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Purified precipitated calcium carbonate and purified calcium silicate compounds, a method for their production, and their use as paper fillersPurified precipitated calcium carbonate and purified calcium silicate compounds, a method for their production, and their use as paper fillers description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060272549, Purified precipitated calcium carbonate and purified calcium silicate compounds, a method for their production, and their use as paper fillers. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED PATENT APPLICATIONS [0001] This application claims priority from and is a Continuation-In-Part of prior allowed U.S. patent application Ser. No. 09/797,173, filed Feb. 28, 2001, which issued as U.S. Pat. No. 7,048,900 on May 23, 2006, entitled "METHOD AND APPARATUS FOR PRODUCTION OF PRECIPITATED CALCIUM CARBONATE AND SILICATE COMPOUNDS IN COMMON PROCESS EQUIPMENT" which claimed priority from prior U.S. Provisional Patent Application Ser. No. 60/265,657, filed on Jan. 31, 2001, and the disclosures of each of the above identified applications and patents are incorporated herein in their entirety by this reference, including their specification, drawing figures, and claims. COPYRIGHT RIGHTS IN THE DRAWING [0002] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The applicant no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. TECHNICAL FIELD [0003] This disclosure is with respect to improved precipitated calcium carbonate compositions, to improved calcium silicate hydrate compositions, as well as to methods for their manufacture, and to methods for their use as paper fillers. BACKGROUND [0004] The new "internet" economy has created a need for better appearing and for higher performance papers. Desirable aesthetic qualities require papers to be brighter, more opaque, and to have a smoother printing surface. Better qualities of these properties are useful to accommodate increasingly important uses of papers, such as ink jet printing and desktop publishing. And, higher performance requirements are sought in industrial papers like paper board and packaging (used to ship items ordered via the internet) which paper types require components with very high mechanical strength. At the same time, escalating shipping and postal costs mean that users would also benefit from lighter weight papers. In other words, it would be desirable to provide industrial paper with higher mechanical strength, higher brightness, higher opacity, yet still having improved printability, weigh less, and made at a lower basis weight. With paper fillers and paper manufacturing techniques known or practiced heretofore, the juxtaposition of these requirements has not been feasible. [0005] Presently, the paper industry adds filler to paper in order to improve some of the key performance attributes. However, nearly all of the paper fillers currently available have some drawbacks associated with their use. For example, the best known filler for improving the optical properties of paper is titanium dioxide (TiO.sub.2). Although it can be used to dramatically improve the optical properties of paper, unfortunately, TiO.sub.2 has some major disadvantages. First, it is very expensive, on the order of about US$2,000 per ton at time of filing of this patent application. Second, it is highly abrasive to processing machinery. Third, it is usually shipped in a slurry form, which requires dispersant additives to prevent settling; that both adds cost and creates paper machine runnability issues. Finally, TiO.sub.2 must be produced off-site, remotely from the paper mill, shipped to customers, thus adding a large transportation cost. [0006] Other fillers, like silica and calcium silicate, are sometimes used to improve sheet bulk, print quality, and other paper properties. Here again, one of the major disadvantages to these products is that they reduce sheet strength and are expensive (silica at about US$3,000 to about US$4,000 per ton, and calcium silicate at about US$800 to about US$1,000 per ton at time of filing this patent application). These products, like TiO.sub.2, are also typically produced off-site, and carry a large transportation cost. [0007] In an effort to reduce production costs, the industry is increasingly switching to commodity fillers such as ground or precipitated calcium carbonate. Precipitated calcium carbonate is perhaps best suited for improving the optical and print qualities of paper. It can also be produced on-site (at a paper mill), thus reducing or eliminating transportation costs. Unfortunately, calcium carbonate is not as effective as TiO.sub.2 or silica based fillers. Moreover, it significantly reduces the strength performance of paper, in addition to causing undesirable dusting. [0008] Importantly, it must also be appreciated that the conventional process for the manufacture of PCC also has several limitations. First, the reaction takes place at atmospheric pressure in an "open" vessel, using a batch process technique. Such processes also require a high CO.sub.2 concentration (15%-20% by volume) in a combustion gas waste stream, and require a long reaction time (often from about 180 to about 200 minutes) to achieve the formation of the desired carbonate species. Conventional PCC manufacturing also requires large size reactors, (about 200 USgal/ton/day of PCC capacity). Additionally, a large building is required to house such PCC reactors, and consequently, a large sized site is a requirement for such a reactor building. Resultantly, capital for the building, equipment, and construction is significant. [0009] In view of the above, there is a definite and as yet unmet need in the paper industry for a high performance specialty filler manufacturing process, especially for such a process that can produce important commodity fillers like PCC. Moreover, it would be desirable for such a high performance process to be technologically superior, i.e., produce better quality filler products at lower costs than are presently available. [0010] Also, it would be desirable to find a new, high performance specialty filler that would, among other things, improve the aesthetic properties of paper (brightness, opacity, smoothness, print quality, etc.) as well as, and at the same time, and the mechanical properties of paper, (bulk, stiffness, etc.), without decreasing any strength properties. Even more desirably, such a filler would be available for supply as a slurry that is free of dispersant. Finally, it would be desirable that such a high performance filler be available from an on-site production facility, in order to eliminate transportation costs for the finished filler. [0011] With regard to the production of precipitated calcium carbonate, it would also be desirable to provide improvements over conventional batch process so as to reduce or eliminate certain current limitations. For example, in an ideal situation, it would be desirable to produce precipitated calcium carbonate using very low concentration CO.sub.2 (as low as about 5.0% CO.sub.2 by volume, or less), while nonetheless significantly increasing the reaction rate, in order to reduce the size of reactors required from the current 200 gal/ton/day by at least half, and more preferably, by at least one fourth, i.e, to as low as about 50 gal/ton/day or less reactor size. Moreover, it would be desirable to reduce required building size, and thus reduce both process equipment costs and overall capital costs for such plants. [0012] Also, it would be highly desirable to provide a method and apparatus that, with common capital equipment, is capable of both the production of the above mentioned high performance specialty filler as well as the production of precipitated calcium carbonate. [0013] In many situations, it would be advantageous to provide fillers useful for producing both wood free papers (normally alkaline, manufactured at wet end pH>7.0), and wood containing papers (normally acidic, manufactured at wet end pH<7.0). [0014] Further, it would often be advantageous to provide a method and apparatus, including equipment design, and process equipment configuration that produces both purified precipitated calcium carbonate and purified calcium silicate hydrates utilizing, at least in part, common process reactors. [0015] Moreover, it would often be useful to provide an improved, purified precipitated calcium carbonate product that can be utilized in paper to improve brightness, opacity, and bulk. [0016] Further, in many applications, it would be useful to provide an improved, purified multiphase calcium silicate hydrate that, when used in the manufacture of paper will: [0017] Improve opacity over precipitated calcium carbonates; [0018] Improve scattering power over precipitated calcium carbonates; [0019] Improve brightness over precipitated calcium carbonates; [0020] Improve sheet caliper over precipitated calcium carbonates; [0021] Improve sheet bulk over precipitated calcium carbonates; [0022] Improve sheet stiffness over precipitated calcium carbonates; [0023] Improve sheet porosity over precipitated calcium carbonates; [0024] Improve surface smoothness over precipitated calcium carbonates; [0025] Improve sheet tensile over precipitated calcium carbonates; [0026] Improve sheet formation over precipitated calcium carbonates; [0027] Improve the intrinsic sheet water and oil absorption over precipitated calcium carbonates; [0028] Improve print quality over paper filled with precipitated calcium carbonates; [0029] Reduce print show through over paper filled with precipitated calcium carbonates; [0030] Finally, in spite of a myriad of prior art attempts at providing acid stable precipitated calcium carbonate compositions, there remain various paper manufacturing situations wherein a purified, acid resistant precipitated calcium carbonate composition would be advantageous in the manufacture of various paper grades. BRIEF DESCRIPTION OF THE DRAWING [0031] The present invention will be described by way of exemplary embodiments, some aspects of which are illustrated in the various accompanying drawing figures, in which like references denote similar elements, and in which: [0032] FIG. 1 is a brightness reversion curve, illustrating the loss of brightness as pH is increased, with respect to a particular grade of paper manufactured with 25% Kraft pulp and 75% wood containing fiber. Continue reading about Purified precipitated calcium carbonate and purified calcium silicate compounds, a method for their production, and their use as paper fillers... 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