PRINTING SYSTEM WITH INK RESERVOIR

Abstract

 The invention relates to a printing system comprising a printing roller (10), in particular an anilox roller, and an ink reservoir (20), the ink reservoir (20) having a sealing portion (32, 34) which is in a sealing surface contact with the surface (12) of the printing roller (10), the sealing portion (32, 34) being made from graphite.

Description

[0001] The invention relates to a printing system comprising an ink reservoir and a printing roller, in particular an anilox roller.

[0002] The ink reservoir is intended to contain a certain amount of ink which is presented to the surface of the anilox roller. The surface of the anilox roller has small depressions which are filled with the ink so that the ink is transported by the anilox roller in a circumferential direction from an area in which the ink reservoir is arranged, to an area in which the ink is transferred to a printing medium or a transfer medium.

[0003] For preventing the ink to escape from the ink reservoir, doctor blades are arranged at the outer edge of the ink reservoir, extending in parallel with the axis of rotation of the printing roller. The doctor blades are in line contact with the surface of the anilox roller and shave excess ink from the surface of the anilox roller so that only the desired amount of ink remains on the surface of the roller. At the axial ends of the ink reservoir, seals are provided which contact the surface of the printing roller and prevent leakage of the ink.

[0004] An example of such arrangement can be seen in EP 2 602 111 A.

[0005] The problem with the doctor blades is that they are subject to significant wear. Typically, they have to be replaced every 3 to 4 days.

[0006] The object of the invention is to improve the seal of the ink reservoir.

[0007] In order to solve this object, the invention provides for a printing system having a printing roller and an ink reservoir, the ink reservoir having a sealing portion which is in a sealing surface contact with the surface of the printing roller, the sealing portion being made from graphite. The invention is based on the idea of completely avoiding the sharp doctor blades. Instead, a sealing portion is used which is in surface contact with the surface of the printing roller and which consists of a material which has "self-lubricating" properties. Accordingly, there is no damage to the surface of the printing roller, and no separate sealing elements are necessary. Another advantage is that the sealing effect of the sealing portion is independent from the direction of rotation of the printing roller.

[0008] According to an embodiment of the invention, the sealing portion has two longitudinal sealing surfaces which extend in parallel with the axis of rotation of the printing roller, and two circumferential sealing surfaces which extend in a circumferential direction of the printing roller. The sealing surfaces are configured to have a curvature which corresponds to the curvature of the surface of the printing roller so that there is a smooth surface contact "around" the space in which the ink is contained, preventing the ink from leaking from the ink reservoir.

[0009] The longitudinal surfaces and/or the circumferential surfaces have a substantial width so as to provide a comparatively large surface area in contact with the surface of the printing roller. Preferably, the width of the surfaces (measured in a circumferential direction for the longitudinal surfaces and in an axial direction for the circumferential surfaces) is more than 5 mm, preferably more than 10 mm and most preferred more than 20 mm.

[0010] The surface area covered by the sealing portion associated with the surface of the printing roller is at least 20% of the surface area of the printing roller, preferably more than 30% and most preferred more than 40% so that a significant portion of the surface area of the printing roller is covered by the ink reservoir. The surface area is measured in a curved condition and is defined by the outer dimensions of the sealing surfaces. As an example, a surface area of 50% is a result of an ink reservoir contacting the printing roller over an angle of 180° (and the entire width).

[0011] The surface area over which the ink within the ink reservoir is in contact with the surface of the printing roller is at least 10% of the surface area of the printing roller so that there is sufficient time for the ink to fill the depressions in the surface of the printing roller when the depressions are moved in a circumferential direction over the ink contained within the ink reservoir.

[0012] According to one embodiment, the sealing portion is a frame made from graphite and connected to an ink container, the ink container being made from a material which is different from graphite. The ink container can be made from steel or another suitable material which fulfills the requirements regarding mechanical stability and chemical resistance while the frame provides the desired sealing property. Should the frame be worn, it can be removed and exchanged against a new frame.

[0013] According to another embodiment, the sealing portion is formed in one piece with the remainder of the ink reservoir. In other words, the entire ink reservoir is made from graphite, thereby avoiding the necessity to mount a frame or other element made from graphite to the ink reservoir.

[0014] In order to guide the ink within the ink reservoir and to prevent turbulences, at least one guiding wall is arranged within the ink reservoir. The guiding wall can contact the surface of the printing roller in the same manner as the sealing portion of the ink reservoir.

[0015] Preferably, the guiding wall extends in parallel with the axis of rotation of the printing roller, thereby dividing the inner volume of the ink reservoir in narrow chambers which are parallel to each other and arranged in parallel with the axis of rotation of the printing roller.

[0016] The ink reservoir preferably contains an ink inlet and an ink outlet which are arranged at opposite sides of the ink reservoir, thereby creating a circulation of the ink through the ink container.

[0017] The invention will now be described with reference to an embodiment which is shown in the enclosed drawings. In the drawings,

Figure 1 is a cross section through a printing system according to the invention, and

Figure 2 is a view onto the sealing surfaces of the ink reservoir of Figure 1.

[0018] In Figure 1, a printing roller 10 is shown which has an axis of rotation R. Printing roller 10 is in particular an anilox roller. It has a plurality of small depressions in its circumferential surface 12 as is known from the prior art.

[0019] An ink reservoir 20 is provided which receives an amount of ink 22 for applying it to the surface of printing roller 10.

[0020] Ink reservoir 20 has outer walls 24 and a bottom wall 26 which together define an interior volume in which ink 22 is received. On the side which is opposite bottom wall 26, surface 12 of printing roller 10 "closes" the interior volume of ink reservoir 20.

[0021] The free ends of outer walls 24 form a sealing portion 30 which is adapted for sealingly contacting surface 12 of printing roller 10. As can be seen in Figure 2, sealing portion 30 comprises longitudinal sealing surfaces 32 and circumferential sealing surfaces 34.

[0022] Both longitudinal sealing surfaces 32 and circumferential sealing surfaces 34 are curved, with the center of curvature coinciding with the axis of rotation R of printing roller 10.

[0023] As can be seen from the drawings, the width of the sealing surfaces 32, 34 is significant. Sealing surfaces 32 have a width, measured in a circumferential direction, of more than 20 mm. Sealing surfaces 34 have a width, measured in an axial direction, of also at least 20 mm.

[0024] Ink reservoir 20 is here formed in one piece from graphite. Accordingly, sealing surfaces 32, 34 are also formed from graphite. They contact surface 12 of printing roller 10 in a surface contact (as opposed to line contact which would be the case if doctor blades were used).

[0025] The percentage of surface 12 which is covered by ink reservoir 20 is quite large as compared to prior art designs. Preferably, the surface area defined by ink reservoir (being the curved surface within the 4 outer corners of the sealing surfaces 32, 34) is preferably 40% or more of the surface area of surface 12.

[0026] The percentage of the surface 12 which is in contact with ink 22 is also higher than in prior art design. Here, at least 10% of the surface area of surface 12 is in contact with the ink contained in ink reservoir 20.

[0027] Because of the material for the sealing surfaces, there is a smooth sliding contact, and because of the width of sealing surfaces 32, 34, there is contact over a large surface area similar to the contact between a steel shaft and a graphite bearing bushing in a sliding bearing. On the one hand, this results in no wear at the side of printing roller 10 and in almost no wear on the side of ink reservoir 20. On the other hand, this results in a reliable sealing effect between printing roller 10 and ink reservoir 20, preventing the ink 22 from leaking from ink reservoir 20.

[0028] Within ink reservoir 20, two guiding walls 28 are provided which extend from bottom wall 26 towards the printing roller. They extend in a longitudinal direction and are slightly shorter than the interior volume of ink reservoir 20. Guiding walls 28 serve for preventing turbulence within the ink volume of ink reservoir 20.

[0029] The guiding walls 28 preferably also contact the surface of printing roller10 with a curved surface 29 similar to the sealing surfaces 32.

[0030] Ink 22 is supplied to ink reservoir 20 by means of an ink inlet 40 and is discharged by means of an ink outlet 42. As can be seen in Figure 2, ink inlet 40 and ink outlet 42 are connected to the inner volume of ink reservoir 20 at opposite sides (viewed in a longitudinal direction) so that, assisted by guiding walls 28, a circulation of the ink 22 in the interior of ink reservoir is created in a longitudinal direction.

[0031] As can be seen in Figure 1, an overflow 50 is arranged downstream of ink outlet 42 from which ink 22 can be guiding towards further processing stations.

[0032] In an embodiment not shown in the drawings, sealing portion 30 is in the form of a separate frame made from graphite, which is connected to an ink container consisting of a different material, e.g. steel. The frame can be screwed to the ink container so as to present to the surface of the printing roller the sealing surfaces.

Claims

1. A printing system comprising a printing roller (10), in particular an anilox roller, and an ink reservoir (20), the ink reservoir (20) having a sealing portion (32, 34) which is in a sealing surface contact with the surface (12) of the printing roller (10), the sealing portion (32, 34) being made from graphite.

2. The printing system of claim 1 wherein the sealing portion (32, 34) has two longitudinal sealing surfaces (32) which extend in parallel with the axis of rotation (R) of the printing roller (10), and two circumferential sealing surfaces (34) which extend in a circumferential direction of the printing roller (10).

3. The printing system of claim 2 wherein the longitudinal surfaces (32) and/or the circumferential surfaces (34) have a width which is more than 5 mm, preferably more than 10 mm and most preferred more than 20 mm.

4. The printing system of any of the preceding claims wherein the surface area covered by the sealing portion (32, 34) associated with the surface (12) of the printing roller (10) is at least 20% of the surface area of the printing roller, preferably more than 30% and most preferred more than 40%.

5. The printing system of any of the preceding claims wherein the surface area within the ink reservoir (20) is at least 10% of the surface area of the printing roller (10).

6. The printing system of any of the preceding claims wherein the sealing portion is a frame made from graphite and connected to an ink container, the ink container being made from a material which is different from graphite.

7. The printing system of any of claims 1 to 5 wherein the sealing portion (32, 34) is formed in one piece with the remainder of the ink reservoir.

8. The printing system of any of the preceding claims wherein at least one guiding wall (28) is arranged within the ink reservoir.

9. The printing system of claim 8 wherein the guiding wall (28) extends in parallel with the axis of rotation (R) of the printing roller (10).

10. The printing system of any of the preceding claims wherein an ink inlet (40) and an ink outlet (42) are provided which are arranged at opposite sides of the ink reservoir (20).

Drawing