Method of feeding particulate material to a heated vaporization surface

Abstract

A method for the vaporization of particulate material includes providing one or more containers each containing possibly distinct particulate materials each having at least one component, fluidizing the particulate material in at least one of the containers, and providing a vaporization zone that is thermally isolated from at least one of the containers. The method further includes delivering particulate material received from each container to the vaporization zone, and applying heat to vaporize the delivered particulate materials at the vaporization zone.

Description

FIELD OF THE INVENTION

The present invention relates to making organic light emitting diode (OLED) devices and more particularly to controllably feeding organic particulate material to a heated surface.

BACKGROUND OF THE INVENTION

An OLED device includes a substrate, an anode, a hole-transporting layer made of an organic compound, an organic luminescent layer with suitable dopants, an organic electron-transporting layer, and a cathode. OLED devices are attractive because of their low driving voltage, high luminance, wide-angle viewing and capability for full-color flat emission displays. Tang et al. described this multilayer OLED device in their U.S. Pat. Nos. 4,769,292 and 4,885,211.

Physical vapor deposition in a vacuum environment is the principal means of depositing thin organic material films as used in small molecule OLED devices. Such methods are well known, for example Barr in U.S. Pat. No. 2,447,789 and Tanabe et al. in EP 0 982 411. The organic materials used in the manufacture of OLED devices are often subject to degradation when maintained at or near the desired rate-dependent vaporization temperature for extended periods of time. Exposure of sensitive organic materials to higher temperatures can cause changes in the structure of the molecules and associated changes in material properties.

To overcome the thermal sensitivity of these materials, only small quantities of organic materials have been loaded in sources and they are heated as little as possible. In this manner, the material is consumed before it has reached the temperature exposure threshold to cause significant degradation. The limitations with this practice are that the available vaporization rate is very low due to the limitation on heater temperature, and the operation time of the source is very short due to the small quantity of material present in the source. In the prior art, it has been necessary to vent the deposition chamber, disassemble and clean the vapor source, refill the source, reestablish vacuum in the deposition chamber and degas the just-introduced organic material over several hours before resuming operation. The low deposition rate and the frequent and time consuming process associated with recharging a source has placed substantial limitations on the throughput of OLED manufacturing facilities.

A secondary consequence of heating the entire organic material charge to roughly the same temperature is that it is impractical to mix additional organic materials, such as dopants, with a host material unless the vaporization behavior and vapor pressure of the dopant is very close to that of the host material. This is generally not the case and as a result, prior art devices frequently require the use of separate sources to co-deposit host and dopant materials.

A consequence of using single component sources is that many sources are required in order to produce films containing a host and multiple dopants. These sources are arrayed one next to the other with the outer sources angled toward the center to approximate a co-deposition condition. In practice, the number of linear sources used to co-deposit different materials has been limited to three. This restriction has imposed a substantial limitation on the architecture of OLED devices, increases the necessary size and cost of the vacuum deposition chamber and decreases the reliability of the system.

Additionally, the use of separate sources creates a gradient effect in the deposited film where the material in the source closest to the advancing substrate is over represented in the initial film immediately adjacent the substrate while the material in the last source is over represented in the final film surface. This gradient co-deposition is unavoidable in prior art sources where a single material is vaporized from each of multiple sources. The gradient in the deposited film is especially evident when the contribution of either of the end sources is more than a few percent of the central source, such as when a co-host is used.

A further limitation of prior art sources is that the geometry of the interior of the vapor manifold changes as the organic material charge is consumed. This change requires that the heater temperature change to maintain a constant vaporization rate and it is observed that the overall plume shape of the vapor exiting the orifices can change as a function of the organic material thickness and distribution in the source, particularly when the conductance to vapor flow in the source with a full charge of material is low enough to sustain pressure gradients from non-uniform vaporization within the source. In this case, as the material charge is consumed, the conductance increases and the pressure distribution and hence overall plume shape improve.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an effective way to vaporize powders.

This object is achieved by a method for the vaporization of particulate material, comprising:

(a) providing one or more containers each containing possibly distinct particulate materials each having at least one component;

(b) fluidizing the particulate material in at least one of the containers;

(c) providing a vaporization zone that is thermally isolated from at least one of the containers;

(d) delivering particulate material received from each container to the vaporization zone; and

(e) applying heat to vaporize the delivered particulate materials at the vaporization zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first embodiment of the invention;

FIG. 2 is a cut-away illustration of a second embodiment of the invention;

FIG. 3 is a detailed view from a different direction of a portion of the embodiment shown in FIG. 2;

FIG. 4 is a section view of an alternative embodiment of the invention;

FIG. 5 is a detailed view of a variation of the embodiment in FIG. 2; and

FIG. 6 illustrates an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to FIG. 1, an apparatus 5 for precision controlled evaporation of a particulate material 10 is shown. The apparatus includes a container 15 which contains particulate material 10 having at least one component, such as an organic material. A transporting arrangement, implemented here as a rotating disk 40, receives particulate material 10 from the container 15. Particulate material 10 is transported by the rotating disk 40 to a vaporization zone 50 where a heat source 55 flash evaporates the transported particulate material. The vaporization zone 50 is defined to be isolated from the container 15 by eliminating conductive heat paths between heat source 55 and container 15. For OLED applications, the apparatus 5 would be placed in a vacuum which eliminates convective transport as well. Further isolation is achieved by utilizing low thermal mass, low specific heat, low thermal conductivity materials to produce the rotating disk 40. Radiative heating of the container 15 can be reduced or eliminated by appropriate design of the heat source 55 or by interposing a thermally grounded shield between the heat source 55 and the container 15.

The rotating disk 40 is positioned so that a portion of the rotating disk 40 can rotate through the container 15. The rotating disk 40 is charged with an electrostatic charge so that as it rotates through particulate material 10 and particulate material 10 is attracted to the rotating disk 40. As the rotating disk 40 rotates, the electrostatically attracted particulate material 10 is carried to the heating zone 50 and between a pair of heat sources 50. The rotating disk 40 is maintained at a temperature below the vaporization temperature of particulate material 10 and is preferably made of a material with low thermal conductivity, low specific heat, and low thermal mass.

Turning now to FIG. 2, an alternative embodiment of the invention is shown. The apparatus 5 includes a container 15 which contains particulate material 10 having at least one component material that is to be vaporized. An agitator screw 75 can be placed in the container 15 to fluidize particulate material 10. In addition, one or more vibratory actuators 80 can be placed on a funnel 85 (formed by the container 15) to improve the flow of the fluidized particulate material 10 from the container 15 into an auger enclosure 22. In this context, fluidized particulate material is a material that is capable of flowing in a fluid-like manner. In this embodiment the transporting arrangement includes a first transporting mechanism and a second transporting mechanism. The first transporting mechanism, is implemented here as a rotatable auger 20 and is disposed in the auger enclosure 22 which in turn is disposed in a material receiving relationship with the container 15. The auger enclosure 22 has openings 24 for receiving particulate material 10 from the container 15. The rotatable auger 20 moves particulate material 10 along a feed path 25 to a delivery zone 30. Rotation of the rotatable auger 20 by a motor 45 causes the particulate material 10 to be subject to pressure at the delivery zone 30; such pressure forces the particulate material 10 through one or more openings 35 formed in a member 36. The member 36 can be a part of the auger enclosure 22 and forces the particulate material 10 into contact with the second transporting mechanism, implemented here as a rotating disk 40. The particulate material 10 is transported by the rotating disk 40 to a heating zone 50 where a heat source 55 flash evaporates the particulate material 10 transported by the second transporting mechanism.

The rotating disk 40 is maintained at a temperature below the effective vaporization temperature of the component materials of particulate material 10 and its rotation carries a controllable quantity of particulate material 10 at a controllable velocity from the auger screw 20 to a location where heat is applied so as to rapidly vaporize a component portion of the transported particulate material 10 at a very localized portion of the rotating disk 40. Choosing a rotating disk 40 having low thermal conductivity, low specific heat and low thermal mass concentrates the heat in a localized area and produces a high thermal gradient that permits flash vaporization to occur. As in the previous embodiment, the particulate material 10 is thermally isolated from the heat source 55 by the elimination of conductive and convective paths. Alternatively, there is an option of interposing a shield that acts to block radiative heating.

FIG. 3 provides a detailed view of the rotating disk 40. A plurality of recesses 60 are apparent from this viewpoint. Each recess 60 carries a predetermined quantity of particulate material 10 from the delivery zone 30 to the heating zone 50 as the rotating disk 40 rotates. A doctor blade 90 is utilized to ensure a repeatable fill in each of the recesses 60 in the face of the rotating disk 60 as well as to remove particulate material 10 adhering to the rotating disk 40 in the regions between recesses 60. A recess 60 in the rotating disk 40 is not the only way particulate material 10 may be carried from the heating source 55. The face of the rotating disk 40 can be featured so as to retain a determinate volume of powder much like a Gravure roll. The rotating disk 40 can be constructed of a flexible or rigid porous material such as an electroform, a sintered material or a screen, all of which may contain openings or recesses designed to capture particulate material 10. Alternately, a thin rotating disk 40 can have a non-porous construction where features are embossed, cut, or etched into at least one of its faces to acquire and retain particulate material 10 in a number of voids. Electrostatic attraction can be used effectively to cause essentially all of the particulate material 10 to adhere to the rotating disk 40 as it is abraded off of the extruded particulate material 10. The rotating disk 40 can be covered by a screen, providing a plurality of recesses into which particulate material 10 may be received at the delivery zone 30 and carried to the heating zone 50. Although the recesses 60 are shown as having substantially the same size, it can be desirable to have recesses of different sizes. The transporting mechanisms can be single stage or a plurality of stages and can take any of the many forms known within the field of particulate material transport.

FIG. 4 shows a section view of an alternative embodiment of the invention. In this embodiment a translational mechanism, implemented as a belt 65, replaces the auger in the feed path 25. At the end of the feed path 25 in the delivery zone 30 the force of gravity feeds the particulate material 10 from the belt 65 onto the rotating disk 40 which is horizontally configured. The rotating disk 40 takes the particulate material 10 from the delivery zone 30 to the heating zone 50 where it is flash evaporated. The belt 65 can contain individual recesses for receiving particulate material 10, it can be a smooth belt, or it can have any of the powder retention mechanisms discussed in the description of FIG. 3.

FIG. 5 shows another embodiment of the invention including two containers 95. The containers 95 can each contain the same or different particulate materials 10. The rotating disk 40 contains recesses 60 which in this figure are two distinct sizes, permitting a controlled, but distinct, amount of particulate material 10 to be dispensed from separate augers disposed in auger enclosures similar to FIG. 2.

FIG. 6 illustrates another embodiment of the invention that utilizes a single stage of transport. The apparatus 5 includes a container 15 containing a fluidized particulate material 10. A translational mechanism in the form of a belt 65 receives particulate material 10 from the container 15. The particulate material 10 drops onto the belt and into recesses 60. A doctor blade 90 insures that each recess 60 contains a uniform amount of particulate material 10 while also removing excess particulate material 10 from the surface of the belt 65 around and between the recesses 60. In this particular embodiment the heat source 55 takes the form of one of the support rollers for the belt 65. A heat sink 100 is interposed as an idler roller to provide thermal isolation between the heat source 55 and the container 15 having the fluidized particulate material 10.

Particulate material 10 can include a single component or can include two or more vaporizable components, such as organic material components, each one having a different vaporization temperature.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, namely for delivery of organic particulate materials to a vaporization zone. However, it can be appreciated that the present invention applies more broadly to particulate materials, including organic and other types of particulate materials. The term “particulate materials” can include a broad range of substances in particulate form, including, but not limited to, crystals, nanotubes, powders, needles, flakes, and other solid materials that can be classified as discontinuous, for example. Moreover, the particulate materials may be provided in a mixture containing a quantity of inert material or materials acting as a carrier for the component material. Inert carriers could include other types of solid materials as well as pastes and liquids, particularly liquid materials having higher viscosities. Any inert material selected must be compatible with the vaporization process, such that the inert carrier is appropriately discarded before or during the vaporization of the component particulate material. For example, the inert carrier can be selected from materials having a much higher vaporization temperature than the desired particulate component material. It can thus be understood that variations and modifications can be effected within the spirit and scope of the invention.

PARTS LIST

• 5 Apparatus
• 10 Particulate material
• 15 Container
• 20 Rotatable auger
• 22 Auger enclosure
• 24 Auger enclosure opening
• 25 Feed path
• 30 Delivery zone
• 35 Opening
• 36 Member
• 40 Rotating disk
• 45 Motor
• 50 Vaporization zone
• 55 Heat source
• 60 Recess
• 65 Belt
• 75 Agitator screw
• 80 Vibratory actuator
• 85 Funnel
• 90 Doctor blade
• 95 Containers
• 100 Heat sink

Claims

1. A method for the vaporization of particulate material, comprising: (a) providing one or more containers each containing possibly distinct particulate materials each having at least one component;(b) fluidizing the particulate material in at least one of the containers;(c) providing a vaporization zone that is thermally isolated from at least one of the containers;(d) delivering particulate material received from each container to the vaporization zone; and(e) applying heat to vaporize the delivered particulate materials at the vaporization zone.

2. The method according to claim 1 wherein the delivery step is provided by transporting means divided into a first stage and a second stage.

3. The method of claim 2 wherein the first stage transporting means includes an auger mechanism or a translational member.

4. The method of claim 2 wherein the second stage transporting means includes a rotating disk or a translational member.

5. The method according to claim 1 wherein the delivery step is provided by a single stage and includes a rotating disk or translational member.

6. The method according claim 1 further including providing a plurality of cells, each cell receiving a predetermined amount of particulate material.

7. The method according to claim 6 wherein the cells have at least one first size receiving a first predetermined amount of particulate material and at least a second size receiving a second predetermined amount of particulate material.

8. The method according to claim 7 wherein the particulate material in the cell of the first size is delivered from a first container of particulate material and the particulate material in the cell of the second size is delivered from a second container of particulate material, where the particulate material of the first container is different from the particulate material of the second container.

9. The method according to claim 1 further including providing a screen having openings and the openings are sized to capture particulate material.

10. The method according to claim 6 further including removing excess particulate material from the cells and from interstitial areas between cells.

11. The method according to claim 1 wherein the delivery step is provided by a moveable member and further including electrostatically transferring particulate material to the moveable member from the container.