Manufacture of composite web having absorbent properties

Abstract

 A method of dispersing droplets of a polymerizable, cross-linkable material (M), in a liquid carrier (12, 16), within a fibrous web (W), in which the material (M) is to be polymerized and cross-linked, as a part of a method of manufacturing a composite web (W¹), which comprises the fibrous web (W) dispersed inclusions of the material (M), as polymerized and cross-linked. Droplets of the material (M) are dispersed within the fibrous web by moving the fibrous web (W) through a droplet-flicking zone (Z₁) and flicking droplets of the material (M), in the liquid carrier (12, 16), onto opposite sides of the fibrous web (W) as the fibrous web is moved through the droplet-flicking zone (Z₁). On each of opposite sides of the fibrous web (W), a rotating brush (2, 6) has bristles (4, 8), picking up the material (M), in the liquid carrier (12, 16), and flicking droplets thereof as the brush (2, 6) rotates. Each brush (2, 6) picks up the material (M), in the liquid carrier (12, 16), from a rotating roller (10, 14) wiped by the bristles (4, 8) of such brush (2, 6). Each brush (2, 6) and the roller (10, 14) wiped by the bristles (4, 8) of such brush (2, 6) rotate, in opposite rotational senses, about parallel axes. The material (M) is polymerized and cross-linked in situ, so as to form the composite web (W¹).

Description

Technical Field of the Invention

[0001] This invention pertains to an improved method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web. The improved method, which effects dispersion of the droplets through the use of a brush roller, may be advantageously employed as a part of a method of manufacturing a composite web. If the material, as polymerized and cross-linked, has absorbent or superabsorbent properties, so that the material is capable of absorbing liquid human excreta, such as urine, menses, or wound excreta, the composite web may be advantageously employed in or as an absorbent article, such as a disposable diaper, tampon, sanitary napkin, wound dressing, or similar product requiring such properties.

Background of the Invention

[0002] Detailed discussions of absorbent articles employing superabsorbent materials in disposable diapers and other products are included in Pieniak et al. U.S. Patents No. 4,500,315, No. 4,540,454, No. 4,537,590, and No. 4,573,988, which collectively provide useful background for this invention.

[0003] As discussed in the Pieniak et al. patents noted above, absorbent articles can be advantageously made with absorbing layers and wicking layers. The absorbing layers can be advantageously made from polyester fibers, within which particles of a superabsorbent material are dispersed. The wicking layers can be advantageously made from cellulosic fibers, such as wood pulp, and can include or take the form of a densified, paper-like layer, such as is disclosed in Burgeni U.S. Patent No. 3,017,304, on one side or each side. See, also, Mesek et al. U.S. Patent No. 3,612,055 and Repke U.S. Patent No. 3,938,522.

[0004] As also discussed in the Pieniak et al. patents noted above, the superabsorbent material can be advantageously formed from a polymerizable, cross-linkable material, e.g., a water-soluble monomer exemplified by sodium, potassium, or ammonium acrylate, which is coated, in a liquid carrier, e.g., in an aqueous solution, onto a fibrous web, and which is polymerized and cross-linked in situ, so as to form a hydrophyllic polymer having superabsorbent properties.

[0005] Conventional coating techniques involve flooding the fibrous web with the material, in the liquid carrier, while the fibrous web is supported on a screen, so as to saturate the fibrous web, and exposing the saturated web to a partial vacuum, which removes excess amounts of the material, in the liquid carrier. Typically, there is about a 7 to 1 ratio between the weight of liquid retained by the fibrous web and the weight of the fibrous web, and the retained liquid is distributed as fragments of continuous film bridging adjacent fibers, and being held by fiber-to-fiber capillaries. It has been heretofore known to remove excess amounts of liquid by means of a padder or a squeeze roll, after the fibrous web has been saturated, with similar results.

[0006] It has been heretofore known that polymerization and cross-linking in situ can be advantageously effected by electron beam, chemical, or heat initiation. Chemical initiation may require a catalyst or initiator of a known type.

[0007] As polymerized and cross-linked in situ, the material tends to retain whatever morphology, i.e., size and shape, the material has as retained, in the liquid carrier, within the fibrous web before the material is polymerized and cross-linked. As an example, if the material is retained by the fibrous web in fragments of continuous film including the liquid carrier, the material tends to occur as fragments of continuous film after the material has been polymerized and cross-linked.

[0008] Conventional techniques for coating a fibrous web with a polymerizable, cross-linkable material, in a liquid carrier, so that the material can be then polymerized and cross-linked in situ, tend to result in polymerized, cross-linked particles that do not have optimal morphologies for absorbency.

[0009] Smaller, nearly spherical particles have preferred morphologies, since such particles have higher surface-to-volume ratios, as compared to fragments of continuous film, and since such particles may have lower internal stresses when swollen with absorbed liquids, as compared to such fragments. Small diameter particles, with optimal spatial distribution, give minimal interference with adjacent, swollen particles. The spheres of swollen gel also create a capillary infrastructure which is effective in immobilizing additional free liquid.

[0010] Smaller, nearly spherical particles are also preferred because such particles are less prone to cause gel blocking when swollen with a liquid being absorbed, e.g., urine being absorbed in a diaper. Gel blocking occurs if particles of a superabsorbent material tending to form a gel when swelling with absorbed liquid are too densely distributed within an absorbent article, so that the swelling particles tend to form a gel layer, which blocks additional liquid from penetrating.

[0011] It also has been heretofore known to spray the aqueous solution by means of nozzles, which typically spray globules of the aqueous solution in circular or oval patterns. Although such globules tend to be more nearly spherical, such spraying techniques employing nozzles have not been entirely satisfactory alternatives to conventional coating techniques discussed above, since nozzles used in such spraying techniques tend to provide nonuniform coverage and to plug or clog intermittently.

[0012] Although the Pieniak et al. patents noted above disclose useful products and useful methods of manufacturing such products, there has been a need, heretofore, for an improved method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web. Moreover, there has been a need, heretofore, for such an improved method as a part of a method for manufacturing a composite web comprising such a fibrous web and dispersed inclusions of such a material, as polymerized and cross-linked.

Summary of the Invention

[0013] This invention provides an improved method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web, in which the material is to be polymerized and cross-linked in situ. The method contemplates use of a brush and roller combination, which is operated so that its brush bristles flick such material, in the liquid carrier, on and penetratingly into the fibrous web. The improved method may be advantageously employed as a part of a method of manufacturing a composite web, which comprises the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked. If the polymerized, cross-linked material has absorbent or superabsorbent properties, the composite web may be further processed, e.g., compressed and cut down to a useful size, and employed as or in an absorbent article useful in a disposable diaper, tampon, sanitary napkin, wound dressing, or similar or dissimilar product requiring such properties.

[0014] The improved method tends to produce from the material, as polymerized and cross-linked, smaller inclusions, which tend to be more nearly spherical, as compared with fragments of continuous film produced by conventional coating techniques discussed above. If the polymerized, cross-linked material has absorbent or superabsorbent properties, such smaller inclusions have more preferable morphologies for absorbency or superabsorbency, as compared to such fragments. Moreover, the improved method tends to provide more uniform coverage and eliminates plugging and clogging, as compared to spraying techniques employing nozzles.

[0015] Pursuant to the improved method, droplets of the material, in the liquid carrier, are dispersed within the fibrous web by moving the fibrous web through a zone wherein droplets of the material, in the liquid carrier, are flicked onto the fibrous web as the fibrous web is moved through the zone, which may be conveniently called a droplet-flicking zone. Droplets flicked onto the fibrous web tend to become dispersed within the fibrous web, as dispersed inclusions, which tend to be nearly spherical, as retained by the fibrous web. Such inclusions tend to be more nearly spherical, as compared to fragments of continuous film resulting from conventional coating techniques.

[0016] Pursuant to the improved method, droplets of the material, in the liquid carrier, are flicked onto the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of a rotating element picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto the fibrous web as the element rotates. Preferably, the rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates. Preferably, the bristles pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles as the brush and the roller rotate. The brush and the roller may rotate, in opposite rotational senses (i.e., counter-rotate), about parallel axes.

[0017] Being resilient, the bristles are deflected, or deformed, from their normal orientation as they wipe the associated roller and receive the polymerizable, cross-linkable material, in the liquid carrier. As the bristles leave the roller, they return to their normal orientation, whereby their resiliency and centrifugal forces combine to cause the liquid on the bristles to be energetically flicked, i.e., flung or projected, onto the moving fibrous web.

[0018] It is desirable, particularly if the fibrous web is thick, for droplets of the material, in the liquid carrier, to penetrate from opposite sides of the fibrous web. Hence, droplets of the material, in the liquid carrier, may be so flicked onto opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zones, by rotating elements picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the elements rotate. At least one of the rotating elements may be then adapted to flick droplets onto a respective side of the fibrous web as the fibrous web is moved through the droplet-receiving zone. Each of the rotating elements may be a brush, which may have bristles wiping a rotating roller, as described above.

[0019] By varying the rotational speed of such a brush, the nominal diameter of the droplets (i.e., the largest cross-sectional dimension of such a droplet, regardless of its shape) flicked by its bristles can be readily controlled within useful ranges, e.g., nominal diameters ranging from less than 0.1 mm to greater than 1 mm. The resulting inclusions, which tend to be nearly spherical, tend to have nearly uniform diameters. It is possible, therefore, to disperse droplets tending to have smaller nominal diameters and droplets tending to have larger nominal diameters respectively onto the fibrous web, either onto a given side or onto opposite sides, in two successive passes of the fibrous web through the droplet-flicking zone. It is possible, moreover, to disperse droplets tending to have smaller nominal diameters and droplets tending to have larger nominal diameters respectively onto opposite sides of the fibrous web in a single pass of the fibrous web through the droplet-flicking zone.

[0020] It is possible, furthermore, to disperse droplets of two different materials, in liquid carriers, one on each side of the fibrous web, either in two successive passes of the fibrous web through the droplet-flicking zone or in a single pass through such zone. Consequently, after such materials have been polymerized and cross-linked, the respective sides of the resultant, composite web can have different characteristics, such as different rates of absorbency or different capacities to absorb liquids.

[0021] When the improved method is employed as a part of a method of manufacturing a composite web, which comprises the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked, the manufacturing method further involves polymerizing and cross-linking the material in situ, so as to form the composite web. If the polymerized, cross-linked material has superabsorbent properties, the composite web may be advantageously employed with superior results, possibly in a compressed and cut-down form, in or as an absorbent article useful in a tampon, sanitary napkin, wound dressing, or similar or dissimilar product requiring absorbent properties. If used in such an article, the composite web can be also provided with a wicking layer or wicking layers, as discussed above, one or more densified, paper-like layers, as discussed above, or both.

[0022] Herein, each reference to a polymerizable, cross-linkable material, in a liquid carrier, is intended to refer to any suitable monomer, oligomer, or polymer of low molecular weight, as exemplified by but not limited to a sodium, potassium, or ammonium salt of acrylic or methacrylic acid, together with a sufficient quantity of any catalyst or initiator needed to catalyze or initiate polymerizing and cross-linking of the monomer, oligomer, or polymer of low molecular weight, in a solution or suspension in a liquid carrier, as exemplified by not limited to water. Moreover, as and where appropriate, each reference to a polymer is intended to refer to a heteropolymer or a polymer of a usual structure.

[0023] Herein, each reference to a material having absorbent properties is intended to refer to a material capable of absorbing liquid human excreta, such as urine, menses, or wound excreta. Moreover, each reference to a material having superabsorbent properties is intended to refer to a material capable of absorbing many times its own weight of such human excreta.

[0024] These and other objects, features, and advantages of this invention are evident from the following description of a preferred mode of carrying out this invention with reference to the accompanying drawing.

Brief Description of the Drawing

[0025] 

FIGURE 1 is a schematic diagram of a fibrous web being moved upwardly through a lower zone, wherein droplets of a polymerizable, cross-linkable material, in a liquid carrier, are being dispersed onto the fibrous web, and through an upper zone, wherein the material, as retained by the fibrous web, is being polymerized and cross-linked. An edge of the fibrous web is shown.

Detailed Description of the Preferred Embodiment

[0026] While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.

[0027] As shown in the schematic diagram, a fibrous web W is being moved upwardly through a lower zone Z₁, wherein droplets D of a polymerizable, cross-linkable material M are being flicked onto opposite sides of the fibrous web W, and through an upper zone Z₂, wherein the material is being polymerized and cross-linked in situ. The lower zone Z₁ may be conveniently called a droplet-flicking zone. The upper zone Z₂ may be conveniently called a polymerizing and cross-linking zone. Any suitable means (not shown) may be used to move the fibrous web W upwardly through the successive zones. Although it is preferred for the fibrous web W to be moved upwardly because the droplets D tend to be better retained by the fibrous web W when the fibrous web is moved upwardly, the fibrous web W may be moved downwardly, or in any other direction, so long as the fibrous web W is moved through such droplet-flicking zone before the fibrous web W is moved through such a polymerizing and cross-linking zone.

[0028] As an example of one type of fibrous web useful with this invention, the fibrous web W may comprise (a) 80% by weight of a fiber blend being a blend of (1) 75% by weight of poly(ethylene terephthalate) fiber (5.5 denier x 1.5 inches/6,11·10⁻⁷ Kg/m x 38.1 mm) and (2) 25% of a first composite fiber (4.1 denier x 1.5 inches/4.55·10⁻⁷ Kg/m x 38.1 mm) having a solid core of poly(ethylene terephthalate) and a sheath of a poly(ethylene terephthalate) copolymer, as available commercially under the trade designation DuPont D-280W from E.I. DuPont de Nemours and Company, Wilmington, Delaware, and (b) 20% by weight of a second composite fiber (3.0 denier x 2 inches/3.33·10⁻⁷ Kg/m x 50.8 mm) having a solid core of poly(ethylene terephthalate) and a sheath of a copolymer of poly(ethylene terephthalate) and polyethylene, as available commercially under the trade designation Enka Bico from BASF Corporation, Parsippany, New Jersey, as carded into a nonwoven web having a basis weight of about (1.25 oz/yd²/42.382 g/m²) and thermally bonded by subjecting the nonwoven web to air heated to about (350° F/176,67°C) as the nonwoven web is pulled through a forced air oven while the nonwoven web is supported on a screen (not shown) in a known manner. This invention, however, is not limited to the type of fibrous web given as an example.

[0029] As an example of one type of polymerizable, cross-linkable material useful with this invention, in a liquid carrier useful therewith, an aqueous solution of 60% concentration of 65% neutralized (on a weight basis) potassium acrylate, as neutralized with potassium hydroxide, may constitute the polymerizable, cross-linkable material, in the liquid carrier, i.e., in water. When such material is polymerized and cross-linked, a majority, e.g., approximately 80%, of the liquid carrier, i.e., water, is evolved. This invention, however, is not limited to the polymerizable, cross-linkable material given as an example, or to the liquid carrier given as an example. Other examples of a polymerizable, cross-linkable material useful with this invention, in a liquid carrier useful therewith, are disclosed in Pieniak et al. U.S. Patents No. 4,500,315, No. 4,540,454, No. 4,537,590, and No. 4,573,988, the disclosures of which patents are incorporated herein by reference.

[0030] In the droplet-flicking zone Z₁, droplets D of the material M in the liquid carrier are flicked onto a given side of the fibrous web W, i.e., its left side as shown, by a rotating brush 2, which is at least as wide as the fibrous web W, and which has bristles 4 picking up the material M, in the liquid carrier, and flicking droplets D of the material M in the liquid carrier onto the given or left side of the fibrous web W as the brush 2 rotates. The brush 2 is rotated in a counterclockwise sense, as shown, by any suitable means (not shown) so as to rotate about a horizontal axis parallel to the fibrous web W moving through the droplet-flicking zone Z₁. Similarly, droplets D of the material M, in the liquid carrier, are flicked onto the other side of the fibrous web W, i.e., its right side as shown, by a rotating brush 6, which is at least as wide as the fibrous web W, and which has bristles 8 picking up the material M, in the liquid carrier, and flicking droplets D of the material M, in the liquid carrier, onto the other or right side of the fibrous web W as the brush 6 rotates. The brush 6 is rotated in a clockwise sense, as shown, by any suitable means (not shown) so as to rotate about a horizontal axis parallel to the fibrous web W moving through the droplet-flicking zone Z₁. The horizontal axes of the brushes 2, 6, respectively are at similar elevations, as shown, but may be at different elevations.

[0031] In the droplet-flicking zone Z₁, the bristles 4 of the brush 2 pick up the material M, in the liquid carrier, by wiping a rotating roller 10 as the brush 2 and the roller 10 rotate. The roller 10 picks up the material M, in the liquid carrier, from a pan 12 containing a supply of the material M, in the liquid carrier, as the roller 10 rotates. The roller 10 is rotated in a clockwise sense, as shown, by any suitable means (not shown) so as to rotate about a horizontal axis parallel to and disposed vertically beneath the horizontal axis of the brush 2. Similarly, the bristles 8 of the brush 6 pick up the material M, in the liquid carrier, by wiping a rotating roller 14 as the brush 6 and the roller 14 rotate. The roller 14 picks up the material M, in the liquid carrier, from a pan 16 containing a supply of the material M, in the liquid carrier, as the roller 14 rotates. The roller 14 is rotated in a counterclockwise sense, as shown, by any suitable means (not shown) so as to rotate about a horizontal axis parallel to and disposed vertically beneath the horizontal axis of the brush 6. The horizontal axes of the rollers 10, 14, respectively are at similar elevations.

[0032] The aforesaid means rotating the brush 2 may be also used to rotate the roller 10 via wiping action of the bristles 4 of the brush 2 against the roller 10. The aforesaid means rotating the brush 6 may be also used to rotate the roller 14 via wiping action of the bristles 8 of the brush 6 against the roller 14. Any suitable, level-controlled or other means (not shown) may be also provided for replenishing the supplies of the material M, in the liquid carrier, in the pans 12, 16, respectively.

[0033] Droplets D flicked by the bristles of the brushes 2, 6, onto opposite sides of the fibrous web W tend to be nearly spherical, to penetrate the fibrous web W from opposite sides, and to be well dispersed within and among the fibers of the fibrous web W, as dispersed inclusions, which tend to be nearly spherical. Such inclusions tend to be more nearly spherical when compared to fragments of continuous film, as produced by conventional coating techniques noted above.

[0034] Typically, the rotational speeds of the brushes 2, 6, are at least 200 rpm. Typically, the rotational speeds of the rollers 10, 14, are from about 50 rpm to about 200 rpm depending on throughput, preferably about 125 rpm. By varying the rotational speeds of the brushes 2, 6, the nominal diameters of droplets D flicked by the bristles of the brushes 2, 6, onto opposite sides of the fibrous web W can be readily controlled within useful ranges, e.g., nominal diameters ranging from less than 0.1 mm to greater than 1 mm.

[0035] Each brush can have a bristle diameter (thickness) from about (0.004 inch/0.1016 mm) to about (0.025 inch/0.635 mm), a bristle diameter (thickness) of about (0.012 inch/0.3048 mm) being preferred, and a bristle length from about (0.5 inch/12.7 mm) about (3 inches/76.2 mm), a bristle length of about (1.875 inches/47.625 mm) being preferred. Depending on the overall diameter of the brush, each brush can have a rotational speed from about 200 rpm to about 2000 rpm, a rotational speed of about 900 rpm being preferred. Preferably, as supplied to the brushes 2, 6, the polymerizable, cross-linkable material, in the liquid carrier, has a water-like viscosity, i.e., a viscosity from about one centipoise to about 10 centipoise.

[0036] If the material M, when polymerized and cross-linked, results in a superabsorbent polymer tending to form a gel as such polymer becomes swollen with a liquid being absorbed, judicious selection of the rotational speeds of the brushes 2, 6, entails that droplets D of the material M, in the liquid carrier, do not tend to be too densely distributed within the fibrous web W. This invention, therefore, enables gel blocking to be largely avoided or minimized.

[0037] Care is taken to avoid agglomeration or smearing of droplets D of the material M, in the liquid carrier, as retained by the fibrous web W. Therefore, spacing between each of the brushes 2, 6, and the fibrous web W is suitably selected for the rotational speeds of the brushes 2, 6, so as to avoid agglomeration of droplets D as droplets D are flicked onto the fibrous web W. Higher rotational speeds require greater spacings. Lower rotational speeds permit lesser spacings. Suitable spacings for given rotational speeds may be readily selected by trial and error. Care is taken, moreover, to avoid touching the fibrous web W retaining droplets D of the material M, in the liquid carrier, before the material M is polymerized and cross-linked.

[0038] In the polymerizing and cross-linking zone Z₂, the material M, as retained in the liquid carrier by the fibrous web W, in dispersed inclusions, is polymerized and cross-linked in situ, whereby the liquid carrier is evolved, so as to form a composite web W′, which comprises the fibrous web W and dispersed inclusions of the polymerized, cross-linked material. Any suitable means (not shown) for electron beam irradiation is preferred as a means for polymerizing and cross-linking the material M; an example is an Energy Sciences™ (Model) CB300 accelerator, as available from Energy Sciences, Inc. If electron beam irradiation is used, the fibrous web W retaining the material M, in the liquid carrier, in dispersed inclusions may be initially exposed to 2 MRAD of such radiation on each side of the fibrous web W, and finally exposed to a curing dose of 8 MRAD on each side of the fibrous web W. Any other suitable technique for electron beam irradiation may be instead used.

[0039] The composite web W′ resulting from electron beam irradiation of the fibrous web W retaining dispersed inclusions of the material M, in the liquid carrier, contains dispersed inclusions of the polymerized, cross-linked material, from which substantially all of the liquid carrier has evolved. If the polymerizable, cross-linkable material, in the liquid carrier, is an aqueous solution of 60% concentration of 65% neutralized (on a weight basis) potassium acrylate, as neutralized with potassium hydroxide, as in the example given above, such inclusions in the composite web W′ are inclusions of a potassium polyacrylate, from which a substantial part of the liquid carrier, i.e., water, has evolved.

[0040] If the inclusions of the polymerized, cross-linked material have superabsorbent properties, the composite web W′ may be further processed in known ways, e.g., compressed and cut-down to a useful size, whereupon the composite web W, as further processed, may be advantageously employed in or as an absorbent article useful in a disposable diaper, tampon, sanitary napkin, wound dressing, or similar of dissimilar product requiring absorbent properties. The composite web W′ may be also provided with one or more densified, paper-like layers (not shown) in a manner disclosed in the Burgeni, Mesek et al., and Repke patents noted above.

EXAMPLE 1

[0041] Two comparative samples were made respectively by the improved method described above and by one of the conventional techniques discussed above.

[0042] For each comparative sample, the fibrous web comprised 80% by weight of the first composite fiber noted above, and 20% by weight of the second composite fiber noted above, as carded into a nonwoven web having a basis weight of about (1.25 oz/yd²/42.382 g/m²) and thermally bonded by subjecting the nonwoven web to air heated to about (350°F/76.67°C) as the nonwoven web was pulled through a forced-air oven while the nonwoven web was supported on a screen.

[0043] For each comparative sample, the polymerizable, cross-linkable material, in a liquid carrier, was an aqueous solution of 60% concentration of 65% neutralized (on a weight basis) potassium acrylate, as neutralized with potassium hydroxide.

[0044] For one such sample, the aqueous solution was flooded onto the fibrous web while the fibrous web was supported on a screen, which served as a carrier, until the fibrous web was saturated. The saturated web, while supported on the screen serving as a carrier, was passed over a slot so as to be there exposed to a partial vacuum, which removed excess amounts of liquid until there was about a 7 to 1 ratio between the volume of liquid retained by the fibrous web and the weight of the fibrous web.

[0045] For the other sample, the fibrous web was moved through a zone wherein droplets of the aqueous solution were flicked onto opposite sides of the fibrous web, as the fibrous web was moved through the zone, by the improved method described above. Two rotating brushes were used, one at each side of the fibrous web. Each brush had a diameter of about (10.5 inches/266.7 mm) at the tips of its bristles, which were made of nylon, as noted above, each having an exposed length of about (1.875 inches/47.625 mm) and a diameter of about (0.012 inch/0.3048 mm). Each brush was rotated, in the rotational senses described above, so that its bristles picked up the aqueous solution from a rotating roller wiped by the bristles. Each roller had a diameter of about (6.5 inches/165.1 mm) and a rotational speed of about 80 rpm. Each brush was above its associated roller. There was interference of about (0.2 inch/5.08 mm) between each brush and its associated roller. Each brush was rotated at a rotational speed of about 600 rpm. The fibrous web W was moved upwardly at a linear speed of about (60 fpm/15.24 m/min).

[0046] For each comparative sample, the fibrous web retaining the aqueous solution was subjected to electron beam irradiation with an initial exposure of (2 MRAD/500·10⁻⁵) on each side of the fibrous web, and with a curing dose of (8 MRAD/125·10⁻⁵) on each side of the fibrous web.

[0047] Demand absorbency of each comparative sample and free swell absorbency of each comparative sample were determined, in each instance with a test liquid, which was an aqueous solution of 1% sodium chloride. Demand absorbency of each comparative sample was determined under a sample pressure of (0.5 psig/3.447·10³ Pag) and a 15 cm negative head of the test liquid for thirty minutes, after which the absorbed volume was measured. Free swell absorbency of each comparative sample was determined by allowing such comparative sample to swell to its absorbent capacity for two hours, after which the swollen sample was drained through filter paper until no more liquid drained from the swollen sample, whereupon absorbed volume was measured.

[0048] The following results were obtained:

Web Preparation	Demand Absorbency	Free Swell Absorbency
Improved Method	13.7 ml/gm	27.0 ml/gm
Conventional Technique	12.6 ml/gm	20.6 ml/gm
-	-	-
% Improvement	8.7%	31.1%

EXAMPLE 2

[0049] Two comparative samples were made by taking webs made per Example 1 and grinding them into powder.

[0050] Each comparative sample was ground into a powder, which passed through a 20 mesh (U.S. mesh) screen.

[0051] Demand absorbency and free swell absorbency of each comparative sample were determined, as in Example 1 discussed above.

[0052] The following results were obtained:

Web Preparation	Demand Absorbency	Free Swell Absorbency
Improved Method	18.0 ml/gm	23.0 ml/gm
Conventional Technique	14.8 ml/gm	19.9 ml/gm
-	-	-
% Improvement	21.6%	15.6%

[0053] As given above, examples 1 and 2 are believed to indicate that, if physical differences tend to be largely nullified as by grinding, a polymer having a given composition and resulting from the improved method used in each example has a molecular structure providing better absorbency, as compared to a polymer having the same composition but resulting from the conventional technique used in each example.

[0054] These examples demonstrate that the improved method is superior to the conventional coating technique used in these examples. The improved method is believed to be similarly superior to conventional coating techniques employing padders or squeeze rolls.

[0055] Moreover, the improved method is believed to be also superior to known spraying techniques employing nozzles, particularly nozzles spraying in circular or oval patterns. As mentioned above, nozzles used in such techniques tend to provide non-uniform coverage, whereas the improved method can be readily controlled so as to provide more uniform coverage. Moreover, nozzles used in such spraying techniques tend to plug or clog intermittently, whereas the improved method does not require any element capable of plugging or clotting.

[0056] From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiment illustrated herein is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Claims

1. A method of dispersing droplets of a polymerizable, cross-linkable material, in a liquid carrier, within a fibrous web, in which the material is to be polymerized and cross-linked, comprising the steps of:

(a) moving the fibrous web through a droplet-flicking zone; and

(b) flicking droplets of the material, in the liquid carrier, onto the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of a rotating element picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto the fibrous web as the element rotates.

2. The method of claim 1 wherein the rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

3. The method of claim 2 wherein the bristles pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles as the brush and the roller rotate.

4. The method of claim 3 wherein the brush and the roller rotate about parallel axes.

5. The method of claim 4 wherein the brush and the roller rotate in opposite rotational senses.

6. The method of claim 1 wherein the flicking step comprises flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of rotating elements picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, onto opposite sides of the fibrous web as the elements rotate, at least one of the rotating elements being adapted to flick droplets onto a respective one of opposite sides of the fibrous web as the fibrous web is moved through the droplet-flicking zone.

7. The method of claim 6, wherein each rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

8. The method of claim 7 wherein the bristles of each brush pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.

9. The method of claim 8 wherein each brush and the roller wiped by the bristles of such brush rotate about parallel axes.

10. The method of claim 9 wherein each brush and the roller wiped by the bristles of such brush rotate in opposite rotational senses.

11. A method of forming a composite web from a fibrous web and a polymerizable, cross-linkable material, in a liquid carrier, comprising the steps of:

(a) dispersing droplets of the material, in the liquid carrier, within the fibrous web, by the method of claim 1; and

(b) polymerizing and cross-linking the material in situ, so as to form a composite web comprising the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked.

12. The method of claim 11 wherein the rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

13. The method of claim 12 wherein the bristles pick up the material in the liquid carrier, from a rotating roller wiped by the bristles as the brush and the roller rotate.

14. The method of claim 13 wherein the brush and the roller rotate about parallel axes.

15. The method of claim 14 wherein the brush and the roller rotate in opposite rotational senses.

16. The method of forming a composite web from a fibrous web and a polymerizable, cross-linkable material, in a liquid carrier, comprising the steps of:

(a) dispersing droplets of the material, in the liquid carrier, within the fibrous web, by the method of claim 6; and

(b) polymerizing and cross-linking the material in situ, so as to form a composite web comprising the fibrous web and dispersed inclusions of the material, as polymerized and cross-linked.

17. The method of claim 15 wherein each rotating element is a brush with bristles picking up the material, in the liquid carrier, and flicking droplets of the material, in the liquid carrier, as the brush rotates.

18. The method of claim 17 wherein the bristles of each brush pick up the material, in the liquid carrier, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.

19. The method of claim 18 wherein each brush and the roller wiped by the bristles of such brush rotate about parallel axes.

20. The method of claim 19 wherein each brush and the roller wiped by the bristles of such brush rotate in opposite rotational senses.

21. A method of dispersing droplets of two different, polymerizable, cross-linkable materials, each material in a liquid carrier for such material, within a fibrous web, in which said materials are to be polymerized and cross-linked, comprising the steps of

(a) moving the fibrous web through a droplet-flicking zone; and

(b) flicking droplets of a different one of said materials, in the liquid carrier therefor, onto each side of the fibrous web as the fibrous web is moved through the droplet-flicking zone, by means of a rotating element picking up the said one of said materials, in the liquid carrier therefor, onto such side of the fibrous web as the element rotates.

22. The method of claim 21 wherein each rotating element is a brush with bristles picking up a different one of said materials, in the liquid carrier therefor, as the brush rotates.

23. The method of claim 22 wherein the bristles of each brush pick up a different one of said materials, in the liquid carrier therefor, from a rotating roller wiped by the bristles of such brush as such brush and the roller wiped by the bristles of such brush rotate.

Drawing