Composition for holographic recording medium, and holographic recording medium

Abstract

A composition for a holographic recording medium, and a holographic recording medium using same. Structural design is carried out on a substrate film-forming substance contained in the composition for the holographic recording medium, and the overall refractive index difference is increased by reducing the refractive index of the substrate, so that a VHG having high performance is prepared.

Description

Composition for holographic recording medium and holographic recording medium

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 14, 2023, with application number 202311187537.9, and invention name “A composition for holographic recording medium and holographic recording medium”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of holographic technology, and more particularly to a composition for a holographic recording medium and a holographic recording medium using the composition. Background Art

[0003] Holographic technology, an optical information technology that utilizes the principles of optical coherence to record optical properties such as lightwave amplitude and phase, is widely used in fields such as holographic anti-counterfeiting and data storage. In this process, the holographic recording medium, as the carrier of holographic recording, is particularly critical. It primarily utilizes the material's refractive index modulation during photopolymerization to convert image information into structural differences between exposed and non-exposed areas, and then recovers the stored information through the principle of diffraction imaging. Therefore, an ideal holographic recording material should possess a high refractive index modulation, a wide spectral response range, excellent photosensitivity, and low haze. Furthermore, it must possess good stability, excellent processing properties, and be inexpensive.

[0004] Typical holographic recording media currently include silver halide emulsion, dichromated gelatin, photodegradable polymers, photoconductive thermoplastics, photoisomerized materials, photorefractive materials (including liquid crystals), metasurface materials, and photopolymers. Silver halide emulsions have complex post-processing and are prone to generating large amounts of wastewater, which pollutes the environment. Dichromated gelatin, photodegradable polymers, photoconductive thermoplastics, and photoisomerized materials suffer from low photosensitivity and refractive index modulation. Photorefractive materials typically require an external electric field, resulting in complex equipment and poor safety. Metasurface materials are difficult to fabricate and involve complex processes. Consequently, these media are unable to produce high-performance volume holographic gratings (VHGs). In contrast, photopolymers offer the advantages of high photosensitivity, high resolution, and excellent light transmittance, as well as excellent processability. They are becoming the most promising recording medium for volume holographic recording devices.

[0005] Typically, a photopolymer formulation consists of a photoinitiator system, a film-forming resin, a recording monomer, and other additives. The absorption characteristics of the photoinitiator system and the quantum yield of free radicals generated determine the speed of the photopolymerization reaction. The film-forming resin acts as a substrate, providing mechanical support for the holographic recording medium and creating a refractive index difference with the recording monomer. The recording monomer provides a high refractive index. Other additives, such as toughening agents and leveling agents, assist in film formation or inhibit shrinkage. To produce high-performance VHGs, a recording monomer with a higher refractive index is usually required. This poses a problem because the solubility of the high-refractive-index monomer in the substrate is limited, limiting the overall performance improvement.

[0006] In view of this, the present invention designs the structure of the substrate from the perspective of the refractive index difference between the substrate and the recording monomer, and improves the overall refractive index difference by reducing the refractive index of the substrate, thereby preparing a high-performance VHG. Summary of the Invention

[0007] The object of the present application is to provide a composition for a holographic recording medium and a holographic recording medium using the composition for a holographic recording medium, so as to at least partially solve the above-mentioned technical problems.

[0008] To achieve the above-mentioned purpose, as one aspect of the present invention, a composition for holographic recording media is provided, wherein the composition for holographic recording media comprises the following components: a substrate film-forming substance, an active monomer, a photoinitiator, and a plasticizer. In one embodiment of the present invention, the substrate film-forming substance is a compound having a group selected from a urethane group, an amide group, a urea group, and an epoxy group, or any combination thereof. In a preferred embodiment of the present invention, the film-forming substrate substance is a compound having two or more methyl carbamate structures. In addition, in order to increase the refractive index difference with the recording monomer, a special structural design of the film-forming substrate substance is required. In the present invention, the refractive index of the substrate is regulated by introducing fluorine element, and the fluorine element content and the molecular weight of the substrate are controlled. The substrate film-forming substance has the general structure shown below: Where R2 is C1-C 10 The carbon chain may be linear, cyclic, branched or heterocyclic; R1 and R3 are independently C1-C 25 The present invention relates to a polyol having a carbon chain, wherein at least one of R1 and R3 is an organic carbon chain containing a fluorine atom, preferably a primary carbon chain with polyfluorine substitution; the mass fraction of fluorine is 5-40%, preferably 10-30%. The polyol can be synthesized by reacting an isocyanate with a polyol or a fluorine-modified polyol. It should be noted that the functionality of the selected isocyanate must be greater than that of the selected polyol, and the isocyanate content must be in excess.

[0009] In one embodiment of the present invention, the active monomer is a C4-C 20 In a preferred embodiment of the present invention, the active monomer is an acrylate substance having an allophanate or urethane structure. In a preferred embodiment of the present invention, in order to increase the refractive index difference with the base film-forming material, the refractive index of the active monomer is ≥1.5.

[0010] Photoinitiators, as sensitizing substances at specific wavelengths, have a significant impact on the photosensitivity of materials in holographic technology, being governed by their absorption of specific wavelengths. In one embodiment of the present invention, the photoinitiator is a known, commercially available compound. For example, using a 520nm light source, a combination of Rose Bengal, rhodamine, and N-aminoglycine or ethylenediamine is a suitable photoinitiator. Alternatively, a boron-containing quaternary ammonium salt combined with Rose Bengal may be used.

[0011] To facilitate subsequent processing, the present invention may also incorporate small molecules with high boiling points as plasticizers. In a preferred embodiment of the present invention, the plasticizer has a boiling point greater than 200 degrees Celsius. In a preferred embodiment of the present invention, the plasticizer is dioctyl phthalate (DOP) or dibutyl phthalate (DBP). Without wishing to be bound by theory, it is believed that the holographic recording medium composition may also contain a catalyst for matrix reactions known to those skilled in the art.

[0012] In addition, as another aspect of the present invention, the various components of the holographic recording medium composition have requirements for their content. In a preferred embodiment of the present invention, based on the total weight of the holographic recording medium composition, the base film-forming substance comprises 15%-60%, preferably 30%-50%; the reactive monomer comprises 20%-50%, preferably 35%-40%; the photoinitiator and co-initiator comprise 0.01%-1%, preferably 0.1%-0.3%; and the plasticizer comprises 2%-20%, preferably 2%-8%.

[0013] The present application also relates to a holographic recording medium prepared from the composition for holographic recording medium of the present invention.

[0014] Beneficial effects of the present invention:

[0015] The present invention designs the structure of the substrate from the perspective of the difference in refractive index between the substrate and the recording monomer, which can significantly improve the refractive index modulation and is relatively easy to operate; the significance of improving the refractive index modulation is that it can significantly improve the resolution and clarity of optical waveguide components and enhance customer comfort. By reducing the refractive index of the substrate, the overall refractive index difference is increased, thereby preparing a high-performance VHG. By fluorination grafting modification of the substrate film-forming material, it was found that the refractive index of the unmodified substrate film-forming material was significantly reduced, and there was a certain effect on the diffraction efficiency and refractive index modulation of the prepared holographic recording medium. The inventors also found that the fluorination modification of the substrate film-forming material is not simply linearly related to the number of fluorine atoms. Only under a specific range of fluorination modification conditions can the ideal effects of the diffraction efficiency and refractive index modulation of the prepared holographic recording medium be achieved. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0017] Example 1: Under red light protection, 30-35% polyether diol (molecular weight 2000), 40% acrylate reactive monomer, and 0.1% rose bengal and 0.3% N-phenylglycine were premixed. Plasticizer DOP was then added and mixed thoroughly. 8-12% triisocyanate monomer and 0.1% organotin were then added and mixed again to obtain a clear photosensitive solution. 5-10% of a modifying compound (undecafluoro-n-hexane-1-ol) with varying fluorine contents was then added to modify the substrate. Under red light protection, a fixed amount of the photosensitive solution was pipetted into a glass box of a specified thickness (10 μm) to form a film. After the siphoning was complete, the glass box was covered with tin foil to protect it from light and then dried in an oven at 72°C for 3 hours to obtain a holographic recording medium.

[0018] Example 2: Under red light protection, 30-35% polyether diol (molecular weight 2000), 40% acrylate reactive monomer, and 0.1% rose bengal and 0.3% N-phenylglycine were premixed. Plasticizer DOP was then added and mixed thoroughly. 8-12% triisocyanate monomer and 0.1% organotin were then added and mixed again to obtain a clear photosensitive solution. 5-10% of a modifying compound (hexafluorobutanol) with varying fluorine contents was then added to modify the substrate. Under red light protection, a fixed amount of the photosensitive solution was pipetted into a glass box of a specified thickness (10 μm) to form a film. After the siphoning was complete, the glass box was covered with tin foil to protect it from light and then dried in an oven at 72°C for 3 hours to obtain a holographic recording medium.

[0019] Example 3: Under red light protection, 30-35% polyether diol (molecular weight 2000), 40% acrylate reactive monomer, and 0.1% rose bengal and 0.3% N-phenylglycine were premixed. Plasticizer DOP was then added and mixed thoroughly. 8-12% triisocyanate monomer and 0.1% organotin were then added and mixed again to obtain a clear photosensitive solution. 5-10% of a modified compound with varying fluorine contents (2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctan-1-ol) was then added to modify the substrate. Under red light protection, a fixed amount of the photosensitive solution was pipetted onto a glass box of a specified thickness (10 μm) to form a film. After the siphoning was complete, the glass box was covered with tin foil to protect it from light and then dried in an oven at 72°C for 3 hours to obtain a holographic recording medium.

[0020] Comparative Example 1: Under a red light protection environment, 35-45% of a polyether diol (molecular weight of 2000), 40% of an acrylate reactive monomer, and 0.1% of Rose Bengal + 0.3% of N-phenylglycine were premixed, and then a plasticizer, DOP, was added and mixed thoroughly. 5-10% of a triisocyanate monomer and 0.1% of an organotin were then added and mixed again to obtain a clear photosensitive solution. Subsequently, under red light protection, a predetermined amount of the photosensitive solution was aspirated and siphoned into a glass box of a specific thickness (box thickness: 10 μm) to form a film. Finally, after the siphoning was completed, the glass box was protected from light with tin foil, placed in an oven, and dried at 72°C for 3 hours to obtain a holographic recording medium.

[0021] The diffraction efficiency was measured using a UV spectrophotometer, and the refractive index was measured using an Abbe refractometer. Test results

[0022] Table 1: Test results of Examples 1-3 and Comparative Examples

[0023] As can be seen from Table 1, the holographic recording media in Examples 1-3, due to the fluorination grafting modification of the substrate film-forming material, have a significantly lower refractive index than the unmodified substrate film-forming material, and have a certain effect on the diffraction efficiency and refractive index modulation of the prepared holographic recording media. This is because by reducing the refractive index of the substrate, the refractive index difference with the active monomer can be effectively widened. At the same time, a comparison of Examples 1-3 shows that the fluorination modification of the substrate film-forming material is not simply linearly correlated with the number of fluorine atoms. As the number of fluorine atoms grafted onto the substrate film-forming material increases to a certain value, the compatibility between the substrate film-forming material and the polymerized reactants of the active monomer is reduced, causing phase separation of the two phases, thereby increasing the haze of the holographic recording medium and affecting the diffraction efficiency and refractive index modulation of the medium.

[0024] 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 them. 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A composition for a holographic recording medium, characterized in that: It contains a substrate film-forming substance, wherein the substrate film-forming substance has a general structure as shown below: Where R2 is C1-C 10 The carbon chain is linear, cyclic, branched or heterocyclic; R1 and R3 are independently C1-C 25 and at least one of R1 and R3 is an organic carbon chain containing a fluorine atom.

2. The composition for holographic recording media according to claim 1, wherein At least one of R1 and R3 is a primary carbon chain having polyfluorine substitution.

3. The composition for holographic recording media according to claim 1 or 2, characterized in that: The mass fraction of fluorine element in the substrate film-forming material is 5% to 40%.

4. The composition for holographic recording media according to claim 1 or 2, characterized in that The substrate film-forming material is prepared by reacting isocyanate with polyol or fluorine-modified polyol.

5. The composition for holographic recording media according to claim 1, wherein It also includes: Reactive monomers; a photoinitiator; and Plasticizer.

6. The composition for holographic recording media according to claim 5, wherein The active monomer is a C4-C 20 Carbon chain; and / or The photoinitiator is a combination of Rose Bengal or rhodamine and N-aminoglycine or ethylenediamine, or a combination of a boron-containing quaternary ammonium salt and Rose Bengal; and / or The plasticizer has a boiling point greater than 200 degrees Celsius.

7. The composition for holographic recording media according to claim 5 or 6, characterized in that The active monomer is an acrylate substance having an allophanate or urethane structure; and / or The plasticizer is dioctyl phthalate or dibutyl phthalate.

8. The composition for holographic recording media according to claim 5 or 6, characterized in that The refractive index of the active monomer is ≥1.

5.

9. The composition for holographic recording media according to claim 5 or 6, characterized in that Based on the total weight of the composition for holographic recording media, the content of the substrate film-forming substance is 15%-60%; the content of the active monomer is 20%-50%; the content of the photoinitiator is 0.01%-1%; and the content of the plasticizer is 2%-20%.

10. A holographic recording medium, characterized in that: The holographic recording medium is prepared by the composition for holographic recording medium according to any one of claims 1 to 9.

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