Paper-strengthening agent and paper

Abstract

This paper-strengthening agent contains a polymer (A) including, as essential components, a (meth)acrylamide (a1), an ethylenically unsaturated monomer (a2) having an amino group and an α-methyl group, an ethylenically unsaturated monomer (a3) having a carboxy group, and an ethylenically unsaturated monomer (a4) having a sulfonic acid group. In a 1H-NMR spectrum of the polymer (A), a high-field-side absorption band X and a low-field-side absorption band Y that are attributable to the α-methyl group of the (a2) component are present in the range of 0.9-1.35 ppm, and the ratio of the area (Xs) of X to the sum of the area (Xs) of X and the area (Ys) of Y is not less than 5% to less than 20%. The potential of an aqueous solution having a pH of 6.8 and containing the polymer (A) with a nonvolatile content concentration of 0.1 wt% at 25°C is 0-300 mV as measured by a PCD electrometer.

Description

Paper strength enhancer, paper

[0001] This invention relates to a paper strength enhancer and paper.

[0002] Paper strength enhancers are chemicals used to increase the strength of paper. In the paper industry in particular, as papermaking systems become more closed off (e.g., recycling of waste pulp), the strength of the raw pulp fibers decreases, making it easier for the strength of the resulting paper to decrease as well. This has increased the importance of paper strength enhancers.

[0003] Incidentally, (meth)acrylamide polymers are commonly used as paper strength enhancers, and they are classified into anionic, cationic, and amphoteric types depending on their ionic properties. Among these, the mainstream amphoteric (meth)acrylamide polymers are obtained by copolymerizing acrylamide with various ethylenically unsaturated monomers (Patent Document 1).

[0004] Furthermore, as a technology to address the closed-loop nature of papermaking systems, the applicant has developed the following: １ A paper strength enhancer is known in which the area ratio of the absorption band derived from α-methyl groups obtained by 1H-NMR spectroscopy is identified (Patent Document 2). However, when this paper strength enhancer is added to pulp slurry, it causes excessive foaming, and insufficient dewatering in subsequent processes results in a high water content in the paper, making it susceptible to drying loads.

[0005] Japanese Patent Publication No. 2012-251252 Japanese Patent Publication No. 2014-196588

[0006] The present invention aims to provide a paper strength enhancer that efficiently dewaters paper during papermaking due to its low foaming properties, and also provides paper that exhibits good paper strength.

[0007] The inventors, through diligent research, have found a solution to the aforementioned problem and have completed the present invention. Specifically, the present invention relates to the following paper strength enhancer and paper.

[0008] (Item 1) A polymer (A) comprising (meth)acrylamide (a1), an ethylenically unsaturated monomer having an amino group and an α-methyl group (a2), an ethylenically unsaturated monomer having a carboxyl group (a3), and an ethylenically unsaturated monomer having a sulfonic acid group (a4) as essential components, wherein the polymer (A) １ A paper strength enhancer wherein, in the H-NMR spectrum, there are high-field absorption bands X and Y on the low-field side that belong to the α-methyl group of component (a2) in the range of 0.9 ppm to 1.35 ppm, and the ratio of the area of ​​absorption band X (Xs) to the total area of ​​the area of ​​absorption band Y (Ys) [Xs / (Xs+Ys)] is 5% or more and less than 20%, and the measured potential by a PCD electrometer at a temperature of 25°C of an aqueous solution of the polymer (A) with a non-volatile content of 0.1% by weight is 0 to 300 mV. (Item 2) The paper strength enhancer according to item 1, further comprising a crosslinkable monomer (a5). (Item 3) Paper containing the paper strength enhancer according to item 1 or 2.

[0009] According to the paper strength enhancer of the present invention, the reduced foaming allows for efficient dewatering during papermaking, and the resulting paper also exhibits good paper strength.

[0010] Polyacrylamide composed of acrylamide and N,N-dimethylaminoethyl methacrylate １ This is a schematic diagram showing that in the 0.9 ppm to 1.35 ppm range of the 1H-NMR spectrum, high-field absorption band X and low-field absorption band Y appear, attributed to the α-methyl group of N,N-dimethylaminoethyl methacrylate. In Figure 1, when no peak appears on the high-field side above high-field absorption band A... １ This is a schematic diagram of an H-NMR spectrum.

[0011] The paper strength enhancer of the present invention comprises a polymer (A) whose essential components are (meth)acrylamide (a1) (hereinafter referred to as component (a1)), an ethylenically unsaturated monomer having an amino group and an α-methyl group (a2) (hereinafter referred to as component (a2)), an ethylenically unsaturated monomer having a carboxyl group (a3) ​​(hereinafter referred to as component (a3)), and an ethylenically unsaturated monomer having a sulfonic acid group (a4) (hereinafter referred to as component (a4)). In the following, (meth)acrylic means methacrylic and acrylic, (meth)acrylate means methacrylate and acrylate, and (meth)acryloyl means methacryloyl and acryloyl.

[0012] (a1) The components are methacrylamide and acrylamide. These may be used individually or in combination.

[0013] (a1) The molar ratio of component is preferably 60 to 95 mol%, more preferably 75 to 95 mol%, and even more preferably 80 to 93 mol%, with the total constituent components being 100 mol%.

[0014] (a2) Component is an ethylenically unsaturated monomer having an amino group and an α-methyl group. An ethylenically unsaturated monomer is one which has one or more carbon-carbon double bonds and / or one or more carbon-carbon triple bonds in the monomer (the same applies hereinafter). Also, "α-methyl group" refers to a methyl group bonded to the α-carbon of the ethylenically unsaturated group.

[0015] (a2) Examples of components include: ethylenically unsaturated monomers having a primary amino group and an α-methyl group, such as 2-methylallylamine; methacrylates having a tertiary amino group, such as N,N-dimethylaminoethyl methacrylate and N,N-diethylaminoethyl methacrylate; methacrylamides having a tertiary amino group, such as N,N-dimethylaminopropyl methacrylamide and N,N-diethylaminopropyl methacrylamide; quaternary salts of methacrylates having a tertiary amino group, such as methyl chloride, benzyl chloride, dimethyl sulfate, and epihalohydrin salts of the aforementioned methacrylates having a tertiary amino group; and quaternary salts of methacrylamides having a tertiary amino group, such as methyl chloride, benzyl chloride, dimethyl sulfate, and epihalohydrin salts of the aforementioned methacrylamides having a tertiary amino group. These may be used individually or in combination of two or more.

[0016] In particular, polymer (A) exhibits the area ratio and PCD potential values ​​described later, produces less foam, and when papermaking is carried out with a paper strength enhancer containing polymer (A), it is more likely to be efficiently dewatered from the pulp slurry. Therefore, it is preferable to include methacrylate having a tertiary amino group, a quaternary salt of methacrylate having a tertiary amino group, more preferably methacrylate having a tertiary amino group, a methyl chloride salt of methacrylate having a tertiary amino group, a benzyl chloride salt of methacrylate having a tertiary amino group, and even more preferably methacrylate having a tertiary amino group.

[0017] (a2) The molar ratio of component (A) is preferably 3.5 to 22 mol%, more preferably 4 to 18 mol%, and even more preferably 6 to 16 mol%, with the total constituent components being 100 mol%, because polymer (A) exhibits the ratio of area and PCD potential values ​​described later, produces less foam, and when papermaking is performed using a paper strength enhancer containing polymer (A), it is easily and efficiently dewatered from the pulp slurry.

[0018] The above-mentioned components may also include an ethylenically unsaturated monomer (a2') (hereinafter also referred to as component (a2')) that does not have an α-methyl group but has an amino group, in addition to component (a2).

[0019] (a2') Examples of component (a2') include: ethylenically unsaturated monomers having a primary amino group but lacking an α-methyl group, such as vinylamine and allylamine; ethylenically unsaturated monomers having a secondary amino group, such as N-methylvinylamine and diallylamine; acrylates having a tertiary amino group, such as N,N-dimethylaminoethyl acrylate and N,N-diethylaminoethyl acrylate; acrylamides having a tertiary amino group, such as N,N-dimethylaminopropyl acrylamide and N,N-diethylaminopropyl acrylamide; quaternary salts of acrylates having a tertiary amino group, such as methyl chloride, benzyl chloride, dimethyl sulfate, and epihalohydrin salts of the aforementioned acrylates having a tertiary amino group; and quaternary salts of acrylamides having a tertiary amino group, such as methyl chloride, benzyl chloride, dimethyl sulfate, and epihalohydrin salts of the aforementioned acrylamides having a tertiary amino group. These may be used individually or in combination of two or more.

[0020] In particular, it is preferable to include a quaternary salt of an acrylate having a tertiary amino group, and more preferably to include a methyl chloride salt of an acrylate having a tertiary amino group and a benzyl chloride salt of a methacrylate having a tertiary amino group.

[0021] The molar ratio of component (a2') is preferably 5 mol% or less, more preferably 4 mol% or less, and even more preferably 3 mol% or less, with the total constituent components being 100 mol%.

[0022] (a3) Component is an ethylenically unsaturated monomer having a carboxyl group.

[0023] (a3) Components include, for example, ethylenically unsaturated monocarboxylic acids such as (meth)acrylic acid, 3-butenoic acid, 4-pentenoic acid, 5-hexenoic acid, and 4-methylhexene; ethylenically unsaturated dicarboxylic acids such as itaconic acid, fumaric acid, maleic acid, citraconic acid, and muconic acid; ethylenically unsaturated monocarboxylic acid anhydrides such as (meth)acrylic anhydride; ethylenically unsaturated dicarboxylic acid anhydrides such as itaconic acid anhydride, maleic acid anhydride, and citraconic acid anhydride; and (meth)acrylamide alkanes such as N-(meth)acryloylglycine (2-((meth)acryloylamino)acetic acid), 3-(meth)acrylamidepropionic acid, 4-(meth)acrylamidebutanoic acid, 5-(meth)acrylamidepentanoic acid, and 6-(meth)acrylamidehexanoic acid. Examples include (meth)acrylamide alkylalkanoic acids such as 3-(meth)acrylamide-2-methylbutanoic acid, 3-(meth)acrylamide-3-methylbutanoic acid, and 4-(meth)acrylamide-3,3-dimethylhexanoic acid; and 2-(meth)acrylamide-N-glycolic acid. These (a3) ​​components may also be used as salts of alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium salts and calcium salts; ammonium salts such as ammonia; and organic amine salts such as trimethylamine, triethylamine, trimethanolamine, and triethanolamine. These may be used individually or in combination of two or more.

[0024] In particular, polymer (A) exhibits the area ratio and PCD potential values ​​described later, produces less foam, and when papermaking is carried out with a paper strength enhancer containing polymer (A), it is more readily dehydrated from the pulp slurry. Therefore, it is preferable to include ethylenically unsaturated monocarboxylic acid, ethylenically unsaturated dicarboxylic acid, and 2-(meth)acrylamide-N-glycolic acid, more preferably (meth)acrylic acid, acrylic anhydride, itaconic acid, and 2-(meth)acrylamide-N-glycolic acid, and even more preferably itaconic acid.

[0025] Of the components of (a3), (meth)acrylamide alkanoic acid, (meth)acrylamide alkyl alkanoic acid, and 2-(meth)acrylamide-N-glycolic acid may be used as is after adding one or more selected from monoalkanoic acid, alkyl monoalkanoic acid, alkanedicarboxylic acid, hydroxycarboxylic acid, aldehyde alkanoic acid and the salts thereof to the reaction components and reacting with component (a1).

[0026] Examples of monoalkanoic acids include acetic acid, propionic acid, butanoic acid, pentanoic acid, and hexanoic acid. Examples of alkylmonoalkanoic acids include 2-methylbutanoic acid, 3-methylbutanoic acid, and 3,3-dimethylhexanoic acid. Examples of alkanedicarboxylic acids include succinic acid and oxalic acid. Examples of hydroxycarboxylic acids include citric acid and glycolic acid. Examples of aldehydecarboxylic acids include glyoxylic acid. Examples of salts of these include alkali metal salts of the monoalkanoic acid, alkylmonoalkanoic acid, alkanedicarboxylic acid, hydroxycarboxylic acid, or aldehydealkanoic acid, such as lithium, sodium, and potassium; alkaline earth metal salts such as magnesium salts and calcium salts; ammonium salts such as ammonia; and organic amine salts such as trimethylamine, triethylamine, trimethanolamine, and triethanolamine. These may be used individually or in combination of two or more.

[0027] (a3) The molar ratio of component (A) is such that polymer (A) exhibits the ratio of area and PCD potential values ​​described later, produces less foam, and when papermaking is carried out with a paper strength enhancer containing polymer (A), it is easily and efficiently dewatered from the pulp slurry. Therefore, with the total constituent components at 100 mol%, a molar ratio of 0.5 to 5 mol%, more preferably 1 to 4.5 mol%, and even more preferably 1.5 to 4.5 mol%, is preferred.

[0028] (a4) Component is an ethylenically unsaturated monomer having a sulfonic acid group.

[0029] Examples of component (a4) include vinyl sulfonic acid, methallyl sulfonic acid, and p-styrene sulfonic acid. These components (a4) may also be used as alkali metal salts such as sodium and potassium, or as salts such as ammonium salts. These may be used individually or in combination of two or more.

[0030] (a4) The molar ratio of component is preferably 0.1 to 5 mol%, more preferably 0.3 to 3 mol%, and even more preferably 0.5 to 2 mol%, with the total constituent components being 100 mol%.

[0031] The aforementioned components may further include a crosslinkable monomer (a5) (hereinafter also referred to as component (a5)).

[0032] (a5) Examples of components include N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and N-t-butyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, and N,N-diisopropyl(meth)acrylamide; N,N'-alkylenebis(meth)acrylamides such as N,N'-methylenebis(meth)acrylamide and N,N'-ethylenebis(meth)acrylamide; crosslinkable monomers having a trialyl group such as triallyl isocyanurate, triallyl trimellitate, triallylamine, and triallyl(meth)acrylamide; and triazines having a (meth)acryloyl group such as 1,3,5-triacryloyl-1,3,5-triazine and 1,3,5-triacryloylhexahydro-1,3,5-triazine. These may be used individually or in combination of two or more. In particular, it is preferable to include N,N-dialkyl(meth)acrylamide, N,N'-alkylenebis(meth)acrylamide, and triazine having a (meth)acryloyl group, and more preferably to include N,N-dialkyl(meth)acrylamide and triazine having a (meth)acryloyl group, as this makes it easier to exhibit excellent paper strength by introducing a branched structure into polymer (A) to increase its molecular weight.

[0033] The molar ratio of component (a5), based on 100 mol% of all constituent components, is preferably 5 mol% or less, more preferably 2 mol% or less, and still more preferably 0.5 mol% or less.

[0034] As the constituent components, a monomer (a6) other than components (a1) to (a5) (hereinafter referred to as component (a6)) may further be contained.

[0035] Examples of component (a6) include: ethylenically unsaturated monomers having an aromatic ring such as styrene, α-methylstyrene, and vinyltoluene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate; vinyl carboxylates such as vinyl acetate and vinyl propionate; nitriles such as acrylonitrile; mercaptans such as 2-mercaptoethanol and n-dodecyl mercaptan; alcohols such as ethanol, isopropyl alcohol, and n-pentyl alcohol; aromatic compounds such as α-methylstyrene dimer, ethylbenzene, isopropylbenzene, and cumene; and carbon tetrachloride. These may be used alone or in combination of two or more kinds thereof.

[0036] The molar ratio of component (a6), based on 100 mol% of all constituent components, is preferably 3 mol% or less, more preferably 1 mol% or less, and still more preferably 0.5 mol% or less.

[0037] In the production of the polymer (A), there may be added: organic acids such as acetic acid, propionic acid, butanoic acid, citric acid, succinic acid, oxalic acid, glycolic acid, and glyoxylic acid; inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; inorganic acid salts such as sodium sulfate, potassium sulfate, and ammonium sulfate; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; starches such as oxidized starch, phosphate esterified starch, urea phosphate esterified starch, etherified starch, crosslinked starch, APS-modified starch, enzyme-modified starch, cationized starch, and amphoteric starch; resins such as polyvinyl alcohol; and additives such as urea, defoaming agents, antioxidants, preservatives, and bactericides. These may be used alone or in combination of two or more kinds thereof.

[0038] The content of the additive is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, relative to 100 parts by weight of all constituent components.

[0039] The polymer (A) is obtained by polymerizing component (a1), component (a2), component (a3) and component (a4) as essential components, and optionally component (a5), component (a6) and the above additives in a solvent in the presence of a polymerization initiator.

[0040] Examples of the above polymerization method include a method using only a dropping polymerization method, a method using only a simultaneous polymerization method (in which a monomer mixed solution is charged all at once), or a method combining a simultaneous polymerization method and a dropping polymerization method.

[0041] The dropping polymerization method is a method in which a monomer mixed solution is dropped into a reaction system pre-charged with a solvent, and examples of the method using only this polymerization method include the following (1) to (3). Note that the dropping may be performed continuously, or may be stopped in the middle of dropping, and resumed after polymerization is carried out for a certain period of time. (1) A method of dropping a monomer mixed solution obtained by mixing all monomer components (2) A method of separately preparing two or more types of monomer mixed solutions and then dropping them simultaneously (3) A method of separately preparing two or more types of monomer mixed solutions and then dropping them sequentially

[0042] Further, examples of the method combining the simultaneous polymerization method and the dropping polymerization method include the following (4) to (7). (4) A method of mixing respective polymers after separately simultaneously polymerizing respective monomer mixed solutions (5) A method of dropping the remaining monomer mixed solution after completing simultaneous polymerization of one or more types of monomer mixed solutions (6) A method of carrying out polymerization by dropping the remaining monomer mixed solution starting from the middle of simultaneous polymerization of one or more types of monomer mixed solutions (7) A method of carrying out dropping polymerization of one or more types of monomer mixed solutions, adding the remaining monomer mixed solution all at once, and then carrying out simultaneous polymerization

[0043] In the present invention, the manufacturing method is preferably carried out by (3) to (7), and more preferably by (3), (5), and (6), because the polymer (A) exhibits the area ratio and PCD potential value described later, produces less foam, and when papermaking is performed using a paper strength enhancer containing the polymer (A), it is easily and efficiently dewatered from the pulp slurry.

[0044] Furthermore, in the above method, when monomer mixture (1) and monomer mixture (2) are prepared and polymerized in this order, the molar ratios of component (a2) and component (a3) ​​contained in each mixture are preferably set as follows, in order to facilitate the polymer (A) from exhibiting the area ratio and PCD potential values ​​described later: • Component (a2): monomer mixture (1) / monomer mixture (2) = preferably 0 / 100 to 40 / 60, and more preferably 5 / 95 to 30 / 70. • Component (a3): monomer mixture (2) / monomer mixture (1) = preferably 0 / 100 to 40 / 60, and more preferably 5 / 95 to 30 / 70.

[0045] Furthermore, monomer mixture (1) and monomer mixture (2) may be polymerized independently using either a simultaneous polymerization method or a dropwise polymerization method.

[0046] Examples of the aforementioned solvents include water and organic solvents. These may be used individually or in combination of two or more.

[0047] Examples of water types include hard water, soft water, tap water, pure water, ultrapure water, ion-exchanged water, and industrial water. These can be used individually or in combination of two or more types.

[0048] Examples of organic solvents include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-octyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and diacetone alcohol; and ethers such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether.

[0049] The solvent content is adjusted so that the polymerization concentration is preferably 5 to 50% by weight, more preferably 10 to 35% by weight.

[0050] Examples of polymerization initiators include inorganic peroxides such as ammonium persulfate and potassium persulfate; organic peroxides such as benzoyl peroxide, dicumyl peroxide, and lauryl peroxide; azo compounds such as 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride, and 2,2'-azobis[2(2-imidazolin-2-yl)propane] hydrochloride; and hydrogen peroxide. These may be used individually or in combination of two or more. Among these, ammonium persulfate, potassium persulfate, and 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride are preferred, and 2,2'-azobis(2-methylpropionamidinopropane) dihydrochloride is more preferred, from the viewpoint of allowing solution polymerization to proceed sufficiently. Furthermore, the method of adding the polymerization initiator can be appropriately selected, such as adding it all at once, adding it in stages, or adding it continuously dropwise.

[0051] The polymerization initiator content is typically 0.01 to 1 part by weight, preferably 0.03 to 0.5 parts by weight, per 100 parts by weight of the total components.

[0052] Polymerization conditions include, for example, a reaction temperature of typically 50 to 100°C (preferably 60 to 90°C). The reaction time is also typically 1 to 10 hours (preferably 1 to 6 hours).

[0053] In the present invention, the obtained polymer (A) is described later. １ From the standpoint of obtaining the desired area ratio in the H-NMR spectrum and the desired PCD measurement potential, it is preferable to carry out the process using the manufacturing methods described in (3), (5), and (6) above.

[0054] The resulting polymer (A) may further contain inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; sulfates such as sodium sulfate, potassium sulfate, and ammonium sulfate; metal hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; resins such as polyvinyl alcohol; and additives such as starch, urea, defoamers, antioxidants, preservatives, and disinfectants.

[0055] The physical properties of the paper strength enhancer of the present invention are as follows: polymer (A) １ In the 1H-NMR spectrum, there are high-field absorption bands X and Y on the low-field side, both attributable to the α-methyl group of component (a2), in the range of 0.9 ppm to 1.35 ppm, and the ratio of the area of ​​absorption band X (Xs) to the total area of ​​absorption band Y (Ys) [Xs / (Xs+Ys)] is 5% or more and less than 20%. Since polymer (A) is a high-molecular-weight compound, both absorption band X and absorber Y have a mountain-shaped profile with broad tails.

[0056] In this measurement, if the polymer (A) does not contain any additives that affect the ratio of the area, it can be measured as is. On the other hand, if it contains additives that affect the ratio of the area, such as an antifoaming agent, the polymer (A) should be precipitated with acetone or the like, and the polymer (A) from which the additives have been removed by vacuum drying should be used for measurement. Note that the removal of additives can also be carried out by methods other than those described above.

[0057] Here, the chemical shift range (0.9 ppm to 1.35 ppm) is the value obtained when 3-(trimethylsilyl)-1-propanesulfonate sodium (DSS) is used as the internal standard.

[0058] The aforementioned chemical shift range (0.9 ppm to 1.35 ppm) is a range voluntarily determined by the applicant. As shown in Figure 1, the upper limit of 1.35 ppm was set based on the minimum point on the left edge of absorption band Y. The area Xs of absorption band X and the area Ys of absorption band Y are demarcated with the minimum point on the right edge of absorption band Y as the boundary. The lower limit of 0.9 ppm was set based on the minimum point on the right edge of absorption band X when a peak appears on the higher magnetic field side than absorption band X, as shown in Figure 1. On the other hand, even when no peak appears on the higher magnetic field side than absorption band X, the lower limit was set to 0.9 ppm. In this case, as shown in Figure 2, the point of contact between the right edge of absorption band X and the baseline of the NMR spectrum is approximately around 0.9 ppm.

[0059] Absorption bands X and Y are both absorption bands derived from the α-methyl groups of component (a2), a constituent component of polymer (A). When the units of component (a2) are more continuous (localized) on the molecular chain of polymer (A), and the protons on the α-methyl groups of component (a2) are adjacent to each other, the relative intensity of absorption band X increases and the relative intensity of absorption band Y decreases. On the other hand, when the units of component (a2) are more ubiquitous on the molecular chain of polymer (A), and the protons on their α-methyl groups are not adjacent to each other, the relative intensity of absorption band X decreases and the relative intensity of absorption band Y increases.

[0060] Therefore, the smaller the ratio of the area of ​​absorption band X to the total area of ​​absorption bands X and Y [Xs / (Xs+Ys)], the more ubiquitous the cationic moieties are on the molecular chain of polymer (A).

[0061] The aforementioned ratio [Xs / (Xs+Ys)] is a commercially available １ Using a 1H-NMR analyzer, the polymer (A) １ This can be calculated by measuring the H-NMR spectrum and determining the integral ratios of As and Bs according to the partitioning procedure described above.

[0062] When the ratio of the area of ​​absorbent band X (Xs) to the total area of ​​absorbent band Y (Ys) [Xs / (Xs+Ys)] is 5% or more and less than 20%, foaming of the paper strength enhancer is reduced, and when the paper strength enhancer is added to the slurry and papermaking is performed, it is efficiently dewatered, which reduces drying efficiency and makes it easier to exhibit a high paper strength effect. Similarly, the ratio [Xs / (Xs+Ys)] is preferably 5% or more and 18% or less, and more preferably 5.5% or more and 17% or less.

[0063] Furthermore, regarding other physical properties, the measured potential of an aqueous solution containing polymer (A) with a non-volatile content of 0.1% by weight, at a pH of 6.8 and a temperature of 25°C, is 0 to 300 mV, as measured by a PCD electrometer. This measured potential is obtained by diluting or volatilizing the paper strength enhancer containing polymer (A) with deionized water, etc., so that the non-volatile content of polymer (A) is 0.1% by weight, and adjusting the pH to 6.8 using an acid or base, and then measuring the aqueous solution with a PCD electrometer. Note that this does not necessarily match the measured potential of the paper strength enhancer itself that is actually used.

[0064] If the measurement potential is less than 0 mV, when added to the pulp slurry, the polymer (A) (or paper strength enhancer) is less likely to self-adsorb, resulting in foaming from unadsorbed components and making it difficult to dewater from the pulp slurry. Furthermore, the paper strength effect tends to be reduced. On the other hand, if it exceeds 300 mV, the strong cationic properties of the polymer (or paper strength enhancer) make it easier for the potential of the pulp slurry to become positive, reducing mutual adsorption, resulting in foaming from unadsorbed components and making it difficult to dewater from the pulp slurry. Furthermore, the paper strength effect tends to be reduced. Similarly, the measurement potential is preferably 15 to 220 mV, and more preferably 30 to 185 mV.

[0065] Other properties of polymer (A) include, for example, a weight-average molecular weight which is preferably 1 million to 10 million, more preferably 1.5 million to 7 million, and even more preferably 2 million to 6 million. Here, "weight-average molecular weight" refers to the value obtained by gel permeation chromatography (GPC).

[0066] Furthermore, the viscosity of polymer (A) is preferably 300 to 20,000 mPa·s, more preferably 500 to 15,000 mPa·s, and even more preferably 1,000 to 12,000 mPa·s. Here, "viscosity" refers to the value measured with a B-type viscometer of a solution with a non-volatile content of 20% by weight, which has been pre-adjusted to a temperature of 25°C.

[0067] The paper strength enhancer of the present invention contains polymer (A), and may further contain inorganic acids such as sodium sulfate, hydrochloric acid, sulfuric acid, and phosphoric acid; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; inorganic salts such as potassium sulfate, ammonium sulfate, aluminum sulfate, aluminum chloride, basic aluminum sulfate, basic aluminum chloride, aluminum silicate, polyaluminum chloride, polyaluminum hydroxide, titanium chloride, titanium sulfate, titanium phosphate, iron nitrate, iron chloride, polyferrous chloride, iron sulfate, polyferrous sulfate, iron phosphate, polyferrous silicate, and polyferrous silicate; starches such as oxidized starch, phosphate-esterified starch, urea-phosphate-esterified starch, etherified starch, cross-linked starch, APS-modified starch, enzyme-modified starch, cationized starch, and amphoteric starch; and additives such as polyvinyl alcohol, urea, defoamers, antioxidants, preservatives, and disinfectants.

[0068] The paper of the present invention contains the paper strength enhancer, and methods for producing it include, for example, adding the paper strength enhancer to a raw pulp slurry (hereinafter also referred to as internal addition), spraying it onto the surface of wet paper, or coating it onto the surface of base paper. The paper strength enhancer may be used as is at the non-volatile content concentration described above, but it can also be further diluted with the water described above to adjust the non-volatile content concentration to 0.1 to 10% by weight before use.

[0069] In the case of internal addition into raw pulp slurry, a paper strength agent is added to the pulp slurry and papermaking is carried out. The amount of the paper strength agent used (in terms of non-volatile content of the polymer (A)) is about 0.01 to 4% by weight based on the dry weight of the pulp. Examples of the type of pulp include chemical pulps such as hardwood pulp (LBKP) and softwood pulp (NBKP); mechanical pulps such as groundwood pulp (GP), refiner ground pulp (RGP) and thermomechanical pulp (TMP); and waste paper pulps such as corrugated cardboard waste paper. When internally adding the paper strength agent, other additives may also be added, including aluminum sulfate as a fixing agent, pH adjusters such as sulfuric acid and sodium hydroxide, papermaking chemicals such as sizing agents and wet strength agents, and fillers such as talc, clay, kaolin, titanium dioxide and calcium carbonate.

[0070] In the case of spraying onto the surface of wet paper, the paper strength agent is sprayed onto the surface of one or more layers of wet paper before combining, and then the wet paper layers are combined. The paper strength agent in this case is used after being diluted to a non-volatile content concentration of about 0.1 to 7% by weight. The viscosity after dilution is about 2 to 50 mPa·s at a temperature of 25°C (1% by weight non-volatile content, 25°C), and the amount used (in terms of non-volatile content) is usually 0.05 to 10% by weight based on the total pulp (weight of non-volatile content).

[0071] In the case of coating onto the surface of base paper, the paper strength agent is coated onto the surface of base paper by various known means. Here, the paper strength agent coated onto the surface of the base paper is referred to as "coating liquid". The viscosity of the coating liquid is usually 1 to 50 mPa·s at a temperature of 50°C. As the type of base paper, uncoated paper using wood cellulose fibers as raw material can be used, and examples of coating means include bar coaters, knife coaters, air knife coaters, calenders, gate roll coaters, blade coaters, two-roll size presses and rod metering. The coating amount of the coating liquid (in terms of non-volatile content) is usually 0.001 to 2 g / m ２ , preferably 0.005 to 1 g / m ２ .

[0072] The paper of the present invention can be used in a variety of products, such as coated paper, newsprint, liners, cores, paper tubes, printing and writing paper, form paper, PPC paper, cup paper, inkjet paper, thermal paper, and the like.

[0073] The present invention will be described below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, "parts" and "%" are based on weight unless otherwise specified.

[0074] The following compounds are abbreviated as follows: AM: Acrylamide DM: N,N-dimethylaminoethyl methacrylate DML: Benzyl chloride of N,N-dimethylaminoethyl methacrylate DMC: Methyl chloride of N,N-dimethylaminoethyl methacrylate IA: Itaconic acid AA: Acrylic acid AGA: 2-acrylamido-N-glycolic acid SMAS: Sodium methallyl sulfonate DMAA: N,N-dimethylacrylamide TAF: 1,3,5-triacryloyl-1,3,5-triazine MBAA: N,N'-methylenebisacrylamide DMAEA-Q: Methyl chloride of N,N-dimethylaminoethyl acrylate DMAEA-BQ: Benzyl chloride of N,N-dimethylaminoethyl acrylate APDM: Dimethylaminopropyl acrylamide APS: Ammonium persulfate

[0075] Example 1 A reaction apparatus equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet tube, and three dropping funnels was filled with 308 parts of deionized water. After removing oxygen from the reaction system by passing nitrogen gas through it, the mixture was heated to 90°C. Dropping funnel (1) was filled with 228 parts AM (27.66 mol%), 4 parts DM (0.5 mol%), 12 parts IA (1.8 mol%), 4.4 parts SMAS (0.54 mol%), 2 parts 62.5% sulfuric acid, 0.3 parts DMAA (0.06 mol%), and 123 parts deionized water. The pH was adjusted to around 3.0 with sulfuric acid (monomer mixture (1)). Next, 455 parts (64.53 mol%) of AM, 37 parts (4.5 mol%) of DM, 1.4 parts (0.2 mol%) of IA, 0.5 parts (0.06 mol%) of SMAS, 0.7 parts (0.14 mol%) of DMAA, 0.13 parts (0.01 mol%) of TAF, and 229 parts of deionized water were charged into dropping funnel (2), and the pH was adjusted to around 3.0 with sulfuric acid (monomer mixture (2)). 0.6 parts of APS and 180 parts of deionized water were charged into dropping funnel (3). Then, the in-system catalyst was added dropwise from dropping funnel (3) over approximately 3 hours. In parallel, monomer mixture (1) and monomer mixture (2) from dropping funnels (1) and (2) were added dropwise at a constant flow rate over approximately 3 hours in that order. After the dropwise addition was complete, 0.4 parts of APS and 10 parts of deionized water were added and kept warm for 1 hour. Deionized water was then added to achieve a non-volatile content of 20% to obtain an aqueous solution of polymer (A-1). The molar ratios of all monomer components are shown in Table 1, and the molar ratios of the monomer components added to each monomer mixture are shown in Table 2.

[0076] Examples 2-15 and Comparative Examples 1-5: The compositions and molar ratios shown in Tables 1 and 2 were changed, and the polymers were synthesized in the same manner as in Example 1 to obtain aqueous solutions of polymers (A-2) to (A-15) and polymers (A'-1) to (A'-5) with a non-volatile content of 20%.

[0077] Example 16 A reaction apparatus equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet tube, and dropping funnel was charged with 228 parts AM (27.66 mol%), 4 parts DM (0.5 mol%), 12 parts IA (1.8 mol%), 4.4 parts SMAS (0.54 mol%), 2 parts 62.5% sulfuric acid, 0.3 parts DMAA (0.06 mol%), and 431 parts deionized water. The pH was adjusted to around 3.0 with sulfuric acid, and oxygen in the reaction system was removed by passing nitrogen gas through it (monomer mixture (1)). Separately, 455 parts AM (64.53 mol%), 37 parts DM (4.5 mol%), 1.4 parts IA (0.2 mol%), 0.5 parts SMAS (0.06 mol%), 0.7 parts DMAA (0.14 mol%), 0.13 parts TAF (0.01 mol%), and 229 parts deionized water were charged into a dropping funnel, and the pH was adjusted to around 3.0 with sulfuric acid (monomer mixture (2)). Next, monomer mixture (1) in the reaction apparatus was heated to 60°C, 0.6 parts APS and 10 parts deionized water were charged, and after reaching 90°C due to polymerization heat, monomer mixture (2) in the dropping funnel was added dropwise over 2 hours. After the dropwise addition was complete, 0.4 parts APS and 10 parts deionized water were added and kept warm for 1 hour, and deionized water was added to obtain an aqueous solution of polymer (A-16) with a non-volatile content of 25%.

[0078]

[0079]

[0080] <Weight-average molecular weight> The weight-average molecular weight of polymer (A) was measured by gel permation chromatography (GPC) under the following measurement conditions. The results are shown in Table 3 (the same applies below). (Measurement conditions) Column: One Guard column PWXL and two GMPWXL columns manufactured by Tosoh Corporation Eluent: Phosphate buffer (0.05 mol / L phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) + 0.13 mol / L sodium dihydrogen phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution, pH approximately 2.5) Flow rate: 0.8 ml / min Temperature: 40°C RI detector: Shodex RI-101 manufactured by Showa Denko K.K. MALS detector: DAWN HELEOS-II manufactured by WYATT Measurement sample: Polymer (A) was diluted with the above eluent so that the non-volatile content concentration of polymer (A) was 0.1% before measurement.

[0081] < １ Area ratio [Xs / (Xs+Ys)] determined by H-NMR measurement > 6.7 mg of each polymer (A) and heavy water (D ２ O) Mix 0.8 ml with the mixture to obtain a solution to which 40.23 mg of 3-(trimethylsilyl)-1-propanesulfonate sodium (DSS) and D ２ A sample for measurement was prepared by adding 1 μl of an internal standard solution, which was mixed with 1.0 ml of O, using a microsyringe. Using the obtained sample for measurement, under the following conditions: １ The 1H-NMR spectrum was measured.

[0082] (Measurement conditions) NMR instrument: 400MR Agilent Technologies 400MHz Probe: AutoX PFG probe (5mm) Probe temperature: 70℃ Measurement frequency: 399.75MHz Measurement solvent: Heavy water (D ２ O) Pulse sequence: presaturation Standard parameters used Number of integrations: 128

[0083] <Calculation of signal area ratio [As / (As+Bs)]> Using the analysis software included with the NMR measuring device (product name: "vNMRJ", manufactured by Agilent Technologies) and a computer, the signal areas <Xs> and <Ys> were determined, and the area ratio [Xs / (Xs+Ys)] was calculated.

[0084] <PCD Potential> An aqueous solution of polymer (A) was mixed with deionized water to which the non-volatile content concentration was 0.1%. The pH was then adjusted to 6.8 with a 0.1% sodium hydroxide aqueous solution to obtain a potential measurement sample. After keeping the sample at a constant temperature of 25°C in a constant temperature bath, the PCD potential was measured using a commercially available PCD electrometer (device name: "PCD02", manufactured by MUTEC).

[0085] The aqueous solutions of each polymer (A) were used directly as paper strength enhancers, and the following evaluations were performed.

[0086] <Foaming> A paper strength enhancer was added to deionized water with a non-volatile content concentration of 1%, and 100 g of the mixture was prepared. 40 g of the mixture was measured into a 70 ml glass bottle, and the pH was adjusted to 6.8 with a 1% sodium hydroxide solution. The mixture was kept warm in a constant temperature bath at 40°C to obtain a measurement sample. The sample was shaken by hand for 30 seconds, allowed to stand for 30 seconds, and then the height from the liquid surface to the top of the foam was measured with a ruler.

[0087] <Dehydration Time> Corrugated cardboard waste paper was beaten using a Niagara-type beater, and calcium chloride was added to a pulp slurry prepared in 350 ml of Canadian Standard Freeness (C.S.F.) to adjust the electrical conductivity to 2.0 mS / cm. Aluminum sulfate was added to this slurry at a concentration of 1.0% (non-volatile content) relative to the weight of the non-volatile content of the pulp slurry and stirred for 30 seconds. Then, each of the above paper strength enhancers was added at a concentration of 1.0% relative to the weight of the non-volatile content of the pulp slurry, based on the non-volatile content of polymer (A). The pH of each pulp slurry was adjusted to 6.8. The pulp slurries were placed in a DDA (Dynamic Drainage Analyzer, manufactured by AB Akribi Kemikonsulter) container and dehydrated under reduced pressure while stirring at a rotation speed of 800 rpm, and the dehydration time was measured for each.

[0088] <Papermaking Evaluation> Prepare a pulp slurry with a pH of 6.8 using the same method as above, dewater it using a tappy sheet machine, and weigh 5 kg / cm³. ２ Press for 2 minutes, resulting in a basis weight of 150 g / m². ２ The paper was prepared in the following manner. Next, it was dried in a rotary dryer at 105°C for 4 minutes, and then conditioned for 24 hours under conditions of 23°C and 50% humidity to obtain the finished paper. The specific burst strength of the finished paper was measured by the following method.

[0089] <Electrical conductivity> Measured using a pH / COND METER D-54 (manufactured by Horiba, Ltd.). <Specific burst strength> Using the paper obtained above, the specific burst strength (kPa·m) was measured in accordance with JIS P 8131. ２ The amount (per g) was measured.

[0090]

Claims

1. A polymer (A) comprising (meth)acrylamide (a1), an ethylenically unsaturated monomer having an amino group and an α-methyl group (a2), an ethylenically unsaturated monomer having a carboxyl group (a3), and an ethylenically unsaturated monomer having a sulfonic acid group (a4) as essential components, wherein the polymer (A) １ A paper strength enhancer wherein, in the 1H-NMR spectrum, there are high-field absorption bands X and Y attributed to the α-methyl group of component (a2) in the range of 0.9 ppm to 1.35 ppm, and the ratio of the area of ​​absorption band X (Xs) to the total area of ​​absorption band Y (Ys) [Xs / (Xs+Ys)] is 5% or more and less than 20%, and the measured potential by a PCD voltmeter at a temperature of 25°C of an aqueous solution with pH 6.8 containing the polymer (A) with a non-volatile content of 0.1% by weight is 0 to 300 mV.

2. The paper strength enhancer according to claim 1, further comprising a crosslinkable monomer (a5).

3. Paper containing the paper strength enhancer described in claim 1 or 2.

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