JPH11286900A - Binder for fiberboard, fiberboard and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a binder for fiberboard excellent in fixing property to fiber by synthesizing an ionic poly(meth)acrylamide containing a polyfunctional monomer and/or N-substituent (meth)acrylamides as constituent monomers. SOLUTION: This binder comprises an amphoteric poly(meth)acrylamide obtained by copolymerizing (meth)acrylamide with an ionic vinyl monomer such as an anionic vinyl monomer, e.g. (meth)acrylic acid and a cationic vinyl monomer, e.g. dimethylaminoethyl (meth)acrylate, a polyfunctional monomer such as ethylene glycol di(meth)acrylate and/or N-substituted (meth)acrylamide represented by CH2 =C(R')-CONR<2> (R<3> ) (R<1> is H or methyl; R<2> is H or a 1-4C alkyl; R<3> is a 1-4C alkyl). The binder in an amount of 1-3 wt.% as solid content based on dried weight of fiber is added to water dispersion of fiber substance such as wooden fiber and the mixture is formed to provide the objective fiber board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fiberboard binder, a fiberboard using the fiberboard binder, and a method for producing the same. Examples of the fiber board to which the present invention can be applied include various boards such as an insulation board and a rock wool board. In particular, the present invention is useful when applied to an insulation board.

[0002]

2. Description of the Related Art Conventionally, as a fiberboard, for example,
2. Description of the Related Art An insulation board manufactured by using a plant fiber such as a wood fiber as a main raw material by a wet method is known. Normal,
In producing an insulation board, a binder is used because the strength of the formed board is insufficient because the raw plant fiber has a weak fiber entanglement. Starch or its derivatives are widely used as binders for such insulation boards.
However, the starch-based binder has a low fixing rate to the fiber, so that the drainage load is high, and the drying efficiency in the drying step is low, so that the production efficiency of the insulation board is low.

[0003] In order to solve the problems of such starch-based binders, cationic polyacrylamides have been used. However, cationic polyacrylamide has a poor fixation to fibers, and an insulation board having sufficient strength cannot be obtained. As a method of improving the fixation of the cationic polyacrylamide to the fiber,
It is conceivable to increase the molecular weight. However, in general, when the molecular weight of the cationic polyacrylamide is increased, the viscosity increases and the cohesive strength increases, so that when added to the plant fiber, a strong floc is generated, and the strength of the molded insulation board is rather reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a binder for a fiberboard which has good fixation to a fiber material and can impart excellent strength to a formed fiberboard.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on ionic polyacrylamide conventionally used as a fiberboard binder. As a result, ionic polyacrylamide containing the following specific monomers as constituent monomers,
Even when it is a high molecular weight material, since it has a low viscosity, by using the specific ionic polyacrylamide as a fiberboard binder, it is possible to improve fixation to fibers,
In addition, they have found that a fiberboard having excellent strength can be obtained, and have accomplished the present invention.

That is, the present invention relates to a polyfunctional monomer and / or a compound of the general formula (1): CH ₂ ＣC (R ¹ ) -CO
NR ² (R ³ ) (R ¹ is a hydrogen atom or a methyl group, R ²
Is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a linear or branched alkyl group having 1 to 4 carbon atoms). Fiberboard binder containing ionic poly (meth) acrylamide containing as a constituent monomer; Fiberboard obtained by adding the above fiberboard binder to an aqueous dispersion liquid containing a fiber substance and molding; Fiber substance; The present invention relates to a method for producing a fiberboard, comprising adding the binder for a fiberboard to an aqueous dispersion containing

[0007]

DETAILED DESCRIPTION OF THE INVENTION The ionic poly (meth) acrylamide used in the present invention includes, for example, (a) (meth) acrylamide, (b) an ionic vinyl monomer and (c) a polyfunctional monomer and / or a compound of the general formula (1): CH ₂ ＣC (R ¹ ) -CONR ² (R ³ ) (R
¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a linear or branched alkyl group having 1 to 4 carbon atoms) Obtained by copolymerizing N-substituted (meth) acrylamides.

(A) (meth) acrylamide refers to acrylamide or methacrylamide, which can be used alone or in combination. From the viewpoint of economy, acrylamide is preferably used alone. Hereinafter, in the present invention, (meta) has the same meaning. (A) The amount of (meth) acrylamide used is ionic poly (meth)
With respect to the total molar sum of the monomers constituting acrylamide,
Usually, it is about 58 mol% or more, preferably 70 mol% or more. If the amount of the component (a) is less than 58 mol%, it is difficult to obtain a sufficient strength improving effect as a fiberboard binder.

(B) The ionic vinyl monomer means an anionic vinyl monomer and a cationic vinyl monomer. (B) The ionic vinyl monomer can impart ionicity to poly (meth) acrylamide by using at least one of an anionic vinyl monomer and a cationic vinyl monomer, but is excellent in the effect of improving the strength of the fiberboard. For this reason, it is preferable to use both anionic vinyl monomers and cationic vinyl monomers to impart amphoteric properties to poly (meth) acrylamide.

Examples of the anionic vinyl monomer include monocarboxylic acids such as (meth) acrylic acid, crotonic acid and (meth) allyl carboxylic acid; dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid and muconic acid; vinyl sulfone Acid, styrenesulfonic acid, 2-acrylamide-
Organic sulfonic acids such as 2-methylpropanesulfonic acid and (meth) allylsulfonic acid; and alkali metal salts such as sodium salt and potassium salt of these various organic acids, and ammonium salts. One or two or more of these anionic vinyl monomers can be used without any particular limitation.
Use of a monomer having an allyl group, in particular, (meth) allylsulfonic acid or a salt thereof is preferred in that the obtained ionic polyacrylamide has a high molecular weight. Especially,
It is preferable to combine (meth) acrylic acid and / or itaconic acid with (meth) allylsulfonic acid or a salt thereof.

As the cationic vinyl monomer, for example, vinyl having a tertiary amino group such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, etc. By reacting monomers or their salts of inorganic or organic acids such as hydrochloric acid, sulfuric acid and acetic acid, or the tertiary amino group-containing vinyl monomer with quaternizing agents such as methyl chloride, benzyl chloride, dimethyl sulfate and epichlorohydrin; Examples of the obtained quaternary ammonium salt-containing vinyl monomer include:

(B) The amount of the ionic vinyl monomer (total of the anionic vinyl monomer and the cationic vinyl monomer) to be used is usually 1 to 1 with respect to the total molar amount of the monomers constituting the ionic poly (meth) acrylamide. 40
It is about mol%, preferably 3 to 40 mol%, more preferably 3 to 30 mol%. When using an anionic vinyl monomer and a cationic vinyl monomer as the ionic vinyl monomer, it is preferable to use about 0.5 to 20 mol% of the anionic vinyl monomer and about 0.5 to 20 mol% of the cationic vinyl monomer. preferable.

The means for imparting a cationic group to the ionic poly (meth) acrylamide can be obtained by copolymerizing a cationic vinyl monomer as described above, or by adding formalin to polyacrylamide or anionic polyacrylamide. Cationic groups can also be introduced by Mannich modification in which a secondary amine is reacted, or by Hoffman reaction in which a hypohalite is reacted.

(C) polyfunctional monomers and / or general formula (1): CH ₂ ＣC (R ¹ ) -CONR ² (R ³ )
(R ¹ is a hydrogen atom or a methyl group; R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms;
N-substituted (meth) acrylamides represented by ( ³ is a linear or branched alkyl group having 1 to 4 carbon atoms) give a crosslinked structure or a branched structure to ionic poly (meth) acrylamide, Even when (meth) acrylamide is used as a high molecular weight material, a relatively low viscosity material is used. One of the polyfunctional monomer and the N-substituted (meth) acrylamide represented by the general formula (1) may be used, or both may be used.

The polyfunctional monomer is a compound having at least two functional groups in a molecule and capable of cross-linking ionic polyacrylamide. Specifically, di (meth) acrylates such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, Bis (meth) acrylamides such as hexamethylenebis (meth) acrylamide, divinyl esters such as divinyl adipate and divinyl sebacate, allyl (meth) acrylate, diallylamine, diallyldimethylammonium, diallyl phthalate, diallyl chlorendate, divinyl Bifunctional vinyl monomers such as benzene, N, N-diallylacrylamide, 1,3,5-triacryloylhexahydro-S-triazine, triallyl isocyanurate, tria Triethanolamine, trifunctional vinyl monomers such as triallyl trimellitate, tetra methylol methane tetraacrylate, tetraallyl pyromellitate, N, N,
N ′, N′-tetraallyl-1,4-diaminobutane,
Examples include tetrafunctional vinyl monomers such as tetraallylamine salts and tetraallyloxyethane, and N-methylolacrylamide. Among these polyfunctional monomers, 1,3,5-triacryloylhexahydro-
S-triazine, triallyl isocyanurate and the like are preferred. The amount of the polyfunctional monomer is usually about 0.001 to 2 mol%, preferably 0.01 to 2 mol%, based on the total mol of the monomers constituting the ionic polyacrylamide.
It is 2 mol%, more preferably 0.01 to 1 mol%.

The general formula (1): CH ₂ ＣC (R ¹ )
—CONR ² (R ³ ) (R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a linear or N-substituted (meth) acrylamides represented by a (branched alkyl group) have a methyl or methylene group in the N-alkyl group acting as a chain transfer point, and many ionic poly (meth) acrylamides Introduce a branch structure,
It is a branched polymer without gelation. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms for R2 or R3 in the general formula (1) include a methyl group, an ethyl group, an isopropyl group and a t-butyl group.
-Specific examples of substituted (meth) acrylamides include:
N, N-dimethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N
-Isopropyl (meth) acrylamide and Nt-
Butyl (meth) acrylamide. Among these, N, N-dimethylacrylamide is preferred in terms of copolymerizability and chain transfer. The amount of the N-substituted (meth) acrylamides to be used is usually 0.1 to the total molar sum of the monomers constituting the ionic poly (meth) acrylamide.
It is about 1 to 10 mol%, preferably 0.1 to 5 mol%.

Further, ionic polyacrylamide includes:
In order to impart hydrophobicity, an alkyl ester of the anionic vinyl monomer (having 1 to 8 carbon atoms in the alkyl group),
Nonionic vinyl monomers such as acrylonitrile, styrenes, vinyl acetate and methyl vinyl ether can also be used. When a nonionic vinyl monomer is used, the amount of the nonionic vinyl monomer is usually 30 to the total molar amount of the monomers constituting the ionic poly (meth) acrylamide.
It is about mol% or less, preferably 20 mol% or less.

The synthesis of the ionic poly (meth) acrylamide can be carried out by various conventionally known methods. For example, the desired water-soluble ionic poly (meth) acrylamide can be obtained by charging the various monomers and water in a predetermined reaction vessel, adding a radical polymerization initiator, and heating under stirring. The reaction temperature is usually 50
The reaction time is about 1 to 5 hours. The reaction concentration (monomer concentration) can be usually performed at about 10 to 40% by weight, and polymerization can be performed even at a high concentration. Note that the obtained aqueous solution of ionic poly (meth) acrylamide can be used and stored without dilution even in a high concentration. In addition, the monomer can be charged by various conventionally known methods such as simultaneous polymerization and continuous drop polymerization. As the radical polymerization initiator, potassium persulfate,
Usual radical polymerization initiators such as persulfates such as ammonium persulfate, or redox polymerization initiators in the form of a combination of these with a reducing agent such as sodium bisulfite can be used. Further, an azo-based initiator may be used as the radical polymerization initiator. The amount of the radical polymerization initiator used is about 0.05 to 2.0% by weight, preferably 0.1 to 0.5% by weight of the total weight of the monomers. The Mannich modification, Hoffman reaction, and the like are performed by a known means after producing poly (meth) acrylamide or anionic poly (meth) acrylamide.

The weight-average molecular weight of the ionic poly (meth) acrylamide is 300,000 in consideration of workability and economy.
It is preferable to be about 4,000,000. More preferably, 1
One million to four million. If the weight average molecular weight is less than 300,000, fixation to fibers is insufficient, while if it exceeds 4,000,000, it is not preferable in terms of workability. The viscosity of the ionic poly (meth) acrylamide is preferably about 10,000 cps (25 ° C.) or less in terms of handleability. Incidentally, the papermaking additive of the present invention,
The solid content concentration is adjusted to 10 to 40% by weight. Even when the solid content concentration is 40% by weight, the viscosity is 10,000c.
It can be adjusted to about ps (25 ° C.) or less. Normally, the solid content concentration is preferably set to 30% by weight or less. Such an ionic poly (meth) acrylamide of the present invention has a low viscosity, despite its high molecular weight, and can be used at a high solids concentration.

In the present invention, the ionic poly (meth) acrylamide is used as a binder, and the binder is added to an aqueous dispersion containing a fibrous substance, followed by molding to produce a fiberboard.

For example, when manufacturing an insulation board, plant fibers are usually used as the fibrous substance. Various types of plant fibers such as wood fiber, straw fiber, and wastepaper pulp fiber can be used. Also, a small amount of synthetic fiber can be used in combination with the fiber material in addition to the plant fiber. Mineral fibers such as rock wool and slag wool are used as fiber materials used in boards other than the insulation board.

The amount of the binder relative to the fiber material is usually about 0.1 to 3% by weight, preferably 0.2% by weight or more and 1.5% by weight, based on the dry weight of the fiber. % Or less.

In general, a general method can be employed for producing the fiberboard. For example, when manufacturing an insulation board, it can be performed by a wet method. That is, an insulation board is obtained by preparing a wet sheet from a dispersion liquid containing plant fibers to which a binder has been added and drying the wet sheet. In addition, a sulfuric acid band, a sizing agent, a retention aid, and the like can be added to the dispersion as needed. Further, another binder such as a starch-based binder can be used in combination.

The obtained fiber board such as an insulation board has a certain thickness, but the thickness can be appropriately adjusted according to various uses. In the case of an insulation board, it is appropriate that the thickness is about 8 mm or more.
The fiber board after the drying step may be impregnated with an adhesive, a flame retardant, or the like.

[0025]

The binder for a fiberboard of the present invention has good fixation to fibers and can impart excellent strength to a molded fiberboard. Further, since the binder for the fiberboard of the present invention and the fixation to the fibers are good, the drainage load is small.

[0026]

The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In each example, all parts and percentages are by weight unless otherwise specified.

Example 1 291.4 powdered acrylamide was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube.
Parts (86.8 mol%, based on the total moles of monomers, the same applies hereinafter), 62.5% sulfuric acid 10 parts, dimethylaminoethyl methacrylate 22.3 parts (3 mol%), 80% acrylic acid aqueous solution 42.6 Parts (10 mol%), 2.4 parts (0.2 mol%) of 1,3,5-triacryloylhexahydro-S-triazine and 1300 parts of ion-exchanged water (monomer concentration: 21%), and the mixture was passed through nitrogen gas. Oxygen in the reaction system was removed. The temperature of the system was adjusted to 40 ° C., and 0.49 part of ammonium persulfate and 0.2 part of sodium hydrogen sulfite were added as a polymerization initiator with stirring. After the temperature was raised to 90 ° C., the temperature was kept for 2 hours. After the polymerization is completed, ion-exchanged water 100
Parts (adjusted to a solid content concentration of 20%), pH 4.2,
Solid content 20.1%, viscosity (25 ° C) 9700 cps,
An amphoteric copolymer aqueous solution having a weight average molecular weight of 2.4 million was obtained. The weight average molecular weight was measured by a low angle light scattering method (GPC-LALLS (manufactured by Tosoh Corporation)).
The measurement was performed at a sample concentration of 0.0125% using an aqueous solution containing acetic acid and sodium acetate of H4.2 as a mobile phase (the method for measuring the weight average molecular weight is the same hereinafter).

Example 2 A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet tube was charged with 289 parts of powdered acrylamide (89.1 mol% based on the total mol of monomers, and the same hereinafter). ), 18.0 parts of 78.0% sulfuric acid, dimethylaminopropylacrylamide 42.7. Parts (6 mol%), 80%
16.4 parts (4 mol%) of an aqueous solution of acrylic acid, 2.3 parts (0.5 mol%) of N, N-dimethylacrylamide, 2.9 parts (0.4 mol%) of sodium methallylsulfonate, and ions 1293 parts of exchanged water (monomer concentration 2
1%), and oxygen in the reaction system was removed through nitrogen gas. The temperature of the system was adjusted to 61 ° C., and 0.35 part of ammonium persulfate was added as a polymerization initiator with stirring. After the temperature was raised to 90 ° C., the temperature was kept for 2 hours. After polymerization is completed, ion-exchanged water 1
50 parts (adjusted to a solid content concentration of 20%) were added, and pH4.
2. Solid content 20.1%, viscosity (25 ° C) 6200 cp
s and an amphoteric copolymer aqueous solution having a weight average molecular weight of 3.4 million were obtained.

Example 3 180.9 powdered acrylamide was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube.
Parts (90 mol% based on the total mol of monomers, the same applies hereinafter), 2.7 parts of 62.5% sulfuric acid, 5.3 parts (1.2 mol%) of dimethylaminoethyl methacrylate, and 70% of dimethylamino methacrylate. Benzyl chloride salt 3
2.1 parts (2.8 mol), 80% acrylic acid aqueous solution 1
5.3 parts (6 mol%), allyl methacrylate 0.14
Parts (0.04 mol%), 48% sodium hydroxide 8.5
Parts and 981 parts of ion-exchanged water (monomer concentration 18%)
And oxygen in the reaction system was removed through nitrogen gas.
The system was heated to 50 ° C. and 0.6 parts of ammonium persulfate and 0.25 part of sodium hydrogen sulfite were used as a polymerization initiator with stirring.
And 2.2 parts of isopropyl alcohol. 90
After heating to ℃, 0.7 parts of potassium persulfate was added,
It was kept warm for 3 hours. After completion of the polymerization, 260 parts of ion-exchanged water (adjusted to a solid content of 15%) were added, and the pH was 4.9, the solid content was 15.3%, the viscosity (25 ° C.) was 8600 cps, and the weight average molecular weight was 2.1 million. An aqueous polymer solution was obtained.

Example 4 A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 620 parts of deionized water.
The temperature of the deionized water was maintained at 97 ° C. while removing oxygen in the reaction system through nitrogen gas. Here, 203.3 parts of powdered acrylamide (9
1.3 mol%, the same applies hereinafter), 62.5% sulfuric acid 13.7
Parts, dimethylaminopropylacrylamide 28 parts (6
Mol%), 8.7 parts of itaconic acid (2.2 mol%), N-
A monomer aqueous solution consisting of 1.5 parts (0.5 mol%) of N, dimethylacrylamide and 417 parts of ion-exchanged water, and a 83.4% aqueous solution of 2,2-azobis (2-amidinopropane) hydrochloride 83.4% Was added dropwise over 3 hours. After the polymerization, 343 parts of ion-exchanged water and 6
9.7 parts of 2.5% sulfuric acid (adjusted to a solid content of 15%) was added, and the pH was 3.5, the solid content was 15.3%, and the viscosity was 25 ° C.
Was 4000 cps, and an amphoteric copolymer aqueous solution having a weight average molecular weight of 3,000,000 was obtained.

Example 5 A four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with 582 parts of deionized water.
The temperature of the deionized water was maintained at 97 ° C. while removing oxygen in the reaction system through nitrogen gas. Here, 150.3 parts of powdered acrylamide (9 parts with respect to the total
3.97 mol%, the same applies hereinafter), 62.5% sulfuric acid 7.1
Parts, dimethylaminoethyl methacrylate 14.2 parts (4 mol%), itaconic acid 3.9 parts (1.33 mol%), N—N, dimethylacrylamide 1.56 parts (0.7 mol%), and ion Aqueous monomer solution consisting of 344 parts of exchanged water and 0.66% of ammonium persulfate
69.5 parts of the aqueous solution was added dropwise over 3 hours. After the completion of the polymerization, 46 parts of ion-exchanged water (adjusted to a solid content of 15%) were added, and the pH was 4.8, the solid content was 15.2, and the viscosity was 25 ° C.
Was 8200 cps, and an amphoteric copolymer aqueous solution having a weight average molecular weight of 3,000,000 was obtained.

Comparative Example 1 In a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, 75.8 parts of powdered acrylamide (85 mol% based on the total mol of monomers, hereinafter the same) ), 5 parts of 62.5% sulfuric acid, 19.7 parts (10 mol%) of dimethylaminoethyl methacrylate, 5.6 parts (5 mol%) of an 80% aqueous solution of acrylic acid, and 56 parts of ion-exchanged water.
Five parts were charged, and oxygen in the system was removed through nitrogen gas. The temperature in the system is brought to 50 ° C, and 5%
After adding 2.5 parts of an aqueous ammonium persulfate solution and 1.1 parts of a 5% aqueous sodium bisulfite solution, the mixture
The temperature was raised to 0 ° C. and kept for 3 hours. Thereafter, 333 parts of ion-exchanged water was added, the pH was 4.4, the solid content was 10.0%, the viscosity (25 ° C.) was 6300 cps, and the weight average molecular weight was 11
There were obtained 100,000 amphoteric copolymer aqueous solutions.

Comparative Example 2 Powdered acrylamide 154.6 was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube.
62.5% sulfuric acid 20.7 parts, N, N-dimethylaminopropylacrylamide 41.2 parts (10 mol%), 80% 17.8 parts (7.5 mol%) of an acrylic acid aqueous solution and 1380 parts of ion-exchanged water were charged, and oxygen in the system was removed through nitrogen gas. The system was heated to 50 ° C., and 0.65 parts of a 5% aqueous ammonium persulfate solution and a 5% aqueous sodium hydrogen sulfite solution were added as a polymerization initiator under stirring.
After charging 27 parts, the temperature was raised from room temperature to 80 ° C. and kept for 3 hours. Then, add 1490 parts of ion-exchanged water,
pH 3.3, solid content 7.3%, viscosity (25 ° C) 800
An aqueous amphoteric copolymer aqueous solution having 0 cps and a weight average molecular weight of 1.5 million was obtained.

(Manufacture of fiberboard) Sulfuric acid bands were added to an aqueous dispersion containing wood fibers at a concentration of 2% per fiber solid content by 0.5%.
%, And after adding 0.5% in terms of solid content of any of the copolymer aqueous solutions obtained in Examples 1 to 5 or Comparative Examples 1 to 2, a wet mat having a thickness of 13 to 14 mm was formed according to a wet method. After drying at 150 ° C for 90 minutes, press working and 12 mm thick fiberboard (inflation board)
It was created. The following tests were performed on the obtained fiberboard to evaluate the performance. Table 1 shows the evaluation results. Comparative Example 3
A starch paste solution (concentration: 0.5%) was added at 5% in terms of solid content, and a fiberboard was prepared in the same manner.

Density: Calculated from the following equation. {(Weight per m2) / thickness (mm)} × 1000

Bending strength: This was performed in accordance with JIS A 5905.

Fixing ratio: Determined by (polyacrylamide fixing amount / polyacrylamide addition amount) × 100 (%). The fixing amount of polyacrylamide is determined by measuring the amount of nitrogen contained in the fiberboard with a trace nitrogen analyzer TN-10 (Mitsubishi Chemical Corporation).
Manufactured by the company) and converted from the increase from the board without the addition of polyacrylamide.

COD of white water: Measured according to JIS K0102.

[0039]

[Table 1]

Claims (4)

[Claims] 1. A polyfunctional monomer and / or a general formula (1): CH ₂ ＣC (R ¹ ) -CONR ² (R ³ ) (R
¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a linear or branched alkyl group having 1 to 4 carbon atoms) A ionic poly (meth) acrylamide containing N-substituted (meth) acrylamides as a constituent monomer. 2. The fiberboard binder according to claim 1, wherein the ionic poly (meth) acrylamide is amphoteric poly (meth) acrylamide. 3. A fiberboard obtained by adding the binder for a fiberboard according to claim 1 or 2 to an aqueous dispersion containing a fibrous substance and molding the resultant. 4. A method for producing a fiberboard, comprising: adding the binder for a fiberboard according to claim 1 or 2 to an aqueous dispersion containing a fibrous substance, followed by molding.