Device and method for transferring flowable printing substances onto a printing material

Abstract

A printer's form for transferring a flowable printing substance onto a printing material to be printed on includes a body having a surface, which surface has a plurality of openings, a plurality of cavities in the body, which cavities end in the openings of the surface of the body and contain gas, wherein each cavity is bounded by a wall, which adjoins the opening and surrounds the cavity, and devices associated with each cavity for producing an overpressure in the cavity in question. At least parts of the surface of the body and/or the wall surfaces of the walls of at least some cavities include a first wall region, which is near the opening and which is composed of a surface that can be wetted with the printing substance.

Claims

1. A printing plate for transferring a flowable printing substance onto a printing material to be printed on, comprising a body having a surface, which surface has a plurality of openings, a plurality of cavities in the body, which cavities end in the openings of the surface of the body and contain gas, wherein each cavity is bounded by a wall which adjoins the opening and surrounds the respective cavity, and devices associated with each cavity for producing an overpressure in said each cavity, wherein wall surfaces of the walls of at least some cavities include a first wall region near the opening and a first wall surface that can be wetted with the printing substance, wherein, at a second wall region remote from the opening, the wall surfaces of the walls of at least some cavities include a second wall surface less wettable with the printing substance than the first wall surface that can be wetted with the printing substance, and wherein the second wall region adjoins the first wall region.

2. The printing plate of claim 1, wherein, with the printing substance applied on the printing plate, a contact angle between the printing substance and the surface of the body or between the printing substance and the first wall surface in the first wall region of a wall is less than 45.

3. The printing plate of claim 1, wherein the device for generating an overpressure in a cavity comprises a heating device for heating the gas in the cavity.

4. The printing plate of claim 3, wherein the heating device for heating the gas in the cavity includes a resistance heating element.

5. The printing plate of claim 3, wherein the heating device for heating the gas in the cavity includes an end portion or a sleeve respectively heating up by absorbing electromagnetic radiation.

6. The printing plate of claim 1, wherein protrusions are arranged on the surface to act as spacers for the printing material.

7. The printing plate of claim 6, wherein the protrusions are formed by the roughness of the surface.

8. The printing plate of claim 1, wherein a maximum diameter of the openings is smaller than a capillary length of the printing substance.

9. A method for transferring the flowable printing substance from the printing plate of claim 1 onto the printing material, comprising: drawing by capillary forces the printing substance into at least a portion of the plurality of cavities into which the openings in the surface of the body open, wherein the printing substance is located in the openings and in regions of the at least a portion of the plurality of cavities near the openings and the printing substance wets the first wall surface that can be wetted with the printing substance, wherein the printing substance closes at least some of the openings in a gas-tight manner, expelling the printing substance from the at least a portion of the plurality of cavities onto the printing material by applying overpressure.

10. The method of claim 9, wherein the printing substance is drawn into the openings and the regions of all cavities of a group of the plurality of cavities, which regions are close to the openings, and the printing substance closes the openings of all cavities of the group of cavities in a gas-tight manner, and the expelling is realized by selectively applying overpressure in selected cavities of the group of cavities.

11. A printing plate for transferring a flowable printing substance onto a printing material to be printed on, comprising a body having a surface, which surface has a plurality of openings, a plurality of cavities in the body, which cavities end in the openings of the surface of the body and contain gas, wherein each cavity is bounded by a wall which adjoins the opening and surrounds the respective cavity, and devices associated with each cavity for producing an overpressure in said each cavity, wherein wall surfaces of the walls of at least some cavities include a first wall region near the opening and a first wall surface that can be wetted with the printing substance, wherein, at a second wall region remote from the opening, the wall surfaces of the walls of at least some cavities include a second wall surface not wettable with the printing substance that forms a contact angle with the printing substance that is larger than 90, wherein the first wall surface that can be wetted with the printing substance forms a contact angle with the printing substance that is less than 90, wherein the second wall region adjoins the first wall region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic perspective illustration of a printing plate of the present invention,

(2) FIGS. 2a and 2b are schematic illustrations of details of the surface of a printing plate,

(3) FIGS. 3a-3d show a schematic illustration of a printing method of the present invention,

(4) FIG. 4 is a schematic illustration of a detail of another embodiment of the surface of a printing plate,

(5) FIGS. 5a-5c show another embodiment of a printing plate of the present invention with protrusions, as well as a printing method of the present invention, and

(6) FIGS. 6a and 6b show another embodiment of a printing plate of the present invention with protrusions on the surface.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) FIG. 1 schematically illustrates a printing plate 1 of the present invention. In the embodiment illustrated the printing plate 1 is in the form of a hollow cylinder. The printing plate 1 has a body 2 with a surface 3 that has openings 5 that are illustrated only schematically in FIG. 1. As is seen best in FIGS. 2a and 2b which show the surfaces 3 of two different embodiments of the present invention printing plate in a schematic illustration of a detail, cavities 7 are arranged behind the openings 5, which open into the openings 5. Each cavity 7 ends but in a single opening 5.

(8) The printing plate 1 serves to print on a printing material 100 with a printing substance, which printing material may be pressed against the surface 3 by means of a roller 102, while it is also possible to keep the roller 102 at a defined distance from the surface 3.

(9) The printing roller 1 further comprises a heating apparatus 104 by which gas in the cavities 7 may be heated using individual heating devices. The heating apparatus 104 may be controlled via a control device 106.

(10) The printing substance is applied onto the surface 3 of the printing plate 1 by means of a printing substance application device 108 including an associated printing substance application control device 110. A doctor blade, not illustrated herein, may be provided, for example a doctor knife, by which excess printing substance can be wiped off prior to printing on the printing material.

(11) Further, a cooling device 112 may be provided by which the cavities 7 heated by the heating apparatus 104 can be cooled.

(12) As is best seen in FIGS. 2a and 2b, the openings are arranged in a raster-like pattern on the surface 3. The cavities 7 opening into the openings 5 are provided as blind holes and are delimited by a wall 9. In a first wall region 11 near the opening, the wall surface 13a is designed as a well wettable surface. In a second wall region 15 remote from the opening, the wall surface 13b is designed as a surface that is poorly wettable with the printing substance. Further, the openings 5 preferably have a maximum diameter D that is smaller than the capillary length of the printing substance. When the printing substance is applied onto the surface 3, the printing substance is drawn into the cavity 7 by the capillary effect and closes the respective opening 3 in a gas-tight manner.

(13) Due to the gas present in the cavities 7, a counter pressure is built as the printing substance enters into the cavities 7, the counter pressure allowing the printing material to enter only to a certain depth, since the counter pressure of the gas in the cavity 7 counteracts the capillary effect. At the same time or as an alternative, the transition from the well wettable surface of the first wall surface 13a to the poorly wettable surface of the second wall surface 13b forms a barrier against further intrusion of printing substance.

(14) The embodiments in FIGS. 2a and 2b only differ in that, in the embodiment in FIG. 2a, the surface 3 of the printing plate 1 forms a planar surface, whereas the surface 3 of the embodiment in FIG. 2b forms a curved surface.

(15) For printing, the gas in the cavity 7 is heated so that the same expands and generates an overpressure. For the purpose of heating he gas, it is possible to heat end portions 17 of the cavities 7, for example.

(16) FIGS. 3a-3d schematic detail illustrations of a printing method of the invention.

(17) The printing substance 200 is applied onto the surface 3 of a printing plate 1. Due to the capillary forces, the printing substance is drawn through the opening 5 into the cavity 7, with the above described design of the wall surface 13a causing the printing substance to remain only in the region near the opening (FIG. 3b). Thereafter, the printing substance may be wiped off (FIG. 3c). The printing substance 200 closes the opening 5 in a gas-tight manner. By subsequent heating of the gas in the cavity 7 by means of a heating device 19 associated with the cavity 7, an overpressure builds in the cavity 7. Given a sufficiently strong and quick heating of the gas and due to the resulting pressure increase, the printing substance is then forced away from the opening 5, accelerated and, assisted by a commencing gas flow, flung from the cavities 7 onto the printing material 100 (FIG. 3d).

(18) A printing method of the present invention using a printing plate 1 of the present invention thus allows a very exact printed image, where it is possible, for example, to selectively heat individual cavities 7 so that a desired printed image is obtained.

(19) In addition or as an alternative to the design of the wall surfaces 13a, 13b, it is possible to design the surface 3 of the printing plate 1 as a well wettable surface.

(20) With a printing plate 1 of such a design, the surface 3 is wetted with printing substance 200, whereby the openings 5 are closed in a gas-tight manner. In an embodiment, the printing plate 1 in which only the surface 3 is designed as a well wettable surface, all of the printing substance 200 remains on the surface 3 and does not or only slightly enter into the cavities 7 through the openings 5. With a printing plate 1 in which both the surface 3 and the wall surface 13a in the wall region 11 near the opening are designed as well wettable surfaces, the printing substance 200 covers the surface 3 and at the same time enters into the cavities 7 through the openings 5.

(21) With a well wettable surface, the contact angle between the printing substance and the surface is less than 90, preferably less than 45.

(22) FIG. 4 is a schematic illustration of a detail of a surface of another embodiment of a printing plate 1 according to the present invention. The embodiment illustrated in FIG. 4 generally corresponds to the embodiment illustrated in FIG. 2a. The embodiment differs in that the cavity 7 is surrounded by a sleeve 21. The sleeve 21 is part of the heating device 19, wherein, due to the sleeve 21, it is possible to heat the gas in the cavity 7 in a particularly advantageous and quick manner, since the entire cavity 7 is surrounded by the sleeve 21 so that the gas can be heated almost from all sides.

(23) In FIGS. 5a-5c, a method is illustrated using a printing plate 1 having a surface 3 designed as a surface well wettable with the printing substance 200. Further, also the wall surface 13a in the wall region 11 near the opening is designed as a well wettable surface. The printing plate 1 illustrated in FIGS. 5a-5c generally corresponds to the printing plate 1 illustrated in FIG. 2a. It only differs in that the surface 3 is designed as a well wettable surface and that, further, the surface 3 is formed with protrusions 23 acting as spacers for a printing material.

(24) The printing substance 200 is applied on the surface 3 (FIG. 5b). Here, printing substance 200 is applied only in such a quantity that the protrusions 23 protrude from the printing substance 200. The printing substance 200 wets the surface 3 of the printing plate 1 and enters in part into the cavities 7 through the openings 5. Thereby, the openings 5 of the cavities 7 are closed in a gas-tight manner.

(25) The protrusions 23 on the surface 3 may be omitted if the distance between the surface 3 and the printed material 100 can be adjusted by an alternative device. For this purpose it is possible to use the roller 102, for example.

(26) As illustrated in FIG. 5c, a printing material 100 rests on the protrusions 23 and thus does not contact the printing substance 200 applied on the surface 3. Thereby, a clean printed image is obtained, since the printing substance 200 cannot reach the printing material 100 in an uncontrolled manner. Using a doctor blade, it can be achieved that the ends of the protrusions 23 are free of printing substance.

(27) In selectively chosen cavities 7 or in all cavities 7, the gas in the cavities 7 is heated, whereby overpressure is generated that forces the printing substance 200 out of the cavity 7 and away from the openings and flings it onto the printing material 100. The cavities 7 may be heated, for example, by heating the end portions 17. This may be effected, for example, by means of laser radiation 25 schematically indicated in FIG. 5c. The material of the end portion 17 absorbs laser radiation of suitable wavelengths, whereby the end portion is heated.

(28) When laser radiation is used, the wavelength of the laser radiation and the optical properties of the material of the printing plate 1 surrounding the cavities can be selected such that the laser radiation is absorbed primarily by the end portion 17. The end portion 17 may for example include finely dispersed metal inclusions absorbing laser radiation by excitation of plasmons. In this regard it may advantageously be provided that the material of the printing plate does not absorb the laser radiation, whereby the same can be focused on selected end portions 17 through the material so as to heat the gas filling in the relevant cavities 7 in a targeted manner. The sleeves 21 in an embodiment illustrated in FIG. 4 may be heated in a similar manner.

(29) Preferably it is provided that the thermal conductivity of the end portion 17 or of the sleeve 21 is higher than the thermal conductivity of the material of the printing plate 1, whereby the thermal input into the material of the printing plate 1 is reduced when the end portion 17 or the sleeve 21 is heated by the absorbed laser radiation.

(30) FIGS. 6a and 6b illustrate another embodiment of a printing plate 1 according to the present invention with protrusions 23. The protrusions 23 are provided on the surface 3 of the printing plate 1 and may differ in size. As in the above described embodiments, the surface 3 of the printing form 1 has openings 5 with adjoining cavities 7. In this printing plate 1, the cavities 7 are formed as blind holes with a large aspect ratio (depth of the blind hole divided by the diameter thereof). This means that the cavity holds a large gas volume that can be heated. Thus, it is possible to fling the printing substance onto the printing material in an advantageous manner, since a strong gas flow can be generated. The protrusions 23 are not arranged uniformly on the surface 3. It is merely necessary to provide a sufficient number of protrusions 23 per unit area to allow them to serve as stops for the printing material 100 and to reliably support the printing material 100. The protrusions 23 are formed by the roughness of the surface 3. Here, the openings 5 are not arranged exclusively in the surface 3 between the protrusions 23, but also in the surface of the protrusions 23 themselves. Thereby, it is possible to form a very fine raster of openings 5, where only small free areas remain that are formed by the tips of the protrusions 23 with which no printing can be performed.

(31) In embodiments illustrated in FIGS. 6a and 6b the surface 3, as well as the wall surface in the cavities 7 are designed as well wettable surfaces. FIG. 6b shows the printing plate of FIG. 6a with printing substance 200 applied thereon. This may be achieved, for example, by wiping with a doctor blade. It is thus achieved that a printing material resting thereon cannot get into direct contact with the applied printing substance 200.

(32) Printing plates, such as illustrated in FIGS. 6a and 6b, may be produced for example in an electrolyte by anodic oxidation of aluminum plates, with the blind holes forming in a matrix of aluminum by self-organization. A printing plate 1 manufactured by this method has cavities in the form of blind holes of a diameter of about 400 nm and a depth of about 100 m, with the distances between the openings 5 of the blind holes 5 being about 500 nm. Large protrusions 23 have a height of about 0.5 m and a mean distance between adjacent large protrusions 23 of about 150 m, for example. In such a printing plate, the bordering of the cavities is made of aluminum oxide enriched in anions which surrounds the cavities in the manner of a sleeve. The matrix of the printing plate surrounding the sleeve is formed by pure aluminum oxide. Laser radiation of a wavelength of 808 nm is absorbed by these sleeves. Using suitable coatings on the wall surfaces of the cavities 7, their properties for wetting with the printing substance can be predetermined, whereby the above described wetting barrier is obtained.