JP2004137653A - Method for producing bleached pulp for papermaking - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating pulp in a high concentration ozone bleaching using a high pulp concentration, improving efficiency of ozone bleaching, and maintaining a sufficiently high pulp strength. <P>SOLUTION: This method for producing bleached pulp is provided by alkaline oxygen-bleaching an unbleached pulp obtained by steam cooking of wood chips, treating the pulp after the oxygen bleaching with an acid at ≤pH 2.5, then adjusting to 1-5% concentration, and having a sequence of dehydrating the pulp concentration up to 32-38mass%, ozone-bleaching and then performing an alkaline extraction of the pulp which is fiber-opened by a pre-breaker. Further bleaching the pulp in ECF and TCF-bleaching processes is provided by ozone-bleaching the pulp adjusted to have the manganese content of ≤10mg/kg of absolutely dried pulp, in the dehydrated pulp. <P>COPYRIGHT: (C)2004,JPO

Description

【００４５】
【表２】

【００４６】
結果表１から明らかなように、ｐＨ２．５以下で酸処理を行なう高濃度オゾン漂白において、脱水後のパルプ濃度が３２〜３８質量％の範囲でかつオゾン漂白時のＭｎ含有量が１０ｍｇ／パルプｋｇ以下の場合ではアルカリ抽出段後のカッパー価が十分低下し、また漂白パルプも高白色度でかつ高粘度が得られており、オゾン漂白の効率を向上させることが可能となった。さらに、オゾン漂白段に続くアルカリ抽出段の洗浄ろ液をアルカリ酸素漂白段の希釈水として使用する場合の酸素漂白の効率が上がり、粘度も向上した。
【００４７】
【発明の効果】
以上の様に、本発明は高白色度でカッパー価の低いパルプが得られ、効率の良い製紙用オゾン漂白パルプの製造が可能となった。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing bleached pulp for papermaking, and more particularly, to a method for producing bleached pulp that improves bleaching efficiency in high-concentration ozone bleaching with high pulp concentration and does not reduce pulp strength. is there.
[0002]
[Prior art]
Conventionally, as a method for bleaching paper pulp, there is a multi-stage bleaching method such as C (molecular chlorine) -E (alkali extraction) -H (sodium hypochlorite) -D (chlorine dioxide). Chemicals have been used, but organic chlorine compounds such as dioxins that are harmful to the environment generated by the reaction of chlorine with organic matter in the pulp poses a problem, and the bleaching stage using oxygen is used in the first stage. Have been adopted. Further, in recent years, ECF (Elemental Chlorine Free) bleaching without using molecular chlorine and TCF (Totally Chlorine Free) bleaching without using any chlorine-based chemicals have been put into practical use. The system chemicals are effective bleaching chemicals.
[0003]
Compared to chlorine-based chemicals, bleaching of pulp with ozone has the advantage that, unlike chlorine-based bleaching, it does not generate organic chlorine compounds in the bleaching process, in addition to the high reactivity of ozone with lignin.
[0004]
For this reason, ozone bleaching has been attracting attention from an early stage.However, ozone has drawbacks such as high production cost, and its oxidizing power tends to damage pulp fibers, and these are major factors that hinder the practical use of ozone bleaching. Was. However, in recent years, the ozone production cost has been drastically reduced due to the improvement of the performance of the ozone generator, and the bleaching method has been improved, so that the ozone bleaching method of performing ozone bleaching at a pulp concentration of 7 to 15% by mass, or pulp A high-concentration ozone bleaching method for performing ozone bleaching at a concentration of 38 to 42% is being introduced.
[0005]
It is important and generally known that ozone bleaching is performed under acidic conditions and that transition metal ions that decompose ozone gas are removed as much as possible. For example, in "Paper and Peripheral Technologies" (4) P2-9, (1987) (see Non-Patent Document 1), in Takagi's paper entitled "On Ozone Bleaching of Pulp", regarding the pH, "Ozone is acidic. Is relatively stable, but when the pH is 4 or higher, it is easily decomposed as the pH increases, and ozone bleaching at a pH of about 2 to 3 is also effective in suppressing the decrease in pulp viscosity. " It is recommended that ozone treatment be performed under acidic conditions. In connection with this, a technique for removing metal ions that decompose ozone gas by adding a washing stage after acidification as a pretreatment of ozone treatment has also been proposed.
[0006]
Further, as a bleaching sequence including ozone, Japanese Patent Application Laid-Open No. 6-346391 (see Patent Literature 1) discloses a technique including performing an ozone treatment at an acidic pH of 1 to 3. Japanese Patent Application Laid-Open No. 5-148785 (Patent Document 2) discloses that a chemically digested lignocellulose-containing pulp is treated with a complexing agent within a pH range of 3.1 to 9.0. Discloses a method of changing the state of the pulp containing trace metals, and then subjecting the pulp to ozone treatment. However, the ozone treatment conditions disclosed in the above documents and publications are intended to suppress the decomposition of ozone or the decrease in pulp viscosity in the ozone stage. Not specified.
[0007]
Further, Japanese Patent Application Laid-Open No. 57-154489 (Patent Document 3) discloses a method of performing ozone treatment of pulp at an acidic pH with a pulp concentration of about 20% to about 45%. However, when the pulp concentration is changed from 20% to 45%, the amount of liquid accompanying the pulp varies greatly, and it is difficult to control the amount of Mn brought into the ozone stage.
[0008]
On the other hand, in recent years, with increasing awareness of environmental issues, a closed technology for collecting all of the bleaching wastewater and a semi-closed technology for collecting a part of the bleaching wastewater have been receiving attention. Bleaching using chlorine-based chemicals such as chlorine and chlorine dioxide is difficult to close because chlorine ions generated in the bleaching process cause corrosion of piping in the recovery process, but ozone bleaching does not generate chlorine ions. It is characterized by being easily closed and semi-closed. However, also in ozone bleaching, when closed or semi-closed, accumulation of metal ions called non-process elements becomes a problem. For example, it is known that metal ions such as manganese and calcium not only have an effect on ozone bleaching property but also have an adverse effect on closedness such as clogging and corrosion of pipes. In addition, when the wastewater from the ozone bleaching stage and the alkali extraction stage is used as dilution water or washing water in the preceding alkaline oxygen bleaching stage, metal ions in the wastewater reduce the efficiency and the yield, viscosity, and strength in oxygen bleaching. Will bring.
[0009]
In the alkaline oxygen bleaching stage, lignin is ionized in an alkaline atmosphere to generate a large amount of phenolic hydroxyl groups, reacts with oxygen molecules and is decomposed into carboxylic acids and the like, and the lignin molecules are reduced in molecular weight and dissolved in alkali. Hydrogen peroxide is partially generated in the course of this reaction, and a hydroxyl radical is generated by the catalytic action of a transition metal such as manganese, iron, or copper. The hydroxyl radical is the strongest one-electron oxidizing agent in an aqueous system, and reacts with cellulose to cause a decrease in pulp yield and a decrease in viscosity and strength.
[0010]
[Patent Document 1] JP-A-6-346391 [Patent Document 2] JP-A-5-148785 [Patent Document 3] JP-A-57-154489 [Non-Patent Document 1] "Paper and peripheral technology" ( 4), p2-9, (1987)
[0011]
[Problems to be solved by the invention]
An object of the present invention relates to high-concentration ozone bleaching having a high pulp concentration, and it is an object of the present invention to provide a processing method for improving ozone bleaching efficiency and maintaining pulp strength sufficiently high.
[0012]
[Means to solve the problem]
The present inventors have studied various methods for improving the efficiency of ozone bleaching in high-concentration ozone bleaching with a high pulp concentration. As a result, before ozone bleaching comprising treatment with an acid having a pH of 2.5 or less and dehydration of the pulp by a twin roll press. By processing, the pulp concentration is adjusted to 32 to 38% by mass, the Mn content in the pulp at that time is adjusted to 10 mg / pulverized pulp or less, and ozone bleaching is performed, thereby greatly improving the efficiency of ozone bleaching. And found the present invention.
[0013]
The present invention includes the following inventions.
(1) Unbleached pulp obtained by digesting wood chips is subjected to alkaline oxygen bleaching, and the resulting pulp after oxygen bleaching is acid-treated at a pH of 2.5 or less, adjusted to a concentration of 1 to 5%, and then pulp. The method has a sequence in which the pulp which has been dewatered to a concentration of 32 to 38% by mass, defibrated by a pre-breaker is ozone bleached, and then alkali-extracted. A method for producing bleached pulp for papermaking, wherein ozone bleaching is performed on pulp in which the manganese content of the post-pulp is adjusted to 10 mg / kg or less.
[0014]
(2) The method for producing bleached pulp for papermaking according to (1), wherein the pre-breaker has serrated teeth on the upper part of the press.
[0015]
(3) The method for producing bleached pulp for papermaking according to (1), wherein the dewatering is performed using a twin-roll press-type dehydrator, and the twin-roll press-type dehydrator has a roll clearance of 8 to 12 mm.
[0016]
(4) The alkali extraction stage after ozone bleaching is performed in the dilution tank without washing after ozone treatment, and the treatment conditions are pulp concentration of 2 to 6% by mass, treatment temperature of 30 to 50 ° C, and treatment time of 5 to 60 minutes. A method for producing bleached pulp for papermaking according to (1).
[0017]
(5) The method for producing bleached pulp for papermaking according to (1), wherein the ozone addition rate in the ozone bleaching is 0.4 to 0.7% by mass per pulp.
[0018]
(6) The bleaching for papermaking according to (1), wherein the difference between the Kα value after oxygen bleaching and the Kα value after 1 kg of ozone added to 1 ton of air-dried pulp after the alkali extraction stage is in the range of 1.2 to 1.7. Pulp manufacturing method.
[0019]
(7) The method for producing bleached pulp for papermaking according to (1), wherein the ECF bleaching step after ozone bleaching is performed in an alkali extraction stage (E), a hydrogen peroxide bleaching stage (P), and a chlorine dioxide bleaching stage (D).
[0020]
(8) The method for producing pulp for papermaking according to (1), wherein the washing filtrate in the alkali extraction stage is used as dilution water and / or washing water in the alkali oxygen bleaching stage.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
As raw pulp used in the present invention, wood chips may be modified continuous cooking (Modified Continuous Cooking), extended modified continuous cooking (Extended Modified Continuous Cooking), all-can isotherm cooking, and isothermal cooking-oil cooking. Chemical pulp obtained by a kraft cooking (including a polysulfide method) such as a cooking method, a super batch cooking method, a Compact cooking method, a KOBUDO ^MARI cooking method, or a sulphite cooking method can be used. Further, the wood chips used in the present invention are not particularly limited, and are preferably hardwood materials such as aspen, beech, acacia, eucalyptus, mangrove, pine, spruce, softwood materials such as Douglas fir, and further bagasse, It goes without saying that the present invention can be applied to lignocellose materials derived from herbaceous plants such as kenaf, esparto grass, rice and reed as long as the conditions are satisfied.
[0022]
In the present invention, unbleached hardwood pulp having a kappa number of 15 to 25 (hereinafter referred to as LUKP) is mainly used as a raw material pulp. Of course, unbleached softwood pulp (NUKP) can be used as long as it satisfies the claims. When the kappa number of LUKP is less than 15, the bleachability of the pulp is improved, but the pulp yield is lowered and the pulp strength is lowered. If the copper value after the digestion exceeds 25, not only is it necessary to use a large amount of bleaching chemicals, but also the post-digestion rate increases and the final product becomes more dusty, so this is also used in actual operations. Is difficult.
[0023]
In the present invention, LUKP obtained by a known cooking method is subjected to an oxygen bleaching step so that the kappa number becomes 6 to 14. This oxygen bleaching step is preferably a step of providing pulp having a kappa number of 8 to 12. If the kappa number of the pulp in this treatment step exceeds 14, it is not preferable because chemicals are unnecessarily consumed in the subsequent bleaching step. Conversely, if the kappa number is less than 6, the strength and yield of the pulp at the stage before bleaching are reduced. This is not preferable because it significantly decreases.
[0024]
Pulp that has undergone oxygen bleaching is first acid-treated at a pH of 2.5 or less. The acid used in the present invention may be any of inorganic acids and organic acids as long as it can be adjusted to pH 2.5 or less.Sulfuric acid, nitric acid, hydrochloric acid, sulfurous acid, inorganic acids such as nitrous acid, among which sulfuric acid is obtained It is preferably used because it is easy to handle and easy to handle. The time of the acid treatment is not particularly limited as long as it is 5 minutes or more, and there is no particular problem as long as the pulp concentration is in the range of 1 to 15% by mass. % Is preferred. Further, the place where the acid is added is not particularly limited, but it is also possible to use the filtrate of the twin roll press type dehydrator in the next step as dilution water after oxygen bleaching, and to add the acid to the circulation line of this filtrate. is there.
[0025]
The pulp that has been subjected to the acid treatment is adjusted to a pulp concentration of 1 to 5% by mass and then sent to a twin roll press type dehydrator to be dehydrated to a pulp concentration of 32 to 38% by mass. By setting the pulp concentration before dehydration to 1 to 5% by mass, metals in the pulp are easily eluted to the solution side, and metals such as Mn can be effectively removed by subsequent dehydration. When the pulp concentration after dehydration is lower than 32% by mass, the moisture inhibits the reaction of ozone, which is not preferable. When the pulp concentration exceeds 38% by mass, the pulp mass is firmly tightened, and the ozone and the pulp react uniformly. It is not preferable because it becomes difficult. For dewatering the pulp, a twin roll press type dehydrator having a roll clearance of 8 to 12 mm is used. If the roll clearance is smaller than 8 mm, the pulp mass is too narrow, which is not preferable. If it is larger than 12 mm, the pulp is insufficiently dewatered and is not practical.
[0026]
The pulp dewatered by the twin roll press dewatering machine is defibrated by a pre-breaker having serrated teeth provided on the upper part of the press, and then sent to an ozone reactor by a conveying screw to be ozone bleached. In the ozone bleaching, the ozone addition rate is 0.4 to 0.7% by mass with respect to the pulp, and the ozone gas concentration is not particularly limited. However, the ozone concentration of 8 to 13 mass which is the capacity of the current general ozone generator is used. % Ozone gas can be used. If the ozone addition ratio is lower than 0.4% by mass, the load in the subsequent bleaching stage becomes high, which causes an increase in the chemical addition ratio and a decrease in pulp strength, which is not preferable. On the other hand, if the ozone addition rate exceeds 0.7% by mass, the pulp strength is undesirably reduced. Ozone is known to decompose upon contact with heavy metals such as manganese, iron, copper, nickel and cobalt. Of these metals, Mn has a significant effect on ozone bleaching because unbleached pulp contains about 20 to 100 mg / kg of absolutely dried pulp. When the amount of Mn contained in the pulp exceeds 10 mg / kg of pulp absolutely dry during ozone bleaching, the decomposition of ozone becomes remarkable. Can be done.
[0027]
The ozone bleached pulp is diluted with a washing filtrate of an alkali extraction stage to which an alkali is added by a dilution screw, and sent to a dilution tank below the ozone reactor. The substantial alkali extraction in the present invention is performed in this dilution tank, and the pulp concentration is 2 to 6% by mass, the treatment temperature is 30 to 50 ° C, and the treatment time is 5 to 60 minutes. Pulp that has undergone such a treatment step has a sufficiently reduced kappa number. In a factory where general ozone bleaching is introduced, the difference between the kappa number after oxygen bleaching and the kappa number after alkali extraction, which is generated per kg of added ozone, per ton of air-dried pulp is about 1.0. However, in the present invention, since ozone bleaching is carried out efficiently, this difference is very high at 1.2 to 1.7. Here, pulp containing 10% of water is referred to as air-dried pulp.
[0028]
In the present invention, preferably, the washing filtrate after the alkali extraction stage is sent to a black liquor recovery step, whereby organic matter generated in ozone bleaching and alkali extraction is recovered as heat energy, and the emission COD can be reduced. The load can be greatly reduced. On the other hand, when the washing filtrate is used for dilution water or washing water in the pre-alkali oxygen bleaching stage, the efficiency, viscosity and strength of oxygen bleaching decrease due to the effects of metal ions such as manganese brought in. Must be removed.
[0029]
The bleaching sequence after ozone bleaching is not particularly limited as long as it is ECF bleaching or TCF bleaching. For example, AZED, AZ-Eo-D, AZ-EDP, A -Z-Eo-DP, AZ-E-DD, AZ-Eo-DD, AZ-E-P-D, and the like. Here, (A) is an acid treatment stage, (Z) is an ozone treatment stage, (E) is an alkali extraction stage, and (Eo) is an alkali extraction stage reinforced with oxygen. In addition, (D) shows a chlorine dioxide stage, and (P) shows a hydrogen peroxide stage. (-) Between each stage indicates a washing step. Further, an enzymatic treatment (Ez) stage may be provided in a part of the bleaching step for the purpose of adding chemicals and improving pulp quality in the above sequence, and a chlorine dioxide stage of D stage is divided and added (dnD, DND, dED etc.).
[0030]
The method for measuring the kappa number, the method for measuring the Mn content, and the method for measuring pulp whiteness of the pulp used in the present invention are as follows.
[0031]
Method for measuring kappa number Kappa number of pulp was measured according to JIS P 8211.
[0032]
Mn content measurement method Mn content in pulp is measured by precisely weighing a pulp sample of about 5 g in absolute dryness to three decimal places, ashing the pulp sample and then dissolving the ash in an aqueous hydrochloric acid solution. And measured by the atomic absorption method. The Mn content in the solution was measured by an atomic absorption method after being appropriately diluted after filtration.
[0033]
Pulp whiteness measurement method The whiteness of pulp was measured according to JIS P8212.
[0034]
Pulp viscosity measurement method The pulp viscosity was measured according to JIS P8215.
[0035]
【Example】
Next, examples of the present invention will be described, but the present invention is not limited thereto. The chemical addition rates in Examples and Comparative Examples represent pulp mass% unless otherwise specified.
[0036]
Example 1
Unbleached pulp obtained by kraft digestion of a mixture of 30% domestic hardwood / 70% eucalyptus wood was washed and oxygen bleached to obtain pulp having a kappa number of 9.7. The pulp was diluted with the filtrate of a twin roll press dehydrator so that the pulp concentration was 4% by mass, adjusted to pH 2.2 by adding sulfuric acid, and then subjected to an acid treatment at 35 ° C. for 10 minutes. Next, the pulp was dewatered to a pulp concentration of 37.2% by mass with a twin-roll press type dewatering machine (roll clearance 10 mm), defibrated with a pre-breaker having saw-shaped teeth on the upper part of the press, and then in an ozone reactor. Ozone bleaching. At this time, the Mn content in the pulp was 5.8 mg / kg of pulp, and the ozone addition rate was 0.5%. Next, the pulp after ozone bleaching was diluted with the washing filtrate after alkali extraction, and alkali extraction was performed in a dilution tank.
[0037]
The conditions for the alkali extraction stage were as follows: an alkali addition rate of 0.9%, a pulp concentration of 4% by mass, and a residence time of 15 minutes. The whiteness after the alkali extraction stage was 67.2% and the kappa number was 3.2. The difference between the kappa number after oxygen bleaching per kg of added ozone and the kappa number after the alkali extraction stage was 1 ton of air-dried pulp. .44. Next, hydrogen peroxide bleaching and chlorine dioxide bleaching were sequentially performed to obtain bleached pulp having a final whiteness of 86.2% and a viscosity of 14.3 mPa · s. The conditions of the hydrogen peroxide bleaching stage were as follows: alkali addition rate 0.4%, hydrogen peroxide addition rate 0.30%, pulp concentration 12 mass%, treatment temperature 65 ° C, residence time 70 minutes. The chlorine dioxide bleaching stage conditions were as follows: chlorine dioxide addition rate 0.25%, pulp concentration 12 mass%, treatment temperature 70 ° C, residence time 150 minutes. The results are shown in Table 1. The degree of reduction in the kappa number per kg of ozone in the table indicates the difference between the kappa number after oxygen bleaching and the kappa number after the alkali extraction stage per kg of added ozone per 1 ton of air-dried pulp.
[0038]
Example 2
The same pulp after oxygen bleaching as in Example 1 was used, the treatment was performed under the same conditions as in Example 1, except that the pH during acid treatment was set to 2.4 and the pulp concentration after dehydration was set to 33.5% by mass. Was. The Mn content during ozone bleaching at this time was 8.6 mg / kg pulp, the whiteness after the alkali extraction stage was 66.9%, and the kappa number was 4.0. The difference between the kappa number after oxygen bleaching and the kappa number after the alkali extraction stage per kg of added ozone per 1 ton of air-dried pulp was 1.27. The bleached pulp after the hydrogen peroxide bleaching and the chlorine dioxide bleaching had a whiteness of 85.9% and a viscosity of 13.9 mPa · s. The results are shown in Table 1.
[0039]
Example 3
Using the filtrate of the alkali extraction stage obtained in Example 1 as dilution water, it was used in Example 1 under the conditions of 100 ° C., oxygen pressure 0.5 MPa, alkali addition rate 2.0%, and reaction time 60 minutes. Unbleached pulp having a kappa number of 18 was subjected to alkaline oxygen bleaching. Table 2 shows the Mn concentration of the dilution water used for oxygen bleaching, and the Kappa number and viscosity after oxygen bleaching.
[0040]
Example 4
Oxygen bleaching was carried out in the same manner as in Example 3 except that the alkaline extraction filtrate obtained in Example 2 was used as dilution water. Table 2 shows the Mn concentration of the dilution water used for oxygen bleaching, and the Kappa number and viscosity after oxygen bleaching.
[0041]
Comparative Example 1
The same treatment as in Example 1 was performed, except that the same pulp after oxygen bleaching as in Example 1 was used, the pH during acid treatment was 3.2, and the pulp concentration after dehydration was 36.8% by mass. The Mn content during ozone bleaching at this time was 15.6 mg / kg pulp, the whiteness after the alkali extraction stage was 64.1%, and the kappa number was 5.1. The difference between the kappa number after oxygen bleaching and the kappa number after alkali extraction per kg of added ozone per 1 ton of air-dried pulp was 1.02. The bleached pulp after the hydrogen peroxide bleaching and the chlorine dioxide bleaching had a whiteness of 83.1% and a viscosity of 11.8 mPa · s. The results are shown in Table 1.
[0042]
Comparative Example 2
The same treatment as in Example 1 was performed, except that the same pulp after oxygen bleaching as in Example 1 was used, and the pulp concentration at the time of pulp dewatering by a twin roll press dehydrator was 40.5%. The Mn content during ozone bleaching at this time was 5.8 mg / kg pulp, the whiteness after the alkali extraction stage was 65.4%, and the kappa number was 4.8. The difference between the Kappa number after oxygen bleaching and the Kappa number after the alkali extraction stage per kg of added ozone per 1 ton of air-dried pulp was 1.08. The bleached pulp after the hydrogen peroxide bleaching and the chlorine dioxide bleaching had a whiteness of 83.8% and a viscosity of 12.0 mPa · s. The results are shown in Table 1.
[0043]
Reference Example The alkali extract filtrate obtained in Comparative Example 1 was used as diluting water, and was not exposed to a kappa number of 18 at 100 ° C., an oxygen pressure of 0.5 MPa, an alkali addition rate of 2.0%, and a reaction time of 60 minutes. The pulp was subjected to alkaline oxygen bleaching. Table 2 shows the Mn concentration of the dilution water used for oxygen bleaching, and the Kappa number and viscosity after oxygen bleaching.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
Results As is clear from Table 1, in high-concentration ozone bleaching in which acid treatment is performed at pH 2.5 or lower, the pulp concentration after dehydration is in the range of 32 to 38% by mass, and the Mn content during ozone bleaching is 10 mg / pulp. In the case of less than kg, the kappa number after the alkali extraction stage was sufficiently reduced, and the bleached pulp was also obtained with high whiteness and high viscosity, making it possible to improve the efficiency of ozone bleaching. Further, the efficiency of oxygen bleaching when the washing filtrate of the alkali extraction stage following the ozone bleaching stage was used as dilution water for the alkali oxygen bleaching stage was increased, and the viscosity was also improved.
[0047]
【The invention's effect】
As described above, according to the present invention, pulp having high whiteness and low kappa number was obtained, and efficient production of ozone bleached pulp for papermaking became possible.

Claims (8)

The unbleached pulp obtained by digesting the wood chips is subjected to alkaline oxygen bleaching, and the obtained pulp after oxygen bleaching is acid-treated at a pH of 2.5 or less, and then adjusted to a concentration of 1 to 5%. A pulp that has been dehydrated to about 38% by mass, defibrated by a pre-breaker, has a sequence of ozone bleaching and then alkali extraction, and further, in a method of producing pulp for papermaking that is bleached in an ECF and TCF bleaching step, A method for producing bleached pulp for papermaking, wherein pulp whose manganese content is adjusted to 10 mg / kg or less of pulp absolute dryness is ozone bleached. The method for producing bleached pulp for papermaking according to claim 1, wherein the prebreaker has serrated teeth on an upper part of the press. The method for producing bleached pulp for papermaking according to claim 1, wherein the dewatering is performed using a twin-roll press type dehydrator, and the twin-roll press type dehydrator has a roll clearance of 8 to 12 mm. The alkali extraction stage after ozone bleaching is performed in a dilution tank without washing after ozone treatment, and the treatment conditions are that the pulp concentration is 2 to 6% by mass, the treatment temperature is 30 to 50 ° C, and the treatment time is 5 to 60 minutes. The method for producing bleached pulp for papermaking according to claim 1, characterized in that: The method for producing bleached pulp for papermaking according to claim 1, wherein the ozone addition rate in ozone bleaching is 0.4 to 0.7% by mass per pulp. 2. The papermaking process according to claim 1, wherein the difference between the K.alpha. Value after oxygen bleaching and the K.alpha. Value after 1 kg of ozone added to 1 ton of air-dried pulp after the alkali extraction stage is in the range of 1.2 to 1.7. For producing bleached pulp. The bleaching pulp for papermaking according to claim 1, wherein the ECF bleaching step after the ozone bleaching is performed in an alkali extraction stage (E), a hydrogen peroxide bleaching stage (P), and a chlorine dioxide bleaching stage (D). Production method. The method for producing pulp for papermaking according to claim 1, wherein the washing filtrate of the alkali extraction stage is used as dilution water and / or washing water of the alkali oxygen bleaching stage.