EP0648288A1

EP0648288A1 - Method for reducing fibre interaction in a tissue, and uses thereof, in particular for manufacturing multilayer tissues.

Info

Publication number: EP0648288A1
Application number: EP93914804A
Authority: EP
Inventors: Claude Lesas
Original assignee: Kaysersberg SA
Current assignee: Essity Operations France SAS
Priority date: 1992-07-03
Filing date: 1993-07-02
Publication date: 1995-04-19
Anticipated expiration: 2013-07-02
Also published as: FR2693213A1; ES2108283T3; FR2693213B1; WO1994001620A1; EP0648288B1

Abstract

A method for reducing fibre interaction in a tissue paper sheet produced by a wet paper making process. The method comprises the steps of treating the paper fibres with a polycationic product, and dispersing said fibres in a medium consisting of a foam obtained by finely dispersing air bubbles in a medium containing water and an anionic surface-active foaming agent.

Description

PROCESS FOR REDUCING THE INTERACTION BETWEEN FIBERS IN A TISSUE AND IMPLEMENTING THE SAME, IN PARTICULAR FOR MANUFACTURING MULTI-STRAT FABRICS

The present invention relates to a new process intended to reduce the interaction between fibers in tissue paper and the implementation of this process, in particular for the manufacture of multi-layered tissue paper.

Tissues or crepe paper based on cellulose wadding

10 find numerous applications in the household or domestic field. Depending on the intended applications, it is sought to control their mechanical properties, in particular their resistance, their feel to improve in particular their softness, their absorbent nature or their bulk.

15 For certain applications, it is sought to make sheets which, inside the same fold, have several layers of different properties and structures, for example a layer providing a fluffy effect on the surface of the sheet and a central layer providing bouffant. We know different processes

20 for the preparation of paper sheets by the wet method. All of them use a dispersion of the paper fibers in an aqueous medium.

A particularly advantageous improvement of this type of process with a view to improving the homogeneity of the dispersion of

25 fibers consists in using as an aqueous medium a foam obtained by the introduction of foamable, water-soluble surfactants, and in carrying out the dispersion of the fibers within this foam. Such processes called "foam processes" are in particular described in US patent 4443297.

In general, the sheets of crepe paper are prepared in machines of the FOURDRINIER type, for example or double cloth or other, from cellulose fibers previously dispersed in an aqueous medium and distributed over a cloth where the pulp is drained and then dried between rollers. Leaf,

35 after having been dried by passage through a hot air hood, is then creped and then calendered. It has been observed that the step of passing through the hot air hood induces on the face of the sheet situated on the hood side a certain roughness effect which is contrary to the generally desired softness effect.

The present invention, by offering a general solution for reducing the bonds between the fibers, makes it possible to provide a particular solution to the problem indicated above by providing ^r j with a means of obtaining a sheet whose fluffy effect on the surface is increased. due to the decrease in the bonds between the fibers in this zone.

Thus, the present invention provides a means which can be used in particular to improve the smoothness of the surface layer of a

10 multi-layer paper such as one can for example prepare using a paper machine with a multi-head box, known per se.

Thus, the present invention provides a solution to the problems in which it is sought to provide a gain in softness read either to the whole of a sheet, or to one of its layers.

In addition, the solution provided is very particularly compatible with the foam processes.

According to one of its essential characteristics, the invention relates to a process intended to reduce the interaction between fibers 20 in a sheet of tissue paper obtained in a wet papermaking technique, characterized in that it comprises a step for treating paper fibers by a polycationic product followed by a step of dispersing said fibers in a medium used to ensure the dispersion of the fibers consisting of a 2 * 3 foam resulting from the fine dispersion of air bubbles in a medium containing water and an anionic surfactant with foaming effect.

One such method in which the surfactant is used to generate a foam by absorbing air in the aqueous mixture will be referred to as a "foam" method.

The polycationic products useful according to the invention are advantageously nitrogen-based polymer compounds generally used in the prior art to improve the wet or dry resistance of the paper, or the retention of the fibers in the

35 paper.

By way of examples of such products, special mention will be made of the reaction products of amines and aminopolyamines with epichlorohydrin, polyacrylamides, polymers of the quaternary polyamine type having in particular a molecular mass of between 50,000 and 100,000.

Among the polycationic products useful according to the invention, mention will be made of commercial products such as, for example, the product marketed under the brand name KYMENE which is a reaction product of epichlorohydrin with a condensing polyamine obtained from adipic acid and di-ethylene-triamine and where the cationic sites are formed by conversion of the secondary amine into quaternary ammonium by alkylation of epichlorohydrin. This product, well known to those skilled in the art, is generally used as an additive intended to increase the characteristics of dry and wet resistance. Mention may also be made of the products sold under the trade mark CYPRO which are products of the reaction of epichlorohydrin on diinethylamine. We also know the product sold under the PAREZ brand which is a melamine formaldehyde resin. As far as the applicant can know, none of these products is currently used to obtain an unbinding effect from paper fibers. These polycationic products will be used in proportions such that a part of their positive sites is fixed on the negative sites carried by the cellulose fibers during the first stage of the process while the other part of these sites remains available to react during the step of dispersing the fibers with the negative sites carried by the anionic surfactant contained in the aqueous dispersion medium, thus leading to bridging between the fiber and the surfactant. As an anionic surfactant, any anionic surfactant known to a person skilled in the art can be used. Among the anionic surfactants with a foaming effect, mention will be made of sulfonates, sulfates, carboxylates and phosphates. It is advantageous to choose surfactants containing a long aliphatic hydrocarbon chain, for example a chain of

^C 10 ^'C 18- The process according to the invention is applicable to all types of cellulose fibers conventionally used for the preparation of tissue paper. We could in particular apply it to unrefined than refined pasta.

The amount of polycationic product used for the pretreatment of the fibers is determined according to the number of negative sites available on the cellulose and the more or less large unbinding effect sought.

This quantity will therefore depend essentially on the origin of the fibers used as well as on their degree of refining.

Thus, by way of example, with a resinous pulp with a fairly low calcium demand, therefore having few anionic sites available, the saturation of these anionic sites with the polycationic product will be reached for much lower doses than those observed with birch paste, for example, with a significantly higher calcium demand.

The effect of refining on the fiber is to generate new anionic sites. It is therefore understandable that this will have the consequence of requiring greater quantities of polycationic products to obtain the maximum delinking effect.

According to one of these advantageous variants, the invention relates to the use of the method, as just explained, within the framework of a method making it possible to obtain a multi-layer sheet and more particularly its use for improving the touch qualities of one of the external layers of such a product.

The Applicant has been able to observe that, in traditional systems for preparing paper sheets, the step of creping the sheet at the outlet of the drying hood induces a certain roughness on the face situated on the hood side of the sheet.

The Applicant has now discovered that by using a process allowing a multi-layer sheet to be produced and by implementing the process according to the invention as described above for the production of the layer situated on the side situated on the side hood of said sheet, one could compensate for the unpleasant effect noted on the hood side face and in particular create the fluffy character of touch generally desired.

Among the processes making it possible to produce multi-layered sheets, there will be mentioned in particular a process which uses a multi-jet injection system to arrange on the canvas successive layers of fiber suspensions of different compositions. In this process, a system consisting of a box of cloisonne head allows to send on the canvas three layers of fibrous suspension of different compositions. By using to form the hood side layer of the sheet fibers previously treated with a polycationic product and suspended in a medium containing an anionic surfactant, one obtains, on the surface of the paper, hood side, a layer whose fluffy character is found considerably increased.

Thus, using a conventional tissue machine provided with a headbox allowing multi-jet injection and intended for the preparation of multi-layer sheets, provided that a carrier fluid containing an anionic surfactant is used, we will prepare , for example, a multi-layer paper, one of the layers of which will contain fibers previously treated with a polycationic product, so as to obtain, in this layer, an increased unbinding effect of the fibers in accordance with the invention.

As an example, we will prepare a paper made up of three layers of different compositions, for example:

- the stratum, in contact with the drying cylinder, contains only pulp of softwood or hardwood which can be refined or not;

- the central stratum includes a non-negligible percentage of highly resilient wet pulp, which gives bulk to the leaf;

- Finally, the opposite layer, known as the hood side, is previously treated with a polycationic product. This product, which binds to the fibers, also reacts with the anionic surfactant to generate a product with a deliant effect.

This produces a sheet of tissue paper having on one of its faces a very fluffy appearance to overcome the rough appearance caused by the doctor blade of the paper machine.

In the example above, the surfactant is chosen from anionic foaming surfactants allowing the implementation of a process, of the "foam process" type.

The examples which follow, given without limitation of the present invention, clearly illustrate its principle by highlighting the unbinding effect obtained, characterized by the reduction in the breaking force of the sheets of tissue, during the implementation of the method of the invention. Examples

The examples which follow were carried out on different kinds of fibers, refined or not.

The tests were carried out on 25 g / m ² paper sheets prepared on a device of the FRANK type, known to those skilled in the art.

Example 1

In this example, the pretreatment of the fibers was carried out with a polycationic product of the quaternary polyamine type sold under the brand CYPRO by AMERICAN CYANAMID. This product is known from the prior art as a promoter used when it is desired to carry out bridging between cellulose and anionic materials; it is not known to have been used for the purpose of modifying the resistance properties, both wet and dry. The anionic surfactant chosen in the examples is an alpha-olefin sulfonate.

In the various tests, we firstly demonstrated the separate effect of the two treatments: pretreatment of the fibers with a polycationic product on the one hand, and action of an anionic surfactant on the other hand. We then show the unbinding effect obtained when implementing the process of the invention.

Effect of the polycationic product alone

This test was carried out on a FRANK machine with a softwood pulp, for three different concentrations of polycationic product (0.1 kg / t, 3 kg / t).

The observed breaking forces, represented in meters according to the usual standard, are recorded in Table I below. We also indicate in percentage how the breaking force varies compared to that (1676) observed with untreated fibers, for different quantities of polycationic product expressed in kg per ton of fibers. TABLE I

There is a slight gain in breaking strength, dry, on the unrefined dough, but this disappears after refining. Effect of the presence of a surfactant in the aqueous medium The tests were carried out in the presence of 200 pp of alpha-olefin sulfonate (designated here by AOS).

Table II below gives the values of the breaking forces (in meters), by comparing them with those obtained under the same conditions but in the absence of surfactant; it illustrates the reduction in the breaking forces linked to this treatment.

TABLE II

There is therefore a certain unbinding effect produced by the surfactant under the conditions of preparation of the sheet (FRANK machine).

It should be noted, however, that such an effect would not necessarily be observed with other conditions for forming the sheet (in an industrial paper machine for example).

Effect of the process according to the invention

Tables III and III 'below collate the results observed concerning the lowering of the breaking strength of different sheets of tissue paper obtained from different types of softwood or unrefined hardwood fibers (table

III) or refined softwood pulp (Table III ').

The sheets were formed with pastes treated beforehand by the addition of polycationic polymer at the rate of 1 and 3 kg / t of fibers respectively. The sheets were then formed in the presence of 200 ppm of anionic surfactant.

TABLE III

From these examples, it appears that the quantity of poly¬ cationic product is to be added as a function of the anionic sites available on the cellulose. If the paste has a high calcium demand, like the birch paste used, the unbinding effect increases with the dose of reagent.

The softwood pulp used has a fairly low calcium demand, so there are few sites available. These sites are already saturated with 1 kg / t of CYPRO and may be less (Table III). When this pulp is refined, new anionic sites are generated on the cellulose, which explains the additional deliant effect noted with 3 kg per ton (Table III '). Example 2 25 g / m ² formulas were prepared as before on a FRANCK type apparatus, with different unrefined hardwood pulps; these pastas are sold under the brands ALIZAY, KOTLAS, OSTRAND. TOFTE, respectively.

The following Table IV summarizes the values of the breaking length obtained for each of the pastes according to whether the formation was carried out in an aqueous medium or else in a foam medium. In the latter case, an anionic surfactant medium of the alpha-olefin sulfonate type was used. TABLE IV

The purpose of the test is to compare the results obtained with two polycationic agents: KYMENE, CYPRO, with those obtained with a cellulose unbinding agent of the prior art: a quaternary amine sold under the brand BEROL 595. The latter's formula is of the type:

RI CH3 -

\

N Cl ^'

R2 CH3

The products are added at 1, 3, 5, 10, 20 kg / t, counted commercial product, to ^'the pulp suspension in a water medium which was then added 200 ppm of anionic surfactant.

The break lengths were measured as a function of the amount of product added. The results are collated in Table V.

It is found that the effects are identical for each paste. KYMENE gives its maximum effect at 5 kg / T, then the resistances are constant.

CYPRO gives its maximum effect at 3 kg / T then the resistance is constant. Berol gives its maximum effect at 10 kg / t, but the inflection zone of the curve representing the decrease in resistances as a function of the quantity of product is around 3 kg / T.

In general, CYPRO has a very powerful effect on resistance from the addition of 1 kg / T. At 2.5 kg / T, its effect is identical to that of the debonding agent of the prior art, BEROL.

The latter then continues to decrease the resistance value as the CYPRO reaches a limit. As for KYMENE, it induces a loss of resistance, but in a much less pronounced way.

TABLE V

Note the case of Ostrand Birch dough. It is a paste which, in an anionic surfactant medium, is much more resistant than the others. We already knew that unrefined birch pulp was very resistant.

For this paste, the delinking effect of BEROL is negligible.

But that of CYPRO and KYMENE much more pronounced. In all cases, CYPRO, by bridging the surfactant and the cellulose, gives a strong unbinding effect, for addition rates between 1 and

3 kg / T. Adding more is useless.

The bridging effect of the polycationic products is confirmed by the dosages of the anionic surfactant fixed on the fiber as is clearly seen in Table VI.

Ostrand Birch pulp: anionic surfactant fixed in g / kg of paper.

TABLE VI

L.

Claims

1) Process intended to reduce the interaction between fibers in a sheet of tissue prepared according to a wet papermaking technique, characterized in that it comprises a step of treating the papermaking fibers with a polycationic product followed by a step of dispersion of said fibers in a medium consisting of a foam resulting from the fine dispersion of air bubbles in a medium containing water and an anionic surfactant with foaming effect.

2) Method according to claim 1, characterized in that the polycationic product is a nitrogen-based polymer product of the type generally used to improve the wet or dry resistance of the paper, or the retention of fibers on the paper machine.

3) Method according to claim 2, characterized in that the polycationic product is a quaternary polyamine.

4) Method according to one of claims 1 to 3, characterized in that the surfactant is an alpha-olefin sulfonate. 5) Method according to one of claims 1 to 4, characterized in that the polycationic product is a quaternary polyamine and the surfactant an alpha-olefin sulfonate.

6) Use of the method according to one of claims 1 to 5, to obtain an increased unbinding effect in one or less of the layers of a sheet of tissue resulting from a multi-jet process.

7) Sheet of multi-layer tissue from a process using multi-jet injection, characterized in that the fibers constituting at least one of the layers were treated with a polycationic product and then were dispersed in a medium consisting of 'A foam resulting from the fine dispersion of air bubbles in a medium containing water and an anionic surfactant with foaming effect.

8) Sheet according to claim 7, characterized in that the stratum located on the hood side during the drying operation of said sheet contains fibers previously treated with a polycationic product.