WO1991011256A1

WO1991011256A1 - Functional complex microgels with rapid formation kinetics

Info

Publication number: WO1991011256A1
Application number: PCT/US1990/001649
Authority: WO
Inventors: Adam F. Kaliski
Original assignee: Industrial Progress, Inc.
Priority date: 1990-01-31
Filing date: 1990-03-28
Publication date: 1991-08-08
Also published as: ZA905091B; AU5546190A; MX173809B; EP0512986A1; IN171538B; CA2075194A1; EP0512986A4; IL94920A0; AU655753B2; CN1031988C; CN1053780A; IL94920A

Abstract

Process for synthesizing complex functional microgels with a rapid formation kinetics in aqueous media and the resulting compositions.

Description

FUNCTIONAL COMPLEX MICROGELS WITH RAPID FORMATION KINETICS

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a process for the synthesis of complex functional microgels with a rapid formation kinetics in aqueous media and the resulting composi¬ tions.

More particularly, the present invention relates to in- situ synthesis of such microgels with flocculating, cementing and surface-chemistry modifying functions in aqueous disper- sions of quantitatively predominant particulate matter to be used essentially non-reactive therewith, to affect the properties of this particulate matter in an advantageous manner.

The complex functional microgels of the present invention are synthesized from subcolloidal reactive silico-aluminate and similar hydrosols and bivalent and multivalent inorganic salts and/or organic, cationically-active, chemical compounds with at least two reactive groups in each molecule. Discussion of the Relevant Art

The scope of prior art relating to the synthesis and practical applications, both of continuous, and discrete gels obtained by interaction of alkali-metal silicates with sodium aluminate, soluble metal salts and/or free acids in different proportions and combinations is simply enormous, involving many thousands of patented gel products.

Most of these products differ from each other only in minor details, such as pH conditions, reaσtant concentrations, sequence of reagent additions, thermal regimes or particular variations in the otherwise very similar preparation proce¬ dures. Yet, these seemingly minor differences may bring about improved, or even novel, material or performance properties of the resultant end products, whose applications encompass such different fields as catalysis, pharmaceuticals, adhesives, water treatment, dehumidification of gases, soil conditioning or ion exchange.

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

In the following, certain general fields of manufacture and utilization of various types of gels shall be discussed in some detail using examples found in the literature. While continuous single and mixed gels (mechanical blends of two or more separate gels) are inherently foreign to the principal idea of the present invention, they will be included in the general discussion for the sake of better clarity. In-situ formation of silica and silico-aluminate gels in aqueous media for the purpose of surface coating of mineral particles has been used commercially ' for many years. For example, virtually all titanium dioxide pigments on the market today are coated with a more or less dense layer of silica or silico-aluminate gels deposited in situ by a controlled inter¬ action 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 coatings mentioned represent continuous gels which are fundamentally different from the instantaneously in-situ formed microparticulate gels (microgels) of the present invention. 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 cementation of individual particles into very abrasive, oversized aggregates can not be avoided. This particle aggregation is by far the most undesirable side effect of surface coating with continuous gels having as a rule very 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 additionally employed.

U.S. Patent No. 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 were also 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 tetra- chloride in WO 87/00544 to Jones.

Hoffmann, in U.S. Patent .3,476,692 describes the prepara¬ tion of a silicomagnesium-aluminate-hydrate gel .("antacid") for use in treatment of gastric hyperacidity. In particular, the above invention pertains to a silicomagnesium-aluminate-hydrate gel, certain properties of which are improved compared to those of other patented antacid products of virtually identical compositions. It should be emphasized rather strongly, however, that the terminology routinely used in colloidal- technological descriptions leaves much to be desired. For example, Hoffmann's so-called "silicomagnesium-aluminate- hydrate" gel is factually a mechanical blend of a separately prepared silico-aluminate gel and a subsequently prepared magnesium-hydroxide gel, hence, fundamentally different from true complex (multicomponent) gels synthesized according to the present invention. Specifically, Hoffmann's antacid gel was prepared by mixing concentrated solutions of sodium silicate and an aluminum salt under alkaline conditions for extended periods of time, e.g., 30 min., to form a solidified silico- aluminate cogel. In the subsequent step, this cogel was crushed and homogenized into a flowable pulp into which a concentrated solution of magnesium sulfate was introduced gradually over a period of time lasting 3 hours. As a conse- quence, the in-situ precipitated magnesium hydroxide hydrate became mechanically, though intimately, dispersed within the previously fluidized pulp of the continuous silico-aluminate cogel.

Inorganic anion-exchangers and a process for their synthesis are disclosed by Duwell in U.S. Patent No. 3,002,932. The above anion exchangers were prepared by .... "coprecipi at- ing mixed hydrated oxides of a pair of homolomorphic metals chosen from the group consisting -of aluminum, silicon, titanium, zinc, and zirconium, the lower-valent member of said pair being present in major amount, in an aqueous medium at a pH in the range of about pH 5 to 7, drying the aqueous mixture at a temperature below 150^βC, and washing the dried mixture with water to remove soluble impurities therefrom." The above technology, as quoted, is based again on physical mixtures of separately prepared gels.

U.S. Patent No. 4,239,615 to Tu is typical of a vast group of patents pertaining to the manufacture and use of zeolites in catalytic cracking of hydrocarbon charges (crude oils). All such zeolite catalysts are based in principle on various modifier^* ions and extensions of continuous silico-aluminate cogels described extensively in textbook literature. It is because of the "memory" effects associated with colloidal systems, mentioned previously, that such endless varieties of related gel products with material or functional-performance differences of practically significant magnitudes can be synthesized with the aid of only two principal ingredients, namely, sodium silicate and sodium aluminate (or aluminum sulfate). As documented amply in everyday industrial ex¬ perience, relatively small differences in the preparation, handling or post-treatment of such gels, the incorporation of various transient or permanent adjuvants notwithstanding, will often result in significant modification of such important product features as abrasion resistance, catalytic activity and selectivity, inhibition resistance or pore-size distribution. In addition to using silica-alumina cogels as cracking- catalyst precursors, Tu also employed a certain specific brand of anionic polyacrylamide (transient adjuvant) to modify the mechanical structure of the catalyst matrix. Accordingly, after a subsequent burnout of the organic substance occluded in the latter matrix, Tu was able to obtain a more favorable pore- size distribution. As far as purely chemical functions of the anionic polyacrylamide with regard to formation of the catalyst matrix are concerned, Tu cautiously- offers the following hypothesis proposed also in " other similar patents: "it is believed that the anionic form chemically react with the silica-alumina gel framework, rather than being physically dispersed in the gel, and thus contributes to the desired pore structure formation." A well known, fact is, however, that concentrated solutions of strongly alkaline reagents, used without exceptions in the synthesis of silica-alumina gels for catalyst precursors, coagulate immediately virtually all organic water-soluble polymers available commercially, indicated clearly by phase separation. Hence, the overwhelming likelihood is that the polyacrylamide adjuvant mentioned above was de facto dispersed mechanically in the gel, much in the same way though perhaps not as intimately as the in-situ formed, molecularly precipitated, magnesium hydroxide hydrate in Hoffmann's silico-aluminate antacid-gel matrix described in U.S. Patent No. 3,476,692. As far as zeolites' reactivity on a molecular scale is concerned, it should be pointed out that small amounts of metallic cations, such as magnesium or calcium ions, can be accepted indeed into the zeolite matrix, albeit by the reversible mechanism of ion-exchange rather than irrever¬ sible chemical reaction. Kaliski in U.S. Patent No. 3,484,271 describes the formation of functional (release) coatings on moving paper webs by an insitu interaction between consecutively applied separate solutions of organic anionic and cationic compounds with at least two functional groups in each molecule. These release coatings are made in the form of continuous, totally imper¬ vious, gel films devoid of any particulate occlusions. As a matter of fact, a particulate matter embedded in such films would more or less completely destroy these films' useful release properties. U.S. Patent No. 2,974,108 to Alexander discloses a method of synthesis of stable alumino-silicate aquasols (hydrosols), with ion-exchange capacities equivalent to those of better zeolites and also very good antisoiling properties. These aquasols are synthesized with the aid of intricate thermal regimes and time-consuming procedures, using silicic acid (rather than alkali-metal, or quaternary ammonium, silicate used in practicing the present invention) and sodium aluminate as the principal reagents. The preferred end product, according to Alexander, contains 5% to 20% of substantially spheroidal porous particles, with particle diameters ranging optimally from 10 milimicrons to 50 milimicrons (nanometer) and particle porosity between 10% and 70%, suspended in an aqueous medium with pH between 5 and 10. The fundamental difference between Alexander's aquasols^{" *} (hydrosols), which are end products by design and, as such, chemically non-reactive, and the hydrosols of the present invention, is that the latter are transient intermediate products of high chemical reactivity, made for the sole purpose of synthesizing complex functional microgels, and serve no practical purpose by themselves. Additional comparisons with the prior art will be made hereinafter, wherever applicable. It should be noted, however, that in reviewing the existing art Applicant is not aware of any references pertaining to systems that are true complex gels, with all principal molecular constituents being chemical- ly bound within the same complex macromolecules, as differen¬ tiated from purely physical mixtures of two or more separate gels. In particular, no references were found in the litera¬ ture with regard to complex, multicomponent, micro-particulate gels (microgels) with a rapid formation kinetics, or conditions under which these microgels can be synthesized and/or utilized. More specifically, no references whatsoever have been found in the literature with regard to the use of complex microgels toward the manufacture of improved products, or any other application for that matter.

SUMMARY OF THE INVENTION

The complex functional microgels of the present invention, characterized by a rapid formation kinetics, are synthesized by a process comprising the steps of: (a) blending separate aqueous solutions of hydrosol- forming reagents, one of which contains an alkali-metal, or quaternary ammonium, silicate and the other one . of which contains an alkali -metal aluminate and/or alkali-metal zincate, to form a subcolloidal reactive hydrosol;

(b) blending an aqueous solution containing at least one bivalent or multivalent inorganic salt and/or organic, cationi- cally-active, chemical compounds with at least two reactive groups in each molecule with the system obtained from step (a) to crosslink said hydrosol and form in situ a complex function¬ al microgel.

The ratio of alkali-metal, or quaternary ammonium, silicates to the combined mass of alkali-metal aluminates and/or zincates may range from 1:10 to 10:1, by weight, while the concentrations of said silicates and aluminates (zincates) in the reaction medium should range from 0.1% to 2.0%, by weight.

The dosage of crosslinking agents in relation to the com¬ bined hydrosol mass may range from less than 0.5:1 to more than 1:1, by weight, for bivalent and multivalent inorganic salts and from 0.1:1 to 1:1, by weight, for organic, cationically- active, chemical compounds with at least two reactive groups in each molecule.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the preferred form of practicing the present invention, complex functional microgels are synthesized in situ in aqueous media to manufacture products which are improved compared with the present ones or which can not be manufactured with the aid of technologies and/or materials of the present art.

The principal reagents of commercial significance for the synthesis of complex functional microgels of the present inven¬ tion are: (1) alkali-metal silicates and quaternary ammonium silicates, preferably sodium silicate; (2) alkali-metal alumi- nates, alkali-metal zincates, and blends thereof in any propor¬ tions, preferably sodium aluminate; and (3) water-soluble, bi¬ valent and multivalent inorganic salts, preferably calcium chloride and calcium nitrate, but equally well other similar salts of calcium, magnesium, barium, aluminum, zinc and zircon¬ ium, as well as cationically-active organic compounds with at least two reactive groups in each molecule, capable of perform¬ ing the same gel-setting functions as bivalent or multivalent inorganic salts. Of course, both anionic and cationic organic additives used in the process must be compatible with their respective anionic and cationic process streams, as indicated by absence of phase separation, clouding, or premature gelling.

Hereinafter shall be demonstrated how the complex functional microgels of the present invention, synthesized in situ, can be employed toward the manufacture of a multitude of valuable novel and improved products. The following example deals with the inherent properties, as well as colloidal- chemical behavior, of these microgels synthesized in plain water, while the subsequent examples deal with more complex reaction media.

EXAMPLE I

A calcium-silico-aluminate microgel was synthesized in water in two chemically and colloidally distinctly different stages. A transient, subcolloidal, reactive sodium-silico- aluminate hydrosol was formed in the first stage and cross- linked in the second stage with a solution of calcium chloride. The synthesis was carried out by injecting simultaneously 40 g of a 5% aqueous solution of sodium silicate (Brand "N"- clear grade, by Philadelphia Quartz Co.) and 40 g of a 5% aqueous solution of sodium aluminate into a beaker containing 250 g of rapidly stirred distilled water, using plastic syringes positioned at diametrically opposite sides of the beaker (the latter precaution was intended to avoid a direct contact of jets of concentrated reagent solutions). Immediately afterwards, 80 g of a 5% aqueous solution of calcium chloride was injected into the beaker while maintaining the stirring at full intensity, causing an "instantaneous" formation of . the microgel. . The freshly formed microgel was extremely fine, but a progressive particle (grain) growth became clearly visible within a few seconds. When agitation of the medium was ceased, the entire disperse phase settled to the bottom of the beaker after a couple of minutes in the form of a relatively thin, very fluffy layer under a pool of crystal-clear supernatant. It was very easy to restore the original state of dispersion by agitation; however, the cycle of progressive particle growth and settling set-in again when agitation was discontinued. The above cycle could be repeated countless numbers of times without any noticeable indication of permanent particle enlargement, or other signs of irreversible aging.

The unusual colloidal behavior of complex microgels, demonstrated in Example I, is deemed essential to their unique ability to flocculate any particulate matter dispersed in an aqueous medium instantaneously, indiscriminately and complete¬ ly, regardless of the particulate matter's physical, chemical or colloidal make-up. This behavior is also essential to the ability of complex microgels to intimately cement the floccu¬ lated (aggregated) particulate matter upon subsequent dewater- ing and drying.

The visual effects associated with the synthesis of complex microgels in water are most impressive due to lightn¬ ing-fast process kinetics. It is estimated that the chemical reaction of crosslinking of sodium-silico-aluminate, or similar, hydrosols by bivalent and multivalent cations, leading to the formation of complex macromolecules (such as calcium- silico-aluminates in Example I), occurs in less than one microsecond. The primary colloidal consequences of the latter reaction, i.e., formation of particulate microgels, are estimated to occur in less than one millisecond. Some instructive microexperi ents carried out with the aid of an ultramicroscope have demonstrated that complex microgels of the present invention can be prepared in less than one-fifth of one second, from three separate drops of dilute reagent solutions aligned in a proper order on a microscopical glass slide. By a single, continuous, rapid sweep of a hand-held rubber-tipped glass rod, the first drop containing a solution of sodium silicate was combined with the second drop containing a solution of sodium aluminate, to synthesize a sodium-silico- aluminate hydrosol. Within the same continuing glass-rod sweep, the freshly created micro-reservoir of the reactive hydrosol was combined with the third drop containing a solution of calcium chloride, to precipitate the calcium-silico- aluminate microgel in an instantaneous manner. According to all indications, considerably shorter time intervals than one- fiftieth of one second, mentioned above, would be sufficient to carry out the described reaction, if not for the experimental difficulties involved.

The quantitative proportions of water and microgel-forming reagents in Example I were selected so as to simulate a reaction medium for synthesizing new types of aggregate pigment products invented by the Applicant and disclosed in the name of Adam F. Kaliski in co-pending U.S. Patent Applications Nos. 07/420,388 and 07/420,472; filed October 12, 1989. The aggregate pigments mentioned have vastly improved optical and other performance properties, compared with those of the pigmentary raw materials from which they were derived. Specifically, the amount of water and proportions of microgel- forming reagents used in Example I were the same as would be used typically per 100 g of pigmentary raw material in actual plant manufacturing operations.

The sodium-silico-aluminate hydrosol in Example I, as well as similar hydrosols of sodium-silico-zincate and sodium- silico-alu inate-zincate types, are formed instantly by simply blending separate solutions of sodium silicate and sodium aluminate (and/ or sodium zincate) in water. From a colloid- chemical standpoint, these hydrosols represent transient, low- molecular-weight, highly reactive inorganic, polymers of anionic polyelectrolyte ^" ype_* Prepared and utilized according to the present invention, they remain completely clear to the eye for several hours devoid of a visually perceptible Tyndall effect. The advent of a readily perceptible Tyndall effect, resembling faint "clouding," signals an advanced stage of polymerization (excessive growth of molecular weight) which renders the polymer (hydrosol) chemically non-reactive, hence, unsuitable for the synthesis of complex microgels of the present inven¬ tion.

The loss of hydrosol reactivity occurs gradually and can be avoided by reducing the time interval between hydrosol formation and its crosslinking by cationic gel-setting agents. The duration of this time interval in laboratory experiments is maintained usually between one and twenty seconds. In large scale batch manufacturing operations the duration of the time interval in question may extend to several minutes, but is considerably shorter (ranging from approximately 20-30 seconds to a couple of minutes) with continuous manufacturing proces¬ ses. Since molecular weights of freshly formed hydrosols grow avalanche-like when high concentrations of hydrosol-forming reagents are involved, the concentrations of sodium silicate and sodium aluminate in the reaction medium should not exceed 2% each, by weight. At the latter upper limit it is already necessary to reduce the time interval between hydrosol formation and crosslinking to a minimum, as can be demonstrated quite spectacularly, e.g., by blending together 5%-solids solutions of sodium silicate and sodium aluminate. At the reagent concentrations mentioned, a strongly light-scattering, ultrahigh-molecular-weight, silico-aluminate polymer is formed very rapidly, which is totally useless for the synthesis of complex microgels of the present invention. As the matter of fact, the entire reaction medium becomes solidified into a rigid continuous gel after only a few seconds.

At the lower end of the spectrum of useful concentrations of hydrosol-forming reagents, sodium silicate and sodium aluminate (zincate) should be present in reaction media containing particulate matter at concentrations of at least

0.1%, by weight.

The latitude with regard to relative proportions of sodium silicate and sodium aluminate, and/or zincate, which can be employed in forming hydrosols suitable for the synthesis of complex functional microgels, is extremely broad. Although certain specific ratios of hydrosol-forming reagents may be preferable for certain purposes, ratios of sodium silicate to the combined mass of sodium aluminate, and/or zincate, ranging from 1:10 to 10:1, by weight, are adequate for most practical applications.

The above-described, chemically reactive, hydrosols are fundamentally different from hydrosol (aquasol) products of the present art. The former are transient intermediate products with a relatively short useful life span, serving exclusively for the purpose of synthesizing the complex functional microgels in question and having no practical use on their own. They belong to the class of "amicrons" (subcolloids) with average particle dimensions smaller than 5 nm, which, according to the nomenclature accepted in many textbooks of colloid chemistry, occupy a boundary position between molecular solutions and conventional colloids. It should be pointed out, however, that the hydrosols of the present invention, which lack any visual indication of the existence of a particulate phase, can remain in the amicron category for only a limited period of time. Upon a certain maximum permissible period of aging, which, depending on the concentration of hydrosol- forming reagents in the reaction medium, may extend from a couple of minutes to several hours, these hydrosols become intrinsically coarser (acquire excessive molecular weight) and fall out from the category of subcolloids. The consequence of this excessive molecular-weight growth is loss of chemical reactivity, which renders the sodium-silico-aluminate (zincate) hydrosols unsuitable for the . synthesis of complex functional microgels. Typical hydrosols (aquasols) of the present art, having average particle diameters ranging from 5 nm to 200 nm, can be classified as "submicrons. " They are represented, for example, by aquasols disclosed by Alexander in U.S. Patent 2,974,108 consisting of solid particles of definite (fixed) shapes, dispersed in aqueous media. Most importantly, these systems are chemically non-reactive final products in their own rights, e.g., ion exchangers in the case of Alexander's aquasols.

The freshly formed subcolloidal reactive hydrosols become crosslinked with gel-setting agents, such as bivalent and multivalent inorganic salts and/or organic, cationically- active, chemical compounds with at least two reactive groups in each molecule, to form the complex (multi-component) microgels mentioned previously. From a chemical standpoint, the above crosslinking of hydrosols by gel-setting agents is a reaction of polycondensation, with simple salts, e.g., NaCl, Na2SU , aNU3, and/or similar ammonium compounds, being formed as by¬ products. Hence, purely inorganic complex microgels of the present invention represent hybrid macromolecules of a polymer- polycondensate type, while the organic/inorganic ones (with organic compounds built intrinsically into the molecular structure) represent hetero-macromolecules of the same polymer- polycondensate type.

The complex functional microgels of the present invention are formed in a virtually instantaneous manner. It is estimated that the chemical reaction between low-molecular- weight, subcolloidal, hydrosols (anionic polyelectrolytes) and bivalent or multivalent inorganic salts, or equivalent organic crosslinking agents, resulting in the formation of hybrid, polymer-polycondensate, macromolecules, occurs in less than one microsecond. The rapid growth of these macromolecules into giant formations with a useful molecular weight of many billion units is estimated to take place within an interval of a couple of milliseconds. This rapid continuous "sweep" of the molecular weight of freshly formed complex functional microgels across an enormously broad molecular-weight range is capable of satisfying the entire potential spectrum of specific floccula- tion requirements of aqueous dispersions of particulate matter, regardless of physical, chemical or colloidal make-up of the latter. It is this molecular-weight "sweep" mentioned, which is deemed responsible for the instantaneous, indiscriminate and complete flocculating action toward even the most polydisperse and heterodisperse colloidal systems known in science and technology. While organic polymeric flocculants become also more efficient with increasing molecular weight, the solubility of these materials in water is reduced strongly when the molecular weight exceeds about ,15,000,000 units. Moreover, the latter flocculants have a relatively narrow molecular-weight distribution, hence, are incapable of satisfying widely diversified flocculation requirements inherent to many polydisperse and heterodisperse colloidal systems, encountered routinely in paper, pigment, and many other industries.

It should be emphasized that the formation of the intermediate reactive subcolloidal hydrosols and resultant complex microgels of the present invention are not stoichio- metric. Identical hydrosols and/or microgels are synthesized each time, however, when the reagent concentrations and proportions, as well as reaction conditions maintained during synthesis, are the same. On the other hand, the principal quantitative and qualitative compositions of above hydrosols and microgels may be varied within unusually broad ranges without detriment to these hydrosols', or microgels', intended functional performance. For example, the ratio of sodium silicate to sodium aluminate, sodium silicate to sodium zincate, and sodium silicate to the combined mass of sodium aluminate and sodium zincate, in forming the subcolloidal reactive hydrosols (sodium-silico-aluminate, sodium-silico- zincate, and sodium-silico-aluminate-zincate, respectively), may range from 10:1 to 1:10, by. weight, the preferred ratio for most practical applications being 1:1. As was established by systematic experimentation, a simple 1:1 ratio, by weight, of calcium chloride and/or equivalent bi¬ valent and multivalent inorganic salts to the combined hydrosol mass is adequate, for a well balanced functional performance of complex microgels synthesized in situ in aqueous dispersions of particulate matter, with respect to flocculation and subsequent cementation and surface-chemical modification. When floccula¬ tion alone is the main objective, the above weight ratio may be reduced to 0.5:1, or even lower.

In plant operations employing large reactors in which incorporation of reagent solutions into the reaction medium is much slower than in laboratory vessels, the considerations of process kinetics often require that some excess of inorganic crosslinking ions be employed. Chemical assays of filtrate liquids from filtration of complex microgels have indicated that the concentration of calcium, or equivalent, ions in the reaction medium should preferably exceed by at least 50% the amount of such ions actually bound chemically by the reactive hydrosols. The reason for this is that the excess of cross- linking ions mentioned does effectively reduce the concentra- tion of unreacted silicon and aluminum (zinc) ions to just a few parts per million.

Unlike with bivalent and multivalent inorganic salts, the ratio of organic, cationically-active, crosslinking agents to hydrosol mass must be determined empirically for each par- ticular agent and specific application. The reason for this is that the chemical properties of organic crosslinking agents mentioned are vastly more differentiated from the standpoint of their effect upon end-use properties of products obtained by flocculation and cementing with complex functional microgels, than are those of corresponding inorganic crosslinking agents. The need for selective screening is perhaps best exemplified by the fact that even small proportions of certain organic crosslinking agents, e.g., 0.1% to 0.2%, by weight, on the total hydrosol mass, may deprive the resultant complex microgels of adhesive properties or even render them completely hydrophobic, hence, of limited applicability in aqueous media. When synthesizing in situ complex functional microgels in dispersions of particulate matter, the relative proportions of properly screened organic crosslinking agents should range, according to present indications, from 0.1% to 5% of the mass of particulate matter. The above, almost boundless, latitude with respect to chemical composition of complex functional microgels of the present invention is very unique, in that practically all methods of gel and hydrosol (aquasol) manufac- ture known in the present art rely on very strictly and narrowly defined compositions, both with regard to the synthesis as well as end-use properties of these systems.

Another uniquely broad latitude with regard to the reaction conditions in general pertains to the pH range, extending from 3.5 to more than 12, under which the complex microgels of the present invention can both be synthesized and perform their intended functions. To synthesize the complex microgels in an acidic medium, e.g., at any pH above 3.5, the solutions of crosslinking reagents must be acidified first, using predetermined amounts of sul"furic acid, alum, or other inorganic or organic acidifying agents. The quantity of acidifying agent needed must be 'assessed independently by titrating beforehand an aliquot sample of a normally prepared, alkaline, microgel. Of course, the acidifying agents can also be added to an already formed (alkaline) microgel, such as may be preferred in certain practical applications.

As is typical of all ultrafast reactions in aqueous media, the formation of the complex functional microgels mentioned is virtually totally independent from the temperature of the reaction medium. As a consequence; the above microgels can be formed in principle within the entire temperature interval in which water remains fluid, i.e., from above the freezing point to below the .boiling point.. With complex microgels synthesized in situ in dispersions of particulate matter, the practical temperature limits depend only on the thermal stability of particulate matter present in the system and considerations of process economy and convenience.

The virtual independence from thermal conditions and regimes is a unique feature of the above microgels, which becomes readily apparent when comparisons are made with technologies of gel and hydrosol synthesis according to the present art. For example, countless patents pertaining to the manufacture of ion exchangers, catalysts, pharmaceutical preparations and other products based on in-situ, or separately, prepared gels and/or hydrosols, sometimes of virtually identical chemical compositions, frequently differ only with respect to small variations in the thermal regimes.

The broad latitudes with respect to reaction conditions, mentioned above, constitute a clear indication of the immense overriding power of the colloidal-chemical reactions controll¬ ing the formation of the complex functional microgels of the present invention. As is well known in colloidal-chemical science and technology, similar latitudes could not be tolerated with procedures of the present art, according to which hydrosols and continuous gels, or products made with their use, must always be manufactured under very strictly defined reagent concentrations and proportions, pH conditions, as well as thermal and procedural regimes.

Many alkali-compatible organic anionic polyelectro- lytes, such as sodium salts of polyacrylic acid or carbox-y- methyl cellulose, or anionically-active monomolecular organic compounds with two or more reactive groups in each molecule, such as sodium salts of N-(l,2-dicarboxyethyl)-N-alkyl sulpho- succinamate (Aerosol 22), can be built chemically into the microgel structure by adding them to the aqueous medium before. or along with, the hydrosol-forming reagents. Similarly, organic cationic polymers, such as polyacrylamides, or cationically-active organic monomolecular compounds with two or more reactive groups in each molecule, such as methyl-dodecyl- benzyl-trimethyl ammonium chlorid-methyldodecylxylene bis(tri- methyl) ammonium chloride (Hyamin 2389), can be built chemical¬ ly into the microgel structure by adding them to the solutions of bivalent or multivalent inorganic salts used for crosslink¬ ing of the subcolloidal reactive (poly-anionic) hydrosols of the present invention, or using them as independent crosslink¬ ing agents. The existence Of true chemical bonding between inorganic and organic constituents in the resultant microgels (made-up of hetero-macromolecules of a hybrid polymer-polycon- densate type) was verified experimentally, in that the organic constituents could not be removed from the gel structure by either a solvent extraction or dialysis.

The application of in-situ synthesized microgels of the present invention to flocculation and retention of polymer- emulsion adhesives is demonstrated in the following example:

EXAMPLE II

The microgel synthesis was carried in essentially the same way as in Example I, except that other materials were also present in the reaction medium. Hence, the latter consisted of 249 g distilled water and 1 g polyacrylic-emulsion adhesive with an average particle size of 45 nm and glass-transition temperature of -40° C. The latter .material is representative of a new class of water-borne emulsion adhesives developed by the Applicant and disclosed in the name of Adam F. Kaliski in the co-pending U.S. Patent 'Application Serial No. 07/333,435; filed April 4, 1989, encompassing acrylic, styrene-butadiene and vinylacetate polymers and copolymers with ultrafine particles ranging from 20 nm to 55 nm in diameter, and having glass-transition temperature ranging from -60°C to +20°C. The freshly synthesized microgel settled to the bottom of the beaker after a short period of time, the supernatant being crystal clear and completely devoid of particles of the polymer-emulsion adhesive. The microgel filtered rapidly through a qualitative filter paper (coarse openings), the filtrate being as crystal clear as the supernatant mentioned above.

Identical results were obtained using various conventional polymer-emulsion adhesives (latexes), and also when sodium zincate was used instead of sodium aluminate, or calcium nitrate instead of calcium chloride. It should be pointed out that no flocculating agents known in the present art are capable of flocculating instantaneously, indiscriminately and completely such difficult-to-handle colloids as polymer emulsion adhesives.

The subsequent example demonstrates the unique instan¬ taneous, indiscriminate and complete flocculating action of the complex functional microgels of the present invention in application to another class of difficult-to-handle colloids, such as organic dyes:

EXAMPLE III

The principal reaction medium in this example consisted of

249.5 g of distilled water and 0.5 g of Helmerco Blue MGW (American Cyanamid), the quantities of sodium silicate, sodium aluminate and calcium chloride being the same as in Examples I and II.

The freshly synthesized microgel behaved in the same manner as microgels synthesized in the two previous examples, the supernatant being similarly crystal clear. A subsequent filtration yielded a completely uniformly colored residue ("filter cake") and a crystal clear filtrate, identical results being obtained with numerous other commercial dyes.

The enormous commercial significance of Examples II and III is comprehended readily by those skilled in the art. For example, most cellulosic fibers used in paper making are notoriously color deficient, revealing undesirable yellow undertones, particularly those contained in groundwood pulps and low-brightness chemical pulps, making the use of blue and red dyes combinations virtually mandatory with papermaking furnishes. While the normally very expensive and water- polluting organic dyes attach very inefficiently to cellulosic fibers, the quantitative balance of blue and red dyes combina¬ tions changes incessantly with each ^furnish recirculation on the paper machine which presents serious operational problems. These problems are totally non-existent with the papermaking process invented by the Applicant and disclosed in the name of Adam F. Kaliski in the copending U.S. Patent Application Serial No. 07/445,366; filed December 4, 1989, based on the use of complex functional microgels of the present invention as the principal papermaking (wet-end) chemicals.

The papermaking process mentioned above permits one to use simultaneously unlimited numbers of dyes, all of these dyes being retained 100% with the microgel-flocculated furnish. This is especially advantageous in the manufacture of colored papers, the dye-related expenses being always very substantial. It is not unusual for the cost of dyes used in the manufacture of intensely-colored paper products^"-, e.g., cocktail napkins, to be two or three times higher than the cost of all other raw materials combined.

Color tones, as well as mechanical strength, of paper webs containing large proportions of organic dyes can be strikingly improved when dyes are used together with the novel ultrafine polymer-emulsion adhesives mentioned previously, or even with conventional latexes, which becomes feasible with the aid of the papermaking process based on the use of complex functional microgels of the present invention. Polymer-emulsion ad¬ hesives, which are among the most efficient "glues" applicable both to cellulosic fibers and mineral pigments as the principal papermaking raw materials, are practically excluded from a direct use in papermaking furnishes because of prohibitively low retention, poor dewatering, picking, and other operational difficulties, the virtually uncombatable contamination of waste water notwithstanding. The instantaneous, indiscriminate and complete flocculat¬ ing action of the in-situ formed complex functional microgels of the present invention makes possible to use even most polydisperse and heterodisperse furnishes, such as could not be handled in a practical manner by any of the acidic, or neutral- to-alkaline, papermaking processes of the present art. Virtually no limits to potential furnish diversities are envisaged in that, in the Applicant's extensive experimenta¬ tion, a water-based colloidal system able to resist the overpowering instantaneous, indiscriminate and complete flocculating action of the in-situ formed complex functional microgels has not yet been encountered.

As is readily understood by those skilled in the art, the complex functional microgels of the present invention may also be applied to the manufacture of wet-laid nonwoven products. The complex functional microgels of the present invention are also uniquely suited for the manufacture of practically unlimited numbers of types of structural aggregate pigments with vastly improved optical properties, also equipped with a- priori designed functional properties. The technology for the synthesis of such pigments was invented by the Applicant and disclosed in the name of Adam F. Kaliski in co-pending U.S. Patent Applications Serial Nos. 07/420,388 and 07/420,472; filed October 12, 1989.

While the primary purpose of the complex functional, in- situ formed, microgels of the present invention is to induce an instantaneous, indiscriminate and complete flocculation (aggregation) of all particulate components of a slurry, their secondary purpose is to provide an arbitrary level of intrinsic cementation to the aggregated particulates, such as pigments, fibers, dyes, etc., upon subsequent drying or other finishing operations. The desired level of cementation may be obtained by varying the composition, and/or dosage, of the complex microgels, such as to provide the end products, e.g., paper webs or composite pigments, with sufficient mechanical integrity to withstand the customary shearing (loading) and/or comminution regimes to which they may be exposed in practical handling and end-use operations. 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, as well as deformability, enabling the microgel particles to orient themselves effectively as discrete ultrathin formations at the interfaces between adjacent particulates (pigment particles, cellulosic fibers) to be cemented.

The tertiary purpose of the complex functional microgels of the present invention, synthesized in situ in dispersions of particulate matter, 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 products' end-use applications. The above effects can be realized through a purposeful modification of the chemical composition, and/or physical properties, of the complex functional microgels. For example, a surface-chemical modification providing an enhanced compatibility of the end product (composite pigment, paper web) with organic media may be attained by an intrinsic incorporation of suitable, anionically and/or cationically active organic compounds with at least two reactive groups in each molecule, into the macromolecules making up the complex microgels of the present invention. An indirect surface-chemical modification of the end products (composite pigments, paper webs) can be attained by co-aggregation of such powerful surface-chemical modifiers in their own right as organic dyes or polymer-emulsion adhesives, possible due to the instantaneous, indiscriminate and complete flocculating action of the complex functional microgel_.s of the present invention.

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

Claims

What is claimed is:

1. A process for synthesizing complex functional microgels with ultrarapid formation kinetics in aqueous media comprising the steps of: (a) preparing a subcolloidal reactive hydrosol by blending aqueous solutions, one of which contains at least one compound selected from the group consisting of alkali-metal silicates and quaternary ammonium silicates and the other of which contains at least one compound selected from the group consisting of alkali-metal aluminates. and alkali-metal zincates; (b) blending an aqueous solution containing at least one gel-setting agent selected from the group consisting of bivalent and multivalent inorganic salts _.and organic cation- ically-active chemical compounds with at least two reactive groups in each molecule with the resultant system from step (a) to crosslink said subcolloidal reactive hydrosol and synthesize said complex functional microgels; and (c) recovering said complex functional microgel from step (b).

2. The process according to Claim 1, further including the step of dewatering said complex functional. microgel.

3. The process according to Claim 1, wherein the silicate is selected from the group consisting of sodium and potassium silicates and quaternary ammonium silicates, the aluminate is selected from the group consisting of sodium and potassium aluminates, and the zincate is selected from the group consisting of sodium and potassium zincates.

4. The process according to Claim 1, wherein the bivalent and multivalent inorganic salts employed are selected from the group consisting of water-soluble salts of calcium, magnesium, barium, aluminum, zinc and zirconium.

^• 5. The process according to Claim 1, wherein the compound selected from the group consisting of alkali-metal silicates and quaternary ammonium silicates is present in the reaction medium at concentrations ranging from 0.1% to 2.0%, by weight.

6. The process according to Claim 1, wherein said at least one compound selected from the group consisting of alkali-metal aluminates and alkali-metal-zincates is present in the reaction medium at concentrations ranging from 0.1% to 2.0%, by weight.

7. The process according to Claim 1, wherein said bivalent and multivalent inorganic salts used for crosslinking of the system resulting from step (a) are introduced into the reaction medium in amounts which are equal to at least one-half of the combined mass of said subcolloidal reactive hydrosol.

8. The process according to Claim 1, wherein the ratio of said silicate to said at least one compound selected from the group consisting of aluminates and zincates in step (a) ranges from 10:1 to 1:10, by weight.

9. The process according to Claim 1, wherein the pH of the reaction medium containing said complex functional microgel, after completion of step (b), ranges from 8 to more than 12.

10. The process according to Claim 1, wherein acidifying agents are introduced to the solution of said crosslinking agents, before completion of step (b).

11. The process according to Claim 1, wherein acidifying agents are introduced to the reaction medium containing said complex functional microgels, after completion of step (b) .

12. The process according to Claim 1, wherein said complex functional microgels are synthesized in situ in the presence of a quantitatively predominant amount of particulate matter to obtain novel and improved products.

13. The process according to Claim 12, wherein said complex functional microgels constitute up to 10%, by weight, as determined by ashing, of the total mass of said particulate matter.

14. The process according to Claim 12, wherein the amount of bivalent and multivalent inorganic salts used to form in situ said complex functional microgels ranges from 0.5% to 10% of the total mass of said particulate matter.

15. The process according to Claim 12, wherein the amount of organic, cationically-active, chemical compounds with at least two reactive groups in each molecule used to form in situ said complex functional microgels ranges from 0.1% to 5.0% of the total mass of said particulate matter.

16. Complex functional microgels comprising subcolloidal reactive hydrosols formed of: (a) at least one reagent selected from the group consisting of alkali-metal silicates and quaternary ammonium silicates; and (b) at least one reagent selected from the group consisting of alkali-metal aluminates and alkali-metal zincates, the ratio of the reagents of (a) to the reagents of (b) ranging from 1:10 to 10:1, by weight, said hydrosols being crosslinked by at least one gel-setting agent selected from a first group consisting of bivalent and multivalent inorganic salts, used in an amount equal to at least 0.5 of the combined mass of said hydrosol, and a second group consisting of organic, cationically-active, chemical compounds with at least two reactive groups in each molecule, used in an amount equal to at least 0.1 of the combined mass of said hydrosol.