ITMI20110209A1 - NON-FABRIC DUCT WITH REDUCED SURFACE EXPANSION OF LIQUID FOR THE PRODUCTION OF HYGIENIC ABSORBENTS AND ITS PROCESS OF OBTAINING - Google Patents

Description

â € œNON-WOVEN DUCTED WITH REDUCED SURFACE EXPANSION OF LIQUID FOR THE PRODUCTION OF HYGIENIC ABSORBENTS AND RELATED PROCESS OF OBTAINMENTâ €

DESCRIPTION

The present invention relates to hygienic absorbents for physiological liquids, with high absorbency, having a reduced surface expansion of the liquid absorbed by capillarity thanks to the particular processing of the surface layer (topsheet) in cotton or similar absorbent materials in natural fibers.

Cotton pads are more breathable than conventional pads made of synthetic materials, and therefore generally more comfortable. Furthermore, these cotton absorbents are suitable for all those who experience dermatological problems in contact with synthetic materials.

The cotton absorbents currently on the market are formed by a thin porous surface layer, in perforated or non-perforated non-woven cotton, also called top-sheet, which has a coating function with the sole purpose of forming a hypoallergenic contact layer. Below this top-sheet there is an intermediate absorbent / filtering layer in cotton or in airlaid of cellulosic fibers, with greater thickness, which forms the core, and a basic polymeric film as a support also having the function of providing a surface on which to apply the adhesive strips for fixing said absorbent to the slip.

These pads can also be equipped with the so-called â € œwingsâ €, which are also adhesive, which guarantee an even better fixing of the pad to the slip. These wings are formed by the top-sheet supported by the aforementioned polymeric film without any intermediate absorbent layer.

To date, this top-sheet is obtained from cotton fibers, in the form of a mat, which is subsequently subjected to hydrointerlacing or water needling (spunlace) thus forming a layer of cotton where the fibers are bound together.

The â € œSpunlaceâ € technology binds the fibers using jets of water coming out of a high pressure nozzle chain, generally 60-80 bar, suitably spaced, for example by 0.8 mm, with a diameter of about 0.08 mm. Said jets of water cross the fibrous mat, binding together the underlying fibers to the high pressure jets and the non-woven thus obtained is resistant and at the same time soft, with a weight that generally varies from 20 to 60 g / m < 2>.

Since cotton is notoriously an absorbent material with high capillarity, this type of absorbent suffers from the drawback of showing a high expansion of the liquid that passes through it with the consequent disadvantage of having an enlargement of the liquid stain up to the wings, making them dirty.

The object of the present invention is to provide an absorbent capable of overcoming, at least in part, the drawbacks that the known art complains of, in particular a cotton absorbent having a reduced surface expansion of the absorbed liquid, in particular on the wings, while ensuring a high absorbency of liquid.

A further object is to provide such an absorbent which can be made with a simple, economical and easy to implement process.

These purposes are achieved by the absorbent with wings in absorbent material of natural fibers such as cotton or viscose, microperforated or smooth, which has the characteristics of the attached independent claim 1.

Advantageous embodiments of the invention appear from the dependent claims.

An object of the present invention is an absorbent with wings comprising as a surface layer or â € œtop-sheetâ € a layer of absorbent material made of natural fibers such as cotton and / or any other natural fiber and their mixtures with viscose or polylactic acid or other suitable fiber. for this purpose, in the form of non-woven fabric, said top sheet having a transversely variable density and equipped with a first plurality of longitudinal lines (grooves) along which said fabric has a density of fibers greater than the rest of the fabric, each of said lines of said first plurality of lines being alternated with a respective longitudinal line of a second plurality of lines along which said fabric has a lower density of fibers.

The greater density of fibers along the first plurality of lines is due to the fact that the fibers are more flattened there and the fabric has a smaller thickness: this means that the capillarity due to the greater proximity between fiber and fiber tends to increase in the sense longitudinal creating lines or bands of canalization for the liquid.

The lower density of fibers that occurs along each line of said second plurality of lines is due to the fact that the fibers therein are less crushed and more spaced from each other: this means that the transfer of liquid from one side ¬brella (fiber) to the other is more difficult, slowing down the flow of capillarity in the transverse direction.

In practice, the longitudinal lines with lower density represent barrier lines to the flow of the liquid in a transverse direction (perpendicular to these lines) coming from the adjacent lines with higher density, thus facilitating the channeling of the liquid along the lines with higher density (and high absorbency) .

The specific alternation of lines with different density of fibers is obtained by means of a specific process of preparation of the non-woven fabric that forms the top sheet that will now be described.

This process includes

- a first step (a) of water hydrointerlacing of a layer of fibers with jets of water adjacent to each other designed to apply pressures lower than or equal to 60 bar to said layer, to obtain a slight cohesion between the fibers, and

- a second phase (b) of water-based hydrointerlacing of the hydrointerlaced mat obtained from the first phase (a), using jets of water at pressures greater than or equal to 100 bar or with a higher flow rate than phase (a), suitably spaced between them, with a pitch (along the transverse line L of the top sheet of fig. la) of at least 0.5 mm from each other, preferably of at least 1 mm, more preferably of at least 2 mm.

The jets of water at high pressure or with a greater flow rate of phase (b) ensure that the fibers more internal to the top-sheet layer are also cohesive, which does not happen in the first phase where the pressures are low and the binding is superficial.

The high pressure or higher flow rate water jets of phase (b) are generally more spaced apart and with a larger nozzle diameter than the low pressure or lower flow rate water jets of phase (a): in this way the jets high pressure water hits again only a part of the areas previously affected by the lower pressure jets, thus creating a fabric with more flattened areas (of high density) alternating with less flattened areas (of lesser density).

Steps (a) and (b) are applied from the same side 30 of the top sheet (Fig. 1b). These phases can be carried out in a single phase using both high and low pressure water jets at the same time through the simultaneous use of different nozzles, with different diameters, as will be described in detail below.

The layer of fibers to be subjected to step (a) can be pre-needled, needled in the form of a mat or even only consist of a plurality of folded or carded plies.

The treatment with water jets used in phases (a) and (b) of this process is a technology known in the art also called water binding (also called spunlacing, hydroentangling, etc.). See for example US 3,485,706 or what described in patent application EP 1359241 incorporated herein by reference.

In the art, interlacing is generally carried out at pressures generally around 60-80 bar, using small diameter nozzles, for example 0.08 mm, placed almost in contact with each other, therefore with a different arrangement than in phase b ).

Reference will now be made to the attached figures which are purely exemplary, and therefore not limitative, of embodiments of the present invention, in which:

fig. la is an enlarged top view, partially interrupted transversely, of a top sheet according to the present invention;

fìg. lb is an enlarged sectional view of the top sheet of fig. the socket along the I-I line;

figs. 2a-2b are schematic perspective views of the hydrointerlacing unit in two different stages of preparation of the top-sheet of the present invention;

figs. 3a-3b are views from the top of the top-sheet of the invention respectively at the moment of formation of the liquid stain and at a subsequent moment of expansion of said stain;

figs. 4 a) -e) are seen from the top of a conventional top sheet a), in microperforated cotton of 35 gr / m <2>, and of some top-sheets b) -e) of the invention, in cotton 35 gr / m <2> microperforated, after a predetermined time from the addition of test liquid;

fig. 5 is an enlarged and partially interrupted top view of an arrangement of low pressure nozzles in the respective nozzle holder chain;

fig. 6 is an enlarged and partially interrupted top view of an arrangement of high pressure nozzles in the respective nozzle holder chain;

figs. 7 a) -b) are seen from above, enlarged and partially interrupted, of two different arrangements of high pressure nozzles in the respective nozzle-holder chain;

fig. 8 is an enlarged and partially interrupted top view of a single arrangement of high and low pressure nozzles in a single nozzle chain.

As illustrated in figs. la and lb, the top sheet layer 10 according to the present invention is a layer provided with a first plurality of longitudinal lines 1, along which the fibers are more flattened (higher density of fibers and lower thickness), and of a second plurality of longitudinal lines 2, alternating with the longitudinal lines 1, along which the fibers are less flattened (lower density of fibers and greater thickness).

With reference to figs. 2a- 2b, the top sheet 10 in non-woven cotton is prepared according to the following procedure: the starting layer that will form the top sheet is a layer of fibers generally coming from a carding plant, also called â € 'veil', which is placed on a conveyor belt 3 which feeds the hydrointerlating section 100.

In said section 100 the fibers of said layer (web) are subjected to a first phase of water interlacing by means of pressure jets which allow the fibers to cohere with each other: this is necessary as in the web coming from the carding the fibers are only joined by mutual adhesion but they break and separate if subjected to traction.

With reference to figs. 2b) and 5, in this first hydrointerlacing phase a plurality of nozzles 4 with a diameter (Φ) of about 0.08 mm and a distance between nozzle and nozzle (pitch, p) are used (along the transverse line L in fig . 5) equal to about 0.8 mm. These nozzles 4 are holes made on a steel plate 5 which acts as a die, and can be arranged on a single row (fig. 5) or on several rows, for example two (fig. 2a) suitably spaced apart.

Other examples of diameter (Φ) of nozzle 4 are 0.06 mm and 0.10 mm,

In one embodiment, said rectangular die 5 generally has a width of 20-25 mm, a thickness of about 0.5 mm and a length of about 2.5 m, and is perforated according to design with holes of different pitch and diameter depending on the type of binding you want to make and the average weight you want for the top sheet 10.

The above dimensions of the spinneret 5 are not binding for the purposes of the present invention and can also vary from a few centimeters up to even 3/6 meters depending on the size of the type of machine on which it will be mounted.

Said die 5 (jet strip) is mounted on a nozzle holder injector 6 which acts as a distributor of the water flow, which is placed, in a fixed position, above the conveyor belt 3 which advances the material in the direction of the arrow indicated in fig. 2a. Said distributor 6 feeds with water the plate 5 on which the holes of the nozzles 4 have been made.

In this first phase a) low pressure water is used, generally between 30 and 40 bar, up to about 60 bar.

The interlaced fiber layer obtained in said first phase (a) is then passed to an area where it can discharge part of the absorbed water, and subsequently sent back to the interlacing unit where the first die 5 has been replaced with a second spinneret 7 (figs. 2b, 6, 7a), 7b)) suitable for supporting nozzles 8 with a larger diameter than the previous nozzles 4 and spaced apart with a greater pitch (P) (along the transverse line L in fig, 6 ).

By way of example, the high pressure nozzles 8 can have a diameter (Φ) of 0.8 mm or 0.12 mm, 0.14 mm, 016 mm, and can be spaced with a pitch (P) that varies from 1 mm up to 5 mm, preferably 2-3 mm. Said nozzles 8 can also be arranged in several horizontal rows.

Figures 6, 7a), 7b) illustrate different arrangements of high pressure nozzles 8 in as many nozzle holder dies 7.

In fig. 6 shows a first embodiment of the spinneret 7 containing nozzles 8 with a diameter of 0.12 mm, which are arranged at a distance P of 2 or 3 mm from each other. The nozzles 8 are also arranged on two horizontal rows (along the line L), which have a distance (d), one from the other, of approximately 1 mm.

In fig. 7a shows a second embodiment of the die 7 containing nozzles 8 with a diameter of 0.12 mm, arranged in two rows which have a distance (d), one from the other, of about 1 mm,

A second nozzle 8 is placed next to each nozzle 8 of each row, at a distance (f) for example of about 0.8 mm. In this way, groups of nozzles 8 are formed along line L, each formed by four nozzles 8 practically adjacent to each other. Each grouping is distant from the other by a pitch (P) which can be equal to 2, 3, 5 mm.

In fig. 7b shows a third embodiment of the spinneret 7 containing nozzles 8 with a diameter of 0.12 mm, arranged in two rows which have a distance (d), one from the other, of about 1 mm.

Next to each nozzle 8 of each row there are two other nozzles 8, at a distance (f) for example of about 0.8 mm. In this way groupings of nozzles 8 are formed, each formed by six nozzles 8. Each grouping is one step away from the other (P), along line L, which can be equal to 2, 3, 5 mm.

In the embodiments of figs. 6, 7 a), 7b) the distance f between the high pressure nozzles 8, placed side by side, can also be equal to 0.6 mm instead of 0.8 mm.

The above dimensions of the spinneret 7 are not binding for the purposes of the present invention and can also vary from a few centimeters up to even 3/6 meters depending on the size of the type of machine on which it will be mounted.

Both dies 5 and 7 are placed transversely to the movement of the conveyor belt 3, as indicated in figs. 2a and 2b with the arrow, so that when the belt 3 moves, the jets of water coming out of the nozzles 4 and 8 hit the entire fiber mattress along the longitudinal lines. The dimensions of these dies 5 and 7 can be for example 2 m in length and 25 cm in width.

In practice, hydrointerlacing at higher pressures, generally greater than 100 bar, or at higher flow rates than the first interlacing (a), occurs only in some specific points or areas (longitudinal lines 1) of the top sheet thanks to the arrangement of the nozzles 8 in the spinneret 7: it is for this reason that the density in said longitudinal lines 1 is greater than in the areas (longitudinal lines 2) not affected by the high pressure jets.

Through the nozzle holder device 6 and the alternation of nozzles 4 and 8 operating at different pressures, a mat of fibers of different pressures are applied along the longitudinal lines of the nozzles: these lines represent bonding lines (or lines) along which the superficial fibers bind more or less with the underlying fibers depending on the pressure used. Subsequently, the top-sheet obtained from said second phase (b) is air dried and wound on a reel.

As mentioned above, it is also possible that said phases (a) and (b) can be carried out at the same time in a single phase using jets of water that hit the mattress with different water flows and therefore with different hydraulic powers, by means of a single die 7 where both types of nozzles 4 and 8 are arranged, as illustrated in fig, 8.

In fact, considering a die 7 of the type of fig. 8 with holes of different diameters, for example 0.08 mm 0.12 mm, at the same pressure there will be greater hydraulic energy for holes with a larger diameter of about double the power, as the expression of the power on the hole diameter is squared. For example, with 1000 holes with a diameter of 0.08 mm at a pressure of 100 bar there is a flow rate of 361 It / h, the same 1000 holes with a diameter of 0.12 mm at the same pressure of 100 bar will have a flow rate of 811 l / h: a 125% increase in hydraulic energy.

In practice, using the same pressure but a single die with two different types of holes, it is possible to have the same effect obtained at the end of phase b).

In said embodiment referred to fig. 8, the low pressure nozzles 4 have a diameter (Φ) of about 0.08 mm and a distance between nozzle and nozzle (p) of about 0.8 mm and are placed only along a single row, while the nozzles 8 have a diameter of 0.12 mm, are arranged in two rows which have a distance (d), one from the other, of about 1 mm, each nozzle 8 being placed at a pitch P from each other, along line L, which can be equal to 2, 3, 5 mm.

In practice, using the same pressure but using 4 low pressure / flow nozzles and 8 high pressure / flow nozzles at the same time, we have

- Greater binding effect with the holes 8 having a larger diameter for greater hydraulic power of the water flow due to a greater passage: a greater and more extensive barrier effect with greater longitudinal capillarity due to the greater proximity of the large holes 8;

- Lower binding effect with the holes 4 having a smaller diameter, in the design with a diameter of 0.08: the holes 4 with a smaller diameter have a lower water flow rate and therefore a lower hydro-interlacing energy.

However, the spinneret embodiments 7 illustrated in fig. 7a and 7b where at each step P there is a grouping of 8 nozzles placed very close to each other.

In fact, using a die 7 where the largest holes 8 are arranged on several horizontal rows and form groups, and where each grouping is distant from the other by a pitch P, there will be a density of holes per cm greater than the configuration on a € ™ single row.

In this grouping configuration, the distance of the holes 8, inside the grouping, is an important process parameter: in fact, the holes 8 with a pitch of 0.8 mm will have a hole density of 12.5 holes per cm, while the holes 8 with 1.0 mm pitch will have a density of 10 holes per cm.

As illustrated in figs. 3a and 3b, while the lower density lines 2 represent longitudinal channels for the liquid along which it can expand, the higher density lines 1 constitute a barrier to the passage of the liquid in a transverse direction with respect to said longitudinal lines 2.

The Applicant has surprisingly found by means of tests that the transverse expansion of liquid is considerably reduced when a non-woven natural absorbent material such as cotton is subjected to the process of the present invention.

In fact, as reported in figures 4 a) -e), the transversal diffusion of the stain is greatly reduced by passing from a conventional top sheet (fig. 4a)) to top sheets made according to the invention (figs. 4 b) -e )).

Furthermore, the top sheets of figs. 4 b) -d) according to the invention show a diffusion of liquid substantially similar to each other: said top sheets have been obtained using the spinneret 7 of fig. 6 respectively with pitch P = 3 mm, P = 3 mm and P = 2 mm.

The top sheet of fig. 4e) according to the invention, which shows the lowest transverse diffusion of liquid was obtained using the spinneret 7 of fig. 7 with a pitch (P) equal to 5 mm.

Without wishing to be bound by any theory, it is presumable that the wider the areas with greater density and binding 1 (made with more nozzles 8 adjacent to each other) the greater the orientation of the capillarity in a longitudinal rather than transverse direction. This prevents the fluid from spreading by transversal capillarity to the sides of the top sheet, and therefore towards the wings of the absorbent, with considerable advantages.

This is illustrated schematically in figs. 4 a) -e) where the stains are reported on various top-sheet samples after a predetermined time after the addition of a suitable test liquid that simulates the behavior of blood: in figure 4a) the conventional cotton top sheet 35 gr / m microperforated, hydro-interlaced at a single pressure of 60-80 bar with nozzles of the same diameter, it has a much larger stain than some top-sheet b) -e) of the invention, in cotton 35 gr / m microperforated.

The cotton fibers used for the formation of the top-sheets can be of any micronage, for example from 2 to 5 (micronaire), or they can be a mixture of fibers with different micronage.

Similarly to the above, in the case of natural fibers other than cotton or in the case of blends of fibers of cotton, viscose, polylactic acid (PLA) or other similar fibers, the dimensions of the fibers used can be any.

With this process it is possible to obtain a top-sheet of conventional weight where the weight is constant over the entire surface, but the density and thickness are different depending on whether you are in a high density area along the longitudinal lines 1 or in a low density zone along the longitudinal lines 2.

In practice, these areas along the longitudinal lines 1 create a transverse barrier effect and diffuse the fluid in a longitudinal direction: the greater the density differential between lines 1 and lines 2, the greater the channeling of the flows in the longitudinal direction.

Therefore the greater or lesser difference in density (g / cm) between said first plurality of longitudinal lines 1 and said second plurality of lines 2 will be chosen on the basis of the final use of the top sheet.

Generally, in order to have a good channeling, the difference in density is at least 5%, preferably at least 10%, more preferably around 15-20%, even if these values are not binding for the purposes of the present invention.

Using the nozzles 8 described in fig. 7a with a P pitch of 3 mm for each group of nozzles, a sample of top sheet was obtained with a density differential equal to about 15% which showed a good longitudinal channeling of the flow.

In particular the density obtained on a 35 gr. of cotton using 4 nozzles as in fìg. 5 with pressure at 60 bar, and nozzles 8 as in fig. 7a with a pressure of 100 bar, a density of 0.095 gr / cm <3> was obtained in the high density areas (longitudinal lines 1) shown in figs. la, and a density of 0.082 gr / cm <3> in the low density areas (longitudinal lines 2) resulting in a density differential equal to approx. 16%.

In practice, the Applicant, by means of tests, has noticed that the transverse diffusion of the liquid seems to be further reduced when, in addition to a greater differentiation of density, there is also

- a greater possible width of the low density zones and the high density zones, and / or

- a greater number of high and low density areas in the transversal sense. In fact, the Applicant observed that

- the greater the difference in density between the high and low density areas, the greater the channeling of fluids in the longitudinal direction;

- the greater the width of the low and high density zones (lines), the greater the barrier effect obtained;

- the greater the number of low and high density zones (lines) per linear centimeter in the transversal direction, the greater the barrier effect.

Numerous modifications and variations of detail within the reach of a person skilled in the art can be made to the present embodiment of the invention, however falling within the scope of the invention expressed by the appended claims.

Claims (11)

CLAIMS 1. Absorbent for physiological liquids comprising as a top-sheet layer (10) a layer of absorbent material made of natural fibers, preferably cotton and / or any other natural fiber and their mixtures with viscose, polylactic acid (PLA) or other similar fibers, in form of non-woven, characterized in that said topsheet has a variable density in a transverse direction and is equipped with a first plurality of longitudinal lines (1) and a second plurality of longitudinal lines (2), the lines of said first plurality of longitudinal lines (1) being interspersed with the lines of said second plurality of longitudinal lines (2) and having a density of fibers greater than said lines (2). 2. Absorbent according to claim 1 wherein the difference in density (g / cm <3>) between said first plurality of longitudinal lines (1) and said second plurality of lines (2) is at least 5%, preferably at least 10%, more preferably around 15-20%. Absorbent according to claim 1 or 2, wherein the micronage of the cotton fibers of the absorbent material used for the formation of the top-sheet (10) is between 2 and 5, or it is a mixture of fibers with different micronage. 4. Absorbent according to any one of the preceding claims, characterized in that it has opposite wings in said transversal direction. 5. Top-sheet (10) for sanitary napkins of physiological liquids as defined in any one of the preceding claims 1-4. Process for preparing a natural fiber absorbent material top sheet (10) for an absorbent as defined in any one of claims 1-5 comprising (a) a first hydrointerlacing of a layer of fibers with pressures lower than or equal to 60 bar, preferably between 30 and 40 bar, with jets of water adjacent to each other, to obtain a slight cohesion between the fibers, (b) a second hydro-interlacing of the slightly indro-interlaced mat obtained from step (a), using pressures greater than or equal to 100 bar and / or with higher flow-rate water jets, said jets being spaced apart with a pitch of at least 0.5 mm, preferably at least 1 min, 7. Process according to claim 6 in which the layer of fibers to be used in step (a) is pre-needled, needled in the form of a mat or constituted by a plurality of folded or carded plies. 8. Process according to claim 6 or 7 in which the layer of fibers to be used in step (a) is fed onto a conveyor belt (3) coming from a carding plant. 9. Process according to any one of the preceding claims 6-8 in which the nozzles (4) for the water jets used in step (a) have a diameter (Φ) of about 0.08 mm, are mounted on a first rectangular die (5) placed above the conveyor belt (3) and are spaced from each other by a distance (pitch, d) equal to about 0.8 mm, 10. Process according to any one of the preceding claims 6-9 in which the nozzles (8) to be used in step (b) have a diameter between 0.8 mm and 0.12 mm (Φ), are mounted on a second die (7), and are spaced apart by a pitch (P) between 1 mm and 5 mm, preferably 2 mm, each of said nozzles (8) being able to also be placed side by side with one or more nozzles (8) at each pitch (P). 11. Process according to claim 10 in which in the die (7) the nozzles (8) are placed on several horizontal rows at a distance (d) from each other, each nozzle (8) of each row being flanked by one or more nozzles (8) at a distance (f) from each other so as to form groups of nozzles (8), each group being distant from the other by a pitch (P) ranging from 1 mm to 5 mm.