US2079470A - Method of making imbibition films - Google Patents

Description

Patented May 4, 1937 UNITED STATES METHOD OF MAKING IMBIBI'I'ION FILMS" Bertha Sugden Tuttle,

West Newton, Masa, as-

signor to Technicolor Motion Picture Corporation, Hollywood, Calif., a corporation of Maine No Drawing.

8 Claims.

This invention relates to films or film surfaces, especially suitable for the reception of imbibition images, as in the manufacture of motion picture films, and to a method for the prepara tion of the same.

In the manufacture of films for cinematographic purposes, and more especially by the method of printing blank films from a dye-wetted matrix film by imbibition, it is of critical importance not only that the matrix film shall take up the dye proportionately to the intensities'represented by the respective images which it contains but that such dye images shall be accurately transferred to the blank film to be printed therefrom. This transfer entails, briefly, the maximum practicable transposition of the dye from the matrix film, thedirect imbibition and intimate adherence of the dye to the printed blank, and the prevention of lateral or irregular diffusion of the dye either during or after the printing operation. 7

It will therefore be manifest that the specific character and condition of both the surface and the structure of the film blank which is to be printed are of primary and determinative importance with respect to the result to be achieved.

In prior practices of imbibition printing, it has been customary to employ a blank of hardened gelatine film or coating and such hardening of the gelatine'has been. carried out in a number of well known 'ways. But such preparations have been qualitative in character and, in conjunction with the variability of gelatine manufacture, have resulted in the obtainment of a variable product, the properties of which (at least in respect of the criterion of superficial characteristics and structural properties demanded for dependable results in imbibition printing) have been nonuniform throughout the surface of long strips and not dependable between different lots of manufacture, especially when derived from different lots of raw material.

Moreover, it has also been observed that, as a result of such variations in the blank film as heretofore manufactured, further variations have developed during storage so that, of blank films which might be substantially the same, those films which are used at one time will differ materially from those used at a later time. The latter films, for example, tend to show a greater degree of hardness than the former. Hence, with varia-' tions in age, film blanks exhibit a variability in their wetting characteristics and penetrability to the dye images impressed thereon. They also tend to croceinate or promote residual accumu- Application September 12, 1934, Serial No. 143,718

lations of dye upon the matrix film, which is detrimental. Other variations, leading to troublesome and unreliable operation of the printing process, have been incurred bydifferences in the properties of the blank film.

Accordingly, it is an object of the present invention to provide an improved and more reliable film blank for imbibition printing and to provide an improved and more determinative method for its manufacture. Other objects will appear from the following disclosure.

In accordance with the present invention it is found that the conditioning of the film blank prior to the hardening treatment (and more especially when the treatment is effected with chrome hardening agents) has a definite influence upon the hardening solution and upon the hardening operation effected upon the film.

This is, for example, especially manifest in the preparation and use of motion picture film blank having a sound track. In one form of such film blanks the sound track is provided along one margin of the film while the remainder of the film surface is left blank for the subsequent printing (by imbibition) of the picture images to be reproduced. The sound track is formed by making the margin (or the whole) of the film light-sensitive and photographing a sound-variable beam of light thereon. The silver image is then developed and the film washed in the customary way to remove surplus reagents.

The blank film having the silver image sound track thus developed along its margin is next hardened and finally printed, (by imbibition) with the series of pictures which are to form the finished motion picture film of the talkie type. It was found, however, that film blank of this type possessed variable properties and that its properties varied with aging, so that its printing characteristics were not dependable. Moreover, it presented the difiiculty of fouling the matrix film so that dye accumulations built up thereon, which hinders obtaining satisfactory impressions upon the printed films.

In this connection it was found, as a part of this invention, that such sound track film blank, after hardening, continued to harden spontaneously. It was further found that, upon aging for a long period of time, an ultimate degree of hardening was reached which was substantially permanent. But such long aging of the film after the application of the sound track and before imprinting the picture images thereon was obviously undesirable. Moreover, the only certain control over the effects of aging in this way was to age all films for a maximum period, suificiently long to insure the permanency of the most unstable .film blank likely to be present.

' But whether the film blanks were thus aged or diificulty lay in the fact that, in spite of inter-' mediate washing, the developed sound track film,

upon passing into the hardening reagent solution, contained and transferred 8. small amount of the fixing reagent to the hardening solution. Such transfer need be but very slight in amount but has the effect of changing (i. e., accelerating) the hardening action of the hardening solution. Moreover, such transfers are cumulative in the hardening solution and thus progressively increase its hardening action.

Such accelerative action upon the hardening agent may be attributed primarily to the alkaline characteristics of the sodium thlosulphate, which' is usually used infixing the sound trackimage, though it may also be affected by the reducing action uponth'e chromium, or the molecular migration of the thiosulphate radical into the chromium nucleus ofthe chromium salts contained in the hardening solution. But, whatever the mechanism of its accelerative action, it is deleterious in respect of the hardening of the film, if it is not limited or controlled.

Athird alternative is that the hardening action may be controlled and also carried to completion. In this aspect of the invention, it was found that the continued hardening action would ultimately spend itself. For example, if such hardened films were storedfor a month (preferably longer) the hardening action would usually be complete and continued hardening action would substantially cease. But the period of time required for thus obtaining a stable film (i. e. not subject to appreciable further harden- .ing action) would still vary considerably with different lots of films.

It has been further found that under such circumstances (whether one uses the film at once or permits the hardening action to go to substantial completion) the film may be found to contain an excess of hardening agent, so that a residual amount of the same will be left free, either upon or in the film or both. This is frequently an insoluble chromium compound such as chromium hydroxide. Such free reagent, es-

pecially in the case of chrome hardening agents,

acts as a mordanting agent upon the dye. This mordanting action is deleterious, because in rendering the dye which is first imparted to the blank insoluble, it forms a solid deposit which interrupts and prevents dye from the matrix film.

From such discoveries it may be postulated as desirable, to overcome the difiiculties of procedure and deleterious characteristics of film blanks resulting in poorly printed films, that the film blank, before hardening shall contain controlled amounts of reagents which are reactive upon the hardening solution; that the hardening action shallbe prompt and completed in the hardening treatment; that thehardened film shall consist substantially exclusively (in the plain areas and apart from the sound track) of hardened gelatine or of hardened and unhardened gelatine, and conversely that it shall be free from or uniformly controlled in respect of amounts of residual deadequate absorption of 4 posits of hardening reagent or any other chromium compounds.

It is now generally believed that the chromehardening of gelatine involves the chemical reac-. tion and combination of the chromium and gelatine and that the resulting compound constitutes the hardened gelatine. The chromium thus combined does not appear to enter into further reaction with the dye image impressed thereon or to affect the dye upon the matrix film from which it is printed. Moreover, it is more resistant to the softening or dissolving action of water than unhardened gelatine and also assumes a structural formation which is especially suitable to the accurate reception, by imbibition, of a dye image, or a succession of superimposed dye images without migration or difiusion. And if there is any reaction of the chromium-gelatine upon the dye image it does not interfere with the accurate production of images thereon.

It was further found, in connection with the present invention, that the hardening solution (e. g. chrome alum) is most effective upon the gelatine or gelatine film, if the latter is so conditioned, (with respect to hydrogen ion concentration) as to be at or approximately at the isoelectric point of gelatine,nam ely pH 4.7-4.8. At

this point also the gelatine manifests a minimum tendency to swell and to react with or absorb acid or basic reagent materials with which it may be associated. On the other hand, it appears to be capable of undergoing metathetical reaction at this point with salts of chromium such as chrome alum or basic chromium salts or salts of chromium in which activating substituent radicals have been introduced into the chromium nucleus in accordance with Werners theory of tanning.

However, since it is not possible to adjust the chromium salt solution to a pH value of 4.,7 by the direct addition of alkalies or ammonia without very heavy precipitation, the presence of a controllable amount of alkalinity in the gelatine at the time when it enters the chrome solution is advantageous. There are several strong alkali salts of weak acids which may be used, although different salts react in different ways. In general they retard precipitation in proportion to the affinity of their constituents for the chromium nucleus. On the other hand, if sumciently high concentrations of salts of this type are used they may check the tanning or hardening action and in the case of certain organic salts may even reverse it. Such high concentrations and organic salts are therefore to be avoided.

In the present invention residual traces of hypo are conveniently used to condition the film in a mildly alkaline state prior to passage into the chrome solution. The alkalinity is controlled within a working range which is favorable to rapid hardening in the chrome but is definitely below the point where precipitation of chrome occurs. Governed also by the rate of penetration of the chrome into the gelatine and the bufiered condition of the latter, the chrome solution becomes gradually more alkaline as it enters the gelatine under conditions favorable to reaction with the protein rather than precipitation. 'It is therefore efiectively provided that the hardening reaction takes place for the most part in acid surroundings which approximate the isoelectric point of gelatine.

After leaving the chrome solution the film is washed in plain water whose pH is lowered from a normal value of 7.3 to about 6.9 due to the traces of-chrome carried over by the film. This water is alkaline enough to precipitate chrome from solution carried over by the film, and it serves also to wash out in a controllable way the soluble excess reagents from the gelatine.

At the same time, the presence of excess of reagent, as byusingan unnecessarily concentrated solution of chrome alum or continuing the treatment for too long a time is to be avoided, since it not only tends to promote the absorption of such salt by the hardened (or unhardened) gelatine but involves a waste of reagent and labor in that it must subsequently be removed by washing, if a thoroughly satisfactory result is to be accomplished.

While chrome alum is more freely soluble in an acidic solution, it is found to be more reactive and more effective as a hardening agent if its acidity is reduced as much as may be expedient without decomposition and consequent separation of solid matter, which is indicated by the appearance and increase of turbidity. For example, in practice a chrome alum solution having pH value adjusted to 3.45 by addition of ammonia has been found highly satisfactory at a concentration of 5.0 to 5.25 grains chrome alum per 100 c. c. of solution.

The period of contact of the film with the hardening solution and the concentration of the hardening solution are kept as low as possible, and. after the treatment residual reagents or solutions are promptly removed. These results may be effected by washing the hardened gelatine film with a neutral or slightly alkaline .wash

water.

The results of such precautions in-the hardening treatment are to effect promptly and to as high a degree of completion as possible the hardening action of the chrome alum solution upon the gelatine, under conditions favorable to such reaction, the avoidance of an excess of reagents, the avoidance'of absorption of the reagents by the gelatine,. and the complete or substantially complete removal of the residual excess of the hardening agent. The resulting product is accordingly uniformly and completely hardened, not subject to further spontaneous hardening action, and not accompanied by absorbed (or adsorbed) salts or other residues. It is, moreover, adjustable to an acidic or even alkaline condition by correspending control of the pH of the hardening solution and of the subsequent wash waters, in accord-ance with the desired condition appropriate to the dye solution with which it is to be printed. It may also be finished substantially at the isoelectric point of gelatine or chrome hardened or chromated gelatine.

A feature of the hardened gelatine blank thus obtained is the sharpness of transfer of a dye image thereon which is possible to obtain by imbibition printing, and also its ability directly to absorb such dye quickly and without irregular diffusion. For example, the sharpness of such images may be measured by the resolving power of the transfer process. By providing an improved resolving power equal to or greater than that of the cameras, one obtains a sharpness and accuracy of detail suflicient to insure the best possible results from high (as well as low) quality of the commercially available negatives. It also is an index of the completeness with which the dye image is transferred from the matrix film and the elimination of croceination or dye accumulation upon the matrix film, evenafter many successive transfers have been made therefrom.

1A typical instance of carrying out the method of the invention will be described with reference to the preparation of the usual standard imbibition film blank. (With sound track film as described above. the procedure will be the same if after development of the sound track record, complete removal of reagents and appropriate readjustment of the pH value of the film is effected.)

A transparent cellulosic film may be first coated with an aqueous solution or emulsion of gelatine,

I which is then preferably-allowed to gel. Before if the hardening reaction be over alkaline. With a substantially neutral gelatine,-the chrome alum solution may conveniently be prepared as above indicated, in a concentration of 5.4% and with a. pH value of 3.45, at which the chrome alum will be retained in solution and yet the acidity of the solution will not be excessive.

The film will be conducted uniformly and rapidly through the hardening solution.

It is then promptly washed, preferably with wash water having a hydrogen ion concentration approximating the isoelectric' point of the gelatine, with pure water, or with a slightly alkaline wash water which tends to neut'ralize and thus offset the acidifying effect of the liberation of free acid from the reactant chrome alum in the hardening reaction.

By thus approaching and maintaining the isoelectric condition of the menstruum surrounding the gelatine, the hardening reaction proceeds more freely and completely under such conditions of the gelatine. Such rapid hardening is convenient, but its greater advantages lie in the reduction of concentration of the hardening solution required, the presence of a minimum of reagents which are susceptible to absorption by the gelatine, uniformity of hardening in the gelatine structure and throughout the surface, the uniformity in degree of hardening produced even while passing from one lot of gelatine to an other, the obtainment of the hardened gelatine in a condition in which it manifests a minimum tendency to swell and absorb other materials, and hence in a condition to facilitate rapid and complete removal of any soluble reagents which may be superficially carried upon the surface by washing, without altering the characteristics either of the gel structure or of thegelatine surface thereby.

Moreover, the finished, hardened film is especially suitable for the reception of dye images by imbibition printing, and preserves such characteristics substantially without changeby aging. And while the dye image is rapidly absorbed by such gelatine surface, which facilitates rapid and complete transfer from the matrix, it does not appear to manifest that tendency toward lateral diffusion which lowers or destroys the resolving power of the transfer process and which is characteristic of hardened films containing residual deposits of reagent materials, such as insolin solid solution. Hence, printed films are obtained in which sharpness of detail and accuracy of shade values (in monochrome reproductions) and of color qualities and intensities (in polychrome reproductions) are not only obtainable but may be dependably and uniformly reproduced;

A further advantage of the procedure herein described is that it yields a film which is substantially without any residue of free chrome alum or by-products of the hardening reaction or other salts, which might, if present, tend to alter,

the surface characteristics or structural properties of the gelatine and also affect the imbibition transfer of dye thereto.

I claim:

1. Method of making gelatinefilm blanks for imbibition printing, comprising conditioning the film to a pH value substantially at one side of the isoelectric point of the gelatine and subjecting the film to a chromic hardening agent conditioned to a pH value substantially at theother side of said isoelectric point, the said pH values being controlled to efiect hardening at approximately the isoelectric point of the gelatine upon contact between said gelatine and hardening agent.

2. Method of making gelatine fihn blanks for imbibiti n printing, comprising the steps of conditioning the gelatine to a pH value substantially above its isoelectric point, and subjecting the film to a chromic hardeningv agent having a pH value substantially below the isoelectric point of the gelatine, the pH values of film and hardening agent being regulated to maintain the film gelatine at approximately its isoelectric point during the hardening treatment.

3. Method of making gelatine film blanks for imbibition printing, comprising the steps of conditioning the gelatine to a pH value substantially below its isoelectric point,.and subjecting the.

film to a chromic hardening agent having a pH value substantially above the isoelectric point of the gelatine, thepH values of film and hardening agent being regulated to maintain the film gelatine at approximately its isoelectric point during the hardening treatment.

4. Method of making gelatine film blanks for imbibition printing, comprising conditioning the film to a pH value substantially at one side of the isoelectric point of the gelatine, subjecting the film to a chromic hardening agent conditioned to a pH value substantially at the other side of said isoelectric point, the said pH values being controlled to effect hardening at approximately the isoelectric point of the gelatine upon contact between said gelatine and hardening agent, and subsequently removing excess reagents and byproducts from the film while maintaining the gelatine approximately at its isoelectric point.

5. Method of making gelatine film blanks for imbibition printing, comprising conditioning the film to a pH value substantially at one side of the isoelectric point of the gelatine and subjecting the film to a chromic hardening agent conditioned to a pH value substantially at the other side of said isoelectric point, the said pH values being controlled to effect hardening at approximately the isoelectric point of the gelatine upon contact between said gelatine and hardening agent, and

subsequently removing excess reagents and byproducts from the film with slightly alkaline wash water.

6. Method of making film blanks for imbibition printing containing a sound record, comprising the steps of printing a sound track on the silver halide gelatine emulsion of a film,developing and fixing'the film, conditioning the pH value of the gelatine with the reagents imparted to the film upon developing and fixing to a value substantially difierent from the isoelectric point of the gelatine, and treating the film with a chromic hardening agent having a controlled pH value which, with the pH value of the said reagents, produces upon contact between gelatine and hardening agent an efiective pH value approximating said isoelectric point.

7. Method of making colored film having a photographic sound track, comprising the steps of printing a sound track on the silver halide gelatine emulsion of a film, developing and fixing the film; conditioning the pH value of the gelatine with the reagents imparted to-the film upon developing and fixing to a value substantially difierent from the isoelectric point of the gelatine, treating the film with a chromic hardening agent having a controlled pH value which, with the pH value of the said reagents, produces upon contact between gelatine and hardening agent an eiiective pH value approximating said isoelectric point, and transferring picture records to said film by imbibition printing.

8. Method of making gelatine film blanks for imbibition printing, comprising conditioning the film to a pH value substantially at one side of the isoelectric point of the gelatine and subjecting the -film to a chromic hardening agent conditioned to a pH value substantially at the other side of said isoelectric point, the said pH values being controlled to efiect hardening at approximately the isoelectric point of the gelatine upon contact between said gelatine and hardening agent, and subsequently washing the film 55 to remove excess reagents and by-products.

BERTHA SUGDEN TU'ITLE.