Photosensitive Silver Halide Emulsions Comprising Coating Aids

Abstract

Photographic element comprising a support and a light-sensitive silver halide emulsion layer is described. The element includes in a water-permeable layer, which may be the silver halide emulsion layer, a hydrophilic colloid binder and as a surface-active agent a monoether or monoester of a polyglycol having oxyethylene units and oxypropylene units in a ratio of at least 2 oxyethylene units to 1 oxypropylene units, the terminal hydroxyl group of said polyglycol monoether or monoester being carboxyalkylated and the carboxyl group being in acid or salt form. The photographic elements do not exhibit hydrophobic inclusions which lead to repellency spots or comets and, additionally, are resistant to yellowing upon development.

Description

This invention relates to film-forming coating compositions comprising a hydrophilic colloid and a carboxy-alkylated polyglycol ether or ester.

In the application of film-forming coating compositions comprising a hydrophilic colloid to surfaces, particularly in the photographic industry, it is desirable to apply such coating compositions uniformly and at good production speeds. In many cases it is even desirable to apply such coatings over other previous layers, which are either wet or dry. For this purpose the use of surface active agents as coating aids in these hydrophilic colloid coating compositions has been widely adopted.

In the United Kingdom Patent Specification 1,178,546 it has been proposed to use as coating aids for hydrophilic colloid coating compositions carboxyalkylated monoethers and monoesters of polyethylene glycol in acid or salt form.

Though these carboxyalkylated monoethers and monoesters of polyethylene glycol have excellent properties for use as coating aids in coating compositions comprising a hydrophilic film-forming colloid they pose a number of difficulties when used in photographic light-sensitive silver halide materials in that they may have a disadvantageous effect on the photographic characteristics of said materials. Indeed, it has been observed that in photographic paper material they give rise to yellowing and in other material produce fogging upon storage.

It has now been found that the disadvantageous photographic effects of the above coating aids can be reduced or eliminated while not influencing the favourable coating characteristics of these coating aids by introducing in the oxyethylene chain one or more oxypropylene units, the ratio of oxyethylene units to oxypropylene units being at least two.

Therefore, in accordance with the present invention coating compositions are provided that comprise a hydrophilic colloid binder material and as surface active agent a monoether or monoester of a polyglycol having oxyethylene units and oxypropylene units in a ratio of at least 2 to 1, the terminal hydroxyl group of said polyglycol monoether or monoester being carboxyalkylated.

Particularly suitable coating aids for use according to the present invention can be represented by the following general formula: ##SPC1##

wherein:

A represents methylene optionally substituted by an alkyl group comprising from one to five C-atoms or ethylene,

M stands for hydrogen, an alkali metal such as sodium or potassium, ammonium or an organic ammonium e.g. diethanolammonium, triethanolammonium, morpholinium, and

R represents an aliphatic carboxylic acyl radical or a hydrocarbon radical including substituted hydrocarbon, more particularly an aliphatic straight-chain or branched-chain radical, in particular an alkyl or alkenyl radical with 6 to 24 and preferably an alkyl or alkenyl radical with 10 to 18 carbon atoms, or an alkylaryl radical, in which the aryl radical may be mononuclear or multinuclear, e.g. an alkylated phenyl or naphthyl radical, and in which the alkyl radical, which is a straight-chain or branched alkyl radical contains preferably 4 to 10 carbon atoms when the aryl radical is naphthyl and 6 to 14 carbon atoms when the aryl radical is phenyl,

each of n and m stands for 0 to 40,

p stands for 1 to 20, and

q stands for an integer such that pxq is at least 1 and at most 20,

the total number of oxyethylene units i.e. (n.times.q)+m being at least 5 and at most 40 and the ratio of oxyethylene units to oxypropylene units i.e. [(n.times.q)+m]/[ p.times.q] being at least 2.

The compounds of use according to the present invention can be prepared by methods well known to those skilled in the art of organic synthesis for instance by condensation of the appropriate alcohol or acid (ROH) alternatively with ethylene oxide and isopropylene oxide (cfr. M.J. Schick -- Nonionic Surfactants -- Marcel Decker Inc., New York, 1967, Chapter 10) whereupon the resulting polyoxyalkylene ether or ester alcohol is carboxyalkylated by means of the appropriate .alpha.-halocarboxylic acid, .beta.-halopropionic acid or salts of these acids.

Examples of suitable coating aids according to the present invention are: ##SPC2##

Coating compositions containing a hydrophilic colloid binder material and a coating aid corresponding to the above general formula can be applied to dry surfaces as well as to wet surfaces and form layers that can be easily overcoated in wet as well as in dry state, the said layers being either light-sensitive layers or not. The coating aids according to the present invention have good anticomet properties and thus prevent the formation of repelency spots and give less rise to foaming and resulting air-bubbles than saponin and other conventional synthetic coating aids; said foaming mainly results from the presence of sulphate or sulphonate groups in the latter coating aids.

The coating aids of use according to the present invention can also be used in combination with other coating aids e.g. coating aids that strongly reduce repellency spots but that render the layer containing them difficult to overcoat. By the presence of the coating aids according to the present invention the latter disadvantage is overcome and the mentioned strong reduction of repellency spots formation is maintained. Moreover, the coating aids according to the present invention have also favourable dispersing or emulsifying properties so that they can be used for dispersing or emulsifying substances in hydrophilic colloid compositions, which as a result of the presence of said coating aids also show improved coating characteristics. For instance they are suitable as dispersing agent or emulsifying agent for substances that are to be incorporated into layers comprising a hydrophilic colloid and that would give rise to the formation of repellency spots in said layers when no compounds according to the invention were present. Other properties of the coating aids according to the present invention will appear hereinafter.

Although the coating aids according to the present invention are mainly intended for use in coating compositions comprising gelatin as hydrophilic colloid, they can also be used as coating aid for coating compositions comprising other colloidal materials or mixtures of them, e.g. hydrophilic natural colloids, modified hydrophilic natural colloids or synthetic hydrophilic polymers. More particularly these colloids may be selected of such film-forming natural or modified natural hydrophilic colloids, as e.g., glue, casein, zein, hydroethylcellulose, carboxymethyl-cellulose, methylcellulose, carboxymethyl-hydroxyethylcellulose, gun arabic, sodium alginate and hydrophilic derivatives of such colloids. They may also be selected of such synthetic hydrophilic polymers as e.g. polyvinyl alcohol, poly-N-vinyl pyrrolidone, polyvinyl amine, polethylene oxide, polystyrene sulphonic acid, polyacrylic acid, and hydrophilic copolymers and derivatives of such polymers. In this connection reference is made, e.g. to United Kingdom Patent Specification 1,139,891 filed Dec. 5, 1963 by Gevaert Photo-Producten N.V. and French Patent Specification 1,507,874 filed Jan. 10, 1967 by Gevaert-Agfa N.V., which relate among others to heat- and/or pressure-sensitive materials comprising a recording layer mainly consisting of a dispersion of hydrophobic thermoplastic polymer particles in a hydrophilic colloid binder.

The compounds according to the above general formula are good coating aids for use in coating compositions as defined above either alone or in admixture with other coating aids e.g. dialkyl sulphosuccinic acid salts and salts of alkyl sulphuric acids, salts of alkyl sulphonic acids, salts of alkylarly polyether sulphuric acids, salts of alkylarly polyether sulphonic acids, the fluorinated coating-aids described in Belgian Patent Specification 742,680 filed Dec. 5, 1969 by Gevaert-Agfa N.V. It has been found that coating aids according to the present invention improve the coating characteristics of coating compositions even at a concentration as low as 0.01 bt weight relative to the weight of solids. Larger concentrations, however, can also be used but generally the concentration is not higher than 5 percent by weight based on the weight of solids. In coating compositions intended for being coated as hydrophilic colloid layers in photographic silver halide materials said coating aids are generally present in amounts from 0.01 to 2 percent based on the weight of dry colloid.

The coating aids according to the invention are particularly suitable for use in a coating composition comprising gelatin as hydrophilic colloid, either as an aqueous solution of gelatin or as a photographic emulsion which ordinarily is composed of an aqueous solution of gelatin containing as the light-sensitive material therein, a silver halide such as silver bromide, silver chloride, silver iodide, or mixtures thereof or another light-sensitive substance. The silver halide emulsions may be coarse, medium or fine grain emulsions and may contain other added substances as sensitizing dyes, hardeners, stabilizers, pH-adjusting compounds, colour couplers, anti-fogging agents, development accelerators, thickening agents, developing agents, softening agents, or the like. For instance, the coating aids of the invention are useful in gelatin photographic emulsions, not only those which are non-optically sensitized for example X-ray emulsions, but also in orthochromatic and panchromatic emulsions. This also includes gelatin emulsions intended for colour photography including colour radiography for example emulsions containing colour forming couplers.

The coating aids corresponding to the above general formula and their mixtures with other coating aids are also very useful in various other types of coating compositions in which gelatin is an important constituent, for example, in gelatin coating compositions to be applied as antihalation layer to the back or front of the base in a photographic material, as protective layer, as filter layer, as intermediate layer, as anticurling layer, etc., which layers can also contain all kinds of other ingredients such as filling agents, hardening agents, antistatic agents, anti-friction agents, or in any other type of gelatin layer, which is coated from a composition comprising an aqueous solution of gelatin, for example a gelatin receptor layer of a blank film for producing multicolour images by imbibition printing.

The coating compositions in accordance with our invention may be coated on a transparent support e.g. of glass, cellulose esters, polyethylene terephthalate or on a non-transparent reflecting material such as paper or an opaque cellulose ester. It is often desirable first to coat a subbing layer to the support, this practice of subbing being well known in the art.

The coating procedure may comprise any of the standard procedures employed in industry, such as roller coating, brush coating, dip-coating, spraying, using a doctor blade or an air blade to control the thickness and distribution of the coating composition.

The following examples illustrate the present invention.

EXAMPLE 1

A series of 11 conventional gelatin silver chloride emulsion samples all having the same composition was prepared. To ten of these samples a certain amount of coating aid was added as listed in the following table whereas to one of these samples no coating aid at all was added. These 10 emulsions were then coated on a baryta coated paper support with grained surface whereupon the emulsion layers formed were overcoated while still wet with a protective gelatin layer containing only saponin as coating aid.

In each case the "critical speed" for applying the protective layers on the wet emulsion layers was determined and the number of repellency spots i.e. "comets" per sq.m were counted for each material.

By "critical speed" is understood the maximum speed of the moving base to be coated, at which the composition for forming the protective layer can still be coated. Indeed, the layers of air carried along by the moving base are capable, at a certain speed, of preventing in large areas, contact of the material to be coated with the wet emulsion layer whereby uncoated portions remain on the moving emulsion layer. On decreasing the speed of coating, contact of the emulsion layer with the protective gelatin layer takes place over the entire area, the instability of the coated layer, because of the incomplete wetting of the base, does not occur and uniformity of the layer thickness is maintained.

The results obtained are listed in the following table.

Criti- Repel- Coating aid used in the emulsion and cal len- concentration thereof in % by weight of speed in cy spots dry gelatin m/min per sq.m none 4 10 0.2 % of saponine 4 1 0.01 % of n-C.sub.18 H.sub.37 -(OCH.sub.2 CH.sub.2 --).sub.9 OCH.sub.2 COONa 7 1 0.025 % do. 16 0 0.05 % do. 20 0 0.01 % of compound 4 6 1 0.025 % of compound 4 17 0 0.05 % of compound 4 19 0 0.01 % of compound 5 5 1 0.025 % of compound 5 15 0 0.05 % of compound 5 18 0

From the results listed in the table it appears that the critical speed obtained with coating aids according to the present invention was markedly higher than when saponin was used and was almost the same as when using compounds according to the United Kingdom Patent Specification 1,178,546. The coating aids of the invention had also the same favourable anti-comet action as the compounds of the United Kingdom Specification.

When the materials formed were developed in a standard 1-phenyl-3-pyrazolidone/hydroquinone developer, stopped, rinsed, fixed and dried in the usual way and than exposed for one hour to U.V.-light, the materials comprising n--C.sub.18 H.sub.37 (OCH.sub.2 CH.sub.2 --).sub.9 OCH.sub.2 COONa showed strong yellowing whereas the materials comprising compounds 4 and 5 remained unaffected.

EXAMPLE 2

A series of fine-grain gelatino silver halide emulsions intended for being coated on a film support and all having the same composition, was prepared. To each of these emulsion samples a certain amount of coating aid or mixture of coating aids was added as listed in the following table, except for one sample to which no coating aid at all was added. After having been coated on a conventional polyethylene terephthalate film support the emulsion layers while still wet were overcoated with a protective gelatin layer. In each case the critical speed for applying the protective layers on the wet emulsion layers was determined and the number of repellency spots per sq.m. were counted for each material. The results obtained are listed in the following table.

Criti- Repel- Coating aid used in the emulsion and cal len- concentration thereof in % by weight of speed in cy spots dry gelatin m/min per sq.m none 15 50 0.2 % of saponine 15 15 0.01 % of sodium isotetradecyl sulphate 4 2 0.01 % of sodium isotetradecyl sulphate + 0.01 % of ##SPC3## 16 2

0.01 % of sodium isotetradecyl sulphate + 0.025 % of ##SPC4## 38 3

0.01 % of sodium isotetradecyl sulphate + 0.05 % of ##SPC5## 40 2

0.01 % of sodium isotetradecyl sulphate + 0.01 % of compound 1 tn 15 3 0.01 % of sodium isotetradecyl sulphate + 0.025 % of 37 2 ompound 1 0.01 % sodium isotetradecyl sulphate + 0.05 % of compound 1 39 2 0.01 % of sodium isotetradecyl sulphate + 0.01 % of compound 2 16 4 0.01 % of sodium isotetradecyl sulphate + 0.025 % of compound 2 37 3 0.01 % of sodium isotetradecyl sulphate + 0.05 % of compound 2 39 1

From the results listed in the table the following can be learned. The formation of repellency spots was reduced when replacing saponin by sodium isotetradecyl sulphate as coating aid. The latter coating aid however, had the disadvantage of lowering the critical speed markedly, which means that the emulsion layer becomes difficult to overcoat. By the use of a combination of sodium isotetradecyl sulphate and a coating aid according to the present invention the critical speed was markedly increased while the number of "comets" remained low, the increase in critical speed and reduction of number of comets being of the same order of magnitude as when using coating aids according to the United Kingdom Patent Specification 1,178,546.

EXAMPLE 3

To a conventional gelatin silver chloride emulsion were added per kg, in addition to saponin, 5 ml of a 5 percent aqueous solution of the coating air with formula: ##SPC6##

The emulsion was applied to a baryta-coated paper support whereupon the emulsion layer was overcoated while still wet with a protective gelatin layer containing saponin as coating aid.

After drying the material was developed for six min. at 28.degree.C in a developing bath of the following composition:

water 800 ml

anhydrous sodium sulphite 50 g

anhydrous sodium carbonate 40 g

sodium hexametaphosphate 2 g

1-phenyl-3-pyrazolidone 0.2 g

hydroquinone 6 g

potassium bromide 2 g

The developed material was then stopped, rinsed, fixed and dried.

Upon overall exposure for one hour to U.V.-light, the exposed and developed material showed heavy yellowing whereas a material of the same composition but comprising instead of the above coating aid, 5 ml of a 5 percent aqueous solution of compound 2 showed no yellowing at all after processing and exposure to U.V.-light as described above.

Claims

We claim:

1. A coating composition comprising a light-sensitive silver halide; a hydrophilic colloid and a surface active agent wherein said surface active agent is a monoether or monoester of a polyglycol having oxyethylene units and oxypropylene units in a ratio of at least 2 oxyethylene units to 1 oxypropylene unit, the terminal hydroxyl group of said polyglycol monoether or monoester being carboxyalkylated and the carboxyl group being in acid or salt form.

2. A photographic element comprising a support and a light-sensitive silver halide emulsion layer, said element including in a water-permeable layer a hydrophilic colloid binder material and a surface active agent having a hydrophilic and hydrophobic portion, and being a monoether or monoester of a polyglycol having oxyethylene units and oxypropylene units in a ratio of at least 2 oxyethylene units to one oxypropylene unit, the terminal hydroxyl group of said polyglycol monoether or monoester being carboxymethylated or carboxyethylated and the carboxyl group being in acid or salt form.

3. A photographic element according to claim 2, wherein said surface active agent corresponds to the formula: ##SPC7##

wherein:

A stands for methylene optionally substituted by C.sub.1 --C.sub.5 alkyl, or ethylene,

R stands for an aliphatic radical having 6 to 24 carbon atoms, or an alkyl aryl radical having from four to 14 carbon atoms in the alkyl moiety,

M stands for hydrogen, an alkali metal atom, ammonium or organic ammonium,

each of n and m stands for 0 to 40,

p stands for 1 to 20, and

q stands for an integer such that p.times.q is at least 1 and at most 20, the total number of recurring oxyethylene units being at least 5 and at most 40, and the ratio of oxyethylene units to oxypropylene units being at least 2.

4. A photographic element according to claim 2, wherein R stands for alkyl or alkenyl comprising from 10 to 18 carbon atoms or for alkylaryl in which the alkyl radical comprises from four to 14 carbon atoms.

5. A photographic element according to claim 2, wherein the hydrophilic colloid binder material is gelatin.

6. A photographic element according to claim 2, wherein the said water-permeable layer is a light-sensitive silver halide emulsion layer.

7. A photographic element according to claim 2, wherein the said support is a paper support.

8. A photographic element according to claim 2, wherein the said support is a paper support and the said water-permeable layer is a light-sensitive silver halide emulsion layer.

9. A photographic element according to claim 2 wherein the surface active agent is present in said element in an amount of from 0.01 to 2 percent by weight based on the weight of the dry hydrophilic colloid.

10. A photographic element according to claim 2 wherein said element comprises, in addition to said surface active compound, a surface active agent selected from the group consisting of dialkyl sulphosuccinic acid salts, salts of alkyl sulphuric acids, salts of alkyl-sulphonic acids, salts of alkylaryl polyether sulphuric acids and salts of alkylaryl polyether sulphonic acids.