EP0958418A1

EP0958418A1 - Method and installation for fixing particles on the surface fibres of a fibre lap, resulting fibre lap, and article comprising such a lap

Info

Publication number: EP0958418A1
Application number: EP98906984A
Authority: EP
Inventors: Achille Duflot
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-02-10
Filing date: 1998-02-06
Publication date: 1999-11-24
Also published as: WO1998035084A1; AU6298698A; FR2759388B1; FR2759388A1

Abstract

The invention concerns a method consisting in: a) generating a suspension of fine droplets of a binder dispersion in a given volume (9) above a fibre lap (2); b) spraying the particles (1) in said volume (9), whereby said particles (1) are coated by the binder dispersion (11) and drop on the fibre lap (2); c) and subjecting the assembly fibre lap /particle coated with the dispersion to a treatment, in particular thermal, for fixing the binder on the fibres of the lap (2). The installation comprises: a) an endless belt (5) provided with driving means; b) means for atomising (8) a binder dispersion (11) for generating a suspension of fine droplets of said dispersion in a given volume (9) above the endless belt; c) means (10) for spraying the particles (1) towards said volume (9); and d) a treating chamber (7) arranged on the path of the endless belt (5), downstream of the atomising (8) and spraying (10) means.

Description

METHOD AND INSTALLATION FOR FIXING PARTICLES ONTO

SURFACE FIBERS OF A FIBER TABLECLOTH. FIBER TABLECLOTH

OBTAINED AND ARTICLE INCLUDING

SUCH A TABLECLOTH The present invention relates to the field of fiber sheets, in particular but not exclusively fiber sheets which are intended for hygiene articles of the diaper type. It relates more particularly to a method and an installation for fixing particles on the surface fibers of such a sheet, in particular fixing particles of a super absorbent material.

In the field of hygiene articles, it is sought to constantly improve the comfort of the user, in particular by reducing the thickness of the absorbent mattress, such a reduction in thickness being made possible by the use of a super absorbent material, that is to say a material capable of absorbing a very large quantity of liquid. It may in particular be a hydroexpandable polymer capable of absorbing at least fifteen times its own weight of water.

Such a super absorbent material is generally in the form of particles, that is to say solid grains. When one seeks to reduce the thickness of the absorbent mattress, for example a diaper, it is necessary that these particles are in one way or another integral with the sheet of fibers constituting the absorbent mattress, failing what there would be strong risks of loss of particles during the various stages of manufacture of the diaper and during handling thereof by the user.

One solution aimed at joining the particles of a super absorbent material to the absorbent mat consists in trapping said particles between two layers of fibers. Another solution, proposed by document EP.676. 96, consists in fixing said particles to the surface of the fiber web using a binder formed from a dispersion of polymers. According to the process described in this document, a sheet of fibers which are not bonded together is treated with an aqueous dispersion of a binder, then the particles thus impregnated with particles of a super-absorbent material are deposited, the excess of dispersion by aspiration and preferably the whole is dried. There is therefore obtained both the bonding of all the fibers of the sheet and the bonding of the particles of the super absorbent material on at least the surface fibers of said sheet. According to the applicant, the process described in document EP.676.496 has drawbacks, however. It requires the use of a very large amount of the aqueous dispersion of binder because it is the whole of the sheet which is impregnated with this dispersion. Furthermore, the fixing of a given particle can only be done if it is in contact with a fiber impregnated with binder; this fixing cannot take place in particular in the cases where a particle is in contact with an unimpregnated area, being a fiber or another particle of the super absorbent material.

In general, what has just been described for fixing the particles of a super absorbent material on a sheet of fibers intended to constitute an absorbent mattress for a hygiene article applies in the same way for fixing of particles whatever they are on the surface fibers of a sheet of fibers, whatever its destination.

The aim that the applicant has set is to propose a method for fixing particles on the surface fibers of a sheet of fibers which overcomes the drawbacks mentioned above.

This object is perfectly achieved by the method of the invention which, in known manner, uses a binder in the form of a dispersion and which typically consists of: a) creating a suspension of fine droplets of the dispersion of binder in a given volume above the sheet of fibers, b) projecting the particles into said volume, whereby said particles are coated with the dispersion of binder and fall on the fiber web, c) and subject the fiber web / particles coated with the dispersion to a treatment capable of fixing the binder on the fibers of the web .

What makes the originality of this process is to associate the binder with the particle to be fixed rather than associating the binder with the fibers of the sheet as is the case of document EP.676.496. The particle which crosses the space in which the suspension of fine droplets of the binder dispersion is found, thus presenting itself as a mist, comes into contact with said droplets and takes charge of them until it is coated with the dispersion. of binder. The fact that the particle is loaded with binder dispersion has incidental advantages, due to its relative weighting; on the one hand when it falls on the sheet the particle can penetrate further among the surface fibers thereof and on the other hand the projection in the volume of the suspension is not necessarily vertical to the sheet but can be done from a different angle.

According to the particular arrangement of the process of the invention, it is the binder which coats the particle which comes into contact with one or more fibers of the sheet and which, after the fixing treatment, performs the bonding between the particle and the sheet. . Of course in the case where several particles are in contact with each other, they are in the same way linked to each other and to the fibers of the sheet, which would not necessarily have been the case in the process described in document EP.676.496.

Preferably, the suspension of fine droplets of the binder dispersion is obtained by spraying an aqueous dispersion containing on the order of 5 to 20% of binder. With this proportion, a homogeneous mist of fine droplets of the dispersion is obtained under good conditions, by using spraying means of the type Airless gun (without air).

As regards particles of a super absorbent material, preferably the dispersion is an aqueous dispersion of a water-soluble binder, for example of carboxy methyl cellulose (CMC). The fixing treatment is preferably a heat treatment, making it possible to evaporate the solvent.

When the particles are in a super absorbent material, and the dispersion of the binder is an aqueous dispersion, it is important that the conditions of the heat treatment are determined so that the evaporation of the water from the dispersion takes place within a time which is less than the expansion time of the super absorbent material under the action of water. In fact, otherwise, an expansion of the super absorbent material could occur under the effect of the water contained in the dispersion. In practice, the expansion time of a super absorbent material is variable and can depend in particular on its particle size. In general for the super absorbents which are used in hygiene articles of the diaper type, the expansion time is of the order of a few tens of seconds. However, it can be much shorter when using smaller particles.

Advantageously, in the case of an aqueous dispersion of a carboxy methyl cellulose, this dispersion has a slightly acidic pH, for example between 4 and 6.8. This particular arrangement has the effect of delaying the expansion of the super absorbent material and therefore of being able to implement the method of the invention with much finer particles of such a material.

It is another object of the invention to provide an installation specially designed for the continuous implementation of the above process. This installation for the continuous fixing of particles on at least surface fibers of a sheet of fibers typically comprises: a) an endless belt equipped with drive means, b) means for spraying a dispersion of binder capable of creating a suspension of fine droplets of said dispersion in a given volume above the endless strip, c) means for the projection of particles, towards the aforementioned volume and d) a treatment enclosure arranged on the path of the endless strip, downstream of the spraying and projection means.

Preferably the spraying means consist of two guns arranged on either side of the endless band and directed obliquely towards it so as to form a mist in the determined volume.

Preferably, the particle projection means consist of an Airless spray gun (without air) placed on one side of the endless band and directed obliquely towards the determined volume.

It is another object of the invention to provide a sheet of fibers obtained by the process of the invention which comprises, in known manner, particles fixed at least to the surface fibers of said sheet by means of a binder ; typically said particles are completely coated with said binder.

According to a preferred embodiment, the particles are in a super absorbent material and the sheet of fibers is of the order of 45 to 1 1 Og / m ² at a rate of 20 to 6Og / m ² of fibers, from 10 to 2Og / m ² of binder and 15 to 3Og / m ² of particles. It is another object of the invention to provide a hygiene article which comprises an absorbent mattress, an impermeable outer film placed under the absorbent mattress, a sheet of fibers according to the invention which is arranged on the absorbent mattress as well as an interior permeable veil covering said sheet of fibers; in this article the surface fibers on which the particles of a super absorbent material are fixed are in contact with the permeable veil interior.

Of course, the present invention is not limited to the sole application of a sheet of fibers to which particles of a super absorbent material are attached intended to form the absorbent mattress of a hygienic article of the diaper type. . In particular the present invention can be applicable in the field of clothing, the particles then being in a heat-bonding material.

The present invention will be better understood on reading the description which will be given of a preferred embodiment of a sheet of fibers intended to constitute the absorbent mattress of a diaper, on which sheet are fixed particles of '' a super absorbent material, illustrated by the appended drawing in which:

FIG. 1 is a schematic perspective representation of an installation for fixing superabsorbent particles on the surface fibers of the sheet and,

- Figure 2 is a schematic sectional representation of the sheet.

The object of the present invention is to fix particles 1 on a sheet 2 and more particularly on the surface fibers 3 of said sheet 2. The installation 4 which is illustrated comprises an endless band 5 which is stretched between cylinders 6 whose at least one is driven by a drive motor, not shown. The upper strand 5a of the endless belt 5, in the horizontal state, passes through an enclosure 7 inside which heating means are provided. Upstream of the enclosure 7 are arranged two pistols 8, on either side of the endless strip 5 directed obliquely towards the upper strand 5a. These spray guns 8 are supplied with an aqueous dispersion of a binder. The operating conditions of the guns and their relative arrangement with respect to each other and with respect to the central strip 5 are determined so that the fine droplets projected by the two guns 8 create a suspension, fog type, in a determined volume 9, above the upper strand 5a of the endless belt 5. In the example illustrated in FIG. 1, this volume 9 covers the entire width of the ply 2 during its movement over the upper strand 5a of the endless belt 5. In addition, the installation 4 comprises a gun 10 for projecting the particles 1. It may in particular be an Airless type gun (without air). This gun 10 is directed towards the volume 9 in which the suspension of the fine droplets of the binder dispersion is located. When they enter the volume 9, the particles 1 come into contact with the fine droplets of the binder dispersion, they take charge of this dispersion until they are at least partially coated. Being thus charged, the particles become heavier and fall naturally towards the upper strand 5a on which is the layer of fibers 2. The particles 1 coated with the dispersion of binder 1 1, during their fall, are stopped by the surface fibers 3 of the sheet 2. The assembly constituted by the sheet 2 and the particles 1 coated with the dispersion of binder 1 1 penetrate, during the movement of the strip 5, into the enclosure 7, the function of which is to evaporate the solvent and optionally polymerize the binder. Thus, after this treatment, the particles 1 are bonded to the surface fibers 3 with which they were in contact thanks to the binder. The sheet 2 'thus formed is then wound at the outlet of the endless belt 5.

In the case of a sheet 2 intended to enter into the composition, at least partially of an absorbent mattress for diaper, the particles 1 are made of a super absorbent material, of the hydro-expandable polymer type, for example particles of carboxy methyl cellulose, polyacrylamide, grafted starch, modified acrylic polymer. These hydro-expandable polymers are capable of absorbing at least fifteen times their own weight of water or aqueous dispersion. By way of non-exhaustive example, the applicant has used particles of the super absorbent product called ATOCHEM HP2OO. In this same application, it is essential that the binder is water-soluble, so that after drying or polymerization, it does not create a barrier on the surface of each particle that the liquid could not penetrate. This water-soluble binder can in particular be an acrylic resin, in aqueous dispersion; for example it is a resin sold by the company HOECHST under the name ARKOFIL AVR

To obtain a suspension of fine droplets, behaving like a mist, it is preferable that the aqueous dispersion of the binder has a concentration which is between 5 and 20% by weight. The ARKOFIL A.V.R. is offered with a concentration of 25%; it has therefore been diluted in water until the concentration reaches, for example, 5%.

In a specific embodiment, the sheet 2 is a nonwoven obtained from a polyester fiber, produced by carding, spreading and stretching until a sheet of 5Og / m ^{2 is} obtained. The speed of movement of the endless belt 5, the operating conditions of the guns 8, the conditions of projection of the particles 1 by the gun 10 have been adjusted so that the respective amounts of particles and of the dispersion of binder have been 23g of particles / m ² and 15g of binder / m ² , which corresponds for a concentration of 5% to 3OOg / m ² of binder dispersion before drying.

It can be seen that on the sheet 2 ′ obtained, the particles 1 are included and fixed firmly in a surface layer 2 ′ a of the sheet 2. It is moreover possible manually to disintegrate this surface layer 2 ′ relative to the rest of tablecloth 2 '. This fixation is sufficiently solid for there to be no loss of particles 1 during subsequent manipulations of the sheet 2 ′.

The purpose of the heat treatment which is carried out in enclosure 7 is to remove the solvent contained in the binder dispersion and optionally to polymerize said binder, so that at the outlet of enclosure 7 the binder effectively ensures the connection between the surface fibers 3 and the particles 1. When the particles 1 are in a super absorbent material, it is important that contact with the aqueous dispersion of binder cannot achieve the expansion of the particles. For this it is necessary that the heat treatment is sufficiently effective and rapid for the elimination of the solvent to be obtained, at least in large part, within the time which is normally necessary for the particle of super absorbent to react upon contact with a medium. liquid. For super absorbent materials usually used in diapers, this reaction time is of the order of ten to several tens of seconds. On the other hand there are super absorbent materials, of fine particle size, which react in much shorter times which can be less than one second. In the latter case, it is almost impossible with conventional heating means to obtain the elimination of the solvent contained in the dispersion of binder in this short time. One solution to this problem may consist in modifying the pH of the dispersion of binder, a modification which aims to make this dispersion acidic, which has the effect of delaying the reaction of the superabsorbent material brought into contact with a liquid. This change in pH must however be controlled, otherwise the super absorbent material would lose its effectiveness. The applicant has determined a pH range between 6.8 and 4 as being acceptable.

In its application to diapers, the sheet 2 ', on the surface fibers 3 of which are fixed particles 1 of a super absorbent material according to the invention made of the order of 45 to 1 1 Og / m ² with a distribution of 20 to 6Og / m ² of fibers, 15 to 3Og / m ² of super absorbent particles and 10 to 2Og / m ² of binder. This sheet 2 ′ is arranged above the absorbent mattress of the diaper and below the interior permeable veil, with the surface fibers 3 on which the particles 1 are fixed which are contact with said interior permeable web. This arrangement makes it possible to obtain an extremely rapid diffusion of the liquid coming onto the internal permeable veil, during successive urinations, this diffusion being for three successive urinations less than 1 second, compared with diffusion times which can go up to 12 seconds. on the third urination with a diaper having a conventional absorbent mattress. In addition, in this same comparison, a much less humidification, up to ten times less, of the inner permeable veil is observed. The present invention is not limited to the embodiment which has just been described. A sheet of fibers with superabsorbent particles attached to these surface fibers can find application in other areas such as drainage, oil absorption, liquid absorption for horticulture or agriculture, without this list is exhaustive.

Furthermore, the invention is not limited to the use of super absorbent particles. For example, in the case of particles of a fusible material, such a sheet could be used in the field of clothing. In another variant of application to diapers, the drainage support is produced, commonly called the loft, to be placed on the absorbent mattress with a diaper from a sheet according to the invention. More precisely, a first card equipped with a spreader is supplied with first fibers of a given titration, for example polyester fibers 6,6 dtex, so as to form a crossed ply; a second card, without spreader, is supplied with second fibers with a lower titration than that of the first fibers, for example 1, 7 dtex, so as to form a parallel sheet; the parallel ply is juxtaposed with the crossed ply, the lower face of the crossed ply being in contact with the parallel ply, and particles of a super-absorbent material are fixed on the upper face of the crossed ply, according to the method of the invention. In the diaper, the parallel sheet, of finer fibers, corresponds to the permeable veil which is intended to come into contact with the skin, while particles of super-absorbent come into contact with the absorbent mat. In this application, the quantity of superabsorbent particles can be of the order of 200 g / m ² .

Claims

1. Method for fixing particles to the surface fibers of a sheet of fibers, using a binder in the form of a dispersion, characterized in that it consists of: a) creating a suspension of fine droplets of the dispersion of binder in a given volume (9) above the sheet (2) of fibers, b) spraying the particles (1) into said volume (9), whereby said particles (1) are coated with the dispersion (1 1) of binder and fall onto the web (2) of fibers, c) and subject the web of fibers / particles coated with the dispersion to a treatment capable of fixing the binder on the fibers (3 ) of the tablecloth (2).

2. Method according to claim 1, characterized in that the suspension of fine droplets of the binder dispersion is obtained by spraying an aqueous dispersion containing on the order of 5 to 20% of binder.

3. Method according to one of claims 1 or 2, characterized in that, being particles of a super absorbent material, the dispersion is an aqueous dispersion of a water-soluble binder, for example of carboxy methyl cellulose (CMC) .

4. Method according to one of claims 1 to 3, characterized in that the fixing treatment is a heat treatment, allowing the solvent to evaporate from the dispersion.

5. Method according to claims 3 and 4, characterized in that the conditions of the heat treatment are determined so that the evaporation of water from the dispersion occurs within a time which is less than the time of expansion of the super absorbent material under the action of water.

6. Method according to claim 5, characterized in that being an aqueous dispersion of a carboxy methyl cellulose, this dispersion has a slightly acidic pH, for example between 4 and 6, 8.

7. Installation for the continuous fixing of particles on the at least superficial fibers of a sheet of fibers, characterized in that it comprises: a) an endless belt (5) equipped with drive means, b) means for spraying (8) a dispersion of binder (1 1) capable of creating a suspension of fine droplets of said dispersion in a given volume (9) above the endless belt (1 5), c) of the means (10) for the projection of particles (1), towards the aforementioned volume (9) and d) a treatment enclosure (7) disposed on the path of the endless belt (5), downstream of the spraying means ( 8) and projection (10).

8. Installation according to claim 7, characterized in that the spraying means consist of two guns (8) arranged on either side of the endless belt (5) and directed obliquely towards the latter so as to form a fog in the determined volume (9).

9. Installation according to one of claims 7 or 8, characterized in that the means (10) of particle projection consist of an Airless gun (without air) directed obliquely towards the determined volume.

10. fiber mat (2 ') obtained by the method of claim 1 which comprises particles (1) fixed at least on the surface fibers (3) of said sheet (2) by means of a binder (1 1) , characterized in that said particles (1) are completely coated with said binder (1 1).

1 1. Tablecloth according to claim 10, characterized in that the particles are in a super absorbent material, the sheet of fibers made of the order of 45 to 1 10g / m ² at the rate of 20 to 6Og / m ² of fibers, of 10 2Og / m ² of binder and 1 5 to 3Og / m ² of particles.

1 2. tablecloth according to claim 10, intended to constitute the drainage support or loft of a hygiene article, characterized in that it is formed by the superposition of a first crossed ply obtained from first titration fibers given on a card equipped with a spreader and a second parallel ply obtained from second titration fibers lower than the first fibers on a card without spreader and in that the particles of a super material absorbent are fixed on at least the surface fibers of the face of the first crossed ply which is not in contact with the second parallel ply.

13. The tablecloth according to claim 10 for an article of clothing in which the particles are made of a fusible material.

14. Hygiene article which comprises an absorbent mattress, an impermeable outer film placed under the absorbent mattress, a sheet of fibers according to one of claims 10 or 1 1 which is arranged on the absorbent mattress and an inner permeable veil covering said sheet of fibers, characterized in that the surface fibers (3) on which the particles (1) of a super absorbent material are fixed are in contact with the interior permeable web.