GB2033596A - Dulled photographic materials - Google Patents

Abstract

Dulled, black and white and colour photographic materials include in at least one layer, for example a silver halide, protective, filter or NC layer, from 5 to 50%, preferably from 7.5 to 20%, by weight, calculated on the dry weight of the binding agent in the layer, of a dispersion of a polyvinyl chloride or vinyl chloride copolymer produced by micro-suspension or seed polymerisation.

Description

SPECIFICATION Dulled photographic materials The invention relates to dulled photographic materials.

It has been proposed to dull the surfaces of photographic layers by incorporating therein inorganic or organic pigments or synthetic polymers. In this manner, there is obtained a certain surface roughness which ensures good retouchability and which suppresses the occurrence of Newton's rings during copying. It is desirable to select a dulling substance that is photographically inert and has a refractive index that is similar to that of dry gelatin so that clouding phenomena and losses of definition caused by scattered light are avoided. The dulled surfaces should also have a good abrassion resistance and be resistant to finger-prints.

In DT-AS 1 547 639 it is proposed to use amorphous silicic acid as the dulling agent. This has the disadvantage, however, that it tends to agglomerate at fairly high temperatures and is therefore difficult to filter. Alkaline earth metal salts, such as those described in US-PS 2 823 136, also have an unsatisfactory effect in that they have too great a density and too strong a covering ability, as a result of which the photographic properties are impaired. Other possible ways of dulling photographic materials consist of the addition of wax (DD-PS 35 234), hardened gelatin (DT-OS 2 522 692), cellulose derivatives (DRP 725 698) or dispersions of synthetic polymers. These known processes, however, are subject to a number of defects.

Layers dulled with wax have an unsatisfactory roughness since the latter is to some extent lost during the drying process. Starch, cellulose derivatives and hardened gelatin can be obtained in the desired grain size range only with difficulty and to some extent lose their dulling effect at high humidities. Synthetic polymer dispersions have the advantage that their dulling effect is not reduced as a result of rapid deposition during the coating operation. Such known polymer dispersions are polystyrene dispersions (GB-PS 645 954) and dispersions based on styrene copolymers (BE-PS 634 174, DT-OS 2 628 643) and on polymethyl methacrylate. With polystyrene resins, however, it is possible only with great difficulty to produce stable dispersions having a uniform particle size distribution.

Since polystyrene, in the same way as polymethyl methacrylate, differs considerably from gelatin in its refractive index, photographic materials dulled with these dispersions show increased clouding and losses of definition. In additon, their production is very expensive and difficult to reproduce.

Another disadvantage of several dulling agents is also that they do not have the desired spherical shape.

The present invention seeks to eliminate the disadvantages of known dulling agents, that is to say clouding and losses of definition caused by light scattering and the unfavourable refractive index of the dulling agent, insufficient stability during the coating process and defective dulling or coating faults caused by an unfavourable particle size distribution of the dulling agent, and to avoid the use of dulling agents which are expensive to produce.

The present invention provides a photographic material which includes inat least one layer from 5 to 50% by weight, preferably from 7.5 to 20% by weight, calculated on the dry weight of the binding agent in the layer, of a dispersion of a polyvinyl chloride or a vinyl chloride copolymer which has been produced by micro-suspension polymerisation or by seed polymerisation.

The polymer dispersions used as dulling agents in accordance with the present invention have a narrow particle size distribution; they can be produced with particle sizes of from 0.1 to 5 Zm according to the procedure described in DT-AS 1 301 529 or GB-PS 978 875 (micro-suspension polymerisation) or in DT-OS 2 054108 (seed polymerisation).

In the aqueous phase without additional protective colloids, the solids in such dispersions tend to settle without forming agglomerates. By adding from 20 to 500% by weight of protective colloid, preferably from 100 to 200% by weight of gelatin, calculated on the polymer, it is possible to obtain very stable dispersions.

Such dispersions can be used as dulling agents in liquid form without previous congelation. It is also possible, however, to allow the dispersions to congeal after adding the gelatin solution and to store the resulting gels. Even after several months' storage at SOC, there is no change in either the particle size or the particle size distribution. The gels melt readily and can be diluted with water or gelatin solution. It is also possible to dry the gels. In order to achieve subsequent rapid re-dispersion, it is advantageous to granulate the gels after or during the drying operation.

The present invention is especially useful for the dulling of silver halide layers, protective layers, filter layers and NC-layers.

The dulling technique of the present invention is distinguished by the fact that the dulling dispersions can be produced in the desired particle size and in a narrow particle size distribution in a simple manner without using high-speed dispersing apparatus. As a result, effective roughening is achieved with particle sizes of from 0.1 to 5clam, even at low concentrations of the dulling agents.

Since the refractive index of the vinyl chloride polymers, being 1.538, almost corresponds to that of gelatin, clouding phenomena and losses of definition are avoided.

The dispersed polymer particles are very stable with regard to agglomeration in the form of dispersions and are also dimensionally stable even at high humidities. Stabilised with gelatin and dried after congelation, the particles can be stored for long periods without low temperatures being required and can be re-dispersed in water or an aqueous protective colloid solution when required. The present invention makes it possible to produce especiallyfine-grained, dulled gelatin layers.

The following Example 1 describes the production of various dulling dispersions, and Examples 2 to 9 illustrates the invention.

EXAMPLE 1 Dulling dispersion A (for comparison) 1 kg of gelatin is swelled and melted in 14 1 of water. 2 kg of polymethyl methacrylate, dissolved in 11.4 1 of methylene chloride are added thereto at 45 C and dispersed by means of a high-speed stirring apparatus.

After dispersion has been completed the methylene chloride is removed and the dispersion is congealed at 10 C. The average particle diameter of the polymer particles is 0.478 Rm. The refractive index of the polymer particles is 1.492.

Dulling dispersion B 1 kg of gelatin is swelled and melted in 9.5 1 of water.6.45 of ora 31% by weight polyvinyl chloride dispersion, produced by micro-suspension polymerisation, having an average particle diameter of 0.4811lem are added thereto at 550C while stirring with a conventional low-speed stirring apparatus. After the addition has been completed the mixture is congealed at 10 C. The refractive index of the polymer particles is 1.538.

Dulling dispersions C- E.

Dulling dispersions C to 3 are produced in a manner similar to dulling dispersion B, polyvinyl chloride dispersions of differing particle sizes being used.

dulling dispersion average particle diameter C 0.789 Mm D 0.948#m E 1.312 um Dulling gelatin 101 of dulling dispersion B are poured into a congealing mould and congealed at 10 C. The resulting gel is cut into cubes of approximately 2 cm3 and air-dried for 48 hours at 350C. It is then reduced in size once more by means of a granulating apparatus. A faintly cloudy granulate is obtained which is referred to below as dulling gelatin.

EXAMPLE 2 1.2 kg of dulling dispersion A are dissolved in 100 1 of a 2% aqueous gelating solution at 40 C. This dispersion is poured, as a protective layer, onto a silver halide emulsion layer.

The dried protective layer has a good retouching ability, a peak-to-valley height of 1.1,am and exhibits few Newton's rings during copying.

EXAMPLE 3 The procedure described in Example 2 is repeated, but using 1.2 kg of dulling dispersion B. The dried protective layer has the following characteristics: retouching ability: very good peak-to-valley height: 1.2 Rm Newton's rings: none EXAMPLE 4 The procedure described in Example 2 is repeated, but using 4.8 kg each of dulling dispersions A and B.

The dried protective layers have the following characteristics: A B retouching ability: very good very good peak-to-valley height: 1.6#m 1.7 Clm Newton's rings: none none The material having the protective layer incorporating dulling dispersion A was very cloudy and showed very great losses of definition.

EXAMPLES 5-7 The precedure described in Example 2 is repeated, but using 4.8 kg each of dulling dispersions C, D and E.

The dried protective layers have the following characteristics: dulllng dispersion C D E retouching ability: very good very good very good peak-to-valley height: 2.8#m 3.lem 3.0-3.2 Rm Newton's rings: none none none EXAMPLE 8 The procedure described in Example 2 is repeated, but using 0.45 kg of dulling gelatin swelled in 1001 of a 1.5% gelatin solution for 20 minutes at 400C and then re-dispersed while stirring.The dried protective layer has the following characteristics: re-touching ability: very good peak-to-valley height: 1.4#m Newton's rings: none EXAMPLE 9 A Aprotective layer produced described in Example 3 is poured onto a multiple-layer colour material of which the green-sensitive silver halide/colour coupler/emulsion layer contains a stabiliser, a hardening agent, a wetting agent, the purple coupler Z 169 (Bios Final Rep. 721, 21, 1946) and other conventional additives. Dulling with dulling dispersion B leads to no impairment of the photographic properties. When the material is stored at 90% relative humidity, no tendency of the backing to adhere to the protective layer is observed.

In contrast, a comparison material without dulling dispersion B in the protective layer shows a considerable tendency to adhere, which, in the case of mechanical stress, results in damage to the backing and to the protective layer.

Claims (5)

1. A photographic material which includes in at least one layer from 5 to 50% by weight, calculated on the dry weight of the binding agent in the layer, of a dispersion of a polyvinyl chloride or a vinyl chloride copolymer which has been produced by micro-suspension polymerisation or by seed polymerisation.

2. A photographic material according to claim 1, which includes in at least one layer from 7.5 to 20% by weight of the dispersion.

3. A photographic material according to claim 1 or claim 2, wherein the binding agent is gelatin.

4. A photographic material according to any one of claims 1 to 3, wherein the layer which includes the dispersion is a silver halide layer, a protective layer, a filter layer or an NC layer.

5. A photographic material according to claim 1 produced substantially as described in any one of Examples 2 to 9 herein.