US2494053A - Photolithographic printing materials - Google Patents

Description

Jan. l0, 1950 c. H. MlTsoN ETAL v 2,494,053

PHOTOLITHOGRAPHIC PRINTING MATERIALS Filed March 17', 1944l F/GJ;

Patented Jan. 10, 1,950

PHOTOLITHOGRAPHIC PRINTING MATERIALS Charles Howard Mitson and Erich Eduard Loening, Wealdstone, England, assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 17, 1944, Serial No. 526,984 In Great Britain March '22, 1943 14 Claims.

This invention is primarily concerned with the formation of designs in sheets to enable them to be used as the printing surfaces for greasy inks in rotary offset printing machines for oflice use, but it is also applicable to the formation of designs in other lithographie (particularly photolithographie) printing materials and in addition to the formation of designs in materials for other purposes. rThe term "design in this specification is used in the widest sense to include lettering, maps, pictures and any other matter normally capable of representation by black and white or other contrasting colours.

If parts of a cellulose derivate, e. g. a cellulose acetate, are hydrolysed, their physical properties become different fro-m those of the remaining parts. It is known to make use of this fact in the preparation of printing surfaces, but the processes proposed hitherto suffer from various disadvantages. Thus in a process described in British Specification No. 368,083 a photographically produced, chrome-albumen reproduction of the desired design is superposed on a hydrolysable sheet and the hydrolysis takes place over the areas not covered by this reproduction; it is necessary to protect the chrome-albumen itself from the hydrolysing agent, e. g. by asphalt or lithographie ink (which is a greasy ink), and this introduces diiculty. Again, in a process described in German Specification No. 509,010 a cellulose acetate surface is hydrolysed all over and coated with a light-sensitive layer in which the desired image is produced and then part of the layer is removed image-Wise so as to leave an image in gum for printing purposes, but such gum images are liable to Wear out when a number of prints are taken from them. One reason for this is that in this process as in that of British Specification No. 368,083, the parts Whichtake the ink are those superposed on the foundation and so are particularly liable to Wear away, Whereas if the foundation itself takes the ink and an ink-repellent design is formed the printing properties can be maintained much longer.

The present invention is based essentially on the idea of using a stencil of the design as a temporary measure to enable some areas of a hydrolysed surface to be so treated that they display surfaces of different chemical composition, use being directly made of the resulta-nt different properties of the different areas. For our purposes the eifect of the treatment is the same as if the treated areas were less hydrolysed than the others. Thus if the product is to be used for photolithographic printing the areas that are to accept the printing ink must be of an ink-receptive composition and the remaining areas must be hydrolysed to a sufficient degree to repel ink when they are wet. If, on the other hand, the product is, for instance,.to be differentially coloured the areas to be coloured must by virtue of their diiference in chemical composition have the property of absorbing a dye to a greater extent than thewother areas. l

According to the invention the stencil is superposed on a surface that has been-uniformly.hy-v drolysed and serves to protect areas of that surface while the other areas are selectively removed or lconverted to a diiferent chemical composition and thereafter the stencil is removed tov expose the protected hydrolysed areas. At .thevtime'of the removal or rconxv/ersion the surface is a uniform .state of hydrolysis, that-is to say,-is hydrolysed ythroughout the Whole Working surface to a substantially uniform depth and degree of hydrolysis.

The stencil is preferably photographically produced and it may be formed in situ -or a preformed lstencil may be applied to the hydrolysed surface, e. g. by a transfer process of the kind used in photography, and if it is formed in situ the surface may .be hydrolysed before the formation of the stencil or hydrolysis may be effected during or after the formation of the stencil. If the stencil is formed after the hydrolysis or a preformed stencil is used, a prehydrolysed layer may be usedas the starting material.

In producing a printing surface the hy drolysable substance may be in the form of a simple ink-receptive layer, and then of course the.

depth of the hydrolysis must be controlled so that there is non-hydrolysed-material left beneath it to form the ink-receptive areas. Alternatively a multi-layer sheet having a hydrolysable layer as Aa face layer may be used, and then the-hydrolysis may proceed through the Whole or only part of the face layer. If it does not penetrate through the Whole of the face layer, the layer or layers underneath simply form a reinforcing support, but if it penetrates through the Whole of the face layer the supporting layer, though it may or may lnot be hydrolysable, must provide the inkreceptive areas of the final surface, and it may for instance be cellulose nitrate.

In any case, the substance from which the hydrolys-able (or hydrolysed) layer is formed preferably consists of cellulose acetate. However other materials may be used, provided that they hydrolyse to give a solid or jelly-like product and that if s. printing surface is being produced they 3 are ink-receptive and can be hydrolysed to an ink-repellent state. Further, if the hydrolysis is to be effected before or during the formation of the stencil and an alkaline developer is used the hydrolysed product, while being hydrophilic, must be insoluble in dilute alkali solutions such as are used in developers. Examples of materials which may be used instead of cellulose acetates are other esters such as cellulose esters (especially organic esters for instance fatty acid esters e. g. cellulose butyrates and cellulose propionates and any mixture of acetates,n propionates and butyrates of cellulose) and resins of an ester character. Further examples are polyvinyl acetates, polyvinyl butyrates and polyvinyl propionates, which may be used alone or mixed with a non-hydrolysable material, e. g. a polyvinyl acetal, in order to impart additional strength to the final hydrolysed sheet. Cellulose nitrate may also be used if a suiciently strong hydrolysing agent is employed.

Fig. 1 is a sectional view through a multi-layer strip or sheet used in forming a stencil;

Fig. 2 is a view similar to Fig. 1 showing the sheet after exposure and development;

Fig. 3 shows the sheet after the unprotected portions of the hydrolysed layer are removed to expose the non-hydrolysed layer;

Fig. 4 shows the sheet after the removal of the stencil layer to expose the previously protected hydrolysed layer;

Fig. 5 is a view similar to Fig. 2 but in which the exposed portions of the hydrolysed'layer'are converted to a different chemical composition;

Fig. 6 is a view of the sheet shown in Fig. 5 with the stencil layer removed;

Fig. '7 is a view similar to Fig. 1 but-showing a multi-layer sheet the layers of which areY formed of diierent materials, only one of which is hydrolysable;

Fig. 8 shows the strip of Fig. '7 when the hydrolysable layer is hydrolysed and a photographic emulsion layer applied;

Fig. 9 shows a sheet with a metal base coated with a hydrolysable layer carrying a gelatine photographic emulsion;

Fig. l0 shows the sheet of Fig. 9 after the emulsion layer has been exposed and developed; and

Fig. 11 shows the sheet of Fig. 10 after'V the hydrolysable layer has been hydrolysed.

An example of a process for preparing a printing material in which the surface is hydrolysed before the formation of the stencil will now be described with reference to Figures 1 to 4 of the accompanying purely diagrammatic drawings.

The starting material is a single-layer sheet about 0.005" thick of a cellulose acetate that has an ink-receptive surface.` This is hydrolysed in an aqueous solution of caustic alkali (50% solution of sodium hydroxide) for from 2 to 5 minutes to bring about hydrolysis of the surface to a uniform extent and thus convert the sheet into a layer l (probably less than 0.001" thick), hydrolysed to such an extent that when wet it will repel ink, and a layer 2 that has been unaffected by the treatment. The alkali is washed out and the sheet is coated with a layer 3 of an unhardened light-sensitive gelatine emulsion containing silver halide, that is to say, a layer in which a stencil may be formed by photography. The material at this stage is shown in Figure 1. After exposure of the layer 3 under a positive of the desired design (preferably through the layer 2) the material is subjected to the action of a tanning developer. Ihis leads to hardening of the parts on which the light has acted, and the unhardened parts of the layer 3 are removed in the usual way, leaving a stencil 4, as shown in Figure 2. The stencil is dried and the areas of the layer I not protected by it are then removed. This is done with a solution of zinc chloride (60 B.), which is poured on the sheet and distributed over its surface, and

. rubbed with cotton wool.

the surface is then immediately and vigorously By this means, areas of the layer I are removed and cellulose acetate areas 5 underneath are laid bare, as shown in Figure 3. These areas 5 match the design and correspond, for instance, to the lines of a map. The stencil is then entirely removed to expose the protected hydrolysed areas having ink-repellent surfaces beneath it; this may be done by treatment with a solution of sodium hypochlorite, and after a short rinsing and removal of the surplus Water the sheet, as shown in Figure 4, presents the lines 5 of the design as an engraved intaglio which easily accepts fatty inks, Whereas the surrounding areas E when wet repel the ink.

A particular advantage of the process just described is that the starting material is a readily available commercial product and that the process is simple and produces an excellent printing surface.

In the example described above the hydrolysed areas are removed by being dissolved and as is indicated by the example this is preferably done by means of a solution containing zinc chloride. It may be desirable to add ethyl lactate to the zinc chloride, as it serves to etch the acetate and to facilitate the removal of the hydrolysed material. Other solvents which are suitable for dispersing or dissolving the hydrolysed surface layer, such for example as lactic acidor copper ammonium hydroxide or any other cellulose hydrate solvent, may also be used. Alternatively solvents can be used which do not actually dissolve the hydrolysed surface layer, but which are able to penetrate this layer and to attack the layer beneath it, and which thereby loosen the hold of the surface layer, which can then be mechanically removed by rubbing. If the layer beneath consists of cellulose acetate or cellulose nitrate such solvents as acetone, ethyl acetate, amyl acetate or its mixtures are suitable for this purpose.

Instead of removing the areas 5 they may be converted into a different chemical composition by treatment with a liquid containing a solvent for a constituent of the material presenting those areas. For instance it is found that if a solution of Zinc chloride and ethyl lactate (two volumes of Zinc chloride of 55 B. and one volume of commercial ethyl lactate) is used, but the surface is only lightly rubbed with cotton wool wetted with the solution, the areas 5 undergo some chemical conversion, the nature of which is not at present understood and which may or may not involve chemical reaction, but which leaves them ink-receptive. It seems likely that this change in chemical composition involves an alteration in the ratio of hydrate to ester, possibly by the solvent action of the ethyl lactate on the underlying ester with subsequent dispersion of the ester throughout the hydrate. However this may be, it will be understood that the different areas must be substantially different in their chemical composition if effective use is to be made of them for printing or other purposes. Thus the material instead of being as shown in Figure 3 is as shown in Figure 5, in which the converted' parts are show'n" at 2A. The stencil isinextremoved by treatment with a hypochlorite solution to expose the hydrophilic parts 6, as show-nin Figure 6. Again, a resin, e. g'. a phenolald'ehyd'e resin, dissolved in a solvent for a constituent of the material may be rubbed over' the surface untill it forms a coating on the hydrolysed areas'. rf course, the resin must be so chosen thatv at' the most it forms on thev stencil only a coating which will permit the subsequent removal of the stencil with the coating by, for example, ahypochlorite solution. Naturally the resin must be or must form with the hydrolysed areas an ink-receptive surface if printing plates are being made.

An example of the use of a multi-layer sheet isillustrated in Figures '7 and 8. Here there is a supporting layer l of cellulose nitrate or other ink-accepting material that either cannot be hydrolysed' or can be hydolysed only with diiculty, and itis covered with a sheet of cellulose acetate 2B or other easily hydrolysable material, this sheet then being hydolysed throughout its whole depth. Figure 8 shows the material after the Whole ofthe acetate layer has been hydrolysed into a layer IB and a photographic emulsion layer 3` has been applied. Thereafter the method may be the same as that described with reference to Figures 2 to 4. This method has the advantage that the hydrolysis is more easily controlled as it cannot easily penetrate further than through theA layer ofv cellulose acetate andthe back of the material is not aifected by the hydrolysis. The support layer 'l will then offer greater mechanical resistance during the printing operation than a sheet of hydrolysed cellulose acetate, which would normally havel been acted upon at both surfaces. Alternatively a protective lacquer may be used on the reverse side' of the cellulose acetate or other hydrolysable layer for the same purpose.

If the hydrolysis is effectedv after a gelatine stencil has been formed, the hydrolysis takes place through the stencil. The sheet may be immersed in a` hydrolysing solution, preferably while it is still wet after being developed with a tanning developer and washed. It is found that a gelatine. photographic emulsion does not unduly impede the hydrolysis. This method is illustrated in Figures 9, 1'0 and 11. Figure 9 shows a cellulose acetate layer 2C carried by a support l of cellulose nitrate or metal, e'. g. zinc, and coated with a layer 3 of a gelatine emulsion containing a silver halide. After an image has been formed and developed in a tanning developer the untanned parts are removed so that a stencil 4 is formed as shown in Figure l0. Next the whole sheet is immersed in a hydrolysing solution. Care must be taken not to soften or destroy the stencil, which is needed for the subsequent operations. Concentrated' caustic solutions (20 to 50%) are unsuitable but efficient hydrolysis can be effected by solutions of low concentration, e. g. 2%, especially if they are mixed with solvents capable of penetrating into the surface of cellulose acetate, for example, alcohol or acetone. As an example the following solution can be used:

Cc. sodium hydroxide 200 Commercial alcohol 400 Acetone v r 10 Water to 1,000

The sheet is immersed in such a solution until the desired state of hydrolysis is obtained, the necessary time usually being from 5 to 10 minutes.

Cil

The resultant sheet with the whole acetate layer- 2C so hydrolysed converted into a layer IC' is shown in-Figure 11.v The remainingsteps may be as described with reference to Figures 3 and 4.

If the hydrolysis is effected duringv the formation of the stencil, a solution may be usedv which acts'. simultaneously as a tanning developer and as a hydrolysing agent, consisting,.for example', of equal parts of a 2.5% aqueous solution of pyrocatecholv and a solution containing:

Cc. 2% sodium hydroxide 500 Commercial alcohol 450 Acetone 50 The alkali content of this developer being unusually high, the tanning action of the developer should be interrupted after, say, 30' to 40 seconds by' the addition of strong sodium sulphite solution, and in order to'allow sufficient time for the hydrolysis the sheet may remain for further 4 to 5 minutes in the developer if necessary.

In these methods in' which the hydrolysis takes place during or after the formation of the` stencil the substance that is hydrolysed' must not be one which is so dincult tohydrolyse that it requires such a powerful hydrolysing solution that theA solution destroys the stencil. When substances that need such solutions are used the hydrolysis must be performed before the photographic layer is applied. For instance, cellulose nitrate cannot be employed in the above examples of thev process unless the hydrolysis is performed before the photographic layer is applied.

The stencil itself may be formed in any suitable way and not merely in the way described inthe' example. For instance, a bichromated colloid may be used instead of a silver halide emulsion, or non-tanning development of a silver halide emulsion followed by imagewise bichromat'e hardening may be used instead of tanning development. Again any reversal process can be used, such for example as etch-bleaching with the wellknown solution containing hydrogen peroxide when a negative stencil is formed from a negative original. If necessary the stencil may be hardened by a hardening agent after being. formed and before being treated further.

When a preformed stencil is used it is still preferably photographically produced and it may be transferred in the form of a light-sensitive emulsion layer containing a latent image, a developed and unxed image or a developed and xed image, or it may be a completely finished stencil layer. In any of these cases, the material that is being transferred may be soaked and then pressed onto the hydrolysed surface by a squeegee.

As indicated above the invention is useful for other purposes in addition to printing. As an example a coloured design may be: produced by treating a sheet in which the design areas are cellulose acetate and the other areas are hydrolysed cellulose acetate with the dyes known as Methyl Violet (Colour Index No. 680)y and Malachite' Green (Colour Index No. 657). If it is the hydrolysed areas that are to be coloured preferentially to areas of cellulose acetate, Cotton Blue (Colour Index 706; Schultz No. 816. second volume, 7th edition) (Hopkins and Williams Ltd), Congo Red (Colour Index No.A 370) and Chrysophenine (Colour Index No. 365) may be used. Any of these dyes may be appliedv by simply wiping an aqueous solution of the dye over the sheet.

We claim:

l. A method of producing a printing surface containing a design by treating a layer of an inkreceptive substance which can be hydrolysed to be ink-repellent when Wet, characterised in that a surface of the layer that is in the ink-receptive state is coated With a light-sensitive layer in which a stencil may be formed by photography, the surface is uniformly hydrolysed to the inkrepellent state, a stencil of the design is photographically produced in the layer coated on the hydrolysed surface, the hydrolysed material not protected by the stencil is removed to expose inkreceptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it. 2. A method of producing a printing surface containing a design by treating a layer of an inkreceptive substance which can be hydrolysed to be ink-repellent when wet, characterised in that a surface of the layer that is in the ink-receptive state is coated with a light-sensitive layer in which a stencil may be formed by photography, this layer is exposed to form a latent image of the design in it, the composite sheet is'then subjected to the action of a solution which acts simultaneously as a tanning developer and a hydrolysing agent so as to produce a stencil corresponding to the latent image and to hydrolyse the Whole surface beneath the layer containing the stencil to a uniform extent and into the ink-repellent state, the hydrolysed material not protected by the stencil is removed to expose ink-receptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it.

3. A method of producing a printing surface containing a design by treating a layer of an inkreceptive substance which can be hydrolysed to be ink-repellent when Wet, characterised in that a surface of the layer that is in the ink-receptive state is coated with a layer of a gelatine emulsion containing a silver halide, a stencil of the design is then photographically produced in the emulsion layer, the composite sheet is immersed in a hydrolysing solution to hydrolyse the surface of the layer of the hydrolysable substance uniformly to the ink-repellent state, the hydrolysed material not protected by the stencil is removed to expose ink-receptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it.

4. A method of producing a printing surface containing a design by treating a layer of cellulose acetate which can be hydrolyzed to be inkrepellent When Wet, characterized in that a surface of said layer that is in the ink-receptive state is coated with a layer of gelatin emulsion containing a silver halide, a stencil of the design is then photographically produced in the emulsion layer, the composite sheet is immersed in a hydrolyzing solution to hydrolyze the surface of a layer of cellulose acetate uniformly to the inkrepellent state, the hydrolyzed material not protected by the stencil is removed to expose inkreceptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it.

5. A method of producing a printing surface containing a design by treating a layer of cellulose acetate which can be hydrolyzed to be inkrepellent when Wet, characterized in that a surface of said layer that is in the ink-receptive state is coated with a layer of gelatin emulsion containing a silver halide, a stencil of the design is then photographically produced in the emulsion layer, the composite sheet is immersed in a hydrolyzing solution to hydrolyze the surface of a layer of cellulose acetate uniformly to the inkrepellent state, the hydrolyzed material not protected by the stencil is removed by zinc chloride to expose ink-receptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it.

6. A method of producing a printing surface containing a design by treating a layer of cellulose acetate which can be hydrolyzed to be ink-repellent When Wet, characterized in that a surface of said layer that is in the ink-receptive state is coated with a layer of gelatin emulsion contaning a silver halide, a stencil of the design is then photographically produced in the emulsion layer, the composite sheet is immersed in a hydrolyzing solution to hydrolyze the surface of a layer of cellulose acetate uniformly to the inkrepellent state, the hydrolyzed material not protected by the stencil is removed by a mixture of zinc chloride and ethyl lactate to expose ink-receptive areas, and the stencil is then removed to expose the ink-repellent areas beneath it.

'7. A method of forming a design in a printing sheet of an ink-receptive material which comprises uniformly hydrolyzing a surface of said sheet to render said surface ink-repellent when wet; selectively removing areas of the surface -that has been uniformly hydrolysed While protecting the remaining areas of said surface by means of a stencil of an image superposed on the hydrolyzed surface, and thereafter removing the stencil to expose the protected hydrolysed areas.

8. A method of forming a design in a printing sheet of an ink-receptive material which comprises unformly hydrolysing the Whole Working surface of a layer of a hydrolysable substance, selectively removing areas of the hydrolysed surface While protecting the remaining areas by means of a stencil of an image superposed on the hydrolysed surface, said removal extending entirely through said surface to expose the inkreceptive portions of the sheet below said removed areas; and thereafter removing the stencil to expose the protected hydrolysed areas.

9. A method of producing a printing surface containing a design by treating a layer of an inkreceptive substance that can be hydrolysed to be ink-repellent when wet, characterized in that areas of a surface of the layer that has been uniformly hydrolysed to be ink-repellent when Wet are selectively removed to leave ink-receptive areas while the remaining areas are protected by a photographically produced stencil of a design, and the stencil is thereafter removed to expose the protected hydrolysed areas.

10. A method of producing a printing surface containing a design by treating a layer of an inkreceptive substance that can be hydrolysed to be ink-repellent when Wet, characterised in that a stencil of the design is photographically formed in a light-sensitive layer applied to a layer of the hydrolysable substance, the surface being uniformly hydrolysed into the ink-repellent state in timed relation to the formation of the stencil,

the areas not protected by the stencil are removed to expose ink-receptive areas, and the stencil is thereafter removed to expose the protected ink-repellent areas.

11. A method of forming a design in a printing sheet of an ink-receptive material Which comprises uniformly hydrolyzing a surface of said sheet to render said surface ink-repellent when wet; selectively removing areas of said surface While protecting the other areas by means of a photographically produced stencil of an image superposed on the hydrolysed surface, said removal extending completely through said surface to expose ink-receptive portions below said removed areas; and thereafter removing the stencil to expose the protected hydrolysed areas.

12. A method of producing a printing surface containing a design by treating a layer of an ink-receptive substance that can be hydrolysed to be ink-repellent when Wet, characterized in that areas of a surface of the layer that has been uniformly hydrolysed to be ink-repellent when Wet are selectively removed to leave exposed inkreceptive areas While the other areas are protected by a photographically produced stencil of the design, said layer being thick enough to leave a non-hydrolysed ink-receptive layer beneath the hydrolysed surface on being subjected to controlled hydrolyses, and thereafter removing the stencil to expose the protected hydrolysed areas.

13. A printing member comprising, a sheet of a cellulose derivative, a hydrolysed surface on said sheet, said surface being ink-repellent when wet, portions of said surface corresponding to a design to be printed being removed to expose an underlying ink-receptive layer of said sheet.

14. A printing member comprising, a sheet of a cellulose derivative, a hydrolysed surface on said sheet, said surface being ink-repellent when wet, and portions of said sheet below said surface and corresponding to a design to be printed being of a composition to receive ink.

CHARLES HOWARD MITSON. ERICH EDUARD LOENING.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 556,380 Stevens Mar. 17, 1896 992,898 Payne May 23, 1911 1,943,486 Ostwald Jan. 16, 1934 2,013,116 Troland Sept. 3, 1935 2,110,496 Babcock Mar. 8, 1936 2,179,245 Wood Nov. 7, 1939 2,276,151 Brandenberger Mar. 10, 1942 2,311,086 Salo Feb. 16, 1943 2,312,499 Lierg Mar. 2, 1943 2,346,008 Clark Apr. 4, 1944 FOREIGN PATENTS Number Country Date 3,453- Great Britain Oct. 5, 1875 509,010 Germany Oct. 4, 1930 337,868 Great Britain Nov. 13, 1930 385,274 Great Britain Mar. 16, 1931 368,083 Great Britain Mar. 3, 1932 599,897 Germany July 11, 1934 648,333 Germany July 28, 1937 650,372 Germany Sept. 18, 1937 496,049 Great Britain Nov. 21, 1948

Claims (2)

1. 7. A METHOD OF FORMING A DESIGN IN A PRINTING SHEET OF AN INK-RECEPTIVE MATERIAL WHICH COMPRISES UNIFORMLY HYDROLYZING A SURFACE OF SAID SHEET TO RENDER SAID SURFACE INK-REPELLENT WHEN WET; SELECTIVELY REMOVING AREAS OF THE SURFACE THAT HAS BEEN UNIFORMLY HYDROLYSED WHILE PROTECTING THE REMAINING AREAS OF SAID SURFACE BY MEANS OF A STENCIL OF AN IMAGE SUPERPOSED ON THE HYDROLYZED SURFACE, AND THEREAFTER REMOVING THE STENCIL TO EXPOSE THE PROTECTED HYDROLYSED AREAS.
2. 13. A PRINTING MEMBER COMPRISING, A SHEET OF A CELLULOSE DERIVATIVE, A HYDROLYSED SURFACE ON SAID SHEET, SAID SURFACE BEING INK-REPELLANT WHEN WET, PORTIONS OF SAID SURFACE CORRESPONDING TO A DESIGN TO BE PRINTED BEING REMOVED TO EXPOSE AN UNDERLYING INK-RECEPTIVE LAYER OF SAID SHEET.

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