DE102004023864B4 - Surface-modified inorganic fillers and pigments - Google Patents

Abstract

Process for the preparation of surface-modified inorganic fillers or pigments with a particle size distribution of
50 to 100 wt. % of particles < 2 µm,
27 to 99 wt. % of particles < 1 µm
each based on the equivalent diameter,
characterized by the fact that
Filler or pigment slurries with a filler or pigment content of 10 to 95% by weight, based on the slurry of natural and/or precipitated calcium carbonate, kaolin, artificial and/or natural aluminum silicates and oxide hydrates, titanium dioxide, satin white, dolomite, mica, metal flakes, bentonite, rutile, magnesium hydroxide, gypsum, layered silicates, talc, calcium silicate and other minerals and earths or mixtures thereof
under the influence of shear forces,
using aqueous polymer dispersions selected from natural rubber, synthetic rubber, synthetic resins and plastics with a solids content of 40 to 60% by weight of natural and/or synthetic polymers with a particle size of 0.005 to 6 µm in aqueous phases with an amount of 0.1 to 15% by weight of polymer dispersion (solid substance), based on the amount of pigment and further with polyacrylates as grinding aids and/or dispersants (active substance) in an amount of 0.1 to 2.0% by weight, based on the fillers or pigments,
ground to the desired grain size.

Description

The invention relates to a process for producing surface-modified inorganic fillers and pigments of defined grain size, the fillers and pigments thus obtained and their use.

In many areas of technology, inorganic pigments or fillers are bound with binders in the form of polymer dispersions, for example in the production of emulsion paints, adhesives or paper.

DE 693 03 877 T2 relates to a process for producing filler pigments on an inorganic basis, in which a compact mineral and a lamellar mineral and/or a plastic pigment are ground together in an aqueous medium in the presence of at least one grinding aid. The comminution is advantageously carried out in the presence of a colloidal protective agent. Preparations of filler pigments obtained by this process and their uses, in particular in the paper industry.

DE 23 44 388 A1 relates to a process for hydrophobizing silicon dioxide.

EN 38 39 900 A1 relates to a process for hydrophobizing particulate solids containing Si-OH groups by reacting a hydrophobizing agent based on organosilicon compounds with particulate solids containing Si-OH groups while simultaneously subjecting the reaction mixture to mechanical stress, which is characterized in that 5 to 50% by weight of the particulate solids containing Si-OH groups, based on the total weight of the reaction mixture consisting of particulate solid and hydrophobizing agent, are used, and the use of the hydrophobic particulate solid obtained in a process for producing compositions based on diorganopolysiloxanes which can be cured to form elastomers.

The EP 0 515 928 B1 relates to surface-modified platelet-shaped pigments with improved stirring behavior as well as their production process and use. The platelet-shaped pigments, for example platelet-shaped metals, metal oxides, mica pigments and other platelet-shaped substrates, are coated in a mixing vessel with a polyacrylate or polymethacrylate or their water-soluble salts and optionally a solvent or solvent mixture while stirring.

For example, a large amount of fillers are used in the production of paper. Almost all papers are mixed with fillers, which give printing and writing paper in particular a uniform formation, better softness, whiteness and feel.

Natural printing papers (uncoated papers) contain up to 35% by weight of fillers, while coated papers contain 25% to 50% by weight. The amount of filler depends very much on the intended use of the paper. Heavily weighted papers have lower strengths and poorer sizing properties.

The filler content in the paper pulp is usually between 5 and 35% by weight and consists of primary pigments or recirculated coating pigments, which can come from leftover coating colors or coated rejects. In addition to the whiteness of the filler, which is important for white-tinted papers, the grain size plays a key role, as it has a strong influence on the filler yield and the physical properties of the paper, particularly the porosity. The filler content remaining in the paper is between 20 and 80% by weight of the amount added to the fiber suspension. The yield depends on the type of filler as well as the material composition, the degree of grinding, the fixation of the filler particles by resin and aluminum sulfate, the paper weight, the paper machine speed, the type of water removal and the fineness of the screen.

According to consumption, the following products are now more important as fillers and coating pigments: kaolin, calcium carbonate, artificial aluminium silicates and oxide hydrates, titanium dioxide, satin white, talc and calcium silicate.

DE 1 96 27 623 C1 ( WO 98/01621 ) describes a process for recycling fillers and coating pigments from paper, cardboard and carton production from the residual water sludge of coating wastewater, deinking plants, internal sewage treatment plants or separation devices as well as the use of a pigment slurry thus obtained to produce a coating slip for the paper industry or for use in the mass of paper production. An essential element of the invention is a process for recycling fillers and coating pigments from paper, cardboard and carton production from the residual water sludge of coating waste water, deinking plants, internal sewage treatment plants or separation devices, which is characterized in that the residual water sludge containing fillers and coating pigments is mixed and then ground to form a pigment slurry with fresh pigment or fresh filler as a powder, slurry containing fresh pigment and/or fresh filler.

The object of the present invention is to improve the contact of inorganic fillers and pigments and binding agents (binders) in the form of polymer dispersions and thus to reduce the necessary amount of binding agents or to improve the bonding of the fillers or pigments to one another and to the substrate, for the production of filler or pigment slurries, in particular in the paper industry and other fields of application, such as the paint industry or the adhesive industry.

According to the invention, it has been found that inorganic pigments of defined grain size, the surface of which during grinding with binders, hereinafter referred to as polymer dispersions, can be used advantageously in many areas of technology, for example in the paper industry and the paint industry or the adhesives industry.

Accordingly, a first embodiment of the present invention consists in a process for producing surface-modified inorganic fillers or pigments having a particle size distribution of
50 to 100 wt. % of particles < 2 µm,
27 to 99 wt. % of particles < 1 µm
each based on the equivalent diameter,
which is characterized by the fact that

Filler or pigment slurries with a filler or pigment content of 10 to 95% by weight, based on the slurry of natural and/or precipitated calcium carbonate, kaolin, artificial and/or natural aluminum silicates and oxide hydrates, titanium dioxide, satin white, dolomite, mica, metal flakes, bentonite, rutile, magnesium hydroxide, gypsum, layered silicates, talc, calcium silicate and other minerals and earths or mixtures thereof
under the influence of shear forces,
using aqueous polymer dispersions selected from natural rubber, synthetic rubber, synthetic resins and plastics with a solids content of 40 to 60 wt.% of natural and/or synthetic polymers with a particle size of 0.005 to 6 µm in aqueous phases with an amount of 0.1 to 15 wt.%, polymer dispersion (solid substance), based on the amount of pigment and
further with polyacrylates as grinding aids and/or dispersants (active substance) in an amount of 0.1 to 2.0% by weight, based on the fillers or pigments,
ground to the desired grain size.

It has been found that polymer dispersions, which should normally have an adhesive effect, are suitable for providing inorganic fillers and pigments in a form which imparts an increased binding capacity compared to fillers and pigments known from the prior art with the same grain size distribution when binding agents are brought into contact with surfaces of inorganic fillers and pigments during the grinding of the fillers and pigments to the desired grain size. The binding agents can come from recyclable materials, for example residual water sludge, or can also be added directly.

Surprisingly, it was found that the polymer particles do not lead to a sticking or agglomeration of the filler particles and pigment particles, but apparently form a fine film on the surface of the fillers or pigments, which have a much better adhesion to each other and to the substrate, for example fibers in the paper industry.

A particularly preferred filler or pigment for modification in the sense of the present invention is calcium carbonate, in particular natural and/or precipitated calcium carbonate.

In addition to calcium carbonate, other fillers and pigments known in the art can also be used, such as kaolin, artificial and/or natural aluminum silicates and oxide hyde rate, titanium dioxide, satin white, dolomite, mica, metal flakes, especially aluminium flakes, bentonite, rutile, magnesium hydroxide, gypsum, layered silicates, talc, calcium silicate and other stones and earths.

For the purposes of the present invention, the fillers and pigments defined above are used in an amount of 10 to 95 wt.%, in particular 30 to 70 wt.%, based on the slurry, in particular water.

When fillers or pigments are applied, for example as a component of coating color in paper production, a high proportion of the binding agent usually migrates into the paper surface. A large proportion of the binding agent is absorbed into the raw paper before it forms a film. The top coating layer becomes depleted of binding agents and so-called picking occurs. However, if the polymer binding agent is ground onto the filler or pigment, migration of the binding agent does not occur or only occurs to a small extent; this means that the offset resistance (resistance to picking) is higher because no (or little) binding agent is lost through absorption. In the current state of the art, however, the loss of binding agent must be compensated by an increased binding agent content in the coating color.

Polymer dispersions in the sense of the present invention comprise the resin solids themselves and their dispersions (latices) of finely divided natural and/or synthetic polymers, with a particle size of 0.005 to 6 µm. These are usually in the form of aqueous, less frequently non-aqueous dispersants. This includes dispersions of polymers such as natural (rubber latex) and synthetic rubber (synthetic latex), as well as synthetic resins (synthetic resin dispersions) and plastics (plastic dispersions) such as polymers, polycondensates and polyaddition compounds, in particular based on polyurethane, styrene/butadiene, styrene/acrylic acid or ester, styrene/butadiene/acrylic acid or ester and vinyl acetate/acrylic acid or ester as well as suspensions containing acrylonitrile.

Corresponding polymer dispersions are commercially available under the product names Basonal ^® , Acronal ^® and Styronal ^® as binders for the emulsion paint industry and also for paper and cardboard coating. In the prior art, these polymer dispersions are incorporated into the filler or pigment slurries, which are usually neutral to alkaline, by stirring without any strong shearing, without any change in the grain size of the filler particles or pigment particles. In the sense of the present invention, however, these are brought into direct contact with the inorganic fillers and pigments by the action of pressure and shear forces. The same naturally also applies to the production of filler or pigment slurries, for example in adhesive production, in which no water is added separately. Under the action of pressure and shear forces during grinding, surface-modified inorganic fillers and pigments are obtained which have an improved binding effect compared to the prior art. It is particularly preferred in the context of the present invention to wet-grind the inorganic fillers or pigments to the desired grain size in the presence of the polymer dispersions. This makes it possible to produce a large variation in the whiteness and size distribution of the fillers or pigments in the case of white fillers or pigments, and this variation can be controlled in particular by the type and duration of the grinding.

The amount of polymer dispersions that are brought into contact with the inorganic fillers or pigments is of some importance. Thus, in the context of the present invention, the inorganic fillers or pigments are brought into contact with an amount of 0.1 to 15% by weight of polymer dispersion (solids), based on the amount of pigment. The polymer dispersions are in aqueous or non-aqueous form with a solids content of 40 to 60% by weight, in particular 50% by weight.

In addition to the polymer dispersions, it is also necessary for the purposes of the present invention that the inorganic fillers or pigments are brought into contact with known dispersants or grinding aids, namely polyacrylates. Such polyacrylates are described, for example, in the above-mentioned EP 0 515 928 B1 described, to which reference is made in full.

In the sense of the present invention, the fillers or pigments are brought into contact with the above-mentioned dispersant active substance in an amount of 0.1 to 2.0, in particular 0.2 to 0.4 wt. %, based on the solid substance.

In paper production, it is usual to use fillers and coating pigments either as powder or in the form of a concentrated slurry containing 50 to 80% by weight of solids. These fillers and pigments are usually provided by the manufacturers with the desired whiteness and particle size distribution. An essential element of the present invention is the use of the inorganic fillers and pigments in a type of “basic grain”, preferably as a solid or also as a highly concentrated slurry, for example with a solids content of 70 wt.% to 85 wt.% or more, for example with an average grain diameter of 50% <1 µm to 50 010 <15 µm, in particular 50 010 <3 µm to 50 010 <8 µm and grinding in the presence of the polymer dispersion, in particular in an aqueous phase, to the desired grain size.

Preferably, a slurry with a solids content of 10 to 95 wt.%, in particular 40 to 80 wt.%, is ground.

This allows a flexible and rapid response to quality and production requirements, for example the various paper raw materials for the paper pulp, the fillers or pigments or slurries for the precoat, topcoat and single coat or the pigmentation alone, as well as the mixing with other fillers or pigments.

For the purposes of the present invention, additives known per se such as wetting agents, stabilizing agents, grinding aids and dispersing aids can be used during the mixing and/or grinding of the inorganic fillers and pigments.

The pigment slurries obtainable with the aid of the present invention can be used particularly advantageously in the paper industry, in particular for producing a coating color for the paper coating or in the paper pulp. Use for producing a coating pigment slurry for offset paper is particularly preferred. In addition, the slurries according to the invention are also suitable for producing a coating color for lightweight, coated papers, in particular at high application speeds, and for producing web offset papers, in particular for producing lightweight, coated web offset papers, coating cardboard and specialty paper, such as labels, wallpaper, silicone base paper, carbonless paper, packaging papers, and for admixture with gravure papers. In this sense, the coating pigment slurries obtainable according to the invention can be used in particular in sheet-fed offset, in particular for sheet-fed offset single coating, sheet-fed offset double coating: sheet-fed offset pre-coat and sheet-fed offset top coat; - in web offset, in particular for the LWC web offset single coat, web offset double coat: web offset precoat and web offset top coat; - in gravure printing, in particular for the LWC gravure single coat, gravure double coat: gravure precoat and gravure top coat; - in cardboard, in particular for the cardboard double coat: cardboard precoat and cardboard top coat as well as flexographic printing and for special papers, in particular for labels and flexible packaging. The fillers and pigments according to the invention can also be used advantageously in paper for digital printing processes.

The process offers the possibility of using the pigment slurries produced according to the invention without any loss of quality in the base papers, coatings and in particular the final qualities produced therewith.

The present invention can also be used in particular for the production of adhesives. Adhesives are known to be non-metallic substances that connect parts to be joined by surface adhesion and internal strength (cohesion). Adhesive is a generic term and includes other common terms for types of adhesive that are chosen according to physical, chemical or processing-related aspects, such as glue, paste, dispersion, solvent, reaction, contact adhesives. The names of the adhesives often contain additions to identify basic materials (for example starch paste, synthetic resin glue, hide glue), processing conditions (for example cold glues, hot-seal or hot-melt adhesives, assembly glue), intended use (for example paper glue, wood glue, metal glue, wallpaper paste, rubber glue) and delivery form (for example liquid glue, glue solution, glue powder, board glue, glue jelly, putty, adhesive tape, adhesive film).

Adhesives are mainly based on organic compounds, but inorganic adhesives are also used.

DIN 16 920 divides adhesive types into physically setting adhesives (glues, pastes, solvents, dispersion, plastisol and hot melt adhesives) and chemically setting adhesives (e.g. cyanoacrylate adhesives). Physically setting adhesives can be solvent-free (hot melt adhesives) or contain solvents. They set by changing the state of aggregation (liquid ⇒ solid) or by evaporating the solvent before or during the bonding process and are generally single-component.

The chemically setting, single- or multi-component reaction adhesives can be based on all polymerization reactions: two-component systems made of epoxy resins and acid anhydrides or polyamines react according to polyaddition mechanisms, cyanoacrylates or methacrylates according to polymerization mechanisms and systems based on aminoplasts or phenolplasts according to polycondensation mechanisms.

The range of monomers or polymers that can be used as adhesive raw materials is very variable and makes it possible to bond almost all materials. Bonding plastics is often problematic.

The dominant goal of ongoing adhesive developments is the (necessary from an ecological and economic point of view) conversion of systems containing organic solvents to solvent-free systems or systems containing water as a solvent.

The fillers or pigments according to the invention are also suitable for the production of paints and varnishes. The fillers or pigments are particularly preferably used for the production of emulsion paints and emulsion dyes. The latter refers to a group of synthetic dyes that are poorly soluble in water (in most cases azo dyes or anthraquinone derivatives, also naphthol AS dyes), which are ground very finely together with dispersants and used for dyeing and printing acetate, polyester, polyamide, polyacrylonitrile, PVC and polyurethane fibers. During dyeing, the dye components dissolved molecularly in the dye bath penetrate the fiber by diffusion, form a solid solution there and thus produce real colors. A modern variant is so-called transfer printing, in which emulsion dyes are thermally transferred from paper to fabrics.

This makes it possible to finely grind relatively coarse inorganic fillers or pigments. The user of the fillers and pigments according to the invention is not bound to the particle sizes specified by the raw material suppliers. In many areas of the state of the art, it is common practice to characterize the raw material suppliers' finished filler or pigment slurries with the number of percent by weight of particles smaller than 2 µm, for example as quality, fineness or type 95, 90, 75, 60, 50 etc.

In many areas of technology, the particle size distribution plays a particular role when using fillers or pigments. For the purposes of the present invention, it is particularly preferred to use fillers or pigments which have a particle size distribution of 10 to 99% by weight of particles < 10 µm, in particular 10 to 95% by weight of particles < 1 µm, in each case based on the equivalent diameter.

The surface-modified inorganic fillers or pigments obtainable according to the invention have a particle size distribution of
50 to 100 wt. % of particles < 2 µm,
27 to 99 wt. % of particles < 1 µm
each based on the equivalent diameter.

1. a) 95 bis 100 Gew.-% an Teilchen < 20 µm und/oder
2. b) 50 bis 100 Gew.-% an Teilchen < 2 µm, insbesondere 50 bis 95 Gew.-% an Teilchen < 2 µm und/oder
3. c) 27 bis 99 Gew.-% an Teilchen < 1 µm, insbesondere 27 bis 75 Gew.-010 an Teilchen < 1 µm und/oder
4. d) 0,1 bis 55 Gew.-% an Teilchen < 0,2 µm, insbesondere 0,1 bis 35 Gew.-% an Teilchen < 0,2 µm,

jeweils bezogen auf den Äquivalentdurchmesser.Particularly preferred in the context of the present invention are fillers or pigments with a particle size distribution of

1. a) 95 to 100 wt.% of particles < 20 µm and/or
2. b) 50 to 100% by weight of particles < 2 µm, in particular 50 to 95% by weight of particles < 2 µm and/or
3. c) 27 to 99 wt.% of particles < 1 µm, in particular 27 to 75 wt.% of particles < 1 µm and/or
4. d) 0.1 to 55% by weight of particles < 0.2 µm, in particular 0.1 to 35% by weight of particles < 0.2 µm,

each based on the equivalent diameter.

Preferred areas of application of the process according to the invention and the fillers or pigments thus obtained are discussed below.

Paint industry:

The classic recipe for an interior emulsion paint usually contains around 10% of a polymer dispersion based on styrene acrylate. A classic facade paint recipe usually has 18 to 25% of a polymer dispersion.

According to the invention, it was found that by using a filler slurry coated with polymer dispersion, the proportion of the total dispersion or the resin proportion in the final recipe can be reduced while maintaining the same strength of the recipe as before, or that the strength increases significantly with the same resin proportion in the recipes as before. In the present case, a standard recipe is therefore equipped in such a way that 50% of the binder contained in the recipe is replaced. Due to the need to use a coated calcium carbonate slurry as the basis for the tests, the solids content of the calcium carbonate in the standard recipe is then used analogously and modified in the comparison recipe in such a way that the fillers previously introduced dry into the dispersion are adequately replaced by the same amount of slurry calculated on a solid basis. This means that there are two identical recipes, with adequately equal amounts of binders and equal amounts of inorganic fillers. In the latter case, however, a portion of the previous standard recipe portion was replaced by the coated carbonate slurry newly designed according to the invention, as described above. This proved that the strength of the paint increases adequately, by taking washability according to DIN as a basis. The paints produced using the fillers or pigments according to the invention showed significantly improved resistance.

In another case, the resin content in the recipe was reduced by 20% by weight compared to the standard recipe. The remaining 80% by weight of the resins contained in the recipe were replaced by adding half of these remaining 80% by weight of normal standard dispersion and the other half of the carbonate slurry coated according to the invention using the new process. Here, too, the washability was measured in comparison to the standard. The paints produced using the fillers or pigments according to the invention showed significantly improved resistance.

Adhesives industry

An adhesive formulation for a typical floor adhesive for bonding textiles or other floors typically contains 35% of a terpolymer dispersion with a resin content of 50%.

In the present case, part of the binder was replaced with a part based on the present invention, so that the total proportion of resin in the recipe remained the same as before, and the filler proportion in the recipe remained the same as in the standard. It was to be proven that the strength had improved significantly compared to the standard.

The formulations produced in this way were used by bonding a previously determined standard carpet to a solid substrate and then comparing the force required to delaminate the layers bonded together in this way. The adhesives produced using the fillers and pigments according to the invention had significantly higher delamination forces.

Paper industry

In the paper industry, coating colors containing approximately 10% by weight of a polymer dispersion (solids) are usually used for surface coating. In the present case, the standard coating color was based on calcium carbonate with 10% by weight of polymer dispersion (solids). As an alternative, the same recipe was produced with the same amounts of carbonate and binder, but part of the previous recipe was modified by replacing both binder and calcium carbonate with calcium carbonate slurry coated according to the invention, using the same polymer dispersion for coating that had previously only been added as a component in the recipe. The pick resistance of the coating was then compared, with a base paper of approximately 14 to 15 g/m ² being coated with the above recipe, one with the standard and the other with the alternative. The pick resistance provides information about which coating film adheres better to the base paper. paper. The pick resistance of the papers using the fillers and pigments according to the invention was significantly improved compared to standard fillers and pigments.

With these three examples, it was then possible to prove from an application point of view that a coating in the liquid phase of the inorganic filler results in a significant improvement in the strength values of the coating compared to the traditional application in which dispersions and inorganic fillers are simply mixed.

A particularly preferred application of the present invention relates to the use of residual water sludge, in particular in the paper industry.

In paper production, losses of coating colours or coating colour components occur which range between 4% and 12% by weight of the material used.

• • an den Streichaggregaten z.B. durch Sortenwechsel, Abrisse, Abstellen und Wiederanfahren der Anlage,
• • in der Streichfarbenaufbereitung, z.B. bei Fehlchargen, Filtrieren,
• • im Rohstofflager, beim Entladen von Tankzügen, Befüllen und Entleeren von Behältern.

These residual coating colors or rejects mainly occur at position A in the figure:

• • on the coating units, e.g. due to grade changes, tear-offs, shutdown and restart of the system,
• • in coating color preparation, e.g. in the case of incorrect batches, filtering,
• • in raw material storage, when unloading tank trucks, filling and emptying containers.

Such disruptions are associated with cleaning work, so that the reject water usually only has low solids contents of around 1 - 2 wt.%. The rejects are usually collected without separation in a "residue collection container" at position B, as in the present case study.

1. a) Der Weg zur Deponie
   • In den meisten Fällen - wie auch in dem hier beschriebenen Anwendungsfall - werden die Rejekte z.B. mittels Zentrifuge (Pos. C) oder Sedimentationsprozess (Pos. D) geflockt, entwässert und auf maximalen Feststoffgehalt (> 55%) gebracht und in dieser Form auf der Deponie „entsorgt“. Hochwertige Einsatzstoffe wie Pigmente und Bindemittel gehen dem Produktionsprozess verloren.
2. b) Rückführung in den Papierstreichprozess mit Hilfe der vorliegenden Erfindung, bei gleichzeitigem Qualitätszugewinn für das Calciumcarbonatpigment. Dazu wird die vorliegende Erfindung in den Produktionskreislauf der Papierfabrik integriert.

At this point, the paper mill can take different paths, e.g.

1. a) The route to the landfill
   • In most cases - as in the application described here - the rejects are flocculated, dewatered and reduced to a maximum solids content (> 55%) using a centrifuge (item C) or sedimentation process (item D), for example, and then "disposed of" in this form at the landfill. High-quality input materials such as pigments and binding agents are lost in the production process.
2. b) Return to the paper coating process using the present invention, with a simultaneous increase in the quality of the calcium carbonate pigment. For this purpose, the present invention is integrated into the production cycle of the paper mill.

First, the rejects are flocculated with the addition of cationic products. Pigments and coagulated binders are separated from the water. Sedimentation devices (item D) or decanters (item E) can be used for this. The centrate from the centrifuge (item C) can also be used; the resulting clear water is used as production water or goes to the sewage treatment plant without polluting it.

Positions C and D are usually parts of the paper mill, position E is part of the present invention. In the application described here, the concentrated reject from the factory's own sedimentation hopper comes into the grinding plant. This consists of the following elements: Pos. F Buffer tank for flocculated and concentrated reject, Pos.G Silo for CaCO ₃ powder Pos.H Mixer for mixtures of dry CaCO ₃ and reject Pos. I Storage tank for CaCO ₃ slurry Pos. K 2-stage ball mill Pos. L if applicable if necessary, intermediate container for finished ground CaCO ₃ slurry

• • Aufkonzentriertes Rejekt wird im Pufferbehälter F gesammelt. Fällt kein Rejekt an, wird der Behälter mit Wasser beschickt.
• • Im Mischer H wird Rejekt und gegebenenfalls Dispergiermittel vorgelegt und dann das CaCO₃-Pulver aus dem Silo G bei 75 bis 80 Gew-% Feststoff dispergiert.
• • Im Vorratsbehälter I wird die Slurry zwischengelagert und von da aus
• • die Kugelmühle K kontinuierlich beschickt. In der Mühle wird die Slurry unter der Zugabe von Mahlhilfsmittel auf die gewünschte Feinteiligkeit vermahlen. Diese Calciumcarbonat-Slurry wird im
• • Behälter L zwischengelagert und dieselbe Slurry anschließend, nach Kontrolle von Teilchengröße, Feststoff, Viskosität und pH-Wert mit Polymerdispersion in der Streichküche versetzt und die so geschaffene Streichfarbe in den
• • Vorratsbehälter M der Streichanlage transportiert. Bei kontinuierlichem Betrieb kann in dem erfindungsgemäßen Verfahren auch auf die Behälter F und I verzichtet werden.

As in the application, the procedure is as follows:

• • Concentrated reject is collected in buffer tank F. If no reject is produced, the tank is filled with water.
• • Reject and, if necessary, dispersant are placed in mixer H and then the CaCO ₃ powder from silo G is dispersed at 75 to 80 wt.% solids.
• • The slurry is temporarily stored in storage tank I and from there
• • the ball mill K is continuously fed. In the mill, the slurry is ground to the desired fineness with the addition of grinding aids. This calcium carbonate slurry is
• • Container L is temporarily stored and the same slurry is then mixed with polymer dispersion in the coating kitchen after checking particle size, solids, viscosity and pH value and the coating color created in this way is added to the
• • Storage container M of the coating system. In continuous operation, the containers F and I can also be dispensed with in the process according to the invention.

When reusing the rejects according to the present invention, the pigments alone can theoretically be separated and recycled. However, the process according to the invention also provides for recycling of the binder, because the grinding of the pigment with the binder is of crucial importance for the quality of the carbonate pigment produced. It is irrelevant whether the binder is in its original form as a finely distributed polymer dispersion or in a flocculated, i.e. coagulated, state as a cluster of balls, because the binder also has its potential as a coagulum. During grinding, the mechanical grinding work between the balls of the binder - regardless of whether it is an individual particle or an agglomerate - rubs onto the pigment particles and forms a film due to the high temperature. The filler or pigment particles are therefore covered with a film of binder.

This binder component is therefore already firmly anchored and can no longer be absorbed into the absorbent substrate (base paper or cardboard). Absorption means loss of binder or depletion of the coating in binder, and this reduces, for example, picking resistance and print gloss. Absorption can also occur irregularly if there are zones of varying levels of absorption in the base paper. This then leads to a spotty print image (mottle).

If, however, as in the process according to the invention, a filler or pigment is applied to the paper/cardboard that is already coated with a binder, there is no migration of this binder. The "yield" of the binder is higher; denser coatings, higher pick resistance and better print gloss are obtained with less binder used. If the coating pigment is distributed homogeneously, the binder is also evenly distributed, which leads to even ink absorption and counteracts mottle. This has been proven by tests and experience with different binders, both in the form of stabilized polymer dispersion and in the form of destabilized binders, i.e. binder agglomerates.

Examples of implementation

• • Papierfabrik mit einer Papiermaschine und einer Jahresproduktion von 100.000 t gestrichenem Papier.
• • Papiermaschine mit on-line Streichaggregaten versehen für Vorstrich und Deckstrich.
• • Gesamtpigmentverbrauch 40.000 t, davon 20.000 t CaCO₃ einer 60-er Feinheitsqualität für den Vorstrich.
• • Rejektanfall 3.200 t/Jahr
• • Kapazität der Anlage zur Durchführung des erfindungsgemäßen Verfahrens 24 t/Tag mit CaCO₃ (60-er Feinheit*)
• • Ziel: Vermahlung von 20 t Frischpigment mit 1 t Rejekt bei einem Feststoffgehalt von 75 Gew.-%. *(60-er Feinheit bedeuten einen Anteil von 60 Gew.-% Teilchen kleiner als 2 µm)

The following studies were confirmed in a practical test:

• • Paper mill with one paper machine and an annual production of 100,000 tonnes of coated paper.
• • Paper machine equipped with on-line coating units for precoating and topcoating.
• • Total pigment consumption 40,000 t, of which 20,000 t CaCO ₃ of a fineness of 60 for the primer.
• • Reject volume 3,200 t/year
• • Capacity of the plant for carrying out the process according to the invention 24 t/day with CaCO ₃ (fineness 60*)
• • Objective: Grinding of 20 t of fresh pigment with 1 t of reject at a solids content of 75 wt.%. *(60 fineness means a proportion of 60 wt.% of particles smaller than 2 µm)

The integration of the grinding plant begins with the collection of the rejects in the buffer tank F, which have already been flocculated and thickened to approx. 40 wt.% and already contain the polymer dispersion.

The reject and dispersant were placed in mixer H and dry CaCO ₃ (grade 30) was added from silo G until 75% solids by weight were reached. The resulting suspension was pumped into storage container I and 1.8 wt.% of a commercially available grinding aid (polyacrylate), based on pigment, was added there.

The 2-stage ball mills K were then continuously fed from storage container I. The CaCO ₃ 30 quality was ground to CaCO ₃ 60 quality. 85 kW per tonne had to be used for the grinding. The 60 quality slurry produced in this way was stored in the intermediate container L until the particle size, viscosity, solids content and pH value had been recorded and then pumped into the storage container M for primer pigment in the coating kitchen. This primer pigment was then also mixed with approx. 16% by weight (commercial product) of a commercially available polymer dispersion (Acronal ^® ) to produce a primer colour.

In the application described here, the primer in the operational test consisted of 60 wt.% standard carbonate 60 fineness plus 40 wt.% AlphaCarb ^® 60 fineness, whereby this 40 wt.% portion consisted of 15 wt.% reject and 25 wt.% CaCO ₃ 30 fineness, so that the proportion of reject in the primer was approximately 7 wt.% reject. At a coating speed of 820 m/min., 10 - 11 g/m ² /side were applied in the primer on the film press. The coating ran perfectly on the film press and the top coat was applied without streaks.

The coated test paper was compared with standard coated paper.

Result:

• • einen höheren Rupfwiderstand bei Offsettest von Note 1 gegenüber Note 2,
• • einen höheren Druckfarbenglanz von 82 gegenüber 75,
• • ein langsameres Wegschlagverhalten der Druckfarbe um ca. 15 sec. nach dem Prüfbau Wegschlagtest,
• • eine bessere Druckgleichmäßigkeit (visuell beurteilt) von Note 2 gegenüber Note 3.

Compared to the standard 60 pigment, strokes with the pigment according to the invention produced

• • a higher resistance to picking in offset test of grade 1 compared to grade 2,
• • a higher ink gloss of 82 compared to 75,
• • a slower absorption behaviour of the printing ink by approx. 15 seconds after the Prüfbau absorption test,
• • better print uniformity (visually assessed) of grade 2 compared to grade 3.

The optical and sensory testing of papers produced using the process according to the invention also revealed excellent quality in the test papers.

Examples of grinding CaCO ₃ with coating color:

To produce a calcium carbonate pigment slurry with a fines fraction of more than 90% by weight < 2 µm, an aqueous anionic copolymer dispersion based on N-butyl acrylate, acrylonitrile and styrene, free from plasticizers and solvents (Acronal®S360 D) was used in a ball mill using ^Calcicell® 30. This polymer dispersion had a solids content of approximately 50% by weight and a pH of approximately 8.

The amount of calcium carbonate Calcicell ^® 30 in the slurry was 75% by weight. SAZ balls with a diameter of 1.6 to 2.5 mm were used as grinding balls. The usable capacity of the mill was 3 l. The working power was 1.3 kW at a speed of 400 to 1500 rpm.

A concentrated coating color (68.7 wt.% solids content) was added to the calcium carbonate and water in the amounts listed in Table 1. To produce the slurry, 1 wt.% of the above-mentioned polymer dispersion (based on the filler content calculation) was added to each batch.

The following Table 1 shows the test program: Table 1: Example Water Coating color Filler Calcicell ^® 30 2 500g 0g 1500g 3 971g 29g 3000g 4 706.5g 43.5g 2250g 5 663g 87g 2010g 6 619.5g 130.5g 1890g 7 576g 174g 1320g

The fineness of the materials used was determined using the laser diffraction method with Cilas device:

Measurement of the raw calcium carbonate used:

D50 4.63 µm D100 27.83 µm < 1µm 15.30% < 2µm 30.20%

Measurement of the coating color used:

D50 1.17 µm D100 9.95 µm < 1µm 41.50% < 2µm 76.10%

Example 2:

The following analysis results were obtained with pure water: Ball quantity: 2.0l Slurry quantity: 0.9l Speed: approx. 1100 rpm

The samples for measuring the grain distribution were taken after 20, 40, 60, 80, 100 and 120 minutes respectively. During the grinding test, the mill was cooled with water. Table 2: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2 µm/% 20 1.85 8.98 53.4 40 1.70 7.97 58.2 60 1.31 5.96 73.0 80 1.13 4.48 81.9 100 1.04 4.46 84.9 120 1.20 7.84 81.6

Colour values (Elrepho measuring device) of the filler from the slurry after 120 min:

$$\text{Rx}=90.3/\text{Ry}=90.1/\text{Rz}088.8/\text{BGW}=-1.7$$

Viscosity measurement (sample after 120 min):

Temperature: 20°C Viscometer: Brookfield HBTD Table 3: Spindle 2: speed 100 50 20 Advertisement 2.2 1.0 0.4 viscosity 70.4 mPa*s 64.0 mPa*s 64.0 mPa*s

Example 3:

Table 4: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 1.83 8.96 53.9 40 1.52 6.97 63.2 60 1.27 6.43 72.8 80 1.09 4.97 80.3 100 1.00 4.48 84.2 120 0.97 4.47 85.3 130 0.97 3.99 86.5 140 0.97 4.43 86.1

Example 4:

Table 5: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 1.81 10.0 54.3 40 1.51 8.0 64.9 60 1.27 8.0 75.0 80 1.15 7.0 80.7 100 1.08 4.96 84.1 110 1.03 4.48 85.9

Colour values (Elrepho measuring device) of the filler from the slurry after 110 min:

$$\text{Rx}=92.2/\text{Ry}=92.0/\text{Rz}=90.7/\text{BGW}=-1.6$$

Viscosity measurement (sample after 110 min):

Temperature: 20°C Viscometer: Brookfield HBTD

Table 6: Spindle 2: speed 100 50 20 Viscosity display 2.0 64.0 mPa*s 1.1 70.4 mPa*s 0.4 64.0 mPa*s

Example 5:

Table 7: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 1.94 9.96 51.1 40 1.53 7.96 64.2 60 1.32 6.94 72.7 80 1.20 7.65 77.5 100 1.08 4.97 80.6 120 0.99 3.98 87.6

Colour values (Elrepho measuring device) of the filler from the slurry after 120 min:

$$\text{Rx}=92.4/\text{Ry}=92.2/\text{Rz}=90.9/\text{BGW}=-1.6$$

Viscosity measurement (sample after 120 min):

Temperature: 20°C Viscometer: Brookfield HBTD Table 8: Spindle 2: speed 100 50 20 Viscosity display 1.7 54.4 mPa*s 0.8 51.2 mPa*s 0.3 48.0 mPa*s

Example 6:

Table 9: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 1.77 9.96 55.5 40 1.47 8.91 65.8 60 1.26 6.95 74.5 80 1.15 4.98 80.2 100 1.06 4.96 84.3 120 1.02 4.92 86.4

Slight sieve residue on 40 µm sieve, foam formation, slight sticking of the balls.

Colour values (Elrepho measuring device) of the filler from the slurry after 120 min:

$$\text{Rx}=91.7/\text{Ry}=91.6/\text{Rz}=90.4/\text{BGW}=-1.4$$

Viscosity measurement (sample after 120 min):

Temperature: 20°C Viscometer: Brookfield HBTD Table 10: Spindle 2: speed 100 50 20 Viscosity display 1.3 41.6 mPa*s 0.6 38.4 mPa*s 0.3 48.0 mPa*s

Example 7:

Table 11: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 1.72 8.96 57.2 40 1.47 7.94 67 60 1.28 5.95 74.7 80 1.21 5.46 77.7 100 1.18 5.96 77.9 120 1.02 4.95 86.3

Greater sieve residue than in example 6 on the 40 µm sieve. Stronger foam formation and stronger sticking of the balls.

Colour values (Elrepho measuring device) of the filler from the slurry after 120 min:

$$\text{Rx}=90.6/\text{Ry}=90.4/\text{Rz}=89.1/\text{BGW}=-1.7$$

Viscosity measurement (sample after 120 min):

Temperature: 20°C Viscometer: Brookfield HBTD Table 12: Spindle 2: speed 100 50 20 Viscosity display 1.3 41.6 mPa*s 0.6 38.4 mPa*s 0.3 48.0 mPa*s

Table 13: Evaluation of the Cilas 850/1 measurements: Time/min D50/µm D100/µm <2µm 20 2.14 10.96 47.4 40 1.72 8.96 57.2 60 1.36 7.92 69.9 80 1.24 7.83 76.2 100 1.16 4.98 80.3 120 1.08 4.96 84.9

Colour values (Elrepho measuring device) of the filler from the slurry after 120 min:

$$\text{Rx}=92.0/\text{Ry}=91.8/\text{Rz}=90.9/\text{BGW}=-1.2$$

Viscosity measurement (sample after 120 min):

Temperature: 20°C Viscometer: Brookfield HBTD Table 14: Spindle 2: speed 100 50 20 Viscosity display 1.1 35.2 mPa*s 0.4 25.6 mPa*s 0.2 32.0 mPa*s

Claims (9)

Process for producing surface-modified inorganic fillers or pigments with a grain size distribution of 50 to 100% by weight of particles < 2 µm, 27 to 99% by weight of particles < 1 µm, each based on the equivalent diameter, characterized in that filler or pigment slurries with a filler or pigment content of 10 to 95% by weight, based on the slurry of natural and/or precipitated calcium carbonate, kaolin, artificial and/or natural aluminum silicates and oxide hydrates, titanium dioxide, satin white, dolomite, mica, metal flakes, bentonite, rutile, magnesium hydroxide, gypsum, layered silicates, talc, calcium silicate and other stones and earths or mixtures thereof under the action of shear forces, using aqueous polymer dispersions which are selected from natural rubber, synthetic rubber, synthetic resins and plastics with a solids content of 40 to 60% by weight of natural and/or synthetic polymers with a particle size of 0.005 to 6 µm in aqueous phases with an amount of 0.1 to 15% by weight of polymer dispersion (solid substance), based on the amount of pigment, and further with polyacrylates as grinding aids and/or dispersants (active substance) in an amount of 0.1 to 2.0% by weight, based on the fillers or pigments, ground to the desired grain size. Procedure according to Claim 1 , characterized in that aluminum flakes are used as mall flakes. Procedure according to Claim 1 or 2 , characterized in that filler or pigment slurries having a filler or pigment content of 30 to 70 wt.%, based on the slurry, are used. Procedure according to one of the Claims 1 until 3 , characterized in that polymer dispersions are used, the plastics being selected on the basis of polyurethane, styrene/butadiene, styrene/acrylic acid or ester, styrene/butadiene/acrylic acid or ester and vinyl acetate/acrylic acid or ester. Procedure according to Claim 4 , characterized in that the dispersants are brought into contact with the fillers or pigments in an amount of 0.2 to 0.4 wt.%, based on these. Procedure according to one of the Claims 1 until 5 for producing a filler and/or pigment slurry with a solids content of 10 to 90 wt.%. Procedure according to Claim 6 for producing a filler and/or pigment slurry with a solids content of 40 to 80 wt.%. Surface-modified inorganic fillers and/or pigments, obtainable by a process according to one of the Claims 1 until 7 . Use of surface-modified fillers and/or pigments according to Claim 8 for the production of emulsion paints, adhesives, coatings or coating slips for the paper industry, in particular coating slips for various segments such as sheet-fed offset, web offset, gravure printing, cardboard and specialty papers.

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