CA1253752A - Method for uniformly distributing discrete particles on a moving porous web - Google Patents

Abstract

METHOD FOR UNIFORMLY DISTRIBUTING DISCRETE PARTICLES ON
A MOVING POROUS WEB

ABSTRACT
The present invention comprises method and apparatus for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface of a moving porous web so that the particles occupy less than 100% of the predetermined portion of the uppermost surface of said moving web. The method preferably comprises the steps of (a) entraining the particles into a moving gaseous stream;
(b) passing the gaseous stream through a conduit having a discharge end with a nozzle exit positioned adjacent the uppermost surface and oriented so as to discharge the gaseous stream containing said entrained particles in a direction substantially parallel to the direction of travel of the moving porous web;
(c) mixing the particles entrained in the gaseous stream inside the conduit to provide a substantially uniform distribution of the particles, as measured across the width of the nozzle exit of said conduit In a direction perpendicular to the direction of travel of said moving porous web;
(d) discharging the gaseous stream containing the uniformly distributed entrained particles from the conduit adjacent the predetermined portion of the uppermost surface of the moving porous web; and (e) maintaining the fluid pressure adjacent the lowermost surface of the moving porous web at a level lower than that adjacent the uppermost surface of the web in an area coinciding in width to the predetermined portion of the web, said area being located near the nozzle exit of the conduit, whereby the bulk of the uniformly distributed particles entrained in the discharged gaseous stream are substantially uniformly deposited onto the predetermined portion of the uppermost surface of the moving porous web as the bulk of the gas in the gaseous stream is drawn from the uppermost to the lowermost surface of said porous web.

Description

~ 2~3'7~
METHOD FOR UNIFORMLY DISTRIBUTING DISCRETE PARTICLES ON
A MOVI NG POROUS WEB

TECHNICAL FIELD
The present invention relates to a method for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost 5 surface of a moving porous web. The present invention relate$ particularly to such a method wherein the particles occupy less than 10096 of a predetermined portion of the uppermost surface of said moving web.

The present invention has particular relation to a 10 method for substantiaily uniformly distributing a layer of discrete particles comprised of superabsorbent polymeric materiai onto a predetermined portion of the uppermost surface of a moving web of absorbent material, such as a tissue ply, a layer of airlaid comminuted wood pulp fibers, a 15 three-dimensional absorbent batt or the like. In a partlcularly preferred embodiment, the particle lay down process is followed by superposing a second moving web of porous material, such as a tissue ply or the like, and three-dimensionally embossing said webs to form a uniformly 20 three-dimensional absorbent laminate structure, _ _ _ Method and apparatus for distributing particulate over a given subs.rate are generally known in the art.
Typical applications for such method and apparatus 25 are found in the field of agriculture where particulate spreaders ara utili7ed to deposit seed and fertilizer.
Other prior art applications Include the distributlon of particulate in the form of gravel and/or de-lcing compounds onto the surfaces of rQadways during periods of 30 inclement weath~r.

~*

Still other applications include the delivery of a powder coating reactant to the surface of a glass sheet while the glass sheet is maintained in an oxidizing atmosphere at a temperature sufficient to pyrolize the coating reactant to 5 deposit a metal oxide film on the surface of the glass. One such method is disclosed in U.S. Patent 4,3~14,986 issued to Henery on August 17, 1982. In the disclosed embodiment, Henery employs a screw feeder for the reactant powder and an eductor to entrain the powder into a gaseous stream. A
10 series of baffles project into the entrance of the coating chamber to create turbulence in the powder/gas mixture, thereby allegedly improving the uniformity of coating. The discharge of the slotted nozzle is oriented substantially perpendicular to the surface of the glass sheet, which 15 preferably moves beneath the nozzle to provide a complete coating by the discharged powder.
Recent advances in the field of absorbent strwctures such as disposable diapers have, however, given rise to a need for method and apparatus to substantially uniformly distribute discrete particles within a predetermined portion of the absorbent cores utilized in such structures so that the particles occupy less than 100% of the area in which they are distributed.
Although prior art absorbent structures useful as 25 absorbent cores in products such as disposable diapers, incontinent pads, catamenlal proclucts, and the like have generally been comprised primarily of absorbent fibrous materials such as absorbent papers, absorbent cloths, fibrous batts, and the like, a relatlvely new class of compounds 30 commonly known as superabsorbent polymers have been cieveloped and are gaining increasing use as at least a part of such absorbent structures. Such superabsorbent polymers are normally water insoluble polymeric materials capable of absorblng at Ieast i 5 times their welght ef water. Such 35 superabsorbent polymers are available in a varie~y of forms, ~5~

including flakes, powders and granules. Superabsorbent polymers generally dif~er from many conventional absorbent materials in that once an aqueous fluid is absorbed by most superabsorbent polymers, it generally cannot be expressed from the superabsorbent polymer under moderate pressure. This is often highly desirable in an absorbent structure such as a disposable diaper in that it prevents absorbed fluid from being expressed out of the structure.
When most superabsorbent polymers absorb aqueous fluids, they swell substantially, often to double their dry dimensions or more at saturation. As most superabsorbent polymers absorb fluid and swell, they generally become a gelatinous mass. If the superabsorbent polymer is in a particulate form and the particles are close to one another, they can coalesce and form a gel barrier which can block the flow of ~luid.
Thus, for maximum effectiveness of the superabsorbent polymers, absorbent structures which include such materials in particulate form preferably maintain separation of the particles from ona another to permit maximum absorption and swelling without allowing the particles to coalesce and form a gel barrier.
Prior art particle distribution techniques such as those described earlier hexein have not been successful in providing substantially uniform distribution of the particulate superabsorbent polymer when employed on converting lines which are typically utilized to construct abæorbent fibrous core structures at speeds of over 500 feet per minute.
OBJECTS OF ASPECTS OF THE INVENTION
Accordingly, it is an object of an aspect of the present invention to provide method and apparatus which will uniformly distribute discrete particles along a predetermined portion oE the uppermost surface of a moving porous web æo that the particles occupy less than 100% o~ ~aid precletermlned portion of the uppermost ~ur~ace o~ the moving w~b.

:

~253~5~
-~ 4 It is an object of an aspect of the present invention to provide such method and apparatus which will permit the distrihution of particulate onto a moving first porous web and thereafter securement of the distributed particulate in position by combining said first porous web with a second web, thereby encapsulating said distributed particulate between said first and second webs.
It is an object of an aspect of the present invention to provide method and apparatus whereby particulate may be uniformly distributed onto any desired number of parallel moving porous webs positioned over one another, and a laminate structure thereafter created by passing said webs either simultaneously or sequentially through one or more sets of combining rolls, such as three-dimensional embossing rolls, to maintain the particulate in its substantially uniformly distributed condition intermediate the respective webs.
SUMMARY OF THE INVENTION
In a particularly preferred embodiment, the present invention comprises method and apparatus ~or substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface of a moving porous web so that the particles occupy less than 100% of the predetermined portion of the uppermost surface of said moving web. The method preferably comprises the steps of (a) entraining the particles into a moving gaseous stream;
(b) passing the gaseous stream through a conduit having a discharge end with a nozzle exit positioned ad~acent the uppermost surface and oriented so as to discharge the gaseous stream containing said entrained particles in a 3~
`~

direction substantially parallel to the direction of travel of the moving porous web;
(c) mixing the particles entrained in the gaseous stream inside the conduit to provide a substantially uniform distribution of the particles, as measured across the width of the nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(cl) discharging the gaseous stream containing the uniformly distributed entrained particles from the conduit adjacent the predetermined portion of the uppermost surface of the moving porous web; and (e) maintaining the fluid pressure adjacent the lowermost surface of the moving porous web at a level lower than that adjacent the uppermost surface of the web in an area coinciding in width to the predetermined portion of the web, said area being located near the nozzle exit of the conduit, whereby the bulk of the uniformly distributed particles entrained in the discharged gaseous stream are substantially uniformly deposited onto the predetermined ~5 portion of the uppermost surface of the moving porous web as the bulk of the gas in the gaseous stream is drawn from the uppermost to the lowermost surface of sald porous web, I n a particularly preferred embodiment, a second porous web is thereafter superposed over said flrst web and the uniformly distributed particles deposited thereon and the two p~rous webs are passed simultaneously between a pair of matlng embossing rolls to three-dimensionally expand and fix the palr of w~bs to one another by fibrous entanglement, 7S~ -thereby substantially locking the particulate in a uniformly distributed conditîon between the webs.
In still another preferred embodiment of the present invention, recycling apparatus is provided at the lateral edges of the first porous web to collect any particulate which is not deposited directly onto the uppermost surface of the first moving porous web and to recycle the particulate thus collected back to the particle entrainment portion of the system. A similar recovery system may, if desired, be employed for particulate pulled completely through the porous web.
This not only minimizes losses which would otherwise be encountered duriny the particle distribution operation, but provides a m~re dust-free and sanitary operating environment.
Other aspects of this invention are as ~ollows:
A method for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface o~ a moving porous web traveling at a ~irst velocity so that said particles occupy less than 100% of said predetermined portion of the uppermost surface of said moving web, said method comprising the steps of:
(a) feeding said particles in a substantially uniform stream to the inlet of a gas eductor;
(b) entraining said particles in a moving gaseous stream;
(c) passing said gaseous stream through a conduit having a nozæle exit positioned adjacent the uppermost sur~ace of and oriented so as to discharge said gaseous stream containing said entrained particles in a direation substantially parallal to the direction of travel o~
said moving porous web, (d) mixing said particles entrained in said ga~eou~ stream inside said aonduit to ~0 provide a substantially uniform .

6a ~ ~5 3~ 5~
distribution of said particles, as measured across the width of said nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(e) discharging said gaseous stream containing said uniformly distributed entrained particles from said conduit adjacent said predetermined portion of the uppermost surface of said moving porous web at a second velocity which is greater than said first velocity; and (f) maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a level below the fluid pressure adjacent the uppermost surface of said moving porous web in an area coinciding in width to said predetermined portion of said web and located near the nozzle exit of said conduit, whereby the uniformly distributed particles entrained in said discha:rged gaseous stream are substantially uniformly deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas in said gaseous ætream is drawn from the uppermost to the lowermost surface of said web.
An apparatus for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface o~ a moving porous web traveling at a first velocity so that said particles occupy less than 100~ of said predetermined portion of the uppermost surface of said moving web, said apparatus comprising:
(a) means Por feeding said partiales in a substantially uniPorm stream to the inlet oP a gas eductor;
~b) means Por entraining said parti~les in a ~0 moving gasQous stream;

~37~
6b (c) conduit means for passing said gaseous stream through a nozzle exit positioned adjacent the uppermost surface of and oriented so as to discharge said gaseous stream containing. said entrained particles in a direction substantially parallel to the dire.ction of travel of said moving porous web;
~d) means for mixing said particles entrained in said gaseous stream inside said conduit to provide a substantially : uniform distribution of said particles, as measured across the width o:E said nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(e) nozzle exit means at the discharge end of said conduit means for discharging said gaseous stream containing said uniformly distributed entrained particles from said conduit adjacent said predetermined portion of the uppermost surface o~ said moving porous web at a second velocity which is greater than said first velocity; and (f) means for maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a level below the fluid pressure adjacent the uppermost surface of said moving porous web in an area coinciding in width to said pr~determined portion of said web and located near the noæzle exit of said conduit, whereby the uniformly distributed particles entrained in said : discharged gaseous stream are substantially uniformly deposited on said predetermined portion of the uppermost sur~ace of said moving porous web as the bulk of the gas in said gaseous stream is ~2~;37~3~
6c drawn from the uppermost to the lowermost surface of said web.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the present invention will be better understood from the following description in conjunction with tha accompanying drawings in which:
Figure 1 is a simplified perspsctive representation of preferred particle distribution and three-dimensional embossing apparatus of the present invention;
Figure 2 is a simplified schematic illustration of method and apparatus for substantially uniformly distributing particulate intarmediate the layers of a three-layer laminate structure in accordance with the present invention;
Figure 3 is an enlarged cross-sectional illustration of a two-layer laminate structure of the type generally disclosed in Figure 1, said cross-section being taken along section line 3-3 of Figure l; and Figure 4 is an enlarged cross-sectional illustration of a three-layer laminate structure taken at a point corresponding to section line 4-4 of Figure

2.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
While the present invention will be described in detail in the context of providing an absorbent laminate structure for use as an absorbent core in an absorbent 5 bandage such as a disposable diaper, the present invention is in no way limited to such application. For example, the present invention may be employed with equal facility to provide a substantially uniform, but spaced distribution of superabsorbent polymer ,oarticles on the uppermost surface of 10 a porous three-dimensional absorbent batt for later incorporation into disposable absorbent structures such as diapers and sanitary napkins.
Figure 1 discloses a particularly preferred system for constructing a two-layer laminate having discrete particles 15 of superabsorbent polymer substantially uniformly distributed along a predetermined portion of its width. In the embodiment illustrated in Figure 1, a first porous web 20 is delivered from a powered supply roll 21 supported on shaft 22 to a first idler roll 23 which preferably extends across the 20 width of the entire web 20.
Web 20 is preferably comprised of a porous material which is preferably fibrous in nature. It is most preferably comprised of thin, substantially contiguous material having two substantially parallel surfaces. Although the web of 25 porous material, as used herein, need not be flat or smooth, it is or can be laid out in a substantially planar, two-dimensional arrangement of indefinite length and indefinite width projectin~ in these two dimensions. The direction perpendlcular to the substantially planar, two-dimensional 30 arrangement of such a web of material will be referred to herein as the Z-direction of the web o-f material. The Z-direction structure of the webs of fibrous materials is an important attribute of the resultant layered absorbent structure described hereln.

7~i~

A web of porous material as used herein may be considered to have a true thickness and an apparent thickness. The true thickness of such a web of material is the distance between its two substantially parallel surfaces.
5 Because the webs are preferably comprised of fibrous materials, the microscopic surfaces of the webs of material are very irregular. Therefore, when the surfaces of these webs are described as substantially planar, the webs are being viewed on a macroscopic scale. The surfaces of the webs are 10 also described as substantially parallel; this does not mean that the webs cannot have thick and thin areas and even some discontinuous areas, e.g., holes. Instead, substantially parallel surfaces, as used herein, means that when there is a substantial macroscopic change of direction of one surface of 15 a web of material, the other surface of the web makes a substantially parallel change of direction.
Examples of porous webs used in absorbent bandages of the type herein describ&d include many papers and non-woven materials. The webs of fibrous materials used 20 in practiclng of the present invention are preferably webs of absorbent materials, more preferably webs of absorbent papers, more preferably still webs of absorbent tissues. The webs of fibrous materials of a layered absorbent structure of the type generally disclosed herein may all be the same 25 fibrous material or may be different flbrous materials.
In yet other embodiments o~ the present invention, the porous web on which the particles are deposited may comprise a layer of airlaid commlnuted wood pulp flbers or the like. Dependlng upon the coheslve strength of the particular 30 absorbent web selected, it may be necessary to utilize traveling support means, such as a foramlnous belt, or a tissue ply to convey the absorbent web during the particle distribution process. Sltuatlons of this type may or may not involve lamlnating of multlple web5 to produce an absorbent 35 core structure. For example, it may be sufflcient to provide ~,Z~7~i ~

uniformly distributed superabsorbent polymer particles throughout the uppermost region of a conventional absorbent web, such as a layer of airlaid comminuted wood pulp fibers.
Such a structure provides the ability to substantially instantaneously contain and temporarily store large volumes of rapidly discharged fluid within the void volume of the airlaid web. rhis ability to quickly contain and temporarily store rapidly discharged fluid, minimizes run-off and provides sufficient exposure time to effectively utilize the very large total absorbent capacity of the superabsorbent polymer particles which tend to absorb the fluid from the void volume of the airlaid web. This combination of properties is particularly desirable in structwres such as disposable diapers where urine is rapidly and periodically discharged over the lS entire useful life of the structure.
If desired, an additional web of similar or dissimilar type may be superposed on the first web after the particles have been distributed thereon.
Particularly preferred webs of absorbent tissue for making a layered absorbent structure of the type generally disclosed in the Drawing Figures exhibit a basis weight of from about 10 grams per square meter to about 100 grams per square meter, more preferably from about 15 grams per square meter to about 40 grams per square meter.
In the embodiment disclosed in Figure 1, the porous web 20 is fed from idler roll 23 across a particle deposition zone comprising a suction chamber 28 having an uppermost lattice type support grid 29, The lattice type support grid 29 exhibits a pattern of openings or apertures which will 3Q permlt a pre-determined portion oF the web having a width "W" to be exposed to a fluid pressure differentlal at some point durin~ its traverse of the vacuum chamber 28. Because of the porous nature of the web 20, vacuum blower 46 which is connect~d to vacuum chamber 28 vla conduit 45 draws air and gas present adjacent the uppermost surface of the porous ~537~.~

web 20 through that predetermined portion of the web corresponding to width "Y~" and discharges it through exhaust port 47, as generally shown in Figure 1. Thus the fluid pressure differential created by vacuum blower 46 causes the 5 particles 10 antrained in the gaseous stream adjacent thè
uppermost surface of porous web 20 to be deposited on that portion of the web corresponding to width "W" when the gas is drawn through the web.
The absorbent particles 10 used in layered 10 absorbent structures of the type disclosed herein may be any fluid absorbent material that swells when it absorbs fluid. It is highly preferred that the absorbent particles be water insoluble polymeric materials (superabsorbent polymers) having a water absorption capacity of 15 times their dry t5 weight or more, preferably having a water absorption capacity of 30 times their dry weîght or more, more preferably having an aqueous saline solution absorp-tion capacity of 30 times their dry weight or more o~ a solution of 19~ sodium chloride in water, There is a wide variety of materials which are or can be physically structured to perform as superabsorbent polymers. Although the following list is not meant to be inclusive of all superabsorbent polymers, such materials are disclosed in the following U.S. Patents; 2,798,053 issued to Brown on July 2, 1957; 2,988,539 issued to Gohen, Spaulding ~ Jones on June 13, 1961; 3,220,960 issued to Wichterle ~ Lim on November 30, 1965: 3,247,171 issued to Walker ~ Pillepich on April 19, 1966; 3,393,168 issued to Johnson on July 16, 1968; 3,419,006 issued to l~ing on December 31, 1968;

3,425,971 Issued to Gugliemelli, YVeaver ~ Russell on February

4, 1969; 3,514,419 issued to Darlow ~ Gibb on May 26, 1970 3,628,534 issued to Donohue on December 21, 1971; 3,661,815 issued to Smith on May 9, 1972; 3,664,343 Issued to Assarsson on May 23, 1972; 3,669,103 issued to Harper, Bash~w ~ Atkins on June 13, 1972; 3,670,731 3ssueci to 3P7~i~
. . .

Harmon on June 20, 1972; 3,783,872 issued to King on January 8, 1974; 3,810,4~8 issued to Harper, Bashaw Atkins on May 14, 1974; 3,926,891 issued to Gross McFadden on December 16, 1975; 3,935,099 issued to Weaver, Bagley, Fanta ~ Doane on January 27, 1976; 3,954,721 issued to Gross on May ~, 1976; 3,971,379 issued to Chatterjee on July 27, 1976; 3,980,663 issued to Gross on September 14, 1976; 3,993,553 issued to Assarsson ~ King on November 23, 1976; 3,997,484 issued to Weaver, E~acJley, Fanta ~ Doane on December 14, 1976; 4,017,653 issued to Gross on April 12, 1977; 4,018,951 issued to Gross on April 19, 1977; 4,044,766 issued to Kaczmarzyk, Hlaban ~ Bernardin on August 30, 1977; 4,045,387 issued to Fanta ~ Doane on August 30, 1977;
4,051,086 issued to Reid on September 27, 1977 L~,05~,124 issued to Yen ~ ~sterholtz on November 15, 1977; 4,076,673 issued to Burkholder, Jr. on February 28, 1978; 4,090,013 issued to Ganslaw ~ Katz on l~/lay 16, 1978; 4,093,776 issued to Aoki ~ Yamasaki on June 6, 1978; 4,102,340 issued to Mesek ~ Repke on July 25, 1978; 4,105,033 issued to Chatterjee ~ Morbey on August 8, 1~78; 4,117,1~4 issued to Erickson ~ Krajewski on September 2~, 1978; 4,190,562 issued to Westerman on ~ebruary 26, 1980; 4,200,557 issued to Chatterjee ~ Schwenker, Jr. on April 29, 1980; and 4,232,674 issued to Melican on November 11, 1~80~
Particularly preferred superabsorbent polymers for use in layered absorbent structures of the type herein disclosed comprise saponified starch-polyacrylonitrile graft copolymers, starch-polyacrylic acid graft copolymers, cross-llnked/grafteci cellulose, saponified vinyl acetate-acrylic acid copolymers, starch grafted polyvinyl acetate, acrylic acid polymers, cross-linked polyethylene oxide, and the like. The superabsorbent polymer particles used in such structures may all be the same or a mlxture of di fferent superabsorbent pol ymers .

7~

In the absorbent laminate structures disclosed in the Drawing Figures, absorbent particles 10 are preferably incorporated as a discontinuous layer between webs of porous materials. The absorbent particles 10 may be in a form such

5 as flakes, powders, or granules. Particularly preferred superabsorbent polymer particles comprise flakes or granules.
I n the resultant absorbent structures, it is preferable to minimize the amount of absorbent particles 10 that can substantially shift position in or escape from the 10 absorbent structure. Therefore, the particles are preferably larger than any openings in the porous webs. In addition to minimizing particle loss in the resultant absorbent structure, this helps to ensure rapid and even particle distribution on the uppermost surface of the porous web during the 15 deposition process, since the larger particles cannot pass through the web.
To minimize waste in practicing the present invention, it is particularly preferred that any particles drawn through the porous web 20 during the deposition 20 process be collected and recycled to the infeed end of the particle handling system.
For absorbent str uctures where the preferred absorbent tissues are used as the webs of fibrous materials, it is preferred that the si~e distribution of the particles be 25 such that about 90g6 (by weight) or more of the particles comprise two perpendicular dimensions of from about 0 . 05 mm to about 1.0 mm, more preferably such that about 7096 tby welght) or more of the particles comprise two perpendicular dimensions of from about 0 .15 mm to about 0. 6 mm. Many 30 absorbent structures disclosed in the references cited hereinbefore are comprised of layered webs of fibrous materials with superabsorbent polymer particles between the web layers. One reason the superabsorbent particles are incorporated In such structures is because they have a 35 grea~er water absorbing capaclty per gram than conventional ~2~i37~

absorbent fibrous materials. Because of this greater absor bing capacity of the superabsorbent polymer particles, such absorbent structures can be made thinner, less bulky and lighter in weight than absorbent structures macle entirely from conventional absorbent fibrous materials. Such thinner, Iess bulky, lighter weight absorbent structures provide potential benefits when incorporated in absorbent bandage products such as disposable diapers, disposable incontinent briefs, sanitary napkins, wound and/or surgical dressings, and the like.
For such absorbent products, the absorbing capacity of the product is a primary concern. However, the rate of absorption of fluid is also generally of importance for such products. I)isposable diapers, incontinent briefs, anci catamenial products, in particular, must be capable of handling gushes of fluid in short periods of time. In the layered absorbent structures disclosed herein, a primary function of the webs of porous materials is to initially absorb the gushes of fluid and transport the fluid to the superabsorbent polymer particles for absorption and retention by them. Thus the webs of fibrous materials preferably have sufficient void volume to handle such gushes of fluid and good wicking properties to quickly disperse the fluid throughout the absorbent structure and to the absorbent particles constrained between the webs. Absorption of the Flu~d from the fibrous materials by the superabsorbent polymer par~icles regenerates the absorbing capacity of the fibrous material so that it is capable of absorbing additional g~shes of fluid. .
A rapici absorption of the fluid by the superabsorbent particlas is desirablQ. The rate of absorption of fluid by the particles is, of course, dependent on the superabsorbent polymer employed; however, it is also dependent on the physical attributes of the particles and 35 their relatlonshlp to the webs of fibrous materials. The rate 5;3~S~2 of absorption of fluid by such a particle is proportional to the surface area of the particle exposed to the fluid being absorbed. Therefore, a maximum absorption rate is achieved by the particie when it is surrounded by the fluid being S absorbed. This can be accomplished in layered absorbent - structures of the present invention if each particle is surrounded by the fibrous material which transports the fluid to the particle.
As superabsorbqnt polymer particles absorb fluid, they swell substantially. Such a particle will exhibit its maximum rate of absorption and maximum absorbing capacity if it is free floating, totally unconstrained in the fluid being absorbed. If such particles are constrained such that they are not free to swell in an uninhibited manner, either the rate of absorption of fluid by the particle, or the capacity of the particle to absorb fluid, or both, will be adversely affected. The absorption rate andlor çapacity of many commercially available superabsorbent polymer particles are adversely affected by process conditions which affect their structure, partlcularly those involving wetting and drying, excessive heating, excessive pressure, or direct contact with adhesives. Such process steps, particularly those which involve the wetting and drying of the particles, can 31so increase the cost of making layered absorbent structures.
If the superabsorbent polymer partlcles 10 in an absorbent structure are constralned such that they are in contact with one another, bo~h the rate of absorption and absorption capacity of the particles will be adversely affected.
I f the particles are in contact with one another, fluid cannot totally surround each particle, and its maximum rate of absorption cannot be achieved. As the contacting particles absorb fluid and begin to swell, they are not free to swell to th&ir fullest extent because of their contact with one another;
thus they are unable to achieve thelr maximum absorblng 35 capacity. Also, as such contactin~ partlcles absorb water i397S~

and s~vell, they will often coalesce to form a gel layer which may block the flow of fluid to other particles, thus reducing the absorption rate and capacity of the structure as a whole.
It is therefore preferable to have the superabsorbent polymer particles separated within a layered absorbent structure with sufficient spacing between the particles to allow -them to swell to their maximum size without contacting neighboring particles .
It is therefore preferable that particles 10 are spaced sufficiently far enough from one another that if the resultant layered absorbent structure is subsequently wetted by a fluid such that particles 10 absorb the fluid and swell to saturation, the saturated particles would cover less than 1 Q0~
of the surface area of each of the interfaces between the superposed webs; more preferably the saturated particles would cover less than 90% of the surface area of each of said interfaces. Such a dispersed spacing of absorbent particles is preferred to ensure that even when the absorbent particles are saturated with fluid and swollen, there is still room between the swollen particles for fluid to pass through all the layers of the absorbent structure. This enables fluid to freely transport through such absorbent structures until it contacts and is absorbed by absorbent particles which are unsatu rated .
Since many superabsorbent polymer particles swell such that their dimensions when saturated with fluid are double or more their dry dimensions, it is preferred that such dry particles cover no more than 50% of the surface area of each of said interfaces; more preferably that the particles cover no more than 2096 of the surface area of each of the interfaces .
The foregoing targets for substantially uniform particle dlstrlbutlon wlthln a predetermined portion of the uppermost surfacs of the porous web 2Q can be achieved in ~5 accordance wlth the process generally dlsclosed in Flgure t~

75.~

In particular, the superabsorbent polymer particles 10 are fed from a bulk hopper 1 into a horizontal chamber in which is mounted a continuously rotating auger 3 which advances the particles 10 along the length of chamber 2 and discharges 5 them by gravity out discharge conduit 4. The speed of rotation of the auger 3 determines the rate of particle flow through discharge conduit 4.
Upon discharge from conduit 4, the particles 10 are entrained in a fast moving stream of air. In the illustrated 10 embodimen~, this is accomplished by discharging the metered particles 10 into an eductor 6 such as a Vortec Model No. 913 available from Vortec Corporation of Cincinnati, Ohio. The eductor 6 contains an internally located, circumferential slot 5 having a downwardly projecting orientation. The internally 15 located, downwardly projecting, circumferential slot 5 is connected to a pressure source, such as an air compressor (not shown), via conduit 71 which supplies compressed gas, preferably air, at a regulated pressure P1. Thus the eductor provides an internal, downwardly directed flow of gas about 20 the Interiar peripheral edge of the slot 5. The downwardly projecting gas flow issuing from the circumferential slot 5 draws ambient air from about the periphery of the eductor 6 and discharges it, along with the uniformly distributed entrained particles 10, at the noz;zle exit 13 of distribution 25 conduit 7, as generally shown in Figure 1. Use ~f the eductor 6 permits a substantially constant volume of particles 10 to be metered into the distribution conduit 7 without air disturbance of the particle meterin~ system.
The eductor 6 is preferably sized to provide an 30 adequate CFM tcubic feet per minute) rating at nozzle exit 13 at reasonably available compresseci air pressures. For any particular application, the CFM requirements are dependent upon the cross-sectional area of the nozzle exit 13 of dlstrlbutlon conduit 7 and the velocity needed to e~fectively 35 transport the particular partlcles 10 being spread. For small lightweight particles 10, i . e ., superabsorbent polymer particles of the type generally described herein, a nozzle exit velocity V2 in the range of about ~,000-3,000 feet per minute is typically sufficient. For higher flow rates (approaching 5 dense flow~ and more dense particles, higher velocities are generally found to work better. In addition to the foregoing, the size of the eductor is also determined by output area considerations of the distribution conduit 7. Since continual cross-sectional area reduction is required throughout the 10 traverse of the discharge conduit 7, the cross-sectional flow area existing at the slot 5 of the eductor 6 is preferably about double the cross-sectional flow area at no~zle exit 13.
As can be seen in the embodiment shown in Figure 1, distribution conduit 7 preferably comprises discrete straight segments 8, 9, 11 and 12 which convert the direction of particle discharge from vertical at the point of introduction to the eductor 6 to substantially horizontal and parallel to the upperrnost surface of moving web 20 at nozzle exit 13. Close coupling the vertically metered particles 10 with a nozzle exit 20 13 oriented parallel to a horizontally oriented, movin~ web not only minimizes turbulence, which could otherwise cause particle surging inside the conduit 7, but also minimizes the incidence of particle bounce at the web which typically results when the particles are discharged in a direction substantially 25 perpendicular to the direction of web travel.
In the illustrated embodiment, the direction of the particles 10 is changed from substantially vertical to substantially horizontal by means of lowermost sections 9, 11 and 12 of distribution conduit 7, each of the three segments 30 involving a 30 angle change to provide a 90 reorientation of the particle flow. The 30 straight sectlons provide riffling surfaces to spread particles by gravity as well as by airflow.
~s particles change direction at the 30 bends, they tend to spread. ~lowever, gravity and centrifugal ~orce cause the 35 partlcles to impact against the bottom side o~ the condult 7 7~

and thereby enhance the spreading action of the particles across the entire width of the noz21e.
In a particularly preferred embodiment of the present invention, a 10 to 1596 gas velocity increase occurs with each 30 angle change to prevent particle makeup in the corners of the distribution conduit 7.
Thus, through each discrete straight segment, i.e., segments 8, 9 and 11, the cross-sectional area, as measured in a direction substantially perpendicular to flow, decreases slightly so that the air velocity is increased slightly over the length of the segment. However, a 25-50% area reduction preferably occurs over segment 12 to create the primary pressure drop at nozzle exit 13. This is done to compensate for the fact that particles issuing from either lateral extremity of nozzle exit 13 must traverse a longer path in conduit 7 than particles issuing from the center of nozzle exit 13. The longer path at the lateral extremities of conduit 7 produces a greater pressure drop and would reduce air veloclty at the lateral extremities of the nozzle exit if the primary drop were not at the point of discharge. Thus, the higher air velocity, and hence the higher pressure differential, existing at nozzle exit 13 as a result of the reducti~n in cross-sectional area promotes uniform air and particle flow across the fuil width "W" of the nozzle exit.
For flow rates from about 5 to about 25 grams per second using particles 10 having a maximum density on the order of about 0.7 grams per cubic centimeter and a maximum size of about 1,000 microns, the no~zle exit height "T" is preferably at least 1/8 inch hlgh, regardless of its wldth "W"
so that particle clogging is prevented.
As will be apparent from Figure 1, the latter portlon of conduit 7, i.e., segment 12, employs straight sldewalls allgned substantially parallel to the lateral edges of the movlng web 20. Thls provldes parallel flow of the unlformly distrlbutecl ~as/partlcle stream whlch Issues from 37~ ~

no7zle exit 13 at velocity V2. In order to ensure that the gas/particle flow does not spread in a direction perpendicular to the no~zle exit 13, straight segment 12 of conduit 7 has sidewalls with a length at least 8 times the height T of the 5 nozzle exit, as measured in the direction of particle flow.
As will be appreciated by those skilled in the art, the maximum included spreading angle in conduit 7, as viewed from overhead, should not exceed about 30 in order to prevent sidewall turbulence. For a given no~zle exit width 10 W , smaller included angles work better since they result in a longer nozzle with more overall length and consequently more opportunity for riffling of the particles 10 to occur.
If desired, the conduit 7 can be vibrated ~by means not shown) to further enhance particle distribution and to 15 avoid particle hang-up within the conduit.
Using the process and apparatus disclosed in Figure 1, small volumes of superabsorbent particles 10 of the type generally described herein can be spread onto a predetermined portion corresponding to width W of the 20 uppermost surface of a porous tissue paper web 20 so as to occupy less than 100% of the predetermined portion of said web. For example, at a web speed V1 of 100 ~eet per minute, the flow rate of said superabsorbent particles 10 to be spread out over a 12 inch wide portion of the web may be 25 as low as 1 gram per second.
Since the no2~1e dischar~e velocity V2 is typically in the 2 ,000 to 4,000 foot per minute range, the particle spreading process herein disclosed is not speed limited. This spreading process has been successfully demonstrated on 30 superabsorbent polymer particles of the type generally described herein at a web speed V1 in the range of 50 to 1,000 feet per minute. i~ue to web handling limitations, the requlred particle conveylng veloclty V2, as measured at no2:zle exlt 13, is typically greater than the velocity Vl of the 35 web. However, glven sultable web handllng means, a web ;j3~

velocity V1 approaching, equaling or even exceeding the particle velocity V2 is believed feasible in practicing the present invention.
High speed photography has been utilized to verify 5 that the particle discharge at the nozzle exit 13 is uniformly distributed across the width W of the nozzle. Furthermore, the aforementioned high speed photography analysis has demonstrated that known pulsations introduced from the auger actuated metering system are somewhat dampened out in the 10 lateral spreading process which takes place in distribution conduit 7.
As can be observed from Figure 1, the particles 10 entraineci in the gaseous stream discharged at velocity V2 from nozzle exit 13 of conduit 7 are deposited onto that 15 portion of the uppermost surface of porous web 20 corresponding to width W by drawing the gas contained in the stream through the porous web 20. This is preferably accomplished by maintaining a negative pressure within chamber 28, such that the bulk of the gas in the stream 20 discharged from nozzle exit 13 is drawn into chamber 28 through porous web 20 and lattice type support grid 29 via conduit 45 and blower 4~ which thereafter ejects the gas through discharge conduit 47. In a particularly preferred embodiment of the present invention, the overall len~th of the 25 chamber 28 and the lattice type support grid 29 as measurad in the direction of web travel, is approximately two feet and is positioned so that its leading edge coincides with nozzle exit 13.
It is of course recognized that particles 10 which 30 are smaller In size than the pores in the web 10 may be drawn through the web 10 along with the gas. If desired, these could be removed by means of a cyclone type separator ~not shown) and returned to the part~cl~ Infeed hopper 1.
I n an exemplary embodiment of the type herein 35 clescribed In relation to Figure 1, approximately '~0 CFhl of air ~2~7S~

are removed from the gaseous stream by blower 46. The vacuum thus created inside chamber 28 not only prevents the porous web 20 from developing wrinkles, but helps to prevent excess air from blowing particles 10 out the sides of the 5 tissue layer 20. It also tends to stabilize the particles in the position in which they are initially deposited until a secondary porous web 30, which may be identical to porous web 20, is fed about idler roll 31 and into converging relation with porous web 20 at mating embossing rolls 35 and 39.
10The process iliustrated in Figure 1 is particularly suitable for producing a layered absorbent structure for use in disposable absorbent bandages such as diapers, incontinent pads, sanitary napkins, and the like. For such an absorbent structure, web 30 is preferably a porous web generally 15simi~ar to porous web 20. Webs 20 and 30 are both fed into the nip between mating embossing rolls 35 and 3~ at velocity Vl. The uppermost surface of web 20 has a predetermined portion of width W over which is distributed a substantially even, but discontinuous layer of particles 10. The 20 predetermined portion of web 20 exhibits a width "W"
corresponding in width to that of chamber 28 and nozzle exit 13.
Although the bulk of the particles 10 initially entrained in the gaseous stream which issues from nozzle exit 25 13 at velocity V2 are collected on the uppermost surface of porous web 20, a recycl ing system is preferably employed to provide a sanltary working environment and to avoid waste of any particles 10 which do not find their way inta contact with the predeterrnlned portion of porous web 20. In the 30 illustrated embodiment, any particles 10 which do not deposit onto the predetermined centrally located portion of porous web 20 are collected by a pair of vacuum nozzles 14 and 15 via their inlet ports 16 and 17, respectively. Vacuum nozzles 14 and 15 are prefera~ly connected vla conduits 1~ and 19, 35 respectively, to a cyclone type separator 25, such as a i)ucon ~ ~j37~i~

Series ''VMI', Model 700, as available from Ducon Company of Mineoia, Long Island, New York. In the separator 25 the air is separated from the particles 10 and the particles are deposited back into the bulk hopper 1 for recycling to the 5 particle deposition zone. Air which is separated from the stream is drawn through conduit 26 by blower 27 and is ultimately discharged to the atmosphere through a filter ~not shown). Thus, the deposition process described herein wastes li~tle or none of the often expensive particles 10.
Webs 20 and 30 with discontinuous layer of particles 10 located therebetween in a prede~ermined portion of width "Y~" are preferably crimped together to form a laminate structure 60 by means of rolls 35 and 39 which have mating Z-direction geometrical protrusions and concavities. As can 15 be generally seen from Figure 1, the outer cylindrical crimping surfaces of rolls 35 and 39 have multiple identical Z-direction protrusions, i.e., protuberances 38 and 41, respectively. In the illustrated embodiment, the protrusions are all substantially square based pyramids. Each square 20 based pyramid meshes with a corresponding concavity on the surface of the opposite roll; therefore, the mating Z-direction concavities mesh with the protuberances on the opposite roll.
Figure 3 is a simplified, greatly enlarged cross-sectional illustration of absorbent laminate structure 60 25 taken along sectlon line 3-3 of Figure i. In the illustrated embodiment only the centrally located portion 61 of the laminate having a width "W" has be&n three-dimensionally embossed by rolls 35 and 39, while the peripheral edges 62 and 63 remain In a substantially planar, und~formed 30 condition, It is of course recognized that the width "W" of the nozzle exit 13, the particle depositlon zone and/or the embossing rolls may be any desired dimension up to and includlng the entire width of web ~0 and/or w&b 30, The latt~r situation may in fact be preferred in situations 35 invol\~lng rewlndlng of the resultant laminate structure 50.

5;2 The protrusions 38 on embossing roll 35 correspond to the valleys 51 located on the uppermost surface of the absorbent laminate structure 60, while the protrusions 41 on roil 39 correspond to the peaks 53 on the lowermost surface of the absorbent laminate structure.
As a result of the substantially uniform distribution of particles 10 across the predetermined portion of width "W"
of porous web 20, the crimping action imparted to webs 20 and 30 by simultaneous passage between rolls 35 and 39 effectively fixes the particles in spaced relation to one another at the interface of the two webs. The fibrous entanglement of the three-dimensionally expanded webs provides a frangible bond between the web surfaces that will permit the discrete absorbent particles 10 to swell in a substantially uninhibited manner when contacted by liquid.
This, in combination with the discrete separation of the particles 10 from one another assures that the full absorptive capacity of the particles can be effectively utilizeci without gel blockage or physical constraint.
As will be appreciated, the strength of the bond between opposed adjacent surfaces of webs 20 and 30 will depend upon such factors as the number and shape of the intermeshing Z-direction protrusions and concavities, the surface properties of the webs of materials 20 and 30, and the density of the absor~ent p;~rticles at the interfaces between the webs.
In general, a greater numbar of such protrusions and concavities having a given height, or a higher height of such protrusions having a given base wldth will result in a stronger bond between opposed adJacent surfaces of ad3acent webs. In a particularly preferred embodiment, a density of about 16 protrusions per square centimeter of laminate web surface has been found effective. Uslng the length of one side of the square base of the pyramidal shaped protrusions as the base wicith of the protrusion, the height to basa width ~2537~

ratio of the protrusions of crimping surfaces of the respective rolls 35 and 39 is preferably about 1.1 to 1, Although the configuration of crimping surfaces shown in Figure 1 are preferred, an almost infinite variety of 5 protrusion and concavity shapes and patterns could be provided in order to produce the desired intermeshing Z-direction protrusions and concavities in layered absorbent structures of the type herein disclosed. It is particularly preferred that at least one of such surfaces have from about 10 10 to about 50 protrusions per square centimeter, more preferably from about 15 to about 25 protrusions per square centimeter. It is preferred that the Z-direction height of such protuberances be from about 1 millim&ter to about 5 millimeters, more preferably from about 2 millimeters to about 15 3 millimeters. It is preferred that such protrusions taper substantially entirely from their base to their tip. The preferred protrusions are pyramidal or conical shaped;
however, a large variety of shapes which would be suitable can readily be concaived by a skilled artisan. Processes of 20 the present invention are not limited to any particular size or shape of protrusion or concavity.
If desired, the strength of the bond between opposed adjacent surfaces of webs 20 and 30 can be further increased by passing the laminate structure 60 between a pair 25 of low pressure calender rolls (not shown~ However, the increased bond strength is normally accompanied by some reduction in Z-direction caliper from the laminate structure's initially crimped condition.
Layered absorbent structures comprised of more 30 than a single pair of porous webs have been found eFfective for use in various disposable absorbent structures. An exemplary process of the present invention for producing a three-layer structure Is generally disclosed in Figure 2, In the slmplifl~d schematlc Illustration disclosed In Figure 2, the 35 system generally discloseci in Figure 1 is flrst utilized to form 37~

a two layer absorbent laminate structure 160 which is thereafter fed about idler rolls 270, 271 and 272 in an S-wrap configuration to yet another idler roll 231 which aligns the two-layer laminate structure 1~0 for feeding toward a S secondary pair of embossing rolls 235 and 239. The latter are generally similar to rolls 35 and 39, respectively.
However, in the embodiment disclosed in Figure 2, a secondary particle feeding system comprising hopper 201, horizontal conduit 202, continuously rotating auger 203 and discharge conduit 204, all generally similar to the corresponding elements shown in Figure 1, is also employed.
As can be seen from Figure 2, particles 10 are fed into an eductor 206 having a circumferential slot 205 which is also supplied by a source of compressed gas at pressure P1.
These elements are generally similar to those described in conjunction with the embodiment of Figure 1. The particles 10 and air from the surrounding atmosphere are distributed throughout conduit 207 which is generally similar to distribution conduit 7 shown in Figure l . The particles 10 are uniformly distributed within conduit 207 and are dischargecl at nozzle exit 213 in a manner generally similar to that disclosed with respect to the embodiment of Figure 1.
An additional porous web 220, which is preferably similar to porous web 20, is fed from supply roll 221 which is supporteci ~y shaft 222. The porous web 220 passes about idler roll 223 and across the surface of a suction chamber 228 generally similar to vacuum chamber 28 shown in Figure 1.
As with the embodiment disclosed in Figure l, the gas contained in the gas/partlculate stream dlscharged from nozzle exit 213 Is drawn through a predetermined portion of width W
of porous web 220 and the particulate 1 Q is deposited onto said predetermined portion of the uppermost surface of porous web 220.
Porous web 220, with the uniformly distributed partlcles 10 deposlted on its surface, is simultaneously fed at 7~

veloeity V1 with the top layer laminate structure 160 into the nip between mating embossing rolls 235 and 239 which are generally similar to rolls 35 and 39, respectively, shown in Figure 1, Embossing roll 239 supported by shaft 240 is 5 preferably vertically stationary, while embossing roll 235 supported on shaft 236 is preferably vertically movable and adjustably loaded by means o~ hydraulic or pneumatic cylinders (not shownl which apply equalized forces to opposite ends of sha~t 236. As a result of passage between the pressure loaded embossing rolls 235 and 239, a three-layer absorbent laminate structure 260 having particulate 10 substantially uniformly distributed at all of its interfaces is created .
Figure 4, which is an enlarged cross-sectional illustration of absorbent structure 260 taken along section line 4-4 of Figure 2, discloses an overall cross-sectional appearance generally similar to that of absorbent laminate structure 60. The ernbossed portion of the structure 261 is centrally located, while the peripheral edges 262 and 263 remain substantially undeformed. The valleys 251 of the absorbent laminate structure correspond to peaks of the protuberances 238 on embossing roll 235, while peaks 253 on the lowermost surface of the structure correspond to peaks of the protuberances 241 on mating embossing roll 239 As will be appreciated, the process generally disclosed in Figure 2 may be repeated any number o~ times to provide the desired number of layers in the resultan~ laminate structure, the only requTrement being that the web or webs onto whlch the particulate is dlstributed must be sufficiently porous to permlt drawing the gas contained in the gas/particulate stream through the thickness of the web or webs and thereby deposit the entrained particles in a substantlally uniformly dlstributed condition along a predetermined portlon of the uppermQst porous web.

Z~37~

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit S and scope of the invention. It is intended to cover, in the appended claims, all such modifications and contemplated uses .
What is claimed is:

Claims (50)

1. A method for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface of a moving porous web traveling at a first velocity so that said particles occupy less than 100% of said predetermined portion of the uppermost surface of said moving web, said method comprising the steps of:
(a) entraining said particles in a moving gaseous stream;
(b) passing said gaseous stream through a conduit having a nozzle exit positioned adjacent the uppermost surface of and oriented so as to discharge said gaseous stream containing said entrained particles in a direction substantially parallel to the direction of travel of said moving porous web;
(c) mixing said particles entrained in said gaseous stream inside said conduit to provide a substantially uniform distribution of said particles, as measured across the width of said nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(d) discharging said gaseous stream containing said uniformly distributed entrained particles from said conduit adjacent said predetermined portion of the uppermost surface of said moving porous web at a second velocity; and (e) maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a level below the fluid pressure adjacent the uppermost surface of said moving porous web in an area coinciding in width to said predetermined portion of said web and located near the nozzle exit of said conduit, whereby the uniformly distributed particles entrained in said discharged gaseous stream are substantially uniformly deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas in said gaseous stream is drawn from the uppermost to the lowermost surface of said web .

2. The method of Claim 1 wherein said gaseous stream and said particles entrained therein undergo a change of direction of approximately 90° as they pass through said conduit .

3. The method of Claim 2 wherein the velocity of said gaseous stream and said particles entrained therein increases during their passage through said conduit.

4. The method of Claim 3 wherein said increased velocity results from a decrease in cross-sectional flow area, as measured in a direction substantially perpendicular to the direction of flow, said decrease in flow area occurring between the inlet to said conduit and the nozzle exit of said conduit .

5. The method of Claim 1 wherein said second velocity of said gaseous stream and said particles entrained therein is greater than said first velocity of said moving porous web, as measured at the nozzle exit of said conduit.

6. The method of Claim 1 wherein the fluid pressure adjacent the lowermost surface of said moving porous web is subatmospheric.

7, The method of Claim 1 including the step of recycling particles which are not deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas contained in said gaseous stream is drawn from the uppermost to the lowermost surface of said web.

8. The method of Claim 1 wherein mixing of said particles entrained in said gaseous stream while said particles are inside said conduit is carried out as said particles strike the walls of said conduit.

9. The method of Claim 1 wherein said moving porous web comprises a three-dimensional absorbent batt and the particles deposited on said predetermined portion of the uppermost surface of said moving porous web become entangled in the lattice of said web.

10. The method of Claim 1 wherein said moving porous web comprises a paper tissue ply.

11. The method of Claim l wherein said moving porous web comprises a nonwoven material.

12. The method of Claim l including the step of superposing a second web on said first moving porous web after said particles have been substantially uniformly deposited on said predetermined portion of the uppermost surface of first moving porous web.

13. The method of claim 12 including the step of three-dimensionally embossing said first and second webs to secure them to one another and fix the position of said uniformly distributed particles therebetween.

14. The method of Claim 1 including the step of feeding a uniform stream of particles into said moving gaseous stream .

15. The method of Claim 14 wherein said uniform stream is provided by means of a rotating auger.

16. The method of Claim 1 wherein said particles are entrained in said moving gaseous stream by means of an eductor .

17. The method of Claim 1 wherein the width of said nozzle exit corresponds to the width of said predetermined portion of the uppermost surface of said moving porous web onto which said particles are deposited and is in vertical alignment with said predetermined portion of said web.

18. The method of Claim 1 wherein said discrete particles are comprised of superabsorbent polymer and are on the average greater in size than the pores in said moving porous web.

19 The method of Claim 1 including the step of vibrating said conduit as said gaseous stream and the particles entrained therein pass through said conduit.

20. The method of Claim 1 wherein said particles are substantially uniformly distributed onto the predetermined portion of said moving porous web so that they occupy less than 50% of said predetermined portion of the uppermost surface of said moving web.

21. The method of Claim l wherein the width of said predetermined portion of said moving porous web comprises the entire width of said web.

22. A method for substantially uniformly distributing a layer of discrete particles along predetermined portion of the uppermost surface of a moving porous web traveling at a first velocity so that said particles occupy less than 100% of said predetermined portion of the uppermost surface of said moving web, said method comprising the steps of:
(a) feeding said particles in a substantially uniform stream to the inlet of a gas eductor;
(b) entraining said particles in a moving gaseous stream;
(c) passing said gaseous stream through a conduit having a nozzle exit positioned adjacent the uppermost surface of and oriented so as to discharge said gaseous stream containing said entrained particles in a direction substantially parallel to the direction of travel of said moving porous web;
(d) mixing said particles entrained in said gaseous stream inside said conduit to provide a substantially uniform distribution of said particles, as measured across the width of said nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(e) discharging said gaseous stream containing said uniformly distributed entrained particles from said conduit adjacent said predetermined portion of the uppermost surface of said moving porous web at a second velocity which is greater than said first velocity, and (f) maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a level below the fluid pressure adjacent the uppermost surface of said moving porous web in an area coinciding in width to said predetermined portion of said web and located near the nozzle exit of said conduit whereby the uniformly distributed particles entrained in said discharged gaseous stream are substantially uniformly deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas in said gaseous stream is drawn from the uppermost to the lowermost surface of said web .

23. The method of Claim 22 wherein said gaseous stream and said particles entrained therein undergo a change of direction of approximately 90° as they pass through said conduit .

24. The method of Claim 23 wherein the velocity of said gaseous stream and said particles entrained therein increases during their passage through said conduit.

25. The method of Claim 24 wherein said increased velocity results from a decrease in cross-sectional flow area as measured in a direction substantially perpendicular to the direction of flow said decrease in flow area occurring between the inlet to said conduit and the nozzle exit of said conduit.

26. The method of Claim 22 wherein said second velocity of said gaseous stream and said particles entrained therein is at least twice said first velocity of said moving porous web as measured at the nozzle exit of said conduit.

27. The method of Claim 22 wherein the fluid pressure adjacent the lowermost surface of said moving porous web is subatmospheric.

28. The method of Claim 22 including the step of recycling particles which are not deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas contained in said gaseous stream is drawn from the uppermost to the lowermost surface of said web.

29. The method of Claim 22 wherein mixing of said particles entrained in said gaseous stream while said particles are inside said conduit is carried out as said particles strike the walls of said conduit.

30. The method of Claim 22 wherein said moving porous web comprises a three-dimensional absorbent batt and the particles deposited on said predetermined portion of the uppermost surface of said moving porous web become entangled in the lattice of said web.

31. The method of Claim 22 wherein said moving porous web comprises a paper tissue ply

32. The method of Claim 22 wherein said moving porous web comprises a nonwoven material.

33. The method of Claim 22 including the step of superposing a second web on said first moving porous web after said particles have been substantially uniformly deposited on said predetermined portion of the uppermost surface of first moving porous web.

34. The method of Claim 33, including the step of three-dimensionally embossing said first and second webs to secure them to one another and fix the position of said uniformly distributed particles therebetween.

35. The method of Claim 22 wherein said uniform stream is provided by means of a rotating auger,

36. The method of Claim 22 wherein the width of said nozzle exit corresponds to the width of said predetermined portion of the uppermost surface of said moving porous web onto which said particles are deposited and is in vertical alignment with said predetermined portion of said web.

37. The method of Claim 22 wherein said discrete particles are comprises of superabsorbent polymer and are on the average greater in size than the pores in said moving porous web .

38. The method of Claim 22 including the step of vibrating said conduit as said gaseous stream and the particles entrained therein pass through said conduit.

39. The method of Claim 22 wherein said particles are substantially uniformly distributed onto the predetermined portion of said moving porous web so that they occupy less than 50% of said predetermined portion of the uppermost surface of said moving web.

40. The method of Claim 22 wherein the width of said predetermined portion of said moving porous web comprises the entire width of said web.

41. An apparatus for substantially uniformly distributing a layer of discrete particles along a predetermined portion of the uppermost surface of a moving porous web traveling at a first velocity so that said particles occupy less than 100% of said predetermined portion of the uppermost surface of said moving web, said apparatus comprising:
(a) means for feeding said particles in a substantially uniform stream to the inlet of a gas eductor;
(b) means for entraining said particles in a moving gaseous stream;
(c) conduit means for passing said gaseous stream through a nozzle exit positioned adjacent the uppermost surface of and oriented so as to discharge said gaseous stream containing said entrained particles in a direction substantially parallel to the direction of travel of said moving porous web;
(d) means for mixing said particles entrained in said gaseous stream inside said conduit to provide a substantially uniform distribution of said particles, as measured across the width of said nozzle exit of said conduit in a direction perpendicular to the direction of travel of said moving porous web;
(e) nozzle exit means at the discharge end of said conduit means for discharging said gaseous stream containing said uniformly distributed entrained particles from said conduit adjacent said predetermined portion of the uppermost surface of said moving porous web at a second velocity which is greater than said first velocity; and (f) means for maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a level below the fluid pressure adjacent the uppermost surface of said moving porous web in an area coinciding in width to said predetermined portion of said web and located near the nozzle exit of said conduit, whereby the uniformly distributed particles entrained in said discharged gaseous stream are substantially uniformly deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas in said gaseous stream is drawn from the uppermost to the lowermost surface of said web.

42. The apparatus of Claim 41 wherein said conduit means causes said gaseous stream and said particles entrained therein to undergo a change of direction of approximately 90°
as they pass through said conduit.

43 The apparatus of Claim 42 wherein said conduit means exhibits a decrease in cross-sectional flow area as measured in a direction substantially perpendicular to the direction of flow between its inlet end and its nozzle exit end.

44. The apparatus of Claim 43 including means for maintaining the fluid pressure adjacent the lowermost surface of said moving porous web at a subatmospheric c level.

45. The apparatus of Claim 41 including means for recycling particles which are not deposited on said predetermined portion of the uppermost surface of said moving porous web as the bulk of the gas contained in said gaseous stream is drawn from the uppermost to the lowermost surface of said web.

46. The apparatus of Claim 41, including means for superposing another web on said first moving porous web after said particles have been substantially uniformly deposited on said predetermined portion of the uppermost surface of first moving porous web.

47. The apparatus of Claim 46, including means for three-dimensionally embossing said first and second webs to secure them to one another and fix the position of said uniformly distributed particles therebetween.

48. The apparatus of Claim 41 wherein said means for feeding said uniform stream of particles comprises a rotating auger.

49. The apparatus of Claim 41 wherein the width of said nozzle exit corresponds to the width of said predetermined portion of the uppermost surface of said moving porous web onto which said particles are deposited and is in vertical alignment with said predetermined portion of said web.

50. The apparatus of Claim 41 including means for vibrating said conduit as said gaseous stream and the particles entrained therein pass through said conduit.