DE102021005047A1 - Polyelectrolyte system, composition having a polyelectrolyte system and method of manufacture - Google Patents

Abstract

The invention relates to a composition for the production of paper, comprising a polyelectrolyte system and microfibrillated cellulose, wherein the polyelectrolyte system comprises cellulose fibers and at least some of the individual cellulose fibers are at least partially coated alternately with at least one first cationic electrolyte layer and at least one first anionic electrolyte layer. The mechanical properties are improved by the cationic and anionic electrolyte layer and the cellulose fibers are mechanically more resistant.

Description

The invention relates to a composition with a polyelectrolyte system, the production of such a composition, and paper produced from such a composition.

The economic production of paper requires good runnability of a paper machine. In order to achieve good runnability, the paper must run well with a low number of web breaks in every sub-process along the entire paper machine line. It has been found that many of the runnability problems occur when the paper web is still wet. Good runnability at the beginning of the paper machine, i.e. when the paper is still wet, is an advantage for high production efficiency of the entire paper manufacturing line. Wet paper runnability can be increased by increasing the strength of the wet web. A number of solutions are known for increasing the strength of the wet paper web, such as increasing the degree of beating of the pulp, varying the overall stock composition or web tension in the process.

At the same time, however, many of these solutions lead to a deterioration in the properties of the finished paper produced or to a significant increase in production costs. For example, an increase in the degree of beating can increase the tendency to curl and have a negative impact on the properties of the final paper.

Traditional wet strength additives used to increase the wet strength of the final dried paper web do not increase the strength of the wet paper web, i.e. the strength of never dried wet webs. This is because wet strength additives typically must be heated and cured before they exhibit strength enhancing properties.

Furthermore, depending on the paper produced, additional production steps may be necessary, which represent a limiting factor in production capacity. For example, in the production of foil base paper, a size press step has to be added due to the nature of the paper, which has a significant impact on production efficiency. The size press process requires rewetting and drying of the material.

It is known from the prior art that polyelectrolyte complexes can increase the bursting strength of paper. For example, describes WO 2018/229333 A1 a process for increasing the strength properties of paper using polyelectrolyte complexes. However, the use of complexes leads to a locally concentrated charge density, which can lead to different strengths within the paper.

It is therefore an object of the invention to overcome the disadvantages of the prior art. In particular, it is an object of the invention to provide a composition for the manufacture of paper which enables mechanical strength paper to be manufactured efficiently. It is a further object of the invention to provide paper made from such a composition.

At least some of the objects are solved by the subject matter of the independent claims. Further preferred embodiments are set out in the dependent claims.

A first aspect of the invention relates to a polyelectrolyte system comprising cellulose fibers. The pulp fibers are preferably suspended in water. The pulp fibers can be beaten and/or unbeaten. At least some of the individual cellulose fibers are at least partially encased alternately with at least one first cationic electrolyte layer and at least one first anionic electrolyte layer. Pulp fibers usually have an anionic surface, therefore the first layer of electrolyte directly attached to this surface of the pulp fibers is always cationic. This cationic electrolyte layer is then followed by an anionic electrolyte layer. The cellulose fibers can be covered only partially or completely by the layers. Complete encapsulation is preferred.

The pulp fibers can be eucalyptus, hardwood, softwood, cotton, bamboo, virgin pulp or recycled pulp. For example, the cellulose fibers can be secondary fibers from waste paper or waste cardboard. The production of pulp is known to the person skilled in the art from the prior art.

The polyelectrolyte system is characterized by the fact that the individual electrolyte layers are evenly distributed over the fibers and an even distribution of the charge density is guaranteed.

Preferably, at least some of the cellulose fibers are coated with at least one second cationic electrolyte layer. Thus, on the one hand, the fibers have an evenly distributed charge density and, on the other hand, the negatively charged surface of the pulp fibers can be changed into a positively charged surface, which expands the possibilities for further surface modification.

In principle, it is possible to apply several cationic electrolyte layers and anionic electrolyte layers alternately to the individual cellulose fibers, so that depending on the application, a different charge density can be applied to the fibers. It is therefore possible that the individual pulp fibers have two or more cationic and anionic electrolyte layers. The outer layer can be cationic or anionic. The selection of the charge of the outer layer is geared in particular to the desired application.

Preferably, the first and/or second cationic electrolyte layer comprises cationic starch. The starch can be potato starch with DS 0.065 and a charge density of 0.38 meq/g or DS 0.065 and a charge density of 0.525 meq/g. Other cationic electrolytes can include cationized microfibrillated cellulose, polyallylamine hydrochloride (PAH), polyethyleneimine (PEI), polyvinylamine (PVAm), polyamidamine-epichlorohydrin resin (PAAE), chitosan, hydroxyethylcellulose ethoxylate (HECE), cationic polyacrylamides, polyacrylamide-co-diallyldimethylammonium chloride (PAM -DADMAC), polyacrylamide-co-[3-(2-methylpropionamido)propyl]-trimethylammonium chloride (PAM-MAPTAC), or combinations thereof. The advantage of cationic starch is that it is a product based on a natural raw material and is therefore more environmentally friendly than fully synthetic electrolytes on the one hand and easily accessible on the other. However, the use of synthetic cationic electrolytes is possible.

In particular, if several cationic electrolyte layers are present, it is conceivable that all of these layers comprise cationic starch. However, it is also possible for the layers to be different cationic electrolyte layers.

The first anionic electrolyte layer preferably comprises anionic starch, preferably aldehyde potato starch. However, other anionic electrolyte layers are also conceivable, for example anionic synthetic polymers such as polyacrylic acid (PAA). It is also possible to use carboxymethyl cellulose (CMC), PAAE, heparin or other anionic polysaccharides or combinations thereof, for example TEMPO-oxidized microfibrillated cellulose. In the case of several anionic electrolyte layers, these can each comprise the same anionic electrolyte or have different anionic electrolytes.

The advantage of anionic starch is that it is a product based on a natural raw material and is therefore more environmentally friendly than fully synthetic electrolytes on the one hand and easily accessible on the other. The use of synthetic anionic electrolytes is nevertheless possible.

A further aspect of the invention relates to a composition for the production of paper comprising a polyelectrolyte system as described above and microfibrillated cellulose. At least some of the individual cellulose fibers of the polyelectrolyte system are at least partially encased alternately with at least one first cationic electrolyte layer and at least one first anionic electrolyte layer. Complete encapsulation is preferred, as explained above.

Surprisingly, it has been shown that such a composition increases the paper structure strength, the so-called Scott Bond, of paper, which in turn makes the paper more mechanically resistant. But other mechanical properties, such as tensile stress, are also improved.

The cellulose fibers of the polyelectrolyte system of the composition can be alternately surrounded by further electrolyte layers, as previously described.

The concentration of the microfibrillated cellulose in the composition is preferably in the range from 1 to 10% by weight, more preferably 2 to 7% by weight and particularly preferably 5% by weight, based on the dry mass of the pulp.

Microfibrillated cellulose in this concentration range gives particularly good results in terms of paper structure strength (Scott Bond).

The composition preferably comprises other mineral fillers and/or pigments. The fillers and/or pigments are preferably selected from the group: aluminum, aluminum oxide, aluminum silicate, calcium, calcium carbonate, chromium, clay, iron, iron oxides, kaolin, corundum, magnesium, magnesium carbonate, magnesium silicate, silicon, silicon dioxide, talc, titanium dioxide, zinc , zinc sulfide, tin oxide or mixtures thereof. Also conceivable are inorganic substances such as diatomite. Titanium dioxide is particularly preferred. The addition of titanium dioxide is particularly advantageous in the production of decorative paper. Surprisingly, it has been shown that the retention can be improved by up to 90% with titanium dioxide. This is a significant increase over the 30 to 40% known in the prior art. It is also possible to use modified titanium dioxide pigment, for example titanium dioxide pigment doped with aluminum, antimony, niobium, zinc or silicon.

The composition may include other additives. The additives are preferably selected from the group consisting of: microfibrillated cellulose, wet strength agents, guar, starch, alginate, polyacrylamide, organic substances such as melamine-formaldehyde resin, urea-formaldehyde resin, acrylates, polyvinyl alcohols, modified polyvinyl alcohol, polyvinyl acrylates, polyacrylates, synthetic binders, binders of natural origin such as Starch, modified starch, carboxymethyl cellulose or mixtures thereof. Examples of suitable wet strength agents are polyamide/polyamine-epichlorohydrin resins, other polyamine derivatives or polyamide derivatives, cationic polyacrylate, modified melamine-formaldehyde resin, or cationic starch.

By adding other additives, the paper properties or the properties of the paper can be adjusted for different applications. For example, the air permeability is reduced in the order MFC > guar > starch > alginate > PAM, which means that the air permeability can be adjusted, especially with paper.

1. a) Bereitstellen einer ersten Suspension aus Zellstofffasern,
2. b) Vermischen der ersten Suspension mit einer ersten kationischen Elektrolytlösung zur Bildung einer zweiten Suspension, wobei zumindest ein Teil der Zellstofffasern in der zweiten Suspension von einer ersten kationischen Elektrolytschicht zumindest teilweise, bevorzugt vollständig, umhüllt werden,
3. c) Vermischen der zweiten Suspension aus Schritt b) mit einer ersten anionischen Elektrolytlösung zur Bildung eines Polyelektrolytsystems,
4. d) Hinzufügen von mikrofibrillierte Zellulose zu dem Polyelektrolytsystem.

The invention further relates to a method for preparing a composition as described above. The procedure includes the steps:

1. a) providing a first suspension of cellulose fibers,
2. b) mixing the first suspension with a first cationic electrolyte solution to form a second suspension, at least some of the pulp fibers in the second suspension being at least partially, preferably completely, encased by a first cationic electrolyte layer,
3. c) mixing the second suspension from step b) with a first anionic electrolyte solution to form a polyelectrolyte system,
4. d) adding microfibrillated cellulose to the polyelectrolyte system.

The process can be carried out as a continuous process or as a batch process.

Surprisingly, it has been shown that this method enables the polyelectrolyte system to be formed layer by layer and thus counteracts the disadvantageous formation of a polyelectrolyte complex. This enables an even distribution of the charges over the pulp fibers. The addition of the microfibrillated cellulose makes it possible to provide a composition for making paper stock having a high internal papermaking strength.

Optionally, a rinsing step can be inserted between step b) and c). Excess material can be removed by the rinsing step and additional formation of polyelectrolyte complexes is avoided. It is conceivable that the surplus material will be processed in order to be used again. The processing steps are known to those skilled in the art from the prior art.

Preferably, the polyelectrolyte system from step c) is mixed with at least one second cationic electrolyte solution to form a third suspension. At least part of the pulp fibers in the third suspension can thus be at least partially, preferably completely, surrounded by a second cationic electrolyte layer.

Alternatively, it is also conceivable that the suspension is alternately brought into contact with at least two cationic and at least two anionic electrolyte solutions. More than two electrolyte solutions are also conceivable. The suspension is preferably rinsed with the electrolyte solutions between the respective contacts. The cationic or anionic electrolyte solutions can be the same electrolyte solution or different electrolyte solutions. Optionally, the final electrolyte solution can be cationic or anionic depending on the intended application.

The more electrolyte solutions that are used, and thus the layers of electrolyte on the fibers, the higher the Scott Bond of the paper.

In order to allow sufficient time for the adsorption of the electrolytes during mixing, the mixing time is preferably up to 30 minutes, particularly preferably between 1 and 30 minutes, very particularly preferably between 5 and 20 minutes and even more preferably 10 minutes take place at room temperature. However, it is also possible to work at elevated temperature. However, the temperature should not exceed 60 °C.

The first and/or the second cationic electrolyte solution may comprise a cationic starch. It is possible that both electrolyte solutions comprise cationic starch. Preferably, the first and/or second cationic electrolyte solution consists of a suspension of cationic starch and water. However, it is also conceivable that the cationic electrolyte solutions include different electrolytes. For example, the first cationic electrolyte solution comprises cationic starch and the second cationic electrolyte solution comprises cationic microfibrillated cellulose.

Advantageously, the first cationic electrolyte of the electrolyte solution from step b) has a concentration of 1-3% by weight and the first anionic electrolyte of the electrolyte solution from step c) has a concentration of 0.3-1.5% by weight. The concentration always refers to the dry amount of pulp in the suspension.

The second cationic electrolyte preferably has a concentration of 0.1-1% by weight, based on the dry amount of pulp in the suspension.

Surprisingly, it has been shown that the electrolytes are particularly well adsorbed at these concentration ratios. The use of overdosed electrolyte solutions can thus be avoided.

Preferably, the concentrations of successively decreasing electrolytes relative to the dry amount of pulp in the suspension. For example, the concentration of the first cationic electrolyte can be 1.25% by weight, the first anionic electrolyte 0.4% by weight and the second cationic electrolyte 0.2% by weight. Another conceivable concentration series would be 2.5% by weight: 1.0% by weight: 0.75% by weight.

The anionic electrolyte solution may include an anionic starch. Other, for example fully synthetic, electrolyte solutions are also conceivable. If multiple anionic electrolyte solutions are used, they can all include anionic starch, or optionally only one or two. If there are several electrolyte solutions, they can have different compositions.

The use of cationic or anionic starch has the advantage that it is based on a natural raw material and is easily accessible. A method using such electrolytes is also environmentally friendly and resource-friendly.

Preferably the pulp is suspended in water and the starch is dissolved in water.

The concentration of the microfibrillated cellulose can be in the range from 1 to 10% by weight, based on the total dry mass of the suspension, preferably 2 to 7% by weight, particularly preferably 3 to 6% by weight and in particular 5% by weight.

Other additives can be added to the composition. The additives are preferably selected from the group consisting of: mineral fillers and/or pigments as previously described, wet strength agents as previously described; guar; Strength; alginate; polyacrylamide or mixtures thereof.

The addition of additives has the advantage that the properties of the paper can be adjusted according to the application.

The invention further relates to paper made from a composition as previously described. The paper can, for example, be a decorative paper, in particular foil base paper; Paper for packaging of all kinds, such as food; printing paper; be insulating paper or sanitary paper. The insulating paper can be, for example, paper with acoustic insulating properties and/or heat insulating properties.

For example, in a specific embodiment, the paper can be made from a composition of 5% by weight of microfibrillated cellulose, based on the total dry matter in the suspension, as well as 30% by weight of TiO ₂ and 65% by weight of cellulose. Such a paper is particularly suitable as decorative paper. In addition, it has surprisingly been found that the retention is significantly improved by up to 90% compared to compositions and methods known in the prior art which provide a retention of 30 to 40%.

• 1: Entstehung eines Polyelektrolytsystems.
• 2: Schematische Darstellung eines Verfahrens zur Herstellung eines Polyelektrolytsystems im Labor.
• 3: Schematische Darstellung eines industriellen Verfahrens zur Herstellung eines Polyelektrolytsystems.
• 4 - 6: Steigerung des Scott Bonds im Vergleich zu Zellstoff.
• 7: Steigerung der Luftdurchlässigkeit und Rauigkeit.

The invention is explained in more detail below using figures and exemplary embodiments. The invention is not limited to these examples. Show it:

• 1 : Formation of a polyelectrolyte system.
• 2 : Schematic representation of a process for the production of a polyelectrolyte system in the laboratory.
• 3 : Schematic representation of an industrial process for the production of a polyelectrolyte system.
• 4 - 6 : Increase in Scott Bond compared to pulp.
• 7 : Increase in air permeability and roughness.

1 shows schematically the gradual coating of a cellulose fiber with polyelectrolyte. The surface of the pulp fiber carries negative charges (A). After applying a first cationic electrolyte layer to the negatively charged surface of the cellulose fiber, the cellulose fiber is coated with a cationic electrolyte layer (B).

An anionic electrolyte layer is then applied to the fiber (C), followed by another cationic electrolyte layer.

2 shows schematically a method 1 for producing a polyelectrolyte system according to the invention on a laboratory scale. Pulp fibers 2 and a cationic electrolyte solution 3 are mixed together to form a suspension 4 . Then the fibers 5 covered by a cationic electrolyte layer are separated from the electrolyte solution 3 . The fibers 5 are mixed together with an anionic electrolyte solution 6 to form a second suspension 7 . The fibers 8 , which are now surrounded by an anionic electrolyte layer, are then separated from the electrolyte solution 6 . A further cationic electrolyte solution 12 can now be added to the fibers 8 .

3 shows schematically the industrial production of a polyelectrolyte system. In a first step, a cationic electrolyte is added to a pulp suspension in a first device 21 . The suspension is stirred for 10 minutes and then pumped into a second device 23 via a first line 22 . An anionic electrolyte is added to this suspension and the mixture is again stirred for 10 minutes. The suspension formed in this way is pumped again via a second line 24 into a third device 25 . The second cationic electrolyte is added. The suspension is stirred again for 10 min and pumped into a device that allows the addition of MFC (not shown).

EXAMPLES

Materials and Methods

A eucalyptus pulp was used. Sheets were made from unrefined pulp and pulp with a drainage resistance of 25 and 35 SR°, respectively. Solbond PC60 (cationic starch from potatoes) and Soljet P500 as anionic starch (derivative of potato starch) from Solam GmbH were used as the cationic starch.

EXAMPLE 1 - SHEETS OF A COMPOSITION ACCORDING TO THE INVENTION

Pulp with SR° 35 was diluted to a consistency of 0.3% by weight. Then, in a first step, 1.25% by weight of cationic starch was added. The suspension was stirred for 10 minutes. Then 0.4% by weight of anionic starch was added. The resulting suspension was again stirred for 10 min. A further 0.2% by weight of cationic starch was then added. The starch solutions used all had a concentration of 1% by weight of cationic or anionic starch. 5% by weight of microfibrillated cellulose, based on the dry mass of cellulose in the suspension, was then added to the suspension. The final concentration of pulp in the suspension was 0.24% by weight. Sheets with a weight of approx. 2.4 g otro (area weight 80 g/m ² ) were then produced using the Rapid-Kothen process (ISO 5269-2:2004). After a sufficiently long period of conditioning (23° C. until paper moisture content corresponds to an atmospheric humidity of 50%), the sheets were characterized.

EXAMPLE 2 TO 8

The production was carried out according to the description of example 1. In the case of example 2, no microfibrillated cellulose was added. For Examples 3 through 8, the additional additives were added after the addition of the microfibrillated cellulose (MFC). The information relates to the total dry amount of solids in the suspension. Example Pulp -PES MFC TiO ₂ /kaolin wet strength agent additive 1 65% 5% + 2 70% 30% + 3 65% 5% 30% + 4 65% 5% 30% + 5% MFC 5 65% 5% 30% + 1% guar 6 65% 5% 30% + 5% strength 7 65% 5% 30% + 1% alginates 8th 65% 5% 30% + 0.15% PAM

CHARACTERIZATION

The characterization was carried out according to ISO 1924-22:1994.

First, the Scott Bond was determined for sheets made from only a polyelectrolyte system and compared to sheets made from a composition of the invention. The digits in the 4 until 7 reflect the composition according to Table 1.

4 shows the increase in Scott Bond compared to paper made from pure pulp. The Scott Bond of paper made from a polyelectrolyte system (PES) shows an increase of approximately 130%, while the Scott Bond for paper made from a composition (1) of polyelectrolyte system and microfibrillated cellulose according to the invention increases by a further 40% and thus a 170% improved Scott Bond over paper made from pure pulp.

5 shows, however, that a polyelectrolyte system with TiO ₂ (2) shows a significant drop in Scott Bond, which is generally due to the TiO ₂ . However, TiO ₂ is necessary for the production of decorative paper. It has now surprisingly been shown that in accordance with a polyelectrolyte system Example 3, when MFC is added to the polyelectrolyte system and TiO ₂ , the Scott Bond improves significantly (3). In addition, it has been found that the retention of TiO ₂ increases up to 90% when MFC is present. This makes it possible to reduce the excess TiO ₂ that is normally required in the production of decorative paper.

From the 6 it can be seen that the addition of other additives can further increase the Scott Bond. The best results were obtained when the composition contained a total of 10% by weight of MFC based on the total dry amount of solid (4). But the addition of guar (5), starch (6), alginate (7) and PAM (8) also leads to very good results.

Out of 7 the porosity of the sheets can be seen. It turns out that 10% by weight MFC (4) has the lowest air permeability, while 0.15% by weight PAM (8) shows the highest permeability. The air permeability thus increases in the order MFC-guar-starch-alginate-PAM.

reference list

1

Proceedings

2

pulp fiber

3

electrolyte solution

4

suspension

5

fibers

6

electrolyte solution

7

suspension

8th

fibers

12

electrolyte solution

21

contraption

22

Management

23

contraption

24

Management

25

contraption

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2018229333 A1 [0006]

Claims (15)

Composition for the manufacture of paper, comprising a polyelectrolyte system and microfibrillated cellulose, wherein the polyelectrolyte system comprises cellulose fibers and at least a portion of the individual cellulose fibers are at least partially coated alternately with at least a first cationic electrolyte layer and at least a first anionic electrolyte layer. composition after claim 1 wherein at least a portion of the pulp fibers is coated with at least a second cationic electrolyte layer, and/or wherein the first and/or second cationic electrolyte layer comprises cationic starch. Composition according to any one of the preceding claims, wherein the first anionic electrolyte layer comprises anionic starch or TEMPO-oxidized microfibrillated cellulose, and/or wherein the microfibrillated cellulose is present at a concentration in the range of 1 to 10% by weight, preferably 2 to 7% by weight and particularly preferably 5% by weight, based on the dry mass of pulp in the composition. Composition according to one of the preceding claims further comprising mineral fillers, in particular titanium dioxide, and/or further comprising additives, preferably selected from the group consisting of: wet strength agents, guar, starch, alginate, polyacrylamide or mixtures thereof. Process for the preparation of a composition according to any one of Claims 1 until 4 , comprising the steps: a) providing a first suspension of cellulose fibers b) mixing the first suspension with a first cationic electrolyte solution to form a second suspension, at least some of the cellulose fibers in the second suspension being at least partially encased by a first cationic electrolyte layer, c) mixing the second suspension from step b) with a first anionic electrolyte solution to form a polyelectrolyte system, d) adding microfibrillated cellulose to the polyelectrolyte system. procedure after claim 5 , wherein a rinsing step is inserted between step b) and c). Procedure according to one of Claims 5 or 6 , wherein the polyelectrolyte system from step c) is mixed with at least one second cationic electrolyte solution to form a third suspension, wherein at least some of the pulp fibers in the third suspension are at least partially encased by a second cationic electrolyte layer. procedure after claim 7 , wherein the first cationic electrolyte solution and/or the second cationic electrolyte solution comprises a cationic starch. A method according to any one of the preceding claims, wherein the first anionic electrolyte solution comprises an anionic starch or TEMPO oxidized microfibrillated cellulose. Procedure according to one of Claims 5 until 9 , wherein the first cationic electrolyte in step b) has a concentration of 1-3% by weight and the first anionic electrolyte in step c) has a concentration of 0.3-1.5% by weight, each based on the dry mass of cellulose in the composition. Procedure according to one of Claims 7 until 10 , wherein the second cationic electrolyte has a concentration of 0.1-1% by weight based on the dry mass of pulp in the composition. Procedure according to one of Claims 5 until 11 , with the concentrations of successive electrolytes decreasing. Procedure according to one of Claims 5 until 12 , wherein the concentration of the microfibrillated cellulose is in the range of 1 to 10% by weight based on the dry matter of the pulp. Procedure according to one of Claims 5 until 13 wherein further additives are added to the composition, selected from the group consisting of: mineral fillers, for example titanium dioxide; Wet strength agents, guar, starch, alginate, polyacrylanide (PAM) or mixtures thereof. Paper made from a composition according to any one of Claims 1 until 4

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