EP2227596B1 - Method for the production of paper, cardboard or the like and related paper or cardboard product - Google Patents

Description

The invention relates to a process for the production of paper, paperboard or similar products, according to which a mixture or pulp of cellulose fibers, at least one retention agent, at least one mineral filler of filler fibers and a solvent, for. Water, is prepared and dried on a wire to produce a product web.

In the manufacture of paper, paperboard or similar products, the ingredients that later represent the product or product web in question are added as a dilute slurry to the mentioned sieve and filtered. The slurry is usually the pulp, ie the pulp of paper or pulp dissolved in water. In order to improve the process of filtration on the screen, retention aids are usually used.

These retention agents essentially ensure that the fillers (and optionally fines) in the slurry are provided with a higher affinity for the cellulose fibers, thus reducing the drainage of these valuable substances through the sieve. That is, by the retention agent, the fillers are retained (retention of Latin "retentio" = retain), so that they are not lost with the process water. This allows the fillers to fulfill their original function of being able to positively influence the smoothness, color, flexibility, etc. of the paper or paperboard product produced.

Fillers according to the invention usually refer to those based on mineral, which are composed of filler fibers. In addition to these mineral fillers of filler fibers, however, it is also possible to add fines such as, for example, kaolin, ie powdery or granular additives, to the paper or paperboard product. The term filler now includes according to the invention Both the previously mentioned mineral fillers as Füllstotffasern and powdery or granular fines.

In fact, the fillers usually have only a low affinity for the cellulose fiber, which explains the effect described. This results in both ecological and economic damage, since the fillers can be mainly minerals for filling but also pigments. In addition, retention agents in the neutral PH range favor the glue adhesion and fiber balling of the cellulose fibers. In this way, not only fillers, but also larger amounts of fine or residual fibers of cellulose fibers are retained, which represent a significant load factor for wastewater, especially in waste paper recycling with a high proportion of multi-shortened cellulose fibers.

The effectiveness of the retention agent is measured as a relative proportion of retained on the screen fiber, fillers and optionally fines against complete retention of these substances in the wastewater. A high retention corresponds to a high percentage of remaining additives or fillers in the paper. From the foregoing, it is immediately apparent that high retention is generally desired in papermaking or paperboard production.

The use of mineral fillers in the manufacture of paper, paperboard or similar products has long been known. An example of this describes the WO 03/093578 A1 , The use of such mineral fillers is intended, on the one hand, to replace all or part of the expensive cellulose fibers and, on the other hand, to bring about a positive effect on the whiteness, the opacity, the smoothness or the printability of the product web produced. The opacity is a measure of the opacity or turbidity of substances and represents mathematically the reciprocal of the transmittance.

Opacity and transmittance describe the same material property. For example, a fully transmissive fabric has an opacity of 1, because the transmittance of a non-light-reinforcing material can be 1 or less. An infinitely opaque, ie impermeable, substance has an opacity of 0. The same applies to the transmittance. In any case, mineral fillers serve, inter alia, to improve the opacity, ie turbidity, mostly in the sense of reducing the opacity and thus increasing the transmittance.

Although mineral fillers are currently used in practice with a weight fraction of several 10 wt .-% in the production of product webs made of paper, cardboard or the like. This massive addition of mineral fillers, however, requires that the strength of the product web be reduced, so that the quality deteriorates. Consequently, the further addition of fillers are limited. In addition, the fillers in the slurry must be retained on the screen, so that with increased use of mineral fillers and the need for retention agents increases. This increases the costs and also has a negative effect on the strength of the paper.

In the generic state of the art according to the CN 1515739 A describes the use of modified mineral fibers of wollastonite as a mineral filler. Although the properties of the filler in question are given in detail, but missing information on the associated paper or cellulose base material.

As part of the DE 40 07 060 A1 is a single-surface structure is addressed, which expands when fired and consists of capable of forming paper fiber material and proportions of 1 to about 98 wt .-% expandable graphite based on the total weight of the fabric. In this context also comes a mixture of cellulose fibers and inorganic fibers for use. In this case, silicate fibers are used as inorganic fibers.

A capacitor paper according to the DE 18 17 334 A finally resorts to a mixture of cellulose fibers with mineral fibers. The diameter of the mineral fibers corresponds to the diameter of the fibrils, which have arisen due to a grinding process of the cellulose fibers.

The invention is based on the technical problem of further developing such a method so that the mineral filler can be added in large quantities and without significant loss of strength, so that overall the production costs are reduced.

1. a) Länge,
2. b) Durchmesser und
3. c) Längenverhältnis (Länge/Durchmesser)

aneinander angepasst werden.To solve this technical problem is provided in a generic method for the production of paper, cardboard or the like products that the cellulose fibers and the filler fibers in terms of at least one of the properties

1. a) length,
2. b) diameter and
3. c) aspect ratio (length / diameter)

be adapted to each other.

In the context of the invention, it is therefore important to adapt the filler fibers of the mineral filler and the cellulose fibers of the cellulose or of the cellulose base material to one another in terms of their dimensions. That is, the respective cellulosic fibers and filler fibers are in their length and / or their respective diameter and / or length ratio (Length / diameter) are substantially identical or are adapted to each other. In this context, it has been found that the cellulose fibers and the filler fibers each have a maximum deviation of 20 times, in particular 10 times, preferably 5 times, more preferably 3 times, and expressly 2 times the same properties.

This applies at least to more than 50% by weight of the cellulose fibers and the filler fibers, in particular even more than 60% by weight of the cellulose fibers and filler fibers. That is, more than 50% by weight and more than 60% by weight, respectively, are within the specified limits in terms of one or more properties. Deviations of at most ten times or in particular a maximum of fivefold have proven to be favorable. That is, the filler fibers may be formed in the example, five or a maximum of ten times as long as the cellulose fibers and vice versa. This then applies to at least 50% by weight, usually even more than 60% by weight of the cellulose fibers and filler fibers. In order to make this adjustment, the filler fibers are usually adapted to the cellulose fibers mostly known properties. For this purpose, scanning tunnel recordings of the filler fibers can be carried out and a corresponding selection made by appropriate screening processes. Within the scope of such scanning tunneling microscopy images, it is easy to determine properties such as length, diameter and length ratio of the filler fibers, and in this way the selection can be made. Of course, this also applies to the cellulose fibers, although these are usually supplied and processed with specific properties.

In the context of the invention, it is thus preferred for the cellulose fiber to be formed twice as long or three times as long as compared to the filler fibers be or vice versa. The same applies to the diameter, which in the case of the filler fibers, for example, can be three times greater compared to the cellulose fibers, if the diameter is the same property. Of course this is not mandatory. Finally, the respective fibers may alternatively or additionally have the mating aspect ratio within the specified ranges.

Tetraeder, die zu eindimensionalen unendlichen Ketten miteinander verknüpft sind. Aufgrund dieser kettenförmigen Strukturmerkmale erklären sich auch die morphologischen Eigenschaften der betreffenden Inosilikate. Denn solche Inosilikate bzw. Kettensilikate zeigen in der Regel einen prismatisch stengeligen bis nadeligen Habitus. Außerdem verfügen sie über eine gute Spaltbarkeit und lassen sich parallel zu den Kettenachsen faserig absondern. Die meisten Inosilikate bauen sich aus eindimensional unendlichen Ketten oder Bändern auf, deren Periodizität zwei Tetraederlängen umfasst. Als besonders bevorzugter Füllstoff hat sich in diesem Zusammenhang das pseudohexagonale Wollastonit erwiesen, welches Dreierketten bildet.It has proven useful if a silicate, in particular an inosilicate, is used as the mineral filler. In fact, such inosilicates have each ${\mathrm{SiO}}_4^{-}$

Tetrahedra linked to one-dimensional infinite chains. These chain-shaped structural features also explain the morphological properties of the inosilicates in question. Because such inosilicates or chain silicates usually show a prismatic stem-like to needle-like habit. In addition, they have good cleavability and can be separated fibrous parallel to the chain axes. Most inosilicates are composed of one-dimensionally infinite chains or bands whose periodicity comprises two tetrahedral lengths. As a particularly preferred filler in this context, the pseudohexagonal wollastonite has been found, which forms triples.

In general, the cellulose fibers and the filler fibers are each formed as short fibers and have a length of less than 2 mm, in particular one which is located below 1 mm. It has proven useful if the filler fibers are equipped with an aspect ratio (length / diameter) of 3 to 50, in particular 3 to 30, preferably 6 to 20 and very particularly preferably 10 to 20. That is, the length of the respective filler fiber is three to fifty times its diameter.

The cellulose fibers are equipped with an aspect ratio of up to about 100 or more. In fact, aspect ratios up to 150 are observed. That is, the length of the cellulose fibers may be 150 times as large as their diameter. As a result, it is ensured in each case that the aspect ratios are adapted to one another in the context of the previously described range. For example, assuming the maximum aspect ratio for the filler fibers of 50, the corresponding aspect ratio for the cellulosic fibers is at most three times, hence 150. Of course, the reverse can also be used.

As cellulose fibers, the invention recommends those made of natural fibers, for example short fibers such as eucalyptus fibers or birch fibers or long fibers such as spruce fibers, etc. The cellulose fibers have a length of up to 1 mm and may be equipped with a diameter of up to 100 .mu.m, wherein the diameter of the cellulose fibers is preferably in the range between about 5 microns and 80 microns settled.

The same applies to the filler fibers. These are usually also equipped with a length of up to 1 mm, preferably up to 0.5 mm. Their diameter is generally at most 100 microns and preferably in the range between 5 microns and 80 microns, in particular between 6 microns and 75 microns.

The filler of the filler fibers or inosilicate fibers and in particular wollastonite fibers has an extraordinary degree of whiteness, which can assume values between 70% and 95%. In particular, a whiteness between 75% and 92% is observed. As usual, the whiteness indicates the reflectivity of the product in question for white light. Due to this fact can be completely or partially dispensed with the addition of color pigments such as titanium dioxide and the inventive mineral filler replaces the respective color pigments wholly or partly.

According to the method of the invention, it is possible with particular preference to produce so-called SC papers (super-calandered). These are uncoated, woody papers, which are advantageously used for the production of magazines.

As a result, a method is described in which the filler fibers of the mineral filler and the cellulose fibers of the cellulosic base material are matched to each other. This applies with regard to the respective length of the fibers and / or their diameter and / or with regard to their aspect ratio. In this case, the invention with respect to the matching property in each case permits a deviation of at most twenty times, in particular ten times, and preferably five times or even less.

In this way, in principle, the level content in the products produced by the process according to the invention can be increased, wherein at the same time the observed in the prior art loss of strength does not occur or not so pronounced. This is ensured by the adaptation of the fibers to one another. In fact, the filler fibers readily insert into the slurry and are capable of replacing the cellulosic fibers to a large extent. This can be attributed to the fact that the individual cellulose molecules are designed as chain-like macromolecules and have a similar morphology to the filler-added inosilicates. As a result of the mutual adaptation of the fibers to one another, the filler fibers are as it were integrated into the molecular bundles that form during the paper making, from which the fibrils are built up.

That is, the filler fibers and the cellulose fibers form a coherent network, so that the strength against paper products with no or reduced proportion of the respective mineral fillers only insignificantly decreases or even remains the same. The use of the filler or of the filler fibers advantageously increases the drying speed in papermaking, because the filler fibers are less hydrophilic than the cellulose fibers and consequently the water absorption is reduced compared to a conventional mixture.

At the same time, the filler fibers increase the porosity of the product web thus produced, so that the application of paint is facilitated and the reprocessing is favored. In addition, the mineral filler used in the filler fibers or the inosilicate fibers generally has a high flash point. This is in the case of wollastonite well above 1000 ° C. This significantly increases the refractoriness of a so-equipped paper or paperboard product.

Furthermore, it is advantageous that inosilicates in general and wollastonite in particular - as already mentioned - are less hydrophilic than cellulose fibers, so that not only the drying, but also the filtration rate can be increased in the production of the product web. As a result, energy can be saved during the drying process and the production speed can be increased. It has proven to be altogether good if the mineral filler or the filler fibers is added directly to the pulp or be taken into account as starting material in the production of the pulp.

As a result of the rod-shaped or needle-shaped fiber shape of the inosilicate fibers, the retention is also improved over previous paper or paperboard products with other mineral fillers. Because the filler fibers and cellulose fibers combine easily. The proportion of the mineral filler with the specially adapted filler fibers in the range of a few wt .-%, for example, 5 wt .-% to 20 wt .-%, preferably up to 10 wt .-% in the pulp. In most cases, additional fillers, such as kaolin, will be used to fill in interstices between the fibers to soften and soften the product produced and give it a smooth surface.

Example 1:

To a pulp of 60 wt .-% birch sulfate and 20 wt .-% spruce sulfate are about 0.2 wt .-% retention aid and nearly 20 wt .-% (actually 19.8 wt .-%) wollastonite with a diameter of about 20 microns and different lengths and an aspect ratio (length U diameter D) of 6 to 20 added.

The following results are observed: No filler 20% by weight of kaolin 20% by weight wollastonite whiteness % 69.78 67.64 76.86 breaking force N 144.2 73.8 94.2 Burst pressure kPa 439.1 173.8 249.0 smoothness ml / min 1524 1419 1593 porosity ml / min 118 156 373

The breaking load has been determined in each case in the machine direction.

Example 2:

To a pulp of pulp is added a coarsely ground wollastonite having fiber lengths up to 0.5 mm and an aspect ratio (L / D) of 10 to 20, in different proportions. In fact, the content of wollastonite is 0.0% by weight, 1.8% by weight, 5.0% by weight and 8.3% by weight in the table below. Accordingly, the proportion of pulp in the pulp is 100% by weight, 98.2% by weight, 95.0% by weight and 91.7% by weight. The following properties are observed: Wollastonite proportion breaking force (%) MR * QR * F (N) % F (N) % 0.0 136.4 0.0 67.6 0.0 1.8 140.1 2.7 72.0 6.6 5.0 140.8 3.2 73.9 9.3 8.3 139.9 2.6 67.4 -0.2 * MR = machine direction, * QR = transverse direction

Claims (8)

1. Process for the production of paper, cardboard or similar products, according to which a mixture of cellulose fibres, at least one retention agent, at least one mineral filler made of filler fibres, and one solvent, e.g. water, is produced and dried on a sieve in order to obtain a paper web, characterised in that the cellulose fibres and the filler fibres are adapted to each other with regards to at least one of the properties

   a) length,

   b) diameter and

   c) length ratio (length/diameter).
2. Process according to claim 1, characterised in that the cellulose fibres and the filler fibres have a deviation of at most twenty-fold, in particular ten-fold, preferably five-fold, particularly preferably three-fold and especially preferably twofold with regards to the corresponding property/properties.
3. Process according to claim 1 or 2, characterised in that a silicate, in particular an inosilicate, preferably wollastonite, is employed as the mineral filler.
4. Process according to one of claims 1 to 3, characterised in that the cellulose fibres and the filler fibres are in the form of short fibres with a length of less than 2 mm, in particular below 1 mm.
5. Process according to one of claims 1 to 4, characterised in that the filler fibres are employed with a length ratio (L/D) of 3 to 50, in particular of 6 to 20 and preferably of 10 to 20.
6. Process according to one of claims 1 to 5, characterised in that the filler fibres are in the form of having a diameter up to 100 µm, in particular 6 µm to 75 µm, and a length up to 1 mm, in particular up to 500 µm.
7. Process according to one of claims 1 to 6, characterised in that the filler has a whiteness of 70 % to 95 %, in particular 75 % to 92 %.
8. Process according to one of claims 1 to 7, characterised in that the mixture contains up to a maximum of 40 wt.-%, preferably up to a maximum of 20 wt.-%, and most preferably up to a maximum of 10 wt.-% filler.