EP0495777A1 - Structural aggregate pigments - Google Patents

Abstract

Structural aggregate pigment products having functional properties of intrinsic construction comprising particulate matter treated with complex functional microgels.

Description

1 STRUCTURAL AGGREGATE PIGMENTS

BACKGROU P OF THE INVENTION

1. Field of the Invention

This invention relates to structural aggregate pigm products comprising a quantitatively predominant particul matter and complex functional microgels which are essentia non-reactive therewith.

In particular, this invention relates to novel structu aggregate pigment products which are manufactured from aque dispersions of particulate matter treated with in-situ fo complex functional microgels.

More particularly, this invention relates to structural gregate pigment products which comprise particulate matter fl culated and cemented with complex (multicomponent) functio microgels.

2. Discussion of the Relevant Art.

The scope of prior art relating to the synthesis practical applications both of continuous and discrete g obtained by interaction of alkali-metal silicates with sod -fcfcianinate, soluble metal salts and/or free acids in different ^~? proportions and combinations is simply enormous, involving man thousands of patented gel products.

Most of these products differ from each other only in min details, such as pH conditions, reagent concentrations, sequen of reagent additions, thermal regimes or particular variatio in the otherwise very similar preparation procedures. Ye these seemingly minor differences may bring about improved, even novel, material or performance properties of the resulta end products, whose applications encompass such different fiel as catalysis, pharmaceuticals, adhesives, water treatment, i exchange, dehumidification of gases or soil conditioning.

The above can probably be comprehended best by consideri that colloids are the lowest-rank systems known in nature equi ped with "memory." As such, they "remember" their history chronological detail and react accordingly in terms of the resultant properties and functional behavior. As a consequenc any intentional or accidental deviation from an establish synthesis procedure or reaction conditions will inescapab cause certain differences, mostly quantitative but sometim profoundly qualitative, in the constitution and/or function properties of the resultant colloidal systems.

In the following, certain general fields of manufacture a utilization of various types of gels shall be discussed in so detail using examples found in the literature. While continuo single and mixed gels (mechanical blends of two or mor- separa gels) are inherently foreign to the principal idea of the pre ent invention, they will be included in the general discussi for the sake of better clarity.

In-situ formation of silica or silico-alu inate gels in aqueous media for the purpose of surface coating of mineral particles has been utilized commercially for many years. For example, virtually all titanium dioxide pigments on the market are coated with a more or less dense layer of silica, or silico- aluminate, gels deposited in situ by a controlled interaction between relatively highly concentrated solutions of sodium silicate and appropriate gel-setting agents such as sulfuric or hydrochloric acids, ammonium sulfate, alum or sodium aluminate, in aqueous dispersions of the pigment. However, the surface coa¬ tings mentioned represent continuous gels which are fundamental¬ ly different from the instantaneously in-situ formed microparti- culate gels (microgels) used in practicing the present invention developed by the Applicant and disclosed in co-pending patent application (Serial No. 07/350,4_.68 ; Filed May 11, 1989 ). Moreover, because of the slow formation kinetics and continuous structure of gels used in surface coating of titanium dioxide pigments in accordance with the present art, excessive uncon¬ trollable cementation of individual particles into very abrasive oversized aggregates can not be avoided. This particle aggrega¬ tion is by far the most undesirable side effect of surface coat¬ ing with continuous gels, having as a rule strongly pronounced cementing properties, since too close a proximity of individual titanium dioxide particles is most detrimental to their light- scattering efficacy. As a consequence, expensive fluid-energy comminution, and/or cumbersome ball milling, must be additional- ly employed.

U.S. Patent 3,726,000 to Wildt, relating to the use of in-situ formed continuous alumino-silicate gels as intrinsic cements toward the preparation of composite pigments, may be considered as typical of the general prior art in this area of technology dating back for over half a century. Many other intrinsic cementing media have also been used for the same purpose, e.g., sodium silicate and aluminum chloride in U.S. Patent No. 2,176,876 to Alessandroni, aliphatic acid in U.S. Patent No. 3,453,131 to Fadner, ethylenediamine and citric acid in U.S. Patent No. 4,075,030 to Bundy, urea-formaldehyde in U.S. Patent No. 4,346,178 to Economou, or silicon tetrachlor- ide in WO 87/00544 to Jones.

Wildt*s composite pigments were intended for latex-paint applications in which the resultant excessive aggregate hardness (abrasiveness) , restricting or even prohibiting the e of these pigments in paper filling and coating, does not constitute a real disadvantage. Principal gel compositions and experimental procedures for in-situ formation of continuous gel cements dis¬ closed in the patent to Wildt, are identical to those utilized commercially for many decades toward surface coating of titanium dioxide pigments mentioned previously. It should be pointed out in this context that while a certain controlled level of residu¬ al particle cementation (permanent aggregation) is quite essen¬ tial to synthesis of composite pigments, any permanent aggrega¬ tion is totally undesirable when continuous gels are used for surface coating of titanium dioxide pigments. Unfortunately, all procedures of the present art relying on the use of continu¬ ous gels toward pigment aggregation or surface coating are lack¬ ing inherent mechanism allowing one to exercise effective con¬ trol over the extent, or patterns, of the residual cementation of individual particles.

Continuous gels with particle-immobilizing and cementing functions were synthesized according to Wildt by an interaction between sodium silicate and aluminum sulfate in aqueous disper¬ sions of particulate raw materials used for preparation of com¬ posite pigments, using relatively high concentrations of gel forming reagents. The particulate raw materials mentioned con¬ sisted of titanium dioxide as the principal optically-active in¬ gredient, as well as coarse-particle-size, very abrasive, cal¬ cined clays (Engelhard^fs Satintone No.l or No.4) and/or coarse delaminated clay as extenders. The procedure described involved several independent critical processing steps, such as heating of the reaction medium (to speed up the formation of continuous gel) , alkaline pH adjustments, and long digestion periods (last¬ ing from 30 to 60 minutes) followed by additional acidic pH ad¬ justments. To convert the resultant reacted, dried, solidified, very hard "cake" into a particulate form suitable for use as composite pigment in latex paints, expensive fluid-energy commi¬ nution was again necessary.

The concept of immobilization of individual particles of titanium dioxide pigments and extenders (e.g., calcined clays) relative to each other is unquestionably ^"valid and advantageous for latex paints and other related applications. However, the detrimental fractionation of pigmentary components and select particle aggregation of Ti0₂/Ti0₂ and extender/extender type not be avoided in composite pigments prepared in accordance w the patent to Wildt because of the slow kinetics of the floc lation process employed. As a consequence, the resultant conf urations of aggregated particles are not conducive to effici light scattering. This has been indeed verified experimental composite pigments made in accordance with procedures set fo in the patent to Wildt having significantly poorer optical p formance in paper filling and coating applications than anal ous blends of identical titanium dioxide and calcined clay u in loose (non-aggrega ^~\ά) state.

Hoffmann, in U.S. Patent 3,476,692, describes the prepa tion of a "silicomagnesium-aluminate-hydrate" gel (antacid) f use in treatment of gastric hyperacidity. In particular, t above invention pertains to a silicomagnesium-aluminate-hydra gel certain properties of which are improved compared to tho of other patented antacid products of virtually identical comp sitions. It should be emphasized rather strongly, however, th the terminology used routinely in colloidal-technologic descriptions leaves much to be desired. For example, Hoffmann so-called silicomagnesium-aluminate-hydrate gel is factually mechanical blend of separately prepared silico-aluminate gel a a magnesium hydroxide gel, hence, fundamentally different fr true complex gels used in practicing the present invention. specific terms, Hoffmann's antacid gel was prepared by mixi concentrated solutions of sodium silicate and an aluminum sa 1 under alkaline conditions for extended periods of time, e.g., minutes, to form a solidified silico-aluminate cogel. Th cogel was subsequently crushed and homogenized into a flowab pulp, into which a concentrated solution of magnesium sulfa was introduced gradually over a period of time lasting 3 hour As a consequence, the in-situ precipitated magnesium hydroxi hydrate became mechanically, though intimately, dispersed with the previously fluidized pulp of the continuous silico-alumina cogel.

Inorganic anion-exchangers and a process for their synthes are disclosed by Duwell in U.S. Patent No. 3,002,932. The abo ion exchangers are prepared by "coprecipitating mix hydrated oxides of a pair of homolomorphic metals chosen fr the group consisting of aluminum, silicon, titanium, zinc, a zirconium, the lower-valent member of said pair being present major amount, in an aqueous medium at a pH in the range of abo pH 5 to 7, drying the aqueous mixture at a temperature bel 150°C, and washing the dried mixture with water to remo soluble impurities therefrom." The above technology, as quote is based again on physical mixtures of separately formed ge rather than true complex microgels made up of intrinsical chemically bound complex macromolecules.

U.S. Patent No. 4,239,615 to Tu is typical of a vast gro of patents pertaining to the manufacture and use of zeolites catalytic cracking of hydrocarbon charges (crude oils) . A such zeolite catalysts are based in principle on vario modifications and extensions of continuous silico-alumina cogels described extensively in textbook literature. It because of the "memory" effects associated with colloid systems, mentioned previously, that such endless varieties related gel products with material or functional-performan differences of practically significant magnitudes can synthesized with the aid of only two principal ingredient namely, sodium silicate and sodium aluminate (or alumin sulfate) . As documented amply in everyday industrial experienc relatively small differences in the preparation, handling post-treatment of such gels, the incorporation of vario transient or permanent adjuvants notwithstanding, will oft result in significant modification of such important produ features as abrasion resistance, catalytic activity a selectivity, inhibition resistance or pore-size distribution.

In addition to using silica-alumina cogels as crackin catalyst precursors, Tu also employed certain specific brand anionic polyacrylamide (transient adjuvant) to modify t mechanical structure of catalyst matrix. Accordingly, after subsequent burnout of the organic substance occluded in t latter matrix, Tu was able to obtain a more favorable pore-si distribution. As far as purely chemical functions of t anionic polyacrylamide with regard to catalyst formation a concerned, Tu cautiously offers the following hypothes proposed also in other similar patents: "it is believed that t anionic form chemically react with the silica-alumina g framework, rather than being physically dispersed in the ge and thus contributes to the desired pore structure formation. A well known fact is, however, that concentrated solutions strongly alkaline reagents used without exceptions in t synthesis of silica-alumina gels for catalyst precurso immediately coagulate virtually all organic water-solub polymers available commercially, indicated clearly by pha separation. The overwhelming likelihood is, therefore, that t polyacrylamide adjuvant mentioned above was de facto dispers mechanically in the gel, much in the same way though perhaps n as intimately as the in-situ formed molecularly precipitat magnesium hydroxide hydrate in Hoffmann's silico-alumina antacid-gel matrix described in U.S. Patent No. 3,476,692. far as zeolites' reactivity on a molecular level is concerne small amounts of metallic cations such as magnesium or calci ions can be accepted indeed into the zeolite matrix, albeit reversible ion-exchange mechanism rather than (irreversibl chemical reaction.

Dumoulin in U.S. Patent No. 4,247,420 and Tu in U. Patent No. 4,239,615, discussed previously, describe the use auxiliary extraneous disperse phase(s) in the preparation catalyst precursor gels. These particulate materials, us mainly as diluents or catalyst-matrix modifiers, are select from among natural or synthetic zeolite powders and/or kaol clays. Embedded in the continuous gel body, the relati proportion of these auxiliary particulates is restricted as rule to less than 25% of the total mass of the catalyst.

Kaliski in U.S. Patent No. 3,484,271 describes the formati of functional (release) coatings on moving paper webs by an i l o situ interaction between consecutively applied separa solutions of organic anionic and cationic compounds with a least two functional groups in each molecule. These releas coatings are made in the form of continuous, totally impervious gel films devoid of any particulate occlusions. As a matter o fact, a particulate matter embedded in such films would destro more or less completely these films' useful release properties.

U.S. Patent No. 2,974,108 to Alexander discloses synthesis o stable aluraino-silicate aquasols (hydrosols) with ion-exchang capacities equivalent to those of better zeolites, and also ver good antisoiling properties. These aquasols are prepared wit the aid of rather intricate thermal regimes and time-consumin procedures, using silicic acid (rather than straight alkali metal silicate, or quaternary ammonium silicate, used in prac ticing the present invention) and sodium aluminate as the prin cipal reagents. According to Alexander, the end product contain preferably from 5% to 20% of substantially spheroidal porou particles suspended in an aqueous medium with pH ranging betwee 5 and 10, the preferred diameter of aquasol particles rangin from 10 to 50 milimicron (nanometer) and particle porosity fro 10% to 70%. Most importantly, however, the aquasols (hydrosols according to Alexander are end products in themselves and chemi cally non reactive, whereas the hydrosols used in practicing th present invention are short-lived intermediate products charac terized by a high level of chemical reactivity.

Additional comparisons with the prior art will be mad hereinafter, wherever applicable. It should be noted, however, II that in reviewing the existing art Applicant is not aware of references pertaining to systems that are true complex ge with all principal molecular constituents being chemically bo within the same complex macromolecules, as differentiated f purely physical mixtures of two or more separate gels. In par cular, no references have been found in the literature perta ing to complex, multicomponent, rapidly forming, micro-parti late gels (microgels) used in practicing the present inventi or conditions under which these microgels can be synthesiz and/or utilized. More specifically, no references whatsoev were found in the literature regarding the use of complex mic gels toward the manufacture of structural aggregate, singl component or multiple-component, pigment products for pa filling and coating, or any other application for that matter.

SUMMARY OF THE INVENTION

The single-component and multi-component structural agg gate pigment products of the present invention comprise:

(a) particulate matter; and

(b) 0.5% to 10%, by weight, as determined by ashing, complex functional microgels which are products of crosslink reaction between: (1) aqueous solutions containing from 0.5 to 10 parts, the total mass of resultant aggregate pigments, of gel-setti agents selected from the group consisting of bivalent and ult valent inorganic salt;?, and/or 0.1 to 5 parts, on the total ma of resultant aggregate pigments, of gel-setting agents select from the group consisting of organic, cationically-activ chemical compounds with at least two reactive groups in ea molecule; and

(2) 0.5 to 10 parts, on the total mass of resultant a gregate pigments, of subcolloidal reactive hydrosols formed blending aqueous solutions of:

(i) a reagent selected from the group consisting alkali-metal silicates and quaternary ammoni silicates; and (ii) at least one reagent selected from the gro consisting of alkali-metal aluminates a alkali-metal zincates;

wherein the ratio of said reagents employed in (i) to said rea gents employed in (ii) ranges from 1:10 to 10:1, by weight, an the ratio of total reagents in (2) to gel-setting agents in (1 ranges from 1:10 to 10:1. DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the preferred form of practicing the present inventio novel structural aggregate pigment products for paper fillin paper coating, and many other applications, are manufactured synthesizing in situ complex functional microgels in aqueo dispersions of quantitatively predominant particulate matte also containing water-soluble functional adjuvants. The princ pal particulate raw materials for the manufacture of structur aggregate pigments include a variety of mineral and organ pigment products of the present art, as well as ultrafine whi or colorless mineral and/or organic particles with dimensio ranging from 0.01 μ to 0.1 ^ιm e.s.d. (equivalent spheric diameter) which are too small to be classified as white pigmen in the conventional sense due to low light-scattering efficac Upon practicing the present invention, however, these ultrafi particles become aggregated into assemblies with sufficient large dimensions to render them optically active in a commerci sense. The above, and other, particulate raw materials for t manufacture of structural aggregate pigments mentioned shall described in more detail hereinafter.

Structural aggregate pigments may be made from a sing principal particulate species, e.g., kaolin clay. Such pigmen shall be called further on "simple aggregate pigments," differentiation to "composite pigments" which shall relate structural aggregate pigments made from two or more differe principal particulate mineral species. The primary purpose of the in-situ formed complex microgels is to induce instantaneous (ultrarapid) , indiscriminate and complete flocculation of all disperse phases present in the reaction medium. Flocculation phenomena play fundamental and indispensable roles in the manufacture of all structural aggregate pigments. The flocculation processes of the present art, however, are slow, selective (rather than indiscriminate) , and incomplete. As a consequence, these processes are not well suited for the manufacture of even simple structural aggregate pigment products free of significant performance deficiencies, and are even less suited for the manufacture of more exotic com¬ posite aggregate pigments assembled from physically, chemically and colloidally highly differentiated particulate components.

Particulate raw materials for the manufacture of such exotic composite pigments encompass, for example, various naturally oc¬ curring and synthetic minerals with particle sizes ranging from 0.01 urn to 10 μnx e.s.d., non-film-forming (high glass-transition temperature) organic emulsion polymers with particle diameters ranging from 0.03 p^~& to 1 Jm, latex adhesives with particle diameters ranging from 0.07 μm to 0.3 ^ιm, and color pigments with particle diameters even smaller than 0.01 jam. The enormous quantitative and qualitative heterogeneity of above furnishes are realized best when considering that the linear dimensions of individual particles span over 3 orders of magnitude, hence, the corresponding volu. or weights of these particles may differ by a factor of one .lion! Moreover, the relative densities of particulate matter may vary from about 1 g/cm³ for certain IS plastics to 4.2 g/cm³ for titanium dioxide pigments, while th surface-chemical properties of particulates may range from ver hydrophilic to extremely hydrophobic.

It is not surprising, therefore, that the detrimental sepa ration and selective fractionation of qualitatively and quanti tatively highly differentiated particulate matter used for syn thesis of composite pigments can not be prevented with the ai of slow, incomplete, and selective flocculation processes an inefficient flocculating agents of the present art. As a matte of fact, many ultrafine water-based colloidal systems can not b flocculated (precipitated) at all with the use of means known i the present art. In the Applicant's own diversified experimen tation, on the other hand, no water-based colloidal system ha yet been encountered, regardless how complex or difficult, abl to resist the overpowering instantaneous, indiscriminate, an complete, flocculating action of the in-situ formed comple functional microgels used in practicing the present invention.

The secondary purpose of the complex microgels disclose herein is to provide an arbitrary level of intrinsic cementatio to aggregated pigment particles upon subsequent drying, or othe finishing operations. The desired level of cementation can b attained by varying composition and/or dosage of the functiona complex microgels, such as to provide structural aggregate pig ment products with sufficient mechanical integrity to withstan the customary shearing (loading) and/or comminution regimes t which they may be exposed in practical handling and end-us operations. It

It should be pointed out in this context that the adhesive action of above microgels is possible only due to the extremely small particle size, enabling the microgel particles to orient themselves effectively as discrete ultrathin formations at the interfaces between adjacent pigment particles to be cemented. Although particles of above microgels are obviously larger than those of silico-aluminate, silico-zincate, or silico-aluminate- zincate hydrosols from which they were derived through cross- linking (polycondensation) with bivalent or multivalent inorgan¬ ic salts and/or organic cationically-active chemical compounds with two o_r more reactive groups in each molecule, they could not be detected visually under 50,000 X magnification in elec- tronphotomicrographs of dried and pulveri∑ ..d composite pigments prepared with the aid of these microgels. Spheroidal hydrosol particles with diameters ranging from 10 nm to 50 nm described in U.S. Patent No. 2,974,108 to Alexander, on the other hand, can be seen clearly in similar electronphotomicrographs.

It is apparent that solid inorganic particles of the latter size, i.e., 10 nm to 50 nm, would not only be useless as inter- facial cements or adhesives, but would actually interfere physi¬ cally with the formation of adhesive joints between adjacent microparticulates. In-situ precipitated solid mineral particles of similar or larger dimensions have been found useful, however, in synthesizing certain kinds of composite pigments, for exam¬ ple, of coprecipitated/coaggregated type disclosed in U.S. Patent No. 4,026,721 to Kurrle. According to this patent, soli¹ spherical hydrous metal-silicate particles were precipitated on \ 1 the surface of kaolin clay platelets improving the end product's optical performance.

The tertiary purpose of the complex microgels disclosed herein is to impart directly, by virtue of their inherent physical and surface-chemical properties, certain specific material and functional properties to the aggregated and cemented products, important from the standpoint of these prod¬ ucts' end-use applications. The above effects can be realized through purposeful modification of the chemical composition, and/or physical properties, of the complex functional microgels. For example, surface-chemical modification providing enhanced compatibility with organic media may be attained by intrinsic incorporation of suitable organic polyelectrolytes, and/or other specialized agents, into macromolecules which make up the complex microgels of the present invention. Composite pigments synthesized with the aid of such microgels with built-in organic groups (functionalities) are especially well suited as fillers for plastics, since they can be easily and uniformly dispersed in oleophilic media.

Anionic polyelectrolytes with microgel-modifying functions, encompassing, among other things, sodium salts of polyacrylic acid or carboxymethyl cellulose, may be introduced into the system through the anionic stream, e.g., along with sodium silicate or sodium aluminate, or added directly to the particu¬ late dispersion. Cationic modifying agents encompassing, among other things, selected bivalent or multivalent inorganic salts, as well as organic cationically-active compounds with at least \i two reactive groups in each molecule, may be introduced into th system along with the solution of the principal bivalent o multivalent inorganic salt(s) used for microgel formation.

The indirect system-modifying action of complex microgels made possible by the indiscriminate and complete flocculatin and retention of such powerful surface-chemical modifiers i their own right as organic dyes and polymer-emulsion adhesives is also important. Other examples of functional modificatio of inherent properties, or functional characteristics, of struc tural aggregate pigments through the in-situ precipitated comp lex microgels used in practicing the present invention shall b discussed hereinafter.

The principal reagents of commercial significance for th in-situ synthesis of the complex functional microgels unde discussion are: (1) alkali-metal silicates and quaternar ammonium silicates, preferably sodium silicate; (2) alkali metal aluminates, alkali-metal zincates, and blends thereof i any proportions, preferably sodium aluminate; and (3) water soluble, essentially colorless, bivalent and multi-valen inorganic salts, preferably calcium chloride and calcium nitrat but equally well other similar salts of calcium, magnesium barium, aluminum, zinc and zirconium, as well as cat onically active organic compounds with at least two reactive groups i each molecule, capable of performing the same gel-settin functions as bivalent or multivale*- inorganic salts. Of course both anionic and cationic organic ditives used in the proces must be compatible with their respective anionic and cationi 14 reaction streams, as indicated by absence of phase separati clouding, or premature gelling.

From a chemical standpoint the above complex microgels a made up of macromolecules of hybrid polymer-pσlycondensate ty the polymerization reaction being at the foundations of hydros formation while polycondensation takes place during crossli ing of the reactive hydrosols by cationic gel-setting agen Inorganic/organic hetero-macromolecules of the same polym polycondensate type are formed when organic chemical compou with at least two reactive groups in each molecule are built i trinsically into the microgel structure.

Since the primarily auxiliary functions of the comp microgels are limited to flocculation, cementation and surfa chemical modification of disperse particulates, these gels used as a rule at the smallest possible dosages needed to p form the intended tasks, ranging from 0.5% to 10%, by weight, determined by ashing, of the total mass of aggregate pigmen the particulate matter being quantitatively predominant phase the overall material balance. On the basis of extensive expe mentation with various simple, as well as most intricate com site, structural aggregate pigment formulations, it has been tablished that the relative weight content of complex microg in a vast majority of end products, determined by ashing af washing out electrolyte by-products such as NaCl, NaN0₃, Na₂S0₄, needs to approach 6% to 10% in only most demandi cases, e.g., those involving high levels of addition of organ particulates, dyes, and the like. In majority of practic applications, however, the relative weight content of comple functional microgels in structural aggregate pigment product ranging from 1% to 6%, as determined by ashing, will be suffi cient for adequate handling and end-use performance. In som less demanding applications, e.g., those which do not involv filtration and subsequent dewatering and comminution of th floccul ted medium, a relative weight content of complex func tional microgels in the resultant pigment products as low a 0.5 %, as determined by ashing, is adequate.

It should be emphasized that formation of intermediate hydro sols, and final microgels, used in practicing the present inven tion are not stoichiometric. The same hydrosols and/or microgel are synthesized each time, however, when the reagent concentra tions and proportions, as well as reaction conditions durin synthesis of these hydrosols and/or microgels, are the same. O the other hand, the principal qualitative and quantitative com positions of above hydrosols and microgels may be varied withi unusually broad ranges without detriment to these hydrosols' , o microgels*, intended functional rerformance. For example, the ratio of sodium silicate to sodium alum.nate, sodium silicate to sodium zincate, or sodium silicate to the combined mass of sodium aluminate and sodium zincate in forming the subcolloidal reactive hydrosols (sodiu -silico-aluminate, sodium-silico-zin- cate, and sodium-silico-aluminate-zincate, respectively) may range from 10:1 to 1:10, by weight, the preferred ratio for most applications pertaining to the synthesis of structural aggregate pigments being 1:1. The concentration^* of sodium silicate in aqueous slurries of particulate matter should vary optimal from 0.1% to 2%, by weight, the same pertaining also to sodi aluminate, sodium zincate, or combination thereof. Reage concentrations significantly higher than 2%, by weight, wou lead in a short period of time to formation of high-molecula weight hydrosols with reduced reactivity relative to crosslin ing agents, necessitating a drastic increase of throughput rat of the reaction medium through the reactors.

As far as the formation of complex microgels is concerned, simple 1:1 ratio, by weight, of calcium chloride or equivale crosslinking salts to the combined hydrosol mass is adequate f a well balanced performance encompassing both flocculation a subsequent cementation of particulate matter used for synthes of structural aggregate pigments of the present invention. should be pointed out, however, that some excess of crosslinki ions is necessary from the standpoint of process kinetics, pa ticularly in plant operations employing large mixers-reactor As has been determined by chemical analysis, the concentrati of calcium, or equivalent, ions in the reaction medium shou exceed by at least 50% the amount of such ions actually bou chemically by the reactive hyrosols. As a matter of fact, it sometimes advantageous to use an even higher excess of bivale and/or multivalent inorganic salts for hydrosol crosslinkin e.g., by employing of up to 10%, by weight, of these salts the total mass of particulate matter.

Unlike with bivalent and multivalent inorganic crosslinki salts, the ratio of organic, cationically active, crosslinki 3Α agents to hydrosol mass must be determined empirically for eac individual compound and specific application. The reason fo this is that the chemical properties of above organic material are vastly more differentiated from the standpoint of thei effect upon end-use properties of structural aggregate pigmen products than are those of corresponding inorganic crosslinkin agents. As a general rule, the relative proportion of the abov organic crosslinking agents should range from 0.1% to 5% of th mass of particulate matter.

As is understood readily by those .skilled in the art, th anionic and cationic streams in the process for synthesizin structural aggregate pigments of the present invention may b reversed by blending solutions of bivalent and multivalen inorganic salts and/or organic, cationically active, chemica compounds with at least two reactive groups in each molecul with aqueous dispersions of particulate matter in step (a) preparing subcolloidal reactive sodium-silico-alu inate (silico zincate or εilico-aluminate-zincaie) hydrosols independently i step (b) ; and blending in step (c) systems resulting fro steps (a) and (b) to form in situ complex functional microgel to flocculate the particulate matter instantaneously, indiscrim inately and completely to synthesize structural aggregate pig ment products. It should be pointed out, however, that the abov reversion of process streams is feasible only in such instance in which the colloidal stability of dispersions of particulat ir :ter is not impaired intolerably by a short period of contac with solutions of cationic agents employed. The pH of the flocculated structural aggregate pigment pro ucts from step (c) above ranges usually from 10 to 12. In cas in which neutral, or slightly subneutral, pH is preferred, p determined amounts of sulfuric acid, or other inorganic or o ganic acidifying agents, may be added to the dispersion of pa ticulate matter in step (a) . The amount of agents necessary lower pH to the desired level must be assessed independently, titrating a sample of the alkaline medium from step (c) wi solutions of the acidifying agents to be employed. Though principle the resultant pH of the flocculated medium in st (c) could be lowered to 3.5, the colloidal stability of mo dispersions of particulate matter used for synthesis of stru tural aggregate pigments of the present invention will be im paired intolerably below pH of 5, or even 5.5.

The complex functional microgels used in practicing t present invention may also be prepared independently, in pla water, and then blended with a dispersion of particulate matt to flocculate the latter indiscriminately and completely, b not instantaneously, to form a structural aggregate pigme product. It should be emphasized, however, that the proce version in which subcolloidal reactive hydrosols are synthesiz first in aqueous dispersions of particulate matter, follow by addition of cationic crosslinking agents, is preferred f the synthesis of structural aggregate pigments according to t present invention.

The above, almost boundless, latitude with respect chemical composition of complex microgels used in practicing t present invention is very unique, in that practically a methods of gel synthesis known in the present art rely on ve strictly and narrowly defined compositions, both with regard these gels' synthesis as well as end-use properties.

Another uniquely broad latitude with regard to the reacti conditions in general pertains to the pH range, extending fr 3.5 to more than 12, under which the complex microgels of t present invention can both be synthesized and perform the intended functions.

As is typical of ultrafast reactions in aqueous media, t in-situ formation of the complex functional microgels mention is virtually independent from temperature. This means that, principle, the above microgels could be formed within the enti temperature interval in which water remains fluid, i.e., fr above the freezing point to below the boiling point. From purely practical standpoint, however, the temperature at whi composite pigments can be manufactured will be determined prim rily by the thermal stability of dispersions of particulate r materials.

The virtual independence from thermal conditions and regim is a very unusual and unique feature of above microgels, whi becomes readily apparent when comparisons are made with oth technologies of gel formation in accordance with the prese art. For example, countless patents pertaining to the manufa ture of catalysts, ion exchangers, pharmaceutical preparatio and other products based on in-situ formed gels, sometimes virtually identical compositions, frequently differ only wi respect to small variations of the thermal regimes. The broad latitudes with respect to reaction condition mentioned above, constitute a clear indication of the incredib overriding power of the principal colloidal-chemical system us in practicing the present invention. It is worth noting th similar latitudes are intolerable with procedures of the prese art, according to which continuous gels and hydrosols, and pro ucts made with their use, must be manufactured always under ve strictly defined reagent concentrations and proportions, pH co ditions, as well as thermal and procedural regimes.

The potential role of structural aggregate pigments of t present invention in future paper making technologies can perhaps illustrated best against a background of present ind trial practices relying on the use of conventional mineral pi ments. For use in paper making, the latter pigments are ma down as a rule in the form of concentrated, optimally dispers slurries. In their final destination, on the other hand, th pigments exist in a highly aggregated and/or flocculated sta e.g., encased within a paper-coating matrix or filled pa webs. This terminal aggregation/flocculation is particula strongly pronounced in coatings, especially those made with t aid of highly poly-disperse and anisometric kaolin pigmen characterized by very fine particle size.

The latter pigments are typified by No. 1 V.F. (Number O Very Fine) , high-glossing, hydrous coating clays which conta 95% - 100%, by weight, of particles smaller than 2 m e.s. (equivalent spherical diameter), less than 10%, by weight, particles smaller than 0.1 urn e.s.d., and have an avera particle size ranging from 0.2 i to 0.4 ym e.s.d. Briefly, above clay products may be described as being manufactured f inherently very fine particle size crudes by blunging the lat in water, removing particulate impurities larger than 44 e.s.d. with the aid of appropriate screens, followed by centr fugation to obtain a useful fraction with particles 95% to 98 by weight, finer than 2 ^ιm e.s.d. The latter fraction is s sequently beneficiated by physical methods such as high-gradie magnetic separation, colloidal-chemical methods such as flot tion and selective flocculation, and chemical methods such oxidation and reduction bleaching important also from the stan point of chemical stabilization of the end product.

The above very fine particle size clays are used by the selves almost exclusively for the manufacture of glossy printi papers, representing a relatively small market, and as feedsto for making fine particle size calcined clay pigments. In t state "as is," these clays are practically unusable toward pap filling applications due to poor retention on the paper machin inferior optical efficacy, and strong fiber debondi-*g action.

At the present, very fine particle size clays are used mai ly as diluents for regular coating clays derived from substa tially more valuable, coarser, more crystalline "white" cl crudes. The light-scattering coefficients of clay pigments ma 100% from the latter crudes are about two to three times high than those of very fine particle size, high-glossing clays. U fortunately, white crudes, particularly those having good rhe logical properties, are progressively more scarce. As a cons SI quence, admixing of up to 50% of optically inferior very fi particle size clays into commercial coating clay products h become a virtual necessity throughout the clay industry. It not surprising, therefore, that the optical properties of su hybrid coating clays constituting the bulk of present mark sales deteriorate progressively as the deposits of better crud become depleted. Indeed, the light-scattering coefficients clay products marketed some 15 years ago were an the avera 40% to 50% higher than those of analogous products market today, the foregone conclusion being that the situation wi only get worse in the future.

The limited usefulness of very fine kaolin clay crudes most unfortunate in that the vast majority of clay deposits the United States belong to this category. Moreover, there a no realistic prospects for a broader utilization of such cla within the context of pigment manufacturing, or other commerci applications, relying on technologies of the present art. Henc the technology of the present invention utilizing these abunda very fine particle size, low-value, crudes as a most valuab raw material toward the manufacture of high-performance, hig value added, structural aggregate pigments constitutes de fac a major breakthrough in the utilization of otherwise inferio or even useless, raw materials.

It is known from optical physics that the highest intensi of light scattering by a spherical particle is attained when t diameter of the particle is equivalent to one-half of the wav length of impinging light, i.e., approximately 200 nm to 300 n With platy clay particles, the light is scattered by variou solid irregularities, such as particle edges or corners, o surface protrusions. Under practical end-use condition encountered in paper filling and coating, with the individua pigment particles being compacted (by way of flocculation an aggregation) into integral formations existing within fille webs or paper-coating matrices, the light is scattered both b internal as well as external structural (solid) details of thes formations. The closer are the dimensions of these structura details to those needed for optimum light scattering, the bette is the resultant optical performance of the entire formation.

It becomes apparent, therefore, that a method enabling on to effectively control the process of forming optimized aggre gate pigment structures represents an enormous commercia potential. As demonstrated by Kaliski in the article entitle "Performance of Some Commercial Clays in Starch-Containing Pape Coating Films" - Part 1, appearing in The Journal of the Techni cal Association of the Pulp and Paper Industry (TAPPI) Vol. 53 No. 11, page 2077 (1970), the light-scattering coefficients o coating formations consisting of kaolin clay pigments and starc adhesives initially increase, and after passing through maximum decrease, with increasing levels of the adhesive. Th explanation of this phenomenon given by Kaliski is that under sized pigment particles, which are incapable of efficient ligh scattering individually, become progressively aggregated b incremental additions of the adhesive into formations whos structural details are dimensionally closer to those needed fo 41 optimum light scattering. After certain critical level of t adhesive in the coating is exceeded, however, the progressi coarsening of structural details of the resultant coati formation by additional adhesive increments becomes excessiv thus reducing the overall light-scattering efficacy of t system. This progressive intrinsic coarsening of the intern structural details with increasing adhesive levels, w demonstrated clearly with the aid of the "rho" factor develop by Kaliski and described in the above-mentioned TAPPI article.

The aggregation and flocculation processes occurring paper filling and coating are not amenable to effective contro within the scope of technologies of the present art, thou attempts to develop such controls have been reported in t literature for more than five decades. The most attractive these approaches were directed towards development of so-call bulking pigments intended to at least duplicate the optic performance of old-fashioned satin white pigments, without t latters' numerous undesirable features. From the standpoint optical performance and printability, satin white admixed conventional coating clays has indeed a unique ability to indu favorable intrinsic structures in the resultant coating form tions. The preparation, handling and application of coati colors containing satin white, however, are rather cumberso and difficult.

New concepts relating to the improvement of pigment perfo mance in paper coatings were developed by Kaliski and describ in the article entitled "Performance of Some Commercial Cla in Starch-Containing Paper-Coating Films" - Part 2 appearing TAPPI, Vol. 55, No. 1, page 102 (1972), as well as in Chapter of "Physical Chemistry of Pigments in Paper Coating" (copyri 1977 by TAPPI) in which he pointed out the importance of "ea setting of transient coating structures in freshly applied co ing films." Such early setting arrests progressive deterio tion of the initial, statistically uniform, transient coat structures in wet coating films and eliminates the detrimen separation and selective fractionation of individual coat ingredients.

Hereinafter shall be demonstrated how structural aggreg pigments of the present invention, as well as scientific c cepts discussed above, can be used to obtain many practi results superior to those attainable with the aid of filling coating pigments of the present art.

The in-situ formed complex functional microgels mentio above make possible to synthesize new types of structural agg gate pigment products uniquely suited toward paper coating filling applications, filling of plastics, and many other pra tical uses. The optical performance of such structural aggrega pigments synthesized from a variety of commercial pigment pro ucts and other mineral and organic particulates, as well as so uble components, is substantially better than that of the orig nal raw materials used in non-aggregated form. Many unique pe formance properties, as well as structural and surface-chemic features, can be imparted to these aggregate pigments almost will by purposeful a-priori design. One of such unique perfo mance properties is, for example, ultrahigh bulking which brin about spectacularly rapid setting of coating films on paper su face. The above setting is fully independent of dewatering, su as is normally indispensable to setting of wet films containi standard coating pigments or conventional bulking pigments. contrast, coating formations containing ultrahigh bulki pigments of the present invention become immobilized (se rapidly without dewatering, yielding smoother and more unifo coatings with higher gloss, brightness and opacity, as well better glueability and printability, than analogous coating fo mations containing pigments of the present art.

Special types of structural aggregate pigments equipped pu posely with maximum bulking properties (very high level thixotropy) are extremely valuable in paper filling applic tions. A complete, but totally reversible, gelling can be o tained with aqueous slurries of such specialized pigments ev upon dilution to 20% solids, or even lower. Accordingly, the pigments begin to display structure-forming (bulking) tendenci during web consolidation on the paper machine even before wat drainage on the forming wire is completed. The practical effec of this heretofore unknown ultrahigh bulking are manifested substantially increased levels of filler retention, vastly i proved uniformity of spatial distribution of pigment particl within consolidating paper webs, and drastic reduction of t normally difficult-to-avoid detrimental web two-sidedness.

Surface-chemical modification of structural aggregate pi ments of the present invention can be affected by building i organic groups into macromolecules making up the microgels an through incorporation of organic particulates into the aggregat pigment structure, thus imparting controlled levels of affinit toward organic (non-polar) media in addition to the inheren affinity of (polar) mineral pigments toward water. In the abov manner, the structural aggregate pigments acquire intrinsi dual-matrix surface characteristics of hydrophilic/organophili type well suited, for example, toward uniform and efficien dissipation both of water and ink solvents in offset printing.

There are hundreds of anionic and cationic organic polymer in daily use by the paper and pigment industries identified onl by trade names, molecular weights, and ionic type, which can b employed toward microgel formation if they are compatible wit the respective ionic streams. For example, anionic polymers suc as sodium salts of polyacrylic acid or carboxymethyl-cellulos are compatible with the anionic process stream if they are no coagulated, or salted out, by strongly alkaline solutions o sodium silicate, aluminate or zincate. Similarly, cationic poly mers, e.g., polyacrylamides, are compatible with the cationi stream if they are not coagulated, or salted out, by solution of bivalent and mutivalent inorganic salts. A vast number o organic monomolecular anionic and cationic chemical compound with two or more reactive groups in each molecule can be used i addition to, or instead of, organic ionic polymers mentione above. Examples of such anionic compounds are sodium salts o N-(l,2-dicarboxyethyl)-N-alkyl sulpho-succinamate (Aerosol 22) or ethylenediamine tetraacεtic acid, while methyl-dodecylbenzyl 53 trimethyl ammonium chloride-methyldodecylxylene bis(tri eth ammonium chloride (Hyamin 2389) is representative of orga cationic compounds with two reactive groups in each molecul Depending on the intended end-use applications of structu aggregate pigments synthesized with the aid of polymeric monomeric organic adjuvants, addition levels of the latter vary from 0.1% to 5%, on the total mass of mineral particulat Lower addition levels of these agents may suffice, for examp with structural aggregate pigments intended for coating of pa for offset printing, higher levels of addition being prefer with composite pigments intended for filling of plastics, paper substrates to be saturated with solutions of organ resins. Of course, organic particulates, e.g., polystyre pigments or polymer-emulsion adhesives, incorporated into t aggregate pigment structure modify the surface chemistry of t resultant pigments in an indirect fashion by forming a du matrix of polar/non-polar type.

Carbon black and organic color dyes can be incorporated in structural aggregate pigments at levels ranging from 0.001% 0.25% and 0.001% to 5%, by weight, respectively. Although bo above materials have notoriously poor affinity toward polar su faces, such as mineral pigments or cellulosic fibers, they a retained and distributed uniformly within aggregate structur of pigments made with the aid of in-situ synthesized compl functional microgels used in practicing the present invention.

Very low levels of addition of carbon black and/or organ color dyes, e.g., ranging from 0.001% to 0.01%, by weight, a J4 often sufficient to correct the inherent "yellowness" typical virtually all mineral raw materials used for synthesis of stru tural aggregate pigments. Somewhat higher levels of additio e.g., ranging from 0.1% to 0.3%, by weight, for color dyes, a from 0.005% to 0.12%, by weight, for carbon black, yield high opacifying structural aggregate filler pigments which can al be used to mask the inherent yellowness of groundwood papers. similar level of dye addition, i.e., 0.1% to 0.3%, by weigh eventually in combination with up to 0.03%, by weight, of carb black, will mask the pronounced yellowness of unbeneficiat kaolin clay making possible to use the latter as is, or aft only inexpensive magnetic beneficiation, toward the manufactu of economical structural aggregate pigments for paper filli and coating.

Still higher levels of color-dye addition, e.g., of up 5%, by weight, make possible to synthesize intensively color aggregate filler pigments for the manufacture of most uniform colored papers devoid of objectionable two-sidedness, such as common with color papers of the present art. The above approa relies on easily controllable mechanical retention of colore filler particles in the web, eliminating the need for difficul to-control quantitative and qualitative balancing of loose dy in recirculating furnishes on the paper machine. The outstandi economy of the above approach should also be pointed out in th retention of mineral fillers in the sheet is from 10 to 40 tim higher than that of loose, incomparably more expensive, dyes.

Decorative gray papers, totally opaque for all practic 3? purposes, can be manufactured with the aid of structural aggr gate filler pigments containing up to 0.25%, by weight, carbon black. Very attractive, "metallised" appearance paper surface can be obtained by incorporation both of metall and color pigments into structural aggregate filler pigments.

It should be borne in mind also that most organic dyes a carbon black, particularly the latter, are pronouncedly hydr phobic while the in-situ formed complex functional microgels the present invention are very hydrophilic unless cured abo 220°C. In the course of the manufacturing process structur aggregate pigments are exposed to drying temperatures whi rarely exceed 150°C, hence, the microgel cement retains a hi degree of hydrophilicity not conducive to a total immobilizati of hydrophobic dyes or carbon black. Since even traces of abo colorants dispersed or dissolved in water can be noted readi at concentrations as low as one part per billion, the need f complete (100%) permanent attachment of these agents to the su face of structural aggregate pigments is rather obvious. Su irreversible attachment (immobilization) can be obtained by i corporation of suitable latex adhesives, along with organic dy and carbon black, into the structural aggregate pigments. T most effective immobilizing agents for carbon black and organ dyes were found to be the novel ultrafine polymer-emulsi adhesives to be discussed in more detail hereinafter. In t absence of immobilizing adhesives, traces of carbon black a organic dyes detach from the mineral (polar) surface when co centrated slurries of structural aggregate pigments are expos to intensive shearing, becoming noticeable especially aft subsequent dilution and aging of the slurries.

Broadly diversified functional properties were imparted structural aggregate pigments of the present invention by inco poration of the above-mentioned novel polymer-emulsion adhesiv developed by the Applicant and disclosed in co-pending pate application (Serial No.07/333,435 ; Filed April A_* 1989) These adhesives, encompassing acrylic, vinylacetate and styren butadiene polymers and copolymers, have ultrafine particles wi diameters ranging from 20 nm to 55 nm, and glass-transition te peratures ranging from +20°C to -60°C. Coated papers for offs printing made with the aid of structural aggregate pigments co taining from 0.25% to 5%, by weight, of the ultrafine polyme emulsion adhesives were found to have better dry and wet coati pick, as well as higher blistering resistance, than analogo coatings made with the aid of conventional pigments. Furth Furthermore, structural aggregate filler pigments containi these adhesives cause much less fiber debonding than conventio al fillers, this positive effect being amplified by hot cale dering of the filled paper.

The above ultrafine polymer-emulsion adhesives, along wit relatively fine particle size (essentially 100% finer than 5 u e.s.d.), high specific surface area (at least 50 m²/g) , strongl gelling minerals such as montmorillonite and bentonite, are th primary functional constituents of ultrahigh bulking pigment mentioned previously. The latter pigments are uniquely suite as fillers for uncoated printing papers, particularly newsprin and papers for ink-jet printers, as well as size-press coatin pigments, because of spectacular ink holdout resulting in excel lent print gloss. Furthermore, these pigments are ideal carrie for ink-curing promoters (driers) , such as manganese, cobalt, lead naphthenates, which should be incorporated into these pi ments in proportions ranging from 0.1% to 5%, by weight.

Calciu -silico-aluminate, and other related, microgels us in practicing the present invention exert by themselves a pr nounced surface-chemical activity. For example, cellulosic we filled with structural aggregate pigments made with the aid above microgels are virtually immune to aging phenomena relat to intrinsic acidity and light exposure.

The instantaneous, indiscriminate and complete flocculati action of the complex functional microgels of the present inve tion makes possible to synthesize multiple-component structur aggregate pigments of virtually any arbitrary morphology a chemical composition, with all particulate ingredients bei statistically and spatially uniformly distributed within t resultant aggregate structures, not attainable with the aid technologies of the present art. The selection of raw materia suitable for the manufacture of structural aggregate pigments extremely broad, encompassing, for example, virtually all typ of conventional "hydrous" kaolin clay products, as well as fi particle size calcined clay pigments derived from very fine pa ticle size kaolin clay feeds; precipitated calcium carbonat calcium silicate, calcium alurainate, calcium sulfate, hydrat alumina, hydrated silica, and silico-aluminates, with equivale spherical diameter ranging from 0.01 urn to 10 ym ^~ naturall occurring calcium carbonate, gypsum, talcum, mont orillonit 3-^* and bentonite, with equivalent spherical diameter ranging fro 0.1 im to 5 um; conventional (commercially available) titaniu dioxide pigments, as well as titanium dioxide products obtaine by special intensive comminution of commercial materials to in crease substantially the relative proportion of particles wit diameters between 0.2 urn and 0.4 um, and reduce the largest par ticles to a diameter essentially smaller than 0.9 um, but pref erably finer than 0.7 -xm or even 0.6 um. ; naturally occurrin rutile and anatase minerals comminuted intensively to' an averag particle size essentially finer than 1 um; organic polymeri pigments; synthetic and natural (cellulosic) microfibrils; conventional latexes as well as novel ultrafine polymer-emulsio adhesives; ink-curing promoters; color dyes and carbon black and particulate phenolic resins of the type used in the manufac ture of carbonless paper.

Interesting steric effects of practical significance can b obtained if a proportion of particulate mineral raw material for the manufacture of structural aggregate pigments are ver fine, or even ultrafine (i.e., 0.01 um to 0.1 um e.s.d.). Fo example, with composite pigments consisting of 30% conventiona titanium dioxide pigment and 70% ultrafine precipitated calciu silicate, by weight, each individual particle of titanium diox ide immobilized in the resultant aggregate structure may be sur rounded by up to 20,000, or even 30,000, particles of calciu silicate. The net effects of such unique steric configuration are manifested by vastly increased light-scattering efficacy o titanium dioxide particles independent of crowding conditions i 3 a filled sheet, or a coating, excellent first-pass retention the paper machine, highly increased oil absorption, and oth important performance advantages.

The use of functional complex microgels of the present inve tion toward manufacture of structural aggregate pigments wi vastly improved optical and other performance properties sha be illustrated hereinafter by way of laboratory examples. T following Example I demonstrates the preparation of a simp structural aggregate pigment from a very fine particle si centrifugal fraction (100% finer than 2 um e.s.d.) of a lo quality Georgia clay crude, using specially developed laborato batch process intended to simulate continuous synthesis proce to be used preferably in large-scale plant operations.

EXAMPLE I

A 100 g batch of the above-mentioned very fine particle si kaolin clay fraction was made down into a slurry of about 7 solids, by weight. The batch of concentrated slurry was dilut subsequently to about 20% solids, by weight, and divided in two equal portions. A 5%-solids solution containing 2 g (d basis) of sodium silicate was added under agitation into o portion of above clay slurry. Similarly, a 5%-solids soluti containing 2 g (dry basis) of sodium aluminate was added in the second portion of the above slurry.

In the subsequent step both above portions of clay slur were recombined rapidly under vigorous agitation, whereby a su 604

-f<5 colloidal reactive sodium-silico-aluminate hydrosol (ani polyelectrolyte) was formed instantly by the interaction bet sodium silicate and sodium aluminate.

Immediately afterwards, a 5%-solids solution containing (dry basis) of calcium chloride was added, under very st agitation, into the recombined clay slurry containing the ab mentioned hydrosol. Instantaneous flocculation of the sl manifested by a total disappearance of vortex in the agita medium was observed upon the introduction of the very first p tion of calcium chloride solution into the system. It thus necessary to increase the agitation rate promptly and stead to restore the vortex without which a useful distribution the remaining portion of calcium chloride solution (the wh process of addition lasting from start to end about 2 secon would not be possible.

The instantaneous flocculation of the system could be rec nized immediately by immersing a spatula in the slurry, with pigment floes being clearly visible in the thin layer of liq retained on the spatula. A narrow layer of clear supernat above the bulk of flocculated slurry formed after a couple minutes, while a thick crystal-clear layer of supernatant observed after a couple of hours.

The flocculated slurry could be filtered right away, tho a controlled period of aging enhances the filtration rate alm invariably with all flocculated particulate systems. Dewater of the above slurry on a Buechner funnel at filter-cloth load of 2000 g/m² was extremely fast. As a matter of fact, 20%-sol slurry of above pigment having pH of 12 needed under above c ditions about 30 minutes for complete filtration and rinsing compared to 30 hours for a 20% solids slurry of non-aggrega raw material flocced with sulfuric acid to pH of 2.5. It worth noting that filtration of alkaline slurry of a very f particle size kaolin clay pigment would be totally impractica

To obtain the final product (simple structural aggregate p ment) , the rinsed and dried filter cake was pre-crushed and c minuted with the aid of conventional pulverizing equipment u routinely in the clay industry. The comminution regime, defi by the number of passes through the pulverizer and the size screen openings, was chosen so as to maintain the dimensions largest particles in the resultant pigment product only sligh larger than they were in the raw material employed, limiting permanent aggregation effectively to the finer particulate fr tions present in the starting material.

The optical performance of the structural aggregate pigm product obtained was rather impressive. The light-scatter coefficients of binderless coating films on black glass plat determined with the aid of techniques described by Kaliski TAPPI 53(11)1970, were 0.170 m²/g for the aggregate pigment compared with 0.050 m /g for the starting material (very f particle size kaolin clay) .

Similar results were obtained when sodium aluminate in reactive hydrosol was replaced partially or totally with equi lent amounts of sodium zincate, or when calcium chloride was placed with calcium nitrate. 4 $-

Dosages of microgel-forming reagents employed in Exampl are preferable both with simple, as well as many composi structural aggregate pigments made according to the present vention. One can comprehend readily, however, that other reag dosages and/or proportions will often be called for consider the virtually countless types of structural aggregate pigm products which can be synthesized by the described method various specific uses.

It should be pointed out also that the flocculated slurry Example I was dewatered by vacuum filtration (Buechner funnel In plant operations, however, the vacuum filtration/rinsing c bination intended to remove electrolyte by-products of micro formation should be followed up preferably by a pressure-filt tion step. .staining highest possible filtercake solids le in the latter step is helpful in eliminating "fine-end tail" the resultant pigment products, encompassing the optically l efficient but strongly debonding aggregates smaller than 0.2 or so. It has also been established experimentally that fla drying, in which both the drying and pulverizing operations intrinsically combined, is advantageous in large scale manuf turing of structural aggregate pigment products of the pres invention, from the standpoint of ease of dispersion, reduct of detrimental screen residue, and overall process economy.

As is readily understood by those skilled in the art, t laboratory batch manufacturing process descr bed in Example I applicable also to plant-scale manufacturing. As far as produ quality and versatility of product design are concerned, ho +3 ever, best results are obtained with the aid of continuous ma facturing processes which provide optimum control of the cri cal crosslinking step and allow one to use higher concentrati of hydrosol-forming reagents in the reaction medium, one of m possible versions of continuous processes for the manufacture structural aggregate pigments of the present invention, invo ing continuous passage of the reaction medium through a ser of in-line mixers reactors (stations) , is described below i simplified fashion as consisting of the following process steps:

(a) metered quantities of slurries of mineral particula are introduced continually into first station to obtain compl homogenization of the medium at high shearing rates;

(b) metered quantities of dilution water, soluble (anion organic agents, polymer-emulsion adhesives, soluble and dispe dyes, and the like, are injected continually into the in-com reaction stream and homogenized at lower shearing rates t those employed in the previous station;

(c) metered quantities of hydrosol forming reagents are jected into the reaction stream entering a third station, form the subcolloidal reactive hydrosol; and

(d) metered quantities of crosslinking agent(s) are injec into the in-coming stream of the hydrosol-containing react medium at a forth station under precisely controlled shear regime, to form in situ continually and reproducibly the desi complex functional microgel, thus flocculating the react medium instantaneously, indiscriminately and completely obtain a structural aggregate pigment product.

Even moderate admixtures of simple structural aggregate pi ment products to conventional coating clays improve substantia ly the latters' optical performance, as shall be demonstrated the following example:

EXAMPLE II

A pigment blend containing 75 parts, by weight, of comme cial delaminated clay and 25 parts, by weight, of the simp structural aggregate pigment from Example I, was made down in a 55%-solids coating formulation of the type used in the man facture of gravure papers. A styrene-butadiene latex was us as the coating adhesive in proportion of 5 parts (dry weigh per 100 parts of total pigment. Analogous control coating fo mulation was prepared using above delaminated clay as the sol pigment.

Both above formulations were applied separately onto typical commercial lightweight publication paper base sheet wit a basis weight of 28 lbs/3300 sq.ft., at a rate of 5 lbs/330 sq.ft., CIS (coated one side). The coated paper was dried an supercalendered under conditions such as to impart a gloss o approximately 50% to the control sample.

It was established by means of visual inspection that pape coated with the formulation containing 25/75 blend of structura aggregate pigment and delaminated clay had better surface cover age, coating lay, and K&N ink-stain uniformity than paper coate with control formulation containing delaminated clay as the sol 4 pigment. It was further established with the aid of instrument measurements that gloss, brightness and opacity of paper coat with formulation containing 25% of the experimental aggrega pigment were higher by 5; 2.5; and 1.5 percentage-points, re pectively, than corresponding values obtained with paper coat with the control formulation.

The make-down of aqueous slurries of structural aggrega pigments, e.g., those described in Examples I and II, diffe fundamentally from that of the high-glossing, very fine partic size, clays from which they were derived. For example, mo coating clay products made from Georgia crudes can be made do with the aid of phosphate and/or polyacrylate dispersants in 70%-solids slurries, characterized by a more or less pronounc dilatancy. The structural aggregate pigments mentioned requi up to five-times higher levels of dispersants, yet, can be ma into slurries with a maximum solids content only slightly high than 60%. The slurries in question are highly thixotropic, fl most readily under shearing, and gel immediately when the shea ing forces are removed. This unique rheological behavior can sustained if above slurries are made down into properly form lated coating colors, or even relatively low-solids pigment sizepress formulations, which is not possible with the coati pigments of the present art.

The practical consequences of the above unique rheologic behavior are quite significant. For example, coating formul 4lo tions containing shear-thinning structural aggregate pigments the present invention can be applied at highest speeds attai able with the fastest, most advanced, coaters of the prese art. Indeed, coating formulations of the above-mentioned ty have been applied on a commercial coater at speeds of near 5000 feet per minute, the empirical indications being that t coating speed could yet be increased very considerably. Mor over, since rapid setting (immobilization) of freshly appli coating films containing above structural aggregate pigments c be obtained without dewatering, the normally unavoidable disa rangement of the initial, more uniform, coating-film structure caused by water drainage currents and contour-following phenom na taking place during setting of wet films, is nearly total eliminated. The important practical consequences of this rap setting are lack of objectionable coating mottle, better fib coverage and smoother coating surface.

A simple structural aggregate pigment similar to that pr pared in Example I, but containing additionally 2 parts of t ultrafine polymer-emulsion adhesive (polybutylacrylate with average particle size below 55 nm and glass-transition te perature of -50°C) per 100 parts of pigment, by weight, w evaluated in a paper filling experiment described in the follo ing example:

EXAMPLE III

Handsheets with dimensions of 30 cm x 30 cm ^~nd basis weig of 60 g/m² were prepared with the aid of laboratory mold usi furnish consisting of a 50:50 softwood/hardwood combinati The system was flocculated with alum at a rate of 20 lbs. ton of furnish, with a high-molecular-weight polyacrylam being used as the retention aid at a rate of 1 lb. per ton furnish. The acidity of the system was maintained at pH of with the aid of sulfuric acid.

A set of filled handsheets was prepared with the aid of simple structural aggregate pigment mentioned above, furt referred to as the "principal" system, an analogous cont system being prepared with the aid of a delaminated clay.

The brightness of unfilled handsheets was about 86% and not change appreciably with increasing filler levels both the principal as well as control systems. The opacity unfilled handsheets was 71%, increasing to 84.4% with the c trol system and 85.1% with the principal system at a fill loading level of 10%, by weight. Since optical properties filled sheets should be compared at equal sheet strength, much stronger principal sheets had to be brought up to a fill loading level of 16.5%, by weight, to reduce their strength the level of the control sheets containing only 10% of dela nated clay. At the increased filler content of 16.5%, opacity of principal sheets was 88.2%, i.e., 3.8 percenta points higher than that possible to obtain with control she of acceptable strength (i.e., containing 10%, by weight, delaminated-clay filler) . The additional advantage reali with the aid of the simple structural aggregate filler -mentio was replacement of 130 lbs. of expensive chemical fibers per Λ2, of paper product with incomparably less expensive and ecol cally preferable mineral matter.

The goal of maximizing the use of mineral fillers in p has been pursued by the paper industry for many years. The obstacles to the above goal have been progressive deteriora of sheet strength and decay of fillers' opacifying efficacy increasing filler loading level, as well as filler abrasiven There is obviously no realistic chance that the above obsta can be overcome in foreseeable future with the aid of mater and technologies of the present art. No such limitations connected with the use of structural aggregate pigments of present invention, however, which offer immediately a variet performance features and advantages going a long way tow attaining of substantial increases of filler-loading levels paper webs above the current industrial practice. As is known, one of the main culprits in fiber debonding are free ment fines present abundantly in all conventional mineral fi products. These fines are eliminated effectively in struct aggregate pigments made with the use of the complex functi microgels, especially with pressure filtration used as one the intrinsic elements of aggregate-pigment manufactu process.

All types of structural aggretjα e filler pigments of present invention have, without exception, lower fiber-debon tendency than conventional filler pigments because of effec elimination of mineral fines. The above performance advan can be enhanced still further with the use of the novel ult fine polyacrylic emulsion adhesives, which are capable of exe ing a distinct filler/fiber cementing action when incorpora into the structure of aggregate filler pigments. This cement action is manifested first, however, when the adhesive cont reaches at least 2% of the total mass of aggregate pigments m of very fine particle size kaolin clays. The above indica that an intrinsic "sink capacity" of the aggregate pigments w respect to the adhesive must be exceeded for some adhesive "s plus" to become available for external use, such as formation microscopically sized adhesive joints between aggregate pigm particles and cellulosic fibers in the surrounding paper w With structural aggregate pigments consisting primarily of f particle size calcined clay and/or synthetic ultrafine preci tated minerals characterized by high oil absorptivity, the trinsic demand (sink capacity) for the above ultrafine polym emulsion adhesives is usually higher than 2%, by weight. As- understood readily, the latter sink-capacity inherent to hi specific-surface-area minerals, such as raontmorillonite or b tonite, is considerably higher than that of any other miner and may require adhesive levels of up to 5%, by weight, of total mass of structural aggregate pigments. It should be no that the filler/fiber cementing action of the ultrafine polym emulsion adhesives seems to be very unique and could not be plicated thus far with the use of conventional latex adhesive

The low fiber-debonding characteristics of structural agg gate pigments used in Example III can be used to full advant so in "high-ash" filling applications, referring to filler-loadin levels in excess of 30%, by weight, due to these pigments' ex tremely low abrasiveness. Multiple assays carried out with th aid of Einlehner's tester have shown that the abrasiveness men tioned ranges from 0 (zero) mg to 0.5 mg, qualifying thes pigments as perhaps the softest mineral fillers ever used in th paper industry. The importance of low abrasiveness can perhap be illustrated best by the fact that fine particle size calcine clay, without question the most attractive single filler pigmen of the present art from the standpoint of opacifying efficac and overall economy, is rarely used at loading levels exceedin 4% of the total mass of paper, by weight, primarily because o the prohibitive abrasiveness.

The manufacture of high-ash papers is hampered by many othe problems in addition to fiber debonding and filler abrasiveness For example, it is necessary as a rule to preflocculate the fil ler system before adding it to the paper furnish, in order t obtain satisfactory first-pass retention when using high filler loading levels in the sheet. Unfortunately, the detrimenta side effects of the above-mentioned filler preflocculation ar invariably overall excessive flocculation of the furnish, whic causes the deterioration of sheet formation quality, as well a essentially total decay of the opacifying efficacy of the fille manifested by lack of sheet opacity increase when the filler loading level in the sheet is increased above certain critica level.

The structural aggregate pigments of the present inventio have significantly higher first-pass retention potential on paper machine, thus eliminating the need for preflσcculatio high-ash paper filling applications. Moreover, ultrahigh le of first-pass retention, well in excess of 90%, can be atta with the aid of 0.1% to 5%, by weight, of synthetic an cellulosic microfibrils incorporated into structural aggre filler pigments. Cellulosic microfibrils suitable for the a purpose can be obtained with the aid of new technology devel by the Applicant and disclosed in co-pending patent applica (Serial No.: 07/165,759 ; Filed: March 9, 1988). The la technology involves cascade processing of cellulosic fib preferably cotton and well-fibrillating cellulosic pulps, sequential processing steps consisting of:

(a) dry or wet chopping of fibers to a length preven hydraulic spinning in subsequent wet processing;

(b) very high consistency (30% to 40% solids, by wei refining, preferably in the presence of sodium silicate, Co red, and/or other inorganic and organic adjuvants enhancing rillization;

(c) precision finishing refining with the aid of colloi mills; and

(d) processing of the system resulting frcm step (c) w the aid of Gmolin homogenizer or equivalent equipment employ very-high-compression/rapid-decompression (adiabatic expansi cycles to separate residual bundles of fibrils without furt appreciable reduction of fibril length.

Fibrils up to 10 um long, or so, can be built into structural aggregate filler pigments to provide extra-high fir pass retention on the paper machine, in addition to considerab web reinforcement badly needed in high-ash paper filling appl cations. It is apparent that synthetic fibrils used instead cellulosic ones will provide extra-high first pass filler rete tion without contributing appreciably to web reinforcement.

Opacifying characteristic of structural aggregate pigmen of the present invention differs fundamentally from that of t pigments of the present art. The opacifying efficacies of t latter pigments, including such powerful opacifiers as titani dioxide and calcined clay, deteriorate rapidly with increasi filler loading, at any level of filler addition. The reason f above performance deterioration is progressively denser crowdi of filler particles leading to avalanche-like flocculation, pa ticularly in the presence of abundant mineral fines with dime sions below 0.2 to 0.25 e.s.d. By contrast, the opacifyi efficacy of structural aggregate filler pigments, essential devoid of free fines and thus not prone to excessive floccul tion even in crowded high-ash paper furnishes, deteriorates mu more slowly with increasing filler loading levels.

The most pronounced decay of opacifying efficacy wi increasing filler-loading level has been observed with inheren ly very fine titanium dioxide pigments. Thus, the opacity handsheets prepared under conditions similar to those describ in Example III increased by 4.8 percentage-points above th of unfilled control sheets when the relative content of titani dioxide in the sheet was increased from 0% to 1%, by weight, b 63 only by 0.6 percentage-points when above relative content w increased from 9% to 10%, by weight. In graphical terms th means that a curve representing opacity of Ti0₂-filled shee as a function of loading level ascends initially very steepl but then flattens rapidly, as the filler-loading level of t sheet increases. The latter is understandably the chief reas why this expensive pigment is rarely used at loading levels excess of 2 or 3 %. By comparison, analogous curves represen ing the opacity of handsheets filled with structural aggrega filler pigments of the present invention as a function of fill loading level ascend initially at significantly lower rates th those obtained with titanium dioxide, but retain steeper slop at higher filler-loading levels, particularly those exceedi considerably 10 or 15%. This slow decline of opacifying pow with increasing filler-loading level combined with low fib debonding, very low abrasiveness and high first-pass retentio make above structural aggregate pigments ideally suited f high-ash filling applications directed toward manufacture very opaque, high-quality, paper products such as could not manufactured heretofore with the aid of pigments and technol gies of the present art.

Outstanding results with respect to optical performance ha been obtained with the use of structural composite pigments sy thesized from blends of fine particle size calcined clay a very fine particle size "hydrous" kaolin clays. This can illustrated well with a single example of a composite fill pigment, consisting of 25% fine particle size calcined clay a 75% very fine particle size kaolin clay, by weight, having nea ly the same opacifying power as the fine particle size calcin clay used by itself. "Synergistic" effects with respect to t opacifying power of very-fine-particle-size hydrous clay/fin particle-size calcined clay blends used for the manufacture above composite pigments have been observed with ratios of the two materials ranging from 95:5 to 5:95, by weight. Most i portantly, however, composite pigments made of blends oi hydro and calcined clays have considerably lower abrasiveness a fiber-debonding tendency than straight calcined clay, hence, m be employed at considerably higher filler-loading levels th the latter pigment by itself, especially with ultrafine polyme emulsion adhesives being built in into aggregate structure.

It should be pointed out in this context that aggregation fine particle size calcined clay as the sole mineral compone of structural aggregate pigments is counterindicated. The reas for this is that the above fine particle size calcined clay derived from very fine particle size kaolin clay fe ds, ha been exposed already to thermal aggregation during the calcini process, in which the "very fine" particles of the feed beco sintered-on to larger platelets, or sintered to each other in "fine" aggregates. This is comprehended readily by consideri that a typical very fine particle size calcining feed has average particle size ranging from 0.2 p^~& to 0.4 "im e.s.d. a virtually no particles larger than 2 j e.s.d., whereas typic fine particle size calcined clay product has, after the therm aggregation, an average particles size ranging from 0.6 um ss

0.8 μm e.s.d. and contains from 2% to 12%, by weight, of par cles larger than 2 um e.s.d., and less than 10%, by weight, particles smaller than 0.2 um e.s.d.

Incomparably more favorable circumstances emerge when inh ently very fine particle size titanium dioxide pigments bec interspaced ("extended") by, and co-aggregated with, relativ much coarser fine particle size calcined clays mentioned abo Hence, composite pigments of the present invention whose miner fraction consists of 2% to 50%, by weight, of titanium dioxi pigments with the balance provided by the above-mentioned fi particle size calcined clays, were found to have excellent opt cal performance in paper filling and coating applicatio demonstrating enormous advantages of the instantaneous, indi criminate and complete flocculation (aggregation of fines) well as subsequent irreversible cementation, obtained with t aid of in-situ formed complex functional microgels used in pra ticing the present invention.

Particularly outstanding results with respect to optic performance and economy were obtained with composite pigmen consisting of 40% titanium dioxide and 60% fine particle si calcined clay, by weight. The application of this composi pigment, referred to in the following Example IV as "composi pigment (40/60)", as a full-fledged titanium-dioxide substitu in coating formulations for lightweight publication paper is i illustrated below:

EXAMPLE IV

Two coating formulations were prepared at 60% solids havi 5^"ώ

compositions shown in Table 1.

Table 1

Formulation Ingredients, Control Composite Pig¬ Parts by Weight Formulation ment Formulation

Delaminated Clay 44 44 No. 2 Coating Clay 44 44 Titanium Dioxide (loose) 12 Composite Pigment 40/60 12 Starch 9

The above formulations were applied to a lightweight publication base sheet with a basis weight of 32 lb per 3300 sq.ft. using a laboratory coating machine. The coated sheets were passed four times through a laboratory supercalender at 300 pli and 140° F. The resultant data are listed in Table 2.

s1

Printing properties of sheets obtained with both above for mulations, such as smoothness, print gloss, optical density an ink show-through, were identical for all practical purpose duplicating the parity of optical properties tabulated above.

Example IV shows clearly that titanium dioxide pigment ca be substituted on "one-for-one" basis with composite pigments o the present invention containing only a fraction of the expen sive high-refractive index material. Similar one-for-one sub stitution of titanium dioxide with the same composite pigmen has been obtained in paper filling applications in a variety o paper products.

Still better optical performance has been obtained wit identically formulated composite pigment (40:60 Ti02:calcine clay) in which the commercial titanium dioxide component wa first subjected to intensive comminution, e.g., with the aid o attrition grinder and zirconia balls with a diameter of approx 1 mm. As the result of above comminution the diameter of larges particles was reduced to p out 0.7 "im, bringing the dimension of the entire pigment population closer to those needed fo optimum light scattering. By contrast, titanium dioxide pigment of the present art contain from 1.5% to 2%, by weight, of par ticles larger than 1 in diameter.

It should be emphasized that, the fundamental differences i the method of synthesis itself notwithstanding, there are prin 5B cipal differences in the composition of matter between titani dioxide/calcined clay composite pigments disclosed by wildt U.S. 3,726,700 and analogous pigments of the present inventio Composite pigments prepared according to Wildt were based Engelhard's Satintones No. 1 and No. 4, which are substantial coarser and 5 to 10 times more abrasive than fine particle si calcined clays used for synthesis of analogous composite pi ments according to the present invention. Unlike fine partic size calcined clays derived from very fine particle size, poor crystallized, "gray" clay crudes, Satintone products used Wildt, intended primarily for paint applications, are obtain by calcining of feeds derived from relatively coarse, high crystalline, "white" clay crudes.

As it is understood readily, other high brightness extend products of appropriate particle size, e.g. synthetic precip tated minerals, can be used in addition to, or instead of, fi particle size calcined clay for synthesizing titanium dioxid containing structural composite pigments of the above-describ type. It is further advantageous to incorporate at least 2%, weight, of precipitated calcium carbonate into all composi filler pigments intended for alkaline papermaking applications

Esthetically very pleasing, cream-colored, ultraopaque pap has been obtained with the aid of composite filler pigments co sisting of fine particle size calcined clay and naturally ocu ring rutile or anatase minerals comminuted intensively to average particle size smaller than 1 Very best results we obtained, however, with composite pigments containing natural Si occurring rutile or anatase comminuted to a particle size 10 finer than 0.7 μ , or even 0.6 um, whose opacifying power w found to be 5 to 6 times higher than that of commercial whi titanium dioxide pigments. Because of their extraordinary colo ing power, intensively comminuted naturally occurring rutile a anatase incorporated into structural aggregate pigments beco practically useful at concentrations considerably lower than i by weight. For applications which require both very high leve of opacification and intensive coloring, the relative content^" intensively comminuted rutile and anatase in structural compo ite pigments may be increased to 50%, by weight.

The highest levels of opacifying efficacy have been obtain thus far by incorporation of specially prepared dispersions carbon black, along with suitable combinations of blue and r (violet) dyes, into the aggregate pigment structure. With ma important paper products, such as newsprint, lightweight publ cation paper, or the groundwood-containing portion of No. merchant papers, the brightness requirements range merely f 58% to 75%, whereas the brightness of most commercial fille ranges from 85% to 99%. The superfluous sheet brightness sulting from application of fillers which are much brighter th the cellulosic fibers is now routinely toned down with the of black dyes, such as nigrosine. The use of latter dyes p vides some limited improvement of sheet opacity but often lea to objectionable hue of the end product and other technical pr blems, e.g., poor ink holdout resulting in excessive ink strik through during printing. By contrast, structural aggregate pi ments containing built-in carbon black and properly balan blue and red dye combinations provide considerably higher opa fying effects at equivalent l_^.εls of sheet brightness and, the same time, make possible to control precisely the hue, well as improve ink holdout, of the end product.

Elementary particle dimensions of the finest commercia available carbon black products are on the order of 9 nm, even the best carbon black dispersions of the present art c tain these elementary particles in the form of "undispersabl multi-particle aggregates. According to paper industry's com experience, aqueous dispersions of such fine carbon bla used for opacifying purposes in combination with white pigme are from 100 to 150 times more opacifying than titanium dioxi pigments. By contrast, specially prepared dispersions of carb black incorporated into structural aggregate pigments of t present invention are from 2000 to 5000 times more opacifyi than titanium dioxide pigments. To attain above levels of opac fying efficacy, commercially available aqueous dispersions carbon black must be de-agglomerated into elementary particl with the use of a special method developed by the Applicant, r ferred to in the following Claims as the "masterbatch." Accor ing to this masterbatch method, an auxiliary aqueous dispersi of mineral pigment, such as hydrous or calcined clay, or prec pitated silicate, is first prepared at highest possible soli attainable with the aid of "heavy-duty" industrial mixing kneading equipment. For ex& pie, aqueous slurries of kaolin ci ?-hould be prepared at solids levels ranging from 78% to 82%, weight, which generates excessive heat and requires jacket cool ing of mixing vessels. Conventional aqueous dispersions of car bon black, such as are possible to prepare by procedures of th present art, are then incorporated under maximum shearing int the auxiliary concentrated pigment slurries mentioned to brea down aggregates of elementary carbon black particles and for completely uniform pastes. Since these auxiliary slurries ma become fluid upon introduction of the conventional carbon blac dispersions, some additional dry pigment must be added to th system to restore its consistency to the previous level. The re¬ sultant, de-agglomerated, carbon black masterbatch is used in the preparation of structural aggregate pigments in essentially the same manner as other predispersed pigmentary raw materials. The opacifying power of structural aggregate pigments con¬ taining carbon black de-agglomerated by the above-described mas¬ terbatch method is demonstrated in the following example:

EXAMPLE V

A set of control handsheets, designated as Sheets A-l and A-2, filled with titanium dioxide pigment was prepared using a conventional acidic papermaking process.

A parallel set of handsheets, designated as Sheets B-1 and B-2, was filled with a composite pigment, synthesized by the procedure described in Example I, consisting of 40 parts titan¬ ium dioxide, 60 parts calcined clay, 0.12 parts carbon black (active basis) , and 2 parts ultrafine polybutylacrylate emulsion adhesive. The handsheets B-1 and B-2 were prepared with the aid of the alkaline papermaking process developed by the Applicant and disclosed in co-pending patent application (Serial No.: 0.7/165,759 ■ Filed: March 9, 1988 ).

Optical data obtained with both above sets of handsheets, intended for satutation with melamine-resin solutions, are pre¬ sented in Table 3.

Table 3 SHEET DESIGNATION

SHEET PROPERTIES MEASURED A-l A-2 B-1 B-2

Basis Weight, lb/3000 sq.ft. 54.3 57.0 54.2 54.8

Filler Content in the sheet, percent by weight 42.0 40.1 37.2 37.5

Net Lbs. of Filler per 3000 sq.ft. 22.8 22.9 20.1 20.6

GE Brightness, % 93.8 92.3 62.7 62.2

HUNTER L -:

L 97.4 96.8 79.6 79.0

*a -0.3 -0.4 -0.3 -0.1

*b 1.1 1.3 0.8 0.5

TAPPI Opacity, % Before Saturation 97.2 96.5 99.6 99.0

TAPPI Opacity, % After Saturation 90.9 89.5 98.5 98.6

Opacity Reduction upon Saturation, %-point 7.3 7.0 1.1 0.4

The differences between Sheets B-1 and B-2 and control sheets regarding opacity reduction brought about by saturation of the sheets with melamine-resin solutions are striking on the bas of numerical data alone. To appreciate fully the enormous between opacity of 99.6% or 99.0% for unsaturated Sheets B-1 a B-2 containing the composite filler, and opacity of 97.2% 96.5% for corresponding control sheets A-l and A-2, listed Table 3, an additional demonstration will be helpful. Hen another set of titanium-dioxide filled sheets, equivalent to control sheets designated as A-l and A-2 in Table 3, was p prepared to assess quantitatively the spectacularly high le of difficulty in obtaining even a minute incremental opacity i crease within the range of very high opacity values. Since ti nium dioxide is the principal opacifier in the above, hig loaded, sheets, its concentration has been expressed direc in terms of net content in lbs. per 3000 sq. in the followi Table 4.

Table 4

Fϋ?is weight. Net TiO, Content, TAPPI Opacit lbs/3000 ft² lbs/3000 ft² %

opacity increase: (+ 1.00 %-pt)

As shown by data in Table 4, doubling (folding) of Sheet with opacity of 98.38% provides an incremental opacity increas of a mere 1.06 percentage-point, analogous doubling of Sheet with opacity of 98.24% providing similarly an incremental opaci ty increase of a mere 1.0 percentage-point. With a triple stac of sheets obtained by doubling Sheet A and adding a single pl of Sheet B, with a combined basis weight of 182.9 lbs/3000 s ft., and a net Ti0₂ content of 94.8 lbs/3000 sq.ft, the incre mental opacity increase was still lower, namely, 0.12 percentag point above the opacity of doubled Sheet A (to a resultant leve of 99.56%), demonstrating clearly the enormous difficulties mentioned previously, associated with gaining incremental opac ity increase within the interval of high opacity values. Show clearly by data in Table 3, on the other hand, a single shee (A-l) with a basis weight of 54.2 lbs/3000 sq.ft., with a ne content of 20.1 lbs/3000 sq.ft. of composite filler pigment con sisting of only 40% titanium dioxide (amounting to 8 lbs. Ti0 per 3000 sq. ft) had an unusually high opacity of 99.6% combine with a brightness of 62.7%, such as would be considered respec table with even high quality newsprint.

The enormous opacifying power of the type of composite pigment described in Example V makes it particularly well suited fo newsprint filling applications. As is well known by those skil led in the art, the basis weight of newsprint is declinin steadily from a 36 lbs/3000 sq.ft. standard prior to 1973 to 3 lbs/3000 sq.ft., and even 28 lbs/3000 sq.ft., in recent years Extensive research work is going on worldwide to lower t basis weight still further, preferably to 26 lbs/3000 sq.ft.

The principal difficulty in reaching the latter goal is t newsprint opacity should range optimally from 92% to 95% adequate printing results, yet such high levels of opacity difficult to maintain systematically even with present newspr of heavier basis weight. A significant relaxation of newspr opacity specifications is unthinkable, however, in that t would necessitate a gigantic task of developing entirely printing technology. The general consensus is that futu ultralightweight, generation of newsprint will rely on the of the most opacifying filler systems available, at substanti ly higher loading levels than are employed presently. The b such filler system of the present art, both from the standpoi of opacifying power and economy, consists of 30 % titanium di xide and 70 % calcined clay, by weight. The above system highly abrasive and debonding, however, and almost 35 .-poi brighter than present-day newsprint whose brightness ranges f 59% to 62%. Using Ti0₂/calcined clay blend would thus necess tate extensive dying-back of the sheet with the aid of organ dyes which, as previously mentioned, drastically reduce ne print's ink holdout when deposited on cellulosic fibers, t detrimental esthetic side effects notwithstanding.

Realistically, however, the opacifying power of Ti0₂/calcin clay blend is simply too low to compensate effectively for t reduction of basis weight with ultralightweight newsprint, ev if used above practically acceptable filler-loading levels. should be boime in mind, though, that many newsprint mills not have water treatment facilities, hence, are not capable using fillers at loading levels above 2% of the fiber mass. T problem is compounded further by the fact that newsprint ink which are immobilized by absorption, require a certain minim of fiber/filler bulk, i.e., minimum adequate sink capacity f containment of ink, such as may be expressed in terms of surfa area and pore volume per unit of newsprint mass. In the absen of adequate sink capacity, a disastrous ink strike-through wi occur.

There appears to be nothing within the scope of materia and technologies of the present art capable of dealing with t above-mentioned problems. Experimental data obtained duri evaluation of structural aggregate pigments of the present i vention indicate clearly, however, that a satisfactory soluti to these problems can be obtained with the aid of appropriate formulated composite fillers, e.g., such whose mineral porti consists of 40% titanium dioxide and up to 25% high-specifi surface-area bentonite (montmorillonite) with fine particle si calcined clay making up the mineral balance, further containi appropriate dose of built-in cellulosic microfibrils along wi up to 0.12 parts of specially de-agglomerated carbon black, a up to 5 parts of ultrafine polymer-emulsion adhesives, per 1 parts of mineral components.

While certain preferred practices and embodiments of t present invention have been set forth in the foregoing specif cation, it is understood readily by those skilled in the a that other variations and modifications may be employed wi the scope of the claims to follow.

Claims

604(, 1What is claimed is:

1. Structural aggregate pigment products comprising:

(a) particulate matter; and

(b) a complex functional microgel, in an amount of 0. to 10%, by weight, as determined by ashing, wherein constitue of said microgel are:

(1) from 0.5 to 10 parts of a hydrosol formed of:

(i) at least one reagent selected from group consisting of alkali-metal silica and quaternary ammonium silicates; and (ii) at least one reagent selected from t group consisting of alkali-metal alum nates and alkali-metal zincates, the rat of the reagents of (i) to the reagents (ii) being from 1:10 to 10:1, by weight;

crosslinked by:

(2) at least one gel-setting agent selected from first group consisting of bivalent and multi-vale inorganic salts in an amount of from 0.5% to 10% the total mass of the structural aggregate pigme and a second group consisting of organic, cationi ally-active, chemical compounds with at least t reactive groups in each molecule, in an amount ( i from 0.1% to 5% of the total mass of the structur aggregate pigment, the ratio, by weight, of the ge setting agent to the hydrosol ranging from 1:10 10:1.

2. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes kaolin cl derived by centrifugal fractionation of kaolin clay crudes.

3. Structural aggregate pigment products according Claim 2, wherein the kaolin clay is beneficiated.

4. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes from 95 to parts of kaolin clay and from 5 to 95 parts of fine partic size calcined clay.

5. Structural aggregate pigments products according Claim 4, wherein the fine particle size calcined-clay pigmen are derived from very fine particle size kaolin clay feeds.

6. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes fine partic size calcined-clay pigments with up to 50%, by weight, of tit nium dioxide pigments.

7. Structural aggregate pigment products according Claim 6, wherein the fine particle size calcined-clay pigmen are derived from very fine particle size kaolin clay feeds.

8. Structural ._agregate pigment products according Claim 6, wherein the titanium dioxide pigment is employed in amount of up to 50%, by weight, and is comminuted to reduce t largest particle diameter below 0.9 and increase substantia no ly the relative proportion of particles with diameters ranging from 0.2 μ . to 0.4 um.

9. Structural aggregate pigment products according to Claim 6, wherein the titanium dioxide is employed in an amount of up to 50%, by weight, and is selected from the group consist¬ ing of naturally occurring rutile and anatase minerals commi¬ nuted to an average particle diameter smaller than 1.0 um.

10. Structural aggregate pigment products according to Claim 1, wherein the particulate matter includes at least one synthetic, separately precipitated, mineral selected from the group consisting of calcium carbonate, calcium silicate, calcium sulfate, hydrated alumina, hydrated silica and metal silicates, having particle dimensions ranging from 0.01 um to 10 um e.s.d., together with up to 50%, by weight, of titanium dioxide pigments.

11. Structural aggregate pigment products according to Claim 10, wherein the titanium dioxide employed is comminuted to reduce the largest particle diameter below 0.9 um and increase substantially the relative proportion of particles with diameters ranging from 0.2 μ to 0.4 u .

12. Structural aggregate pigment products according to Claim 10, wherein the titanium dioxide is employed in an amount of up to 50%, by weight, and is selected from the group consist¬ ing of naturally occurring rutile and anatase minerals commi¬ nuted to an average particle diameter smaller then 1.0 um.

13. Structural aggregate pigment products according to Claim 1, wherein the particulate matter includes up to 50%, m by weight, of titanium dioxide pigments which are comminuted reduce the largest particle diameter below 0.9 μ and incre substantially the relative proportion of particles with dia ters ranging from 0.2 μm to 0.4 μm.

14. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes up to 50%, by weight, of naturally occurring rutile and anatase miner comminuted to an average particle size essentially finer t 1.0 jim.

15. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes at least mineral pigment selected from the group consisting of natura occurring talcum, calcium carbonate and gypsum, having parti dimensions ranging from 0.1 jam to 5 um e.s.d.

16. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes at least synthetic, separately precipitated, mineral selected from group consisting of calcium carbonate, calcium silicate, calc sulfate, hydrated alumina, hydrated silica and metal silicat having particle dimensions ranging from 0.01 um to 10 um e.s.

17. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes from 0.5% 25%, by weight, of particulate minerals finer than 5 um e.s selected from the group consisting of montmorillonite bentonite, said minerals having specific surface area in exc of 50 m²/g.

18. Structural aggregate pigment products according 5604

11

Claim 1, wherein the particulate matter includes from 1% 20%, by weight, of non-film-forming emulsion polymers ha particle diameters ranging from 0.03 um to 1.0 um.

19. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes from 0.25 5%, by weight, of latex adhesives having average particle di ters ranging from 0.07 um to 0.3 um.

20. Structural aggregate pigment products according Claim 1, wherein the particulate matter includes from 0.25% 5%, by weight, of ultrafine polyacrylic-emulsion adhesi having average particle diameters smaller than 55 nm and gl transition temperatures ranging from +20°C to -60°c

21. Structural aggregate pigment products according Claim 1, said products including from 0.1% to 5%, by weight, organic anionic compounds with at least two reactive groups each molecule.

22. Structural aggregate pigment products according Claim 1, said products including from 0.1% to 5%, by weight, organic cationic compounds with at least two reactive groups each molecule.

23. Structural aggregate pigment products according Claim 1, said products including from 0.001% to 5%, by weig of organic color dyes.

24. Structural aggregate pigment products according Claim 1, said products including from 0.001% to 0.25%, weight, of carbon black.

25. Structural aggregate pigment products according 13

Claim 1, said products including at least one material selected from the group consisting of carbon black and color dyes together with a polymer-emulsion adhesive.

26. Structural aggregate pigment products according to Claim 25, wherein the adhesive is an ultrafine polyacrylic-emul- -Hnr. adhesive.

27. Structural aggregate pigment products according to Claims 24, 25 or 26, wherein the carbon black employed is de- agglomerated by the masterbatch method.

28. Structural aggregate pigment products according to Claim 1, said products including from 0.1% to 5%, by weight, of ink-curing promoters.

29. Structural aggregate pigment products according to Claim 1, wherein the particulate matter includes from 0.1% to 5%, by weight, of microfibrils with a length of up to 10 selected from the group consisting of synthetic microfibrils and cellulosic microfibrils derived through fibrillation of natural¬ ly occurring fibers.

30. Structural aggregate pigment products according to Claim 1, wherein the reagent selected from the group consisting of alkali-metal silicates and quaternary ammonium silicates is sodium silicate.

31. Structural aggregate pigment products according to Claim 1, wherein the reagent selected from the group consisting of alkali-metal aluminates and alkali-metal zincates is sodium aluminate.

32. Structural aggregate pigment products according to Claim 1, wherein the bivalent or multivalent inorganic salts ar selected from the group consisting of calcium chloride and cal ciui titrate.