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  Grinding methodUSPTO Application #: 20060106118Title: Grinding method Abstract: The invention provides a method of grinding an inorganic particulate material such as calcium carbonate or kaolin in an aqueous suspension, preferably at a solids level below about 50% by weight, wherein the aqueous suspension includes a sub-effective amount of a dispersing agent for the inorganic particulate material. (end of abstract)
Agent: Finnegan, Henderson, Farabow, Garrett & Dunner LLP - Washington, DC, US Inventors: John Claude Husband, Nigel V. Jarvis, Charles Desmond Payton, David Robert Skuse USPTO Applicaton #: 20060106118 - Class: 516078000 (USPTO) Related Patent Categories: Colloid Systems And Wetting Agents; Subcombinations Thereof; Processes Of, Continuous Liquid Or Supercritical Phase: Colloid Systems; Compositions An Agent For Making Or Stabilizing Colloid Systems; Processes Of Making Or Stabilizing Colloid Systems; Processes Of Preparing The Compositions (e.g., Micelle; Thickening Agent; Protective Colloid Agent; Composition Containing An Emulsifying Agent With No Dispersant Disclosed; Organic Liquid Emulsified In Anhydrous Hf), Aqueous Continuous Liquid Phase And Discontinuous Phase Primarily Solid (e.g., Water Based Suspensions, Dispersions, Or Certain Sols*, Of Natural Or Synthetic Ester-wax, Beeswax, Carnauba Wax; Or Latex Dispersion), The Solid Is Primarily Inorganic Material (e.g., Mercurous Halide) The Patent Description & Claims data below is from USPTO Patent Application 20060106118. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] This invention relates to a method of grinding an aqueous suspension of an inorganic particulate material and to products obtained thereby. BACKGROUND OF THE INVENTION [0002] Aqueous suspensions containing inorganic particulate material, for example an alkaline earth metal (e.g. calcium) carbonate or kaolin, are used widely in a number of applications. These include, for example, the production of pigment or filler containing compositions which may be used in paper manufacture or paper coating, and the production of filled compositions for paints, plastics and the like. [0003] The inorganic particulate material typically has a known particle size distribution (psd), dictated by the intended end use in ways which are well known in the art. Generally, the required psd is obtained by a method which includes grinding the inorganic particulate material in an aqueous suspension. The suspension may contain a high (e.g. above about 50% by weight) or low (e.g. below about 50% by weight) content of the inorganic particulate solids. [0004] Where the aqueous suspension has a high solids content, it is necessary to disperse the inorganic particulate material using an effective amount of a dispersing or deflocculating agent (dispersant). High solids grinding typically produces a relatively high proportion of ultra-fine particles (e.g. having an equivalent spherical diameter smaller than about 0.25 .mu.m. To maintain an acceptably low viscosity of the suspension, one either needs to use relatively high levels of common dispersants, or lower levels of specialized--and thus relatively expensive--dispersants. [0005] Where the aqueous suspension has a low solids content, a dispersant can be avoided. This enables the suspension to be dewatered cost-effectively, but problems can be encountered when mixing dispersant into the suspension later. [0006] It is often desirable to produce a product which has a "steep" psd, in the sense that a large proportion of the particles are within a narrow size range. As used herein, a "steep" psd refers to a steepness factor greater than about 35, more particularly above about 40, steepness factor being defined as the ratio of the d.sub.30 equivalent spherical diameter (at which 30% by weight of the particles are finer) to the d.sub.70 equivalent spherical diameter (at which 70% by weight of the particles are finer), multiplied by 100. [0007] In order to obtain this desired steepness, it is the present practice to grind the aqueous suspension at low solids in order to minimize the formation of ultra-fine particles. It is also desirable to perform the grinding stage in the absence of any dispersant in order to maintain a flocculated or aggregated state and so facilitate subsequent flocculated dewatering. In some cases, effective amounts of specialized dispersants are added to the dewatered, relatively high solids, suspension, to minimize flocculation and provide an acceptable viscosity for handling at that stage. It is also common practice to recirculate the water removed at the dewatering stage, to dilute the fresh feed. However, a number of problems can arise. For example, there can a significant loss in brightness (discoloration) due to corrosion products (e.g. iron-based corrosion products) from the system piping and equipment. Typically brightness values can be reduced by about 2-3 ISO units lower, with yellowness values about 1-2 ISO units higher. This discoloration is probably exacerbated in the low solids method, because the recirculated water becomes relatively highly aerated. Moreover, it can be difficult to introduce the dispersants in effective amounts at the high solids stages. In addition, the use of specialized dispersants can result in materials which may then not be compatible in mixtures with materials including conventional dispersants such as polyacrylates. [0008] The present invention aims to go at least some way towards overcoming the above problems, or at least to provide an acceptable alternative method of grinding an aqueous suspension of an inorganic particulate material. BRIEF DESCRIPTION OF THE INVENTION [0009] The present invention is based on the finding that the problems referred to above can be alleviated by performing the grinding of an inorganic particulate material in an aqueous suspension which includes a very small amount of a dispersant. [0010] In accordance with a first aspect of the present invention, there is provided a method of grinding an inorganic particulate material in an aqueous suspension, wherein the said aqueous suspension includes a sub-effective amount of a dispersant for the inorganic particulate material. The term "sub-effective" means that the dispersant is present in a finite amount, but that amount is not sufficient to give rise to deflocculation of the particulate inorganic material, so that the flocculation characteristics of the suspension are substantially the same as would be found in the complete absence of any dispersant. Such an amount of the dispersant may typically be up to about 0.25% by weight, based on the weight of dry inorganic particulate, for example up to about 0.15% by weight, e.g. up to about 0.1% by weight. [0011] In accordance with a second aspect of the present invention, there is provided a method of grinding an aqueous suspension of a particulate inorganic material to obtain a particulate inorganic material of reduced particle size and increased steepness, wherein the grinding is carried out in the presence in the aqueous suspension of a sub-effective amount of a dispersant for the inorganic particulate material. [0012] The method may, for example, be used in the grinding of an inorganic particulate material at a low solids level in the suspension, e.g. the amount of the inorganic particulate solids being less than about 50% by weight, based on the total weight of the suspension. [0013] The method preferably further comprises grinding the inorganic particulate material under grinding conditions such as to raise the steepness of the inorganic particulate material to a steepness factor above about 35, more particularly above about 40, for example above about 45. [0014] The method preferably further comprises dewatering the aqueous suspension to raise the solids content thereof, more preferably to a content of inorganic particulate material above about 50% by weight, based on the total weight of the suspension. [0015] In accordance with a third aspect of the present invention, there is provided an aqueous suspension of a ground particulate inorganic material comprising a sub-effective amount of a dispersant for the inorganic particulate material. The aqueous suspension may suitably be prepared by a grinding method according to the first or second aspect of the present invention. The particulate inorganic material suitably has a steepness factor above about 35, more particularly above about 40, for example above about 45. The dispersant is suitably present in the aqueous suspension in an amount up to about 0.25% by weight, based on the weight of dry inorganic particulate, for example up to about 0.15% by weight, e.g. up to about 0.1% by weight. The aqueous suspension may be at a high or low solids content. [0016] In accordance with a fourth aspect of the present invention, there is provided an aqueous suspension of a ground inorganic particulate material comprising a dispersant-effective amount of a dispersant for the inorganic particulate material, when prepared by a method according to the first or second aspect of the present invention and which includes the addition, after grinding, of an amount of a dispersant to the aqueous suspension. [0017] In accordance with a fifth aspect of the present invention, there is provided a dry ground inorganic particulate material comprising an amount of a dispersant for the inorganic particulate material, the material being the dry residue of an aqueous suspension according to the third or fourth aspect of the present invention. [0018] In accordance with a sixth aspect of the present invention, there is provided the use of a sub-effective amount of a dispersant as a corrosion inhibitor in a low solids aqueous suspension of an inorganic particulate material. DETAILED DESCRIPTION OF THE INVENTION The Inorganic Particulate Material [0019] The inorganic particulate material may, for example, be an alkaline earth metal carbonate such as calcium carbonate, a hydrous kandite clay such as kaolin or ball clay, an anhydrous (calcined) kandite clay such as metakaolin or fully calcined kaolin, wollanstonite, bauxite, talc, mica, titanium dioxide, silicon dioxide or carbon. Continue reading... Full patent description for Grinding method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Grinding method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Grinding method or other areas of interest. ### Previous Patent Application: Compound and method for prevention and/or treatment of vaginal infections Next Patent Application: Novel integration for co and h2 recovery in gas to liquid processes Industry Class: Colloid systems and wetting agents; subcombinations thereof; processes of ### FreshPatents.com Support Thank you for viewing the Grinding method patent info. IP-related news and info Results in 1.24615 seconds Other interesting Feshpatents.com categories: Electronics: Semiconductor , Audio , Illumination , Connectors , Crypto , |
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