MXPA00011201A - Method and apparatus for engraving solid articles with laser beams and the articles produced - Google Patents

Abstract

The process and apparatus engrave a solid article to provide on at least a portion of a surface of the article a plurality of spaced-apart engraved cells. It generates a laser beam and splits the laser beam into at least two beams. Each of the beams forms a focused spot at the surface. The focused spots spaced apart from each other form beam pairs with each pair of the beams being arranged for simultaneously engraving a new cell. The focused spot of a first of the beam pair engraves the new cell and a second focused spot re-engraves the previously engraved cell. The splitting comprises passing the laser beam through an optical device having a diffractive optical element to form the first beam and the second beam having the spaced apart focused spots.

Description

METHOD AND APPARATUS FOR RECORDING ARTICLES. SOLID WITH LASER MACHINES AND THE ARTICLES PRODUCED TECHNICAL FIELD The present invention relates to the etching of solid surfaces by multiple laser beams wherein the laser beams are formed from a single beam source using a diffractive optical device.

BACKGROUND TECHNIQUE Liquid transfer articles have numerous applications, including without limitation, such as plates or rollers for printing, measuring plates or rollers for offset printing, flexography or engraving or plates and rollers for applying liquid such as ink, lacquer or liquid resin to surfaces that are going to be coated with such liquids. In all cases the liquid or ink to be transferred is kept in a plurality of cells etched on the surface of the plate or roller with the amount of liquid to be transferred depending on the number, size and depth of the cells per unit area of the engraved surface. In practice, cells are formed together closely in a defined pattern of parallel lines of cells. In the case of a cylinder, they are preferably formed in a continuous spiral on the cylindrical surface. Although the engraved surface may be in the form of a plate, by far the most common and usual form is that of a cylinder having a continuous spiral of cells engraved on its surface. The spiral of cells is engraved so that a plurality of lines are produced *. * ..... ** _ - _, - ... .._-- ._,, .__. _-, _ .. *., ___, _., ü_, B_fc _ * - * _.

Parallel of cells all forming the same angle (usually called the screen angle) with a surface line parallel to the long axis of the cylinder or roller, whose angle can be from about 0 ° to 90 ° , for example 30 ° or 60 °, but more commonly 5 45 °. Although a variety of engraved surfaces are used to transfer the liquid, ceramic and metal carbide surfaces are generally used for liquid transfer, due to their extreme hardness and excellent wear resistance with subsequent. Due to its use, however, the only practical method of grinding such surfaces has been by means of a laser beam. Although continuous laser beams are used to etch some surfaces, the pulse laser beam is used much more commonly since it gives the production of discrete cells on the engraved surface by itself. The cells that are formed are of specific diameter and depth and can be used to measure liquids with a high degree of accuracy and prediction. In a prior art method each pulse of the laser beam produces a cell. In producing the cell, however, the pulse also produces a raised portion (i.e., above the original surface of the roller) called "recast" around the periphery of each cell which is generally ring-shaped, but wide and irregular height. When the pulse of the laser light is focused on the surface of the roller, the ceramic material is evaporated and expelled from the surface of the rollers. During this process some of the expelled material solidifies around the edge of the cells producing an appearance of ? _lÍ ________ Éi _______________________ ¿_l___i ___________________ ..... ..i. . .i. », -_-. t ___ a _._,. a crater This edge of re-solidified material, is the recast. Remelting makes it impossible to reduce, by conventional methods, the distance between cells along the spiral engraving line to less than about 2 times that along a line perpendicular to the longitudinal axis of the cylindrical roller. The remelting can be partially or entirely eliminated by polishing the engraved roller. Due to the irregularity in the height of the remelting, the movement of the liquid between adjacent cells is possible if a post polishing or insufficient polishing is not undertaken to reduce the remelting in flat areas between the cells. When it is possible for the liquid to pass between adjacent cells, this type of structure is called "an open cell structure". When enough polishing is done to produce flat areas of recast of the same height above the original surface or the original surface itself, then the cells approach as the movement of the liquid between them is no longer possible. This is referred to as a closed cell structure, which is preferred. The recast is usually irregular in shape and is typically irregular with sharp peaks. These characteristics cause many problems in addition to those already described. For example, a plastic or metal sheet is used in a printing press to remove excess ink from an ink roller surface before measuring the ink for the rest of the process. These sheets can be worn or damaged prematurely by the irregularities of the recast. The material of the sheet can also end up being deposited in the roller cells ^^^ & Inker, causing inconsistent measurement of roller ink. Another problem has to do with the aesthetic quality of the engraving The irregularities of the recast give many engravings a rough "unfinished" appearance and poor symmetry for the cells. This causes the overall appearance of the recorded patterns are inconsistent across the surface of the rollers. Examples of laser beam etching of liquid transfer articles can be found in U.S. Patent Nos. 4,108,659 for Dmi, 4,504,354 for George et al., 10 4,566,938 for Jenkins et al., 5,193,180 for Morgan, and 5,143,178 and 5,236,763 for Luthi. The descriptions of these patents are specifically incorporated by reference herein. It has been found that many of these problems can be avoided by rewriting an area of the roll surface that has already been recorded. 15 The re-recorded cells (re-recorded at least twice) can be made much more symmetrical and the recast can be smoothed and rounded. This must also allow the walls of the cell-to-cell cells to become thinner and smoother. The bottoms of the cells must also be smoother and more open. The depth of the cells 20 can be 20 to 30% or more, more produndas than the cells "beaten" by a laser beam only once. This re-engraving process overcomes many of the problems associated with the conventional one-shot engraving process. A re-engraving process of the prior art is described in the patents of Luthi discussed above. In this process the pulses of the beam of "d *» »- ^ * - - • * > * - - - ^ ~ - > ._- -.- ....,. ...., - .., .. faith The laser is formed in a series of consecutive groups with each group comprising two or more consecutive separate pulses.The incidence of each group of pulses on the solid surface that is recorded forms an individual cell in the transfer article. Other methods are known for re-recording.An approach is to record the roller a first time and then return the focusing optics to its starting point.The entire roller is then recorded again.A difficulty with this approach is to ensure registration or appropriate overlap between the first and second engravings In addition, the process is slow and expensive since the engraving process must be repeated 2 times to produce the final re-engraved roller.Other approach uses conventional optical refractive elements to divide a laser beam into 2 you have a separate focus point for each beam, adjusting mirrors in the optical trajectory of this approach, the second focus point can be placed on a previously recorded cell. This approach requires a controller to position the mirrors as the engraving patterns are changed. Typically use 2 beam splitters which can produce an energy loss of 50% because the second beam splitter divides the energy of the two beams a second time. The more commercial lasers would not have sufficient power to tolerate such a 50% loss in power without slowing the engraving processing speed for the liquid transfer rolls. Refracting the 2 laser beams through a common focusing lens using this technique can also cause distortion of the shape of the beams which can cause the cells _ ^ __ _¡_ ._ ~ _ ^ _ i ^^ i L_? * '-' J - • - - - - «- '~ ¿, ¿I_ ___. E. of gravure are slightly the optical instead of round as desired. This approach is also very expensive, costing as much as US $ 60,000 for the laser machining device and as much as US $ 50,000 for the controller and software to operate it. 5 Another approach still uses an acousto-optic modulator to modulate a continuous beam of laser energy to re-record a cell. For example, a cell is recorded by the laser beam and then the beam is diverted to the next cell position in the circle of the roller to record that cell. Then the beam is diverted back to the original cell which is hit a second time. The process is then repeated around the circumference of the rod. It is not believed that this approach produces the desired quality of roll engraving that is possible with the other approaches. Ceramic materials commonly used for anilox rolls, for example, are poor heat conductors. It has been found that the initially recorded cell needs time to cool and fully solidify to take full advantage of the second "stroke". This approach does not provide sufficient time for proper cooling, refuting the quality compared to other re-engraving processes. This system is very expensive too, costing as much as 20 US $ 90,000.00 each. The systems of beam splitting and beam modulation also have limited back-adjustability with many of the existing engraving machines. The physical size and necessary characteristics of the beam of these machines usually require modifications significant of the machines at high cost in order to retrofit ? á & ^^ tU ^^^^^^ * such systems to the machines. It would be highly desirable to find a re-engraving process that has improved efficiency and production without decreasing the quality of the etched product. As will be described later, the present invention achieves those improvements at significantly lower cost than the prior art approaches by using an optical system. which uses an optical diffraction element. Optical diffraction elements or binary grids have found several applications as described in certain patents and publications as follows: U.S. Patent Nos. 4,436,398 to Endo et al., 5,786,560 to Tatah et al., And 5,914,814 to Ang. Diffractive Optics Move Into The Commercial Arena, by MR Feldman, who appeared in the October 1994 issue of Focus World Laser, published by PennWell Publishing Co. Diffractive Optics Improve Product Design, by MR Feldman and collaborators, which appeared in the number of September 1995 by Photonics Spectra, published by Laurin Publising Co., Inc., Laser Beam Shapes For The Future, by G. Sharp, and collaborators, which appeared in the December 1994 issue of Industrial Laser Review, published by PennWell Publishing Co., and Binary Optics: New Diffractive Elements for The Designer's Tool Kit, by A. Kathman, which appeared in the September 1992 issue of Photonics Spectra, published by Laurin Publishing Co., Inc. In particular the Endo and collaborators and Tatah and ¿Í Í Í Í L L L | | | | |......... ______ -.-. - _- _ > ___. », __ _ _ __. A _ ^ ...._ t ._.__ * collaborators and publication # 2 shows, for example, that diffraction optics can convert a simple laser beam into several beams of light. departure . They do not show, however, the use of diffraction optics to provide divided beams for recording and regrouting, particularly for making a liquid transfer art. The descriptions of the three patents and publications 1 to 4 are intended to be incorporated by reference herein with their description of the fabrication and application of diffraction optical elements.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to the etching of solid surfaces by means of multiple laser beams wherein the laser beams are formed from a single laser beam source using an element. optical diffraction. 5 According to a preferred embodiment of the invention, a process for recording a solid article is provided to provide at least a portion of a surface of the article with a plurality of separate etched cells. A laser beam is generated, preferably a laser beam of pulses. The laser beam is divided into at least two beams, with each beam forming a point focused on the surface. The focused points are separated from each other. The beams generally form pairs of beams with each pair of beams being arranged to simultaneously record a new cell with the focused point of a first of the pair of beams and re-record a previously recorded cell with the focused point of one second of the pair of beams. The division of the original laser beam is carried out by passing the laser beam through an optical device having a diffraction optical element to form at least the first beam and the second beam having the focused points separated. The process employs divided beams to engrave and re-record a plurality of cells on the surface of the article. In a further preferred embodiment, more than two beams are formed so that for each divided beam that is recording a new cell there is another divided beam that is regaring a previously opened cell g. The processes of this invention are particularly useful for making articles for liquid transfer which have numerous applications as described above. In a still preferred embodiment of the invention each cell defines an opening in the surface of the article having a first central axis and a second central axis normal to the first axis, the axes intersecting at a central point of the axis. In this modality, the step of cutting comprises the cells arranged in at least two rows, in which a line drawn through the first axes of the cells in a row is substantially parallel to a traced line. through the first axes of the cells in an adjacent cell; and wherein at least a portion of the cells in a row each has its second axes aligned between the second axes of the two separate cells in an adjacent row. Preferably, the length of the non-etched space between two cells in a row along a line containing its first axes is between about 1 to about 1.3 times the length of a space not recorded between 1 of the cells in the row and an adjacent cell in an adjacent row, along a line containing the points on the central axis of the cells. Also preferably, the cells are aligned so that a line drawn through the center-axis point of a cell in a cell and through a point of the central axis of an adjacent cell in an adjacent cell forms an angle. between more than about 0 ° and less than about 90 ° with a line drawn parallel to the longitude axis of the inductive cylindrical item. Most preferably, the angle is between more than about 60 ° and less than about 90 °. In a particularly preferred embodiment, the cells are disposed equally substantially apart from one another; and the length of the space not recorded between two cells in a row along a line containing its first axes is substantially equal to the length of the space not recorded between one of the cells and an adjacent cell in an adjacent row. along a line that contains the points of the central axis of the cells. Preferably, the optical diffraction element is formed of a material that is transparent to the laser beam. Advantageously, the sling length is from about 0. 1 to about 15 μm (microns or microns) and most advantageously from about 1 to about 15 μm. Most preferably, the sling length of the laser beam is approximately 10.6 μm. According to an alternate embodiment of the invention, an apparatus is provided for engraving a solid article so as to provide at least a portion of a surface of the article with a plurality of separate grooved cells. The apparatus includes a laser beam generator to generate a laser beam. Preferably the laser beam that is generated is a laser beam of pulses. An optical device having an optical diffraction element is provided for dividing the laser beam into at least two beams, with each of the beams forming a point focused on the surface. Preferably the optical element of diffraction is arranged along the axis d of the laser beam as it is generated to divide the beam into at least two beams which are then passed through a refractive lens for provides r points focused on the surface. Preferably, each of the beams is separated from the other beams. The optical device generally forms the beams in pairs with each pair of beams being arranged to simultaneously record a new cell with the focused point of a first of the bundle and re-record a previously recorded cell with the focused point of one second of the beam. pair of beams. Medium is provided to use each pair of beams to record and re-record a plurality of cells on the surface of the article. Preferably, the article is an article for transferring the liquid. Preferably, the optical device provides more than two beams and for each divided beam to record a new cell another split beam is provided to re-record a previously recorded cell. Preferably, the optical diffraction element is formed of a material that is transparent to the laser beam. •? - ^ a - The product produced by the process of this invention also comprises a preferred embodiment of the invention. It is therefore an object of the present invention to provide a re-engraving process that has improved efficiency and production without diminishing the quality of the finished product. It is another object of the present invention to provide such a process that uses a diffraction optical device to divide a laser beam from the engraving apparatus. It is another object of the present invention to provide an improved recording apparatus for carrying out the re-engraving process using a diffraction optical device for dividing the laser beam used for engraving. It is another object of the present invention to produce an article for transfer of liquid by the process of the invention, which has a reduced manufacturing cost. The foregoing and additional objects and advantages of this invention will be made apparent by the consideration of the following description thereof.

BRIEF DESCRIPTION OF THE DIAMETERS Figure 1 is a schematic view of a laser engraving apparatus according to a preferred embodiment of this invention. Figure 2 is a schematic partial perspective view of a recorded surface of a delivered product. Figure 3 is a schematic view of the apparatus of Figure 1 which .; ac _t > - Illustrates a preferred cell pattern which can be produced by the apparatus and process according to the preferred embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be incorporated in many forms of alternate embodiments. In addition, any size, shape or type of materials or elements could be used. adequate. Referring to Figure 1, this invention relates to a method and apparatus 10 for recording and re-recording a series of consecutive cells 12 on a solid surface 14 by striking the solid surface 14 with laser beams 16 in relative movement with the surface 14. In particular, the present invention relates to the engraving and re-engraving of solid surfaces 14 by multiple laser beams 16 having separate focus points 24 and 26 on the surface 14. Laser beams 16 having points 24 and 26 of Separate focus are formed from a single laser beam 15 provided by a laser generator 18 using an optical diffraction element 20 and refractive lens 22. The relative motion of the focus points 24 and 26 of the laser beams and the surface 14 can be provided by any conventional desired means as are well known in the art. The generated laser 18 and optical system 30, or the surface 14, or some combination of them, could be moved, for example, by a servo or _______________ computer controlled devices 28 and 29, to provide the relative motion required to record the cells 12. The mechanisms for traversing the working surface 14 under a laser beam are very well known and do not form part of this invention In accordance with a preferred embodiment of the invention, the laser beam that is generated is a pulse laser beam. The optical device 30 includes an optical diffraction element 20 for the laser beam 1 5 in at least 2 beams 1 6, with each of 16 together forming 24 or 26 in focus or the si- milar in the surface 14. Preferably, the diffraction optical element 20 is arranged along the axis 34 of the laser beam 1 5 which is generated by the generator 18 and divides the beam into at least two beams which are then passed through a refractive lens 22 to provide the points 24 and 26 focused on the surface 14. Preferably, each of the beams 16 is separated from each of the other beams 16 The optical device 30 preferably forms the beams 16 in pairs with each pair of the beams 16 being arranged to simultaneously record a new cell 12 with the focused point 22 of a first of the pairs 16 of beams and re-record a cell 12 previously recorded with the focused point 24 of a second of the beam pairs 16. Preferably, control means 32 is provided to use each pair of beams 16 to record and re-record a plurality of cells 12 on the surface 14 of article 36. Preferably, article 36 is a transfer article of the liquid. ¡ÉÉÍ_IIÍÍÍÍÍlÍÍÉÍ ----_________----------------------------- ^ '"" ""' T M-Tt. »_ .? - l III «l? . T in The diffraction optical elements (sometimes called a diffraction grating or a binary grid) are fully described in the patents and publications noted thus far. The characteristics of a laser beam (15) in any given image plane can be defined as the sum of the phase relationships of the photons comprising the beam 15. Altering the phase relationships in the beam 15 with an optical element 20 of diffraction the beam can be divided into multiple beams 16 with little loss of power because the energy of the beam 15 is reareglado essentially to provide the resulting beams 16. An optical defraction element 20 breaks the light slings entering the beam 15 into a large number of slings which recombine and form new slings on the other side of the optical element 20. The new slings can be moved in a different direction to the light that enters. The optical diffraction element 20 can therefore convert a single beam 15 into several output beams 16. The optical diffraction element 20 breaks the sling or light beam by forcing it through a microscopic pattern which is typically etched on the surface of the diffraction element 20 using conventional photolithography. The optical diffraction element 20 is designed to alter the phase relationship of the incident beams (15) so that the focusing lens 22 produces at least two focus points 24 and 26 of equal intensity substantially at a fixed spacing to allow that a focus point 24 engrave the cells 12 on a surface 14 of virgin materials while the second focus point 26 re-recorded the cells 12 g previously cut, all in a single pass through the surface 14. The optical element 20 The diffraction pattern alters the phase relationship of the beam 1 5 so that the lens 22 of at least two beams 16 at an angle with the pitch of the lens 22. This causes the lens 22 to produce a number of points 24 and 26. of focus that correspond to the number of beams 16 that it receives. Since the diffraction element 20 can accurately alter the phase relationships of the beam 1 5, the separation of the focus points 24 and 26 can be set in a repeatable and predictable manner. The cost of an optical diffraction element is a few dollars. It is also retro-fitted to existing engraving equipment, since it is compatible with most engraving systems. In addition, improvements in the efficiency of the engraving / re-engraving process of at least about 30% have been observed. The diffraction element 20 in combination with the focusing lens 20 does not add apparent distortions to the focus points 24 and 26, maintaining good symmetry of the cell 12. The engraving quality provided by the use of an optical element 20 diffraction in the optical device 30 to divide the beam 1 5 into multiple beams 16 is significantly improved compared to other re-engraving technology. There are three improved aspects of re-engraving with the optical system 30, are the smoothness of the walls and remelting of cell 12, better geometric definition of the shape of cell 12 and increased depth of cell 12. The depth of cell 12 is increases because the second bulbs 26 are able to focus below the surface 14 in the pre-recorded cell 12. Further, the beam splitting 15 with one element Optical diffraction provides greater energy in each of the divided beams 16 compared to the optical beam splitters of the prior art, due to the efficiency of the optical diffraction element. This makes it possible to increase the speed of the engraving operation thereby improving the productivity significantly. Preferably, the diffraction optical element 20 is designed to divide the has 15 into more than two beams 16. In such preferred arrangement, for each beam 16 divided to record a new cell 12 another beam 16 is provided divided to re-record a cell 12 previously recorded. According to a preferred alternate embodiment of the invention, there is provided a process for engraving a solid article to provide at least a portion of a surface 14 of article 16 with a plurality of separate engraved cells 12. A laser beam 15 is generated, preferably as a pulse laser beam. The laser beam 15 is divided into at least two beams 16, with each of the beams 16 forming a focus point 24 or 26 on the surface 14. The focused points 24 and 26 are spaced apart from each other. The beams 16 generally form pairs of beams with each pair of beams being arranged to simultaneously record a new cell 12 with the focused point 24 of a first 16 of the beams and re-record a cell 12 previously recorded with the focus point 26 of a second pair 16 of the beams. The division of the original laser beam 15 is achieved by passing it through an optical device 30 having a diffraction optical element 20 to form at least the first beam and the second beam, having the focus points 24 and 26 separated . The process uses split beams 16 to engrave and re-record a plurality of cells 12 on the surface of the article. Preferably, the process is computer controlled so that an appropriate relative movement is provided between the surface 14 of article 36 and the beams 16 to provide the desired array of cells 12 around the surface 14. Any desired controller can be used. By computer and its associated software as is known in the engraving technique In a preferred fashion the preferred form is formed by two beams 16 so that for each divided beam that is branching a new cell there is another divided beam that is reg- arving a cell previously saved. The processes of this invention are particularly useful for making transfer articles 36 which have numerous applications as described above. With reference now to Figures 2 and 3, in an even more preferred embodiment of the invention each cell 12 defines an aperture 40 in the surface 14 of the article 36 having a first central axis 42 and a second central axis 44 normal to the first axis, the axes that intersect at a point 46 of the central axis. In this embodiment the engraving step comprises engraving the cells 12 arranged in at least two rows 48, in which a line drawn through the first axes 42 of the cells 12 in a row 48 is substantially parallel to one line. traced through the first axes 42 of the cells in an adjacent row 48 '. At least a portion and preferably all cells 12 in a cell 48 each have their second axes 44 aligned - * "" "- * - * -" • * - • - - - - - between the second axes 44 of the two cells 12 separated into an adjacent row 48 '. Preferably the length of the space 50 not recorded between two cells 12 in a row 48 or 48 'along a line containing its first axes 42 is between about 1 and about 1.3 times the length of a space 52 not etched between one of the cells 12 in the row 48 and an adjacent cell in an adjacent row 48 ', along a line 54 containing the points 46 of the central axis of the cells s 12. Also preferably the cells 1 2 are aligned more closely than a line 42 traced through the points 46 of the central axis of a cell 1 2 in a cell 48 and a line 54 traced through the points 46 of the central axis of a cell in a row 48 and an adjacent cell 12 in an adjacent cell 48 'forms an angle a from 0 ° to 90 ° with a line drawn parallel to a long axis of the inductive article. Advantageously, the angle a is between more than about 0 ° and less than about 90 °. The most advantageous, the angle is between more than approximately 60 ° and less than approximately 90 °. When the article 36 is on a roller the shaft 42 falls parallel to the axis of the roller 36. The angle a is usually referred to as a screen angle. In a particularly preferred embodiment the cells 12 are disposed equally substantially apart from each other and the length of the space 50 not recorded between two cells 12 in a row 48 along a line containing their first axes 42 is substantially equal to the length of the space 52 not recorded between one of the cells 1 2 in the row 48 and an adjacent cell 12 in a row 48 'adjacent along a line containing the points 46 of the central axis of the cells 12. Referring to Figures 1-3 and Figure 3 in particular, lines 54 are divided into a sequence of lines "A" and "B" as shown. A line "B" 54 appears on each side of a line "A" 54 and vice versa. 4 focus points 24 or 26 can be provided by the diffraction element 20. Such a diffraction element has been successfully employed in a preferred alternate mode of the process and apparatus 10 In the process of four focus points and apparatus 10, two focus points 24 are used to record cells 12 and two focus points 26 are used to re-record the cells 12. In this preferred embodiment the controller 32 is programmed to accommodate two engraving points 24, one which records only the "A" lines and the other to record only the "B" lines. Similarly, the two re-engraving points 26 are arranged with one recording only the "A" lines and the other recording only the "B" lines. For example, the four-point diffraction element 20 can take advantage of this configuration by having the first and third points 24 record the lines "A" and "B" and the second and fourth points 26 re-engrave these lines. This has the advantage of doubling the speed of the etching process while retaining the improvements provided by this invention. Six and eight point diffraction elements 20 using this approach could give three and four times the engraving speed improvements as long as the laser generator 18 is capable of generating sufficient energy for all the focus points 24 and 26.

The etched product produced by the process of this invention also comprises a preferred embodiment of the invention. Preferably, the product is a liquid transfer article 36 and most preferably a liquid transfer roller. Because the diffraction element 20 is a simple optical element with dimensions similar to the lens 22 of FIG. In the approach, few are required if there are some modifications for the optical system 30 for your application. This makes it compatible with almost any system that is easily and easily retro- fitted in such systems. Although a diffraction element 20 is preferably used in the optical system 30, multiple diffraction elements could be used if desired. The optical diffraction element 20 is mounted just behind the focusing lens 22 between the lens 22 and the beam generator 18. The position of the two focus points 24 and 25 can be made with the engraving patterns by rotating the element 20. optical lens and focusing lens 22 in a common lens assembly (not shown). The separation of the two focus points 24 and 26 depends on the design of the diffraction element 20 and the focal length of the lens 22. The equation for calculating the separation is as follows: H = F tan?. where H is the half-angle separation, F is the focal length of the lens and? is the diffraction angle designated to the optical diffraction element 20. For conventional etching of anilox transfer rollers 36 there are three cell patterns 12 that are commonly used, namely those with screen angles equal to 30 °, 45 ° and 60 °. Lines per Centimeter (LPC) or screen count, is determined by counting the number of cells 12 that falls along the specified screen angle a. The computer 32 calculates the number of cells 12 that will accommodate around the circumference of the roller (36) based on the input information comprising: the diameter of the roller 36, the screen angle a and the LPC The controller 32 calculates the positions for two complete rows 54 of cells 12 around the circumference of the roller (36) These rows or lines 54 have been previously noted as lines "A" and "B" When the first row of cells, line "A", is produces, the computer advances the position of the optical system 30, to place the next row of cells, line "B", so as not to overlap with the line "A" prior to engraving. Changing the position of the line "B" with respect to the line "A" around the circumference of the roller (36), and advancing the optical system 30 less than a full width of cell 12, the two lines "A" and " B "are interspersed producing a pattern similar to that of a honeycomb as shown in Figure 2. This process of advancing the position of the optical system 30 and alternating between the position of the line" A "and the line" B "is repeated towards down the axial length 56 of the roller 36. The computer can alter the space 50 or 52 of the cells 12 around the circumference and along the axis 56 of the roller 36 to produce the desired LPC and screen angle a. According to a preferred embodiment of this invention, which employs at least two focal points 24 and 26 produced by the optical system 30, the points 24 and 26 are preferably aligned ___? _______ ^ _____ are parallel to the lines "A" and "B" or most preferably parallel to the axis 56 of the line 36. The two points 24 and 26 produced by the diffraction element 20 rotate at around a point that falls between the two points. The two points 24 and 26 are placed 1 80 ° apart between them. The diffraction element 20 can be rotated slightly in an attempt to align the second 26 or trailing point directly in the middle of the cells 12 produced by the first point 24 or forward so that a point 24 is g The virgin surface 14 of the material is scratched and the second point 26 is grouping the cells previously formed with the two points almost parallel to the lines "A" and "B", with the diffraction element 20 dropping a few tenths The degree moves the points along the axis 56 of the rod. Changing the LPC moves the placement of the 12 more cells along the circumference of the rod (36). Combining the rotation of the diffraction element 20 and changing In the LPCs, it is possible to place the backing point 26 directly in the middle of the previously cracked cells 1 2 g, producing the desired re-engraving effects of this invention. The optical system 30 is compatible with any controller 32 used for the engraving of liquid transfer rolls 36 because All employ techniques of similar processes to generate the desired patterns of cells 12. However, because the separation between points 24 and 26 is fixed, computers 32 are capable of generating these patterns with high accuracy and accuracy. consistency in the placement of cells 12 are preferred to ensure that the second point 26 remain centered in cells 12 previously recorded in ^^^ s ^ * ji ^ ai * j & »g? * ^ írí ^ all the engraving of roller 36. Most preferably, points 24 and 26 are aligned with the axes 56 of roller 36. For example, for a pattern of cells 12 recorded having a screen angle of 60 ° the ratio of the count of line 54 to the relative advance between surface 14 and beams 16 along the axis 56 of the roller can be expressed as: cosine = the amount of the advance along the axis 56 of the roller 36 divided by the line count. For example, if the engraving is a pattern of a of 60 ° and 200 LPC, eos 60 = 0.5 and the number of lines along the axis of the roller is 100 LPC. This means that if the engraving were to be made with two focus points 24 and 26 separated by approximately 1 mm, and the two points 24 and 26 were aligned along the axis 56 of the roller, not the screen angle, the first point 24 would record the virgin surface 14 while the second point 26 would re-register the cells 12 ten lines 44 behind the first point 24 following the same pattern. Aligning the two points 24 and 26 to the axis 56 of the roller instead of the screen angle a means that the separation between them can remain fixed for all the accounts of line 54 and screen angles, provided the advance is calculated and rounded for each angle. The axial space of line ten 44 between the first and second strokes in a cell 12 increases the cooling time of cell 12 between strokes that improve the aesthetics of cell 12. Alternatively, if the engraving is a pattern of a 45 ° and 200 LPC, the number of lines 44 along the axis 56 of the roller is 141.4 HJktMi ________________ É ____ l LPC, (eos 45 ° = 0.707). If the advance is rounded to the nearest whole number of LPC, 140 and recalculated, the actual LPCs to do the separation work from 1 mm to 45 degrees is 198. (1% error). The same mathematical process can be used for engravings of a of 30 °. Advantageously, the spacing between the focus points 24 and 26 is from about 0.1 mm (millimeter) to about 25 mm and most advantageously from about 0.5 mm to about 5 mm. Approximately a gap of 1 mm between focus points 24 and 26 has been found to work well. Because the second point 26 will increase the depth of previously recorded cells 12, it will be necessary during the preparation to measure the results in a test band area. A spacing from point 24 to 26 of focus of about 1 mm or less will decrease the amount of test band required. A different diffraction element 20 must be used for each focal length of the lens 22 used since the separation of the point 24 to 26 is a function of the focal length.

In order to illustrate a preferred embodiment of this invention, a diffraction element 20 of 2.8 cm (centimeters) in diameter was obtained. When the diffraction element 20 was placed along the axis 34 of the beam 15, behind the lens 22 having a focal length (FL) of 3.8 cm as shown in Figure 1, two points 24 and 26 of focus by the lens 22. The binary grid or diffraction element 20 preferably had a grating period of 812 ± 1 μm, which for a focusing lens 22 of / = 3.8 cm and a sling length of the laser beam 15 of 10.6 μm, translates to a separation of 0.995 mm _tt_i_t _? _____________ ______ ¡___ between beams 16 of the order of +1 and -1 in points 24 and 26 of focus. Advantageously, the laser beam 15 has a sling length between about 0.1 μm and about μm. The target depth of the slots 38 for the grid 20 was 1.77 μm ± 0.089 μm (± 5%). In this example, a depth of 1.83 μm was obtained. The engraving uniformity through the diffraction element 20 of 2.8 cm in diameter was approximately ± 1%. The diffraction element was AR / AR V (antireflective) coated at 10.6μm. The diffraction element 20 of this example is for use with a laser beam having a sling length equal to 10.6 μm produced by the carbon dioxide laser generator 18. Preferably, the optical diffraction element is formed of a material that is transparent to the laser beam. In this example the difractor was made of germanium in order to satisfy this requirement. The optical diffraction element 20 produced according to this example had an efficiency of 80% and produced cells 12 which exhibit all the characteristics of the re-recorded cells 12. The preferred diffractor used in this example was made from germanium because the crystalline structure is more dense. The microstructure of this material is best defined so that it produces less dispersion or loss of energy for points 24 and 26 of primary focus. Similar diffraction patterns can be recorded in other materials away from the infrared such as zinc selenide. This etching technique can also be applied to Garnet lasers of Neodymium Yttrium Aluminum, or Nd: YAG, which have become more commonly used for engraving liquid transfer articles 36. This laser produces a beam 15 of light with a sling length of 1.06 μm which requires that the difractor 20 be fabricated from transparent materials at this sling length, such as quartz or synthetic quartz, commonly referred to as fused silica. It should be possible to apply this etching technique to any sling length of the desired laser beam 15 considered for engraving articles 36 for liquid transfer, provided a suitable transparent material can be found, which can support the necessary diffraction structures, which are engraved or milled on the surface of the materials. The diffraction element of this example was separated from the focus lens by a 2 mm spacer. The assembly was rotated to align the first order points 24 and 26 with the axis 56 of the roller 36. The optical system 30 produced two points 24 and 26 of first order focus separated by approximately 995 microns. The distribution of the intensity between the two points 24 and 26 of the first order was approximately 50/50. Cell pattern engravings 12 to 180 LPC and smaller were produced with excellent engraving quality. The cells 12 re-recorded showed an increase in depth 58 of cell 12 as in Figure 2 of about 18%, which should improve engraving speeds. There appeared to be no aberration introduced by the optical diffraction element. The efficiency of the optical system 30 was measured as approximately 90%. Approximately 10% of beam energy 15 went to points of second order which do not participate in the ___._ ^^ to__. ____.-__ _MIÉ__Í _____ ^ __ á - l ------ i engraving process. The optical system 30 of this example was designed to align the first order focus points 24 and 26 from one line "A" to the next. This means that the combinations of line counts 5 must be multiple, 1, 3, 5, 7. At a distance of 1 mm from point 24 to 26, this is equal to reaching line counts for an engraving of a of 60 ° of 60, 100, 140 LPC. Reducing the separation from point 24 to 26 reduces the line count resolution. Therefore, 1 mm was used preferentially to minimize the separation of points and maintain the appropriate resolution. The surface 14 of article 36 preferably has a ceramic, metallic or cermet coating that is etched in accordance with this invention. Suitable ceramic, metallic or cermet coatings, such as refractory oxide coating or carbides ico, can be applied to the roller surface 36. For example, can be used r alloys tungsten carbide-cobalt, tungsten carbide-n íquel carbide tungste non-cobalt chromium, tungsten carbide-n nickel chrome, chrome-nickel, aluminum oxide, chromium nickel chromium carbide, chromium cobalt chromium carbide, tungsten-titanium carbide-nickel, cobalt alloys, alloys oxide dispersion in cobalt, alumina-titania, alloys based on copper, dispersed oxides alloys based on iron, alloys of n íquel and based on n íquel , and the like. Chromium oxide (Cr2O3), aluminum oxide (AI2O3), oxide of silicon or its mixtures as the coating material, the oxide being askááj & ^ & f chrome the most preferred. Preferred coatings of metal carbide can be applied to the metal surface of the roll by any well-known technique; for example, the gun detonation process, the plasma coating process, the high-speed oxy-fuel process or thermal spray coating in general. The gun detonation process is well known and fully described in US Patents. Nos. 2,714,563; 4,173,685; and 4,519,840, the descriptions of which are incorporated herein by reference The techniques Conventional plasma for coating a substrate is described in U.S. Patents. Nos. 3,016,447; 3,914,573; 3,958,097; 4,173,685; and 4,519,840, the descriptions of which are incorporated herein by reference. The thickness of the coating applied by the plasma process or the gun detonation process can vary from about 0.0127 to about 2.54 mm and the roughness ranges from about 50 to about 1000 Ra depending on the process, ie detonation gun or plasma, the type of coating material and coating thickness. The ceramic or metal carbide coating on the roller can preferably be treated with a suitable pore sealer such as an epoxy sealer. Such a sealant is UCAR 100 epoxy available from Praxair Surface Technologies, Inc. (UCAR is a registered trademark of Union Carbide Corporation). The treatment seals the pores to prevent moisture or other corrosive materials from penetrating through the ceramic or metal carbide coating to attack and degrade the ^^^^ tój ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ and underlying steel structure of the roll is to be understood that the foregoing description is only illustrative of the invention can be devised alternatives and modifications by those skilled in the art without departing of the spirit of invention. Accordingly, the present invention seeks to encompass all such alternatives, modifications and variants that fall within the spirit and scope of the appended claims. _ ^ «^ -» ____ l ______-: ._ .. «.._ _._ .., __._.._, _ ....., * __., __._.,. _ - »__-__-__._.

Claims (10)

1. R E IVI N DICAC ION ES 1. A process for engraving a solid article to provide in at least a portion of a surface of the article a plurality of separate etched cells comprising: generating a laser beam; d) dividing said laser beam into at least two beams, with each of said beams forming a point focused on said surface, said focused points being spaced apart from each other, said beams forming generaly bundle pairs with each pair of d said beams being arranged to simultaneously record a new cell with said focused point of a first of said pair of beams and re-record a previously recorded cell with said focused point of a second of said pair of beams, said division step comprising, passing said laser beam through an optical device having a diffraction optical element to form at least said first beam and said second beam having said focused points separated; and recording and re-recording a plurality of cells on the surface of the article.
2. 2. The process of claim 1 wherein more than two beams are formed so that for each divided beam that is recording a new cell there is another divided beam that is re-recording a previously recorded cell.
3. The process of claim 1 wherein each cell defines an opening in the surface of the article having a first central axis and a second central axis normal to said first axis, said axes being & & __; __, Are located at a central point of the axis, and where said step of engraving comprises recording said cells arranged in at least two rows, in which a line drawn through the first The mere axes of the cells in a row are substantially parallel to a line drawn through the first axes of the rows in an adjacent row; and wherein at least a portion of the cells in a row each have their second axes aligned between the second axes of two cells separated in an adjacent row.
4. 4. The process of claim 3 wherein the length of a space not recorded between two cells in a row along a line containing its first axes is between about 1 to 1.3 times the length of a space not recorded between one of said cells in said row and an adjacent cell in an adjacent row, along a line containing the points of the central axis of the cells.
5. The process of claim 4 wherein the solid article is a cylindrical liquid transfer roll and the cells are aligned such that a line drawn through the center line point of a cell in a row and through a point of the central axis of an adjacent cell in an adjacent shaft forms an angle of between more than about 0 ° and less than about 90 ° with a line drawn parallel to a longitudinal axis of the cylindrical article.
6. The process of claim 5 wherein the angle is between more than about 60 ° and less than about 90 °.
7. The process of claim 1 wherein said laser beam has a sling length of about 0. 1 μm to about 15 μm.
8. 8 An apparatus for recording a solid article to provide on at least a portion of a surface of the article a plurality of separate etched cells comprising: a laser beam generator for generating a laser beam, an optical device having a optical diffraction element for dividing said laser beam into at least two beams, with each of said beams forming a point focused on said surface, said focused points of said beams being separated between them, said beams generally forming pairs of beams with each pair of said beams being arranged to simultaneously record a new cell with said focused point of a first of said pair of beams and re-record a previously recorded cell with said focused point of one second of said pair of beams; and means for employing said at least two beams to record and re-record a plurality of cells in the superie of article
9. 9. The apparatus of claim 8 wherein said optical device provides more than two beams and for each divided beam for recording one. new cell is provided another split beam to re-record 20 a previously recorded cell.
10. 10. The apparatus of claim 8 wherein said article is an article for transferring liquids. _- .., .. ,, ..... _-_-_ - _-__-_. »_ ... ......... *.-...-. . , .., -,, ". , »_ R n; < tf 'H, - < • r - f 1 t < The process and apparatus record a solid article to provide in at least a portion of a surface of the article a plurality of separate gutted cells, it generates a laser beam and divides the laser beam into minus two beams Each of the beams forms a focused point on the surface The focused points separated from each other form pairs of beams with each pair of beams being arranged to simultaneously record a new cell The focused point of a first of the pair The beam comprises the new cell and a second focused point re-recorded the previously recorded cell.The division comprises passing the laser beam through an optical device that has a diffraction optical element to form the first beam and the second beam which has the points focused separately. ^ t ^^^^^^^^^^^ & ^^^^^^^^^^^^^^^^ gg ^ ^^^^^^ j ^ ^^ ^ tÍBßAMi ----- ------ ¿^^