JP4823317B2 - Method for producing chemical mechanical pulp - Google Patents

Description

  The present invention relates to a method for producing chemical mechanical pulp from raw wood containing wood chips according to the preamble of claim 1.

  In such a method, under the condition that the impregnation solution penetrates into the wood chips and soaks into the wood chips, the wood chips constituting the raw wood are brought into contact with the alkaline impregnation solution, and the wood chips soaked with the impregnation solution are beaten. To produce mechanical pulp.

  The invention also relates to a chemical mechanical pulp according to the preamble of claim 14.

  Chemical mechanical pulp is produced by beating wood chips pretreated with chemicals, typically alkaline liquids, to the desired freeness. Chemical treatment facilitates beating and improves the properties of mechanical pulp. Also in chemical cooking, the wood chips are pretreated with an alkaline solution to facilitate fiber disaggregation.

  In the manufacture of mechanical and chemical pulp, both chemical absorption well into the pulp and uniform absorption into the pulp are essential. Non-uniform absorption increases the percentage of fine shards in the pulp and reduces the latent strength.

  Two mechanisms allow the absorption of liquids and chemicals into the wood, namely penetration and diffusion. Osmosis occurs as a result of pressure differences, whereas diffusion occurs as a result of concentration differences. At the beginning of the impregnation phase, the pressure difference is mainstream inside the wood chip, whereas the pressure outside the wood chip is a factor that promotes penetration to the point where the pressure difference can be balanced. When the entire wood chip is filled with liquid, diffusion prevails instead, and chemicals move into the wood chip and provide a means for reaction products to exit the wood chip.

  There are two types of penetration: natural and forced. In natural penetration, a pressure difference is generated by capillary force, while in forced penetration, a pressure difference is generated by external pressure or by generating a vacuum inside the wood chip.

  The alkaline impregnation solution swells the fiber walls and narrows the capillaries. This reduces longitudinal penetration. At the same time, however, the alkaline solution dissolves the fiber components, which accelerates the penetration.

  Diffusion is much slower than penetration. Increasing the temperature improves the diffusion rate, but it is known that increasing the rate of reaction is much faster than increasing the rate of diffusion. Thus, for example, it is noted in the literature that during the sulfate cooking process, calculations using diffusion coefficients and activation energies indicate that the diffusion rate at 170 ° C is about 4 times higher than at 100 ° C. ing. At the same time, the reaction rate is increased by a factor of 900 (Talton, J., diffusion of sodium hydroxide in wood at high pH as a function of temperature and degree of pulping, M. Sc. Thesis. , North Carolina State University, 1986, 45s).

  As the reaction rate increases, the consumption of alkali also increases.

  And the alkali dose and the size of the wood chip affect the diffusion. To avoid generating more waste, the alkali dose must be increased when the wood chip thickness is increased. Increasing the alkali dose also increases the alkali gradient between the wood chip and the surrounding solution (same liquid / wood ratio), resulting in an increase in diffusion rate.

  It should also be noted that the amount of alkali administered for impregnation is the most important factor affecting the yield of chemical mechanical pulp (CTMP). Fiber loss occurs primarily as a result of acetic acid destruction, lignin dissolution and acidic polysaccharide dissolution, all of which are caused by alkali. The effect of alkali dose is greater on hardwood than on softwood. When the alkali dose (eg, the amount of NaOH) is increased from 0.5% to 3%, the yield from the aspen material decreases linearly from about 95% to 89% in the conventional process.

  Part of the yield loss already occurs during impregnation, and part of it occurs during the subsequent high temperature beating stage.

  In fact, to ensure maximum impregnation, the amount of alkali used must be increased. The penetration of the alkaline solution into the wood chips is slow and the alkali tends to be consumed on the outside part of the wood chips, leaving no sufficient alkali for the inside of the wood chips. In the beating stage, this is indicated by a higher percentage of fine wood pieces.

The effect of alkali on the scattering quality of chemical mechanical pulp is particularly problematic. Scattering quality decreases with increasing alkali dose, and at the same level of beating, scattering is always smaller with higher alkali doses. Bleaching also further reduces scattering. In order to produce high-quality printing paper, it is essential that the pulp has good scattering and whiteness characteristics. It is possible to produce hardwood CTMP pulp with high whiteness, i.e. up to 88% ISO whiteness.
Tarton, J.A. Diffusion of sodium hydroxide in wood at high pH as a function of temperature, degree of pulping, M. Sc. Cesis, North Carolina State University, 1986, 45s

  The object of the present invention is to eliminate at least some of the disadvantages associated with the prior art and to provide a novel solution for producing chemical mechanical pulp.

The present invention is based on the principle that impregnation of chips is carried out at an absolute pressure of 1.5 bar or more when producing chemical mechanical pulp.

  Richardson and LeMahieu provide a method for producing super-ground wood pulp in which aspen chips are impregnated with a mixture of sodium hydroxide and sodium sulfite at a temperature of about 75 ° C. and a pressure of 4 bar before beating the chips. [Tappy 1965 (48), pp. 344-346]. According to the described matter, the strength of the pulp can be improved by increasing the alkali concentration, and at the same time the energy consumption is reduced. However, a problem with the known solution is that the addition of alkali reduces the bleachability of the pulp.

  In the context of the present invention, we unexpectedly found that impregnation is more efficient when combined with efficient degassing of chips, most suitably performed by steaming, and pressure impregnation. It has also been found that the alkaline dose can be greatly reduced. When compared at the same level of freeness, a much lower alkaline dosage can be employed to make the percentage of fine wood the same or lower, while at the same time pulp scattering is the case with conventional non-pressure impregnation Can be higher.

The method according to the invention is carried out by successively arranging the following equipment: a chip degassing unit, a chip impregnation unit and a chip beating unit, in which case the impregnation unit is a sealed container. And impregnation treatment is carried out in the sealed container at an absolute pressure of 1.5 bar or more .

  More specifically, the method according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

  The pulp according to the invention is also characterized by what is stated in the characterizing part of claim 14.

  Notable advantages are obtained with the present invention. In a pilot experiment, it was demonstrated that the alkali dose can be reduced by 50% or more by using pressure impregnation. In addition, the present invention improved pulp scattering, i.e., in the experiment, the scattering was significantly higher than in the TMP reference example (0% alkali). It should also be noted that the scattering can be improved without increasing the percentage of fine wood pieces. With the same level of freeness, the bulk is improved.

  Pressure impregnation creates a permeability of over 95% in laboratory level experiments. At the reference point used in the experiment, the maximum penetration was 63-74%. In conducting the pilot test, the alkali concentration is reduced from the conventional level of 0.8-1.2% / Adt (1 ton of air-dried pulp) to a level of 0.25% / Adt without increasing the percentage of fine wood chips. I was also able to. Scattering was clearly higher than the reference example at all test points.

  Pressure impregnation can improve the quality of chemical mechanical refiner pulp for different end use applications.

  In the following, the invention will be examined more closely with the aid of a detailed description and with reference to the application examples given below.

  The accompanying drawings show a simplified diagram of the equipment used in the method according to the invention.

As explained above, the method according to the invention comprises three steps:
First, remove at least most of the air contained in the raw wood containing the wood chips (ie degas the wood chips),
Second, in order to efficiently absorb the alkali in the wood chip, the obtained raw material is impregnated with an alkaline solution at an absolute pressure of 1.5 bar or more ,
Third, it involves beating the treated wood chips to a predetermined freeness.

  As can be seen from the above, pulp is produced using a chemical mechanical process. In the present invention, the production of chemical mechanical pulp generally means a process that includes both a chemical fiber disaggregation stage and a mechanical fiber disaggregation stage, as described above. The CMP and CTMP processes are chemical mechanical processes. In the CMP process, the raw wood is beaten at standard atmospheric pressure, while in the CTMP process, pressurized refiner groundwood pulp is produced. Since CMP uses higher doses of chemicals, its yield is generally lower (less than 90%) than that of the CTMP process. In both cases, the chemical treatment of wood is traditionally carried out with sodium sulfite (sulphonation treatment), in which case hardwood can be treated with sodium hydroxide. In this case, typical chemical doses in the CTMP process are about 0-4% sodium sulfite and 1-7% sodium hydroxide, and the temperature is about 60-120 ° C. On the other hand, in the CMP process, the chemical dosage is 10-15% for sodium sulfite and / or 4-8% for sodium hydroxide (calculated from dry wood) and the temperature is about 130- 160 ° C, correspondingly 50-100 ° C.

  In the chemical mechanical process, it is also possible to impregnate the chip with an alkaline peroxide solution (APMP process). The dosage of peroxide is generally 0.1-10% (by dry pulp weight), typically about 0.5-5%. Alkaline feed, such as sodium hydroxide, is about the same, i.e. about 1-10% by weight.

  The present invention particularly relates to a CTMP process. In the CTMP process, fibers are disaggregated by using a pressure refiner groundwood pulp method on chips derived from impregnation.

  In the process according to the invention, the initial material is a chip comprising coniferous or hardwood wood. In particular, hardwood chips are used for production, and the chips are prepared from birch (generally Betula wood species), Populus wood species, or mixtures thereof. Examples of suitable wood species of the genus Birch are: B. pendula and B. pendula. Examples of suitable wood species of B. pubescens and of the genus Poplar are: P. tremula, P. P. tremuloides, P balsamea, P. Balsamifera, P. balsamifera P. trichocarpa, P.M. Heterophila (P. heterophylla), P. P. deltoides and P. deltoides P. grandidentata. Aspen (European Aspen, P. Tremura; Quake Aspen, P. Trem Roides), aspen species crossed from different stock aspen, hybrid aspen (eg, P. Tremura x Trem Roides, P. Tremura x Tremura) P. del toides * Trichocarpa, P. trichocarpa x Del Toydes, P. del Toydes x nigra, P. maximowiczii x Trichocarpa), and other species created by genetic technology are particularly preferred it is conceivable that.

  Along with birch and poplar species, other broadleaf species such as eucalyptus and mixed tropical hardwoods can also be used as raw materials. Among the conifers, mention should be made of spruce (Picea abies) and pine (Pinus silvestris), and other wood species of the genus Spruce and Pinus.

  According to one application, chemical mechanical pulp containing up to 100% of coniferous fibers is produced. However, according to the present invention, it is possible to produce a chemical mechanical pulp consisting of a mixture of hardwood and coniferous fibers and containing at least 5% of coniferous fibers, for example 50-99% hardwood fibers and 1-50% Of coniferous fibers. By using coniferous fibers, especially by using spruce fibers, the bulk, strength properties and stiffness of the pulp can be improved.

  The size of the wood chips of the raw wood is generally about 20-50 mm × 1-10 mm, typically about 35-40 mm × 3-5 mm.

  First, remove as much of the air in the wood chips as possible. In general, the aim is to remove at least 70% of the air contained in the chip, especially about 80-100%. Air is usually present in gaseous form. As can be seen from the attached flow sheet, this degassing can be carried out in the evaporator 1 by applying steam to the chip. In the process according to the figure, chips of initial material are fed into a steaming silo 1 by means of a screw conveyor 2, into which steam is fed from a single supply nozzle or, as shown, chips in the silo. Water vapor is supplied from several nozzles 3a-3c in order to distribute the water evenly.

  The purpose of the steam treatment is to remove air from the wood chips. At the same time, water vapor remains in the wood chips.

  The steam treatment can be carried out, for example, in the continuous evaporator 1 shown in the figure, in which the wood chips move through the steam treatment silo 1 and in the steam treatment silo 1 are saturated with approximately saturated or nearly saturated steam. Contact is allowed for 0.5-20 minutes, in particular about 1-10 minutes. The steam treatment can be carried out at an overpressure, but generally a steam treatment at standard atmospheric pressure is quite sufficient. Specifically, depending on how saturated the steam used is, a high temperature, for example, a temperature of about 50-100 ° C., particularly about 80-100 ° C. is employed.

  Instead of steam treatment, degassing can be carried out in low pressure / vacuum, or the steam treatment can be made more efficient by vacuum treatment.

  The treated tip is removed from the steam silo through the outlet nozzle 4, and most preferably the tip is then compressed in the plug screw 5. After this stage, usually at least 95%, preferably at least 98% of the air is removed and at the same time a part of the vapor is also removed.

  For completeness, it should be mentioned that steam treatment of chips can be used in the manufacture of both sulfate pulp and chemical mechanical refiner pulp. However, until the present invention, it has not been suggested that the combination of steaming and pressure impregnation of wood chips can be used in the production of chemical mechanical pulp.

  After the deaeration stage, the wood chips are led to the impregnation stage 6. According to a preferred embodiment of the invention, the steamed wood chips are taken to the impregnation stage which is carried out in the absorber 6 in particular at the temperature of the steam treatment stage. The temperature of the impregnation solution used in the impregnation stage is kept lower than the temperature of the steam in the steam treatment stage.

  In practice, the impregnation stage is carried out in a closed vessel, i.e. a pressure vessel, which is arranged downstream of the steamer. The illustrated absorber basically comprises an elongated absorber, the longitudinal axis of the absorber being arranged essentially vertically, the absorber having an upper part and a lower part, in this case degassing Wood chips coming from the unit can be fed into the upper part of the absorber and taken out via the lower part of the absorber. In the absorber, according to the present invention, an absolute pressure of generally at least 1.5 bar, preferably about 1.5-15 bar, can be created.

  If wood chips are fed quickly into the impregnation vessel, the temperature of the wood chips can drop by up to about 10-20 ° C. before the impregnation stage begins.

  In the absorber 6 there is an upper separator 7. Through the inlet nozzle 7a, the chips are supplied to the absorber, and the liquid is separated from the wood chips in the separator. This liquid is recycled into the waste stream of the steaming silo 1.

  According to a preferred embodiment, steamed wood chips are supplied to the impregnation stage together with the impregnation chemical, in which case the impregnation chemical is supplied to the pipeline 11 from separate inlet nozzles 10a-10c. Is connected to the outlet nozzle 4 of the steamer 1 and the inlet nozzle 7 a of the absorber 6. Most suitably, pumps 20, 21 or similar devices are placed in the pipeline to create pressure.

In the impregnation step, an impregnation solution containing an aqueous solution of an alkaline material is used, and the solution may optionally contain a sulfonated chemical. Usually, an aqueous solution of an alkali metal hydroxide such as NaOH or KOH, or an alkaline earth metal hydroxide such as magnesium hydroxide, Mg (OH) ₂ or calcium hydroxide, or a mixture thereof is used. If desired, the solution also contains a sulfite compound such as, for example, sodium sulfite. The dose of the alkali hydroxide is usually about 2-12 kg / Adt (1 ton of air-dried pulp), preferably about 6 kg / Adt at maximum, more preferably about 4 kg / Adt at maximum. Alkaline earth metal hydroxides are used in corresponding doses (in moles). The pH value of the solution is about 9-11. The consumption of sulfite compounds is about 1-20 kg / Adt, suitably up to 3 kg / Adt for hardwoods.

  In addition to pure solutions, aqueous solutions of blends of alkaline materials such as cooking liquor obtained from cooking of pulp such as white liquor and green liquor can also be used for impregnation. The temperature of the impregnation stage is about 30-95 ° C., preferably about 40-90 ° C., which can be achieved at least in part with heat carried by the chip. In general, the temperature of the impregnation stage is lower than the temperature of the degassing stage. According to the invention, the pressure in the impregnation stage is an absolute pressure of about 1.5-15 bar, preferably about 2-10 bar. Consequently, impregnation utilizes an overpressure of at least about 0.5 bar. The ratio between wood and liquid (p / p) is generally about 1:20 to 1: 4, in particular about 1:15 to 1: 6.

  The dosage of impregnating chemical can be adjusted depending on the chip to be treated and can be increased as required.

  The duration of the impregnation treatment is about 1-240 minutes, preferably about 5-120 minutes, in particular about 10-60 minutes.

  During the impregnation stage, the wood chips are impregnated with alkali to the maximum extent possible. Generally, at least 85%, preferably at least 90%, more preferably at least 95% of the pore volume of the wood chip should be filled with the impregnation solution.

  Impregnation can be carried out in one or several stages, in which case at least one stage is carried out at overpressure. According to a preferred embodiment, the hot chips are first impregnated at the overpressure under the conditions described above, and then the impregnation is continued in an open container or container at the same or different temperature. About 10-80% of the duration of the impregnation process can be carried out under pressurized conditions. In the applications shown below, the duration of pressurized and unpressurized processing is similarly long, with a total duration of 40 minutes.

  Wood chips coming from the impregnation stage are taken out through the outlet nozzle 6a. Reference number 6b refers to the discharging device of the absorber. With this discharge device, the residue collected at the bottom of the device can be taken out. Thereafter, the chips are fed to a conventional chemical mechanical pulp beating stage 12, which can be carried out, for example, in a beating machine comprising a grooved beating blade. The raw wood is beaten to a predetermined freeness, ie 50-500 ml CSF, more preferably 90-150 ml CSF.

  Basic FIG. 1 shows how the chip flow generated from the impregnation stage is actually further processed before beating. In line therewith, first the excess impregnation solution can be removed in the screw press 13 and then the chemical reaction can be continued in the reaction silo 14 before the chips are brought to beating on the screw conveyors 15a and 15b. When using such a silo, the reaction time in the reaction silo 14 is usually about 0.1-10 hours.

  In the screw press 13, impurities and fiber material unsuitable for beating can be separated, and they are taken out through a sieve 16 into a waste channel. The liquid phase 17 resulting from the screw press can be recirculated through the pipeline 10, optionally in combination with unused feed water.

  Reference numbers 22 and 23 refer to pumps arranged for liquid phase supply. As shown, the impregnation solution is most preferably recycled to the process, and its alkali concentration can be adjusted (increased) with fresh alkali feed.

  It should be pointed out that the two essential factors of the present invention are to achieve a good degassing prior to combining the impregnation solution and the chip and to pressurize the impregnation. Together, these two factors allow for efficient penetration of the impregnation solution into the wood chips. The holding time and temperature in the pressure vessel are selected in such a way that the diffusion time and reaction time can be adjusted. There must be sufficient time for diffusion to occur and the rate of reaction should not be too high.

  The chemical mechanical pulp described above has exceptionally good properties. As described in the introduction, the light scattering quality of the pulp has been improved, and an improvement in light scattering quality has been achieved without increasing the percentage of bound fibers. Thus, at the same level of freeness, the light scattering quality of the pulp according to the invention is at least 5% and even 10% better than the high alkali reference example. At the same time, the percentage of sliver in the pulp according to the present invention is lower than that of the TMP reference example, and unexpectedly lower than that of the high alkali reference example. At the same level of freeness, the bulk is improved by about 5%.

A notable example is that the scattering quality of CTMP pulp prepared from aspen is higher than 45 m ² / kg and the percentage of fine wood pieces is lower than 0.3%. Correspondingly, it is possible to produce pulp from straw that has a scattering quality higher than 45 m ² / kg and a small piece percentage lower than 1.5%. These are just examples of the nature of the pulp, and the pulp manufacturer is free to choose the desired level of scattering or percentage of swarf within the limits of the present invention, and with the help of the present invention the parameters It should be pointed out that one of these can be improved considerably.

  The pulp according to the invention can be used for the production of paper or cardboard products.

  Thus, after the above-mentioned fiber disaggregation, the pulp is generally bleached, for example, with hydrogen peroxide under alkaline conditions to a whiteness of about 75-88%.

  If desired, the properties of the initial material can be adjusted by mixing the pulp with the chemical pulp in such a way that a slashable initial material can be achieved, but the initial material is a significant amount (at least 30% by weight). Of chemical mechanical pulp. Preferably, softwood pulp is used as the chemical pulp, in which case the percentage is 1-50% of the dry weight of the raw fibers. However, it is also possible to use only chemical mechanical aspen pulp.

  First, the pulp for papermaking is slushed by a method known per se to an appropriate consistency (usually to a solid content percentage of about 0.1 to 1%), and then developed on a plow net and converted into a web. Form a paper or cardboard web. Fillers such as calcium carbonate can be added to the fiber slash, generally about 1-50% by weight of the fiber.

  The paper web can be surface sized and / or provided with a coating layer and may be calendered if desired. A coating paste can be used for single-layer coating, pre-coating, and surface coating. Triple coating is also possible. In general, the coating according to the invention comprises 10-100 parts by weight of at least one pigment or mixture of pigments, 0.1-30 parts by weight of at least one binder, and other additives known per se. Contains 10 parts by weight.

  In the manner described above, according to the present invention, a web having excellent printability, good smoothness, and high opacity and whiteness can be produced from the pulp material. Examples of applications are fine paper, coated printing paper and catalog paper, and multilayer cardboard lining.

  The following non-limiting examples illustrate the invention.

Example 1
Aspen CTMP pulp was prepared in the laboratory under the following conditions.

  Aspen wood chips exposed to steam at 100 ° C. for 2-5 minutes were impregnated with different amounts of sodium hydroxide in a sealed container at a pressure of 5 bar (a) at 80 ° C. for 20 minutes. Thereafter, impregnation was further continued at 80 ° C. for 20 minutes in an open reaction silo.

Among other things, the properties of the pulp were determined using the following method.
- bulk cm ³ / g: EN 20534
-Scattering m ² / kg: ISO 9416
-CSF ml: ISO 5267-2
-Binding fiber: "Pulmac binding fiber", sample size 3g, 0.08mm gap plate for 150ml CSF pulp, 0.10mm gap plate for 325ml CSF pulp

  Table 1 shows what happened when aspen chips were beaten to a 150 ml CSF drainage level in this manner.

  As shown in the table, the use of the present invention makes it possible to reduce the dose of alkali hydroxide, in which case the scattering is clearly increased without increasing the percentage of fine wood pieces. The scattering increases by more than 10% compared to the case where alkali is used in the conventional amount. Unexpectedly, the percentage of fine wood pieces was significantly lower than the 1.2% alkaline reference example.

  Table 2 shows the bulk of the above pulp.

  It can be seen that the bulk is slightly improved at the same CSF level.

  The above experiment was repeated with a wood chip. The following scattering values were obtained by pressure impregnation (80 ° C., 5 bar, 20 minutes) of the brazing material at a 325 ml CSF level.

  Again, a significant improvement in scattering was achieved, although the percentage of fine wood in the experiment remained high. However, it was 1/3 lower than the reference example.

  In the case of cocoons, there was no significant effect on bulk by reducing the alkali dose.

Example 2 Laboratory impregnation In the laboratory, impregnation with aspen and brazing material was carried out at standard atmospheric pressure using alkaline doses of 2.5, 5 and 10 kg NaOH / Adt tips. The wood / liquid ratio was 1: 8 and the temperature was 80 ° C.

  Samples were taken from the impregnation solution 15 minutes, 30 minutes, 1 hour, and 3 hours after the start of the impregnation process. As the alkaline dose increased, the organic material dissolved in the impregnation solution increased dramatically as a function of impregnation time. At the same time, the dissolved COD increased dramatically.

  The results of the effect of alkali dose on fiber loss achieved in this example for 40 minutes laboratory scale impregnation of aspen are shown in the table below.

  It should also be pointed out that the fiber loss was determined from the impregnation solution before beating. The amount of dissolved material increased by beating, and the fiber loss increased correspondingly, and the loss increased as the alkali dose increased.

Figure 2 shows a simplified diagram of the equipment used in the method according to the invention.

Claims (14)

Contacting the wood chips with an alkaline impregnation solution in an impregnation step under conditions where the impregnation solution penetrates the wood chips;
In order to produce pulp, according to a method of beating wood chips treated with the impregnation solution to a desired freeness,
In a method for producing chemical mechanical pulp from raw wood containing wood chips,
Deaerate the wood chips,
Before beating the wood chips, impregnating the obtained degassed wood chips with an alkaline impregnation solution at an absolute pressure of 1.5 bar or more in such a manner that the impregnation solution is efficiently absorbed by the wood chips A method for producing chemical mechanical pulp. The method according to claim 1, wherein steam is applied to the raw wood at a temperature of 50 ° C. or more to remove air from the wood chips. Bringing the steamed wood chips into the impregnation stage essentially at the temperature of the steam treatment,
The method according to claim 2, wherein, in the impregnation step, the temperature of the impregnation solution is maintained lower than the temperature of the steam treatment.   4. The method according to claim 2, wherein the steamed wood chips are fed to the impregnation stage through a screw press. 5. The impregnation solution according to claim 1, wherein an impregnation solution containing an alkali metal hydroxide and having a maximum dose of 6 kg / Adt is used in the impregnation step. Method. 6. The aqueous solution of alkali metal hydroxide , cooking liquid obtained by cooking of chemical pulp, or sulfite compound, or a mixture thereof is used as the impregnation solution. Method. The wood chips, 1-240 minutes, The method according to any one of claims 1 to 6, characterized in that impregnating the alkaline impregnation solution. The method according to claim 1, by beating the wood raw material, characterized in that the freeness of 50-500ml CSF. The method according to claim 1 where the temperature of the impregnation stage is characterized by a 30-95 ° C.. 10. The method according to claim 1, wherein the pressure in the impregnation step is 1.5-15 bar in absolute pressure. 11. A method according to any preceding claim, wherein in the impregnation step, at least 85% of the pore volume of the wood is filled with the impregnation solution. The impregnation is carried out in several stages, wherein at least one of the stages is carried out at an absolute pressure of 1.5 bar or more and at least one stage is carried out at standard atmospheric pressure. Item 12. The method according to any one of Items 1 to 11. The steaming of the wood chips, by using a water vapor saturation The method according to any of claims 1 to 12, which comprises carrying out at least essentially normal atmospheric pressure.   Chemical mechanical pulp manufactured using the method according to any one of claims 1 to 13.

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