Paper strength enhancer and paper

Abstract

To provide a paper-strengthening agent having excellent storage stability and showing good paper strength when formed into a paper.SOLUTION: A paper-strengthening agent is a mixed liquid involving a (meth)acrylamide-based polymer (A) containing (meth)acrylamide (a1), cationic group-bearing polymerizable monomer (a2), anionic group-bearing polymerizable monomer (a3) and cross-linkable monomer (a4) as reactive components, a water-soluble aluminum compound (B), an inorganic acid salt (C) (in the (C) component, those belonging to (B) component are excluded), and an inorganic acid (D). When a viscosity of the mixed liquid initially after its preparation (concentration 15 wt.%, temperature: 25°C) is shown as X1 mPa s, and a viscosity of the mixed liquid after 3-days storage at a temperature of 60°C (concentration 15 wt.%. temperature: 25°C) is shown as X2 mPa s, 30≤X1≤30,000 and 0.8≤X2 / X1≤2 are satisfied.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a paper strength enhancer and paper obtained using the same.

Background Art

[0002] A paper strength enhancer is a chemical used to increase the strength of paper itself. Especially in the paper manufacturing industry, with the progress of closed-loop papermaking systems (such as recycling of waste paper pulp), the strength of the obtained paper is more likely to decrease due to the reduction in the strength of pulp fibers as raw materials, and the importance of paper strength enhancers is increasing.

[0003] By the way, as paper strength enhancers, (meth)acrylamide-based polymers are widely used, and depending on their ionic properties, they are classified into anionic type, cationic type, and amphoteric type. Among these, the mainstream amphoteric type (meth)acrylamide-based polymer is obtained by copolymerizing acrylamide with polymerizable monomers such as cationic monomers and anionic monomers (Patent Document 1).

[0004] When the polymer is added to a pulp slurry in a papermaking system, aluminum sulfate is also added as a fixing agent. However, with the progress of closed-loop papermaking systems, the fixing effect of aluminum sulfate decreases, and there is also a movement in paper mills to reduce the amount of aluminum sulfate added from the perspective of environmental load, which makes it difficult to further exert the paper strength effect of the paper strength enhancer itself. As a solution to this problem, a method of adding a paper strength enhancer obtained by mixing a (meth)acrylamide polymer and a water-soluble aluminum compound such as aluminum sulfate has been known for a long time (Patent Document 2). Such a mixed paper strength enhancer has advantages in, for example, reducing the amount of aluminum sulfate added to the pulp slurry and enhancing the paper strength effect.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] However, a paper strength enhancer containing both a (meth)acrylamide-based polymer and a water-soluble aluminum compound predominantly forms a cross-linked structure in which a plurality of polymers are ionically bonded to aluminum atoms due to the electrostatic interaction between the anionic groups in the polymer and the cationicity of the aluminum atoms (hereinafter referred to as "metal cross-linking"). As a result, there has been a problem in so-called storage stability, which tends to thicken over time.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a paper strength enhancer having excellent storage stability and exhibiting a good paper strength effect on paper.

Means for Solving the Problems

[0008] The present inventor has intensively studied the components contained in the paper strength enhancer, found a solution to the above problems, and completed the present invention. That is, the present invention relates to the following paper strength enhancer and paper.

[0009] 1. A mixed solution containing a (meth)acrylamide-based polymer (A) containing (meth)acrylamide (a1), a polymerizable monomer (a2) having a cationic group, a polymerizable monomer (a3) having an anionic group, and a cross-linkable monomer (a4) as reaction components, a water-soluble aluminum compound (B), an inorganic acid salt (C) (excluding those belonging to the (B) component among the (C) components), and an inorganic acid (D), When the viscosity of the mixed solution immediately after preparation (concentration: 15% by weight, temperature: 25°C) is X1 mPa·s, and the viscosity of the mixed solution after storage at 60°C for 3 days (concentration: 15% by weight, temperature: 25°C) is X2 mPa·s, 30 ≦ X1 ≦ 30,000 and 0.8 ≦ X2 / X1 ≦ 2 and the content of the component (D) is 1 to 12 parts by weight based on 100 parts by weight of the component (A) in terms of solid content weight Paper strength enhancer.

[0010] 2. The molar ratio of the reaction components is 55 to 98 mol% of component (a1), 0.5 to 20 mol% of component (a2), 0.5 to 20 mol% of component (a3), and 0.002 to 2 mol% of component (a4). The paper strength enhancer according to claim 1.

[0011] 3. The paper strength enhancer according to the preceding item 1 or 2, wherein component (B) is aluminum sulfate and / or its hydrate.

[0012] 4. The content of component (B) is 0.3 to 20 parts by weight as the amount of aluminum ions with respect to 100 parts by weight of component (A) in terms of solid content weight. The paper strength enhancer according to any one of the preceding items 1 to 3.

[0013] 5. Component (C) contains one or more selected from the group consisting of sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, potassium sulfate, sodium hydrogen sulfate, and potassium hydrogen sulfate. The paper strength enhancer according to any one of the preceding items 1 to 4.

[0014] 6. The content of component (C) is 1 to 70 parts by weight with respect to 100 parts by weight of component (A) in terms of solid content weight. The paper strength enhancer according to any one of the preceding items 1 to 5.

[0015] 7. Component (D) is sulfuric acid and / or phosphoric acid. The paper strength enhancer according to any one of the preceding items 1 to 6.

[0016] 8. The pH at 25°C in an aqueous solution with a solid content concentration of 1% by weight is 2 to 3.5. The paper strength enhancer according to any one of the preceding items 1 to 7.

[0017] 9. Paper obtained by using the paper strength enhancer according to any one of the preceding items 1 to 8.

Advantages of the Invention

[0018] The paper strength enhancer of the present invention suppresses the increase in viscosity over time and exhibits an excellent paper strength effect on paper.

Embodiments for Carrying Out the Invention

[0019] The paper strength enhancer of the present invention is a mixed solution containing a (meth)acrylamide polymer (A) (hereinafter referred to as component (A)), a water-soluble aluminum compound (B) (hereinafter referred to as component (B)), an inorganic acid salt (C) (excluding those belonging to component (B) among components (C)) (hereinafter referred to as component (C)), and an inorganic acid (D) (hereinafter referred to as component (D)).

[0020] (A) component is a component that exhibits an excellent paper strength effect. In the present invention, it means a polymer containing (meth)acrylamide (a1) (hereinafter referred to as component (a1)), a polymerizable monomer (a2) having a cationic group (hereinafter referred to as component (a2)), a polymerizable monomer (a3) having an anionic group (hereinafter referred to as component (a3)), and a crosslinkable monomer (a4) (hereinafter referred to as component (a4)) as reaction components. Here, the polymerizable monomer refers to a monomer having one or more double bonds and / or carbon-carbon triple bonds in one molecule of the monomer.

[0021] Examples of component (a1) include methacrylamide and acrylamide. These can be used alone or in combination of two.

[0022] Component (a2) is not particularly limited as long as it has a cationic group, and various known ones can be used. For example, polymerizable monomers having a secondary amino group, polymerizable monomers having a tertiary amino group, quaternized salts of these polymerizable monomers, etc. can be mentioned.

[0023] The polymerizable monomer having a secondary amino group is not particularly limited, and examples thereof include diallylamine. The polymerizable monomer having a tertiary amino group is not particularly limited, and examples thereof include (meth)acrylates having a tertiary amino group such as N,N-dimethylaminoethyl (meth)acrylate and N,N-diethylaminoethyl (meth)acrylate; (meth)acrylamides having a tertiary amino group such as N,N-dimethylaminopropyl (meth)acrylamide and N,N-diethylaminopropyl (meth)acrylamide. The quaternized salts of these monomers mean those obtained by reacting the polymerizable monomer having a secondary amino group or the polymerizable monomer having a tertiary amino group with a quaternizing agent. The quaternized salts may be inorganic acid salts such as hydrochlorides and sulfates, or organic acid salts such as acetates. Examples of the quaternizing agent include methyl chloride, benzyl chloride, dimethyl sulfate, epichlorohydrin, etc. These may be used alone or in combination of two or more. Among them, the polymerizable monomer having a tertiary amino group and / or its quaternized salt is preferable, and it is more preferable to contain (meth)acrylate having a tertiary amino group and / or the quaternized salt of the (meth)acrylate. N,N-dimethylaminoethyl (meth)acrylate and the quaternized salt of N,N-dimethylaminoethyl (meth)acrylate are more preferable, and N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl acrylate benzyl chloride, and N,N-dimethylaminoethyl methacrylate benzyl chloride are particularly preferable. Note that "(meth)acrylate" means methacrylate or acrylate.

[0024] (a3) component, as long as it has an anionic group, is not particularly limited, and various known ones can be used. For example, polymerizable monomers having a carboxyl group such as (meth)acrylic acid, itaconic acid, itaconic anhydride, fumaric acid, maleic acid, etc.; polymerizable monomers having a sulfonic acid group such as vinyl sulfonic acid, methallyl sulfonic acid, etc. These (a3) components may be used as salts such as alkali metal salts of sodium, potassium, etc. and ammonium salts. These may be used alone or in combination of two or more. Among them, (meth)acrylic acid, itaconic acid, and sodium methallyl sulfonate are preferred.

[0025] (a4) component is a component for introducing a branched structure into the polymer. The (a4) component is not particularly limited. For example, N-alkyl(meth)acrylamides such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-t-butyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide; N,N'-alkylenebis(meth)acrylamides such as N,N'-methylenebis(meth)acrylamide, N,N'-ethylenebis(meth)acrylamide; crosslinkable monomers having a triallyl group such as triallyl isocyanurate, triallyl trimellitate, triallyl amine, triallyl(meth)acrylamide; triazines having a (meth)acryloyl group such as 1,3,5-triacryloyl-1,3,5-triazine, 1,3,5-triacryloyl hexahydro-1,3,5-triazine, etc. These may be used alone or in combination of two or more. Among them, at least one selected from the group consisting of N,N-dialkyl(meth)acrylamide, N,N'-alkylenebis(meth)acrylamide, and triazine having a (meth)acryloyl group is preferred, and N,N-dimethylacrylamide and N,N'-methylenebisacrylamide are more preferred.

[0026] The amounts of use of the respective reaction components are not particularly limited, but from the viewpoint that the obtained paper exhibits excellent paper strength effects, they are set as follows in terms of molar ratio. · Component (a1): Preferably 55 to 98 mol%, more preferably 77.8 to 93.5 mol% · Component (a2): Preferably 0.5 to 20 mol%, more preferably 3 to 10 mol% · Component (a3): Preferably 0.5 to 20 mol%, more preferably 1 to 10 mol% · Component (a4): Preferably 0.002 to 2 mol%, more preferably 0.004 to 0.5 mol%

[0027] The reaction components may further contain a monomer (a5) other than the components (a1) to (a4) (hereinafter referred to as component (a5)). The component (a5) is not particularly limited. For example, polymerizable monomers having an aromatic ring such as styrene, α-methylstyrene, vinyltoluene; alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate; vinyl carboxylates such as vinyl acetate, vinyl propionate; nitriles such as acrylonitrile; mercaptans such as 2-mercaptoethanol, n-dodecyl mercaptan; alcohols such as ethanol, isopropyl alcohol, n-pentyl alcohol; aromatic compounds such as α-methylstyrene dimer, ethylbenzene, isopropylbenzene, cumene; carbon tetrachloride and the like. These may be used alone or in combination of two or more. Further, the content of the component (a5) is less than 5 mol% in all the constituent monomers.

[0028] In the production of the polymer, for the purpose of adjusting the pH of the monomer solution, suppressing the hydrolysis of the monomer (polymerization stabilization), etc., organic acids such as citric acid, succinic acid, and oxalic acid; inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; additives such as antifoaming agents and antioxidants may be added. These may be used alone or in combination of two or more, and as the content thereof, 15 parts by weight or less, preferably 10 parts by weight or less, is preferable with respect to 100 parts by weight of all constituent monomers.

[0029] Component (A) is not particularly limited and can be obtained by polymerizing a monomer component containing component (a1), component (a2), component (a3), and component (a4), and optionally component (a5) and the additive in a solvent.

[0030] The polymerization method is not particularly limited, and examples thereof include a method using only the dropping polymerization method, or a method combining the simultaneous polymerization method (charging the monomer mixture all at once) and the dropping polymerization method.

[0031] The dropping polymerization method is a method of dropping a monomer mixture into a reaction system charged with a solvent such as water in advance. Examples of the method using only this polymerization method include the following (1) to (3). Note that the dropping may be continuous, or the dropping may be stopped during the dropping, polymerization may be carried out for a certain period of time, and then the dropping may be resumed. (1) A method of dropping a monomer mixture in which all monomer components are mixed (2) A method of separately preparing two or more types of monomer mixtures and then dropping them simultaneously (3) A method of separately preparing two or more types of monomer mixtures and then dropping them in sequence

[0032] Examples of the method combining the simultaneous polymerization method and the dropping polymerization method include the following (4) to (7). (4) A method of separately carrying out simultaneous polymerization of each monomer mixture and then mixing each polymer (5) A method of carrying out simultaneous polymerization of one or more types of monomer mixtures and then dropping the remaining monomer mixtures (6)A method of polymerizing while simultaneously polymerizing two or more types of monomer mixtures and then dropping and polymerizing the remaining monomer mixtures (7)A method of carrying out dropwise polymerization of two or more types of monomer mixtures, adding the remaining monomer mixtures all at once, and then carrying out simultaneous polymerization

[0033] Here, when preparing two or more types of monomer mixtures, it is more preferable to increase the amounts of the (a2) component and the (a3) component in some of the mixtures and sequentially react these mixtures, or to add the (a2) component and the (a3) component at a certain point during the polymerization reaction, etc., and perform an operation such that the concentrations of the (a2) component and the (a3) component involved in the reaction become higher in any of the monomer mixtures.

[0034] Examples of the solvent include water, organic solvents, etc., and these may be used alone or in combination of two or more. The organic solvent is not particularly limited, and examples thereof include alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-octyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, diacetone alcohol; and ethers such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether. Among them, it is usually preferable to use water from the viewpoint of dissolving the (a1) to (a5) components.

[0035] The polymerization initiator is not particularly limited. For example, persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; azo compounds such as 2,2'-azobis(2-amidinopropane) hydrochloride and 2,2'-azobis[2(2-imidazolin-2-yl)propane] hydrochloride; hydrogen peroxide, etc. can be mentioned. These can be used alone or in combination of two or more. Among them, from the viewpoint of allowing solution polymerization to proceed sufficiently, ammonium persulfate, potassium persulfate, and 2,2'-azobis(2-amidinopropane) hydrochloride are preferred. Also, the method of adding the polymerization initiator is not particularly limited, and batch addition, divided addition, continuous dropping, etc. can be appropriately selected. Also, the content of the polymerization initiator is not particularly limited, and it is usually about 0.001 to 5 parts by weight, preferably about 0.01 to 1 part by weight, based on 100 parts by weight of the components (a1) to (a5).

[0036] The polymerization conditions are not particularly limited. For example, the temperature is about 50 to 100 °C and the time is about 1 to 8 hours.

[0037] As the physical properties of the obtained component (A), for example, the weight average molecular weight is usually 500,000 to 7,000,000, preferably 1,000,000 to 6,000,000, from the viewpoints of the fixing property to pulp and the effect of improving paper strength. The "weight average molecular weight" here refers to the value obtained by the gel permeation chromatography (GPC) method.

[0038] Also, the viscosity of the component (A) is usually 500 to 150,000 mPa·s, preferably 1,500 to 100,000 mPa·s. The "viscosity" here refers to the value measured with a B-type viscometer for a solution with a solid content concentration of 15% by weight that has been adjusted to a temperature of 25 °C in advance (the same applies hereinafter).

[0039] (B) component is a water-soluble aluminum compound, which forms a metal crosslink through electrostatic interaction with component (A) and promotes the excellent paper strength effect of paper. Examples of component (B) include aluminum sulfate, aluminum chloride, basic aluminum sulfate, basic aluminum chloride, aluminum silicate, polyaluminum chloride, polyaluminum hydroxide, etc. Note that hydrates can also be used for component (B). These can be used alone or in combination of two or more. Among them, aluminum sulfate, aluminum chloride, and polyaluminum chloride are preferred, and aluminum sulfate is more preferred, in terms of easy availability.

[0040] The content of component (B) is not particularly limited. However, from the perspective that the viscosity of the paper strength enhancer does not increase excessively and an excellent paper strength effect is also shown, the amount of aluminum ions relative to 100 parts by weight of component (A) in terms of solid content weight is preferably 0.3 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, and even more preferably 0.75 to 5 parts by weight.

[0041] (C) component is an inorganic acid salt, which has the function of weakening the electrostatic interaction between component (A) and component (B), and is a component used to exhibit excellent storage stability of the paper strength enhancer. Examples of component (C) include nitrates such as ammonium nitrate, sodium nitrate, potassium nitrate; nitrites such as ammonium nitrite, sodium nitrite, potassium nitrite; hypo-nitrites such as ammonium hypo-nitrite, sodium hypo-nitrite, potassium hypo-nitrite; sulfates such as ammonium sulfate, sodium sulfate, potassium sulfate, ammonium bisulfate, sodium bisulfate, potassium bisulfate; sulfites such as ammonium sulfite, sodium sulfite, potassium sulfite; hypo-sulfites such as ammonium hypo-sulfite, sodium hypo-sulfite, potassium hypo-sulfite; phosphates such as ammonium phosphate, sodium phosphate, potassium phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate; Phosphites such as ammonium phosphite, sodium phosphite, potassium phosphite, diammonium hydrogen phosphite, disodium hydrogen phosphite, dipotassium hydrogen phosphite, ammonium dihydrogen phosphite, sodium dihydrogen phosphite, potassium dihydrogen phosphite; Hypophosphites such as ammonium hypophosphite, sodium hypophosphite, potassium hypophosphite, diammonium hydrogen hypophosphite, disodium hydrogen hypophosphite, dipotassium hydrogen hypophosphite, ammonium dihydrogen hypophosphite, sodium dihydrogen hypophosphite, potassium dihydrogen hypophosphite, etc. are included. These may be used alone or in combination of two or more. In addition, hydrates may be used for inorganic acid salts.

[0042] Among these (C) components, sulfates and / or phosphates are preferred from the viewpoint of weakening the electrostatic interaction between the (A) component and the (B) component and the paper strength enhancer showing excellent storage stability. More preferably, it contains one or more selected from the group consisting of sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, potassium sulfate, sodium hydrogen sulfate and potassium hydrogen sulfate, and even more preferably contains two or more selected from the above group.

[0043] The content of the (C) component is not particularly limited, but from the viewpoint of weakening the electrostatic interaction between the (A) component and the (B) component and the paper strength enhancer showing excellent storage stability, based on the solid content weight, with respect to 100 parts by weight of the (A) component, 1 to 70 parts by weight is preferred, 1 to 50 parts by weight is more preferred, and 1 to 30 parts by weight is even more preferred.

[0044] (D) component is an inorganic acid. When the (D) component is blended, the pH of the paper strength enhancer decreases, and the anion component contained in the paper strength enhancer (for example, derived from the (a3) component in the (A) component) dissociates (for example, R-COOH → R-COO - +H +It becomes difficult to (e.g., etc.). As a result, the electrostatic interaction between the (A) component and the (B) component weakens, and the paper strength enhancer exhibits excellent storage stability. Examples of the (D) component include hydrochloric acid, nitric acid, nitrous acid, hyponitrous acid, sulfuric acid, sulfurous acid, hyposulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, etc. These may be used alone or in combination of two or more. Among them, sulfuric acid and phosphoric acid are preferred from the viewpoint of suppressing the increase in the pH of the paper strength enhancer and enabling the paper strength enhancer to exhibit excellent storage stability.

[0045] The content of the (D) component is not particularly limited, but in addition to adjusting the pH of the paper strength enhancer, from the viewpoint of suppressing the increase in its pH and enabling the paper strength enhancer to exhibit excellent storage stability, based on the solid content weight, with respect to 100 parts by weight of the (A) component, 1 ~12 parts by weight is more preferable, and 1~10 parts by weight is even more preferable.

[0046] The paper strength enhancer of the present invention may further contain organic acids such as citric acid, succinic acid, and oxalic acid; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; and additives such as urea, polysaccharides (e.g., starch), defoamers, antioxidants, polymerization inhibitors, and preservatives.

[0047] The paper strength enhancer of the present invention can be obtained by mixing the (A) component, the (B) component, the (C) component, and the (D) component, and optionally the above additives, at room temperature. Water may also be added for dilution. Regarding the (A) component, two or more polymers produced under different compositions and conditions such as the type and / or amount of use of the monomer may be mixed, or those previously diluted with water may be used. Also, these mixing methods and mixing orders are not particularly limited.

[0048] When the viscosity of the paper strength enhancer obtained as described above is X1 mPa·s for the mixed solution immediately after preparation (concentration: 15% by weight, temperature: 25°C), and the viscosity of the mixed solution after storage at 60°C for 3 days is X2 mPa·s (concentration: 15% by weight, temperature: 25°C), 30 ≤ X1 ≤ 30,000 and 0.8 ≤ X2 / X1 ≤ 2. Here, "immediately after preparation" means within 2 hours after the preparation is completed in order to stabilize the temperature of the obtained paper strength enhancer at 25°C.

[0049] (Regarding viscosity X1) If the viscosity X1 is less than 30 mPa·s, the paper strength enhancer will dissolve in a large amount of water in the papermaking system and will fall off during dehydration, making it difficult to exhibit the paper strength effect of the paper. Also, if it exceeds 30,000 mPa·s, it will be difficult to mix uniformly when the paper strength enhancer is diluted with a solvent such as water, or it will be difficult to pump out the paper strength enhancer with a pump or the like during papermaking, and the desired amount of the paper strength enhancer will not be added to the pulp slurry. As a result, the paper strength effect of the paper is likely to deteriorate in terms of operation. Also, from the same point of view, for viscosity X1, 100 ≤ X1 ≤ 25,000 is preferable, and 300 ≤ X1 ≤ 20,000 is more preferable.

[0050] (Regarding X2 / X1) X2 / X1 is an index of the storage stability of the paper strength enhancer. If X2 / X1 exceeds 2, the viscosity will continue to increase over time, making it impossible to add the paper strength enhancer stored for a long time to the pulp slurry. Also, from the same point of view, for the viscosity X2 / X1, 0.8 ≤ X2 / X1 ≤ 1.8 is preferable, and 0.8 ≤ X2 / X1 ≤ 1.5 is more preferable.

[0051] As other physical properties of the paper strength enhancer of the present invention, from the point of maintaining excellent storage stability, the pH at 25°C in an aqueous solution with a solid content concentration of 1% by weight is preferably 2 to 3.5, more preferably 2 to 3, and still more preferably 2 to 2.5.

[0052] The paper of the present invention is obtained by using the above paper strength enhancer. As its manufacturing method, for example, adding the paper strength enhancer into the raw pulp slurry (hereinafter also referred to as internal addition), or coating it on the surface of the base paper, etc. can be mentioned. The paper strength enhancer is preferably diluted with water and adjusted so that its solid content concentration becomes 0.1 to 2.0% by weight.

[0053] When adding it internally into the raw pulp slurry, the paper strength enhancer is added to the pulp slurry and then papermaking is carried out. The usage amount of the paper strength enhancer (in terms of the solid content conversion of component (A)) is not particularly limited, but it is about 0.01 to 4% by weight based on the dry weight of the pulp. Also, the type of pulp is not particularly limited, and examples include chemical pulps such as hardwood pulp (LBKP) and softwood pulp (NBKP); mechanical pulps such as groundwood pulp (GP), refiner ground pulp (RGP), and thermomechanical pulp (TMP); wastepaper pulps such as corrugated wastepaper, etc. When adding the paper strength agent solution internally, in addition, as a fixing agent, pH adjusters such as aluminum sulfate, sulfuric acid, and sodium hydroxide; papermaking chemicals such as sizing agents and wet strength agents; fillers such as talc, clay, kaolin, titanium dioxide, and calcium carbonate can be added.

[0054] When coating on the surface of the base paper, the paper strength enhancer is coated on the surface of the base paper by various known means. Here, the paper strength enhancer coated on the surface of the above base paper is called a "coating liquid". The viscosity of the coating liquid is usually 1 to 40 mPa·s at a temperature of 50°C. As the type of the base paper, uncoated paper made from wood cellulose fibers can be used, and the coating means is not particularly limited. Examples include bar coater, knife coater, air knife coater, calendar, gate roll coater, blade coater, two-roll size press, rod metering, etc. Also, the coating amount (in terms of solid content conversion) of the coating liquid is not particularly limited, but it is usually 0.001 to 2 g / m 2 degree, preferably 0.005 to 1 g / m 2 degree.

[0055] The paper of the present invention is used for various products, such as base paper for coating, newsprint, liner, core, paper tube, printing and writing paper, foam paper, PPC paper, base paper for cup, inkjet paper, thermal paper, etc.

Example

[0056] The present invention will be described below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, "parts" and "%" are based on weight unless otherwise specified.

[0057] The following compounds are represented by abbreviations. AM: Acrylamide DM: N,N-Dimethylaminoethyl methacrylate DML: N,N-Dimethylaminoethyl methacrylate benzyl chloride IA: Itaconic acid AA: Acrylic acid SMAS: Sodium methallyl sulfonate DMAA: N,N-Dimethylacrylamide MBAA: N,N’-Methylenebisacrylamide TAF: 1,3,5-Triacryloylhexahydro-1,3,5-triazine APS: Ammonium persulfate

[0058] <Weight average molecular weight of component (A)> The weight average molecular weight of component (A) was measured by gel permeation chromatography (GPC) under the following measurement conditions. Column: One guard column PWXL and two GMPWXL columns manufactured by Tosoh Corporation Eluent: Phosphate buffer (0.05 mol / L phosphoric acid (manufactured by FUJIFILM Wako Pure Chemical Corporation) + 0.13 mol / L sodium dihydrogen phosphate (manufactured by FUJIFILM Wako Pure Chemical Corporation) aqueous solution, pH about 2.5) Flow rate: 0.8 ml / min Temperature: 40°C RI detector: Shodex RI-101 manufactured by Showa Denko K.K. MALS detector: DAWN HELEOS-II manufactured by Wyatt Measurement sample: Diluted with the above eluent so that the concentration of the polymer was 0.1% and then measured.

[0059] <Viscosity of component (A) and paper strength enhancer> Using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), the viscosities of component (A) adjusted to a temperature of 25°C and the paper strength enhancer were measured.

[0060] <ph> Using a commercially available measuring instrument (product name: "pH METER F-14", manufactured by Horiba, Ltd.), the pH of the sample at 25°C in an aqueous solution of the paper strength enhancer with a concentration of 1% was measured.

[0061] Production Example 1 162 parts of ion-exchanged water were placed in a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas inlet tube, and two dropping funnels. After removing the oxygen in the reaction system through nitrogen gas, the mixture was heated to 90°C. 512 parts of 50% AM (92.5 mol%), 30.6 parts of DM (5 mol%), 10.1 parts of IA (2 mol%), 2.5 parts of SMAS (0.4 mol%), 15 parts of 62.5% sulfuric acid, 0.4 parts of DMAA (0.1 mol%), and 286 parts of ion-exchanged water were charged into dropping funnel (1), and the pH was adjusted to around 3.0 with sulfuric acid (monomer mixture). 0.3 parts of APS and 180 parts of ion-exchanged water were charged into dropping funnel (2). Next, the catalyst in dropping funnel (2) was dropped into the system over about 3 hours. In parallel, the monomer mixture in dropping funnel (1) was dropped at a constant flow rate over about 3 hours. After the dropping was completed, 0.6 parts of APS and 10 parts of ion-exchanged water were added and kept warm for 1 hour, and then 853 parts of ion-exchanged water were added to obtain an aqueous solution of component (A-1) with a solid content concentration of 15%. The weight average molecular weight and viscosity of component (A-1) are shown in Table 1 (the same applies hereinafter).

[0062] Production Examples 2 to 17, Comparative Production Examples 1 to 3 With the compositions shown in Table 1, synthesis was carried out in the same manner as in Production Example 1, and aqueous solutions of component (A) with a solid content concentration of 15% were obtained respectively.

[0063]

Table 1

[0064] Example 1 667 parts (100 parts of solid content) of an aqueous solution of component (A-1), 17.5 parts of aluminum sulfate hexadecahydrate (weight conversion of aluminum ions: 1.5 parts), 1.05 parts of sodium dihydrogen phosphate hydrate, 10 parts of sodium sulfate, 0.70 parts of phosphoric acid, and 2.25 parts (1.4 parts of solid content) of a sulfuric acid aqueous solution with a solid content concentration of 62.5% were mixed at room temperature for 15 minutes, and then ion-exchanged water was added to adjust the solid content concentration to 15% and mixed to obtain a paper strength enhancer. The viscosity X1 (mPa·s) and pH of the paper strength enhancer are shown in Table 2 (the same applies hereinafter).

[0065] Examples 2 to 7, 9 to 27, Comparative Examples 1 to 9 Using the compositions shown in Table 2, the same procedure as in Example 1 was carried out to obtain paper strength enhancers with a solid content concentration of 15% respectively. Note that the paper strength enhancers of Comparative Examples 4 and 5 had a high viscosity immediately after synthesis, and the paper strength enhancer of Comparative Example 7 had a low molecular weight, so they were not used for the following evaluations.

[0066] Example 8 667 parts (100 parts of solid content) of an aqueous solution of component (A-1), 94.4 parts of an aqueous solution of polyaluminum chloride (weight conversion of aluminum ions: 5.0 parts), 2.1 parts of sodium dihydrogen phosphate hydrate, 30 parts of sodium sulfate, 1.4 parts of phosphoric acid, and 13.8 parts (8.6 parts of solid content) of a sulfuric acid aqueous solution with a solid content concentration of 62.5% were mixed at room temperature for 15 minutes, and then ion-exchanged water was added to adjust the solid content concentration to 15% and mixed to obtain a paper strength enhancer.

[0067] Example 28 333 parts (50 parts of solid content) of an aqueous solution of component (A-2), 333 parts (50 parts of solid content) of an aqueous solution of component (A-3), 17.5 parts of aluminum sulfate hexadecahydrate (weight conversion of aluminum ions: 1.5 parts), 1.05 parts of sodium dihydrogen phosphate hydrate, 10 parts of sodium sulfate, 0.7 parts of phosphoric acid, and 2.25 parts (1.4 parts of solid content) of a sulfuric acid aqueous solution with a solid content concentration of 62.5% were mixed at room temperature for 10 minutes, and then ion-exchanged water was added to adjust the solid content concentration to 15% and mixed to obtain a paper strength enhancer.

[0068] <Storage Stability> Each paper strength enhancer was allowed to stand in a constant temperature machine at 60 °C for 3 days. After adjusting the temperature to 25 °C, the viscosity of each paper strength enhancer was measured, and the value was designated as X2 (mPa·s), and X2 / X1 was calculated. The results are shown in Table 2.

[0069] <Paper making evaluation> Each paper strength enhancer (A) shown in Table 2 was diluted by adding ion-exchanged water so that the solid content concentration became 1.0%. Then, the following paper making evaluation was carried out. Note that the paper strength enhancers (Comparative Examples 3, 6, and 8) in which X2 / X1 exceeded 2 in the above storage stability test were not evaluated.

[0070] The corrugated waste paper was beaten in a Niagara-type beater, calcium chloride was added to the pulp slurry adjusted to Canadian Standard Freeness (C.S.F) of 350 ml, and the electrical conductivity was adjusted to 4.0 mS / cm. After adding 0.5% by solid content of aluminum sulfate to this slurry liquid based on the pulp slurry solid content weight, the paper strength enhancer of Example 1 was added in an amount such that the solid content of the (A) component became 0.5% based on the pulp slurry solid content weight. The pH of each pulp slurry was adjusted to 6.5. It was dehydrated with a TAPPI sheet machine and pressed at 5 kg / cm 2 for 2 minutes to make paper with a basis weight of 150 g / m 2 Next, it was dried at 105 °C for 4 minutes with a rotary dryer, conditioned for 24 hours under the conditions of a temperature of 23 °C and a humidity of 50%, and then the burst strength was measured. The same evaluation was also carried out for the paper strength enhancers of Examples 2 to 24 and Comparative Examples 1 to 2. Note that the electrical conductivity, water filtration amount, and burst strength were measured by the following methods. The results are shown in Table 2.

[0071] <Electrical conductivity> It was measured using a pH / COND METER D-54 (manufactured by Horiba, Ltd.).

[0072] <Water filtration amount> It was measured in accordance with JIS P 8121 using Canadian Standard Freeness (C.S.F).

[0073] <Specific burst strength> Using the paper obtained above, in accordance with JIS P 8131, the specific bursting strength (kPa·m 2 / g) was measured.

[0074] [Table 2]

[0075] ※1: Indicated by the parts by weight of aluminum ions with respect to 100 parts by weight (solid content) of component (A). ※2: Indicated by the parts by weight of component (C) and component (D) with respect to 100 parts by weight (solid content) of component (A).< / ph>

Claims

1. A sizing agent for paper, which is a mixed solution containing a (meth)acrylamide-based polymer (A) containing (meth)acrylamide (a1), a polymerizable monomer (a2) having a cationic group, a polymerizable monomer (a3) having an anionic group, and a crosslinkable monomer (a4) as reaction components, a water-soluble aluminum compound (B), an inorganic acid salt (C) (excluding those belonging to the component (B)), and an inorganic acid (D), Let the viscosity of the mixed solution immediately after preparation (solid content concentration: 15% by weight, temperature: 25°C) be X １ mPa·s, and when the viscosity of the mixed solution after storage at 60°C for 3 days (solid content concentration: 15% by weight, temperature: 25°C) is X ２ mPa·s, then 30 ≤ X １ ≤ 30,000, and 0.8 ≤ X ２ / X １ ≤ 2, and wherein the content of the component (D) is 1 to 12 parts by weight based on 100 parts by weight of the component (A) in terms of solid content weight.

2. The sizing agent for paper according to claim 1, wherein the molar ratio of the reaction components is 55 to 98 mol% of the component (a1), 0.5 to 20 mol% of the component (a2), 0.5 to 20 mol% of the component (a3), and 0.002 to 2 mol% of the component (a4).

3. The sizing agent for paper according to claim 1 or 2, wherein the component (B) is aluminum sulfate and / or its hydrate.

4. The sizing agent for paper according to any one of claims 1 to 3, wherein the content of the component (B) is 0.3 to 20 parts by weight as the amount of aluminum ions based on 100 parts by weight of the component (A) in terms of solid content weight.

5. The sizing agent for paper according to any one of claims 1 to 4, wherein the component (C) contains one or more selected from the group consisting of sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, potassium sulfate, sodium hydrogen sulfate, and potassium hydrogen sulfate.

6. The sizing agent for paper according to any one of claims 1 to 5, wherein the content of the component (C) is 1 to 70 parts by weight based on 100 parts by weight of the component (A) in terms of solid content weight.

7. The sizing agent for paper according to any one of claims 1 to 6, wherein the component (D) is sulfuric acid and / or phosphoric acid.

8. The sizing agent for paper according to any one of claims 1 to 7, wherein the pH at 25 °C in an aqueous solution with a solid content concentration of 1% by weight is 2 to 3.

5.

9. Paper obtained by using the sizing agent for paper according to any one of claims 1 to 8.

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