Application of fluidized material to a substrate using intermittent charges of compressed air

A venturi slot applicator for applying a fluidized material to a moving web during application cycles, while said moving web passes underneath said venturi slot applicator in a direction of travel, comprising:

• a feedblock positioned above said moving web, said feedblock having an applicator slot and at least one supply slot, said feedblock having at least one cavity reservoir for holding said fluidized material, said at least one cavity reservoir communicating with said applicator slot through said at least one supply slot, said feedblock having at least one orifice for admitting said fluidized material into said at least one cavity reservoir;
• wherein:
• said applicator slot has an inlet for admitting a charge of compressed air during each of said application cycles, said applicator slot having at least one ledge adjacent to said at least one supply slot for accumulating said fluidized material between each of said application cycles, said applicator slot having a venturi region adjacent to said at least one ledge, width of said applicator slot decreasing to a minimum in said venturi region and then increasing again, said applicator slot having an outlet above said web;
• said venturi slot applicator further comprising:
• supply means for continuously supplying said fluidized material to said orifice of said feedblock under pressure, said pressure of said fluidized material forcing said fluidized material through said cavity reservoir and supply slot and into said applicator slot;
• a rotary air valve comprising a rotor and a stator, said rotor and stator cylindrical in cross section and hollow, said rotor mounted coaxially within said stator, said rotor and stator having a common axis;
• wherein:
• said rotor has an outer surface with at least one channel machined in said outer surface and extending through to said hollow interior of said rotor, said at least one channel parallel to said common axis, said rotor adapted for rotation;
• and
• said stator has an outer surface and an inner surface, said inner surface abutting and covering said outer surface of said rotor, said stator having a channel machined in said outer surface of said stator, said channel extending through to said hollow interior of said stator, said channel parallel to said common axis, said channel having an inlet adjacent to said rotor and an outlet adjacent to said inlet of said applicator slot;
• said venturi slot applicator further comprising:
• compressed air supply means for supplying compressed air to said hollow interior of said rotor;
• drive means for rotating said rotor at an angular velocity, said drive means bringing said at least one channel in said rotor into periodic alignment with said channel in said stator during each of said application cycles, allowing a charge of compressed air to travel from said hollow interior of said rotor through said channels in said rotor and said stator into said applicator slot, said venturi region creating a region of low pressure in said charge of compressed air, thereby entraining said fluidized material on said at least one ledge in said charge of compressed air, said charge of compressed air discharging said material entrained in said charge through said outlet of said applicator slot and onto said moving web.

A method of applying spaced-apart transverse bands of fluidized material onto a web, said method comprising the steps of:

• moving a web along a first path;
• at a location along said path discharging a fluidized material repetitively from a slotted outlet extending transversely across said web path, said discharging step comprising the steps of:
• including a venturi with said slotted outlet;
• accumulating fluidized material in proximate relation along said slotted outlet while maintaining open communication between said accumulating fluidized material and said venturi of said slotted outlet through a supply slot, said slotted outlet remaining open during said accumulating step;
• repetitively drawing a predetermined amount of said accumulating fluidized material through said supply slot and out said slotted outlet onto said web by repetitively discharging a charge of compressed gas through said venturi and said slotted outlet.