Holographic material, volume holographic grating, holographic device, and preparation method

Abstract

A holographic material and a preparation method therefor, a holographic optical element, a holographic device, and a preparation method for a volume holographic grating. The preparation method for a holographic material comprises: providing a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives; and uniformly mixing the components under a light-proof condition to obtain a holographic material. In this way, a second-order holographic material can be pre-mixed for long-term storage, a start timing of a first-order reaction can be controlled, and a preparation process can be improved.

Description

Holographic materials, volume holographic gratings, holographic devices and their preparation methods

[0001] This application claims priority to Chinese Patent Application No. 2024117118625, filed on November 26, 2024, entitled "Holographic Material, Volume Holographic Grating, Holographic Device and Preparation Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of optical technology, and in particular to a holographic material and its preparation method, a volume holographic grating, a holographic device, and a method for preparing a volume holographic grating. Background Technology

[0003] Photopolymerizable holographic polymer materials (also known as holographic photopolymerizable materials) can be used to prepare volumetric holographic gratings through the principle of phase separation induced by coherent beam polymerization. They have advantages such as high photosensitivity and strong processing adaptability, and are considered ideal materials for holographic optical elements in the fields of VR (Virtual Reality) and AR (Augmented Reality).

[0004] Among related technologies, there are methods to prepare stable holographic polymer materials using orthogonal reaction design strategies and achieve industrial applications. Taking the polyurethane / acrylate orthogonal two-stage reaction type as an example, in the first stage, the polyol reacts with the isocyanate to form a cross-linked polymer network. In the second stage, the high-refractive-index monomer undergoes a holographic photopolymerization reaction under coherent light irradiation to form a volume holographic grating. However, due to the high chemical reactivity of isocyanates and their prepolymers, they can react with compounds containing active hydrogen (such as water vapor in the air), leading to inconveniences in use and storage. Summary of the Invention

[0005] Based on this, this application provides a holographic material and its preparation method, a volume holographic grating, a holographic device, and a volume holographic grating preparation method, which enables the pre-mixing and long-term storage of second-order holographic materials, controls the first-order reaction, and improves the entire volume holographic grating preparation process.

[0006] In a first aspect, this application provides a holographic material comprising: a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives; the blocked polyisocyanate comprises -NCO groups blocked by a blocking agent containing active hydrogen, and the blocked -NCO groups can be deblocked; the first compound can undergo a first polymerization reaction with the deblocked blocked polyisocyanate; the polymerizable monomer can undergo a second polymerization reaction in the presence of light and the photoinitiator.

[0007] Secondly, this application provides a method for preparing holographic materials, the method comprising:

[0008] Blocked polyisocyanates, first compounds, polymerizable monomers, photoinitiators, and other additives are available.

[0009] The blocked polyisocyanate, the first compound, the polymerizable monomer, the photoinitiator, and the other additives are mixed evenly under light-protected conditions to obtain the holographic material.

[0010] Thirdly, this application provides a volume holographic grating, which is made of the holographic material described above.

[0011] Fourthly, this application provides a holographic device, which includes the volume holographic grating described above.

[0012] Fifthly, this application provides a method for fabricating a volume holographic grating, the method comprising:

[0013] Provide holographic materials, wherein the holographic materials are as described above;

[0014] The holographic material is uniformly distributed on the surface of the substrate;

[0015] A substrate with holographic material uniformly distributed on its surface is placed under deblocking conditions, which causes the blocked -NCO groups of the blocked polyisocyanate in the holographic material to be deblocked into new -NCO groups, and the new -NCO groups to undergo a first polymerization reaction with the first compound to form a first-order cross-linked polymer network.

[0016] A light beam is used to illuminate a substrate placed under unsealed conditions, causing the polymerizable monomers in the bright area of ​​the holographic material to undergo a second polymerization reaction, and causing the polymerizable monomers in the unilluminated dark area to migrate to the bright area, thereby obtaining the volume holographic grating.

[0017] This application provides a holographic material and its preparation method, a volume holographic grating, a holographic device, and a method for preparing a volume holographic grating. The holographic material includes: a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives. The blocked polyisocyanate includes -NCO groups blocked by a blocking agent containing active hydrogen, and the blocked -NCO groups can be deblocked. The first compound can undergo a first polymerization reaction with the deblocked blocked polyisocyanate. The polymerizable monomer can undergo a second polymerization reaction in the presence of light and a photoinitiator. Because the holographic material does not use chemically reactive isocyanates, but rather blocked polyisocyanates, the polymerization reaction between the blocked polyisocyanates and the first compound in the holographic material can be avoided as much as possible. This allows the second-order holographic material to be pre-mixed and stored for a long time under room temperature and light-protected conditions, avoiding fluctuations and changes in the basic physical parameters of the holographic material. This also eliminates the need for freshly prepared holographic materials and pre-mixed AB glue, thus reducing the corresponding process costs and making it easier to control batch stability. When using holographic materials to prepare volume holographic gratings, the first polymerization reaction between the first compound and isocyanate is controlled by controlling the deblocking of the blocked -NCO groups to form a first-stage cross-linked polymer network. Then, the polymerizable monomers are controlled by light to undergo a second polymerization reaction to obtain the volume holographic grating, thereby improving the entire volume holographic grating preparation process. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the chemical structure of each component in the polyurethane / acrylate orthogonal second-order reactive system in the related technology;

[0019] Figure 2 is a schematic diagram of the isocyanate protection and deprotection chemical process in the embodiments of this application;

[0020] Figure 3 is a flowchart illustrating an embodiment of the method for preparing holographic materials according to this application;

[0021] Figure 4 is a flowchart illustrating another embodiment of the method for preparing holographic materials according to this application;

[0022] Figure 5 is a schematic flowchart of an embodiment of the fabrication method of the volume holographic grating of this application;

[0023] Figure 6 is a schematic diagram of the chemical process of the blocking and deblocking of the -NCO group of isocyanate in one embodiment of the preparation method of the volume holographic grating of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] The flowchart shown in the attached diagram is for illustrative purposes only and does not necessarily include all content and operations / steps, nor does it necessarily have to be performed in the order described. For example, some operations / steps can be broken down, combined, or partially merged, so the actual execution order may change depending on the actual situation.

[0026] In the following description, the use of suffixes such as "module," "part," or "unit" to denote elements is solely for the purpose of illustration and has no inherent meaning. Therefore, "module," "part," or "unit" may be used interchangeably.

[0027] Photopolymerizable holographic polymers (also known as holographic photopolymers) can be used to fabricate volumetric holographic gratings through the principle of phase separation induced by coherent beam polymerization. They possess advantages such as high photosensitivity and strong processing adaptability, and are considered ideal materials for holographic optical elements in VR (Virtual Reality) / AR (Augmented Reality) technologies. DuPont, Inc. in the United States was the first to use linear polymers with low refractive indices as binders to stabilize aryl acrylates with high refractive indices, successfully developing a series of commercially available holographic polymers that are easy to transport and suitable for roll-to-roll production processes. However, using linear polymers to stabilize photopolymerizable monomers leads to problems such as high volatile solvent consumption, large thickness, and poor dimensional stability caused by thermal chain relaxation.

[0028] To address the aforementioned issues, second-order reactive holographic polymer materials utilize in-situ chemical reactions to form cross-linked polymer networks, replacing linear polymer binders to stabilize photopolymerizable monomers. These in-situ chemical reactions include, but are not limited to, sol-gel reactions, addition reactions between polyols and polyisocyanates, addition reactions between polyamines and polyepoxides, Michael addition reactions between polythiols and polyacrylates, and addition reactions between polythiols and polyepoxides. These in-situ chemical reactions forming the cross-linked polymer network exhibit an orthogonal relationship with the free radical photopolymerization reactions during holographic recording, meaning the two reactions do not interfere with each other. Covestro AG in Germany has utilized this orthogonal reaction design strategy to prepare the high-performance Bayfol@HX series of holographic polymer materials and has achieved industrial applications.

[0029] Taking the Bayfol@HX series from Covestro in Germany as an example, it is a polyurethane / acrylate orthogonal two-stage reaction type. In the first stage, the polyol reacts with the isocyanate to form a first-stage cross-linked polymer network. In the second stage, the high-refractive-index monomer undergoes a holographic photopolymerization reaction under coherent light beam irradiation to form a volume holographic grating. The common chemical components of the corresponding system are shown in Figure 1, including: polyol, isocyanate, TBPA (tetrabromophthalic anhydride), BPTPA (1,3-diphenylthio-2-acrylate), and photoinitiator TPO (trimethylbenzoyl-diphenylphosphine oxide).

[0030] Due to the high chemical reactivity of isocyanates and their prepolymers, they can react with compounds containing active hydrogen (such as moisture in the air), leading to inconveniences in use and storage (mixed holographic materials cannot be stored for long periods). For example, the first-order reaction can typically be completed either by baking at high temperature (e.g., 70°C) for 12 hours or by slow curing at room temperature for more than three days. Therefore, it is best to prepare the holographic material immediately before coating or pouring, or premix it using AB glue. Both methods increase process costs and batch stability control issues. Furthermore, during mixing, the isocyanate-polyol reaction inevitably begins slowly, causing fluctuations and changes in fundamental physical parameters such as viscosity.

[0031] To address the aforementioned challenges, this application provides a holographic material and its preparation method, a holographic optical element, a holographic device, and a method for preparing a volume holographic grating. The holographic material comprises: a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives. The blocked polyisocyanate includes -NCO groups blocked by a blocking agent containing active hydrogen, and the blocked -NCO groups can be deblocked. The first compound can undergo a first polymerization reaction with the deblocked blocked polyisocyanate. The polymerizable monomer can undergo a second polymerization reaction under illumination and with a photoinitiator. Since the holographic material does not use highly chemically reactive isocyanates but rather blocked polyisocyanates, polymerization reactions between the blocked polyisocyanates and the first compound in the holographic material can be minimized. This allows for long-term storage of the holographic material, avoiding fluctuations and changes in its fundamental physical parameters. Furthermore, the holographic material does not require immediate preparation or pre-mixing with AB glue, thus reducing process costs and facilitating batch stability control. In summary, this approach facilitates the use and storage of holographic materials.

[0032] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0033] This application provides a holographic material comprising: a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives; the blocked polyisocyanate includes -NCO groups blocked by a blocking agent containing active hydrogen, and the blocked -NCO groups can be deblocked; the first compound can undergo a first polymerization reaction with the deblocked blocked polyisocyanate; the polymerizable monomer can undergo a second polymerization reaction in the presence of light and the photoinitiator.

[0034] Blocked polyisocyanates are compounds formed by blocking the -NCO group of polyisocyanates with blocking agents containing active hydrogen (such as phenol, ε-caprolactam, etc.). Blocked polyisocyanates are stable at room temperature.

[0035] Isocyanates are a class of organic compounds with active nucleophilic properties and reversible structures; polyisocyanates have multiple -NCO groups. A blocking reaction refers to the reaction of isocyanates with nucleophiles (blocking the -NCO groups) to form a blocked structure (e.g., urea structure, etc.), thus protecting the isocyanate. A deblocking reaction refers to the reversal of these blocked structures under specific conditions, reopening them and thus deprotecting the isocyanate, as shown in Figure 2.

[0036] The blocked -NCO groups in blocked polyisocyanates can be unblocked, that is, blocked polyisocyanates undergo unblocking reactions. The conditions for unblocking include, but are not limited to: (1) heating, raising the temperature to the unblocking temperature of the blocked polyisocyanate. Under high temperature conditions, the blocked structure can be reopened by heating reaction and restored to isocyanate; different blocking agents will result in different unblocking temperatures; (2) hydrogenation reaction, the blocked structure can undergo hydrogenation reaction in the presence of hydrogen gas and reopen to isocyanate; (3) the unblocking process also requires a certain amount of time to complete; (4) the unblocking conditions are also affected by factors such as solvent type and blocking agent type.

[0037] The first compound can undergo a first polymerization reaction with the unblocked blocked polyisocyanate. The first compound is a compound having multiple isocyanate reactive functional groups, which are usually hydroxyl groups. The first compound includes, but is not limited to: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, trimethylolpropane, trimethylolethane, glycerol, triethanolamine, pentaerythritol, dipentaerythritol, sorbitol, and at least one of polyester polyols, polycarbonate polyols, and polyether polyols with a molecular weight of 200 to 10,000.

[0038] Polymerizable monomers are typically high-refractive-index monomers, and may include, but are not limited to: alkenyl naphthalene monomers, alkenyl anthracene monomers, alkenyl benzene monomers, acrylic monomers, acrylate monomers, etc.

[0039] Photoinitiators are initiators that can be activated by light radiation and initiate polymerization reactions of corresponding polymerizable groups, including but not limited to: aromatic ketone compounds, benzoin and its derivatives, acylphosphine oxides, ammonium arylboronic acid, organometallic compounds, etc.

[0040] Other additives include, but are not limited to, at least one of the following: chain transfer agents, plasticizers, leveling agents, and defoamers.

[0041] Because the holographic material does not use highly reactive isocyanates, but rather blocked polyisocyanates, the polymerization reaction between the blocked polyisocyanates and the first compound in the holographic material can be minimized. This allows for long-term storage of the holographic material and avoids fluctuations and changes in its fundamental physical parameters. Furthermore, the holographic material does not require on-the-spot preparation or pre-mixing with AB glue, thus reducing processing costs and making batch stability easier to control. In short, it facilitates the use and storage of holographic materials.

[0042] In some embodiments, the holographic material may also include a photosensitizer.

[0043] In some embodiments, the content of the blocked polyisocyanate is 10%-65% by mass, for example: 10%, 30%, 50%, 65%, etc.; the content of the first compound is 10%-40%, for example: 10%, 20%, 30%, 40%, etc.; the content of the polymerizable monomer is 20%-75%, for example: 20%, 40%, 60%, 75%, etc.; the content of the photoinitiator is 0.1%-4%, for example: 0.1%, 1%, 2.5%, 4%, etc.; and the content of the other additives is 0.1%-3%, for example: 0.1%, 1%, 2%, 3%, etc.

[0044] In some embodiments, the blocking agent includes at least one of the following: alcohols (e.g., diethylene glycol monobutyl ether), phenols (e.g., 2,4,6-trichlorophenol), amines and amides (e.g., ε-caprolactam, cyclobutyrylimide), oximes (e.g., methyl ethyl ketone oxime, butanone oxime), heterocyclic or other nitrogen-containing compounds (e.g., imidazole, 2-methylimidazole, 4-nitroimidazole), and reactive methylene compounds (e.g., diethyl malonate). It may also be other blocking agents (e.g., cyclodiurea, methyl methacrylate, etc.).

[0045] In some embodiments, the first compound comprises a polyol. The polyol may be a low-refractive-index compound with two or more hydroxyl functional groups, such as tetraethylene glycol, trimethylolethane, glycerol, triethanolamine, polyester polyols with a molecular weight of 200-2000, polycarbonate polyols, polyether polyols, etc.

[0046] In some embodiments, the polymerizable monomer comprises an acrylate monomer. The polymerizable monomer may also be at least one of the following: alkenylnaphthalene compounds, alkenylanthracene compounds, alkenylbenzene compounds, acrylic compounds, methacrylic acid compounds, acrylate compounds, methacrylate compounds, N-vinylpyrrole, N-vinylcarbazole, N-vinylimidazolium, N-vinylindole, N-vinylpyrrolidone, and trans-N-3-yntynebutenylcarbazole.

[0047] In some embodiments, the other additives include at least one of chain transfer agents, plasticizers, leveling agents, and defoamers.

[0048] Chain transfer agents can be thiol compounds, including but not limited to one or more of the following: dodecyl mercaptan, mercaptoethanol, hexamethylene mercaptan, phenylethyl mercaptan, etc.

[0049] Plasticizers can be one or more of toluene, xylene, dimethylformamide, dimethylacetamide, glycerol, and phthalates.

[0050] The leveling agent can be a silicone surface additive, including but 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 mixture of these surface additives manufactured by BYK Corporation.

[0051] The defoamer can be an organosilicon defoamer, including but not limited to: BYK-011, BYK-012, BYK-023, and BYK-1610 produced by BYK Corporation, and DC65 and AFE-7820 produced by Dow Corning Corporation.

[0052] Referring to Figure 3, which is a flowchart of an embodiment of the preparation method of holographic materials of this application, the preparation method includes steps S101 and S102.

[0053] Step S101: Provide a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives.

[0054] Step S102: The blocked polyisocyanate, the first compound, the polymerizable monomer, the photoinitiator, and the other additives are mixed evenly under light-protected conditions to obtain the holographic material.

[0055] This holographic material can be stored for a long time under normal temperature and light-protected conditions. Because a blocked polyisocyanate is used instead of a chemically highly reactive isocyanate in its preparation, polymerization reactions between the blocked polyisocyanate and the first compound are minimized. This allows for long-term storage of the holographic material and avoids fluctuations and changes in its fundamental physical parameters. Furthermore, the holographic material does not require immediate preparation or pre-mixing with AB glue, thus reducing processing costs and facilitating batch stability control. In short, it facilitates the use and storage of holographic materials.

[0056] In some embodiments, step S101, which involves providing a blocked polyisocyanate, may include sub-steps S1011 and S1012, as shown in FIG4.

[0057] Sub-step S1011: Provide a polyisocyanate and a blocking agent containing active hydrogen.

[0058] Sub-step S1012: Block the polyisocyanate using the blocking agent to obtain the blocked polyisocyanate.

[0059] In some embodiments, the content of the blocked polyisocyanate is 10%-65% by mass, the content of the first compound is 10%-40%, the content of the polymerizable monomer is 20%-75%, the content of the photoinitiator is 0.1%-4%, and the content of the other additives is 0.1%-3%.

[0060] In some embodiments, the blocking agent includes at least one of alcohols, phenols, amines and amides, oximes, heterocyclic or other nitrogen-containing compounds, and active methylene compounds.

[0061] In some embodiments, the first compound comprises a polyol.

[0062] In some embodiments, the polymerizable monomer includes an acrylate monomer.

[0063] In some embodiments, the other additives include at least one of chain transfer agents, plasticizers, leveling agents, and defoamers.

[0064] This application also provides a holographic optical element, which is made of any of the holographic materials described above.

[0065] In some embodiments, the holographic optical element includes a volume holographic grating.

[0066] This application also provides a holographic device, which includes the holographic optical elements described above.

[0067] This application also provides a holographic storage optical disc, which is made of any of the holographic materials described above.

[0068] Referring to Figure 5, which is a flowchart of an embodiment of the fabrication method of the volume holographic grating of this application, the fabrication method includes steps S201 to S204.

[0069] Step S201: Provide holographic material, wherein the holographic material is any of the holographic materials described above.

[0070] Step S202: Distribute the holographic material evenly on the surface of the substrate.

[0071] The substrate can be a plate or film with a certain thickness. The holographic material can be distributed on the substrate surface by coating or encapsulation.

[0072] Step S203: Place the substrate with holographic material uniformly distributed on its surface under deblocking conditions, so that the blocked -NCO groups of the blocked polyisocyanate in the holographic material are deblocked into new -NCO groups, and the new -NCO groups react with the first compound to form a first-order cross-linked polymer network.

[0073] Step S204: Illuminate the substrate placed under the unsealed condition using a light beam, causing the polymerizable monomers in the bright area of ​​the holographic material to undergo a second polymerization reaction, and causing the polymerizable monomers in the dark area that were not illuminated to migrate to the bright area, thereby obtaining the volume holographic grating.

[0074] Because the holographic material uses a blocked polyisocyanate to chemically protect the -NCO groups, the polymerization reaction between the blocked polyisocyanate and the first compound in the prepared holographic material can be avoided as much as possible. This allows the holographic material to be stored for a long time without fluctuations or changes in its basic physical parameters. After being uniformly distributed on the substrate surface, the blocked -NCO groups are deblocked by placing the substrate under deblocking conditions, thereby controlling the initiation of the first-order reaction between the isocyanate and the first compound. This forms a first-order cross-linked polymer network that stabilizes the polymerizable monomers. Then, coherent light exposure is performed, and the polymerizable monomers undergo a second polymerization reaction, separating from the cross-linked polymer network to form a volume holographic grating.

[0075] In some embodiments, the deblocking conditions include raising the temperature to the deblocking temperature of the blocked isocyanate.

[0076] In some embodiments, the content of the blocked polyisocyanate is 10%-65% by mass, the content of the first compound is 10%-40%, the content of the polymerizable monomer is 20%-75%, the content of the photoinitiator is 0.1%-4%, and the content of the other additives is 0.1%-3%.

[0077] In some embodiments, the blocking agent includes at least one of alcohols, phenols, amines and amides, oximes, heterocyclic or other nitrogen-containing compounds, and active methylene compounds.

[0078] In some embodiments, the first compound comprises a polyol.

[0079] In some embodiments, the polymerizable monomer includes an acrylate monomer.

[0080] In some embodiments, the other additives include at least one of chain transfer agents, plasticizers, leveling agents, and defoamers.

[0081] Referring to Figure 6, on the left, a) malonic ester (i.e., the blocking agent) reacts with the -NCO groups of isocyanate to form a malonic ester blocking product (i.e., blocked isocyanate), which is inert and stable at room temperature; on the right, b) the malonic ester blocking product (i.e., blocked isocyanate) is deblocked under high temperature conditions and reacts with other hydroxyl-containing molecules (i.e., the first compound) (i.e., the deblocked blocked isocyanate undergoes a first polymerization reaction with the first compound). Therefore, the holographic material using the malonic ester blocking product exhibits inertness and non-reaction at room temperature in the dark. After thorough mixing, this holographic material can be stored for a long time. When preparing a volumetric holographic grating, after coating or instilling the substrate, it can undergo a first polymerization reaction with other hydroxyl-containing molecules (i.e., the first compound) after heating to form a first-order cross-linked polymer network.

[0082] In some embodiments, step S204, which involves illuminating the substrate after it has been placed under the unsealed condition with a light beam, may include: controlling the light beam to form interference fringes on the surface of the substrate without a grating structure.

[0083] In the fabrication of volume holographic gratings, one method requires a substrate with a grating structure. This necessitates meticulous pre-processing of the substrate to obtain the grating structure, increasing the fabrication steps and complexity. To simplify the fabrication process and reduce complexity, the substrate used in this embodiment does not have a grating structure. By controlling the light beam to form interference fringes on the surface of the substrate, the polymerizable monomers in the bright areas of the holographic material illuminated by the light undergo a second polymerization reaction, causing the polymerizable monomers in the unilluminated dark areas to migrate to the bright areas, thereby obtaining the volume holographic grating. This approach simplifies the fabrication process and reduces complexity.

[0084] The embodiments of this application are illustrated below with several specific examples.

[0085] Part 1: Storage Stability Experiment of Holographic Materials

[0086] Example A:

[0087] S1: Using 2-chloro-4-nitrophenol as a blocking agent, an equimolar isocyanate-terminated polyurethane prepolymer was chemically protected to obtain a 2-chloro-4-nitrophenol-blocked polyisocyanate.

[0088] S2: The 2-chloro-4-nitrophenol-blocked polyisocyanate obtained in step S1 is mixed with other components in the proportions shown in Table 1 under light-protected conditions. This mixture can be stored for a long time at room temperature under light-protected conditions as a holographic material mixture.

[0089] Table 1

[0090] Comparative Example A:

[0091] S1: Mix the unclosed isocyanate-terminated polyurethane prepolymer with other components according to the proportions in Table 2, mix them evenly under light-protected conditions, and store the mixture as a holographic material mixture at room temperature under light-protected conditions for a long period of time.

[0092] Table 2

[0093] The appearance and parameters of Example A and Comparative Example A were observed and tested according to the time intervals in Table 3.

[0094] Table 3

[0095] The holographic material mixed in Example A of Table 1, the holographic material stored for three months, the holographic material mixed in Comparative Example A, and the holographic material stored for one day were used to prepare a volume holographic grating. The relevant parameters of the volume holographic grating were detected to test the holographic material stored for three months.

[0096] Part Two: Fabrication of a bulk holographic grating using the holographic material of Example A and the material of Comparative Example A:

[0097] Example A1 (using the holographic material mixed from Example A)

[0098] S3: The holographic material mixture from Example A is coated onto a glass substrate to form a uniform film of 50 μm thickness. The temperature is then raised to the isocyanate deblocking temperature of 70°C to generate new -NCO groups that react with polyols to form a first-order cross-linked polymer network, thereby stabilizing the polymerizable monomers.

[0099] S4: Expose the film or sheet material obtained in step S3 to coherent light to induce the polymerization of polymerizable monomers with high refractive index, which then separate from the cross-linked polymer network that has been formed into a film, forming a volume holographic grating. Measure the diffraction efficiency, transmittance, and haze (according to ISO 17901-2: Methods for measurement of hologram recording characteristics).

[0100] Example A11 (Using holographic material stored for three months after Example A)

[0101] S3: The holographic material mixture stored for three months in Example A is coated to form a uniform film of 50 μm thickness on the surface of a glass substrate. The temperature is raised to the isocyanate deblocking temperature of 70°C to generate new -NCO groups that react with polyols to form a first-order cross-linked polymer network to stabilize the polymerizable monomers.

[0102] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce the polymerization of polymerizable monomers with high refractive index, which then separate from the cross-linked polymer network that has been formed into a film to form a volume holographic grating. Measure the diffraction effect, transmittance, and haze.

[0103] Comparative Example A1 (using the holographic material mixed from Comparative Example A)

[0104] S3: The holographic material mixture after mixing in Comparative Example A is coated onto the surface of a glass substrate to form a uniform film with a thickness of 50 μm. The temperature is then increased to 70 degrees Celsius to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network, thereby stabilizing the polymerizable monomers.

[0105] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce the polymerization of polymerizable monomers with high refractive index, which then separate from the cross-linked polymer network that has been formed into a film to form a volume holographic grating. Measure the diffraction efficiency, transmittance, and haze.

[0106] Comparative Example A11 (using holographic material stored for 1 day as described in Comparative Example A)

[0107] S3: The holographic material mixture of Comparative Example A, after being stored for 1 day, is coated onto the surface of a glass substrate to form a uniform film with a thickness of 50 μm. The temperature is then increased to 70 degrees Celsius to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network, thereby stabilizing the polymerizable monomers.

[0108] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce polymerization of polymerizable monomers with high refractive index, separate them from the cross-linked polymer network that has been formed into a film, form a volume holographic grating, and measure the diffraction efficiency, transmittance, and haze.

[0109] The specific test results are shown in Table 4:

[0110] Table 4

[0111] Part Three: Fabrication of Holographic Gratings Using Multiple Different Sets of Holographic Materials According to Embodiments of This Application:

[0112] Example 1:

[0113] S1: Using 2-methylimidazole as a blocking agent, an equimolar hexamethylene diisocyanate was chemically protected to obtain a 2-methylimidazole-blocked polyisocyanate.

[0114] S2: After mixing the 2-methylimidazolium-blocked hexamethylene diisocyanate obtained in step S1 with other components in the proportions shown in Table 5 under light-protected conditions, it can be used as a holographic material mixture and stored for a long time at room temperature under light-protected conditions.

[0115] Table 5

[0116] S3: After storing the mixed holographic material solution for one month, a 50µm thick uniform film is formed on the surface of a glass substrate by coating. The temperature is raised to 130 degrees to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network to stabilize polymerizable monomers.

[0117] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce polymerization of polymerizable monomers with high refractive index, separate them from the cross-linked polymer network that has been formed into a film, form a volume holographic grating, and measure the diffraction efficiency, transmittance, and haze.

[0118] Example 2:

[0119] S1: Using 2,4-dichlorophenol as a blocking agent, an equimolar amount of butane-1,4-diisocyanate was chemically protected to obtain 2,4-dichlorophenol-blocked polyisocyanate.

[0120] S2: After mixing the 2,4-dichlorophenol-blocked butane-1,4-diisocyanate obtained in step S1 with other components in the proportions shown in Table 6 under light-protected conditions, it can be used as a holographic material mixture and stored for a long time at room temperature under light-protected conditions.

[0121] Table 6

[0122] S3: After storing the mixed holographic material solution for one month, a 50µm thick uniform film is formed on the surface of a glass substrate by coating. The temperature is raised to 80 degrees to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network to stabilize polymerizable monomers.

[0123] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce the polymerization of polymerizable monomers with high refractive index, which then separate from the cross-linked polymer network that has been formed into a film to form a volume holographic grating. Measure the diffraction efficiency, transmittance, and haze.

[0124] Example 3:

[0125] S1: Methyl ethyl ketone oxime was used as a blocking agent to chemically protect an equimolar amount of trimethylhexamethylene diisocyanate to obtain methyl ethyl ketone oxime-blocked trimethylhexamethylene diisocyanate.

[0126] S2: After the methyl ethyl ketone oxime-blocked trimethyl hexamethylene diisocyanate obtained in step S1 is mixed with other components in the proportions shown in Table 7 under light-protected conditions, it can be used as a holographic material mixture and stored for a long time under normal temperature and light-protected conditions.

[0127] Table 7 Example 3 (Unsealing Temperature) 90℃

[0128] S3: After storing the mixed holographic material solution for 1 month, a 50µm thick uniform film is formed on the surface of a glass substrate by coating. The temperature is raised to 90 degrees to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network to stabilize polymerizable monomers.

[0129] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce the polymerization of polymerizable monomers with high refractive index, which then separate from the cross-linked polymer network that has been formed into a film to form a volume holographic grating. Measure the diffraction efficiency, transmittance, and haze.

[0130] Examples 4-6:

[0131] S1: Methyl 3-chloro-4-hydroxybenzoate was used as a blocking agent to chemically protect an equimolar molar isocyanate-terminated polyurethane prepolymer to obtain a methyl 3-chloro-4-hydroxybenzoate-blocked polyisocyanate.

[0132] S2: After the methyl 3-chloro-4-hydroxybenzoate blocked polyisocyanate obtained in step S1 is mixed with other components in the proportions shown in Table 8 under light-protected conditions, it can be used as a holographic material mixture for long-term storage at room temperature under light-protected conditions. The proportions of the blocked polyisocyanate compounds are 15%, 25%, and 40%, respectively.

[0133] Table 8

[0134] S3: After storing the mixed holographic material solution for one month, a 50µm thick uniform film is formed on the surface of a glass substrate by coating. The temperature is raised to 70 degrees to promote the reaction of -NCO groups with polyols to form a first-order cross-linked polymer network to stabilize polymerizable monomers.

[0135] S4: Expose the film or sheet material obtained in step S3 with coherent light to induce polymerization of polymerizable monomers with high refractive index, separate them from the cross-linked polymer network that has been formed into a film, form a volume holographic grating, and measure the diffraction efficiency and transmittance.

[0136] The specific test results are shown in Table 9:

[0137] Table 9

[0138] As can be seen from Examples 1 to 6 above, protecting the polyisocyanate compound with a sealing agent can significantly improve the storage time of the holographic photopolymer. After one month of storage, the optical performance of the prepared grating is comparable to that before storage. If the unsealing temperature of the sealed isocyanate is too high, as in Example 1, it will cause some high-refractive-index monomers to thermally polymerize during the unsealing process, resulting in a decrease in the performance of the grating prepared later.

[0139] It should be understood that the terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application.

[0140] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0141] The above description is merely a specific embodiment of this application, but the scope of protection of this application 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 this application, and such modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A holographic material, comprising: The invention comprises a blocked polyisocyanate, a first compound, a polymerizable monomer, a photoinitiator, and other additives; the blocked polyisocyanate includes -NCO groups blocked by a blocking agent containing active hydrogen, and the blocked -NCO groups can be deblocked; the first compound can undergo a first polymerization reaction with the deblocked blocked polyisocyanate; and the polymerizable monomer can undergo a second polymerization reaction in the presence of light and the photoinitiator.

2. The material of claim 1, wherein, The content of the blocked polyisocyanate is 10%-65% by mass percentage, the content of the first compound is 10%-40%, the content of the polymerizable monomer is 20%-75%, the content of the photoinitiator is 0.1%-4%, and the content of the other additives is 0.1%-3%.

3. The material of claim 1, wherein, The blocking agent includes at least one of alcohols, phenols, amines and amides, oximes, heterocyclic or other nitrogen-containing compounds, and active methylene compounds.

4. The material of claim 3, wherein, The alcohol compounds include diethylene glycol monobutyl ether; And / or, the phenolic compounds include 2,4,6-trichlorophenol; And / or, the amine and amide compounds include at least one of ε-caprolactam and cyclobutyrylimide; And / or, the oxime compounds include at least one of methyl ethyl ketone oxime and butanone oxime; And / or, the heterocyclic or other nitrogen-containing compound includes at least one of imidazole, 2-methylimidazolium, and 4-nitroimidazolium; And / or, the active methylene compound includes diethyl malonate.

5. The material of claim 1, wherein, The first compound includes polyols.

6. The material of claim 1, wherein, The polyols include at least one of tetraethylene glycol, trimethylolethane, glycerol, triethanolamine, polyester polyols with a molecular weight of 200-2000, polycarbonate polyols, and polyether polyols.

7. The material of claim 1, wherein, The polymerizable monomers include acrylate monomers.

8. The material of claim 1, wherein, The other additives include at least one of chain transfer agents, plasticizers, leveling agents, and defoamers.

9. The material of claim 8, wherein, The chain transfer agent includes thiols; And / or, the plasticizer comprises at least one of toluene, xylene, dimethylformamide, dimethylacetamide, glycerol, and phthalates; And / or, the leveling agent includes an organosilicon surface additive; And / or, the defoamer includes silicone defoamers.

10. A method for preparing a holographic material, the method comprising: Blocked polyisocyanates, first compounds, polymerizable monomers, photoinitiators, and other additives are available. The blocked polyisocyanate, the first compound, the polymerizable monomer, the photoinitiator, and the other additives are mixed evenly under light-protected conditions to obtain the holographic material.

11. The method of claim 10, wherein, The provision of the blocked polyisocyanate includes: Provides polyisocyanates and blocking agents containing active hydrogen; The polyisocyanate is blocked using the blocking agent to obtain the blocked polyisocyanate.

12. A volume holographic grating, wherein the volume holographic grating is made of the holographic material according to any one of claims 1-9.

13. A holographic device comprising the volume holographic grating of claim 12.

14. A method for fabricating a volume holographic grating, the method comprising: A holographic material is provided, the holographic material is described in any one of claims 1-9; The holographic material is uniformly distributed on the surface of the substrate; The substrate with the surface uniformly distributed with the holographic material is placed in a deblocking condition, so that the blocked -NCO groups of the blocked polyisocyanate in the holographic material are deblocked into new -NCO groups, and the new -NCO groups react with the first compound to form a first-order cross-linked polymer network; The substrate after being placed in the deblocking condition is irradiated by a light beam, so that the polymerizable monomers in the bright area of the holographic material irradiated by the light beam are subjected to a second polymerization reaction, and the polymerizable monomers in the dark area not irradiated are migrated to the bright area, and then the volume holographic grating is obtained.

15. The method of claim 14, wherein, The deblocking condition includes increasing the temperature to the deblocking temperature of the blocked isocyanate.

16. The method of claim 14, wherein, The irradiation of the substrate after being placed in the deblocking condition by the light beam comprises: Controlling the light beam to form interference fringes on the surface of the substrate without grating structure.

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