US2910358A

US2910358A - Printing plates for use in offset printing

Info

Publication number: US2910358A
Application number: US336402A
Authority: US
Inventors: Coles Derek Harrison
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-04-09
Filing date: 1953-02-11
Publication date: 1959-10-27
Anticipated expiration: 1976-10-27
Also published as: BE520057A; FR1083534A; NL81835C; GB756847A; CH324699A

Description

0a. 27-, 1959 D. H. COLES 2,

PRINTING PLATES FOR USE IN OFF SET PRINTING Filed Feb. ll. 1955 Fig.1

,11 Fig. 2 v 1 zzzr .7 A -12 Fig. 4

Fig. 5

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.INVENTOR. DEREK HARRISON 6015s BY ATTORNEYJ' United States Patent PRINTING PLATES FOR USE IN OFFSET PRINTING Derek Harrison Coles, London, England Application February 11, 1953, Serial No. 336,402

5 Claims. (Cl. 96-33) The present invention relates to the production of printing plates for use in offset printing and is concerned with a method of producing such plates of the type in which an original in the form of an image on a translucent or transparent carrier is transferred to a printing plate by making the plate sensitive to light, placing the carrier in contact with the light-sensitive plate, directing light through the carrier onto the sensitized plate, and subsequently developing the plate to form an offset printing plate. 1

According to the present invention, in producing an offset printing plate by a method of the type specified, the said image is initially produced without lateral reversal on the face of the tissue of a sheet of duplex paper, the said face of the tissue is then afiixed to a face of the said carrier, the backing sheet of the duplex paper is removed, the side of the carrier bearing the said tissue is placed in close contact with the sensitized printing plate and light is directed through the carrier bearing the tissue on to the sensitized plate.

The term duplex paper used in this specification means a paper comprising a thin tissue paper sheet superimposed on, and removably secured by an adhesive to a single heavier backing sheet.

The method according to the invention enables printing down to be effected with the side of the carrier bearing the image in contact with the light sensitized printing plate and the use of the duplex paper enables this to be effected quickly and easily and without the need for preparating a laterally reversed image in the first instance. Furthermore the printing plate is produced Without the use of a camera and dark room equipment and without the cost of making photographic negatives or positives and retouching is unnecessary.

The carrier may conveniently be of paper such as baryta paper althoughin many cases glass, a trans parent foil, or a translucent material such as a cellulose acetate film may be used alternatively. The instability of film is well known and since this is not used as an intermediate step in reproducing the image onto the sensitized surface of the metal plate, the image will tend to remain more stable particularly if the carrier be of glass or a stable film such as the material known as Astrafoil. The exposure time when using a paper carrier may be reduced by treating the paper with a suitable oil. This has the further effect of improving the stability of the image.

The invention is particularly suitable for producing ofiset lithographic printing plates.

The invention can be carried out as described by way of example with reference to the accompanying diagrammatic drawings in which:

i Fig. 1 illustrates a sheet of duplex paper in perspective with the tissue and backing sheet separated at one corner,

Figs. 2 to 9 inclusive are diagrams illustrating successive stages in the'production of a printing plate, and

l ice Fig. 10 illustrates a variant of the method illustrated by Figs. 2 to 9.

In the embodiment of the invention illustrated in Figs. 1 to 9 of the drawings, the first step in the production of a printing plate for use in offset printing is to form the required opaque image, without lateral reversal, on the face of the tissue 11 of a sheet of duplex paper.

The tissue 11 is constituted by a thin sheet of tissue paper which is superimposed on and removably secured by an adhesive to a heavier backing sheet 12. In Fig. 1, the tissue 11 and backing sheet 12 of the duplex paper are shown separated at one corner.

One method of forming the above-mentioned opaque image is by printing, as follows. Type is set up and made ready on a letter-press machine. A pull is then taken on the tissue 11 of the sheet of duplex paper, using any suitable printing ink which need not be black. As will be noted in Figs. 2 to 4 of the drawings, the ink which is applied to one surface of the tissue sheet in forming the image 11 thereon, is absorbed through the tissue sheet so that it extends to the other surface of the latter. A duplex paper which has been found to give satisfactory results is the paper sold by Brittains Limited of Cheddleton Paper Mills, Near Leek, Stafiordshire, England, under the designation W.P.D.W. Paper. A proof thus obtained is next dusted over with black or metallic dusting powder, which may conveniently be lamp black, by dabbing lightly with cotton wool dipped in the powder. French chalk is then dusted over the surface with cotton wool, and the whole wiped clean with fresh cotton wool or brushed oif with a soft brush. Thus the image '11 (Figs. 2 to 4) is rendered opaque.

The duplex paper is then affixed by means of an adhesive to a carrier sheet 13 of baryta paper with the tissue side to the carrier sheet, as illustrated in Fig. 2. The TAPPI Monograph SeriesNo. 7, entitled Pigments for Paper Coating and published 1948 by the Technical Association of the Pulp and Paper Industry, New York, N.Y., on pages 14-16 thereof in an article entitled Barium Sulphate Pigments indicates that baryta paper is a paper coated with barium sulphate using a high grade gelatin as the adhesive and refers to a discussion by Dr. Th. Bentzen on haryta paper in Tech. Assoc. Papers 8:4952 (1925) regarding the fundamentals involved in the preparation of the coating mix, its application to the raw stock'and the testing of the finished paper. This article also points out that barium sulphate is a heavy white pigment which is formed from the mineral, barytes, occurring in the United States or witherito, a barium carbonate ore mined in Europe and England. According to this article, the barium sulphate coating on paper is a dense compact film and does not take a high gloss but is useful for dull or matte finishes which have a characteristic satiny feel. As is hereinafter indicated the barium sulphate coating on the baryta paper provides a good drawing or printing surface. Barium sulphate readily absorbs ink, without blurring like blotting paper. As a result of the substantial quantity of ink that this coating will absorb, the lines are dense and thus effectively interrupt the passage of light and produce a sharp image on the printing plate.

The backing sheet of the duplex paper is now removed, leaving only the tissue 11 face down on the carrier sheet 13, see Fig. 3. The carrier sheet 13 and the tissue 11 carried thereby are next rendered translucent by means of medicinal paraffin thinned with benzene, excess oil being removed with the aid of blotting paper.

An aluminium printing plate is then prepared with a 2%% solution of glacial acetic acid, rinsed in water and coated in a whirler at say 60 r.p. m. with a coating 15 'of gum arabic and ammonium dichlormate solution.

When dry, the sensitized plate 14 so produced is placed in a printing down frame with the carrier sheet 13 hearing the tissue 11 in close contact with the coating 15, the side of the carrier sheet 13 hearing the tissue 11 being placed in contact with the sensitized coating 15, as illus trated diagrammatically in Fig. 4.

The sensitized coating 15 on the plate 14 is then exposed. Fig. 5 shows the plate after it has been exposed and after the carrier sheet 13 and tissue 11 have been removed. The exposed areas 16 have been hardened by the action of the light whilst the unexposed areas 17 remain soft.

During the subsequent development, the unhardened areas 17 of the coating are removed, leaving the exposed areas 16 in relief as illustrated in Fig. 6.

After developing the plate 14 with a developing solution such as one consisting of a solution of calcium chloride and lactic acid, the plate 14 is etched from 2 to 4 minutes in a solution such as calcium chloride, zinc chloride, iron perchloride and hydrochloric acid with the result that the level of the uncoated portions of the plate is depressed as at 18 (Fig. 7) below the level of the metal surface. When etching has been completed, the etching solution is removed with several applications of waterfree alcohol 200 proof and the plate is dried.

The plate 14 is then based with an azeotropic mixture and inked in with lithographic ink, so that the depressed areas 18 (Fig. 7) are thereby coated with ink as at 19 (Fig. 8). After French chalk has been applied, the lighthardened portions 16 of the coating are removed by rinsing or soaking in warm water followed, if necessary, by light brushing. When this operation has been completed, the plate is dried and is gummed and washed out with asphaltum solution in the usual way. In the finished plate those parts of the surface of the plate 14 from which the hardened coating 16 has been removed constitute metallic water-receptive areas 20 between the inked printing areas 19.

In the example described above, the plate is developed (see Fig. 6 et seq.) by the deep etch process. The exposed plate can however be developed by other known processes in which a laterally reversed positive is normally used or could be used, such as for example the gum reversal process or the so-called Vandyck process.

It will be understood that the duplex paper, instead of being affixed to the carrier sheet 13 by means of a separate coating of adhesive, may alternatively be of the kind in which the tissue side is already gummed or coated with a thermoplastic adhesive.

An alternative method of forming the original opaque image on the face of the tissue of the duplex paper, is to apply it by means of a typewriter or the like in the form of an ink impression having a tacky or greasy surface to which the lamp black subsequently dusted over it will adhere.

The typewriter is preferably an electrically-operated typewriter or type-setting machine capable of producing justified lines of copy, such as any one of the typewriters sold under the following trade marks and trade descriptions: Orotype, Vari-Typer, I.B.M. Typewriter, Justowriter, Lithotype and Underwood Justifying Typewriter. An ordinary typewriter of the kind now widely used at the present time may, however, be used.

Any ribbon used for typing direct onto an offset plate for duplicating would be found suitable for use in those cases where the type impressions are struck with a ribbon.

In the case of machines which operatewith one time paper ribbons, the ribbon may be a paper ribbon coated with soft, greasy carbon.

The image can alternatively be drawn or written with an opaque ink which would not require subsequent dustmg.

The subsequent procedure is the same as that already described with reference to Figs. 2 to 9.

It will be apparent to those skilled in the art that the invention may also be applied to the production of a series of offset printing plates for reproducing coloured images. The several colour component images are formed on the tissue of duplex paper without lateral reversal and transferred to a suitable carrier as in the example already described. This is particularly suitable for adapting a series of letterpress colour blocks for lithographic printing. The letterpress colour blocks may be used to form images on the tissue of duplex paper and the images may be transferred to offset lithographic printing plates in the manner already described.

Furthermore a duplicate offset lithographic printing plate can readily be produced from an existing plate by employing the existing plate to print an image on the tissue of a sheet of duplex paper. The image may be transferred from the duplex paper to an offset lithographic printing plate in the manner already described.

The invention may also be employed to add type, a drawing or other image to an existing positive or photographic transparency for use in producing an offset lithographic printing plate.

If it is required to reverse the original that is to print a white image on a black or coloured background from the original black image on white background the sensitised coating on the lithographic printing plate will be other than that described and may be, for example, the well known emulsion containing egg albumen, ammonium dichromate and water. The areas of emulsion not exposed to light are washed out during developing.

The invention may be used with advantage in producing offset printing plates for printing images formed partly of lines and partly of words or symbols. For

example, it can be used for printing musical compositions or business forms consisting of lines with box headings. In such cases, it will generally be desirable to apply the image to the duplex paper or to the duplex paper and carrier sheet in two separate operations. For example, the staves may first be printed without lateral reversal on the face of a tissue of the duplex paper which is then fixed to the face of the carrier, after which the backing sheet is removed. The musical notations may then be superimposed in a similar manner in the required positions in relation to the staves on to the above-mentioned tissue, the backing being thereafter removed to producev a laterally reversed positive combining both parts of the image to be printed.

Alternatively, the lines or staves may be printed or drawn laterally reversed on the carrier sheet, to which the face of the tissue of the duplex paper is to be affixed subsequently, and the notes, box headings and the like drawn or printed without lateral reversal on the face of the tissue and stuck in the required positions, on the face of the carrier or vice versa.

In Fig. 10, which illustrates this variant, 21 represents the laterally reversed lines or staves on the carrier sheet,

While the other references indicate parts corresponding.

to those bearing the same references in Fig. 4. The caliper of the tissue is such that it is insuificient to cause distortion by light diffusion or creep and will not aided the clear reproduction of the lines or staves 21.

The last-mentioned procedure may be used with appropriate modifications for producing images in the form of lines and box headings, such as are required in busi-- Although particular reference has been made to the these may be of paper.

production of offset lithographic printing plates, it will be understood that the method according to the invention can also be used in the production of photogravure plates or cylinders or any other process, such as offset-letterpress or dry oifset lithography where a reversed positive can be used. Furthermore although reference has been made to an aluminum plate it will be understood that plates of other materials such as zinc, copper, magnesium, tri-metal and bi-metal with the appropriate chemicals, may also be employed.

The invention facilitates storage of originals since Furthermore, in the event of say a first edition of a book being made and it being desired to ensure that a second edition can be printed later, the letterpress type or the plates themselves need not be kept neither need the originals. All that is required is that a duplicate set of duplex papers be produced taking care that both sets are dusted with the opaque powder before they are dry. The duplicate set may then be stored indefinitely in a dry place and may be used at any later date to prepare a fresh set of printing plates. Thus the plates or type used for the first edition may be melted down and used again. A duplicate set of duplex papers is also easily transportable. An additional advantage is that the signatures of the book have the pages already imposed in the correct position for subsequent printing.

While the invention has been described above by way of example with reference to line subjects, it should be understood that it is equally applicable for the reproduction of half-tones.

I claim:

1. The method of producing a printing plate for use in offset printing, which comprises taking a duplex paper composed of a thin tissue paper sheet removably secured throughout its entire area by adhesive to a backing sheet of heavier paper and applying to the outer surface of the tissue sheet of such duplex paper an opaque right-reading image of part of an original to be transferred to a printing plate, applying to a paper carrier sheet a laterally reversed image of another part of said original, securing such outer surface of the tissue sheet of the duplex paper to the image bearing surface of said carrier sheet so that both parts of such image are sandwiched therebetween, separating the backing sheet of the duplex paper from the tissue sheet thereof, leaving the tissue sheet adhered to the carrier sheet with the image therebetween, rendering the paper carrier sheet capable of transmitting light rays therethrough, placing the other surface of the tissue sheet in close contact with the light sensitive material of a sensitized printing plate, then directing light through both the carrier and tissue sheets and onto the light sensitive material of such printing plate, and then developing and cleaning said printing plate.

2. The method of producing a printing plate for use in offset printing, which comprises taking a duplex paper composed of a backing sheet to which a thin tissue paper sheet is removably secured throughout its entire area by an adhesive and applying a right-reading image to the outer surface of the tissue sheet of such duplex paper, applying to one surface of a carrier constituted of material capable of transmitting light rays therethrough a second laterally reversed image, then securing the outer surface of the tissue sheet of the duplex paper to said one surface of said carrier so that said right-reading image and said laterally reversed image are both sandwiched between the tissue sheet and the carrier, separating the backing sheet of the duplex paper from the tissue sheet thereof, leaving the tissue sheet adhered to the carrier with the images therebetween, placing the other surface of the tissue sheet in close contact with the light sensitive material of a sensitized printing plate, and then directing light through both the carrier and the tissue sheet and onto the light sensitive material of such printing plate,

whereby the matter of both images is combined on the finished printing plate.

3. The method of producing a printing plate for use in offset printing, which comprises taking a duplex paper composed of a thin tissue paper sheet removably secured, throughout the area thereof to which an image is to be applied, to a backing sheet of stiffer material and applying to the outer surface of the tissue sheet thereof in such area and with ink an original in the form of a rightreading image, dusting the outer surface of the tissue sheet with an opaque powder before the ink is dry, removing the powder except where it adheres to the ink, adhering such outer surface of the tissue sheet to a surface of a sheet of baryta paper, stripping said backing sheet from the tissue sheet leaving the latter adhered to the baryta paper, increasing the translucency of the composite baryta and tissue paper in the image bearing area thereof by the application of oil, placing the other surface of the tissue sheet in contact with the light sensitive material of a sensitized printing plate, and then directing light through both the baryta paper and tissue sheet and onto such light sensitive material.

4. The method of producing a printing plate for use in offset printing, which comprises taking a duplex paper composed of a thin tissue paper sheet removably secured, throughout the area thereof to which an image is to be applied, to a backing sheet of stiffer material and mechanically applying to the outer surface of the tissue sheet thereof in such area an original in the form of an opaque right-reading image, adhering such outer surface of the tissue sheet to a surface of a sheet of baryta paper, stripping said backing sheet from the tissue sheet leaving the latter adhered to the baryta paper, increasing the translucency of the composite baryta and tissue paper in the image bearing area thereof by the application of oil, placing the other surface of the tissue sheet in contact with the light sensitive materialof a sensitized printing plate, and then directing light through both the baryta paper and tissue sheet and onto such light sensitive material.

5. The method of producing a printing plate for use in ofiset printing, which comprises taking a duplex paper composed of a thin tissue paper sheet removably secured, throughout the area thereof to which an image is to be applied, to a backing sheet of stiffer material and mechanically applying to the outer surface of the tissue sheet thereof in such area an original in the form of an opaque right-reading image using an ink that is capable of being absorbed through the tissue sheet so that such image extends to the other surface of said tissue sheet, adhering such outer surface of the tissue sheet to a surface of a carrier constituted of a sheet of baryta paper having substantially greater stiffness and strength than the paper of the tissue sheet, stripping said backing sheet from the tissue sheet leaving the latter adhered to the carrier baryta sheet, increasing the translucency of the baryta sheet by the application of oil, placing the other surface of the tissue sheet in contact with the light sensitive material of a sensitized printing plate and with the inner surface of said image against such light sensitive material to substantially eliminate light creep, and then directing light through both the oiled baryta and tissue sheets and onto such light sensitive material in the area of said sheets in which the outer surface of said image at the outer surface of said tissue sheet is not opposed to such directed light.

References Cited in the file of this patent UNITED STATES PATENTS 729,803 St. John June 2, 1903 971,009 Ippers Sept. 20, 1910 (Other references on following page) 7 UNITED STATES PATENTS Seyfierth July 1, 1924 Wheelright Oct. 15, 1935 Buckingham Jan. 30, 1951 FOREIGN PATENTS Great Britain of 1895 8 OTHER REFERENCES Modern Photoengraving, by Flader, pub. Modern Photoengraving, 1948, page 167. G.P.O., Transparent Proofs from Type Forms, Bulletin C3, Government Printing Oflice, 1951, pages 1-18.

G.P.O., Transparent Proofs from Type Forms, Bulletin C-3, Government Printing Oflice, 1951, pages 1-2.

Claims

4. THE METHOD OF PRODUCING A PRINTING PLATE FOR USE IN OFFSET PRINTING, WHICH COMPRISINGS TAKING A DUPLEX PAPER COMPOSED OF A THIN TISSUE PAPER SHEET REMOVABLY SECURED, THROUGHOUT THE AREA THEREOF TO WHICH AN IMAGE IS TO BE APPLIED, TO A BACKING SHEET OF STIFFER MATERIAL AND MECHANICALLY APPLYING TO THE OUTER STIFFER MATERIAL AND SHEET THEREOF IN SUCH AREA AN OPRIGINAL IN THE FORM OF AN OPAQUE RIGHT-READING IMAGE, ADHERING SUCH OUTER SURFACE OF THE TISSUE SHEET TO A SURFACE OF A SHEET OF BARYTA PAPER, STRIPPING SAID BACKING SHEET FROM THE TISSUE SHEET LEAVING THE LATTER ADHERED TO THE BARYTA PAPER, INCREASING TRHE TRANSLUCENCY OF THE COMPOSITE BARYTA AND TISSUE PAPER IN THE IMAGE BEARING AREA THEREOF BY THE APPLICATION OF OIL PLACING THE OTHER SURFACE OF THE TISSUE SHEET IN CONTACT WITH THE LIGHT SENSITIVE MATERIAL OF A SENSITIZED PRINTING PLATE, AND THEN DIRECTING LIGHT THROUGH BOTH THE BARYTA PAPER AND TISSUE SHEET AND ONTO SUCH LIGHT SENSITIVE MATERIAL