CN107366182B

CN107366182B - Paper strength enhancer for high-ash paper, method for producing high-ash paper, and high-ash paper

Info

Publication number: CN107366182B
Application number: CN201710202049.9A
Authority: CN
Inventors: 井冈浩之; 西浦尚吾; 廣濑国博; 藤冈大辅
Original assignee: Arakawa Chemical Industries Ltd
Current assignee: Arakawa Chemical Industries Ltd
Priority date: 2016-03-31
Filing date: 2017-03-30
Publication date: 2020-12-01
Anticipated expiration: 2037-03-30
Also published as: CN107366182A; JP6897227B2; JP2017186725A

Abstract

The purpose of the present invention is to provide a novel amphoteric polyacrylamide which can be easily fixed in pulp even in a high-ash environment, is less likely to cause disorder into a paper texture, and has an excellent paper strength effect. Comprises the following key elements [1]]、[2]、[3]、[4]And [5]]The amphoteric polyacrylamide paper strength enhancer for high-ash paper: [1]The component (1) contains acrylamide (a), cationic vinyl monomer (b) containing alpha methyl and anionic vinyl monomer (c); [2]Wherein the component (b) in the component (1) accounts for 1-15 mol%, and the component (c) accounts for 1-10 mol%; [3]At it¹An H-NMR spectrum having a high magnetic field side absorption band A and a low magnetic field side absorption band B of an alpha methyl group assigned to the component (B) in the range of 0.9 to 1.35ppm, and the ratio of the area of the signal As/(As + Bs) being 10 to 35%; [4]15% by weight aqueous solution thereof (25 ℃ C.)The viscosity of (A) is 2,000 to 60,000 mPas; [5]The ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) is 3.5 or less.

Description

Paper strength enhancer for high-ash paper, method for producing high-ash paper, and high-ash paper

Technical Field

The present invention relates mainly to a paper strength enhancer for high ash paper, a method for manufacturing high ash paper, and high ash paper.

Background

Inorganic fillers such as talc, kaolin, and calcium carbonate are generally used for paper such as printing paper and note paper. In particular, calcium carbonate is excellent in opacity, whiteness, and smoothness of paper, and can improve printing suitability, and therefore the amount used in the paper industry tends to increase year by year. Hereinafter, paper containing a large amount of inorganic filler is referred to as "high ash paper".

However, high ash paper tends to have a reduced tensile strength, internal strength, and the like as the content of the inorganic filler increases. As a result of the large amount of inorganic filler present between pulp fibers, it is believed that entanglement and hydrogen bond-mediated interaction between fibers may be hindered.

Therefore, various improvements have been made to the paper strength enhancers such as polyacrylamide and cationized starch for the purpose of compensating for the strength of high-ash paper. Particularly, amphoteric polyacrylamide has a high paper strength-enhancing effect because its cationic group is directly fixed to pulp and its anionic group is indirectly fixed to pulp (via an auxiliary material such as aluminum sulfate).

On the other hand, the demand for recycled paper from waste paper in this field is still increasing. However, amphoteric polyacrylamide is difficult to fix because waste paper pulp is a product of short fiber formation and deterioration development. From this point of view, it is conceivable to increase the amount of cationic groups, but the paper quality is disturbed and the paper strength effect is reduced due to the strong cohesive force of the amphoteric polyacrylamide as described above.

Therefore, in patent document 1, the present inventors reported that a paper strength enhancer using amphoteric polyacrylamide having predetermined parameters does not disturb the paper quality and exhibits excellent paper strength. However, it has been found that the paper strength enhancer is suitable for the high ash paper, particularly for paper containing a large amount of calcium carbonate as an inorganic filler, but the desired effect may not be achieved.

Documents of the prior art

Patent document

Japanese unexamined patent publication No. 2014-196588

Disclosure of Invention

Technical problem to be solved by the invention

The invention provides a paper strength agent containing novel amphoteric polyacrylamide, which is easy to be fixed on pulp fibers even if added to pulp slurry containing a large amount of inorganic filler, has excellent paper strength enhancing effect and does not cause disorder of paper quality.

Means for solving the problems

The present inventors have made studies to solve the above-mentioned problems of the amphoteric polyacrylamide defined under the predetermined parameters in patent document 1. As a result, it is considered that, in the case where the amphoteric polyacrylamide is applied to, in particular, a pulp slurry containing a large amount of calcium carbonate as an inorganic filler, one of the reasons for the decrease in the effect is because the amphoteric polyacrylamide significantly hinders the fixation to the pulp fiber.

Accordingly, the present inventors have found that a paper strength enhancing agent for solving the above problems can be obtained by optimizing the above parameters and specifying physical property conditions which are not explicitly described in the document 1.

That is, the present invention relates to a paper strength enhancer for high ash paper, a method for producing high ash paper, and high ash paper as described below.

1. A paper strength enhancing agent for high-ash paper, which comprises an amphoteric polyacrylamide having the following requirements [1], [2], [3], [4] and [5 ]:

[1] the component (1) of the amphoteric polyacrylamide contains acrylamide (a), cationic vinyl monomer (b) containing alpha methyl and anionic vinyl monomer (c);

[2] the proportion of the component (b) in the component (1) of the amphoteric polyacrylamide is 1-15 mol%, and the proportion of the component (c) is 1-10 mol%;

[3]of said amphoteric polyacrylamides¹An H-NMR spectrum in the range of 0.9 to 1.35ppm, having a high magnetic field side absorption band A and a low magnetic field side absorption band B of an alpha methyl group which are assigned to the component (B), and a ratio As/(As + Bs) of an area (As) of the absorption band A to a sum of an area (As) of the absorption band A and an area (Bs) of the absorption band B being 10 to 35%;

[4] the viscosity of a 15 wt% aqueous solution (25 ℃) of the amphoteric polyacrylamide is 2,000 to 60,000 mPas;

[5] the amphoteric polyacrylamide has a ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of 3.5 or less.

2. The paper strength additive as described in the above item 1, wherein the proportion of the component (a) in the component (1) is 55 to 97.8 mol%.

3. The paper strength additive according to the above item 1 or 2, wherein the component (b) is at least one selected from the group consisting of a tertiary amino group-containing methacrylate, a tertiary amino group-containing methacrylamide, a quaternary ammonium salt structure-containing methacrylate, and a quaternary ammonium salt structure-containing methacrylamide.

4. The paper strength additive according to any one of the preceding items 1 to 3, wherein the component (1) further contains a cationic vinyl monomer (b') not containing an α -methyl group.

5. The paper strength additive as described in the above item 4, wherein the component (b') is at least one selected from the group consisting of a tertiary amino group-containing acrylate, a tertiary amino group-containing acrylamide, a quaternary ammonium salt structure-containing acrylate, and a quaternary ammonium salt structure-containing acrylamide.

6. The paper strength additive as described in the above item 4 or 5, wherein the proportion of the component (b') in the component (1) is 0.1 to 3 mol%.

7. The paper strength additive according to any one of the preceding items 1 to 6, wherein the component (c) contains an unsaturated carboxylic acid.

8. The paper strength additive as described in the above item 7, wherein the unsaturated carboxylic acid contains an unsaturated carboxylic acid containing no α -methyl group.

9. The paper strength additive as described in the above item 8, wherein the unsaturated carboxylic acid containing no α -methyl group contains an unsaturated monocarboxylic acid containing no α -methyl group, and the proportion of the unsaturated monocarboxylic acid containing no α -methyl group is 50 mol% or more.

10. The paper strength additive as described in the above item 9, wherein the unsaturated monocarboxylic acid containing no α -methyl group contains acrylic acid and/or a salt thereof.

11. The paper strength additive as described in any one of the above items 1 to 10, wherein the component (1) may further contain a crosslinkable monomer (d).

12. The paper strength additive according to the above item 11, wherein the component (d) contains at least one selected from the group consisting of N, N-dimethylacrylamide and methylenebisacrylamide.

13. The paper strength additive as described in the above 11 or 12, wherein the proportion of the component (d) in the component (1) is 0.01 to 1 mol%.

14. The paper strength agent as described in any one of the preceding items 1 to 13, wherein the component (1) further contains a chain-transfer vinyl monomer (e).

15. The paper strength additive as described in the above item 14, wherein the component (e) contains a (meth) allylsulfonate.

16. The paper strength additive as described in the above item 14 or 15, wherein the proportion of the component (e) in the component (1) is 0.05 to 2 mol%.

17. A method for producing high ash paper, characterized by adding the paper strength enhancer as defined in any one of the above items 1 to 16 to a papermaking system containing an inorganic filler at a concentration of 10 to 50% by weight relative to pulp.

18. The method of manufacturing high ash paper according to the item 17, wherein the inorganic filler is at least one selected from the group consisting of talc, kaolin, and calcium carbonate.

19. A high ash paper obtained by the method for producing a high ash paper described in the above item 17 or 18.

20. The high ash paper according to the item 19 above, wherein the ash content in the paper is 10% by weight or more.

Effects of the invention

The paper strength agent of the present invention can be easily fixed to pulp even when applied to pulp slurry containing a large amount of inorganic filler, particularly calcium carbonate. In addition, the paper strength enhancement effect is better, and the paper quality disorder is reduced. The same effect is obtained when the used paper pulp slurry is used.

Further, the paper strength enhancer of the present invention can be used as a surface treatment agent for an inorganic filler, and when the obtained coated inorganic filler is used, excessive aggregation of the inorganic filler can be suppressed, so that paper to which the paper strength enhancer of the present invention is added is excellent in paper strength (tensile strength, internal strength) and has reduced texture disorder.

Drawings

Fig.1 shows a schematic diagram of a polyacrylamide prepared from acrylamide and a cationic vinyl monomer containing an α -methyl group in both fig.1 and fig.2, the former showing a case where the unit of the cationic vinyl monomer containing an α -methyl group is uniformly distributed, and the latter showing a case where the unit is locally distributed.

FIG.2 shows polyacrylamide prepared from acrylamide and dimethylaminoethyl methacrylate¹An H-NMR spectrum is in the range of 0.9ppm to 1.35ppm, and a schematic diagram showing a high magnetic field side absorption band A (signal A) and a low magnetic field side absorption band B (signal B) which are attributed to the α -methyl group of dimethylaminoethyl methacrylate appears.

FIG. 3 shows a case where no peak is generated on the higher magnetic field side than the signal A in FIG.2¹H-NMR spectrum.

FIG. 4 is a graph showing the relationship between the ratio of ash content and the specific tensile strength in paper sheets 1 and 2 prepared by adding the same amphoteric polyacrylamide.

Detailed Description

The amphoteric polyacrylamide which constitutes the paper strength additive of the present invention is characterized by satisfying the requirements [1], [2], [3], [4] and [5] defined above.

The requirement [1] specifies that the amphoteric polyacrylamide is as follows: the component (1) contains acrylamide (a) (hereinafter referred to as component (a)), a cationic vinyl monomer (b) containing an α -methyl group (hereinafter referred to as component (b)), and an anionic vinyl monomer (c) (hereinafter referred to as component (c)).

In the present invention, acrylamide is used as the component (a). This is because the paper strength-enhancing effect of the amphoteric polyacrylamide in the present invention is more contributed than to methacrylamide.

The proportion of the component (a) in the component (1) is not particularly limited, and from the viewpoint of ensuring the excellent paper strength-enhancing effect of the amphoteric polyacrylamide of the present invention and further suppressing the effect of disturbing the paper texture, the proportion of the component (a) in the component (1) is usually about 55 to 97.8 mol%, preferably about 70 to 97 mol%, and more preferably about 80 to 95 mol%.

The component (b) is not particularly limited as long as it is a cationic vinyl monomer containing an α -methyl group, and various known ones can be used. The "α -methyl group" as used herein means a methyl group bonded to the α -carbon atom of a vinyl group in a monomer having the vinyl group and a cationic functional group.

[ solution 1]

The component (b) includes, for example, at least one selected from the group consisting of a tertiary amino group-containing methacrylate, a tertiary amino group-containing methacrylamide, a quaternary ammonium salt structure-containing methacrylate, and a quaternary ammonium salt structure-containing methacrylamide. The latter compounds are obtained by reacting the former compounds with quaternizing agents. Specific examples of the tertiary amino group-containing methacrylic acid ester and the tertiary amino group-containing methacrylamide include dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, and diethylaminopropyl methacrylamide. Examples of the quaternary ammonium agent include methyl chloride, benzyl chloride, dimethyl sulfate, and epichlorohydrin.

In the present invention, the component (1) may contain various known cationic vinyl monomers (b') not containing an α -methyl group. Specifically, there may be mentioned an acrylic ester having a quaternary ammonium salt structure and an acrylamide having a quaternary ammonium salt structure, which are obtained by reacting an acrylic ester having a tertiary amino group and an acrylamide having a tertiary amino group with a quaternizing agent, respectively. Examples of the tertiary amino group-containing acrylic ester and the tertiary amino group-containing acrylamide include dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropylacrylamide, and diethylaminopropylacrylamide. The quaternary ammonium agent may be the one described above.

The proportion of the component (b ') in the component (1) is not particularly limited, but the proportion of the component (b') in the component (1) is usually less than 3 mol%, preferably less than 2 mol%, and more preferably less than 1 mol%, from the viewpoint of the paper strength-enhancing effect of the amphoteric polyacrylamide in the present invention.

In addition, from the viewpoint of the fixing property to pulp and the paper strength enhancing effect of the amphoteric polyacrylamide in the present invention, it is preferable to use only the component (b) without using the component (b'). This is considered to be because the amphoteric polyacrylamide obtained as described above is easily made into particles by intermolecular interaction and can be fixed by pulp fibers.

As the component (c), any of various known vinyl monomers having an anionic group in the molecule can be used without particular limitation. Specific examples thereof include unsaturated carboxylic acids and unsaturated sulfonic acids.

The unsaturated carboxylic acid can be classified into an unsaturated carboxylic acid containing no alpha methyl group and an unsaturated carboxylic acid containing an alpha methyl group. Examples of the former include acrylic acid, itaconic acid, maleic anhydride, and fumaric acid. Examples of the latter include methacrylic acid and crotonic acid. Salts may also be formed for the above-mentioned substances. Examples of the salt-forming species include alkali metal salts such as sodium salts and potassium salts, amines such as trimethylamine and tributylamine, and ammonia. Among the above, in particular, from the viewpoint of having an excellent paper strength-enhancing effect and further suppressing the disturbance of the paper quality, an α -methyl group-free unsaturated carboxylic acid (salt) is preferable, and acrylic acid and/or a salt thereof is more preferable.

Examples of the unsaturated sulfonic acid include vinylsulfonic acid, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof.

When the proportion of the unsaturated monocarboxylic acid having no α -methyl group (preferably, acrylic acid and/or a salt thereof) in the unsaturated carboxylic acid having no α -methyl group is 50 mol% or more, the paper strength-enhancing effect and the texture disorder-suppressing effect tend to be improved.

The component (1) may contain a crosslinkable monomer (d) (hereinafter also referred to as component (d)) for the purpose of increasing the molecular weight of the amphoteric polyacrylamide in the present invention and improving the paper strength-enhancing effect thereof. As the component (d), any known crosslinking monomer can be used without particular limitation as long as it can be used for producing polyacrylamide. Examples thereof include monofunctional monomers such as allyl acrylate, diethylene glycol monoacrylate and N, N-dimethylacrylamide; difunctional vinyl monomers such as ethylene glycol diacrylate, diallylamine, N-methylolacrylamide, methylenebisacrylamide and the like; trifunctional vinyl monomers such as triallyl isocyanate; tetrafunctional vinyl monomers such as tetraallyloxyethane, and the like. Among the above, the monofunctional monomer and/or the bifunctional monomer are preferable because a branched structure and/or a crosslinked structure can be easily introduced into the objective amphoteric polyacrylamide to easily increase the molecular weight thereof, and particularly, at least one selected from the group consisting of N, N-dimethylacrylamide and methylenebisacrylamide is preferably contained, and N, N-dimethylacrylamide is more preferably contained.

The proportion of the component (d) in the component (1) is not particularly limited, but the proportion of the component (d) in the component (1) is usually about 0.01 to 1 mol%, preferably about 0.02 to 0.8 mol%, and more preferably about 0.05 to 0.6 mol%, from the viewpoints of attaining a high molecular weight without gelation of the amphoteric polyacrylamide in the present invention, providing excellent fixation of the polyacrylamide to pulp and excellent paper strength-enhancing effect, and further suppressing the disorder of the paper quality.

The component (1) may contain various known chain transfer vinyl monomers (e) (hereinafter also referred to as component (e)). By using the component (e), the amphoteric polyacrylamide of the present invention can be increased in molecular weight without gelling, and the viscosity of the aqueous solution thereof can be reduced. Further, the amphoteric polyacrylamide has good fixing property to pulp, paper strength enhancing effect, and paper quality disorder suppressing effect. The component (e) may be (meth) allylsulfonate (i.e., allylsulfonate and/or methallylsulfonate), and examples of the salt-forming species include alkali metal salts such as sodium salt and potassium salt.

The proportion of the component (e) in the component (1) is not particularly limited, and from the viewpoint of ensuring that the amphoteric polyacrylamide of the present invention has a high molecular weight without gelling, and at the same time, the amphoteric polyacrylamide has fixing properties to pulp, a paper strength-enhancing effect, and a paper texture disorder-suppressing effect, the proportion of the component (e) in the component (1) is usually about 0.1 to 2 mol%, preferably about 0.15 to 1 mol%, and more preferably about 0.2 to 0.8 mol%.

The component (1) may further contain other monomers which may react with the components (a) to (e), and examples thereof include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and octadecyl (meth) acrylate; nonionic vinyl monomers such as acrylonitrile, styrenes, vinyl acetate, and methyl vinyl ether. The number of carbon atoms of the alkyl group of the alkyl (meth) acrylate is not particularly limited, and is usually about 1 to 8. Further, the proportion of the nonionic vinyl monomer in the aforementioned components is not particularly limited, and in the case of 100 mol% of the component (1), the proportion of the nonionic vinyl monomer is usually 10 mol% or less, preferably 5 mol% or less.

The requirement [2] specifies that the proportion of the component (b) in the component (1) is 1 to 15 mol%, and the proportion of the component (c) is 1 to 10 mol%.

(b) When the proportion of the component (c) is less than 1 mol%, the amphoteric polyacrylamide of the present invention tends to be insufficient in the fixation of pulp and paper strength-enhancing effect. When the proportion of the component (b) exceeds 15 mol%, the amphoteric polyacrylamide tends to have too strong an aggregation property and to have a disturbed paper texture. From the same viewpoint as above, the proportion of the component (b) is preferably about 2 to 12 mol%, and more preferably about 3 to 10 mol%.

(c) When the proportion of the component (c) is less than 1 mol%, the amphoteric polyacrylamide of the present invention tends to be insufficient in the fixation of pulp and paper strength-enhancing effect. When the proportion of the component (c) exceeds 10 mol%, the amphoteric polyacrylamide tends to have too strong an aggregation property and to have a disturbed paper texture. From the same viewpoint as above, the proportion of the component (c) is preferably about 1 to 9 mol%, and more preferably about 2 to 8 mol%.

Essential element [3]The parameters of the amphoteric polyacrylamide in the present invention are defined values. In particular, of the amphoteric polyacrylamides¹In the H-NMR spectrum, a high magnetic field side absorption band A (hereinafter referred to as signal A) and a low magnetic field side absorption band B (hereinafter referred to as signal B) of the α -methyl group which is the component (B) appear in the range of 0.9ppm to 1.35 ppm. Further, it is characterized in that a ratio As/(As + Bs) of an area (As) of the absorption band a to a sum of the area (As) of the absorption band a and an area (Bs) of the absorption band B is 10 to 35%. In addition, since the amphoteric polyacrylamide is a polymer compound, both the signal a and the signal B have a peak shape having a wide peak width.

Here, the above chemical shift range (0.9ppm to 1.35ppm) is a numerical value in the case of 3-trimethylsilane-1-propanesulfonic acid sodium (DSS) as an internal standard substance.

Although the above-described range of chemical shifts (0.9ppm to 1.35ppm) is a range defined by the present inventors, as shown in fig.2, the upper limit value (1.35ppm) is set based on the lowest point (local lowest value) on the left side of the peak of the signal B. The boundary between the lowest point on the right side of the peak of the signal B is defined by the area As of the signal a and the area Bs of the signal B. The lower limit value (0.9ppm) of the chemical shift range is set based on the lowest point on the right side of the peak of the signal a when the peak appears on the higher magnetic field side than the signal a (see fig. 2). However, even in the case where no peak appears on the higher magnetic field side than the signal a, the lower limit value is set to 0.9 ppm. In this case, as shown in FIG. 3, the intersection (contact point) between the right side of the signal A and the NMR spectrum base line is approximately 0.9 ppm.

Both the signal a and the signal B are absorption bands specific to the α methyl group constituting the component (B) of the amphoteric polyacrylamide in the present invention. In addition, on the molecular chain of the amphoteric polyacrylamide, the unit of the component (B) is continuous (localized), the alpha methyl of the unit is in a close-coupled environment, the relative intensity of the signal A is increased, and the relative intensity of the signal B is reduced. On the contrary, the unit of the component (B) is homogenized on the molecular chain of the amphoteric polyacrylamide, and the proton in the alpha methyl group is in a non-adjacent environment, so that the relative intensity of the signal A is reduced, and the relative intensity of the signal B is increased.

Therefore, the smaller the ratio As/(As + Bs) of the signal A to the total area of the signals A and B, the more uniform the cationic sites on the molecular chain of the amphoteric polyacrylamide in the present invention.

Using commercially available¹Method for measuring amphoteric polyacrylamide in the invention by H-NMR analyzer¹In the H-NMR spectrum, the integrals of As and Bs are obtained respectively according to the division standard, and the proportional relation As/(As + Bs) of the areas can be calculated.

Unlike the invention described in patent document 1, the amphoteric polyacrylamide in the present invention is applicable to high-ash paper, and the area ratio As/(As + Bs) is preferably 10% or more and less than 35%, more preferably 12% or more and less than 25%, and still more preferably 15% or more and less than 20%, for the purpose of self-fixing of pulp fibers in pulp slurry containing a large amount of inorganic filler, particularly calcium carbonate.

In addition, under papermaking conditions where the amount of the inorganic filler is large, that is, the proportion of pulp fibers is relatively low, it is considered that the use of amphoteric polyacrylamide having highly localized cationic sites will cause excessively strong aggregation of pulp fibers. From this viewpoint, in the present invention, it is considered that the proportional relationship As/(As + Bs) is set to a value smaller than that described in patent document 1, and the desired effect can be obtained by optimizing the viscosity condition and the polydispersity condition described later.

The requirement [4] specifies the viscosity of the amphoteric polyacrylamide in the form of an aqueous solution in the present invention. The amphoteric polyacrylamide in the present invention is different from the amphoteric polyacrylamide in patent document 1 in that the value of the aforementioned proportional relationship As/(As + Bs) is relatively small. That is, the amphoteric polyacrylamide of the present invention is partially eliminated in localization of the cationic site. As a result, the self-fixing ability to the pulp fiber is relatively lowered. Further, since the pulp slurry for high-ash paper making contains a large amount of inorganic filler, the contact point between the amphoteric polyacrylamide and the pulp fiber is small. Therefore, in the present invention, in order to compensate for such a deficiency, the viscosity of a 15 wt% aqueous solution is defined to be 2,000 to 60,000 mPas. According to the above-mentioned regulation, the amphoteric polyacrylamide of the present invention can be easily brought into contact with pulp fibers, and a predetermined paper strength effect can be exhibited under papermaking conditions containing a large amount of inorganic filler because more hydrogen bonds are formed at the contact points. From this viewpoint, the viscosity of the 15 wt% aqueous solution is preferably about 3,000 to 30,000 mPas, and more preferably about 4,000 to 15,000 mPas.

The viscosity can be measured by various known means. Specifically, a capillary viscometer, a falling ball viscometer, a rotary viscometer, and the like are mentioned, and a rotary viscometer is preferable from the viewpoint of directly measuring the viscosity at a predetermined concentration. As the measuring instrument, for example, a B-type viscometer can be cited. As the measurement conditions, a 15 wt% aqueous solution at 25 ℃ and 6rpm under the rotor No. 3 condition or 6rpm under the rotor No. 4 condition is preferable.

The requirement [5] specifies the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the amphoteric polyacrylamide in the present invention, that is, the range of the molecular weight distribution (hereinafter referred to as polydispersity) of the amphoteric polyacrylamide. When the paper strength enhancer described in patent document 1 is used in paper making under high ash conditions, the paper quality (high ash paper) tends to be disturbed and the paper strength tends to be lowered, and one of the reasons for this is that the content of the amphoteric polyacrylamide having a high molecular weight, which tends to disturb the paper quality, and the low molecular weight, which has a small contribution degree to the paper strength, is considered to be large because the molecular weight distribution of the amphoteric polyacrylamide constituting the paper strength enhancer is relatively wide. Therefore, in the present invention, in order to compensate for the disadvantage, the molecular weight distribution (Mw/Mn) is defined to be 3.5 or less. By limiting the content to this range, the proportion of the high molecular weight fraction which causes excessive aggregation of pulp fibers and causes disorder of the paper quality can be reduced, and the proportion of the low molecular weight fraction which has a low contribution to the self-fixing property of pulp fibers and the paper strength effect can be reduced. From this viewpoint, the ratio is 3.5 or less, preferably 3 or less, and more preferably 2.8 or less. The lower limit is usually 1 or more, preferably 1.5 or more.

Mw and Mn are measured by various known methods, and both are preferably determined by a Gel Permeation Chromatography (GPC) method.

The method for producing the paper strength agent of the present invention is not particularly limited, and as described above, the amphoteric polyacrylamide from which the paper strength agent is produced can be controlled in localization of cationic sites in its molecular chain, and various known polymerization methods (dropping polymerization method, simultaneous polymerization method, multi-step polymerization method, and the like) can be used as long as they satisfy the requirement for producing amphoteric polyacrylamide having a predetermined viscosity and molecular weight distribution.

The amphoteric polyacrylamide satisfies the requirements [3], [4] and [5], and for example, an operation of dividing all vinyl monomers constituting the amphoteric polyacrylamide into a plurality of monomer mixtures, and reacting the above mixtures sequentially by increasing the amount of the component (b) in a part of the mixture, or adding a large amount of the component (b) to the reaction system at a certain time point in the polymerization reaction to increase the concentration of the component (b) involved in the polymerization reaction to some extent can be performed.

Further, a preferable production method of the paper strength additive of the present invention is as follows. In this manner, it was further confirmed that amphoteric polyacrylamide having the following regions was obtained: the cationic position on the molecular chain of the amphoteric polyacrylamide in the invention is a region localized to a certain degree.

That is, this embodiment is characterized by comprising the following steps (a) and (B):

step (A): polymerizing a monomer mixture (I) containing acrylamide (a) and a cationic vinyl monomer (b) having an alpha methyl group as essential components, wherein the proportion of the component (b) is 5 to 87 mol% (preferably 5 to 60 mol%, and more preferably 10 to 40 mol%);

step (B): a monomer mixture (II) containing acrylamide (a) and an anionic vinyl monomer (c) as essential components and having a proportion of the anionic vinyl monomer (c) of 1 to 20 mol% (preferably 1 to 15 mol%, more preferably 1 to 10 mol%) is polymerized.

If necessary, the monomer mixture (I) and/or the monomer mixture (II) may contain a cationic vinyl monomer (b') not containing an α -methyl group.

In addition, it is preferable that the monomer mixture (I) contains the anionic vinyl monomer (c) from the viewpoints of excellent fixation of the obtained amphoteric polyacrylamide to pulp and paper strength enhancing effect, and further suppression of paper quality disorder.

The monomer mixture (I) and/or the monomer mixture (II) may further contain a crosslinkable monomer (d), and the component (d) may be added to the reaction system separately in the middle of the step (a) and the step (B) or may be added to the reaction system after the completion of the step (a) and/or the step (B).

From the same viewpoint as described above, it is preferable that the monomer mixture (I) and/or the monomer mixture (II) further contain a chain transfer vinyl monomer (e).

The composition other than the component (b) in the monomer mixture (I) is not particularly limited, and from the viewpoint of excellent fixation of the obtained amphoteric polyacrylamide to pulp, excellent paper strength-enhancing effect, further suppression of paper quality disorder, and the like, the total proportion of the monomer components in the monomer mixture (I) is usually about 30 to 90 mol% for the component (a), (about 0 to 15 mol% for the component (b'), (about 0 to 40 mol% for the component (c), (about 0.01 to 3 mol% or 0 mol% for the component (d), and about 0 to 20 mol% for the component (e), as 100 mol%; preferably, the component (a) is about 40 to 85 mol%, the component (b') is about 0 to 10 mol%, the component (c) is about 0.1 to 30 mol% or 0 mol%, the component (d) is about 0.01 to 2.5 mol% or 0 mol%, and the component (e) is about 0.1 to 15 mol%; further, it is preferable that the component (a) is about 50 to 80 mol%, the component (b') is about 0 to 5 mol%, the component (c) is about 1 to 20 mol% or 0 mol%, the component (d) is about 0.1 to 2 mol% or 0 mol%, and the component (e) is about 0.1 to 10 mol%.

The composition other than the component (c) in the monomer mixture (II) is not particularly limited, and from the viewpoint of excellent fixation of the obtained amphoteric polyacrylamide to pulp, excellent paper strength-enhancing effect, further suppression of paper quality disorder, and the like, the total proportion of the monomer components in the monomer mixture (II) is usually about 20 to 98.8 mol% for the component (a), about 0 to 15 mol% for the component (b'), about 0.001 to 1 mol% or 0 mol% for the component (d), and about 0 to 1 mol% for the component (e), based on 100 mol% of the monomer components; preferably, the amount of the component (a) is about 60 to 98.8 mol%, the amount of the component (b) is about 0 to 10 mol%, the amount of the component (b') is about 0 to 10 mol%, the amount of the component (d) is about 0.01 to 0.5 mol% or 0 mol%, and the amount of the component (e) is about 0.01 to 0.5 mol%; further, it is preferable that the component (a) is about 70 to 98.8 mol%, the component (b) is about 0 to 5 mol%, the component (b') is about 0 to 8 mol%, the component (d) is about 0.1 to 0.4 mol% or 0 mol%, and the component (e) is about 0.01 to 0.4 mol%.

In order to obtain an amphoteric polyacrylamide satisfying the requirement (3) in a high yield, the molar ratio ((I)/((I) + (II))) of the monomer mixture (I) is usually 25 mol% or less (preferably about 8 to 24 mol%, and more preferably about 10 to 22 mol%) relative to the total number of moles of all monomers constituting the monomer mixture (I) and the monomer mixture (II).

Further, both the monomer mixture (I) and the monomer mixture (II) can be used as a solution. The solvent is preferably water, and an organic solvent such as methanol, ethanol, or 2-propanol may be used in combination as a cosolvent. When the monomer mixture (I) and/or the monomer mixture (II) contains a monomer which is easily hydrolyzed, sulfuric acid may be used to prevent the hydrolysis.

The polymerization conditions in the step (A) and the step (B) are not particularly limited. For example, the polymerization temperature is usually about 50 to 100 ℃ and the polymerization time is about 1 to 5 hours. In addition, in the step (A) and/or the step (B), conventionally known polymerization initiators such as potassium persulfate and ammonium persulfate, redox polymerization initiators prepared by using the initiators with a reducing agent such as sodium bisulfite, azo type initiators, and the like can be used. The amount of the polymerization initiator used is not particularly limited, and is usually about 0.01 to 2% by weight, preferably about 0.05 to 0.5% by weight, based on the total weight of all the constituent monomers of the amphoteric polyacrylamide in the present invention.

In the step (a), the monomer mixture (I) may be polymerized dropwise, simultaneously, or in combination. However, in order to easily control the polymerization reaction, dropwise polymerization is preferred.

In the step (B), the monomer mixture (II) may be polymerized dropwise, simultaneously, or in combination. However, the dropwise polymerization is also preferable for easy control of the polymerization reaction.

Further, the order of the step (A) and the step (B) is not particularly limited under the condition that the purpose of forming a region in which the cationic site on the molecular chain of the amphoteric polyacrylamide is localized to some extent can be achieved. Examples thereof include: after step (a) is completed, starting the method of step (B); after completion of step (B), the method of step (a) and the like are started. Further, the time interval of step (a) and step (B) is not particularly limited, for example: after step (a) or step (B) is completed, another step may be directly started; after the completion of step (a) or step (B), another step may be started after a lapse of a certain time. In addition, after the step (a) or the step (B) is started, another step may be started in the same reaction system before the completion of the above step, and in this case, amphoteric polyacrylamide having a uniform cationic site to some extent can be obtained.

Further, for example, the monomer mixture (I) and/or the monomer mixture (II) may or may not contain an initiator in advance. When the initiator is not contained, for example, the initiator is dropped into the reaction system from the outside during both the step (A) and the step (B). In this case, the initiator may be used as an aqueous solution.

The most preferable production method of the paper strength enhancer of the present invention is: a mode in which after completion of the step (A) of polymerizing dropwise addition of the monomer mixture (I), the monomer mixture (II) is added dropwise to the same reaction system to polymerize it. In this embodiment, by polymerizing the monomer mixture (I) containing a relatively large amount of the component (b) through the step (a), a polyacrylamide precursor having a high density of cationic sites to some extent can be produced at a time. Then, by polymerizing the monomer mixture (II) containing relatively little or no component (b) in the presence of the precursor, amphoteric polyacrylamide having a region in which cationic sites are localized to some extent in the molecular chain can be easily obtained. In this embodiment, it is preferable that the initiator is added dropwise to the reaction system during both the step (a) and the step (B).

The Mw of the amphoteric polyacrylamide in the present invention is usually about 500,000 to 10,000,000, preferably about 1,000,000 to 7,000,000, and the Mn is usually about 200,000 to 6,000,000, preferably about 400,000 to 4,000,000.

The paper strength agent of the present invention contains the amphoteric polyacrylamide, and an aqueous solution is preferably used. The solid content concentration is not particularly limited, but is usually about 0.01 to 2% by weight.

The paper strength agent of the present invention may contain other paper strength agents. Specifically, there may be mentioned: modified starches such as cationized starch and amphoteric starch; modified celluloses such as carboxymethyl cellulose and hydroxyethyl cellulose; polyvinyl alcohol; urea-formaldehyde resin; melamine-formaldehyde resins; polyamide polyamine epichlorohydrin; polyvinylamine, and the like. The amount of these other paper strength agents is not particularly limited, and the total amount of the paper strength agent of the present invention and the other paper strength agents is 100 wt%, and the other paper strength agents are usually about 0.1 to 40 wt%.

The method for producing high ash paper of the present invention is characterized by adding the paper strength enhancer of the present invention to a pulp slurry containing 10 to 50 wt% of an inorganic filler based on the weight (solid content) of the pulp to make paper.

As the inorganic filler, for example, at least one selected from the group consisting of talc, kaolin and calcium carbonate can be cited. Examples of calcium carbonate include ground calcium carbonate and light calcium carbonate.

As the pulp slurry, kraft pulp; bleached or unbleached chemical pulp such as sulfite pulp; bleached or unbleached pulp such as groundwood pulp, mechanical pulp, thermomechanical pulp and the like; waste paper pulp such as waste newspaper, magazine waste paper, cardboard waste paper, deinked waste paper, etc.

The amount of the paper strength agent of the present invention to be added is not particularly limited, and may be suitably determined depending on the kind of paper and pulp slurry and the papermaking conditions, and usually, the solid content of the amphoteric polyacrylamide contained in the paper strength agent is usually 0.1% by weight or more, preferably about 0.1 to 3% by weight, based on the weight (solid content) of the pulp slurry. In addition, aluminum sulfate, a sizing agent, and other additives for papermaking may be added to the pulp slurry.

The high ash paper of the present invention can be obtained by the aforementioned manufacturing method. The obtained high ash paper can be used as lining base paper, middle base paper, paper tube base paper, white cardboard, kraft paper, high quality paper, newsprint paper, etc. In the high ash paper, the content of the inorganic filler is not particularly limited, but is usually 10% by weight or more, and preferably about 10 to 30% by weight.

Examples

The present invention will be described in detail below by referring to reference examples, examples and comparative examples, but the present invention is not limited to the examples. In each example, parts and% are by weight unless otherwise specified. The physical property values of the respective examples are values measured by the following methods.

Example 1

An 401.4 portion of ion-exchanged water was charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas introduction tube, and 3 dropping funnels (hereinafter referred to as funnel 1, funnel 2, and funnel 3 in this order), and after oxygen in the reaction vessel was removed by introducing nitrogen gas directly into the ion-exchanged water, the temperature of the ion-exchanged water was set to 90 ℃.

Then, in the funnel 1, as the monomer mixture (I), an aqueous solution prepared by adding 79.04 parts of a 50% acrylamide aqueous solution, 24.37 parts of dimethylaminoethyl methacrylate, 3.99 parts of 80% acrylic acid, 0.18 part of N, N-dimethylacrylamide, 0.292 part of sodium methallylsulfonate, 11.91 parts of 62.5% sulfuric acid, and 61.42 parts of ion exchange water was further adjusted to a mixture of pH 4.5 with sulfuric acid.

Then, in the funnel 2, as a monomer mixture (II), 386.98 parts of a 50% acrylamide aqueous solution, 10.44 parts of dimethylaminoethyl methacrylate, 13.27 parts of benzyl chloride quaternary ammonium salt of 75% dimethylaminoethyl acrylate, 9.31 parts of 80% acrylic acid, 0.18 parts of N, N-dimethylacrylamide, 0.292 parts of sodium methallylsulfonate, 5.10 parts of 62.5% sulfuric acid, and 231.16 parts of ion exchange water were added to prepare an aqueous solution, which was further adjusted to a mixture of pH 4.5 with sulfuric acid.

Then, to funnel 3, an initiator solution prepared from 0.21 parts of ammonium persulfate and 180 parts of ion-exchanged water was added.

Then, the stopcocks of the funnel 1 and the funnel 3 were opened simultaneously, and the whole amount of the monomer mixture (I) and a half amount of the initiator solution were added dropwise over 2 hours. Thereafter, the stopcock of funnel 2 was opened directly, and the aforementioned monomer mixture (II) and the remaining half amount of the initiator solution were added dropwise over 2 hours.

Then, the reaction system was incubated at 90 ℃ for 1 hour, and 562 parts of ion-exchanged water was further added to obtain an amphoteric polyacrylamide having a weight-average molecular weight of 121 ten thousand and a viscosity of 8,900 mPas (solid content concentration: 15.0%).

Examples 2 to 15

Amphoteric polyacrylamide (any solid content concentration was 15.0%) was obtained in the same manner as in example 1, except that the monomer mixture (I), the monomer mixture (II) and the initiator solution were changed to the compositions shown in table 1.

Comparative examples 1 to 9 and comparative example 11

Amphoteric polyacrylamide (any solid content concentration was 15.0%) was obtained in the same manner as in example 1, except that the monomer mixture (I) and the monomer mixture (II) were changed to a mixture having the composition shown in table 1.

Comparative example 10

276.2 parts of ion-exchanged water was charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas introduction tube, and 3 dropping funnels (hereinafter referred to as funnel 1, funnel 2, and funnel 3 in this order), and after oxygen in the reaction vessel was removed by introducing nitrogen gas directly into the ion-exchanged water, the temperature of the ion-exchanged water was set to 90 ℃.

Then, as the monomer mixture (I), an aqueous solution prepared by adding 193.00 parts of a 50% acrylamide aqueous solution, 40.20 parts of dimethylaminoethyl methacrylate, 24.20 parts of benzyl chloride quaternary ammonium salt of 60% dimethylaminoethyl methacrylate, 1.40 parts of 80% acrylic acid, 0.300 parts of N, N-dimethylacrylamide, 0.250 parts of methylenebisacrylamide, 3.200 parts of sodium methallylsulfonate, 19.70 parts of 62.5% sulfuric acid, and 168.1 parts of ion exchange water to the funnel 1 was further adjusted to a mixture of pH 4.5 with sulfuric acid.

Then, in the funnel 2, as the monomer mixture (II), 469.00 parts of a 50% acrylamide aqueous solution, 9.200 parts of 80% acrylic acid, 0.30 parts of N, N-dimethylacrylamide, 0.250 parts of methylenebisacrylamide, 0.800 parts of sodium methallylsulfonate, and 212.30 parts of ion exchange water were added as an aqueous solution.

Then, to funnel 3, an initiator solution prepared from 0.6 parts of ammonium persulfate and 180 parts of ion-exchanged water was added.

Then, the reaction system was incubated at 90 ℃ for 1 hour, and then 400 parts of ion-exchanged water was further added to obtain an amphoteric polyacrylamide (solid content concentration: 20.3%) having a weight-average molecular weight of 300 ten thousand and a viscosity of 8,500 mPas. This sample was diluted to 15.0% with ion-exchanged water and the viscosity was measured to be 1,200 mPas.

For the examples and comparative examples, the molar ratio of each component is shown in table 2 for 100 mol% of the total ratio of the monomer components in the monomer mixture (I) or the monomer mixture (II), and the molar ratio of each component is shown in table 3 for 100 mol% of the total monomer components.

The symbols in tables 1 to 3 for the compounds are as follows.

AM: acrylamide (molecular weight 71.1)

DM: dimethylaminoethyl methacrylate (molecular weight 157.2)

DML: benzyl chloride Quaternary ammonium MethylaminoEthyl methacrylate (molecular weight 283.8)

APDM: dimethylaminopropyl acrylamide (molecular weight 156.2)

DMAEA-BQ: benzyl chloride Quaternary ammonium salt of dimethylaminoethyl acrylate (molecular weight 269.8)

IA: itaconic acid (molecular weight 130.1)

AA: acrylic acid (molecular weight 72.1)

DMAA: n, N-dimethylacrylamide (molecular weight 99.1)

MBAA: methylene bisacrylamide (molecular weight 154.2)

SMAS: sodium methallyl sulfonate (molecular weight 158.2)

APS: ammonium persulfate (molecular weight 228.2)

V-50: 2, 2' -azobis (2-amidinopropane) dihydrochloride (molecular weight 271.2)

¹Determination of H-NMR spectra

Amphoteric Polyacrylamide 26.7mg and deuterium oxide (D) for examples 1 to 15 and comparative examples 1 to 11₂O)0.8ml, dripping 1 mul of internal standard liquid into the mixed liquid by a micro syringe, wherein the internal standard liquid is 40.23mg of 3-trimethylsilyl-1-sodium propanesulfonate (DSS) and D₂O1.0 ml was mixed to prepare a sample for measurement (concentration: 0.5%).

Then, the sample was used to measure under the following conditions¹H-NMR spectrum.

NMR measurement apparatus: 400MHz manufactured by 400MR Agilent Technologies

A probe: AutoX PFG probe (5mm)

Temperature of the probe: 70 deg.C

Measuring frequency: 399.75MHz

And (3) determination of a solvent: heavy water (D)₂O)

Pulse sequence: using pre-saturation criterion parameters

The accumulation times are as follows: 128 times

Calculation of the ratio of Signal area As/(As + Bs)

The areas (As) and (Bs) of the signals were obtained on a computer using analysis software vNMRJ (manufactured by Agilent Technologies) attached to the NMR measuring apparatus, and the area ratio As/(As + Bs) was calculated. The results are shown in Table 4.

Weight average molecular weight

The weight average molecular weight and the polydispersity (Mw/Mn) of the amphoteric polyacrylamides of examples 1 to 15 and comparative examples 1 to 11 were measured under the following conditions. The results are shown in Table 4.

GPC host: manufactured by imperial ソー strain

A chromatographic column: protection column PWXL 1 and GMPWXL 2 (column temperature 40 ℃ C.) made by Chinese envoys ソー (strain)

Mobile phase: n/2 acetic acid buffer solution (N/2 acetic acid (made by pure Chinese Co., Ltd.)) and N/2 sodium acetate (made by chemical キシダ Co., Ltd.)) aqueous solution, pH 4.2)

Flow rate: 0.8 ml/min

A detector:

the RALLS method; ビスコテック TDA MODEL 301 (concentration detector, 90 ℃ light scattering detector and viscosity detector each having a temperature of 40 ℃ C.)

Viscosity of the oil

The amphoteric polyacrylamides of examples 1 to 15 and comparative examples 1 to 11 were measured for viscosity at 25 ℃ with a spindle number 3 at 6rpm using a B-type viscometer (product name: ビストメトロン, manufactured by Toba 12471; \\12473 テム. The results are shown in Table 4.

TABLE 4

Preparation of pulp slurry

Bleached Kraft Pulp (LBKP) was pulped with a nija beater to give a finished pulp with a canadian standard freeness (c.s.f) of 350 ml. Then, sodium sulfate was added to the slurry, and the conductivity thereof was adjusted to 0.5mS/cm, thereby producing a pulp slurry 1 of 1% slurry. Further, this conductivity was measured using a commercially available measuring instrument (product name "pH/COND METER D-54", (strain) horiba).

Then, while stirring the pulp slurry 1, aluminum sulfate (1.0% by weight of the pulp), cationized starch (0.8% by weight of the pulp) (Japanese food chemical: ネオタック 30T), and amphoteric polyacrylamide (0.3% by weight of the pulp) of example 1 were added in this order, followed by addition of calcium carbonate (15% by weight of the pulp) (Ordomo : タマパール TP 121). Using the resulting pulp slurry, 80g/m of weight per square meter of paper was formed using a TAPPI cube-making machine²And (5) making paper. The resulting wet paper was pressed in a standard manner to give dry finished paper 1. Paper sheets 1 were obtained in the same manner as in the amphoteric polyacrylamides of examples 2 to 15 and comparative examples 1 to 11, respectively.

While stirring the pulp slurry 1, aluminum sulfate (1.0% by weight of the pulp), cationized starch (0.8% by weight of the pulp) (JP food chemical: ネオタック 30T), and amphoteric polyacrylamide (0.3% by weight of the pulp) of example 1 were added in this order, followed by calcium carbonate (30% by weight of the pulp) (Omoduomo : タマパール TP 121). Using the resulting pulp slurry, 80g/m of weight per square meter of paper was formed using a TAPPI cube-making machine²And (5) making paper. The resulting wet paper is pressed in a standard manner to give a dry finished paper 2. Paper sheets 2 were obtained in the same manner as in the amphoteric polyacrylamides of examples 2 to 15 and comparative examples 1 to 11, respectively.

Paper 3 was obtained in exactly the same manner as paper 2 except that the amphoteric polyacrylamide was not added.

Determination of specific tensile Strength

The specific tensile strength of the paper 1 and the paper 2 was measured according to JIS P8113. The paper strength such as the specific tensile strength is greatly influenced not only by the kind of amphoteric polyacrylamide added but also by the amount of ash in the paper. The paper has different filler yields due to different types of amphoteric polyacrylamides, different coagulability and interaction with fillers, and different ash contents in paper to which various amphoteric polyacrylamides are added. As described above, since the paper force is affected by the amount of paper ash, it is necessary to compare the difference in the paper force improvement effect by adding the amphoteric polyacrylamide after correcting the paper ash amount to the same amount. The specific tensile strength was corrected according to the following method.

The strength of 20% ash in paper was estimated from the relationship between the proportion of ash in paper and the specific tensile strength of paper sheets 1 and 2 (FIG. 4) prepared by adding the same amphoteric polyacrylamide. The results are shown in Table 5.

Y(20％)＝Y₂-a(X₂-20)

a＝(Y₂-Y₁)/(X₂-X₁)

Y (20%): specific tensile strength in terms of 20% ash in paper

X₁: paper ash ratio example of finished paper 1

X₂: paper ash ratio example of finished paper 2

Y₁: specific tensile Strength of the finished paper 1

Y₂: specific tensile Strength of the finished paper 2

Internal strength determination

The internal strength of the aforementioned paper 1 and paper 2 was measured in accordance with J.TAPPI No. 18-2. The results of calculating the internal strength of 20% ash in paper in the same manner as the specific tensile strength are shown in table 5.

Measurement of coefficient of variation of texture

The value obtained by inputting the light transmittance (brightness) of the paper 2 into a commercially available test instrument (product name "システム Hyper-700 for パーソナル paper", manufactured by OBS) and performing statistical analysis of the brightness distribution was used as the texture variation coefficient (variation coefficient) of the paper 2. The smaller the value of the texture variation coefficient, the better the texture. The results are shown in Table 5.

Immobilization rate of amphoteric Polyacrylamide

The nitrogen content of each of the paper-forming sheets 2 and 3 was determined using a commercially available measuring apparatus (trade name "TN-110", manufactured by Mitsubishi chemical corporation), and the nitrogen content was expressed by the following equation to calculate the immobilization ratio of the amphoteric polyacrylamide. The results are shown in Table 5.

The fixation ratio (%) × 100 [ ("nitrogen component of paper 2 — nitrogen component of paper 3) ]/(theoretical nitrogen component of amphoteric polyacrylamide in example 1 × addition ratio of the amphoteric polyacrylamide) ]

TABLE 5

Claims

2. The paper strength agent according to claim 1, wherein the component (a) in the component (1) is present in an amount of 55 to 97.8 mol%.

3. The paper strength additive according to claim 1 or 2, wherein the component (b) is at least one selected from the group consisting of a tertiary amino group-containing methacrylate, a tertiary amino group-containing methacrylamide, a quaternary ammonium salt structure-containing methacrylate, and a quaternary ammonium salt structure-containing methacrylamide.

4. The paper strength agent according to claim 1 or 2, wherein the component (1) further contains a cationic vinyl monomer (b') not containing an α -methyl group.

5. The paper strength agent according to claim 3, wherein component (1) further contains a cationic vinyl monomer (b') not containing an α -methyl group.

6. The paper strength additive according to claim 4, wherein the component (b') is at least one selected from the group consisting of an acrylic acid ester having a tertiary amino group, an acrylamide having a tertiary amino group, an acrylic acid ester having a quaternary ammonium salt structure, and an acrylamide having a quaternary ammonium salt structure.

7. The paper strength additive according to claim 5, wherein the component (b') is at least one selected from the group consisting of an acrylic acid ester having a tertiary amino group, an acrylamide having a tertiary amino group, an acrylic acid ester having a quaternary ammonium salt structure, and an acrylamide having a quaternary ammonium salt structure.

8. The paper strength agent according to claim 4, wherein the proportion of the component (b') in the component (1) is 0.1 to 3 mol%.

9. The paper strength agent according to any one of claims 5 to 7, wherein the proportion of the component (b') in the component (1) is 0.1 to 3 mol%.

10. The paper strength additive according to claim 1 or 2, wherein the component (c) contains an unsaturated carboxylic acid.

11. The paper strength additive according to claim 3, wherein the component (c) contains an unsaturated carboxylic acid.

12. The paper strength additive according to claim 4, wherein the component (c) contains an unsaturated carboxylic acid.

13. The paper strength agent according to claim 10, wherein the unsaturated carboxylic acid contains an unsaturated carboxylic acid containing no α -methyl group.

14. The paper strength agent according to claim 11 or 12, wherein the unsaturated carboxylic acid contains an unsaturated carboxylic acid containing no α -methyl group.

15. The paper strength additive according to claim 13, wherein the unsaturated carboxylic acid containing no α -methyl group contains an unsaturated monocarboxylic acid containing no α -methyl group, and the proportion of the unsaturated monocarboxylic acid containing no α -methyl group is 50 mol% or more.

16. The paper strength additive according to claim 14, wherein the unsaturated carboxylic acid containing no α -methyl group contains an unsaturated monocarboxylic acid containing no α -methyl group, and the proportion of the unsaturated monocarboxylic acid containing no α -methyl group is 50 mol% or more.

17. The paper strength agent according to claim 15 or 16, wherein the unsaturated monocarboxylic acid containing no α -methyl group contains acrylic acid and/or a salt thereof.

18. The paper strength additive according to claim 1 or 2, wherein the component (1) may further contain a crosslinkable monomer (d).

19. The paper strength additive according to claim 3, wherein the component (1) may further contain a crosslinkable monomer (d).

20. The paper strength additive according to claim 4, wherein component (1) may further contain a crosslinkable monomer (d).

21. The paper strength additive according to claim 10, wherein component (1) may further contain a crosslinkable monomer (d).

22. The paper strength agent according to claim 18, wherein the component (d) contains at least one selected from the group consisting of N, N-dimethylacrylamide and methylenebisacrylamide.

23. The paper strength agent according to any one of claims 19 to 21, wherein the component (d) contains at least one selected from the group consisting of N, N-dimethylacrylamide and methylenebisacrylamide.

24. The paper strength agent according to claim 18, wherein the proportion of the component (d) in the component (1) is 0.01 to 1 mol%.

25. The paper strength agent according to any one of claims 19 to 22, wherein the proportion of the component (d) in the component (1) is 0.01 to 1 mol%.

26. The paper strength agent according to claim 23, wherein the proportion of the component (d) in the component (1) is 0.01 to 1 mol%.

27. The paper strength agent according to claim 1 or 2, wherein component (1) further comprises a chain-transfer vinyl monomer (e).

28. The paper strength agent according to claim 3, wherein component (1) further comprises a chain-transfer vinyl monomer (e).

29. The paper strength agent according to claim 4, wherein component (1) further comprises a chain-transfer vinyl monomer (e).

30. The paper strength agent according to claim 10, wherein component (1) further comprises a chain-transfer vinyl monomer (e).

31. The paper strength agent according to claim 18, wherein component (1) further comprises a chain-transfer vinyl monomer (e).

32. The paper strength agent according to claim 27, wherein the component (e) contains a (meth) allylsulfonate.

33. The paper strength agent according to any one of claims 28 to 31, wherein the component (e) contains (meth) allyl sulfonate.

34. The paper strength agent according to claim 27, wherein the component (e) is contained in the component (1) in an amount of 0.05 to 2 mol%.

35. The paper strength agent according to any one of claims 28 to 32, wherein the component (e) is contained in the component (1) in an amount of 0.05 to 2 mol%.

36. The paper strength agent as claimed in claim 33, wherein the proportion of the component (e) in the component (1) is 0.05 to 2 mol%.

37. A method for producing high ash paper, characterized in that the paper strength enhancer as defined in any one of claims 1 to 36 is added to a papermaking system containing an inorganic filler at a concentration of 10 to 50% by weight based on the pulp.

38. The method of manufacturing high ash paper according to claim 37, wherein the inorganic filler is at least one selected from the group consisting of talc, kaolin, and calcium carbonate.

39. A high ash paper obtained by the method for producing a high ash paper according to claim 37 or 38.

40. The high ash paper according to claim 39, wherein the ash content in the paper is 10% by weight or more.