (FIG. 8).

The seal regions 256 are substantially weakened, and in some instances are torn, in the same manner as the seal regions 156 of the prior art absorbent pads. However, the weakened seal regions 256 in the transverse end seal band 14, in the plane of the absorbent pad 10, extend in the elongate direction of said pad, and not transverse to said elongate direction as is the case in the prior art absorbent pad described above (FIG. 5). Therefore, the transverse dimension of the regions of weakness, i.e., seal regions 256, as viewed transversely to the elongate direction of the absorbent pad 10, is extremely small, being approximately equal to the thickness of the webs of the fibrous envelope 18 in the seal regions 256 (FIG. 9). These weakened regions of narrow transverse dimension are interconnected by unweakened ridges 250 and valleys 252 which define the major transverse extent of the transverse end seal bands. This transverse end seal band 14 has been found to have a tensile strength in the direction of elongation of the absorbent pad 10 which is approximately twice the tensile strength of the end seal bands of the prior art absorbent pad described above in connection with FIGS. 5 and 6. This increase in tensile strength has proven sufficient to prevent separation of discrete sections from the continuous composite structure as a result of the tension forces applied to the continuous composite structure as it is fed through the various pad forming operations.

Claims

I claim:

1. A method for continuously manufacturing elongate, disposable absorbent pads comprising the steps of:

a. continuously forming discrete, elongate, absorbent fluff batts of cellulosic fibers;

b. feeding said fluff batts in their direction of elongation in spaced relation to each other, said fluff batts being spaced from each other in said direction of elongation;

c. disposing said fluff batts within a fibrous envelope as said fluff batts are fed in their direction of elongation to form a continuous composite structure comprising said spaced fluff batts disposed within said fibrous envelope;

d. maintaining sufficient tension on said fibrous envelope in the direction of feed to prevent undesirable movement of said continuous composite structure in a direction transverse to said feed direction;

e. transversely closing and sealing said fibrous envelope in regions intermediate adjacent fluff batts by:

1. forming a transversely extending seal band having a seal row of transversely adjacent ridges and valleys interconnected by lateral walls on each of the opposed surfaces of said fibrous envelope, and

2. transversely compressing the lateral walls of said seal row to form weakened seal regions only in said lateral walls, said weakened seal regions, in the plane of said composite structure, being disposed only in the direction of feed of the composite structure, said weakened seal regions being characterized by interlocked fibers of said fibrous envelope for maintaining the seal band in a closed condition; and

f. transversely severing said continuous composite structure within the confines of said transversely extending seal band to form individual elongate absorbent pads having sealed end margins.

2. The method according to claim 1, wherein said fibrous envelope is formed by the steps of: feeding a continuous backing cover web and a fluid pervious, continuous facing cover web adjacent opposed surfaces of said spaced fluff batts; folding opposed side margins of said facing cover web into overlying relationship with said backing cover web; and securing said facing cover web to said backing cover web in their overlying regions.

3. The method according to claim 2, wherein the step of securing said facing cover web to said backing cover web includes the step of applying conditions securing stripes to the backing cover web in regions which are in overlying relationship with the side margins of said facing cover web.

4. The method according to claim 2 including the additional steps, prior to transversely severing said continuous composite structure into individual elongate absorbent pads, of: folding elongate, side regions of the continuous composite structure into overlying relationship with the continuous facing cover web in a center region of said composite structure to form side panels, and securing said side panels to said facing cover web.

5. The method according to claim 1 including the additional steps, prior to transversely severing said continuous composite structure into individual elongate absorbent pads, of: folding elongate, side regions of the continuous composite structure into overlying relationship with the fibrous envelope in a center region of said composite structure to form side panels, and securing said side panels to said fibrous envelope in said center region.

6. The method according to claim 5, wherein the step of securing said side panels to said facing cover web includes the step of applying securing tacks between the side panels and the center region of said continuous composite structure adjacent each transversely extending seal band.