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Title:
CONTINUOUS INK JET PRINTING GUTTER ASSEMBLY
Document Type and Number:
WIPO Patent Application WO/1990/006855
Kind Code:
A1
Abstract:
A gutter (13) for colecting unwanted droplets in an ink jet printing machine comprises a narrow front slot which leads through a manifold (14) to a suction outlet (15). The dimension of the manifold parallel to the length of the slot diminishes towards the outlet and the dimension perpendicular to the length of the slot increases towards the outlet whereby the cross sectional area through which the ink flows from the gutter (22) to the outlet is substantially constant or varies substantially smoothly.

Inventors:
GRAY COLIN (GB)
Application Number:
PCT/GB1989/001519
Publication Date:
June 28, 1990
Filing Date:
December 20, 1989
Export Citation:
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Assignee:
ELMJET LTD (GB)
International Classes:
B41J2/185; (IPC1-7): B41J2/185
Foreign References:
US4268836A1981-05-19
Download PDF:
Claims:
£ MS
1. A gutter assembly for a continuous multijet ink jet printer, the assembly having a gutter (22) with an elongate inlet slot (24), the gutter opening into an ink collection manifold (14) having an outlet for coupling to a suction passage (15), the manifold cross sectional perpendicular to the direction of flow from the gutter to the outlet having, adjacent to the gutter, a dimension parallel to the length of the slot substantially equal to the length of the slot and diminishing towards the outlet, and a. dimension perpendicular to the length of the slot which increases from the gutter to the outlet whereby the cross sectional area through which the ink flows from the gutter to the outlet is substantially constant or varies substantially smoothly.
2. An assembly according to claim 1, in which the manifold (14) is formed between a flat plate (23) and a profiled surface of a block (10).
3. An assembly according to claim 2, in which the inlet slot (24) is formed by a slot in the plate (23), or between a flange (22) at the end of the plate and an end wall of the block or an electrode (9) carried by the block.
Description:
DESCRIPTION

CONTINODS INK JET PRINTING COTTER ASSEMBLY

in multi-jet ink jet printers a plurality of trains of ink droplets are passed in a substantially planar array through an electrostatic field and the individual droplets are, or are not, individually deflected depending upon whether they have been given a charge or not, as they have passed, upstream of the field, a charging electrode assembly. The uncharged droplets impinge on a substrate for printing and the charged droplets are deflected and caught in a primary gutter, or vice versa. Some printers also have a secondary gutter which is advanced to a position in which it catches charged or uncharged droplets for printing, during a start up period during which monitoring is carried out, for example to check proper break up of the ink jets into the droplets and alignment of the trains of droplets with the charging electrode. The secondary gutter is . retracted so that the trains pass the secondary gutter during normal operation for printing.

Both types of gutter normally comprise an inlet slot arranged parallel to the plane of the droplet trains and facing opposite to the direction of droplet flight. The ink collected in a gutter coalesces and is subsequently drawn through a suction pipe back to an ink reservoir for reuse. Problems can occur in ensuring that there are no stagnant zones where the quick drying ink may set, or abrupt changes in cross section which impede flow, thus impeding free flow back through the suction pipe;

In accordance with the present invention, a gutter assembly for a continuous multi-jet ink jet printer has an elongate inlet slot, the gutter opening into an ink collection manifold having an

outlet for coupling to a suction passage, the manifold cross sectional perpendicular to the direction of flow from the gutter to the outlet having, adjacent to the gutter, a dimension parallel to the length of the slot substantially equal to the length of the slot and diminishing towards the outlet, and a dimension perpendicular to the length of the slot which increases from the gutter to the outlet whereby the cross sectional area through which the ink flows from the gutter to the outlet is substantially constant or varies substantially smoothly.

With this arrangement the ink will coalesce and flow at substantially constant velocity, or with controlled acceleration or deceleration, through the manifold to the outlet.

The manifold is preferably formed between a flat plate and a profiled surface of a block, and the inlet slot for the gutter may be formed either by a slot in the plate or between a flange at the end of the plate and an end wall of the block or an electrode carried by the block.

The manifold may be divided into a number of parts, such as two parts, each of which collects ink from a corresponding length of the gutter and leads to a respective outlet.

An ink jet printer incorporating a gutter assembly in accordance with the invention is illustrated diagrammatically in the accompanying drawings, in which:-

Figure 1 is a vertical section through the printer;

Figure 2 is a section taken on the line II-II in Figure 1; and; Figure 3 is a section taken on the line III-III in Figure 2.

Figure 1 represents a conventional ink jet printer comprising an ink modulating device 5 which

produces a co-planar array of downwardly directed streams 6 of ink droplets. The individual streams 6 pass through respective slots 7 in a charging electrode 8 so that individual droplets may be individually charged or left uncharged. The trains of droplets then pass down between an earth electrode

9 carried by a support block 10 and a deflection electrode 11 carried by a support block 12. The electrode 11 is continuously charged with the same positive or negative charge which is selectively applied to the droplets so that uncharged droplets continue in a straight path 6A whereas charged droplets are deflected along a path 6B and are caught in a gutter 13, from which they are drawn through an ink collection manifold 14 to suction outlets 15.

During start up and adjustment of the machine, the undeflected droplets passing along the paths 6A are caught in a secondary gutter 16 and withdrawn through a manifold 17 and suction outlet 18 in a support block 19. For printing, the block 18 and secondary gutter are moved to the left as indicated by the arrow 20 so that the undeflected droplets impinge on a moving web 21 to be printed.

The invention is concerned with the construction of the assembly consisting of primary gutter 13, manifold 14 and suction outlet 15. A forward flange 22 of a gutter plate 23 is curved upwards in front of the earth electrode 9 and defines with the electrode and the bottom of the support block 10 a narrow elongate inlet slot which leads into a cavity forming the manifold 14. This cavity is formed between profiling in the bottom of the support block 10 and the plate 23 as shown in Figures

2 and 3. As is apparent from Figures 1 and 2, the height of the cavity increases gradually from the front slot to the rear, and simultaneously the cavity converges from the front slot towards the

rear, where it leads into the suction outlet 15. Consequently, the cross sectional area of the cavity remains substantially constant between its front edge and its rear connection to its suction outlet 15.

The manifold 17 may be similarly constructed to the manifold 14.