US2734298A

US2734298A - Mechanical negative process and resist

Info

Publication number: US2734298A
Authority: US
Priority date: 1952-06-21
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

United States Patent MECHANICAL NEGATIVE PROCESS AND RESIST Harold A. Molz, Arlington, Va., and James Edward Peake, Bladenshurg, Md.

No Drawing. Application June 21, 1952, Serial No. 294,934

8 Claims. (Cl. 41-46) This invention relates to processes of producing films adapted for use in the preparation of photolithographic plates and the like. More specifically, the invention relates to processes of preparing either positives or negatives of such films directly from hot type without the aid of lenses, cameras, dark rooms or other specialized photographic equipment. The films produced in accordance with the teachings of the present invention are comparable in use and quality to conventional films in use in the art of producing lithographic printing plates and are even superior in some respects.

The invention contemplates the production of lithographic negatives and/or positlvesdirectly from hot type, that is, type produced from a linotype machine, a monotype machine or hand-set machine-cast type, or type hand-set from a case of type. The negative or positive is produced without the use of a camera and without the use of any equipment other than that normally used in the process of preparing and set-ting type and pulling proofs on paper or acetate sheets, with the exception however that the present process uses ordinary commercial photographic film and more particularly those films now normally used in the lithographic art, which films are characterized in that they have a fine grain, relatively thin emulsion coating and an. extremely high contrast. In the processing of such films, commercially available developing and fixing baths and dissolving solutions are used. However, a special resist may be employed under certain conditions as indicated hereinafter.

In the conventional method of preparing films for use in the preparation of lithographic printing plates, it is customary to set up the type or other material to be copied end, after inking the type a page proof is made. The

impression made on the page proof is. then photographed with a commercial type camera having lenses particularly adapted for the type of work in question and as a result of the photographing of the material on. the page proof a film negative is prepared in the usual mannor by employing a dark room and the. successive chemical treatments ordinarily used in developing conventional films. Care must be taken to see. that the film is not pre-exposed before it is placed in the camera and care must also be taken to. see thatthe film is not exposed to light uponor after being removed from the camera until the. developing process has been completed under dark room eonditions..

An important aspect of the present invention is that any photosensitive, article. comprising a transparent or trans- ,lucentbase; being provided on one. surface thereof with a highrcontrast emulsion such as. that known in the trade as Eastman Kodalitlr Film or Duponts LithoTransparent paperfilrn may be used as the photographic film. The light-sensitive emulsion such as silver halide, on the surface of such-a film is printed from a blanket with a certain typeresist, ina manner such as referre'd to as dry offset to impress. thereon the image desired. in the ultimate photolithographic plate. Thepresentfinvention contemplates that a resist comprise a fluorescein of the Rhodamine type since such resist has proved most successful in the present process. The film, after having an image printed thereon is, before or after impression, subjected to exposure to normal room light (or stronger) and is treated with certain developing and fixing baths to produce a lithographic film capable of use directly in the lithographic printing art, that is, a lithographic printing plate can be made directly from the film so produced.

An important object of the invention is to provide a particular class of resists which will be stable and insoluble in the presence of either a developing solution or hypo solution, and yet be capable of being removed by nonaqueous solvents. Thus when the printed or impressed film, having been printed or impressed on its, emulsion side, is placed in one of the well known developers, such as Eastman Kodalith Developer, the resist will stand up, that is, not react with or be dissolved by the developer whereby the emulsion lying directly beneath such resist is protected and preserved .until a later stage in the process. Upon further treatment of the resist with a non aqueous solvent such as varsol, gasoline, turpentine, or the like, the resist will be dissolved and removed from the surface of the film. Thereafter, the film is placed in a fixing bath such as sodium thiosulphate solution and afterwards washed and dried to produce the desired negative.

if it is desired to produce a positive film, it may be done by reversing the sequence of the developing and fixing steps. Thus, when the printed or impressed film, having been printed or impressed on its emulsion side, is placed first in a fixing bath such as sodium thiosulphatc solution, the resist will stand up, that is, not be altered or dissolved whereby the emulsion lying directly beneath such resist is protected and preserved until it is desired to remove the resist. The resist is removed with a nonaqueous solvent such as a solution of varsol, gasoline, turpentine or the like, in the manner indicated in connectionwith the preparation of the negative. After removal of the resist, the film is placed in a developer, such as Eastman Kodalith Developer, to develop the previously protected portions of the film and afterwards the film is washed and dried in the usual manner to produce the desired positive.

A further object of the invention is to provide either a wrong reading negative or positive as the film is viewed from the emulsion side. Whether the film produced is a negative or a positive is determined bythe particular sequence in which the particular film treating steps are used as pointed out hereinbefore.

A further object of the invention is to provide a particular type resist which is particularly adapted'for use in the process of the present invention, said resist preferably comprising as a pigment one of the fluorescein dyes which dyes are well known in the art relating to printing inks. It has been found that the resist which isbest adapted to the present process consists of a Rhodamine B toner resist which is approximately 30% pigment by weight.

A further object of the invention is to provide methods of producing lithographic film negatives and/ or positives from hot type. Whether or not the negatives and/or positives thus produced are wrong reading or right reading when viewed from the emulsion'surf'ace can be determined, first, as towhether or not the emulsion surface of the film was impressed by dry offset from the blanket of a proof press, or secondly, whether or not the emulsified surface was'irnpressed directly from the type of a proof press, and further the fact that the thus impressed films can be made positive or negative" as determined by selection of the particular sequence of steps to which the films are subjected. A

A further object of the invention is to provide methods of producing either multiple wrong reading" negatives from a right reading positive, or multiple wrong reading positives from a right reading negative.

A further object of the invention comprises the production of lithographic film positives or negatives from a well known type proof press in which the emulsion surface of the film is impressed with an image from the blanket of such a machine, the film having been delivered to the grippers emulsion side down or impressed from the type of such a press. In the latter instance, the film is delivered to the grippers emulsion side up to take the impression directly from the type.

Now, describing the process more particularly with re spect to the features of novelty therein, printing type of any construction is set up in the bed of any proof press designed to print simultaneously both sides of a sheet of paper, acetate, etc. such as a Vandercook 4T. It will be understood that such type, when so set, is known in the art as wrong reading. The surface of the type form is then inked up in the normal manner with the novel resist which the present invention discloses, such resist, by way of example, consisting of 30% Rhodamine B, 30% No. 1 varnish and 30% blanc fixe" (extender) plus about of other extender (inorganic salts or other materials used to make ink commercially practical) such resist being a quick setting, non-drying, high tact resist. The type of resist we have found to be best suitable for our process and by way of example consists by weight of 11% parts lithographic linseed varnish #1 (regular); 13 parts blanc fixe (precipitated barium sulphate); 2 parts precipitated calcium carbonate; 10% parts Rhodamine B, pigment toner and a very small amount of a chemical anti-skinning" agent. Next, in the process, an impression is transferred on the usual blanket, which impression is right reading. That is, the impression onto the blanket is an image of the type which was set up in the proof press, which type was set up wrong reading and thus when the impression was transferred to the blanket the same was right reading in that the impression was reversed end for end, or as a mirror image so to speak. Of course, it would be possible to set the type in the press in right reading form and the impression thus produced from such would be wrong reading, wherein, if desired, the impression on the emulsion surface of the film would be right reading. After the blanket has been thus impressed with the type, the image on the blanket is then transferred to the emulsion side of the film, which impression, as viewed from the emulsion side of the film, will be wrong reading. The same could be impressed in right reading form if so desired by using right reading type as explained above.

The next step in the process is to expose the impressed film to normal room light (or stronger) if the same has not already been so exposed to thereby fully and completely expose the same. Thereafter, the film is deposited in a tray of film developer such as Eastman Kodalith Developer or to any developer recommended by the manu facturer of the particular film being used, and we have found that excellent results have been obtained by a developer consisting of the following formula, by way of example:

Water, about 90 F 64 oz. (Avd. or U. S. Liq.)

This developer develops to a dense black color all portions of the emulsion surface of the film other than those portions covered by the resist image. The importance here is the fact that the resist is so composed as to resist attack by the developer and consequently that portion .4 of the emulsion covered by the resist is not developed.

The next step in the process is to wash off from the surface of the film as much of the developer solution as possible by immersing the film for a short time in tap water. Thereafter, the film which now carries the resist only on those portions of the film Whereon the image was impressed is immersed in a bath of a non-aqueous resist-dissolving solution, such as a solution of varsol, gasoline, turpentine or the like, and at the same time swabbing the film gently with a cotton wad or the like to facilitate removal of the resist.

The next step in the treatment of the film comprises placing the film in a so-called hypo bath. For this purpose, there may be employed a fixing bath such as a solution of sodium thiosulphate consisting of the followmg:

Water, about 125 F oz Sodium thiosulfate lbs 3 Ammonium chloride oz 6% Sodium sulfite, dessicated oz 2 Acetic acid (28%) fiuid oz 6 Boric acid crystals oz 1 Potassium alum oz 2 Cold water to make gallon 1 Action of the hypo bath on the film will remove the emulsion in those portions which were protected by the resist and which were consequently not developed, dissolved or attacked by the developer. In this manner, there is produced a clear, sharp negative which is wrong reading when viewed from the emulsion side of the film. Thereafter, the film is washed in water for a few minutes to remove the excess hypo and is hung to dry.

In the event a positive print is desired, as where the same is to be used in a deep etch plate-making procedure, it is only necessary to first apply to the emulsion surface of the film the resist image desired and then to treat the film with the aforementioned sodium thiosulphate solution (hypo). The hypo solution in this procedure removes all of the salts of the emulsion carried on the film except those portions protected by the resist, which of course would be the matter transferred from the impression blanket, it being understood that the resist is so composed as to be insoluble in and unaffected by the hypo. Such treatment makes the film entirely transparent except for the portions protected and covered by the resist. After the hypo treatment has been completed, the film is washed in water, and is then deposited in a tray of a non-aqueous dissolving solution such as a solution of varsol, gasoline, turpentine or the like, which solution will dissolve the resist from the emulsion which has been protected thereby. The film is then Washed in water and thereafter placed in a developing bath of the type described hereinbefore. As a result of this step, that portion of the emulsion which was directly beneath the resist will show black on a translucent background and thereby produce a positive film having a wrong reading impression thereon when viewed from the emulsion side of the film. It will therefore readily be seen that in the production of such a positive film that no camera is needed, and no photographic negative need be produced to make such a positive therefrom as is the usual practice. The wrong reading positive thus produced is particularly suitable for use in making deep etch lithographic printing plates.

As heretofore stated, if it is found to be desirable to produce a negative or positive lithographic film from a film which has had its emulsion surface impressed directly from a type, it is possible to do so. During the process of producing such films, it should be understood that a proof press of any well known type may be used and the type may be set up in the bed of the press and then covered with the particular resist of the present invention by the usual inking rollers. Thereafter, the usual tympan or blanket cylinder is passed over the type to. impress the film and, in this feature of the invention,- the lithographic film is inserted in the grippers on the t-ympan or blanket cylinder with the emulsion side of the film facing away from thetympan or blanket so that when the tympan or blanket cylinder is moved across the type bed, the resist image is impressed to the emulsion surface of the film directly from the type. The film impressed in this manner is right reading because it has taken an impression from the wrong reading type. When this film. is treated in either of the sequence of steps set forth above, we. obtain either a negative or positive, both right reading, depending upon the. sequence selected. Whether the film is negative or positive. is determined by whether the film is treated first with the developer, next with the solvent, and next with the hypo to produce a right reading negative or by treating the film in the sequence of first with the hypo, next with the solvent and finally with the developer to thereby produce a right reading positive. It will be understood that the film may be washed with ordinary tap water between the various steps of the process. It can not readily be seen that if the right reading negative thus produced is placed with its emulsion surface adjacent or in contact with the emulsion surface of an unimpressed and unexposed film and light is passed through the negative film to the unimpressed film, a wrong reading positive will be produced. Conversely, if the impressed surface'emulsion side of the positive right reading film is positioned in contact with or adjacent the emulsion surface of an unimpressed and unexposed film, and light is passed through from the side of the positive, a wrong reading negative will be produced. Therefore, such right reading negatives or positives are used when it is desired to make multiples or duplicates of like subject matter. The wrong reading negatives produced from the positive film may be used for making albumin process plates while the wrong reading positives can be used in deep-etch work. It should be understood that the application of the resist to the emulsion surface of the film can be done by hand rather than from type or by a machine and the type can be set by hand or otherwise and therefore no proof press is essential in carrying out the process insofar as the present method of producing right reading negatives and positives is concerned.

In order to produce a white opaque positive, it is only necessary to perform first the step of placing the film in a hypo which will remove all of the salts of the emulsion other than that protected by the resist, then, dissolve the resist by placing the film in a bath of a dissolving solution such as varsol, gasoline, or the like, and after using the developing bath a bleaching bath containing some well known silver bleaching chemical such as sodium hypochlorite can be used. The bleaching bath bleeches the developed portions of the impressed image and such portions are rendered partially opaque.

It will therefore be understood that in the process outlined above, that there have been disclosed a number of processes of producing and making either positive or negative films for use with lithographic printing, first of all by providing methods in which either a photolith negalive for producing albumen plates or a photolith positive for producing deepetch plates may be prepared in both of which the reading is wrong reading when viewed from the emulsion side. Inasmuch as lithographic plates are normally right reading, it is highly desirable that the impressed fihn be wrong reading when viewed from the emulsion side so that the emulsion side of the film can be placed directly in contact with the sensitized surface of the lithographic plate and thereby avoid any spread or undercutting of the light when using the present film for producing the printing plates.

Dark room conditions are not necessary and as a matter of fact the entire sheet of film must be preexposed before the processes can be performed.

With the processes above disclosed corrections are much simplified in that all that is necessary is to correct the type and pull a new negative which will eliminate the time consuming step of stripping-in appropriate corrections.

And again in the present method, the negative may be ruled with the resist by a scriber directly on the negative.

While the particular resist above disclosed has been found entirely satisfactory for the present process, it is contemplated that many other fluorescein pigments may be used in place of the Rhodamine B above disclosed to obtain a similar result.

What is claimed is:

1. A protective resist for use in the preparation of a film for making lithographic plates comprising approximately 30% Rhodamine B pigment and approximately 60% of a carrier therefor comprising approximately equal parts of varnish and blanc fixe and approximately 10% inorganic salt extenders.

2. The method of making from a uniformly preexposed silver halide emulsion coated lithographic film a negative from which printing plates may be produced, comprising the steps of applying tothe face of type an image-producing resist of the composition set forth in claim 1, transferring the resist from the type face to a printing blanket, transferring the resist from the printing blanket to the emulsion side of said uniformly preexposed film, completely exposing the film to light, subjecting the exposed film to a first chemically active agent reactive with the emulsion surface of the film but not reactive with said resist, dissolving the resist, reacting the protected portion with a second agent to produce an image of said type face on said film, and finally washing and drying the negative thus produced.

3. The process of making, for use in producing multiple positives, a right reading negative from a uniformly pre-exposed silver halide emulsion coated lithographic film comprising the steps of impressing a protective resist of the composition set forth in claim 1 on selected areas of the emulsion surface of the film, treating the film so impressed with a silver halide developer to develop that portion of the emulsion not covered by the resist, applying a solvent to the resist to remove said resist from said surface, treating the film with a thiosulfate solution to remove from the film the previously protected portion of said emulsion, and washing the negative thus produced.

4. The process of making, for use in producing multiple negatives, a right reading positive from a uniformly pre-exposed silver halide emulsion coated lithographic film comprising the steps of impressing a protective rcsist of the composition set forth in claim 1 on selected areas of the emulsion surface of the film, treating the film so impressed with a thiosulfate solution to remove from the film that portion of the emulsion not covered by the resist, applying a solvent to said resist to remove said resist from said surface, treating the film with a silver halide developer to develop the previously protected portion of said surface, and washing the positive thus produced.

5. The method of making a film for use in the production of lithographic plates comprising the steps of impressing on selected areas of the uniformly pre-exposcd silver halide emulsion surface of a light sensitive photographic film a water-insoluble protective resist of the composition set forth in claim 1 which is non-reactive with silver halide photographic developers and thiosulfate solutions, fully exposing the film to light, treating the film with a first chemically reactive photographic solution which is a silver halide developer for the unprotected areas of said emulsion surface, removing the resist with a non-aqueous solvent therefor which is non-reactive with said emulsion surface, treating the previously pro tected areas with a second chemically reactive photographic solution which is a thiosulfate solution reactive with said previously protected areas to produce an image, and then Washing and drying the negative thus produced.

6. The method of making a film for use in the production of lithographic plates comprising the steps of applying to selected areas on the coating of a film having a chemically reactive silver halide coating on one side thereof, in the presence of light, a protective resist of the composition set forth in claim 1, subjecting the film to the action of a solution selected from the class consisting of silver halide developer and thiosulfate solution, removing said resist from said selected areas and subjecting the film to the action of the other member of said class to produce an image on said film corresponding to the selected areas to which said protective resist is applied.

7. The method of making a film for use in the production of lithographic plates comprising the steps of impressing on selected areas of the uniformly pre-exposed silver halide emulsion surface of a light sensitive photographic film a water-insoluble protective resist which is non-reactive with silver halide photographic developers and thiosulfate solution, said resist having the composition set forth in claim 1, fully exposing the film to light, treating the film with a first chemically reactive photographic solution which is reactive with the unprotected areas of said emulsion surface, removing the resist with a non-aqueous solvent therefor which is non-reactive with said emulsion surface, treating the previously protected areas with a second chemically reactive photographic solution which is reactive with said previously protected areas to produce an image, and then washing and drying the negative thus produced.

8. The method of making a film for use in the production of lithographic printing plates, comprising the steps of coating a type face with a resist of the composition set forth in claim 1, transferring said resist from said type face to the silver halide emulsion side of a uniformly pre-exposed light sensitive photographic film, completely exposing the film to light, treating the film with a first agent which reacts with the portion of the emulsion not protected by the resist, washing and treating the film with a solvent for said resist, treating the film with a second agent which reacts with the portion of the emulsion previously protected by the image-resist to render the image permanent, and washing and drying the positive film thus produced.

References Cited in the file of this patent UNITED STATES PATENTS 868,779 Hammer Oct. 22, 1907 1,700,262 Heinecke Jan. 29, 1929 1,892,875 Dietz Jan. 3, 1933 1,901,799 Brooks et al Mar. 14, 1933 1,913,881 Heinecke June 13, 1933 1,922,548 Mattin Aug. 15, 1933 2,152,856 Switzer Apr. 4, 1939 2,306,887 Klose Dec. 29, 1942 2,319,079 Murray et al. May 11, 1943 2,503,790 Yule Apr. 11, 1950