NO151308B - PROCEDURE FOR FIXING A SUPER-ABSORBING POWDER BETWEEN TWO Lanes - Google Patents

Abstract

Insertion process of pulverulent products (3) so called "super absorbing" in a fiber structure. The powder of the super absorbing product (3) is deposited on a fiber layer (1), a fiber mat (2) comes on top for covering and the fiber mat is bound to said fiber layer, according to cohesion lines and/or points (4), so as to define between said layer and said mat spaces in which a certain amount of powder of super absorbing product (3) is trapped. Application to absorbing fiber structures, particularly sanitary towels.

Description

The present invention relates to a method for fixing a superabsorbent powder (13) between a first web (11) of any hydrophobic, liquid-permeable web material and a second web material (12) by applying the superabsorbent powder (13) to the first web (11) in the desired width and thickness, after which the deposited powder (13) is covered by the second web material (12), by anchoring the first web (11) and the second web (12) to each other, along cohesion lines and/or points.

The products called "super absorbents" are mixtures which swell in the presence of the liquid to be absorbed, but which do not dissolve in it, the liquid is thus absorbed in a quasi-irreversible manner. They are mainly cellulose ethers, alignates or modified polyacrylates.

Their production has been the object of many attempts, and

many methods are known for introducing them into a carrier.

According to most of the prior art, super-absorbent products are attached to the surface of the carrier or mixed into the carrier mass, the terms "attached" or "mixed in" signifying that there is a solid connection.

see between the essentially powdery product and the carrier. This solid connection is achieved by the presence of an addition product responsible for the adhesion.

This additive, according to a first series of known methods,

can be water, one then speaks of fission of the super-absorbent by wetting. According to the method described in French patent no. 2,319,434, the support is thus moistened, after which particles of a modified cellulose ether are applied

res on the carrier. The particles swell and adhere to the carrier, after which the liquid is removed by drying. A variant is described in a similar method in US Patent No. 3,919,042, which consists in pulverizing starch particles with electrostatic agents on a cellulosic fiber sheet containing at least 25% water.

According to other methods, in contrast to the ones mentioned above, are

it' the "super-absorbent" product that is moistened. The method described in French patent no. 2,122,432 consists, for example, in applying a gel which is swollen with water (cross-linked polyacrylamide) on a cellulose carrier, after which the resulting laminate is dried. And further the method described in BRD patent no. 489,308, according to which a layer of powdered starch is moistened (or dextrin or gelatin) to fix it.

Other methods make use of the addition of water as a fixing agent for the super absorbent, both to the carrier and to the absorbent product. Thus, according to the technique described in GB Patent No. 1,354,406, sheets of cellulose wadding impregnated or not impregnated with a cationic compound are coated with a powder of a water-absorbing polymer, stacked and subjected to a treatment with water vapor.

The combination consisting of the fibrous support and the absorbent powder is likewise moistened by treatment with water vapor according to the method in French patent no. 2,066,234.

Fixation techniques involving wetting generally have the advantage of being cheap and simple, except for certain methods described above which involve drying. But they have the disadvantage that they cause the absorbent particles to swell before drying. This leads to a loss of efficiency with the absorbent particles, as their surface condition changes.

Among other things, several particles can stick to each other, which in this case leads to the formation of a film, and most likely to the deposition of a mono-layer. In order to avoid "partial gelation" which is unavoidable in methods involving fixation by wetting, other fixation techniques make use of the use of a solvent other than water.

According to US patent 3,903,389, the surface of the fiber structure is thus coated with a layer of adhesive material, after which said adhesive layer is "sprinkled" with particles of liquid-absorbing material.

According to another example in the present applicant's French application No. 77.27569, the order of addition is reversed. The solvent, which is preferably an aqueous solution of polyvinyl alcohol, is placed on the surface of the product obtained after pulverizing or transferring the superabsorbent onto the carrier.

All methods for fixing liquid absorbent products using an adhesive other than water also have the advantage of being simple and inexpensive and the disadvantage that they weaken the absorption capacity of the absorbent product due to the presence of adhesive on part of the grain's surface.

For this reason, attempts have been made to hold the powder firmly in a fiber structure without using any solvent.

US Patent No. 4,055,180 discloses a layered fiber structure particularly intended for sanitary napkins and baby diapers, consisting of a fiber mat surrounded by a sheet of fabric wadding on which is placed a hydrocolloidal compound in the form of an unfixed powder. The obtained product is covered with a polyethylene sheet in which many cavities or pockets of hemispherical shape are formed, which form many closed spaces for expansion of the gel. In this embodiment, the powder is not "fixed", i.e. it is not glued to the carrier. In each formed cavity, however, a limited amount of powder is simply enclosed. In order for the liquid to be absorbed to reach the absorbent powder, the polyethylene sheet is perforated with many small holes.

Such a structure only compensates for part of the aforementioned disadvantages of gluing using a solvent or wetting the powder and/or the carrier. The super-absorbent product is known to retain fluids as its volume increases significantly. Considering that the volume of the pre-formed pockets is necessarily limited, the amount of absorbent product that can be introduced into each of them is also limited. If this quantity is too large, the walls of the pockets formed in the polyethylene sheet constitute an obstacle to the expansion of the gel and, as a result, the absorption capacity of the structure is reduced.

Secondly, the polyethylene sheet is pre-manufactured, which makes it much more difficult to carry out the method for obtaining a multi-layer product. Finally, the outflow of liquid from the many small holes in the polyethylene sheet, which can be easily blocked, is very precarious.

There is likewise known a method belonging to the National Starch Company, according to which a thermoplastic grid is placed between two sheets of fabric wadding, the powder of super-absorbent being simply placed in the meshes of the grid,• and the two folds of the wadding held in the intervening grid by heat binding. According to this method, the pre-formation of a number of pockets is avoided.

However, as in the already cited US Patent No. 4,055,180, the amount of powder of the "super absorbent" that can be placed between the cotton pads is limited. In this embodiment, it is limited due to the relative inextensibility of the fabric wadding folds.

Although the powder is thus no longer fixed, the main obstacle to expansion of the gel is to be found in the inelastic walls of the pockets containing the powder.

The purpose of the present invention is to remedy the aforementioned disadvantages by providing a new method for fixing a powdery, super-absorbent product in a fiber mat, which enables the introduction of significant doses of said product which fully fulfills its task as an absorbent and this in a simple and continuous way.

To achieve this, proceed as follows:

The powder of the super-absorbent product is placed

on a fiber mat in the form of ribbons whose length depends on the product to be manufactured,

the complex obtained is covered with a fiber cloth,

said fiber cloth is connected to said fiber mat along lines and/or points in such a way that they limit cavities between said mat and cloth and where a certain amount of super absorbent is enclosed.

The method is thus characterized by the fact that the elastic webs (11, 12) are anchored by cold embossing or by heat calendering, so that a cavity is defined between the first web (11) and the second web (12) in which a certain amount of the absorbent powder (13).

According to a first embodiment of the invention, the powder is placed on a mat of super-curled, hydrophobic or hydrophilic fibers, depending on the desired results, after which the whole is covered with a second mat of synthetic polyester or polypropylene fibers.

The obtained complex is then hot calendered. In this case, the fixing of the fibers to each other is carried out by thermo-melting to enclose the powder. ^

The second mat is preferably made up of a carded veil.

According to a variant of the preferred method, powders are applied in several ribbons, after which at least these powder ribbons are covered with a second fiber mat or cloth and finally, after heat calendering, the obtained complex is cut into ribbons according to cutting lines that divide the zones that are not covered

in

with powder, lengthwise.

Said tape is then wound on spools which form a very advantageous form of product containing the powder.

It is possible to use such a fibrous structure containing a super absorbent in powder form in a wide range of absorbent articles, such as e.g. diapers, sanitary napkins, "alezes", etc.

The description is made complete by means of the following drawings. Figure 1 illustrates the structure of the product obtained by means of the first embodiment of the invention. Figure 2 illustrates the engraving design on the calendering cylinders. Figure 3 illustrates a variant of the second embodiment.

According to a variant of the embodiment of the method

as shown in Figures 1, 2 and 3, the super-absorbent powder 13 is deposited in the form of a band on a cloth 11, preferably with a basis weight of approx. 40 g/m 2 of said super-crimped fibres, then the whole is covered with a second fiber mat 12 of synthetic polypropylene or polyester fibers which are likewise super-crimped.

The former super-curled fiber mat can consist of hydrophobic or hydrophilic fibers depending on the desired result.

The second mat, with a weight of 30 g/m, consists of fibers with a length of close to 60 mm. The obtained product is hot calendered. The connection between the fibers is achieved by hot melting in order to enclose the powder 13 which is deposited as bands on the fiber mass by means of cavities formed by the engraving in the used cylinder (these cavities can, for example, have the same shape as those described above in the description of the first embodiment of the invention, see fig. 2). In relation to the first embodiment, this variant has the advantage that it provides a fiber structure which proves to be very favorable. Referring to the drawing in figure 3, where the deposition of powder is seen in three bands 13a, 13b and 13c, it is actually easy to cut along the cutting lines 14.1 and 14.2, which are in zones without powder, to obtain bands of super-absorbent product based on the structure 10

which is formed according to the above-mentioned method.

The tapes are then rolled up to be able to offer the product in a very practical form. The fiber structure obtained in this way is very easy to use because it is available on coils whose width can be varied depending on the final product to be produced.

As for the fixation of the super-absorbent itself, the method offers many advantages, the super-absorbent can perform its task completely, the grains are free in an expandable cavity (super-curled fibers). The liquid to be absorbed is moved and held in the super-absorbent tape due to the complex structure (hydrophilic or hydrophobic, textured fibers).

The product obtained by means of the second embodiment of the invention is very pleasant to the touch, it remains soft, flexible and resistant.

As a variant, a similar product can be obtained without hot calendering, but by feeding the fiber structure after application of the second mat into an oven with hot air passage. The connection between the fibers is carried out by hot melting without calendering. In this case, the product exhibits a somewhat better volume.

The fibrous structures which contain the super absorbent and which are produced according to one of the methods described above, are preferably used in the production of sanitary napkins.

Claims (7)

1. Method for fixing a superabsorbent powder (13) between a first web (11) of any hydrophobic, liquid-permeable web material and a second web material (12) by applying the superabsorbent powder (13) to the first web (11) in the desired width and thickness, after which the deposited powder (13) is covered by the second web material (12), in that the first web (11) and the second web (12) are anchored to each other, along cohesion lines and/or points, characterized in that they elastic webs (11,12) are anchored by cold embossing or by heat calendering, so that between the first web (11) and the second web (12) a cavity is defined in which a certain amount of the absorbent powder (13) is enclosed. 2. Method according to claim 1, characterized in that the paths (11,12). connected with a lattice-like pattern, so that each mask will contain a certain amount of super absorbent powder. 3. Method according to claim 1, characterized in that a single or multi-layer carded veil is used as the second web (12) which at least partially consists of super-crimped synthetic fibers and that a corresponding material is used as the first web (11). 4. Method according to claim 1, characterized in that the heat calendering is carried out using a patterned gravure roller. 5. Method according to claims 1-4, characterized in that a fiber mat of hydrophilic fibers is used as the first web (11). 6. Process according to claims 1-5, characterized in that the first web (11) is used with a basis weight of approx. 40 g/m2. 7. Method according to claim 3, characterized in that a fiber veil consisting of polyester and polypropylene fibers with an average length of 60 mm is used as the second web (12).