WO2015181700A1 - Method for making pads of absorbent products and pad made with the method - Google Patents

Abstract

Described is a method for making pads (13) of absorbent products, comprising the steps of making a plurality of filaments (4) starting from an extruded polymeric material, with these filaments (4) at a temperature close to the melting temperature of the polymer, depositing these filaments (4) on the outer surface (7a) of a first rotary cylinder (7) shaped to form on it a main layer (6) of non-woven fabric, rolling the surface (7a) of the first cylinder (7) with the outer surface (8a) of a second cylinder (8) rotating with the main layer (6) of non-woven fabric interposed between the surfaces (7a, 8a), crystallising the filaments (4) of polymeric material.

Description

DESCRIPTION

METHOD FOR MAKING PADS OF ABSORBENT PRODUCTS AND PAD MADE WITH THE METHOD.

Technical field

This invention relates to a method for making pads of absorbent products. More specifically, this invention relates to a method for making pads of absorbent products in non-woven fabric.

Background art

Absorbent products (wipes, sanitary towels, nappies) are known in the sector which use layers of non-woven fabric and aim to achieve a high thickness with a consequent reduction in density.

The ability to obtain products with a high specific volume brings numerous advantages.

A first of these advantages, particularly felt in the sector of nappies, in the making of the so-called acquisition products, regards the obtaining, with the same weight of material used, of greater thicknesses which constitute more effective barriers relative to the lower layer, thus determining a greater speed of acquisition of the liquid and consequent reductions in the return to the surface of the liquid itself (wet back).

In the sector of products for both personnel and household hygiene, an increase in volume with the same weight results in an improvement of the so-called "feel", that is, the sensation to touch, which becomes advantageously softer and denser.

An advantage which is sought in all the sectors is that linked to obtaining a more voluminous product at a lower cost. However, currently, the materials available do not allow these advantages to be obtained in an economically convenient manner.

Sometimes, in effect, processing aimed at increasing the specific volume of the layers of the pad is so onerous and expensive that it results in being inapplicable to normal manufacturing processes.

Disclosure of the invention

The aim of this invention is to overcome the drawbacks of the prior art, proposing a method for making pads of absorbent products which allows large volumes to be obtained at reduced costs.

A further aim of this invention is to propose a method for making pads of absorbent products which is effective, practical and inexpensive to implement.

According to the invention, these aims are achieved by a heating station comprising the technical features described in one or more of the appended claims.

Brief description of drawings

The technical features of the invention, according to the above aims, are clearly described in the appended claims and its advantages are apparent from the detailed description which follows, with reference to the accompanying drawings which illustrate non-limiting example embodiments of it, and in which:

Figure 1 is a schematic side elevation view of a portion of a system wherein steps of the method according to this invention are implemented;

- Figures 2 to 4 illustrate respective variant embodiments of the method according to the invention;

- Figure 5 is a perspective view from above of a detail of the system of Figure 1 . Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes in its entirety a system for making pads of absorbent articles according to the method according to this invention.

The system 1 comprises, upstream, a station 2 for extruding polymeric material from which the non-woven fabric originates.

At the extrusion station 2 an initial step of conditioning the polymeric material is actuated, which is brought to the liquid/viscous state and then fibres or filaments are formed.

Downstream of the extrusion station 2 the system 1 comprises a station 3 for spinning.

The polymeric material at the outfeed from the extrusion station 2 in the form of fibres or filaments is fed to the spinning station 3 at the outfeed of which a plurality of filaments 4 of predetermined limited diameter is made available.

The diameter of the filaments 4, or better, their linear density, measured in denier (den) where 1 den is equivalent to 1 g/9km, is advantageously between 1 den and 100den.

Preferably, the linear density of the filaments 4 is between 1 den and 30den.

Even more preferably, the linear density of the filaments 4 is between 1 den and 10den.

Downstream of the spinning station 3 the system 1 comprises a station 5 for forming a main layer 6 of non-woven fabric.

The forming station 5 comprises a first cylinder 7 shaped at a relative external cylindrical surface 7a.

The forming station 5 comprises a second cylinder 8 shaped at a relative external cylindrical surface 8a. The external surfaces 7a, 8a of the first and second cylinders 7, 8 have a plurality of respective protrusions and cavities.

The filaments 4 of thermoplastic material at the outfeed from the spinning station 3 transfer, by gravity, towards the first cylinder 7, depositing on the relative cylindrical surface 7a.

During the relative falling towards the first cylinder 7 and the depositing on it, the filaments 4 are still at a temperature close to the melting temperature.

Thanks to this thermal state, the filaments 4, when superposing, are capable of stably connecting with each other, determining those interconnections which are designed to generate the non-woven fabric. A sort of sealing therefore occurs at the points of superposing between the filaments 4.

The superposing of adjacent filaments 4 just described is favoured by means of known techniques and not described further, such as, for example, the relative translation of first cylinder 7 and spinning station 3 along a direction parallel to the axis of rotation of the first cylinder 7. With reference to the accompanying drawings, the axis of rotation of the first cylinder 7 is perpendicular to the plane of the figure, as is also the axis of rotation of the second cylinder 8.

The above-mentioned protrusions and cavities made on the external cylindrical surfaces 7a, 8a of the first and second cylinder 7, 8 are shaped to match each other and positioned in such a way as to allow the two cylinders 7, 8 to mesh during their rotation about the respective axes.

As illustrated in Figure 5, a preferred but not exclusive embodiment of above-mentioned protrusions and cavities is of a truncated pyramid form. According to an alternative embodiment, not illustrated, the above- mentioned protrusions and cavities are hemispherical in shape.

According to further alternative embodiment, also not illustrated, the above-mentioned protrusions and cavities are frusto-conical in shape. The first and the second cylinder 7, 8 therefore engage in rotation, counter-rotating about the respective axes in the direction of the arrows indicated in Figure 1.

During the rotation of first and second cylinders 7, 8 the main layer 6 of non-woven fabric is interposed between them and driven downstream, according to the direction indicated by the arrow F.

Due to the presence of the cavities and protrusions on the external cylindrical surfaces 7a, 8a of the two cylinders 7 and 8, the main layer 6 of non-woven fabric undergoes a consequent deformation by which it adopts a substantially three-dimensional shape.

In other words, the main layer 6 of non-woven fabric is subjected to a forming by the above-mentioned protrusions in its the passage across the two first and second cylinders 7, 8.

In the contact with the two cylinders 7, 8 the main layer 6 is cooled, according to substantially known cooling methods not described further. Following this cooling, the temperature of the filaments 4 of polymeric material drops considerably below the melting temperature of the polymeric material, thus determining a substantial crystallisation of filaments 4.

Following this crystallisation of the filaments 4 which make up the main layer 6 of non-woven fabric, the forming imparted to the main layer 6 adopts a final character, determining the stability its above-mentioned shape which is substantially three-dimensional.

As illustrated in Figure 2, the main layer 6 of non-woven fabric is superposed, on opposite sides of the layer 6 itself, by a first and a second containment layer 9, 10.

This superposing occurs at a predetermined zone 1 1 , using respective means not illustrated.

The first and second containment layers 9, 10 advantageously have a plane extension. These containment layers 9, 10 are made with prior art technologies not described in detail in this specification.

In this regard, for example, the containment layers 9, 10 may consist of card webs, webs of continuous filaments of the "spunbond" type, webs formed by short fibres of the "air-laid" type, or even compositions of each of these.

The term "card web," means a thin layer of fibres individually spun, which are partly linear. The card web is obtained by removal from a card cylinder.

The term "spunbond" means a particular processing consisting in the melting of the polymer, which is then perforated and pressed.

Lastly, the term "air-laid" identifies a technology for processing non-woven fabric characterised by a web formed by a dry compound consolidated by latex, resins or heat.

Alternatively to what was just described above, the containment layers 9, 10 may also consist of layers of non-woven fabric already finished, that is to say, layers wherein the random fibres have already been bonded together, thus acquiring consistency and resistance similar to that of a fabric.

The accompanying drawings schematically illustrate, by way of an example, groups of card cylinders 12 designed to make card webs. This example does not limit the scope of the invention in any way regarding the type of web used for making the containment layers 9, 10.

Returning to the superposition of the containment layers 9, 10, they, regardless of their particular type, are connected stably to the main layer 6.

The assembly of the main layer 6 and of the two containment layers 9, 10, all integrally connected with each other, defines a pad 13 for absorbent products made according to this invention. A simplified embodiment, not illustrated, of the pad 13 according to this invention comprises a single containment layer combined with the main layer 6 with a three-dimensional extension.

A stable connection between the containment layers 9, 10 and the main layer 6 is advantageously sought for imparting stability to the pad 13, in particular to prevent the flattening of the main three-dimensional layer 6. In effect, considering any longitudinal section of the pad 13 according to this invention, the resulting shape is not unlike that of a normal lattice beam structure where tie rods and struts effectively contribute to the non- deformability of the system.

A further and maybe also more focussed analogy is to be found with the structure of the corrugated cardboard, where a corrugated layer is interposed between two flat layers, thereby giving shape to a particularly strong structure compared with the layers taken individually.

As illustrated in Figures 2 and 3, downstream of the above-mentioned zone 1 1 of superposing the containment layers 9, 10 on the main layer 6, the system 1 has a station 14 for connecting these layers.

The connection station 14 may actuate different methods for connecting between the fibres of the different layers 6, 9, 10.

With reference to Figure 2, the connection station 14 comprises hot air bonding means 15, also known in the sector as "air through bonding" systems.

These hot air bonding means 15 make, with the aid of jets of hot air which strike the pad 13, a stable connection between adjacent fibres 4 of the various layers 6, 9, 10 which make up the pad 13.

In other words, the hot air which strikes the layers brings the fibres with low melting points to a melting or softening point. The vicinity of these fibres in any of the layers 6, 9, 10 with other similar fibres implies that a sort of bonding is created in the points of contact between the relative softened parts. In the system 1 shown in Figure 3 the connection station 14 comprises hydrobonding or hydrobinding means 16.

The hydrobonding means 16, according to substantially known methods, stably interlace, tying them together, adjacent fibres 4 of the various layers 6, 9, 10 which make up the pad 13.

Figure 4 shows a variant of the system of Figure 2 wherein the pad 13 comprises two main layers 6 with a third containment layer 17 interposed between them.

For this purpose, the system 1 of Figure 4 comprises two units 18 for forming a main layer 6 and three separate groups 12 of web cylinders designed to make the respective card webs constituting the three containment layers 9, 10, 17.

The definition of the unit for forming a main layer 6 refers to the set of stations and apparatuses already described above and illustrated in Figure 1 .

The system 1 comprises, downstream of a respective zone 1 1 of superposing all the above-mentioned main 6 and containment layers 9, 10, 17, a connection station 14 at which these layers are connected together with the methods described above with reference to the variant embodiments of Figures 2 and 3.

Further variant embodiments comprise the making of systems 1 designed to assemble multiple main layers 6 interposed with respective containment layers.

According to variants embodiments, not illustrated, of the method according to this invention, the above-mentioned step of stably connecting the main layer 6 to the respective containment layers 9, 10, 17 is actuated by a thermal bonding process with bending or by a needle punching process. Both these processes, although used in different contexts from that of this invention, are to be considered of substantially known type with regards to their respective construction modes. The pad 13 obtained with the method according to this invention has a thickness between 1 and 30 mm.

Preferably, the thickness of the pad is between 1 and 15 mm.

Even more preferably, the thickness of the pad is between 1 and 9 mm. The invention brings important advantages.

In effect, for example, the cost of the textile fibres from carding is significantly greater that of the original unworked polymeric material. The fact of being able to add to the carded material used for the containment layers 9, 10 a main internal layer 6 made with a less costly raw material, provides, with the same finished weight of the pad 13, a product which is more voluminous and less costly by a percentage proportional to the quantity in weight of the main layer 6 which is inserted in the pad 13.

Also, advantageously, by using the method according to this invention, it is possible modify the form of the main layer as desired according to the requirements simply by varying the shape of the external cylindrical surfaces of the first and second shaped cylinders.

The term pad in this specification refers both to structures in which the three-dimensionality is required for the functional need of draining liquids (for example, the so-called acquisition layer or absorbent layers of nappies and the like) and to structures in which this aspect is basically required for commercial or marketing needs (for example, tissues and wipes for which voluminosity and softness to touch are sought).

Claims

1 . A method for making pads (13) of absorbent products, comprising the steps of:

- making a plurality of filaments (4) starting from an extruded polymeric material, the filaments (4) being at a temperature close to the melting temperature of the polymer,

- placing the filaments (4) on the outer surface (7a) of a shaped rotary cylinder (7) to form on the cylinder (7) a main layer (6) of non-woven fabric,

- engaging in a rotary fashion the surface (7a) of the first cylinder (7) with the outer surface (8a) of a second rotary cylinder (8) with the main layer (6) of non-woven fabric interposed between the surfaces (7a, 8a), the outer surfaces (7a, 8a) of the first and second cylinder (7, 8) having a plurality of respective protrusions and cavities shaped to match,

- crystallising the filaments (4) of polymeric material to give the main layer (6) of non-woven fabric interposed between the outer surfaces (7a, 8a) of the first and second cylinder (7, 8) a respective three-dimensional shape,

- superposing on the main three-dimensional layer (6) a first containment layer (9) in a substantially flat extension.

2. The method according to claim 1 , characterised in that it comprises the step of superposing on the main layer (6) of non-woven fabric with a three- dimensional extension a second containment layer (10) on the opposite side of the main layer (6) relative to the first containment layer (9).

3. The method according to claim 1 or 2, characterised in that it comprises the step of preparing a plurality of main layers (6) with three-dimensional extension alternated with the containment layers (9, 10, 17).

4. The method according to any one of the preceding claims, characterised in that the at least one containment layer (9, 10, 17) comprises "spunbond" or "airlaid" filaments.

5. The method according to any one of the preceding claims 1 to 3, characterised in that the at least one containment layer (9, 10, 17) is made of non-woven fabric.

6. The method according to any one of the preceding claims, characterised in that it comprises the step of stably connecting the main layer (6) with the at least one containment layer (9, 10, 17).

7. The method according to claim 6, characterised in that the connecting step is actuated by a process of through-air thermal bonding.

8. The method according to claim 6, characterised in that the connecting step is actuated by a process of hydrobonding.

9. The method according to claim 6, characterised in that the connecting step is actuated by a process of thermal bonding with bending machine.

10. The method according to claim 6, characterised in that the connecting step is actuated by a process of needle punching.

1 1 . An absorbent product comprising a pad (13) made with the method according to any one of claims 1 to 10.

12. The absorbent product according to claim 1 1 characterised in that the pad (13) has a thickness of between 1 and 30 mm.