Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PHOTOGRAPHIC HARDENERS
Document Type and Number:
WIPO Patent Application WO/1999/022271
Kind Code:
A1
Abstract:
Tris(hydroxymethyl)phosphine and tetrakis(hydroxymethyl)phosphonium salts and condensates are useful in photography to harden proteinaceous peptizers and surface coatings.

Inventors:
GILBERT PAUL DOUGLAS (GB)
TALBOT ROBERT ERIC (GB)
Application Number:
PCT/EP1998/006788
Publication Date:
May 06, 1999
Filing Date:
October 26, 1998
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ALBRIGHT & WILSON UK LTD (GB)
GILBERT PAUL DOUGLAS (GB)
TALBOT ROBERT ERIC (GB)
International Classes:
C09H7/00; G03C1/30; (IPC1-7): G03C1/30; C09H7/00
Foreign References:
US3501311A1970-03-17
US4138256A1979-02-06
GB1203215A1970-08-26
EP0638842A11995-02-15
GB1272070A1972-04-26
GB1061134A1967-03-08
Attorney, Agent or Firm:
Savidge, Roger Gordon Madgwick (Albright & Wilson UK Limited Patents Dept. 210-222 Hagley Road West Oldbury West Midlands B68 0NN, GB)
Download PDF:
Claims:
CLAIMS
1. The use of organic compound containing one or more phosphorus atoms and a plurality of hydroxymethyl groups each attache to said phosphorus atom or one of said phosphorus atoms as hardeners of proteinaceous peptizers and surface coatings in the photographic industry.
2. The use according to claim 1 of THP, THP salts or THP condensates.
3. A method of hardening a layer of water soluble protein deposited on a support for the production of photographic images, which comprises contacting said protein, before, during or after deposition with a hardener, characterised in that said hardener is, or comprises an organic compound having one or more phosphorus atoms and at least two hydroxymethyl groups, each of said hydroxymethyl groups being attache to said phosphorus atom or one of said phosphorus atoms.
4. A method according to claim 3 wherein said hardener is THP, a THP salt or a THP condensate.
5. A method according to claim 4 which comprises the steps of forming an aqueous solution comprising a water soluble protein and THP, a THP salt or a water soluble THP condensate, depositing said solution on a photographic support, gelatinising said solution and drying it to form a hardened layer.
6. A method according to claim 3 of manufacturing a photographic medium which comprises precipitating a photosensitive salt in the presence of an aqueous proteinaceous peptizer to form grains of said salt disperse in said peptizer, depositing said disperse grains in said peptizer as a layer on a support and contacting said peptizer before, during and/or after deposition with a hardener characterised in that said hardener is THP, a THP salt or a water soluble THP condensate.
7. A method according to claim 3 of preparing support surfaces for photographic printing which comprises coating said surfaces with a dispersion of a pigment in a water soluble protein and contacting the protein with a hardener, before or after formation of the coating characterised in that said hardener is THP, a THP salt or a THP condensate.
8. A method according to any of claims 3 to 7 wherein the hardener is used in a proportion of from 0.05 to 20% based on the weight of protein.
9. A method according to any of claims 3 to 8 wherein said hardener is applied to the proteinaceous layer as an aqueous solution containing 0.01 to 8% by weight of said hardener.
10. A film or plate comprising at least one layer of photographic mulsion and optionally one or more protective layers of gelatin, at least one of said layers being hardened by THP or THP salt or a THP condensate.
Description:
PHOTOGRAPHIC HARDENERS The present invention provides novel photographic hardeners for use in hardening proteinaceous peptizing and coating agents used in the preparation and development of photographic mulsions and preparing photographic prints.

For convenience the term"photography"is used broadly herein to include radiography, thermal imaging and the formation of images by all forms of energetic radiation e. g. ultra violet, infra red, alpha, beta, gamma and x-rays, and the tracking of atomic or sub-atomic particles. The prefix"photo"should be construed accordingly wherever the context permit.

Photographic mulsion is prepared by precipitating grains of photosensitive salt, usually comprising silver halides, in the presence of an aqueous peptizing agent. The latter is usually a water soluble protein or proteinaceious material, typically gelatin. For convenience the peptizer will be referred to in the following description as"gelatin". But it is understood that the term is used broadly when the context permits to include other water soluble proteins which can be applied in a similar manner to gelatin.

The mulsion is coated onto a support to form one or more photosensitive layers. The support may be coated with a layer comprising gelatin, before and/or after deposition of the mulsion. After exposure the photosensitive layer is typically developed by contact with a reducing agent which is capable of reducing exposed grains to metallic silver more rapidly that unexposed grains. The image is fixed by dissolving off the unreduced salt to form a negative. Typically the image is then transferred photographically from the negative to a print which is usually supporte on paper or card which has been coated with a dispersion of white pigment such as barium sulphate in, e. g., gelatin.

Hardeners are used to harden the gelatin by cross linking active sites within the protein molecule. This is essential if the photographic film or plate is to survive high temperatures or alkaline solutions during processing, and be resistant to surface abrasion. The hardener is normally added to the mulsion prior to coating and may additionally be applied after coating. It may also be used to harden any layer of gelatin applied to the support as a substrate or any protective layer applied over the photosensitive layer. The hardener may also be applied during or after development and/or fixing, and to harden any layers comprising gelatin which may be formed in the course of printing.

Hitherto the main hardeners used in photography have been metal salts such as chrome alum, and, increasingly, aldehydes such as glutaraldehyde. Neither of these materials is desirable from the point of view of health, safety, and environmental protection. Chrome salts are a potentially serious source of pollution and glutaraldehyde is a powerful allergen.

There is therefore a need for a safer and more environmentally acceptable hardener for use in the photographic industry.

We have now discovered that organic compound containing one or more phosphorus atoms and a plurality of hydroxymethyl groups attache to said phosphorus atom or atoms, such as tris (hydroxymethyl) phosphine, referred to herein as THP, tetrakis (hydroxymethyl) phosphonium salts, referred to herein as THP salts and condensates of the type formed when THP salts react with nitrogenous comonomers such as urea, amines and/or ammonia to form copolymers or cooligomers (herein referred to as THP condensates), are all very effective and environmentally acceptable hardeners for proteinaceous peptizers, substrats and protective layers used in the preparation of photographs.

THP condensates, prepared from THP salts, especially the chloride (THPC), sulphate (THPS) and phosphate (THPP), have been widely used in the preparation of fire retardant for use in the textile industry. THP salts have found extensive use as biocides in water treatment. They have also been used in the leather industry to inhibit shrinkage of skions during acid degreasing, as curing agents in leather finishing, and as components of tanning liquors.

Our invention therefore provides the use of organic compound containing one or more phosphorus atoms and a plurality of hydroxymethyl groups each attache to (one of) said phosphorus atom (s), e. g. THP, THP salts or THP condensates as hardeners of proteinaceous peptizers and surface coatings in the photographic industry.

Generally the invention provides: a method of hardening a layer of water soluble protein deposited on a support for the production of photographic images, which comprises contacting said protein, before, during or after deposition with a hardener, characterised in that said hardener is, or comprises an organic compound having one or more phosphorus atoms and at least tAo hydroxymethyl groups, each of said hydroxymethyl groups being attache to said phosphorus atom or one of said phosphorus atoms, for example THP, a THP salt or a THP condensate.

According to one embodiment the invention comprises the steps of forming an aqueous solution comprising a water soluble protein and THP, a THP salt or a water soluble THP condensate, depositing said solution on a photographic support, gelatinising said solution and drying it to form a hardened layer.

According to a particular embodiment the invention provides a method of manufacturing a photographic medium which comprises precipitating a photosensitive salt in the presence of an aqueous proteinaceous peptizer to form grains of said salt disperse in said peptizer, depositing said disperse grains in said peptizer as a layer on a support and contacting said peptizer before, during and/or after deposition with a hardener characterised in that said hardener is THP, a THP salt or a water soluble THP condensate.

According to a further embodiment the invention provides a method of preparing support surfaces for photographic printing which comprises coating said surfaces with a dispersion of a pigment in a water soluble protein and contacting the protein with a hardener, before or after formation of the coating characterised in that said hardener is THP, a THP salt or a THP condensate.

According to a further embodiment the invention provides a film or plate comprising at least one layer of photographic mulsion and optionally one or more protective layers of a water soluble protein such as gelatin, at least one of said layers being hardened by THP, THP salt or THP condensate.

Any water soluble THP salt may be used in accordance with the invention. On economic grounds we prefer to use THPS or alternatively THPC. However, other salts such as, for example, the phosphate, bromide, nitrate, sulphite, acetate, citrate, formate, lactate, tartrate, carbonate, borate, or silicate could equally be used. The nature of the counter ion is not critical provided that it does not adversely affect any other component of the system.

THP may be formed by raising the pH of a solution of THP salt above 3.5, e. g. above 4, especially above 5.

THP condensates may contain 2 or more phosphorus atoms, so long as the phosphorus compound is water soluble to a concentration of at least 0.1, preferably more than 0.5, g/l at 25°C. Such phosphorus compound contain a total of at least 2 hydroxymethyl groups, usually at least one per phosphorus atom, and preferably at least 2 hydroxymethyl groups per phosphorus atom. The group or groups joining the phosphorus atoms together may be of the formula-R-,-R-O-,-R-O-R-,-R-NH-R or-R-R"-R-where R is an alkylene group of 1 to 4 carbon atoms and R"is the residue formed by removal of two hydrogen atoms, bonded to nitrogen, from a di or polyamide or an amine or di or polyamine, such as urea, a Cl 20 alkylamine, dicyandiamide, thiourea or guanidine. Such compound with 2 or more, e. g. 3, hydroxyalkyl groups per phosphorus atom may be made by self condensation off THP salts with a compound of general formula R"H2 such as urea, or a Cl to 2o alkylamine, e. g. by heating at 40 to 120°C.

The hardener of the invention is typically used in a proportion of from 0.05 to 20% based on the weight of gelatin, preferably 0.1 to 10%, e. g. 0.5 to 5%.

In post exposure treatments, such as developing, fixing and printing we prefer to contact the exposed film with a solution containing 0.005% to 10% by weight THP, THP salt or THP condensate, more preferably 0.01 to 8%, especially 0.1 to 5%, e. g. 0.2 to 2%.

The hardener is preferably added to the photosensitive mulsion before coating of the latter onto the support medium. The mulsion preferably comprises the photosensitive grains which are typically fine (e. g. 0.01 to 50 microns, especially 1 to 20 microns) crystals of silver bromide and/or silver chloride or a mixture of silver chloride and/or silver bromide with silver iodide. The grains are disperse in the aqueous protein, which is usually gelatin. The mulsion may additionally contain any known photographic mulsion additives, such as coating aids, sensitisers, dyes and mulsion stabilisers.

Coating may be effected in conventional manner, e. g. by depositing a layer of mulsion on the support substrate, which layer is gelatinised, e. g. by chilling and drying. The support will normally be a film such as cellulose triacetate or polyethylene terephthalate but could alternatively be a glass or ceramic plate, paper or card, printed circuit board or other solid substrate. The support may be precoated with a gelatin layer which may have been hardened by including a hardener of the invention. The mulsion may be deposited in several layers, which may have different compositions in order to provide different photochemical responses. Optionally a support layer of gelatin may be deposited to protect the surface. Hardener may be applied to the coated substrate after, or at any stage during, the coating process if it is desired to toughen the photosensitive layer.

The hardener may also be applied during or after developing and fixing in order to toughen J the negative or print.

When printing, it is conventional to coat the card or other printing substrate with a layer of gelatin containing disperse white pigment, in order to improve its reflectivity before depositing the mulsion, and this coating too may be hardened by applying a THP salt.

The invention is not limited to conventionally developed film, but may be applied to any process which employs gelatin or other water soluble protein as peptizer or as a substrate or protective layer for a photosensitive medium, including, but not limited to, monochrome, colour, radiographic and self developing films and plates, and particle detectors.

The invention will be illustrated by the following examples:- Examole 1 Equivalent proportion of two saturated solutions, of silver nitrate and of silver halides (equal weights of chloride and bromide) respectively were added slowly with vigorous agitation to a concentrated solution of gelatin, all at 70°C. To the mixed solutions was added a 78% aqueous solution of THPS in a proportion of 5% active THPS by weight based on the weight of gelatin. The mixture was coated onto cellulose triacetate film, chilled to gelatinise the mulsion and dried.

A similar mulsion was prepared using glutaraldehyde as the hardener. The example of the invention showed satisfactory robustness in comparison with the control.

Example 2 The hardening action of a 75% aqueous solution of THPS at 40°C and an addition of 1.8% active ingredient based on the weight of gelatin was compare with glutaraldehyde and formaldehyde at various pH values. The hardening time was measured and recorde in Table 1.

Table 1 HARDENING AGENT pH THPS Glutaraldehyde Formaldehyde 10.6 < 10 sec < 10 sec ND 7.0 < 10 sec < 10 sec 2 hrs 6.0 2.0 min 1.5 min > 6 hrs 5.0 11.5 min 6.5 min > 6 hrs 4.0 > 6 hrs 33 min > 6 hrs This demonstrates hardening times equivalent to glutaraldehyde but without the adverse environmental impact.

Visual comparison between gelatins treated with THPS and glutaraldehyde respectively showed that the former was substantially clear while the latter had a marked reddish discoloration.