High speed vacuum porting

This invention proposes a new, improved method and apparatus for applying web segments to a traveling web. These web segments, sometimes called ears or wings, may be asymmetrical or otherwise incompatible with the usual slip-and-cut method. The asymmetrical shape may have differing web tensions which can cause the web segments to be improperly engaged with the vacuum holes on an anvil roll. The present invention utilizes both circumferential rows of vacuum holes and an additional pattern of ear retaining vacuum holes. The circumferential rows of vacuum holes are activated consecutively by vacuum commutation, however, the pattern of ear retaining vacuum holes are activated simultaneously to counter the effects of differing web tensions on the ear portions.

BACKGROUND OF THE INVENTION

The present invention relates to disposable hygiene products and more specifically, to methods and apparatuses for processing disposable hygiene products. More specifically, the invention relates to cutting and applying segments of one web to attach to a disposable hygiene product. Various types of automatic manufacturing equipment have been developed which produce the desired results with a variety of materials and configurations.

When manufacturing hygiene products, such as baby diapers, adult diapers, disposable undergarments, incontinence devices, sanitary napkins and the like, a common method of applying discrete pieces of one web to another is by use of a slip-and-cut applicator. A slip-and-cut applicator is typically comprised of a cylindrical rotating vacuum anvil, a rotating knife roll, and a transfer device. In typical applications, an incoming web is fed at a relatively low speed along the vacuum face of the rotating anvil, which is moving at a relatively higher surface speed and upon which the incoming web is allowed to “slip”. A knife-edge, mounted on the rotating knife roll, cuts a off a segment of the incoming web against the anvil face. This knife-edge is preferably moving at a surface velocity similar to that of the anvil's surface. Once cut, the web segment is held by vacuum drawn through holes on the anvil's face as it is carried at the anvil's speed downstream to the transfer point where the web segment is transferred to the traveling web.

Typical vacuum rolls used in the prior art have rows of vacuum holes which are fed by cross-drilled ports, each being exposed to the source of vacuum by commutations, as the ports move into a zone of negative pressure in a stationary manifold. Such a configuration serves to apply vacuum sequentially to each successive row of holes.

A common problem associated with slip-and-cut applicators occurs at the point of cut. Since the web being cut is traveling at a very low velocity compared to the anvil and knife velocity (perhaps 1/20th), the engagement of the knife with infeeding web tends to induce a high tensile stress in the infeeding web. Having been placed under such a high level of stress, the infeeding web can recoil violently when the cut is finally completed, causing loss of control of the infeeding web. This “snap-back” effect increases with the thickness of the infeeding web. Thicker webs tend to prolong the duration of engagement with the knife before completion of the cut, thereby increasing the build-up of stress. This is a common process problem that is usually addressed by the provision of various shock-absorbing devices. One possible solution might have been to reduce the surface velocity of the knife, but substantially different velocities between the knife and anvil result in rapid wear of the knife edge and/or anvil face, depending on relative hardness.

Continual improvements and competitive pressures have incrementally increased the operational speeds of disposable diaper converters. As speeds increased, the mechanical integrity and operational capabilities of the applicators had to be improved accordingly. As a further complication, the complexity of the fastener tabs being attached to those products has also increased. Consumer product manufacturers are now offering tapes which are die-cut to complex profiles and which may be constructed of materials incompatible with existing applicators. For instance, a proposed fastener tab may be a die-profiled elastic textile, instead of a typical straight-cut stiff-paper and plastic type used in the past. Consequently, a manufacturer may find itself with a slip-and-cut applicator which cannot successfully apply die-cut tape segments. Existing applicators cannot successfully apply fastener whose boundaries are fully profiled, as may be desired to eliminate sharp corners, which might irritate a baby's delicate skin. This demonstrates a clear need for an improved applicator capable of applying new fastener configurations and overcoming other shortcomings of prior art applicators.

Slip-and-cut apparatus are well known for their ability to cut relatively short segments of one web and place them accurately on another, higher speed web. Certain materials, however, behave badly in these applications. The tension pulsation caused by the cutting may cause the material to snap back, losing its natural track down the moving surface of the anvil roll. This is especially common with thick webs. Other materials, such as nonwoven fabrics, may be difficult to control because they are very porous and provide little resistance to air flow to keep the material on track. Still other materials, such as certain perforated films may possess texture qualities which tend to be very unstable on the anvil surface, acting instead like a puck on an air hockey table.

These problems are further exacerbated by using materials with a very low modulus of elasticity. Here, even very low levels of vacuum at the anvil surface may cause the material to stretch with the advancing movement of the anvil. The sudden change of tension seen when the knife cuts this over-stretched web can result in severe snap-back and complete loss of position, relative to the intended centerline. Likewise, webs with very high moduli may snap back violently when the web is cut.

The prior art is quite successful when processing full-width or symmetrical webs, which are drawn uniformly forward by the sliding vacuum surface on which they are held. Attempts to process asymmetrical webs on such a surface are less successful, as the draw of the advancing vacuum pattern will act differently on parts of the web which have differing lines of tension. For instance, a die-cut ear web for a disposable diaper may have only a narrow continuous portion along one edge, with the opposite edge being more or less scalloped in shape.

It is therefore an object of this invention to provide an apparatus which can maintain control over die cut web sections of various shapes.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus which provides high speed vacuum porting to selected vacuum pattern areas on a rotating cylindrical roll. This invention has the advantage of being able to “switch on” selected areas rather than discrete rows.

In a typical configuration of a slip-and-cut applicator, there is a pattern of vacuum holes distributed to evenly draw the entering web onto the anvil's surface and thence into a cut point where a knife edge engages an anvil, thus severing the web into discrete segments if so desired. The invention provides a generally cylindrical anvil body connected to a source of vacuum. The anvil roll has an ear retaining portion on its outer surface. This ear retaining portion is formed with a plurality of vacuum holes. A vacuum slot is provided on an end face surface (commutating surface) of the anvil roll and is adapted to put the plurality of vacuum holes in communication with the vacuum source. The anvil roll is utilized in connection with a rotary knife to cut small segments of an incoming web. The anvil roll then transfers those cut segments to an additional web.

It is desired to immediately grasp and hold the ear at the instant of the cut of the continuous web as it is separated into discrete segments. As soon as the ear is cut from the infeeding web, instantaneous control must be established.

One embodiment of this invention provides a cylindrical anvil roll which is symmetrical about a center circumferential plane. This embodiment allows two incoming webs to be utilized, allowing two segments to be cut, one on either end of the anvil roll, each time the rotary knife engages the anvil roll.

Additionally, the anvil roll may have an additional set of ear retaining portions formed in diametric opposition to the first set of ear retaining portions. In such an embodiment, the knife roll would engage the anvil roll two times for each rotation of the anvil roll, thus producing up to four cut segments per rotation of the anvil roll.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings there is seen inFIG. 1a diagrammatic illustration of a prior art process for applying tabs to webs in a diaper making process. The present invention can use this prior art method of affixing the ears12to the web10, with a different anvil, the new anvil114described below. Web10is a composite material used in formation of diapers which is generally formed of various layers of material such as plastic back sheets, absorbent pads and nonwoven topsheets. A series of ears12are applied to web10. In the illustrated process a rotatable vacuum anvil14is used to supply the ears12to web10. Anvil14has internally reduced air pressure or vacuum (not shown), and a plurality of openings24are provided through its surface to enable suction of the tab segments13against the anvil surface14. A web of the ear tab forming material16is fed by rollers20and22against the anvil surface14where it is cut into segments by a rotary knife18.

In the prior art, the surface of the anvil roll14has vacuum holes24on its smooth surface. In a typical configuration of a slip-and-cut applicator, there is a pattern of vacuum holes24distributed to evenly draw the entering web onto the surface of anvil14and thence into the cut point where the knife edge18engages the anvil14.

It can be seen fromFIG. 1that in the prior art, the infeed of the ear tab forming material16can be at a first speed (with individual ears12spaced together), after which the individual ears gain speed to the speed of the anvil14. Typical infeed speeds could be 120 mm/product for the infeed, while anvil speeds could be 450 mm/product on the anvil. This transition from the slower first speed to the quicker second speed takes place at the cut point, the ear tab forming material16slipping on the anvil14until cut. However, immediately at the transition cut point19from the slower speed to the faster speed, it is desired to place vacuum on the ears because centrifugal force would try to throw the ears off of the vacuum anvil14.

In both the prior art and the present invention, a continuous ear forming web16is provided to the system. The web16is comprised of two portions13and15, as shown inFIG. 2. Segment13is more specifically referred to as the tab section of the ear12, segment15is the ribbon section of the ear12. The ear forming material16is cut into individual ears12by the rotary knife18as shown inFIG. 1, along lines such as the dashed lines shown inFIG. 2.

Referring now toFIG. 3, a front view of an anvil roll114of the present invention is shown carrying ear forming material16(and later, an ear12) in phantom. The anvil roll114is preferably formed with two vacuum portions116separated by a center groove portion118. The vacuum portions116are preferably mirror images of each other. The anvil roll114is symmetrical about a center plane through its circumference. Each vacuum portion116contains several circumferential rows of circular vacuum holes24. Each vacuum portion116may also contain a circumferential groove120with an additional circumferential row of vacuum holes24located in the circumferential groove120.

The preferred embodiment of the anvil roll114of the present invention is also formed with two diametrically opposed anvil pockets122and two diametrically opposed pairs of ear retaining portions124. The ear retaining portions can be created as inserts, with different vacuum patterns applied as the user deems necessary. Each anvil pocket122is a groove which extends across the face of the entire anvil roll114. One ear retaining portion124is located on each of the vacuum portions116. Each ear retaining portion124has an ear vacuum hole pattern126made of a plurality of vacuum holes24located at or near the surface of the anvil roll144. The preferred embodiment, as shown inFIG. 3is a plurality of rows of vacuum holes24, each row having a plurality of vacuum holes24, although more or less than those configurations or patterns shown can be used.

In operation, two webs of ear material16are carried by the anvil114. One web of ear material16is located on each vacuum portion116. A single ear12is cut from the ear web16when the rotary knife18engages the anvil roll114at the anvil pocket122. Immediately after a single ear12is cut from the ear web16, the single ear12is located on the ear retaining portion124, particularly the tab portion13of the ear12as shown inFIG. 2. At this point the vacuum in the ear retaining portion124has been engaged to secure the single ear12to the anvil roll114. As the anvil roll114rotates the vacuum is released at a predetermined location so that the single ear12can be applied to the diaper web10. Because this configuration has two vacuum portions116, a pair of two ears12is cut each time the rotary knife18engages the anvil toll114. This allows for two pair of ears12to be cut with each revolution of the anvil roll114. Shown in dotted line inFIG. 3is a vacuum slot128, described below.

Referring now toFIG. 4, a perspective view of the anvil114is shown. The anvil114will be described in relation to its endface and its outer surface, the outer surface that surface shown onFIG. 3and the endface the two ends of the anvil114.

The vacuum slot128contains a plurality of vacuum holes24that allow commutation of the vacuum to the entire ear vacuum hole pattern126, allowing the pattern126to be activated simultaneously, as opposed to each of the rows that comprise the vacuum of vacuum holes24being enabled one at a time. The vacuum pattern126is activated utilizing drilled ports28that communicate the vacuum from the slot128to the individual holes24of the pattern126. It should be noted that the pattern126can also be provided with a depressed slot configuration so that it too is all simultaneously enabled with vacuum.

The remaining vacuum holes24provided on the anvil roll114are enabled sequentially, by known vacuum commutation method utilizing cross drilled ports28.

The vacuum slot128is provided at a first radius R1on the anvil roll114, the remaining vacuum holes provided at a different R2. The differing radii R1and R2allow two vacuum manifolds (not shown) to communicate each at a different radius, R1or R2, thus selectively applying vacuum to the anvil.

Referring now toFIG. 5, a cross sectional view of the anvil roll114of the present invention. In this embodiment, the slot128has been placed at R2. It is appreciated that the slot128communicating with the pattern126can be placed at either R1or R2, and the remaining vacuum holes24communicating with drilled ports28can be interchanged at either R1or R2. For machining purposes, it is likely preferable to place the slot128communicating with the pattern at R2for simplicity in machining.

Referring now toFIG. 6, a side view of the anvil roll114is shown, showing the endface of the anvil, or the circular portion of the cylindrical body114. The ear web16is shown infeeding to the anvil114, where it is then cut with the rotary knife18. It is desired to apply the vacuum to the pattern126simultaneously with the knife cut.

The range of vacuum application is provided for with a manifold (not shown) that continuously applies vacuum to vacuum patterns V1and V2. Vacuum pattern V1is at R1, Vacuum pattern V2is at R2. Vacuum pattern V1applies vacuum to the slot128each time the slot128rotates through the vacuum pattern V1provided on the manifold. When the slot128is in communication with V1, vacuum is applied to vacuum holes24associated in the slot128on the endface of the anvil for commutation to the pattern126on the outer surface of the anvil114. When the slot128is not in communication with V1, the vacuum to the pattern126is turned off.

Vacuum pattern V2is applied to the vacuum holes24disposed on the endface of the anvil114and the associated circumferential ribbon vacuum hole pattern on the outer surface of the anvil114throughout V2. As each successive vacuum hole24rotates through V2, the vacuum is on. As each successive vacuum hole24leaves V2, its vacuum is turned off.

From the center of the endface, a radius extending to the contact point of the knife18with the anvil roll114can be extended, and as the anvil roll rotates through angle B as shown, the rotation of the ear12will be from the knife point to the transfer point TP. It is throughout this angle B that vacuum is desired across the pattern126and onto the ear12. To accomplish this, a smaller angle C has vacuum applied to it. The angle C can be expressed mathematically as the angle B minus twice the width128′ of the slot128. This is because pattern126is placed in communication with the slot128, the slot128communicates vacuum simultaneously to the pattern126. Therefore, the leading edge of the ear12and the trailing edge of the ear12will receive vacuum at the same time. Therefore, the user must allow the leading edge of the ear12to pass by the knife18the desired length of the ear12prior to engaging the vacuum onto the ear12. Similarly, prior to arriving at the transfer point TP, the vacuum will have to be released on both the leading and trailing edges of the ear12simultaneously, allowing the ear12to continue on its downstream path.

An angle A, larger than angle B, is provided to define V2, as it is desired to draw the web16into contact with the anvil both prior to and during cutting by the knife18.