Printing machine with pressurized fluid backing

Abstract

A rotary printing machine is disclosed which eliminates an impression roller and creates a fluid force which urges the material to be imprinted against the printing plate.

Description

BACKGROUND

In the rotary printing machine industry it has long been established that the printing cylinder should be backed by a rotating back-up or so-called "impression", cylinder such that the web, or individual sheets, upon which the printing is to be effected, is/are held and supported against the imprinting force of the rotary printing cylinder. Such conventional printing and impression cylinders are disclosed, for example, in U.S. Pat. Nos., 5,154,602, and 5,103,732 which are hereby incorporated by reference.

SUMMARY

It has now been discovered that, contrary to all prior teachings and beliefs in the rotary printing industry, the impression cylinder may be eliminated entirely. That is, it has been discovered that the impression cylinder may be replaced by a non-rotating backing element which is not only of substantially lower cost, but which may easily and readily vary the optimum backing pressure against the sheets or web to be imprinted. In one preferred embodiment, the non-rotating backing element ejects a pressurized fluid such as gas against the web or sheets to be imprinted. The pressure of the gas against the web or sheets may be easily varied, and such pressurized fluid virtually eliminates friction or possible scuffing by any impression cylinder.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side view of a printing machine of the Prior Art;

FIG. 2 is a schematic, fragmentary side view of one printing stage of one embodiment of the present invention;

FIG. 2-A is a schematic, fragmentary side view of a second embodiment;

FIGS. 3 and 4 are views along view line 3--3 of FIG. 2 illustrating different shapes of apertures;

FIGS. 5 and 6 are schematic, fragmentary side views of third and fourth embodiments;

FIGS. 7 and 8 are schematic representations of two modes of fluid flow in the practice of the invention;

FIGS. 9-A and 9-B are schematic, fragmentary side views of two further embodiments; and

FIGS. 10 and 11 are schematic, fragmentary side views of an additional embodiment showing a roller element in two positions during operation.

DETAILED DESCRIPTION

Referring to FIG. 1, first and second stages of a conventional, prior art rotary printing machine are illustrated schematically. FIG. 1 is particularly illustrative of a flexographic printing machine which imprints very high-resolution, multi-colored images on either a web, or a succession of individual sheets such as "container blanks". Container blanks are sheets of cardboard, and typically corrugated cardboard, which become folded to form containers for products. By way of background, it will be understood that high speed flexographic printing has become so efficient and precise that beautifully multi-colored images of products such as meats or fruits may be printed directly upon a container blank without first printing the image on a sheet of high resolution paper, and then pasting such sheet upon the container. At the same time, present requirements for printing high quality indicia such as images, text and designs on individual container blanks requires speeds of the blanks through the printing machine in the order of 1,000 board-feet per minute. This requires that the printing and impression cylinders shown in FIG. 1 rotate at very high speeds. This is not a severe problem for printing cylinders 10, 10' because their large diameters are such that they can withstand the high speeds without flexing along their axes. However, this is not true with respect to impression cylinders 12 and 12'. Only a few years ago, such impression cylinders generally had diameters in the order of 6 to 8 inches. Presently, because of the requirements for increasingly higher speeds, the impression cylinders have had to have their diameters increased to the order of 14" or larger. This not only substantially increases the cost of each impression cylinder, but it becomes increasingly more and more difficult to provide an impression cylinder which will not flex at its longitudinal center and thereby produce impressions of uneven density on the web or sheets 11 being imprinted. The present invention solves these severe problems by completely eliminating the impression cylinder(s).

As further illustrated schematically in FIG. 1, sheets of material 11 to be imprinted are typically conveyed to the nip between printing cylinder 10 and impression cylinder 12 by a feed conveyor 14. Such feed conveyors are well known in the printing art, and disclosed for example in U.S. Pat. No. 5,782,183 incorporated herein by reference, such that a detailed description is not necessary for those skilled in the printing art. However, it will be noted that in FIG. 1 material 11 is illustrated as being conveyed by the bottom reach 16a of the conveyor against which they are held by a pressure differential above and below the material. It will also be understood that conveyors 14, 14' and 14" may be replaced by conveyors which convey the material on their upper reaches 16b, and that for certain applications, one or all of the conveyors may be replaced by pairs of feed rollers (not shown) all as is well known in the printing art. The critical fact is that, as the diameters of the impression cylinders have increased, the feed conveyors, or pairs of feed rollers, must be moved farther and farther away from each other. This means that when individual sheets are being imprinted, they are held less firmly such that the clarity of the printed image may suffer. Also, the minimum length of each sheet to be printed is increased such that some very short sheets can no longer be imprinted in such machines. The present invention unexpectedly solves all of these critical problems as well.

Referring to FIG. 2, print cylinder 10" is shown as having a conventional printing plate 18 which rotates in the direction of arrow A and imprints images on material 11. Material 11 is illustrated as being one of a continuous series of individual sheets or blanks, such as container blanks, which pass through one or more printing stages. However, it will also be apparent that material 11 may be a continuous web of material to be imprinted as previously described, and it will be understood that printing cylinder 10" may be a single-stage cylinder or one of a plurality of like printing cylinders in a multi-stage machine.

On the side of material 11 which is opposite to printing plate 18, there is disposed a transverse element 20 which extends across the width of the machine generally perpendicular to the direction of travel of material 11. Transverse element 20 may be referred to as an elongated element or "beam" since it does not rotate, and it extends as a stationary element across the lateral extent or width of the printing machine between side walls 25 of the machine as shown schematically in FIG. 3.

Transverse element or beam 20 may be of various cross-sectional shapes and preferably includes a longitudinally extending hollow chamber 22. Chamber 22 is supplied with a gas, such as air, at superatmospheric pressure from a compressor or other source of pressurized gas. The compressed gas in chamber 22 flows out of the chamber through one or more passages 26 to orifices 28. Orifices 28 are located adjacent the backside of material 11 and directly opposite to the point at which material 11 is contacted by printing plate 18. Therefore, as will be more fully explained hereafter, the fluid pressure of the gas forces material 11 against the printing plate. As a result, the rotating impression cylinder of the prior art is completely eliminated, as is all mechanical contact with the backside of the material, and all such elements are replaced by an entirely fluid pressure force which produces substantially no friction against the forward motion of the material through the machine.

In FIG. 2, elongated element 20 is illustrated as having a generally rectangular cross-section, and chamber 22 is shown as being a groove in the beam covered by a sealed cap or strip 23. However, it will apparent that the operation and performance of the present invention is not dependent upon the specific cross-sectional shape of beam or element 20, nor upon the provision of three separate elements such as chamber 22, passage(s) 26 and orifice(s) 28. Rather, as illustrated in FIG. 2-A for example, element 20 may be of circular cross-section, and may be a hollow tube of metal or plastic composition. Furthermore, orifice(s) 28 and passages 26 may simply comprise one or more ports 28' which direct the pressurized gas against the backside of material 11. With regard to the term "backside", it will be clear to those skilled in the printing art that the backside is the side opposite to the side which is to be imprinted. It will also be readily understood that the material to be imprinted may be fed to the bottom portion of a print cylinder, below which a conventional impression cylinder may be positioned, as in the known manner of some printing machines which print on the top side of the material as opposed to the bottom side as illustrated.

As illustrated in FIGS. 3 and 4, orifices 28 may comprise a series of individual openings or ports 28', or they may be in the shape of one or more elongated slots 28". That is, depending upon the size, shape and weight of material 11 and the pressure in chamber 22, the shape and number of orifices 28 extending along the longitudinal length of beam 20 may be preferred to be a large plurality of small, individual ports 28', or one or more slots 28". Also, beam 20 may be composed of any suitable metal, or even plastic, so long as it is sufficiently rigid to extend across the width of the machine.

Referring to FIG. 5, beam or elongated element 20 is illustrated as including a layer 30 of low coefficient of friction composition, such as well known plastic materials for example. Layer 30 is positioned immediately adjacent the backside of material 11 between the material and beam 20. In this embodiment, any of the material which may be warped, bent, creased or otherwise distorted and non-planar such as to instantaneously contact the end of beam 20 instead contacts low friction layer 30. Thus, the material is not scuffed or otherwise damaged as it passes through the printing stage while the majority of the surface of the backside is maintained out of contact with layer 30 by the high pressure gas. The problem of warpage can be particularly serious with cardboard and corrugated cardboard where uncontrollable ambient moisture levels may create warps in the cardboard material to be imprinted. Therefore, instead of requiring a fluid pressure of such magnitude as to prevent any possibility of any warped materials contacting the pressurized beam, the present invention includes the provision of a low coefficient layer which enables the use of much lower fluid pressures which substantially reduces compressor energy.

Referring to FIG. 6, this figure illustrates that the orifices may include enlarged areas or lands 32 such that the high pressure gas in high pressure passages 26 may be diffused over a larger area by expansion in the increased surface area of lands 32. Of course, it will be apparent that enlarged surface area lands 32 may be formed directly in beam 20, as in FIG. 6, or in a low coefficient of friction layer such as layer 30 shown in FIG. 5.

It has also been discovered that, depending upon the pressure of the gas in chamber 22, the exit velocity of the gas from orifices 28 or lands 32, and the total volumetric flowrate of the gas, the present invention may operate in different modes. For example, as schematically illustrated in FIG. 7, high velocity jet(s) 36 may be directed against the backside of the material whereby it is primarily the dynamic fluid pressure of the jet which forces material 11 against the printing plate on the print cylinder. Such jets of gas may be produced by utilizing narrow passages 26, and/or high velocity nozzles 38, and/or the use of high pressures in chamber 22. At the same time, as shown schematically in FIG. 8, beam 20 may be positioned closer to the backside of material 11 so as to form a very thin film 37 of pressurized gas between the backside of material 11 and the adjacent surface of the beam. In this mode, passage 26 may be made larger, and/or a land such as land 32 of FIG. 6 may be provided so as to diffuse the gas over a larger area and form the very thin film. In either mode, whether the fluid jet mode or the fluid film mode, it will be apparent that it is pressurized gas which contacts the backside of the material and forces it against the print plate of the printing cylinder; i.e., as opposed to the rotating impression cylinder of the prior art. As shown in FIGS. 9-A and 9-B, the film mode may also be promoted by the provision of multiple passages 26 along the direction of material movement, and the film may be formed with a land area 32' as illustrated in FIG. 9-A, or with a flat, non-recessed surface as shown in FIG. 9-B.

In each of the foregoing illustrative embodiments, the material to be printed is maintained out of contact with a solid element by virtue of pressurized gas, except of course, for possible non-planar portions as previously explained. FIG. 10 schematically illustrates a further embodiment of the present invention in which the material to be printed does contact a solid element, but the solid element is maintained in contact with the material by fluid pressure such as a film of pressurized fluid.

Referring to FIGS. 10 and 11, numeral 20 continues to indicate an elongated element or beam as previously described, and numeral 22 continues to indicate a chamber of compressed gas. However, numeral 40 indicates a freely rotating roller, such as a ball or elongated cylinder, which is mounted in a chamber 42 in beam 20, and it will be understood that roller 40 may be solid or hollow as shown. The compressed gas from high pressure chamber 22 is conducted to chamber 42 by one or more passages 44, and it will be noted that the diameter of the upper portion of chamber 42 is slightly larger than that of roller 40. As a result, the pressurized gas around the upper portion of rotating element 40 forces roller 40 downwardly as viewed in FIGS. 10 and 11. The bottom portion of chamber 42 is the same diameter as that of roller 40 whereby roller 40 acts as a valve head which seats against opposing surface 46 on the lower portion of chamber 42 as shown in FIG. 10. This essentially prevents the escape of pressurized gas from chamber 42 so long as no force urges roller 40 upwardly against the pressure of the fluid in chamber 42. However, as shown in FIG. 11, when material 11 passes between the print plate and roller 40, the thickness of the material forces the roller upwardly against the fluid pressure in the upper portion of chamber 42. This movement lifts the lower portion of roller 40 away from seating against surface 46 which causes the roller to rotate in a surrounding film of pressurized fluid. That is, roller 40 floats in a fluid film and offers virtually no frictional resistance to the passage of the material.

In addition, when roller 40 moves away from seat 46, pressurized fluid can flow around roller 40 and exit between the back surface of the material and the bottom surface 48 of the beam. This pressurized fluid layer further assists in forcing the material against the printing cylinder and away from contact with the beam.

From the foregoing explanation of several embodiments of the present invention, it will be clear to those skilled in the printing art that the invention removes all of the serious problems of impression cylinders, and also provides a system in which the pressure of the fluid can easily be adjusted so as to vary the pressure against the backside of the material. In addition, all frictional contact with the backside of the material can be eliminated, as well as all scuffing and other damage to the material. Moreover, the distance between the feed conveyors or feed rollers and the printing cylinder may be substantially decreased such that the material is held more securely during printing. It will also be understood that the foregoing description of several preferred embodiments is intended to be illustrative of the principles of the present invention rather than exhaustive of the invention, and it will be apparent that many variations will be obvious to those skilled in the printing art. Accordingly, it is to be understood that the foregoing description is not intended to limit the invention to the illustrated embodiments, and that the true invention is not intended to be limited other than as expressly set forth in the following claims interpreted under the doctrine of equivalents.

Claims

1. A printing machine for printing indicia on material comprising:

(a) a printing plate;

(b) feed means for feeding said material in contact with said printing plate; and

(c) fluid pressure means for urging said material against said printing plate.

2. The printing machine of claim 1 wherein said feed means comprise conveyor means for feeding said material, and said conveyor means are positioned immediately adjacent said fluid pressure means.

3. The printing machine of claim 1 wherein said fluid pressure means eject pressurized gas against said material for urging said material into contact with said printing plate.

4. The printing machine of claim 3 wherein said fluid pressure means eject a plurality of jets of gas against said material.

5. The plurality machine of claim 3 wherein said fluid pressure means eject gas at superatmospheric pressure and form a pressurized film of gas between said material and said fluid pressure means.

6. The printing machine of claim 1 wherein said fluid pressure means include hollow lands for diffusing said pressurized gas against said material.

7. A printing machine for imprinting indicia on material passing therethrough comprising:

(a) printing means for printing indicia on a first side of said material;

(b) roller means for engaging said material on a second side of said material and urging it into contact with said printing means; and

(c) fluid pressure means urging said roller means into engagement with said material.

8. The printing machine of claim 7 wherein said fluid pressure means comprise means forming a pressurized fluid chamber, and wherein said roller means is positioned in said chamber, and wherein said pressurized fluid in said chamber urges said roller means in a direction toward said material.

9. The printing machine of claim 7 wherein said fluid pressure means comprise means forming a valve seat, and wherein said pressurized fluid urges said roller means against said valve seat.

10. The printing machine of claim 9 wherein said roller means are positioned such as to be moved away from said valve seat by said material passing through said machine.

11. The printing machine of claim 10 wherein said roller means and said valve seat are positioned so as to eject pressurized gas against said material when said material moves said roller means away from said valve seat.

12. A printing machine comprising at least one printing stage for printing indicia on material as said material passes through said printing stage comprising:

(a) a rotary printing cylinder;

(b) a printing plate mounted on said cylinder;

(c) feed means for feeding said material through said printing stage in contact with said rotary printing plate, said printing plate being positioned adjacent a first said of said material; and

(d) fluid pressure means for exerting a fluid pressure against the second side of said material for forcing said material into firm contact with said printing plate.

13. The printing machine of claim 12 wherein said fluid pressure means comprise an elongated element extending substantially transversely to the direction of travel of said material, and orifice means for ejecting pressurized fluid against said second side of said material.

14. The printing machine of claim 13 wherein said elongated element includes a high pressure chamber and fluid passage means connecting said chamber to said orifice means.

15. The printing machine of claim 13 wherein said orifice means comprise a plurality of apertures positioned along the length of said elongated element.

16. The printing machine of claim 13 wherein said orifice means comprise at least one elongated slot extending parallel to the length of said elongated element.

17. The printing machine of claim 13 including a layer of low coefficient of friction means adjacent said orifice means for momentarily engaging any non-planar portions of said material.

18. The printing machine of claim 13 wherein said elongated element comprises an elongated hollow duct.

19. The printing machine of claim 13 wherein said orifice means comprise a plurality of apertures positioned along the direction of travel of said material.

20. A rotary printing machine for printing indicia on material having first and second sides including at least one printing stage comprising in combination:

(a) a rotary printing cylinder positioned adjacent said first side of said material as it passes through said printing machine;

(b) a printing plate mounted on said printing cylinder;

(c) an elongated element positioned adjacent said second side of said material and extending generally perpendicularly relative to the direction of travel of said material; and

(d) said elongated element including fluid pressure means for ejecting superatmospheric pressure fluid against said second side of said material for forcing said material against said printing plate as said material passes through said printing stage.

21. The printing machine of claim 20 wherein said printing cylinder comprises a flexographic printing cylinder.

22. The printing machine of claim 20 wherein said machine includes conveyor means for printing on a continuous web of material to be imprinted.

23. The printing machine of claim 20 wherein said machine includes conveyor means for printing on a plurality of unconnected sheets.