EP1331308A1 - A creped sheet of absorbent paper, a roll for the embossing and a process incorporating the same - Google Patents

Abstract

Disclosed is a cotton cellulose sheet comprising at least one first embossed area (A<sb>1</sb>, A<sb>2</sb>) with protrusions on one side and corresponding indentations on the other side. The indentations have an essentially polygon-shaped base. The inventive sheet comprises at least one second non-embossed area (B). According to the invention: - the indentations 101', 102' are arranged at least according to one alignment; - the sides facing two adjacent indentations define a bridge (P) with straight or substantially straight edges having a length L which is greater than the greatest width D thereof. One or several interlinked bridges define a path between preferably two second non-embossed areas (B) which are separated by at least one embossed area (A<sb>1</sb>, A<sb>2</sb>). The invention also relates to a cylinder for embossing such a sheet.

Description

The invention relates to the field of absorbent papers for use sanitary or domestic. It particularly targets single-use products such as napkins, tablecloths, paper towels or paper toilet, made of cellulose wadding.

Cellulose wadding is an absorbent paper of grammage, preferably between 15 and 35 g / m ² , which can be manufactured so as to have a certain elongation capacity. A common technique is to apply and stick the sheet still wet on a drying cylinder, and then detach it using a blade forming a doctor blade to create crimping undulations. It can then be rewound pending processing into a finished product. This technique presented in summary is said to be conventional. It is designated in the field by (CWP).

Another technique is to dry the sheet after draining without apply pressure, at least in part, until it is dry enough to freeze the fibers within the leaf. If necessary, drying ends by applying the sheet to a heated cylinder. Thanks to this first drying, the sheet can be pressed on the cylinder without destroying its structure. It retains part of its volume. This cylinder also allows its crepe. The first drying is carried out without pressure by blowing air hot through the foil after draining. This technique, which we designates in the field under the acronym (TAD), allows to obtain a sheet thicker, and of greater mass volume than the technique conventional. It is characterized by a more open structure and a greater permeability.

Then, by the known technique of embossing, it can be improved or at the very least, modify one or other of its characteristics, such as as softness, suppleness, absorption, thickness or appearance. The mode processing is then a function of the use for which it is intended. The embossing pattern is most commonly made up of protrusions or bosses in the shape of pyramids with round, oval or square section, distributed regularly on the surface of the leaf. We observe that at a protuberance on one side of the sheet corresponds a cavity or cell on the other side.

To emboss the cellulose wadding, we generally use a cylinder rigid having spikes on the surface, obtained by etching or by machining, of appropriate shape, size and density. We apply the sheet on the cylinder and it is pressed by means of another cylinder having a deformable coating, for example of rubber. She thus marries the relief. For the same reason, one obtains a more deformation or less important according to the parameters that we have chosen, such as flexibility of rubber, for its ability to deform and conform to relief of the engraving, and the embossing pressure.

The Applicant is currently marketing a paper product paper towels with protuberances distributed in circles concentric. The paper towel consists of two plies of cellulose wadding which have been embossed separately and assembled so that the protrusions are in a position known as "nested". The protuberances of one fold face the other fold and are placed between the protrusions of this latest. The two folds are nested in this way one inside the other, and provide air pockets, improving absorption. The sheet has alveoli on its two visible sides. Leaving aside the state of the surface at the microscopic level, but considering its appearance with the naked eye, the sheet has a relief on two levels. A first level is defined by the bottom of the cells (the bottom of the cells is in one plane if the embossing pins were all on the same level). The second level corresponds to that of the part of the sheet which is not embossed.

To improve the absorption capacity of a paper towel product, can work on the sheet at the time of its manufacture, i.e. at level of the paper machine, on its formation, its drying mode or additives that are incorporated, for example.

The embossing mode of the sheet is also an important parameter on which we can act for this purpose.

The Applicant has set itself the objective of creating a mode of embossing improving the absorption properties of cotton wool paper cellulose.

The Applicant has also set itself the objective of creating a embossing mode producing an attractive and attractive visual effect at the same time.

• les alvéoles sont disposés selon au moins un alignement
• les côtés en vis à vis de deux alvéoles adjacentes définissent un pont à bords rectilignes ou sensiblement rectilignes, de longueur L supérieure à sa plus grande largeur D, le dit pont reliant préférentiellement deux secondes zones non gaufrées, disposées de part et d'autre d'au moins une première zone gaufrée.

According to the invention, this objective is achieved with a cellulose wadding sheet comprising at least a first embossed zone having protuberances on one side corresponding to cells on the other face, the cells having a base of substantially polygonal shape. , and at least one second non-embossed zone, characterized in that

• the cells are arranged in at least one alignment
• the opposite sides of two adjacent cells define a bridge with rectilinear or substantially rectilinear edges, of length L greater than its greatest width D, the said bridge preferably connecting two second non-embossed zones, arranged on either side d '' at least a first embossed zone.

We call "bridge" the part which is between two cells adjacent. In a preferred arrangement of the invention, the bridges have straight edges. The edges of the bridges can be curved without leaving the part of the invention. The edges are preferably parallel but they can also be slightly tilted relative to each other, as it will be explained in more detail below.

We define the width D of the bridge by the distance between the edges of two adjacent cells. When the edges are not parallel, we consider the average distance along the bridge.

In this case, the width can vary in a plane parallel to the surface of the sheet. The width of the bridge can also vary in a plane perpendicular to the leaf surface, between the leaf surface in top of the cell and the bottom of the cell. The largest width is determined both in the plane parallel to the surface of the sheet and in the plane perpendicular to the surface of the sheet.

This width can be very small when the bridges are not planar but are curved transversely, which is the most frequent.

The structure according to the invention is new compared to that that can be found in the state of the art. Surprisingly, we notes that the bridges stand out visually and create a pattern distinct from the pattern from the alveoli, while in the patterns of the prior art, the pattern apparent was that of the alveoli themselves. The embossed motif of the invention evokes a textile product with an embroidered ornament. Indeed, the bridge with its rectilinear edges, evokes the gathering of several fibers or threads of a woven or simply textile product.

In particular, the sheet of the invention has at least three distinct levels of relief which bring out the motif defined by the cell alignments.

A first level corresponds to the bottom of the cells, a second level corresponds to the non-embossed area and a third level to the surface bridges.

This solution differs from the prior art where the alveoli, protrusions respectively, forming alignments, have a oval or round base. Admittedly, in this case too, we see that between two adjacent cells, the level of the leaf is lower than that of the second zone, but this part has a rounded hollow shape which cannot be compared to a bridge. The invention makes it possible to create frank breaks in level, sources of contrast. The edges formed by these edges, straight or substantially straight, also contribute to enhance the contrast effect.

Preferably, the cellulose wadding sheet is such that the L / D ratio is greater than 1, preferably greater than 1.5, and in particular greater than 3.

The sheet can also be characterized in that the distance between two adjacent first zones (A ₁ , A ₂ ), separated by an unembossed zone (B) is between one and three times, preferably between one and two times , the width of said first zones (A ₁ , A ₂ ).

Embossed paper with a pattern of square cells is already known. For example, US Patent 4,293,990 describes an embossed sheet of paper for wiping. The embossing consists of flat portions separated by valleys. The distance (width and length) between the cells is always the same in this case. Bridges do not exist. In addition, well that the sides of the valleys are straight, we do not find in this pattern of part corresponding to the second zones of the invention, therefore a fortiori three areas at different levels.

In particular, according to one embodiment, the section cells can be triangular with the advantage of having these in alignments forming portions of curves without losing ownership of bridges.

Advantageously, the slope (α) of at least one of the walls of the cells measured with respect to the vertical to the plane of the sheet is included between 20 ° and 45 °.

In addition, the linear density of the cells is between 2 and 20 per cm; their surface density is between 4 and 50 per cm ² , preferably between 4 and 20 per cm ² .

The sheet according to the invention can be associated with a second sheet of cellulose wadding to form a sheet of double thickness.

So the second sheet can be a cellulose wadding sheet, of the type blown through.

In accordance with an advantageous characteristic of the invention, the alignments are concentric.

The cylinder for the embossing of a sheet comprises pins with polygonal base forming alignments in which two pins adjacent are arranged so that two respective sides of the base polygonal of said two pins are arranged opposite one another and are substantially parallel to each other.

Preferably, the pins have a triangular base.

The cylinder according to the invention is in particular characterized by the fact that the angle (β) defined by the said two sides of the pins substantially parallels is between 0 and 35 °.

Preferably, each of the faces of the pins form an angle (α) between 20 and 45 ° with a plane perpendicular to a generator of the cylinder defined at the level of said face.

The process for making a sheet, whereby a sheet on an engraved embossing cylinder, of course is part of the present invention.

The invention also relates to the method for obtaining in particular the product defined above. Surprisingly, we see that it is possible to make a pattern comprising alignments cells forming such a relief on three levels, embossing the cotton wool cellulose on an engraved cylinder with a single depth level of engraving. This avoids the complex and expensive engravings of cylinders.

• la figure 1 représente schématiquement une installation de gaufrage,
• la figure 2 représente une partie d'un exemple de motif de gaufrage du cylindre conforme à l'invention,
• la figure 2 A est une partie agrandie de la figure 2,
• la figure 3 est une représentation en perspective d'un picot du motif de la figure 2,
• la figure 4 représente une vue partielle photographique, en perspective, d'un produit gaufré selon le motif de la figure 2,
• la figure 5 représente une vue photographique, en perspective, d'un produit gaufré de l'art antérieur,
• la figure 6 représente une vue photographique, en perspective, d'un produit gaufré selon un autre mode de réalisation de l'invention,
• la figure 7 montre un graphique sur lequel on a reporté des vitesses d'absorption mesurées sur un produit de l'invention et sur un produit de l'art antérieur.

Other advantages and characteristics will become apparent on reading the following description of a nonlimiting embodiment of the invention, accompanied by drawings in which:

• FIG. 1 schematically represents an embossing installation,
• FIG. 2 represents part of an example of the embossing pattern of the cylinder according to the invention,
• FIG. 2 A is an enlarged part of FIG. 2,
• FIG. 3 is a perspective representation of a pin of the pattern in FIG. 2,
• FIG. 4 represents a partial photographic view, in perspective, of an embossed product according to the pattern in FIG. 2,
• FIG. 5 represents a perspective photographic view of an embossed product of the prior art,
• FIG. 6 represents a perspective photographic view of an embossed product according to another embodiment of the invention,
• FIG. 7 shows a graph on which absorption rates measured on a product of the invention and on a product of the prior art have been reported.

Figure 1 gives a schematic representation of an element of an industrial unit for embossing plies of cellulose wadding and transform into a sheet of product for sanitary or domestic use. This element comprises an embossing cylinder 1, generally made of metal, with a surface engraved according to the desired embossing pattern, and a cylinder 2 coated with rubber or any other material liable to deform. Both cylinders have parallel axes of rotation and roll on top of each other. We guides the sheet of cellulose wadding between the two cylinders at the same time time that drive means rotate the two cylinders in opposite direction relative to each other, and pusher means bring together the two cylinders from each other under a determined force. By deforming in the contact area, the rubber follows the relief of the engraving of the first cylinder 1. The sheet 3 placed between the two cylinders undergoes the same deformation. The engraving consists of pins 10, which we see at an enlarged scale compared to the diameter of the cylinder, distributed according to the chosen motif. The width of the contact area between the two cylinders, which forms a rectangular band, is designated by the term imprint and is expressed in centimeters.

In Figure 2, there is shown, in top view, a portion of the pattern engraved on cylinder 1 and in accordance with an embodiment of the invention.

This pattern can preferably consist of pins 10 with a triangular base. The pins are placed in alignments A ′ ₁ , A ′ ₂ which in this example are essentially in arcs of a circle and constitute the first embossed zones A ₁ , A ₂ . Between two alignments A ' ₁ , A' ₂ , there is a second zone B 'which does not have pins 10.

The pins preferably have a pyramidal shape with triangular base as seen more precisely in Figure 3. Their vertex is not pointed and is truncated. It forms a flat. The height (H) spikes is measured from their top to the bottom of the engraving and varies from about 0.1 to 2.5 mm. It depends on the intended application.

Preferably, we choose a lower height for the products which aim for a soft touch such as toilet paper or towels table. On the other hand, for a product which we want to make the most of absorption capacity of cellulose wadding, we choose a height H more high.

The faces of the adjacent spikes in the form of pyramids may have different or identical slopes. Their base is polygonal or substantially polygonal and two adjacent pins are arranged in such a way so that their bases have 2 parallel rectilinear sides or substantially parallel as defined below.

The angle (α) (as visible in Figure 3) of the slopes of the pins is preferably between 20 ° and 45 °, measured relative to the vertical of the base of the pin and which on the cylinder is perpendicular to the axis of this latest.

Finally, although the pin 10 in FIG. 3 for example has edges frank, it is also within the scope of the invention to provide pyramidal spikes with rounded edges. Other forms of pins with a polygonal base can be considered as trapezoids, diamonds ....

According to the embodiment shown, the pins on the same alignment are arranged so that the vertices 101, 102 of any two adjacent pins can be slightly offset from the general direction of alignment. As illustrated in particular in FIG. 2 at the level of the alignment zones A ' ₁ or A' ₂ .

Considering the space provided between two pins, we observe that this is defined by the sides 101m and 102m of their triangular base. Preferably, the two adjacent sides 101m, 102m of two spikes form an angle (β) between them which, in accordance with a characteristic of the invention is between 0 ° and 35 °: cf. figure 2A

Here, in the case of triangular-based pins arranged in an arc, two adjacent pins are oriented in an opposite direction. In others terms, a first and a third spike of the alignment are oriented towards the center of the circle defined by the alignment while the second pin arranged between the first and the third is oriented towards the outside of the defined circle by alignment and is inserted between the first and second pins.

The angle (β) formed by the two sides is preferably less than 35 ° so that it can form a bridge on the embossed product. The distance between two successive pins is quite small. It is such that, on the product embossed, the length L of the bridge part is related to its width D greater than 1, but the result is more marked with a ratio higher, 1.5 for example, 2 or 3 in particular.

By the width D, it is necessary to understand the distance between two sides of two adjacent cells. This width can be taken at one level any one between the base and the top of the cell; the width D thus varies according to the angle (α).

The length L of a bridge corresponds substantially to the length of two adjacent sides 101m, 102m of two neighboring pins 10.

The embodiment of the patterns of the invention is of interest especially when the folds are arranged in nested mode and the first zones separated from each other by second non-embossed zones substantially equal. The widths are preferably equal in this layout because there is then a very clear difference in level between the first and second zones.

Without departing from the scope of the invention, two or more than two alignments can be adjacent, i.e. close to each other, to form a embossed area which itself is surrounded by unembossed areas. Bridges are thus created, between the cells of the different alignments, which allow communication from an unembossed area to a another non-embossed area disposed on the other side of the embossed area.

In Figure 4, there is shown a partial perspective view of a product obtained by embossing on a cylinder with the motif of the figure 2.

We recognize the cells 101 'and 102' arranged in alignments A ₁ , A ₂ here in the form of circles. The cells are separated by parts forming p zigzag bridges according to the pattern of the embodiment shown. It is observed that the bridges P are curved and do not have a flat upper surface. This comes from the small spacing between the protrusions placed along the alignments. When embossing, the paper does not touch the bottom of the engraving. The protuberance alignments are separated by unembossed areas B. It is observed that the bridges are at a level slightly set back from that of the zones B. This relief accentuates the contrast between the embossed zones A ₁ , A ₂ and the non-embossed zones B.

Thus (see Figures 4 and 6), we observe the formation of very bridges visible. Each bridge P has a length L and a width D. Des additional patterns thus created give a new effect to the product.

Not only a visual effect of contrast is obtained but a technical improvement of the product has been highlighted concerning absorption properties.

It was surprisingly observed that the products according to the invention exhibited significantly improved absorption properties.

This effect is very advantageous in particular for the use of the sheet as a paper towel.

Thus, we were able to demonstrate by different tests that not only the absorption capacity is increased, the diffusion of the liquid is thus improved both in the cross direction and in the running direction and finally, the rate of absorption of liquids by the sheet according to the invention is superior to the products of the prior art.

1) Test de mesure de la capacité d'absorption et de la vitesse d'absorption sous pression Pour ce test, l'échantillon est posé à plat sur une plaque poreuse en verre fritté dont la taille des pores a été déterminée à 40 µm. Un plateau portant des poids est posé sur l'échantillon. L'échantillon est ainsi légèrement comprimé. La plaque poreuse repose sur un plateau qui comporte un orifice en son centre dans lequel débouche par en dessous un tube souple. Le tube souple met de cette façon le volume de la plaque poreuse en communication avec un réservoir de liquide dont le niveau peut être ajusté en hauteur par rapport à celui de la plaque poreuse. Le réservoir est lui-même posé sur une balance. Ce moyen permet de connaítre la quantité de liquide qui est passée dans l'échantillon quand on a soulevé le réservoir par rapport à la plaque poreuse.Le liquide est en général de l'eau à 9g/l de chlorure de sodium.La procédure consiste à imprégner l'échantillon au travers de la plaque poreuse en abaissant le niveau de l'échantillon par rapport au réservoir. On mesure la quantité de liquide absorbée simplement en mesurant la perte d'eau dans le réservoir. On procède avec différents poids.On peut procéder à des mesures de capacité d'absorption également sans pression.Les échantillons étaient les suivants

• Référence L1, un papier essuie-tout gaufré, composé de deux plis de grammage 23g/m² chacun disposés en position nested l'un par rapport à l'autre. Il est actuellement commercialisé par la société Georgia-Pacific. Le produit est représenté en photographie sur la figure 5. Les alvéoles PA₁ sont circulaires et disposés en cercles concentriques laissant entre eux des zones non gaufrées PA₂
     Diamètre des alvéoles : 1 mm, mesuré au fond
     Nombre d'alvéoles par cm²: 7 environ.
     Nombre d'alvéoles le long d'un alignement : environ 4 par cm linéaire.
• Référence M1, même papier de base que celui de la référence L1, mais gaufré conformément à l'invention et composé également de deux plis.

Les alvéoles ont une base triangulaire équilatérale dont les côtés ont 1 mm de long. Le produit est celui représenté en photographie à la figure 4.
   Les alvéoles sont disposés en cercles concentriques selon le motif de la figure 2. La densité du motif est la même que pour la référence L1. On trouve le même nombre par unité de surface et le même nombre par unité de longueur, le long des alignements.

• Référence N1, on fabrique une feuille composée de deux plis à partir du même papier et avec un motif unitaire composé des mêmes alvéoles que dans le cas MB1, mais la disposition des alignements n'est plus en cercles. Les cercles sont remplacés par des hexagones.
  Le produit est représenté sur la figure 6 et donne un effet de motif différent.

Le tableau ci-dessous rapporte les valeurs de l'absorption mesurée successivement pour des pressions croissantes de 5, 55 et 105g/cm² puis revenant à une pression de 5 g/cm². On note que la valeur de 5 g/cm² correspond, estime-t-on, à la pression à laquelle est soumis le papier essuie-tout en utilisation normale.Les caractéristiques du papier tissue, de base avant gaufrage, papier 1 ainsi que celle des papiers en ouate de cellulose L1, M1, N1 sont rassemblées sur le tableau ci-dessous. Grammage g/m² Ep. mm Résistance à la traction sèche N/m/2plis Résistance à la traction humide N/m/2plis Absorption (g/g) sous différentes pressions (g/cm²) SM ST SM ST 5 55 105 5 Papier 1 46 0,18 1151 627 307 174 3,8 3,2 2,9 3,4 L1 6,2 3,2 2,7 3,8 M1 6,7 3,4 2,8 4,0 N1 6,6 3,4 2,8 4,0 Le grammage est exprimé en g/m². L'épaisseur est mesurée sur une pile de 12 feuilles et ramenée à une feuille. La résistance à la traction est mesurée sur des éprouvettes, découpées dans une feuille à deux plis, de 5 cm de large, et est rapportée en N/m. l'absorption est mesurée en gramme de liquide absorbé par gramme de papier (g/g)On observe pour les références M1 et N1 de l'invention une amélioration de l'absorption par rapport à un motif constitué d'alvéoles à base circulaire (réf. L1). L'amélioration est plus marquée à faible charge, soit 5 g/cm². Cela s'explique par le fait que l'effet du motif diminue avec l'augmentation de la pression d'appui sur la feuille d'essuie-tout. On constate cette même différence entre les feuilles gaufrées et le même papier non gaufré.

2) On a procédé à un deuxième test, dit de diffusion, destiné à évaluer la capacité de mouillage d'un échantillon par diffusion de liquide. En général, le liquide est de l'eau salée à 0,9 %. Les échantillons de forme rectangulaire (par exemple 12 cm x 2,5 cm) sont placés sur un plateau inclinable et des électrodes (espacées d'1 cm) sont disposées sur chaque échantillon dont une extrémité est plongée dans l'eau. L'ensemble des électrodes est relié à un ordinateur qui enregistre notamment le temps à chaque cm mouillé. Un programme met en forme ces données, ce qui permet d'obtenir le tableau suivant : la première ligne de chiffres (de 1 à 9) correspond au nombre de cm mouillés. Dans ce tableau, L correspond à un produit connu ; M et N correspondent respectivement aux produits M1 et N1 du test d'absorption Temps de diffusion sens SM (s) Temps de diffusion sens ST (s) 1 2 3 4 5 6 8 9 1 2 3 4 5 6 8 9 L 0,8 3,3 7,7 16 25 36 64 86 0,7 2,5 5 7,7 12 16 28 36 M 1,1 3,9 6,9 15 21 28 52 66 1 2,9 5,5 10 14 19 34 43 N 1,2 3,7 8,8 13 21 29 56 68 0,9 2,6 4,6 8 14 20 33 42 On observe que pour les produits M et N comportant le motif de l'invention, les temps de diffusion dans le sens marche et dans le sens travers sont plus proches l'un de l'autre que ceux du produit L. Cela signifie que le liquide diffuse plus efficacement dans toutes les directions que sur un produit L présentant un motif de gaufrage de l'art antérieur.

3) On a procédé à un test de vitesse d'absorption visant à vérifier dans quelle mesure la géométrie des alvéoles et leur alignement permettant la création de ponts intervenaient dans le processus d'absorption. On dispose un cylindre horizontal au dessus d'une lame revêtue de teflon. On fixe une feuille de papier sur le cylindre face à la lame. On dépose un goutte d'eau colorée sur la lame et on approche lentement cette dernière de la feuille qui se trouve sur le cylindre. On éclaire fortement la goutte et on enregistre au moyen d'une caméra que l'on déclenche juste avant l'absorption. La durée maximum de l'enregistrement est de 5,4 secondes avec une image toutes les 4 ms.Les images obtenues permettent de mesurer l'évolution du diamètre de la goutte au cours du tempsOn mesure le temps mis par une goutte qui se trouve sur la lame pour passer à l'intérieur du substrat papier, et on répète l'opération autant de fois qu'il est nécessaire pour obtenir un échantillonnage de résultats représentatifs statistiquement. On a procédé à ces mesures sur des échantillons des mêmes papiers que dans les exemples précédents en deux endroits différents. On a d'abord mesuré le temps d'absorption par le papier aux points PI₁ (figure 4) et PA₁ (figure 5) dans la zone centrale des motifs, puis aux points PI (figure 4) et PA (figure 5) c'est à dire dans la zone non gaufrée (mais correspondant à une zone gaufrée du second pli).On a pu ainsi mesurer le temps moyen d'absorption des gouttes. Sur la figure 7 on a tracé les courbes d'absorption du diamètre d'une goutte dans le temps.Ces quatre courbes indiquent chacune l'évolution en pourcentage du diamètre d'une goutte en fonction du temps, la goutte étant initiée en différents endroits de deux types de feuilles.

• Courbe 1 est la trace pour une goutte initiée au point PA1 de la figure 5
• Courbe 2 est la trace pour une goutte initiée au point PI1 de la figure 4
• Courbe 3 est la trace pour une goutte initiée au point PA2
• Courbe 4 est la trace pour une goutte initiée au point PI2.

Ainsi, il apparaít que, aux points comparables d'initiation, le diamètre d'une goutte diminue plus rapidement lorsqu'elle est appliquée sur un produit de l'invention. On peut en déduire que la vitesse d'absorption des liquides appliqués en surface est plus rapide.On observe que l'amélioration de la vitesse d'absorption est obtenue en surface du pli aussi bien sur une zone gaufrée que sur une zone qui elle-même n'est pas gaufrée. En fait, il faut prendre en considération le pli sous-jacent qui respectivement est gaufré et non gaufré. L'invention a donc un effet global sur la feuille double (comprenant deux plis).

Tests have been carried out aimed at showing that products in accordance with the invention have an improved absorption capacity compared to products of the prior art.

1) Test for measuring the absorption capacity and the speed of absorption under pressure For this test, the sample is placed flat on a porous sintered glass plate, the pore size of which has been determined at 40 μm. A weighing plate is placed on the sample. The sample is thus slightly compressed. The porous plate rests on a plate which has an orifice in its center into which opens out from below a flexible tube. The flexible tube in this way puts the volume of the porous plate in communication with a liquid reservoir whose level can be adjusted in height relative to that of the porous plate. The tank is itself placed on a scale. This means it is possible to know the quantity of liquid which has passed into the sample when the reservoir has been raised in relation to the porous plate. The liquid is generally water containing 9 g / l of sodium chloride. The procedure consists impregnating the sample through the porous plate by lowering the level of the sample relative to the reservoir. We measure the amount of liquid absorbed simply by measuring the loss of water in the tank. We use different weights. We can also measure absorption capacity without pressure. The samples were as follows

• Reference L1, an embossed paper towel, composed of two 23g / m ² grammage plies each arranged in a nested position relative to each other. It is currently marketed by the Georgia-Pacific company. The product is represented in photography in FIG. 5. The cells PA ₁ are circular and arranged in concentric circles leaving between them unembossed zones PA ₂
  Cell diameter: 1 mm, measured at the bottom
  Number of cells per cm ² : about 7.
  Number of cells along an alignment: approximately 4 per linear cm.
• Reference M1, same basic paper as that of reference L1, but embossed in accordance with the invention and also composed of two folds.

The cells have an equilateral triangular base, the sides of which are 1 mm long. The product is that shown in photography in Figure 4.
The cells are arranged in concentric circles according to the pattern in Figure 2. The density of the pattern is the same as for the reference L1. We find the same number per unit area and the same number per unit length along the alignments.

• Reference N1, we make a sheet composed of two folds from the same paper and with a unitary pattern composed of the same cells as in case MB1, but the arrangement of the alignments is no longer in circles. The circles are replaced by hexagons.
  The product is shown in Figure 6 and gives a different pattern effect.

The table below reports the absorption values measured successively for increasing pressures of 5, 55 and 105 g / cm ² then returning to a pressure of 5 g / cm ² . Note that the value of 5 g / cm ² corresponds, it is estimated, to the pressure to which the paper towel is subjected in normal use. The characteristics of tissue paper, basic before embossing, paper 1 as well as that of the cellulose wadding papers L1, M1, N1 are collated in the table below. Weight g / m ² Thickness mm Dry tensile strength N / m / 2 ply Wet tensile strength N / m / 2 ply Absorption (g / g) under different pressures (g / cm ² ) SM ST SM ST 5 55 105 5 Paper 1 46 0.18 1151 627 307 174 3.8 3.2 2.9 3.4 L1 6.2 3.2 2.7 3.8 M1 6.7 3.4 2.8 4.0 N1 6.6 3.4 2.8 4.0 The grammage is expressed in g / m ² . The thickness is measured on a stack of 12 sheets and reduced to one sheet. The tensile strength is measured on test pieces, cut from a two-ply sheet, 5 cm wide, and is reported in N / m. absorption is measured in grams of liquid absorbed per gram of paper (g / g) An improvement in absorption is observed for the references M1 and N1 of the invention compared to a pattern made up of circular-based cells ( ref. L1). The improvement is more marked at low load, ie 5 g / cm ² . This is explained by the fact that the effect of the pattern decreases with the increase in the pressing pressure on the paper towel. This same difference is noted between the embossed sheets and the same unembossed paper.

2) A second so-called diffusion test was carried out, intended to evaluate the wetting capacity of a sample by liquid diffusion. In general, the liquid is 0.9% salt water. The rectangular-shaped samples (for example 12 cm x 2.5 cm) are placed on a tilting tray and electrodes (spaced 1 cm apart) are placed on each sample, one end of which is immersed in water. All of the electrodes are connected to a computer which records in particular the time at each wet cm. A program formats these data, which makes it possible to obtain the following table: the first line of figures (from 1 to 9) corresponds to the number of wet cm. In this table, L corresponds to a known product; M and N correspond respectively to the products M1 and N1 of the absorption test Diffusion time direction SM (s) ST direction diffusion time (s) 1 2 3 4 5 6 8 9 1 2 3 4 5 6 8 9 The 0.8 3.3 7.7 16 25 36 64 86 0.7 2.5 5 7.7 12 16 28 36 M 1.1 3.9 6.9 15 21 28 52 66 1 2.9 5.5 10 14 19 34 43 NOT 1.2 3.7 8.8 13 21 29 56 68 0.9 2.6 4.6 8 14 20 33 42 It is observed that for the products M and N comprising the motif of the invention, the diffusion times in the forward direction and in the transverse direction are closer to each other than those of the product L. This means that the liquid diffuses more effectively in all directions than on a product L having an embossing pattern of the prior art.

3) An absorption speed test was carried out to verify to what extent the geometry of the cells and their alignment allowing the creation of bridges intervened in the absorption process. There is a horizontal cylinder above a teflon-coated blade. A sheet of paper is fixed on the cylinder facing the blade. A drop of colored water is placed on the slide and the slide is slowly approached from the sheet on the cylinder. We strongly illuminate the drop and record by means of a camera which is triggered just before absorption. The maximum duration of the recording is 5.4 seconds with an image every 4 ms. The images obtained make it possible to measure the evolution of the diameter of the drop over time. We measure the time taken by a drop that is on the blade to pass inside the paper substrate, and the operation is repeated as many times as necessary to obtain a sampling of statistically representative results. These measurements were carried out on samples of the same papers as in the previous examples in two different places. We first measured the absorption time by the paper at points PI ₁ (figure 4) and PA ₁ (figure 5) in the central area of the patterns, then at points PI (figure 4) and PA (figure 5) i.e. in the non-embossed area (but corresponding to an embossed area of the second fold). We were thus able to measure the average absorption time of the drops. In FIG. 7, the absorption curves of the diameter of a drop have been plotted over time. These four curves each indicate the percentage change in the diameter of a drop as a function of time, the drop being initiated in different places. of two types of leaves.

• Curve 1 is the trace for a drop initiated at point PA1 in Figure 5
• Curve 2 is the trace for a drop initiated at point PI1 in Figure 4
• Curve 3 is the trace for a drop initiated at point PA2
• Curve 4 is the trace for a drop initiated at point PI2.

Thus, it appears that, at comparable points of initiation, the diameter of a drop decreases more quickly when it is applied to a product of the invention. We can deduce that the absorption speed of the liquids applied on the surface is faster. We observe that the improvement of the absorption speed is obtained at the surface of the fold both on an embossed area and on an area which it- not even embossed. In fact, consideration must be given to the underlying fold which is embossed and unembossed respectively. The invention therefore has an overall effect on the double sheet (comprising two plies).

Claims (15)

Cellulose wadding sheet comprising at least a first embossed zone (A ₁ , A ₂ ) with protuberances on one side corresponding to cells (101 ', 102') on the other face, the cells having a form base substantially polygonal, and at least one second non-embossed zone (B), characterized in that the cells (101 ', 102') are arranged in at least one alignment the opposite sides of two adjacent cells define a bridge (P) with rectilinear or substantially rectilinear edges of length L greater than its greatest width D, said bridge preferentially connecting two second non-embossed zones (B) separated by at least one first embossed area (A ₁ , A ₂ ). Cellulose sheet according to the preceding claim, characterized in that L / D is greater than 1, preferably greater than 1.5, and in particular greater than 3. Sheet according to one of the preceding claims, characterized in that the distance between two adjacent first zones (A ₁ , A ₂ ), separated by an unembossed zone (B), is between one and three times, preferably between once and twice, the width of said first zones (A ₁ , A ₂ ). Cellulose wadding sheet according to any one of the preceding claims, characterized in that the base of the said cells (101 ', 102') is triangular. Cellulose wadding sheet according to one of the preceding claims, characterized in that the slope (α) of at least one of the walls of the cells measured with respect to the vertical to the plane of the sheet is between 20 ° and 45 °. Cellulose wadding sheet according to one of the preceding claims, characterized in that the density of the cells is between 4 and 50 per cm ² and preferably between 4 and 20 per cm ² . Cellulose wadding sheet according to any one of the preceding claims, characterized in that the linear density of the cells is between 2 and 20 per cm. Cellulose wadding sheet according to one of the preceding claims, characterized in that it is associated with a second cellulose wadding sheet to form a sheet of double thickness, Cellulose wadding sheet according to the preceding claim, characterized in that the second sheet is a cellulose wadding sheet, of the type blown through. Cellulose sheet according to any one of the preceding claims, characterized in that said alignments are concentric. Roller for embossing a sheet according to one of the preceding claims, characterized in that it comprises pins (10) with a polygonal base forming alignments (A ' ₁ , A' ₂ ), in which two pins ( 101, 102) adjacent are arranged so that two respective sides (101m, 102m) of the polygonal base of said two pins are arranged opposite one another and are substantially parallel to each other. Cylinder according to the preceding claim, characterized in that the pins (10) have a triangular base. Cylinder according to one of claims 11 or 12, characterized in that the angle (β) between said two sides (101 m, 102 m) substantially parallel to the pins (101, 102) is between 0 and 35 ° . Cylinder according to one of Claims 11 to 13, characterized in that each of the faces of the pins form an angle (α) between 20 and 45 ° with a plane perpendicular to a generatrix of the cylinder defined at the level of said face. Method for manufacturing a sheet according to one of Claims 1 to 10, according to which the sheet is pressed on an engraved embossing cylinder (1), characterized in that the cylinder (1) is defined according to any one of Claims 11 to 14.

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