EP0972110B2 - Method for producing high dry-strength paper, pulpboard and cardboard - Google Patents

Abstract

Paper, board and cardboard having high dry strength are produced by the addition of cationic, anionic and/or amphoteric starch as dry strength agents to the paper stock and drainage of the paper stock with sheet formation in the presence of cationic polymers as retention aids for starch, and cationic polymeric retention aids are used for increasing the retention of dry strength agents comprising cationic, anionic and/or amphoteric starch in the production of paper, board and cardboard.

Description

The invention relates to a process for the production of paper, paperboard and cardboard with high dry strength by adding cationic, anionic and / or amphoteric starch as a dry strength agent to the paper stock and dewatering of the stock under sheet formation.

To increase the dry strength of paper, for example Ullmann's Encyclopedia of Technical Chemistry, 4th Edition, Verlag Chemie, Weinheim-New York, 1979, Volume 17, page 581 It is known to use aqueous slurries of native starches, which are converted by heating into a water-soluble form, as a mass additive in the production of paper. However, the retention of the starches dissolved in water to the paper fibers in the pulp is low. An improvement in the retention of natural products of cellulose fibers in the production of paper, for example, from US-A-3,734,820 known. Therein graft copolymers prepared by grafting dextran, a naturally occurring polymer having a molecular weight of 20,000 to 50 million, with cationic monomers, eg diallyldimethylammonium chloride, mixtures of diallyldimethylammonium chloride and acrylamide or mixtures of acrylamide and basic methacrylates, such as dimethylaminoethyl methacrylate become. The graft polymerization is preferably carried out in the presence of a redox catalyst.

From the US-A-4 097 427 For example, there is known a process for cationizing starch which comprises starch cooking in an alkaline medium in the presence of water-soluble quaternary ammonium polymers and an oxidizing agent. Suitable quaternary ammonium polymers include, inter alia, quaternized diallyldialkylaminopolymers or quaternized polyethylenimines. As the oxidizing agent used, for example, ammonium persulfate, hydrogen peroxide, sodium hypochlorite, ozone or tert-butyl hydroperoxide. The modified cationic starches which can be prepared in this way are added as a dry strength agent in the production of paper to the paper stock. However, the wastewater is burdened by a very high COD (chemical oxygen demand).

From the US-A-4,146,515 For example, there is known a process for producing cationic starch which is used for surface sizing and coating of paper and paper products. According to this method, an aqueous slurry of oxidized starch is digested together with a cationic polymer in a continuous digester. Suitable cationic polymers are condensates of epichlorohydrin and dimethylamine, polymers of diallyldimethylammonium chloride, quaternized reaction products of ethylene chloride and ammonia and quaternized polyethyleneimine.

From the US-A-3,467,608 For example, there is known a process for producing a cationic starch which comprises heating a slurry of starch in water together with a polyalkyleneimine or polyalkylenepolyamine having a molecular weight of at least 50,000 at a temperature of about 70 to 110 ° C for about 0.5 to 5 hours , The mixture contains from 0.5 to 40% by weight of polyalkyleneimine or polyalkylenepolyamine and from 99.5 to 60% by weight of starch. According to Example 1, a polyethyleneimine having an average molecular weight of about 200,000 in dilute aqueous solution with potato starch is heated at a temperature of 90 ° C for 2 hours. The modified potato starch can be precipitated in a mixture of methanol and diethyl ether. The in the US-A-3,467,608 described reaction products of starch and polyethyleneimine or polyalkylenepolyamines are used as flocculants.

From the EP-A-0 282 761 and the DE-A-3 719 480 Manufacturing methods for paper, cardboard and cardboard with high dry strength are known. In this process, the dry strength agent used is reaction products obtained by heating native potato starch with cationic polymers such as polymers containing vinylamine, N-vinylimidazoline or diallyl dimethyl ammonium units or polyethyleneimines in aqueous medium to temperatures above the gelatinization temperature of the starch in the absence of oxidizing agents, Polymerization initiators and alkali are available.

From the EP-B-0 301 372 a similar process is known in which correspondingly modified, enzymatically degraded starches are used. Under the digestion conditions for native starch given there, in addition to an incomplete digestion (spectroscopic investigations show undissolved, sometimes only swollen starch granules), a larger amount of degradation products (degradation rates> 10%) are also found.

From the US-A-4,880,497 and the US-A-4,978,427 discloses a process for producing high dry and wet strength paper comprising adding to the surface of the paper or to the stock prior to sheet formation a hydrolyzed copolymerization solidifying agent which is prepared by copolymerizing N-vinylformamide and ethylenically unsaturated monomers, such as For example, vinyl acetate, vinyl propionate or alkyl vinyl ethers and hydrolyzing from 30 to 100 mol% of the formyl groups of the copolymer to form amino groups is available. The hydrolyzed copolymers are used in amounts of 0.1 to 5 wt .-%, based on dry fibers.
From the GB 1,110,004 discloses a method for producing paper with improved solidification, wherein as a solidifier water-soluble polysaccharides such as natural or chemically-modified polysaccharides, in particular starches, are used. The flocculation and retention agent is then followed by the addition of a polyalkyleneimine.

From the DE-A-4127 733 Hydrolyzed graft polymers of N-vinylformamide and saccharide structures containing natural substances are known, which are used as dry and wet strength agents. However, the hydrolysis of the graft polymers under acidic conditions has a strong molecular weight degradation of the polysaccharides result.

From the WO-A-96/13525 is a method for the cationic modification of starch by reacting starch with polymers containing amino and / or ammonium groups in aqueous medium at temperatures of 115 to 180 ° C under elevated pressure known, wherein at most 10 wt .-% of the starch used are degraded ,

HR Hernandez describes in EUCEPA 24th Cont.Proc.Pap.Technol., May 1990, pages 186-195 the use of cationic or amphoteric starch together with cationic or anionic retention aids in the manufacture of paper. In a paper machine test, paper production takes place in the alkaline pH range with alkenyl succinic anhydride, alum, amphoteric waxy maize starch and an anionic retention agent.

By adding a cationically modified starch as a dry strength agent to the stock, an undesirable decrease in the dewatering rate of the stock occurs. At the same time, an increase in the COD value in the waste water of the paper machine is observed. This increase in the COD value occurs mainly in high-salty paper machine wastewater.

The invention is therefore based on the object to provide a process for the production of paper, paperboard and cardboard with high dry strength, wherein one achieves an increased retention of starch in the paper and thus lower COD values in paper machine wastewater and wherein also compared to the state The technique achieves an acceleration of the drainage rate.

The object is achieved according to the invention by a process for the production of paper, paperboard and cardboard with high dry strength by adding starch obtainable by reaction of native, cationic, anionic and / or amphoteric starch with synthetic cationic polymers, as a dry strength agent to the paper stock and Dewatering the stock in the presence of sheet retention aids when employing polymers containing cationic vinylamine unit starch.

The invention further provides the use of polymers containing vinylamine units as cationic polymeric retention aids for increasing the retention of dry strength agents from starch obtainable by reacting native, cationic, anionic and / or amphoteric starch with synthetic cationic polymers in the manufacture of paper , Cardboard and cardboard. Particularly preferred is the use of hydrolyzed homo- or copolymers of N-vinylformamide having a degree of hydrolysis of 1 to 100% and a K value of at least 30 (determined according to H. Fikentscher in aqueous solution at a polymer concentration of 0.5% by weight). %, a temperature of 25 ° C and a pH of 7) in amounts of 0.01 to 0.3 wt .-%, based on dry pulp, as a retention aid for cationic, anionic and / or amphoteric starch.

Suitable pulps for the production of the pulps are all qualities customary for this purpose, for example wood pulp, bleached and unbleached pulp and pulps from all annual plants. Wood pulp includes, for example, groundwood, thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressure groundwood, semi-pulp, high yield pulp and refiner mechanical pulp (RMP). Suitable pulps are, for example, sulphate, sulphite and soda pulps. Suitable annual plants for the production of paper stocks For example, rice, wheat, sugarcane and kenaf. Waste paper is also used alone or in admixture with other fibers to make the pulps. Waste paper also belongs to waste paper, which gives rise to the white pitch due to the content of binders for coating and printing inks. The reason for the formation of so-called stickies is given by adhesives derived from self-adhesive labels and envelopes, as well as glues from the backsliding of books and so-called hotmelts.

The fibers mentioned can be used alone or mixed with one another. The pulps of the type described above contain varying amounts of water-soluble and water-insoluble impurities. The impurities can be detected quantitatively, for example, with the aid of the COD value or else with the aid of the so-called cationic requirement. Cationic requirement is understood to be that amount of a cationic polymer which is necessary in order to bring a defined amount of the white water to the isoelectric point. Since the cationic requirement depends very much on the composition of the cationic polymers used in each case for the determination, one uses according to Example 3 of the standardization DE-B-2 434 816 obtained condensation product obtainable by grafting a polyamidoamine of adipic acid and diethylenetriamine with ethyleneimine and subsequent crosslinking with a Polyethylenglykoldichlorhydrinether. The pulps containing impurities have, for example, COD values of 300 to 40,000, preferably 1,000 to 30,000 mg of oxygen per kg of the aqueous phase and a cationic requirement of more than 50 mg of said cationic polymer per liter of white water.

Thickeners used are starches which are obtainable by reaction of native cationic, anionic and / or amphoteric starch with synthetic cationic polymers. Cationic, anionic and amphoteric starches are known and commercially available. Cationic starches are prepared, for example, by reacting native starches with quaternizing agents such as 2,3- (epoxypropyl) trimethylammonium chloride. For example, starch and starch derivatives are described in detail in U.S. Pat Book by Günther Tegge, Starch and Starch Derivatives, Behr's-Verlag, Hamburg 1984 , For example, corn starch, potato starch, wheat starch, rice starch, tapioca starch, sago starch, sorghum starch, manioc starch, pea starch, rye starch or mixtures of the native starches mentioned can be used as native starches. As a starch also rye flour and other flours comes into consideration. In addition, protein-containing starches of rye, wheat and legumes are suitable. For the cationic modification with polymers, those native starches which have an amylopectin adhesion of at least 95% by weight are also suitable. Preferred are starches having an amylopectin content of at least 99% by weight. Such starches can be obtained, for example, by starch fractionation of conventional native starches or by plant growth techniques from plants which produce substantially pure amylopectin starch. Starches having an amylopectin content of at least 95, preferably at least 99% by weight are available on the market. They are offered, for example, as waxy maize starch, waxy potato starch or waxy wheat starch. The native starches can be modified either alone or in admixture with cationic polymers.

The modification of the native starches and of cationic, anionic and / amphoteric starch with synthetic cationic polymers is carried out by known methods by heating starches in an aqueous medium in the presence of cationic polymers at temperatures above the gelatinization temperature of the starches. Methods of this type are, for example, from the references cited in the prior art EP-B-0 282 761 and the WO-A-96/13525 known. For the cationic modification of the abovementioned starches, all synthetic polymers which contain amino and / or ammnium groups are suitable. These compounds are referred to below as cationic polymers.

in der R und R¹ gleich oder verschieden sind und H oder C₁- bis C₆-Alkyl bedeuten, allein oder in Gegenwart von anderen damit copolymerisierbaren Monomeren und Hydrolyse der entstehenden Polymerisate mit Säuren oder Basen unter Abspaltung der Gruppierung

und unter Bildung von Einheiten der Formel

in der R die in Formel (I) angegebene Bedeutung hat, hergestellt.Suitable cationic polymers are, for example, homopolymers and copolymers containing vinylamine units. Polymers of this type are prepared by known processes by polymerizing N-vinylcarboxamides of the formula

in which R and R ^{1 are} identical or different and are H or C ₁ - to C ₆ -alkyl, alone or in the presence of other monomers copolymerizable therewith and hydrolysis of the resulting polymers with acids or bases with elimination of the grouping

and forming units of the formula

in which R has the meaning given in formula (I).

1. 1) 99 bis 1 Mol-% N-Vinylcarbonsäureamide der Formel (I) und
2. 2) 1 bis 99 Mol-% andere, damit copolymerisierbare monoethylenisch ungesättigte Monomere,

wie beispielsweise Vinylester von gesättigten Carbonsäuren mit 1 bis 6 Kohlenstoffatomen, z.B. Vinylformiat, Vinylacetat, Vinylpropionat und Vinylbutyrat. Geeignet sind auch ungesättigte C₃- bis C₆-Carbonsäuren, wie z.B. Acrylsäure, Methacrylsäure, Maleinsäure, Crotonsäure, Itaconsäure und Vinylessigsäure sowie deren Alkalimetall- und Erdalkalimetallsalze, Ester, Amide und Nitrile, beispielsweise Methylacrylat, Methylmethacrylat, Ethylacrylat und Ethylmethacrylat oder mit Glykol- bzw. Polyglykolestem ethylenisch ungesättigter Carbonsäuren, wobei jeweils nur eine OH-Gruppe der Glykole und Polyglykole verestert ist, z.B. Hydroxyethylacrylat, Hydroxyethylmethacrylat, Hydroxypropylacrylat, Hydroxybutylacrylat, Hydroxypropylmethacrylat, Hydroxybutylmethacrylat sowie die Acrylsäuremonoester von Polyalkylenglykolen eines Molgewichts von 1.500 bis 10.000. Weiterhin sind geeignet die Ester von ethylenisch ungesättigten Carbonsäuren mit Aminoalkoholen, wie z.B. Dimethylaminoethylacrylat, Dimethylaminoethylmethacrylat, Diethylaminoethylacrylat, Diethylaminoethylmethacrylat, Dimethylaminopropylacrylat, Dimethylaminopropylmethacrylat, Diethylaminopropylacrylat, Diethylaminopropylmethacrylat, Dimethylaminobutylacrylat und Diethylaminobutylacrylat. Die basischen Acrylate werden in Form der freien Basen, der Salze mit Mineralsäuren wie z.B. Salzsäure, Schwefelsäure und Salpetersäure, der Salze mit organischen Säuren wie Ameisensäure oder Benzolsulfonsäure, oder in quaternisierter Form eingesetzt. Geeignete Quaternisierungsmittel sind beispielsweise Dimethylsulfat, Diethylsulfat, Methylchlorid, Ethylchlorid oder Benzylchlorid.Suitable monomers of the formula (I) are, for example, N-vinylformamide, N-vinyl-N-methylformamide, N-vinyl-N-ethylformamide, N-vinyl-N-propylformamide, N-vinyl-N-isopropylformamide, N-vinyl-N -butylformamide, N-vinyl-N-sec-butylformamide, N-vinyl-N-tert-butylformamide, N-vinyl-N-pentylformamide, N-vinylacetamide, N-vinyl-N-ethylacetamide and N-vinyl-N-methylpropionamide , Preference is given to using N-vinylformamide in the preparation of polymers which contain units of the formula (III) in copolymerized form. The hydrolyzed polymers containing units of the formula (III) have K values of 15 to 300, preferably 30 to 200, determined according to H. Fikentscher in aqueous solution at pH 7, a temperature of 25 ° C. and a polymer concentration of 0 , 5 wt .-%. Copolymers of the monomers (I) contain, for example

1. 1) 99 to 1 mol% of N-vinylcarboxamides of the formula (I) and
2. 2) 1 to 99 mol% of other monoethylenically unsaturated monomers copolymerizable therewith,

such as vinyl esters of saturated carboxylic acids having 1 to 6 carbon atoms, for example vinyl formate, vinyl acetate, vinyl propionate and vinyl butyrate. Also suitable are unsaturated C ₃ - to C ₆ -carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, crotonic acid, itaconic acid and vinylacetic acid and their alkali metal and alkaline earth metal salts, esters, amides and nitriles, for example methyl acrylate, methyl methacrylate, ethyl acrylate and ethyl methacrylate or with glycol - or polyglycol esters of ethylenically unsaturated carboxylic acids, wherein in each case only one OH group of the glycols and polyglycols is esterified, for example hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and the acrylic acid monoesters of polyalkylene glycols of a molecular weight from 1,500 to 10,000. Also suitable are the esters of ethylenically unsaturated carboxylic acids with aminoalcohols such as dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate, diethylaminopropyl acrylate, diethylaminopropyl methacrylate, dimethylaminobutyl acrylate and diethylaminobutyl acrylate. The basic acrylates are used in the form of the free bases, the salts with mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, the salts with organic acids such as formic acid or benzenesulfonic acid, or in quaternized form. Suitable quaternizing agents are, for example, dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride or benzyl chloride.

Also suitable as comonomers are 2) unsaturated amides such as, for example, acrylamide, methacrylamide and N-alkyl mono- and diamides with alkyl radicals of 1 to 6 carbon atoms, such as, for example, N-methylacrylamide, N, N-dimethylacrylamide, N-methylmethacrylamide, N-ethylacrylamide, N-propylacrylamide and tert-butylacrylamide and basic (meth) acrylamides, e.g. Dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide, diethylaminoethylacrylamide, diethylaminoethylmethacrylamide, dimethylaminopropylacrylamide, diethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and diethylaminopropylmethacrylamide.

Further suitable comonomers are N-vinylpyrrolidone, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, N-vinylimidazole and substituted N-vinylimidazoles, e.g. N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole, N-vinyl-5-methylimidazole, N-vinyl-2-ethylimidazole, and N-vinylimidazolines, e.g. Vinylimidazoline, N-vinyl-2-methylimidazoline, and N-vinyl-2-ethylimidazoline. N-vinylimidazoles and N-vinylimidazolines are also used, except in the form of the free bases, in neutralized or quaternized form with mineral acids or organic acids, the quaternization preferably being carried out with dimethyl sulfate, diethyl sulfate, methyl chloride or benzyl chloride.

In addition come as comonomers 2) sulfo-containing monomers such as vinyl sulfonic acid, Allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid or 3-sulfopropyl acrylate in question.

When using basic comonomers 2), e.g. Basic acrylic esters and amides can often be dispensed with hydrolysis of the N-vinylcarboxamides. The copolymers include terpolymers and those polymers which additionally contain at least one further monomer in copolymerized form.

1. 1) N-Vinylformamid und
2. 2) Vinylformiat, Vinylacetat, Vinylpropionat, Acrylnitril und N-Vinylpyrrolidon sowie hydrolysierte Homopolymerisate von N-Vinylformamid mit einem Hydrolysegrad von 2 bis 100, vorzugsweise 30 bis 95 Mol-%.

Preferred cationic polymers are hydrolyzed copolymers

1. 1) N-vinylformamide and
2. 2) Vinyl formate, vinyl acetate, vinyl propionate, acrylonitrile and N-vinylpyrrolidone and hydrolyzed homopolymers of N-vinylformamide having a degree of hydrolysis of 2 to 100, preferably 30 to 95 mol%.

In the case of copolymers which contain copolymerized vinyl esters, in addition to the hydrolysis of the N-vinylformamide units, hydrolysis of the ester groups occurs to form vinyl alcohol units. Polymerized acrylonitrile is also chemically altered on hydrolysis, e.g. Amide, cyclic amidine and / or carboxyl groups are formed. The hydrolyzed poly-N-vinylformamides may optionally contain up to 20 mole% of amidine structures formed by reaction of formic acid with two adjacent amino groups in the polyvinylamine or by reaction of a formamide group with an adjacent amino group.

Suitable cationic polymers furthermore include ethyleneimine units in copolymerized form. Preferably these are polyethyleneimines obtainable by polymerizing ethyleneimine in the presence of acidic catalysts such as ammonium bisulfate, hydrochloric acid or chlorinated hydrocarbons such as methyl chloride, ethylene chloride, carbon tetrachloride or chloroform. Such polyethyleneimines have, for example, in 50 wt .-% aqueous solution has a viscosity of 500 to 33,000, preferably 1,000 to 31,000 mPa · s (measured according to Brookfield at 20 ° C and 20 rpm). The polymers of this group also include polyamidoamines grafted with ethyleneimine, which may optionally be crosslinked by reaction with an at least bifunctional crosslinker. Products of this type are prepared, for example, by condensing a dicarboxylic acid such as adipic acid with a polyalkylenepolyamine such as diethylenetriamine or triethylenetetramine, optionally grafting with ethyleneimine and reaction with an at least bifunctional crosslinker, eg bischlorohydrin ether of polyalkylene glycols, cf. US-A-4,144,123 and U.S.-A-3,642,572 ,

Further suitable for the modification of the starch poly-Diallyldimethylammoniumchloride into consideration. Polymers of this type are known. By polymers of diallyldimethylammonium chloride are meant primarily homopolymers and copolymers with acrylamide and / or methacrylamide. The copolymerization can be carried out in any monomer ratio. The K value of the homo- and copolymers of diallyldimethylammonium chloride is at least 30, preferably 95 to 180.

in der R₁, R₂=H, C₁- bis C₁₈-Alkyl, Benzyl, Aryl, R₃, R₄=H, C₁- bis C₄-Alkyl und X- ein Säurerest bedeutet, gegebenenfalls zusammen mit Acrylamid und/oder Methacrylamid in wäßrigem Medium bei pH-werten von 0 bis 8, vorzugsweise von 1,0 bis 6, 8 in Gegenwart von Polymerisationsinitiatoren, die in Radikale zerfallen, polymerisiert.Also suitable as cationic polymers are homopolymers and copolymers of optionally substituted N-vinylimidazolines. These are also known substances. You can, for example, according to the procedure of DE-B-1 182 826 be prepared by reacting compounds of the formula

in which R ₁ , R ₂ = H, C ₁ - to C ₁₈ -alkyl, benzyl, aryl, R ₃ , R ₄ = H, C ₁ - to C ₄ -alkyl and X- represents an acid radical, optionally together with acrylamide and / or methacrylamide in an aqueous medium at pH values of 0 to 8, preferably from 1.0 to 6.8 in the presence of polymerization initiators which decompose into free radicals, polymerized.

in der R₁, R₂=H, CH₃, C₂H₅, n- und i-C₃H₇, C₆H₅ und X- ein Säurerest ist. X- steht vorzugsweise für Cl-, Br, SO₄ ^2-, CH₃-O-SO₃ ^-, R-COO- und R₂=H, C₁- bis C₄-Alkyl und Aryl.1-vinyl-2-imidazoline salts of the formula (V) are preferably used in the polymerization,

in which R ₁ , R ₂ = H, CH ₃ , C ₂ H ₅ , n- and iC ₃ H ₇ , C ₆ H ₅ and X- is an acid radical. X- is preferably Cl, Br, SO ₄ ^2- , CH ₃ -O-SO ₃ ^- , R-COO- and R ₂ = H, C ₁ - to C ₄ -alkyl and aryl.

The substituent X - in the formulas (IV) and (V) can in principle be any desired acid radical of an inorganic and an organic acid. The monomers of formula (IV) are obtained by neutralizing the free bases, ie 1-vinyl-2-imidazolines, with the equivalent amount of an acid. The vinylimidazolines can also be neutralized with trichloroacetic acid, benzenesulfonic acid or toluenesulfonic acid, for example. Apart from salts of 1-vinyl-2-imidazolines, quaternized 1-vinyl-2-imidazolines are also suitable. They are prepared by reacting 1-vinyl-2-imidazolines, which may optionally be substituted in the 2-, 4- and 5-position, with known Quaternisierungsmittein. Suitable quaternizing agents are, for example, C ₁ -C ₁₈ -alkyl chlorides or bromides, benzyl chloride or bromide, epichlorohydrin, dimethyl sulfate and diethyl sulfate. Preferably used epichlorohydrin, benzyl chloride, dimethyl sulfate and methyl chloride.

To prepare the water-soluble homopolymers, the compounds of the formulas (IV) or (V) are preferably polymerized in an aqueous medium.

1. 1) 70 bis 97 Gew.-% Acrylamid und/oder Methacrylamid,
2. 2) 2 bis 20 Gew.-% N-Vinylimidazolin oder N-Vinyl-2-methylimidazolin und
3. 3) 1 bis 10 Gew.-% N-Vinylimidazol

einpolymerisiert enthalten. Diese Copolymerisate werden durch radikalische Copolymerisation der Monomeren 1), 2) und 3) nach bekannten Polymerisationsverfahren hergestellt. Sie haben K-Werte im Bereich von 80 bis 150 (bestimmt nach H. Fikentscher in 5 %iger wäßriger Kochsalzlösung bei 25°C und einer Polymerkonzentration von 0,5 Gew.-%).Since the compounds of the formula (IV) are relatively expensive, copolymers of compounds of the formula (IV) with acrylamide and / or methacrylamide are preferably used as cationic polymers for economic reasons. These copolymers then contain the compounds of the formula (IV) only in effective amounts, ie in an amount of 1 to 50% by weight, preferably 10 to 40% by weight. Particularly suitable for the modification of native starches are copolymers of 60 to 85% by weight of acrylamide and / or methacrylamide and 15 to 40% by weight of N-vinylimidazoline or N-vinyl-2-methylimidazoline. The copolymers can be further prepared by copolymerizing other monomers such as styrene, N-vinylformamide, vinyl formate, vinyl acetate, vinyl propionate, C ₁ - to C ₄ -alkyl vinyl ether, N-vinylpyridine, N-vinylpyrrolidone, N-vinylimidazole, ethylenically unsaturated C ₃ - to C ₅ -Carbonsäuren and their esters, amides and nitriles, sodium vinyl sulfonate, vinyl chloride and vinylidene chloride in amounts up to 25 wt .-% be modified. For example, one can use for the modification of native starches copolymers, the

1. 1) from 70 to 97% by weight of acrylamide and / or methacrylamide,
2. 2) 2 to 20% by weight of N-vinylimidazoline or N-vinyl-2-methylimidazoline and
3. 3) 1 to 10 wt .-% N-vinylimidazole

incorporated in copolymerized form. These copolymers are prepared by free-radical copolymerization of the monomers 1), 2) and 3) by known polymerization. They have K values in the range of 80 to 150 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25 ° C. and a polymer concentration of 0.5% by weight).

Other suitable cationic polymers are copolymers of 1 to 99 mol%, preferably 30 to 70 mol% of acrylamide and / or methacrylamide and 99 to 1 mol%, preferably 70 to 30 mol% of dialkylaminoalkyl acrylates and / or methacrylates , eg Copolymers of acrylamide and N, N-dimethylaminoethyl acrylate or N, N-diethylaminoethyl acrylate. Basic acrylates are preferably present in acids neutralized or quaternized form. The quaternization can be carried out, for example, with methyl chloride or with dimethyl sulfate. The cationic polymers have K values of 30 to 300, preferably 100 to 180 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25 ° C. and a polymer concentration of 0.5% by weight). At a pH of 4.5, they have a charge density of at least 4 meq / g polyelectrolyte.

Also suitable are copolymers of 1 to 99 mol%, preferably 30 to 70 mol% acrylamide and / or methacrylamide and 99 to 1 mol%, preferably 70 to 30 mol% Dialkylaminoalkylacrylamid and / or -methacrylamid. The basic acrylamides and methacrylamides are also preferably present in acids neutralized or quaternized form. Examples which may be mentioned are N-trimethylammoniumethylacrylamide chloride, N-trimethylammoniumethylmethacrylamidechloride, trimethylammoniumethylacrylamidemethosulphate, trimethylammoniumethylmethacrylamidemethosulphate, N-ethyldimethylammoniumethylacrylamideethosulphate, N-ethyldimethylammoniumethylmethacrylamidethosulphate, trimethylammoniumpropylacrylamidechloride, trimethylammoniopropylmethacrylamidechloride, trimethylammoniopropylacrylamidemethosulphate, trimethylammoniumpropylmethacrylamidemethosulphate and N-ethyldimethylammoniumpropylacrylamidethosulphate. Preferred is trimethylammonium propylmethacrylamide chloride.

As cationic polymers are also polyallylamines into consideration. Polymers of this type are obtained by homopolymerization of allylamine, preferably in acids neutralized or in quaternized form or by copolymerizing allylamine with other monoethylenically unsaturated monomers, corresponding to the previously described copolymers with N-vinylcarboxamides.

For cationic modification of starch according to the present invention, for example, an aqueous suspension of at least one kind of starch with one or more of the cationic polymers is heated to temperatures above the gelatinization temperature of the native or modified starches, e.g. to temperatures of 90 to 180 ° C, preferably 115 to 145 ° C. At temperatures above the boiling point of water, the reaction is carried out under elevated pressure, the reaction being carried out in such a way that at most 10% by weight of the starch undergoes a molecular weight reduction. Aqueous slurries of starch contain, for example, per 100 parts by weight of water 0.1 to 10, preferably 2 to 6 parts by weight of starch. To 100 parts by weight of starch is used, for example 0.5 to 10 parts by weight of at least one cationic polymer. Suitable cationic polymers are preferably partially or completely hydrolyzed homo- or copolymers of N-vinylformamide, polyethyleneimines, ethyleneimine-grafted and crosslinked polyamidoamines and / or polydiallyldimethylammonium chlorides.

When heating the aqueous starch suspensions in the presence of cationic polymers, the starch is first digested. By starch digestion is meant the conversion of the solid starch granules into a water-soluble form whereby superstructures (helix formation, intramolecular hydrogen bonds, etc.) are abolished without degradation of the starch-building amylose and / or amylopectin moieties to oligosaccharides or glucose. The aqueous starch suspensions containing a cationic polymer dissolved are heated in the reaction to temperatures above the gelatinization temperature of the starches. In the method according to the invention, the starch used is digested to at least 90, preferably to> 95 wt .-% and modified with the cationic polymer. The strength is clearly solved. Preferably, after the conversion of the starch from the reaction solution using a cellulose acetate membrane having a pore diameter of 1.2 μm, it is no longer possible to filter off any unreacted starch.

The reaction is preferably carried out at elevated pressure. This is usually the pressure which the reaction medium has in the temperature range above the boiling points of water, e.g. developed at 115 to 180 ° C. It is for example at 1 to 10, preferably 1.2 to 7.9 bar. During the reaction, the reaction mixture is subjected to shear. If the reaction is carried out in a stirred autoclave, stirring the reaction mixture, for example, with 100 to 2,000, preferably 200 to 1,000 revolutions / minute. The reaction can be carried out in virtually all apparatuses in which starch is digested in the art, e.g. in a jet cooker. The residence times of the reaction mixture at the above-mentioned temperatures of 115 to 180 ° C, for example, 0.1 seconds to 1 hour and are preferably in the range of 0.5 seconds to 30 minutes.

Under these conditions, at least 90% of the starch used is digested and modified. Preferably, less than 5 wt .-% of the starch are degraded.

The native starch types may also be subjected to a pretreatment, e.g. oxidatively, hydrolytically or enzymatically degraded or chemically modified. Again, the wax strengths, such as waxy potato starch and waxy maize starch are of particular interest.

The reaction products thus obtainable have, for example, at a solids concentration of 3.5% by weight, a viscosity of 50 to 10,000, preferably 80 to 4,000 mPa.s, measured in a Brookfield viscometer at 20 revolutions / minute and a temperature of 20 ° C. , The pH of the reaction mixtures is, for example, in the range of 2.0 to 9.0, preferably 2.5 to 8.

The starches modified with cationic polymers are used as dry strength agents in the amount of, for example, from 0.5 to 10, preferably from 0.5 to 3.5, and particularly preferably from 1.2 to 2.5,% by weight, based on dry paper stock , added. According to the invention, the paper stock is additionally metered with a cationic vinylamine units-containing polymer as retention aid for the above-described starches which have been modified with a polymer. Preferably, first the dry strength and then the retention agent. However, it is also possible to add dry strength agent and retention agent to the stock at the same time, wherein dry strength agent and retention agent are metered separately from one another. It is also possible to dose a mixture of dry strength agent and retention agent to the paper. Such mixtures can be prepared, for example, by adding to the disrupted starch retention aid, after cooling to 50 ° C or below. However, the retention aid may also be added to the stock before the addition of the modified starch. This order of addition makes use of, for example, the processing of paper stocks which have a high level of impurities.

As a retention aid for starch according to the invention cationic vinylamine units containing polymers into consideration.

The dry strength agent used is preferably a cationic starch which is obtainable by reacting 100 parts by weight of a native, cationic, anionic and / or amphoteric starch with 0.5 to 10 parts by weight of a polymer comprising vinylamine units with a Value of 60 to 150 at temperatures above the gelatinization temperature of the starch. As polymers containing vinylamine units, e.g. hydrolyzed homopolymers and copolymers of N-vinylformamide having a degree of hydrolysis of at least 60% are preferably used. These homopolymers and copolymers are added not only to the cationization of starch but also to the paper stock as a retention aid for the cationically modified starches.

The hydrolyzed homo- and copolymers of N-vinylformamide considered as retention aids for starch may generally have a degree of hydrolysis of from 1 to 100%.

• Polydiallyl-dimethylammoniumchlorid
• wasserlöslichen, mit Epichlorhydrin vernetzten Polyamidoaminen
• wasserlöslichen, mit Ethylenimin gepfropften und mit Bis-chlorhydrinethem von Polyalkylenglykolen vernetzten Polyamidoaminen und/oder
• wasserlöslichen Polyethyleniminen und wasserlöslichen, vernetzten Polyethyleniminen

bei Temperaturen oberhalb der Verkleisterungstemperatur der Stärken bis 180°C.Other preferred cationic starches are obtainable, for example, by reacting 100 parts by weight of a native, cationic, anionic and / or amphoteric starch with 0.5 to 10 parts by weight

• Polydiallyl dimethyl
• water-soluble, with epichlorohydrin cross-linked polyamidoamines
• water-soluble, with ethyleneimine grafted and crosslinked with bis-chlorohydrinethem of polyalkylene glycols polyamidoamines and / or
• water-soluble polyethyleneimines and water-soluble, crosslinked polyethyleneimines

at temperatures above the gelatinization temperature of the starches up to 180 ° C.

The starches to be used as dry strength agents are used in amounts of from 0.5 to 10, preferably from 1 to 5,% by weight, based on dry paper stock. The dewatering of the paper stock is carried out according to the invention always in the presence of at least one polymers containing vinylamine units as a retention aid for starch, wherein the retention agents are used in amounts of 0.01 to 0.3 wt .-%, based on dry paper pulp. This results in a considerably improved retention of the starch and an increase in the dewatering rate of the paper stock on the paper machine compared to the known methods.

As a retention aid for starch, it is also possible to use so-called microparticle systems in which a high molecular weight cationic synthetic polymer is added to the paper stock, the macroflakes formed are cut by shearing the stock and then bentonite is added. This method is for example from the EP-A-0 335 575 known. For such a microparticle system, cationic polymers used are a mixture of a polymer comprising vinylamine units, for example polyvinylamine and a cationic polyacrylamide, for example a copolymer of acrylamide and dimethylaminoethyl acrylate methochloride, and bentonite after the shear stage. Further preferred combinations of cationic polymers as retention aids for starches are mixtures of polymers containing vinylamine units and crosslinked polyamidoamines grafted with ethyleneimine and mixtures of polymers containing vinylamine units with polydiallyldimethylammonium chlorides.

Unless otherwise indicated, percentages in the examples are percent by weight. The K values were after H. Fikentscher, Cellulose Chemistry, Vol. 13, 58-64 and 71-74 (1932 ) at a temperature of 25 ° C in aqueous solution at a polymer concentration of 0.5 wt .-% determined.

Examples

The following cationic polymers were used:

Polymer 1:

Polyamidoamine of adipic acid and diethylenetriamine grafted with .. Ethylenimin and then with polyethylene glycol dichlorohydrin as described in Example 3 of DE-B-2 434 816 was networked.

Polymer 2:

Hydrolyzed polyvinylformamide having a K value of 90 and a degree of hydrolysis of 95 mol%.

Polymer 3:

Hydrolyzed polyvinylformamide having a K value of 90 and a degree of hydrolysis of 75 mol%.

Polymer 4:

Hydrolyzed polyvinylformamide having a K value of 90 and a degree of hydrolysis of 50 mol%.

Consolidator 1

An aqueous suspension of native potato starch was cooked continuously in the presence of 1.5% polymer 2 in a laboratory jet cooker from Werkstättenbau GmbH at a temperature of 130 ° C. and a pressure of 2.3 bar.

Examples 1 to 4

A paper stock having a stock consistency of 7.6 g / l was prepared from an open finished commercial wave raw material based on recovered paper. The pH of the stock was 8.0. In order to determine the starch retention, in each case the amounts of solidifier 1 and the polymers 1-4 indicated in Table 1 were added in succession to samples of this paper stock. After mixing the paper stock with the additives, it was filtered off with suction and the starch content was determined from the absorbance measurement of the starch-iodine complex. The results obtained are shown in Table 1. Another part of the paper stock was dewatered after metering solidifier 1 and the polymers indicated in Table 1 in each case with the aid of a Schopper-Riegler apparatus. The dewatering time was determined according to DIN ISO 5267 for 700 ml filtrate. The results are given in Table 1, Example 1 being a comparison.

Comparative Example 1

Example 1 was repeated with the exception that only solidifier 1 in an amount of 2%, based on dry pulp, metered to the pulp. Starch content of the filtrate and the dewatering time are shown in Table 1. Table 1 example Additive to paper stock, based on dry stock Starch content in the filtrate [mg / l] Drainage time [sec / 700 ml] 1 (comparison) 2% strength agent 1 + 0.08% polymer 1 38 92 2 2% strength agent 1 + 0.08% polymer 2 34 49 3 2% strength agent 1 + 0.08% polymer 3 30 55 4 2% strength agent 1 + 0.08% polymer 4 30 67 Comparative example 1 2% strength agent 1 50 136

Example 5

An open finished commercial wave raw material based on waste paper with a consistency of 0.76% was first mixed with 2% strength agent 1 and then with 0.08% polymer 3 as a cationic starch retention aid. After addition of solidifier and polymer, the stock was mixed in each case. Part of this pulp was sucked off. From the filtrate, the COD value and the starch retention by enzymatic degradation to glucose were determined by HPLC. From the other part of the pulp, the dewatering time for 500 ml of filtrate was determined using a Schopper-Riegler apparatus. The results are shown in Table 2.

Comparative Examples 2 to 4

Example 5 was repeated with the changes shown in Table 2. The results are shown in Table 2. Table 2 example Additive to paper stock, based on dry stock COD value [mgO ₂ / l] Strong retention (enzymatic method) Drainage time [sec / 500 ml] 5 2% strength agent 2 + 0.08% polymer 3 134 93 20 Comparative example 2 2% strength agent 1 313 43 72 3 2% commercial cationic starch DS 0.035 162 92 78 4 - 135 68

Example 6

An open finished commercial wave raw material based on waste paper with a substance concentration of 0.76% was successively mixed with 2% strength promoter 2 and 0.08% polymer 3. After mixing, paper sheets having a basis weight of 120 g per m ^{2 are} produced on a Rapid-Köthen sheet former. The sheets were tested for dry strength, namely the dry tear length according to DIN ISO 1924, dry burst pressure according to DIN ISO 2758 and flat crush resistance CMT according to DIN EN 23035 equal to ISO 3035. The results are given in Table 3.

Comparative Examples 5 to 7

First, Example 6 was repeated with the changes shown in Table 3, working in the absence of Polymer 3 (Comparative Example 5). In further tests, commercial cationic starch (Comparative Example 6) was used and found to be zero (Comparative Example 7). The results are shown in Table 3. Table 3 example Additive to paper stock, based on dry stock Dry breaking length [m] Dry burst pressure [kPa] CMT [N] 6 2% strength agent 1 + 0.08% polymer 3 4433 296 209 Comparative example 5 2% strength agent 1 4353 278 190 6 2% commercial cationic starch DS 0.035 4488 296 194 7 - 3757 241 160

Polymer 5:

Hydrolyzed poly-N-vinylformamide having a K value of 90 and a degree of hydrolysis of 30%.

Polymer 6:

High molecular weight, cationic polyacrylamide with a charge density of 1.7 at pH 4.5 and an average molecular weight of 8.5 million D.

Example 7

A waste paper stock having a COD of 8000 mg oxygen / l and a 1% stock concentration was sequentially added with 2% Solidifier 1, 0.12% Polymer 2, and 0.02% Polymer 6. After mixing, paper sheets with a basis weight of about 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The sheets were tested for dry strength, namely the strip crush resistance (SCT) value according to DIN 54518 (ISO 9895), dry burst pressure according to DIN ISO 2758 and flat crush resistance CMT according to DIN EN 23035 (ISO 3035). The results are shown in Table 4

Example 8

A paper stock based on waste paper with a COD of 8000 mg oxygen / l and a substance concentration of 1% was added successively with 2% strength agent 1, with 0.12% polymer 3 and 0.02% polymer 6. After mixing, paper sheets with a basis weight of about 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for dry strength by the methods given in Example 7. The results are shown in Table 4.

Example 9

A paper stock based on waste paper with a COD of 8000 mg oxygen / l and a substance concentration of 1% was added successively with 2% strength agent 1, with 0.13% polymer 4 and 0.02% polymer 6. After mixing, paper sheets with a basis weight of about 110 g / m ² are placed on the Rapid-Köthen sheet former ago. The leaves were tested for dry strength by the methods given in Example 7. The results are shown in Table 4.

Example 10

A paper stock based on waste paper with a COD of 8000 mg oxygen / l and a substance concentration of 1% was added successively with 2% strength agent 1, with 0.13% polymer 5 and 0.02% polymer 6. After mixing, paper sheets with a basis weight of about 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for dry strength by the methods given in Example 7. The results are shown in Table 4.

Comparative Example 8

A paper stock based on recovered paper with a COD of 8000 mg oxygen / l and a substance concentration of 1% was added successively with 2% strength agent 1 and 0.02% polymer 6. After mixing, paper sheets with a basis weight of about 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for dry strength by the methods given in Example 7. The results are shown in Table 4. Table 4 example Additive to the pulp; based on dry pulp COD value of the filtrate (mg O ₂ / l) Intensive retention (enzymatic method) in% of the starch offered Stripping resistance to 110 g / m ² Dry burst pressure (kPa) to 110 g / m ² CMT (N) to 110 g / m ² 7 2% solidifier 1, 0.12% polymer 2 and 0.02% polymer 6 7680 87 2, 87 295 172 8th 2% solidifier 1, 0.12% polymer 3 and 0.02% polymer 6 6860 91 2.86 280 174 9 2% solidifier 1, 0.13% polymer 4 and 0.02% polymer 6 7020 86 2.81 289 177 10 2% strength modifier 1, 0.13% polymer 5 and 0.02% polymer 6 7010 94 2.83 296 166 Comparative Example 8 2% solidifier 1, and 0.02% polymer 6 7180 66 2.77 282 172

Claims (11)

1. A process for the production of paper, board and cardboard having high dry strength by the addition of starch which is obtainable by reacting natural, cationic, anionic and/or amphoteric starch with synthetic cationic polymers as a dry strength agent to the paper stock and drainage of the paper stock in the presence of retention aids with sheet formation, wherein polymers containing cationic vinylamine units are used as a retention aid for starch.
2. A process as claimed in claim 1, wherein a cationic starch is used in combination with cationic polymers which contain vinylamine units and have K values of at least 30 (determined according to H. Fikentscher in aqueous solution at a polymer concentration of 0.5 % by weight, at 25°C and at a pH of 7).
3. A process as claimed in claim 1 or 2, wherein a cationic starch which is obtainable by reacting 100 parts by weight of a natural, cationic, anionic or amphoteric starch with from 0.5 to 10 parts by weight of a polymer containing vinylamine units and having a K value of from 60 to 150 at above the glutinization temperature of the starch is used.
4. A process as claimed in claim 3, wherein hydrolyzed homo- or copolymers of N-vinylformamide having a degree of hydrolysis of at least 60 % are used as the polymers containing vinylamine units.
5. A process as claimed in any of claims 1 to 4, wherein hydrolyzed homo- or copolymers of N-vinylformamide having a degree of hydrolysis of from 1 to 100 % are used as retention aids for starch.
6. A process as claimed in any of claims 1 to 5, wherein the dry strength agents are used in amounts of from 0.5 to 10 % by weight, based on dry paper stock.
7. A process as claimed in any of claims 1 to 6, wherein the dry strength agents are used in amounts of from 1 to 5 % by weight, based on dry paper stock.
8. A process as claimed in any of claims 1 to 7, wherein the retention aids for starch are used in amounts of from 0.01 to 0.3 % by weight, based on dry paper stock.
9. A process as claimed in claim 1 or 2, wherein a cationic starch which is obtainable by reacting 100 parts by weight of a natural, cationic, anionic or amphoteric starch with from 0.5 to 10 parts by weight of

   - polydiallyl-dimethylammonium chloride,

   - water-soluble polyamidoamines crosslinked with epichlorohydrin

   - water-soluble ethyleneimine-grafted polyamidoamines crosslinked with bischlorohydrin ethers of polyalkylene glycols or

   - water-soluble polyethyleneimines and water-soluble crosslinked polyethyleneimines

   at from above the glutinization temperature of the starch to 180°C is used.
10. The use of polymers containing vinylamine units as cationic polymeric retention aid for increasing the retention of dry strength agents comprising starch which is obtainable by reacting natural, cationic, anionic and/or amphoteric starch with synthetic cationic polymers in the production of paper, board and cardboard.
11. The use as claimed in claim 10, wherein hydrolyzed homo- or copolymers of N'-vinylformamide having a degree of hydrolysis of from 1 to 100 % and a K value of at least 30 (determined according to H. Fikentscher in aqueous solution at a polymer concentration of 0.5 % by weight, at 25°C and at a pH of 7) are used as retention aids in amounts of from 0.01 to 0.3 % by weight.