FIELD OF THE INVENTION

The present invention relates generally to systems and methods for dispensing liquid materials, for example, as may be used in applications for coating flexible films and the like, and in particular such systems as are configured for dispensing multiple liquid materials from multiple reservoirs.

BACKGROUND

There exist many systems for the dispensing of liquid materials onto substrates. Generally, two regimes for such dispensing apparatus exist: “drop on demand” and “continuous.” In a drop-on-demand regime, the substrate is coated with material that is dispensed in the form of individual droplets delivered from a nozzle. In a continuous coating regime, the material is dispensed onto the substrate in a continuous flow. Regardless of the dispensing method, it is typically the case that precision control over dispensing pressures are required. Different materials to be dispensed require different dispensing pressures due to their differing rheological properties. Consequently, it is difficult to employ a single dispensing apparatus in connection with a wide range of liquid materials.

SUMMARY

Embodiments of the present invention provide for the dispensing of a precise amount of liquid material, with constant volume and at tunable frequencies, without high tolerance requirements on the pressures used for such dispensing or on the materials being dispensed. Systems configured in accordance with the present invention are characterized by relatively fast open/close switch times, which enable rapid switching between materials for dispensing. The dispensing is accomplished by two separate liquid flow mechanisms, one being an imprecise pressure transfer dispenser, and the other a piston transfer mechanism. In one embodiment, the dispensing system may be used within an apparatus for coating thin and precise layers of rheological material on a flexible film. In such apparatus, the thickness of the layer applied to the film is controlled by the separation distance or gap between two rollers, with the gap width being maintained by two or more microwires disposed in the gap between the rollers. The coating apparatus may also be used without the multi-material dispensing system, e.g., when only a single material is being deposited on the film, and may, in some embodiments, utilize a conventional syringe as a dispenser. Accordingly, aspects of the multi liquid dispensing system and the coating system will be described separately as well as in combination with one another.

In one embodiment of the invention, a coating apparatus includes a dispensing unit arranged to apply rheological material on a flexible film. The film is arranged so as to be drawn through a gap between a pair of rollers of the coating apparatus. The gap defines a thickness of a layer of rheological material applied to the film by being positioned after a coating area in which the rheological material is applied to the film in a direction of film travel. The gap has a width maintained at a desired separation distance between the rollers by microwires suspended through the gap.

The coating apparatus may include a plurality of microwire holders mounted on rack that is slidably secured to a first track formed of one or more rails and secured to a rail holder such that a selected microwire holder with a microwire having a desired thickness is positionable adjacent to the gap between the pair of rollers. Each microwire holder may be displaceable along respective second tracks in a direction perpendicular to an extent of the first track. In such arrangements, each microwire holder may include a holder frame to which drums and wire supports are mounted, one end of a respective microwire of each microwire holder being secured to a respective first drum and another end of the respective microwire being secured to a respective second drum, with a middle portion of the respective microwire being supported by wire supports, such that rotation of respective first and second drums about respective axes of rotation adjusts tension of the respective microwire. The gap width is then defined by two microwire sub-assemblies, each microwire sub-assembly including racks linearly translatable along rails so as to position selected microwire holders having microwires of desired thickness adjacent to surfaces of said rollers.

In various embodiments of the invention, the microwires may be suspended through the gap and in contact with the film, in contact with one of the rollers, but not the film, or in contact with each of the pair of rollers but not the film.

Further, the film to which the rheological material is applied may be opposed across the gap by a second film. Thus, the microwires may be suspended through the gap and in contact with the film to which the rheological material is applied and the second film, in contact with one of the rollers, but not the film to which the rheological material is applied, or in contact with each of the pair of rollers but not the film to which the rheological material is applied or the second film.

Another embodiment of the invention provides for coating a film by dispensing a first rheological material onto a surface of a flexible film while drawing the film through a gap between a pair of rollers. The gap defines a thickness of a layer of the rheological material applied to the film by being positioned after a coating area in which the rheological material is applied to the film in a direction of film travel, and is maintained at a width by positioning first microwires through the gap as the dispensing of the rheological material takes place.

As indicated above, the film to which the first rheological material is applied may be opposed across the gap by a second film and a contact area of the second film across the gap from the film to which the rheological material is applied may be adjusted. In some cases, after adjusting the contact area of the second film, a second rheological material is dispensed onto the surface of the flexible film.

During dispensing of the rheological material onto the film, the width of the gap may be adjusted by exchanging the first microwires for second microwires of different thickness than the first microwires through the gap. Thereafter, the contact area of the second film across the gap from the film to which the rheological material is applied may be adjusted. Or, the dispensing of the first rheological material may be paused while exchanging the first microwires for second microwires of different thickness than the first microwires through the gap, and, thereafter, the contact area of the second film across the gap from the film to which the rheological material is applied may be adjusted. In still other instances, dispensing of the first rheological material may be suspended in favor of dispensing a second rheological material onto the surface of the film, and adjusting the width of the gap by exchanging the first microwires for second microwires of different thickness than the first microwires through the gap.

In another embodiment of the invention, a dispensing unit for dispensing liquid material includes a hollow reservoir configured to accommodate a syringe and having an elongated nipple at one end of the reservoir, a piston including a shaft disposed therein, and a bracket adapted to receive the nipple of the reservoir and the piston. The nipple of the reservoir provides a fluid path for liquid material dispensed from the syringe when supported in said reservoir and the bracket is adapted to receive the nipple of the reservoir such that the fluid path for the liquid material is oriented towards a nozzle disposed in the bracket. The nipple also has holes disposed near an end thereof, and the bracket is adapted to receive the piston oriented with respect to the nipple of the reservoir such that the shaft of the piston is aligned with the holes in the nipple and the nozzle. The shaft is thereby displaceable through the holes in the nipple towards the nozzle.

In some embodiments, the bracket includes rail mounts adapted to interface with rails of a dispenser system. Further, the piston may include a nib at a its top and an air nipple positioned along its longitudinal length. A hollow shaft of the piston that extends through the shaft being in fluid communication with the air nipple. The dispensing unit may also include the syringe received within the reservoir, and the syringe may have a plunger and a cap.

A further embodiment of the invention provides a dispensing system have one or more of the above-described dispensing units. These dispensing units are arranged so as to be laterally displaceable along a length of the dispensing system defined by a lead screw. A first motor is configured to drive the lead screw clockwise or counterclockwise, thereby displacing the dispensing units along the length of the dispensing system. The dispensing system also includes means for selectively actuating pistons of the dispensing units so as to displace respective ones of the shafts of the pistons with respect to the nozzles of the brackets they are received in.

In various embodiments, the means for selectively actuating pistons of the dispensing units include a piston nib capture unit translatable within a piston capture block parallel to a longitudinal axis of respective ones of the pistons of the dispensing units. A second motor is coupled to rotate a piston displacement shaft clockwise or counterclockwise, and the piston displacement shaft has at one end thereof a piston displacement cam. The piston nib capture unit contains a cam recess to receive the piston displacement cam and also includes a slotted recess to receive a nib of a respective one of the shafts of the pistons when disposed over that respective shafts. Thus, when the piston displacement cam rotates with the piston displacement shaft, the piston nib capture unit is translated in a direction defined by the longitudinal axis of the pistons and any respective piston nib that is secured within the slotted recess of the piston nib capture unit is also translated along that respective piston's longitudinal axis.

The end of the piston displacement shaft may be offset from an axis of rotation of the piston displacement shaft and the piston displacement cam may be oval in shape. Preferably, the piston nib capture unit containing the cam recess is fixed so as to remain stationary along an axis orthogonal to the longitudinal axis of the respective ones of the pistons.

In some instances, the dispensing system includes a third motor coupled to rotate a piston stroke shaft, which has at one end a piston stroke cam positioned so as to engage a displaceable cam along the piston displacement shaft. The displaceable cam abuts a spring-loaded wedge connected to the piston displacement cam so that movement of the displaceable cam through engagement with the piston stroke cam forces open the wedge thereby moving a center of rotation of the piston displacement cam radially away from an axis of rotation of the piston displacement shaft. In this way, the length of the stroke of the piston shafts may be adjusted.

A further embodiment of the invention provides a process for dispensing materials. According to the process, one or more syringes are filled with liquid materials of interest and subsequently placed in respective ones of a plurality of reservoirs of a dispenser unit. Respective pressures of the syringes for dispensing droplets of the liquid materials of interest when respective piston shafts of pistons associated with the plurality of reservoirs are activated are set (e.g., by adjusting positions of respective plungers of the one or more syringes), and a control unit of the dispenser unit is programmed with a desired print pattern of the liquid materials of interest. The eccentricity of a piston displacement cam of the dispenser unit is set so as to define a piston shaft stroke length of the pistons. Thereafter, a printing operation according to the desired print pattern is run, wherein during that printing operation actuators coupled to the control unit effect dispensing of the liquid materials from the reservoirs by displacing the respective piston shafts of the pistons associated with the plurality of reservoirs along their longitudinal lengths, thereby creating said droplets of the liquid materials. The liquid materials of interest may be replaced as needed during the printing operation.

In one instance, displacement of each respective piston shaft is achieved by way of one of the actuators rotating a shaft, one end of which is offset from its axis of rotation, forcing a piston nib capture unit to be displaced in a direction parallel to an axis of the longitudinal lengths of the pistons as the shaft rotates. The piston nib capture unit captures a top nib of a selected respective piston in a slotted recess within which top nib is positioned as the piston nib capture unit moves, thereby causing movement of the shaft of the selected respective piston as well. Also, a second of the actuators may displace the plurality of reservoirs of the dispensing unit along a length of the dispensing unit between movements of the shafts of each selected respective piston by rotating a lead screw clockwise or counterclockwise. And, a third of the actuators may change the piston shaft stroke length by changing an offset distance of the end of shaft from its axis of rotation.

Yet another embodiment of the invention provides a coating apparatus having one or more dispensing units of the kind discussed above. The dispensing units are arranged so as to apply rheological material from syringes accommodated within respective hollow reservoirs of the dispensing units on a flexible film drawn between a pair of spools, under respective nozzles of the dispensing units and through a gap defined by a pair of rollers of the coating apparatus. The gap defines a thickness of a layer of rheological material applied to the film by being positioned after a coating area in which the rheological material from the syringes is applied to the film in a direction of film travel, and the gap is maintained at a desired separation distance between the rollers by microwires suspended through the gap. So as to allow for gap widths of different dimensions, a plurality of microwire holders may be mounted on rack, and the rack slidably secured to a first track formed of one or more rails secured to a rail holder such that a selected microwire holder with a microwire having a desired thickness is positionable adjacent to the gap between the pair of rollers.

Each microwire holder may be displaceable along respective second tracks in a direction perpendicular to an extent of the first track. Further, each microwire holder may include a holder frame to which drums and wire supports are mounted. In such instances, one end of a respective microwire of each microwire holder is secured to a respective first drum and another end of the respective microwire is secured to a respective second drum, with a middle portion of the respective microwire being supported by wire supports such that rotation of respective first and second drums about respective axes of rotation adjusts tension of the respective microwire. In still other embodiments, the gap may be defined by two microwire sub-assemblies, each including racks linearly translatable along rails so as to position selected microwire holders having microwires of desired thickness adjacent to surfaces of said rollers.

These and further embodiments of the invention are described in detail below.

