US2733655A - Microscopic printing ey planographic means - Google Patents

Description

Feb. 7, 1956 A. BONI 2,733,655

1 MICROSCOPIC PRINTING BY PLANOGRAPHIC MEANS Filed May 15, 1951 'INVENTOR.

A TTORN EV United States Patent MICROSCOPIC PRINTING BY PLANOGRAPHIC MEANS Albert Boni, Chester, Vt., assignor to Readex Microprint Corporation, New York, N. Y., a corporation of New York a Application May 15, 1951, SerialNo. 226,505 Claims. (Cl. 10-1----149) This invention relates to the art of planographic printing and has for its principal object the provision of a process by which lithographic or other planographic print of extremely small size can be produced on paper or other sheet material, with sufiicient clarity to be read with the use of a simple optical enlarger or viewer.

There are many instances in which it would bedesirable to make microscopic reproductions of plano graphic printing, as, for example, when space requirements do not permit maintaining extensive records, publications, etc., having print ofordinary sizes. In the past, many attempts have been made to provide such reproductions, as by making greatly reduced photographs of printed matter. The results of these attempts, however, have involved limitations, particularly with respect to cost, which either restrict greatly the field of commercial use of the technique or make it unsuitable for any commercial-use.

The principal difliculty encountered in microscopic printing with ink is the lack of sharpness in the definition of the small printed characters, so that they take on a blurred appearance when viewed through the optical enlarger. That is, the microscopic characters appear to have a mottled texture and jagged or feathery edges, which may be referred to as a low 'fidelity efiect. This efiect becomes more pronounced the greater the reduction in the size of the characters, and has been a limiting factor in the extent to which the printing can be reduced in size as compared with ordinary printing. For example, a reduction of five diameters in ten-point type has usually be considered the maximum reduction possible without an intolerable sacrifice in the clarity of the print.

I have discovered a process for high-fidelity microscopic, planographic printing which enables the characters to be made much smaller than has been possible commercially heretofore and still retain their sharpness even when magnified 1S and more diameters. According to my process, the printing is made directly upon the paper or other sheet from a lithographic or pianographic printing plate having ink-receptive images of small size. However, the ink is applied repeatedly to the plate prior to each printing impression on-the paper, with only a light coating of ink at each application to the plate, and the printing impression on the paper is made by the plate under a pressure considerably in excess of those conventionally used in planographic printing. in other words, the microscopically printed characters are made up of accurately superimposed, relatively thin ink layers built up on the planographic printing plate and then impressed upon the sheet "by heavy pressure. The thickness or heaviness of the ink coating applied to the printing plate at each of the repeated inkings of the plate is determined by the number of the repeated ink-ings and the amount of ink which can be applied under the heavy printing pressure without causing smudg'ing or "spreading of the ink on :the paper. That is, when the inking of the plate is 'repeatedonly 2,733,655 1 C3 Patented Feb. 7, 1956 once, each ink coating applied to the plate will generally be heavier than when several repeated inkings are made; and when heavier printing pressures are used, the ink coatings will generally be thinner and applied more times to the plate. The more times the inkings of the plate are repeated before each printing impression, and hence the lighter the ink coating at each application of ink to the plate, the finer will be the ultimate detail obtainable in the microscopic printing.

The repeated inkings can be made conveniently with conventional duplicating machines of the direct printing type. I have found that the Davidson Dual Duplicator, equipped for direct printing, can be used for this purpose, since it permits easy control of the thickness of the ink coating applied to the printing plate, enables repeated inkings of the printing plate before the impress'ion is made on the paper from the plate, and allows adjustment of the printing pressure to the relatively high range required by my process. Since this Davidson machine is "well-known in the printing art, it is not described or illustrated in detail here. Briefly, when the Davidson machine is used in the practice of the prese'nt invention, it is set .up for direct printing so that the blanket cylinder constitutes the impression cylinder or platen, and the segment for holding the lithographic or other planographic printing plate bearing the microscopic .in'kereceptive images is attached to the large cylinder in place of the impression segment. The lead edge of the paper is gripped by grippers operating on continuous chains, rather than on a cylinder, and the grippers are opened by a cam which determines the point at which the paper is released after passing between the cylinders, apparatus of this type being disclosed in W. W. Davidson Pa-tents -No. "2,436,165 of February 24, 1948', and No. 2,374,668 of May 1, 1945. The paper may be inserted into and removed from the grippers manually at the beginning and .end of the complete operation. The thickness of the ink coating applied to the printing plate at each revolution may regulated in any conventional manner, by adjusting the pressure of the doctor blade on 'the ink fountain roller. The pressure of the printing plate .or large cylinder against the blanket cylinder maybe adjusted in the usual manner by a lever movement "which yaries the spacing between the parallel axes of the cylinders. The inter-cylinder pressure is .a .direct function :of the distance through which this spacing is decreased after initial contact between the plate and blanket. Thus, if the setting of the lever gives a 3 thousandthscof an inch movement of the plate against the blanket, after the initial contactfthe intercylinder or printing pressure is referred :to as 3 thousandths of an inch.

The pressure :at which the printing impression is made, following the repeated inkin gs of the plate, is a critical .factor in :obtaining fineness of detail of the microscopic printing. Atthe pressures ordinarily used-in planographic printing =(about2 or '3 thousandths of an inch), there is no noticeable or appreciable improvement in the fineness .of detail when making repeated inkings. I have discovered that there is no appreciable improvement in this respect until the pressure is increased to about 18 'thousandthsof an'inch. For best results, the pressure should be within 'the range of 28 to '35 thousandths of -an inch. 1 have found that the above-specified pressures are applicable for commercially available blankets of different degreesof hardness, evidently because the blankets are very thin (in the-order of 78 t housandths of an inch).

I have found that the type of printing plate used in the process is also a factor affecting the clarity of fineness of detail .of the microscopic printing. For best results, the printing .plate should be a lithographic plate having the finest possible grained surface, preferably so fine as to give the surface a substantially mirror-like surface.

The process can be practiced with good results when printing on commercially available paper stock. I have found that the most satisfactory results are obtained when using coated papers, such as Kromekote, which isa product of Champion Paper and Fiber Company, of Hamilton, Ohio, the coating of thispaper being nonporous and showing no surface roughness or hills and valleys under a lX lens, and being of uniform thickness throughout its area.

The new process produces'striking'results in the fineness of detail of the microscopic printing when viewed through a magnifying glass or enlarger. For example, when a direct printing'plate is made to duplicate a full page of The New York Times (which uses 6 point type) with a reduction of 717 /2 diameters, the microscopic printing from this plate in accordance with my invention can be read very easily with a magnifying glass giving a corresponding enlargement. In fact, the printing has extremely fine detail when viewed through the enlarger. In this manner, I have been able to reprint, microscopically, 25

pages of The New York Times on a sheet space measuring only 5 inches by 7%' inches, with excellent results in the clarity of the print when viewed through the enlarger. From this example, it will be appreciated that the new process can be used to greatadvantage for many purposes, particularly in view of its simplicity, the fact that it can be practiced with conventional duplicating equipment, and the fact that it does not require expensive materials.

In the accompanying drawing-I have illustrated schematically an apparatus for use in carrying out the process. As there shown, the apparatus comprises a plate cylinder 1 mounted for rotation on its axis by fixed bearings at each end, one of the end bearings being shown at 2. On the periphery 'of the-cylinder is a lithographic printing plate 3 in the form .of a segment, which is releasably secured to the cylinder in any desired manner. This plate carries the microscopic inkareceptive images and is preferably a lithographic plate having a smooth, substantially grainless surface. A blanket or impression cylinder 4 is mounted for rotation adjacent andparallel to the plate cylinder on axial end bearings, one of which is shown at 5. These bearings, however, are movable on arms slidable in fixed bushings, thesupporting arm for the bearing 5 being shown at 6 and its fixed bushings at 77a. To

each arm 6, intermediate itsbushings 7-7a, a lever 8 is pivotally connected at its lower end, the lever being adapted to swing on a fixed pivot 9 above the arm. By swinging the levers 8, the impression cylinder 4 may be moved bodily toward or away. from the plate cylinder 1, to move the cylinders into and out of engagement. levers 8 also serve .to adjust theintercylinder pressure to and within the range previously specified. When the pressure adjustment has been made, the pressure is maintained by nuts 10-1011 threaded on each arm 6 and adapted to be tightened against the ends of its bushing 7a. As previously mentioned, the pressure is here considered as the distance (in thousandths of an inch) through which the cylinder 4 is moved toward and against the cylinder 1 after initial contact between the periphery of cylinder 4 and the periphery of plate 3.

The impression cylinder 4 is of the same diameter'as the plate cylinder 1, and the two cylinders are driven at equal speeds in opposite directions (as shown by the arrows) by any suitable or conventional driving mechanism (not shown), such as the mechanism used in the aforesaid Davidson machine, which permits adjustment of the spacing between the axes of the cylinders. The impression cylinder 4 has a resilient covering or blanket and may be the type of cylinder referred to as the blanket cylinder in' the Davidson machine, the blanket being preferably of the standard'hard classification. The paper is held on the blanket cylinder 4 by a gripping device .11, which may be of conventional form to clamp the paper The ' along itsleading edge against the periphery of cylinder 4.

This gripping device, as shown, is hinged to the cylinder 4 at 11a and its lagging or free end is held in its clamping position against cylinder 4 by a spring 12. The gripping device may be lifted against the spring 12 to permit insertion or removal of the paper.

During the initial rotation of the cylinders 1 and 4, the lovers 8 are adjusted to provide a space between the cylinders, so that no printing impression will be made by the printing plate 3. During this initial rotation of the spaced cylinders, a thin coating of ink is applied repeatedly to the plate 3 by ink transfer rolls 13 which receive ink from a fountain or reservoir 14. The thickness of each ink coating may be regulated in any suitable manner, as by adjusting the pressure of the doctor blade 17 against the ink roll 13 in the fountain 14, to squeeze more or less of the ink from this roll. Before each application of ink to the plate, the plate is dampened with the usual moistening solution applied from a reservoir 15 by transfer rolls 16. During each revolution of the cylinders, a light coating of ink is applied to the plate 3 from the ink rolls 13, after moistening of the plate by the rolls 16. After .the desired number of repeated inkings (preferably 3-5),

the plate is ready for the printing impression. The latter is eiiected by operating the levers 8 to engage the cylinders and adjust the inter-cylinder pressure to the relatively high range, as previously described. The paper may be fed to and released from the gripper 11 manually, or it may be fed and released automatically, after the required number of cylinder rotations under the ink rollers 13. For example, the stationary cams for releasing the gripper at the feeding station in the Davidson Dual Duplicator, may be made movable so that they can be projected into their operating positions only after the desired number of rotations of the cylinders.

'The thickness of each ink coating applied to the plate 3 by the transfer rollers 13 is, as previously mentioned, considerably less than is used normally, that is, with only asingle application of ink to the plate prior to each printing impression. In general, the thickness of each of the superimposed ink coatings on the plate will be roughly l/n of the thickness normally used, where n is the number of the superimposed inkings. When the number of these inkings is 4, for example, the thickness of the ink coating applied to the plate at each cylinder revolution will generally be about A of the ultimate thickness of the composite super-imposed ink layers on the plate.

I claim:

1. A planographic printing process for producing fine print on a sheet'with the use of a rotary planographic printing plate, a parallel rotary cylinder and a resilient blanket, which comprises moistening and applying a light coating of 'ink repeatedly to the plate before impressing ,the plate against the sheet, the thickness of each ink coating being generally l/n of the ultimate thickness of the .composite superimposed ink layers applied to the plate,

where n is the number of said ink coating applications, and then passing the sheet between the cylinder and plate, to make the printing impression on the sheet, while maintaining between the cylinder and plate a heavy pressure equal to the pressure obtained by displacing the axis ,of the plate toward the parallel axis of the cylinder through making a printing impression on the sheet from the plate 'under'a heavy pressure obtained by moving the plate against the blanket through a distance of at least about 18 thousandths of an inch, after initial contact of the plate and blanket.

3. A process according to claim 2, in which said pressure is obtained by moving the plate against the blanket through a distance of 28 to 35 thousandths of an inch, after initial contact of the plate and blanket.

' 4. A process according to claim 2, in which the number of said ink coatings is between 3 and 5.

5. A process according to claim 2, comprising also the step of forming the printing plate from a smooth, substantially grainless lithographic plate.

6. A process according to claim 2, in which said pressure is obtained by moving the plate against the blanket through a distance of 28.to 35 thousandths of an inch,

, after initial contact of the plate and blanket, said printing plate being formed from a smooth, substantially grainless lithographic plate.

7. A planographic printing process for producing fine print on a sheet with the use of a planographic printing plate and a resilient blanket, which comprises moistening the plate and coating it with a layer of ink, and then pressing the plate against the sheet on the blanket under a heavy pressure equal to the pressure obtained by displacing the plate against the blanket through a distance of at least .018",-after initial contact of the plate and blanket, to make a printing impression on the sheet from the plate.

8. In the production of fine printing on a sheet with the use of a smooth, substantially grainless lithographic printing plate and a resilient blanket, the process which comprises forming small ink-receptive images on the plate, moistening and making repeated inkings upon the printing plate while maintaining the plate out of contact with the sheet, the thickness of each inking being generally l/n of the ultimate thickness of the composite superimposed inkings, where n is the number of said inkings, and then pressing the plate against the sheet under a heavy pressure equal to the pressure obtained by displacing the axis of a rotary printing plate toward the parallel axis of a rotary resilient blanket cylinder through a distance of at least about 18 thousandths of an inch, after initial contact of the plate and cylinder, whereby the print is built up from thin, superimposed ink layers from the plate.

9. A planographic direct printing process for producing fine print on a sheet with the use of a planographic printing plate and a resilient blanket which comprises moistening the plate and coating it repeatedly with a thin layer of ink before contacting the plate with the sheet, the thickness of each ink layer being generally 1/ n of the ultimate thickness of the composite superimposed ink layers, where n is the number of said coatings, and then making a printing impression on the sheet directly from the plate under aheavy pressure of at least the magnitude obtained by displacing the axis of a rotary printing plate toward the parallel axis of a rotary resilient blanket cylinder through a distance of about 18 thousandths of an inch, after initial contact of the plate and cylinder.

10. A microscopic reproduction of printed matter which comprises a sheet, and microscopic inked characters each applied to the sheet as a pre-formed layer of ink by coating a moistened planographic printing plate with a layer of ink and then pressing the plate against the sheet on a resilient blanket under a heavy pressure equal to thepressure obtained by displacing the plate against the blanket through a distance of at least .018", after initial contact of the plate and the blanket.

References Cited in the file of this patent UNITED STATES PATENTS 129,176 Savage July 16, 1872 148,530 Waddie Mar. 10, 1874 476,135 Elsenhardt May 31, 1892 1,227,557 Cochran et al May 22, 1917 2,040,129 Hagelin May 12, 1936 2,046,959 Mehl July 7, 1936 2,302,816 Toland et al 2.. Nov. 24, 1942 OTHER REFERENCES Art and practice of printing, volume III, Montague, published by Sir Isaac Pitman & Sons, Ltd., London, page 151. (Copy in Div. 17, U. S. Patent Ofiice.)

Printing Inks, Ellis, published by Reinhold Publishing Corp., New York, N. Y., page 475. (Copy in Div. 17, U. S. Patent Oflice.)

The Lithographers Manual (Soderstrom) published by Walton Publishing Co., New York, N. Y., pages 186-195 and 301. (Copy in Div. 17, U. S. Patent Oflice.)

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