EP0279313B1 - Process for preparing a pigmentary agent suited for use in the paper-making industry, said agent improving the printability of paper or board, the agent and its use - Google Patents

Abstract

Pigment-based agent (I) for increasing the printability of paper or cardboard is produced by: (a) making an aq. colloidal system (II) from pigment(s) (III) and water-soluble or swellable hydrogel(s) (IV) contg. anionic gps.; (b) coacervation of (II) with a quat. organic ammonium salt (V); and (c) concn. by sedimentation, centrifuging and/or press filtration. The claims also cover (I). Pref. (III) is kaolin. Pref. (IV) is produced from a hydrated cation-exchangeable smectic laminar silicate with an ion exchange capacity of 50-120 milliequiv./100 g, pref. Na bentonite; or a natural or synthetic organic polymer. (V) has 8-22 C alkyl gp(s). and pref. is stearyldimethylbenzylammonium chloride or distearyldimethylammonium chloride. (II) has a total solids content of 2-15, pref. 3-5 wt.%; and the (III):(IV) ratio is such that 5-40, pref. 10-20% of the (III) particles are coated by coacervation. Coacervation is carried out in the presence of a fat- or oil-soluble optical whitener.

Description

The invention relates to a process for producing a pigment-based agent suitable for the paper and board industry, which improves the printability of paper and board, the agent produced by this process and the use thereof.

From EP-A-0 016 465 a process for the production of coated paper and cardboard and coating slip for carrying out the process is known, whereby aqueous coating slips are also mentioned, the hydrogels containing anionic groups from synthetic organic polymers, an aqueous pigment dispersion and the aqueous solution contain a quaternary ammonium compound. These coating slips are said to lead to better printability in the gravure printing process in LWC papers which have been coated in accordance with the claimed process.

• (a) einem wasserunlöslichen hydratisierten kationenaustauschfähigen filmbildenden smektischen Schichtsilikat mit einer Ionenaustauschfähigkeit von wenigstens 50 mVal/100 g und
• (b) einem daran gebundenen, aus einer Oniumverbindung abgeleiteten organischen Rest in die Fasermasse oder in die Oberfläche des Fasergebildes einbringt, wobei der organophile Komplex durch Reaktion mit dem organischen Lösungsmittel eine Sperrschicht bildet.

DE-OS 35 06 278 (US Ser. No. 831.638) describes a method for improving the holdout of printing inks, lacquers and coating compositions containing organic solvents on fabrics made of fibers, in particular on paper, by introducing water-insoluble substances into them the fiber mass or known in the surface of the fiber structure, which is characterized in that an organophilic complex

• (a) a water-insoluble, hydrated, cation-exchangeable film-forming smectic layered silicate with an ion exchange capacity of at least 50 meq / 100 g and
• (b) an attached organic residue derived from an onium compound into the fiber mass or into the surface of the fiber structure, the organophilic complex forming a barrier layer by reaction with the organic solvent.

The reasons why such an organophilic complex can influence the holdout behavior of a surface have not yet been completely clarified.

In the magazine "Wochenblatt für Papierfabrikation" 114 , 1986, No. 6, pages 177-181, G. Dessauer considers the penetration behavior of gravure inks and reports on preliminary results with the use of such organophilic complexes. In the same journal 114 , 1986, No. 6, pages 182-187, A. Breunig reports on laboratory tests to improve the holdout of printing inks, which confirm the effectiveness of the organophilic complexes described in DE-OS 35 06 278.

It has been shown that the best holdout results are achieved when the reactive organophilic complex of organic solvents is applied directly to the paper surface. It has been found that an application of 0.3 to 1.0 g per square meter (calculated dry) is sufficient to achieve an optimal holdout effect for printing inks and varnishes. Scanning electron micrographs show that a layer of the reactive organophilic complex lies finely and uniformly on the entire surface. The autoadhesion is sufficient to form a closed and sufficiently adherent film.

A disadvantage of this method of application, however, is that the coating must be carried out from an organic solution, whereas there is a strong reluctance for environmental reasons alone.

Attempts to use the reactive organophilic complex from the water phase failed e.g. T. that the entry in the stock suspension requires such substantial amounts that an economic use of the the process described in DE-OS 35 06 278 no longer exists or a coating from the water phase only leads to a usable result if the complex is pre-swollen by means of a minimum amount of 30% of a water-dilutable solvent so that a sufficiently fine dispersion is possible . The coating achieved with this led to a result equivalent to the pure solvent coating only when the paper was satinized at approx. 90 ° C. The order quantities then required were again of a similar order of magnitude as for pure solvent application, but the tendency was somewhat higher.

The application of a water-solvent mixture may be acceptable in some cases, but this is certainly not the cheapest way.

After it had been shown that the efforts to use the reactive organophilic complex in the paper or cardboard mass only brought about 5 - 8%, based on the total substance, of the desired holdout effect, it also became clear that this is possible, but it may be difficult to enforce for cost reasons.

The older German patent application P 36 34 277.7 dated October 8, 1986 deals with the task of applying a reactive complex which improves the holdout of printing ink from the water phase and without any solvent to paper with the title "Means for improving paper and cardboard ".

The object of the present invention is to achieve a simplification and improvement of the method known from DE-OS 35 06 278 and, in particular, an environmentally friendly method which is easy to carry out and avoids the use of organic solvents for the production of a paper and board industry suitable, pigment-based agents that improve the printability of paper and cardboard.

• a) eine wäßrige Pigmentdispersion entweder zunächst mit einer quarternären Ammoniumverbindung versetzt und dann ein wasserlösliches oder wasserquellbares, anionische Gruppen enthaltendes Hydrogel aus der kolloidalen Dispersion eines hydratisierten, kationenaustauschfähigen, filmbildenden smektistischen Schichtsilikats, das eine Ionenaustauschfähigkeit von 50 bis 120 mVal/100 g aufweist, zugibt oder
• b) die wäßrige Pigmentdispersion zunächst mit einem wasserlöslichen oder wasserquellbaren, anionische Gruppen enthaltenden Hydrogel aus der kolloidalen Dispersion eines hydratisierten, kationenaustauschfähigen, filmbildenden smektistischen Schichtsilikats, das eine Ionenaustauschfähigkeit von 50 bis 120 mVal/100 g aufweist, versetzt und dann eine quarternäre Ammoniumverbindung zugibt und gegebenenfalls das dabei durch Koazervation erhaltende Produkt aufkonzentriert.

It has now been found that the task can be solved with the aid of a means which can be produced by

• a) an aqueous pigment dispersion is either first mixed with a quaternary ammonium compound and then a water-soluble or water-swellable hydrogel containing anionic groups from the colloidal dispersion of a hydrated, cation-exchangeable, film-forming smectic layered silicate which has an ion exchange capacity of 50 to 120 mVal / 100 g is added or
• b) the aqueous pigment dispersion is first mixed with a water-soluble or water-swellable hydrogel containing anionic groups from the colloidal dispersion of a hydrated, cation-exchangeable, film-forming smectic layered silicate which has an ion exchange capacity of 50 to 120 meq / 100 g, and then adds a quaternary ammonium compound and if necessary, the product obtained by coacervation is concentrated.

The invention is therefore based on the finding that the printing properties of paper, in particular of thin printing papers which are used in gravure printing, can be considerably improved if the paper, but also cardboard, is treated in bulk or on the surface with an agent, which essentially consists of particles obtained by coacervation from at least one pigment, a water-soluble or water-swellable hydrogel containing anionic groups and a quaternary ammonium salt, and in which the solid pigment particles are "microencapsulated" by a kind of shell from the two other components.

According to the method of the invention, a pigment or pigment mixture with a water-insoluble envelope, e.g. B. a water-insoluble organophilic silicate, in such a finely dispersed form that a coating is applied to practically every pigment grain.

The invention achieves organophilic solvents, e.g. B. isopropanol-free, organophilic phyllosilicates both to be introduced into the paper stock and to produce coating compositions.

Although it is known to coat solid particles by coacervation with gelatin, it is not known to develop modified pigments for the paper industry by means of coacervation.

It has proven to be advantageous if the coacervation or microencapsulation of the pigment particles carried out according to the invention at low consistencies of preferably 2 to 15% total substance content, in particular 3 to 5% solids content, i. H. with comparatively strong dilution.

In addition, you can also work at higher concentrations, for example in a caddy mixer with solids contents of approx. 65 to 70%.

An agent produced according to the method of the invention can be spread onto a paper, cardboard, cardboard or non-woven surface by conventional methods and then smoothed on a calender. However, the agent can, for example, also be mixed into a paper stock and moved out in a known manner on a paper, cardboard or wet fleece machine, with the finished product being filled with e.g. B. 10 to 35 wt .-% of the reactive properties of the particle shells or capsule walls can be used to improve the holdout and the printing work.

When coating paper and cardboard, it is known that it is customary and, for optical reasons, also desirable to add pigments, in particular kaolins, calcium carbonate, titanium dioxide and talc. From the unpigmented application to a line with approx. 94% pigment and 6% binder content, the most varied variants are possible.

If a mixture of an inert white pigment, e.g. B. kaolin, and a reactive, printability-improving complex, it follows logically that with the increase in the percentage of the inert pigment, the opacity, the volume or the whiteness of the coating are improved, but at the same time the desired holdout effect decreases, d. H. is watered down.

DE-OS 35 06 278 describes a coating slip in Example 3 which consists of 96 parts of kaolin and 4 parts of mechanically finely dispersed reactive organophilic bentonite. As usual, this coating slip is bound with a plastic dispersion. After the hot satin, an improvement is evident, but only with a line application of 7 g / m² and side. If one starts from the simplified idea that the dispersed reactive organophilbentonite particles are of the same order of magnitude as the kaolin particles, then in this example 26 kaolin particles have a particle made of reactive organophilic complex.

If you the organophilic bentonite in the presence of the kaolin presented at the usual concentrations in industry of 200 g / l in the ratio of z. B. 10 parts by weight of bentonite to 1 part by weight of kaolin to the reactive complex, so you get a hydrophobic product with full ion exchange, which is just as difficult to disperse as a pure organophilic silicate.

For really perfect dispersion, the addition of a water-miscible solvent, such as. B. isopropanol, necessary to arrive at a finely dispersed stable homogeneous dispersion.

Surprisingly, it has now been found that the problem of fine dispersity takes care of itself if one works according to the inventive method. You can conveniently proceed in such a way that first a pigment, for. B. kaolin, talc, calcium carbonate or another conventional pigment or a mixture of pigments predispersed in water in a comparatively strong dilution.

The coacervation takes place by reacting the three components, namely hydrogel, quaternary ammonium salt and in pigment in water, it being possible for the three components to be added in any order. It is preferred first to react the pigment with the quaternary ammonium salt and then to add the hydrogel.

The implementation of the hydrogel containing anionic groups, e.g. B. Na bentonite, with quaternary ammonium salt in the presence of the pigment is preferably carried out in a comparatively strong dilution in water. In this way, a finely dispersed, comparatively very thin suspension is obtained, in which the pigment and the organophilic silicate are contained, the latter enveloping the pigment particles. The fact that the formation of the organophilic silicate takes place can be seen from the phase separation between the colloid and the pure water which settles on top. The product obtained sediments, if not very quickly. But you can also first prepare a suspension of quaternary salt and pigment particles and add dad hydrogel. You can typically proceed as follows, for example:
From the quaternary ammonium salt, e.g. B. dimethyldioctadecylammonium chloride, is first prepared by heating in water to about 70 ° C, based on the active substance, 1 wt .-% solution. This solution is then z. B. added to a 5% kaolin suspension, in an amount necessary to form 10% organophilic silicate is. The quaternary salt is absorbed on kaolin, especially since it itself has approx. 3 to 5 mVal ion exchange capacity, which must be taken into account when calculating the amounts. A 2% by weight colloidal dispersion in water is prepared from Na bentonite, whereupon it is slowly added to the suspension of the kaolin with the quaternary salt with constant stirring.

About 132 molar equivalents are exchanged in this way with respect to bentonite. A phase separation of the resulting mixture is observed. A warming, e.g. B. to 70 to 80 ° C, accelerates the phase separation. After standing in a separating funnel for several hours, half of the total amount can be drawn off as a clear aqueous, slightly saline solution. The product obtained in this way has a dry content of approximately 6 to 8%. It can be further thickened using any method. Also the opposite way, namely the addition of the Na bentonite dispersion to the pigment and the subsequent reaction with the quaternary ammonium compound in z. B. 1% solution leads to the same result.

The phenomenon that agglomerates which are difficult to disperse no longer occur in the reaction of inorganic layered silicate and quaternary ammonium compound with a sufficient free path length because work is carried out in extreme dilution can only be explained by the fact that a kind of coating of the disperse pigment particles provided has occurred.

Since, among other things, a maximum of opacity is generally sought when coating paper and cardboard, it is often advantageous to use the coacervate made from a known inorganic layered silicate.

When carrying out the process according to the invention, it is advantageous to start from a hydrogel from the colloidal dispersion of a hydrated, cation-exchangeable, film-forming smectic layered silicate which has an ion exchange capacity of 50 to 120 meq / 100 g. Layered silicates of this type are, for example, montmorillonite, hectorite, saporite, sauconite, beidellite, nontronite and preferably bentonite.

Advantageously, customary, known, water-insoluble optical brighteners can also be added, i. H. can be used together with the quaternary ammonium salt. These water-insoluble optical brighteners are then found on the outside of the pigment in the organophilic complex formed.

worin R C₈-C₂₂-Alkyl, C₈-C₂₂-Alkenyl oder eine Gruppe der Formel -(A-O)_y-C₈-C₂₂-Alkyl, R₁ C₁-C₄-Alkyl oder Benzyl, R₂ Wasserstoff, C₁-C₂₂-Alkyl, C₁-C₂₂-Alkenyl oder eine Gruppe der Formel -(A-O)_y-B oder der Formel -(A-O)_y-C₈-C₂₂-Alkyl, R₃ Wasserstoff, C₁-C₄-Alkyl oder eine Gruppe der Formel -(A-O)_y-B, A C₁-C₄-Alkylen, B Wasserstoff oder eine Gruppe der Formel -COR, y eine Zahl von 1 bis 25 und X ein Anion bedeuten;

worin X, R, R₁ und R₂ die oben angegebenen Bedeutungen haben;

worin z jeweils eine Zahl von 1 bis 10 bedeutet und X, R₁, A und B die oben angegebenen Bedeutungen haben;

worin p 1 oder 2 bedeutet und X, R und R₁ die oben angegebenen Bedeutungen haben;

worin die Gruppen R₄ gleich oder verschieden sein können und Wasserstoff C₁-C₄-Alkyl, Benzyl oder eine Gruppe der Formel -(A-O)_z-B, m 2 oder 3 und n 0 oder 1 bedeuten und X, R, R₁, A, B und z die oben angegebenen Bedeutungen haben;

worin R₅ Wasserstoff, C₁-C₄-Alkyl oder Benzyl bedeutet und X, R, R₁ und m die oben angegebenen Bedeutungen haben;

worin R₆ OH, NH₂ oder eine Gruppe der Formeln -OCOR oder -NHCOR bedeutet und X, R und R₁ die oben angegebenen Bedeutungen haben;

worin X, R und R₁ die oben angegebenen Bedeuten haben.Suitable quaternary organic ammonium salts are those of the following formulas (1) to (8)

wherein R is C₈-C₂₂-alkyl, C₈-C₂₂-alkenyl or a group of the formula - (AO) _y -C₈-C₂₂-alkyl, R₁ C₁-C₄-alkyl or benzyl, R₂ is hydrogen, C₁-C₂₂-alkyl, C₁- C₂₂-alkenyl or a group of the formula - (AO) _y -B or of the formula - (AO) _y -C₈-C₂₂-alkyl, R₃ is hydrogen, C₁-C₄-alkyl or a group of the formula - (AO) _y -B, A C₁-C₄alkylene, B is hydrogen or a group of the formula -COR, y is a number from 1 to 25 and X is an anion;

wherein X, R, R₁ and R₂ have the meanings given above;

wherein z each represents a number from 1 to 10 and X, R₁, A and B have the meanings given above;

wherein p is 1 or 2 and X, R and R₁ have the meanings given above;

in which the groups R können can be identical or different and are hydrogen C₁-C₄ alkyl, benzyl or a group of the formula - (AO) _z -B, m 2 or 3 and n are 0 or 1 and X, R, R₁, A, B and z have the meanings given above;

wherein R₅ is hydrogen, C₁-C₄ alkyl or benzyl and X, R, R₁ and m have the meanings given above;

wherein R₆ is OH, NH₂ or a group of the formulas -OCOR or -NHCOR and X, R and R₁ have the meanings given above;

wherein X, R and R₁ have the meanings given above.

Of all quaternary organic ammonium salts, the compounds of formula 1 are preferred. The following group is preferred in the compounds of the formulas 1 to 8: R = C₁₂-C₁₈-alkyl or C₁₂-C₁₈-alkenyl, R₁ = methyl or ethyl, R₂ = methyl, ethyl, C₁₂-C₁ oder-alkyl or C₁₂-C₁₈-alkenyl , A = C₂H₄ or C₃H₆ and n = 1 or 2. Insofar as substituents consist of C₈-C₂₂-alkyl or C₈-C₂₂-alkenyl groups, groups which are derived from natural fatty acids and their mixtures are particularly suitable here. such as tallow fatty acid, coconut fatty acid, oleic acid, palmitic acid, stearic acid. Possible anions are, for example, chloride, bromide, sulfate, methosulfate, dimethophosphate, phosphate or anions of organic acids such as acetic acid, propionic acid, trichloroacetic acid, lactic acid, citric acid, tartaric acid, tartonic acid, oxalic acid, malonic acid.

Appropriately, the procedure is such that the weight fraction of the pigment core covering or capsule wall formed by the coacervation, i. H. the proportion of hydrogel, based on the total amount of solid matter of all components, is set to 5 to 40% by weight, preferably 10 to 20% by weight. The proportion by weight of quaternary ammonium salt in the pigment core coating or capsule wall can be different. It depends on the ion exchange ability of the hydrogel, e.g. B. the layered silicate, and the degree of ion exchange. This means that, depending on how much ammonium salt is added, practically a complete ion exchange or an incomplete ion exchange is effected. Sufficient ammonium salt can also be used so that the "microencapsulated" particles obtained are cationic and repel each other. Based on the hydrogel, the agents according to the invention consist of 1 to 50% by weight of quaternary ammonium salt and 50 to 99% by weight of the hydrogel or layered silicate.

With the pigments coated by the method of the invention under comparatively strong dilution, after thickening via sedimentation, centrifuge or the like, surface preparations can be applied to paper or cardboard by known methods. If e.g. B. the ratio of pigment to formed reactive organophile complex is 10 to 1, z. B. at 3 g / m² and page 0.27 g / m² organocomplex. If this order is hot satinized, the z. B. on the kaolin reactive complexes an excellent holdout for gravure ink. The function of the reactivity with the printing ink can be combined in this way with the need for optical coverage of the paper surface without the layer thickness having an influence on the printing behavior. If one assumes that a normal coating kaolin has a specific surface of 6 to 8 m² / g, the reactive organophilic complex will have a specific surface of the same order of magnitude in the pigment coating. This means a very substantial increase in the specific surface area of the reactive complexes compared to a simple mixture.

The pigments coated by the process of the invention are hydrophobic. This means that they are no longer bound to the usual strengths. Plastic dispersions adjusted to hydrophilic pigments can no longer be used. With plastic dispersions, such as. B. based on methyl methacrylate (Rohagit SD 25) or styrene-acrylate (Dow Latex 695), the coated hydrophobic pigments can be bound perfectly. For example, 6% of the binder, based on the coated pigment, is sufficient to achieve a line binding suitable for gravure printing. As a result of the thermoplastic deformability of the organophilic silicates, adhesion to the outer layer of the pigments occurs during the hot satinization. For manipulation in production, however, binding by means of a binder which is compatible with the coated pigment appears expedient. For a surface treatment of the paper with the agent to be produced according to the invention, this agent is incorporated into a suitable binder such as polyvinyl alcohol or styrene-acrylate dispersion and applied to the paper in a conventional manner. The proportion of binder here is approximately 5 to 20% by weight, the application amounts of these mixtures to the paper are generally 0.1 to 10 g / m². The pigments encased by the process of the invention can also be used in the stock of a paper to be treated in bulk. Due to the significantly increased specific surface area, one comes obviously with smaller amounts of the reactive substance. The amount of the agent produced according to the invention is about 12 to 35% by weight, based on the fiber content.

If Na bentonite is used as the hydrogel containing anionic groups to carry out the process according to the invention, it is not necessary to start from a purified Na bentonite. Rather, it is e.g. B. also possible, commercial, about 75% active ingredient containing simple Na bentonite, as z. B. is used in wastewater treatment as a coacervable colloid. Strangely enough, the strong intrinsic color of this material does not play the expected negative role in the case of coating a pigment which is whiter per se.

By coating CaCO₃ according to the proposal of this invention, the durability of this pigment in an aluminum sulfate-containing paper mill circuit is obviously improved, which is an extremely desirable side effect.

The pigment-based compositions which can be prepared by the process of the invention can also advantageously be used for the production of paints based on plastic dispersions, for the production of water-based paints, for the production of wallpaper primers and wallpaper paints, i.e. H. For example, use with advantage wherever an improvement in weather resistance, wipability or washability or the like is important.

The following examples are intended to illustrate the invention:

example 1

50 g of a commercially available fine paper kaolin (Dorfner FP 75) are finely dispersed in one liter of water using a high-shear mixer (Ultraturrax, manufacturer: Jahnke and Kunkel) for 15 minutes. A dispersing agent is not added since practically all commercially available paper kaolins already contain such, mostly anionic ones.

2.3 g of commercially available dimethyldioctadecylammonium chloride with 77% active ingredient content (Präpagen WK, manufacturer: Hoechst AG) are dissolved in 230 ml of water at 70 ° C. The solution of the strongly cationic quaternary ammonium salt obtained is added with continued stirring of the kaolin suspension.

4.3 g of commercially available Na bentonite (Opazil) which has not been cleaned from quartz and heavy spar is dispersed in 215 ml of water and likewise sheared intensively in a high-shear mixer of the type specified for 15 to 20 minutes until a homogeneous hydrosol is obtained.

The fully hydrated, film-forming water-Na-bentonite mixture obtained has an active substance content of reactive and ion-exchangeable bentonite of 3.23 g. About 5 g of an organophilic layered silicate which is insoluble in water are deposited on the kaolin. The total amount of the aqueous dispersion of almost 1,500 ml obtained separates into a water phase and a sedimenting dispersion phase. This separation is accelerated at 70 ° C. The reaction mixture obtained can be concentrated in a separating funnel overnight to about 700 ml, which then contain 55 g of solid substance. This corresponds to a solids content of approx. 7.86% by weight. For this purpose, based on the solids content, 6% by weight of a styrene-acrylate latex (3.3 g solid or 6.6 g of a commercially available plastic dispersion with a solids content of 50%). After carefully and gently stirring in this binder, a line of 3.5 g / m² and page is applied in the customary manner to a conventional wood-containing coating base paper of 38 g / m². After drying, the satin is calendered to an optimal gloss at a temperature of 90 ° C in a conventional calender. This line now contains approximately 8.63% by weight of a reactive organophilic silicate, corresponding to approximately 0.3 g / m² per side. An intaglio print from a toluene solution attached to it shows an outstanding holdout for the color and an excellent print gloss.

Example 2

Starting from the reaction mixture of kaolin and an organophilic phyllosilicate prepared according to Example 1, a mixture consisting of 40% by weight of this mixture and 60% by weight of a fiber mixture is stirred together. The fiber mixture consists of 25% long fiber sulfate pulp, ground on 23 ° Schopper-Riegler and 75% of a softwood cut with 74 ° S.R.

A sheet of 45 g / m 2 with a filler content of 32% by weight is produced from this mixture on a Rapid Koethen sheet former. After calendering on a calender with roller temperatures of 110 ° C, the paper is printed in a test printer. This shows a significantly improved acceptance of the gravure printing ink, an improved gloss, a greater depth of color and a reduced tendency to missing dots.

Example 3

35 g of a commercially available calcium carbonate (Durcal) are added to one liter of water without the addition of an auxiliary dispersed using an intensive stirrer. A 2% dispersion of a purified Na bentonite in water is produced with vigorous stirring. 162 ml of this calcium carbonate dispersion are mixed into the calcium carbonate dispersion with intensive stirring. Starting from commercially available dimethyldistearylammonium chloride, a 2% by weight solution is prepared using hot water. This solution is added while stirring to the mixture of carbonate and Na bentonite until approximately 120 to 125 ml have been added. This corresponds to an equimolar amount, based on bentonite, of approx. 130 to 135 meq. This means that in addition to the amount that can be converted via the ion exchange, a small excess of the strongly cationic quaternary ammonium salt was used. This improves the repulsion of the enveloped particles formed with one another.

After settling and decanting the excess water, a suspension of coated carbonate particles in water with a solids content of 8% is obtained. With 4.5% by weight of a plastic binder based on methyl methacrylate (Rohagit SD 25, manufacturer: Röhm GmbH), registered as a conventional plastic dispersion, a spreadable coating composition is obtained which is applied in the usual way to paper or cardboard. With a line application of 4 g / m², the line contains 0.5 g / m² reactive organophilic layered silicate, an amount which is sufficient for an almost complete holdout of solvents and thus also printing ink containing solvents. In this example too, satin coating at high temperature is necessary so that the density of the packaging of the coated pigments in this line is sufficient.

Waste paper obtained from this coated paper or cardboard has an increased resistance to the Calcium carbonate in paper mixtures containing aluminum sulfate. The deinkability of this line is also improved according to the invention, since less printing ink is required to achieve the same depth of color.

Example 4

40 g of a high quality spreadable kaolin (type SPS, manufacturer: English China Clay Corp.) are finely dispersed in 1000 ml of water. 0.7% of an optical brightener for oils and fats, dissolved in isopropanol in a ratio of 1 to 2, is mixed into a stock paste of dimethyldistearylammonium chloride, based on the active ingredient content, and stirred vigorously. It is recommended to heat the paste in a water bath to approx. 60 to 70 ° C. The quaternary ammonium salt is then diluted down in hot water to a concentration of 1% by weight. 245 ml of this solution are mixed into the kaolin suspension with stirring. Then 215 ml of a 2% commercial Na bentonite slurry are added (Opazil, manufacturer: Südchemie AG).

In this way, pigments coated with the organophilic silicate are obtained which are already highly white, the pigment coating containing the water-insoluble optical brightener. Using a compatible plastic binder, as described in Example 3, a bright white, optically brightened line is obtained which shows a particularly good holdout for gravure and web offset printing inks. Here too, a good hot satin finish is to be carried out after the stroke and drying of the paper web. The packing density of the coated kaolin particles is also of great importance here

Example 5

375 g of commercial kaolin are dispersed with 500 ml of water in a twin-screw kneader. Separately, 15 g of dimethyldioctadecylanmonium chloride (commercially available) are diluted in water to give a 50% dispersion, and this dispersion is introduced into the twin-screw kneader together with 28 g of sodium bentonite. The mixture is then homogenized for one hour and the mass obtained is diluted with water to give a slurry with a solids content of 25%. So much of a 10% aqueous solution of polyvinyl alcohol is added to this slurry that the total content of polyvinyl alcohol is 7% by weight or 14% by weight. This gives a completely homogeneous coating composition for gravure printing (binder content 7%) or offset printing (binder content 14%).

Claims (8)

1. A process for the production of an agent suitable for the paper and board industry and improving the printability of paper and board, which comprises

   a) either treating an aqueous pigment dispersion first with a quaternary ammonium compound and then adding a water-soluble or water-swellable hydrogel containing anionic groups and composed of the colloidal dispersion of a hydrated, cation-exchangeable, film-forming smectic phyllosilicate having an ion exchange capacity of 50 to 120 meq./100 g, or

   b) treating the aqueous pigment dispersion first with a water-soluble or water-swellable hydrogel containing anionic groups and composed of the colloidal dispersion of a hydrated, cation-exchangeable, film-forming smectic phyllosilicate having an ion exchange capacity of 50 to 120 meq./100 g and, if appropriate, concentrating the product obtained by coacervation.
2. The process as claimed in claim 1, wherein the quaternary organic ammonium salt used is stearyldimethylbenzylammonium chloride or distearyldimethylammonium chloride.
3. The process as claimed in claim 1, wherein the smectic phyllosilicate used is sodium bentonite.
4. The process as claimed in claim 1, wherein a colloidal system having a total solids content from 2 to 15 % by weight is subjected to coacervation.
5. The process as claimed in any of claims 1 to 4, wherein the pigment/hydrogel weight ratio, relative to solids, is selected such that the proportion of the coverings, formed via the coacervation, of the pigment particles, relative to the latter, is 5 to 40 % by weight.
6. An agent, produced as claimed in any of claims 1 to 5.
7. The use of an agent, produced as claimed in any of claims 1 to 5, for producing a paper- or board-coating composition.
8. The use of an agent, produced as claimed in any of claims 1 to 5, as a filler for mixing into a raw paper pulp.