US3455239A - Method and article for printing and engraving - Google Patents

Description

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July 15, 1969 l J. E. SMITH 3,455,239

METHOD AND ARTICLE FOR PRINTING AND ENGRAVING 3 Sheets-Sheet 1 Filed May 2, 1966 MMWMWE@ MMMEWMEEE WDD MD MU MDGEEEH@ MDEHEE MEEMMHM@ METHOD AND ARTICLE FOR PRINTING AND DNGRAVTNG Filed May 2, 196e -sheet :a

3 Sheets J. E. SMITH July 15, 1959 A nnnwmmm i@ mmmmwmmmm y UUUDD@ @D Dm M nmnnnmnmnm DUUUDDUDDUUD W munnnnnnmn mmmmmmmmm M y mudnnnnn nu mummmummmm y DUDDDDDDDD mmmwmwmmwm. WJ Unnmmmmmm mmmmmmmwm fr M mmmmmmmm mmwmmwm Z M Z f i n ff d H W @T 4 A 6.

July l5, 1969 J. E. SMITH 3,455,239

METHOD AND ARTICLE FOR PRINTING AND DNGRAVING Filed May 2, 1966 3 Sheets-Sheet 3 llls 3,455,239 METHOD AND ARTICLE FOR PRINTING AND ENGRAVING James E. Smith, Avon, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed May 2, 1966, Ser. No. 546,996 Int. Cl. B41n 1/00; G01d 15/10; G03f 7/00 U.S. Cl. 101-395 20 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of making printing plates, a blank printing plate employed in the method, and the product of the method. An electron beam is swept across the surface of the blank printing plate having a plurality of uniformly shaped projections to selectively remove the projections and leave printing intelligence on the blank. The projections are suficiently small and so densely packed that the projections can impart high resolution, half-tone characteristics to the blank. A printing plate made from the blank plate can print both text material and pictorial material in greytones. Widely separated, individual projections may be preserved at otherwise void areas of the plates to support the printed page during the printing process.

This invention relates to a plate for printing and the method for producing it. More specifically it relates to a plate for halftone printing with high quality resolution.

Most engraving or etching processes used today are aimed at producing a stipple pattern of either minute projections or depressions on an engraving plate. The engraved patterns then consist of arrays of very small holes or projections which simulate the intelligence being reproduce-d on the printing plate. The degree of fidelity which can be achieved and the faithfulness of the tone which can be accomplished in the reproduction heavily depends upon the resolution in these arrays of dots. For example, if large dots are used they must generally be fairly widely spaced. The word dots is used here in a generic sense to indicate ink carrying areas such as small depressions, cavities, projections, etc., irrespective of the shape of the dots which can, of course, be either round, rectangular or any other convenient shape. The number of large surface area dots which can occupy a given area on the plate is quite limited, and a large dot array would appear to the eye as a very coarse pattern. On the other hand, if the dots are small, more of them can be packed into a given area and the dot array would then appear as a fine pattern. In fact, if the dots are extremely small and densely packed, the pattern would appear to the eye as one continuous tone in which the eye could no longer distinguish the individual dots. Obviously then, if one could carry the dot representtation to its extreme, for example using millions of microscopic dots in a closely packed array, even very small ordinary text letters in addition to the customary pictorial material could be reproduced faithfully, clearly and with good resolution.

The techniques available today to produce such closely packed arrays are generally slow, require meticulous care in their application, and their resolution is limited to pictorial displays and large text letters, but cannot be used with very small text letters. Hence, today high resolution dot arrays have not been used to any extent wherein time or economics play a dominant role.

The high resolution capabilities of energized beams such as lasers and including charged particle beams such as electron or ion beams can be as small as one micron or less and have demonstrated their utility in various l United States Patent elds such as microscopy, microchemistry, and precision cutting or welding of a variety of materials. The demonstrated capabilities of the energized beam in achieving extremely high lpower densities would ordinarily lead one to assume that vit can be used with convenience in a high speed engraving system which could produce a printing plate having a closely packed dot array by utilizing the beam as a cutter or evaporator. However, there are a number of problems associated with using an energized beam for these purposes which to date have inhibited the application thereof to the manufacturing of printing plates.

The use of an electron beam for cutting various materials by evaporation methods, is well known as for instance described in the patent to Steigerwald, No. 2,793,281. The method of reproducing an image with an electron beam by melting is described in the patent to Groak, No. 2,630,484. The production of a printing plate with a laser beam is described in an article by William T. Reid entitled Laser-Etching Printing Plates May Soon Be a Reality, Inland Printer/American Lithographer, December, 1964, pages 57 and 113. The patent to Griswold, No. 2,107,294, discloses any intaglio printing plate having cells with narrow walls and wherein the material in the cells responds chemically differently to an etch bath compared to the Walls which are substantially impervious to the bath. The use of an energized beam to cut printing plates and write thereon as disclosed in the prior art is generally slow in comparison with chemical methods of producing a printing plate. This is due to the fact that a large amount of material must be removed within a very short time by the energized beam.

The chemical etching art, which is a large-area material removal process as in contrast with the energized beam point-by-point removal process, has been applied in the production of printing plates for many years. Despite the fact that extremely high power densities, for instance 109 watts per square inch can be achieved with energized beams, the point-to-point approach of the energized beam cutting methods poses some real and practical problems when one tries to achieve high plate making speeds comparable with the chemical etching art.

Some insight can be obtained to this problem by reviewing the phenomena actually involved. For instance, when an energized beam strikes the workpiece as in FIGURE 13, the thermal energy transferred to the workpiece is free to spread outward and downward from the point of impingement due to the thermal conductivity of the material constituting the workpiece. Thermal conduction continues as long as the thermal gradients persist and there is a path for the heat to flow away from the point of impingement. As the material in the impingement larea becomes vaporized, which occurs rather rapidly due to the high power density of the beam, the thermal conductive path from the center of the beam impingement area to the periphery of the hole is broken. This doe-s not mean necessarily that the thermal energy transferred to the hole periphery or the surrounding material has ceased. In fact, thermal diffusion through the vapor created as Well as the radiant heat transfer persist to such an extent that the periphery of the hole continues to heat up due to the presence of the beam. But being in direct line of impingement, the bottom of the hole continues-to vaporize so long as the beam is applied or until a hole is drilled through the workpiece.

The size, shape, as well as the depth of the hole, which are very important factors for printing, created in this manner are dependent upon a number of interrelated factors. The amount of energy required to vaporize the volume of material to be removed consists not only of the amount of heat needed to take care of the heat of vaporization of the material, but also the amount required to raise that volume of material to its boiling point and to replenish any heat which is lost to the surrounding material during the time it takes to vaporize the given volume. In general, when using the extreme power densities and microscopic beam spot diameters which can be achieved with modern energized beam equipment, the drilling of various materials can be accomplished in a short enough time period to minimize the heat loss to the surrounding material. Similarly, if only microscopic volumes of materials have to be removed from the workpiece, the dwell time of the beam over a given portion of the workpiece can be sufliciently short to minimize such side losses. The cutting or engraving of thin-sheet materials thus can be done fairly rapidly. On the other hand, if deep cuts are to be made, of for example .030, and the volume of the material to be removed is substantial, then the cumulative dwell time of the beam over any particular spot of the workpiece becomes appreciable. For a given power level and beam density the beam ON time must be appreciably longer in order to supply the higher total heat required for vaporization of the larger volume of material which is to be vaporized. In such instances, thermal conductive influences can cause appreciable heat losses to the surrounding areas. One can, of course, go to higher beam powers to compensate for these losses and/ or increase the beam power density by decreasing the beam spot diameter with a constant beam power or increase the beam power with the spot diameter kept constant. To do so, however, generally leads to more expensive equipment although it may tend to improve the cutting speed. Furthermore, there are definite practical considerations which limit the extent to which this avenue for employing energized beams for the cutting of printing plates can be followed.

One of those practical problems, as illustrated in FIG- URE 14, resides in the actual thermal distribution within the vicinity of the beam impingement area. Generally, the symmetrical distribution of the heat from the point of impingement depends to a large extent upon the previous thermal history of the area, the uniformity of the thermal properties of the material, the geometry of the workpiece as well as its thickness and, of course, the uniformity of the energized beam itself. Under such circumstances there can be sufficient differences in the boiling rate, that is the vaporization about the periphery of the hole being drilled, to cause a certain amount of raggedness in the shape of the hole itself. Recondensations around the edges can occur which further accentuate the raggedness. What usually results in most materials and is specifically more pronounced in some others, is a hole the edges of which are irregular and the shape of which is difficult to control as is illustrated in FIGURE 15. There are several ways in which the raggedness can be smoothed, for example, where one goes to a smaller spot diameter and sweeps the hole circumference with the beam and thus averages the irregularities. Another possibility is to repeatedly pulse the beam over the same spot using short enough beam ON times and long enough OFF times to minimize thermal conductivity influences. A third possibility would be to increase the beam power density to a sufficiently high level that one very short burst of power is all that is needed to drill the hole. But as previously mentioned, the latter would be an expensive approach and the former increases the time required to make a printing plate with an energized beam.

Unsymmetrical thermal distributions have `a great imn pact on the energized beam engraving process. If, for exn ample, the engraving is to consist of a series of closely spaced holes, the degree of closeness of two adjacent holes is largely dependent upon the edge definition of the holes themselves. As illustrated in FIGURE 16, lack of thermal symmetry can lead to breakovers between two adjacent holes. The combined effects of hole edge raggedness and breakover forces one to keep the holes well separated, thereby reducing the lidelity and .resolution of the hole pattern. The most obvious approach (aside from the techniques referred to earlier for controlling edge raggedness) that would overcome this difficulty would be to go to a smaller spot diameter and space the holes closer together but still sutiiciently far enough apart to preclude breakover. However, decrease in spot size is consistent with decreasing beam power for any particular power density. Hence, unless power density is increased as Well, one is faced with longer beam dwell times in order to penetrate to a given depth in the material being engraved. This again is contrary to the goal of achieving high engraving speeds.

One solution proposed to solve this dilemma is to revert to a blank plate workpiece which has a low melting point. Materials frequently mentioned are plastics and low melting point primary metals or eutectics thereof. At first glance one would think that this would be a plausible solution since little power is needed to evaporate such materials. Hence, the cutting speeds could be increased to a high degree. Aside from the lack of durability in these materials which perhaps could be improved somewhat by use of a higher strength backing material, there is an even more important reason why they do not fulll the bill as the workpiece in a high speed engraving system. This has to do with the degree of resolution which can be achieved on the resultant printing plate. The problem is again one of edge definition wherein the hole formed in the plastic material cannot withstand a large thermal gradient before it tends to disintegrate. Hence, even though the temperature at the point is low enough to preclude vaporization, it may be high enough to melt the edges and destroying the edge definition of leach hole as illustrated in FIGURE 17. One therefore tends to prevent this Iproblem by reducing the temperature at the edges, and again, the dwell time for producing the printing plate has to be increased rather than decreased.

Although it has been suggested that the use of a backing material would resolve some of these ditiiculties because the backup plate would rapidly conduct the heat away from the hole edges before the edges could melt, it should be clear that any heat passing from the vaporization region must pass through the low melting material to reach the backup plate and therefore, in the absence of an enormous thermal conductivity of the top layer material, the speed of thermal transfer to the backup plate will be insuicient to prevent the destruction of the edges of the holes.

In summary, if a high melting point material is used as the workpiece in order to withstand the high thermal gradients, the dwell time required to remove any appreciable amount of material is suiicient ly high to cause an undesirable spread of energy from the beam into the surrounding material. Since there are no barriers to quench this spread of thermal energy deposited by the energized beam, increased beam power to reduce dwell time of the energized beam is required to compensate for these losses.

Also, in the event a low melting point material is used on the workpiece in order to decrease the beam power requirement and decrease dwell time, the material surrounding the vaporization region is incapable of withstanding the high thermal gradients. Consequently, edge definition becomes poor and the delity of the engraved pattern deteriorates.

Furthermore, local irregularities in the thermal distribution pattern around the beam impingement area. foster Unsymmetrical and nonuniform vaporization thereby preventing the formation of smooth hole edges and leading to problems such as breakover between adjacent holes. If the hole separation is increased to compensate for this phenomena, the density of the pattern is reduced to an extent where the resolution of the pattern again has deteriorated.

Energized beams such as electron or ion beam devices and lasers are inherently high resolution tools. Resolutions on the order of one micron have been achieved to date with such beams and better resolutions are theoretically possible. If it is possible to utilize such high resolution tools and at the same time avoid the practical diiculties as described heretofore, a substantial contribution to the printing art can be made.

With these observations in mind, it appears that the energized -beam alone cannot eliminate these problems; hence, one must look to the workpiece also.

It is an object of this invention to provide a hal'ftone printing plate.

It is another object of this invention to provide a printing plate on which high quality text material is inscribed in halftone.

It is still another object of this invention to provide a halftone printing plate through the use of an energized beam.

It is still another object of this invention to provide a method for establishing intelligence with an energized beam on a blank plate having a high density of dots uniformly distributed thereon.

It is still further an object of this invention to provide a method for establishing intelligence on a blank plate having a plurality of minute isolated projections.

It is a further object of this invention to provide a method for establishing intelligence on a blank Iplate by removing portions of the workpiece material which are isolated from one another.

It is a lfurther object of this invention to produce a blank plate for establishment thereon of intelligence andy having a dense array of projections.

These and other objects of this invention will become more readily apparent upon a review of the drawings and the description thereof as follows. In the drawings:

FIGURE 1 shows a blank plate for engraving and with a plurality of isolated projections.

FIGURES 2 and 3 show a method of making a printing plate from a blank plate as shown in FIGURE 1.

FIGURES 4, 5, 6, 7 and 8 show an alternate method for producing a printing plate from a blank plate of the type shown in FIGURE l. n

FIGURES 9 and 10 show the preparations involved 1n producing a blank plate having a plurality of cavities lled with a second material.

FIGURES 11 and 12 show the method of producing intelligence on a blank plate of FIGURE by means of an energized beam.

FIGURE 13 shows the thermal energy spread from an energized beam during an engraving operation.

FIGURE 14 shows the typical thermal gradients encountered in the workpiece at the start of the engraving c cle.

yFIGURE l5 shows the ragged appearance of a cavity cut with an energized beam.

FIGURE 16 shows the breakover between adjacent cavities cut with an energized beam.

FIGURE 17 shows the poor edge definition of a cavity cut with an energized beam.

FIGURE 18 shows an enlarged perspective view of a relief letter engraved on a blank plate.

As will be obvious from the figures and the descriptions which follow, the use of the word blank in the terminology blank plate, as used herein, refers to the fact that there is an absence of intelligence on the plate initially and that said intelligence must then be added to the plate for it to become an actual printing plate.

Two types of blank plates for engraving thereon are described herein. Each is provided with a plurality of tiny dots (projections or cavities) which are isolated from one another. FIGURE l shows a blank plate having a plurality of projections 10 each of which is isolated from its adjacent projections by a groove typically presented at 12. Such a blank plate 14 may be manufactured from a smooth metallic plate made of copper, zinc, aluminum, magnesium or nickel and may be of any desirable thickness, but preferably with sucient bulk to be capable of absorbing and conducting away the thermal loads occurring during the evaporation of the projections with an energized beam. The top surface of the smooth metallic plate must be fairly flat so that the projections 10 will have their top surfaces lying in a common plane. However, where variations in the surface of the plate exist after the formation of the projections 10, a further process for smoothing and flattening the projections into a common plane could easily be carried out by conventional machining or standing processes.

In the event that the blank plate 14 is curved for placement on a roller, then the top surfaces of the projections 10 must be equidistant from the base material from which they arise. In the case where the blank plate is part of a cylindrical section, then the tops of the projections must lie on a surface substantially concentric with the cylinder. These latter conditions are necessary for eventual use of the plate with rotary presses.

The blank plate of FIGURE 1 may be made by an energized beam which has sufcient power and the diameter of which is sufficiently small so that the grooves 12 may be cut into the base material 16. By carefully controlling the relative movement of the plate 14 with respect to the beam and with transverse cuts, isolated projections 10 are produced on the plate 14. Common chemical removal processes may, of course, also be employed to produce the blank plate 14.

An energized beam capable of cutting plate 14 could, for example, be a beam of charged particles as described in the patent to Steigerwald, No. 2,793,281. The power density of the electron beam is adjusted so high that it evaporates a small layer of the material on which it impinges. By repeatedly pulsing the beam in accordance with the teachings of the patent to Steigerwald, No. 2,902,583, a well-defined hole may be made in the workpiece material. Displacing the workpiece relative to the beam then produces the grooves in the blank plate of FIGURE 1. It is, of course, possible to make projections 10 in the blank plate' v14 having different shapes such as circular or oval or other shapes by the proper control of the plate relative to the beam. The grooves 12 can be arranged in different ways so that a triangular pattern of projections 10 are formed. It should be realized, of course, that the time involved in producing the blank plate 14 with an energized beam will be substantial, depending primarily upon the type of material and volume to be cut. However, the process for making the blank plates takes place off line so that the on line time of establishing intelligence on the blank plate is not affected. A multitude of these plates can be prepared beforehand and stocked until needed.

The density of the projections in FIGURE 1 is so high that a sufficient number of individual imprints of dots can be made across the width of a typical character in a common text to permit the halftone printing thereof with high resolution.

Thus, one of the advantages of such a printing plate is that very tine text material as well as pictorial material can be represented by a dot pattern. The use of dot halftones to represent pictorial material is a common practice within the printing industry today. However, one has not been able to devise a practical system for representing very iine text material in this manner. The problem becomes clear upon examining a typical line screen wherein dots are produced for the pictorial representation in newspapers and where the dot diameters of the order of ve to ten thousandths of an inch. Typically, the widths of text letters in todays newspapers are of the order of twelve thousandths of an inch. To represent a text letter by a pattern of these standard dots, it is not possible to use more than one or two dots to cover this width. The resultant effect isthat the text characters appear ragged and poorly defined and unpleasing to the human eye.

The projections on the blank plate of FIGURE 1 have a much liner resolution so that even small text characters such as 12 points or less may be printed in halftone. The top surface areas of the projections that will be used to carry ink should -be no less than 16x106 square inches and normally are 1 to 9 l06 square inches with groove widths approximately from to 10X10"4 inches. Exact sizes and spacings depend upon the type of paper and ink used during printing, and consequently, all text material may be produced in halftone on the plate with significant resolutions.

Furthermore, there is a distinct advantage in having the entire printing surface initially covered with these projections. For instance, several areas on the printing surface may be designated for bright tones such as white and the ink carrying projections must be removed from these areas. If these white areas are large, the paper on which the print is to be made may dip into these areas and contact the base material and pick up any stray ink present thereon.

Prior art techniques avoided this problem by depressing or etching these areas down at. least .030 inch below bordering raised printing surfaces. These deep cuts are not needed any longer with the printing plate of FIGURE l. By providing these large white areas with widely spaced, discrete, microscopic projections, the paper bridges these large areas without the usual sagging and resultant ink pickup from the depressed surfaces. Since the projections are so minute their imprints will affect the coloring of the white areas very little and at most provide the paper with a very light gray background. As a result, one may make a printing plate from the blank plate of FIGURE 1 with projections as short as .002 to .003 inch and generally less than .005 inch.

The beam 20 is generated with a device as shown in Patent No. 2,793,281 and directed at the blank plate 22. The power and the power density of the beam 20 are arn justed together with the focus of the beam at the plate so that individual projections may be removed by the beam. FIGURE 2 shows the beam 20 evaporating the projection 24, and projections such as 23 have already been evap orated. The control of the movement of the beam 20 relative to the blank plate 22 and its intensity will cause preselected projections to be evaporated. A final configuration such as the letter T in FIGURE 3 is made wherein the T is produced in relief and consists of minute dis-1 crete projections.

The beam spot size may be as small :as one micron in diameter, but generally will be adjusted to a size corn-s mensurate with the size of a projection. With such a beam size, one projection may be evaporated without affecting adjacent ones. Generally the dots of the blank are also chosen to have surface areas commensurate with normal beam spot size and acceptable printing speeds.

Generally the plate 22 is made of sufficient bulk and of a good thermal conducting material so that the heat lost to the lplate during the removal of any one projection will not affect adjacent projections. The projections are effectively thermally isolated from one another.

Herein resides one of the unique advantages of this invention. The application of inherent high resolution halftone characteristics to a blank plate beforehand makes possible the subsequent engraving thereon with an ener-= gized beam such as an electron beam, ion beam, or laser without the previously mentioned disadvantages.

The height of the projections and their cross-sectional areas are optimized keeping in mind the type of material, the desired printing speed and the method of printing. Where an energized beam such an an electron beam is used, its power, power density, spot size and intensity are preferably controlled to allow removal of a projection 'with a single pass. The shape of a projection bears a strong factor on this and its height-to-average-width ratio is general-= ly held to less than three. For practical height .003 inch apn pears acceptable. The ratio, however, should not then become too large lest the projections become too slender and incapable of standing up under a printing press operation.

FIGURES 4 through 8 show an alternate method inn volving a chemical removal process for using a blank plate of FIGURE l. The optimum height and cross-sectional dimensions of the projections now are determined by other considerations than when an energized beam issued. There are unique advantages also in the chemical removal of the projections.

The blank plate 14 in FIGURE 4 is rst covered with a chemical resist material 30. Material 30 may be, for instance, a lacquer, acid-resist or a standard photoresist material such as KPR which becomes insoluble to a rinse after exposure to either light passing through a photographic 32 or exposure by an energized beam which is modulated as it passes over the material. The material 30 will cover all of the projections as well as the grooves and form a smooth layer across the whole of the plate 14.

After exposure in FIGURE 4, the material 30 will have an exposed T, 34 and an unexposed section 36. FIGURE 6 shows the cross-sectional View.

Thereupon the unexposed section 36 is rinsed away in a bath to which the exposed T is not affected. The underlying projections of section 36, being stripped of their protec tive coating, may then be chemically removed by insertion in a strong etching bath. The final cross-sectional view after etching is shown in FIGURE 7. Note that the material 38 protected the projections completely with but minor inconsequential undercutting occurring adjacent to the foot of projections 40 and 42.

Subsequently, the protective material is removed and the exposed projections show the letter T in FIGURE 8. It should be clear that the coating material 30 need not be a photosensitive one when a high power density beam such as an ion, electron, or laser beam is used to expose the plate. The material 30 need only be resistive to the etchant to be used in subsequent chemical removal process, with the high power density beam being used to selectively remove the coating over those projections which are to be chemically eliminated from the matrix plate. Note that the particular advantage of using a blank plate as in FIG- URE l in the chemical removal. process of FIGURES 4 through 8 is the substantial avoidance of undercutting problems. The tops of the projections 40 and 42 are protected since the protective coating 38 extends down to the base material. In the event the protective material covers a portion of the top of a projection, undercutting thereof will, of course, occur. But the adjacent projection will fully be protected and the deterioration of one projection will not materially and visibly affect the delity of the text material. This advantage will-become clearly ap`1 parent where the area density of the projections are so high (for example. projections of 4 106 square inches in area and separated by .0005 inch), that the loss of a row of projections on each side of a text character will not affect its fidelity. Very fast etching baths may be employed with`= out concern with undercutting.

The need for paper supports on large etched areas may be served by leaving every seventh or eighth projection intact in these wide areas having less than 5 percent grey tone. When using a photographic negative 32 to expose the plate, this may be accomplished by incorporating a background of dots of appropriate size and spacing in the negative. Where an energized beam is used to expose the material 30, the Ibeam may be so controlled as to be modulated periodically to an OFF state, thereby leaving a pattern of widely spaced unexposed projections in the background areas of the plate. Said modulations would be superimposed on the variable modulations carrying the intelligence to be imparted to the plate.

Another method for providing a printing plate contain-1 ing isolated areas is illustrated in FIGURES 9', l0, ll and l2. A blank plate is provided with a multitude of isolated cavities 62 which are separated from one anu other by land areas 64. These land areas are made up of the basic material from which the printing plate is made and provide a fence or barrier between the various cavities. These cavities, as shown in FIGURE 10, are iilled with a second material 66 that is different from the material from which the blank plate 60 is made up and has a lower melting point or a lower evaporating point. A typical material that could be used for lilling the cavities 62 is a low melting plastic. After the cavities have been filled with the lovver melting material 66, an energized beam 70 is applieduto the plate with such power and power densities that if can readilyl evaporate the material 66 within the cavities without melting or affecting the base material of the blank plate. Since the energized beam 70 has a small cross section, it is capable of evaporating the lower melting material in one cavity without affecting the material in adjacent cavities. Any heat imparted by the beam onto the blank plate 60 is readily carried away from the cavity to the base metal without upsetting the temperature in the adjacent cavities which are therefore eifec tively thermally isolated. A blank plate provided with the low melting material contains a high density of cavities for the same purpose as the blank plate 14 in FIGURE 1. Upon the removal by the energized beam of the low melting material and the formation of characters such as the letter T in FIGURE 12, an intaglio printing process can be applied whereby the ink is carried in the cavities and imparted to the printing paper according to standard printing processes. The cavity depth, size, and other characteristics can be determined beforehand based upon the type of ink and paper to be printed with. The plate can be made up from a very ne screen mesh having a smooth top surface so that all of the cavities have their entrances located in substantially the same plane.

The material 66 is applied to the printing surface of the blank plate and is substantially ush therewith.

A sandwich-type construction could also be used in this instance to provide a base plate for good heat sink qualities. The lower layer of the sandwich could be removed after the cutting operation so as to leave a pattern of very small through-holes, in other words, a screen pat-I tern for screen-type printing. Again it should be realized that the shape of the cavities need not be rectangular or that the cavities should be arranged in any particular recm tangular pattern. In fact, to obtain optimum thermal isolation and the highest packing density of the cavities, a triangular array is the preferred geometry. In such an array any three adjacent projections would be equidistant from one another. The triangular array is a welll-known geometry for high density packing and is described in moreJ detail in Slater, Introduction to Chemical Physics 415 (1st ed. 1939).

In FIGURE 18 a letter t is shown made up from a plurality of projections arranged in a square array. The letter t is greatly exaggerated to provide an indication of the perspective of a relief text character made according to this invention.

The methods described in relation to FIGURES 9 through 12 wherein dissimilar materials are used to pro-1 vide isolation between the individual printing dots require a very small amount of power where an electron beam is used to evaporate the material with the lower melting point. Hence, the dwell time of the beam can be exceedingly low, leading to very high engraving speeds. The total beam power requirement may be quite modest, such as 100 watts for materials 66 like parafiin, etc., and with dwell times of the order of 100 microseconds or less. These parameters are well within the capabilities of presu ent electron beam equipment and may very soon be available in other precision, energized beam devices, such as laser and ion beams. The printing plate has the fur ther advantage in that it is reusable so that it may again be filled with the secondary material to make up a new blank plate.

It is to be understood that the invention is not limited l0 to the specific embodiments herein illustrated and described but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. A printing plate blank comprising:

a blank plate provided with at least one surface working area for the placement thereon of intelligence,

said surface working area covered with a plurality of minute separate projections each having a minute surface area less than 16 10r6 square inches,

said projections being substantially alike in shape and height and being substantially uniformly distributed over said surface working area, the separation of the surface areas being no greater than 10 104 inches to impart high resolution halftone character istics to the blank plate.

2. A device as recited in claim 1 wherein each proiection surface area is substantially at to accept ink thereon.

3. A device as recited in claim 1 wherein the blank plate is curved and the projection surface areas lie on a surface substantially parallel to the curve of the blank plate.

4. A device as recited in cla-im 3 wherein the blank plate is shape-d and curved as a section of the curved surface of a cylinder and the surface areas of the projections lie substantially in a cylindrical surface concentric with the cylinder.

5. A device as recited in claim 1 wherein the projections are uniformly distributed over the entire surface working area according to a predetermined pattern.

6. A device as recited in claim 5 wherein the projections are distributed in a triangular pattern.

7. A device as recited in claim 1 wherein the height of 'the projections is approximately or less than .O05 in.

8. A printing plate blank comprising:

a blank plate made of a base material having good thermal conductivity and provided with at least one surface working area for the placement thereon of intelligence,

said surface working area being covered with a plurality of separate projections each having a, minute surface area at the top of the projections,

the base material of said blank plate having suilicient bulk to effectively thermally isolate adjacent projections, p

the minute surface area of the projections being substantially at, substantially equidistant from said base material, and beingv less than 16x10-6 square inches, and

the spacing between the surface areas being no greater than 10X 104 inches to impart high resolution halftone characteristics to the blank plate.

9. A device as recited in claim 8 wherein the height of the projections is approximately or less than .005 inch.

10. A device as recited in claim 9 wherein the ratio of the height of each projection to the average-width of each projection is less than three.

11. A master halftone printing plate with supports for the material to be printed on comprising:

a single printing plate having its entire printing surface covered with halftone intelligence thereon,

said printing. surface being provided with relief text material and blank spaces,

said text material including a plurality of minute, separate projections, having a top surface area less than 16 l06 square inches separated by no ,more than 10X 10-4 inches, and

said blank spaces including minute separate widely spaced projections to support the material.

12. A device as recited in claim 11 wherein the blank spaces include a plurality of widely spaced uniformly distributed projections.

13. A device as recited in claim 11 wherein the area l l density of the projections in the blank spaces is less than percent greytone.

14. A device as recited in claim 13 wherein the height of the projections is approximately or less than .005 inch.

15. A master printing plate for printing on paper or other thin materials comprising:

a single printing plate having a printing surface entirely covered with a plurality of minute projections each having a height no greater than .005 inch a-nd a surface area on top less than 16x10-6 square inches,

the area density of the projections varied to form rem lief printings, the separation between projections being no greater than X104 inches in 100% greyn tone regions of the printings, and

where the density of the projections between the printings is decreased to a level no greater than 5% greytone for sharp contrast and for support of the material being printed upon,I

16. A method for making a printing plate comprising generating an energized beam,

directing the energized bea-m at a blank plate having a printing surface entirely covered with a plurality of minute, thermally isolated projections,

moving the blank plate relative to the energized beam,

adjusting the power and the power density of the ener" gized `beam within a range suicient to remove a projection, and

selectively deenergizing the beam as the blank plate moves relative to the beam to preserve preselected projections.

17. A method as recited in claim 16 and further inm cluding:

adjusting the cross-sectional area of the energized bea-m at the printing surface to be commensurate with the cross-sectional area of aprojection..

18 A method for making a printing plate comprising:

generating a beam of charged particles,

focussing the beam on a blank plate having a printing Surface entirely covered with a plurality of minute, thermally isolated projections having crossesectional areas no greater than 16x106 square inches, moving the blank plate relative to the beam of charged 5 particles,

adjusting the power and the power density of the beam `within a range sufficient to remove a projection with out affecting adjacent projections, and selectively deenergizing the beam as the blank plate moves relative to the beam to preserve preselected projections, 19., A method as recited in claim 18 wherein the focussing step further comprises:

adjusting the focus of the beam of charged particles to produce a spot size of the beam at the printing surface that is commensurate with the cross-sectional area of a projection.I 20. A method as recited in claim 16 wherein the projectons are separated by a `distance no greater than 10X10-4 inches Iand have cross-sectional areas less than 16x10* square inches and the beam cross-sectional area is adjusted to be commensurate with the cross-sectional area of the projection,

References Cited UNITED STATES PATENTS 384,586 6/1888 Norman. 1,459,669 6/1923 Berold lOl-395 2,234,997 3/1941 Yanes lOl-401.1 XR

FOREIGN PATENTS 866,070 4/1961 Great Britain.

t: DAVID KLEIN, Primary Examiner U.Sc Cl. X.R.

96-36.3, 86; lOl-401, 401.1; l78-6.6; 219-69, 121; 346-76

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