WO2024185662A1

WO2024185662A1 - Paper manufacturing method and agent

Info

Publication number: WO2024185662A1
Application number: PCT/JP2024/007668
Authority: WO
Inventors: Jiayi Chen
Original assignee: Kurita Water Industries Ltd
Current assignee: Kurita Water Industries Ltd
Priority date: 2023-03-03
Filing date: 2024-03-01
Publication date: 2024-09-12
Anticipated expiration: 2025-09-03
Also published as: CN120813740A; TW202436244A; KR20250159029A; JP2024124869A

Abstract

A paper manufacturing method using a pulp slurry prepared by reusing, as a paper raw material, a part of a low-quality raw material discharged in a papermaking step, wherein the low-quality raw material to be reused as a paper raw material is a reformed raw material treated with a specific agent, and the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are superior to those of a pulp slurry containing an untreated low-quality raw material not treated with the specific agent.

Description

PAPER MANUFACTURING METHOD AND AGENT

The present invention relates to a paper manufacturing method and an agent, and more particularly, to a technology for reusing a part of a low-quality raw material discharged in a papermaking process, as a paper raw material.

For example, demand for paper packaging materials such as corrugated board has increased with an increase in electronic commerce. From the viewpoints of environmental conservation and effective resource reuse, these packaging materials are recycled as much as possible and reused as paper. However, as recycling of these packaging materials progresses, fibers as raw materials deteriorate, and there is a tendency for productivity (e.g., water filterability) to decrease and for white-water concentration (turbidity) to increase during production, often leading to issues. Further, even if waste discharged in a conventional papermaking process is returned to the papermaking process as is and used, similar issues occur.

For example, Patent Document 1 discloses a method for treating a papermaking sludge, characterized in that deodorizing treatment and reforming treatment are applied to the papermaking sludge with one or more inorganic oxidizing agents selected from a specific oxidizing agent group, then nonionic water-soluble polymers containing acrylamide as a main component and a vinyl polymerization cationic water-soluble polymer and/or a vinyl polymerization amphoteric water-soluble polymer are sequentially added in this order to perform aggregating treatment, and then dehydration is performed by a dehydrator.

Patent Document 2 discloses a method in which lime or quicklime is added to a papermaking sludge to adjust the pH value of the sludge to greater than 9.5 and equal to or less than 11.0, whereby generation of hydrogen sulfide and mercaptans can be suppressed over a long period of time and the papermaking sludge can be used without any issue in firing in a cement plant.

However, these methods are completely different from the present invention because reuse of the papermaking sludge as paper is not mentioned at all. For this reason, there has been not known a paper manufacturing method in which waste material discharged in a conventional paper manufacturing process is used without any issue in manufacturing.

Japanese Unexamined Patent Application, Publication No. 2010-149033 Japanese Unexamined Patent Application, Publication No. 2005-161165

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a paper manufacturing method capable of maintaining or improving characteristics of a pulp slurry by reforming, among low-quality materials discharged in a papermaking step, a low-quality material to be reused as a paper raw material so as to be suitable for reuse, and an agent to be used for reforming the low-quality material so as to be suitable for reuse.

The present inventors have intensively studied to solve the above-mentioned issues. As a result, the inventors have found that in a paper manufacturing method using a pulp slurry prepared by reusing, as a paper raw material, a part of a low-quality raw material discharged in the papermaking step, if the low-quality raw material to be reused as a paper raw material is converted to a reformed raw material by treating it with a specific agent, and this reformed raw material is added to the pulp slurry, the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are superior to those of the pulp slurry containing an untreated low-quality raw material not treated with the specific agent, and stable manufacturing of good quality paper is possible, arriving at the completion of the present invention. Specifically, the present invention provides the following.

A first aspect of the present invention relates to a paper manufacturing method including using a pulp slurry prepared by reusing, as a paper raw material, a part of a low-quality raw material discharged in a papermaking step, in which the low-quality raw material to be reused as a paper raw material is a reformed raw material treated with a specific agent, and the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are superior to those of a pulp slurry containing an untreated low-quality raw material not treated with the specific agent.

A second aspect of the present invention relates to the paper manufacturing method as described in the first aspect, in which the pulp slurry containing the reformed raw material has characteristics of the same or higher water filterability and turbidity than the pulp slurry which does not reuse the low-quality raw material.

A third aspect of the present invention relates to the paper manufacturing method as described in the first or second aspect, in which the specific agent is any one of the following (1), (2), or (3):
(1) a reaction product obtained by subjecting an acrylamide-based polymer to Hoffman degradation;
(2) a copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g, a cationization degree of 0.6 to 2.0 meq/g, an anionization degree of 0.20 meq/g or less, and a ratio of cation charge density/anion charge density of 5 to 20; and
(3) a copolymer of (meth)acrylamide and a compound represented by the following chemical formula (I), the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g and a cationization degree of 0.6 to 3.0 meq/g,
chemical formula (I): R¹-COO-C₂H₄-N(CH₃)₂-R²,
wherein R¹ is CH₂=CH- or CH₂=C(CH₃)-, R² is an alkyl group having 1 to 3 carbon atoms or a benzyl group, and they may be the same type or different types.

A fourth aspect of the present invention relates to the paper manufacturing method as described in the third aspect, in which a benzyl group moiety portion of the agent (3) has a cationization degree of 0.1 to 1.2 meq/g and R² is a benzyl group.

A fifth aspect of the present invention relates to the paper manufacturing method as described in any one of the first to fourth aspects, in which the paper raw material is waste paper, paperboard, or kraft paper.

A sixth aspect of the present invention relates to the paper manufacturing method as described in any one of the first to fifth aspects, in which the reformed raw material obtained by treating the low-quality raw material with the specific agent is mixed with the pulp slurry.

A seventh aspect of the present invention relates to the paper manufacturing method as described in the sixth aspect, in which the specific agent is further added to the pulp slurry even after the reformed raw material is mixed with the pulp slurry.

An eighth aspect of the present invention relates to an agent for treating a low-quality raw material to be reused as a paper raw material of a pulp slurry, in which the agent converts the low-quality raw material to be reused to a reformed raw material, so that characteristics of water filterability and turbidity of the pulp slurry improve.

A ninth aspect of the present invention relates to the agent as described in the eighth aspect, in which the agent is any one of the following (1), (2), or (3):
(1) a reaction product obtained by subjecting an acrylamide-based polymer to Hoffman degradation;
(2) a copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g, a cationization degree of 0.6 to 2.0 meq/g, an anionization degree of 0.20 meq/g or less, and a ratio of cation charge density/anion charge density of 5 to 20; and
(3) a copolymer of (meth)acrylamide and a compound represented by the following chemical formula (I), the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g and a cationization degree of 0.6 to 3.0 meq/g:
chemical formula (I): R¹-COO-C₂H₄-N(CH₃)₂-R²,
wherein R¹ is CH₂=CH- or CH₂=C(CH₃)-, R² is an alkyl group having 1 to 3 carbon atoms or a benzyl group, and they may be the same type or different types.

A tenth aspect of the present invention relates to the agent as described in the ninth aspect, in which a benzyl group moiety portion of the agent (3) has a cationization degree of 0.1 to 1.2 meq/g and R² is a benzyl group.

According to the present invention, it is possible to provide a paper manufacturing method capable of maintaining or improving characteristics of a pulp slurry by treating a part of a low-quality raw material discharged in a papermaking step using a specific agent to convert the part of a low-quality raw material to a reformed raw material which can be reused as a paper raw material and adding this reformed raw material to the pulp slurry, as well as to provide an agent for use in converting a low-quality raw material to a reformed raw material.

Hereinafter, specific embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and can be carried out with appropriate modifications within the scope of the object of the present invention.

The paper manufacturing method of the present invention is a method of manufacturing paper including use of a pulp slurry prepared by reusing, as a paper raw material, a part of a low-quality raw material discharged in a papermaking step, in which the low-quality raw material to be reused as a paper raw material is a reformed raw material treated with a specific agent, and the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are superior to those of a pulp slurry containing an untreated low-quality raw material not treated with the specific agent.

In the above-mentioned paper manufacturing method, the pulp slurry containing a reformed raw material has the same or higher characteristics of water filterability and turbidity than the pulp slurry which does not reuse a low-quality raw material.

Further, the agent of the present invention is an agent for treating a low-quality raw material to be reused as a paper raw material of a pulp slurry, and the agent treats the low-quality raw material to be reused and converts it to a reformed raw material, so that characteristics of water filterability and turbidity of the pulp slurry improve.

In the above-mentioned paper manufacturing method and the above-mentioned agent, waste paper, paperboard or kraft paper is suitable as the paper raw material.

<Low-Quality Raw Materials>
In the present invention, the low-quality raw material to be treated refers to a raw material having an anion trash, i.e., PCD (cation demand) of -200 μeq/L or less, and having a value of an amount of filtrate for 10 seconds in the following freeness test 10 ml or more smaller as compared with a papermaking raw material used in the papermaking step.

Examples of the low-quality raw materials include raw materials such as low-quality waste paper, DIP floss, coat broke, recovery raw materials in manufacturing processes, drainage scum, a paper sludge, a drainage treatment facility sludge, a biotreated surplus sludge, floating scum by pressurizing drainage prior to treatment, pulp containing a drainage sludge, and the like.

<Cationic Demand>
A sample is filtered through a 150 μm-pass filter cloth, and a filtrate is collected. The obtained filtrate is charged into a flow potentiometer (PCD (Particle Change Detector)-03, manufactured by Mutec Corporation), and a cationic demand is measured from the amount of titration solution (manufactured by Poly-DADMAC Kishida Chemical Co., Ltd.).

<Freeness Test>
By using a freeness tester including a tube with a diameter of 60 mm having an 80 mesh wire attached to the tube bottom and a tube through which water exits, a sample (180 ml) accumulated in the tube is dropped downward through the mesh wire by opening and closing a valve. An amount of filtrate for 10 seconds at this time is measured by a graduated cylinder. The greater the amount of filtrate, the faster the dehydration speed during the papermaking process, which means improved productivity.

<Specific Agent>
As the (specific) agent of the present invention, any cationic substance is satisfactory, as long as it is capable of neutralizing an anionic substance contained, for example, in the low-quality raw material. A cationic polymer is particularly preferable. This cationic polymer is capable of adjusting charge of a pulp slurry to an optimal state by neutralizing anionic substances. Further, the agent is a polymer, whereby impurities such as pitch can be fixed to fibers.

<Cationic Polymer>
The cationic polymer is not particularly limited as long as it is a cationic polymer, but above all, the cationic polymer described in any one of the following (1), (2), or (3) is preferable because an effect is achieved by a smaller addition amount:

(1) a reaction product obtained by subjecting an acrylamide-based polymer to Hoffman degradation,
hereinafter, this reaction product being also referred to as an agent (1);

(2) a copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g, a cationization degree of 0.6 to 2.0 meq/g, an anionization degree of 0.20 meq/g or less, and a ratio of cation charge density/anion charge density of 5 to 20,
hereinafter, this copolymer being also referred to as an agent (2); and

(3) a copolymer of (meth)acrylamide and a compound represented by the following chemical formula (I), the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g and a cationization degree of 0.6 to 3.0 meq/g,
hereinafter, this copolymer being also referred to as an agent (3):
chemical formula (I): R¹-COO-C₂H₄-N(CH₃)₂-R²,
wherein R¹ is CH₂=CH- or CH₂=C(CH₃)-, R² is an alkyl group having 1 to 3 carbon atoms or a benzyl group, and they may be the same type or different types.

<Agent (1)>
The intrinsic viscosity and molecular weight of the acrylamide-based polymer are generally correlated to each other. That is, as the intrinsic viscosity decreases, the molecular weight may decrease, and the water filterability and yield may decrease. Therefore, in order to improve the water filterability and yield, the intrinsic viscosity of the acrylamide-based polymer is preferably 10.0 dl/g or more, and more preferably 12.5 dl/g or more. The intrinsic viscosity of the acrylamide-based polymer is more preferably 13.0 dl/g or more, more preferably 14.0 dl/g or more, and most preferably 14.5 dl/g or more. If the intrinsic viscosity of the acrylamide-based polymer is too high, the molecular weight becomes too large, and when the agent (1) is added in the papermaking step, the agent (1) may act as an aggregating agent, which may incur collapse of the balance of the papermaking. Therefore, in order to suppress aggregation, the intrinsic viscosity of the acrylamide-based polymer is preferably 40.0 dl/g or less, and more preferably 28.0 dl/g or less. The intrinsic viscosity of the acrylamide-based polymer is more preferably 24.0 dl/g or less, more preferably 20.0 dl/g or less, and most preferably 16.0 dl/g or less.

If a degree of anionization of the acrylamide-based polymer is too high, an ionic reaction between the cationic group and the anionic group occurs in the acrylamide-based polymer molecule, and thus the yield and water filterability may decrease. Therefore, the degree of anionization of the acrylamide-based polymer for improving the yield and water filterability is preferably 0.30 meq/g or less, more preferably 0.10 meq/g or less, more preferably 0.05 meq/g or less, more preferably 0.03 meq/g or less, and most preferably 0.01 meq/g or less.

The intrinsic viscosity is calculated by measuring flow-down time using a Cannon Fenske viscometer, and calculating the intrinsic viscosity from the measured values using Huggins equation and Mead-Fuoss equation. The degree of anionization is denoted by a colloid equivalent value, which is measured according to the following method as described in paragraph 0029 of Japanese Unexamined Patent Application, Publication No. 2009-228162.

<Method of Measuring Colloid Equivalent Value of Anion>
An anionic polymer compound diluted to a 50 ppm aqueous solution (diluted with pure water) is collected in a 100 ml graduated cylinder and transferred into a 200 ml beaker. While stirring the solution with a rotor, an N/10 sodium hydroxide solution (produced by Wako Pure Chemical Industries Ltd.) is added by whole pipette, whereby pH is adjusted to 10.5, then several drops of toluidine blue indicator (produced by Wako Pure Chemical Industries) are added, and titration is performed with an N/400 polyvinyl alcohol potassium sulfate solution (produced by Wako Pure Chemical Industries Ltd.). Before titration, 5 ml of N/200 methyl glycol chitosan solution (manufactured by Wako Pure Chemical Industries Ltd.) is added by whole pipette. The time point at which blue color turns into reddish purple color, and the reddish purple color does not disappear even after several seconds, is determined as an end point. Similarly, a blank test is performed using pure water (blank).
Colloid equivalent value (meq/g) of anion = [measured value (ml) of anionic polymer compound - titrated amount (ml) of blank test]/2

In the present invention, the acrylamide-based polymer refers to a polymer obtained by polymerizing acrylamide, and may contain another cationic monomer. Furthermore, the acrylamide polymer may or may not include an anionic monomer; however, it is preferable, as described above, that the acrylamide-based polymer obtained by polymerization reaction has an intrinsic viscosity of 10.0 to 40.0 dl/g and a degree of anionization of 0.3 meq/g or less. However, in order to increase the product yield by lowering the degree of anionization and suppressing hydrolytic degradation of the acrylamide polymer during polymerization, it is preferable that an anionic monomer is not included.

Examples of the cationic monomer which may be included in the acrylamide-based polymer include acrylonitrile, diallyldimethylammonium chloride (DADMAC), N,N-dimethyl-1,3-propanediamine (DMAPA), and the like.

The acrylamide-based polymer preferably has a linear structure (linear polymer) in order to further improve water filterability and yield of a pulp slurry containing a reformed raw material and to reduce a moisture content of wet paper. That is, it is more preferable not to subject a cross-linkable monomer to the polymerization as a monomer other than the acrylamide to be used for the polymerization reaction of the acrylamide-based polymer.

Examples of solvents to be used in the polymerization reaction of the acrylamide-based polymer include water, alcohol, and dimethylformamide. In view of cost, water is preferred.

A polymerization initiator of the acrylamide-based polymer is not particularly limited as long as it is soluble in a solvent. Examples include azo compounds such as 2,2'-azobis-2-amidinopropane hydrochloride, azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile and the like. Also, peroxides such as ammonium persulfate, potassium persulfate, hydrogen peroxide, ammonium peroxodisulfate, benzoyl peroxide, lauroyl peroxide, succinic peroxide, octanoyl peroxide, and t-butyl peroxy-2-ethylhexanoate are exemplified. Examples include redox systems in which ammonium peroxodisulfate is combined with sodium sulfite, sodium bisulfite, tetramethylethylenediamine or trimethylamine. A chain transfer agent is preferably used in combination in the polymerization reaction. Examples of the chain transfer agent include alkyl mercaptans, thioglycolic acid and esters thereof, isopropyl alcohol, and a monomer having a (meth)allyl group such as allyl alcohol, allylamine and (meth)allylsulfonic acid, and salts thereof.

Temperature and time of the polymerization reaction of the acrylamide-based polymer may be adjusted so that the resulting acrylamide-based polymer has a desired intrinsic viscosity and a desired degree of anionization. For example, in order for the resulting acrylamide-based polymer to have an intrinsic viscosity of 12.5 to 28.0 dl/g and a degree of anionization of 0.30 meq/g or less, the acrylamide polymer that satisfies the above-described conditions can be polymerized, for example, by setting the starting temperature to a low temperature and gradually increasing the temperature. If the starting temperature is too high, the intrinsic viscosity is lowered, and during reaction, a hydrolysate of the acrylamide is produced, which increases the degree of anionization. Therefore, a low starting temperature is desired. More specifically, the starting temperature of the polymerization reaction is preferably 10°C to 30°C, more preferably 15°C to 25°C, and most preferably 18°C to 22°C. Further, from the viewpoint of easy control of heat generation during polymerization, the upper limit of temperature increasing after the start of polymerization is preferably 80°C or lower, more preferably 70°C or lower, and most preferably 65°C or lower.

<Reaction Product Generation Step>
In a reaction product generation step, by subjecting the above-mentioned acrylamide-based polymer to the Hoffman degradation, it is possible to produce an agent which treats a low-quality raw material to be reused as a paper raw material of a pulp slurry, and which can be used as an agent to treat a low-quality raw material to be reused and convert it to a reformed raw material so that characteristics of water filterability and turbidity of the pulp slurry improve.

When the Hofmann degradation is performed, a solution obtained by polymerizing the acrylamide-based polymer may be used as is or may be used after dilution. If necessary, a solution may be prepared separately, as required.

When a concentration of the acrylamide-based polymer to be subjected to the Hofmann degradation is set high, a non-uniform reaction occurs, and sufficient effects, improvement in yield or water filterability cannot be obtained. In order to sufficiently obtain these effects, a concentration of the acrylamide-based polymer is preferably 35% by mass or less, more preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably 2% by mass or less. When the concentration of the acrylamide-based polymer is too low, efficiency of the Hoffman degradation is lowered, and therefore, the concentration of the acrylamide-based polymer is preferably 0.001% by mass or more, more preferably 0.010% by mass or more, and most preferably 0.100% by mass or more.

The Hoffman degradation is preferably performed by causing a hypohalous acid to act on an amide group of the acrylamide-based polymer under alkali conditions. Specifically, the Hofmann degradation is preferably carried out in a pH range of 8.0 or more, and preferably in a pH range of 11.0 to 14.0. To obtain alkali conditions, for example, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are used. In order to cause a hypohalous acid to act, for example, a hypohalite salt such as hypochlorite, hypobromite, or hypoiodite is used.

Examples of the hypochlorite, hypobromite, and hypoiodite include alkali metal salts and alkaline earth metal salts thereof. Examples of the alkali metal salts of hypochlorite include sodium hypochlorite, potassium hypochlorite and lithium hypochlorite.

An amount of hypohalite to be subjected to the Hoffman degradation is not particularly limited, but if an amount of the acrylamide-based polymer relative to an amount of the hypohalite is too small or too large, an amount of the acrylamide-based polymer or the hypohalite which is not involved in the reaction increases, so that efficiency of the reaction decreases. In order to efficiently perform the reaction, a molar ratio of hypohalite relative to the acrylamide-based polymer is preferably 0.1:10 to 10:10, more preferably 1:10 to 10:10, and most preferably 2:10 to 10:10.

In the Hofmann degradation of the present invention, it is preferable that hypohalite is mixed with a liquid containing an acrylamide-based polymer under a condition of pH 8.0 or more. Thereby, gelation of the reaction product can be prevented. In the Hofmann degradation, alkali is preferably added together with hypohalite to a liquid containing the acrylamide-based polymer. This also prevents the reaction product from gelling. As the alkali, conventionally known alkali (alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and the like described above) can be used.

The temperature in the Hofmann degradation can be appropriately selected in the range from 0°C to 110°C, but may be selected in combination with reaction time in order to obtain the desired degree of cationization described above. For example, when the reaction product is supplied within 24 hours, the Hofmann degradation is preferably performed in the range of from 10°C to 50°C, and more preferably 10°C to 30°C.

In the reaction product generation step described above, a neutralizing agent may be added before the next step of supplying the reaction product, but it is preferable that the neutralizing agent is not added. Addition of the neutralizing agent tends to improve water filterability and yield and to reduce a moisture content of wet paper. Examples of the neutralizing agent include a pH adjusting agent (e.g., hydrochloric acid) used for neutralizing conventionally well-known Hoffman degradation.

A degree of cationization of the acrylamide-based polymer is preferably 0.01 meq/g or more, more preferably 0.10 meq/g or more, more preferably 0.30 meq/g or more, more preferably 0.50 meq/g or more, and most preferably 1.00 meq/g or more. In addition, the higher the degree of cationization of the acrylamide-based polymer, the higher the effect, which is preferable because the addition amount can be reduced. A degree of cationization of the acrylamide-based polymer is usually 2.00 meq/g or less.

A degree of cationization of the reaction product is represented by a colloid equivalent value similarly to the degree of anionization, and is measured by the following method.

<Method of Measuring Colloid Equivalent Value of Cation>
A reaction product diluted to a 50 ppm aqueous solution (diluted with pure water) is collected in a 100 ml graduated cylinder and transferred into a 200 ml beaker. While stirring the solution with a rotor, an N/10 hydrochloric acid solution is added by whole pipette, whereby the pH is adjusted to 4, then several drops of toluidine blue indicator (produced by Wako Pure Chemical Industries) are added, and titration is performed with an N/400 polyvinyl alcohol potassium sulfate solution (produced by Wako Pure Chemical Industries Ltd.). Before titration, 5 ml of N/200 methylglycol chitosan solution (manufactured by Wako Pure Chemical Industries) is added by whole pipette. The time point at which blue color turns into reddish purple color, and the reddish purple color does not disappear even after several seconds, is determined as the end point. Similarly, a blank test is performed using pure water (blank). Colloid equivalent value (meq/g) of cation = [measured value of reaction product (ml)- titrated amount of blank test (ml)]/2

<Agent (2)>
The intrinsic viscosity and molecular weight of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct are generally correlated to each other. That is, as the intrinsic viscosity decreases, the molecular weight may decrease, and the water filterability and yield may decrease. Therefore, in order to improve the water filterability and yield, the intrinsic viscosity of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is preferably 8.0 dl/g or more, and more preferably 12.5 dl/g or more. The intrinsic viscosity of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is more preferably 13.0 dl/g or more, more preferably 14.0 dl/g or more, and most preferably 14.5 dl/g or more. If the intrinsic viscosity of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is too high, the molecular weight becomes too large, and when the agent (2) is added in the papermaking step, the agent (2) may act as an aggregating agent, which may incur collapse of the balance of the papermaking. Therefore, in order to suppress aggregation, the intrinsic viscosity of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is preferably 28.0 dl/g or less, more preferably 24.0 dl/g or less, more preferably 20.0 dl/g or less, and most preferably 16.0 dl/g or less.

If a degree of anionization of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is too high, an ionic reaction between the cationic group and the anionic group occurs in the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, and thus the yield and water filterability may decrease. Therefore, the degree of anionization of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct for improving yield and water filterability is preferably 0.20 meq/g or less, more preferably 0.10 meq/g or less, more preferably 0.05 meq/g or less, more preferably 0.03 meq/g or less, and most preferably 0.01 meq/g or less.

An intrinsic viscosity and a degree of anionization in the copolymer of (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct are measured in the same manner as in the above acrylamide-based polymer.

A degree of cationization of the copolymer of (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct is preferably 0.6 meq/g or more and 2.0 meq/g or less, more preferably 0.8 meq/g or more and 1.5 meq/g or less.

The degree of cationization of the copolymer of (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct is measured in the same manner as in the above acrylamide-based polymer.

The copolymer of (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct is preferably cationic rich, and more specifically, the ratio of cationic charge density/anion charge density is more preferably in the range of 5 to 20.

The dimethylaminoethyl acrylate quaternary adduct is obtained by reacting dimethylaminoethyl acrylate with a quaternizing agent. Examples of the quaternization agent include alkyl halides such as methyl chloride and dialkyl sulfates such as dimethyl sulfate. When these quaternization agents are reacted with dimethylaminoethyl acrylate, an alkyl group of the quaternization agent is introduced into a nitrogen atom of the dimethylaminoethyl acrylate to form a salt of a quaternary ammonium ion and a halogen ion or a monoalkyl sulfate ion. An alkyl group introduced by the quaternization agent is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, and particularly preferably a methyl group. Quaternization of dimethylaminoethyl acrylate can be carried out by a well-known method.

Examples of solvents to be used in the polymerization reaction of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct include water, alcohol, and dimethylformamide. In view of cost, water is preferred.

A polymerization initiator of the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct is not particularly limited as long as it is soluble in a solvent. Examples include azo compounds such as 2,2'-azobis-2-amidinopropane hydrochloride, azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile and the like. Also, peroxides such as ammonium persulfate, potassium persulfate, hydrogen peroxide, ammonium peroxodisulfate, benzoyl peroxide, lauroyl peroxide, saccharinic peroxide, octanoyl peroxide, and t-butylperoxy2-ethylhexanoate are exemplified. Also exemplified are redox systems in which ammonium peroxodisulfate is combined with sodium sulfite, sodium bisulfite, tetramethylethylenediamine or trimethylamine. A chain transfer agent is preferably used in combination in the polymerization reaction. Examples of the chain transfer agent include alkyl mercaptans, thioglycolic acid and esters thereof, isopropyl alcohol, and a monomer having a (meth)allyl group such as allyl alcohol, allylamine and (meth)allylsulfonic acid, and salts thereof.

The temperature and time of the polymerization reaction of the copolymer of (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct may be adjusted such that the copolymer of the obtained (meth)acrylic acid, (meth)acrylamide, and dimethylaminoethyl acrylate quaternary adduct has a desired intrinsic viscosity, degree of cationization, degree of anionization, ratio of cation charge density/anion charge density. For example, in order for the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct to have an intrinsic viscosity of 8.0 to 28.0 dl/g, a degree of cationization of 0.6 to 2.0 meq/g, and a degree of anionization of 0.20 meq/g or less, a ratio of cation charge density / anion charge density of 5 to 20, the copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct that satisfies the above-described conditions can be polymerized, for example, by setting the starting temperature to a low temperature and gradually increasing the temperature. If the starting temperature is too high, the intrinsic viscosity is lowered, and during reaction, a hydrolysate of (meth)acrylamide is produced, which increases the degree of anionization. Therefore, a low starting temperature is desired. More specifically, the starting temperature of the polymerization reaction is preferably 10°C to 30°C, more preferably 15°C to 25°C, and most preferably 18°C to 22°C. Further, from the viewpoint of easy control of heat generation during polymerization, the upper limit of the temperature increasing after the start of polymerization is preferably 80°C or lower, more preferably 70°C or lower, and most preferably 65°C or lower.

<Agent (3)>
The intrinsic viscosity and molecular weight of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) are generally correlated to each other. That is, as the intrinsic viscosity decreases, the molecular weight may decrease, and the water filterability and yield may decrease. Therefore, in order to improve the water filterability and yield, the intrinsic viscosity of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is preferably 8.0 dl/g or more, and more preferably 12.5 dl/g or more. The intrinsic viscosity of the copolymer of (meth)acrylamide and the compound represented by the chemical formula (I) is more preferably 13.0 dl/g or more, more preferably 14.0 dl/g or more, and most preferably 14.5 dl/g or more. If the intrinsic viscosity of the copolymer of (meth)acrylamide and the compound represented by the chemical formula (I) is too high, the molecular weight becomes too large, and when the agent (3) is added in the papermaking step, the agent (3) may act as an aggregating agent, which may incur collapse of the balance of the papermaking. Therefore, in order to suppress aggregation, the intrinsic viscosity of the copolymer of (meth)acrylamide and the compound represented by the chemical formula (I) is preferably 28.0 dl/g or less, more preferably 24.0 dl/g or less, more preferably 20.0 dl/g or less, and most preferably 16.0 dl/g or less.

If a degree of anionization of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is too high, an ionic reaction between a cationic group and an anionic group occurs in a molecule of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I), and thus the yield and water filterability may decrease. Therefore, the degree of anionization of the copolymer of (meth)acrylamide and the compound represented by the chemical formula (I) for improving the yield and water filterability is preferably 0.20 meq/g or less, more preferably 0.10 meq/g or less, more preferably 0.05 meq/g or less, more preferably 0.03 meq/g or less, and most preferably 0.01 meq/g or less.

An intrinsic viscosity and a degree of anionization of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) are measured in the same manner as in the acrylamide-based polymer described above.

A degree of cationization of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is preferably 0.6 meq/g or more and 3.0 meq/g or less, and more preferably 0.8 meq/g or more and 1.5 meq/g or less.

A degree of cationization of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is measured in the same manner as in the acrylamide-based polymer described above.

Specific examples of the compound represented by the chemical formula (I) include quaternary salts such as a hydrochloride salt and a sulfate salt of dialkylaminoalkyl (meth)acrylate such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; alkyl halide adducts such as methyl chloride; benzyl halide adducts such as benzyl chloride; dialkyl sulfate adducts such as dimethyl sulfate, and the like.

When the benzyl halide adduct of dialkylaminoalkyl (meth)acrylate (hereinafter sometimes referred to as a benzyl group moiety) is included as the compound represented by the chemical formula (I) (that is, when R² of the chemical formula (I) is a benzyl group), a degree of cationization of the benzyl group moiety portion of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is preferably 0.1 meq/g or more, more preferably 0.2 meq/g or more, more preferably 0.2 meq/g or more, more preferably 0.4 meq/g or more, and most preferably 0.6 meq/g or more. A cationization degree of the benzyl group moiety portion of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is preferably 1.2 meq/g or less, more preferably 1.0 meq/g or less, and most preferably 0.9 meq/g or less.

The degree of cationization of the benzyl group moiety portion in the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) can be calculated from DAB mol% and DAA mol% determined by C¹³NMR.

As a solvent to be used in a polymerization reaction of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I), for example, water, alcohol, dimethylformamide, or the like can be used. In view of cost, water is preferred.

A polymerization initiator of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) is not particularly limited as long as it is soluble in a solvent. Examples include azo compounds such as 2,2'-azobis-2-amidinopropane hydrochloride, azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile and the like. Also, peroxides such as ammonium persulfate, potassium persulfate, hydrogen peroxide, ammonium peroxodisulfate, benzoyl peroxide, lauroyl peroxide, succinic peroxide, octanoyl peroxide, and t-butyl peroxy-2-ethylhexanoate are exemplified. Examples include redox systems in which ammonium peroxodisulfate is combined with sodium sulfite, sodium bisulfite, tetramethylethylenediamine or trimethylamine. A chain transfer agent is preferably used in combination in the polymerization reaction. Examples of the chain transfer agent include alkyl mercaptans, thioglycolic acid and esters thereof, isopropyl alcohol, and a monomer having a (meth)allyl group such as allyl alcohol, allylamine and (meth)allylsulfonic acid, and salts thereof.

Temperature and time of the polymerization reaction of the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) may be adjusted so that the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) has a desired intrinsic viscosity and a desired degree of anionization. For example, in order for the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I), in which R² is a benzyl group, to have an intrinsic viscosity of 8.0 to 28.0 dl/g, a degree of cationization of 0.6 to 3.0 meq/g, and a degree of cationization of the benzyl group moiety portion of 0.1 to 1.2 meq/g, for example, the copolymer of (meth)acrylamide and a compound represented by the chemical formula (I) can be polymerized by setting the starting temperature to a low temperature and gradually increasing the temperature. If the starting temperature is too high, the intrinsic viscosity is lowered, and during reaction, a hydrolysate of the (meth)acrylamide is produced, which increases the degree of anionization. Therefore, a low starting temperature is desired. More specifically, the starting temperature of the polymerization reaction is preferably 10°C to 30°C, more preferably 15°C to 25°C, and most preferably 18°C to 22°C. Further, from the viewpoint of easy control of heat generation at the time of polymerization, the upper limit of the increasing temperature after the start of polymerization is preferably 80°C or lower, more preferably 70°C or lower, and most preferably 65°C or lower.

Note that each of the physical property values represented by the intrinsic viscosity, the degree of cationization, the degree of anionization, and the ratio of cation charge density/anion charge density of the agents (2) and (3) means a content with respect to the net of polymer.

The polymerization method of the agents (1) to (3) is not particularly limited, but may be, for example, aqueous solution polymerization, reverse phase emulsion polymerization, dispersion polymerization, solution polymerization, or the like.

Forms of the agents (1) to (3) are not particularly limited, and examples thereof include aqueous solutions, dispersions in salt water, water-in-oil emulsions, powders, and the like.

<Method of Selection of Agents for Low-Quality Raw Materials>
With regard to a combination of an agent and a low-quality raw material to be treated in the selection of an agent of the present invention, it is sufficient to select an agent having good reactivity with the low-quality raw material. That is, a low filtrate turbidity and large filtrate amount serves as an index of good reactivity. At this time, in order to consider not only the filtrate turbidity and filtrate amount, but also chemical costs, for example, a difference in the unit prices of each agent in each supply area should be considered. Therefore, it is preferable to comprehensively evaluate and select, including economic performance after performing a test selected by the method disclosed in the Examples.

An addition amount of the above-mentioned agent can be expected to be effective only by adding a small amount to the low-quality raw material, but is preferably 10 ppm or more, more preferably 100 ppm or more, more preferably 250 ppm or more, more preferably 500 ppm or more, and most preferably 1000 ppm or more. The upper limit of the addition amount of the above-mentioned agent is not particularly limited, but since a processing cost increases as the addition amount increases, the upper limit is preferably 10,000 ppm or less, more preferably 8,000 ppm or less, more preferably 6,000 ppm or less, and more preferably 4,000 ppm or less from the viewpoint of the processing cost.

As a method of adding the above-mentioned agent, a well-known method can be used, and a method can be mentioned, in which the above-mentioned agent is added to a slurry containing a low-quality raw material to produce a reformed raw material, and the reformed raw material is added to a pulp slurry of a papermaking raw material to make paper. An order in which the above agents are added to the slurry containing a low-quality raw material is not particularly limited. A method of adding these agents is not particularly limited, and the agents may be diluted with industrial water or the like and added or may be added as they are.

After mixing the reformed raw material with the pulp slurry, the agent may be further added to the pulp slurry. The method of adding these agents is not particularly limited, and the agents may be diluted with industrial water or the like and added, or the agents may be added as they are.

An amount of the reformed raw material obtained by chemical treatment of the low-quality raw material to the pulp slurry is preferably 0.01% by weight to 20.00% by weight, more preferably 0.10% by weight to 10.00% by weight, more preferably 0.30% by weight to 5.00% by weight, and most preferably 0.50% by weight to 3.00% by weight.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.

<Examples 1 to 6>
Since a paper sludge (hereinafter, it is also referred to as "PS".) is a low-quality raw material, if the paper sludge is used as a paper raw material for papermaking (papermaking raw material) as it is, the dehydration speed in the papermaking machine decreases, and the production efficiency decreases. Thus, in each of Examples 1 to 6, a pulp slurry (reformed raw material) was prepared by treating 5 mass% of PS in an addition content shown in Table 1 of the agent (1) (PD-3820). Then, each prepared pulp slurry was subjected to a freeness test, and the filtrate turbidity and the filtrate amount were measured. The preparation conditions and results of the pulp slurries are shown in Table 1 below.

<Comparative Example 1, Reference Example 1>
In Comparative Example 1, an untreated pulp slurry of 5 mass% PS which had not been treated with the agent (1) was prepared. Further, in Reference Example 1, a pulp slurry of 95 mass% papermaking raw material containing no PS nor agent (1) was prepared. Then, the pulp slurry was subjected to a freeness test, and the filtrate turbidity and the filtrate amount were measured. The preparation conditions and results of the pulp slurries are shown in Table 1 below.

<Freeness Test>
By using a freeness tester including a tube with a diameter of 60 mm having an 80 mesh wire attached to the tube bottom and a tube through which water exits, a pulp slurry (180 ml) accumulated in the tube was dropped downward through the mesh wire by opening and closing a valve. An amount of filtrate for 10 seconds at this time was measured by a graduated cylinder.

<Turbidity>
A turbidity of the filtrate obtained in the above freeness test was measured using a portable turbidity meter (2100Q, manufactured by DKK-TOA CORPORATION). Note that as compared with Comparative Example 1 in which the agent (1) had not been added, as the turbidity was lower, stains in the system were reduced, and defects and the risk of paper breakage could be reduced.

The following agent was used as the agent (1).
PD-3820: A reaction product obtained by subjecting an acrylamide-based polymer to the Hoffman degradation at polymer:hypohalous acid = 10:4, manufactured by Kurita Water Industries Ltd.

As shown in Table 1, in Comparative Example 1 in which an untreated paper sludge was blended/ contained, the amount of filtrate was only 2 ml. When the pulp slurry prepared in Comparative Example 1 was blended as a raw material to another raw material in an amount of, for example, 1% by weight or more, dehydration speed of the paper machine was significantly lowered, resulting in a poor efficiency of paper production. Contrary to this, in each of Examples 1 to 6 where treatment with the agent (1) was performed, the filtrate amount was larger and the filtrate turbidity was lower than in Comparative Example 1. Among them, Examples 4 to 6 had the characteristics of the water filterability and the filtrate turbidity that were the same as or better than Reference Example 1. As described above, the agent treatment significantly improved the filtrate amount and significantly reduced the filtrate turbidity, and thus, the treatment effect of the agent could be recognized.

Characteristics of the low-quality raw materials other than the paper sludge and characteristics of the papermaking raw materials as comparison targets are shown in Table 2.

As shown in Table 2, it was found that the low-quality raw materials were significantly inferior in the water filterability and the like to the papermaking raw material.

<Examples 7 to 15>
To a slurry raw material collected in the production process of a papermaking and paperboard factory, a predetermined amount of a reformed raw material obtained in each of the above-described Examples was added, as shown in Table 3, and then 200 ppm of PD-1230 (manufactured by Kurita Water Industries) was added as a yield and water filterability improving agent of cationic polyacrylamide, which is generally used in the production of paper, to obtain a pulp slurry. Then, the pulp slurry was subjected to the freeness test in the same manner as in Examples 1 to 6, and the filtrate turbidity and the filtrate amount were measured. In Examples 7 to 15, the concentration of the slurry raw material was set to 1% by weight.

<Comparative Examples 2 to 3, Reference Example 2>
A pulp slurry was obtained in the same manner as in Examples 7 to 15, except that the slurry raw material collected in the production process of the papermaking and paperboard factory was changed to the reformed raw material shown in Table 3. Then, the pulp slurry was subjected to the freeness test in the same manner as in the above-described Examples 7 to 15, and the filtrate turbidity and the filtrate amount were measured. In Comparative Examples 2 and 3 and Reference Example 2, the concentration of the slurry raw material was set to 1% by weight.

As shown in Table 3, in the pulp slurry of each of Examples 7 to 15 containing the reformed raw material, the improvement in the water filterability and turbidity of the filtrate was observed as compared with Comparative Examples 2 and 3. With regard to cases where 5% by weight of the reformed raw material was blended, Examples 9 to 11 were recognized to have the same or better effect than Reference Example 2, and the addition amount of the agent (1) of 2,000 ppm or more is considered to be more preferable. In addition, with regard to cases where 10% by weight of the reformed raw material was blended, Examples 13 to 15 were recognized to have the same or better effect than Reference Example 2, and the addition amount of the agent (1) of 2,000 ppm or more is considered to be more preferable, similarly to cases where 5% by weight of the reformed raw material was blended. Note that regardless of presence or absence of addition of a yield and water filterability improving agent, no influence was observed on the effect of the means for solving the issue of the low-quality raw material.

<Examples 16 to 24 and Comparative Examples 4 to 6>
In the syntheses, the following monomers were used.
“AM”: (meth)acrylamide
“DAA”: dimethylaminoethyl acrylate quaternary adduct (methylene chloride salt)
“AA”: (meth)acrylic acid
“DAB”: N-(2-acryloyloxyethyl)-N-benzyl-N,N-dimethylammonium chloride

(Example 16)
To a 300 ml four-necked flask equipped with a stirrer, a nitrogen introduction tube, a cooler, and a thermometer, AM=11.2 g, DAA=9.7 g, AA=0.14 g, and 164.0 g of demineralized water were added. After passing through nitrogen gas, the temperature was raised to 50°C, 2 g of a 1% aqueous solution of 2,2'-azobis-2-amidinopropane 2 hydrochloride salt was added, and the mixture was kept at 60°C for 6 hours under stirring at 300 rpm. A part of the resulting polymer was taken and vacuum-lyophilized to synthesize a solid polymer (agent (2)). A colloid equivalent value and intrinsic viscosity of the anion or cation of the agent (2) were measured by the following method. A pulp slurry treated by adding 2,000 ppm of a solid polymer (agent (2)) to 5 mass% of paper sludge was prepared, and the freeness test of the pulp slurry was performed in the same manner as in Examples 1 to 6, and the filtrate turbidity and the filtrate amount were measured.

(Examples 17 to 24 and Comparative Examples 4 to 6)
A solid polymer (the polymers of Examples 17 to 18 were agents (2) and the polymers of Examples 19 to 24 were agents (3)) was synthesized in the same manner as in Example 16 and the same measurement was performed, except that the monomers shown in Tables 4 and 5 below were added instead of AM=11.2 g, DAA=9.7 g, and AA=0.14 g in Example 16 and each solid polymer shown in Tables 4 and 5 below was added in a content of 2,000 ppm to the 5% by mass paper sludge. A degree of cationization of the benzyl group moiety portion of each solid polymer of Examples 19 to 24 was measured by the following method.

<Colloid Equivalent Value of Anion>
The sample diluted to 50 ppm aqueous solution (diluted with pure water) was collected in a 100 ml graduated cylinder and transferred to a 200 ml beaker. While stirring the solution with a rotor, an N/10 sodium hydroxide solution (produced by Wako Pure Chemical Industries Ltd.) was added by whole pipette, whereby pH was adjusted to 10.5, then several drops of toluidine blue indicator (produced by Wako Pure Chemical Industries) were added, and titration was performed with an N/400 polyvinyl alcohol potassium sulfate solution (produced by Wako Pure Chemical Industries Ltd.). Before titration, 5 ml of N/200 methyl glycol chitosan solution (manufactured by Wako Pure Chemical Industries Ltd.) was added by whole pipette. The time point at which blue color turned into reddish purple color, and the reddish purple color did not disappear even after several seconds, was determined as the end point. Similarly, a blank test was performed using pure water (blank). Colloid equivalent value (meq/g) of anion = [measured value (ml) of anionic polymer compound - titrated amount (ml) of blank test]/2

<Colloid Equivalent Value of Cations>
The sample diluted to 50 ppm aqueous solution (diluted with pure water) was collected in a 100 ml graduated cylinder and transferred to a 200 ml beaker. While stirring the solution with a rotor, an N/10 hydrochloric acid solution was added by whole pipette, whereby the pH was adjusted to 4, then several drops of toluidine blue indicator (produced by Wako Pure Chemical Industries) were added, and titration was performed with an N/400 polyvinyl alcohol potassium sulfate solution (produced by Wako Pure Chemical Industries Ltd.). Before titration, 5 ml of N/200 methylglycol chitosan solution (manufactured by Wako Pure Chemical Industries) was added by whole pipette. The time point at which blue color turned into reddish purple color, and the reddish purple color did not disappear even after several seconds, was determined as the end point. In the same manner, a blank test was performed with pure water (blank). Colloid equivalent value (meq/g) of cation = [measured value of reaction product (ml)- titrated amount of blank test (ml)]/2

<Intrinsic viscosity>
Flow-down time of each sample was measured using a Cannon Fenske viscometer, and the intrinsic viscosity was calculated from the measured value using Huggins equation and Mead-Fuoss equation.

<Degree of Cationization of Benzyl Group Moiety Portion>
A degree of cationization of the benzyl group moiety portion was calculated from DAB mol% and DAA mol% determined by ¹³CNMR based on the following formula. Degree of cationization of benzyl group moiety portion = DAB mol%×cation degree/(DAA mol% DAB mol%)

As shown in Tables 4 and 5, it was found that the water filterability and filtrate turbidity of the pulp slurry treated with the agent (2) or the agent (3) were significantly improved, similarly to the case of the agent (1).

Next, the effect when the agents of the present invention were used was confirmed, using a DIP floss as the low-quality raw material other than the paper sludge.

<Examples 25 to 33, Comparative Example 7 and Reference Example 3>
A DIP floss generated from a papermaking and paperboard factory was used as the low-quality raw material. A pulp slurry used in the production of paperboard in the same papermaking and paperboard factory was used as the papermaking raw material. In each of Examples 25 to 33, an agent shown in Table 6 was added in the content shown therein to the DIP floss to obtain a reformed raw material, which was blended with the papermaking raw material to obtain a solution with a DIP floss content shown in Table 6, and PD-1230 was added to the solution in a content of 200 ppm to prepare a pulp slurry. Then, the pulp slurry was subjected to the freeness test in the same manner as in Examples 1 to 6, and the filtrate turbidity and the filtrate amount were measured. In Comparative Example 7, a pulp slurry was prepared in the same manner as in Examples 25 to 33 except that the reformed raw material was not blended and the DIP floss content was adjusted as shown in Table 6, and the filtrate turbidity and the filtrate amount were measured. In Reference Example 3, a pulp slurry was prepared in the same manner as in Examples 25 to 33 except that the reformed raw material and the DIP froth were not blended, and the filtrate turbidity and the filtrate amount were measured.

As shown in Table 6, it was found that even when 5 to 10% by weight of the DIP floss as the low-quality raw material was blended to the pulp slurry, the water filterability and the turbidity of the filtrate were improved by the chemical treatment of the DIP floss by the agents (1) to (3) of the present invention. When the DIP floss of 5% by weight was blended, a sufficient effect was observed even when the addition amount was 2,000 ppm, and when the DIP floss of 10% by weight was blended, the effect was further improved by setting the addition amount to 4,000 ppm. In addition, improvement in the water filterability by the treatment with the agent (3) was observed, and the filtrate turbidity exhibited the best result, though the water filterability by the agent (1) was slightly poor.

<Examples 34 to 42, Comparative Example 8 and Reference Example 4>
A surplus sludge (biotreated surplus sludge) generated from the papermaking and cardboard factory was used as the low-quality raw material. A pulp slurry used in the production of paperboard in the same papermaking and cardboard factory was used as the papermaking raw material. In each of Examples 34 to 42, an agent shown in Table 7 was added in the content shown therein to the surplus sludge to obtain a reformed raw material, which was blended with the papermaking raw material to obtain a solution with a surplus sludge content shown in Table 7, and PD-1230 was added to the solution in a content of 200 ppm to prepare a pulp slurry. Then, the pulp slurry was subjected to the freeness test in the same manner as in Examples 1 to 6, and the filtrate turbidity and the filtrate amount were measured. In Comparative Example 8, a pulp slurry was prepared in the same manner as in Examples 34 to 42, except that the reformed raw material was not blended and the surplus sludge content was adjusted as shown in Table 7, and the filtrate turbidity and the filtrate amount were measured. In Reference Example 4, a pulp slurry was prepared in the same manner as in Examples 34 to 42 except that the reforming raw material and the surplus sludge were not blended, and the filtrate turbidity and the filtrate amount were measured.

The surplus sludge, which is a low-quality raw material, has a large economic benefit as the recovery and utilization thereof are advanced. However, it is known that recovery and utilization are the most difficult. As shown in Table 7, it was found that from the results of Examples 34 to 42 that even when 5 to 10% by weight of the surplus sludge as the low-quality raw material was blended in the pulp slurry, the water filterability and turbidity of the filtrate were improved by the chemical treatment of the surplus sludge using the agents (1) to (3) of the present invention. When the surplus sludge of 5% by weight was blended, a sufficient effect was observed even when the addition amount was 2,000 ppm, and when the surplus sludge of 10% by weight was blended, the effect was further improved by setting the addition amount to 4,000 ppm. With the agent (1), further improvement was achieved by setting the addition amount to 6,000 ppm. The agent treatment by the agent (2) showed the best result in the water filterability.

From the above results, it was found that the optimum agent varies depending on the type of the low-quality raw material. It became also apparent that the higher the concentration of the agent, the more remarkable the effect. The reason for this is considered that the amount and charge state of the anionic substance vary depending on the type of the low-quality raw material, and expression of the effect varies depending on the type of the agent.

According to the present invention, it is possible to manufacture paper using a pulp slurry prepared by reusing, as the paper raw material, a part of a low-quality raw material, which is normally processed as waste; the low-quality raw material is a reformed raw material obtained by treatment with a specific agent; and the pulp slurry obtained by reusing the reformed raw material has an effect that the characteristics of water filterability and turbidity are the same as or better than those of the pulp slurry obtained by not reusing the reformed raw material.

Claims

A paper manufacturing method, comprising using a pulp slurry prepared by reusing, as a paper raw material, a part of a low-quality raw material discharged in a papermaking step,
wherein the low-quality raw material to be reused as a paper raw material is a reformed raw material treated with a specific agent, and
the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are superior to those of a pulp slurry containing an untreated low-quality raw material not treated with the specific agent.
The paper manufacturing method according to claim 1, wherein the pulp slurry containing the reformed raw material has characteristics of water filterability and turbidity that are the same as or better than those of the pulp slurry which does not reuse the low-quality raw material.
The paper manufacturing method according to claim 1 or 2, wherein the specific agent is any one of the following (1), (2), or (3):
(1) a reaction product obtained by subjecting an acrylamide-based polymer to Hoffman degradation;
(2) a copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g, a cationization degree of 0.6 to 2.0 meq/g, an anionization degree of 0.20 meq/g or less, and a ratio of cation charge density/anion charge density of 5 to 20; and
(3) a copolymer of (meth)acrylamide and a compound represented by the following chemical formula (I), the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g and a cationization degree of 0.6 to 3.0 meq/g,
chemical formula (I): R¹-COO-C₂H₄-N(CH₃)₂-R²,
wherein R¹ is CH₂=CH- or CH₂=C(CH₃)-, R² is an alkyl group having 1 to 3 carbon atoms or a benzyl group, and they may be the same type or different types.
The paper manufacturing method according to claim 3, wherein a benzyl group moiety portion of the agent (3) has a cationization degree of 0.1 to 1.2 meq/g and R² is a benzyl group.
The paper manufacturing method according to claim 1 or 2, wherein the paper raw material is waste paper, paperboard, or kraft paper.
The paper manufacturing method according to claim 1 or 2, wherein the reformed raw material obtained by treating the low-quality raw material with the specific agent is mixed with the pulp slurry.
The paper manufacturing method according to claim 6, wherein the specific agent is further added to the pulp slurry even after the reformed raw material is mixed with the pulp slurry.
An agent for treating a low-quality raw material to be reused as a paper raw material of a pulp slurry,
wherein the agent converts the low-quality raw material to be reused to a reformed raw material, so that characteristics of water filterability and turbidity of the pulp slurry improve.
The agent according to claim 8, wherein the agent is any one of the following (1), (2), or (3):
(1) a reaction product obtained by subjecting an acrylamide-based polymer to Hoffman degradation;
(2) a copolymer of (meth)acrylic acid, (meth)acrylamide, and a dimethylaminoethyl acrylate quaternary adduct, the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g, a cationization degree of 0.6 to 2.0 meq/g, an anionization degree of 0.20 meq/g or less, and a ratio of cation charge density/anion charge density of 5 to 20; and
(3) a copolymer of (meth)acrylamide and a compound represented by the following chemical formula (I), the copolymer having an intrinsic viscosity of 8.0 to 28.0 dl/g and a cationization degree of 0.6 to 3.0 meq/g:
chemical formula (I): R¹-COO-C₂H₄-N(CH₃)₂-R²,
wherein R¹ is CH₂=CH- or CH₂=C(CH₃)-, R² is an alkyl group having 1 to 3 carbon atoms or a benzyl group, and they may be the same type or different types.
The agent according to claim 9, wherein a benzyl group moiety portion of the agent (3) has a cationization degree of 0.1 to 1.2 meq/g and R² is a benzyl group.