WO2000043209A1

WO2000043209A1 - Print head having air suction

Info

Publication number: WO2000043209A1
Application number: PCT/NL2000/000022
Authority: WO
Inventors: Henricus Wilhelmus KRÜS
Original assignee: Stork Digital Imaging B.V.
Priority date: 1999-01-19
Filing date: 2000-01-13
Publication date: 2000-07-27
Also published as: AU2331400A; NL1011065C2

Abstract

A print head (1) for an inkjet printer comprises a body (2) for positioning ink nozzle units (3) which are directed towards the front side (F) of the print head (1), and guide members (7) in order to guide a movement of the print head (1) parallel to the front side (F). In order to remove a mist of ink in the vicinity of the print head, the print head is provided with at least one air-removal element (4), which is like wise directed towards the front side (F) and is arranged behind the ink nozzle units (3) as seen in the direction of movement. In order for the ink mist to be removed more efficiently, the print head (1) is furthemore provided with at least one air-supply element (5), which is directed towards the front side (F), for supplying air behind the air-removal elements (4), as seen in the direction of movement. Preferably, the air-removal elements (4) and the air-supply elements (5) are each arranged in the immediate vicinity of one another at one end of the print head (1).

Description

Print head having air suction

The invention relates to a print head for an inkjet printer, comprising a body for positioning ink nozzle means which are directed towards the front side of the print head, air-removal means which are directed towards the front side for removing air, and air-supply means which are directed towards the front side for supplying air, and guide means in order to guide a movement of the print head parallel to this front side. A print head of this nature is known from US patent 4,369,450.

Inkjet printers are in widespread use for printing various types of substrates, such as paper and textiles. These printing appliances enable a very high printing quality to be achieved at a high printing speed.

However, one problem of inkjet printers is that a mist of minuscule ink droplets may form in the vicinity of the substrate. A so-called "ink mist" of this nature is caused by charged ink drops impinging on the substrate; the ink drop "splashes" when it strikes the substrate and thus produces a number of small ink droplets which remain suspended in the air in the vicinity of the substrate. Ink mist is also caused by ink drops which only partially strike the collecting element and thus break up into a plurality of small ink drops. A collecting element of this nature, for example a so- called beam gutter, is used to collect ink drops which are not to reach the substrate.

In the inkjet printer according to US patent 4,369,450, it is attempted to minimize the formation of ink mist and to remove the ink mist which is still inevitably formed efficiently by, firstly, arranging the ink nozzle means at a slight angle in the direction of movement of the print head. It is stated that this inclined arrangement minimizes the formation of ink mist. Secondly, an air-removal chamber is provided, arranged in front of the ink nozzle means in a specified direction of movement of the print head. The air-removal chamber is connected to a fan, which sucks in the air which is laden with ink mist from the front side of the print head via a filter element arranged in the air-removal chamber, for the purpose of withdrawing the ink mist. The fan allows the air which has been sucked in and filtered to flow back out via a second chamber with an opening in the front surface of the print head, from which opening the ink also passes outwards, so that the ink mist is prevented from being deposited on the deflection electrodes arranged in the second chamber. One drawback of this known inkjet printer is that the filtered air flows out in the immediate vicinity of the deflected ink drops, which may cause interference with the direction of flow of the ink drops. Furthermore, no additional measures are taken to ensure that ink mist formed is actually sucked out. In fact, there is a considerable risk with the embodiment shown in this patent that ink mist will not enter the air-removal chamber. Only some of the ink mist is removed, with the result that ink mist remains in the surrounding area. As a result of the movement of the print head, not all of the ink mist will be sucked into the air-removal chamber, and therefore some of the mist will bypass this chamber. Using a greater suction force does not provide any solution to this problem, since this will cause a greater and more intensive flow of air in the vicinity of the ink nozzle means, which will have an adverse affect on the printing quality. Also, this known system is unsuitable for a (bidirectional) inkjet printer, which is active both when moving forwards and when moving backwards .

Furthermore, US-A-5, 877, 788 (corresponds to WO 96/35584) has disclosed a device for cleaning the front surface of an inkjet printer using a fluid. In the embodiments shown in Figs. 6 and 7 of this document, air is blown over the front surface of the print head along the ink nozzle means from a first side and is removed on the opposite side. The abovementioned drawbacks also apply to this known device.

The object of the invention is to avoid the abovementioned and other drawbacks of the prior art and to provide a print head for inkjet printers which allows air and ink mist to be removed completely. A further object of the invention is to provide a print head which allows effective removal in the direction of movement of the print head. According to the invention, for this purpose a print head of the type described in the preamble is characterized in that the air-removal means are arranged to remove air behind the ink nozzle means, as seen in the direction of movement, and the air-supply means are arranged to supply air behind the air-removal means, as seen in the direction of movement. Supplying air using the air- WO 00/43209 ^J PCT/NLOO/00022 supply means, which are arranged behind the air-removal means as seen in the direction of movement of the print head, causes a local excess pressure which stops ink mist from penetrating. Generating this local excess pressure behind the air-removal means as seen in the direction of movement therefore effectively prevents the ink mist from being able to bypass the air-removal means.

Preferably, the print head according to the invention is designed in such a manner that the air-removal means and the air- supply means are arranged in the immediate vicinity of one another at one end of the print head. Arranging the air-supply and air- removal means in the immediate vicinity of one another results in an optimum utilization of the local excess pressure. Moreover, a compact structure of the print head is obtained. Arranging the assemblies of the air-removal means and the air-supply means at one end of the print head results in the maximum possible effectiveness of this assembly.

Advantageously, air-removal means and air-supply means are arranged at both ends of the print head. This ensures that in the case of a print head which executes a reciprocating movement, ink mist is removed in both directions of movement.

The air-removal means may comprise a discharge element which is connected to a discharge pump by means of a hose. Then, an essentially constant reduced pressure is generated, resulting in uniform suction. Preferably, the print head according to the invention is designed in such a manner that the air-supply means comprise a supply nozzle which is connected to an air-collecting member which is directed in the direction of movement. Providing an air- collecting member which is directed in the direction of movement allows air to be collected during the movement of the print head and to be guided to the supply nozzle, which is connected to the air-collecting member. As a result, the air supply is made dependent on the speed of the print head, i.e. the local excess pressure which is brought about by the air-supply means increases as the speed of the print head rises. Obviously, it is possible to use an air pump and a hose instead of an air-collecting member.

Advantageously, a shield plate with openings arranged therein for the ink nozzle means is arranged on the front side of the print head. In this way, it is possible for the ink mist to be, as it were, enclosed between the substrate and the shield plate, making it possible for the ink mist to be removed more effectively.

The invention furthermore provides an inkjet printer which is provided with a print head with air-supply means and air- removal means. Moreover, the invention provides a method for printing a substrate using an inkjet printer which comprises at least one print head which can move with respect to the substrate and has ink nozzle means at a jetting position, excess pressure being created at a first position and reduced pressure being created at a second position in the immediate vicinity of the print head, in which method, as seen in the direction of movement, the second position is located between the jetting position and the first position.

In the following text, the invention will be explained in more detail with reference to an exemplary embodiment which is illustrated in the figures, in which:

Fig. 1 shows an outline sketch of the print head according to the invention.

Fig. 2 diagrammatically depicts a front view of a print head according to the invention. Fig. 3 diagrammatically depicts a plan view of the print head shown in Fig. 2.

Fig. 4 diagrammatically depicts a side view of the print head shown in Fig . 2.

The print head 1, which is only diagrammatically depicted in Fig. 1, comprises an ink nozzle unit 3 which is located at a certain distance from a substrate 15. During operation, the print head 1 moves with respect to the substrate 15 in the direction indicated by A (to the left in the drawing) . The print head 1 furthermore comprises an air-removal element 4 with a removal nozzle 8 which is directed towards the substrate 15. As seen in the direction of movement A, the air-removal element 4 is situated behind the ink nozzle unit 3. A reduced pressure is formed at a position in the vicinity of the removal nozzle 8 under the influence of the air-removal element 4, which may be connected to an air-removal pump (not shown) . Under the influence of this reduced pressure, ink mist 10 which is situated between the ink nozzle unit 3 and the substrate 15 will be removed via the air- removal element 4.

According to the invention, the print head 1 also comprises an air-supply element 5 which is arranged behind the ink nozzle unit 3 and the air-removal element 4, as seen in the direction of movement A. Air is supplied under the influence of air-supply element 5, which may be connected to an air-supply pump (not shown) and has a supply nozzle 9 facing towards the substrate 15. Under the influence of this air, a local excess pressure is generated at a position in the vicinity of the supply nozzle 9.

The generation of an excess pressure in the vicinity of the substrate 15, at the rear side of the print head 1 as seen in the direction of movement A, has the advantage of forming a "sweeping effect", with the result that the ink mist 10 can be removed very effectively. The excess pressure forms an air cushion which prevents the print head 1 from moving past the ink mist 10 without removing the latter.

Moreover, an air flow along the substrate 15 is formed between the supply nozzle 9 and the removal nozzle 8, the direction of which air flow corresponds to the direction of movement A of the print head. This air flow contributes to very effective removal of the ink mist 10.

Moreover, supplying air in the vicinity of the substrate ensures that contaminated air is displaced out of this environment. This way, the influence of dust and the like on the printing result is reduced.

Fig. 2 shows a front view, partially in section, of an embodiment of a print head according to the invention. The front side of the print head 1 shown in Fig. 2 is directed towards the substrate in operation.

The print head 1 comprises a body 2 for ink nozzle elements (not shown) to be arranged on. A guide element 7 is connected to the body 2. This guide element 7 allows a reciprocating movement in the directions of movement A and B to take place.

A combined air-removal and air-supply element 4, 5 is attached to each end of the body 2. In the embodiment shown, the air-removal element 4 has an approximately square removal nozzle 8, while the air-supply nozzle 9 of the air-supply elements is relatively narrow. However, the length of the air-supply nozzle 9 corresponds to the length of the air-removal nozzle 8.

The air-removal elements 4 are connected to an air- removal pump (not shown) via a removal pipe 6, while the air-supply elements 5 are in communication with air-collecting members 11, as will be explained in more detail with reference to Fig 3.

The side view illustrated in Fig. 3 also shows the body 2 to which the guide element 7 is attached. As can be seen from Fig. 3, the guide element 7 comprises a hollow tube through which a guide pin (not shown) can be fitted.

The air-collecting member 11 is provided with an inlet opening 14, which is in each case directed towards a direction of movement A, B, cf. Fig. 2. During the movement of the print head 1, the inlet opening 14 of the air-collecting member 11 will collect air which is guided to the supply nozzle 9 from the air-supply element 5. As can be seen from Fig. 3, the supply nozzle 9 is directed towards the substrate 15.

Although in the embodiment illustrated an air-removal element 4, an air-supply element 5 and an air-collecting member in each case form a single unit, it is, of course, possible for these elements to be designed as separate elements.

As can be seen from Fig. 2, the cross section of the air- collecting member 11 decreases gradually from the inlet opening 14 towards the air-supply nozzle 9. However, as can be seen from Fig. 3, the diameter actually increases transversely with respect to the front side F. The shape shown makes it possible to achieve highly effective guidance of air.

As shown in Fig. 4, the air-removal elements 4 are substantially triangular in cross section and each open out in a removal pipe 6 which is connected to a removal hose (not shown) of a discharge pump.

The use of the air-collecting members 11 provides an air supply which is dependent on the speed of the print head. In other words, if the print head 1 is at a standstill, no air will be supplied. In this way, the so-called "sweeping effect" of the local excess pressure is only generated when required.

As can be seen from Fig. 4, a shield plate 12 is provided for the ink nozzle units 3 (cf . also Fig. 2) . This shield plate 12 is used to stop the ink mist from spreading. As shown in Fig. 2, there are openings 13 in the shield plate 12, through which openings ink drops can reach the substrate. "

Claims

1. Print head (1) for an inkjet printer, comprising a body (2) for positioning ink nozzle means (3) which are directed towards the front side (F) of the print head (1), air-removal means (4) which are directed towards the front side (F) for removing air, and air-supply means (5) which are directed towards the front side (F) for supplying air, and guide means (7) in order to guide a movement of the print head (1) parallel to this front side (F) , characterized in that the air-removal means (4) are arranged to remove air behind the ink nozzle means (3), as seen in the direction of movement (A; B) , and the air-supply means (5) are arranged to supply air behind the air-removal means (4), as seen in the direction of movement (A; B) .

2. Print head according to claim 1, characterized in that the air-removal means (4) and the air-supply means (5) are arranged in the immediate vicinity of one another at one end of the print head ( 1) .

3. Print head according to claim 2, characterized in that air-removal means (4) and air-supply means (5) are arranged at both ends of the print head (1) .

4. Print head according to one of the preceding claims, characterized in that the air-removal means (4) comprise a removal nozzle (8) which is connected to a discharge pump by means of a hose.

5. Print head according to one of the preceding claims, characterized in that the air-supply means (5) comprise a supply nozzle (9) which is connected to an air-collecting member (11) which is directed in the direction of movement.

6. Print head according to claim 5, characterized in that the air-collecting member (11), as seen in the direction of flow of the air, has a diameter which decreases in a first direction and increases in a second direction, the first and second directions being perpendicular to one another, in order to form a supply nozzle (9) which is directed towards the front side (F) , is narrow as seen in the direction of movement and is wide as seen transversely with respect to the direction of movement.

7. Print head according to one of the preceding claims, characterized in that a shield plate (12) with openings (13) arranged therein for the ink nozzle means (3) is arranged on the front side ( F ) .

8. Print head according to one of the preceding claims, characterized in that the ink nozzle means (3) comprise at least one row of ink nozzle openings, which row is arranged at an angle with respect to the direction of movement (A; B) which angle is preferably approximately 30°.

9. Inkjet printer, provided with a print head (1) according to one of the preceding claims.

10. Method for printing a substrate (15) using an inkjet printer which comprises at least one print head (1) which can move with respect to the substrate (15) and has ink nozzle means (3) at a jetting position, excess pressure being created at a first position and reduced pressure being created at a second position in the immediate vicinity of the print head (1) characterized in that, as seen in the direction of movement (A; B) , the second position is located between the jetting position and the first position.