US1631421A - Photographic film - Google Patents

Description

Jun 7, 1927.

- w. LO'HOFER PHOTOGRAPIHIC FILM Filed Nov. 5. 1923 TRANSPARENT suP dfi'r w wov EMULSION SENSITIVE To VISIBLE Lmn-r finvs COLLOID LAYER CONTA'NING- F'INELY GRAINED PARTICLES AND IF DESIRED AN ANTIHALATION DYE Patented June 7, 1927.

UNITED STATES wnznnmr Lonorna, or were,

axrmnensnnnscnarr, or

GERMANY, assrenoa '1:0 I. c. rnauxroa'r-ou-rna-mam,

FARBENINDUSTBIE GERMAN-Y.

PHOTOGRAPHIC 'FILM.

Application filed November 8,1928, Serial No. 672,650,..apd in Germany March 9, 1923.

Photographic films are known in which the back is provided with a gelatine coating to stop curling. Dyed coatings on the bac of supports for photographic purposes are also known in order to avoid halation.

he object of the present invention is a photographic film, the back of which is provided with a coating which not only fulfils the requirements for protection against curlm ing and'halation but which aifords at the same time a suitable ground for retouching. This iseifected-by a layer of a colloid in which substances are embedded that absorb or diffuse any light transmitted through the coating and thesupport and impart to the coating a more .or less rough surface. The layer furthermore imparts a greater clearness and softness to the picture, while the softer lights show more clearly on the sub clued background and stand out in better relief. Softness is desired in photography and is obtained according tov the invention by the facility afforded by the film coating for retouching. For this purpose one uses ;hitherto a background of a dull varnish which, however, introduced difliculties in the case of films.

The possibility of retouching depends entirely upon the graininess of the layer. The

least size of grain just enabling retouching is within the range of sizes of the silver rams in a developed photographic image. he grain size of the layer may be varied according to the desired degree of retouch,

a as to whether a strong change of the original values of the photographic image is necessar or whetherthere shall only be applied a litt e correction of a few lines. For example,

a film tor portrait work requires a size of grain difierent from that suitable for photo- -mechanical work. Furthermore, the grain size will be regulated as to whether the film will be used in enlargement or not. In the first case too big a size of grain. would cause trouble. The grain size is increased if the possibility of a strong and sharp retouch is desired. \v

The

raininess is determined approximately by t e size and the quantity of the single grains present. It has'been found that a layenfitting satisfactorily for retouch must have at least 15 l to 20 percent of roughening material in the substratum, the particles having an average grain size of l or 2 thousandths of a millito the invention as hereinbefore described.

graphic material,

xin

meter. Opaque coatings now on the market have a grain size of about 3 ten-thousandths of a millimeter, Although these coatings have an optical efiect since they scatter visual rays, they are not at all suitable for retouch.

It is to be understood that theminimum percentage above indicated of roughening material in the substratum is onlyapproxir mate, since the size of grains varies not only with the quantity of roughening material, but also insome way with the method of mixing the solution from which the coating In the accompanying drawing, which is a 7 diagrammatical sectional view, 1 represents an ordinary flexible support of nitrocellulose or the like; 2 is'a gelatine-silver halid emulsionlayer and 3 is a back coating according As the colloid can that can be entirely other elements which be used mainly gelatine or partly replaced by are insoluble in water when the applied solution is dried, for instance albumen, caseine, and the like treat- 50 ed with formaldehyde. As embedded substances can be used insoluble compositions in a very fine state of division, such as car-' bonates', sulphates and phosphates of the' alkaline earths, also suitable compounds of 35 the heavy metals and the like. The back coating can be applied in the same manner as, for instance, in roll-films.

To enhance the antihalation efiect dyes or other combinations may be added, preferablythose which can easily beremoved at the usual later treatment of the photofor instance in the acid g baths. Suitable dyes for this purpose are, for example, acid fuchsine, aurin or tartrazine.

. It is to be understood that the. data given below is merely by way of example and that the invention is not limited to the use of the articular substances or proportions speci ed therein.

- Example 1.-A preparation of 1 kilo of rice starch in 5 litres of water is poured into 30 litresof a solution of 10per cent gelatine and is ap lied in the usual manne'rf 10a Ewmnp 2.The material for the back coating isv prepared by stirring freshly pre-fi cipitated and washed calcium sulphate ends.

5 to 10% solution of sodium .caseinogenate,

adding a small quantity of formaldehyde.

Example 3.To a solution of- 450 grams of gelatine in 2 litres of-water is addeda solution of 750 grams of barium chloride in 1.5 litres of water, and, While stirring a solution of 420 grains of anhydrous sodium ing a solution of 80 grams of acid fuchsine in 2 litres of water. Instead thereof 125 grams of aurin in 1.5 litres of alcohol of 40 to strength may be employed.

What I claim is,

1. A film for photographic work with visible 1i ht re s comprisin a su' orting flexible sgeet hgving on one side tligreof a coating of'material sensitive to visible light rays and upon the other side a coating of a coating of material sensitive to visible light rays and upon the other side a coating of gelatine containing finely grained particles-- in an amount and with a retouching.

grain size enabling 3. A film in accordance with claim and having incorporated'in the colloid layer an antihalation dye.

4. A fihn in accordance with claim 2 and having incorporated in the 'gelatine layer an antihalation dye.

In testimony whereof I affix my signature.

DR; WILHELM LoHoFER.

Images