US3218165A - Process for producing continuoustone transparencies - Google Patents

Description

3,218,165 PROCESS FOR PRODUCING CONTINUOUS- TONE TRANSPARENCIES Harold Francis Foote, Ipswich, Mass., assignor of one-half to Lawrence David MacKenzie, Belmont, Mass. No Drawing. Filed May 16, 1962, Ser. No. 195,329 3 Claims. (Cl. 9648) The present invention relates to film transparencies and to processes for producing the same.

Particularly in the commercial photography field, it has long been desired to produce monochromatic and color transparencies having continuous tones in the image, but with absolutely crystal-clear and colorless areas surrounding the image. Numerous approaches to the attainment of these ends have been tried throughout the years, but the art has had to content itself with a residual tone or hue in the so-called White areas of the transparency surrounding the image, primarily because continuous-tone film, in view :of its characteristics for producing continuoustone images, must inherently have a background tonal quality that is not completely clear and colorless. Where, indeed, absolute background clarity and colorlessness is essential, such prohibitively expensive techniques as actually cutting out the images and mounting the same on a colorless transparent surface, have been proposed.

An object of the present invention is to provide a new and improved continuous process for producing monochromatic and/or color transparencies that, while having all of the continuous-tone-film advantages with regard to producing true continuous-tone images, eliminates the previously inherent and disadvantageous tonal background in the so-called white areas of the film surrounding the continuous-tone images, and there provides, to the contrary, an absolutely crystal-clear, colorless background, free from haze and visible imperfections, transparent and optically homogenous.

A further object is to provide such a novel continuous process that obviates both the background-tone and highcost disadvantages above described, and does so with the further advantages of faster processing and more true fine detail.

Still another object is to provide new and improved monochromatic and/ or color transparencies.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims. In summary, however, from one of its broad aspects, the process underlying the invention comprises the steps of exposing a high-contrast photographic film of the type normally used for line and screened negatives and positives; briefly submersing the film in a fast-acting de veloper until just prior to the appearance of white areas of the latent image impressed thereon by the exposure; immediately thereupon rapidly submersing the film in a high-contrast developer provided with low-density cut-off characteristics and, preferably, with means for bleaching heavily exposed areas of development; maintaining the last-named submersion until substantially crystal-clear nontonal colorless transparency of the said white areas is attained; and thereupon short-stopping and fixing the film. Preferred details and transparencies are hereinafter discussed.

In contravention of established practice, the present invention, while concerned with the development of a continuous-tone image, does not, however, follow the convention of employing a continuous-tone film; but, as before nited States Patent explained, employs, to the contrary, so-called line films that have heretofore been employed substantially exclusively for the very different purpose of copying line and screened negatives and positives. The line film is readily distinguishable from the continuous-tone film in several particulars. Line film has a steep low-to-high density characteristic sensitometric curve (i.e. density vs. exposure), which is essential to provide clean edges on lines and half-tone dots, as described, for example, on page 12 of Films and Plates for The Graphic Arts, Kodak Graphic Arts Data Book Q2, Eastman Kodak Company, Fourth edition, 1961. The angular slope of such almost vertical line-film sensitometric curves is of the order of about -85 degrees, more or less, on graphs plotting ensity units (ordinate) as a function of the logarithm of exposure( abscissa), with the units of density and exposure having the same scale. Typical curves of this character are presented, for example, on data sheet D4 of the said book.

Continuous-film, on the other hand (page 10 of the said Data Book), generally has an angular slope in its sensitometric curve that is much less steep, of the order of about 30 to 45 degrees, more or less, in the initial portion thereof. Reference may be made, for example, to data page D-19 of the said book. Other well-known characteristic differences between line and continuous-tone film are the following:

about 4 to 5 erally about 1.5 to 2. Slow emulsion High-speed emulsion. Small grains of quite uniform Large grains of mixed size sizes.

High contrast Low contrast.

Several present-day commercial examples :of line film are those sold under the trademark Kodalith Ortho-Estar Base (Eastman Kodak-data pages D-9 thruogh 9l7 of the said book); under the trade name Reprolith (Ansco); under the mark Photolith (Du Font); and under the name Process Extra Ortho (Gevaert).

Examples of continuous-tone film include those sold under the name Commercial Ortho (Eastman Kodak data pages D41, 42 of the said book); under the name Commercial Sheet Film (Ansco); and under the name Commercial (Du Pont).

For purposes of illustration, the invention Will be described in terms of producing a transparency from a photographic film negative, though the broader applications are obvious. Almost any type of film negative is useable, but soft" or flat negatives seem to give the best results. The negative is placed in the normal manner in a standard enlarger, together with the line-type film to be exposed and used for the positive. As before stated, the line film is an extremely high-contrast, orthochromatic film, preferably provided with a polyester plastic base to reduce shrinkage to a minimum and with an abrasion-resistant surface, such as is embodied in the previously mentioned commercial line films.

Exposure is best accomplished with a soft, cold, fluorescent light, with the time of exposure depending upon the density of the negative and the aperture of the enlarger lens. Normally, for purposes of the present invention,

an exposure time of between about 5 to seconds is satisfactory, generally constituting a deliberate underexposure of the film.

Following such exposure, the film is subjected to two critical development processes. For the initial development, the exposed film, contrary to usual practice with line film, is submersed in' a fast-acting soft developer, as of the elon-hydroquinone type. Preferred chemical compositions for such developers follow:

Example 1 Water cc 500.0 p-Methylaminophenol sulfate grams 3.1 Sodium sulfite (desiccated) do 45.0 Hydroquinone' do 12.0 Sodium carbonate, monohydrated do 80.0 Potassium bromide do 1.9 Add water to make liter 1.0

A similar developer is commercially available under the Eastman Kodak tradename Dektol D72.

Example II Water (about 90 F. or 32 C.) cc 500.0 Sodium sulfite, desiccated grams 37.5 p-Methylaminophenol sulfate do 2.5 Sodium carbonate, monohydrated do 44.0 Hydroquinone do 10.0 Potassium bromide do 5.0 Add water to make "liters" 1.0

This developer is commercially available under the Du Pont tradename Professional Portrait Developer 55-D.

Example III Water (125 F. or 52 C.) cc 750.0 p-Methylaminophenol sulfate grams 3.5 Sodium su-lfite, desiccated do 45.0 Hydroquinone -do 11.5 Sodium carbonate, monohydrated do 78.0 Potassium bromide do 1.2 Add water to make liter 1.0

A similar developer is commercially available under the Ansco tradename Paper Developer 103.

The emulsion of the film is completely covered by the developer in a very short time in order to prevent uneven development, and the time of development is determined by the following critical criterion, established, as by observation, under correct safe-light conditions. The exposed film must remain in the developer only until just prior to the appearance of the white areas of the latent image, impressed on the film emulsion by the exposure. This time duration, from submersion in the developer until just prior to the appearance of the white image, is determined either by making test films, or by prc-judging by an experienced technician observing the low tones on the film. The time duration has been found to range from about 5 to seconds, depending upon the density of the low tones or shades desired.

While it is unnecessary to advance a theory of operation, it being sufficient to describe the precise steps necessary to attain the novel results, it is believed that this first development step above-described constitutes a very rapid, accelerated development of the surface image content which, as before explained, is generally underexposed. Through this action, it appears that a large boost to the development of the image is generated without even initiating the development of the background. It is further believed that operation is thereby had on the lower knee portion of the characteristic sensitometric curve. 7

Whether this theoretical analysis is or is not correct, it is the experimental fact that, when such critical initial development is correctly accomplished, there is only surface development on the film. The temperature of the Example I Water cc 500.0 Sodium sulfite (desiccated) grams 30.0 Paraformaldehyde do Sodium bisulfate do Boric acid (crystals) do Hydroquinone z do Potassium bromide do Add water to make 1iter This developer is commercially available under the Eastman Kodak tradename Kodalith D-85. However, the commercial developer is improved by adding sufiicient amounts of potassium bromide to improve restraining and bleaching action.

Example 11 Water (125 F. or 52 C.) cc l-lydroquinone "grams" Sodium sulfite, desiccated do Sodium carbonate, monohydrated do Citric acid do Potassium bromide do 10.0 Add cold water to make liter 1.0

A similar developer is commercially available under the Ansco traden'ame Long-Life Reprolith Developer 81.

Example 111 40 Water (90 F. or 32 C.) cc Sodium sulfite, desiccated grarns-.. Paraformaldehyde do Potassium metabisulfate do Boric acid, crystals do Hydroquinone do Potassium bromide do Add cold water to make liters A similar developer is commercially available under the Du Pont trade name Paraformaldehyde Developer 7 I! V The second developer allows the continuation of contrast development that was initiated in the first developer. It also bleaches the heavily exposed areas of development so that white tones will appear on the film as absolutely colorless, providing a true, clear transparency. While this colorless, transparently clear condition is not completely apparent at this stage of development, an experienced technician can judge the correct degree of opacity on the white areas of the film that is required to obtain the desired transparent clarity in the finished product. The time of the second-stage development is not as critical as in the time of developing in the first developer. Depending upon the desired density of the image on the film, the second development time can vary from about 30 seconds to 180 seconds with a temperature of about 68 degrees F. After the second development is completed, the film is short-stopped and fixed in the usual manner.

In accordance with this process, a continuous-tone image is developed on line film, resulting in a transparency that combines the advantages of the two films (line and continuous-tone) into a single superior product without the disadvantageous background tonal color of the continuous-tone film. As before explaine t e White areas of the photographic original develop as clear and colorless areas in the line film; whereas, in continuoustone film, the white areas are never completely colorless because the film itself has a tonal quality. By developing continuous-tone images on line film, therefore, there is no distortion of the tones of the image and there is no residual tone in the film surrounding the image. Line film dries faster than continuous-tone film, so that the use of line film offers the further advantage of quicker processing. The line film, moreover, is more sensitive to fine detail than continuous-tone film, providing a truer copy, and the line film, in addition, is less expensive than continuous-tone film.

Optical densitometer measurements comparing the colorless background produced in transparencie prepared in accordance with the process of the present invention with the so-called transparency of the background of conventional half-tone or continuous-tone films, show that great improvement is attained toward the goal of a truly clear background void of any detectable tonal hue:

Density (arbitrary relative units) Present Continuousinvention tone transparency Film base developed without exposure- O. 00 0. 015 Film base developed after exposure to white surface (standard white of the fgrey scale) 0.00 0.03 Film base developed after exposure to white (on grey scale) 0.02 0.10

The last-mentioned all-important advantage of the ability to produce continuous-tone positives on a film that has no intrinsic background tones is important, also, in the development of diazo methods for reproducing multicolored slides with a photographic image. For now, by making color-separated positives through the above-described developing method of the invention, and using the positives as masters, individual monochrome diazo films can be made in the four basic process-color (1 black, 1 blue, 1 magenta, 1 yellow). These are superimposed on each other with their images in registration, as is well known, producing a full color transparency that for the first time provides an absolutely colorless, clear background.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A process for producing continuous-tone images on high-contrast photographic line film, that comprises, the successive steps of exposing such high-contrast line film; briefly submersing the film in a fast-acting developer to which water has been added selected from the group consisting substantially of:

Water cc 500.0 p-Methylaminophenol sulfate grams 3.1 Sodium sulfite (desiccated) do 45.0 Hydroquinone d0 12.0 Sodium carbonate, monohydrated do 80.0 Potassium bromide do 1.9

Water (about 90 F.) cc ,500.0 Sodium sulfite, desiccated grams 37.5 p-Methylaminophenol sulfate do 2.5

6 Sodium carbonate, monohydrated do 44.0 Hydroquinone do 10.0 Potassium bromide do 5.0

Water F.) cc 750.0 p-Methylaminophenol sulfate grams 3.5 Sodium sulfite, desiccated do 45.0 Hydroquinone do 11.5 Sodium carbonate, monohydrated do 78.0 Potassium bromide do 1.2

maintaining the said submersing only until just prior to the appearance of white areas of the latent image impressed thereon by the exposure; substantially immediately thereupon submersing the film in a high-contrast developer to which water has been added provided with low-density cut-off characteristics and selected from the group consisting substantially of:

Water cc 500.0 Sodium sulfite (desiccated) grams 30.0 Paraformaldehyde do 7.5 Sodium bisulfate do 2.2 Boric acid (crystals) do 7.5 Hydroquinone do 22.5 Potassium bromide do 1.6

Water (125 F.) cc 750.0 Hydroquinone grams 35.0 Sodium sulfite, desiccated do 55.0 Sodium carbonate, monohydrated do 80.0 Citric acid do 5.5 Potassium bromide do 10.0

(iii) Water (90 F.) cc 500.00 Sodium sulfite, desiccated grams 60.0 Paraformaldehyde do 15.0 Potassium metabisulfate do 5.0 Boric acid, crystals do 15 .0 Hydroquinone do 45.0 Potassium bromide do 3.0

maintaining the last-named submersion until substantially colorless and clear transparency of the said white areas is attained; and short-stopping and fixing the film.

2. A process as claimed in claim 1 and in which the said exposing step is limited to a period of time up to about 10 seconds.

3. A process as claimed in claim 1 and in which the step of submersing in the fast-acting developer is limited to a period of time from about 5 to about 30 seconds.

References Cited by the Examiner UNITED STATES PATENTS 1,273,435 7/1918 Williams 96--42 1,428,009 9/1922 Crowe 9643 1,928,579 9/1933 Walker 9642 2,028,863 1/1936 Briel 9642 X 2,339,482 l/ 1944 Huttkay 9690' 2,541,490 2/1951 Yule 96-66 2,544,910 3/1951 Yule 9666 OTHER REFERENCES Kodak Data Book, Copying 6th ed., page 25, 1958, TR E3KO.

NORMAN G. TORCHIN, Primary Examiner.

Claims (1)

1. A PROCESS FOR PRODUCING CONTINUOUS-TONE IMAGES ON HIGH-CONTRAST PHOTOGRAPHIC LINE FILM, THAT COMPRISES, THE SUCCESSIVE STEPS OF EXPOSING SUCH HIGH-CONTRAST LINE FILM; BRIEFLY SUBMERSING THE FILM IN A FAST-ACTING DEVELOPER TO WHICH WATER HAS BEEN ADDED SELECTED FROM THE GROUP CONSISTING SUBSTANTIALLY OF: