MXPA00000059A - Process for manufacturing wet laid fibrous structures comprising substantially non swellable particles added to the slurry - Google Patents

Abstract

A process for manufacturing fibrous structures comprising a wet laid fibre web comprising substantially water insoluble, substantially non water swellable particles that are added directly to the slurry. A fibrous structure according to this method is also described.

Description

PROCESS FOR MANUFACTURING FIBROUS STRUCTURES PLACED IN MOISTURE THAT DOES NOT SUBSTANTIALLY INCLUDE PARTICLES CAPABLE OF SWELLING ADDED TO SUSPENSION FIELD OF THE INVENTION The present invention relates to a process for manufacturing fibrous structures comprising a wet stretched fibrous web comprising substantially water insoluble particle material, which substantially can not swell in water, and fibrous structures manufactured in accordance with this process. The structures preferably must acquire / distribute and / or absorb aqueous fluids and the particulate material comprised therein also gives the structure additional benefits, for example, odor control; the structures are particularly suitable for use in disposable absorbent articles.

BACKGROUND OF THE INVENTION Fibrous structures, in particular fibrous structures for absorbing liquids, are manufactured for many uses, for example, they are incorporated in absorbent articles, such as disposable diapers, incontinence pads and sanitary napkins, as fluid or transmission absorption elements and / or diffusion of fluid, for example, as absorbent cores that must absorb and retain body fluids. Fibrous structures, and more specifically fibrous structures used in absorbent articles such as fluid absorption or fluid transmission and / or diffusion elements, may comprise one or more components in order to improve their specific performances; for example, absorbent structures comprising fibers and a particulate material, such as a particulate odor control material, are known in the art. Other components can also be included to give the structure additional benefits. Wet laying processes are widely used to produce fibrous webs when using papermaking techniques. In the wet laying process, natural or manufactured fibers are suspended in water to obtain a uniform distribution. As the fiber and the suspension in water, or "suspension", flows in a moving wire screen, the water passes leaving the fibers spread randomly in a uniform band. Then, additional water is withdrawn from the band and the remaining water is removed by drying. The bond can be completed by drying or bonding an agent, for example, an adhesive, which can be subsequently added to the dry band and the cured band. The fibrous webs produced by the wet laying process are particularly suitable for use as fluid absorption or transmission and / or fluid diffusion elements in absorbent articles, such as disposable diapers, sanitary napkins, incontinence pads and handkerchiefs. Wet laid structures have a number of advantages compared to similar types of structures that are prepared, for example, by laying in air. Wet laid structures discard body fluids much better than similar air laid structures. This is because wet laid structures suffer less wet collapse than structures laid in air. This, in turn, allows wet laid structures to better maintain their capillary channels and hollow spaces. Wet laid structures are also stronger than structures laid in air, from the point of view of tensile strength. Said comparatively high tensile strength is manifested when the wet laid structures are wet or dry. In general, they show a higher density and a lower thickness compared to structures laid in air that have the same base weight. The inclusion of particle material in fibrous webs wet-laid is known, but suffers from some disadvantages. According to a known method, particles are added to wet laid structures after the drying step; usually, water or other liquid is sprayed, such as an adhesive, to a dry sheet made by the wet laying process, before applying the particle material to the sheet and optionally an additional layer, for example, a fibrous layer is superimposed on the sheet, in order to form a laminated structure of mixed body. The added liquid helps the particles to attach to the leaves, preventing their migration during manufacturing or transport, and also helps in the lamination. This type of manufacturing is expensive, since re-wetting the dry base sheet to promote adhesion of the particles and optionally lamination, involves another drying step to remove the additional water. The alternative use of an adhesive, while being able to provide a stronger bond between the fibers and the particles, requires an additional curing step, possibly a drying step in the case of water-based or solvent-based adhesives, and It is also not suitable if there are high amounts of particles added to the sheet. In fact, the particles would form a type of continuous layer, and the adhesion of these particles to the sheet, and to the additional optional layer, requires a proportionally high amount of adhesive, which impairs the characteristics of the active particles, and of the entire structure of mixed body. A method for the latter type for manufacturing a wet laid structure comprising an aggregate particle material after the drying step of the wet laying process is described, for example, in the U.S. Patent. 5,300,192 from Weyerhaeuser Company, according to which the particles are bound to the fibers by means of a binder provided during the production of the web. The binder can be reactivated at a later stage, so that particles can be added during the web forming process or, preferably, when the web is subsequently used in a production line, for example, by fiber deformation of the web. the band and then lying in air. However, the wet laid structure still has the same disadvantages mentioned above. European patent applications EP-A-359 615 and EP-A-719 531 of James River Corporation of Virginia and Kao Corporation, respectively, describe alternative processes for forming absorbent sheets comprising wet laid fibrous layers and particles of absorbent material of gel solidification, also known in the art as "superabsorbent" particles. Typically, the particles of gel-solidifying absorbent material are distributed in a wet-laid fibrous web when it is still wet, i.e., before the drying step, and then the web is covered with another layer, possibly a fibrous layer, so that the particles are not present on the surface of the absorbent sheet. The incorporation of particles of gel-solidifying absorbent material in the wet laid strip before the drying step is considered advantageous since the fibers constituting the strip have a high degree of freedom when they are still wet, and therefore , particles of solidifying gel-absorbing material spread over the fibrous web can penetrate, at least to some degree, from the surface into the fibrous web. The incorporation of gel-solidifying absorbent material particles in the wet band also takes advantage of the swelling of the particles during the absorption of water still present in the band; the particles become sticky and adhere to the fibers of the web, thus acting as a binder for the web, which therefore does not necessarily require another specific binder.

The incorporation of gel-solidifying absorbent material particles in a wet laid structure prior to the drying step still shows some disadvantages due to the behavior of the gel-solidifying absorbent materials. The swelling of this type of material during the absorption of water can in fact impair the ability of the swollen particles of solidifying gel-absorbing material to easily penetrate the thickness of the band, due to the increase in volume and the stickiness of the fibers. particles. Therefore, said particles can not achieve a more uniform distribution, from the surface where they are spread. This is particularly true when relatively high amounts of particles are spread on the wet laid strip; in this case, the swollen particles, instead of penetrating inside the fibrous layer, can tend to form an almost continuous layer superimposed on the wet fibrous band, with a result similar to that already described with reference to the incorporation of stretched bands. wet before dried, also hinting at the need for a drying step quite expensive to remove water from the fibers and swollen particles. Another disadvantage of this type of structure is that the swollen particle material incorporated in the fibrous web performs a binding action on the fibrous web during drying, which changes according to the percentage and distribution of the particles in the fibrous web. The degree to which a wet-laid fibrous web, or level of bonding, is attached, usually correlates with the stiffness of the resulting structure, therefore, in order to have structures with different amounts of superabsorbent particles with a level of Even quite uniform bonding involving the stiffness values that are commonly preferred, for example, in the field of disposable absorbent articles, it may be necessary to somehow adjust this level of bonding. For example, it may be necessary to add another means of attachment to the structure, if the level of bond provided by the superabsorbent particles is insufficient, and therefore, the combined effect of two different binding media must be taken into consideration. Alternatively, a reduction with known means, for example, mechanically, of a very high level of bonding may be necessary, since a rigid structure generally results in higher amounts of superabsorbent particles that are incorporated in wet laid strips. The incorporation of gelling absorbent material, preferably in the form of particles, into wet laid fibrous structures by adding the material directly into the suspension has also been proposed in European Patent EP-A-528248. The absorbent material swells preferably in the dispersion medium, usually water, of the suspension, but it is said that by reducing the duration of exposure of this absorbent material to the dispersion medium and / or by selecting an absorbent material having a gel strength. At the top it is possible to keep the inflation to a relatively low degree, thus preventing the bond between the absorbent particles and the fibers. However, this requires a manufacturing process that is difficult to optimize, because this duration of exposure usually depends on the type of material incorporated in the suspension. On the other hand, a duration of the exposure that is sufficient to avoid or at least reduce the bond between the fibers and the particles can still lead to the union between the particles themselves, due to their sticky surface, with the possible formation of agglomerates or agglomerates. , especially when they are going to incorporate amounts of high particles in the fibrous structure laid wet. This can also lead to the entrapment of particles or agglomerates of particles in the forming wire used in the wet laying process; the particles or the agglomerates of trapped particles in the forming wire remain in contact with the water for a longer time and therefore would swell to a much higher level as compared to the level of swelling accepted in the process. Eventually it may result in partial obstruction of the forming wire. Therefore, an object of the present invention is to provide a process for manufacturing fibrous structures for acquiring / distributing and / or absorbing aqueous fluids comprising a wet laid fibrous web obtainable from a suspension comprising a binder and a material of particle. Another object of the present invention is to provide said process wherein the bonding of the wet-laid fibrous web is carried out exclusively by the binder means, and can be controlled independently of the amount of the particle material incorporated in the wet laid fibrous web. The process is therefore simpler since no adjustments are needed depending on the type of particle material that is incorporated. Still another object of the present invention is to provide a fibrous structure made in accordance with this method comprising a wet laid fibrous web incorporating a particulate material and having the above mentioned advantages. It has been found that the incorporation of substantially water-insoluble particle material and that it can not substantially swell in water in a wet-laid fibrous web when added to the suspension prior to deposition in the wire screen results in a better distribution of the particles within the fibrous web, even in the case of high amounts of particles that are incorporated into the structure, without the risk of particle agglomeration. The easier and more precise control of the process can also be achieved, with particular reference to the joining of the structure by means of binding means provided in the suspension or in the wet laid fibrous web.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process for manufacturing a fibrous structure comprising fibers, a binder medium, and a substantially water insoluble particle material which substantially can not swell in water. The process comprises the steps of: a) providing a wet laid fibrous web that is prepared by a wet process of an aqueous suspension comprising fibers and the particulate material, b) providing the fibrous web wet laid with the binder medium, c) drying the fibrous web, and d) joining the fibrous web when activating the binder medium. The invention further relates to a fibrous structure obtainable from a suspension comprising fibers, a binder means and a particle material substantially insoluble in water and which can not substantially swell in water.

BRIEF DESCRIPTION OF THE DRAWINGS Although the specification concludes with claims that point in particular and distinctly claim the present invention, it is believed that the present invention will be better understood from the following description along with the following drawings: Figure 1 is a side elevational view, in fragment , schematic of an apparatus for making a fibrous structure in accordance with the present invention; Figure 2 is an elongated, cross-sectional view of a fibrous structure in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for manufacturing a fibrous structure preferably intended to acquire / distribute and / or absorb aqueous fluids, and fibrous structures manufactured in accordance with the process. The structure comprises a wet stretched fibrous web comprising substantially water insoluble particle material and which can not substantially swell in water. In a preferred embodiment, the structures of the present invention are incorporated into absorbent articles, preferably as fluid acquisition / distribution structures, which must receive and distribute various aqueous body fluids. The structures can also be incorporated as absorbent structures that must absorb and retain body fluids. Particle material substantially insoluble in water and which can not substantially swell in water comprised in the wet laid fibrous web provides additional benefits to the structure, for example, odor control. Absorbent articles, and more specifically disposable absorbent articles, refers to items such as sanitary napkins, disposable diapers, incontinence pads, which a wearer uses adjacent to the body and must absorb and contain different fluids that the body discharges (e.g., vaginal discharges) , menstruation, sweat and / or urine) and that should be discarded after a single use. By "particle material" is meant a substance in the form of discrete particles. The particles can be configured in a varied manner such as spherical, round, angular, acicular or irregular.

As used herein, "substantially insoluble in water" refers to substances that substantially do not dissolve in water, and therefore, retain their solid particle form after contact with water. By "substantially not swelling in water" is meant materials which, although capable of absorbing water, usually in relatively low amounts, for example by surface adsorption and / or pore filling via capillary flow, do not swell, is say, these materials do not substantially increase their volume in absorption. The swelling mechanism is well known from the field of so-called superabsorbent materials; said materials are typically constituted by a three-dimensional polymer network which, upon contact with a solvent, usually water, unwinds polymer chains to more open conformations., so that each chain maximizes its contact with the solvent molecules, and thus swelling of the network occurs with the formation of a gel structure. Therefore, the absorption involves a partial solubilization of the absorbent material. Suitable materials according to the present invention are those which preferably do not form gels with water and absorb less than 5 times their own weight of water, more preferably less than 1.5 times. In any case, materials that can not substantially swell in water, in accordance with the present invention, do not form a sticky surface upon contact with water, even when they are capable of absorbing a limited amount thereof. Said materials may comprise pure substances or agglomerates thereof, provided that together they satisfy the preferred requirement of the lack of substantial swelling capacity. In a preferred embodiment, the fibrous structures according to the present invention can integrally comprise an element of a disposable absorbent article, for example, the absorbent core or a fluid acquisition / distribution element, or they can be included therein as part of said element. The particle material comprised therein is capable of providing the fibrous structure with an additional benefit, for example, control of odors typically associated with the body fluids that make contact with the fibrous structure. Disposable absorbent articles, such as, for example, sanitary napkins, pantiliners, incontinence pads, or diapers, typically comprise a fluid-permeable topsheet, a fluid-impermeable backsheet, which may optionally be vapor permeable and / or gas, an absorbent core therebetween, and, preferably, a fluid acquisition / distribution layer, usually placed between the topsheet and the absorbent core. The fibrous structures of the present invention can be made by using conventional equipment designed for wet laying process. The invention will be described below as a process for manufacturing a fibrous structure constituted by a wet stretched fibrous web comprising the particle material, which is capable of providing acquisition / distribution of aqueous fluids, in particular body fluids, and furthermore control of the odors associated with the absorbed fluids, and as a fibrous structure manufactured in accordance with this process, said structure should be incorporated as an acquisition / distribution layer in a disposable absorbent article, for example, a sanitary napkin. Figure 1 is a simplified schematic illustration of a preferred embodiment of the fabrication of a fibrous structure 8 of the present invention. Techniques are known in the art for the wet laid fibrous material to form sheets such as dry mesh and paper. These techniques are generally applicable to the wet laying of fibers to form wet laid fibrous webs in accordance with the process of the present invention. Suitable wet laying techniques include manual sheet forming, and wet laying with the use of papermaking machines as described, for example, by L.H. Sanford et al. In the U.S. Patent. No. 3,301,746. In general, as illustrated in FIG. 1, wet-laid fibrous webs can be made by depositing an aqueous suspension of fibers from an apparatus 14 known in the art as the main box in a foraminous forming wire 12, by draining the suspension from the suspension. wet laid to form a wet band 11, and drying the wet band. Preferably, aqueous suspensions of wetwear fibers will have a fiber consistency of between about 0.05% and about 2.0%, preferably between about 0.05% and about 0.2% of the total weight of the suspension. Particle material substantially insoluble in water and substantially not swellable in water 18 is added directly to the suspension in the main box 14, being fed for example from a reservoir 20. A homogeneous mixture of fibers and particulate material 18 is therefore obtained in the suspension 10. The main case 14 has an opening, known as a slice, for supplying the aqueous suspension 10 of fibers and particulate material 18 in the foraminous forming wire 12. The foraminous forming wire 12 is often referred to in the art as a Fourdrinier wire. The Fourdrinier wire may be of a construction and mesh size used for dry mesh or other papermaking processing. Preferably, mesh sizes of about 70 to about 100 (standard Tyler sieve scale) are used (all mesh sizes referred to herein should be based on the standard Tyler sieve scale, unless specifically indicated otherwise) . Conventional case designs can be used known in the art for dry mesh and tissue sheet formation. Suitable commercially available main boxes include, for example, fixed roof, double wire, and main drum boxes. Once formed, the wet strip 11 is drained and dried. The drain can be made with suction boxes 16 or other vacuum devices. Typically, the drain increases the fiber consistency to between about 8% and about 45%, total weight of the wet web and not considering the weight of the particulate material 18, preferably between about 8% and about 22%. Drainage to consistencies over about 22% may require wet pressing and is less preferred. Because a fraction of the particulate material 18 can possibly be drained with the water from the fiber web 11 deposited on the forming wire 12, this fraction can preferably be recovered from the water and fed back into the suspension, by means of a suitable recovery apparatus, not illustrated in Figure 1. Any risk of entrapment in the forming wire 12 of the drained fraction of the particulate material 18 can be avoided, for example, by simply selecting a material of particles 18 of such average dimensions with respect to the mesh size of the forming wire that the particulate material 18 drains with the water from the wet laid fiber web 11 can substantially pass through the openings of the wire 12. Any preferred size of the particulate material can be really used in any way, since the ability to not substantially swell the particle material 18 is not it avoids a substantial increase in volume in the particulate material, but also any possible agglomeration of particles due to surface tack, and eventually prevents the particles from sticking to the forming wire itself. Minor amounts of particulate material 18 drained from the fiber web 11 which must nevertheless remain in the forming wire 12 due to the intrinsic, non-swollen size of the particles can therefore be easily washed, for example with water, after of the separation of the fiber band 11 of the forming wire 12, and then preferably recovered. Any natural or synthetic fiber can be used in the fibrous structures made in accordance with the process of the present invention, such as cellulose, rayon, nylon, polyester, polyolefin, or bicomponent fibers.; also compressed fibers or synthetic wood pulp fibers can be used. Chemically hardened cellulosic fibers such as those described in US Patents may also be used. 4,889,597 and 5,217,445. In particular, wood pulp fibers are preferred. In the process and in the product of the present invention, any type of particle material which is substantially insoluble in water and which substantially can not swell in water, and which can provide benefit to the fibrous structure can be used. Particularly suitable is the particle material capable of providing the fibrous structure without odor control, but other activities are also possible, for example, particle material to provide ion exchange capacity, in connection or not with odor control. In its preferred use for acquisition / distribution and / or absorption of fluid in disposable absorbent articles, the fibrous structures according to the present invention must make contact with body fluids. Therefore, the preferred particle materials are those capable of controlling unpleasant odors associated with body fluids. Any suitable odor control agent known in the art can preferably be incorporated in the form of particle material into fibrous structures according to the present invention, provided that it is substantially insoluble in water and that it can not substantially be swollen in water. Water. For example, substantially water-insoluble particle material, which substantially can not be swollen in water for odor control may comprise chlorophyll particles, activated carbon granules, carbon, ion exchange resin, activated alumina, and zeolite, including the well-known "molecular sieve" zeolites of type A and X and the zeolite materials made under the tradename ABSCENTS by Union Carbide Corporation and UOP. Another suitable odor control particle material used in the present invention may also comprise other compounds such as chitin, silica gel, diatomaceous earth, polystyrene derivatives, starches and the like, or agglomerates thereof, for example, agglomerated particles of zeolite and silica with a binder. A substantially water insoluble particle material, which substantially can not swell in preferred water to provide odor control is a mixture of zeolite and silica particles, preferably in the form of silica gel. The average dimensions of substantially water insoluble particle material, which can not substantially swell in water used in accordance with the present invention, given as a percentage by weight of the smallest dimensions of the individual particles, can be between 50 microns and 1500 microns, preferably between 100 microns and 800 microns. The substantially water-insoluble particle material, which can not substantially swell in water 18 can only become wet, and possibly absorb even a certain amount of water when it comes into contact with water in suspension 10, but does not substantially swell and not becoming sticky, unlike the swelling materials, for example the particles of gelling absorbent material of the prior art, and irrespective of the time of contact with water. In the embodiment of the present invention illustrated in Figure 1, the particle material is mixed uniformly with the fibers in the suspension 10 and therefore a uniform distribution of the particle material 18 is obtained between the fibers 24 through the The total thickness of the fiber web 11, as illustrated in Figure 2, shows a fibrous structure 8 already complete according to the present invention. Due to the absence of swelling, the particle material 18 is not impeded from distributing between the fibers 24 by the increased volume and by the stickiness of the surface of the particles, as the swelling particles of the prior art are; on the other hand, the particles 18 do not even tend to stick to one another, with the possible formation of agglomerates or agglomerates, which is likely to occur with the processes of the prior art, also in the case of very short contact times with Water. This means that larger amounts of particle material 18 can be added to the wet laid fiber web 11, without the risk of the formation of agglomerates of particles 18 distributed unevenly in the wet laid fiber web 11, as this may be the case when using the material of swelling particles, for example superabsorbents, the contact time of the particle material 18 with the water is therefore not of greater interest in the process of the present invention. The process of the present invention also allows other preferred distributions of the particle material 18 within the thickness of the fiber web 11, starting from the same uniform mixture of fibers and particles in the suspension. In fact it is possible to take advantage of the drainage effect of the water during the drainage stage in order to achieve a non-uniform distribution of the particle material 18 within the thickness of the strip 11, with the highest concentration close to the surface of the strip 11 which is adjacent to the forming wire 12, and possibly showing a more or less pronounced concentration gradient. The ability to not substantially swell the particle material 18 prevents the formation of agglomerates, and prevents the particles from sticking to the forming wire 12, due to its non-tacky surface. These alternate distributions may be beneficial for certain uses of the resulting fibrous structure. After drainage, the fibrous web 11 comprising the substantially water-insoluble particle material, which can not substantially swell in water 18 can be transferred, but not necessarily, from the forming wire 12 to a drying cloth 26 which carries the fibrous web 11 to drying apparatuses 28. The drying web 26 is thicker than the forming wire 12, for increased drying efficiency. The drying fabric 26 preferably has from about 30% to about 50% open area and from about 15% to about 25% closed area, such as a 31.25 S (satin fabric) that has been sanded for increase the closed area within the preferred scale. The wet microcontraction is preferably implemented during the transfer of the forming wire to the fabric. The wet microcontraction can be achieved by running the forming wire 12 at a speed that is about 5% to about 20% faster than the speed at which the fabric 26 runs. Drying can be achieved with a thermal blow dryer 28 or a vacuum device such as a suction box, although drying by thermal blow is preferred. The wet-laid webs are preferably dried (usually at fiber consistency between about 90% and about 95% based on the weight of the web without the particles) by the dryers through thermal blow 28. It is also it can use a steam drum dryer apparatus known in the art, such as Yankee drum dryers. The dry bands preferably do not curl. As an alternative to the drying described above, the waterless web can be removed from the forming wire placed on a drying and drying screen (without restriction) in a charge drying process, for example, by a thermal blow dryer or a furnace heated with forced convection steam. As is known in the art, fibers in wet laying processes may have a tendency to flocculate, or form granules, in aqueous solution. In order to inhibit flocculation, the aqueous suspension must be pumped to the main case 14 at a linear velocity of at least about 0.25 m / sec. Also, it is preferred that the linear velocity of the suspension 10 upon leaving the main box slice is from about 2.0 to about 4.0 times the speed of the forming wire 12. Another method to reduce the flocculation of fibers in a laying process wet is described in the US Patent No. 4, 889,597, issued December 26, 1989, wherein jets of water are directed to the wet laid fibers just after deposition in the forming wire. The presence of particulate material substantially insoluble in water, which can not substantially swell in water dispersed with the fibers in the suspension does not promote flocculation, due to the non-tacky surface of the particles when in contact with water, which can not adhere to the fibers and cause the formation of agglutination. Known processes for producing the wet laid fibrous webs 11 of the present invention, which comprise the substantially water-insoluble particle material, which substantially can not swell in water 18, usually form lower tensile strength sheets, particularly in the not dry condition. Furthermore, not much bonding action can be performed by the particle material 18 comprised therein, due to the fact that it is substantially insoluble in water, that it can not substantially swell in water, and therefore can not stick to the fibers, as is the case, for example, of the swellable particle material, for example, gel-solidifying absorbent material in the form of a particle, of the prior art. Therefore, in order to facilitate processing and to increase the integrity of the wet-laid web after drying, a binder means can be integrally incorporated into the web. This can be done by adding the binder to the fibers before forming the band, when applying the binder (binders chemical additives) to the fibrous web wet laid after depositing on the forming wire and before drying, then to dry, or a combination thereof. For example, suitable binding means for increasing the physical integrity of the fibrous structures 8 of the present invention constituted by a wet-laid fibrous web comprising substantially water insoluble particle material, which substantially can not be swollen in water include chemical additives, such as resinous binders, latex, and starch known in the art to provide increased integrity to fibrous webs. Suitable resinous binders include those that are known for their ability to provide moisture resistance in paper structures, such as can be found in the TAPPI series No. 29, Wet Strength in Paper and Paperboard, Technical Association of the Pulp and Paper Industry (New York, 1954). Suitable resins include polyamide-epichlorohydrin and polyacrylamide resins. Other resins which have utility in this invention are urea formaldehyde resins and melamine formaldehyde. The most common functional groups of these polyfunctional resins are nitrogen containing groups such as amino groups and methylol groups attached to nitrogen. Resins of the polyethylenimine type can also find utility in the present invention. Starches, in particular, modified, cationic starches as chemical additives in the present invention may also be useful. Said cationic starch materials, usually modified with nitrogen-containing groups such as amino groups and methylol groups attached to nitrogen, can be obtained from Natural Starch and Chemical Corporation, located in Bridgewater, N.J. Other suitable binders include, but are not limited to, polyacrylic acid polyacrylic acid. The level of chemical additive binders that are added will typically be from about 0.25% to about 2% based on the weight of the band without the particles. However, chemical additive binders that are hydrophilic can be used in larger amounts. Chemical additive binders can be applied to dry or non-dry webs by printing, spraying or other methods known in the art. Preferred chemical binders are liquid hot curing compositions that can be activated by heat treatment, such as emulsions or water-based dispersions of synthetic polymers or copolymers (latex) which can be coagulated. In another embodiment, the binder means of the wet laid fibrous web comprises from about 10% to about 50%, preferably from about 25% to about 45%, more preferably from about 30% to about 45%, with based on the weight of the strip without the particles, of a thermoplastic binder material, wherein the thermoplastic binder material provides binding sites at intersections of the fibers, and possibly involves the particle material distributed therein. Said thermally bonded webs can be made, in general, by wet-laying a fibrous web comprising, for example, hydrophilic fibers and thermally fusible binder fibers, which are preferably evenly distributed therein. The thermoplastic fibrous material may be intermixed with hydrophilic fibers, for example, cellulosic fibers, in a preferred embodiment of the present invention, in the aqueous suspension prior to the formation of the web. Once formed, the wet stretched fibrous web is thermally bonded by heating the web until the thermoplastic fibers melt. Upon melting, at least a portion of the thermally fusible link fibers will migrate to intersections of the cellulosic fibers and, to a lesser degree, of the fibers with the particle material. These intersections become link sites for the thermoplastic material. The band is then cooled, and the thermoplastic material joins the cellulosic fibers together at the bonding sites, at the same time stabilizing the particle material comprised in the structure. The thermoplastic binder materials useful for the wet laid fibrous web of the present invention herein include any thermoplastic polymer that can be melted at temperatures that will not damage the fibers and the particulate material. Preferably, the melting point of the thermoplastic binder material will be less than about 175 ° C, preferably between about 75 ° C and about 175 ° C. In any case, the melting point should not be less than the temperatures at which the articles of this invention will be stored, whereby the melting point will typically be not less than about 50 ° C. The thermoplastic binder material may be, for example, polyethylene, polypropylene, polyester, polyvinyl chloride, polyvinylidene chloride. Preferably, the thermoplastic material will preferably not damage or absorb aqueous fluid. However, the surface of the thermoplastic material can be hydrophilic or hydrophobic (as used herein, the terms "hydrophilic (a)" and "hydrophobic (a)" should refer to the degree to which the surfaces are wetted by water). The hydrophobic material is made more preferred as a percentage of higher thermoplastic binder material, particularly at percentages above about 40%. The thermoplastic fibers for use herein may be in the order of about 0.1 cm to about 6 cm in length, preferably from about 0.3 cm to about 3.0 cm. A preferred type of thermoplastic fibrous material is commercially available and available as PULPEX ™ (Hercules, Inc., Washington, Del., USA). PULPEX is a polyolefin material that has a very high surface to mass ratio, which, in general, is made by spraying molten polymer and gas through a vacuum nozzle. PULPEX is available in polyethylene and polypropylene forms. The thermally fusible binder fibers can be replaced by a thermoplastic polymer material in finely divided form, for example, in powder form. It is preferred that the thermoplastic polymer material in finely divided form have flow characteristics to allow the necessary bonds between the fibers, and, to a lesser degree, between the fibers and the particle material, form quickly.

These characteristics can be achieved by a thermoplastic polymer material in finely divided form with a melt flow index (MFI) evaluated by the method ASTM D 1238-85 under conditions 190 / 2.16, of at least 25 g / 10 min., preferably at least 40 g / 10 min., and even more preferably at least 60 g / 10 min. If the fibers of the wet-laid fibrous web are short cellulosic fibers, it is preferred to use a thermoplastic polymeric material composed of high density polyethylene powder with maximum particle dimensions of about 400 microns, characterized by a melt flow index of approximately 50 g / 10 min. The thermoplastic binder material is preferably melted by air binding, however, other methods such as infra red light, etc., should not be excluded. In another variation, the band can be subjected to heat embossing on one or both sides of the band. This technique is described in more detail in the U.S. Patent. No. 4,590,114. In a preferred embodiment, the activation of the binder means is carried out by a heating step intended to cure a liquid hot curing binder, or alternatively to melt a thermoplastic binder material, either in fibrous or powder form. More preferably, as shown in the embodiment of the present invention illustrated in Figure 1, the heating step is performed during the drying of the wet laid fibrous web 11 in the dryer with thermal blow passage 28, where the fibers Thermally fusible binders comprised in the wet laid fibrous web are melted so as to bond the dry web of wood pulp fibers comprising the particle material 18, thus avoiding the risk of losing particles of the fibrous web 11 during the step of drying In a less preferred alternative embodiment of the present invention, the binder means can only refer to a hydrogen binding capacity of the fibers comprised in the wet laid fibrous web. The fibers with hydrogen bonding capacity, for example, the preferred wood pulp fibers, can in fact form a wet stretched fibrous web where bonding occurs between the fibers, due to hydrogen bonds. In this case, the activation of the binder means corresponds to the formation of the hydrogen bonds between the fibers during the drying step, and then the addition of any additional specific binder means is required. Fabrics such as tissue sheets and other water-permeable non-woven sheets can be used as external support in addition to or in place of the binder medium described above. In the process of the present invention for manufacturing fibrous structures, the level of bonding of the wet-laid fibrous web comprising the particle material is carried out exclusively by the binder means and is not influenced by the particle material itself, even when it is present in a relatively high quantity and with a not very uniform distribution, due to its insolubility characteristics in substantial water and lack of being able to swell in water which make the particle material almost inert to the fibers. Therefore, the desired degree of bonding level can be easily provided and can be controlled by the incorporation of suitable binder medium, substantially independent of the amount of particulate material comprised in the wet laid fibrous web, as can be determined one skilled in the art. Wet-laid fibrous webs which in a preferred embodiment integrally constitute the fibrous structures of the present invention, will preferably have dry basis weights of less than about 1000 g / m2 and dry densities of less than about 0.60 / cm3. Although the scope of the invention should not be limited, fibrous structures having dry basis weights ranging from about 10 g / m2 to about 1000 g / m2, preferably from about 100 g / m2 to about 800 g / m2, more preferably from about 150 g / m2 to about 400 g / m2, and dry densities between about 0.02 g / cm3 and 0.20 g / cm3, more preferably between about 0.02 g / cm.sup.3 and about 0.15 g / cm.sup.3, are suitable as fluid acquisition / distribution layers in disposable absorbent articles. All values are based on the dry band without the particles. The density and the basis weight may be substantially uniform, although the non-uniform density and / or basis weight, and the density and / or basis weight gradients, should be encompassed herein. In this way, the fibrous structure may contain regions of relatively higher or relatively lower density and basis weight, preferably without exceeding the above scales. According to one embodiment of the present invention, the wet-laid fibrous web constituting the fibrous structure comprises from about 50% to 100% hydrophilic cellulosic fibers, typically wood pulp fibers, and from 0% to about 50% of a binder medium, based on the weight of the dry web without the particles, to increase the physical integrity of the web, to facilitate processing in the web and / or dry state, and to provide increased integrity by wetting the web during its use. Preferably, the wet laid fibrous web will comprise at least about 2% fibrous binder media. Chemical additives can also be used as binder media, and are incorporated into the acquisition / distribution layer at levels typically from about 0.2% to about 2.0%, basis weight of the dry band without the particles. Particle material substantially insoluble in water, which substantially can not swell in water, for example, to provide odor control, can be incorporated into the fibrous structures according to the present invention in an amount varying from 20 g / m2 at 400 g / m2, preferably from 100 g / m2 to 300 g / m2, more preferably from 150 g / m2 to 250 g / m2, with reference to the total surface area of the fibrous structure. Preferably, the fibrous structures of the present invention can comprise from 2% to 80% by weight of the particle material, based on the weight »Total dry of the structure. The weight of the particle material that can actually be used in various fibrous structures intended for different uses can be determined by the skilled artisan considering the size and type of the fibrous structure, and its intended use. The fibrous structures of the present invention can be integrally constituted by a wet-laid fibrous web comprising substantially water insoluble particle material, which can not substantially swell in water, or can comprise at least one other fibrous web, for example , another fibrous band stretched wet. In an alternative embodiment of the present invention, not illustrated, the particle material can be distributed unevenly in the fibrous structure, for example with different concentrations throughout the thickness of the structure. For example, the particle material may be more concentrated at the center of the fibrous structure, at an intermediate part of the outer surfaces of the fibrous structure itself, or near one of the outer surfaces. This can be achieved by means known in the art, for example by adding the particle material to the suspension in a position closer to the opening through which the suspension is deposited from the main layer towards the forming wire, so that such that the particles can be properly directed to a desired position in the suspension outlet opening (slice), instead of being randomly distributed in the same suspension.

In a further alternative embodiment of the present invention, not illustrated, another fibrous web wet laid on the surface of the wet laid fibrous web may be provided where the particle material has been distributed, comprising another binder medium which, when activated and in combination with the binder comprised in the wet-laid fibrous web, it performs the union of the other fibrous web and the fibrous web laid wet, which together constitute the fibrous structure. Preferably, the other fibrous web is another wet laid fibrous web formed directly on the fibrous web wet laid after the distribution of the particle material. The other fibrous web may also be constituted by a preformed nonwoven layer, or a polymeric film may also be attached to the wet laid fibrous web in order to form a mixed body structure comprising the fibrous structure of the present invention. Of course, the substantially water-insoluble but swellable particle material, such as, for example, particles of gel-solidifying absorbent material, can also be added to the fibrous structures of the present invention after the stage of drying the wet stretched fibrous web, included in the fibrous structure and linked with one of the methods known in the art. As an alternative, other liquids other than water may also be used in the wet laying process of the present invention in order to provide the suspension. Therefore, the characteristics and type of the particles to be distributed in the wet-laid fibrous web may be different, compared to those described above, at the same time maintaining substantial insolubility and lack of substantial swelling capacity. with respect to the liquid used as a dispersion medium to provide the fibrous suspension.

Claims (14)

1. - A process for manufacturing a fibrous structure comprising fibers, a binder, and a particle material, said particle material being substantially insoluble in water and substantially unsupportable in water, said process comprising the steps of: a) providing a wet laid fibrous web that is prepared by a wet process from an aqueous suspension comprising fibers and said particulate material, b) providing said fibrous web wet laid with said binder means, c) drying said fibrous web , and d) joining said fibrous web when activating said binder means.

2. A process according to claim 1, wherein said particle material comprises odor control compounds, preferably zeolites and silica.

3. A process according to any preceding claim, wherein said union of said fibrous web is made exclusively by said binder means.

4. A process according to any preceding claim, wherein said binder means is provided either in said suspension or, alternatively, after the wet laying of said fibrous web.

5. A process according to any preceding claim, wherein said binder means comprises thermally fusible link fibers and can be activated by heat treatment.

6. - A process according to any of claims 1 to 4, wherein said binder means comprises a curable liquid composition, preferably at least one liquid hot cure composition that can be activated by heat treatment.

7. A process according to any preceding claim, wherein said fibrous web stretched wet comprises hydrophilic cellulosic fibers.

8. A fibrous structure that can be obtained by the process of claim 1, comprising a wet laid fibrous web that can be obtained from a suspension comprising fibers, a binder, and a particulate material, the fibrous structure characterized in that said particulate material is substantially insoluble in water and that it can not substantially swell in water.

9. A fibrous structure according to claim 8, characterized in that said particle material comprises odor control compounds, preferably zeolites and silica.

10. A fibrous structure according to claim 8 or 9, characterized in that the union of said fibers is carried out exclusively by said binder means.

11. A fibrous structure according to any of claims 8 to 10, characterized in that said binder means comprises thermally fusible bonding fibers.

12. A fibrous structure according to any of claims 8 to 10, characterized in that said binder means comprises a curable liquid composition, preferably a liquid hot cure composition.

13. - A fibrous structure according to any of claims 8 to 12, characterized in that said fibrous web stretched wet comprises hydrophilic cellulosic fibers.

14. An absorbent article for absorbing body fluids comprising a liquid permeable upper sheet, an absorbent element, and a back sheet, characterized in that said absorbent article comprises the fibrous structure according to any of claims 8 to 13.