CA1301540C - Engraved printing rolls and process of making - Google Patents

Abstract

ENGRAVED PRINTING ROLLS AND PROCESS OF MAKING

ABSTRACT
An engraved printing roll is formed by sequential indentations in the roll surface by a stylus. Each indentation is a diamond shape with a longer axis of each indentation overlapping each circumferentially adjacent indentation but the shorter axis not overlapping any other indentation.

Description

~3~

ENGRAVED PRINTING ROLLS AND PROCESS OF ~AKING

FIELD OF THE INVENTION:
This invention relates to printing rolls which are mechanically engraved ~o produce cells on the roll surface to receive printing ink as well as the process of engraving the surface~

BACKGROUND C)F TEIE INVENTION:
Engraved printing rolls of the modern type are cylindrical in shape. Engraved on the cylindrical surface are a large number of cavities designed to hold ink which will be deposited on the desired printing mediumr for example, paper, fabric, or plastic. The engraved cavities are called ~Icells~ in the industryl and several hundrecl such cells or recesses are formed per linear inch; their depkh may range from about 0.0015 inches to about 0.0008 inches.
The general operating characteristics of a printing operation of the type being considered in this invention are disclosed in the patent to Heurich, U.S. Patent No.
3,613,578.
The earliest form of engraved printing roll had a pattern of cixcular shaped cells. This produced a substantial "corner post" between the cells. In the industry a "corner post" is the area between cells where ink will not print, for example, with four cells in a square pattern the "corner post'~ is the flat area at the center of the square where no ink will be deposited.
Subsequently s~uare shaped and hexagon shaped cells were developed. This obviously served to reduce the size of the corner post.
Another development included tri-helical grooving.
This further reduced "corner post" problems but sufered the side effect vf causing lateral ink migration with less control over the coating application~

~p r ~3~

So called "electronic engraving" (where a detector "reads" a black and white print of a design pattern to control a cutting stylus) can be programmed 50 that the stylus drags between one cell and the next to create a relatively shallow interconnecting channel; this aids the flow of ink. There is also known ~see U.S. Patent No.
4,301,583) a mechanical engraving process in which a shallow V~cut channel exists between adjacent cells.
A patent to Hieber et al. (U.S. Patent No.
104,155,766) shows a screen for engraving having interconnection of cells via channels which is another way the prior art has tried to improve the engraving procedure, to reduce the corner post and improve the resulting printing.

S~MMA~Y OF THE INVENTION:
15The present invention provides printing rolls which have an extended print life while maintaining a given quality of printing. Generally speaking, the invention provides a mechanically engraved cylindrical printing roll having cells interconnected at weirs in a line defining a circumference of the roll, to form a plurality of circumferentially extending chains around the roll, the walls defining each cell form an elongated rhombus outline with a major axis and a minor axis, the major axis having a length greater than the length of the minor axis, the major axis extending in the direction of the circumference of the roll, the corners of each circumferentially adjacent rhombus at both ends of the major axis overlapping to the extent that no rhombus includes an outline of a sharp point along the major axis, the circumference being coextensive with the major axis of each rhombus in the circumference, the weirs defining a sharp dividing line between cellsr the weirs comprising the highest elevation on the circumference, the circumferential line substantially bisecting each weir, the depth of each of the cells increasing i~ both directions from the weirs, each chain being spaced from adjacent chains by a zig-zag shaped wall of uniform elevation and width, each wall extending ~ l9 circumferentially around the roll such that no wall contacts any other wall, and each wall is configured to be a mirror image of any next adjacent wall.

BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will now be described further with reference to the accompanying drawings in which:
Fig. 1 is a portion of a microphotograph of the engraved surface of a cylindrical printing roll, in accordance with the invention;
~ig. 2 is a section on the line II - II of Fig. 1;
Fig. 3 is an explanatory diagram showing the formation of a master die;
Fig. 4 is a section elevation supplementing Fig. 3;
Figs. 5A and 5B show a portion of the surface of two prior art forms of roll and the e~`fect of use; and Fig. 6 shows a portion of the surface shown in Fig.
1 and the effect of use.

DESCRIPTION OF THE P~EFERRED EMBODIMENT:
A printing roll i~ conventionally cylindrical in shape. To carry ink on the roll it is customary to engrave thousands of minute cells on the roll surface. This invention is concerned with the shape, orientation and arrangement of these cells.
In Fig. 1 the lands or walls 10 between cells or indentations 13 are of zig-zag shape and of constant width.
Any two adjacent zig-zags are mirror images of ,~,,~

~L3~

each other but they do not touch. Thereby, an opening 12 exists between cells 13 taken in the direction 14 of the cir umference of the roll surface. The cells 13 are elongate diamond pyramidal in shape and form having a depth of in the range fifteen micron~ to ninety microns.
They could also have a quadrilateral base~ A form of weir 15, best seen in Fig. 2, exists between adjacent cells at the opening 12. The depth of the weir below the land or cell wall 10 is about one-half the depth of the cell 13.
In Fig. 2 a fraction of a cylindrical roll 16 is shown in section having at its surface the cells 13.
Preferably the cells will number about sixty-five to two hundred per cîrcumferential inch and a roughly corrssponding number in a transverse direction. The surface 17 of the roll ~which is swept by a doctor blade in use to remove excess ink) is shown and this, of course, defines the cell wall areas 10.
In Figs. 3 and 4 the pyramidal indentation making up each cell 13 is shown as an elongate diamond shape 19. As each indentation overlaps its adjacent indentations a form of circumferentially extending chain is created. Of course, the leading and trailing points 18 of the indentations becom~ obliterated as each succeeding indentation is made and the eventual outline of the cells is completed - i.e. the diamond shaped cell aperture 13 as shown in Fig. 1. Indentations in the roll are made using a mill which is formed from a stylus or master die 20 made as shown in Fig. 4. The pitch between successive positions of the stylus or punch is represented by the letter ~p~. The path taken by the punch is shown by the chain line 21.
The deformation of the surface 17 of the roll by the stylus 20 during the formation of the cells 13 will obviously displace =aterial in a radial direction. The ~3~

means for main~aining or refo~ming the wall or land 10 at a uniform radial distance from the roll axis is known in the art and need not be de~cribed., Fig. 5A shows a prior art roll having l~itially isolated square cells 22 (dash lines) on a square matrix and having cell walls 23. With burnishing and wear smaller cells 24 (continuo.us lines~ are formed with a somewhat irregular outline. At the same time a significantly enlarged ~corner post~ 25 ~as represented by arrows 25A) is built up at the merger of the cell walls which is a serious impediment to any ink flow.
In Fig. 5B another prior art arrangement is shown.
In this figure the cells 26 (dash lines) are of approximately similar shape as in Fig. 5A initially but include narrow shallow connecting channels 27 between adjacent cells in the direction 28 o~ the circum~erence o~ the roll so that ink can flow between cells. As with the burnishing and wear mentioned in relation to Fig.
5A, the cell wall increases in width and the cell 26 decreases in size to a cell 29. When these channels 27 are blocked due to wear, to produce cells 29, a significant ncorner postn 30 is again created (as represented by arrows 31).
In Fig. 6, the arrangement o~ the present invention, the initial cells 13 are shown as dash-lines and the cell shape with burnishing and wear is shown as cells 32. Whilst the general burnishing and wear has occurred to the same extent as in Figs. 5~ and 5B, the ~corner pOstn 33 (as represented by arrows 3~) is not so excessive and ink can still flow easily across the corner post so that the quality of pxinting is not badly damaged. ~Note particularly the small distance between the vertical arrows 34.) ~L3~S~

Having thus descrihed the invention in its preferred embodiment it will be clear to those having ordinary skill in the art that modifications may be made to the apparatus and the procedural steps without departing from the spirit of the invention. It is not intended that the words used to describe the invention in the specification nor the drawings illustrating the same be used in a limiting sense. Rather it is intended that the invention be limited only by the scope of the appended claims.

Claims (8)

1. A mechanically engraved cylindrical printing roll having cells interconnected at weirs in a line defining a circumference of the roll, to form a plurality of circumferentially extending chains around the roll, the walls defining each cell form an elongated rhombus outline with a major axis and a minor axis, said major axis having a length greater than the length of the minor axis, said major axis extending in the direction of said circumference of the roll, the corners of each circumferentially adjacent rhombus at both ends of the major axis overlapping to the extent that no rhombus includes an outline of a sharp point along said major axis, said circumference being coextensive with the major axis of each rhombus in said circumference, said weirs defining a sharp dividing line between cells, said weirs comprising the highest elevation on said circumference, said circumferential line substantially bisecting each weir, the depth of each of said cells increasing in both directions from said weirs, each chain being spaced from adjacent chains by a zig-zag shaped wall of uniform elevation and width, each said wall extending circumferentially around the roll such that no wall contacts any other wall, and each wall is configured to be a mirror image of any next adjacent wall.

2. The printing roll of claim 1 wherein the cells are shaped as one of a whole or truncated pyramid form when viewed in cross-section.

3. The printing roll of claim 2 wherein each cell has a depth in the range of about 15-90 microns.

4. The printing roll of claim 3 wherein about 65 to 200 cells are formed per circumferential inch around the roll.

5. The printing roll of claim 1 wherein the depth of each weir below wall elevation is about one-half the depth of each cell.

6. The printing roll of claim 2 wherein the depth of each weir below wall elevation is about one-half the depth of each cell.

7. The printing roll of claim 3 wherein the depth of each weir below wall elevation is about one-half the depth of each cell.

8. The printing roll of claim 4 wherein the depth of each weir below wall elevation is about one-half the depth of each cell.