Pitch Impairment Suppression Method

Abstract

To provide a pitch trouble suppression method, that is useful for suppressing / preventing pitch stains in the papermaking process.SOLUTION: The pitch trouble suppression method is a pitch trouble suppression method for controlling the size of a pitch contained in the pulp slurry in the pulping step and / or the preparation step to suppress the occurrence of pitch trouble in the papermaking process, including an oxidizing agent addition step in which an oxidizing agent is added to at least one location pulp slurry in the pulping step and the preparation step so that the average particle size of the pitch contained in the pulp slurry is less than 150 μm, and / or a pitch dispersing agent addition step in which a pitch dispersing agent is added to at least one location pulp slurry in the pulping step and the preparation step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for suppressing pitch trouble in the papermaking process.

Background Art

[0002] Conventionally, in the papermaking process (especially in the paper-making process), troubles due to pitch have occurred, and in order to suppress and prevent this, various chemicals have been developed. Pitch refers to a water-insoluble sticky substance mainly composed of organic substances derived from natural resins and gum substances released from wood, pulp, and paper, as well as additives used in the manufacturing process of paper and pulp.

[0003] Generally, pitch is dispersed in a colloidal state in the process water (pulp slurry or white water) in the manufacturing process of paper and pulp. However, due to some external actions, such as a large shearing force, a sudden change in pH, an excessive addition of a sulfate band (aluminum sulfate), etc., its colloidal state is considered to be destroyed, and it aggregates and grows larger. This aggregated and enlarged pitch, due to its adhesiveness, not only adheres to manufacturing equipment such as paper, pulp, fan pumps, inside pipes, chests, wires, felts, rolls, etc., but also the adhered matter peels off and re-adheres to paper and pulp. And the formed dirt and defects on the paper reduce the quality of paper products, and the resulting paper breaks cause troubles such as reducing productivity and workability.

[0004] In recent years, due to the diversification of paper, the types and usage amounts of additives have increased, the usage ratio of waste paper has increased, and as the degree of water closure in the papermaking process becomes higher, the occurrence of pitch trouble has increased more than ever, and its occurrence form has become more complicated. For example, problems with pitch originating from recycled paper materials are increasing, not only from conventional mechanical pulps such as grand pulp (GP) and thermomechanical pulp (TMP), and from chemical pulps such as kraft pulp (KP). Examples of pitch originating from recycled paper materials include synthetic resins such as magazine spine glue (polyvinyl acetate) and labels (acrylic adhesive). Furthermore, in order to improve productivity, the enlargement of equipment and the increase in papermaking speed, combined with other factors, have led to the emergence of pitch contamination problems on the wire section, press section rolls, blankets, and blanket suction boxes.

[0005] To suppress such pitch problems, methods have been proposed and put into practical use, including methods of adsorbing pitch components onto inorganic compounds such as fine talc, methods of fixing pitch particles to pulp fibers before aggregation, methods of dispersing pitch particles, and methods combining these methods.

[0006] For example, Patent Document 1 discloses a pitch disorder inhibitor for paper and pulp manufacturing processes, which contains as active ingredients a cationic polymer selected from polydiallyldimethylammonium salts with molecular weights of 20,000 to 100,000 and epichlorohydrin-dialkylamine condensates with molecular weights of 20,000 to 100,000, and a nonionic surfactant obtained by adding ethylene oxide or ethylene oxide and propylene oxide to a higher aliphatic amine. However, conventional additives and methods are not sufficiently effective in preventing pitch damage, and more effective chemicals and methods are desired.

[0007] Furthermore, Patent Document 2 describes a method for suppressing pitch defects in a paper manufacturing system that produces paper from paper raw materials, and discloses that pitch adhesion can be suppressed by performing a treatment that suppresses the increase in calcium ion concentration in the aqueous system of the paper manufacturing system.

[0008] Furthermore, Patent Document 3 describes a method for controlling pitch in the papermaking process using a combination of lipase and an oxidizing agent, thereby controlling deposit-forming contaminants including pitch or other fiber components. It also describes controlling deposit-forming contaminants by releasing organic contaminants from the fibers by contacting the fibers with a combination of lipase and at least one peroxide-free oxidizing agent.

[0009] Thus, while methods for suppressing pitch defects in the papermaking process have been studied for some time, there has been little study on pulp slurries in which pitch defects in the papermaking process are suppressed, that is, pulp slurries containing pitch controlled to such an extent that pitch defects do not occur in the papermaking process. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2004-044067 [Patent Document 2] Japanese Patent Publication No. 2011-226032 [Patent Document 3] Patent No. 6084689 [Non-patent literature]

[0011] [Non-Patent Document 1] "Method for reducing pitch in cardboard," Journal of the Japan Paper and Paper Technology Association, Vol. 58, No. 4, pp. 468-477, April 2004. [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] Therefore, the object of the present invention is to provide a method for suppressing pitch defects that is useful for suppressing and preventing pitch contamination in the papermaking process. [Means for solving the problem]

[0013] Generally, the papermaking process is divided into four stages: 1) pulping, 2) chemical mixing, 3) papermaking, and 4) finishing. Conventional methods for suppressing pitch defects have involved adding pitch control agents to the pulp slurry in the mixing and papermaking stages, primarily to suppress pitch defects that occur in the papermaking stage. However, such methods are not sufficiently effective in preventing pitch defects in the papermaking stage, and a more effective method for suppressing pitch defects is desired.

[0014] The inventors of the present invention conducted extensive research to solve the above problems and found that by controlling the size of the pitch particles in the pulp slurry before it is introduced into the papermaking process so that it does not exceed a certain size, the occurrence of pitch problems in the papermaking process can be suppressed. They then discovered that by adding a specific oxidizing agent to the pulp slurry at least one point in the pulping process and / or adding a pitch dispersant to the pulp slurry at least one point in the pulping process and / or the pulp slurry, the expansion of pitch beyond a certain size can be suppressed, resulting in an excellent suppression and prevention effect of pitch contamination in the papermaking process, and thus completed the present invention. Furthermore, the inventors have discovered that the occurrence of pitch defects in the papermaking process can be suppressed by controlling the particle size of the pitch in the pulp slurry after it is introduced into the papermaking process to be below a specific size. They have found that by adding a specific oxidizing agent and a pitch dispersant to the pulp slurry at least one location in the papermaking process, the pitch is reduced to below a specific size, exhibiting an excellent suppression and prevention effect of pitch contamination in the papermaking process, and have thus completed the present invention. Furthermore, the inventors have found that the occurrence of pitch problems in the papermaking process can be suppressed by controlling the particle size of pitch in the pulp slurry before and / or after its introduction into the papermaking process so that it is below a specific size. They have found that by adding a specific oxidizing agent and / or pitch dispersant to the pulp slurry at least one point in the pulping process and / or preparation process, and further adding a specific oxidizing agent and / or pitch dispersant to the pulp slurry at least one point in the papermaking process, the pitch in the pulp slurry in the papermaking process is reduced to below a specific size, exhibiting an excellent suppression and prevention effect of pitch contamination in the papermaking process, thus completing the present invention.

[0015] The present invention relates to a method for suppressing pitch defects in a papermaking process by controlling the size of pitch contained in a pulp slurry during a pulping process and / or a mixing process, and is characterized by comprising an oxidizing agent addition step of adding an oxidizing agent to a pulp slurry at least at one location in the pulping process and / or the mixing process, such that the average particle size of the pitch contained in the pulp slurry is less than 150 μm, and / or a pitch dispersant addition step of adding a pitch dispersant to a pulp slurry at least at one location in the pulping process and / or the mixing process. Furthermore, the present invention is a method for suppressing pitch defects in a papermaking process, which controls the size of pitch contained in a pulp slurry in the papermaking process and suppresses the occurrence of pitch defects in the papermaking process, and is characterized by comprising an oxidizing agent addition step of adding an oxidizing agent to the pulp slurry at least one location in the papermaking process so that the average particle size of the pitch contained in the pulp slurry is less than 150 μm, and a pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at least one location in the papermaking process. Furthermore, the present invention is a method for suppressing pitch defects in a papermaking process, which controls the size of pitch contained in a pulp slurry in a pulping process and / or a mixing process and a papermaking process, thereby suppressing the occurrence of pitch defects in the papermaking process, comprising: a first oxidizing agent addition step of adding a first oxidizing agent to a pulp slurry at least one location in the pulping process and the mixing process, and / or a first pitch dispersant addition step of adding a first pitch dispersant to a pulp slurry at least one location in the pulping process and the mixing process, such that the average particle size of the pitch contained in the pulp slurry of the papermaking process is less than 150 μm; and further comprising a second oxidizing agent addition step of adding a second oxidizing agent to a pulp slurry at least one location in the papermaking process, and / or a second pitch dispersant addition step of adding a second pitch dispersant to a pulp slurry at least one location in the papermaking process. The oxidizing agent is preferably at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, hydrogen peroxide, and combined halogens. Furthermore, it is preferable that the first oxidizing agent and the second oxidizing agent are at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, hydrogen peroxide, and combined halogens. Furthermore, in the pitch dispersant addition step described above, it is preferable to add the pitch dispersant to a pulp slurry having a residual chlorine concentration of 0.5 mg / L or more and 30 mg / L or less. Furthermore, in the first pitch dispersant addition step and the second pitch dispersant addition step, it is preferable to add the pitch dispersant to a pulp slurry having a residual chlorine concentration of 0.5 mg / L or more and 30 mg / L or less. Furthermore, the pitch damage suppression method of the present invention comprises the above-mentioned oxidizing agent addition step and the above-mentioned pitch dispersant addition step, wherein the oxidizing agent is preferably at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, and combined halogen. Furthermore, it is preferable that the pitch dispersant is at least one selected from the group consisting of surfactants, cationic polymers, and organic solvents. Further, it is preferable that the first and second pitch dispersants are at least one selected from the group consisting of a surfactant, a cationic polymer, and an organic solvent. Hereinafter, the present invention will be described in detail.

[0016] The present invention is a pitch defect suppression method for controlling the size of pitch contained in a pulp slurry in a pulping step and / or a conditioning step and suppressing the occurrence of pitch defects in a papermaking step, wherein the average particle size of the pitch contained in the pulp slurry is less than 150 μm, an oxidizing agent addition step of adding an oxidizing agent to at least one location of the pulp slurry in the pulping step and the conditioning step, and / or a pitch dispersant addition step of adding a pitch dispersant to at least one location of the pulp slurry in the pulping step and the conditioning step. By providing an oxidizing agent addition step of adding an oxidizing agent to at least one location of the pulp slurry in the pulping step and the conditioning step, the pitch size in the pulp slurry can be miniaturized. Therefore, the enlargement of pitch is suppressed, and the occurrence of pitch defects in the papermaking step can be suppressed. Further, by providing a pitch dispersant addition step of adding a pitch dispersant to at least one location of the pulp slurry in the pulping step and the conditioning step, the dispersibility of the pitch can be improved before the pitch size in the pulp slurry enlarges, and the aggregation of the pitch is suppressed. Therefore, it can be maintained at a minute size without causing enlargement of the pitch. Therefore, the occurrence of pitch defects in the papermaking step can be suppressed.

[0017] The present invention is also a pitch defect suppression method for controlling the size of pitch contained in a pulp slurry in a papermaking step and suppressing the occurrence of pitch defects in the papermaking step, characterized in that an oxidizing agent addition step of adding an oxidizing agent to at least one location of the pulp slurry in the papermaking step and a pitch dispersant addition step of adding a pitch dispersant to at least one location of the pulp slurry in the papermaking step are provided so that the average particle size of the pitch contained in the pulp slurry is less than 150 μm. By including an oxidizing agent addition step of adding an oxidizing agent to the pulp slurry at at least one location in the papermaking process, the pitch size in the pulp slurry in the papermaking process can be minimized. Therefore, the growth of pitch is suppressed and the minimization is promoted, so that the occurrence of pitch defects in the papermaking process can be suppressed. Also, by including a pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at at least one location in the papermaking process, the dispersibility of the pitch can be improved before the pitch size in the pulp slurry in the papermaking process grows, and the aggregation of the pitch is suppressed, so that it can be maintained at a small size without causing the growth of the pitch. Therefore, the occurrence of pitch defects in the papermaking process can be suppressed.

[0018] The present invention is also a pitch defect suppression method for controlling the size of the pitch contained in the pulp slurry in the pulping process and / or the preparation process and the papermaking process, and suppressing the occurrence of pitch defects in the above papermaking process. The method includes a first oxidizing agent addition step of adding a first oxidizing agent to the pulp slurry at at least one location in the pulping process and the preparation process so that the average particle size of the pitch contained in the pulp slurry in the papermaking process is less than 150 μm, and / or a first pitch dispersant addition step of adding a first pitch dispersant to the pulp slurry at at least one location in the pulping process and the preparation process. Further, it includes a second oxidizing agent addition step of adding a second oxidizing agent to the pulp slurry at at least one location in the papermaking process, and / or a second pitch dispersant addition step of adding a second pitch dispersant to the pulp slurry at at least one location in the papermaking process. By including a first oxidizing agent addition step of adding an oxidizing agent to the pulp slurry at least one location in the pulping process and / or the mixing process, the pitch size in the pulp slurry can be reduced, and pitch enlargement can be suppressed. Furthermore, by including a first pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at least one location in the pulping process and / or the mixing process, the dispersibility of the pitch can be improved before the pitch size in the pulp slurry enlarges, pitch aggregation can be suppressed, and the pitch can be maintained at a small size without causing pitch enlargement. In addition, by including a second oxidizing agent step of adding an oxidizing agent to the pulp slurry at least one location in the papermaking process, and / or a second pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at least one location in the papermaking process, the pitch size in the pulp slurry in the papermaking process can be reduced, and / or the dispersibility of the pitch can be improved before the pitch size enlarges. This suppresses the aggregation of pitch in the pulp slurry during the papermaking process, allowing it to be maintained at a minute size without becoming excessively large.

[0019] The pitch damage suppression method of the present invention may be either a method for controlling the pitch size contained in the pulp slurry in the pulping process and / or the mixing process, or a method for controlling the pitch size contained in the pulp slurry in the papermaking process, or a combination thereof. The explanation of terms used in the pitch damage suppression method of the present invention is common to the method for controlling the pitch size contained in the pulp slurry in the pulping process and / or the mixing process, and / or the method for controlling the pitch size contained in the pulp slurry in the papermaking process. In this specification, the compounds, addition methods, and preferred embodiments used in the oxidizing agent addition step, the first oxidizing agent addition step, and the second oxidizing agent addition step are common. Therefore, in the following description, all will be referred to as the oxidizing agent addition step, and the oxidizing agent, the first oxidizing agent, and the second oxidizing agent used therein will be referred to as the oxidizing agent. Also, the compounds, addition methods, and preferred embodiments used in the pitch dispersant addition step, the first pitch dispersant addition step, and the second pitch dispersant addition step are common. Therefore, in the following explanation, all steps will be referred to as the pitch dispersant addition step, and the pitch dispersant used here, the first pitch dispersant, and the second pitch dispersant will be referred to simply as the pitch dispersant. Furthermore, in this specification, the papermaking process includes a pulping process, a compounding process, and a papermaking process.

[0020] The pitch disorder suppression method of the present invention may use either wood or recycled paper as the pulping raw material.

[0021] For example, when recycled paper is used as raw material, the pulping process of recycled paper mainly consists of a disintegration process, a rough sorting / refining process, and a dewatering / washing process. In addition, it may also include a deinking process to remove ink contained in the recycled paper and a bleaching process to chemically bleach the pulp. Specifically, each process is as follows: a disintegration (pulpering) process in which the recycled paper used as raw material is mixed with water using mechanical force to form a pulp slurry; a rough sorting (dust removal) process in which foreign matter contained in the recycled paper is removed; a deinking process in which ink components are removed by adding a deinking agent; a refinement process in which foreign matter contained in the recycled paper and pulp components are separated by a screen; a washing process in which the pulp slurry is washed with water; a dewatering process in which the pulp is dewatered; and a bleaching process in which bleaching agents are added to bleach the pulp. The water used in each of the above processes and the water that is discharged are called white water. Furthermore, the mixture of recycled paper and white water in the pulpering process is called pulp slurry.

[0022] Furthermore, when wood is used as a raw material, for example, the pulping process for chemical pulp mainly consists of a wood preparation process, a digestion process, a selection and washing process, and a dewatering process. In addition, a bleaching process in which the pulp is chemically bleached may also be included. In the digestion process, chemicals are added to the chips, and they are boiled at high temperature and pressure to dissolve the resin (lignin) and extract the fibers, thus pulping the chips. In other words, the pulp raw material becomes a pulp slurry after going through the digestion process. Furthermore, the pulping process for mechanical pulp consists of a wood crushing process, a dust removal process, and a concentration process. In addition, a bleaching process in which the pulp is chemically bleached may also be included. In the above process, the material is mechanically fibrousized to become a pulp slurry.

[0023] In the pitch defect suppression method of the present invention, it is preferable that the oxidizing agent addition step and / or pitch dispersant addition step be added to the pulp slurry in at least one of the devices that apply mechanical shear to the pulp slurry, and / or to the pulp slurry upstream of the above device. By adding the oxidizing agent and / or pitch dispersant in at least one of the devices that apply mechanical shear, and / or upstream thereof, the oxidizing agent and / or pitch dispersant and the pulp slurry are thoroughly stirred and mixed, the pitch components contained in the pulp slurry and the oxidizing agent and / or pitch dispersant come into sufficient contact, promoting the miniaturization and / or dispersibility of the pitch components, and allowing the pitch components to remain stably dispersed in minute sizes. Therefore, the occurrence of pitch defects in the papermaking process can be further suppressed. In this invention, the terms "upstream" and "downstream" are determined by the flow direction of pulp slurry or white water in piping and equipment. The direction in which the pulp slurry or white water flows is downstream, and the opposite direction is upstream. For example, in a raw material line for pulping raw materials, the side closer to the pulping raw materials is upstream. Also, for example, in a white water supply line for supplying white water, the side closer to the white water pit is upstream.

[0024] In this invention, a device that applies mechanical shear refers to, for example, a device that agitates pulp slurry at a rotational speed of 50 rpm to 3000 rpm within the device, and refers to a point where the stress acting on the pulp slurry within the device is greater than the stress acting on the pulp slurry flowing through the piping. Specifically, examples include pulpers, refiners, screw presses, double separators, refining screens, rotary screens, washers, thickeners, and fan pumps. Preferred specific devices include pulpers, refiners, and fan pumps.

[0025] Furthermore, in the present invention, it is more preferable that the oxidizing agent addition step and / or pitch dispersant addition step occur upstream of the drainage line. As described above, by adding the oxidizing agent and / or pitch dispersant to the pulp slurry upstream of at least one of the mechanical shearing devices, the miniaturization and / or dispersibility of pitch components in the pulp slurry is promoted. Subsequently, the dispersed pitch components are discharged along with white water from the raw material lines of the pulping and mixing processes via the drainage line, thereby reducing the amount of pitch components in the pulp slurry. As a result, pitch problems in the papermaking process can be prevented more effectively.

[0026] The above-mentioned drainage lines refer to lines that discharge white water from the raw material line through which the pulp slurry flows, to the pulping process, mixing process, and papermaking process, and do not include lines that recover white water for reuse. Furthermore, in addition to the method of discharging the pitch component from the pulping and mixing processes to the outside of the system via a drainage line, as described above, there is also a method of transferring the pitch component together with the pulp slurry to the papermaking process that follows the pulping and mixing processes. However, the "drainage line" mentioned above refers to the line that discharges the pitch component together with the white water from the raw material line.

[0027] The specific oxidizing agent used in the present invention is preferably at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, hydrogen peroxide, and combined halogen.

[0028] Examples of the above-mentioned hypochlorites include sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite, and in the present invention, one of these can be used alone or two or more in combination.

[0029] Examples of the above-mentioned chlorites include sodium chlorite, potassium chlorite, and calcium chlorite, and in the present invention, one of these can be used alone or two or more in combination.

[0030] Because the chlorine dioxide mentioned above is an extremely unstable chemical substance, its storage and transportation are very difficult. Therefore, it is preferable to manufacture (generate) chlorine dioxide on-site using a known method and adjust its concentration for use. For example, chlorine dioxide can be produced by the following reaction, and commercially available chlorine dioxide generators (devices) can also be used. (1) Reaction of sodium hypochlorite, hydrochloric acid, and sodium hypochlorite NaOCl+2HCl+2NaClO2→ 2ClO2+3NaCl+H2O (2) Reaction of sodium chlorite with hydrochloric acid 5NaClO2+4HCl → 4ClO2+5NaCl+2H2O (3) Reactions with sodium chlorate, hydrogen peroxide and sulfuric acid 2NaClO3+H2O2+H2SO4→ 2ClO2+Na2SO4+O2+2H2O

[0031] Examples of the above-mentioned bound halogens include bound chlorine and bound bromine, and specifically, monochloramine and / or monobrolamine are preferred. The monochloramine and monobroramine described above are mild oxidizing agents produced by reactions such as OCl-(Br-) + NH4+ → NH2Cl(Br) + H2O. For example, monochloramine can be produced by mixing sodium hypochlorite with an ammonium compound. Specific examples of ammonium compounds include ammonium sulfate, ammonium bromide, ammonium chloride, and ammonium sulfamate, which can be used individually or in combination of two or more. In one or more embodiments, the molar ratio of sodium hypochlorite to ammonium compound is preferably 1:1 to 1:2 as the molar ratio of residual chlorine to nitrogen.

[0032] In this invention, the amount of oxidizing agent added can be appropriately set depending on the state of the pulp slurry, but generally, in the case of recycled paper pulp, it is preferable to add the oxidizing agent to the pulp slurry at locations where mechanical shearing occurs, such as the pulper in the pulping process, and in the case of chemical pulp or mechanical pulp, at locations where mechanical shearing occurs, such as the stage before the washing process, so that the concentration of the oxidizing agent in the pulp slurry is 5 ppm or more and 100 ppm or less, more preferably 10 ppm or more and 80 ppm or less, and even more preferably 50 ppm or less from an economic standpoint. Furthermore, it is preferable to add the above-mentioned oxidizing agent so that the amount of residual chlorine in the pulp slurry (in the case of monobroramine, as a value equivalent to the amount of residual chlorine) is 0.5 mg / L or more and 30 mg / L or less, more preferably 1 mg / L or more and 30 mg / L or less, and even more preferably, from an economic standpoint, so that it is 1 mg / L or more and 10 mg / L or less, or 1 mg / L or more and 5 mg / L or less.

[0033] Furthermore, the oxidizing agent used in the pitch damage suppression method of the present invention is particularly preferably one that contains a bound halogen. This is because the amount of residual chlorine in the pulp slurry is sustained, and the pitch damage suppression effect is sustained.

[0034] In this invention, the term "amount of residual chlorine" refers to the "value converted to the amount of residual chlorine" when monobroramine is used.

[0035] The pitch dispersant used in the present invention is preferably at least one selected from the group consisting of surfactants, cationic polymers, and organic solvents, and more preferably two or more, in order to reduce aggregation and stickiness of pitch components.

[0036] The above-mentioned surfactant is preferably at least one selected from the group consisting of cationic surfactants, nonionic surfactants, and amphoteric surfactants.

[0037] Examples of the cationic surfactants mentioned above include quaternary ammonium compounds such as alkyldimethylbenzylammonium salts and dialkyldimethylammonium salts having an alkyl group with 10 to 18 carbon atoms, and dihydroxyethylalkylamines having 10 to 18 carbon atoms. Specifically, examples include decyldimethylbenzylammonium chloride, decyldimethylbenzylammonium bromide, dodecyldimethylbenzylammonium chloride, dodecyldimethylbenzylammonium bromide, tetradecyldimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium bromide, hexadecyldimethylbenzylammonium chloride, hexadecyldimethylbenzylammonium bromide, octadecyldimethylbenzylammonium chloride and octadecyldimethylbenzylammonium bromide, lauryldimethylbenzylammonium chloride, lauryldimethylbenzylammonium bromide, dihydroxyethylstearylamine and dihydroxyethyloleylamine, and in the present invention, one of these can be used alone or two or more in combination. Furthermore, among these, alkyldimethylbenzylammonium salts having a C12-C18 alkyl group and dihydroxyethylalkylamines having a C12-C18 alkyl group are preferred in terms of their effect on improving the dispersibility of pitch components in pulp slurry, and alkyldimethylbenzylammonium chlorides having a C12-C18 alkyl group and dihydroxyethylstearylamines are particularly preferred.

[0038] Examples of the nonionic surfactants mentioned above include ethylene oxide of a higher aliphatic amine or an adduct of ethylene oxide and propylene oxide, and ethylene oxide of a higher alcohol ether or an adduct of ethylene oxide and propylene oxide.

[0039] As for the ethylene oxide or ethylene oxide and propylene oxide adduct of a higher aliphatic amine, a saturated or unsaturated aliphatic amine having 10 to 20 carbon atoms to which 10 to 30 moles of ethylene oxide or 0 to 15 moles of propylene oxide are preferred in terms of improving the dispersibility of the pitch component, and a mixture to which 10 to 20 moles of ethylene oxide or 0 to 5 moles of propylene oxide are even more preferred.

[0040] Examples of saturated or unsaturated aliphatic amines having 10 to 20 carbon atoms include decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, oleylamine, tallow alkylamine, and coconut alkylamine. Here, tallow alkylamine and coconut alkylamine refer to a mixture of amines (mixed alkylamines) in which linear or branched saturated or unsaturated aliphatic hydrocarbon groups having 12 to 20 carbon atoms, produced by known means from coconut oil or coconut fat, tallow, etc., are the main component.

[0041] The ethylene oxide or ethylene oxide-propylene oxide adducts of higher aliphatic amines are particularly preferred, specifically, a stearylamine-ethylene oxide 20-mol adduct and a tallowamine-ethylene oxide-propylene oxide adduct with an adduct ratio of 85 / 15 (31 moles of ethylene oxide and 4 moles of propylene oxide).

[0042] As for ethylene oxide or adducts of ethylene oxide and propylene oxide to higher alcohol ethers, those obtained by adding 4 to 50 moles of ethylene oxide or 0 to 15 moles of propylene oxide to saturated or unsaturated fatty acids having 12 to 18 carbon atoms are preferred in terms of improving the dispersibility of the pitch component, and examples include fatty acid esters of polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl ethers, and polyoxyethylene glycol.

[0043] Examples of higher alcohol ethers that are ethylene oxide or adducts of ethylene oxide and propylene oxide include polyoxyethylene lauryl ether, polyoxyethylene tetradecyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octyldodecyl ether, polyoxyethylene laurylphenyl ether, polyoxyethylene tetradecylphenyl ether, polyoxyethylene cetylphenyl ether, polyoxyethylene stearylphenyl ether, polyoxyethylene oleylphenyl ether, and polyoxyethylene octyldodecylphenyl ether. Of these, the use of polyoxyethylene alkylphenyl ethers is preferred, and polyoxyethylene nonylphenyl ethers with 10 to 16 moles of ethylene oxide added are particularly preferred.

[0044] Examples of the above-mentioned amphoteric surfactants include alkyldimethylaminoacetic acid betaine having a saturated or unsaturated alkyl group with 10 to 18 carbon atoms. Specifically, examples include decyldimethylaminoacetic acid betaine, dodecyldimethylaminoacetic acid betaine, tetradecyldimethylaminoacetic acid betaine, hexadecyldimethylaminoacetic acid betaine, octadecyldimethylaminoacetic acid betaine, lauryldimethylaminoacetic acid betaine, and stearyldimethylaminoacetic acid betaine. In the present invention, one of these can be used alone or in combination of two or more. Among these, lauryldimethylaminoacetic acid betaine is preferred in terms of its effect on improving the dispersibility of pitch components in pulp slurry.

[0045] Examples of the cationic polymers mentioned above include water-soluble aluminum compounds, polydiallyldimethylammonium salts, and epichlorohydrin-dialkylamine condensates. Examples of the above-mentioned water-soluble aluminum compounds include polyaluminum chloride and polyhydroxyammonium chloride. Examples of the polydiallyldimethylammonium salts mentioned above include polydiallyldimethylammonium chloride, polydiallyldimethylammonium bromide, polydiallyldimethylammonium nitrate, polydiallyldimethylammonium sulfate, and polydiallyldimethylammonium phosphate, all with molecular weights of 20,000 to 100,000. Among these, polydiallyldimethylammonium chloride is particularly preferred. Examples of the epichlorohydrin-dialkylamine condensates mentioned above include epichlorohydrin-dimethylamine condensates and epichlorohydrin-diethylamine condensates with molecular weights of 10,000 to 200,000. In the present invention, one of these can be used alone or in combination of two or more. Among these, polyaluminum chloride and / or polydiallyldimethylammonium chloride with a molecular weight of 20,000 to 100,000 are more preferred in terms of their effect on improving the dispersibility of pitch components in pulp slurry.

[0046] Examples of the above-mentioned organic solvents include higher fatty acid alkylamides, glycols, glycol ethers, dimethyl sulfoxides, and tetrahydrofurans. Specifically, examples of the above-mentioned higher fatty acid alkylamides include tall oil fatty acid dimethylamide. Examples of the glycols mentioned above include ethylene glycol, propylene glycol, diethylene glycol, and dipropylene glycol. Examples of the glycol ethers mentioned above include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propoxypropanol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and tripropylene glycol methyl ether. In the present invention, one of these can be used alone or in combination of two or more. Among these, tall oil fatty acid dimethylamide, ethylene glycol, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether are preferred in terms of their effect on improving the dispersibility of pitch components in pulp slurry.

[0047] The oxidizing agent and / or pitch dispersant used in the present invention is preferably at least two selected from the group consisting of the above-mentioned oxidizing agent, the above-mentioned surfactant, the above-mentioned cationic polymer, and the above-mentioned organic solvent. The preferred combination varies depending on the type of pitch and the composition of the pulp slurry, but a combination of an oxidizing agent and a nonionic surfactant, a combination of an oxidizing agent, a nonionic surfactant and a cationic polymer, or a combination of an oxidizing agent and a cationic polymer is more preferred. Specifically, as the oxidizing agent, at least one selected from the group consisting of hypochlorite, chlorine dioxide and monochloramine is preferred, and as the cationic surfactant, lauryldimethylbenzylammonium chloride and / or dihydroxyethyl stearylamine is preferred. As the nonionic surfactant, polyoxyethylene stearylamine with 10 to 30 moles of ethylene oxide added and / or polyoxyethylene nonylphenol ether with 10 to 16 moles of ethylene oxide added is preferred. As the amphoteric surfactant, lauryldimethylaminoacetic acid betaine is preferred. As the cationic polymer, polyaluminum chloride and / or polydiallyldimethylammonium chloride with a molecular weight of 20,000 to 100,000 is preferred. As the organic solvent, at least one selected from tall oil fatty acid dimethylamide, ethylene glycol, ethylene glycol monobutyl ether, and diethylene glycol monobutyl ether is preferred.

[0048] Particularly preferred combinations of at least two pitch dispersants include the combination of polyoxyethylene stearylamine and polyaluminum chloride, the combination of polyoxyethylene stearylamine and tall oil fatty acid dimethylamide, the combination of polyoxyethylene stearylamine, tall oil fatty acid dimethylamide, and polyaluminum chloride, the combination of polyoxyethylene stearylamine and polydiallyldimethylammonium chloride, the combination of polyaluminum chloride and ethylene glycol monobutyl ether, the combination of polyaluminum chloride and tall oil fatty acid dimethylamide, and the combination of polyoxyethylene stearylamine, tall oil fatty acid dimethylamide, and polydiallyldimethylammonium chloride. Preferred combinations of oxidizing agents and pitch dispersants include monochloramine and polyaluminum chloride, monochloramine and tall oil fatty acid dimethylamide and polyaluminum chloride, monochloramine and polyoxyethylene stearylamine, monochloramine and tall oil fatty acid dimethylamide and polyoxyethylene stearylamine, sodium hypochlorite and polyaluminum chloride, sodium hypochlorite and tall oil fatty acid dimethylamide and polyaluminum chloride, sodium hypochlorite and polyoxyethylene stearylamine, sodium hypochlorite and tall oil fatty acid dimethylamide and polyoxyethylene stearylamine, hydrogen peroxide and polyoxyethylene stearylamine, hydrogen peroxide and sodium hypochlorite and polyoxyethylene stearylamine, monochloramine and diethylene glycol monobutyl ether, monochloramine and polyoxyethylene stearylamine and polyaluminum chloride, and chlorine dioxide and tall oil fatty acid dimethylamide and polyaluminum chloride.

[0049] When the pitch dispersant is a surfactant and / or an organic solvent, the total amount of the pitch dispersant added to the pulp slurry at at least one point in the pulping and preparation processes is preferably 1.5 kg / t as an upper limit, more preferably 1.0 kg / t as an upper limit, and even more preferably 0.5 kg / t as an upper limit from an economic standpoint. The lower limit is preferably 0.1 kg / t and more preferably 0.25 kg / t. When the pitch dispersant is a cationic polymer, the total amount added is preferably 3.0 kg / t as an upper limit, more preferably 1.5 kg / t as an upper limit, and even more preferably 1.0 kg / t as an upper limit from an economic standpoint. The lower limit is preferably 0.1 kg / t and even more preferably 0.25 kg / t. Adding the pitch dispersant to the pulp slurry in the above amounts maintains the dispersibility of the pitch components in the pulp slurry and prevents the growth of pitch due to aggregation.

[0050] The present invention's method for suppressing pitch defects suppresses the occurrence of pitch defects in the papermaking process by controlling the average particle size of the pulp slurry pitch in the papermaking process to less than 150 μm. As mentioned above, in the papermaking process, pitch not only adheres to manufacturing equipment such as fan pumps, piping, chests, wires, felt, and rolls, but this adhered material also peels off and reattaches to the paper and pulp. This results in stains and defects in the formed paper, degrading the quality of the paper product, and causing problems such as paper breaks that reduce productivity and work efficiency. The average particle size of pitch is 150 μm, which is the size that can be found on the paper surface, and anything larger than this has a very high probability of being detected as a defect, so it serves as a benchmark value. For this reason, one method of pitch analysis in the papermaking process is to pass the pulp slurry through a mesh wire with a mesh opening of 150 μm. Therefore, by controlling the size (particle size) of the pitch in the pulp slurry and maintaining the state of the pitch in the pulp slurry before it is introduced into the papermaking process in a dispersed state with an average particle size of less than 150 μm, and / or maintaining the state of the pitch in the pulp slurry after it is introduced into the papermaking process in a dispersed state with an average particle size of less than 150 μm, the adhesion of pitch in the papermaking process is suppressed, and because the pitch is in a stably dispersed state when it comes into contact with the pulp fibers, the pitch in a micronized state of a specific size is uniformly incorporated into the paper, and the pitch is discharged outside the papermaking process. As a result, pitch contamination is prevented, and various pitch problems that occur in the papermaking process, such as the occurrence of defective products and paper breakage caused by the adhesion of enlarged pitch to the paper product, can be suppressed overall. Furthermore, because the pitch component is incorporated into the paper and discharged outside the papermaking process, the amount of pitch component in the white water that is recycled throughout the papermaking process is reduced. In other words, the total amount of pitch in the papermaking system can be reduced, and pitch problems can be effectively suppressed. Therefore, the pitch defect suppression method of the present invention is preferably used for pulp slurries in the pulping and / or mixing processes in which the average particle size of pitch contained in the pulp slurry introduced into the papermaking process is 150 μm or more. Furthermore, it is preferable to use the method for pulp slurries in the papermaking process in which the average particle size of pitch contained in the pulp slurry after it has been introduced into the papermaking process is 150 μm or more. As described above, pitch components with large particle sizes cause pitch defects in the papermaking process. Moreover, the pitch defect suppression method of the present invention includes a pitch size measurement step for measuring the average particle size of pitch in the pulp slurry introduced into the papermaking process, and it is preferable that the oxidizing agent addition step and / or the pitch dispersant addition step be performed at least at one location in the pulping and / or mixing process when the average particle size of pitch in the pulp slurry introduced into the papermaking process is 150 μm or more. The pitch size measurement step may be performed at least at one location in the pulping and / or mixing processes, but it is preferable that it be performed in the mixing process. Furthermore, the pitch defect suppression method of the present invention includes a pitch size measurement step for measuring the average particle size of pitch in the pulp slurry introduced into the papermaking process, and it is preferable that the oxidizing agent addition step and / or the pitch dispersant addition step be performed at least one location in the papermaking process when the average particle size of pitch in the pulp slurry introduced into the papermaking process is 150 μm or more. The pitch size measurement step may be performed at least one location in the papermaking process, but it is preferable that it be performed upstream of the inlet.

[0051] As a result of the above oxidizing agent addition step and / or pitch dispersant addition step, the average particle size of the pitch in the pulp slurry before being introduced into the papermaking process is less than 150 μm, but preferably less than 120 μm, more preferably less than 77 μm, and even more preferably less than 23 μm. Furthermore, when the above-mentioned oxidizing agent addition step and / or pitch dispersant addition step is performed in the papermaking process, the average particle size of the pitch in the pulp slurry introduced into the papermaking process will be less than 150 μm, but it is preferable that the average particle size of the pitch be less than 120 μm, more preferably less than 77 μm, and even more preferably less than 23 μm.

[0052] The average particle size of the pitch in the pulp slurry can be measured based on common technical knowledge typically used by those skilled in the art in the field to which this invention belongs. For example, the average particle size of the pitch can be calculated using image analysis as follows.

[0053] The following describes a method for measuring the average particle size of pitch using image analysis.

[0054] (Acquisition of images of pitch particles in aqueous solution) From the pulp slurry in a beaker or similar container, collect a sample of white water, taking care to avoid including pulp fibers. For example, this can be done by using a dropper and visually inspecting the sample to avoid pulp fibers, or by using centrifugation. Next, dilute the obtained white water to an appropriate concentration with pure water, and record an image of the pitch particles using an imaging device such as a microscope (for example, an Olympus fluorescence microscope). In this case, if the pitch particles are difficult to see, add a hydrophobic staining solution to stain the pitch components, and then record a color image of the pitch particles using a microscope or similar device.

[0055] (Method for calculating the average particle size of pitch using image analysis) Using analysis software (Image J / provided by the National Institutes of Health), the pitch is isolated and the particles are clearly visible to the naked eye. The average particle size and number of pitch particles are then calculated through image analysis.

[0056] The above oxidizing agent addition step is performed at least one location in the pulping process and the preparation process, and the above pitch dispersant addition step is performed at least one location in the pulping process and the preparation process, but it is preferable that it is performed on the pulp slurry upstream of at least one of the devices that apply mechanical shear to the pulp slurry. Furthermore, it is preferable that it is performed on the pulp slurry downstream of the pulper process (disintegration process) and / or the deinking process. By adding an oxidizing agent, the miniaturization of pitch components contained in the pulp slurry is promoted. In addition, by adding a pitch dispersant, the aggregation of pitch components is suppressed and the dispersibility is improved. As a result, the pitch components in the pulp slurry are stably dispersed in a miniaturized state.

[0057] The pulpering process is the upstream step in the pulping process. By adding an oxidizing agent at this stage, the reduction of pitch particles can be accelerated, resulting in a lower average particle size. Furthermore, by adding a pitch dispersant during the pulping process, the reduced pitch particles can be stably dispersed, preventing aggregation and suppressing particle size increase. Furthermore, although some pitch components are discharged outside the pulping system during the deinking process, a certain amount of pitch components remains in the pulp slurry after the deinking process. Therefore, by performing an oxidizing agent addition step and / or a pitch dispersant addition step in the pulp slurry downstream of the deinking process, the pitch components can be further reduced in size and / or stably dispersed to suppress aggregation and enlargement. By performing an oxidizing agent addition step and / or a pitch dispersant addition step in such a process, pitch problems in the papermaking process can be prevented more effectively. Furthermore, it is preferable that the above-mentioned oxidizing agent addition step and / or pitch dispersant addition step be performed at least one location in the pulping process and at least one location in the mixing process. This is because, by performing the above-mentioned oxidizing agent addition step and / or pitch dispersant addition step in the pulping process, the pitch components contained in the pulp slurry are miniaturized upstream of the papermaking process, and further miniaturization can be promoted by performing the above-mentioned step in the mixing process as well, thereby suppressing the enlargement of the miniaturized pitch components.

[0058] Furthermore, if the above-mentioned oxidizing agent addition step and / or pitch dispersant addition step is performed at at least one location in the papermaking process, it is preferable that it be performed on the pulp slurry upstream of at least one of the devices that apply mechanical shear to the pulp slurry in the papermaking process. Specifically, it is preferable that it be performed on the pulp slurry upstream of the fan pump. Adding an oxidizing agent promotes the miniaturization of pitch components contained in the pulp slurry. Adding a pitch dispersant suppresses the aggregation of pitch components and improves dispersibility. As a result, the pitch components in the pulp slurry are stably dispersed in a miniaturized state.

[0059] When adding an oxidizing agent and a pitch dispersant in the papermaking process, one example is to add the oxidizing agent to the pulp slurry upstream of the fan pump, and then add the pitch dispersant to the white water that circulates from the wire-under-wire white water pit and is used as concentration adjustment water at the inlet. The pitch components brought from the pulping process through the preparation process to the papermaking process become fine particles when the oxidizing agent is added and the mixture is stirred by the fan pump. Furthermore, the fine pitch components that come into contact with the pitch dispersant at the inlet and come into contact with the pitch dispersant when paper is made in the wire section are carried by the flow of white water, pass through the wire-under-wire white water pit, and circulate within the system from the collection tank. However, because the pitch size is kept small due to the effect of the pitch dispersant, pitch problems are not caused within the system.

[0060] The pitch dispersant addition step described above is preferably performed on a pulp slurry with a residual chlorine concentration of 0.5 to 30 mg / L, and more preferably on a pulp slurry with a residual chlorine concentration of 1 to 10 mg / L. By adding a pitch dispersant to a pulp slurry having a specific residual chlorine concentration, aggregation of finely milled pitch can be suppressed, and finely milled pitch can be uniformly dispersed in the pulp slurry. This makes it possible to suppress pitch problems in the papermaking process.

[0061] Furthermore, in the pitch damage suppression method of the present invention, which comprises the above-mentioned oxidizing agent addition step and the above-mentioned pitch dispersant addition step, when the pitch dispersant is added to a pulp slurry with a residual chlorine concentration of 0.5 to 30 mg / L, the oxidizing agent is preferably at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, and combined halogen. More preferably, it is a combined halogen. Also, the pitch dispersant addition step is preferably located downstream of the oxidizing agent addition step.

[0062] Furthermore, if the pitch disorder suppression method of the present invention comprises the above-mentioned oxidizing agent addition step and the above-mentioned pitch dispersant addition step, and at least one selected from the group consisting of hydrogen peroxide, hypochlorite, chlorite, and chlorine dioxide is used as the oxidizing agent, it is preferable that the above-mentioned oxidizing agent addition step and the above-mentioned pitch dispersant addition step are carried out at the same location at least one of the pulping process and the preparation process. This is because hydrogen peroxide, hypochlorite, chlorite, and chlorine dioxide are consumed when added to the pulp slurry and promote pitch miniaturization, but by adding a pitch dispersant at the same time, the miniaturized pitch can be effectively dispersed and the miniaturized state of the pitch can be maintained.

[0063] Furthermore, the above-mentioned oxidizing agent addition step and / or pitch dispersant addition step may be carried out by continuous addition or by intermittent addition, but it is preferable to carry it out by continuous addition.

[0064] Furthermore, in the present invention, continuous addition means supplying continuously, which means continuously supplying the pitch dispersant and / or oxidizing agent to the pulp slurry, and even if supply and stop are repeated, if the stop time is less than 30 minutes, the supply is considered continuous.

[0065] In the pitch damage suppression method of the present invention, the oxidizing agent addition step and / or pitch dispersant addition step are preferably performed on a pulp slurry having a pulp concentration of 0.5 to 50%, and more preferably on a pulp slurry having a pulp concentration of 2.0 to 20%.

[0066] Figure 1 is a block diagram illustrating a recycled paper pulp processing step that describes one embodiment of the present invention. The recycled paper raw material is turned into pulp slurry in pulper 1, dewatered in screw press 2, and then stored in maturation tower 3. Next, the pulp slurry sent from maturation tower 3 passes through double separator 4, is deinked in fall washer 5 and rotary screen 6, and is stored in stock chest 7a. After that, the pulp slurry is bleached in hydrogen peroxide bleaching tower 8, washed and dewatered in washer 9 and thickener 10, and stored in finished chest 7b. The white water discharged at each stage is collected by white water recovery line 12 and collected in white water pit 11. The white water collected in the white water pit 11 is supplied to the recycled paper pulp manufacturing process and reused via a white water supply line 13 that supplies white water to the pulper 1, the channel connecting the pulper 1 and the maturation tower 3, the channel connecting the bleaching tower 8 and the washer 9, etc.

[0067] Thus, the pulping process generally involves multiple washing and dewatering steps, and the pulp slurry is agitated in various pieces of equipment such as pulpers, refiners, screw presses, double separators, refining screens, rotary screens, washers, thickeners, and fan pumps. In the pitch disorder suppression method of the present invention, it is preferable to perform the oxidizing agent addition step and / or pitch dispersant addition step on the pulp slurry upstream of the stirring step, which is located upstream of the drainage line. This is because the pitch components in the pulp slurry are miniaturized by the oxidizing agent, and aggregation is suppressed and dispersibility is improved by the pitch dispersant, so that the pitch components are discharged together with white water in the subsequent drainage line.

[0068] Furthermore, in the pitch defect suppression method of the present invention, it is preferable to further perform the oxidizing agent addition step and / or pitch dispersant addition step on the pulp slurry downstream of the discharge line. This is because further miniaturization of the pitch components remaining in the pulp slurry and / or suppression of aggregation results in the pitch components being stably dispersed in a miniaturized state, thereby more effectively preventing pitch defects in the subsequent papermaking process.

[0069] Furthermore, it is even more preferable that the oxidizing agent addition step and / or pitch dispersant addition step be performed at least once for each white water loop. Here, a white water loop refers to a white water recirculation system formed when white water drained from the raw material line is collected in a white water pit, and the white water collected in the white water pit is supplied to the raw material line, with one white water loop formed for each white water pit. If there are multiple white water supply lines from one white water pit, the white water recirculation system formed by the upstream white water supply line that supplies white water from the white water pit to the upstream side of the raw material line is called a white water loop, and white water supply lines branching off from the upstream white water supply line are also included as part of the white water loop.

[0070] Furthermore, in another embodiment of the pitch defect suppression method of the present invention, instead of providing the above oxidizing agent addition step and / or the above dispersant addition step so that the average particle size of the pitch contained in the pulp slurry is less than 150 μm, the above oxidizing agent addition step and / or the above pitch dispersant addition step may be provided so that the content of pitch with a particle size of less than 150 μm is 50% or more of the total amount of pitch contained in the pulp slurry. As described above, when the particle size of the pitch is 150 μm or more, pitch defects in the papermaking process and pitch defects throughout the papermaking process are more likely to occur, so the effects of the present invention can also be obtained when the pitch component with a particle size of less than 150 μm accounts for 50% or more of the total amount of pitch.

[0071] The amount of pitch components with a particle size of less than 150 μm can be measured based on common technical knowledge ordinarily used by those skilled in the art to which this invention belongs. For example, the amount and proportion of pitch components with a particle size of less than 150 μm can be calculated by taking water from the pulp slurry before it is introduced into the papermaking process and / or after it has been introduced into the papermaking process, and measuring the pitch in the white water, which is collected in a way that does not include pulp fibers, using image analysis.

[0072] In this case, it is preferable that pitch components with a particle size of less than 150 μm account for 60% or more of the total amount of pitch components in the pulp slurry, and more preferably 70% or more. Furthermore, it is preferable that the particle size of pitch components accounting for 50% or more of the total amount of pitch is less than 120 μm, more preferably less than 77 μm, and even more preferably less than 23 μm. [Effects of the Invention]

[0073] The pitch defect suppression method of the present invention makes it possible to prevent pitch defects in the papermaking process. [Brief explanation of the drawing]

[0074] [Figure 1] Figure 1 is a block diagram illustrating a recycled paper pulp processing step that describes one embodiment of the present invention. [Figure 2] Figure 2 is a graph showing the amount of hydrophobic substance (pitch) contained in the pulp slurry in the seed box during the papermaking process in Examples 31 and 32 and Reference Example 7. [Figure 3] Figure 3 is a graph showing the amount of hydrophobic substance (pitch) in the white water during the papermaking process in Examples 31 and 32 and Reference Example 7. [Figure 4] Figure 4 is a flowchart illustrating the pulping and mixing processes of the papermaking process in Test Example 8.

[0075] The present invention will be described based on the following examples, comparative examples, and reference examples, but the present invention is not limited thereto. In the following examples, the reduction of pitch size may be expressed as pitch size refinement or pitch miniaturization. [Examples]

[0076] [Test Example 1] (Examples 1-7 and Comparative Example 1) One liter of recycled paper pulp slurry, mainly composed of ethylene vinyl acetate copolymer as the pitch component, was weighed out and used as the sample. The obtained sample was mixed with each of the drugs at the concentrations shown in Table 1 below, and stirred at room temperature for 3 minutes (2000 rpm) using a tabletop pulper (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a sample containing the drugs. Next, the sample containing the obtained drug was kept warm in a 35°C bath and gently stirred for 72 hours using a three-one motor, simulating a pulp slurry flowing through a pipe. Next, the average particle size of the pitch in the sample after stirring for 72 hours was measured using a Thermo Fisher automatic cell counter (Countess II FL). The measurement conditions for the cell counter were a particle count of 10^6 or more and fluorescence intensity of 100%. The measurement conditions for the cell counter were the same for all the following test examples. The measurement results are shown in Table 1 below. In the following tables, when the unit of the amount of additive is (kg / T), it indicates the amount added to the pulp, and when the unit of the amount added is (ppm), it indicates the amount added to the pulp slurry. Furthermore, the classification of the additives in the test is shown as follows: pitch dispersant is A, and oxidizing agent is B.

[0077] The liquid concentrations of each agent used in Examples 1-12 and Reference Examples 1-6 are as follows. In each test, the agents were added so that the concentration indicated in the table equaled the concentration of the active ingredient. Monochloramine was prepared by a known method (for example, the method described in Japanese Patent Publication No. 2017-53054), then diluted with pure water to the drug concentration shown in Table 1 below, and added. Polyoxyethylene stearylamine ethylene oxide 20 molar adduct (30% aqueous solution) Tall oil fatty acid dimethylamide (95% aqueous solution) Polyaluminum chloride (32% aqueous solution) Hydrogen peroxide (35% aqueous solution)

[0078] [Table 1]

[0079] Examples 1 to 4 confirmed that the pitch size can be refined whether a pitch dispersant such as a surfactant, cationic polymer, or organic solvent is used alone, or whether an oxidizing agent is used alone. Furthermore, Examples 5-7 confirmed that using combinations of oxidizing agents and pitch dispersants, as well as combinations of cationic polymers (pitch dispersants) and surfactants, resulted in superior pitch refinement effects.

[0080] [Test Example 2] (Examples 8-10, Comparative Example 2, and Reference Examples 1-4) The pitch component is a recycled paper pulp slurry mainly composed of acrylic ester polymers, at a basis weight of 100 g / m². 2 We measured out the amount to achieve the desired result, and this was used as the sample. The obtained samples were mixed with the agents at the concentrations shown in Table 2 below, kept warm in a 40°C bath, and stirred for 1 hour using a stirrer to obtain samples containing the agents according to Examples 8-10 and Reference Examples 1-4, and a sample without added agents according to Comparative Example 2. Next, the pitch size of each obtained sample was measured using a Thermo Fisher automated cell counter (Countess II FL) after being stored in a cool, dark room at 4°C for one week. The results of the pitch refinement rate, based on the pitch size of the sample without chemical additives after one week, are shown in Table 2 below.

[0081] [Table 2]

[0082] When the pitch size was checked one week after treatment, an increase in pitch size due to pitch aggregation was observed when only a surfactant or oxidizing agent was used. This is thought to be because aggregation occurred due to the influence of inorganic components present in the recycled paper pulp slurry after being left to stand for one week, resulting in a larger pitch size than when no chemicals were added. In actual production environments, the pulp slurry is not left to stand for a week, and the pitch does not enlarge to the extent that pitch damage occurs as in this test; these are test results under more stringent conditions. On the other hand, from Examples 8 to 10, it was confirmed that a superior pitch refinement effect can be continuously obtained by using a pitch dispersant (surfactant) and an oxidizing agent in combination.

[0083] [Test Example 3] (Examples 11, 12, Reference Examples 5, 6, and Comparative Example 3) Except for using the concentrations of each agent listed in Table 3 below, the same procedure as in Test Example 2 was performed to obtain samples containing the agents related to Examples 11 and 12 and Reference Examples 5 and 6, and a sample without the agent related to Comparative Example 3. Next, papermaking was performed using each of the obtained samples to produce sheets. Organic solvent extraction was performed on the obtained sheets, and the amount of pitch contained in the sheets was measured. Then, using the amount of sheet pitch produced from the sample without the agent related to Comparative Example 3 as a reference, the percentage reduction in pitch due to the addition of the agent was defined as the pitch washing rate on the sheet. Furthermore, the pitch refinement rate was measured using an automatic cell counter after storing each of the above samples in a cool, dark room at 4°C for one week, as in Test Example 2. The measurement results are shown in Table 3 below.

[0084] [Table 3]

[0085] When the pitch size was checked one week after treatment, it was confirmed that, similar to the results in Test Example 2, the use of a surfactant alone resulted in an enlargement of the pitch size due to pitch aggregation. On the other hand, from Examples 11 and 12, it was confirmed that a superior pitch refinement effect could be continuously obtained by using a pitch dispersant (surfactant) in combination with an oxidizing agent. Furthermore, it was confirmed that a superior cleaning effect can be obtained by using a pitch dispersant and an oxidizing agent in combination, even with respect to the amount of pitch contained in the resulting sheet.

[0086] [Test Example 4] (Examples 13-22 and Comparative Example 4) One liter of recycled paper pulp slurry, mainly composed of ethylene vinyl acetate copolymer, was weighed out and used as the sample. The same test procedure as in Test Example 1 was performed on the obtained sample, except that instead of adding each agent at the concentrations shown in Table 1 above, the agents at the concentrations shown in Table 4 below were added, and the average particle size of the pitch in the sample was measured using an automated cell counter. The measurement results are shown in Table 4 below.

[0087] The liquid concentrations of each agent used in the following examples are as follows. In each test, the agents were added so that the concentration indicated in the table equaled the concentration of the active ingredient. Chlorine dioxide was produced by a known method (for example, the method described in Japanese Patent No. 5879596), then diluted with purified water as appropriate to adjust the concentration of the agent shown in Table 4 below, and added to the mixture. Polyoxyethylene stearylamine ethylene oxide 10 molar adduct (100% purity) Polyoxyethylene stearyl ether ethylene oxide 20 molar adduct (100% purity) Sodium hypochlorite (12% aqueous solution) chlorine dioxide Ethylene glycol monobutyl ether (purity 99% or higher) Ethylene glycol (purity 99% or higher)

[0088] [Table 4]

[0089] Examples 13 to 18 confirmed that the pitch size can be refined even when a pitch dispersant such as a surfactant, cationic polymer, or organic solvent is used alone on the sample. Furthermore, Examples 19-22 confirmed that using combinations of an organic solvent as a pitch dispersant and a cationic polymer, as well as combinations of an oxidizing agent, a cationic polymer, and a surfactant, resulted in a superior pitch refinement effect.

[0090] [Test Example 5] (Examples 23-27 and Comparative Example 5) Unbleached kraft pulp, primarily containing rosin as a natural pitch, was diluted to 0.3% with tap water to prepare a pulp slurry. The pulp slurry was adjusted to pH 4 using hydrochloric acid and used as the sample. After adding the chemicals at the concentrations shown in Table 5 to 1 L of the obtained sample, the mixture was stirred at 150 rpm using a three-one motor for 72 hours while maintaining the temperature in a 40°C bath. Next, the average pitch particle size in each sample after stirring for 72 hours was measured using a Thermo Fisher automated cell counter (Countess II FL), as in Test Example 1. The measurement results are shown in Table 5 below.

[0091] [Table 5]

[0092] Examples 23-25 ​​confirmed that pitch can be refined even with natural pitch, whether using a pitch dispersant or an oxidizing agent alone. Furthermore, Examples 26 and 27 confirmed even better pitch refinement effects with combinations of pitch dispersants and combinations with oxidizing agents.

[0093] [Test Example 6] (Example 28 and Comparative Example 6) A paperboard raw material mainly containing ethylene vinyl acetate copolymer as pitch was diluted to 0.3% with tap water to prepare a pulp slurry, which was used as the sample. 300 mL of the resulting sample was mixed with monochloramine at a concentration of 15 ppm relative to the slurry, and this sample was designated as the sample for Example 28. A sample without monochloramine was designated as the sample for Comparative Example 6. Each sample was stirred at 600 rpm for 3 minutes using a three-one motor, then placed in a 100 mL plastic bottle, sealed, and the average pitch particle size was measured using an automatic cell counter after 1 week in a rotary incubator at 150 rpm and 30°C. The measurement results are shown in Table 6 below.

[0094] [Table 6]

[0095] Example 28 confirmed that even with a large pitch size, the pitch can be refined by adding an oxidizing agent.

[0096] [Test Example 7] (Examples 29, 30 and Comparative Example 7) Corrugated cardboard waste paper, mainly containing ethylene vinyl acetate copolymer as pitch, was diluted to 0.3% with tap water to prepare a pulp slurry, which was used as the sample. Two samples were prepared by adding monochloramine at a concentration of 15 ppm relative to the slurry to 300 mL of the obtained sample, and these were used as the samples for Examples 29 and 30. The sample without monochloramine was used as the sample for Comparative Example 7. After gently stirring each sample with a stirrer for 15 minutes, a dispersant was added to the sample for Example 30 at a concentration of 0.5 kg / t relative to the pulp. After gently stirring each sample with a stirrer for a further 30 minutes, the average pitch particle size was measured using an automatic cell counter. The measurement results are shown in Table 7 below.

[0097] [Table 7]

[0098] From Example 29, it was found that the pitch size can be refined even when using an oxidizing agent alone. However, from the results of Example 30, it was confirmed that when an oxidizing agent and a surfactant are used in combination, the pitch size can be further refined even in tests simulating the case where the two agents are added at more distant locations.

[0099] [Test Example 8] (Examples 31, 32 and Reference Example 7) In the papermaking process of a certain paper mill producing toilet paper, as shown in Figure 4, the pitch size in the papermaking process was measured when a pitch dispersant (surfactant-based or cationic polymer-based) was added at either the pulping or mixing stage. This test was conducted to confirm how the amount of pitch of a specific size in the papermaking process changes depending on the location of the chemical addition in an actual papermaking process. The test from the start to day 5 was designated as Reference Example 7, the test from day 13 to day 24 was designated as Example 31, and the test from day 36 to day 62 was designated as Example 32.

[0100] (Reference example 7) From the start of the experiment until the fifth day, a cationic polymer-based pitch dispersant was added to the total chest 51 in the papermaking process at a rate of 1.0 kg / t per pulp. (Example 31) From day 13 to day 24 of the experiment, a surfactant-based pitch dispersant was added to a tank 43 located at the outlet of the maturation tower 42 in the papermaking process at a rate of 0.5 kg / t relative to the pulp, and a cationic polymer-based pitch dispersant was added to the total chest 51 at a rate of 0.5 kg / t relative to the pulp. (Example 32) Between 36 and 62 days from the start of the experiment, a surfactant-based pitch dispersant was added to a tank 43 located at the outlet of the maturation tower 42 in the papermaking process at a rate of 0.5 kg / t per pulp, and a cationic polymer-based pitch dispersant was added to the total chest 51 at a rate of 0.3 kg / t.

[0101] (Measurement of the amount of hydrophobic material (pitch) of a specific size in the papermaking process) In the papermaking process of toilet paper production at a certain paper mill, circulating white water and pulp slurry from seed boxes were collected from the papermaking stage. These were fractionated using a 150 μm or 23 μm mesh, and the filtrate was collected. 6 μL of 0.01% dye was added to 3 mL of the filtrate and stirred for 30 seconds to stain the hydrophobic substance (pitch). The fluorescence intensity was measured using a hydrophobicity tester (Turner Designs, Handheld Fluorometer) and determined as the amount of hydrophobic substance (pitch). The seed box is a chest located downstream of the main chest 51, and is the stage before pulp concentration adjustment water is added to send the pulp slurry to the inlet. For example, it may be located before the fan pump. (Not shown in Figure 4) Figures 2 and 3 show the changes over time in the amount of hydrophobic substances less than 150 μm and less than 23 μm in the filtrate of pulp slurry in white water and seed boxes.

[0102] Figures 2 and 3 show that, compared to Reference Example 7 in which the pitch dispersant is added only to the general chest 51 in the actual papermaking process, adding the pitch dispersant to the tank 43 located at the outlet of the maturation tower 42 in addition to the general chest 51 increased the amount of hydrophobic material (pitch) with a pitch size of less than 150 μm in the pulp slurry and white water during the papermaking process. Furthermore, an increase in the amount of hydrophobic material (pitch) with a pitch size of less than 23 μm was confirmed. From these results, it was confirmed that adding the pitch dispersant to both the pulping process and the mixing process, rather than adding the pitch dispersant only to the general chest in the mixing process, resulted in finer micronization of hydrophobic material (pitch) during the papermaking process. This is thought to be because mechanical shear is applied at the separator 44 in the pulping process, and by adding the pitch dispersant upstream of this, the hydrophobic material (pitch) in the pulp slurry is effectively micronized. Furthermore, by adding the pitch dispersant to the general chest in the mixing process, the micronized state of hydrophobic material (pitch) is maintained. This effect reduced pitch adhesion within the system, significantly decreasing the number of times the paper machine needed to be stopped for cleaning. Furthermore, the reduced adhesion of the finer pitch reduced the transfer of felt and other materials into the system, resulting in a decrease in the number of defects. [Explanation of symbols]

[0103] 1 pulper 2 Screw press 3 Aging Tower 4 Double Separator 5 Fall Washer 6 Rotary Screens 7a Stock Chest 7b Completed Chest 7c Chest 8. Hydrogen peroxide bleaching tower 9 Washer 10 Thickener 11 Shiramizu Pit 12. White water recovery line 13 White water supply line 41 Pulper 42 Aging Tower 43 tanks 44 Separators 45 Fall Washer 46 screens 47 Screw Press 48 Finescreen 49 Washer 50a Tank a 50b Tank b 51 General Chest

Claims

1. A method for suppressing pitch defects in a papermaking process in which white water is recycled, wherein the size of the pitch contained in the pulp slurry in the pulping process and / or the mixing process is controlled to suppress the occurrence of pitch defects in the papermaking process, The process includes an oxidizing agent addition step of adding an oxidizing agent to the pulp slurry at least one location in the pulping process and / or the mixing process, and / or a pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at least one location in the pulping process and / or the mixing process, so that the average particle size of the pitch contained in the pulp slurry of the pulping process and / or the mixing process is maintained at less than 150 μm, or The process includes a step of adding two or more pitch dispersants, in which two or more pitch dispersants are added to the pulp slurry at least at one location in the pulping process and / or the mixing process, so that the average particle size of the pitch contained in the pulp slurry of the pulping process and / or the mixing process is maintained at less than 150 μm. The pitch dispersant addition step involves adding at least one pitch dispersant selected from the group consisting of surfactants, cationic polymers, and organic solvents to a pulp slurry having a residual chlorine concentration of 0.5 mg / L or more and 30 mg / L or less. The aforementioned step of adding two or more pitch dispersants involves adding at least two pitch dispersants selected from the group consisting of surfactants, cationic polymers, and organic solvents to the pulp slurry. The papermaking process includes a pitch size measurement step for measuring the average particle size of pitch in the pulp slurry introduced into the papermaking process. A method for suppressing pitch defects, characterized by the following features.

2. A method for suppressing pitch defects in a papermaking process in which white water is recycled, wherein the size of the pitch contained in the pulp slurry in the papermaking process is controlled, and the occurrence of pitch defects in the papermaking process is suppressed, The papermaking process includes an oxidizing agent addition step of adding an oxidizing agent to the pulp slurry at least one location in the papermaking process, and a pitch dispersant addition step of adding a pitch dispersant to the pulp slurry at least one location in the papermaking process, so that the average particle size of the pitch contained in the pulp slurry of the papermaking process is maintained at less than 150 μm. The pitch dispersant addition step involves adding at least one pitch dispersant selected from the group consisting of surfactants, cationic polymers, and organic solvents to a pulp slurry having a residual chlorine concentration of 0.5 mg / L or more and 30 mg / L or less. The papermaking process includes a pitch size measurement step for measuring the average particle size of pitch in the pulp slurry introduced into the papermaking process. A method for suppressing pitch defects, characterized by the following features.

3. A method for suppressing pitch defects in a papermaking process in which white water is recycled, wherein the size of the pitch contained in the pulp slurry in the pulping process and / or the mixing process and the papermaking process is controlled, and the occurrence of pitch defects in the papermaking process is suppressed. The papermaking process comprises a first oxidizing agent addition step of adding a first oxidizing agent to the pulp slurry at least one location in the pulping process and the mixing process, and / or a first pitch dispersant addition step of adding a first pitch dispersant to the pulp slurry at least one location in the pulping process and the mixing process, so that the average particle size of the pitch contained in the pulp slurry of the papermaking process is maintained at less than 150 μm, and further comprises a second oxidizing agent addition step of adding a second oxidizing agent to the pulp slurry at least one location in the papermaking process, and / or a second pitch dispersant addition step of adding a second pitch dispersant to the pulp slurry at least one location in the papermaking process. The process comprises at least one of the first pitch dispersant addition step and the second pitch dispersant addition step, The first pitch dispersant addition step and / or the second pitch dispersant addition step involves adding at least one pitch dispersant selected from the group consisting of surfactants, cationic polymers, and organic solvents to a pulp slurry having a residual chlorine concentration of 0.5 mg / L or more and 30 mg / L or less, or adding at least two pitch dispersants selected from the group consisting of surfactants, cationic polymers, and organic solvents. The papermaking process includes a pitch size measurement step for measuring the average particle size of pitch in the pulp slurry introduced into the papermaking process. A method for suppressing pitch defects, characterized by the following features.

4. The pitch damage suppression method according to claim 1 or 2, wherein the oxidizing agent is at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, hydrogen peroxide, and combined halogen.

5. The pitch damage suppression method according to claim 3, wherein the first oxidizing agent and the second oxidizing agent are at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, hydrogen peroxide, and combined halogen.

6. A method for suppressing pitch damage according to claim 1, 2, or 4, comprising an oxidizing agent addition step and a pitch dispersant addition step, wherein the oxidizing agent is at least one selected from the group consisting of hypochlorite, chlorite, chlorine dioxide, and combined halogen.

7. The pitch damage suppression method according to claim 1, 2, or 3, wherein the oxidizing agent addition step, the pitch dispersant addition step and / or the addition of two or more pitch dispersants step are performed by adding the oxidizing agent and / or pitch dispersants to the pulp slurry in at least one of the devices that apply mechanical shear to the pulp slurry, and / or to the pulp slurry upstream of the device.

8. The pitch size measurement step is performed using image analysis, as described in Claim 1, 2, or 3.

Images