Photopolymer type holographic recording medium and its applications, use of compounds

Abstract

The application discloses a photopolymer type holographic recording medium and application thereof, and a use of a compound, and raw materials of the photopolymer type holographic recording medium comprise: a film-forming resin, the film-forming resin comprises a compound and a polyisocyanate; a reactive functional group of the compound is a hydroxyl group or an amino group, and a main chain of the compound comprises a diphenyl disulfide main chain or a dinaphthyl disulfide main chain. The photopolymer type holographic recording medium is generated by a polymerization reaction of hydroxyl or amino of the compound and isocyanate groups of the polyisocyanate, and has a secondary amine and a-S-S- bond; under the action of light, the-S-S- bond of the film-forming resin in a partially coherent bright area is broken, free radicals generated serve as a photoinitiator to start polymerization of a writing monomer in the coherent bright area at the end of the S free radical, a covalent bond is formed between part of the film-forming resin and the writing monomer after reaction, small molecule migration is reduced, the phase separation degree between the coherent bright area and a coherent dark area is reduced, and haze is reduced.

Description

Technical Field

[0001] This invention relates to the field of holographic materials technology, and more particularly to photopolymer-type holographic recording media and their applications, as well as the uses of compounds thereon. Background Technology

[0002] The components in the raw materials used to make holographic recording media, such as photosensitive dyes, photoinitiators, chain transfer agents, writing monomers, film-forming resins, and plasticizers, work together to determine the performance of the holographic recording media. The photosensitive dyes and photoinitiators use photoinitiation to polymerize the writing monomers in the coherent bright region, while the writing monomers in the coherent dark region remain largely unreacted. The concentration difference of the writing monomers between the coherent bright and dark regions causes unreacted writing monomers in the dark region to migrate to the bright region, squeezing the film-forming resin from the bright region into the dark region. This makes the refractive index of the bright region close to that of the writing monomers, and the refractive index of the dark region close to that of the film-forming resin. The refractive index difference between the writing monomers and the film-forming resin allows for the formation of a refractive index-modulated volume holographic grating.

[0003] Existing photoinitiation systems composed of photosensitive dyes and photoinitiators suffer from low photoinitiation efficiency. After the photoinitiator decomposes, it produces free small molecules such as benzaldehyde and benzoic acid. If these free small molecules migrate to the surface of the molded product, they will volatilize and produce an unpleasant odor. If the human body comes into contact with these small molecules, it will affect health. Some residual small molecules will further oxidize, causing the material to gradually turn yellow after a period of use, affecting the appearance and user experience.

[0004] There is a significant difference between the structure of the polymerized bright stripe region and the structure of the polymerized dark stripe region. Therefore, phase separation is likely to occur between the two, resulting in increased haze of the prepared material. Summary of the Invention

[0005] In view of this, the present invention proposes a photopolymer-type holographic recording medium and its application, as well as the use of the compound, aiming to reduce or eliminate the migration problem of small molecules generated by the decomposition of photoinitiators, reduce the probability of unpleasant odors, reduce the degree of yellowing of materials, and reduce material haze.

[0006] The first aspect of the invention provides the use of a compound for reacting with a polyisocyanate to form a film-forming resin, wherein the compound and / or the film-forming resin simultaneously serve as a photoinitiator; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound comprises a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

[0007] As can be seen from the above technical solution, the compound proposed in the first aspect of this invention has two uses. It can not only polymerize with the isocyanate groups of polyisocyanates via hydroxyl or amino groups to generate film-forming resins with secondary amines and -SS- bonds, but also induce the breaking of -SS- bonds on the main chain of some film-forming resins or the breaking of -SS- bonds on the main chain of some unreacted compounds under light irradiation, generating free radicals. This allows it to act as a photoinitiator, selectively and efficiently initiating the polymerization of components of the writing monomer in the coherent bright region at the S-terminus, causing some of the film-forming resin to form covalent bonds with the reacted writing monomers. This reduces the migration of small molecules generated after the -SS- bonds break, thus reducing the probability of unpleasant odors and the degree of yellowing of the material. Furthermore, the film-forming resin achieves a certain degree of connection with the writing monomers after the reaction in the coherent bright region, making the structure of the polymerized coherent bright region similar to the structure of the film-forming resin in the coherent dark region, thereby reducing phase separation and lowering the haze of the material.

[0008] The second aspect of the present invention provides a photopolymer-type holographic recording medium, wherein the raw materials of the photopolymer-type holographic recording medium include: a film-forming resin, wherein the film-forming resin includes a compound and a polyisocyanate; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound includes a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

[0009] As can be seen from the above technical solutions, the photopolymer-type holographic recording medium proposed in the second aspect of this invention allows the compound to undergo a polymerization reaction with the isocyanate groups of polyisocyanates via hydroxyl or amino groups to generate a film-forming resin with secondary amines and -SS- bonds. Furthermore, under illumination, it can induce the breakage of the -SS- bonds on the main chain of the film-forming resin in the coherent bright area, generating free radicals. These free radicals can then act as photoinitiators, selectively and efficiently initiating the polymerization of the writing monomers in the coherent bright area at the S-terminus. This results in the formation of covalent bonds between a portion of the film-forming resin and the reacted writing monomers, reducing the migration of small molecules generated after the -SS- bond breakage. This reduces the probability of unpleasant odors and decreases the degree of yellowing of the material. Because the film-forming resin acting as a photoinitiator achieves a certain connection with the reacted writing monomers in the bright area, the structure of the coherent bright area after polymerization has a certain similarity to the structure of the film-forming resin squeezed into the coherent dark area. This reduces the degree of phase separation between the coherent bright and dark areas, effectively reducing the haze of the material.

[0010] The third aspect of the present invention provides a volume holographic recording grating, wherein the volume holographic recording grating is prepared by holographic exposure of the holographic recording medium described in the foregoing embodiments.

[0011] The fourth aspect of the present invention provides a holographic optical element, which includes the volume holographic recording grating of the foregoing embodiments.

[0012] As can be seen from the above technical solutions, the volume holographic recording grating proposed in the third aspect and the holographic optical element proposed in the fourth aspect of the present invention have good holographic performance, high diffraction efficiency, high sensitivity, small required exposure amount, and low haze.

[0013] The optical device proposed in the fifth aspect of the present invention includes the holographic optical element of the foregoing embodiments.

[0014] As can be seen from the above technical solutions, the optical devices proposed in the fifth aspect of the present invention, such as head-up display devices, augmented reality devices, virtual reality devices, and photopolymer holographic storage optical discs, have excellent holographic performance.

[0015] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the disclosure of the embodiments of the present invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 These are holographic exposure characteristic curves of the photopolymer-type holographic recording medium proposed in Examples 2-4 of this invention; Figure 2 These are holographic exposure characteristic curves of the photopolymer-type holographic recording medium proposed in Examples 7-9 of this invention; Figure 3 This is a graph showing the holographic exposure characteristics of a typical photopolymer holographic recording medium. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0019] Photopolymer materials used for holographic recording mainly include components such as photoinitiating systems, chain transfer agents, writing monomers, film-forming resins, and plasticizers. Among them, the photoinitiating system is an important component of holographic photopolymers, and it mainly includes photosensitive dyes, photoinitiators (or co-initiators), and other components.

[0020] The working principle of the photoinitiation system is as follows: photons are captured by a photosensitive dye, and then, through electron transfer and hydrogen transfer mechanisms in synergy with the photoinitiator, free radicals are generated controllably and efficiently in the coherent bright region, such as the bright interference fringes, thereby selectively initiating the polymerization of writing monomers. The writing monomers in the coherent dark region are essentially unreacted. The concentration difference of writing monomers between the coherent bright and dark regions causes unreacted writing monomers in the coherent dark region to migrate to the coherent bright region, ultimately forming the refractive index modulation grating that determines the performance of the hologram. The coherent bright region mainly consists of polymerized writing monomers, while the coherent dark region mainly consists of polymerized film-forming resin.

[0021] The polymers in the coherent bright region and coherent dark region of the related technology have significant structural differences, so they are prone to phase separation, which leads to increased haze in the prepared material.

[0022] In related technologies, photoinitiation systems involving photosensitive dyes and photoinitiators suffer from low photoinitiation efficiency. After the photoinitiator decomposes, it produces free small molecules such as benzaldehyde and benzoic acid. If these free small molecules migrate to the surface of the molded product, they will volatilize and produce an unpleasant odor. If the human body comes into contact with these small molecules, it will affect health. Some residual small molecules will further oxidize, causing the manufactured material to gradually turn yellow after a period of use, affecting the appearance and user experience.

[0023] In view of this, the present invention proposes the use of a compound, a photopolymer-type holographic recording medium, a volume holographic recording grating, a holographic optical element, and an optical device, aiming to reduce or eliminate the migration problem of small molecules generated by the decomposition of photoinitiators, reduce the probability of unpleasant odors, reduce the degree of yellowing of materials, and reduce material haze.

[0024] Where there is no conflict, the following embodiments and features can be combined with each other.

[0025] The use of the compounds in the embodiments of this application will now be described by way of example.

[0026] The present invention discloses the use of a compound for reacting with polyisocyanates to generate a film-forming resin, wherein the compound and / or the film-forming resin simultaneously serve as a photoinitiator; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound includes a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

[0027] The following diagram illustrates the structural formula of the compound's main chain: The structural formula of the diphenyl disulfide backbone is as follows: The structural formula of the main chain of dinaphthyl disulfide is: .

[0028] As can be seen from the above, the compound proposed in the embodiments of the present invention has two uses. It can not only produce a film-forming resin that has a secondary amine and retains the main chain of the compound and the unreacted groups in the polyisocyanate through polymerization reaction of hydroxyl or amino groups with the isocyanate group of the polyisocyanate, but also retains the main chain of the compound and the unreacted groups in the polyisocyanate.

[0029] For example, R2-N=C=O represents polyisocyanate, and R1-NH2 and R1-OH represent compounds with amino and hydroxyl functional groups, respectively. The reaction equation for the formation of the film-forming resin is illustrated below: R2-N=C=O + R1-NH2→ R2-NH-CO-NH-R1; where R1 includes a diphenyl disulfide backbone or a dinaphthyl disulfide backbone, that is, it has a -SS- structure that can be broken under light. The R1-NH2 of the original compound also has a -SS- structure that can be broken under light.

[0030] R2-N=C=O + R1-OH → R2-NH-COO-R1; where R1 includes a diphenyl disulfide backbone or a dinaphthyl disulfide backbone, that is, it has a -SS- structure that can be broken under light. The R1-OH of the original compound also has a -SS- structure that can be broken under light.

[0031] The -SS- bonds in R1-NH2 and / or R2-NH-CO-NH-R1, or R1-OH and / or R2-NH-COO-R1, can rapidly absorb light energy in the presence of ultraviolet and / or visible light. The bond energy of the -SS- bonds themselves is relatively weak, and the absorbed photon energy enables the film-forming resin to overcome the bond energy of the disulfide bond. After absorbing light energy, the non-bonded electrons of the sulfur atom transition from the ground state to the excited state, thereby forming small molecular groups with sulfur free radicals. R1-NH2 and / or R2-NH-CO-NH-R1 with -SS- bonds, and R1-OH and / or R2-NH-COO-R1 with -SS- bonds are easily excited under light irradiation to form free radicals that can initiate the polymerization of writing monomers, with high initiation efficiency.

[0032] For example, the film-forming resin formed by the reaction of the compound with polyisocyanate, under light irradiation, experiences partial breakage of the -SS- bonds on the main chain of the film-forming resin, generating free radicals. These free radicals can act as photoinitiators in the system, selectively and efficiently initiating the polymerization of writing monomers in the coherent bright region at the S-terminus. This allows some of the film-forming resin to form covalent bonds with the reacted writing monomers, reducing and preventing the migration of small molecule groups generated after the -SS- bond breakage, thus lowering the probability of unpleasant odors and reducing the degree of yellowing of the material. For example, the film-forming resin generated by the reaction of the aforementioned compound with polyisocyanate, in addition to forming a refractive index difference with the writing monomers, can also simultaneously act as a photoinitiator for photopolymer holographic recording media. That is, the compounds in the aforementioned embodiments are used to prepare photopolymer holographic recording media, and the compounds are one component in the raw materials of photopolymer holographic recording media.

[0033] Because some of the film-forming resins are linked to the writing monomers after the reaction in the coherent bright region, the structure of the coherent bright region after polymerization has a certain similarity to the structure of the film-forming resin in the coherent dark region, thereby reducing the degree of phase separation and lowering the haze of the material.

[0034] In some embodiments, the compound is selected from at least one of 4,4'-dihydroxydiphenyl disulfide, 6,6′-dihydroxy-2,2′-dinathyl disulfide, 3,3'-dihydroxydiphenyl disulfide, di(2-hydroxy-1-naphthyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, 3,3'-diaminodiphenyl disulfide, and 4,4'-disulfidedimethylbis(4,1-phenylene)diethanol. The compounds illustrated in these embodiments all have a -SS- group capable of photolysis and a reactive functional group of hydroxyl or amino; since each of these substances has two reactive functional groups, one equivalent of the compound can react with a maximum of two equivalents of isocyanate groups. These compounds contain phenyl and sulfur or naphthyl and sulfur, and have a high refractive index, allowing the refractive index of the compound to reach above 1.7 or even greater than 1.8; for example, some of these compounds have a refractive index of 1.7 to 1.85.

[0035] In some embodiments, the polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, terephthalic diisocyanate, bitoluidine diisocyanate, and diphenylmethylene diisocyanate. These polyisocyanates have isocyanate groups as their reactive functional groups, each molecule containing two isocyanate groups. One equivalent of the polyisocyanate can react with two equivalents of amino groups or two equivalents of hydroxyl groups, resulting in higher reactivity and faster reaction with the compound. These polyisocyanates contain aromatic rings, giving them a refractive index higher than 1.55. The film-forming resin synthesized from the reaction of these polyisocyanates with the compound has a high refractive index, thereby increasing the refractive index difference between the film-forming resin and the writing monomer. Exemplarily, toluene diisocyanate, abbreviated as TDI, includes 2,4-TDI and 2,6-TDI isomers. Exemplarily, diphenylmethane diisocyanate, abbreviated as MDI, includes 4,4'-MDI, 2,4'-MDI, and polymeric MDI thereof. In the examples, 1,5-naphthalene diisocyanate is abbreviated as NDI, terephthalic diisocyanate as PPDI, benzyl toluidine diisocyanate as TODI, and diphenylmethylene diisocyanate as XDI. In other examples, the polyisocyanate is selected from butane-1,4-diisocyanate (refractive index 1.453), isophorone diisocyanate (refractive index 1.484), dicyclohexylmethane diisocyanate (refractive index 1.496), etc., as long as the refractive index difference between the film-forming resin and the writing monomer is sufficiently large, and the refractive index difference between the film-forming resin and the writing monomer must be at least greater than 0.1.

[0036] The photopolymer-type holographic recording medium of this application will now be described by way of example.

[0037] The photopolymer-type holographic recording medium proposed in this invention comprises the following raw materials: a film-forming resin, which includes a compound and a polyisocyanate; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound includes a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

[0038] As can be seen from the above, the photopolymer-type holographic recording medium proposed in this embodiment of the invention allows the compound to undergo a polymerization reaction with the isocyanate groups of polyisocyanates via hydroxyl or amino groups to generate a film-forming resin containing secondary amines and -SS- bonds. The specific reaction principle can be found in the preceding text and will not be repeated here.

[0039] The formed film-forming resin can induce the breakage of -SS- bonds on the main chain of the film-forming resin in some coherent bright areas under light irradiation, generating free radicals. It has high photoinitiation efficiency, which is very important for photopolymer holographic recording media, directly endowing the photopolymer holographic recording media with excellent comprehensive performance. On the one hand, it can convert more photon energy into free radicals, significantly reducing the required exposure energy, thereby significantly improving the photosensitivity of photopolymer holographic recording media and enabling fast recording and low-power operation.

[0040] On the other hand, high efficiency ensures that the polymerization of writing monomers can be initiated quickly and thoroughly in the bright stripe region of the coherent bright area. This not only accelerates the diffusion process of writing monomers from the dark area to the bright area, but also speeds up the phase separation process of the film-forming resin and the writing monomers. This results in high-contrast refractive index modulation, higher diffraction efficiency, and a larger dynamic range. It can effectively suppress monomer residues and photoinitiator byproducts caused by incomplete reactions or side reactions, thereby reducing the volume shrinkage, optical scattering, and background noise of the photopolymer holographic recording medium. Ultimately, it enables the hologram of the photopolymer holographic recording medium to achieve high fidelity. The photopolymer holographic recording medium has excellent optical quality and good long-term stability.

[0041] It is understood that the film-forming resin in the embodiments of this application can also serve as a photoinitiator in a photopolymer-type holographic recording medium, selectively and efficiently initiating the polymerization of writing monomers in the coherent bright region at the end of S, so that a portion of the film-forming resin and the reacted writing monomers form covalent bonds. This strong chemical bonding significantly reduces the degree of phase separation between the "polymer generated in the bright stripe region" and the "film-forming resin in the dark stripe region"; it can also reduce the migration of small molecules generated after the -SS- bond breaks, thereby reducing the probability of unpleasant odors and the degree of yellowing of the material, reducing the potential toxicity of the material, and improving the long-term stability and environmental friendliness of the material.

[0042] If there are residual small free radical molecules from the photolysis reaction, these free radicals can further couple with each other to reform disulfides; or, the small free radical molecules can participate in other reactions in the system.

[0043] Because the film-forming resin, which acts as a photoinitiator, achieves a certain connection with the writing monomer after the reaction in the bright area, the structure of the coherent bright area after polymerization has a certain similarity to the structure of the film-forming resin that is squeezed into the coherent dark area. This reduces the degree of phase separation between the coherent bright area and the coherent dark area, effectively reducing the haze of the material.

[0044] In some embodiments, the compound has at least two reactive functional groups, and the polyisocyanate has at least two isocyanate groups. Multiple amino or hydroxyl groups can react rapidly with multiple isocyanate groups to form a polymer compound with a certain degree of polymerization. This allows the film-forming resin to provide a certain mechanical strength to the entire photopolymer holographic recording medium and to serve as a framework. And / or, the compound accounts for 15% to 40% of the mass percentage of the photopolymer holographic recording medium. For example, the mass percentage can be 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 33%, 35%, 40%, or a range consisting of any two of the above specific values ​​as endpoints. The polyisocyanate accounts for 15% to 40% of the mass percentage of the photopolymer holographic recording medium. For example, the mass percentage can be 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 33%, 35%, 40%, or a range consisting of any two of the above specific values ​​as endpoints. The compound and the polyisocyanate together form a film-forming resin with a low refractive index, thereby providing support for the other components. In a more specific embodiment, the compound is controlled at 21.61% to 39.19%; the polyisocyanate-based compound is controlled at 17.2% to 39.7%.

[0045] In some embodiments, the compounds are selected from at least one of 4,4'-dihydroxydiphenyl disulfide, 6,6′-dihydroxy-2,2′-dinathyl disulfide, 3,3'-dihydroxydiphenyl disulfide, di(2-hydroxy-1-naphthyl)disulfide, 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, 3,3'-diaminodiphenyl disulfide, and 4,4'-disulfidedimethylbis(4,1-phenylene)diethanol. The properties of these compounds are as described above and will not be repeated here. Each compound either has two amino groups or two hydroxyl groups. The refractive indices of the compounds are relatively high, generally above 1.7; for example, the refractive index of 6,6′-dihydroxy-2,2′-dinathyl disulfide is approximately 1.835, the refractive index of 4,4'-dihydroxydiphenyl disulfide is approximately 1.71, and the refractive index of 3,3'-dihydroxydiphenyl disulfide is approximately 1.752. In other embodiments, the polyisocyanate is selected from butane-1,4-diisocyanate (refractive index 1.453), isophorone diisocyanate (refractive index 1.484), dicyclohexylmethane diisocyanate (refractive index 1.496), etc., as long as the refractive index difference between the film-forming resin and the writing monomer is sufficiently large. The refractive index difference between the film-forming resin and the writing monomer must be at least greater than 0.1. For example, when 6,6′-dihydroxy-2,2′-dinathyl disulfide is used as the compound and isophorone diisocyanate is used as the polyisocyanate, with a molar ratio of hydroxyl to isocyanate groups of 1:1, the refractive index of the resulting film-forming resin is approximately 1.698.

[0046] In some embodiments, the polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, terephthalic diisocyanate, benzyl toluidine diisocyanate, and phenylene diisocyanate. The properties of these polyisocyanates are as described above and will not be repeated here. These polyisocyanates all have two isocyanate groups. Each polyisocyanate has a high refractive index, generally above 1.55.

[0047] When examples of compounds having two amino groups or two hydroxyl groups are combined with examples of polyisocyanates having two isocyanate groups, the compounds having two amino groups and the polyisocyanates having two isocyanate groups can undergo rapid polymerization under catalyst-free conditions, for example, forming polyurea-type film-forming resins with -NH-CO-NH- groups; compounds having two hydroxyl groups and polyisocyanates having two isocyanate groups can undergo relatively mild polymerization, for example, forming polyurethane-type film-forming resins with -NH-CO-O- groups. The film-forming resins formed after the above polymerization reactions have certain mechanical strength and can serve as a skeleton and carrier, which is beneficial for film formation.

[0048] In some embodiments, the raw materials for the photopolymer-type holographic recording medium further include: polymerizable monomers, photosensitive dyes, catalysts, and additives. The polymerizable monomers serve as writing monomers, and the refractive index of the writing monomers is lower than that of the film-forming resin.

[0049] In the embodiments, the polymerizable monomers can undergo polymerization under the action of free radicals formed after photo-induced fracture of part of the film-forming resin, generating a polymer. Specifically, the monomers in the bright region, i.e., the polymerizable monomers in the bright region, are consumed and their concentration decreases as they polymerize, while the polymerizable monomers in the dark region hardly react. The difference in monomer concentration between the bright and dark regions causes the high concentration of polymerizable monomers in the dark region to migrate to the bright region, while most of the film-forming resin in the bright region is squeezed into the dark region. This makes the refractive index of the bright region close to the refractive index of the polymer after the polymerizable monomers are polymerized, while the refractive index of the dark region close to the refractive index of the polymer after the reaction of the polyisocyanate and the compound, forming a phase-type volumetric holographic grating with refractive index modulation.

[0050] In a further embodiment, the polymerizable monomer accounts for 20% to 50% of the mass of the photopolymer holographic recording medium, for example, values ​​such as 20%, 23%, 25%, 26%, 30%, 31%, 32%, 35%, 36%, 37%, 39%, 40%, 42%, 45%, 47%, 50%, and a range of values ​​between any two of the above specific values.

[0051] For example, the photosensitive dye accounts for 0.01% to 1% of the mass of the photopolymer-type holographic recording medium; for example, it can be 0.01%, 0.02%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1%, etc., or a range of values ​​between any two of the above specific values. In these embodiments, the photosensitive dye can be combined with polyurethane (a polyurethane-type film-forming resin having -NH-CO-O-) or polyurea (a polyurea-type film-forming resin having -NH-CO-NH-) as a photoinitiator in the aforementioned embodiments to realize a visible light initiation system, and adapt it to lasers of different wavelengths. Under irradiation with light within a specific wavelength range, the photosensitive dye in the photoinitiation system is activated by the corresponding light and absorbs light energy, transferring the light energy to the polyurethane or polyurea acting as a photoinitiator. This allows the polyurethane or polyurea acting as a photoinitiator to be activated under light radiation within a wider wavelength range, broadening the range of selectable light sources. Under irradiation with a matching wavelength light source, the photosensitive dye absorbs light energy and transfers it to the photoinitiator, causing the -SS- bonds of the polyurethane or polyurea to break, generating free radical small molecule groups with initiation functions. These free radical small molecule groups can initiate the polymerization of polymerizable monomers to achieve the construction of holographic gratings, thereby improving the photosensitivity of photopolymer-type holographic recording media.

[0052] For example, the photosensitive dye is 1 / 10 to 1 / 3 of the mass of the film-forming resin used as a photoinitiator, such as 1 / 10, 1 / 9, 1 / 8, 1 / 7, 1 / 6, 1 / 5, 1 / 4, or 1 / 3, and a range including any two of the aforementioned specific values. Effective control of the photosensitive dye concentration ensures that the number and speed of photons absorbed by the film-forming resin during holographic exposure are controlled within a suitable range, the rate of the photo-initiated polymerization reaction is controlled within a reasonable range, and the grating formation speed is controlled within a certain range, thus guaranteeing the light transmittance of the photopolymer-type holographic recording medium and achieving excellent diffraction efficiency.

[0053] For example, the catalyst accounts for 0.1% to 5% of the mass of the photopolymer-type holographic recording medium; for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.6%, 0.8%, 1.0%, 1.5%, 2.0%, 2.2%, 2.5%, 2.8%, 3%, 3.4%, 3.7%, 4.0%, 4.2%, 4.4%, 4.7%, 5%, etc., or a range of values ​​between any two of the above specific values. This can effectively increase the reaction rate of the relevant components, increase the consumption rate of the relevant components after exposure, thereby quickly forming a concentration difference of monomers in the bright and dark areas, and realizing a phase-type volume holographic grating with refractive index modulation. In a specific embodiment, the catalyst is controlled at 0.19% to 5%.

[0054] For example, the additive accounts for 0.1% to 10% of the mass of the photopolymer-based holographic recording medium. For instance, it can be 0.1%, 0.2%, 0.3%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4%, 5%, 6%, 6.5%, 7%, 7.4%, 7.7%, 8.0%, 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.1%, 9.3%, 9.5%, 9.7%, 10%, etc., or a range of values ​​between any two of the above specific values. Taking the additive as a leveling agent as an example, it can effectively improve the uniformity of the mixture, enhance its flowability, and reasonably control costs. Taking the additive as a chain transfer agent as an example, it can control the polymer chain length within a reasonable range and effectively prevent excessive polymerization. In a specific embodiment, the additive is controlled at 2.8% to 10%.

[0055] In the above embodiments, the components of the photopolymer holographic recording medium are controlled within a reasonable range, which can achieve full synergy among the components and prevent the holographic performance of the final photopolymer holographic recording medium from deteriorating due to too much or too little of a certain component, thus ensuring that the overall holographic performance of the final photopolymer holographic recording medium is better.

[0056] The following describes the mass percentage of each component in the photopolymer holographic recording medium in some specific embodiments: For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 22.8%, 17.2%, 50%, 1%, 1.2%, and 7.8%, respectively.

[0057] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 27.97%, 21.03%, 40%, 0.05%, 4%, and 6.95%, respectively.

[0058] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 31.6%, 28.4%, 30%, 0.8%, 1%, and 8.2%, respectively.

[0059] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 37.3%, 39.7%, 20%, 0.01%, 0.19%, and 2.8%, respectively.

[0060] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 40%, 25%, 28.9%, 1%, 5%, and 0.1%, respectively.

[0061] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 33.91%, 23.59%, 29%, 0.5%, 3%, and 10%, respectively.

[0062] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 15%, 40%, 33%, 1%, 3%, and 8%, respectively.

[0063] For example, the mass percentages of the compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, and additive in the photopolymer holographic recording medium are 40%, 15%, 43.9%, 0.5%, 0.5%, and 0.1%, respectively.

[0064] The selection of polymerizable monomers is described below as an example.

[0065] In some embodiments, the polymerizable monomer is at least one of acrylate monomers and methacrylate monomers. The polymerizable monomers in these embodiments all have polymerizable reactive functional groups such as acrylate groups or methacrylate groups, and have a refractive index lower than that of the film-forming resin. Exemplarily, the acrylate monomer includes fluorinated acrylates, and the methacrylate monomer includes fluorinated methacrylates. When fluorinated acrylates or fluorinated methacrylates are used as components of the writing monomer, they can effectively reduce the refractive index of the writing monomer and create a larger refractive index difference between the film-forming resin and the writing monomer, for example, a refractive index difference of at least 0.1, a refractive index difference greater than 0.2 in some film-forming resins and the writing monomer, and a refractive index difference greater than 0.3 in others, resulting in high diffraction efficiency of the fabricated holographic optical element.

[0066] Unless otherwise specified, when multiple substances in the embodiments of this application are combined to form the same component, the ratio between the multiple substances is any ratio or any ratio in which they are compatible.

[0067] For example, the acrylate monomer is selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, isobornyl acrylate, lauryl acrylate, octadecyl acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, octafluoropentyl acrylate, and 1,1,1,3,3,3-hexafluoroisopropyl acrylate. The monomers are selected from at least one of the following: 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 1H,1H,7H-dodecylheptyl acrylate, 1H,1H-perfluorooctyl acrylate, 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane, tetrafluoropropyl acrylate, 1H,1H,11H-eicofluoroundecyl acrylate, heptafluoroisopropyl acrylate, 2-2,2-difluoroethyl acrylate, and methacrylate monomers. All monomers in these examples have reactive acrylate functional groups and low refractive indices, less than 1.5. In these examples, trifluoroethyl acrylate, hexafluorobutyl acrylate, octafluoropentyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 1H,1H,7H-dodecylheptyl acrylate, 1H,1H-perfluorooctyl acrylate, 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane, tetrafluoropropyl acrylate, 1H,1H,11H-eicofluoroundecyl acrylate, heptafluoroisopropyl acrylate, and 2-2,2-difluoroethyl acrylate are all fluorinated acrylate monomers, and their refractive indices are usually lower, some even below 1.4.

[0068] For example, the methacrylate monomer is selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate. The following are included in the list of esters, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, bisphenol A dimethacrylate, 1H,1H-perfluorooctyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecylfluorononyl methacrylate, 2,2-difluoroethyl 2-methyl-2-acrylate, octafluoropentyl methacrylate, dodecafluoroheptyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 1H,1H-perfluoropropyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, hexafluorobutyl methacrylate, and 2,2,3,3-tetrafluoropropyl methacrylate. The monomers in these examples all have reactive functional groups (methacrylate groups) and low refractive indices, with most being less than 1.5. For example, methyl methacrylate has a refractive index of 1.412, and ethyl methacrylate has a refractive index of 1.4147. The monomers in these examples—1H,1H-perfluorooctyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecylfluorononyl methacrylate, 2-methyl-2-acrylate, 2,2-difluoroethyl methacrylate, octafluoropentyl methacrylate, dodecafluoroheptyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 1H,1H-perfluoropropyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, hexafluorobutyl methacrylate, and 2,2,3,3-tetrafluoropropyl methacrylate—are all fluorinated methacrylate monomers, and their refractive indices are generally even lower, some being less than 1.4.

[0069] In some embodiments, a compound with a refractive index of 1.7 to 1.85 and a polyisocyanate with a refractive index of 1.55 to 1.65 are selected as components of the film-forming resin, and a polymerizable monomer with a refractive index of 1.3 to 1.35 is selected as a component of the writing monomer. This allows the film-forming resin and the writing monomer to form a significant refractive index difference, for example, Δn ≥ 0.3. When the refractive index difference is sufficiently significant, the diffraction efficiency of the volume holographic recording grating can be improved.

[0070] For example, when 6,6′-dihydroxy-2,2′-dinathyl disulfide is used as the compound (refractive index approximately 1.835), and 1,5-naphthalene diisocyanate is used as the polyisocyanate (refractive index approximately 1.6), wherein the molar ratio of hydroxyl and isocyanate groups is 1:1, and fluorinated methacrylate monomers such as octafluoropentyl methacrylate (refractive index approximately 1.358) or dodecafluoroheptyl methacrylate (refractive index approximately 1.349) are used, the refractive index difference between the formed film-forming resin and the writing monomer can be greater than 0.3, approximately 0.39.

[0071] For example, when 3,3'-dihydroxydiphenyl disulfide is used as the compound (refractive index approximately 1.75), diphenylmethane diisocyanate is used as the polyisocyanate (refractive index approximately 1.59), wherein the molar ratio of hydroxyl to isocyanate groups is 1:1, and a fluorinated methacrylate monomer such as 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecylfluorononyl methacrylate (refractive index approximately 1.344) is used, the refractive index difference between the formed film-forming resin and the writing monomer can be greater than 0.3, approximately 0.326.

[0072] For example, when 4,4'-dihydroxydiphenyl disulfide is used as the compound (refractive index approximately 1.71~1.75), terephthalic diisocyanate is used as the polyisocyanate (refractive index approximately 1.567), wherein the molar ratio of hydroxyl to isocyanate groups is 1:1, and a fluorinated acrylate monomer such as 1,1,1,3,3,3-hexafluoroisopropyl acrylate (refractive index approximately 1.319) is used, the refractive index difference between the formed film-forming resin and the writing monomer can be greater than 0.3, approximately 0.33.

[0073] For example, when 6,6′-dihydroxy-2,2′-dinathyl disulfide (refractive index approximately 1.835) is selected as the compound and isoflurane diisocyanate (refractive index approximately 1.484) is selected as the polyisocyanate, the molar ratio of hydroxyl and isocyanate groups is 1:1, and a fluorinated acrylate monomer such as trifluoroethyl acrylate (refractive index approximately 1.35) is used, the refractive index difference between the formed film-forming resin and the writing monomer can be greater than 0.3, approximately 0.34.

[0074] The selection of photosensitive dyes will be described below as an example.

[0075] In some embodiments, the photosensitive dye is selected from at least one of xanthracene dyes, cyanine dyes, phenothiazine dyes, and phenoxazine dyes. These photosensitive dyes are used in conjunction with a photoinitiator RSSR, comprising R2-NH-CO-NH-R1 or R2-NH-COO-R1, enabling R2-NH-CO-NH-R1 or R2-NH-COO-R1 to cleave the -SS- group in the diphenyl disulfide backbone or dinaphthyl disulfide backbone under illumination across a wider range of light wavelengths, further generating free radicals to initiate polymerization. Exemplarily, xanthracene dyes have strong absorption in the visible light region, for example, stronger absorption in the green light band. Exemplarily, cyanine dyes can have absorption wavelengths extending from the visible light region to the near-infrared region. Exemplarily, phenothiazine and phenoxazine dyes have strong absorption in the near-ultraviolet / visible region, transferring energy to the photoinitiator RSSR via electron transfer, causing SS- cleavage to generate small free radical molecules, further initiating polymerization.

[0076] For example, xanthracene dyes include, but are not limited to, eosin Y, fluorescein, Bengal rose red, and erythrosine B. Fluorescein absorbs blue-green light, while eosin Y, Bengal rose red, and erythrosine B absorb green light.

[0077] For example, cyanine dyes include, but are not limited to, quinoline blue and other cyanine dyes. Quinoline blue is sensitive to green light; other cyanine dyes are sensitive to red or near-infrared light.

[0078] For example, phenothiazine dyes or phenotoxazine dyes include, but are not limited to, methylene blue, Laureth violet, and Nile red. Methylene blue is sensitive to blue light. Laureth violet and Nile red are sensitive to green light.

[0079] Understandably, by using different photosensitive dyes, it is possible to adapt to more commonly used laser light sources, reducing equipment investment costs; and making the photoinitiation system more flexible. After absorbing light energy, the photosensitive dye transfers the light energy to the RSSR, which has the function of a photoinitiator. This enables the -SS- bond to break and initiate subsequent polymerization under the irradiation of a laser light source of the selected wavelength, without relying on the use of a short-wavelength laser light source that is compatible with the RSSR with the function of a photoinitiator.

[0080] In other embodiments, the photosensitive dye can also be combined with the compound to achieve the breaking of the -SS- bond in the main chain of the compound. The photoinitiation principle is similar to the combination of RSSR with photoinitiator function and photosensitive dye.

[0081] The selection of catalysts will be described below as an example.

[0082] In some embodiments, the catalyst is selected from at least one of tertiary amine catalysts or organometallic catalysts.

[0083] In specific examples, the catalyst is selected from at least one of triethylenediamine, bis(dimethylaminoethyl) ether, dimethylethanolamine, 2-(2-dimethylamino-ethoxy)ethanol, trimethylhydroxyethylpropanediamine, N,N-bis(dimethylaminopropyl)isopropanolamine, dibutyltin dilaurate, stannous octoate, potassium carboxylate catalysts, and bismuth carboxylate catalysts. The catalyst is not limited to the types listed above; any catalyst capable of catalyzing the polymerization reaction of the aforementioned components under light irradiation is acceptable. Those skilled in the art should understand that these all fall within the scope of protection of this invention.

[0084] The selection of additives will be described below as an example.

[0085] In some embodiments, the additive is selected from at least one of chain transfer agents, defoamers, leveling agents, plasticizers, and dehydrating agents. When the additive includes a chain transfer agent, the chain transfer agent accounts for less than or equal to 3% of the mass of the photopolymer holographic recording medium, and the chain transfer agent is a thiol-based chain transfer agent. When the additive includes a defoamer, the defoamer accounts for less than or equal to 3% of the mass of the photopolymer holographic recording medium. When the additive includes a leveling agent, the leveling agent accounts for less than or equal to 3% of the mass of the photopolymer holographic recording medium. When the additive includes a plasticizer, the plasticizer accounts for less than or equal to 3% of the mass of the photopolymer holographic recording medium. When the additive includes a dehydrating agent, the dehydrating agent accounts for less than or equal to 3% of the mass of the photopolymer holographic recording medium. In embodiments using chain transfer agents, the polymer chain length can be controlled within a reasonable range, effectively preventing excessive polymerization and ensuring that the final holographic recording medium has the required optical properties and diffraction efficiency. In embodiments using defoamers, the defoamer can reduce the surface tension of the liquid and remove foam, improving the flowability of the mixture of components. In embodiments using leveling agents, the uniformity of the mixture can be effectively improved, the flowability enhanced, and costs reasonably controlled. In embodiments using plasticizers, the plasticizers increase the plasticity of the polymer by intercalating between polymer molecular chains, weakening intermolecular stress, increasing chain mobility, and reducing crystallinity. In embodiments using dehydrating agents, the dehydrating agents can remove excess water during the reaction, allowing for better mixing of the components and preventing stratification. The mass percentage of each of the aforementioned chain transfer agent, defoamer, leveling agent, plasticizer, and dehydrating agent in the photopolymer holographic recording medium is less than or equal to 3%, and the mass percentage can be 3%, 2.9%, 2.8%, 2.7%, 2.6%, 2.5%, 2.4%, 2.3%, 2.2%, 2.1%, 2.0%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, or 0%; and at least one of the chain transfer agent, defoamer, leveling agent, plasticizer, and dehydrating agent in the photopolymer holographic recording medium is not 0.

[0086] In some embodiments, the additive includes a chain transfer agent, which includes a thiol chain transfer agent. The addition of a thiol chain transfer agent enables more uniform polymer chain formation and controlled chain growth during the polymerization of polymerizable monomers under free radical initiation. It also reduces volume shrinkage after polymerization and can regulate the molecular weight of the polymerizable monomers after polymerization.

[0087] For example, the thiol chain transfer agent is selected from at least one of n-dodecylthiol, n-octylthiol, n-butylthiol, tert-dodecylthiol, mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, ethyl mercaptoacetate, isooctyl mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), tri(3-mercaptopropionic acid) trimethylolpropane, dipentaerythritol hexa(3-mercaptopropionate), mercaptopropyltrimethoxysilane, and mercaptopropyltriethoxysilane.

[0088] In some embodiments, when the additive includes a defoamer, the defoamer is a silicone defoamer and / or a silicone-free polymeric defoamer.

[0089] More specifically, one can choose, for example, BYK-011, BYK-012, BYK-014, BYK-023, BYK-051N, BYK-085, BYK-1610, BYK-1707, BYK-1740, and BYK-1760 manufactured by BYK Corporation, or DC65 and AFE-7820 manufactured by Dow Corning Corporation, or any mixture of these defoamers in any proportion. The BYK series of defoamers have excellent defoaming performance, good compatibility with other components, and good dispersibility; among them, BYK-011, BYK-012, BYK-014, and BYK-051N are silicone-free polymeric defoamers. DC65 is a water-based ink that dries quickly, provides good printing results, and is not easily peeled off. AFE-7820 has highly efficient defoaming performance.

[0090] In some embodiments, when the additive includes a leveling agent, the leveling agent is a silicone surface aid.

[0091] In specific embodiments, leveling agents include, but are not limited to, BYK-302, BYK-306, BYK-307, BYK-327, BYK-329, BYK-333, BYK-356, BYK-358, BYK-378, BYK-3455, BYK-3566, or any mixtures of these surface additives manufactured by BYK Corporation. The BYK series of leveling agents exhibits excellent leveling properties.

[0092] In some embodiments, the additive includes a plasticizer selected from at least one of toluene, xylene, dimethylformamide, dimethylacetamide, glycerol, and phthalates. When multiple plasticizers are selected, they can be in any proportion.

[0093] In some embodiments, the additive includes a dehydrating agent. In specific examples, the dehydrating agent includes, but is not limited to, p-toluenesulfonyl isocyanate, triethyl orthoformate, CUWR-WB20 dehydrating agent from Guangzhou Yourun Synthetic Materials Co., Ltd., ALT-201 dehydrating agent from Anxiang Elite Chemical Co., Ltd., and PCCI dehydrating agent from Shanghai Luer Chemical Trading Co., Ltd.

[0094] The solvent will now be described by way of example.

[0095] In some embodiments, the raw materials of the photopolymer holographic recording medium further include: a solvent, which is used to dissolve other components in the raw materials of the photopolymer holographic recording medium; the solvent accounts for 20% to 500% of the total amount of other substances in the raw materials of the photopolymer holographic recording medium; the solvent enables other components in the raw materials of the photopolymer holographic recording medium, such as compounds, polyisocyanates, polymerizable monomers, photosensitive dyes, catalysts, and additives, to remain mixed before being coated onto the substrate surface; and after being coated onto the substrate surface and cured, the solvent evaporates, leaving the remaining components.

[0096] For example, the solvent is selected from at least one of dichloromethane, ethyl acetate, petroleum ether, n-hexane, toluene, xylene, N,N-dimethylformamide, N,N-dimethylacetamide, diethyl ether, pentane, acetone, dichloroethane, chloroform, methanol, tetrahydrofuran, trichloroethane, carbon tetrachloride, ethanol, butanone, benzene, cyclohexane, acetonitrile, isopropanol, ethylene glycol dimethyl ether, propionitrile, heptane, pyridine, butanol, ethylene glycol-methyl ether, octane, butyl acetate, chlorobenzene, ethylene glycol-diethyl ether, cyclohexanone, and dimethyl sulfoxide. Selecting the above solvents allows for sufficient wetting of other components and ensures miscibility between the components, forming a relatively homogeneous mixture system, which facilitates application and fabrication of photopolymer-type holographic recording media.

[0097] The following describes an exemplary method for preparing a photopolymer-based holographic recording medium.

[0098] A method for preparing a photopolymer-based holographic recording medium includes the following steps: Step S100: Weigh the raw materials of each component of the photopolymer holographic recording medium: compound, polyisocyanate, polymerizable monomer, photosensitive dye, catalyst, additive, and solvent into a container, and stir thoroughly until all components are dissolved.

[0099] Step S200: Filter the mixture using a filter membrane to obtain the mixture.

[0100] Step S300: The mixture is coated onto a substrate and dried to obtain a photopolymer-type holographic recording medium. In some embodiments, drying is carried out in a darkroom with a humidity of 10% to 85% and a temperature of 20°C to 50°C. For example, the humidity includes specific values ​​such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, and 85%, as well as a range consisting of any two of the above specific values ​​as endpoints; the temperature includes specific values ​​such as 20°C, 25°C, 30°C, 35°C, 40°C, or 50°C, as well as a range consisting of any two of the above specific values ​​as endpoints. The conditions are simple and easy to operate, and the solvent can be evaporated after drying.

[0101] By employing the aforementioned method for preparing photopolymer holographic recording media, the preparation process involves fewer steps, is simpler to operate, is easier to implement, and facilitates the acquisition of photopolymer holographic recording media with high photosensitivity, high diffraction efficiency, and good weather resistance.

[0102] The application of the photopolymer-type holographic recording medium of the foregoing embodiments of the present invention is described below.

[0103] The present invention proposes a volume holographic recording grating, which is prepared by holographic exposure of the holographic recording medium of the aforementioned embodiment.

[0104] The present invention proposes a holographic optical element, which includes the volume holographic recording grating of the aforementioned embodiment.

[0105] As can be seen from the above, the volume holographic recording grating and holographic optical element proposed in this embodiment of the invention, since they include the aforementioned photopolymer-type holographic recording medium of this invention, also possess the advantages of the photopolymer-type holographic recording medium of this invention. They can achieve high photoinitiation efficiency and realize a more uniform and dense recording medium microstructure. While suppressing phase separation, they effectively reduce light scattering centers, thereby achieving low haze (<0.2%). Combining an efficient initiation and polymerization mechanism, this volume holographic recording grating and holographic optical element simultaneously exhibit high sensitivity and high diffraction efficiency: sensitivity >100 cm / mJ; diffraction efficiency >95%; and required exposure amount less than 10 mJ / cm. 2 This gives holographic optical elements better holographic performance.

[0106] The optical device of the present application embodiment will now be described by way of example.

[0107] This invention provides an optical device comprising the holographic optical element described in the preceding embodiments. This optical device includes, but is not limited to, head-up displays (HUDs), augmented reality (AR) devices such as AR glasses, virtual reality (VR) devices such as VR glasses, and photopolymer holographic storage discs. Photopolymer holographic storage discs enable erasable rewriting and real-time recording, making them suitable for storing large amounts of data and offering very fast data transfer speeds. Taking AR glasses as an example, due to the use of the holographic optical element described in the preceding embodiments, the high diffraction efficiency of the holographic optical element results in a brighter virtual display and better color display for the same power consumption. To achieve the same display brightness, the power required by the optical engine is lower, reducing overall power consumption, extending battery life, and reducing heat generation. Incident light can efficiently penetrate the medium, greatly reducing energy loss due to scattering, resulting in a brighter holographic image, more saturated colors, and higher holographic quality.

[0108] As can be seen from the above, the optical device proposed in the embodiments of the present invention, since it includes the aforementioned holographic optical element of the present invention, also has the advantages of the holographic optical element of the present invention, and the optical device has excellent holographic performance.

[0109] Unless otherwise specified, the raw materials of the photopolymer holographic recording medium in the embodiments of the present invention, such as compounds, polyisocyanates, polymerizable monomers, photosensitive dyes, catalysts, additives, solvents, etc., can all be obtained from conventional commercial sources.

[0110] The photopolymer-type holographic recording medium of the present invention will be described below with reference to specific embodiments.

[0111] Example 1 In this embodiment, the photopolymer holographic recording medium is designated as 1-1. The specific components of 1-1 are shown in Table 1 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0112] Table 1

[0113] Example 2 In this embodiment, the photopolymer holographic recording medium is designated as 1-2. The specific components of 1-2 are shown in Table 2 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0114] Table 2

[0115] Example 3 In this embodiment, the photopolymer holographic recording medium is designated as 1-3. The specific components of 1-3 are shown in Table 3 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0116] Table 3

[0117] Example 4 In this embodiment, the photopolymer holographic recording medium is designated as 1-4. The specific components of 1-4 are shown in Table 4 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0118] Table 4

[0119] Example 5 In this embodiment, the photopolymer holographic recording medium is designated as 1-5. The specific components of 1-5 are shown in Table 5 below, wherein the equivalent ratio of the amino group of the compound to the isocyanate group of the polyisocyanate is 1:1.

[0120] Table 5

[0121] Example 6 In this embodiment, the photopolymer holographic recording medium is designated as 1-6. The specific components of 1-6 are shown in Table 6 below, wherein the equivalent ratio of the amino group of the compound to the isocyanate group of the polyisocyanate is 1:1.

[0122] Table 6

[0123] Example 7 In this embodiment, the photopolymer holographic recording medium is designated as 1-7. The specific components of 1-7 are shown in Table 7 below, wherein the equivalent ratio of the amino group of the compound to the isocyanate group of the polyisocyanate is 1:1.

[0124] Table 7

[0125] Example 8 In this embodiment, the photopolymer holographic recording medium is designated as 1-8. The specific components of 1-8 are shown in Table 8 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0126] Table 8

[0127] Example 9 In this embodiment, the photopolymer holographic recording medium is designated as 1-9. The specific components of 1-9 are shown in Table 9 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0128] Table 9

[0129] Example 10 In this embodiment, the photopolymer holographic recording medium is designated as 1-10. The specific components of 1-10 are shown in Table 10 below, wherein the equivalent ratio of the hydroxyl groups of the compound to the isocyanate groups of the polyisocyanate is 1:1.

[0130] Table 10

[0131] Comparative Example The composition is roughly the same as that of the photopolymer holographic recording medium 1-1 in Example 1, except that the compound in the photopolymer holographic recording medium 1-1 is replaced with 2,4-dihydroxybiphenyl, and the mass percentage is adjusted to 29.71%; the mass percentage of toluene diisocyanate is adjusted to 27.79%; the mass percentage of leveling agent is adjusted to 1%; and the mass percentage of photoinitiator α,α-dialkoxyacetophenone in the photopolymer holographic recording medium is increased to 2%, resulting in a common photopolymer holographic recording medium, denoted as 2-1.

[0132] Experimental Example 1 The performance of photopolymer holographic recording media 1-1 to 1-10 in Examples 1-10 and the conventional photopolymer holographic recording media 2-1 in the comparative example were tested, and the results are shown in Table 11. During the test, different wavelengths of laser light were selected for exposure of each holographic recording medium in each example, depending on the photosensitive system, with an exposure intensity of 3 mW / cm². 2 .

[0133] Using the photopolymer holographic recording media 1-2 to 1-4 in the embodiments, corresponding holographic performance diagrams were plotted to obtain... Figure 1 Using the photopolymer-type holographic recording media 1-7 to 1-9 in the embodiments, corresponding holographic performance diagrams were plotted to obtain... Figure 2 .

[0134] Specifically, for the aforementioned photopolymer-type holographic recording media 1-2, 1-3, 1-4, 1-7, 1-8, and 1-9, solid-state lasers with wavelengths of 532 nm, 532 nm, 633 nm, 532 nm, 457 nm, and 457 nm were used as light sources. After passing through a beam expander, beam splitter, and half-wave plate, two beams with the same intensity and a diameter of 8 mm were obtained. The two beams were intersected within the prepared holographic recording medium for exposure, with a light intensity of 3 mW / cm². 2 The detection light source uses a 785 nm wavelength solid-state laser that does not react with the recording medium. The detection light is incident on the exposure area from the Bragg angle. The transmitted light and diffracted light are monitored in real time by a photodetector. The single grating diffraction efficiency (η) and the photosensitivity (S) of the photopolymer holographic recording medium are calculated by formulas (1) to (3).

[0135]

[0136] In the formula, η is the diffraction efficiency, η max For the highest diffraction efficiency, I d I represents the optical power of the diffracted light, measured in W. t Ω represents the transmitted light power, measured in W; S represents the photosensitivity, measured in cm / mJ; and E represents the exposure energy, measured in mJ / cm².

[0137] The haze of the photopolymer holographic recording media 1-1 to 1-10 of each embodiment and the ordinary photopolymer holographic recording media 2-1 of the comparative example were tested using a haze meter. The test results are shown in Table 11.

[0138] like Figure 1 , Figure 2 As shown, the final measured diffraction efficiency of the photopolymer holographic recording medium of this invention is greater than 95%, and the exposure dose is less than 10 mJ / cm². 2 The sensitivity is greater than 100 cm / mJ.

[0139] And such Figure 3 As shown, a conventional photopolymer holographic recording medium 2-1, used as a comparative example, was exposed at a wavelength of 532 nm and an exposure intensity of 3 mW / cm². 2 The diffraction efficiency of the ordinary photopolymer holographic recording medium 2-1 in the comparative example was found to be less than 32%, requiring an exposure dose greater than 73 mJ / cm². 2 Its sensitivity is relatively low, less than 8 cm / mJ.

[0140] The holographic performance tests of the photopolymer holographic recording media 1-1 to 1-10 in each embodiment and the ordinary photopolymer holographic recording media 2-1 in the comparative example are shown in Table 11 below.

[0141] Table 11

[0142] In summary, for reference Figure 1 , Figure 2 , Figure 3 According to Table 11, the diffraction efficiency of the photopolymer holographic recording medium in the embodiments of the present invention is greater than or equal to 95.99%, which is much higher than that of the comparative example. This indicates that when AR glasses are made using the photopolymer holographic recording medium of the embodiments of the present application, the virtual display screen will be brighter, the color display will be better, and the imaging will be clearer under the same power consumption. Under the same display brightness, the power required by the optical engine is lower, the power consumption of the whole machine is reduced, the battery life is extended, and the device generates less heat.

[0143] The photopolymer holographic recording medium of this application has a sensitivity greater than or equal to 101.59 cm / mJ, which is much greater than that of the comparative example. This indicates that only a small amount of light energy is needed to complete the curing and photopolymerization process of the photopolymer holographic recording medium, making the fabrication of bulk holographic recording gratings faster, significantly improving production efficiency and reducing manufacturing costs. The high-sensitivity holographic recording medium is compatible with more exposure equipment, making it more user-friendly in terms of equipment and process investment.

[0144] The exposure required for the photopolymer holographic recording medium in this application embodiment is less than or equal to 9.7 mJ / cm². 2 The difference is much smaller than that of the comparative example, indicating that the holographic recording medium using the embodiments of this application only requires extremely low exposure energy to form a stable volume holographic recording grating, which can shorten the exposure time under the premise of the same exposure power, or reduce the laser power requirement during exposure under the premise of the same exposure time.

[0145] The haze of the photopolymer holographic recording medium in this embodiment of the invention is less than or equal to 0.19%, which is significantly lower than that of the comparative example. This indicates that the phase separation between the polymerized structures in the bright fringe region and the polymerized structures in the dark fringe region of the photopolymer holographic recording medium of this application is relatively small. The smaller haze can achieve low scattering loss, allowing the photopolymer holographic recording medium to diffract more incident light to the required first-order diffraction direction during the hologram recording process during exposure, thus achieving high diffraction efficiency. The smaller haze can also allow incident light to penetrate the medium efficiently, greatly reducing energy loss caused by scattering, making the holographic image brighter, the colors more saturated, and the hologram of higher quality, thereby improving holographic performance.

[0146] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. Use of a compound, characterized in that, The compound is used to react with polyisocyanates to generate a film-forming resin, and the compound and / or the film-forming resin simultaneously act as a photoinitiator; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound includes a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

2. The use of the compound as claimed in claim 1, characterized in that, The compound is used to prepare a photopolymer holographic recording medium, wherein the film-forming resin serves as a photoinitiator for the photopolymer holographic recording medium; and / or, the refractive index of the compound is 1.7 to 1.

85.

3. A photopolymer-based holographic recording medium, characterized in that, The raw materials of the photopolymer holographic recording medium include: a film-forming resin, which includes a compound and a polyisocyanate; the reactive functional group of the compound is hydroxyl or amino, and the main chain of the compound includes a diphenyl disulfide main chain or a dinaphthyl disulfide main chain.

4. The photopolymer-type holographic recording medium as described in claim 3, characterized in that, The compound has at least two reactive functional groups, and the polyisocyanate has at least two isocyanate groups; and / or, The compound accounts for 15% to 40% of the mass of the photopolymer holographic recording medium; the polyisocyanate accounts for 15% to 40% of the mass of the photopolymer holographic recording medium.

5. The photopolymer-type holographic recording medium as described in claim 4, characterized in that, The compound is selected from at least one of 4,4'-dihydroxydiphenyl disulfide, 6,6′-dihydroxy-2,2′-dinathyl disulfide, 3,3'-dihydroxydiphenyl disulfide, di(2-hydroxy-1-naphthyl) disulfide, 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, 3,3'-diaminodiphenyl disulfide, and 4,4'-disulfidedimethylbis(4,1-phenylene)diethanol; and / or, the refractive index of the compound is 1.7 to 1.

85.

6. The photopolymer-type holographic recording medium as described in claim 3, characterized in that, The polyisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, terephthalic diisocyanate, benzyl toluidine diisocyanate, and diphenylmethylene diisocyanate.

7. The photopolymer-type holographic recording medium according to any one of claims 3 to 6, characterized in that, The raw materials of the photopolymer holographic recording medium also include: polymerizable monomers, photosensitive dyes, catalysts, and additives; The polymerizable monomer is used as a writing monomer, and the refractive index of the writing monomer is less than that of the film-forming resin.

8. The photopolymer-type holographic recording medium as described in claim 7, characterized in that, The polymerizable monomer accounts for 20% to 50% of the mass percentage of the photopolymer-type holographic recording medium; The photosensitive dye accounts for 0.01% to 1% of the mass of the photopolymer-type holographic recording medium; The catalyst accounts for 0.1% to 5% of the mass of the photopolymer-type holographic recording medium; The additive accounts for 0.1% to 10% of the mass of the photopolymer holographic recording medium.

9. The photopolymer-type holographic recording medium as described in claim 8, characterized in that, The polymerizable monomer is at least one of acrylate monomers and methacrylate monomers.

10. The photopolymer-type holographic recording medium as described in claim 9, characterized in that, The acrylate monomers are selected from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, isobornyl acrylate, lauryl acrylate, octadecyl acrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, trifluoroethyl acrylate, hexafluorobutyl acrylate, octafluoropentyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 2 At least one of the following monomers: 2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl acrylate, 1H,1H,7H-dodecylfluoroheptyl acrylate, 1H,1H-perfluorooctyl acrylate, 1,6-bis(acryloyloxy)-2,2,3,3,4,4,5,5-octafluorohexane, tetrafluoropropyl acrylate, 1H,1H,11H-eicosyl undecyl acrylate, heptafluoroisopropyl acrylate, 2-2,2-difluoroethyl acrylate, and methacrylate. The methacrylate monomers are selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, and neopentyl glycol dimethacrylate. At least one of the following: trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, bisphenol A dimethacrylate, 1H,1H-perfluorooctyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecylfluorononyl methacrylate, 2,2-difluoroethyl 2-methyl-2-acrylate, octafluoropentyl methacrylate, dodecafluoroheptyl methacrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 1H,1H-perfluoropropyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, hexafluorobutyl methacrylate, and 2,2,3,3-tetrafluoropropyl methacrylate.

11. The photopolymer-type holographic recording medium as described in claim 8, characterized in that, The photosensitive dye is selected from at least one of oxanthracene dyes, anthocyanin dyes, phenothiazine dyes, and phenotoxazine dyes; The catalyst is selected from at least one of tertiary amine catalysts or organometallic catalysts; The additive is selected from at least one of chain transfer agents, defoamers, leveling agents, plasticizers, and dehydrating agents; When the additive includes a chain transfer agent, the chain transfer agent accounts for less than or equal to 3% of the mass percentage of the photopolymer holographic recording medium, and the chain transfer agent is a thiol chain transfer agent; when the additive includes an antifoaming agent, the antifoaming agent accounts for less than or equal to 3% of the mass percentage of the photopolymer holographic recording medium; when the additive includes a leveling agent, the leveling agent accounts for less than or equal to 3% of the mass percentage of the photopolymer holographic recording medium; when the additive includes a plasticizer, the plasticizer accounts for less than or equal to 3% of the mass percentage of the photopolymer holographic recording medium; when the additive includes a dehydrating agent, the dehydrating agent accounts for less than or equal to 3% of the mass percentage of the photopolymer holographic recording medium.

12. The photopolymer-type holographic recording medium as described in claim 11, characterized in that, The additive includes a chain transfer agent selected from at least one of the following: n-dodecyl mercaptan, n-octyl mercaptan, n-butyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, ethyl mercaptoacetate, isooctyl mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), tri(3-mercaptopropionic acid)trimethylolpropane, dipentaerythritol hexa(3-mercaptopropionate), mercaptopropyltrimethoxysilane, and mercaptopropyltriethoxysilane.

13. The photopolymer-type holographic recording medium as described in claim 7, characterized in that, The raw materials of the photopolymer holographic recording medium further include: a solvent, which is used to dissolve other components in the raw materials of the photopolymer holographic recording medium; the solvent accounts for 20% to 500% of the total amount of other substances in the raw materials of the photopolymer holographic recording medium.

14. A volume holographic recording grating, characterized in that, The volumetric holographic recording grating is prepared by holographic exposure of the photopolymer holographic recording medium as described in any one of claims 3 to 13.

15. A holographic optical element, characterized in that, Includes the volume holographic recording grating as described in claim 14.

16. An optical device, characterized in that, Includes the holographic optical element as described in claim 15.

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