MXPA98004814A - Method and apparatus for elaborating absorbent structures that have divided zones of particu - Google Patents

Abstract

The present invention provides a method and apparatus for making absorbent structures having a layer of discrete particulate absorbent material, which is divided into two or more strips (9) separated by a substantially particle-free zone (11). The method for making these absorbent structures comprises the steps of first generating an initial particle suspension comprising a two phase fluid of gelling absorbent particles suspended in a gas (such as air), which flows in an inlet duct. The initial suspension of particles is then divided into multiple final suspensions of particles in corresponding multiple branching ducts, each of the final particle suspensions having a given percentage of particles as a function of the cross-sectional area of the inlet duct. The particles in the final particle suspensions are distributed substantially uniformly as a function of the cross-sectional position of the branch ducts. Finally, the suspended particles are filtered from the final suspensions of particles by capturing them in a substrate such as a tissue layer. An apparatus according to the present invention for practicing the above method comprises an inlet duct. A particle suspension generator in fluid communication with the inlet duct to generate the initial suspension of particles, at least two branch ducts in fluid communication with the inlet duct, and a particle suspension divider disposed within the input duct to divide the initial suspension of particles into final suspensions of multiple particles in the branch ducts. In a preferred embodiment, the apparatus further comprises an adhesive supplying device for adhesively coating the particles in the final suspensions of particles to form adhesively coated particles.

Description

METHOD AND APPARATUS FOR ELABORATING STRUCTURES ABSORBENTS THAT HAVE DIVIDED PARTICLE ZONES FIELD OF THE INVENTION The present invention relates to an absorbent structure comprising at least one layer of discrete particulate absorbent material. More particularly, the present invention relates to a method and apparatus for making absorbent structures having a layer of discrete particulate absorbent material, which is divided into two or more separate bands by a substantially particle-free zone.

BACKGROUND Absorbent articles such as disposable diapers, incontinence pads, and catamenial towels generally include an absorbent core to receive and maintain exudates from the body. Typically the absorbent core includes a fibrous web, which may be a web of natural or synthetic fibers, placed by air, non-woven, or combinations thereof. A class of particulate absorbent materials known as super absorbent polymers or gelling absorbent materials can be incorporated into the fibrous web to improve the absorption and retention characteristics of the fibrous web. Because gelling absorbent materials are generally significantly more expensive than readily available natural or synthetic fiber materials (eg, cellulose fibers), it is advantageous to reduce the amount of the gelling absorbent material in the core. Instead of evenly distributing these particles throughout the entire core, it is desirable to distribute the particles in the absorbent core in a predetermined manner such that it is located in the particles where they will be most effective in acquiring and retaining the exudates. of the body. Although various means for forming uniformly distributed particle streams and applied to the portions of the absorbent core (such as individual particles discharged in an air stream) have been developed, these methods typically either require multiple feed mechanisms or on particle applications. to the core areas selectively coated with adhesive. The use of multiple feeding mechanisms multiplies the cost of capital required to produce these absorbent cores, while the over application of particles to the selective adhesive zones increases material waste and accompanying material costs. Accordingly, it would be desirable to provide an improved method and apparatus for making absorbent structures having discrete bands or regions of particulate absorbent gelling materials separated by substantially particle-free zones that minimizes the required equipment. It would also be desirable to provide an improved method and apparatus for making absorbent structures having discrete bands or regions of particulate gelling absorbent materials that reduces the amount of lost gelling absorbent material particles generated by the manufacturing process and provides waste. reduced of the material.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method and apparatus for making absorbent structures having a layer of discrete particulate absorbent material, which is divided into two or more bands separated by a substantially particle-free zone. The method for making these absorbent structures comprises the steps of first generating an initial particle suspension comprising a two-phase fluid of gelling absorbent particles suspended in a gas (such as air), which flows in an inlet duct. The particles are distributed substantially evenly in the gas as a function of the cross-sectional position in the inlet duct. The initial suspension of particles is then divided into final suspensions of multiple particles in corresponding multiple branching ducts, each of the final suspensions of particles having a given percentage of particles as a function of the given area as a function of the cross-sectional area of the inlet duct. These particles in the final particle suspensions are distributed substantially uniformly as a function of the cross-sectional position of the branch ducts. Finally, the suspended particles are filtered from the final suspensions of particles by capturing them in a substrate such as a tissue layer. In a preferred embodiment of this method, the final particle suspensions are directed through a stream of adhesive to form adhesive coated particles before being filtered from the final particle suspensions, followed by the deposition of the adhesively coated particles on the substrate. . The initial suspension of particles can be divided into two, three or more final suspensions of particles, and can preferably have at approximately equivalent percentages of particles there as a function of the cross-sectional area of the inlet duct. An apparatus according to the present invention for practicing the above method comprises an inlet duct, a particle suspension generator in fluid communication with the inlet duct to generate the initial particle suspensions, at least two branch ducts in fluid communication with the inlet duct, and a particle suspension divider disposed within the inlet duct to divide the initial suspension of particles into final suspensions of multiple particles in the branch ducts. In a preferred embodiment, the apparatus further comprises an adhesive delivery device for adhesively coating the particles in the final suspensions of particles to form adhesively coated particles. The particle suspension divider preferably comprises a duplicator plate for dividing the initial suspension of particles into two, three, or more final suspensions of particles in the branch ducts.

BRIEF DESCRIPTION OF THE DRAWINGS Although the description concludes with the claims pointing out in a particular manner, and claiming differently from the present invention, it is believed that the present invention will be better understood from the following description in combination with the figures of the accompanying drawings, in which similar reference numbers identify similar elements, and wherein: Figure 1 shows a partially cut away plan view of an absorbent article according to the present invention; Figure 2 shows a top view of an absorbent structure in accordance with the present invention; Figures 3 and 4 show respectively a transverse cross-sectional view and a longitudinal cross-sectional view of the absorbent structure of the Figure 2, wherein the laminar unit is placed on the side facing the user of the absorbent structure; Figures 5 and 6 show respectively a cross-sectional view and a longitudinal cross-sectional view of the absorbent structure of Figure 2, wherein the sheet unit is placed on the side facing the backsheet of the absorbent structure; Figure 7 shows a schematic transverse cross-sectional view of an absorbent article comprising an absorbent structure in accordance with the present invention, which includes a dedusting layer; Figure 8 schematically shows a production line for forming the absorbent articles comprising an absorbent structure in accordance with the present invention; Figure 9 is a plan view of a nozzle assembly in accordance with the present invention; Figure 10 is an elevation view of the nozzle assembly of the Figure 9; Figure 11 is a cross-sectional view of the inlet 106 of the nozzle of Figure 9, illustrating the bifurcation plate 104; Figure 12 is a cross-sectional view similar to Figure 11 illustrating an alternate configuration of the diffuser plate; and Figure 13 is an enlarged, perspective view illustrating the relationship between the air gun 56 and the adhesive nozzle 53 illustrated in Figure 9 in the operation.

DETAILED DESCRIPTION OF THE INVENTION As used herein, the term "absorbent article" refers to devices that absorb and contain exudates from the body and, more specifically refers to devices that are placed against or close to the user's body to absorb and contain the different exudates discharged from the body. The term "disposable" is used herein to describe absorbent articles that are not intended to be washed or otherwise restored or reused as an absorbent article (ie, they are intended to be discarded after a single use and , preferably to be recycled, composted or otherwise disposed of in an environmentally compatible manner). A "unitary" absorbent article refers to absorbent articles that are formed of separate parts joined together to form a coordinated entity, such that they do not require separately manipulated parts such as a liner and a separate fastener. A preferred embodiment of an absorbent article of the present invention is the unitary disposable absorbent article, diaper 20, shown in Figure 1. As used herein, the term "diaper" refers to an absorbent article generally worn by infants and toddlers. incontinent that is used around the user's lower torso. However, it should be understood that the present invention is also applicable to other absorbent articles such as incontinence briefs, incontinence undergarments, diaper bras and liners, training pants, climbing diapers, feminine hygiene garments such as sanitary napkins and the like.

Absorbing Article Figure 1 is a plan view of the absorbent article 20, in particular a diaper, in accordance with the present invention in its flattened, non-contracted state (i.e., with the contraction induced by the elastic pulled outwards), with portions of the structure that are cut to show more clearly the diaper construction 20, and with the portion of the diaper 20 that gives or makes contact with the wearer, the interior surface, facing the viewer. As shown in Figure 1, diaper 20 comprises a liquid-permeable topsheet 21 of which a portion has been cut away to show the underlying structure. The core 1 is comprised between the upper sheet 21 and the back sheet 23. The diaper 20 further comprises elasticized side panels 30 which can elastically extend in the direction of the transverse center line 16, elasticized leg folds 32, an elastic waist feature 3. 4; a generally multiple fastener system designated 36. Figure 1 shows a preferred embodiment of the diaper 20 in which the top sheet 21 and the back sheet 23 have length and width dimensions generally greater than those of the absorbent structure 1. The top sheet 21 and the backsheet 23 extend beyond the edges of the absorbent structure 1 to thereby form the periphery of the diaper 20. Although the top sheet 21, the backsheet 23 and the absorbent structure 1 can be assembled in a variety of configurations Well-known diaper configurations are generally described in the United States patent. 3,860,003 entitled "Shrinkable side portions for disposable diaper" which was issued to Kenneth B. Buell on January 14, 1975; and United States Patent Application Serial No. 07 / 715,152, issued "Absorbing article with dynamic elastic waist characteristic having a predisposed elastic flexion joint" Kenneth B. Buell et al. filed June 13, 1991; each of which is incorporated herein by reference.

Figure 2 shows a plan view of an absorbent structure 1, comprising storage areas 13, 13 'and a central acquisition zone 11. Figures 3 and 4 show a cross-sectional view of the absorbent structure 1 throughout of the transverse centerline 16 and the longitudinal centerline 17, respectively. The absorbent structure comprises an upper layer 3 and a lower layer 5. The upper layer 3, comprises a substrate 7 and a layer of particles of gelling absorbent material 9, attached to the substrate 7. The combination of the substrate 7 and the particles of gelling absorbent material attached thereto is also referred to as a "laminar unit". The upper layer 3 comprises a central acquisition zone 11 and a storage area 13, 13 'that surrounds the acquisition zone 11 on either side. The average basis weight of the particles of gelling absorbent material 7 in the acquisition zone is relatively low compared to the average basis weight of the particles of gelling absorbent material in the 13,13 'storage zone. Preferably, the particles of gelling absorbent material are not present in the acquisition zone 11. The storage zone 13, 13 'may comprise an average basis weight of the particles of gelling absorbent material greater than 25 g / m2, preferably greater than 40 g / m2, the average basis weight of the particles in the acquisition zones 11 being below 25 g / m2. The lower layer 5 comprises a mixture of particles of gelling absorbent material and fibers, which may be a pulp of cellulose fluff, than the synthetic or combinations thereof. The lower layer 5 is preferably formed by placement by air. The upper layer 3 is preferably placed on the upper layer of the lower layer 5., in such a way that the particles of the gelling absorbent material 9, are included in 3 substrates 7 and the lower layer 5. The substrate 7 prevents the particles of gelling absorbent material, if they get to detach from the substrate, migrate towards the side facing the user 15 of the structure 1 and prevents the particles from contacting the user's skin. Figures 5 and 6 show cross-sectional views along the transverse centerline 16 and the longitudinal centerline 17 of an embodiment of the absorbent structure, wherein the laminar unit 3 is located below the mixed layer 5. The layer of particles of gelling absorbent material 9 is distributed non-uniformly through the substrate 7. When desired, strips, channels or other variations in the basis weight of the particles of gelling absorbent material can be applied in the laminar unit 3 Figure 7 shows a schematic cross-sectional view of a preferred embodiment of an article 20 comprising an absorbent structure 1 according to the present invention. The absorbent structure 1 is preferably enclosed between a liquid-permeable upper sheet 21 and a liquid-impermeable back sheet 23.

The Top Sheet The top sheet 21 is placed adjacent to the surface facing the body 15 of the absorbent structure, or core 1, and is preferably attached to it and to the backsheet 23 by attachment means (not shown), such as those well known in the art. Suitable fixing means are described with respect to the attachment of the backsheet 23 to the absorbent structure 1. As used herein, the term "attached" embraces configurations with which one element is directly secured to the other element, securing the element directly to the other element, and configurations with which the element is directly secured to the other element by fixing the element to a member or intermediate members, which in turn are fixed to the other element.

In a preferred embodiment of the present invention, the topsheet 21 and the backsheet 23 are directly bonded together at the periphery of the absorbent article 20, and are bonded together indirectly by attaching them directly to the absorbent structure 1 by the attachment means (not shown). The upper sheet 21 is docile, of soft feeling and non-irritating to the wearer's skin. In addition, the topsheet 21 is permeable to liquid allowing liquids (eg urine) to easily penetrate through its thickness. A suitable top sheet can be manufactured from a wide range of materials, such as porous foams, cross-linked foams; plastic films with openings; or woven or nonwoven webs of natural fibers (e.g., wood or cotton fibers), synthetic fibers (e.g. polyester or polypropylene fibers), or a combination of natural and synthetic fibers. Preferably, the topsheet 21 is made of a hydrophobic material to isolate the user's skin from the liquids contained within the absorbent core 1. Preferably, the top sheet is coated with a hydrophilic coating which is removed by washing the top sheet after that gets wet. There are a number of manufacturing techniques that can be used to manufacture the top sheet 21. For example, the top sheet 21 can be a non-woven web of spunbonded, carded, wet-laid, melted and hydroentangled-blown fibers, combinations of the above or similar. A preferred top sheet is carded and thermally bonded by means well known to those skilled in the art of fabrics. A preferred top sheet comprises a short length polypropylene fiber web, as manufactured by Veratec, Inc., a division of the International Paper Company of Walpole, Massachusetts under the designation P-8.

The Backsheet The backsheet 23 is placed adjacent to the garment surface of the absorbent structure 1 and is preferably bonded thereto by attachment means (not shown), such as those well known in the art. For example, the backsheet 23 can be secured to the absorbent structure 1 by a uniform, continuous adhesive layer, a patterned adhesive layer, or an array of separate lines, coils or dots of adhesives. The adhesives that have been found to be satisfactory are manufactured by H.B. Fuller Company of St. Paul, Minnesota and marketed as HL-1258. The fixing means preferably comprise a network of open-pattern adhesive filaments as disclosed in U.S. Patent 4,573,986 entitled "Waste containment garment, disposable", which was issued to Minetola et al. On March 4, 1986, more preferably several lines of adhesive filaments twisted in a spiral pattern as illustrated by the apparatus and methods shown in U.S. Patent No. 3,911,173 issued to Sprague, Jr. on October 7, 1975; U.S. Patent 4,785,996, issued to Ziecker et al. on November 22, 1978; and U.S. Patent 4,842,666 issued to Werenicz on June 27, 1989. Each of these patents is incorporated herein by reference. Alternately, the fixing means may comprise heat junctions, pressure junctions, ultrasonic junctions, dynamic mechanical joints or any other means of attachment or combinations of these fixation means as are known in the art. The backsheet 23 is impervious to liquids (eg urine), and is preferably manufactured from a thin plastic film, although other flexible liquid impervious materials may also be used. As used herein, the term "flexible" refers to materials that are docile and that will readily conform to the shape and general contour of the human body. The backsheet 23 prevents the exudates absorbed and contained in the absorbent structure 1 from wetting the articles that come into contact with the absorbent article 20, such as sheets and undergarments. The backsheet 23 can thus comprise a woven or non-woven material, polymeric films such as polyethylene or polypropylene thermoplastic films or composite materials such as a film-coated nonwoven material. Preferably, the backsheet is a thermoplastic film having a thickness of from 0.012 mm to about 0.051 mm. Particularly preferred materials for the backsheet include the RR8220 blown films and the RR5475 cast films as manufactured by Tredegar Industries, Inc., of Terre Haute, IN. The backsheet 23 is preferably embossed and / or dull finished to provide a more fabric-like appearance. In addition, the backsheet 23 can allow the vapors to escape from the absorbent structure 1, (ie, breathable), while still preventing the exudates from passing through the backsheet 23. The Acquisition Layer In the embodiment of the Figure 7, the absorbent structure 1, comprises an upper acquisition layer 25. The acquisition or collection layer 25 serves to rapidly collect large discharges of liquids and isolate them from the user's body, until these liquids have been absorbed by the underlying layers 5,7,9. The density of the acquisition layer 25 is preferably between 0.02 and 0.13 grams per cubic centimeter, the basis weight being between 50 and 500 grams per square meter, depending on the volume of the discharge to be captured. A preferred material for the acquisition layer 25 is a chemically hardened cellulosic material as described in EP-A-0 429 112 (Herrón) United States Patent 4,898,642 (Moore) and 4,889,597 (Bourbon). The most useful acquisition layers comprise open networks of thermally bonded synthetic air-laid fibers, also referred to as "TBAL", as described in patent applications No. 08/141, 156 and EPA-A-513 148. Other Useful materials for use as an acquisition layer are described in the application PCT / EP94 / 01814, filed on June 3, 1994. Materials most suitable for the acquisition layer are air filters, air filter mixes and synthetic fibers, or for example, raised floor nonwovens as produced by Corovin GmBH, Postfach 1107, D-31201 Peine, Germany, under the trade name COROLOFT. An important property of the acquisition layer 25 is its ability to maintain a sufficient hollow volume for uptake of liquid, even when wet. The fibers in the layer 25 must be sufficiently elastic so as not to collapse in its wet state upon compression.

The Mixed Layer The mixed layer 5 can comprise any fibrous absorbent medium that is generally compressible, conformable, non-irritating to the user's skin and capable of absorbing and retaining liquids such as urine, and other certain exudates from the body. The lower layer 5 can be manufactured in a wide variety of sizes and shapes (eg, rectangular, hourglass, capital T, asymmetric, etc.), and from a wide variety of commonly used liquid absorbent materials. in disposable diapers and other absorbent articles such as crushed wood pulp which is generally referred to as an air filter. Examples of other suitable absorbent materials that can be used in addition to the fibrous material included in layer 5 are, for example, accreted cellulose wadding; blown polymers in the molten state, including coform; chemically modified or cross-linked cellulose fibers; tissue, including tissue wraps and laminates, absorbent foams, absorbent sponges; etc. the configuration and construction of the absorbent core can also be varied (for example, the absorbent core can have zones of variable gauge, a hydrophilic gradient, a superabsorbent gradient, or acquisition zones of lower average density and lower average basis weight; one or more layers or structures). The total absorbent capacity of the absorbent structure 1, however, must be compatible with the intended design load and intended use of the diaper 20. In addition, if the size and absorbent capacity of the absorbent structure 1 can be varied to encompass varying users from babies to adults. Mixed Layers 5 copies are described in U.S. Patent 4,610,678 entitled "High Density Absorbing Structures", issued to Wesiman et al. On September 9, 1986; U.S. Patent 4,673,402, entitled "Absorbent articles with cores with double layers", issued to Wesiman on June 16, 1987; U.S. Patent 4,834,735, entitled "High density absorbent members having lower density and lower basis weight catchment areas", issued to Alemany et al. on May 30, 1989. Each of these patents is incorporated herein by reference. In the embodiment as illustrated in Figure 7, a fibrous layer 10 that is substantially free of particles of absorbent gelling material, also referred to as a dedusting layer, is located below the mixed layer 5. The dedusting layer 10 and the The fibrous matrix of the mixed layer 5 can be parts of a single homogenous fibrous layer that has been formed by placing with air. However, for the purpose of the present invention, the dedusting layer 10 is not considered as a part of the mixed layer 5. Forming an absorbent core comprising a mixed layer 5 and a dedusting layer 10 has been described in the US Pat. the states No. 4,88,231, entitled "Absorbent Core Having a Dust Cap" issued to Angstadt on December 19, 1989.

The laminar unit The substrate layer 7 of the laminar unit 3 can, for example, be formed by a non-woven layer or by a tissue layer such as the BOUNTY tissue as marketed by The Procter & Gamble Company, or such as a high wet strength tissue of a basis weight of 22.5 g / m2 as produced by STREPP HmbH & Co. KG, D 5166 Kreuzau-Untermaubach Germany, under the NCB reference. Alternatively, the substrate layer 7 is formed by a three-dimensional apertured thermoplastic film as described in EP-A-0 203 820 (Curro), EP-A-0 156 471 (Curro) and in EP-A-0 141 654 (Koger II). Other suitable materials for forming the substrate layer 7 are high wet strength nonwoven materials, such as high wet strength nonwovens, such as polyolefin nonwovens. The particles of gelling absorbent material can be fixed to the substrate by applying a layer of adhesive to the substrate 7, followed by deposition of the particles on the adhesive layer. The acquisition or acquisition zone 11 is preferably substantially free of both adhesive and particles of gelling absorbent material in such a way that it maintains its ability to function in the acquisition role. In a presently preferred configuration, the basis weight of the particles 9 in the storage zone 13, 13 'is approximately 25 g / m2. In a preferred baby diaper 1, the laminar unit 3 of the absorbent structure comprises a total of between 1 to 4 grams of particles of gelling absorbent material, such that the combined weight of the particles of gelling absorbent materials in the laminar unit 3 in the mixed layer 5 form at least 40% of the weight of the fibers in the mixed layer 5. The acquisition zones 11 can be formed by any pattern of open areas such as a number of channels or a number of circles, squares , etc.

Method and apparatus for making an absorbent article Figure 8 shows schematically a process for making an absorbent article according to the present invention. A first tissue 50 is unwound from a supply roll 51. The tissue 50 forms the side facing the user 15 of the absorbent structure. Heat-melt adhesive supplied from a tank 54 is applied to a nozzle 53 and sprayed as fibers blown in the molten state by the nozzle 53 into two longitudinal strips parallel to the longitudinal direction of the tissue 50. The particles of absorbent gelling material are supplied from a container 58 and are blown by an air pistol 56 through spray of the adhesive leaving the nozzle 53. The absorbent particles are directed by the air pistol 56 according to the present invention on the same longitudinal parallel strips of the Tissue 50 as the adhesive. The suction device 55 assists in the placement of the particulate material on the tissue and also serves to collect lost particles. The particles of adhesive-coated gelling absorbent material are deposited in the storage zone of the substrate and form, in combination with the tissue, the laminar unit 52. The functionality of the air pistol 56 according to the present invention is as described in FIG. the next section. The cellulosic fibers are deposited on a conduit 63 on a positioning screen 62 of a rotating positioning drum 61. The particles of gelling absorbent material are shown in a stream of air that carries the fibers from the storage container 64. the positioning drum 61, the mixed layer 63 is formed. The particles of container gelling absorbent material 64. Are introduced into the fiber stream, such that they are predominantly located on the right-hand side of the material discharge conduit. 63. As a consequence, the fibers that are first deposited on the positioning screen 62 when the positioning cavity 64 is rotated below the material fall pipe, are not mixed with the particles of absorbent gelling material and form the dedusting layer 74. The absorbent element comprising the dedusting layer 74 and the mixed layer 73, are placed on the laminar unit 52. A suction device 66, 68 draws the fibrous absorbent member 73 onto the laminar unit and keeps the absorbent elements in a defined position. In a tightening space or inlet formed by a pair of calendering rollers 70 and 71, the absorbent elements 73 are compressed to the desired thickness and density. From an additional supply roller 75, a preformed web unit 76 of any configuration is unwound and placed on the side facing the backsheet of the absorbent member 73. The use of a preformed web unit 76 is optional and may be omitted when only a single laminar unit is desired on the side facing the user of the absorbent structure. Alternatively, the laminar unit 76 that faces the backsheet can be made in an in line manner similar to the way in which the laminar unit 52 was formed. Then the backsheet 78 and the topsheet 80 are supplied from rolls of supply 76 and 81, respectively, and are combined with the absorbent element 73 which now comprises the laminar unit 76 that faces towards the backsheet, the dedusting layer 74, the mixed layer 73 and the laminar unit 52 facing the top sheet The web of absorbent articles is then cut to form individual absorbent articles in a cutting unit that has not been illustrated in this figure. The individual absorbent articles are folded into a bending unit 83 and are stacked, compressed and packaged in a packing unit 85. The process for forming the absorbent article according to the invention has been described only schematically. The steps of the process for fixing the elastic elements and the provision of a tape fastening system have been omitted. A detailed description of a process for forming a mixed layer have been described in U.S. Patent Nos. 4,765,780 and 4,764,325 (Angstadt).

Method and apparatus for making an absorbent structure (laminar unit having divided zones of particles) Figures 9 and 10 illustrate in greater detail the construction of an air pistol 56 according to the invention, which is particularly useful for forming structures absorbers such as the laminar unit 3. As stated above, the laminar unit 3 preferably includes parallel strips or bands 9 of particles of absorbent gelling material adhered on the substrate layer 7, separated by an acquisition or collection zone substantially free of charge. adhesive and particle-free 11. While it is preferred that the acquisition zone 11 be substantially free of adhesive, a relatively small amount of adhesive can be applied to the acquisition zone to join this zone to the underlying mixed layer to improve the integrity of the adhesive. absorbent structure. A suitable adhesive is, for example, the thermal melt adhesive as produced by Findley, Roosendal, Netherlands, under reference H 2127. The adhesive can be deposited through the adhesive nozzle 53 as a melt blown film that it is blown at such high air velocities that the film breaks in an open network of filaments as described in U.S. Patent 4,573,986 (Minetola). Alternatively, a spiral pattern of adhesive can be deposited to obtain a network impervious to the liquid of adhesive filaments as described in the US patent.

United States 3,911, 173, 4,031, 854 and 4,098,632 (all issued to Sprague). In order to adhere the particles of the gelling absorbent particles to the substrate 7 according to the invention, the particles are directed through a stream of adhesive before being contacted with the substrate to form adhesively coated particles. Subsequently, the adhesive coated particles of the suspension are filtered to be captured or deposited on the substrate. In this way, good liquid permeability of the laminar unit is maintained, and very little fluid blockage takes place by the adhesive. The acquisition or acquisition zones 11 can be kept substantially free of adhesive by the selective application of the adhesive to the substrate, for example, by application of two parallel adhesive strips covering the acquisition areas 13, 13 '. The adhesive can be applied by a single nozzle through a shield element which blocks the part of the glue stream that is directed to the acquisition zone 11, or can be applied by two separate glue nozzles. In the acquisition zone 11, particles of gelling absorbent material are preferably not present. Accordingly, regardless of whether the acquisition zone 11 is totally free of adhesive, the air pistol 56 according to the present invention provides multiple streams of particles of gelling absorbent material, and a record with the deposition regions. 13,13 '. Of the desired laminar unit, and in register with the adhesive pattern produced by the multiple adhesive nozzles or the unfolded regions of the nozzle. As illustrated more clearly in Figure 9, the air gun 56 preferably includes two elements: an eductor or ejector 101 and a bifurcation nozzle 100. The eductor 101 dispenses the individual particles of the gelling absorbent material in an air stream to form an air stream. or generate a suspension of substantially evenly distributed particles. The eductors or ejectors of this variety are commercially available under the trade designation Fox Venturi Eductor 1 1/12"Model 300-SCE-55, Stainless Steel Version, manufactured by Fox Valve Development Corporation of Dover, NJ The bifurcation nozzle 100 dividing the suspension of substantially evenly distributed particles into multiple suspensions of substantially uniformly distributed particles As used herein, suspensions of substantially uniformly distributed particles are those where the particles are distributed substantially uniformly as a function of the cross-sectional position at any given cross-sectional location in a duct. In the configuration illustrated in Figures 9 and 10, the bifurcation nozzle 100 includes two branch ducts 102 and 103 of approximately equal cross-sectional area. In the inlet duct (nozzle inlet 106) a particle suspension divider (bifurcation plate 104) is placed to divide the suspension of substantially uniform input particles based on the cross-sectional area into multiple particle suspensions, which then proceed through the corresponding branched ducts. The nozzle inlet 106, and the bifurcation plate 104 can be sized and configured to produce multiple suspensions of equal, proportional particles or different particle content and mass flow. For example, in the configuration illustrated more clearly in Figure 11 (a cross section of the nozzle inlet 106), the bifurcation plate 104 is positioned at the inlet of the nozzle 106 to divide the inlet area in cross section equally into two. passages of equal cross-sectional area (50%) of the original cross-sectional area), which feeds the branch ducts 102 and 103. Accordingly, the particle suspension that enters the bifurcation nozzle 100 from the eductor 101 is divided also in two suspensions of particles for deposition on the substrate 7. The branching ducts 102 and 103 preferably have a length and geometry to balance the particle distributions in the multiple streams after division in the event of any non-uniformity that is enter in the flows, and are set up to download the particle suspensions in the desired orientation with re to each other and to the receiving surface. As illustrated in Figure 13, it is presently preferred that the branching ducts direct the suspensions of particles divided away from one another (being originally adjacent to one another in the same suspension) and then parallel to each other again to form the multiple suspensions of parallel separated particles). In this separation of itself it provides the substantially particle-free zone in the finished laminar unit corresponding to the catchment area 11. Figure 13 illustrates the air gun 56 of Figure 9 in operation when installed in a manufacturing frame as illustrated in Figure 8. Note the relationship between the air gun 56 and the adhesive nozzle 53, and the divided particle streams 201 and 202. In the event that in more than two streams of particles of If desired, the configurations of the bifurcation plate can be developed to divide the inflow in a sectional manner into 3 or more particle suspensions of the desired relative ratios and / or multiple bifurcation nozzles 100 can be used in sequence to subdivide the flows and divided. A configuration of the bifurcation plate to divide an inflow into 3 flows is illustrated in Figure 12, where the entry area in cross section, each 33% of the original area in cross section, each of which can feeding a branch of the nozzle and thus generating 3 assorted bands of gelling absorbent material particles in a laminar unit. If two, three, or more resulting flows are desired, it is currently preferred to achieve flow division through the orientations of the bifurcation plate, which are circumferentially separated asymmetrically. In the event that some non-uniformity of incoming particle suspension occurs, this deviation of uniformity is frequently but typically asymmetric circumferentially, that is, a comparable distribution would be observed at several circumferential locations at a constant radius from the center of the entrance duct. Therefore, by achieving the division of the flow over an asymmetric circumferential base, the probability of the resulting variations in the volume of flow / density is reduced. It is also possible to join the particles of gelling absorbent material without the use of an adhesive. The particles can be deposited on a moist substrate 7 such that the particles absorb moisture on their surface and become sticky. The subsequent drying of the moist substrate 7 under the application of pressure results in the fixation of the particles 9 to the substrate 7. In this manufacturing method, the adhesive nozzle 53 would be omitted from the schematic illustration of Figure 8, but the shape and function of the air pistol 56 would remain the same. In another alternate configuration, where the particles are interconnected by the application of an interparticle crosslinking or interlacing agent to form an interparticularly interlaced aggregate, the particles of the gelling absorbent material can be attached to the substrate by the interparticle interlacing agent. This has been described in United States patent application 08/142258 (Hseuh). A method for forming a multilayer layered unit having a multiplicity of tissue layers and layers of gelling absorbent particles enclosed between the tissue layers is described in U.S. Patent 4,578,068 (Kramer). In this structure the particles of gelling absorbent material are bonded to the tissue layers substantially completely by fiber entrapment. A method for depositing the particles of gelling absorbent material on a substrate has been described in U.S. Patent 4,551,191 (Kock). Both of the aforementioned US patents are incorporated herein by reference. Although embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, attempts are made to protect all these changes and modifications that are within the scope of the invention.

Claims (10)

1. A method for making an absorbent structure, characterized in that said method comprises the steps of: a) generating an initial suspension of particles comprising a two-phase fluid of particles, preferably comprising gelling absorbent material, suspended in a gas, preferably air , which flows in an inlet duct, said particles being substantially uniformly distributed in said gas as a function of the cross-sectional position in said inlet duct; b) dividing the initial suspension of particles into multiples, preferably two or three, final suspensions of particles in correspondence with multiple branching ducts, each of the final suspensions of particles having a percentage of particles as a function of the cross-sectional area of the particles. entrance duct, said particles being substantially evenly distributed in said gas as a function of the cross-sectional position of said branch ducts; c) preferably, directing the final suspensions of particles through a stream of adhesive to form adhesively coated particles; and d) filtering the adhesively coated particles from said final particle suspensions by depositing the adhesively coated particles on a substrate. The method for making an absorbent structure, according to claim 1, further characterized in that said final particle suspensions have approximately equal percentages of particles as a function of the cross-sectional area of said inlet duct. The method for making an absorbent structure, according to claim 1 or claim 2, further characterized in that the initial suspension of particles is circumferentially divided symmetrically in the final suspensions of particles. The method for making an absorbent structure, according to any of claims 1 to 3, further characterized in that the final suspensions of particles are directed away from each other and then directed parallel to each other to form suspensions of separate particles, parallel, before capturing said particles. The method for making an absorbent structure, according to any of claims 1 to 4, further characterized in that the final particle suspensions are directed through the corresponding multiple adhesive streams. 6. An apparatus for making an absorbent structure, the apparatus including an inlet duct and a particle suspension generator, preferably an eductor, in fluid communication with the inlet duct to generate an initial suspension of particles comprising a fluid of two phases of particles suspended in a gas flowing into said duct, the particles being substantially evenly distributed in said gas as a function of the cross-sectional position in said inlet duct, characterized in that the apparatus comprises, in combination a) at least two branching ducts in fluid communication with the inlet duct, said branching ducts preferably having separate outlets to provide suspensions of separate, parallel particles; b) a particle suspension divider, preferably a bifurcation plate, disposed within the inlet duct to divide the initial suspension of particles in the inlet duct into multiple, preferably two or three, final suspensions of particles in said branch ducts, said particle suspension divider preferably circumferentially dividing symmetrically said initial suspension of particles in the final suspensions of particles, each said final particle suspensions having a percentage of particles as a function of the cross-sectional area of the entrance duct, said final particle suspensions preferably having approximately equal percentages of particles as a function of the cross-sectional area of the inlet duct; and c) preferably, an adhesive supplying device for adhesively coating the particles in said final particle suspensions to form adhesive coated particles. The apparatus for making an absorbent structure, according to claim 6, further characterized in that the final particle suspensions have approximately equal percentages of particles as a function of the cross-sectional area of the inlet duct. The apparatus for making an absorbent structure, according to claim 6 or claim 7, further characterized in that the particle suspension divider circumferentially symmetrically divides the initial suspension of particles in the final particle suspensions. The apparatus for making an absorbent structure, according to any of claims 6 to 8, further characterized in that the adhesive supplying device comprises multiple glue nozzles. The apparatus for making an absorbent structure, according to any of claims 6 to 8, further characterized in that the adhesive dispensing device comprises a single glue nozzle.