JPH09143894A - Production of neutral paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce neutral paper in a neutral region in the good yields of pulp fibers and a filler by adding a specific aqueous additive to a pulp slurry containing the filler. SOLUTION: An amphoteric crosslinked acrylamide copolymer produced by copolymerizing 0.005-5mol.% of a crosslinking monomer such as methylolacrylamide as an essential component, 1-20mol% of an anionic vinylic monomer such as acrylic acid, 0.5-10mol% of a cationic vinylic monomer such as dimethylaminoethyl acrylate, and 60-98mol% of acrylamide and/or methacrylamide, and a cation-modified acrylamide polymer produced by adding a hypohalite salt and an alkali catalyst such as potassium hydroxide to the aqueous solution of an acrylamide polymer and subsequently subjecting the mixture to a Hoffmann decomposition reaction are added to prepare an aqueous additive mixture for paper making. A pulp slurry containing calcium carbonate as a filler and having a pH of 6-9 is mixed with the above-described additive mixture in an amount of 0.01-2% based on the dry weight of the pulp, and subsequently subjected to the production of the neutral paper in a neutral region.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing neutral paper, and more particularly to a method for producing neutral paper from a pulp slurry containing a filler. More specifically, the present invention relates to a method for producing neutral paper with improved yields of pulp fiber and filler.

[0002]

2. Description of the Related Art Generally, in the papermaking process, the whiteness and opacity of papermaking are improved, the smoothness and finish of the paper are improved, and the ink absorption and printability are further improved. Various fillers are used for the purpose of imparting flexibility to the.

However, if only the filler is added, most of the filler will flow out into white water during papermaking, the yield will be extremely low, the initial effect will not be exhibited, and there will be a large economical disadvantage. Bring For this reason, in the industry, it is common to use some kind of filler yield improver in the general papermaking process in which the filler is added.

Conventionally, acidic papermaking has been popularly carried out by adding a sulfuric acid band as a filler and making paper in an acidic region. However, in recent years, from the viewpoint of long-term storage of printed matter, neutral paper making without using the sulfuric acid band at all or using a very small amount in a weakly acidic to weakly alkaline region of pH 6 to 9 is widely used. It has become to.

As a method for improving the yield in the above-mentioned neutral paper making, for example, the following various methods have been proposed. (1) JP-A-57-77399 proposes a polymer copolymer of (meth)acrylic acid ester and acrylamide as a filler retention agent. (2) JP-A-57-51900 discloses that a binder composed of a complex of cationic starch and colloidal silicic acid is effective in improving the filler yield and paper strength. (3) JP-A-62-125096 discloses the combined effect of using an amphoteric acrylamide polymer and an aluminum compound. (4) Japanese Patent Application Laid-Open No. 62-191598 discloses that addition of bentonite and a synthetic cationic polymer improves yield and drainage. (5) JP-A-62-110998 discloses that a pulp slurry contains a colloidal silicic acid and a cationic or amphoteric acrylamide derivative, and further contains a cationized starch to provide a sufficient filler for a neutral papermaking system. A technique for obtaining a yield is disclosed. (6) JP-A-5-51895 discloses a method for improving retention and drainage by using a specific starch and a zwitterionic acrylamide copolymer in combination in a high-yield pulp neutral papermaking system. Has been done. (7) Japanese Unexamined Patent Publication (Kokai) No. 5-78997 discloses a method in which an amphoteric polyacrylamide copolymer is used in combination with a polymer having a cationic group to improve the filler yield and drainage.

[0006]

Generally, in order to make neutral paper without problems, it is necessary to secure a good yield of pulp fibers and fillers in the pulp slurry. That is,
Generally, when the yield is low, papermaking system stains, paper breaks, etc. are induced, and the operability is significantly deteriorated. Therefore, as described above, various yield improving agents and yield improving systems have been proposed in the art.

As mentioned above, a method for producing neutral paper from a pulp slurry containing calcium carbonate having a pH of 6 to 9 is actively used in the art, and in that case, it is important to improve the yield of calcium carbonate. It goes without saying that it is an issue. We have
An intensive study was conducted on the improvement of the yield of neutral pulp fibers and fillers using a pulp slurry containing calcium carbonate as the filler. As a result, the present inventors use an aqueous mixture-based additive for papermaking comprising a zwitterionic crosslinkable acrylamide polymer prepared by using a crosslinkable vinyl monomer as an essential constituent monomer and a cation-modified acrylamide polymer. As a result, it was found that the yields of pulp fiber and filler are remarkably improved, and the present invention has been completed.

[0008]

SUMMARY OF THE INVENTION The present invention will be described in brief. In the method for producing neutral paper from a pulp slurry containing a filler, the present invention provides the pulp slurry with a crosslinkable vinyl monomer as an essential constituent monomer. The present invention relates to a method for producing neutral paper, which comprises adding an aqueous mixture type additive comprising a zwitterionic cross-linking type acrylamide polymer and a cation-modified acrylamide polymer, and making paper in a neutral range.

The technical constitution of the present invention will be described in detail below.

First, in the pulp slurry system containing a filler, which is the object of the papermaking method of the present invention, as the filler, any of various known fillers used in conventional papermaking processes can be used. Kaolin, titanium dioxide, clay, calcined clay, synthetic silica, aluminum hydroxide, talc, heavy calcium carbonate, light calcium carbonate and the like can be used. In the present invention, of the above-mentioned fillers, heavy calcium carbonate or light calcium carbonate is particularly preferable. Further, a mixture of these calcium carbonate and the above-mentioned other fillers is also preferable. In the method for producing neutral paper of the present invention, the pH of the pulp slurry at the time of paper making containing the filler is preferably in a substantially neutral region, specifically, in the range of 6 to 9. The aqueous mixture-based additive comprising the amphoteric cross-linking acrylamide polymer and the cation-modified acrylamide polymer of the present invention has a markedly high yield of pulp fiber and filler in the pH range of the pulp slurry system in the neutral region. It is possible to exert an excellent effect.

Next, the zwitterionic cross-linking type acrylamide polymer which is one of the essential components of the aqueous mixture type additive of the present invention will be explained. The amphoteric crosslinkable acrylamide polymer of the present invention is prepared by using a crosslinkable vinyl monomer as an essential constituent monomer. That is,
The amphoteric crosslinkable acrylamide polymer of the present invention, (a) crosslinkable vinyl monomer, (b) anionic hynyl monomer, (c) cationic vinyl monomer, and (d)
It is composed of a copolymer prepared by copolymerizing a monomer mixture consisting of acrylamide and/or methacrylamide.

In the present invention, it is used to prepare the above-mentioned zwitterionic cross-linked acrylamide polymer (a).
Examples of the crosslinkable vinyl monomer as a component include bis(meth)acrylamides such as methylolacrylamide, methylenebis(meth)acrylamide, and ethylenebis(meth)acrylamide; diglycols such as ethylene glycol di(meth)acrylate and diethylene glycol di(meth)acrylate. (Meth)acrylates; divinyl adipate,
Divinyl esters such as divinyl sebacate; epoxy acrylates; urethane acrylates; divinylbenzene, 1,3,5 triacryloylhexahydro-S
-Triazine, triallyl isocyanurate, triallyl trimellitate, triallyl amine, N,N-diallyl acrylamide, tetramethylol methane tetraacrylate, tetraallyl pyromellilate, N,N-dimethyl acrylamide having an N-substituted amide group, etc. Can be mentioned.

In the above-mentioned (a) crosslinkable vinyl monomer, methylol acrylamide, methylene bis acrylamide, diethylene glycol dimethacrylate,
1,3,5 triacryloylhexahydro-S-triazine, tetramethylolmethane tetraacrylate,
N,N-dimethylacrylamide is preferred, and methylolacrylamide, methylenebisacrylamide, 1,3,5 triacryloylhexahydro-S-triazine, N,N-dimethylacrylamide are particularly suitable. In the present invention, the above-mentioned (a) crosslinkable vinyl monomer may be used alone or in combination of two or more.

In the present invention, it is used to prepare the above-mentioned zwitterionic crosslinked acrylamide polymer (b).
Examples of the anionic vinyl monomer as a component include acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, or vinyl monomers such as sodium, potassium and ammonium salts thereof. Is mentioned.

In the present invention, it is used to prepare the above-mentioned zwitterionic crosslinked acrylamide polymer (c).
As the component cationic vinyl monomer, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide, diethylaminopropyl acrylamide, diethylaminopropyl methacrylamide, acrylamine, Vinyl monomers having tertiary amine groups such as diallylamine or salts thereof with inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and sulfamic acid, or salts of organic acids or vinyl monomers containing tertiary amine groups and methyl chloride, benzyl chloride, Examples thereof include vinyl monomers containing a quaternary ammonium salt obtained by a reaction with a quaternizing agent such as dimethylsulfate, epichlorohydrin, glycidyltrimethylammonium chloride, and 3-chloro-2-hydroxypropyltrimethylammonium chloride.

In the present invention, the anionic vinyl monomer (b) and the cationic vinyl monomer (c) described above are used.
Can be used alone or in combination of two or more in each category.

In the amphoteric cross-linking type acrylamide polymer of the present invention, the molar ratio of the components (a) to (d) is 0.005 to 5 mol% for the component (a), and 1 to 1 for the component (b). 20 mol%, the component (c) is 0.5 to 10 mol%,
The component (d) is preferably in the range of 60 to 98 mol %. When the component (a) is less than 0.005 mol %, the effect of the present invention is not improved, and when it exceeds 5 mol %, a gelation phenomenon occurs.

The characteristic feature of the present invention is that when the use ratio (molar ratio) of each of the components (a) to (d) is out of the above range (out of the above range), the pulp fiber targeted by the present invention is That is, the yield effect of the filler cannot be sufficiently obtained.

In the present invention, in addition to the above-mentioned essential constituent monomers, the effects of the present invention are not substantially impaired,
A monomer copolymerizable with the above-mentioned constituent monomers can be used. As the above-mentioned copolymerizable monomer,
Nonionic vinyl monomers such as (meth)acrylic acid ester, vinyl acetate and acrylonitrile can be used.

As the method for producing the zwitterionic cross-linking type acrylamide polymer of the present invention, various conventionally known methods can be adopted. For example, a reaction vessel equipped with a stirrer and a nitrogen gas introduction tube is charged with the constituent monomers (a), (b), (c) and (d) of the present invention and water.
As a polymerization initiator, hydrogen peroxide, ammonium persulfate,
Peroxides such as potassium persulfate and ammonium hydroperoxide, or redox initiators combining these peroxides with a reducing agent such as bisulfite, or 2,2'azobis(2-aminodibropane) hydrochloride Such as a water-soluble azo polymerization initiator, etc., and if necessary, a polymerization regulator or a chain transfer agent such as isopropyl alcohol, allyl alcohol, sodium hypophosphite, mercaptoethanol, thioglycolic acid, etc. is appropriately used to react. Temperature 40-8
The desired amphoteric crosslinked acrylamide polymer may be prepared by reacting at 0° C. for 1 to 5 hours. In the above-mentioned polymerization method, when N,N-dimethylacrylamide having an N-substituted amide group is used as the crosslinkable vinyl monomer as the component (a), N,N-dimethylacrylamide prepared by the above-mentioned polymerization method is included. It is necessary to add an oxidizing radical catalyst to the copolymer and to carry out a crosslinking reaction at a temperature of 60 to 80° C. for 1 to 5 hours. Examples of the oxidizing radical catalyst include inorganic peroxides such as hydrogen peroxide and persulfates (ammonium persulfate, potassium persulfate, etc.).

Next, the cation-modified acrylamide polymer, which is the other essential component of the aqueous mixture-based papermaking additive of the present invention, will be described. Examples of the cation-modified acrylamide polymer of the present invention include a cation-modified acrylamide polymer by a Hoffmann decomposition reaction and a cation-modified acrylamide polymer by a Mannich reaction. The former method for preparing the cation-modified acrylamide polymer by the Hoffman decomposition reaction may be the same as the conventional method. For example, by adding a hypohalite and an alkali catalyst to an aqueous solution of an acrylamide polymer, the acrylamide polymer and the hypohalite are reacted in an alkaline region, and then an acid is added to adjust the pH to 3 It may be adjusted to 0.5 to 5.5.

In the present invention, the cation-modified acrylamide polymer is not limited to the above-mentioned Hoffman decomposition reaction, and may be one prepared by utilizing the Hoffman decomposition reaction of the following modes. That is, a cation-modified product prepared by Hofmann decomposition reaction of polyacrylamide in the presence of choline chloride (JP-A-53-109594),
A cation-modified product prepared by adding a quaternization reaction product of a tertiary amine having a hydroxyl group and benzyl chloride or its derivative in the Hoffman decomposition reaction (Japanese Patent Publication No. 58-868).
No. 2), a cation-modified product prepared by adding an organic polyvalent amine as a stabilizer in the Hoffman decomposition reaction (Japanese Patent Publication No.
0-17322), or a cation-modified product prepared by adding a specific cationic compound as a stabilizer in the Hoffmann decomposition reaction (Japanese Patent Publication No. 62-45884). The polymer prepared by the Hoffmann decomposition reaction generally contains about 5 to 5 cationic monomer units.
40 mol% and acrylamide units are contained in about 60 to 95 mol %. The average molecular weight of the cation-modified acrylamide polymer prepared by the Hoffmann decomposition reaction is preferably about 5 to 1,000,000.

In the present invention, the cation-modified acrylamide polymer may be one obtained by the Mannich reaction. For the preparation of the cation-modified acrylamide polymer by the Mannich reaction, a method similar to the conventional method may be adopted. For example, conditions may be adopted in which a secondary amine such as formalin and dimethylamine is added to an aqueous solution of an acrylamide polymer and the reaction is performed at a temperature of about 40 to 60° C. for about 1 to 5 hours. The polymer prepared by the Mannich reaction generally contains about 10 to 60 mol% of cationic monomer units and about 40 to 90 mol% of acrylamide units.

In the present invention, when a cation-modified acrylamide polymer prepared by a Hoffmann decomposition reaction is used as the cation-modified acrylamide polymer, a very excellent yield effect of pulp fiber and filler can be obtained. There is.

The method for producing neutral paper according to the present invention is carried out under the water-soluble mixture type papermaking additive comprising the above-mentioned specific zwitterionic cross-linking type acrylamide polymer and cation-modified acrylamide polymer. In addition, it is essential to make paper in the neutral range. The use mode of the aqueous mixture-based papermaking additive of the present invention is used in the form of an aqueous mixture prepared by previously mixing the essential components constituting the additive, or the essential components are added immediately before being added to the pulp slurry. When mixed and used in the form of an aqueous mixture, the yield effect of pulp fibers and filler can be significantly improved. Such an effect cannot be obtained when only one of the above-mentioned essential components is used and when both components are separately added to the pulp slurry.

As described above, the method for producing neutral paper according to the present invention is, for example, an aqueous mixture system in which an aqueous solution of a zwitterionic cross-linking type acrylamide polymer and a water-soluble cation-modified acrylamide polymer are mixed in advance. This is to prepare a papermaking additive and add it to a pulp slurry containing a filler for papermaking in a neutral region. Needless to say, the high-concentration aqueous mixture-based papermaking additive prepared in advance can be appropriately diluted with water if necessary. The concentration of the above-mentioned aqueous mixture-based papermaking additive is not particularly limited.

In the method for producing neutral paper of the present invention, the use ratio of each component of the aqueous mixture-based papermaking additive, that is,
The mixing ratio of the amphoteric crosslinkable acrylamide polymer and the cation-modified acrylamide polymer can be selected from a wide range depending on the papermaking conditions such as raw pulp, papermaking pH, and the amount of band added, but in terms of solid content weight ratio. , Usually the former:
The latter may be about 95:5 to 5:95. The preferable mixing ratio is the former:the latter=80:20 to 20:80. The specific amphoteric cross-linking acrylamide polymer and the cation-modified acrylamide polymer of the present invention form a stable and uniform colloidal mixed aqueous solution in the water-soluble mixed system. When a zwitterionic acrylamide polymer other than the above-mentioned specific zwitterionic cross-linking acrylamide polymer of the present invention is used in combination with a cation-modified acrylamide polymer, the diluted solution immediately after mixing becomes cloudy and insoluble. , Aggregates may precipitate over time.

When the aqueous mixture-based papermaking additive of the present invention is used in the papermaking process, it may be used in a desired amount in terms of dry weight of pulp. Generally, 0.001% to 2%, preferably 0.01% to 0.5%, based on the dry weight of the solid matter, is added to the raw material pulp, and the paper is dried in the neutral region. Then, the neutral paper may be manufactured. In the present invention, a cationized starch-based paper strengthening agent, a neutral sizing agent, a dye, an antifoaming agent, a sulfuric acid band, etc. can be used as required.

Under the aqueous mixture-based additive for papermaking of the present invention, an excellent effect is exhibited in the yield of the pulp fiber and the filler. The present inventors have inferred the following about the mechanism of expression of the above-mentioned excellent effect. The zwitterionic crosslinkable acrylamide polymer containing the crosslinkable vinyl monomer of the present invention as an essential component has a relatively high molecular weight and has a highly branched structure. It is presumed that it forms a very stable complex with an acrylamide polymer. And
It is considered that the stable water-soluble composite described above is an important factor in exhibiting the excellent pulp fiber and filler retention effect.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to Preparation Examples, Examples and Comparative Examples.

[0031]

[Preparation example of zwitterionic cross-linked acrylamide polymer]

(Preparation example R-1) 62.3 g of acrylamide (d component) and itaconic acid (b component) 5.9 were placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube.
g, trimethylmethacryloyloxyethylene ammonium chloride (component c) 3.8 g, 1% 1.3.5-triacryloylhexahydro-S-triazine (component a) 2.2 g, and soft water 430 g were charged, and then the pH was adjusted. 3.
Adjust to 5, raise the temperature to 50°C while passing nitrogen gas, and
% Ammonium persulfate 1.5 ml, 5% sodium bisulfite 1.
5 ml was added and reacted at 50 to 80° C. for 3 hours to prepare a zwitterionic crosslinked acrylamide polymer. The properties are shown in Table 1.

(Preparation Example R-2/R-3/R-4/R-6
/R-7/R-8) Preparation Example R-1 except that any one of the types of components (a) to (d) or the amount thereof used was changed as shown in Table 1. The same operation as in Example R-1 was performed to prepare a zwitterionic crosslinked acrylamide polymer. The properties are shown in Table 1.

Preparation Example R-5 In Preparation Example R-1,
A copolymer is prepared by performing the same operation as in Preparation Example R-1 except that one of the types of the components (a) to (d) or the amount thereof is changed as shown in Table 1. did. Ammonium persulfate was added to the above-mentioned copolymer in an amount corresponding to equimolar amount of dimethylacrylamide and reacted at 70 to 80° C. for 1 hour to prepare a zwitterionic crosslinked acrylamide polymer. The properties are shown in Table 1.

In Table 1, each symbol means the following. a-1: TAF (1.3.5, triacryloylhexahydro-S-triazine) a-2: MBA (methylenebisacrylamide) a-3: DMAA (dimethylacrylamide) a-4: MAA (methylolacrylamide) b -1: itaconic acid b-2: acrylic acid b-3: maleic anhydride c-1: DMC (trimethylmethacryloyloxyethyl ammonium chloride) c-2: DM (dimethylaminoethyl methacrylate) c-3: DMAPAA (dimethylamino) Propyl acrylamide)

[0035]

[Table 1]

[0036]

[Preparation example of cation-modified acrylamide polymer by Hoffmann degradation]

(Preparation Example H-9) Effective chlorine concentration of 12% with respect to 300 g of an acrylamide polymer having an average molecular weight of 100,000 and a concentration of 15%
Sodium hypochlorite 37.5g and 48% caustic potash 15g
An aqueous alkaline sodium hypozincate solution containing water is added dropwise while cooling and stirring, and after completion of the addition, the temperature is kept at 25°C for another 60 minutes.
Hold at ℃ to carry out the reaction. After completion of the reaction, the pH of the reaction solution was adjusted to 4.5 with dilute hydrochloric acid to obtain a cation-modified acrylamide polymer with a Hofmann decomposition reaction having a polymer concentration of 10%. The properties are shown in Table 2.

Preparation Example H-10/H-11 Preparation Example H-
In Example 9, the same operation as in Preparation Example H-9 was conducted except that the acrylamide polymer was replaced with an average molecular weight of 500,000, and sodium hypochlorite and caustic potash were used in amounts corresponding to the cation modification rate shown in Table 2. Thus, a cation-modified acrylamide polymer obtained by the Hoffman decomposition reaction was obtained. The properties are shown in Table 2. In Table 2, the cation modification rate mol% (cation monomer unit) is an actual measurement value quantified by the colloid titration method. Also, the values in parentheses in the same column are
The theoretical value is shown.

[0038]

[Table 2]

[0039]

[Preparation example of cation-modified acrylamide polymer by Mannich reaction]

(Preparation Example M-12) 37% formalin 19.2% g with respect to 400 g of an aqueous solution of anionic acrylamide polymer having an average molecular weight of 400,000 and a concentration of 7% (anion degree 5 mol %),
25 g of 50% dimethylamine aqueous solution was added, and thereafter the same operation as in Preparation Example M-12 was carried out to obtain a cation-modified acrylamide polymer by Mannich reaction. The properties are shown in Table 3. In Table 3, the cation modification rate mol% (cation monomer unit) is a value determined by the colloid titration method.

[0040]

[Table 3]

(Examples 1 to 10) Pulp L-BKP (4
00 ml C.I. S. Place 500 ml of a 0.6% strength pulp slurry of F) in a Brit jar tester. Next, the mixture is stirred at 1500 rpm, and 0.5% of sulfuric acid band (dry weight of pulp: the same applies hereinafter) is added. After 40 seconds, 0.7% of pearl gum HMS (Cationic tapioca starch manufactured by Hoshiko Kagaku Kogyo Co., Ltd.) was added, and after 40 seconds,
Add 20% of light calcium carbonate. Furthermore, after 20 seconds, stirring was reduced by 750 rpm, and 20 seconds after that, the amphoteric cross-linked acrylamide polymers of Preparation Examples R1 to R6 and the cations of Preparation Examples H-9, H-10, H-11, and H-12. 0.05% of an aqueous mixture prepared by mixing the modified acrylamide polymer with each of the mixing ratios shown in Table 4 is added.
Then, draining is started after 5 seconds and 100 ml of water is collected after 10 seconds. It was filtered using Toyo filter paper No. 3 whose weight was measured, and dried at 105°C (Pufnarot) to obtain the solid content weight, which was designated as (f). Next, electric furnace 550°C
The ash content was determined by baking the ash to obtain ash, which was designated as (t). The exact weight of the solid content (fiber+filler) in 100 ml of the original pulp suspension polymerization liquid was determined, and this was designated as (F). Using the measured values, the total yield (%) and the filler yield (%) were determined as follows. The results are also shown in Table 4. Total Yield=[(F−f)/(F)]×100 Filler Yield=[(T−t)/(T)]×100 The configuration and operating conditions of the brit jar tester are 60 mesh plastic wire. , Drainage flow rate 150
ml/min.

Comparative Examples 1 to 7 Instead of the aqueous mixed solution of the zwitterionic cross-linking type acrylamide polymer and the cation-modified acrylamide polymer used in the examples, (i) Preparation Examples R-7 and H- When using an aqueous mixture prepared by mixing the compounds No. 10 and M-12 in the mixing ratio shown in Table 4, (ii) When the compounds of Preparation Example R-1 and H-10 were added separately in sequence (i)
ii) Preparation Examples R-1, H-10, Pearl Flock FR-C
(Hoshiko Kagaku Kogyo Co., Ltd.; high-molecular-type zwitterionic acrylamide polymer, concentration 4%) was used alone, and (iv) no addition was conducted. The retention effect of pulp fiber and filler was measured in the same manner as in the example. The results are also shown in Table 4.

[0043]

[Table 4]

[0044]

EFFECT OF THE INVENTION The method for producing neutral paper according to the present invention has a specific method
Aqueous mixture type papermaking additive mixed with two kinds of acrylamide polymers, specifically, (1) a zwitterionic crosslinkable acrylamide polymer prepared by using a crosslinkable vinyl monomer as an essential constituent monomer, and (2) ) The paper is characterized in that it is produced in a neutral region under an aqueous mixture type papermaking additive which is used in combination with a Hofmann decomposition reaction or a Mannich reaction, particularly a cation-modified acrylamide polymer by the former reaction.

In particular, in the method for producing neutral paper according to the present invention, the aqueous mixture-based additive for papermaking exerts a remarkable effect in improving the yield of pulp fibers and fillers. There is no effect in the mode in which they are added separately (sequentially), and the mode in which both components are mixed in advance and added in the form of an aqueous solution in which a complex is formed is characterized in that excellent effects are exhibited. And, the method for producing neutral paper of the present invention is such that the pH containing calcium carbonate as a filler is
It exhibits an excellent pulp fiber and filler retention effect in neutral paper made from 6 to 9 pulp slurries.

Claims (4)

[Claims] 1. A method for producing a neutral paper from a pulp slurry containing a filler, wherein the pulp slurry comprises a zwitterionic crosslinked acrylamide polymer prepared by using a crosslinkable vinyl monomer as an essential constituent monomer, and a cation-modified acrylamide. A method for producing neutral paper, which comprises adding an aqueous mixture-based additive for papermaking comprising a base polymer, and making paper in a neutral region. 2. An amphoteric crosslinkable acrylamide polymer prepared by using a crosslinkable vinyl monomer as an essential constituent monomer, comprising: (a) a crosslinkable vinyl monomer, (b) an anionic vinyl monomer, and (c) a cationic vinyl monomer. And (d) acrylamide and/or methacrylamide, which is a copolymer obtained by copolymerizing the neutral paper. 3. The method for producing neutral paper according to claim 1, wherein the cation-modified acrylamide polymer is a cation-modified acrylamide polymer by a Hoffman decomposition reaction. 4. The method for producing neutral paper according to claim 1, wherein the pulp slurry is a pulp slurry containing calcium carbonate as a filler and having a pH of 6 to 9.