US3087818A

US3087818A - Photographic emulsions, elements, and processes

Info

Publication number: US3087818A
Application number: US82683A
Authority: US
Inventors: Jr Vaughan Crandall Chambers
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1961-01-16
Filing date: 1961-01-16
Publication date: 1963-04-30
Anticipated expiration: 1980-04-30

Description

Unite States This invention relates to photographic gelatinosilver halide emulsions and emulsion layers and to photographic elements embodying the same. More particularly, it rehates to such emulsion layers and elements having improved photographic characteristics. Still more particularly, the invention relates to a process for increasing.

the covering power of developed silver and improving the maximum density, contrast-and effective speed of gelatino-silver halide emulsions.

It:i-s known to add certain chemical compounds, .e.g., heavy metal and noble" metal salts to improve the sensitomeric characteristics of I photographic gelatino-silver halidecmulsions. a practical. limit to-the. advantages which can be obtained bythe addition of suchcompounds without accompanyingg deleterious eiiects such as uncontrollable fog and instability on tropical aging.

It-has been proposed to add to, or replace all or part of-theigelatin in the gelatino-silver halide system with various polymeric colloid materials for various reasons including attempts to overcome the well-known disadvantages of gelatin. However, a few of these proposals have overcome these disadvantages in a satisfactory manner, and gelatin is still-used in most commercial photographic-films. In general, when all ofthe gelatin is-replaced by the synthetic polymers suggested by the prior art, many of the-outstanding photographic and colloidchemical properties of gelatin are lost.

An object of this invention is to provide improved r Still'further objects will be apparent from the following description of the invention.-

It has now beenfounthin' accordance with this invention, .thatg'elatino-silver halide emulsions of increased covering power and enhanced properties can be made by adding to the emulsions an amount of at least one water-soluble pectic polysaccharide taken from the group consistingrof araba'n, arabogalactan and galactan and having arr-"average molecular weight of about 6,000 to 100,000 so that the pectic polysaccharide constitutes 20 to 80 parts and preferably 30 to 70 parts per 100 parts of gelatin in. a gelatino-s'ilver halide emulsion. The amount of pectic polysaccharide present is based on finished emulsion ready for coating onto a film, paper, metal foil, glass plate or other support.

The pectic polysaccharides, araban, galactan and aminogalactan, are polymers of L-arabinose and D-galactose and are present in the tissues and seeds of the higher orderof plants from which they may be extracted.

In general, the finished emulsion will contain 20 to 80 parts of one or more of the pectic polysaccharides per 100 parts of gelatin and the gelatin may be in a ratio to silver halide of from 1:06 to -1':1.5 (60 to 150 parts by weight per 100 parts by weight of gelatin). The emulsions may, of course, contain small amounts of conventional adjuvants. The final emulsions show markedly increased silver covering power (e.g., to 40% greater) There is, however, at the present time,

atent ree over all gelatin emulsions. To' be more specific, with re spect to coveringpower for the same quantity of silver halide, large increases in maximum density and contrast can be obtained in the developed image. Covering power of developed silver can be-expressed as the numerical result of dividing optical density by the grams of silver per square decimeter in the developed image layer. The

covering power will, of course, vary with the amount of" utilized in any gelatinosilver halide system to improve its efliciency. The invention isalso very useful in the socalled graphic arts films, i.e., lithographic films. In all cases when the pectic polysaccharide is present in the amounts set forth above, a higher density is obtained from a given amount of metallic silver in the developed photographic layer, although the effect is more noticeable in large-grain silver halide emulsions than in smallgrain emulsions.

The processes of the invention'are quitesimple and consist of rr'ierely'admixi'rig with'the" molten or liquefied emulsion, after the digestion step, an aqueous solution of one or more of the water-soluble pectic polysaccharides. dobromide emulsion useful for X-ray films is prepared by conventional methods. The silver halides are precipitated in gelatin and the resulting dispersion or'emulsion ripened. The emulsion is then washed, either after chilling and noodling, or after coagulation, by decanting the supernatant liquid. The emulsion is redispersed and then it is digested to bring it to maximum speed. Following digestion, a water-soluble pectic polysaccharide having an average molecular weight of 6,000 to 100,000 (usually in aqueous solution) is added to the molten emulsion in an amount sufficient to provide the desired ratio of pectic polysaccharide to gelatin. 7 The usual final additions, e.g., of hardener, anti-fogging agents, sensitizing agent and spread-ing agent, are made and the emulsion is coated on a suitable support and dried inthe usual manner. To test the effectiveness of the-pectiopolysaccharide the element is exposed in a sensitometer accord ing to a procedure based on the American Standard Method for the Sensitometry of Medical X-ray Films PH 2.9-1956."

The sensitometer used in' the following examples was equipped with a neutral density /2 step wedge. The density of. a selected step, as set forth in the tables, was measured and the quantity of metallic silver per square decimet'er was determined by analysis. The dens= ity divided by the quantity of silver in grams per square decirneter was taken as an expression of covering power of the developed silver.

The invention will now be illustrated further by, but is not intended to be limited to, the following examples. The quantities of the pectic polysaccharides are given as parts by weight per parts" by weight of gelatin in the emulsion.

Example I A high speed gelatino-silver iodobromide emulsion was made in the usual manner and digested with an organic sulfur compound and gold chloride. It contained approximately 1.6 mol percent of silver iodide and 98.4 mol percent of silver bromide and the ratio 015 gelatin to As an exemplary procedure, a gelatino-silver io- Grams p-N-methylaminophenol hydrosulfate 3.0 Anhydrous sodium sulfite 50.0 Hydroquinone 9.0 Anhydrous sodium carbonate 50.0 Potassium bromide 4.5

Water to make 1,000 ml.

Following development, the films were fixed, washed and dried in the conventional manner. The results of the sensitometric tests and measurements of covering power are shown in the following table:

Parts of Covering Arabo- Power of galactan Maximum Developed per 100 Density Silver at parts of Densities Gelatin o1 1.33:.1

1 (Control) 1.23 29 2 17 1.76 37 3 35. 5 1. 78 36 Example 11 An emulsion was made and treated in the same manner as in Example I except that a 5% aqueous solution of the pectic polysaccharide, araban, an extract of apple pectin having an average molecular weight 6,500, was added in place of the arabogalactan. The results are shown in the following table. The relative coating weights of silver halide are given to show that the last emulsion containing araban was coated at 74% of the coating weight of the control.

Covering Parts of Power of Arabian Relative Maximum Developed Per 100 Coating Density Silver at parts of Weight Densities Gelatin of 1.3 :l: .1

1 (Control) 0 100 1. 23 29 17 103 1. 37 31 35. 5 106 1. 49 33 68 74 1. 21 35 It will be seen that, although substantially less sliver halide was used in the last coating containing araban, as indicated by the relative coating weight, the maximum density obtained was close to that of the control by virtue of the higher covering power of the developed silver. Substantial savings in silver cost can be realized by this more efficient use of developed silver.

It has been found that the increased covering power of the silver in developed photographic emulsion layers is not limited to adding the water-soluble pectic polysaccharides to the gelatino-silver halide emulsion layer. The beneficial results also can be attained by incorporating the pectic polysaccharides in a gelatin composition to be coated next to a gelatino-silver halide emulsion layer, e.g., in a gelatin sublayer, a separator or lightfiltering layer or in an antiabrasion layer. The amount of araban, galactan, arabogalactan or mixtures thereof so used can be based on the total gelatin in the contiguous layers. A layer essentially composed of gelatin and one or more of the pectic polysaccharides in an amount of 20 to 80 parts per 100 parts by weight of the total gelatin in the contiguous layers can be used.

As will be apparent from the above description, the invention is not limited to the specific quantities or types of water-soluble pectic polysaccharides as shown in the examples. According to the technical reference Polysaccharide Chemistry by Whistler and Smart, Academic Press, Inc., New York 1953, pages 198-207, the pectic polysaccharides of this invention are composed of 01,4- D-galactopyranose units, i.e., galactan; approximately l--% 5-l,6'-D-galactopyranose and [i-1,3'-D-galactopyranose units, and approximately 12% terminal L- arabofuranose units, i.e., arabogalactan; and a-1,5-L- arabofuranose units and a-1,3-L-arabofuranose units, i.e., araban. The latter material, araban, is a polymer of L-arabinose which can be extracted from apple pectin and peanuts. Generally, araban contains small amounts of pectic acid and galactan. Galactan is present in numerous plant tissues and can be obtained in reasonable purity from the seeds of the shrubby plant, white lupine. The arabogalactan can be extracted from larch wood.

The invention is not limited to photographic gelatinosilver halide emulsions of the silver iodobromide type. The invention may be applied to other gelatino-silver halide emulsions e.g., gelatino-silver bromochloride emulsions of the lithographic type as well as silver bromide emulsions. This invention is particularly efficacious in photographic emulsions where the average silver halide grain size is relatively large.

The pectic polysaccharides are useful not only with black and white photographic and X-ray emulsions, but with photographic emulsions used in color photography. Suitable emulsions can contain color-formers in addition to gelatin and at least one of the water-soluble pectic polysaccharides. Examples of useful gelatino-silver halide emulsions and color-formers useful therein are disclosed in Middleton and Jennings US. 2,319,426; Dorough, U.S. 2,380,032, Dorough, US. 2,380,033 and Woodward and C'hu, US. 2,927,024. In the case of emulsions containing pectic polysaccharides which are to be used for color photography, the emulsion layers may be developed in color developers containing the color-formers. The invention may also be applied to photographic elements useful in dye imbibition and wash-01f reliefi processes for colour photography.

The emulsions may contain any of the well-known optical sensitizing dyes as well as non-optical sensitizers such as sulfur sensitizers containing labile sulfur, e.g., allyl isothiocyanate, allyl diethyl thiourea, phenyl isothiocyamate and sodium thiosulfate, the polyoxyalkylene others in Blake et al. US. Patent 2,400,532 and the polyglycols disclosed in Blake et al. US. Patent 2,432,549. Other optical sensitizers such as amines as taught by Staud et al. U. S. Patent 1,925,508 and metal salts as taught by Baldsiefen US. Patent 2,540,085 and Baldsicfen et al. US.

Patent 2,540,086 may also be used. Antifoggants, e.g., benzotriazole and triazaindenes, can be used as well as the usual hardeners, i.e., chrome alum, formaldehyde, etc. Pigments, matting agents and other well-known photographic emulsion adjuvants also may be used in conjunction with the pectic polysaccharides.

The emulsion may be coated on any suitable support such as paper or films composed of cellulose esters, e.g., cellulose triacetate, cellulose acetate/butyrate; superpolymers, e.g., polyvinyl chloride (co) vinyl acetate; polyvinyl acetals, e.g., formals, acetals; polystyrene; polyamides, e.g., polyhexamethylene adipamide, and polyesters, e.g., polyethylene terephthalate, polyethylene terephthalate/isophthalate, esters formed by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclohexane-l,4-dimethanol (hexahydro-p-Xylene alcohol). The vinylidene chloride copolymer-coated oriented polyester films of Alles et al. US. Patent 2,627,088 and Alles US. Patent 2,779,684 are especially suitable.

An advantage of the invention is that it provides a simple, dependable and effective means for providing gelatino-silver halide photographic emulsions of enhanced covering power 015 developed silver. The efticiency of the resulting developed silver is increased, that is, it can provide greater density per quantity of metallic silver which results from development. I

Another advantage of the invention is that the addition of pectic polysaccharides to photographic emulsions requires no special technique and can he carried out by the ordinary technician with conventional appacatus. Since :the pectic polysaccharides can he added from aqueous solutions, it does not provide the problems of solvent recovery and the resulting modified gelatino-silver halide emulsions can be coated and dried in the conventional coating and drying apparatus which ofiers commercial advantages. Still \iurther advantages will be apparent from the foregoing description of the invention.

What is claimed is:

1. A photographic silver halide emulsion having increased covering power of developed silver comprising, on a dry basis per 100 parts by weight of gelatin, 20 to 80 parts by weight of at least one water-soluble pectic polysaccharidetaken from the group consisting of araban, arabogalactan and galact-an having a molecular weight of 6,000 to 100,000, and 60' to 150 parts by weight of a light-sensitive silver halide.

2. An emulsion as defined in claim 1 wherein said pectic polysaccharide is ama bogalactan.

3. An emulsion as defined in claim 1 wherein said silver halide is silver iodobromide.

4. A photographic element having increased covering power ofi developed silver comprising a support and a gelatino-lsilver halide emulsion layer comprising, on a dry basis per 100 parts by weight of gelatin, 20 to 80 parts by weight of at least one water-soluble pectic polysaccharide takenfrom the group consisting of araban, arabogalaotan and galactan having an average molecular weight of 6,000 to 100,000, and 60 to 150 pants by weight of a light-sensitive silver halide. t

5. An element as defined in claim 4 wherein said pectic polysaccharide is arabogalactan.

6. An element as defined in claim 4 wherein said silver halide is silver iodobromide. t

7. A photographic element having increased covering power of developed silver comprising a support, a gelatino-silver halide emulsion layer and a layer contiguous the silver halide emulsion layer, the said contiguous layer containing, on a dry basis per 100 pants by weight of total gelatin in said layers, 20 to 80 parts by weight of at least one watersoluble pectic polysaccharide taken irom the group consisting of araban, arahogalactan and galactan having a molecular weight of 6,000 to 100,000, any remaining constituent of the contiguous layer being gelatin.

8. A process for increasing the covering power of developed sil-ver which comprises admixing with a gelatinosilver halide emulsion containing, on a dry weight basis per 100 parts by weight of gelatin, to 150 parts by weight ofi light-sensitive silver halide, from 20m parts by weight of at least one water-soluble pectic polysaccharide taken from the group consisting of anaban, a-rabogalactan and galactan per parts lay weight of gelatin, said pectic polysacoharide having an average molecular Weight of 6,000 to 100,000.

9. A process as defined in claim 8 wherein said pectic polysaccharide is arabogal-actan.

10. A process as defined in claim 8 wherein said silver halide is silver iodobromide.

References Cited in the file of this patent UNITED STATES PATENTS Nicholes et al May 11, 1948 lllingsworth et a1 Oct. 10, 1961 Whistler et al: Polys-accharide Chemistry, Academic Press, Inc, New York, 1953, pages 198-207.

Claims

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION HAVING INCREASED COVERING POWER OF DEVELOPED SILVER COMPRISING ON A DRY BASIS PER 100 PARTS BY WEIGHT OF GELATIN, 20 TO 80 PARTS BY WEIGHT OF AT LEAST ONE WATER-SOLUBLE PECTIC POLYSACCHARIDE TAKEN FROM THE GROUP CONSISTING OF ARABAN, ARABOGALACTAN AND GALACTAN HAVING A MOLECULAR WEIGHT OF 6,000 TO 100,000, AND 60 TO 150 PARTS BY WEIGHT OF A LIGHT-SENSITIVE SILVER HALIDE.