JP2014012903A - Production method of bleach pulp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide bleached pulp in which unbleached pulp obtained by performing digestion of a lignocellulosic material is performed by alkali oxygen delignification, then performed by persulfuric acid treatment in which mirabilite or sesquicarbonate mirabilite inclusion solution is added in an acidic region, and then performed by an (ECF,TCF) multistage bleach process in which chlorine and hypochlorite are not used to produce the bleached pulp, and lowering of a pulp viscosity is little.SOLUTION: An unbleached pulp obtained by performing digestion of a lignocellulosic material is performed by alkali oxygen delignification, pulp after the alkali oxygen delignification is performed by hydrogen peroxide treatment by an initial reaction at pH of 1.5-4.5 and at a reaction temperature of 50-85°C, and is performed by persulfuric acid treatment under the existence of mirabilite and/or sesquicarbonate mirabilite, and an amount of hexeneuronic acid in the bleach pulp is made at most 15 mmol per 1 kg of bone dry pulp.

Description

  The present invention relates to a method for producing bleached pulp derived from lignocellulosic material. More specifically, in the present invention, the unbleached pulp obtained by digesting the lignocellulosic material is subjected to alkaline oxygen delignification, and then subjected to persulfuric acid treatment with addition of mirabilite or sesqui mirabilite containing solution in the acidic region, The present invention relates to a method for producing a bleached pulp that is treated in a multi-stage bleaching step that does not use chlorine or hypochlorite (ECF, TCF) and has a low decrease in pulp viscosity.

  In order to use lignocellulosic material as a papermaking raw material in many applications, after pulping by chemical action such as cooking, or pulping by mechanical action using a refiner, etc., the resulting pulp is bleached by chemicals. Need to be bleached to increase whiteness. For example, kraft pulp is usually subjected to alkaline oxygen delignification after use in applications that require strength, such as packaging materials, and then chlorine, hypochlorite, chlorine dioxide, oxygen, ozone, hydrogen peroxide It is generally used as bleached kraft pulp after bleaching with bleaching agent and bleaching aid such as persulfuric acid, peracetic acid, caustic soda, etc. .

  When producing bleached pulp from unbleached pulp, it is necessary to maintain a certain level of strength of the pulp fiber itself, so that the decomposition of carbohydrates such as cellulose and hemicellulose constituting the pulp fiber is minimized. In addition, it is common to employ a three- to six-stage multi-stage bleaching method in which bleaching is carried out gently by avoiding radical one-step bleaching and various combinations of bleaching chemicals and bleaching conditions.

Conventionally, in the multi-stage bleaching method, the pulp is first treated with chlorine, lignin contained in the pulp is chlorinated, and after adding solubility to the lignin, the chlorinated lignin is dissolved and extracted with an alkali, A method has been employed in which lignin is separated and removed from the pulp, and a small amount of residual lignin is decomposed and removed by using hypochlorite, chlorine dioxide, or the like to obtain a pulp with high whiteness.
However, in recent years, there is concern about the environmental impact of organochlorine compounds (hereinafter abbreviated as AOX) contained in the bleaching effluent from the pulp chlorination stage, and there is an increasing trend of not using chlorine for pulp bleaching. In addition, when hypochlorite is used, chloroform is generated during pulp bleaching, which may adversely affect the environment, so a bleaching sequence that does not use hypochlorite for pulp bleaching is required. It is coming.

  At present, oxygen-based bleaching chemicals such as ozone, oxygen, hydrogen peroxide, and peracids such as peracetic acid and persulfuric acid are attracting attention as an alternative to chlorine and hypochlorite. However, peracetic acid is widely used because it has a low selectivity to delignification and there is a risk of impairing pulp strength, a high chemical cost, or explosiveness and difficulty in handling. It has not yet reached. Therefore, at present, as a substitute for chlorine and hypochlorite, chlorine dioxide and alkaline hydrogen peroxide, which have already been used, are generally used. In particular, there are increasing examples of replacing bleaching starting from the chlorine bleaching-alkali extraction sequence with chlorine dioxide bleaching and alkaline hydrogen peroxide bleaching. However, since chlorine dioxide and alkaline hydrogen peroxide have a different reaction bleaching mechanism from chlorine, especially when hard paper is made from hardwood, the bleaching of the pulp after bleaching is extremely severe under practical conditions. There was a problem that it was inferior.

  Bleaching with a general bleaching sequence that does not use chlorine or hypochlorite (for example, D-EDP: D = chlorine dioxide stage, E = alkali extraction stage, P = alkali hydrogen peroxide stage) When the amount of hexeneuronic acid in the pulp obtained is higher than 15 mmol per kg of absolutely dry pulp, there is a problem that the fading of the pulp is remarkably inferior.

  As a method for improving fading, it is known to perform xylanase treatment before or after oxygen bleaching of pulp (for example, see JP-A-2-264087 and JP-A-2-293486). There is also a proposal for improving fading (for example, see JP-A-6-101185), but there is a problem that the effect of improving fading is not so great for the cost of prescription. Further, in the method of performing acid pretreatment (for example, see British Patent No. 1062734, JP 10-508346 A), unbleached pulp is subjected to a temperature of 80 ° C. or higher under acidity before the bleaching stage ( For example, refer to British Patent No. 1062734) or processed at 85 to 150 ° C. (for example, refer to Japanese Patent Publication No. 10-508346), and then bleached in multiple stages to improve pulp fading. It has been reported.

  However, when the present inventors processed and bleached under these conditions, it was found that, although the color fading was improved at a temperature exceeding 85 ° C., the strength was greatly reduced. Furthermore, the acid pretreatment method at this high temperature has a large decrease in whiteness after acid treatment. Therefore, the decrease in bleaching chemicals is less as the kappa number decreases, and the pulp yield decreases and the wastewater COD increases. However, there is also a problem that the equipment cost is high due to the necessity of equipment capable of withstanding high temperature and low pH.

  On the other hand, a dry heating method (heating at 105 ° C. for 24 hours) is used for evaluating the fading property (see, for example, Japanese Patent Publication No. 10-508346), but in order to see the actual fading property, In spite of the fact that it is essential to perform the fading test under heat / humidity conditions (for example, 80 ° C. and relative humidity 65%), this evaluation method is a fading evaluation only by heat treatment. Considering climatic conditions, it is difficult to evaluate the fading characteristics of products using this evaluation method.

  The PC value (post-color number) that is usually used for evaluation of fading is obtained from the difference in whiteness before and after the fading process. Photographic materials using pulp having a low PC value (for example, see JP-A-56-54436), and photographic materials excellent in fading using pulp bleached by a sequence including oxygen bleaching (for example, special materials There is a report example about Kaisho 63-303191.) All are examples using pulp produced by chlorine-based bleaching, and from the characteristics of photographic materials, Since the whiteness is as high as ISO 90% or more, the bleaching pulp is naturally excellent in fading. However, as in the present invention, a pulp having excellent strength and fading is not produced by a bleaching method that does not use chlorine and hypochlorite.

  On the other hand, in the hydrogen peroxide treatment in the acidic region, there is a method (Patent Document 1) using mirabilite or a sesqui mirabilite-containing solution in order to prevent a decrease in pulp viscosity. However, maintenance of pulp viscosity and removal efficiency of hexeneuronic acid Considering that, persulfuric acid is clearly more effective. When persulfuric acid treatment was carried out without using mirabilite or a sesqui mirabilite-containing solution, although fading was excellent, there was a point to be improved from the test results of the inventors regarding prevention of pulp viscosity reduction.

  In the bleached pulp manufacturing process, as a method for preventing a decrease in pulp viscosity, alkaline pulp is heat-treated by adding nitrite and nitrate at about 80 ° C. in an acidic treatment liquid having a pH of 1.0 to 1.6, There is a method of performing alkali extraction treatment of lignin without adding oxygen (for example, see Patent Document 2), but it only proposes an alternative to oxygen bleaching and prevents viscosity reduction in multi-stage bleaching stages. is not.

  In addition, there are several patent documents (Patent Documents 3, 4, 5, 6, and 7) regarding a method of bleaching pulp using persulfuric acid, but all of them are insufficient to prevent a decrease in pulp viscosity. .

  On the other hand, the composition and amount of waste liquid discharged from chlorine dioxide production facilities using chlorate, sulfuric acid, and methanol as raw materials, and used in coagulation-precipitation treatment tanks for factory waste liquids, bleaching processes, etc., or dumped into the ocean Is generally 1.2 to 1.4 tons for 1 ton of chlorine dioxide production, 0.5 to 5 kg of sodium chlorate to 1 ton of chlorine dioxide production, and sodium chloride to produce chlorine dioxide The ratio is 0.1 to 0.5 kg per 1 ton. Therefore, in the ECF bleaching method which does not normally use elemental chlorine, for example, when a production amount of 1000 tons per day is produced in a normal ECF sequence such as D / E / OPD, The amount of use is 5 to 15 tons, and the amount of sesqui-sodium salt in the waste liquid that accompanies it is discharged 6 to 21 tons per day, and the amount of discharge from the chlorine dioxide facility is considerable. . Methods for producing chlorine dioxide by reducing chlorate with methanol include Nippon Carlit's R-8 method and Hodogaya Engineering's SVP-LITE method.

  As a waste liquid treatment method from a chlorine dioxide production facility, a method of producing aluminum sulfate by adding aluminum or an aluminum compound (see, for example, JP-A-51-96796), a method of using in a cooking chemical (for example, (See JP-A-52-107302.) In a two-chamber electrodialysis apparatus composed of a bipolar membrane and a cation exchange membrane, the sulfate is decomposed into sulfuric acid and alkali, and the sulfuric acid is reused in the chlorine dioxide production facility. (For example, refer to Japanese Patent Laid-Open No. 5-58601.) However, all of them are expensive in production and equipment, and in most actual pulp manufacturing factories, pH adjustment of the coagulation sedimentation treatment tank of the factory waste liquid It is currently used for pH adjustment in the bleaching process.

Japanese Patent No. 4039308 Japanese Patent No. 3265036 JP 2007-169831 A JP 2007-308815 A JP 2008-88606 A JP 2011-1636 A JP 2011-1637 A

  The inventors of the present invention have previously described bleached pulp obtained by subjecting unbleached pulp obtained by digesting lignocellulosic material to alkaline oxygen delignification and then bleaching without using elemental chlorine in a multistage bleaching step. In the production method, the pulp after alkaline oxygen delignification is treated with hydrogen peroxide at a reaction initial pH of 1.5 to 4.5 and a reaction temperature of 50 ° C. to 85 ° C., and the amount of hexeneuronic acid in the bleached pulp is A method for producing bleached pulp with improved fading has been proposed, characterized in that it is 15 mmol or less per kg of absolutely dry pulp.

  According to the present invention, in the above method, by setting the amount of hexeneuronic acid in the bleached finished pulp to 15 mmol or less per kg of the dry pulp, not only the bleaching property of the bleached pulp is improved, but also the pulp viscosity is reduced. The purpose is to reduce the number. Another object of the present invention is to make it possible to effectively use the waste liquid discharged from the chlorine dioxide production facility.

The present invention capable of achieving the above object includes the following inventions.
(1) Unbleached pulp obtained by digesting lignocellulosic material is subjected to alkaline oxygen delignification, and the pulp after the alkaline oxygen delignification is subjected to persulfuric acid at an initial reaction pH of 1.5 to 4.5 and a reaction temperature of 50 to 85 degrees. A method for producing bleached pulp in which the amount of hexeneuronic acid in the bleached pulp is 15 mmol or less per kg of absolutely dry pulp, and the hydrogen peroxide treatment is carried out in the presence of sodium sulfate and / or sesqui sodium salt A method for producing a bleached pulp characterized by having reduced viscosity and improved fading.

(2) The method for producing bleached pulp according to (1), wherein the presence ratio of mirabilite and / or sesqui mirabilite in the persulfuric acid treatment is 0.01% by mass to 10% by mass per dry pulp.

(3) The method for producing bleached pulp according to any one of (1) and (2), wherein the mirabilite and / or sesqui mirabilite is a sesqui mirabilite-containing waste liquid discharged from a chlorine dioxide production facility as a waste liquid.

(4) The method for producing bleached pulp according to any one of (1) to (3), wherein a chelating agent is added to the persulfuric acid treatment.

(5) The bleached pulp is a hardwood pulp, wherein the bleached pulp has a reduced viscosity and improved fading as described in any one of (1) to (4).

(6) Acidic paper containing, as a main component, bleached pulp having a reduced viscosity and improved fading, which is produced by the method according to any one of (1) to (5).

  Unbleached pulp obtained by digesting lignocellulosic material is subjected to alkaline oxygen delignification, followed by persulfuric acid treatment with addition of sesqui mirabilite, and processed in a multi-stage bleaching process using neither chlorine nor hypochlorite. Using the bleached finished pulp manufacturing method, the bleached finished pulp has a hexeneuronic acid amount of 15 mmol or less per absolutely dry pulp, so that the bleached pulp is disaggregated, and then a pulp sheet is produced, and the relative humidity is 80 ° C. The PC value treated for 48 hours under a constant temperature and humidity condition of 65% was 10.0 or less, and it was possible to remarkably improve the fading property of the bleached pulp and greatly increase the pulp viscosity. Furthermore, in general, it is used to adjust the pH of the factory waste liquid to the coagulation sedimentation treatment tank, to adjust the pH to the bleaching process, etc., or to recover and effectively use the waste liquid containing sesqui-nitrate discharged from the chlorine dioxide production facility. It is also possible to do.

  The lignocellulosic material used in the present invention is not particularly limited. As the cooking method for obtaining the pulp used in the present invention, known cooking methods such as kraft cooking, polysulfide cooking, soda cooking, alkali sulfite cooking, etc. can be used, considering pulp quality, energy efficiency, etc. Then, the kraft cooking method or the polysulfide cooking method is suitably used. For example, when kraft cooking of wood, the sulfidity of the kraft cooking liquid is 5 to 75%, preferably 15 to 45%, and the effective alkali addition rate is 5 to 30% by weight, preferably 10 to 25% by weight of the absolutely dry wood. %, The cooking temperature is 130-170 ° C., and the cooking method may be either a continuous cooking method or a batch cooking method. When a continuous cooking kettle is used, a modified cooking method in which a cooking solution is added at multiple points may be used. The method is not particularly limited.

  In cooking, as a cooking aid in the cooking solution to be used, known cyclic keto compounds, for example, benzoquinone, naphthoquinone, anthraquinone, anthrone, phenanthroquinone, and quinone-based alkyl substitutes such as alkyl and amino, or the quinone series 1 selected from hydroquinone compounds such as anthrahydroquinone, which is a reduced form of the compound, and a 9,10-diketohydroanthracene compound which is a stable compound obtained as an intermediate of an anthraquinone synthesis method by the Diels-Alder method A seed | species or 2 or more types may be added, and the addition rate is 0.001-1.0 mass% per the absolute dry weight of a wood chip.

  In the present invention, unbleached chemical pulp obtained by a known digestion method is delignified by a known alkaline oxygen delignification method through washing, rough selection, and selection steps. As the alkaline oxygen delignification method used in the present invention, a known medium concentration method or high concentration method can be applied as it is, but a medium concentration method in which the pulp concentration currently used for general purposes is 8 to 15% by mass. Is preferred.

  In the alkali oxygen delignification method based on the medium concentration method, caustic soda or oxidized kraft white liquor can be used as the alkali, and oxygen gas from oxygen, PSA (Pressure Swing Adsorption) can be used as the oxygen gas. Or oxygen from VSA (Vacuum Swing Adsorption) can be used. The oxygen gas and alkali are added to a medium-concentration pulp slurry in a medium-concentration mixer and mixed sufficiently, and then sent to a reaction tower capable of holding a mixture of pulp, oxygen, and alkali for a certain period of time under pressure, and delignified. Is done.

  The oxygen gas addition rate is 0.5 to 3% by mass per mass of dry pulp, the alkali addition rate is 0.5 to 4% by mass, the reaction temperature is 80 to 120 ° C., the reaction time is 15 to 100 minutes, and the pulp concentration Is 8 to 15% by mass, and other known conditions can be applied. In the present invention, in the alkaline oxygen delignification step, the alkaline oxygen delignification is continuously performed a plurality of times, and the delignification is preferably advanced as much as possible. The pulp that has been subjected to alkaline oxygen delignification is then sent to a washing step. The pulp is sent to the persulfuric acid treatment step after washing.

  The reaction temperature during the treatment with persulfuric acid in the present invention is preferably 50 to 85 ° C. When the temperature is less than 50 ° C., the fading property is not sufficiently improved. On the other hand, when the temperature exceeds 85 ° C., the fading property is improved, but the viscosity and strength of the bleached pulp are remarkably lowered. The initial reaction pH is preferably 1.5 to 4.5. If the initial reaction pH is less than 1.5, the pulp strength is greatly adversely affected, and it is difficult to find a durable lining at a pH of less than 1.5 at the above temperature, even if very expensive. It ’s not practical. When the pH is higher than 4.5, the effect of removing hexeneuronic acid is reduced and the scaling of calcium oxalate in the process becomes severe.

On the other hand, the addition rate of persulfuric acid is preferably 0.05 to 5% by mass per absolutely dry pulp, and is preferably 0.1 to 2% by mass in consideration of effects and damage to pulp fibers.
Further, the retention of the persulfuric acid treatment is preferably 30 to 300 minutes considering the effect and damage to the pulp fiber, and the treatment concentration is not limited as long as it is a general in-process concentration, but 8 to 15%. The medium concentration method or the high concentration method of 25 to 40% is preferable. In the present invention, the acid used for maintaining the acidic region may be used in combination with either an inorganic acid or an organic acid. The pH during the acid treatment is 1.5 to 4.5, and specifically, inorganic acids such as sesquiz salt silicate discharged from sulfuric acid, nitric acid, hydrochloric acid, sulfurous acid, nitrous acid, or chlorine dioxide generating equipment can be used. . As an acid other than sesqui mirabilite, sulfuric acid is preferably used because it is easy to obtain and handle. In addition, a general formulation is used for acid treatment. On the other hand, the addition rate of mirabilite or sesqui mirabilite is 0.01 to 10% by mass, preferably 0.1 to 5% by mass, and preferably 0.1 to 5% by mass per dry pulp. If it is less than 10%, the effect of increasing the viscosity is thin, and if it exceeds 10% by mass, the production cost increases.

In the persulfuric acid treatment in the acidic region of the present invention, a chelating agent may be added. Type chelating ^agents, Fe ^2+, Cu ^2+, as long as it can sequester metal ions ^{Mn 2+,} etc. EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), DTPMP (diethylene triamine pentamethylene phosphonic acid), PHAS ( (Poly-α-hydroxyacrylate) and the like, and various chelating agents may be used in combination. Moreover, the addition rate of a chelating agent is generally added in the range of 0.001% by mass to 5% by mass with respect to absolutely dry pulp, and the addition of the chelating agent may be added before or after the addition of hydrogen peroxide. However, in order to maximize the chelating effect, it is more effective before the addition of persulfuric acid.

  In the persulfuric acid treatment of the present invention, pressurization can be performed using an oxygen-containing gas or a nitrogen-containing gas. The oxygen-containing gas used for pressurization during processing can be used on an industrial scale, such as oxygen from a cryogenic separation method, oxygen from PSA, oxygen from VSA, etc. Currently, alkaline oxygen desorption is possible. Oxygen or oxygen-containing gas having an oxygen purity of 85% by volume or more used in lignin, an oxygen-containing gas adjusted to an oxygen content of more than 21% by volume using an oxygen production facility using the molecular sieve, Examples thereof include an oxygen-enriched gas produced by mixing an oxygen-containing gas having an oxygen purity of 85% by volume or more and air, an air having an oxygen content of 20% by volume or more, and the like. Can be used. The pressure applied during the acid treatment with the oxygen-containing gas or the nitrogen-containing gas during the persulfuric acid treatment is 0.05 to 0.9 MPa (gauge pressure), preferably 0.15 to 0.7 MPa.

  Moreover, when it has an ozone bleaching stage in a multistage bleaching process, the exhaust gas containing oxygen can also be used suitably. The nitrogen-containing gas used in the persulfuric acid treatment stage of the present invention may be any gas as long as the nitrogen gas content is 95% or more, but from an economic standpoint, it is a depth used for alkaline oxygen delignification. A nitrogen-containing gas by-produced when producing oxygen gas such as oxygen from the cold separation method, oxygen from PSA, oxygen from VSA, etc. is preferably used.

  In the present invention, an enzyme treatment step can be provided after the persulfuric acid treatment step in the acidic region. The enzyme used in the enzyme treatment step may be any enzyme as long as the potassium permanganate value of the pulp measured by JIS P 8206 is decreased by reacting with the pulp. For example, xylanase, lignin peroxidase, manganese peroxidase, laccase and the like are known. Of course, these enzymes may be used, and it is needless to say that enzymes that are not yet known may be applicable enzymes. In addition, these enzymes may be used alone, or may be combined, mixed, and further divided into a plurality of times. Among these enzymes, a xylan-degrading enzyme called xylanase has a bleaching promoting effect and is preferably used.

  In the present invention, a persulfuric acid treatment step is provided after the alkaline oxygen bleaching step, but it is also possible to provide an acid treatment step at a later stage. The acid treatment in the acid treatment step of the present invention is preferably performed under conditions of pH 2.5 to 3.5, temperature of preferably 85 to 110 ° C., and retention time of preferably 20 to 90 minutes. The acid used in the acid treatment of the present invention may be either an inorganic acid or an organic acid as long as the pH during the acid treatment can be adjusted to a predetermined value. Specifically, sulfuric acid, nitric acid, hydrochloric acid, sulfurous acid, etc. Among them, sulfuric acid is preferably used because it is easy to obtain and handle. In addition, a general prescription is adopted for acid treatment.

  In the multi-stage bleaching process of the present invention, the first stage is a chlorine dioxide bleaching stage (D), an ozone bleaching stage (Z), or a bleaching stage (Z / D) in which ozone bleaching and chlorine dioxide bleaching are continuously combined. Is preferably used, the alkali extraction stage (E) is used in the second stage, and a combination of chlorine dioxide, alkali hydrogen peroxide and the like is preferably used in the third and subsequent stages. The chlorine dioxide used in the first stage chlorine dioxide bleaching stage of the present invention can be selected from chlorine dioxide obtained from many chlorine dioxide generation methods known to those skilled in the art, but is preferably a generation method that does not produce chlorine as a by-product. Chlorine dioxide obtained from The pH in the first chlorine dioxide stage of the present invention is 2 to 6, preferably 2.5 to 4, and any acid or alkali can be supplementarily added to adjust the pH. Moreover, well-known conditions can be employ | adopted for all other chlorine dioxide bleaching conditions, such as chlorine dioxide processing time, processing temperature, and a pulp density | concentration.

  In the alkaline extraction stage following the chlorine dioxide bleaching stage of the present invention, many alkaline compounds known to those skilled in the art can be used, but caustic soda is the easiest to use and is preferably used. In the alkali extraction stage of the present invention, oxygen and / or hydrogen peroxide can be used in combination. In addition, the alkali extraction stage of the present invention can be performed under known conditions.

  Any bleaching chemical other than chlorine and hypochlorite may be used in the third and subsequent bleaching stages following the chlorine dioxide bleaching stage and the alkali extraction stage used in the multistage bleaching process of the present invention. However, general bleaching chemicals such as chlorine dioxide, alkaline hydrogen peroxide, ozone, etc. are preferably used. The number of stages after the third stage is not particularly limited, but considering energy efficiency, productivity, etc., it is preferable to finish in three or four stages in total.

  The chemicals used in the present invention include persulfuric acid (Px), chlorine dioxide (D), alkali (E), oxygen (O), alkaline hydrogen peroxide (P), ozone, excluding chlorine and hypochlorite. Known bleaching agents and bleaching assistants such as (Z), enzymes (Ez) and organic peracids can be mentioned. As the bleaching sequence, after oxygen delignification, for example, the sequence starting from the persulfate stage (Px) is Px-DE / OD, Px-DE / O-PD, Px-DE. / O-D-D, Px-D-E / O-D-P, Px-D-E / OP-D, Px-D-E / O-Z-D, Px-Z-E / O-D , Px-ZE / OP-D, Px-ZE / OP-DP, Px-ZE / OP-PD, Px-ZDE / OD, Px-Z -DE / OP-D, Px-Z / DE / OD, Px-Z / DE / OP-D and the like, and Px-Ez-DE / OD including the enzyme, Px-Ez-DE / OPD, Px-Ez-DE / ODD, Px-Ez-DE / ODP, Px-Ez-DE / OP-D, Px-Ez-DE / O-Z-D, Px- z-ZE / OD, Px-Ez-ZE / OP-D, Px-Ez-ZE / OP-DP, Px-Ez-ZE / OP-PD, Px-Ez-ZDE / OD, Px-Ez-ZDE / OP-D, Px-Ez-Z / DE / OD, Px-Ez-Z / D- E / OP-D etc. can also be mentioned.

  Further, the Px stage in the present invention may be performed anywhere in the multi-stage bleaching process as long as it is after alkaline oxygen delignification, but it is more effective immediately after alkaline oxygen delignification. Examples of sequences in which the persulfuric acid stage (Px) is in the multi-stage bleaching process include D-Px-E / OD, D-E / O-Px-D, D-Px-E / OP-D, D -E / OP-Px-D, D-E / O-D-Px, Z-Px-E / OD, ZE / O-Px-D, ZE / OP-Px-D, Z -D-Px-E / OD, Z-DE / O-Px-D, Z / D-Px-E / OD, Z / DE / O-Px-D, etc. Can do. Further, a chelating agent treatment stage with ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) or the like may be inserted in the multistage bleaching step.

Also, chelation with EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), DTPMP (diethylenetriaminepentamethylenephosphonic acid), PHAS (poly-α-hydroxyacrylate), etc. before the Px stage in the multistage bleaching process An agent treatment stage (Q) may be provided. For example, Q-Px-DE / OD, Q-Px-DE / O-PD, Q-Px-DE / ODD, Q-Px-DE / OD-P, Q-Px-DE / OP-D, Q-Px-DE / O-ZD, Q-Px-ZE / OD, Q-Px-Z- E / OP-D, Q-Px-ZE / OP-DP, Q-Px-ZE / OP-PD, Q-Px-ZD-E / OD, Q- Px-ZDE / OP-D, Q-Px-Z / DE / OD, Q-Px-Z / DE / OP-D, etc. are mentioned.

  In the present invention, bleaching of unbleached pulp with alkaline oxygen, followed by persulfuric acid treatment, and then bleached in a multi-stage bleached hexeneuronic acid amount of 15 mmol or less per 1 kg of absolutely dry pulp results in fading. We have to wait for further research on the reason for the improvement, but if hexeneuronic acid remains in the finished pulp of acid paper, it will turn into a chromophore under conditions of high humidity and high temperature. However, the whiteness is expected to decrease. Therefore, hardwood with a higher content of hexeneuronic acid is more susceptible to fading than softwood.

Further, in the present invention, a detailed reaction mechanism in which persulfuric acid decomposes hexeneuronic acid must also be studied in the future, but persulfate partially reacts with lignin and the like, and is a radical species that easily decomposes hexeneuronic acid. It is considered that there is also a reaction in which hydrooxonium ions (OH +) that are expected to be produced from persulfuric acid are involved in the decomposition of hexeneuronic acid.
Recent studies have also proposed that hexeneuronic acid groups can be epoxidized to form an acid-stable form, which can prevent fading.

  On the other hand, in the present invention, it is necessary to wait for further research on the reaction mechanism in which sesqui mirabilite retains the pulp viscosity. However, the production of (OH) radicals generated by some influence is suppressed or captured. It is thought that the reaction is happening.

In the method of preparing acid paper using the bleached pulp of the present invention, the bleached pulp is beaten with a beater to about CSF (Canadian Standard Freeness, Canadian Standard Freeness) 350 ml to 550 ml, and then a sulfuric acid band of about 2.5 is added. %, Rosin sizing agent (eg, Size Pine E, Arakawa Chemical) approx. 0.5%, Talc (eg, Illite, Nihon Talc, Inc.) approx. 20%, Yield improver (eg, Percoll 182, Kyowa Sangyo) There is a method of blending in an order of about 0.02% and making an acidic paper having a basis weight of about 64 g / m ² by a conventional method. When making acidic paper, it is of course possible to mix and use other bleached pulp as long as the excellent properties of the acidic paper of the bleached pulp of the present invention are not impaired.

Moreover, the method of preparing neutral paper using the bleached pulp of this invention is beaten bleached pulp to about CSF350ml-550ml with a beater, and then cationized starch (for example, ace K100, Oji Cornstarch) about 0 0.5%, sulfate band about 0.5%, AKD (for example, SPK902, manufactured by Arakawa Chemical) about 0.05%, light calcium carbonate (for example, TP121, manufactured by Okutama Kogyo) about 20%, yield improver (for example, , Percoll 182, Kyowa Sangyo Co., Ltd.) in the order of about 0.02%, and there is a method of making neutral paper with a basis weight of about 64 g / m ² by a conventional method.
The fading improvement effect of the present invention is large in the case of acid paper, but there is no problem using the pulp treated in the present invention for neutral paper.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is of course not limited to these examples. Examples 1 to 5 and Comparative Examples 1 to 3 shown below are obtained by bleaching hardwood kraft pulp after factory alkaline bleaching with Px-DED sequence.
Unless otherwise indicated, the following methods were used to measure the kappa number, the amount of hexeneuronic acid in the pulp, the measurement of the pulp whiteness, the evaluation of the fading of the pulp, and the measurement of the pulp viscosity. In addition, the addition rate of the chemical | medical agent in an Example and a comparative example shows the mass% per absolute dry pulp mass.

1. Measurement of pulp kappa number The kappa number was measured according to JIS P8211.

2. Quantification of the amount of hexeneuronic acid in the pulp 5 g of completely dried pulp was weighed into a 500 ml SUS container, and made into a total of 300 ml using a formic acid-sodium formate buffer 10 mmol / l solution. After that, the inside of the SUS container was replaced with nitrogen gas, and treated in an oil thermostat at 110 ° C. for 5 hours. After cooling the SUS container with running water, the treated pulp suspension including the washing liquid was made up to 500 ml and filtered, and the liquid was analyzed by HPLC (high performance liquid chromatography). -Carboxy-2-furaldehyde was quantified. In quantification, the following formulas and references were used.

Calculation formula: (concentration of 20 μl of each sample) = a, b (ng / μl).
1) Amount of 2-furoic acid (mmol / kg) = a × (500/1000) / (10 × 10 ⁻³ ) /112.08
2) 5-carb-2-hydroxydehydride amount (mmol / kg) = b × (500/1000) / (10 × 10 −3) /140.1
3) Amount of hexeneuronic acid (mmol / l) = 2-furoic acid amount + 5-carboxy-2-furaldehyde

References: Authors Vuolinen, T .;
Selective hydration of hexenuronic acid groups and it's application in ECF and TCF bleaching of craft pulls
International Pulping Bleaching Conference, April 14-18, 1996, P43-51

3. Measurement of whiteness of bleached pulp After bleaching the bleached pulp, a sulfuric acid band was added to the pulp slurry at 3.0% to the pulp, and a sheet having a basis weight of 60 g / m ² was prepared according to Tappi test method T205os-71 (JIS P 8209). . Thereafter, the whiteness of the pulp was measured according to JIS P 8123.

4). Evaluation of Pulp Fading Property The pulp sheet for measuring whiteness was faded for 48 hours under the conditions of 80 ° C. and 65% relative humidity, and the PC value was calculated and evaluated from the pulp whiteness before and after fading. PC value = 100 × [{(1−whiteness after fading) ² / (2 × whiteness after fading)} − (1−whiteness before fading) ² / (2 × whiteness before fading)}]

5. Measurement of viscosity of bleached pulp It carried out according to TAPPI 44.
6). Measurement of specific tear strength of bleached pulp After separating the pulp, a sheet having a basis weight of 60 g / m ² was prepared according to Tappi test method T205os-71 (JIS P 8209), and the specific tear strength of the pulp was measured according to JIS P 8116. .

Example 1
Cooking hardwood cooking-Alkali oxygen delignified kraft pulp (whiteness 48.1%, copper number 10.7) of dry weight 80.0g in a plastic bag, using ion-exchanged water to adjust the pulp concentration After adjusting to 10%, 0.1% sesqui mirabilite and 0.5% persulfuric acid were added per mass of dry pulp, and the mixture was immersed in a thermostatic bath at 65 ° C for 120 minutes to perform persulfuric acid treatment. (Hereinafter abbreviated as Px stage). The initial reaction pH of the Px stage was 3.2. The obtained pulp was diluted to 3% with ion-exchanged water and then dehydrated and washed using a Buchner funnel to obtain a Px-staged pulp. Next, the pulp after Px is put in a plastic bag, the pulp concentration is adjusted to 10% using ion exchange water, 0.7% of chlorine dioxide is added per mass of absolutely dry pulp, and the temperature is kept at 65 ° C. The first chlorine dioxide stage (hereinafter abbreviated as D stage) was bleached by immersion for 40 minutes. The obtained pulp was diluted to 3% with ion-exchanged water, then dehydrated and washed with a Buchner funnel.

The pulp after stage D is put in a plastic bag, the pulp concentration is adjusted to 10% using ion-exchanged water, caustic soda is added 1.2% per mass of dry pulp, and the temperature is 65 ° C. as in stage D. The treatment was performed for 110 minutes, and an alkali extraction stage (hereinafter abbreviated as E stage) was performed. The obtained pulp was diluted with ion-exchanged water to adjust the pulp concentration to 3%, and then dehydrated and washed using a Buchner funnel to obtain a pulp after stage E.
Subsequently, the pulp after stage E is put in a plastic bag, adjusted to a pulp concentration of 10% using ion-exchanged water, 0.25% of chlorine dioxide is added per mass of dry pulp, and the temperature is the same as in stage D. The treatment was carried out at 65 ° C. for 240 minutes, and the second stage D was bleached. The obtained pulp was diluted to 3% with ion-exchanged water, washed with a Buchner funnel and dehydrated to obtain a bleached pulp having a whiteness of 83.9%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 2
After the alkaline oxygen delignification, the same operation as in Example 1 was performed except that the sesqui mirabilite in the persulfate treatment of kraft pulp was changed to 2.0%. The initial reaction pH of the Px stage was 2.5, and the whiteness of the pulp after multistage bleaching was 84.4%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 3
After alkaline oxygen delignification, the same operation as in Example 1 was performed except that the sesqui mirabilite in the persulfate treatment of kraft pulp was changed to 2.0% and the persulfate addition rate was 0.4%. The initial reaction pH of the Px stage was 2.7, and the pulp whiteness after multistage bleaching was 84.3%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 4
After alkaline oxygen delignification, the same operation as in Example 1 was performed, except that the sesqui mirabilite in the persulfate treatment of kraft pulp was 2.0% and the hydrogen peroxide addition rate was 0.3%. The initial reaction pH of the Px stage was 2.8, and the pulp whiteness after multistage bleaching was 84.1%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 5
After the alkaline oxygen delignification, the same operation as in Example 1 was performed except that the sesqui mirabilite in the persulfate treatment of kraft pulp was changed to 3.7%. The initial reaction pH of the Px stage was 2.3, and the pulp whiteness after multistage bleaching was 84.0%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 6
After the alkaline oxygen delignification, the same operation as in Example 1 was performed except that 2.0% of sodium sulfate was added in the persulfuric acid treatment of kraft pulp. The initial reaction pH of the A / P stage was 2.6 and the pulp whiteness after multistage bleaching was 84.4%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Example 7
After alkaline oxygen delignification, the same operation as in Example 2 was performed except that 0.30% of DTPA was added by persulfuric acid treatment of kraft pulp. The initial reaction pH of the Px stage was 2.7, and the pulp whiteness after multistage bleaching was 84.3%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Comparative Example 1
After alkaline oxygen delignification, the same operation as in Example 1 was performed except that the sesqui mirabilite in the persulfate treatment of kraft pulp was 0% and the sulfuric acid addition rate was 0.70%. The initial reaction pH of the Px stage was 2.6, and the pulp whiteness after multistage bleaching was 84.1%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Comparative Example 2
After the alkaline oxygen delignification, the same operation as in Example 1 was carried out except that the sesqui mirabilite in persulfate treatment of kraft pulp was 0%, the sulfuric acid addition rate was 0.70%, and the persulfate addition rate was 0.1%. It was. The initial reaction pH of the Px stage was 3.0, and the pulp whiteness after multistage bleaching was 84.6%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Comparative Example 3
After the alkaline oxygen delignification, the same operation as in Example 1 was performed except that the addition rate of sesqui mirabilite in the persulfate treatment of kraft pulp was 2.0%, the addition rate of sulfuric acid was 0.30%, and no persulfate was added. It was. The initial reaction pH of the Px stage was 2.8, and the pulp whiteness after multistage bleaching was 83.6%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Comparative Example 4
After alkaline delignification, the same operation as in Example 2 was performed except that the reaction temperature in the persulfuric acid treatment of kraft pulp was 40 ° C. The initial reaction pH of the Px stage was 2.5, and the whiteness of the pulp after multistage bleaching was 83.6%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

Comparative Example 5
After alkaline oxygen delignification, the same operation as in Example 2 was performed except that the reaction temperature in the persulfuric acid treatment of kraft pulp was 90 ° C. The initial reaction pH of the Px stage was 2.5, and the whiteness of the pulp after multistage bleaching was 84.5%. The amount of hexeneuronic acid of the obtained bleached pulp, the PC value of the bleached pulp sheet after 48 hours, the viscosity of the bleached pulp and the specific tear strength were measured and shown in Table 1.

  As is apparent from a comparison of Examples 1 to 7 and Comparative Example 1 in Table 1, it can be seen that the viscosity and the specific tear strength are reduced when no sodium sulfate or sesqui sodium salt is used during the persulfuric acid treatment. Further, when a chelating agent is added as in Example 7, the viscosity is further improved. On the other hand, as is clear when Examples 1 to 7 and Comparative Example 2 are compared, even if the addition rate of persulfuric acid is decreased in order to improve the viscosity, the amount of hexeneuronic acid increases, the PC value increases, and fading occurs. The pulp is inferior in nature. Further, as apparent from comparison between Examples 2 to 4 and Comparative Example 3, even if sesqui mirabilite was added, if hexeneuronic acid was not added, the amount of hexeneuronic acid was still increased, the PC value was high, and the color fading was observed. The pulp becomes inferior. In addition, as apparent from comparison between Example 2 and Comparative Examples 4 to 5, even when sesqui mirabilite or persulfuric acid is added, if the reaction temperature is low, the amount of hexeneuronic acid increases, the PC value is high, and the color fading property is poor. Pulp. On the contrary, it can be seen that when the reaction temperature is increased, the viscosity and the specific tear strength are significantly reduced.

Claims (6)

Unbleached pulp obtained by digesting lignocellulosic material is subjected to alkaline oxygen delignification, and the pulp after the alkaline oxygen delignification is subjected to persulfuric acid treatment at a reaction initial pH of 1.5 to 4.5 and at a reaction phoneme of 50 to 85 ° C. And the bleached pulp has a hexeneuronic acid content of 15 mmol or less per kg of dry pulp, wherein the persulfuric acid treatment is performed in the presence of mirabilite and / or sesqui mirabilite. A method for producing bleached pulp. 2. The method for producing bleached pulp according to claim 1, wherein an abundance ratio of salt cake and / or sesqui salt salt in the persulfuric acid treatment is 0.01% by mass to 10% by mass per dry pulp. The method for producing bleached pulp according to any one of claims 1 and 2, characterized in that the mirabilite and / or sesqui mirabilite is a sesqui mirabilite-containing waste liquid discharged as a waste liquid from a chlorine dioxide production facility. The method for producing bleached pulp according to any one of claims 1 to 3, wherein a chelating agent is added to the persulfuric acid treatment. The method for producing bleached pulp according to any one of claims 1 to 4, wherein the bleached pulp is hardwood pulp and has a reduced viscosity and improved fading. The acid paper which has as a main component the bleached pulp manufactured by the method of any one of the said Claims 1-5.