JP2022080874A - Paper-strengthening agent, and paper - Google Patents

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

The present invention relates to a paper strength enhancer and the paper obtained by using the same.

Paper strength enhancers are chemicals used to increase the strength of the paper itself. Especially in the paper industry, the papermaking system is becoming more closed (recycling of used paper pulp, etc.), and the strength of the obtained paper is likely to decrease due to the decrease in the strength of the pulp fiber used as the raw material. The sex is increasing.

By the way, as a paper strength enhancer, a (meth) acrylamide-based polymer is widely used, and is classified into an anionic type, a cationic type, and an amphoteric type according to its ionicity. Among these, the mainstream amphoteric type (meth) acrylamide-based polymer can be obtained by copolymerizing acrylamide with a polymerizable monomer such as a cationic monomer or an anionic monomer (Patent Document 1).

When the polymer is added to a papermaking-based pulp slurry, aluminum sulfate is also added as a fixing agent, but the fixing effect of aluminum sulfate decreases as the papermaking system becomes closed, and the environmental load also increases. From this point of view, there is a movement to reduce the amount of aluminum sulfate added in paper mills, and it is a problem that the paper strength effect of the paper strength enhancer itself is less likely to be exhibited. As a solution to this problem, a method of adding a paper strength enhancer in which a (meth) acrylamide polymer and a water-soluble aluminum compound such as aluminum sulfate are mixed has been known for a long time (Patent Document 2). Such a mixed paper strength enhancer is advantageous in that, for example, the amount of aluminum sulfate added to the pulp slurry is reduced and the paper strength effect is enhanced.

Japanese Unexamined Patent Publication No. 2012-251252 Japanese Unexamined Patent Publication No. 2001-101787

However, the paper strength enhancer containing both the (meth) acrylamide polymer and the water-soluble aluminum compound has a plurality of aluminum atoms due to the electrostatic interaction between the anionic group in the polymer and the cationic property of the aluminum atom. The polymer predominantly forms an ionically bonded crosslinked structure (hereinafter referred to as “metal crosslink”), and as a result, there is a problem in so-called storage stability, which tends to thicken with time.

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.

The present inventor has diligently studied the components contained in the paper strength enhancer, and found that the above-mentioned problems can be solved, and has completed the present invention. That is, the present invention relates to the following paper strength enhancer and paper.

1. 1. A (meth) acrylamide-based polymer 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 mixed solution containing (A), a water-soluble aluminum compound (B), an inorganic acid salt (C) (excluding those belonging to the component (B) among the components (C)), and an inorganic acid (D).
The viscosity of the mixed solution immediately after preparation (concentration 15% by weight, temperature: 25 ° C.) was X ₁ mPa · s, and the viscosity of the mixed solution after storage at a temperature of 60 ° C. for 3 days (concentration 15% by weight, temperature: 25 ° C.) A paper strength enhancer having 30 ≤ X ₁ ≤ 30,000 and 0.8 ≤ X ₂ / X ₁ ≤ 2 when (° C.) is X ₂ mPa · s.

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

3. 3. The paper strength enhancer according to item 1 or 2 above, wherein the component (B) is aluminum sulfate and / or a hydrate thereof.

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

5. The components (C) are sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, potassium sulfate, sodium hydrogen sulfate and hydrogen sulfate. The paper strength enhancer according to any one of the above items 1 to 4, which contains at least one selected from the group consisting of potassium.

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

7. The paper strength enhancer according to any one of the above items 1 to 6, wherein the component (D) is sulfuric acid and / or phosphoric acid.

8. The paper strength enhancer according to any one of the above items 1 to 7, wherein the pH of an aqueous solution having a solid content concentration of 1% by weight at a temperature of 25 ° C. is 2 to 3.5.

9. Paper obtained by using the paper strength enhancer according to any one of the above items 1 to 8.

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

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

The component (A) is a component that exerts an excellent paper strength effect, and in the present invention, (meth) acrylamide (a1) (hereinafter referred to as the component (a1)) and a polymerizable monomer having a cationic group (hereinafter referred to as the component (a1)) ( a2) (hereinafter referred to as (a2) component), a polymerizable monomer (a3) having an anionic group (hereinafter referred to as (a3) component) and a crosslinkable monomer (a4) (hereinafter referred to as (a4) component. ) Is included in the reaction component. Here, the polymerizable monomer means a monomer having one or more double bonds and / or carbon-carbon triple bonds in one molecule.

Examples of the component (a1) include methacrylamide and acrylamide. These may be used alone or in combination of two.

The component (a2) is not particularly limited as long as it has a cationic group, and various known substances can be used. For example, a polymerizable monomer having a secondary amino group and a tertiary amino group may be used. Examples thereof include polymerizable monomers having, and quaternized salts of these polymerizable monomers.

The polymerizable monomer having a secondary amino group is not particularly limited, and examples thereof include diallylamine and the like. The polymerizable monomer having a tertiary amino group is not particularly limited, and has, for example, a tertiary amino group such as N, N-dimethylaminoethyl (meth) acrylate and N, N-diethylaminoethyl (meth) acrylate ( Meta) Acrylate; Examples thereof include (meth) acrylamide having a tertiary amino group such as N, N-dimethylaminopropyl (meth) acrylamide and N, N-diethylaminopropyl (meth) acrylamide. The quaternary salt of these monomers means a product obtained by reacting a polymerizable monomer having a secondary amino group or a polymerizable monomer having a tertiary amino group with a quaternizing agent, and the like. The graded salt may be an inorganic acid salt such as a hydrochloride or a sulfate, or an organic acid salt such as an acetate. Examples of the quaternary agent include methyl chloride, benzyl chloride, dimethyl sulfate, epichlorohydrin and the like. These may be used alone or in combination of two or more. Among them, a polymerizable monomer having a tertiary amino group and / or a quaternized salt thereof is preferable, and it is more preferable to contain a (meth) acrylate having a tertiary amino group and / or a quaternized salt of the (meth) acrylate. Preferably, a quaternized salt of N, N-dimethylaminoethyl (meth) acrylate and N, N-dimethylaminoethyl (meth) acrylate is more preferable, and N, N-dimethylaminoethyl acrylate and N, N-dimethylaminoethyl are more preferable. Acrylatebenzyl chloride and N, N-dimethylaminoethyl methacrylatebenzyl chloride are particularly preferred. In addition, "(meth) acrylate" means methacrylate or acrylate.

The component (a3) is not particularly limited as long as it has an anionic group, and various known components can be used. For example, a polymerizable monomer having a carboxyl group such as (meth) acrylic acid, itacon acid, anhydrous itaconic acid, fumaric acid, maleic acid; a polymerizable monomer having a sulfonic acid group such as vinyl sulfonic acid and methallyl sulfonic acid. Can be mentioned. In addition, these (a3) components may be used as alkali metal salts such as sodium and potassium, and salts such as ammonium salts. These may be used alone or in combination of two or more. Of these, (meth) acrylic acid, itaconic acid, and sodium methallyl sulfonate are preferable.

The component (a4) is a component for introducing a branched structure into the polymer. The component (a4) is not particularly limited, and for example, N such as N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, and Nt-butyl (meth) acrylamide. -Alkyl (meth) acrylamide; N, N-dialkyl (meth) acrylamide such as N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide; N, N, N'-alkylene bis (meth) acrylamide such as N'-methylenebis (meth) acrylamide, N, N'-ethylenebis (meth) acrylamide; triallyl isocyanurate, triallyl trimellitate, triallylamine, triallyl ( Meta) Crosslinkable monomer having a triaryl group such as acrylamide; 1,3,5-triacrylloyl-1,3,5-triazine, 1,3,5-triacrylloylhexahydro-1,3,5-triazine and the like. Examples thereof include triazine having an (meth) acrylamide group. 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'-alkylene bis (meth) acrylamide, and triazine having a (meth) acryloyl group is preferable, and N, N-dimethyl is preferable. Acrylamide, N, N'-methylenebisacrylamide is more preferred.

The amount of each reaction component used is not particularly limited, but is set as follows in terms of molar ratio from the viewpoint that the obtained paper exhibits an excellent paper strength effect.
(A1) component: preferably 55 to 98 mol%, more preferably 77.8 to 93.5 mol%.
(A2) component: preferably 0.5 to 20 mol%, more preferably 3 to 10 mol%.
(A3) component: preferably 0.5 to 20 mol%, more preferably 1 to 10 mol%.
(A4) component: preferably 0.002 to 2 mol%, more preferably 0.004 to 0.5 mol%.

The reaction component may further contain a monomer (a5) (hereinafter referred to as a component (a5)) other than the components (a1) to (a4). The component (a5) is not particularly limited, and is, for example, a polymerizable monomer having an aromatic ring such as styrene, α-methylstyrene, vinyltoluene, etc .; methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth). ) Alcohol (meth) acrylates such as acrylates, n-butyl (meth) acrylates, 2-ethylhexyl (meth) acrylates and cyclohexyl (meth) acrylates; vinyl carboxylates such as vinyl acetate and vinyl propionates; nitriles such as acrylonitrile; Melcaptans such as 2-mercaptoethanol and n-dodecyl mercaptan; alcohols such as ethanol, isopropyl alcohol and n-pentyl alcohol; aromatic compounds such as α-methylstyrene dimer, ethylbenzene, isopropylbenzene and cumene; carbon tetrachloride and the like Can be mentioned. 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.

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

The component (A) is not particularly limited, and the component (a1), the component (a2), the monomer component containing the component (a3) and the component (a4), and if necessary, the component (a5) and the additive are used as a solvent. Obtained by polymerizing in.

The above-mentioned polymerization method is not particularly limited, and examples thereof include a method using only a drop polymerization method, a method in which a simultaneous polymerization method (collectively charging a monomer mixed solution) and a drop polymerization method are combined.

The dropping polymerization method is a method of dropping a monomer mixed solution into a reaction system in which a solvent such as water is charged in advance, and examples of the method using only the dropping polymerization method include the following (1) to (3). Be done. It should be noted that the dropping may be continued, or the dropping may be stopped in the middle of the dropping, polymerized for a certain period of time, and then the dropping may be restarted.
(1) A method of dropping a monomer mixed solution in which all the monomer components are mixed (2) A method of separately preparing two or more kinds of monomer mixed solutions and then dropping them at the same time (3) Separately adding two or more kinds of monomer mixed solutions After preparing to, the method of dropping in order

In addition, examples of the method in which the simultaneous polymerization method and the dropping polymerization method are combined include the following (4) to (7).
(4) A method of simultaneously co-polymerizing each monomer mixed solution and then mixing each polymer (5) A method of dropping the remaining monomer mixed solution after the simultaneous polymerization of one or more kinds of monomer mixed solutions is completed (5) 6) Method of dropping and polymerizing the remaining monomer mixed solution from the middle of simultaneous polymerization of one or more kinds of monomer mixed solution (7) Drop-polymerizing one or more kinds of monomer mixed solution and the remaining monomer mixed solution A method of simultaneous polymerization after adding all at once

Here, when preparing a mixture of two or more types of monomers, the amount of the component (a2) or the component (a3) in some of the mixed solutions may be increased, and these mixed solutions may be reacted in sequence (. The concentration of the component (a2) and the component (a3) involved in the reaction is increased in any of the monomer mixed solutions, such as adding the component (a2) or the component (a3) at a certain point during the polymerization reaction. It is more preferable to perform various operations.

Examples of the solvent include water, an organic solvent and the like, and these may be used alone or in combination of two or more. The organic solvent is not particularly limited, and is, for example, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, isobutyl alcohol, n-hexyl alcohol, n-octyl. Alcohols such as alcohols, ethylene glycols, propylene glycols, diethylene glycols, triethylene glycols and diacetone alcohols; ethers such as ethylene glycol monobutyl ethers, propylene glycol monomethyl ethers and propylene glycol monoethyl ethers can be mentioned. Above all, it is usually preferable to use water from the viewpoint of dissolving the components (a1) to (a5).

The polymerization initiator is not particularly limited, and is, for example, persulfate such as ammonium persulfate, potassium persulfate, sodium persulfate; 2,2'-azobis (2-amidinopropane) hydrochloride, 2,2'-azobis. [2 (2-imidazolin-2-yl) propane] azo compounds such as hydrochloride; hydrogen peroxide and the like can be mentioned. These may be used alone or in combination of two or more. Of these, ammonium persulfate, potassium persulfate, and 2,2'-azobis (2-amidinopropane) hydrochloride are preferable from the viewpoint of sufficiently advancing solution polymerization. Further, the method of adding the polymerization initiator is not particularly limited, and batch addition, partial addition, continuous dropping, or the like can be appropriately selected. The content of the polymerization initiator is also not particularly limited, and 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). Is.

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

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

The viscosity of the component (A) is usually 500 to 150,000 mPa · s, preferably 1,500 to 100,000 mPa · s. Here, "viscosity" refers to a solution having a solid content concentration of 15% by weight, adjusted to a temperature of 25 ° C. in advance, and measured with a B-type viscometer (the same applies hereinafter).

The component (B) is a water-soluble aluminum compound, which is a component that crosslinks with a metal by electrostatic interaction with the component (A) and promotes the excellent paper strength effect of paper. Examples of the component (B) include aluminum sulfate, aluminum chloride, basic aluminum sulfate, basic aluminum chloride, aluminum silicate, polyaluminum chloride, polyaluminum hydroxide and the like. A hydrate can also be used as the component (B). These may be used alone or in combination of two or more. Of these, aluminum sulfate, aluminum chloride, and polyaluminum chloride are preferable, and aluminum sulfate is more preferable because of their availability.

The content of the component (B) is not particularly limited, but the viscosity of the paper strength enhancer does not increase excessively, and an excellent paper strength effect is also exhibited. Therefore, the solid content weight is 100 parts by weight of the component (A). The amount of aluminum ions is preferably 0.3 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, still more preferably 0.75 to 5 parts by weight.

The component (C) is an inorganic acid salt, has a function of weakening the electrostatic interaction between the component (A) and the component (B), and is used to show excellent storage stability of the paper strength enhancer. It is an ingredient.
As the component (C), for example, nitrates such as ammonium nitrate, sodium nitrate, and potassium nitrate;
Nitrite such as ammonium nitrite, sodium nitrite, potassium nitrite;
Hyponitrites such as ammonium nitrite, sodium nitrite, potassium nitrite;
Sulfates such as ammonium sulfate, sodium sulfate, potassium sulfate, ammonium hydrogensulfate, sodium hydrogensulfate, potassium hydrogensulfate;
Sulfites such as ammonium sulfite, sodium sulfite, potassium sulfite;
Hyposulfites such as ammonium hyposulfite, sodium hyposulfite, potassium hyposulfite;
Phosphorus such as ammonium phosphate, sodium phosphate, potassium phosphate, disammonium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, etc. salt;
Ammonium phosphite, sodium phosphite, potassium phosphite, diammonium hydrogen phosphite, disodium hydrogen phosphite, dipotassium hydrogen phosphite, ammonium dihydrogen phosphite, sodium dihydrogen phosphite, sub Subphosphates such as potassium dihydrogen phosphate;
Ammonium hypophosphite, sodium hypophosphite, potassium hypophosphite, diammonium hydrogen hypophosphite, disodium hydrogen hypophosphite, dipotassium hydrogen hypophosphite, ammonium dihydrogen hypophosphite, next Examples thereof include hypophosphite such as sodium dihydrogen phosphite and potassium dihydrogen hypophosphite. These may be used alone or in combination of two or more. As the inorganic acid salt, a hydrate may be used.

Among these components (C), sulfates and / or phosphates are sulfates and / or phosphates because they weaken the electrostatic interaction between the components (A) and (B) and the paper strength enhancer exhibits excellent storage stability. Is preferable, and it is composed 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. It is more preferable to include one or more species selected from the group, and it is further preferable to include two or more species selected from the group.

The content of the component (C) is not particularly limited, but the solid content is such that the electrostatic interaction between the component (A) and the component (B) is weakened and the paper strength enhancer exhibits excellent storage stability. By weight, 1 to 70 parts by weight is preferable, 1 to 50 parts by weight is more preferable, and 1 to 30 parts by weight is further preferable with respect to 100 parts by weight of the component (A).

The component (D) is an inorganic acid. When the component (D) is blended, the pH of the paper strength enhancer is lowered, and the anionic component contained in the paper strength enhancer (for example, the one derived from the component (a3) in the component (A)) is dissociated (for example, R-. COOH → R ^- COO- + H ⁺ etc.) becomes difficult. As a result, the electrostatic interaction between the component (A) and the component (B) is weakened, and the paper strength enhancer exhibits excellent storage stability. Examples of the component (D) include hydrochloric acid, nitrate, nitrite, hyponitrite, sulfuric acid, sulfite, hyposulfate, phosphoric acid, nitrous acid, hypophosphoric acid and the like. These may be used alone or in combination of two or more. Of these, sulfuric acid and phosphoric acid are preferable because they suppress the increase in pH of the paper strength enhancer and the paper strength enhancer exhibits excellent storage stability.

The content of the component (D) is not particularly limited, but in addition to adjusting the pH of the paper strength enhancer, it suppresses the increase in the pH, and the paper strength enhancer has excellent storage stability. In terms of solid content weight, 0.5 to 15 parts by weight is preferable, 1 to 12 parts by weight is more preferable, and 1 to 10 parts by weight is further preferable with respect to 100 parts by weight of the component (A).

The paper strength enhancer of the present invention further includes organic acids such as citric acid, succinic acid, and oxalic acid; inorganic bases such as sodium hydroxide, potassium hydroxide, and calcium hydroxide; urea, polysaccharides (for example, starch), and the like. Additives such as a defoaming agent, an antioxidant, a polymerization inhibitor, and an antiseptic may be added.

The paper strength enhancer of the present invention can be obtained by mixing the component (A), the component (B), the component (C) and the component (D), and if necessary, the additive at room temperature. Water may also be added for dilution. As for the component (A), two or more kinds of polymers produced under different compositions and conditions such as the type and / or the amount of the monomer used may be mixed, and those diluted with water in advance are used. You may. Further, the mixing method and mixing order thereof are not particularly limited.

The paper strength enhancer obtained above has a viscosity (concentration: 15% by weight, temperature: 25 ° C.) of the mixed solution immediately after preparation of X1 mPa · s, and _a mixed solution after storage at a temperature of 60 ° C. for 3 days. When the viscosity (concentration: 15% by weight, temperature: 25 ° C.) of is X ₂ mPa · s, 30 ≦ X ₁ ≦ 30,000 and 0.8 ≦ X ₂ / X ₁ ≦ 2. note that. 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.

(About viscosity X ₁ )
If the viscosity X ₁ is less than 30 mPa · s, the paper strength enhancer dissolves in a large amount of water in the papermaking system and falls off during dehydration, making it difficult for the paper strength effect to be exhibited. If it exceeds 30,000 mPa · s, it becomes difficult to mix the paper strength enhancer uniformly when diluted with a solvent such as water, or it becomes difficult to send out the paper strength enhancer by a pump or the like when making paper. , A desired amount of the paper strength enhancer is not added to the pulp slurry, and as a result, the paper strength effect of the paper tends to be inferior, which tends to be deteriorated in terms of operation. Further, from the same point of view, the viscosity X ₁ is preferably 100 ≦ X ₁ ≦ 25,000, and more preferably 300 ≦ X ₁ ≦ 20,000.

(About X ₂ / X ₁ )
X ₂ / X ₁ is an index of storage stability of the paper strength enhancer. When X ₂ / X ₁ exceeds 2, the viscosity continues to increase over time, so that the paper strength enhancer stored for a long period of time cannot be added to the pulp slurry. Further, the viscosity X ₂ / X ₁ is preferably 0.8 ≦ X ₂ / X ₁ ≦ 1.8, more preferably 0.8 ≦ X ₂ / X ₁ ≦ 1.5 from the same point of view.

As another physical property of the paper strength enhancer of the present invention, the pH at a temperature of 25 ° C. in an aqueous solution having a solid content concentration of 1% by weight is preferably 2 to 3.5 from the viewpoint of maintaining excellent storage stability. Yes, more preferably 2-3, still more preferably 2-2.5.

The paper of the present invention is obtained by using the paper strength enhancer, and as a method for producing the paper, for example, the paper strength enhancer is added to the raw material pulp slurry (hereinafter, also referred to as internal addition), or For example, painting on the surface of the base paper. The paper strength enhancer is preferably diluted with water, and its solid content concentration is adjusted to 0.1 to 2.0% by weight.

When internally added to the raw material pulp slurry, a paper strength enhancer is added to the pulp slurry to make paper. The amount of the paper strength enhancer used (converted to the solid content of the component (A)) is not particularly limited, but is about 0.01 to 4% by weight with respect to the dry weight of the pulp. The type of pulp is not particularly limited, and for example, chemical pulp such as broadleaf pulp (LBKP) and coniferous pulp (NBKP); crushed wood pulp (GP), refiner ground pulp (RGP), thermomechanical pulp (TMP) and the like. Mechanical pulp; used paper pulp such as used cardboard paper and the like can be mentioned. In addition, when adding a paper strength agent solution, as a fixing agent, a pH adjuster such as aluminum sulfate, sulfate or sodium hydroxide; a paper-making chemical such as a sizing agent or a wet paper strength agent; talc or clay. , Kaolin, titanium dioxide, calcium carbonate and other fillers can be added.

When applying to the surface of the base paper, a paper strength enhancer is applied to the surface of the base paper by various known means. Here, the paper strength enhancer applied to the surface of the base paper is referred to as 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 base paper, uncoated paper made from wood cellulose fiber can be used, and the coating means is not particularly limited. For example, bar coater, knife coater, air knife coater, calender, gate. Examples include roll coaters, blade coaters, 2-roll size presses and rod metering. The coating amount (in terms of solid content) of the coating liquid is also not particularly limited, but is usually about 0.001 to 2 g / m ² , preferably about 0.005 to 1 g / m ² .

The paper of the present invention is used in various products, for example, coated base paper, newspaper paper, liner, core, paper tube, printing writing paper, foam paper, PPC paper, cup base paper, inkjet paper, heat-sensitive paper and the like. Can be mentioned.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, "part" and "%" in Examples and Comparative Examples are based on weight unless otherwise specified.

The following compounds are indicated 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-triacrylloylhexahydro-1,3,5-triazine APS: ammonium persulfate

<Weight average molecular weight of component (A)>
By the gel permeation chromatography (GPC) method, the weight average molecular weight of the component (A) was measured under the following measurement conditions.
Column: 1 guard column PWXL and 2 GMPWXL manufactured by Toso Co., Ltd. Eluent: Phosphoric acid buffer (0.05 mol / L phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) + 0.13 mol / L sodium dihydrogen phosphate (Made by Fujifilm Wako Pure Chemical Industries, Ltd.) Aqueous solution, pH approx. 2.5)
Flow velocity: 0.8 ml / min Temperature: 40 ° C
RI detector: Showa Denko Corporation Shodex RI-101
MALS detector: WYATT DAWN HELEOS-II
Measurement sample: The polymer was diluted with the above eluent and measured so that the concentration of the polymer was 0.1%.

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

<pH>
Using a commercially available measuring machine (product name "pH METER F-14", manufactured by HORIBA, Ltd.), the pH of the sample at a temperature of 25 ° C. in an aqueous solution of a paper strength enhancer having a concentration of 1% was measured.

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

Production Examples 2 to 17, Comparative Production Examples 1 to 3
The compositions shown in Table 1 were synthesized in the same manner as in Production Example 1, and aqueous solutions of the component (A) having a solid content concentration of 15% were obtained.

Example 1
(A-1) 667 parts of aqueous solution (solid content 100 parts), 17.5 parts of aluminum sulfate 16hydrate (weight conversion of aluminum ions: 1.5 parts), sodium dihydrogen phosphate hydrate 1 After mixing 0.05 parts, 10 parts of sodium sulfate, 0.70 parts of phosphoric acid and 2.25 parts of a sulfuric acid aqueous solution having a solid content concentration of 62.5% (solid content 1.4 parts) at room temperature for 15 minutes, ion-exchanged water. The mixture was added so that the solid content concentration was 15%, and the mixture was mixed to obtain a paper strength enhancer. _The viscosities X1 (mPa · s) and pH of the paper strength enhancer are shown in Table 2 (the same applies hereinafter).

Examples 2 to 7, 9 to 27, Comparative Examples 1 to 9
With the composition shown in Table 2, the same procedure as in Example 1 was carried out to obtain paper strength enhancers having a solid content concentration of 15%. The paper strength enhancers of Comparative Examples 4 and 5 had a high viscosity immediately after synthesis, and the paper strength enhancers of Comparative Example 7 had a low molecular weight, so that they were not subjected to the following evaluation.

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

Example 28
333 parts of aqueous solution of (A-2) component (50 parts of solid content), 333 parts of aqueous solution of (A-3) component (50 parts of solid content), 17.5 parts of aluminum sulfate / hexahydrate (weight of aluminum ions) Conversion: 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 of sulfuric acid aqueous solution with a solid content concentration of 62.5% (solid content). 1.4 parts) was mixed at room temperature for 10 minutes, and then added and mixed with ion-exchanged water so that the solid content concentration became 15% to obtain a paper strength enhancer.

<Storage stability>
Each paper strength enhancer was allowed to stand in a thermostat at 60 ° C. for 3 days. The viscosity of each paper strength enhancer after adjusting the temperature to 25 ° C. was measured, and the value was set to X ₂ (mPa · s), and X ₂ / X ₁ was calculated. The results are shown in Table 2.

<Papermaking evaluation>
Each paper strength enhancer (A) shown in Table 2 was diluted by adding ion-exchanged water so as to have a solid content concentration of 1.0%. After that, the following papermaking evaluation was performed. In the above-mentioned storage stability test, the paper strength enhancer (Comparative Examples 3, 6 and 8) in which X ₂ / X ₁ exceeded 2 was not evaluated.

Calcium chloride is added to a pulp slurry prepared by beating waste paper from a step ball with a Niagara beater and adjusting to 350 ml of Canadian Standard Freeness (CSF) to increase the electrical conductivity to 4.0 mS / cm. It was adjusted. After adding a sulfuric acid band to this slurry liquid with a solid content of 0.5% based on the weight of the solid content of the pulp slurry, the paper strength enhancer of Example 1 is added to the solid content of the pulp slurry to have the solid content of the component (A). An amount of 0.5% was added. The pH of each pulp slurry was adjusted to 6.5. It was dehydrated with a tappy sheet machine, pressed at 5 kg / cm ² for 2 minutes, and made into paper to a basis weight of 150 g / m ² . Then, it was dried in a rotary dryer at 105 ° C. for 4 minutes, and the humidity was adjusted for 24 hours under the conditions of a temperature of 23 ° C. and a humidity of 50%, and then the burst strength was measured. In addition, the same evaluation was performed on the paper strength enhancers of Examples 2 to 24 and Comparative Examples 1 and 2. The electrical conductivity, the amount of drainage, and the burst strength were measured by the following methods. The results are shown in Table 2.

<Electrical conductivity>
It was measured using pH / COND METER D-54 (manufactured by HORIBA, Ltd.).

<Amount of drainage>
Measurements were made according to JIS P 8121 using Canadian Standard Freeness (CSF).

<Ratio burst strength>
Using the paper obtained above, the specific burst strength (kPa · m ² / g) was measured according to JIS P 8131.

* 1: Shown by the weight part of aluminum ion with respect to 100 parts by weight (solid content) of (A) component.
* 2: Shown by the weight part of the component (C) and the component (D) with respect to 100 parts by weight (solid content) of the component (A).

Claims (9)

A (meth) acrylamide-based polymer containing (meth) acrylamide (a1), a polymerizable monomer having a cationic group (a2), a polymerizable monomer having an anionic group (a3), and a crosslinkable monomer (a4) as reaction components. A mixed solution containing (A), a water-soluble aluminum compound (B), an inorganic acid salt (C) (excluding those belonging to the component (B)), and an inorganic acid (D).
The viscosity of the mixed solution immediately after preparation (solid content concentration 15% by weight, temperature: 25 ° C.) was X ₁ mPa · s, and the viscosity of the mixed solution after storage at a temperature of 60 ° C. for 3 days (solid content concentration 15% by weight). , Temperature: 25 ° C.) is X ₂ mPa · s, and 30 ≦ X ₁ ≦ 30,000 and 0.8 ≦ X ₂ / X ₁ ≦ 2. The molar ratios of the reaction components are (a1) component 55 to 98 mol%, (a2) component 0.5 to 20 mol%, (a3) component 0.5 to 20 mol%, and (a4) component 0.002 to. The paper strength enhancer according to claim 1, which is 2 mol%. The paper strength enhancer according to claim 1 or 2, wherein the component (B) is aluminum sulfate and / or a hydrate thereof. The paper strength enhancer 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 with respect to 100 parts by weight of the component (A) in terms of solid content weight. .. The components (C) are sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, potassium sulfate, sodium hydrogen sulfate and hydrogen sulfate. The paper strength enhancer according to any one of claims 1 to 4, which comprises at least one selected from the group consisting of potassium. The paper strength enhancer according to any one of claims 1 to 5, wherein the content of the component (C) is 1 to 70 parts by weight with respect to 100 parts by weight of the component (A) in terms of solid content weight. The paper strength enhancer according to any one of claims 1 to 6, wherein the component (D) is sulfuric acid and / or phosphoric acid. The paper strength enhancer according to any one of claims 1 to 7, wherein the pH of an aqueous solution having a solid content concentration of 1% by weight at a temperature of 25 ° C. is 2 to 3.5. Paper obtained by using the paper strength enhancer according to any one of claims 1 to 8.