EP2069135B1 - Process and assembly for manufacturing an absorbent sheet, and absorbent sheet obtained - Google Patents

Description

The present invention relates to the field of absorbent papers based on cellulose wadding, for sanitary or domestic use such as toilet paper, towels or any paper wiping, napkins ...

For the production of such products, cellulose wadding, also known as tissue paper, is generally used. It is a low weight absorbent paper, between 10 and 45 g / m ² , obtained wet from paper fibers. It includes, possibly, chemical additives in small proportions, according to the use for which it is intended. It can be obtained by pressing the still wet sheet on a heated cylindrical element of large diameter, on which it is dried and from which it is then detached by means of a metal blade applied against it, transversely to its direction of rotation. . This operation is intended to crepe the sheet which then has transverse corrugations to its direction walk. The crepe gives the sheet a certain elasticity at the same time as it increases its thickness and gives it tactile properties.

Another known method of manufacture comprises a first step of drying the sheet, at least in part, by means of a stream of hot air therethrough. This can then be creped or not.

In general, the sheet thus manufactured is then transformed into another distinct phase of production known as transformation or conversion and associated with other sheets then called folds to form the final absorbent paper product.

Indeed, when it is desired to confer particular properties on a sheet such as thickness, softness, swelling, one can choose to associate several plies between them.

The association can be of a chemical nature by gluing, for example, or of a mechanical nature.

As regards bonding, the known methods consist in depositing a film of glue on all or part of the surface of one of the plies, and then in contacting the glued surface with the surface of at least one other ply.

This type of association requires specific equipment, additional in the production line which represents a cost, additional technical difficulties. In addition, the glue itself is expensive, clogs the cylindrical elements of the embossing unit and can induce additional rigidity, unwanted on the final product whose softness will be also diminished by the presence of the glue. These disadvantages have led some manufacturers to turn to mechanical type associations.

In this case, the combination of the folds can be performed by knurling or by compression, in the conversion or conversion phase.

Knurling consists of compressing the folds to be associated between a wheel (or engraved wheel, provided with elements in relief) and a smooth cylindrical element.

Each knurled band corresponds to the width of a wheel. The bands can form decorative strips on the sheet.

As an illustration, the patent US 3,377,224 describes a "tissue" paper made by such a method. Since a very limited width of paper is knurled, a significant disadvantage lies in the delamination of the non-knurled areas.

In addition, the association by knurling is limited when it is desired to make patterns across the width of a width. Indeed, even if a large number of knurls are arranged side by side (thus creating a large number of bands) there may be areas without knurling.

The document EP 1 362 953 illustrates a particular example of an installation and method using knurling. The major difference with respect to the basic method described above is that the combination of folds takes place in wide parallel bands (machine running direction) on the sheet, and in that one applies an additive film such as oil on at least one side of the sheet.

On the other hand, knurling generally creates problems of readability of the embossed pattern if it exists, because the knurling overwrites the embossing patterns.

In addition, in the case where a large number of rollers is used, adjusting and / or setting the rollers makes the manufacture difficult and complex.

Embossing is also known which is a deformation in the thickness of the sheet or fold, which gives it a particular relief or hollow. The thickness of the sheet or fold is increased after embossing compared to its initial thickness.

If the embossing adds thickness to each fold or sheet, it does, however, induce a substantial reduction in the breaking strength of the sheet. Indeed, the mechanical work on the fold (or the sheet) is accompanied by loosening interfiber bonds embossed areas.

In the case of a multi-ply sheet, the embossing can be carried out individually on each ply, then the plies already embossed are combined by means of a marrying cylinder. Requirement WO 2004/065113 illustrates an example of this type of association.

However, such a marrying cylinder is complex in particular when its entire outer surface must be covered with a hard material band wound helically.

In one or the other embodiment of a multiply sheet, the two (or more) folds are embossed then associated by passing the sheet thus treated and formed, between an engraved cylinder and a marrying cylinder.

Requirement WO01 / 38078 discloses an analogous method for autogenously bonding two cellulosic sheets to form a multilayer multilayer laminate by high pressure rolling. Fixation occurs at selected wet connection points prior to association with a functional fluid such as water. The method is applicable to multilayer substrates formed from sheets treated with chemical softening agents.

The association can cause problems including wear of the engraved cylinder and / or the marrying cylinder.

Wear is accentuated when high pressures and / or speeds are needed.

A first known approach is to cover the outer surface of the marrying cylinder, for example, a ferrule.

Requirement FR 2 801 833 discloses a marrying cylinder (for example) on which is mounted a sleeve, a so-called securing layer being interposed between the cylinder and the sleeve. The bonding layer can be considered as an "elastic" underlayer that dampens the pressure variations and also the manufacturing differences of each of the cylinders.

However, in use, it has been found that manufacturing differences and pressure variations damped by this type of cylinder are not sufficient. Early wear and punctual wear occurred, especially if the cylinders operate at high speeds, from about 300 m / min.

In addition, the pressure on the sheet at the passage (or nip) between the cylinders increases their wear; the outer layer is damaged in places.

Of course, all these deficiencies have negative consequences on the formed leaves which, for example, are not sufficiently associated (they delaminate); so we end up with a production of uneven quality, even overall bad.

This is not acceptable for the manufacturer or the user.

There is therefore a need to combine folds of cellulose wadding in a manner that is both reliable, simple, without bonding and which obviates the problems mentioned above.

The present invention provides a solution which relates to a process for producing an absorbent sheet comprising at least two plies of cellulose wadding, comprising associating said plies under pressure by passing between two cylindrical elements made of steel, the former being externally smooth and the second being externally provided with elements in relief and the hardness of the first cylindrical element being smaller than that of the second cylindrical element.

According to the invention, the first cylindrical element has a treated, hardened surface layer and a deformable underlayer; the second cylindrical member has a hardened outer surface, and the sheet as it passes between the two cylindrical members is compressed to a specific pressure of 40 to 250 N / mm ² .

The features set out above advantageously make it possible to work at high pressures and thus to obtain multi-ply products of good quality which furthermore have various, varied and perfectly visible embossing patterns.

Advantageously, the difference in external hardness between the first and the second cylindrical element is between 2 and 20 HRC, preferably between 5 and 15 HRC.

This difference in hardness makes it possible to operate at high speeds and / or pressures while obtaining a perfect combination of folds.

In addition, this difference in hardness creates a wear of the engraved cylindrical element slower than that of the first cylindrical element, which is an advantage because the engraved cylindrical element is an expensive element of the installation, more expensive than the first one. smooth cylindrical element.

With regard to the external hardness of the first cylindrical element, values between about 30 and about 65 HRC may be chosen.

The method according to the invention advantageously allows to associate folds of width between 0.3 and 4 m, without wear problem of the cylindrical elements or variation in the quality of the association, regardless of the scrolling speeds folds.

The sheet obtained by such a method is further covered by the invention.

In addition, the subject of the invention is a set of cylindrical elements made of steel intended for the combination of multi-ply absorbent sheets, the first cylindrical element being externally smooth and the second cylindrical element being externally provided with elements in relief. outer hardness of the first cylindrical element being lower than that of the second cylindrical element, and said assembly for associating under pressure the different folds of the sheets by passing in the gap between their generatrices.

According to the invention, the first cylindrical member has a hardened surface layer and a deformable underlayer, the second cylindrical member has a hardened outer surface, the first cylindrical member being pressed against the second cylindrical member so as to exert on the absorbent sheet a specific pressure of between 40 and 250 N / mm ² .

In addition to the advantages already mentioned, the invention allows great flexibility in the choice of marking patterns, in the type of embossing, the arrangement and / or the quantity of patterns.

Moreover, the first cylindrical element may comprise a cylinder, or a set of several coaxial cylinders.

According to an advantageous characteristic of the invention, the outer (surface) layer of the first cylindrical element has a thickness of between 3 and 30 mm, while the deformable underlayer, which is thinner, may have a thickness of between 0.5 and 10 mm.

A hardness gradient of said outer layer of the first cylindrical element may advantageously be provided, depending on its thickness.

Without departing from the scope of the invention, said outer surface layer of the first cylindrical element may comprise two layers associated and superimposed on one another, the outermost being treated, cured.

The outer surface (or ferrule) of the first cylindrical element, mounted on the deformable underlayer is a kind of shield that resists perfectly to mechanical stresses while maintaining overall flexibility to the cylindrical element.

Thus for widths of large size, the arrow in the center of the cylindrical element can be compensated by the relative general flexibility of said cylindrical element.

Similarly manufacturing tolerances of each of the cylindrical elements can be compensated including but not exclusively by said flexibility created by the deformable underlayer.

It is also conceivable, without departing from the scope of the invention, said deformable sub-layer comprises at least two layers having different mechanical characteristics.

• la figure 1 est une coupe simplifiée d'un « nip » entre deux éléments cylindriques, selon un premier mode de réalisation de l'invention ;
• la figure 2 est une coupe simplifiée d'un « nip » selon un deuxième mode de réalisation de l'invention ;
• la figure 3 est un schéma montrant les principaux éléments nécessaires à la mise en oeuvre d'un mode de réalisation de l'invention ; et
• la figure 4 est un schéma montrant les principaux éléments nécessaires à la mise en oeuvre d'un autre mode de réalisation de l'invention.

Other features, details, and advantages of the present invention will appear better on reading the following description, given by way of illustration and in no way limiting, with reference to the appended drawings, in which:

• the figure 1 is a simplified section of a "nip" between two cylindrical elements, according to a first embodiment of the invention;
• the figure 2 is a simplified section of a "nip" according to a second embodiment of the invention;
• the figure 3 is a diagram showing the main elements necessary for the implementation of an embodiment of the invention; and
• the figure 4 is a diagram showing the main elements necessary for the implementation of another embodiment of the invention.

According to one embodiment of the invention, as schematized on the figure 1 , the set of two cylindrical elements allowing the association of the folds comprises a first cylindrical element 1 commonly known as a marrying cylindrical element which cooperates with a second cylindrical element 2 called embossing element.

As is known, the marrying cylindrical element 1 has a smooth outer surface, and the cylindrical embossing element 2 externally has protuberances such as lines, spikes having only one or two different depths, or more.

As is also known, the first marrying cylindrical element has an external hardness of hardness lower than that of the second cylindrical element.

According to an embodiment as illustrated on the figure 1 , the first cylindrical member 1 has an outer surface formed of two layers 111, 112 associated and superimposed on one another, the outermost 112 being treated, cured.

According to another embodiment of the invention, as illustrated in figure 2 , the first marrying cylindrical element has a hardened outer surface 11 which rests on a deformable underlayer 12 which itself may for example be made of a polymer.

Without departing from the scope of the invention said sub-layer 12 may comprise at least two layers having different mechanical characteristics, in particular hardnesses and / or different resilience.

The external hardness of the first cylindrical element can be achieved through a treated steel sleeve; or through a sleeve externally coated with a cured treated layer.

Any conventional treatment known to those skilled in the art can be performed here in order to impart the required external hardness to said cylindrical element 1.

In all cases, it is sought to obtain an external hardness (on the surface) greater than about 30 HRC, preferably between 30 and 55 HRC.

Furthermore, the outer surface of the engraved cylindrical element 2 has a hardness greater than 2 to 20 HRC to that of the first matching cylindrical element 1. A hardness difference of between 5 and 15 HRC may be preferred.

• On fait pénétrer un corps pointu dans une éprouvette en métal.

The HRC unit is a unit of hardness according to the test developed by ROCKWELL based on the following principle:

• A pointed body is penetrated into a metal test tube.

Specifically, a penetrating body is used a slightly rounded diamond tip whose apex angle is 120 °; this diamond point is gradually pushed into the metal and the residual indentation (e, in μm) of the tip under a given load is measured.

The value of the hardness is then given by $$\mathrm{100}-\frac{\mathrm{<figure-callout\; id="2"\; label="e"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">e</figure-callout>}}{\mathrm{2}}$$

Thus the harder the metal, the more its hardness expressed in HRC units is close to 100;

These hardness tests known to those skilled in the art are for example disclosed in the book "General professional technology for mechanics" - Volume II - Class of 1st - Editions FOUCHER, pages 35 to 38 .

In addition, ISO 6508 - 1: 1999 provides a comprehensive definition of ROCKWELL hardness tests.

The external hardness of the cylindrical element 2 etched can be achieved by a surface treatment which preferably relates to a thickness 22 greater than the height of the protuberances (or the highest protuberances) forming the etching.

It is also conceivable that the steel of the engraved cylindrical element 2 inherently has the required hardness, in its entirety, as illustrated in FIG. figure 2 .

One or the other solution will be chosen depending on the cost and / or the difficulty of producing the cylindrical elements 1, 2, or any other technical constraint.

According to the invention, at the level of the nip between the cylindrical elements 1 and 2 there is contact along the common generatrix of the cylindrical elements, and the absorbent sheet to be associated passes between these cylindrical elements where it undergoes a specific specific pressure, including between 40 and 250 N / m ² .

The specific pressure can be defined as the ratio between the total force applied by the first cylindrical element 1 on the second cylindrical element 2 at the nip, on the sum of the surfaces in contact at this point, at a given instant.

It is therefore easy to understand that this pressure varies as a function of the geometry of the distal surfaces (ends) of the protuberances of the engraved cylindrical element 2, and that it can thus be controlled and controlled.

The present invention advantageously allows a great freedom in the choice of protuberances, that is to say in fact embossing patterns of the absorbent sheet to be manufactured.

It is even conceivable to carry out the embossing by means of a type of protuberances and the association by means of another type of protuberances, those which are actually in contact under pressure with the external surface of the marrying cylindrical element 1.

A great flexibility in the choice is possible according to the invention.

Furthermore, the characteristics mentioned above allow an association on relatively wide sheets of width, that is to say between 0.3 and 4 m, without particular problem.

Regarding the nature of the deformable underlayer 12, it may be made of a compressible polymer such as an elastomer.

This underlayer may have a thickness of between 0.5 and 10 mm; tests with thicknesses ranging from 2 to 4 mm gave very interesting results.

The arrangement according to the invention makes it possible to reduce the deflection of the cylindrical embossing element 2 as well as the vibrations and other associated disadvantages.

As an example, the marrying cylindrical element 1 is coated with a sleeve 11, which has a hardness of 47 HRC and is in contact with the engraved cylindrical element 2 which itself has an external hardness of 57 HRC . The elastic underlayer 12 has a thickness of 4 mm and is made of a compressible polymer such as an elastomer, known per se.

The underlayer 12 advantageously makes it possible to dampen manufacturing defects, wear and / or vibrations at high speeds.

At high speeds it is necessary to understand speeds greater than or equal to about 300 m / min for the manufacture of toilet paper; and from 150 to 350 m / min for handkerchiefs.

It has furthermore been found that a hardness difference of approximately 10 HRC between the external surfaces of the two cylindrical elements 1, 2 makes it possible to obviate all the aforementioned drawbacks, and in particular to preserve a relatively low wear of each of the cylindrical elements given their rotational speeds and their respective dimensions.

For purposes of illustration of a method of manufacturing a sheet according to the invention, the figures 3 and 4 schematize two examples of possible installations.

The figure 3 shows a first example according to which the elements used comprise, in addition to the marrying cylindrical element 1 and the embossed cylindrical element (embossing) 2, a cylindrical rubber element 3 intended to cooperate with the cylindrical element 2 in order to emboss one of the folds (or groups of folds) P1 constituting the sheet F, according to a procedure known per se and which, therefore, will not be further explained.

In the example illustrated by the figure 3 a second fold (or group of folds) P2 is brought into the gap (or nip) between the cylindrical elements 1 and 2 where it is associated with the first fold P1, as already described. This second fold is not embossed.

A sheet F comprising two plies P1, P2 (or group of plies) is thus produced, with a first embossed ply and a second non-embossed ply.

The figure 4 shows the elements used to manufacture an absorbent sheet according to another embodiment of the invention, and which comprise, in addition to a marrying cylindrical element 1 and an engraved cylindrical element 2, a second cylindrical element etched 4 and two cylindrical elements in rubber 31, 32 which are counterparts to each of the cylindrical engraved elements 2, 4.

Thus the first fold (or group of folds) P1 passes first between the first cylindrical rubber member 31 and the cylindrical element engraved 2 where it is embossed. Simultaneously and symmetrically, the second fold P2 passes between the second cylindrical rubber element (counterpart) 32 and the second cylindrical element engraved 4 for embossing purposes.

The two plies (or group of plies) thus embossed separately, are joined between the first and second cylindrical engraved elements 2, 4 which are wedged so that the protuberances (or markings) of each of the plies are embedded in one another. other. This particular arrangement, called nested, is well known to those skilled in the art and will not be further described.

Thus positioned with respect to each other, the plies are then associated at the level of the nip 5 between the first etched cylindrical element 2 and the marrying cylindrical element 1, under conditions in accordance with the invention mentioned above.

Without departing from the scope of the invention, the first cylindrical element (1), smooth, may comprise a set of coaxial cylinders carried by one or more axes. In the latter case, the axes are angularly offset around the second engraved cylindrical element (2). A priori two axes are preferentially provided, diametrically opposed.

Of course each of the coaxial cylinders has characteristics in accordance with the invention, namely in particular a surface layer (11) treated, cured and a deformable underlayer (12).

Without departing from the scope of the invention, it is conceivable to associate at least two plies without these being previously treated and / or embossed.

Claims (14)

1. Process for manufacturing an absorbent sheet comprising at least two plies of cellulose wadding, consisting in associating said plies under pressure by passing between two cylindrical steel elements, the first (1) being externally smooth and the second (2) being externally provided with raised elements and the hardness of the first cylindrical element being less than that of the second cylindrical element, the first cylindrical element (1) having a treated, hardened surface layer (11), and a deformable sublayer (12), the second cylindrical element (2) having a hardened outer surface, and the sheet during its passage between the two cylindrical elements (1, 2) being compressed to a specific pressure of between 40 et 250 N/mm².
2. Manufacturing process according to claim 1, characterised in that the difference in external hardness between the first (1) and second (2) cylindrical elements is between 2 and 20 HRC, preferably between 5 and 15 HRC.
3. Manufacturing process according to any one of the preceding claims, characterised in that the external hardness of the first cylindrical element (1) is between about 30 and about 65 HRC.
4. Process according to any one of the preceding claims for associating a sheet of width of between 0.3 and 4 m.
5. Set of cylindrical steel elements (1, 2) for associating multi-ply absorbent sheets, the first cylindrical element (1) being externally smooth and the second cylindrical element (2) being externally provided with raised elements, the external hardness of the first cylindrical element (1) being less than that of the second cylindrical element (2), and said set for associating the various sheet plies under pressure by passing in the gap between their generatrices, the first cylindrical element (1) having a hardened surface layer (11) and a deformable sublayer (12) and the second cylindrical element (2) having a hardened outer surface, the first cylindrical element being pressed against the second cylindrical element so as to exert on the absorbent sheet a specific pressure of between 40 and 250 N/mm².
6. Assembly of cylindrical elements according to claim 5, characterised in that the first cylindrical element is a cylinder.
7. Assembly of cylindrical elements according to claim 5, characterised in that the first cylindrical element comprises several coaxial cylinders.
8. Assembly of cylindrical elements according to any one of claims 5 to 7, characterised in that the difference in external hardness between the first (1) and second (2) cylindrical elements is between 2 and 20 HRC, preferably between 5 and 15 HRC.
9. Assembly of cylindrical elements according to any one of claims 5 to 8, characterised in that the external hardness of the first cylindrical element (1) is between about 30 and about 65 HRC.
10. Assembly of cylindrical elements according to any one of claims 5 to 9, characterised in that the thickness of the outer layer (11) of the first cylindrical element (1) is between 3 and 30 mm.
11. Assembly of cylindrical elements according to any one of claims 5 to 10, characterised in that the thickness of the deformable sublayer (12) of the first cylindrical element is between 0.5 and 10 mm.
12. Assembly of cylindrical elements according to any one of claims 5 to 11, characterised in that the hardness gradient of the outer surface layer of the first cylindrical element (1) depends on its thickness.
13. Assembly of cylindrical elements according to any one of claims 5 to 12, characterised in that the outer surface layer (11) of the first cylindrical element comprises two associated layers (111) and (112) superimposed on each other, the outermost (112) being treated, hardened.
14. Assembly according to any one of claims 5 to 13, characterised in that the deformable sublayer (12) comprises at least two layers having different mechanical characteristics.

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