1. Field of the Invention
This invention relates to novel aggregate pigment products comprising low-refractive-index pigmentary materials.
More specifically, this invention relates to aggregate pigment products in which particles of single and multiple pigmentary species and other subpigmentary and nonpigmentary components are coflocculated and cemented intrinsically with the aid of in-situ synthesized complex (multicomponent) functional microgels.
2. Discussion of the Relevant Art
White pigments encompass a class of particulate materials which are essentially colorless, insoluble, nontoxic, reasonably nonabrasive, and have dimensions favoring a diffuse reflection, or scattering, of light constituting the visible portion of the electromagnetic spectrum with wavelengths ranging from 420 nm for violet to 660 nm for red.
In accordance with the laws of physical optics, maximum scattering of light occurs when a propagating light wave encounters in its path an obstacle, a pigment particle as the case in point, whose dimensions are equal to one-half of the length of the impinging wave. At equal particle dimensions, pigmentary materials with higher refractive indexes, whose values range from 1.41 for silica to 2.73 for rutile, scatter the light more efficiently than those with lower ones.
The most elementary physical model of light scattering may be considered one in which monochromatic light is diffracted by a single spherical particle. Maximum diffraction of the blue, green and red portions of the light spectrum (additive primary components of light) by spherical particles is obtained when the latter have diameters of about 150 nm, 200 nm and 250 nm, respectively. By integrating the comprehensive spectral response of a single spherical particle scattering polychromatic light, mapped as a function of particle diameter, one can calculate that the maximum light scattering occurs with a particle having a diameter of about 200 nm.
A universally useful physical model of light scattering by pigments must, understandably, be applicable both to any arbitrary pigment shape (virtually all inorganic pigments, other than TiO.sub.2, are nonspherical) as well as to integral end-use formations containing these pigments, such as paper-coating and paint films, filled paper or pigmented plastics. Let us consider, for example, a single, highly anisometric particle of kaolin clay in the form of a hexagonal platelet. The light waves of different lengths impinging upon such a multifaceted platelet are scattered with different intensities depending on how closely the dimensions of a particular facet of this platelet approximate one-half of the length of the impinging light wave. Among the multitude of geometrical facets by which the impinging light may be scattered are, for example, platelet faces (in the x,y plane) or edges and protrusions from platelet surfaces (in z direction). Moreover, the impinging light waves are scattered independently by each of the six triangular tips of the hexagonal platelet, the shorter waves being scattered more efficiently closer to the tips, across shorter distances, while the longer waves are being scattered more efficiently farther from the tips, across longer distances.
The ability to scatter light is a universal property both of particulate and extensive matter. Hence, even an "infinitely" large, most precisely polished mirror also scatters light, though only to a very negligible extent. In general, all light waves, regardless of length, will scatter with different intensities across all physical obstacles encountered in their path, such as individual particles or parts of aggregated matter, grain boundaries, or sites of localized stress concentrations giving rise to elasto-optical effects.
As far as white pigments are concerned, it should be emphasized that the latter represent a pragmatic class of particulate materials, useful in the trade, whose features are defined by a convention. In the very minimum, pigments must consist to a predominant extent of particles whose dimensions uniquely favor the scattering of light, not so much with regard to the performance of individual particles but primarily with regard to the performance of the resultant end-use formations containing these particles. The latter requirement necessitates that pigments additionally possess certain specific features and performance properties, whose scope is not fixed, however, but expands in keeping pace with the scientific and technological advancements in the field of pigments.
Whether a solid particle can be classified as pigmentary depends not only upon raw physical dimensions but also upon the particle's morphology. Hence, monolithic, spherical, virtually perfectly isometric, single-faceted particles of TiO.sub.2, or organic pigments, cease to be pigmentary for all practical purposes when their particle diameters exceed about 1 .mu.m. Overall, the spherical shape is disadvantageous for pigment particles in geometric bodies scatter the light more selectively, hence, less efficiently, than analogous anisometric particles of an equivalent mass. Furthermore, spheres have an inherent tendency to form closely packed structures characterized by a low void volume and poor light-scattering efficacy. A closely packed ensemble of monodisperse spheres has a maximum void volume of only about 26% which, for polydisperse spheres, can fall below 15%, or even 10%.
Multifaceted pigment particles, such as inherently aggregated clusters of elementary, ultrafine (subpigmentary) particles of precipitated silica or metal silicates, on the other hand, can be as large as 10 .mu.m, or even 20 .mu.m, e.s.d. (equivalent spherical diameter) and still be pigment worthy. Regardless of morphological features, however, all ultrafine particulate materials with dimensions finer than 0.1 .mu.m e.s.d. are not pigment worthy, being classified as "subpigmentary." It should be pointed out, though, that inherently fine-particle-size pigment products, such as titanium dioxide or high-glossing kaolin clay, may contain a substantial proportion of subpigmentary particles.
White pigments traditionally have been divided in the art into "primary," having a refractive index of about 2.0 or higher, and "secondary," with a refractive index ranging from approximately 1.4 to 1.65. Following the example of lithopone, introduced on the market around 1875, interspacing of particles of high-refractive-index primary pigments with particles of low-refractive-index secondary ones has become a standing practice in the paper and paint industries. As the first composite pigment ever, obtained by coprecipitating birefringent zinc sulfide (refractive indexes of 2.356 and 2.378), used in proportion of from 30 to 60%, by weight, with barium sulfate (refractive index 1.64), lithopone represents a classical case of a virtually perfect interspacing ("extension") of a primary pigment with a secondary one.
As titanium dioxide (TiO.sub.2) was introduced on the market in 1919, rapidly becoming the dominant high-refractive-index white pigment on the market, it became instantly clear that the most economical performance is obtained when TiO.sub.2 is used in blends with less expensive, low-refractive-index co-pigments. It was also recognized, however, that a great deal of detrimental selective fractionation and flocculation occurs in practical applications involving the use of such loose pigment blends. Various composite pigments were thus developed in which the primary pigments, e.g., titanium dioxide or zinc sulfide (ZnS), were first intimately blended with, and subsequently affixed to, secondary pigments (extenders) to achieve a permanent immobilization of both particulate species relative to each other.
It should be emphasized that the aggregation, as such, was never considered as a goal in itself in making composite pigment products from extraneous primary and secondary pigments as the raw materials. Instead, the primary goal has been to permanently immobilize the particles of primary pigments and extenders relative to each other to prevent a detrimental separation (fractionation) of the pigmentary components according to species and size in the subsequent end-use applications. The second attempted goal was to obtain an optimum spacing between the immobilized TiO.sub.2 particles equal to about one half of an "average" light wavelength with the aid of commercial extender pigments. As is now well understood in the trade, however, the above doctrine was a misconception, the dimensional considerations clearly revealing that a true interspacing of TiO.sub.2 particles with the incomparably coarser particles of the commercial extender pigments is physically impossible.
As is now also well known in the art, a great deal of detrimental (uncontrolled) aggregation of pigment particles, particularly TiO.sub.2, was unavoidable during the synthesis of the prior-art composite pigments under discussion. Since the prevailing doctrines in the art postulate that all TiO.sub.2 particles must be separated from each other by an optimal distance to obtain the highest possible optical-performance efficacy, an aggregation of TiO.sub.2 particles being tantamount to a technological anathema, it is not surprising that the inventors of TiO.sub.2 -based composite pigments have refrained from even mentioning, by name, the aggregation of pigmentary components in all respective patent descriptions known to the applicant.
While the concept of a mutual interspacing of particles of primary and secondary pigments has at least a nominal justification based on the consideration of the well-known laws of physical optics, a purposeful aggregation of low-refractive-index pigments by themselves had never been contemplated in the prior art, to the best of the applicant's knowledge, until after the phenomenon of beneficial in-situ aggregation of pigment fines, discovered by the applicant, was published in 1970. As a matter of fact, the iron-clad doctrine in the pigment science and technology of the prior art has always been that pigments must be optimally deaggregated and dispersed to yield the best optical and other performances.
According to the above-mentioned publication appearing in the Journal of the Technical Association of the Pulp and Paper Industry (TAPPI), Vol. 53, No. 11, November 1970, Pages 2077-2084 ("Performance of Some Commercial Clays in Starch-Containing Paper-Coating Films; Part I. Black Glass Plates as Model Substrates"), preceded by a presentation at the TAPPI Coating Conference held in Houston, Tex., May 3-4, 1970, the light-scattering properties of entire pigment populations can be improved by aggregating in situ pigment fines whose dimensions in a discrete state are too small for efficient light scattering. For example, the light-scattering performance at two different wavelengths (457 nm and 577 nm) for coating formulations prepared from three different clay products in films deposited on optically flat black glass plates as coating substrates was presented graphically as a function of the binder-volume fraction in FIGS. 6 and 7 of the above publication. The slopes of the curves representing the light-scattering coefficients of No. 1 and No. 2 clays as the function of the binder-volume content in the coating ascend initially with the increasing binder-volume fraction and, after reaching the maximum value at a binder-volume fraction corresponding to about 5 parts of starch per 100 parts of clay, by weight, descend as the binder-level is further increased.
This initial increase of light-scattering coefficients is explained in the above publication "...by an aggregation of clay fines effected by the initial addition of binder. The aggregates of ultrafine particles, which are understood here as assemblies of a very few such particles, should scatter the light more effectively than the individual components." The subsequent steady decline of the magnitude of the light-scattering coefficients is explained as follows: "An increase of the binder content of the coating systems beyond the F.sub.bv (binder volume fraction--explanation added by the applicant) value of 0.080 (5 parts starch per 100 parts clay, by weight) appears to cause a further growth of the assemblies of pigment particles, so that the optimum dimensions of the light-scattering sites are exceeded." With the relatively coarse mechanically delaminated clay having only minor proportions of particles smaller than 0.1-0.2 .mu.m, e.s.d., the light-scattering efficacy of the coatings declined from the very first incremental addition of the binder because of the scarcity of ultrafine particles amenable to a beneficial aggregation.
The relatively coarser intrinsic structure of the coating films containing the mechanically delaminated clay, compared to those containing No. 1 and No. 2 clays, was verified with the aid of a new empirical parameter, called "Rho" (after the Greek letter .rho.), defined in the above publication as the ratio of the numerical values of the light-scattering coefficients assessed at 577 nm and 457 nm for the same coating film. With coating films having a relatively fine intrinsic structure, such as binderless coatings or coatings with a low binder-volume fraction, the magnitudes of the corresponding "Rho" parameters are low. As the intrinsic coating structure becomes coarser, as was the case with all coatings discussed in the above publication in which the binder content was continuously increased, the magnitude of "Rho" increases accordingly. Below a certain specific binder-volume concentration (about 5-8%, by weight), the coarsening of the coating structure is beneficial; hence, an increasing Rho value is associated with the increase of the light-scattering coefficients. Above this specific binder-volume concentration, however, the coarsening in question becomes excessive, the increasing Rho value being associated with a decrease of the light-scattering coefficients.
As is evident from the above considerations, the light-scattering efficacy of both high- and low-refractive-index pigments can be significantly improved by a purposeful, in-situ aggregation of pigment fines. The publication by Kaliski (TAPPI Journal, Vol. 53, No. 11, November 1970, Pages 2077-2084) thus provided the scientific foundation for an entirely new pigment technology, opening the way to designing and manufacturing new lines of pigment products with an improved optical performance.
Indeed, the first patent pertaining to the manufacture of an aggregate pigment with improved optical properties, made of a single, low-refractive-index pigmentary raw material, namely, U.S. Pat. No. 4,075,030 ("High Bulking Clay Pigments and Methods for Making the Same"), was issued to Bundy et al. in 1978. According to this patent, a fine-particle-size kaolin clay, also containing 0.1-0.7% platy mica with a diameter below 100 .mu.m (passing through a 150-mesh screen) as an auxiliary material, was treated with ethylenediamine and citric acid and then flocculated with sulfuric acid. After filtration and rinsing, the resultant filter cake was dried at 65.degree. C. The improved optical performance of the resultant pigment product was explained speculatively in terms of incorporation of voids "...to form a high bulking clay." However, the contribution of the "voids" in question to the improved optical performance of the high-bulking pigment product under discussion was not documented by Bundy et al. with any experimental data.
As is readily understood by those skilled in the art, the colloid-chemical action of the above-mentioned reagents leads to the flocculation of the slurry of the clay raw material employed, resulting in the formation of essentially only two types of aggregates: the first type consists of clay fines alone, clustered together by themselves; the second type consists of discrete (individual) clay fines and/or small clusters of such fines attached to the coarser kaolin platelets. However, as is well known to those skilled in the art, the flocculating system employed by Bundy et al. is quite inefficient, necessitating that its action be enhanced with the aid of the coarse mica platelets. That platy mica particles, with diameters of up to 100 .mu.m, do indeed enhance the flocculation of the much finer clay pigment employed in U.S. Pat. No. 4,075,030 (96.4% finer than 2 .mu.m according to the Example I therein) shall be made clear from the considerations to follow.
The enhanced flocculation of small particles in the presence of coarser ones is well known in the art, being first described by V. D. Samygin et al. in the article titled "Mechanism of Mutual Flocculation of Particles Differing in Size" (translated from Kolloidnyi Zhurnal, Vol. 30, No. 4, pp. 581-586, July-August, 1968), dealing with flocculation phenomena in flotation processes. According to the above article, the rate of adhesion of fine particles to coarser ones may be higher by a factor of 10.sup.3 -10.sup.4 than the rate of cohesion between finer particles.
An analysis of the functional aspects of the above-mentioned "high bulking clay pigments" clearly points to the lack of a viable adhesive (cementing) mechanism capable of providing an adequate level of mechanical integrity to the individual pigment aggregates. As a consequence, the aggregates break down under high-shearing conditions encountered routinely during the makedown of pigment slurries or high-speed blade-coating, the enhanced optical-performance efficacy acquired through aggregation being strongly reduced. It is worth noting in the above context that, as documented amply by industrial experience, imparting an adequate mechanical integrity to the aggregate pigments while simultaneously generating in a controlled manner beneficial aggregate pigment structures has never been accomplished satisfactorily in the entire technology of the aggregate pigments of the prior art.
It should also be pointed out that the term "high bulking" is used incorrectly with the aggregate pigment disclosed in U.S. Pat. No. 4,075,030 as well as in other similar disclosures to be discussed hereinafter. Traditionally, the term "bulking" has been applied only to thixotropic pigments , e.g., satin white, which have shear-thinning properties. Hence, satin-white containing coating formulations applied to a web of paper with the aid of a doctor blade become very fluid in the high-shear zone under the blade but set immediately after emerging from that zone. As a consequence, the freshly applied coating films resist the shrinking (compaction) caused by the dewatering process and, at the same coating weight, are thicker (more bulky) than analogous films formed from non-thixotropic coating formulations. In terms of additional benefits, the thixotropic, rapidly setting coating films are mottle-free, the detrimental binder migration being more or less completely eliminated. The common feature of all true bulking (thixotropic) pigments is that their aqueous slurries gel readily and do not settle, or settle only partially, forming very soft, "bulky" sediments.
In contrast, the aqueous slurries of aggregate pigments of the prior art, including slurries of thermally aggregated (by sintering) calcined clays, do not gel, forming instead rock-hard sediments upon settling. Although the latter pigments do indeed provide some limited "bulking" action, they do so solely by virtue of flow hindrance induced by dilatancy rather than by thixotropic setting. Because of this dilatancy, the flow of freshly applied coating films containing the flow-hindering pigments is hampered momentarily so that a thermal setting, induced by drying, can take effect before a major disarrangement of the coating-film structure occurs. However, the latter pigments are not even nearly as effective in preventing the detrimental binder migration as the thixotropic bulking pigments.
Aggregate pigments virtually identical to those of Bundy et al., except for the cementing medium employed, were disclosed in WO 87/00544 to Jones et al. Called "structured kaolin pigments," with the emphasis being placed on structure rather than aggregation, the latter are manufactured in a "dry state" by saturating a fine-particle-size kaolin clay with metal chlorides, e.g., silicon tetrachloride, which are then hydrolyzed in situ and converted into cements bonding the pigment fines to each other and to the coarser clay platelets. The optical-performance efficacy of these pigments, made from fine-particle-size kaolin clay raw materials, is essentially identical to that of analogous pigments disclosed by Bundy et al. Although the mechanical integrity of the structured kaolin pigments made in accordance with WO 87/00544 is higher than that of the pigments disclosed by Bundy et al., the approach used by Jones et al. makes it inherently difficult to generate in situ sufficiently high levels of cement needed for a truly adequate mechanical strength of the resultant pigment aggregates.
As is understood by those skilled in the art, other approaches already employed in synthesizing TiO.sub.2 - or ZnS-containing composite pigments of the prior art are also applicable to synthesizing aggregate pigments made solely of low-refractive-index pigmentary raw materials. One such viable approach, for example, was disclosed in U.S. Pat. No. 2,176,876 to Alessandroni. In accordance with the latter, an anionically dispersed slurry of a low-refractive-index pigmentary raw material is flocculated with the aid of a cationic agent. Although not taken into consideration by Alessandroni, some beneficial in-situ aggregation of pigment fines present in the system is inescapable due to the above-mentioned flocculation.
The inherent difficulty of the above-mentioned approach is, however, that the initial increments of cationic flocculants introduced into the pigment furnish induce an excessive local flocculation of particulate matter, inhibiting a uniform mechanical distribution of the remaining portion of the flocculant throughout the furnish. It is thus impossible to always synthesize an identical pigment product since even moderate differences in raw material properties, such as may be brought about by a mere change of the mining location of a kaolin-clay crude, strongly affect the flocculation kinetics of the furnish, notoriously causing major variations in the end-use properties of the resultant aggregate pigment products.
Other potential approaches applicable to the manufacture of aggregate pigments can be patterned on a modification of the spray-drying or freeze-drying approaches suggested by Fadner in U.S. Pat. No. 3,453,131. The modification in question relies upon adding suitable polymer-emulsion adhesives to pigment furnishes to be submitted to spray-drying or freeze-drying.
As is readily understood by those skilled in the art, the three key processing elements indispensable to a successful synthesis of aggregate pigments of any type, regardless of the method employed, are as follows:
(a) Inducing a statistically uniform spatial distribution of all particulates present in a well-dispersed composite pigment furnish (slurry of pigmentary raw materials), using the best available dispersants and adequate agitation regimes.
(b) Instantly "freezing" the statistically uniform spatial distribution induced in (a), to ensure an equivalent statistically uniform distribution of particulate components in the resultant composite pigment products.
(c) Imparting an adequate mechanical integrity to the resultant pigment aggregates to enable the composite pigment products to withstand the shearing regimes to which they may be exposed in the customary handling and end-use applications.
It should be borne in mind, however, that a truly optimal pigment dispersion, such as is indispensable for generating a statistically uniform spatial distribution of all particulates in the furnish in accordance with requirement (a) can be obtained only with a single monodisperse particulate species. In a slurry of a polydisperse pigment, for example, one can distinguish three classes of particulates which differ considerably with regard to colloidal behavior, namely, the fine fraction encompassing pigment fines with particles smaller than 0.15-0.2 .mu.m e.s.d.; the intermediate fraction encompassing particles with equivalent spherical diameters ranging from about 0.2 .mu.m to about 0.5-0.7 .mu.m; and the remaining "coarse" fraction. Although the commercial slurries of polydisperse pigments (no commercial monodisperse pigments have ever been offered on the market) are commonly referred to in the art as being "optimally" dispersed, in reality each individual size fraction is characterized by an inherently different state of dispersion and thus also by a different dispersion stability and resistance to flocculation.
The overall colloidal picture becomes yet more complicated with pigment dispersions that are both polydisperse and hetero-disperse (consisting of two or more pigment species), such as are used for the synthesis of composite pigments. As is well known in the art, it is fundamentally impossible to obtain an "optimal" dispersion of such composite slurries in that each individual pigment fraction and species has a different optimum dispersant demand, both quantitatively and qualitatively, and a different equilibrium between the dispersant adsorbed on the pigment and dissolved in the carrier medium (water). Hence, even if optimally dispersed slurries of individual pigment species were prepared separately and then blended, a progressive destabilization of the dispersion of the resultant composite slurry would commence immediately. As a consequence, a separation (fractionation) and selective flocculation of the polydisperse and heterodisperse phases according to species and size would immediately set in, starting with the relatively least stable disperse fraction and progressing toward the relatively more stable ones. As a matter of fact, the better the initial dispersion of a composite pigment slurry, the more pronounced become the phenomena of fractionation and selective flocculation when the slow and inefficient flocculation processes of the prior art are employed in the synthesis of composite pigments.
It is thus obvious from the above considerations that composite pigments are considerably more difficult to synthesize than those consisting of a single pigmentary species. For the best possible end results, it is virtually mandatory to first start with optimally dispersed, separately prepared, raw material slurries, blend these slurries within the shortest possible time interval at the highest practical solids, using a vigorous agitation, dilute the resultant pigment furnish to the solids level called for by the synthesis procedure, and then instantly flocculate the furnish to "freeze" the dynamically maintained uniform spatial distribution of all particulates present in the furnish before a detrimental fractionation and selective flocculation of the particulates can set in.
As is readily understood, the cementing (adhesive) medium needed to impart the desirable level of mechanical strength to the resultant pigment aggregates must either be already present in the pigment furnish or be synthesized in situ, regardless of whether the aggregate pigment is synthesized from a single or multiple raw material species.
It should be pointed out in the above context that a successful process scheme for synthesizing aggregate pigments, encompassing all three above-mentioned key elements, was never fully realized in the prior art, as shall become clear from the considerations to follow.
Firstly, while the state of an optimal (for all practical purposes) dispersion is clearly indispensable to attaining a uniform spatial distribution of all particulate components present in a disperse system, the flocculating agents and processes of the prior art are incapable of completely overriding the action of the powerful modern dispersants.
Secondly, because of the detrimental progressive destabilization of composite slurries, the total homogenization of all particulate components in pigment furnishes used for synthesizing composite pigments should be accomplished very rapidly, preferably within an interval shorter than 2-5 minutes. The latter requires, however, that the homogenization be carried out at the highest attainable solids, such as can be handled only with the aid of advanced powerful in-line mixers. Powerful mixers are also indispensable to speedily carry out the dilution of the furnish in that the dispersion stability of diluted slurries deteriorates much faster than that of high-solids ones.
Thirdly, a continuous introduction (metering) of the flocculating agents into the diluted pigment furnish is virtually mandatory. The use of batch processes, such as are commonly employed in the manufacture of pigments in accordance with the prior art, will invariably result in synthesizing non-uniform, non-reproducible inferior end products.
Fourthly, the kinetics of the flocculation process employed must be instantaneous, for all practical purposes. With a non-instantaneous process, of course, the particulates present in the furnish will flocculate sequentially, the least stable fractions being the first ones to be flocculated. Furthermore, the flocculation mechanism must also be indiscriminate, i.e., unaffected by either the physical, chemical or colloidal makeup of the disperse phases present in the furnish. As is rather obvious, a discriminatory flocculation mechanism would invariably lead to a detrimental selective flocculation of the particulates according to species and size. The flocculation must also be complete, manifested by a clear separation of the flocculated phase from a clear supernatant.
As is well known by those skilled in the art, a flocculation process having all the above-mentioned attributes was unknown in the prior art before it was first disclosed in U.S. Pat. No. 5,116,418 issued May 26, 1992 and the co-pending patent application Ser. No. 07/919,831 ("Functional Complex Microgels with Rapid Formation Kinetics"), Filed Jul. 27, 1992 now abandoned, both above applications being incorporated herein by reference.
As is readily understood, the above instantaneous, indiscriminate and complete flocculation process, combined with the intrinsic cementing mechanism, makes it possible to synthesize countless numbers of aggregate pigments from a wide variety of pigmentary, subpigmentary and nonpigmentary raw materials. As a consequence, the novel aggregate pigments of the present invention provide not only an improved optical performance (the primary goal of all analogous aggregate pigment products known in the prior art), but also extend into the hitherto untapped domain of functional pigments. The latter functional pigments are designed to provide a variety of novel material as well as performance properties, such as reduced fiber debonding and increased first-pass retention in paper-filling applications, intrinsic pitch-combating ability, reduced abrasivity, paper-coloring ability, shear-thinning (thixotropy) of coating colors in high-speed coating applications, or affinity to (compatibility with) organic media.
It should be emphasized strongly herein that all composite pigments known in the prior art consisted of high-refractive-index primary pigments, such as TiO.sub.2 or ZnS, in blends with low-refractive-index secondary (extender) pigments, but none was known consisting solely of blends of low-refractive-index particulate components, such as those synthesized in accordance with the present invention. It should be emphasized also that, to the best of the applicant's knowledge, all aggregate pigments of the prior art, regardless of the composition or type, were intended exclusively for the improvement of optical-performance efficacy, aggregate pigments intended for improved or novel functional properties being unknown heretofore.
In accordance with the foregoing and disclosures to follow, it is an object of the present invention to provide compositions for novel aggregate pigment products made of raw materials encompassing solely low-refractive-index inorganic and/or organic pigments, subpigmentary mineral particulates, and non-pigmentary particulate and/or water-soluble materials.
In particular, it is an object of the invention to provide compositions for aggregate pigment products synthesized by the general method disclosed in the previously mentioned U.S. Pat. No. 5,116,418 to.
It is a further object of the invention to provide compositions for aggregate pigment products synthesized from virtually all low-refractive-index pigmentary raw materials applicable to paper making and having a higher optical-performance efficacy and lower abrasivity than the individual materials employed for their synthesis.
It is a yet further object of the invention to provide compositions for aggregate pigment products which, regardless of their predominant kaolin-clay or calcined-clay content, are uniquely suitable for use in the alkaline papermaking process.
It is a still further object of the invention to provide compositions for aggregate pigment products with improved optical-performance efficacy and extra-high bulking properties, synthesized from commercial precipitated pigmentary raw materials deagglomerated mechanically to a subpigmentary particle size, used alone or in blends with pigmentary raw materials and/or other constituents.
It is a yet further object of the invention to provide compositions for aggregate pigment products having intrinsic pitch-combating properties in papermaking furnishes.
It is a yet further object of the invention to provide compositions for aggregate pigment products containing, in addition to pigmentary and/or subpigmentary and other constituents, water-soluble and/or disperse polymer adhesives to reduce fiber debonding in paper-filling applications and improve solvent dissipation in printing.
It is a still further object of the invention to provide compositions for aggregate pigment products for paper-coating applications containing, in addition to pigmentary and/or subpigmentary and other constituents, non-film-forming organic-polymer particulates for improved ink receptivity.
It is a yet further object of the invention to provide compositions for aggregate pigment products for newsprint-filling applications containing, in addition to pigmentary and/or subpigmentary and other constituents, high-surface-area, high-oil-absorption pigmentary raw materials for both improved ink absorbency and immobilization.
It is a yet further object of the invention to provide compositions for extra-high-opacifying aggregate pigment products containing intrinsically dispersed carbon black, thus rendering them particularly suitable for the manufacture of lightweight newsprint and groundwood specialty papers.
It is a still further object of the invention to provide compositions for aggregate pigment products containing intrinsically incorporated color dyes to eliminate the residual yellow hue, inherent to virtually all commercial pigments, and/or render the resultant aggregate pigment products directly applicable to the coloring of paper, paints and the like.
It is a yet further object of the invention to provide compositions for aggregate pigment products containing chemically built-in organic, cationically active compounds with at least two reactive groups in each molecule to impart controlled levels of oleophilic properties to the resultant pigment products, thus rendering them uniquely compatible with, and dispersible in, organic media such as plastics, synthetic fibers and solvent-based lacquers and paints.
It is a yet further object of the invention to provide compositions for aggregate pigment products containing cellulosic and/or synthetic microfibrils to maximize first-pass retention and decrease fiber debonding in paper-filling applications, especially high-ash applications.
A yet further object of the invention is to provide compositions for aggregate pigment products in which the particulate ingredients are coflocculated in a controlled manner into aggregates whose intrinsic structure, as well as spatial distribution of the light-scattering and functional sites, provides an overall performance efficacy of the resultant products that is superior, in terms of the light-scattering efficacy, functional properties and economy of use, to that of the equivalent blends of loose ingredients.
It is also a particularly special object of the invention to provide general principles of qualitative, quantitative and functional formulating of the ingredients of aggregate pigments as well as principles of inducing intrinsic, optically favorable spatial and structural configurations, enabling one to design at will aggregate pigment products suited for the specific needs and preferences of individual customers.