Continuous coatings are prepared using novel two part compositions and methods. The two part compositions of the invention comprise, in separate containers, a powder polymer composition and a coalescing agent. The powder composition has preferred particle size distribution and composition for use in the compositions or methods of the invention. The coalescing agents of the invention cooperate with the powder part to result in a excellent finish having the appropriate drying hardness, durability, etc. The novel method of the invention involves contacting a coalescing agent with polymer particles in a variety of coating methods. The particles and the coalescing agent interact to form a continuous coating layer or finish layer. The basic coating formation methods of the invention can be embodied in a number of methods or protocols including applying a solid polymer to the liquid coalescing agent, applying the agent to the polymer particulate or applying the liquid and polymer simultaneously. In any protocol, a desirable floor finish can be easily formed. This invention is particularly suitable for a floor finish composition.

The invention relates to compositions and methods used in the formation of a polymer coating from a polymer particulate. The coatings of the invention can be made in a uniform continuous structure. Further, floor finishes having appropriate predetermined properties such as hardness, thickness, resiliency, and integrity can be made. One aspect of the invention is a two part coating system. A second aspect of the invention is a method for forming the polymer coating of the invention using the two part system and a number of distinct coating forming protocols. Another aspect of the invention is a floor finish system that results in substantial labor savings.
Coating compositions are generally well known and have been formulated using a variety of technologies such as solvent based, aqueous liquid and powder systems. Powder coatings have been electrostatically applied to hard surfaces such as metals and then baked into a hard resistant finish. Reactive liquid coatings have been made by combining reactive materials (such as reactive isocyanates, ethylenically unsaturated reactive systems, reactive epoxy systems, etc.). Such systems have been applied to surfaces and then reacted to form a crosslinked hard surface. Further, coatings have been formed by dissolving typically polymeric materials in organic solvents at a solids concentration of about 10 to 50 wt.- %. Such solutions are applied and the solvent borne materials dry to a hard surface by the evaporation the solvent leaving a polymer coating. In order to increase the add-on of polymeric solids, polymer materials have been dispersed in aqueous media to form finish compositions. Lastly, aqueous technologies are used with active materials at concentrations typically higher than solvent systems. Such aqueous dispersions have been applied to surfaces for the purposes of forming a finish layer by serial application and evaporation of the water. Once the water is removed, the polymer materials form a useful film typically in a multi-coating layer. Solvent or aqueous based systems typically leave a residue of the medium in the coating.
Typical compositions and methods include those in Michio et al., Japanese Patent No. 92243309A. Michio et al. teach a aqueous/solvent coating composition for floors comprising a polymeric material combined with an ether solvent material adapted for reduced odor. Feigin, U.S. Pat. No. 4,131,585, teaches a polyether leveling agent adapted for use in aqueous self-polishing, dry bright coating compositions. Hacket et al., U.S. Pat. Nos. 4,363,835 and 4,704,429 and Zdanowski et al., U.S. Pat. No. 4,517,330, teach a method of forming floor finishes by applying an aqueous dispersion of polymer and materials and then dry buffing the resulting coating at high temperature to either fuse or crosslink the waxy or reactive coating composition. Bolgiano et al., U.S. Pat. No. 4,421,782, teach the formation of a coating from an aqueous system which after drying is radiation cured into a hard tough surface. Craven, U.S. Pat. No. 3,776,752, teaches compositions and methods for finishing surfaces. The method comprises applying a solvent dispersion of a polymer coating material, drying the applied material to form a coating and then forming the resulting coating with a finishing agent. Such finishing agents disclosed by Craven include typical plasticizing compositions. Lovell, Canadian Patent No. 717,495 (U.K. Patent No. 930,919), teaches the application of an organosol polish composition. Lovell discloses that the organosol material, when cosprayed with a solvent material, forms a combined coating which dries to a hard floor surface. Lewis et al., U.S. Pat. No. 4,168,255, and Gehman et al., U.S. Pat. No. 4,017,662, teach a polishing method involving the application of an aqueous coating composition containing a polymer material and finish forming agents. The polymeric materials combine with the agents as the aqueous material evaporates leaving a hard floor finish. Berrido, U.S. Pat. No. 4,747,880, teaches a dry granular floor care product. The dry granular material is formulated such that it can be combined with water to form an aqueous solution or dispersion which can be applied to form a clean shiny appearance after drying.
The prior art coating technology involves heat melted or fused coatings, reactive crosslinking coatings, or coatings that rely on a carrier liquid, an evaporating liquid aqueous or solvent medium for film formation. Such media involve solvents which must evaporate upon application to initiate coalescing the finish layer. Further the prior art aqueous compositions typically require two or more applications to form a finished surface having two or more distinct layers for a complete floor treatment. The typical applications of coatings to floors, walls, ceilings and other environmental hard surfaces can involve rolling, mopping, spray coating and other conventional methods. A combination of a resin, solvent (aqueous or organic), diluent, additives and pigment can be used. A survey of conventional coating composition and techniques is shown in Kirk-Othmer Concise Encyclopedia of Chemical Technology, Fourth Edition, Wiley Interscience Publications, pp. 469-482 (John Wiley and Sons, Inc. 1999).
A need exists for floor coating systems that can be used with minimal labor in forming a reliable coating with as little as one application of the coating system. The coating systems of the invention can be used without substantial heat input for curing or a substantial proportion of an organic carrier solvent or an aqueous medium.
We have found a two-part system that can be used in a method for forming a continuous hard durable coating on virtually any surface. The two-part system comprises a polymer first part in the form of a finely divided flowable powder or particulate that can be delivered to a surface without an aqueous or organic solvent or other carrier liquid. The second part is a liquid part comprising a liquid coalescent or coalescing agent. In use, the parts are combined on the floor surface or as they are being delivered to the floor surface. The coalescing agent causes the polymer powder uniformly distributed in a finely divided state to coalesce and form a uniform film or coating within a short time after it came in contact with the coalescent. The materials can be applied in one of three application regimens we have defined to date, others may be developed and used. The powder can be uniformly placed on a target surface first followed by a careful uniform application of the coalescing agent. Second, the coalescing agent can be placed on the target surface followed by a careful uniform application of the powder particle. Lastly, the materials can be formed into a fine dispersion of the material in air, combined in an application device and simultaneously delivered to the surface. In such a process, the powder and coalescing agent can be atomized in separate atomizers and combined after atomization to form a spray of the final coating components.
One important application of the coating technology of this invention is to form hard, uniform coatings with regular thickness and integrity on floors. These coatings are typically 1 to 20 microns, preferably 3 to 12 microns, most preferably 4 to 10 thickness. The floor finishes can have properties such as hardness, thickness, resiliency, integrity and wear resistance that meet or exceed requirements of current floor finish technology. Two or more coatings can be made if each coating provides a unique property. Layers of different hardness can be used. A first layer can be formed from a colored layer with a second uncolored clear layer. A first layer can be used with a second layer having a COF additive or biocide. A first acrylic layer can be used with a second urethane layer.
Floor surfaces that can be treated include installed floors, uninstalled sheet vinyl or uninstalled flooring units. The coatings can be applied during manufacture of the flooring as one of the final steps in manufacture, can be applied to the flooring at an installation site just prior to installation, can be applied to the floor after installation or during routine maintenance. The primary substrates or supports for conventional coating systems include paper and paperboard, polymer films such as polyethylene, polyethylene terephthalate, metal foils, woven and non-woven fabrics, fibers, metal coils and a variety of environmental surfaces including floors, walls, ceilings, hard surfaces, exterior walls and other rough, curved or flat surfaces. Each of these kinds of surfaces utilizes coating compositions and methods adapted for each coating environment. Many coating processes are used in the industry including methods that create single and multiple layers. The precision and uniformity of the coating is important for consistent coverage, uniform appearance and wear properties.
For the purpose of this patent application, the term xe2x80x9ccoatingxe2x80x9d refers to a single or multiple coating of a polymer material in a substantially uniform layer. In this application uniform indicates the thickness does not vary more than about xc2x13 microns, preferably xc2x12 microns, from place to place in the coating. Such a coating can be applied under factory conditions or in the field. The term xe2x80x9cfloor finishxe2x80x9d typically connotes a floor coating having a thickness of greater than 1 micron but typically less than 12 microns, preferably less than 5, microns having a single layer formed from the coalesced distribution of the polymer particles. Such floor finishes can be applied during floor tile manufacture or at a building location. Traditional floor finish methods use multiple (typically 4 or 5) applications of the finish forming liquid to result in a multi-layer or laminate structure. Each layer typically have a thickness less than 2 microns, often as little as 1 micron. The technology of the invention, however, can be used to form multiple layers. The term xe2x80x9cpolymer particlexe2x80x9d typically connotes a polymer material typically made by polymerizing ethylenically unsaturated monomers and then comminuting such a polymeric material into a particle or particulate collection. The particles in the particulate can have a major dimension less than about 40 microns, preferably less than about 25 microns but preferably greater than about 10 microns. The term xe2x80x9ccoalescing agentxe2x80x9d typically connotes an organic or silicone liquid material that causes the polymer particle to coalesce into a single layer floor finish film having a dimension greater than about 1 micron but less than about 12 microns. Such coalescing agents are materials that can cause the polymer particles to flow of fuse into a continuous layer before evaporation and are typically organic materials with a relatively low VOC (volatile organic compound content), typically less than about 10 mm-Hg preferably less than 5 mm-Hg, often less than 1 mm-Hg. More volatile, higher VOC coalescing agents can be used in a factory location where dying speed is important. In such locations, higher VOC coalescing agents can be recovered and recycled during coating operations. The more volatile solvent coating media carrier materials typically have a VOC greater than 20 mm-Hg and more 25 to 80 mm-Hg. A coalescing agent can be identified as a coalescing agent using the following procedure. The polymer floor finish particulate or powder material can be placed on a surface of a glass dish or microscope slide. About 0.5 grams, or less, sufficient to thinly cover the glass surface, of the slide or dish is used. Onto the particulate or powder is added about an equal amount by weight of a candidate coalescing agent. The test or candidate coalescing agent can be lightly sprayed or added drop-wise to the polymer powder and lightly mixed to form a uniform glaze of the wetted polymer. Visual and microscopic observations will confirm if the candidate coalescing agent can form a coating. The coating should be formed within about 30 minutes, preferably less than 5 minutes.
The coating compositions of the invention can be used to form a finish on an individual flooring unit. A flooring unit is defined as sheet vinyl with a defined width and an optional or indeterminate length, a single uninstalled quarry tile, composite tile, vinyl tile, wooden flooring component such as pine strips or oak strips having milled tongue and groove installation components and other common stone, thermoplastic, linoleum, wood flooring components, etc. Such flooring units are designed to be delivered to an installation site and individually installed onto a rough floor or subfloor surface using adhesive compositions, mastic, metallic fasteners such as nails, wooden pegs, etc. Such flooring units are typically used to cover a rough floor or subfloor with a large number of units to form the final floor surface.
Each flooring unit can be covered with the compositions of the invention leasing a uniform continuous coating layer. The flooring unit can comprise sheet vinyl or an individual flooring unit that can have an area that range from about 5 to 2000 cm2, more commonly 10 to 1000 cm2. The most typical flooring unit comprises vinyl flooring made in the form of large rolled sheets with a width of 2 meters to 5 meters and an indeterminate length, about 5 to 6 cm2. ceramic tile, a about 15 cm by 15 cm vinyl tile, a quarry tile having dimensions of from about 200 cm2 to 1000 cm2, flooring components having tongue and groove installation features that can have a width of from about 2 to about 20 cm and variable length from 25 inches to 350 cm. The surface area of each flooring unit can range from about 5 to about 5000 cm2., commonly 10 to 4000 cm2, commonly 20 to 1000 cm2. When used in forming a coating layer on a flooring unit, the coalescing agent and the polymer particulate are typical materials of the invention. However, the coalescing agent used in a factory formed floor finish on a flooring unit can be of higher volatility than typical coalescing agents used in field applications. Factory manufacture of coating units using higher volatility coalescing agents can involve processes in which the volatilized coalescing agents are recovered, recycled and reused in the application rendering the higher volatility less problematic than their use in field applications. Further, factory application of the coating compositions on flooring units can involve the use of relatively high heat flux of incident energy. Such high heat energy use can result in more rapid coating formation and more rapid evaporation of the coalescing agent from the finished floor unit. The use of the methods and compositions of the invention in coating flooring units involves coating one substantially planar surface of the flooring unit without applying a coating to an installation, surface of the flooring unit. In other words, the surface of the flooring unit that is used to attach the flooring unit either to the rough floor or subfloor or to other flooring units are preferably not coated with the compositions of the invention. However, the exposed surface of the flooring unit obtains a complete continuous uniform coating of the compositions of the invention.
The coatings and finishes of the invention appear to the eye be substantially identical in gross appearance and when conventionally tested have properties similar to those of the prior art. In the coatings of the invention, however, the microscopic structure of the inventive coatings of this invention appears to be substantially different. In practice, the coating layers can appear substantially different under cross-sectional microscopic examination. The prior art coating are typically made with four or more applications of the liquid coating material forming a layered structure. This is a result of the limits of the application methods. Each individual layer has a thickness controlled by the viscosity of the liquid coating mixture. Useful viscosity materials require several applications. A coating of this invention is typically a single uniform layer structure greater than 1 micron, but typically less than 20 microns in thickness.
The polymer particulate compositions of the invention are typically substantially free of liquid organic or aqueous media, however, the coalescing agent can contain some proportion of water or solvent but rarely has greater than about 10 wt % water based on the total amount of coalescing agent. Further, the polymer particles can contain some water as a matter of impurity or residue from water based polymerization techniques, however, the amount of water present in the polymer particulate is typically less than 10 wt % of the total polymer material. Certainly, little or no free or flowalble water is used as an aqueous medium or carrier liquid to carry either the coalescing agent or the polymer particle onto the floor surface. For the purpose of this patent application, the term xe2x80x9cfloor surfacexe2x80x9d typically relates to a ceramic, terrazzo, concrete, quarry tile, vinyl, linoleum, wood composite or other conventional floor surface material. The compositions of the invention are typically used to coat a large area of floor in a single step. Accordingly, the processes of the invention are typically used in coating more than about 100 cm2, preferably more than 0.9 m2, most preferably more than 10 m2, of floor surface area in a single step. Typically, the polymer and coalescent can be simultaneously applied to a surface. The compositions of the invention can also be applied using devices designed to cover 100 m2 of floor surface in a good amount of time. One of ordinary skill in the art will readily appreciate that the polymer particulate or the coalescing agent can be distributed over a relatively small or large area of floor followed by a careful application of the other part of the two-part coating systems. Such a coating technique is substantially different than the application of a solvent or aqueous based medium in which the combined one-part materials are applied typically using a mop to distribute the combined materials in a relatively small location in building up a continuous coating on the floor surface. Lastly, one of ordinary skill in the art will readily appreciate that there is a substantial difference between the form of the materials typically considered to be coatings in an aqueous media or coatings in an organic solvent media when compared to coating materials of the invention comprising a flowable powder polymeric composition and a liquid considered to be a coalescing agent. Solvents typically do not become involved in coalescing polymer particles into a final coating. Coalescing agents, however, are comparatively lower in volatility than solvents. Coalescents are intimately involved in penetrating polymer particles, causing the polymer to fuse or flow, leaving a coated surface as the coalescent evaporates. The resulting coating exhibits coverage, consistency and uniform coating properties. Commonly, solvents or other liquid carrier media evaporate without causing any important change in polymer properties. A coalescing agent operates to modify the polymer properties of a coating system during fusing and coating formation. A plasticizer is different than a coalescing agent because after a plasticizer is incorporated into a polymer it is an essentially permanent part of the formulation. A plasticizer results in a permanent change in polymer properties including Tg (glass transition temperature), rheology, tensile strength, film forming properties, etc. Lastly, the coatings of the invention are substantially free of aqueous or solvent residue in the coating layer.
The essential components of the compositions and methods of the invention can be found first in a powder particulate polymer part and second in a liquid coalescing agent part. The powder particulate polymer part typically comprises a flowable substantially dry particulate material made into a composition having a dimension of from about 3 to about 50 microns, preferably about 3 to about 15 microns. Often a blended particulate can have an advantage in friction or appearance. Such a blend can comprise a particulate with an average particle size of about 25 microns with a particulate of about 40 microns. The material is typically a dry, flowable, non-caking particulate. The polymer can be reduced to the desired particle size by spray drying from an emulsion or milled from a solid. Typically, the polymer particulate material of the invention are prepared by first polymerizing the material using conventional techniques such as those commonly employed in aqueous/solvent emulsion polymerization systems. The resulting product is then spray dried in conventional spray drying equipment to a dry polymer particle with the desired dimensions. Also, if the size of the polymer particles need adjusting to a reduced polymer particle size, the polymer can be comminuted in typical dry grinding/ball milling technology and then classified into particle sizes conventionally. The polymer materials are kept dry to a degree such that the polymer particulate material does not cake, but retains its free flowing characteristic. The polymer particles of the invention can be conventional coating polymers and can be made from a number of useful monomer materials and polymerization systems.
One advantage of the invention is that the coating powders useful in the practice of the invention can be prepared by non-conventional methods of preparing powders. Many critical properties of the coatings such as thickness, chargeability, fluidizing bed pressures, build thicknesses, percent overspray, etc., are determined by the shape, size, and size distribution of the powder. Conventional powders result from limited control over these parameters. The powders of the invention can be made by spray drying of coating powder composition or spray congealing of an atomized coating powder composition. The resulting product provides preferred particles with controlled size and narrow particle size distributions. These physical properties result in high powder transfer to a surface or substrate, and in uniform robust coatings.
Blends of monomers are used in a balanced ratios to obtain the desired glass transition temperature, hydrophobic/hydrophilic qualities, and in particular a desired minimum film forming temperature. Suitable monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, 3,5,5-trimethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate, isotridecyl acrylate, cetyl acrylate, octadecyl acrylate and n-butoxyethyl acrylate. Further n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylbutyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, 3,5,5-trimethylhexyl methacrylate, n-decyl methacrylate, n-dodecyl methacrylate, isotridecyl methacrylate, octadecyl methacrylate and butoxyethyl methacrylate, can be used. Further, tert-butyl acrylate or methacrylate, tert-amyl acrylate or methacrylate, 1,1-dimethylbutyl acrylate or methacrylate and 1,1-dimethylhexyl acrylate or methacrylate. Further, isobornyl acrylate or methacrylate, cyclohexyl acrylate or methacrylate, acrylate or methacrylate, and phenyl acrylate or methacrylate can be used. Further, methyl methacrylate, but also ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate and sec-butyl methacrylate can be used. Further, vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate, vinyl octanoate and vinyl 2-ethylhexanoate can be used. Further, styrene, xcex1-methylstyrene,2-, 3- or 4-vinyltoluene, 2,4-dimethylstyrene and l-phenylpropene. Further, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, citraconic acid, fumaric acid, maleic acid and maleic anhydride. Of these, acrylic acid and methacrylic acid are particularly suitable. Multifunctional hydrophilic monomers having at least one further functional group are monomers with amido groups, including N-substituted derivatives, such as alkoxyalkylamido- and alkylolamido(meth)acrylates, (meth)acrylamidoglycolic acid and esters and/or ethers thereof, with further olefinic double bonds, for example divinylbenzene, butanediol di(meth)acrylate or (meth)allyl(meth)acrylate, and with hydroxyl, amino, epoxy, oxazolinidyl, oxazinyl or ureido groups in the side chain. In an emulsion component, the cation M+is preferably ammonium, potassium or in particular sodium, but may also be lithium, trimethylammonium, triethylammonium, tri-n-butylammonium, tetra-n-butylammonium, triethanolammonium or triisopropanolammonium. Multifunctional monomers can be employed to crosslink polymer chains either through irreversible covalent bonding or through reversible coupling with divalent, trivalent, etc. metal ions. The polyvalent metal compound, if employed in the coatings, may be either a metal complex or a metal chelate. The polyvalent metal ions may be those of beryllium, cadmium, copper, calcium, magnesium, zinc, zirconium, barium, strontium, aluminum, bismuth, antimony, silver, lead, cobalt, iron, nickel or any other polyvalent metal or mixture thereof which can be added to the composition by means of an oxide, hydroxide, or basic, acidic, or neutral salt or complex or clathrate thereof which has appreciable solubility in water, such as at least about 1% by weight therein. The selection of polyvalent metal and the anion are governed by the solubility of the resultant meal complex in order. Zinc and cadmium are particularly preferred polyvalent metal ions. The ammonia and amine complexes (and especially those coordinated with NH3) of these metals are particularly useful. Amines capable of so complexing include morpholine, monoethanol amine, diethylaminoethanol, and ethylenediamine. Polyvalent metal complexes (salts) or organic acids that are capable of solubilization in an alkaline pH range may also be employed. Such anions as acetate, glutamates, formate, carbonate, salicylate, glycollate, octoate, benzoate, gluconate, oxalate and lactate are satisfactory. Polyvalent metal chelates where ligand is a bidentate amino acid such as glycine or alanine may also be employed. The polyvalent metal compound must be such that the metal is available to serve its crosslinking function, i.e., it is dissociable to form polyvalent metal-containing ions. Preferred polyvalent metal compounds, complexes and chelates include zinc acetate, cadmium acetate, zinc glycinate, cadmium glycinate, zinc carbonate, cadmium carbonate, zinc benzoate, zinc salicylate, zinc glycollate and cadmium glycollate. Although the polyvalent metal compound may be added to the polish composition in dry form such as a powder, it is preferred to first solubilize the polyvalent metal compound using a fugitive ligand such as ammonia. For purposes of this invention a ligand is considered fugitive if at least a portion of said ligand tends to volatilize under normal film forming conditions. Since the ammonia may complex with the polyvalent metal compound, a compound such as zinc glycinate, when solubilized in dilute aqueous ammonia solution, may be named zinc amine glycinate.
The polyvalent metal compound when used is employed in an amount so that the ratio of polyvalent metal to the xcex1,xcex2-ethylenically unsaturated acid of the addition polymer varies from about 0.05 to 0.5, and preferably from about 0.2 to 0.3. This is expressed as the ratio of metal, such as Zn++, to xe2x80x94COOH or xe2x80x94COONH4 groups, a ratio of 0.5 being stoichiometric.
The polymer particulate materials of the invention can be formulated in a particle having a dimension of from 3 to 50 microns, or other preferred particle size as are discussed herein, with other compatible materials that aid in coating, film or finish formation and/or characteristics. Such ingredients include cooperative polymer materials, plasticizers, waxes, small amounts of solvents or liquids that aid in particle formation but do not act as liquid media. The compositions can also include biocides, gloss agents, deglossing agents, matte forming agents, friction (TiO2, silica or other COF additives) modifiers and other additives common in coating formulations. Typical particulate formulations for the coating polymer is set forth in the following table. Further blending polymers with different Tg can have useful properties. Relatively higher Tg polymers can aid in forming regions of increased friction on the coating surface. Clearly film forming materials can be combined with both film forming and non-film forming materials. These materials can have a variety of particle sizes depending on desired properties.
Some polymers which would be useful are 60/40 MMA/MA, 55/40/5, MMA/MA/DMAM, 70/30 MMA/EA, 80/20 MMA/BA, 60/40 MMA/2EHA, 75/25 EMA/MA, 90/10 EMA/EA, 50/50 MMA/BMA, 88.5/715.5/88.5 MAA/Sty/AA. 60/39/1 MMA/MA/MAA, 34/28/25/5/8 MMA/BA/Sty/AN/MAA; wherein AA=Acrylic acid, MMA=Methyl methacrylate, MA=Methyl acrylate, EA=Ethyl acrylate, EMA=Ethyl methacrylate, AN=acrylonitrile, Sty=Styrene BA=Butyl acrylate, 2EHA=2-Ethylhexyl acrylate, BMA=Butyl ethacrylate, DMAM=Dimethylaminoethyl methacrylate and MAA=Methacrylic acid. Other Polymers include cellulosic types including cellulose acetate phthalate (CAP), cellulose acetate trimellitate (CAT), hydroxypropylmethyl cellulose phthalate (HPMCP), hydroxy propylmethyl cellulose acetate succinate (HPMCAS) and carboxymethylethyl cellulose (CMEC) vinyl types including polyvinyl alcohol acetate phthalate (PVAP) acryl types including copolymers of methacrylic acid and ethyl acrylate are used. Further, hydroxypropyl methylcellulose phthalate, cellulose acetate phthalate, methyl methacrylate/methacrylic acid copolymer, polyvinyl acetate phthalate, carboxymethyl ethylcellulose, polyvinyl alcohol phthalate, starch acetate phthalate cellulose acetate succinate, styrene/maleic acid copolymer, polyvinyl acetyl diethylaminoacetate, poly(dimethylaminoethyl methacrylate), benzylaminomethylcellulose, diethylaminomethylcellulose, benzylaminoethyl hydroxyethylcellulose, cellulose acetate diethylaminoacetate, cellulose acetate dibutylaminohydroxypropyl ether, sodium carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, polyvinyl alcohol, gelatin, polyvinylpyrrolidone, pyrrolidone/vinyl acetate copolymer, polyethylene glycol, hydroxypropyl methylcellulose, hydroxypropylcellulose, vinylpyrrolidone/vinyl acetate copolymer, ethylcellulose, methylvinylpyridine/methyl acrylate methacrylate copolymer, acetylcellulose, nitrocellulose, polyvinyl acetate, shellac and mixtures of two or more thereof are useful.
Blends of the addition copolymers may be used. The polymers may also be graft copolymers including grafts of the monomers mentioned on shellac. The copolymer containing acid groups may be soluble or dispersible in aqueous alkaline media having a pH from 7.0 to 11, usually at least 7.5, and preferably from about 8.0 to 9.5, the pH being adjusted to achieve a water clear appearance.
The second necessary component, a coalescing agent or coalescent, is necessary in the production of a coherent film layer from the polymer particles. The fugitive coalescent agent enables or promotes the film forming characteristics of the polymer particles in the coating compositions. The term fugitive means the material eventually evaporates or escapes the coating during or after film formation. Some small proportion of coalescent residue can remain in the layer. The fugitive material which are preferred are at least partially water soluble higher boiling (about 150xc2x0 to 200xc2x0 C.) monohydric and polyhydric alcohols; and monoalkyl and dialkyl ethers of glycols, diglycols ether alcohols, and polyglycols where alkyl is straight or branched and has from 1 to 5 carbon atoms. Examples of such fugitive materials include diglyme, 2-butoxyethanol, 3-methoxybutanol-1, the monomethyl, monoethyl and monobutyl ether of diethyleneglycol, dipropylene glycol or polypropylene glycols, ethylene glycol, propylene glycol and polypropylene glycols. An evaporative coalescent temporarily reduces the film formation temperature and softens the polymer particulate. This allows the particles to fuse and form a continuous film layer. The final properties of the polymer film layer are established or expressed as the coalescent evaporates from the particles. Additional energy could be added to the coating to aid in the removal of the coalescing agent. The coalescent is used with the polymer at an amount of about 0.2 to 2 or about 0.5 to 1 part by weight of the coalescent for each part of the polymer. Additive materials can be added to the coalescent liquid to enhance the coalescent action. Such additives reduce surface tension at the particle coalescent interface. Such materials may include minor amounts of low molecular weight or lower (a C1-6 linear or branched alcohol) or a surfactant.
A wide variety of materials capable of performing the aforementioned role in the film formation process. Some examples of liquids used in conjunction with acrylic based polymers include but are not limited to glycol ethers or ether alcohols, mono alkyl ether alcohols, etc. including diethylene glycol C1-6 mono- or dialkyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, dipropylene glycol methyl ether, tripropylene glycol ethyl ether, propylene glycol ethyl ether, glycol ether, triethylene glycol ethyl ether, etc. selected other coalescents can include texanol (isobutyrate), benzyl alcohol, 3-methoxybutanol-1. Examples of low volatility fugitive coalescents include the monomethyl, monoethyl and monobutyl ethers of diethylene glycol, triethylene glycol, dipropylene glycol and tripropylene glycol and also benzyl alcohol, isophorone and methoxybutanol.
A wide variety of materials can be used as a plasticizer. Any material that reduces the glass transition temperature can be defined as plasticizer. Plasticizers can enhance the properties of the polymer films and to ease their film formation. A plasticizer incorporates itself into the polymer matrix and permanently educes the polymer""s glass transition temperature. This obtains a reduction in the polymer hardness and an increase in the polymer flexibility. The plasticizer also aids in he film formation process. While permanent plasticizers are not necessary in the film formation process plasticizers can provide useful properties. The polymer materials of the invention can be combined with plasticizers in a variety of ways. When the polymeric materials are spray dried, the polymers can be combined with plasticizers in the aqueous or solvent form solution prior to spray drying. During spray drying, the permanent plasticizers can combine with the polymers in the final flow of particles. Alternatively, the plasticizer can be added to the polymer particles during comminution or during milling prior to classification of the polymer/plasticizer composition into the correct particle size. Other ways of combining plasticizer and polymer are known in the art and can be used to result in a combined polymer plasticizer flowable particle. Examples of non-fugitive permanent plasticizers are pure or mixed diesters of phthalic acid with benzyl alcohol, butanol, hexanol, 2-ethylhexanol, cyclohexanol or octanol as alcohol component, pure or mixed benzoic and fatty esters of monohydric or polyhydric alcohols such as pentaerythritol, glycols and propylene glycols. Examples are polypropylene glycol adipate benzoate, diethylene glycol dibenzoate, dibenzyl sebacate, acetyl tributyl citrate and butyl phthalate-butyl glycolate. A structurally different group are triphenyl phosphate, tributyl phosphate and tributyoxyethyl phosphate. Tributoxyethyl phosphate is frequently also used as flow control agent.
Waxes are often used in conjunction with a polymer in the production of polymer films used as floor finishes. However, they are not a necessary component. They can serve a few purposes in a polymer film. Among these are modifications in the film durability, the buffability, the reparability, and the coefficient of friction. Waxes are oftentimes added to surface coatings. This is particularly true of acrylic floor finishes. In floor finish formulations, the emulsified wax should be added to the base polymer prior to drying to solid. In the case of acrylic floor finishes, the emulsified wax should be mixed with the acrylic latex and then spray dried. The resulting dry polymer is comprised of both wax and acrylic polymer. One could also envision the addition of wax along with the coalescing fluid. Furthermore, the addition of more liquid would result in longer cure times and therefore is not the preferred embodiment.
It is important that the wax remain as discrete particles in the film. It is that discrete particle character that manifests itself in film""s properties. In the compositions of the present invention, the relative proportions of the polymer to wax are from 100:0 to 30:70 by weight. The variation in these relative proportions provides for various buffing characteristics. The wax used may be either natural or synthetic and of vegetable, animal or mineral origin and should have a melting point of at least 75xc2x0 C. and preferably of at least 82xc2x0 C. Some examples of these waxes include both high and low density polyethylene and polypropylene waxes, carnuba, montan, palm waxes, Chinese insect, ceresin, azocerite, microcrystalline waxes, Fisher-Tropsch wax. Mixtures of the waxes may be used. Waxes of lower melting points should not be used as the sole wax component, but can be blended with higher melting point waxes such that the aggregate melting point is about 75xc2x0 C.
An alkali soluble resin may aid in film formation in floor finishes. These usually acid-functional resins may if desired also be used in a partially neutralized form. In floor finish formulations of the invention, the resin should be added to the base polymer prior to drying to solid. This is the preferred embodiment. The resulting polymer is comprised of both the base polymer and the resin. Examples of such alkali soluble resins are shellac, Manilla gum, Loba gum and alkali soluble alkyd resins which essentially represent polyesters of aliphatic dicarboxylic acids with aliphatic polyhydric alcohols, which may be modified with a C8-C18-fatty acid, glycerol esters of C8-C18-fatty acids and resin acids, for example abietic acid or rosin. But it is particularly advantageous to use addition copolymers of olefinically unsaturated acids and aromatic vinyl compounds, for example copolymers of acrylic acid, methacrylic acid and/or maleic anhydride with styrene.
In the methods of the invention, the coatings are made by combining the polymer particulate with a coalescing liquid agent at preferred proportions. Since certain agents are more or less effective as a coalescing agent, there is a broad range of proportions useful in the invention that can result in the formation of an excellent coating of beneficial properties. The coatings of the invention can be formed on flooring materials at a floor manufacturing plant. In such a process, flooring units, such as a vinyl tile, ceramic tile, milled oak or pine board, etc. can be coated as described in this application. Onto the tile unit or wood flooring unit is placed typically simultaneously the particulate and coalescing agent of the invention. As described above, the polymer particle or the coalescing agent can be separately added. The coalescing agent is permitted to form the continuous finish layer during processing. The coalescing agent is typically removed by evaporation during the operations or immediately thereafter. In a flooring manufacturing location, additional energy can be applied to the flooring to speed coalescing agent removal. Typical factory applications permit the use of higher VOC coalescing agents. Such agents can be substantially recovered in recovery systems after evaporation and recycled. The ratio of combining the polymer with a coalescing agent are shown in the following table of coating systems.
The following coating examples highlight the coating formation characteristics of the compositions of the invention. We have provided a number of examples that illustrate the spirit of the invention using three different acrylic based polymers, a cellulosic polymer and a number of different coalescing agents. The coatings exhibit useful hardness, uniformity, resiliency, integrity, durability, and flexibility. The coatings in the examples are evaluated for gloss. Gloss provides an indication of proper film formation. A discussion of the results of scanning electron microscopy (SEM) analysis of the coatings are also included. The SEM analysis is used to confirm coherent film formation. Examples using three conventional Rohm and Haas polymeric coating compositions other coating agents and differing coalescing agents are provided. The examples include the coating of glass microscopic slides, ceramic tile, and vinyl composite tile.

Polymer surface coating made by coalescing a polymer particulate with a coalescing agent


A implant for a cervical vertebra comprises two branches adapted to extend respectively substantially along the two cervical laminae of a given cervical vertebra that have been spaced apart from each other after osteotomy of the laminae, and a rigid body interconnecting the two branches.

The invention relates to cases of compression syndrome in the spine of the neck.
Compression syndrome in the cervical vertebrae can arise because of injury or of malformation.
An object of the invention is to provide a device for responding to cases of compression syndrome.
In order to achieve this object, the invention provides an implant for a cervical vertebra, the implant comprising two branches adapted to extend respectively substantially along the two cervical laminae of a given cervical vertebra that have been spaced apart from each other after osteotomy of the laminae, and a rigid body interconnection the two branches.
Thus, after osteotomy of the cervical laminae and after they have been spread rearwards, the branches of the implant can be fixed to the respective laminae to hold them apart, thereby putting an end to compression on the cavity.
Advantageously, the implant has a deformable link between the body and at least one of the branches.
Thus, the implant adapts appropriately to the morphology of the vertebra.
Advantageously, the link is elastically flexible.
Advantageously, the body has a zone of thickness that is reduced compared with the thickness of the remainder of the body and that defines the link.
Advantageously, the body is generally curved in shape, having a center of curvature situated on the same side as the branches.
Thus, the size of the implant is matched to the shape of the cavity.
Advantageously, the body has a curved inner face situated facing the branches and an outer face opposite from the branches, the inner face having curvature with a center of curvature that is situated on the same side as the branches and a radius of curvature that is smaller than the radius of curvature of the outer face.
Here again, the shape of the implant leaves the necessary volume for the cavity.
Advantageously, at least one of the branches has portions in relief.
Advantageously, the portions in relief form abutments preventing link elements that extend substantially perpendicularly to the longitudinal direction of the branch from moving along the branch.
This facilitates fixing the branches to the laminae and increases the lifetime of the fixings.
Advantageously, the portions in relief comprise notches.
Advantageously, the branches are suitable for being engaged in holes formed in the cervical laminae, and the portions in relief comprise barb-forming teeth.
Advantageously, the branch is of a width measured between the tips of the teeth that tapers towards the free end of the branch.
Advantageously, the portions in relief extend over two opposite longitudinal faces of the branch.


Intumescent laminate with high heat transfer resistance composed of a glass-fiber web or glass-fiber fabric each of which has been coated with a four-component intumescent composition comprising a) a phosphate compound, b) a melamine compound, c) a polyol and d) an inorganic framework-forming compound.

Intumescent materials in the form of paints, lacquers, coatings, pastes, putties, mortars, seals, boards, blanks or cut sections, strips, foams, webs, films, profiles and other semi-finished products are used for fire protection in buildings. When intumescent materials are exposed to heat they expand and form an insulating flame-retardant foam which protects underlying surfaces and substances from exposure to the fire.
The classic three-part mixture is composed of substances contributing carbon, dehydrators and blowing agents (expanders).
DE 27 03 022, DE 28 17 268, DE 28 27 828, U.S. Pat. No. 4,375,516 or DE 30 42 788, for example, disclose porous backing materials coated with intumescent compositions.
All of the patent applications cited describe layer materials, such as boards, films or webs, with a sealed surface which is intrinsically unsuitable for certain sectors, such as sound insulation or fire-protection bulkheads of open conduits.
It was also apparent that, although a wide variety of intumescent materials is available in the market, it is not yet possible to achieve satisfactory impregnation of microporous backing materials.
Since in many potential application sectors it is impossible to exclude the formation of condensation, the only impregnating agents which can be used are those which form compounds insoluble, or at least nearly insoluble, in water. The selection is therefore restricted to a few fire-protection paints and fire-protection lacquers which form water-resistant films on drying.
However, experiments to saturate mineral-fiber boards or microporous melamine-resin foams with water-resistant fire-protection paints gave no industrially useful results. The pulverulent fire-protection components became concentrated at the surface of the backing materials, and only the binder diffused into the interior of the backing boards. The adhesion of the fire-protection components was only slight and they crumbled away on drying.
The obvious use of non-pigmented fire-protection lacquers also failed to achieve any substantial improvement. These high-viscosity formulations cannot be used to saturate microporous backing materials. Thorough saturation of the backing materials was achieved only after appropriate dilution. However, the proportions introduced of the fire-protection components were too low for favorable results to be achieved in subsequent fire tests after drying.
It was an object of the present invention to provide flexible laminates having a high degree of expansion and high heat transfer resistance but not having the abovementioned disadvantages.
Surprisingly, the object was achieved by means of a laminate made from a glass backing material and a four-component layer.
The invention therefore provides an intumescent laminate with high heat transfer resistance, which is composed of a glass-fiber web or glass-fiber fabric coated with a four-component intumescent composition comprising
a) a phosphate compound
b) a melamine compound
c) a polyol
and
d) an inorganic framework-forming compound.
The novel laminate has a coating made from four components. For the purposes of the invention, phosphate compounds (component a) are compounds selected from the class consisting of ammonium polyphosphate, melamine resin phosphate, polyol phosphates, such as, for example pentaerythritol phosphate, glycerol phosphate, sorbitol phosphate, mannitol phosphate, dulcitol phosphate, neopentyl glycol phosphate, ethylene glycol phosphate, dipentaerythritol phosphate, etc. For the purposes of the invention, melamine resin phosphates are compounds such as the reaction products of Lamelite C with phosphoric acid.
Preferred phosphate compounds are polyol phosphates and ammonium polyol phosphates.
Component b) is a melamine compound selected from the class consisting of melamine, hexamethoxymethylmelamine (HMMM), dimelamine pyrophosphate, melamine polyphosphate and melamine phosphate. Preference is given to HMMM or melamine.
Suitable polyols (component c) are those selected from the class consisting of sugars, pentaerythritol, dipentaerythritol, polyvinyl acetate, polyvinyl alcohol, sorbitol and EO-PO polyols. Preference is given to pentaerythritol, dipentaerythritol or polyvinyl acetate.
The fourth component, d), is an inorganic framework-forming compound selected from the class consisting of titanium dioxide, aluminum silicate, clay, zinc borate, calcium borate, sodium phosphate, sodium silicate, zeolite, wollastonite, boron phosphate, serpentine, kaolin, talc, sepiolite, alkaline earth and plagioclases, such as albite and anorthite.
Preference is given to titanium dioxide or aluminum silicate.
The amount of component a) used here is from 5 to 50% by weight, preferably from 10 to 30% by weight. The proportion of component b) is also from 5 to 50% by weight, preferably from 5 to 30% by weight.
The amount of component c) added is from 5 to 40% by weight, preferably from 10 to 30% by weight, and the amount of component d) used is from 5 to 30% by weight, preferably from 5 to 20% by weight.
There is a proviso that all of the components a) to d) always total to 100% by weight.
In each case here, it is possible to use only one compound per component, but it is also possible, for one or more of the components, to use two or more of the listed compounds.
In a specific embodiment, phosphate compound, component a), and polyol, component c), may be present in combination. In this case polyol partial phosphates are present as combined components a)+c).
For the purposes of the invention, polyol partial phosphates are compounds obtained, for example, by esterifying polyols with phosphoric acid or polyphosphoric acids. Examples of these are combination products made from phosphoric acid, ethylene glycol and pentaerythritol.
The four-component composition may, if desired, comprise conventional auxiliaries, such as wetting agents, antifoams, thickeners, dyes, fungicides, plasticizers, binders, flame retardants or various fillers.
The proportion of the individual additives is in each case from 0 to 10% by weight, preferably from 0.1 to 6% by weight. It is again important here that all of the constituents do not give more than 100% by weight in total.
Examples of suitable auxiliaries are conventional wetting agents based on polyacrylates and/or on polyphosphates, alginate thickeners, silicone antifoams; binders, such as polyvinyl acetates, polyvinyl alcohols, polyvinyl butyrals and polyvinyl chloride, styrene-acrylate, vinyltoluene-acetate, etc.; plasticizers, such as chlorine-containing waxes, fillers, such as vermiculite, inorganic fibers, quartz sand, glass microspheres, mica, silica, mineral wool, etc.; flame retardants, such as phosphoric esters, Hostaflam TPOP 920 (Clariant), Amgard V 490 (Albright+Wilson), triethyl phosphate, tris(chlorpropyl) phosphate etc.
The coating is applied in the form of a solution or paste to the backing, and, if desired, an amount of from 10 to 50% by weight, preferably from 15 to 45% by weight, of water is added to the mixture of components, again with the proviso that all of the components should not give more than 100% by weight in total.
The backing used for the novel laminate is a glass-fiber web or a glass-fiber fabric. The weight per unit area of the backing is preferably from 50 to 500 g/m2.
The coating process is carried out on a horizontal spreading and coating (or drying) unit.
The temperature during the coating procedure is from about 10 to 30xc2x0 C., and the drying temperature is from about 70 to 170xc2x0 C.
According to the invention, preferred laminates have a thickness of from 0.5 to 15 mm. The preferred overall thickness of the laminate is from 1 to 5 mm.
The novel laminates feature high heat transfer resistance. This value is above 0.3 Km2/W at 800xc2x0 C. The laminates also feature a high expansion factor. For example, at 300xc2x0 C. this factor is mostly above 20. The novel laminates are therefore suitable, for example, as a hot-gas seal for fire doors, as fire-protection curtaining for apertures in masonry walls, as door panels [lacuna] as windings surrounding individual cables or cable runs, etc.

Intumescent laminates with high heat transfer resistance

DSM Fine Chemicals Austria Nfg GmbH and CoKG


In a gas-generating chemical reaction carried out in a borehole that is largely filled with water, substantial pressure increases can be generated. This pressure can be used to fracture rocks around the borehole and, hence, stimulate water, oil or gas wells in tight rock formations. This pressure increase can also be used to fracture coal seams for enhanced in-situ gasification or methane recovery. This invention discloses the use of a new, novel system, based on the homogeneous reaction of aluminum alkyls with water, to create a controlled pressure increase. The most appropriate reaction mixture, as characterized by the rise of time of the generated pressure pulse and the energy content per unit length of borehole charge, is disclosed in this new invention.

There are currently three technologies to stimulate water, oil and gas flow in a tight rock formation. These include: downhole explosives, propellant combustion and, the most frequently used, hydraulic fracturing. Each of these techniques has limitations. For example, with downhole explosives, the pressure rise is often too rapid, tending to create a zone of compact rock around the borehole which can actually decrease production. Hydraulic fracturing is characterized by a slow pressure rise which tends to create long single fractures parallel to existing natural fractures, often resulting in marginal stimulation. Propellant combustion, where propellant charges burned downhole are used to generate a high-pressure gas, produces the desired multiple fracture pattern, however the cost is high and the system remains contaminated with the propellant (generally nitrogen-based) until large volumes have flushed the borehole. These limitations can be overcome with the use of the novel new invention of this disclosure, chemical reaction-induced pressure pulses. Here, a gas-generating chemical reaction is carried out in a borehole that is largely filled with water and substantial pressure increases can be generated. This pressure can be used to fracture rocks around the borehole and, hence, stimulate water, oil and gas wells in tight rock formations. This pressure increase can also be used to fracture coal seams for enhanced in-situ gasification. This invention discloses the use of a new, novel system, based on the homogeneous reaction of aluminum alkyls with water, to create a controlled pressure increase. The most appropriate reaction mixture as characterized by the rise time of the generated pressure pulse and the energy content per unit length of borehole charge, is disclosed in this new, non-obvious invention.
Rock fracturing to stimulate water, oil or gas flow in a tight rock formation can be carried out by three methods. The first method is downhole explosives. In this case, an explosive charge is detonated in the hole. The highly concentrated stresses produced by such an explosion tend to create a zone of highly compacted rock around the borehole, a stress cage, and do not necessarily propagate fractures such that fluid flow is stimulated. In some cases, this method can damage the formation, resulting in a decreased production rate.
The second method is hydraulic fracturing. This is the chosen method of industry and is carried out by high pressure pumping of fluid with proppants into the rock formation. Normally, a single fracture is produced which is with or parallel to existing natural fractures, often resulting in marginal stimulation.
The third method is propellant combustion, a recent approach which uses propellant charges burned downhole to generate high pressure gas. The charges are tailored to provide a range of burning rates and can be used to produce a multiple fracture pattern. Fractures of this type are useful in linking natural formation fractures and increasing fluid flow to or from the borehole. However, the cost is high and groundwater would remain contaminated with the propellant (generally nitrogen-based) until large volumes of water have flushed the borehole.
In all three methods, the active system is confined to a specific region of the borehole, i.e. a region expected to produce. This isolation is accomplished by using hydraulic and mechanical packers, squeeze cementing and sundry other procedures.
The literature suggests that the pressure rise time, the time for 90% of the pressure rise to occur, is the important parameter in determining the fracture pattern. The longest pressure rise times are found in the second method, hydraulic fracturing, in which case a single long radial fracture is obtained. The shortest rise times are found when the first method, downhole explosives, is used, in which case compacted zones with few, if any, long radial fractures are created. The intermediate rise times, on the other hand, give the multiple fracture pattern, which consists of several radial fractures. With this in mind, it is apparent that in any new system developed, it is important to be able to control the rise time in order to control the fracture pattern. The new, novel present invention discloses a new rock fracturing system which has significant advantages over the three methods of current technology just discussed. This new, novel invention is one in which control of rise time can be readily effected. This disclosure uses chemical reaction-induced pressure pulses to stimulate water, oil and gas production.
In a closed space of fixed volume, a chemical reaction which produces heat and gas will increase the pressure of the system. A particular group of such reactions are those in which a material combines with water. These reactions can be divided into two broad categories, heterogeneous and homogeneous reactions.
The first category is heterogeneous solid/liquid reactions. The first type of reactions discussed involves metals of the Periodic Table, Groups I & II. The most common of these is probably sodium (Na), which reacts with water to produce hydrogen gas. In this case, the reaction is one between a solid and a liquid to produce solid sodium hydroxide and gaseous hydrogen, with sodium hydroxide tending to form a solid film around the sodium and hydrogen a gas film. These films have two significant effects, the first being buoyancy which is caused by the gas film, and the second being a diffusional resistance for the water moving through the film. This diffusion is the rate controlling process in the reaction so that rise time is probably predetermined by the diffusivities of the reacting species.
The second type of reactions in this category involves metal carbides. Many carbides of metals, particularly the salt-like carbides of metals in Periodic Table, Groups I, II & III, react readily with water to produce hydrocarbon gas. These materials may be divided into two main groups:
Carbides containing discrete atoms or C.sup.- ions and carbides which contain C.sub.2.sup.2- ions. Carbides of the first group yield methane on hydrolysis. A typical example is aluminum carbide. Those of the second group yield acetylene and the most common example is calcium carbide. Again, the reactions which take place are between a solid and a liquid and diffusion rates of water through the gas and hydroxide films control the reaction rate and, thus, the pressure rise time. However, in both cases gas evolution is probably so vigorous that this film layer is constantly disturbed, so it should not be thought of as quiescent. The third type of reactions in this category involve other organometallics which are solids and show the same or similar reaction characteristics as those of the types above and will not be discussed further.
Solids of all three types may be passivated if these materials, on exposure to moist air, form oxide and/or insoluble hydroxide films. If these films are coherent and relatively nonporous, the "aged" materials may be unreactive unless the film is ruptured. Experiments in our laboratory with aluminum carbide show no reactivity with water unless the water was heated to 60.degree. C.-100.degree. C. This suggests that differential thermal expansion between unreacted aluminum carbide and the aluminum oxide/hydroxide film, both of which are water insoluble, caused rupture and exposure of fresh surface for reaction. These problems are not present in calcium carbide as the hydroxide formed in this case is water soluble.
With aluminum carbide, it was found that, even after heating the reactants to 100.degree. C. prior to reaction, the rate was too slow to be considered feasible for rock fracturing. The pressure rise time for this aluminum carbide reaction was found to be just under one hour. The slowed rate of this reaction is probably the result of diffusional resistance through the aluminum hydroxide/oxide film and the methane gas film. This is not a problem with this present disclosure's novel use of aluminum alkyls.
The second large category of reactions producing heat and gas that increase the pressure of the system discussed in this disclosure is Homogeneous Liquid/Liquid Reactions. Many of the problems of reaction rate prediction and control associated with the heterogeneous solid/liquid reactions can be avoided in homogeneous liquid/liquid reactions. The most likely candidates in this category for gas producing agents are the aluminum alkyls of this disclosure, which are organometallic compounds of the general formula A1R.sub.3, where R stands for a hydrocarbon radical. These compounds react violently with water to produce heat and the corresponding hydrocarbon gas. Some aluminum alkyls are available commercially in quantities as large as rail tank car amounts.
In the absence of oxygen, the aluminum alkyl reaction with water is shown in equation (1): EQU A1R.sub.3 +3H.sub.2 O.fwdarw.A1(OH).sub.3 +3RH (1)
so that one mole of aluminum in this case produces three moles of hydrocarbon gas compared to the A1.sub.4 C.sub.3 system in which four moles of aluminum are necessary to produce the same amount of gas. In this case, there are no diffusional resistance problems, and violence of the reaction keeps the two liquids in a well-mixed state. When examined in detail, the gas bubbles produced in these reactions actually increase the reaction rate via turbulent mixing of the reactants.
Most aluminum alkyls produced commercially have a small amount of hydrogen incorporated into them due to incomplete alkylation. Hence, small amounts of hydrogen will likely be formed upon hydrolysis.
This new, nonobvious invention disclosure proposes the gas generating reaction of aluminum alkyls with water as an alternative to these three current technology methods. Aluminum alkyls, such as triethylaluminum, cost on the order of one dollar/lb., and they are available in tank car deliveries. Therefore these aluminum alkyls are inexpensive when compared to the use of propellants. In addition, aluminum alkyls can release more energy per unit length of borehole than do propellants such as M5. Studies with propellants as gas generators have shown that the pressure rise time will control the fracture pattern. Aluminum alkyls such as triethylaluminum, TEA, and trimethylaluminum, TMA, are ideally suited for tailored pressure rise times. For example, aluminum alkyls can be easily diluted. Very slow rise times can be effected by dissolving the aluminum alkyls in a solvent not miscible with water, creating a multiphase reaction.
Chemical reaction-induced pressure pulses using aluminum alkyls represent an ideal low-cost stimulant. The energy content of aluminum alkyls is high and the reaction with water can be easily tailored to produce the optimum pressure rise times.
This new, novel invention disclosure uses aluminum alkyls as high pressure gas producing agents in gas fracturing technology. A review of the properties and reactions of aluminum alkyls, relevant to the generation of high pressure gases is presented here. Aluminum alkyls are produced in large quantities by several companies. Aluminum alkyls, AA, are highly reactive compounds. Their main use is as catalysts in the polymerization industry, however their high reactivity has captured the interest of researchers in many fields. AA compounds react vigorously with air and water, producing large quantities of heat and gas. Undiluted, they are pyrophoric in nature, igniting spontaneously in air, particularly the lower formula weight homologs, i.e. trimethylaluminum, TMA, and triethylaluminum, TEA.
All AA compounds react explosively with liquid water. The presence of air further intensifies this reaction. In reacting with oxygen, aluminum oxide is produced along with water and carbon dioxide as the major products. Reaction with water produces, as the major products, aluminum hydroxide and the corresponding hydrocarbon gas, which can ignite.
The focus of the present invention disclosure is on the reaction of aluminum alkyls with water in the absence of oxygen to produce hydrocarbon gases at elevated pressures. The organo-aluminum reactions most important are TMA and TEA with water.
Of interest is the fact that the liquid specific heat of AA compounds is about half that of water, and all react exothermically with water and air. A few AA compounds freeze at normal atmospheric conditions so that thawing must be accounted for in some facilities if ambient temperature falls below certain values.
In the TMA and TEA reactions with water, methane and ethane are produced respectively. The Virial equation of state can be used to predict the state variables for the methane and ethane produced in these reactions. The Virial equation is shown below as equation (2): EQU PV=RT(1+B/V.sup.2 +C/V.sup.3 +D/V+ . . .) (2)
The first three virial coefficients for methane and ethane are available and should cover temperatures up to 623.degree. K. and pressures to about 5000 psig. Below this temperature, all higher order terms can be neglected. Also, if excess water is used to adjust the initial gas volume of the reactions, solubility data for the methane/water system and the ethane/water system must be used to predict the final equilibrium conditions. Using this data, which is based on thermodynamic equilibrium, and by applying simplifying assumptions, the final pressures attained can be predicted and, by manipulating the initial gas volume, can be controlled.
Monitoring the pressure versus time response of constant volume reactions of AA compounds with water documents the dynamic characteristics of aluminum alkyl reactions with water. This response, known as the pressure rise time (time to achieve 90% of the final pressure), determines whether the reaction is considered to be an explosive or slower reaction.
Triethylaluminum, TEA, and Trimethylaluminum, TMA, are the most logical choices of material for development of a homogeneous downhole gas generating system. While the TMA reaction with water is more energetic than that of TEA, after considering the physical properties and cost of each, TEA is preferable. TMA is a solid below 59.5.degree. F. and would be solid on a cold day. TEA melts at -49.9.degree. F., a 100.degree. F. difference. TMA is also currently ten times more expensive compared with TEA. Heats of reaction with water are substantial in both cases, with TMA at 2939 BTU/lbm and TEA at 1811 BTU/lbm, both at 77.degree. F. A mixture of the two or even with other aluminum alkyls can be used to tailor the pressure rise time and expand the temperature range in which the system is a liquid. A further point is that critical properties of methane and ethane can be important at the conditions of a downhole pressure pulse. The critical temperature and pressure for CH.sub.4 are -117.degree. F. and 667 psi, while for C.sub.2 H.sub.6 they are 90.degree. F. and 708 psi.
If the energy available for fracturing using aluminum alkyls can be taken as the heat of reaction at room temperature, then a comparison can be made between TMA, TEA and propellants previously studied by the literature. Literature has proposed that the volume of rock which contains the fracture is proportional to the total energy released so that EQU .pi.R.sup.2 L=BE
where:
R=radial length of the major fracture measured from the center of the borehole PA1 L=length of borehole section PA1 E=energy density of reactants (energy/volume) PA1 B=proportionality constant that depends on the mechanics and structural properties of the formation
For ash fall tuff rock formation, B=0.193. Comparison for 6" diameter borehole, 1' long in ash fall tuff rock is given below to compare TMA and TEA with M5 propellant. This comparison assumes that the hole is filled per unit-length with the stoichiometric amount of water and aluminum alkyl.
______________________________________ Comparison of M5 Propellant with Aluminum Alkyls Material (E/L)Btu/ft R(ft) ______________________________________ M5 10,400 19.7 TEA 13,238 22.0 TMA 17,237 25.3 ______________________________________
This data shows that, from values of the energy released per unit length (E/L), aluminum alkyls are better than the propellant.
To compare the various possible reactions of TEA with proton donors, the stoichiometric volume of reactants needed to produce one mole of hydrocarbon gas has been calculated for several candidate reactants. The minimum volume required was for the TEA/water system. The maximum volume is open-ended and would be attained by dilution of the TEA with an appropriate solvent. Table I summarizes these calculations.
TABLE I ______________________________________ Reaction of TEA with Various Reactants to produce one mole of Ethane Total Volume Volume of TEA Volume of Reactant Reactant (cm3) (cm3) (cm3) ______________________________________ H.sub.2 O 63.6 45.5 18.1 HF 65.5 45.5 20.0 HNO.sub.3 87.2 45.5 41.7 H.sub.2 SO.sub.4 72.3 45.5 26.8 HBr 75.4 45.5 29.9 ______________________________________
In studies on the use of propellants as gas generators, it was shown that pressure rise time controlled the fracture pattern. There is a need, therefore, in the gas generation system chosen, to be able to control this parameter in order to determine the fracture characteristics. This is obviously currently a choice between hydraulic and multiple fracture regimes, since explosive fracture is seldom desired for stimulation.
The nonobvious invention of this disclosure, use of aluminum alkyls such as TEA and TMA, is ideally suited for tailored pressure rise times. This can be effected in several ways.
The first way is by solvent dilution. The rate of reaction with water or alcohol, in the absence of oxygen, can be reduced significantly by dilution of the aluminum alkyl with an appropriate solvent. By controlling the rate of reaction, the pressure rise time is also controlled. The main drawback of this method is that the energy density of the system is also reduced.
The second way is by using different proton donors, thus replacing water with alcohols of varying chain length and/or steric hindrance. The use of less reactive proton donors can achieve the desired buffering effect also. In this case the rate is decreased due to an increased difficulty in obtaining protons. Also, the use of higher molecular weight proton donors decreases the molar concentration, hence the reaction rate decreases. Again, energy density is also decreased. The addition of an acid to any of the above systems would likely speed the reaction. For example, if the TEA/water system is not "fast" enough for a certain application, 5% by weight H.sub.2 SO.sub.4 may be used to increase the rate. Some acids that may be used are Sulfuric (H.sub.2 SO.sub.4), Nitric (HNO.sub.3), Hydrobromic (HBr) and Hydrochloric (HCl) acids.
A third way is by using different aluminum alkyls. Different aluminum alkyls can exhibit different reaction dynamics. A fourth and final way is by using multi-phase reactions. By using immiscible reactants, a diffusional resistance can be introduced. This interfacial type reaction can be controlled by varying parameters such as surface tension.

Aluminum alkyls used to create multiple fractures

The Board of Supervisors of Louisiana State University and Agricultural and Mechanical College


Methods of treating superconducting composites to enhance their wettability in solder, and composites having enhanced wettability. It has been found that wettability can be substantially enhanced by stripping a thin layer off the surface of the composite before incorporating it into a laminated component. This layer can be stripped, for example, by chemically etching the composite, for example in a solution of nitric acid and ammonium bifluoride.

The present invention is related to methods of enhancing the wettability of composite materials, and in particular to composite materials that may be easily laminated to form components which can withstand thermal cycling.
High temperature superconductors (HTS materials) have increasing utility as power conductors, fault current limiters, and other applications. Since HTS materials are generally brittle oxides, it is common to produce them in composite form, wherein superconducting filaments are supported by a noble metal matrix. The matrix is most commonly silver-based, but any metal or alloy which will withstand superconductor processing conditions and which does not act to poison the superconductor may be used.
It has been observed that in use, superconducting composites often exhibit xe2x80x9cballooning.xe2x80x9d When the composite is immersed in liquid nitrogen or another cryogen suitable for achieving superconducting properties, a certain amount of cryogen collects in interstices between the matrix and the superconducting filaments. When the composite is allowed to return to room temperature, the cryogen expands and causes portions of the composite to deform to form balloons. This deformation subjects the delicate superconducting filaments to fatigue and possibly fracture, degrading or destroying superconductor filaments. A strong need thus exists for a method of preventing ballooning from occurring.
When a superconducting composite is to be laminated by soldering it to another material (e.g., a metal tape which can provide mechanical and/or thermal stabilization), it is important that the laminate be sealed against any infiltration by liquid cryogen to prevent ballooning, and further that it be in good thermal and mechanical contact with the solder in order to avoid the creation of hot spots or stress concentrations. Similarly, when a composite is protectively encapsulated (e.g., with solder or with a polymer), the encapsulating material should be free of defects that might compromise the integrity of the seal. Also, when forming multistrand cables, solder or another material may be used to hold the strands together, and again, a good contact between the solder and the strands should be achieved.
In one aspect, the invention comprises methods of preparing superconducting composites for lamination, encapsulation, or any other process that requires wetting of the composite by a liquid. The method comprises removing a thin layer of matrix material to expose a surface having a low concentration of oxide particles. The layer may be removed, for example, by chemical etching or by electrolytic cleaning. If it is removed by etching, the etchant may be, for example, nitric acid, hydrochloric acid, ferric chloride, ammonia, a caustic solution, or a mixture of these, and may contain other salts such as ammonium bifluoride. The thin layer may be on the order of 0.013 mm thick, or as thick as can be achieved without excessively degrading the properties of the superconductor (e.g., degrading the critical current by more than about 10%). The exposed surface may subsequently be coated with solder, which may wet the surface with a wettability of at least 250 xcexcN/mm, 300 xcexcN/mm, or 350 xcexcN/mm. The solder may be, for example, lead-tin, silver-tin, silver-lead-tin, or lead-indium solder. When the thin layer is removed electrolytically, an electrolyte such as nitric acid, hydrochloric acid, sulfuric acid, sodium hydroxide, ferric chloride, or ferrous chloride may be used. The removal process may leave the exposed surface at least 97% free of foreign particles, at least 99% free, at least 99.5% free, or at least 99.8% free.
By xe2x80x9cnoble metalxe2x80x9d as it is used herein, it is meant any metal whose reaction products are thermodynamically unstable under the reaction conditions employed relative to the desired superconducting ceramic, or which does not react with the superconducting ceramic or its precursors under the conditions of manufacture of the composite. A noble metal matrix may be a metal different from the metallic elements of the superconducting ceramic, such as silver, gold, or their alloys, or it may be a stoichiometric excess of one of the metallic elements of the superconducting ceramic, such as copper.
By xe2x80x9cdesired superconducting ceramicxe2x80x9d as it is used herein, it is meant the oxide superconductor intended for eventual use in the finished article. Typically, the desired oxide superconductor is selected for its superior electrical properties, such as high critical temperature or critical current density. The desired oxide superconductor is typically a member of a superconducting oxide family which has demonstrated superior electrical properties, for example, BSCCO 2223 (including BSCCO (2.1)223) or BSCCO 2212 in the BSCCO family. By xe2x80x9cprecursorxe2x80x9d is meant any material that can be converted to an oxide superconductor upon application of a suitable heat treatment. Precursors may include any combination of elements, metal salts, oxides, suboxides, oxide superconductors which are intermediate to the desired oxide superconductor, or other compounds which, when reacted in the stability field of a desired oxide superconductor, produces that superconductor. For example, there may be included elements, salts, or oxides of copper, yttrium, and barium for the YBCO family of oxide superconductors; elements or oxides of copper, bismuth, strontium, and calcium, and optionally lead, for the BSCCO family of oxide superconductors; elements, salts, or oxides of copper, thallium, calcium and barium or strontium, and optionally, bismuth and lead, for the thallium (TBSCCO) family of oxide superconductors; elements, salts, or oxides of copper, mercury, calcium, barium or strontium, and optionally, bismuth and lead, for the mercury (HBSCCO) family of oxide superconductors. The YBCO family of oxide superconductors is considered to include all oxide superconductors of the type comprising barium, copper, and a rare earth selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. By xe2x80x9coxide superconductor intermediate to the desired oxide superconductorxe2x80x9d is meant any oxide superconductor which is capable of being converted to the desired oxide superconductor. The formation of an intermediate may be desired in order to take advantage of desirable processing properties, for example, a micaceous structure amenable to texturing, which may not be equally possessed by the desired superconducting oxide. Precursors are included in amounts sufficient to form an oxide superconductor. In some embodiments, the precursor powders may be provided in substantially stoichiometric proportion. In others, there may be a stoichiometric excess or deficiency of any precursor to accommodate the processing conditions used to form the desired superconducting composite. For this purpose, excess or deficiency of a particular precursor is defined by comparison to the ideal cation stoichiometry of the desired oxide superconductor. Thalliation, the addition of doping materials, including but not limited to the optional materials identified above, variations in proportions and such other variations in the precursors of the desired superconducting oxides as are well known in the art, are also within the scope and spirit of the invention.


A method allocates resource in an Orthogonal Frequency-Division Multiple Access (OFDMA) network, including a set of Base Stations (BSs) and a set of Mobile Stations (MSs) for each BS. OFDMA frame are constructed as multiple resource blocks, and each resource block contains symbols transmitted on different subcarriers. A cluster is formed from adjacent sectors of different neighboring cells to jointly optimize the resource allocation in multiple frames, and three non-overlap zones are sequentially identified in cluster: cell center zone, cell edge zone, and cluster corner zone. Resource allocation includes intra-cluster proportional fair scheduling and inter-cluster interference mitigation. Intra-cluster scheduling further includes resource allocation for cell center zone and resource allocation for cell edge zone.

OFDMA
Orthogonal frequency-division multiplexing (OFDM) is a modulation technique used at the physical layer (PHY) of a number of wireless networks, e.g., networks designed according to the well known IEEE 802.11a/g and IEEE 802.16/16e standards. Orthogonal Frequency-Division Multiple Access (OFDMA) is a multiple access scheme based on OFDM. In OFDMA, separate sets of orthogonal tones (sub-channels) and time slots are allocated to multiple transceivers (users or mobile stations) so that the transceivers can communicate concurrently. OFDMA is widely adopted in many next generation cellular networks such as 3GPP Long Term Evolution (LTE) and IEEE 802.16m due to its effectiveness and flexibility in radio resource allocation.
OFDMA Resource Allocation
The radio spectrum is a scarce resource in wireless communications, and therefore an efficient use of it is needed. The rapid growth of wireless applications and subscriber users have called for a good radio resource management (RRM) scheme that can increase the network capacity and, from a commercial point of view, save deployment cost. Consequently, developing an effective radio resource allocation scheme for OFDMA is of significant interest for industry.
The fundamental challenge in resource allocation is the inequality between the scarce spectrum that is available, and the vast area to be covered and large number of users to be served. In other words, the same frequency spectrum must be reused in multiple geographical areas or cells. This will inevitably incur inter-cell interference (ICI), when users or mobile stations (MSs) in neighboring cells use the same spectrum. In fact, ICI has been shown to be the predominant performance-limiting factor for wireless cellular networks. As a result, a significant amount of research has been devoted to developing ICI-aware radio resource allocation for cellular networks.

Clustering based resource allocation in multi-cell OFDMA networks

Mitsubishi Electric Research Laboratories, Inc.


The invention relates to drawn pieces made of steel plate, particularly for motor vehicles bodies, and to a process for manufacturing such drawn pieces. In order to be able to manufacture drawn pieces with a high piece strength but of a low weight and with a low susceptibility to denting in a simple manner, according to the invention, a spring steel plate which is already hardened in the initial state, particularly bainitizedxe2x80x94for example, CK60 or C63 or 67SiCr5xe2x80x94is used during the drawing of the vehicle body parts. The yield point of the heat-treated plate bar material is approximately in the range of from 800 to 1,800 N/mm2; the tensile strength is above that. Because of these strength values, plate bars of a plate thickness of approximately 0.3 mm to 0.6 mm can be used, whereby approximately 20 to 60% of the previous piece weight can be saved. The drawn piece according to the invention is therefore a definite lightweight part. In addition to being bainitized, the spring steel plate can be mechanically hardened, for example, by cold rolling or by a heat treatment.

The invention relates to drawn parts made of steel plate, particularly for motor vehicle bodies, such as vehicle body outer skin parts and load-bearing structural parts, but also to comparable lightweight construction parts of different applications as well as to a corresponding manufacturing process.
Preferably high-quality drawn steel types are used nowadays in vehicle body construction for the exterior covering parts. Since, because of the low yielding point of the material, these steel types can be deformed very easily, minor damages during the manufacturing, but particularly during the use of the finished vehicle will necessarily lead to permanent deformations. Minor bumps, for example, when parking on parking lots, the impact of rocks, hail, or the like, result in dents which can be removed only at relatively high expenditures.
It is known (Krafthand Journal, Volume 4, Feb. 15, 1986, Pages 151 to 159) to use high-strength steel types in vehicle body construction for exterior covering parts of vehicle bodies which, although they require higher expenditures for repair work, are nevertheless less susceptible to damage. However, no detailed information is supplied there with respect to the recommended higher-strength steel types. Neither concrete materials, nor characteristic values, nor a pretreatment of the materials are mentioned. The different characteristic processing values to which reference is made there with respect to xe2x80x9cstandard sheet metalxe2x80x9d in comparison to xe2x80x9chigher-strength sheet metalxe2x80x9d indicate, because of the relative small difference, that the xe2x80x9chigher-strength sheet metalsxe2x80x9d are those which have an inherently higher material strength in the unhardened state.
German Patent Document DE 195 29 881 C1 suggests the deep drawing of vehicle body parts made of a hardenable spring steelxe2x80x94preferably in the hot statexe2x80x94and bringing the workpiece to spring steel hardness only in the finished drawn condition. This method of operation requires high-expenditure heatable deep-drawing tools and a quenching system integrated in the pressing facility, which is cumbersome and results in expectations of a high fault rate in the series operation with such a heterogeneous manufacturing using a hot deforming and a heat treatment.
In a contribution from the German journal Bleche Rohre Profile, 40 (1993), Page 906 and on, with the title xe2x80x9cNew Developments in the Manufacturing of Motor Vehicle Partsxe2x80x9d, the term xe2x80x9chigher-strength steel typesxe2x80x9d is also used for vehicle body steel plates, which, however, are steel materials which are not heat-treated and which, because of their alloy composition, inherently, that is, in the unhardened state, of a higher material strength than conventional sheet metal steels. In this context, the following steel types are mentioned: Age-hardening steel, Ti- and Nb-micro-alloyed steel as well as martensitic and bainitic polyphase steel. It is explicitly mentioned there that generally the deformability decreases as the strength rises. Problems in this respect are discussed there in detail.
It is an object of the invention to be able to manufacture in a simple manner drawn pieces of the initially mentioned type which have a high strength.
According to the invention, this object is achieved by means of the characterizing features of Claim 1 (drawn piece) and by those of Claim 6 (process). Accordingly, for drawn pieces, particularly for vehicle body parts, a spring steel is used in the heat-treated, specifically bainitized state, and this spring steel is deep-drawn or stretch-formed. This can be achieved surprisingly well despite the hardened metal plate by means of a corresponding tool design, press design and process forces. However, for this purpose, significantly higher process forces are required than previously. All process parameters required for the deformation have to be newly determined empirically, which can, however, easily be achieved within the scope of normal optimizing tests and as a function of the respective component.
Because of the fact that, during the deforming process, the spring steel can be stressed without failing by a significantly higher hold-down force and deforming forcexe2x80x94in comparison to conventional deep-drawn steel typesxe2x80x94, surprising large deforming degrees or deep drawing can be achieved. Because of the characteristic mechanical values of the hard spring steel plate, which are usually poor for a suitability for deep drawing, specifically a low uniform elongation and elongation at rupture, a low consolidation index, a low vertical anisotropy, a high deformability could definitely not be expected. Because of the nevertheless possible, high degrees of deformation, not only less deep-drawn outer skin pieces can be deep-drawn without any problems, but also load-bearing structural parts for which greater degrees of deformation are required. In the case of the latter, it is useful to superimpose a fine structuringxe2x80x94honeycomb or waffle structurexe2x80x94at least in slightly curved areas of the drawn piece, so that a high stiffness can be achieved here.
As the strength increases, that is, as the elastic limit rises, hardened metal plates generally lose deforming capacity. The measurable mechanical characteristic values, such as the uniform elongation or the elongation at rupture usually diminish as the strength of the plate bar material increases. This also applies to the bainitized spring steel recommended according to the invention. However, surprisingly, this material has unusually high characteristic deforming values xe2x80x9cvertical anisotropyxe2x80x9d and xe2x80x9cconsolidation indexxe2x80x9d, which are not customary for conventionally hardened spring steel. Because of the high characteristic deforming values of the bainitized spring steel recommended according to the invention, it is possible that very high process forces can be transmitted without cracks. The process forces occurring or to be used in this case may reach approximately ten to twenty times the process forces during the deep drawing of conventional deep-drawn steel. Because of these surprisingly high characteristic deforming values of the bainitized spring steel recommended according to the invention, the good deep-drawing results could be achieved in an interaction with the abnormal process forces.
In this context, it should be pointed out that the deep drawing or stretch forming of metal plate components makes significantly higher demands on the deformability of a material than other deforming processes, such as bending or punching. In the case of deformation-critical materials, the deep drawing or stretch forming is only slightly more difficult to control than the bending, because the drawing results in a surface enlargement with respect to the starting plate bar. Not every material which can easily be cold-bent is also easily suitable for use as a drawn material.
The heat treatment of the bainitizing of spring steel is known per se. In older German-language literature references, this type of heat treatment is also called isothermal hardening or austempering. It is also known that bainitized spring steel can be cold-deformed (compare, for example, a contribution from the technical journal Draht, 3 (1992), Pages 307 to 310). However, as far as the applicant knows, only bending or punching are known as deforming methods of such materials, but not deep drawing or stretch forming, for which a much higher degree of stretching and upsetting and mainly a multidimensional stretching and upsetting is demanded.
During the bainitizing, the steel has to be cooled from the austenization temperature and from the austenized condition very rapidlyxe2x80x94approximately within one secondxe2x80x94to a temperature which is clearly above the martensite starting temperature, thus, for example, to approximately 300 to 350xc2x0 C., for which salt baths or lead baths can be used. The steel must then be maintained at this temperature for a certain time which depends on the alloying of the steelxe2x80x94for approximately 2 to 10 minutesxe2x80x94until the austenite is transformed completely into a bainitic structure. Only then can the steel cool to room temperature, which can take place by allowing it to stand or by blower cooling.
The yield point of the hardened bainitized spring steel is approximately in the range of from 800 to 1,800 N/mm2, preferably 900 to 1,200 N/mm2; the tensile strength is by approximately 100 to 200 N/mm2 above it. Althoughxe2x80x94as mentioned abovexe2x80x94, the deforming capacity of a material decreases with its increasing yield point, of the bainitized spring steels from the PT group known to the applicant, the spring steel with the name PT120 with a tensile strength of 1,200 N/mm2 and a yield point of 1,000 N/mm2 is particularly recommended because, according to the applicant""s knowledge, it has a very good strength in this group combined with very good deforming characteristics. Spring steel may be used which is made of conventional carbon steelxe2x80x94, for example, of the DIN (standard) designations CK60 or C63xe2x80x94or of stainless alloyed spring steelxe2x80x94such as 67SiCr5xe2x80x94. The use of stainless steel plate is recommended in this case particularly because the expected durability of the less dent-susceptible motor vehicle body parts is higher than previously and because a rusting-through in the case of non-stainless steel types with a high durability and smaller wall thickness is possible earlier than previously.
The spring steel with the designation Ck60 (according to DIN) or 2 C 60 (according to Euronorm 83), which, for example, is recommended, has the following composition in weight percent:
Because of the high strength of the material, a metal plate which is clearly reduced in its thicknessxe2x80x94approximately 0.3 mm to 0.5 mmxe2x80x94in comparison to previously customary metal plate thicknessesxe2x80x940.8 mmxe2x80x94can be processed to form vehicle body parts. Simultaneously, the vehicle body parts according to the invention exhibit an improved denting behavior; that is, the tendency for a plastic deformation in the event of minor damage is clearly lower than previously. As a rule, minor indentations rebound elastically to their original shape. As the result of the smaller metal plate thickness, the vehicle body parts produced therefrom, while the denting behavior is improved and the overall strength is the same, can be designed to be approximately 20% to 60% lighter than previously.
Because of the high denting resistance of the drawn pieces according to the invention, these are of interest not only for outer skin parts. On the contrary, the present invention opens up new application possibilities under the aspect of a lightweight vehicle body construction. The previously thinnest vehicle body metal plates had a thickness of approximately 0.7 mm. As a result of the invention, metal plate thicknesses of approximately 0.3 mm definitely seem possible with respect to aspects of strength, particularly when a fine structuring is superimposed on less curved workpiece areas. Because of a metal plate thickness reduction by up to 0.5 mm or to approximately one third of the previous wall thickness which seems possible, considerable reductions of weight should be possible on the motor vehicle body structure which are at least equal to the use of light metals. If, in addition, a spring-hard stainless steel is used, the corrosion disadvantage of thin steel plates can also be compensated.

Deep-drawn parts made of spring sheet steel which are especially used as a lightweight structural member or vehicle body part, and a method for the production thereof