EP0972110B1 - 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 method for producing paper, Cardboard and cardboard with high dry strength by adding cationic, anionic and / or amphoteric starch as a dry strength agent for paper stock and dewatering of the paper stock with leaf formation.

To increase the dry strength of paper, e.g. out Ullmann's Encyclopedia of Technical Chemistry, 4th edition, publisher Chemie, Weinheim - New York, 1979, volume 17, page 581, known, aqueous slurries of native starches by heating be converted into a water-soluble form as a mass additive use in the manufacture of paper. The retention of in Starch is dissolved in water to the paper fibers in the paper stock however slight. An improvement in the retention of natural products of cellulose fibers in the manufacture of paper, for example known from US-A-3 734 820. It contains graft copolymers described by grafting dextran, one in the naturally occurring polymer with a molecular weight from 20,000 to 50 million, with cationic monomers, e.g. 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 In the presence of a redox catalyst.

From US-A-4 097 427 is a process for cationization of starch, where you can cook the starch in one alkaline medium in the presence of water-soluble quaternary Performs ammonium polymers and an oxidizing agent. As quaternary ammonium polymers include also quaternized Diallyldialkylaminopolymerisate or quaternized polyethyleneimines into consideration. The oxidizing agent used is, for example Ammonium persulfate, hydrogen peroxide, sodium hypochlorite, Ozone or tert-butyl hydroperoxide. The ones that can be produced in this way modified cationic starches are used as dry strength agents in the manufacture of paper the paper stock added. However, the wastewater is very high COD (chemical oxygen demand) burdened.

From US-A-4 146 515 a method for the production of cationic starch known for surface sizing and coating of paper and paper products is used. According to This process uses an aqueous slurry of oxidized Starch together with a cationic polymer in a continuous Cooker open minded. Coming as cationic polymers Condensates of epichlorohydrin and dimethylamine, polymers of diallyldimethylammonium chloride, quaternized reaction products of ethylene chloride and ammonia as well as quaternized Polyethyleneimine into consideration.

From US-A-3 467 608 is a method for producing a cationic starch known as a slurry of Starch in water together with a polyalkyleneimine or polyalkylene polyamine with a molecular weight of at least 50,000 to a temperature of about 70 to about 0.5 to 5 hours Heated to 110 ° C. The mixture contains 0.5 to 40 wt .-% polyalkyleneimine or polyalkylene polyamine and 99.5 to 60% by weight starch. According to Example 1, a polyethyleneimine with an average Molecular weight of about 200,000 in dilute aqueous Potato starch solution at temperature for 2 hours heated from 90 ° C. The modified potato starch can be in one Mixture of methanol and diethyl ether can be precipitated. In the of the reaction products of starch and described in US-A-3,467,608 Polyethyleneimine or polyalkylene polyamines are used as flocculants used.

Manufacturing processes are known from EP-A-0 282 761 and DE-A-3 719 480 for paper, cardboard and cardboard with high dry strength known. This process is used as a dry strength agent Implementation products used by heating native Potato starch with cationic polymers such as vinylamine, Containing N-vinylimidazoline or diallyldimethylammonium units Polymers or polyethyleneimines in an aqueous medium Temperatures above the gelatinization temperature of the starch in Absence of oxidizing agents, polymerization initiators and Alkali are available.

Such a process is known from EP-B-0 301 372, at the correspondingly modified, enzymatically degraded starches for Come into play. Under the digestion conditions specified there for native starch is next to an incomplete digestion (Spectroscopic studies show unresolved, sometimes only swollen starch granules) also a larger amount of breakdown products (Degradation rates> 10%) found.

A process is known from US-A-4 880 497 and US-A-4 978 427 for the production of paper with high dry and wet strength known, either on the surface of the paper or a hydrolyzed to the paper stock before sheet formation Add copolymer as a solidifying agent by copolymerization of N-vinylformamide and ethylenically unsaturated Monomers such as vinyl acetate, vinyl propionate or Alkyl vinyl ether and hydrolyzing from 30 to 100 mol% of the Formyl groups of the copolymer with formation of amino groups is available. The hydrolyzed copolymers are in quantities from 0.1 to 5% by weight, based on dry fibers.

DE-A-4 127 733 describes hydrolyzed graft polymers of Natural products containing N-vinylformamide and saccharide structures known to apply as a dry and wet strength agent Find. Hydrolysis of the graft polymers under acidic conditions However, the polysaccharides have a strong molecular weight reduction result.

WO-A-96/13525 describes a method for cationic modification of starch by reacting starch with polymers that Amino and / or ammonium groups contain in an aqueous medium Temperatures 115 to 180 ° C known under increased pressure, wherein a maximum of 10% by weight of the starch used can be broken down.

HR Hernandez describes in EUCEPA 24 ^th Cont.Proc.Pap.Technol., May 1990, pages 186-195 the use of cationic or amphoteric starch together with cationic or anionic retention agents 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.

If you add a cationically modified starch to the paper stock as a dry strength agent, an undesirable occurs Decrease in the drainage rate of the paper stock on. At the same time, an increase in the COD value is observed Waste water from the paper machine. This increase in COD occurs especially with heavily saline paper machine wastewater.

The invention is therefore based on the object of a method for Manufacture of paper, cardboard and cardboard with high dry strength to provide, with increased retention of starch in paper and therefore lower COD values in paper machine waste water reached and also compared to the stand the technology an acceleration of the drainage speed is achieved.

• Vinylamineinheiten enthaltende Polymere
• Polyethylenimine
• vernetzte Polyamidoamine
• mit Ethylenimin gepfropfte und vernetzte Polyamidoamine
• Polydiallyldimethylammoniumchloride
• N-Vinylimidazolineinheiten enthaltende Polymere
• Dialkylaminoalkylacrylat- oder Dialkylaminoalkylmethacrylat enthaltende Polymere
• Dialkylaminoalkylacrylamid-Einheiten oder Dialkylaminoalkylmethacrylamid-Einheiten enthaltende Polymere und
• Polyallylamine

einsetzt.The object is achieved according to the invention with a process for the production of paper, cardboard and cardboard with high dry strength by adding cationic, anionic and / or amphoteric starch as a dry strength agent for the paper stock and dewatering the paper stock in the presence of retention agents with sheet formation, if at least for starch a cationic polymer from the group of

• Polymers containing vinylamine units
• polyethyleneimines
• cross-linked polyamidoamines
• Polyamidoamines grafted and crosslinked with ethyleneimine
• polydiallyldimethylammonium
• Polymers containing N-vinylimidazoline units
• Polymers containing dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate
• Polymers containing dialkylaminoalkyl acrylamide units or dialkylaminoalkyl methacrylamide units and
• polyallylamine

starts.

• Vinylamineinheiten enthaltenden Polymere
• Polyethylenimine
• vernetzten Polyamidoamine
• mit Ethylenimin gepfropften und vernetzten Polyamidoamine
• Polydiallyldimethylammoniumchloride
• N-Vinylimidazolineinheiten enthaltenden Polymere
• Dialkylaminoalkylacrylat- oder Dialkylaminoalkylmethacrylat enthaltende Polymere
• Dialkylaminoalkylacrylamid-Einheiten oder Dialkylaminoalkylmethacrylamid-Einheiten enthaltenden Polymere und
• Polyallylamine

zur Erhöhung der Retention von Trockenfestigkeitsmitteln aus kationischer, anionischer und/oder amphoterer Stärke bei der Herstellung von Papier, Pappe und Karton. Besonders bevorzugt ist die Verwendung von hydrolysierten Homo- oder Copolymerisaten von N-Vinylformamid mit einem Hydrolysegrad von 1 bis 100 % und einem K-Wert von mindestens 30 (bestimmt nach H. Fikentscher in wäßriger Lösung bei einer Polymerkonzentration von 0,5 Gew.-%, einer Temperatur von 25°C und einem pH-Wert von 7) in Mengen von 0,01 bis 0,3 Gew.-%, bezogen auf trockenen Papierstoff, als Retentionsmittel für kationische, anionische und/oder amphotere Stärke.The invention also relates to the use of cationic polymeric retention agents from the group of

• Polymers containing vinylamine units
• polyethyleneimines
• cross-linked polyamidoamines
• Polyamidoamines grafted and crosslinked with ethyleneimine
• polydiallyldimethylammonium
• Polymers containing N-vinylimidazoline units
• Polymers containing dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate
• Dialkylaminoalkylacrylamid units or dialkylaminoalkyl methacrylamide units containing polymers and
• polyallylamine

to increase the retention of dry strength agents made of cationic, anionic and / or amphoteric starch in the manufacture of paper, cardboard and cardboard. The use of hydrolyzed homo- or copolymers of N-vinylformamide with 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) is particularly preferred. %, a temperature of 25 ° C and a pH of 7) in amounts of 0.01 to 0.3 wt .-%, based on dry paper stock, as a retention agent for cationic, anionic and / or amphoteric starch.

All of them come as fibrous materials for the production of the pulps common qualities, e.g. Wood pulp, bleached and unbleached pulp and pulp from all annual plants. For example, wood pulp includes thermomechanical substance (TMP), chemothermomechanical substance (CTMP), pressure cut, semi-pulp, high-yield pulp and Refiner Mechanical Pulp (RMP). As pulp come for example Sulphate, sulphite and sodium pulp into consideration. suitable Annual plants for the production of paper materials are, for example Rice, wheat, sugar cane and kenaf. For the production the pulp is also used alone or as a mixture with waste paper other fibers used. Waste paper also includes so-called deleted committee, due to the content of binder for coating and printing inks gives rise to the white pitch. The so-called stickies give rise to stickies and envelopes derived from glue and adhesives from the back sizing of books and so-called hotmelts.

The fiber materials mentioned can be used alone or as a mixture with one another be used. The pulps of the above Art contain varying amounts of water-soluble and water-insoluble Impurities. The contaminants can, for example with the help of the COD value or also with the help of the so-called cationic needs are recorded quantitatively. Under cationic The quantity of a cationic is required Polymers understood that is necessary to a defined amount to bring the white water to the isoelectric point. Because the cationic Requires very much from the composition of each depends on the cationic polymers used for the determination, is used for standardization according to Example 3 of DE-B-2 434 816 condensation product obtained by Grafting a polyamidoamine from adipic acid and diethylene triamine with ethyleneimine and subsequent crosslinking with a polyethylene glycol dichlorohydrin ether is available. The contaminants containing pulps have, for example, COD values of 300 to 40,000, preferably 1,000 to 30,000 mg of oxygen per kg of aqueous phase and a cationic requirement of more than 50 mg of the cationic polymer mentioned per liter of white water.

Cationic, anionic and amphoteric starches are known and available in the stores. For example, cationic strengths by implementing native strengths with quaternizing agents such as 2,3- (epoxypropyl) trimethylammonium chloride. Strength and starch derivatives are described in detail, for example in the book by Günther Tegge, starch and starch derivatives, Behr's Verlag, Hamburg 1984.

Starches are particularly preferred as dry strength agents used by the implementation of native, cationic, anionic and / or amphoteric starch with synthetic cationic Polymers are available. One can, for example, as native strengths Corn starch, potato starch, wheat starch, rice starch, Tapioca starch, sago starch, sorghum starch, cassava starch, pea starch, Rye starch or mixtures of the named native Use strengths. Rye flour and others come as a starch Flour into consideration. Proteins containing proteins are also suitable Starches from rye, wheat and legumes. For the cationic Modification with polymers also come native Starches that have an amylopectin content of at least 95% by weight. Starches containing are preferred Amylopectin of at least 99% by weight. Such strengths can for example by starch fractionation of common native starches or obtained from plants through breeding measures, which produce practically pure amylopectin starch. Strengthen with an amylopectin content of at least 95, preferably at least 99% by weight is available on the market. you will be for example as waxy corn starch, wax potato starch or Waxy wheat starch offered. The native strengths can either modified alone or in a mixture with cationic polymers become.

Modifying native strengths as well as cationic, anionic and / amphoteric starch with synthetic cationic Polymers are made according to known methods by heating Starches in an aqueous medium in the presence of cationic polymers to temperatures above the gelatinization temperature of the Strengthen. Methods of this type are, for example, from the References cited in the prior art EP-B-0 282 761 and WO-A-96/13525. For the cationic modification of the Above mentioned strengths come in all synthetic polymers Consider that contain amino and / or ammonium groups. This Compounds are referred to below as cationic polymers designated.

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, homo- and copolymers containing vinylamine units. Polymers of this type are obtained by known processes by polymerizing N-vinylcarboxamides of the formula

in which R and R ^{1 are the} same 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 to form units of the formula

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

1) 99 bis 1 Mol-% N-Vinylcarbonsäureamide der Formel (I) und

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. Polyglykolestern 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-vinyl acetamide, N-vinyl-N-ethyl acetamide and N-vinyl-N-methyl propionamide , N-vinylformamide is preferably used in the preparation of polymers which contain units of the formula (III) in copolymerized form. The hydrolyzed polymers which contain 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% by weight. Copolymers of the monomers (I) contain, for example

1) 99 to 1 mol% of N-vinylcarboxamides of the formula (I) and

2) 1 to 99 mol% of other monoethylenically unsaturated monomers copolymerizable therewith,

such as, for example, vinyl esters of saturated carboxylic acids having 1 to 6 carbon atoms, for example vinyl formate, vinyl acetate, vinyl propionate and vinyl butyrate. Unsaturated C ₃ - to C ₆ -carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, crotonic acid, itaconic acid and vinyl acetic 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, are also suitable - or polyglycol esters of ethylenically unsaturated carboxylic acids, in each case only one OH group of the glycols and polyglycols being esterified, for example hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate and the acrylic acid monoesters of 1,500 molexylene glycols of a polyalkylene glycol of 1,500 moles of polyalkylene glycol. Also suitable are the esters of ethylenically unsaturated carboxylic acids with amino alcohols, such as, for example, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropylacrylate, dimethylaminopropyl methacrylate, diethylaminopropylacrylate, diethylaminopropylaminatylaminate aminobutyl acrylate, diethylaminopropyl methacrylate, 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 2) are 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 N-methyl acrylamide, N, N-dimethylacrylamide, N-methyl methacrylamide, N-ethyl acrylamide, N-propylacrylamide and tert-butyl acrylamide as well basic (meth) acrylamides, e.g. dimethylaminoethyl, Dimethylaminoethyl methacrylamide, diethylaminoethyl acrylamide, Diethylaminoethyl methacrylamide, dimethylaminopropylacrylamide, Diethylaminopropylacrylamide, dimethylaminopropylmethacrylamide and Diethylaminopropylmethacrylamide.

Also suitable as comonomers are N-vinylpyrrolidone, N-vinylcaprolactam, acrylonitrile, methacrylonitrile, N-vinylimidazole as well as substituted N-vinylimidazoles such as e.g. N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole, N-vinyl-5-methylimidazole, N-vinyl-2-ethylimidazole, and N-vinylimidazolines such as e.g. vinylimidazoline, N-vinyl-2-methylimidazoline, and N-vinyl-2-ethylimidazoline. N-vinylimidazoles and N-vinylimidazolines are excluded in the form of the free bases also with mineral acids or organic Acids neutralized or used in quaternized form, the quaternization preferably using dimethyl sulfate, Diethyl sulfate, methyl chloride or benzyl chloride is made.

In addition, the comonomers 2) contain sulfo groups Monomers such as vinylsulfonic acid, allylsulfonic acid, Methallylsulfonic acid, styrene sulfonic acid or 3-sulfopropyl acrylate in question.

When using basic comonomers 2) such as e.g. basic acrylic esters and amides can often be due to hydrolysis the N-vinylcarboxamides are dispensed with. The copolymers include terpolymers and those polymers that additionally contain at least one further monomer in copolymerized form.

1) N-Vinylformamid und

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 of

1) N-vinylformamide and

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

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

Ethyleneimine units also come as cationic polymers polymerized-containing compounds into consideration. Preferably these are polyethyleneimines, which by polymerize 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 a viscosity of 500 to 33,000, preferably 1,000 up to 31,000 mPa · s (measured according to Brookfield at 20 ° C and 20 RPM). The polymers in this group also include those grafted with ethyleneimine Polyamidoamines, which may still be by reaction can be crosslinked with an at least bifunctional crosslinker. Products of this type are, for example, condensed a dicarboxylic acid such as adipic acid with a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine, if appropriate Grafting with ethyleneimine and reacting with at least one bifunctional crosslinker, e.g. Bischlorohydrin ether of polyalkylene glycols manufactured, cf. US-A-4 144 123 and US-A-3 642 572.

Starch modification also includes poly-diallyldimethylammonium chlorides into consideration. Polymers of this type are known. Among polymers of diallyldimethylammonium chloride should primarily homopolymers and copolymers with Acrylamide and / or methacrylamide can be understood. The copolymerization can be made in any monomer ratio become. 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.Homopolymers and copolymers of optionally substituted N-vinylimidazolines are also suitable as cationic polymers. These are also known substances. They can be prepared, for example, by the process of DE-B-1 182 826 in that 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 ^{- is} an acid residue, optionally together with acrylamide and / or methacrylamide are polymerized in an aqueous medium at pH values from 0 to 8, preferably from 1.0 to 6.8, in the presence of polymerization initiators which break down into free radicals.

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 residue. 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 acid residue 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, for example, with trichloroacetic acid, benzenesulfonic acid or toluenesulfonic acid. In addition to salts of 1-vinyl-2-imidazolines, quaternized 1-vinyl-2-imidazolines can also be used. They are prepared by reacting 1-vinyl-2-imidazolines, which may optionally be substituted in the 2-, 4- and 5-position, with known quaternizing agents. Examples of suitable quaternizing agents are C ₁ -C ₁₈ -alkyl chlorides or bromides, benzyl chloride or bromide, epichlorohydrin, dimethyl sulfate and diethyl sulfate. Epichlorohydrin, benzyl chloride, dimethyl sulfate and methyl chloride are preferably used.

To produce the water-soluble homopolymers, the Compounds of the formulas (IV) or (V) preferably in aqueous Medium polymerizes.

1) 70 bis 97 Gew.-% Acrylamid und/oder Methacrylamid,

2) 2 bis 20 Gew.-% N-Vinylimidazolin oder N-Vinyl-2-methylimidazolin und

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. 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 are particularly suitable for modifying native starches. The copolymers can also be polymerized by copolymerizing other monomers such as styrene, N-vinylformamide, vinyl formate, vinyl acetate, vinyl propionate, C ₁ -C ₄ -alkyl vinyl ether, N-vinyl pyridine, N-vinyl pyrrolidone, N-vinyl imidazole, ethylenically unsaturated C ₃ -C _5- carboxylic acids and their esters, amides and nitriles, sodium vinyl sulfonate, vinyl chloride and vinylidene chloride can be modified in amounts of up to 25% by weight. For example, one can use copolymers for the modification of native starches

1) 70 to 97% by weight of acrylamide and / or methacrylamide,

2) 2 to 20% by weight of N-vinylimidazoline or N-vinyl-2-methylimidazoline and

3) 1 to 10% by weight of N-vinylimidazole

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

Copolymers also come as cationic polymers from 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 in Question, e.g. Copolymers of acrylamide and N, N-dimethylaminoethyl acrylate or N, N-diethylaminoethyl acrylate. Basic acrylates are preferably in neutralized with acids or in quaternized Form before. Quaternization can, 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% aqueous Saline at 25 ° C and a polymer concentration of 0.5% by weight). At pH 4.5 they have a charge density of at least 4 meq / g polyelectrolyte.

Copolymers of 1 to 99 mol% are also suitable, preferably 30 to 70 mol% of acrylamide and / or methacrylamide and 99 to 1 mol%, preferably 70 to 30 mol% of dialkylaminoalkylacrylamide and / or methacrylamide. The basic acrylamides and methacrylamides are also preferably in neutralized with acids or in quaternized form. Examples are given N-trimethylammonium ethyl acrylamide chloride, N-trimethylammonium ethyl methacrylamide chloride, Trimethylammoniumethylacrylamidmethosulfat, Trimethylammonium ethyl methacrylamide methosulfate, N-ethyldimethylammonium ethyl acrylamide ethosulfate, N-Ethyldimethylammoniumethylmethacrylamidethosulfat, Trimethylammoniumpropylacrylamidchlorid, Trimethylammonium propyl methacrylamide chloride, trimethylammonium propyl acrylamide methosulfate, Trimethylammoniumpropylmethacrylamidmethosulfat and N-ethyldimethylammonium propylacrylamide ethosulfate. Trimethylammonium propyl methacrylamide chloride is preferred.

Polyallylamines are also suitable as cationic polymers. Polymers of this type are obtained by homopolymerization of allylamine, preferably in acid neutralized or in quaternized form or by copolymerizing allylamine with other monoethylenically unsaturated monomers, accordingly of the copolymers described above with N-vinylcarboxamides.

For the cationic modification of starch according to the invention for example an aqueous suspension of at least one type of starch with one or more of the cationic polymers Temperatures above the gelatinization temperature of the native or the modified starches, e.g. to temperatures of 90 to 180 ° C, preferably 115 to 145 ° C. At temperatures above of the boiling point of water, the reaction is increased Pressure carried out, the reaction being carried out in the manner is that at a maximum of 10 wt .-% of the starch a molecular weight reduction entry. For example, aqueous starch slurries contain per 100 parts by weight of water 0.1 to 10, preferably 2 to 6 parts by weight of starch. For example, 100 parts by weight of starch is used. 0.5 up to 10 parts by weight of at least one cationic polymer. Partially or preferably come as cationic polymers fully hydrolyzed homo- or copolymers of N-vinylformamide, Polyethyleneimines, grafted with ethyleneimine and crosslinked polyamidoamines and / or polydiallyldimethylammonium chlorides into consideration.

When heating the aqueous starch suspensions in the presence of The starch is first digested by cationic polymers. Starch is the transfer of the fixed Starch grains in a water-soluble form, with superstructures (Helix formation, intramolecular hydrogen bonds, etc.) canceled be without the degradation of those who build strength Amylose and / or amylopectin units to oligosaccharides or Glucose is coming. The aqueous starch suspensions, which are cationic Contain polymer dissolved, are in the implementation Temperatures above the gelatinization temperature of the starches heated. In the method according to the invention, the one used At least 90, preferably> 95% by weight of starch digested and modified with the cationic polymer. The strength is clearly resolved. Preferably you can go to the conversion of the starch from the reaction solution in use a cellulose acetate membrane with a pore diameter of 1.2 µm no more filter unreacted starch.

The reaction is preferably carried out at elevated pressure. in this connection it is usually the pressure that the reaction medium in the temperature range above the boiling point of water, e.g. developed at 115 to 180 ° C. For example, it lies at 1 to 10, preferably 1.2 to 7.9 bar. During the implementation the reaction mixture is subjected to shear. If one If the reaction is carried out in a stirred autoclave, this is stirred Reaction mixture, for example with 100 to 2,000, preferably 200 to 1,000 revolutions / minute. The reaction can be practical be carried out in all equipment in which starch in open to technology, e.g. in a jet cooker. The Residence times of the reaction mixture at the above temperatures from 115 to 180 ° C, for example, 0.1 seconds to 1 hour and is preferably in the range of 0.5 seconds up to 30 minutes.

Under these conditions, at least 90% of the used Strength open-minded and modified. Preferably be less than 5% by weight of the starch is broken down.

The native starch types can also be pretreated e.g. degraded oxidatively, hydrolytically or enzymatically or be chemically modified. Here too are Wax starches, such as waxy potato starch and waxy corn starch from of special interest.

The reaction products obtainable in this way have, for example a viscosity at a solids concentration of 3.5% by weight from 50 to 10,000, preferably 80 to 4,000 mPa · s, measured in a Brookfield viscometer at 20 rpm and one 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 so available modified with cationic polymers Starches are used as dry strength agents in paper pulp Amounts of, for example, 0.5 to 10, preferably 0.5 to 3.5 and particularly preferably 1.2 to 2.5% by weight, based on dry Paper stock, added. According to the invention, one doses to Pulp additionally a cationic polymer as a retention agent for the strengths described above, such as cationic Starch, preferably those starches modified with a polymer were, anionic and / or amphoteric starches. Preferably first meter the dry strength agent and then the Retention agents. However, it is also possible to use dry strength agents and adding retention aids to the paper stock at the same time, whereby dry strength agent and retention aid are separated from one another be dosed. It is also possible to choose a mix Dosage of dry strength agents and retention aids to the paper. Such mixtures can be produced, for example, by this be that the retention agent of the digested starch after cooling to 50 ° C or below. The retention aid can also before adding the modified starch Paper stock can be added. From this order of addition is done, for example, when processing paper stock Use that have a high content of contaminants.

• Vinylamineinheiten enthaltende Polymere
• Polyethylenimine
• vernetzte Polyamidoamine
• mit Ethylenimin gepfropfte und vernetzte Polyamidoamine
• Polydiallyldimethylammoniumchloride
• N-Vinylimidazolineinheiten enthaltende Polymere
• Dialkylaminoalkylacrylat- oder Dialkylaminoalkylmethacrylat enthaltende Polymere
• Dialkylaminoalkylacrylamid-Einheiten oder Dialkylaminoalkylmethacrylamid-Einheiten enthaltende Polymere und
• Polyallylamine.

All cationic polymers which have already been described above for the cationic modification of native starch can be used as cationic polymers which can be considered as retention agents for starch

• Polymers containing vinylamine units
• polyethyleneimines
• cross-linked polyamidoamines
• Polyamidoamines grafted and crosslinked with ethyleneimine
• polydiallyldimethylammonium
• Polymers containing N-vinylimidazoline units
• Polymers containing dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate
• Polymers containing dialkylaminoalkyl acrylamide units or dialkylaminoalkyl methacrylamide units and
• Polyallylamine.

Condensates of dimethylamine and epichlorohydrin are also suitable, Condensates of dimethylamine and dichloroalkanes such as Dichloroethane or dichloropropane and condensation products Dichloroethane and ammonia.

In a preferred embodiment of the invention The process uses a cationic starch in combination with cationic polymers containing vinylamine units and the K values 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).

A cationic is preferably used as the dry strength agent Strength that is available through implementation of 100 parts by weight of a native, cationic, anionic and / or amphoteric starch with 0.5 to 10 parts by weight of a vinylamine unit containing polymers with a K value of 60 to 150 at temperatures above the gelatinization temperature of the Strength. Polymers containing vinylamine units are e.g. hydrolyzed homo- and copolymers of N-vinylformamide with a degree of hydrolysis of at least 60% is preferably used. These homopolymers and copolymers are not only used for cationization of starch but also the paper stock as a retention agent added for the cationically modified starches.

Those considered as retention agents for starch hydrolyzed homo- and copolymers of N-vinylformamide can generally have a degree of hydrolysis of 1 to 100%.

• Polydiallyl-dimethylammoniumchlorid
• wasserlöslichen, mit Epichlorhydrin vernetzten Polyamidoaminen
• wasserlöslichen, mit Ethylenimin gepfropften und mit Bis-chlorhydrinethern 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 polyamidoamines crosslinked with epichlorohydrin
• water-soluble polyamidoamines grafted with ethyleneimine and crosslinked with bis-chlorohydrin ethers of polyalkylene glycols
  and or
• water-soluble polyethyleneimines and water-soluble, crosslinked polyethyleneimines

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

Have preferred commercial cationic starches e.g. a degree of substitution D.S. up to 0.15. As Starches to be used in dry strength agents are given in Amounts of 0.5 to 10, preferably 1 to 5 wt .-%, based on dry paper stock used. The drainage of the paper stock according to the invention always takes place at least in the presence a retention aid for starch, the retention aid in Quantities of 0.01 to 0.3 wt .-%, based on dry paper stock be used. This gives you compared to the known Process significantly improved retention of starch and an increase in the rate of drainage of the paper stock on the paper machine.

So-called microparticle systems can also be used as retention agents for starch use, with the paper stock a high molecular weight cationic synthetic polymer adds to the formed Macro flakes cut up by shearing the paper stock and then adds bentonite. This method is for example known from EP-A-0 335 575. For such a microparticle system can be used, for example, as cationic polymers Mixture of a polymer containing vinylamine units, e.g. Polyvinylamine and a cationic polyacrylamide, e.g. a copolymer of acrylamide and dimethylaminoethyl acrylate methochloride insert and add bentonite after the shear step. Other preferred combinations of cationic polymers as Retention agents for starches are mixtures of vinylamine units containing polymers and grafted with ethyleneimine cross-linked polyamidoamines and mixtures of vinylamine units containing polymers with polydiallyldimethylammonium chlorides.

Unless otherwise stated, the percentages mean weight percent in the examples. The K values were calculated according to H. Fikentscher, Cellulose-Chemie, Volume 13, 58 to 64 and 71 to 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 from adipic acid and diethylene triamine, which with .. Grafted ethyleneimine and then with polyethylene glycol dichlorohydrin ether according to the information in Example 3 DE-B-2 434 816 has been networked.

Polymer 2:

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

Polymer 3:

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

Polymer 4:

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

Solidifier 1

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

Examples 1 to 4

A paper stock with a stock density of 7.6 g / l was prepared from an open, ready-made commercially available shaft raw material based on waste paper. The pH of the paper stock was 8.0. To determine the starch retention, samples were taken of this Paper pulp each have the amounts of hardener given in Table 1 1 and the polymers 1-4 added in succession. After this Mixing the paper stock with the additives was suction filtered and the starch content from the extinction measurement of the starch-iodine complex certainly. The results obtained are in Table 1 given. Another part of the pulp was after dosing of solidifier 1 and those in Table 1 specified polymers using a Schopper-Riegler device dewatered. The drainage time was determined according to DIN ISO 5267 for 700 ml filtrate. The results are shown in Table 1.

Comparative Example 1

Example 1 was repeated with the exception that only pulping agent 1 was added to the paper stock in an amount of 2%, based on dry paper stock. The starch content of the filtrate and the drainage time are given in Table 1. example Addition to paper stock, based on dry paper stock Starch content in the filtrate
[Mg / l] drainage time
[sec / 700 ml] 1 2% hardener 1 + 0.08% polymer 1 38 92 2 2% hardener 1 + 0.08% polymer 2 34 49 3 2% hardener 1 + 0.08% polymer 3 30 55 4 2% hardener 1 + 0.08% polymer 4 30 67 Comparative example 1 2% hardener 1 50 136

Example 5

An open, ready-made, commercially available shaft raw material Waste paper base with a consistency of 0.76% was initially with 2% hardener 1 and then with 0.08% polymer 3 as Retention agent for cationic starch added. After encore The pulp of the strengthener and polymer was mixed together. Part of this paper stock was sucked off. From the The COD value and the starch retention by enzymatic became filtrate Degradation to glucose determined by HPLC. From the other Part of the paper stock was determined using a Schopper-Riegler device the drainage time for 500 ml of filtrate. 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. example Addition to paper stock, based on dry paper stock COD
[mgO ₂ / l] strength retention
(enzymatic method) drainage time
[sec / 500 ml] 5 2% hardener 2 + 0.08% polymer 3 134 93 20 Comparative example 2 2% hardener 1 313 43 72 3 2% commercial cationic starch DS 0.035 162 92 78 4 - 135 68

Example 6

A whipped finished commercial wave raw material based on waste paper with a substance concentration of 0.76% was successively mixed with 2% hardener 2 and 0.08% polymer 3. After mixing, paper sheets with a basis weight of 120 g per m ^{2 are} produced on a Rapid-Köthen sheet former. The sheets were tested for their 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 shown 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, commercially available cationic starch was used (comparative example 6) and the zero value was determined (comparative example 7). The results are shown in Table 3. example Addition to paper stock, based on dry paper stock Dry breaking length
[M] dry bursting
[KPa] CMT
[N] 6 2% hardener 1 + 0.08% polymer 3 4433 296 209 Comparative example 5 2% hardener 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 with a K value of 90 and a degree of hydrolysis of 30%.

Polymer 6:

Commercially available modified PEI with a charge density of 14.7 at pH 4.5 and 10.8 at pH 7 and an average molecular weight of approximately 700,000 D.

Polymer 7:

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 paper dye based on waste paper with a COD value of 8000 mg oxygen / l and a substance concentration of 1% was successively mixed with 2% hardener 1, with 0.245% polymer 6 and 0.02% polymer 7. After mixing, paper sheets with a basis weight of approx. 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for their 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 waste paper-based paper stock with a COD value of 8000 mg oxygen / l and a substance concentration of 1% was mixed in succession with 2% hardener 1, 0.12% polymer 2 and 0.02% polymer 7. After mixing, paper sheets with a basis weight of approx. 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for their dry strength using 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 value of 8000 mg oxygen / l and a substance concentration of 1% was successively mixed with 2% hardener 1, 0.12% polymer 3 and 0.02% polymer 7. After mixing, paper sheets with a basis weight of approx. 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for their dry strength using the methods given in Example 7. The results are shown in Table 4.

Example 10

A paper material based on waste paper with a COD value of 8000 mg oxygen / l and a substance concentration of 1% was mixed with 2% hardener 1, 0.13% polymer 4 and 0.02% polymer 7 in succession. After mixing, paper sheets with a basis weight of approx. 110 g / m ^{2 are} produced on the Rapid-Köthen sheet former. The leaves were tested for their dry strength using the methods given in Example 7. The results are shown in Table 4.

Example 11

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

Comparative Example 8

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

Claims (12)

1. A process for the production of paper, board and cardboard having high dry strength by the addition of cationic, anionic or amphoteric starch 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 at least one cationic polymer from the group consisting of

   polymers containing vinylamine units

   polyethyleneimines

   crosslinked polyamidoamines

   ethyleneimine-grafted and crosslinked polyamidoamines

   polydiallyldimethylammonium chlorides

   polymers containing N-vinylimidazoline units

   polymers containing dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate

   polymers containing dialkylaminoalkylacrylamide units or dialkylaminoalkylmethacrylamide units and

   polyallylamines

   is 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 a cationic starch having a degree of substitution D.S. of up to 0.15 is used.
7. A process as claimed in any of claims 1 to 6, wherein the dry strength agents are used in amounts of from 0.5 to 10 % by weight, based on dry paper stock.
8. A process as claimed in any of claims 1 to 7, wherein the dry strength agents are used in amounts of from 1 to 5 % by weight, based on dry paper stock.
9. A process as claimed in any of claims 1 to 8, wherein the retention aids for starch are used in amounts of from 0.01 to 0.3 % by weight, based on dry paper stock.
10. 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.
11. The use of a cationic polymeric retention aid from the group consisting of

    polymers containing vinylamine units

    polyethyleneimines

    crosslinked polyamidoamines

    ethyleneimine-grafted and crosslinked polyamidoamines

    polydiallyldimethylammonium chlorides

    polymers containing N-vinylimidazoline units

    polymers containing dialkylaminoalkyl acrylate or dialkylaminoalkyl methacrylate

    polymers containing dialkylaminoalkylacrylamide units or dialkylaminoalkylmethacrylamide units and

    polyallylamines.

    for increasing the retention of dry strength agents comprising cationic, anionic or amphoteric starch in the production of paper, board and cardboard.
12. The use as claimed in claim 11, 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.