Holographic recording medium

Abstract

The invention relates to a holographic recording medium which is characterized in that active monomers are structurally modified by introducing sulfur atoms and aromatic ring groups with relatively large molar refractive indexes, and the overall refractive index difference is improved by improving the refractive index of the active monomers, so that a volume holographic grating with high performance is prepared.

Description

Technical Field

[0001] The present application belongs to the technical field of recording materials for AR holographic display devices, and specifically relates to a holographic recording medium. Background Art

[0002] Holographic technology refers to an optical information technology that uses the principle of optical coherence to record the amplitude, phase and other optical properties of light waves. It is widely used in the fields of holographic anti-counterfeiting and data storage. In this process, as the carrier of holographic recording, the holographic recording medium is particularly critical. It mainly converts the image information into the difference in structure between the exposure area and the non-exposure area through the difference in refractive index modulation of the material under photopolymerization reaction, and restores the stored information through the principle of diffraction imaging. Therefore, the ideal holographic recording material should have a high refractive index modulation, a wide spectral response range, excellent photosensitivity, and low haze. In addition, it should also have good stability, excellent processing performance and cheap raw materials.

[0003] The typical holographic recording media at present mainly include: silver halide emulsion, dichromated gelatin, photodegradable polymer, photoconductive thermoplastic material, photoisomerized material, photorefractive material (including liquid crystal), metasurface material, photopolymer, etc. Among them, the post-processing process of silver halide emulsion is complicated and it is easy to produce a large amount of waste liquid to pollute the environment; dichromated gelatin, photodegradable polymer, photoconductive thermoplastic material and photoisomerized material have the problem of low photosensitivity and refractive index modulation; photorefractive material usually requires an additional external electric field, the equipment is complex and the safety is poor; metasurface material has the problems of difficult construction and complex process. As a result, these media cannot produce high-performance volume holographic gratings. Summary of the invention

[0004] The purpose of this application is to solve the problems existing in the above-mentioned prior art. This application provides a holographic recording medium, including: a substrate film-forming material, an active monomer and a photoinitiator;

[0005] The refractive index of the active monomer is not less than a preset value, and the structural formula of the active monomer is:

[0006]

[0007] Among them, R1 is a Cn skeleton, which can be a saturated carbon chain or an unsaturated carbon chain, or a benzene ring or other cyclic structure, where n is 1 to 10; R2 is H or a hydrocarbon or unsaturated acrylic ester structure containing one or more sulfur atom carbon chains; and R3 is H or -CH4.

[0008] As a preferred embodiment of the present application, the active monomer includes one or more of the following structural formulas:

[0009]

[0010] As a preferred embodiment of the present application, the substrate film-forming material is at least one of a homopolymer of vinyl acetate, a styrene / butadiene block copolymer or a polyurethane.

[0011] As a preferred embodiment of the present application, the polyurethane is prepared by reacting a polyether alcohol having a relative molecular mass of 200 to 4000 with isocyanate.

[0012] As a preferred embodiment of the present application, the sulfur atom content accounts for 5% to 50%.

[0013] As a preferred embodiment of the present application, a toughening agent is also included.

[0014] As a preferred embodiment of the present application, the boiling point of the toughening agent is greater than 200 degrees Celsius.

[0015] As a preferred embodiment of the present application, the content of the substrate film-forming substance is 10% to 60%; the content of the active monomer is 20% to 50%; the content of the initiator is 0.01% to 1%; and the content of the plasticizer is 2% to 20%.

[0016] As a preferred embodiment of the present application, the content of the substrate film-forming substance is 20% to 50%; the content of the active monomer is 30% to 45%; the content of the initiator is 0.1% to 0.3%; and the content of the plasticizer is 2% to 8%.

[0017] As a preferred embodiment of the present application, the photoinitiator is a combination of Rose Bengal, rhodamine and n-aminoglycine / ethylenediamine, or a combination of a boron-containing quaternary ammonium salt and Rose Bengal.

[0018] This application has the following beneficial effects:

[0019] A holographic recording medium provided in the present application is structured by introducing sulfur atoms and aromatic ring groups with a large molar refractive index to modify the active monomers, and the refractive index of the active monomers is increased to increase the overall refractive index difference, thereby preparing a high-performance volume holographic grating. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the scheme of the present application, the technical scheme in the embodiment of the present application will be clearly and completely described below in conjunction with the embodiment of the present application. Obviously, the described embodiment is only an embodiment of a part of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work should belong to the scope of protection of this application. In the following embodiments, unless otherwise stated, the specific conditions of the test method are generally implemented according to conventional conditions or conditions recommended by the manufacturer; raw materials and reagents are obtained commercially or prepared using public information.

[0021] Unless otherwise specified in the following examples, all reagents and materials used were commercially available.

[0022] The applicant has found through research that photopolymers not only have the advantages of high photosensitivity, high resolution, and good light transmittance, but also have excellent preparation process performance, and have gradually become the most promising recording medium in the field of volume holographic recording devices.

[0023] Usually, the photopolymer formulation mainly includes substances such as photoinitiator system, film-forming resin, recording monomer and other additives. Among them, the absorption characteristics of the photoinitiator system and the quantum yield of the free radicals generated determine the speed of the photopolymerization reaction; the film-forming resin is used as a base film-forming material, on the one hand, it provides mechanical support for the holographic recording medium, and on the other hand, it forms a refractive index difference with the recording monomer; the recording monomer provides a high refractive index; other additives include toughening agents, leveling agents, etc., which play a role in assisting film formation or inhibiting shrinkage. In order to prepare high-performance volume holographic gratings, recording monomers with higher refractive index are usually required. According to the relationship between the refractive index of the material and the molar refractive index and molar volume of the monomer revealed by the Lorentz-Lorenz relationship, it can be seen that introducing atoms or groups with a large molar refractive index is one of the effective means to increase the refractive index of the material. Among them, the Lorentz-Lorenz formula is used to determine the refractive index of a substance and its change process in the medium.

[0024] In view of this, the present application modifies the structure of the active monomer by introducing sulfur atoms and aromatic ring groups with a large molar refractive index, and improves the overall refractive index difference by increasing the refractive index of the active monomer, thereby preparing a high-performance volume holographic grating.

[0025] The purpose of the present application is to provide a holographic recording medium and a display device with a high refractive index modulation degree, so as to improve at least part of the above technical problems.

[0026] The present application provides a holographic recording medium, comprising: a substrate film-forming substance, an active monomer and a photoinitiator;

[0027] The refractive index of the active monomer is not less than a preset value, and the structural formula of the active monomer is:

[0028]

[0029] Among them, R1 is an alkane or an aromatic hydrocarbon, wherein the number of carbon atoms in R1 is 1 to 10; R2 is a hydrogen atom or an alkane or an unsaturated acrylic ester structure containing one or more sulfur atoms; and R3 is H or CH4.

[0030] Further, R1 is a Cn skeleton, which can be a saturated carbon chain or an unsaturated carbon chain, or a benzene ring or other cyclic structure, wherein n is 1 to 10; R2 is H or a hydrocarbon or unsaturated acrylic ester structure containing one or more sulfur atom carbon chains; the preferred sulfur atom content is 5% to 50%;

[0031] In the embodiment of the present application, the refractive index of the active monomer of the present application is not less than 1.6.

[0032] In the embodiment of the present application, the film-forming material is selected from at least one of a homopolymer of vinyl acetate, a styrene / butadiene block copolymer and a polyurethane material. In the present application, a polyurethane having a methyl carbamate structure is preferably used as the base film-forming material. In addition, in order to ensure that the base film-forming material has a certain degree of flexibility and self-support, a polyether alcohol having a relative molecular mass of 200 to 4000 and an isocyanate are preferably used to prepare a polyurethane base film-forming material.

[0033] In the embodiments of the present application, the highly reactive monomer may be one or more of the following structures:

[0034]

[0035] In order to facilitate subsequent processing, as a preferred embodiment of the present application, a toughening agent is also included. The toughening agent is a small molecule substance with a high boiling point, and preferably the boiling point of the toughening agent should be greater than 200 degrees Celsius.

[0036] In the embodiments of the present application, the composition of each substance has requirements on the content. Based on the total amount of the composition, the content of the film-forming substance is 10% to 60%, preferably 20% to 50%; the content of the active monomer is 20% to 50%, preferably 30% to 45%; the content of the initiator is 0.01% to 1%, preferably 0.1% to 0.3%; the content of the plasticizer is 2% to 20%, preferably 2% to 8%;

[0037] In the embodiments of the present application, the photoinitiator is a combination of Rose Bengal, rhodamine and n-aminoglycine / ethylenediamine, or a combination of a boron-containing quaternary ammonium salt and Rose Bengal.

[0038] It should be noted that the photoinitiator, as a sensitizing substance at a certain wavelength, has a very important influence on the photosensitivity of the material in holographic technology, which is subject to the absorption of a specific wavelength. In the present application, the photoinitiator is a compound known per se and commercially available on the market. Taking a light source with a wavelength of 520nm as an example, the photoinitiator that can be selected is a combination of substances such as rose bengal, rhodamine and n-aminoglycine / ethylenediamine, and substances such as a combination of boron-containing quaternary ammonium salt and rose bengal can also be selected.

[0039] The following is a detailed introduction to the preparation method of highly active monomers:

[0040] Embodiment 1:

[0041] Preparation of highly reactive monomer 1:

[0042]

[0043] According to the above chemical synthesis method, an active monomer 1 is first prepared for use, wherein the refractive index of the active monomer is 1.63; secondly, under a red light protection environment, 10-35% of a polyether diol, 40% of an active monomer 1, and 0.1% of rose red + 0.3% of N-phenylglycine are pre-mixed, and after uniform mixing, 8-12% of a triisocyanate monomer and 0.1% of an organic tin are added thereto and mixed again to obtain a clear photosensitive liquid; then, under red light protection, a quantitative amount of the above photosensitive liquid is absorbed and siphoned into a glass box of a specific thickness to form a film (the box thickness in this application is uniformly 10 μm); finally, after the siphoning is completed, the glass box is protected from light with tin foil and placed in an oven at 72° C. for 1 hour.

[0044] Embodiment 2:

[0045] Preparation of highly reactive monomer 2:

[0046]

[0047] According to the above chemical synthesis method, an active monomer 2 is first prepared for use, wherein the active monomer has a refractive index of 1.65; secondly, under a red light protection environment, 10-35% of a polyether diol, 40% of an active monomer 1, and 0.1% of rose red + 0.3% of N-phenylglycine are pre-mixed, and after uniform mixing, 8-12% of a triisocyanate monomer and 0.1% of an organic tin are added thereto and mixed again to obtain a clear photosensitive solution; then, under red light protection, a quantitative amount of the above photosensitive solution is absorbed and siphoned into a glass box of a specific thickness to form a film (the box thickness in the present invention is uniformly 10 μm); finally, after the siphoning is completed, the glass box is protected from light with tin foil and placed in an oven at 72° C. for 1 hour.

[0048] Comparative Example 1:

[0049] In a red light protection environment, 10-35% of polyether diol, 40% of commercially available acrylate monomer (2-phenylethyl acrylate) and 0.1% of rose bengal + 0.3% of N-phenylglycine are pre-mixed, and then 8-12% of triisocyanate monomer and 0.1% of organic tin are added thereto and mixed again after being evenly mixed to obtain a clear photosensitive liquid. Then, under the protection of red light, a certain amount of the above-mentioned photosensitive liquid is absorbed and siphoned into a glass box of a specific thickness (the box thickness in the present invention is uniformly 10 μm) to form a film. Finally, after the siphoning is completed, the glass box is protected from light with tin foil and placed in an oven at 72° C. for 1 hour.

[0050] Comparative Example 2:

[0051] Under the red light protection environment, 10-35% of polyether diol, 40% of commercially available acrylate monomer (ethyl acrylate) and 0.1% of rose bengal + 0.3% of N-phenylglycine are pre-mixed, and then 8-12% of triisocyanate monomer and 0.1% of organic tin are added thereto and mixed again after being evenly mixed to obtain a clear photosensitive liquid. Then, under the red light protection, a quantitative amount of the above-mentioned photosensitive liquid is absorbed and siphoned into a glass box of a specific thickness (the box thickness in the present invention is uniformly 10 μm) to form a film. Finally, after the siphoning is completed, the glass box is protected from light with tin foil and placed in an oven at 72° C. for 1 hour.

[0052] Table 1: Test results of Examples 1-2 and Comparative Examples 1-2

[0053] Serial number Refractive index of active monomer Diffraction efficiency Refractive index modulation Δn Example 1 1.63 90％ 0.0314 Example 2 1.65 95％ 0.0363 Comparative Example 1 1.57 63％ 0.0186 Comparative Example 2 1.41 25％ 0.009

[0054] It can be seen from Table 1 that the holographic recording medium in Example 1-2 has a significantly improved refractive index modulation compared with the active monomer in Comparative Example 1-2, since the refractive index of the active monomer is significantly greater than that of the active monomer in Comparative Example 1-2, which is beneficial for preparing high-performance volume holographic gratings.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A holographic recording medium, characterized in that: include: Base film-forming substances, reactive monomers and photoinitiators; The refractive index of the active monomer is not less than a preset value, and the structural formula of the active monomer is: Among them, R1 is a Cn skeleton, which can be a saturated carbon chain or an unsaturated carbon chain, or a benzene ring or other cyclic structure, where n is 1 to 10; R2 is H or a hydrocarbon or unsaturated acrylic ester structure containing one or more sulfur atom carbon chains; and R3 is H or -CH4.

2. A holographic recording medium according to claim 1, characterized in that: The active monomers include one or more of the following structural formulas:

3. A holographic recording medium according to claim 1, characterized in that: The substrate film-forming material is at least one of a homopolymer of vinyl acetate, a styrene / butadiene block copolymer or a polyurethane.

4. A holographic recording medium as claimed in claim 2, characterized in that: The polyurethane is prepared by reacting a polyether alcohol with a relative molecular mass of 200 to 4000 with isocyanate.

5. A holographic recording medium according to claim 1, characterized in that: The sulfur atom content accounts for 5% to 50%.

6. A holographic recording medium according to claim 1, characterized in that: Toughening agents are also included.

7. A holographic recording medium according to claim 6, characterized in that: The boiling point of the toughening agent is greater than 200 degrees Celsius.

8. A holographic recording medium according to claim 7, characterized in that: The content of the substrate film-forming substance is 10% to 60%; the content of the active monomer is 20% to 50%; the content of the initiator is 0.01% to 1%; and the content of the plasticizer is 2% to 20%.

9. A holographic recording medium according to claim 7, characterized in that: The content of the substrate film-forming substance is 20% to 50%; the content of the active monomer is 30% to 45%; the content of the initiator is 0.1% to 0.3%; and the content of the plasticizer is 2% to 8%.

10. The holographic recording medium according to claim 1, characterized in that: The photoinitiator is a combination of rose bengal, rhodamine and n-aminoglycine / ethylenediamine, or a combination of a boron-containing quaternary ammonium salt and rose bengal.

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