Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H19/00—Coated paper; Coating material
  • D21H19/36—Coatings with pigments
  • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent

Definitions

• the invention relates to cationically adjusted pigment dispersions and coating colors for paper coating.
• the coating pigments used to produce coating colors which are supplied in the dry state, generally have an anionic interfacial charge, and the pigment particles are usually in the form of agglomerates or coarse-particle aggregates, which are disadvantageous both in terms of the processing of the coating color and on the coating quality impact.
• the individual particles should be used as primary particles, i.e. deflocculated, present.
• a combined application of suitable dispersing devices and the use of chemical auxiliaries is required to disperse the agglomerates.
• Optimal dispersion ensures that the attractive forces between the particles are eliminated or counteracted, so that the pigment particles do not re-agglomerate after the dispersion has been produced.
• the most common inorganic and organic dispersants used in the paper industry are almost exclusively polyanionic (e.g. polyphosphates and polyacrylates). These dispersants break up the pigment agglomerates into primary particles, which improves the optical properties of the papers coated with the coating colors, since finer particles give better paper and printing gloss.
• the dispersion also enables pigment slurries and thus coating colors with a high solid are obtained which do not tend to flocculate prematurely even at elevated storage and processing temperatures.
• the anionic dispersants have a number of disadvantages.
• the negative effects of the anionic dispersants can be remedied to a certain extent by reducing the charge with appropriate binders (eg binders rich in carboxyl groups) and by adding low molecular weight cationic auxiliaries, so-called immobilizing agents.
• appropriate binders eg binders rich in carboxyl groups
• low molecular weight cationic auxiliaries so-called immobilizing agents.
• the anionic dispersants interact undesirably with the cationic auxiliaries, which leads to an increase in need for cationic aids.
• the resulting coacervate acts as a contaminant in the papermaking process.
• a coating color in a weakly acidic medium has the advantage that low dispersant amounts are sufficient for pigment dispersion, owing to the good dispersing action of the protons.
• a broader range of binders can be used in the weakly acidic medium, e.g. Amphoteric binders and binders based on proteins, which are also cationic in the weakly acidic range.
• the acidic mode of operation is not possible with CaCO3, due to the decomposition of the carbonate.
• the object of the present invention was to provide cationically adjusted pigment dispersions or coating colors in which pigments are used, their use in the required high concentration because of their high viscosity in aqueous dispersion hitherto was impossible.
• the calcium sulfate can be present as anhydrous calcium sulfate, as a hemihydrate or as a dihydrate.
• the aluminum hydroxide can be present with a cationic surface or, due to grinding aids, with an anionic surface.
• Talc is generally difficult to disperse without wetting agents.
• the pigment components mentioned can also be blended with other pigments, such as kaolin and / or calcium carbonate, the blended pigments also being able to predominate.
• Aqueous dispersions of the starting pigments used according to the invention have very high viscosities even at relatively low solids contents if they are dispersed in a conventional manner.
• Brookfield viscosities of approximately 50% dispersions are between approximately 5000 and 8000 mPa.s (spindle 5 at 50 rpm).
• the pigment dispersions according to the invention are notable for low viscosities, even at high solids contents.
• the pigment dispersions according to the invention can be stored in their cationic form.
• the proportions of expensive transshipment agents can be kept significantly lower.
• the protective colloids also have water-retentive properties and good pigment-binding properties. This water-retentive effect is particularly important for coating color processing on high-speed coating machines, since under the high hydrodynamic loads in coating dosage and leveling, the coating ink loses mobilizing water, binding agents and auxiliaries to the base paper when water retention is poor, which means that strong processing and Final quality problems, as described above, occur.
• the pigment dispersions according to the invention are preferably characterized in that the cationized polymer (c) has been obtained in situ by cationization of the pigment particles (a) coated with the hydrophilic starting polymers.
• the dispersant used as component (b) is preferably an oligomeric or polymeric quaternary ammonium compound. Compared to low molecular weight quaternary ammonium compounds with a low charge density, such compounds have the advantage that the charge reversal takes place more quickly with lower addition amounts and a positive zeta potential is achieved.
• the cationic polymer is preferably obtained by reacting the hydrophilic starting polymers with nitrogen-containing compounds and quaternizing the reaction products.
• a particular advantage of the present invention is that the pigment dispersions can also be used at a weakly acidic pH. This has the advantage that the amount of dispersant (b) can be reduced or coating colors with higher solids contents can be achieved.
• the protective colloids (c) are preferably cationized by reacting the hydrophilic starting polymers with nitrogen-containing compounds and quaternizing the reaction products or by reacting with a cationic polymer or copolymer from the group of the melamine-formaldehyde resins, epichlorohydrin resins, dicyandiamide resins, quaternary acrylates, the polymeric diallyl compounds or of the polymeric guanidine compounds.
• These cationic polymers are also preferably used for the cationic polymer (b).
• the protective colloid (c) can also be cationized from the outset. These compounds include, for example, proteins at a weakly acidic pH.
• the protective colloid is preferably a reaction product of one or more hydrophilic starting polymers with an originally anionic character from the group of Polyacrylates and methacrylates, degraded starches or degraded modified starches, degraded galactomannans, degraded modified galactomannans, methyl celluloses, hydroxymethyl celluloses, carboxymethyl celluloses, degraded alginates and one or more cationic polymers or copolymers from the group of the melamine-formaldehyde resins, epichlorohydrin resins, polymeric epichlorohydrin compounds, polymeric compounds and dicyandiamide resins.
• Polyvinyl alcohols are non-ionic compounds from which cationized protective colloids can also be produced.
• the cationized protective colloid (c) can also be the reaction product of one or more of the above-mentioned substances with originally anionic character and a quaternary ammonium compound of the general formula HN+R3X ⁇ wherein R is an alkyl group with up to 20 carbon atoms and X ⁇ is an anion, in particular a chloride ion.
• the cationic polymer or copolymer (b) used according to the invention is preferably a poly (diallyldimethylammonium chloride) and preferably has a molecular weight corresponding to a viscosity of 500 to 1500 mPa.s (Brookfield viscosity at 15% solids content, 20 rpm and room temperature).
• the cationic polymer or copolymer (b) is preferably a polymeric quaternary ammonium compound according to one of the following structure types: where x is 1 to 3.
• the cationic polymer or copolymer (b) is a poly (diallylammonium chloride) or a poly (3,5-methylene-piperidinium chloride), the nitrogen atoms optionally being substituted by lower alkyl groups.
• the invention further relates to a method for producing a cationically adjusted pigment dispersion, as described above; This process is characterized in that an aqueous suspension of the pigment particles (a) which are optionally coated with the cationized polymer (c) is dispersed with the cationic polymer (b).
• the procedure is such that the pigment particles (a) are coated with the cationized polymer (c) before dispersing until the zeta potential of the dispersion containing the coated pigment particles (a) has a value at the isoelectric point or in has reached the cationic range. It is therefore favorable that the pigment particles are first coated with the cationized protective colloid (c) before they are dispersed with the dispersing and transfer agent (b).
• the pigment component (a) can also be coated with the hydrophilic starting polymer and cationized in situ with the cationic polymer or with the quaternary ammonium compound (b).
• the invention further relates to a coating color for paper coating, a pigment dispersion as described above, and (d) a binder or mixture of binders for connecting the dispersed and optionally coated with the cationized polymer (c) pigment particles (a) to one another and to one another of the paper surface.
• the binder or binder mixture (d) is preferably also cationic or amphoteric in the neutral or alkaline range.
• amphoteric binders are generally only used for coating colors with a weakly acidic pH.
• the amount of the binder (d) can be kept relatively low if the protective colloid (c) is used since it has a co-binder function.
• Preferred synthetic binders (d) are styrene-butadiene or styrene-acrylate copolymers with functional cationic groups and / or cationic polyvinyl acetates, cationic polyvinyl alcohols or their copolymers.
• the binder (d) can be selected from the group of degraded and native galactomannans, starches, methyl celluloses, hydroxymethyl celluloses, carboxymethyl celluloses, alginates, proteins and polyvinyl alcohols and contain cationic groups. Proteins are particularly suitable for the weakly acidic area because of their amphoteric nature they have a cationic charge from the outset. The isoelectric point is included pH 5 to 6. If proteins are used in the alkaline range, they should be slightly cationized (eg by coacervate formation or by real cationization).
• starch If starch is used, it should be cationized for both the acidic and the alkaline range.
• the binders also affect the water retention of the coating color.
• the coating color according to the invention can further contain, as auxiliaries, cationic or nonionic thickeners (e.g. galactomannans or synthetic thickeners), and / or water retention aids.
• the coating color may also contain auxiliaries, such as lubricants (e.g. fatty acid derivatives, waxes or paraffins in emulsion form), optical brighteners (e.g. stilbene derivatives) and / or wet strength agents (e.g. cationic or nonionic resins).
• a preferred coating color contains the components, based on 100 parts by weight of dry pigment (a) in the following parts by weight: Gravure printing Offset / letterpress (c) protective colloids 0.1-6.0 0.1 - 6.0 (b) dispersant 0.0-3.0 0.0 - 3.0 (d) Natural binder 0.0-10.0 1.0 - 20.0 (e) Synthetic binder 1.0-7.0 1.0 - 15.0 (f) Aids as indicated above 0.2-4.0 0.2 - 5.0 (g) wet strength agent 0.0-3.0 0.0 - 5.0
• the coating slip according to the invention is preferably prepared by placing the pigment dispersion according to the invention in a suitable mixing unit, adding the dilution water required for the desired final solids content of the coating slip and, if the mixing intensity is high, adding the natural binder, if appropriate dissolved in a separate operation, and / or subsequently adding the synthetic binder .
• the binders if necessary, the thickener and the water retention aid and then the other auxiliaries, such as lubricants and, if necessary, optical brighteners, and finally the wet strength agent are added.
• the order given has proven particularly useful for the production of an agglomerate-free, easy-to-process coating color.
• the coating color according to the invention has good adhesion to the normally negatively charged paper fiber. This property can be used by using excess coating color, e.g. when changing the paper type, which adds paper pulp as a filler.
• the cationic coating slip according to the invention can safely enter the paper machine cycle since the interaction with the cationic auxiliaries does not occur or wastewater problems are avoided in this way.
• the coating colors according to the invention when added to the paper pulp as fillers, have the side effect that they are also used in the pulping of wood for the production of paper bind resulting anionic degradation products, such as dextrins, lignins, hemicellulose, etc.
• the anionic impurities are adsorbed on the cationic pigment interface and discharged with the paper, so that the wastewater pollution is also lower in this regard.
• This adsorption improves the base paper properties such as opacity, strength, porosity, etc.
• the talc was mixed with water and the PVA solution (hydrophilic starting polymer) and mixed thoroughly. Then the dispersant solution (b) was added, whereby the initially anionic pigment was reloaded.
• the dispersion obtained had the following properties: Ex. 1 Ex. 2 Solids content (% by weight) 58.3 49.8 PH value 8, 2 8.6 Brookfield viscosity at 50 rpm, spindle 5, room temperature mPa.s 880 48 Brookfield viscosity at 100 rpm, spindle 5, room temperature mPa.s 600 60 Zeta potential (mV) +87 +63
• a dispersion with untreated talc had the following properties: Solids content 49.2% by weight pH 8.6 Brookfield viscosity at 50 rpm, spindle 5, room temperature 6600 mPa.s Brookfield viscosity at 100 rpm, spindle 5, room temperature 3900 mPa.s Zeta potential -22 mV
• the dispersions according to the invention therefore had a significantly lower viscosity than the comparative dispersion despite a higher solids content or with practically the same solids content.
• the talc was mixed thoroughly with water. Then the dispersant solution (b) was added, whereby the initially anionic pigment was reloaded.
• the dispersion obtained had the following properties: Solids content 64.4% by weight pH 7.9 Brookfield viscosity at 50 RPM, spindle 4, room temperature 620 mPa.s Brookfield viscosity at 100 RPM, spindle 4, room temperature 510 mPa.s Zeta potential +96 mV
• the gypsum was mixed with water and the phosphated starch solution (hydrophilic starting polymer) and mixed thoroughly. Then the dispersant solution (b) was added, whereby the initially anionic pigment was reloaded.
• the dispersion obtained had the following properties: Solids content 66.6% by weight pH 6.6 Brookfield viscosity at 50 RPM, spindle 5, room temperature 1040 mPa.s Brookfield viscosity at 100 rpm, spindle 5, room temperature 760 mPa.s Zeta potential + 8 mV
• a dispersion with untreated gypsum had the following properties: Solids content 57.0% by weight pH 7.5 Brookfield viscosity at 50 RPM, spindle 6, room temperature 8000 mPa.s Brookfield viscosity at 100 rpm, spindle 6, room temperature 4300 mPa.s Zeta potential -26 mV
• the dispersion according to the invention therefore had a significantly lower viscosity than the comparative dispersion.
• the dispersant solution (b) was added to the PVA solution (hydrophilic starting polymer) and mixed thoroughly, whereby the PVA was cationized. Then the aluminum hydroxide was added.
• the dispersion obtained had the following properties: Solids content 67.4% by weight pH 9.5 Brookfield viscosity at 50 rpm, spindle 5, room temperature 2520 mPa.s Brookfield viscosity at 100 rpm, spindle 5, room temperature 1500 mPa.s Zeta potential +67 mV.
• a dispersion with untreated aluminum hydroxide had the following properties: Solids content 48.7% by weight pH 9.4 Brookfield viscosity at 50 rpm, spindle 5, room temperature 4500 mPa.s Brookfield viscosity at 100 rpm, spindle 5, room temperature 2750 mPa.s Zeta potential +68 mV.
• the dispersion according to the invention therefore had a significantly lower viscosity than the comparison dispersion.
• the reduction in viscosity which apparently has nothing to do with a change in the zeta potential, is probably due to the fact that the agglomerates of the very finely divided pigment components are broken up by the cationized protective colloid.
• the cationic pigment dispersion according to Example 5 was with a cationic kaolin dispersion (extender pigment) of the following composition Water 135 g Kaolin (90% ⁇ 2 ⁇ m) 306 g 21% PVA solution 60 g 45% solution of poly (diallyldimethylammonium chloride) 13 g mixed in such an amount that the weight ratio between aluminum hydroxide and kaolin was 15:85.
• the mixed dispersion obtained had the following properties: Solids content 62.0% by weight pH 7.0 Brookfield viscosity at 50 RPM, spindle 5 room temperature 1920 mPa.s Brookfield viscosity at 100 rpm spindle 5, room temperature 1050 mPa.s Zeta potential + 58 mV.
• the viscosity of the mixed dispersion remained unchanged even after a long storage period.
• Coating colors were prepared with the pigment dispersions according to Examples 1, 4 and 6, the composition of which is given in the table below.

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• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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Citations (2)

• 1987
  • 1987-09-14 DE DE19873730833 patent/DE3730833A1/de not_active Withdrawn
• 1988
  • 1988-09-08 EP EP88114669A patent/EP0307795A3/fr not_active Withdrawn
  • 1988-09-14 JP JP63228885A patent/JPH0197296A/ja active Pending
  • 1988-09-14 FI FI884222A patent/FI884222A/fi not_active IP Right Cessation

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