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  Electro-static dissipative ceramic products and methodsUSPTO Application #: 20060014627Title: Electro-static dissipative ceramic products and methods Abstract: The invention provides partially stabilised zirconia and alumina based electro-static dissipative or ESD ceramic compositions. The proposed ceramic compositions include specific amounts of dopants comprising one or more metal oxides selected from iron oxide, chromium oxide and titanium oxide. The proposed ESD ceramic materials are made into useful industrial products by injection moulding and sintering technology. A novel binder system may optionally be used to make injection mouldable feedstock. Useful products produced by the invention include, for example, ESD ceramic tweezers tips, ESD ceramic dispensing needles, ESD ceramic scissors and blades and ESD ceramic wire bonding capillaries which retain their ESD properties at relatively low temperatures, for example, service temperatures from 25 to 500° C. (end of abstract) Agent: Albert Wai-kit Chan Law Offices Of Albert Wai-kit Chan, LLC - Whitestone, NY, US Inventors: Jian Guo Zhang, Hwey Eng Liow, Bo Zhang USPTO Applicaton #: 20060014627 - Class: 501103000 (USPTO) Related Patent Categories: Compositions: Ceramic, Ceramic Compositions, Refractory, Zirconium Compound Containing, Zirconium Oxide The Patent Description & Claims data below is from USPTO Patent Application 20060014627. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention pertains to low resistivity or semi-conductive ceramic materials, methods of making them and their applications. Specifically, the invention relates to new ceramic materials in which the electrical surface resistivity is controlled to be within a range that allows for the fabrication of useful articles that absorb and dissipate electrostatic charges. Such articles include injection moulded and sintered electro-static dissipative (ESD) and/or antistatic tools, such as tweezers, scissors, dispensing needles and wire bonding capillaries. BACKGROUND OF THE INVENTION [0002] Currently on the market ESD products are dominantly those made of ESD plastic materials. These are basically polymer based composite materials with conductive fillers such as carbon and/or metal powders or fibres at various amounts, generally around 20-30 wt %, depending on the required conductivity and density of the fillers. Polymer based composites are generally injection moulded to form specific parts or products. U.S. Pat. No. 5,409,968 illustrates such a material used as an ESD material. This group of plastic composite materials has limited applications owing to its limited intrinsic mechanical performance, heat resistance and chemical resistance. [0003] Efforts have been reported over the past twenty years with regards to the development of functional ceramic materials and ESD ceramic materials. It is known that by adding conductive materials it is possible to make a ceramic based ESD composite. U.S. Pat. No. 4,866,016 depicts aluminium oxide, titanium oxide and tin oxide composite based ceramics with additives of tantalum oxide, forming a useful dielectric material. U.S. Pat. No. 5,830,819 reports an alumina based ceramic sintered product, with additions of multiple oxides including manganese oxide, iron oxide and niobium oxide, having ESD and antistatic properties, with volume resistivity varying from 1.times.10.sup.7 to 1.times.10.sup.13 ohm-cm and an absolute value of the temperature coefficient of volume resistivity of not larger than 1.8%/degree C. at 25 to 75.degree. C. More recently, U.S. Pat. No. 6,136,232 describes an ESD ceramic material comprising stabilised zirconia with additions of lanthanum chromate. These inventions provide materials with limited performance particularly at lower temperatures, and complicated compositions. They are difficult to make and process, with certain additives being cost prohibitive and toxic in practical commercial applications. The prior art also presents U.S. Pat. No. 4,110,260. That patent teaches electroconductive composite ceramics composed of an independent phase of conglomerates having a specific particle diameter of at lease 20.mu. and also 2-50% by weight of a continuous phase of an electroconductive substance. The present invention does not rely on the addition of any electroconductive substance or electroconductive phase. U.S. Pat. No. 4,931,214 shows ceramic bodies with electronic conductivity for use in oxygen concentration cells, oxygen probes, fuel cells and electrolysis cells. Unlike the present invention, that patent teaches nothing about ESD bonding capillaries, tweezers or anti-static tools and the like and also relies on relatively exotic dopant oxides of metals from Groups Va and VIa of the Periodic System of Elements. U.S. Pat. No. 6,354,479 teaches the fabrication of capillary bonding tips in broad terms but fails to teach either the specific compositions or the specific heat treatment steps or fabrication steps which are disclosed in this specification. In addition, that patent teaches elaborate machining and manufacturing processes which are obviated by the techniques taught in this disclosure. [0004] In the prior art, the electro-conductivity or electro-static dissipativeness of the composite is obtained through the connectivity of the second phase within the base matrix, where the base material is insulative and the second phase is usually a conductive material. By adjusting the appropriate volume percentage of the second phase fillers, the composite can be made electro-conductive or ESD or antistatic. Because the material is a composite, non-uniform dispersions and/or agglomerations of the second phases render so-called hot-spots in the material, which are undesirable for ESD applications. OBJECTS AND SUMMARY OF THE INVENTION [0005] It is an object of the present invention to provide simple ESD ceramic material compositions and processes for manufacturing them, which compositions can be used at temperatures from 25 to 500.degree. C. without degradation of their required properties. [0006] It is another object of the present invention to provide a novel and specific binder system, for use with the above referenced compositions, which enable the ESD ceramic materials to be made into products using injection moulding and sintering. [0007] Accordingly, the present invention provides that all raw materials are ceramic powders and they are insulative at the beginning of the process. There are no conductive phases or materials added to the insulative base ceramic materials. The electro-static dissipative properties are obtained through the interaction of the base and added oxides under the controlled process conditions, creating an oxygen deficiency within the matrix. This results in the second phase being totally "dissolved" in the base material, producing a new non-stoichiometric compound, which has metallic interstitial atoms, which lead to n-type of electrical conductivity. DETAILED DESCRIPTION OF THE INVENTION [0008] Electrostatic discharge has a considerable destructive potential during the manufacturing of disc-drives, micro-electronics, semiconductor devices and generally in the telecommunications device manufacturing industries. Control over electro-static discharge is of the utmost importance in these types of manufacturing operations. Manufacturers thus provide ESD wire bonding capillaries, tweezers, scissors, dispensing needles, pushing rods, and so on as means for controlling unintentional high voltage discharges. It will be understood that tools of this type are expected to be electrically dissipative, having rates of conductivity which are sufficient to prevent charge accumulation yet incapable of overloading the very devices being bonded or otherwise handled. In addition manufactured ESD tools and articles are often expected to be very stiff, wear resistant, clean and chemically inert. [0009] The doping of ceramic compositions is seen in the prior art as a solution to the problem of manufacturing of ceramic articles with adequate conductivity, particularly at high temperatures such as 800-1000.degree. C. In contrast, ESD ceramics are required not just to demonstrate conductivity, but controlled rates of conductivity, particularly at lower temperatures such as 25-500.degree. C. [0010] Having regard for the above referenced considerations, the disclosure of the present invention now teaches novel ESD ceramic materials and processes for their fabrication based on either or both partially stabilised zirconia and pure alumina. In some preferred embodiments, compositional economy and simplicity are attained by requiring just one addition of a metal oxide at 2-25 wt %. This allows for the first time, blending of readily available ceramic non-conductive powders together for application in injection moulding process technology. Binders and undesirable processing agents are then conveniently removed before sintering in air or in a reducing atmosphere and/or in a vacuum. When sintering is done in air, a favourable heat treatment follows. The instant disclosure provides a specific and novel binder system especially for the said ESD ceramic materials, enabling the successful production of the said products free from defects, without compromising their mechanical property requirements. It will be understood that while this binder is both new and useful, it is not absolutely essential to the practice or application of the invention. [0011] In accordance with the present invention, and as shown in Table 1 there is provided partially stabilised zirconia based ESD ceramic compositions A and B, and pure alumina based ESD ceramic compositions C and D. TABLE-US-00001 TABLE 1 Zirconia and alumina based ESD ceramic compositions Metal Zirconium Aluminium oxide Composition Description oxide oxide dopant A (wt %) Zirconia 80-98 0 2-20 based B (wt %) Strengthened 70-85 5-25 10-25 zirconia based C (wt %) Alumina 0 80-95 5-20 based D (wt %) Toughened 5-25 65-85 10-25 alumina based [0012] According to the first aspect of the present invention, a dopant oxide at a quantity of 2-25 wt % is admixed with a pure alumina, or a partially stabilised zirconia (stabilised with preferably 5.2 wt % of yttria), or a toughened alumina (toughened with 5-25 wt % partially stabilised zirconia), or a strengthened zirconia (strengthened with 5-25 wt % of pure alumina) producing alumina based ceramic ESD compositions and zirconia based ceramic ESD compositions. The zirconia based ESD ceramic compositions contain 80-98 wt % zirconia partially stabilised with preferably 5.2 wt % of yttria and 2-20 wt % of dopants. Said dopants consist of at least one (and preferably one) metal oxide selected from oxides including iron oxide, chromium oxide and titanium oxide. The strengthened zirconia based ESD ceramic compositions contain 70-85 wt % zirconia partially stabilised with preferably 5.2 wt % of yttria (strengthened with 5-25 wt % of pure alumina) and 10-25% by weight of dopants. Said dopants consist of at least one (and preferably one) metal oxide selected from oxides including iron oxide, chromium oxide and titanium oxide. The alumina based ESD ceramic compositions contain 80-95 wt % pure alumina (purity >99.95%) and 5-20% by weight of dopants. Said dopants consist of at least one (and preferably one) metal oxide selected from oxides including iron oxide, chromium oxide and titanium oxide. The toughened alumina based ESD ceramic compositions contain 65-85 wt % pure alumina (purity >99.95%, toughened with 5-25 wt % partially stabilised zirconia) and 10-25% by weight of dopants. Said dopants consist of at least one (and preferably one) metal oxide selected from oxides including iron oxide, chromium oxide and titanium oxide. [0013] Further to another aspect of the present invention, the ESD ceramic compositions disclosed above are applied to injection moulding process by blending the dry powdered oxide ceramic ingredients with a novel (but non-essential) binder system. The preferred binder system comprises a composition of thermal degradable polymers, polyolefin, surfactants and waxes, specifically the said polymers are high density polyethylene (HDPE) and ethylene vinyl alcohol (EVA), in the range of 40-70 wt %. Said polyolefin includes peanut oil, vegetable oil, or fish oil, in the range of 0-10 wt %, more preferably 2-10 wt %. Said surfactant is stearic acid, in the range of 1-10 wt %, more preferably 1-5 wt %. The preferred waxes are polyethylene wax, paraffin wax, and bee wax and the like, in the range of 25-50 wt %. The ESD compositions and the binder components are mixed under heat and vacuum to produce injection mouldable feedstock. [0014] The method for the invention proceeds generally as follows. The ESD ceramic materials are mixed sufficiently and uniformly using attrition mill. Thereafter, the mixed ESD ceramic materials are mixed with the binder system under vacuum of about 10.sup.-2 torr using a planetary kneading mixer. The feedstock produced is made into useful industrial products using injection moulding and sintering. The sintering is done in air or in a vacuum of about 1 to 10.sup.-2 torr or in a reducing atmosphere, heating to 1300 to 1600.degree. C. and holding for 1 to 4 hours followed by controlled cooling down to below 1000.degree. C. then followed by natural furnace cooling. In sintering in air, a heat treatment of about 1000.degree. C. in hydrogen (reducing atmosphere) or in a vacuum of about 1 to 10.sup.-2 torr and holding for 1 to 3 hours before cooling down naturally also in a hydrogen reducing atmosphere or in a vacuum of about 1 to 10.sup.-2 torr to room temperature. In sintering in a vacuum or in a reducing atmosphere, the said after heat treatment is not required. [0015] According to another aspect of the present invention, the said ESD ceramic materials are made into useful industrial products using powder injection moulding technology. The said products include ESD ceramic tweezers tips; ESD ceramic scissors blades; ESD ceramic dispensing needles and ESD ceramic wire bonding capillaries. The said ESD ceramic tweezers tips are made of 80-90 wt % of yttria partially stabilised zirconia and 10-20 wt % of titania (purity >99.9%), formed using injection moulding and sintering, ideally having electrical surface resistivity in the range of 3.times.10.sup.6 to 8.times.10.sup.9 ohm/square at 10V and 100V of applied voltages; static decay time of <1.0 s from +/-1000V to +/-10V and discharge current at 500V being <10 mA. The said ESD ceramic dispensing needles are made of 85-95 wt % of yttria partially stabilised zirconia and 5-15 wt % of titania (purity >99.9%), formed using injection moulding and sintering, having electrical surface resistivity in the range of 2.times.10.sup.7 to 9.times.10.sup.9 ohm/square at 10V and 100V of applied voltages. The said ESD ceramic scissors blades are made of 80-90 wt % of strengthened zirconia (strengthened with 5-20 wt % of pure alumina) and 10-20 wt % of titania (purity >99.9%), formed using injection moulding and sintering, having electrical surface resistivity in the range of 5.times.10.sup.6 to 9.times.10.sup.9 ohm/square at 10V and 100V of applied voltages. The said ESD ceramic wire bonding capillaries are made of 80-95 wt % of toughened alumina (purity >99.95%, toughened with 5-25 wt % of yttria partially stabilised zirconia) and 5-20 wt % of titania (purity >99.9%), formed using injection moulding and sintering and finishing, having electrical surface resistivity in the range of 6.times.10.sup.6 to 8.times.10.sup.9 ohm/square at 10V and 100V of applied voltages, which remains unchanged when subjecting to service temperatures from 25 to 500.degree. C. [0016] Unless defined otherwise all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. [0017] The present invention is hereinafter described specifically by way of Examples. The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the present invention, and are not intended to limit the scope of what is regarded as the invention nor are they intended to represent that the experiments below are all and only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight and temperature is in degrees Celsius. EXAMPLES Example 1 [0018] The partially stabilised zirconia (with 5.2 wt % yttria) and titania powders obtained commercially were weighed according to the weight ratios as defined in Table 2. TABLE-US-00002 TABLE 2 Composition 1- zirconia based ESD ceramic composition for Example 1 zirconia titania Composition 1 80-90 wt % 10-20 wt % Continue reading... Full patent description for Electro-static dissipative ceramic products and methods Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electro-static dissipative ceramic products and methods 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. 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