FR2492997A1 - Hologram recording material - by coating a rigid or flexible support with gelatin, and sensitising with aq. ammonium di:chromate soln. - Google Patents

Abstract

Process for prodn. of a hologram recording material with a flexible or rigid support, consists of preparing a 12-18% suspension of pure gelatin in water and mixing to cause complete dissoln. at 20 deg.C, followed by mixing for 5-10 mins. at 70 deg.C; filtering the soln. using a filter maintained at 50 deg.C; cooling to 40 deg.C and maintaining the temp. at this; adding 0.5 wt.% ammonium dichromate w.r.t. gelatin and mixing to achieve complete dissoln. The bath is then maintained at 40 deg.C and the support is immersed in the bath for ca. 1 min. and withdrawn at 1-5 cm/min. The coated support is dried in air in the vertical position for 1 hr., then the material is hardened in an oven for 2 hrs. at 150 deg.C. The material is then sensitised by immersion for 5 mins. in a 4-10% aq. ammonium dichromate soln. and stored in darkness at 20-30 deg.C for a max. of 48 hrs. in air at 30-40% humidity. Prods. have improved efficiency of diffraction and signal/noise ratio than previous materials based, e.g. on silver halide materials and give holograms with high resolution.

Description

 The present invention relates to the field of supports for recording and developing a hologram, and relates to a process for manufacturing a material on a rigid or flexible support, for developing and protecting the latter.

 Currently, the supports used for recording and developing holograms are generally photographic emulsions that are not very sensitive, but of high resolution, thermoplastic supports based on the interaction of electric charges with light, photoresists in which s modulates the surface of the support by chemical development, or photopolymers in which polymerization of a monomer takes place under the effect of light.

 However, these existing supports have a relatively low diffraction efficiency, namely around 60% for whitened silver emulsions and even less for the others, and the signal / noise ratio is poor. In addition, the resolution of these supports is often insufficient and their cost is relatively high.

 The present invention aims to overcome these drawbacks.

 It relates, in fact, to a process for manufacturing a material on a rigid or flexible support for recording a hologram, characterized in that it consists in preparing 12 to 18% by weight of pure gelatin in suspension in water by carrying out an initial mixing until complete dissolution at a temperature of 20 C, then a final mixing for approximately 5 to 10 minutes at 70 C, to filter the solution obtained by means of a filter heated to 50 C, â lower the temperature and maintain it at 40 ° C., then add ammonium dichromate in a proportion of 0.5% by weight of the gelatin, and carry out mixing until complete dissolution, then, still maintaining the bath obtained at 40 ° C., immerse in the latter, for about one minute, a rigid or flexible support, then remove it vertically at a speed of 1 to 5 cm / min., dry the support in a vertical position, air, for one hour, then harden the entire support, in the oven for d them hours at 150 C, then sensitize the hardened support by soaking for 5 minutes in a 4 So water solution at 10% ammonium dichromate and then store the support at 20 CC at dark 30 C for a maximum duration of 48 hours in air at 30 = 0 to 40% humidity.

 The support thus obtained is then prepared by passage through running water, followed by passage with stirring in isopropyl alcohol and drying in an upright position, and finally, by passage through a vacuum oven for 1 to 2 hours at 90 o C.

 The subject of the invention is also a process for developing the material on an impressed rigid or flexible support which consists in first dipping the support in a solution at 0.5% by weight of ammonium dichromate and of fixative diluted with l distilled water, rinse for 10 minutes under running water at 20 C, then immerse the support for 3 minutes with stirring in a solution of 50% isopropyl alcohol and 50% distilled water, then immerse the support for 2 minutes in a 90% solution of isopropyl alcohol and 10% of distilled water, then immerse it, with stirring, for approximately 10 to 20 minutes in isopropyl alcohol, and finally dry the support for at least 2 minutes in a jet of hot air, then pass it in a vacuum oven for 1 to 2 hours at 90 C.

 According to an alternative embodiment of the invention, the support can be immersed only in pure isopropyl alcohol for about 10 to 20 minutes after rinsing with running water, then be dried.

 The process for manufacturing the material on a rigid or flexible support in accordance with the invention gives excellent results for gelatin layer thicknesses of 1 to f5 r on supports of 3 cm x 8 cm and from 1 to 40 for supports 12 cm x 12 cm.

 The process for manufacturing the material on a rigid or flexible support may also consist, in accordance with an alternative embodiment of the invention, in preparing 4% by weight of pure gelatin suspended in water by carrying out an initial mixing up to complete dissolution at a temperature of 20 ° C., then a final mixing for approximately 5 to 10 minutes at 70 ° C., filtering the solution obtained by means of a filter heated to 50 ° C., then adding 0.5% by weight, relative to the weight of gelatin, ammonium dichromate, and to carry out a mixture until complete dissolution while maintaining the temperature at approximately 50 ° C., then to apply the product obtained by means of any applicator at a temperature of 50 ° C. by depositing said product on the rigid or flexible support to then worm the excess product with a blade spaced from the support by a distance of 0.5 to 1 mm so as to achieve a uniform distribution, to dry the support in a strictly horizontal position at the ambient air for about 24 hours, and finally to harden it in the oven at 150 o C for 2 hours, to sensitize it by soaking for 5 minutes in a solution of water at 4% to 10% of ammonium dichromate, then store it in the dark for a maximum of 48 hours at 20 C to 30 C in air at 30% to 40% humidity.

 This method of manufacturing the material s7Xr rigid or flexible support allows thicknesses of gelatin layers of 6 to 15 thread to be obtained on supports of 12 cm x 12 cm. The development of the support is identical to that of the supports obtained by immersion.

 The methods of manufacturing materials on rigid or flexible support described above make it possible to obtain supports which can be used up to limit wavelengths of 540 nm due to the spectral sensitivity of the material.

 For longer wavelengths, namely 633 nm and 647 nm, the manufacturing methods described above are supplemented by an sensitization step which consists in preparing a sensitizing solution comprising 0.06 M of ammonium dichromate and 10 mg / ml of green or blue methylene dye, stir this solution for approximately 2 minutes until the green or methylene blue dissolves completely, filter the solution with a Whatman No. 541 rapid filter to sensitize the support in the darkness by soaking with stirring for 6 minutes, then passing the gelatin side to a wringing roller, the substrate side being wiped, and then drying the support in air at 40% humidity, the support can then undergo holographic exposure within 48 hours and be developed.

 For the protection against humidity of a hologram recorded on a rigid or flexible support, the invention provides a method which consists in applying to the support, after development, by means of an epoxy-based adhesive. resin, a glass plate or a flexible transparent film. This protection can also be obtained by coating the rigid or flexible support with a protective varnish.

 It is thus possible, in the case of the use of a flexible support, to obtain a hologram with high brightness, which can itself be glued on any other support such as paper, or an airplane windshield. to form holographic mirrors in head-up control systems.

 The materials on rigid or flexible support obtained by application of the process in accordance with the invention make it possible to record or produce three-dimensional images of three-dimensional diffusing or specular objects by reflection or by transmission. This process allows mass production, at low cost, of holograms for various scientific, industrial, bio-medical, artistic and commercial applications. In addition, thanks to the invention, it is possible to carry out, with the same type of support, recordings at wavelengths reaching 647 nm.

 Of course, the invention is not limited to the embodiments described. Modifications remain possible, without departing from the scope of protection of the invention.

Claims (7)

CLAIMS-  1. A method of manufacturing a material on a rigid or flexible support for recording a hologram, characterized in that it consists in preparing 12 to 18% by weight of pure gelatin suspended in water by performing a initial mixing until complete dissolution at a temperature of 20 C, then a final mixing for approximately 5 to 10 minutes at 70 C, to filter the solution obtained by means of a filter heated to 50 C, to lower the temperature and to maintain it at 40 ° C., then add ammonium dichromate in a proportion of 0.5% of the weight of the gelatin, and mix until complete dissolution, then, still maintaining the bath obtained at 40 ° C. , immerse in the latter, for about one minute, a rigid or flexible support, then remove the latter vertically at a speed of 1 to 5cm / min., dry the support in the vertical position, in air, for one hour , then harden the entire support in the oven for two hours at 150 C, to sensitize then insert the hardened support by soaking for 5 minutes in a 4% to 10% water solution of ammonium dichromate and then store the support at 20 C to 30 C in the dark for a maximum period of 48 hours in air at 30% to 40% humidity.  2. Method according to claim 1, characterized in that it consists in preparing 4 X by weight of pure gelatin suspended in water by carrying out an initial mixing until complete dissolution at a temperature of 20 C, then a mixing final for approximately 5 to 10 minutes at 70 ° C., to filter the solution obtained by means of a filter heated to 50 ° C., then to add 0.5 So by weight, relative to the weight of gelatin, of ammonium dichromate, and mixing until complete dissolution while maintaining the temperature at around 50 ° C., then applying the product obtained by means of any applicator at a temperature of 50 ° C. by depositing said product on the rigid or flexible support, then remove the excess product with a blade spaced from the support by a distance of 0.5 to 1 mm so as to achieve a uniform distribution, to dry the support in a strictly horizontal position in ambient air for about 24 hours , and finally to harden it in the oven at 150 C for 2 hours, to sensitize it by soaking for 5 minutes in a solution of water at 4% to 10 lo of ammonium dichromate, then to store it in the dark for a maximum period of 48 hours at 20 C to 30 C in air at 30% to 40% humidity.  3. Method according to any one of claims 1 and 2, characterized in that, for wavelengths greater than 540 nm, namely 633 and 647 nm, it consists, after storage of a maximum duration 48 hours, to prepare a sensitizing solution comprising 0.06 M of ammonium dichromate and 10 mg / ml of dry methylene green or blue dye, to stir this solution for approximately 2 minutes until the green or blue of methylene, to filter the solution with a Whatman No. 541 rapid filter, to sensitize the rigid or flexible support in the dark by soaking with stirring for 6 minutes, then passing the gelatin side with a spin roller, the substrate side being wiped off, and then drying the support in unqair at 40% humidity, the support can then undergo holographic exposure within 48 hours and be developed.  4. Method for developing supports obtained by applying the methods according to any one of claims 1 to 3, characterized in that it consists in first dipping the support in a solution at 0.5% by weight of dichromate d ammonium and fixative diluted with distilled water, rinse for 10 minutes under running water at 20 C, then immerse the support for 2 minutes with stirring in a 50% solution of isopropyl alcohol and 50 X distilled water, then immerse the support for 2 minutes in a solution of 90% isopropyl alcohol and 10% distilled water, then immerse it, with stirring, for about 10 to 20 minutes in alcohol isopropyl and finally drying the support for at least 2 minutes in a jet of hot air, then passing it in a vacuum oven at 90 C for 1 to 2 hours.  5. Method according to claim 4, characterized in that after rinsing with running water at 20 C, the support is only immersed in pure isopropyl alcohol for about 10 to 20 minutes, then is dried.  6. Method for protecting a hologram on a guide or flexible support obtained by applying the methods according to claims 1 to 5, characterized in that it consists in applying to the support, after development, a glass plate or flexible transparent film using an epoxy-resin adhesive.  7. Method according to claim 6, characterized in that it consists in coating the rigid or flexible support by means of a protective varnish.