|
(11) | EP 0 428 332 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Colour holograms |
| (57) There is described holographic material which comprises coated on a photographic
supporting base at least one silver halide emulsion which has a mean grain size of
less than 0.1µm and at least one emulsion of which has been optically sensitised with
at least one green sensitising dye of the following general formula I :
wherein R₁ is an optionally substituted alkyl group, R₂ is hydrogen or an alkyl group having 1 to 6 carbon atoms and D represents the atoms needed to complete an optionally substituted 5- or 6- membered heterocyclic ring and at least one emulsion of which has been optically sensitised with at least one red sensitising dye of the general formula II :- wherein R₁ is an alkyl group having 1 to 4 carbon atoms, R₂ and R₃ are each hydrogen, alkyl groups having 1 to 4 carbon atoms or aryl, R₄ is an optionally substituted alkyl group and Y represents the atoms necessary to complete a benzothiazole or benzoselenazole nucleus, the benzene ring of which is optionally substituted. The silver halide emulsion used in the holographic material of the present invention can be used to produce a record of a holographic exposure which has been made using a laser which emits in the blue, green or red regions of the spectrum. If three exposures are made to the three regions of the visible spectrum a record of all three exposures can be obtained. |
[0002] It should be possible to prepare a multicolour hologram by incorporating a plurality of optical sensitising dyes in the silver halide emulsion and exposing the material holographically to three laser exposures, one in the blue, one in the green and one in the red regions of the spectrum. After processing to develop the latent silver image followed by a rehalogenating bleach, on white light reconstruction a multi-colour hologram should be visible. However in practice it has been found very difficult to discover a mixture of optical sensitizing dyes which can be used to prepare such a multicolour hologram.
[0003] To begin with as the crystal size of the silver halide crystals in the emulsion is required to be less than 0.1 µm, that is to say a Lippmann emulsion, only a limited number of optical sensitizing dyes are able to be used. Secondly as at least two optical sensitizing dyes are required to be present in the mixture often one dye is adsorbed preferentially on to the silver halide and the optical sensitizing effect of the non-adsorbed dye is almost completely negated. Thus it is necessary to choose two dyes which are adsorbed equally well on to the silver halide crystals.
[0004] Thirdly because it is necessary to process the material using a rehalogenating bleach it is necessary to choose dyes which do not inhibit the bleaching of the silver. A large number of sensitizing dyes which sensitise strongly in normal photographic material can not be used for this reason.
[0005] However we have discovered a mixture of sensitizing dyes which do not suffer from any of the above listed defects either individually or when in admixture and which can be used to prepare multi-colour holograms.
[0006] Therefore according to the present invention there is provided holographic material which comprises coated on a photographic supporting base at least one silver halide emulsion which has a mean grain size of less than 0.1 µm and at least one emulsion of which has been optically sensitized with at least one green sensitizing dye of the following general formula I:-
wherein R₁ is an optionally substituted alkyl group, R₂ is hydrogen or an alkyl group having 1 to 6 carbon atoms and D represents the atoms needed to complete an optionally substituted 5- or 6- membered heterocyclic ring and at least one emulsion of which has been optically sensitized with at least one red sensitizing dye of the general formula II :-
wherein R₁ is an alkyl group having 1 to 4 carbon atoms, R₂ and R₃ are each hydrogen, alkyl groups having 1 to 4 carbon atoms or aryl, R₄ is an optionally substituted alkyl group and Y represents the atoms necessary to complete a benzothiazole or benzoselenazole nucleus, the benzene ring of which is optionally substituted.
[0007] Preferably there is one silver halide emulsion layer which has been sensitised with at least one dye of formula I and with at least one dye of formula II.
[0008] Preferably in the dyes of formula I R₁ is a sulphor-alkyl group and most preferably a sulpho-butyl group. Preferably in the dyes of formula I R₂ is hydrogen or methyl.
[0009] Preferably in the dyes of formula I D completes an unsubstituted rhodanine or thiohydantoin ring.
[0010] Preferably in the dyes of formula II Y represent the atoms necessary to complete an unsubstituted benzothiazole ring.
[0013] Preferably in the dye of formula II R₄ is an optionally substituted alkylene chain -Z-CO₂H, wherein Z is an alkyl moiety of from 1 to 4 carbon atoms.
[0014] The optional substitution on the benzene ring of the benzothiazole or benzoselenazole ring is preferably selected from at least one alkyl or alkoxy group having from 1 to 4 carbon atoms and a halogen atom. Very useful substituents are (one or more) methyl or methoxy groups or chlorine atoms.
[0015] Optional substitution on the alkylene chain Z preferably is selected from an alkyl group having from 1 to 4 carbon atoms, preferably a butyl radical such as -CH₂CH(CH₃)₂, an aryl group, preferably phenyl and an aralkyl group wherein the alkyl moiety has from 1 to 4 carbon atoms such as benzyl, phenylethyl, phenylpropyl. Preferably, these groups are substitutents on a methylene group Z.
[0016] The dyes of formula II where R₄ is -Z-CO₂ H are described in British Patent Application No. 2162855.
[0017] The dyes of formula I are included in the dyes described in British Patent Specification No. 1317139.
[0018] The dyes of formula I have an absorption which stretches from 440 nm to 550 nm. An argon ion laser can be tuned to emit at 458 nm and also at 528 nm (as well as other wavelengths).
[0019] The dyes of formula II are red sensitizing dyes and their absorption stretches from 600 nm to 710 nm. A helium-neon laser has its emission at 633 nm.
[0020] The silver halide emulsion used in the holographic material of the present invention can be used to produce a record of a holographic exposure which has been made using a laser which emits in the blue, green or red regions of the spectrum. If three exposures are made to the three regions of the visible spectrum a record of all three exposures can be obtained.
[0021] Therefore according to another aspect of the present invention there is provided a process for the production of a hologram which on reconstruction exhibits a multi-colour holographic image which process comprises exposing the holographic material hereinbefore described which comprises at least one dye of formula I and at least one dye of formula II to three holographic laser exposures one in the blue region of the visible spectrum, one in the green region and one in the red region developing the latent silver image using a silver halide developing agent and removing the developed silver using a rehalogenating bleach bath.
[0022] Preferably the binder for the silver halide emulsion or emulsions is gelatin. The laser exposures can be sequentially in any order or simultaneously. As long as care has been taken to avoid gross shrinkage of the emulsion during processing then the holographic image obtained on reconstruction comprises a blue image which represents the object of the holographic exposure when using the blue light emitting laser, a green image which represents the object of the holographic exposure when using the green light emitting laser and a red image which represents the object of the holographic exposure when using the red light emitting laser.
[0023] The overlapping of these colour images enables the whole visible image colour range to be obtained for example where the red and the green images overlap a yellow image is obtained.
[0024] A tuned Krypton laser can be used to effect all three exposures. Such a laser emits at 476.5 nm in the blue region of the spectrum, at 520.8 nm in the green region of the spectrum and at 647.1 nm in the red region of the spectrum. Using the holographic material of the present invention after three holographic exposures using the tuned Krypton laser at these wavelengths, followed by silver development and a rehalogenating bleach to remove the developed silver a holographic record can be obtained which on white light reconstruction exhibits a hologram which is in all three colours blue, green and red.
[0025] But however much care is taken during the processing to prevent emulsion shrinkage some shrinkage usually takes place and this leads to a decrease in replay wavelength of up to 70 nm in the record obtained in all three exposures. Thus in this case the record obtained by the green exposure will replay at as low as 450 nm instead of at 520 nm the exposing wavelength during the green exposure. Thus the hologram reconstruction would exhibit all the replay wavelengths hypsochromically shifted. A bathochromic shift in the replay wavelength of a hologram can be effected by treating the emulsion after silver halide development with a gelatin swelling agent such as triethanolamine however this is not a lasting effect thought to be due to evaporation of the triethanolamine. Certain gelatin hardening agents such as aluminium salts have also been used but with very unpredictable results.
[0026] However there is described in European patent application 225 852 a method of preparing a hologram in which the binder is gelatin which exhibits a permanent and reproducible bathochromic shift in the replay wavelength.
[0027] In this patent application there is described a method of preparing a hologram which is of the silver halide in gelatin binder type which method comprises holographically exposing the material by use of coherent light, developing the holographic image by a chemical process and before processing, simultaneously or subsequently, treating the material with a solution of a compound which has a molecular weight of over a 100 and which reacts with the gelatin to form covalent bonds therewith to increase the molecular bulk of gelatin. A compound of this type is hereinafter referred to as a gelatin reactive compound. Preferably the solvent for the gelatin reactive compound is water.
[0028] A large number of compounds can be used in the process, but particularly useful compounds are those compounds which are used to treat fibrous materials of animal origin such as wool and silk. Such compounds are used to treat wool and silk to increase their dye-ability and to render fabrics treated with them more crease resistant.
[0029] A particularly useful class of compounds are the aldehyde condensation compounds described in European patent application 225 852.
[0030] These compounds have a very complex structure and can be best defined by their process of manufacture as set forth in British Patent No. 814288 wherein it states that there, is provided a process for the manufacture of condensation products, wherein a non-cyclic compound containing at least once the atomic grouping
is condensed in a first stage with an aldehyde and a salt of an aliphatic amine containing at least two primary or secondary amino groups at a temperature above 100 C, and the product so obtained is further condensed in a second stage with an aldehyde and a water-soluble ammonium salt or amine salt in the presence of a solvent.
[0031] A particularly useful range of condensation compounds are obtained when the aldehyde used in the first stage condensation and in the second stage condensation is in each case formaldehyde.
[0032] Preferably the salt of an alphatic amine used is a salt of ethylene diamine. Also preferably the water-soluble ammonium salt used in the second stage condensation is ammonium chloride.
[0033] As non-cyclic compounds which contain at least once the
grouping there may be used, guanidine, acetoguanidine, biguanide or substitution products of those compounds such as alkyl-biguanides or aryl-biguanides. Most preferably, however, the non-cyclic compund used is dicyandiamide.
[0034] An especially useful compound is obtained which is the reaction product of formaldehyde, ammonium chloride, dicyandiamide and ethylene diamine in a molar ration of 2:1:1:0.1. This compound is hereinafter referred to as Condensate 1 and is used in the Examples which follow.
[0035] Another useful class of compounds are the so-called reactive dyestuffs which comprise at least one hydrophilic group and at least one group which can react with a textile such as wool, cotton or silk.
[0036] Reactive dyes comprise both a chromophore group and a reactive group and there are also described in E.P. 225 852.
[0037] Examples of reactive groups are substituted mono-azine, diazine, triazine- oxazine- pyridine-, pyrimidine-, pyridazine-, pyrazine- and thriazine-rings of this type which are annelated for example, phthalazine, quinoline, quinazoline, quainoxaline and acridine rings.
[0038] Other examples of reactive groups are acryloyl and mon-, di-or trichloroacryloyl for example -COCH=CHCl and other substituted acryloyl groups such as -methylsulphonylacryloyl and protected acryloyl groups. Also vinyl sulphone groups and protected vinyl sulphone groups.
[0039] Other compounds which cause a permanent and reproducible bathochromic shift in the replay wavelength of gelatin binder holograms and which are described in European Patent Application 230 208 can also be used in this aspect of the present invention. Also the compounds described in European patent application No. 226542 can be used.
[0040] By rehalogenating bleach bath is meant a bath which oxidises the developed silver to a silver halide. It appears that this silver halide deposits on the undeveloped silver halide present in the material so reinforcing the holographic image on reconstruction.
[0041] Examples of useful rehalogenating bleach baths are aqueous solutions of ferric ammonium E.D.T.A. together with potassium bromide or p-benzoquinone and potassium bromide.
[0042] Therefore according to a further aspect of the present invention there is provided a process for the production of a hologram which on reconstruction exhibits a multi-colour holographic image which process comprises exposing the holographic material hereinbefore described which comprises at least one dye of formula I and at least one dye of formula II the silver halide emulsion or emulsions having a gelatin binder to three holographic laser exposures one in the blue region of the visible spectrum, one in the green region of the visible spectrum and one in the red region of the visible spectrum, developing the latent silver image using a silver halide developing agent, removing the developed silver using a rehalogenating bleach bath and before the bleach step, at the same time as the bleach step or after the bleach step treating the holographic material with an aqueous solution of a compound which causes a permanent swelling of the gelatin.
[0043] Preferably this compound has a molecular weight of over 100 and reacts with the gelatin to form covalent bonds therewith to increase the molecular bulk of the gelatin.
[0044] Most preferably the strength of the solution of this compound and the length of treatment are just sufficient to counteract the shrinkage of the gelatin due to the photographic processing so that no appreciable shift is observed on reconstruction of the hologram and the blue, green and red parts of the hologram when reconstructed exhibit substantially the same wavelengths as those of the three laser exposures. It requires some experimentation to enable this to be done.
[0045] The holographic material of the present invention has been described in particular for the production of reflection holograms however, it is also of use for the production of transmission holograms.
Example 1
[0047] A gelatino silver iodobromide emulsion having a median crystal size of 0.04 µm was prepared having a gelatin content of 162g/mole of silver. The emulsion was gold and sulphur sensitised and 0.8g/mole of silver of the green sensitizer A of the formula set forth below was added, followed by 0.4g/mole of silver of the red sensitizer B of the formula set forth below was added.
[0048] After a period for sensitization at an elevated temperature the emulsion was stabilized using a tetrazaindene stabilizer and wetting agents and coating aids added. The emulsion was then coated on 100 µm polyester base, which had been subbed, at a silver coating weight of 3.0g/m². A gelatin supercoat of 1.1g/m² was coated on the dried emulsion layer.
[0049] A strip of the thus prepared holographic material was exposed in three separate areas to three laser exposures performed by a tuned Krypton laser, the first exposure being at 647.1 nm in the red region of the visible spectrum, the second being at 520.8 nm in the green region of the visible spectrum and the third being at 476.5 nm in the blue region of the visible spectrum. The intensity of exposure in each case was between 300 - 600 µ J/cm². In each case the object of the holographic exposure was a plane mirror positioned parallel to the holographic material plane. Each exposure was made in the Denisyuk mode.
[0050] The material was then developed for 2 minutes at 30°C in a solution of the following formulation :-
| Sodium Sulphite Anhydrous | 30 g |
| Hydroquinone | 10 g |
| Sodium Carbonate | 60 g |
| Water to | 1000 ml |
[0051] The samples were then transferred to a rehalogenating bleach bath of the following composition :-
| Fe(NH₄)EDTA(1.8 M Solution) | 150 ml |
| KBr | 20 g |
| Water to | 1000 ml |
[0052] The samples were then water washed in running water for 1 minute and transferred to an aqueous bath which consisted of a 3% by weight solution of condensate 1 for 2 minutes.
[0053] After drying, the hologram in the holographic material was reconstructed using white light. This reconstruction showed that in the area of the first laser exposure a red hologram of the mirror was seen in the area of the second laser exposure a green hologram of the mirror was seen and in the area of the third exposure a blue hologram of the mirror was seen.
[0054] Table 1 shows the exposing and replay wavelengths of these three exposures at maximum reflectivity.
Table 1
| Exposure Number | Exposing nm | Replay nm |
| first | 647.1 | 647.9 |
| second | 520.8 | 525.9 |
| third | 476.5 | 478.6 |
[0055] This shows that the three primary colours were accurately reproduced by holographic exposures on a single piece of film.
Example 2
[0056] This example illustrates the effect of not treating the material with a swelling agent and with using a red sensitizing dye not of formula II or using a green sensitizing dye not of formula I.
[0057] There was used in this example a strip of the holographic material as prepared in Example 1 called emulsion 1.
[0058] Three other emulsions were prepared as in Example 1 except the emulsion 2 comprised 0.4 g/mole silver of the red sensitizing dye C as hereinafter formulated and emulsion 3 comprised 0.4 g/mole silver of the red sensitizing dye D as hereinafter formulated instead of red dye B. Both dyes C and D are well known red sensitizing dyes for photographic silver halide emulsions. Emulsion 4 comprised 0.8 g/mole silver of green sensitizing dye E as hereinafter formulated instead of dye A.
[0060] Samples of coating of emulsions 1,2,3 and 4 were exposed and developed to produce a wedge spectrogram. In all cases the wedge spectrogram indicated that the emulsions had a high sensitivity over the range 400 - 650 nm. Relative speeds to white light were determined at an exposure time of 10⁻⁴ seconds followed by development in a standard metol-hydroquinone developing solution.
[0061] Holographic evaluation was carried out by making a Denisyuk exposure of a brushed aluminium plate using a HeNe laser with an emitting wavelength of 633 nm. The holographic materials were developed in the developer used in Example 1 and bleached in the same ferric EDTA rehalogenating bleach. The reflectivity of the holograms and replay wavelengths were determined in a spectro-photometer. Relative reflectivity is expressed as a percentage of the reflectivity of the brushed aluminium target. The results of evaluation are given in the table below.
| EMULSION | RELATIVE SPEED AT D=1.0 (WHITE LIGHT) | RELATIVE REFLECTIVITY % | REPLAY WAVELENGTH nm |
| 1 | 1.71 | 78 | 569 |
| 2 | 1.63 | 9 | 561 |
| 3 | 1.68 | 14 | 560 |
| 4 | 1.53 | 24 | 580 |
[0062] Whereas the holographic material using emulsion 1 was completely bleached and therefore virtually transparent to transmitted light those using emulsion 2,3 and 4 contained a heavy deposit of unbleached silver in the exposed areas and therefore the relative reflectivity of emulsions 2 - 4 are significantly reduced.
1. Holographic material which is characterised in that it comprises coated on a photographic
supporting base at least one silver halide emulsion which has a mean grain size of
less than 0.1µm and at least one emulsion of which has been optically sensitized with
at least one green sensitizing dye of the following general formula I :
wherein R₁ is an optically substituted alkyl group, R₂ is hydrogen or an alkyl group having 1 to 6 carbon atoms and D represent the atoms needed to complete an optionally substituted 5- or 6- membered heterocyclic ring and at least one emulsion of which has been optically sensitised with at least one sensitizing dye of the general formula II :-
wherein R₁ is an alkyl group having 1 to 4 carbon atoms, R₂ and R₃ are each hydrogen, alkyl groups having 1 to 4 carbon atoms or aryl, R₄ is an optionally substituted alkyl group and Y represents the atoms necessary to complete a benzothiazole or benzoselenazole nucleus, the benzene ring of which is optionally substituted.
wherein R₁ is an optically substituted alkyl group, R₂ is hydrogen or an alkyl group having 1 to 6 carbon atoms and D represent the atoms needed to complete an optionally substituted 5- or 6- membered heterocyclic ring and at least one emulsion of which has been optically sensitised with at least one sensitizing dye of the general formula II :-
wherein R₁ is an alkyl group having 1 to 4 carbon atoms, R₂ and R₃ are each hydrogen, alkyl groups having 1 to 4 carbon atoms or aryl, R₄ is an optionally substituted alkyl group and Y represents the atoms necessary to complete a benzothiazole or benzoselenazole nucleus, the benzene ring of which is optionally substituted.
2. Holographic material according to claim 1 which is characterised in that it comprises
one silver halide emulsion layer which has been sensitized with at least one dye of
formula I and with at least one dye of formula II.
3. Holographic material according to either claim 1 or claim 2 which is characterised
in that in the dyes of formula I R₁ is a sulpho-alkyl group.
4. Holographic material according to claim 3 characterised in that the sulpho-alkyl
group is sulphobutyl group.
5. Holographic material according to any one of claims 1 to 4 characterised in that
in the dyes of formula I R₂ is hydrogen or methyl.
6. Holographic material according to any one of claims 1 to 5 characterised in that
in the dyes of formula I D completes an unsubstituted rhodanine or thiohydantoin ring.
7. Holographic material according to any one of claims 1 to 6 characterised in that
in the dyes of formula II Y represent the atoms necessary to complete an substituted
benzothiazole ring.
8. Holographic material according to any one of claims 1 to 7 characterised in that
in the dyes of formula II R₁ is methyl or ethyl.
9. Holographic material according to any one of claims 1 to 8 characterised in that
in the dyes of formula II R₂ and R₃ are each methyl.
10. Holographic material according to any one of claims 1 to 9 characterised in that
in the dyes of formula II R₄ is an optionally substituted alkylene chain -Z-CO₂H wherein
Z is an alkyl moiety of from 1 to 4 carbon atoms.
11. A process for the production of a hologram which on reconstruction exhibits a
multi-color holographic image which process is characterised in that it comprises
exposing the holographic material as claimed in any one of claims 1 to 10 which comprises
at least one dye of formula I and at least one dye of formula II to three holographic
laser exposures, one in the blue region of the visible spectrum, one in the green
region and one in the red region, developing the latent silver image using a silver
halide developing agent and bleaching the developed silver using a rehalogenating
bleach bath.
12. A process for the production of a hologram which on reconstruction exhibits a
multi-color holographic image which process is characterised in that it comprises
exposing the holographic material as claimed in any one of claims 1 to 10 which comprises
at least one dye of formula I and at least one dye of formula II and in which the
silver halide emulsion or emulsions has a gelatin binder to three holographic laser
exposures one in the blue region of the visible spectrum, one in the green region
of the visible spectrum and one in the red region of the visible spectrum, developing
the latent silver image using a silver halide developing agent, removing the developed
silver using a rehalogenating bleach bath and before the bleach step, at the same
time as the bleach step of after the bleach step treating the holographic material
with an aqueous solution of a compound which causes a permanent swelling of the gelatin.
13. A process according to claim 12 which is characterised in that the compound which
causes a permanent swelling of the gelatin has a molecular weight of over 100 and
reacts with the gelatin to form covalent bonds therewith to increase the molecular
bulk of the gelatin.