US2358060A

US2358060A - Photographic materials

Info

Publication number: US2358060A
Application number: US407487A
Authority: US
Inventors: Edward P Davey
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1940-09-03
Filing date: 1941-08-19
Publication date: 1944-09-12
Anticipated expiration: 1961-09-12

Description

Patent ed Sept. 12, 19,44

UNITED "STATES PATENT orricsi Edward Titli figlffrrsiignor to Eastman Kodak Company, Rochester, N. Y., a I I corporation of New Jersey I No Drawing. Application August 19, 1941, Serial '8 Claims.

(a) Silver chloride is naturally more contrasty than silver bromide.

(b) Silver chloride develops much more rapidly (usually 20 to 40 secs.) than silver bromide (usually 1 /2 to 2 mins.)

If the brightest possible print with good transparency in the shadows are required from flat negatives, it is customary to use silver chloride which is superior to silver bromide in this particularrespect. On 'theother hand, in view of (a) mentioned above, very soft prints are more easily made on silver bromide paper.

It has been the practice .of all photographic manufacturers for morethan twenty years to sell numerous different sensitive papers.

Even as long ago as 1912 in British Specification-No. 15,054, Fischer proposed to make a In Great Britain September 3,

judge the development and readjust the exposure ,both as to amount and colour of light if it was found to be incorrect the first time. For exif the exposure has been too great, say double the correct exposure, then when development is cut short in an endeavour to save the, print from being wasted, the contrast obtained is much too high which would not have occurred when using.

ordinary single emulsion papers. Moreover, it is diflicult, in fact usually impossible, to obtaina satisfactory printif development is cut short as can be done in the case of standard single emuls ion papers, and which is in fact veryfrequently done to avoid waste when making prints. Home the user is compelled to learn a new technique of judging the making of prints-by visual inspection.

Moreover, if the emulsions are coated as superposed layers, theimage which develops in the lower emulsion layer is, during development, considerably'obscured by the upper emulsionlayer and, as seen from above in the case of photographic paper, the highlights or shadows, whichphotographic sensitive paper by mixing or coating one overthe other two emulsions giving differing contrasts under the same development conditions but with differing coloured lights for exposure. This result can be achieved'by using silverv chloride which as indicated above, lends itself to making a contrasty emulsion in conjunction with silver bromide which lends itself to making a soft emulsion. In fact, in an endeavour to produce such a variable contrast sensitive paper, it has 'been proposed by Renwick in U. S. Patent No. 2,202,026 to mirror coat in separate layers, a dye-sensitised contrasty silver chloride emulsion and an ordinary soft silver bro-' mideor chloro bromide emulsion.

This method suffers from the serious disadvantage of giving a sensitive material which when exposed for different contrasts gives con-' siderable inconvenience in processing. When printing most negatives which do not fall at the absolute extremes of contrast (i. e. fullyv soft or fully contrasty) where both emulsions come into play to varying degrees, the relation between therates of appearance of the highlights and the heavy shadows in the same print is distorted, and moreover to add to the difficulty, differs from one negative to another. This makes it difficult to tages referred to such as the restricted choice of v ever develop first in the lower layer are obscured and give again an unpleasant and inconvenient rate of appearance of the different parts of the image and also fromone kind of negativeto another, especially in the case of the large bulk of negatives which print between the extremes where both emulsions areutilised in varying degrees, all of which is of course additional to the effects already mentioned as resulting from using different halides. Hencewhile the use of the same halides in superposed layers overcomes some disadvantages it does not overcome .all of them.

It follows that inall the above proposals difliculty is entailed in attempting to develop by inspection to say nothing of ,the other disadvanconvenient developingsolutions and in particular I am not aware of any proposal to overcome this difliculty of inspection development.

It is an object of my inventionto produce a sensitive photographic paper which is eminently suitable for development by inspection as well as having other advantages, such as ease of making a mixture which gives, uniform image colours and uniform times of development over the whole range of contrasts.

According to my invention I employ a mixture of an emulsion of a silver halide which is optidescribe.

cally sensitised to a region of the spectrum and another emulsion of the same halide but of different contrast which has its maximum sensitivity in another region of the spectrum whereby the mixture gives a difference in gradation of at least 2.5, the lowest gradation being below 1.8,

by exposing .tolights of ditlerent colours.- I may make both emulsions of silver bromide or both of silver chloride, or even of chlorobromide, providing the halide compositions of the two emm sions are for all practical purposes the same: a

I shallnow refer to various forms of my invention, each of which achieves a-special object. Another disadvantage of'the use of halides is thatit is not possible to make a satis factory sensitive paper which is sufliciently hightised that its natural sensitivity is sufliciently low. If the use of the natural sensitivity in this way could beavoided a wider scope would be permitted in the production of the two emulsions of the mixture. I am not aware of any prior P p sal to avoid using the natural sensitivity in thi way while atthe same time the material can be proowith a sharpEcutoif at say 580 dmerem, l5

: In all forms" of my invention I preferably emly sensitive for use in very rapidly operating Ina- P chines or where only a weak light exposure is possible. According to a special form of my invention'" this dimculty is overcome by employing -a mixture of two silver bromide emulsions.

For some purposes it is desired to make a series -of. prints from various negatives with a'very high a degree of brilliance and clarity." This was not achieved in the prior proposals of using a silver chloride emulsion mixed with a silverbromide emulsion, since the images formed. in the silver chloride emulsion are-more brilliant than those formed inthesilver bromide emulsion. f-According toanother special form of my in- =vention I achievethisobject by employing'a mixture oftwo silverchlorideemulsions. I *If 'onee-mulsion is sensitised-to green and the -"other is not sensitised. such a combination can- 1 not be processed in a yellow or yellowish-green or orange'light but must be processedin the more inconvenient red light. Sometimesthis does not matter, but, for some purpossit-isuridoubtedly inconvenient. This is overcome, as well as all the disadvantagesol' prior proposals by' a,pre-' ferred form of my invention which I shall now essed in an orange or light red light. I achieve this desirable result in a preferred form of using two silver chloride-emulsions in which both emulsion are optically sensitised, one with a maximum at about 470 m and the other at about550 ma Ijshallno'w describe the ways of performing the several forms of my invention referred to above.

ploy' one emulsion which gives a gradation (measured as herein described) less than 1.8 and the other emulsion which gives a gradation of at least 2.5 greater than that of the other emulsion and 'ofwhich one of such emulsionslhereafter referredto as the former emulsion) is sensitised to haveitsmaximum speed at least 60. m further towards the longwavelengths than the maximum speed of the other of such emulsions, the speed of the former emulsion measured at about the wavelength of the maximum speedof theother emu1 "sion being not greater than hair the speed or the other emulsion measured at the same'f wavelengths, while measured at about the wavelength of maximum speed of the former emulsion the speed thereof is at least twice the speed of the other emulsion. For most purposes .it is preferable that both emulsions should be substantially insensitive to wavelengths beyond 600 m The said gradations are tobe measured by means of 7 light of about the-wavelength (as herein defined) In this preferred form which exhibit these special further advantages I employ a silver chloride emulsion which hasnotbeen specially u tically sensitised, and therefore'has a natural sensitivity which-is high at- 390v m withv a silver 1 chloride emulsion which has been sensitised to have its-maximum optical sensitisation at about 520 m or less but preferably between 420 and 490 m for example 4'70 m with a low natural'sensitivity. When such maximum isat about 520 im the material: can be processedv in an orange light, but when it isabout 47011111 it can be processed inarelatively brightyellow. I

My invention achieves aspecial advantage in, respect of producing warm tone prints with the same developing solutions containing large quantities of a restrainer both by visual inspec without. The use of different halides renders it extremely diflicult to obtain satisfactory or at least similar brown or :warm-toned prints over the whole range of contrasts. Even the use of a silver chlorobromide emulsion as proposed by Renwick does not give satisfactory warm tone over 1 the whole range of contrasts. because "he mixes it with a silver chloride emulsion, and in fact I am not aware of any prior proposals to enable such prints to b made.

I achieved this result in another special form of tionand Q of maximum speed of the emulsion concerned.

WhereI refer herein to about a certain wavelength, I mean the range of wavelengths covering 40 m each side thereof. 'To ascertain the wavelength of maximum speed there should be employed-a spectrogram made by-using a, neutral wedgewith a tungsten filament, at 2700K as the light source,,and wavelengths below 390 m are excludedirom such measurements. 1

I By the term silver bromide emulsion as used herein, I mean an emulsion which consists of at least 90% of AgBr based on the total silver halide.

By the tenn "silver chloride emulsion I means an emulsion which consists of at least 90% iAgCl based on the total silver halide.

By thetermsilver-chloro-bromide emulsion wherever used herein Imean silver-halide emulsions which contain over 10% and less than 90% (but preferably over 30% and lessthan of 1 silver chloride based on the total silver halide. It is'desirable that the percentage silver chloride content of the two emulsion should not differ by more than 25, but preferably not more than 10.

' Itis the practice to add sometimes some silver iodide to silver bromide, silver chloride and silverchloro-bromide emulsions, and such emulsions are included within the terms of the present invention.

In order to produce a sensitive photographic element of the greatest convenience. and simmy invention by employing two silver chlorobromide emulsions as will be described hereinafter.

All the above methods referred to, make use of the natural sensitivity of one emulsion, hence it is important to have the other emulsion so sensiplicity in use for most purposes (i. e. with most negatives commonly met in practice) I have sions'and the'optically sensitising dye should be found'that it is preferable that the coated emulso chosen that the speed in the blue region of the non-optically sensitised blue sensitive emulsion should beat least 1.8 (and preferably at least twice) the speed of the optically sensitised emulsion in the blue region, while the speed of the optically sensitised emulsion in the green to yellow region should be between one-third and one-anda-quarter (preferably between three quarters and one-and-a-quarter) times the speed of the non-optically sensitised emulsion in the blue region and the gradation of the non-optically sensitised emulsion in the blue portion should be between 0.8 and 1.8 (preferably between 1.0 and 1.6) while the gradation of the optically sensitised emulsion in the yellow to green region of the spectrum should be at least 2.5 greater (preferably 3.5 greater). It is usually desirable that both emulsions be substantially insensitive beyond 600 mu.

Usually the gradation of the optically sensitised emulsion will not be more than 7.

All speeds herein referred to are measured by taking theexposure necessary to give a density of 1.0.

Whenever I refer herein to the gradation of an emulsion I mean the average slope of the characteristic H. & D. curve between densities of 0.4 to 1.6.

It is to be understood that when the emulsions are to be coated on an opaque support such as white paper, the density measurements which are made to arrive at the aforesaid measurements are to be done by reflected light.

In all measurements referred'to or implied herein, development is done at 68 1. for 1 /2 minutes with the following solution:

Metol grams- 2.2 NazSOs cryst do.. 150.0 Hydroquinone do 17.0 NazCOa cryst -..q do 175.0 KBr. -do 2.8 Water ccs 1,000.

This solution is diluted with an equal part of water, for use.

Whenever I refer herein to the various characteristics (including speed and gamma) of each emulsion I mean when measured on the emulsion coated as a layer by itself at a quantity per square foot which is the same as is used for that emulsion in the composite emulsion layer.

The measurements specifically referred to as in the blue portion of the spectrum are made byv exposing to a tungsten light (27003000 K) through a Wratten No. 47A filter, and in the green to yellow portion of the spectrum by exposing to sfiilich a tungsten light through a Wratten No. 5

ter.

Preferably the non-optically sensitised blue sensitive emulsion should be one having a characteristic H & D curve whose straight portion is as'long as possible.

For the. emulsion or emulsions which are optically sensitised there may be used one or more sensitising dyes, and since the emulsions are to be mixed, such dyes must be incorporated in that emulsion before it is mixed with the non-optically sensitised emulsion in such manner that after the emulsions are mixed, any tendency of the dye or dyes to wander from the one emulsion to the other is avoided or minimised for example, by adopting the procedure described in my application Serial No. 387,437. The procedure described in the co-pending application of Edward B. Knott and myself Serial No. 391,375 may be utilised in the production of the optically. sensitised emulsion. Dyes having little tendency to wander are described in the co-pending application of Leslie G. S. Brooker Serial No. 321,370 filed March 1, 1940.

' Example 1 danine or St (2-ethyl-1 (2) -benzoxazolylidene) ethylidenel -3-nh e p t y l-l-phenylQ-thiohydantoin. The emulsion so optically sensitised had a speed in the blue region of 2.0 with a speed in the green to yellow of 5.7 and gradation in the green to yellow of 5.5. This emulsion was allowed to stand while adding soft lac to the nonoptically sensitised emulsion. This latter was a silver bromide emulsion (containing 3% silver iodide calculated on the total silver halide content but free from silver chloride) having aspeed in the blue region of 5.4 and a gradation 1.5. To an amount of this emulsion made from 200 grams of silver nitrate there was added 500 cos. of ethyl alcohol containing 10'grams of soft lac (at 35 C.).' The emulsions at 35 C. were mixed and coated immediately on a paper support.

Example 2 An optically sensitised emulsion of silver bromide without any other silver halide was prepared as follows; take an amount of an emulsion giving a high gradation and made from 200 grams of silver nitrate and immediately after formation of the silver bromide there was added 0.03 gram of the second named dye of Example 1. This was ripened at 40 C. for ten minutes; then allowed to set and washed; more gelatine was added and then digested at 55 C. for 30 minutes.

The emulsion so prepared had a speed in the blue of 1.0 with a speed in the green to yellow of 2.7 and gradation in the green to yellow of 4.4.

A non-optically sensitised emulsion for mixing therewith was prepared so as tohave a speed in the blue region of 4.7 and a gradation of 1.3. The two emulsions were mixed and coated immediately on a paper support.

Example 3 A bromide emulsion giving a high gradation and containing the equivalent of 200 grams of silver nitrate was adjusted to a pH of 7 and sensitised with 0.05 gram of 3-ethyl-5-(2-ethyl-1- benzoxazylidene-ethylidene) 1-phenyl-2-thiohy dantoin and allowed to stand for 30-minutes at- 35" C. A suspension containing 50 grams of magnesium hydroxide was then added, followed by a 5% alcoholic solution of 50 grams of soft lac resin, and then followed by addition of 50 grams of potassium chloride. The product was then kept at 35 C. until the speed of the emulsion had reached the required figure (say minutes). The emulsion so prepared had a speed in the blue of 1.5 with a speed in the green to yellow of 3.0 and gradation in the green to yellow of 4.5. The same quantities of magnesium hydroxide and resin were added to a bromide emulsion to have a speed in the blue of 4.0 and a gradation of 1.2. These two emulsions were port. I

30 C. and coated.

Erample 4 of silver bromide and 1% of silver iodide calculated on its total silver halide content and having a speed in the violet of 0.3 and a gradation of 1.5. The two emulsions were mixed in equal proportions at 30 C. and coated.

Example 5 An amount of a silver chloride emulsion was made from 200 grams of silver nitrate and immediately after formation of the silver chloride there was added 0.1 gram of the same dye as used in Example 2. This emulsion was then ripened at about 60 C. for about v40 minutes and then more gelatine added. The emulsion so prepared had a speed in the violet of 0.1 with a speed in the green to yellow of 0.8 and gradation in the green to yellow of 5.0. Also there was prepared a silver chloride emulsion in like manner except using the dye 3-n-heptyl-5(1-methyl-3-5-naphthoxazolylidene) rhodanine; this emulsion had a speed in the violet of 0.3, and in the blue of 1.1 with'a gradation in the blue of 1.4. The two emulsions were mixed in equal proportions at Example 6 An amount of a silver chloro-bromide emulsion of 50% silver-chloride and 0 to.%% silver-iodide content (the remainder thus being silver bromide) was made from 200 grams of silver nitrate and immediately after formation of the silver halide 0.1 gram of the same dye as used in Example 2 was added. This was ripened at about 60 C.

' for about 40 minutes and then more gelatine added, allowed to set and washed well. The emulsion so prepared had a speed in the blue to violet of 0.2 with a speed in the green to yellow of 0.7 and gradation in the green to yellow of 5.0. There was also prepared a silver chloro-bromide emulsion of the same halide composition which was not optically sensitised but had a speed in the blue to violet of 0.8 and gradation of 1.4. These two emulsions were mixed in equal proportions at about 30 C. and coated on paper.

I claim:

1. A photographic printing material for making prints of substantially the same contrast and same density range from negatives of widely. differing contrasts containing a sensitive layer comprising a mixture of two emulsions of the same silver halide, each emulsion being present in quantity suflicient to give a density of at least 1.6, at least one emulsion being optically sensitized before mixing the emulsions so that after mixing the two emulsions their maximum sensitivities lie in diiferent spectral regions, one emulsion hava ing in its region of maximum sensitivity before mixing a gradation of less than 1.8 over a density range of 0.4 to 1.6 and the other emulsion having inits region of maximum sensitivity before mixing a gradation at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6.

2. A photographic printing material for making prints of substantially the same contrast and 7 prising a mixture of two silver bromide emulsions, each emulsion being present in quantity suificient to give a density of at least 1.6, at least one emulsion being optically sensitized before mixing the emulsions so that after mixing the two emulsions their maximum sensitivities lie in different spectral regions, one emulsion having in its region of maximum sensitivity before mixing a gradation of less than 1.8 over a density range of 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6. V

3. A. photographic printing material for making prints of substantially the same contrast and same density range from negatives of widely differing contrasts containing a sensitive layer comprising a mixture of two silver chloride emulof 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6.

4. A photographic printing material for making prints of substantially the same contrast and the same density range from negatives of widely differing contrasts containing a sensitive layer comprising a mixture of two silver chlorobromide emulsions, each emulsion being present in quantity sufficient to give a density of at least 1.6, at least one emulsion being optically sensitized before mixing the emulsions so that after mixing the two emulsions their maximum sensitivities lie in dilferent spectral regions, one emulsion having in its region of maximum sensitivity before mixing a gradation of less than 1.8 over a density range of 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6.

5. A photographic printing material for making prints of substantially the same contrast and same density range from negatives of widely differing contrasts containing a sensitive layer comprising a mixture of a silver chlorobromide emulsion whose chloride content lies between 10 per cent and 25 per cent of the total halide in the emulsion and another silver chlorobromide emulsion Whose chloride content lies between 10 per cent and 25 per cent of the total halide in the emulsion, each emulsion being present in quantity suflicient to give a density of at least 1.6, at leastone emulsion being optically sensitized before mixing the emulsions so that after mixing the two emulsions their maximum sensitivities lie in different spectral regions, One emulsion havemulsion being optically sensitized with a maximum at about 4'70-"m and the other emulsion being not optically sensitized, the one emulsion having in its region of maximum sensitivity before mixing a gradation of less than 1.8 over a density range of 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation of at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6.

7. A photographic printing material for making prints of substantially the same contrast and same density range from negatives of widely differing contrasts containing a sensitive layer comprising a mixture of two silver chloride emulsions, each emulsion being present in quantity sufiicient to give a density of at least 1.6, the one emulsion being optically sensitized with a maximum at about 550 m and the other emulsion being optically sensitized. with a maximum at about 470 ml, the other emulsion having in its region of maximum sensitivity before mixing a gradation of less than 1.8 over a density range of 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation at least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6.

8. A photographic printing material for making prints of substantially the same contrast and same density range from negatives of widely differing contrasts containing a sensitive layer comprising ,a mixture of two emulsions of the samev silver halide, each emulsion being present in quantity sufllcient to give a density of at least 1.6, at least one emulsion being optically sensitized before mixing the emulsions so that after mixing the 'two emulsions their maximum sensitivities lie in difierent spectral regions, the one emulsion having in its region of maximum sensitivity before mixing a gradation of less than 1.8 over adensity range of 0.4 to 1.6 and the other emulsion having in its region of maximum sensitivity before mixing a gradation at-least 2.5 greater than that of the first emulsion over a density range of 0.4 to 1.6, the one emulsion being optically sensitized to have its maximum speed at least m further toward the longer wavelengths than the maximum speed of the other emulsion, the speed of the first emulsion measured at about the wavelength ,of the maximum speed of the other emulsion being not greater than half the speed of the other emulsion measured at the same wavelength, while measured at about the wavelength of the maximum speed of the first emulsion, the speed of the first emulsion is at least twice the speed of the other emulsion, both emulsions being substantially insensitive to wavelengths beyond 600 m EDWARD P. DAVEY.