Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F5/00—Screening processes; Screens therefor
  • G03F5/20—Screening processes; Screens therefor using screens for gravure printing

Definitions

• This invention relates to the art of gravure printing and concerns more particularly (a) a unique positive of the subject to be reproduced, used in the making of the printing-plate and its method of production, (b) a novel intaglio print-- lug-plate and its process of manufacture from such positive, (c) a new printirm procedure resulting in ,(d) an improved print presenting the original subject with great fidelity as to all tonal 1n gradations.
• Intaglo printing involves the employment ;of a printingplate made from a continuous-tone positive and a gravure-screen and in which plate the picture is 16 depicted by a series of dots formed as wells or depressions in the'printing surface of the plate,
• Such gravure printing comprises the employment or an intaglio 25 printing-plate in which such ink-wells are allot thesame area but which vary in depth in conformity with the tones of the original interpreted, the wells representing the blacks of the subject being deepest, those corresponding to the lightest 3d tones being shallowe'st, and those'representing the intermediate tones being of harmonizing intervening depths. Since the deeper wells accomim ate a greater quantity of ink than the shallow r ones, the former, or course, ,willdepoeit 35 more'ink on the paper and therefore will produce darker tones. v
• the image or design to be reproduced is transferred to the printing-plate by means of an intermediate medium, such as the so-called fcarbontissue, throughwhich the plate is etched'difl'erentially to produce the ink-wells oi varying depths, this being the only method employed commercially heretofore in making a gravure plate.
• an intermediate medium such as the so-called fcarbontissue
• Such printing-plate is ordinarily produced by first making a continuous-tone negative of the subject and then making a continuous-tone positive therefrom, the positivebeing photographically printed on the lisht-sensitive gelatinous layer of the paper-backed carbon-tissue, and a rotogravure screen is also photographically printed thereover on the same light-responsive stratum of the carbon-tissue by a secondexposure.
• Such double-exposed carbon-tissue stratum or layer is thereupon secured face down on the sur- 55 face of the metal printing-plate, its paper backingltolthe darkest zones ing om's! such coating developed, the veloped coating being known in the trade as a carbon-resist".
• a process of producing an intaglio printingplate comprising photographing the subject in negative through a line-screen with the camera initially focused to obtain a checker-board effect of the screen on the ground-glass of the camera, overexposing such negative plate sufficiently to cause the shaded and dark portions of the design of the subject to appear on the negative as variable size, entirely-disconnected, transparent dots, the largest dots corresponding in tone and position to the darkest zones of the subject, such excessive or unusual light-exposure causing the negative, except for the dots, to be substantially opaque, and thereafter using this negative, through the" medium of a positive plate or film made therefrom, an etch-resist, and an etchingfluid to form the intaglio printing-plate; or, stated solids, to represent the darkest parts of the subject.
• the half-tone screen is spaced at its correct focal distance in front of the sensitive plate which is to form the negative and the excessive lightexposure of the plate is depended upon entirely to lessen or restrict the effect of the screen so that the negative carries only in half intensity the tones of the original subject.
• the over-exposure eliminates all dot effects in the negative where the original subject was entirely white, so that the negative in those areas is completely We.
• a leading purpose of the present new invention is to provide an improved method of printing in which the several above-specified and other disadvantages apparent to a person skilled in the art are avoided or eliminated, an especial object of the invention being to supply a different an better procedure to overcome the deficiency of the second of the prior art processes described, in that the new method is capable of making prints correctly and exactly representing all tones of the subject, from the lightest to the darkest.
• a positive transparency (hereinafter referred to as a positive) is made by photographing a continuous-tone negative of the subject through a conventional half-tone screen under such conditions of screenposition and of exposure that the dots on the positive are all of the same intensity but vary in area or size from the darkest to the lightest tones, the blacks or solids of the original subject being represented by practically unconnected dots and the whites of the subject being entirely free from dots in the positive, while the dots representing the intermediate tones are of correspondingly graduated areas.
• This positive is unique in that, although it represents the entire range of tone values of the initial subject, all such values are actually present in the positive at about half intensity of the original, except pure whites which are the same in each.
• This peculiar positive is produced, not by over-exposure, but by placing the screen in front of the light-sensitive plate at the correct distance, differing somewhat from its true focal distance, to produce the indicated result.
• the spacing of the screen in front of the photographic plate and the period of exposure of such plate are both less than would be used to produce an ordinary half-tone positive with all other conditions the same.
• the screen distance may be about three-fourths that which would be used for the production of a half-tone and the exposure may be in the neighborhood of approximately one-third that which could .be satisfactorily employed for the making of a half-tone;
• tone-value or its equivalent has been used in reference to the original subject, it is intended to mean the relative position of the tone of any particular color in a scale which represents the full range of the color in question; when employed in relation to the continuous-tone negative, it signifies the value of the densityor opaqueness of the tone; when used in reference to the hemi-tone positive, it specifies the relation between the total area of the opaque dots to the area of the transparent surface in a unit area of the tone under consideration of the positive, it being home in mind *that all dots in the positive are of equal density regardless of size; and when employed in reference to the hemi-tone gravure printingplate, hereinafter referred to in more detail, it means the relation between the area of the inkwells to the area of the non-printing surface ina unit area of the tone under consideration in the printing-plate.
• the etching of the intaglio printing-plate is carried out long enough to assure that the many practically independent etched wells in the surface of the plate are deep enoughtoaccommodatemilicientinksotbat when the printing is done there will be enough inkappliedtotheprintbyailwellstopermita proper spreading thereof whereby to give the print a full range of tone gradation from the darkest shadows or solids to the brightest highlights; this ink enlargement or spread of the dots on the print making good or overcoming the lack of full intensity of the positive. Such spreading of the ink on the print takes place in more or less degree for all printed dots.
• vmode of practising the invention which procedure is not however essential, but which has certain advantages of afl'ording more leeway or greater latitude in the time of light exposure in making the positive and of the production of sharper and more clearly defined dots and which may be accomplished by a slight change in the indicated distance between the screen and the film which is to form the positive, or by a slightly longer exposure, or both, comprises making a positive under conditions such that the whites of the subject have extremely fine dots in the positive which are capable of being entirely removed by an ordinary reducing operation, and, in eliminating these by such reduction, all of the remaining dots of the positive will be reduced a certain uniform extent, the specified reduction being controlled so as to remove the dots on the whites without entirely eradicating the dots representing the next darker shade. In this way, all of the tone values of the picture are preserved, although the positive, when viewed by itself, as stated above, shows less contrast and appears flatter than the original subject.
• An additional feature of the invention is the production of a composite-positive of illustrations and type-matter in which the illustrations appear as described above and the type-matter is presented as black letters carrying crossed white.
• a further principle of the invention resides in the transferring of the single or of the composite positive directly to the printing-plate without the use of carbon-tissue and in such a way that the subsequent etching can be easily controlled.
• the surface of the printing-plate is coated with a resist of such a nature that it remains substantially unimpaired and intact during the entire etching period, whereby the etching may be interrupted at any time, the plate examined, and certain areas painted out with a protective varnish or the like, as desired, before continuing the etching.
• the intaglio printing-plate itself, which possesses a non-printing surface corresponding to the whites of the picture and the remainder of which contains a plurality or ag egation of ink-wells representing the tone dots of the picture, these wells being of different areas and approximately uniformly etched as to depth, the wells representing the darkest tones being practically separate and distinct, the tones next to white being represented by small wells, and the areas representing the whites being entirely free from wells. All of the wells, however, are sufliciently deep to permit the plate to be topped, as by means of an ink roll-up, Without filling in of the liner wells, and re-etched as desired. As long as the kind of resist employed remains on the plate, such inking prior to re-etching is not required, but after the resist has been removed, the applied ink acts as a resist whereby the wells may be etched deeper.
• a continnous-tone negative is made from the original subject to be reproduced in the manner common in the photographic art; but if the original be a photograph, the negative from which it was made may be employed for this purpose, and in either instance, the negative may be retouched if desired.
• a set of continuous-tone separation negatives one for each color, is made photographically through color-filters in the usual way, and these are retuched or corrected as required so that each negative contains its proper color values.
• Each negative, produced in this manner, is then placed before a camera, and while properly illuminated, is photographed through an ordinary half-tone or equivalent screen, the exposure being such and the screen being so positioned with reference to the positive being made that the clot formation is produced on the positive in which the largest dots, representing the blacks, are practically separate and distinct from, and do not touch, one another except possibly at their corners as in a checker-board efiect, while the smallest dots on the whites are so fine that they may be readily cut or removed in a reducing step.
• This desirable dot arrangement is obtained by selecting the proper distance between the halftone or other screen (for example 150 lines to the inch) and the sensitized plate undergoing exposure and using the correct lens aperture and time for the exposure.
• This positive may be made on a wet-plate, if preferred. in order that the subsequent development thereof may be more readily controlled:
• each of the positives may be made by contact printing on a dry-plate using a half-tone or similar screen in a manner such that the above-mentioned dot formation is secured.
• the positive is developed and then reduced by any standard reagent, depending upon the type of plate employed, and during this procedure the entire positive is reduced a sufficient amount to eliminate entirely or substantially completely the minute dots on the whites, but not enough to eradicate the dots representing any of the next darker tones of the picture, this ieduction step also tending to remove the fringe effect of the dots and to cause them to be more clearly defined and with sharper demarcation.
• this positive will appear to have less contrast than the original subject or the negative, this characteristic being of material importance in the subsequent step of printing with the corresponding printing-plate, inasmuch as it provides a continuous support in the heavily inked gags of the plate for the ink-wiping doctor-
• this peculiar and noteworthy hemi-tone positive is produced by using a half-tone or analogous screen at such a chosen distance from the light-sensitive film as to provide the specified result with proper exposure, the positive not truly depicting the negative from which it is made, because it displays the tones of the continuous-tone, preferably but not necessarily somewhat thin, negative in discontinuous dots of about one-half less value or area than they should be, the result being that such positive looks unduly shallow or more or less lifeless as it is without the full tone contrasts present in the corresponding negative.
• a positive of the type or printed matter is made by taking a press-proof of the printed matter, a negative is made thereof, a. negative of a gravure-screen is placed over the type negative, and a positive is photographically made therefrom on a film by contact printing, the resultant positive reproducing the type in black on which the screen appears as crossed white lines.
• This positive is stripped and mounted on a glass-plate together with the hemi-tone positives of the illustrations in correct relative positions, thereby providing a suitable compoundpositive which can be placed in a vacuum printing-frame and printed on the light-sensitive surface of the metal printing-plate, as hereinafter set forth.
• the crossed white lines of the typematter in the final printing-plate perform the same function as do the walls of the larger wells in the etched printlng-plate in that they prevent the doctor-blade from removing the ink from the cells, representing the type-matter, or, stated otherwise, the white lines divide the typematter into practically separate dots in the positive and practically separate wells in the plate.
• the gravure-screen is preferably used in connection with the letters instead of the conventional half-tone screen because it provides pockets or wells in the plate of larger area resulting in a letter of sharper outline than it would be possible to obtain by the employment of a half-tone screen.
• Other screens, such as a line screen may be used, if desired.
• a single positive or a composite positive having been produced in the manner above stated it will be understood that it can be transferred to the metal printing-plate in any standard manner and the plate then used for printing in accordance with the intagllo process, but this is preferably carried out in the following manner in conformity with the present invention:
• the surface of a copper-plate which is to form its printing surface is sensitized by applying thereto a lightsensitive coating of a solution of shellac and a bichromate commonly called cold-enamel.” If the surface of the plate were covered with a thin coating of light-sensitive glue or gelatin, then exposed through a positive to the action of light.
• the positive having been previously stripped from its support and placed face down on the coating to assure that the flnal print will not be reversed right to left, whereupon such coating is developed, for example, as by the use of alcohol, leaving on the plate a coating impervious to the action of the etching medium but containing numerous free small passages therethrough corresponding to the dots of the positive and through which the etching fluid has free and unimpeded access to the surface of the copperplate.
• the positive design or picture is then etched through such resist apertures into the surface of the underlying plate to the required depth, a suitable single strength only of the etching agent being required, thus avoiding the necessity for the great care heretofore essential in etching gravure plates.
• a composite-positive obtained as above indicated is used. it is photographically printed on such light-impressionable copper-plate coating in any convenient manner, as by the step-and-repeat method of photo composition; or, in the case of a large composite, by a vacuum printing-frame, the
• step-and-repeat procedure permitting an accurate tosecure registration of all parts of cooperating intagllo plates, this being particularly essential in the case of large subjects.
• Precise registration is facilitated by placing dependence on the employment for each color of the cold-enamel light-sensitive coating on its copper printingplate, which procedure entirely overcomes the normal and intrinsic uncertainties incident to the use of a deformable or distortable carbon-tissu such customary intermediate tissue agency employed in the production of gravure plates being subject to serious inaccuracies which prevent the securing of faithful reproductions, because the gelatin and its paper support of the carbon-tissue cannot be depended upon to aflord correct registration due to the vagaries of variable expansion with or across the grain of the paper, the humidity and the temperature, of course, entering into the situation.
• Any areas of the printing-plate, whether single or composite, such as borders, to be protected from the action of the etching-fluid, may be preliminarily painted over with asphalt-varnish, after which the unvarnished parts of the plate are etched with a standard etching solution for a suflicient period of time, this operation requiring from three to eight minutes, depending upon the solution employed.
• Such etching may be interrupted at any time to permit the plate to be washed, dried, and examined, because the resist has remained in place in uninjured condition, and any portions of the plate that have been adequately etched may be painted over with asphaltvarnish before continuing the etching, which is then prolonged untfl the entire printing-plate has been etched the needed amount.
• the plate After a proof has been taken, the plate may be topped with ink and re-etched or corrected as needed, the ink, under thesecircumstances, acting as a resist.
• the various ink-wells are of different areas corresponding in position and size to the dots of the hemi-tone positive from which they were formed, but these wells are of approximately the same depth. It will be understood, therefore, that use is made of conventional disconnected middle-tone dots in the positive and corresponding conventional practically disconnected middle-tone wells in the printing-plate for thedeepest shadows and regular gradations from those to dot-free or well-free whites, as the case may be, which aredesigned and adapted to faithfully and correctly reproduce all the tonal changes of the original in the print.
• Th centers of any four, adjacent, checkerboardarranged ink-wells, with their corners in close proximity, representing the solids of the sub- Ject, constitute the corners of a square and the distance between the centers of any pair of such ink-wells will be equal to the length of one side of such square or to the length of its diagonal, the former distance being necessarily somewhat shorter than the latter distance.
• the centers of any four adjoining ink-wells also form a square and the distance between the centers of any pair of such wells may be equal to the length of the side of the square or to the length of its diagonal, the former distance obviously being shorter than the diagonal distance.
• the length of the non-printing portion of the printing-plate between wells measured along the diagonal line and the length of the non-printing portion between wells measured along the side-line of the square are substantially different, and, from the geometrical construction, it is apparent that the ratio between the two can be equal to, but cannot exceed, l.4142+ in the case of the standard gravure formation of ink-wells, leaving out of account any rounding out of the sides of the ink-wells during etching whereas, in the patentees approximate-checkerboard arrangement of ink-wells the ratio must inevitably be greater than 1.4l42+.
• the ink-wells in the plate representing the blackest or deepest shadows shall be of such size and capacity that, although they are practically unconnected, the spreading of their ink on the paper will be sufficient to cover the entire area of the printed surface corresponding to such portions of the subject, and the ink employed should be of such viscosity, determined by the depth of the etching and of the separation of the wells, that the dispersion of the ink on the printed surface will thus faithfully duplicate all tones and shades of the original.
• the conventional middle-tone dots are present as virtually or to all intents and purposes disconnected ink-wells in the intaglioplate, they are lost on the print through the spreading of the ink which produces a rich ink layer forming a desirable continuous tone.
• step-and-repeat machines may be employed for composing the matter to be reproduced directly on the printing-plates.
• local re-etching of the plate, and continuation of the etching may be resorted to, if
• said space and exposure both being sufliciently less than would produce an ordinary half-tone positive-transparency with the other conditions the same, that the exposed plate, when developed, will represent the solids, ii any, of the subject at substantially one-halt tone value by relatively-large practically-unconnected dots and will represent all lesser tones of the subject by dots of corresponding lesser areas, and developing said exposed plate to produce a positive-transparency having said characteristics, all said dots being of substantially the same density.
• the dots of said positive-transparency representing the solids are arranged in approximate-checkerboard design, in which said plate light-sensitive coating is cold-enamel, and
• etching is performed solely by a single-strength etching-reagent.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)
• Printing Methods (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=26248839

Family Applications (1)

Country Status (4)

Cited By (1)

• 1935
  • 1935-05-14 FR FR790457D patent/FR790457A/fr not_active Expired
  • 1935-08-13 US US36019A patent/US2155458A/en not_active Expired - Lifetime
• 1936
  • 1936-02-24 GB GB12175/35A patent/GB470385A/en not_active Expired
• 1937
  • 1937-07-31 BE BE422922D patent/BE422922A/xx unknown

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