EP0765215B1 - Absorbent paper multilayered sheet and method of manufacture - Google Patents

Abstract

PCT No. PCT/FR95/00786 Sec. 371 Date Jan. 14, 1997 Sec. 102(e) Date Jan. 14, 1997 PCT Filed Jun. 15, 1995 PCT Pub. No. WO95/35205 PCT Pub. Date Dec. 28, 1995An absorbent multi-layer sheet, with at least two layers each constituted of at least one embossed ply of creped absorbent paper having a specific surface weight between 10 and 40 g/m2 per ply, with an external surface forming the outer side of the multi-layer sheet and an inner surface, the inner surface of the first layer including first and second protrusions and the inner surface of the second layer including third protrusions nested between the-protrusions of the first layer, the two layers being bonded together by at least part of the protrusion tips of one layer adhesively joined to the other layer between two protrusions, is characterized in that the bonding is implemented by the first protrusions of the first layer, the second protrusions having a lesser height than the first ones and their tips being adhesive-free.

Description

The present invention relates to the field of absorbent papers for use sanitary and domestic, and targets a multilayer sheet for products such as toilet paper, handkerchiefs, towels, or wiping cloths, as well as its method of manufacturing

In the sanitary and domestic paper industry, we use, for the realization products, a low-weight creped absorbent paper such as cellulose wadding. We takes advantage of its elongation capacity conferred by the crêpe to emboss it. Indeed, the embossing gives bulk to the sheet, and induces an improvement in the absorption liquids, touch and softness.

We tried to further increase the absorption capacity by creating sheets multilayer, obtained by combining two or more sheets

US Pat. No. 3,867,225, for example, describes a process for producing such a product consisting in embossing two sheets of cellulose wadding separately according to a pattern consisting of projections or protuberances at a rate of 2 to 30 per cm ² , applying an adhesive substance on the top of part of these projections, to bring the two sheets together by the embossed faces, that is to say having the protuberances, by arranging the protuberances of one between the protuberances of the other, and glue the vertices of one sheet with the recessed areas of the other sheet. By the voids formed between the two sheets, a structure is thus produced having an improved absorption capacity compared to absorbent sheets not thus transformed. In certain applications of the product obtained, where softness is an important criterion, it would be desirable to avoid the presence of too large a number of connection points between the two sheets, since the total surface linked to it is proportional and this constitutes an important stiffness factor. As the gluing is carried out by deposition by means of a gluing cylinder, the number of connection points is equal to that of the protuberances of the sheet receiving the glue. To reduce this number of connection points, this patent proposes partial gluing by the use of a glue applicator cylinder whose surface is hollowed out with cells. Unfortunately, such a solution has proven to be impractical industrially because it leads to rapid fouling of the cylinders by agglomeration of material in the cells.

US Patent 4320162 describes a multilayer sheet structure consisting of two embossed sheets. Each sheet includes a wide pattern of firsts relatively deep embossed protrusions surrounded by a tighter pattern of second protrusions embossed less deeply. The two sheets are associated, according to a first example, by the vertices of the first protrusions, and, according to a second embodiment, by the vertices of the first projections for one leaf and the vertices of the second projections for the other leaf. Such a structure in theory offers a greater internal vacuum volume than in the layout presented in patent US 3867225 since the two sheets are joined by the top protrusions. However, it is less resistant to crushing; there is indeed a sagging of the projections already under low contact pressure.

The present invention provides a multilayer structure combining the advantages of the two methods mentioned above without presenting the disadvantages, as well as its manufacturing process

The subject of the invention is a multilayer absorbent sheet with at least two layers each consisting of at least one embossed sheet of creped absorbent paper weighing between 10 and 40 g / m ² per sheet, with an external face forming the external face of the multilayer sheet and an internal face, the internal face of the first layer comprising first and second protrusions, and the internal face of the second layer comprising third overlapping protuberances between the protuberances of the first layer, the two layers being linked together by at least part of the tops of the protrusions of a layer made integral by bonding to the other layer between two protrusions. This multilayer sheet is characterized in that said connection is provided by the first protuberances of the first layer, said second protuberances having a lower height than the first and their top having received no adhesive substance.

Thanks to the invention, a sheet is obtained whose rigidity is lower than that of a sheet having the same number of protrusions also nested, but where these are all the same height. In addition, we do not penalize the crush resistance. We can easily define the total surface glued from the surface of the peaks of the first protuberances. So the glued surface can vary from 0.1 to 20% depending on the application for which the product obtained is intended. For a sheet intended to be transformed into toilet paper, we will choose a surface glued between 1 and 5% to obtain optimal softness.

According to another characteristic, the height of the second protrusions is greater than 50% of the height of the first protrusions. In effect, optimal resistance to crushing is obtained if the second protrusions are substantially at the same level as the surface of the adjacent layer.

According to another characteristic, the first protrusions are distributed in a spaced pattern, at least two second protrusions being arranged between two successive first protrusions. The first protrusions will advantageously reproduce a drawing combining a plurality of lines pleasing to the eye, that of a flower for example. These drawings will be surrounded by points constituted by the second protrusions and each occupying a small area, the density of these points may be relatively high, up to 80 or 100 points per cm ² .

According to another characteristic, the height of the third protrusions is less than or equal to the height of the first protrusions. To to ensure satisfactory crush resistance it is desirable that the height of these protuberances is at least half that of the first protuberances.

According to another characteristic, the vertices of the third protrusions form a bond, by gluing, with the first layer.

The present invention also relates to a method making it possible to manufacture the multilayer sheet presented above. The method for making a multilayer sheet, consisting of embossing a first sheet of paper, itself single or multiple, on a first cylinder comprising on its surface first and second elements in relief and a second sheet, which can also be simple or multiple, on a second cylinder comprising third elements in relief, with apply glue to at least part of the tops of the protuberances on one of the sheets, bring the two sheets together so that the protrusions of the first leaf overlap between the protrusions of the second leaf, and that the glued tops adhere to the other sheet between two protrusions, is characterized in that the first elements have a height H, measured in relation to the surface of the cylinder, greater than the height h of the second elements, the difference between the heights H and h being greater than 0.05 mm: H-h> 0.05 mm and what, on the first sheet, said deposit glue is only made on the first protrusions.

According to another characteristic, the difference between said heights H and h is less than 50% of H, in particular for H between 1 and 2 mm, and especially when the height of the elements is between 1.2 and 1.5 mm. We thus obtains a multilayer sheet whose second protrusions will fill with their role as a strut and resistance to crushing.

In accordance with another characteristic, the third elements in relief, on the second cylinder, have a height H 'less than or equal to the height H: H' ≤ H

According to another characteristic, the second cylinder has fourth elements in relief, the height h 'of the fourth elements being less than the height H 'of the third elements.

According to another characteristic, H 'and h' are linked by the relation: 0.5 x H '≤h' ≤ H'- 0.05.

According to another characteristic, an adhesive substance is applied both on the first and third protrusions.

La figure 1 représente une installation pour la mise en oeuvre du procédé de l'invention.

La figure 2 représente le motif des éléments en relief, selon un mode de réalisation, apparaissant à la surface d'un cylindre de gaufrage.

La figure 3 représente le motif des éléments en relief sur l'autre cylindre de gaufrage coopérant avec le cylindre de la figure 2.

La figure 4 représente, vue en coupe partielle , la feuille multicouche obtenue selon le procédé.

Other characteristics and advantages will appear on reading the nonlimiting embodiments of the invention, with reference to the appended drawings in which:

FIG. 1 represents an installation for implementing the method of the invention.

FIG. 2 represents the pattern of the elements in relief, according to one embodiment, appearing on the surface of an embossing cylinder.

FIG. 3 represents the pattern of the elements in relief on the other embossing cylinder cooperating with the cylinder of FIG. 2.

FIG. 4 represents, seen in partial section, the multilayer sheet obtained according to the method.

There is shown schematically in Figure 1 a machine, now conventional, used to manufacture the product of the invention.

This installation comprises two embossing units, each consisting of a elastomer-coated cylinder, 1 and 3 respectively, cooperating with a cylinder engraved steel, 2 and 4 respectively. Cylinders 2 and 4 are engraved so that present on the surface elements in relief or spikes, distributed regularly as well machine direction than cross direction.

A first sheet of cellulose wadding 5, absorbent crepe paper used as sanitary or household paper, such as toilet paper, handkerchief, towel, or wiping cloth, is driven from a reel not shown and guided around of cylinder 1; according to the embodiment shown, it is a double sheet. The cylinder is pressed against cylinder 2 by suitable means not shown of so that the sheet, passing between them, is caused to deform and marry the relief of the engraving of the cylinder 2. The sheet is then driven by the latter. A sizing device 8, known per se, deposits with an applicator cylinder a adhesive substance 9 on the top of the raised elements or protuberances of the sheet 5.

A second sheet 6, driven from a coil, undergoes embossing similar passing between cylinders 3 and 4. Cylinder 4 is arranged at a slight distance from cylinder 2 so that the sheet can come off the surface of cylinder 4. It comes into contact with the first leaf, over a portion of its course where it is still applied against the surface of cylinder 2. The two cylinders are driven to synchronous and opposite speeds, they are set in rotation relative to each other so that the protrusions of the sheet 6 are housed between the protrusions of sheet 5. A cylinder 7, said matchmaker, with smooth surface, rotated against the cylinder 2 ensures the union of the two sheets by pressing sheet 6 by its zones in indentation - between two adjacent protuberances - against the vertices provided with glue 9 of the protrusions of the sheet 5. The multilayer sheet obtained is then cut into sheets of small width and put in rolls, of toilet paper for example.

According to the invention, the cylinder has first and second elements in relief of different heights. An enlarged, partial and perspective view of the surface of the cylinder 2 is reproduced in FIG. 1. The first elements in relief 10, on which the first protuberances form the first sheet, have a height H, and are distributed on the surface of the cylinder according to a regular pattern or not. When the reliefs are obtained by engraving or by machining, the height is measured from the top of the element which is substantially planar in general, to the bottom of the engraving. If the elements are reported, we proceed from the same way by difference in heights, the reference being the top of the highest elements.

These first elements can be of any shape. They are advantageously constituted so as to form the imprint of a linear design, for example that of a flower such as that shown in FIG. 2. The first elements 10 are relatively distant from each other. This spacing will depend in particular on the surface occupied by the drawing on the sheet. For example, for a drawing falling within an area of 100 mm ² , the distance between the first two elements will be 15 mm. The height H is between 1 and 2 mm. A particularly suitable value, for the production of toilet paper from cellulose wadding weighing between 10 and 40 g / m ² , is between 1.2 and 1.5 mm, for example 1.3 mm . Obviously, the depth of the embossing and the height of the resulting protrusions on the sheet will depend on the hardness of the coating of the cylinder 1 and the pressure it exerts on the cylinder 2.

Between these first elements, relatively distant from each other, are arranged in second relief elements 12 whose height h is lower. In practical, the height h is measured by difference with H.

These second elements in the structure of the multilayer sheet must fulfill, as the first elements, the function of strut, to contribute to compressive strength and give volume; however they must be sufficiently set back from these so that the sizing device only apply the adhesive substance to the tops of the first protrusions of the first sheet. In practice, the height h of the second elements will be at least 0.05 mm less than H but preferably will remain greater than half of H: 0.5 x H ≤ h ≤ H- 0.05.

These elements 12 are distributed, between the elements 10, in a regular pattern tighter. In Figure 2, there is shown a partial plan view of the distribution first and second elements on the surface of cylinder 2.

The cylinder 4 is engraved according to a pattern in agreement with that of the cylinder 2 in such a way that the protuberances of the second sheet overlap between the protuberances of the first sheet when the two sheets are assembled according to the method of Figure 1. Figure 3 shows a partial top view of the pattern of the elements in relief 14 on the surface of the cylinder 4. Their height H 'is equal to or lower than that of the first elements of the first sheet: H '≤ H. Indeed, if it was greater, the protrusions would be crushed and brought to height H at passage in the interval between the matching cylinder 7 and the cylinder 2. As is notes, in this example, the raised elements of the cylinder 4 have a distribution identical to that of the second elements 12 of the first cylinder. They leave areas 16 non-embossed in which the first relief elements 10 fit.

Figure 4 is a partial sectional view of the multilayer sheet 100 obtained. The sheet 5 has first protrusions 51, and second protrusions 52 of slightly lower height obtained with the elements in relief 10 and 12 respectively. As can be seen according to the embodiment of the figure, the latter is greater than half that of the protrusions 51. The sheet 6 itself has protrusions 61, called third protrusions obtained with the elements in relief 14. According to the embodiment shown, they have substantially the same height as the first protrusions 51, and, apart areas occupied by the first protuberances, they overlap between the second protrusions 52 of the sheet. Sheet 5 is linked to sheet 6, between two protrusions 61, by the top of the protrusions 51 by means of a layer adhesive 9.

Thanks to the solution of the invention with two-level embossing of one of the sheets, it is also possible to obtain multilayer sheets whose appearance can be further improved by coloring the adhesive substance

According to another embodiment of the invention not shown, the second cylinder has third and fourth raised elements which after embossing of the second leaf produce third and fourth protuberances at the surface of the latter. The heights H 'and h' of said elements in relief will be preferably linked by the same relation as H and h, namely: 0.5 x H '≤ h' ≤ H'- 0.05.

According to another embodiment not shown, the two cylinders are placed steel so that they mesh with each other. Compared to the solution of figure 1, this guarantees correct positioning of the protrusions of the sheet 6 - the one that is carried by the cylinder with which the matching cylinder is not associated - compared to protuberances of the other leaf. Indeed, by the meshing of the cylinders the two sheets are guided towards each other until they are assembled. This provision is of particular interest when a glueer is planned for each of the groups embossing. The bringing together of the steel cylinders so that they mesh one in the other already allows a certain association of folds at this level. This provision, thanks to the second glue, is useful if you want to increase the number of stitches of connection between the two layers.

Claims (14)

1. Multilayer absorbent sheet having at least two layers, each consisting of at least one embossed sheet of absorbent crepe paper having a weight of between 10 and 40 g/m² per sheet, with an outer face forming the outer face of the multilayer sheet, and an inner face, the inner face of the first layer (5) having first (51) and second (52) protuberances, and the inner face of the second layer (6) having third protuberances (61) interlaced between the protuberances of the first layer, the two layers being bonded together by at least part of the tops of the protuberances of one layer secured by gluing to the other layer between two protuberances, characterized in that the said bond is provided by the first protuberances of the first layer, the said second protuberances being less high than the first and their tops not having received the adhesive substance.
2. Sheet according to the preceding claim, characterized in that the height of the second protuberances is greater than 50 % of the height of the first protuberances.
3. Sheet according to one of the preceding claims, characterized in that the first protuberances are distributed in a spaced pattern, more than one second protuberance being positioned between two successive first protuberances.
4. Sheet according to one of the preceding claims, characterized in that the glued area of the tops of the first protuberances represent between 0.1 and 20 % of the area of the sheet.
5. Sheet according to the preceding claim, characterized in that the said glued area represents between 1 and 5 % of the total area of the sheet.
6. Sheet according to one of the preceding claims, characterized in that the height of the third protuberances is less than or equal to the height of the first protuberances.
7. Sheet according to the preceding claim, characterized in that the second layer has fourth protuberances of which the height is at least 50 % of the height of the third protuberances.
8. Sheet according to either of claims 6 or 7, characterized in that the tops of the third protuberances form a bond by gluing with the first layer.
9. Process for producing a multilayer sheet according to one of the preceding claims, consisting of embossing a first sheet of paper on a first cylinder having on its surface first and second raised elements, and a second sheet on a second cylinder having third raised elements, of depositing glue on at least part of the tops of the protuberances produced on one of the sheets, of bringing the two sheets together so that protuberances of the first sheet are interlaced between the protuberances of the second sheet, and in that the glued tops adhere to the other sheet between two protuberances, characterized in that the first elements have a height H greater than the height h of the second elements, the difference between the heights H and h being greater than 0.05 mm : H - h > 0.05, and in that, on the first sheet, the said glue deposit is only applied to the first protuberances.
10. Process according to claim 9, characterized in that the difference between the said heights H and h is less than 50 % of H for a value of H of between 1 and 2 mm.
11. Process according to either of claims 9 or 10, characterized in that the third raised elements on the second cylinder have a height H' less than or equal to the height H : H' ≤ H.
12. Process according to claim 11, characterized in that the second cylinder has fourth raised elements, the height h' of the fourth elements being less than the height H' of the third elements.
13. Process according to claim 12, characterized in that H' and h' are associated by the relationship : 0.5×H'≤h'≤H' -0.05.
14. Process according to claim 12 or 13, characterized in that the heights of the first and third raised elements being equal : H = H', an adhesive substance is applied to ensure a bond between the two sheets on the tops of the third protuberances.

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