HK1091785B - Apparatus for depositing droplets - Google Patents

Description

Device for depositing ink drops

Technical Field

The present invention relates to the deposition of ink droplets on a substrate.

Background

An ink jet printer is a device for depositing (depositing) ink droplets on a substrate. Ink jet printers typically include an ink path from an ink supply to a nozzle path. The nozzle path terminates in a nozzle orifice from which ink drops are ejected. Ink drop ejection is controlled by pressurizing ink in the ink path with an actuator, which may be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printing device has an array of ink paths with corresponding nozzle openings and associated actuators. Ink drop ejection from each nozzle hole can be independently controlled. In drop-on-demand printing devices, each actuator is fired to selectively eject a drop at a particular pixel location of an image as the printing device and a print substrate are moved relative to each other. In high performance printing devices, the nozzle holes typically have a diameter of 50 microns or less, e.g., about 25 microns, are dispersed at a pitch of 100 to 300 nozzles/inch, have a resolution of 100 to 3000dpi or more, and provide ink droplets having a volume of about 1 to 70 picoliters (pl) or less. The drop ejection frequency is typically 10kHz or higher.

U.S. patent No.5265315 to Hoisington et al, the entire contents of which are incorporated herein by reference, describes a printing apparatus having a semiconductor body and a piezoelectric actuator. The body is composed of silicon that is etched to form the ink chamber. The nozzle holes are formed by a separate nozzle plate attached to the silicon body. Piezoelectric actuators have a layer of piezoelectric material that changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber disposed along the ink path. Fishbeck et al, U.S. Pat. No. 4825227 and Hine, U.S. Pat. No.4937598, both of which are incorporated herein by reference in their entirety, describe piezoelectric ink jet printing devices.

Printing accuracy is affected by many factors, including the size and velocity uniformity of ink drops ejected by nozzles in a device or among multiple devices in a printer. The drop size and drop velocity uniformity are in turn affected by factors such as the dimensional uniformity of the ink paths, acoustic interference effects, contamination in the ink flow paths, and the actuation uniformity of the actuators.

Commercial printing paper may have loose particles that can reduce the quality of the print.

Disclosure of Invention

In general, one aspect of the invention features an apparatus for depositing ink droplets on a substrate. The apparatus includes a support for a substrate, a droplet ejection assembly positioned above the support for depositing droplets of ink on the substrate, an enclosure, and a source of pressurized gas connected to the enclosure. The enclosing structure forms, together with the support, an enclosed area through which ink droplets are ejected onto the substrate. The closure structure, together with the support, also forms an inlet gap and an outlet gap through which the substrate travels. Pressurized gas associated with the enclosure provides a flow of gas from the enclosure through the apertures.

In some embodiments, the enclosure includes a hood disposed over the droplet ejection assembly. The inlet and outlet apertures and the gas pressure may be adjusted to deliver gas through the apertures at a velocity that is higher than the velocity of the substrate. The inlet gap and outlet gap may be between about 0.006 to about 0.100 inch for a 0.004 inch substrate. It may be advantageous to purge particulate matter and moisture from a pressurized gas source. In some cases, the pressure of the pressurized gas is about 0.1 inches to about 10 inches of water above normal atmospheric pressure.

In other embodiments, the enclosure includes a manifold distribution system that delivers pressurized gas to each of the slots adjacent to each of the apertures.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

Drawings

FIG. 1 is a schematic side view of an apparatus for printing on a substrate.

Fig. 2 is a perspective view of one of the printing stations shown in fig. 1.

FIG. 2A is a cross-sectional view of the printing station shown in FIG. 2 taken along line 2A-2A.

Fig. 3 is a perspective view of an alternative printing station.

FIG. 3A is a cross-sectional view of the printing station shown in FIG. 3 taken along line 3A-3A.

Like reference symbols in the various drawings indicate like elements.

Detailed Description

Fig. 1 shows an apparatus 10 for continuously depositing ink droplets on a substrate 12 (e.g., paper). The substrate 12 is pulled from a roll 14 on a supply support 16 and supplied to a series of droplet deposition stations 18 for placing a large number of droplets of different colors on the substrate 12. Each droplet deposition station 18 has a stationary droplet ejection assembly (ink jet) 20 positioned above the substrate 12 for depositing droplets on the substrate 12. Beneath the substrate 12 in each deposition station 18 is a substrate support structure 22 (e.g., a porous platen). After the substrate 12 leaves the final deposition station 24, it may reach a pre-processing station 26. A pre-processing station 26 may be used to dry the substrate 12. It may also be used for UV treatment or other radiation treatment of the substrate 12. Next, the base substrate 12 proceeds to a processing station 28 where it is folded and cut into finished products 30. The substrate feed rate is about 0.25 to 5.0 meters/second or higher. The droplet ejection assembly may eject droplets of ink. It is also possible to eject UV-treatable materials, radiation-treatable materials or other materials that can be delivered as droplets.

Fig. 2 shows an apparatus 32 in which the printable substrate 12 is advanced in the machine's longitudinal direction under the droplet ejection assembly 20. In this embodiment, droplet ejection assembly 20 is comprised of a large number of discrete print units 21 mounted and sealed in a print unit support 23. The unprinted substrate 12 enters the inlet side 36 and the printed substrate 38 exits the outlet side 40. A substrate support structure 22 (e.g., a porous platen) supports the printable substrate 12. The substrate support structure 22 may also be a curved non-porous platen or a rotating drum (not shown). Mounted above the droplet ejection assembly is a hood 42 for receiving pressurized gas 44 through an inlet 46.

Figure 2A shows the device shown in figure 2, taken along the line 2A-2A. Pressurized gas entering hood 42 travels to a proximal edge 52 and a distal edge 54 of enclosed area 50 formed by print unit support 23 and support structure 22. From here, the pressurized gas exits the paper inlet gap 56 and the paper outlet gap 58. This arrangement allows debris to be removed before it has a chance to enter the print zone. In addition, the pressurized gas may help keep the substrate flat against the support structure. The pressure in enclosure 42 is between about 0.1 inches and about 10 inches of water above nominal atmospheric pressure. Having both the paper feed gap 56 and the paper exit gap 58 will maintain pressure balance under the enclosed area 50, for example to reduce the risk of paper jams.

The gas pressure should be adjusted so that the gas velocity through the gap is between about 0.25 and about 5 meters/second. If the air pressure is too high, the image may be damaged, the energy requirements may be limited, and excessive noise may be present. Excessive noise may be generated by turbulence, and as the velocity becomes higher, the turbulence becomes greater, and then the noise becomes greater. The energy required for a given flow rate is proportional to the gas flow, so that as the flow rate becomes higher, the energy demand becomes greater.

For a 0.004 inch substrate (e.g., paper), the inlet gap is about 0.006 to about 0.100 inch and the outlet gap is about 0.006 to about 0.100 inch. If the gap is too large, the energy requirements may be limited, if the gap is too small, the image may be smeared or a paper jam may be present.

The substrate may be paper, plastic or other printable substrate. Typical substrates are about 0.002 to about 0.008 inches thick.

The pressurized gas may be filtered, for example, with a HEPA filter to remove particulate matter and excess moisture. In some cases, water or other solvents may be added to prevent clogging of the droplet ejection assembly. In some cases, an inert gas environment may be required to help treat the ink droplets. In other cases, other gases may be required to help treat the ink droplets.

Fig. 3 shows an alternative apparatus 60 for cleaning the print path. In this embodiment, pressurized gas is delivered to a manifold distribution system 62 contained in print unit support 23. FIG. 3A shows this alternative apparatus 60 taken along line 3A-3A and shows the pressurized gas advancing from a manifold distribution system 62 through a slit 64 in the distribution system. In this embodiment, slit 64 is continuous along the entire lateral length of print unit support 23. The slit 64 delivers pressurized gas to the enclosed area 50 and then to the paper entry gap 56 and the paper exit gap 58.

The inlet and outlet gaps are adjusted together with the gas pressure and the slit width so that the gas velocity through the gaps is preferably about 1.0 m/s.

For a 0.004 inch substrate (e.g., paper), the inlet gap and the outlet gap are about 0.006 to about 0.100 inch.

Various embodiments of the present invention have been described above. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the apparatus shown in FIG. 3 may be modified by using a plurality of small holes (not shown) in print unit support 23, rather than slits 64, for delivering pressurized gas to enclosed area 50. The orifices may be configured so that the pressurized gas does not interfere with the deposition of ink droplets on the substrate 12. The deposited droplets may be ink or other material. For example, the deposited droplets may be a material that can be UV treated or otherwise radiation treated or other material that can be delivered as droplets. Accordingly, other embodiments are within the scope of the following claims.

Claims (22)

1. An apparatus for depositing ink droplets on a substrate, the apparatus comprising:

a support for the substrate;

a droplet ejection assembly disposed above the support for depositing the droplets on the substrate on the support;

a closed structure forming an enclosed area with the support through which the ink droplets are ejected onto the substrate, the closed structure further forming an inlet gap and an outlet gap with the support through which the substrate travels; and

a source of pressurized gas connected to the enclosure to provide a flow of gas from the enclosure through the inlet and outlet apertures;

wherein the velocity of the gas stream flowing through the inlet and outlet apertures is greater than the velocity of the substrate.

2. The apparatus of claim 1, wherein the enclosure structure comprises a hood disposed above the droplet ejection assembly.

3. The apparatus of claim 2, wherein the pressurized gas has a pressure of 0.1 inches to 10 inches of water above normal atmospheric pressure.

4. The apparatus of claim 2 wherein said inlet gap is between 0.006 and 0.100 inches.

5. The device of claim 2 wherein the outlet gap is between 0.006 and 0.100 inches.

6. The apparatus of claim 1, wherein the enclosure structure comprises a manifold distribution system that delivers pressurized gas to respective slots of the manifold distribution system located adjacent the inlet and outlet apertures.

7. The apparatus of claim 6, wherein the pressurized gas has a pressure of 0.1 inches to 10 inches of water above normal atmospheric pressure.

8. The apparatus of claim 6 wherein said inlet gap is between 0.006 and 0.100 inches.

9. The device of claim 6 wherein the outlet gap is between 0.006 and 0.100 inches.

10. The apparatus of claim 1, wherein the ink drops comprise ink.

11. The device of claim 1, wherein the substrate comprises paper.

12. The apparatus of claim 1, the support being a continuously moving support.

13. The apparatus of claim 1, further comprising a filter for removing particulate matter from the pressurized gas source.

14. The apparatus of claim 1, further comprising adding moisture to the source of pressurized gas.

15. The apparatus of claim 1, further comprising adding a solvent to the source of pressurized gas.

16. The apparatus of claim 1, wherein the inlet and outlet gaps and the pressure of the pressurized gas are sized to deliver the gas through the inlet and outlet gaps at a velocity greater than the velocity of the substrate.

17. The apparatus of claim 1, wherein the gas is air.

18. The apparatus of claim 1, wherein the gas has an oxygen content lower than air.

19. The apparatus of claim 1, wherein the gas has a higher oxygen content than air.

20. The device of claim 1 wherein said inlet gap is between 0.006 and 0.100 inches.

21. The device of claim 1 wherein said outlet gap is between 0.006 and 0.100 inches.

22. The apparatus of claim 1, wherein the inlet and outlet gaps and the pressure of the pressurized gas are sized to lay the substrate flat on the support.