JPH1044404A - Liquid catching apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid droplet catching apparatus (for continuous ink jet printing apparatus) equipped with a vacuum port minimizing an air stream necessary for feeding back ink without generating falling or dripping. SOLUTION: A catching apparatus has a catching surface 20 receiving a selectively charged ink droplet and a curved part 28 guiding the flow of the selectively charged ink droplet from the catching surface to a throat part 22 and the throat part 22 receives the flow of the selectively charged ink droplet. The throat part 22 has a short and narrow gap equipped with a suddenly expanded part on its downstream side and two converged/diffused channels 33 formed from an oval island part 30 and an oval side wall 32. The vacuum port 26 consisting of the catching surface 20, the curved part 28 and the throat part 22 forms a decelerated air stream and returns the selectively charged ink liquid droplet from a printing head to a fluid apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a droplet capture device for a continuous ink jet printing device, and more particularly to an improved capture device structure for controlling the flow of captured ink.

[0002]

2. Description of the Related Art Generally, a continuous ink jet printing apparatus has a print head manifold for supplying pressurized ink, and ejects a stream of ink from a print head orifice plate communicating with the manifold. By applying a periodic wobble (e.g., vibration) to the liquid stream with an electromechanical transducer, the stream is broken into droplets of uniform size and shape.

A charge plate comprising an array of addressable electrodes is located near a stream breakpoint and selectively charges adjacent droplets in response to a print information signal. The charged droplet is deflected from its normal trajectory. For example, in a typical binary printing mode, charged droplets (ie, droplets not used for printing) are deflected and captured by a capture device, and uncharged droplets reach the print media.

[0004] Various capture devices have been proposed as structures for capturing and recirculating droplets not used for printing from the print head on the way.

[0005]

In such a capture device, several potential problems must be considered. First, the capture device intercepts ink droplets that are not used for printing in a manner that prevents splashing of the ink droplets onto the print media and the generation of ink fog that can contaminate the print media. Must. Second, the capture device must effectively remove the captured droplet from the droplet capture area so that the ink film formed on the capture surface does not obstruct the flight path of the printed droplet.

To achieve these objectives, some existing capture devices for existing printheads are designed to prevent ink from falling off the printhead when the printhead is operated at various heights and angles. About 3 scfh of air flow is required. The two-phase airflow condition is a slug flow, in which the foamy ink slug moves at a speed greater than the average liquid velocity. As a result, 12 to 24 feet of ink (360-7
Upon returning to the fluidic device at a speed of 20 cm), the ink is agitated by the air flow and evaporates or atomizes. Such an air flow creates several problems.

First, existing capture device constructions require a screen to regulate the high velocity air flow to the capture device. The location and shape of the screen is important for the proper functioning of the printhead and requires extremely high precision. Second, the high evaporation rate requires a refill device that uses a specially formed fluid to replenish the evaporated ink. Third, variable (i.e., machine-to-machine, environment-to-environment) high evaporation rates affect ink density control using droplet counting methods. In addition, exposing the ink to air can create an ink mist in the fluidic device, requiring a replaceable filter to protect the elements of the vacuum device from the ink mist. In some inks, exposing the ink to air causes a slight aging phenomenon, which causes ink deterioration. Further, for some inks, exposing the ink to air causes bubbles to form, which adversely affect the function of the fluidic device and / or printhead. In addition, the high-speed air flow in the capturing device may take in paper dust and dust and interfere with print droplets to cause printing failure. Also, the high velocity airflow in the trapping device may alter the printing droplets in cooperation with the malformed screen, which may result in poor printing.

[0008] One way to improve the structure of the capture device is to provide a capture device having a screen located on the throat of the capture device for flowing ink into the throat of the capture device. However, capture device assemblies with screens located in the throat of the capture device are difficult to manufacture. Regulation of ink flow and air flow to the throat of the capture device is very sensitive to screen position and shape.

[0009] In view of the above problems, low speed airflow in the capture device is desirable. However, with respect to the slow air flow in the capture device, ink is retained in the print head, especially when the print head is operating at an angle to the direction of gravity, when the print head operates at a low air flow. Is difficult to do.

[0010] Therefore, there is a need to provide a low-speed airflow type capture device that can solve the above-mentioned conventional problems.

[0011]

SUMMARY OF THE INVENTION The above requirements are fulfilled by a capture device according to the invention, in which the non-printing ink (for printing) is simple in construction and with minimal agitation. A vacuum port is provided that can return unused ink) to the fluidic device and requires minimal air intake to control ink removal at any orientation of the printhead. The configuration of the capture device of the present invention does not require a screen to regulate mixing of air and ink at the throat of the capture device. In addition, this novel capture arrangement allows for operation of the printhead in all orientations, as well as operation of the printhead with slow airflow. Thus, the advantages of low speed airflow in the capture device can be realized without affecting the flexibility of the printing device.

In accordance with one aspect of the present invention, there is provided a capture device for a continuous ink jet printing device of the type that generates a row of selectively charged droplet streams, the capture device comprising a charged ink liquid. Capture the drops. The capture device has a vacuum port with a capture surface for receiving selectively charged ink droplets. The radius or curvature of the capture device relative to the capture surface directs a stream of selectively charged ink droplets from the capture surface to the throat of the capture device. The throat of the capture device associated with the bend of the capture device accepts a stream of selectively charged ink droplets from the bend of the capture device.
The throat of the trap has a short, narrow gap with a downstream abrupt divergence and two converging / diffusing channels formed by elliptical islands and elliptical sidewalls.
The vacuum port of the capture device creates a decelerated airflow, returning a stream of selectively charged ink droplets from the printhead to the fluidic device.

Accordingly, it is an object of the present invention to provide a droplet (for a continuous ink jet printing device) with a vacuum port that minimizes the airflow required to return the ink without causing drops or drops. The purpose is to provide a capture device. Another object of the present invention is to provide a capture device with a vacuum port for returning non-printing ink to the fluidic device for reuse.

[0014]

DETAILED DESCRIPTION OF THE INVENTION One important object of the present invention is to provide a low-speed airflow capture device that minimizes the airflow required to return ink without dripping it. It is to be.

Referring to the drawings, FIG. 1 is a schematic side view of an ink jet printhead of the type used in the present invention, FIG.
FIG. 4 is a sectional view of a vacuum port of the capture device. Print head 1
0 has a resonator assembly 12 with an orifice plate for generating an ink filament 14 and an ink manifold (not shown). The resonator stimulates the filament and breaks the filament into droplets in the region of the charge electrode 16 of the capture assembly 18. The ink droplets are selectively charged by a charge electrode, and the charged droplets are deflected onto a capture surface 20 of the capture device and reach a throat 22 of the capture device. The uncharged droplets reach the print medium (not shown) without being deflected. The collected ink is withdrawn through the capture device tube 24 and recycled.

It is an object of the present invention to provide a non-printing ink that can be returned to a fluid device with a simple structure, with minimal agitation, and a minimum for controlling ink removal in any orientation of the printhead. The purpose of the present invention is to provide a capture device with a vacuum port which requires only a small air intake. FIG. 3 is a perspective view showing the underside of the capture device assembly 18 showing the major geometric features of the vacuum port 26 according to the present invention. The vacuum port 26 has a capture surface 20, a curved portion (radius) 28, and a throat portion 22. Surface 20 and curve 28 have the same geometry and function as known and existing vacuum ports. The capture surface 20 receives the selectively charged ink droplets, and the bend 28 directs the flow of the selectively charged ink droplets from the capture surface to the throat. Non-printing droplets from the inkjet array strike the capture surface 20 of the capture device, forming a film of ink adhered to the capture surface. Due to the momentum from the impinging droplet, the ink film flows toward the curve 28.
Due to the Coanda effect, i.e., the tendency to flow to adhere to the wall or to adhere to each other, ink adhesion to the wall occurs under various conditions, and the ink film turns around the curved portion toward the opening in the throat. Even when flowing along the surface, the ink film remains attached to the capture device.
The throat 22 receives a stream of selectively charged ink droplets from the capture surface. The capture device is covered by a plate (not shown) that constitutes one wall of the vacuum port.

As shown in FIG. 2, the throat 22 has a short narrow gap 34 with an abrupt enlargement 36 downstream, both of which (34, 36) reduce the width of the port 26 of FIG. Extends across. The elliptical island 30 splits the flow into two paths, and along the elliptical sidewall 32, two converging /
A diffusion channel or passage 33 is formed. The narrow gap 34, the abrupt expansion 36 and the passage 33 establish the desired flow in the capture device and form a return line for the capture device.

To avoid agitation of the ink, the capture device must operate in a different stream than the slag stream. If the air flow decreases while the liquid flow is maintained, the flow enters another state, known as bubble flow. In this state of the two-phase flow, the air flow is in the form of individual discrete bubbles entrained in the liquid phase and moving at the speed of the liquid. Thus, the bubble flow provides an effectively decelerated air flow and less agitation than the slag flow. The vacuum port of the capture device establishes this bubble flow condition in the return line of the capture device while at the same time allowing operation of the print head in any orientation without dripping ink. Abrupt expansion 36 on the downstream side
A narrow gap 34 with two and two converging / diffusing channels 33 make this possible.

In a preferred embodiment of the present invention,
The throat 22 has a gap 34 of about 0.25 mm (0.010 inches) and the length of the gap in the flow direction is about 0.76 mm (0.030 inches). About 0.2
5mm (0.010 inch) gap is about 0.76m
m (0.030 inch) abrupt enlargement 36.
As the ink film enters the throat 22, capillarity occurs, causing the ink film to fill the gap and limit air entry. At the center of each flow path around island 30, about 0.76 mm (0.03 mm) downstream of the gap
Bubbles are individually formed at a sudden expansion of 0 inches. These bubbles remain discrete as they enter the capture device return tube 24, creating a stable bubble flow through the tube to the fluidic device. In this mode of operation, the airflow entering the throat of the capture device differs from 3 scfh in existing printheads, from 0.2 to 0.
7 scfh.

The shape of the islands and sidewalls controls the inflow of air in various orientations. In the most difficult orientations (i.e., where the printhead flow path is one above the other)
The upper flow path takes in more air than the lower flow path, and the lower flow path is more prone to dripping. The converging structure provides a low pressure area at the center of each channel, limiting the air intake imbalance between the two flow paths. In the upper flow path, the bubble formation point moves toward the outer wall, but the bubble flow is maintained. The configuration of the capture device according to the present invention allows operation of the printhead in all directions and also allows operation of the printhead with a slow airflow.

INDUSTRIAL APPLICABILITY AND EFFECTS The present invention is useful in the field of ink jet printing and provides a droplet capture device that minimizes the airflow required for ink return without dropping or dripping. It has the advantage that. Another advantage of the present invention is that the capture device has a vacuum port for returning non-printing ink to the fluidic device with little agitation. Yet another advantage of the present invention is that the vacuum port of the capture device requires a minimal amount of air intake to control ink removal at any orientation of the printhead.

Although the present invention has been described with reference to the preferred embodiments, it is needless to say that various modifications and variations are possible within the gist of the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an inkjet printhead useful for a capture device according to the present invention.

FIG. 2 is a sectional view of a vacuum port of the capture device according to the present invention.

FIG. 3 is a bottom perspective view of the capture device showing the major geometry of the vacuum port of the capture device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 18 Capture device 20 Capture surface 22 Throat part 26 Vacuum port 28 Curved part 30 Island part 32 Side wall 33 Channel 34 Gap 36 Enlarged part

Claims (10)

[Claims] 1. A droplet capture device in a continuous ink jet printing device for generating a row of parallel, selectively charged droplet streams from a fluidic device, a capture surface for receiving selectively charged ink droplets. And a curved portion associated with the capture surface and guiding a flow of ink droplets selectively charged from the capture surface; and an ink droplet selectively charged from the curved portion related to the curved portion. A narrow, narrow gap throat adapted to accommodate the flow of air and having a downstream abrupt enlargement;
A droplet capturing device comprising: 2. A droplet capture device according to claim 1, further comprising a vacuum port for forming a decelerated airflow and returning selectively charged ink droplets to said fluidic device. 3. The droplet capture device according to claim 2, wherein said vacuum port has said capture surface, said curved portion and said throat portion. 4. The droplet capture device according to claim 1, wherein the short, narrow gap of said throat is about 0.25 mm (0.010 inch). 5. The droplet capture device of claim 1 wherein said short narrow gap in said throat has a length of about 0.76 mm (0.030 inch). 6. The droplet capture device of claim 1 wherein the abrupt widening downstream of the gap is about 0.76 mm (0.030 inch). 7. The droplet capture device according to claim 1, wherein said throat has two converging / diffusing channels formed by elliptical islands and elliptical sidewalls. 8. A droplet capture device according to claim 7, wherein the balance of the ingested air flow between said two converging / diffusing channels is maintained by the converging / diffusing geometry of said channels. 9. The method according to claim 1, wherein when the flow of the selectively charged ink droplets enters the throat, the gap is filled with a film of ink by capillary action to restrict the invasion of air. Item 6. The droplet capturing device according to Item 1. 10. The droplet capturing device according to claim 1, wherein bubbles are individually formed in the enlarged portion on the downstream side of the gap.