PAPER-STRENGTHENING AGENT, PAPER, AND METHOD OF PRODUCING PAPER

Abstract

A paper-strengthening agent comprising an amphoteric (meth)acrylamide polymer and an amphoteric (meth)acrylamide polymer, wherein each of constituent monomers of the amphoteric (meth)acrylamide polymer and the amphoteric (meth)acrylamide polymer comprises (meth)acrylamide, a cationic unsaturated monomer, an anionic unsaturated monomer, and a crosslinkable unsaturated monomer, and has a specific weight-average molecular weight, and wherein each viscosity of the paper-strengthening agent, the polymer, and the polymer satisfies a specific relationship.

Claims

1. A paper-strengthening agent comprising an amphoteric (meth)acrylamide polymer (A1) and an amphoteric (meth)acrylamide polymer (A2), wherein each of constituent monomers of the amphoteric (meth)acrylamide polymer (A1) and the amphoteric (meth)acrylamide polymer (A2) comprises (meth)acrylamide (a1), a cationic unsaturated monomer (a2), an anionic unsaturated monomer (a3), and a crosslinkable unsaturated monomer (a4), wherein each of weight-average molecular weights of the amphoteric (meth)acrylamide polymer (A1) and the amphoteric (meth)acrylamide polymer (A2) is 1,500,000 to 10,000,000, and wherein, where a viscosity (25° C.) of an aqueous solution (pH: 4) of 15% by mass of paper-strengthening agent is defined as X.sub.AmPa.Math.s, a viscosity (25° C.) of an aqueous solution (pH: 4) of the amphoteric (meth)acrylamide polymer (A1) with 15% by mass of concentration is defined as X.sub.A1mPa.Math.s, and a viscosity (25° C.) of an aqueous solution (pH: 4) of the amphoteric (meth)acrylamide polymer (A2) with 15% by mass of concentration is defined as X.sub.A2mPa.Math.s, the paper-strengthening agent satisfies the following inequality 1:
1.1≤X.sub.A/(m.sub.A1×X.sub.A1+m.sub.A2×X.sub.A2)≤6  (Inequality 1) (wherein, m.sub.A1 is a ratio of a solid content weight of the amphoteric (meth)acrylamide polymer (A1) to a total weight of the amphoteric (meth)acrylamide polymer (A1) and the amphoteric (meth)acrylamide polymer (A2), m.sub.A2 is a ratio of a solid content weight of the amphoteric (meth)acrylamide polymer (A2) to the total weight of the amphoteric (meth)acrylamide polymer (A1) and the amphoteric (meth)acrylamide polymer (A2), and m.sub.A1+m.sub.A2=1.)

2. The paper-strengthening agent of claim 1, wherein the viscosity X.sub.A is 1,100 to 40,000 mPa.Math.s.

3. The paper-strengthening agent of claim 1, wherein the viscosity X.sub.A1 is 1,000 to 12,000 mPa.Math.s.

4. The paper-strengthening agent of claim 1, wherein the viscosity X.sub.A2 is 1,000 to 12,000 mPa.Math.s.

5. The paper obtained by using a paper-strengthening agent of claim 1.

6. The method of producing paper, the method comprising adding a paper-strengthening agent of claim 1 to a pulp slurry.

7. The method of producing paper of claim 6, wherein the pulp slurry has an electrical conductivity of 3 mS/cm or more.

Description

EXAMPLE

[0104] Hereinafter, the present invention will be described with reference to Examples. The present invention is not limited these Examples. Besides, unless otherwise specified, “part(s)” and “%” in Examples and Comparative examples are based on weight.

[0105] Abbreviations of compounds are shown below.

[0106] AM: Acrylamide

[0107] DM: N,N-dimethylaminoethyl methacrylate

[0108] DML: N,N-dimethylaminoethyl methacrylate benzyl chloride

[0109] BQ: N,N-dimethylaminoethyl acrylate benzyl chloride

[0110] APDM: N,N-dimethylaminopropyl acrylamide

[0111] IA: Itaconic acid

[0112] AA: Acrylic acid

[0113] SMAS: Sodium methallylsulfonate

[0114] DMAA: N,N-dimethylacrylamide

[0115] MBAA: N,N′-methylenebisacrylamide

[0116] APS: Ammonium persulfate

<Weight-Average Molecular Weights of Polymer (A1) and Polymer (A2)>

[0117] A weight-average molecular weight of the paper-strengthening agent was measured by gel permeation chromatography (GPC) method under the following measurement conditions.

[0118] Column: One Guard column PWXL and two GMPWXL manufactured by Tosoh Corporation

[0119] 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)

[0120] Flow rate: 0.8 mL/min

[0121] Temperature: 40° C.

[0122] RI detector: Shodex RI-101 manufactured by Showa Denko K.K.

[0123] MALS detector: DAWN HELEOS-II manufactured by Wyatt Technology

[0124] Measurement sample: Measured by diluting with the above-described eluent so that a concentration of a polymer became 0.1%.

<Viscosity of Polymer (A1) and Polymer (A2) Immediately after Synthesis>

[0125] A viscosity of a sample at a temperature of 25° C. was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.). Besides, the viscosity here represents a viscosity obtained immediately after synthesis.

<pH>

[0126] A pH of a sample at a temperature of 25° C. was measured using a commercially available measuring machine (product name: “pH METER F-14”, manufactured by HORIBA, Ltd.).

Production Example 1-1

[0127] 69.1 parts of ion-exchanged water were put into a reactor equipped with a stirrer, a thermometer, a reflux cooling tube, a nitrogen gas introduction tube, and three dropping funnels, removed of oxygen in a reaction system through nitrogen gas, and then heated to 90° C. 43.6 parts (23.96 mol %) of 50% AM, 10.0 parts (5.0 mol %) of DM, 0.8 parts (0.50 mol %) of IA, 0.6 parts (0.30 mol %) of SMAS, 4.8 parts of 62.5% sulfuric acid, 0.06 parts (0.05 mol %) of DMAA, and 35.3 parts of ion-exchanged water were charged into the dropping funnel (1), and pH was adjusted to around 3.0 with sulfuric acid (a monomer mixed solution (I)). Moreover, 121.7 parts (66.93 mol %) of AM, 2.0 parts (1.0 mol %) of DM, 3.3 parts (2.0 mol %) of IA, 0.4 parts (0.20 mol %) of SMAS, 1.0 part of 62.5% sulfuric acid, 0.06 parts (0.05 mol %) of DMAA, 0.02 parts (0.01 mol %) of MBAA, and 62.0 parts of ion-exchanged water were charged into the dropping funnel (2), and pH was adjusted to around 3.0 with sulfuric acid (a monomer mixed solution (II)). 0.14 parts of APS and 45.0 parts of ion-exchanged water were charged into the dropping funnel (3). Next, a catalyst in a system was dropped with the dropping funnel (3) over about 3 hours. In parallel, the monomer mixed solution (I) in the dropping funnel (1) and the monomer mixed solution (II) in the dropping funnel (2) were dropped in this order at a constant flow rate over about 3 hours. After completion of the dropping, 0.1 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 1 hour, and 112 parts of ion-exchanged water were charged to obtain an aqueous solution of a polymer (A1-1) having a pH of 4. The physical properties are shown in Table 2 (the same applies hereinafter).

Production Examples 1-2 to 1-3, Production Examples 1-6 to 1-11, Production Examples 2-1 to 2-3, Production Examples 2-6 to 2-10, Comparative Production Examples 1 to 5

[0128] Aqueous solutions of polymers each having a pH of 4 were obtained in the similar manner of synthesis as in Production example 1-1 with compositions shown in Table 1.

Production Example 1-4

[0129] An aqueous solution of a polymer (A1-4) having a pH of 4 was obtained in the similar manner as in Production example 1-2 except that, after completion of dropping, 0.28 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 3 hours.

Production Example 1-5

[0130] An aqueous solution of a polymer (A1-5) having a pH of 4 was obtained in the similar manner as in Production example 1-1 except that, after completion of dropping, 0.14 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 0.5 hours.

Production Example 2-4

[0131] An aqueous solution of a polymer (A2-4) having a pH of 4 was obtained in the similar manner as in Production example 2-2 except that, after completion of dropping, 0.28 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 3 hours.

Production Example 2-5

[0132] An aqueous solution of a polymer (A2-5) having a pH of 4 was obtained in the similar manner as in Production example 2-1 except that, after completion of dropping, 0.14 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 0.5 hours.

Production Example 1-12

[0133] 69.1 parts of ion-exchanged water were put into a reactor similar with that in Production example 1-1, removed of oxygen in a reaction system through nitrogen gas, and then heated to 90° C. 43.6 parts (23.96 mol %) of AM, 10.0 parts (5.0 mol %) of DM, 0.8 parts (0.50 mol %) of IA, 0.6 parts (0.30 mol %) of SMAS, 4.8 parts of 62.5% sulfuric acid, 0.06 parts (0.05 mol %) of DMAA, and 35.3 parts of ion-exchanged water were charged into the dropping funnel (1), and pH was adjusted to around 3.0 with sulfuric acid (a monomer mixed solution (I)). Moreover, 60.8 parts (33.61 mol %) of AM, 1.0 part (0.50 mol %) of DM, 1.7 parts (1.0 mol %) of IA, 0.2 parts (0.10 mol %) of SMAS, 0.5 parts of 62.5% sulfuric acid, 0.04 parts (0.03 mol %) of DMAA, and 31.0 parts of ion-exchanged water were charged into the dropping funnel (2), and pH was adjusted to around 3.0 with sulfuric acid (a monomer mixed solution (II)). Furthermore, 60.8 parts (33.33 mol %) of AM, 1.0 part (0.50 mol %) of DM, 1.7 parts (1.0 mol %) of IA, 0.2 parts (0.10 mol %) of SMAS, 0.5 parts of 62.5% sulfuric acid, 0.03 parts (0.02 mol %) of DMAA, 0.02 parts (0.01 mol %) of MBAA, and 31.0 parts of ion-exchanged water were charged into the dropping funnel (3), and pH was adjusted to around 3.0 with sulfuric acid (a monomer mixed solution (III)). 0.14 parts of APS and 45 parts of ion-exchanged water were charged into the dropping funnel (4). Next, a catalyst in a system was dropped with the dropping funnel (4) over about 3 hours. In parallel, the monomer mixed solutions (I), (II), and (III) in the dropping funnels (1), (2), and (3) were dropped in this order at a constant flow rate over about 3 hours. After completion of the dropping, 0.1 parts of APS and 2.0 parts of ion-exchanged water were charged and kept warm for 1 hour, and 112 parts of ion-exchanged water were charged to obtain an aqueous solution of a polymer (A1-12) having a pH of 4.

Production Example 2-11

[0134] An aqueous solution of a polymer (A2-11) having a pH of 4 was obtained in the similar manner of synthesis as in Production example 1-12 with compositions shown in Table 1.

<Viscosity of Polymer (A1) and Polymer (A2) at Concentration of 15% and pH of 4>

[0135] The obtained polymers (A-1) to (A1-12), polymer (A2-1) to (A2-11), and polymer (B-1) to (B-5) were diluted by adding a deionized water so as to have a concentration of 15%. Moreover, after adjusting pH to 4 with a 5% sulfuric acid aqueous solution, a viscosity at a temperature of 25° C. was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.). The results are shown in Table 3.

TABLE-US-00001 TABLE 1 Monomer composition (mol %) Component (a2) component (a3) component (a4) component No. AM DM DML BQ APDM IA AA SMAS DMAA MBAA Production example 1-1 A1-1 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 1-2 A1-2 91.09 6.0 — — — 2.5 — 0.30 0.10 0.01 Production example 1-3 A1-3 90.35 6.0 — — — 2.5 — 1.0 0.10 0.05 Production example 1-4 A1-4 91.09 6.0 — — — 2.5 — 0.30 0.10 0.01 Production example 1-5 A1-5 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 1-6 A1-6 78.89 18.0 — — — 2.5 — 0.50 0.10 0.01 Production example 1-7 A1-7 90.89 4.0 1.0 1.0 — 2.5 — 0.50 0.10 0.01 Production example 1-8 A1-8 90.89 3.0 1.0 1.0 1.0 2.5 — 0.50 0.10 0.01 Production example 1-9 A1-9 81.39 6.0 — — — 12.0  — 0.50 0.10 0.01 Production example 1-10 A1-10 71.39 6.0 — — — 22.0  — 0.50 0.10 0.01 Production example 1-11 A1-11 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 1-12 A1-12 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 2-1 A2-1 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 2-2 A2-2 91.09 6.0 — — — 2.5 — 0.30 0.10 0.01 Production example 2-3 A2-3 90.35 6.0 — — — 2.5 — 1.0 0.10 0.05 Production example 2-4 A2-4 91.09 6.0 — — — 2.5 — 0.30 0.10 0.01 Production example 2-5 A2-5 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Production example 2-6 A2-6 84.89 12.0 — — — 2.5 — 0.50 0.10 0.01 Production example 2-7 A2-7 90.89 4.0 1.0 1.0 — 2.5 — 0.50 0.10 0.01 Production example 2-8 A2-8 90.89 3.0 1.0 1.0 1.0 2.5 — 0.50 0.10 0.01 Production example 2-9 A2-9 90.89 6.0 — — — — 2.5 0.50 0.10 0.01 Production example 2-10 A2-10 75.39 6.0 — — — 18.0  — 0.50 0.10 0.01 Production example 2-11 A2-11 90.89 6.0 — — — 2.5 — 0.50 0.10 0.01 Comparative B-1 93.39 6.0 — — — — — 0.50 0.10 0.01 production example 1 Comparative B-2 94.39   — — — 5.0 — 0.50 0.10 0.01 production example 2 Comparative B-3 89.65 6.0 — — — 2.5 — 1.5 0.10 0.25 production example 3 Comparative B-4 91.0 6.0 — — — 2.5 — 0.50 — — production example 4 Comparative B-5 91.4 6.0 — — — 2.5 — — 0.10 — production example 5

TABLE-US-00002 TABLE 2 Monomer composition (mol %) Monomer mixed solution (I) (a2) (a3) (a4) Symbol AM DM DML BQ APDM Total IA AA SMAS DMAA MBAA Total Production example 1-1 A1-1 23.96 5.0 — — — 5.0 0.5 — 0.30 0.05 — 0.05 Production example 1-2 A1-2 24.32 5.0 — — — 5.0 0.5 — 0.10 0.05 — 0.05 Production example 1-3 A1-3 22.83 5.0 — — — 5.0 0.5 — 0.90 0.05 — 0.05 Production example 1-4 A1-4 23.96 5.0 — — — 5.0 0.5 — 0.20 0.05 — 0.05 Production example 1-5 A1-5 23.96 5.0 — — — 5.0 0.5 — 0.30 0.05 — 0.05 Production example 1-6 A1-6 6.69 15.0  — — — 15.0  0.5 — 0.30 0.05 — 0.05 Production example 1-7 A1-7 22.28 3.0 1.0 1.0 — 5.0 0.5 — 0.30 0.05 — 0.05 Production example 1-8 A1-8 22.28 2.0 1.0 1.0 1.0 5.0 0.5 — 0.30 0.05 — 0.05 Production example 1-9 A1-9 22.01 5.0 — — — 5.0 3.0 — 0.30 0.05 — 0.05 Production example 1-10 A1-10 21.12 5.0 — — — 5.0 5.0 — 0.30 0.05 — 0.05 Production example 1-11 A1-11 26.17 3.0 — — — 3.0 0.5 — 0.30 0.05 — 0.05 Production example 1-12 A1-12 23.96 5.0 — — — 5.0 0.5 — 0.30 0.05 — 0.05 Production example 2-1 A2-1 30.06 1.0 — — — 1.0 2.0 — 0.30 0.05 — 0.05 Production example 2-2 A2-2 30.42 1.0 — — — 1.0 2.0 — 0.10 0.05 — 0.05 Production example 2-3 A2-3 28.93 1.0 — — — 1.0 2.0 — 0.90 0.05 — 0.05 Production example 2-4 A2-4 30.06 1.0 — — — 1.0 2.0 — 0.20 0.05 — 0.05 Production example 2-5 A2-5 30.06 1.0 — — — 1.0 2.0 — 0.30 0.05 — 0.05 Production example 2-6 A2-6 28.06 3.0 — — — 3.0 2.0 — 0.30 0.05 — 0.05 Production example 2-7 A2-7 30.62 1.0 — — — 1.0 2.0 — 0.30 0.05 — 0.05 Production example 2-8 A2-8 30.61 1.0 — — — 1.0 2.0 — 0.30 0.05 — 0.05 Production example 2-9 A2-9 31.01 1.0 — — — 1.0 — 2.0 0.30 0.05 — 0.05 Production example 2-10 A2-10 10.56 1.0 — — — 1.0 15.0  — 0.30 0.05 — 0.05 Production example 2-11 A2-11 30.06 1.0 — — — 1.0 2.0 — 0.30 0.05 — 0.05 Comparative B-1 24.18 5.0 — — — 5.0 — — 0.30 0.05 — 0.05 production example 1 Comparative B-2 31.45 — — — — — 1.5 — 0.30 0.05 — 0.05 production example 2 Comparative B-3 21.87 5.0 — — — 5.0 1.0 — 1.00 0.05 0.10 0.15 production example 3 Comparative B-4 23.1 5.0 — — — 5.0 1.0 — 0.30 — — — production example 4 Comparative B-5 24.42 5.0 — — — 5.0 0.5 — — 0.05 — 0.05 production example 5 Monomer composition (mol %) Monomer mixed solution (II) (a2) (a3) (a4) Symbol AM DM DML BQ APDM Total IA AA SMAS DMAA MBAA Total Production example 1-1 A1-1 66.93 1.0 — — — 1.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-2 A1-2 66.77 1.0 — — — 1.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-3 A1-3 67.52 1.0 — — — 1.0 2.0 — 0.10 0.05 0.05 0.1  Production example 1-4 A1-4 66.93 1.0 — — — 1.0 2.0 — 0.10 0.05 0.01 0.06 Production example 1-5 A1-5 66.93 1.0 — — — 1.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-6 A1-6 72.2 3.0 — — — 3.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-7 A1-7 68.61 3.0 1.0 1.0 — 5.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-8 A1-8 68.61 2.0 1.0 1.0 1.0 5.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-9 A1-9 59.38 1.0 — — — 1.0 9.0 — 0.20 0.05 0.01 0.06 Production example 1-10 A1-10 50.27 1.0 — — — 1.0 17.0  — 0.20 0.05 0.01 0.06 Production example 1-11 A1-11 64.72 3.0 — — — 3.0 2.0 — 0.20 0.05 0.01 0.06 Production example 1-12 A1-12 33.61 0.5 — — — 0.5 1.0 — 0.10 0.03 — 0.03 Production example 2-1 A2-1 60.83 5.0 — — — 5.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-2 A2-2 60.67 5.0 — — — 5.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-3 A2-3 61.42 5.0 — — — 5.0 0.5 — 0.10 0.05 0.05 0.1  Production example 2-4 A2-4 60.83 5.0 — — — 5.0 0.5 — 0.10 0.05 0.01 0.06 Production example 2-5 A2-5 60.83 5.0 — — — 5.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-6 A2-6 56.83 9.0 — — — 9.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-7 A2-7 60.27 3.0 1.0 1.0 — 5.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-8 A2-8 60.28 2.0 1.0 1.0 1.0 5.0 0.5 — 0.20 0.05 0.01 0.06 Production example 2-9 A2-9 59.88 5.0 — — — 5.0 — 0.5 0.20 0.05 0.01 0.06 Production example 2-10 A2-10 64.83 5.0 — — — 5.0 3.0 — 0.20 0.05 0.01 0.06 Production example 2-11 A2-11 30.56 2.5 — — — 2.5  0.25 — 0.10 0.03 — 0.03 Comparative B-1 69.21 1.0 — — — 1.0 — — 0.20 0.05 0.01 0.06 production example 1 Comparative B-2 62.94 — — — — — 3.5 — 0.20 0.05 0.01 0.06 production example 2 Comparative B-3 67.78 1.0 — — — 1.0 1.5 — 0.50 0.05 0.15 0.20 production example 3 Comparative B-4 67.9 1.0 — — — 1.0 1.5 — 0.20 — — — production example 4 Comparative B-5 66.98 1.0 — — — 1.0 2.0 — — 0.05 — 0.05 production example 5 Monomer composition (mol %) Monomer mixed solution (III) (a2) (a3) (a4) Symbol AM DM IA SMAS DMAA MBAA Total Production example 1-1 A1-1 Production example 1-2 A1-2 Production example 1-3 A1-3 Production example 1-4 A1-4 Production example 1-5 A1-5 Production example 1-6 A1-6 Production example 1-7 A1-7 Production example 1-8 A1-8 Production example 1-9 A1-9 Production example 1-10 A1-10 Production example 1-11 A1-11 Production example 1-12 A1-12 33.33 0.50 1.0 0.10 0.02 0.01 0.03 Production example 2-1 A2-1 Production example 2-2 A2-2 Production example 2-3 A2-3 Production example 2-4 A2-4 Production example 2-5 A2-5 Production example 2-6 A2-6 Production example 2-7 A2-7 Production example 2-8 A2-8 Production example 2-9 A2-9 Production example 2-10 A2-10 Production example 2-11 A2-11 30.28 2.5 0.25 0.10 0.02 0.01 0.03 Comparative B-1 production example 1 Comparative B-2 production example 2 Comparative B-3 production example 3 Comparative B-4 production example 4 Comparative B-5 production example 5

TABLE-US-00003 TABLE 3 Viscosity immediately after Weight-average synthesis Viscosity (mPa .Math. s) molecular weight Concentration Viscosity (pH: 4, Symbol (Unit: 10K) (%) (mPa .Math. s) concentration: 15%) Production example 1-1 A1-1 280 20 8500 2300 Production example 1-2 A1-2 160 20 8500 2300 Production example 1-3 A1-3 890 20 8600 2400 Production example 1-4 A1-4 350 15 10000 10000 Production example 1-5 A1-5 230 20 5000 1500 Production example 1-6 A1-6 250 20 8500 2300 Production example 1-7 A1-7 280 20 8700 2400 Production example 1-8 A1-8 280 20 8500 2300 Production example 1-9 A1-9 320 20 8500 2300 Production example 1-10 A1-10 340 20 8600 2400 Production example 1-11 A1-11 290 20 8500 2300 Production example 1-12 A1-12 320 20 8500 2300 Production example 2-1 A2-1 270 20 8500 2300 Production example 2-2 A2-2 160 20 8800 2500 Production example 2-3 A2-3 910 20 8500 2300 Production example 2-4 A2-4 340 15 10000 10000 Production example 2-5 A2-5 220 20 5000 1500 Production example 2-6 A2-6 260 20 8500 2300 Production example 2-7 A2-7 270 20 8600 2400 Production example 2-8 A2-8 290 20 8500 2300 Production example 2-9 A2-9 300 20 8500 2300 Production example 2-10 A2-10 360 20 8500 2300 Production example 2-11 A2-11 320 20 8500 2300 Comparative B-1 290 20 8500 2300 production example 1 Comparative B-2 320 20 8500 2300 production example 2 Comparative B-3 1250 20 8500 2300 production example 3 Comparative B-4 185 20 3400 1000 production example 4 Comparative B-5 85 20 8300 2250 production example 5

Influence of Weight Ratio of Each Polymer (1) (Viscosity of Polymer (1) and Viscosity of Polymer (2) are the Same)>

Examples 1 to 5, Comparative Examples 1 to 2

[0136] The polymer (A1-1) and the polymer (A2-1) were added in the weight ratios shown in Table 4 and mixed to obtain a paper-strengthening agent (A), respectively.

<Viscosity of Paper-Strengthening Agent (A), Polymer (A1) and Polymer (A2)>

[0137] Using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.), a viscosity of the paper-strengthening agent at a temperature of 25° C. was measured, which value was defined as X.sub.A (hereinafter, also referred to as a measured value X.sub.A). Moreover, a viscosity (pH: 4, concentration: 15%) of the polymer (A1) shown in Table 4 was defined as X.sub.A1, and a viscosity (pH: 4, concentration: 15%) of the polymer (A2) was defined as X.sub.A2.

[0138] Besides, an arithmetic mean value of the viscosity of the polymer (A1) and the viscosity of the polymer (A2) was calculated from

(Equation 2).

(Arithmetic mean value)=m.sub.A1×X.sub.A1+m.sub.A2×X.sub.A2  (Equation 2)

[0139] (m.sub.A1 is a ratio of a solid content weight of the polymer (A1) to a total weight of the polymer (A1) and the polymer (A2), m.sub.A2 is a ratio of a solid content weight of the polymer (A2) to the total weight of the polymer (A1) and the polymer (A2), and m.sub.A1+m.sub.A2=1.)

[0140] In this evaluation, (measured value X.sub.A)/(arithmetic mean value) was used as a value. The results are shown in Table 4.

<Preparation of Paper-Strengthening Agent for Evaluation on Papermaking>

[0141] Each paper-strengthening agent (A) shown in Table 4 was diluted by adding a deionized water so as to have a solid content concentration of 1.0%. Then, the following evaluation on papermaking was performed.

(Evaluation on Papermaking)

[0142] A waste corrugated fiberboard was beaten with a Niagara beater, and calcium chloride was added to a pulp slurry adjusted to have 350 ml of Canadian Standard Freeness (C.S.F) to adjust an electrical conductivity to 4.0 mS/cm. An alum (aluminum sulfate) was added to this slurry liquid in a solid content of 1.0% based on a solid content weight of the pulp slurry, and then paper-strengthening agent (A) shown in Table 4 was added in a solid content of 0.5% based on the solid content weight of the pulp slurry. The pH of each pulp slurry was adjusted to 6.5. The slurry was dehydrated with a tappi sheet machine and pressed at 5 kg/cm.sup.2 for 2 minutes for papermaking with a basis weight of 150 g/m.sup.2. Next, the paper was dried in a rotary dryer at 105° C. for 4 minutes and subjected to humidity control for 24 hours under a condition of a temperature at 23° C. and a humidity of 50%, and then a specific burst strength was measured. Besides, electrical conductivity and specific burst strength were measured by the following methods. The results are shown in Table 4.

<Electrical Conductivity>

[0143] An electrical conductivity was measured using pH/COND METER D-54 (manufactured by HORIBA, Ltd.).

<Freeness>

[0144] The freeness was measured according to JIS P 8121 using Canadian Standard Freeness (C.S.F).

<Specific Burst Strength>

[0145] Using the paper obtained above, a specific burst strength (kPa.Math.m.sup.2/g) was measured according to JIS P 8131.

TABLE-US-00004 TABLE 4 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 1 A1-1 2300 A2-1 2300 90/10 Example 2 A1-1 2300 A2-1 2300 75/25 Example 3 A1-1 2300 A2-1 2300 50/50 Example 4 A1-1 2300 A2-1 2300 25/75 Example 5 A1-1 2300 A2-1 2300 10/90 Comparative A1-1 2300 A2-1 2300 97/3  example 1 Comparative A1-1 2300 A2-1 2300  3/97 example 2 Viscosity (pH: 4, concentration: 15%) (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 1 3000 2300 1.30 388 3.20 Example 2 4750 2300 2.07 397 3.25 Example 3 6000 2300 2.61 411 3.26 Example 4 4900 2300 2.13 385 3.19 Example 5 3200 2300 1.39 382 3.16 Comparative 2490 2300 1.08 383 3.14 example 1 Comparative 2500 2300 1.09 378 3.12 example 2

<Influence of Weight Ratio of Each Polymer (2) (Viscosity of Polymer (1) and Viscosity of Polymer (2) are the Same)>

Examples 6-10

[0146] The polymer (A1-4) and the polymer (A2-4) were added in the weight ratios shown in Table 5 and mixed to obtain a paper-strengthening agent (A), respectively. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. The results are shown in Table 5.

TABLE-US-00005 TABLE 5 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 6 A1-4 10000 A2-4 10000 90/10 Example 7 A1-4 10000 A2-4 10000 75/25 Example 8 A1-4 10000 A2-4 10000 50/50 Example 9 A1-4 10000 A2-4 10000 25/75 Example 10 A1-4 10000 A2-4 10000 10/90 Viscosity (pH: 4, concentration: 15%) (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 6 19000 10000 1.90 498 3.28 Example 7 33500 10000 3.35 545 3.24 Example 8 41500 10000 4.15 597 3.19 Example 9 35000 10000 3.50 559 3.23 Example 10 21000 10000 2.10 505 3.27

<Influence of Weight-Average Molecular Weight of Each Polymer>

Examples 11-19, Comparative Examples 3-9

[0147] The polymer (A1) and the polymer (A2) each having a different weight-average molecular weight were added in the weight ratios shown in Table 6 and mixed to obtain a paper-strengthening agent, respectively. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. The results are shown in Table 6.

TABLE-US-00006 TABLE 6 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 11 A1-1 2300 A2-1 2300 50/50 Example 12 A1-1 2300 A2-2 2500 50/50 Example 13 A1-1 2300 A2-3 2300 50/50 Example 14 A1-2 2300 A2-1 2300 50/50 Example 15 A1-2 2300 A2-2 2500 50/50 Example 16 A1-2 2300 A2-3 2300 50/50 Example 17 A1-3 2400 A2-1 2300 50/50 Example 18 A1-3 2400 A2-2 2500 50/50 Example 19 A1-3 2400 A2-3 2300 50/50 Comparative A1-1 2300 — 100/0  example 3 Comparative A1-2 2300 — 100/0  example 4 Comparative A1-3 2400 — 100/0  example 5 Comparative — A2-1 2300  0/100 example 6 Comparative — A2-2 2500  0/100 example 7 Comparative — A2-3 2300  0/100 example 8 Comparative A1-1 2300 A1-2 2300 50/50 example 9 Viscosity (pH: 4, concentration: 15%) (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 11 6000 2300 2.61 411 3.26 Example 12 5700 2400 2.38 395 3.24 Example 13 6300 2300 2.74 437 3.31 Example 14 5850 2300 2.54 389 3.23 Example 15 5300 2400 2.21 375 3.22 Example 16 6100 2300 2.65 411 3.28 Example 17 6300 2350 2.68 449 3.32 Example 18 6250 2450 2.55 410 3.26 Example 19 6700 2350 2.85 443 3.35 Comparative 2300 2300 — 381 3.14 example 3 Comparative 2300 2300 — 367 3.08 example 4 Comparative 2400 2400 — 395 3.18 example 5 Comparative 2300 2300 — 376 3.10 example 6 Comparative 2500 2500 — 365 3.04 example 7 Comparative 2300 2300 — 393 3.14 example 8 Comparative 2350 2300 1.02 376 3.11 example 9

<Influence of Weight Ratio of Each Polymer (3) (Viscosity of Polymer (1) and Viscosity of Polymer (2) are Different)>

Examples 20 to 24, Comparative Examples 10 to 11

[0148] The polymer (A1-4) and the polymer (A2-1) were added in the weight ratios shown in Table 7 and mixed to obtain a paper-strengthening agent (A), respectively. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. The results are shown in Table 7.

TABLE-US-00007 TABLE 7 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 20 A1-4 10000 A2-1 2300 90/10 Example 21 A1-4 10000 A2-1 2300 75/25 Example 22 A1-4 10000 A2-1 2300 50/50 Example 23 A1-4 10000 A2-1 2300 25/75 Example 24 A1-4 10000 A2-1 2300 10/90 Comparative A1-4 10000 A2-1 2300 98/2  example 10 Comparative A1-4 10000 A2-1 2300  2/98 example 11 Viscosity (pH: 4, concentration: 15%) (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 20 14000 9230 1.52 467 3.27 Example 21 17300 8075 2.14 484 3.26 Example 22 16100 6150 2.62 464 3.28 Example 23 8900 4225 2.11 434 3.23 Example 24 4500 3070 1.47 410 3.19 Comparative 10500 9769 1.07 441 3.19 example 10 Comparative 2730 2531 1.08 389 3.15 example 11

<Influence of Changing of Type of Polymer (A1)>

Examples 25 to 33, Comparative Examples 12 to 20

[0149] The polymer (A1-4) and the polymer (A2-1) were mixed in the weight ratios shown in Table 8 to obtain a paper-strengthening agent, respectively. Moreover, the polymer (A1-5) to the polymer (A1-12) were mixed in the similar manner to obtain paper-strengthening agents. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. Moreover, as a comparison, only the polymer (A1-4) to the polymer (A1-12) were used for evaluation in the similar manner. The results are shown in Table 8.

TABLE-US-00008 TABLE 8 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 25 A1-4 10000 A2-1 2300 50/50 Example 26 A1-5 1500 A2-1 2300 50/50 Example 27 A1-6 2300 A2-1 2300 50/50 Example 28 A1-7 2400 A2-1 2300 50/50 Example 29 A1-8 2300 A2-1 2300 50/50 Example 30 A1-9 2300 A2-1 2300 50/50 Example 31 A1-10 2400 A2-1 2300 50/50 Example 32 A1-11 2300 A2-1 2300 50/50 Example 33 A1-12 2300 A2-1 2300 50/50 Comparative A1-4 10000 — 100/0  example 12 Comparative A1-5 1500 — 100/0  example 13 Comparative A1-6 2300 — 100/0  example 14 Comparative A1-7 2400 — 100/0  example 15 Comparative A1-8 2300 — 100/0  example 16 Comparative A1-9 2300 — 100/0  example 17 Comparative A1-10 2400 — 100/0  example 18 Comparative A1-11 2300 — 100/0  example 19 Comparative A1-12 2300 — 100/0  example 20 Viscosity at pH of 4.0 (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 25 16100 6150 2.62 464 3.28 Example 26 4700 1900 2.47 392 3.24 Example 27 5400 2300 2.35 420 3.21 Example 28 6350 2350 2.70 414 3.27 Example 29 6350 2300 2.76 416 3.28 Example 30 8000 2300 3.48 463 3.34 Example 31 13800 2350 5.87 514 3.19 Example 32 2800 2300 1.22 356 3.18 Example 33 6400 2300 2.78 418 3.28 Comparative 10000 10000 — 430 3.18 example 12 Comparative 1500 1500 — 372 3.10 example 13 Comparative 2300 2300 — 399 3.07 example 14 Comparative 2400 2400 — 385 3.15 example 15 Comparative 2300 2300 — 390 3.16 example 16 Comparative 2300 2300 — 411 3.17 example 17 Comparative 2400 2400 — 442 3.14 example 18 Comparative 2300 2300 — 354 3.11 example 19 Comparative 2300 2300 — 397 3.15 example 20

<Influence of Changing of Type of Polymer (A2)>

Examples 34 to 41, Comparative Examples 21 to 28

[0150] The polymer (A1-1) and the polymer (A2-4) were mixed in the weight ratios shown in Table 9 to obtain a paper-strengthening agent, respectively. Moreover, the polymer (A2-5) to the polymer (A2-11) were mixed in the similar manner to obtain paper-strengthening agents. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. Moreover, as a comparison, only the polymer (A2-4) to the polymer (A2-11) were used for evaluation in the similar manner. The results are shown in Table 9.

TABLE-US-00009 TABLE 9 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 34 A1-1 2300 A2-4 10000 50/50 Example 35 A1-1 2300 A2-5 1500 50/50 Example 36 A1-1 2300 A2-6 2300 50/50 Example 37 A1-1 2300 A2-7 2400 50/50 Example 38 A1-1 2300 A2-8 2300 50/50 Example 39 A1-1 2300 A2-9 2300 50/50 Example 40 A1-1 2300 A2-10 2300 50/50 Example 41 A1-1 2300 A2-11 2300 50/50 Comparative — A2-4 10000  0/100 example 21 Comparative — A2-5 1500  0/100 example 22 Comparative — A2-6 2300  0/100 example 23 Comparative — A2-7 2400  0/100 example 24 Comparative — A2-8 2300  0/100 example 25 Comparative — A2-9 2300  0/100 example 26 Comparative — A2-10 2300  0/100 example 27 Comparative — A2-11 2300  0/100 example 28 Viscosity at pH of 4.0 (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 34 15900 6150 2.59 459 3.28 Example 35 4700 1900 2.47 391 3.24 Example 36 5000 2300 2.17 463 3.32 Example 37 6300 2350 2.68 407 3.27 Example 38 6300 2300 2.74 411 3.28 Example 39 4900 2300 2.13 376 3.22 Example 40 7050 2300 3.07 457 3.18 Example 41 6400 2300 2.78 416 3.28 Comparative 10000 10000 — 419 3.16 example 21 Comparative 1500 1500 — 364 3.08 example 22 Comparative 2300 2300 — 449 3.14 example 23 Comparative 2400 2400 — 387 3.11 example 24 Comparative 2300 2300 — 390 3.12 example 25 Comparative 2300 2300 — 350 3.08 example 26 Comparative 2300 2300 — 454 3.07 example 27 Comparative 2300 2300 — 404 3.12 example 28

<Influence of Polymer (B) in Comparative Production Example>

Comparative Examples 29 to 34

[0151] Using the polymer (B-1) to the polymer (B-5), two types of polymers shown in Table 10 were added in the predetermined weight ratios and mixed to obtain a paper-strengthening agent, respectively. A viscosity measurement and evaluation on papermaking with each paper-strengthening agent were performed in the similar manner as in the above-described method. The results are shown in Table 10.

TABLE-US-00010 TABLE 10 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Comparative B-1 2300 A2-1 2300 50/50 example 29 Comparative B-3 2300 A2-1 2300 50/50 example 30 Comparative B-4 1000 A2-1 2300 50/50 example 31 Comparative B-5 2250 A2-1 2300 50/50 example 32 Comparative A1-1 2300 B-2 2300 50/50 example 33 Comparative B-1 2300 B-2 2300 50/50 example 34 Viscosity at pH of 4.0 (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Comparative 5600 2300 2.43 376 2.89 example 29 Comparative 11400 2300 4.96 568 2.93 example 30 Comparative 3100 1650 1.88 382 3.13 example 31 Comparative 5000 2275 2.20 368 3.09 example 32 Comparative 5500 2300 2.39 375 2.90 example 33 Comparative 10300 2300 4.48 566 2.88 example 34
<Evaluation in Papermaking Environment with Low Electrical Conductivity>

Examples 42 to 46, Comparative Examples 35 to 36

[0152] The similar evaluation was performed using a pulp slurry in which calcium chloride was added to adjust an electrical conductivity to 1.0 mS/cm in the above-described evaluation on papermaking. Besides, as paper-strengthening agents, those obtained by mixing two types of polymers shown in Table 11 in the predetermined polymerization ratios were used. The results are shown in Table 11.

TABLE-US-00011 TABLE 11 Polymer (1) Polymer (2) Viscosity X.sub.A1 Viscosity X.sub.A2 (pH: 4, concentration: 15%) (pH: 4, concentration: 15%) Weight ratio No. (mPa .Math. s) No. (mPa .Math. s) (solid content) Example 42 A1-1 2300 A2-1 2300 50/50 Example 43 A1-2 2300 A2-1 2300 50/50 Example 44 A1-3 2400 A2-1 2300 50/50 Example 45 A1-4 10000 A2-1 2300 50/50 Example 46 A1-5 1500 A2-1 2300 50/50 Comparative A1-1 2300 — 100/0  example 35 Comparative — A2-1 2300  0/100 example 36 Viscosity (pH: 4.0, concentration: 15%) (mPa .Math. s) Measured Arithmetic Measured value Specific burst value X.sub.A mean value X.sub.A/arithmetic Freeness strength (mPa .Math. s) (mPa .Math. s) mean value (mL) (kPa .Math. m.sup.2/g) Example 42 6000 2300 2.61 450 3.24 Example 43 5850 2300 2.54 432 3.22 Example 44 6300 2350 2.68 488 3.22 Example 45 16100 6150 2.62 522 3.19 Example 46 4700 1900 2.47 435 3.22 Comparative 2300 2300 — 414 3.16 example 35 Comparative 2300 2300 — 409 3.13 example 36