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
  • D21H19/38—Coatings with pigments characterised by the pigments
  • D21H19/40—Coatings with pigments characterised by the pigments siliceous, e.g. clays
• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/68—Water-insoluble compounds, e.g. fillers, pigments siliceous, e.g. clays

Definitions

• This invention relates to improving the properties of paper filling pigments obtained by bulking kaolin clay by addition to the clay of a cationic polyelectrolyte,e.g. as a polyamine or a quaternary ammonium polyelectrolyte. More specifically, this invention relates to improvements in cationically bulked kaolin of the type described in U.S. 4,738,726, Pratt et al, U.S. 4,767,466, Nemeh et al, and U.S. 4,772,332, Nemeh et al.
• Coated printing paper possessing superior printability especially by rotogravure and offset methods has been obtained by coating with coating formulations containing bulked pigments.
• Cationically bulked kaolin is enjoying widespread commercial success for coating paper, but the desired degree of improvement in opacification when used to fill paper has not been realized - see, for example, data in EXAMPLE VI of US-A-4738726, supra.
• High bulking clay pigments offer the opportunity of maintaining or improving the opacity, brightness, gloss and printability of coated paper having lower coating weights, thereby reducing the pigment cost for coating colors; and improving the opacity of paper filled with kaolin.
• bulking is achieved by introducing voids in a pigment structure which contribute to increased light scatter. Controlled calcination of kaolin clays results in one type of bulking clay pigment.
• Calcined bulked kaolin clay such as the material supplied under the registered trademark ANSILEX has enjoyed widespread commercial success for more than a decade especially as paper filler. For many years attempts have been made to bulk hydrous kaolin clays, thereby avoiding the increase in pigment abrasivity that appears to be an inherent result of calcination.
• U.S. Patent Nos. 4,075,030, 4,076,548 and 4,078,941 teach procedures for increasing the opacifying power of hydrous kaolin clays by "selectively flocculating" ultrafine clay particles with a low molecular weight polyamine flocculating agent (e.g., ethylene diamine or hexamethylene diamine) or with long carbon chain amines or certain quaternary ammonium salts (e.g. "ditallowdimethyl” ammonium chloride) in the presence of a mineral acid flocculating agent, e.g., sulfuric acid, and optionally with the adding presence of citric acid or mica or both.
• a low molecular weight polyamine flocculating agent e.g., ethylene diamine or hexamethylene diamine
• certain quaternary ammonium salts e.g. "ditallowdimethyl” ammonium chloride
• the selective flocculation treatment allegedly incorporates voids in the clay to form a low density, high-bulking pigment which when used as a coating color pigment improves the opacity of paper coated therewith.
• U.S. Patent No. 4,640,716 teaches the use of certain zirconium compounds such as zirconium ammonium carbonate to bulk clay.
• printer and publishers are requiring paper with improved optical and printing properties. These properties sometimes cannot be achieved without the aid of filler pigments.
• filler pigments Another reason for the use of filler pigments is the desire to produce lighter basis weight papers with optical and printing properties comparable to higher basis weights.
• the pigment compensates for the reduction in fiber content of the lighter papers and the consequent loss of opacity and printing properties.
• the present invention provide means for improving the opacifying properties of cationically bulked kaolin clay pigments when used as fillers for paper and paperboard.
• a bulked hydrous kaolin clay paper filler is prepared by adding water soluble cationic organic material such as polyamine or quaternary ammonium polyelectrolyte, in amount in excess of that required to flocculate the kaolin, but insufficient to redeflocculate the previously flocculated kaolin.
• the median particle size of the clay particles that are treated with the cationic polyelectrolyte preferably ranges from 0.4 to 0.7 micrometers, equivalent spherical diameter (e.s.d), more preferably 0.5 to 0.6 micrometers, as determined by conventional sedimentation techniques using the SEDIGRAPH particle size analyzer, supplied by Micromeritics, Inc. From about 50 to 95 wt.% of the particles are preferably finer than 2 micrometers, e.s.d. The content of fines below 0.3 micrometer e.s.d. may be below 35 weight percent, preferably below 25 weight percent, and most preferably 20 weight percent or below. It should be understood that the measurements of the size of clay particles that are 0.3 micrometer or finer are of limited reproducibility.
• the value for weight percent may be ⁇ 5% when tested by another operator or a different SEDIGRAPH analyzer is employed.
• median particle size is 0.5 to 0.6 micrometers, e.s.d., with 85 to 90% by weight of the particles finer than 2 micrometers, e.s.d., and less than about 20% by weight or less finer than 0.30 micrometers, e.s.d.
• a hydrous kaolin fraction that is about 80 to 88% finer than 2 micrometers. Most preferably, about 80 to 85% finer than 2 micrometers with from 10% to 19% by weight finer than 0.3 micrometers.
• the amount of cationic polyelectrolyte employed is carefully controlled to be sufficient to achieve maximum opacification potential of the clay as a result of forming a bulked (aggregated) structure in which the aggregates are sufficiently strong to survive mechanical forces exerted during manufacture and end use and is carefully controlled.
• the amount of cationic polyelectrolyte exceeds that required to flocculate the kaolin, but is insufficient to redeflocculated the previously flocculated clay.
• the specific amount of the cationic polyelectrolyte salt used to treat the kaolin clay may vary with characteristics of the polyelectrolyte, the particle size distribution of the clay and solids content of the clay slurry to which the polyelectrolyte is added.
• dimethyldiallyl ammonium salt polyelectrolyte with clay having a median size in the range of about 0.5 to 0.6 micrometers, and having less than 20% finer than 0.3 micrometers and adding polyelectrolyte to a previously deflocculated clay-water suspension having a clay solids content of about 20-40% by weight, useful amounts range from about 0.12% to about 0.20% by weight of the moisture free weight of the clay, most preferably about 0.15% to about 0.16% by weight. An excessive amount of the polyelectrolyte will redeflocculate the clay.
• the polyelectrolyte which is water soluble, is best added to the slurry as a dilute aqueous solution, e.g., 0.25-2.0 wt.% concentration, with agitation to achieve good distribution in the slurry.
• Ambient temperature can be used. It may be advantageous to heat the slurry of clay, solution of polyelectrolyte, or both to about 150° to 180°F.
• the cationic polyelectrolyte flocculants that are used have closely spaced charged centers and therefore represent high charge density material. Because of this, the reaction with the clay mineral is extremely rapid and appears to be complete in a relatively short time.
• Water soluble cationic polyelectrolyte flocculants are well known in the art and many are known to increase the rate at which clay slurries filter. See, for example, US. Patent No. 4,174,279.
• Cationic polyelectrolyte flocculants are characterized by a high density of positive charge. Positive charge density is calculated by dividing the total number of positive charges per molecule by the molecular weight. Generally the high charge density of polyelectrolyte flocculants exceeds 1X10- 3 and such materials do not contain negative groups such as carboxyl or carbonyl groups.
• alkyl diallyl quaternary ammonium salts are obtained by copolymerizing aliphatic secondary amines with epichlorohydrin - see U.S. Patent No. 4,174,279.
• Still other water-soluble cationic polyelectrolytes are poly(quaternary ammonium) polyether salts that contain quaternary nitrogen in a polymeric backbone and are chain extended by ether groups. They are prepared from water-soluble poly(quaternary ammonium salts) containing pendant hydroxyl groups and bifunctionally reactive chain extending agents; such polyelectrolytes are prepared by treating N, N.
• N( 1 ), N( 1 ) tetraalkylhydroxyalkylenediamine and organic dihalide such as dihydroalkane or dihaloether with epoxy haloalkane Such polyelectrolytes and their use in flocculating clay are disclosed in U.S. Patent No. 3,663,461.
• Other water soluble cationic polyelectrolyte flocculants are polyamines. Polyamine flocculants are usually supplied commercially under trade designations; chemical structure and molecular weight are not provided by the suppliers.
• the invention is not limited to Polymer 261 LV since other cationic flocculants appear to provide equivalent, if not superior results.
• the suspension is substantially thickened as a result of flocculation.
• the resulting thickened system can then be acidified, typically to pH 2 to 6, preferably 3 to 5, and bleached using a convention bleach reagent (hydrosulfite salt such as sodium dithionite) and then at least partially dewatered to remove free water and place the recovered bulked clay in a form such that is can be washed to remove ions in the flocculated clay suspension.
• a filter for example a rotary vacuum filter.
• Bleaches are usually preferred which reduce any color forming ferric iron constituents to a more water soluble and therefore more easily removable ferrous state (Fe 2+ )
• suitable bleaching agents include water soluble dithionite salts, and borohydride salts which are advantageously added to the clay mineral slurry in an amount in the range of from 1 to 15 lbs., most preferably about 4 to 6 lbs., of bleaching agent per ton of dry clay.
• the slurry of polymer treated clay can be acidified before filtration to enhance filtration even if bleaching is not carried out. Viscosity stability of bulked kaolin products is poor unless bleach residues are removed by washing or sulfonates are used as dispersants.
• the clay suspension can be dewatered by filtering to a moist filter cake having a solids content of about 50 to 60% by weight.
• the filter cake can be washed to remove soluble material and then fluidized by the addition of a secondary dispersing agent which, in accordance with a preferred embodiment of the invention, comprises a mixture of anionic sulfonates and polyacrylate salt described in U.S. 4,772,332. If the previously described acid bleaching step is omitted, only minimal if any pH adjustment may be necessary to bring pH into the desired range of 6.0 to 7.5 pH can be adjusted to a value between 6.0 and 7.5, preferably 6.8 to 7.5, using a suitable base such as sodium hydroxide.
• the dewatered and washed filter cake may be fluidized by adding a deflocculant and supplied for shipment in slurry form as mentioned above.
• the filter cake can be fluidized by addition of a deflocculant and then spray dried to produce a dry so-called "predispersed" product in dustless form.
• the resultant bulked polyelectrolyte treated clay product can be used as a filler for paper webs by making a furnish comprising pulp, kaolin, retention aid and other ingredients.
• a clay slurry having a higher solids content than the filter cake it will be necessary to add dry, previously bulked clay to build up the solids content of the slurry obtained by adding dispersants to fluidize the filter cake.
• dry previously bulked clay should be mixed with the dispersed filter cake.
• the solids concentration of the slurry that is acceptable to the papermaker depends upon the properties that the pigment will impart to the paper.
• the kaolin clay pigments bulked in accordance with practice of the present invention are especially useful in filling paper, but are generally not optimized for use in coating paper, due to difficulties in making high solids coating colors.
• Typical pigments of the invention have the following properties:
• Light scattering is assessed by coating the kaolin clay suspensions onto black glass plates at a coat weight of 7.0-14.0 g/m 2 (expressed as dry clay).
• the reflectance of the coatings after drying in air is measured at wavelengths 457 nm and 577 nm by means of an Elrepho reflectometer.
• the reflectance values are converted by the use of Kubelka-Munk equations to light scattering values ( M 2 /g).
• the light scattering values are a measure of the opacity potential of the clay because the higher values indicate that light, rather than passing through the pigment coating, is reflected and scattered back.
• the higher the light scattering value the higher the opacity potential of the clay. Reflectance is measured at two different wavelengths.
• the 457 nm wavelength used is the TAPPI brightness measurement, and the 572 nm wavelength is used to measure opacity.
• CALGON 261 LV polymer was added to the suspension of purified clay at the 0.08, 0.10, 0.12, 0.16 and 0.20% level, based on dry weight of clay.
• the polyelectrolyte was added as an aqueous solution of 0.5% (wt.) concentration.
• the bulked slurries were mixed for one half hour, bleached with 5 Ib/ton K-brite at pH 3.0, aged for about 18 hours, filtered, washed with 0.5 to 1 water/dry kaolin and dispersed with a mixture of sulfonates and sodium polyacrylate dispersant as shown in Table 1.
• the slurries were then spray dried and made down at 55% solids without additional dispersant. Brookfield viscosity and black glass scattering of the sample were measured. As expected, scattering and Brookfield viscosities of bulking pigments increase with increasing the polymer dosage. At the bulking level of 0.2%, the viscosity of the aqueous slurry can be reduced by adding more dispersant as can be seen from data on Table 2.

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• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Paper (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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Publications (1)

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Cited By (4)

Citations (3)

• 1990
  • 1990-11-14 CA CA 2029955 patent/CA2029955A1/fr not_active Abandoned
  • 1990-11-19 AU AU66849/90A patent/AU6684990A/en not_active Abandoned
  • 1990-11-22 EP EP90312718A patent/EP0430582A1/fr not_active Withdrawn
  • 1990-11-22 BR BR9005918A patent/BR9005918A/pt unknown

Patent Citations (3)

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