Modifier for inorganic fillers in papermaking

Abstract

To provide a modifier of an inorganic filler for paper making that can produce paper with reduced strength loss while containing inorganic filler.SOLUTION: This invention relates to a modifier of an inorganic filler for paper making containing a polycarboxylic acid copolymer, wherein the polycarboxylic acid copolymer contains a constituent unit 1 and a constituent unit 2 derived from a monomer represented by a specific formula, and wherein the weight ratio of the constituent unit 1 to the constituent unit 2 is 65 / 35 to 99 / 1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a modifier for inorganic fillers for papermaking. [Background technology]

[0002] In general, inorganic fillers are sometimes added to paper made of cellulosic fibers to improve optical properties, primarily whiteness and opacity, which tend to be insufficient with cellulosic fibers alone. In recent years, due to growing environmental awareness and the need to reduce production costs, efforts have been made to reduce the amount of cellulosic fibers used, which are made from wood, and instead increase the amount of fillers used to increase the filler content in paper.

[0003] For example, Patent Document 1 describes a filler having an average particle diameter of 4.0 to 15.0 μm and a BET specific surface area of ​​5.0 to 10 m 2 It has been proposed to use precipitated calcium carbonate consisting of primary particles and / or aggregates thereof having a needle-like and columnar shape of 0.1g / g.

[0004] Patent Document 2 describes paper with a filler added thereto, which contains light calcium carbonate, which is formed by flocculating spindle-shaped primary particles of calcium carbonate, and has a secondary particle diameter of 1 to 10 μm and a BET specific surface area of ​​8 to 20 m. 2 / g, pore volume 1.5 to 3.5 cm 3 / g range of precipitated calcium carbonate has been proposed.

[0005] Furthermore, Patent Document 3 proposes reducing the drying load during paper production by using rosette-type calcium carbonate, which is made by agglomerating primary particles of spindle-shaped calcium carbonate into a burr-like shape, in combination with talc as a filler.

[0006] Furthermore, Patent Document 4 proposes that the use of a reaction product of a compound obtained by adding an alkylene oxide having 2 to 4 carbon atoms to the active hydrogen of a polyalkyleneimine having a weight-average molecular weight of 500 to 10,000 with a higher fatty acid having 12 to 24 carbon atoms and / or an ester compound of a higher fatty acid having 12 to 24 carbon atoms as a paper modifier can impart various added value, such as optical properties and flexibility, while suppressing a significant decrease in paper strength.

[0007] Furthermore, Patent Document 5 proposes that a copolymer obtained by reacting a hydrophobic vinyl monomer such as styrene or a (meth)acrylic acid ester with a carboxyl group-containing vinyl monomer in a weight ratio of 30 / 70 to 90 / 10 is used as a filler modifier for papermaking, thereby imparting an excellent effect of improving opacity and suppressing print-through after printing while maintaining paper strength. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-060692 [Patent Document 2] International Publication No. WO2004 / 108597 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-172287 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-082949 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-332512 Summary of the Invention [Problem to be solved by the invention]

[0009] When the amount of filler added to paper is increased, the optical properties improve, but the strength of the paper, such as tensile strength and tear strength, decreases. This is thought to be because inorganic fillers have poor affinity with pulp fibers, inhibiting hydrogen bonding between the pulp fibers.

[0010] In view of the above circumstances, an object of the present invention is to provide a technique for suppressing a decrease in strength of paper containing an inorganic filler. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that the above problems can be solved by modifying the inorganic filler by adding a specific polycarboxylic acid copolymer. The present invention includes, but is not limited to, the following aspects. [1] A modifier for inorganic fillers for papermaking, containing a polycarboxylic acid copolymer, The polycarboxylic acid copolymer is (1) Constitutional unit 1 derived from a monomer represented by the following formula 1:

[0012] [ka]

[0013] [In the formula, R 1 , R 2 and R 3 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, x represents an integer of 0 to 2, y represents 0 or 1, R 4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, and R 5 O are the same or different and represent an oxyalkylene group having 2 to 18 carbon atoms, and n is the average number of moles of oxyalkylene groups added and represents a number from 1 to 100. (2) Constitutional unit 2 derived from a monomer represented by the following formula 2:

[0014] [ka]

[0015] [In the formula, R 6 , R 7 and R 8are each independently a hydrogen atom, a methyl group, or -(CH2)rCOOM 2 represents M 1 and M 2 are the same or different and represent a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group, or a substituted alkylammonium group, and r is an integer of 0 to 2, where -(CH2)rCOOM 2 -COOM 1 or other -(CH2)rCOOM 2 When an anhydride is formed, the group M 1 and M 2 does not exist] wherein the weight ratio of structural unit 1 to structural unit 2 is 65 / 35 to 99 / 1. [2] The modifier according to [1], wherein the copolymer has a weight average molecular weight (Mw) of 5,000 to 100,000, and a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw / Mn, of 1.0 to 10.0. [3] The modifier according to [1] or [2], which is used in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the inorganic filler. [4] The modifier according to [1] or [2], which is added to an inorganic filler before mixing with pulp. [5] The modifier according to [1] or [2], which is used by adding it to paper stock. [6] The modifier according to [5], wherein the paper stock contains 5 to 50 parts by weight of an inorganic filler per 100 parts by weight of pulp. [Effects of the Invention]

[0016] According to the present invention, it is possible to produce paper that contains an inorganic filler such as precipitated calcium carbonate but that does not experience a decrease in strength. The details of why the present invention provides such excellent effects are not clear, and the present invention is not bound by the following speculation, but it is thought that the copolymer according to the present invention adsorbs to the inorganic filler and also to the pulp fibers, thereby allowing the inorganic particles to be uniformly fixed to the pulp fibers and enhancing interfiber bonding, thereby suppressing the decrease in paper strength that accompanies the internal addition of the inorganic filler. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to a modifier for inorganic fillers for papermaking. By adding the modifier of the present invention to inorganic fillers, it is possible to suppress a decrease in paper strength when the inorganic filler is internally added to paper. Polycarboxylic acid copolymer The modifier according to the present invention comprises a polycarboxylic acid copolymer containing at least the structural unit 1 and structural unit 2 described below. The weight ratio of structural unit 1 to structural unit 2 in the polycarboxylic acid copolymer according to the present invention is 65 / 35 to 99 / 1, preferably 70 / 30 to 97 / 3, more preferably 80 / 20 to 95 / 5, and may be 85 / 15 to 93 / 7. Here, the ratio of each structural unit contained in the copolymer basically corresponds to the charging ratio of each structural unit when synthesizing the copolymer. It is expected that having the structural ratio within this range makes it easier to uniformly disperse the inorganic filler as fine particles.

[0018] From the viewpoints of fluidity and workability, the weight average molecular weight Mw of the copolymer is preferably 5000 to 100000. The lower limit of the weight average molecular weight may be 10000 or more or 15000 or more, and the upper limit of the weight average molecular weight may be 90000 or less or 80000 or less.

[0019] Regarding the molecular weight distribution of the copolymer, Mw / Mn is preferably 1.0 to 10.0, and may be 1.2 to 8.0 or 1.5 to 6.0. Here, the weight average molecular weight and the like can be measured by a known method using gel permeation chromatography (GPC) in terms of polyethylene glycol.

[0020] (Constituent unit 1) The copolymer according to the present invention comprises a structural unit 1 derived from a monomer represented by formula 1.

[0021] [ka]

[0022] where R 1 , R 2 , R 3 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, x represents a number from 0 to 2, y represents 0 or 1, R 5 O's may be the same or different and each represent an oxyalkylene group having 2 to 18 carbon atoms, and n is the average number of moles of oxyalkylene groups added, which is a number from 1 to 100. 4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms.

[0023] R 1 , R 2 , R 3 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. R 5 O's may be the same or different and represent an oxyalkylene group having 2 to 18 carbon atoms. Examples of the oxyalkylene group include an oxyethylene group (ethylene glycol unit), an oxypropylene group (propylene glycol unit), and an oxybutylene group (butylene glycol unit), with an oxyethylene group (ethylene glycol) and an oxypropylene group (propylene glycol) being preferred.

[0024] Here, "same or different" means that the general formula R 5 If multiple Os are included (n is 2 or more), each R 5 This means that the O may be the same oxyalkylene group or different (two or more types of) oxyalkylene groups. 5When multiple O's are contained, examples include a mixture of two or more oxyalkylene groups selected from the group consisting of oxyethylene groups (ethylene glycol units), oxypropylene groups (propylene glycol units), and oxybutylene groups (butylene glycol units).Preferably, an oxyethylene group (ethylene glycol unit) and an oxypropylene group (propylene glycol unit) are mixed, or an oxyethylene group (ethylene glycol unit) and an oxybutylene group (butylene glycol unit) are mixed, and more preferably, an oxyethylene group (ethylene glycol unit) and an oxypropylene group (propylene glycol unit) are mixed.In a mixture of different oxyalkylene groups, the addition of two or more types of oxyalkylene groups may be block-like addition or random addition.

[0025] n is the average number of moles of oxyalkylene groups added, and represents a number from 1 to 100. n is preferably from 1 to 50, more preferably from 1.5 to 40, and even more preferably from 2 to 30. The average number of moles added means the average value of the number of moles of alkylene glycol units added to 1 mole of monomer.

[0026] The copolymer according to the present invention may contain only one type of structural unit 2, or may contain a combination of two or more types. In particular, it preferably contains two types of monomers having different average numbers of moles of oxyalkylene groups added, and more preferably contains a combination of a monomer having an average number of moles of oxyalkylene groups added, n, of 1, and a monomer having an average number of moles of oxyalkylene groups added, n, of more than 1 and 100 or less.

[0027] In a preferred embodiment, when n is 1, for example, R 4 is a hydrogen atom, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, with 2-hydroxyethyl (meth)acrylate being particularly preferred.

[0028] When a monomer in which n is 1 and a monomer in which n is greater than 1 and 10 or less are used in combination, the weight ratio of the two is preferably 1 / 99 to 99 / 1, more preferably 3 / 97 to 50 / 50, and even more preferably 5 / 95 to 30 / 70. This weight ratio corresponds to the weight ratio of the monomers charged when synthesizing the copolymer.

[0029] R 4 represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. The effect of the present invention can be fully achieved if the number of carbon atoms is not too large. 4 is preferably a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, and most preferably a hydrogen atom or a methyl group.

[0030] Examples of the above-mentioned monomer include esters of unsaturated monocarboxylic acids such as (meth)acrylate (hereinafter, "(meth)acrylate" means "acrylate or methacrylate") with (poly)alkylene glycols such as (poly)ethylene glycol, (poly)ethylene (poly)propylene glycol, (poly)ethylene (poly)butylene glycol, methoxy(poly)ethylene glycol, methoxy(poly)ethylene (poly)propylene glycol, and methoxy(poly)ethylene (poly)butylene glycol.

[0031] Specific examples include (poly)alkylene glycol (meth)acrylates such as (poly)ethylene glycol (meth)acrylate, (poly)ethylene (poly)propylene glycol (meth)acrylate, (poly)ethylene (poly)butylene glycol (meth)acrylate, methoxy(poly)ethylene glycol (meth)acrylate, methoxy(poly)ethylene (poly)propylene glycol (meth)acrylate, and methoxy(poly)ethylene (poly)butylene glycol (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate. As the monomer of formula 2, one or a combination of two or more of these may be used, but it is preferable to use a (poly)alkylene glycol (meth)acrylate, and it is more preferable to use a (poly)ethylene glycol (meth)acrylate or a methoxy(poly)ethylene glycol (meth)acrylate. When the monomer is a (poly)alkylene glycol (meth)acrylate, the average number of moles of (poly)alkylene glycol added is preferably 1 to 50. When the monomer has n of 1 and is a (poly)alkylene glycol (meth)acrylate, the average number of moles of (poly)alkylene glycol added in the monomer is preferably 1. Furthermore, when n is greater than 1 and 10 or less and is a (poly)alkylene glycol (meth)acrylate, the average number of moles of (poly)alkylene glycol added in the monomer is preferably greater than 1 and 100 or less, more preferably 1.5 to 50, and even more preferably 2 to 20.

[0032] The above-mentioned monomers can be produced by known methods without any particular limitation, such as esterification of an unsaturated monocarboxylic acid such as (meth)acrylic acid with a (poly)alkylene glycol such as (poly)ethylene glycol, (poly)ethylene (poly)propylene glycol, (poly)ethylene (poly)butylene glycol, methoxy(poly)ethylene glycol, methoxy(poly)ethylene (poly)propylene glycol, or methoxy(poly)ethylene (poly)butylene glycol.

[0033] (Constituent unit 2) The copolymer according to the present invention comprises a structural unit 2 derived from a monomer represented by formula 2.

[0034] [ka]

[0035] where R 6 , R 7 , R 8 are each independently a hydrogen atom, a methyl group, or -(CH2)rCOOM 2 represents -(CH2)rCOOM 2 -COOM 1 or other -(CH2)rCOOM 2 When an anhydride is formed, the group M 1 and M 2 does not exist. M 1 and M 2 are the same or different and represent a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group or a substituted alkylammonium group, and r represents an integer of 0 to 2.

[0036] Examples of the above-mentioned monomers include unsaturated monocarboxylic acid monomers and unsaturated dicarboxylic acid monomers. Examples of the unsaturated monocarboxylic acid monomers include acrylic acid, methacrylic acid, and crotonic acid, as well as their salts (e.g., monovalent metal salts, ammonium salts, and salts with organic amines). Examples of the unsaturated dicarboxylic acid monomers include maleic acid, itaconic acid, citraconic acid, and fumaric acid, as well as their salts (e.g., monovalent metal salts, ammonium salts, and salts with organic amines), and their anhydrides.

[0037] The copolymer according to the present invention may contain only one type of structural unit 2, or may contain two or more types. (Synthesis of copolymer) The copolymer of the present invention can be produced by copolymerizing each of the predetermined monomers by a known method, such as polymerization in a solvent or bulk polymerization.

[0038] Examples of solvents used in polymerization in a solvent include water, lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, aromatic hydrocarbons such as benzene, toluene, and xylene, alicyclic or aliphatic hydrocarbons such as cyclohexane and n-hexane, esters such as ethyl acetate, and ketones such as acetone and methyl ethyl ketone. From the viewpoint of the solubility of the raw material monomers and the resulting copolymer, it is preferable to use one or more solvents selected from the group consisting of water and lower alcohols, and among these, it is more preferable to use water.

[0039] When copolymerization is carried out in a solvent, each monomer and the polymerization initiator may be continuously added dropwise to a reaction vessel, or a mixture of each monomer and the polymerization initiator may be continuously added dropwise to a reaction vessel. Alternatively, a solvent may be charged into a reaction vessel, and a mixture of the monomers and the solvent and a polymerization initiator solution may be continuously added dropwise to the reaction vessel, or some or all of the monomers may be charged into a reaction vessel, and the polymerization initiator may be continuously added dropwise.

[0040] The polymerization initiator that can be used for the copolymerization is not particularly limited. When copolymerization is performed in an aqueous solvent, examples include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; and water-soluble organic peroxides such as t-butyl hydroperoxide. In this case, an accelerator such as sodium bisulfite or Mohr's salt may be used in combination. Furthermore, when copolymerization is performed in a solvent such as a lower alcohol, aromatic hydrocarbon, alicyclic or aliphatic hydrocarbon, ester, or ketone, examples of the polymerization initiator that can be used include peroxides such as benzoyl peroxide and lauryl peroxide; hydroperoxides such as cumene peroxide; and aromatic azo compounds such as azobisisobutyronitrile. In this case, an accelerator such as an amine compound may be used in combination. Furthermore, when copolymerization is performed in a water-lower alcohol mixed solvent, for example, the aforementioned polymerization initiators or combinations of polymerization initiators and accelerators can be appropriately selected and used. The polymerization temperature varies depending on polymerization conditions such as the solvent and polymerization initiator used, but is typically performed in the range of 50 to 120°C.

[0041] In the copolymerization, a chain transfer agent may be used to adjust the molecular weight, if necessary. Examples of chain transfer agents that can be used include known thiol compounds such as mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, octyl thioglycolate, and 2-mercaptoethanesulfonic acid; phosphorous acid, hypophosphorous acid, and salts thereof (e.g., sodium hypophosphite, potassium hypophosphite); sulfurous acid, hydrogen sulfite, dithionous acid, metabisulfite, and salts thereof (e.g., sodium sulfite, potassium sulfite, sodium hydrogen sulfite, potassium hydrogen sulfite, sodium dithionite, potassium dithionite, sodium metabisulfite, potassium metabisulfite); and lower oxides and salts thereof. These may be used alone or in combination. Furthermore, to adjust the molecular weight of the copolymer, a monomer with higher chain transfer properties may be used in addition to the above-mentioned monomers as the monomer for obtaining the copolymer. Examples of monomers with high chain transfer properties include (meth)allylsulfonic acid (salt) monomers. The content of such monomers in the copolymer is usually 20% by weight or less, and preferably 10% by weight or less.

[0042] When copolymerization is performed in an aqueous solvent to obtain a copolymer, the pH during polymerization typically becomes strongly acidic due to the influence of the monomers having unsaturated bonds. However, this can be adjusted to an appropriate pH. If pH adjustment is required during polymerization, the pH can be adjusted using an acidic substance such as phosphoric acid, sulfuric acid, nitric acid, alkyl phosphoric acid, alkyl sulfuric acid, alkyl sulfonic acid, or (alkyl)benzenesulfonic acid. Among these acidic substances, phosphoric acid is preferred due to its pH buffering effect. However, to eliminate the instability of the ester bonds in ester-based monomers, polymerization is preferably performed at a pH of 2 to 7. While there are no particular limitations on the alkaline substance that can be used to adjust the pH, alkaline substances such as NaOH and Ca(OH)2 are commonly used. pH adjustment can be performed on a solution containing the monomers before polymerization, or on a solution containing the copolymer after polymerization. Alternatively, a portion of the alkaline substance can be added before polymerization, followed by polymerization, and then the pH of the solution containing the copolymer can be further adjusted.

[0043] Inorganic filler for paper making The modifier according to the present invention is used together with an inorganic filler for papermaking. The inorganic filler for papermaking is not particularly limited, but examples thereof include calcium carbonate such as heavy calcium carbonate and light calcium carbonate, kaolin such as engineered kaolin, calcined kaolin, and delaminated kaolin, calcium sulfite, gypsum, talc, white carbon, amorphous silica, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and papermaking sludge. The average particle size of the inorganic filler is not particularly limited, but is preferably 0.1 to 10 μm, more preferably 0.5 to 7 μm, and even more preferably 1 to 5 μm.

[0044] In the present invention, the inorganic filler and the copolymer are used in combination, and the amount of the copolymer used is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 15 parts by weight, and even more preferably 1 to 10 parts by weight, per 100 parts by weight of the inorganic filler.

[0045] In the present invention, the ash content of the paper is preferably 3 to 50% by weight, more preferably 5 to 40% by weight, and may be 8 to 30% by weight or 10 to 20% by weight, from the viewpoint of improving the optical properties of the paper, mainly whiteness and opacity. The ash content of the paper can be adjusted by increasing or decreasing the amount of filler blended into the paper stock, taking into account factors such as filler retention.

[0046] In the present invention, paper can be produced by using organic fillers in addition to inorganic fillers such as calcium carbonate. Examples of organic fillers include urea-formalin resin, vinyl chloride resin, polystyrene resin, urea / formalin resin, melamine resin, styrene / butadiene copolymer resin, phenolic resin, and hollow plastic particles. The ratio of inorganic and organic fillers used together is not particularly limited and can be adjusted depending on the quality of the paper.

[0047] As the inorganic filler, calcium carbonate such as precipitated calcium carbonate is particularly preferred. However, the calcium carbonate is not particularly limited as long as it is suitable for papermaking applications, and for example, calcium carbonate in the shape of a needle, column, spindle, sphere, cube, rosette, or the like can be used.

[0048] The precipitated calcium carbonate used in the present invention may be calcite-based or aragonite-based, and may be produced by any method. The average particle size of calcium carbonate is not particularly limited, but is preferably 0.1 to 10 μm, more preferably 0.5 to 7 μm, and even more preferably 1 to 5 μm.

[0049] The amount of calcium carbonate to be blended into the paper stock is preferably 2 to 30% by weight relative to the pulp weight in terms of opacity, etc. The filler content in the paper (ash content in the paper) is preferably 10% by weight or more and 40% by weight or less.

[0050] In the present invention, the amount of calcium carbonate used is not particularly limited. When calcium carbonate is used as an internal filler, it is preferable to use 10 parts by weight or more of calcium carbonate per 100 parts by weight of the internal filler used, more preferably 50 parts by weight or more, and even more preferably 70 parts by weight or more.

[0051] According to the present invention, paper containing an inorganic filler such as calcium carbonate can effectively suppress a decrease in strength. The use of paper in the present invention is not particularly limited, and examples of the paper include various coating base papers, newsprint, high-quality paper, medium-quality paper, electrophotographic transfer paper, inkjet paper, thermal paper, pressure-sensitive paper, kraft paper, pressure-sensitive recording paper, packaging paper, paper containers, cardboard, wallpaper, fiberboard, photographic base paper, impregnation base paper, and flame-retardant paper. In one embodiment, the paper of the present invention is suitable as printing paper for various printing methods such as offset printing and gravure printing.

[0052] The basis weight of the paper according to the present invention is not particularly limited, but is, for example, 30 to 650 g / m 2 The range can be about 35 to 200 g / m 2 , 40~120g / m 2 , 45~80g / m 2 The paper of the present invention may also be made into thick paper such as multi-layer paperboard or card exceeding the above range.

[0053] Pulp for papermaking may be, for example, bleached chemical pulp such as commonly used hardwood bleached kraft pulp (LBKP) or softwood bleached kraft pulp (NBKP), unbleached pulp such as hardwood unbleached kraft pulp (LUKP) or softwood unbleached kraft pulp (NUKP), mechanical pulp such as groundwood pulp (GP), pressure groundwood pulp (PGW), refiner groundwood pulp (RGP), or thermomechanical pulp (TMP), deinked recycled paper pulp (DIP), or broke. Furthermore, one or more types of pulp fiber obtained from non-wood fiber materials such as kenaf, synthetic pulp, or inorganic fiber may also be blended into the base paper. Mechanical pulp and DIP can be bleached as needed, and the degree of bleaching can be adjusted as desired.

[0054] In addition to pulp and fillers, papermaking chemicals may also be used in the paper stock as needed. Examples of internal papermaking chemicals include internal sizing agents, retention aids, drainage aids, paper strength agents, dyes, fluorescent dyes, and bulking agents. Specific examples of internal sizing agents include alkyl ketene dimers, alkenyl succinic anhydride sizing agents, styrene-acrylic sizing agents, higher fatty acid sizing agents, petroleum resin sizing agents, and rosin sizing agents. Specific examples of retention aids, drainage aids, and paper strength agents include polyvalent metal compounds such as aluminum (e.g., aluminum sulfate, aluminum chloride, sodium aluminate, and basic aluminum compounds), various starches, cellulose nanofibers, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and methyl cellulose, polyacrylamides, urea resins, polyamide / polyamine resins, polyethyleneimine, polyamines, polyvinyl alcohol, and polyethylene oxide.

[0055] In the present invention, when the filler is added to the pulp raw material, it is preferable to add the filler while thoroughly stirring the pulp raw material. Examples of the location where the filler is added include the inlet of the machine chest and the suction port of the fan pump.

[0056] The papermaking conditions are not particularly limited, and examples of the papermaking machine include commercial-scale papermaking machines such as a Fourdrinier papermaking machine, a twin-wire papermaking machine, an on-top papermaking machine, a cylinder papermaking machine, and a short-wire papermaking machine, and can be appropriately selected depending on the purpose. Any of the papermaking methods, such as acidic papermaking, neutral papermaking, and weakly alkaline papermaking, can be used, but since calcium carbonate dissolves in the acidic range, when calcium carbonate is added internally, it is desirable to make the paper in a neutral to weakly alkaline range.

[0057] A surface treatment agent may be applied to paper to improve surface strength, water resistance, ink receptivity, etc. The type of surface treatment agent is not particularly limited, but preferred examples include starches such as raw starch, oxidized starch, esterified starch, cationized starch, and self-modified starch produced in a paper mill by thermochemical or enzymatic modification using acetylated tapioca starch as a raw material, as well as modified starches such as aldehyde starch and hydroxyethylated starch. It is also possible to use cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and cellulose nanofibers; modified alcohols such as polyacrylamide, polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, and acetoacetylated polyvinyl alcohol; styrene-butadiene copolymers, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, and polyacrylic esters in combination. Furthermore, to improve sizing properties, it is also possible to use surface sizing agents such as styrene-based sizing agents, olefin-based sizing agents, acrylate-based sizing agents, styrene-acrylic sizing agents, and cationic sizing agents in combination. In the present invention, various auxiliary agents that are typically blended in clear coatings, such as dispersants, thickeners, water-retaining agents, antifoaming agents, water-resistant agents, colorants, and conductive agents, may also be used as needed.

[0058] As a device for applying the surface treatment coating liquid, known size press devices such as two-roll type, three-roll type, gate roll type, and film transfer type can be used. Film transfer types are systems in which a wet coating film is formed on an applicator roll and then transferred to the surface of the base paper, and examples include a transfer roll coater and a rod metering size press coater. Coating may also be performed using a coater (applicator) such as a curtain coater, spray coater, or blade coater.

[0059] These coating devices apply the surface treatment coating liquid to the paper at a rate of 0.1 to 5.0 g / m per side. 2 After application, the surface can be dried with a dryer and finished, but to improve printability, it is preferable to treat it with a calendering device such as a machine calender, soft calender, or shoe calender. The surface treatment liquid may also be applied to both sides.

[0060] The present invention can also provide coated paper having at least one coating layer primarily composed of a pigment and an adhesive. The present invention improves the strength of the paper, resulting in excellent blister resistance and good sizing properties, resulting in coated paper with excellent surface smoothness.

[0061] In one embodiment, a base paper coated with a coating liquid containing a surface treatment agent may be used as the coated base paper for producing pigment coated paper. This surface treatment has the effect of improving the surface strength of the base paper or cleaning foreign matter from the surface of the base paper, thereby suppressing the occurrence of streaks and the like. However, in the case of an on-machine coater in which the base paper is made, a coating layer composed mainly of pigment and adhesive is applied, and then dried, the surface treatment is sometimes omitted to avoid limitations in drying capacity and the risk of paper breakage.

[0062] The coated base paper can also be subjected to a smoothing finish treatment using a machine calender, soft calender, or the like. The pigment used in the coating layer is not particularly limited, and may be one or more pigments commonly used in the field of coated paper, such as heavy calcium carbonate, light calcium carbonate (whether of the present invention or not), calcium sulfite, gypsum, talc, kaolin, engineered kaolin, calcined kaolin, white carbon, amorphous silica, delaminated kaolin, diatomaceous earth, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, inorganic fillers such as recycled inorganic particles from papermaking sludge and deinking froth, and organic fillers such as urea-formalin resin, vinyl chloride resin, polystyrene resin, urea / formalin resin, melamine resin, styrene / butadiene copolymer resin, phenolic resin, and hollow plastic particles. The mixing ratio can be adjusted depending on the paper quality and is not particularly limited.

[0063] The pigment coating solution can use adhesives typically used in the field of coated paper, or various surface treatment agents used in uncoated paper. These adhesives can also be used alone or in combination. The amount of adhesive to be added is not particularly limited, but is usually 1 to 50 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of pigment.

[0064] Furthermore, various auxiliary agents such as colored dyes, colored pigments, fluorescent whitening dyes, thickeners, water retention agents, antioxidants, antiaging agents, conductivity inducers, antifoaming agents, ultraviolet absorbers, dispersants, pH adjusters, mold release agents, water-resistant agents, and water-repellent agents may be appropriately blended as needed.

[0065] The solids concentration of the pigment coating liquid can be selected from the range of 25 to 80% by mass, and in consideration of adjustment of the coating amount and operability, a range of 50 to 70% by mass is preferable. There is no particular restriction on the number of coating layers provided on the coated base paper, whether it is one layer or two or more layers. In the case of multiple layers, they do not all need to be the same, and can be adjusted appropriately depending on the required quality level. The amount of coating in the coating layer is also not particularly restricted, and can be adjusted depending on the white paper quality and printing quality of the coated paper, but is generally 0.5 to 40.0 g / m per side. 2 That's about it.

[0066] In the present invention, various coating devices commonly used in the field of coated paper manufacturing, such as air knife coaters, various blade coaters, gate roll coaters, roll coaters, die coaters, curtain coaters, and spray coaters, can be used as appropriate for the coating method used to provide the coating layer.

[0067] After the pigment coating liquid is applied to the base paper, the coating layer is dried to obtain the coated paper. The drying method can be selected from any of the usual methods, such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer.

[0068] The coated paper thus obtained may be passed through any of various known and commonly used finishing devices, such as a supercalender, gloss calender, soft calender, or matte calender, to give it a finished product. [Example]

[0069] The present invention will be described in detail below using specific examples, but the present invention is not limited to the following specific examples. Unless otherwise specified in this specification, concentrations and the like are based on weight, and numerical ranges include their endpoints.

[0070] Experiment 1: Preparation and evaluation of modifiers 1-1. Sample 1 291 parts of water and 7.5 parts of polyethylene glycol monoallyl ether (average number of ethylene oxide added moles: 10) were added to a glass reactor equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropping device, and the atmosphere in the reactor was replaced with nitrogen while stirring. After heating to 100°C under a nitrogen atmosphere, a monomer aqueous solution containing 3.9 parts of methacrylic acid, 0.072 parts of acrylic acid, 22 parts of methoxypolyethylene glycol methacrylate (average number of ethylene oxide added moles: 25), 36 parts of 2-hydroxypropyl acrylate, and 33.5 parts of water was added dropwise to the reactor over 2 hours, while the temperature was maintained at 100°C. A mixture of 1.2 parts of ammonium persulfate and 44 parts of water was then added dropwise to the reactor over 2 hours. After the addition, the temperature was maintained at 100°C and the reaction was continued for another hour, yielding a 40% copolymer aqueous solution.

[0071] The resulting copolymer was analyzed by gel permeation chromatography (GPC), and found to have a weight average molecular weight of 21000 and Mw / Mn of 2.42. The analysis conditions were as follows: Measuring equipment: Tosoh Columns used: Shodex Column OH-pak SB-806HQ, SB-804HQ, SB-802.5HQ Eluent: 0.05 mM sodium nitrate / acetonitrile 8 / 2 (v / v) Standard substance: polyethylene glycol (manufactured by Tosoh) Detector: Differential refractometer (Tosoh) 1-2. Sample 2 A glass reactor equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropping device was charged with 254 parts of water, and the reactor was purged with nitrogen while stirring. After heating to 100°C under a nitrogen atmosphere, a monomer aqueous solution containing 215 parts of methoxypolyethylene glycol methacrylate (MPEG-MA, average ethylene oxide addition moles: 13.5), 3.1 parts of 3-mercaptoprionic acid, 33 parts of methacrylic acid (MAA), and 42 parts of water was added dropwise over 2 hours while maintaining the temperature at 100°C. At the same time, a mixture of 2.7 parts of ammonium persulfate and 38 parts of water was added dropwise over 2.5 hours. The reaction was continued for another hour while maintaining the temperature at 100°C. The mixture was then cooled to 70°C, neutralized to pH 7 with sodium hydroxide, and water was added simultaneously to obtain a 43% copolymer aqueous solution. Analysis using GPC revealed that the copolymer had a weight-average molecular weight of 12,000 and an Mw / Mn ratio of 1.62.

[0072] 1-3. Sample 3 218 parts of water and 13.9 parts of polyethylene glycol monoallyl ether (average number of moles of ethylene oxide added: 10) were added to a glass reactor equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropping device, and the atmosphere in the reactor was replaced with nitrogen while stirring. After heating to 100°C under a nitrogen atmosphere, a monomer aqueous solution containing 7.2 parts of methacrylic acid, 0.07 parts of acrylic acid, 41 parts of methoxypolyethylene glycol methacrylate (average number of moles of ethylene oxide added: 25), 67.2 parts of 2-hydroxypropyl acrylate, and 43.5 parts of water was added dropwise over 2 hours while maintaining the temperature at 100°C. At the same time, a mixture of 0.01 parts of ammonium persulfate and 37.7 parts of water was added dropwise over 2.5 hours. The temperature was maintained at 100°C and the reaction was continued for another hour, yielding a 30% copolymer aqueous solution. Analysis by GPC revealed that the copolymer had a weight average molecular weight of 73,000 and Mw / Mn of 6.55.

[0073] 1-4. Sample 4 (Comparative Example) A glass reactor equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropping device was charged with 315 parts of water, and the reactor was purged with nitrogen while stirring. After heating to 100°C under a nitrogen atmosphere, a monomer aqueous solution containing 325 parts of 2-hydroxypropyl acrylate and 216 parts of water and a mixture of 2.85 parts of ammonium persulfate and 77 parts of water were each added dropwise to the reactor over 2 hours while maintaining the temperature at 100°C. The reaction was continued for another hour while maintaining the temperature at 100°C, yielding a 40% aqueous polymer solution. Analysis using GPC revealed that the weight-average molecular weight of the polymer was 11,000 and the Mw / Mn ratio was 3.16.

[0074] 1-5. Sample 5 (Comparative Example) A glass reactor equipped with a thermometer, stirrer, reflux device, nitrogen inlet tube, and dropping device was charged with 198 parts of water. The reactor was purged with nitrogen while stirring. The temperature was raised to 100°C under a nitrogen atmosphere. While maintaining the temperature at 100°C, an aqueous monomer solution containing 72 parts of acrylic acid, 70 parts of a 31% NaOH solution, and 54 parts of water was added dropwise over 2 hours. The reaction was continued for another hour while maintaining the temperature at 100°C, yielding a 36% homopolymer solution. Analysis using GPC revealed that the weight-average molecular weight of the polymer was 14,000 and the Mw / Mn ratio was 1.71.

[0075] [Table 1]

[0076] Experiment 2: Production and evaluation of inorganically filled paper An aqueous slurry containing inorganic filler was prepared by adding the polymer synthesized in Experiment 1 as a modifier to light calcium carbonate (average particle size 0.49 μm, acicular light calcium carbonate) produced in-house. The weight ratio of the light calcium carbonate (inorganic filler) to the modifier was 100:1.

[0077] The inorganic filler slurry was added to a pulp slurry containing bleached hardwood kraft pulp (LBKP, CSF: 370 ml) and bleached softwood kraft pulp (NBKP, CSF: 510 ml) in a weight ratio of 90:10. Then, 200 ppm of cationic polyacrylamide (Hakuto, Percoll 3045) and 0.1% of anionic inorganic pigment (Heimo, Heimonite-01) based on the pulp solids were further added and stirred to prepare a paper stock (paper stock solids: approximately 0.55%).

[0078] Next, using this paper stock as a raw material, hand-made paper containing inorganic fillers was produced using a circular hand-made papermaking machine in accordance with JIS P8222 (basis weight: approximately 60 g / m 2 ). The properties of the produced handsheets were measured based on the following criteria. Basis weight: JIS P8124 Paper thickness: JIS P8118 Density: JIS P8118 Ash content: JIS P8251 Bursting strength: JIS P8112 Tear strength: JIS P8116 Number of folding times: JIS P8115 Air permeability: JAPAN TAPPI No.5 Smoothness: JIS P8119 Whiteness: JIS P8148 Opacity: JIS P8149

[0079] [Table 2]

[0080] As is clear from the above results, by adding the modifier of the present invention to the inorganic filler in advance, the decrease in paper strength, such as burst strength index and tear strength index, of the inorganic filler-added paper was suppressed. In particular, when the modifiers of Samples 1 to 3 were added to the inorganic filler, the tear strength index of the paper was significantly improved compared to when no modifier was added (Sample 2-1) or when a homopolymer was added (Sample 2-5). As can be seen from the above results, adding the modifier of the present invention to the inorganic filler not only suppresses the decrease in paper strength, but can also be expected to improve paper strength.

[0081] Experiment 3: Production and evaluation of inorganic filled paper The modifier synthesized in Experiment 1 was added to precipitated calcium carbonate (Okutama Kogyo Co., Ltd., Tamapearl TP121-6S, average particle size: 1.8 μm, spindle-shaped precipitated calcium carbonate) to prepare an aqueous slurry containing an inorganic filler. The weight ratio of the inorganic filler (prepared precipitated calcium carbonate) to the modifier was 100:1.

[0082] Next, the inorganic filler slurry and aluminum sulfate were added to a pulp slurry consisting of 100% bleached hardwood kraft pulp (LBKP, CSF: 360 ml) to prepare a paper stock. The amount of aluminum sulfate added was 0.5% of the total solids content of the pulp slurry.

[0083] This paper stock was used as a raw material to make hand-made paper using a circular hand-made papermaking machine (basis weight: approximately 73 g / m 2 The handsheets were prepared in accordance with JIS P 8222, but the wet paper after dewatering was dried using a laboratory-scale cylinder dryer, rather than by the method prescribed in JIS P 8222 in which the paper was placed in close contact with a metal plate.

[0084] The tear strength index of the paper thus produced was measured in the same manner as in Experiment 2, and it was found that when the modifier according to the present invention was added, the strength of the paper was greatly improved.

[0085] [Table 3]

[0086] Experiment 4: Evaluation of fixation of modifier to inorganic filler The fixation of the modifier of the present invention to inorganic fillers was evaluated. Specifically, an aqueous slurry (20% concentration) was prepared by mixing light calcium carbonate (PC-35, average particle size 50 μm, manufactured by Sankyo Seifun) and the modifier (Sample 1 or 5) in a weight ratio of 200:1. The aqueous slurry was stirred for 5 minutes at 400 rpm using a stirring device (ZZ-1200, manufactured by Tokyo Rikakikai). The stirred aqueous slurry was then centrifuged (15 minutes at 10,000 rpm) using a centrifuge (H-2000B, manufactured by Kokusan).

[0087] The amount of the modifier contained in the supernatant solution after separation was determined using GPC under the above-mentioned conditions, and the amount of the modifier fixed to the precipitated precipitated calcium carbonate was calculated.

[0088] [Table 4]

[0089] When the fixation to inorganic fillers was evaluated, it was revealed that the modifier of the present invention (Sample 1) had significantly better fixation to inorganic particles than Sample 5, which was a comparative example.

Claims

1. A modifier for inorganic fillers for papermaking, comprising a polycarboxylic acid copolymer, The polycarboxylic acid copolymer is (1) Structural unit 1 derived from a monomer represented by the following formula 1: 【Chemical 1】 [In the formula, R １ , R ２ and R ３ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, x represents an integer of 0 to 2, y represents 0 or 1, R ４ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms, R ５ O are the same or different and each represents an oxyalkylene group having 2 to 18 carbon atoms, and n is the average number of moles of oxyalkylene groups added and is a number from 1 to 100. (2) Structural unit 2 derived from a monomer represented by the following formula 2: 【Chemistry 2】 [In the formula, R ６ , R ７ and R ８ are each independently a hydrogen atom, a methyl group, or —(CH ２ ) rCOOM ２ represents M １ and M ２ are the same or different and represent a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group, or a substituted alkylammonium group; r is an integer of 0 to 2; and ２ ) rCOOM ２ Is -COOM １ or other -(CH ２ ) rCOOM ２ When an anhydride is formed, the group M １ and M ２ does not exist] wherein the weight ratio of structural unit 1 to structural unit 2 is 65 / 35 to 99 / 1.

2. The copolymer has a weight average molecular weight (Mw) of 5,000 to 100,000, and a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) Mw / Mn is 1.0 to 10.

0. The modifier according to claim 1.

3. 3. The modifier according to claim 1, which is used in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the inorganic filler.

4. 3. The modifier according to claim 1, which is added to an inorganic filler before mixing with pulp.

5. The modifier according to claim 1 or 2, which is used by being added to paper stock.

6. The modifier according to claim 5, wherein the paper stock contains 5 to 50 parts by weight of an inorganic filler per 100 parts by weight of pulp.

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