JP2012012727A - Pulp bleaching aid and pulp bleaching method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bleaching aid and a method for bleaching pulp which are capable of well bleaching both of a chemical pulp and a mechanical pulp under an alkali condition of pH 11 or higher in a bleaching treatment of pulp using hydrogen peroxide.SOLUTION: A bleaching aid comprises a component (a): a polymer compound having a constitutional unit represented by the following general formula (I) and a component (b): a copper compound, and is used in a bleaching treatment of pulp such that the mass of the component (a) is 5 to 1000 mass ppm based on the dry mass of the pulp, the mass of the copper is 0.12 to 30 mass ppm based on the dry mass of the pulp, and the mass ratio of the component (a)/the copper is 4 to 800. (Formula 1)

Description

  The present invention relates to a pulp bleaching assistant and a pulp bleaching method using the same.

  Pulp is a vegetable fiber that is a raw material for paper made mainly from wood, and is roughly classified into chemical pulp and mechanical pulp depending on the production method.

Chemical pulp is a general term for pulp produced by decomposing a pulp material (raw material) by a chemical reaction and separating lignin and the like. Among them, many kinds of trees including broad-leaved trees can be used as raw materials, and kraft pulp having high whiteness is most widely used by being bleached.
Since kraft pulp is characterized by high strength, it has been used as packaging paper that requires strength, such as cement bags and rice bags. In recent years, kraft pulp has high whiteness when subjected to a bleaching treatment, so that it is generally used as a high-quality paper subjected to a multistage bleaching treatment.
Conventionally, chlorine has been used as a bleaching agent for bleaching unbleached pulp. However, since chlorine produces organic chlorine compounds (by-products) such as dioxins, its impact on the environment is a problem. It was.
In recent years, so-called ECF (Elemental Chlorine Free) bleaching, in which oxygen, chlorine dioxide, hydrogen peroxide, or the like, acts in stages instead of chlorine, has become the mainstream.

Since chlorine dioxide has high bleaching power, bleaching treatment using chlorine dioxide is essential in current ECF bleaching. In the bleaching treatment using chlorine dioxide, compared with the bleaching treatment using conventional chlorine, although the production amount of the organic chlorine compound is greatly reduced, the influence on the environment is still regarded as a problem.
For this reason, reduction of the amount of chlorine dioxide used in ECF bleaching is required, but hydrogen peroxide used together with chlorine dioxide in ECF bleaching has a weaker bleaching power than chlorine and chlorine dioxide. Increasing the amount does not lead to a reduction in the amount of chlorine dioxide used.
Therefore, ECF bleaching requires a means for greatly improving the bleaching power of hydrogen peroxide in order to reduce the amount of chlorine dioxide.

  Mechanical pulp is a general term for pulp that is manufactured by mechanically grinding wood logs and chips with physical force, and is pulped while containing wood components such as lignin and hemicellulose. Pulp yield from 80% or more. Mechanical pulp is inexpensive and rich in opacity and high-speed papermaking, so it is mainly used for lower grade paper such as newsprint and renewal paper and fiberboard. However, the strength of the paper is low because the fiber is rigid. There is a drawback.

  Therefore, as a method of improving the strength of paper while maintaining a high pulp yield, the wood chip is placed under high temperature and high pressure, and the lignin acting as a fiber-to-fiber adhesive is ground and softened. The method is used. Pulp produced by this method is called thermomechanical pulp (TMP), and there is less damage to the fiber compared to mechanical pulp produced by other methods, and the fiber is long, so that high strength paper is obtained. Can do. TMP is currently the mainstream of mechanical pulp, and its use is expanding to high-value-added products such as lightweight coated paper and high gloss paper in addition to newspaper paper.

  Mechanical pulp such as TMP contains a large amount of lignin and the like in the fiber, so a large amount of hydrogen peroxide is required to improve the whiteness of the mechanical pulp, and it is altered by sunlight, heat, and oxygen. It's easy to do. For this reason, from the viewpoint of cost and quality, means for improving the bleaching power of hydrogen peroxide is strongly demanded in the production of mechanical pulp as well as ECF bleaching.

In response to such demands, conventionally, pulp bleaching assistants have been proposed for improving the bleaching power of bleaching agents in the pulp manufacturing process.
For example, Patent Literatures 1 and 2 propose pulp bleaching assistants that combine copper and specific ligands. According to the inventions of Patent Documents 1 and 2, the pulp can be satisfactorily bleached in the range of weak acid acidity to weak alkalinity (pH 6 to 10).
Patent Documents 3 to 4 propose pulp bleaching assistants that combine copper, nickel and the like with specific ligands.
Patent Document 5 proposes a pulp bleaching assistant composed of copper ions and a ligand compound capable of forming a complex with copper ions and used for bleaching chemical pulp after cooking.

JP 2008-202197 A JP 2009-68143 A JP 2007-126775 A JP-T-2001-515136 JP 2004-183170 A

However, the above-described conventional pulp bleaching assistant has not yet obtained a satisfactory bleaching effect.
In addition, pulp bleaching in the industrial production of pulp usually decomposes and removes non-cellulosic components such as lignin in the pulp with hydrogen peroxide, and increases the whiteness of the pulp (bleaching effect). It is performed under the condition of pH 11 or higher. On the other hand, the inventions of Patent Documents 1 and 2 exhibit effects in a weakly acidic to weakly alkaline region and are not adapted to actual industrial production. Moreover, although the invention of patent documents 3-5 shows a high effect with respect to the kraft pulp from which most non-cellulose components, such as lignin, were removed by alkali digestion, the effect with respect to the mechanical pulp containing a large amount of non-cellulose components is It is not satisfactory. Furthermore, the invention of Patent Document 5 assumes that after adding a pulp bleaching assistant to chemical pulp, heat treatment is performed by adding pressurized oxygen in an alkaline medium, and hydrogen peroxide is used as a bleaching agent. Not.
An object of the present invention is to provide a bleaching assistant and a pulp bleaching method capable of satisfactorily bleaching both chemical pulp and mechanical pulp even under alkaline conditions of pH 11 or higher in pulp bleaching using hydrogen peroxide.

  As a result of intensive studies, the present inventors have combined a copper compound and a specific polymer compound, and added a specific amount of the copper compound and the specific polymer compound to the pulp, respectively. The inventors have found that either pulp or mechanical pulp can be satisfactorily bleached, and have reached the present invention.

That is, the pulp bleaching assistant of the present invention comprises the following component (a) and component (b) below, and is a pulp bleaching assistant used for pulp bleaching with hydrogen peroxide. The mass of the component (a) is 5 to 1000 ppm by mass with respect to the dry mass of the pulp, the mass of copper is 0.12 to 30 ppm by mass with respect to the dry mass of the pulp, and [(a) component] / [copper ] Is used as the mass ratio represented by 4-800.
Component (a): a polymer compound having a structural unit represented by the following general formula (I), the polymer compound may be composed of the same structural unit, or two or more structural units The copolymer which consists of may be sufficient.

（前記一般式（Ｉ）中、Ａは、ＣＨ又はＮであり、Ｘは、Ｈ又は下記一般式（ＩＩ）で表される置換基であり、全てのＸは、同一であってもよいし、相互に異なっていてもよいが、少なくとも１つが下記一般式（ＩＩ）で表される置換基である。）

(In the general formula (I), A is CH or N, X is H or a substituent represented by the following general formula (II), and all Xs may be the same. These may be different from each other, but at least one is a substituent represented by the following general formula (II).)

（前記一般式（ＩＩ）中、Ｙはカルボキシル基又は１級〜３級のアミノ基のいずれかであり、ｎは０〜２の整数である。Ｙが２級又は３級のアミノ基の場合、一般式（Ｉ）で表される構成単位同士を結合させる架橋種となっていてもよい。）

(In the general formula (II), Y is either a carboxyl group or a primary to tertiary amino group, and n is an integer of 0 to 2. When Y is a secondary or tertiary amino group And may be a cross-linking species that bonds the structural units represented by the general formula (I).)

(B) Component: Copper compound.
In the general formula (I), A is N, and Y represented by the general formula (II) is preferably a carboxyl group, and may be used for mechanical pulp.

The pulp bleaching method of the present invention is a pulp bleaching method for bleaching pulp using a pulp bleaching assistant containing the following component (a) and component (b) below and hydrogen peroxide, wherein the component (a): The mass ratio is 5 to 1000 mass ppm with respect to the dry mass of the pulp, the mass of copper is 0.12 to 30 mass ppm with respect to the dry mass of the pulp, and [(a) component] / [copper]. The pulp bleaching assistant is added so that the value becomes 4 to 800.
Component (a): a polymer compound having a structural unit represented by the following general formula (I), the polymer compound may be composed of the same structural unit, or two or more structural units The copolymer which consists of may be sufficient.

（前記一般式（Ｉ）中、Ａは、ＣＨ又はＮであり、Ｘは、Ｈ又は下記一般式（ＩＩ）で表される置換基であり、全てのＸは、同一であってもよいし、相互に異なっていてもよいが、少なくとも１つが下記一般式（ＩＩ）で表される置換基である。）

(In the general formula (I), A is CH or N, X is H or a substituent represented by the following general formula (II), and all Xs may be the same. These may be different from each other, but at least one is a substituent represented by the following general formula (II).)

（前記一般式（ＩＩ）中、Ｙはカルボキシル基又は１級〜３級のアミノ基のいずれかであり、ｎは０〜２の整数を表す。Ｙが２級又は３級のアミノ基の場合、一般式（Ｉ）で表される構成単位同士を結合させる架橋種となっていてもよい。）

(In the general formula (II), Y represents either a carboxyl group or a primary to tertiary amino group, and n represents an integer of 0 to 2. When Y is a secondary or tertiary amino group, And may be a cross-linking species that bonds the structural units represented by the general formula (I).)

  (B) Component: Copper compound.

 In this paper, “the dry mass of the pulp” is the mass of the pulp obtained by drying the pulp before bleaching with hydrogen peroxide at 105 ° C. for 4 hours.

  According to the present invention, in the bleaching treatment of pulp using hydrogen peroxide, both chemical pulp and mechanical pulp can be satisfactorily bleached even under alkaline conditions of pH 11 or higher.

It is a flowchart which shows one Embodiment of the manufacturing process of the kraft pulp using the pulp bleaching method of this invention.

(Pulp bleaching aid)
The pulp bleaching assistant of the present invention comprises (a) component: polymer compound and (b) component: copper compound, and is used for bleaching pulp with hydrogen peroxide.
The pulp bleaching assistant may be a two-component type in which the component (a) and the component (b) are independent from each other, a mixture of the component (a) and the component (b), The complex in which the component (a) is coordinated to the copper derived from the component (b) as a ligand may be formed, or a mixture of these may be used.
In addition, for example, the pulp bleaching assistant includes a first aqueous solution that includes the component (a) and does not include the component (b), and a second aqueous solution that includes the component (b) and does not include the component (a) 2. It may be a liquid type.

In the pulp bleaching aid of the present invention, the component (a) and the component (b) are represented by a mass ratio represented by [(a) component] / [copper] (hereinafter referred to as (a) / The (copper) mass ratio) is 4 to 800, preferably 20 to 320, and more preferably 35 to 80. If the (a) / (copper) mass ratio is less than 4, the amount of copper dissolved alone increases, the decomposition of hydrogen peroxide itself is accelerated, and the bleaching effect of hydrogen peroxide cannot be improved. When the mass ratio of (a) / (copper) exceeds 800, the blending effect of the component (B) is lost and the whiteness of the pulp is not improved.
In this article, the mass of “copper” is not only the copper derived from component (b) but also the mass containing copper ions present in water.

<(A) Component: Polymer Compound>
The component (a) is a polymer compound represented by the following general formula (I). In addition, (a) component may be comprised from the same structural unit, and may be a copolymer which consists of 2 or more types of structural units.

  In the general formula (I), A is CH (methine group) or N (nitrogen), and among them, N is preferable. When A in the general formula (I) is N, the component (a) can easily form a complex with copper, and the bleaching effect of hydrogen peroxide by the pulp bleaching assistant can be further enhanced.

  In the general formula (I), X is H (hydrogen) or a substituent represented by the following general formula (II), and at least one X is a substituent represented by the following general formula (II). . In the general formula (I), all Xs may be the same or different from each other. Among them, all Xs are preferably a substituent represented by the following general formula (II). By having such a substituent, the component (a) can easily form a complex with copper, and the bleaching effect of hydrogen peroxide by the pulp bleaching assistant can be further enhanced.

In the general formula (II), Y is either a carboxyl group or a primary to tertiary amino group, and among them, a carboxyl group is preferable. By having such a substituent, the component (a) can easily form a complex with copper, and the bleaching effect of hydrogen peroxide by the pulp bleaching assistant can be further enhanced.
In addition, when Y is a secondary or tertiary amino group, Y may be a cross-linking species that bonds the structural units represented by the general formula (I).
n is an integer of 0 to 2, and 1 or 2 is preferable because formation of a complex between the component (a) and copper is facilitated.

  Among such components (a), A in the general formula (I) is N, X is a substituent represented by the general formula (II), and Y in the general formula (II). Are those in which is a carboxyl group, such as aminopolycarboxylic acid polymers. If it is such a structure, (a) component becomes easy to form a complex with copper, and can improve the bleaching effect of hydrogen peroxide by a pulp bleaching adjuvant more.

The molecular weight of (a) component is 2000 or more as a weight average molecular weight, Preferably it is 2000-200000, More preferably, it is 5000-100000, More preferably, it is 10000-50000. When the weight average molecular weight is less than 2,000, decomposition of hydrogen peroxide may be promoted, and when it exceeds 200,000, handling becomes difficult as the viscosity increases.
Here, the weight average molecular weight of the component (a) is measured by gel permeation chromatography (GPS) using a pullulan standard (P-82, manufactured by Showa Denko KK) having a molecular weight of 5,800 to 853,000 as a standard substance. Value. The weight average molecular weight can be measured, for example, by the following procedure. First, a dried sample is dissolved in an aqueous solution (sodium acetate concentration: 10 mM, acetonitrile concentration: 20 vol%) to prepare a 0.5 mass% sample solution. TSK-GelG2500PWXL and TSK-GelGMPWXL (both manufactured by Tosoh Corporation) are connected and installed in a column oven. Using the aqueous solution (sodium acetate concentration: 10 mM, acetonitrile concentration: 20 vol%) as an eluent, the weight average molecular weight can be measured under the conditions of a column oven set temperature: 40 ° C., a flow rate: 0.5 mL / min, and detection: RI. .

Examples of the component (a) include (1) a copolymer of maleic acid and acrylic acid, and (2) an aminopolycarboxylic acid in which a side chain containing a carboxyl group is introduced into a main chain composed of a polyethyleneimino group. Polymer, (3) polyethyleneimine and the like. Examples of such commercially available products of component (a) include Aqualic TL (trade name, manufactured by Nippon Shokubai Co., Ltd.), which is the copolymer of (1), and aminopolycarboxylic acid high (2). Examples thereof include TrilonP (trade name, manufactured by BASF) which is a molecule, Epomin series (manufactured by Nippon Shokubai Co., Ltd.) and Lupasol series (manufactured by BASF) which are polyethyleneimines of (3) above.
These (a) components can be used individually by 1 type or in combination of 2 or more types as appropriate.

  The blending amount of the component (a) in the pulp bleaching assistant can be determined in consideration of the amount of pulp that is to be bleached in the bleaching process described later.

<(B) Component: Copper compound>
The copper compound as component (b) is not particularly limited as long as it can dissociate copper ions in water, and is particularly preferably highly water-soluble.
As the component (b), for example, a water solution containing divalent copper such as copper sulfate, copper chloride, copper nitrate, copper acetate, copper formate, copper perchlorate, copper iodate, copper phosphate, copper trifluoroacetate and the like. Salt, and particularly preferred are copper sulfate and copper chloride. Copper sulfate or copper chloride has a high water solubility, facilitates the formation of a complex with the component (a), and can further enhance the bleaching effect of hydrogen peroxide by the pulp bleaching aid. The component (b) may be an anhydride or a hydrate. These (b) components can be used individually by 1 type or in combination of 2 or more types.

  The blending amount of the component (b) in the pulp bleaching assistant can be determined in consideration of the amount of pulp that is to be bleached in the bleaching process described later.

<Other ingredients>
The pulp bleaching aid of the present invention can be blended with a pH adjuster, a buffering agent, etc., if necessary, as long as the effects of the present invention are not impaired.

(Pulp bleaching method)
The pulp bleaching method of the present invention bleaches pulp to be bleached using a pulp bleaching assistant containing component (a) and component (b) in combination with hydrogen peroxide. The bleaching treatment means a treatment stage for bleaching the pulp, and may include, for example, other steps aimed at removing lignin remaining in the pulp and improving the whiteness of the pulp.

The pulp bleaching method of the present invention will be described below with reference to FIG. FIG. 1 is a flowchart showing an embodiment of a process for producing kraft pulp using the pulp bleaching method of the present invention.
As shown in FIG. 1, this manufacturing process includes a cooking process (reference numeral 10 in the figure), a first cleaning / dehydration process (reference numeral 12 in the figure), an oxygen bleaching process (reference numeral 14 in the figure), The second cleaning / dehydration process (reference numeral 16 in the figure), the hydrogen peroxide bleaching process (reference numeral 18 in the figure), and the third cleaning / dehydration process (reference numeral 20 in the figure). ing.
In the present embodiment, the bleaching process includes an oxygen bleaching step 14, a second washing / dehydrating step 16, a hydrogen peroxide bleaching step 18, and a third washing / dehydrating step 20.

<Cooking process>
In the cooking step 10, wood chips obtained by pulverizing wood raw materials such as conifers and hardwoods are dispersed in water together with an alkaline agent, and the cooking dispersion is heated to remove lignin from the raw material chips. It is a step of obtaining pulp. That is, lignin is removed from the bundled fibers bound by lignin, and the bundled fibers are loosened to promote pulping into individual fibers.

The cooking method in the cooking step 10 is kraft cooking, and a conventionally known method can be used. The kraft cooking method is performed, for example, by mixing raw material chips with an alkali agent and water in a digester and heating at 150 to 170 ° C. for 1 to 3 hours.
Examples of the alkaline agent include sodium hydroxide and sodium sulfide.

<First cleaning / dehydration process>
The first washing / dehydrating step 12 is a step of washing and dehydrating the unbleached pulp obtained in the cooking step 10. In this step, impurities such as lignin separated in the cooking step are removed from the unbleached pulp.
As the washing / dehydrating method, a conventionally known method can be used, and examples thereof include a method in which unbleached pulp is dispersed in water, mixed and washed, and then pressed and dehydrated.

<Oxygen bleaching process>
The oxygen bleaching step 14 is a step of performing oxygen delignification treatment on the washed and dehydrated unbleached pulp to obtain oxygen bleached pulp.
For the oxygen delignification treatment, a conventionally known method can be used. For example, unbleached pulp is mixed with an alkali agent and water, oxygen pressurized to 0.4 to 0.7 MPa is supplied, and 90 to 120 What heats at ° C is mentioned.
As the alkaline agent, sodium hydroxide, sodium sulfide, potassium hydroxide, sodium metasilicate, potassium metasilicate, or the like can be used.

<Second cleaning / dehydration process>
The second washing / dehydrating step 16 is a step of dehydrating the oxygen bleached pulp obtained in the oxygen bleaching step after washing with water. In this step, impurities such as lignin separated in the oxygen bleaching step 14 are removed from the unbleached pulp.
The method of washing / dehydrating is the same as the first washing / dehydrating step 12.

<Hydrogen peroxide bleaching process>
The hydrogen peroxide bleaching step 18 is a step of bleaching oxygen bleached pulp using hydrogen peroxide and a pulp bleaching assistant to obtain a bleached pulp dispersion containing bleached pulp. In the hydrogen peroxide bleaching step 18, for example, together with oxygen bleached pulp, pulp bleaching assistant and hydrogen peroxide, if necessary, alkali agent or acid is dispersed in water to form an oxygen bleached pulp dispersion. And bleaching oxygen bleached pulp.

The order in which the components in the hydrogen peroxide bleaching step 18 are added to the oxygen-bleached pulp dispersion is not particularly limited, but it is preferable that the alkali agent or acid, the pulp bleaching assistant, and hydrogen peroxide be in this order. By adopting such an addition order, decomposition of hydrogen peroxide can be suppressed.
The method of adding each component to the oxygen-bleached pulp dispersion is, for example, adding an alkali agent or acid to water to make a dispersion medium for bleaching, and then introducing the oxygen-bleached pulp into this bleaching dispersion medium, And hydrogen peroxide is added. At this time, the method of adding the pulp bleaching assistant can be determined according to the dosage form. For example, if the pulp bleaching assistant is a two-component type or a two-component type, the component (a) and the component (b) are added. You may add each separately, and may add, after previously mixing (a) component and (b) component.

  The concentration of oxygen-bleached pulp in the oxygen-bleached pulp dispersion, that is, the pulp to be bleached is not particularly limited, but is preferably 5 to 20% by mass, more preferably 7 to 15% by mass, for example, in terms of absolute dryness. The absolute dry rate is a value measured by the absolute dry rate test method (JIS P8203) (the same applies hereinafter).

  The amount of hydrogen peroxide added to the oxygen-bleached pulp dispersion is preferably 1 to 10% by mass and more preferably 2 to 5% by mass with respect to the dry mass of the oxygen-bleached pulp, that is, the pulp to be bleached. If the amount of hydrogen peroxide used is less than 1% by mass, the bleaching effect may be insufficient. If it exceeds 10% by mass, the bleaching effect by hydrogen peroxide is high, and it is used in combination with a pulp bleaching aid. The effects of may not be seen.

  The amount of the pulp bleaching auxiliary added to the oxygen bleached pulp dispersion is such that the mass of the component (a) is 5 to 1000 ppm by mass, preferably 20 to 800 ppm by mass, more preferably the dry mass of the oxygen bleached pulp. It is 20-500 mass ppm. If it is less than 5 ppm by mass, decomposition of hydrogen peroxide by copper occurs and the bleaching effect becomes insufficient. If it exceeds 1000 ppm by mass, the bleaching effect becomes insufficient due to an increase in the viscosity of the oxygen-bleached pulp dispersion.

  In addition, the amount of pulp bleaching assistant added to the oxygen bleached pulp dispersion is such that the weight of copper is 0.12 to 30 ppm by weight, preferably 0.5 to 20 ppm by weight, based on the dry weight of the oxygen bleached pulp. More preferably, it is 1.3-13 mass ppm. If it is less than 0.12 ppm by mass, the bleaching effect will be insufficient, and if it exceeds 30 ppm by mass, the decomposition of hydrogen peroxide by copper will be accelerated and the bleaching effect will be insufficient.

  Furthermore, (a) / (copper) mass ratio in oxygen bleached pulp dispersion liquid is 4-800, Preferably it is 20-320, More preferably, it is 1.3-13. When the (a) / (copper) mass ratio is less than 4, the amount of the component (b) dissolved alone increases, the decomposition of hydrogen peroxide itself is promoted, and the whiteness of the pulp cannot be improved. When the mass ratio of (a) / (copper) exceeds 800, the blending effect of the component (b) is lost and the whiteness of the pulp is not improved.

The pH of the oxygen bleached pulp dispersion is not particularly limited, but is preferably pH 7 to 12, more preferably pH 8 to 12, and still more preferably pH 11 to 12, for example. If the pH is 7 or more, an excellent bleaching effect can be obtained, and if the pH is 12 or less, the pulp fibers can be prevented from deteriorating. Furthermore, if it is pH 11-12, while further improving a bleaching effect, the conditions of the conventional hydrogen peroxide bleaching process can be diverted as it is. The pH was measured using a pH meter (product name: IQ200, manufactured by IQ Scientific Instruments) and a pH electrode (product name: PH15-SS, manufactured by IQ Scientific Instruments) at about 25 ° C. This is done by inserting a pH electrode therein and reading the indicated value after 60 seconds.
The pH of the oxygen bleached pulp dispersion can be adjusted by adding an alkali agent or an acid.
Examples of the alkaline agent include the same as those in the oxygen bleaching step 14. The addition amount of the alkaline agent can be determined according to the pH required for the oxygen bleached pulp dispersion, and is preferably 0.01 to 10% by mass, more preferably 0.1 to 5%, based on the dry mass of the oxygen bleached pulp. Mass%.
Examples of the acid include hydrochloric acid and sulfuric acid.

Although the temperature conditions in the hydrogen peroxide bleaching process 18 are not specifically limited, For example, 40-90 degreeC is preferable and 50-80 degreeC is more preferable. If it is 40 degreeC or more, the shortening of the reaction time of this process can be aimed at, and if it is 90 degrees C or less, discoloration by browning etc. of oxygen bleached pulp can be prevented.
Although the reaction time in the hydrogen peroxide bleaching process 18 is not specifically limited, For example, after preparing an oxygen bleached pulp dispersion liquid, 30 to 300 minutes are preferable and 120 to 180 minutes are more preferable.

<Third cleaning and dehydration process>
In the third washing / dehydrating step 20, the bleached pulp dispersion obtained in the hydrogen peroxide bleaching step 18 is subjected to solid-liquid separation, and the obtained solid is washed with water and then dehydrated. In this step, the color components, pulp bleaching assistant, hydrogen peroxide and the like contained in the bleached pulp dispersion are removed to obtain a solid bleached pulp.

  Although the above-mentioned embodiment demonstrated the pulp bleaching method of the kraft pulp which uses a raw material as a raw material, this invention is not limited to what uses a raw material as a timber. It may be a wood raw material, or a mixture of these and a wood raw material.

  In addition, a cooking process can be determined according to the kind of raw material, and well-known cooking methods, such as polysulfide cooking, soda cooking, alkali sulfite cooking, can be used besides kraft cooking. Of these, kraft cooking is preferably used in view of pulp quality, energy efficiency, and the like.

  In the above-described embodiment, bleaching treatment is performed on the unbleached pulp in the order of the oxygen bleaching step 14 and the hydrogen peroxide bleaching step 18. For example, the hydrogen peroxide bleaching step 18 and the oxygen bleaching step 14 In order, unbleached pulp may be bleached.

Furthermore, a bleaching step using a bleaching agent other than hydrogen peroxide may be provided in both or one of the preceding stage and the subsequent stage of the hydrogen peroxide bleaching process 18. Thus, the whiteness of the paper made from a pulp can be made higher by bleaching in multiple steps using a plurality of bleaching agents.
As bleaching agents other than hydrogen peroxide, chlorine dioxide, ozone, sodium hypochlorite and the like can be used.

In the above-described embodiment, the pulp bleaching method for kraft pulp, that is, chemical pulp, is applicable to the production of mechanical pulp.
The pulp bleaching method in the mechanical pulp manufacturing process will be described below.
The manufacturing process of mechanical pulp is roughly composed of a grinding step, a separation step, a hydrogen peroxide bleaching step, and a washing / dehydrating step.

<Crushing process>
The grinding step is a step of grinding the raw material chips into a pulp. As the grinding method, a conventionally known method can be used, for example, grinding of raw material chips with a pocket grinder, chain grinder, ring grinder, pressure grinder, etc., or grinding of raw material chips with a single disc refiner, double disc refiner, or the like. Crushing and the like.

 In the grinding process, if necessary, a pretreatment operation may be provided in which the raw material chips are heat-treated at 100 to 125 ° C. for several minutes before grinding, or further immersed in chemicals for several minutes before heating. it can. Examples of chemicals used in the pretreatment operation include sodium sulfite and sodium hydroxide.

<Separation process>
A separation process is a process of removing a foreign material from the raw material ground and pulped, and obtaining a finely selected pulp. Examples of the separation step include a classification method using a screen with various openings.

<Hydrogen peroxide bleaching process>
The hydrogen peroxide bleaching step in the mechanical pulp manufacturing process is the same as the hydrogen peroxide bleaching step in the kraft pulp manufacturing process described above, except that the selected pulp obtained in the separation step is used instead of the oxygen bleached pulp. Also in the mechanical pulp manufacturing process, a bleaching step using a bleaching agent other than hydrogen peroxide may be provided in either or both of the preceding stage and the subsequent stage of the hydrogen peroxide bleaching process.

<Washing and dehydration process>
The washing and dehydration step is a step of solid-liquid separation of the bleached pulp dispersion obtained in the hydrogen peroxide bleaching step, and washing and dehydrating the obtained solid with water to obtain a bleached pulp. This is the same as the third cleaning / dehydrating step in the manufacturing process.

  According to the pulp bleaching aid of the present invention, the addition amount of the component (a) and the component (b) with respect to the dry mass of the object to be bleached is in a specific range, and the mass ratio of (a) / (copper) is specific. By making it into the range, the bleaching effect of hydrogen peroxide can be enhanced. The action to enhance the bleaching effect is not clear, but the copper released from (a) component and (b) component forms a metal complex in water, and this metal complex promotes the oxidation reaction with hydrogen peroxide. This is considered to be an appropriate amount.

The present invention can be applied not only to the production of chemical pulp but also to the production of mechanical pulp, and can enhance the bleaching effect of hydrogen peroxide.
In addition, since the present invention can be applied to the hydrogen peroxide bleaching process under the condition of pH 11 or higher, it is possible to carry out peroxidation by a simple method of adding a pulp bleaching assistant to the hydrogen peroxide bleaching process in conventional pulp production. The hydrogen bleaching effect can be improved.

 In addition, the pulp bleaching aid of the present invention has a low environmental impact compared to conventionally proposed pulp bleaching aids, has a relatively simple structure, excellent industrial productivity, and is inexpensive. Suitable for large-scale pulp production.

 Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

(Raw material)
The raw materials used in this example are as follows.
<(A) Component: Polymer Compound>
A-1: Aminopolycarboxylic acid polymer in which a side chain containing a carboxyl group is introduced into a main chain composed of a polyethyleneimino group (trade name: Trilon P, weight average molecular weight: about 50,000, manufactured by BASF) )
A-2: Copolymer of maleic acid and acrylic acid (trade name: Aqualic TL, weight average molecular weight: about 50000, manufactured by Nippon Shokubai Co., Ltd.)
A-3: polyethyleneimine (trade name: Lupasol HF, weight average molecular weight: about 25000, manufactured by BASF)

<(A ′) component: a chelating agent which is a comparative product of the component (a)>
A′-1: n-dibutylamine (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
A′-2: Acetoxime (special grade reagent, manufactured by Kanto Chemical Co., Inc.)
A'-3: Pyridine (special grade reagent, manufactured by Kanto Chemical Co., Inc.)
A′-4: Catechol (special grade reagent, manufactured by Kanto Chemical Co., Inc.)
A′-5: Mercaptosuccinic acid (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.)
A′-6: 2,2′-dipyridylamine (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.)

<(B) Component: Copper compound>
CuSO ₄ · 5H ₂ O: Copper (II) sulfate pentahydrate (special grade reagent, Mw = 249.68, manufactured by Kanto Chemical Co., Inc.)
CuCl ₂ · 2H ₂ O: Copper (II) chloride dihydrate (special grade reagent, Mw = 170.48, manufactured by Wako Pure Chemical Industries, Ltd.)
<(B ′) Component: Metal Compound as a Comparative Product of Component (b)>
MnSO4 · 5H2O: Manganese (II) sulfate pentahydrate (special grade reagent, Mw = 241.07, manufactured by Kanto Chemical Co., Inc.)
FeSO4 · 7H2O: Iron (II) sulfate heptahydrate (special grade reagent, Mw = 278.01, manufactured by Kanto Chemical Co., Inc.)
In Tables 1 to 7, the mass ratio (mass ppm) of Cu (Mw = 63.54) with respect to the dry pulp is used for the component (b), and Mn (Mw = 54.93) or Fe for the component (b ′). The mass ratio (mass ppm) with respect to the dry pulp of (Mw = 55.84) was shown in [].

<Hydrogen peroxide>
・ Hydrogen peroxide: 30% hydrogen peroxide solution (reagent, manufactured by Kanto Chemical Co., Inc.)

<Others>
H ₂ SO ₄ : sulfuric acid, concentration 1N (special grade reagent, manufactured by Kanto Chemical Co., Inc.)
・ NaOH: Sodium hydroxide, concentration 1N (special grade reagent, manufactured by Kanto Chemical Co., Inc.)
・ Na ₂ SiO ₃ : No. ₃ sodium silicate solution (reagent, manufactured by Showa Chemical Co., Ltd.)

(Evaluation of bleaching effect)
The bleaching effect was evaluated by obtaining the difference in whiteness for the bleached pulp obtained in each example by the following method.

<Production of evaluation paper>
The bleached pulp obtained in each example was washed with tap water and collected by filtration. The bleached pulp collected by filtration is dispersed in 400 mL of tap water, and an EDTA solution (EDTA-2Na concentration 5 g / L) is added at a rate of 0.5 mL per 1 g of the absolute dry mass of the bleached pulp, and sodium hydroxide (1 mol / L) or A test pulp dispersion having a pH of 4.0 to 5.5 was prepared using a sulfuric acid (about 0.5 mol / L) solution.
The test pulp dispersion was suction filtered to 200 g / m ² and then press dehydrated and dried overnight to produce an evaluation paper.

<Measurement of whiteness of evaluation paper>
The whiteness of the evaluation paper was measured according to Japanese Industrial Standard JIS P8211.
Four predetermined positions on the evaluation paper are set, and the whiteness of the four predetermined positions is measured using SE-2000 (product name, manufactured by Nippon Denshoku Industries Co., Ltd.), and the average value (ISO whiteness) ) For each example.
Separately, with respect to bleached pulp bleached without adding the components (a), (b) and (a ′), the whiteness was measured in the same manner as the whiteness of each example, and this was used as the standard whiteness.

<Whiteness difference>
The evaluation of the bleaching effect was calculated by the following formula (1).
Whiteness difference = [each example whiteness]-[reference whiteness] (1)

When the whiteness difference shows a positive value, it indicates that the bleaching effect has been improved by the addition of the pulp bleaching assistant, and the higher the value, the higher the effect. On the other hand, when the difference in whiteness shows a negative value, it means that the whiteness has decreased due to the addition of the pulp bleaching aid.
If the whiteness difference is 1.0 point or more, the difference in whiteness can be clearly seen even by visual observation. Moreover, if it exceeds 0.5, it can be evaluated that the bleaching effect was significantly improved.

(Examples 1-10, Comparative Examples 1-10)
As the material to be treated, softwood kraft pulp, which is a chemical pulp with a whiteness of 41.9, was used as a kraft pulp obtained by subjecting coniferous trees to alkali digestion, oxygen delignification treatment, and chlorine dioxide bleaching treatment by a conventional method.
1 g (solid content) of softwood kraft pulp was weighed into a cylindrical 50 mL glass bottle.
Subsequently, according to Tables 1-2, after adding sodium hydroxide, (a) component or (a ') component and (b) component or (b') component were added separately, respectively. In addition, the addition amount of each component in a table | surface is the mass ratio of each component with respect to the dry mass of softwood kraft pulp (it is the same below).
Next, an aqueous hydrogen peroxide solution and tap water were added so that the pulp concentration would be 10% by mass, and adjusted to pH 11 with sulfuric acid or sodium hydroxide as necessary to obtain a chemical pulp dispersion. In addition, the amount of hydrogen peroxide in the table is a value for pure hydrogen peroxide. In addition, the mass ratio of [(a ′) component] / [copper] and the mass ratio of [(a) component] / [(b ′) component-derived metal] are “(a) / (copper) mass ratio”. Described (the same applies hereinafter).
And the chemical pulp dispersion liquid was left still for 120 minutes in a 60 degreeC temperature bath, and the softwood kraft pulp was bleached. After leaving still for 120 minutes, the chemical pulp dispersion was filtered, and the solid content separated by filtration was washed with 100 times the mass of tap water to obtain bleached pulp. About the bleached pulp obtained in this way, a whiteness difference was calculated | required and the result is shown in a table | surface.

(Examples 11-29, Comparative Examples 11-28)
The processed material is a thermomechanical pulp (TMP) in which softwood chips are heated at 120 ° C. for 2 minutes and then subjected to two stages of refining with a single disc refiner. The softwood TMP which is a pulp was used.
1 g (solid content) of conifer TMP was weighed into a cylindrical 50 mL glass bottle.
Subsequently, according to Tables 3-7, after adding sodium hydroxide and sodium silicate, (a) component or (a ') component and (b) component or (b') component were added separately, respectively.
Next, an aqueous hydrogen peroxide solution and tap water were added so that the pulp concentration was 7% by mass, and the pH was adjusted to 11 with sulfuric acid or sodium hydroxide as necessary to obtain a mechanical pulp dispersion.
And mechanical pulp dispersion liquid was left still for 180 minutes in a 60 degreeC warm bath, and the softwood TMP was bleached. After standing for 120 minutes, the mechanical pulp dispersion was filtered, and the solid content separated by filtration was washed with tap water having a mass of 100 times to obtain bleached pulp. About the bleached pulp obtained in this way, a whiteness difference was calculated | required and the result is shown in a table | surface.

As shown in Table 1, in Examples 1 to 10 to which the present invention was applied, the difference in whiteness was 0.9 or more. In particular, Examples 1 to 4 in which the component (a) was a-1 (aminopolycarboxylic acid polymer) were relatively different from Examples 5 to 10 using other a-2 or a-3. The whiteness difference was high.
On the other hand, as shown in Table 2, in Comparative Example 1 in which the pulp bleaching assistant was only the component (b), the whiteness difference was −3.4, and bleached pulp bleached without adding the pulp bleaching assistant. It was inferior in whiteness. Moreover, although the whiteness difference was 0.5, the comparative example 2 which made the pulp bleaching adjuvant only the (a) component was inferior to the whiteness difference of Examples 1-10. In addition, in Comparative Examples 3 to 8 using the component (a ′) instead of the component (a), the whiteness difference is −1.9 to −3.0, and the improvement of the bleaching effect is not observed. It was a thing. Further, in Comparative Examples 9 to 10 using the component (b ′) instead of the component (b), the whiteness difference was 0.5 or less. From these results, it was found that by using the pulp bleaching aid of the present invention, the bleaching effect of hydrogen peroxide can be synergistically enhanced in the bleaching treatment under the condition of pH 11.

As shown in Table 3, in Examples 11 to 14 to which the present invention was applied, the difference in whiteness was 1.5 or more.
On the other hand, as shown in Table 3, in Comparative Example 11 in which the pulp bleaching assistant was only the component (b), the whiteness difference was −2.9, and bleached pulp bleached without adding the pulp bleaching assistant. It was inferior in whiteness. Moreover, although the whiteness difference was 0.5, the comparative example 12 which made the pulp bleaching assistant only the (a) component was inferior to the whiteness difference of Examples 11-14. In addition, in Comparative Examples 13 to 18 using the component (a ′) instead of the component (a), the whiteness difference is −1.4 to −2.5, and the improvement of the bleaching effect is not observed. It was a thing. Furthermore, instead of the component (b), Comparative Examples 19 to 20 using the component (b ′) had a whiteness difference of 0.5 or less. From these results, it was found that by using the pulp bleaching aid of the present invention, the bleaching effect of hydrogen peroxide can be synergistically enhanced even for mechanical pulp.

As shown in Table 5, Examples 15 to 22 in which the ratio of the component (a) to the dry weight of mechanical pulp was 5 to 1000 mass ppm and the ratio of copper was 0.127 to 25.4 mass ppm were bleached. The improvement of the effect was seen.
On the other hand, in Comparative Examples 21 to 26 in which the ratio of the component (a) to the dry mass of the mechanical pulp or the ratio of copper to the dry mass of the mechanical pulp is outside the scope of the present invention, the components (a) and (b) The bleaching effect of hydrogen peroxide by the addition of was not observed.

As shown in Table 6, in Examples 23 to 29 in which the (a) / (copper) mass ratio was 3.9 to 787, an improvement in the bleaching effect was observed. In particular, in Examples 24-28 in which the mass ratio (a) / (copper) was 20-315, the whiteness difference was a high value of 2.1-2.8.
On the other hand, in Comparative Examples 27 to 28 (Table 7) in which the (a) / (copper) mass ratio is outside the scope of the present invention, the bleaching effect of hydrogen peroxide by the addition of the (a) component and the (b) component is present. I couldn't see it.

10 Cooking Process 12 First Cleaning / Dehydration Process 14 Oxygen Bleaching Process 16 Second Cleaning / Dehydration Process 18 Hydrogen Peroxide Bleaching Process 20 Third Cleaning / Dehydration Process

Claims (4)

A pulp bleaching auxiliary agent comprising the following component (a) and the following component (b), which is used for bleaching a pulp with hydrogen peroxide,
During the bleaching treatment of the pulp, the mass of the component (a) is 5 to 1000 ppm by mass with respect to the dry mass of the pulp, the mass of copper is 0.12 to 30 ppm by mass with respect to the dry mass of the pulp, and [(a ) Component] / [copper] The mass ratio represented by 4 to 800 is used as a pulp bleaching assistant.
Component (a): a polymer compound having a structural unit represented by the following general formula (I), the polymer compound may be composed of the same structural unit, or two or more structural units The copolymer which consists of may be sufficient.

(In the general formula (I), A is CH or N, X is H or a substituent represented by the following general formula (II), and all Xs may be the same. These may be different from each other, but at least one is a substituent represented by the following general formula (II).)

(In the general formula (II), Y is either a carboxyl group or a primary to tertiary amino group, and n is an integer of 0 to 2. When Y is a secondary or tertiary amino group And may be a cross-linking species that bonds the structural units represented by the general formula (I).)
(B) Component: Copper compound.   The pulp bleaching assistant according to claim 1, wherein A in the general formula (I) is N, and Y represented by the general formula (II) is a carboxyl group.   The pulp bleaching auxiliary according to claim 1 or 2, wherein the pulp bleaching auxiliary is for mechanical pulp. A pulp bleaching method for bleaching pulp using a pulp bleaching assistant comprising the following component (a) and component (b) below, and hydrogen peroxide,
The mass of the component (a) is 5 to 1000 mass ppm with respect to the dry mass of the pulp, the mass of copper is 0.12 to 30 mass ppm with respect to the dry mass of the pulp, and [(a) component] / [copper]. The pulp bleaching method, wherein the pulp bleaching assistant is added so that the expressed mass ratio is 4 to 800.
Component (a): a polymer compound having a structural unit represented by the following general formula (I), the polymer compound may be composed of the same structural unit, or two or more structural units The copolymer which consists of may be sufficient.

(In the general formula (I), A is CH or N, X is H or a substituent represented by the following general formula (II), and all Xs may be the same. These may be different from each other, but at least one is a substituent represented by the following general formula (II).)

(In the general formula (II), Y is either a carboxyl group or a primary to tertiary amino group, and n is an integer of 0 to 2. When Y is a secondary or tertiary amino group And may be a cross-linking species that bonds the structural units represented by the general formula (I).)
(B) Component: Copper compound.

Images