JP7100315B2 - How to make bleached pulp - Google Patents

Description

The present invention relates to a method for producing bleached pulp using a lignocellulosic substance derived from wood or the like as a material.

Conventionally, a method for producing bleached pulp for papermaking is known (for example, Patent Documents 1 to 5). In the conventional method for producing bleached pulp, various treatments are applied to the unbleached pulp to produce the bleached pulp.

WO2009 / 081714A WO2007 / 132836 Japanese Unexamined Patent Publication No. 2010-270410 Japanese Unexamined Patent Publication No. 2010-265564 Japanese Unexamined Patent Publication No. 2008-08606

In the conventional method for producing bleached pulp, there are various treatment steps for unbleached pulp, and the combinations thereof are also various. Then, from the viewpoints of prevention of decrease in viscosity of pulp, improvement of bleaching effect, reduction of molecular chlorine, reduction of cost and the like, development of a new method for producing bleached pulp is required.

The present invention provides the following method for producing bleached pulp.
(1) A cooking process for cooking lignocellulosic substances and
An alkaline oxygen bleaching step in which the unbleached pulp obtained by evaporating the lignocellulosic substance is treated with alkaline oxygen bleaching,
A monosulfuric acid treatment process that performs monosulfuric acid treatment on pulp that has been bleached with alkali oxygen,
A method for producing bleached pulp, which comprises a hydrogen peroxide treatment step of performing hydrogen peroxide treatment on pulp that has been bleached with alkali oxygen.
A method for producing bleached pulp, which uses chlorine dioxide in an amount of 0.1% by mass or less per mass of absolute dry pulp in the monosulfuric acid treatment step.
(2) The method for producing bleached pulp according to (1) above, wherein 0.01 to 2.00% by mass of monosulfuric acid is added per mass of absolute dry pulp in the monosulfuric acid treatment step.
(3) The method for producing bleached pulp according to (1) or (2) above, wherein 0.01 to 0.09% by mass of chlorine dioxide is added per mass of absolute dry pulp in the monosulfuric acid treatment step.
(4) The method for producing bleached pulp according to any one of (1) to (3) above, wherein in the cooking step, 5 to 30% by mass of active alkali is added per mass of absolute dry pulp.
(5) The value of the viscosity of the pulp (cP) obtained after the monopersulfuric acid treatment step is 60% or more of the value of the viscosity of the pulp (cP) immediately before the monopersulfate treatment step (1). )-(4). The method for producing bleached pulp according to any one of (4).
(6) The production of the bleached pulp according to any one of (1) to (5) above, wherein the viscosity value (cP) of the pulp obtained after the monosulfuric acid treatment step is 10 or more and 30 or less. Method.
(7) The method for producing bleached pulp according to any one of (1) to (6) above, wherein the hydrogen peroxide treatment step is a subsequent stage of the monosulfuric acid treatment.
(8) The method for producing bleached pulp according to any one of (1) to (7) above, wherein at least one of magnesium sulfate and sodium silicate is used in the hydrogen peroxide treatment step.
(9) The bleaching according to any one of (1) to (8) above, wherein 0.5 to 3.0% by mass of hydrogen peroxide is added per mass of absolute dry pulp in the hydrogen peroxide treatment step. How to make pulp.
(10) Any of the above (1) to (9), further using an alkaline component in an amount of 0.1 to 5.0% by mass based on the mass of the hydrogen peroxide in the hydrogen peroxide treatment step. The method for producing bleached pulp according to item 1.
(11) The method for producing bleached pulp according to any one of claims 1 to 10, wherein the viscosity value (cP) of the pulp obtained after the hydrogen peroxide treatment step is 5.0 or more and 15 or less.
(12) The method for producing bleached pulp according to any one of (1) to (11) above, wherein the monosulfuric acid treatment step of adding chlorine dioxide is only one step.
(13) A second monopersulfate treatment step of further monopersulfating the alkali-oxygen bleached pulp and / or a second hydrogen peroxide treatment step of performing hydrogen peroxide treatment is performed. The method for producing bleached pulp according to any one of the above (1) to (11).
(14) The method for producing bleached pulp according to any one of (1) to (13) above, which does not include an ozone treatment step of treating the unbleached pulp with ozone.
(15) The method for producing bleached pulp according to any one of (1) to (14) above, wherein the bleached pulp is a melting pulp.

According to the method for producing bleached pulp of the present invention, it is possible to prevent a decrease in the viscosity of the pulp, improve the bleaching effect, and produce the bleached pulp while reducing the amount and cost of molecular chlorine used. ..

It is a graph which shows the whiteness (ISO%) of the bleached pulp of each Example and the comparative example. It is a graph which shows the viscosity (cP) of the bleached pulp of each Example and the comparative example. It is a graph which compares the value of the whiteness (ISO%) in each step which manufactures a bleached pulp in some Examples. 3 is a graph comparing the values of viscosity (cP) in each step of producing bleached pulp in some examples.

Hereinafter, the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be arbitrarily modified and carried out within the scope of the effect of the invention.

[Manufacturing method of bleached pulp]
The method for producing bleached pulp of the present invention includes an alkali oxygen bleaching step of bleaching a predetermined unbleached pulp with alkali oxygen bleaching, a monopersulfuric acid treatment step and hydrogen peroxide treatment for the pulp bleached with alkali oxygen, which will be described in detail later. Including the process. In the method for producing bleached pulp, chlorine dioxide of 0.1% by mass or less per mass of absolute dry pulp is used in the monosulfuric acid treatment step.

[Lignocellulosic substance]
As the lignocellulosic substance used in the present invention, a hardwood material containing a large amount of methylglucuronic acid that produces hexenuronic acid is suitable, but a softwood material may also be used. Further, the lignocellulosic substance may be a non-wood such as bamboo or hemp, and may be a mixture of the above-mentioned hardwood, softwood, and non-wood, and is not particularly limited.

[Creating process]
In the present invention, unbleached pulp is obtained by a cooking step of cooking a lignocellulosic substance. As a cooking method for obtaining unbleached pulp used in the cooking step, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, acidic sulphite cooking, and alkaline sulphite cooking can be used. Considering quality, energy efficiency and the like, a kraft steaming method or a polysulfide steaming method is preferably used.

For example, when lignocellulosic made of 100% broad-leaved lumber is kraft-evaporated, the sulfide degree of the kraft cooking solution is 5 to 75% by mass, preferably 15 to 45% by mass, and the effective alkali addition rate is 5 to 30% by mass per absolute dry wood mass. %, preferably 10 to 25% by mass. The cooking temperature is 130 to 170 ° C., and the cooking method may be either a continuous cooking method or a batch cooking method. In the case of using a continuous cooking kettle in the cooking, a modified cooking method in which the cooking liquid is added at multiple points may be used, and the method is not particularly limited.

In the step of cooking the lignocellulosic substance, delignin treatment is performed. Finally, when a pulp for dissolution is obtained as a bleached pulp, it is preferable to remove hemicellulose derived from a lignocellulosic substance together with lignin in the cooking step. As described above, when the dehemicellulose treatment is desired, for example, a hydrolysis treatment step may be provided before the step of removing lignin by adopting an alkaline steaming method such as a kraft steaming method to remove the hemicellulose. .. Further, when lignin is removed by the acidic sulfite cooking method, hemicellulose can also be removed together with the lignin. Therefore, the cooking step using the acidic sulfite cooking method is preferably used as a part of the manufacturing method of the pulp for dissolution.

In the cooking step, it is preferable to add 5 to 30% by mass of active alkali per mass of absolute dry pulp. In the cooking step, preferably 10 to 25% by mass of active alkali is used, more preferably 12 to 20% by mass, still more preferably 15 to 18% by mass of active alkali. The active alkali in the cooking step is not particularly limited, but for example, sodium hydroxide, potassium hydroxide and the like are used. In the cooking step, sodium hydroxide is preferably used as the active alkali.

Further, in the cooking step of the lignocellulose substance, known cyclic keto compounds such as benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone and the quinone-based compounds such as alkyl and amino can be used as a cooking aid in the cooking liquid used. A nuclear substituent or a hydroquinone-based compound such as anthraquinone, which is a reduced form of the quinone-based compound, can be used. Further, one or more selected from 9,10-diketohydroanthracene compounds and the like, which are stable compounds obtained as intermediates of the anthraquinone synthesis method by the Diels-Alder method, may be added. The addition rate of these cooking aids is a normal addition rate, for example, 0.001 to 1.0% by mass per absolute dry pulp mass of a lignocellulosic substance such as wood chips.

[Alkaline oxygen bleaching process]
The unbleached pulp obtained by the above-mentioned cooking is subjected to a further delignin treatment and bleached by an alkaline oxygen bleaching step after undergoing a washing, rough selection and selection steps, if necessary.
As the alkaline oxygen bleaching step, a known medium concentration method or high concentration method can be applied, but the pulp concentration is preferably 8 to 40% by mass, and the pulp concentration is more preferably 10 to 35% by mass.

As the alkali added to the pulp in the alkaline oxygen bleaching step, sodium hydroxide (caustic soda), potassium hydroxide, oxidized kraft white liquor and the like can be used. Further, in the alkaline oxygen bleaching step, oxygen gas may be added together with the alkali. As the oxygen gas, oxygen from the cold separation method, oxygen from PSA (Pressure Swing Adsorption), oxygen from VSA (Vacum Swing Adsorption) and the like can be used.

In the alkaline oxygen bleaching step, oxygen which may be used in combination with alkali is added to the pulp slurry in a mixer, for example, and after sufficient mixing, the mixture of pulp, oxygen and alkali is held under pressure for a certain period of time. It is sent to the reaction tower where it can be made, and delignin is removed. The reaction conditions of the alkaline oxygen bleaching step are as follows, for example. That is, the addition rate of oxygen gas is 0.5 to 3% by mass per mass of bonedry pulp, the addition rate of alkali is 0.5 to 4% by mass, the reaction temperature is 80 to 120 ° C., and the reaction time is For 15 to 100 minutes, the pulp concentration is 8 to 40% by mass, preferably 10 to 35% by mass, and other known conditions can be applied.

In the alkaline oxygen bleaching step, it is preferable to carry out the alkaline oxygen bleaching treatment a plurality of times in succession to promote delignin as much as possible to reduce the content of heavy metals. After the alkali oxygen treatment is carried out, the pulp is preferably sent to a washing step.

The washed pulp is subjected to chlorine-free bleaching treatment as follows. The chlorine-free bleaching treatment includes at least an alkali oxygen bleaching treatment, a monosulfuric acid treatment step in which the washed pulp is treated with monosulfuric acid, and a hydrogen peroxide treatment step in which hydrogen peroxide treatment is performed. included.

[Monosulfurous acid treatment process]
In the monosulfuric acid treatment step, monosulfuric acid and chlorine dioxide are added to the washed pulp.
In the monopersulfate treatment step, the amount of monopersulfate added per mass of absolute dry pulp is preferably 0.01 to 2.00% by mass, more preferably 0.02 to 1.00% by mass. It is more preferably 0.05 to 0.80% by mass, and particularly preferably 0.1 to 0.5% by mass.

In addition, monosulfuric acid is also called peroxymonosulfuric acid, and can be produced by hydrolyzing peroxydisulfuric acid, or by mixing hydrogen peroxide and sulfuric acid in an arbitrary ratio. However, the manufacturing method thereof is not particularly limited. Further, oxonone or the like, which is a _double salt of monosulfuric acid (2KHSO ₅ , KHSO ₄ , K2 SO ₄ ), can also be used. However, in consideration of economic efficiency, it is preferable to produce and use monosulfuric acid at low cost by mixing inexpensive high-concentration hydrogen peroxide and inexpensive high-concentration sulfuric acid.

As a method for producing monopersulfuric acid by mixing high-concentration hydrogen peroxide and high-concentration sulfuric acid, a hydrogen peroxide solution having a concentration of 20 to 70% by mass, preferably 35 to 70% by mass is mixed with 80 to 98% by mass. A method of dropping and mixing concentrated sulfuric acid having a concentration of%, preferably 93 to 98% by mass is preferable. The mixed molar ratio of sulfuric acid and hydrogen peroxide is preferably 1: 1 to 5: 1, and more preferably 2: 1 to 4: 1. If both hydrogen peroxide solution and sulfuric acid have low concentrations, the production efficiency of monosulfuric acid will decrease, so it is not suitable. Further, if these concentrations are too high, the risk of ignition or the like increases, which is not suitable. Further, when the mixed molar ratio of sulfuric acid and hydrogen peroxide deviates from 1: 1 to 5: 1, the production efficiency of monosulfuric acid is lowered, which is not preferable.

Further, in the monosulfuric acid treatment step, chlorine dioxide is used for the washed pulp together with the monosulfuric acid. The amount of chlorine dioxide used in the monosulfuric acid treatment step is 0.1% by mass or less, or less than 0.1% by mass, per mass of absolute dry pulp. The amount of chlorine dioxide used in the monopersulfate treatment step is preferably 0.09% by mass or less, and the lower limit may be 0, but the more preferable amount of chlorine dioxide added is the mass of absolute dry pulp. It is 0.01 to 0.09% by mass, more preferably 0.020 to 0.085% by mass per absolute dry pulp mass.
As described above, in the monosulfuric acid treatment step used in the present invention, it is possible to suppress the amount of expensive chlorine dioxide used, which is advantageous in terms of cost. Further, in the present invention, not only the molecular chlorine is unnecessary, but also the amount of chlorine dioxide, which is a chlorine-based compound, used is minimal, and the effect that safety can be easily ensured is recognized.

In the monosulfuric acid treatment step, the pH is preferably adjusted to 1.5 to 6, more preferably 2 to 4. And known alkalis and acids can be used for pH adjustment. In the monosulfuric acid treatment step, the treatment time is, for example, 1 minute to 5 hours, preferably 10 to 180 minutes, and more preferably 30 to 100 minutes. In the monosulfuric acid treatment step, the treatment temperature is preferably 20 to 100 ° C, more preferably 40 to 90 ° C. The concentration of the pulp to be treated in the monopersulfuric acid treatment step is not particularly limited, but is usually 5 to 30% by mass, and preferably 8 to 15% by mass from the viewpoint of operability.

Retention rate of the viscosity value (cP) of the pulp in the monopersulfation treatment step, that is, the viscosity of the pulp immediately before the monopersulfuric acid treatment step of the viscosity value A ₁ (cP) of the pulp obtained by the monopersulfuric acid treatment step. The value (cP) of the ratio (A ₁ / A ₂ × 100 (%)) to the value A ₂ (cP) is preferably 60% or more. The retention rate is more preferably 62% or more, still more preferably 65% or more.
The viscosity value (cP) of the pulp obtained by the monosulfuric acid treatment step is preferably 10 or more and 30 or less, and more preferably 15 or more and 25 or less.

[Hydrogen peroxide treatment process]
In the hydrogen peroxide treatment step, hydrogen peroxide is added to the washed pulp. Further, the hydrogen peroxide treatment step is preferably a subsequent stage of the monopersulfuric acid treatment step, and in this case, the pulp that has been subjected to the monopersulfuric acid treatment at least once is the target of the hydrogen peroxide treatment step.

The addition rate of hydrogen peroxide in the hydrogen peroxide treatment step is preferably 0.5 to 3.0% by mass, more preferably 1.0 to 2.5% by mass, based on the mass of the absolute dry pulp.
The treatment temperature in the hydrogen peroxide treatment step is preferably 20 to 100 ° C, more preferably 40 to 90 ° C. In the hydrogen peroxide treatment step, the pH value of the reaction system is preferably adjusted to 8 to 14, and more preferably adjusted to 10.5 to 12.0. Known alkalis and acids can be used to adjust the pH. The pulp concentration in the hydrogen peroxide treatment step is not particularly limited, but is preferably 8 to 15% by mass from the viewpoint of operability.

Further, in the hydrogen peroxide treatment step, it is preferable to use at least one of a magnesium salt and sodium silicate (sodium silicate). As the magnesium salt, for example, magnesium sulfate is preferably added to the pulp. Further, as sodium silicate, for example, it is preferable to add any of compounds such as Na ₂ SiO ₃ , Na ₄ SiO ₄ , Na ₂ Si ₂ O ₅ , Na ₂ Si ₄ O ₉ and the like to the pulp. When a magnesium salt or sodium silicate is added to a reaction system containing pulp, heavy metals such as copper, iron and manganese and transition metals act on oxygen or hydrogen peroxide in an alkaline system to generate active oxygen radicals. It is possible to prevent a decrease in the viscosity of the pulp due to the above.
The addition ratio of the magnesium salt in the hydrogen peroxide treatment step is preferably an amount in which Mg is 0.01 to 1.0% by mass with respect to the mass of the absolute dry pulp, and more preferably Mg is added with respect to the mass of the absolute dry pulp. The amount is 0.02 to 0.5% by mass, and more preferably 0.05 to 0.2% by mass of Mg with respect to the mass of the absolute dry pulp.
The addition rate of the sodium silicate compound in the hydrogen peroxide treatment step is preferably 0.1 to 2.0% by mass with respect to the mass of the absolute dry pulp, and more preferably 0.2 with respect to the mass of the absolute dry pulp. It is about 1.5% by mass, more preferably 0.5 to 1.0% by mass with respect to the mass of the absolute dry pulp.

In the hydrogen peroxide treatment step, it is preferable to keep the reaction system alkaline as described above, and the amount is 0.1 to 5.0% by mass based on the mass of hydrogen, more preferably 0.2 to 0.2. It is preferable to use an amount of 3.0% by mass, more preferably 0.3 to 2.0% by mass of an alkaline component. As the alkaline component, sodium hydroxide (caustic soda), potassium hydroxide and the like can be used.

The viscosity value (cP) of the pulp obtained by the hydrogen peroxide treatment step is preferably 5.0 or more and 15 or less, more preferably the viscosity value (cP) of the pulp obtained by the monosulfuric acid treatment step. Is 6.5 or more and 12 or less.
Further, the retention rate of the viscosity value (cP) of the pulp in the hydrogen peroxide treatment step, that is, the pulp immediately before the hydrogen peroxide treatment step having the viscosity value B ₁ (cP) of the pulp obtained by the hydrogen peroxide treatment step. The value of the ratio (B ₁ / B ₂ × 100 (%)) to the viscosity value B ₂ (cP) is preferably 30% or more, and more preferably, the pulp immediately before the monopersulfuric acid treatment step. The viscosity value (cP) is 35% or more, more preferably 40% or more, and particularly preferably 42% or more.

[Types of various processes and number of stages]
In the method for producing bleached pulp, it is preferable that the monosulfuric acid treatment step is only one step. In this case, the process of producing the bleached pulp can be simplified. However, in the method for producing bleached pulp, a second monosulfuric acid treatment step in which monosulfuric acid is further applied to the pulp that has been bleached with alkali oxygen may be included. Further, in addition to the above-mentioned hydrogen peroxide treatment step, a second hydrogen peroxide treatment step for further performing hydrogen peroxide treatment may be included. In the method for producing bleached pulp including the second monosulfuric acid treatment step and the second hydrogen peroxide treatment step, at least one of the hydrogen peroxide treatment steps is performed after the monosulfuric acid treatment. It is preferable to have.

Further, in the method for producing bleached pulp, a treatment step for bleaching other than the hydrogen peroxide treatment step and the monopersulfate treatment step, for example, an ozone treatment step for treating unbleached pulp with ozone, a chlorine treatment step, and the like. It may include a hypochlorite treatment step and the like. However, from the viewpoint of simplifying the process of producing bleached pulp and ensuring safety, it is preferable that the ozone treatment step, the chlorination step, and the hypochlorite treatment step are not included.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not construed as being limited to the following examples.

1. 1. Preparation of monopersulfuric acid At 70 ° C., 95% by mass sulfuric acid (Wako Pure Chemical Industries, Ltd.) was added dropwise to 45% by mass hydrogen peroxide solution (manufactured by Mitsubishi Gas Chemical Industries, Ltd.). The concentrations in the prepared monosulfuric acid aqueous solution were 0.19 mmol / L for monosulfuric acid, 0.81 mmol / L for sulfuric acid, and 0.14 mmol / L for hydrogen peroxide.

2. 2. Preparation of Chlorine Dioxide Water Chlorine dioxide water was prepared by the methanol method (R8 method).

3. 3. Measurement of Pulp Whiteness The measurement of pulp whiteness was performed according to TAPPI Test Methods T452 om-92 (1996).

4. Measurement of Pulp Viscosity The measurement of pulp viscosity was performed according to TAPPI Test Methods T230 om-94 (1996).

5. Wood chips used: Eucalyptus globulus from Chile, A. mearnsii from South Africa, Acacia mangium from Vietnam and A. hybrid mangium and auriculiformis from Japan. Chips of a mixed hardwood (Quercus spp.) Material were used.

6. Kraft Steaming For each chip, 195 mL of water was added to an absolute dry weight of 50 g, and pre-hydrolysis treatment was performed at 150 ° C. for 2.5 hours. The pre-hydrolyzed wood chips were subjected to E.I. Globulus has an active alkali addition rate of 18%, A. marunsii, A. hybrid mangium and auriculiformis, Quercus spp. Was kraft-melted at 150 ° C. for 3 hours at an active alkali addition rate of 17% and at a sulfurization degree of 30% (sodium sulfide: Na _2S addition rate). The liquid ratio was 4 mL / g (melting step).

7. Alkaline oxygen bleaching The steamed chips were mixed and subjected to alkaline oxygen bleaching at 115 ° C. for 60 minutes under the conditions of pulp concentration 30%, oxygen pressure 0.5 MPa, and caustic soda addition rate 0.6% (alkaline oxygen bleaching step). ).

8. Cleaning method after bleaching The bleached pulp is hand-squeezed to contain twice the amount of water with respect to the mass of absolute dry pulp, and 20 times the amount of water (about 40 ° C) with respect to the mass of absolute dry pulp is added. After sufficient stirring, it was dehydrated by filtration until it contained twice the amount of water with respect to the mass of the absolute dry pulp. Next, twice the amount of water (about 40 ° C.) as in the 18-fold amount of the filtrate was added to the mass of the absolute dry pulp and stirred sufficiently, and then the state contained twice the amount of water with respect to the mass of the absolute dry pulp. It was dehydrated by filtration until it became. This was repeated once again for washing after bleaching.

Example 1
Chlorine oxygen bleaching and washed pulp are placed in a polyethylene bag, water required for bleaching at a pulp concentration of 10% is added, and monopersulfate is 0.2% of the absolute dry pulp mass. A mixture of chlorine dioxide water having a chlorine dioxide mass of 0.083% with respect to the absolute dry pulp mass was added. After adjusting the pH to 3.0 with a small amount of caustic soda, the mixture was sufficiently mixed by hand and bleached at 70 ° C. for 70 minutes (monosulfuric acid treatment step). The treated pulp was washed by the above washing method.
Put the washed pulp in a polyethylene bag, add the amount of water required for bleaching at a pulp concentration of 10%, and add hydrogen peroxide, which is 2% of the absolute dry pulp mass, and the mass of the hydrogen peroxide. Add 0.7% by mass of caustic soda and magnesium sulfate in an amount of 0.1% by mass of Mg with respect to the mass of absolute dry pulp, mix well by hand, and bleach at 70 ° C. for 60 minutes (hydrogen peroxide). Hydrogen peroxide treatment step). The treated pulp was washed by the above-mentioned washing method, and a pulp sheet was prepared from the obtained bleached pulp, and the whiteness and viscosity were measured.

Examples 2-5
Except for changing the addition rate of active alkali to wood chips in the kraft cooking process (melting process) and the amount of chlorine dioxide added in the monosulfuric acid treatment process based on the mass of absolute dry pulp as shown in Table 1 below. Was bleached in the same manner as in Example 1.

Comparative Example 1
Same as Example 1 except that the addition rate of active alkali to wood chips in the kraft cooking treatment was changed and the amount of chlorine dioxide added to the wood chips in the monosulfuric acid treatment step was 0.124% based on the mass of absolute dry pulp. Bleached.

The results of Examples 1 to 5 and Comparative Example 1 are shown in Table 1. Regarding the whiteness and viscosity, the results of Examples 1 to 4 in which the active alkali addition rate to the wood chips in the kraft cooking treatment (melting step) is common are shown in FIGS. 1 and 2.
In Example 1 and Comparative Example 1, the whiteness is the same, but in Comparative Example 1, the viscosity is lower than that in Example 1 in the monosulfuric acid treatment step, and an appropriate amount of chlorine dioxide is added. Therefore, it was possible to suppress the decrease in viscosity. Further, in each example in which a smaller amount of chlorine dioxide was added than in Example 1, the effect of preventing the decrease in the viscosity of the pulp while maintaining the whiteness at a good level was recognized.

Example 6
The bleached pulp obtained in Example 1 is placed in a polyethylene bag, water required for bleaching at a pulp concentration of 10% is added, and monopersulfuric acid, which is 0.1% based on the absolute dry pulp mass, is added. rice field. After adjusting the pH to 3.0 with a small amount of caustic soda, the mixture was sufficiently mixed by hand and bleached at 70 ° C. for 70 minutes (monosulfuric acid treatment step). The treated pulp was washed by the above washing method.
Put the washed pulp in a polyethylene bag, add the amount of water required for bleaching at a pulp concentration of 10%, and add hydrogen peroxide, which is 1% of the mass of absolute dry pulp, and the mass of hydrogen peroxide. Add 0.7% by mass of caustic soda and magnesium sulfate in an amount of 0.1% by mass of Mg with respect to the mass of absolute dry pulp, mix well by hand, and bleach at 70 ° C. for 60 minutes (hydrogen peroxide). Hydrogen peroxide treatment step).
As described above, the final bleached pulp of Example 6 further bleached as compared with Example 1 and the whiteness of the pulp obtained in each treatment step of Example 6 (including the treatment steps up to Example 1). Table 2 shows the values of degree (ISO%) and viscosity (cP).
In the table below, "O" indicates an alkaline oxygen bleaching step, "MPS" indicates a monosulfuric acid treatment step, "Ep" indicates a hydrogen peroxide treatment step, and "ClO ₂ " indicates the addition of chlorine dioxide. The numerical values in the right column of each abbreviation are the values of the whiteness (ISO%) and the viscosity (cP) of the pulp obtained immediately after the step indicated by each abbreviation.

また、上述の実施例６の各工程におけるパルプの白色度（ＩＳＯ％）、及び、粘度（ｃＰ）の値と、実施例７における各値とを比較した結果を図３、及び、図４に示す。 Example 7
The bleached pulp obtained in Example 4 was further subjected to monosulfuric acid treatment and hydrogen peroxide treatment in the same manner as in Example 6 except that chlorine dioxide was not used in the monosulfuric acid treatment step. As described above, the final bleached pulp of Example 7 further bleached as compared with Example 4 and the whiteness of the pulp obtained in each treatment step of Example 7 (including the treatment steps up to Example 4). Table 3 shows the values of degree (ISO%) and viscosity (cP).

Further, the results of comparing the whiteness (ISO%) and viscosity (cP) values of the pulp in each step of Example 6 and the respective values of Example 7 are shown in FIGS. 3 and 4. show.

Example 8
The bleached pulp obtained in Example 5 was further subjected to monosulfuric acid treatment and hydrogen peroxide treatment in the same manner as in Example 6 except that chlorine dioxide was not used in the monosulfuric acid treatment step. As described above, the final bleached pulp of Example 8 further bleached as compared with Example 5 and the whiteness of the pulp obtained in each treatment step of Example 8 (including the treatment steps up to Example 5). Table 4 shows the values of degree (ISO%) and viscosity (cP).

Based on the results of Examples 6 to 8, even if the steps of monosulfuric acid treatment (MSP) and hydrogen peroxide treatment (Ep) are repeated a plurality of times, a significant decrease in the viscosity of the pulp can be prevented and the pulp is white. The effect of further improvement was confirmed. In particular, Examples 6 and 7, in which only the conditions of the chlorine dioxide addition rate in the first monopersulfate treatment step are different, that is, the chlorine dioxide addition rate in the first monopersulfuric acid treatment step is 0.083% by mass. Comparing Example 6 with Example 7 to which chlorine dioxide is not added, by adding a small amount of chlorine dioxide, the viscosity level of the pulp is maintained better even after the subsequent steps. It was confirmed that the whiteness could be greatly improved.

Claims (15)

The cooking process for cooking lignocellulosic substances and
An alkaline oxygen bleaching step in which the unbleached pulp obtained by evaporating the lignocellulosic substance is treated with alkaline oxygen bleaching,
A monosulfuric acid treatment process that performs monosulfuric acid treatment on pulp that has been bleached with alkali oxygen,
A method for producing bleached pulp, which comprises a hydrogen peroxide treatment step of performing hydrogen peroxide treatment on pulp that has been bleached with alkali oxygen.
A method for producing bleached pulp, in which 0.01 to 0.09 % by mass of chlorine dioxide is added per mass of absolute dry pulp in the monosulfuric acid treatment step. The method for producing bleached pulp according to claim 1, wherein in the monosulfuric acid treatment step, 0.01 to 2.00% by mass of monosulfuric acid is added per mass of absolute dry pulp. The method for producing bleached pulp according to claim 1 or 2, wherein 0.020 to 0.085 % by mass of chlorine dioxide is added per mass of absolute dry pulp in the monosulfuric acid treatment step. The method for producing bleached pulp according to any one of claims 1 to 3, wherein in the cooking step, 5 to 30% by mass of active alkali is added per mass of absolute dry pulp. The viscosity value (cP) of the pulp obtained after the monosulfuric acid treatment step is 60% or more of the viscosity value (cP) of the pulp immediately before the monosulfuric acid treatment step .
The method for producing bleached pulp according to any one of claims 1 to 4 , wherein the viscosity of the pulp is a value measured according to TAPPI Test Methods T230 om-94 (1996) . The viscosity value (cP) of the pulp obtained after the monosulfuric acid treatment step is 10 or more and 30 or less.
The method for producing bleached pulp according to any one of claims 1 to 5 , wherein the viscosity of the pulp is a value measured according to TAPPI Test Methods T230 om-94 (1996) . The method for producing bleached pulp according to any one of claims 1 to 6, wherein the hydrogen peroxide treatment step is a subsequent stage of the monopersulfuric acid treatment. The method for producing bleached pulp according to any one of claims 1 to 7, wherein at least one of magnesium sulfate and sodium silicate is used in the hydrogen peroxide treatment step. The method for producing bleached pulp according to any one of claims 1 to 8, wherein 0.5 to 3.0% by mass of hydrogen peroxide is added per mass of absolute dry pulp in the hydrogen peroxide treatment step. The bleaching according to any one of claims 1 to 9, wherein in the hydrogen peroxide treatment step, an alkaline component having an amount of 0.1 to 5.0% by mass based on the mass of the hydrogen peroxide is used. How to make pulp. The viscosity value (cP) of the pulp obtained after the hydrogen peroxide treatment step is 5.0 or more and 15 or less.
The method for producing bleached pulp according to any one of claims 1 to 10 , wherein the viscosity of the pulp is a value measured according to TAPPI Test Methods T230 om-94 (1996) . The method for producing bleached pulp according to any one of claims 1 to 11, wherein the monosulfuric acid treatment step of adding chlorine dioxide is only one step. The claimed pulp further comprises a second monopersulfate treatment step of monopersulfating the alkali oxygen bleached pulp and / or a second hydrogen peroxide treatment step of hydrogen peroxide treatment. Item 1 A method for producing bleached pulp according to any one of Items 1 to 11. The method for producing bleached pulp according to any one of claims 1 to 13, which does not include an ozone treatment step of treating the unbleached pulp with ozone. The method for producing bleached pulp according to any one of claims 1 to 14, wherein the bleached pulp is a melting pulp.

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