Patent GB-1005311-A (GB)
Title: Multiple lead faceplate for electrostatic printing devices
IPC: C03B37/15
Filed: 1961-09-20
Abstract: A method of producing an electrostatic printing member having a matrix of conductors insulated from each other and extending from one side of the face-plate to the other side thereof, comprises arranging a plurality of wires having a uniform coating of insulating material adhered thereto in an enclosure wherein the coatings on adjacent wires are contiguous and the wires are parallel to each other and to the top opening of the enclosure, fusing the insulating material to form a bundle, slicing a relatively thin array from the bundle wherein the conductors extend from one side of the array to the other side.  The wires are coated by heating a length of tubing to about 140-150 DEG  C. above the softening temperature and drawing the line through the tubing at such a rate that a 1.5-2.5 mil. coating of glass is deposited on the wire.  The coated wires are stacked parallel to the major axis of a rectangular die which is lined with refractory material and an inner coating of pieces of glass of the same material as the coating of the wires. A piece of glass is placed on top of the bundle and a weight placed thereon to maintain a constant pressure.  The firing cycle is accomplished in four stages; outgassing by heating in a vacuum of 50-200 microns of mercury at a temperature of 150-200 DEG  C. below the softening point of the glass for half an hour and then raised at a uniform rate to 10-20 DEG  C. below the softening temperature at which point the vacuum is broken; sealing by continuing the uniform rate of temperature rise to a temperature of 50-60 DEG  C. above the softening point of the glass, e.g. at a rate of 10 DEG  C. per minute, and holding this temperature for 5-15 minutes; homogenizing by plunging the die into a furnace which is at a temperature of 50-100 DEG  C. above the liquidus temperature of the die for about five minutes to remove any crystals that may have been formed; and annealing by rapidly lowering the temperature to a point somewhat above the annealing point of the glass, removing the bundle from the die and placing the bundle in a furnace slightly above the annealing temperature for two hours, after which the bundle is allowed to cool to room temperature.  The bundle is sliced using a diamond saw, and the resulting arrays ground and polished to a thickness of 0.05-0.075 inches, both surfaces being flat and accurately parallel.  The array is then sealed to the tube envelope by placing them in position in an open top furnace at a temperature of 100 DEG  C. above the annealing point of the envelope and softening the edges of the array with a flame. The wire used is preferably of tungsten having a coefficient of expansion of about 47.10-7/ DEG  C. at the setting point of the coating glass and a diameter of 0.001 inches \sB3%.  The coating glass is composed of 76% by weight of SiO2, 4% of Na2O, 14% of B2O3, 2% K2O, 2% of Al2O leaving 2% miscellaneous, and has a coefficient of expansion of 40.10-7/ DEG  C. and softening, annealing and liquidus temperatures of 780 DEG  C., 560 DEG  C. and 1070 DEG  C. respectively.  The envelope glass is composed of 70% SiO2, 4% Na2O, 20% B2O3 and 6% PbO and has a coefficient of expansion of 36.10-7/ DEG  C. and softening and annealing temperatures of 756 DEG  and 518 DEG  C. respectively.