WO2008077450A1

WO2008077450A1 - Method for the production of tissue paper

Info

Publication number: WO2008077450A1
Application number: PCT/EP2007/010165
Authority: WO
Inventors: Hans-Ludwig Schubert; Frank Peter Meltzer; Esa-Matti Aalto
Original assignee: Voith Patent Gmbh
Priority date: 2006-12-23
Filing date: 2007-11-23
Publication date: 2008-07-03
Also published as: JP2010514946A; EP2126195A1; BRPI0718883A2; US20090266500A1; RU2009128370A; CA2673175A1

Abstract

The invention relates to a method for the production of a tissue web (1) produced from a material suspension comprising fibers. To this end, the volume and the tear length is to be improved, with minimized freeness degree, such that the material suspension comprises lignocellulosic pulp of wood or annuals, which has a tear length of more than 6.5 km at 12 °SR, or a tear length of more than 8.0 km at 15°SR, and a lignin content of at least 15% in relation to the otro pulp for coniferous wood in an unbleached state, or a tear length of more than 4.5 km at 20 °SR, and a lignin content of at least 12% in relation to the otro pulp for hardwood in an unbleached state, or a tear length of more than 3.5 km at 20 °SR, and a lignin content of at least 10% in relation to the otro pulp for annuals in an unbleached state.

Description

Process for the production of tissue paper

The invention relates to a method for producing a tissue web, which is produced from a fiber suspension comprising fibers.

The invention also relates to a process for the preparation of a stock suspension for the particular use for the production of tissue webs.

Tissue products today are mainly produced from whole pulps, preferably kraft pulps.

Mechanically produced fibrous materials are used only to a limited extent because the yellowing tendency and the poor strength of the substances prevent widespread use here.

Typical mixing ratios between long fiber and short fiber pulps are in the 50:50 range.

The porosity and permeability of the tissue paper are critically determined by the degree of freeness of the fibers in the stock suspension from which the tissue paper is made.

In this case, a high freeness causes a high fines content in the suspension, resulting in a low porosity and permeability.

Furthermore, a high freeness causes a high water retention value for the fibers of the pulp suspension, whereby the tissue paper is poorly dewatered during its production.

The poor drainability often results in too low a dry content during production at high machine speeds. Thus, for example, a certain dry content is necessary in front of the Yankee drying cylinder in order to prevent lifting of the tissue paper web by its contact with the hot jacket surface of the tissue drying cylinder.

In addition, the tissue web must be tear-resistant.

Tear resistance is determined by both the manufacturing process and the degree of beating of the fibers. To increase the tear strength, the tissue paper must be compacted during its production. Furthermore, in order to obtain a high tear strength, the fines content must be high.

The requirements for tensile strength thus contradict the requirements for water absorption, absorbency and drainability.

The object of the invention is therefore to enable the production of tissue paper with a high specific volume, the highest possible tear length with the lowest possible degree of grinding.

According to the invention, this object is achieved in that the pulp suspension contains lignocellulosic pulp of wood or annual plants having a tearing length of more than 6.0 km at 12 ⁰ SR or a tearing length of more than 7.5 km at 15 ° SR and a lignin content of at least 15% in relation to otro pulp for unbleached softwood or a breaking length of more than 4,5 km at 20 ⁰ SR and a lignin content of at least 12% related to the otro pulp for hardwood in the unbleached state or a breaking length of more than 3.5 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for annual plants in the unbleached state.

The fibers show high strength values even at a much lower degree of grinding compared with previously used fibers. The fibrous material according to the invention is able to build up a good bond to adjacent fibers even at a low degree of grinding and thus also less expenditure of grinding energy. The lignin content of the unbleached pulp may advantageously be at least 15%, preferably at least 18%, especially at least 21% of the otro pulp, in hardwood at least 12%, preferably at least 14%, especially at least 16% of the otro pulp and in annual plants at least 10% %, preferably at least 12% and in particular at least 19% of the otro pulp.

The higher the lignin content of the pulp, the lower the losses of wood pulp in the manufacture of the pulp.

It is also possible to achieve higher strength values. Therefore, the breaking length for softwood fiber mass at 12 ^° SR should be greater than 7 km, preferably greater than 7.5 km and in particular greater than 8 km. The tenacity for softwood fiber mass at 15 ^° SR should be greater than 9 km, preferably greater than 9.5 km and in particular greater than 10 km.

The tensile for Hardwood pulp should be at a lignin content of at least 12% and a freeness of 20 SR ⁰ greater than 6 km, preferably greater than 7 kilometers and in particular greater than 7.5 km away.

The tenacity for annual plant fiber mass should be greater than 3.5 km, preferably greater than 4 km and in particular greater than 4.5 km, at 20 ^° SR.

However, the fibrous material according to the invention is not only characterized by high breaking lengths. Rather, the strength level is high overall.

If the pulp according to the invention is subjected to a bleaching treatment, the fiber properties improve considerably. Bleaching treatment is required for some applications with higher whiteness requirements. It also aims to adjust and improve fiber properties. The bleaching treatment increases the breaking lengths. - A -

Thus, the pulp suspension lignocellulosic pulp from wood or annual plants should contain, a tenacity of greater than 7.5 km at 15 ⁰ SR and a lignin content of at least 13% based on the oven-dry pulp for softwood in the bleached state or a tenacity of greater than 5 , 0 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for hardwood in bleached condition or a breaking length of more than 5.5 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for annual plants in the bleached state.

Again, higher tear lengths are beneficial.

Thus, the breaking length for softwood fiber mass at 15 ^° SR should be greater than 9 km, preferably greater than 10 km.

The tenacity for hardwood pulp should be greater than 5.5 at 20 ^° SR and the tenacity for annual plant fiber mass at 25 ^° SR should be greater than 5 km, preferably greater than 5.5 km, and more preferably greater than 6 km.

In order to make optimal use of the advantages in terms of a high specific volume and a high strength with the lowest possible freeness, the pulp suspension should contain exclusively lignocellulosic pulp as described above.

For many applications, however, it is sufficient if the stock suspension is only partially formed by such lignocellulosic pulp. It is advantageous if between 20 and 80%, preferably between 30 and 50% of the pulp of the pulp suspension of lignocellulosic pulp are formed as described above.

After the formation of a tissue web, it is preferably passed in a dewatering step between an upper, structured and permeable belt and between a lower permeable belt, along which Drainage section pressure is exerted on the upper band, the tissue web and the lower band.

The pressure exerted on the arrangement of upper band, tissue web and lower band pressure can be effected by a gas flow and / or by a mechanical pressing force.

Preferably, in a dewatering step, a gas flows through first the upper band, then the tissue web and then the lower band. The drainage takes place in the direction of the lower band.

In addition or as an alternative to the gas flow, it may be advantageous if, in the dewatering step, the arrangement of upper belt, tissue web and lower belt is guided at least in sections between a tensioned press belt and a smooth surface, wherein the press belt acts on the upper belt and the lower band is supported on the smooth surface.

Preferably, the arrangement of upper belt, tissue web and lower belt is at least partially flowed through in the region of the dewatering section of the gas stream, so that the dewatering takes place simultaneously by the pressing force of the press belt and the flow of the gas.

Experiments have shown that the gas flow through the tissue web should be about 150 m ³ per minute and meter length along the drainage path.

In the interests of adequate dewatering of the tissue web, the press belt should be under a tension of at least 30 kN / m, preferably at least 60 kN / m and in particular 80 kN / m.

To both a good drainage of the tissue web by the mechanical tension of the press belt as well as due to the gas flow through the To achieve press belt, the press belt should have an open area of more than 50% and a contact area of at least 15%.

The smooth surface is preferably formed by the lateral surface of a roller. The generation of the gas flow can advantageously take place via a suction zone in the roll and / or via an overpressure hood arranged above the upper strip.

In the preparation of the lignocellulosic pulp-containing pulp suspension according to the invention, it is essential that at least one suspension component of wood or annual plants with a lignin content of at least 15% for softwood and 12% for hardwood and 10% for annual plants, in each case based on the otro pulp with the following Steps is made:

- Make a chemical solution with more than 5% chemicals (calculated as NaOH) for softwood or with more than 3.5% chemicals (calculated as NaOH) for hardwood or with more than 2.5% chemicals (calculated as NaOH), each purchased on the otro amount of wood used,

Mixing the chemical solution with the wood or annual plants in a predetermined liquor ratio,

- Heating the chemical solution and the wood or annual plants to a temperature above room temperature and then either (1st alternative)

- removal of free-flowing chemical solution and - digestion of the wood or annual plants in the vapor phase or (2nd alternative)

- Harvesting the wood or annual plants in the presence of the chemical solution in the liquid phase and

- Separating the free-flowing chemical solution and the wood or annual plants. The method according to the invention is based on the fact that higher quantities of chemicals are used for the production of high-yield fibers than has hitherto been customary. More than 5% of softwood chemicals are well above the hitherto common chemicals levels for engineering pulp production, also more than 3.5% for hardwood and 2.5% for annual plants. This high use of chemicals yields fibers with good yield and excellent strength properties. Thus, for softwood at grinding degrees of only 12 ⁰ SR to 15 ⁰ SR, breaking lengths of more than 8 km, but also breaking lengths of more than 9 km and more than 10 km are measured. For deciduous trees, values of more than 5 km, but also breaking lengths of more than 6 km and more than 7 km are measured at only 20 ⁰ SR. This achieves the desired high level of strength.

It is to be regarded as an extraordinary advantage of the method according to the invention that these strength values are achieved even at extremely low degrees of grinding, which were previously unavailable for high-yield fibers. Fibrous materials according to the prior art exhibit an unacceptable level of strength at freenesses of 12 ⁰ to 15 ⁰ SR SR for softwood pulps or 20 ⁰ SR for hardwood. Known pulps have so far yielded fibers at these low degrees of grinding which have not exhibited sufficient binding power and which accordingly have not provided sufficient strength properties for economical use of such fibers.

Suitable annual plants are, in particular, bamboo, hemp, rice straw, bagasse, wheat, miscanthus or the like.

By contrast, the fibrous materials produced by the process according to the invention have tear lengths of more than 8 km up to 11 km and tear strengths of more than 70 cN up to more than 110 cN, even at degrees in the range from 12 ^° SR to 15 ^° SR Leaf weight of 100 g / m ² . These low levels of grinding are moreover achieved with a low specific requirement of grinding energy, which is less than 500 kWh / t of pulp for softwood pulps, and in hardwood pulps the demand for grinding energy may even be less than 300 kWh / t Fibrous amount. The realization that the high level of strength is already achieved at low grinding degrees of 12 ⁰ SR to 15 ⁰ SR for softwood and 20 ⁰ SR for hardwood and below, is an essential part of the invention.

These high strength values combined with low levels of grinding are not yet known for pulps with a lignin content of more than 15% for softwood pulps, more than 12% for hardwood pulp or more than 10% for annual plants. However, the high strength level can also be maintained for fibers with an even higher lignin content. The inventive method is also suitable for the production of softwood pulps with a lignin content of more than 18%, preferably more than 21%, advantageously more than 24% based on the otro fiber mass. Hardwood fibers with a lignin content of more than 14%, preferably more than 16%, more preferably more than 18% and annual plants with a lignin content of more than 10%, preferably more than 12%, in particular more than 19% can also with the lignin are prepared according to the invention and show a high level of strength.

The composition of the chemical solution used for the digestion can be determined in accordance with the wood to be broken or the annual plants and the desired pulp properties. As a rule, only one sulfite component is used. Alternatively or in addition, a sulfide component may be added. Digestion with a sulfite component is not disturbed by the presence of sulfide components. Technically, sodium sulfite is usually used, but also the use of ammonium or potassium sulfite or magnesium bisulfite is possible. In particular, when high amounts of sulfite are used, can be dispensed with the use of an alkaline component, because even without the addition of alkaline components, a high pH value sets, which favors the digestion.

To adjust the pH and to support the delignification, an acidic and / or an alkaline component can be added. The alkaline component is usually sodium hydroxide (NaOH) is used. Is possible but also the use of carbonates, especially sodium carbonate. All information on chemical quantities of the digestion process in this document, eg. B. for the total use of chemicals or for the distribution of the sulfite component and the alkaline component, unless otherwise stated, each calculated and reported as sodium hydroxide (NaOH).

As an acid component, acids can be added to adjust the desired pH. However, preference is given to the addition of SO ₂ , if appropriate in aqueous solution. It is inexpensive and readily available, especially if the spent chemical solution z. B. based on sodium sulfite, after digestion is prepared for further use.

It is considered an independent inventive achievement to have recognized the advantages of using a quinone component for the high yield digestion of the invention. Quinone components, particularly anthraquinone, have heretofore been used in the manufacture of pulps with minimal lignin content to prevent unwanted attack on the carbohydrates towards the end of the digestion. The addition of quinone components makes it possible to continue the digestion of wood until almost complete degradation of the lignin. It has been found to be an unprecedented, unexpected property of quinone components that significantly increase the rate of lignin degradation in the production of high yield pulps. The duration of the digestion can z. B. in the production of softwood pulps by more than half, depending on digestion conditions shortened by more than three quarters. This remarkable effect is achieved with minimal use of quinone. Optimal is a use of z. As anthraquinone, which is between 0.005% and 0.5%. Use of anthraquinone of up to 1% also provides the desired effect. A use of more than 3% anthraquinone is usually uneconomical.

From single or several of the aforementioned chemicals, a chemical solution is prepared. Mostly an aqueous solution is used. When Option can also be provided for the use or addition of organic solvents. Alcohol, especially methanol and ethanol, in combination with water, result in particularly effective chemical solutions for the production of high-quality high-yield fibers. The mixing ratio of water and alcohol can be optimized for the respective raw material in a few experiments.

The amount of chemicals to be used according to the invention for producing a pulp with a yield of at least 70% is at least 5% for softwood, at least 3.5% for hardwood and at least 2.5% for annual plants, in each case based on the otro wood or annual plant mass to be broken up. The quality of the produced pulp shows the best results with a chemical use of up to 15% for softwoods up to 10% for hardwood and up to 10% for annual plants. Preference is given to between 9% and 11% chemicals based on the used otro wood in softwood added. For hardwoods, the use of chemicals is rather lower, preferably between 4% and 10%, more preferably between 6% and 9% and in annual plants between 3 and 10%.

As already explained above, setting a specific pH is by no means required. Only if, for example, special properties of the pulps (particularly high whiteness, a certain ratio of breaking lengths and tear strength) are to be achieved with the digestion, it may be useful to add acid or an alkaline component before or during the digestion. According to an advantageous embodiment of the method according to the invention, regardless of the chosen use of chemicals as a whole, a ratio between an alkaline component and sulfur dioxide (SO ₂ ) can be adjusted within a wide range. SO ₂ is mentioned here as representative of the above-mentioned acidic component. So it can be used instead of SO ₂ and an acid. Since the possibly added quinone component is used only in minimal amounts, usually well below 1%, it is negligible for setting this ratio. A ratio of alkaline component: SO ₂ in a range of 5: 1 to 1, 6: 1 is well suited to carry out the inventive method and to achieve fibers with high strength properties. A customary, particularly suitable range is between 2: 1 and 1, 6: 1. The adjustment of the proportionate components takes place depending on the raw material to be digested and the respectively selected process control (digestion temperature, digestion time, impregnation).

The process of the invention can be carried out in a wide pH range. The ratio of alkaline component to acidic component or the use of an acidic or an alkaline component can be adjusted so that at the beginning of the process, a pH between 6 and 11, preferably between 7 and 11, more preferably between 7.5 and 10 is set. The more alkaline pH's between 8 and 11, which are beneficial to the process of the invention, also favor the effect of the quinone moiety. The method according to the invention is tolerant with regard to the pH; There are few chemicals required for pH adjustment. This has a favorable effect on the costs of chemicals.

Without further addition of acid or alkaline component arises, for. For example, for softwood, at the end of the digestion, a pH between 5 and 9, usually between 6.5 and 9 in the free-flowing chemical solution and the dissolved organic components that have been liquefied by the digestion, a. Among the dissolved organic components are mainly lignosulfonates.

The liquor ratio, ie the ratio of the amount of otro wood or annual plants to the chemical solution, is set between 1: 1, 5 and 1: 6. A liquor ratio of 1: 2 to 1: 4 is preferred. In this range, a good and simple mixing and impregnation of the material to be digested is ensured. For softwood, a liquor ratio of 1: 3.5 is preferred. For wood chips with a large surface, the liquor ratio can also be significantly higher, to allow rapid wetting and impregnation. At the same time, the concentration of the chemical solution can be kept so high that the liquid volumes to be circulated are not too large.

The mixture or impregnation of the wood or Einjähraufschlussgut preferably takes place at elevated temperatures. A heating of the wood chips and the

Chemical solution to up to 110 ⁰ C, preferably up to 120 ⁰ C ₁ particularly preferably up to 130 ⁰ C leads to a rapid and uniform digestion of the wood. For the mixing or impregnation of the chips, a period of up to 30 minutes, preferably of up to 60 minutes, particularly preferably of up to 90 minutes, is advantageous. The optimal period of time depends among other things on the

Amount of chemicals, liquor ratio, selected temperature and

Type of digestion (liquid or vapor phase).

The digestion of the mixed or impregnated with the chemical solution lignocellulosic material is preferably carried out at temperatures between 120 ⁰ C and 190 ⁰ C, preferably between 140 ⁰ C and 180 ⁰ C. For most woods decomposition temperatures between 150 ⁰ C and 170 ⁰ C. set. Higher or lower temperatures can be adjusted, but in this temperature range, the energy required to heat and accelerate the digestion are in an economic relationship. Higher temperatures can also have a negative effect on the strength and whiteness of the fibers. The pressure generated by the high temperatures can be easily absorbed by appropriate design of the digester. Usually, the duration of the heating is only a few minutes, usually up to 30 minutes, advantageously up to 10 minutes, in particular when heated by means of steam. The duration of the heating can take up to 120 minutes, preferably up to 60 minutes, z. B. when it is digested in the liquid phase and the chemical solution is to be heated together with the wood chips.

The duration of the digestion is chosen especially depending on the desired pulp properties. The duration of the digestion can be shortened to up to 2 minutes, z. B. in the case of a vapor phase digestion of a Hardwood with low lignin content. But it can also be up to 180 minutes, if z. B. the digestion temperature low and the natural lignin content of the aufzuschließenden wood is high. Even if the initial pH of the digestion is in the neutral range, a long digestion time may be required. Preferably, the digestion time is up to 90 minutes, especially in coniferous wood. Particularly preferably, the digestion time is up to 60 minutes, advantageously up to 30 minutes. A digestion time of up to 60 minutes is mainly considered for hardwoods.

In annual plants, the digestion time is up to 90 minutes. The use of a quinone component, in particular anthraquinone, allows a reduction of the digestion time to up to 25% of the time required without the addition of anthraquinone. If the use of quinone components is omitted, the digestion time is extended by more than one hour, for example from 45 minutes to 180 minutes, for comparable digestion results.

According to an advantageous embodiment of the method according to the invention, the duration of the digestion is set as a function of the selected liquor ratio. The lower the liquor ratio, the shorter the process duration can be set.

The production of high yield pulp with high chemical input of more than 5% for softwood, of more than 3.5% for hardwood and at least 2.5% for annual plants initially appears uneconomical. Experiments have shown, however, that only some of the chemicals are consumed during the partial digestion of the lignocellulosic material. The majority of the chemicals are discharged unused, either before digestion (vapor phase digestion) or after digestion (digestion in the liquid phase). The actual consumption of chemicals is below the amounts used in the digestion solution. Chemical consumption is recorded as the amount of chemicals measured in terms of the original amount of chemicals after removal or separation of the chemical solution and, if necessary, detection of chemical solution measured after defibration or in conjunction with detection of the chemical solution. The consumption of chemicals depends on the absolute amount of chemicals used for the digestion, based on the otro wood mass to be digested. The higher the use of digestion chemicals, the lower the direct sales of chemicals. When using 27.5% of chemicals based on otro wood pulp, for example, only about 30% of the chemicals used are consumed. However, when 15% of the chemicals are used in relation to otro wood, 60% of the chemicals used are consumed, as demonstrated in laboratory tests. The consumption of chemicals for the process according to the invention is according to a preferred embodiment of the process during digestion up to 80%, preferably up to 60%, more preferably up to 40%, advantageously up to 20%, particularly advantageously up to 10% of the chemical use, the is used at the beginning of the digestion.

The chemical consumption for producing a ton of pulp is about 6%

14% sulfite and / or sulfide component and optionally alkaline and / or acidic component and optionally quinone component based on otro pulp (deciduous and

Softwood or annual plants). According to the invention, this quantity is sufficient

Chemicals to produce a pulp with the given properties.

However, in order to ensure a uniform process result and possibly to obtain special, desired pulp properties, it may prove useful to use higher amounts of chemicals for the digestion, z. As the above-mentioned up to 30% chemicals based on otro wood or

Annuals mass.

The use of these amounts of chemicals at the beginning of the digestion shows advantageous effect, since the fibers obtained in this way previously unavailable

Properties, in particular high strength properties and high whiteness. In particular, no digestion method is currently available that has a broad pH range from neutral to alkaline produces fibers with high strengths. As economically particularly attractive has been found that the fibers produced according to the invention are to be ground with much lower energy consumption to predetermined degrees of grinding than known fibers. In addition, they develop the high strengths even at unusually low grinding grades from 12 ⁰ SR to 15 ⁰ SR for softwood and 20 ⁰ SR for hardwood.

Excess chemicals are present after mixing and impregnating the wood with the chemical solution or after digestion in the free flowing liquid. This excess is deducted before digestion (1st alternative) or after digestion (2nd alternative). According to an advantageous embodiment of the method, the composition of the removed chemical solution is detected and then adjusted to a predetermined composition for re-use for the production of fibers. The chemical solution that is removed before or after the decomposition of the wood or annual plants no longer has the original composition. At least some of the chemicals used for digestion have - as described above - penetrated into the material to be digested and / or has been consumed in the digestion. The unused chemicals can easily be used again for the next digestion. However, it is proposed according to the invention to first determine the composition of the removed chemical solution and then the consumed proportions of z. As sulfite, alkaline component, quinone component or water or alcohol to supplement to restore the predetermined composition for the next digestion. This supplementary step is also called strengthening.

It is to be regarded as a considerable advantage of this measure that the chemical solution even when removed before digestion, but also when removed after digestion contains no or only very few substances resulting from reuse of the strengthened chemical solution to interfere with the next digestion. The method according to the invention, which aims to provide an oversupply of digestion chemicals during impregnation, can thus be extremely economical despite the initially uneconomic approach of high chemical use, because the removal or separation and the strengthening of the chemical solution can be carried out easily and inexpensively.

The process of the invention is specifically controlled so that only as little of the starting material used is degraded or dissolved. The aim is to produce a pulp which has a lignin content of at least 15% based on the otro fiber mass for softwood, preferably a lignin content of at least 18%, more preferably 21%, advantageously at least 24%. For hardwood is sought to achieve a lignin content of at least 12% based on the otro fiber mass, preferably of at least 14%, more preferably of at least 16%, advantageously of at least 18%. In annual plants, the preferred lignin content is between 10 and 28%, in particular between 12 and 26%.

The yield of the process according to the invention is at least 70%, preferably more than 75%, advantageously more than 80%, in each case based on the wood used. This yield correlates with that given above

Lignin content of the pulp. The original lignin content of wood is specific to the species. In the present process, the yield loss is predominantly a loss of lignin. In the case of nonspecific digestion processes, the proportion of carbohydrates is markedly increased, eg. B. because digestion chemicals in an undesirable manner also bring cellulose or hemicelluloses in solution.

A further, advantageous measure is to remove after defibering and optionally grinding the lignocellulosic material, the remaining chemical solution and feed it to a further use. In a preferred embodiment, this reuse can include two aspects. On the one hand, the decomposed during the partial digestion or dissolved in organic material, predominantly lignin, further used. It is burned, for example, to gain process energy. Or it is prepared to be used elsewhere. On the other hand, the used and unused chemicals are reprocessed so that they can be used for a renewed, partial digestion of lignocellulosic material. This includes the treatment of used chemicals.

According to a particularly preferred variant of the method according to the invention, the chemical solution used is used extremely efficiently. After defibering and optionally grinding, the pulp is washed to displace the chemical solution as much as possible through water. The filtrate produced in this washing or displacement process contains considerable amounts of chemical solution and organic material. According to the invention, this filtrate is supplied to the removed or separated chemical solution before the chemical solution is fortified and fed to the next digestion. The chemicals and organic components contained in the filtrate do not disturb the digestion. To the extent that they still contribute to delignification during the next digestion, their content is recorded in the chemical solution and taken into account in determining the amount of chemicals required for this digestion. The further contained in the filtrate chemicals behave inert during the pending digestion. They do not bother. The organic constituents contained in the filtrate are also inert. They will continue to be used in the processing of the chemical solution after the next digestion, either to generate process energy or otherwise.

It is considered to be particularly advantageous that less filtrate water and fewer chemicals are used for digestion by this filtrate. At the same time a maximum of dissolved organic material is detected. This improved use of the dissolved organic material also improves the economy of the process according to the invention. The invention will be explained in more detail below with reference to several exemplary embodiments. In the attached drawing shows:

Figure 1: an apparatus for performing the method according to the invention and

Figure 2: a second device.

First, however, the details of the method according to the invention for producing the stock suspension will be explained in more detail below using exemplary embodiments.

The following tests were evaluated according to the following rules:

The yield was calculated by weighing the raw material used and the pulp obtained after the pulping, in each case dried at 105 ^° C. to constant weight (atro).

The lignin content was determined as Klason lignin according to TAPPT T 222 om-98. The acid-soluble lignin was determined according to TAPPI UM 250

- The paper technology properties were determined on test sheets, which were prepared according to Zellcheming leaflet V / 8/76. - The degree of grinding was recorded according to Zellcheming leaflet V / 3/62.

- The density was determined according to Zellcheming regulation V / 11/57.

The breaking length was determined according to Zellcheming regulation V / 12/57.

- The tear resistance was determined according to DIN 53 128 Elmendorf.

Tensile, Tear and Burst Index were determined according to TAPPI 220 sp-96.

- The whiteness was determined by preparing the test sheets according to Zellcheming leaflet V / 19/63, measured according to SCAN C 11: 75 with a Datacolor elrepho 450 x photometer; the whiteness is given in percent according to ISO standard 2470. - The viscosity was determined according to the leaflet IV / 36/61 of the Association of Pulp and Paper Chemists and Engineers (Zellcheming). - All% figures in this document are to be read as weight percent unless otherwise specified.

The term "otro" in this document refers to "oven-dry" material which has been dried at 105 ^° C. to constant weight. - The chemicals for the digestion are given in percent by weight as sodium hydroxide, unless otherwise stated.

Example 1 - Softwood pulping in the liquid phase

A mixture of spruce wood and Douglas fir wood chips was after a damping (30 minutes in saturated steam at 105 ⁰ C) with a sodium sulfite pulping solution at a liquor ratio of wood: digestion solution 1: 3 added. The total use of chemicals was less than 15% based on otro woodchips. The pH at the beginning of the digestion was adjusted to pH 8.5-9 by addition of SO ₂ .

The impregnated with chemical solution spruce wood chips were heated over a period of 90 minutes at 170 ° C and digested for 60 minutes at this maximum temperature.

Subsequently, the free-flowing liquid was removed by centrifugation, collected and analyzed and strengthened in an arrangement for recycling unconsumed liquid and thus provided for the next digestion.

The open-ended wood chips were shredded. Aliquots of the pulp so produced were ground for different lengths to determine the strength at different degrees of grinding. The energy required to shred the partially digested chips was less than 300 kWh / t of pulp.

The yield in this experiment was 77% based on the wood pulp used. This corresponds to a pulp with a lignin content of well over 20%. The average lignin content for spruce wood is given as 28% in relation to the otro wood mass (Wagenführ, Anatomie des Holzes, VEB Fachbuchverlag Leipzig, 1980). The actual lignin content of the pulp is higher than 20%, because during digestion mainly but not exclusively lignin is broken down. Carbohydrates (cellulose and hemicelluloses) are also dissolved in small amounts. The values given show that the digestion has a good selectivity with regard to lignin and carbohydrate degradation.

The whiteness is unexpectedly high with values of over 55% ISO and thus provides a good starting point for a possible subsequent bleaching, in the whiteness of 75% ISO can be achieved.

At a starting grinding degree of 12 ^° SR, these substances already have 6 km of breaking length with a specific weight of 1.87 cm ³ / g.

To grind the fibers to a degree of grinding of 15 ⁰ SR, a grinding time of 20 to 30 minutes is required. Up to a grinding time of 20 minutes (freeness SR 12 ⁰ - 15 ⁰ SR), the freeness independent of pH (pH 6 to pH 9.4) developed at the beginning of the pulping process in a narrow range.

Also regardless of the initial pH of the digestion and the grinding time required to reach the degree of grinding a high level of strength is achieved at a freeness of 15 ⁰ SR.

Example 2

The pulp was made from spruce wood chips with the pH at the beginning of the digestion being 9.4.

In addition to the 15% total chemicals (sulfite and NaOH in predetermined proportions), the chemical solution 0.1 anthraquinone was added based on the amount of wood used. The duration of the digestion was 60 minutes.

The following values resulted:

Yield (%): 81, 1

Lignin content: 22.7

Whiteness (% ISO): 53.7

Tear length (km): 9.6

Tear resistance (cN, 100 g / m ² ): 75.0

By adding 0.1% anthraquinone, the duration of digestion can be reduced from approx. 180 minutes to 60 minutes under otherwise unchanged digestion conditions. This time saving is valuable, above all because the plants for producing pulp can be made smaller. Further savings potential lies in the fact that the temperature required for digestion only needs to be maintained for a much shorter period of time.

Furthermore, it was determined that with decreasing use of total chemicals up to values of between 5 and 15% softwood pulp is produced with largely equally good properties. These results are not dependent on the use of anthraquinone. The anthraquinone causes an acceleration of the digestion, the desired pulp can also be digested without the addition of anthraquinone.

Example 3: Hardwood pulping in the liquid phase

Eucalyptus chips were added after attenuation with a sodium sulfite digestion solution at a liquor ratio of wood digestion solution 1: 3. The use of chemicals here was 10.5% (as NaOH) on otro woodchips. In the period of 90 minutes, the pulp was impregnated and the food was heated to the maximum digestion temperature of 170 ⁰ C. The cooking time was 50 minutes.

Digestions with eucalyptus wood show that these substances can be produced with a specific energy input for defibration of less than 250 kWh / t.

The yield in these experiments was 77% based on the wood pulp used. In an initial freeness of 14 SR these substances have 3.5 km tearing length at a specific of 2.05 cm ³ / g. These substances bleached to whiteness of 79.6% ISO in the following bleach.

Experiments have shown that the vapor phase digestions have a low overall time requirement. Compared to the digestion in the liquid phase, the heating up to the maximum digestion temperature takes place much faster. The actual digestion then takes the same duration as a boiling in the liquid phase. There is no free-flowing chemical solution during vapor phase digestion, which is removed after impregnation and before digestion. It is therefore less mixed with organic material than the chemical solution, which is withdrawn after digestion in the liquid phase. However, this does not affect the quality of the pulp produced.

While in the case of vapor-phase digestions similar values can be achieved in the yield, the whiteness of the fibers produced during the steam digestion is significantly lower. A significant effect is the reduction of the maximum digestion temperature from 170 ⁰ C to 155 ⁰ C: the whiteness increases.

The fibers produced in the vapor phase have excellent strengths. The tenacity was measured, for example, 10 km and 11 km at 15 ⁰ SR. The tear resistance was measured, for example, at 82.8 cN and 91.0 cN. These values correspond to the best values for high fiber pulps Lignin content that has been achieved for digestions in the liquid phase or is even higher. For prior art high lignin content pulps, comparable strength values are not known.

It can be seen particularly clearly from the examples that the fibrous materials according to the invention require only a small amount of energy during grinding in order to build up high breaking lengths without reducing the tear propagation resistance. Grinding 12 ⁰ SR was achieved in 0-10 minutes; Grinding degree 13 ⁰ SR 5-30 minutes, usually 10-20 minutes. In order to reach grind level 14 ⁰ SR, the Jokro mill had to work for 30-40 minutes and for grind level 15 ⁰ SR it took between 35 and 40 minutes. It is obvious that a grinding up to Mahlgrade by 40 ⁰ SR would require an enormous amount of grinding energy. A particular advantage of the method according to the invention is therefore to be seen in the fact that with low energy consumption to be milled fibers are produced with high strengths.

The device for providing a pulp suspension, which is used in the process according to the invention for the production of a tissue web, comprises a pulper in which the dry raw materials and pulp and waste paper are dissolved in water and converted into a pumpable state. Subsequently, the substance thus formed is fed to a mixing vessel

In the subsequent grinding process, the stock suspension is ground to a freeness of 12 ° SR or more.

After the machine chest, the stock suspension is very strongly diluted with white water and fed to a headbox 13.

Regardless of how the stock suspension is obtained, it is important for the production of tissue paper that the material emerging from the headbox 13 Pulp has a freeness of less than 20 ⁰ SR and has a tearing length of more than 4.5 km.

A stock suspension 1 with the above-mentioned properties emerges from the headbox 13 in such a way that it is injected into the incoming gap between a forming fabric 14 and a structured, in particular 3-dimensionally structured, band 3, whereby a tissue web 1 is formed.

The Formiersieb 14 has a directed to the tissue web 1 side, which is smooth relative to that of the structured band 3.

In this case, the side of the structured band 3 facing the tissue web 1 has recessed areas and elevated areas relative to the recessed areas, so that the tissue web 1 is formed in the recessed areas and the raised areas of the structured band 3. The height difference between the recessed

Areas and raised areas is preferably 0.07mm and 0.6mm.

The area formed by the raised areas is preferably 10% or more, more preferably 20% or more, and most preferably 25% to 30%.

In the illustrated embodiments, the assembly of upper belt 3, tissue web 1 and forming fabric 14 is directed around a forming roll 15 and the tissue web 1 is substantially dewatered through the forming fabric 14 before the forming fabric 14 is removed from the tissue web 1 and the tissue web 1 on the Volume 3 is transported on.

The voluminous sections of the tissue web 1 formed in the recessed areas of the band 3 have a higher volume and a higher basis weight than the sections of the tissue web 1 formed in the raised areas of the band 3.

The tissue web 1 therefore already has a 3-dimensional structure due to its formation on the structured band 3. The sheet formation can, however, also take place between two smooth forming fabrics 14, so that a substantially smooth tissue web 1 is formed without a 3-dimensional structure.

In one of the formation of the tissue web 1 subsequent dewatering step, the tissue web 1 between the structured band 3, which is arranged at the top, and a lower, permeable and formed as a felt band 2, wherein in the dewatering step along a Entwässerungsstrecke pressure on the structured band. 3 , the tissue web 1 and the band 2 is exercised such that the

Tissuebahn 1 is drained in the direction of the belt 2, as indicated by the arrows in both figures.

During the dewatering, the tissue web 1 wraps around the rolls 2, 3 a roll 5.

By dewatering the tissue web 1 in the direction of the belt 2 during this dewatering step and by dewatering the tissue web 1 on the structured belt 3 on which it has already been formed, the voluminous sections are compressed less than the other sections, so that As a result, the voluminous structure of these sections is retained.

The pressure for dewatering the tissue web 1 is generated at least in sections at the same time by a gas flow and by a mechanical pressing force in the dewatering step according to FIG.

The gas stream flows through first the structured band 3, then the tissue web 1 and then the formed as a felt lower band 2. The gas flow through the tissue web 1 is about 150 m ³ per minute and meter web length. In the present case, the gas flow is generated by a suction zone 10 in the roller 5, wherein the suction zone 10 has a length in the range between 200 mm and 2500 mm, preferably between 800 mm and 1800 mm, more preferably between 1200 mm and 1600 mm.

The negative pressure in the suction zone 10 is between -0.2bar and -0.8bar, preferably between -0.4bar and -0.6bar.

With regard to the performance of the dewatering step performed by mechanical pressing force and optionally or additionally with gas flow, as well as the various configurations of devices for carrying out such a dewatering step, PCT / EP2005 / 050198 should be fully incorporated in the disclosure of the present application.

According to FIG. 1, the mechanical pressing force is produced by guiding the arrangement of structured band 3, tissue web 1 and band 2 of a dewatering section 11 between a press belt 4 under tension and a smooth surface during the dewatering step, the press belt 4 being structured Band 3 acts and the band 2 is supported on the smooth surface.

The smooth surface is formed by the lateral surface of the roller 5.

The dewatering section 11 is essentially defined by the wrap area of the press belt 4 around the lateral surface of the roller 5, wherein the wrap area is determined by the distance between the two guide rollers 12.

The press belt 4 is under a tension of at least 30 kN / m, preferably at least 60 kN / m or 80 kN / m and has an open area of at least 25% and a contact surface of at least 10% of its entire surface facing the upper band 3.

In the concrete case, the press belt 4, designed as a spiral link fabric, has an open area of between 51% and 62% and a contact area of between 38% and 49% of its total area facing the upper belt 3.

With regard to the structure of the press belt, PCT / EP2005 / 050198 should be included in full in the disclosure of the present application.

The tissue web 1 leaves the dewatering section 11 with a dry content of between 25% and 55%.

Subsequently, the tissue web 1 is guided in a subsequent dewatering step further dewatering step together with the structured band 3 through a press nip, wherein the tissue web 1 is arranged in the press nip between the structured band 3 and a smooth roll surface of a Yankee drying cylinder 7. The press nip here is an extended press nip formed by the Yankee dryer cylinder 7 and a shoe press roll 8.

The tissue web 1 rests on one side with a relatively large area on the lateral surface of the Yankee drying cylinder 7, the tissue web 1 resting on the other side on the structured band 3.

The recessed areas and the relatively elevated areas of the structured band 3 are in this case designed and arranged relative to one another such that the voluminous sections in the press nip are essentially not pressed. On the other hand, the other sections are pressed, whereby the strength of the tissue web 1 is further increased. Between the two described dewatering steps, a further dewatering step can be provided, which can be carried out by means of a device 9.

Optionally, it can be provided that the tissue web 1, before it passes through the press nip, is guided together with the structured band 3 around an evacuated deflection roller, the structured band 3 being arranged between the tissue web 1 and the evacuated deflection roller (not shown).

From Figure 2 it can be seen that the gas flow can be generated in addition by a arranged above the structured band 3 Überdruckhabe 6, wherein the dewatering step takes place in this case without mechanical pressing force, i. In contrast to FIG. 1, no press belt 4 is provided which wraps around the roller 5 in sections.

Claims

claims

Anspruch [en] A process for producing a tissue web (1) which is produced from a pulp comprising a pulp, characterized in that the pulp suspension comprises lignocellulosic pulp of wood or

Annual plants containing a tearing length of more than 6.0 km at 12 ⁰ SR or a tearing length of more than 7.5 km at 15 ° SR and a lignin content of at least 15% based on the otro pulp for unbleached softwood or a Tear length of more than 4.5 km at 20 ⁰ SR and a lignin content of at least 12% based on the otro pulp for

Hardwood in the unbleached state or a tearing length of more than 3.5 km at 20 ⁰ SR and a lignin content of at least 10% based on the otro pulp for annual plants in the unbleached state.

2. The method according to claim 1, characterized in that the lignin content of the unbleached pulp in coniferous wood at least 15%, preferably at least 18%, in particular at least 21% of otro pulp, in hardwood at least 12%, preferably at least 14%, in particular at least 16% of the otro pulp and in annual plants at least 10%, preferably at least 12% and in particular 19% of the otro pulp.

3. The method according to claim 1 or 2, characterized in that the breaking length for softwood fiber mass at 12 ⁰ SR is greater than 7 km, preferably greater than 7.5 km and in particular greater than 8 km.

4. The method according to any one of the preceding claims, characterized in that the breaking length for softwood fiber mass at 15 ⁰ SR is greater than 9 km, preferably greater than 9.5 km and in particular greater than 10 km.

5. The method according to any one of the preceding claims, characterized in that the breaking length for hardwood fiber mass at a freeness of 20 ⁰ SR is greater than 6 km, preferably greater than 7 km and in particular greater than 7.5 km.

6. The method according to any one of the preceding claims, characterized in that the breaking length for annual plant fiber mass at 20 0SR is greater than 3.5 km, preferably greater than 4 km and in particular greater than 4.5 km.

7. A process for producing a tissue web (1), which is prepared from a pulp comprising pulp, characterized in that the pulp suspension contains lignocellulosic pulp of wood or annual plants having a tearing length of more than 7.5 km at 15 ⁰ SR and a Lignin content of at least 13% based on the otro pulp for

Softwood bleached or having a breaking length of more than 5,0 km at 20 ^° SR and a lignin content of at least 10% related to the otro pulp for hardwood in bleached condition or a breaking length of more than 5,5 km at 20 ⁰ SR and has a lignin content of at least 10% based on the otro pulp for annual plants in the bleached state.

8. The method according to claim 7, characterized in that the breaking length for softwood fiber mass at 15 ⁰ SR is greater than 9 km, preferably greater than 10 km.

9. The method according to claim 7 or 8, characterized in that the breaking length for hardwood fiber mass at 20 ⁰ SR is greater than 5.5.

10. The method according to any one of claims 7 to 9, characterized in that the breaking length for annual plant fiber mass at 20 ⁰ SR is greater than 4 km, preferably greater than 4.5 km and in particular greater than 5 km.

11. A process for producing a tissue web (1), characterized in that the pulp suspension contains only lignocellulosic pulp according to one of the preceding claims.

12. A process for producing a tissue web (1), characterized in that the pulp suspension is only partially formed by lignocellulosic pulp according to one of claims 1 to 11.

13. The method according to claim 12, characterized in that between 20 and 80%, preferably between 30 and 50% of the pulp of

A pulp suspension of lignocellulosic pulp according to one of claims 1 to 11 is formed.

14. The method according to any one of the preceding claims, characterized in that the tissue web (1) is guided in a dewatering step between an upper, structured and permeable belt (3) and between a lower permeable belt (2), wherein along a Entwässerungsstrecke (11 ) Pressure on the upper band (3), the tissue web (1) and the lower band (2) is applied.

15. The method according to claim 14, characterized in that in a dewatering step (11) first of the upper band (3), then the tissue web (1) and then the lower band (2) is flowed through by a gas.

16. The method according to claim 14 or 15, characterized in that in the dewatering step, the arrangement of the upper belt (3), tissue web (1) and lower belt (2) at least partially between a tensioned press belt (4) and a smooth surface is guided, wherein the press belt (4) acts on the upper band (3) and the lower

Band (2) supported on the smooth surface.

17. The method according to claim 15 or 16, characterized in that the arrangement of upper belt (3), tissue web (1) and lower belt (2) is at least partially flowed through in the region of the dewatering section (11) of the gas stream.

18. The method according to any one of claims 15 to 17, characterized in that the gas flow through the tissue web (1) is about 150 m ³ per minute and meter length along the dewatering section (11).

19. The method according to any one of claims 16 to 18, characterized in that the press belt (4) is under a tension of at least 30 kN / m, preferably at least 60 kN / m and in particular 80 kN / m.

20. The method according to any one of claims 16 to 19, characterized in that the press belt (4) has an open area of more than 50% and a

Contact area of at least 15%.

21. The method according to any one of claims 16 to 20, characterized in that the smooth surface is formed by the lateral surface of a roller (5).

22. The method according to claim 21, characterized in that the gas flow through a suction zone (10) in the roller (5) is formed.

23. The method according to any one of claims 15 to 22, characterized in that the gas flow through a above the upper band (3) arranged over-pressure hood (6) is generated.

24. A process for the production of a pulp comprising material suspension for use in particular for producing a tissue web (1), wherein at least a proportion of wood or annual plants with a lignin content of at least 15% for softwood, of at least 12% for hardwood and of at least 10% for annual plants, in each case based on the otro fiber mass, using the following steps:

- manufacture a chemical solution with more than 5% chemicals (calculated as NaOH) for softwood or with more than 3.5% chemicals (calculated as NaOH) for hardwood or with more than 2.5% chemicals (calculated as NaOH) for annual plants, each related to the otro amount of wood

- Mixing the chemical solution with wood or annual plants in a given liquor ratio

- Heating the chemical solution and the wood or the annual plants to a temperature above room temperature and then

- either (1 st alternative) removing free-flowing chemical solution and digesting the wood or annual plants in the vapor phase - or (second alternative) digesting the wood or annual plants in the liquid phase and separating the free-flowing chemical solution and the wood or the annual plants.

25. The method according to claim 24, characterized in that a fibrous material with a content of at least 15% lignin, preferably at least 18% lignin, advantageously at least 21% lignin, in particular at least 24% lignin based on otro pulp for softwood or with a content of At least 14% lignin, preferably at least 16% lignin, more preferably at least 18% lignin based on otro pulp for hardwood or containing at least 10% lignin, preferably at least 12% lignin, especially at least 19% lignin based on otro pulp for annual plants will be produced.

26. The method according to claim 24 or 25, characterized in that for the preparation of the chemical solution, a quinone component is used.

27. The method according to any one of claims 24 to 26, characterized in that for the decomposition of softwood at most 15% chemicals, preferably between 9 and 11% chemicals are used.

28. The method according to any one of claims 24 to 27, characterized in that for the digestion of hardwood at most 10% chemicals, preferably between 4 and 10% chemicals, in particular between 6 and 9% chemicals are used.

29. The method according to any one of claims 24 to 28, characterized in that for the digestion of annual plants at most 10%, preferably between 3 and 10% chemicals are used.

30. The method according to any one of claims 24 to 29, characterized in that for the preparation of the chemical solution sulfites and sulfides, individually or in

Mixture be used.

31. The method according to claim 30, characterized in that for the preparation of the chemical solution, an acidic and / or an alkaline component, in particular an acid, sulfur dioxide, sodium hydroxide and / or a carbonate is used.

32. The method according to any one of claims 24 to 31, characterized in that for the digestion of an alkaline component and an acidic component, in particular SO ₂ are used, wherein the ratio is alkaline

Component: SO _{2 is} adjusted in a range of 5: 1 to 1, 6: 1, preferably 2: 1.

33. The method according to any one of claims 24 to 32, characterized in that the method at a pH between 6 and 11, preferably between

7 and 11, more preferably between 7.5 and 10 is performed.

34. The method according to any one of claims 24 to 33, characterized in that a liquor ratio wood: chemical solution between 1: 1, 5 and 1: 6, preferably between 1: 2 and 1: 4 is set.

35. The method according to any one of claims 24 to 34, characterized in that the heating of the chemical solution and the wood or annual plants up to 130 ⁰ C, preferably up to 120 ⁰ C, advantageously up to 110 ⁰ C.

36. The method according to any one of claims 24 to 35, characterized in that the heating of the wood or the annual plants and optionally the chemical solution for up to 120 minutes, preferably up to 60 minutes, advantageously up to 30 minutes, particularly advantageously up to 10 Takes minutes.

37. The method according to any one of claims 24 to 36, characterized in that the digestion of the wood or annual plants at temperatures between 120 ⁰ C and 190 ⁰ C, preferably at temperatures between 150 ⁰ C and 180 ⁰ C, particularly preferably at temperatures between 160 ⁰ C and 170 ⁰ C is performed.

38. The method according to any one of claims 24 to 37, characterized in that the digestion of the wood or annual plants up to 180 minutes, preferably up to 90 minutes, more preferably up to 60 minutes, advantageously up to 30 minutes, particularly advantageous to takes 2 minutes.

39. The method according to claim 38, characterized in that the duration of the digestion is selected as a function of the liquor ratio.

40. The method according to any one of claims 24 to 39, characterized in that the consumption of chemicals during digestion up to 80%, preferably up to 60%, more preferably up to 40%, advantageously up to 20%, Particularly advantageous is up to 10% of the chemical use at the beginning of the digestion.

41. The method according to any one of claims 24 to 40, characterized in that the composition of the removed or separated chemical solution is detected and then adjusted for reuse for the production of fibers to a predetermined composition.

42. The method according to any one of claims 24 to 41, characterized in that after the pulping and possibly grinding the digested lignocellulosic material released chemical solution is removed and is fed to a further use.