EP1362953B1 - Process for marking a paperweb, paperweb having a watermark pattern - Google Patents

Abstract

The marking procedure, for use on paper with at least one layer of cellulose wadding, consists of deforming the paper under pressure between a first rigid roller (1) with a smooth surface, and at least one secondary rigid roller (2) with relief elements, and includes the cold application of an additive coating that promotes the formation of a watermark on at least one surface of the paper or rollers during the marking operation. The additive is based on mineral oil, e.g. a white mineral oil with a dynamic viscosity of 15 - 80 mPa.s. at about 25 deg C, and can be applied by spraying, atomisation or coating at a preferable rate of 0.2 and 0.5 per cent by weight in relation to the paper. The motifs formed by the roller relifs are preferably between 30 and 40 sq mm in area each.

Description

The present invention relates to the field of papers for sanitary purposes or domesticated. Examples include toilet paper, paper towels or any paper wiping, napkins, etc.

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 cylinder 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.

The subject of the invention is a process for marking a sheet consisting of one or several folds of cellulose wadding to obtain a pattern simulating a watermark.

The term marking refers to the compression of certain parts on one side of the sheet to thereby form compacted areas, and significantly reduce its thickness in these areas, without forming a corresponding relief on the opposite side of the sheet.

A watermark is the impression of a drawing in the thickness or body of the paper, which is visible by transparency. The watermark is called "wet" or "true" watermark when it is produced during the manufacture of the paper, in the wet phase of the process before drying. It is produced, for example, by the imprint of a pattern on a cylinder rotating in contact with the still wet sheet.

A dry or simulated watermark is an impression of appearance similar to a true watermark, produced on paper after its manufacture. We have already proposed various embodiments, but generally suitable for different applications of papers for sanitary or domestic use.

The applicant, in its patent EP-B-0 864 014, proposed the application of a motive pattern simulating a watermark to a sheet of absorbent paper made of cellulose wadding. The method consists in deforming the sheet under stress by passing between a hard etched roll and a receiving roll having a surface hardness greater than 40 Shore D under a specific pressure of at least 150 kg / cm ² with a marking speed of at least 50m / min. Preferably, the engraved cylinder is made of steel and heated to a temperature ranging from 50 ° C. to 100 ° C. A small quantity of water is optionally provided.

The method makes it possible to obtain a product with a pattern simulating a watermark, the marked surface being smooth, shiny and translucent with a small thickness compared to its extent.

US Patent 4,166,758 discloses a method for making transparent paper of submitting a sheet in the wet state under pressure by means of a cylinder engraved heated.

Patent Application WO 94/06623 describes the marking of a paper for sachet of tea with application of a melt additive to improve the appearance of the pattern and the sheet resistance.

Patent application WO 01/47699 describes a method for binding several plies tissue paper on which a lotion is applied. According to this process, one exercises a hot pressing by means of heated cylinders.

The applicant has sought to improve its previous process, and in particular to to obtain a strongly contrasting filigree pattern without having to implement heating means.

The method of the invention achieves this objective.

The method of the invention for marking a pattern simulating a watermark on a sheet composed of at least one ply of cellulose wadding, consisting of deforming constrains the sheet between a first smooth surface rigid roll and at least one second rigid roller provided with relief elements, is characterized by the fact that it applies to a film of an additive based on mineral oil, favoring the formation of the watermark on at least one of the surfaces of the sheet during the marking operation.

The additive is applied on the surface and penetrates into the thickness of the sheet at the same it is distorted. It is applied cold, ie without heat outside, at room temperature. This results in an optimum result with Simple.

Preferably, the additive is applied to the first roll, to the elements relief of the second roll or on both rolls. In the latter case, we notice that the decoration stands out perfectly, both on the marked side and on the opposite side.

Different means of application of the additive can be envisaged: coating, spraying, atomization in particular. In the case of a spray, the additive may be applied directly to the roll or rolls during the marking operation. However according to an advantageous embodiment, the additive is applied by coating. The coating can be performed by means of a device comprising a screened cylinder. In the description which follows, the additive is applied by contact of the surface to be coated, here the rollers, with an absorbent means impregnated with the additive. The additive is then transferred from the surface (s) of the roll or rolls on the surface (s) of the sheet, during the operation of marking.

It suffices to apply a rather small quantity of additive, so that the finished product contains less than 1% by weight, preferably between 0.2 and 1% and preferentially still between 0.2 and 0.5% of additive in mass relative to the mass of the leaf.

Preferably, the additive is a white mineral oil, suitable for medicinal or food applications. Its dynamic viscosity at room temperature, of the order of 25 ° C, is between 15 and 80, preferably between 20 and 30 mPa.s, according to the NFT60-100 standard.

This process makes it possible to create patterns with various shapes. In particular, the elements in relief on the second roll form units unitary surface area between 20 and 50 mm ² and preferably between 30 and 40 mm ² . In particular, the raised elements comprise portions of continuous shape, preferably linear. Preferably, the ratio of the marked area to the total area of the sheet is less than 20%.

On the other hand, a force is exerted on the second roller corresponding to a linear pressure on the sheet of between about 20 and about 100 kg / cm 2, preferably between 40 and 90 kg / cml.

According to an advantageous embodiment, for the marking of a sheet of width included between 250 and 3200 mm, the sheet is deformed between a first roll extending across the width of the width of the sheet and at least one second roll of width between 15 and 90 mm.

In particular, a plurality of second rollers distributed over the length of the first roll. Each roll can be formed of an assembly of several discs.

The sheet obtained comprising at least one ply of cellulose wadding weighing between 10 and 45 g / m ² , having a marked zone simulating a watermark, is characterized in that it is impregnated with additive, in particular with mineral oil. Advantageously, the amount of additive is less than 1% by weight relative to the mass of the sheet.

• La figure 1 est une vue en perspective schématique d'un mode de réalisation de l'invention,
• La figure 2 est une coupe d'une feuille réalisée selon l'invention,
• La figure 3 est une illustration d'un décor sur une feuille selon l'invention.

The invention will be better understood on reading the following description, given by way of illustration and in no way limiting, with reference to the appended drawings in which:

• FIG. 1 is a schematic perspective view of an embodiment of the invention,
• FIG. 2 is a section of a sheet made according to the invention,
• Figure 3 is an illustration of a decor on a sheet according to the invention.

As seen in FIG. 1, a sheet 8 composed of at least one fold cellulose wadding, here two, is unwound from at least one coil. She is guided, via at least one detour or guide roll (not referenced) up to pass between a first roll 1 whose surface is smooth and a plurality of second rollers 2 provided with relief elements. The first roll presents a rotation axis YY '. The rollers 2 are etched and are for example mounted on a common axis XX ', which is parallel to YY'. It is also part of the the invention to have the second rollers 2 on two or more axes parallel. They can thus be arranged along two axes diametrically opposed, with the advantage of ensuring a better balancing of efforts exerted on the first roll 1. The second rollers 2 may each have a width between 15 and 90 mm, for example 80 mm. They can be spaced apart others to form decorated strips on the sheet to be treated.

The elements in relief on the engraved wheels 2 are of complex shape, continuous or formed of continuous assemblies (open or closed). Without leaving the framework of the invention, it is possible to wedge the knurls 2 so as to obtain a pattern which extends over all or part of the surface of the sheet. Between rolls 1 and 2, there is compression of the sheet 8. Means for exerting force on the second rolls corresponding to a linear pressure between about 20 and 100 kg / cm 2, preferably between 40 and 90 kg / cm 2.

Moreover, at this level, the sheet 8 is covered on at least one of its surfaces of an additive based on mineral oil, such as petroleum jelly. According to a mode of preferred embodiment, using a white mineral oil, medicinal or food, in any case suitable for use in direct, indirect or indirect food contact occasional. For example, an oil marketed under the trade name Primol is used. or Marcol by ESSO SAF. It is a colorless liquid whose viscosity dynamic at 25 ° C is advantageously between 20 and 25 mPa.s.

Means 3 and 4 for applying the additive are provided. These means may coat either the engraved rollers 2, the smooth roll 1, or the two types of rollers. Depending on the case, they are in contact with one and / or the other of said rolls.

The means 3 and 4 may be of any type known per se, with a reserve 5 for the additive and an absorbent material which makes it possible to transfer the additive from the reserve 5 to the associated roller 1 or 2. The absorbent material may be based on textile fibers with a density of between 200 and 450 g / m ² / mm, for example 225 g / m ² / mm.

With regard to the smooth roll 1, the additive is preferentially applied to its entire contact surface and oriented along the generator.

For the engraved rolls 2, using the coating means above, the vertices of the relief patterns are coated with additive. The process of the invention is particularly advantageous in installations which mark downtime after winding a log or rolls, known in the art as "Stop & go".

When the two surfaces of a sheet 8 are totally or partially impregnated with an additive, it is possible to obtain, for example, a product as schematized in section in Figure 2 with two layers 6 and 7 of additive. Advantageously, this double application of additive helps to reinforce the visual contrast of the patterns marked. Visual aspects and aesthetics are reinforced by the mechanical action of compressing the second means 2 against the sheet to be treated which, during this step, is impregnated with the additive based on mineral oil, and bears on the first medium (roll 1 smooth).

On the other hand, in a new and unexpected way, the visual contrast effect is really accentuated when the quantity of additive deposited and measurable on the sheet, is less than 1% by weight relative to the total mass of the sheet.

This quantity not only allows to have a visual contrast effect reinforced but also not to create traces or spots around the boundaries of the pattern. We obtain a product whose pattern is of excellent quality.

By way of illustration, the application pressure of the means 2 against the means 1 is at least 60 kg / cml (kg per linear cm measured along the generator of contact).

Advantageously, the elements in relief on the rollers 2 have surfaces of the order of 20 to 50 mm ² , and preferably 30 to 40 mm ² . They are arranged on the second roller 2 so that it remains in continuous support on the smooth roller 1 so as to avoid vibrations.

The patterns are of any shape, linear or not; an example is given on the Figure 3 where 9 feather patterns appear in dark on a light background. In made on a sheet of cellulose wadding, the patterns form a contrast with the bottom of the sheet 8.

The sheet 8 may be formed of one or more plies. In the latter case, notes an association of the folds between them in the zones containing the decor. of the wide sheets can be decorated by the method according to the invention. A example of decor is given in Figure 3.

An appropriate implementation of the invention then consists in providing at least a first set of etched means 2 arranged along a first axis XX ', and that a second set of engraved means arranged along a second axis different and parallel to the first (XX '), the axes being parallel to the axis YY' of the smooth roll 1. The first and second axes of the second engraved means can for example, to be arranged diametrically opposed with respect to the smooth roll. each of the first axes (XX '), the engraved means such as knurled wheels, are placed at a certain distance from each other. So, in case of damage or wear, the replacement of a wheel is easy. If they are arranged along two axes, the engraved rollers 2 are preferably placed in staggered rows.

The products covered by the invention are, for example, rolls of paper hygienic, napkins, towels or rolls for industrial wiping. In the case of products such as towels or towels table, a localized decoration for example at the edge of the product can be provided.

A decoration distributed over the entire surface of the product may, however, be provided for hygienic paper or industrial wiping applications.

Application tests of an additive, Marcol 82 oil, were carried out on a installation as shown in Figure 1 with coating on the rollers 1 and 2. The marking pressure was 60 kg / cml. The scroll speed of the sheet was 100 m / min.

Paper image analysis was carried out in the marked areas and the unmarked areas. It is thus possible to evaluate the contrast and the visibility of the watermark in determining the difference between the gray levels measured. This method is repeated patent EP 0864014 B1 of the Applicant. Results are reported in the table below.

Finally, the quantity of additive impregnated on the sheet, that is to say the percentages by mass of additive present in the sheet thus obtained by the device described. The measure consisted in extracting the additive by chloroform gravimetrically. This method is recalled below.

A control sample with additive and a sample without additive are made. We take 4 g of paper which is introduced into an extraction cartridge. We extract the additive by solvent with 50 ml of chloroform in a "Soxlhet" apparatus automatic. After a soaking step of half an hour and a rinse of a hour, the evaporation of the solvent takes place, and the rate of extract is quantified. The rate of additive corresponds to the rate of extract of the sample with additive reduced by Sample extract without additive. The quantities thus measured of additive are indicated in% in the table below.

The thickness of a sheet is determined according to ENV 12625-3 and is not increased by the process according to the invention. The thickness of the unlabelled base sheet is about 0.224 mm. Linear pressure Kg / cml Sheet speed m / min Thickness of the sheet mm Differences in gray levels Additive% face (6) face (7) 43.75 100 0.226 + - 0.01 34 36 0.37 65.62 100 0.237 + - 0.01 56 54 0.45 87.5 100 0.239 + - 0.01 60 54 0.35

The differences in gray levels measured on each of the faces illustrate the good visibility of the pattern simulating a watermark. In addition, training of a watermark both on the face coming into contact with the smooth roller and the engraved rolls.

The method described in patent EP 864014 consists in illuminating the sheet means of an optical fiber and a light diffuser, and to measure the level of gray using a CCD camera and a Leica Quantilet 600S image analyzer. We adjusts settings such as brightness and contrast. We delimit a surface to get an image. The image is divided into pixels. Each pixel of this surface has a gray level. The average value of all pixels in the image gives a value average gray level of the surface. In the gray scale, the white has a level 256 and black 0. The average gray level of a marked surface is measured in delimiting a small closed area. We delimit an unmarked area of surface corresponding to this marked area and measure the average level of Grey. We calculate the difference between the averages of the two images that we postpone In the picture. In common, a watermark is obtained when the value of the difference in gray levels is greater than 20.

Claims (16)

1. A method for marking a watermark-simulating pattern onto a sheet (8) comprising at least one ply of tissue paper, said method comprising deforming under stress said sheet against a rigid first roll (1) exhibiting a smooth outer surface and at least one rigid second roll (2) having salient elements, characterised by the fact that an unheated film of additive material comprising mineral oil is applied in such a manner so as to enhance watermark formation on at least one side of the sheet.
2. Method as claimed in claim 1, wherein the additive material is applied to the first roll (1).
3. Method as claimed in claim 1 or 2, wherein the additive material is applied to the salient elements of the second roll (2).
4. Method as claimed in claim 1, wherein the additive material is applied to both the first roll (1) and the second roll (2).
5. Method as claimed in any of the preceedings claims wherein the additive material is applied by spraying, atomizing, coating, or preferably by contact with an absorbent means impregnated with said additive material.
6. Method as claimed in any of the preceedings claims, wherein less than 1% by wt. preferably between 0,2 and 1 % most preferably between 0,2 and 0,5 % of additive material is applied relative to said sheet.
7. Method as claimed in claim 1, wherein the additive material is a white mineral oil having a dynamic viscosity at 25°C of between 15-80 mPa.s, preferably between 20-30 mPa.s.
8. Method as claimed in any of the preceedings claims, wherein the salient elements of the second roll subtend unit patterns exhibiting a surface of between 20-50 mm², preferably between 30-40 mm².
9. Method as claimed in any of the preceedings claims, wherein the salient elements comprise segments of a continuous shape.
10. Method as claimed in any of the preceedings claims, wherein a force corresponding to a linear pressure between 20-100 kg/cml, preferably between 40-90 kg/cml is exerted on the second roll (2).
11. Method as claimed in any preceedings claims, wherein the sheet is between 250 and 3200 mm wide, the first roll runs across a full width of said sheet, and at least one second roll is between 15 and 90 mm wide.
12. Method as claimed in any preceedings claims, wherein the sheet is deformed between the first roll and a plurality of the at least one second roll which are arrayed along a length of the first roll.
13. A sheet comprising at least one tissue paper ply having a specific surface weight between 10-45 g/m², said sheet being manufactured according to the method of one of the preceedings claims, said sheet exhibiting a marked zone simulating a watermark, characterised by the fact that it is impregnated with a mineral oil bond additive.
14. Sheet as claimed in claim 13, wherein the additive material is present at a zone of a marked surface in said sheet.
15. Sheet as claimed in claim 13 or 14, wherein the quantity of additive material is less than 1% by weight relative to said sheet.
16. Sheet as claimed in claims 13, 14 or 15, wherein a marked surface of the sheet relative to total sheet surface is less than 20%.

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