EP0828602B1 - Method for making an absorbent structure - Google Patents

Abstract

The invention relates to a manufacturing method for an absorbent structure (10) having at least two plies (P1, P2) each constituted of at least one embossed sheet of creped absorbent paper, wherein the plies (P1, P2) engage between two engraved metal cylinders (CG1, CG2) fitted with protrusions (R1, R2), driven in synchronized rotation, and mutually nesting with a play (J) between the tops of the protrusions (R1, R2) of one metal cylinder (CG1, CG2) and the opposite trough surface (F2, F1) of the engraving of the other cylinder (CG2, CG1), the method being characterized in that the play (J) is less than the depth of the cylinder engravings and larger than the sum of the thicknesses (E1, E2) of the plies (P1, P2) which were previously shaped in such a matching manner that the plies (P1, P2) are not compressed when being engaged between the nested engraved cylinders (CG1, CG2).

Description

The present invention relates to a method for producing a absorbent structure or sheet with at least two plies, each consisting of at least minus an embossed sheet of crepe absorbent paper.

The invention relates in particular to the production of fibrous products, in the form of absorbent paper for sanitary and domestic use.

The invention thus relates more particularly to a structure multi-ply absorbent, also called multi-layer structure for products such as toilet paper, handkerchiefs, towels, or wiping cloths.

In the sanitary and domestic paper industry, for the realization of the different products, a low crepe absorbent paper weight such as cellulose wadding or cotton wool. We take advantage of the elongation capacity of this material, conferred by creping, for the emboss.

Indeed, the embossing gives bulk to the sheet and it induces a improved absorption of liquids, touch and softness. Attempts have been made to further increase the absorption capacity by creating multilayer structures obtained by combining at least two layers, also called folds each consisting of at least one embossed sheet of crepe absorbent paper.

• du type dans lequel on engage les plis entre deux cylindres métalliques gravés pourvus de protubérances, entraínés en rotation de manière synchronisée et s'imbriquant mutuellement avec un jeu J entre les sommets des protubérances d'un cylindre métallique et la surface en vis-à-vis du fond de la gravure de l'autre cylindre,
• du type dans lequel chaque pli est, préalablement à son engagement entre les deux cylindres gravés, conformé à la surface de celui des cylindres gravés qui lui est associé en appliquant le pli sur ce dernier au moyen d'un cylindre presseur associé à revêtement souple, notamment en matériau élastomère ou en caoutchouc,
• du type dans lequel on applique une substance adhésive sur les zones en relief d'au moins un pli préalablement à l'engagement des plis entre les cylindres gravés,

French patent application 93 00366 has already proposed a method for producing an absorbent structure with at least two plies,

• of the type in which the folds are engaged between two engraved metal cylinders provided with protuberances, driven in rotation in a synchronized manner and interlocking with a clearance J between the tops of the protuberances of a metal cylinder and the surface facing screw of the bottom of the engraving of the other cylinder,
• of the type in which each ply is, prior to its engagement between the two engraved cylinders, conformed to the surface of that of the engraved cylinders which is associated with it by applying the ply to the latter by means of a pressure cylinder associated with flexible coating, especially made of elastomeric material or rubber,
• of the type in which an adhesive substance is applied to the raised areas of at least one fold prior to the engagement of the folds between the engraved cylinders,

According to the method described in this document, the value of the clearance J is chosen at most equal to the thickness of the sheet to be embossed so as to ensure calendering of the sheet at the tops of the bosses obtained with the association of folds at this level. This process presents however the drawback of requiring the use of cylinders whose machining tolerances of engravings are very tight, which is not easy industrially.

The process commonly designated in the art is also known. anterior by "nested" according to which the two cylinders are sufficiently distant from each other so that one of the folds after embossing is peeled off from the cylinder and applied to the second engraved cylinder carrying the second fold of so that the protrusions of the first fold overlap between the protrusions of the second fold. A matched cylinder with rubber presses the first fold against the second so as to guarantee the contact between the glued vertices of the second fold and the first fold, and their association. This technique is illustrated by US patent 3,867,225.

The Applicant has however been able to observe that such a process, when is used at very high embossing pressures, sometimes results in a floating phenomenon, upstream of the engagement between the cylinder matchmaker and the engraved metal cylinder associated with it, that of the folds which is peeled off from its metallic embossing cylinder for its course in this area towards the match cylinder.

This floating phenomenon results in the formation of a loop causing a gap between the two folds, and therefore to defects of manufacturing due to the mismatch of the two plies at the time of their association by bonding by the matching cylinder.

Besides the difficulty of maintaining synchronization of displacement the two folds before their association by gluing by means of the cylinder This technique also has the disadvantage of requiring a match. sufficiently high pressure between the matching cylinder and one of the engraved cylinders to obtain a good association by bonding the two folds previously embossed.

The use of a relatively high pressure then results, in because of the resilience of the matching cylinder, to an embossing phenomenon additional, or embossing again, of the outer ply relative to the engraved cylinder associated with the matching cylinder which affects the aesthetics of the product as well as its softness to the touch.

The object of the present invention is to propose a method which takes advantage of of the advantages of the two methods mentioned above while remedying to the disadvantages which have just been mentioned.

To this end, the invention proposes a method where the engraved cylinders are distant from each other with a clearance J measured between the vertices of the protrusions of one cylinder and the etching bottom surface of the other cylinder, said clearance J being greater than the sum of the thicknesses of the folds previously shaped, characterized in that this clearance is less than the depth of cylinder engraving.

The invention also provides an installation for setting up work of the method according to the invention of the type comprising two cylinders engraved metal with protrusions, rotated by synchronized and with a clearance J between the vertices of the protrusions of a metal cylinder and the surface facing the bottom of the engraving of the other cylinder, greater than the sum of the thicknesses of the folds previously embossed, characterized in that said clearance J is less than the depth of the engraving of cylinders.

The invention also provides an absorbent structure with at least two plies produced according to the invention and characterized in that it has an absorption capacity measured according to AFNOR NFQ 03068 standard greater than 10 cm ³ / g, in particular between 11 and 14 cm ³ / g when it is produced from two sheets of crepe absorbent paper each having an absorption capacity of between 4 and 6 cm ³ / g.

• la figure 1 représente en coupe transversale une structure absorbante à deux plis ;
• la figure 2 est un schéma illustrant la conception d'une installation pour la mise en oeuvre du procédé de fabrication conforme aux enseignements de l'invention ;
• la figure 3 est une vue schématique en coupe selon la ligne 3-3 de la figure ; et
• la figure 4 est un diagramme permettant d'illustrer les performances d'une feuille multicouches absorbante réalisée conformément aux enseignements de l'invention.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

• Figure 1 shows in cross section an absorbent structure with two plies;
• Figure 2 is a diagram illustrating the design of an installation for the implementation of the manufacturing process according to the teachings of the invention;
• Figure 3 is a schematic sectional view along line 3-3 of the figure; and
• FIG. 4 is a diagram making it possible to illustrate the performance of an absorbent multilayer sheet produced in accordance with the teachings of the invention.

There is shown in Figure 1, in cross section, a sheet or structure 10 with two plies P1 and P2 nested one inside the other.

The fold P1 has bosses B1 obtained by embossing which are spaced from each other and oriented towards the fold P2 which has also, symmetrically, bosses B2 oriented towards the fold P1.

The bosses B2 are fitted between the bosses B1 and the spacing between the bosses B1 and B2 is sufficient to provide between them a space 12.

Each ply or sheet P1, P2 is a sheet of cellulose wadding, crepe absorbent paper used as sanitary or domestic paper weighing between 10 and 40 g / m ² .

The thickness E1, E2 of each of the plies P1, P2, which can be identical for the two folds, is for example of the order of 0.1 mm.

The sheet 10 illustrated in FIG. 1 is produced by means of the installation shown in Figure 2.

This installation comprises two embossing units made up each of a pressure cylinder CP1, CP2 coated with flexible material elastomer, cooperating with an engraved steel cylinder CG1, CG2 respectively.

The cylinders CG1 and CG2 are engraved so as to present in surface of the elements in relief and / or of the pins R1, R2 distributed as well on the circumference, machine direction, than on the width of each cylinder, cross direction.

In accordance with the teachings of the invention, and as can be see it in figures 2 and 3, the metallic cylinders engraved CG1 and CG2 parallel axes are positioned relative to each other so that overlap at the level of their opposite zone, that is to say that the parts in relief R1 of one of the cylinders is inserted between the parts in relief R2 of the other cylinder, the overlap C also called engagement of two cylinders, being however such that there is a clearance J between the cylinders engraved CG1 and CG2 allowing the engagement of folds P1 and P2 between the engraved cylinders.

More precisely, the clearance J measured between the vertices of the protrusions, for example R1, of one of the metallic cylinders CG1 and the surface facing the bottom, for example F2, of the engraving of the other cylinder CG2 is greater than or equal to the sum of the thicknesses E1 and E2 of the folds P1 and P2 when the latter are engaged in the nesting zone mutual fund CG1 and CG2.

We thus have the relation J> E1 + E2.
E1 and E2 are the thicknesses of the folds P1 and P2 in the nesting zone, that is to say of the folds P1 and P2 previously embossed before their simultaneous engagement between the cylinders CG1 and CG2, due to their prior passage in the two embossing units.

The installation illustrated in Figure 2 includes a device size 14, known per se, which deposits by an applicator cylinder 16 a adhesive substance A on the tops of the raised protrusions B2 of one of the two folds, here the fold P2, after the embossing of this fold by the CP2 cylinder associated with CG2 cylinder but before the engagement of the fold P2 between the two engraved cylinders CG1 and CG2.

Thanks to the characteristic of the invention according to which the clearance J is greater than the sum of the thicknesses E1, E2 of the folds P1 and P2 beforehand embossed, the folds are not compressed during their simultaneous engagement between the engraved cylinders CG1, CG2 but they are on the other hand nested in the other and are ready to be bonded by means of a cylinder matchmaker CM which, like the pressure cylinders CP1 and CP2, is a cylinder with flexible coating of elastomeric material which, in the mode of embodiment illustrated in the figures, cooperates with the engraved metal cylinder CG2 to apply the two folds P1 and P2, previously embossed, glued and nested one inside the other, against the CG2 cylinder.

Thanks to the nesting of the two folds ensured during their phase mutual engagement between the two cylinders CG1 and CG2, there is no risk of relative offset of the two folds between the time they leave their mutual engagement zone between the engraved cylinders CGI and CG2 and the moment when the two overlapping folds engage between the matching cylinder CM and the engraved cylinder CG2.

In addition, due to the prior intimate nesting of the two folds P1 and P2, but without pressure, the pressure provided by the matching cylinder CM against the engraved metal cylinder CG2 can be reduced thus avoiding phenomenon of "etching again" of the fold P1 by the raised portions R2 of the metallic cylinder engraved CG2.

The installation allowing the implementation of the method according to the invention of course has adjustment means (not shown) of the distance between the two engraved cylinders CG1 and CG2 and therefore of adjusting the distance D separating the bottoms F1 and F2 from the engravings of the two cylinders in their mutual nesting area.

The method according to the invention makes it possible to produce stronger imprints in each of the two folds P1 and P2 by using, for example, an embossing pressure corresponding substantially to the limit of the flexible material of the cylinders CP1 and CP2 and for example of the order of 14 kg / cm ² .

The method according to the invention makes it possible to produce, from paper reliably, i.e. flawlessly, creped from fibrous products to high absorption capacity and very soft to the touch.

The diagram in Figure 4 illustrates these performances.
On this diagram, the absorption capacity of an absorbent structure measured according to AFNOR standard NFQ 03068 and which is expressed in cm ³ / g has been indicated on the ordinate.

On the abscissa, we have shown the transverse wet resistance expressed in cN for 15 mm.

The measurements were carried out after aging for 15 min at 125 ° C.

As can be seen in the diagram, the basic sheet or fold, before any embossing, has an absorption capacity of between 4 and 6 cm ³ / g.

An absorbent structure with two overlapping plies P1 and P2 produced according to the state of the art has an absorption capacity generally between 6 and 10 cm ³ / g and it is, in all cases, less than the limit value 20 d '' about 11 cm ³ / g.

On the contrary, when the multilayer absorbent structure is produced in accordance with the method according to the invention, one obtains point values, indicated on the left part of curve 18 of FIG. 4 which are above the limit value 20 and which are in particular between 12 and 14 cm ³ / g.

The invention is not limited to the process which has just been described. It is in particular possible without departing from the scope of the invention, to apply the adhesive substance A on the vertices of the protrusions B1, B2 of the two folds P1 and P2 prior to their mutual engagement between the cylinders metallic engraved CG1 and CG2.

The invention is also not limited to the production of a structure absorbent with two plies, a third ply, previously embossed and arranged between folds P1 and P2, which can be engaged simultaneously between the engraved cylinders CG1 and CG2, the clearance J then being of course greater or equal to the sum of the thicknesses of the three plies previously embossed.

Claims (4)

1. Process for making an absorbent sheet (10) with at least two plies (P1, P2), each consisting of at least one embossed sheet of absorbent crepe paper,

   of the type in which the plies (P1, P2) are threaded between two engraved metal cylinders (CG1, CG2) provided with protuberances (R1, R2), driven in rotation in a synchronized manner, a play J being provided between the tops of the protuberances (R1, R2) of one metal cylinder (CG1, CG2) and the opposite surface of the bottom (F2, Fl) of the engraving of the other cylinder (CG2, CG1),

   of the type in which each ply (P1, P2), prior to it being threaded between two engraved cylinders (CG1, CG2), is made to conform totally or partially to the surface of the engraved cylinders with which it is associated by applying the ply (P1, P2) onto the latter (CG1, CG2) by means of a pressure cylinder (CP1, CP2) associated with a flexible covering, in particular made of elastomeric material or rubber,

   of the type in which an adhesive substance (A) is applied to the zones in relief (B2) of at least one ply (P2) prior to the plies (P1, P2) being threaded between the engraved cylinders (CG1, CG2),

   and of the type in which the two plies (P1, P2) are associated by gluing, subsequent to the plies being threaded between the engraved cylinders (CG1; CG2), by applying the two nested plies (P1, P2) onto one (CG2) of the two engraved cylinders by means of a marrying cylinder (CM) with a flexible covering, made in particular of an elastomeric material or of rubber, the said play (J) being greater than the sum of the thicknesses (E1, E2) of the previously formed plies (P1, P2), characterized in that the said play J is less than the depth of the engraving of the cylinders.
2. Process according to claim 1, characterized in that the adhesive substance (A) is applied on the zones in relief on one of the two plies (P1, P2), prior to the plies being threaded between the engraved cylinders.
3. Installation for implementing the process according to one of the preceding claims 1 or 2, of the type comprising two engraved metal cylinders (CG1, CG2) provided with protuberances (R1, R2), driven in rotation in a synchronized manner with a play (J) between the tops of the protuberances (R1, R2) of one metal cylinder and the facing surface of the bottom (F2, F1) of the engraving of the other cylinder, greater than the sum of the thicknesses (E1, E2) of the previously embossed plies, characterized in that the play J is less than the depth of the engravings of the cylinders.
4. Absorbent structure (10) with at least two plies (P1, P2), each consisting of at least one embossed sheet of absorbent crepe paper, characterized in that it is made by a process according to one of claims 1 or 2, and in that its absorptive capacity, measured according to AFNOR standard NFQ 03068 lies between 11 and 14 cm³/g when it is made from two sheets of absorbent crepe paper each possessing an absorptive capacity of between 4 and 6 cm³/g.

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