The present invention relates to a method and to apparatus for producing a material web which has a generally flat upper surface and a pattern of perforated recesses which project downwardly from the flat upper surface.

Such webs are often used as the top sheets of disposable absorbent articles, such as diapers, sanitary napkins, or incontinence guards, and include a plurality of holes which impart good liquid-permeability to the sheet. The top sheets are also often made of a plastic material, partly to be able to provide a dry surface in contact with the wearer's skin, and partly for reasons of cost. The holes are normally formed in the plastic materials by vacuum-forming, wherein recesses or hollows are formed in the material in conjunction with forming the holes. These recesses reduce the skin contact area of an article provided with such a top sheet, causing the article to be less plastic-like to the touch and to be more airy than when the holes are placed in the same plane as the upper surface of the top sheet.

SE-B-449 298 describes a top sheet of the aforedefined kind, which includes a pattern of recesses in which there are formed holes which are orientated in a plane extending generally perpendicular to the upper side of the sheet. In addition to the aforesaid advantages, such a top sheet has the additional advantage that underlying absorbent material and therewith material absorbed therein will be less visible than if the holes had lain in a plane which extends parallel with the upper side of said sheet, particularly when the article is seen from above.

Swedish Patent Application No. J. , filed on the same day as the instant application, describes a method of the kind defined in the introduction in which a pattern of cuts is produced with the aid of a cutting roller and an

anvil or counterpressure roller.

The primary object of the present invention is to simplify and improve the aforesaid method.

This object is achieved with a method of the kind defined in the introduction which is characterized by providing a flat web of elastic material with a pattern of discrete cuts with the aid of an ultrasonic welding device, and thereafter producing a recess on one side of each cut in the web. The positions of the cuts are determined solely by the positions of the anvils on the anvil holder of the welding device as distinct to the aforesaid method in which the cuts made by the cutting device must be aligned very accurately in relation to the anvils, meaning that the method according to the present invention is much simpler than the aforesaid known method. Furthermore, the known cutting or clipping roller constitutes a component which must be changed often due to wear whereas an ultrasonic welding device has a long useful life span, and consequently the inventive method reduces the standstill or idling time of the process line in comparison with the aforesaid known method. The edges of the cuts produced with the aid of an ultrasonic welding device are softer and more rounded than the edges of conventionally made cuts, meaning that the cut top sheet will be less coarse, i.e. smoother.

According to one preferred embodiment of the invention, subsequent to being cut the web is supported by flat top surfaces on a member which projects out from an anvil roller and the recesses are formed by virtue of a projection on a press roller pressing those regions of the web which lie outside the flat top surfaces of the projection on the anvil roller into the spaces between adjacent projections on the anvil roller.

The invention also relates to apparatus for producing a

material web having a generally flat upper side and a pattern of perforated recesses which project downwardly from said flat upper side, said apparatus being characterized by an ultrasonic welding device which includes an anvil roller having a pattern of anvils that stand out from projections on the peripheral surface of the roller, and one or more ultrasonic horns which extend radially outside the anvil roller in its axial direction across the width of the anvil pattern, a press roller which coacts with the anvil roller and which is provided with projections which are intended to penetrate into the spaces between the projections on the anvil roller in the nip between said rollers, and means for moving a material web through the device. In addition to an arrangement of this kind having a long useful life and being readily adjustable in comparison with a cutting roller, the patterns of cuts can be readily varied, by simply changing an anvil roller.

According to a first variant of one embodiment of said apparatus, the anvil roller is comprised of a peg roller having a plurality of peg rows extending peripherally around the roller, wherein each of the pegs has a flat top surface, and wherein the anvil surfaces are comprised of outwardly projecting ridges which extend along a peripheral edge of the flat top surface of each peg. An outwardly projecting ridge preferably extends along each peripheral edge of the flat top surfaces of the pegs.

According to another variant of said embodiment, the anvil roller includes a plurality of axially separated rows of outwardly projecting ribs which extend peripherally around the anvil roller and have flat top surfaces, and rows of outwardly projecting ridges which extend along a peripheral edge of the top surface of each rib. Preferably, rows of outwardly projecting ridges extend along each peripheral edge of the outwardly projecting ribs.

The invention will now be described with reference to the accompanying drawings, in which

Fig. 1 illustrates schematically a perforating arrangement according to a first embodiment of the invention;

Fig. 2 is a sectioned view of the lower part of the ultrason¬ ic horn and a part of the anvil roller of the arrangement shown in Figure 1;

Fig. 3 is a sectional view taken on the line III-III in Figure 2;

Fig. 4 is a view similar to the view of Figure 2 and illus- trates a preferred embodiment of the anvil roller;

Fig. 5 is a sectioned view illustrating the coaction between an anvil roller and a press roller of the arrangement shown in Figure 1; and

Figs. 6 and 7 are cut-away perspective views of a web of material produced by the arrangement shown in Figure 1 and with the aid of an anvil roller constructed in accordance with Figure 2 and Figure 4 respectively.

The apparatus illustrated in Figure 1 includes an ultrasonic welding device 1 having a welding unit 2 and an anvil roller 3. A press roller 4 is mounted adjacent to and coacts with the anvil roller 3. The welding unit 2 includes conventional- ly an electric high-frequency generator, a transducer for converting electric energy to vibratory movement of an ultrasonic horn 5 at an ultrasonic frequency, and an amplifi¬ er for increasing the amplitude of the vibratory movement generated. A first web 6 of elastic and weldable material, preferably plastic material, is passed through the device l and runs first between the ultrasonic horn 5 and the anvil roller 3, and then through the nip defined between the press

roller 4 and the anvil roller. The web 6 is preferably taken from a storage reel (not shown) and moved to the welding device on a conveyor, for instance a suction conveyor.

The welding unit 2 may be of any suitable kind, for instance of the kind marketed by Branson or Dukane. Although only one welding unit is shown in the Figures, it will be understood that several such units may be arranged transversely adjacent to one another, when the web 6 is to be cut over a width which requires the use of several units.

Figures 2 and 3 are respectively a partial longitudinal section view and a cross-section view of the anvil roller 3 and the ultrasonic horn 5. By longitudinal direction is meant here the direction A in which the web 6 moves. As seen from the drawings, the anvil roller is a peg roller having radially projecting pegs 7 which are disposed in a plurality of peg rows which are each separated in the axial direction of the roller. Each row of pegs includes a succession of pegs which extend around the full circumference of the roller. Each peg 7 has a flat top surface 8. The anvils on the anvil roller 3 coacting with the ultrasonic horn are comprised of ridges 9, 10 which project out from each peripheral edge of the top surface 8 and which extend along the major part of these edges. The web 6 is indicated in broken lines in the Figure and rests on the top surfaces 8 of the pegs 7 when passing the horn 5.

Figure 4 is a view similar to Figure 2 and shows an anvil roller 3' in which the ridges 10' project out from the peripheral edges of axially separated rows of ribs 7' which extend sequentially in the circumferential direction of the roller 3'. A cross-sectional view similar to Figure 3 of the section of the anvil roller 3' and the ultrasonic horn shown in Figure 4 would have the same appearance as that shown in Figure 3 and is therefore not shown in the drawings.

The ultrasonic horn 5 is positioned at such a mean distance from the anvil ridges 9, 10 and 10' respectively and is driven with such power as to achieve complete through-melting of the plastic material in the web 6 at the anvil locations as the anvils pass the horn. Thus, after passing between anvil and horn, the web 6 will exhibit a pattern of longitu¬ dinally extending cuts where each cut has an extension which corresponds to the extension of the ridges.

When cutting with the aid of an ultrasonic welding device, the edges of the cuts will be softer and more rounded than when cutting with conventional knives or like devices, therewith imparting to the material 6 a smoother surface than that obtained when using conventional cutting tools. Further- more, the material can be cut without physical contact between horn and anvil, therewith resulting in only slight wear on the equipment in comparison with conventional cutting or clipping tools, whose cutting edges need to be sharpened at regular intervals. Since the exchange of knives requires the anvil roller and the knife carrier to be accurately realigned, which is a time-consuming task, the use of an ultrasonic welding device will result in far less standstill time occasioned by maintenance requirements.

The press roller 4 has around its periphery a number of projections in the form of ribs 11 which fit into the spaces between the rows of pegs 7 on the anvil roller (see Figure 3).

Figure 5 illustrates schematically and in longitudinal section view the manner in which recesses are produced in the nip between the press roller 4 and the anvil roller 3. As will be seen from this Figure, the flat web 6 is deformed by the ribs 11 on the press roller as the web passes through the nip between press roller and anvil roller, so that those parts of the web 6 that are located between adjacent rows of pegs 7 on the anvil roller will be pressed by the ribs 11

down into the spaces between adjacent rows of pegs. Those parts of the web 6 that are located between adjacent pegs 7 in the peg rows will accompany the movement of the trans¬ versely outwardly-lying parts, this accompanying movement of said parts being facilitated by the cuts made in the web, . Consequently, those parts of the web that are located outside the top surfaces 8 of the pegs 7 will be moved down to the position shown in broken lines in Figure 5. Thus, the cut surfaces of the cuts produced along each peripheral edge of the top surfaces 8 will be separated from one another to form holes 12, as indicated in broken lines in Figure 5.

Figure 6 is a schematic perspective view of part of the web shown in Figure 5 after leaving the press roller 4. The web 6 produced by the apparatus shown in Figure 1 thus includes a pattern of recesses 13 in which two opposing openings 12 in the web 6 extend generally perpendicular to the upper side of said web.

Figure 7 is a view analogous with the view of Figure 6 and shows part of the web 6 produced when using the anvil roller 3' illustrated schematically in Figure 4. In this particular case, the ribs on the press roller penetrate into the space between the ribs 7' as the web passes the nip between the press roller 4 and the anvil roller 3', therewith producing U-shaped recess channels 14, the walls of which extending perpendicular to the upper surface of the web 6 include a row of pair-wise opposing openings 12' in the web 6.

As the web passes through the nip between the press roller 4 and the anvil roller 3 and 3' respectively, the web 6 is deformed plastically so as to obtain the configuration illustrated in Figures 6 and 7 respectively. However, the cuts enable the parts located between two opposing cuts in the web to move more easily than remaining parts, and consequently the plastic deformation and therewith the thickness of the material will be different in different

parts of the web. This phenomenon can be utilized to control the elasticity of the web, for instance by displacing all the pegs in the rows of pegs or the ribs in the rows of ribs on the anvil roller in relation to one another.

It will be understood that the described embodiments can be modified in several ways within the scope of the invention. For instance, the longitudinally extending ridges on the top surfaces of the pegs or the ribs may extend solely along one peripheral edge. The projections on the anvil roller and the press roller may also have forms other than those shown. Neither need the projections on the rollers complement one another hand in a glove. For instance, the cross-section of the press roller may be such as to fill only a part of the space between the rows of pegs or ribs on the anvil roller, particularly when only the anvils extend along a peripheral edge of the top surfaces of the pegs or ribs. The welding unit or units may be movable vertically from an active position, so as to enable the web to be cut intermittently in a simple manner. The web may be comprised of other elastic materials than plastic material or may be comprised of a composite sheet, such as a plastic nonwoven laminate. The invention is therefore restricted solely by the content of the following Claims.