CA2065282C - Method for papermaking and additives for papermaking - Google Patents

Abstract

An additive for papermaking comprising a cationic acrylamide polymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions at 50 - 110°C for a short time and an anionic inorganic substance or a cationic polyacrylamide (s) produced by co-polymerizing (a) a cationic monomer (acrylic acid ester derivative or acrylamide derivative), (b) an ?,.beta. -unsatu-rated carboxylic acid or salts thereof and (c) an acryl-amide, and papermaking using such additive.

Description

- l- 2~282 DESCRIPTION
METHOD FOR PAPERMAE;ING AND ADDITIVES
FOR PAPERMAE~ING

Technical Field The present invention relates to a method for paper-making, and more particularly to, a method for papermak-ing comprising using both a cationic acrylamide polymer obtained by Hofmann decomposition reaction at an elevated temperature for a short time and an anionic inorganic sub-stance or a cationic polyacrylamide produced by copoly-meri:~ation, and an additive for papermaking comprising a cationic acrylamide polymel- produced by Hofmann decomposi-tion reaction and an anioni c inorganic substance or a cationic polyacrylamide prepared by copolymeri~ation.
Background Art Since it has recently become difficult to obtain raw materials for paper, the amount ratio of old papers in pulp raw materials has increased. As a result, there are de-manded paper strength imprc~vers capable of imparting higher paper strength. On the ot~Ler hand, in practical operations there are demanded chemicals capable of improving freeness due to requirement of imcreasing the pulp dehydration speed and chemicals capable of intproving drying- property to meet requirement of decreasing t he amount of steam to be used.
A Hofmann decomposition reaction product of polyacryl-amide (hereinafter referred to as "Hofmann PAM") is a ca-tionic resin having a primary amino group directly bonded to the polymer main chain, and has been conventionally used as a freeness improver and a paper strength improver in a step of papermaking.
A f eature of Hofmann ]?AM resides in the high aggrega-tion power, and it not onl~ improves freeness, but also improves the strength between flbers due to the hydrogen bond of the prlmary amino group which is also a cationic group .
However, when the Hofmann PAM is used alone, sometimes 5 an ef f ective f ixation to pulp f ibers can not be attained depending on the papermaking conditions and the feature of the Hofmann PAM can not be fully exhibited.
In such a case, problem of freeness can be solved by increasing the amount of Hofmann PAM to be added, but on 10 the other hand, the formation of paper is deteriorated.
Therefore, satisfactory results are not always obtained as to paper strength and printing characteristics.
Disclosure of Invention In view of the above-mentioned points r the present in-ventors have investigated various additives capable of ex-hibiting a desirable effect when used together with Hofmann PAM, and as a result, have found that when an anionic in-20 organic substance or a cationic acrylamide polymer producedby copolymerization is used together therewith, freeness can be controlled without lowering paper strength charac-teristics, and the present invention has been completed.
That is, the present invention is concerned with a 25 method for papermaking which comprises adding to a pulp slurry a cationic acrylamide polymer produced by reacting an acrylamide polymer with a hypohalogenite at 50 - 11 O~C
for a short time at an alkaline region and an anionic in-organic substance or a cationic polyacrylamide produced by 30 the copolymerization of (a) a cationic monomer of the generai~formula (I) C = o R2 - (I) ( C ) N /

where R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, n is an integer of 2 - 4, and/o]^ organic or inorganic acid salts thereDf, or quaternary ammonium salts produced by the reac-5 tion of the compound of the formula (I) with a quaterniz-ing agent, (b) an D( ,~ -unsaturated carboxylic acid and/or salts thereof, and 10 (c) an acrylamide monomer of the general formula (II), CHz C (R5) CONH2 ~II) where R5 is hydrogen or methyl , and an additive for paperma]{ing comprising a cationic acryl-amide polymer produced by reacting an acrylamide polymer with a hypohalognite at an alkaline region at 50 - 11 0C
20 for a short time and an anionic inorganic su]~stance or ~
a cationic polyacrylamide produced by the copolymerization of (a) a cationic monomer of the general formula (I) C = O R2 (I) X - (CH2)]1 - N

where~ R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, n is an integer of 2 - 4, and/o:r organic or inorganic acid salts 3 5 thereof, or quaternary ammonium salts produced by the reac-tion of the compound of the formula (I) with a quaterniz-ing agent, ~ 206~2~2 (b) an ~, ~ -unsaturated carboxylic acid and/or salts thereof, and (c) an acrylamide monomer of the general formula (II), CH2 = C (Rs) - CONH2 (II) where R5 is hydrogen or methyl.
In the following, the present invention is .-Ypl;~n 10 in detail.
~ he acrylamide polymers used in the present invention include homopolymers of acrylamides ( or methacrylamides ), copolymers of acrylamides (or methacrylamides) and at least one unsaturated monomer capable of copolymerizing there-15 with, and further graft copolymers of the acrylamides (ormethacrylamides) with water-soluble polymers such as starch and the like.
As the copolymerizable monomers, there may be mentioned hydrophilic monomers, ionic monomers, lipophilic monomers 20 and the like, and at least one monomer may be used.
Concretely the hydrophilic monomers are, for example, diacetone acrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, 25 N-ethylmethacrylamide, N-ethylacrylamide, N,N-diethylacrylamide, N-propylacrylamide, N-acryloylpyrrolidine, 30 N-acryloylpiperidine, N-acryloylmorphorine, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydL~cy~ yl methacrylate, 35 hydro,cy~L"~yl acrylate, various methoxypolyethylene glycol (meth) acrylates, N-vinyl-2-pyrrolidone, ~ 2~6!~282 and the like.
As ionic monomers, there may be mentioned, for ex-ample, 5 acids such as acrylic acid, methacrylic acid, vinylsulfonic acid, allylsulfonic acid, 10 methallylsulfonic aicd, styren~ sulfonic acid, 2-acrylamido-2-phenylpropane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and the like, and salts thereof, 1 5 and amines such as N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, 20 N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl acrylamide, and the like, and salts thereof.
As lipophilic monomers, there may be mentioned, for example, 25 N-alkyl (meth)acrylamide derivatives such as N,N-di-n-propyl acrylamide, N-n-butyl acrylamide, N-n-hexyl acrylamide, N-n-hexyl methacrylamide, 30 N-n-octyl acrylamide, N-n-octyl methacrylamide, N-tert-octyl acrylamide, N-dodecyl acrylamide, N-n-dodecyl methacrylamide, 35 and the like, N-(~J-glycidoxyalkyl) (meth)acrylamide derivatives such as N,N-diglycidyl acrylamide, -- 6 _ 20~52~2 N,N-diglycidyl methacry~ amide, N- ( 4-glycidoxybutyl ) ac~ ylamide, N- ( 4-glycidoxybutyl ) methacrylamide, N- ( 5 -glycidoxypentyl ) acrylamide, N- ( 6-glycidoxyhexyl ) ac} ylamide, and the like, (meth)acrylate derivatives such as methyl ( meth ? acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, lauryl (meth) acrylate, 2-ethylhexyl (meth)acrylate, glycidyl ( meth ) acrylate and the like, acrylonitrile, methacrylonitrile r vinyl acetate, vinylidene chloride, olefins such as ethylene, propylene, butene and the like, 2 0 s tyrene, divinyl benzene, ~, -methylstyrene, butadi ene, i soprene, and the like.
The amount of the unsaturated monomer used for copoly-merization varies depending on the types of unsaturated monomers and combination thereof, but is usually O - 50 5 by weight.
As water-fioluble polymers to be used for graft copoly-merization with the above-mentioned monomers, there may be used both natural ones a]ld synthetic ones.
As natural water-soluble polymers, there may be used starches of different orLgin and modified starches such as oxidized starch, carboxy:L starch, dialdehyde starch, cation-modified starch and the like, cellulose derivatives such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, - 7 - 2Q6~2~2 hydroxyethylcellulose and the like, alginic acid, agar, pectin, carrageenan, dextran, pururan, arum root, Arabia rubber, caseln and gelatin.
As synthetic water-soluble polymers, there may be 5 mentioned polyvinyl alcohol, polyvinyl ether, polyvinyl pyrrolidone, polyethylene imine, polyethylene imine, poly-ethylene glycol, polypropylene glycol, polymaleic acid copolymer, polyacrylic acid, polyacrylamides and the like.
The amount of the monomer to be added to the above-mentioned water-soluble polymer is 0 .1 - 10 . 0 times the weight of the water-soluble polymer Then the above-mentioned monomers are polymerized to prepare polyacrylamide. As the methods for polymerization, free-radical polymerization is preferable, and as the poly-merization solvent, polar solvents such as water, alcohols, dimethylformamide and the like are usable, but since Hof-mann decomposition reaction is carried out in an aqueous solution. It is preferable to effect the polymerization in an aqueous solution.
The concentration of monomers is such a case as above is 2 - 30 % by weight, preferably 5 - 30 % by weight.
As the polymerization initiator, there is not any limitation as far as it is water-soluble. The polymeriza-tion initiator is usually dissolved in an aqueous solution of monomers and used.
Concretely, as peroxide initiators, there may be men-tioned, for example, ammonium persulfate, potassium per-sulfate, hydrogen peroxide, tert-butyl peroxide and the like .
In such a case, the peroxide can be used alone, but may be slso used as a redox polymerization agent by com-bining with a reducing agent.
As the reducing agent, there may be used, for example, sulfites, hydrogen sulfi tes, salts of low order ionization metals such as iron, copE)er, cobalt and the like, organic amines such as N,N,N' ,N' -tetramethyl ethylenediamine and -- 8 _ 20~i282 the like, and reducing sugars such as aldose, ketose and the like.
As azo compounds, there may be used 2,2'-azobis-2-amidinoprapane hydrochloride, 2, 2 ' -azobis-2, 4- dimethyl-5 valeronitrile, 4, 4 ' -azobis-4-cyanovaleric acid, salts thereof and the like.
Further, two or more of the above-mentioned polymeri-zation initiator may be used in combination.
When graft polymerization is effected to a water sol-10 uble polymer, other than the above-mentioned polymeriza-tion initiator, there may be also used transition metal ions such as ceric ion, ferric ion and the like, and fur-ther, such ions may be used in combination with the above-mentioned polymerization initiators.
The amount of the initiator to be added may be 0.01 -10 9i by weight based on the weight of monomers, preferably O . 02 - 8 9~ by weight . In the case of a redox initiator, the amount of the reducing agent to be added may be 0.1 100 %, preferably 0.2 - 80 % based on the initiator in terms of mole.
The polymerization temperature is as low as 30 to 90C
in the case of a single polymerization initiator, and much lower such as about -5 to 50C in the case of a redox poly-merization initiator.
In addition, it is not necessary to keep the tempera-ture at a constant temperature, and the temperature may be changed accordingly as the polymerization proceeds. In general, as the polymerization proceeds, the temperature rises due to the generated polymerization heat.
The atomosphere in the polymerization vessel at that time is not particularly limited, but it is desirable to replace the atmosphere with an inert gas such as nitrogen gas for the purpose of accelerating the polymerization.
The polymerization time is not critical, but is usually 1 20 hours.
Then, the polyacrylamide produced by the above-mention-ed method is subj ected to Hofmann decomposition reaction .

206S2~2 ' . g When the polyacrylamide as a starting material is prepared in an aqueous solution, it can be directly used or, if necessary, it is dilute~ and then used for the reaction.
In the case of graft copolymerization, there is pro-duced polyacrylamide not grafted as a by-product, but the product is directly used for the reaction without removing the non-graf ted one .
Hofmann decomposition reaction is effected by acting a hypohalogenite on the amido group of polyacrylamide in the presence of an ~lk~lin~ substance.
As a hypohalogenous acid, there may be mentioned hy-pochlorous acid, hypobromous acid, and hypoiodous acid.
As a hypohalogenite, there may be used metal or al-kaline earth metal salts. Concretely, they may be sodium hypochlorite, potassium hydrochlorite, lithium hypochlo-rite, calcium hypochlorite, magnesium hypochlorite, barium hypochlorite and the like. Similarly, there may be men-tioned alkali metal or alkaline earth metal hypobromite and hypoiodite in case of hypobromite and hypoiodite.
It is also possible to produce hypohalogenite by blow-ing a halogen gas into an alkaline solution.
On the other hand, as alkaline substances, there may be mentioned alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate and the like.
Among them, alkali metal hydroxides are preferable, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide and the like are mentioned.
The amount of the above-mentioned substance to be added to polyacrylamides is 0.05 - 2.0 mol, preferably 0.1 - 1 . 5 mol per amido group in the case of hypohalogenous acid, 0.05 - 4.0 mol, preferably 0.1 - 3.0 mol per amido group in the case of alkaline substance. The pH in such a case is usually 11 - 14.
The concentration of polyacrylamide in such a case is usually 0.1 - 17.5 % by weight, but preferably 0.1 - 10 9 by weight since a high reaction concentration results in 20~5282 difficult agitation or causes gelation.
Further, when the reactlon concentration is less than 1 %, the reaction speed becomes so slow that it is more preperable that the reaction concentration is 1 - 10 % by 5 weight. The reaction temperature may be S0 - 11 0C, prefer-ably 60 - 1 00C. The Hofmann decomposition reaction is carried out at the above-mentioned temperature range within a short time. The reaction time varies depending on reac-tion temperature and polymer concentration in the reaction 10 solution, and therefore, the reaction time can not be de-finitely mentioned, but, for example, when the polymer con-centration is 1 % by weight, it is within ten and several minutes at 50C and within several minutes at 65C and suf-ficiently within several tens sec. at 80C. Further, when 15 the polymer concentration is high, the reaction time can be shorter .
The relation between the reaction time and the reaction temperature may be generally within the range defined by the following two formulas, and when the reaction is carried out within such range, a good result can be obtained, 15,150 t (sec) ~ e 273+T x 2.5 x 10-2 (1) 15,15C
t (sec) ~e 273+T x 10-18 + 30 (2) T: Reaction temperature ( C) 50 ~ T ~ 110 Cationic polyacrylamides produced under the above-mentioned conditions have a cation eqivalent determined by colloid titration at pH 2 of about 0 - 10 . 0 meq/g, and said cation equivalent can be controlled by the amount of 35 hypohalogenite added.

20~5282 Since the reaction ls carried out in an alkaline region, the amino group is hydrolyzed to produce carboxyl group as a by-product. The amount of the by- production is about 0 - 10 . 0 meq/g in terms of anion equivalent meas-5 ured by colloid titration at pH 10. The amount of by-production can be controlled by ad~usting the amount o~ the alkaline substance added.
After effecting the reaction under the above-mentioned conditions, it is preperable to stop the reaction so as to 10 suppress the proceeding of a side-reaction. Howeverr when the product is used immediately after the reaction, some-times it is not necessary to stop the reaction.
The procedure of stopping the reaction may be (1 ) add-ing a reducing agent, (2) cooling, (3) lowering the pH of 15 the solution by adding an acid, or the like. These pro-cedur~es may be used alone or in combination. (1 ) is a method for deactivating the remaining hypohalogenite and the like by the reaction with a reducing agent.
In general, when the Hofmann decomposition reaction 20 has completed, there still remain compounds having active chlorine such as unreacted hypohalogenites and the like.
When such a reaction solution is used as a paper strength agent, it causes rust on paper-making machines, and there-fore, usually the active chlorine is deactivated by using 25 a reducing agent.
However, when a hyl?ohalogenite is reacted in an amount of equivalent mol. or less based on mol. of acrylamide unit of the polymer and at a high temperature, after com-pletion of the reaction, unreacted hypohalogenite hardly 3 0 remains .
Therefore, the product can be used as a paper strength agent without deactivating active chlorine by using a re-ducing agent.
( 2 ) is concerned with a method for suppressing the pro-3 5 ceeding of reaction . As a procedure thereof, there may becooling with heat exchar~ger, diluting with cold water and the like.

- 12 - 20~282 The temperature is usually 50C or less, preferably 45C
or less,more preferably 40C or less.
According to ( 3 ), Hofmann decomposition reaction is stopped by lowering the pH of the solution after completion 5 of the reaction which is usually alkaline such as pH 12 -13 by using an acid and the progress of hydrolysis reaction is simultaneously suppressed.
At that point, it is necessary only that the pH is neutral or less, preferably 4 - 6.
A reaction stopping method may be appropriately se-lected from (1 ) - (3) depending on the reaction conditions, and the methods may be ~sed in combination.
Anionic inorganic ~ubstances which can be used together with Hofmann decomposition PAM produced by the above-men-tioned method may be sodium silicate, anionic particule-like inorganic substances and mixtures thereof.
Sodium silicate ca l be produced by melting silicon dioxide with sodium car]~onate or sodium hydroxide at an el-evated temperature, and commercially available water glass also may be used. The structure is shown by the following general f ormula:
NaO nSiO2 xH2O
where n is 1 - 4. The examples are sodium metasilicate, sodium orthosilicate, No. 1, No. 2 and No. 3 water glasses and the like.
The form to be used may be such that flake or powder thereof or the like is dissolved in water, or commercially 3 0 available aqueous solution products also may be used .
As an anionic partlcle-like inorganic substance, it is necessary only that it ls not soluble in water and is anionically charged in ~ater, and various materials can be used .
Concretely, the examples may be silicon dioxide, alu-minum oxide, antimony o~ide, titanium oxide, and oxides ~ 2065282 .

such as clay minerals, ~or example, alminosilicates such as montmorillonite, bentonite, kaolin, activated clay, silica sand, diatomaceous earth and the like, magnesia-silicates such as talc, and further carbonates such as 5 calcium carbonate and the like.
When the size of the above-mentioned particles is too large, the composite effect becomes small. The particle size is usually 100 ym or less, preferably 50 ym or less, more preferably 10 ym or less.
The ratio of anionic inorganic s~bstance to Hofmann decomposition PAM when both are added may be such that the amount of anionic inorganic substance is 1 - 500 % by weight, preferably 2 _ 400~ 96 by weight, more preferably 3 -300 Y6 by weight based on Hofmann decomposition PAM. When 15 the ratio is too small, the effect due to the combined use is not obtained while when it is too large, the function of Hofmann decomposition PAM is deteriorated.
The Hofmann decomposition rate is not particularly critical, but usually 5 - 60 mol 96, preferably 10 - 50 mol 20 96.
A practical procedure for adding anionic inorganic substances in combination with Hofmann decomposition PAM
is such that Hofmann dec~mposition PAM used in the present invention is produced by the reaction at a high temperature 25 for a short time and the product can be directly used, and since the resulting reaction fluid is strongly alkaline, the combined addition may be effected by any procedure.
Concretely, (i) upo]n effecting Hofmann decomposition reaction, the anionic inorganic substance is added to and 30 dissolved in soaium hydroxide, sodium hypochlorite or mix-ture solutions thereof ill advance and the mixture is used for Hofmann decompositioll reaction.
( ii ) After Hoffmann decornposition reaction, the anionic inorganic substance is added to the reaction fluid.
35 (iii) Both are added separately.

~ 14 ~ - 20~282 The amount of Hofmann decomposition PAM and anionic inorganic substance added to pulp is usually 0.005 - 5.0 %, preferably 0.01 - 2.0 % based on the dry weight of pulp.
In such a case, the ratio of Hofmann decomposition PAM
to anionic inorganic substance varies depending on paper-making conditions. Concretely, for example, when it is in-tended to increase freeness so as to accelerate the paper-making speed, the ratio of anionic inorganic substance is rendered small while when it is intended to control the formation and make uniform paper, the ratio of anionic in-organic substance is increased.
According to the process o~ the present invention, sometimes the effect is further enhanced when aluminum sulfate or water-soluble anionic resins is used in combi-1 s nation .
The water-soluble anionic resins used here may be water-soluble resins having an anionic substituent such as carboxyl group, sulfonic acid group, phosphoric aicd group and the like, or salts thereof.
Examples of said resins are:
anionic acrylamide resins, anionic polyvinyl alcohol resins, carboxymethylcellulose, carboxymethylated starch, sodium alginate, and the like.
The point when the addition is effected is not criti-cal, that is, the addition may be effected before or after Hofmann decomposition PA~ and sodium silicate are added to a pulp slurry, or simult~neously. Further, the addition may be effected to each ~f Hofmann decomposition PAM and sodium silicate or to a mixture solution thereof.
The place where the addition is effected may be any-where as far as it is before forming a wet sheet.
It is preferable to add to a place where chemicals can be sufficiently mixed with and diluted with the pulp slurry and which is near the papermaking wire part, for _ 15 - 2~2~2 example, machine chest, Inixing box, seed box, white water pit, outlet of screen an,~ the like.
As a papermaking machine, there may be used either Fourdrinier paper machine or cylinder paper machine.
After the present a~ditive for papermaking is added to a pulp slurry having a concentration of 0.5 - 5.0 96, a pH 4.0 - 9.0 at a temperature of 20 - 70C, a wet sheet is formed at a wire part an,~ then water is squeezed at a press part. The nip pressure at the press part ranges from 20 to 400 kg/cm. After passing the press part, the wet sheet is transferred to a dry part and dried with steam.
The steam pressure is 2 - 15 kg¦cm2 and the drying is carried out in a drum at 80 - 200C. After this process, chemical treatments may be effected at a size press or calender so as to improve printing property, surface strength, water resistance, and water repellency.
The additive for papermaking in the present invention comprising a Hofmann decomposition PAM and an anionic in-organic substance as ef f ective components . The concentra-tion of the effective co!nponents may be 0.001 - 50 %.
The amount ratio of anionic inorganic substance to Hofmann decomposition PA~ may be 1 - 500 % by weight, pref-erably 2 - 400 %, more preferably 3 - 300 %. When the mixing ratio is too low, the mixing effect due to the mix-ing is not obtained while when the ratio is too high, the property of the Hofmann PAM is deteriorated. The Hofmann decomposition rate here is not particularly critical, but usually 5 - 60 mol 96, preferably 10 - 50 mol %.
As a procedure for mixing a Hofmann decomposition PAM
and an anionic inorganic substance, (i) upon carrying out Hofmann decomposition reaction, they may be added to or dissolved in sodium hydroxide, sodium hypochlorite or a mixture solution thereof in advance and the resulting mix-ture is used for the Hoflnann decomposition reaction.
(ii) After Hofmann decoml?osition reaction, they may be mixed with the resulting reaction fluid.

2~6~282 The solution after the Hofmann decomposition reaetion is usually of pH 12 - 13, but the pH may be lowered wtih an inorganic or organic acid before it is mixed with an anionic inorganie substance, and further, it is possible 5 to lower the pH after mixing with an anionie inorganie substanee. The additive for papermaking of the present invention may have pH 2 - 14.
Aceording to the present invention, the eationic monomers of the general formula (I) as above are, for ex-10 ample, (meth)acrylic acid ester derivatives represented bydimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate, and (meth)acrylamide derivatives represent-ed by dimetkylaminopropyl (meth)acrylamide and diethyl-ami nopropyl ( meth ) acrylamide .
The organie or inor~anic acid salts may be salts of inorganie aeids such as sulfuric acid, hydrochloric acid, phosphorie aeid and the Like, or salts of organie aeids such as acetic acid, forrnic acid ana the like.
As quaternary ammonium salts obtained by the reaction of the compound of the general formula ( I ) above with a quaternizing agent, there may be mentioned, for example, vinyl monomers having a quaternary ammonium salt produced by the reaetion of a vin}~l monomer having a tertiary amino group with a quat,~rn~71ng agent such as methyl chloride, methyl bromide, methyl ic~dide, dimethyl sulfuric acid, epichlorohydrin, benzyl chlorlde and the like, Aeeording to the present invention, a vinyl monomer having a tertiary amino sroup, or organie or inorganic salts thereof may be usecd in combination with a quaternary ammonium salts obtained k~y the reaction with a quaternizing agent. The mixing ratio of these components is not crit-i eal .
The amount of the eationie monomer is usually 0 . 5 - 70 mol %, preferably 2 - 50 mol 96.
The ~, f3 -unsaturated earboxylie aeids or salts there-of, for example, alkali metal salts or ammonium salt there-of are vinyl monomers having anionieity, for example, un-_ 17_ 20~282 saturated carboxylic acids such as maleic acid, fumaric acid, itaconlc acid, 5 (meth) acrylic acid, crotonic acid, citraconic acid, and the like, and alkali metal salts thereof such as sodium salts, potas-sium salts and the like, and ammonium salts thereof.
The amount of the monomer may be 0 . 5 - 20 mol 96, pref-erably 2 - 20 mol 96.
The monomer represented by the general formula (II) of the present invention may be acrylamide and methacrylamide, and commercially available such monomers in the form of powder or an aqueous solution may be sufficiently used.
The amount of the monomer used may be 10 - 9 0 mol % .
According to the present invention, as a fourth com-ponent other than (a) - (c), there may be used a crosslink-ing monomer (d).
The crosslinking mol~omer may be a monomer having at least two double bonds i]l the molecule and an N-alkoxy-methyl (meth)acrylamide derivative.
Concretely, examples of the former include methylene bisacrylamide, diallyl acrylamide, tri acryl f ormal, diacryloylimide, ethylene glycol acrylate, ethylene giycol dimethacrylate, propylene glycol diacrylate 1 ,3-butylene glycol dimethacrylate, 1 ,4-butylene glycol methacrylate, glycerol dimethacrylate, neopentyl glycol dimethacrylate, , trimethylol propane triacrylate, - 18 - 20652~2 divinylbenzene, diallyl phthalate, and the like.
The N-alkoxymethyl ( meth ) acrylamide derivatives in-5 clude N-hydroxymethyl (meth)acrylamide, for example, N-methylol (meth)acrylam.ide, N-methoxymethyl (meth)acrylamide, N-ethoxymethyl (meth)acrylamide, N-n-butoxymethyl (metha)acrylamide, 10 N-tert-butoxymethyl (meth)acrylamide, and the like.
The amount of the crosslinking agent varies depending on the type of crosslinking monomer, but is usually 0.0001 - 20 mol %~ preferably 0.001 - 10 mol %.
When the amount is less than 0.0001 mol %~ the paper strength effect can not be sufficiently exhibited. On the contrary, when the amount exceeds 20 mol %, gelation is liable to occur.
As methods for obtaining the cationic polyacrylamide (B) of the present invention, there may be used conventional methods for polymerizing such type of water-soluble vinyl monomers .
For example, fr~e-radical polymerization is preferable.
The concentration of the monomer may be 2 - 30 % by weight, preferably 5 - 30 96 by weight.
The polymerization initiator is not particularly criti-cal as far as it is water-soluble, and is usually used by dissolving it in an aqueous solution of the monomer.
Examples of polymerization initiators are peroxides such as hydrogen peroxide, benzoyl peroxide and the like;
persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate and the like, bromates such as sodium bromate, potassium bromate and the like, perborates such as sodium perborate, potassium perborate, ammonium perborate, and the like;
percarbonates such as sodium percarbonate, potassium per-carbonate, ammonium percarbonate and the like;

~ 19 ~ 2~6~282 perphosphates such as sodium perphosphate, potassium per-phosphate, ammonium perphosphate, and the like;
tert-butyl peroxide and the like.
The above-mentioned initiators may be used alone or in combination with a reducing agent as a redox type poly-merization agent.
As the reducing agent, there may be mentioned, for example, sulfites, hydrogensulfites, salts of iron, copper, cobalt and the like of a low order ionization, organic amines such as N,N,N',N'-tetramethyl ethylenediamine and the like, and reducing sugars such as aldose and ketose.
As azo compounds, there may be used 2,2'-azobis-4-amidinopropane hydrochloride, 2,2'-azobis-2,4-dimethyl-valeronitrile, 4,4'-azobis-4-cyanovaleric acid, salts thereof and the like.
Further, two or more of the above-mentioned polymeri-zation initiator may be used in combination.
The polymerization temperature is as low as 30 to 90C
in the case of a single polymerization initiator, and much lower such as about 5 to 50C in the case of a redox poly-merization initiator.
In addition, it is not necessary to keep the tempera-ture at a constant temperaturer and the temperature may be changed accordingly as the polymerization proceeds. ~n general, as the polymerization proceeds, the temperature rises due to the generated polymerization heat.
The atmosphere in the polymerization vessel at that time is not particularly limited, but it is desirable to replace the atmosphere with an inert gas such as nitrogen gas for the purpose of accelerating the polymerization.
The polymerization time is not- critical, but is usually 1 - 20 hours.
The method of the present invention is used for making paper from pulp, and is effective to improve remarkably freeness for draining water upon papermaking and improve paper strength serving to enhance the mer~hAn; ~ strength f of paper.

~ 206~282 The amount ratio of Elofmann decomposition PAM and cationic polyacrylamide (B) is optional depending on pulp raw material and white ~ater. However, from the stand-point of mixing effect, it may range ~rom 95: 5 to 5: 95, preferably from 80 :20 ~:o 20 :80.
The cationic polyacrylamide may be added to pulp in such a monner that Hofmclnn decomposition PAM and cationic polyacrylamide (B) are separately added to pulp slurry, or Hofmann decomposition PAM and cationic polyacrylamide (B) are firstly mixed and t~len added to pulp slurry. Either may be used.
In combination of Hofmann decomposition PAM and ca-tionic polyacrylamide (~), sometimes the effect is further enhanced when aluminum culfate or water-soluble anionic resins is used in combination.
The water-soluble anionic resins used here may be water-soluble resins ha~ing an anionic substituent such as carboxyl group, sulfonic acid group, phosphoric acid group and the like, or salts thereof.
Examples of said resins are:
anionic acrylamide resins, anionic polyvinyl alcohol resins, carboxymethylcellulose, carboxymethylated starch, sodium alginate, and the like.
The point where the agents are to be added is not particularly critical. The agents may be added before or after or simultaneously with adding Hofmann decomposition PAM and cationic polyacrylamide~ (B) to pulp slurry.
Further, the agents may be mixed separately with each of Hofmann decomposition PAM and cationic polyacrylamide (B), or may be mixed with a mixture solution of Hofmann decom-position PAM and cationic polyacrylamide (B).
The place where the addition is effected may be any-where as far as it is before forming a wet sheet.
It is preferable to add to a place where chemicals can be sufficiently mixe~ with and diluted With the pulp slurry and which is near the papermaking wire part, for .

206~282 ~- 21 -example, machine chest, mixing box, seed box, white water pit, outlet of screen arld the like.
As a papermaking machine, there may be used either ~ourdrinier paper machirle or cylinder paper machine.
After the present additive for papermaking is added to a pulp slurry having a concentration of 0 . 5 - 5 . 0 9~i, p~ 4.0 - g.o at a tempel~ature of 20 - 70C, a wet sheet is formed at a wire part and then water is squeezed at a press part. The nip pressure at the press part ranges from 20 to 400 kg/cm. After passing the press part, the wet sheet is transferred to a dry part and dried with steam.
The steam pressure is 2 - 15 kg/cm2 and the drying is carried out in a drum at 80 - 200C.
After this process, chemical treatments may be effected at a si2e press or calerlder so as to improve printing pro-perty, surface strength~ water resistance, and water re-pellency .
The additives for papermaking according to the present invention may be in the form of a water-soluble liquid mixture comprising Hofmann decomposition PAM and cationic polyacrylamide (B) as active components. The concentration of the active components may range from 0.001 to 50 %.
The amount ratio of Hofmann decomposition PAM to cationic polyacrylamide (s) may range, in terms of weight, from 95: 5 to 5: 95, E~referably from 80: 20 to 20: 80.
When the mixing ratio is too small, the effect due to using in combination is not obtained. On the contrary, when the mixing ratio is too large, the function of the Hofmann decomposition PP~M is deteriorated. ~lere~ the de-composition rate of Hof~lann decomposition is not partic-ularly critical, but is usually 5 - 60 mol 96, preferably 10 - 50 mol %.
A method for mixing Hofmann decomposition PAM and cationic polyacrylamide (B) may be as shown below. ~Che solution after Hofmann decomposition reaction is usually of pH 12 - 13, but the pH may be lowered with an inorganic _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . . . . . . .

~ - 22 - 2~5282 or organic acid before or after mixing with cationic poly-acrylamide ( B ) .
The additives for ]~apermaking according to the present invention may range from 2 to 14.
When paper is manufactured by the above-mentioned meth-od, freeness can be improved without deteriorating paper strength such as rupture strength, internal bond strength, compression strength an(~ the like.
Therefore, when the method of the present invention is used for manufacturillg paper products where the content of waste paper in the raw materials is high, such as cor-rugated board, newspape~^ and the like, very good results are obtained and paper of high strength can be produced.
Other than corrugal ed board and newspaper, when the present invention is ap~lied to manufacturing of high strength paper or the case where excellent freeness is re-quired at a papermaking step, there can be produced papers of high strength in a good productivity.

- 23 - 20~282 Best Mode fnr Carrying Out the Invention The present invention is explained referring to the following examples, but is not restricted by the examples.
5 The ll%ll in the following is ~O by weight" unless otherwise specif ied .

24 . 0 g of a 10 wt . % aqueous polyacrylamide solution (Brookfield viscosity at 25C: 3,400 cps) was placed in a 500 ml beaker, diluted with 36.0 g of distilled water, and heated to 80C with stirring, and to the resulting solution was added 14 . 8 g of a mixture solution of sodium hypochlo-rite and NaOH ( concentration of sodium hypochlorite : 1 . 0 mol/kg; concentration oE NaOH: 2.0 mol/kg). The reaction was stopped 15 sec. after the addition of the above-mention-ed mixture solution, and there was obtained a 1 wt. % acryl-amide polymer (Hofmann PAM (A~ ) .
A part of the reaction product was added to an aqueous solution of pH 2 and a colloid titration by means of a 1/
400 N aqueous solution of potassium polyvinyl sulfonate using toluidine blue as indicator. The resulting cationi-city was 4 . 4 meq. /g .
In the following tests the Hofmann PAM ~A) was used immediately af ter the preparation .

24 . 0 g of a 12 . 5 wt. % aqueous polyacrylamide solution (Brookfield viscosity at 25C: 12,400 cp) was placed in a 500 ml beaker, diluted ~ith 36.0 g of distilled water, and to the resulting solution was added with stirring at 20C
14 . 8 g of a mixture sol~ltion of sodium hypochlorite and NaOH (concentration of ~30dium hypochlorite: 1.0 mol/kg;
concentration of NaOH: 2.0 mol/kg). Two hours later, 225.2 g of a 0.001 % aqueous solution of sodium sulfite was added thereto to stop t~le reaction and a 1 wt. % acrylamide ~,, . 20652~2 polymer (hereinafter called "Hofmann PAM (B) ") .
A part of the reaction product was added to an aqueous solution of pH 2 and a colloid titration was carried out using a 1/400 N aqueous solution of potassium polyvinyl 5 sulfonate with toluidine blue as indicator and the cation-city was 4 . 4 meq. /g .

To a pulp slurry ( concentration of 1 . 0 % ) having 0 t'AnAA~ i~ln Standard Freeness (hereinafter called "CSF" ) of 450 ml and 1.0% concentration obtained from waste paper of cor-rugated board was added a commercially available rosin emul-sion sizing agent in an amount of 0.15% based on the dry weight of pulp followed by stirring for two minutes.
Then, aluminum sulfate was added thereto in an amount of 1 . 0 % based on the dry weight and then stirring was ef-fected for one minute. The pH of the resulting pulp slurry was 5.1.
Then, No. 3 water glass was added thereto in an amount of 0.30 % based on the dry weight of pulp, and stirring was effected for one minute. Hofmann PAM (A) obtained in Prep-aration Example 1 was added in an amount of 0 . 60 % based on the dry weight of pulp, and stirring was continued for fur-ther one minute.
Part of the resulting pulp slurry was taken to meas-ure CSF according to JIS-P-8121 r and the remainder was used to make paper in a TAPPI square sheet machine, and then the resulting paper was dried for two hours at 11 O'C by a hot air blowing dryer to obtain a hand-made paper with a basis weight of 150 i 3 g/m2 To evaluate the resulting hand-made paper, its "spe-cific compression strength" was measured according to JIS-P-8126, its "specific rupture strength" according to JIS-P-8112 and its "internal bond strength" by a Kumagaya Riki 35 Internal Bond Tester. Table 1 shows the result.

The procedure of Example 1 was repeated to effect the hand-making paper test except that No. 3 water glass was added in an amount of 0 . 60 ~6 based on the dry weight.
Table 1 shows the result.

The procedure of Example 1 was repeated to effect the hand-maklng paper test except that No. 3 water glass was added in an amount of 0.90 % based on the dry weight.
Table 1 shows the result.

The procedure of Example 1 was repeated to effect the hand-making paper test except that No. 3 water glass was added in an amount of 1 . 50 % based on the dry weight. Table 1 shows the result.

The procedure of Example 1 was repeated to effect the hand-making paper test except that No. 3 water glass was added in an amount of 0.003 % based on the dry weight.
Table 1 shows the resul t .

The procedure of Example 1 was repeated to efiect the hand-making paper test except that No. 3 water glass was added in an amount of 5 . 00 96 based on the dry weight. Table 1 shows the result.
COMPARISON EXAMPLES 3 a]1d 4 The procedures of Comparison Examples 2 and 4 were re-peated respectively except that Hofmann PAM (B) was used in place of Hofmann PAM (A) used in Comparison Examples 1 and 35 2. Table 1 shows the results.

EXAMPLE 5 ~
To a pulp slurry o~- Canadian Standard Freeness (hereinafter called "CS~") of 543 ml and 1.0 % concentra-tion obtained from waste paper of corrugated board was added aluminum sulfate in an amount of 0.5 % based on the dry weight of pulp, and stirring was effected for a ~urther minute. The p~ of the F)ulp slurry was 5 . 8 .
Then, colloidal silica (Snowtex 40, particle size 10 - 20 nm, manufactured by Nissan Kagaku K.K. ) was added thereto in an amount of 0 . 25 % based on the dry weight of pulp followed by stirring for 30 sec, and Hofmann PAM (A) obtained in Preparation Example 1 was added thereto in an amount of 1.50 % based on the dry weight of pulp. The stirring was continued for further 30 sec.
A part of the resulting pulp slurry was taken to measure CSF according to JIS-P-8121, and the remainder was used to make paper in a TAPPI square sheet machine. The product was then dried b ~ a hot air blowing dryer at 110 C
for two hours to produce a hand-made paper with a basis weight of 150 + 3 g/m2.
To evaluate the resulting hand-made paper, the spe-cific compression strength was measured according to JIS-P-8126, the specific rupt:ure strength according to JIS-P-8112, and the internal bond strength by a Kumagaya Riki Internal Bond Tester. Table 2 shows the result.

The procedure of Example 5 was repeated to effect the hand-making paper test except that colloidal silica was added in an amount of 0.50 % based on the dry weight.
Table 2 shows the result.

The procedure o~ Exal~ple 5 was repeated to effect the hand-making paper test except that colloidal silica was added in an amount of 1.00 ~6 based on the dry weight.
Table 2 shows the result.
. . _ . . . , _ _ _ 27 --2~652~2 The procedure of Example 5 was repeated to effect the hand-making paper test e~ccept that colloidal silica was added in an amount of 0.001 % based on the dry weight.
Table 2 shows the result.

The procedure of Example 5 was repeated to effect the hand-making paper test e~ccept that colloidal silica was added in an amount of 10 0 % based on the dry weight.
Table 2 shows the result.

In a four-necked flask equipped with stirrer, reflux condenser, thermometer, and n~ trogen inlet pipe were placed 675 g (94 mol %) of 40 % acrylamide, 23.1 % (4 mol %) of dimethylaminoethyl methacrylater 5.8 g (2 mol %) of acrylic acid, 62.3 mg (0.01 mol ~) of bismethylene acrylamide and 1 .004 g of waterr and the pH of the resulting mixture was adjusted to 4.5 with a 10 % aqueous solution of sulfuric acid. Then the inner temperature was raised to 40C while blowing nitrogen gas thereinto. A 10% aqueous solution of ammonium persulfate and a 10% aqueous solution of sodium hy-drogen sulfite were added to the above-mentioned mixture with stirring and polymerization was initiated.
Then, the reaction ~nixture was kept at 85C, and three hours after the beginnin~ of the polymerization, water was added to stop the polymerization reaction and there was obtained a stable aqueous solution of acrylamide polymer having 15.3 % of non-volcltile matter, Brookfield viscosity of 6,800 cps at 25C and pEI 4.3.

30 . 0 g of a 10 wt . % aqueous solution of polyacrylamide (Brookfield viscosity at 25C: 3,400 cp) was placed in a 500 ml beaker, diluted with distilled water, heated to 80C
with stirring, and then 14.3 g of a mixture solution of - 28 _ 2~652~2 sodium hypochlorite and NaOH (concentration of sodium hypochlorite: 1.0 mol/ky; concentration of NaOH: 2.0 mol/kg) was added to the resulting solution and 15 sec.
later, 225.7 g of cold water at 5C was added to stop the 5 reaction. As a result, a 1 wt. % acrylamide polymer (Hofmann PAM (C) ) was obtained.
A part of the reaction product was added to an aqueous solution of pH 2 and a colloia titration was then carried out using a 1/400 N aqueous solution of potassium poly-10 vinyl sulfonate with toluidine blue as indicator and thecationicity was 3 . 8 meq. /g.
In the following test, Hofmann PAM (C) was used im-mediately after the preparation.

To a pulp slurry of '~n~ n Standard Freeness (here-inafter called "CSF") of 400 ml and 1.0 % concentration obtained from waste paper of corrugated board was added a commercially available rosin emulsion sizing agent in 20 an amount of 0.15 % based of the dry weight of pulp fol-lowed by stirring for two minutes.
Then, aluminum sulf~te was added to the resulting mixture in an amount of l . 0 % based on the dry weight of pulp and stirring was effected for a further minute. At 25 this time, the pH of the pulp slurry was 5.1.
Further, the acryla~ide polymer obtained in Prepara-tion Example 3 was added to the resulting mixture as above in an amount of 0.30 % based on the dry weight of pu~lp.
Stirring was effected for one minute and then Hofmann PAM
30 (C) obtained in Preparation Example 4 was added thereto in an amount of 0.10 96 based on the dry weight of pulp.
The stirring was corltinued for a further one minute and then a part of the resulting pulp slurry was taken to measure CSF according to ,JIS-P-8121, and the remainder was 35 used to make paper in a TAPPI square sheet machine. The resulting product was dri ed by a hot air blowing dryer at - 29 _ 2~6~2~2 11 0C for 2 hours to obtain a hand-make paper with a basis weight of 125 + 3 g/m2.
To evaluate the hand-made paper, the specific com-pression strength was measured according to JIS-P-81 26r the specific rupture strength according to JIS-P-8112 and the i~ternal bond strength by a Kumagaya Riki Internal Bond Tester. Table 3 shows the result.

The procedure of Example 8 was repeated to effect the hand-making paper test except that the polyacrylamide poly-mer obtained in Preparation Example 3 was added in an amount of 0.20 ~ based ~n the dry weight and Hofmann PAM
(C) obtained in Preparation Example ~ was added in an amount of 0.20 % based on the ary weight. Table 3 shows the result .

The procedure of E~cample 8 was repeated to effect the hand-making paper test except that the polyacrylamide poly-mer=obtained in Prepara~ion Example 3 was added in an amount of 0.10 % based on the dry weight and Hofmann PAM
(C) obtained in Preparation Example 4 was added in an amount of 0.30 % based on the dry weight. Table 3 shows the result.

The procedure of E~cample 8 was repeated to effect the test except that the acrylamide polymer obtained in Prepa-ration Example 3 was added in an amount of 0.40 96 based on the dry weight and Hofmann PAM (C) obtained in Preparation Example 4 was not added, Table 3 shows the result.

The procedure of Example 8 was repeated to effect the test except that Hofmann PAM (C) obtained in Preparation _ 30 _ 2~52~2 Example 4 was added in an amount of 0 . 40 % based on the dry weight and the acrylamide polymer obtained in Prepa-ration Example 3 was not added. Table 3 shows the result.
As shown in Tables 1 - 2, papers manufactured ac-5 cording to the conditions of the present invention exhibitrather a tendency of improved paper strength by the addi-tion of anionic inorganic s~bstances though addition of anionic lnorganic substances usually changes the freeness.
It appears that when a proper amount of an anionic 10 inorganic substance is 1?resent, the aggregation force of Hofmann PAM is lowered to an appropriate level so that the formation is controlled and the paper strength character-istics such as specific rupture strength, specific com-pression strength, inte~-nal bond strength and the like 5 become excellent.
This effect is remarkable when the ~ofmann decomposi-tion reaction was carried out in a temperature range of 50C - 11 0C for a short time. The mechanism is not yet clarified, but it is clear that the paper strength effect 20 of PAM obtained by the l~ofmann decomposition reaction car-ried out at a high temperature for a short time can be en-hanced by using an anionic inorganic substance.
Therefore, when it is contemplated that the formation is controlled and a paper of excellent strength is made 25 even if the freeness is adversely affected to some extent, the present-invention exhibits a great effect.
In addition, as shown in Table 3, papers made under the conditions within th e scope of the present invention can exhibit excellent characteristics such as specific 30 rupture strength, specific compression strength, internal bond strength and the like as compared with the case where an acrylamide polymer obtained in Preparation Example 3 or 4 is used alone while the papers made according to the present invention retains the same level of freeness as 35 that in the case where the acrylamide polymer obtained in Preparation Example 4 is used alone.
.

- 31 - . 20~282 ~ _ Ln ~ , 0 ,~ N N N N N N
N ~ I~ U~
I~ 0 0 0 ~` 1 N ~ ~_ a); ~.0 0 0 0 ~D 1`
~ - N N 1'7 0 N N
0 0 cr~ ~ u7 1--Ln N O ~D ~ Ln - ~ U) DO~ Ln ~D Ln o o o ~ O ~
E~ L i~ ~3 ,D --' ,~ :
æ~ O O O
~ ~ U~ U~
Ln ~n Ln Ln ~ ~
U ~~ ~ ~ N N
I~ o o o o o o æ r ~ 00 0 0 N N
~ N1~1 ~ - ~ - N

~- 32 - 206~282 TABL:~ - 2 P~ate of addition Freeness Specific Specii~ic Internal (%/pipe) rupture cc~npression ~ond ~ofrnann C~lloidal strength strength strength PAM silica ~ (kg/cm) Ecample 5 : 1.50 0.25 603 2.78 21.8 2.40 EXample 6 1.50 0.50 606 2.83 2f.7 2.51 E~ample 7 1.5b 1.00 592 3.03 22.3 2.26 Ccmparison ~mple 3 1.50 - 550 2.48 ~ 20.1 2.09 'r~r~ q~n Example 4 - 10.0 542 2.07 18.2 1.23 ~ 33 ~ 206~282 TABL~ - 3 Rate of Addition Freeness Specific Sp cific Internal (96/pipe) rupture ~nrF~qC~nn ~ond Copolymeri- Hofmarn strength strength strength zation PAM ~A~5 (C) (ml) (kg/cm) Example 8 0.30 0.10 645 2.72 14.5 2.99 Example 9 0.20 0.20 645 2.70 14.4 3.07 E~cample 10 0.10 0.30 648 2.69 14.0 3.15 Cnparison Example 5 0.40 - 469 2.47 12.6 1.92 t' ' snn Example 6 - 0.40 650 2.48 13.0 2.78 Industrial Applicability The paper produced by the method of the present in-vention exhibits excellent specific rupture strength, spe-cific compression strength, internal bond strength and the l ike .
~ ddition of the anionic inorganic substance is suit-able for controlling the formation and producing a paper of high strength even if the freeness is somewhat adversely affected. When the cationic polyacrylamide is added, the level of freeness attained by using an acrylamide polymer .
alone can be retained, the formation is not lowered despite of good fre~eness which usually indicates lowering thereof, and the paper strength characteristic is excellent as com-pared with that when the acrylamide polymer is used alone.

Claims (8)

1. A method for papermaking which comprises adding to a pulp slurry both an anionic inorganic substance and a cationic acrylamide polymer produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions at 50 - 110°C for a short time, and then form-ing a wet pulp sheet followed by dehydration with a press and drying with a drier.

2. A method for papermaking which comprises adding to a pulp slurry both an anionic inorganic substance and a cationic acrylamide polymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions of at least about pH 11 at a reaction tempera-ture T (°C): 50°C ? T ? 110°C for a short reaction time t (sec) as shown in the following formulas, t (sec) ? e x 2.5 x 10-20 t (sec) ? e x 10-18 + 30 and then forming a wet pulp sheet followed by dehydration with a press and drying with a dryer.

3. An additive for papermaking which comprises an anionic inorganic substance and a cationic acrylamide pol-ymer produced by reacting an acrylamide polymer with a hy-pohalogenite under alkaline conditions at 50 - 110°C for a short time.

4. An additive for papermaking which comprises an anionic inorganic substance and a cationic acrylamide pol-ymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions of at least about pH 11 at a reaction temperature T (CC): 50°C ? T
? 110°C for a short reaction time t (sec) as shown in the following formulas, t (sec) ? e x 2.5 x 10-20 t (sec) ? e x 10-18 + 30

5. A method for papermaking which comprises adding to a pulp slurry both a cationic acrylamide polymer (A) produced by, reacting an acrylamide polymer with a hypo-halogenite under alkaline conditions at 50 - 110°C for a short time and a cationic polyacrylamide (B) produced by copolymerizing (a) a cationic monomer of the general formula (I), (I) where R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, and n is an integer of 2 - 4, and/or organic or inorganic acid salts thereof, or quaternary ammonium salts produced by the reac-tion of the compound of the general formula (I) with a quaternizing agent, (b) an ?, .beta.-unsaturated carboxylic acid and/or salts thereof, and (c) an acrylamide monomer of the general formula (II) CH2 = C (R5) - CONH2 (II) where R5 is hydrogen or methyl, and then forming a wet pulp sheet followed by dehydration with a press and drying with a dryer.

6. A method for papermaking which comprises adding to a pulp slurry both a cationic acrylamide polymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions of at least about pH 11 at a reaction tempera-ture T (°C): 50°C ? T ? 110°C for a short reaction time t (sec) as shown in the following formulas, t (sec) ? e x 2.5 x 10-20 t (sec) ? e x 10-18 +30 and a cationic polyacrylamide (s) produced by copolymerizing (a) a cationic monomer of the general formula (I), (I) where R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, and n is an integer of 2 - 4, and/or organic or inorganic acid salts thereof, or quaternary ammonium salts produced by the reac-tion of the compound of the general formula (I) with a quaternizing agent, (b) an ? , .beta.-unsaturated carboxylic acid and/or salts thereof, and (c) an acrylamide monomer of the general formula (II) CH2 = C (R5) - CONH2 (II) where R5 is hydrogen or methyl, and then forming a wet pulp sheet followed by dehydration with a press and drying with a dryer.

7. An additive for papermaking which comprises a cationic acrylamide polymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions at 50 - 110°C for a short time and a cationic polyacrylamide (B) produced by copolymerizing (a) a cationic monomer of the general formula (I), (I) where R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, and n is an integer of 2 - 4, and/or organic or inorganic acid salts thereof, or quaternary ammonium salts produced by the reac-tion of the compound of the general formula (I) with a quaternizing agent, (b) an ? , .beta.-unsaturated carboxylic acid and/or salts thereof, and (c) an acrylamide monomer of the general formula (II) CH2 = C (R5) - CONH2 (II) where R5 is hydrogen or methyl.

8. An additive for papermaking which comprises a cationic acrylamide polymer (A) produced by reacting an acrylamide polymer with a hypohalogenite under alkaline conditions of at least about pH 11 at a reaction tempera-ture T (°C): 50°C ? T ? 110°C for a short reaction time t (sec) as shown in the following formulas, t (sec) ? e x 2.5 x 10-20 t (sec) ? e x 10-18 + 30 and a cationic polyacrylamide (B) produced by copolymerizing (a) a cationic monomer of the general formula (I), (I) where R1 is hydrogen or methyl, R2 and R3 are hydrogen or alkyl having 1 - 6 carbon atoms, X is O or NH, and n is an integer of 2 - 4, and/or organic or inorganic acid salts thereof, or quaternary ammonium salts produced by the reac-tion of the compound of the general formula (I) with a quaternizing agent, (b) an ?, .beta. -unsaturated carboxylic acid and/or salts thereof, and .

(c) an acrylamide monomer of the general formula (II) CH2 = C (R5) - CONH2 (II) where R5 is hydrogen or methyl.