WO2008087337A2

WO2008087337A2 - Tracing paper production method

Info

Publication number: WO2008087337A2
Application number: PCT/FR2007/052586
Authority: WO
Inventors: David Botterill
Original assignee: Arjowiggins
Priority date: 2006-12-22
Filing date: 2007-12-20
Publication date: 2008-07-24
Also published as: WO2008087337A3; FR2910500A1; ES2719628T3; FR2910500B1; EP2122053A2; EP2122053B1

Abstract

The invention relates to a method for producing a sheet of tracing paper having a darkness index of less than 40 % measured in accordance with ISO 2469, in which a paper pulp based on virgin cellulose fibres in aqueous suspension is subjected to the action of a cellulase-based enzyme product for a pre-determined period of time prior to the mechanical refining thereof.

Description

Method of manufacturing a paper slams

The present invention relates to a method of manufacturing a tracing paper from a cellulosic fiber composition including a step of enzymatic treatment of fibers. For the purposes of the present invention, the term "tracing paper" is used traditionally in the paper industry to refer to a so-called "natural" tracing paper obtained from an aqueous suspension of paper pulp which has undergone extensive refining of cellulose fibers which 'it contains.

In fact, paper pulps must undergo a refining step in order to hydrate and fibrillate the fibers. This step densifies the fibrous mat forming on the web of the paper machine and controls the physical and optical characteristics of the paper sheet. During the manufacture of tracing paper, this refining step is pushed to obtain a very dense sheet almost free of air (voids), which gives transparency to the paper. In the manufacture of tracing paper, the mechanical refining of a paste in aqueous suspension is then carried out before it is used on the paper machine. This fibrillation step is carried out in mechanical refiners which are large energy consuming devices.

Moreover, the high degree of refining of the fibers causes machinability problems, in particular problems of drainability of the dough during the formation of the sheet on the paper machine. However, it is known that the dewatering of paper pulp on the web of a paper machine plays a particularly important role in productivity, especially for tracing paper. Indeed, it is necessary to heat the refined pulp at temperatures of 80 to 95 ⁰ C for example to facilitate drainage and thus increase the productivity of the paper machine. This also leads to some energy consumption.

In addition, despite this heating of the dough, the dewatering time can be quite long compared to the dewatering time of a poorly refined dough (to make a conventional non-transparent paper). French patent application FR 2 557 894 describes a process for treating paper pulps with a particular enzymatic solution based on xylanases promoting fibrillation. According to this treatment method, a solution of xylanases is added to a fibrous suspension of paper pulp. The dough thus treated is then refined mechanically. This enzymatic treatment of the pulp causes a loosening of the fiber structure, loosening which favors the subsequent action of the refining step.

European Patent Application EP 0 262 040 discloses a process for treating a paper pulp based on recycled fibers with an enzyme preparation containing cellulases and / or hemicellulases. The purpose of this document is to improve the drainage of the aqueous suspension of fibrous material without any undesirable effect on the mechanical characteristics of the paper made from this paste. The technique used to improve the dewatering of the aqueous fiber suspension fed to the web of a paper machine does not make use of a virgin fiber paper pulp having low fibrillation and fine rates. In addition, this document does not describe the manufacture of a tracing paper.

The present invention aims to solve the disadvantages of the prior art of the manufacture of a tracing paper, in particular to reduce the energy costs of this manufacture while maintaining good mechanical and optical characteristics of the tracing paper.

The invention thus provides a method for manufacturing a sheet of tracing paper having good mechanical characteristics and a low opacity index, the pulp of which is based on virgin cellulosic fibers in aqueous suspension is subjected to the action of an enzyme preparation based on cellulases prior to mechanical refining.

The Applicant has found, surprisingly, that the process according to the invention makes it possible, on the one hand, to improve the dewatering of the suspension paste by accelerating the dewatering, and / or to reduce the temperature of the suspension pulp in headbox that will be drained, and secondly to have a gain in energy during the production of tracing paper, in particular by reducing the amount of refining energy required.

Those skilled in the field of stationery know that the refining step of cellulosic fibers needs to be particularly pushed when one wants to make tracing paper. Moreover, those skilled in the art know that the fibrils and fines thus created slow down the dripping speed of the dough.

As a result, one skilled in the art thought that improving the refining process by an enzymatic action would not make it possible to increase the speed of dewatering. pulp in suspension. However, the Applicant, contrary to the prejudices of the skilled person, was able after much research to develop a tracing paper manufacturing process, namely a paper comprising cellulosic fibers very refined and having good mechanical characteristics and a low opacity index, which allows both to improve the drip of the dough and to reduce the energy consumption, in particular of the energy of refining and the energy related to the decrease of some degrees Celsius of the temperature of the dough suspension for dripping.

The method of manufacturing a sheet of tracing paper having an opacity index of less than 40%, measured according to ISO 2469, according to the invention is characterized in that it comprises the following steps: a) acting on an aqueous suspension of pulp whose fibrous composition comprises at least 50% by dry weight of virgin cellulosic fibers, an enzymatic preparation containing cellulases; b) after an enzymatic action time on said pulp of not more than 60 minutes (in step a)), the enzymatic action of the cellulases on said paper pulp is inhibited; c) the pulp is mechanically refined; paper mill obtained in step b), d) said fine paper pulp is drained onto the fabric of the paper machine, e) the sheet thus formed is dried so as to obtain said sheet of tracing paper.

According to a particular case of the invention, a tracing paper is manufactured which can have an opacity index of less than 30%, measured according to the ISO 2469 standard.

The process according to the invention applies to paper pulp based on virgin cellulosic fibers. Thus, the fibrous composition of the paper pulp according to the invention may comprise at least 50% of virgin cellulosic fibers in dry weight, preferably at least 70% of virgin cellulosic fibers in dry weight, relative to the total dry weight of the fibrous composition. pulp. More preferably still the composition may comprise 100% virgin fibers.

The term "virgin fibers" in the sense of the present invention, as usually used in the paper industry, non-recycled fibers, these fibers may in addition come from broken manufacturing. Broken manufacturing is paper removed at any stage of manufacture on the paper machine and generally pulped. One distinguishes on the one hand the wet manufacturing breaks, that is to say accumulated in the wet part of the paper machine and on the other hand the dry manufacturing breaks, accumulated at any point of the dryness of the machine. paper machine, trimmings from winding, re-slitting and cutting operations as well as paper rejected in sorting.

Typically, papermaking pulps used for the manufacture of tracing paper are selected from bleached northern softwood kraft pulp, bleached softwood kraft pulp from the South and blend thereof. These papermaking pulps may possibly be associated with small quantities of hardwood type pulp. Bleached sulphite pulps can also be used for the manufacture of tracing paper.

The enzymatic action in step a) is performed on the pulp at the required pH and temperature conditions for the enzymes to be active, according to the knowledge in the field of biotechnology.

Preferably, the enzymatic preparation of the invention utilizes endo-1,4-β-glucanase cellulases, which are commonly referred to as "endoglucanases".

In a particular embodiment of step a) of the process of the invention, the pulp is added to the paper pulp composed of at least 50% of virgin cellulosic fibers in aqueous suspension at a rate of 50 g / l, the enzyme preparation containing the cellulases.

According to a particular case of the invention, 0.05 to 1 gram of a cellulase, in particular of endoglucanase type, is added to said aqueous suspension based on virgin cellulosic fibers per kilogram of paper pulp on a dry weight basis, and the whole is mixed for a time not exceeding 60 minutes.

Indeed, the Applicant has found that the enzymatic treatment of the paper pulp in suspension of step a) of the process does not need to be continued beyond 60 minutes. The enzymatic reaction of the cellulases is therefore stopped, preferably by inhibiting it by addition of a chemical inhibitor to the pulp suspension. According to step b) of the process of the invention, the enzymatic action of the cellulases is inhibited by adding to said aqueous suspension of paste a chemical inhibitor so that the enzymatic treatment time of said aqueous suspension of dough does not exceed 60 minutes. According to an advantageous embodiment of the invention, said chemical inhibitor is a strong oxidizer. More particularly, said chemical inhibitor is chosen from sodium hypochlorite and hydrogen peroxide, especially used in the form of an aqueous solution. According to the invention, the enzymatic action time of the cellulases on the aqueous pulp suspension is preferably between 5 and 45 minutes, more preferably between 5 and 30 minutes.

One method to determine that enzyme inhibition has occurred is to track the viscosity of CMC (carboxymethylcellulose) solutions made with the water of dough samples taken before and after the addition of the inhibitor, according to the method described later after the examples.

The CMC solution for the sample taken before adding the inhibitor

(once brought to the activity temperature of the enzymes) quickly loses its viscosity due to the action of the enzymes on the cellulose chains whereas the CMC solution relating to the sample taken after the addition of the inhibitor (when brought to the activity temperature of the enzymes) remains stable in viscosity.

This method makes it possible to optimize the concentration and quantity of the inhibitor as well as the inhibition time.

Once the enzymatic action of the cellulase-based enzyme preparation is inhibited, the pulp thus treated, resulting from step b) of the process, is subjected according to step c) of the process of the invention to a mechanical refining. Usually, the mechanical refining is carried out by means of refiner (s). According to one aspect of the invention, the paper pulp is refined to a Schopper-Riegler degree greater than 80.

A reduction in the consumption of the refining energy during the mechanical refining of the pulp could be observed following the enzymatic action of the cellulases on the pulp in aqueous suspension.

According to step d) of the process of the invention, the aqueous pulp suspension obtained is deposited on the fabric of a paper machine, generally a flat-bed paper machine, and the water is drained by gravity and by means of foils and other dewatering devices. Step d) of the tracing paper manufacturing method according to the invention is characterized by an improvement in the drip rate of the dough on the fabric of the paper machine compared to the same dough not treated with enzymes. Speed dewatering of the aqueous suspension of paste obtained at the end of step c) of the process is characterized by a dewatering time determined according to the test described below in the paragraph "DESCRIPTION AND CONDITIONS OF REALIZATION OF THE MEASUREMENT OF "DRAINAGE" for a given volume, between 40 and 60 seconds. An improvement in the drip speed of the dough on the web of the paper machine during step d) of the method according to the invention was observed for a tracing paper having a given opacity index and less than 40 %. Indeed, the dewatering speed of said processed and refined pulp, which is characterized by a dewatering time determined according to the test described below in the paragraph "DESCRIPTION AND CONDITIONS OF REALIZATION OF THE SEWING MEASUREMENT" for a given volume, can be improved by at least 10% with respect to the dewatering speed of a paste that has not been previously treated enzymatically, but refined so as to obtain a tracing paper of opacity value identical, said dewatering speed being characterized by a dewatering time determined according to the same test described below in the paragraph "DESCRIPTION AND CONDITIONS OF REALIZATION OF THE MEASUREMENT OF DRAINAGE".

In general, during the manufacture of a tracing paper, the temperature of the suspension of the dough is adjusted between about 80 and 95 ° C to allow better drainage of the paper sheet. However, the inventors have surprisingly found, during their many experiments, that not only the drip rate of the dough on the fabric of the paper machine was significantly improved but also that the temperature of the dough suspension could be reduced by a few degrees Celsius, namely from 2 to 10 ⁰ C for dripping. Thus, during the manufacture of a tracing paper according to the method of the invention, the temperature of the dough in suspension can be adjusted to a temperature of less than or equal to 80 ^° C., preferably between 70 ° and 75 ° C., and the dripping speed on the fabric of the paper machine of the dough resulting from step d) remains significantly improved. This decrease in the temperature of the pulp suspension as well as the reduction of the pulp refining energy represents an energy gain.

More particularly, according to the invention, the refined paste obtained at the end of step c) is heated to said temperature, in the short circuit of the paper machine leading to the headbox of the machine paper. Then, during step e) of the process of the invention, the sheet of tracing paper obtained in step d) of the process is dried on drying rollers.

The sheet of tracing paper thus obtained has a relatively low opacity index specific to the tracing paper sheets, more specifically an opacity index of less than 40%, preferably less than 30%, measured according to the ISO 2469 standard.

This gives a sheet of tracing paper according to the method of the invention which has good mechanical characteristics and a low opacity index, and which has a basis weight of between about 30 and 200 g / m ² or even up to 300 g / m2. A dye may be added, for example, in the aqueous suspension of the dough before the head box of the paper machine, so as to obtain a colored sheet of tracing paper.

The appended figures and the nonlimiting example and the comparative example below will make it possible to better understand the invention.

Example 1 according to the invention

70 kg in dry weight (ie 80% relative to the weight of the sheet) of the long virgin fibers of a bleached Kraft softwood pulp are suspended in hot water at approximately 70 ^° C. in a pulper. 180 kg dry weight of broken (ie 20% relative to the dry weight of the sheet), so as to obtain a concentration of 50g / l.

0.2 gram of endo-1,4-β-glucanase cellulase enzymes per kilogram of the dough mixture on a dry weight basis is added to said aqueous fiber dispersion. The enzymatic activity is maintained for 15 minutes and then stopped by adding an aqueous solution of sodium hypochlorite to said aqueous slurry. The fiber suspension is at a temperature of about 50 ⁰ C and its pH was adjusted between 6 and 8 to be in the activation conditions of the enzymes.

The pulp suspension is refined in a mechanical refiner by applying a refining energy of 500 kWh / ton so as to obtain a level of fibrillation leading to a final opacity of the paper sheet of 36%. Thus refined pulp is heated in short circulation of the paper machine at a temperature of about 80 ⁰ C, and is fed to the headbox and depositing the paste on the wire of a machine flat-table paper, it is drained and pressed. Then, the sheet of tracing paper thus obtained is dried on drying rollers at approximately 100 ^° C.

This gives a sheet of tracing paper having an opacity index of 36% and a basis weight of 110 g / m ² .

Comparative Example 2 According to the Prior Art

750 kg dry weight (ie 80% relative to the weight of the sheet) of long virgin fibers of a bleached Kraft softwood pulp and 180 kg of dry weight are suspended in water in a pulper. broken down (ie 20% relative to the dry weight of the sheet), so as to obtain a concentration of 50 g / l.

This pulp suspension is refined in a mechanical refiner by applying a refining energy of 800 kWh / ton so as to obtain a level of fibrillation leading to a final opacity of the paper sheet of 36%. The dough thus refined is heated in the short circuit of the paper machine at a temperature of about 85 ° C., and it is brought to the headbox and then deposited on the fabric of a machine. flat-table paper, it is drained and pressed. Then, the sheet of tracing paper thus obtained is dried on drying rollers at approximately 100 ^° C. This gives a sheet of tracing paper having an opacity index of 36% and a basis weight of 110 g / m ² .

Figures:

FIG. 1 represents the curve of the opacity index as a function of the refining energy of a sheet of tracing paper resulting from an enzyme-treated paste according to the invention (example 1) and that of a sheet of tracing paper resulting from an untreated paste according to the prior art (example 2).

FIG. 2 represents the curve of the dewatering time (denoted Dv) as a function of the refining energy of a sheet of tracing paper resulting from an enzyme-treated paste according to the invention (example 1) and that of a sheet of tracing paper obtained from an untreated dough by enzyme according to the prior art (example 2). Results interpretation

Figure 1 shows the influence of enzymatic treatment on the refining energy of the pulp in aqueous suspension.

As can be seen in FIG. 1, the opacity index of 36% of a sheet of tracing paper obtained according to the same process as that of the invention but whose paste in aqueous suspension is free from any enzymatic treatment. (Example 2), requires a refining energy of 800 kWh / ton while the same opacity index of 36% can be obtained for a sheet of tracing paper as described in Example 1, the pulp in aqueous suspension has was subjected to enzymatic treatment at the rate of 0.2 gram of an endo-l, 4-β-glucanase cellulase per kilogram of pulp with a refining energy of the order of 500 kWh / ton. Therefore, a tracing paper obtained according to the method of the invention allows a reduction in the energy consumption of refining of about 38%.

Figure 2 shows the influence of enzymatic treatment on the dewatering time (Dv). The tracing paper manufacturing method according to the invention, as previously described, makes it possible to improve the dripping speed of the dough on the fabric of the paper machine, the dripping speed of the dough which is characterized by a time of dyeing. determined according to the test described below in the paragraph "DESCRIPTION

AND CONDITIONS FOR PERFORMING THE MEASUREMENT OF DRAINAGE "for a given volume.

As can be seen in the curve representing the dewatering time as a function of the refining energy of FIG. 2, the dewatering time (in seconds) determined according to the test described below, of a sheet of tracing paper as described in Example 1 according to the invention, the paste in aqueous suspension was subjected to enzymatic treatment at a rate of 0.2 gram of an endo-l, 4-β-glucanase-type cellulase by kilogram of pulp for a refining energy (in kWh / ton) of 500 kWh / ton, is 48 s. However, it is found that the dewatering time (in seconds) determined according to the same test described below, a sheet of tracing paper obtained according to the same process as that of the invention but whose pulp in aqueous suspension is free of any enzymatic treatment according to Example 2 for a refining energy of 800 kWh / ton, is 95 s. Therefore a tracing paper obtained according to the method of the invention allows a marked improvement in the dripping speed of the dough on the fabric of the paper machine, by about 50%, in addition to the gain in refining energy. about 38%, for an opacity equivalent of 36%.

DESCRIPTION AND CONDITIONS OF REALIZATION OF THE SELECTION MEASUREMENT:

The measurement of the drip rate of the dough is characterized by the determination of the water flow time by gravitation in seconds for a given volume, this dewatering time of the dough is determined as follows: withdraws a sample of pulp in aqueous suspension and determines its concentration in g / 1, then is prepared from this sample, a liter of aqueous suspension of pulp concentration equal to 0.5 g / l, and its temperature is from 15 ^° C. - the Schöpper-Riegler apparatus, standardized according to the international standard ISO5267-1: 1999, is closed and the (two) dripping outlets of the apparatus are put in a standard container according to the same standard, then the liter of the preparation of aqueous paste suspension at 0.5 g / l in the bowl of the Schöpper-Riegler, - the drip outlets of the apparatus are opened and a stopwatch is started simultaneously, the stopwatch as soon as the volume of water Drained in the standardized container reaches 610ml, we note the dewatering time, expressed in seconds, necessary to reach the volume of 610ml of drained water.

The g / l concentration of the dough is typically determined by filtration of a given volume of the sample of the dough suspension, the recovered dough is dried and weighed. DESCRIPTION OF THE DETERMINATION OF INHIBITION OF ENZYMES:

Two dough samples, A and B, are taken from the pulper. Sample A contains the enzymes before inhibition and Sample B (taken at the same place 5 minutes later) contains the enzymes and the inhibitor. Both dough samples are dewatered to recover their respective waters which are then chilled to deactivate any uninhibited enzyme in both batches.

Once cold, at 4 ° C, these waters are used to dissolve CMC (carboxymethylcellulose) to have two respective solutions A and B of CMC. The CMC solutions are then brought to the activity temperature of the enzymes (around 50 ^° C.) and the viscosities are measured regularly.

CMC solution A, without inhibitor (once brought to the enzyme activity temperature), rapidly loses its viscosity by the action of enzymes on the cellulose chains whereas CMC solution B, with inhibitor, remains stable in viscosity. We can therefore conclude that the inhibition has taken place.

Claims

1. A method of manufacturing a sheet of tracing paper having an opacity index of less than 40%, measured according to ISO 2469, characterized in that it comprises the following successive steps: a. acting on an aqueous suspension of pulp whose fibrous composition comprises at least 50% by dry weight of virgin cellulosic fibers, an enzyme preparation containing cellulases, b. after an enzymatic action time on said pulp of not more than 60 minutes, the enzymatic action of the cellulases on said pulp, c. mechanical refining of the pulp obtained in step b), d. said refined paste is drained onto the web of a paper machine, e. the sheet thus formed is dried so as to obtain said sheet of tracing paper.

2. Method according to claim 1, characterized in that the paper pulp comprises at least 70% virgin cellulosic fibers by dry weight, relative to the total dry weight of the fibrous composition of the pulp.

3. Method according to claim 1, characterized in that said pulp is made of 100% virgin cellulosic fibers dry weight, relative to the total dry weight of the fibrous composition of the pulp.

4. Process according to any one of claims 1 to 3, characterized in that the cellulases of the enzymatic preparation of step a) are of endo-1,4-β-glucanase type.

5. Method according to any one of claims 1 to 4, characterized in that, in step a), is reacted with 0.05 to 1 gram of cellulases per kilogram of pulp paper dry weight.

6. Method according to any one of claims 1 to 5, characterized in that inhibits the enzymatic action of cellulases in step b) by means of a chemical inhibitor.

7. The method of claim 6, characterized in that said chemical inhibitor is a strong oxidizer.

8. The method of claim 7, characterized in that said chemical inhibitor is selected from sodium hypochlorite and hydrogen peroxide, especially in the form of an aqueous solution.

9. Process according to any one of claims 1 to 8, characterized in that the enzymatic action time of the cellulases on the aqueous pulp suspension is between 5 and 45 minutes, more preferably between 5 and 30 minutes.

10. Process according to any one of claims 1 to 9, characterized in that the refined paste resulting from step c) is heated to a temperature less than or equal to 80 ⁰ C, before step d) dewatering .

11. Method according to the preceding claim 10, characterized in that said temperature is between 70 and 75 ⁰ C.

12. Method according to one of claims 10 to 11, characterized in that the refined paste obtained at the end of step c) is heated to said temperature, in the short circuit of the paper machine leading up to 'to the headbox of the paper machine.

13. Process according to any one of Claims 1 to 12, characterized in that the aqueous pulp suspension is drained onto the fabric of a flat-bed paper machine during step d) of said process.

14.. Process for manufacturing a sheet of tracing paper according to any one of Claims 1 to 13, characterized in that the dewatering speed of the aqueous pulp suspension in step d) corresponds to a dewatering time included between 40 and 60 seconds, the said dewatering time being determined as follows: a sample of paste is taken in aqueous suspension and its concentration in g / 1 is determined, and then, from this sample, a liter is prepared. of an aqueous suspension of paste of concentration equal to 0.5 g / l, the Schöpper-Riegler apparatus is closed, standardized according to the international standard ISO5267-1: 1999, and the drip outlets of the apparatus are put in the same standardized container according to the same standard, is then introduced the liter of the preparation of aqueous suspension of paste to 0.5 g / l in the bowl of Schöpper-Riegler device, it opens the drip outlets of the device Schöpper- Riegler and trigger simultaneously ment a stopwatch, stop the timer as soon as the volume of water drained in the standardized container reaches 610ml, we note the dewatering time, expressed in seconds, necessary to reach the volume of 610ml of water drained.