EP3863860A1

EP3863860A1 - Circulation apparatus for a liquid mixture of substances in a container

Info

Publication number: EP3863860A1
Application number: EP19805379.5A
Authority: EP
Inventors: Jan Franck
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-10-08
Filing date: 2019-10-08
Publication date: 2021-08-18
Also published as: KR102554112B1; IL282009A; KR20210069649A; US11801684B2; WO2020075058A1; CA3115183A1; DE102018007916A1; US20210347182A1; JP2022514149A; JP7224686B2; CN112839822A; CN112839822B

Abstract

The invention relates to an apparatus for circulating a liquid mixture of substances, for example a solution, emulsion or suspension, between a container and a pressure-sensitive component which is supplied from the container, for example for circulating an ink between an ink storage container and a print head of a printing system, comprising a pump, which allows the liquid mixture of substances to circulate in the container through an external conduit circuit, a Venturi tube, the main conduit of which is connected into the external conduit circuit, and also a conduit which connects the output connection of the pressure-sensitive component to the suction connection of the Venturi tube.

Description

Circulation device for a liquid mixture in a container

The invention relates to a device for circulating a liquid substance mixture stored in a container, for example a solution, emulsion or suspension, comprising a circulation pump which allows the liquid substance mixture to circulate in the container through an external line circuit, so that segregation within the Container is avoided, even if no mechanical stirring device is arranged in this.

Various liquids, in particular liquid mixtures of substances, including inks for digital printing, are sometimes not stable, and pigments, dissolved substances, etc. can settle out if the liquid is not kept in motion - not just in a storage container, e.g. in a container Ink tank, but also in a processing device, for example in a printhead.

In the prior art, for example in laboratories, stirrers are used in order to avoid segregation of such liquid substance mixtures. There are also such integrated stirrers in ink tanks, which keep the ink constantly in motion, as shown in the attached FIG. 2, which describes a typical prior art: Within the framework of a printing system 21, an ink reservoir 22 becomes a printhead 24 via a line 23 fed with ink 25. So that the ink 25 does not separate in the ink reservoir 22, a stirrer 26 is provided there, the shaft 27 of which is guided to the outside through the housing 28 of the ink reservoir 22. Such a stirrer 26 is complex, however, because the ink reservoir 22 should mostly be sealed airtight from the atmosphere, while the mechanics or electrics of the stirrer 26 - that is, the shaft 27 or cable, etc. - must be led out of the ink reservoir 22. A circulation of the ink 25 through the print head 24 is not provided. For this reason, magnetic stirrers have already been provided in JP H05-185600, that is to say magnetic bodies within an ink tank, which react to a magnetic field applied from outside and rotate and thereby mix the ink. On the other hand, each time an ink supply container is changed, the magnetic body must first be removed and inserted in a new ink supply container, which is extremely cumbersome.

DE 600 11 928 T2 describes another way; here there is no need for a stirrer within an ink container, and instead an ink circulation is provided, a first of two tubes opening into the container being connected to the suction connection of a pump, the pressure connection of which is connected to the second tube. As a result, the ink is kept in circulation and segregation is avoided, so that a stirrer is no longer required.

However, none of these documents is devoted to the further problem of how, within a pressure-sensitive component, in particular within a print head, a pressure that is as uniform as possible and constant over time can be maintained so that the print head always prints with the same quality.

In currently available printing systems, an attempt is either made to install an actively operated pump device within the inflow line of an ink print head or an actively operated suction device in the outflow line. However, this technique has not proven itself because pumping or suction devices can hardly be technically enabled to achieve a really constant, i.e. Maintain pressure difference free of pressure vibrations or waves permanently.

On the other hand, attempts have also already been made to provide two ink containers which are operated with different internal pressures, so that an ink flow occurs as a result of this pressure difference. However, this requires a constantly active pressure control in order to compensate for the increasing empty volume above the liquid of the container with higher internal pressure as a result of the ink consumption and the empty volume which likewise decreases in the other container.

There is also a variant in which two ink containers are provided at different heights or with different fill levels, the pressure difference being caused by the different water levels. However, this requires a constantly active fill level control in order to compensate for the volume of liquid in the upstream tank which decreases as a result of the ink consumption and the liquid volume which increases in the other tank in equal measure.

In addition, two ink containers are required for each print head or printing ink in these two cases, which means an increased space requirement. Furthermore, such a system makes it difficult to actively change the flow rate, since fill levels and pressures in the containers cannot be changed easily without the printhead dripping or drawing air, etc. Finally, such systems cannot be easily retrofitted to ink containers without circulation , because a standard ink tank without circulation only has a maximum of one heater and one full / empty display with refill function; when upgrading the pressure system for circulation using two tanks, everything has to be replaced. This results from the disadvantages of the prior art described

Problem initiating the invention to develop a generic circulation device in such a way that a pressure which is constant over time and constant can always be maintained in the pressure-sensitive component - for example in a print head.

This problem is solved in a generic circulation device by a Venturi tube, the main line in the external circuit is switched on; and a line which connects an output connection of the pressure-sensitive component with the suction connection of the Venturi tube. With such an arrangement it is possible to circulate liquid, in particular ink, through a pressure-sensitive component, in particular through a printhead; With such a printing system, the ink virtually flows past the nozzles and is kept in constant motion to prevent pigments, etc. from settling. At the same time, nozzle failures due to air bubbles can be prevented or remedied, because the small bubbles are transported through the circulation, etc.

There are different printheads in the prior art; for example those that require a flow rate of 1-5 ml / min; others require a flow of 100-300 ml / min.

The circulation through the printhead should be as pulse-free as possible, i.e. a continuous ink flow, since pump impulses or pressure impulses, due to the inertia of the ink, would cause the head to drip or air to be drawn in, so that the printhead no longer prints properly. A pump that is as pulseless as possible is therefore required, e.g. a diaphragm pump or propeller pump, and a venturi tube with suction connection, the pump in question pumps from the ink tank in a circle back into the ink tank; this means that the ink is constantly in motion and a stirrer is not required.

At the point where the ink is pumped from the pump back into the tank, a venturi tube is connected, which is connected to the circulation outlet of the print head. Using this Venturi tube, ink is sucked through the print head continuously and almost pulse-free and ends up in a container again; preferably in the same container that also feeds the printhead with ink. By setting the delivery rate of the pump used, and / or by using different Venturi tubes and / or flow restrictors, you can achieve any circulation rates. With the arrangement according to the invention, it may be possible to dispense with active negative pressure or negative pressure control in the ink container, provided the suction pressure of the venturi tubes is sufficient for the print head, in particular if the ink container is arranged above the print head.

The system according to the invention is very small, can be retrofitted at any time, is easy to control and implement and requires virtually no monitoring.

It is irrelevant whether the liquid is circulated in a small container or returned to a larger one, etc.

Of course, a degassing unit can also be provided in the container, and / or a filter, and / or a heater, etc. It has proven to be advantageous that the external line circuit is not closed via the pressure-sensitive component, but rather is closed directly, that is represents a bypass to the pressure-sensitive component. As a result, the mixing process within the storage and food container is completely decoupled from the operation of the pressure-sensitive component - in particular a printhead.

For this very reason, the line circuit between the storage and / or food container and the pressure-sensitive component should not be closed via the circulation pump, but should represent a bypass to the circulation pump. It has also proven useful that the main line of the Venturi tube downstream of the circulation pump is switched on in its line circuit. Thus, the two circuits - the circuit of the circulation pump on the one hand and the circuit of the pressure-sensitive component on the other - only combine in the venturi tube and flow back together from there to the container. Apart from this flow union, the two flows are largely decoupled, so that pressure fluctuations that may be caused by the circulation pump, despite all countermeasures, cannot reach the pressure-sensitive component.

The pressure-sensitive component is fed directly from the container at its inlet connection; ideally, no pump device is required for this, but a simple line connection is sufficient; even a pressure drop - such as could be caused by an elevated arrangement of the container relative to the print head - is not required.

Rather, the pressure drop required for the formation of a flow is caused by the venturi tube, which produces a negative pressure at its suction connection. In other words, the flow within the closed circuit via the pressure-sensitive component is only maintained via a pressure drop which is attributable to the suction power of the Venturi tube.

By connecting a return line from the pressure-sensitive component to the container via the venturi tube, the circuit through the pressure-sensitive element is closed and unused liquid is returned to the container, where it is immediately available for subsequent use.

If the closed circuit via the pressure-sensitive component is free of pumps, an optimally uniform pressure drop across the valve results pressure sensitive component so that it finds optimal operating conditions.

A non-return valve can be provided in the suction line between the output connection of the pressure-sensitive component and the suction connection of the venturi tube, which prevents a backflow to the output connection of the pressure-sensitive component. This completely prevents a reversal of flow within the pressure-sensitive part, even if the circulation pump should fail.

Furthermore, it is possible to provide a reducing device in the suction line between the outlet connection of the pressure-sensitive component and the suction connection of the Venturi tube, in order to limit the flow rate from the outlet connection of the pressure-sensitive component. As a result, the circulation speed can be individually adapted to the requirements of the pressure-sensitive component.

Such a reducing device is preferably designed as an adjustable reducing valve, so that the circulation speed can be readjusted at any time by the pressure-sensitive component.

It is within the scope of the invention that the inlet and outlet lines open at the storage or food container in the area of the housing base thereof, so that circulation can be maintained as long as there is still so much liquid in the container that the outlet line outlet does not falls dry.

Since no stirrer is required in the storage container, the inside of the storage container can be kept free of moving elements. Therefore, the ink container can also be designed as an exchangeable reusable or disposable container and can be quickly replaced at any time so that the printing process only has to be interrupted briefly. Furthermore, the invention recommends using a continuously conveying pump as the circulation pump, for example a diaphragm pump or a propeller pump. The fewer pressure fluctuations such a pump generates, the less the operation of the pressure-sensitive assembly is impaired.

Finally, it corresponds to the teaching of the invention that the container is an ink supply container and / or that the pressure-sensitive component is an ink printhead. In the case of printing systems, the invention can be used with particular advantage because it usually requires a high degree of consistency in the pressure gradient across the ink print head in order to achieve optimum printing results.

Further features, details, advantages and effects based on the invention will become apparent from the following description of a preferred embodiment of the invention and from the drawing. Here shows:

Fig. 1 shows a schematic piping plan of an inventive

Ink printing system; such as

Fig. 2 shows an ink printing system according to the prior art.

In the context of a printing system 1 according to the invention, an ink reservoir 2 is provided which feeds a print head 4 with ink 5 via a line 3.

However, no agitator is provided in the ink reservoir 2. Instead, segregation of the ink 5 is avoided by keeping it constantly in motion via an external circuit 6. For this purpose, a circulation pump 7 is used, which via its suction line 8 as well as its Pressure line 9, 10 is each connected to the ink reservoir 2, so that the ink 5 circulates through the external circuit 6.

In the pressure line 9, 10 of the circulation pump 7, that is to say downstream thereof, a Venturi tube 11 is switched on in such a way that the ink 5 circulating in the circuit 6 flows through it.

The venturi tube 11 consists of a smooth-walled tube piece, the inner lumen of which narrows at one point in cross section, for example to 90% of the normal inner tube cross section or less, preferably to 80% of the normal inner tube cross section or less, preferably to 60% of the normal inner tube cross section or less, in particular to 40% of the normal inner tube cross section or less, or even to 30% of the normal inner tube cross section or less. Even more severe constrictions are conceivable, for example to 25% of the normal inner tube cross section or less, preferably to 20% of the normal inner tube cross section or less, preferably to 15% of the normal inner tube cross section or less, in particular to 10% of the normal inner tube cross section or less.

The narrowing of the cross-section of the venturi tube 11 can be brought about, for example, by two pipe sections 12, 13 directed towards one another, conical or tapering in some other way from their peripheral ends to their mutually facing ends, which are connected to one another at the point of their smallest diameter. At this point, a third, lateral connection 14 is provided, at which a vacuum is present during operation of the Venturi nozzle 11 and which is therefore to be referred to as a suction connection 14.

In addition to the peripheral openings of its two pipe sections 12, 13 and the suction connection 14, the Venturi tube 11 preferably has no further openings Openings, is therefore independent of the ambient atmospheric pressure in the interior.

The Venturi tube 1 1 should consist of a solid material, such as metal or a solid, structure-stable plastic, so that it does not deform under the influence of a pressure difference between the outside and the inside.

In addition, the jacket of the Venturi tube 1 1 should be both liquid-tight, so that no ink can escape, and gas-tight, so that, with an internal suppression, neither air nor any other gas diffuses into the interior.

Another special feature of the invention is that the central, tapered area of the venturi tube 11 should preferably be at the same level as the two tube sections 12, 13. This can be achieved, for example, by the venturi tube. 11 is aligned horizontally as shown in Fig. 1.

The peripheral ends of the conical tube sections 12, 13 are switched into the pressure line 9, 10 of the circulation pump 7 and form the main line of the Venturi nozzle or the Venturi tube 1 1. The suction connection 14 of the Venturi tube is via a suction line 15 with the outlet-side connection 16 of the printhead 4 connected, so that the negative pressure against the normal operating pressure at the inlet-side connection 17 of the print head 4 causes a pressure difference which results in a flow.

In order to be able to set this pressure difference exactly to the value required by the relevant print head 4, a reducing device can be switched on in the suction line 15. This can be an adjustable reducing valve 18. Furthermore, the invention provides that a non-return valve 19 is also switched on in the suction line 15 in order to avoid backflow of ink in the suction line 15, even if the circulation pump 7 is switched off or fails.

Since the pressure difference r _D across the print head 4 is from the level of the liquid level 20 of the ink 5 in the ink supply and / or supply container 2, this container 2 can be operated without refilling as long as the lines 3, 8 do not fall dry .

For the venturi tube. 11, the Bernoulli equation applies, where index 1 refers to the parameters in the inlet connection or pipe section 12, index 2 to the parameters in the suction connection 14:

(p ₁ - p ₂ ) + p * g * (h ₁ - h ₂ ) = ½ * p * v ₂ ² * [1 - (A ₂ / A ₁ ) ² ], where p is the pressure at the respective location, h the height at the respective location, A the clear flow cross-section at the respective location, V the flow velocity at the respective location, and p the density of the ink and g the gravitational acceleration, or p ₂ - p ₁ = p * g * (h ₁ - h ₂ ) - ½ * p * v ₂ ² * [1 - (A ₂ / A ₁ ) ² ]; p ₂ = p ₁ + p * 9 * (h ₁ - h ₂ ) - ½ * p * v ₂ ² * [1 - (A ₂ / A ₁ ) ² ],

If the height difference (hi - h ₂ ) is negligibly small - in particular if the Venturi tube 1 1 is aligned horizontally or if its dimensions are small - the formula is simplified to: p ₂ = p ₁ - ½ * p * v ₂ ² * [1 - (A ₂ / A ₁ ) ² ], Furthermore, it should be assumed that the density p of the ink is approximately 1 kg / dm ³ . Furthermore, it can be assumed that the pressure p ₁ when the circulation pump 7 is running is greater than the weight pressure p _t at the bottom of the ink reservoir 2 and also greater than the surrounding atmospheric pressure p _a . In particular, with the pressure increase p _z resulting from the output of the circulation pump 7: p ₁ = p _t + p * g * (h _t - h ₁ ) + p _z .

The weight pressure p _d at the inlet-side connection 17 of the print head 4 is dependent on the height h _{d of} the inlet-side connection 17 of the print head 4 in relation to the height h _{t of} the outlet at the bottom of the ink reservoir 2: p _d = p _t + p * g * (h _t - h _d ).

However, a suction p ₂ should be present at the suction connection 14, such that a suction r _d <0 prevails at the outlet-side connection 16 of the pressure head 4 compared to the weight pressure p _d at the inlet-side connection 17 of the print head 4: p ₂ = p _d + p _D = p _t + p * g * (h _t - h _d ) + r _D , more than the difference p * g * (h ₂ - h _d ) reduced: p ₂ + p * g * (h ₂ - h _d ) = p _d + r _D = p _t + p * g * (h _t - h _d ) + p _D , ie,

If h ₁ »h ₂ , the following applies:

Accordingly, the cross-sectional ratio (A ₁ / A ₂ ) between the inlet 12 of the venturi 11 and its suction connection 14 can be according to the above formula from the pump pressure p _{z of} the circulation pump 7, the desired pressure difference r _D above the print head 4 and the flow velocity v ₁ in the feed line 12, taking into account the density p of the ink. Various modifications of the arrangement according to the invention are possible. In particular, different valves and / or cross-sectional reductions can also be inserted at another point in the circuit in question. In addition, according to this principle, several printheads of a printing system can be connected to a common venturi tube or each printhead is connected to its own venturi tube.

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Reference list

1 pressure system 26 stirrers

2 ink reservoir 27 shaft

3 line 28 housing

4 printhead

5 ink

6 cycle

7 circulation pump

8 suction line

9 pressure line

10 pressure line

11 Venturi tube

12 inlet pipe section

13 outlet-side pipe section

14 suction connection

15 suction line

16 outlet connection

17 inlet connection

18 reducing valve

19 check valve

20 liquid levels

21 printing system

22 ink reservoir

23 line

24 printhead

25 ink

Claims

Claims. Device for circulating a liquid substance mixture (5) stored in a container (2), for example a solution, emulsion or suspension, comprising a circulation pump (7) which pumps the liquid substance mixture (5) in the container (2) through an external circuit (6) can be circulated so that segregation within the container (2) is avoided, even if no mechanical stirring device is arranged therein;

marked by

a) a Venturi tube (11), the main line (12, 13) of which is switched on in the external line circuit (6); such as

b) a line (15) which connects an output connection (16) of the pressure-sensitive component (4) to the suction connection (14) of the Venturi tube (1 1).

2. Device according to claim 1, characterized in that the external line circuit (6) is not closed via the pressure-sensitive component (4), but is closed immediately, that is to say it is a bypass to the pressure-sensitive component (4).

3. Apparatus according to claim 1 or 2, characterized in that the line circuit between the container (2) and the pressure-sensitive component (4) is not closed via the circulation pump (7), but represents a bypass to the circulation pump (7).

4. Device according to one of claims 1 to 3, characterized in that the main line (12, 13) of the Venturi tube (1 1) downstream of the circulation pump (7) in the external Line circuit (6) is switched on, especially in the pressure line (9, 10) of the circulation pump (7).

5. Device according to one of the preceding claims, characterized in that the pressure-sensitive component (4) is fed at its input connection (17) from the container (2).

6. Device according to one of the preceding claims, characterized in that a return line from the pressure-sensitive component (4) to the container (2) is connected via the Venturi tube (1 1).

7. Device according to one of the preceding claims, characterized in that the closed circuit via the pressure-sensitive component (4) is free of pumps.

8. Device according to one of the preceding claims, characterized in that the flow within the closed circuit via the pressure-sensitive component (4) is maintained only over a pressure drop which is attributable to the suction power of the venturi tube (11).

9. Device according to one of the preceding claims, characterized in that a check valve (19) is provided in the suction line (15) between the outlet connection (16) of the pressure-sensitive component (4) and the suction connection (14) of the venturi tube (11), which prevents backflow to the output connection (16) of the pressure-sensitive component (4).

10. Device according to one of the preceding claims, characterized in that a reducing device in the suction line (15) between the output connection (16) of the pressure-sensitive component (4) and the suction connection (14) of the Venturi tube (1 1) is provided in order to limit the flow quantity from the outlet connection (16) of the pressure-sensitive component (4).

11, Device according to claim 10, characterized in that the reducing device is designed as an adjustable reducing valve (18),

12. Device according to one of the preceding claims, characterized in that the inlet and / or outlet line (s) (3, 8, 10) opens onto the storage container (2) in the region of its housing base

(-en).

13. Device according to one of the preceding claims, characterized in that no stirrer is arranged in the storage container (2), but that the storage container (2) is free of movable elements inside.

14. Device according to one of the preceding claims, characterized in that the circulation pump (7) is a continuously pump, for example a diaphragm pump or propeller pump.

15. Device according to one of the preceding claims, characterized in that the container (2) is an ink reservoir.

16. Device according to one of the preceding claims, characterized in that the pressure-sensitive component (4) is an ink pressure pot.

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