Paper additive, and paper

Abstract

To provide an additive for paper having excellent stability as an aqueous dispersion, paper thickness improving effect, and foam suppression effect in the paper making system.SOLUTION: An additive for paper in the form of an aqueous dispersion of the invention includes: a fatty acid monoalkanolamide (A); a (meth)acrylamide polymer (B) containing (b-1) anionic monomers in a specific proportion; salts (C) consisting of (c -1) polybasic acids, (c -2) alkali metals or the like; and water (D), wherein the mass ratio of (A) to (B) is (A):(B)=97-80:3-20, and a mass ratio of (C) to (D) is (C):(D)=3-25:97-75.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a paper additive excellent in stability as an aqueous dispersion, a paper thickness improving effect, and a foaming suppressing effect in a papermaking system, and paper using the same.

Background Art

[0002] In recent years, due to the deterioration of the raw log supply situation and environmental protection, there is a demand for paper that maintains the conventional quality while reducing the amount of pulp used. However, simply reducing the amount of pulp for the purpose of reducing the weight of paper may cause the paper to become thinner, resulting in a decrease in opacity, and printing may be visible through the back. Therefore, there is a demand for a chemical that can reduce the amount of pulp while maintaining the paper thickness, that is, a chemical that can improve the paper thickness.

[0003] As chemicals for improving paper thickness, reaction products of amide compounds obtained by the reaction of fatty acids and polyalkylene polyamines with epihalohydrin (see, for example, Patent Documents 1 and 2), paper additives containing compounds obtained by urea-crosslinking these amide compounds (see, for example, Patent Document 3), paper thickeners composed of ester reaction products of polyhydric alcohols and fatty acids (see, for example, Patent Document 4), and paper thickeners containing linear fatty acid monoamides as a main component (see, for example, Patent Document 5) are known. However, the paper thickness improving effect is not at a sufficiently satisfactory level, and there are problems such as a large amount of foaming in the papermaking system, poor stability of the aqueous dispersion, the paper becoming slippery, and the sizing effect of the paper being significantly reduced depending on the type of sizing agent used in combination.

[0004] Furthermore, there is known a papermaking paper quality improver (see Patent Document 6) containing a compound having a water separation degree of 4% or more and having a hydrophilic group and a hydrophobic group that bring about all paper quality improvement effects of bulk, whiteness, and opacity, and a water-soluble polymer selected from the group consisting of polyacrylamide-based polymers and cationized starches that satisfy at least one of an average molecular weight of 10 million to 100 million or a viscosity of 1 to 4000 mPa·s in a 1% aqueous solution. However, when used as an aqueous dispersion, there are problems such as an increase in foaming in the papermaking system, an increase in the viscosity of the aqueous dispersion over time, and separation of the aqueous dispersion. Therefore, it is necessary to lower the effective component concentration to obtain a stable aqueous dispersion, which is not preferable.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Disclosure of the Invention

Problems to be Solved by the Invention

[0006] The present invention provides a paper additive excellent in stability as an aqueous dispersion, a paper thickness improvement effect, and a foaming suppression effect in a papermaking system, and paper using the same.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that a fatty acid monoalkanolamide having a specific number of carbon atoms, an acrylamide and / or methacrylamide polymer having a specific composition, and a paper additive containing specific salts are excellent in stability and exhibit excellent paper thickness improvement effect and foam suppression effect when added to a pulp slurry, and have completed the present invention. That is, the present invention is <1> An aqueous dispersion containing the following compound (A), the following (meth)acrylamide polymer (B), the following salts (C), and water (D), wherein the mass ratio of compound (A) to (meth)acrylamide polymer (B) is (A):(B) = 97 to 80:3 to 20, and the mass ratio of salts (C) to water (D) is (C):(D) = 3 to 25:97 to 75, which is a paper additive. Compound (A): A fatty acid monoalkanolamide represented by the following general formula (1). R1-C(=O)NH-R2-OH…(1) R1: An alkyl group or alkenyl group having 7 to 21 carbon atoms, R2: An alkylene group having 2 to 3 carbon atoms. (Meth)acrylamide polymer (B): (b-1) An anionic monomer and (b-2) (meth)acrylamide are contained in a ratio of (b-1):(b-2) = 2 to 30:98 to 70 (mol%), and (b-3) a hydrophobic chain transfer agent is contained in an amount of 0.1 to 3 (mol%) based on the total of (b-1) and (b-2), which is a polymer of monomers. Salts (C): (c-1) A polybasic acid and (c-2) at least one alkaline substance selected from alkali metals, alkaline earth metals, ammonia, alkylamines, alkanolamines, and alkylalkanolamines, which are salts. <2> The paper additive according to <1>, wherein the (b-1) anionic monomer is at least one selected from monomers having a carboxyl group, monomers having a sulfonic acid group, and salts thereof. <3> The polybasic acid in (c-1) is at least one selected from sulfuric acid, phosphoric acid, citric acid, and succinic acid, and (c-2) the alkaline substance is one or more selected from sodium and ammonia. The paper additive according to any one of <1> or <2>. <4> The paper additive according to any one of <1> to <3>, which is a paper thickness improver. <5> Paper containing the paper additive according to any one of <1> to <4>. It is.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a paper additive that is excellent in stability as an aqueous dispersion, has an excellent paper thickness improving effect and a foam suppressing effect in a papermaking system, and can reduce the amount of pulp raw material used when manufacturing paper products.

Best Mode for Carrying Out the Invention

[0009] The paper additive of the present invention contains compound (A), (meth)acrylamide polymer (B), salts (C), and water (D). In the present invention, "(meth)acryl" means "acryl or methacryl".

[0010] Compound (A) of the present invention is mainly composed of a fatty acid monoalkanolamide which is a dehydration condensation reaction product of (a-1) a monovalent fatty acid having 8 to 22 carbon atoms (hereinafter referred to as "monovalent fatty acid (a-1)") and (a-2) a monoalkanolamine having 2 to 3 carbon atoms (hereinafter referred to as "monoalkanolamine (a-2)"). In the structure of compound (A), the long-chain alkyl group or alkenyl group having 7 to 21 carbon atoms, which is a fatty acid residue, is considered to play a role in hydrophobizing pulp fibers. Further, since the hydroxyl group at the terminal of the alkanol group has an affinity for the pulp fiber surface, the hydroxyl group is oriented toward the pulp side and the long-chain alkyl group or alkenyl group is oriented toward the side opposite to the pulp, so that the pulp fiber surface can be hydrophobized more efficiently with a smaller amount, and as a result, an excellent paper thickness improving effect is exhibited.

[0011] As the monovalent fatty acid (a-1) having 8 to 22 carbon atoms, it may be saturated or unsaturated, and may be linear or branched. Specifically, octanoic acid (caprylic acid) having 8 carbon atoms, 2-ethylhexanoic acid, decanoic acid (capric acid) having 10 carbon atoms, dodecanoic acid (lauric acid) having 12 carbon atoms, tetradecanoic acid (myristic acid) having 14 carbon atoms, hexadecanoic acid (palmitic acid) having 16 carbon atoms, octadecanoic acid (stearic acid) having 18 carbon atoms, 16-methylheptadecanoic acid (isostearic acid), cis-9-octadecenoic acid (oleic acid), cis,cis-9,12-octadecadienoic acid (linoleic acid), 9,12,15-octadecatrienoic acid ((9,12,15)-linolenic acid), 6,9,12-octadecatrienoic acid ((6,9,12)-linolenic acid), eicosanoic acid (arachidic acid) having 20 carbon atoms, docosanoic acid (behenic acid) having 22 carbon atoms, and esterified products or acid halides of these fatty acids can be mentioned. Also, as mixed fatty acids and hydrogenated fatty acids, beef tallow fatty acid, coconut fatty acid, palm oil fatty acid, castor oil fatty acid, soybean oil fatty acid, tall oil fatty acid, and their hydrogenated products can be mentioned. Among these, monovalent fatty acids having 12 to 22 carbon atoms are preferable in terms of being industrially easily available and having a more excellent paper thickness improvement effect. More preferably, it is a monovalent fatty acid having a saturated linear alkyl group having 12 to 20 carbon atoms. The monovalent fatty acid (a-1) may be used alone or in combination of two or more.

[0012] Examples of the monoalkanolamine (a-2) having an alkyl group having 2 to 3 carbon atoms include monoethanolamine and monopropanolamine. Among these, monoethanolamine is preferable in terms of being industrially easily available and inexpensive. The monoalkanolamine (a-2) may be used alone or in combination of two or more.

[0013] The compound (A), which is a reaction product of a monovalent fatty acid (a-1) having 8 to 22 carbon atoms and a monoalkanolamine (a-2) having an alkyl group with 2 to 3 carbon atoms, may be produced by any method. For example, there is a method in which the monovalent fatty acid (a-1) and the monoalkanolamine (a-2) are reacted at 100 to 200 °C for 0.5 to 10 hours using a known amidation catalyst as necessary. Other examples include the reaction of a monovalent fatty acid anhydride and the monoalkanolamine (a-2), the reaction of a monovalent fatty acid halide and the monoalkanolamine (a-2), and the reaction of a monovalent fatty acid ester and the monoalkanolamine (a-2).

[0014] In the reaction of the monovalent fatty acid (a-1) and the monoalkanolamine (a-2), in addition to the fatty acid monoalkanolamide formed by the dehydration condensation of the carboxyl group of the monovalent fatty acid (a-1) and the amino group of the monoalkanolamine (a-2), an ester compound, which is a dehydration condensate of the carboxyl group of the monovalent fatty acid (a-1) and the hydroxyl group of the monoalkanolamine (a-2), is formed as a by-product. Furthermore, an amide-ester compound in which both the amino group and the hydroxyl group of the monoalkanolamine (a-2) have undergone a dehydration condensation reaction with the carboxyl group of the monovalent fatty acid (a-1) is also formed as a by-product. In addition, a small amount of the unreacted substances of the monovalent fatty acid (a-1) and the monoalkanolamine (a-2) remains. If these by-products and unreacted substances are contained in a large amount in the compound (A), it may inhibit the paper thickness improvement effect of the compound (A), and may also impair the emulsifying dispersibility and stability of the additive for paper, which is an aqueous dispersion. Therefore, the content of these by-products and unreacted substances is preferably small, preferably 50% by mass or less with respect to the compound (A), and more preferably 20% by mass or less. The mass ratio of the compound (A), the by-products, and the unreacted substances can be calculated by known methods such as size exclusion chromatography and nuclear magnetic resonance method. In the present invention, the by-products and the unreacted substances are included in the parts by mass of the compound (A). When a monovalent fatty acid anhydride, a monovalent fatty acid halide, or a monovalent fatty acid ester is used instead of the monovalent fatty acid (a-1), the corresponding by-products and unreacted substances are also included in the parts by mass of the compound (A).

[0015] (Meth)acrylamide polymer (B) (hereinafter referred to as "polymer (B)") contains an anionic monomer (b-1) and (meth)acrylamide (b-2) in a ratio of (b-1):(b-2) = 2 to 30:98 to 70 (mol%), and is a polymer of monomers containing a hydrophobic chain transfer agent (b-3) in an amount of 0.1 to 3 (mol%) based on the total of (b-1) and (b-2).

[0016] The additive for paper is an aqueous dispersion using water as a medium, and polymer (B) is considered to function as an emulsifying and dispersing agent for compound (A). When the anionic monomer (b-1) is introduced into the polymer chain of polymer (B), it contributes to the stabilization of the aqueous dispersion due to electrostatic repulsion between dispersed particles. Furthermore, when the additive for paper is added to the papermaking system, the additive for paper can be more efficiently fixed on the pulp surface via cationic substances such as sulfate bands, various metal salts present in the papermaking system, and retention aids, and it is considered that the effect of improving paper thickness and the effect of suppressing foaming can be enhanced. Also, when the hydrophobic chain transfer agent (b-3) is introduced into polymer (B) (theoretically mainly introduced at the polymer terminal), polymer (B) adheres more firmly to the particle surface of compound (A) due to the high affinity caused by hydrophobic-hydrophobic interaction with compound (A). This contributes to the emulsifying and dispersing properties of the additive for paper (suppression of the formation of coarse particles and aggregation of particles in the aqueous dispersion during and after emulsification, and suppression of the generation of sediment and floating matter due to aggregation), viscosity stability (storage stability) such as suppression of thickening over time during storage at high temperatures, mechanical stability against shear force during pump feeding, and contributes to the foaming suppression effect by preventing polymer (B) from desorbing from the particle surface. It is considered that the improvement of these stabilities contributes to the improvement of the fixing efficiency of the additive for paper to pulp fibers in the papermaking system and the prevention of contamination of the paper machine.

[0017] The anionic monomer is at least one selected from monomers having a carboxyl group, monomers having a sulfonic acid group, and salts thereof. Examples of the salts of the carboxyl group and the sulfonic acid group include alkali metal salts such as sodium and potassium, ammonium salts, alkylamine salts, etc. Among these, sodium, potassium, and ammonium salts are preferred. Among the monomers having a carboxyl group (hereinafter referred to as "carboxylic acid-based monomers"), monobasic carboxylic acid monomers, dibasic carboxylic acid monomers and their acid anhydrides are preferred. Specifically, monobasic carboxylic acid monomers such as (meth)acrylic acid, maleic anhydride, maleic acid, fumaric acid, itaconic anhydride, itaconic acid, citraconic anhydride, citraconic acid, etc. dibasic carboxylic acid monomers and their acid anhydrides can be exemplified. Among these, acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, maleic acid, fumaric acid are preferred. Specific examples of the monomer having a sulfonic acid group (hereinafter referred to as "sulfonic acid-based monomer") include sulfonic acid-based monomers such as styrene sulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic acid, sulfonylethyl (meth)acrylate, (meth)allyl sulfonic acid, etc. and / or sulfate-based monomers such as sulfate ester of hydroxyethyl (meth)acrylate. Among these, styrene sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, sulfonylethyl methacrylate, methallyl sulfonic acid are preferred.

[0018] (b-1) The anionic monomer can be used alone or in combination of two or more. In the present invention, while the sulfonic acid-based monomers contribute to the dispersion stability compared with the carboxylic acid-based monomers, the carboxylic acid-based monomers are superior to the sulfonic acid-based monomers in terms of the fixing of the pulp surface of the additive for paper, which is an aqueous dispersion. Therefore, it is preferable to use the sulfonic acid-based monomer and the carboxylic acid-based monomer in combination. However, the sulfonic acid-based monomers are preferably less than half the amount of the carboxylic acid-based monomers.

[0019] (b-2) (Meth)acrylamide is acrylamide and / or methacrylamide.

[0020] (b-1) The usage ratio of the anionic monomer to (b-2) (meth)acrylamide needs to be (b-1):(b-2) = 2 to 30:98 to 70 (mol%), and preferably (b-1):(b-2) = 5 to 20:95 to 80 (mol%). By emulsifying and dispersing compound (A) in water with polymer (B) where the usage amount of the (b-1) anionic monomer is in the range of 2 to 30 mol% of the total molar sum of the monomers constituting polymer (B), a paper additive with excellent stability and paper thickness improvement effect can be obtained. When the usage amount of the (b-1) anionic monomer is less than 2 mol%, the ability to emulsify and disperse compound (A) due to insufficient electrostatic repulsion force between particles caused by insufficient anionicity is not sufficiently imparted to polymer (B), resulting in the generation of foreign substances due to aggregation of dispersed particles during the production or storage of the paper additive, or the floating of dispersed particles or thickening of the paper additive itself, leading to a decrease in the paper thickness improvement effect, concerns about the contamination of manufacturing equipment, storage containers, papermaking equipment, and an increase in the pump load during liquid feeding. Also, due to insufficient anionicity, when the paper additive is added to the papermaking system, the amount of salt formation between polymer (B) on the particle surface and (polyvalent) metal derived from sulfate bands will be insufficient, resulting in a decrease in the fixing of the paper additive to the pulp, and insufficient paper thickness improvement effect and foam suppression effect cannot be obtained. Conversely, when the usage amount of the (b-1) anionic monomer is more than 30 mol%, it causes the floating of dispersed particles or thickening of the paper additive itself during the production or storage of the paper additive. In the papermaking system, substances with cationic groups such as polyvalent metal salts derived from polymer (B) and sulfate bands, cationized starch added separately, and dry paper strength agents form excessive salts, causing aggregation etc. in the dispersion of this paper additive, and the paper thickness improvement effect decreases. Furthermore, since the water solubility of polymer (B) increases, it is easy to desorb from the particle surface of compound (A), and the desorbed polymer (B) increases the foaming in the papermaking system, adversely affecting the operability during papermaking.

[0021] (b-3) As the hydrophobic chain transfer agent, specifically, mercaptopropionic acid esters such as 2-ethylhexyl mercaptopropionate and n-octyl mercaptopropionate, thioglycolic acid esters such as 2-ethylhexyl thioglycolate and n-octyl thioglycolate, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan can be mentioned. Also, 2,4-diphenyl-4-methyl-1-pentene, which is an unsaturated dimer of α-methylstyrene, can be used as the hydrophobic chain transfer agent. Among these, mercaptopropionic acid esters and mercaptans are preferred, and 2-ethylhexyl mercaptopropionate, n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-octyl mercaptan are more preferred. These can be used alone or at least two or more kinds can be used. The amount of the hydrophobic chain transfer agent used needs to be 0.1 to 3 mol% based on 100 mol% of the total molar sum of the monomers of (b-1) and (b-2). If it is less than 0.1 mol%, the amount of the hydrophobic group introduced to the end of the polymer (B) is too small, and the adhesion of the polymer (B) to the particle surface of the compound (A) becomes insufficient, impairing the stability of the paper additive. Also, if it exceeds 3 mol%, the polymer (B) is too low in molecular weight, which may impair the protective colloid property of the dispersed particles and deteriorate the emulsifying dispersibility and storage stability of the paper additive.

[0022] Unless it inhibits the effects of the present invention, other monomers can be added as copolymerization components of the polymer (B) within a non-obstructive range in addition to the above (b-1) to (b-3). Examples of other monomers include nonionic monomers, cationic monomers, hydrophilic chain transfer agents, and crosslinking agents.

[0023] As nonionic monomers, there are hydrophilic hydroxyalkyl (meth)acrylates, vinylformamide, polyalkylene glycol (meth)acrylates, methoxypolyethylene glycol (meth)acrylates, etc., and hydrophobic ones such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, normal octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, etc., which are alkyl (meth)acrylates or cycloalkyl (meth)acrylates having an alkyl group or cycloalkyl group with 1 to 20 carbon atoms; other (meth)acrylate esters such as allyl (meth)acrylate and benzyl (meth)acrylate; styrene, α-methylstyrene, vinyltoluene, divinylbenzene, and styrenes having an alkyl group with 1 to 4 carbon atoms on these aromatic rings; vinyl carboxylate esters of carboxylic acids with 1 to 20 carbon atoms such as vinyl acetate, vinyl propionate, and vinyl neodecanoate, etc. These are preferably included in an amount of at most 5 mol% or less, per 100 mol% of the total molar sum of (b-1) and (b-2), either alone or in combination of at least two or more.

[0024] As cationic monomers, specifically, there are aminoalkyl (meth)acrylates, amino-hydroxyalkyl (meth)acrylates, aminoalkyl (meth)acrylamides, vinylimidazole, allylamine, diallylamine, etc., and furthermore, quaternary ammonium salts thereof, etc. These are preferably included in an amount of at most 5 mol% or less, per 100 mol% of the total molar sum of (b-1) and (b-2), either alone or in combination of at least two or more.

[0025] As the hydrophilic chain transfer agent, specifically, 2-mercaptoethanol, mercaptopropanol, mercaptobutanol, mercapto glycol, thioglycerol, cysteamine hydrochloride, mercaptopropionic acid and its salts, thioglycolic acid and its salts, thioacetic acid and its salts, etc. may be mentioned. It is preferable that these are contained at most 3 mol% or less with respect to 100 mol% of the total molar sum of the monomers of (b-1) and (b-2), either alone or at least two or more kinds. If it exceeds 3 mol%, the polymer (B) is excessively reduced in molecular weight, so that the protective colloid property of the dispersed particles is impaired, and the emulsifying dispersibility and storage stability of the additive for paper containing the polymer (B) may be impaired.

[0026] The crosslinking agent is not particularly limited as long as it is a polyfunctional monomer having two or more radical polymerizable functional groups, and known ones can be used. Specifically, polyfunctional (meth)acrylamides such as methylene bisacrylamide, hexanediol diacrylate, tetraethylene glycol diacrylate, hexaethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 1,3,5-triacryloylhexahydro-1,3,5-triazine and other polyfunctional (meth)acrylates, and aromatic vinyl compounds such as divinylbenzene may be mentioned. It is preferable that these are contained at most 5 mol% or less with respect to 100 mol% of the total molar sum of (b-1) and (b-2), either alone or at least two or more kinds. By using a crosslinking agent exceeding 5 mol%, the branched (crosslinked) structure is excessively introduced into the polymer (B), so that the emulsifying dispersibility, storage stability, mechanical stability, and dilution stability of the additive for paper may be impaired.

[0027] As a method for producing the polymer (B), generally, solution polymerization using water as a medium can be employed, and it can be obtained by copolymerizing the monomers. In solution polymerization, in addition to water, solvents such as isopropyl alcohol, ethyl alcohol, and methyl isobutyl ketone can be used alone or in a mixture of two or more. Further, the polymerization initiator used in the polymerization is not particularly limited, and various ones such as persulfates, peroxides, azo compounds, and redox initiators can be used. Further, an acid, an alkali, and a buffer solution can be added as a pH adjuster. The acid is not particularly limited, and various ones such as inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, organic acids such as acetic acid, lactic acid, and citric acid, and acidic salts such as aluminum sulfate and aluminum chloride can be used. The alkali is not particularly limited, and various ones such as sodium hydroxide, potassium hydroxide, ammonia, alkylamine, and alkanolamine can be used. The buffer solution is not particularly limited, and various ones such as phosphate buffer solution, acetate buffer solution, and citrate buffer solution can be used. The acid, alkali, and buffer solution can be used alone or in a combination of two or more. The acid, alkali, and buffer solution used here are not included in the salts (C).

[0028] The mass ratio of the compound (A) to the polymer (B) in the paper additive of the present invention needs to be (A):(B)=97 to 80:3 to 20 as solid content, and among them, 95 to 85:5 to 15 is preferable. When the content of the polymer (B) in the paper additive is less than 3% by mass, the emulsifying and dispersing ability is not sufficient and the mechanical stability is poor. Further, when it is used in excess of 20% by mass, the viscosity of the paper additive increases, and the product solid content has to be lowered to obtain a viscosity that can be pumped, leading to an increase in cost, and further, the storage stability is poor. In addition, an excess polymer (B) that does not contribute to the dispersion of the compound (A) causes foaming in the papermaking system.

[0029] The salts (C) are salts composed of (c-1) a polybasic acid and (c-2) at least one alkaline substance selected from alkali metals, alkaline earth metals, ammonia, alkylamines, alkanolamines, and alkylalkanolamines.

[0030] Salts (C) showed an effect of significantly reducing the increase in viscosity over time during the storage of the additive for paper, which is an aqueous dispersion. Compound (A) of the additive for paper has a hydroxyl group in its structure. Therefore, when compound (A) is used as the dispersed substance in an aqueous dispersion, due to the affinity between the hydroxyl group and water molecules, compound (A) is likely to elute into the aqueous phase, and the viscosity of the aqueous dispersion increases over time and its stability is easily impaired. On the other hand, by dissolving salts (C) in the aqueous phase, it is considered that the elution of compound (A) into the aqueous phase is significantly suppressed, and accordingly, the increase in viscosity over time is also suppressed.

[0031] (c-1) A polybasic acid is an acid that can donate multiple protons to a base in one molecule, and either inorganic acids or organic acids can be used. Examples of inorganic acids include oxoacids such as sulfuric acid, carbonic acid, metasilicic acid (the above are dibasic acids), phosphoric acid (tribasic acid), etc., and polyoxoacids such as polysilicic acid and polyphosphoric acid formed by dehydration condensation of these oxoacids. Examples of organic acids include oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, sebacic acid, malic acid, tartaric acid, glutamic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, phthalic acid, tetrahydrophthalic acid (the above are dibasic acids), 1,2,3-propanetricarboxylic acid, citric acid, aconitic acid, trimellitic acid (the above are tribasic acids), 1,2,3,4-butanetetracarboxylic acid, pyromellitic acid, naphthalenetetracarboxylic acid (the above are tetrabasic acids), etc. Dibasic acids and tribasic acids are preferred in terms of easy availability. Sulfuric acid, phosphoric acid, citric acid, and succinic acid are more preferred because of their excellent storage stability of the additive for paper due to the effect of suppressing the elution of compound (A) into the aqueous phase and their low cost.

[0032] (c-2) An alkaline substance is a substance that forms a salt by exchanging protons with an acid, and examples include alkali metals such as lithium, sodium, and potassium, alkaline earth metals such as magnesium and calcium, alkylamines such as dimethylamine, trimethylamine, monoethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, and diethylethanolamine, alkanolamines, alkylalkanolamines, and ammonia. Since it is commercially available as a salt, it is easily obtainable and inexpensive, and because the solubility of the salt in water is high, sodium, potassium, magnesium, and ammonia are preferred as alkaline substances. Sodium and ammonia are more preferred because of the excellent storage stability of the paper additive due to the elution suppression effect of compound (A) into the aqueous phase and their low cost.

[0033] Salts (C) are preferably those having a solubility in water at 20 °C of 5 g / 100 g-water or more, more preferably 10 g / 100 g-water or more, because the crystals of the salts themselves do not precipitate in the aqueous dispersion and the elution suppression effect of compound (A) into the aqueous phase can be sufficiently exerted. Specifically, sodium sulfate, potassium sulfate, magnesium sulfate, ammonium sulfate, monoethanolamine sulfate salt, triethanolamine sulfate salt, dimethylaminoethanol sulfate salt, disodium hydrogen phosphate, diammonium hydrogen phosphate, tripotassium phosphate, disodium succinate, trisodium citrate, triammonium citrate, and their hydrates can be mentioned. These may be used alone or in combination of two or more. When using the hydrate of the salts (C), the mass excluding the water of hydration is taken as the mass of the salts (C).

[0034] In the production of the aqueous dispersion of the paper additive of the present invention, in order to improve the emulsifying dispersibility and storage stability, known surfactants can be appropriately used. For example, sorbitan fatty acid esters, sugar fatty acid esters, fatty acid polyglycol esters, fatty acid amides, sugar esters, and various polyalkylene oxide type nonionic surfactants, etc., in which the carbon number of the alkyl group and / or alkenyl group is 4 to 20; anionic surfactants such as long-chain alkyl sulfonates, sulfate esters, alkylbenzene sulfonates, and sodium naphthalene sulfonate formalin condensates, in which the carbon number of the alkyl group and / or alkenyl group is 4 to 20; cationic surfactants such as long-chain alkylamine salts, polyoxyalkylene amines, tetraalkyl quaternary ammonium salts, trialkylbenzyl quaternary ammonium salts, alkylimidazolium salts, alkylpyridinium salts, alkylquinolinium salts, alkylphosphonium salts, and alkylsulfonium salts, in which the carbon number of the alkyl group and / or alkenyl group is 4 to 20; and amphoteric surfactants such as various betaine type surfactants. Since the polymer (B) is anionic and the particle surface of the paper additive is negatively charged, nonionic surfactants and anionic surfactants are preferred.

[0035] The above-mentioned surfactant can be used alone or in combination of two or more. When using a surfactant, the amount used is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, based on 100% by mass of the compound (A), in order to suppress foaming and enhance the emulsifying dispersibility. The mass of the surfactant is included in the mass of the water (D).

[0036] The usage amount of salt (C) requires that the mass ratio of salt (C) to water (D) be (C):(D) = 3 to 25:97 to 75. If the mass ratio of salt (C) is less than 3, the effect of suppressing the elution of compound (A) into the aqueous phase is insufficient, and a stable aqueous dispersion cannot be obtained. Also, when the mass ratio of salt (C) is more than 25, the electrostatic repulsion of polymer (B) is insufficient due to the salt, and the emulsifying dispersibility and storage stability may be impaired. Among them, (C):(D) = 10 to 25:90 to 75 is preferable. However, even within the above mass ratio range, it is preferable to use within the range that does not exceed the solubility of salt (C) in water because the stability of the paper additive is good.

[0037] In the present invention, the method for preparing the paper additive comprising the compound (A), the polymer (B), the salts (C) and water (D) is not particularly limited. For example, as described in Japanese Patent Publication No. 54-36242, a solution obtained by previously dissolving the compound (A) in an oil-soluble solvent is mixed with the polymer (B) and water (D), and after homogenizer treatment, the solvent is distilled off to produce a water-in-oil emulsion, i.e., the so-called solvent method. As described in Japanese Patent Publication No. 53-32380, the molten compound (A) is mixed with the polymer (B) and water (D) under high temperature and high pressure, and a water-in-oil emulsion is produced through a homogenizer, i.e., the so-called mechanical method. As described in Japanese Patent Application Laid-Open No. 52-77206, after mixing the molten compound (A) component with the polymer (B) and a part of water, further water (D) is added to form a water-in-oil emulsion, and then reverse water (D) is added to cause a phase transition to a water-in-oil emulsion, i.e., the so-called phase inversion method is used. Also, a mechanical method of forming a water-in-oil emulsion using a high-shear rotary emulsifying and dispersing machine as described in Japanese Patent Application Laid-Open No. 10-226981 is also used. The salts (C) can be added either before or after at least one of the mechanical treatment steps such as the homogenizer and the phase inversion step. However, considering the improvement of the emulsifying and dispersing properties due to the effect of suppressing the elution of the compound (A) into the aqueous phase and the stability of the aqueous dispersion, it is preferably contained at least before the mechanical treatment step and the phase inversion step. And additives to water (D) can be added at least one of before and after the mechanical treatment steps such as the homogenizer and the phase inversion step under the condition that the effects of the additives are not lost.

[0038] Without impairing the effects of the present invention and within the range not affecting the stability during storage, etc., other water-soluble organic solvents, defoamers, thickeners, preservatives, rust inhibitors, the pH adjuster, fillers, antioxidants, fillers, dyes and other various additives may be contained.

[0039] The solid content of the paper additive of the present invention is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 50% by mass or less from the viewpoints of cost and stability.

[0040] In the present invention, the solid content is defined as the percentage of the mass after heating and drying the object to be measured at 150°C for 20 minutes with respect to the mass before heating and drying.

[0041] The viscosity of the paper additive of the present invention is preferably low. A lower viscosity requires less energy for liquid delivery, and when diluted and added to the papermaking system, a uniform diluted solution can be obtained quickly. Preferably, it is 100 mPa·s or less, and more preferably 60 mPa·s or less. The viscosity in the present invention is the measured value by a Brookfield rotational viscometer.

[0042] From the viewpoint of storage stability, the average particle diameter of the paper additive of the present invention is preferably 0.3 to 1.0 μm. The average particle diameter in the present invention is the particle diameter (D50) at which the cumulative volume frequency is 50%, measured by a laser diffraction / scattering particle size distribution measuring device LA-960V2 (manufactured by Horiba, Ltd.).

[0043] The paper additive of the present invention can be used as a paper thickness improver. Depending on the type of paper or paperboard and the desired paper thickness improvement effect, usually, by adding 0.1 to 1.5% by mass of solid content based on the dry mass of the pulp slurry, the desired paper thickness improvement effect can be obtained. It can also be used as a surface treatment agent for paper. In this case, it is applied to the pre-made wet paper or paper by conventional methods such as spraying, dipping, clear coating, and pigment coating.

[0044] The paper containing the additive for paper of the present invention is not particularly limited, and examples include various papers and paperboards. Examples of paper types include recording papers such as PPC paper, inkjet printing paper, laser printer paper, foam paper, thermal transfer paper, thermal recording base paper, and pressure-sensitive recording base paper; photographic printing paper and its base paper; coated base papers such as art paper, cast-coated paper, and high-quality coated paper; packaging papers such as kraft paper and pure white roll paper; household tissue papers such as tissue paper, toilet paper, towel paper, and kitchen paper; other various papers (Western papers) such as notebook paper, book paper, various printing papers, and newsprint; paperboards for paper containers such as manila board, white board, and chip board; paperboards such as liner, core, and gypsum board base paper; paper containers; and pulp molds such as cushioning materials. In addition to paper, modified wood and inorganic building materials can be mentioned, for example, particle board, hard board, insulation board, and rock wool board. Among them, various printing papers and book papers that can improve printing suitability and readability, paperboards and paperboards for paper containers that can improve folding strength, household tissue papers that can give a good touch, and pulp molds that require buffering properties against impact are preferred because the paper thickness improvement effect can impart thickness and flexibility to the paper.

[0045] The paper of the present invention can contain kraft pulp or sulfite pulp, etc., bleached or unbleached chemical pulp, groundwood pulp, mechanical pulp or thermomechanical pulp, etc., bleached or unbleached high-yield pulp, waste newsprint, waste magazines, waste corrugated cardboard or deinked waste paper, etc. as pulp raw materials. Further, a mixture of the above pulp raw materials and synthetic fibers such as polyamide, polyimide, polyester, polyolefin, and polyvinyl alcohol, regenerated cellulose fibers, and cellulose-based fibers other than pulp such as cotton may be contained.

[0046] In manufacturing the paper of the present invention, additives generally used in papermaking, such as fillers, sizing agents, dry paper strength improvers, wet paper strength improvers, yield improvers, drainage improvers, and sulfuric acid bands, may also be used as needed to achieve the physical properties required for each paper type. These may be used alone or in combination of two or more. Further, these may be premixed with the additive for the paper of the present invention and added to the pulp for use, and the mixing method is not particularly limited.

[0047] Examples of the filler include clay, talc, white carbon, titanium oxide, calcium carbonate, etc., and these may be used alone or in combination of two or more.

[0048] Examples of the sizing agent include sizing agents of fatty acid soaps such as sodium stearate, rosin, fortified rosin, and rosin ester sizing agents (hereinafter referred to as "rosin sizing agents"), aqueous emulsions of alkenyl succinic anhydride (hereinafter referred to as "ASA sizing agents"), aqueous emulsions of 2-oxetanone (hereinafter referred to as "AKD sizing agents"), aqueous emulsions of paraffin wax, cationic sizing agents obtained by the reaction of carboxylic acids and polyamines, aqueous emulsions of reaction products of aliphatic oxyacids and aliphatic amines or aliphatic alcohols other than the additive for the paper of the present invention, cationic styrene sizing agents, etc. These may be used alone or in combination of two or more. Among these, the use of rosin sizing agents, ASA sizing agents, and AKD sizing agents, which are generally used frequently, is preferred, and the use of AKD sizing agents is more preferred because the sizing effect may be improved by combining them with the additive for the paper of the present invention.

[0049] Examples of the dry paper strength improver include anionic polyacrylamide, cationic polyacrylamide, amphoteric polyacrylamide, cationized starch, and amphoteric starch, etc., and these may be used alone or in combination of two or more.

[0050] Examples of wet strength improvers include polyamide-epichlorohydrin resins, polyvinylamine, melamine-formaldehyde resins, and urea-formaldehyde resins. These may be used alone or in combination with anionic polyacrylamide.

[0051] Examples of yield improvers include anionic, cationic, or amphoteric high molecular weight polyacrylamide, polyvinylamine, a combination of silica sol and cationized starch, and a combination of bentonite and cationic high molecular weight polyacrylamide. These may be used alone or in combination of two or more.

[0052] Examples of drainage improvers include polyethyleneimine, cationic, amphoteric, or anionic polyacrylamide, polyvinylamine, etc. These may be used alone or in combination of two or more.

[0053] Since the sulfate bond has the effect of increasing the fixing amount of the paper additive in the paper, it is preferably added. It is more preferable to add 0.1 to 2% by mass based on the pulp dry mass. The sulfate bond may be added before, after, or simultaneously with the addition of the paper additive of the present invention.

[0054] Also, surface strength improvers such as starch, polyvinyl alcohol, and acrylamide-based polymers, dyes, coating colors, surface sizing agents, and anti-slip agents may be applied as needed using a size press, a gate roll coater, a blade coater, a calendar, etc. These may be used alone or in combination of two or more.

Examples

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Also, parts and % in the following are all based on mass unless otherwise specified.

[0056] (Synthesis of A) Synthesis Example 1 In a separable flask equipped with a thermometer, a cooling tube, and a stirrer, 275.0 g (1.0 mol) of stearic acid sakura 275 (manufactured by NOF Corporation, a stearic acid / palmitic acid mixture) as the monovalent fatty acid (a-1) and 1.3 g (0.01 mol) of 75% phosphoric acid as the amidation catalyst were added, and the temperature was raised to 145 °C to dissolve the stearic acid. After confirming the dissolution, 67.2 g (1.1 mol) of monoethanolamine as the monoalkanolamine (a-2) was added dropwise, the temperature was raised to 160 °C, and the reaction was carried out for 6 hours while removing the generated water, and 325.2 g of compound (A) M-1 with a solid content of 100% was obtained.

[0057] Synthesis Examples 2 to 5 and Comparative Synthesis Examples 2 to 4 As shown in Table 1, the synthesis was carried out in the same manner as in Synthesis Example 1 except that the type of the monovalent fatty acid (a-1) and the type of the monoalkanolamine (a-2) were changed, and M-2 to M-5 and RM-2 to RM-4, which are compound (A), were obtained.

[0058] Comparative Synthesis Example 1 As the stearic acid amide, which is a reaction product of stearic acid and ammonia, Alflow (registered trademark) S-10 manufactured by NOF Corporation was used as RM-1.

[0059] [Table 1]

[0060] (Synthesis of (B)) Synthesis Example 6 Into a flask equipped with a stirrer, a thermometer, and a nitrogen gas inlet tube, 199.6 g of ion-exchanged water, 367.5 g of isopropyl alcohol (IPA), 62.7 g (12 mol%) of itaconic acid (IA) as an anionic monomer (b-1), 25.0 g (3 mol%) of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 3.2 g (0.5 mol) of sodium methallylsulfonate (SMAS), 482.6 g (84.5 mol%) of a 50% aqueous acrylamide (AAm) solution as (meth)acrylamide (b-2), 4.1 g of normal dodecyl mercaptan (NDM) as a hydrophobic chain transfer agent (0.5 mol% based on the sum of (b-1) and (b-2)) and 4.4 g of 2-ethylhexyl mercaptopropionate (MPAO) (0.5 mol% based on the sum of (b-1) and (b-2)), 3.1 g of mercaptoethanol (MET) as a hydrophilic chain transfer agent (1.0 mol% based on the sum of (b-1) and (b-2)), and 11.1 g of a 25% aqueous sodium hydroxide solution as a pH adjuster were charged under a nitrogen atmosphere with stirring at 25°C. After heating to 65°C, 2.8 g of azobisisobutyronitrile was added as an initiator to start the polymerization reaction, and the reaction was carried out at 80°C for 5 hours. Then, isopropyl alcohol was distilled off, and by cooling to room temperature, 1000 g of polymer (B) P-1 with a solid content of 35% was obtained.

[0061] Synthesis Examples 7 to 22 and Comparative Synthesis Examples 5 to 8 As shown in Table 2, except for changing the type and amount of the anionic monomer (b-1), the amount of acrylamide (AAm) which is acrylamide / and methacrylamide (b-2), the amount and type of the hydrophobic chain transfer agent (b-3), other chain transfer agents, nonionic monomers, hydrophobic monomers, crosslinking agents, and the type and amount of cationic monomers, the synthesis was carried out in the same manner as in Synthesis Example 6 to obtain polymers (B) P-2 to P-17 and RP-1 to RP-4 with a solid content of 35%.

[0062] [Table 2]

[0063] Explanation of the symbols in Table 2 IA: Itaconic acid AA: Acrylic acid MAA: Methacrylic acid AMPS: 2-Acrylamido-2-methylpropanesulfonic acid NaSS: Sodium styrenesulfonate SMAS: Sodium methallylsulfonate AAm: Acrylamide MPAO: 2-Ethylhexyl mercaptopropionate NDM: n-Dodecyl mercaptan tDM: tert-Dodecyl mercaptan MET: Mercaptoethanol HEMA: 2-Hydroxyethyl methacrylate CHMA: Cyclohexyl methacrylate DPA: Dimethylaminopropyl acrylamide HEGDA: Hexaethylene glycol diacrylate ※ Mole % based on the total of (b-1) and (b-2)

[0064] (Manufacture of paper additive) Production Example 1 200.0 g of M-1, which is the compound (A) obtained above, was charged into a four-necked flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 95 °C for heating and dissolution. After confirming the melting, 63.4 g (22.2 g of solid content) of P-1, which is a polymer (B) with a solid content concentration of 35%, 81.7 g of ammonium sulfate, which is a salt (C), 35.0 g of sodium sulfate, and then 119.9 g of ion-exchanged water at 90 °C were gradually added to prepare a coarse dispersion. The prepared coarse dispersion was emulsified using a high-pressure emulsifier (a homogenizer manufactured by Manton Gorin) to obtain a high-temperature emulsion. The emulsion was gradually mixed with 500 g of water at about 10 °C and cooled to obtain an additive E-1 for paper with a solid content of 33.7% and a concentration of compound (A) of 19.8%. The concentration of compound (A) in the additive E-1 for paper was determined by subtracting the solid content of the polymer (B) (2.2%) and the solid content of the salt (C) (11.7%) from the solid content of the additive E-1 for paper. In the additive E-1 for paper, the mass ratio is (A):(B) = 90:10, (C):(D) = 15:85.

[0065] Production Examples 2 to 30 and Comparative Production Examples 1 to 15 As described in Table 3 and Table 5, except for changing the type and amount of the compound (A), the type and amount of the polymer (B), and the type and amount of the salt (C), the production was carried out in the same manner as in Production Example 1 to obtain additives E-2 to E-30 and RE-1 to RE-15 for paper.

[0066] Production Example 31 200.0 g of M-1, which is the compound (A) obtained above, was charged into a four-necked flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 95 °C for heating and dissolution. After confirming the melting, 63.4 g (22.2 g of solid) of P-1, which is the polymer (B), 81.7 g of ammonium sulfate, which is the salt (C), 35.0 g of sodium sulfate, 10.0 g (4.0 g of solid) of Self Flow 120 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), which is a surfactant, and then 109.9 g of ion-exchanged water at 90 °C were added to prepare a crude dispersion. The prepared crude dispersion was emulsified using a high-pressure emulsifier to obtain a high-temperature emulsion. The emulsion was gradually mixed with 500 g of water at about 10 °C and cooled to obtain an additive E-31 for paper with a solid content of 33.9% and a concentration of the compound (A) of 20.0%. The concentration of the compound (A) in the additive E-31 for paper was determined by subtracting the solid content of the polymer (B) (2.2%), the solid content of the salt (C) (11.7%), and the solid content of the surfactant (0.4%) from the solid content of the additive E-31 for paper. In the additive E-31 for paper, the mass ratio is (A):(B) = 90:10, (C):(D) = 15:85.

[0067] Production Example 32 E-32, an additive for paper, was obtained in the same manner as in Production Example 31 except that the type of surfactant was changed as shown in Table 3.

[0068] The solid content, viscosity, average particle diameter, and viscosity after storage for 2 weeks in a constant temperature bath at 36°C (hereinafter referred to as viscosity after 2 weeks at 36°C) of the paper additives E-1 to E-32 obtained in Production Examples 1 to 32 and the paper additives RE-1 to RE-15 for comparative examples obtained in Comparative Production Examples 1 to 15 are shown in Tables 4 and 6. The solid content was calculated as the percentage of the mass after heating and drying for 20 minutes in a dryer at 150°C with respect to the mass before heating. The viscosity was the value measured at 25°C using a Brookfield rotational viscometer, and it can be used if it is 500 mPa·s or less, but if it is higher, it indicates poor fluidity and cannot be used. If the viscosity after 2 weeks at 36°C is 500 mPa·s or less, it indicates good storage stability. The average particle diameter was measured using a laser diffraction / scattering particle size distribution measuring device LA-960V2 (manufactured by Horiba, Ltd.) to measure the particle diameter (D50) at which the cumulative volume frequency is 50%. An average particle diameter of 0.3 to 1.0 μm indicates good emulsification dispersibility and storage stability.

[0069] Note that for the paper additives RE-1, 7, 9 to 15 for comparative examples, a uniform aqueous dispersion could not be obtained due to poor emulsification during production, or the resulting aqueous dispersion had no fluidity. Therefore, the solid content, viscosity, particle diameter, and viscosity after 2 weeks at 36°C were not measured and they are not evaluated as comparative examples.

[0070] [Table 3]

[0071] [Table 4]

[0072] [Table 5]

[0073] [Table 6]

[0074] (Example 1) The hardwood kraft pulp (LBKP) was beaten to a Canadian Standard Freeness of 400 ml, and a pulp slurry with a pulp concentration of 2.5% was prepared. While stirring this pulp slurry, based on the dry mass of the pulp, the above paper additive E-1 was added sequentially at a concentration of 0.4% by solid mass of compound (A), 1.5% by solid mass of aluminum sulfate, 0.5% by solid mass of cationized starch, 0.1% by solid mass of AD1614 (manufactured by Starlight PMC Co., Ltd.) as an AKD sizing agent, and 16% by solid mass of light calcium carbonate to prepare a paper stock. Note that the concentration of compound (A) was calculated as the value obtained by subtracting the solid mass of polymer (B), the solid mass of salt (C), and the solid mass of the additive from the total solid mass of the paper additive E-1. Using this paper stock, a hand-sheet was made on a rectangular sheet machine to obtain a hand-sheet with a basis weight of 80 g / m 2 ². The obtained hand-sheet was conditioned at 23 °C and 50% relative humidity for 24 hours, and then the density, sizing degree, specific volume, and specific volume improvement degree were measured and calculated by the following methods. The value of the specific volume improvement degree is an index of the paper thickness improvement effect, and the higher the value, the higher the paper thickness improvement effect. The results of the specific volume improvement degree and the sizing degree are shown in Table 7.

[0075] Sizing degree... JISP8122 Method for Testing the Sizing Degree of Paper Density... JISP8118 Paper and Paperboard - Test Methods for Thickness and Density Specific volume... The reciprocal of density Specific volume improvement degree... "(Specific volume) / (Specific volume in the case of no paper additive ※) × 100 - 100" ※ Specific volume in Reference Example 1 below Foaming test... The same paper stock as the paper stock before sheet formation in Example 1 above was diluted to a pulp concentration of 0.25% with tap water at pH 7.5 and placed in a cylindrical container. A part of the pulp slurry in the cylindrical container was circulated by a pump and dropped into the container from a height of 1 m continuously for 10 minutes, and the determination was made according to the following criteria based on the ratio of the liquid surface area covered with foam to the entire liquid surface area after 10 minutes. ×: The liquid surface area covered with foam is 50% or more of the whole, and it is easy to foam. △: The liquid surface area covered with foam is more than 10% and less than 50% of the whole, and it foams slightly. ○: The liquid surface area covered by bubbles is less than 10% of the whole, and foaming is suppressed. Regarding foamability, ○ to △ are at a practical level.

[0076] (Examples 2 to 32, Comparative Examples 2 to 6, 8) As shown in Table 7, for the hand-sheet paper obtained in the same manner as in Example 1 except that the type of paper additive was changed, the specific volume improvement degree and sizing degree were measured, and a foaming test was carried out. The results are shown in Table 7.

[0077] (Reference Example 1) For the hand-sheet paper obtained in the same manner as in Example 1 except that no paper additive was added in Example 1, the specific volume and sizing degree were measured, and a foaming test was carried out. The results are shown in Table 7.

[0078]

Table 7

[0079] From the comparison between Production Examples 1 to 5 and Comparative Production Examples 1 to 3, and between Examples 1 to 5 and Comparative Examples 2 to 3 respectively, it can be confirmed that when monoalkanolamine is not used, the emulsifying and dispersing properties of Compound (A) are inferior, and a sufficient paper thickness improvement effect cannot be obtained.

[0080] From the comparison between Production Examples 1 to 5 and Comparative Production Example 4, and between Examples 1 to 5 and Comparative Example 4, it can be confirmed that when the carbon number of the monovalent fatty acid (a-1) is less than 7, the emulsifying property and storage stability are inferior, and a sufficient paper thickness improvement effect cannot be obtained.

[0081] From the comparison between Production Examples 6 to 17 and Comparative Production Example 5, and between Examples 6 to 17 and Comparative Example 5, when the ratio of the anionic monomer (b-1) to the (meth)acrylamide (b-2) is such that the amount of the anionic monomer (b-1) becomes small outside the range of (b-1):(b-2) = 2 to 30:98 to 70 (mol%), it can be confirmed that the electrostatic repulsion decreases, resulting in poor storage stability and causing foaming in the papermaking system.

[0082] From the comparison between Production Examples 6 to 17 and Comparative Production Example 6, and between Examples 6 to 17 and Comparative Example 6, it was confirmed that when the ratio of the (b-1) anionic monomer to the (b-2) (meth)acrylamide is such that the amount of the (b-1) anionic monomer is larger than the range of (b-1):(b-2) = 2 to 30:98 to 70 (mol%), it causes thickening of the paper additive itself during storage and increases foaming in the papermaking system.

[0083] From the comparison between Production Examples 6 to 17 and Comparative Production Example 7, it was confirmed that when the (b-3) hydrophobic chain transfer agent was not used in Polymer (B), the hydrophobicity was insufficient, resulting in a significant deterioration of the emulsifying dispersibility and the inability to obtain an aqueous dispersion.

[0084] From the comparison between Production Examples 6 to 17 and Comparative Production Example 8, and between Examples 6 to 17 and Comparative Example 8, when the ratio of the (b-1) anionic monomer in Polymer (B) is less than the range of (b-1):(b-2) = 2 to 30:98 to 70 (mol%) and a cationic monomer is used instead of the anionic monomer, it was confirmed that Compound (A) is not sufficiently dispersed and stabilized in water, the particles aggregate, and a sufficient paper thickness improvement effect cannot be obtained, causing foaming in the papermaking system.

[0085] From the comparison between Production Examples 22 to 27 and Comparative Production Example 9, between Production Examples 22 to 27 and Comparative Production Example 10, and between Production Examples 22 to 27 and Comparative Production Example 11, it was confirmed that when salts (C) containing no (c-1) polybasic acid and at least one alkaline substance selected from (c-2) alkali metals, alkaline earth metals, ammonia, alkylamines, alkanolamines, and alkylalkanolamines are used, deterioration of the emulsifying property and an increase in the viscosity of the aqueous dispersion occur, and a stable aqueous dispersion cannot be obtained.

[0086] From the comparison between Production Examples 6 to 17 and Comparative Production Example 12, it was confirmed that when the amount of Polymer (B) is less than the range of Compound (A):Polymer (B) = 97 to 80:3 to 20, Compound (A) is not sufficiently dispersed and stabilized in water, and an aqueous dispersion cannot be obtained.

[0087] From the comparison between Production Examples 6 to 17 and Comparative Production Example 13, it can be confirmed that when the amount of Polymer (B) is increased from the range of Compound (A):Polymer (B) = 97 to 80:3 to 20, the viscosity of the aqueous dispersion increases and a stable aqueous dispersion cannot be obtained.

[0088] From the comparison between Production Examples 28 to 30 and Comparative Production Example 14, it can be seen that when the amount of Salts (C) is decreased from the range of the mass ratio of Salts (C) to Water (D) = (C):(D) = 3 to 25:97 to 75, the emulsifying property deteriorates significantly and an aqueous dispersion cannot be obtained.

[0089] From the comparison between Production Examples 28 to 30 and Comparative Production Example 15, it can be seen that when the amount of Salts (C) is increased from the range of the mass ratio of Salts (C) to Water (D) = (C):(D) = 3 to 25:97 to 75, the viscosity of the aqueous dispersion increases due to the high solid content and a stable aqueous dispersion cannot be obtained.

Claims

Claim 1 An aqueous dispersion containing the following compound (A), the following (meth)acrylamide-based polymer (B), the following salts (C), and water (D), wherein the mass ratio of compound (A) to (meth)acrylamide-based polymer (B) is (A):(B) = 97 to 80:3 to 20, and the mass ratio of salts (C) to water (D) is (C):(D) = 3 to 25:97 to 75, which is a paper additive. Compound (A): A fatty acid monoalkanolamide represented by the following general formula (1). R １ -C(=O)NH-R ２ -OH…(1) R １ : An alkyl group or alkenyl group having 7 to 21 carbon atoms, R ２ : An alkylene group having 2 to 3 carbon atoms. (Meth)acrylamide-based polymer (B): A polymer of monomers containing (b-1) an anionic monomer and (b-2) (meth)acrylamide in a ratio of (b-1):(b-2) = 2 to 30:98 to 70 (mol%), and containing (b-3) a hydrophobic chain transfer agent in an amount of 0.1 to 3 mol% based on the total of (b-1) and (b-2). Salts (C): Salts composed of (c-1) a polybasic acid and (c-2) at least one alkaline substance selected from alkali metals, alkaline earth metals, ammonia, alkylamines, alkanolamines, and alkylalkanolamines. Claim 2 The paper additive according to claim 1, wherein (b-1) the anionic monomer is at least one selected from monomers having a carboxyl group, monomers having a sulfonic acid group, and salts thereof. Claim 3 The paper additive according to any one of claims 1 or 2, wherein (c-1) the polybasic acid is at least one selected from sulfuric acid, phosphoric acid, citric acid, and succinic acid, and (c-2) the alkaline substance is one or more selected from sodium and ammonia. Claim 4 The paper additive according to any one of claims 1 to 3, which is a paper thickness increasing agent. Claim 5 A paper containing the paper additive according to any one of claims 1 to 4.

Images