JP2017186725A - Paper durability promoter for high ash content paper, manufacturing method of high ash content paper and high ash content paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide amphoteric polyacrylamide making pulp easy to fix, hardly disturbing formation and excellent in paper durability effect even with high ash content.SOLUTION: There is provided a paper durability promoter that contains an amphoteric polyacrylamide having requirements [1] to [5]. [1] acrylamide (a), an α methyl group-containing cationic vinyl monomer (b) and an anionic vinyl monomer (c) are contained. [2] a ratio of the (b) component is 1-15 mol% and a ratio of the (c) component is 1-10 mol%. [3] There are high magnetic field side absorption band A and low magnetic field side absorption band B assigned to an α methyl group of the (b) component ofH-NMR spectrum and an area of A (As) and an area of B (Bs) is [As/(As+Bs)]=10-35%. [4] a viscosity of 15 wt.% solution (25°C) is 2,000-60,000 mPa a. [5] a ratio between a weight average molecular weight (Mw) and a number average molecular weight (Mn), (Mw/Mn) is 3.5 or less.SELECTED DRAWING: Figure 2

Description

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

  In general, inorganic fillers such as talc, kaolin and calcium carbonate are used for paper such as printing paper and writing paper. In particular, calcium carbonate is excellent in opacification, whitening and smoothing of paper and enhances printability, so that the amount used in the papermaking industry tends to increase year by year. Hereinafter, paper containing a large amount of inorganic filler is referred to as “high ash paper”.

  However, the high ash content paper tends to decrease the tensile strength, the internal strength, and the like as the content of the inorganic filler increases. As a result of the presence of a large amount of inorganic filler between the pulp fibers, it is considered that the entanglement between the fibers and the interaction through hydrogen bonding are inhibited.

  Therefore, conventionally, paper strength enhancing agents such as polyacrylamide and cationized starch have been used for the purpose of supplementing the strength of high ash content paper, and various improvements have been repeated. In particular, amphoteric polyacrylamide has a high paper strength enhancing effect because it is directly fixed to the pulp by its cationic group and the anionic group is indirectly fixed to the pulp (via an auxiliary material such as a sulfate band).

  On the other hand, there is still a growing demand for recycled paper made from waste paper. However, because waste paper pulp has been shortened and deteriorated, amphoteric polyacrylamide is difficult to be fixed. In this regard, it is conceivable to increase the amount of the cationic group. However, such amphoteric polyacrylamide has a strong cohesive force, so that the formation of the paper is disturbed and the paper strength effect is rather inferior.

  Therefore, the present applicant has shown in Patent Document 1 that a paper strength enhancer using amphoteric polyacrylamide having a predetermined parameter does not disturb the texture of the paper and is excellent in paper strength. However, it has been found that when the paper strength enhancer is applied to the high ash paper, particularly paper containing a large amount of calcium carbonate as an inorganic filler, the desired effect may be impaired.

JP 2014-196588 A

  The present invention provides a novel amphoteric polyacrylamide that is easily fixed to pulp fibers even when added to a pulp slurry containing a large amount of inorganic filler, has an excellent paper strength enhancing effect, and does not disturb the formation of the formed paper. It is a main subject to provide a paper strength enhancer including the same.

  The present inventor has studied to solve the above problem in amphoteric polyacrylamide defined by the predetermined parameters of Patent Document 1. As a result, it is considered that the amphoteric polyacrylamide is remarkably hindered from fixing the amphoteric polyacrylamide to the pulp fiber as one of the reasons that the effect decreases when applied to an inorganic filler, particularly a pulp slurry containing a large amount of calcium carbonate. It was.

  Therefore, the present inventor has found that a paper strength enhancer capable of solving the above-mentioned problems can be obtained by optimizing the parameters and specifying physical property conditions not explicitly described in the document 1. It was.

  That is, the present invention relates to a high ash paper strength enhancer, a high ash paper manufacturing method, and a high ash paper shown below.

1. A high ash paper strength enhancer containing amphoteric polyacrylamide having the following requirements [1], [2], [3], [4] and [5].
[1] The component (1) includes acrylamide (a), an α-methyl group-containing cationic vinyl monomer (b), and an anionic vinyl monomer (c). [2] Component (b) in the component (1) The ratio of the component (c) is 1 to 10 mol%. [3] In the range of 0.9 ppm to 1.35 ppm of the ¹ H-NMR spectrum, (b) ) There are a high magnetic field side absorption band A and a low magnetic field side absorption band B belonging to the α-methyl group of the component, and the total area of the absorption band A area (As) and the absorption band B area (Bs) The ratio [As / (As + Bs)] of the area (As) of the absorption band A is 10 to 35%. [4] The viscosity of the 15 wt% aqueous solution (25 ° C.) is 2,000 to 60,000 mPa · s. [5] Its weight average molecular weight (Mw) and number average The ratio of the molecular weight (Mn) (Mw / Mn) is 3.5 or less

2. Item 2. The paper strength enhancer according to Item 1, wherein the ratio of component (a) in component (1) is 55 to 97.8 mol%.

3. 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 salt structure-containing methacrylate, and a quaternary salt structure-containing methacrylamide. The paper strength enhancer according to item 1 or 2.

4). Item 4. The paper strength enhancer according to any one of Items 1 to 3, wherein Component (1) further contains an α-methyl group-free cationic vinyl monomer (b ′).

5. The component (b ′) is at least one selected from the group consisting of tertiary amino group-containing acrylates, tertiary amino group-containing acrylamides, quaternary salt structure-containing acrylates, and quaternary salt structure-containing acrylamides. Item 5. The paper strength enhancer of Item 4.

6). Item 6. The paper strength enhancer according to Item 4 or 5, wherein the proportion of component (b ') in component (1) is 0.1 to 3 mol%.

7). (C) The paper strength enhancer according to any one of Items 1 to 6, wherein the component contains an unsaturated carboxylic acid.

8). Item 8. The paper strength enhancer according to Item 7, wherein the unsaturated carboxylic acid comprises an α-methyl group-free unsaturated carboxylic acid.

9. Item 9. The paper strength enhancer according to Item 8, wherein the α-methyl group-free unsaturated carboxylic acid contains α-methyl group-free unsaturated monocarboxylic acid, and the occupation ratio is 50 mol% or more.

10. Item 10. The paper strength enhancer according to Item 9, wherein the α-methyl group-free unsaturated monocarboxylic acid comprises acrylic acid and / or a salt thereof.

11. Item 11. The paper strength enhancer according to any one of Items 1 to 10, wherein the component (1) further contains a crosslinkable monomer (d).

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

13. Item 13. The paper strength enhancer according to Item 11 or 12, wherein the ratio of component (d) in component (1) is 0.01 to 1 mol%.

14 Item 14. The paper strength enhancer according to any one of Items 1 to 13, wherein the component (1) further comprises a chain transfer vinyl monomer (e).

15. (E) The paper strength enhancer according to Item 14, wherein the component comprises (meth) allyl sulfonate.

16. Item 16. The paper strength enhancer according to Item 14 or 15, wherein the ratio of component (e) in component (1) is 0.05 to 2 mol%.

17. A method for producing a high ash content paper, wherein the paper strength enhancer according to any one of Items 1 to 16 is added to a papermaking system containing an inorganic filler in an amount of 10 to 50% by weight with respect to pulp.

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

19. High ash paper obtained by the method for producing high ash paper according to Item 17 or 18.

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

  The paper strength enhancer according to the present invention is easily fixed to a pulp even when applied to a pulp slurry containing a large amount of an inorganic filler, particularly calcium carbonate. In addition, the effect of enhancing paper strength is good and there is little disturbance in the formation of the paper. This effect is the same when using waste paper pulp slurry.

  Further, the paper strength enhancer according to the present invention can be used as a surface treatment agent for inorganic fillers, and even when the obtained coated inorganic filler is used, excessive aggregation of the inorganic filler can be suppressed. Paper to which a paper strength enhancer is added has excellent paper strength (tensile strength and internal strength) and has little formation disturbance.

FIG. 1 and FIG. 2 is a schematic diagram of polyacrylamide composed of acrylamide and an α-methyl group-containing cationic vinyl monomer. The former shows that the α-methyl group-containing cationic vinyl monomer unit is ubiquitous, and the latter shows that the unit is localized. It shows the state of being present. In the range of 0.9 ppm to 1.35 ppm of ¹ H-NMR spectrum of polyacrylamide composed of acrylamide and dimethylaminoethyl methacrylate, a high magnetic field side absorption band A (signal A belonging to α methyl group of the dimethylaminoethyl methacrylate is included. ) And a low magnetic field side absorption band B (signal B). In FIG. 2, it is a schematic diagram of the 1H-NMR spectrum when no peak appears on the higher magnetic field side than Signal A. It is a relationship figure of the ash content in paper and specific tensile strength of the formed paper 1 and the formed paper 2 which prepared by adding the same amphoteric polyacrylamide.

  The amphoteric polyacrylamide constituting the paper strength enhancer of the present invention is characterized in that it satisfies all the predetermined requirements [1], [2], [3], [4] and [5].

  Requirement [1] is that the amphoteric polyacrylamide is composed of acrylamide (a) (hereinafter also referred to as component), α-methyl group-containing cationic vinyl monomer (b) (hereinafter referred to as component (b)). Also anionic vinyl monomer (c), hereinafter referred to as component (c). ) Is included.

  In the present invention, acrylamide is used as the component (a). This is because it contributes to the paper strength enhancing effect of the amphoteric polyacrylamide according to the present invention as compared with methacrylamide.

  The ratio of the component (a) in the component (1) is not particularly limited, but the amphoteric polyacrylamide according to the present invention is excellent in the paper strength enhancing effect and further ensures the effect of suppressing the formation of the formed paper from being disturbed. More usually, it is about 55-97.8 mol%, preferably about 70-97 mol%, more preferably about 80-95 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. Here, the “α methyl group” means a methyl group bonded to the α carbon of the vinyl group in a monomer having a vinyl group and a cationic functional group.

  As the component (b), for example, at least selected from the group consisting of a tertiary amino group-containing methacrylate, a tertiary amino group-containing methacrylamide, a quaternary salt structure-containing methacrylate, and a quaternary salt structure-containing methacrylamide. One kind is mentioned. The latter compound is obtained by reacting the former with a quaternizing agent. Specific examples of the tertiary amino group-containing methacrylate and the tertiary amino group-containing methacrylamide include dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylate and diethylaminopropyl methacrylate. Examples of the quaternizing agent include methyl chloride, benzyl chloride, dimethyl sulfate and epichlorohydrin.

  In the present invention, the component (1) can further contain various known α-methyl group-free cationic vinyl monomers (b ′). Specific examples include quaternary salt structure-containing acrylates and quaternary salt structure-containing acrylamides obtained by reaction of tertiary amino group-containing acrylates and tertiary amino group-containing acrylamides with quaternizing agents, respectively. . Examples of the tertiary amino group-containing acrylate and tertiary amino group-containing acrylamide include dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl acrylamide, and diethylaminopropyl acrylamide. Examples of the quaternizing agent include those described above.

  The ratio of the component (b ′) in the component (1) is not particularly limited, but is usually less than 3 mol%, preferably less than 2 mol%, more preferably from the viewpoint of the paper strength enhancing effect of the amphoteric polyacrylamide according to the present invention. Is less than 1 mol%.

  Note that it is preferable to use only the component (b) without using the component (b ') from the viewpoint of the fixability of the amphoteric polyacrylamide according to the present invention to the pulp and the effect of enhancing paper strength. This is considered to be because the amphoteric polyacrylamide obtained in this way is likely to be formed into particles due to the association between molecules, thereby being fixed by pulp fibers.

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

  Unsaturated carboxylic acids can be classified into α-methyl group-containing unsaturated carboxylic acids and α-methyl group-containing unsaturated carboxylic acids. Examples of the former include acrylic acid, itaconic acid, maleic acid, maleic anhydride, and fumaric acid. Examples of the latter include methacrylic acid and crotonic acid. These may form a salt. Examples of the salt-forming species include alkali metal salts such as sodium salt and potassium salt, amines such as trimethylamine and tributylamine, ammonia and the like. Among these, α-methyl group-free unsaturated carboxylic acid (salt) is preferable, and acrylic acid and / or a salt thereof are particularly preferable from the viewpoint of excellent paper strength enhancing effect and further suppressing disturbance of the formation of the formed paper. More preferred.

  Examples of the unsaturated sulfonic acid include vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and salts thereof.

  When the proportion of α-methyl group-free unsaturated monocarboxylic acid (preferably acrylic acid and / or salt thereof) in the α-methyl group-free unsaturated carboxylic acid is 50 mol% or more, the paper strength enhancing effect and There exists a tendency for the disorder suppression effect to become favorable.

  Component (1) includes a crosslinkable monomer (d) (hereinafter also referred to as component (d)) for the purpose of increasing the molecular weight of the amphoteric polyacrylamide according to the present invention and enhancing its paper strength enhancing effect. It's okay. As the component (d), various known monomers can be used without particular limitation as long as they are crosslinkable monomers that can be used in the production of polyacrylamide. For example, monofunctional monomers such as allyl acrylate, diethylene glycol monoacrylate, N, N-dimethylacrylamide; bifunctional vinyl monomers such as ethylene glycol diacrylate, diallylamine, N-methylolacrylamide, and methylenebisacrylamide; trifunctional monomers such as triallyl isocyanate Vinyl monomers; and tetrafunctional vinyl monomers such as tetraallyloxyethane. Among these, the monofunctional monomer and / or the bifunctional monomer is preferable because it is easy to introduce a branched structure and / or a crosslinked structure into the target amphoteric polyacrylamide and easily achieve a high molecular weight thereof. It is preferable to include at least one selected from the group consisting of N-dimethylacrylamide and methylenebisacrylamide, and more preferable to include N, N-dimethylacrylamide.

  The ratio of the component (d) in the component (1) is not particularly limited, but the amphoteric polyacrylamide according to the present invention is made to have a high molecular weight without gelation, and the polyacrylamide has a fixability to pulp and a paper strength enhancing effect. From the viewpoint of excellent and further suppressing the formation of the formed paper from being disturbed, it is usually about 0.01 to 1 mol%, preferably about 0.02 to 0.8 mol%, more preferably 0.05 to 0. It is about 6 mol%.

  The component (1) may contain various known chain transfer vinyl monomers (e) (hereinafter sometimes referred to as component (e)). By using the component (e), the amphoteric polyacrylamide according to the present invention can be made to have a high molecular weight without being gelled, and the aqueous solution can be made to have a low viscosity. In addition, the fixability of the amphoteric polyacrylamide to the pulp, the paper strength enhancing effect, and the effect of suppressing disturbance of the texture of the formed paper are also improved. Examples of the component (e) include (meth) allyl sulfonate (that is, allyl sulfonate and / or methallyl sulfonate), and examples of the salt-forming species include alkali salts such as sodium salt and potassium salt. Metal salts are mentioned.

  The ratio of the component (e) in the component (1) is not particularly limited, but the amphoteric polyacrylamide according to the present invention is increased in molecular weight without gelation, and the fixability of the polyacrylamide to the pulp and the paper strength enhancing effect From the viewpoint of securing the effect of suppressing the disorder of the texture of the formed paper, and usually from about 0.1 to 2 mol%, preferably from about 0.15 to 1 mol%, more preferably from 0.2 to It is about 0.8 mol%.

  The component (1) may further contain other monomers that can react with the components (a) to (e), such as methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acrylic. N-propyl acid, iso-propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, stearyl (meth) acrylate, Nonionic vinyl monomers such as (meth) acrylic acid alkyl esters, acrylonitrile, styrenes, vinyl acetate, methyl vinyl ether and the like. In addition, although carbon number of the alkyl group of this (meth) acrylic-acid alkylester is not specifically limited, Usually, it is about 1-8. Further, the ratio of the nonionic vinyl monomer in the constituent component is not particularly limited, but is usually 10 mol% or less, preferably 5 mol% or less, when the constituent component (1) is 100 mol%.

  Requirement [2] prescribes that the proportion of component (b) in component (1) is 1 to 15 mol% and the proportion of component (c) is 1 to 10 mol%.

  When the ratio of the component (b) is less than 1 mol%, the fixability of the amphoteric polyacrylamide according to the present invention to the pulp and the effect of enhancing paper strength tend to be insufficient. On the other hand, when it exceeds 15 mol%, the cohesiveness of the amphoteric polyacrylamide becomes too strong, and the texture of the formed paper tends to be disturbed. Further, from the same viewpoint as described above, the ratio of the component (b) is preferably about 2 to 12 mol%, more preferably about 3 to 10 mol%.

  When the ratio of the component (c) is less than 1 mol%, the fixability of the amphoteric polyacrylamide according to the present invention to the pulp and the paper strength enhancing effect tend to be insufficient. On the other hand, if it exceeds 10 mol%, the cohesiveness of the amphoteric polyacrylamide becomes too strong and the texture of the formed paper tends to be disturbed. Further, from the same viewpoint as described above, the ratio of the component (c) is preferably about 1 to 9 mol%, more preferably about 2 to 8 mol%.

The requirement [3] defines the parameters of the amphoteric polyacrylamide according to the present invention. Specifically, the ¹ H-NMR spectrum of the amphoteric polyacrylamide has a high magnetic field absorption band A (hereinafter referred to as signal) belonging to the α-methyl group of the component (b) in the range of 0.9 ppm to 1.35 ppm. A) and a low magnetic field side absorption band B (hereinafter referred to as signal B) appear. And the ratio [As / (As + Bs)] of the area (As) of the absorption band A to the total area of the area (As) of the absorption band A and the area (Bs) of the absorption band B is 10 to 35%. There is a feature in the point. Since the amphoteric polyacrylamide is a high molecular compound, both the signal A and the signal B have a mountain shape with a broad hem.

  Here, the range of chemical shift (0.9 ppm to 1.35 ppm) is a numerical value when sodium 3- (trimethylsilyl) -1-propanesulfonate (DSS) is used as an internal standard substance.

  In addition, the range of the chemical shift (0.9 ppm to 1.35 ppm) is a range voluntarily determined by the applicant, but as shown in FIG. 2, the upper limit (1.35 ppm) is The minimum point (local minimum) on the left foot side of signal B was set as a guide. In addition, the area As of the signal A and the area Bs of the signal B are partitioned with the minimum point on the right skirt side of the signal B as a boundary. In addition, the lower limit (0.9 ppm) of the chemical shift range is a guideline when the peak appears further on the higher magnetic field side than the signal A (see FIG. 2). Set to. However, even when no peak appears on the higher magnetic field side than the signal A, the lower limit is set to 0.9 ppm. In this case, as shown in FIG. 3, the contact point (a point of contact) between the right tail of the signal A and the baseline of the NMR spectrum is approximately 0.9 ppm.

  Signals A and B are both absorption bands specific to the α-methyl group of the component (b) constituting the amphoteric polyacrylamide according to the present invention. When the unit of the component (b) is more continuous (localized) on the molecular chain of the amphoteric polyacrylamide and the proton in the α-methyl group is placed in an adjacent environment, the relative intensity of the signal A is The relative intensity of signal B becomes smaller. Conversely, when the unit of component (b) is more ubiquitous on the molecular chain of the amphoteric polyacrylamide and placed in an environment where protons in the α-methyl group are not adjacent, the relative intensity of signal A decreases. The relative intensity of signal B is increased.

  Therefore, the ratio of the area of signal A to the total area of signals A and B [As / (As + Bs)] indicates that the smaller this is, the more ubiquitous cationic sites on the molecular chain of the amphoteric polyacrylamide according to the present invention. Means.

The ratio [As / (As + Bs)] was determined by measuring the ¹ H-NMR spectrum of the amphoteric polyacrylamide according to the present invention using a commercially available ¹ H-NMR measuring instrument, and following the above-described compartment procedure, the integration ratio of As and Bs. Can be calculated by obtaining each of them.

  Unlike the invention described in Patent Document 1, the amphoteric polyacrylamide according to the present invention is applied to high ash paper, and is self-fixing to pulp fibers in a pulp slurry containing a large amount of inorganic filler, particularly calcium carbonate. For this purpose, the ratio [As / (As + Bs)] is preferably about 10% to less than 35%, more preferably about 12% to less than 25%, and more preferably about 15% to less than 20%. .

  In addition, it is considered that the aggregation of pulp fibers becomes too strong when amphoteric polyacrylamide having a highly localized cation site is used under papermaking conditions with a large amount of inorganic filler, that is, with a relatively small proportion of pulp fibers. In this regard, in the present invention, the area ratio [As / (As + Bs)] is set to be relatively smaller than the value described in Patent Document 1, and the viscosity conditions and polydispersity conditions described below are optimal. It is thought that the expected effect is produced by becoming.

  The requirement [4] defines the viscosity of the amphoteric polyacrylamide according to the present invention in an aqueous solution state. Unlike the amphoteric polyacrylamide according to Patent Document 1, the amphoteric polyacrylamide according to the present invention has a relatively small area ratio [As / (As + Bs)]. That is, in the amphoteric polyacrylamide according to the present invention, the localization of the cationic site is eliminated to some extent. As a result, the ability to self-fix to pulp fibers is relatively lowered. Furthermore, since the pulp slurry for paper making of high ash content contains a large amount of inorganic filler, there are few contact points between the amphoteric polyacrylamide and the pulp fiber. Therefore, in the present invention, the viscosity of the 15% by weight aqueous solution is defined as 2,000 to 60,000 mPa · s for the purpose of compensating for the shortage. By doing so, the amphoteric polyacrylamide of the present invention is easy to come into contact with the pulp fiber, and more hydrogen bonds are formed at the contact point, so that it exerts a predetermined paper strength effect under the papermaking conditions containing a large amount of inorganic filler. I think that. From this viewpoint, the viscosity is preferably about 3,000 to 30,000 mPa · s, more preferably about 4,000 to 15,000 mPa · s.

  The viscosity can be measured by various known means. Specific examples include a capillary viscometer, a falling ball viscometer, a rotary viscometer, and the like, but a rotary viscometer is preferable in that a viscosity at a predetermined concentration can be directly measured. An example of the measuring instrument is a B-type viscometer. As measurement conditions, a 15 wt% aqueous solution, 25 ° C., 3 rotors at 6 rpm, or no. 6 rotors with 4 rotors are preferred.

  Requirement [5] is the ratio (Mw / Mn) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the amphoteric polyacrylamide according to the present invention, that is, the spread of the molecular weight distribution of the amphoteric polyacrylamide (hereinafter referred to as polydispersion). (Also called degrees). One of the reasons is that the paper strength enhancer described in Patent Document 1 tends to cause turbulence of the formed paper (high ash content paper) and decrease in paper strength when applied to papermaking under high ash content conditions. The amphoteric polyacrylamide that constitutes the paper strength enhancer has a relatively wide molecular weight distribution, and it contains a high molecular weight amphoteric polyacrylamide that easily causes disturbance of formation, and a low molecular weight amphoteric polyacrylamide that contributes little to paper strength. I thought it was because of the large amount. Therefore, in the present invention, the molecular weight distribution (Mw / Mn) is regulated to 3.5 or less for the purpose of compensating for such drawbacks. By limiting to this range, the ratio of the high molecular weight category that causes overcoagulation of the pulp fiber and the formation disturbance of the formed paper, and the low self-fixing property to the pulp fiber, the contribution to the paper strength effect is relatively low. The ratio of the molecular weight classification can be reduced. From this viewpoint, the ratio is 3.5 or less, preferably 3 or less, more preferably 2.8 or less. Moreover, a lower limit is 1 or more normally, Preferably it is 1.5 or more.

  Mw and Mn can be measured by various known means, but it is preferable that both are determined by gel permeation chromatography (GPC).

  The production method of the paper strength enhancer according to the present invention is not particularly limited, but as described above, the amphoteric polyacrylamide forming the paper strength enhancer can control the localization of the cationic site on the molecular chain, Various known polymerization methods (drop polymerization method, simultaneous polymerization method, multi-stage polymerization method, etc.) can be adopted as long as the method can produce amphoteric polyacrylamide satisfying the viscosity and molecular weight distribution.

  In order to satisfy the requirements [3], [4] and [5] for the amphoteric polyacrylamide, for example, the total vinyl monomer constituting the amphoteric polyacrylamide is divided into a plurality of monomer mixtures, and ( b) The amount of the component used is increased and these mixtures are reacted sequentially, or the component (b) is added to the reaction system at a certain point in the polymerization reaction to participate in the polymerization reaction. It is preferable to carry out an operation that increases the concentration of the component (b) to some extent.

  Moreover, the preferable manufacturing method of the paper strength enhancer which concerns on this invention is the following aspects. According to this aspect, amphoteric polyacrylamide having a region where a cationic site is localized to some extent on the molecular chain according to the present invention can be obtained more reliably.

  That is, the said aspect contains acrylamide (a) and alpha methyl group containing cationic vinyl monomer (b) as an essential component, and the ratio of this (b) component is 5-87 mol% (preferably 5-60 mol%). The monomer mixture (I) is more preferably 10 to 40 mol%), the acrylamide (a) and the anionic vinyl monomer (c) as essential components, and the anionic vinyl monomer And (B) polymerizing the monomer mixture (II) in which the ratio of (c) is 1 to 20 mol% (preferably 1 to 15 mol%, more preferably 1 to 10 mol%). To do.

  Either one or both of the monomer mixture (I) and the monomer mixture (II) may contain an α-methyl group-free cationic vinyl monomer (b ′), if necessary.

  In addition, the monomer mixture (I) has an amphoteric polyacrylamide obtained with excellent fixability to pulp and paper strength-enhancing effect, and further suppresses the formation of paper from being disturbed. It is preferable to include a functional vinyl monomer (c).

  In addition, one or both of the monomer mixture (I) and the monomer mixture (II) may further contain a crosslinkable monomer (d). The component (d) is separately provided in the process (A) and the process (B). It can also be added to the reaction system or after the completion of one or both of step (A) and step (B).

  Further, from the same viewpoint as described above, the monomer mixture (I) and the monomer mixture (II) preferably further include a chain transfer vinyl monomer (e) in one or both of them.

The composition other than the component (b) in the monomer mixture (I) is not particularly limited, but the amphoteric polyacrylamide obtained has excellent fixability to the pulp and a paper strength enhancing effect, and further suppresses the formation of the formed paper from being disturbed. From the viewpoint of the above, assuming that the total proportion of the monomer components in the monomer mixture (I) is 100 mol%, the component (a) is usually about 30 to 90 mol%, the component (b ′) is about 0 to 15 mol%, (c ) Component 0-40 mol%, (d) component 0.01-3 mol% or 0 mol%, and (e) component 0-20 mol%, preferably (a) component 40-85 mol. %, (B ') component 0-10 mol%, (c) component 0.1-30 mol% or 0 mol%, (d) component 0.01-2.5 mol% or 0 mol% And (e) about 0.1 to 15 mol% of the component,
More preferably, 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%, and the component (d) is 0.1 to 2%. About mol% or 0 mol%, and (e) about 0.1-10 mol% of component.

  The composition other than the component (c) in the monomer mixture (II) is not particularly limited, but the amphoteric polyacrylamide obtained has excellent fixability to the pulp and a paper strength enhancing effect, and further suppresses the formation of the formed paper from being disturbed. From the viewpoints of the above, assuming that the total proportion of the monomer components in the monomer mixture (II) is 100 mol%, the component (a) is usually about 20 to 98.8 mol%, the component (b) is about 0 to 15 mol%, ( b ') about 0-15 mol% of component, (d) about 0.001-1 mol% or 0 mol% of component, and (e) about 0-1 mol% of component, preferably (a) component 60- About 98.8 mol%, (b) about 0-10 mol% of component, (b ′) about 0-10 mol% of component, (d) about 0.01-0.5 mol% or 0 mol% of component, and (E) component is about 0.01 to 0.5 mol%, more Preferably, (a) component 70 to 98.8 mol%, (b) component 0 to 5 mol%, (b ′) component 0 to 8 mol%, (d) component 0.1 to 0.4. It is about mol% or 0 mol%, and (e) component is about 0.01-0.4 mol%.

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

  Moreover, both monomer mixture (I) and monomer mixture (II) can be used as a solution. As the solvent, water is usually preferable, and an organic solvent such as methanol, ethanol, 2-propanol or the like can be used as a cosolvent. Moreover, when monomer mixture (I) and / or monomer mixture (II) contain the monomer which is easy to hydrolyze, in order to prevent this, a sulfuric acid can be used.

  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 ° C., and the polymerization time is about 1 to 5 hours. In the step (A) and / or the step (B), a redox system comprising a conventionally known polymerization initiator such as potassium persulfate or ammonium persulfate, or a reducing agent such as the initiator and sodium bisulfite. An initiator such as a polymerization initiator or an azo initiator can be used. The amount used is not particularly limited, but is usually about 0.01 to 2% by weight with respect to the total weight of all constituent monomers of the amphoteric polyacrylamide according to the present invention, preferably 0.05 to 0.00%. About 5% by weight.

  In the step (A), the monomer mixture (I) may be subjected to drop polymerization, simultaneous polymerization, or a combination thereof. However, drop polymerization is preferred because the polymerization reaction is easily controlled.

  Also in the step (B), the monomer mixture (II) may be subjected to drop polymerization, simultaneous polymerization, or a combination thereof. However, since the polymerization reaction is easy to control, dropping polymerization is also preferable.

  The order of the step (A) and the step (B) is not particularly limited as long as the purpose of forming a region where a cationic site is localized to some extent on the molecular chain of the amphoteric polyacrylamide can be achieved. For example, the method of starting a process (B) after completing a process (A), or starting a process (A) after completing a process (B), etc. are mentioned. Further, the time interval between the step (A) and the step (B) is not particularly limited. For example, the other step may be started immediately after the step (A) or the step (B) is completed. You may start another process, after completing (A) or a process (B) and progressing for a fixed time. In addition, after the start of the step (A) or the step (B), the other step may be started in the same reaction system before the completion thereof. In this case, the amphoteric poly having a cationic site partially ubiquitous to some extent. Acrylamide can be obtained.

  The initiator may be included in the monomer mixture (I) and / or the monomer mixture (II) in advance or may not be included, for example. If not included, for example, the initiator may be dropped into the reaction system from the outside over both step (A) and step (B). In this case, the initiator can be used as an aqueous solution.

  The most preferable production method of the paper strength enhancer according to the present invention is an embodiment in which the monomer mixture (II) is dropped into the same reaction system after completion of the step (A) of dropping the monomer mixture (I). is there. In this embodiment, a monomer mixture (I) containing a relatively large amount of component (b) is polymerized in step (A) to once produce a polyacrylamide precursor with a certain degree of cationic site density. Then, in the presence of the precursor, by polymerizing the monomer mixture (II) having a relatively small amount of component (b) or zero, a region in which the cationic site is localized to some extent is formed on the molecular chain. It is possible to easily obtain amphoteric polyacrylamide. Moreover, in this aspect, it is preferable that the said initiator is dripped at a reaction system over both a process (A) and a process (B).

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

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

  The paper strength enhancer of the present invention may include other paper strength agents. Specific examples include 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 resin, polyamide polyamine epichlorohydrin, and polyvinylamine. The mixing amount of the other paper strength agent is not particularly limited, but is usually about 0.1 to 40% by weight, where the total of the paper strength enhancer of the present invention and the other paper strength agent is 100% by weight.

  The method for producing a high ash content paper according to the present invention comprises adding the paper strength enhancer of the present invention to a pulp slurry containing 10 to 50% by weight of an inorganic filler in terms of the weight of pulp (solid content). Features.

  Examples of the inorganic filler include at least one selected from the group consisting of talc, kaolin and calcium carbonate. Examples of calcium carbonate include heavy calcium carbonate and light calcium carbonate.

  Pulp slurry includes bleached or unbleached chemical pulp such as kraft pulp, sulfite pulp, bleached or unbleached pulp such as groundwood pulp, mechanical pulp, thermomechanical pulp, newspaper wastepaper, magazine wastepaper, cardboard wastepaper, deinked wastepaper, etc. Used paper pulp and the like.

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

  The high ash content paper of this invention is obtained with the above-mentioned manufacturing method. The resulting high ash paper can be used as liner base paper, core base paper, paper tube base paper, white board paper, kraft paper, fine paper, newspaper, and the like. The content of the inorganic filler in the high ash paper is not particularly limited, but is usually 10% by weight or more, preferably about 10 to 30% by weight.

  Hereinafter, the present invention will be described more specifically with reference examples, examples and comparative examples, but the present invention is not limited to these examples. In each example, all parts and% are based on weight unless otherwise specified. The physical property value of each example is a value measured by the following method.

Example 1
A reaction vessel equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet tube and three dropping funnels (hereinafter referred to as funnel 1, funnel 2, and funnel 3) was charged with 401.4 parts of ion-exchanged water, After removing oxygen in the reaction vessel by directly blowing nitrogen gas into the ion exchange water, the temperature of the ion exchange water was set to 90 ° C.
Next, in funnel 1, as monomer mixture (I), 79.04 parts of 50% acrylamide aqueous solution, 24.37 parts dimethylaminoethyl methacrylate, 3.99 parts 80% acrylic acid, 0.18 parts N, N-dimethylacrylamide An aqueous solution consisting of 0.292 parts of sodium methallyl sulfonate, 11.91 parts of 62.5% sulfuric acid and 61.42 parts of ion-exchanged water was further adjusted to pH 4.5 with sulfuric acid.
Next, in Funnel 2, as monomer mixture (II), 386.98 parts of 50% aqueous acrylamide, 10.44 parts of dimethylaminoethyl methacrylate, 13.27 parts of benzyl chloride quaternized product of 75% dimethylaminoethyl acrylate, 80% An aqueous solution comprising 9.31 parts of acrylic acid, 0.18 parts of N, N-dimethylacrylamide, 0.292 parts of sodium methallyl sulfonate, 5.10 parts of 62.5% sulfuric acid, and 231.16 parts of ion-exchanged water was further added. A solution adjusted to pH 4.5 with sulfuric acid was charged.
Subsequently, the funnel 3 was charged with an initiator solution consisting of 0.21 part of ammonium persulfate and 180 parts of ion-exchanged water.
Subsequently, the cocks of the funnel 1 and funnel 3 were opened simultaneously, and the entire amount of the monomer mixture (I) and half of the initiator solution were added dropwise over 2 hours. Immediately after that, the cock of the funnel 2 was opened, and the entire amount of the monomer mixture (II) and the remaining half of the initiator solution were dropped over 2 hours.
Next, after the reaction system was kept at 90 ° C. for 1 hour, 562 parts of ion-exchanged water was further added to thereby prepare an amphoteric polyacrylamide having a weight average molecular weight of 1,120,000 and a viscosity of 8,900 mPa · s (solid content concentration: 15.0%). Got.

Examples 2-15
Amphoteric polyacrylamide (both solid content concentration of 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. Obtained.

Comparative Examples 1-9, 11
Amphoteric polyacrylamide (both solid content concentration 15.0%) was obtained by the same method as Example 1 except having changed the monomer mixture (I) and monomer mixture (II) into the composition shown in Table 1.

Comparative Example 10
Into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas introduction pipe and three dropping funnels (hereinafter referred to as funnel 1, funnel 2 and funnel 3), 276.2 parts of ion-exchanged water was charged. After removing oxygen in the reaction vessel by directly blowing nitrogen gas into the ion exchange water, the temperature of the ion exchange water was set to 90 ° C.
Subsequently, in the funnel 1, as a monomer mixture (I), 193.00 parts of 50% acrylamide aqueous solution, 40.20 parts of dimethylaminoethyl methacrylate, 24.20 parts of benzyl chloride quaternized product of 60% dimethylaminoethyl methacrylate, 80% 1.40 parts of acrylic acid, 0.300 part of N, N-dimethylacrylamide, 0.250 part of methylenebisacrylamide, 3.200 parts of sodium methallyl sulfonate, 19.70 parts of 62.5% sulfuric acid, and 168 ion-exchanged water An aqueous solution consisting of 1 part was further adjusted to pH 4.5 with sulfuric acid.
Next, in the funnel 2, as a monomer mixture (II), 469.00 parts of 50% aqueous acrylamide, 9.200 parts of 80% acrylic acid, 0.30 parts of N, N-dimethylacrylamide, 0.250 parts of methylenebisacrylamide, An aqueous solution consisting of 0.800 parts of sodium methallyl sulfonate and 212.30 parts of ion-exchanged water was charged.
The funnel 3 was then charged with an initiator solution consisting of 0.6 parts ammonium persulfate and 180 parts ion-exchanged water.
Subsequently, the cocks of the funnel 1 and funnel 3 were opened simultaneously, and the entire amount of the monomer mixture (I) and half of the initiator solution were added dropwise over 2 hours. Immediately after that, the cock of the funnel 2 was opened, and the entire amount of the monomer mixture (II) and the remaining half of the initiator solution were dropped over 2 hours.
Next, the reaction system was kept at 90 ° C. for 1 hour, and further charged with 400 parts of ion-exchanged water, whereby an amphoteric polyacrylamide having a weight average molecular weight of 3 million and a viscosity of 8,500 mPa · s (solid content concentration: 20.3%) Got. The viscosity of this sample diluted to 15.0% with ion-exchanged water was measured and found to be 1,200 mPa · s.

  Regarding Examples and Comparative Examples, Table 2 shows the molar ratio of each component when the total ratio of the monomer components in the monomer mixture (I) or the monomer mixture (II) is 100 mol%. The molar ratio of each component when all the monomer components were 100 mol% was represented, respectively.

The symbols representing the compounds in Tables 1 to 3 have the following meanings.
AM: acrylamide (molecular weight 71.1)
DM: dimethylaminoethyl methacrylate (molecular weight 157.2)
DML: benzyl chloride quaternized product of dimethylaminoethyl methacrylate (molecular weight 283.8)
APDM: dimethylaminopropylacrylamide (molecular weight 156.2)
DMAEA-BQ: benzyl chloride quaternized product 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: Methylenebisacrylamide (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)

<Measurement of ¹ H-NMR spectrum>
After mixing 26.7 mg of amphoteric polyacrylamide of Examples 1 to 15 and Comparative Examples 1 to 11 and 0.8 ml of heavy water (D ₂ O), 3- (trimethylsilyl) -1-propanesulfonic acid was added to the mixture. 1 μl of an internal standard solution obtained by mixing 40.23 mg of sodium (DSS) and 1.0 ml of D 2 O was dropped using a microsyringe to prepare a measurement sample (concentration: 0.5%).

Subsequently, the ¹ H-NMR spectrum was measured using the sample under the following conditions.

NMR measuring device: 400 MHz manufactured by Agilent Technologies 400 MHz
Probe: AutoX PFG probe (5mm)
Probe temperature: 70 ° C
Measurement frequency: 399.75 MHz
Measuring solvent: heavy water (D2O)
Pulse sequence: prestration Standard parameter use count: 128 times

<Calculation of signal area ratio [As / (As + Bs)]>
Using the analysis software vNMRJ (manufactured by Agilent Technologies) attached to the NMR measuring instrument, the area <As> and <Bs> of the signal were obtained on a computer, and the area ratio [As / (As + Bs)] was calculated. did. The results are shown in Table 4.

<Weight average molecular weight>
About the amphoteric polyacrylamide of Examples 1-15 and Comparative Examples 1-11, the weight average molecular weight and polydispersity (Mw / Mn) were measured on condition of the following. The results are shown in Table 4.

GPC body: Tosoh Corp. column: Tosoh Corp. guard column PWXL 1 and GMPWXL 2 (column temperature 40 ° C.)
Eluent: N / 2 acetate buffer (N / 2 acetic acid (Wako Pure Chemical Industries, Ltd.) + N / 2 sodium acetate (Kishida Chemical Co., Ltd.) aqueous solution, pH 4.2)
Flow rate: 0.8 ml / min Detector:
RALLS method; TDA MODEL301 manufactured by Biscotech (concentration detector, 90 ° light scattering detector, and viscosity detector are each set to 40 ° C.)

<Viscosity>
For the amphoteric polyacrylamides of Examples 1 to 15 and Comparative Examples 1 to 11, using a B-type viscometer (product name “Vistometron”, manufactured by Shibaura System Co., Ltd.), 25 ° C., rotation speed 6 rpm, rotor No. The viscosity was measured under the condition of 3. The results are shown in Table 4.

[Preparation of paper materials]
Bleached kraft pulp (LBKP) was beaten with a Niagara-type beater to obtain a slurry prepared so that Canadian Standard Freeness (CSF) was 350 ml. Next, sodium sulfate was added to the slurry, and the electrical conductivity was adjusted to 0.5 mS / cm, whereby a 1% slurry paper stock 1 was prepared. In addition, the said electrical conductivity was measured using the commercially available measuring device (Brand name "pH / COND METER D-54", Horiba, Ltd. make).

Next, while stirring the stock 1, a sulfuric acid band (1.0% by weight of pulp), cationized starch (0.8% by weight of pulp) (Nippon Food Kako: Neotac 30T), amphoteric polyacrylamide of Example 1 After adding in order of (vs. pulp weight 0.3%), calcium carbonate (vs. pulp 15%) (Okutama Kogyo: Tama Pearl TP121) was added. Using the obtained pulp slurry, paper was made using a TAPPI square sheet machine so that the basis weight of the resultant paper was 80 g / m ² . The obtained wet paper was pressed and dried according to a conventional method to obtain an adult paper 1. Similarly, the amphoteric polyacrylamides of Examples 2 to 15 and Comparative Examples 1 to 11 were used in the same manner to obtain the respective papers 1.

While stirring the stock 1, the sulfuric acid band (1.0% pulp weight), cationized starch (0.8% pulp weight) (Nippon Food Kako: Neotac 30T), the amphoteric polyacrylamide of Example 1 (vs. After adding in order of pulp weight 0.3%), calcium carbonate (30% to pulp) (Okutama Kogyo: Tama Pearl TP121) was added. Using the obtained pulp slurry, paper was made using a TAPPI square sheet machine so that the basis weight of the resultant paper was 80 g / m ² . The obtained wet paper was pressed and dried according to a conventional method to obtain an adult paper 2. Similarly, the amphoteric polyacrylamides of Examples 2 to 15 and Comparative Examples 1 to 11 were used in the same manner to obtain the respective papers 2.

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

[Measurement of specific tensile strength]
The specific tensile strengths of the resultant paper 1 and the resulting paper 2 were measured in accordance with JIS P8113. Paper strength such as specific tensile strength is greatly influenced not only by the type of amphoteric polyacrylamide added, but also by the amount of ash in the paper. Since the agglomeration and interaction of the filler differ depending on the type of amphoteric polyacrylamide, and the yield of the filler in the paper changes, the amount of ash content in the paper to which various amphoteric polyacrylamides are added is usually not the same. As described above, since the paper strength is affected by the amount of ash in the paper, the difference in the paper strength improvement effect due to the addition of amphoteric polyacrylamide needs to be compared by correcting to the equivalent amount of ash in the paper. The specific tensile strength was corrected according to the following.
The strength of ash content in paper 20% was estimated by the following formula from the relationship between the percentage of ash content in paper 1 and the strength of specific paper 2 prepared by adding the same amphoteric polyacrylamide (FIG. 4). The results are shown in Table 5.

_{Y (20%) = Y 2} -a (X 2 -20)
a = (Y ₂ −Y ₁ ) / (X ₂ −X ₁ )

Y (20%): Specific tensile strength X ₁ in terms of ash content in paper X ₁ : Ratio of ash content in paper X ₂ : Ratio of ash content in paper 2 Y ₁ : Specific tensile strength of paper 1 Y ₂ : Specific tensile strength of the formed paper 2

[Measurement of internal strength]
The internal strength of the above-mentioned formed paper 1 and the formed paper 2 was determined according to J. TAPPI No. It measured based on 18-2. Table 5 shows the results of calculating the internal strength at 20% ash content in the paper in the same manner as the specific tensile strength.

[Measurement of formation variation coefficient]
Passing light (luminance) from the adult paper 2 was taken into a commercially available measuring instrument (trade name “Personal Image Processing System Hyper-700”, manufactured by OBS), and a value obtained by statistical analysis of the luminance distribution was obtained. The formation variation coefficient (variation coefficient) of the grown paper 2 was used. The formation variation coefficient means that the smaller the value, the better the formation. The results are shown in Table 5.

[Fixing rate of amphoteric polyacrylamide]
The nitrogen content of each of the resultant paper 2 and the mature paper 3 is determined using a commercially available measuring device (product name “TN-110”, manufactured by Mitsubishi Chemical Corporation), and the nitrogen content is calculated as follows: And the fixing rate of amphoteric polyacrylamide was calculated. The results are shown in Table 5.

Fixing rate (%) = [(nitrogen content of the resulting paper 2−nitrogen content of the formed paper 3) ÷ (theoretical nitrogen content of the amphoteric polyacrylamide according to Example 1 × addition rate of the amphoteric polyacrylamide)] × 100

Claims (20)

A high ash paper strength enhancer containing amphoteric polyacrylamide having the following requirements [1], [2], [3], [4] and [5].
[1] The component (1) includes acrylamide (a), an α-methyl group-containing cationic vinyl monomer (b), and an anionic vinyl monomer (c). [2] Component (b) in the component (1) The ratio of the component (c) is 1 to 10 mol%. [3] In the range of 0.9 ppm to 1.35 ppm of the ¹ H-NMR spectrum, (b) ) There are a high magnetic field side absorption band A and a low magnetic field side absorption band B belonging to the α-methyl group of the component, and the total area of the absorption band A area (As) and the absorption band B area (Bs) The ratio [As / (As + Bs)] of the area (As) of the absorption band A is 10 to 35%. [4] The viscosity of the 15 wt% aqueous solution (25 ° C.) is 2,000 to 60,000 mPa · s. [5] Its weight average molecular weight (Mw) and number average The ratio of the molecular weight (Mn) (Mw / Mn) is 3.5 or less The paper strength enhancer of Claim 1 whose ratio of the (a) component in a structural component (1) is 55-97.8 mol%. 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 salt structure-containing methacrylate, and a quaternary salt structure-containing methacrylamide. The paper strength enhancer of claim 1 or 2. The paper strength enhancer according to any one of claims 1 to 3, wherein the component (1) further contains an α-methyl group-free cationic vinyl monomer (b '). The component (b ′) is at least one selected from the group consisting of tertiary amino group-containing acrylates, tertiary amino group-containing acrylamides, quaternary salt structure-containing acrylates, and quaternary salt structure-containing acrylamides. The paper strength enhancer according to claim 4. The paper strength enhancer according to claim 4 or 5, wherein the ratio of the component (b ') in the component (1) is 0.1 to 3 mol%. (C) The paper strength enhancer in any one of Claims 1-6 in which a component contains unsaturated carboxylic acid. The paper strength enhancer according to claim 7, wherein the unsaturated carboxylic acid comprises an α-methyl group-free unsaturated carboxylic acid. The paper strength enhancer according to claim 8, wherein the α-methyl group-free unsaturated carboxylic acid contains α-methyl group-free unsaturated monocarboxylic acid, and the occupation ratio is 50 mol% or more. The paper strength enhancer according to claim 9, wherein the α-methyl group-free unsaturated monocarboxylic acid comprises acrylic acid and / or a salt thereof. The paper strength enhancer according to any one of claims 1 to 10, wherein the component (1) further comprises a crosslinkable monomer (d). The paper strength enhancer according to claim 11, wherein the component (d) includes at least one selected from the group consisting of N, N-dimethylacrylamide and methylenebisacrylamide. The paper strength enhancer of Claim 11 or 12 whose ratio of (d) component in a structural component (1) is 0.01-1 mol%. The paper strength enhancer according to any one of claims 1 to 13, wherein the component (1) further comprises a chain transfer vinyl monomer (e). The paper strength enhancer of claim 14, wherein component (e) comprises (meth) allyl sulfonate. The paper strength enhancer of Claim 14 or 15 whose ratio of the (e) component in a structural component (1) is 0.05-2 mol%. A method for producing a high ash content paper, wherein the paper strength enhancer according to any one of claims 1 to 16 is added to a papermaking system containing an inorganic filler in a concentration of 10 to 50% by weight with respect to pulp. The method for producing a high ash paper according to claim 17, wherein the inorganic filler is at least one selected from the group consisting of talc, kaolin and calcium carbonate. A high ash content paper obtained by the method for producing a high ash content paper according to claim 17 or 18. The high ash content paper of Claim 19 whose ash content in paper is 10 weight% or more.