FIELD OF THE INVENTION
[1]This invention relates to structured pigment compositions formed by the reaction of colloidal silicas and clays, and more particularly relates to structured composite pigments which are reaction products of clay, colloidal silicas, and optional spacer particles such as titanium dioxide, methods for preparation of the structured composite pigment, and paper and paint compositions containing such composite pigments.
BACKGROUND ART
[2]Coatings are applied to paper and fillers are utilized in paints or paper to improve various qualities including printing quality and optical properties such as brightness, opacity and gloss. Sodium aluminosilicates are well known as paper pigments. An important group of sodium aluminosilicates are the composite products produced by the hydrothermal reaction between kaolin clay and alkali metal silicates as described in U.S. Pat. No. 4,812,299. These composite products are described as altered kaolin clay platelets which have an integral rim or protuberance of essentially amorphous alkali metal silicate-kaolin clay reaction product. The composite compositions are structured materials in which the degree of structure is controlled depending on reaction conditions.
[3]An improved structured sodium aluminosilicate composite paper pigment is described in PCT Publication WO92/03387 and U.S. Pat. No. 5,186,746. The structured sodium aluminosilicates described in these publications are produced by the reaction of sodium silicates and kaolin clay under hydrothermal conditions. The composite products are characterized by having low oil absorption values and high total pore volumes. These products offer high performance properties despite their low oil absorption characteristics.
[4]The present invention provides an improved group of structured pigments which have optimum pore structures and improved slurry rheology at higher solids contents than the prior art.
SUMMARY OF THE INVENTION
[5]It is accordingly one object of the present invention to provide a novel class of composite pigments which are useful as paper coating pigments and as paper and paint fillers.
[6]A further object of the invention is to provide novel composite structured pigments produced from the reaction of clays and colloidal silica, which pigments have improved slurry rheology and morphology for use as paper coating pigments and as paper and paint fillers.
[7]A still further object of the invention is to provide an improved composite pigment which has better rheology than known sodium aluminosilicate paper pigments, which pigments can be provided to the paper industry as higher solids slurries than those known to the art, and can be provided with spacer particles to control product porosity at desired levels.
[8]An even further object of the invention is to provide a method for preparation of the novel pigments of this invention comprising the reaction of a clay with a colloidal silica to produce a structured aggregate clay product, which product can be further reacted with a spacer particle such as TiO2 to modify its pore size distribution, increase its total pore volume, and thereby improve pore structure properties pertinent to providing opacity.
[9]It is a still further object of the invention to provide modified clays of low colloidal silica treatment levels through slurry make-down shear, which are no longer structured pigments but are surface modified slurry products offering higher solids, improved Hercules viscosity and improved IGT values as compared to untreated clays.
[10]Other objects and advantages of the present invention will become apparent as the description thereof proceeds.
[11]In satisfaction of the foregoing objects and advantages, the present invention provides structured pigments comprising the reaction product of a clay and colloidal silica.
[12]In a further aspect of the invention, a paper pigment having an optimum pore structure is prepared by the reaction of a clay, a colloidal silica and a spacer particle such as titanium dioxide.
[13]In a still further embodiment, the present invention provides a structured pigment in slurry form, which pigment comprises the reaction product of a clay, colloidal silica, and a spacer particle such as titanium dioxide, and optionally contained in an aqueous suspension or slurry in admixture with a clay such as kaolin clay, natural clays, delaminated clays, structured sodium aluminosilicates or calcined clay. Also provided by the present invention are paper and paint products which contain the structured composite pigments of the present invention.
[14]The present invention also provides processes for the preparation of the structured pigments of this invention, which processes comprise the reaction of kaolin clay with a colloidal silica to form a structured pigment comprising a colloidal silica/clay reaction product. In a further embodiment, the structured colloidal silica/clay reaction product is spray dried to powder form, and optionally formed as an aqueous slurry. In a still further embodiment, the structured colloidal silica/clay reaction product is further reacted with spacer particles such as titanium dioxide to increase the optimum pore structure. In a further process embodiment, the clay slurry may be combined with the colloidal silica and spacer particles such as titanium dioxide simultaneously via in-line metering of the colloidal silica and titanium dioxide for reaction with the clay.
[15]The present invention also provides processes for preparation of novel paper products by incorporation of about 1-50 wt. % of the structured pigments of this invention into the paper as coatings and fillers. Included in the embodiments of the invention are methods for extending titanium dioxide in paper board coatings by incorporation of about 1-50 wt. % of the composite pigments of the present invention into the paper board coating.
BRIEF DESCRIPTION OF THE DRAWINGS
[16]Reference is now made to the drawings accompanying the application, wherein:
[17]FIG. 1a is a graph comparing different treatment levels of colloidal silicas in weight percent on the particle size of a modified clay pigment of the invention;
[18]FIG. 1b is a graph comparing the effect of surface area of the colloidal silica reagent in two different treatment concentrations on the particle size of a modified clay pigment of the invention;
[19]FIG. 1c is a graph comparing the treatment levels of colloidal silica on the surface area of a modified clay pigment of the invention;
[20]FIG. 2a is a graph illustrating the particle size histograms for a colloidal silica modified HG-90 clay pigment indicating the chemical structuring which occurs at low colloidal silica treatment levels;
[21]FIG. 2b is a sedigraph showing the chemical structuring of a colloidal silica modified HG-90 clay pigment when treated at low colloidal silica treatment levels;
[22]FIG. 2c is a graph showing the relative sediment density as a measure of bulking properties of a clay pigment modified with a specific colloidal silica;
[23]FIG. 3a is a graph showing the comparative pore structure in terms of cumulative pore volume of a clay-titanium dioxide composite compared with a colloidal silica modified clay pigment of the invention;
[24]FIG. 3b is a graph showing the comparative pore structure in terms of pore size populations of a clay-titanium dioxide composite compared with a colloidal silica modified clay pigment of the invention;
[25]FIG. 4 is a graph showing the comparative pore structure of two different clay-titanium dioxide composite pigments;
[26]FIG. 5 is a schematic of a preferred process for producing the structured pigment slurries of this invention;
[27]FIG. 6 is an X-ray diffraction pattern of a clay-titanium dioxide composite pigment of this invention with reference patterns;
[28]FIGS. 7a and 7b are graphs showing the comparative pore structure properties of a clay-titanium dioxide composite pigment versus that of a blend of the composite pigment with calcined clay as per the invention;
[29]FIG. 8 is a graph showing the comparative pore structure of slurry product mixtures of this invention;
[30]FIG. 9 is a graph of the comparative pore structure of a colloidal silica treated pigment mixture slurry of this invention compared with the commercial structured product SAMPAQUE 5002; and
DESCRIPTION OF THE INVENTION
[31]The present invention is concerned with a novel group of structured composite pigments which have particular utility as paper pigments and paint pigments. The pigments of the invention in the basic embodiment are reaction products of a clay and colloidal silica. The pigments are structured aggregate clays which have excellent properties as paper pigments.
[32]The structured aggregate clays of this invention are prepared by the treatment of a clay, preferably a kaolin clay, preferably in the form of a filter cake slurry. The kaolin clay is initially treated with colloidal silica, preferably in suspension form at ambient temperatures. After treatment, a particularly advantageous procedure is to inject the clay slurry/colloidal silica reaction mixture into a spray dryer to initiate the bonding reaction and thereby produce the structured aggregate clays.
[33]The clay to be used as a reaction product in the invention may be any commercially available clay mineral but preferably is a product known as kaolin clay. Included in this definition, however, are Tertiary clays, delaminated clays, primary clays, and Cretaceous clays but including any clay product which is effective to react with colloidal silica in accordance with the teachings of this invention.
[34]The colloidal silica reactant can be any of several colloidal silicas known to the prior art and available commercially. Such liquid colloidal silicas usually contain about 5-50% SiO2 by weight in water and can be of any desired particle size. It is preferred in this invention that the colloidal silica be a fine particle size colloidal silica.
[35]Particularly useful colloidal silicas for use in the invention are sold commercially by DuPont as Ludox® Colloidal Silica and by Eka Nobel as Bindzil. Such colloidal silicas have typical properties such as SiO2 contents of about 30-50 wt. %, surface areas ranging from 140-360 m2 /g, and average particle diameters ranging from 7-22 nm. The preferred colloidal silica is a silica containing about 30 wt. % SiO2 with an average particle diameter of 7 nm and a surface area of 360 m2 /g. For purposes of this invention, the smaller the particle size of the colloidal silica used, the higher the extent of clay aggregation obtained in the final structured product. A preferred colloidal silica is sold by DuPont as Ludox® Grade SM.
[36]The treatment of a kaolin clay with colloidal silica is conducted in an aqueous medium at room temperature. In general, an aqueous suspension of the kaolin clay preferably containing 15-60% clay solids is thoroughly mixed with the colloidal silica under low shear mixing conditions. In a preferred embodiment, the kaolin clay is treated with about 0.2-12 wt. % of the colloidal silica. Preferably the treatment level of colloidal silica is about 0.5-5 wt. %.
[37]After the low shear mixing is concluded, the treated clay is then preferably dried by introducing the reactant mixture in suspension into a spray drier under conventional spray drying conditions. Preferred conditions include an entrance temperature of about 1100° F. and an exit temperature of about 250° F.
[38]The products recovered at this stage are structured aggregate reaction products in which the colloidal silica particles appear to act as an adhesive agent or binder to bind the clay particles together. The spray drying process appears to drive the bonding reaction nearly to completion wherein the active surface hydroxyl groups on the clay react with those on the colloidal silica particles. As a result of the reaction, the surface of the clay is modified and the aggregate product comprises clay particles aggregated by layers of silica so as to provide a product having a larger BET surface area than the starting clay material. At typically useful levels of colloidal silica, the product surface area will have a BET surface area of 1-30 m2 g, preferably 2-10 m2 /g higher than the original clay surface area. In general, the surface area of the composite products will range from 10-35 m2 /g depending on the choice of starting clay.
[39]The pigment products of this invention are described as structured aggregates. The structured products correlate to total pore volume of the products. Total pore volume is measured by mercury intrusion porosimetry in accordance with the teachings of U.S. Pat. No. 5,186,746. The pigment structure definitions are described herein in Table VIII-b. In general a very high structure product will have a total pore volume as measured in ml/g of above 3.3, a high structure pigment will have a total pore volume of 2.5-3.3, a medium structure pigment will have a pore volume of 1.6-2.5, a low structure pigment will have a total pore volume of 0.8-1.6, and a very low structure pigment will have a total pore volume of less than 0.8.
[40]A novel feature of the products of the present invention is the ability to form high solids content slurries or high solids suspensions with the structured products. The modified structured clays of the present invention can be provided in slurry form having solids contents of as high as 67%. This important characteristic is made possible by the improved Hercules viscosity of the products. Hercules viscosity is a measurement of high shear viscosity and correlates to product slurry pumpability and paper coating runnability. In general, under Hercules measurement conditions of A-Bob at 1100 rpm, a slurry having a Hercules viscosity value below 18±400 rpm is not pumpable with a high speed centrifugal pump as are typically employed in paper mills. A preferred product will have a Hercules viscosity of at least 18±500 rpm. The structured modified clays of this invention repeatedly demonstrate Hercules viscosity values greater than 18±500 rpm at high slurry solids.
[41]The product recovered from the spray dryer is a structured aggregate clay in dry powder form containing the reaction product of clay particles and colloidal silica particles. The structured aggregate product is a useful paper pigment. However, it has been found that light scattering characteristics of the clay/colloidal silica structured aggregate clay are not optimum and insufficient opacity may be imparted to the paper by this pigment. An optimum structured pigment would have substantial porosity wherein the mean pore size is about 0.3 microns in diameter, which equals one-half the wavelength of visible light. Accordingly, in a further embodiment of the invention, the structured clay/colloidal silica aggregate is further modified so as to shift the diameter pore size into the most effective opacifying range. In these experiments it was found in one embodiment that optical properties could be improved by the use of fine particle delaminated clays such as the clay sold by J. M. Huber Corporation under the designation Hydrafine-90DL. This is a Number 1 clay having a median Malvern particle size of about 2.0 microns. The use of this clay improves the porosity of the structured pigment.
[42]A further and significant modification to improve porosity and optical properties is to add a third component to the reaction which has a particular particle shape and particle size. This increases the amount of total pore volume by 10-25% but more importantly increases the amount of porosity with pore diameters near 0.3 micron in size. It was discovered that if 0.2-0.3 micron size particles in the form of spheres or blocks or similar shapes, such as those of TiO2, SiO2, ATH (aluminum tri hydroxide), CaCO3, ZrO2, or mixtures thereof, are added to the reaction, the particles will act as spacers between the clay platelets so that the clay particles will not be predominantly bonded together in face to face fashion in the aggregate product. The spacer particles will create additional voids within the structure aggregates in the 0.2-0.3 micron diameter size range.
[43]The addition of the spacer particles provides sufficient improvements in pore structure to result in a product which has a porosity of about 0.3 microns in diameter. About 3-25 wt. % of the spacer particles are preferably added to the reaction, based on the weight of the clay. While any particles of the type mentioned may be used, titanium dioxide is particularly preferred because of availability and because TiO2 provides certain refractive index advantages. Rutile TiO2 or Anatase TiO2 may be used and alumina coated versions of these TiO2 forms are preferably used. Therefore, in a further embodiment of the invention, there is provided a process for the preparation of an aggregate or composite pigment product which has optimum porosity characteristics for use as a paper pigment, which product is produced by the reaction of a kaolin clay, colloidal silica, and a spacer particle such as titanium dioxide. It is preferred that the clay be a fine particle delaminated kaolin clay such as the J. M. Huber Corporation's Hydrafine™ 90-DL, and that the colloidal silica reagent be one of the colloidal silicas discussed above. Titanium dioxide is the preferred spacer particle in the form of spheres or blocks. In the structuring reaction, the components are used in a preferred weight ratio of about 82-89 parts clay, about 1-3 parts colloidal silica, and about 10-15 parts of spacer particle (titanium dioxide).
[44]In preparing the products of the invention, the preferred colloidal silica to be reacted with the clay is negatively charged and has a colloidal size ranging from 2-100 nm in particle size (0.002-0.1 microns). The preferred particle size is 7-9 nm. The composition of the colloidal silica is preferably essentially all silica. Some commercially available silicas may be surface altered such as by reaction with alumina, and altered colloidal silicas may also be used in the process. In general, the finer the particle size of the colloidal silica, the higher its surface area and resultant greater reactivity in producing the structured pigments. Further, the higher the surface area of the colloidal silica reagent, the lower its available SiO2 wt. % activity in water. Also, on the other hand, the higher the surface area, the greater the high shear rheological benefits provided to the modified clay up to a colloidal silica surface area of about 360 m2 /g.
[45]It is a feature of the invention that the colloidal silica/clay reaction products and the colloidal silica/TiO2 /clay reaction products can be mixed or blended with commercially available clays to obtain special properties. Thus, the structured silica modified clays of this invention may be blended with 1-99 wt. %, preferably 5-60 wt. % of other clay products such as calcined clays, delaminated clays, processed clays, Cretaceous clays, fine particle Tertiary clays, structured sodium aluminosilicates, such as those sold by J. M. Huber Corporation under the tradename SAMPAQUE, and mixtures thereof. It is particularly useful to provide blends of the colloidal silica modified clays of this invention with other clays in slurry form as it enables the preparation of higher solid slurries which are desired by the paper industry.
[46]In the paper industry, paper pigments are preferably purchased in slurry form for direct addition to the paper furnish or to the coating formulation. Because the silica modified clays of this invention often exhibit more thixotropic-like slurry behavior, blends of these silica modified clays with delaminated clays, calcined clays, or structured sodium aluminosilicates (SAMS) of the type described in U.S. Pat. Nos. 4,812,299 and 5,186,746 are particularly beneficial. Blends of these clays in slurry form provide a stable slurry product. Delaminated clays and structured clays typically exhibit very dilatant slurry rheology, which can be greatly moderated when they are used in blends with the products of this invention. Dilatancy limits slurry solids and decreases the runnability of paper coating.
[47]A preferred procedure for blending with structured sodium aluminosilicates (SAMS) is to provide a sodium aluminosilicate as described in U.S. Pat. No. 4,812,299 or 5,186,746 in dispersed filter cake form. The dispersed filter cake contains substantial water and generally will contain about 15-30 wt. % solids. To this dispersed filter cake slurry is added the dry composite structured modified clay of this invention to build solids via blending. The resulting make-down blend produces a product slurry which can be maintained at a solids content of as high as 67% solids. A preferred slurry product will contain about 88 parts by weight of the clay/silica/TiO2 reaction product aggregate of this invention and about 12 parts of sodium aluminosilicate or calcined clay. The slurry product of this invention provides a better high-shear rheology at higher solids than structured products known to the art.
[48]A preferred process for producing the silica modified clays of this invention comprises in-line treatment using a continuous in-line injection system. The selected clay filter cake slurry is treated in a continuous manner with the colloidal silica and a spacer particle such as titanium dioxide Just prior to the spray-drying step. In a preferred batch type procedure, a mixing vessel is provided into which a slurry or suspension of the selected clay is introduced. The suspension or slurry of the clay is maintained under low shear mixing conditions, preferably at an ambient temperature and neutral pH conditions. The selected amounts of colloidal silica and titanium dioxide are then preferably added simultaneously to the clay slurry. In the preferred procedure, the colloidal silica and titanium dioxide are metered into the clay slurry in the selected controlled ratios using flow meters. After being well mixed, the resulting mixture is then continuously introduced into a spray drier under the drying conditions set forth herein and the dried product recovered from the spray drier.
[49]A feature of this process is the continuous contact between the clay suspension, the titanium dioxide and silica. Uniform mixing is highly desirable in production of products having uniform characteristics in that the colloidal silica and titanium dioxide would be uniformly aggregated with the clay particles.
[50]A preferred process scheme for producing structured pigment slurries of this invention is shown in FIG. 5 accompanying the application. In this Figure, the indicated clay is a Hydrafine-90 DL filter cake slurry maintained at about 55% solids at a pH of 6.5 to 7.0. To this slurry is added rutile titanium dioxide pigment slurry and the colloidal silica reagent. Good mixing is achieved and the mixture passes through the spray drier to produce the dried, structured titanium dioxide containing Hydrafine-90 composite pigment (Str. TiHF-90). This composite pigment can then be further processed to provide preferred slurry products as described in FIG. 5. In one embodiment, the composite dry pigment is made-down with a slurry of dispersed Hydramatte filter cake which is a very coarse particle size delaminated clay. This make-down results in a structured delaminated clay slurry of 65% solids and contains a 60/40 mixture of the Hydramatte clay and the structured composite pigment.
[51]In an alternative embodiment, the Str. TiHF-90 dry composite pigment is made-down with the commercial calcined clay, Hycal, into water to form a structured pigment slurry blend containing 67% solids in a weight ratio of 88 parts composite pigment and 12 parts Hycal. This structured slurry may be post blended with an ultrafine particle size clay slurry by low shear blending to produce a new structured slurry having a solids content of 69% with the solids being in a 75/25 weight ratio of Hydragloss-90 clay and structured composite clay of the invention.
[52]In still a further embodiment, the dry composite pigment is made-down with a commercial structured sodium aluminosilicate, SAMPAQUE 5002 dispersed filter cake slurry, to form a structured silica pigment slurry containing 67% solids in a 88/12 weight ratio of the composite pigment Str. TiHF-90 and SAMS-5002.
[53]The structured compositions of the present invention have a structure level as defined by porosity and other characteristics which render said products distinct from other paper coating pigments of the prior art. The structured composite products of the present invention have an oil absorption of less than about 50 g/100 grams and preferably about 40 g/100 grams and a total pore volume and defined structured level in the range of 0.85-1.15. The products of the invention are therefore low structured materials as defined herein.
[54]On the other hand, the commercial product SAMPAQUE 5002, a structured sodium aluminosilicate has an oil absorption value of 105 g/100 grams and a total pore volume of 2.85. Therefore, this SAMPAQUE 5002 product is a high structured material. In addition, the calcined clay commercial product Hycal, has an oil absorption value of 80 g/100 grams and a total pore volume of about 1.60, thus, being a medium structured material.
[55]It is also a feature that the new structured clay agregate pigment of this invention has an oil absorption value which is no higher than the starting clay reactant and also has a low pore structure as defined by porosimetry. On the other hand, the product of this invention yields a product slurry which equals or exceeds the performance of a slurry of the calcined clay Hycal or the SAMPAQUE-5002 product. It is also a feature of the invention that the silica modified clays of this invention, which have been treated with low treatment levels of colloidal silica, can under certain high shear mixing conditions be attritioned back to their starting clay particle size. This yields a slurry of silica-coated clay particles which provide unique properties as paper coating compositions.
[56]The invention thus provides a broad range of useful clay products. The colloidal silica modified clays and colloidal silica modified clays containing spacer particles, preferably of titanium dioxide, find wide use because of their unique properties. Blends of these products with conventional clays provide additional benefits.
[57]The following examples are presented to illustrate the invention, but it is not to be considered as limited thereto.
[58]Table I below sets forth examples of colloidal silica reagents useful in producing the modified structured clays of this invention. In this Table, colloidal silicas are identified by their product tradename, by the manufacturer, and by characteristics including the stabilizing counter ion, specific surface area, particle charge, silica weight percent, titratable alkali weight percent, pH, specific gravity, and average particle diameter. It will be noted that the preferred silicas are all negatively charged and those having particle sizes of 7-9 nm (0.007 microns) are highly preferred. Preferred colloidal size is 2-100 nm (0.002-0.1 microns) in particle size. From a compositional viewpoint, these colloidal silicas are essentially SiO2 but can be altered by surface modification as shown by the products identified as Bindzil 159/500 and Ludox AM. In the products shown, with numerical suffixes such as Bindzil 15/500, the first number shows the SiO2 activity in wt. percent and the second number shows the specific surface area in M2 /g. Table I is as follows:
EXAMPLE 1
[60]In this example, a starting kaolin clay identified as HG-90, was treated with varying treatment levels of colloidal silica. The kaolin clay, HG-90, is a Number 1 high brightness fine particle Tertiary kaolin clay of the J. M. Huber Corporation. The designation HG means Hydragloss. This clay is available as a dispersed filter cake slurry at 52% solids concentration with a pH of 6.5-7.0.
[61]In this example, samples of HG-90 kaolin clay were treated at the treatment levels of colloidal silica in active weight percent as shown in FIG. 1a. The treatment was carried out by contacting the colloidal silica reagent with the kaolin clay using low shear mixing at ambient temperature. The active treatment level of colloidal silica ranged from 0.2-12% by weight. This range is considered to be the useful treatment level.
[62]After low shear mixing of the kaolin clay and colloidal silica, the resulting treated clay was subjected to spray drying at an inlet temperature of 1000°-1100° F. and an outlet temperature of 250° F. The spray drying process dries the product and also is believed to cause the bonding reaction between the kaolin clay particles and colloidal silica to proceed rapidly and nearly to completion. It is believed that active hydroxyl groups on the clay react with those on the colloidal silica to produce a structured aggregate product.
[63]As may be seen in FIG. 1a, the colloidal silica agents selected were Ludox TM, Ludox AM, and Ludox SM. These colloidal silicas differ in surface area and their specific surface areas are indicated in the graph of FIG. 1a. The HG-90 kaolin clay was treated with the three colloidal silicas in accordance with the amounts and procedure discussed above.
[64]In FIG. 1a, the treatment level of each colloidal silica is plotted against the Malvern Median particle size of the silica modified clay in microns. FIG. 1a shows the product particle size trends based on the different treatment levels. Aggregate product particle size is observed to increase as a function of increasing silica treatment level. Also, FIG. 1a shows that the higher the specific surface area of the colloidal silica reagent employed means greater reactivity in producing structured pigments by the colloidal silica acting as an inorganic binder.
[65]The product produced as a result of this bonding reaction is a structured clay in which the colloidal silica appears to act as a binder or adhesive for the clay particles. The rheological benefits obtained from the colloidal silica treatment of the clay are best measured by the advantages achieved by providing the product as a much higher solids slurry than can be made available by similar products.
[66]On the other hand, the colloidal silica treated clay of this invention is available in solids content of 67-68% as a paper coating.
[67]FIG. 1b is a graph showing the particle size properties of the colloidal silica modified Hydragloss 90 clay pigments plotted against the specific surface area of various colloidal silica reagents. This graph shows particle structuring as a function of the colloidal silica type. In this graph a 4.0% treatment level of each colloidal silica is compared to a 6.0% treatment level of the same colloidal silicas in regards to their effect on Malvern Median particle size in microns. This is a different way of plotting the data of FIG. 1a and demonstrates the effect of the specific surface area of the colloidal silica reagent resulting product on particle size.
[68]FIG. 1c demonstrates that as a result of modifying the surface of the Hydragloss 90 clay with a colloidal silica to provide layers of SiO2, a substantial increase in the clay's BET surface area is obtained. The product surface area, by BET measurement of the modified clay, will be as much as 30 m2 /g higher than the original clay surface area given the use of colloidal silica treatment levels of up to 12% by weight.
EXAMPLE 2
[69]In this example, products according to the invention are prepared by reaction of Hydragloss 90 clay, a Number 1 high brightness East Georgia fine particle Tertiary clay, by treatment with colloidal silica at the treatment levels shown in the following Table II as Experiments A, B, C, D, E and F. These treatment levels ranged from 0 (control) to treatment levels of 2.5% in 0.5% increments. Experiment F, showing an average treatment level of 2.0%, was obtained by mixing a dry silica modified product of 3.1% treatment level with untreated clay in dispersed filter cake slurry formed via Cowles make-down.
[70]Also shown in Table II is the make-down procedure employed, the BF viscosity, the Hercules viscosity and the Malvern Median particle size of the modified clays. The Hercules viscosity is a measurement of high shear viscosity and correlates to slurry pumpability. This is an important characteristic in paper mills in that the slurry must be pumpable by a high speed centrifugal pump. The Hercules viscosity, as determined under conditions using A-Bob at 1100 rpm, should provide a measurement of at least 18±500 rpm. A value below 18±400 rpm is not pumpable.
[71]In Table II it will be noted that the control Experiment A had a Hercules viscosity reading of 18±170 rpm at a 74.5 solids concentration, and a reading of 18±490 rpm at a solids concentration of 73.5% Only the latter slurry is barely pumpable.
[72]On the other hand, Experiments C, D, E and F all provide pumpable slurries at 74.5% solids because of the colloidal silica treatments. In Table II, make-down of the slurry products was at 75% solids.
[73]A Hercules viscosity of at least 18±500 rpm is desired. Therefore the preferred colloidal silica treatment levels to provide this Hercules viscosity should be a minimum of about 1.0% by weight, and preferably about 1-1.5% by weight of colloidal silica, based on the amount of clay being treated.
[74]FIGS. 2a, 2b and 2c are graphs demonstrating other properties associated with these silica modified HG-90 pigments, including: particle size Histograms in FIG. 2a; sedigraph particle size curves in FIG. 2b;, and bulking properties as measured by relative sediment density in FIG. 2c for products produced in accordance with the procedures of Table II except that the modified clays were all slurried at 50% solids. In FIG. 2a, the Malvern particle size Histograms show the results of chemical structuring provided by the low colloidal silica treatment levels of from 0.5-1.5% as compared with the Hydragloss 90 untreated control. FIG. 2b shows the sedigraph particle size curves for the indicated modified clays and the resulting degree of chemical structuring. The sedigraph curves are a plot of the particle diameter in microns against the weight percent of particles finer than the indicated amount in microns.
[75]FIGS. 2a and 2b both show that most structuring occurs on the fine particles because they have the largest surface available for aggregation via reaction with the colloidal silica binder.
[76]FIG. 2c is a plot of the treatment level of the colloidal silica against the relative sediment density of the products.
EXAMPLE 3
[78]This example sets forth data and results from a pilot scale-up run of a colloidal silica modified Hydragloss 90 product. This work was basically a pilot plant scale-up based on the experiments of Example 2, specifically a scale-up of Example D of Table II in which the colloidal silica treatment was 1.5 wt. %. This product had optimum rheological benefits in terms of improved Hercules viscosity while maintaining the BF viscosity below 2000 cps. Physical property data are set forth in Table III-a.
[79]As indicated in the NOTE following Table III-a, production of this modified Hydragloss 90 clay slurry was carried out on a 150 gallon batch slurry basis using a conventional 100 horsepower Cowles Dissolver makedown system operating at a tip speed of 4000 FPM.
[80]The resulting slurry product from this experiment was compared with the starting Hydragloss 90 clay for the properties shown in Table III-a. It will be noted that the modified Hydragloss 90 clay has an increased BET surface area and an increased solids content.
[81]In Table III-b, the coating performance of the basic Hydragloss 90 clay and the colloidal silica-modified Hydragloss 90 clay are compared in an LWC/Rotogravure application. The top portion of this table shows the coating ingredients. The bottom portion of this table shows the performance data for the coated paper sheets. In an LWC/Rotogravure application, the coating weight is normally in the range of 6-8 lbs. per ream per side. As shown in the performance data, the total coat weight used was 12 lbs. per ream. A major performance difference seen in the data of Table III-b is in the increase in the IGT value in centimeters per second from 81 cm/sec for the control to 127 cm/sec for the coated sheet containing colloidal silica modified clay. The IGT measurement is a measure of coating strength. The most expensive part of a paper coating formulation is the latex binder. The IGT value shows that the colloidal silica treated clay of this invention can potentially reduce the amount of latex binder needed to maintain coating strength properties and could therefore substantially reduce costs in paper production. An additional side benefit of being able to reduce latex binder levels in a coating formulation is added opacity, since less binder is available to fill air microvoids in the coating that provide significant light scattering properties. The performance relationship of binder level on coating opacity is well known to those skilled in the art.
[82]It can be concluded from the results shown in Table III-b that the colloidal silica modified clay of this invention improves the coating strength of paper so as to represent a significant source of cost reduction via the removal of latex binder.
EXAMPLE 4
[85]In this example, Hydragloss 90 clay is treated with the colloidal silica reagents, Bindzil 30-360 and Bindzil 15-500 in Experiments A and B as shown in following Table IV. Experiment C is the control. The colloidal silica treatment level is 1.5% in both Experiments A and B and the initial make-down solids were all at 75%. The make-down temperature and slurry pH are also indicated.
[86]The modified products were prepared by reaction of a Hydragloss 90 slurry at 55% solids with the colloidal silica reagent followed by spray drying to produce the dry colloidal silica modified Hydragloss 90 clay. The clay was then made down in water to provide the modified product slurry.
[87]Table IV shows that the higher surface areas provided by the colloidal silica reagent of Experiment B do not improve results. The product of Experiment A using the colloidal silica Bindzil 30/360 appears to provide the maximum benefits with respect to Hercules viscosity.
EXAMPLE 5
[89]In this example, Experiments A, B, C, D and E described in following Table V, are provided in which Example A is a control. The colloidal silica reagent employed was Bindzil 30/360. The treatment levels are as indicated ranging from 0.6-1.8. In this case the clay was a Hydrafine™-90 ND, a non-delaminated Number 1 high brightness cretaceous kaolin clay. The slurry products were produced by reaction of the Hydrafine clay slurry at 55% solids with the colloidal silica reagent followed by spray drying to provide the dry colloidal silica modified clay. The clay was then made-down in water to produce the product. The data and results are shown in following Table V.
[90]This example shows the difference in clay rheology using a different type of clay. In this case, the high anatase content of the non-delaminated clay appears to negate the benefits of colloidal silica treatment.
EXAMPLE 6
[92]In this example, a similar clay treatment to Example 5 was carried out using the colloidal silica treatment levels indicated. The clay used in this experiment was a delaminated kaolin clay product Hydramatte™, normally used for Matte paper applications. The delaminated clay was treated at 52% solids concentration with a dry Hydramatte™ clay which had been treated with 1% of colloidal silica, the colloidal silica being Bindzil 30/360. A delaminating clay normally provides print gloss properties. This Example shows that on a delaminated clay, the 1-2% colloidal silica treatment level provides optimum benefits for high shear rheology. The conditions and results are show in the following Table VI.
EXAMPLE 7
[94]In this Example, comparisons are made in following Table VII between a Hydragloss 90 clay feed stock in Experiment A which has not been treated with colloidal silica with a composite pigment of the invention in Experiment B. The composite pigment in Experiment B is a Hydragloss 90 clay feed stock which has been treated with 4.0 wt. % of colloidal silica under the conditions described herein. The colloidal silica reagent employed was Ludox SM, described in Table I. The Hydragloss 90 clay was also treated simultaneously with 3.0% of titanium dioxide. The titanium dioxide used was an alumina-coated, rutile-based TiO2 pigment slurry described in the NOTE to Table VII. The resulting composite pigment was 97% of colloidal silica modified clay and 3.0% of titanium dioxide. The titanium dioxide particles appear to act in the clay pigment as spacer particles. The composite pigment shown in Experiment B of Table VII is a colloidal silica modified clay which has a low titanium dioxide content.
[95]The composite pigment was spray dried in accordance with procedures described herein and evaluated for physical properties. As shown in Table VII, the Malvern Median particle size of the spray dried product was 0.50 microns for the untreated Hydragloss 90 clay feed stock as compared to 6.04 microns for the composite pigment of Experiment B. Further, pigment brightness remains the same, the surface area is increased, and the slurry Ph is increased. This increase in Malvern Median particle size is dramatic and shows production of a superior composite structured pigment.
EXAMPLE 8
[97]This Example prepares composite pigments having high titanium dioxide contents and compares those pigments with basic Hydragloss 90 clay and a blend of Hydragloss 90 clay and titanium dioxide. As may be noted from the following Table VIII-a, Experiment A sets forth the characteristics of the basic Hydragloss 90 clay feed stock. Experiment B sets forth the characteristics of a blend of Hydragloss 90 clay and titanium dioxide in which the clay has not been treated with colloidal silica.
[98]Experiment C sets forth the characteristics of a composite pigment produced by blending 75 parts of a Hydragloss 90 clay which has been treated with 1.0% of colloidal silica and 25 wt. % of titanium dioxide in the same manner as in Example 7. Experiment D is a composite pigment of the invention in which the Hydragloss 90 clay has been treated with 1.5% of colloidal silica and the resulting composite treated with 25 wt. % of titanium dioxide.
[99]Table VIII-a sets forth various characteristics, the important characteristics being the dramatic increase in Malvern Median particle size of the resulting spray dried product and the final slurry product of the composite pigments in Column C and D. Therefore, Table VIII-a demonstrates the advantages achieved by treating the colloidal silica modified clay with high amounts of titanium-dioxide.
[100]Table VIII-a also sets forth the total pore volume for the products. The composite pigment of Experiment C is indicated as having a total pore volume of 0.854 ml/gm and the composite pigment of Experiment D has a total pore volume of 0.890 ml/gm.
[101]The following Table VIII-b sets forth the pigment structure definitions based on mercury intrusion porosimetry as described in U.S. Pat. No. 5,186,746. From this Table it will be seen that the composite pigments of Experiments C and D of Table VIII-a are low structure pigments.
[102]In treating the colloidal silica modified clay product with titanium dioxide, it has been found that the optimum amount of titanium dioxide is about 10-15% based on the total amount of silica modified clay. In the Examples, rutile titanium dioxide was used because of the higher refractive index. However, anatase titanium dioxide could also be used. It is also an advantage that rutile TiO2 is available in slurry form, either untreated or surface modified. The surface modification of the titanium dioxide is application of low levels of alumina to provide better dispersion properties. The treated titanium dioxide provides better bonding composites. Low levels of alumina on the rutile titanium dioxide are preferred.
EXAMPLE 9
[105]In this Example a comparison is made in the following Table IX between composite pigments of the invention based on different types of clay pigments. In Experiment A, the clay was Hydragloss 90; in Experiment B the clay was Hydrasperse 90 and in Experiment C, the clay was Hydrafine 90. The different clays are explained in the NOTE to Table IX. In each of Experiments A, B and C, the colloidal silica treatment was identical, the treatment amount being 1.8 wt. % based on the total clay pigment. The weight ratio of modified clay to titanium dioxide was 87.5-12.5 respectively. The modified titanium containing clay pigment of this invention was then blended in the ratios set forth with commercial sodium aluminosilicate product sold commercial as SAMS 5002, at a blending ratio of 90/10 for Experiment A, 88/12 for Experiment B, and 88/12 for Experiment C. The physical properties of the products of Experiments A, B and C are set forth in Table IX.
[106]The results from Table IX show that the products of Experiments B and C have more structure and more structure in the optimum range. An important characteristic is the differential pore volume (DPV) and where the most beneficial pore volume will exist. The most beneficial pore volume is between 0.1 and 0.4 and all of these products fall within that range, being 0.3, 0.44 and 0.46 respectively.
[107]Reference should be made to FIG. 3a with respect to porosity. Comparisons of the pore structure of a clay-titanium dioxide composite is made against a colloidal silica modified clay. Since porosity is on a gram or weight basis, this Figure becomes more significant because of the density differences in the product. In addition, FIG. 4 should be noted with respect to this Example as FIG. 4 shows the net effect of the clay particle size.
EXAMPLE 10
[109]This Example sets forth the comparative performance of HSS (high structured silica) pigment slurries in a paper filler application. In following Table X-a, comparisons are made between the structured pigments A, B, C and D which are blends of structured clays which have been modified with colloidal silica and titanium dioxide and a SAMS 5002 commercial product. The SAMS 5002 product is a 50% solid slurry in Experiment D. The top part of this Table X-a shows the conditions for the tests.
[110]The properties of the filled paper sheet are set forth at the bottom of Table X-a. Two different levels of filler were maintained, 6.0% and 13.0%. The opacity, brightness, whiteness index and yellowness index were generally the 'same for all of Experiments A, B and C. The yellowness index for pigments A, B and C was superior to the control of Example D at both filler levels. A significant property of Experiments A, B and C in this invention is found in the Scott Bond measurements, which measurements were substantially higher than the control Experiment D. Scott bond measures internal sheet strength and correlates the particle size. The results of this Table show that the product of Experiment C out performs the other pigments because of the superior optical properties.
[111]Table X-b compares the coating performance of various high structured pigment slurries in paper coating formulations. The top part of this Table shows the pigments compared and the other components of the formulation. The bottom part of Table X-b shows the performance data. From this performance data Coating III appears superior in opacity, in paper gloss, brightness and the whiteness index.
EXAMPLE 11
[114]In this Example as shown in Table XI-a, an untreated Hydrafine™ clay feed stock in Experiment A was compared with a composite pigment of the invention in Experiment B. The composite pigment in Experiment B was a mixture of 87.5 parts by weight of a Hydrafine™ 90 clay pigment which had been modified by treatment with 1.8 wt. % of colloidal silica and 12.5 wt. % of titanium dioxide. The physical properties are set forth in the last few columns of the table. This Table shows that the composite pigment of the invention of Experiment B provides an improved brightness, an improved whiteness index, and surface area. Further, the Malvern Median particle size of the spray dried product was substantially increased as was the total pore volume. Therefore, the composite pigment of Experiment B is a significantly improved product as a paper coating pigment.
[115]The following Table XI-b compares the product of Experiment B from Table X-a with the commercial product SAMPAQUE 5002 and the commercial product, Hycal, a fine particle size calcined clay. Table XI-b shows that the composite product of Experiment B is the product with improved characteristics.
[116]Reference should be made to FIG. 6 accompanying this application with respect to the X-ray diffraction pattern of the three products of Table XI-b. The X-ray diffraction pattern of the product of Experiment B at the top of this FIG. 6 is clearly a distinct X-ray diffraction pattern from the reference patterns.
EXAMPLE 12
[119]The following Table XII sets forth comparative physical properties of various blends of the modified structured clay pigments of this invention with other clay products. The blends are important in the clay industry in providing an ability to tailor properties for particular end uses, especially for use as paper pigments. The blends set forth in Table XII are mixtures of high structured silica pigments of this invention with high structured clays known to the prior art. The high structured silica of this invention is a colloidal silica modified Hydrafine™-90 clay which is the pigment described in Experiment B of Table XI-a. The pigment in Experiment E of Table XII is an 88/12 by weight blend of the pigment of this invention with commercial product SAMS-5002. The pigment in Experiment F is an 88/12 by weight blend of the pigment of this invention with the commercial calcined clay, Hycal, sold by J. M. Huber Corporation. The pigment in Experiment G is a 75/25 blend of the pigment of this invention with the commercial product SAMS-5002, a structured paper pigment available from J. M. Huber Corporation. The pigment in Experiment H is 100% of the pigment of this invention and corresponds to the pigment of Experiment B of Table XI-b.
[120]In the comparisons of Table XII, it will be noted that all the products have excellent Hercules viscosity and good optical properties. Thus, the high structured silica pigment of this invention, when blended with commercial clay pigments, provides excellent products to the paper industry wherein characteristics can be tailored for particular needs of the customer.
[121]FIG. 7a, 7b and 8 are graphs showing the comparative pore structure of the pigment of this invention with Experiment F of Table XII in FIG. 7a and 7b and a comparison of the products of Experiments F and G of Table XII.
EXAMPLE 13
[123]This Example is a coating study comparing the performance of a high structure silica of this invention with high structured clay products in paper coating formulations. The comparisons as may be noted from the top part of following Table XIII, are between a delaminated clay, a Number 1 clay, and the commercial high structured product SAMPAQUE 5002, blends of products of E, F or G of Table XII, and the silica pigment of this invention which is Product H of Table XII. The performance data is set forth in the bottom part of Table XIII.
EXAMPLE 14
[125]This Example presents a comparison of physical properties for higher structure analogs of the high structured silicas of this invention with blends with the calcined commercial clay, Hycal. The product in Experiment A is a Hydrafine™-90 delaminated clay which has been treated with 1.5 wt. % of the colloidal silica, Bindzil 30-360, and rutile titanium dioxide in an amount of 12.5 wt. %. The clay composition of Experiment B is the same composition wherein the clay treated with the colloidal silica and titanium dioxide is a mixture of the Hydrafine™-90 clay blended with 17 wt. % of the calcined clay, Hycal as shown in Table XIV. The product in Experiment C is an 80/20 blend of the pigment of Experiment A and Hycal. The pigment in Experiment D is a 96/4 blend of the pigment of Experiment B and Hycal.
[126]The physical properties of these pigments of Experiments A, B, C and D are set forth in Table XIV.
EXAMPLE 15
[128]In this Example, the following Table XV-a compares the physical properties for structured pigment slurries of high structured silica product of this invention with a commercial SAMPAQUE-5002 product slurry. The product in Experiment A is a pigment slurry which is a blend of 88 parts of a structured pigment of this invention with 12 parts of the commercial calcined clay, Hycal. The pigment of Experiment B is the commercial high structured clay SAMPAQUE-5002 at a 50% solid slurry. The pigment of Experiment A utilizes the structured pigment of Experiment E of Table XII.
[129]Table XV-a shows that the product of Experiment A provides a high solids pigment having higher opacity and higher Scott Bond.
[130]These pigments are further compared in Table XV-b for hand sheet parameters and filled sheet parameters. The comparative pore structure is shown in FIG. 9 for these two products.
EXAMPLE 16
[134]This Example in Table XVI-a provides the comparative performance of high structured clays and calcined clay pigments in extending titanium dioxide in a LWC formulation. Coatings I, II, and III contain the coating ingredients indicated. Properties for the coated sheets are set forth at the bottom of the Table. This Table shows the effects of titanium dioxide extension and indicates that Coating III provides optimum extension and better results for IGT. Coating II results show extension of titanium dioxide.
[135]The following Table XVI-b provides similar results for indicated Coatings I and II.
EXAMPLE 17
[138]This Example provides in Tables XVII-a and XVII-b typical physical properties of structured pigment blends designed for board coating applications. The Table compares the Hydragloss™-90 clay pigment slurry with a structured pigment blend of this invention which comprises 75% of the Hydragloss-90 clay with 25% of the 88/12 high structured clay product of this invention. Table XVII-b illustrates TiO2 extension.
EXAMPLE 18
[142]This Example provides in Table XVIII comparative properties of various clay slurries made-down in combination with various structured pigment.
EXAMPLE 19
[144]This Example provides in following Tables XIX-a, XIX-b, XIX-c and XIX-d data on comparative slurry properties of various delaminated clay/structured pigment combinations.
EXAMPLE 20
[149]This example sets forth coating performance data for a Hydramatte™/structured clay pigment blend of this invention in a latex flat paint application. A comparison of Formulations A and C show significant advantages in Formulation C. Formulation C utilizes the high structured silica pigment of this invention.
[151]The invention has been described with reference to certain preferred embodiments. However, it is obvious variations thereon will become apparent to those skilled in the art, the invention is not to be considered as limited thereto.
