Means and process for achieving a controlled particle size range of cathode ray tube phosphors

Claim 1

A process for achieving a cathodoluminescent phosphor suspension of predeterminately controlled particle size for use in a cathode ray tube screening formulation to achIeve a high resolution type screen having uniform thickness, said process comprising the steps of: preparing a first aqueous suspension of diverse-particle-size phosphor material; selectively sizing said diverse-particled suspension by transferring at least a portion thereof into a walled micromesh sieve means oriented in a shallow quantity of collector liquid at a depth sufficient to cover the foraminous area of said sieve, said collector liquid being confined in an open flat-bottom container of a substantially rigid smooth surface material freely supported in a temperature controlled liquid bath agitated by a source of ultrasonic energy, said collector liquid container being positioned in a manner that the bottom exterior surface thereof is at least in even fractional wavelength relationship with said energy source; moving said sieve means substantially vertically in said collector liquid in a substantially reciprocating manner combined with a slowly and slightly tilting motion to provide a gentle pumping action, whereupon an exchange of suspension liquid, collector liquid and sieve-sized particles is effected through said foraminous sieve area, said movement and said ultrasonic agitation being continued until said first suspension liquid and the phosphor particles therein passable by said sieve are substantially transferred to said collector liquid to form a second suspension of sieve-sized phosphor particles; removing said sieve means with the residual phosphor particles therein from said second suspension; transferring said second suspension from said ultrasonic energy environment; and adjusting the phosphor solids concentration of said second suspension to that required for utilization in said cathode ray tube screening formulation.