Abstract: A process for multi-layer, co-coating preparation of a silver halide color light sensitive material comprising co-coating at least eight coating liquid compositions simultaneously onto a traveling support to form at least eight total layers comprising a lowermost layer adjacent to the support and at least seven outer layers adjacent to the lowermost layer, wherein the at least eight coating liquid compositions comprise a lowermost layer coating liquid composition and at least seven outer coating liquid compositions; the lowermost layer coating liquid composition has a viscosity of 15 to 100 cp; each outer layer coating liquid composition of the at least seven outer layer liquid compositions has a viscosity of at least 30 cp; and the at least seven outer layer coating liquid compositions have an arithmetic mean viscosity of 60 to 300 cp.

Abstract: A process for preparing a photopolymerizable printing element includes feeding a layer of a photopolymerizable composition, calendering the layer to form a web, applying tension to the web, and cooling the web wherein during cooling, a gripping force is applied at side edges of the web. The application of the gripping force to the web substantially reduces non-uniformities in the thickness of the photopolymerizable layer.

Abstract: There is disclosed a process for heat treatment of a photographic polyester film support, comprising steps of winding a biaxially oriented polyester film into a roll so that the thickness of a gas layer lying between the film layers continually becomes 1.5 .mu.m to 10 .mu.m, and then subjecting the roll of the polyester film to heat treatment at a temperature between 50.degree. C. and the glass transition temperature of the polyester. According to the above process, a photographic polyester film support, which is excellent in flatness of the film and does not cause unevenness of coating, can be provided.

Abstract: Low melting point epoxy scavenger compounds are disclosed which contain a pH dependent ionizable group to facilitate migration of the scavenger from an adjacent scavenger layer (that does not contain any coupler) to an imaging layer (containing coupler and emulsion) of a photographic element at the pH of development. One aspect of the invention comprises a process of forming an aqueous dispersion of an epoxy compound of the structural formula SI: ##STR1## wherein: R is H, an alkyl group, or an aryl group; L.sub.1 is an alkyl group or an aryl group; L.sub.2 is --O--, --CO--, --S--, --SO.sub.2 --, --PO.sub.2 --, --CO.sub.2 --, --NHCO-- or --NHSO.sub.2 --, wherein L.sub.2 may be orientated in either direction; L.sub.3 is an alkyl group; m is 0 or 1; p is 0 or 1; and X is ##STR2## wherein R' is H or an alkyl or aryl group, with the proviso that where L.sub.2 comprises an ionizable group, X may also be an alkyl group or an aryl group; wherein the compound has a melting point of less than about 50.degree. C.

Abstract: An improved method of hardening a hydrophilic colloid is detailed. The hardening results in a stronger matrix and less water pickup. These and other advantages are obtained by hardening with a combination of at least one hardener chosen from Formula I either alone or in combination with at least one hardener chosen from Formula II: ##STR1## The substituents are defined.

Abstract: Photographic emulsions are quickly chilled to a homogeneous, particulate gel by injection of carbon dioxide coolant, while the emulsion is agitated. This process is carried out in a housing having a pair of parallel auger screws to transport emulsion circuitously within the housing. Carbon dioxide coolant is injected through a plurality of nozzles in the housing and is then removed from the housing through a vent line.

Abstract: This invention provides composition and method to overcome the very high viscosity of prior small-particle dispersions when admixed with gelatin in aqueous solution for coating a photographic film element.The invention is generally accomplished by the utilization of a second surfactant in the melt formulated by the admixture of the small-particle dispersion and the gelatin solution. The surfactants of this invention, that is, utilized to control the rheology of such said melts, have the following general structure: ##STR1## wherein n=5 to 20 andx=1 to 4.

Abstract: A silver halide photographic material comprises a plastic support, a silver halide emulsion layer and an antistatic backing layer. A process for the preparation of the photographic material comprises the steps of: coating a silver halide emulsion on one side of the support to form the silver halide emulsion layer; and coating an aqueous coating solution on the other side of the support to form the antistatic backing layer. The coating solution contains electroconductive particles, a binder and a specific nonionic surface active agent represented by the formula (Ia), (Ib), (II), (III) or (IV).

Abstract: A support sheet for a photographic printing sheet having enhanced anti-fogging and anti-yellowing properties comprises a pulp paper substrate sheet, a front coating layer formed on a front surface of the substrate sheet and comprising a cured resinous material produced from electron beam-curable unsaturated organic compound by an electron beam irradiation thereto and mixed with a white pigment, and a back coating layer formed on a back surface of the substrate sheet and comprising a film-forming synthetic resinous material, in which a magnesium compound is contained, as an anti-fogging agent, in the substrate sheet and/or the front coating layer.

Abstract: The present invention is a biaxially oriented polyester film support in which the surface has been subjected to an energetic treatment to produce amine groups on the polyester surface. The treated surface is then coated with a dilute amine reactive hardener solution. After drying the hardener solution a photographic emulsion is coated to the surface. The resulting film element has better adhesion of the photographic emulsion after photoprocessing than previous known methods.

Abstract: Photographic elements comprising loaded latex compositions are prepared by (a) combining under conditions of low or moderate shear, in the presence of surfactant, and in the substantial absence of water-miscible or volatile organic solvents, a liquid organic composition comprising at least one photographically useful compound with an aqueous polymer latex, (b) holding the combination resulting from (a) in a liquid state for sufficient time for substantial loading of the organic coposition into the polymer latex to occur, and (c) coating the loaded latex resulting from (b) on a support.

Abstract: Disclosed is a process for producing a titanium dioxide pigment used for a resin-coated paper type photographic support, comprising the following steps:(a) a step of adding at least one alkaline earth metal compound in an amount of 0.01-2.0% by weight in terms of a metal oxide based on the titanium dioxide before calcination step and(b) an acid-washing step of washing the titanium dioxide at acidic state after the calcination step and before a step of surface treatment with a hydrated metal oxide,and wherein particle size of the titanium dioxide pigment is 0.110-0.150 .mu.m shown by number-average diameter obtained by measuring the diameter in a certain direction using an electron microscope. A photographic support which comprises the above titanium dioxide pigment is also disclosed. Occurrence of die lip stain and microgrit are substantially reduced in the photographic support and a photographic material made thereof exhibits improved image sharpness.

Abstract: Methods and compositions are provided for hardening with fast-acting hardeners the colloidal carrier materials, such as gelatin, in the layers of photographic materials, such as photographic film. The methods of the invention comprise coating, with a conventional coating technique, among the layers of a photographic material a layer of a composition of the invention. The compositions of the invention are aqueous solutions which comprise a fast-acting hardener and a polymeric thickener, have concentrations of thickener less than about 50 mg/cm.sup.3 and, at 40.degree. C. and shear rates between about 1000 sec.sup.-1 and 10,000 sec.sup.-1, have viscosities from about 5 cp to about 20 cp and power law indices greater than about 0.90.

Abstract: An imaging element comprising a light-sensitive imaging layer and a polyester film support having coated thereon greater than 0.17 gm/m.sup.2 of a layer of a self-crosslinking polyurethane derived from an isocyanate terminated prepolymer extended with an aliphatic polyamine and end-capped with N-methylol hydrazide groups, the prepolymer being derived from (a) a diisocyanate, and (b) a polyester polyol and having pendant water dispersing, carboxylic salt groups on the polymer chain.

Abstract: A coating method for producing a photographic light-sensitive element without unevenness of coating, even when coating is carried out with at least one coating composition containing a low boiling point solvent as an outermost layer and coating is carried out at a high speed using a multi-layer simultaneous coating method. In accordance with the invention, the following relationship is maintained:C<0.2Lwhere C (wt %) is the concentration of a low boiling point solvent in a coating composition forming an outermost one of the coating layers, and L (cc/m.sup.2) is a quantity of a wet coating per web unit area in a thickness from an inner surface of the outermost layer adjacent to the outer surface of the silver halide layer to a surface of said outermost layer.

Abstract: A base film having dimensional stability and high transparency, which comprises (A) a plastic film having on either one or both sides thereof (B) a thin film layer comprising (1) an oxide of silicon and (2) a fluoride of alkaline earth metal, or comprising (1) an oxide of silicon, (2) a fluoride of alkaline earth metal, and (3) an oxide of magnesium, the thin film layer (B) being formed by a vacuum film forming process. A photographic light-sensitive material comprising the base film having dimensional stability and high transparency, having on either one or both sides thereof (C) a photographic layer.

Abstract: The improvement in photoprinting on metallic surfaces which comprises masking the yellowish tint on the polyurethane coating on the metallic surface by including in the solution of the polyurethane coating being applied a Violet dye and a Dark Green dye.

Abstract: To prepare a screen printing stencil, a pattern of resist, having a complementary design to the final screen printing stencil, is applied to a conductive mandrel. A patterned layer is electroformed onto the exposed surface of the mandrel such that the layer corresponds to the exposed orifices of the pattern of resist. The resulting screen printing stencil can have an overgrowth geometry or a straight-wall geometry depending on the type of photoresist employed, and can be used in the electronic substrate fabrication and electronic assembly industries.

Abstract: A method of manufacturing a photosensitive element which can be exposed and enveloped by diffusion transfer processes to form a lithographic printing plate, said method comprising the steps of:(a) providing a support layer,(b) coating a negative acting silver halide emulsion layer onto said support layer, and(c) coating a physical development nucleation layer comprising particles onto said silver halide emulsion layer,wherein the coating of said physical development nucleation layer is performed with a coating composition which is at a temperature above 0.degree. C. and below 30.degree. C.

Abstract: A silver halide photographic light-sensitive material is disclosed, which comprises a support and provided thereon, a hydrophilic colloid layer comprising a silver halide emulsion layer wherein the hydrophilic colloid layer contains a compound having a solubility of not less than 1 g based on 100 g of water of 25.degree. C.

Abstract: An optical disc includes a recording film formed on one surface of a disc-shaped plastics substrate having light transmission properties, and a coating film formed on the other surface of the substrate to which an optical beam is applied, in which the plastics substrate is made by injection molding and a barrier, such as a U-shaped annular groove or ridge, is circumferentially formed on the other surface, at a radial distance which is the distance from a center position to a joint position of an injection mold, and a method for manufacturing the same.

Abstract: A silver halide photographic light-sensitive material is disclosed. The light-sensitive material comprises a support comprising a substrate and an electron beam-cured resin layer provided on a surface of the substrate, and a hydrophilic colloid layer provided on said resin layer. The resin layer comprises an electron beam-curable composition cured by electron beam radiation and a white pigment in an amount of 20% to 70% by weight. The hydrophilic colloid layer includes at least one silver halide emulsion layer and optionally a non-light-sensitive hydrophilic colloid layer, and contains gelatin and an oil component. In the light-sensitive material, the curling degree of the support R m.sup.-1, the coating amount of the gelatin G g/m.sup.2, and the coating amount of the oil component Oi g/m.sup.2 are each -8.ltoreq.R.ltoreq.-1, 2.ltoreq.G.ltoreq.20 and 0.ltoreq.Oi.ltoreq.20, respectively, and a value Y calculated by the following equation is -3.ltoreq.Y.ltoreq.5;Y=0.9G-0.

Abstract: The photographic paper support sheet having enhanced resistance to yellowing and satisfactory flexibility includes a front surface coating layer formed on a substrate paper sheet and having a laminate structure which includes an inside electron-beam-cured resin layer and an outermost electron-beam-cured resin layer derived from an electron-beam-curable coating liquid composition containing compounds (A) and (B) of the formulae (I) and (II). ##STR1## wherein R=--H or --CH.sub.3, a, b and c=0 or 1 to 4, a+b+c=1 to 4, a', b' and c'=0 or 1 to 8, and a'+b'+c'=5 to 8, in a weight ratio (A)/(B) of 30/70 to 90/10.

Abstract: The invention is directed to a process for forming a chromogenic photographic heat-transferable non-aqueous dye-diffusion-transfer photographic element comprising the steps of: providing, separately, a melt comprising a spectrally dye-sensitized silver halide emulsion and a dry diffusion transfer facilitating thermal solvent; mixing said spectrally dye sensitized silver halide emulsion melt and said dry diffusion transfer facilitating thermal solvent with a mixing means to create a mixed melt; providing a coating substrate; coating said mixed melt on said substrate to form a coated photographic element, wherein said coating takes place less than about 10 minutes after mixing.The heat-transferable photographic element thus formed has improved photographic sensitivity and increased sensitometric uniformity.

Abstract: The support member for photographic printing paper of the present invention has a coating layer which comprises white pigment and hydrophobic binder soluble in an organic solvent on a base material, whereby voids are formed in said coating layer. The support member increases whiteness degree and gives an image with excellent sharpness.

Abstract: Process for forming a microcrystalline coupler dispersion comprising the steps of: providing crystalline coupler in an aqueous suspension; dispersing said coupler with mechanical shear, combining said coupler dispersion with an activating water-immiscible organic solvent; and mixing said combined dispersion is disclosed.

Abstract: In a photographic paper production method, a photographic paper support is coated with one or more photographic silver halide emulsion layers and one or more other hydrophilic colloid layers, at least one of the layers including a hardener. The coated support is then dried and conditioned to a temperature of from 24.degree. C. to 33.degree. C. The photographic and other layers on the support are conditioned to an equilibrium relative humidity of from 55% to 70%. The coated support is then stored at the conditioned temperature until the photographic and other layers have achieved a predetermined hardness. The new photographic paper production method reduces the post-production storage time required for photographic paper to achieve an acceptable level of abrasion resistance.

Abstract: A photographic emulsion containing: a photosensitive silver halide; a light-insensitive, reducible silver source; a reducing agent for the light-insensitive, reducible silver source; and a binder consisting essentially of poly(vinyl butyral) having a poly(vinyl alcohol) content of about 17.5 to 21.0 wt. % and at least one solvent selected from the group consisting of: toluene, methyl ethyl ketone, acetone, tetrahydrofuran, and 1,4-dioxane. Additionally, a process for coating a substrate involving applying at least one layer of a molten thermoreversible organogel layer; causing it to gel; and removing residual solvent.

Abstract: A manufacturing process for a light-sensitive material having thereon a magnetic recording layer, the magnetic recording layer having excellent optical transparency, a high magnetic recording performance (S/N ratio) and good graininess. After applying a coating solution on a support, the coating solution containing a magnetic substance, the support is dried while it is passed through an orienting magnetic field to orient the magnetic substance contained in the coating solution in a fixed direction.

Abstract: A coating composition for applying a layer to a photographic element and the resulting photographic element comprising gelatin, water and from 0.3 to 1 gm/100 gms of the composition of a surfactant mixture of 15 to 70 percent by weight of a dioctyl sulfosuccinate, sodium salt or di-fluoroalkylsulfosuccinate, sodium salt, from 35 to 75 percent by weight of a nonylphenoxy polyglycidyl alcohol, and from 3 to 14 percent by weight of perfluoro-octyl sulfonamido, N-hydrogen, N-propylene trimethylammonium iodide based on the total weight of the surfactant mixture; when a dioctyl sulfosuccinate, sodium salt is used, the minimum amount thereof is 0.15 gm/100 gm of coating composition.

Abstract: A process is provided for preparing improved aqueous gelatin compositions for improved coatings, particularly light sensitive photographic coatings, wherein a viscosity increasing amount of a copolymer of an alkali metal or ammonium salt of a sulfonic acid containing polymer with an unsaturated monomer, particularly a copolymer of acrylamide and sodium-2-acrylamido-2-methylpropanesulfonate, is added to an aqueous gelatin composition at a point immediately before any point which requires a high viscosity after and a low viscosity before the addition.

Abstract: A process for the manufacture of a photothermographic element comprising the steps of:a) providing a substrate,b) coating a first layer on said substrate, said first layer comprising an organic polymeric binder, silver halide, reducible silver salt or silver complex, and an organic solvent,c) before 70% of the solvent in said first layer is removed from said first layer, coating a second layer comprising a solvent and a second polymeric binder onto said first layer, said second polymeric binder comprising at least one cellulose ester, at least one of said first layer and said second layer containing a reducing agent for silver ion.

Abstract: A photoimageable composition and process for use of the same. The composition comprises a binder that is a mixture of a phenolic resin and a multifunctional epoxy or vinyl compound and a curing system comprising a photoactive compound capable of generating a curing catalyst capable of crosslinking the binder components. The process for use of the composition comprises application of the composition to a substrate, drying of the same, exposing the dried coating to activating radiation, curing the binder in light exposed areas, developing the coating and thermally curing the developed image. The composition is especially useful as a solder mask.

Abstract: There is provided a method for preparing a biaxially oriented polyester sheet or web, with improved antistatic properties, comprising the steps of(i) stretching said polyester sheet or web first in one direction and second in a direction perpendicular thereto(ii) coating said hydrophobic polyester sheet or web, either before stretching or between said first and second stretching operation, on one or both sides, with a transparent antistatic primer layer, wherein the coating composition of said transparent antistatic primer layer comprises (1) a dispersion of a polythiophene with conjugated polymer backbone and a polymeric polyanion compound and (2) a latex polymer having hydrophilic functionality.The primer layer is coated from an aqueous composition and does not show a substantial change in resistivity depending on relative humidity or wet processing.

Abstract: The invention discloses a continuous method of manufacture of gelled dispersion melts of "small-particle" microprecipitated photographic agents. The continuous melt manufacturing process of this invention provides dispersion melts that are invariant in agent concentration, melt viscosity, and turbidity as a function of the run time and are also very reproducible and robust in repetitive preparations. Many photographic melts of this invention exhibit high photographic activity and light stability of the agents when exposed to light.

Abstract: A photographic material and a preparing method thereof are disclosed, the material comprising a photographic print and a protective layer provided on an image layer of the photographic print by coating latex comprising a resin having a glass transition temperature of 30.degree. to 70.degree. C.

Abstract: A support sheet for a photographic printing sheet having enhanced anti-fogging and anti-yellowing properties comprises a pulp paper substrate sheet, a front coating layer formed on a front surface of the substrate sheet and comprising a cured resinous material produced from electron beam-curable unsaturated organic compound by an electron beam irradiation thereto and mixed with a white pigment, and a back coating layer formed on a back surface of the substrate sheet and comprising a film-forming synthetic resinous material, in which magnesium hydroxide is contained, as an anti-fogging agent, in the substrate sheet.

Abstract: This invention provides composition and method to overcome the very high viscosity of prior small-particle dispersions when admixed with gelatin in aqueous solution for coating a photographic film element.The invention is generally accomplished by the utilization of a second surfactant in the melt formulated by the admixture of the small-particle dispersion and the gelatin solution. The surfactants of this invention, that is, utilized to control the theology of such said melts, have the following general structure: ##STR1## wherein n=5 to 20 andx=1 to 4.

Abstract: Sensitometric Quality Indicator Parameters (SQIP), including Color Radial Error (1), Average Density Error (2), Contrast Mismatch Error (3), HUE (4), and related Auxiliary Quality Parameters, are derived primarily from the deviations in aim values of the red, green, and blue density values over the standard range of exposure steps for a color photographic product. Normalized tolerance limit values common to SQIP 1-3 are established at one exposure reference level within the standard range of exposure steps. A composite graphical display of density deviations versus LOG H exposure, of SQIP 1-4 with associated tolerance limit values versus LOG H exposure, and of the Auxiliary Quality Parameters enables the rapid analysis and disposition of a batch of color photographic product with regard to sensitometric quality.

Abstract: A method for fabricating a photoconductor coupled liquid crystal valve comprising the step of; deposing a transparent electrode on a transparent substrate; forming on said transparent electrode a photoconductive layer formed of amorphous silicon by the ECR; forming on said photoconductive layer an optical shielding layer formed of amorphous silicon by the ECR; forming on said optical shielding layer an optical reflection layer; forming an orientation film on said optical reflection layer; laminating on said orientation film a transparent substrate having a transparent electrode and another orientation film stoked thereon by the above method in such a manner that the two orientation films face each other with a spacer interposed therebetween; and disposing liquid crystals into said spacer.

Abstract: A conformal, substantially uniform thickness layer of photoresist is deposited on a semiconductor wafer by causing photoresist solids to "sediment" out of solution or suspension. Generally, the more conformal the layer, the more uniform the reflectance of the layer and the less variation in underlying feature critical dimension (cd). In order to accommodate possible resulting deviations in photoresist layer thickness causing undesirable reflectance nonuniformities (and cd variations), a top antireflective coating may be applied to the photoresist layer. In the case of a point-by-point lithography process, such as e-beam lithography, the thickness/reflectance variations can be mapped, and exposure doses adjusted accordingly.

Abstract: Hydrophilic organic colloids such as collagen or gelatin are modified for use in photographic elements such as film or paper, or for use as reagents in automated dry chemical analyzers. The modification comprises reaction of some of the carboxy groups attached to the polypeptide with (i) a amide bond forming agent, e.g. 1-pyrrolidinylcarbonylpyridinium chloride, and (ii) a di- or triamine, such as piperazine, diethylenetriamine or ethylenediamine. Such modification enables that colloid to react faster with a gelatin hardener such as bis(vinylsulfonyl)methane (BVSM). When coated over an equal amount of unmodified gelatin, and both layers imbibed with BVSM, a modified gelatin layer showed an enzyme resistance greater than that of the unmodified gelatin. This demonstrates that the modified gelatin hardened preferentially.

Abstract: The invention provides radiation sensitive compositions that comprise an amphoteric polymer, the polymer comprising at least two distinct carrier groups so that the polymer is positively polarized or negatively polarized upon treatment with an acid or base, respectively, enabling the compositions to be electrodeposited either anaphoretically or cataphoretically. Employing this amphoteric polymer in a radiation sensitive composition also allows the use of either an acid or base solution to image and remove the deposited composition irrespective of whether the composition was applied cataphoretically or anaphoretically. The compositions of the invention are also suitably formulated as liquid coating compositions or used to form dry film resists.

Abstract: In preparing an optical recording disk by spin coating a dye-containing solution to an annular substrate to form a recording layer thereon, a circular channel is preformed in the substrate in proximity to the inner peripheral edge of the substrate for defining an inner boundary of the recording layer. Then the recording layer is free of corrugations near its inner boundary, leading to improved adhesion of an overlying protective film and a minimal variation in reflectivity.

Abstract: Photographic materials, such as films and papers, include a support and coatings on the support. The coatings often contain hardeners which cause gelation cross links in the binder in the coating. The extent to which the cross-links have formed at the time of processing of the film or paper affects the appearance of the image produced by processing. Conventionally the cross-links have been allowed to form with time in normal atmospheric conditions. According to the invention, the formation of the cross links is accelerated to substantial completion by a process including incubating the material at a temperature above the glass transition temperature of the coating and below the melting point of the coating in an atmosphere having a relative humidity which causes a moisture content of the coating of 0.1 to 0.25 for a period of time sufficient to substantially complete the hardening, that is, the formation of the cross-links.

Abstract: A photoimageable composition and process for use of the same. The composition comprises a binder that is a mixture of a phenolic resin and a multifunctional epoxy or vinyl ether pound and a curing system comprising a photoactive compound capable of generating a curing catalyst capable of crosslinking the binder components. The process for use of the composition comprises application of the composition to a substrate, drying of the same, exposing the dried coating to activating radiation, curing the binder in light exposed areas, developing the coating and thermally curing the developed image. The composition is especially useful as a solder mask.

Abstract: A method of reducing the tendency toward formation of ripple imperfections in the coating of multilayer photographic elements is disclosed. Coating compositions are prepared for upper, middle, and lower gelatin-containing layers of a layered mass. The middle layer has a gelatin concentration within three weight percent of each of the upper and lower layers and the upper, middle, and lower layers each have a viscosity that differs from a norm by no more than 15%. A laminar flow of a layered mass including the coating compositions is formed and then received as a layered coating on a moving support. A multilayer photographic element is also disclosed.

Abstract: The present invention relates to a device for preparing a photographic liquid which is to be applied in the manufacture of a photographic photosensitive material wherein multiple layers of photographic liquids are applied simultaneously. The present invention has at least one chemical measuring station which measures various kinds of chemicals sent from chemical storage tanks and prepares a photographic liquid which is to be applied to a film, supplies the measured chemicals to a pot and a conveys the chemicals in the pot to a hopper from which the chemicals are supplied to a liquid preparation tank.

Abstract: An optical recording medium comprises a substrate and a recording layer provided on the substrate, and the recording layer contains a recording material having a property in that a difference in temperature between decomposition point of the recording material and melting point thereof is not more than 100.degree. C. In result, the recording layer is capable of forming a complete pit, and the medium has superior reproduction characteristics.

Abstract: A semiconductor wafer 11 is mounted on an elongated member 18, one end of which is rotatable about a transverse axis (14), thereby to distribute a liquid on the upper surface of the wafer more evenly. In order to stabilize the rotation of the elongated member, a second elongated member is preferably attached end-to-end to the elongated member (18) and rotates with it. A counterweight (26) in the second elongated member moves during the rotation such that the distance between the wafer and the central axis and the distance between the center of the counterweight and the axis are substantially equal. The weight distribution is approximately symmetrical about the axis and the structure is dynamically stabilized. The counterweight and the wafer assembly may be moved during rotation by applying air pressure from a source (23) to pistons (13, 26) in the two elongated members.