DE69109639T2 - METHOD FOR PRODUCING PAPER AND ADDITION TO IT. - Google Patents

Description

Technical area

The present invention relates to a process for producing paper, in particular to a process for producing paper using both a cationic acrylamide polymer obtained by Hofmann decomposition reaction at elevated temperature for a short period of time and an anionic inorganic substance or a cationic polyacrylamide prepared by copolymerization, and a papermaking additive containing or consisting of a cationic acrylamide polymer obtained by Hofmann decomposition reaction and an anionic inorganic substance or a cationic polyacrylamide prepared by copolymerization.

Description of the state of the art

Since the procurement of raw materials for paper has recently become difficult, the proportion of waste paper in the raw material pulp has increased. As a result, agents for improving the strength of the paper are needed. On the other hand, in practical application, chemicals for improving the dewatering tendency are needed to increase the dewatering speed of the pulp, as well as chemicals for improving the drying property to meet the requirement for reducing steam consumption.

A polyacrylamide obtained by Hofmann decomposition reaction (hereinafter referred to as Hofmann PAA) is a cationic resin having a primary amino group directly bonded to the polymer main chain, which is commonly used as a drainage improver and paper strength agent in a stage of papermaking.

A characteristic of Hofmann's polyacrylamide is its high aggregation power, and it not only improves drainage, but also the strength between the fibers through the hydrogen bonding of the primary amino group, which is also a cationic group.

However, when Hofmann's PAA is used alone, sometimes depending on the conditions of papermaking, effective fixation to the fibers of the pulp cannot be achieved, so that the feature of Hofmann's polyacrylamide cannot be fully utilized.

In this case, the drainage problem can be solved by increasing the addition of Hofmann PAA, but on the other hand, paper formation is impaired. In terms of paper strength and printing properties, therefore, satisfactory results are not always achieved.

From JP-A-62-015391 and JP-A-60-065195 it is known how the yield of fillers in paper production is increased by adding Hofmann PAA in combination with additives to the pulp.

Disclosure of the invention

In view of the above points, the present inventors have studied various additives which have the desired effect when used together with Hofmann's PAA. They have found that by using an anionic inorganic substance or a cationic acrylamide polymer prepared by copolymerization, drainage can be controlled without restricting the paper strength. The present invention is the result.

The present invention thus relates to a process for papermaking in which a pulp the following substances may be added:

a cationic acrylamide polymer prepared by reacting an acrylamide polymer with a hypohalite for a short time at 50 - 110ºC under alkaline conditions, and an anionic, inorganic substance or a cationic polyacrylamide prepared by copolymerization

(a) a cationic monomer of the general formula

wherein 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 from 2 to 4 and/or organic or inorganic acid salts thereof or quaternary ammonium salts prepared by reacting the compound of formula (I) with a quaternizing agent,

(b) an α, β-unsaturated carboxylic acid and/or its salts and

(c) an acrylamide monomer of the general formula (II),

CH2=C(R5)-CONH2 (II)

where R5 is hydrogen or methyl, and

a papermaking additive containing or consisting of a cationic acrylamide polymer obtained by reacting an acrylamide polymer with a hypohalite was produced over a short period of time at 50 - 110ºC in the alkaline range, and

an anionic, inorganic substance or a cationic polyacrylamide, prepared by copolymerization

(a) a cationic monomer of the general formula

wherein 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 from 2 to 4 and/or organic or inorganic acid salts thereof or quaternary ammonium salts prepared by reacting the compound of formula (I) with a quaternizing agent,

(b) an α, β-unsaturated carboxylic acid and/or its salts

and

(c) an acrylamide monomer of the general formula (II),

CH2=C(R5)-CONH2 (II)

wherein R�5 is hydrogen or methyl.

The present invention is explained in more detail below.

The acrylamide polymers used in the present invention include homopolymers of acrylamides < or methacrylamides), copolymers of acrylamides (or methacrylamides) and at least one unsaturated monomer copolymerizable therewith, and also graft copolymers of acrylamides (or methacrylamides) with water-soluble polymers, e.g. starch and the like.

Copolymerizable monomers include hydrophilic monomers, ionic monomers, lipophilic monomers and the like, of which at least one may be used.

In detail, the hydrophilic monomers are e.g.

Diacetoneacrylamide,

N,N-dimethylacrylamide,

N,N-dimethylmethacrylamide,

N-ethylmethacrylamide,

N-ethylacrylamide,

N,N-diethylacrylamide,

N-propylacrylamide,

N-acryloylpyrrolidine,

N-acryloylpiperidine,

N-acryloylmorpholine,

Hydroxyethyl methacrylate,

Hydroxyethyl acrylate,

Hydroxypropyl methacrylate,

Hydroxypropyl acrylate,

various methoxypolyethylene glycol (meth)acrylates

N-vinyl-2-pyrrolidone

and similar.

Ionic monomers are e.g.

Acids such as

Acrylic acid,

Methacrylic acid,

Vinylsulfonic acid,

Allylsulfonic acid,

Methallylsulfonic acid,

Styrenesulfonic acid,

2-Acrylamido-2-phenylpropanesulfonic acid,

2-Acrylamido-2-methylpropanesulfonic acid

and similar and their salts

and

Amines like

N,N-dimethylaminoethyl methacrylate,

N,N-diethylaminoethyl methacrylate,

N,N-dimethylaminoethyl acrylate,

N,N-dimethylaminopropylmethacrylamide,

N,N-dimethylaminopropylacrylamide

and similar and their salts.

Lipophilic monomers are e.g.

N-alkyl(meth)acrylamide derivatives such as

N,N-di-n-propylacrylamide,

N-n-butylacrylamide,

N-n-hexylacrylamide,

N-n-hexylmethacrylamide,

N-n-octylacrylamide,

N-n-octylmethacrylamide,

N-tert-octylacrylamide,

N-dodecylacrylamide

N-n-dodecylmethacrylamide

and similar,

N-(ω-glycidoxyalkyl)(meth)acrylamide derivatives such as pN,N-diglycidylacrylamide,

N,N-diglycidylmethacrylamide,

N-(4-glycidoxybutyl)acrylamide,

N-(4-glycidoxybutyl)methacrylamide,

N-(5-glycidoxypentyl)acrylamide,

N-(6-glycidoxyhexyl)acrylamide,

and similar,

(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 similar,

Acrylonitrile,

Methacrylonitrile,

Vinyl acetate,

Vinylidene chloride,

Olefins such as ethylene, propylene, butene and similar,

Styrene,

Divinylbenzene,

α-methylstyrene,

Butadiene,

Isoprene

and similar.

The amount of unsaturated monomer used for copolymerization depends on the type and combination of unsaturated monomers, but is usually 0 - 50 wt%.

The water-soluble polymers to be used for graft copolymerization with the above-mentioned monomers can be natural or synthetic.

Suitable natural, water-soluble polymers include, for example, starches of various origins and modified starches such as oxidized starch, carboxylated starch, dialdehyde starch, cation-modified starch and the like, cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose and the like, alginic acid, agar, pectin, carrageenan, dextran, puran, aronia root, gum arabic (gum arabic), casein and gelatin.

Synthetic, water-soluble polymers include polyvinyl alcohol, polyvinyl ether, polyvinylpyrrolidone, polyethyleneimine, polyethylene glycol, polypropylene glycol, Polymaleic acid copolymer, polyacrylic acid, polyacrylamides and the like.

This monomer is added to the above-mentioned water-soluble polymer in an amount of 0.1 to 10 times the weight of the water-soluble polymer.

The above-mentioned monomers are then polymerized to produce polyacrylamide. The preferred polymerization process is radical polymerization. Polar solvents, e.g. water, alcohols, dimethylformamide and the like, can be used as solvents for the polymerization. However, since the Hofmann decomposition reaction takes place in aqueous solution, the polymerization is preferably carried out in aqueous solution.

In a case such as the above, the monomer concentration is 2 - 30 wt%, preferably 5 - 30 wt%.

Any initiator is suitable for polymerization, provided it is water-soluble. Normally it is dissolved in an aqueous solution of monomers before use.

Specifically, ammonium persulfate, potassium persulfate, hydrogen peroxide, tert-butyl peroxide and the like can be used as peroxide initiators.

In this case, the peroxide can be used alone or as a redox polymerization agent by combining it with a reducing agent.

Reducing agents that can be used include sulphites, bisulfites, salts of weakly ionised metals such as iron, copper, cobalt and similar, organic amines such as N,N,N',N'-tetramethylethylenediamine and similar. as reducing sugars e.g. aldose, ketose and similar.

As azo compounds, 2,2'-azobis-2-amidinopropane hydrochloride, 2,2'-azo-bis-2,4-dimethylvaleronitrile, 4,4'-azobis-4-cyanovaleric acid, their salts and the like can be used.

In addition, two or more of the above polymerization initiators can be used together.

When graft polymerization is carried out on a water-soluble polymer other than the above-mentioned polymerization initiator, transition metal ions such as cerium (IV) ion, ferric ion, and the like can also be used, and furthermore, these ions are usable in combination with the above-mentioned polymerization initiators.

0.01 to 10% by weight of initiator, based on the weight of the monomers, can be added, preferably 0.02 to 8% by weight. When using a redox initiator, the reducing agent can be added in amounts of 0.1 - 100%, preferably 0.2 - 80%, based on molar proportions of initiator.

The polymerization temperature when using a single polymerization initiator is only 30 - 90ºC and is even lower when using a redox polymerization initiator, namely approximately -5 to 50 ºC.

In addition, the temperature does not have to be kept constant. Rather, it can be adapted to the course of the polymerization. In general, the temperature rises during the polymerization due to the heat of polymerization released.

Any atmosphere is suitable in the polymerization vessel at this time, but to accelerate polymerization it is better to replace the atmosphere with an inert gas, such as nitrogen. There is no time specified for polymerization. It usually takes 1 to 20 hours.

The polyacrylamide prepared by the above-mentioned process is then subjected to the Hofmann decomposition reaction.

If the polyacrylamide feedstock is prepared in aqueous solution, it can be used directly, or it can be diluted if necessary and then used for the reaction.

In the case of graft copolymerization, an ungrafted polyacrylamide is produced as a by-product, but the product is used directly for the reaction without removing the ungrafted product.

The Hofmann decomposition reaction is carried out by allowing the hypohalite to act on the amido group of the polyacrylamide in the presence of an alkaline substance.

Examples of hypohalous acids are hypochlorous acid, hypobromic acid and hypoiodic acid.

Hypohalites are, for example, metal or alkaline earth metal salts. Specifically, sodium hypochlorite, potassium hydrochlorite, lithium hypochlorite, calcium hypochlorite, magnesium hypochlorite, barium hypochlorite and the like can be used. Similarly, alkali metal or alkaline earth metal hypobromite and hypoiodite can also be used in the case of hypobromite and hypoiodite.

Hypohalite can also be formed by bubbling a halogen gas into an alkaline solution.

Alkaline substances that can be used include, for example, alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate and similar.

Preferred are alkali metal hydroxides, e.g. sodium hydroxide, potassium hydroxide, lithium hydroxide and the like.

When using a hypohalous acid, 0.05 to 2.0 moles, preferably 0.1 to 1.5 moles of the above-mentioned substance are added to the polyacrylamides per amido group. When using alkaline substances, 0.05 to 4.0 moles, preferably 0.1 to 3.0 moles, are added per amido group. The pH value in this case is usually 11-14.

The polyacrylamide concentration in such cases is usually 0.1-17.5 wt%, preferably 0.1 to 10 wt%, since a high concentration during the reaction makes stirring more difficult or the product gels.

If the concentration during the reaction is less than 1%, the reaction becomes slow, so that a concentration of 1 to 10% by weight is preferred. The reaction temperature may be 50 to 110°C, preferably 60 to 100°C. The Hofmann decomposition reaction is carried out for a short time in the above-mentioned temperature range. The reaction time may vary depending on the reaction temperature and the polymer concentration of the reaction solution. The reaction time cannot therefore be specified exactly. However, if the polymer concentration is, for example, 1% by weight, the reaction time is 10 minutes or less at 50°C, several minutes at 65°C and several tenths of a second at 80°C. If the polymer concentration is high, the reaction time may be shorter.

The relationship between reaction time and reaction temperature can be generally expressed by the following two equations. If the reaction takes place within these limits, a good result can be obtained.

T: reaction temperature (ºC)

50&le;T&le;110

The number of cation equivalents of the cationic polyacrylamides produced under the above conditions is approximately 0-10.0 meq/g (determined by colloid titration at a pH of 2). The number of cation equivalents can be regulated by controlled addition of the amount of hypohalite.

Since the reaction takes place in the alkaline range, the amino group is hydrolyzed, resulting in a carboxyl group as a byproduct. Approximately 0 to 10.0 meq/g of byproduct are obtained as anion equivalent (determined by colloid titration at a pH of 10). The amount of byproduct can be regulated by adjusting the amount of alkaline substance added.

After carrying out the reaction under the above conditions, it is preferable to stop the reaction to suppress side reactions. However, if the product is used immediately after the reaction, the reaction may not need to be stopped in some cases.

The reaction can be stopped by

(1) Addition of a reducing agent

(2) Cooling or

(3) Lowering the pH of the solution by adding an acid or something similar.

These methods can be used individually or in combination. In method (1), the remaining hypohalite and the like are deactivated by reaction with the reducing agent.

In general, after completion of the Hofmann decomposition reaction, compounds containing active chlorine, e.g. unreacted hypohalites and the like, remain as residue. If such a reaction solution is used as a paper strengthening agent, this leads to rust on the paper machines, so active chlorine is normally deactivated by a reducing agent.

However, if a hypohalite is reacted with the same amount molar equivalents or less, based on the acrylamide unit of the polymer, and at high temperature, practically no unreacted hypohalite remains after completion of the reaction.

The product can therefore be used as a paper strengthening agent without deactivation of active chlorine by a reducing agent.

With method (2) the continuation of the reaction is suppressed, e.g. by cooling with a heat exchanger, dilution with cold water and similar methods.

The temperature is normally 50ºC or below, preferably 45ºC or less, more preferably 40ºC or less.

In method (3), the Hofmann decomposition reaction is stopped by lowering the pH value of the solution, which is normally alkaline (pH12-13), after the reaction has been terminated by an acid. At the same time, the hydrolysis reaction is suppressed.

At this point the pH only needs to be neutral or below neutral, preferably 4-6.

Depending on the reaction conditions, any of the methods (1) to (3) can be chosen to terminate the reaction. The methods can also be used in combination.

Anionic, inorganic substances that can be used together with Hofmann decomposition polyacrylamide prepared by the process described above are sodium silicate, anionic, inorganic substances in particle form and mixtures thereof.

Sodium silicate can be prepared by melting silicon dioxide with sodium carbonate or sodium hydroxide at elevated temperature. Commercially available sodium silicate solution can also be used. The following general formula shows the structure:

NaO nSiO₂ xH₂O

where n is 1-4. Examples include sodium metasilicate, sodium orthosilicate, water glass No. 1, No. 2 and No. 3 and the like.

They can be used in the form of flakes or powder or similar, dissolved in water, or as aqueous solutions, as are commercially available.

For anionic, inorganic substances in particle form, it is important that they are insoluble in water and be anionically charged in water. Various materials can be used.

In detail, for example, silicon dioxide, aluminum oxide, antimony oxide, titanium oxide and oxides such as clay minerals, e.g. aluminum silicates such as montmorillonite, bentonite, kaolin, activated clay, quartz sand, diatomaceous earth and similar, magnesia silicates such as talc, but also carbonates such as calcium carbonate and similar can be used.

If the above particles are too large, the bonding effect is reduced. The particles usually have a size of 100 µm or less, preferably 50 µm or less, particularly preferably 10 µm or less.

The ratio of anionic, inorganic substance to Hofmann's decomposition polyacrylamide, when both are added, can be 1 to 500 wt. %, preferably 2 to 400 wt. %, particularly preferably 3 to 300 wt. % of anionic, inorganic substance, based on Hofmann's decomposition polyacrylamide. If the ratio is too small, the effect achievable by the combined use is not achieved, while if the ratio is too large, the function of Hofmann's decomposition polyacrylamide is impaired.

The Hofmann decomposition rate is not fixed. It is normally between 5 and 60 mol %, preferably 10 to 50 mol %.

In practice, the anionic inorganic substances combined with Hofmann's decomposition polyacrylamide can be added so that the Hofmann's decomposition polyacrylamide used according to the present invention is prepared by reaction for a short time at high temperature and can be used directly, and due to the high alkalinity of the obtained Reaction liquid the joint addition can be carried out by one of the following methods.

Specifically, the procedure can be selected as follows:

(i) In the Hofmann decomposition reaction, the anionic inorganic substance is previously added to and dissolved in sodium hydroxide, sodium hypochlorite or mixed solutions thereof, and the mixture is used for the Hofmann decomposition reaction.

(ii) The anionic inorganic substance is added to the reaction liquid after the Hofmann decomposition reaction.

(iii) Both are added separately.

Normally, the Hofmann decomposition polyacrylamide and the anionic inorganic substance are added to the pulp in an amount of 0.005 to 5.0%, preferably 0.01 to 2.0%, based on the dry weight of the pulp.

In this case, the ratio of Hofmann decomposition polyacrylamide to anionic, inorganic substance depends on the conditions of paper production. If, for example, the tendency to dewater is to be increased in order to speed up paper production, the proportion of anionic, inorganic substance is kept low. However, if paper formation is to be regulated and a uniform paper is to be produced, the proportion of anionic, inorganic substance is increased.

According to the process of the invention, the effect is sometimes further increased when aluminum sulfate or water-soluble anionic resins are used in combination.

The water-soluble anionic resins used here may be water-soluble resins having an anionic substituent, e.g. a carboxyl, sulfonic acid, phosphoric acid and similar group or their salts.

Examples of such resins are:

anionic acrylamide resins,

anionic polyvinyl alcohol resins,

carboxymethyl cellulose,

carboxymethylated starch,

Sodium alginate

and similar.

The time of addition is not specifically prescribed. The addition can be made before, after or at the same time as the addition of Hofmann decomposition polyacrylamide and sodium silicate to the pulp. It can also be made to the Hofmann decomposition polyacrylamide and sodium silicate or a solution mixture thereof.

The addition can be made at any point, but before the wet web is formed.

A location is preferred where the chemicals can be well mixed and diluted with the pulp and which is close to the wire section of the paper machine, e.g. machine chest, mixing box, knot catcher, white water pit, wire drain and similar.

Either a fourdrinier machine or a cylinder machine can be used as a paper machine.

After adding the additive for paper production according to the invention to the pulp (concentration 0.5 to 5.0%, pH value 4.0 to 9.0 at a temperature of 20 to 70ºC), a wet web is formed in the wire section and the water is pressed out in the press section. The nip pressure in the press section ranges from 20 to 400 kg/cm. After passing through the press section, the wet web is transported to the drying section and dried with steam.

The steam pressure is 2-15 kg/cm² and drying is carried out at 80-200ºC in a roller. Subsequently, chemical treatments can be carried out in the size press or in the polishing machine to improve the printing properties, surface strength, water resistance and water-repellent properties.

The additive according to the invention for paper production has a Hofmann decomposition polyacrylamide and an anionic, inorganic substance as active ingredients. The concentration of these active ingredients is 0.001 to 50%.

The ratio of anionic, inorganic substance to Hofmann decomposition polyacrylamide is 1-500% by weight, preferably 2-400%, particularly preferably 3-300%. If the mixing ratio is too low, the effect is not achieved. If the ratio is too high, the properties of the Hofmann decomposition polyacrylamide deteriorate. The decomposition rate is not specified. However, it is normally 5 to 60 mol%, preferably 10 to 50 mol%.

Hofmann decomposition polyacrylamide can be mixed with an anionic, inorganic substance as follows:

(i) In the Hofmann decomposition reaction, they can be preliminarily added to or dissolved in sodium hydroxide, sodium hypochlorite or a mixture of solutions thereof. The mixture is then used for the Hofmann decomposition reaction.

(ii) They can be mixed with the reaction liquid after the Hofmann decomposition reaction.

The solution obtained after the Hofmann decomposition reaction normally has a pH of 12-13, which, however, can be lowered by an inorganic or organic acid before mixing with an anionic, inorganic substance. The pH can also be lowered after mixing with an anionic, inorganic substance. The papermaking additive according to the invention can have a pH of 2-14.

According to the present invention, the cationic monomers of the above-mentioned general formula (I) may be, for example, (meth)acrylic acid ester derivatives such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate and (meth)acrylamide derivatives such as dimethylaminopropyl (meth)acrylamide and diethylaminopropyl (meth)acrylamide.

The organic or inorganic acid salts can be salts of inorganic acids, e.g. sulfuric acid, hydrochloric acid, phosphoric acid and the like, or salts of organic acids, e.g. acetic acid, formic acid and the like.

The quaternary ammonium salts obtained by reacting the compound according to the above general formula (I) with a quaternizing agent are, for example, vinyl monomers having a quaternary ammonium salt prepared by reacting a vinyl monomer having a tertiary amino group with a quaternizing agent such as methyl chloride, methyl bromide, methyl iodide, dimethylsulfuric acid, epichlorohydrin, benzyl chloride and the like.

According to the present invention, a vinyl monomer having a tertiary amino group or its organic or inorganic salts in combination with a quaternary ammonium salt obtained by reaction with a quaternizing agent. The mixing ratio is not specified.

The proportion of cationic monomer is normally 0.5-70 mol%, preferably 2-50 mol%.

The α, β-unsaturated carboxylic acids or their salts, e.g. alkali metal salts or ammonium salts, are anionic vinyl monomers such as unsaturated carboxylic acids, e.g.

Maleic acid,

Fumaric acid,

Itaconic acid,

(Meth)acrylic acid,

Crotonic acid,

Citraconic acid,

and similar,

and their alkali metal salts, e.g. sodium salts,

Potassium salts and similar, and their ammonium salts.

The amount of monomer can be 0.5 to 20 mol %, preferably 2 to 20 mol %.

The monomer represented by the general formula (II) of the present invention may be acrylamide and methacrylamide, and any of the commercially available monomers in the form of powder or aqueous solution. The monomer may be used in amounts of 10 to 90 mol%.

According to the present invention, a crosslinking monomer (d) can be used as the fourth component other than (a) to (c).

The crosslinking monomer can be a monomer with at least two double bonds in the molecule and an N-alkoxymethyl(meth)acrylamide derivative.

In detail, these can be, for example:

Methylenebisacrylamide

Diallylacrylamide,

Triacrylformal,

Diacryloylimide,

Ethylene glycol acrylate,

Ethylene glycol dimethacrylate,

Propylene glycol diacrylate,

1,3-Butylene glycol dimethacrylate,

1,4-Butylene glycol methacrylate,

Glyceryl dimethacrylate,

Neopentylglycerin dimethacrylate,

Trimethylolpropane triacrylate,

Divinylbenzene,

Diallyl phthalate

and similar.

N-alkoxymethyl(meth)acrylamide derivatives include N-hydroxymethyl(meth)acrylamide, e.g.

N-methylol(meth)acrylamide,

N-methoxymethyl(meth)acrylamide,

N-ethoxymethyl(meth)acrylamide,

N-n-butoxymethyl(meth)acrylamide,

N-tert-butoxymethyl(meth)acrylamide

and similar.

The amount of crosslinking agent depends on the type of crosslinking monomer, but is normally 0.0001-20 mol%, preferably 0.001-10 mol%.

If it is less than 0.0001 mol %, the paper-strengthening effect is not fully achieved. On the other hand, if it exceeds 20 mol %, gelling is likely to occur.

The cationic polyacrylamide (B) according to the invention can be prepared by conventional methods for polymerizing such water-soluble vinyl monomers.

Radical polymerization, for example, is preferred.

The monomer concentration can be 2-30 wt%, preferably 5 to 30 wt%.

There are no special requirements for the polymerization inhibitor, except that it must be water-soluble. It is usually used dissolved in an aqueous solution of the monomer.

Polymerization initiators include:

Peroxides such as hydrogen peroxide, benzoyl peroxide and similar;

Persulfates such as sodium persulfate, potassium persulfate, ammonium persulfate and similar;

Bromates such as sodium bromate, potassium bromate and similar;

Perborates such as sodium perborate, potassium perborate, ammonium perborate and similar;

Percarbonates such as sodium percarbonate, potassium percarbonate, ammonium percarbonate and similar;

Perphosphates such as sodium perphosphate, potassium perphosphate, ammonium perphosphate and similar;

tert-butyl peroxide and similar.

The above-mentioned initiators can be used alone or in combination with a reducing agent as redox polymerization agents.

Reducing agents can be, for example: sulfites, bisulfites, salts of iron, copper, cobalt and similar, weakly ionized metals, organic amines such as N,N,N',N'-tetramethylethylenediamine and similar and reducing sugars such as aldose and ketose.

As azo compounds, 2,2'-azobis-4-amidinopropane hydrochloride, 2,2'-azo-bis-2,4-dimethylvaleronitrile, 4,4'-azobis-4-cyanovaleric acid, their salts and the like can be used.

In addition, two or more of the above polymerization initiators can be used in combination.

In the case of a single polymerization initiator, the polymerization temperature is only 30 to 90ºC and when using a redox polymerization initiator it is even only 5 to 50ºC.

In addition, the temperature does not need to be kept constant. It can be adjusted to the polymerization process. In general, the temperature rises during the polymerization process due to the heat of polymerization generated.

There are no special requirements for the atmosphere in the polymerization vessel at this stage, but to accelerate polymerization it is better to replace the atmosphere with an inert gas, e.g. nitrogen. There is no time specified for polymerization. It usually lasts from 1 to 20 hours.

The process according to the invention is used to produce paper from pulp. It effectively allows the drainage during paper production to be significantly improved and the strength and mechanical strength of the paper to be increased.

The ratio of Hofmann decomposition polyacrylamide to cationic polyacrylamide (B) depends on the raw material for the pulp and the white water. With regard to the mixing effect, it can be between 95:5 and 5:95, preferably 80:20 and 20:80.

The cationic polyacrylamide can be added to the pulp in such a way that the Hofmann decomposition polyacrylamide and the cationic polyacrylamide (B) are added to the pulp separately or the Hofmann decomposition polyacrylamide and the cationic polyacrylamide (B) are first mixed and then added to the pulp. Both methods are possible.

The effect of the combination of Hofmann decomposition polyacrylamide and cationic polyacrylamide (B) is sometimes further increased when aluminum sulfate or water-soluble anionic resins are used.

The water-soluble anionic resins used here may be water-soluble resins having an anionic substituent, e.g. a carboxyl, sulfonic acid, phosphoric acid and similar group or their salts.

Examples of such resins are:

anionic acrylamide resins,

anionic polyvinyl alcohol resins,

carboxymethyl cellulose,

carboxymethylated starch,

Sodium alginate

and similar.

The time of addition is not specifically prescribed. The addition can be made before, after or at the same time as the addition of the Hofmann decomposition polyacrylamide and the cationic polyacrylamide (B) to the pulp. In addition, the agents can be mixed separately with the Hofmann decomposition polyacrylamide and the cationic polyacrylamide (B) or a solution mixture of the Hofmann decomposition polyacrylamide and the cationic polyacrylamide (B).

The addition can be made at any point, but before the wet web is formed.

A location is preferred where the chemicals can be well mixed and diluted with the pulp and which is close to the wire section of the paper machine, e.g. machine chest, mixing box, knot catcher, white water pit, wire drain and similar.

Either a fourdrinier machine or a cylinder machine can be used as a paper machine.

After adding the additive according to the invention for paper production to the pulp (concentration 0.5 to 5.0%, pH value 4.0 to 9.0 at a temperature of 20 to 70°C), a wet web is formed in the wire section and the water is pressed out in the press section. The roller nip pressure in the press section ranges from 20 to 400 kg/cm. After passing through the press section, the wet web is transported to the drying section and dried with steam.

The steam pressure is 2-15 kg/cm² and the drying is carried out at 80-200ºC in a roller.

Subsequently, chemical treatments can be carried out in the size press or in the polishing machine to improve the printing properties, surface strength, water resistance and water-repellent properties.

The additive for papermaking according to the invention can be a water-soluble, liquid mixture containing as active ingredients a Hofmann decomposition polyacrylamide and a cationic polyacrylamide (B). The concentration of the active ingredients is 0.001-50%.

The ratio of Hofmann decomposition polyacrylamide to cationic polyacrylamide (B) is 95% to 5:95, preferably 80:20 to 20:80%, based on weight.

If the mixing ratio is too low, the desired effect of the combination will not be achieved. If the ratio is too high, the function of the Hofmann decomposition polyacrylamide deteriorates. The decomposition rate is not specified, but is normally 5-60 mol%, preferably 10-50 mol%.

The Hofmann decomposition polyacrylamide can be mixed with a cationic polyacrylamide (B) as described below. The solution obtained after the Hofmann decomposition reaction normally has a pH of 12-13, but this can be lowered by an inorganic or organic acid before or after mixing with cationic polyacrylamide (B).

The additives for paper production according to the invention can have a pH value of 2-14.

When paper is manufactured using the process described above, drainage can be improved without affecting the paper’s strength, e.g. tear resistance, internal bonding, press strength, etc.

If the process according to the invention is used to produce paper products in which the raw materials consist largely of waste paper, for example corrugated cardboard, newspapers, etc., very good results are obtained and paper of high strength can be produced.

In addition to corrugated cardboard and newspapers, high-strength paper can be produced with good productivity or excellent dewatering can be achieved in one production stage when the process according to the invention is applied.

Best mode for carrying out the invention

The present invention is explained using the following examples, but is not limited thereto. Unless otherwise stated, the percentages hereinafter mean % by weight.

Manufacturing example 1

In a 500-ml beaker, 24.0 g of a 10% aqueous polyacrylamide solution (Brookfield viscosity at 25°C: 3,400 cps) was added, diluted with 36.0 g of distilled water and heated to 80°C with stirring. To the resulting solution was added 14.8 g of a mixed solution of sodium hypochlorite and NaOH (sodium hypochlorite concentration: 1.0 mol/kg; NaOH concentration: 2.0 mol/kg). The reaction was stopped 15 seconds after the addition of the mixed solution. 1 wt% acrylamide polymer (Hofmann PAA (A)) was obtained.

A portion of the reaction product was added to an aqueous solution with a pH of 2. A colloid titration was carried out using 1/400 N aqueous potassium polyvinylsulfonate solution and toluidine blue as an indicator. The cation concentration thus obtained was 4.4 meq/g.

In the following experiments, Hofmann’s polyacrylamide (A) was used immediately after preparation.

Manufacturing example 2

24.0 g of a 12.5% aqueous polyacrylamide solution (Brookfield viscosity at 25ºC: 12,400 cp) was added to a 500 ml beaker and diluted with 36.0 g of distilled water. 14.8 g of a mixed solution of sodium hypochlorite and NaOH (sodium hypochlorite concentration: 1.0 mol/kg; NaOH concentration: 2.0 mol/kg) was added to the resulting solution at 20ºC while stirring. Two hours later, 225.2 g of a 0.001% aqueous sodium sulfite solution was added to terminate the reaction. 1 wt.% of acrylamide polymer (hereinafter referred to as Hofmann's PAA (13)) was obtained.

A portion of the reaction product was added to an aqueous solution with a pH of 2. A colloid titration was carried out using 1/400 N aqueous potassium polyvinylsulfonate solution and toluidine blue as an indicator. The cation concentration thus obtained was 4.4 meq/g.

example 1

To a pulp with a Canadian Standard Freeness (hereinafter abbreviated to CSF) of 450 ml and a concentration of 1.0% waste paper made from corrugated cardboard, 0.15% of a commercially available rosin emulsion size, based on pulp dry weight, was added and stirred for two minutes.

Then 1.0% aluminum sulfate, based on dry weight, was added and stirred for 1 minute. The resulting pulp had a pH value of 5.1.

Then 0.30% of water glass No. 3, based on the dry weight of the pulp, was added and the mixture was stirred for 1 minute. Thereafter, 0.60% of the Hofmann polyacrylamide (A) obtained according to Preparation Example 1, based on the dry weight of the pulp, was added and the mixture was stirred again for 1 minute.

A part of the pulp obtained was used for the determination of CSF according to JIS-P-8121. From the rest, square paper was made in a TAPPI machine. The paper was dried in a hot air dryer at 110ºC for two hours. A handmade paper with a basis weight of 150 ± 3 g/m² was obtained.

To evaluate the handmade paper, the specific press strength was measured according to JIS-P-8126, the specific tear strength according to JIS-P-8112 and the internal bond was measured using a 'Kumagaya Riki Internal Bond Tester'. The result is shown in Table I.

Example 2

Example 1 was repeated, but 0.60% of water glass No. 3 was added, based on dry weight. The result is shown in Table I.

Example 3

Example 1 was repeated, but 0.90% of water glass No. 3, based on dry weight, was added. The result is shown in Table I.

Example 4

Example 1 was repeated, but 1.50% of water glass No. 3 was added, based on dry weight. The result is shown in Table I.

Comparison example 1

Example 1 was repeated, but 0.003% Waterglass No. 3, based on dry weight, was added.

Comparison example 2

Example 1 was repeated, but 5.00% Waterglass No. 3, based on dry weight, was added.

Comparative examples 3 and 4

Examples 2 and 4 were repeated, but instead of the compound used in Comparative Examples 1 and 2, Hofmann's polyacrylamide (A) and Hofmann's polyacrylamide (B) were used. The results are shown in Table I.

Example 5

To a pulp with a Canadian Standard Freeness (hereinafter abbreviated to CSF) of 543 ml and a concentration of 1.0% waste paper made from corrugated cardboard, 0.5% aluminum sulfate, based on pulp dry weight, was added and stirred for 1 minute. The pulp had a pH of 5.8.

Then 0.25% colloidal silica (Snowtex 40, particle size 10-20 nm, manufacturer: Nissan Kagaku K.K.) based on pulp dry weight was added and stirred for 30 seconds. Then 1.50% of Hofmann's polyacrylamide (A) obtained according to Preparation Example 1 based on pulp dry weight was added and stirred for a further 30 seconds.

A part of the pulp obtained was used for the determination of CSF according to JTS-P-8121. From the rest square paper was produced in a TAPPI machine. The paper was dried in a hot air dryer at 110ºC for two hours. A handmade paper with a basis weight of 150 ± 3 g/m² was obtained.

To evaluate the handmade paper, the specific press strength was measured according to JIS-P-8126, the specific tear strength according to JIS-P-8112 and the internal bond was measured using a 'Kumagaya Riki Internal Bond Tester'. The results are shown in Table II.

Example 6

Example 5 was repeated, but 0.50% colloidal silica, based on dry weight, was added. The result is shown in Table II.

Example 7

Example 5 was repeated, but 1.00% colloidal silica on a dry weight basis was added. The result is shown in Table II.

Comparison example 5

Example 5 was repeated, but 0.001% colloidal silica, based on dry weight, was added. The result is shown in Table II.

Comparison example 6

Example 5 was repeated, but 10.0% colloidal silica, based on dry weight, was added. The result is shown in Table II.

Manufacturing example 3

675 g (94 mol%) of 40% acrylamide, 23.1% (4 mol%) of dimethylaminoethyl methacrylate, 5.8 g (2 mol%) of acrylic acid, 62.3 mg (0.01 mol%) of bismethylene acrylamide and 1.004 g of water were placed in a four-necked flask equipped with a stirrer, reflux condenser, thermometer and inlet tube for nitrogen. The pH of the mixture was adjusted to 4.5 with 10% aqueous sulfuric acid solution. The temperature in the flask was increased to 40°C. At the same time, nitrogen gas was introduced. Then, a 10% aqueous ammonium persulfate solution and a 10% aqueous sodium hydrogen sulfite solution were added to this mixture while stirring and the polymerization was initiated.

The reaction mixture was kept at 85°C and 3 hours after the start of the polymerization, it was terminated by adding water. A stable aqueous acrylamide polymer solution with a solids content of of 15.3%, a Brookfield viscosity of 6,800 cps at 25ºC and a pH of 4.3.

Manufacturing example 4

30.0 g of a 10% aqueous polyacrylamide solution (Brookfield viscosity at 25°C: 3,400 cp) was placed in a 500 ml beaker, diluted with distilled water and heated to 80°C with stirring. 14.3 g of a mixed solution of sodium hypochlorite and NaOH (sodium hypochlorite concentration: 1.0 mol/kg; NaOH concentration: 2.0 mol/kg) was added to the resulting solution. After 15 seconds, the reaction was stopped by adding 225.7 g of cold water (5°C). 1 wt% acrylamide polymer (Hofmann PAA (C)) was obtained.

A portion of the reaction product was added to an aqueous solution with a pH of 2. A colloid titration was carried out using 1/400 N aqueous potassium polyvinylsulfonate solution and toluidine blue as an indicator. The cation concentration thus obtained was 3.8 meq/g.

In the following experiments, Hofmann’s polyacrylamide (C) was used immediately after preparation.

Example 8

To a pulp with a Canadian Standard Freeness (hereinafter abbreviated to CSF) of 400 ml and a concentration of 1.0% waste paper made from corrugated cardboard, 0.15% of a commercially available rosin emulsion size, based on pulp dry weight, was added and stirred for two minutes.

Then 1.0% aluminum sulfate, based on the dry weight of the pulp, was added and stirring continued for 1 minute. The resulting pulp had a pH value of 5.1 at this point.

To the mixture was then added 0.30% of the aluminum sulfate obtained in Preparation Example 3, based on pulp dry weight, and stirred for 1 minute. Then, 0.10% of the Hofmann decomposition polyacrylamide (C) obtained in Preparation Example 4, based on pulp dry weight, was added.

Stirring was continued for 1 minute. A portion of the pulp obtained was then used for the determination of CSF according to JIS-P-8121. Square paper was made from the remainder in a TAPPI machine. The paper was dried in a hot air dryer at 110ºC for two hours. A handmade paper with a basis weight of 125 ± 3 g/m² was obtained.

To evaluate the handmade paper, the specific press strength was measured according to JIS-P-8126, the specific tear strength according to JIS-P-8112 and the internal bond was measured using a 'Kumagaya Riki Internal Bond Tester'. The results are shown in Table III.

Example 9

Example 8 was repeated, but 0.20% of the polyacrylamide polymer from Preparation Example 3 and 0.20% of the Hofmann polyacrylamide (C) from Preparation Example 4, each based on dry weight, were added. The result is shown in Table III.

Example 10

Example 8 was repeated, but 0.10% of the polyacrylamide polymer from Preparation Example 3 and 0.30% of Hofmann's polyacrylamide (C) from Preparation Example 4, each based on dry weight, The result is shown in Table III.

Comparison example 7

Example 8 was repeated, but 0.40% of the polyacrylamide polymer from Preparation Example 3, based on dry weight, was added. Hofmann’s polyacrylamide (C) from Preparation Example 4 was not added. The result is shown in Table III.

Comparison example 8

Example 8 was repeated, but 0.40% of the Hofmann polyacrylamide (C) from Preparation Example 4 was added, based on dry weight. The acrylamide polymer from Preparation Example 3 was not added. The result is shown in Table III.

It can be seen from Tables I - II that paper produced under the conditions of the present invention has improved strength by adding anionic, inorganic substances, although the drainage tendency is normally changed by adding anionic, inorganic substances.

It appears that in the presence of the correct amount of anionic, inorganic substance, the aggregation forces of Hofmann's polyacrylamide are reduced accordingly, so that controlled paper formation can take place and the paper properties such as specific tear strength, specific press strength, internal bonding, etc. are excellent.

The effect is remarkable when the Hofmann decomposition reaction is carried out over a short period of time in a temperature range of 50-110ºC. The mechanism is not yet clear, but it is certain that the The paper-strengthening effect of polyacrylamide, which is obtained by Hofmann decomposition reaction over a short time at high temperature, can be increased by using an anionic, inorganic substance.

Therefore, if one wants to have controlled paper formation and paper with excellent strength, even if drainage suffers somewhat, the present invention offers good possibilities.

As shown in Table III, the paper produced under the conditions of the present invention has excellent properties such as specific tear strength, specific press strength, internal bonding, etc., as compared with cases where the acrylamide polymer obtained in Preparation Example 3 or 4 is used alone, while the paper produced according to the present invention has the same degree of dewatering as when the acrylamide polymer obtained in Preparation Example 4 is used alone. Table I Hofmann decomposition conditions Addition (%/pipe) Dewatering (ml) Specific tensile strength Specific compressive strength Internal bond (kg/cm) Temperature ( C) Time Hof PAA Water glass Example Comparative example Hours Legend: Hof PAA= Hofmann polyacrylamide Table II Addition (%/line) Dewatering (ml) Specific tensile strength Specific compressive strength Internal bond (kg/cm) Hof PAA Colloidal Silica Example Comparison example Legend: Hof PAA= Hofman polyacrylamide Table III Addition (%/line) Dewatering (ml) Specific tensile strength Specific compressive strength Internal bond (kg/cm) Copolymer PAA Hof PAA (C) Example Comparison example Legend: Copolymer PAA= Copolymerization polyacrylamide Hof PAA= Hofmann polyacrylamide

Industrial applicability

The paper produced by the process of the invention has excellent specific tear strength, specific press strength, internal bonding, etc.

By adding the anionic inorganic substance, paper formation can be controlled and high-strength paper can be produced even if the drainage tendency is slightly impaired. By adding the cationic polyacrylamide, the drainage degree achieved by adding an acrylamide polymer alone can be maintained, paper formation is not impaired despite good drainage tendency which normally causes deterioration, and paper strength is excellent compared with using the acrylamide polymer alone.

Claims (8)

1. A process for making paper which comprises adding both an anionic inorganic substance and a cationic acrylamide polymer to a pulp prepared by reacting an acrylamide polymer with a hypohalite for a short time at 50-110°C under alkaline conditions, and then forming a wet web of pulp which is subsequently dewatered in a press and dried with a dryer. 2. Process according to claim 1, wherein the cationic acrylamide polymer is prepared by reacting the acrylamide polymer with the hypohalite under alkaline conditions (pH value at least about 11) at a reaction temperature T (ºC) of 50ºC ≤ T ≤ 110ºC for a reaction time t (sec) according to the following formulas: 3. Additive for papermaking consisting of or containing an anionic, inorganic substance and a cationic acrylamide polymer obtainable by reacting an acrylamide polymer with a hypohalite for a short time at 50-110ºC under alkaline conditions. 4. Additive according to claim 3, wherein the cationic acrylamide polymer is prepared by reacting the acrylamide polymer with the hypohalite under alkaline conditions (pH at least about 11) at a reaction temperature T (ºC) of 50ºC &le; T &le; 110ºC for a reaction time t (sec) according to the following formulas: 5. A process for the manufacture of paper, in which a fibre pulp is added both a cationic acrylamide polymer (A) prepared by reacting an acrylamide polymer with a hypohalite for a short time at 50-110ºC under alkaline conditions, and a cationic polyacrylamide (B) prepared by copolymerization (a) a cationic monomer of the general formula (I) wherein 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 from 2-4 and/or organic or inorganic acid salts thereof, or quaternary ammonium salts, prepared by reacting the compound of the general formula (I) with a quaternizing agent, (b) an α, β-unsaturated carboxylic acid and/or their salts and (c) an acrylamide monomer of the general formula (II) CH₂=C(R₅)-CONH₂ (II) wherein R�5 is hydrogen or methyl, is added and then a wet web of pulp is formed, which is subsequently dewatered in a press and dried with a dryer. 6. Process according to claim 5, wherein the cationic acrylamide polymer (A) is prepared by reacting the acrylamide polymer with the hypohalite under alkaline conditions (pH value at least about 11) at a reaction temperature T (ºC) of 50ºC ≤ T ≤ 110ºC for a reaction time t (sec) according to the following formulas: 7. Additive for papermaking consisting of or containing a cationic acrylamide polymer (A), preparable by reacting an acrylamide polymer with a hypohalite for a short time at 50 to 110ºC under alkaline conditions, and a cationic polyacrylamide (B) prepared by copolymerization (a) a cationic monomer of the general formula (I) wherein 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 from 2-4 and/or organic or inorganic acid salts thereof, or quaternary ammonium salts prepared by reacting the compound of formula (I) with a quaternizing agent. (b) an α, β-unsaturated carboxylic acid and/or their salts and (c) an acrylamide monomer of the general formula (II) CH₂=C (R₅)-CONH₂ (II) wherein R�5 is hydrogen or methyl. 8. Additive according to claim 7, wherein the cationic acrylamide polymer (A) can be prepared by reacting an acrylamide polymer with the hypohalite under alkaline conditions (pH value at least about 11) at a reaction temperature T (ºC) of 50ºC ≤ T ≤ 110ºC for a reaction time t (sec) according to the following formulas: