EP0416427B1 - Neutral sizing agent for rough paper masses using cationic polymer dispersions - Google Patents

Description

The invention relates to the use of aqueous cationic plastic dispersions in combination with polymeric retention aids for the mass sizing of raw paper pulps at neutral pH.

As is well known, an important process step in the production of paper is the sizing of the cellulose fibers in the production of base paper. It is used for paper production from the cellulose raw material, among other things. the purpose of making the paper more writable and / or printable by appropriate hydrophobization of the cellulose fibers. Resin glues based on rosin, which e.g. be precipitated from the aqueous phase of the cellulose fiber pulp (paper pulp) by means of aluminum salts, whereupon they attach to the cellulose fibers. Thereafter, after the addition of retention aids and flocculants and, if appropriate, of further auxiliaries and / or fillers to the cellulose pulp, the cellulose fibers hydrophobicized when the resin glue precipitates can easily be removed from the aqueous phase and obtained in the form of raw paper webs.

As is well known, this procedure leads to considerable wastewater problems and can cause severe corrosion on paper machines. It also leads to unsatisfactory storage stability in the finished paper due to the acidic constituents contained in the precipitated paper pulp.

The efforts of the paper manufacturers to add less expensive but acid-sensitive calcium carbonate to the paper coating slips as filler instead of kaolin, and also to be able to use paper waste and waste paper, as well as the lower storage stability of paper, the raw sizing of which took place at pH values in the acidic range, increased the demand for so-called Neutral sizing agents emerge that can exert their effect at a pH of 7 if possible. With regard to a further rationalization of the process, the need to be able to directly adapt the degree of sizing to the respective requirement simply by varying the amount of neutral sizing agent became apparent.

Cationic polymer solutions or polymer dispersions have therefore already been used for the production of sized paper at a neutral pH value, since the product-specific substantivity of polymeric cationic molecules means that they can be voluntarily applied to the cellulose fibers without prior destabilization of their solution or dispersion.

DE-B-1 053 783, for example, discloses cationic copolymers which can be obtained by radical-initiated polymerization in bulk or in solution or in aqueous dispersion. They contain monomer units from esters or amides of acrylic or methacrylic acid which have at least one quaternary ammonium compound in the side chain ester or amide radical of the monomer units, which is bonded to the hetero atom of the ester or amide group via an alkylene group. These copolymers can also contain, as comonomer constituents, monomer units from the group of vinyl acetate, vinyl formate, vinylidene chloride, styrene, isobutylene, butadiene and butyl acrylate and are used for the production of molding compounds, films, fibers, adhesives, Lacquers, textile auxiliaries etc. used. However, it has been shown that practically all of the cationic copolymer dispersions mentioned in DE-AS 1 053 783 are unsuitable for use as paper sizing agents, and that size paper produced therewith has unsatisfactory properties.

DE-C-1 546 236 discloses cationic copolymer dispersions which can be used for the production of sized papers. The copolymers of these products contain 20 to 60% by weight of styrene and / or acrylonitrile, 20 to 60% by weight of (meth) acrylic acid ester and 5 to 50% by weight of cationic monomer units composed of ethylenically unsaturated compounds and quaternary nitrogen atom. However, to obtain usable results, these copolymers require those with a content of at least 20% by weight of cationic monomer units, which, given the limited availability and the high cost of the required cationic starting monomers, prevent their copolymers from being widely used.

Cationic copolymer latices are known from EP-C-119 109 and are said to be suitable as paper sizes. The copolymers of these products mainly consist of vinyl esters, (meth) acrylic acid esters, vinyl aromatics and 1 to 20% by weight of partially nitrogen-containing monomer units which are capable of accepting cationic charges, preferably based on (meth) acrylamides, some of which are quaternized. They also contain nonionic or cationic emulsifiers. With regard to the possible use of these products in papermaking, however, no test results have so far become known.

US-A-4 717 758 describes a paper sizing agent based on a water-soluble polymer of dimethylaminopropyl (meth) acrylamide or its quaternization product, itaconic acid and acrylamide. Good sizing properties can only be achieved with this system up to a solids content of approx. 15% by weight, since a relatively high molecular weight is required for a sufficient sizing degree, which causes a very high viscosity of the sizing agent even with a low solids content.

All cationic recommended so far as a replacement for the acidic resin glue as paper sizing agent Plastic dispersions have obvious significant disadvantages that prevent their practical use as paper sizing agents. You need either a too high proportion of cationic monomer units for full sizing, which is too important as a cost factor, or they require too high amounts of copolymer, z. B. up to 5 wt .-%, based on the cellulose content in the paper. In addition, the products do not offer the paper manufacturer enough options to influence the size of the paper to the required extent with the same sizing agent.

The present invention was therefore based on the object of making available a paper sizing agent for the mass sizing of paper at a neutral pH value, which in particular enables inexpensive sizing, is easy to use and can lead to full sizing even at low application rates. The user should make simple and minor changes, e.g. Concentration variations, also allow you to get to paper with low sizing levels and also to be able to vary the dry strength of the raw sized paper sufficiently.

It has now surprisingly been found that the above-mentioned difficulties can be overcome and that water-thinnable sizing agents which can be used advantageously for mass sizing paper at neutral pH can be obtained by using finely divided aqueous cationic copolymer dispersions with specific properties of the invention in combination with polymeric retention aids.

The invention therefore relates to the use of aqueous cationic plastic dispersions as neutral sizing agents for the mass sizing of raw paper pulps in a conventional aqueous suspension at neutral pH for the production of acid-free raw paper, characterized in that that aqueous cationic copolymer dispersions with a minimum cation activity of 20 μmol / g solid (FS), the cationic charge being more than half on the surface of the dispersion copolymer particles, the minimum film-forming temperature (MFT) of the dispersion being below 50 ° C. the glass transition temperature T _{G of} the copolymer is below 70 ° C. and above 0 ° C. and the average particle diameter of the cationic dispersion copolymer particles is below 0.5 μm, in combination with polymeric retention aids, the weight ratio of the polymeric retention aid to the cationic dispersion copolymer preferably 0.3: 1 to 0.005: 1, at a pH in the range from 6.5 to 7.5 in an amount of up to 2% by weight of cationic dispersion copolymer, based on the dry weight of the raw cellulose fibers, with the raw cellulose fiber suspension mixed intensively with the proviso that ß either the polymeric retention aid is added first and the cationic plastic dispersion is metered in, or the two agents are metered in separately at the same time into the aqueous cellulose fiber suspension with intensive mixing, if appropriate with the addition of inert fillers, pigments, dyes and customary auxiliaries, including fillers Calcium carbonate base, and then the acid-free base paper is isolated and dried from the aqueous suspension in a conventional manner, preferably in the form of base paper webs or sheets of base paper.

The invention further relates to a process for the production of sized acid-free raw paper from raw cellulose fibers in a conventional aqueous suspension using aqueous cationic plastic dispersions and polymeric retention aids as neutral sizing agents at pH values from 6.5 to 7.5, characterized in that the Sizing agents, as specified in the previous paragraph, preferably at normal temperature, with the aqueous cellulose fiber suspension intensively mixed, optionally with the use of inert fillers, pigments, dyes and customary auxiliaries, including fillers based on calcium carbonate, and the sized, acid-free raw paper isolated and dried in the usual manner.

Another object of the invention is acid-free, bulk-sized base paper in the form of flat sheets, sheets or moldings or in the form of flakes or nonwovens, produced by the above-mentioned process, optionally with the use of inert fillers, dyes and conventional auxiliaries, optionally from Calcium carbonate based fillers.

As polymeric retention aids, the products known as polymeric retention aids and drainage accelerators are used in the usual application amounts, optionally in the form of their aqueous solutions or aqueous dilutions. These are either added as such simultaneously with the aqueous cationic copolymer dispersions used according to the invention to the aqueous cellulose fiber suspension in the neutral pH range, or the retention aid is predosed and the cationic copolymer dispersion is then added, the latter variant being preferred.

This combined use of polymeric retention aids and cationic copolymer dispersions according to the invention surprisingly results in an obviously synergistic increase in effectiveness in paper sizing. This enables, inter alia, a sufficiently effective application of very inexpensive application rates of cationic monomer units in the cationic dispersion copolymers with a simultaneously widened concentration-dependent degree of effectiveness.

Retention agents and dewatering accelerators are known to serve the purpose of increasing the fiber, fine and filler retention on the paper machine screen in conventional use. In addition, certain types of products can increase the dewatering speed on the wire and in the wet presses, as well as faster drying of the paper web in the dryer section, which can be used to increase production or save energy. Experience has shown that the effect of the higher to high molecular weight products is based on a reduction in the negative zeta potential of the paper stock suspension and / or on the bridging between paper stock particles by the polymers, which in both cases causes the paper stock suspension to micro-flocculate. However, an effective paper sizing effect cannot be achieved by using the polymeric retention aids alone. It was therefore all the more surprising that the obviously synergistic increase in activity in paper sizing with cationic plastic dispersions was due to the combined use of polymeric retention aids and cationic copolymer dispersions according to the invention.

Possible polymeric retention aids to be used according to the invention are in particular: polyamines, preferably higher molecular weight polyalkylene polyamines, in particular polyethyleneimine, or reaction products such as can be obtained by crosslinking oligoamines with dichloroethane, epichlorohydrin or reaction products from epichlorohydrin and polyetherdiols,
Polyamidoamines, preferably polyamide amines, as can be obtained by reacting adipic acid with diethylenetriamine or similar polyamines and crosslinking with the above-mentioned crosslinking agents, or reaction products based on ethyleneimine / adipic acid / polyamine / epichlorohydrin,
Polyacrylamides, preferably high molecular weight polyacrylamides, such as anionically modified acrylamide / acrylic acid copolymers, cationically modified copolymers of acrylamide with aminoacrylic and methacrylic acid esters with tertiary and quaternary amine functions, cationic products, formed by the MANNICH reaction of polyacrylamide homopolymers,
Polysalts, for example polymers or copolymers of diallyldimethylammonium chloride (poly-DADMAC homo- or copolymers), preferably poly-DADMAC copolymers, with molecular weights in the range from 10⁴ to 10⁶, particularly preferably 10⁵ to 10⁶, in particular copolymers with vinyl acetate and / or acrylamide and / or N-methylolacrylamide, furthermore homopolymeric poly-DADMAC with molecular weights of preferably at least 10,000 is particularly preferred, cationic starch, guar derivatives, cationic polyvinyl alcohol.
Cationic polymeric retention aids are preferred.

According to the invention, 0.05 to 0.2% by weight, in particular 0.05 to 0.1% by weight, based on the dry cellulose weight, of retention aids in combination with a cationic copolymer dispersion of the cellulose fiber suspension are added with the proviso that either Retention aid as such is added simultaneously with the cationic copolymer dispersion, or that the retention aid is pre-dosed and the cationic copolymer dispersion is then added.

Since the polymeric retention aids used in accordance with the invention can generally form colloidal aqueous solutions, they can advantageously be added to the cellulose fiber suspension in the form of colloidal aqueous solutions.

In principle, all aqueous, cationically charged plastic or polymer dispersions are suitable as aqueous cationic plastic dispersions to be used according to the invention for raw paper sizing in the neutral pH range, preferably at pH values from 6.5 to 7.5, but preferably those with a medium dispersion Particle diameter of 0.05 to 0.5 µm and a minimum cation activity of 20 to 200 µmol / g solid (FS), the cationic charge being more than half on the surface of the dispersion copolymer particles, in particular those whose cationic charge is too 60 to 90% is located on the surface of the dispersion copolymer particles. The molecular weight of the dispersion copolymers is not critical and can preferably be from 10,000 to several million. Lower and higher molecular weights are also possible. In general, they are adapted to the requirements and objectives. The amount of cationic plastic dispersions used in combination with the abovementioned retention aids is preferably 0.1 to 2% by weight, in particular 0.5 to 1% by weight, of dispersion copolymer solid (FS), based on the dry weight of the cellulose fiber mass used for sizing in the cellulose fiber suspension or raw paper pulp.

Retention aids and aqueous cationic plastic dispersion, based on the copolymeric solids content (FS) of the cationic dispersion, are particularly preferably used in a weight ratio of 0.2: 1 to 0.01: 1.

• a) 60 bis 95 Gew.-% ethylenisch ungesättigten Monomeren aus der Gruppe Vinylester von (C₁-C₁₈)-Monocarbonsäuren, vorzugsweise Vinylacetat, Vinylpropionat, Vinylversatat, Vinyllaurat, Vinylstearat,
  (Meth-)Acrylester von (C₁-C₂₂)-Alkoholen, vorzugsweise Methylmethacrylat, Butylmethacrylat, Oktylmethacrylat, Ethylacrylat, Isobutylacrylat, 2-Ethylhexylacrylat, Vinylaromaten, vorzugsweise Styrol, Vinyltoluol, Vinylchlorid, Ethylen, (Meth-)Acrylnitril, Diester von Maleinsäure und/oder Fumarsäure mit (C₁-C₁₈)-Alkoholen;
  In einer besonders bevorzugten Variante besteht die Komponente a), bezogen auf die Komponente a), aus 50 bis 70 Gew.-% hydrophoben Monomeren aus der Gruppe (Meth-)Acrylnitril, Vinylaromaten, vorzugsweise Styrol und Vinyltoluol, sowie 25 bis 45 Gew.-% Estern der (Meth-)Acrylsäure, vorzugsweise Butylacrylat, Oktylacrylat, Butylmethacrylat, Oktylmethacrylat;
  Ein weiteres erfindungswesentliches Merkmal besteht ferner darin, daß die erfindungsgemäß verwendeten wäßrigen, kationischen, copolymeren Kunststoffdispersionen eine minimale Filmbildungstemperatur (MFT) im Bereich von 0 bis 50°C besitzen und die Glastemperatur T_G des kationischen Dispersionscopolymerisats zwischen 10 und 65°C, vorzugsweise zwischen 20 und 50°C, liegt,
• b) 2 bis 20 Gew.-%, vorzugsweise 3 bis 10, insbesondere 3 bis 7 Gew.-%, ethylenisch ungesättigten, salzbildenden, wasserlöslichen Monomeren mit Alkylammonium-, Alkylsulfonium- oder Alkylphosphoniumgruppen, vorzugsweise Alkylammoniumgruppen, insbesondere aus der Gruppe Trimethylammoniumethyl(meth-)acrylatchlorid, β-Acetamido-diethyl-aminoethyl(meth-)acrylat-chlorid, (Meth-)Acrylamidopropyltrimethylammonium-chlorid, (Meth-)Acrylamidoethyltrimethylammonium-bromid, Trimethylammoniumneopentyl(meth-)acrylat-chlorid, Diallyl-dimethylammonium-chlorid, Diallyl-butylmethylammonium-bromid,
• c) 2 bis 20 Gew.-%, vorzugsweise 3 bis 15, insbesondere 3 bis 8 Gew.-%, ethylenisch ungesättigten Monomeren mit mindestens einem funktionellen Rest
  
  worin die Substituenten R¹ und R² gleich oder verschieden sein können und mindestens einer für eine durch (C₁-C₆)-Alkyl verätherte oder nicht verätherte (C₁-C₆)-Alkylolgruppe steht, vorzugsweise aus der Gruppe N-Methylol(meth-)acrylamid, Dimethylol(meth-)acrylamid, N-Methoxymethyl(meth-)acrylamid, N-Butoxymethyl(meth-)acrylamid, N-Isobutoxymethyl(meth-)acrylamid, N-(3-Hydroxy-2,2-dimethylpropyl)-(meth-)acrylamid, wobei N-Methylolacrylamid, N-Methoxymethylmethacrylamid und N-Butoxymethylmethacrylamid besonders bevorzugt sind,
• d) 0 bis 5 Gew.-% weiteren, von a) bis c) verschiedenen ethylenisch ungesättigten Monomeren mit funktionellen Resten aus der Gruppe -COOH,
  
  wobei R¹ und R² gleich oder verschieden sein können und für H, (C₁-C₄)-Alkyl, (C₅-C₇)-Cycloalkyl oder (C₆-C₁₈)-Aralkyl stehen, -OH, -Si(OR)₃, wobei R für (C₁-C₄)-Alkyl oder mit (C₁-C₄)-Alkyl veräthertem (C₁-C₄)-Hydroxyalkyl oder für Acetyl steht und die drei Substituenten R gleich oder verschieden sein können,
  
  wobei R³, R⁴ gleich oder verschieden sein können und für (C₁-C₁₈)-Alkyl, (C₅-C₇)-Cycloalkyl oder (C₆-C₁₂)-Aryl bzw. Aralkyl stehen,
  
  wobei R⁵, R⁶, R⁷ gleich oder verschieden sein können und für H, (C₁-C₁₈)-Alkyl, (C₅-C₇)-Cycloalkyl oder (C₆-C₁₂)-Aryl bzw. Aralkyl stehen,
  vorzugsweise Monomere aus der Gruppe ethylenisch ungesättigter Carbonsäuren, insbesondere Acrylsäure, Methacrylsäure, Itakonsäure, Maleinsäure, Fumarsäure sowie der Halbester dieser zweiwertigen Carbonsäuren mit geradkettigen oder verzweigten (C₁-C₈)-Alkoholen,
  ethylenisch ungesättigter Amide, insbesondere Acrylamid, Methacrylamid, N-Methylacrylamid, N-Butylmethacrylamid, N-tert.-Butylmethacrylamid, N-Cyclohexylmethacrylamid, N-Benzylmethacrylamid, Diacetonacrylamid, Methylacrylamidoglykolatmethyläther,
  ethylenisch ungesättigter Hydroxyalkylester, insbesondere Hydroxyethylacrylat, Hydroxypropylacrylat, Hydroxyethylmethacrylat, Hydroxypropylmethacrylat, Polyglykoläther der Acryl- oder Methacrylsäure mit 2 bis 50 Ethylenoxideinheiten, Polypropylenglykoläther der Acryl- oder Methacrylsäure mit 2 bis 50 Propylenoxideinheiten, wobei die Endgruppe der Polyalkylenglykolätherreste mit einem Alkyl- oder Arylrest veräthert sein kann,
  ethylenisch ungesättigter Silane, insbesondere Vinyltrimethoxysilan, Vinyltriethoxysilan, Methacryloxypropyltrimethoxysilan, Methacryloxypropyltris(methoxyethoxy)silan, Vinyltris(methoxyethoxy)silan, Vinyltriacetoxysilan,
  ethylenisch ungesättiger Urethane, insbesondere N-Methylcarbamidoethylmethacrylat, N-Butylcarbamidoisopropylmethacrylat, N-Oktadecylcarbamidoethylacrylat, N-Phenylcarbamidoethylmethacrylat, N-Cyclohexylcarbamidoethylacrylat,
  ethylenisch ungesättigter Harnstoffe, insbesondere 2-Methacryloylethylharnstoff, 2-Oktylmethacryloylethylharnstoff, 2-Phenylmethacryloylethylharnstoff,
  ethylenisch ungesättigter Sulfonsäuren bzw. Sulfonsäurederivate, insbesondere Ethylensulfonsäure, (3-Sulfopropyl)methacrylsäureester oder Acrylamidomethylpropansulfonsäure bzw. deren Salze, vorzugsweise Alkali- oder Ammoniumsalze,
  ethylenisch ungesättigter Phosphonsäuren, insbesondere Vinylphosphonsäure oder Acrylamidomethylpropanphosphonsäure bzw. deren Alkali- oder Ammoniumsalze,
• e) 0 bis 5 Gew.-% ethylenisch ungesättigten fluorhaltigen Monomeren, vorzugsweise Acryl- oder Methacrylester von teil- oder perfluorierten (C₁-C₈)-Alkanolen, teil- oder perfluorierte (C₂-C₁₈)-Alkylene, insbesondere aus der Gruppe Methacrylsäure-2,2,3,4,4,4-hexafluorbutylester, Methacrylsäure-2,2,3,3-tetrafluorpropylester oder Perfluorhexylethylen,
• f) 0 bis 5 Gew.-% ethylenisch ungesättigten Carbonylverbindungen, vorzugsweise aus der Gruppe Vinylmethylketon, Acrolein, Crotonaldehyd, Allylacetoacetat, Acetoacetoxyethyl(meth-)acrylat,
• g) 0 bis 5 Gew.-% ethylenisch ungesättigten und zur Vernetzung befähigten Monomeren, vorzugsweise aus der Gruppe der mehrfach ethylenisch ungesättigten oder mehrfunktionellen Monomeren, insbesondere Divinylbenzol, Diallylphthalat, Butandioldiacrylat,
  Triethylenglykoldimethacrylat, Allylmethacrylat, Bisphenol-A-diethylenglykoldimethacrylat, Triallylcyanurat, Methylen-bis-methacrylamid,
  und die Dispersionen außerdem
• h) 0,1 bis 10 Gew.-%, vorzugsweise 0,2 bis 6 Gew.-%, bezogen auf die Gesamtmenge aller Monomereinheiten in dem Copolymerisat, Emulgatoren und/oder gegebenenfalls Schutzkolloide, vorzugsweise aus der Gruppe der kationischen, amphoteren und insbesondere der nichtionogenen Tenside und/oder Schutzkolloide, enthalten.

Also particularly preferred are aqueous cationic copolymeric polymer dispersions based on ethylenically unsaturated monomers, the dispersion copolymer particles of which are based on% by weight of the total amount of monomer units in the copolymer

• a) 60 to 95% by weight of ethylenically unsaturated monomers from the group of vinyl esters of (C₁-C₁₈) monocarboxylic acids, preferably vinyl acetate, vinyl propionate, vinyl versatate, vinyl laurate, vinyl stearate,
  (Meth) acrylic esters of (C₁-C₂₂) alcohols, preferably methyl methacrylate, butyl methacrylate, octyl methacrylate, ethyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, vinyl aromatics, preferably styrene, vinyl toluene, vinyl chloride, ethylene, (meth) acrylonitrile and diester of maleic acid / or fumaric acid with (C₁-C₁₈) alcohols;
  In a particularly preferred variant, component a), based on component a), consists of 50 to 70% by weight of hydrophobic monomers from the group (meth) acrylonitrile, vinylaromatics, preferably styrene and vinyltoluene, and 25 to 45% by weight. -% esters of (meth) acrylic acid, preferably butyl acrylate, octyl acrylate, butyl methacrylate, octyl methacrylate;
  Another feature essential to the invention is that the aqueous, cationic, copolymeric plastic dispersions used according to the invention have a minimum film-forming temperature (MFT) in the range from 0 to 50 ° C. and the glass transition temperature T _{G of} the cationic dispersion copolymer is between 10 and 65 ° C., preferably between 20 and 50 ° C,
• b) 2 to 20 wt .-%, preferably 3 to 10, in particular 3 to 7 wt .-%, ethylenically unsaturated, salt-forming, water-soluble monomers with alkylammonium, alkylsulfonium or alkylphosphonium groups, preferably alkylammonium groups, in particular from the group trimethylammoniumethyl (meth -) acrylate chloride, β-acetamido-diethylaminoethyl (meth) acrylate chloride, (meth) acrylamidopropyltrimethylammonium chloride, (meth) acrylamidoethyltrimethylammonium bromide, Trimethylammonium neopentyl (meth) acrylate chloride, diallyl dimethylammonium chloride, diallyl butylmethylammonium bromide,
• c) 2 to 20% by weight, preferably 3 to 15, in particular 3 to 8% by weight, of ethylenically unsaturated monomers with at least one functional radical
  
  wherein the substituents R¹ and R² can be the same or different and at least one represents a (C₁-C₆) alkyl etherified or non-etherified (C₁-C₆) alkylol group, preferably from the group N-methylol (meth) acrylamide, Dimethylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-isobutoxymethyl (meth) acrylamide, N- (3-hydroxy-2,2-dimethylpropyl) - (meth -) acrylamide, with N-methylolacrylamide, N-methoxymethyl methacrylamide and N-butoxymethyl methacrylamide being particularly preferred,
• d) 0 to 5% by weight of further ethylenically unsaturated monomers, different from a) to c), with functional radicals from the group -COOH,
  
  where R¹ and R² may be the same or different and represent H, (C₁-C₄) alkyl, (C₅-C₇) cycloalkyl or (C₆-C₁₈) aralkyl, -OH, -Si (OR) ₃, where R represents (C₁-C₄) -alkyl or (C₁-C₄) -alkyl etherified (C₁-CH) -hydroxyalkyl or acetyl and the three substituents R can be identical or different,
  
  where R³, R⁴ may be the same or different and stand for (C₁-C₁₈) alkyl, (C₅-C₇) cycloalkyl or (C₆-C₁₂) aryl or aralkyl,
  
  where R⁵, R⁶, R⁷ may be the same or different and represent H, (C₁-C₁₈) alkyl, (C₅-C₇) cycloalkyl or (C₆-C₁₂) aryl or aralkyl,
  preferably monomers from the group of ethylenically unsaturated carboxylic acids, in particular acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and the half esters of these dibasic carboxylic acids with straight-chain or branched (C₁-C₈) alcohols,
  ethylenically unsaturated amides, especially acrylamide, methacrylamide, N-methyl acrylamide, N-butyl methacrylamide, N-tert-butyl methacrylamide, N-cyclohexyl methacrylamide, N-benzyl methacrylamide, diacetone acrylamide, methyl acrylamide glycolate methyl ether,
  ethylenically unsaturated hydroxyalkyl ester, in particular hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, polyglycol ether of acrylic or methacrylic acid with 2 to 50 ethylene oxide units, polypropylene glycol ether of acrylic or methacrylic acid with 2 to 50 propylene oxide units, the end group of which is the aralkyl ether or polyalkylene glycol ether can,
  ethylenically unsaturated silanes, in particular vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropyltris (methoxyethoxy) silane, vinyltris (methoxyethoxy) silane, vinyltriacetoxysilane,
  ethylenically unsaturated urethanes, in particular N-methylcarbamidoethyl methacrylate, N-butylcarbamidoisopropyl methacrylate, N-octadecylcarbamidoethyl acrylate, N-phenylcarbamidoethyl methacrylate, N-cyclohexylcarbamidoethyl acrylate,
  ethylenically unsaturated ureas, in particular 2-methacryloylethylurea, 2-octylmethacryloylethylurea, 2-phenylmethacryloylethylurea,
  ethylenically unsaturated sulfonic acids or sulfonic acid derivatives, in particular ethylene sulfonic acid, (3-sulfopropyl) methacrylic acid ester or acrylamidomethyl propane sulfonic acid or salts thereof, preferably alkali metal or ammonium salts,
  ethylenically unsaturated phosphonic acids, in particular vinylphosphonic acid or acrylamidomethylpropanephosphonic acid or their alkali metal or ammonium salts,
• e) 0 to 5 wt .-% of ethylenically unsaturated fluorine-containing monomers, preferably acrylic or methacrylic esters of partially or perfluorinated (C₁-C₈) alkanols, partially or perfluorinated (C₂-C₁₈) alkylenes, especially from the group methacrylic acid 2,2,3,4,4,4-hexafluorobutyl ester, 2,2,3,3-tetrafluoropropyl methacrylic acid or perfluorohexylethylene,
• f) 0 to 5% by weight of ethylenically unsaturated carbonyl compounds, preferably from the group vinyl methyl ketone, acrolein, crotonaldehyde, allylacetoacetate, acetoacetoxyethyl (meth) acrylate,
• g) 0 to 5% by weight of ethylenically unsaturated and capable of crosslinking, preferably from the group of polyethylenically unsaturated or polyfunctional monomers, in particular divinylbenzene, diallyl phthalate, butanediol diacrylate,
  Triethylene glycol dimethacrylate, allyl methacrylate, bisphenol A diethylene glycol dimethacrylate, triallyl cyanurate, methylene bis methacrylamide,
  and the dispersions as well
• h) 0.1 to 10 wt .-%, preferably 0.2 to 6 wt .-%, based on the total amount of all monomer units in the copolymer, emulsifiers and / or optionally protective colloids, preferably from the group of cationic, amphoteric and in particular the nonionic surfactants and / or protective colloids.

Cationic dispersion copolymers which contain styrene / butyl acrylate, trialkylammonium alkyl (meth) acrylate chloride and N-methylol (meth) acrylamide as monomer units are particularly preferred.

Suitable emulsifiers which are used in the preparation of the aqueous cationic copolymer dispersions to be used according to the invention, preferably in the emulsion polymerization of the comonomers, are customary nonionic emulsifiers, in particular nonionic surfactants, preferably from the group of the reaction products of aliphatic, cycloaliphatic, araliphatic, aliphatic, aliphatic aromatic carboxylic acids, alcohols, phenols, amines with epoxides, such as Ethylene oxide, and block copolymers of various epoxides, such as Ethylene oxide and propylene oxide.

Preferred emulsifiers are furthermore, for example, primary, secondary and tertiary fatty amines in combination with organic or inorganic acids and also tensioactive quaternary alkylammonium compounds. Amphoteric surfactants with a zwitterionic structure, for example of the beta type such as alkylamidopropylbetaines, are also suitable. Especially preferred emulsifiers are nonionic surfactants, in particular alkyl and alkylaryl polyglycol ethers with 15 to 50 ethylene oxide units. The emulsifiers mentioned can be used either individually or in combination with one another or with one another. The amount of emulsifiers to be used depends on the desired dispersion properties and is preferably 0.1 to 10% by weight, in particular 0.2 to 6, particularly preferably 0.3 to 4% by weight, based on the total amount of all monomer units in the copolymer.

Suitable protective colloids are preferably those based on high molecular weight organic compounds which have hydroxyl, amino or ammonium groups and are water-soluble or water-dispersible, with essentially no or no pronounced interfacial activity and a pronounced dispersibility. Preferred protective colloids are, for example, cationic polyelectrolytes, for example poly-diallyldimethylammonium chloride (poly-DADMAC), cellulose ethers, polyvinyl alcohols, polysaccharides, (chitosan, starch), polyvinylpyrrolidones, it being possible for these compounds to be preferably substituted by amino groups or quaternary ammonium groups. The latter groups can be introduced into the underlying macromolecules, for example by substitution using cationizing reagents, such as, for example, glycidyl trimethyl ammonium chloride. Cationic polyvinyl alcohols can also be obtained, for example, by saponification of corresponding vinyl acetate copolymers containing amino and / or ammonium groups. Particularly preferred protective colloids are cationically modified polysaccharides and cationic polyelectrolytes. The amounts of protective colloid to be used depend on the desired dispersion properties, in particular the fine particle size of the dispersion particles. To be favoured Protective colloid amounts of between 0 and 5% by weight, in particular between 0.1 and 2% by weight, based on the total amount of monomers, may be used in the emulsion polymerization.

The cationic plastic dispersions used according to the invention can be prepared by conventional emulsion polymerization using the feed or pre-emulsion process, preferably at 20 to 100 ° C., in particular at 50 to 90 ° C. Part of the monomer mixture can be prepolymerized in the aqueous liquor in a customary manner and the rest of the monomer mixture can be metered in continuously while maintaining the reaction at the reaction temperature.

The cationic plastic dispersions used according to the invention have a high cation activity of preferably at least 20 to 200 μmol / g solid (FS), measured at pH 7, it being particularly advantageous if more than half, in particular 60 to 90%, of the cationic charges are themselves located on the surface of the copolymer particles.

A high content of cationic surface charge can be achieved, for example, by metering in the cationic, salt-like, ethylenically unsaturated quaternary monomers, preferably alkylammonium compounds, mentioned above under b) during the copolymerization in uneven amounts, preferably larger amounts with the monomer mixture at the start of the copolymerization . The cation activity and the cationic surface charge fraction can be measured, for example, titrimetrically in a known manner (cf. W. Schempp and HT Trau, Wochenblatt für Papierfabrikation 19, 1981, pp. 726-732, or JP Fischer and K. Löhr in GD Parfitt and AV Patsis, Organic Coatings: Science and Technology, Vol. 8, pp. 227-249, Marcel Dekker, Inc., New York, April 1986).

The solids content (FS) of the cationic plastic dispersions used according to the invention is in the range customary for dispersions. For use in the cellulose pulp, the solids content is preferably set to values of 3 to 40% by weight, in particular 5 to 20% by weight, based on the plastic dispersion. In these preferred solid concentration ranges, the cationic dispersions according to the invention have a low viscosity and develop practically no disruptive foam when used.

In contrast to the polymeric retention aids used according to the invention, which can form colloidal aqueous solutions, the dispersion copolymers which can be isolated from the aqueous cationic plastic dispersions used according to the invention are not soluble in water.

In the production of the cationic plastic dispersions by free-radically initiated emulsion polymerization in an aqueous medium, all systems customary in emulsion polymerization, preferably water-soluble, and initiating free radical chains, which can also be anionic in nature, can be used to initiate the copolymerization. Preferred initiators are e.g. 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamidine) dihydrochloride, 4,4'-azobis (4-cyanovaleric acid), H₂O₂, tert. -Butyl hydroperoxide, persulfates such as ammonium persulfate, sodium persulfate, potassium persulfate, redox systems such as H₂O₂ / ascorbic acid, optionally with the addition of small amounts of polyvalent metal salts, such as. B. iron (II) sulfate, as an activator, also high-energy radiation and conventional photoinitiators. Azo compounds such as 2,2'-azobis (2-amidinopropane) dihydrochloride and 4,4'-azobis (4-cyanovaleric acid) are preferably used.

For molecular weight control, the Emulsion polymerization also includes conventional regulators, such as mercaptans or halogenated hydrocarbons for lowering the molecular weight, or, if appropriate, up to 5% by weight, based on the total amount of monomers, of polyethylenically unsaturated or polyfunctional compounds capable of crosslinking, such as divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, butane diisocyanate Butanediol diacrylate, triallyl cyanurate, melamine, isocyanatoethyl methacrylate can be used to increase the molecular weight.

For the quality inspection and evaluation of the paper sizing agents used according to the invention, paper test sheets are produced from base paper treated with the sizing agent to be tested in the usual way (production according to leaflet V / 8/116 of November 26, 1976 by the Association of German Pulp and Paper Chemists and Engineers). The test sheets are dried on a steam-heated cylinder dryer with felt covering. For post-conditioning, the test sheets are dried in a drying cabinet at 120 ° C for 10 minutes.

The sizing factor f is determined from the glued test sheets obtained, which can be calculated using the following formula I:

> 20 bis 20

= hochgeleimtes Papier (Volleimung der Zellulosefasern)

 20 bis 10

= gutgeleimtes Papier

 10 bis 5

= mittelmäßig geleimtes Papier

5 bis 1

= schlecht geleimtes Papier

1 bis < 1

= ungeleimtes Papier

The values of the sizing factor f are evaluated as follows:

> 20 to 20

= highly sized paper (full size of cellulose fibers)

20 to 10

= well-sized paper

10 to 5

= medium sized paper

5 to 1

= badly sized paper

1 to <1

= unsized paper

The quantity "time" contained in the formula I is the time in seconds that a test ink (according to DIN 53 126) needs to act on the paper under constant pressure and without inhibitory influences from the first touch to the first sign of penetration of the paper sample . It is determined with the aid of the glue level testing device PLG-e (Schröder, Weinheim), which registers the reflectivity that changes as a result of the penetration of the ink into the paper photoelectrically as a function of time.

The dry and wet fracture resistance [N] are determined in accordance with DIN 53112, but the washing time is reduced from 24 hours to 1 hour.

The bursting strength according to Mullen can be determined according to DIN 53 141.

The invention is illustrated by the following examples.

example 1

A mixture of 7.5 g of nonylphenol polyglycol ether with 30 ethylene oxide units (30 EO), 37.5 g of methacrylamidopropyltrimethylammonium chloride (MAPTAC) (50% by weight, aqueous), 39.0 g of N-methylolacrylamide (48 wt .-%, aqueous) and 892 g of demineralized water (demineralized water) submitted. After further addition of 37.5 g of a monomer mixture of 37.5 g of styrene, 150 g of methyl methacrylate, 187.5 g of butyl acrylate and 3.75 g of ethylene glycol dimethacrylate, the mixture is heated to 90 ° C. and the polymerization is carried out by adding 2.5 g of one 1 wt .-% aqueous Cu (NO₃) ₂ solution and 15 g 30 wt .-% aqueous H₂O₂ started. The remainder of the monomer mixture is then metered in at 85 ° C. within 2 hours. After the end of the metering, 10 g of 30% by weight aqueous H₂O₂ and 2.5 g of 1% by weight aqueous Cu (NO₃) ₂ solution are added, the mixture is left to polymerize for 1 hour at 90 ° C. and then on Cooled to room temperature. The conversion of the amount of monomers used is practically quantitative and the resulting cationic copolymer dispersion is obtained without coagulum. It has a solids content (FS) of 30% by weight, based on the dispersion, and a cation activity of 153 µmol / g FS, of which 100 µmol is due to the external cation activity. The glass transition temperature (T _G ) of the copolymer is + 20 ° C and the minimum film formation temperature (MFT) of the dispersion is + 10 ° C.

Examples 2-4

Example 1 is repeated, but with different changes. So the proportions are varied in the comonomers and it is used as a polymerization initiator instead of the [Cu (NO₃) ₂ + H₂O₂] catalyst equivalent amounts of 4,4'-azo-bis (4-cyanovaleric acid) (AVS) and the respective monomer mixture added. The postpolymerization is initiated in all Examples 2 to 4 as in Example 1.

In Table 1, the quantitative ratios of the comonomers in the cationic copolymer dispersions of Examples 1 to 4 in% by weight, based in each case on the cationic copolymer content, the emulsifier content in% by weight, based on the copolymer content, the solids content (FS) Dispersion in% by weight, based on the dispersion, the total cation activity of the copolymer in µmol / g FS at pH 7 and the proportion of external cation activity in the total cation activity, and the glass transition temperature T _{G of} the Copolymer, determined by differential thermal analysis (DSC measurement), summarized.

Comparative Example 1

Example 1 is repeated with the modification that the quantitative ratios of the comonomers vary and the methyl methacrylate is omitted entirely. The same polymerization initiators as in Examples 2 to 4 are used. The numerical values are summarized in Table 1. The resulting cationic copolymer dispersion is not in accordance with the invention since, among other things, it has a too high T _G of 73 ° C. In addition, the external cation activity is too low.

Examples 5-8

The aqueous cationic copolymeric polymer dispersions according to the invention obtained according to Examples 1-4 are used both with the sole use of different amounts of cationic copolymer dispersion (1% by weight, 2.5% by weight, 5% by weight of cationic copolymer) Solid (KATCO-FS), based on the raw cellulose dry weight) as well as combined use according to the invention of the aqueous cationic copolymer plastic dispersions according to the invention with an amount of 1% by weight cationic copolymer solid (KATCO-FS), based on the raw cellulose dry weight each with 0.1% by weight of poly-diallyldimethylammonium chloride (100%) (= poly-DADMAC), based on the raw cellulose dry weight, with the addition of the stated agents to the raw cellulose pulp to be sized at pH 7, raw paper test sheets in usual way, according to leaflet V / 8/116 of November 26, 1976 of Ve pure German pulp and paper chemists and engineers. The aqueous cellulose pulp is first admixed with the poly-DADMAC as an aqueous solution with stirring and the aqueous cationic copolymer dispersion is then metered in with stirring and the base paper test sheets are obtained and conditioned in a conventional manner. The simultaneous addition of both agents (retention aid and aqueous cationic copolymer dispersion) via separate feeds gives practically the same advantageous results.

The sizing factor (f), the wet breaking resistance [N] and the dry breaking resistance [N] are determined on the raw paper test sheets obtained. The results are summarized in Table 2.

Comparative Examples 2-4

In an analogous manner to Examples 5-8, the non-inventive aqueous cationic copolymer dispersion of Comparative Example 1 is also tested for its sizing effect in aqueous cellulose fiber pulp at pH 7, both on its own and in combination with Poly-DADMAC, and the corresponding characteristic data the resulting raw paper test sheets determined (Comparative Example 2). The results are summarized in Table 2. In comparative example 3, base paper test sheets are produced with the sole addition of 0.1% by weight of poly-DADMAC without cationic copolymer dispersion, and in comparative example 4 without addition of poly-DADMAC and without addition of cationic copolymer dispersion. The corresponding quality inspection results are listed in Table 2.

As can be seen from the results in Table 2, the combination of 1% by weight of a cationic dispersion copolymer according to the invention and 0.1% by weight of poly-DADMAC etc. an equally good sizing factor (f), namely full sizing of the cellulose fibers, obtained with 2.5 to 5% by weight of the cationic dispersion copolymer according to the invention alone without the retention aid poly-DADMAC. When gluing there is obviously a synergistic increase in activity which is extremely surprising and cannot be derived from the prior art. The wet and dry fracture resistance values [N] according to the invention are also surprisingly significantly more advantageous than those not according to the invention for comparable sizing factors (f).

Claims (8)

1. The use of an aqueous cationic plastics dispersion as a neutral sizing agent for the internal sizing of base paper stuff in a conventional aqueous suspension at a neutral pH for the production of acid-free base paper, which comprises intensively mixing an aqueous cationic copolymer dispersion having a minimum cation activity of 20 µmol/g of solids, more than half of the cationic charge being located on the surface of the dispersion copolymer particles, the minimum film-forming temperature (MFT) of the dispersion being below 50°C, the glass temperature T_G of the copolymer being below 70° and above 0° and the mean particle diameter of the cationic dispersion copolymer particles being below 0.5 µm, with the raw cellulose fiber suspension at a pH in the range from 6.5 to 7.5 in a quantity of up to 2% by weight of cationic dispersion copolymer, relative to the dry weight of the raw cellulose fibers, in combination with a polymeric retention aid, the weight ratio of the polymeric retention aid to the cationic dispersion copolymer being preferably 0.3:1 to 0.005:1, with the proviso that either the polymeric retention aid is added first and the cationic plastics dispersion is metered in afterwards or the two agents are metered separately at the same time into the aqueous cellulose fiber suspension with intensive mixing, if desired with the additional use of inert fillers, pigments, dyes and conventional auxiliaries, if appropriate of fillers based on calcium carbonate, and then isolating the acid-free base paper from the aqueous suspension in the conventional manner, preferably in the form of base paper webs or base paper board, and drying it.
2. The use as claimed in claim 1, wherein a polymeric retention aid from the group comprising polyamines, polyamidoamines, polyacrylamides which may be cationically modified, polymeric or copolymeric polysalts based on diallyldimethylammonium chloride, cationic starch, guar derivatives and cationic polyvinyl alcohol is used.
3. The use as claimed in claim 1 and/or 2, wherein an aqueous cationic copolymeric plastics dispersion is used which is based on ethylenically unsaturated monomers and whose dispersion copolymer particles, in % by weight relative to the total quantity of monomer units in the copolymer, are built up from

   a) 60 to 95% by weight of ethylenically unsaturated monomers from the group comprising vinyl esters of (C₁-C₁₈)-monocarboxylic acids, (meth)acrylates of (C₁-C₂₂)-alcohols, vinylaromatics, vinyl chloride, ethylene, (meth)acrylonitrile and diesters of maleic acid and/or fumaric acid with (C₁-C₁₈)-alcohols,

   b) 2 to 20% by weight of ethylenically unsaturated, salt-forming water-soluble monomers having alkylammonium, alkylsulfonium or alkylphosphonium groups, preferably alkylammonium groups,

   c) 2 to 20% by weight of ethylenically unsaturated monomers having at least one functional radical

   

   in which the substituents R¹ and R² can be identical or different and at least one is a (C₁-C₆)-alkyl-etherified or unetherified (C₁-C₆)-alkylol group,

   d) 0 to 5% by weight of further ethylenically unsaturated monomers, different from a) to c), having functional radicals from the group comprising

   

   in which R¹ and R² can be identical or different and are H, (C₁-C₄)-alkyl, (C₅-C₇)-cycloalkyl or (C₆-C₁₈)-aralkyl,
   -OH, -Si(OR)₃, R being (C₁-C₄)-alkyl or (C₁-C₄)-alkyl-etherified (C₁-C₄)-hydroxyalkyl or acetyl, it being possible for the three substituents R to be identical or different,

   

   in which R³ and R⁴ can be identical or different and are (C₁-C₁₈)-alkyl, (C₅-C₇)-cycloalkyl or (C₆-C₁₂)-aryl or -aralkyl,

   

   in which R⁵, R⁶ and R⁷ can be identical or different and are H, (C₁-C₁₈)-alkyl, (C₅-C₇)-cycloalkyl or (C₆-C₁₂)-aryl or -aralkyl,
   preferably monomers from the group comprising ethylenically unsaturated carboxylic acids, and the half-esters of dibasic unsaturated carboxylic acids with (C₁-C₈)-alcohols, ethylenically unsaturated amides, ethylenically unsaturated hydroxyalkyl esters, it being possible for the end group of esters with polyalkylene glycol ether radicals to be etherified with an alkyl radical or aryl radical, ethylenically unsaturated silanes, ethylenically unsaturated urethanes, ethylenically unsaturated ureas, ethylenically unsaturated sulfonic acids or sulfonic acid derivatives, and ethylenically unsaturated phosphonic acids, or alkali metal salts or ammonium salts thereof,

   e) 0 to 5% by weight of ethylenically unsaturated fluorine-containing monomers, preferably acrylates or methacrylates of partially fluorinated or perfluorinated (C₁-C₈)-alkanols or partially fluorinated or perfluorinated (C₂-C₁₈)-alkylenes,

   f) 0 to 5% by weight of ethylenically unsaturated carbonyl compounds, preferably from the group comprising vinyl methyl ketone, acrolein, crotonaldehyde, allyl acetoacetate and acetoacetoxyethyl (meth)acrylate,

   g) 0 to 5% by weight of ethylenically unsaturated monomers capable of crosslinking, preferably from the group comprising ethylenically polyunsaturated or polyfunctional monomers, in particular divinylbenzene, diallyl phthalate and butanediol diacrylate, triethylene glycol dimethacrylate, allyl methacrylate, bisphenol A diethylene glycol dimethacrylate, triallyl cyanurate and methylene-bis-methacrylamide,
   and the dispersion also contains

   h) 0.1 to 10% by weight, preferably 0.2 to 6% by weight, relative to the total quantity of all monomer units in the copolymer, of emulsifiers and/or, if necessary, protective colloids, preferably from the group comprising the cationic, amphoteric and in particular nonionic surfactants and/or protective colloids.
4. The use as claimed in one or more of claims 1 to 3, wherein 0.05 to 0.2% by weight, preferably 0.05 to 0.1% by weight, relative to the raw cellulose dry weight, of polymeric retention aid is used.
5. The use as claimed in one or more of claims 1 to 4, wherein the aqueous cationic copolymer dispersion possesses a minimum cation activity of 20 to 200 µmol/g of solids, preferably of 50 to 200 µmol/g of solids, and 60 to 90% of the cationic charge is located on the surface of the dispersion copolymer particles.
6. The use as claimed in one or more of claims 1 to 5, wherein 0.5 to 1% by weight of cationic dispersion copolymer, relative to the dry weight of the raw cellulose stuff, is used, the polymeric retention aid and the cationic dispersion copolymer, each relative to the polymer content thereof, being employed in a weight ratio from 0.2:1 to 0.01:1.
7. A process for producing sized acid-free base paper from raw cellulose fibers in a conventional aqueous suspension by internal sizing at a pH from 6.5 to 7.5 with the use of an aqueous cationic plastics dispersion as the sizing agent, which comprises mixing, with intensive stirring, an aqueous cationic copolymer dispersion as the sizing agent, either simultaneously with a polymeric retention aid or after preceding addition of the polymeric retention aid, preferably at normal temperature, with the aqueous raw cellulose fiber suspension, if desired with the additional use of inert fillers, pigments, dyes and conventional auxiliaries, if appropriate of fillers based on calcium carbonate, the combined use of the aqueous cationic copolymer dispersion with the polymeric retention aid, the quantities employed, the compositions and the property features corresponding to the specifications in any of claims 1 to 6, isolating the sized acid-free base paper in the conventional manner and drying it.
8. An acid-free base paper, internally sized at a neutral pH, in the form of two-dimensional webs, boards or moldings or in the form of flocks or nonwovens, produced by the process as claimed in claim 7 with the use of neutral sizing agents as claimed in any of claims 1 to 6.