Holographic photopolymerizable material, holographic photosensitive film, holographic optical element, and display device

Abstract

Provided are a holographic photopolymerizable material, a holographic photosensitive film, a holographic optical element, and a display device, which relate to the field of polymer materials. The holographic photopolymerizable material comprises: a photosensitizer, a photopolymerizable monomer, and a polymer matrix. The photopolymerizable monomer and the photosensitizer are distributed in the polymer matrix, and the photopolymerizable monomer is polymerized under a first condition. The molecular structure of the polymer matrix comprises a linear structure, and a side chain of the polymer matrix comprises secondary reaction functional groups. The conversion rate of the secondary reaction functional groups under the first condition is less than or equal to 30%, so that it is guaranteed that under the first condition, the photopolymerizable monomer can migrate within the polymer matrix having the linear structure, thereby obtaining a holographic optical element having better optical performance. Furthermore, the holographic optical element can be arranged under a second condition to cause cross-linking of the secondary reaction functional groups, such that the thermodynamic performance of the holographic optical element is further improved, thereby enabling the holographic optical element to maintain better optical performance even in a high-temperature environment.

Description

Holographic photopolymer materials, holographic photosensitive films, holographic optical elements, display devices

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on July 31, 2023, with application number 202310953952.4 and application name “Holographic photopolymer materials, holographic photosensitive films, holographic optical elements, and display devices,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of polymer materials, and specifically to holographic photopolymer materials, holographic photosensitive films, holographic optical elements, and display devices. Background Art

[0003] Optical holography is based on the principles of optical interference and diffraction. By introducing a reference light wave and interfering with an object light wave, the amplitude and phase information of the object light wave is recorded as interference fringes on a holographic recording medium. The original object light wave is then reconstructed through diffraction, thereby recreating a three-dimensional image of the original object. Holographic technology can include the holographic recording process, which can be understood as using the principle of interference to record / store the optical information of an object. Holograms can include optical information such as the amplitude and phase of the light wave.

[0004] Holographic technology typically uses holographic photosensitive films to record / store optical information, such as the amplitude and phase of light waves. The material used in holographic photosensitive films can be called a holographic recording medium. Holographic photopolymers are a commonly used holographic recording medium. As a holographic polymer material, holographic photopolymers have attracted considerable attention due to their wide sensitivity range, ease of manufacture and transportation, and excellent long-term storage stability.

[0005] In recent years, with the expansion of the application fields of holographic technology, higher application temperatures have emerged in some fields, such as in-vehicle and airborne displays. Holographic photopolymer materials disclosed in related technologies are prone to random motion of polymer chains under high temperature conditions, resulting in a decrease in the optical performance of the holographic optical element / holographic photosensitive film formed by the holographic photopolymer material. The optical performance degradation can include: decreased diffraction efficiency, decreased transmittance, increased haze, and diffraction peak drift, which limits the application of holographic photopolymer materials in fields such as in-vehicle and airborne displays.

[0006] Summary of the Invention

[0007] This application discloses a holographic photopolymer material, a holographic photosensitive film, a holographic optical element, and a display device. The holographic photopolymer material comprises a photosensitizer, a photopolymerizable monomer, and a polymer matrix. The polymer matrix has a refractive index lower than that of the photopolymerizable monomer, and the side chains of the polymer matrix include secondary reactive functional groups. These secondary reactive functional groups can be cross-linked under a second condition, thereby yielding a holographic optical element with improved thermodynamic properties.

[0008] In a first aspect, the present application discloses a holographic photopolymerizable material comprising: a photosensitizer, a photopolymerizable monomer, and a polymer matrix. The photopolymerizable monomer is polymerized under a first condition; the molecular structure of the polymer matrix comprises a linear structure; and the side chains of the polymer matrix comprise secondary reactive functional groups. The secondary reactive functional groups are cross-linked under a second condition, and the conversion rate of the secondary reactive functional groups under the first condition is less than or equal to 30%.

[0009] In this implementation, the photosensitizer can absorb light waves and produce active intermediates that polymerize the photopolymerizable monomers. During holographic recording (the first condition), the holographic photopolymerizable material can be divided into a coherent bright area and a coherent dark area. The photosensitizer located in the coherent bright area can produce active intermediates that initiate the polymerization of the photopolymerizable monomers. The concentration difference of the photopolymerizable monomers thus produced causes the photopolymerizable monomers to diffuse toward the coherent bright area and polymerize. This ultimately results in monomer polymers having different concentrations in the coherent bright area and the coherent dark area. The refractive index of the photopolymerizable monomer is greater than that of the polymer matrix, and accordingly, the refractive index of the monomer polymer is greater than that of the polymer matrix. Therefore, the coherent bright area and the coherent dark area have different refractive indices, thereby achieving holographic recording / storage.

[0010] A photopolymerizable monomer and a photosensitizer are distributed within a polymer matrix, and the photopolymerizable monomer is polymerized under a first condition. The molecular structure of the polymer matrix comprises a linear structure, and the side chains of the polymer matrix comprise secondary reactive functional groups. The conversion rate of the secondary reactive functional groups is less than or equal to 30% under the first condition, thereby ensuring that the photopolymerizable monomer can migrate within the linear polymer matrix under the first condition, thereby obtaining a holographic optical element with excellent optical properties. Furthermore, the holographic optical element can be subjected to a second condition to crosslink the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element, allowing the holographic optical element to maintain excellent optical properties even in higher temperature environments.

[0011] In combination with an implementation of the first aspect, the first condition includes: irradiation of light waves with a wavelength of 400nm-800nm; the second condition includes: at least one of irradiation of light waves with a wavelength less than 400nm, catalysis, and high temperature.

[0012] In conjunction with an implementation of the first aspect, the side chains of the polymer matrix further include fluorine. In this implementation, the side chains of the polymer matrix include fluorine (F). The presence of F can reduce the refractive index of the polymer matrix, thereby enabling the holographic optical element obtained from the holographic photopolymer material to have better optical properties.

[0013] In combination with an implementation of the first aspect, the polymer matrix includes: at least one monomer.

[0014] In combination with an implementation of the first aspect, the at least one monomer includes: a first monomer; a side chain of the first monomer includes: a fluorine element and a secondary reaction functional group.

[0015] In this embodiment, the side chains of the polymer matrix include F. The presence of F can reduce the refractive index of the polymer matrix, resulting in a holographic optical element fabricated from the holographic photopolymer material having a high diffraction efficiency. The side chains of the polymer matrix also include secondary reactive functional groups. The conversion rate of the secondary reactive functional groups under the first condition is less than or equal to 30%, thereby ensuring that the photopolymerizable monomers can migrate within the linear structure of the polymer matrix under the first condition, resulting in a holographic optical element with excellent optical properties. Furthermore, the holographic optical element can be placed under a second condition to crosslink the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element, allowing the holographic optical element to maintain excellent optical properties even in high-temperature environments.

[0016] In combination with an implementation of the first aspect, the at least one monomer includes: a second monomer and a third monomer; the side chain of the second monomer includes: a fluorine element; and the side chain of the third monomer includes: a secondary reaction functional group.

[0017] In this implementation, the polymer matrix includes a second monomer and a third monomer. The side chain of the second monomer includes: F. The presence of F can reduce the refractive index of the polymer matrix so that the holographic optical element prepared from the holographic photopolymer material has a higher diffraction efficiency. The side chain of the third monomer includes: a secondary reaction functional group. The conversion rate of the secondary reaction functional group is less than or equal to 30% under the first condition, thereby ensuring that under the first condition, the photopolymerizable monomer can migrate within the linear structure of the polymer matrix to obtain a holographic optical element with better optical properties. Furthermore, the holographic optical element can be placed under the second condition to cross-link the secondary reaction functional groups, thereby improving the thermodynamic properties of the holographic optical element, so that the holographic optical element can still maintain better optical properties in a high temperature environment.

[0018] In combination with an implementation of the first aspect, the at least one monomer further includes: a fourth monomer; and a side chain of the fourth monomer includes: at least one of hydrogen and an alkyl substituent.

[0019] In this implementation, the polymer matrix may include: a side chain of a fourth monomer including at least one of hydrogen and an alkyl substituent. The introduction of the fourth monomer may serve to adjust the glass transition temperature of the holographic photopolymer material.

[0020] In combination with an implementation of the first aspect, the secondary reactive functional group includes at least one of vinyl ether, allyl group, epoxy group, carboxyl group, and mercapto group.

[0021] In this embodiment, the secondary reactive functional groups include at least one of vinyl ether, allyl, epoxy, carboxyl, and thiol. These secondary reactive functional groups have a conversion rate of less than or equal to 30% under the first condition and are cross-linkable under the second condition. This ensures that the photopolymerizable monomers can migrate within the linear polymer matrix under the first condition, resulting in a holographic optical element with superior optical properties. Furthermore, the holographic optical element can be subjected to the second condition to cross-link the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element.

[0022] In combination with an implementation of the first aspect, the secondary reaction functional group further includes: isocyanate and hydroxyl.

[0023] In this implementation, the secondary reactive functional groups include isocyanate and hydroxyl groups. Under the first condition, the conversion rate of the isocyanate and hydroxyl groups is less than or equal to 30%, thereby ensuring that the photopolymerizable monomers can migrate within the linear polymer matrix, resulting in a holographic optical element with excellent optical properties. Furthermore, the holographic optical element can be placed under the second condition to crosslink the isocyanate and hydroxyl groups, thereby improving the thermodynamic properties of the holographic optical element.

[0024] In combination with an implementation of the first aspect, the number average molecular weight of the polymer matrix is ​​20,000-300,000.

[0025] In this implementation, the number average molecular weight of the polymer matrix is ​​20,000-300,000. The polymer matrix has both good thermodynamic properties and good compatibility with other components.

[0026] In combination with an implementation of the first aspect, the glass transition temperature of the polymer matrix is: -20°C-120°C.

[0027] In combination with an implementation of the first aspect, the mass fraction of fluorine element in the polymer matrix is ​​5%-30%.

[0028] In this implementation, the mass fraction of fluorine in the polymer matrix is ​​5%-30%. The holographic photopolymer material containing the polymer matrix can have both good film-forming properties and good optical properties.

[0029] In combination with an implementation of the first aspect, the refractive index of the polymer matrix is ​​less than or equal to 1.48.

[0030] The refractive index of the polymer matrix disclosed in the present embodiment is less than or equal to 1.48. The polymer matrix has a relatively low refractive index. The holographic photopolymer material containing the polymer matrix can obtain a holographic optical element with relatively high diffraction efficiency.

[0031] In conjunction with an implementation of the first aspect, the molecular structure of the polymer matrix includes: Wherein R1 includes: hydrogen atom or methyl; R2 includes: hydrogen atom or methyl; R3 includes: hydrogen atom or methyl; R4 includes: -C n H 2n+1 One or more of; R5 includes: fluorine element; R6 includes: secondary reaction functional group; a includes: an integer of 0-500; b includes: an integer of 1-500; c includes: a hydrogen atom or a methyl group.

[0032] A second aspect of an embodiment of the present application discloses a holographic photosensitive film, comprising: a protective layer and a first film layer covering the protective layer, wherein the first film layer is made of the holographic photopolymer material disclosed in the first aspect.

[0033] Among them, the effects that can be achieved in the second aspect can refer to the effects that can be achieved by any implementation method of the first aspect, and will not be repeated here.

[0034] A third aspect of an embodiment of the present application discloses a holographic optical element, comprising: a protective layer and a second film layer covering the protective layer, wherein the materials used for the second film layer include: a polymer matrix and a monomer polymer, and the molecular structure of the polymer matrix includes: a cross-linked structure; the second film layer includes: a coherent bright area and a coherent dark area, wherein the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area, and the monomer polymer is obtained by polymerization of a photopolymerizable monomer.

[0035] The embodiment of the present application also discloses a holographic optical element, comprising: a protective layer and a second film layer covering the protective layer. The second film layer comprises: a polymer matrix and a monomer polymer, and the refractive index of the monomer polymer is greater than the refractive index of the polymer matrix. The molecular structure of the polymer matrix includes a cross-linked structure; the second film layer includes a coherent bright area and a coherent dark area, and the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area. The monomer polymer is used to form a refractive index distribution for recording holograms. The refractive index of the area where the monomer polymer is polymerized (coherent bright area) is relatively high, while the area without monomer polymer or the area with less monomer polymer polymerization (coherent dark area) can be understood as the background. The refractive index of the background is relatively low, and the monomer polymer can be used together with the background to fully record the hologram. The molecular structure of the polymer matrix in the second film layer is a cross-linked structure. Therefore, the holographic optical element has better heat resistance. The holographic optical element can still maintain good optical properties in a high temperature environment.

[0036] A fourth aspect of an embodiment of the present application discloses a method for preparing a holographic optical element, comprising: forming a first film layer on one side of a protective layer, the first film layer comprising: a photosensitizer, a photopolymerizable monomer, and a polymer matrix, the photopolymerizable monomer polymerizing under a first condition: the molecular structure of the polymer matrix comprising: a linear structure, and the side chains of the polymer matrix comprising: secondary reactive functional groups, the secondary reactive functional groups cross-linking under a second condition, and the conversion rate of the secondary reactive functional groups under the first condition being less than or equal to 30%; photopolymerizing the monomer under the first condition to form a monomer polymer to obtain a second film layer, the second film layer comprising: a coherent bright region and a coherent dark region, the density of the monomer polymer in the coherent bright region being greater than the density of the monomer polymer in the coherent dark region; and cross-linking the secondary reactive functional groups under the second condition to form a cross-linked structure to obtain the holographic optical element.

[0037] Among them, the effects that can be achieved in the fourth aspect can refer to the effects that can be achieved in the third aspect, and will not be repeated here.

[0038] The fifth aspect of the embodiments of the present application discloses a display device, comprising: a display screen and an optical element arranged on the display screen; the optical element comprises: the holographic photosensitive film disclosed in the second aspect or the holographic optical element disclosed in the third aspect.

[0039] Among them, the effects that can be achieved in the fifth aspect can refer to the effects that can be achieved in the first to fourth aspects, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a flow chart of a process for preparing a holographic optical element;

[0041] FIG2 is a flow chart of a method for preparing a holographic photosensitive film disclosed in a feasible implementation manner;

[0042] FIG3 is a flow chart of a method for preparing a holographic optical element disclosed in a feasible implementation manner;

[0043] FIG4 is a schematic diagram of a holographic recording system;

[0044] FIG5 is a flow chart of a method for preparing a holographic optical element disclosed in a feasible implementation manner. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0046] Hereinafter, the terms "first," "second," etc., are used solely for descriptive purposes to distinguish between identical or similar items with substantially the same function and effect, and are not to be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Therefore, a feature defined as "first," "second," etc., may explicitly or implicitly include one or more of such features.

[0047] Also, in the description of the present application, unless otherwise specified, “plurality” means two or more than two.

[0048] At the same time, in the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner to facilitate understanding.

[0049] First, the concepts involved in the embodiments of the present application are explained:

[0050] Interference is the phenomenon that when two or more waves meet in space, they superimpose or cancel each other out, forming a new waveform.

[0051] Amplitude: The maximum value a light wave can vibrate to.

[0052] Phase is the position of a light wave at a specific moment in its cycle.

[0053] A light beam is a form of light wave, specifically a beam of light waves.

[0054] Macromolecular compounds generally refer to compounds with a relative molecular mass of several thousand to several million and have excellent mechanical properties.

[0055] Linear structure is a type of structure of polymer compounds. The entire molecule of the linear structure is like a long chain.

[0056] Crosslinked structure, also known as network structure, is a three-dimensional network structure of polymer compounds.

[0057] Haze Haze refers to the percentage of transmitted light intensity that deviates from the incident light by more than 2.5° to the total transmitted light intensity. The greater the haze, the lower the gloss and transparency of the film.

[0058] Diffraction efficiency (DE) is an important parameter of holographic photopolymer materials, which refers to the ratio of the light intensity in a certain diffraction direction to the incident light intensity.

[0059] The refractive index modulation (index of refraction degree of modulation) is an important parameter of holographic photopolymer materials, which reflects the degree to which the holographic photopolymer materials are controlled by light wave signals.

[0060] Transmittance is an important parameter of holographic photopolymer materials and can be expressed as the ratio of the luminous flux passing through the holographic photopolymer material to its incident luminous flux.

[0061] Glass transition temperature (Tg) refers to the temperature corresponding to the transition from glassy state to highly elastic state. Tg is the lowest temperature at which molecular chain segments can move.

[0062] Holographic technology, also known as virtual imaging technology, uses the principles of interference and diffraction to record and reproduce the true three-dimensional image of an object. Holographic projection technology can include: the holographic recording process and the holographic reproduction process.

[0063] The holographic recording process can be understood as using the interference principle to record the optical information of an object. Specifically: a portion of the light wave is irradiated on the object to be photographed to form an object beam related to the object to be photographed; the other portion of the light beam is incident on the holographic film (the holographic film in the embodiment of the present application may also be referred to as a holographic photopolymer material) as a reference beam, and the reference beam can be superimposed on the object beam to produce interference. In the above manner, the phase and amplitude of each point on the object beam related to the object to be photographed are converted into spatially varying intensities, thereby using the contrast and spacing between the interference fringes to record all the optical information of the object beam (referred to as hologram in the embodiment of the present application). The optical information may include: phase and amplitude. In the embodiment of the present application, the holographic film used to record the interference fringes may be referred to as a holographic photosensitive film, or a holographic film.

[0064] The holographic reconstruction process can be understood as an imaging process. After the holographic film recording the interference fringes undergoes processing procedures such as development and fixing, a hologram, or holographic photograph, is obtained. Specifically, a hologram can be understood as a holographic optical element (HOE). Under the irradiation of a coherent light beam, the diffracted light waves of the holographic optical element generally produce two images: the original image (also called the initial image) and the conjugate image. These two images can provide users with a strong sense of three-dimensionality and a realistic visual effect. Each part of the hologram records the optical information of each point on the photographed object. Therefore, in principle, each part can reproduce the entire image of the photographed object. Through multiple exposures, multiple different images can be recorded on the same film, and they can be displayed separately without interfering with each other.

[0065] Visible holography uses holographic optical elements to store optical information, such as the amplitude and phase of light waves. Holographic optical elements can replace lenses, gratings, mirrors, or more complex optical components in optical systems. They are used in high-tech fields such as in-vehicle head-up displays (HUDs), augmented reality (AR) glasses, holographic 3D projection, high-end anti-counterfeiting, and high-density data storage.

[0066] For example, in vehicle-mounted head-up display devices, holographic optical elements are used to create holographic windshields. Leveraging the high diffraction efficiency of holographic optical elements, relevant driving information can be projected onto the vehicle's windshield, effectively enhancing the driving experience and safety. At the same time, their excellent heat resistance can meet the harsh operating environments of vehicles. In AR glasses, optical waveguide technology is used to guide the image light source diffracted by the holographic optical element into glass or resin for total reflection, and finally diffracted by the holographic optical element into the human eye to form an image.

[0067] As a holographic polymer material, holographic photopolymer is often used as the material of holographic optical elements due to its advantages such as wide photosensitivity range, easy manufacturing and transportation, and good long-term storage stability.

[0068] Holographic photopolymers can be prepared using coherent laser technology. They are structurally ordered polymers that can simultaneously store all information, including the amplitude and phase of light waves. Holographic photopolymers can include a photosensitizer, a polymer matrix, and photopolymerizable monomers.

[0069] The polymer matrix can provide mechanical support for the holographic photopolymer material, bond the photopolymerizable monomers, and introduce photosensitizers. The refractive index (index of refraction) of the polymer matrix is ​​usually low (refractive index <1.5). In some application scenarios, the polymer matrix can also be called a resin, a film-forming resin. The photosensitizer can absorb the radiation energy of light waves and produce active intermediates that promote the polymerization of photopolymerizable monomers through chemical changes. Photopolymerizable monomers are monomers that can undergo photopolymerization, and usually photopolymerizable monomers have a high refractive index (refractive index>1.5). During holographic recording, the photopolymerizable monomers can be polymerized into photopolymers (also referred to as monomer polymers in the embodiments of the present application) under the action of the active intermediates generated by the photosensitizer. The refractive index of the photopolymer is greater than the refractive index of the polymer matrix. There is a refractive index difference between the photopolymer and the polymer matrix, forming a holographic optical element with periodic phase separation.

[0070] The following is a further description of the preparation process of the holographic optical element with reference to the accompanying drawings:

[0071] Please refer to (I) in FIG1 . The holographic photopolymer material includes: a photosensitizer (not shown in the figure), a photopolymerizable monomer 100 , and a polymer matrix 200 . The photosensitizer and the photopolymerizable monomer 100 are distributed in the polymer matrix 200 .

[0072] Refer to (2) in FIG1 . A holographic photopolymer material can be irradiated with light wave A, so that some areas of the holographic photopolymer material are exposed and some areas of the holographic photopolymer material are not exposed. The exposed areas can be referred to as coherent bright areas 11, and the unexposed areas can be referred to as coherent dark areas 12.

[0073] Typically, the coherent bright regions 11 and the coherent dark regions 12 are spaced apart. Therefore, in some application scenarios, the coherent bright regions 11 may also be referred to as bright stripe regions, and the coherent dark regions 12 may also be referred to as dark stripe regions.

[0074] Under the action of light wave A, the holographic photopolymer material is divided into interference fringes alternating between coherent bright areas 11 and coherent dark areas 12 .

[0075] Please continue to refer to (2) in Figure 1 . In the coherent dark region 12, the photopolymerizable monomer 100 hardly polymerizes. In the coherent bright region 11, the radiation energy of light wave A prompts the photosensitizer to generate reactive intermediates, i.e., the reactive intermediates are present in the coherent bright region 11. The reactive intermediates cause the photopolymerizable monomer 100 in the coherent bright region 11 to polymerize to form a photopolymer, causing the concentration of the photopolymerizable monomer 100 in the coherent bright region 11 to decrease.

[0076] At this time, there is a concentration difference between the photopolymerizable monomer 100 in the coherent bright area 11 and the photopolymerizable monomer 100 in the coherent dark area 12 .

[0077] Please refer to (3) in FIG. 1 . The concentration difference of the photopolymerizable monomer 100 causes the photopolymerizable monomer 100 in the dark area 12 to migrate toward the bright area 11 .

[0078] The polymer matrix 200 solidifies into a film, halting the migration of the photopolymerizable monomers 100. This results in the holographic optical element shown in (4) of Figure 1 . In the holographic optical element, the refractive index of the coherent bright regions 11 is close to that of the photopolymer, while the refractive index of the coherent dark regions 12 is close to that of the polymer matrix 200. The refractive index of the photopolymer is greater than that of the polymer matrix 200. Consequently, the holographic optical element exhibits a grating structure with periodic refractive index variations.

[0079] Based on the above description, it can be seen that the polymer matrix 200 in the holographic optical element plays the role of providing a baseline refractive index for the holographic optical element. The greater the difference in refractive index between the polymer matrix 200 and the photopolymer in the holographic optical element, the higher the diffraction efficiency of the holographic optical element, that is, the better the optical performance of the holographic optical element.

[0080] One feasible way to improve the optical performance of the holographic optical element is to increase the difference in refractive index between the polymer matrix 200 and the photopolymer.

[0081] One way to increase the refractive index difference between the polymer matrix 200 and the photopolymer may be:

[0082] Large conjugated structures such as sulfur (S), selenium (Se), benzene rings, and naphthalene rings are introduced into the photopolymerizable monomer 100 to increase the refractive index of the photopolymerizable monomer 100, so that the photopolymer obtained by polymerizing the photopolymerizable monomer 100 has a higher refractive index, thereby increasing the refractive index difference between the polymer matrix 200 and the photopolymer.

[0083] Another way to increase the refractive index difference between the polymer matrix 200 and the photopolymer may be:

[0084] Elements such as fluorine (F) and silicon (Si) may be introduced into the polymer matrix 200 to reduce the refractive index of the polymer matrix 200 , thereby increasing the refractive index difference between the polymer matrix 200 and the photopolymer.

[0085] Specifically, the related art discloses a holographic photopolymer material, which may include a film-forming resin (referred to as polymer matrix 200 in the embodiments of this application). The film-forming resin is obtained by polymerizing a fluorinated monomer and a vinyl monomer. The vinyl monomer is selected from vinyl esters, vinyl alcohol, vinyl ether, and vinyl acetal, and the fluorinated monomer is selected from perfluorinated monomers, vinyl fluoride, vinylidene fluoride, fluoroolefins, and fluoroalkyl esters of acrylic acid or methacrylic acid. The mass fraction of fluorine in the film-forming resin is approximately 3% to 25%.

[0086] Due to the presence of fluorine, the film-forming resin has a lower refractive index, which in turn makes the holographic optical element formed by the holographic photopolymer material have a higher refractive index modulation, and thus makes the holographic optical element have a higher diffraction efficiency.

[0087] For example, the film-forming resin in the holographic optical element I is obtained by polymerizing vinyl acetate and a perfluorinated monomer. The refractive index modulation degree of the holographic optical element I can reach more than 0.040-0.076.

[0088] For another example, the film-forming resin in the holographic optical element II is obtained by polymerization of polyvinyl acetate, that is, the film-forming resin does not introduce fluorine element, and the refractive index modulation degree of the holographic optical element II can reach 0.025-0.031.

[0089] It can be seen that the introduction of fluorine element into the film-forming resin of the holographic optical element can improve the refractive index modulation of the holographic optical element, so that the holographic optical element has a higher diffraction efficiency.

[0090] In a solution disclosed in a related art, the film-forming resin contained in the holographic photopolymer material has a linear molecular structure. The holographic photopolymer material has poor thermodynamic properties, resulting in poor stability of the grating structure of the holographic optical element, which affects the optical performance of the holographic optical element.

[0091] Specifically, under high temperature conditions, the film-forming resin is prone to polymer chain movement, causing deformation of the grating structure of the holographic optical element. This deformation can lead to a comprehensive decline in the optical properties of the holographic optical element, including refractive index modulation, transmittance, and haze.

[0092] In order to further improve the optical performance of the holographic optical element, the holographic photopolymer material can adopt a film-forming resin with a cross-linked structure, or the holographic photopolymer material can adopt a film-forming resin that can construct a cross-linked structure, so that the holographic photopolymer material has better thermodynamic properties, thereby ensuring that the holographic optical element has better optical properties.

[0093] For example, Related Art 2 discloses a holographic photopolymerizable material. The film-forming resin employed in this holographic photopolymerizable material is obtained by reacting a polyisocyanate component with an isocyanate-reactive component, such as a polyol. The film-forming resin has a three-dimensional cross-linked structure. The photopolymerizable monomer 100 employed in this holographic photopolymerizable material includes an acrylate compound. The three-dimensional cross-linked structure of the film-forming resin in this holographic photopolymerizable material provides the material with superior thermodynamic properties, and the holographic optical element derived from this holographic photopolymerizable material exhibits excellent optical properties.

[0094] For example, Related Art 3 discloses a photopolymer composition (holographic photopolymer material) for forming a holographic recording medium. The film-forming resin in the photopolymer composition is a polymer formed by crosslinking a siloxane polymer containing at least one silane functional group with an acrylic polyol. The film-forming resin has a crosslinked structure. Related Art 3 further discloses that the temperature and humidity durability of the holographic photopolymer material can be further improved by optimizing the crosslinking density of the film-forming resin.

[0095] The cross-linking density of the cross-linked film-forming resin is high, which inhibits the migration of the photopolymerizable monomer 100 during holographic recording, resulting in a smaller difference in refractive index between the coherent bright area and the coherent dark area of ​​the final holographic optical element, and a lower diffraction efficiency of the holographic optical element.

[0096] In order to solve the technical problems existing in the related art, the embodiment of the present application discloses a holographic photopolymer material. The holographic photopolymer material may include: a polymer matrix, a photopolymerizable monomer and a photosensitizer.

[0097] The polymer matrix can provide mechanical support for the holographic photopolymer material. Photopolymerizable monomers and photosensitizers are dispersed in the polymer matrix. The photosensitizer can absorb light waves and produce active intermediates that polymerize the photopolymerizable monomers. During holographic recording (the first condition), the holographic photopolymerizable material can be divided into coherent bright areas and coherent dark areas. The photosensitizer located in the coherent bright areas can produce active intermediates. The polymerization of the photopolymerizable monomers is initiated, and the concentration difference of the photopolymerizable monomers generated thereby prompts the photopolymerizable monomers to diffuse into the coherent bright areas and polymerize. This ultimately results in monomer polymers with different concentrations in the coherent bright areas and the coherent dark areas. The refractive index of the photopolymerizable monomer is greater than that of the polymer matrix, and accordingly, the refractive index of the monomer polymer is greater than that of the polymer matrix. Therefore, the coherent bright areas and the coherent dark areas have different refractive indices, thereby achieving holographic recording / storage.

[0098] The molecular structure of the polymer matrix includes a linear structure, and the side chains of the polymer matrix include secondary reactive functional groups. The conversion rate of the secondary reactive functional groups is less than or equal to 30% under the first condition, thereby ensuring that the photopolymerizable monomers can migrate within the linear polymer matrix under the first condition, resulting in a holographic optical element with high diffraction efficiency, that is, a holographic optical element with excellent optical performance. Furthermore, the holographic optical element can be subjected to a second condition to crosslink the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element. This allows the holographic optical element obtained from the holographic photopolymer material to exhibit excellent optical performance at higher temperatures, making the holographic optical element suitable for a wide range of applications.

[0099] Optionally, the conversion rate of the secondary reactive functional group under the first condition is less than or equal to 10%.

[0100] The following is a further description of the components of the holographic photopolymer material:

[0101] In the embodiment of the present application, the holographic photopolymer material may include: a polymer matrix.

[0102] In the embodiment of the present application, the polymer matrix includes: a high molecular compound formed by connecting at least one monomer. The polymer matrix can provide mechanical support for the holographic photopolymer material.

[0103] In the embodiments of the present application, the molecular structure of the polymer matrix includes a linear structure, and the side chains of the polymer matrix may include secondary reactive groups. These secondary reactive groups will be further described in subsequent embodiments. Generally, the lower the refractive index of the polymer matrix, the higher the diffraction efficiency of the resulting holographic optical element.

[0104] To further improve the diffraction efficiency of holographic optical elements fabricated from holographic photopolymer materials, as a feasible approach, the side chains of the polymer matrix can include fluorine (F). The presence of F can lower the refractive index of the polymer matrix, resulting in a holographic optical element fabricated from the holographic photopolymer material having a higher diffraction efficiency.

[0105] In some feasible implementations, the polymer matrix may include a homopolymer. A homopolymer can be understood as a high molecular weight compound formed by polymerizing a single monomer (a first monomer). The monomer may include at least one of methyl methacrylate (MMA), butyl acrylate (BA), glycidyl methacrylate (GMA), and dodeca fluoroheptyl methacrylate (DFMA).

[0106] As a possible implementation, the molecular structure of the polymer matrix may include:

[0107] Structural formula 1: Structural formula 2: wait.

[0108] R in Structural Formula 1 and Structural Formula 2 1-1 is a secondary reactive functional group. 1-2 Including: hydrogen atom (H), methyl (-CH3), etc.

[0109] It is worth noting that the examples of this application are merely exemplary introductions of several homopolymers that the polymer matrix may contain, and the types of the aforementioned homopolymers do not constitute a specific limitation.

[0110] In some feasible implementations, the polymer matrix may include a copolymer, wherein a copolymer may be understood as a high molecular compound formed by polymerization of at least two monomers.

[0111] As a feasible implementation, the at least one monomer may include a second monomer and a third monomer. In the embodiment of the present application, the side chain of the second monomer includes fluorine. The side chain of the third monomer includes a secondary reactive functional group.

[0112] As a possible implementation, the molecular structure of the polymer matrix may include:

[0113] Structural formula 3:

[0114] The second monomer is described below:

[0115] In structural formula three, It can be understood as the second monomer. Wherein, R5 includes: a functional group containing F. The functional group containing F can include: a fluoroalkyl group or a fluoroaryl group. Exemplarily, the fluoroalkyl group can include: -CH2F, -CH2CH2F, etc. Exemplarily, the fluoroaryl group can include: wait.

[0116] In the structural formula 3, b can be understood as the degree of polymerization of the second monomer. The present embodiment does not impose a specific limitation on b, and the value of b can be set according to needs.

[0117] Considering that the thermodynamic properties of the polymer matrix are related to b, specifically, the larger b is, the greater the molecular weight of the polymer matrix is, and the better the thermodynamic properties of the polymer matrix are. As a feasible implementation, b can be greater than or equal to 1 to ensure that the polymer matrix has better thermodynamic properties.

[0118] Considering that the migration resistance of the photopolymerizable monomer is related to b, specifically, the larger b is, the greater the migration resistance of the photopolymerizable monomer in the polymer matrix is, and the greater the migration resistance of the photopolymerizable monomer is, the lower the diffraction efficiency of the holographic optical element formed by the holographic photopolymerizable material is.

[0119] In order to make the holographic photopolymer material form a holographic optical element with greater diffraction efficiency, as a feasible implementation, b is less than or equal to 500 so that the holographic photopolymer material disclosed in this implementation can form a holographic optical element with greater diffraction efficiency.

[0120] As a feasible implementation method, b can be in the range of 1-500, so that the holographic photopolymer material can have better thermodynamic properties and the holographic photopolymer material can form a holographic optical element with greater diffraction efficiency.

[0121] Considering that the refractive index of the polymer matrix is ​​related to the mass fraction of the fluorine element in the polymer matrix, specifically, the higher the mass fraction of the fluorine element in the polymer matrix, the lower the refractive index of the polymer matrix, and the higher the diffraction efficiency of the resulting holographic optical element.

[0122] In order to obtain a polymer matrix with a lower refractive index, as a feasible implementation method, the mass fraction of fluorine element in the polymer matrix can be greater than or equal to 5%.

[0123] Considering that the film-forming properties of holographic photopolymer materials are related to the mass fraction of fluorine in the polymer matrix, specifically, the lower the mass fraction of fluorine in the polymer matrix, the better the film-forming properties of the holographic photopolymer material. To obtain a holographic photopolymer material with excellent film-forming properties, as a feasible implementation, the mass fraction of fluorine in the polymer matrix can be less than or equal to 30%.

[0124] In order to take into account both the film-forming properties of the holographic photopolymer material and the refractive index of the polymer matrix, as a feasible implementation method, the mass fraction of the fluorine element in the polymer matrix can be 5%-30%. Alternatively, the mass fraction of the fluorine element in the polymer matrix can be 10%-20%.

[0125] In this implementation, R5 includes F, and the introduction of F can reduce the refractive index of the polymer matrix. In some feasible implementations, the refractive index of the polymer matrix is ​​less than or equal to 1.48.

[0126] The polymer matrix provided by the present embodiment has a relatively low refractive index. The holographic optical element formed by using the polymer matrix has a relatively high diffraction efficiency. The polymer matrix can be used to obtain a holographic optical element with relatively good optical performance.

[0127] The third monomer is described below:

[0128] In structural formula three, It can be understood as the third monomer. Wherein, R6 is a secondary reactive functional group. c can be understood as the degree of polymerization of the third monomer. The present application embodiment does not specifically limit c, and the value of c can be set according to needs.

[0129] Considering that the thermodynamic properties of the polymer matrix are related to c, specifically, the larger c is, the larger the molecular weight of the polymer matrix is, and the better the thermodynamic properties of the polymer matrix are. As a feasible implementation, c is greater than or equal to 1 so that the polymer matrix has better thermodynamic properties.

[0130] Considering that the migration resistance of the photopolymerizable monomer is related to c, specifically, the larger c is, the greater the migration resistance of the photopolymerizable monomer is, and the greater the migration resistance of the photopolymerizable monomer is, the lower the diffraction efficiency of the ultimately formed holographic optical element is.

[0131] In order to enable the holographic photopolymer material to form a holographic optical element with a relatively high diffraction efficiency, as a feasible implementation, c may be less than or equal to 500, so that the holographic photopolymer material disclosed in this implementation can form a holographic optical element with a relatively high diffraction efficiency.

[0132] As a feasible implementation, c can be in the range of 1-500, so that the holographic photopolymer material obtained by this implementation can have better thermodynamic properties, and the holographic photopolymer material can form a holographic optical element with greater diffraction efficiency.

[0133] In order to adjust the glass transition temperature of the holographic photopolymer material, in some feasible implementations, the at least one monomer may include a fourth monomer, and a side chain of the fourth monomer includes at least one of hydrogen and an alkyl substituent.

[0134] For example, as a possible implementation, the molecular structure of the polymer matrix may include:

[0135] Structural formula 4: In structural formula 4, R1, R2, and R3 include hydrogen atoms or methyl groups.

[0136] The second monomer and the third monomer can be found in the above embodiments and will not be described in detail here.

[0137] The fourth monomer is described below:

[0138] Structural formula four, It can be understood as the fourth monomer. a can be understood as the polymer of the fourth monomer. R1 includes: H or -CH3. R4 includes: alkyl substituent (-C n H 2n+1 ) one or more of the following.

[0139] Considering that the glass transition temperature of the holographic photopolymer material is related to the type and content of the fourth monomer (which can be represented by a in Structural Formula 4), in some feasible implementations, R1 and a in Structural Formula 4 can be adjusted to adjust the glass transition temperature of the holographic photopolymer material to between -20°C and 120°C, so that the holographic photopolymer material can meet the needs of different application scenarios. Optionally, the glass transition temperature of the holographic photopolymer material is between 0°C and 80°C.

[0140] The polymer matrix is ​​further described below in conjunction with the number average molecular weight:

[0141] The examples of this application do not impose any specific limitation on the number average molecular weight of the polymer matrix.

[0142] Considering that the thermodynamic properties and film-forming properties of a polymer matrix are related to its number-average molecular weight, a larger number-average molecular weight indicates better thermodynamic properties. As a feasible implementation, the number-average molecular weight of the polymer matrix can be greater than or equal to 20,000 to achieve better thermodynamic properties.

[0143] As a feasible implementation method, the number average molecular weight of the polymer matrix can be less than or equal to 300,000, so that the polymer matrix and other components have good film-forming properties.

[0144] As a feasible implementation method, the number average molecular weight of the polymer matrix can be between 20,000 and 300,000, so that the polymer matrix has both better thermodynamic properties and compatibility with other components.

[0145] The molecular structure of the polymer matrix is ​​further explained below:

[0146] The polymer matrix disclosed in the examples of this application has a linear molecular structure. The polymer matrix has side chains, and the side chains of the polymer matrix include secondary reactive functional groups. In the examples of this application, the secondary reactive functional groups have a conversion rate of less than or equal to 30% under the first condition and can undergo a cross-linking reaction under the second condition.

[0147] In the holographic photopolymer material disclosed in this embodiment, the conversion rate of the secondary reaction functional groups of the polymer matrix under the first condition is less than or equal to 30%, and the polymer matrix exists in the form of a linear structure. The linear structure of the polymer matrix provides less resistance to the migration of photopolymerizable monomers. The photopolymerizable monomers can migrate quickly to the coherent bright region and polymerize there to form a monomer aggregate. Therefore, a holographic optical element formed using the holographic photopolymer material disclosed in this embodiment has a large refractive index difference between the coherent bright region and the coherent dark region, resulting in a high diffraction efficiency.

[0148] After the holographic recording is completed, the holographic optical element can be placed under a second condition to crosslink the secondary reaction functional groups, thereby improving the thermodynamic properties of the holographic optical element.

[0149] The secondary reactive functional groups are further defined below.

[0150] Before introducing the secondary reactive functional group, the first condition and the second condition involved in the embodiments of the present application are first introduced.

[0151] In the embodiment of the present application, the first condition can be understood as a condition that enables polymerization of the photopolymerizable monomer. The first condition can include: visible light. The wavelength of the visible light is in the range of 400nm-800nm.

[0152] The polymerization process of photopolymerizable monomers is generally as follows: upon exposure to visible light, the holographic photopolymerizable material is divided into coherent bright regions and coherent dark regions. Photosensitizers located in the coherent bright regions produce reactive intermediates, which initiate polymerization of the photopolymerizable monomers. This creates a concentration difference between the coherent bright and dark regions, prompting the photopolymerizable monomers to converge and diffuse toward the coherent bright region. Ultimately, the coherent bright region is dominated by the high-refractive-index photopolymer, while the coherent dark region is dominated by the low-refractive-index polymer matrix.

[0153] The second condition is not specifically limited in the present embodiment. For example, the second condition may include: an irradiation condition. However, it is necessary to ensure that the wavelength range of the second condition does not overlap with the wavelength range of the first condition.

[0154] As a feasible implementation, the second condition may include: ultraviolet radiation, wherein the wavelength of the ultraviolet radiation is less than or equal to 400 nm.

[0155] As a feasible implementation, the second condition may include: non-irradiation condition. Exemplarily, the non-irradiation condition may include but is not limited to: high temperature, catalysis, etc.

[0156] This completes the description of the first condition and the second condition.

[0157] The secondary reaction functional groups involved in the examples of this application are introduced below.

[0158] The embodiments of the present application do not specifically limit the types of secondary reactive functional groups. Any functional group that has a conversion rate of less than or equal to 30% under the first condition and undergoes cross-linking under the second condition can be used as a secondary reactive functional group in the embodiments of the present application.

[0159] As a feasible implementation method, the secondary reaction functional groups may include: vinyl ether (the structural formula can be found in Structural Formula 5), ​​N-vinyl (the structural formula can be found in Structural Formula 6), allyl (the structural formula can be found in Structural Formula 7), etc.

[0160] Structural formula 5: Structural formula 6: Structural Formula VII Here, * indicates a bonding site.

[0161] The secondary reactive functional groups can cross-link with each other to generate cationic polymerization under the irradiation of ultraviolet light, so that the polymer matrix is ​​transformed from a linear structure to a cross-linked structure.

[0162] As a feasible implementation method, the secondary reactive functional group may include: epoxy group.

[0163] The present embodiments do not specifically limit the number of ring atoms in the epoxy group. For example, the secondary reactive functional group may include: a three-membered epoxy group (the structural formula of which can be found in Structural Formula 8), a four-membered epoxy group (the structural formula of which can be found in Structural Formula 9), and a five-membered epoxy group (the structural formula of which can be found in Structural Formula 10). In the present embodiments, the secondary reactive functional group containing an epoxy group may be referred to as an epoxy secondary reactive functional group.

[0164] Structural formula eight: Structural formula 9: Structural formula 10:

[0165] As a feasible implementation, the secondary reactive functional groups may include carboxyl groups (-COOH). The conversion rate of the carboxyl groups under irradiation with a wavelength of 400 nm to 800 nm is less than or equal to 30%. The carboxyl groups can undergo an acid condensation reaction under the action of a catalyst, converting the polymer matrix from a linear structure to a cross-linked structure.

[0166] As a feasible implementation, the secondary reactive functional groups may include: thiol (-SH) and double bond (-C=C-). The conversion rate of -SH and -C=C- under irradiation wavelength of 400nm-800nm ​​is less than or equal to 30%. -SH and -C=C- can undergo an addition reaction of thiol (reactive functional group is -SH) and olefin (reactive functional group is -C=C-) under the action of a catalyst, transforming the polymer matrix from a linear structure to a cross-linked structure.

[0167] As a feasible implementation, the secondary reactive functional groups may include isocyanate (-N=C=O) and hydroxyl (-OH). The conversion rate of -N=C=O and -OH under irradiation with a wavelength of 400nm-800nm ​​is less than or equal to 30%. After exposure, -N=C=O and -OH can undergo a condensation reaction with an isocyanate (with the reactive functional group -N=C=O) and an alcohol (with the reactive functional group -OH) under the action of a catalyst, transforming the polymer matrix from a linear structure to a cross-linked structure.

[0168] This completes the description of the secondary reactive functional groups.

[0169] In practical applications, holographic photopolymer materials can be analyzed using material characterization equipment such as gel permeation chromatography, differential scanning calorimetry, nuclear magnetic resonance spectrometer, high performance liquid chromatography-mass spectrometer, Abbe refractometer and elemental analyzer. Specifically:

[0170] Gel permeation chromatography can obtain information on the molecular weight and molecular weight distribution of polymers isolated from holographic photopolymerizable materials.

[0171] Differential scanning calorimetry can be used to obtain the glass transition temperature of polymers.

[0172] The nuclear magnetic resonance spectrometer can obtain the nuclear magnetic resonance spectrum information of each component substance separated from the holographic photopolymer material to analyze the structure of the polymer matrix.

[0173] High performance liquid chromatography-mass spectrometry can obtain the molecular weight of each component substance separated from the holographic photopolymer material.

[0174] The refractive index of polymers can be obtained using an Abbe refractometer.

[0175] Elemental analyzers can obtain information on the ratio of each element in polymers.

[0176] In the embodiment of the present application, the holographic photopolymer material may include: a photosensitizer.

[0177] A photosensitizer can be understood as a substance that can undergo photochemical changes and produce active intermediates when stimulated by light waves.

[0178] The embodiments of the present application do not specifically limit the type of photosensitizer. Any substance that can produce an active intermediate capable of initiating polymerization of photopolymerizable monomers after being excited by light waves can be used as a photosensitizer in the embodiments of the present application.

[0179] As a feasible implementation, the photosensitizer may include at least one of acridine orange, eosin B, erythrosine B, rose bengal, safranin, rhodamine B, methyl blue, methylene blue, 3,3′-carbonylbis(7-diethylaminocoumarin), and 2,5-bis(4-diethylaminobenzylidene)cyclopentanone. These photosensitizers have stable structures, are not prone to yellowing, and are easily bleached, thereby ensuring that the holographic photosensitive film / holographic optical element prepared from the holographic photopolymer material disclosed in this implementation has a high transmittance.

[0180] The aforementioned photosensitizers are capable of generating reactive intermediates under light wavelengths of 400-800 nm. Irradiation can be employed to cause the photosensitizer located in the coherent bright region to generate reactive intermediates, while the photosensitizer located in the coherent dark region generates no or minimal reactive intermediates. The reactive intermediates encourage the diffusion of photopolymerizable monomers into the coherent bright region, where they polymerize to form monomer aggregates. Ultimately, the coherent bright region and the coherent dark region have different monomer aggregate concentrations and different refractive indices, thereby enabling holographic recording / storage.

[0181] In the embodiments of the present application, the active intermediate can be understood as an intermediate that can initiate a polymerization reaction of the photopolymerizable monomer. The active intermediate can include but is not limited to: free radical active species and / or cationic active species.

[0182] For example, the free radical active species may include, but are not limited to, phenyl radicals and alkyl radicals.

[0183] For example, the cationic active species may include, but are not limited to, protons. In the embodiment of the present application, the protons may be derived from acidic substances such as hexafluorophosphoric acid (HPF6) and hexafluoroantimonic acid (HSbF6).

[0184] In order to further improve the optical performance of the holographic optical element formed by the holographic photopolymer material, as a feasible implementation method, the holographic photopolymer material may further include: a co-initiator.

[0185] The use of a co-initiator in conjunction with a photosensitizer can accelerate the rate at which the photosensitizer generates active intermediates under the excitation of light waves, thereby increasing the migration rate of photopolymerizable monomers in the polymer matrix, thereby improving the optical properties of the holographic optical element formed by the holographic photopolymerizable material.

[0186] The embodiments of the present application do not specifically limit the type of coinitiator. Any substance that can accelerate the rate at which the photosensitizer generates active intermediates under the excitation of light waves can be used as a coinitiator in the embodiments of the present application.

[0187] Exemplary coinitiators may include at least one of N-phenylglycine, triethanolamine, triisopropanolamine, methyldiethanolamine, diphenyliodonium chloride, and diphenyliodonium hexafluorophosphate. These coinitiators can accelerate the rate at which the photosensitizer generates reactive intermediates under light excitation, thereby increasing the migration rate of photopolymerizable monomers within the polymer matrix, thereby improving the optical properties of the holographic optical element formed from the holographic photopolymerizable material.

[0188] This completes the description of the photosensitizer / coinitiator.

[0189] In the embodiment of the present application, the holographic photopolymer material may include: a photopolymerizable monomer.

[0190] In the embodiment of the present application, the photopolymerizable monomer is a simple compound that can be polymerized under the action of an active intermediate. The refractive index of the photopolymerizable monomer is greater than the refractive index of the polymer matrix.

[0191] In the embodiment of the present application, the compound formed by polymerization of the photopolymerizable monomer can be referred to as a monomer polymer, and the refractive index of the monomer polymer is greater than the refractive index of the polymer matrix.

[0192] Under the irradiation of a coherent light beam, the photosensitizer in the coherent bright area can produce reactive intermediates, which promote the polymerization of photopolymerizable monomers toward the coherent bright area to form monomer aggregates. Ultimately, the coherent bright area and the coherent dark area have different monomer aggregate concentrations and different refractive indices, thus achieving holographic recording / storage.

[0193] The embodiments of the present application do not specifically limit the types of photopolymerizable monomers. Any substance that can be polymerized under the action of an active intermediate and has a refractive index greater than that of the polymer matrix can be used as a photopolymerizable monomer in the embodiments of the present application.

[0194] As a feasible implementation method, the photopolymerizable monomer may include: chlorine atoms (Cl), bromine atoms (Br), iodine atoms (I), sulfur atoms (S), aromatic rings, and benzene rings. The above atoms or groups can increase the refractive index of the photopolymerizable monomer, so that the coherent bright areas and coherent dark areas of the holographic optical element obtained after holographic processing have a high refractive index contrast. The high refractive index contrast makes it easier to simultaneously achieve high transmittance and high diffraction efficiency of the holographic optical element.

[0195] This completes the description of the holographic photopolymerizable material.

[0196] The present application also discloses a holographic photosensitive film, comprising a protective layer and a first film layer covering the protective layer. The first film layer is obtained by curing the holographic photopolymer material disclosed in the present application. The first film layer may include a polymer matrix, a photopolymerizable monomer, and a photosensitizer. The polymer matrix may provide mechanical support for the first film layer. Under a first condition, the photosensitizer may absorb light waves and produce reactive intermediates that polymerize the photopolymerizable monomers. The reactive intermediates may promote the migration of the photopolymerizable monomers to the coherent bright region of the first film layer, resulting in different refractive indices between the coherent bright region and the coherent dark region of the first film layer.

[0197] In addition, the side chains of the polymer matrix include secondary reactive functional groups. The conversion rate of the secondary reactive functional groups under the first condition is less than or equal to 30%. This ensures that, under the first condition, the photopolymerizable monomers can migrate within the linear polymer matrix. The migration rate of the photopolymerizable monomers within the polymer matrix is ​​high, thereby enabling the holographic photosensitive film to produce a holographic optical element with superior optical properties.

[0198] After holographic recording / storage is complete, the holographic photosensitive film is converted into a holographic optical element. The holographic optical element can be subjected to a second condition to crosslink the secondary reactive functional groups, thereby improving the thermodynamic properties of the holographic optical element. This indicates that the holographic photosensitive film provided in the embodiments of the present application can achieve high information recording / storage efficiency. Furthermore, the holographic photosensitive film disclosed in the embodiments of the present application can produce a holographic optical element with high thermodynamic properties.

[0199] The present invention does not specifically limit the protective layer; any material that can support and protect the first film layer can be used as the protective layer in the present invention. For example, the protective layer may include, but is not limited to, polyester film (PET), triacetyl cellulose film (TAC), glass, ceramic, and composite materials containing multiple of these materials.

[0200] The embodiment of the present application also discloses a holographic optical element, comprising: a protective layer and a second film layer covering the protective layer. The second film layer comprises: a polymer matrix and a monomer polymer, and the refractive index of the monomer polymer is greater than the refractive index of the polymer matrix. The molecular structure of the polymer matrix includes a cross-linked structure; the second film layer includes a coherent bright area and a coherent dark area, and the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area. The monomer polymer is used to form a refractive index distribution for recording holograms. The refractive index of the area where the monomer polymer is polymerized (coherent bright area) is relatively high, while the area without monomer polymer or the area with less monomer polymer polymerization (coherent dark area) can be understood as the background. The refractive index of the background is relatively low, and the monomer polymer can be used together with the background to record the complete hologram. The molecular structure of the polymer matrix in the second film layer is a cross-linked structure. Therefore, the holographic optical element has better heat resistance.

[0201] Based on the same technical concept, the present application also discloses a method for preparing a holographic photosensitive film. As shown in FIG2 , the method includes: S201-S203:

[0202] S201: Mixing a polymer matrix, a photopolymerizable monomer, and a photosensitizer to obtain a holographic photopolymerizable material.

[0203] S202: coating a holographic photopolymer material on the protective layer.

[0204] In some feasible implementations, the holographic photopolymer material can be coated on the surface of the protective layer by techniques such as blade coating, casting, printing, spraying or inkjet printing.

[0205] S203: converting the holographic photopolymer material into a first film layer to obtain a holographic photosensitive film.

[0206] In some feasible implementations, the S203 processing method includes but is not limited to: oven heating and other curing methods.

[0207] It is worth noting that the above S201-S203 should be completed in the dark or under a safelight. In the holographic photosensitive film prepared by this embodiment, the side chains of the polymer matrix include: secondary reactive functional groups. The conversion rate of the secondary reactive functional groups under the first condition is less than or equal to 30%. This ensures that under the first condition, the photopolymerizable monomers can migrate within the linear polymer matrix to achieve information recording / storage efficiency. In other words, the holographic photosensitive film prepared by this embodiment can have a high information recording / storage efficiency. In addition, the secondary reactive functional groups in the holographic photosensitive film obtained in the embodiment of the present application are cross-linked under the second condition, which can further obtain a holographic optical element with high thermodynamic properties.

[0208] Based on the same technical concept, the present application also discloses a method for preparing a holographic optical element. As shown in FIG3 , the method includes: S301-S305:

[0209] S301: Mixing a polymer matrix, a photopolymerizable monomer, and a photosensitizer to obtain a holographic photopolymerizable material.

[0210] S302: coating a holographic photopolymer material on the protective layer.

[0211] S303: Converting the holographic photopolymer material into a first film layer.

[0212] The specific implementation of the above S301-S303 can be found in the above embodiments and will not be repeated here.

[0213] S304: Photopolymerization in the first film layer forms a monomer polymer under the first condition, and the first film layer is converted into a second film layer.

[0214] The second film layer includes: a coherent bright area and a coherent dark area, wherein the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area;

[0215] S305: Under the second condition, the secondary reaction functional groups in the second film layer are cross-linked to form a cross-linked structure, thereby obtaining a holographic optical element.

[0216] The second film layer includes a coherent bright area and a coherent dark area. The density of the monomer polymer in the coherent bright area is greater than that in the coherent dark area. The monomer polymer is obtained by polymerizing a photopolymerizable monomer.

[0217] The embodiment of the present application uses a holographic recording system to convert the first film layer into the second film layer. Referring to FIG4 , the holographic recording system may include: a laser 41 , a shutter (SH), a beam expander 42 , a lens 43 , a reflector 44 , and a beam splitter 45 .

[0218] Laser 41 generates a coherent light beam, while a shutter controls the holographic exposure time. Beam expander 42 modifies the beam diameter and divergence angle. Lens 43 collimates the expanded beam. Mirror 44 controls the beam's propagation direction, ensuring it follows a predetermined path. Beam splitter 45 splits the beam into coherent beams with the same frequency, constant phase difference, and consistent vibration direction.

[0219] Referring to (a) in FIG. 4 , in a reflective holographic recording system, the light beam emitted by the laser 41 is split into two coherent beams by the beam splitter 45 . The coherent beams in these two directions are emitted from the two sides of the holographic photosensitive film toward the first film layer B, respectively. Coherent bright areas and coherent dark areas are formed on the first film layer B, and the first film layer is transformed into the second film layer, thereby achieving holographic storage / recording.

[0220] Referring to (2) in FIG. 4 , in a transmission holographic recording system, when two coherent light beams (46 and 47) are located on the same side of the first film layer B, coherent bright areas and coherent dark areas are formed on the first film layer B, and the first film layer is transformed into the second film layer, thereby achieving holographic storage / recording.

[0221] Based on the same technical concept, the present application also discloses a display device including the holographic optical element or holographic photosensitive film disclosed in the present application. The display device is, for example, a head-up display (HUD) device.

[0222] Based on the same technical concept, the embodiments of the present application also disclose a storage device, including the holographic optical element or holographic photosensitive film disclosed in the embodiments of the present application.

[0223] Based on the same technical concept, the embodiments of the present application also disclose an anti-counterfeiting mark, including the holographic optical element or holographic photosensitive film disclosed in the embodiments of the present application.

[0224] The following is a further explanation of the solutions disclosed in the embodiments of this application with reference to specific embodiments:

[0225] Example 1:

[0226] According to the ratio shown in Table 1, 15 mmol of MMA, 65 mmol of BA, 10 mmol of GMA and 10 mmol of DFMA were weighed into a 100 mL round-bottom flask. The intermediate solution formed can be seen in (1) of Figure 5.

[0227] 0.1 mol % of a thermally initiated free radical initiator 2,2′-Azobis(2-methylpropionitrile, AIBN) and 20 mL of propylene glycol methyl ether acetate (2-Acetoxy-1-methoxypropane, PGMEA) were added to the round-bottom flask.

[0228] Nitrogen was passed through the flask for 15 min to expel oxygen from the flask.

[0229] The round-bottom flask from which oxygen was purged was placed at 70° C. with stirring for 12 h.

[0230] After the reaction is complete, the intermediate solution is diluted and added dropwise to n-hexane to precipitate. This is repeated N times (N is greater than or equal to 1). The solvent is removed by filtration, and the precipitate is dried in a vacuum oven at 60°C for 24 hours to obtain a fluorine-containing film-forming resin 1 (also referred to as a polymer matrix in this embodiment of the present application).

[0231] The molecular weight of the fluorine-containing film-forming resin 1 obtained in Example 1 is 88.3 kg / mol, the molecular weight distribution of the fluorine-containing film-forming resin 1 is 3.98, the glass transition temperature of the fluorine-containing film-forming resin 1 is 27°C, the fluorine mass fraction in the fluorine-containing film-forming resin 1 is 12.1%, and the refractive index n of the fluorine-containing film-forming resin 1 is 1.43.

[0232] Table 1

[0233] 5 , the process of forming a holographic photopolymer material, a holographic photosensitive film, and a holographic optical element from a polymer matrix is ​​described below:

[0234] Please refer to (I) in FIG. 5 , where the reactants disclosed in Example 1 are mixed to obtain a fluorine film-forming resin 200 .

[0235] Referring to FIG. 5 (2), the fluorine-containing film-forming resin 200 is weighed and mixed with the photopolymerizable monomer 100, a photosensitizer (not shown), and a solvent (not shown) according to Table 2 to obtain a holographic photopolymerizable material. The solvent may include dichloromethane (DCM) and methanol.

[0236] The holographic photopolymer material was coated on the surface of a 10 cm×10 cm glass substrate (which may be referred to as a protective layer in this embodiment of the application) using a 100 μm wet film preparation device.

[0237] The solvent was removed by heating at 50°C for 5 minutes to form a 16 μm thick holographic photosensitive film, which was then attached with a PET optical film and stored at room temperature in the dark for future use.

[0238] The holographic photosensitive film is holographically exposed using a reflective optical path A with an exposure wavelength of 460 nm (blue light), an exposure power of 2 mW, and an exposure time of 60 s to form a holographic grating. For details, see (3) in FIG. 5 .

[0239] After the exposure is completed, ultraviolet (UV) bleaching is first performed using a high-pressure mercury lamp. The cationic photoinitiator triggers the ring-opening polymerization of the epoxy functional groups to form a cross-linked network and the unreacted photopolymerization monomers to react completely. Then, the holographic optical element 1 is heated at 80° C. for 10 minutes to achieve a thermal enhancement effect. Finally, white light bleaching is used for 24 hours to obtain the holographic optical element 1. For details, please refer to (4) in Figure 5.

[0240] Various optical properties of the holographic optical element 1 were measured using an ultraviolet-visible spectrophotometer and a haze meter. The test results can be found in Table 3.

[0241] Heat resistance test:

[0242] After the holographic optical element was placed in an oven at 85° C. and heated for 40 hours, various holographic optical properties were tested and listed in Table 3.

[0243] Table 2

[0244] Table 3

[0245] In the solution disclosed in Example 1, the fluorine-containing film-forming resin 1 used achieves both excellent optical properties and heat resistance by forming a cross-linked structure. The resulting holographic optical element achieves a diffraction efficiency of 81.2%, an overall transmittance of 88.1%, and a haze of 1.60. After baking at 85°C for 40 hours, the holographic optical element shows no significant degradation in any of its optical properties.

[0246] Example 2:

[0247] The fluorine film-forming resin 2 was obtained by using the formula shown in Table 4. The fluorine film-forming resin 2 was used to prepare the holographic photosensitive film 2 according to the method of Example 1. The difference from Example 1 is:

[0248] The wavelength of the light source used for exposure was 640 nm (red light) and the exposure power was 2 mW to obtain a holographic optical element. The holographic optical properties and heat resistance test data of the holographic optical element can be found in Table 5.

[0249] Table 4

[0250] Table 5

[0251] In the solution disclosed in Example 2, the diffraction efficiency of the holographic optical element can reach 95.6%, the overall transmittance of the holographic optical element can reach 85.0%, and the haze of the holographic optical element can reach 2.34. After baking at 85°C for 40 hours, the optical properties of the holographic optical element did not show a significant decline.

[0252] Example 3:

[0253] As shown in Table 6, 80 mmol of GMA and 20 mmol of TFMA were weighed into a 100 mL round-bottom flask. 0.1 mol% of AIBN and 30 mL of PGMEA were added. After nitrogen flow for 15 minutes to remove oxygen, the mixture was stirred at 70°C for 12 hours. After the reaction, the polymer solution was diluted to an appropriate concentration and added dropwise to n-hexane to precipitate. This process was repeated twice. The solvent was filtered off, and the precipitate was dried in a vacuum oven at 60°C for 24 hours to obtain purified fluorine-containing film-forming resin 2. The molecular weight of fluorine-containing film-forming resin 2 was 78.3 kg / mol, the molecular weight distribution of fluorine-containing film-forming resin 2 was 2.85, the glass transition temperature of fluorine-containing film-forming resin 2 was 52°C, and the fluorine mass fraction in fluorine-containing film-forming resin 2 was 7.5%.

[0254] Table 6

[0255] Using the formulation shown in Table 7, a holographic photosensitive film 3 was prepared using the fluorine-containing film-forming resin 2 according to the method of Example 1. The differences from Example 1 are:

[0256] The wavelength of the light source used for exposure is 540 nm (green light) and the exposure power is 2 mW to obtain the holographic optical element 3. The holographic optical properties and heat resistance test data of the holographic optical element 3 can be found in Table 8.

[0257] Table 7

[0258] Table 8

[0259] In the solution disclosed in Example 3, the diffraction efficiency of the holographic optical element 3 can reach 89.9%, the overall transmittance of the holographic optical element 3 can reach 82.0%, the haze of the holographic optical element 3 is 0.66, and after baking at 85°C for 40 hours, the optical properties of the holographic optical element 3 do not show a significant decrease.

[0260] Comparative Example 1:

[0261] In Comparative Example 1, a film-forming resin 4 was obtained using the holographic formula shown in Table 9, and a holographic optical element 4 was prepared according to the method of Example 1. Unlike Example 1, film-forming resin 4 was formed from polyvinyl acetate (PVAC). The holographic optical properties and heat resistance test data of holographic optical element 4 are listed in Table 10. The diffraction efficiency of holographic optical element 4 was 89.1%, the overall transmittance of holographic optical element 4 was 72.5%, and the haze of holographic optical element 4 was 3.31.

[0262] Table 9

[0263] Table 10

[0264] In the solution disclosed in Comparative Example 1, the holographic optical element 4 was baked at 85°C for 40 hours. Compared with the fluorine-containing film-forming resins 1 and 2, its optical properties showed a significant decline, including a decrease in diffraction efficiency of 8.3%, a decrease in overall transmittance of 59.6%, and an increase in haze of 23.81, making it unusable as a heat-resistant optical film.

[0265] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

[0266] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A holographic photopolymerizable material, characterized in that: include: Photosensitizers; a photopolymerizable monomer that polymerizes under a first condition; A polymer matrix, wherein the refractive index of the polymer matrix is ​​less than the refractive index of the photopolymerizable monomer, the molecular structure of the polymer matrix comprises a linear structure, and the side chain of the polymer matrix comprises a secondary reactive functional group, the secondary reactive functional group is cross-linked under a second condition, and the conversion rate of the secondary reactive functional group under the first condition is less than or equal to 30%.

2. The holographic photopolymer material according to claim 1, characterized in that: The first condition includes: irradiation with light waves having a wavelength of 400nm-800nm; The second condition includes: at least one of irradiation with light waves having a wavelength less than 400 nm, catalysis, and high temperature.

3. The holographic photopolymer material according to claim 1 or 2, characterized in that: The side chain of the polymer matrix further includes: fluorine element.

4. The holographic photopolymer material according to any one of claims 1 to 3, characterized in that: The polymer matrix includes: at least one monomer.

5. The holographic photopolymer material according to claim 4, characterized in that: The at least one monomer includes: a first monomer; The side chain of the first monomer includes: a fluorine element and the secondary reaction functional group.

6. The holographic photopolymer material according to claim 4, characterized in that: The at least one monomer comprises: a second monomer and a third monomer; The side chain of the second monomer includes: fluorine element; The side chain of the third monomer includes: the secondary reaction functional group.

7. The holographic photopolymer material according to claim 5 or 6, characterized in that: The at least one monomer further comprises: a fourth monomer; The side chain of the fourth monomer includes at least one of hydrogen and an alkyl substituent.

8. The holographic photopolymer material according to any one of claims 1 to 7, characterized in that: The secondary reactive functional group comprises at least one of vinyl ether, allyl group, epoxy group, carboxyl group and mercapto group.

9. The holographic photopolymer material according to any one of claims 1 to 8, characterized in that: The secondary reaction functional groups also include: isocyanate and hydroxyl.

10. The holographic photopolymer material according to any one of claims 1 to 9, characterized in that: The number average molecular weight of the polymer matrix is ​​20,000-300,000.

11. The holographic photopolymer material according to any one of claims 1 to 10, characterized in that: The glass transition temperature of the polymer matrix is ​​between -20°C and 120°C.

12. The holographic photopolymer material according to any one of claims 3 to 11, characterized in that: The mass fraction of the fluorine element in the polymer matrix is ​​5%-30%.

13. The holographic photopolymerizable material according to any one of claims 1 to 12, characterized in that: The polymer matrix has a refractive index less than or equal to 1.

48.

14. The holographic photopolymer material according to any one of claims 1 to 13, characterized in that: The molecular structural formula of the polymer matrix includes: Wherein R1 includes: hydrogen atom or methyl; R2 includes: said hydrogen atom or said methyl; R3 includes: said hydrogen atom or said methyl; R4 includes: -C n H 2n+1 One or more of; R5 includes: fluorine element; R6 includes: the secondary reaction functional group; a includes: an integer of 0-500; b includes: an integer of 1-500; c includes: a hydrogen atom or a methyl group.

15. A holographic photosensitive film, characterized in that: include: A protective layer and a first film layer covering the protective layer, wherein the first film layer is made of the holographic photopolymer material according to any one of claims 1-14.

16. A holographic optical element, characterized in that: include: A protective layer and a second film layer covering the protective layer, wherein the second film layer is made of a material comprising: a polymer matrix and a monomer polymer, wherein the molecular structure of the polymer matrix comprises: a cross-linked structure; and the monomer polymer is obtained by polymerizing a photopolymerizable monomer; The second film layer includes: a coherent bright area and a coherent dark area, and the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area.

17. A method for preparing a holographic optical element, characterized in that: include: A first film layer is formed on one side of the protective layer, wherein the first film layer comprises: a photosensitizer, a photopolymerizable monomer and a polymer matrix, wherein the photopolymerizable monomer is polymerized under a first condition: the molecular structure of the polymer matrix comprises: a linear structure, and the side chain of the polymer matrix comprises: a secondary reactive functional group, wherein the secondary reactive functional group is cross-linked under a second condition, and the conversion rate of the secondary reactive functional group under the first condition is less than or equal to 30%; Under the first condition, the photopolymerizable monomer forms a monomer polymer to obtain a second film layer, wherein the second film layer comprises: a coherent bright area and a coherent dark area, and the density of the monomer polymer in the coherent bright area is greater than the density of the monomer polymer in the coherent dark area; Under the second condition, the secondary reaction functional groups are cross-linked to form a cross-linked structure to obtain a holographic optical element.

18. A display device, characterized in that: include: A display screen and an optical element disposed on the display screen; The optical element comprises: the holographic photosensitive film according to claim 15 or the holographic optical element according to claim 16.

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